Tackling heart failure in the twenty-first century

Heart failure, or congestive heart failure, is a condition in which the heart cannot supply the body's tissues with enough blood. The result is a cascade of changes that lead to severe fatigue, breathlessness and, ultimately, death. In the past quarter century, much progress has been made in understanding the molecular and cellular processes that contribute to heart failure, leading to the development of effective therapies. Despite this, chronic heart failure remains a major cause of illness and death. And because the condition becomes more common with increasing age, the number of affected individuals is rising with the rapidly ageing global population. New treatments that target disease mechanisms at the cellular and whole-organ level are needed to halt and reverse the devastating consequences of this disease.     

Biodiversity conservation: uncertainty in predictions of extinction risk

Thomas et al. model species-distribution responses to a range of climate-warming scenarios and use a novel application of the species-area relationship to estimate that 15-37% of modelled species in various regions of the world will be committed to extinction by 2050. Although we acknowledge the efforts that they make to measure the uncertainties associated with different climate scenarios, species' dispersal abilities and z values (predictions ranged from 5.6% to 78.6% extinctions), we find that two additional sources of uncertainty may substantially increase the variability in predictions.     

Improved estimates of upper-ocean warming and multi-decadal sea-level rise

Changes in the climate system's energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database, even when volcanic and other variable climate forcings are included. The sum of the observed contributions has also not adequately explained the overall multi-decadal rise. Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950-2003, using statistical techniques that allow for sparse data coverage and applying recent corrections to reduce systematic biases in the most common ocean temperature observations. Our ocean warming and thermal expansion trends for 1961-2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993-2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors. On average, the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations, but the modelled multi-decadal trends are smaller than observed. We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 +/- 0.4 mm yr(-1), in good agreement with our updated estimate of near-global mean sea-level rise (using techniques established in earlier studies) of 1.6 +/- 0.2 mm yr(-1).     

Multimodel projections and uncertainties of net ecosystem production in China over the twenty-first century

Ecosystems in China have been absorbing anthropogenic CO2 over the last three decades. Here, we assess future carbon uptake in China using models from phase 5 of Coupled Model Intercomparison Project under four socio-economic scenarios. The average of China＇s carbon sink from 2006 to 2100 represented by multimodel mean net ecosystem production （NEP） is projected to increase （relative to averaged NEP from 1976 to 2005） in the range of 0.137 and 0.891 PgC a^-1 across different scenarios. Increases in NEP are driven by increases in net primary production exceeding increases in heterotrophic respiration, and future carbon sink is mainly attributed to areas located in eastern China. However, there exists a considerable model spread in the magnitude of carbon sink and model spread tends to be larger when future climate change becomes more intense. The model spread may result from intermodel discrepancy in the magnitude of CO2 fertilization effect on photosynthesis, soil carbon turnover time, presence of carbon-nitrogen cycle and interpretation of land-use changes. For better quantifying future carbon cycle, a research priority toward improving model representation of these processes is recommended.     

Remobilization of southern African desert dune systems by twenty-first century global warming

Although desert dunes cover 5 per cent of the global land surface and 30 per cent of Africa, the potential impacts of twenty-first century global warming on desert dune systems are not well understood. The inactive Sahel and southern African dune systems, which developed in multiple arid phases since the last interglacial period, are used today by pastoral and agricultural systems that could be disrupted if climate change alters twenty-first century dune dynamics. Empirical data and model simulations have established that the interplay between dune surface erodibility (determined by vegetation cover and moisture availability) and atmospheric erosivity (determined by wind energy) is critical for dunefield dynamics. This relationship between erodibility and erosivity is susceptible to climate-change impacts. Here we use simulations with three global climate models and a range of emission scenarios to assess the potential future activity of three Kalahari dunefields. We determine monthly values of dune activity by modifying and improving an established dune mobility index so that it can account for global climate model data outputs. We find that, regardless of the emission scenario used, significantly enhanced dune activity is simulated in the southern dunefield by 2039, and in the eastern and northern dunefields by 2069. By 2099 all dunefields are highly dynamic, from northern South Africa to Angola and Zambia. Our results suggest that dunefields are likely to be reactivated (the sand will become significantly exposed and move) as a consequence of twenty-first century climate warming.     

Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms

Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms--such as corals and some plankton--will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean-carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.     

智能机器人:21世纪科技皇冠上的璀璨明珠

 在回顾智能机器人发展历程的基础上,阐述了机器人的过去:人类的幻想,机器人的现在:从幻想走向现实,机器人的未来:智能机器人。介绍了工业机器人、军用机器人、仿生机器人、服务机器人、多指灵巧手和类人机器人的主要功能、研究现状和应用背景。展望了智能机器人的发展前景。     

非全周开口滑阀的节流温升与形变

联合采用FLUENT和ANSYS分析软件对具有典型节流槽的非全周开口滑阀的三维流场、液-固温度场和固体热变形进行数值计算.结果表明:非全周开口滑阀内部流体和固体内的温度分布不均匀,阀口流束在接近固体壁面的区域温度较高,流束中心部位温度较低,阀体和阀芯在阀口附近及流束冲击壁面有局部高温,由此导致的阀芯和阀体不均匀变形量可...     

开关柜母排多点面阵测温与温升异常辨识方法

针对单点传感测温难以全面准确识别高压开关柜过热故障的问题,提出一种以低分辨率多点面阵测温取代传统点测温的新方法及其技术实现.首先,提出低分辨率红外阵列传感器的开关柜温度状态多点传感检测技术,获取开关柜电缆室母排与电缆连接处的多视场温度分布数据.其次,在实现过热区域定位的基础上,建立k最近邻(KNN)算法温度故障辨识模型,识别开关柜母排故障状态.最后,搭建开关柜温度状态监测平台,采集数据并分析.实验结果表明,多点面阵测温不仅适用于开关柜状态监测要求,且其温升异常检测方法可有效实现过热故障的区域定位与识别分类.     

环境负温与升温温差作用下冻土强度特性试验研究

随着西部经济快速发展,冻土区工程日趋活跃,冻土灾害问题愈显突出。为了减少灾害,提高工程耐久性,必须进行冻土区地基承载力的力学特性与温度变化的关系研究。采用青海省果洛州海拔4 200 m处冻土,在室内模拟不同环境负温与升温温差的冻土常规三轴压缩试验,得到冻土在不同环境负温、不同升温温差下的应力-应变曲线以及强度-温度关系曲线。试验结果表明,低温冻土到高温冻土的破坏特征是由脆性破坏过渡到塑性破坏,其应力应变关系由广义双曲线模型变为邓肯-张模型;环境负温与升温温差的不同,使得冻土强度折减不同;设计冻土区地基承载力时,需根据当地温度和升温温差等变化特点修正冻土区地基承载力特征值。     

基于等效时间的混凝土绝热温升

对不同养护温度下的混凝土绝热温升进行了研究,采用化学反应速率描述环境温度对混凝土绝热温升的影响,探讨了化学反应速率与养护温度之间的关系．引入等效时间的概念,根据Arrhenius函数和指数函数研究水化热化学反应速率随温度的变化,最后采用反演分析方法中的最小二乘法回归分析试验数据,确定绝热温升和等效时间的关系式．结果表明,温度对混凝土水化热最高绝热温升影响不大,对于某种混凝土存在唯一的绝热温升与等效时间关系曲线,可以用等效时间描述温度对混凝土绝热温升的影响．     

湿式多盘制动器的温升特性分析

为了全面揭示湿式制动器在持续工况下的温升变化情况,本文以用于矿山机械的湿式多盘制动器作为研究对象,通过仿真分析和台架实验分析持续工况下的摩擦盘的温度变化。并利用正交试验设计和交互作用分析确定影响摩擦盘温升的最显著因素以及各因素之间的交互作用对温升的影响。结果表明：（1）摩擦盘在径向上的温度变化大于在周向上的温度变化。（2）对于无轨胶轮车来说,应避免速度在40km/h附近制动。（3）影响摩擦盘温升的最显著因素为制动速度,其次是制动时间,最小的为制动力。（4）在多因素交互分析中,制动力与制动时间的交互作用最明显,这两个因素的联合作用对摩擦盘温升影响较大。该研究可为湿式制动器的设计、优化提供理论基础,并为如何避免热变形和热失效提供思考角度。     

