27 July 2015

Untranslatable words

I have already written about (im)possible translation on this blog. The series on Genette's Mimologiques (first part here) is also relevant, because Cratylism has strong implications for the theoretical possibility of translation. At some point, I should write something about Steiner's After Babel.

Lately, I've been looking through the monumental Dictionary of Untranslatables: A Philosophical Lexicon. On a lighter note, here are some illustrated examples of hard to translate concepts from several languages. Both sources discuss the term saudade.

P.S. As I'm writing this post, I'm also reading a comment on Slashdot about the different meaning of "government" in British vs. American English...

Postdoc position: numerical simulations for biophysics

A post-doctoral fellowship is available at the MSC laboratory of the Paris Diderot University (Paris, France), in the framework of our ANR project. Apply before October 1st. The contract should begin on January 1st 2016 at the latest.

Title: Modelling the many-body interactions between protein inclusions in cell membranes
Gross salary: ~ 2500 €/month (varies with seniority).
Duration: ~ 12 months.
Summary of the research topic: The MSC laboratory is a research unit at the very heart of Paris working on three main axes: non-linear physics, soft-matter and interface between physics, biology and medicine. The subject proposed here is part of a wider research effort, pursued in collaboration with three other laboratories from the Paris area, in the framework of a project financed by the ANR (French grant agency). In particular, the successful candidate will work in close collaboration with an experimental group in the Laboratory of Solid State Physics (LPS, Orsay).

25 July 2015

Why good research is like fiction literature

It's not that it requires making things up. I mean this quote by David Foster Wallace:

"[A] certain amount of vanity is necessary to be able to do it all, but any vanity above that certain amount is lethal."

 After all, we must be convinced that we can discover something new and important, that nobody else has been able to find, but still remain lucid enough not to fool ourselves.

12 July 2015

Metrics for science

A couple of recent posts at Occam's Typewriter, on journal impact factors and on metrics in general discuss the evaluation of journals, researchers and institutions. In particular, Athene Donald's post links to The Metric Tide, an in-depth evaluation of quantitative indicators.

What I find interesting is that The Metric Tide compares (in Supplementary Report II) various metrics and the REF quality profile, which ranks individual UK researchers in five categories (one to four stars, in increasing order of "originality, significance and rigour" and the bottom drawer, discreetly labeled as "unclassified".)

The authors computed the precision and sensitivity of REF 4* predictions based on each indicator and the Spearman correlation of the indicator with the REF quality profile. In the areas of physics and chemistry, the best predictor seems to be the citation count, with a precision (percentage of correct predictions) of about 50%, a sensitivity (the proportion of REF 4* outputs identified by the metric prediction) of 85% and a correlation of 0.6.

This is fairly imprecise, but the analysis is done over entire thematic fiels (or units of assessment, as they are called in the report). The accuracy would probably improve if the comparison were restricted to sub-fields, which are more homogeneous in terms of audience sizes and citation practices.

What is it clearly missing from the picture (and would be very hard to measure) is the influence of the various metrics themselves on the REF evaluation...

11 July 2015

Weightlifting and the 2/3 power law

At least since Haldane's 1926 paper [1], we know that the various characteristics of an organism scale according to different power laws. For instance, its mass increases as the volume, i.e. as the cube of the length: \(M \sim L^3\). The strength \(S\), however, should be proportional to the muscle section, and thus increase as \(S \sim L^2\). We therefore get \(S \sim M^{2/3}\).

26 June 2015

The structure factor of a liquid - part V

Finite-size effects

In previous posts, we have always considered that the liquid system was infinite and homogeneous. This may no longer be the case if:
  • the particles are confined in relatively small spaces or
  • their attractive interaction leads to the formation of dense aggregates, separated by more dilute regions.
Although physically very different, those two situations have similar effects on the structure and we will treat them together.

29 May 2015

Global cooling: is the paper really claiming it?

A recent paper in Nature finds a strong correlation between ocean circulation and oscillations in Atlantic surface temperatures which could be moving to a negative phase. According to the authors, "[t]his may offer a brief respite from the persistent rise of global temperatures."

This claim has been taken up by various sites, along a much stronger prediction: decades of global cooling by up to 0.5°C. However, I cannot find this second item anywhere in the original paper. Where does it come from?!

25 May 2015

The structure factor of a liquid - part IV

Sum rule for impenetrable systems

The hard sphere liquid is an idealized model, but some of its properties hold for a very large class of systems, those that have an impenetrable core of size \(R_c\) (\(g(r< 2 R_c = 0\)). Let us write the Fourier relation between \(g(r) -1\) and \(S(q) -1\) (the inverse of Eq. (4) in post II):

The structure factor of a liquid - part III

This is the third part in a series. In part I and part II we defined the basic concepts used in the theory of liquids, in particular the radial distribution function \(g(r)\) and the structure factor \(S(q)\).

The simplest system one can imagine is the ideal gas. There is no interaction between particles: \(u(r) = 0\), leading to \(g(r) = 1\) (the particle at the origin does not affect the position of its neighbors) and \(S(q) = 1\). The ideal gas is a trivial case, but it can be seen as the reference state for other systems. In particular, one could say that the functions \(g(r) - 1\) and \(S(q) - 1\) that appear in Equation (4) of part II quantify the difference with respect to the ideal gas (due to the interaction potential \(u(r) \neq 0\).)