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entropy

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entropy


  4  definitions  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Entropy  \En"tro*py\,  n.  [Gr.  ?  a  turning  in  ?  in  +  ?  a  turn, 
  fr  ?  to  turn.]  (Thermodynamics) 
  A  certain  property  of  a  body,  expressed  as  a  measurable 
  quantity,  such  that  when  there  is  no  communication  of  heat 
  the  quantity  remains  constant,  but  when  heat  enters  or  leaves 
  the  body  the  quantity  increases  or  diminishes.  If  a  small 
  amount,  h,  of  heat  enters  the  body  when  its  temperature  is  t 
  in  the  thermodynamic  scale  the  entropy  of  the  body  is 
  increased  by  h  ?  t.  The  entropy  is  regarded  as  measured  from 
  some  standard  temperature  and  pressure.  Sometimes  called  the 
  thermodynamic  function. 
 
  The  entropy  of  the  universe  tends  towards  a  maximum. 
  --Clausius. 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Heat  \Heat\,  n.  [OE.  hete,  h[ae]te,  AS  h?tu,  h?to,  fr  h[=a]t 
  hot;  akin  to  OHG.  heizi  heat,  Dan.  hede,  Sw  hetta.  See 
  {Hot}.] 
  1.  A  force  in  nature  which  is  recognized  in  various  effects, 
  but  especially  in  the  phenomena  of  fusion  and  evaporation, 
  and  which  as  manifested  in  fire,  the  sun's  rays, 
  mechanical  action  chemical  combination,  etc.,  becomes 
  directly  known  to  us  through  the  sense  of  feeling.  In  its 
  nature  heat  is  a  mode  if  motion,  being  in  general  a  form 
  of  molecular  disturbance  or  vibration.  It  was  formerly 
  supposed  to  be  a  subtile,  imponderable  fluid,  to  which  was 
  given  the  name  caloric. 
 
  Note:  As  affecting  the  human  body,  heat  produces  different 
  sensations,  which  are  called  by  different  names  as 
  heat  or  sensible  heat,  warmth,  cold,  etc.,  according  to 
  its  degree  or  amount  relatively  to  the  normal 
  temperature  of  the  body. 
 
  2.  The  sensation  caused  by  the  force  or  influence  of  heat 
  when  excessive,  or  above  that  which  is  normal  to  the  human 
  body;  the  bodily  feeling  experienced  on  exposure  to  fire, 
  the  sun's  rays,  etc.;  the  reverse  of  cold. 
 
  3.  High  temperature,  as  distinguished  from  low  temperature, 
  or  cold;  as  the  heat  of  summer  and  the  cold  of  winter; 
  heat  of  the  skin  or  body  in  fever,  etc 
 
  Else  how  had  the  world  .  .  .  Avoided  pinching  cold 
  and  scorching  heat!  --Milton. 
 
  4.  Indication  of  high  temperature;  appearance,  condition,  or 
  color  of  a  body,  as  indicating  its  temperature;  redness; 
  high  color;  flush;  degree  of  temperature  to  which 
  something  is  heated,  as  indicated  by  appearance, 
  condition,  or  otherwise. 
 
  It  has  raised  .  .  .  heats  in  their  faces.  --Addison. 
 
  The  heats  smiths  take  of  their  iron  are  a  blood-red 
  heat,  a  white-flame  heat,  and  a  sparking  or  welding 
  heat.  --Moxon. 
 
  5.  A  single  complete  operation  of  heating,  as  at  a  forge  or 
  in  a  furnace;  as  to  make  a  horseshoe  in  a  certain  number 
  of  heats. 
 
  6.  A  violent  action  unintermitted  a  single  effort;  a  single 
  course  in  a  race  that  consists  of  two  or  more  courses;  as 
  he  won  two  heats  out  of  three 
 
  Many  causes  .  .  .  for  refreshment  betwixt  the  heats. 
  --Dryden. 
 
  [He]  struck  off  at  one  heat  the  matchless  tale  of 
  ``Tam  o'Shanter.''  --J.  C. 
  Shairp 
 
  7.  Utmost  violence;  rage;  vehemence;  as  the  heat  of  battle 
  or  party.  ``The  heat  of  their  division.''  --Shak. 
 
