1、A Dictionary ofScienceFIFTH EDITION31Great Clarendon Street, Oxford ox2 6dpOxford University Press is a department of the University of Oxford.It furthers the Universitys objective of excellence in research, scholarship,and education by publishing worldwide inOxford New YorkAuckland Cape Town Dar es
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3、a registered trade mark of Oxford University Pressin the UK and in certain other countriesPublished in the United Statesby Oxford University Press Inc., New York Market House Books Ltd. 1984, 1991, 1996, 1999, 2005The moral rights of the author have been assertedDatabase right Oxford University Pres
4、s (maker)First edition, under the title Concise Science Dictionary, 1984Second edition 1991Third edition 1996Fourth edition 1999 retitled A Dictionary of ScienceFifth edition 2005All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any
5、form or by any means,without the prior permission in writing of Oxford University Press,or as expressly permitted by law, or under terms agreed with the appropriatereprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Departm
6、ent, Oxford University Press, at the address aboveYou must not circulate this book in any other binding or coverand you must impose the same condition on any acquirerBritish Library Cataloguing in Publication DataData availableLibrary of Congress Cataloging in Publication DataData availableTypeset b
7、y Market House Books Ltd.Printed in Great Britain on acid-free paper byCox coma. 2. (in astron-omy) The apparent displacement in theposition of a star as a result of the earthsmotion round the sun. Light appears tocome from a point that is slightly dis-placed in the direction of the earths mo-tion.
8、The angular displacement = v/c,where v is the earths orbital velocity andc is the speed of light.abiogenesis The origin of living fromnonliving matter, as by *biopoiesis. Seealso spontaneous generation.abiotic factor Any of the nonliving fac-tors that make up the abiotic environ-mentin which living
9、organisms occur.They include all the aspects of climate,geology, and atmosphere that may affectthe biotic environment. Compare bioticfactor.abomasum The fourth and nal cham-ber of the stomach of ruminants. It leadsfrom the *omasum and empties into thesmall intestine. The abomasum is re-ferred to as
10、the true stomach as it is inthis chamber that protein digestion oc-curs, in acidic conditions. Seeruminantia.ABO system One of the most impor-tant human *blood group systems. Thesystem is based on the presence or ab-sence of *antigens A and B on the surfaceof red blood cells and of *antibodiesagains
11、t these in blood serum. A personwhose blood contains either or boththese antibodies cannot receive a transfu-sion of blood containing the correspond-ing antigens as this would cause the redcells to clump (see agglutination). Thetable illustrates the basis of the system:people of blood group O are de
12、scribed asuniversal donors as they can give bloodto those of any of the other groups. Seealso immune response.abscisic acid A naturally occurringplant *growth substance that appears tobe involved primarily in seed maturation,stress responses (e.g. to heat and water-logging), and in regulating closur
13、e of leafpores (stomata). In seeds, it promotes thesynthesis of storage protein and preventspremature germination. In leaves, abscisicacid is produced in large amounts whenthe plant lacks sufcient water, promot-ing closure of stomata and hence reduc-ing further water losses. It was formerlybelieved
14、to play a role in *abscission,hence the name.abscissa See cartesian coordinates.abscission The separation of a leaf,fruit, or other part from the body of aplant. It involves the formation of an ab-scission zone, at the base of the part,within which a layer of cells (abscissionlayer) breaks down. Thi
15、s process is sup-pressed so long as sufcient amounts of*auxin, a plant growth substance, owfrom the part through the abscissionzone. However, if the auxin ow declines,for example due to injury or ageing, ab-scission is activated and the part becomesseparated.absolute 1. Not dependent on or rela-tive
16、 to anything else, e.g. *absolute zero.2. Denoting a temperature measured onan absolute scale, a scale of temperaturebased on absolute zero. The usual abso-lute scale now is that of thermodynamic*temperature; its unit, the kelvin, was for-merly called the degree absolute (A) andis the same size as t
17、he degree Celsius. InBritish engineering practice an absolutescale with Fahrenheit-size degrees hasbeen used: this is the Rankine scale.absolute alcohol See ethanol.absolute conguration A way of de-noting the absolute structure of an opticalisomer (see optical activity). Two conven-tions are in use:
18、 The dl convention re-lates the structure of the molecule tosome reference molecule. In the case ofsugars and similar compounds, thedextrorotatory form of glyceraldehyde(HOCH2CH(OH)CHO), 2,3-dihydroxy-propanal) was used. The rule is as fol-lows. Write the structure of this moleculedown with the asym
19、metric carbon in thecentre, the CHO group at the top, theOH on the right, the CH2OH at the bot-tom, and the H on the left. Now imaginethat the central carbon atom is at the cen-tre of a tetrahedron with the four groupsat the corners and that the H and OHcome out of the paper and the CHO andCH2OH gro
20、ups go into the paper. The re-sulting three-dimensional structure wastaken to be that of d-glyceraldehyde andcalled d-glyceraldehyde. Any compoundthat contains an asymmetric carbon atomhaving this conguration belongs to thed-series. One having the opposite congu-ration belongs to the l-series. It is
21、 impor-tant to note that the prexes d- and l- donot stand for dextrorotatory and laevoro-tatory (they are not the same as d- and l-).In fact the arbitrary conguration as-signed to d-glyceraldehyde is now knownto be the correct one for the dextrorota-tory form, although this was not knownat the time.
