10 See VB also RB Archimedes NNP computer NN , , Archimedes NNP -LRB- -LRB- disambiguation NN -RRB- -RRB- . .
25 Archimedes NNP of IN Syracuse NNP -LRB- -LRB- circa NN 287 CD BC NNP - - 212 CD BC NNP -RRB- -RRB- , , was VBD a DT Greek JJ mathematician NN , , astronomer NN , , philosopher JJ , , physicist NN and CC engineer NN . .
31 He PRP was VBD killed VBN by IN a DT Roman NNP soldier NN during IN the DT sack NN of IN the DT city NN , , despite IN orders NNS from IN the DT Roman NNP general JJ , , Marcellus NNP , , that IN he PRP was VBD not RB to TO be VB harmed VBN . .
55 1 CD Discoveries NNS and CC inventions NNS 2 CD Writings NNS by IN Archimedes NNP 3 CD Quotes NNPS about IN Archimedes NNP 4 CD Named NNP after IN Archimedes NNP 5 CD See NNP also RB 6 CD External NNP links NNS 7 CD References NNS Discoveries NNS and CC inventions NNS Archimedes NNP became VBD a DT popular JJ figure NN as IN a DT result NN of IN his PRP$ involvement NN in IN the DT defense NN of IN Syracuse NNP against IN the DT Roman NNP siege NN in IN the DT First NNP and CC Second NNP Punic NNP Wars NNPS . .
84 He PRP is VBZ reputed VBN to TO have VB held VBN the DT Romans NNPS at IN bay NN with IN war JJ engines NNS of IN his PRP$ design NN ; ; to TO have VB been VBN able JJ to TO move VB a DT full-size JJ ship NN complete JJ with IN crew NN and CC cargo NN by IN pulling VBG a DT single JJ rope NN ; ; to TO have VB discovered VBN the DT principles NNS of IN density NN and CC buoyancy NN while IN taking VBG a DT bath NN -LRB- -LRB- thereupon NN taking VBG to TO the DT streets NNS naked JJ calling VBG '' '' eureka NN '' '' - - '' '' I PRP have VBP found VBN it PRP ! ! '' '' -RRB- -RRB- ; ; and CC to TO have VB invented VBN the DT irrigation NN device NN known VBN as IN Archimedes NNP ' ' screw NN . .
18 He PRP has VBZ also RB been VBN credited VBN with IN the DT possible JJ invention NN of IN the DT odometer NN during IN the DT First JJ Punic NNP War NNP . .
20 One CD of IN his PRP$ inventions NNS used VBN for IN military JJ defense NN of IN Syracuse NNP against IN the DT invading NN Romans NNP was VBD the DT claw NN of IN Archimedes NNP . .
16 In IN creativity NN and CC insight NN , , he PRP exceeded VBD any DT other JJ mathematician NN prior RB to TO the DT European JJ renaissance NN . .
43 In IN a DT civilization NN with IN an DT awkward JJ numeral JJ system NN and CC a DT language NN in IN which WDT '' '' a DT myriad JJ '' '' -LRB- -LRB- literally RB ten CD thousand CD -RRB- -RRB- meant VBN '' '' infinity NN '' '' , , he PRP invented VBD a DT positional JJ numeral JJ system NN and CC used VBD it PRP to TO write VB numbers NNS up IN to TO 1064 CD . .
31 He PRP devised VBD a DT heuristic JJ method NN based VBN on IN statics NNS to TO do VB private JJ calculation NN that IN we PRP would MD classify VB today NN as IN integral JJ calculus NN , , but CC then RB presented VBD rigorous JJ geometric JJ proofs NNS for IN his PRP$ results NNS . .
16 To TO what WP extent NN he PRP actually RB had VBD a DT correct JJ version NN of IN integral JJ calculus NN is VBZ debat NN able JJ . .
34 He PRP proved VBD that IN the DT ratio NN of IN a DT circle NN ' ' s POS perimeter NN to TO its PRP$ diameter NN is VBZ the DT same JJ as IN the DT ratio NN of IN the DT circle NN ' ' s POS area NN to TO the DT square NN of IN the DT radi NN us PRP . .
33 He PRP did VBD not RB call VB this DT ratio NN but CC he PRP gave VBD a DT procedure NN to TO approximate VB it PRP to TO arbitrary JJ accuracy NN and CC gave VBD an DT approximation NN of IN it PRP as IN between IN 3 CD + + 1/7 CD and CC 3 CD + + 10/71 CD . .
30 He PRP was VBD the DT first JJ , , and CC possibly RB the DT only JJ , , Greek JJ mathematician NN to TO introduce VB mechanical JJ curves NNS -LRB- -LRB- those DT traced VBN by IN a DT moving VBG point NN -RRB- -RRB- as IN legitimate JJ objects NNS of IN study NN . .
26 He PRP proved VBD that IN the DT area NN enclosed VBN by IN a DT parabola NN and CC a DT straight JJ line NN is VBZ 4/3 IN the DT area NN of IN a DT triangle NN with IN equal JJ base NN and CC height NN . .
13 -LRB- -LRB- This DT proposition NN needs VBZ to TO be VB understood VBN consistently RB with IN the DT illustration NN below IN . .
47 The DT '' '' base NN '' '' is VBZ any DT secant JJ line NN , , not RB necessarily RB orthogonal JJ to TO the DT parabola NN ' ' s POS axis NN ; ; '' '' the DT same JJ base NN '' '' means VBZ the DT same JJ '' '' horizontal JJ '' '' component NN of IN the DT length NN of IN the DT base NN ; ; '' '' horizontal JJ '' '' means VBZ orthogonal JJ to TO the DT axis NN . .
20 '' '' Height NNP '' '' means VBZ the DT length NN of IN the DT segment NN parallel NN to TO the DT axis NN from IN the DT vertex NN to TO the DT base NN . .
19 The DT vertex NN must MD be VB so RB placed VBN that IN the DT two CD horizontal JJ distances NNS mentioned VBN in IN the DT illustration NN are VBP equal JJ . . -RRB- -RRB-
59 In IN the DT process NN , , he PRP calculated VBD the DT oldest JJS known VBN example NN of IN a DT geometric JJ series NN with IN the DT ratio NN 1/4 VBZ : : If IN the DT first JJ term NN in IN this DT series NN is VBZ the DT area NN of IN the DT triangle NN in IN the DT illustration NN then RB the DT second NN is VBZ the DT sum NN of IN the DT areas NNS of IN two CD triangles NNS whose WP$ bases NNS are VBP the DT two CD smaller JJR secant JJ lines NNS in IN the DT illustration NN . .
8 Essentially RB , , this DT paragraph NN summarizes VBZ the DT proof NN . .
25 Archimedes NNP also RB gave VBD a DT quite RB different JJ proof NN of IN nearly RB the DT same JJ proposition NN by IN a DT method NN using VBG infinitesimals NNS ; ; that IN different JJ proof NN is VBZ found VBN here RB . .
40 He PRP proved VBD that IN the DT area NN and CC volume NN of IN the DT sphere NN are VBP in IN the DT same JJ ratio NN to TO the DT area NN and CC volume NN of IN a DT circumscribed JJ straight JJ cylinder NN , , a DT result NN he PRP was VBD so RB proud JJ of IN that IN he PRP made VBD it PRP his PRP$ epitaph NN . .
19 Archimedes NNP is VBZ probably RB also RB the DT first JJ mathematical JJ physicist NN on IN record NN , , and CC the DT best JJS before IN Galileo NNP and CC Newton NNP . .
26 He PRP invented VBD the DT field NN of IN statics NNS , , enunciated VBD the DT law NN of IN the DT lever NN , , the DT law NN of IN equilibrium NN of IN fluids NNS and CC the DT law NN of IN buoyancy NN . .
37 Using VBG only RB ancient JJ Greek JJ geometry NN , , he PRP also RB gave VBD the DT equilibrium NN positions NNS of IN floating VBG sections NNS of IN paraboloids NNS as IN a DT function NN of IN their PRP$ height NN , , a DT feat NN that WDT would MD be VB taxing VBG to TO a DT modern JJ physicist NN using VBG calculus NN . .
69 Apart NNP from IN general JJ physics NNS he PRP was VBD an DT astronomer NN , , and CC Cicero NNP writes VBZ that IN in IN the DT year NN 212 CD BC NNP when WRB Syracuse NNP , , Italy NNP was VBD raided VBN by IN Roman NNP troops NNS , , the DT Roman NNP consul NN Marcellus NNP brought VBD a DT device NN which WDT mapped VBD the DT sky NN on IN a DT sphere NN and CC another DT device NN that WDT predicted VBD the DT motions NNS of IN the DT sun NN and CC the DT moon NN and CC the DT planets NNS -LRB- -LRB- i NNP . . e NN . . a DT planetarium NN -RRB- -RRB- to TO Rome NNP . .
10 He PRP credits VBZ Thales NNP and CC Eudoxus NNP for IN constructing VBG these DT devices NNS . .
42 For IN some DT time NN this DT was VBD assumed VBN to TO be VB a DT legend NN of IN doubtful JJ nature NN , , but CC the DT discovery NN of IN the DT Antikythera NNP mechanism NN has VBZ changed VBN the DT view NN of IN this DT issue NN , , and CC it PRP is VBZ indeed RB probable JJ that IN Archimedes NNP possessed JJ and CC constructed VBN such JJ devices NNS . .
34 Pappus NNP of IN Alexandria NNP writes VBZ that IN Archimedes NNP had VBD written VBN a DT practical JJ book NN on IN the DT construction NN of IN such JJ spheres NNS entitled VBD On IN Sphere-Making NNP . . Archimedes NNP ' ' works NNS were VBD not RB very RB influential JJ , , even RB in IN anti JJ quity NN . .
14 He PRP and CC his PRP$ contemporaries NNS probably RB constitute VB the DT peak NN of IN Greek JJ mathematical JJ rig NN our RB . .
18 During IN the DT Middle NNP Ages NNPS the DT mathematicians NNS who WP could MD understand VB Archimedes NNP ' ' work NN were VBD few JJ and CC far RB between IN . .
22 Many JJ of IN his PRP$ works NNS were VBD lost VBN when WRB the DT library NN of IN Alexandria NNP was VBD destroyed VBN and CC survived VBD only RB in IN Latin NNP or CC Arabic NNP translations NNS . .
24 As IN a DT result NN , , his PRP$ mechanical JJ method NN was VBD lost VBN until IN around IN 1900 CD , , after IN the DT arithmetization NN of IN analysis NN had VBD been VBN carried VBN out IN successfully RB . .
31 We PRP can MD only RB speculate VB about IN the DT effect NN that IN the DT '' '' method NN '' '' would MD have VB had VBN on IN the DT development NN of IN calculus NN had VBD it PRP been VBN known VBN in IN the DT 16th JJ and CC 17th JJ centuries NNS . .
37 Writings NNS by IN Archimedes NNP On IN the DT Equilibrium NNP of IN Planes NNP -LRB- -LRB- 2 CD volumes NNS -RRB- -RRB- This DT book NN spells VBZ out RP the DT law NN of IN the DT lever NN and CC uses VBZ it PRP to TO calculate VB the DT areas NNS and CC centers NNS of IN gravity NN of IN various JJ geometric JJ figures NNS . .
16 On IN Spirals NNS In IN this DT book NN , , Archimedes NNP defines VBZ what WP is VBZ now RB called VBN Archimedes NNP ' ' spiral NN . .
25 This DT is VBZ the DT first JJ mechanical JJ curve NN -LRB- -LRB- i FW . . e FW . . , , traced VBN by IN a DT moving VBG point NN -RRB- -RRB- ever RB considered VBN by IN a DT Greek JJ mathematician NN . .
12 Using VBG this DT curve NN , , he PRP was VBD able JJ to TO square VB the DT circle NN . .
43 On IN the DT Sphere NNP and CC The DT Cylinder NN In IN this DT book NN Archimedes NNP obtains VBZ the DT result NN he PRP was VBD most RBS proud JJ of IN : : that IN the DT area NN and CC volume NN of IN a DT sphere NN are VBP in IN the DT same JJ relationship NN to TO the DT area NN and CC volume NN of IN the DT circumscribed JJ straight JJ cylinder NN . .
22 On IN Conoids NNS and CC Spheroids NNS In IN this DT book NN Archimedes NNP calculates VBZ the DT areas NNS and CC volumes NNS of IN sectios NNS of IN cones NNS , , spheres NNS and CC paraboloids NNS . .
40 On IN Floating VBG Bodies NNS -LRB- -LRB- 2 CD volumes NNS -RRB- -RRB- In IN the DT first JJ part NN of IN this DT book NN , , Archimedes NNP spells VBZ out RP the DT law NN of IN equilibrium NN of IN fluids NNS , , and CC proves VBZ that IN water NN around IN a DT center NN of IN gravity NN will MD adopt VB a DT spherical JJ form NN . .
19 This DT is VBZ probably RB an DT attempt NN at IN explaining VBG the DT observation NN made VBN by IN Greek JJ astronomers NNS that IN the DT Earth NNP is VBZ round NN . .
25 Note VB that IN his PRP$ fluids NNS are VBP not RB self-gravitating JJ : : he PRP assumes VBZ the DT existence NN of IN a DT point NN towards IN all DT things NNS fall VBP and CC derives VBZ the DT spherical JJ shape NN . .
20 One CD is VBZ led VBN to TO wonder VB what WP he PRP would MD have VB done VBN had VBD he PRP struck VBD upon IN he PRP idea NN of IN universal JJ gravitation NN . .
19 In IN the DT second JJ part NN , , a DT veritable JJ tour-de-force NN , , he PRP calculates VBZ the DT equilibrium NN positions NNS of IN sections NNS of IN paraboloids NNS . .
13 This DT was VBD probably RB an DT idealization NN of IN the DT shapes NNS of IN ships NNS ' ' hulls NNS . .
35 Some DT of IN his PRP$ sections NNS float VBP with IN the DT base NN under IN water NN and CC the DT summit NN above IN water NN , , which WDT is VBZ reminiscent JJ of IN the DT way NN icebergs IN float NN , , although IN Archimedes NNP probably RB was VBD n't RB thinking VBG of IN this DT application NN . .
38 The DT Quadrature NN of IN the DT Parabola NNP In IN this DT book NN , , Archimedes NNP calculates VBZ the DT area NN of IN a DT segment NN of IN a DT parabola NN -LRB- -LRB- the DT figure NN delimited VBN by IN a DT parabola NN and CC a DT secant JJ line NN not RB necessarily RB perpendicular JJ to TO the DT axis NN -RRB- -RRB- . .
18 The DT final JJ answer NN is VBZ obtained VBN by IN triangulating VBG the DT area NN and CC summing VBG the DT geometric JJ series NN with IN ratio NN 1/4 CD . .
10 Stomachion NNP This DT is VBZ a DT Greek JJ puzzle NN similar JJ to TO Tangram NNP . .
13 In IN this DT book NN , , Archimedes NNP calculates VBZ the DT areas NNS of IN the DT various JJ pieces NNS . .
12 This DT may MD be VB the DT first JJ reference NN we PRP have VBP to TO this DT game NN . .
26 Recent JJ discoveries NNS indicate VBP that IN Archimedes NNP was VBD attempting VBG to TO determine VB how WRB many JJ ways NNS the DT strips NNS of IN paper NN could MD be VB assembled VBN into IN the DT shape NN of IN a DT square NN . .
13 This DT is VBZ possibly RB the DT first JJ use NN of IN combinatorics NNS to TO solve VB a DT problem NN . .
29 Archimedes NNP ' ' Cattle NNP Problem NNP Archimedes NNP wrote VBD a DT letter NN to TO the DT scholars NNS in IN the DT Library NNP of IN Alexand NNP ria NNP , , who WP apparently RB had VBD downplayed RP the DT importance NN of IN Archimedes NNP ' ' works NNS . .
32 In IN these DT letters NNS , , he PRP dares VBZ them PRP to TO count VB the DT numbers NNS cattle NNS in IN the DT Herd NNP of IN the DT Sun NNP by IN solving VBG a DT number NN of IN simultaneous JJ diophantine JJ equations NNS , , some DT of IN them PRP quadratic JJ . .
16 This DT problem NN is VBZ one CD of IN the DT famous JJ problems NNS solved VBD with IN the DT aid NN of IN a DT computer NN . .
20 The DT Sand NNP Reckoner NNP In IN this DT book NN , , Archimedes NNP counts VBZ the DT number NN of IN grains NNS of IN sand NN fitting VBG inside IN the DT universe NN . .
27 This DT book NN mentions VBZ Aristarchus NNP ' ' theory NN of IN the DT solar JJ system NN , , contemporary JJ ideas NNS about IN the DT size NN of IN the DT Earth NNP and CC the DT distance NN between IN various JJ celestial JJ bodies NNS . .
15 From IN the DT inroductory JJ letter NN we PRP also RB learn VBP that IN Archimedes NNP ' ' father NN was VBD an DT astronomer NN . .
