共查询到20条相似文献，搜索用时 46 毫秒
1.
Anders Emrich 《Experimental Astronomy》1990,1(4):227-235
This paper describes a flexible spectrometer architecture consisting of standard units that can be configured to meet different requirements. The spectrometer is a hybrid between an analog filterbank and digital autocorrelator. Two applications are given, one for balloon borne submillimeter radio astronomy employing a compact and low power design, and one for millimeter imaging with a much more powerful and flexible system. The basic hardware and software units are described as well as the overall architecture. Thanks to the modularized approach the spectrometer can easily be modified for other application areas, such as plasma physics or molecular spectroscopy. 相似文献
2.
We investigate, by ray-trace simulation, two hard X-ray telescopes based on microchannel plate (MCP) optics. The first is the, by now well known, lobster-eye geometry, while the second is a novel design. The second design uses a pair of MCPs with square channels packed in a radial fashion and represents a conical approximation to the Wolter type I configuration. We show that such telescopes can provide X-ray imaging at energies up to 100 keV. Effective area may be scaled arbitrarily by co-aligning many MCP optics. As an example, we calculate that 50 parallel Wolter I units each of 60 mm diameter and 5 m focal length yield a sensitivity of 1 milli Crab at 45 keV in a 105 second integration. 相似文献
3.
NASA is proposing a new receiving facility that needs to beamform broadband signals from hundreds of antennas. This is a similar problem to SKA beamforming with the added requirement that the processing should not add significant noise or distortion that would interfere with processing spacecraft telemetry data. The proposed solution is based on an FX correlator architecture and uses oversampling polyphase filterbanks to avoid aliasing. Each beamformer/correlator module processes a small part of the total bandwidth for all antennas, eliminating interconnection problems. Processing the summed frequency data with a synthesis polyphase filterbank reconstructs the time series. Choice of suitable oversampling ratio, and analysis and synthesis filters can keep aliasing below −39 dB while keeping the passband ripple low. This approach is readily integrated into the currently proposed SKA correlator architecture. 相似文献
4.
自1993年乌鲁木齐天文站25m射电望远镜建成以来,除了不断完善VLBI观测系统外,还选择发展了具有科学价值的单天线天体物理观测课题。其中基于常温接收机的脉冲星脉冲到达时间观测系统已经于1999年5～6月间建成。该系统建立在25m射电天线的18cm波段上,消色散采用了2×128×2．5MHz多通道滤波器和数字化器,并由PC机完成数据采集。同时进行的脉冲星工作还有92cm及其它波段的脉冲轮廓监测,对0329+54的多波段观测得到了它的频谱。在25m天线的1．3cm波段上建立了基于声表面波频谱仪和频率综合器的分子谱线观测系统,对水脉泽的观测已经发现了十几个可能的水脉泽源,观测结果正在认证当中。 相似文献
5.
The Crab Pulsar was observed at 1540 MHz with the 25m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy μs were detected in two observing sets. All of these giant pulses are located in the main pulse (MP) and inter pulse (IP) windows of the average profile of the Crab Pulsar. The ratio of the numbers of giant pulses detected in the IP and MP windows is about 0.05. Our results show that, at 1540 MHz, the emission in the IP is contributed by giant and normal pulses, while that in the MP is almost dominated by giant pulses. The distribution of energy of the 2436 giant pulses at 1540 MHz can be described by a power-law with index α=3.13±0.09. The intrinsic threshold of giant pulse energy in the MP window is about 1400 Jy μs at 1540 MHz. 相似文献
6.
Peter Cogan 《Astrophysics and Space Science》2005,297(1-4):275-281
The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the next-generation ground-based gamma-ray observatory
that is being built in southern Arizona by a collaboration of 10 institutions in Canada, Ireland, the UK and the USA. VERITAS
is designed to operate in the range from 50 GeV to 50 TeV with optimal sensitivity near 200 GeV; it will effectively overlap
with the next generation of space-based gamma-ray telescopes. The first phase of VERITAS, consisting of four telescopes of
12 m aperture, will be operational by the time of the GLAST launch in 2007. Eventually, the array will be expanded to include
the full array of seven telescopes on a filled hexagonal grid of side 80 m. A prototype VERITAS telescope with a reduced number
of mirrors and signal channels has been built. Its design and performance is described here. The prototype is scheduled to
be upgraded to a full 499 pixel camera with 350 mirrors during the autumn of 2004.
