高温气体动力学及其前景

高温气体动力学是近代力学中最具活力的新兴分支学科之一。近年来,鉴于航空航天工业飞速发展以及高温化工、无污染燃烧、新材料加工、微机械制造等应用需求,人们必须突破经典气体动力学框架,将研究对象从常温下的完全气体拓展到高温下的真实气体。对高速、高焓等极端条件下高温气体非平衡流动中出现的复杂现象及相应机理的研究,导致了物理、化学与流体力学的相互交缘。这一跨学科领域蕴孕着重大突破的可能。本文简要地介绍了这一分支学科的背景、特点、国内外研究工作现况及其应用前景。

直接散斑法测量各种材料试件的变形

本文给出一种试件表面处理方法,它可以解决对于各种材料试件(例如有色金属、黑色金属、玻璃钢、碳纤维复合材料、陶瓷、岩石、混凝土制品等)使用直接散斑法进行变形测量的问题。文中阐述了基本原理和操作方法,给出了在铝合金材料、碳纤维复合材料、玻璃钢复合材料试件上进行断裂力学实验的结果。

含环向裂纹厚壁圆筒电磁止裂的应力场分析

以具有轴对称性质、端部带有半埋藏环形裂纹的厚壁圆筒为研究对象，通过对长厚壁圆筒内外环面均匀通入超强脉冲电流进行电磁热止裂。采用复变函数方法求解了脉冲放电瞬间裂纹尖端的温度场和热应力场。在一定的超强脉冲电流作用下，由于环形裂纹尖端的电流绕流热集中效应，裂尖温升超过了金属熔点，使裂尖处金属熔化在内部形成堆焊，钝化了裂尖，并且在裂纹前缘形成了热压应力，阻止了裂纹的扩展。在此基础上还讨论了在电载荷和机械载荷共同作用下裂纹前缘的应力场。

A Delphi Process to Optimize Quality and Performance of Drug Evaluation in Neonates

Background: Neonatal trials remain difficult to conduct for several reasons: in particular the need for study sites to have an existing infrastructure in place, with trained investigators and validated quality procedures to ensure good clinical, laboratory practices and a respect for high ethical standards. The objective of this work was to identify the major criteria considered necessary for selecting neonatal intensive care units that are able to perform drug evaluations competently. Methodology and Main Findings: This Delphi process was conducted with an international multidisciplinary panel of 25 experts from 13 countries, selected to be part of two committees (a scientific committee and an expert committee), in order to validate criteria required to perform drug evaluation in neonates. Eighty six items were initially selected and classified under 7 headings: "NICUs description - Level of care'' (21), "Ability to perform drug trials: NICU organization and processes (15), "Research Experience'' (12), "Scientific competencies and area of expertise'' (8), "Quality Management'' (16), "Training and educational capacity'' (8) and "Public involvement'' (6). Sixty-one items were retained and headings were rearranged after the first round, 34 were selected after the second round. A third round was required to validate 13 additional items. The final set includes 47 items divided under 5 headings. Conclusion: A set of 47 relevant criteria will help to NICUs that want to implement, conduct or participate in drug trials within a neonatal network identify important issues to be aware of. Summary Points: 1) Neonatal trials remain difficult to conduct for several reasons: in particular the need for study sites to have an existing infrastructure in place, with trained investigators and validated quality procedures to ensure good clinical, laboratory practices and a respect for high ethical standards. 2) The present Delphi study was conducted with an international multidisciplinary panel of 25 experts from 13 countries and aims to identify the major criteria considered necessary for selecting neonatal intensive care units (NICUs) that are able to perform drug evaluations competently. 3) Of the 86 items initially selected and classified under 7 headings - "NICUs description - Level of care'' (21), "Ability to perform drug trials: NICU organization and processes (15), "Research Experience'' (12), "Scientific competencies and area of expertise'' (8), "Quality Management'' (16), "Training and educational capacity'' (8) and "Public involvement'' (6) - 47 items were selected following a three rounds Delphi process. 4) The present consensus will help NICUs to implement, conduct or participate in drug trials within a neonatal network.

A preliminary assessment of water quality in fish cages on Lake Kariba, Zimbabwe

The water quality in fish cages on Lake Kariba was studied. The Kruskal-Wallis test was used to determine whether the water quality parameters differed significantly among the cage-types (cage-type effect). Secchi disc readings ranged from 2 to 4 metres, while temperature ranged from 23 degree C to 29.5 degree C. The observed conductivity was between 98.7 mu S/cm and 102.3 mu S/cm. The pH was between 6.31 and 7.82. Concentrations of dissolved oxygen varied from 1.55 to 6.47 mg/l, while dissolved oxygen saturation ranged from 22.3% to 83.1%. Within the same month, temperature did not differ significantly among cages. Conductivity, pH, dissolved oxygen concentration and dissolved oxygen saturation differed significantly among the 3 cage-types. Temperature and pH levels in the cages were close to the optimum levels for the culture of cichlids. Sub-optimal levels of dissolved oxygen occurred occasionally in the octagonal cages.