58 '' '' The DT Method NNP '' '' In IN this DT work NN , , which WDT was VBD unknown JJ in IN the DT Middle NNP Ages NNPS , , but CC the DT importance NN of IN which WDT was VBD realised VBN after IN its PRP$ discovery NN , , Archimedes NNP pioneered VBD the DT use NN of IN infinitesimals NNS , , showing VBG how WRB breaking VBG up RP a DT figure NN in IN an DT infinite JJ number NN of IN infinitely NN small JJ parts NNS could MD be VB used VBN to TO determine VB its PRP$ area NN or CC volume NN . .
41 Archimedes NNP did VBD probably RB consider VB these DT methods NNS not RB mathematically RB precise JJ , , and CC he PRP used VBD these DT methods NNS to TO find VB at IN least JJS some DT of IN the DT areas NNS or CC volumes NNS he PRP sought VBD , , and CC then RB used VBD the DT more RBR traditional JJ method NN of IN exhaustion NN to TO prove VB them PRP . .
13 This DT particular JJ work NN is VBZ found VBN in IN what WP is VBZ called VBN the DT Archimedes NNP Palimpsest NNP . .
11 Some DT details NNS can MD be VB found VBN at IN how WRB Archimedes NNP used VBD infinitesimals NNS . .
71 Quotes VBG about IN Archimedes NNP '' '' Perhaps RB the DT best JJS indication NN of IN what WP Archimedes NNP truly RB loved VBD most PRP is VBZ his PRP$ request NN that IN his PRP$ tombstone NN include VBP a DT cylinder NN circumscribing VBG a DT sphere RB , , accompanied VBN by IN the DT inscription NN of IN his PRP$ amazing JJ theorem NN that IN the DT sphere NN is VBZ exactly RB two-thirds NNS of IN the DT circumscribing VBG cylinder NN in IN both DT surface NN area NN and CC volume NN ! ! '' '' -LRB- -LRB- Laubenbacher NNP and CC Pengelley NNP , , p NN . . 95 CD -RRB- -RRB- Named NNPS after IN Archimedes NNP Archimedes NNP crater NN on IN the DT Moon NNP . .
32 Asteroid NNP 3600 CD Archimedes NNP , , named VBN in IN his PRP$ honour NN See VB also RB Archimedean NNP property NN Archimedean NNP solid JJ Archimedean NNP point NN Claw NNP of IN Archimedes NNP External NNP links NNS Wikiquote NNP has VBZ a DT collection NN of IN quotations NNS by IN or CC about IN Archimedes NNP . .
14 Archimedes NNP Home NNP Page NNP -LRB- -LRB- http://www JJ . . mcs NNP . . drexel NNP . . edu/~crorres/Archimedes/contents NNS . . html . -RRB- -RRB-
15 MacTutor NNP biography NN of IN Archimedes NNP -LRB- -LRB- http://www-groups NNS . . dcs NNS . . st-and CC . . ac.uk/~history/Mathematicians/Archimedes NNP . . html NNP -RRB- -RRB-
12 The DT Archimedes NNP Palimpsest NNP -LRB- -LRB- http://www JJ . . thewalters NNS . . org/archimedes/frame NN . . html NN -RRB- -RRB-
8 web NN pages NNS at IN the DT Walters NNP Art NNP Museum NNP . .
14 Archimedes NNP - - The DT Golden JJ Crown NNP -LRB- -LRB- http://www NN . . mcs . . . drexel NNP . . edu/~crorres/Archimedes/Crown/CrownIntro.html NNP -RRB- -RRB-
25 points NNS out IN that IN in IN reality NN Archimedes NNP may MD well RB have VB used VBN a DT more RBR subtle JJ method NN than IN the DT one CD in IN the DT classic JJ version NN of IN the DT story NN . .
17 Archimedes NNP ' ' Quadrature NN Of IN The DT Parabola NNP -LRB- -LRB- http://www JJ . . math NN . . ubc NN . . ca/~cass/archimedes/parabola NN . . html NN -RRB- -RRB-
24 Translated VBN by IN Thomas NNP Heath NNP . . Archimedes NNP ' ' On IN The DT Measurement NN Of IN The DT Circle NNP -LRB- -LRB- http://www JJ . . math NN . . ubc NN . . ca/~cass/archimedes/circle NN . . html NN -RRB- -RRB-
20 Translated VBN by IN Thomas NNP Heath NNP . . Archimedes NNP ' ' Cattle NNP Problem NNP -LRB- -LRB- http://www JJ . . mcs NNP . . drexel NNP . . edu/~crorres/Archimedes/Cattle/Statement NN . . html NN -RRB- -RRB-
10 eTexts NNS -LRB- -LRB- http://www JJ . . gutenberg NN . . net/catalog/world/authrec NN ? ? fk_authors=2545 CD -RRB- -RRB-
34 of IN Archimedes NNP ' ' works NNS , , at IN Project NNP Gutenberg NNP References NNP 1 CD - - Mathematical NNP Expeditions NNS : : Chronicles NNS by IN the DT Explorers NNS by IN Laubenbacher NNP and CC Pengelley NNP -LRB- -LRB- 1999 CD -RRB- -RRB- Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Archimedes NNP '' ''
15 Categories NNS : : Engineers NNS |  Inventors NNS |  Mathematicians NNS |  Physicists NNS |  Hellenistic NNP philosophers NNS |  Ancient JJ mathematicians mathematicians
13 Image NN of IN the DT largest JJS antarctic JJ ozone NN hole NN ever RB recorded VBN in IN September NNP 2000 CD . .
20 Data NNP taken VBN by IN the DT Total JJ Ozone NN Mapping VBG Spectrometer NNP -LRB- -LRB- TOMS NNP -RRB- -RRB- instrument NN aboard IN NASA NNP ' ' s POS Earth NNP Probe NNP satellite NN . .
48 Ozone NN depletion NN refers NNS to TO the DT approximately RB 5 CD % % reduction NN in IN in IN the DT total JJ amount NN of IN ozone NN in IN the DT stratosphere JJ detected VBN from IN 1979 CD to TO 1990 CD , , whereas WRB ozone NN hole NN refers NNS to TO the DT much JJ larger JJR losses NNS - - up RP to TO 70 CD % % over IN Antarctica NNP or CC 30 CD % % over IN the DT Arctic NNP . .
29 This DT reduction NN is VBZ held VBN by IN a DT wide JJ scientific JJ consensus NN to TO be VB due JJ primarily RB to TO an DT increase NN in IN concentrations NNS of IN stratospheric JJ chlorine NN from IN breakdown NN of IN human JJ manufactured VBN CFC NNP emissions NNS . .
8 Ozone NN depletion NN varies NNS geographically RB and CC by IN season NN . .
43 Since IN the DT ozone NN layer NN prevents VBZ most RBS harmful JJ wavelengths NNS of IN ultraviolet NN light NN from IN passing VBG through IN the DT earth NN ' ' s POS atmosphere NN , , observed VBD and CC projected VBD decreases NNS in IN ozone NN have VBP generated VBN worldwide JJ concern NN and CC led VBD to TO speedy JJ adoption NN of IN the DT Montreal NNP Protocol NNP banning VBG CFC NNP use NN . .
45 In IN public JJ policy NN discussions NNS , , the DT term NN ozone NN layer NN depletion NN is VBZ considered VBN synonymous JJ with IN the DT theory NN that IN a DT trend NN of IN global JJ ozone NN depletion NN , , which WDT is VBZ caused VBN by IN CFC NNP emissions NNS , , is VBZ subsequently RB allowing VBG more JJR ultraviolet NN radiation NN to TO reach VB the DT earth NN ' ' s POS surface NN . .
41 It PRP is VBZ suspected VBN that IN a DT variety NN of IN biological JJ consequences NNS , , including VBG , , for IN example NN , , increases NNS in IN melanoma NN and CC the DT destruction NN of IN plankton NN populations NNS in IN the DT ocean NN ' ' s POS photic JJ z NN one CD , , may MD result VB from IN this DT increased VBN UV NN exposure NN . .
17 1 CD History NN of IN the DT research NN 2 CD General NNP 3 CD Observations NNS 4 CD The DT ozone NN hole NN and CC its PRP$ causes NNS 4.1 CD
63 Increased VBN UV NN due JJ to TO the DT ozone NN hole NN 4.2 CD Biological JJ effects NNS of IN increased VBN UV NN 4.3 CD Public NNP policy NN in IN response NN to TO the DT ozone NN hole NN 5 CD Controversy NN regarding VBG ozone NN science NN and CC policy NN 6 CD Related JJ articles NNS 7 CD External JJ links NNS History NN of IN the DT research NN In IN 1970 CD Prof NNP . . Paul NNP Crutzen NNP pointed VBD out RP the DT possibility NN that IN nitrogen NN oxides NNS from IN fertilizers NNS and CC supersonic JJ aircraft NN might MD deplete VB the DT ozone NN layer NN . .
29 In IN 1974 CD Frank NNP Sherwood NNP Rowland NNP and CC Mario NNP J NNP . . Molina NNP realised VBD that IN when WRB CFCs NNP finally RB break VBP apart RP in IN the DT atmosphere NN and CC release NN chlorine NN atoms NNS they PRP cause VBP ozone NN depletion NN . .
15 These DT three CD scientists NNS received VBD the DT Nobel NNP Prize NNP in IN Chemistry NNP in IN 1995 CD for IN this DT work NN . .
44 They PRP calculated VBD that IN if IN CFC NNP production NN continued VBD to TO increase VB at IN the DT going VBG rate NN of IN 10%/year JJ until IN 1990 CD , , then RB remain VBP steady JJ , , CFCs NNP would MD cause VB a DT global JJ 5 CD to TO 7 CD percent NN ozone NN loss NN by IN 1995 CD and CC 30 CD - - 50 CD % % loss NN by IN 2050 CD . .
52 However RB , , the DT discovery NN of IN the DT Antarctic NNP '' '' ozone NN hole NN '' '' by IN Farman NNP , , Gardiner NNP and CC Shanklin NNP -LRB- -LRB- announced VBN in IN a DT paper NN in IN Nature NNP in IN May NNP 1985 CD -RRB- -RRB- was VBD a DT surprise NN - - chemical JJ reactions NNS on IN PSCs NNS in IN the DT cold JJ Antarctic NNP stratosphere JJ caused VBD faster RBR depletion NN than IN expected VBN - - and CC caused VBD worldwide JJ publicity NN . .
24 Ozone NN depletion NN has VBZ been VBN observed VBN all DT over IN the DT globe NN but CC is VBZ greatest JJS at IN high JJ latitudes NNS -LRB- -LRB- that DT is VBZ , , near IN the DT poles NNS -RRB- -RRB- . .
26 The DT best RBS known VBN example NN is VBZ the DT annual JJ thinning NN of IN the DT ozone NN layer NN over IN Antarctica NNP during IN the DT polar JJ winter NN -LRB- -LRB- see VB ozone NN hole NN section NN below IN -RRB- -RRB- . .
17 Since IN 1981 CD the DT UNEP NNP has VBZ sponsored VBN a DT series NN of IN reports NNS on IN scientific JJ assessment NN of IN ozone NN depletion NN . .
7 The DT most RBS recent JJ is VBZ from IN 2002 CD . .
11 General NNP Releasing NNP CFCs NNP into IN the DT atmosphere NN has VBZ caused VBN ozone NN depletion NN . .
29 Since IN the DT ozone NN layer NN absorbs VBZ UV NN , , this DT would MD be VB expected VBN to TO increase VB surface NN UV NN levels NNS , , which WDT could MD lead VB to TO damage NN , , including VBG increases NNS in IN skin NN cancer NN . .
16 This DT is VBZ the DT reason NN for IN the DT Montreal NNP Protocol NNP on IN Substances NNS that IN Deplete NNP the DT Ozone NN Layer NNP . .
50 Although IN decreases NNS in IN stratospheric JJ ozone NN are VBP well-tied JJ to TO CFC NNP ' ' s POS , , and CC there EX are VBP good JJ theoretical JJ reasons NNS to TO believe VB that IN decreases NNS in IN ozone NN will MD lead VB to TO increases NNS in IN surface NN UV NN , , there EX is VBZ not RB much JJ direct JJ observational JJ evidence NN linking VBG ozone NN depletion NN to TO additional JJ skin NN cancer NN in IN human JJ beings NNS . .
38 Ozone NN in IN the DT Earth NNP ' ' s POS atmosphere NN is VBZ generally RB created VBN by IN ultraviolet NN light NN striking VBG oxygen NN molecules NNS , , which WDT consist VBP of IN two CD oxygen NN atoms NNS -LRB- -LRB- O2 CD -RRB- -RRB- , , creating VBG two CD single JJ oxygen NN atoms NNS , , known VBN as IN atomic JJ oxygen NN . .
16 The DT atomic JJ oxygen NN then RB combines VBZ with IN a DT molecule NN of IN O2 CD to TO create VB ozone NN , , O3 NNP . .
34 The DT ozone NN molecule NN is VBZ also RB unstable JJ and CC when WRB hit VBN by IN ultraviolet NN light NN it PRP splits VBZ into IN a DT molecule NN of IN O2 NNP and CC an DT atom NN of IN atomic JJ oxygen NN , , a DT continuing JJ process NN called VBD the DT ozone-oxygen NN cycle NN . .
15 Ozone NN can MD be VB destroyed VBN by IN atomic JJ chlorine NN , , fluorine NN or CC bromine NN in IN the DT atmosphere NN . .
34 These DT elements NNS are VBP found VBN in IN certain JJ stable JJ compounds NNS , , especially RB chlorofluorocarbons NNS -LRB- -LRB- CFCs NNP -RRB- -RRB- , , which WDT may MD find VB their PRP$ way NN to TO the DT stratosphere JJ and CC there EX be VB liberated VBN by IN the DT action NN of IN ultraviolet NN light NN . .
16 Most JJS importantly RB , , the DT chlorine NN atoms NNS so IN generated JJ destroy NN ozone NN molecules NNS in IN a DT catalytic JJ cycle NN . .
38 In IN this DT cycle NN a DT single JJ chlorine NN atom NN would MD keep VB on IN destroying VBG ozone NN forever RB , , were VBD it PRP not RB for IN reactions NNS that WDT remove VBP chlorine NN atoms NNS from IN this DT cycle NN by IN forming VBG reservoir NN species NNS such JJ as IN hydrochloric JJ acid NN and CC chlorine NN nitrate NN . .
40 The DT reactivation NN of IN atomic JJ chlorine NN from IN these DT reservoir NN species NNS is VBZ normally RB slow VB , , but CC is VBZ enhanced VBN by IN the DT presence NN of IN polar JJ stratospheric JJ clouds NNS which WDT appear VBP during IN Arctic NNP winters NNS , , leading VBG to TO a DT strong JJ seasonal JJ cycle NN in IN ozone NN hole NN formation NN . .
28 Ozone NN depletion NN also RB explains VBZ much RB of IN the DT the DT observed JJ reduction NN in IN stratospheric JJ and CC upper JJ tropospheric JJ temperatures NNS -LRB- -LRB- 1 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . grida NNP . . no/climate/ipcc_tar/wg1/223 CD . . htm NN -RRB- -RRB-
13 -LRB- -LRB- 2 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . giss JJ . . nasa.gov/edu/g JJ wdebate NN \/ / -RRB- -RRB- . .
26 This DT is VBZ because IN the DT reason NN for IN the DT warmth NN of IN the DT stratosphere NN is VBZ absorption IN of IN UV NN radiation NN by IN ozone NN , , hence RB reduced JJ ozone NN leads VBZ to TO cooling VBG . .
27 Some DT stratospheric JJ cooling NN is VBZ also RB predicted VBN from IN increases NNS in IN greenhouse NN gases NNS such JJ as IN CO . 2 CD ; ; however RB the DT ozone-induced JJ cooling NN is VBZ found VBN to TO be VB probably RB dominant JJ . .
14 Observations NNS The DT most RBS pronounced JJ decrease NN in IN ozone NN has VBZ been VBN in IN the DT lower JJR stratosphere NN . .
56 However RB , , the DT ozone NN hole NN is VBZ most RBS usually RB measured VBN not RB in IN terms NNS of IN ozone NN concentrations NNS at IN these DT levels NNS -LRB- -LRB- which WDT are VBP typically RB of IN a DT few JJ parts NNS per IN million CD -RRB- -RRB- but CC by IN reduction NN in IN the DT total NN column NN ozone NN , , above IN a DT point NN on IN the DT earth NN ' ' s POS surface NN , , which WDT is VBZ normally RB expressed VBN in IN Dobson NNP units NNS . .