22、 However, all d-compoundsare not dextrorotatory. For instance, theacid obtained by oxidizing the CHOgroup of glyceraldehyde is glyceric acid(1,2-dihydroxypropanoic acid). By conven-tion, this belongs to the d-series, but it isin fact laevorotatory; i.e. its name can bewritten as d-glyceric acid or l
23、-glyceric acid.To avoid confusion it is better to use + (fordextrorotatory) and (for laevorotatory),as in d-(+)-glyceraldehyde and d-()-glyceric acid.abscissa 2aABABOABA and Bneither A nor Banti-Banti-Anoneanti-A andanti-BA, OB, OA, B, AB, OOA, ABB, ABABA, B, AB, OGroup Antigens on redcell surfaceAn
24、tibodiesin serumBlood group ofpeople donor canreceive blood fromBlood group ofpeople donor cangive blood toThe ABO blood group systemThe dl convention can also be usedwith alpha amino acids (compounds withthe NH2group on the same carbon as theCOOH group). In this case the moleculeis imagined as bein
25、g viewed along theHC bond between the hydrogen and theasymmetric carbon atom. If the clockwiseorder of the other three groups is COOH,R, NH2, the amino acid belongs to the d-series; otherwise it belongs to the l-series.This is known as the CORN rule.The rs convention is a conventionbased on priority
26、 of groups attached tothe chiral carbon atom. The order of pri-ority is I, Br, Cl, SO3H, OCOCH3, OCH3,OH, NO2, NH2, COOCH3, CONH2, COCH3,CHO, CH2OH, C6H5, C2H5, CH3, H, with hy-drogen lowest. The molecule is viewedwith the group of lowest priority behindthe chiral atom. If the clockwise arrange-ment
27、 of the other three groups is in de-scending priority, the compound belongsto the r-series; if the descending order isanticlockwise it is in the s-series. d-(+)-glyceraldehyde is r-(+)-glyceraldehyde. Seeillustration.absolute expansivity See expansivity.absolute humidity See humidity.absolute permit
28、tivity See permittiv-ity.absolute pitch (perfect pitch) The abil-ity of a person to identify and reproduce anote without reference to a tuned musicalinstrument.absolute temperature See absolute;temperature.absolute value (modulus) The squareroot of the sum of the squares of the realnumbers in a *com
29、plex number, i.e. theabsolute value of the complex number z = x + iy is |z| = (x2+ y2).3 absolute valueaCHOOHCH2OHH Cplanar formulaCHOCHOHCH2OHCHOCH2OHHCOHstructure in 3dimensionsFischer projectionCCH3NH2COOHHCOOHCH3HNH21C3 21C2 3Rconfiguration SconfigurationDL convention: D-(+)-glyceraldehyde (2,3-
30、dihydroxypropanal)DL convention: D-alanine (R is CH2in the CORN rule); the molecule is viewed with H on topRS system: the lowest priority group is behind the chiral carbon atomabsolute zero Zero of thermodynamic*temperature (0 kelvin) and the lowesttemperature theoretically attainable. It isthe temp
31、erature at which the kinetic en-ergy of atoms and molecules is minimal.It is equivalent to 273.15C or 459.67F.See also zero-point energy; cryogenics.absorbed dose See dose.absorptance Symbol . The ratio of theradiant or luminous ux absorbed by abody to the ux falling on it. Formerlycalled absorptivi
32、ty, the absorptance of a*black body is by denition 1.absorption 1. (in chemistry) The takeup of a gas by a solid or liquid, or the takeup of a liquid by a solid. Absorption dif-fers from *adsorption in that the ab-sorbed substance permeates the bulk ofthe absorbing substance. 2. (in physics)The conv
33、ersion of the energy of electro-magnetic radiation, sound, streams of par-ticles, etc., into other forms of energy onpassing through a medium. A beam oflight, for instance, passing through amedium, may lose intensity because oftwo effects: *scattering of light out of thebeam, and absorption of photo
34、ns byatoms or molecules in the medium. Whena photon is absorbed, there is a transitionto an excited state. 3. (in biology) Themovement of uid or a dissolved sub-stance across a plasma membrane. Inmany animals, for example, soluble foodmaterial is absorbed into cells lining thealimentary canal and th
35、ence into theblood. In plants, water and mineral saltsare absorbed from the soil by the *roots.See osmosis; transport protein.absorption coefcient 1. (in physics)See lamberts laws. 2. (in chemistry) Thevolume of a given gas, measured at stan-dard temperature and pressure, that willdissolve in unit v
