The interpretation of observations of ice and silicate ir features and polarization across it in the spectra of protostellar objects BN and AFGL 2591     

Alex E. Il'In 《Astrophysics and Space Science》1995,224(1-2):233-233

The absorption features of ice at 3µm and of silicate at 10 and 20µm as well as the linear polarization across it have been calculated. The interpretations of data for protostellar objects BN and AFGL 2591 are made.The model of partially aligned spinning spheroidal grains with the Purcell's suprathermal alignment mechanism and the power law size distribution are considered. Core-mantle, porous and composite particles are investigated in the Rayleigh approximation. In the case of composite and porous grains the effective refractive indices are computed with the approximate Bruggeman rule.The influence of grain chemical composition, elongation and structure has been investigated. The distinctions in polarization between composite and core-mantle models are found. The mixing of grain materials smooths the individual spectral features of chemical components. The adding of graphite causes the shift of the 10µm peak position to shorter wavelengths. When the fraction of graphite increases, the peak at 20µm decreases and shifts to shorter wavelengths. The increase of elongation reduces the negative polarization at the 3µm feature, shifts the 10µm and 20µm peak positions to longer wavelengths, and raises the strength of the 20µm band. The porosity leads to similar effects.It was found that the studied grain models are in good agreement with observational data for BN and AFGL 2591 objects. The absence of polarization excess near 3µm for AFGL 2591 is attributable to a decrease in elongation of large grains as a result of coagulation. The attention is attracted to the problem of real distribution of the interstellar dust grains over the elongation parameter. The determination this distribution function and the study of its evolution in the processes of accretion and coagulation are necessary.  相似文献   

THE IMPACT-FLOOD CONNECTION: DOES IT EXIST?*     

Alexander Deutsch  Christian Koeberl  Joel D. Blum  Bevan M. French  Billy P. Glass  Richard Grieve  Peter Horn  Elmar K. Jessberger  Gero Kurat  Wolf Uwe Reimold  Jan Smit  Dieter Stöffler  Stuart Ross Taylor 《地学学报》1994,6(6):644-650

In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research.  相似文献   

Triggering factors,behavior, and social impact of the January 2021 hail-debris flows at the Central Valley of Chile     

Romero  Jorge E.  Vergara-Pinto  Francisca  Aguilar  Germ&#;n  Garc&#;s  Alex  Montserrat  Santiago 《Landslides》2022,19(4):865-883

Landslides - An extreme precipitation event produced catastrophic debris flows in central Chile during 29–31 January 2021 (austral summer). Our study focuses on the triggering factors and...  相似文献   

Multi-factor impact analysis of agricultural production in Bangladesh with climate change   总被引：1，自引：0，他引：1  

Alex C. Ruane  David C. Major  Winston H. Yu  Mozaharul Alam  Sk. Ghulam Hussain  Abu Saleh Khan  Ahmadul Hassan  Bhuiya Md. Tamim Al Hossain  Richard Goldberg  Radley M. Horton  Cynthia Rosenzweig 《Global Environmental Change》2013,23(1):338-350

Diverse vulnerabilities of Bangladesh's agricultural sector in 16 sub-regions are assessed using experiments designed to investigate climate impact factors in isolation and in combination. Climate information from a suite of global climate models (GCMs) is used to drive models assessing the agricultural impact of changes in temperature, precipitation, carbon dioxide concentrations, river floods, and sea level rise for the 2040–2069 period in comparison to a historical baseline. Using the multi-factor impacts analysis framework developed in Yu et al. (2010), this study provides new sub-regional vulnerability analyses and quantifies key uncertainties in climate and production. Rice (aman, boro, and aus seasons) and wheat production are simulated in each sub-region using the biophysical Crop Environment REsource Synthesis (CERES) models. These simulations are then combined with the MIKE BASIN hydrologic model for river floods in the Ganges-Brahmaputra-Meghna (GBM) Basins, and the MIKE21 Two-Dimensional Estuary Model to determine coastal inundation under conditions of higher mean sea level. The impacts of each factor depend on GCM configurations, emissions pathways, sub-regions, and particular seasons and crops. Temperature increases generally reduce production across all scenarios. Precipitation changes can have either a positive or a negative impact, with a high degree of uncertainty across GCMs. Carbon dioxide impacts on crop production are positive and depend on the emissions pathway. Increasing river flood areas reduce production in affected sub-regions. Precipitation uncertainties from different GCMs and emissions scenarios are reduced when integrated across the large GBM Basins’ hydrology. Agriculture in Southern Bangladesh is severely affected by sea level rise even when cyclonic surges are not fully considered, with impacts increasing under the higher emissions scenario.  相似文献   

