26 December 2013

The efficiency of molecular motors

We know since the work of Sadi Carnot that the efficiency \(\eta\) (the fraction of heat converted into work) of a thermal engine cannot exceed a surprisingly simple maximum value, \(\eta_{\text{max}} = 1 - T_c/T_h\), defined in terms of the absolute temperatures of the cold and hot heat sources, \(T_c\) and \(T_h\). This limitation applies to a wide variety of devices, from combustion engines to solar cells: in the latter case, \(T_h \simeq 5800 \, \text{K}\) is that of the Sun and \(T_c\) is the ambient temperature, yielding \(\eta_{\text{max}} = 93\%\) [1].
We also know that living organisms can operate at (or even below) the temperature of their environment. In these conditions, Carnot's formula would yield zero efficiency, and thus no work production. And yet, our muscles can reach an efficiency of above 50% [2], higher than that of our cars! How can we solve this paradox?

22 December 2013

The availability of research data

A recently published paper [1] (free preprint here) warns that research data becomes less accessible with time. The authors tried to retrieve email addresses from articles 2 to 22 years old, sent standard messages requiring the data sets and followed up on the responses. In most cases (63%) the addresses were not working or they received no response. The other outcomes were: no information on the status of the data (6%), claim of data loss (7%), refusal to share (4%) and receipt of data (19%).

10 December 2013

Heidegger's "black books"

[UPDATE 02/03/2014] (via enowning) A short piece in The Chronicle of Higher Education covering pretty much the same ground as the articles below.
[UPDATE 27/01/2014] An interview with Peter Trawny (editor of the "black books") appeared in Die Zeit (in German). An adapted version in French was published in Le Monde (in French).

[First seen here.] The controversy around Heidegger's political position is rekindled in anticipation of the philosopher's personal notebooks being published next spring. Supposedly, they contain clear antisemitic remarks. The debate has already started in the French press [1,2] and on the radio [3].

The more general question is: to what extent is the quality of the work affected by the morals of the author? There are many possible (and partially overlapping) answers, depending on the precise failing imputed to the author. This is where Heidegger's example is instructive, since his relation to national-socialism and antisemitism is not totally clear (among other things, because his work has not yet been completely published).

9 December 2013

Are espressos fast?

Another example of an abstract term with a very concrete Latin origin: express.

5 December 2013

The weight of an hourglass

This seems to be a classical problem [1]: what is the weight of an hourglass? Careful consideration shows that the weight is larger while running than at rest!