47 Marked NNP decreases VBZ in IN column NN ozone NN in IN the DT antarctic JJ spring NN and CC early JJ summer NN compared VBN to TO the DT early JJ 1970s NNS and CC before RB have VBP been VBN observed VBN using VBG instruments NNS such JJ as IN the DT Total JJ Ozone NN Mapping VBG Spectrometer NNP -LRB- -LRB- TOMS NNP -RRB- -RRB- -LRB- -LRB- 3 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . atm.ch.cam NN . . ac.uk/tour/part2 CD . . html NN -RRB- -RRB- . .
50 Substantial JJ reductions NNS of IN up RB to TO 70 CD % % in IN the DT ozone NN column NN observed VBN in IN the DT austral JJ -LRB- -LRB- i NNP . . e NN . . southern JJ hemispheric NN -RRB- -RRB- spring NN over IN Antarctica NNP and CC first RB reported VBD in IN 1985 CD -LRB- -LRB- Farman NNP et NNP al JJ 1985 CD -RRB- -RRB- are VBP continuing VBG -LRB- -LRB- 4 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . wmo.ch/web/arep/reports/o3_assess_rep_2002_front_page NN . . html NN -RRB- -RRB- . .
24 Through IN the DT 1990's NNS , , total NN column NN ozone NN in IN September NNP and CC October NNP have VBP continued VBN to TO be VB 40 IN - - 50 CD % % lower JJR than IN pre-ozone-hole JJ values NN . .
69 In IN the DT arctic NN , , declines NNS are VBP greatest JJS in IN winter/spring NN and CC the DT amount NN is VBZ more RBR variable JJ year-to-year JJ than IN in IN the DT Antarctic NNP : : when WRB the DT stratosphere NN is VBZ colder IN the DT losses NNS are VBP gre JJ ater NN , , up RB to TO 30 CD % % In IN mid JJ latitudes NNS it PRP is VBZ probably RB preferable JJ to TO speak VB of IN ozone NN depletion NN rather RB than IN holes NNS ; ; declines NNS are VBP about IN 3 CD % % below IN pre-1980 JJ values NNS for IN 35-60N JJ and CC about IN 6 CD % % for IN 35-60S JJ . .
10 In IN the DT tropics NNS , , there EX are VBP no DT significant JJ trends NNS . .
45 The DT ozone NN hole NN and CC its PRP$ causes NNS The DT cause NN of IN the DT ozone NN holes NNS is VBZ generally RB agreed VBN to TO be VB CFC NNP -LRB- -LRB- Chlorofluorocarbon NN -RRB- -RRB- compounds NNS which WDT break VBP down RP -LRB- -LRB- due JJ to TO ultraviolet JJ light NN -RRB- -RRB- and CC become VB free JJ radicals NNS containing VBG chlorine NN high JJ in IN the DT Earth NNP ' ' s POS atmosphere NN . .
9 These DT radicals NNS then RB break VB down RP the DT ozone NN catalytically NN . .
45 Ozone NN destruction NN due JJ to TO chlorine NN radicals NNS from IN CFCs NNP can MD take VB place NN in IN the DT gas NN phase NN , , but CC occurs VBZ particularly RB rapidly RB on IN the DT surface NN of IN polar JJ stratospheric JJ clouds NNS -LRB- -LRB- PSC NNP -RRB- -RRB- , , which WDT form VBP over IN the DT poles NNS -LRB- -LRB- particularly RB the DT south JJ pole NN -RRB- -RRB- during IN winter NN . .
27 A DT rise NN in IN CFC NNP production NN has VBZ accompanied VBN the DT ozone NN depletion NN and CC a DT plausible JJ chemical NN mechanism NN for IN CFC NNP ' ' s POS role NN in IN ozone NN depletion NN has VBZ been VBN proposed VBN . .
26 As IN a DT result NN , , a DT worldwide JJ ban NN on IN most JJS uses NNS of IN CFCs NNP , , the DT Montreal NNP Protocol NNP , , was VBD signed VBN and CC entered VBD into IN force NN in IN 1989 CD . .
44 The DT photochemical JJ processes NNS involved VBN are VBP complex JJ but CC well RB understood VBN , , with IN UV NN radiation NN being VBG involved VBN in IN both DT the DT natural JJ production NN and CC destruction NN of IN ozone NN , , as RB well RB as IN the DT breakdown NN of IN CFCs NNP into IN free JJ radicals NNS and CC the DT destruction NN of IN ozone NN by IN chlorine NN radicals NNS . .
45 The DT role NN of IN sunlight NN in IN ozone NN depletion NN is VBZ the DT reason NN why WRB the DT Antarctic NNP ozone NN depletion NN is VBZ greatest JJS during IN spring NN ; ; during IN winter NN , , even RB though IN PSCs NNS are VBP at IN their PRP$ most JJS abundant JJ , , there EX is VBZ no DT light NN over IN the DT pole NN to TO drive VB the DT chemical JJ reactions NNS . .
18 CFCs NNS are VBP a DT byproduct NN of IN some DT chemical NN processes NNS , , and CC were VBD also RB used VBN in IN air NN conditioning/cooling VBG units NNS . .
13 They PRP were VBD also RB widely RB used VBN as IN aerosol JJ propellants NNS prior RB to TO the DT 1980s CD . .
26 What WP makes VBZ CFCs NNP so RB effective JJ in IN breaking VBG down IN ozone NN is VBZ that IN one CD CFC NNP radical JJ acts NNS as IN a DT catalyst NN and CC can MD break VB down RP many JJ ozone NN molecules NNS . .
14 Furthermore RB , , these DT radicals NNS stay VBP in IN the DT atmosphere NN for IN a DT very RB long JJ time NN . .
52 Scientists NNS have VBP increasingly RB been VBN able JJ to TO attribute VB the DT observed JJ ozone NN depletion NN to TO the DT increase NN of IN anthropogenic JJ halogen NN compounds NNS from IN CFCs NNP , , by IN the DT use NN of IN complex JJ chemical NN transport NN models NNS and CC their PRP$ validation NN against IN observational JJ data NNS -LRB- -LRB- e NN . . g NN . . SLIMCAT WDT -LRB- -LRB- http://www JJ . . lec.leeds NNS . . ac.uk/~martyn/slimcat NN . . html NN -RRB- -RRB- -RRB- -RRB- . .
49 These DT models NNS work NN by IN combining VBG satellite NN measurements NNS of IN chemical NN concentrations NNS and CC meteorological JJ fields NNS with IN chemical JJ reaction NN rate NN constants NNS obtained VBD in IN lab JJ experiments NNS , , and CC are VBP able JJ to TO identify VB not RB only RB the DT key JJ chemical JJ reactions NNS but CC also RB the DT transport NN processes NNS which WDT bring VBP CFC NNP photolysis NN products NNS into IN contact NN with IN ozone NN . .
42 Increased VBN UV NN due JJ to TO the DT ozone NN hole NN Although IN ozone NN , , O3 NNP , , is VBZ a DT minority NN constituent NN in IN the DT earth NN ' ' s POS atmosphere NN , , it PRP is VBZ responsible JJ for IN most JJS of IN the DT main JJ absorption NN of IN ultraviolet NN -LRB- -LRB- UV NN -RRB- -RRB- radiation NN in IN the DT atmosphere NN . .
24 Correspondingly NNP , , a DT significant JJ decrease NN in IN atmospheric JJ ozone NN could MD be VB expected VBN to TO give VB rise NN to TO significantly RB increased VBN levels NNS of IN UV NN near IN the DT surface NN . .
70 Increases NNS in IN surface NN UV NN due JJ to TO the DT ozone NN hole NN can MD be VB partially RB inferred VBN by IN radiative JJ transfer NN model NN calculations NNS , , but CC cannot MD be VB calculated VBN from IN direct JJ measurements NNS because IN of IN the DT lack NN of IN reliable JJ historical JJ -LRB- -LRB- pre-ozone-hole JJ -RRB- -RRB- surface VBP UV NN data NNS , , although IN more RBR recent JJ surface NN UV NN observation NN measurement NN programmes NNS exist VBP -LRB- -LRB- e JJ . . g NN . . at IN Lauder NNP , , New NNP Zealand NNP -LRB- -LRB- 5 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . niwa.co.nz/services/uvozone NN \/ / -RRB- -RRB- -RRB- -RRB- . .
97 Because IN it PRP is VBZ this DT same JJ UV NN radiation NN that WDT creates VBZ the DT ozone NN in IN the DT ozone NN layer NN from IN O2 CD -LRB- -LRB- regular JJ oxygen NN -RRB- -RRB- in IN the DT first JJ place NN , , a DT reduction NN in IN stratospheric JJ ozone NN would MD actually RB tend VB to TO increase VB photochemical JJ production NN of IN ozone NN at IN lower JJR levels NNS -LRB- -LRB- in IN the DT troposphere NN -RRB- -RRB- , , although IN the DT overall JJ observed JJ trends NNS in IN total NN column NN ozone NN are VBP still RB a DT decrease NN , , largely RB because IN ozone NN produced VBD lower JJR down RP has VBZ a DT naturally RB shorter JJR photochemical JJ lifetime NN , , so IN it PRP is VBZ destroyed VBN before IN the DT concentrations NNS could MD reach VB a DT level NN which WDT would MD compensate VB for IN the DT ozone NN reduction NN higher JJR up IN . .
24 Biological JJ effects NNS of IN increased VBN UV NN The DT main JJ public JJ concern NN regarding VBG the DT ozone NN hole NN has VBZ been VBN the DT effects NNS of IN surface NN UV NN on IN human JJ health NN . .
38 As IN the DT ozone NN hole NN over IN Antarctica NNP has VBZ in IN some DT instances NNS grown VBN so RB large JJ as IN to TO reach VB southern JJ parts NNS of IN Australia NNP and CC New NNP Zealand NNP , , environmentalists NNS have VBP been VBN concerned VBN that IN the DT increase NN in IN surface NN UV NN could MD be VB significant JJ . .
64 UVB NN -LRB- -LRB- the DT higher JJR energy NN UV NN radiation NN absorbed VBN by IN ozone NN -RRB- -RRB- is VBZ generally RB accepted VBN to TO be VB a DT contributory JJ factor NN to TO malignant JJ melanoma NN -LRB- -LRB- skin NN cancer NN -RRB- -RRB- - - for IN example NN one CD study NN showed VBD that IN a DT 10 CD % % increase NN in IN the DT UVB NN was VBD associated VBN with IN a DT 19 CD % % increase NN in IN melanomas NNS for IN men NNS and CC 16 CD % % for IN women NNS -LRB- -LRB- Fears NNS et FW al JJ , , Cancer NNP Res NNP . .
9 2002 CD , , 62 CD -LRB- -LRB- 14 CD -RRB- -RRB- :3992-6 CD -RRB- -RRB- . .
15 So RB far RB , , ozone NN depletion NN in IN most JJS locations NNS has VBZ been VBN typically RB a DT few JJ percent NN . .
28 Were VBD the DT high JJ levels NNS of IN depletion NN seen VBN in IN the DT ozone NN hole NN ever RB to TO be VB common JJ across IN the DT gl NN obe NN , , the DT effects NNS could MD be VB substantially RB more RBR dramatic JJ . .
15 For IN example NN , , recent JJ research NN -LRB- -LRB- 6 CD -RRB- -RRB- -LRB- -LRB- http://sci NN . . newsfactor.com/perl/story/15776 CD . . html NN -RRB- -RRB-
18 has VBZ analyzed VBN a DT widespread JJ extinction NN of IN plankton NN 2 CD million CD years NNS ago IN that IN coincided VBD with IN a DT nearby JJ supernova NN . .
53 Researchers NNS speculate VBP that IN the DT extinction NN was VBD caused VBN by IN a DT significant JJ weakening NN of IN the DT ozone NN layer NN at IN that DT time NN when WRB the DT radiation NN from IN the DT supernova NN produced VBD nitrogen JJ oxides NNS that WDT catalyzed VBD the DT destruction NN of IN ozone NN -LRB- -LRB- plankton NN are VBP particularly RB susceptible JJ to TO effects NNS of IN UV NN light NN , , and CC are VBP vitally RB important JJ to TO marine JJ food-webs NNS -RRB- -RRB- . .
24 Aside RB from IN the DT direct JJ effect NN of IN ultraviolet NN radiation NN on IN organisms NNS , , increased VBD surface NN UV NN leads VBZ to TO increased VB tropospheric JJ ozone NN , , as IN noted VBN above IN . .
26 Paradoxically RB , , at IN ground-level NN increased VBN ozone NN is VBZ generally RB recognised VBN to TO be VB a DT health NN risk NN , , as IN ozone NN is VBZ toxic JJ due JJ to TO its PRP$ strong JJ oxidant NN properties NNS . .
31 Public NNP policy NN in IN response NN to TO the DT ozone NN hole NN Environmentalists NNS assert VBP that IN the DT CFCs NNS have VBP caused VBN so RB much JJ damage NN to TO the DT ozone NN layer NN that IN the DT use NN of IN CFCs NNP should MD be VB banned VBN . .
35 The DT full JJ extent NN of IN this DT damage NN CFCs NNS have VBP caused VBN is VBZ not RB known VBN and CC will MD not RB be VB known VBN for IN decades NNS ; ; however RB marked VBD decreases NNS in IN column NN ozone NN have VBP already RB been VBN observed VBN -LRB- -LRB- see VB above NN -RRB- -RRB- . .
15 In IN 1987 CD , , the DT Montreal NNP Protocol NNP was VBD signed VBN , , controlling VBG the DT emissions NNS of IN CFCs NNP . .
25 To TO some DT extent NN , , their PRP$ role NN has VBZ been VBN replaced VBN by IN the DT less JJR damaging JJ hydro-chloro-fluoro-carbons NNS -LRB- -LRB- HCFCs NNP -RRB- -RRB- , , although IN concerns NNS remain VBP regarding VBG HCFCs NNS also RB . .
44 Controversy NN regarding VBG ozone NN science NN and CC policy NN Any DT counter-measures NNS which WDT have VBP a DT negative JJ economic JJ impact NN will MD remain VB a DT controversial JJ issue NN due JJ to TO the DT strong JJ economic JJ interests NNS involved VBN , , with IN key JJ questions NNS regarding VBG whether IN the DT scientific JJ understanding NN is VBZ strong JJ enough JJ to TO warrant VB the DT proposed JJ countermeasures NNS . .
36 In IN this DT context NN it PRP is VBZ worth JJ noting VBG that IN it PRP is VBZ commonly RB believed VBN that IN one CD reason NN for IN the DT relative JJ ease NN of IN introduction NN of IN the DT Montreal NNP protocol NN was VBD the DT availability NN of IN CFC NNP replacements NNS at IN little JJ extra JJ cost NN . .
40 The DT consensus NN amongst IN most JJS atmospheric JJ physicists NNS and CC chemists NNS is VBZ that IN the DT scientific JJ understanding NN has VBZ now RB reached VBN a DT level NN where WRB countermeasures NNS to TO control VB CFC NNP emissions NNS are VBP justified VBN , , although IN the DT decision NN is VBZ ultimately RB one CD for IN policy NN - - makers NNS and CC society NN . .
32 Despite IN this DT general JJ consensus NN , , the DT science NN behind IN ozone NN depletion NN remains VBZ complex JJ , , and CC some DT who WP oppose VBP the DT enforcement NN of IN countermeasures NNS point NN to TO some DT of IN the DT difficulties NNS experienced VBN in IN these DT studies NNS . .
14 For IN example NN : : Initial JJ studies NNS of IN the DT ozone NN hole NN were VBD hampered VBN with IN difficulties NNS . .
55 Most RBS notably RB , , satellite NN measurements NNS showing VBG massive JJ depletion NN of IN ozone NN around IN the DT south NN pole NN were VBD initially RB rejected VBN as IN unreasonable JJ by IN data NNS quality NN control NN algorithms NNS ; ; the DT ozone NN hole NN was VBD only RB detected VBN in IN satellite NN data NNS when WRB the DT raw JJ data NN was VBD reprocessed VBN with IN modified VBN processing NN algorithms NNS following VBG evidence NN of IN an DT ozone NN hole NN in IN in IN situ NN observations NNS . .
32 This DT , , however RB , , was VBD simply RB a DT problem NN with IN the DT data-processing NN algorithms NNS for IN the DT satellite NN data NNS and CC has VBZ long RB been VBN corrected VBN , , and CC so RB has VBZ no DT bearing NN on IN the DT current JJ situation NN . .
8 Predictions NNS of IN ozone NN remains VBZ a DT difficult JJ science NN . .
27 The DT World NNP Meteorological NNP Organization NNP Global NNP Ozone NNP Research NNP and CC Monitoring NNP Project NNP - - Report VB No JJ . . 44 CD -LRB- -LRB- http://www JJ . . al NN . . noaa.gov/WWWHD/Pubdocs/Assessment98/executive-summary JJ . . html JJ # # A , -RRB- -RRB- , ,
35 which WDT on IN balance NN comes VBZ out RP strongly RB in IN favour NN of IN the DT Montreal NNP protocol NN , , nonetheless RB notes VBZ that IN projections NNS of IN ozone NN loss NN for IN the DT 1994-1997 CD period NN made VBN in IN the DT UNEP NNP 1994 CD Assessment NNP had VBD been VBN an DT overestimate NN . .
