暗能量研究进展

1998年,美国两个超新星观测团队发现,今天的宇宙是在加速膨胀的,而推动宇宙加速膨胀的是一种不为当时人们所知的物质组分——暗能量。暗能量的存在是近年来粒子宇宙学研究领域最重要的发现之一,并为随后一系列的天文观测实验所支持。暗能量的物理性质已经成为当今宇宙学的一个研究热点,近年来已经取得了巨大的进展。本文将会回顾一下近些年来国内外在暗能量研究方面,特别是在利用天文观测数据限制暗能量性质方面所取得的进展,并展望未来的天文观测实验研究暗能量性质的可行性。     

Spectral analysis of paramagnetic centers induced in human tooth enamel by x-rays and gamma radiation

Based on study of spectral and relaxation characteristics, we have established that paramagnetic centers induced in tooth enamel by x-rays and gamma radiation are identical in nature. We show that for the same exposure dose, the intensity of the electron paramagnetic resonance (EPR) signal induced by x-radiation with effective energy 34 keV is about an order of magnitude higher than the amplitude of the signal induced by gamma radiation. We have identified a three-fold attenuation of the EPR signal along the path of the x-radiation from the buccal to the lingual side of a tooth, which is evidence that the individual had undergone diagnostic x-ray examination of the dentition or skull. We have shown that the x-ray exposure doses reconstructed from the EPR spectra are an order of magnitude higher than the applied doses, while the dose loads due to gamma radiation are equal to the applied doses. The data obtained indicate that for adequate reconstruction of individual absorbed doses from EPR spectra of tooth enamel in the population subjected to the combined effect of x-radiation and accidental external gamma radiation as a result of the disaster at the Chernobyl nuclear power plant, we need to take into account the contribution to the dose load from diagnostic x-rays in examination of the teeth, jaw, or skull.     

Astrophysical Black Holes: A Compact Pedagogical Review

Black holes are among the most extreme objects that can be found in the Universe and an ideal laboratory for testing fundamental physics. Here, the basic properties of black holes as expected from general relativity, the main astronomical observations, and the leading astrophysical techniques to probe the strong gravity region of these objects are reviewed. The main intention is to provide a compact introductory overview on astrophysical black holes to new students entering this research field, as well as to senior researchers working in general relativity and alternative theories of gravity, who wish to quickly learn the state of the art of astronomical observations of black holes.     

模块化天文CCD通用控制器

为满足大规模拼接CCD天文观测应用系统对控制器的特殊要求,开展可扩展的模块化天文CCD通用控制器技术研究,并成功研制了样机系统.该系统采用相关双采样技术及控制技术等手段获得极低的读出噪声,采用全数字化的结构实现系统的通用性以及实现远程观测、远程监控的功能.测试结果表明,该系统的系统噪声小于3e~-,动态范围为16bit,非线性优于1%,满足现阶段大部分天文观测的需要.作为应用实例,利用本系统制作的真空紫外CCD相机,成功获得了He和氘121.5nm、164、193、205、218.6、273.3和294.5nm谱线的光谱图像,完成了对空间天文观测的102nm~320nm光谱仪的检测工作.     

Telescope illumination and beam measurements for submillimeter astronomy

Submillimeter receivers which operate in the highest frequency atmospheric windows must still be mounted on large infrared and optical telescopes. Finding the optimum submillimeter wave illumination for these large telescopes is simplified by their effectively perfect optical surfaces and long focal lengths, but is complicated by telescope optics which have been optimized for non-tapered beams. In order to determine the effects of changing illumination edge taper, we calculated idealized aperture and beam efficiencies for telescopes which are used for submillimeter astronomical observations. The optimum illumination edge taper for the large infrared telescopes is near 10 dB, somewhat less than for classical radio telescopes, and is not very critical as long as it is between 10 and 13 dB.We also present an accurate method for measuring the sizes of, and deviations from, Gaussian beam pattern distributions by using astronomical sources which have sizes comparable with the beam.     