松嫩平原农牧交错区优化生态-生产范式——以长岭县为例

松嫩平原农牧交错区位于松嫩平原的西部，中国北方农牧交错带的最东端;具有独特的地质环境特点，环境问题突出，是我国生态脆弱地区之一，及世界三大苏打盐碱土集中分布区之一。近年来，由于人为的不合理利用和开垦、以及粗放的生产模式，使该地区生态系统严重受损，土地沙漠化、水土流失、盐碱化、土地生产力下降等生态环境问题日益突出。因此，建立一个适合该地区生态环境条件、社会经济发展状况的优化生态-生产范式是必要而紧迫的。 本论文以松嫩平原农牧交错区为研究对象，以其典型地段为切入点，通过大量数据的收集、文献资料的查阅、野外考察与测定、室内分析处理等，得出了以下主要结论： 一、生态-地理环境背景分析 松嫩平原农牧交错区是多种生态-地理环境危害并存的区域，其中包括盐碱化、沙漠化、气候灾害、水资源短缺等等。当前，沙化土地和盐碱化土地的面积已占该地区土地总面积的34.27 %，并且呈逐年递增的趋势。松嫩平原农牧交错区气候灾害频发，主要是旱灾、水灾、风灾。此外，水资源短缺以及水质问题，同样影响着农业生产及社会经济发展。造成松嫩平原农牧交错区多种生态-地质环境危害并存的主要影响机制是：该地区自身的地质-地理环境特点、气候因素和人类活动的综合效应，并且人类活动日益成为主要驱动因子。 二、实例研究 松嫩平原农牧交错区优化生态-生产范式研究是以长岭县为例，通过对长岭县景观格局变化分析、土壤格局分布、农牧业生产特点、以及农业可持续性评价等，得出以下结论： 1、对研究区内土地利用格局分析表明：1980 ~ 2000年，在土地利用类型没有发生变化的基础上，表现为各土地利用类型面积上的增减;草地、林地大面积地向农田转移，农田面积明显增加;大规模地开垦农田，已经导致了景观的优势度增加，破碎度增加，多样性下降，这最终将使整个景观趋于更加不稳定。 2、长岭县土壤总体水平较差，障碍性土壤占长岭县总土地面积的55.38 %。从土地利用变化对不同地势条件下土壤理化性状影响分析，结果表明：（1）地势相对高的平台地，土壤肥力较高，且开垦对土壤理化性质的影响相对较小，更适合农业开发;（2）低地原生植被为草甸草原，其养分状况也比较好，但其地势较低，易发生水渍和盐碱化;（3）坡地是当地土壤养分最为贫瘠地区，也是风沙土较集中分布的区域，对其开垦会增大土壤的风蚀和水蚀，使土壤养分状况严重下降。 3、对研究区牧草资源分布格局、牧草资源承载力和利用现状等进行分析，结果表明：放牧系统提供的牧草资源已不能满足当地畜牧业对牧草资源的需求。草地提供的牧草资源仅能满足总牧草需求的16.6 %，放牧系统提供的牧草仅占总牧草需求的47.3 %;玉米秸秆转化为牧草资源的潜力巨大，经估算，占总牧草资源的78.3 %，其承载力为总牧草需求的2.4倍。当前，农牧交错区牧草资源的粗蛋白含量普遍偏低，不能完全满足动物生产的需要，制约了当地畜牧业发展。根据当地畜牧业现状、牧草资源潜力，我们提出：应在合理利用当地牧草资源的基础上，有计划地建立高产优质、富含粗蛋白的人工牧草基地，实现畜牧业可持续发展与生态保护的协调统一。 4、长岭县是以第一产业为主，即农业生产为主要经济来源。对农业生产结构的分析表明：农牧业生产占总农业产值的90 %以上，并以种植业为主，种植业一直占总农业产值60 %以上。受当地气候条件、土壤格局分布的限制，单一粮食生产、粗放的生产模式以及对天然草地资源的过分依赖，最终导致该地区农牧业发展缓慢，经济条件落后。 5、在上述分析的基础上，作者提出了长岭县优化生态-生产范式，即以高效农业生产、生活圈，水土保持和自然生态保育圈、牧草生产基地及生态功能保护圈的三圈等级系统。以此为依据，对土地利用格局进行调整，通过粮、草、经多元农业结构的建设，在合理利用与保护草地的基础上，使长岭县畜牧业走向产业化的发展模式。

