A reanalysis of the HCO+/HOC+ abundance ratio in dense interstellar clouds     

Jarrold MF  Bowers MT  DeFrees DJ  McLean AD  Herbst E 《The Astrophysical journal》1986,303(1):392-400

New theoretical and experimental results have prompted a reinvestigation of the HCO+/HOC+ abundance ratio in dense interstellar clouds. These results pertain principally but not exclusively to the reaction between HOC+ and H2, which was previously calculated by DeFrees, McLean, and Herbst to possess a large activation energy barrier. New calculations, reported here, indicate that this activation energy barrier is quite small and may well be zero. In addition, experimental results at higher energy and temperature indicate strongly that the reaction proceeds efficiently at interstellar temperatures. If HOC+ does indeed react efficiently with H2 in interstellar clouds, the calculated HCO+/HOC+ abundance ratio rises to substantially greater value under standard dense cloud conditions than in deduced via the tentative observation of HOC+ in Sgr B2.  相似文献   

Ab initio molecular orbital studies of low-energy, metastable isomers of the ubiquitous cyclopropenylidene     

DeFrees DJ  McLean AD 《The Astrophysical journal》1986,308(1):L31-L35

The discovery of cyclopropenylidene in space suggests that other C3H2 isomers may be present and a tentative detection of one such isomer, propargylene (HCCCH), has been reported. Ab initio molecular orbital theory has been used to characterize five low-lying, metastable isomers of cyclopropenylidene. Four are found to be stable minima and their vibrational frequencies are reported, although the stable form of triplet propargylene is not firmly established. Extended calculations including the electron correlation energy, show that the lowest in energy is singlet propadienylidene, followed by propargylene; the singlet and triplet of the latter are too close in energy to allow an assignment of the ground state; triplet propadienylidene is at a significantly higher energy. Rotational frequencies computed to an expected accuracy of +/- 1%-2% do not confirm the tentative detection of propargylene in space, although the discrepancy between theory and the observation is not so great as to unequivocally rule out this possibility.  相似文献   

澳大利亚和新西兰的地震危险性     

Dowr.  DJ 傅建武 《地震科技情报》1997,(7):12-18

作为计划协调澳大利亚和新西兰两国的建筑规范的一个前奏，本文旨在讨论阐明两国的地震危险性状况，给出了４７５年重复周期的峰值地面国速度危险性图，同时给出了新西兰２５００年重复周期的典型钣应诸危险性图。  相似文献   

Concentrations of Cd,Zn and Cu in sediments and brown shrimp (Crangon crangon L.) from the Severn Estuary and Bristol Channel,UK     

Culshaw C  Newton LC  Weir I  Bird DJ 《Marine environmental research》2002,54(3-5):331-334

Cd, Zn and Cu levels were determined in sediments and Crangon crangon from 9 sites in the Severn Estuary/Bristol Channel during winter 1999. Metal levels in both shrimp and sediments varied significantly between sites and were related to proximity of input and/or sediment type. In the upper Estuary, Cd levels in shrimp were 100x higher than other reported values whereas sediment Cd contamination was comparable. It is suggested that high Cd levels in shrimp are due to the high inputs and enhanced bioavailability of metal during winter.  相似文献   

美国东南部边缘磷成因期与海洋δ^13C和δ^18O记录的联系     

Mall  DJ 周立君 《海洋地质前沿》1997,(4):11-13

美国东南部边缘磷成因期与海洋δ￣（１３）Ｃ和δ￣（１８）Ｏ记录的联系ＤａｖｉｄＪ．Ｍａｌｌｉｎｓｏｎ等海洋一大气储库中ＣＯ２的生物迁移在地质年代中受磷的可利用性限制。因此，为了推断出关于碳的生物地球化学循环和潜在的气候控制，了解整个地质时代中磷通量是...  相似文献   

尼罗河三角洲平原沉积物来源和沿岸土壤流失的特例     

Stan.  DJ 程昕 《海洋地质前沿》1996,(8):19-21

尼罗河三角洲平原沉积物来源和沿岸土壤流失的特例Ｄ．Ｊ．Ｓｔａｎｌｅｙ尼罗河三角洲曾经是地中海最大的沉积中心，如今它已基本上成为一个人工改造的沿岸平原，不再向地中海延伸，局部开始后退。尼罗河三角洲不再是一个活动的三角洲（Ｓｔａｎｌｅｙ和Ｗａｒｎｅ，１９...  相似文献   

