Tibetan plateau aridification linked to global cooling at the Eocene-Oligocene transition

Continental aridification and the intensification of the monsoons in Asia are generally attributed to uplift of the Tibetan plateau and to the land-sea redistributions associated with the continental collision of India and Asia, whereas some studies suggest that past changes in Asian environments are mainly governed by global climate. The most dramatic climate event since the onset of the collision of India and Asia is the Eocene-Oligocene transition, an abrupt cooling step associated with the onset of glaciation in Antarctica 34 million years ago. However, the influence of this global event on Asian environments is poorly understood. Here we use magnetostratigraphy and cyclostratigraphy to show that aridification, which is indicated by the disappearance of playa lake deposits in the northeastern Tibetan plateau, occurred precisely at the time of the Eocene-Oligocene transition. Our findings suggest that this global transition is linked to significant aridification and cooling in continental Asia recorded by palaeontological and palaeoenvironmental changes, and thus support the idea that global cooling is associated with the Eocene-Oligocene transition. We show that, with sufficient age control on the sedimentary records, global climate can be distinguished from tectonism and recognized as a major contributor to continental Asian environments.     

Stimulated influences of Lake Agassiz on the climate of central North America 11,000 years ago

Eleven thousand years ago, large lakes existed in central and eastern North America along the margin of the Laurentide Ice Sheet. The large-scale North American climate at this time has been simulated with atmospheric general circulation models, but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere, ice sheet, and proglacial lakes. Here we present simulations of the climate of central and eastern North America 11,000 years ago with a high-resolution, regional climate model nested within a general circulation model. The simulated climate is in general agreement with that inferred from palaeoecological evidence. Our experiments indicate that through mesoscale atmospheric feedbacks, the annual delivery of moisture to the Laurentide Ice Sheet was diminished at times of a large, cold Lake Agassiz relative to periods of lower lake stands. The resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin, thus affecting the routing of fresh water to the North Atlantic Ocean. A retreating ice margin during periods of high lake level may have opened an outlet for discharge of Lake Agassiz into the North Atlantic. A subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet, thereby reducing discharge to the North Atlantic. These variations may have been decisive in causing the Younger Dryas cold event.     

美国西部开发中的城市化

美国西部开发中的城市化，与十叶当时的区域关系、采矿业、横贯大陆铁路铺设联系紧密。这种城市的崛起，推动了西部经济体系的形成和发展。     

埋地热油管道停输温降的CFD模拟

针对埋地热油管道的停输温降过程,分别建立了埋地热油管道的物理模型和数学模型,并应用FLUENT软件模拟了不同土壤导热系数、不同大气温度下的温度场分布。同时在稳态的基础上模拟非稳态,得出停输后温度场、速度场的分布。并对不同油温下的温度分布进行模拟,得出了温度场在不同条件影响下的分布规律。对于优化管道建设和制定科学合理的热油输送工艺具有重要的作用。     

大气温度年周期性变化对集油管道温降的影响研究

油田集油管道的温降计算是否准确直接影响到油田能耗的高低及油田集输管道的安全性。建立了土壤自然温度场模型,并与实测数据进行了比较,结果表明,按大气温度年周期性变化计算土壤温度场方法是可行的,误差在工程允许范围内。同时,分析了油田集输管道温降的影响因素,得出了大气温度年周期性变化对集油管道温降的影响,结果表明:同一埋深管道的温降随大气温度年周期性变化而变化,埋深变化时,集油管道的温降随大气温度年周期性变化时延迟时间不同。     

North Pacific seasonality and the glaciation of North America 2.7 million years ago

In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.     

对北美文化多样性与教育的反思

通过对一群亚裔加拿大社会服务从业者与来自其同一族裔社区的妇女工作的经验的描述 ,就文化适切实践模式对文化的假设提出质疑 ,并论述了文化的复杂性和多变性 ,阐述了文化适切实践的话语如何把殖民和种族权力的关系简约为文化问题。     

Origin of extant domesticated sunflowers in eastern North America

Eastern North America is one of at least six regions of the world where agriculture is thought to have arisen wholly independently. The primary evidence for this hypothesis derives from morphological changes in the archaeobotanical record of three important crops--squash, goosefoot and sunflower--as well as an extinct minor cultigen, sumpweed. However, the geographical origins of two of the three primary domesticates--squash and goosefoot--are now debated, and until recently sunflower (Helianthus annuus L.) has been considered the only undisputed eastern North American domesticate. The discovery of 4,000-year-old domesticated sunflower remains from San Andrés, Tabasco, implies an earlier and possibly independent origin of domestication in Mexico and has stimulated a re-examination of the geographical origin of domesticated sunflower. Here we describe the genetic relationships and pattern of genetic drift between extant domesticated strains and wild populations collected from throughout the USA and Mexico. We show that extant domesticates arose in eastern North America, with a substantial genetic bottleneck occurring during domestication.     