37 Although IN increased VBN UVB NN has VBZ been VBN shown VBN to TO constitute VB a DT melanoma NN risk NN -LRB- -LRB- see VB above NN -RRB- -RRB- , , it PRP has VBZ been VBN difficult JJ for IN statistical JJ studies NNS to TO establish VB a DT direct JJ link NN between IN ozone NN depletion NN and CC increased VBN rates NNS of IN melanoma NN . .
39 Although IN melanomas NNS did VBD increase VB significantly RB during IN the DT period NN 1970-1990 CD , , it PRP is VBZ difficult JJ to TO separate VB reliably RB the DT effect NN of IN ozone NN depletion NN from IN the DT effect NN of IN changes NNS in IN lifestyle JJ factors NNS -LRB- -LRB- e JJ . . g NN . . time NN spent VBD outdoors NNS -RRB- -RRB- . .
45 Some DT atmospheric JJ scientists NNS -LRB- -LRB- for IN instance NN Fred NNP Singer NNP , , founder NN of IN SEPP NNP and CC also RB a DT global JJ warming NN skeptic JJ -RRB- -RRB- and CC industry-sponsored JJ advocacy NN groups NNS question NN or CC completely RB deny VB a DT link NN between IN CFCs NNP and CC ozone NN depletion NN -LRB- -LRB- 7 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . sepp.org/ozone/ozonefranklin NN . . html NN -RRB- -RRB- . .
47 It PRP is VBZ common JJ to TO see VB completely RB nonsensical JJ arguments NNS put VBP forward RB to TO prove VB that IN CFCs NNP cannot MD cause VB ozone NN depletion NN - - for IN example NN , , that IN they PRP are VBP heavier JJR than IN air NN and CC so RB cannot MD reach VB the DT stratosphere JJ -LRB- -LRB- 8 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . junkscience NN . . com/may99/freon NN . . htm NN -RRB- -RRB- . .
45 CFCs NNS are VBP heavier JJR than IN air NN , , but CC just RB like IN argon NN , , krypton NN and CC other JJ heavy JJ gases NNS with IN a DT long JJ lifetime NN they PRP are VBP uniformly RB distributed VBN throughout IN the DT turbosphere NN and CC reach VB the DT upper JJ atmosphere NN -LRB- -LRB- 9 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . so.wustl NN . . edu/science_outreach/curriculum/ozone/info/stratosphere/myths/heavier NN . . html NN -RRB- -RRB- . .
36 Related JJ articles NNS ozone NN ozone NN layer NN ozone-oxygen NN cycle NN Montreal NNP Protocol NNP Scientific NNP assessment NN of IN ozone NN depletion NN CFC NNP melanoma NN , , skin NN cancer NN greenhouse NN gas NN ultraviolet NN External NNP links VBZ NOAA NNP Stratospheric NNP Ozone NNP Webpage NNP -LRB- -LRB- http://www NN . . ozonelayer NN . . noaa.gov NN \/ / -RRB- -RRB-
20 Stratospheric JJ ozone NN depletion NN -LRB- -LRB- Antarctic NNP , , Arctic NNP , , and CC global JJ -RRB- -RRB- -LRB- -LRB- http://www JJ . . al NN . . noaa.gov/WWWHD/Pubdocs/StratO3 JJ . . html NN -RRB- -RRB-
17 at IN NOAA NNP Ozone IN Depletion NNP And CC Global NNP Environmental NNP Change NNP -LRB- -LRB- http://www JJ . . ciesin NN . . org/TG/OZ/oz-home NN . . html NN -RRB- -RRB-
19 at IN Columbia NNP University NNP Scientific NNP Assessment NNP of IN Ozone NNP Depletion NNP : : 1998 CD -LRB- -LRB- http://www JJ . . al NN . . noaa.gov/WWWHD/pubdocs/Assessment98/faq JJ . . html NN -RRB- -RRB-
15 - - by IN WMO NNP , , UNEP NNP , , NOAA NNP Ozone NNP FAQ NNP -LRB- -LRB- http://www JJ . . faqs.org/faqs/ozone-depletion NN \/ / -RRB- -RRB-
12 Methyl NNP Bromide NNP Blues NNPS -LRB- -LRB- http://www JJ . . greens NNS . . org/s-r/32/32-15 IN . . html NN -RRB- -RRB-
15 Five CD Scientific NNP Questions NNPS On IN The DT Cf NNP c-Ozone NN Issue NN -LRB- -LRB- http://www JJ . . sepp.org/ozone/5questions NNS . . html . -RRB- -RRB-
24 by IN S NNP . . Fred NNP Singer NNP A DT Critique NN of IN the DT UN NNP Scientific NNP Assessment NNP of IN Ozone NNP Depletion NNP : : 1994 CD -LRB- -LRB- http://www JJ . . sepp.org/ozone/ozassm NN . . html NN -RRB- -RRB-
21 by IN S NNP . . Fred NNP Singer NNP The DT Ozone-CFC NNP Debacle NNP : : Hasty NNP Action NNP , , Shaky NNP Science NNP -LRB- -LRB- http://www JJ . . sepp.org/ozone/ozonefranklin NN . . html NN -RRB- -RRB-
19 by IN S NNP . . Fred NNP Singer NNP The DT Skeptics NNP vs IN . . the DT Ozone NN Hole NNP -LRB- -LRB- http://www JJ . . wunderground.com/education/ozone_skeptics NNS . . asp VBP -RRB- -RRB-
18 WMO/UNE NNP P NNP Scientific NNP Assessment NNP of IN Ozone NNP Depletion NNP : : 1998 CD -LRB- -LRB- http://www JJ . . al NN . . noaa.gov/WWWHD/Pubdocs/Assessment98 CD . . html NN -RRB- -RRB-
11 The DT Ozone NN Tour NNP -LRB- -LRB- http://www JJ . . atm.ch.cam NN . . ac.uk/tour NN \/ / -RRB- -RRB-
19 at IN the DT Centre NNP for IN Atmospheric NNP Science NNP , , University NNP of IN Cambridge NNP The DT Ozone NNP FAQ NNP -LRB- -LRB- http://www JJ . . faqs.org/faqs/ozone-depletion NN \/ / -RRB- -RRB-
25 - - a DT superb JJ resource NN -LRB- -LRB- but CC last JJ updated VBN in IN 1997 CD -RRB- -RRB- The DT Politics NNS of IN Methyl NNP Bromide NNP -LRB- -LRB- http://www NN . . greens VBZ . . org/s-r/32/32-15 CD . . html NN -RRB- -RRB-
15 Jon NNP Shanklin NNP ' ' s POS Ozone NN pages NNS -LRB- -LRB- http://www NN . . antarctica NNP . . ac.uk/met/jds/ozone NNP \/ / -RRB- -RRB- , ,
13 including VBG a DT pamphlet NN -LRB- -LRB- http://www JJ . . antarctica NNP . . ac.uk/met/jds/ozone/ozpamw7 CD . . htm NN -RRB- -RRB- . .
9 Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Ozone_depletion NN '' ''
40 Caffeine NNP molecular JJ structure NN Caffeine NNP is VBZ a DT chemical NN compound NN found VBN naturally RB in IN such JJ foods NNS as IN coffee NN beans NNS , , tea NN , , cacao VBD beans NNS -LRB- -LRB- chocolate NN , , but CC in IN much RB smaller JJR amounts NNS -RRB- -RRB- , , kola NN nuts NNS , , Yerba NNP mate NN , , and CC guarana NN . .
27 It PRP is VBZ well RB known VBN for IN its PRP$ characteristic JJ , , intensely RB bitter JJ taste NN , , and CC as IN a DT stimulant NN of IN the DT central JJ nervous JJ system NN , , heart NN , , and CC respiration NN . .
6 It PRP is VBZ also RB a DT diuretic JJ . .
23 It PRP is VBZ added VBN to TO some DT soft JJ drinks NNS such JJ as IN colas NNS and CC Mountain NNP Dew NNP . . 1 CD Chemical NNP properties NNS 2 CD Physical NNP properties NNS 3 CD Sources NNS 3.1 CD
53 Chocolate NNP 3.2 CD Coffee NNP 3.3 CD Teas NNP and CC other JJ infusions NNS 3.4 CD Other JJ sources NNS 3.5 CD Equivalents NNS 200 CD mg NN of IN Caffeine NNP 4 CD Metabolism NNP and CC toxicology NN 5 CD Abuse NNP and CC addiction NN 6 CD History JJ 7 CD References NNS 8 CD External NNP links NNS Chemical NNP properties NNS Caffeine NNP is VBZ an DT alkaloid JJ of IN the DT methylxanthine NN family NN , , which WDT also RB includes VBZ the DT similar JJ compounds NNS theophylline NN and CC theobromine NN . .
12 In IN its PRP$ pure JJ state NN it PRP is VBZ an DT intensely RB bitter JJ white JJ powder NN . .
21 Its PRP$ chemical JJ formula NN is VBZ C8H10N4O2 NNP , , its PRP$ systematic JJ name NN is VBZ 1,3,7-trimethylxanthine CD or CC 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione CD , , and CC its PRP$ structure NN is VBZ shown VBN above IN . .
18 Physical JJ properties NNS Pure NNP caffeine NN occurs VBZ as IN odorless JJ , , white JJ , , fleecy NN masses NNS , , glistening VBG needles NNS or CC powder NN . .
66 Boiling NNP point NN : : 178 CD C NNP -LRB- -LRB- sublimes NNS -RRB- -RRB- Melting NNP point NN : : 238 CD C NNP Specific JJ gravity NN : : 1.2 CD Volatility NN : : 0.5 CD % % Vapor IN pressure NN : : 760 CD mm CD Hg NNP @ @ 178 CD C NNP pH NNS : : 6.9 CD -LRB- -LRB- 1 CD % % solution NN -RRB- -RRB- Solubility NN in IN water NN : : 2.17 CD % % Vapor IN density NN : : 6.7 CD Molecular NNP weight NN : : 194.19 CD Sources NNS The DT main JJ source NN of IN caffeine NN in IN food NN industry NN are VBP the DT coffee NN beans NNS . .
7 The DT caffeine NN content NN can MD vary VB significantly RB . .
17 In IN 2004 CD some DT trees NNS were VBD found VBN in IN Ethiopia NN that WDT contain VBP 15 CD times NNS less RBR caffeine JJ than IN average JJ . .
17 Beans NNP from IN such JJ trees NNS may MD be VB used VBN in IN the DT future NN to TO produce VB better JJR quality NN decaffeinated VBD coffee NN . .
34 One CD dose NN of IN caffeine NN is VBZ generally RB considered VBN to TO be VB 100 CD mg NN , , delivered VBN by IN one CD 5 CD fl NN oz NN \/ / 150 CD ml JJ cup NN of IN drip NN coffee NN or CC one CD -LRB- -LRB- or CC one-half NN -RRB- -RRB- caffeine NN tablet NN . .
43 Real-world NNP coffee NN varies NNS considerably RB in IN caffeine JJ content NN per IN cup NN , , from IN about IN 75 CD to TO 250 CD mg NN . . Black NNP tea NN contains VBZ somewhat RB less JJR caffeine NN per IN serving VBG than IN coffee NN , , depending VBG on IN the DT strength NN of IN the DT brew NN , , and CC green JJ tea NN contains VBZ significantly RB less JJR . .
45 Colas NNP also RB typically RB contain VBP less JJR than IN coffee NN , , but CC some DT '' '' energy NN '' '' colas NNS and CC similar JJ drinks NNS can MD have VB considerably RB more RBR -LRB- -LRB- the DT caffeine NN strength NN of IN soft JJ drinks NNS being VBG controlled VBN entirely RB by IN the DT manufacturer NN , , with IN high JJ caffeine NN content NN a DT popular JJ marketing NN feature NN -RRB- -RRB- . .
24 The DT mateine NN described VBD in IN some DT literature NN as IN the DT primary JJ psychoactive JJ constituent NN of IN yerba NNP mate NN is VBZ also RB generally RB considered VBN to TO be VB identical JJ to TO caffeine NN . .
34 Tisanes NNPS -LRB- -LRB- i FW . . e NN . . Herbal NNP teas NNS -RRB- -RRB- , , depends VBZ on IN the DT herb NN , , e.g NN . . Chamomile NNP and CC Rooibos NNP teas NNS have VBP no DT caffeine NN while IN Yerba NNP mate NN and CC Guarana NNP do VBP contain VB varying VBG quantities NNS . .
21 Many JJ tea NN drinkers NNS characterise VBP herbal JJ tea NN simply RB as IN that IN which NNP , , unlike IN black JJ or CC green JJ tea NN , , contains VBZ no DT caffeine NN . .
12 Other JJ sources NNS Energy RB drink VB - - 10 CD mg/floz NN -LRB- -LRB- 340 CD mg/litre NNP -RRB- -RRB- . .
10 Some DT countries NNS limit VBP the DT caffeine NN content NN at IN 135 CD mg/litre NNP . .
19 This DT includes VBZ caffeine NN from IN any DT source NN -LRB- -LRB- including VBG guarana NN , , which WDT is VBZ often RB found VBN in IN energy NN drinks NNS -RRB- -RRB- . .
11 In IN many JJ countries NNS , , caffeine NN is VBZ classified VBN as IN a DT flavouring NN . .
16 Metabolism NN and CC toxicology NN Caffeine NNP is VBZ thought VBN to TO act VB on IN the DT brain NN by IN blocking VBG adenosine NN receptors NNS . .
27 Adenosine NNP , , when WRB bound VBN to TO receptors NNS of IN nerve NN cells NNS , , slows VBZ down RP nerve NN cell NN activity NN ; ; this DT happ JJ ens NNS , , among IN other JJ times NNS , , during IN sleep NN . .
37 The DT caffeine NN molecule NN , , being VBG similar JJ to TO adenosine NN , , binds NNS to TO the DT same JJ receptors NNS but CC does VBZ n't RB cause VB the DT cells NNS to TO slow VB down RB ; ; instead RB , , the DT caffeine NN blocks NNS the DT receptors NNS and CC thereby RB the DT adenosine JJ action NN . .
54 The DT resulting VBG increased VBN nerve NN activity NN causes VBZ the DT release NN of IN the DT hormone NN epinephrine NN , , which WDT in IN turn NN leads VBZ to TO several JJ effects NNS such JJ as IN higher JJR heart NN rate NN , , increased VBD blood NN pressure NN , , increased VBD blood NN flow NN to TO muscles NNS , , decreased VBD blood NN flow NN to TO the DT skin NN and CC inner JJ organs NNS , , and CC release NN of IN glucose NN by IN the DT liver NN . .
20 In IN addition NN , , caffeine NN , , similar JJ to TO amphetamines NNS , , increases VBZ the DT levels NNS of IN the DT neurotransmitter NN dopamine NN in IN the DT brain NN . .
24 Caffeine NNP is VBZ quickly RB and CC completely RB removed VBN from IN the DT brain NN and CC , , unlike IN other JJ CNS NNS stimulants NNS or CC alcohol NN , , its PRP$ effects NNS are VBP short JJ lived VBN . .
28 In IN many JJ people NNS , , caffeine NN does VBZ not RB negatively RB affect VB concentration NN or CC higher JJR mental JJ functions NNS , , and CC hence RB caffeinated JJ drinks NNS are VBP often RB consumed VBN in IN the DT course NN of IN work NN . .
9 Continued NNP consumption NN of IN caffeine NN can MD lead VB to TO tolerance NN . .
25 Upon IN withdrawal NN , , the DT body NN becomes VBZ oversensitive JJ to TO adenosine VB , , causing VBG the DT blood NN pressure NN to TO drop VB dramatically RB , , leading VBG to TO headache NN and CC other JJ symptoms NNS . .
27 Recent JJ studies NNS suggest VBP that IN caffeine JJ intake NN -LRB- -LRB- in IN coffee NN -RRB- -RRB- may MD decrease VB the DT risk NN of IN developing VBG Parkinson NNP ' ' s POS disease NN , , but CC additional JJ study NN is VBZ needed VBN . .
9 Too RB much JJ caffeine NN can MD lead VB to TO caffeine JJ intoxication NN . .
23 The DT symptoms NNS of IN this DT disorder NN are VBP restlessness NN , , nervousness NN , , excitement NN , , insomnia NN , , flushed JJ face NN , , diuresis NN , , and CC gastrointestial JJ complaints NNS . .
15 They PRP can MD occur VB in IN some DT people NNS after IN as RB little JJ as IN 250 CD mg NN per IN day NN . .
28 More JJR than IN 1 CD g NN per IN day NN may MD result VB in IN muscle NN twitching NN , , rambling VBG flow NN of IN thought VBN and CC speech NN , , cardiac JJ arrhythmia NN or CC tachycardia NN , , and CC psychomotor NN agitation NN . .