  8.  Agitation  of  mind;  inflammation  or  excitement; 
  exasperation.  ``The  head  and  hurry  of  his  rage.''  --South. 
 
  9.  Animation,  as  in  discourse;  ardor;  fervency. 
 
  With  all  the  strength  and  heat  of  eloquence. 
  --Addison. 
 
  10.  Sexual  excitement  in  animals. 
 
  11.  Fermentation. 
 
  {Animal  heat},  {Blood  heat},  {Capacity  for  heat},  etc  See 
  under  {Animal},  {Blood},  etc 
 
  {Atomic  heat}  (Chem.),  the  product  obtained  by  multiplying 
  the  atomic  weight  of  any  element  by  its  specific  heat.  The 
  atomic  heat  of  all  solid  elements  is  nearly  a  constant, 
  the  mean  value  being  6.4. 
 
  {Dynamical  theory  of  heat},  that  theory  of  heat  which  assumes 
  it  to  be  not  a  peculiar  kind  of  matter,  but  a  peculiar 
  motion  of  the  ultimate  particles  of  matter. 
 
  {Heat  engine},  any  apparatus  by  which  a  heated  substance,  as 
  a  heated  fluid,  is  made  to  perform  work  by  giving  motion 
  to  mechanism,  as  a  hot-air  engine,  or  a  steam  engine. 
 
  {Heat  producers}.  (Physiol.)  See  under  {Food}. 
 
  {Heat  rays},  a  term  formerly  applied  to  the  rays  near  the  red 
  end  of  the  spectrum,  whether  within  or  beyond  the  visible 
  spectrum. 
 
  {Heat  weight}  (Mech.),  the  product  of  any  quantity  of  heat  by 
  the  mechanical  equivalent  of  heat  divided  by  the  absolute 
  temperature;  --  called  also  {thermodynamic  function},  and 
  {entropy}. 
 
  {Mechanical  equivalent  of  heat}.  See  under  {Equivalent}. 
 
  {Specific  heat  of  a  substance}  (at  any  temperature),  the 
  number  of  units  of  heat  required  to  raise  the  temperature 
  of  a  unit  mass  of  the  substance  at  that  temperature  one 
  degree. 
 
  {Unit  of  heat},  the  quantity  of  heat  required  to  raise,  by 
  one  degree,  the  temperature  of  a  unit  mass  of  water, 
  initially  at  a  certain  standard  temperature.  The 
  temperature  usually  employed  is  that  of  0[deg]  Centigrade, 
  or  32[deg]  Fahrenheit. 
 
  From  WordNet  r  1.6  [wn]: 
 
  entropy 
  n  1:  (thermodynamics)  a  measure  of  the  amount  of  energy  in  a 
  system  that  is  available  for  doing  work  entropy 
  increases  as  matter  and  energy  in  the  universe  degrade 
  to  an  ultimate  state  of  inert  uniformity  [ant:  {ectropy}] 
  2:  (communication  theory)  a  numerical  measure  of  the 
  uncertainty  of  an  outcome;  "the  signal  contained  thousands 
  of  bits  of  information"  [syn:  {information},  {selective 
  information}] 
 
  From  The  Free  On-line  Dictionary  of  Computing  (13  Mar  01)  [foldoc]: 
 
  entropy 
 
    A  measure  of  the  disorder  of  a  system.  Systems  tend 
  to  go  from  a  state  of  order  (low  entropy)  to  a  state  of 
  maximum  disorder  (high  entropy). 
 
  The  entropy  of  a  system  is  related  to  the  amount  of 
  {information}  it  contains.  A  highly  ordered  system  can  be 
  described  using  fewer  {bit}s  of  information  than  a  disordered 
  one  For  example,  a  string  containing  one  million  "0"s  can  be 
  described  using  {run-length  encoding}  as  [("0",  1000000)] 
  whereas  a  string  of  random  symbols  (e.g.  bits,  or  characters) 
  will  be  much  harder,  if  not  impossible,  to  compress  in  this 
  way 
 
  {Shannon}'s  formula  gives  the  entropy  H(M)  of  a  message  M  in 
  bits: 
 
  H(M)  =  -log2  p(M) 
 
  Where  p(M)  is  the  probability  of  message  M. 
 
  (1998-11-23) 
 
 




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