Investigation of the thermal conductivities across metal-insulator transition in polycrystalline VO2

Previous reports about the thermal conductivities of VO2 showed various temperature dependences across metal-insulator transition (MIT) temperature. In this work, polycrystalline VO2 samples were fabricated by spark plasma sintering of VO2 powder. Temperature dependences of their thermal conductivities were investigated using laser flash technique, and the thermal conductivity showed a significant decrease trend from metal-phase to insulator phase. Electrical transport properties were investigated to confirm both carrier and lattice contribution to the thermal conductivity. It is found that the lattice thermal conductivity decreased significantly across MIT point, which may be caused by soft phonon mode in metal phase of VO2 .     

An Arctic mammal fauna from the Early Pliocene of North America

A peat deposit on Ellesmere Island, Nunavut, Canada, allows a unique glimpse of the Early Pliocene terrestrial biota north of the Arctic Circle. The peat accumulated in a beaver pond surrounded by boreal larch forest near regional tree line in coastal hills close to the Arctic Ocean. The ecological affinities of the plant and beetle remains contained in the peat indicate that winter temperatures on Ellesmere Island were nearly 15 degrees C higher and summer temperatures 10 degrees C higher than they are today. Here we show that the mammalian remains buried in the peat represent mainly taxa of Eurasiatic zoogeographic and phyletic affinities, including the first North American occurrence of a meline badger (Arctomeles). This deposit contains direct evidence of the composition of an Early Pliocene (4-5 million years ago) arctic mammalian fauna during an active period of interchange between Asia and North America.     

A transitional snake from the Late Cretaceous period of North America

Snakes are the most diverse group of lizards, but their origins and early evolution remain poorly understood owing to a lack of transitional forms. Several major issues remain outstanding, such as whether snakes originated in a marine or terrestrial environment and how their unique feeding mechanism evolved. The Cretaceous Coniophis precedens was among the first Mesozoic snakes discovered, but until now only an isolated vertebra has been described and it has therefore been overlooked in discussions of snake evolution. Here we report on previously undescribed material from this ancient snake, including the maxilla, dentary and additional vertebrae. Coniophis is not an anilioid as previously thought a revised phylogenetic analysis of Ophidia shows that it instead represents the most primitive known snake. Accordingly, its morphology and ecology are critical to understanding snake evolution. Coniophis occurs in a continental floodplain environment, consistent with a terrestrial rather than a marine origin; furthermore, its small size and reduced neural spines indicate fossorial habits, suggesting that snakes evolved from burrowing lizards. The skull is intermediate between that of lizards and snakes. Hooked teeth and an intramandibular joint indicate that Coniophis fed on relatively large, soft-bodied prey. However, the maxilla is firmly united with the skull, indicating an akinetic rostrum. Coniophis therefore represents a transitional snake, combining a snake-like body and a lizard-like head. Subsequent to the evolution of a serpentine body and carnivory, snakes evolved a highly specialized, kinetic skull, which was followed by a major adaptive radiation in the Early Cretaceous period. This pattern suggests that the kinetic skull was a key innovation that permitted the diversification of snakes.     

北美超低渗致密油藏提高采收率技术现状

在过去的十年中,北美致密油气的开发技术日渐成熟,其中,最具代表性的技术是水力压裂和水平钻井技术的结合。然而,现有依靠天然能量的衰竭式开发只能采出超低渗储层中的少部分原油（采出程度低于10%）,导致致密储层中仍存在大量剩余油。因此,非常规超低渗油藏提高采收率技术的研究日趋重要。目前,全世界90%以上的致密油产量来自美国,其开采技术在非常规致密油的开发领域具有明显优势。并且,在过去的十年间,北美的石油公司已经对针对致密低渗油藏的提高采收率（EOR）技术进行了许多现场测试。鉴于美国在非常规致密油的勘探开发中具有领先地位,重点对北美致密油资源开发中提高采收率措施的现场经验进行了总结和评价,并指出了其目前面临的主要困难和挑战。此项研究对于中国未来超低渗致密油藏提高采收率技术的发展具有指导和借鉴意义。     

Neodymium isotopes distribution and transport in the central North Pacific deep water

