Nonplanar Shock Structures in a Relativistic Degenerate Multi-Species Plasma

A nonlinear propagation of cylindrical and spherical modified ion-acoustic (mIA) waves in an unmagnetized, collisionless, relativistic, degenerate multi-species plasma has been investigated theoretically. This plasma system is assumed to contain non-relativistic degenerate light ions, both non-relativistic and ultra-relativistic degenerate electron and positron fluids, and arbitrarily charged static heavy ions. The restoring force is provided by the degenerate pressures of the electrons and positrons, whereas the inertia is provided by the mass of ions. The arbitrarily charged static heavy ions participate only in maintaining the quasi-neutrality condition at equilibrium. The modified Burgers (mB) equation is derived by using reductive perturbation technique and numerically analyzed to identify the basic features of mIA shock structures. The basic characteristics of mIA shock waves are found to be significantly modified by the effects of degenerate pressures of electron, positron, and ion fluids, their number densities, and various charge state of heavy ions. The implications of our results to dense plasmas in astrophysical compact objects (e.g., non-rotating white dwarfs, neutron stars, etc.) are briefly discussed.     

一种改进的基于混合高斯模型的运动目标检测方法

混合高斯模型方法被广泛应用于运动目标检测,但是现有的混合高斯模型方法在应对噪声和光照突变时效果不佳,其运动目标检测的效果会受到严重影响。为了解决上述问题,提出了一种结合边缘混合高斯模型方法以及改进的基于邻域差方法的综合方法。该方法充分利用了边缘图像对于噪声和光照突变不敏感,以及邻域差方法可以去除部分噪声的特点,对图像序列进行综合处理。实验结果证明,该方法可以提升运动目标的检测率,降低误警率,可以更有效地应对噪声和光照突变的干扰,从而具有更准确的目标检测效果。     

Relativistic compact stars with charged anisotropic matter

In this article, we perform a detailed theoretical analysis of new exact solutions with anisotropic fluid distribution of matter for compact objects subject to hydrostatic equilibrium. We present a family solution to the Einstein-Maxwell equations describing a spherically symmetric, static distribution of a fluid with pressure anisotropy. We implement an embedding class one condition to obtain a relation between the metric functions. We generalize the properties of a spherical star with hydrostatic equilibrium using the generalised Tolman-Oppenheimer-Volkoff (TOV) equation. We match the interior solution to an exterior Reissner-Nordström one, and study the energy conditions, speed of sound, and mass-radius relation of the star. We also show that the obtained solutions are compatible with observational data for the compact object Her X-1. Regarding our results, the physical behaviour of the present model may serve for the modeling of ultra compact objects.     

Properties of gravitationally bound dark compact ultra dense objects

We consider compact astrophysical objects formed from dark matter fermions of mass 250 GeV to 100 TeV or from massless fermions hidden by vacuum structure of similar energy scale. These objects have maximum stable masses of sub-planetary scale and radii of micron to centimeter scale. We describe the surface gravity and tidal forces near these compact ultra dense objects, as pertinent to signatures of their collisions with visible matter objects.     

THE DIFFERENCE OF OPTICAL POLARIZATION PROPERTIES BETWEEN XBLs AND RBLs

On the basis of the beaming model, we have derived a relation between the observed polarization (P^ob) and Doppler-corrected optical magnitude (m^corr), log P^ob=0.4(1-k) m^corr+C. We tested the correlation between P^{ob} and mcorr. The main results are as follows: (1) for both high and low states, there are strong correlations between Pob and mcorr for 29 RBLs with well-observed polarization and Doppler factor, where mcorr=mob+(3+α)logδ/0.4, and δ is the optical Doppler factor; (2) no correlation exists between Pob and the observed optical magnitude, mob, for the 29 RBLs in high state, but there is a close correlation for the 29 RBLs in low state; (3) however, there is an obvious anti-correlation between Pob and mcorr for 35 XBLs with good simultaneous observation data. Our results show that (i) a new difference in polarization is found between RBLs and XBLs; (ii) this difference in polarization between RBLs and XBLs seems really to be physical differences.}     