暗能量:观测证据和理论研究

自1998年发现宇宙的加速膨胀以来,大量的天文观测显示宇宙中存在压强为负的暗能量成分.暗能量已经成为目前宇宙学和理论物理的最重要的研究课题之一.文章介绍了暗能量存在的天文观测证据和理论研究现状与展望.     

The UCB/MPE cassegrain submillimeter heterodyne spectrometer

The UCB/MPE Submillimeter Heterodyne Spectrometer is a system for ascronomical spectroscopy in the high-frequency atmospheric windows from 500 to 1000 GHz. It contains a molecular laser local oscillator, a cooled Schottky open structure mixer, a quasi-optical coupling system, and an acousto-optical spectrometer. The compact receiver mounts at the Cassegrain focus of large infrared astronomical telescopes. The receiver noise temperature on the telescope is approximately 3500 K (DSB) during observations of the CO J=76 line at 806.652 GHz. The spectrometer's frequency resolution and instantaneous bandwidth (<2 MHz resolution across 1.1 GHz) are well suited for observations of molecular emission lines from a variety of astronomical sources.     

三轴稳定GEO卫星漫反射光变特性

利用天文测光方法研究了地球同步轨道卫星可见光波段的反射光变特性.以三轴稳定地球同步轨道通讯卫星为研究样本,进行了可见光波段的光学非高分辨成像观测,并使用天文标准星进行定标.基于相位角序列的测光观测数据表明:在大相位角区域卫星光变曲线分布与漫反射光照数学模型计算结果有很好的一致性,以卫星主体和太阳能电池板的漫反射效应为主;而在小相位角区域与漫反射模型计算结果有明显的差异,为卫星的太阳帆板镜面反射效应影响所致.     

A high efficiency polarizing interferometer for astronomical observations in the submillimetric region

We describe a high efficiency polarizing interferometer for astronomical observations in the submillimetric and millimetric region. The results obtained during tests at the focal plane of TIRGO (Gornergrat) lead to the conclusion that the instrument works with the expected efficiency and can be used for astronomical observations of faint sources.     

Space and astrophysical plasmas: Pervasive problems

The observations and measurements given by Earth orbiting satellites, deep space probes, sub-orbital systems and orbiting astronomical observatories point out that there are important physical processes which are responsible for a wide variety of phenomena in solar-terrestrial, solar-system and astrophysical plasmas. In this review these topics are exemplified both from an observational and a theoretical point of view.     

Crystal optic effects in absorption of x-radiation

In this paper, the effect of crystal anisotropy on absorption of x-radiation is investigated. A formula is obtained describing the absorption of x-radiation by a biaxial crystal. Crystal optic effects are considered in the x-ray region of the spectrum. A mechanism is proposed for the dependence of the fine structure of x-ray absorption on the sample thickness in an anisotropic crystal. The effect of the crystal anisotropy on the x-ray fluorescence is investigated in the case of a uniaxial crystal.Scientific-Research Institute of Physics, Rostov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 115–119, July, 1995.     

Galactic searches for dark matter

For nearly a century, more mass has been measured in galaxies than is contained in the luminous stars and gas. Through continual advances in observations and theory, it has become clear that the dark matter in galaxies is not comprised of known astronomical objects or baryonic matter, and that identification of it is certain to reveal a profound connection between astrophysics, cosmology, and fundamental physics. The best explanation for dark matter is that it is in the form of a yet undiscovered particle of nature, with experiments now gaining sensitivity to the most well-motivated particle dark matter candidates. In this article, I review measurements of dark matter in the Milky Way and its satellite galaxies and the status of Galactic searches for particle dark matter using a combination of terrestrial and space-based astroparticle detectors, and large scale astronomical surveys. I review the limits on the dark matter annihilation and scattering cross sections that can be extracted from both astroparticle experiments and astronomical observations, and explore the theoretical implications of these limits. I discuss methods to measure the properties of particle dark matter using future experiments, and conclude by highlighting the exciting potential for dark matter searches during the next decade, and beyond.     

