Infrared echoes near the supernova remnant Cassiopeia A

Two images of Cassiopeia A obtained at 24 micrometers with the Spitzer Space Telescope over a 1-year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arc minutes. Individual features exhibit apparent motions of 10 to 20 arc seconds per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant.     

The Fermi Gamma-Ray Space Telescope discovers the pulsar in the young galactic supernova remnant CTA 1

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 x 10(-13) seconds per second. Its characteristic age of 10(4) years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.     

Herschel detects a massive dust reservoir in supernova 1987A

We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.     

Bistatic-radar observation of long-period, directional ocean-wave spectra with loran a

Bistatic-radar scattering from medium- to long-wavelength (80 to 200 meters) ocean waves has been observed with the use of loran A (1.85 megahertz) transmissions and a receiver located 280 kilometers away. The received echoes have been converted into a time-delay, Doppler-frequency map in which the effects of anisotropies in the ocean-wave spectra are clearly shown. The distribution of the echoes in delay-Doppler space is consistent with Bragg scattering from trains of dispersed ocean waves.     

ROSAT X-ray detection of a young brown dwarf in the chamaeleon I dark cloud

Photometry and spectroscopy of the object Cha Halpha 1, located in the Chamaeleon I star-forming cloud, show that it is a approximately 10(6)-year-old brown dwarf with spectral type M7.5 to M8 and 0.04 +/- 0.01 solar masses. Quiescent x-ray emission was detected in a 36-kilosecond observation with 31.4 +/- 7.7 x-ray photons, obtained with the Rontgen Satellite (ROSAT), with 9final sigma detection significance. This corresponds to an x-ray luminosity of 2.57 x 10(28) ergs per second and an x-ray to bolometric luminosity ratio of 10(-3.44). These are typical values for late M-type stars. Because the interior of brown dwarfs may be similar to that of convective late-type stars, which are well-known x-ray sources, x-ray emission from brown dwarfs may indicate magnetic activity.     

Detection of circumstellar material in a normal type Ia supernova

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.     

An asymmetric energetic type Ic supernova viewed off-axis, and a link to gamma ray bursts

Type Ic supernovae, the explosions after the core collapse of massive stars that have previously lost their hydrogen and helium envelopes, are particularly interesting because of their link with long-duration gamma ray bursts. Although indications exist that these explosions are aspherical, direct evidence has been missing. Late-time observations of supernova SN 2003jd, a luminous type Ic supernova, provide such evidence. Recent Subaru and Keck spectra reveal double-peaked profiles in the nebular lines of neutral oxygen and magnesium. These profiles are different from those of known type Ic supernovae, with or without a gamma ray burst, and they can be understood if SN 2003jd was an aspherical axisymmetric explosion viewed from near the equatorial plane. If SN 2003jd was associated with a gamma ray burst, we missed the burst because it was pointing away from us.     

Discovery of a compact radio component in the center of supernova 1986J

Very-long-baseline interferometry observations have revealed a bright, compact radio component near the center of the expanding shell of supernova 1986J. The component, not present in earlier images, has an inverted radio spectrum different from that of the shell. Such an inversion has not been seen in the spectrum of any other supernova. The new component is likely radio emission associated either with accretion onto a black hole or with the nebula formed around an energetic young neutron star in the center of SN 1986J, which would directly link either a black hole or a neutron star to a modern supernova.     

A high-brightness source of narrowband, identical-photon pairs

We generated narrowband pairs of nearly identical photons at a rate of 5 x 10(4) pairs per second from a laser-cooled atomic ensemble inside an optical cavity. A two-photon interference experiment demonstrated that the photons could be made 90% indistinguishable, a key requirement for quantum information-processing protocols. Used as a conditional single-photon source, the system operated near the fundamental limits on recovery efficiency (57%), Fourier transform-limited bandwidth, and pair-generation-rate-limited suppression of two-photon events (factor of 33 below the Poisson limit). Each photon had a spectral width of 1.1 megahertz, ideal for interacting with atomic ensembles that form the basis of proposed quantum memories and logic.     