15 Caffeine NNP intoxication NNP can MD lead VB to TO symptoms NNS similar JJ to TO panic NN disorder NN and CC generalized VBN anxiety NN disorder NN . .
24 The DT LD50 NNP is VBZ estimated VBN to TO be VB about IN 192 CD mg/kg NN of IN body NN mass NN , , or CC about RB 72 CD cups NNS of IN coffee NN for IN an DT average JJ adult NN . .
35 While IN safe JJ for IN humans NNS , , caffeine NN and CC its PRP$ related JJ compounds NNS theobromine NN and CC theophylline NN are VBP considerably RB more JJR toxic JJ to TO some DT other JJ animals NNS such JJ as IN dogs NNS and CC horses NNS , , due JJ to TO differences NNS in IN liver NN meta NN bolism NN . .
56 A DT fascinating JJ recent JJ finding NN is VBZ that IN intake NN of IN caffeine NN can MD up RP to TO halve VB a DT patient NN ' ' s POS risk NN of IN diabetes NNS mellitus NN type NN 2 CD . . While IN this DT was VBD originally RB noticed VBN in IN patients NNS who WP consumed VBD high JJ amounts NNS -LRB- -LRB- 7 CD cups NNS a DT day NN -RRB- -RRB- , , the DT relationship NN has VBZ now RB been VBN shown VBN to TO be VB linear JJ -LRB- -LRB- Salazar-Martinez NNP 2004 CD -RRB- -RRB- . .
18 Abuse NNP and CC addiction NN Caffeine NNP , , in IN its PRP$ many JJ forms NNS , , has VBZ been VBN used VBN for IN its PRP$ stimulating JJ effects NNS . .
25 In IN modern JJ times NNS , , though RB , , the DT substance NN can MD be VB produced VBN in IN much RB higher JJR quantities NNS , , and CC has VBZ found VBN its PRP$ way NN into IN many JJ products NNS . .
14 Purer NNP forms NNS , , such JJ as IN those DT in IN caffeine JJ pills NNS , , are VBP available JJ easily RB . .
21 These DT pills NNS are VBP often RB used VBN by IN college NN students NNS and CC graveyard JJ shift NN workers NNS to TO last VB an DT entire JJ night NN with IN no DT sleep NN . .
25 Caffeine JJ pills NNS have VBP been VBN under IN media NNS fire NN for IN recent JJ and CC past JJ deaths NNS of IN students NNS , , usually RB take VBP on IN the DT form NN of IN a DT caffeine NN overdose NN . .
15 One CD such JJ example NN of IN this DT was VBD the DT death NN North NNP Carolina NNP student NN , , Jason NNP Allen NNP . .
19 He PRP swallowed VBD a DT total NN of IN 90 CD such JJ pills NNS , , which WDT is VBZ the DT equivalent NN of IN 250 CD cups NNS of IN coffee NN . .
19 One CD dangerous JJ form NN of IN caffiene JJ use NN is VBZ to TO stay VB alert JJ when WRB one CD is VBZ under IN the DT influence NN of IN alcohol NN . .
16 This DT tricks VBZ one CD into IN thinking VBG one CD is VBZ more RBR alert JJ than IN what WP is VBZ actually RB the DT case NN . .
19 When WRB such JJ persons NNS take VBP part NN in IN dangerous JJ tasks NNS , , like IN driving VBG , , etc FW . . it PRP results VBZ in IN accidents NNS . .
14 History JJ Caffeine NNP was VBD isolated VBN by IN the DT German JJ chemist NN Friedrich NNP Ferdinand NNP Runge NNP in IN 1819 CD . .
23 According VBG to TO the DT legend NN , , he PRP did VBD this DT at IN the DT instigation NN of IN Johann NNP Wolfgang NNP von NNP Goethe NNP -LRB- -LRB- Weinberg NNP & & Bealer NNP 2001 CD -RRB- -RRB- . .
32 References NNS Salazar-Martinez NNP E NNP , , Willet NNP WC NNP , , Ascherio NNP A NNP , , Manson NNP JE NNP , , Leitzmann NNP MF NNP , , Stampfer NNP MJ NNP , , Hu NNP FB NNP . . Coffee NNP consumption NN and CC risk VB for IN type NN 2 CD diabetes NN mellitus NN . .
7 Ann NNP Intern NNP Med NNP 2004 CD ; ; 140:1-8 CD . .
6 Weinberg NNP BA NNP , , Bealer NNP BK NNP . .
5 The DT world NN of IN caffeine NN . .
9 New NNP York NNP & & London NNP : : Routledge NNP , , 2001 CD . .
15 External NNP links NNS Caffeine NNP Content NNP of IN Foods NNP -LRB- -LRB- http://www JJ . . cspinet NN . . org/new/cafchart NN . . htm NN -RRB- -RRB-
9 Caffeine NNP Intoxication NNP -LRB- -LRB- http://www JJ . . digitalnaturopath.com/cond/C569985 CD . . html NN -RRB- -RRB-
11 Caffeine NNP Intoxication NNP -LRB- -LRB- http://www JJ . . drowning NN . . com/caffeine NN . . html NN -RRB- -RRB-
11 Caffeine NNP Health NNP -LRB- -LRB- http://www JJ . . coffeeforums.com/viewforum NN . . php NN ? ? f=4 NNS -RRB- -RRB-
14 Description NN of IN the DT Yerba NNP Mate NNP -LRB- -LRB- http://platense NN . . dyn NN . . dhs NNS . . org/personal/argentina/mate_desc.htm . -RRB- -RRB-
6 Is VBZ Caffeine NNP a DT Health NNP Hazard NNP ? ?
7 -LRB- -LRB- http://www JJ . . benbest.com/health/caffeine NN . . html NN -RRB- -RRB-
6 Why WRB do VBP plants NNS make VB caffeine NN ? ?
8 -LRB- -LRB- http://www JJ . . thenakedscientists.com/html/columnists/dalyacolum NN n2 CD . . htm NN -RRB- -RRB-
14 Stimulants NNS -LRB- -LRB- edit NN -LRB- -LRB- http://en JJ . . wikipedia NNP . . org/w/wiki NNP . . phtml NNP ? ? title=Template:Stimulants&action=edit NN -RRB- -RRB-
23 -RRB- -RRB- -LRB- -LRB- Caffeine NNP -RRB- -RRB- -LRB- -LRB- Nicotine NNP -RRB- -RRB- Sympathomimetic NNP amines VBZ -LRB- -LRB- edit NN -LRB- -LRB- http://en JJ . . wikipedia NNP . . org/w/wiki NNP . . phtml NNP ? ? title=Template:S NNS ympathomimetic_amines&action=edit NN -RRB- -RRB-
60 -RRB- -RRB- -LRB- -LRB- Cathinone NNP -RRB- -RRB- -LRB- -LRB- Chlorphentermine NNP -RRB- -RRB- -LRB- -LRB- Cocaine NNP -RRB- -RRB- -LRB- -LRB- Diethylpropion NNP -RRB- -RRB- -LRB- -LRB- Ephedrine NNP -RRB- -RRB- -LRB- -LRB- Fenfluramine NNP -RRB- -RRB- -LRB- -LRB- Fen-phen NNP -RRB- -RRB- -LRB- -LRB- Mazindol NNP -RRB- -RRB- -LRB- -LRB- Methcathinone NNP -RRB- -RRB- -LRB- -LRB- Methylphenidate NNP -RRB- -RRB- -LRB- -LRB- Pemoline NNP -RRB- -RRB- -LRB- -LRB- Phendimetrazine NNP -RRB- -RRB- -LRB- -LRB- Phenmetrazine NNP -RRB- -RRB- -LRB- -LRB- Phentermine NNP -RRB- -RRB- -LRB- -LRB- Pseudoephedrine NNP -RRB- -RRB- Amphetamines NNP -LRB- -LRB- edit NN -LRB- -LRB- http://en JJ . . wikipedia NNP . . org/w/wiki NNP . . phtml NNP ? ? title=Template:Amphetamines&action=edit NN -RRB- -RRB-
48 -RRB- -RRB- -LRB- -LRB- Amphetamine NNP -RRB- -RRB- -LRB- -LRB- Benzphetamine NNP -RRB- -RRB- -LRB- -LRB- Dexamphetamine NNP -RRB- -RRB- -LRB- -LRB- MDMA NNP -RRB- -RRB- -LRB- -LRB- Methamphetamine NNP -RRB- -RRB- -LRB- -LRB- Paramethoxyamphetamine NNP -RRB- -RRB- This DT article NN is VBZ part NN of IN the DT Wikiproject NNP on IN Drugs NNP , , which WDT is VBZ an DT attempt NN to TO facilitate VB the DT categorization NN and CC creation NN of IN accurate JJ and CC formal JJ drug-related JJ articles NNS on IN Wikipedia NNP . .
27 If IN you PRP are VBP interested JJ in IN editing NN this DT article NN , , please VB see VB its PRP$ talk NN page NN and CC ensure VB your PRP$ edits NNS are VBP consistent JJ with IN the DT goals NNS of IN the DT project NN . .
9 Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Caffeine NNP '' ''
12 Categories NNS : : Alkaloids NNP |  Heterocyclic NNP bases NNS |  Ketones NNP |  Purines NNP |  Stimulants Stimulants
33 The DT principal JJ natural JJ phenomena NNS that WDT contribute VBP acid-producing NN gases NNS to TO the DT atmosphere NN are VBP emissions NNS from IN volcanoes NNS and CC from IN biological JJ processes NNS that WDT occur VBP on IN the DT land NN , , in IN wetlands NNS , , and CC in IN the DT oceans NNS . .
22 The DT effects NNS of IN acidic JJ deposits NNS have VBP been VBN detected VBN in IN glacial JJ ice NN thousands NNS of IN years NNS old JJ in IN remote JJ parts NNS of IN the DT globe NN . .
12 Principal NNP human JJ sources NNS are VBP industrial JJ and CC power-generating JJ plants NNS and CC transportation NN vehicles NNS . .
20 The DT gases NNS may MD be VB carried VBN hundreds NNS of IN miles NNS in IN the DT atmosphere NN before IN they PRP are VBP converted VBN to TO acids NNS and CC deposited VBD . .
20 Industrial NNP acid NN rain NN is VBZ a DT substantial JJ problem NN in IN China NNP , , Eastern NNP Europe NNP , , Russia NNP and CC areas NNS down-wind NN from IN them PRP . .
12 These DT areas NNS all DT burn VBP sulfur-containing NN coal NN to TO generate VB heat NN and CC electricity NN . .
15 Acid JJ rain NN is VBZ defined VBN as IN rain NN with IN a DT pH NN of IN below IN 4.0 CD - - 4.5 CD . .
14 Normal JJ rain NN has VBZ a DT pH NN of IN about RB 5.6 CD , , which WDT is VBZ slightly RB acidic VBN . .
16 This DT natural JJ acidity NN is VBZ caused VBN by IN dissolved JJ carbon NN dioxide NN dissociating VBG to TO form VB weak JJ carbonic JJ acid NN . .
30 ' ' A DT cid JJ rain NN ' ' is VBZ caused VBN by IN sulfur NN from IN impurities NNS in IN fossil JJ fuels NNS and CC nitrogen NN from IN the DT air NN combining NN with IN oxygen NN to TO form VB sulfur NN and CC nitrogen NN diox NN ides NNS . .
24 These DT diffuse NN into IN the DT atmosphere NN and CC react VB with IN water NN to TO form VB sulfuric NN and CC nitric JJ acids NNS which WDT are VBP soluble JJ and CC fall VB with IN the DT rain NN . .
7 Some DT hydrochloric JJ acid NN is VBZ also RB formed VBN . .
31 A DT possible JJ reaction NN for IN the DT production NN of IN acid NN rain NN is VBZ as IN follows VBZ : : Evidence NN for IN an DT increase NN in IN the DT levels NNS of IN acid NN rain NN comes VBZ from IN analysing VBG layers NNS of IN glacial JJ ice NN . .
36 These DT show VB a DT sudden JJ increase NN in IN pH NNS from IN the DT start NN of IN the DT industrial JJ revolution NN of IN 6 CD to TO 4.5 CD or CC 4 CD . . Other JJ information NN has VBZ been VBN gathered VBN from IN studying VBG organisms NNS known VBN as IN diatoms NNS which WDT inhabit VBP ponds NNS . .
17 Over IN the DT years NNS these DT die VBP and CC are VBP deposited VBN in IN layers NNS of IN sediment NN on IN the DT lakes NNS bottom NN . .
29 Diatoms NNP thrive NN in IN certain JJ pHs NNS , , so IN the DT numbers NNS of IN diatoms NNS found VBN in IN layers NNS of IN increasing VBG depth NN give VBP an DT indication NN of IN the DT change NN in IN pH NNS over IN the DT years NNS . .
17 Since IN the DT industrial JJ revolution NN , , emissions NNS of IN sulfur NN and CC nitrogen NN oxides NNS to TO the DT atmosphere NN have VBP increased VBN . .
22 Industrial NNP and CC energy-generating NN facilities NNS that WDT burn VBP fossil JJ fuels NNS , , primarily RB coal NN , , are VBP the DT principal JJ sources NNS of IN increased VBN sulfur NN ox NN ides NNS . .
20 Occasional NNP pH , readings NNS of IN well RB below IN 2.4 CD -LRB- -LRB- the DT acidity NN of IN vinegar NN -RRB- -RRB- have VBP been VBN reported VBN in IN industrialized VBN areas NNS . .
18 These DT sources NNS , , plus CC the DT transportation NN sector NN , , are VBP the DT major JJ originators NNS of IN increased VBN nitrogen NN ox NN ides NNS . .
21 The DT problem NN of IN acid NN rain NN not RB only RB has VBZ increased VBN with IN population NN and CC industrial JJ growth NN , , it PRP has VBZ become VBN more RBR widespread JJ . .
25 The DT use NN of IN tall JJ smokestacks NNS to TO reduce VB local JJ pollution NN has VBZ contributed VBN to TO the DT spread NN of IN acid NN rain NN by IN releasing VBG gases NNS into IN regional JJ atmospheric JJ circulation NN . .
27 Often RB deposition NN occurs VBZ a DT considerable JJ distance NN from IN its PRP$ formation NN , , with IN mountainous JJ regions NNS tending VBG to TO receive VB the DT most RBS -LRB- -LRB- simply RB because IN of IN their PRP$ higher JJR rainfall NN -RRB- -RRB- . .
25 An DT example NN of IN this DT effect NN is VBZ the DT frequent JJ high JJ pH NNS of IN rain NN which WDT falls VBZ in IN Scandinavia NNP compared VBN to TO the DT oxide NN levels NNS it PRP gives VBZ off RP . .
18 There EX is VBZ a DT strong JJ relationship NN between IN higher JJR pHs NNS and CC the DT lowering VBG of IN populations NNS of IN fish NN in IN lakes NNS . .
17 Below RB 4.5 CD virtually RB no DT fish NN survive JJ , , whereas WRB levels NNS of IN 6 CD or CC higher JJR promote VB healthy JJ populations NNS . .
17 Acid NN in IN water NN inhibits IN the DT production NN of IN enzymes NNS which WDT enable VBP trout NN larvae NNS to TO escape VB their PRP$ eggs NNS . .
11 It PRP also RB mobilises VBZ toxic JJ metals NNS such JJ as IN aluminium NN in IN lakes NNS . .
18 Aluminium NNP causes VBZ some DT fish NN to TO produce VB an DT excess NN of IN mucus JJ around IN their PRP$ gills NNS , , preventing VBG proper JJ ventilation NN . .
18 Phytoplankton NNP growth NN is VBZ inhibited VBN by IN high JJ acid NN levels NNS , , and CC animals NNS which WDT feed NN on IN it PRP su VBD ffer NN . .
26 Many JJ lakes NNS are VBP subject JJ to TO natural JJ acid NN runoff NN from IN acid NN soils NNS , , and CC this DT can MD be VB triggered VBN by IN particular JJ rainfall NN patterns NNS that WDT concentrate VBP the DT acid NN . .
13 An DT acid NN lake NN with IN newly-dead JJ fish NN is VBZ not RB evidence NN of IN severe JJ air-pollution NN . .
12 Trees NNS are VBP harmed VBN by IN acid NN rain NN in IN a DT variety NN of IN ways NNS . .
24 The DT waxy JJ surface NN of IN leaves NNS is VBZ broken VBN down RP and CC nutrients NNS are VBP lost VBN , , making VBG trees NNS more RBR susceptible JJ to TO frost NN , , fungus NN and CC insects NNS . .
13 Root NNP growth NN slows VBZ and CC as IN a DT result NN less JJR nutrients NNS are VBP taken VBN up RP . .
27 Toxic JJ ions NNS are VBP mobilised VBN in IN the DT soil NN , , and CC valuable JJ minerals NNS are VBP leached VBN away RB or CC -LRB- -LRB- in IN the DT case NN of IN phosphate NN -RRB- -RRB- become VBP bound VBN to TO clay VB . .
