TypefacesforSymbolsinScientificManuscripts MostwordprocessingsoftwarenowinuseatNISTiscapableofproducinglightface(thatis,regular)orboldfacelettersof theLatinorGreekalphabetsinbothroman(upright)anditalic(sloping)types.Theunderstandabilityoftypedandtypeset scientificandtechnicalpublicationsisfacilitatedifsymbolsareinthecorrecttypeface.Thefollowingrulesaretakenfrom InternationalOrganizationforStandardization(ISO)InternationalStandardISO31-0:1992toISO31-13:1992. Thetypefaceinwhichasymbolappearshelpstodefinewhatthesymbolrepresents.Forexample,irrespectiveofthetypeface usedinthesurroundingtext,“A”wouldbetypedortypesetin —italictypeforthescalarquantityarea: A; —romantypefortheunitampere: A; —italicboldfaceforthevectorquantityvectorpotential:A. Morespecifically,thethreemajorcategoriesofsymbolsfoundinscientificandtechnicalpublicationsshouldbetypedortypeset ineitheritalicorromantype,asfollows: —symbolsforquantitiesandvariables: italic; —symbolsforunits: roman; —symbolsfordescriptiveterms: roman. Theserulesimplythatasubscriptorsuperscriptonaquantitysymbolisinromantypeifitisdescriptive(forexample,ifitisa numberorrepresentsthenameofapersonoraparticle);butitisinitalictypeifitrepresentsaquantity,orisavariablesuchas xinEx oranindexsuchasiinoi xi thatrepresentsanumber.Anindexthatrepresentsanumberisalsocalleda“runningnumber.” Thefollowingfoursectionsgiveexamplesofthepropertypefacesforthesethreemajorcategories. Quantitiesandvariables—italic Symbolsforquantitiesareitalic,asaresymbolsforfunctionsingeneral,forexample,f(x): t=3s ttime,ssecond T=22K Ttemperature,Kkelvin r=11cm rradius,cmcentimeter l = 633 nm l wavelength, nm nanometer Constantsareusuallyphysicalquantitiesandthustheirsymbolsareitalic;however,ingeneral,symbolsusedassubscriptsand superscriptsareromanifdescriptive: NA Avogadroconstant,AAvogadro R molargasconstant uD Debyetemperature,DDebye Z atomicnumber e elementarycharge me mmass,eelectron Runningnumbersandsymbolsforvariablesinmathematicalequationsareitalic,asaresymbolsforparameterssuchasaandb thatmaybeconsideredconstantinagivencontext: m 2 2 2 y=O xi zi x =ay +bz i=1 Symbolsforvectorsareboldfaceitalic,symbolsfortensorsaresans-serifbolditalic,andsymbolsformatricesareboldfaceitalic: a a A?B=C (vectors) T (tensors) A = S 11 12D(matrices) a21 a22 Symbolsusedassubscriptsandsuperscriptsareitaliciftheyrepresentquantitiesorvariables: cp ppressure qm mmass sV Vsolidangle vz zzcoordinate Units—roman ThesymbolsforunitsandSIprefixesareroman: m meter g gram L liter cm centimeter mg microgram mL milliliter (over) Descriptive terms — roman Symbols representing purely descriptive terms (for example, the chemical elements) are roman, as are symbols representing mathematical constants that never change (for example, p) and symbols representing explicitly defined functions or well defined operators (for example, G(x )ordiv): Chemical elements: Ar argon B boron C carbon Mathematical constants, functions, and operators: e base of natural logarithms Sxi S sum of lnx loge natural logarithm of exp x exp exponential of sin x sin sine of lg x log10 common (decimal) logarithm of dx /dt d 1st derivative of loga x log a logarithm to the lb x log2 binary logarithm of base a of Symbols used as subscripts and superscripts are roman if descriptive: (ir) «0 ir irrational Ek k kinetic l Vm m molar, l liquid phase mB B Bohr Sample equations showing correct type q1 q2 F = 2 F = ma pV = nRT 4p«0 r 2 –5 wB = xB Vm,B* /SxAVm,A* Ea = RT d(ln k)/dTc1=l/[exp(c2 /lT) –1] 2 F E = mc p˜ B = lB lim(xB p /lB) =–grad V p→0 Q Greek alphabet in roman and italic type The following table shows the proper form, in both roman and italic type, of the upper-case and lower-case letters of the Greek alphabet. Greek alphabet in roman and italic type alpha A a A a beta B b B b gamma Gg Gg delta Dd Dd epsilon E «,e E «,e zeta Z z Z z eta H h H h theta Q, U(a) u, q(b) Q , U (a) u , q (b) iota I i Ii kappa K k , û(b) Kk,û(b) lambda Ll Ll mu M m M m nu N n N n xi Jj Jj omicron O o Oo pi Pp,Ã Pp,Ã rho P r, (b) P r, (b) sigma Ss Ss tau T t T t upsilon Yy Yy phi Fw,f Fw,f chi Xx Xx psi Cc Cc omega Vv Vv (a) The International Organization for Standardization (ISO) gives only the first of these two letters (see ISO International Standard ISO 31-0:1992). (b) ISO gives these two letters in the reverse order (see ISO International Standard ISO 31-0:1992)..