新石器人类活动反映了中国长江三角洲海平面控制地形的变化     

Stan.  DJ 马建华 《海洋地质前沿》1997,(4):15-17

新石器人类活动反映了中国长江三角洲海平面控制地形的变化Ｄ．Ｊ．Ｓｔａｎｌｅｙ等该地质一考古学综合调查主要研究早、中全新世时期长江三角洲平原上影响新石器人类迁徒的环境限定因素。最近的资料表明：（１）该三角洲最早的新石器文化虽然比中国内陆早期的新石器文化...  相似文献   

Apparent lack of CYP1A response to high PCB body burdens in fish from a chronically contaminated PCB site     

Brammell BF  Price DJ  Birge WJ  Elskus AA 《Marine environmental research》2004,58(2-5):251-255

Chronic exposure to organic contaminants such as polychlorinated biphenyls (PCBs) can lead to the development of resistance to these chemicals, a condition associated with reduced response of CYP1A1, a pollutant-inducible biomarker. We measured CYP1A activity (ethoxyresorufin o-deethylase, EROD) and PCB concentrations in feral fish from the Town Branch/Mud River system (Logan County, KY), a stream historically contaminated with PCBs and partially remediated. As a first step in evaluating the possible development of resistant populations in this system, we measured CYP1A expression and PCB body burdens in resident fish from sites we previously characterized as containing biologically significant levels of CYP1A inducing compounds. Mean PCB concentrations in edible flesh ranged from 75.2 to 16.7 microg/g in fish collected from Town Branch remediated sites and were relatively low (1.23 microg/g) in Town Branch reference site fish. However, hepatic CYP1A activity was similar among individuals of most species collected from reference and contaminated/remediated sites. The absence of elevated CYP1A levels in resident fish species despite the presence of significant PCB body burdens may indicate these fish have developed reduced sensitivity to CYP1A induction, a condition associated with acquired resistance to toxicants.  相似文献   

黔南大贵州滩早三叠世高频旋回堆积型式及其与地球轨道参数变化周期的 …   总被引：7，自引：2，他引：5  

Lehn.  DJ 《中国区域地质》1998,17(1):1-8,15

大贵州滩是右江盆地内的一个三叠纪弧立碳酸盐岩台地。其早三叠世滨潮坪５级小旋回由是潮下泥粒灰岩和潮间条纹岩及蓝藻细菌吉岩等组成。小旋回组合规律为：小旋回按４：的比例组成小旋回束,后者又按３：１的比例组成小旋回组。  相似文献   

Microscale characterization of dissolved organic matter production and uptake in marine microbial mat communities     

Paerl HW  Bebout BM  Joye SB  Des Marais DJ 《Limnology and oceanography》1993,38(6):1150-1161

Intertidal marine microbial mats exhibited biologically mediated uptake of low molecular weight dissolved organic matter (DOM), including D-glucose, acetate, and an L-amino acid mixture at trace concentrations. Uptake of all compounds occurred in darkness, but was frequently enhanced under natural illumination. The photosystem 2 inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) generally failed to inhibit light-stimulated DOM uptake. Occasionally, light plus DCMU-amended treatments led to uptake rates higher than light-incubated samples, possibly due to phototrophic bacteria present in subsurface anoxic layers. Uptake was similar with either 3H- or 14C-labeled substrates, indicating that recycling of labeled CO2 via photosynthetic fixation was not interfering with measurements of light-stimulated DOM uptake. Microautoradiographs showed a variety of pigmented and nonpigmented bacteria and, to a lesser extent, cyanobacteria and eucaryotic microalgae involved in light-mediated DOM uptake. Light-stimulated DOM uptake was often observed in bacteria associated with sheaths and mucilage surrounding filamentous cyanobacteria, revealing a close association of organisms taking up DOM with photoautotrophic members of the mat community. The capacity for dark- and light-mediated heterotrophy, coupled to efficient retention of fixed carbon in the mat community, may help optimize net production and accretion of mats, even in oligotrophic waters.  相似文献