15 The DT toxic JJ ions NNS released VBN due JJ to TO acid NN rain NN forms VBZ the DT greatest JJS threat NN to TO humans NNS . .
31 Mobilised NNP copper NN has VBZ been VBN implicated VBN in IN outbreaks NNS of IN diarrhoea NN in IN young JJ children NNS and CC it PRP is VBZ thought VBN there RB are VBP links NNS between IN water NN supplies NNS contaminated VBN with IN aluminium NN and CC Alzheimer NNP ' ' s POS disease NN . .
27 Solutions NNS In IN the DT U.S NNP . . , , coal-burning NN power NN plants NNS are VBP required VBN to TO use VB flue NN gas NN desulfurisation NN system(FGD NN -RRB- -RRB- to TO remove VB sulfur-containing NN gases NNS from IN their PRP$ stack NN gases NNS . .
21 An DT example NN of IN FGD NNP is VBZ the DT wet NN scrubber NN which WDT is VBZ commonly RB used VBN in IN the DT U.S NNP . . and CC many JJ other JJ countries NNS . .
26 A DT wet NN scrubber NN is VBZ basically RB a DT reaction NN tower NN equipped VBN with IN a DT fan NN that WDT extracts VBZ hot JJ smoky NN stack NN gases NNS from IN a DT power NN plant NN into IN the DT tower NN . .
26 Lime NNP or CC limestone NN in IN slurry NN form NN is VBZ also RB injected VBN into IN the DT tower NN to TO mix VB with IN the DT stack NN gases NNS and CC combine VB with IN the DT sulphur NN dioxide NN present NN . .
18 The DT calcium NN carbonate NN of IN the DT limestone NN produces VBZ pH-neutral JJ calcium NN sulfate NN that WDT is VBZ physically RB removed VBN from IN the DT scrubber NN . .
12 That DT is VBZ , , the DT scrubber NN turns VBZ sulfur NN pollution NN into IN industrial JJ sulfates NNS . .
21 In IN some DT areas NNS the DT sulfates NNS are VBP sold VBN to TO chemical VB companies NNS as IN gysum NN when WRB the DT purity NN of IN calcium NN sulfate NN is VBZ high JJ . .
10 In IN others NNS , , they PRP are VBP placed VBN in IN a DT land-fill NN . .
18 Some DT people NNS oppose VBP regulation NN of IN power-generation NN , , believing VBG that IN power-generation NN and CC pollution NN are VBP required VBN to TO go VB together RB . .
4 This DT is VBZ false JJ . .
48 Nuclear NNP reactors NNS generate VBP less JJR than IN one-millionth JJ the DT toxic JJ waste NN -LRB- -LRB- measured VBN by IN net JJ biological JJ effect NN -RRB- -RRB- per IN watt NN , , when WRB wastes NNS of IN both DT power-generation NN facilities NNS are VBP properly RB handled VBN -LRB- -LRB- USA NNP forbids VBZ nuclear JJ recycling NN , , so IN that DT country NN produces VBZ more RBR '' '' waste VB '' '' than IN other JJ countrie NN s NNS -RRB- -RRB- . .
10 An DT even RB more RBR benign JJ regulatory JJ scheme NN involves VBZ emission NN trading NN . .
20 In IN this DT scheme NN , , every DT current JJ polluting NN facility NN is VBZ given VBN an DT emissions NNS license NN that IN becomes VBZ part NN of IN capital NN equipment NN . .
16 Operators NNS can MD then RB install VB pollution NN control NN equipment NN , , and CC sell VB parts NNS of IN their PRP$ emissions NNS licenses NNS . .
17 The DT main JJ effect NN of IN this DT is VBZ to TO give VB operators NNS real JJ economic JJ incentives NNS to TO install VB pollution NN controls NNS . .
27 Since IN public JJ interest NN groups NNS can MD retire VB the DT licenses NNS by IN purchasing VBG them PRP , , the DT net JJ result NN is VBZ a DT continuously RB decreasing VBG and CC more JJR diffused JJ set NN of IN pollution NN sources NNS . .
25 At IN the DT same JJ time NN , , no DT particular JJ operator NN is VBZ ever RB forced VBN to TO spend VB money NN without IN a DT return NN of IN value NN from IN commercial JJ sale NN of IN assets NNS . .
9 Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Acid_rain NNP '' ''
51 Cryptography NNP -LRB- -LRB- from IN Greek JJ kryptos NNS , , '' '' hidden JJ '' '' , , and CC graphein NN , , '' '' to TO write VB '' '' -RRB- -RRB- is VBZ , , traditionally RB , , the DT study NN of IN ways NNS to TO convert VB information NN from IN its PRP$ normal JJ , , comprehensible JJ form NN into IN an DT incomprehensible JJ format NN , , rendering VBG it PRP unreadable JJ without IN secret JJ knowledge NN the DT art NN of IN encryption NN . .
24 In IN the DT past NN , , cryptography NN helped VBD ensure VB secrecy NN in IN important JJ communications NNS , , such JJ as IN those DT of IN spies NNS , , military JJ leaders NNS , , and CC diplomats NNS . .
16 In IN recent JJ decades NNS , , the DT field NN of IN cryptography NN has VBZ expanded VBN its PRP$ remit NN in IN two CD ways NNS . .
23 Firstly RB , , it PRP provides VBZ mechanisms NNS for IN more JJR than IN just RB keeping VBG secrets NNS : : schemes NNS like IN digital JJ signatures NNS and CC digital JJ cash NN , , for IN example NN . .
44 Secondly RB , , cryptography NN has VBZ come VBN to TO be VB in IN widespread JJ use NN by IN many JJ civilians NNS who WP do VBP not RB have VB extraordinary JJ needs NNS for IN secrecy NN , , although IN typically RB it PRP is VBZ transparently RB built VBN into IN the DT infrastructure NN for IN computing NN and CC telecommunications NNS , , and CC users NNS are VBP not RB aware JJ of IN it PRP . .
17 The DT study NN of IN how WRB to TO circumvent VB the DT use NN of IN cryptography NN is VBZ called VBN cryptanalysis NN , , or CC codebreaking NN . .
18 Cryptography NNP and CC cryptanalysis NN are VBP sometimes RB grouped VBN together RB under IN the DT umbrella NN term NN cryptology NN , , encompassing VBG the DT entire JJ subject NN . .
25 In IN practice NN , , '' '' cryptography NN '' '' is VBZ also RB often RB used VBN to TO refer VB to TO the DT field NN as IN a DT whole JJ ; ; crypto NN is VBZ an DT informal JJ abbreviation NN . .
11 Cryptography NNP is VBZ an DT interdisciplinary JJ subject NN , , drawing VBG from IN several JJ fields NNS . .
13 Before IN the DT time NN of IN computers NNS , , it PRP was VBD closely RB related VBN to TO linguistics NNS . .
32 Nowadays RB the DT emphasis NN has VBZ shifted VBN , , and CC cryptography NN makes VBZ extensive JJ use NN of IN technical JJ areas NNS of IN mathematics NNS , , notably RB number NN theory NN , , information NN theory NN , , computational JJ complexity NN , , statistics NNS and CC finite VB mathematics NNS . .
32 It PRP is VBZ also RB a DT branch NN of IN engineering NN , , but CC an DT unusual JJ one CD as IN it PRP must MD deal VB with IN active JJ , , intelligent JJ and CC malevolent JJ opposition NN -LRB- -LRB- see VB cryptographic JJ engineering NN and CC security NN engineering NN -RRB- -RRB- . .
53 Associated JJ fields NNS are VBP steganography VBG the DT study NN of IN hiding VBG the DT very JJ existence NN of IN a DT message NN , , and CC not RB necessarily RB the DT contents NNS of IN the DT message NN itself PRP -LRB- -LRB- for IN example NN , , microdots NNS , , or CC invisible JJ ink NN -RRB- -RRB- and CC traffic NN analysis NN , , which WDT is VBZ the DT analysis NN of IN patterns NNS of IN communication NN in IN order NN to TO learn VB secret JJ information NN . .
46 1 CD Terminology NN 2 CD Cryptanalysis NNP 3 CD History NN of IN cryptography NN 4 CD Secure JJ communications NNS 5 CD Symmetric NNP key NN cryptography NN 6 CD Public NNP key NN cryptography NN 7 CD Warnings NNS 8 CD Other JJ topics NNS 9 CD See NNP also RB 10 CD External JJ links NNS Terminology NNP The DT original JJ information NN which WDT is VBZ to TO be VB protected VBN by IN cryptography NN is VBZ called VBN the DT plaintext NN . .
22 Encryption NN is VBZ the DT process NN of IN converting VBG plaintext NN into IN an DT unreadable JJ form NN , , termed VBD ciphertext NN , , or CC , , occasionally RB , , a DT cryptogram NN . .
14 Decryption NNP is VBZ the DT reverse JJ process NN , , recovering VBG the DT plaintext NN back RB from IN the DT ciphertext NN . .
7 Enciphering NNP and CC deciphering NN are VBP alternative JJ terms NNS . .
10 A DT cipher NN is VBZ an DT algorithm NN for IN encryption NN and CC decryption NN . .
24 The DT exact JJ operation NN of IN ciphers NNS is VBZ normally RB controlled VBN by IN a DT key NN some DT secret JJ piece NN of IN information NN that WDT customises VBZ how WRB the DT ciphertext NN is VBZ produced VBN . .
22 Protocols NNS specify VBP the DT details NNS of IN how WRB ciphers NNS -LRB- -LRB- and CC other JJ cryptographic JJ primitives NNS -RRB- -RRB- are VBP to TO be VB used VBN to TO achieve VB specific JJ tasks NNS . .
35 A DT suite NN of IN protocols NNS , , ciphers NNS , , key JJ management NN , , user-prescribed JJ actions NNS implemented VBN together RB as IN a DT system NN constitute NN a DT cryptosystem NN ; ; this DT is VBZ what IN an DT end-user NN interacts NNS with IN , , e.g NN . . PGP NNP or CC GPG NNP . .
20 In IN ordinary JJ parlance NN , , a DT -LRB- -LRB- secret JJ -RRB- -RRB- '' '' code NN '' '' is VBZ often RB used VBN synonymously RB with IN '' '' cipher JJ '' '' . .
49 In IN cryptography NN , , however RB , , the DT term NN has VBZ a DT specialised JJ technical JJ meaning NN : : codes NNS are VBP a DT method NN for IN classical JJ cryptography NN , , substituting VBG larger JJR units NNS of IN text NN , , typically RB words NNS or CC phrases NNS -LRB- -LRB- e JJ . . g NNP . . , , '' '' apple NN pie NN '' '' replaces NNS '' '' attack NN at IN dawn JJ '' '' -RRB- -RRB- . .
33 In IN contrast NN , , classical JJ ciphers NNS usually RB substitute VB or CC rearrange VB individual JJ letters NNS -LRB- -LRB- e JJ . . g NNP . . , , '' '' attack NN at IN dawn NN '' '' becomes VBZ '' '' buubdl JJ bu NN ebxo NNS '' '' by IN substitution NN . . -RRB- -RRB- . .
12 The DT secret JJ information NN in IN a DT code NN is VBZ specified VBN in IN a DT codebook NN . .
23 '' '' Cipher NNP '' '' is VBZ alternatively RB spelt VBN '' '' cypher NNS '' '' ; ; similarly RB '' '' ciphertext JJ '' '' and CC '' '' cyphertext JJ '' '' , , and CC so RB forth RB . .
17 Both DT spellings NNS have VBP long JJ histories NNS in IN English NNP , , and CC there EX is VBZ occasional JJ tension NN between IN their PRP$ adherents NNS . .
38 Cryptanalysis NN Main NNP article NN : : Cryptanalysis NNP A DT cryptanalyst NN might MD appear VB to TO be VB the DT natural JJ adversary NN of IN a DT cryptographer NN , , and CC to TO an DT extent NN this DT is VBZ true JJ : : one CD can MD view VB this DT contest NN all DT through IN the DT history NN of IN cryptography NN . .
30 However RB , , it PRP is VBZ possible JJ , , in IN fact NN preferable JJ , , to TO interpret VB the DT two CD roles NNS as IN complementary NN : : a DT thorough JJ understanding NN of IN cryptanalysis NN is VBZ necessary JJ to TO create VB secure JJ cryptography NN . .
17 There EX are VBP a DT wide JJ variety NN of IN cryptanalytic JJ attacks NNS , , and CC it PRP is VBZ convenient JJ to TO classify VB them PRP . .
29 One CD distinction NN concerns VBZ what WP an DT attacker NN can MD know VB and CC do VB in IN order NN to TO learn VB secret JJ information NN , , e.g NN . . does VBZ the DT cryptanalyst NN have VBP access NN only RB to TO the DT ciphertext NN ? ?
12 Does VBZ he PRP also RB know VBP or CC can MD he PRP guess VB some DT corresponding JJ plaintexts NNS ? ?
12 Or CC even RB : : Can MD he PRP choose VB arbitrary JJ plaintexts NNS to TO be VB encrypted VBN ? ?
12 -LRB- -LRB- see VB ciphertext NN only RB , , known VBN plaintext NN and CC chosen VBN plaintext NN -RRB- -RRB- . .
25 While IN these DT example NN scenarios NNS all DT view VBP the DT cipher NN as IN an DT abstract JJ black JJ box NN , , other JJ attacks NNS are VBP based VBN on IN the DT implementation NN of IN the DT cipher NN . .
28 If IN a DT cryptanalyst NN has VBZ access NN to TO , , for IN example NN , , timing NN or CC power NN consumption NN , , he PRP may MD be VB able JJ to TO break VB a DT cipher NN otherwise RB resistant JJ to TO analysis NN . .
30 If IN a DT cryptosystem NN uses VBZ a DT key NN or CC a DT password NN , , it PRP is VBZ at IN risk NN from IN an DT exhaustive JJ search NN ; ; this DT is VBZ very RB commonly RB the DT weakest JJS point NN in IN such JJ systems NNS . .
12 Linear NNP and CC differential JJ cryptanalysis NN are VBP general JJ methods NNS for IN symmetric JJ key JJ cryptography NN . .
29 When WRB cryptography NN relies VBZ on IN hard JJ mathematical JJ problems NNS , , as RB is VBZ usually RB the DT case NN in IN asymmetric JJ cryptography NN , , algorithms NNS for IN tasks NNS such JJ as IN factoring VBG become VBN potential JJ tools NNS for IN cryptanalysis NN . .
18 History NN of IN cryptography NN Main NNP article NN : : History NN of IN cryptography NN Cryptography NNP has VBZ had VBN a DT long JJ and CC colourful JJ history NN . .
20 The DT earliest JJS forms NNS of IN secret JJ writing NN required VBN only RB pen JJ and CC paper NN , , and CC are VBP now RB collectively RB termed VBN classical JJ cryptography NN . .
31 The DT two CD main JJ categories NNS are VBP transposition NN ciphers NNS , , which WDT rearrange VBP the DT order NN of IN letters NNS in IN a DT message NN , , and CC substitution NN ciphers NNS , , which WDT systematically RB replace VB groups NNS of IN letters NNS with IN others NNS . .
31 Classical JJ ciphers NNS tend VBP to TO leak VB varying JJ amounts NNS of IN information NN about IN the DT statistics NNS of IN the DT plaintext NN , , and CC because IN of IN this DT they PRP are VBP easily RB broken VBN , , for IN example NN by IN frequency NN analysis NN . .
16 Classical NNP ciphers NNS still RB enjoy VBP popularity NN today NN , , though RB mostly RB as IN puzzles NNS -LRB- -LRB- see VB cryptogram NN -RRB- -RRB- . .
30 Early RB in IN the DT 20th JJ century NN , , several JJ mechanical JJ devices NNS were VBD invented VBN for IN performing VBG encryption NN , , including VBG rotor NN machines NNS - - most RBS famously RB the DT Enigma NNP cipher NN used VBN in IN World NNP War NNP II NNP . .
17 The DT ciphers NNS implemented VBN by IN these DT machines NNS brought VBD about RB a DT significant JJ increase NN in IN the DT complexity NN of IN cryptanalysis NN . .
15 The DT various JJ attacks NNS on IN Enigma NNP , , for IN example NN , , succeeded VBD only RB after IN considerable JJ effort NN . .
21 Occasionally RB , , these DT devices NNS have VBP featured VBN in IN films NNS , , such JJ as IN in IN the DT James NNP Bond NNP adventure NN From IN Russia NNP with IN Love NNP . .
16 With IN the DT advent NN of IN digital JJ computers NNS and CC electronics NNS , , very RB complex JJ ciphers NNS could MD be VB implemented VBN . .
