A brown dwarf mass donor in an accreting binary

A long-standing and unverified prediction of binary star evolution theory is the existence of a population of white dwarfs accreting from substellar donor stars. Such systems ought to be common, but the difficulty of finding them, combined with the challenge of detecting the donor against the light from accretion, means that no donor star to date has a measured mass below the hydrogen burning limit. We applied a technique that allowed us to reliably measure the mass of the unseen donor star in eclipsing systems. We were able to identify a brown dwarf donor star, with a mass of 0.052 +/- 0.002 solar mass. The relatively high mass of the donor star for its orbital period suggests that current evolutionary models may underestimate the radii of brown dwarfs.     

Flashing superluminal components in the jet of the radio galaxy 3C120

A 16-month sequence of radio images of the active galaxy 3C120 with the Very Long Baseline Array reveals a region in the relativistic jet where superluminal components flash on and off over time scales of months, while the polarization angle rotates. This can be explained by interaction between the jet and an interstellar cloud located about 8 parsecs from the center of the galaxy. The cloud, which rotates the polarization direction and possibly eclipses a section of the jet, represents a "missing link" between the ultradense broad-emission-line clouds closer to the center and the lower density narrow-emission-line clouds seen on kiloparsec scales.     

A gaseous metal disk around a white dwarf

The destiny of planetary systems through the late evolution of their host stars is very uncertain. We report a metal-rich gas disk around a moderately hot and young white dwarf. A dynamical model of the double-peaked emission lines constrains the outer disk radius to just 1.2 solar radii. The likely origin of the disk is a tidally disrupted asteroid, which has been destabilized from its initial orbit at a distance of more than 1000 solar radii by the interaction with a relatively massive planetesimal object or a planet. The white dwarf mass of 0.77 solar mass implies that planetary systems may form around high-mass stars.     

新伪尾柱虫皮层纤毛器的超微结构1）

应用透射电镜术显示了腹毛目纤毛虫新伪尾柱虫（Pseudourostyla nova）的皮层表膜及表膜下细胞质、皮层微管胞器和其他细胞质胞器。结果显示：新伪尾柱虫纤毛器基部附属微管较为短小,细胞表膜下成束排列的微管结构与进化程度较高的纤毛虫的微管胞器表现出诸多差异,认为腹毛目纤毛虫棘毛基部微管的发达程度是与其各类群细胞的分化程度密切联系的。     

Absorption features in the x-ray spectrum of an ordinary radio pulsar

The vast majority of known nonaccreting neutron stars (NSs) are rotation-powered radio and/or γ-ray pulsars. So far, their multiwavelength spectra have all been described satisfactorily by thermal and nonthermal continuum models, with no spectral lines. Spectral features have, however, been found in a handful of exotic NSs and were thought to be a manifestation of their unique traits. Here, we report the detection of absorption features in the x-ray spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings bridge the gap between the spectra of pulsars and other, more exotic, NSs, suggesting that the features are more common in the NS spectra than they have been thought so far.     

Characterization of dwarf mutants and molecular mapping of a dwarf locus in soybean

Plant height is one of the most important traits in soybean. The semi-dwarf soybean cultivars could improve the ability of lodging resistance to obtain higher yield. To broaden the dwarfism germplasm resources in soybean, 44 dwarf mutants were identified from a gamma rays mutagenized M_-2 population. Two of these mutants, Gmdwf1(Glycine max dwarf 1) and Gmdwf2(Glycine max dwarf 2), were investigated in this study. Genetic analysis showed that both mutants were inherited in a recessive manner and their mutated regions were delimited to a 2.610-Mb region on chromosome 1 by preliminary mapping. Further fine mapping study proved that the two mutants had a common deletion region of 1.552 Mb in the target region, which was located in a novel locus site without being reported previously. The dwarfism of Gmdwf1 could not be rescued by gibberellin(GA) and brassinolide(BR) treatments, which indicated that the biosynthesis of these hormones was not deficient in Gmdwf1.     

