Condensed concepts

It is amazing to me how much theoretical physics and chemistry ends with diagonalising a 2 x 2 Hermitian matrix! e.g. from Marcus-Hush theory of electron transfer to the BCS theory of superconductivity... Yet I find I am often scrambling to get the algebra right. Finally, I have written down the eigenvalues and eigenvectors in a form that I find the most useful. I give them below (partly so I won't have to keep finding them...). The version below is actually taken from this paper

I sometimes hear this is the first axiom of management. It features at the end of an interesting article in The Economist, Digital Taylorism: A modern version of “scientific management” threatens to dehumanise the workplace The article is stimulated by a recent controversial New York Times article that chronicled the way that Amazon.com treats their employees. Just a few quotes to stimulate you to look at the Economist article The reaction to the Times piece shows that digital Taylorism is just as unpopular as its stopwatch-based predecessor. Critics make some powerful points. “Gobbetising” knowledge jobs limits a worker’s ability to use his expertise creatively, they argue. Measuring everything robs jobs of their pleasure. Pushing people to their limits institutionalises “burn and churn”. Constant peer-reviews encourage back-stabbing. Indeed, some firms that graded their staff, including Microsoft, General Electric and Accenture, concluded that it is counter-productive, and dr

How can a member of the general public find out if someone is a real theoretical physicist? The end of this amusing clip from The Big Bang Theory gives the answer.

It is surprising and disappointing to me how this issue continues to comes up. Hence, I thought I would write a post about it. Here are a few concrete examples. A student submits an abstract to a conference without the permission of co-authors. A university vice-president signs a letter of support for the application of a faculty member for a prestigious fellowship. The letter was actually written by the applicant and contains ridiculous claims about the international status of the applicant. The senior author of a paper allows a postdoc to submit a paper even though she has not actually looked at the manuscript because she is so “busy.” The manuscript is full of typos and the referencing is poor. A Ph.D student submits a dissertation proposal to a departmental review committee even though he has has not shown the document to his advisor. An advisor shows the results of a student at a conference without letting them know. A student gives a terrible talk at a conference. The ad

This is a question that is sometimes discussed. Can you study physics (biochemistry) if you have not taken a calculus (chemistry) course? Should you be allowed to? At UQ we actually have some solid data that allows a more meaningful discussion about the issue. The following text is taken from a recent review of the Bachelor of Science at UQ  (page 125). As some, but by no means all, students are aware, for about 15 years the university has not enforced completion of prerequisites . That is, students are free to enrol in any courses they choose, irrespective of whether or not they have previously enrolled in, or passed, any prerequisites.  Students generally are not actively advised that prerequisites are effectively optional. However, any student who explicitly asks is usually advised to complete prerequisites, and that they take a significant risk if they attempt a course without the necessary background knowledge. The lack of enforcement of prerequisites means that a significan

It is natural that students and postdocs should come to faculty members to get career advice. Should I do a Ph.D? Should I do a postdoc? Should I leave academia? Some faculty give excellent and balanced advice. Particularly, they give students a realistic picture of the [low] chances of a Ph.D (and postdoc) leading to an academic career, particularly at a leading university in the Western world. A good place to start the discussion is the data here.  A related statistic to consider is that of the local department. What is the ratio of the Ph.D graduation rate to the faculty hiring rate? For example, in the School of Mathematics and Physics at UQ we currently have close to 100 enrolled Ph.D students. That means we graduate about 20-25 per year. We probably hire faculty at roughly the rate of 0-4 per year. Unfortunately, some faculty don't exactly go out of their way to inform students and postdocs of these painful realities and/or they give the impression, either directly or sub

When is a phenomena truly emergent? Is there some objective quantitative criteria that one might use to decide? This is an issue because sometimes discussions of emergence are pretty fuzzy and even flaky. I have now read the full article Asymptotics, Singularities, and the Reduction of Theories  by Michael Berry that I mentioned in passing in a previous post. I highly recommend the article as I think it has a very important insight: singular asymptotic expansions provide a concrete criteria for emergence. Berry considers the specific problem: He then discusses these examples in detail, including discussions of the asymptotic expansions. I recommend reading this article before the one by Hans Primas (reviewed in the previous post ) as the latter is more technical and philosophical than Berry's. One thing I think this highlights is that the problem of emergence in quantum systems is neither more or less challenging or interesting than in classical syst