32 A DT characteristic NN of IN computer NN ciphers NNS is VBZ that IN they PRP operate VBP on IN binary JJ strings NNS unlike IN classical JJ and CC mechanical JJ schemes NNS , , which WDT use VBP an DT alphabet NN of IN around IN 26 CD letters NNS , , depending VBG on IN the DT language NN . .
18 Computer NNP ciphers NNS are VBP also RB much RB more RBR resistant JJ to TO cryptanalysis NN ; ; few JJ are VBP susceptible JJ to TO a DT ciphertext-only JJ attack NN . .
30 Extensive JJ academic JJ research NN into IN modern JJ cryptography NN is VBZ relatively RB recent JJ it PRP only RB began VBD in IN the DT open JJ community NN during IN the DT 1970s NNS with IN the DT specification NN of IN DES NNP and CC the DT invention NN of IN RSA NNP . .
50 It PRP is VBZ well RB that IN much JJ progress NN has VBZ been VBN made VBN in IN a DT short JJ time NN ; ; popular JJ applications NNS such JJ as IN the DT Internet NNP and CC mobile JJ phones NNS have VBP repositioned VBN cryptography NN , , historically RB the DT sole JJ province NN of IN a DT few JJ groups NNS with IN exceptional JJ needs NNS for IN secrecy NN , , into IN a DT mainstream NN technology NN on IN which WDT millions NNS rely VBP . .
18 As RB well RB as IN noting VBG lessons NNS from IN its PRP$ history NN , , cryptographers NNS are VBP also RB careful JJ to TO consider VB the DT future NN . .
25 Moore NNP ' ' s POS law NN is VBZ routinely RB taken VBN into IN account NN when WRB specifying VBG key-lengths NNS , , and CC the DT potential JJ effects NNS of IN quantum NN computing NN have VBP already RB been VBN considered VBN . .
5 Note VB also RB quantum NN cryptography NN . .
15 Secure JJ communications NNS See VB also RB : : Information NN security NN Cryptography NNP is VBZ commonly RB used VBN for IN securing NN communications NNS . .
31 Four CD desirable JJ properties NNS are VBP : : Confidentiality NNP , , also RB known VBN as IN secrecy NN : : only RB an DT authorised JJ recipient NN should MD be VB able JJ to TO extract VB the DT contents NNS of IN the DT message NN from IN its PRP$ encrypted VBN form NN . .
17 Otherwise RB , , it PRP should MD not RB be VB possible JJ to TO obtain VB any DT significant JJ information NN about IN the DT message NN contents NNS . .
18 Integrity NNP : : the DT recipient NN should MD be VB able JJ to TO determine VB if IN the DT message NN has VBZ been VBN altered VBN during IN transmission NN . .
24 Authentication NN : : the DT recipient NN should MD be VB able JJ to TO identify VB the DT sender NN , , and CC verify VB that IN the DT purported JJ sender NN actually RB did VBD send VB the DT message NN . .
14 Non-repudiation NN : : the DT sender NN should MD not RB be VB able JJ to TO deny VB sending VBG the DT message NN . .
12 Cryptography NNP can MD provide VB mechanisms NNS to TO help VB achieve VB all DT of IN the DT above NN . .
17 However RB , , some DT goals NNS are VBP n't RB always RB necessary JJ , , practical JJ or CC even RB desirable JJ in IN some DT contexts NNS . .
23 For IN example NN , , the DT sender NN of IN a DT message NN may MD wish VB to TO remain VB anonymous JJ ; ; clearly RB non-repudiation NN would MD be VB inappropriate JJ in IN that DT case NN . .
45 Symmetric NNP key NN cryptography NN Main NNP article NN : : Symmetric NNP key NN algorithm NN Symmetric NNP key NN ciphers NNS use VBP the DT same JJ key NN for IN encryption NN and CC decryption NN , , or CC a DT little JJ more JJR precisely RB , , the DT key NN used VBN for IN decryption NN is VBZ '' '' easy JJ '' '' to TO calculate VB from IN the DT key NN used VBN for IN encryption NN . .
16 Other JJ terms NNS include VBP '' '' private-key JJ '' '' , , '' '' one-key JJ '' '' and CC '' '' single-key JJ '' '' cryptography NN . .
14 Symmetric JJ key JJ ciphers NNS can MD be VB broadly RB grouped VBN into IN block NN ciphers NNS and CC stream NN ciphers NNS . .
38 Stream NNP ciphers NNS encrypt VBD one CD bit NN at IN a DT time NN , , in IN contrast NN to TO a DT block NN cipher NN , , which WDT operates VBZ on IN a DT group NN of IN bits NNS -LRB- -LRB- a DT '' '' block NN '' '' -RRB- -RRB- of IN a DT certain JJ length NN all RB in IN one CD go NN . .
21 Depending VBG on IN the DT mode NN of IN operation NN , , block NN ciphers NNS can MD be VB implemented VBN as IN self-synchronizing JJ stream NN ciphers NNS -LRB- -LRB- CFB JJ mode NN -RRB- -RRB- . .
18 Likewise RB , , stream NN ciphers NNS can MD be VB made VBN to TO work VB on IN individual JJ blocks NNS of IN plaintext NN at IN a DT time NN . .
10 Thus RB , , there EX is VBZ some DT duality NN between IN the DT two CD . .
24 The DT block NN ciphers NNS DES NNP , , IDEA NNP and CC AES NNP , , and CC the DT stream NN cipher NN RC4 NN , , are VBP among IN the DT most RBS well-known JJ symmetric JJ key JJ ciphers NNS . .
20 Other JJ cryptographic JJ primitives NNS are VBP sometimes RB classified VBN as IN symmetric JJ cryptography NN : : Cryptographic JJ hash NN functions NNS produce VBP a DT hash NN of IN a DT message NN . .
28 While IN it PRP should MD be VB easy JJ to TO compute VB , , it PRP must MD be VB very RB difficult JJ to TO invert VB -LRB- -LRB- one-way JJ -RRB- -RRB- , , though IN other JJ properties NNS are VBP usually RB needed VBN as RB well RB . .
8 MD5 NNP and CC SHA-1 NNP are VBP well-known JJ hash JJ functions NNS . .
30 Message NN authentication NN codes NNS -LRB- -LRB- MACs NNP -RRB- -RRB- , , also RB known VBN as IN keyed-hash JJ functions NNS , , are VBP similar JJ to TO hash JJ functions NNS , , except IN that IN a DT key NN is VBZ needed VBN to TO compute VB the DT hash NN . .
13 As IN the DT name NN suggests VBZ , , they PRP are VBP commonly RB used VBN for IN message NN authentication NN . .
19 They PRP are VBP often RB constructed VBN from IN other JJ primitives NNS , , such JJ as IN block NN ciphers NNS , , unkeyed-hash JJ functions NNS or CC stream NN ciphers NNS . .
34 Public NNP key JJ cryptography NN Main NNP article NN : : Public NNP key JJ cryptography NN \/ / Asymmetric JJ key JJ algorithm NN Symmetric NNP key NN encryption NN has VBZ a DT troublesome JJ drawback NN two CD people NNS who WP wish VBP to TO exchange VB confidential JJ messages NNS must MD share VB a DT secret JJ key NN . .
20 The DT key NN must MD be VB exchanged VBN in IN a DT secure JJ way NN , , and CC not RB by IN the DT means NNS they PRP would MD normally RB communicate VB . .
16 This DT is VBZ usually RB inconvenient JJ , , and CC public-key JJ -LRB- -LRB- or CC asymmetric JJ -RRB- -RRB- cryptography NN provides VBZ an DT alternative NN . .
23 In IN public JJ key NN encryption NN there RB are VBP two CD keys NNS used VBN , , a DT public NN and CC a DT private JJ key NN , , for IN encryption NN and CC decryption NN respectively RB . .
16 It PRP must MD be VB '' '' difficult JJ '' '' to TO derive VB the DT private JJ key NN from IN the DT public JJ key NN . .
29 This DT means VBZ that IN someone NN can MD freely RB send VB their PRP$ public NN key NN out RP over IN an DT insecure JJ channel NN and CC yet RB be VB sure JJ that IN only RB they PRP can MD decrypt VB messages NNS encrypted VBN with IN it PRP . .
11 Public NNP key JJ algorithms NNS are VBP usually RB based VBN on IN hard JJ mathematical JJ problems NNS . .
15 RSA NNP , , for IN example NN , , relies VBZ on IN the DT -LRB- -LRB- conjectured VBN -RRB- -RRB- difficulty NN of IN factorisation NN . .
41 For IN efficiency NN reasons NNS , , hybrid JJ encryption NN systems NNS are VBP used VBN in IN practice NN ; ; a DT key NN is VBZ exchanged VBN using VBG a DT public-key JJ cipher NN , , and CC the DT rest NN of IN the DT communication NN is VBZ encrypted VBN using VBG a DT symmetric-key JJ algorithm NN -LRB- -LRB- which WDT is VBZ typically RB much RB faster RBR -RRB- -RRB- . .
19 Elliptic JJ curve NN cryptography NN is VBZ a DT type NN of IN public-key JJ algorithm NN that WDT may MD offer VB efficiency NN gains NNS over IN other JJ sche NN mes NNS . .
45 Asymmetric NNP cryptography NN also RB provides VBZ mechanisms NNS for IN digital JJ signatures NNS , , which WDT are VBP way NN to TO establish VB with IN high JJ confidence NN -LRB- -LRB- under IN the DT assumption NN that IN the DT relevant JJ private JJ key NN has VBZ not RB been VBN compromised VBN in IN any DT way NN -RRB- -RRB- that IN the DT message NN received VBN was VBD sent VBN by IN the DT claimed VBN sender NN . .
23 Such JJ signatures NNS are VBP often RB , , in IN law NN \/ / by IN implicit JJ inference NN , , as IN the DT digital JJ equivalent NN of IN physical JJ signatures NNS on IN paper NN documents NNS . .
26 In IN a DT technical JJ sense NN , , they PRP are VBP not RB as IN there EX is VBZ no DT physical JJ contact NN nor CC connection NN between IN the DT ' ' signer JJR ' ' and CC the DT ' ' signed VBN ' '
27 Properly RB used VBN high JJ quality NN designs NNS and CC implementations NNS are VBP capable JJ of IN a DT very RB high JJ degree NN of IN assurance NN , , likely JJ exceeding VBG any DT but CC the DT most RBS careful JJ physical JJ signature NN . .
11 Examples NNS of IN digital JJ signature NN protocols NNS include VBP DSA NNP and CC El NNP Gamal NNP . .
28 Digital NNP signatures NNS are VBP central JJ to TO the DT operation NN of IN public JJ key NN infrastructure NN and CC many JJ network NN security NN schemes NNS -LRB- -LRB- eg NN , , Kerberos NNP , , most JJS VPNs NNS , , et CC c JJ -RRB- -RRB- . .
30 Warnings NNS Myths NNS and CC misunderstandings NNS about IN cryptography NN are VBP widespread JJ , , and CC there EX is VBZ an DT abundance NN of IN insecure JJ cryptographic JJ software NN on IN the DT market NN , , sometimes RB pejoratively RB referred VBD to TO as IN snake NN oil NN . .
21 Readers NNS , , buyers NNS , , and CC users NNS should MD therefore RB exercise VB substantial JJ caution NN when WRB selecting VBG books NNS and CC products NNS ; ; self-education NN is VBZ advised VBN . .
15 Even RB software NN with IN known VBN strong JJ algorithms NNS may MD be VB insecure JJ , , because IN of IN poor JJ implementation NN . .
26 Other JJ topics NNS See VB also RB : : Topics NNP in IN cryptography NN The DT security NN of IN all DT practical JJ encryption NN schemes NNS remains VBZ unproven JJ , , both DT for IN symmetric JJ and CC asymmetric JJ sche NN mes NNS . .
30 For IN symmetric JJ ciphers NNS , , confidence NN gained VBD in IN an DT algorithm NN is VBZ usually RB anecdotal JJ e.g NN . . no DT successful JJ attack NN has VBZ been VBN reported VBN on IN an DT algorithm NN for IN several JJ years NNS despite IN intensive JJ analysis NN . .
15 Such JJ a DT cipher NN might MD also RB have VB provable JJ security NN against IN a DT limited JJ class NN of IN attacks NNS . .
28 For IN asymmetric JJ schemes NNS , , it PRP is VBZ common JJ to TO rely VB on IN the DT difficulty NN of IN the DT associated VBN mathematical JJ problem NN , , but CC this DT , , too RB , , is VBZ not RB provably RB secure VB . .
16 Surprisingly RB , , cryptography NN does VBZ have VB provably RB secure JJ ciphers NNS the DT one CD time NN pad NN , , for IN example NN . .
22 However RB , , such JJ schemes NNS require VBP keys NNS as RB long RB as IN the DT plaintext NN , , so IN they PRP are VBP almost RB always RB too RB cumbersome JJ to TO use VB . .
21 When WRB the DT security NN of IN a DT system NN fails VBZ , , it PRP is VBZ rare JJ that IN a DT weakness NN in IN the DT cryptographic JJ algorithms NNS is VBZ exploited VBN . .
20 More RBR often RB , , it PRP is VBZ a DT mistake NN in IN the DT implementation NN , , the DT protocols NNS used VBN or CC some DT other JJ human JJ error NN . .
26 The DT study NN of IN how WRB best JJS to TO implement VB and CC integrate JJ cryptography NN is VBZ a DT field NN in IN itself PRP , , see VBP : : cryptographic JJ engineering NN , , security NN engineering NN and CC cryptosystem NN . .
23 Cryptography NNP can MD be VB used VBN to TO implement VB some DT remarkable JJ protocols NNS : : zero-knowledge JJ proof NN , , secure JJ multiparty JJ computation NN and CC secret JJ sharing NN , , for IN example NN . .
13 See VB also RB Topics NNP in IN cryptography NN an DT analytical JJ list NN of IN articles NNS and CC terms NNS . .
10 Books NNS on IN cryptography NN an DT annotated JJ list NN of IN suggested VBD readings NNS . .
9 List NNP of IN cryptographers NNS an DT annotated JJ list NN of IN cryptographers NNS . .
11 Important JJ publications NNS in IN cryptography NN some DT cryptography NN papers NNS in IN computer NN science NN . .
11 List NNP of IN cryptography NN topics NNS an DT alphabetical JJ list NN of IN cryptography NN articles NNS . .
17 External NNP links VBZ Helger NNP ' ' s POS cryptography NN pointers NNS -LRB- -LRB- http://www JJ . . tcs NNP . . hut NN . . fi/~helger/crypto NN \/ / -RRB- -RRB-
18 RSA NNP Laboratories NNP ' ' FAQ NNP About IN today NN ' ' s POS cryptography NN -LRB- -LRB- http://www JJ . . rsasecurity NN . . com/rsalabs/faq/index NN . . html NN -RRB- -RRB-
20 essentially RB elementary JJ coverage NN sci NN . . crypt RB mini-FAQ JJ -LRB- -LRB- more RBR recent JJ -RRB- -RRB- -LRB- -LRB- http://www NN . . mindspring VBG . . com/~schlafly/crypto/faq JJ . . htm NN -RRB- -RRB-
11 Savard NNP ' ' s POS glossary JJ -LRB- -LRB- http://home NN . . ecn NN . . ab.ca/~jsavard/crypto/jscrypt.htm NN -RRB- -RRB-
24 an DT extensive JJ and CC detailed JJ view NN of IN cryptographic JJ history NN with IN emphasis NN on IN crypto NNS devices NNS Open VBN source NN project NN CrypTool NNP -LRB- -LRB- http://www JJ . . cryptool NN . . org NN -RRB- -RRB-
11 - - Exhaustive JJ educational JJ tool NN about IN cryptography NN and CC cryptanalysis NN , , freeware NN . .
9 Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Cryptography NNP '' ''
10 Categories NNS : : Applied NNP mathematics NNS |  Cryptography NNP |  Mathematical NNP science NN occupations occupations
28 This DT view NN , , taken VBN with IN infrared JJ light NN , , is VBZ a DT false-color JJ image NN of IN a DT quasar-starburst JJ tandem NN with IN the DT most RBS luminous JJ starburst NN ever RB seen VBN in IN such PDT a DT combination NN . .
13 The DT quasar-starburst NN was VBD found VBN by IN a DT team NN of IN researchers NNS from IN six CD institutions NNS . .
39 A DT quasar NN -LRB- -LRB- from IN quasi-stellar JJ radio NN source NN -RRB- -RRB- is VBZ an DT astronomical JJ object NN that WDT looks VBZ like IN a DT star NN in IN optical JJ telescopes NNS -LRB- -LRB- i NNP . . e NN . . it PRP is VBZ a DT point NN source NN -RRB- -RRB- , , and CC has VBZ a DT very RB high JJ redshift NN . .
