A common mass scale for satellite galaxies of the Milky Way

The Milky Way has at least twenty-three known satellite galaxies that shine with luminosities ranging from about a thousand to a billion times that of the Sun. Half of these galaxies were discovered in the past few years in the Sloan Digital Sky Survey, and they are among the least luminous galaxies in the known Universe. A determination of the mass of these galaxies provides a test of galaxy formation at the smallest scales and probes the nature of the dark matter that dominates the mass density of the Universe. Here we use new measurements of the velocities of the stars in these galaxies to show that they are consistent with them having a common mass of about 10(7) within their central 300 parsecs. This result demonstrates that the faintest of the Milky Way satellites are the most dark-matter-dominated galaxies known, and could be a hint of a new scale in galaxy formation or a characteristic scale for the clustering of dark matter.     

A common somitic origin for embryonic muscle progenitors and satellite cells

In the embryo and in the adult, skeletal muscle growth is dependent on the proliferation and the differentiation of muscle progenitors present within muscle masses. Despite the importance of these progenitors, their embryonic origin is unclear. Here we use electroporation of green fluorescent protein in chick somites, video confocal microscopy analysis of cell movements, and quail-chick grafting experiments to show that the dorsal compartment of the somite, the dermomyotome, is the origin of a population of muscle progenitors that contribute to the growth of trunk muscles during embryonic and fetal life. Furthermore, long-term lineage analyses indicate that satellite cells, which are known progenitors of adult skeletal muscles, derive from the same dermomyotome cell population. We conclude that embryonic muscle progenitors and satellite cells share a common origin that can be traced back to the dermomyotome.     

卫星干扰源定位系统中到达时差检测方法研究

为了进一步提高卫星干扰源测时差定位的性能,文章提出了一种基于小波变换和奈曼一皮尔逊准则的到达时间差参数估计方法.该方法利用小波去噪特性,在低信噪比环境下,能够准确估计接收信号的TDOA参数,为提高卫星干扰源定位性能提供了有效方法;通过选择最佳小波基函数对接收信号直接进行加权处理,减小了传统小波变换过程中的运算量,仿真结果验证了算法的可靠性和有效性.     

A stability limit for the atmospheres of giant extrasolar planets

Recent observations of the planet HD209458b indicate that it is surrounded by an expanded atmosphere of atomic hydrogen that is escaping hydrodynamically. Theoretically, it has been shown that such escape is possible at least inside an orbit of 0.1 au (refs 4 and 5), and also that H3+ ions play a crucial role in cooling the upper atmosphere. Jupiter's atmosphere is stable, so somewhere between 5 and 0.1 au there must be a crossover between stability and instability. Here we show that there is a sharp breakdown in atmospheric stability between 0.14 and 0.16 au for a Jupiter-like planet orbiting a solar-type star. These results are in contrast to earlier modelling that implied much higher thermospheric temperatures and more significant evaporation farther from the star. (We use a three-dimensional, time-dependent coupled thermosphere-ionosphere model and properly include cooling by H3+ ions, allowing us to model globally the redistribution of heat and changes in molecular composition.) Between 0.2 and 0.16 au cooling by H3+ ions balances heating by the star, but inside 0.16 au molecular hydrogen dissociates thermally, suppressing the formation of H3+ and effectively shutting down that mode of cooling.     

A scaling law for slow earthquakes

Recently, a series of unusual earthquake phenomena have been discovered, including deep episodic tremor, low-frequency earthquakes, very-low-frequency earthquakes, slow slip events and silent earthquakes. Each of these has been demonstrated to arise from shear slip, just as do regular earthquakes, but with longer characteristic durations and radiating much less seismic energy. Here we show that these slow events follow a simple, unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes. We find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant, with a spectral high-frequency decay of f(-1). This scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category. The observed scale dependence of rupture velocity for these events can be explained by either a constant low-stress drop model or a diffusional constant-slip model. This new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation.     

A novel heterogeneous reaction for generating gaseous nitrous acid

The short-lived reactive specimen nitrous acid HONO was generated in the gas phase by the hetero-geneous reaction of gaseous HCl with AgNO2 which can generate higher concentration of HONO than other methods. We investigated the process from generation to dissociation in the gas phase under different controlled temperatures,and discussed the ionization and reaction on the solid surface by combination of the photoelectron spectroscopy and photoionization mass spectroscopy(PES-PIMS) and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) .     

A novel heteroseneous reaction for generating gaseous nitrous acid

The short-lived reactive specimen nitrous acid HONO was generated in the gas phase by the heterogeneous reaction of gaseous HCl with AgNO2 which can generate higher concentration of HONO than other methods. We investigated the process from generation to dissociation in the gas phase under different controlled temperatures, and discussed the ionization and reaction on the solid surface by combination of the photoelectron spectroscopy and photoionization mass spectroscopy （PES-PIMS） and in situ diffuse reflectance infrared Fourier transform spectroscopy （DRIFTS）.     

基于动态电压调节的高性能业务系统能耗优化

提出一种面向高性能业务主机基于动态电压调节技术的能耗优化方法,该方法测量应用程序在不同频率下的性能和能耗,并建立性能约束下的能耗优化模型,优化业务系统的能耗;利用功率计测试了3种典型计算机系统在不同频率下运行程序的能耗;根据测试数据和系统能耗优化模型,对能耗优化方法进行了实验验证,结果显示:对于不同的时间约束条件和程序,所提方法可以节省16％的系统能耗.     