The VERITAS collaboration consists of universities and institutions from Ireland, UK, USA and Canada. See for a full listing. 相似文献
7.
简述了基于IBOB和Xilinx System Generator平台的射电望远镜宽带数字频谱仪系统的设计与应用;给出了双路400MHz、2048通道、16IP输出数字频谱仪系统的具体设计方案,并对该数字频谱仪器的性能指标进行了分析和测试,验证了方案的可行性;最后初步讨论了滤波器设备对后端系统的影响。 相似文献
8.
Luisa Morales-Rueda Pierre F.L. Maxted Tom R. Marsh 《Astrophysics and Space Science》2004,291(3-4):299-306
We present the results of a 3.5 year long campaign to measure orbital periods of subdwarf-B (sdB) star binaries. We directly compare our observed orbital period distribution with that predicted by using binary population synthesis. Up to now, most of our systems seem to have been formed through two of the formation channels discussed by Han et al. (2003, MNRAS 341, p. 669), i.e. the first and the second common envelope ejection (CE) channels. At this point, thanks to the long baseline of our observations, we are starting to detect also very long orbital period systems. These have probably come from a complete different formation path, the first stable Roche Lobe overflow (RLOF) channel in which the first mass transfer phase is stable. This channel is expected to lead to the formation of very wide binaries with typical orbital periods ranging from 1 month to 1 year. 相似文献
9.
A. V. Dudnik V. K. Persikov I. I. Zalyubovsky T. G. Timakova E. V. Kurbatov Yu. D. Kotov V. N. Yurov 《Solar System Research》2011,45(3):212-220
The STEP-F satellite telescope for measuring electrons and protons of the Photon scientific equipment is described. Its design
features are given. The device detects electrons, protons, and α-particles in the energy range 0.18–2.3, 7.4–55.2, and 298–160.0
MeV, respectively. Geometric factors vary in the range of 12.4–21.7 cm2 sr, depending on the energy of the particles. In addition, there are three channels of mixed recording of particles of different
types and channels of recording of the secondary electromagnetic radiation generated in the construction materials of the
device and spacecraft. Methods and results of the computer simulation of the passage of the particle through detector materials
are presented, along with configuration, calibration measurements, and tests (both standalone and integrated) within the complex
of scientific instrumentation and spacecraft. Updated data on geometric factors of the device and energy ranges of the direct
detection of charged high-energy particles and of channels of mixed recording of several types of particles are given. Special
software is described for the rapid analysis of the processed data of the STEP-F telescope, and the visualization of time
variations of particle fluxes with different time resolution in some periods of high solar activity and in its absence. 相似文献
10.
P. S. Ramkumar T. Prabu Madhu Girimaji G. Marker leyulu 《Journal of Astrophysics and Astronomy》1994,15(3):343-353
A fast digital signal processor has been designed and built for survey and some observations of pulsars. The processor obtains
spectral information over a bandwidth of 16 MHz (256 channels) every 25μsecs Wedescribethe design ofthisprocessor and present
some test observations made with the Ooty Radio Telescope. 相似文献
11.
J. M. Lamarre J. L. Puget F. Bouchet P. A. R. Ade A. Benoit J. P. Bernard J. Bock P. De Bernardis J. Charra F. Couchot J. Delabrouille G. Efstathiou M. Giard G. Guyot A. Lange B. Maffei A. Murphy F. Pajot M. Piat I. Ristorcelli D. Santos R. Sudiwala J. F. Sygnet J. P. Torre V. Yurchenko D. Yvon 《New Astronomy Reviews》2003,47(11-12):1017
The High Frequency Instrument (HFI) of Planck is the most sensitive CMB experiment ever planned. Statistical fluctuations (photon noise) of the CMB itself will be the major limitation to the sensitivity of the CMB channels. Higher frequency channels will measure galactic foregrounds. Together with the Low Frequency Instrument, this will make a unique tool to measure the full sky and to separate the various components of its spectrum. Measurement of the polarization of these various components will give a new picture of the CMB. In addition, HFI will provide the scientific community with new full sky maps of intensity and polarization at six frequencies, with unprecedented angular resolution and sensitivity. This paper describes the logics that prevailed to define the HFI and the performances expected from this instrument. It details several features of the HFI design that has not been published up to now. 相似文献
12.