水化热引起的大体积混凝土墙温度分析

根据已提出的考虑混凝土化学反应速度的热传导方程新理论，分析了水化热引起的大体积混凝土墙的温度场，给出了该问题非线性热传导方程的解析迭代公式，研究中，绝热温升采用了基于Arrhenius理论的有效时间的函数，从而导致求解非线性热传导方程，从计算结果得出如下结论：（a)浇筑温度对大体积混凝土墙的最高温升有显著影响，浇筑温度越高，混凝土墙的内外最大温差越大；（b)由于混凝土的导热系数低，墙中心的温度高于其表面温度，这将导致混凝土墙横断面上不同位置在不同时刻具有不同的水化热化学反应速率；（c）水化热化学反应速率随温度升高而加快，从而使混凝土硬化速度加快，初凝和最终凝固时间缩短，因此，在炎热气候条件下宜采用低热水泥。     

铁道牵引变压器动态温升的仿真计算

针对铁道牵引变压器在各种负荷条件下的温升情况,进行了深入的仿真计算研究,揭示了影响牵引变压器温升的因素,并对如何充分利用牵引变压器容量提出了建议．     

低温升抗裂高性能混凝土的研究与应用

近年来,送变电基础工程发展迅速,大体积砼使用量也日益增加.为解决大体积砼易开裂的问题,本研究依托送电变基础工程,以密实骨架堆积法为基础设计了基准配合比,并进一步对胶凝材料体系及减水剂做出优化.试验表明,在综合考虑砼的强度及较低水化温升情况下,胶凝材料体系中水泥、粉煤灰、矿粉的掺量分别宜为320 kg/m³、39.5 kg/m³、35.6 kg/m³.选择TJE-200减水剂,掺量在2%时最佳.制备出的产品在送变电工程中取得了明显的经济效益.     

全流量自冷却柱塞泵的泵内温升特性分析

为研究新型全流量自冷却柱塞泵的自冷却特点并分析其自冷却性能,基于双端面配流原理提出了全流量自冷却柱塞泵,简述其结构及工作原理,对全流量自冷却柱塞泵和传统CY泵的温升特点进行对比分析,从宏观角度分析温升原因和能量转换关系,得到两种泵在相同工况下的温升差距,利用AMESim软件搭建柱塞泵的热学模型,仿真得到两种泵的温升曲线...     

基于细观尺度的混凝土绝热温升预测

从混凝土的热学性能和细观组成出发,建立混凝土绝热温升和水泥水化程度的关系,将绝热温升表示为水泥水化程度的函数;假定混凝土为随机骨料和水泥净浆组成的二相复合材料,取单元尺寸为100 mm×100 mm的混凝土试件,并将试件剖分为1 mm×1 mm的有限元网格,考虑单个骨料和多个随机骨料2种投放方式,从细观尺度数值模拟混凝土的绝热温升过程,研究混凝土细观结构的温度分布.结果表明,文中给出的模型可较准确地预测混凝土绝热温升;在绝热条件下,由于混凝土细观结构中骨料和砂浆的热学和力学性质差异,试件内部仍会产生温度梯度和温度应力.     

采煤机运动参数对工作面温升的影响

采煤工作面的温度关系到工人的健康、设备的使用性能和煤炭生产的安全。为了研究采煤机运动参数对工作面温升的影响,建立了采煤机设计参数与工作面温升关系的数学模型,分析了采煤机的牵引速度、滚筒转速与工作面温升之间的关系及其影响。模拟结果表明,采煤机的运动参数对工作面的温升有直接的影响,工作面的温度随采煤机牵引速度的提高迅速增加,滚筒转速对工作面的温升影响较大;适当降低采煤机的牵引速度和滚筒转速能降低采煤工作面的温升。该结果为正确选择采煤机的运动参数、减少采煤机工作发热、降低采煤工作面温升、进一步改善采煤工作面的环境提供了依据。     

电阻温度系数实验的不确定度分析

通过对电阻温度系数实验直线拟合结果的不确定度估算,得出增大测量区间和增加测量数据的数量是提高直线拟合质量的关键。