36、olume of a given liquid.absorption indicator See adsorptionindicator.absorption spectrum See spectrum.absorptivity See absorptance.ABS plastic Any of a class of plasticsbased on acrylonitrilebutadienestyrenecopolymers.abundance 1. The ratio of the totalmass of a specied element in the earthscrust to
37、 the total mass of the earths crust,often expressed as a percentage. For ex-ample, the abundance of aluminium inthe earths crust is about 8%. 2. The ratioof the number of atoms of a particular iso-tope of an element to the total number ofatoms of all the isotopes present, often ex-pressed as a perce
38、ntage. For example, theabundance of uranium235 in natural ura-nium is 0.71%. This is the natural abun-dance, i.e. the abundance as found innature before any enrichment has takenplace.abyssal zone The lower depths of theocean (below approximately 2000 metres),where there is effectively no light pene-
39、tration. Abyssal organisms are adapted forliving under high pressures in cold darkconditions. See also aphotic zone.a.c. See alternating current.acceleration Symbol a. The rate of in-crease of speed or velocity. It is measuredin m s2. For a body moving linearly withconstant acceleration a from a spe
40、ed u toa speed v,a =(v u)/t =(v2 u2)/2swhere t is the time taken and s the dis-tance covered.If the acceleration is not constant it isgiven by dv/dt = d2s/dt2. If the motion isnot linear the vector character of displace-ment, velocity, and acceleration must beconsidered. See also rotational motion.a
41、cceleration of free fall Symbol g.The acceleration experienced by any mas-sive object falling freely in the earthsgravitational eld. Experimentally this isalmost constant for all positions near theearths surface, independent of the natureof the falling body (provided air resistanceis eliminated). Th
42、is is taken to indicatethe strict proportionality of *weight (theforce causing the acceleration) and *iner-tial mass, on the basis of *Newtons sec-ond law of motion. There is somevariation of g with latitude, because of theearths rotation and because the earth isnot completely spherical. The standar
43、dvalue is taken as 9.806 65 m s2. The accel-eration of free fall is also called the accel-eration due to gravity.absolute zero 4aaccelerator 1. (in physics) An apparatusfor increasing the kinetic energies ofcharged particles, used for research in nu-clear and particle physics. See cyclotron;linear a
44、ccelerator; synchrocyclotron;synchrotron. 2. (in chemistry) A sub-stance that increases the rate of a chemi-cal reaction, i.e. a catalyst.acceptor 1. (in chemistry and biochem-istry) A compound, molecule, ion, etc., towhich electrons are donated in the forma-tion of a coordinate bond. 2. (in biochem
45、-istry) A *receptor that binds a hormonewithout any apparent biological response.3. (in physics) A substance that is added asan impurity to a *semiconductor becauseof its ability to accept electrons from thevalence bands, causing p-type conductionby the mobile positive holes left. Comparedonor.accep
46、tor levels Energy levels of an ac-ceptor atom in a *semiconductor, such asaluminium, in silicon. These energy levelsare very near the top of the valence band,and therefore cause p-type conduction. Seealso energy band.acclimation The physiological changesoccurring in an organism in response to achang
47、e in a particular environmental fac-tor (e.g. temperature), especially underlaboratory conditions. Thermal acclima-tion studies reveal how such properties asmetabolic rate, muscle contractility, nerveconduction, and heart rate differ betweencold- and warm-acclimated members ofthe same species. These
48、 changes occurnaturally during *acclimatization andequip the organism for living in, say, coldor warm conditions.acclimatization 1. The progressiveadaptation of an organism to any changein its natural environment that subjects itto physiological stress. 2. The overall sumof processes by which an org
49、anism at-tempts to compensate for conditions thatwould substantially reduce the amount ofoxygen delivered to its cells. Compare ac-climation.accommodation 1. (in animal physiol-ogy) Focusing: the process by which thefocal length of the *lens of the eye ischanged so that clear images of objects ata range of distances are displayed on theretina. In humans and some other mam-mals accommodation is achieved by reexadjustments in the shape of the lensbrought about by relaxation and contrac-tion of muscles within the *cilia
