# more barred letters in thermodynamics

• To: math-font-discuss@cogs.susx.ac.uk
• Subject: more barred letters in thermodynamics
• From: vieth@convex.rz.uni-duesseldorf.de (Ulrik Vieth)
• Date: Tue, 31 Aug 93 12:17:51 +0200

Last week I brought up the need for <iotbar> and/or <iotaslash>
in plasma physics. Now, I've seen more barred letters used in some
books on thermodynamics: <deltabar> and <dbar> are sometimes used
to denote differentials in quasistatic processes.  Thus one might
write the second law of thermodynamics as

T dS = \deltabar Q   	(for reversible processes)
and
T dS \geq \delta Q	(for irreversible processes)

While I have no reference for the use of <deltabar> other than the
manuscript of my professor, which is still under preparation, I have
seen the use of <dbar> for a similar purpose in a recent german book

T. Flie{\ss}bach: Statistische Physik,
B.I. Wissenschaftsverlag, 1992

That book was produced in TeX and I guess the <dbar> was constructed
similar to <hbar> in plain.tex by kerning the little bar (actually
the bar accent from cmr used as an ordinary character) and the <d>.

Does anybody have other references in thermodynamics books. J"org?

Similar to <hbar>, <hslash> and <iotabar>, <iotaslash> both a barred
and a slashed version of <delta> and <d> might appear. The slashed
version seems to be prefered in handwriting.

Since the number of symbols in the MC is limited, I wonder if it would
be better to have a little bar and little slash accent'' for the
purpose of crossing letters than a collection of specialized symbols.

Since those barred letters are used as identifiers (mathords), I see
no problems in putting them into macros enclosed in a group. However,
it is always safer to have them as simple character like <hbar> and
<hslash> in MSBM. Surely there must be some reason for their existence
in the AMS fonts.

Greetings,

Ulrik.