从美国的经济衰退看市场失灵

市场经济在发展过程中,往往会出现失灵。当人们分析这个问题时,一般只是从市场本身去寻找原因,妄图依靠市场自身的力量去克服,而忽视了实质问题。在借鉴前人已有成果的基础上,力图从宏观的、深层次的角度出发,结合近年来美国经济发展的实例,去找出引发市场失灵的真正原因,并提出解决它的一些办法。     

Partially Ionized Plasmas in Astrophysics

Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress.     

Particle Acceleration in the Heliosphere: Implications for Astrophysics

There has been a remarkable discovery concerning particles that are accelerated in the solar wind. At low energies, in the region where the particles are being accelerated, the spectrum of the accelerated particles is always the same: when expressed as a distribution function, the spectrum is a power law in particle speed with a spectral index of ?5, and a rollover at higher particle speeds that can often be described as exponential. This common spectral shape cannot be accounted for by any conventional acceleration mechanism, such as diffusive shock acceleration or traditional stochastic acceleration. It has thus been necessary to invent a new acceleration mechanism to account for these observations, a pump mechanism in which particles are pumped up in energy through a series of adiabatic compressions and expansions. The conditions under which the pump acceleration is the dominant acceleration mechanism are quite general and are likely to occur in other astrophysical plasmas. In this paper, the most compelling observations of the ?5 spectra are reviewed; the governing equation of the pump acceleration mechanism is derived in detail; the pump acceleration mechanism is applied to acceleration at shocks; and, as an illustration of the potential applicability of the pump acceleration mechanism to other astrophysical plasmas, the pump mechanism is applied to the acceleration of galactic cosmic rays in the interstellar medium.     

Fundamental Unsolved Problems in Astrophysics

There is given a list and discussion of what are arguably the top 20 unsolved problems in astrophysics today. The list ranges from particle physics to cosmology. Possible resolutions are noted, but without judgement. Perhaps the most remarkable aspect of the discussed problems is that they are closely interrelated. This opens the prospect that a solution to one or a few may lead to a significantly better understanding of modern astrophysics.     

Gravitomagnetism in Physics and Astrophysics

Based on general relativity, the article reviews gravitomagnetism in physics and astrophysics. Emphasis is put on observational effects. Accelerated reference frames in flat spacetime are discussed to illuminate the gravitomagnetic field. Compact insight into the dynamics of gravitationally interacting non-spinning and spinning objects is achieved by employing the Hamilton formalism.     

高阶椭圆齿轮的三维实体设计与线切割加工

非圆齿轮可以实现周期性的非匀速比运动,在各种精密机械中都得到了日益广泛的应用。综合应用CREO的参数化设计功能、ADAMS的运动仿真功能、CAXA线切割的代码生成功能实现了三阶椭圆齿轮的设计与制造,为单件及小批量生产场合创建了典型范式,适用于各种类型非圆齿轮的设计与制造。     

The Astrophysics of Galactic Cosmic Rays

Observations of cosmic rays and their related radio to gamma-ray signatures are surveyed and discussed critically, and compared to theoretical models of the cosmic-ray origin and propagation. The analogous heliospheric processes are included as a well-studied case of the principal physical processes of energetic particle acceleration and propagation. Reinforcements, or conflicts, in the interpretations of cosmic-ray spectral and compositional characteristics arise when cosmic-ray source and propagation models are confronted with astronomical information about the Galaxy as a whole and from potential source sites, i.e., supernova remnants or regions with high massive-star density. This volume represents the outcome of two workshops held at ISSI. In this chapter we summarize the introductory papers presented below, and include insights from the workshop discussions.     

Hysteresis Provides Self-Organization in a Plasma Model

The magnetosphere is a multi-scale spatio-temporal complex dynamical system. Self-organization is a possible solution to the seemingly contradicting observation of the repeatable and coherent substorm phenomena with underlying complex behavior in the plasma sheet. Self-organization, through spatio-temporal chaos, emerges naturally in a plasma physics model with sporadic dissipation.     

Understanding Kappa Distributions: A Toolbox for Space Science and Astrophysics

In this paper we examine the physical foundations and theoretical development of the kappa distribution, which arises naturally from non-extensive Statistical Mechanics. The kappa distribution provides a straightforward replacement for the Maxwell distribution when dealing with systems in stationary states out of thermal equilibrium, commonly found in space and astrophysical plasmas. Prior studies have used a variety of inconsistent, and sometimes incorrect, formulations, which have led to significant confusion about these distributions. Therefore, in this study, we start from the N-particle phase space distribution and develop seven formulations for kappa distributions that range from the most general to several specialized versions that can be directly used with common types of space data. Collectively, these formulations and their guidelines provide a “toolbox” of useful and statistically well-grounded equations for future space physics analyses that seek to apply kappa distributions in data analysis, simulations, modeling, theory, and other work.     

