## In Nature this week

### March 30, 2007

1. Parsi Genes and their databasing K S Jayaraman writes about the efforts of a Bangalore based company to generate the database of genetic information of Parsis and use the information for the study of diseases:

Fleeing persecution by invading Arabs, the Parsis arrived in India from Persia 1,200 years ago, around the same time that a few hundred Vikings arrived in Iceland. They speak a unique Indian dialect and their religion forbids marriage outside the community, so they have remained relatively inbred.

“I realized four years ago that I was sitting on a goldmine or a powder keg,” says Villoo Morawala Patell, a Parsi and molecular biologist who founded the biotech company Avesthagen in 1998. Patell says she refers to a powder keg because of the fear that Parsis will soon become extinct because of inbreeding (the population has shrunk to its present size from a high of 115,000 in 1941).

However, the project is not without its critiques:

Studies suggest that there has been some mixing of Parsi genes with those of other Indians. “It is a bit of a gamble,” says Indraneel Mittra, director of the Bhopal Memorial Hospital and Research Centre in India. “My feeling is that the Parsis are not as pure as Icelanders, and in any case I do not know how fruitful the Icelandic study has been.”

2. The Darwin delay myth, or, is it? Did Darwin really delay his publication of the origin of species for fears of its reception by the public and the estabishment? A historian says no; however, some Darwin scholars seem to take objections to the methodology used in arriving at that answer:

Kohn points out that searching for explicit references to a “delay” is a simplistic approach to the problem, and that other factors should be considered. For example, Darwin often criticized religion in his notebooks, which suggests that he would have been aware of the probable implications of his theory for religion. It is hard to see how the absence of specific references to a delay rules out any influence of cultural and societal factors on Darwin’s decisions, agrees David Quammen, author of The Reluctant Mr Darwin.

3. How mathematical can you get with a renaissance painting? A leading historian of science advances interesting, if controversial theories as to the identities of the people portrayed  in a Renaissance painting, The Flagellation:

King is undaunted by the criticism he has received, and believes that some art historians will dismiss his work because they can’t understand it. “The epigram and painting are mathematical in nature,” he says. “No art historian has ever looked at the basic geometry of the painting”.

But even an expert with mathematical training, such as Kemp, says that drawing any conclusions from measurements alone is fraught with problems. Part of the difficulty is deciding what to measure and where to measure it from and to, especially on a complicated painting like The Flagellation. “You are likely to hit something,” Kemp says. “I want to see direct evidence.” Such evidence might be lines drawn underneath the paint.

Like other art historians approached by Nature, Ellen Handy of the City College of New York worries that King may be jumping too quickly to conclusions, but she acknowledges that art history often ignores mathematics. “Ironically, many of those who consider themselves as art historians don’t have the training that the artists of the time did,” she says. Many Renaissance artists, such as Piero, were skilled geometricians. “We are not. We can learn from those who have that mathematical training now.”

Architect James Bradburne, also a cultural historian and director general of the Palazzo Strozzi in Florence, acknowledges that proof may never be found, but supports King’s ideas nevertheless: “If this is accepted even as a plausible hypothesis, then it says that scientific objects can legitimately be treated as historical documents, in the same way as paintings themselves have been. Scientific objects can be considered part of the puzzle.”

Be sure to take a look at the article at least for the nice pictures of the painting as well as the medieval scientific instrument called astrolabe.

4. Systems biology and simplicity in biology Eric Werner reviews three books on systems biology and finds one of them most practical, while the author of one of the books reviewed, Uri Alon, writes how it is possible to discover general principles in biology.
5. Seeing without eyes No, we are not discussing some Rig Vedic poetry here. Herman Batelan and Kees Uiterwaal, in a News and Views piece, describe one such technique of seeing, namely using electric fields, and apparently, some fish (like sharks) do. Here is the abstract of the piece:

Images of nanoscale structures can be constructed using the flow of electrons ejected from a metal probe tip by a fast laser pulse. The technique adds new dimensions to established methods of microscopy.

Don’t miss the tip-enhanced electron emission microscopic picture of a nanoscale gold (grain boundary?) groove.

6. Electrons in plutonium A high temperature (600 K, $\delta$) phase of plutonium, I understand, is characterized by a 25% increase in its atomic volume as compared to its room temperature(300 K, $\alpha$) phase. Shim et al trace this characteristic to the underlying electronic structure.

The 5f duality similarly has a quantum-mechanical origin, but this time it is in the ‘correlated electron’ problem. Electrons have the same negative charge and so repel each other electrostatically. In simple, crystalline metals, this effect is weak, and the effect of all other electrons on one individual electron can be calculated using an averaged effective repulsive potential.This ‘self-consistent mean-field approximation’ predicts itinerant electronic states, and provides generally accurate predictions of a metal’s bonding, phase stability, equation of state, and so on. But where electrons are more strongly localized (atomic), the approximation starts to fail. New approaches must take into account not only how electron wavefunctions dance round each other in a correlated fashion so as to lower the total energy of the system, but also phenomena, such as the Pauli repulsion between two electrons of the same spin, that affect the metal’s magnetic properties.

I understand that the theoretical approach that Shim et al use to explain the size anamoly is called the dynamical mean-field method, and it overcomes the disadvantages of the usual mean field methods which predict the size correctly, but also predict (wrongly) the plutonium phase to be magnetic. The News and Views section explain all these and much more very lucidly.

7. The handedness at the molecular level An interesting paper about the determination of chirality of a small organic molecule and the News and Views piece that comments on the work:

Were he alive today, Lord Kelvin would be impressed with the work of Haesler et al. … Kelvin was the first to introduce the word ‘chirality’, meaning right- or left-handedness, into science, and was equally adept at experimental and theoretical physics. He would have enjoyed the combination of exquisite instrumentation and advanced theoretical simulation with which the authors have confirmed the absolute configuration (handedness) of a small organic molecule designed to possess structural chirality of the utmost delicacy.

Have a science-filled week!

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