Complex gas hydrate from the Cascadia margin

Natural gas hydrates are a potential source of energy and may play a role in climate change and geological hazards. Most natural gas hydrate appears to be in the form of 'structure I', with methane as the trapped guest molecule, although 'structure II' hydrate has also been identified, with guest molecules such as isobutane and propane, as well as lighter hydrocarbons. A third hydrate structure, 'structure H', which is capable of trapping larger guest molecules, has been produced in the laboratory, but it has not been confirmed that it occurs in the natural environment. Here we characterize the structure, gas content and composition, and distribution of guest molecules in a complex natural hydrate sample recovered from Barkley canyon, on the northern Cascadia margin. We show that the sample contains structure H hydrate, and thus provides direct evidence for the natural occurrence of this hydrate structure. The structure H hydrate is intimately associated with structure II hydrate, and the two structures contain more than 13 different hydrocarbon guest molecules. We also demonstrate that the stability field of the complex gas hydrate lies between those of structure II and structure H hydrates, indicating that this form of hydrate is more stable than structure I and may thus potentially be found in a wider pressure-temperature regime than can methane hydrate deposits.     

柴达木盆地三湖坳陷气钾1井烃源岩地球化学特征分析

对烃源岩的地球化学特性的研究有助于油气的勘测。柴达木盆地三湖坳陷有丰厚的天然气资源,沉积范围广,厚度较大其厚度整体约2 000~3 200 m。选取三湖地区达布逊湖东部气钾1井的烃源岩样品,通过分析生物标志化合物,研究烃源岩的地球化学特征。实验结果表明:饱和烃的中低碳数分子无明显偶奇碳数优势,反映出微生物的降解作用明显改变了常规生物标志物的分布特征;有机质母质,植烷含量丰富,其碳数值接近于主峰碳数值,呈现弱还原的沉积环境特征;气钾1井中天然气有机母质主要来源于以陆生高等植物为主要母源的湖相沉积环境;伽马蜡烷也出峰明显,说明其沉积的水环境主要为高盐特征;正构烷烃C_(31)/C_(29)的比值表明这一期间的气候条件为寒冷干燥。     

Greenhouse gases: low methane leakage from gas pipelines

Using natural gas for fuel releases less carbon dioxide per unit of energy produced than burning oil or coal, but its production and transport are accompanied by emissions of methane, which is a much more potent greenhouse gas than carbon dioxide in the short term. This calls into question whether climate forcing could be reduced by switching from coal and oil to natural gas. We have made measurements in Russia along the world's largest gas-transport system and find that methane leakage is in the region of 1.4%, which is considerably less than expected and comparable to that from systems in the United States. Our calculations indicate that using natural gas in preference to other fossil fuels could be useful in the short term for mitigating climate change.     

烟草中的挥发物对烤烟香气的影响

为探讨烟草中挥发性物质与其烟气质量的关系,采用毛细管气相色谱(GC)和气相色谱-质谱(GC-MS)对国内外约3000多个烤烟样品中的挥发性物质进行了系统分析,研究烟草的产地、品种、种植条件、气候、烟叶位置及陈化对烟草中挥发性物质和烟气质量的影响．结果显示,所有烤烟中的挥发性物质的组分是相同的,但各组分的含量却有很大差别．对产于不同地区的卷烟烟气的强度、刺激性、风味和余味的评价表明,它们之间存在明显的质的差异,说明烟气质量可以根据烟草中含量相对丰富的挥发性物质来进行初步评价。     

