The role of a strong far-infrared radiation field in line excitation and cooling of photodissociation regions and molecular clouds

We have theoretically studied the influence of a far-infrared radiation (FIR) field from H_π region on the cooling by C and O atoms, C⁺ ion and CO molecule in a photodissociation region, and a molecular cloud associated with H_π region (hereinafter referred as H_I region) at low temperatures (T _k≤200 K). Comparisons have been made for cooling with and without FIR for two extreme abundances (10⁻⁴ and 10⁻⁷) of the mentioned species for temperatures ranging between 10 and 200K and an hydrogen particle density range 10 cm⁻³≤n _o≤ 10⁷ cm³. The cooling by the species with low line-splitting (C_I, C_π and CO) is significantly influenced by the radiation field for temperaturesT _k < 100 K while the effect of radiation field on cooling by O_I is significant even at higher temperatures (T _k > 100 K). The effect of FIR field on the cooling of CO from low rotational transitions is negligibly small, whereas it is considerable for higher transitions. In general, the cooling terms related to the short-wavelength transitions are more affected by FIR than those related to longer wavelengths. It is also demonstrated here that in the determination of thermal structure of an HI region the dust grains play an important role in the heating of gas only through photoelectron emission following irradiation by far-ultraviolet (FUV) radiation, as the infrared radiation from the dust is too small to have substantial effect on the cooling. It is found that in the H_π /H_I interface the FIR field from grains in the H_π region is not capable of modifying the temperature of the warmest regions but does so in the inner part where the temperature is low enough.     

Cumulenic and heterocumulenic anions: potential interstellar species?

A recent theoretical investigation by Terzieva & Herbst of linear carbon chains, C _n where n  ≥ 6, in the interstellar medium has shown that these species can undergo efficient radiative association to form the corresponding anions. An experimental study by Barckholtz, Snow & Bierbaum of these anions has demonstrated that they do not react efficiently with molecular hydrogen, leading to the possibility of detectable abundances of cumulene-type anions in dense interstellar and circumstellar environments. Here we present a series of electronic structure calculations which examine possible anionic candidates for detection in these media, namely the anion analogues of the previously identified interstellar cumulenes C _n H and C _{n −1}CH₂ and heterocumulenes C _n O (where n  = 2–10). The extraordinary electron affinities calculated for these molecules suggest that efficient radiative electron attachment could occur, and the large dipole moments of these simple (generally) linear molecules point to the possibility of detection by radio astronomy.     

Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of Calofornia—hydrothermal effects on unconsolidated diatom ooze

The effects of intrusive thermal stress have been studied on a number of Pleistocene sediment samples obtained from Leg 64 of the DSDP-IPOD program in the Gulf of California. Samples were selected from Sites 477, 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions. For comparison purposes, samples from Sites 474 and 479 were selected as representative of unaltered material.The GC and GC-MS data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher-plant detritus. Samples from sill proximities were found to contain thermally-derived distillates and those adjacent to sills contained essentially no lipids. Curie point pyrolysis combined with GC and GC-MS was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin. Pyrograms of the altered kerogens were much less complex than the unaltered samples, reflecting the thermal effects. The kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated, wet sediments resulted in in situ pyrolysis of the organic matter.Examination of the kerogens by ESR showed that spin density and line width pass through a maximum during the course of alteration but ESR g-values show no correlation with maturity. Stable carbon isotope (δ¹³C) values of kerogens decrease by 1–1.5‰ near the sills at Sites 477 and 481 and the atomic N/C decreases slightly with proximity to a smaller sill at Site 478. Differences in maturation behavior between Site 477 and 481 and Site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of Guaymas Basin protokerogen.     

