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1.
D. L. Band L. A. Ford J. L. Matteson D. M. Palmer B. J. Teegarden M. S. Briggs G. N. Pendleton R. D. Preece W. S. Paciesas 《Astrophysics and Space Science》1995,231(1-2):145-148
No absorption lines between 15 and 100 keV have been detected in burst spectra accumulated by BATSE. Almost 250 bursts have been inspected visually, and a computerized search has begun. Our simulations show that BATSE could indeed detect lines similar to those observed byGinga in strong bursts, and our tests of the detectors' actual capabilities demonstrate they function as understood. The apparent discrepancy between BATSE andGinga is not yet compelling, and therefore the BATSE nondetections do not invalidate theGinga detections. Nonetheless, the absence of BATSE line detections indicates a low line-occurrence frequency. 相似文献
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R. D. Preece M. S. Briggs G. N. Pendleton W. S. Paciesas J. L. Matteson D. L. Band L. A. Ford 《Astrophysics and Space Science》1995,231(1-2):207-210
The BATSE Spectroscopy Detectors (SDs) each have a thin beryllium window which allows detection of photons down to 5 keV. Until recently, exploitation of low-energy SD discriminator data has been held up by a lack of knowledge of its energy coverage. A recent series of in-flight changes in the instrument configuration has allowed the SD discriminators to be calibrated fairly accurately. With this in hand, we have surveyed BATSE GRBs for such features as X-ray precursors and after-glows in the roughly 5-10 keV band. For a large percentage of the BATSE bursts, no emission is observed in this energy band. In some cases where low-energy emission has been observed, ratios of flux histories indicate differential spectral evolution. In addition, we have obtained joint spectral fits between the low-energy data and the regular SD data, showing that a single spectral model is sometimes insufficient to fit the entire energy range. 相似文献
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Morgan Gopnik Clare Fieseler Laura Cantral Kate McClellan Linwood Pendleton Larry Crowder 《Marine Policy》2012
From 2009 to 2011, marine spatial planning (MSP) rapidly gained visibility in the United States as a promising ocean management tool. A few small-scale planning efforts were completed in state waters, and the Obama Administration proposed a framework for large-scale regional MSP throughout the U.S. Exclusive Economic Zone. During that same time period, the authors engaged a variety of U.S ocean stakeholders in a series of dialogs with several goals: to share information about what MSP is or could be, to hear stakeholder views and concerns about MSP, and to foster better understanding between those who depend on ocean resources for their livelihood and ocean conservation advocates. The stakeholder meetings were supplemented with several rounds of in-depth interviews and a survey. Despite some predictable areas of conflict, project participants agreed on a number of issues related to stakeholder engagement in MSP: all felt strongly that government planners need to engage outsiders earlier, more often, more meaningfully, and through an open and transparent process. Equally important, the project affirmed the value of bringing unlike parties together at the earliest opportunity to learn, talk, and listen to others with whom they rarely engage. 相似文献
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We have developed a model for reflection nebulae around luminous infrared sources embedded in dense dust clouds. The aim of this study is to determine the sizes of the scattering grains. In our analysis, we have adopted an MRN-like power-law size distribution (Mathis, Rumpl, and Nordsieck) of graphite and silicate grains, but other current dust models would give results which were substantially the same. In the optically thin limit, the intensity of the scattered light is proportional to the dust column density, while in the optically thick limit, it reflects the grain albedo. The results show that the shape of the infrared spectrum is the result of a combination of the scattering properties of the dust, the spectrum of the illuminating source, and foreground extinction, while geometry plays a minor role. Comparison of our model results with infrared observations of the reflection nebula surrounding OMC-2/IRS 1 shows that either a grain size distribution like that found in the diffuse interstellar medium, or one consisting of larger grains, can explain the observed shape of the spectrum. However, the absolute intensity level of the scattered light, as well as the observed polarization, requires large grains (approximately 5000 angstroms). By adding water ice mantles to the silicate and graphite cores, we have modeled the 3.08 micrometers ice band feature, which has been observed in the spectra of several infrared reflection nebulae. We show that this ice band arises naturally in optically thick reflection nebulae containing ice-coated grains. We show that the shape of the ice band is diagnostic of the presence of large grains, as previously suggested by Knacke and McCorkle. Comparison with observations of the BN/KL reflection nebula in the OMC-1 cloud shows that large ice grains (approximately 5000 angstroms) contribute substantially to the scattered light. 相似文献