Previously, I posted about the tricky problem of establishing experimentally that an unconventional superconductor that the Cooper pairs are in a spin triplet state. One basic (but far from definitive) signature is that the upper critical magnetic field is larger than the Clogston-Chandreshakar limit [this is often called the Pauli paramagnetic limit but I think that is a scientific misnomer ]. I am particularly interested in this problem because of recent theoretical work showing how triplet superconductivity may arise in a particular quasi-one-dimensional metal. A new family of materials A2Cr3As3 [A=K,Rb,Cs] is attracting significant interest because some experiments show the desired high upper critical field. I think the "first" paper is a Phys. Rev. X article with the title  Superconductivity in Quasi-One-Dimensional  K 2 Cr 3 As 3  with Significant Electron Correlations I am slowly trying to work through some of the literature. Here are a few observations. I welc

Ernst Mayr was one of the leading evolutionary biologists in the twentieth century and was influential in the development of the modern philosophy of biology. He particularly emphasised the importance of emergence and the limitations of reductionism. In his book, This is Biology: the Science of the Living World  Mayr has the following paragraphs that are embarrassing to physicists. Before turning to the organicist paradigm which replaced both vitalism and physicalism, we might note in passing a rather peculiar twentieth-century phenomenon-the development of vitalistic beliefs among physicists. Niels Bohr was apparently the first to suggest that special laws not found in inanimate nature might operate in organisms. He thought of these laws as analogous to the laws of physics except for their being restricted to organisms. Erwin Schrodinger and other physicists supported similar ideas. Francis Crick (1966) devoted a whole book to refuting the vitalistic ideas of the physicists Walter

Increasingly people are asked in specific contexts to provide their CV in a very specific format. Previously, I noted the bizarre recent requirements of the NSERC in Canada. At UQ there is a standard form " Academic portfolio of Achievement " that has to be completed for annual appraisals, applications for promotion, tenure, and sabbatical. This is particularly arduous for senior people who have to do it for the first time. One cannot simply "cut and paste" a list of 100 publications. Arguably, the value of every applicant putting their CV in the same format is that it makes it much easier for a committee to find specific information they require and to compare candidates. Nevertheless, I used to think this was a bad idea because it simply wastes a lot of time in people reformatting their CV for each new situation. However, I now think that there are other reasons why a standard format CV is a bad idea. Allowing applicants to write a CV in their chosen forma

Seth Olsen kindly lent me his copy of Chemistry, Quantum Mechanics, and Reductionism  by Hans Primas, published in 1981. I has a Foreword by Paul Feyerabend !  [Primas died last October and there will be  a symposium in his honour later this year ] This is a book I had wanted to read for a while since I had seen it referenced in various philosophical contexts. Besides some deep philosophy he has lots of polemical statements about theoretical chemistry. Wanting to find an electronic version I could copy choice quotes from led me to a more dense, broader, and more recent (1998) article Emergence in exact natural science. Here I mention a few highlights. emergence and theory reduction are related. Theory reduction is the process where a more general theory, such as quantum mechanics or special relativity, "reduces" in a particular mathematical limit to a less general theory such as classical mechanics. This is a subtle philosophical problem that is arguably poorly unde

In trying to turn research into an actual journal publication there are several stages at which the process can stall or be significantly delayed (sometimes by months or years). * Combining, selecting, and condensing some specific research results into a publon with a well defined message. * Writing a rough first draft. * Polishing the draft into an acceptable form for submission to a journal. * Revising and resubmitting the paper, possibly to a different journal, if rejected from one. Moving beyond these obstacles can be a significant struggle even for senior scientists. Furthermore,  junior collaborators can be frustrated and anxious as they wait for action. Their survival and careers depend on getting papers published in a timely manner. I even know of cases of students who did not get a Ph.D because a manuscript or draft thesis just sat on the desk of their advisor. I am also struck by the fact that I know senior people who have impressive publication records but if you