Radiogenic Neodymium (Nd) isotopes in the central North Pacific deep water have been generally interpreted as reflecting Pacific arcs input according to previous studies, while little is known about the specific path and mode of radiogenic Nd from these arcs to deep water. In this study, Nd isotopic data from surface scrapings of 17 Fe-Mn crusts from the central North Pacific deep water (around 20°N) have been reported. Based on these data together with recently published data on dissolved Nd isotopes in seawater for this region, we propose that radiogenic Nd isotopes in North Pacific Intermediate Water (NPIW 300–800 m) from the western Pacific margin is an important source for the central North Pacific deep water, while the surface water of this area has little influence on dominating deep water Nd isotopes. Such a view emphasizes the role of vertical mixing and advection of the marginal ocean currents in balancing Nd isotopes in central North Pacific deep water, and helps to understand oceanic Nd cycling. Moreover, the values of ε _Nd from surface scrapings of Fe-Mn crusts are relatively homogenous, with an average value of about −3.4, which is higher than that of modern seawater (∼−3.9). This difference over short time scales reflects the quick evolution of Nd isotopes in central North Pacific deep water.     

北美典型气候区建筑围护结构HM模拟及分析

为明确气候参数、材料参数对建筑围护结构模拟结果的影响,以及热湿耦合传递模型(HM)和被普遍采用的Glaser模型之间的差异,在热湿过程模拟软件WUFI Plus中选择北美典型气候区的20个代表城市,设置15组外墙构件,进行空间单元HVAC需求、室内热湿环境和外墙热湿性能的全年模拟.模拟结果与室外气候参数进行相关性分析,表明室外气温、太阳辐射、相对湿度和风驱雨不同程度地影响相关结果.通过材料参数控制所得2组HM和3组Glaser模型的对比,表明液态水相关参数、含湿量引起的材料参数的变物性取值对模拟结果有显著影响.北美典型气候区HM模拟对我国建筑围护结构热湿过程相关的气候参数、材料参数和评估方法的研究具有借鉴意义.     

基于Fluent的海底输油管道停输温降数值模拟

随着海上油田的大量开发,对海底输油管道停输过程传热问题的研究迫在眉睫。加热输送的原油管道在运行过程中,不可避免地会遭遇油田停电和管线维修等意外,造成停输。这时油管内原油的黏度随油温下降而升高。当油温降到一定值后,会给管道的再启动带来极大的困难,甚至造成凝管事故。为避免凝管事故发生,需要准确预测海底管道管内原油的温降情况及安全停输时间,分析影响停输时间的因素。利用Fluent软件对海底输油管道停输温降进行数值模拟。计算结果表明,保温层厚度和海水温度对停输时间影响非常明显。模拟结果可指导生产实践。     

油田环状集输流程埋地管道温降计算方法研究

以工程热力学、传热学、油气集输、多相流等学科知识为依据,根据能量守恒定律建立油田环状集输流程埋地管道的温降计算模型,找出油田环状集输流程埋地管道的温降计算方法.同时,对油田生产现场的温降进行测试,通过试验数据验证建立的温降计算方法满足工程应用.     

升降温条件对约束钢梁抗火性能的影响

采用有限元方法对约束钢梁的火灾性能进行模拟,并与试验结果进行比较,在验证仿真模型正确的基础上,研究不同升降温条件下钢梁的火灾响应,分析各参数对钢梁抗火性能的影响。结果表明:升温最高温度Tmax和形状系数Sc越大,升温速率越大,梁的耐火时间越短,变形越大;到达最高温度所用时间Tmax越大,升温越慢,且受火时间越长,变形越大,但相应的耐火时间也增长。短热模型较长冷模型耐火时间长,变形小,对抗火有利。降温段约束梁的挠度均有恢复,但升温时变形越大,降温后的残余变形也越大.     

影响蔗糖溶液玻璃化转变温度的几个因素

以蔗糖溶液为样品，试验研究了退火处理、升温速率、溶液浓度等因素对最大冻结浓缩溶液的玻璃化转变温度Ｔｇ′的影响。结果表明，退火处理对Ｔｇ′值影响较大，而另外两种因素对Ｔｇ′无影响。     

Reconciling the temperature dependence of respiration across timescales and ecosystem types

Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem, including both consumers and primary producers. Respiration exhibits an exponential temperature dependence at the subcellular and individual levels, but at the ecosystem level respiration can be modified by many variables including community abundance and biomass, which vary substantially among ecosystems. Despite its importance for predicting the responses of the biosphere to climate change, it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments. Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes, rivers, estuaries, the open ocean and forested and non-forested terrestrial ecosystems, with an average activation energy similar to that of the respiratory complex (approximately 0.65?electronvolts (eV)). By contrast, annual ecosystem respiration shows a substantially greater temperature dependence across aquatic (approximately 0.65?eV) versus terrestrial ecosystems (approximately 0.32?eV) that span broad geographic gradients in temperature. Using a model derived from metabolic theory, these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level, and fundamental differences in the importance of other variables besides temperature—such as primary productivity and allochthonous carbon inputs—on the structure of aquatic and terrestrial biota at the community level.