基于量子化学计算的乙烷、乙烯、乙炔水合物主客体间相互作用特性研究

天然气水合物是一种特殊的笼状化合物,水合物中的客体分子不同,主客体间的相互作用存在差异。为了分析烃类水合物中主客体间相互作用的特征,利用量子化学方法,对乙烷、乙烯、乙炔这3种客体分子占据Ⅰ型水合物T笼时的结构、相互作用能及C—C键伸缩振动频率进行研究,讨论了客体分子在水笼中的赋存形态,揭示了主客体间的相互作用机制。结果表明：客体分子占据T笼后,与占据前相比,T笼会发生微小的膨胀或收缩,客体分子的原子间距减小;通过能量分析,发现主客体间相互作用能(ΔE_host-guest)的大小顺序为：ΔE_T笼-乙烯<ΔE_T笼-乙烷<ΔE_T笼-乙炔,色散矫正的加入使主客体间的相互作用能增大;能量分解结果显示C原子的杂化方式对水合物的主客体间相互作用影响较大,随着客体分子中C原子的杂化方式由sp³→sp²→sp杂化,客体分子与水笼间的相互作用中静电作用先略微减弱、然后增强,色散作用逐渐减弱;与未占据T笼相比,乙烷分子占据T笼后C—C键伸缩振动频率增加了6.79 cm^-1,乙烯和乙炔分子占据T笼后C—C键伸缩振动频率分别减小了5.86 cm^-1和15.87 cm^-1。     

Climate sensitivity constrained by temperature reconstructions over the past seven centuries

The magnitude and impact of future global warming depends on the sensitivity of the climate system to changes in greenhouse gas concentrations. The commonly accepted range for the equilibrium global mean temperature change in response to a doubling of the atmospheric carbon dioxide concentration, termed climate sensitivity, is 1.5-4.5 K (ref. 2). A number of observational studies, however, find a substantial probability of significantly higher sensitivities, yielding upper limits on climate sensitivity of 7.7 K to above 9 K (refs 3-8). Here we demonstrate that such observational estimates of climate sensitivity can be tightened if reconstructions of Northern Hemisphere temperature over the past several centuries are considered. We use large-ensemble energy balance modelling and simulate the temperature response to past solar, volcanic and greenhouse gas forcing to determine which climate sensitivities yield simulations that are in agreement with proxy reconstructions. After accounting for the uncertainty in reconstructions and estimates of past external forcing, we find an independent estimate of climate sensitivity that is very similar to those from instrumental data. If the latter are combined with the result from all proxy reconstructions, then the 5-95 per cent range shrinks to 1.5-6.2 K, thus substantially reducing the probability of very high climate sensitivity.     

黄山风景区能源消费的碳足迹分析

旅游业敏感于全球气候变化,同时旅游业的能源消费所产生的温室气体排放,也影响全球气候变化.旅游地是特殊的人地关系相互作用的区域,旅游地能源消费的碳排放分析,是旅游地制定与实施低碳景区政策与措施的基础.在构建基于能源消费结构的旅游地碳足迹测度模型的基础上,以黄山风景区为例,利用2006-2009年的相关数据进行分析,认为：1）黄山风景区2006-2009年间碳足迹总量上升趋势明显,年均增长率为7％;2）能源消费的碳足迹存在明显的结构差异,5种能源碳足迹从高到低依次为电能、煤、柴油、汽油、液化气;3）能源消费的碳足迹分析表明,2006-2009年黄山风景区呈可持续发展态势.     

用计算机数据采集精确测量气体的摩尔热容比

用计算机快速采集和处理数据，测量了氩气、氧气、二氧化碳气体的摩尔热容比，结果表明：对单原子分子气体实验值与理论值很好地一致；对多原子分子气体实验值与理论值有一定的偏差，说明能均分定理存在一定的局限性。     

Land-atmosphere coupling and climate change in Europe

Increasing greenhouse gas concentrations are expected to enhance the interannual variability of summer climate in Europe and other mid-latitude regions, potentially causing more frequent heatwaves. Climate models consistently predict an increase in the variability of summer temperatures in these areas, but the underlying mechanisms responsible for this increase remain uncertain. Here we explore these mechanisms using regional simulations of recent and future climatic conditions with and without land-atmosphere interactions. Our results indicate that the increase in summer temperature variability predicted in central and eastern Europe is mainly due to feedbacks between the land surface and the atmosphere. Furthermore, they suggest that land-atmosphere interactions increase climate variability in this region because climatic regimes in Europe shift northwards in response to increasing greenhouse gas concentrations, creating a new transitional climate zone with strong land-atmosphere coupling in central and eastern Europe. These findings emphasize the importance of soil-moisture-temperature feedbacks (in addition to soil-moisture-precipitation feedbacks) in influencing summer climate variability and the potential migration of climate zones with strong land-atmosphere coupling as a consequence of global warming. This highlights the crucial role of land-atmosphere interactions in future climate change.     