I like to say, "physicists don't care about the details, chemists say the details do matter, and biologists say the details are a matter of life and death." Bill Parson recently told me about a striking example of how one mutation [substituting a single amino acid for a different one in a protein] can really change things, for better or for worse. I reproduce below the relevant paragraph from this paper. Crystal Structures of Human 108V and 108M Catechol O-Methyltransferase  K. Rutherford, I. Le Trong, R.E. Stenkamp, W.W. Parson Human COMT contains a common polymorphism at residue 108, which can be either valine (V) or methionine (M). 22 ,  23  and  24  Approximately 25% of U.S. and Northern European Caucasians are homozygous for the 108M allele, which is much less common in African and Asian populations. 25  and  26  The 108M allele has been linked with increased risk for breast cancer, 27 ,  28 ,  29  and  30   obsessive–compulsive disorder , 31  and  32  some m

In a previous post I discussed the problem of extracting reliable parameters for tight-binding (and Hubbard) models from ab initio band structure calculations. My comments then were influenced by the figure below, which has now appeared on the arXiv in a short review by Anthony Jacko. First, the band structure for a specific organic material was calculated using a density functional theory (DFT) based approximation. The energy dispersion relations were then fit to a tight-binding model involving 8 different hopping integrals, t0, t1, ....t7.  The horizontal axis indexes the 8 integrals, the vertical axis shows their values determined from a range of different fits, using slightly different fitting methods and different runs of the fitting algorithm.  Note the significant differences. Thus, caution is in order if one uses the common practise of simply performing one fit [which may look impressive to the naked eye]. Jacko notes that this is like getting the elephants t

What is excited state proton transfer (ESPT)? Consider a hydrogen bond A-H...B in a molecular system. Suppose the system absorbs a photon (usually in the visible to near UV range) and undergoes a transition to an electronic excited state. In most cases A-H is an organic molecule containing conjugated bonds and the transition is a pi to pi* transition. Then on the time scale of picoseconds [within a factor of one thousand] the proton transfers from the donor A to the acceptor B, i.e. (A-H)*...B evolves to something like (A-)*...(H-B)+. If A and B are part of the same molecule then this is intramolecular ESPT. If A and B are distinct molecules then this is intermolecular ESPT. If A-H is dissolved in water, and significant ESPT occurs then A-H is called a photoacid. I have started to work on this rich and diverse subject. My goal is to develop several simple diabatic state models that might give a more unified picture of the phenomena and provide some physical insight. Given t

It is hard to make meaningful or reliable generalisations about social trends in a complex world. But, I do want to try. In particular, I would like to suggest that the values that drive university decisions [e.g. about hiring, promotions, and allocation of resources] has shifted in the last twenty years. Here are some potted historical observations, based largely on Australian and US universities. The scholarship era (roughly before the 1960s). People were hired and promoted largely based on letters of reference that evaluated the scholarly contributions of the individual. The emphasis was on quality not quantity. Student tuition was either affordable (in the USA) or non-existent (in Australia). Most administrators were faculty (many on secondment, i.e. temporary) with distinguished scholarly records. The disparity between faculty and senior administrator salaries was small. Departments across the university had roughly equal influence and status. In particular, the humanities [

There is currently a lot of interest in layered materials with extremely large magnetoresistance [XMR], partly stimulated by a Nature paper last year. The figure below shows the data from that paper, which is my main focus in this post. A recent PRL  contains the following paragraph A striking feature of the XMR in  WTe 2  is the turn-on temperature behavior: in a fixed magnetic field above a certain critical value  H c , a turn-on temperature  T ∗  is observed in the  R ( T )  curve, where it exhibits a minimum at a field-dependent temperature  T ∗ . At  T < T ∗ , the resistance increases rapidly with decreasing temperature while at  T > T ∗ , it decreases with temperature  [2] . This turn-on temperature behavior, which is also observed in many other XMR materials such as graphite  [19, 20] , bismuth  [20] ,  PtSn 4   [21] ,  PdCoO 2   [22] ,  NbSb 2   [23] , and NbP  [24] , is commonly attributed to a magnetic-field-driven metal-insulator transition and believed to be a