Archive for March 10th, 2010

Beteille on Raj

March 10, 2010

Here is Beteille on the economist K N Raj:

I cannot assess Raj’s contribution to economic science, nor is this the place or the time to do so. But he certainly was an inspiration to many both within and outside his own discipline. P.N. Dhar, who was both his friend and his rival, was bemused by the admiration Raj was able to attract. Shortly after he joined Indira Gandhi’s office as her adviser, he prepared a note for her with great care and some satisfaction. When he went to see her about the note, the first question she asked him was, “What does Dr Raj think of this?” It mattered to many people what Raj thought of them and their work. It certainly mattered to me.

In 1968, I was awarded a Jawaharlal Nehru Fellowship for two years. I chose as my subject the study of agrarian social structure, at that time a somewhat unusual choice for a sociologist. My choice was influenced to a large extent by my association with Raj. I was determined to show him that sociologists had something to say about class and not just about caste, but that they had their own approach to its study. My colleagues in the department of sociology were a little puzzled by my choice of subject, and some even thought that Raj was turning me into a Marxist.

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Liquid droplet on liquid nitorgen

March 10, 2010

An interesting one from PNAS:

Vitrification and levitation of a liquid droplet on liquid nitrogen

Y S Song et al

The vitrification of a liquid occurs when ice crystal formation is prevented in the cryogenic environment through ultrarapid cooling. In general, vitrification entails a large temperature difference between the liquid and its surrounding medium. In our droplet vitrification experiments, we observed that such vitrification events are accompanied by a Leidenfrost phenomenon, which impedes the heat transfer to cool the liquid, when the liquid droplet comes into direct contact with liquid nitrogen. This is distinct from the more generally observed Leidenfrost phenomenon that occurs when a liquid droplet is self-vaporized on a hot plate. In the case of rapid cooling, the phase transition from liquid to vitrified solid (i.e., vitrification) and the levitation of droplets on liquid nitrogen (i.e., Leidenfrost phenomenon) take place simultaneously. Here, we investigate these two simultaneous physical events by using a theoretical model containing three dimensionless parameters (i.e., Stefan, Biot, and Fourier numbers). We explain theoretically and observe experimentally a threshold droplet radius during the vitrification of a cryoprotectant droplet in the presence of the Leidenfrost effect.

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