Archive for February, 2008
The temperature at the surface of the sun is 6000 kelvin, but the temperature of the sun’s corona is more than 3,000,000 kelvin. But it is still a mystery how the sun’s corona is heated to such a high temperature.
Much of the the 7 December 2007 issue of Science is devoted to the Hinode (“sunrise”) solar space telescope mission. (The web site for the mission is in Japanese, if you read that language.) Hinode was launched in September 2006 and since October 2006 has observed the sun from earth orbit. The initial observations have provide clues for solving the mystery of heating the sun’s corona.
In a perspective, Erdélyi and Fedun (p. 1572) explain that there are at least three fundamental questions to be answered.
Where is the energy generated? How does the generated energy propagate from the energy reservoir to the solar corona? How does the transported energy dissipate efficiently in the solar corona to maintain its multimillion-kelvin temperature?
It is now clear that the powerful magnetic fields in the solar atmosphere play a crucial role in heating the corona. In 1970, Hannes Alfvén was awarded the Nobel prize in physics for his predictions of magnetic waves, now called Alfvén waves, in the solar atmosphere. Many of Hindode’s observations are consistent with the presence of Alfvén waves, and the waves are sufficiently powerful to generate the solar wind and heat the corona.
February 29 2008 | Astronomy | Comments Off
Separate analyses of genetic markers from the mitochondrial genome, the Y chromosome, and autosomes have revealed that all humans are descended from a small group of ancestors that lived in eastern Africa. In the 22 February 2008 issue of Science, Li et al., in a paper titled “Worldwide human relationships inferred from genome-wide patterns of variation”, have taken this analysis to a much more detailed level.
Li et al. examined 642,690 single-nucleotide polymorphisms in the autosomes of 938 individuals representing 51 populations from all over the world. Their analysis was based on the proposition that each person’s genome originated from K different ancestral populations. They performed the analysis with K = 2 through K = 7. With K = 7, they found that the seven components corresponded to populations from Africa, Middle East, Europe, Central/South Asia, East Asia, Oceania, and the Americas. Individuals from the Middle East displayed the most mixed ancestry; Palestinians, for example, displayed ancestry from South/Central Asia, Europe, and the Middle East.
The researchers created a maximum likelihood phylogenetic tree from the 51 populations. The sub-Saharan African populations appeared nearest the root of the tree, which was established by the chimpanzee branch, consistent with the hypothesis that humans first appeared in Africa and then migrated to the other continents. The two most distant branches of the tree represented the populations from Oceania and from the Americas.
The large number of markers allowed the group to distinguish finer differences among the populations. For example, the eight European populations sampled in the study — Adygei (an ethnic group from the Russian Caucasus), Basque, French, Italian, Orcadian, Russian, Sardinian, and Tuscan — were well separated in a principal component plot.
February 28 2008 | Biology | Comments Off
In the 24 January 2008 issue of Nature, Sánchez-Lavega et al. published a paper titled “Depth of a strong jovian jet from a planetary-scale disturbance driven by storms.” The paper reports the results of investigations into the circulation jets in the atmosphere of Jupiter. The paper is accompanied by a News & Views article by Kunio M. Sayanagi. (A subscription or payment of a fee is required to view these.)
Both the paper and the article make special note of the role of amateur astronomers in making regular planetary observations. Amateur astronomers around the world can coordinate to make series of continuous observations of a planet over many weeks. The advancement of optical and image processing technologies has led to astonishing improvements in the quality of the images that can be obtained with relatively modest equipment. Dr. Sayanagi writes:
This coverage from around the world nicely complements the more powerful, but less flexible capabilities of the large ground- and space-based telescopes.
For example, see the website of Chrisopher Go, who is one of the contributing authors to the paper. Mr. Go has a second website devoted to Jupiter’s Red Spot Junior.
February 27 2008 | Astronomy | Comments Off
In a paper in the 15 November 2007 issue of Nature, Lehmann et al. explore in detail the RNA-dependent activity of RNA polymerase II from Saccharomyces cerevisiae. RNA polymerase normally transcribes RNA from a DNA template, but the ability of RNA polymerase to use an RNA template suggests that RNA polymerase could have evolved from an enzyme that replicated viral RNA genomes. It is hypothesized that, during the transition from the RNA world to our DNA-based world, this ancient replication enzyme evolved to use DNA as a template.
There is evidence that RNA polymerase II replicates hepatitis delta virus, which has an RNA genome, but this replication is slow in vitro. The authors speculate that unidentified factors present in the cell increase the processivity of RNA polymerase II when it uses an RNA template.
February 26 2008 | Biology | Comments Off
On January 22, 2008, an international consortium of genome sequencing centers announced the 1000 Genomes Project. The goal of the project is to obtain the sequences of 1000 human genomes. Currently, sequences of three human genomes are publicly available.
The press release details the goals of the project, which are to:
- develop a new, highly detailed map of variation in the human genome, a resource that should enable the association of variation of single nucleotide polymorphisms with diseases
- use new DNA sequencing technologies to reduce the cost of the sequencing effort to only $30-50 million
However, no medical information will be available for the persons whose genomes will be sequenced. This seems to negate the value of a lot of the data, since there will be no way to identify associations of SNPs with specific genetic disorders.
The first phase of the project will involve three pilot studies. In the first pilot study, the project will obtain the sequences of six genomes at 20x coverage from two families using new sequencing technologies. This will provide working experience with the new technologies and will enable the project to choose which sequencing method to move forward with.
In the second pilot study, the project will obtain 2x coverage of 180 genomes to provide experience with data management and interpretation.
The third pilot study will focus on obtaining the sequences of the exons of approximately 1000 genes from 1000 people. This study will provide additional experience in data management and interpretation.
The project will then move on to the production phase, which will take two years. The project leaders anticipate a sequencing throughput of more than 8 billion bases per day. It will be extremely challenging to capture and analyze so much data.
February 25 2008 | Biology | Comments Off
In the February 24, 2008, edition of the New York Times Book Review, James Kaplan reviews Beginner’s Greek by James Collins.
Part comedy of manners, part chick lit in male drag, James Collins’s “Beginner’s Greek” is a great big sunny lemon chiffon pie of a novel, set, for good measure and our sociological titillation, among the WASP ruling classes, people who work at white-shoe investment firms and own villas in southwestern France and can instantly tell the difference between fine Bordeaux and plonk.
I had missed the review, but tonight I listened to the New York Times Book Review Podcast, in which Sam Tanenhaus interviews James Collins. Mr. Collins turns out to be an experienced journalist who decided finally that he had a story to tell in Beginner’s Greek, his first novel.
One of the amusing parts of the interview comes when Mr. Tanenhaus asks Mr. Collins if he is happy living in Virginia. It sounds to me like Mr. Collins (although he doesn’t say so) would much rather be back in New York, but his wife prefers Virginia. Mr. Collins admits, however, that living in Virginia made it easier to write Beginner’s Greek.
This book is going on my wish list.
February 24 2008 | Books | Comments Off
