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排序方式: 共有1906条查询结果,搜索用时 562 毫秒
1.
Jason D. Tambie Madiha Farag-Miller Keith Miller Bheshem Ramlal Michael Sutherland 《Marine Geodesy》2019,42(3):227-245
Using two dimensional continuous wavelet transforms, a novel method for identification of mesoscale eddies is presented to facilitate extraction of characteristics for area, amplitude, type, and location from maps of sea level anomalies. In comparison with the previously established growing method for eddy identification, it is found that the wavelet method identifies more than twice the number of eddies and is particularly better at resolving small eddies down to the 0.25 degree resolution of the data. Such research into eddy identification and tracking is significant to the assessment of eddies with potential to impact on coastlines of small islands. The method is applied to the identification of eddies on tracks towards islands of the Eastern Caribbean over 23?years. Spatial and temporal variation in rate of occurrence and magnitude is established. For Barbados there is an average of 9 anticyclonic incidents a year with maximum amplitude of typically 0.22?m in the dry seasons and 0.16?m in the wet seasons. Seasonal variation is reversed for the other islands with twice the number of anticyclonic incidents having maximum amplitudes of about 0.20?m annually. 相似文献
2.
Creating an isotopically similar Earth–Moon system with correct angular momentum from a giant impact
Bryant M. Wyatt Jonathan M. Petz William J. Sumpter Ty R. Turner Edward L. Smith Baylor G. Fain Taylor J. Hutyra Scott A. Cook John H. Gresham Michael F. Hibbs Shaukat N. Goderya 《Journal of Astrophysics and Astronomy》2018,39(2):26
The giant impact hypothesis is the dominant theory explaining the formation of our Moon. However, the inability to produce an isotopically similar Earth–Moon system with correct angular momentum has cast a shadow on its validity. Computer-generated impacts have been successful in producing virtual systems that possess many of the observed physical properties. However, addressing the isotopic similarities between the Earth and Moon coupled with correct angular momentum has proven to be challenging. Equilibration and evection resonance have been proposed as means of reconciling the models. In the summer of 2013, the Royal Society called a meeting solely to discuss the formation of the Moon. In this meeting, evection resonance and equilibration were both questioned as viable means of removing the deficiencies from giant impact models. The main concerns were that models were multi-staged and too complex. We present here initial impact conditions that produce an isotopically similar Earth–Moon system with correct angular momentum. This is done in a single-staged simulation. The initial parameters are straightforward and the results evolve solely from the impact. This was accomplished by colliding two roughly half-Earth-sized impactors, rotating in approximately the same plane in a high-energy, off-centered impact, where both impactors spin into the collision. 相似文献
3.
Mallory S. E. Roberts Crystal L. Brogan Bryan M. Gaensler Jason W. T. Hessels C.-Y. Ng Roger W. Romani 《Astrophysics and Space Science》2005,297(1-4):93-100
A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be
associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the
pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies
seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM. 相似文献
4.
Shelf-mounted Ocean Thermal Energy Conversion (OTEC) plants require installation of cold-water pipes (CWP) on slopes of40deg to depths of 1000 m. In addition, tower platforms containing OTEC power systems may be located on lesser sloped terrain near shore and exposed to special environmental loading problems affecting foundation design. Shelf-mounted installations require careful attention to site selection and geotechnical considerations for foundation integrity on sloped surfaces. This paper primarily discusses research associated with cold-water pipe and foundation installations on steep slopes, although research continues on tower platforms located on the shelf. At least five nations are in various stages of development of OTEC systems for island applications. Each of their systems is either shelf mounted or land based and requires that a large diameter cold-water pipe be installed on a steep slope to provide cold water from 1000-m depths. In addition to the installation and deployment of the large cold-water pipe, the most significant problem is the design and installation of suitable foundations that will last for several decades. To date there is very little experience in the offshore industry for large installations on steep slopes. A major scale-model research project is underway on the slopes of the island of Hawaii. A section of pipe 2.4 m in diameter and 24 m long was installed using combination concrete foundations and joints. The pipe and foundations are fully instrumented to measure environmental loading forces due principally to currents and waves. Environmental measurements will also be taken in the test area. The measurement data will be used to validate available analytical models for subsequent use in aiding industry in providing more cost-effective designs for OTEC pipes and foundations. 相似文献
5.
6.
Angela C. Taylor 《New Astronomy Reviews》2003,47(11-12):925
We discuss two experiments – the Very Small Array (VSA) and the Arcminute MicroKelvin Imager (AMI) – and their prospects for observing the CMB at high angular multipoles. Whilst the VSA is primarily designed to observe primary anisotropies in the CMB, AMI is designed to image secondary anisotropies via the Sunyaev–Zel’dovich effect. The combined ℓ-range of these two instruments is between ℓ=150 and 10,000. 相似文献
7.
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9.
Daniel P. Glavin Jason P. Dworkin Andrew Aubrey Oliver Botta James H. Doty Zita Martins Jeffrey L. Bada 《Meteoritics & planetary science》2006,41(6):889-902
Abstract— Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β‐alanine, γ‐amino‐n‐butyric acid (γ‐ABA), and α‐aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440–3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α‐dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ?‐amino‐n‐caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon‐6 contamination from the Antarctic sample storage bags may have occurred during collection. 相似文献
10.
Sarah Church Peter Ade James Bock Melanie Bowden John Carlstrom Ken Ganga Walter Gear James Hinderks Wayne Hu Brian Keating John Kovac Andrew Lange Eric Leitch Olivier Mallie Simon Melhuish Anthony Murphy Ben Rusholme Creidhe OSullivan Lucio Piccirillo Clem Pryke Andy Taylor Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083
QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓmax2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005. 相似文献