一类二阶常系数线性椭圆型方程组解的唯一性

本文给出了在相同的三种变换下将三个二阶方阵的对称化部分同时化为正定的条件，从而证明了一类二阶常系数线性椭圆型方程组能化为强椭圆型方程组，并利用这一结论证明了这类方程组在有界闭区域上Dirichlet问题解的是唯一的。     

Nonthermal Radiation Mechanisms

In this paper we review the possible radiation mechanisms for the observed non-thermal emission in clusters of galaxies, with a primary focus on the radio and hard X-ray emission. We show that the difficulty with the non-thermal, non-relativistic Bremsstrahlung model for the hard X-ray emission, first pointed out by Petrosian (Astrophys. J. 557, 560, 2001) using a cold target approximation, is somewhat alleviated when one treats the problem more exactly by including the fact that the background plasma particle energies are on average a factor of 10 below the energy of the non-thermal particles. This increases the lifetime of the non-thermal particles, and as a result decreases the extreme energy requirement, but at most by a factor of three. We then review the synchrotron and so-called inverse Compton emission by relativistic electrons, which when compared with observations can constrain the value of the magnetic field and energy of relativistic electrons. This model requires a low value of the magnetic field which is far from the equipartition value. We briefly review the possibilities of gamma-ray emission and prospects for GLAST observations. We also present a toy model of the non-thermal electron spectra that are produced by the acceleration mechanisms discussed in an accompanying paper Petrosian and Bykov (Space Sci. Rev., 2008, this issue, Chap. 11).     

The dust content of clusters of galaxies

We have statistically investigated the infrared luminosity of clusters of galaxies in comparison with the known tracers of the cluster mass like the X-ray luminosity and the cluster richness (e.g. the number of member galaxies). Our results show that there is a clear positive correlation of the infrared luminosity with the cluster mass. Quantitatively speaking, the infrared luminosity is on average 20 times higher than the X-ray luminosity. Moreover, the infrared luminosity increases with the redshift. This probably shows that a major part of this infrared luminosity is due to star formation in the member galaxies. Another possible contribution would be the thermal emission from dust particles in the diffuse intracluster medium. However our method does not allow us to infer conclusions about this second hypothesis. Depending on their size and abundance, such particles would contribute to the infrared luminosity of galaxy cluster and have an impact on the cooling function of the baryons and thus on the formation of the large scale structures. This is an important cosmological question which still remains open.     

线性相对运动的正切拦截和正切交会轨道研究

针对冲量方向与追踪器速度方向相同的正切轨道问题,用线性相对运动方程研究了正切于初始轨道和正切于目标轨道的共面轨道拦截和轨道交会问题。得到初始和终端时刻的相对速度向量的解析表达式,定义了两个关于目标真近点角的单变量函数,于是正切拦截和正切交会问题等价于这两个函数分别等于零,最后用割线法求解这两个函数的数值解。根据能量最优要求,考虑初始漂移段,分析了一个周期内的最佳初始正切冲量点。仿真结果校验了本文提出的方法。     

The optical emission lines of type 1 X-ray bright Active Galactic Nuclei

A strong X-ray emission is one of the defining signatures of nuclear activity in galaxies. According to the Unified Model for Active Galactic Nuclei (AGN), both the X-ray radiation and the prominent broad emission lines, characterizing the optical and UV spectra of Type 1 AGNs, are originated in the innermost regions of the sources, close to the Super Massive Black Holes (SMBH), which power the central engine. Since the emission is concentrated in a very compact region (with typical size r?0.1$r?0.1$ pc) and it is not possible to obtain resolved images of the source, spectroscopic studies of this radiation represent the only valuable key to constrain the physical properties of matter and its structure in the center of active galaxies. Based on previous studies on the physics of the Broad Line Region (BLR) and on the X-ray spectra of broad (FWHM_Hβ ? 2000 km s⁻¹) and narrow line (1000 km s⁻¹ ?FWHM_Hβ ? 2000 km s⁻¹) emitting objects, it has been observed that the kinematic and ionization properties of matter close to the SMBHs are related together, and, in particular, that ionization is higher in narrow line sources. Here we report on the study of the optical and X-ray spectra of a sample of Type 1 AGNs, selected from the Sloan Digital Sky Survey (SDSS) database, within an upper redshift limit of z=0.35$z=0.35$, and detected at X-ray energies. We present analysis of the broad emission line fluxes and profiles, as well as the properties of the X-ray continuum and Fe Kα emission and we use these parameters to assess the consistency of our current AGN understanding.     

