Loss of ACTN3 gene function alters mouse muscle metabolism and shows evidence of positive selection in humans

More than a billion humans worldwide are predicted to be completely deficient in the fast skeletal muscle fiber protein alpha-actinin-3 owing to homozygosity for a premature stop codon polymorphism, R577X, in the ACTN3 gene. The R577X polymorphism is associated with elite athlete status and human muscle performance, suggesting that alpha-actinin-3 deficiency influences the function of fast muscle fibers. Here we show that loss of alpha-actinin-3 expression in a knockout mouse model results in a shift in muscle metabolism toward the more efficient aerobic pathway and an increase in intrinsic endurance performance. In addition, we demonstrate that the genomic region surrounding the 577X null allele shows low levels of genetic variation and recombination in individuals of European and East Asian descent, consistent with strong, recent positive selection. We propose that the 577X allele has been positively selected in some human populations owing to its effect on skeletal muscle metabolism.     

基于不同分布假设的GARCH模型对上证指数风险值预测能力的比较研究

采用GARCH模型对上海股票市场的潜在风险进行了度量．通过对三种不同分布（Normal，Student-t，GED）进行返回检验，可看出GED分布能更好地刻画上证指数的尖峰厚尾特征，从而也能更准确地预测沪市的风险值．     

复合电流滤序器的谐波特性及其对相差高频保护的影响

谐波对电力系统继电保护的影响是电力部门十分关注的问题.本文就稳态谐波对复合电流滤序器和相差高频保护的影响作了计算与分析,并指出谐波对于相差高频保护影响的严重性.文中的计算、分析和结论可供电力系统继电保护工作者在设计、研究和运行分析时参考.     

Resurrecting ancestral alcohol dehydrogenases from yeast

Modern yeast living in fleshy fruits rapidly convert sugars into bulk ethanol through pyruvate. Pyruvate loses carbon dioxide to produce acetaldehyde, which is reduced by alcohol dehydrogenase 1 (Adh1) to ethanol, which accumulates. Yeast later consumes the accumulated ethanol, exploiting Adh2, an Adh1 homolog differing by 24 (of 348) amino acids. As many microorganisms cannot grow in ethanol, accumulated ethanol may help yeast defend resources in the fruit. We report here the resurrection of the last common ancestor of Adh1 and Adh2, called Adh(A). The kinetic behavior of Adh(A) suggests that the ancestor was optimized to make (not consume) ethanol. This is consistent with the hypothesis that before the Adh1-Adh2 duplication, yeast did not accumulate ethanol for later consumption but rather used Adh(A) to recycle NADH generated in the glycolytic pathway. Silent nucleotide dating suggests that the Adh1-Adh2 duplication occurred near the time of duplication of several other proteins involved in the accumulation of ethanol, possibly in the Cretaceous age when fleshy fruits arose. These results help to connect the chemical behavior of these enzymes through systems analysis to a time of global ecosystem change, a small but useful step towards a planetary systems biology.     

Anhedonia requires MC4R-mediated synaptic adaptations in nucleus accumbens

Chronic stress is a strong diathesis for depression in humans and is used to generate animal models of depression. It commonly leads to several major symptoms of depression, including dysregulated feeding behaviour, anhedonia and behavioural despair. Although hypotheses defining the neural pathophysiology of depression have been proposed, the critical synaptic adaptations in key brain circuits that mediate stress-induced depressive symptoms remain poorly understood. Here we show that chronic stress in mice decreases the strength of excitatory synapses on D1 dopamine receptor-expressing nucleus accumbens medium spiny neurons owing to activation of the melanocortin 4 receptor. Stress-elicited increases in behavioural measurements of anhedonia, but not increases in measurements of behavioural despair, are prevented by blocking these melanocortin 4 receptor-mediated synaptic changes in vivo. These results establish that stress-elicited anhedonia requires a neuropeptide-triggered, cell-type-specific synaptic adaptation in the nucleus accumbens and that distinct circuit adaptations mediate other major symptoms of stress-elicited depression.     

Electrostatic trapping of ammonia molecules

The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems.     

Test of GBAS integrity monitoring system using GPS simulator

In recent years, many countries are developing aircraft navigation systems using GNSS(Global Navigation Satellite System),because GNSS has many technical and economic benefits. International organizations as ICAO(International Civil Aviation Organization) and RTCA(Radio Technical Commission for Aeronautics) set up international standards of GBAS(Ground Based Augmentation System)using GNSS and recommend countries to develop GBAS that is based on the standards. To go with the international stream, Korea Airport Cooperation has also developed GBAS. For evaluating the system,KAC and Seoul National University have performed flight tests of the developed GBAS several times and have concluded that the system has good accuracy enough to be used in aircrafts. At that time, the purpose of tests was focused on accuracy of GBAS. But integrity of the system which is important for safety of aircrafts was not tested sufficiently,because it is impossible to make erroneous situations of real GPS signals. So, at this time, we used GPS simulator which can generate GPS signals with satellite failure scenarios. The GPS simulator used in this test generates GPS signals by the scenarios organized in advance.The scenarios can include pseudorange and carrier phase error, parity error and etc. So we organized several scenarios which can includes potential errors of GPS signals and many possible cases for testing the system effectively and accurately. And we tested integrity function of the GBAS system by using GPS signals generated by the simulator.This paper introduces the implemented integrity monitoring system and algorithms used in the tests. And it describes the scenarios of satellite failure. Finally, this paper shows the results of tests.     

物理知识网络的特性分析

为了研究由物理用语组成的物理知识网络的特性,利用复杂网络理论构建了物理知识的二元网络,通过分析发现物理知识二元网络具有复杂网络的特点:物理用语间的平均距离较短;物理知识网络的度分布满足幂律分布;物理知识网络具有层次性模块结构.因此,通过分析物理知识的二元网络特性,可以理解物理教科书所隐含的抽象的物理知识的结构特征.     

Development & performance analysis of korean WADGPS positioning algorithm

Today, many countries are developing their own WADGPS-type systems. The U.S. WAAS is already available for non-aviation users and its full operation is expected by the end of 2003. The European EGNOS and the Japanese MSAS is also in progress. China now propels the SNAS (Satellite Navigation Augmentation System) project,and India made the plan for its GAGAN (GPS And GEO Augmented Navigation) project. Recently, the Ministry of Maritime Affairs and Fisheries of Korea decided to develop Korean WADGPS. It is a very first step for the implementation of practical system. Till now, we have contrived the algorithm for the WADGPS in Korea & East Asia and evaluated its performance by simulations. In this paper, we complemented the positioning algorithm for the actual data processing. We analyzed the performance of the proposed algorithm with the actual data from the reference stations of Korean NDGPS network, which covers almost the whole country.     

An explanation for a universality of transition temperatures in families of copper oxide superconductors

A remarkable mystery of the copper oxide high-transition-temperature (T(c)) superconductors is the dependence of T(c) on the number of CuO2 layers, n, in the unit cell of a crystal. In a given family of these superconductors, T(c) rises with the number of layers, reaching a peak at n = 3, and then declines: the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers and the latest notion of a competing order nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, T(c) can be raised further.