一种宽带卫星网络路由协议

结合宽带卫星网络系统的特点 ,提出了一种宽带卫星网络路由协议SARP(SatelliteNetworkAdaptiveRoutingProtocol) ,着重介绍了SARP工作范围、主要设计思想及实现 .通过仿真测试了SARP的性能 .结果表明 ,在宽带卫星网络环境下SARP比传统的链路状态协议L S的性能有明显改进     

一类二元算子方程组的公共不动点

利用非线性泛函分析中的锥与半序理论和单调迭代方法,讨论了不具有连续性和紧性条件的非单调二元算子方程组解的存在唯一性,给出了迭代序列收敛于解的误差估计,所得结果是某些已知结果的改进和推广.     

基于效用函数的LEO卫星移动通信系统波束切换

针对提供多种业务的LEO卫星移动通信系统,考虑不同的业务类型和呼叫类型,定义了基于效用函数的系统用户满意度,并用其度量系统服务质量;以最大化系统用户满意度为准则,给出了波束切换策略,建立了有约束的非线性规划模型;该模型的求解结果决定了是否接受一个切换呼叫.仿真结果表明该策略在保证系统服务质量要求的同时,有效地降低了波束小区的切换掉话率,并且算法简单、信令负荷小.     

新型海事卫星通信微带贴片天线单元

结合经验公式和仿真软件,设计了一种双层贴片,两层介质的微带贴片天线单元.该单元天线采用单馈点正方形切角的方式实现圆极化,在频率为1520～1680 MHz、驻波比<1.5时,相对阻抗带宽达到10%,满足了第四代海事卫星通信中BGAN业务的需要.此外,该天线单元舍弃了传统的探针耦合馈电方式,采用特性阻抗为100Ω的微带线馈电,便于实现天线阵微带馈电网路的设计,从而达到改善其方向性及轴比带宽的目的.     

一种低轨卫星星座系统中的路由算法设计

针对低轨(low earth orbit,LEO)卫星星座系统中路由较复杂的问题,结合了最短路径与次选最短路径,提出了一种低轨卫星星座系统中的路由算法设计,通过仿真和分析表明该算法在综合考虑新呼叫和切换呼叫时具有较高的优越性.     

低轨道移动卫星通信DS/CDMA误码性能分析

讨论了非静止轨道移动卫星通信中DS／CDMA(直接序列扩频码分多址)QPSK(Quaternary Phase Shift Keying)调制的误码性能。以莱斯衰落信道为基础,考虑卫星覆盖仰角对误码率的影响,推导了误码率的解析表达式。给出了计算机仿真数值曲线,并对仿真结果进行了讨论。通过在相同误码率以及不同仰角情况下扩频调制同窄带QPSIK调制信噪比恶化量的比较,可以看出扩频调制对误码性能有很大的改善。得出的结论对进一步评价系统的分组错误概率、吞吐量以及抗衰落技术的选择具有重要的意义。     

一种编译指导的实时动态电压调节低功耗算法

提出了一种编译指导的实时动态电压调节低功耗算法.算法在编译器的帮助下,在条件语句,循环语句等影响程序实际执行时间的控制语句结构中设置电压调节点,插入电压调节代码,从而最大限度地利用了程序运行时的空闲时间,达到了降低系统功耗的效果.在RTLPower实时低功耗系统上对算法进行了实验,实验结果表明该算法可以减少50%的能量消耗.     

A compact system of small planets around a former red-giant star

Planets that orbit their parent star at less than about one astronomical unit (1?AU is the Earth-Sun distance) are expected to be engulfed when the star becomes a red giant. Previous observations have revealed the existence of post-red-giant host stars with giant planets orbiting as close as 0.116?AU or with brown dwarf companions in tight orbits, showing that these bodies can survive engulfment. What has remained unclear is whether planets can be dragged deeper into the red-giant envelope without being disrupted and whether the evolution of the parent star itself could be affected. Here we report the presence of two nearly Earth-sized bodies orbiting the post-red-giant, hot B subdwarf star KIC 05807616 at distances of 0.0060 and 0.0076?AU, with orbital periods of 5.7625 and 8.2293 hours, respectively. These bodies probably survived deep immersion in the former red-giant envelope. They may be the dense cores of evaporated giant planets that were transported closer to the star during the engulfment and triggered the mass loss necessary for the formation of the hot B subdwarf, which might also explain how some stars of this type did not form in binary systems.     

设备密集型仿真系统硬件控制接口模式及系统

针对设备密集型仿真系统硬件控制开发存在的无序、依赖、重复等实际工程问题,在硬件控制量的标识、采集、驱动、传输、访问、维护等方面进行研究,实现一种规范、软硬件高效无缝集成的系统化方法和支持该法的可重用产品.硬件控制量的标识采用二维表示法,并采用紧缩二维索引、传输数据压缩技术达到既节省存储空间又不影响访问、传输时间效率的目标.实现一个支持该表示法的通用硬件接口系统,在客户源程序中可以通过该接口系统提供的与二维表示法完全一致的接口实现硬件控制量的访问.在多台全任务飞行模拟器中的应用结果表明,该方法和相关接口系统具有直观、简洁、规范、无缝集成、可重用、易维护扩充、满足实时性要求等特点.