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81.
到目前为止片状模塑料(SMC)的创新技术也仅适用于高体积分数产品的制造,并且由于模具和压力要求而需要高的投资。到目前为止片状模塑料(SMC)的创新技术也仅适用于高体积分数产品的制造,并且由于模具和压力 相似文献
82.
Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution. This requires building a taxonomy of comets from both present-day dynamical reservoirs: the Kuiper Belt (hereafter KB), sampled through observation of ecliptic comets (primarily Jupiter Family comets, or JFCs), and the Oort cloud (OC), represented observationally by the long-period comets and by Halley Family comets (HFCs). Because of their short orbital periods, JFCs are subjected to more frequent exposure to solar radiation compared with OC comets. The recent apparitions of the JFCs 9P/Tempel 1 and 73P/Schwassmann-Wachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class, which is under-represented in studies of cometary parent volatiles. This chapter reviews the latest techniques developed for analysis of high-resolution spectral observations from ~2–5 μm, and compares measured abundances of native ices among comets. While no clear compositional delineation can be drawn along dynamical lines, interesting comparisons can be made. The sub-surface composition of comet 9P, as revealed by the Deep Impact ejecta, was similar to the majority of OC comets studied. Meanwhile, 73P was depleted in all native ices except HCN, similar to the disintegrated OC comet C/1999 S4 (LINEAR). These results suggest that 73P may have formed in the inner giant planets’ region while 9P formed farther out or, alternatively, that both JFCs formed farther from the Sun but with 73P forming later in time. 相似文献
83.
Michael R. Collier Aaron Roberts Adolfo Viñas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(10):1704-1709
We describe a new wave mode similar to the acoustic wave in which both density and velocity fluctuate. Unlike the acoustic wave in which the underlying distribution is Maxwellian, this new wave mode occurs when the underlying distribution is a suprathermal κ-function and involves fluctuations in the power law index, κ. This wave mode always propagates faster than the acoustic wave with an equivalent effective temperature and becomes the acoustic wave in the Maxwellian limit as κ → ∞. 相似文献
84.
Canada is a space power with unique technical niches that support opportunities for collaboration on space technologies. When U.S.-origin space technologies are involved Canada's ability to collaborate internationally may be conditional on US law and policy. As a result, US export control law can be directly linked to the success or failure of Canadian collaboration. This article examines the strategic impact of U.S. export controls on Canadian autonomy to collaborate on international missions, including multi-use missions. Canadian space export control policy is also examined more broadly with the goal of providing specific policy recommendations that will enhance Canada's future as an international space actor. 相似文献
85.
Xu J Ramian GJ Galan JF Savvidis PG Scopatz AM Birge RR Allen SJ Plaxco KW 《Astrobiology》2003,3(3):489-504
We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs. 相似文献
86.
Michael F. A’Hearn Michael J. S. Belton Alan Delamere William H. Blume 《Space Science Reviews》2005,117(1-2):1-21
The Deep Impact mission will provide the first data on the interior of a cometary nucleus and a comparison of those data with
data on the surface. Two spacecraft, an impactor and a flyby spacecraft, will arrive at comet 9P/Tempel 1 on 4 July 2005 to
create and observe the formation and final properties of a large crater that is predicted to be approximately 30-m deep with
the dimensions of a football stadium. The flyby and impactor instruments will yield images and near infrared spectra (1–5
μm) of the surface at unprecedented spatial resolutions both before and after the impact of a 350-kg spacecraft at 10.2 km/s.
These data will provide unique information on the structure of the nucleus near the surface and its chemical composition.
They will also used to interpret the evolutionary effects on remote sensing data and will indicate how those data can be used
to better constrain conditions in the early solar system. 相似文献
87.
Hawkins S. Edward Darlington E. Hugo Murchie Scott L. Peacock Keith Harris Terry J. Hersman Christopher B. Elko Michael J. Prendergast Daniel T. Ballard Benjamin W. Gold Robert E. Veverka Joseph Robinson Mark S. 《Space Science Reviews》1997,82(1-2):31-100
A multispectral imager has been developed for a rendezvous mission with the near-Earth asteroid, 433 Eros. The Multi-Spectral Imager (MSI) on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft uses a five-element refractive optical telescope, has a field of view of 2.93 × 2.25°, a focal length of 167.35 mm, and has a spatial resolution of 16.1 × 9.5 m at a range of 100 km. The spectral sensitivity of the instrument spans visible to near infrared wavelengths, and was designed to provide insight into the nature and fundamental properties of asteroids and comets. Seven narrow band spectral filters were chosen to provide multicolor imaging and to make comparative studies with previous observations of S asteroids and measurements of the characteristic absorption in Fe minerals near 1 µm. An eighth filter with a much wider spectral passband will be used for optical navigation and for imaging faint objects, down to visual magnitude of +10.5. The camera has a fixed 1 Hz frame rate and the signal intensities are digitized to 12 bits. The detector, a Thomson-CSF TH7866A Charge-Coupled Device, permits electronic shuttering which effectively varies the dynamic range over an additional three orders of magnitude. Communication with the NEAR spacecraft occurs via a MIL-STD-1553 bus interface, and a high speed serial interface permits rapid transmission of images to the spacecraft solid state recorder. Onboard image processing consists of a multi-tiered data compression scheme. The instrument was extensively tested and calibrated prior to launch; some inflight calibrations have already been completed. This paper presents a detailed overview of the Multi-Spectral Imager and its objectives, design, construction, testing and calibration. 相似文献
88.
89.
Has the current US space policy improved the USA's overall strategic position? Does it affect favorably international partnerships? These questions are examined in terms of security, political economy, and influence. In today's context, where there are more space players, more options, more potential for unintended consequences, and higher stakes, unilateral action is more limited in its effectiveness than in earlier times. Surveying current US space policy, it is not clear that data-driven, analytically based decisions are being made to affect positively national independence, innovation, market creation, and international perceptions of the USA as a trustworthy partner. More promising are the steps taken to bolster a predictable space operational environment and economic competitiveness. Ultimately, in order to achieve American excellence and leadership, a ‘closed loop’ on the policy system is needed, to gauge regularly and systematically whether the US is achieving the desired national outcomes. 相似文献
90.