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Carefree people may compromise their health by delaying medical treatment. Pulsars Aplenty

Astronomers find the densest concentration of rapidly whirling neutron stars.

Galaxies Surf on Cosmic Waves

Astronomers verify that ripples from the big bang control the distribution of galaxies.

Preparing for International Polar Year.

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Canada: Science on Ice—Canada Readies for International Polar Year A. Fazekas

Canada calls for preproposals for research projects aimed at understanding the world's polar regions.

Germany: Uncovering the Situation of Ph.D. Students in Germany A. Forde The first thorough survey of the plight of German Ph.D. students is published.

Europe: European Science Bytes Next Wave Staff

Read about the latest funding, training, and job market news from Europe.

MiSciNet: NOAA Program Impacts Minority Serving Institutions C. Parks

An educational partnership program is designed to recruit more minorities with quantitative backgrounds.

MiSciNet: Investing in the Future of Science E. Francisco

A program sponsored by Oak Ridge National Lab offers math and science research opportunities for minority students.

US: Careers in Science Web Log J. Austin

Breaking news and observations related to science careers are updated throughout the week.

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► Perspective: Diabetes and Stem Cell Researchers Turn to the Lowly Spleen S. Kodama, M. Davis, D. L. Faustman

Splenic stem cells might offer hope for the treatment of aging-related disease. related Type 2 Diabetes section page 369

News Focus: Pay at the Pump R.J. Davenport

Scans of failing hearts in patients reveal an energy crisis.

The spleen—a fountain of youth?

Targets of insulin action.

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Related Type 2 Diabetes section page 369

► Editorial Guide: Diabetes—Fighting Fat on Multiple Fronts E. M. Adler

Mechanisms of insulin resistance and pathways for stimulation of P-cell growth are highlighted.

► Perspective: Diabetes Outfoxed by GLP-1? G.G.Holz

GLP-1 stimulates multiple pathways to stimulate pancreatic P-cell growth.

^ Perspective: Lipid Microdomains and Insulin Resistance—Is There a Connection? E. Ikonen and S. Vainio

Alterations in plasma membrane lipid composition may alter insulin signaling.

► Perspective: Ser/Thr Phosphorylation of IRS Proteins—A Molecular Basis for Insulin Resistance Y. Zick

S6K1 participates in homeostatic negative feedback mechanisms that can also lead to insulin resistance.

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This Week in Science

Brittle Boundaries

Semiconducting Aerogels

Aerogels are porous, very low density materials that have the appearance of frozen smoke. They are typically made from oxides and are thus insulators. Mohanan et al. (p. 397) have made analogous aerogels from metal chalcogenides (sulfides, selenides, and tellurides), which are materials commonly used for making semiconductor quantum dots. As a result, the aerogels retain semiconducting properties such as photoluminescence, and yet have a porous network structure with pores in the 2- to 50-nanometer-size range.

The addition of sulfur to many metals and alloys causes them to become brittle, but the reason for this weakening is not , - - —

edited by Stella Hurtley and Phil Szuromi ed to understand the tectonics of the region and the strength of the crust. Chevalier et al. (p. 411) estimated a rate of slip of about 11 milli-meters per year over about 20,000 to 140,000 years on one branch of the Karakorum based on offset moraines, which is consistent with the extrusion of western Tibet owing to the collision of India with Eurasia. This rate is higher than some geodetic estimates of recent slip over shorter time periods and suggests that slip rates on the fault have varied over time.

well understood. Yam- ¡ p aguchi et al. (p. 393, -published online 6 January 2005) modeled the embrittlement of nickel by progressively adding sulfur atoms to a grain boundary. First-princi- i ples calculations reveal that the weakening of the boundary is caused by the aggregation of sulfur atoms at the boundary, which repel each other. The sulfur atoms are forced into non-ideal bonding because the nickel-sulfur bonds are stronger than the sulfur-sulfur bonds.

Combing the Ultraviolet

The use of ultrashort, broadband laser pulses, or optical combs, was recently extended from being a reference standard for continuous wave lasers to being a way to probe the energy levels of atoms. The advantage of using the combs is that they combine the high temporal resolution needed to study dynamics with precise frequency measurement. Witte et al. (p. 400;see the Perspective by Udem) have now extended this method to the short-wavelength, deep ultraviolet region of the spectrum by creating a train of the pulses with the fourth harmonic of an optical laser. The authors measured a high-energy transition frequency in Kr atoms with an order of magnitude reduction in uncertainty from prior studies.

Producing Orders Pockets of Spin

The sensitivity of magnetic resonance force microscopy (MRFM) is reaching the point where single spins can be detected. Making measurements on a small ensemble of localized spins created by microwave irradiation of silicon, Budakian et al. (p. 408) show that that MRFM cannot only detect spin fluctuations but can also be used to manipulate them. Pockets of ordered spin can be formed from a background bath of thermally fluctuating spins in the vicinity of the cantilever tip, and these pockets of ordered spin can be stored and read out. The technique itself should prove useful as a probe of the dynamics of nanoscale magnets, and the ability to create, store, and read out small pockets of ordered spin should prove useful in quantum computing.

Slips in Slip Rates

The Karakorum fault is a major strike-slip fault trending northwest just north of the western Himalayan Mountain Range. The rate of slip on the fault is difficult to estimate, but these rates are need

Sudden Changes in Lions' Ranges

Population dynamics of social species can be highly complex because of the interplay of group-level factors and population-level factors. Packer et al. (p. 390;see the Perspective by Ranta and Kaitala) present long-term data from the Serengeti plains of East Africa which show how herbivore populations (wildebeest, buffalo, zebra, and gazelle) influence lion populations directly and indirectly through the herbivores' impact on vegetation. The herbivore population changes are smooth and gradual, but the lion populations show sudden shifts between alternative equilibria. A model that constrained the upper and lower limits of pride size gave rise to the observed patterns of sudden shifts. Thus, population trends cannot necessarily be understood solely on the basis of individual survival and reproduction.

Separation and Speciation

Ring species, which are isolated species connected by intergraded populations, have long been thought to exemplify the occurrence of speciation in the presence of gene flow. However, some taxo-nomic and molecular evidence have cast doubt on this classic model. Irwin et al. (p. 414) conducted a genome-wide survey for the greenish warbler, whose territory encircles the Tibetan plateau. Two genetically distinct and reproductively isolated forms of the warble are indeed connected by a chain of populations through which genetic patterns change gradually.

Big Bacteria Promote Phosphorite Formation

Thiomargarita namibiensis is a colossus among bacteria (almost 1 millimeter in diameter) found off the Namibian coast. Schulz and Schulz (p. 416) show it accumulates intracellular polyphosphates under aerobic conditions and releases phosphate under anoxic conditions, thereby creating pore water supersaturated in phosphate that precipitates as phosphorite. Energy gained by breakdown of polyphosphate under anoxic conditions is used for intracellular accumulation of sulfide and acetate or other organic carbon. The sulfide is oxidized to elemental sulfur by using nitrate as an electron acceptor. The release of phosphate by these organ-

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