简论低碳经济对循环经济的超越

循环经济主要关注与经济活动密切相关的资源和污染问题,由于它可以和消费主义相结合而采用＂大量生产-大量消费-大量再循环＂模式,前途不一定就是可持续的。低碳经济则主要关注与气候变暖密切相关的温室气体排放问题,它紧紧抓住能量转换这个关键环节,指明废弃物的再利用也要花费能量,强调通过＂节能减排＂实现可持续发展,在理念和可操作性上都比循环经济前进了一步。     

气相丙酮分子与带电离子的低激发态特性

采用密度泛函理论中的B3P86方法,在6-311++G(d,p)基组水平上,优化气相丙酮分子及带电离子的基态稳定几何构型,并用含时密度泛函理论(TD-DFT)方法,研究气相丙酮分子和离子的低激发态特性.结果表明:随着分子获得电子数目的增加,体系能量逐渐增加;S1激发态能量与基态能量差值ΔE减小;分子荧光波长急剧增加;电子跃迁轨道数减少.     

含硫杂环化合物的合成与性质

含硫杂环化合物广泛存在于天然产物、香料和药物分子之中,具有特殊的气味以及重要的生物活性,有着广泛的用途。这类化合物也是有机合成中一类非常重要的中间体。因此,含硫杂环化合物的合成研究备受关注。本文阐述了近几年来含硫杂环化合物的合成研究进展,对其相关性能进行了评价,并对该领域的发展前景进行了展望。     

气相半胱氨酸分子与带电离子的低激发态特性

采用密度泛函理论(DFT)中的B3LYP方法, 在6-311++G(-d,p-)基组水平上, 对气相单体半胱氨酸(Cys)分子及离子的基态稳定几何构型进行优化, 并用含时密度泛函理论(TD-DFT)方法, 得到气相单体Cys分子和Cys^2-离子的低激发态特性. 结果表明： 随着分子捕获电子数目的增加, 体系的能量逐渐增加, S1激发态与基态能量的差值Δ E明显减小, 分子的荧光波长由239.35 nm增至1 895.82 nm, S7激发态的电子跃迁轨道数减少.     

Creation of ultracold molecules from a Fermi gas of atoms

Following the realization of Bose-Einstein condensates in atomic gases, an experimental challenge is the production of molecular gases in the quantum regime. A promising approach is to create the molecular gas directly from an ultracold atomic gas; for example, bosonic atoms in a Bose-Einstein condensate have been coupled to electronic ground-state molecules through photoassociation or a magnetic field Feshbach resonance. The availability of atomic Fermi gases offers the prospect of coupling fermionic atoms to bosonic molecules, thus altering the quantum statistics of the system. Such a coupling would be closely related to the pairing mechanism in a fermionic superfluid, predicted to occur near a Feshbach resonance. Here we report the creation and quantitative characterization of ultracold 40K2 molecules. Starting with a quantum degenerate Fermi gas of atoms at a temperature of less than 150 nK, we scan the system over a Feshbach resonance to create adiabatically more than 250,000 trapped molecules; these can be converted back to atoms by reversing the scan. The small binding energy of the molecules is controlled by detuning the magnetic field away from the Feshbach resonance, and can be varied over a wide range. We directly detect these weakly bound molecules through their radio-frequency photodissociation spectra; these probe the molecular wavefunction, and yield binding energies that are consistent with theory.     