The Meteoritical Bulletin,No. 100, 2014 June     

Alex Ruzicka  Jeffrey N. Grossman  Laurence Garvie 《Meteoritics & planetary science》2014,49(8):E1-E101

Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Ko?ice, Silistra, So?tmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/  相似文献   

DUN AND BRADSTREET'S MARKET IDENTIFIERS AND ECONOMIC GEOGRAPHY*     

Alex Schwartz 《The Professional geographer》1987,39(2):166-172

An increasing number of studies of business start-ups, closings, and relocations rely on a single data base, DUNS Market Identifiers. This data file to U.S. business establishments provides researchers with essential information about individual firms and establishments. It also exhibits serveral idiosyncracies and requires careful consideration of the meaning of such basic terms as “location”and “firm.”Drawing from a recent survey of 500 New Jersey firms. I consider some of the methodological amd conceptual issues Dun and Bradstreet data pose for industrial location analysts. The Dun and Bradstreet listings exaggerate the exaggerate the incidence and magnitude of establishment openings and closing.  相似文献   

Evaluation of Inference Adequacy in Cumulative Logistic Regression Models: An Empirical Validation of ISWRidge Relationships     

Cheng-Wu CHEN  Hsien-Chueh Peter YANG  Chen-Yuan CHEN  Alex Kung-Hsiung CHANG  Tsung-Hao CHEN   《中国海洋工程》2008,22(1):43-56

Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p 〈0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to cheek the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height （X1 ） and potential energy （X2 ） significantly impact （p 〈 0. 0001 ） the amplitude-based refleeted rate; the P-values for the deviance and Pearson are all 〉 0.05 （0.2839, 0.3438, respectively）. That is, the goodness-of-fit between ridge height （ X1 ） and potential energy （X2） can further predict parameters under the scenario of the best parsimonious model. Investigation of 6 predictive powers （ R2, Max-rescaled R^2, Sorners＇ D, Gamma, Tau-a, and c, respectively） indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model.  相似文献   

Differentiation and evolution of the IVA meteorite parent body: Clues from pyroxene geochemistry in the Steinbach stony‐iron meteorite     

Alex Ruzicka  Melinda HUTSON 《Meteoritics & planetary science》2006,41(12):1959-1987

Abstract— We analyzed the Steinbach IVA stony‐iron meteorite using scanning electron microscopy (SEM), electron microprobe analysis (EMPA), laser ablation inductively‐coupled‐plasma mass spectroscopy (LA‐ICP‐MS), and modeling techniques. Different and sometimes adjacent low‐Ca pyroxene grains have distinct compositions and evidently crystallized at different stages in a chemically evolving system prior to the solidification of metal and troilite. Early crystallizing pyroxene shows evidence for disequilibrium and formation under conditions of rapid cooling, producing clinobronzite and type 1 pyroxene rich in troilite and other inclusions. Subsequently, type 2 pyroxene crystallized over an extensive fractionation interval. Steinbach probably formed as a cumulate produced by extensive crystal fractionation (?60–70% fractional crystallization) from a high‐temperature (?1450–1490 °C) silicate‐metallic magma. The inferred composition of the precursor magma is best modeled as having formed by ≥30–50% silicate partial melting of a chondritic protolith. If this protolith was similar to an LL chondrite (as implied by O‐isotopic data), then olivine must have separated from the partial melt, and a substantial amount (?53–56%) of FeO must have been reduced in the silicate magma. A model of simultaneous endogenic heating and collisional disruption appears best able to explain the data for Steinbach and other IVA meteorites. Impact disruption occurred while the parent body was substantially molten, causing liquids to separate from solids and oxygen‐bearing gas to vent to space, leading to a molten metal‐rich body that was smaller than the original parent body and that solidified from the outside in. This model can simultaneously explain the characteristics of both stony‐iron and iron IVA meteorites, including the apparent correlation between metal composition and metallographic cooling rate observed for metal.  相似文献   

Periodic long-term X-ray and radio variability of Cygnus X-1     

Pawe&#; Lachowicz  rzej A. Zdziarski  Alex Schwarzenberg-Czerny  Guy G. Pooley  Shunji Kitamoto 《Monthly notices of the Royal Astronomical Society》2006,368(3):1025-1039

  相似文献   

Book review     

Alex Woronow 《Mathematical Geology》1987,19(6):579-581

  相似文献