The ultraviolet view of the Magellanic Clouds from GALEX: A first look at the LMC source catalog

The Galaxy Evolution Exporer (GALEX) has performed unprecedented imaging surveys of the Magellanic Clouds (MC) and their surrounding areas including the Magellanic Bridge (MB) in near-UV (NUV, 1771-2831 Å) and far-UV (FUV, 1344-1786 Å) bands at 5^″$5^{″}$ resolution. Substantially more area was covered in the NUV than FUV, particularly in the bright central regions, because of the GALEX FUV detector failure. The 5σ$\sigma$ depth of the NUV imaging varies between 20.8 and 22.7 (ABmag). Such imaging provides the first sensitive view of the entire content of hot stars in the Magellanic System, revealing the presence of young populations even in sites with extremely low star-formation rate surface density like the MB, owing to high sensitivity of the UV data to hot stars and the dark sky at these wavelengths.     

Highly Elliptical Orbits for Arctic observations: Assessment of ionizing radiation

The ionizing radiation environment was analyzed for a variety of potential Highly Elliptical Orbits (HEOs) with orbital periods ranging from 6 h to 24 h suitable to continuously monitor the Arctic region. Several models available from the ESA Space Environment Information System (SPENVIS) online tool were employed, including the new-generation AE9/AP9 model for trapped radiation. Results showed that the Total Ionizing Dose (TID) has a well-pronounced local minimum for the 14-h orbit, which is nearly identical to the overall minimum observed for the longest orbital period (24 h). The thickness of slab aluminum shielding required to keep the annual TID below 10, 5 and 3.33 krad (i.e. 150, 75 and 50 krad for 15 years of mission duration) for a 14-h orbit is 2.1, 2.7 and 3.1 mm respectively. The 16-h orbit requires an additional 0.5 mm of aluminum to achieve the same results, while the 24-h orbit requires less shielding in the order of 0.2–0.3 mm. Comparison between the AE8/AP8 and AE9/AP9 models was conducted for all selected orbits. Results demonstrated that differences ranged from −70% to +170% depending on orbit geometry.     

Elliptical vibration cutting of large-size thin-walled curved surface parts of pure iron by using diamond tool with active cutting edge shift

Large-size thin-walled curved surface parts of pure iron are crucial in aerospace, national defense, energy and precision physical experiments. However, the high machining accuracy and surface quality are difficult to achieve due to the serious tool wear and deformation when machining the parts with conventional cutting tools. In this paper, an elliptical vibration cutting (EVC) with active cutting edge shift (ACES) based on a long arbor vibration device is proposed for ultra-precision machining the pure iron parts by using diamond tool. Compared with cutting at a fixed cutting edge, the influence of ACES on the EVC was analyzed. Experiments in EVC of pure iron with ACES were conducted. The evolutions of the surface roughness, surface topography, and chip morphology with tool wear in EVC with ACES are revealed. The reasonable parameters of ultra-precision machining the pure iron parts by EVC with ACES were determined. It shows that the ACES has a slight influence on the machined surface roughness and surface topography. The diamond tool life can be significantly prolonged in EVC of pure iron with ACES than that with a fixed cutting edge, so that high profile accuracy and surface quality could be obtained even at higher nominal cutting speed. A typical thin-walled curved surface pure iron part with diameter ∅240 mm, height 122 mm, and wall thickness 2 mm was fabricated by the presented method, and its profile error and surface roughness achieved PV 2.2 μm and Ra less than 50 nm, respectively.     

Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model

We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.