Evolution of the Protosolar Nebula and Formation of the Giant Planets

The formation of planetary systems is intimately tied to the question of the evolution of the gas and solid material in the early nebula. Current models of evolution of circumstellar disks are reviewed here with emphasis on the so-called “alpha models” in which angular momentum is transported outward by turbulent viscosity, parameterized by an dimensionless parameter α. A simple 1D model of protoplanetary disks that includes gas and embedded particles is used to introduce key questions on planetesimal formation. This model includes the aerodynamic properties of solid ice and rock grains to calculate their migration and growth. We show that the evolution of the nebula and migration and growth of its solids proceed on timescales that are generally not much longer than the timescale necessary to fully form the star-disk system from the molecular cloud. Contrary to a widely used approach, planet formation therefore can neither be studied in a static nebula nor in a nebula evolving from an arbitrary initial condition. We propose a simple approach to both account for sedimentation from the molecular cloud onto the disk, disk evolution and migration of solids. Giant planets have key roles in the history of the forming Solar System: they formed relatively early, when a significant amount of hydrogen and helium were still present in the nebula, and have a mass that is a sizable fraction of the disk mass at any given time. Their composition is also of interest because when compared to the solar composition, their enrichment in elements other than hydrogen and helium is a witness of sorting processes that occured in the protosolar nebula. We review likely scenarios capable of explaining both the presence of central dense cores in Jupiter, Saturn, Uranus and Neptune and their global composition. This revised version was published online in August 2006 with corrections to the Cover Date.     

A lightning swept stroke model: A valuable tool to investigate the lightning strike to aircraft

In the context of lightning strike on the Dassault Falcon family of aircraft, the standard zoning of Falcon 50, 900 and 2000, inferred from FAA and EUROCAE WG31 documents [US Department of Transportation, Federal Aviation Administration, Advisory Circular AC 20-53A, 1985; US Department of Transportation, Federal Aviation Administration, Advisory Circular AC 20-53B, Draft, 1991; EUROCAE WG 31, Aircraft Lightning Zoning Standard, ED-91, 1998], has been presented. Zoning proves to be quite similar between the three types of aircraft. Thanks to the feed-back on lightning strikes to Falcon, lightning traces have been observed on the fuselage for different flight conditions and aircraft. Observations are compared with the zoning performed by Dassault. A physical model, developed by ONERA, was used to simulate the sweeping of lightning on the fuselage of a Falcon 900. The results are in good agreement with the lightning traces observed on the fuselages.     

构建高职数控技术应用专业课程体系的改革与实践

课程体系是衡量学校办学水平和教学质量的重要标志，是实现培养目标的基本保证。从构建课程体系前提、人才培养目标、人才培养机制、课程体系构建、课程体系改革的效果等几个方面对数控技术应用专业课程体系建设进行了探讨，初步构建了产学研结合的人才培养途径，建立了理论体系和实践体系相结合的课程体系。     

Modeling of dynamic evolution of coronal loops

Parameters of expanding magnetic loops and arches and of mass flows generated by them in the corona have been computed in a 1D two-fluid approximation. Two possible trigger mechanisms of the coronal transients have been considered: (i) sudden increase of the background magnetic field strength, and (ii) heating and compression plasma inside these magnetic structures. We discuss the formation of shock waves and their dependence on dynamics and geometry of the magnetic structures.     

Solar Gamma-Ray Spectroscopy

Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain a rich set of observables that provides information about both the accelerated ions and the environment where the ions are transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact (typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona, exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric ³He abundance is also discussed.     

The Local Bubble and Interstellar Material Near the Sun

The properties of interstellar matter at the Sun are regulated by our location with respect to a void in the local matter distribution, known as the Local Bubble. The Local Bubble (LB) is bounded by associations of massive stars and fossil supernovae that have disrupted dense interstellar matter (ISM), driving low density intermediate velocity ISM into the void. The Sun appears to be located in one of these flows of low density material. This nearby interstellar matter, dubbed the Local Fluff, has a bulk velocity of ∼19 km s⁻¹ in the local standard of rest. The flow is coming from the direction of the gas and dust ring formed where the Loop I supernova remnant merges into the LB. Optical polarization data suggest that the local interstellar magnetic field lines are draped over the heliosphere. A longstanding discrepancy between the high thermal pressure of plasma filling the LB and low thermal pressures in the embedded Local Fluff cloudlets is partially mitigated when the ram pressure component parallel to the cloudlet flow direction is included.     

Stellar flares

Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are solar-like, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed.     

Evolution of low-mass stars. implications for the dark matter distribution in the halo

We present up-to-date evolutionary models of low-mass stars, from M0.6 M down to the hydrogen burning minimum mass, using recent equation of state and synthetic spectra calculations. Comparison is made with observed luminosity function for these objects. We also present implications for the dark-matter distribution in the galactic halo.     

超声爬波无损检测方法的研究

本文介绍了超声无损检测中一种具有较好应用前景的波型──超声爬波。试验研究了爬波检测时缺陷定位、定性评定的方法，并给出了主要结论。