Selective dynamical imaging of interferometric data

Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The sparse nature of the EHT’s (u, v)-coverage presents a challenge when attempting to resolve highly time-variable sources. We demonstrate that the changing (u, v)-coverage of the EHT can contain regions of time over the course of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT observations of sources with simple orbital variability. We then use these results to make recommendations for imaging the 2017 EHT Sgr A* data sethttp://iopscience.iop.org/2041-8205Physic

First Sagittarius A* Event Horizon Telescope results. II. EHT and multiwavelength observations, data processing, and calibration

We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5–11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ∼50 μas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.http://iopscience.iop.org/2041-8205Physic

First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring

In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24%–28%, peaking at ∼40%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to ≈46° ± 12° rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150°. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow

烧成制度对BaTiO3介电性能的影响

烧成制度对BaTiO3质PTC陶瓷的介电性能有重要影响，详细讨论了烧成温度、保温时间、冷却速度以及烧结气氛等因素对BaTiO3质陶瓷室温电阻和PTC效应的影响，并对其影响机制给出了合理解释。研究结果表明，陶瓷的半导化与烧成温度密切相关，适当保温对传质有很大影响，冷却速度和烧结气氛对室温电阻和PTC效应有一定影响

14.7MeV/u、19.2MeV/u ~(20)Ne诱发反应中转移和碎裂反应过程的竞争

对于在14.7MeV/u、19.2MeV/u ~(20)Ne+~(58)Ni反应中出射的类弹碎片,比较其单举动量分布和与前方向20个塑料闪烁体中带电粒子符合的动量分布,区分来自于碎裂过程和转移反应过程的贡献,并研究随束流能量变化时这两种过程的竞争

中能区~(86)Kr+~(197)Au反应中的能量耗散、π介子阈下产生和流角

用扩展BUU模型计算了中能区~(86)Kr+~(197)Au重系统的能量耗散、π介子阈下产生和流角,定量地拟合了43MeV/u~(86)Kr+~(197)Au实验的能量耗散和类弹碎片核电荷数的关系及类弹类靶碎片核电荷数的关联

中心集体流对带电粒子关联函数的影响

讨论了中心集体流对带电粒子关联函数的影响，采用蒙特卡罗方法研究了热源发射出的单粒子能谱与双粒子关联谱受中心集体流的影响。利用ＱＭＤ模型计算了１００ＭｅＶ／ｕ的Ｍｉ＋Ｎｉ系统在ｂ＝０ｆｍ条件下的双质子关联函数。在计算中发展了一种交换粒子计算方法并证实了在１００ＭｅＶ／ｕｉ＋Ｍｉ的中心碰撞中存在中心集体流。计算结果表明，在中重系统中关联函数对中心集体流是灵敏的，为在１００ＭｅＶ／ｕ以上能区研究中重系统中心碰撞形成的中心集体流提供了一种可行的方法。Influence of the central collective flow on two-pardcle correlation function is di scussed. The Monte-Carlo calculation i s used to describe how the si ngle particle and two-particle spectrum from a hot emission source are effected by the central collectiveflow. The two- proton correlation function for Ni + Ni system withb= 0fm at 100MeV / u is calculated by using QMD model. .The particle interchange model is developed and used to prove the existence of a central collective flow in central sions of 100MeV ...国家自然科学基

七株眼虫基于微卫星DNA指纹图谱的区分和关系分析

尽管以前对眼虫进行过大量的形态发育研究和基于核糖体RNA基因的系统发育分析,但对于株系之间的关系仍然知之甚少．因其形态特征有限并且易变,很难鉴定眼虫的相似种和同种内不同的株．作者利用微卫星DNA指纹图谱,在七株眼虫中扩增了七个微卫星DNA位点,成功扩增的六个微卫星引物都得到了四到八个条带．从微卫星DNA指纹图谱计算得到的相似性系数范围从0．000到0．957．根据相似性系数得到的树状结构,七株眼虫在距离为0．9346处分为三支:E．mutabilis,E．intermedia和E．gracilis．其中

烧成制度对BaTiO3介电性能的影响

烧成制度对BaTiO3质PTC陶瓷的介电性能有重要影响，详细讨论了烧成温度、保温时间、冷却速度以及烧结气氛等因素对BaTiO3质陶瓷室温电阻和PTC效应的影响，并对其影响机制给出了合理解释。研究结果表明，陶瓷的半导化与烧成温度密切相关，适当保温对传质有很大影响，冷却速度和烧结气氛对室温电阻和PTC效应有一定影响