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M. San Miguel de la Cámara Antonio Almela YJ. M. Fúster Casas 《Bulletin of Volcanology》1952,12(1):165-182
While working to construct a geological map. A.Almela, an Engineer of Mines, discovered in Alhama de Murcia a previously unknown volcanic crater. This volcano erupted through the miocene layers and extended above them, thus establishing the date of this eruption as being post-miocene. Since there are no sedimentary rocks in this region of a more recent date it is impossible to fix the date of the eruption any more exactly. The crater is about 1Km. In the surface of the crater one finds slag, scoriaceous lava and compact rocks. The rock is composed of phlogopite, olivine and diopside in phenocrysts in a hyaloid cement with tiny grains of sanidine, olivine and diopside; and a thin layer of phlogopite in a glassy brownish black. A study was made of the chemical constituency of the rocks on the basis of three complete analyses and a comparison was made with the findings already made by Vera-Garrucha and those of Fortuna. All of the data as compiled in the five tables and four diagrams graphically represents the obtained results. The volcanic rocks have a close analogy to those ofOsann’s « Verita » type, which are shown not only by the analytical value of the magmatic parameters but also by the positions of the points shown in diagramsK-mg andLs-Fs-Ks of the three types already analized. In all the samples which have been studied from Barqueros the value of the K2O is superior to that of Na2O; it is also greater than that of Vera-Garrucha and less than in that of Fortuna. 相似文献
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D. L. Band S. Ryder L. A. Ford J. L. Matteson D. M. Palmer B. J. Teegarden M. S. Briggs W. S. Paciesas G. N. Pendleton R. D. Preece 《Astrophysics and Space Science》1995,231(1-2):203-206
We evaluated the significance of the line candidates identified by the visual search of burst spectra from BATSE's spectroscopy detectors. None of the candidates satisfy the detection criteria: anF-test probability less than 10–4 for a feature in one detector and consistency among the detectors which viewed the burst. Most of the candidates are not very significant, and are likely to be fluctuations. Because of the expectation of finding absorption lines, the search was biased towards absorption features. We do not have a quantitative measure of the completeness of the search which would form the basis of a comparison with previous missions. Therefore a more objective computerized search has begun. 相似文献
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David Twichell Elizabeth Pendleton Wayne Baldwin James Flocks 《Geo-Marine Letters》2009,29(6):349-358
The Chandeleur Islands lie on the eastern side of the modern Mississippi River delta plain, near the edge of the St. Bernard
Delta complex. Since abandonment approximately 2,000 years b.p., this delta complex has undergone subsidence and ravinement as the shoreline has transgressed across it. High-resolution
seismic-reflection, sidescan-sonar, and bathymetry data show that seafloor erosion is influenced by locally variable shallow
stratigraphy. The data reveal two general populations of shallow erosional depressions, either linear or subcircular in shape.
Linear depressions occur primarily where sandy distributary-channel deposits are exposed on the seafloor. The subcircular
pits are concentrated in areas where delta-front deposits crop out, and occasional seismic blanking indicates that gas is
present. The difference in erosional patterns suggests that delta-front and distributary-channel deposits respond uniquely
to wave and current energy expended on the inner shelf, particularly during stormy periods. Linear depressions may be the
result of the sandy distributary-channel deposits eroding more readily by waves and coastal currents than the surrounding
delta-front deposits. Pits may develop as gas discharge or liquefaction occurs within fine-grained delta-front deposits, causing
seafloor collapse. These detailed observations suggest that ravinement of this inner shelf surface may be ongoing, is controlled
by the underlying stratigraphy, and has varied morphologic expression. 相似文献