Condensed concepts

For a diverse range of chemical compounds, the strength of hydrogen bonds [parametrised by the binding energy and/or bond length] is correlated with a wide range of physical properties such as bond lengths, vibrational frequencies and intensities, and isotope effects. I have posted about many of these and a summary of the main ones is in this paper. One correlation which is particularly important for practical reasons is the correlation of bond strength (and length) with the chemical shift associated with proton NMR. The chemical shift is the difference between the NMR resonant frequency of the proton in a specific molecule and that of a free proton. The first important point is that although this shift is extremely small (typically one part in 100,000!) one can measure it extremely accurately. More importantly, this shift is quite sensitive to the local chemical bonding and so one can use it to actually identify the bonding in unknown molecules (e.g. protein structure determin

Today I am giving a talk at IISER Kolkata. My host Chiranjib Mitra requested that I include some discussion of this year's Nobel Prize in Physics. This was very helpful as I think the talk now flows better and there are more illustrations of my main points. But, there is less time to talk about my own work... Here is the current version of the slides . I welcome comments.

I like concrete classroom demonstrations. Andrew Boothroyd recently showed me a very elegant demonstration based on this paper Spontaneous Chirality in Simple Systems Galen T. Pickett, Mark Gross, and Hiroko Okuyama It considers hard spheres confined to a cylinder. Different phases depending on the value of D, the ratio of the diameters of the cylinder and the spheres. The phase diagram is below. Andrew has a nice demonstration using ping pong balls and a special transparent plastic cylinder that has the right diameter to produce a chiral phase. He shows it during a colloquium and sometimes even gets an applause! I found a .ppt that has the nice pictures below.

Amongst his one page guides John Wilkins [my postdoc supervisor] has Guidelines for giving a truly terrible talk "Strict adherence to the following time-􏰀tested guidelines will ensure that both you and your work remain obscure and will guarantee an audience of minimum size at your next talk􏰁." Independently, David Sholl has illustrated the problems in concrete ways with an actual talk "The Secrets of Memorably Bad Presentations"   I am not sure if it is funny or just plain painful. But it does drive home the points. All students (and some faculty) should be forced to watch it in full.

A necessary ingredient to surviving and possibly prospering in science is the ability to write clearly in English. Yet many students are not native English speakers and some have had poor education and training. For some, it is even difficult to write basic sentences without grammar and spelling mistakes. This is a serious issue for both students and advisors. Unfortunately, what happens too often is that advisors spend too much time correcting the English in drafts of papers and thesis chapters rather than focusing on the scientific content . Even, worse lazy or over-committed advisors don't do the corrections and referees, examiners, or editors are left with the problem. Advisors, co-authors, and examiners can get quite irritated in the process. Students need to realise they are really hurting themselves in not addressing this issue. Is there a solution? I try to encourage students and postdocs to pair up and read each other's drafts. However, this is not really qui

In my previous post about the 2016 Nobel Prize in Physics I stated that the Kosterlitz-Thouless transition was a classical phase transition (involving topological objects = vortices), in contrast to the quantum phase transitions associated with topological phases of matter. However, on reflection I realised that it should not be overlooked that there is something distinctly quantum about the KT transition. In a two-dimensional superfluid it involves the binding of pairs of vortices and anti-vortices. These each have a quantum of circulation (+/-h/m where h is Planck's constant and m is the particle mass). At the KT transition temperature Tc there is a finite jump in the superfluid density rho. The value just below Tc is related to Tc by Note that Planck's constant appears in this equation. In a classical world (h=0), Tc would be zero and there would be no KT transition! This universal relation was derived by Nelson and Kosterlitz in 1977 The figure below c

Are there any necessary or sufficient conditions for getting a faculty position? Previously, I suggested that a key element is actually dumb luck: being in the right place at the right time. But that is not my focus here. Twenty years ago when I was struggling to find a faculty job the mythology was that you had to have at least two PRLs and get an invited talk at an APS March Meeting. And doing a postdoc at certain places (e.g. ITP Santa Barbara) would help... Now the mythology seems to be that you need to have Nature and Science papers.... But, this in actually not the case. This is not a sufficient condition. Search committees want to hire someone who can lead an independent research program and can move into new areas. Several department chairs have said things to me along the lines of "It is amazing how we interview some candidates who have impressive publication lists involving papers in luxury journals but when we actually talk to them we quickly lose interest.

I was delighted to see this year's Nobel Prize in Physics awarded to Thouless, Haldane, and Kosterlitz  ”for theoretical discoveries of topological phase transitions and topological phases of matter”. A few years ago I predicted Thouless and Haldane , but was not sure they would ever get it. I am particularly glad they were not bypassed, but rather pushed forward, by topological insulators. There is a very nice review of the scientific history on the Nobel site. Here are a few random observations, roughly in order of decreasing importance. First, it is important to appreciate that there are two distinct scientific discoveries here. They do both involve Thouless and topology, but they really are distinct and so Thouless’ contribution in both is all the more impressive. The “topological phase transition” concerns the Kosterlitz-Thouless transition which is a classical phase transition (i.e. driven by thermal fluctuations) which is driven by vortices (topological objects,

There is a very helpful review article Demystifying the Holographic Mystique by Dmitri Khveshchenko In order to motivate a proper full reading I just give a few choice quotes. Thus far, however, a flurry of the traditionally detailed (hence, rarely concise) publications on the topic have generated not only a good deal of enthusiasm but some reservations as well. Indeed, the proposed ’ad hoc’ generalizations of the original string-theoretical construction involve some of its most radical alterations, whereby most of its stringent constraints would have been aban- doned in the hope of still capturing some key aspects of the underlying correspondence. This is because the target (condensed matter) systems generically tend to be neither conformally, nor Lorentz (or even translationally and/or rotationally) invariant and lack any supersymmetric (or even an ordinary) gauge symmetry with some (let alone, large) rank-N non-abelian group.   Moreover, while sporting a truly impressive lev