The importance of new rate coefficients for deuterium fractionation reactions in interstellar chemistry     

Helen Roberts  Eric Herbst  T. J. Millar 《Monthly notices of the Royal Astronomical Society》2002,336(1):283-290

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量子化学方法研究氯代苯酚类化合物对水生物毒性的构效关系     

许旋  罗一帆  李华祥 《广东海洋大学学报》1992,(2)

对20个氯代苯酚类化合物进行了CNDO/2量子化学计算,讨论了化合物电子结构与其对水生物翻车鱼(Bluegill)、花鳉鱼(Guppy)、和虾(Shrimp)半致死量之间的关系,分别获得了表示其构效关系的三个线性方程,它们的显著性均远高于α=0.01水平。结果表明:氯代苯酚化合物苯环上碳原子的兀电荷之和(∑Qπ_R)越大苯环上碳原子的净电荷之和(∑Q_R)越大,或LUMO轨道能(E_(LUMO))越低,均使化合物对Bluegill和Guppy水生物的毒性增大;而化合物苯环上羟基邻位的碳原子的兀电荷布居(P_3)越大,同时HOMO轨道能E_(HOMO)越高,则化合物对Shrimp毒性也越大。据此,可预测氯代苯酚类化合物对上述三种水生物的毒性。  相似文献   

FARMLAND AND URBAN AREA DYNAMICS MONITORING INCHINA USING REMOTE SENSING AND SPATIALSTATISTICS METHODOLOGY     

LIU Ming-liang  ZHUANG Da-fang  LIU Ji-yuan 《中国地理科学(英文版)》2001,11(1):42-49

1 INTRODUCTIONGlobal change research involves much geo-objectsand geo-process, such as climate and environmentalchange, substance and energy cycling, land-use/land-cover change (LUCC), interactivity between human and nature, etc.. So it need cooperation frommany research communities including international research programs groups such as IGBP (InternationalGeosphere-Biosphere Programme IPCC (Intergovemmental Panel on Climate Change), IHDP (InternationalHuman Dimension Program o…  相似文献   

On water ice formation in interstellar clouds     

R. Papoular 《Monthly notices of the Royal Astronomical Society》2005,362(2):489-497

A model is proposed for the formation of water ice mantles on grains in interstellar clouds. This occurs by direct accretion of monomers from the gas, be they formed by gas or surface reactions. The formation of the first monolayer requires a minimum extinction of interstellar radiation, sufficient to lower the grain temperature to the point where thermal evaporation of monomers is just offset by monomer accretion from the gas. This threshold is mainly determined by the adsorption energy of water molecules on the grain material; for hydrocarbon material, chemical simulation places this energy between 0.5 and 2 kcal mol⁻¹, which sets the (true) visible extinction threshold at a few magnitudes. However, realistic distributions of matter in a cloud will usually add to this an unrelated amount of cloud core extinction, which can explain the large dispersion of observed (apparent) thresholds. Once the threshold is crossed, all available water molecules in the gas are quickly adsorbed, because the grain cools down and the adsorption energy on ice is higher than on bare grain. The relative thickness of the mantle, and, hence, the slope of  τ₃( A _v)  depend only on the available water vapour, which is a small fraction of the oxygen abundance. Chemical simulation was also used to determine the adsorption sites and energies of O and OH on hydrocarbons and study the dynamics of formation of water molecules by surface reactions with gaseous H atoms, as well as their chances to stick in situ.  相似文献   

Fragmentation and the formation of primordial protostars: the possible role of collision-induced emission     

E. Ripamonti  T. Abel 《Monthly notices of the Royal Astronomical Society》2004,348(3):1019-1034

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Rhombic Cell Analysis. Ⅱ. Application to the IRAS／PSCz Catalogue     

Tao Kiang  Yong-Feng Wu  Xing-Fen Zhu Dunsink Observatory Dublin Institute for Advanced Studies Dublin Ireland Center for Astrophysics  University of Science  Technology of China  Hefei 《中国天文和天体物理学报》2004,4(3):209-220

Rhombic cell analysis as outlined in the first paper of the present seriesis applied to samples of varying depths and liming luminosities of the IRAS/PSCzCatalogue. Numerical indices are introduced to summarize essential information.Because of the discrete nature of the analysis and of the space distribution of galax-ies, the indices for a given sample must be regarded as each having an irreduciblescatter. Despite the scatter, the mean indices show remarkable variations acrossthe samples. The underlying factor for the variations is shown to be the limitingluminosity rather than the sampling depth. As samples of more and more luminousgalaxies are considered over a range of some 2.5 magnitudes (a factor of some 75in space density), the morphology of the filled and empty regions defined by thegalaxies degrades steadily towards insignificance, and the degrading is faster for thefilled than the empty region.  相似文献   

