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排序方式: 共有102条查询结果,搜索用时 15 毫秒
11.
Peter Wizinowich 《Contemporary Physics》2013,54(4):432-450
Since Galileo’s first observations in 1609, telescopes have grown dramatically in size. Larger telescopes collect more light, allowing astronomers to detect fainter sources and to look further back in time towards the birth of the universe. The angular resolution of these telescopes, however, has been limited by turbulence in the earth’s atmosphere. This limitation can be dramatically reduced with the use of adaptive optics (AO) to measure and correct the blurring introduced by atmospheric turbulence. AO is now routinely used for science observations on the world’s largest telescopes and is providing a much more detailed view of our universe. 相似文献
12.
13.
Summary The perihelic shift of planets due to the charged Sun is calculated. The results when compared with experimental shifts suggest
that the planets Mercury, Venus and Icarus do not possess self-electromagnetic fields
Riassunto Si calcola lo spostamento perielico dei pianeti dovuto al Sole carico. I risultati, se confrontati con gli spostamenti sperimentali, suggeriscono che i pianeti Mercurio, Venere e Icaro non hanno campi elettromagnetici propri.
РезУме Вычисляется сдвиг перигелия планет обусловленный заряженным Солндем. Полученные результаты при сравнении с зкспериментальнЫми сдвигами предполагаУт, что планеты Меркурий, Венера и Икар не имеУт собственных злектромагнитных полей.相似文献
14.
Kimihiro Kimura Hiroyuki Iwashita Shinichiro Asayama Masahiro Sugimoto Gumpei Kikuchi Hideo Ogawa 《International Journal of Infrared and Millimeter Waves》2008,29(8):713-723
We have developed a 150 GHz band corrugated feed horn. These corrugated feed horns have been established by a new machining
method, which involves digging corrugations through a metal material. We were able to realize E plane and H plane symmetry,
low side lobe level, and low cross-polarization level. Measured co-polarization beam patterns above − 35 dB were consistent
with the simulated patterns within a designed frequency range. The peak levels of cross-polarization beam patterns were less
than − 30 dB. And, the performances were uniform in several horns. In the present paper, we describe the corrugated horn produced
by this methods. 相似文献
15.
The ancient record, “During the first year of King Yi, the day dawned twice at Zheng”, has provided important clues to early
Chinese chronicles. The astronomical conditions and visible area distributions related to such a “double dawn” event are discussed,
and the precision and current problems in the calculations of ancient astronomical phenomena are shown. On such a basis, all
the solar eclipses from 1000 BC to 840 BC are calculated and their associated “double dawn” features investigated. The conclusion
that the “double dawn” was a solar eclipse occurring on April 21st, 899 BC is corfirmed to be the most reasonable.
Project supported by the Xia-Shang-Zhou Chronology Project and Director Foundation of the Chinese Academy of Sciences. 相似文献
16.
用宇宙作为物理实验室,探索在地球上无法企及的条件下,例如极早期宇宙或黑洞视界附近强引力场中的物理规律,已成为新世纪物理学和天文学共同的前沿课题;空间天文观测是其中一个最重要的研究途径.自主研制和发放空间硬X射线调制望远镜(HXMT),实现中国空间天文卫星零的突破,是中国《“十一·五”空间科学发展规划》的目标之一. HXMT 将实现宽波段X射线 (1—250 keV) 巡天,其中在硬X射线波段具有世界最高灵敏度和空间分辨率,发现大批被尘埃遮挡的超大质量黑洞和未知类型天体,探测宇宙硬X射线背景辐射;HXMT还将通过对黑洞和其他高能天体宽波段X射线时变和能谱的观测,研究致密天体极端物理条件下的动力学和辐射过程. 基于成像技术创新提出HXMT项目迄今已有15年,能不能抓住技术创新所提供的科学机遇仍然是一个严重的挑战. 相似文献
17.
60年前,里卡多·贾科尼团队用探空火箭首次探测到了来自太阳系以外的X射线辐射,从此打开了人类探索宇宙的一个全新的窗口。与我们所熟悉的可见光天空不同,在“看不见”的X射线宇宙,明亮的发光天体涵盖了黑洞、中子星、白矮星等致密天体,星系团和星系中弥漫的大量不可见的高温气体,以及各种剧烈的灾变事件。它们代表着宇宙中最为奇特的天体和极端的物理条件,如极强引力场、极强磁场和极高温。文章重点介绍最有代表性的X射线源,包括中子星和黑洞X射线双星、超大质量黑洞和活动星系核、星系团,以及伽马暴、超新星和潮汐瓦解恒星事件等爆发天体。 相似文献
18.
Five hundred meter aperture spherical radio telescope (FAST) 总被引:1,自引:0,他引:1
NAN Rendong 《中国科学G辑(英文版)》2006,49(2):129-148
Five hundred meter aperture spherical radio telescope (FAST) will be the largest radio telescope in the world. The innovative
engineering concept and design pave a new road to realizing a huge single dish in the most effective way. Three outstanding
features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical
aberration on the ground to achieve full polarization and a wide band without involving a complex feed system, and the light
focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise
parts of the receivers. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of the science
goals, for example, the neutral hydrogen line surveying in distant galaxies out to very large redshifts, looking for the first
shining star, detecting thousands of new pulsars, etc. Extremely interesting and exotic objects may yet await discovery by
FAST. As a multi-science platform, the telescope will provide treasures to astronomers, as well as bring prosperity to other
research, e.g. space weather study, deep space exploration and national security. The construction of FAST itself is expected
to promote the development in high technology of relevant fields. 相似文献
19.
S. Hudlet M. Saint Jean C. Guthmann J. Berger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):5-10
We propose a very simple method to determine the electrical tip-surface force in Atomic Force Microscopes used to study the
electrical properties of metallic or insulating materials; the analysis of the measurements as well as determination of the
appropriate experimental procedures requiring an analytical model of the tip-surface capacitance. The comparison of force
expressions obtained by this method with those obtained by exact derivation in the case of the sphere-infinite plane system
shows very good agreement. This method is then applied to determine the tip-surface force, the real shape of the tip being
introduced in the derivation. The obtained expression is compared to experimental and numerical data. We emphasize that this
method is very general and can be applied to any axially symmetric capacitor.
Received: 17 June 1997 / Received: 16 September 1997 / Accepted: 7 November 1997 相似文献
20.
Stellar speckle spectroscopy is a speckle interferometric method enabling us to separate point by point spectra on a stellar object with a diffraction-limited spatial resolution of a telescope. We describe observational results obtained with our system for speckle spectroscopy. Data of two binary stars, of which separations are closer than seeing disc, were taken and processed by cross-correlation method. In each object, spectral images of two component stars around the Hα line (656.3 nm) were spatially resolved with nearly diffraction-limited resolution. The separated spectra of ADS940 reveal different spectral types of the component stars. These results demonstrate the ability of the speckle spectroscopic method.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994. 相似文献