iMechanica - thermodynamics - Comments

Dear Henry, Many thanks

Yuhuai Zhang — Sun, 11 Nov 2007 21:16:53 -0500

Dear Henry,

Many thanks to your very meaningful information.

Yuhuai

discussions started in March

Henry Tan — Wed, 07 Nov 2007 02:20:17 -0500

Dear Yuhuai,

You may be interested in our thread of discussions started in March (http://imechanica.org/node/1064). I am puzzled by this issue ever since I worked on molecular dynamics computations. Please give us some of your thoughts. Thanks.

Henry

time-temperature equivalence for a viscouselastic material

Henry Tan — Sat, 08 Sep 2007 15:59:24 -0400

How does the time-temperature equivalence for a viscouselastic material be viewed at molecular scale?

How temperature affects the viscoelastic behaviour?

Henry Tan — Sat, 08 Sep 2007 15:56:04 -0400

How temperature affects the viscoelastic behaviour? especially viewed from the behaviour of molecular movements?

Mr Tan, But it

Aneet — Tue, 15 May 2007 10:38:47 -0400

Mr Tan,

But it should make sense, as the molecules/atoms vibrate or move around, they do so because they have velocity. And when we talk about molecular dynamics wont we say KE = (1/2)mv2 where KE = (3/2)NkT (for a 3D system, K - Boltzmann's constant?)

Then we do have energy and thus 'temperature'.

Aneet

Ortwin Hess

Henry Tan — Sun, 15 Apr 2007 23:18:11 -0400

Professor Ortwin Hess
Department of Physics
University of Surrey

His recent interests include nano-thermodynamics.
http://www.ph.surrey.ac.uk/profiles?s_name=Ortwin_Hess

Thermodynamics and nanotechnology

Henry Tan — Fri, 13 Apr 2007 15:56:23 -0400

Thermodynamics, largely driven into being by the steam engine, should be pushed into a further mature stage, driven by the nanotechnology that controls matter on the atomic scale.

temperature at the tip of the nano-indenter

Henry Tan — Fri, 13 Apr 2007 01:36:15 -0400

Nanoindentation is a fundamental, evolving, and complementary discipline (Michelle, http://imechanica.org/node/1237).

It iis an interesting topic among imechanicians from many different backgrounds:
Experimental Nanomechanics (Xiaodong, http://imechanica.org/node/606);
Viscoelastic Contacts (Michelle, http://imechanica.org/node/842);
On the uniqueness of measuring elastoplasticproperties from indentation (Xiaodong, http://imechanica.org/node/1222).

The nanoindentation measurements can be even more interesting, when accounting for the temperature at the tip of the nano-indenter.

Nanotubes may have no 'temperature'

Henry Tan — Fri, 13 Apr 2007 00:56:28 -0400

An interesting news headline in nanotechwire.com
http://www.nanotechwire.com/news.asp?nid=1064&ntid=133&pg=9

Physicists have made a bizarre discovery: the concept of temperature is meaningless in some tiny objects. Although the concept of temperature is known to break down on the scale of individual atoms, research now suggests that it may also fail to apply in rather larger entities, such as carbon nanotubes.

The blossoming field of nanotechnology relies on being able to manipulate materials that are made from just a few thousand atoms. Carbon nanotubes, for example, are tiny cylinders that could be used to make miniature electronic devices.

Ortwin Hess from the University of Surrey, Guildford, UK and colleagues say that if you took the temperature at one end of a 10-micrometre nanotube, it would not necessarily have the same temperature as the other end, no matter how long it was left to reach a thermal equilibrium. Such a nanotube is about as long as a sheet of paper is thick.

quotation by Thomas Jefferson

Henry Tan — Fri, 23 Mar 2007 12:53:00 -0400

Dear Cetin:

The quotation by Thomas Jefferson was not on “American approach on getting things done”, but on his views of mathematics (he was enthusiastic about mathematics).

A complete quotation should be:

"…… Having to conduct my grandson through his course of mathematics, I have resumed that study with great avidity. It was ever my favorite one. We have no theories there, no uncertainties remain on the mind; all is demonstration and satisfaction."

Callen's thermodynamic text book

Mogadalai Gururajan — Fri, 23 Mar 2007 05:31:45 -0400

H B Callen's Thermodynamics and an introduction to thermostatistics is a wonderful text book too; in fact, we used Callen as the text, and Kittel and Kroemer as a supplementary text (for problems).

nanoscale thermodynamics

Henry Tan — Thu, 22 Mar 2007 23:33:22 -0400

Many thanks to Sukumar for bringing Tsallis's non-extensive statistics into our attention.

As the size of systems becomes smaller to nanoscale, effects of ﬂuctuations and contributions from surface play more important roles.

I searched the literature, there are currently three approaches for nanoscale thermodyamics:

(1) generalizing the Boltzmann-Gibbs statistics as to take account of the non-extensive feature of such systems, e.g., Tsallis statistics (http://en.wikipedia.org/wiki/Tsallis_entropy);

(2) a modiﬁcation of the Boltzmann-Gibbs statistics by adding subdivision energy;

(3) non-equilibrium thermodynamics including work ﬂuctuations.

Boltzmann distribution

Henry Tan — Thu, 22 Mar 2007 21:36:47 -0400

In the derivation of the Boltzmann distribution for a small system, the system and the reservoir are in thermal contact, exchanging energy. All other modes of interactions between the system and the reservoir are blocked: no exchange of molecules, of volume, or anything else.

This block requirement works fine for macroscopic system.

However, for a nanoscale system the energy changes are associated with volume change which cannot be ignored as in macroscopic systems.

Therefore, the Boltzmann distribution needs to be modified to characterize nanoscale systems.

A great book

Henry Tan — Thu, 22 Mar 2007 17:08:59 -0400

I Agree, a great book!

I used the 2nd edition of this book, Thermal Physics by Charles Kittel and Herbert Kroemer, when I was a undergraduate student studying in the Drpartment of Physics at the Tsinghua University.

It was used as a text book for the course taught by Prof. Xingzhong Li (http://www.phys.tsinghua.edu.cn:8080/chinese/personnel/profile.php?id=21).

one has to learn at least three times

Henry Tan — Thu, 22 Mar 2007 17:00:49 -0400

Sommerfeld's words remind me of Zhigang's comment (http://imechanica.org/node/207):

"...... As many people say, thermodynamics is a subject that one has to learn at least three times."