Constraining dark matter properties with gamma-rays from the Galactic Center with Fermi-LAT

We study the capabilities of the Fermi-LAT instrument on board of the Fermi mission to constrain particle dark matter properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels, with gamma-ray observations from the Galactic Center. Besides the prompt gamma-ray flux, we also take into account the contribution from the electrons/positrons produced in dark matter annihilations to the gamma-ray signal via inverse Compton scattering off the interstellar photon background, which turns out to be crucial in the case of dark matter annihilations into μ⁺μ⁻ and e⁺e⁻ pairs. We study the signal dependence on different parameters like the region of observation, the density profile, the assumptions for the dark matter model and the uncertainties in the propagation model. We also show the effect of the inclusion of a 20% systematic uncertainty in the gamma-ray background. If Fermi-LAT is able to distinguish a possible dark matter signal from the large gamma-ray background, we show that for dark matter masses below ∼200 GeV, Fermi-LAT will likely be able to determine dark matter properties with good accuracy.     

银河系的形成和演化

银河系是宇宙中数以百亿计星系中的一员.自威廉.赫歇尔以来,人们对银河系结构和运动状态的认识已有200多年历史,而有关银河系起源和演化的探索则只是在最近半个多世纪内才成为天文学的研究热点.文章在简述银河系认识史的基础上,对有关银河系形成和演化这一重要天体物理问题做了概要的评述,其中包括银河系厚盘的发现及其可能的形成机制.     

Gaia: 3-dimensional census of the Milky Way Galaxy*

Astrometry from space has unique advantages over ground-based observations: the all-sky coverage, relatively stable, and temperature and gravity invariant, operating environment delivers precision, accuracy and sample volume several orders of magnitude greater than ground-based results. Even more importantly, absolute astrometry is possible. The European Space Agency Cornerstone mission Gaia is delivering that promise. Gaia provides 5-D phase space measurements, 3 spatial coordinates and 2 space motions in the plane of the sky, for a representative sample of the Milky Way’s stellar populations (over 2 billion stars, being ~1% of the stars over 50% of the radius). Full 6-D phase space data are delivered from line-of-sight (radial) velocities for the 300 million brightest stars. These data make substantial contributions to astrophysics and fundamental physics on scales from the Solar System to cosmology. A knowledge revolution is underway.     

Pricing techniques for self regulation in Vehicle Sharing Systems

We study self regulation through pricing for Vehicle Sharing Systems (VSS). Without regulation VSS have poor performances. We want to improve the efficiency of VSS using pricing as incentive. We take as base model a Markovian formulation of a closed queuing network with finite buffer and time dependent service time. This model is unfortunately intractable for the size of instances we want to tackle. We discuss heuristics: a scenario approach, a fluid approximation, simplified stochastic models and asymptotic approximations. We compare these heuristics on toy cities.     

多通道光路在气体分析中的应用

本文在不分光红外分析法的基础上,应用一种多通道的光路,研究在一个气室中分析多种气体成分的方法。即研究在一个气室中周期地透射多种特定的带通很狭的红外波时,其光电响应值与相对应气体成分浓度的关系。结果表明,多通道光路系统的检测精度和稳定性方面均达到了较好水平。     

拟连续Domain上的扩张定理

定义了拟定向极小集,并证明了拟连续Domain的每个元都有拟定向极小集,在拟连续Domain中,给出了保拟定向极小集映射的几个等价刻画,并且在此基础上得到了拟连续Domain上的两个相应扩张定理。     

数学方法论在数学教学中的应用

本文介绍了运用数学方法论的观点指导数学教学的一种崭新的数学教育方式,即应用数学的发展规律、数学的思想方法和数学中的发现、发明与创新的观点设计数学教学．     

ELTRA CS 800碳、硫分析仪分析时间过长原因浅析

分析了造成CS 800型C、S分析仪分析时间过长的原因：如氧气的纯度、转化炉的工作效率、气路等；并找到了相应的解决方法。     

模糊度量空间的一些结果

指出在Erceg's伪度量公理中(B3)条件对讨论它的诱导拓扑不是本质的.基于这个结果,给出它的两种诱导拓扑的关系.最后,在Erceg's伪度量集合上构造一个非平凡的一一映射.