A Synchrotron X-ray Study of a Solid-Solid Phase Transition in a Two-Dimensional Crystal

A measurement and interpretation on a molecular level of a phase transition in an ordered Langmuir monolayer is reported. The diagram of surface pressure (pi) versus molecular area of a monolayer of chiral (S)-[CF(3)-(CF(2))(9)-(CH(2))(2)-OCO-CH(2)-CH (NH(3)(+))CO(2)(-)] over water shows a change in slope at about pi(s)= 25 millinewtons per meter. Grazing-incidence x-ray diffraction and specular reflectivity measurements indicate a solid-solid phase transition at pi(s). The diffraction pattren at low pressures reveals two diffraction peaks of equal intensities, with lattice spacings d of 5.11 and 5.00 angstroms; these coalesce for pi >/=pi(s). Structural models that fit the diffraction data show that at pi> pi(s) the molecules pack in a two-dimensional crystal with the molecules aligned vertically. At pi < pi(s) there is a molecular tilt of 16 degrees +/- 7 degrees . Independent x-ray reflectivity data yield a tilt of 26 degrees +/- 7 degrees . Concomitant with the tilt, the diffraction data indicate a transition from a hexagonal to a distorted-hexagonal lattice. The hexagonal arrangement is favored because the -(CF(2))(9)CF(3) moiety adopts a helical conformation. Compression to 70 millinewtons per meter yields a unit cell with increased crystallinity and a coherence length exceeding 1000 angstroms.     

A Spatially Resolved X-ray Image of a Star Like the Sun

Observations made with the x-ray satellite ROSAT (Roentgen Satellite) have produced the first spatially resolved x-ray image of a corona around a star like our sun. The star is the secondary in the eclipsing binary system alpha Coronae Borealis (CrB), which consists of one star of spectral type A0V and one of type G5V. The x-ray light curve of alpha CrB shows a total x-ray eclipse during secondary optical minimum, with the G star behind the A star. The totality of the eclipse demonstrates that the A-type component in alpha CrB is x-ray dark and that the x-ray flux arises exclusively from the later-type companion. The x-ray eclipse ingress and egress are highly asymmetric compared with the optical eclipse, indicating a highly asymmetric x-ray intensity distribution on the surface of the G star. From a detailed modeling of the ingress and egress of the x-ray light curve, an eclipse map of the G star was constructed by a method based on an optimization by simulated annealing.     

强度干扰后退化森林生态系统中保留木的生态效应研究综述

保留木是指森林生态系统受到强度干扰后所存留的树木,保留木对退化森林生态系统结构与功能的维持和恢复具有多方面的生态效应。在生态系统的尺度上总结了退化森林生态系统中保留木的各种生态效应,主要包括保留木对非生物因子和生物因子(附生生物多样性、动物活动和动物多样性、树木更新、空间结构)的影响。森林生态系统经营中,"绿树保留"的经营方式是基于保留木生态效益的实践应用,它可有效减少采伐对生态系统结构和功能所造成的损失。并将有助于深入理解受到强度干扰后森林生态系统中保留木的多种生态效应,可为退化森林生态系统的恢复与重建提供理论依据。     

贵州红水河沟谷残存季雨林蕨类植物区系初步研究

初步研究表明,贵州红水河沟谷残存季雨林共有蕨类植物178种（含变种和变型）,隶属于30科67属。该区蕨类植物中优势科、属明显,优势科有水龙骨科Polypodiaceae,金星蕨科Thelypteridaceae,卷柏科Selaginellaceae,凤尾蕨科Pteridaceae,蹄盖蕨科Athyriaceae,铁角蕨科Aspleniaceae,三叉蕨科Aspidiaceae,鳞毛蕨科Dryopteridaceae,铁线蕨科Adiantaceae;优势属有卷柏属Selaginella,凤尾蕨属Pteris,毛蕨属Cyclosorus,铁线蕨属Adiantun,短肠蕨属Allantadia,铁角蕨属Asplenium,线蕨属Colysis。区系分析结果表明,该区蕨类植物属的地理成分包含世界广布成分、热带成分、热带亚热带成分、亚热带成分、温带成分和东亚成分等6个成分类型,以热带亚热带成分（含26属）为主,频率达44．83％;种的区系成分包含世界广布成分、热带成分、热带亚热带成分、温带成分、东亚成分和中国特有成分等6个成分类型,以热带亚热带成分为主（含103种）,频率达59．54％。聚类分析结果显示,该蕨类区系与深圳南山区蕨类植物区系地理成分的组成最为相似、图1表3参26     

贵州红水河沟谷残存季雨林药用蕨类植物资源调查

对贵州红水河沟谷残存季雨林药用蕨类植物进行调查及标本采集鉴定,初步统计出贵州红水河沟谷残存季雨林分布有药用蕨类植物75种（含2变型）,隶属于26科44属,对该区系药用蕨类植物的多样性、药用价值进行了阐述,并对进一步开发与利用提出了建议。表2参22．