更为有序的库存管理

航空公司和供应商在库存管理系统投入巨资,减少供应链中一切低效率的环节,以期达到节省资金和盈利的目标。因为库存和航材占用大量的资金,而这些被大量库存所占用的资金本可以用在如开发新产品、拓展市场和     

Alteration Assemblages in Martian Meteorites: Implications for Near-Surface Processes

The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between martian crustal fluids and the parent igneous rocks. The resultant secondary minerals — which comprise up to 1 vol.% of the meteorites — provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25 – 150 °C) brines. This is consistent with the simple mineralogy of these assemblages — Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays — and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 "rosettes". Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event post-dating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes.Radiometric dating (K-Ar, Rb-Sr) of the secondary mineral assemblages in one of the nakhlites (Lafayette) suggests that they formed between 0 and 670 Myr, and certainly long after the crystallisation of the host igneous rocks. Crystallisation of ALH84001 carbonate took place 0.5 Gyr after the parent rock. These age ranges and the other research on these assemblages suggest that environmental conditions conducive to near-surface liquid water have been present on Mars periodically over the last 1 Gyr. This fluid activity cannot have been continuous over geological time because in that case much more silicate alteration would have taken place in the meteorite parent rocks and the soluble salts would probably not have been preserved.The secondary minerals could have been precipitated from brines with seawater-like composition, high bicarbonate contents and a weakly acidic nature. The co-existence of siderite (Fe-carbonate) and clays in the nakhlites suggests that the pCO₂ level in equilibrium with the parent brine may have been 50 mbar or more. The brines could have originated as flood waters which percolated through the top few hundred meters of the crust, releasing cations from the surrounding parent rocks. The high sulphur and chlorine concentrations of the martian soil have most likely resulted from aeolian redistribution of such aqueously-deposited salts and from reaction of the martian surface with volcanic acid volatiles.The volume of carbonates in meteorites provides a minimum crustal abundance and is equivalent to 50–250 mbar of CO₂ being trapped in the uppermost 200–1000 m of the martian crust. Large fractionations in ¹⁸O between igneous silicate in the meteorites and the secondary minerals (30) require formation of the latter below temperatures at which silicate-carbonate equilibration could have taken place (400°C) and have been taken to suggest low temperatures (e.g. 150°C) of precipitation from a hydrous fluid.     

Non-Thermal Processes in Cosmological Simulations

Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles and turbulence.     

精益技术在维修上的应用

改变了飞机生产线的精益技术正在维修产品上找到新的应用,可大量节省修理时间。一架美国陆军的AH-64阿帕奇直升机经过在伊拉克长达1年的服役,机上的弹孔多是草草打上补丁     

Injection and Acceleration Processes in Corotating Interaction Regions: Theoretical Concepts

A brief overview on particle injection and acceleration in corotating interaction regions is presented. After introducing the diffusion-convection transport equation for energetic particles we discuss diffusive acceleration at the corotating shocks, stochastic acceleration within the interaction region, and the injection and acceleration of pickup ions at the corotating shocks. This revised version was published online in August 2006 with corrections to the Cover Date.     

俄罗斯航空工业:政令能否确保变革成功?

《国际航空》2006年第一期曾刊载了关于俄罗斯航空制造业意欲合并重组的动向,近来,随着总统令的签署,看来这场变革势在必行,然而,政令之下,是否行之有效,真能一改俄罗斯航空工业颓废没落之势,俄国内争议依然很多。     

Physical Processes in the Outer Heliosphere

This chapter covers the theory of physical processes in the outer heliosphere that are particularly important for the IBEX Mission, excluding global magnetohydrodynamic/Boltzmann modeling of the entire heliosphere. Topics addressed include the structure and parameters of the solar wind termination shock, the transmission of ions through the termination shock including possible reflections at the shock electrostatic potential, the acceleration and transport of suprathermal ions and anomalous cosmic rays at the termination shock and in the heliosheath, charge-exchange interactions in the outer heliosphere including mass and momentum loading of the solar wind, the transport of interstellar pickup ions, and the production and anticipated intensities of energetic neutral atoms (ENAs) in the heliosphere.     

Substorm Trigger Processes in the Magnetotail: Recent Observations and Outstanding Issues

The present article reviews recent studies about near-Earth substorm processes. A focus is placed on the relationship between two fundamental processes, that is, tail current disruption (TCD) and the formation of a near-Earth neutral line (NENL). The former is inferred to cause dipolarization, and the latter is often associated with the fast plasma flow in the plasma sheet. Whereas it is inferred from the directions of fast plasma flows that the NENL is formed at 20–30 R _E from the Earth, dipolarization is most manifest in the near-Earth (6.6–12 R _E) region. The observation of the fast plasma flow prior to substorm (Pi2) onsets favors the idea that the NENL is formed first and dipolarization is the effect of the pile-up of magnetic flux convected earthward from the NENL, which is called the pile-up model. The present paper addresses several outstanding issues regarding this model, including (1) the interpretation of plasma flow deceleration in terms of the flux pile up, (2) highly irregular magnetic fluctuations observed in the near- Earth region, (3) the spatial coherency of the fast plasma flow, (4) the spatial structure and expansion of dipolarization region, and (5) the explosive growth phase. The paper also proposes the possibility that TCD is an independent process, but the formation of the NENL sets a favorable condition for it.