HARRA-MURNION L. K. CULHANE J. L. HUDSON H. S. FUJIWARA T. KATO T. STERLING A. C. 《Solar physics》1997,171(1):103-122
We analyse the physical characteristics of a C5.7 class flare which was observed on 27 September, 1993 using data from the soft X-ray telescope (SXT), the Bragg crystal spectrometer (BCS), and the hard X-ray telescope (HXT) on Yohkoh. The flare takes the form of a simple loop which is much brighter at one of its footpoints than anywhere else for a period of 2 min. During this time there is an increase in the soft X-ray fluxes, and a corresponding peak in hard X-rays. The parameters derived from the hard X-ray and soft X-ray spectra and images are assumed to be from the footpoint. This flare showed two peaks in the non-thermal velocity, the first one simultaneous with the footpoint brightening. The non-thermal velocity corresponding to these first few minutes is unusually large – by a factor of 80%, 68%, and 26% relative to the second peak in the Fexxv, Caxix, and Sxv channels respectively. 相似文献
13.
《New Astronomy Reviews》2002,46(8-10):625-629
High resolution γ-ray spectroscopy at energies around 1 MeV, as with SPI on board INTEGRAL, is a powerful tool for astronomy with radioactivities. We do not expect the SPI signal-to-background ratio for any of the anticipated γ-ray sources to exceed a few percent; hence detailed modelling of the instrumental background will be crucial. We exploit the similarities between TGRS on board WIND and SPI with respect to orbit and radiation environment, as well as detector design and material composition, to anticipate the most important instrumental background lines and their production channels in SPI at the energies of selected γ-ray lines of astrophysical relevance. 相似文献
14.
In the Xanthe Terra region of Mars, two forms of flow fields are observed on the walls of Mojave Crater, a fresh impact site with a maximum age of Late Hesperian. Flow fields with steep, lobate margins are consistent with emplacement of a highly viscous medium. The focus of this report is on fan-shaped landforms that share many morphologic attributes in common with terrestrial alluvial fans, including a semi-conical form, branching tributary networks, distributary channels and incised channels. Collectively, these sub-kilometer-scale landforms have attributes consistent with overland flow of fluids and formation of fans by water and gravity-driven alluvial sedimentation. Superposition and cross-cutting relationships indicate that fan formation occurred in multiple phases that may have been a single event or multiple, temporally distinct episodes. Many aspects of the fan formation are ill-constrained, including the amount and source of fluid as well as the duration of fan formation and modification. Fans are concentrated on the crater walls and the ejecta blanket shows minimal evidence of fluvial erosion. Similar fan-shaped landforms to those in Mojave Crater are extremely rare on Mars. The localization of fans to Mojave Crater implies that the impact event played a role in the formation of these sub-kilometer fans. This is the first geologic evidence on Mars that tentatively supports a link between impact crater events and the liberation of water for surface runoff. 相似文献
15.
16.
Large channels on the Martian surface have been variously attributed to erosional, volcanic, and tectonic processes. Morphometric information shows that large braided Martian channels and islands between those channels are similar in their dimensions to channels and islands of large braided fluvial features on Earth. The information also suggests that braided fractures in solid materials are fundamentally different in morphometry from braided channels of Earth and Mars. Braided tension fractures have characteristically low braiding indices and are much narrower than their irregularly shaped “midchannel” islands. Terrestrial and Martian channels, in contrast, have high braiding indices, and they are wider than their streamlined midchannel islands. Braided volcanic features are known from the earth and the moon, but the absence of volcanic constructs near the large braided channels on Mars indicates that volcanic origin is unlikely. The morphometric information suggests that braided Martian channels are probably of fluvial origin. 相似文献
17.