CS2和COS在y-A12O3表面吸附的密度泛函理论研究

煤气中的有机含硫化合物CS2和COS对环境及后续的反应带来很大的危害,常用Al2O3进行脱硫处理。小分子在固体表面的吸附是研究气固反应的基础。采用量子化学密度泛函理论方法研究了CS2和COS在y-Al2O3（110）表面的吸附,结果表明CS2最稳定的构型为C82的3个原子分别与表面的Al0一Al键中的3个原子作用,形成了（COS2）。一物种,此构型的吸附能为107．98kJ／mol;COS以SC键-9表面的1个Al-O键作用时最稳定,吸附能为99．99kJ／mol。通过分波态密度和小分子吸附前后净电荷的变化可知,在这两个构型中,小分子与表面有很强的相互作用。     

Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000

Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766, these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at ￡1.3 billion (refs 5, 6). Although the flooding was deemed a 'wake-up call' to the impacts of climate change at the time, such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail to account fully for the complex hydrometeorology associated with flooding. Here we present a multi-step, physically based 'probabilistic event attribution' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed computing, we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.     

烷烃、醇、醚的定量结构与保留相关性(QSRR)研究

在邻接矩阵的基础上 ,建立一种新的连接性指数 mL =∑(δi·δj·δk·… ) 0 .5,其中 :0 L =∑(δi) 0 .5,1L =∑(δi·δj) 0 .5,并计算了 146个有机分子的0 L、1L值 .发现 mL不仅对这些化合物具有良好的结构选择性 ,而且与其气相色谱保留指数RI具有很好的相关性 .     

Uncertainty in predictions of the climate response to rising levels of greenhouse gases

The range of possibilities for future climate evolution needs to be taken into account when planning climate change mitigation and adaptation strategies. This requires ensembles of multi-decadal simulations to assess both chaotic climate variability and model response uncertainty. Statistical estimates of model response uncertainty, based on observations of recent climate change, admit climate sensitivities--defined as the equilibrium response of global mean temperature to doubling levels of atmospheric carbon dioxide--substantially greater than 5 K. But such strong responses are not used in ranges for future climate change because they have not been seen in general circulation models. Here we present results from the 'climateprediction.net' experiment, the first multi-thousand-member grand ensemble of simulations using a general circulation model and thereby explicitly resolving regional details. We find model versions as realistic as other state-of-the-art climate models but with climate sensitivities ranging from less than 2 K to more than 11 K. Models with such extreme sensitivities are critical for the study of the full range of possible responses of the climate system to rising greenhouse gas levels, and for assessing the risks associated with specific targets for stabilizing these levels.     

PdY合金氢化反应热力学函数的理论研究

在Pd和Y原子相对论有效原子实势和基函数SDD下,使用密度泛函理论B3LYP方法计算得到PdY和PdYH(D,T)分子的结构、光谱数据、能量E、熵S等性质.计算固体PdY和PdYH(D,T)的能量和熵时,近似以气体分子的电子能和振动能代替固体分子的能量,用电子熵和振动熵代替固体分子的熵.在此近似下,计算了不同温度下PdY合金与氢同位素气体反应的热力学函数,得到氢化反应温度与平衡压力的关系式.     

作为温室气体排放衡量指标的碳排放强度分析

针对美国政府提出的以温室气体排放强度下降率作为其减排目标的建议,分析了影响碳排放强度下降率的因素.利用历史统计数据,定量研究了碳排放强度下降率与国内生产总值(GDP)的增长率、碳排放增长对GDP的弹性、能源消费强度以及能源消费的碳强度等相关关系.对处于不同经济发展阶段国家的碳排放强度以及碳排放强度下降率进行了规律性分析,从而得出结论:以碳排放强度作为各国减缓气候变化贡献的衡量指标,对于发展中国家而言,可以承认和反映其对减缓气候变化的贡献;对发达国家来说,则不能只谈这一单一指标,而必须将碳排放强度的下降率大于GDP增长率作为重要基准.