A cocoon of freshly accelerated cosmic rays detected by Fermi in the Cygnus superbubble

The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little of their escape from the shock and their evolution through the turbulent medium surrounding massive stars. Gamma rays can probe their spreading through the ambient gas and radiation fields. The Fermi Large Area Telescope (LAT) has observed the star-forming region of Cygnus X. The 1- to 100-gigaelectronvolt images reveal a 50-parsec-wide cocoon of freshly accelerated cosmic rays that flood the cavities carved by the stellar winds and ionization fronts from young stellar clusters. It provides an example to study the youth of cosmic rays in a superbubble environment before they merge into the older Galactic population.     

Astronomy and Solar Physics: X-ray Gas Scintillation Spectrometer Experiment

The payload complement on Spacelab 1 included a spectrometer for observations of the brighter cosmic x-ray sources. The primary scientific objective was to study the detailed spectral features of cosmic x-ray sources and their associated temporal variations over a wide energy range from about 2 to 80 kiloelectron volts. The instrument, based on the gas scintillation proportional counter, had a geometrical area of some 180 square centimeters with an energy resolution of about 9 percent at 7 kiloelectron volts. The results presented here show new results from two galactic binary x-ray sources, Cygnus X-3 and Centaurus X-3, and from the Perseus cluster of galaxies. The excellent energy resolution of the instrument permits line features to be identified in these sources with unprecedented quality.     

Hydrogen 21-centimeter emission from a galaxy at cosmological distance

We have detected the neutral atomic hydrogen (HI) emission line at a cosmologically significant distance [redshift (z) = 0.18] in the rich galaxy cluster Abell 2218 with the Westerbork Synthesis Radio Telescope. The HI emission originates in a spiral galaxy 2.0 h65(-1) megaparsecs from the cluster core. No other significant detections have been made in the cluster, suggesting that the mechanisms that remove neutral gas from cluster galaxies are efficient. We infer that fewer than three gas-rich galaxies were accreted by Abell 2218 over the past 10(9) years. This low accretion rate is qualitatively consistent with low-density cosmological models in which clusters are largely assembled at z > 1.     

Particle acceleration on megaparsec scales in a merging galaxy cluster

Galaxy clusters form through a sequence of mergers of smaller galaxy clusters and groups. Models of diffusive shock acceleration suggest that in shocks that occur during cluster mergers, particles are accelerated to relativistic energies, similar to conditions within supernova remnants. In the presence of magnetic fields, these particles emit synchrotron radiation and may form so-called radio relics. We detected a radio relic that displays highly aligned magnetic fields, a strong spectral index gradient, and a narrow relic width, giving a measure of the magnetic field in an unexplored site of the universe. Our observations show that diffusive shock acceleration also operates on scales much larger than in supernova remnants and that shocks in galaxy clusters are capable of producing extremely energetic cosmic rays.     

Magnetism from the atom to the bulk in iron, cobalt, and nickel clusters

Molecular beam deflection measurements of small iron, cobalt, and nickel clusters show how magnetism develops as the cluster size is increased from several tens to several hundreds of atoms for temperatures between 80 and 1000 K. Ferromagnetism occurs even for the smallest sizes: for clusters with fewer than about 30 atoms the magnetic moments are atomlike; as the size is increased up to 700 atoms, the magnetic moments approach the bulk limit, with oscillations probably caused by surface-induced spin-density waves. The trends are explained in a magnetic shell model. A crystallographic phase transition from high moment to low moment in iron clusters has also been identified.     

Stormy weather in galaxy clusters

Recent x-ray, optical, and radio observations coupled with particle and gas dynamics numerical simulations reveal an unexpectedly complex environment within clusters of galaxies, driven by ongoing accretion of matter from large-scale supercluster filaments. Mergers between clusters and continuous infall of dark matter and baryons from the cluster periphery produce long-lived "stormy weather" within the gaseous cluster atmosphere-shocks, turbulence, and winds of more than 1000 kilometers per second. This weather may be responsible for shaping a rich variety of extended radio sources, which in turn act as "barometers" and "anemometers" of cluster weather.     

Clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield, california

The San Andreas fault at Parkfield, California, apparently late in an interval between repeating magnitude 6 earthquakes, is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters (<20-meter radius) of microearthquakes. Within these clusters, which account for 63% of the earthquakes in a 1987-92 study interval, virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes. Sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second. The rate of earthquake occurrence, particularly at depth, increased significantly during the study period, but the fraction of earthquakes that were cluster members decreased.     

An inverse compton process for the excess diffuse EUV emission from the virgo and coma galaxy clusters

The excess extreme-ultraviolet (EUV) emission detected in the Virgo and Coma clusters is explained by inverse Compton scattering of cosmic microwave background photons, which are scattered by the relativistic electrons that account for the extended radio synchrotron emission of these clusters. The lower limits of the average magnetic fields of these clusters estimated from the EUV excess are close to the equipartition magnetic fields derived from radio observations, indicating that the electron energies and magnetic field energies might be close to equipartition. The excess emission suggests energy reservoirs of approximately 10(61) and approximately 10(60) ergs for the Coma and Virgo clusters, respectively.     

Age estimates of globular clusters in the Milky Way: constraints on cosmology

Recent observations of stellar globular clusters in the Milky Way Galaxy, combined with revised ranges of parameters in stellar evolution codes and new estimates of the earliest epoch of globular cluster formation, result in a 95% confidence level lower limit on the age of the Universe of 11.2 billion years. This age is inconsistent with the expansion age for a flat Universe for the currently allowed range of the Hubble constant, unless the cosmic equation of state is dominated by a component that violates the strong energy condition. This means that the three fundamental observables in cosmology-the age of the Universe, the distance-redshift relation, and the geometry of the Universe-now independently support the case for a dark energy-dominated Universe.     

Gas-phase clusters: spanning the States of matter

Gas-phase clusters, which are weakly bound aggregates comprised of either atoms or molecules, often display properties that lie between those of the gaseous and condensed states. Interesting questions arise concerning how large a cluster must be before it will display bulk properties. Currently there is extensive research activity directed toward studies of their formation and varying properties and reactivity as a function of the degree of aggregation. Results serve to elucidate at the molecular level the course of change of a system to be followed from the gas to the condensed state, thereby enabling a spanning of the states of matter.     

Extreme-Ultraviolet Flux from the Virgo Cluster: Further Evidence for a 500,000-Kelvin Component

A surprising discovery in x-ray astronomy was that clusters of galaxies often contain vast quantities of hot (20 million kelvin) diffuse gas. Substantial diffuse extreme-ultraviolet (EUV) emission has recently been detected in the Virgo cluster of galaxies. Depending on the character of the interstellar medium in our galaxy, this emission could be either an aspect of the hot cluster gas or a previously undetected 500,000-kelvin component. Analysis of the observational data in combination with our current knowledge of the interstellar medium revealed that the EUV flux cannot be an effect of the interstellar medium. Hence, a warm cluster component appears likely.     

Giant ringlike radio structures around galaxy cluster Abell 3376

In the current paradigm of cold dark matter cosmology, large-scale structures are assembling through hierarchical clustering of matter. In this process, an important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark matter-dominated collapsing structures such as pancakes, filaments, and clusters of galaxies. Here, we report Very Large Array telescope observations of giant ( approximately 2 Mpc by 1.6 Mpc), ring-shaped nonthermal radio-emitting structures, found at the outskirts of the rich cluster of galaxies Abell 3376. These structures may trace the elusive shock waves of cosmological large-scale matter flows, which are energetic enough to power them. These radio sources may also be the acceleration sites where magnetic shocks are possibly boosting cosmic-ray particles with energies of up to 10(18) to 10(19) electron volts.     