38 The DT general JJ consensus NN is VBZ that IN this DT high JJ redshift NN is VBZ cosmological JJ , , the DT result NN of IN Hubble NNP ' ' s POS law NN , , which WDT implies VBZ that IN quasars NNS must MD be VB very RB distant JJ and CC must MD emit VB more JJR energy NN than IN dozens NNS of IN normal JJ galaxies NNS . .
43 Some DT quasars NNS display VBP rapid JJ changes NNS in IN luminosity NN , , which WDT implies VBZ that IN they PRP are VBP small JJ -LRB- -LRB- an DT object NN cannot MD change VB faster RBR than IN the DT time NN it PRP takes VBZ light NN to TO travel VB from IN one CD end NN to TO the DT other JJ ; ; but CC see VBP J1819+3845 NNP for IN another DT explanation NN -RRB- -RRB- . .
25 The DT highest JJS redshift NN currently RB known VBN for IN a DT quasar NN is VBZ 6.4 CD -LRB- -LRB- 1 CD -RRB- -RRB- -LRB- -LRB- http://www JJ . . sdss NN . . org/news/releases/20030109 CD . . quasar JJ . . html NN -RRB- -RRB- , ,
19 which WDT is VBZ significant JJ because IN it PRP implies VBZ a DT maximum NN distancemore IN distant JJ quasars NNS should MD be VB easily RB observable JJ if IN they PRP existed VBD . .
18 This DT is VBZ taken VBN to TO mean VB that IN the DT oldest JJS observed JJ quasars NNS correspond JJ to TO the DT beginning NN of IN galaxy JJ formation NN . .
31 The DT first JJ quasars NNS marked VBD the DT end NN of IN the DT dark JJ age NN , , the DT period NN after IN the DT emission NN of IN the DT cosmic JJ microwave NN background NN radiation NN where WRB there EX are VBP no DT observable JJ sources NNS of IN radiation NN . .
14 1 CD Properties NNS of IN Quasars NNP 2 CD Quasar NNP Emission NNP Generation NNP 3 CD History NN of IN quasar NN observation NN 3.1 CD
29 See VB also RB Properties NNP of IN Quasars NNP Of IN the DT several JJ hundred CD quasars NNS observed VBD , , all DT spectra NN have VBP shown VBN considerable JJ redshifts NNS , , ranging VBG from IN 0.06 CD to TO the DT recent JJ maximum NN of IN 6.4 CD . .
12 Therefore RB , , all DT known VBN quasars NNS lie VBP at IN great JJ distances NNS from IN us PRP . .
13 The DT closest JJS being VBG 240 CD Mpc IN away RB and CC the DT farthest JJS being VBG 5500 CD Mpc NNP ! !
14 However RB , , most JJS quasars NNS are VBP known VBN to TO lie VB above IN 1000 CD Mpc NNP in IN distance NN . .
33 Since IN light NN takes VBZ such JJ a DT long JJ time NN to TO cover VB these DT great JJ distances NNS , , we PRP are VBP seeing VBG quasars NNS as IN they PRP existed VBD long RB ago RB - - the DT universe NN as IN it PRP was VBD in IN the DT distant JJ past NN . .
25 Although IN faint JJ when WRB seen VBN opti NNS cally RB , , their PRP$ high JJ redshift NN and CC great JJ distance NN imply VBP that IN quasars NNS are VBP the DT brighest JJS objects NNS in IN the DT known VBN universe NN . .
49 In IN a DT general JJ sense NN , , quasars NNS range VBP in IN luminosity NN from IN 10^38 CD W NNP -LRB- -LRB- the DT luminosity NN of IN the DT brightest JJS radio NN galaxy NN -RRB- -RRB- to TO 10^42 CD W NNP . . The DT average JJ quasar NN is VBZ found VBN to TO be VB 10^40 CD W NNP , , which WDT is VBZ comparable JJ to TO 1000 CD Milky NNP Way NNP galaxies NNS , , or CC 10 CD trillion CD Suns NNPS . .
14 When WRB compared VBN to TO active JJ galaxies NNS , , quasars NNS exhibit NN much RB of IN the DT same JJ properties NNS . .
14 Radiation NNP is VBZ nonthermal JJ and CC some DT are VBP shown VBN to TO have VB emission NN jets NNS and CC lobes NNS . .
36 Quasars NNP can MD be VB observed VBN in IN many JJ parts NNS of IN the DT electromagnetic JJ spectrum NN including VBG radio NN , , infrared VBN , , optical JJ , , ultraviolet NN , , X-ray NN and CC even RB gamma NN rays NNS while IN most JJS quasars NNS are VBP found VBN to TO emit VB in IN the DT infrared VBN . .
13 Quasars NNP are VBP also RB found VBN to TO vary VB in IN luminosity NN in IN differing JJ time NN periods NNS . .
15 Some DT vary VBP in IN brightness NN every DT few JJ months NNS , , weeks NNS , , days NNS , , or CC hours NNS . .
43 This DT recent JJ evidence NN has VBZ allowed VBN scientists NNS to TO theorize VB that IN quasars NNS exhibit NN energy NN in IN a DT very RB small JJ region NN , , since IN each DT part NN of IN the DT quasar NN would MD have VB to TO be VB in IN contact NN with IN other JJ parts NNS on IN such JJ a DT timescale NN to TO coordinate VB the DT luminosity NN variations NNS . .
24 As IN such JJ , , a DT quasar JJ varying NN on IN the DT time NN scale NN of IN a DT few JJ weeks NNS cannot MD be VB larger JJR than IN a DT few JJ light JJ weeks NNS across IN . .
31 Quasar NNP Emission NNP Generation NNP Since IN quasars NNS exhibit NN properties NNS of IN all DT active JJ galaxies NNS , , many JJ scientists NNS have VBP compared VBN the DT emissions NNS from IN quasars NNS to TO those DT of IN small JJ active JJ galaxies NNS due JJ to TO their PRP$ likeness NN . .
15 The DT best JJS explanation NN for IN quasars NNS is VBZ that IN they PRP are VBP powered VBN by IN supermassive JJ black JJ holes NNS . .
30 Scientists NNS theorize VBP to TO create VB the DT luminosity NN of IN 10^40 CD W NNP -LRB- -LRB- average JJ brightness NN of IN a DT quasar NN -RRB- -RRB- , , a DT super-massive JJ black JJ hole NN would MD have VB to TO consume VB 10 CD stars NNS per IN year NN . .
16 The DT brightest JJS known VBN quasars NNS are VBP thought VBN to TO devour VB 1000 CD solar JJ masses NNS of IN material NN every DT year NN . .
15 Quasars NNP are VBP thought VBN to TO ' ' turn DT on NNS ' ' and CC off RB depending VBG on IN their PRP$ surroundings NNS . .
33 One CD implication NN is VBZ that IN a DT quasar NN would MD not RB , , for IN example NN , , continue VB to TO feed VB at IN that DT rate NN for IN 10 CD billion CD years NNS , , which WDT nicely RB explains VBZ why WRB there EX are VBP no DT nearby JJ quasars NNS . .
23 In IN this DT framework NN , , after IN a DT quasar NN finishes VBZ eating VBG up RP gas NN and CC dust NN , , it PRP becomes VBZ an DT ord JJ inary JJ , , normal JJ galaxy NN . .
17 Quasars NNP also RB provide VBP some DT clues NNS as IN to TO the DT end NN of IN the DT Big NNP Bang NNP ' ' s POS reionization NN . .
33 The DT oldest JJS quasars NNS -LRB- -LRB- z NN -RRB- -RRB- 4 CD -RRB- -RRB- display NN a DT Gunn-Peterson NNP trough NN and CC clearly RB have VBP absorption NN regions NNS in IN front NN of IN them PRP indicating VBG that IN the DT intergalactic JJ medium NN at IN that DT time NN was VBD neutral JJ gas NN . .
21 More RBR recent JJ quasars NNS show VBP no DT absorption NN region NN but CC rather RB their PRP$ spectra NN contain VBP a DT spiky JJ area NN known VBN as IN the DT Lyman-alpha NNP forest NN . .
22 This DT indicates VBZ that IN the DT intergalactic JJ medium NN has VBZ undergone JJ reionization NN into IN plasma NN , , and CC that IN neutral JJ gas NN exists VBZ only RB in IN small JJ clouds NNS . .
17 One CD other JJ interesting JJ characteristic NN of IN quasars NNS is VBZ that IN they PRP show VBP evidence NN of IN elements NNS heavier JJR than IN helium NN . .
31 This DT is VBZ taken VBN to TO mean VB that IN galaxies NNS underwent IN a DT massive JJ phase NN of IN star NN formation NN creating VBG population NN III NNP stars VBZ between IN the DT time NN of IN the DT Big NNP Bang NNP and CC the DT first JJ observed JJ quasars NNS . .
57 However RB , , this DT prediction NN has VBZ the DT problem NN in IN that DT , , as IN of IN 2004 CD , , no DT evidence NN for IN such JJ stars NNS have VBP been VBN found VBN , , and CC it PRP may MD seriously RB undermine VB our PRP$ current JJ views NNS of IN the DT universe NN if IN no DT such JJ stars NNS are VBP found VBN in IN the DT next JJ few JJ years NNS , , and CC alternate VB mechanisms NNS for IN producing VBG heavy JJ elements NNS cannot MD be VB found VBN . .
17 History NN of IN quasar NN observation NN The DT first JJ quasars NNS were VBD discovered VBN with IN radio NN telescopes NNS in IN the DT late JJ 1950s NNS . .
12 Many JJ were VBD recorded VBN as IN radio NN sources NNS with IN no DT corresponding JJ visible JJ object NN . .
25 Hundreds NNS of IN these DT objects NNS were VBD recorded VBN by IN 1960 CD and CC published VBN in IN the DT Third NNP Cambridge NNP Catalog NNP as IN astronomers NNS scanned VBD the DT skies NNS for IN the DT optical JJ counterparts NNS . .
14 In IN 1960 CD radio NN source NN 3C JJ 48 CD was VBD finally RB tied VBN to TO an DT optical JJ object NN . .
22 Astronomers NNS detected VBD what WP appeared VBD to TO be VB a DT faint NN blue JJ star NN at IN the DT location NN of IN the DT radio NN source NN and CC obtained VBD its PRP$ spectrum NN . .
13 Containing VBG many JJ unknown JJ broad JJ emission NN lines NNS , , the DT anomalous JJ spectrum NN defied VBD interpretation NN . .
7 In IN 1963 CD a DT breakthrough NN was VBD achieved VBN . .
22 Another DT radio NN source NN , , 3C JJ 273 CD , , that WDT was VBD tied VBN with IN an DT optical JJ object NN and CC exhibiting VBG the DT same JJ strange JJ emission NN lines NNS . .
27 These DT were VBD found VBN not RB to TO be VB strange JJ at IN all DT - - but CC rather RB spectral JJ lines NNS of IN hydrogen NN found VBD to TO be VB redshifted VBN at IN the DT rate NN of IN 16 CD percent NN ! !
19 This DT discovery NN by IN Maarten NNP Schmidt NNP found VBD that IN 3C JJ 273 CD was VBD receding VBG away RB at IN a DT rate NN of IN 44,000 CD km/s NNS . .
22 This DT discovery NN revolutionized VBD Quasar NNP observation NN and CC allowed VBN for IN other JJ astronomers NNS to TO find VB redshifts NNS from IN the DT emission NN lines NNS from IN other JJ radio NN sources NNS . .
18 3C JJ 48 CD was VBD found VBN to TO have VB a DT redshift NN of IN 37 CD percent NN - - 1/3 VBZ the DT speed NN of IN light NN . .
13 With IN these DT discoveries NNS , , the DT name NN '' '' Quasar NNP '' '' came VBD into IN light NN . .
18 The DT term NN quasi-stellar JJ object NN came VBD to TO be VB used VBN as IN a DT term NN for IN these DT puzzling JJ objects NNS to TO astronomers NNS . .
27 Later RB it PRP was VBD found VBN that IN not RB all DT -LRB- -LRB- actually RB only RB 10 CD % % or CC so RB -RRB- -RRB- quasars NNS have VBP strong JJ radio NN emission NN -LRB- -LRB- are VBP ' ' radio-loud JJ ' ' -RRB- -RRB- . .
18 The DT name NN ' ' QS NNP O NNP ' ' -LRB- -LRB- quasi-stellar JJ object NN -RRB- -RRB- is VBZ sometimes RB given VBN to TO the DT radio-quiet JJ class NN . .
13 Others NNS use VBP the DT terms NNS ' ' radio-loud JJ ' ' and CC ' ' radio-quiet JJ quasars NNS ' ' . .
23 One CD great JJ topic NN of IN debate NN during IN the DT 1960s NNS was VBD whether IN quasars NNS are VBP nearby JJ objects NNS or CC distant JJ objects NNS as IN implied VBN by IN their PRP$ redshift NN . .
29 It PRP was VBD suggested VBN , , for IN example NN , , that IN the DT redshift NN of IN quasars NNS was VBD not RB due JJ to TO the DT Doppler NNP effect NN but CC rather RB to TO light VB escaping VBG a DT deep JJ gravitational JJ well RB . .
27 One CD strong JJ argument NN against IN cosmologically RB distant JJ quasars NNS was VBD that IN it PRP implied VBD energies NNS that WDT were VBD far RB in IN excess NN of IN known VBN energy NN conversion NN processes NNS , , including VBG nuclear JJ fusion NN . .
22 At IN this DT time NN , , there EX were VBD some DT suggestions NNS that IN quasars NNS were VBD made VBN of IN antimatter JJ and CC that IN this DT accounts NNS for IN their PRP$ brightness NN . .
30 This DT objection NN was VBD removed VBN with IN the DT proposal NN of IN the DT accretion NN disc NN mechanism NN in IN the DT 1970s NNS , , and CC today NN the DT cosmological JJ distance NN of IN quasars NNS is VBZ accepted VBN by IN almost RB all DT researchers NNS . .
23 Although IN most JJS astrophysicists NNS now RB believe VBP that IN quasars NNS are VBP cosmological JJ objects NNS , , there EX remain VBP a DT few JJ who WP cite VBP evidence NN that IN they PRP are VBP nearby RB . .
27 For IN example NN , , Y NNP . . P NNP . . Varshni NNP has VBZ predicted VBN that IN large JJ redshifts NNS attributed VBD to TO quasars NNS are VBP a DT consequence NN of IN natural JJ lasing NN on IN the DT emission NN spectra NN . .
12 Varshni NNP and CC others NNS also RB dispute VB the DT standard JJ explanation NN of IN superluminal JJ motion NN . .
26 Also RB , , Halton NNP Arp NNP has VBZ stated VBN that IN quasars NNS are VBP spawned VBN by IN galaxies NNS and CC has VBZ argued VBN that IN quasars NNS can MD be VB observed VBN to TO be VB interacting VBG with IN galaxies NNS . .
53 In IN the DT 1980s CD , , unified VBN models NNS were VBD developed VBN in IN which WDT quasars NNS were VBD viewed VBN as IN simply RB a DT class NN of IN active JJ galaxies NNS , , and CC a DT general JJ consensus NN has VBZ emerged VBN that IN in IN many JJ cases NNS it PRP is VBZ simply RB the DT viewing NN angle NN that WDT distinguishes VBZ them PRP from IN other JJ classes NNS , , such JJ as IN -LRB- -LRB- blazars NNS and CC radio NN galaxies NNS -RRB- -RRB- . .
52 The DT huge JJ luminosity NN of IN quasars NNS is VBZ believed VBN to TO be VB a DT result NN of IN friction NN caused VBN by IN gas NN and CC dust NN falling VBG into IN the DT accretion NN disks NNS of IN supermassive JJ black JJ holes NNS , , which WDT can MD convert VB about IN half NN of IN the DT mass NN of IN an DT object NN into IN energy NN as IN compared VBN to TO a DT few JJ percent NN for IN nuclear JJ fusion NN processes NNS . .
37 This DT mechanism NN is VBZ also RB believed VBN to TO explain VB why WRB quasars NNS were VBD more RBR common JJ in IN the DT early JJ universe NN , , as IN this DT energy NN production NN ends VBZ when WRB the DT supermassive JJ black JJ hole NN consumes VBZ all DT of IN the DT gas NN and CC dust NN near IN it PRP . .
44 This DT means VBZ that IN it PRP is VBZ possible JJ that IN most JJS galaxies NNS , , including VBG our PRP$ own JJ Milky NNP Way NNP , , have VBP gone VBN through IN a DT quasar JJ stage NN and CC are VBP now RB quiescent JJ because IN they PRP lack VBP a DT supply NN of IN matter NN to TO feed VB into IN their PRP$ central JJ black JJ holes NNS to TO generate VB radiation NN . .
14 See VB also RB List NNP of IN quasars NNS Retrieved VBN from IN '' '' http://en JJ . . wikipedia NNP . . org/wiki/Quasar NNP '' ''
10 Categories NNS : : Astronomy NNP |  Celestial NNP bodies NNS |  Galaxies NNP |  Quasars Quasars