1 December 2016

CNRS positions - the 2017 campaign

The detail of the 2017 campaign for permanent research positions at the CNRS (Centre national de la recherche scientifique) has been published in the Journal Officiel (see links below) and the submission site is open. The submission deadline is January 6th 2017. There are 211 open positions at the CR2 level (4 less than in 2016), 75 CR1 (2 less), 256 DR2 (+3) and 2 DR1 (+2). The total number has been stable over the last five years, as shown in the graph below:

The official texts: CR2, CR1, DR2, DR1.

20 November 2016

The Ewald sphere

The Ewald sphere is a widely used concept, but one that is quite difficult to grasp in the beginning (at least it was for me, as well as for some of my colleagues.) It can be seen as a way of converting vectors between the "real" space, in which the experiment is performed, and "reciprocal" space.

18 November 2016

Solution Self-Assembly of Plasmonic Janus Nanoparticles

Our paper appeared in Soft Matter.

Congratulations to Nicolò Castro for his first paper as first author!

21 October 2016

10 October 2016

Curvature of a planar curve

I have done this calculation several times over the years, so I might as well write it down in detail, in case it may be of use to someone else.

We are interested in the curvature \(C = 1/R\) of a planar curve \(y=f(x)\) at a given point A, where \(R\) is the curvature radius at that particular point, defined with respect to the curvature center \(O\) (intersection of the normals raised to the curve in A and its infinitesimal neighbor B.)

The angle subtending AB is: \(\displaystyle \mathrm{d}\alpha = \mathrm{d}s/R \Rightarrow C = \frac{\mathrm{d}\alpha}{\mathrm{d}s}\)
The length of the curve element AB is: \(\displaystyle \mathrm{d}s = \sqrt{\mathrm{d}x^2 + \mathrm{d}y^2} \Rightarrow \frac{\mathrm{d}s}{\mathrm{d}x } = \sqrt{1+ f'(x)^2}\)

The derivative of \(f\) is directly related to the angle \(\alpha\): \(\displaystyle f'(x) = \frac{\mathrm{d}y}{\mathrm{d}x} = \tan \alpha \Rightarrow \alpha = \arctan \frac{\mathrm{d}y}{\mathrm{d}x} = \arctan [f'(x)] \Rightarrow \frac{\mathrm{d}\alpha}{\mathrm{d}x} = \frac{1}{1+f'(x)^2} f''(x)\)

Putting together the three relations above yields:
\[C = \frac{\mathrm{d}\alpha}{\mathrm{d}s} = \frac{f''(x)}{\left [ 1 + f'(x)^2\right ]^{3/2}}\]

12 August 2016

Identification of a major intermediate along the self-assembly pathway of an icosahedral viral capsid

Our paper appeared in Soft Matter!
The modelling and fitting of the SAXS data required lengthy analysis and intensive calculations. In particular, we used the analytical model for scattering from spherical patches that I had published last year.

2 August 2016


I learned today that the title of the fourth book in Proust's Search of Lost Time (Sodome et Gomorrhe) was translated in English as Cities of the Plain, same as Cormac McCarthy's novel, and that the expression comes from King James Version of the Bible. Looks like most novels in the English language borrow their title from the KJV (Yeats's poems are a close second, though).

I also found out that the title to Wittgenstein's Tractatus Logico-Philosophicus was inspired by Spinoza's Tractatus Theologico-Politicus. Also, 60 years before Spinoza Robert Fludd wrote his Tractatus Theologo-Philosophicus, which is closer in title (although probably not in content).

2 July 2016


Higgs ! En voilà, un nom à particule !

28 June 2016

Climate and Geography

Is aggression correlated to the climate? Researchers from the Vrije Universiteit Amsterdam and Ohio State University seem to think so (read the press release and the preprint of the paper).

They put forward a supposedly new model titled CLimate, Aggression, and Self control in Humans (CLASH). I can't comment on the merits and novelty of this approach, but it reminds me of Montesquieu's remarks in The Spirit of the Laws (book XIV, chapter II):

In northern countries we meet with a people who have few vices, many virtues, a great share of frankness and sincerity. If we draw near the south we fancy ourselves removed from all morality; the strongest passions multiply all manner of crimes, every one endeavouring to take what advantage he can over his neighbour, in order to encourage those passions.