湖南生猪生产波动影响因素的实证分析及政策建议

本文在明确农业产业集群含义的基础上,通过对辽宁省农业产业集群的个案调查研究,总结出农业产业集群有三种成长模式,即基础推动型农业产业集群,企业带动型农业产业集群和市场导向型农业产业集群。这三种成长模式只是广义上的农业产业集群向严格意义的农业产业集群发展中形成的不同路径方式。针对不同成长模式存在的问题,提出相应的对策建议。不同地区在发展本地农业产业集群时,可以依据自身优势,有不同的模式选择。     

基于自组织竞争神经网络的红籽瓜自交系聚类分析

自组织竞争神经网络是一种具有强大的自学习功能、良好的自组织性和自适应性的聚类方法,能够迅速得到聚类结果.本文基于自组织竞争神经网络的聚类功能,依据6个红色籽用西瓜数量性状特征指标,将47份自交系分为4类.聚类结果表明,不同自交系类群间的遗传变异较大,在配置杂交组合时,应尽量在不同类群问选配亲本,为红籽瓜育种提供理论依据.     

Infrared signature of structures associated with the H+(H2O)n (n = 6 to 27) clusters

We report the OH stretching vibrational spectra of size-selected H+(H2O)n clusters through the region of the pronounced "magic number" at n = 21 in the cluster distribution. Sharp features are observed in the spectra and assigned to excitation of the dangling OH groups throughout the size range 6 相似文献   

Numerical simulations unravel the cosmic web

The universe is permeated by a network of filaments, sheets, and knots collectively forming a "cosmic web." The discovery of the cosmic web, especially through its signature of absorption of light from distant sources by neutral hydrogen in the intervening intergalactic medium, exemplifies the interplay between theory and experiment that drives science and is one of the great examples in which numerical simulations have played a key and decisive role. We recount the milestones in our understanding of cosmic structure; summarize its impact on astronomy, cosmology, and physics; and look ahead by outlining the challenges faced as we prepare to probe the cosmic web at new wavelengths.     

History of meteorites from the moon collected in antarctica

In large asteroidal or cometary impacts on the moon, lunar surface material can be ejected with escape velocities. A few of these rocks were captured by Earth and were recently collected on the Antarctic ice. The records of noble gas isotopes and of cosmic ray-produced radionuclides in five of these meteorites reveal that they originated from at least two different impact craters on the moon. The chemical composition indicates that the impact sites were probably far from the Apollo and Luna landing sites. The duration of the moon-Earth transfer for three meteorites, which belong to the same fall event on Earth, lasted 5 to 11 million years, in contrast to a duration of less than 300,000 years for the two other meteorites. From the activities of cosmic ray-produced radionuclides, the date of fall onto the Antarctic ice sheet is calculated as 70,000 to 170,000 years ago.     

物流对农业产业集群发展的影响研究

农业产业集群高效率生产的竞争优势需物流系统的支撑,物流对农业产业集群能够辐射的市场区域大小有很大影响,进行物流对农业产业集群发展的影响研究具有积极意义.对农业产业集群及其物流进行分析,并采用层次分析法分析物流各因素对农业产业集群发展影响的相对重要程度,结果表明物流的专业化程度是影响农业产业集群发展的首要因素.提出农业产业集群与第三方物流从战略适应和功能整合两个维度合作,从而加大第三方物流对农业产业集群发展的推动作用.     

A Possible Intracluster Origin for the Excess Soft X-ray Component in Some Clusters

The soft x-ray spectra of the Virgo and Coma clusters cannot be modeled by emission from the well-known hot intracluster medium attenuated by photoelectric absorption along the line of sight in our galaxy. If the excess soft emission is due to thermal emission in the clusters from gas at about 1 million kelvin, then the gas should be rapidly cooling. The high rate of cooling poses problems for the origin of the gas and its sink. A model in which the component is due to turbulent mixing layers around clouds scattered throughout the intracluster medium may explain the excess emission. The gas in the mixing layer is reheated after cooling, so that the total mass remains relatively small.