A classical nova,V2487 Oph 1998, seen in x-rays before and after its explosion

Classical nova explosions are very energetic and frequent phenomena caused by explosive hydrogen burning on top of an accreting white dwarf. Observations of the recent nova V2487 Oph 1998 by the X-ray Multi-Mirror satellite (XMM-Newton) provide evidence that accretion (probably on a magnetic white dwarf) was reestablished as early as 2.7 years after the explosion. In addition, positional correlation with a source previously discovered by the R?ntgen Satellite (ROSAT) in 1990 suggests that the site of a nova explosion had been seen in x-rays before the outburst.     

A deep 6-centimeter radio source survey

The Very Large Array has been used to survey a small region of sky at a wavelength of 6 centimeters down to a completeness level of 60 microjanskys-about 100 times weaker than the faintest radio sources that have been detected with other instruments. The observed source count at flux densities below 100 millijanskys converges in a manner similar to the lower frequency counts, although there is some evidence for an excess of sources weaker than 100 microjanskys. The sources in the survey are preferentially identified with faint galaxies.     

A radio pulsar spinning at 716 Hz

We have discovered a 716-hertz eclipsing binary radio pulsar in the globular cluster Terzan 5 using the Green Bank Telescope. It is the fastest spinning neutron star found to date, breaking the 24-year record held by the 642-hertz pulsar B1937+21. The difficulty in detecting this pulsar, because of its very low flux density and high eclipse fraction (approximately 40% of the orbit), suggests that even faster spinning neutron stars exist. If the pulsar has a mass less than twice the mass of the Sun, then its radius must be constrained by the spin rate to be <16 kilometers. The short period of this pulsar also constrains models that suggest that gravitational radiation, through an r-mode (Rossby wave) instability, limits the maximum spin frequency of neutron stars.     

Stellar feedback in dwarf galaxy formation

Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major factor shaping the evolution of dwarf galaxies. We present detailed cosmological simulations with sufficient resolution both to model the relevant physical processes and to directly assess the impact of stellar feedback on observable properties of dwarf galaxies. We show that feedback drives large-scale, bulk motions of the interstellar gas, resulting in substantial gravitational potential fluctuations and a consequent reduction in the central matter density, bringing the theoretical predictions in agreement with observations.     

A magnetized jet from a massive protostar

Synchrotron emission is commonly found in relativistic jets from active galactic nuclei (AGNs) and microquasars, but so far its presence in jets from young stellar objects (YSOs) has not been proved. Here, we present evidence of polarized synchrotron emission arising from the jet of a YSO. The apparent magnetic field, with strength of ~0.2 milligauss, is parallel to the jet axis, and the polarization degree increases toward the jet edges, as expected for a confining helical magnetic field configuration. These characteristics are similar to those found in AGN jets, hinting at a common origin of all astrophysical jets.     

水稻黑条矮缩病矮化程度与产量关系研究

对不同时期发病的黑条矮缩病病株矮化程度进行了调查,结果发现不同发病时期的矮化程度存在显著差异,据此将不同时期的病株分为5类。在此基础上对不同类型植株的单株产量、有效分蘖、穗长、秕谷率和千粒重等重要指标进行了考察,采用DPS软件对试验结果进行了相关性和差异显著性分析。数据分析表明,随着病情加重,植株产量、有效分蘖、穗长和千粒重明显下降,秕谷率则显著上升,且不同类型间考察指标达到了显著水平。     

A bright millisecond radio burst of extragalactic origin

Pulsar surveys offer a rare opportunity to monitor the radio sky for impulsive burst-like events with millisecond durations. We analyzed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3 degrees from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. No further bursts were seen in 90 hours of additional observations, which implies that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.     

Very long baseline interferometric observations made with an orbiting radio telescope

An orbiting spacecraft and ground observatories have been used to obtain interferometric observations of cosmic radio sources. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting observatory in conjunction with two 64- meter radio telescopes at ground observatories, one in Australia and one in Japan. The quasars 1730-130 (NRAO 530), 1510-089, and 1741-038 were observed at a frequency of 2.3 gigahertz, and a maximum projected baseline of 1.4 earth diameters was achieved. All quasar observations for which valid data were acquired resulted in detected fringes. Many of the techniques proposed for a dedicated very long baseline interferometry observatory in space were used successfully in this experiment.     