Peaking the current of a microsecond generator operating into a plasma load

A configuration of a plasma flow switch intended for peaking the current of a capacitor bank operating into a liner load has been proposed and tested where the current bridge and the liner are formed with the help of a single pulsed gas valve. The design of the load unit has been optimized for the efficiency of the energy transfer from the energy store to the liner. The peaker was tested in experiments on generation of soft x-radiation and K-radiation of neon. High efficiency of conversion of the magnetic energy of the primary store to x-radiation has been demonstrated. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 36–40, December, 1999.     

X-radiation from a SNOP-1 unit

Experimental and theoretical studies are made of the spatial distribution of a dose of x-radiation from an SNOP-1 accelerator with a diode operating in the electron-beam pinch regime. The Monte Carlo method is used to calculate the spectral distribution of the accelerator radiation, and it is shown that the fraction of ultrahard x-radiation (10–100) keV in the spectrum may reach 40–50%. Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–83, December, 1995.     

On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths

We have measured, using a custom setup, the emissivity of metallic wire-grids, suitable for polarimeters and interferometers at mm and far infrared wavelengths. We find that the effective emissivity of these devices is of the order of a few %, depending on fabrication technology and aging. We discuss their use in astronomical instruments, with special attention to Martin–Puplett Interferometers in low-background applications, like astronomical observations of the Cosmic Microwave Background.     

Antenna measurements of open-structure Schottky mixers and determination of optical elements for a heterodyne system at 184, 214 and 287 μm

Antenna patterns of open structure Schottky mixers were measured at 184, 214 and 287 μm. For use in a heterodyne detector system the antenna pattern must be matched to the signal beam, for example the astronomical signal of a telescope, and the optically coupled local oscillator beam. The procedure of determining a lens system is described and the successful application in astronomical observations with the Kuiper Airborne Observatory (KAO) is shown.     

基于多视场星点椭圆率的望远镜主动准直方法

光学元件的准直失调会引起天文望远镜在观测过程中的像质退化,该问题在大口径快焦比的天文光学系统中更为突出。针对此问题,本文提出一种用于望远镜日常观测过程中的主动准直方法,通过星像解算实时校正副镜位置及姿态达到维持望远镜像质的目的。该方法基于多视场星点椭圆率,利用粒子群优化算法迭代求解望远镜光学元件失调量,从而校正由光学元件失调引起的低阶像差。利用1.6 m多通道测光巡天望远镜光学系统进行模拟仿真,求解副镜失调量残余误差小于1%,在系统设计公差范围以内。利用南极巡天望远镜AST3-3模拟及实验验证,表明该方法可高精度求解望远镜光学元件的失调误差。     

Radiative collapse in Z-pinches

Problems associated with determination of optimum Z-pinch parameters from the standpoint of soft x-radiation yield are considered. The phenomenon of radiative collapse is discussed, in this context, and development times of radiative collapse are calculated for argon Z-pinches. It is shown that in experiments with compression of argon liners conducted on the GIT-4 installation, the pinch mass for which the radiated power is highest is about equal to the mass with the shortest radiative-collapse time. Institute of High-Current Electronics, Siberian Division, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 76–83, December, 1997.     

A criticism of the “absolute space-time theory”

It is argued that the so-called “absolute space-time theory” is inconsistent, in disagreement with some astronomical observations, and improperly titled.     

Blind detection of giant pulses: GPU implementation

Radio astronomical pulsar observations require specific instrumentation and dedicated signal processing to cope with the dispersion caused by the interstellar medium. Moreover, the quality of observations can be limited by radio frequency interference (RFI) generated by Telecommunications activity. This article presents the innovative pulsar instrumentation based on graphical processing units (GPU) which has been designed at the Nançay Radio Astronomical Observatory. In addition, for giant pulsar search, we propose a new approach which combines a hardware-efficient search method and some RFI mitigation capabilities. Although this approach is less sensitive than the classical approach, its advantage is that no a priori information on the pulsar parameters is required. The validation of a GPU implementation is under way.