汉阳锅顶山地区晚泥盆世遗迹化石的发现及其意义

本文描述了12属11种和两个未定种,其中有8个新种。Incisifex,Margaritichnus,Spirophycus(?)在中国首次报道。值得提出的是在五通组发现了海相遗迹化石:Rusophycus,Diplichnites,Chondrites等。作者认为该沉积环境可能属于过渡类型,在河流沉积之间含有一些海相夹层,并非单纯陆相地层。     

Fractionated aromatic petroleums and the generation of gas-condensates

Based on experimental and observational evidence, a mode of origin involving evaporative fractionation is proposed for a class of petroleums enriched in light aromatic and naphthenic hydrocarbons (benzene, toluene, meta-xylene, para-xylene, methylcyclopentane, cyclohexane, and methylcyclohexane). Progressive gas loss from gas-saturated oil is suggested as the causal mechanism, with simultaneous loss of light ends in gaseous solution, and accompanying fractionation. These processes were simulated experimentally.Residual oils exhibit the following changes in their remaining light hydrocarbons, <C₉: (1) increase in aromaticity (in aromatic hydrocarbons relative to normal alkanes of molecular weight); (2) increase in “normality” (in unbranched alkanes and naphthenes relative to branched isomers), and (3) decrease in paraffinicity (in paraffins relative to naphthenes). Retrogressive changes in maturity indicators take place leading to spurious evidence of immaturity in residual oils and the derived evaporative condensates.The phenomena occur in many basins, and are a key to understanding major aspects of petroleum variability. On the basis of aromaticity and paraffinicity relationships, evaporative gas-condensates are distinguishable from those generated by thermal cracking. Unfractionated thermal gas-condensates are rare. Evaporative condensates are the daughter products of oils which have suffered evaporative fractionation.     

中国前寒武纪痕迹化石的分布及其古生物学、地层学意义

近年来，在我国前寒武纪不同时代的地层中发现了大量的痕迹化石，其中前寒武纪冰期前的痕迹化石主要分布于我国北方的长城纪和青白口纪地层中。这些痕迹化石产出时代古老，表明在我国北方１４～１７亿年前的海水中就可能生活有古老的后生动物，这些痕迹化石的发现对于探索后生动物的起源及演化具有重要意义。前寒武纪冰期后所发现的痕迹化石主要分布于我国西南地区震旦纪晚期的地层中，这些痕迹化石在震旦纪地层中的广泛分布，对震旦系及震旦系与寒武系界线的划分对比将提供重要依据。     

塔里木北缘库车坳陷侏罗系阳霞组的双壳类化石及其时代

系统采集并研究了塔里木盆地北缘库车坳陷库车河剖面阳霞组的双壳动物化石，讨论了化石组合特点及其地质时代，根据化石组合面貌、岩性和沉积特征以及剖面结构，认为阳霞组的时代应为早侏罗世晚期，与北缰地区的三工河组相当。     

Structure and chemistry in the hot molecular core G34.3+0.15

New multifrequency spatial and spectral studies of the hot molecular core associated with the ultracompact HII region G34.3+0.15 have demonstrated an extremely rich chemistry in this archetypal hot core and revealed differing spatial structure between certain species which may be a dynamical effect of chemical evolution. The structure of the hot core has been studied with the JCMT in the high excitation J=19-18 and J=18-17 lines of CH₃CN and with the Nobeyama Millimetre Array at 4 arc resolution in the J=6-5 transition. Comparison with a VLA NH₃(3,3) map shows a displacement between peak emission in the two chemical species which is consistent with chemical processing on a time scale comparable to the dynamical time scale of 10⁵ yrs.A 330-360 GHz spectral survey of the hot core with the JCMT has detected 358 spectral lines from at least 46 distinct chemical species, including many typical of shocked chemistry while other species indicate abundances that reflect the chemistry of a previous cold phase. The first unambiguous detection of ethanol in hot gas has been made. Observations of 14 rotational transitions of this molecule yield a temperature of 125 K and column density 2×10¹⁵ cm^–2. This large abundance cannot be made by purely gas-phase processes and it is concluded that ethanol must have formed by grain surface chemistry.     

Dissolved Organic Matter in Oceanic Waters

The amount of information on oceanic dissolved organic matter (DOM) has increased dramatically in the last decade thanks to the advances in chemical characterization. This information has supported the development of some novel and important ideas for DOM dynamics in the ocean. Consequently, we have a better understanding of the importance of DOM in oceanic biogeochemical cycles. Here we review studies published mainly during 1995–2001, synthesize them and discuss unsolved problems and future challenges. The measurement, distribution and turnover of dissolved organic carbon (DOC) are presented as the bulk dynamics of the oceanic DOM. The size spectrum, elemental composition, and chemical compositions at molecular and functional group levels are described. The mechanisms proposed for the survival of biomolecules in DOM are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.