Supershrimp: deep bioturbation in the strait of canso, nova scotia

Axius serratus, a crustacean thought to be extremely rare, was discovered in large numbers in polluted regions of the Strait of Canso. The shrimp may live deeper than 3 meters in the sediment; burrows are kept open to at least 2.5 meters. Sediment contained in old filled burrows is anomalous in its distribution of particle size and its content of water, organic carbon, and trace elements. These anomalous qualitites affect the geotechnical properties of sediments on the sea floor.     

糜子矮秆突变体“819”矮秆基因的遗传学分析

为揭示糜子矮秆突变体“819”矮秆基因的遗传规律,为后续定位矮秆突变基因提供理论基础,研究调查了糜子矮秆突变体“819”与高秆材料J12,以及它们杂交产生的674个F₂代个体的株高、穗长、穗颈长、分蘖数、茎节数、二级枝梗长度1、二级枝梗长度2、二级枝梗长度3、二级枝梗间距1、二级枝梗间距2共10个性状,进一步利用方差分析、卡方检验、相关及回归分析、主成分分析对这些性状进行研究。结果表明,糜子矮秆突变体“819”的矮秆性状是由单基因控制的隐性性状;株高与穗长、穗颈长、分蘖数、茎节数、二级枝梗长度1、二级枝梗长度2、二级枝梗长度3、二级枝梗间距1呈极显著正相关(P<0.01),与二级枝梗间距2呈显著正相关(P<0.05);株高(Y)对其他农艺性状的回归方程为:Y=-18.446+1.491X₁+1.222X₂+6.827X₄+1.319X₇+0.746X₈,回归方程的拟合度为0.811,回归方程经显著性检验达到极显著水平(P<0.01),可以利用回归方程对株高进行预测;糜子F₂群体的10个性状进行主成分分析获得3个主成分,这3个主成分的累积贡献率高达72.656%,3个主成分分别被命名为长度因子、茎节数因子、枝梗间距因子。研究结果为矮秆基因定位、矮秆后代的评价选择提供了依据。     

中国水稻黑条矮缩病研究进展

水稻黑条矮缩病是水稻重要的病毒病,对水稻生产造成严重损失。该病由灰飞虱传播的水稻黑条矮缩病毒引起。本文综述了近年来中国水稻黑条矮缩病病原基因组结构和功能、传毒介体、病害流行以及防治等方面的最新研究进展,为中国水稻黑条矮缩病的综合防控提供依据。     

南方水稻黑条矮缩病毒S6编码一个沉默抑制子

 【目的】分析南方水稻黑条矮缩病毒（SRBSDV）基因组S6编码的SP6蛋白的抑制子活性,明确SRBSDV是否编码RNA沉默抑制子来干扰植物的沉默。【方法】将分别含有SP6与GFP质粒的农杆菌共浸润转GFP基因的16c本氏烟纯合系,观察SP6对局部沉默和系统沉默的抑制作用;将含有SP6,GFP和dsGFP质粒的农杆菌三者共浸润,观察SP6对由dsRNA引起的沉默的抑制作用;在同一植株不同部位接种GFP和SP6,观察SP6对RNA沉默信号传导的影响;通过马铃薯X病毒（Potato virus X,PVX）在本氏烟上表达SP6,观察SP6是否能增强PVX的致病性。【结果】SP6能抑制由GFP正义RNA介导的沉默,但其抑制作用较弱,仅能延缓局部沉默和系统沉默的产生。SP6能灭活RNA沉默信号,阻止沉默信号的长距离传导,回复GFP的沉默,但不能抑制由dsRNA引起的沉默。利用PVX在本氏烟上表达SP6能增强PVX的致病性。【结论】SP6是病毒编码的RNA沉默抑制子,在RNA沉默的起始和信号传导阶段起作用。     

玉米粗缩病观察初报

对玉米粗缩病的危害症状进行了描述, 通过电子显微镜对粗缩病病毒进行了观察,分析了近两年玉米粗缩病暴发的原因,并提出了简明的防治措施.