B. N. Ashoka Kumar V. C. Babu S. Seetha V. Girish S. K. Gupta Ram Sagar S. Joshi P. Narang 《Journal of Astrophysics and Astronomy》2001,22(1):131-144
The design and performance of a portable three channel photometer installed at the Uttar Pradesh State Observatory (UPSO),
Naini Tal is described. The photometer is modular and the whole unit can be disassembled as individual channels such that
the system can also be used as a single channel or two channel photometer. The system also has provision to monitor a guide
star. The instrument was put into operation since November 1999 on the 1m Sampurnanand telescope at UPSO, Naini Tal. Since
then, it is used extensively for the ‘Survey of rapidly oscillating Ap (roAp) stars in the northern sky’ from UPSO. Observational
results using this new photometer in its initial phase of operation are discussed. The advantage of having continuous sky
measurement is demonstrated. 相似文献
18.
S.A. Schumm 《Icarus》1974,22(3):371-384
Large Martian channels have been attributed to fluvial erosion primarily because they widen in a downstream direction, appear to be braided in places, have tributaries, and may be sinuous. However, tension fractures in a variety of materials produce features that superficially resemble the Martian channels at, of course, a very different scale.Based on the morphology of these channels as viewed on Mariner 9 images, it is not possible to determine that these features have a fluvial origin. It is probable that most large Martian channels have a structural origin and reflect local or planet-wide tensional forces. 相似文献
19.
Paul D. Komar 《Icarus》1979,37(1):156-181
Comparisons are undertaken between the hydraulics of channelized water flows on Mars, large terrestrial rivers, deep-sea turbidity currents, and the catastrophic flow of Lake Missoula floods. Expected bottom shear stresses, velocities and discharges, flow powers, and other parameters are computed for each. Sand transport rates and the times required for channel erosion are estimated for Mangala Channel. These calculations indicate that the turbidity currents and Lake Missoula floods were similar to channelized water flow on Mars in their flow characteristics and in their abilities to erode and transport sediments. Like the Lake Missoula floods, deep-sea turbidity currents are catastrophic in character, being formed by the slumping of large masses of sediment trapped in submarine canyons or deposited on the continental slope. The repeated flows originating from submarine canyons have formed deep-sea channels similar in scale and overall morphology to the Martian outflow channels. The submarine canyon can be viewed as the counterpart of the chaotic terrain or crater which serves as sources for many Martian channels. Like most Martian outflow channels, the deep-sea channels generally lack tributaries or have only minor tributaries, instead consisting of a single pronounced channel extending for several hundred kilometers from its origin at the submarine canyon to deep abyssal depths. The channels vary considerably in dimensions, but most commonly have widths in the range 2 to 15 km with reliefs of 50 to 450 meters, again similar in scale to the Martian channels. Other similarities include sections of anastomosing channels, a general lack of pronounced meandering, and a lack of an apparent “delta” where the transported sediments are deposited. The similarities of channel morphology and flow hydraulics indicate the deep-sea channels and turbidity currents can be useful in furthering our understanding of the Martian outflow channels. Physical processes in the deep-sea occur under a reduced effective gravity because of the overlying water with its buoyancy. The deep-sea channels provide another set of Earth-based channels which can be studied to determine the effects of gravity on such factors as channel meandering and anastomosing characteristics. 相似文献
20.
A debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into Chryse Planitia from the adjacent southern uplands of Mars. The debris is thought to have originated through a mechanism of collapse in the chaotic terrains which exist at the head of these channels as well as locally along the channels. This proposition is based on the detailed morphologic similarities between Martian channel source areas and the heads of both subaerial and subaqueous terrestrial debris flows. The downslope movement of the debris produced the channels through (a) modification of earlier collapse areas, (b) active bed erosion, and (c) loading-induced collapse. The large-scale channel geometry and the assemblage of related morphologic features on Mars correspond tto that observed in subaqueous debris flow chutes on the Mississippi delta front. Through various mechanisms of strain-dependent viscosity decrease the debris flow gained mobility downstream, turned into a debris avalanche, and moved onto Chryse Planitia at very high velocities. This high-velocity avalanche eroded a series of streamlined remnants near the channel mouths and deposited its load as a thin blanket over a large area of the basin creating virtually no depositional relief. 相似文献