⁴⁰Ar/³⁹Ar and oxygen isotope studies of polymetamorphism from Tinos Island, Cycladic blueschist belt, Greece     

M. BRÖCKER  H. KREUZER  A. MATTHEWS  M. OKRUSCH 《Journal of Metamorphic Geology》1993,11(2):223-240

Abstract Petrological, oxygen isotope and ⁴⁰Ar/³⁹Ar studies were used to constrain the Tertiary metamorphic evolution of the lower tectonic unit of the Cyclades on Tinos. Polyphase high-pressure metamorphism reached pressures in excess of 15 kbar, based on measurements of the Si content in potassic white mica. Temperatures of 450–500° C at the thermal peak of high-pressure metamorphism were estimated from critical metamorphic assemblages, the validity of which is confirmed by a quartz–magnetite oxygen isotope temperature of 470° C. Some ⁴⁰Ar/³⁹Ar spectra of white mica give plateau ages of 44–40 Ma that are considered to represent dynamic recrystallization under peak or slightly post-peak high-pressure metamorphic conditions. Early stages in the prograde high-pressure evolution may be documented by older apparent ages in the high-temperature steps of some spectra. Eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation. Oxygen isotope thermometry of four quartz–magnetite pairs from greenschist samples gives temperatures of 440–470° C which cannot be distinguished from those deduced for the high-pressure event. The exhumation and overprint is documented by decreasing ages of 32–28 Ma in some greenschists and late-stage blueschist rocks, and ages of 30–20 Ma in the lower temperature steps of the Ar release patterns of blueschist micas. Almost flat parts of Ar–Ar release spectra of some greenschist micas gave ages of 23–21 Ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism. Oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a δ¹⁸O-enriched fluid. Rather, the compositions indicate that fluid to rock ratios were very low, the isotopic compositions being primarily controlled by those of the protolith rocks. We assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid. A quartz–magnetite sample from a contact metamorphic skarn, taken near the Miocene monzogranite of Tinos, gave an oxygen isotope temperature of 555° C and calculated water composition of 9.1%. The value of δ¹⁸O obtained from this water is consistent with a primary magmatic fluid, but is lower than that of fluids associated with the greenschist overprint, which indicates that the latter event cannot be directly related to the monozogranite intrusion.  相似文献   

Challenging a Paradigm: Do We Need Active and Inactive Areas to Account for Near-Nuclear Jet Activity?     

Crifo  J.-F.  Rodionov  A. V.  Szegö  K.  Fulle  M. 《Earth, Moon, and Planets》2002,90(1-4):227-238

We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei. The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley, for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images of the coma.  相似文献   

测绘项目管理实施引论     

龚强 《地理信息世界》2002,(4)

根据我国测绘生产单位的实际情况 ,测绘项目管理的具体实施大致包括对项目的识别、选定、启动与筹集资金、计划、成本估算、执行计划、控制、收尾等主要步骤。当项目确定后 ,需要启动和筹集资金。而计划是项目管理的基本组成部分 ,包括明确项目目标和工作范围。项目成本估算有因素估算法和利用WBS方法的详细估算。项目质量管理规划的依据有质量目标、范围说明、标准和规范等。  相似文献   

Detection of rovibrationally excited H2 formed through the heterogeneous recombination of H atoms on a cold HOPG surface     

J.S.A. Perry  S.D. Price 《Astrophysics and Space Science》2003,285(3-4):769-776

This paper reports results from an experiment designed to measure the nascent rovibrational population of H₂ molecules that have formed through the heterogeneous recombination of H atoms on the surface of cosmic dust analogues under conditions approaching those of the interstellar medium (ISM). H₂ that has formed on a highly oriented pyrolytic graphite (HOPG) surface has been detected, using laser induced resonance-enhanced multi-photon ionization (REMPI), in the v = 1 (J= 0–3) rovibrational states at surface temperatures of 30 K and 50 K. These excited product molecules display rotational temperatures significantly higher than the target surface temperature. These first results suggest that a considerable proportion of the binding energy released on formation of the H₂ is deposited in the surface, in addition to internal excitation of the product molecules. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献