基于均值漂移实现非发射线天体光谱的谱线自动提取

非发射线天体的光谱是天体光谱谱线提取中最难处理的一种。针对非发射线天体,给出了一种基于均值漂移的谱线自动提取方法。首先,利用均值漂移总是指向局部密度最大点也即密度的模式点这一性质,提取出较为满意的伪连续谱;其次,均值漂移滤波同时工作在空间域和幅度域上,是一种非线性的边缘保持滤波方法,在去除噪声的同时,能够较好地保持特征谱线的信息,文章在连续谱归一化后,采用均值漂移去噪得到谱线光谱;最后,对谱线光谱设置局部阈值提取出特征谱线。通过对恒星、正常星系等的实验表明：该方法是有效的, 这将对后续的参数测量和基于谱线的光谱分类非常有利。     

γ噪Blazar天体的γ射线和近红外光辐射研究

收集了29个有γ噪的Blazar天体(其中有16个BL Lac天体和13个平谱射电类星体)的近红外流量密度和γ射线流量密度,获得以下主要结果:1)23个天体中的γ射线流量密度和近红外流量密度在低态时存在较强的相关性而在高态时有弱的相关性.2)在29个天体中,有6个天体只有一个观测数据点,将其认为是高态时,γ射线流量密度与近红外光流量密度之间有弱相关性,而认为是低态时有强相关性.3)29个源的γ射线流量密度与X射线流量密度在低态时有相关性,但是γ射线流量与光学流量密度,γ射线流量与射电流量密度均没有相关性.4)在16个BL Lac天体中γ射线流量与近红外光流量不论在高态还是低态都有相关性,而13个平谱射电类星体没有相关性.讨论了γ噪Blazar天体的γ射线辐射机制,认为γ射线的辐射机制主要是同步自康普顿散射.而逆康普顿散射来自绕中心核且温度约为2000K的尘埃,这些尘埃的区域大约有r=3pc,聚束的相对论电子也可能是这种尘埃模型辐射机制的一个重要补充.平谱射电类星体和BL Lac天体的γ辐射机制可能有些不同. 关键词： Blazar天体 星系γ射线观测辐射机制 非热辐射     

旋转物体温度的非接触检测原理

本文讨论了利用交流电桥作感温部件及旋转变压器原理实验对旋转体温度的非接触检测。     

一种利用窗口结构提取红外弱小目标的方法

在分析红外弱小目标检测的检测概率和虚警率的基础上,引入了一种基于窗口结构的红外弱小目标检测方法.该方法无需进行图像差分,利用局部小范围内目标相对背景的灰度变化检测目标,可以在较低信噪比的情况下获得较高的检测概率和较低的虚警率.实验表明了该方法的有效性.     

回转体表面条纹沟槽减阻水洞实验研究

本文在条纹沟槽表面减阻理论分析的基础上,对条纹沟槽表面回转体进行了大量的水洞实验研究。实验模型表面条纹沟槽采用直接加工方法,头部线型为双参数平方根圆头曲线,尾部线型为双参数尖尾曲线。实验结果分析表明,与相同形状、尺寸的光滑表面回转体相比,条纹沟槽表面回转体在一定速度范围内存在很好的减阻效果,最大减阻量超过6%,且在小攻角范围内减阻量基本稳定,对回转体升力特性也没有影响。对比不同尺寸条纹沟槽的减阻效果发现,降阻量不但随条纹沟槽宽度S变化,而且随来流速度U∞变化,即与无因次沟槽宽度S (文中近似取S =S.LRe2Ckx,其中k为总阻力Cx的修正因子)存在着一定的关系。对于V型条纹沟槽具有减阻效果的S 的范围在10到60之间。本文研究证明,条纹沟槽表面减阻技术在水下航行器设计领域有着很好的应用前景,同时文中所取得的研究成果对该技术的应用具有一定的促进作用。