黄绵土不同形态有机氮径流流失规律

利用不同坡度径流小区 ,在自然降水条件下 ,研究侵蚀泥沙不同形态有机氮的流失规律 ,结果表明 :在 4次产流泥沙中 ,除氨基糖氮含量减少外 ,其它有机形态氮均存在增加趋势 ,以氨态氮含量增加最为显著。随坡度的下降 ,水解全氮、氨态氮和氨基酸氮含量呈增加趋势 ;泥沙中水解全氮、氨基酸氮、氨态氮、非酸水解氮均存在不同程度的富集 ,其富集率随坡度的下降而增大 ,以氨基酸氮富集程度高 ,泥沙中氨基糖态氮反而无富集现象存在 ;当坡度分别为 2 5°、2 0°、15°、10°和 5°时 ,水解全氮流失量分别为 1135 .0、76 3.7、485 .5、313.0和 15 4.4kg/ km2 ,而氨基酸氮流失量则为 2 34.8、182 .7、12 1.1、76 .8和 33.9kg/ km2 ,占水解全氮的 2 0 .6 %～ 2 4.9%。氨态氮流失量为 742 .5、5 0 3.3、32 2 .2、2 0 8.9、97.4kg/ km2 ,占水解全氮的 6 3.1%～ 6 6 .7%。氨基糖氮占酸水解氮 1.1%～ 2 .9%。非鉴别氮占水解全氮的 5 .8%～ 12 .6 %。而酸水解氮与非酸水解氮之比分别为 ...

HDPE／Surlyn共混体系的热学行为及相转变研究

利用示差扫描热量仪（ＤＳＣ）、热机械分析装置（ＴＭＡ）、电子拉力机和扫描电镜等方法对ＨＤＰＥ／Ｓｕｒｌｙｎ共混体系的热学行为和相态结构进行了研究，证实该共混体系属部分相容的非均相体系，当Ｓｕｒｌｙｎ含量在３０％到５０％时，该共混物发生了明显的相转变。

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the diurnal course of CO2 flux were -9.38 and 5.02 μmol•m-2•s-1, respectively. The largest daily CO2 uptake was 1.7 g C•m-2•d-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.

贵州省遵义市大气降水中有机和无机地球化学特征研究

正确认识降水中的化学组分是评价酸雨和大气环境质量的重要途径，降水中低分子有机酸的研究是认识C、H、O等元素生物地球化学循环和酸雨成因的重要内容。贵州省遵义市作为我国酸雨高发地区，是降水化学组成尤其是低分子有机酸地球化学循环研究的典型区域。我们在遵义市进行了为期一年(2006年5月~2007年4月)的降水采集(共76个样品)，对pH值、电导率和主要的阴离子(包括有机和无机)、阳离子进行了测定，并进行了分析和讨论。 (1) pH和电导率的雨量加权平均值分别为4.11(范围：2.30~ 6.04)和62.10 μs•cm-1 (范围：6.60 ~ 1630.00 μs•cm-1)，酸雨频率高达93.2%，pH存在着显著的季节变化，其中冬季pH值最低，表明遵义市酸雨污染较为严重，冬季为最。 (2) 遵义市监测期间离子浓度的大小顺序为SO42-> Ca2+> H+> NH4+> NO3-> Cl-> F->HCOO-> Mg2+> K+> CH3COO-> Na+> (COO)22-> PO43-> NO2-，其中SO42-、Ca2+、H+、NH4+、NO3-是最主要离子，浓度分别为148.15 μmol•L-1、81.89 μmol•L-1、77.74 μmol•L-1、43.80 μmol•L-1和31.50μmol•L-1，它们分别占离子总量的31.97%、17.67%、16.78%、9.45%和6.54%；遵义市大气降水中主要的致酸物质是SO42-和NO3-，主要的缓冲物质是Ca2+和NH4+，大气污染类型属硫酸钙型。相对酸度和中和因子结果表明降水中仅有77%的降水酸度被碱性物质(以Ca2+和NH4+为主)中和；因子分析中H+、NO3-、nss-SO42-(非海源性硫酸根)、NH4+归为一组，再次表明SO42-和NO3-对降水酸度的重要贡献。富集系数和源的贡献分析表明，SO42-和NO3-主要来自人为活动的贡献，SO42-来源主要包括工业、民用的燃煤燃烧释放的SO2，NO3-主要是遵义市电厂和其它工厂向大气中排放的NOx的化学转化而成。Ca2+主要来自于遵义市的土壤及水泥厂等的排放；Mg2+主要来自陆源输入，部分来自海水的贡献。氮肥生产、大面积农田化肥的使用以及生物排放源很可能是该地区降水中NH4+的主要污染源。值得注意的是，作为海盐性离子的Cl-，在遵义市降水中重要的部分还是人为活动，主要是遵义工厂(如碱厂和钛厂)向大气中排放的HCl和Cl2转化而成。无机离子浓度的季节变化表明，对于遵义市，需要逐步改变能源结构尤其是冬季工业、居民燃煤的使用，才能有效地改善遵义市当前的环境污染。 (3) 遵义市降水中含量较高的常见有机酸是[HCOO-]T、[CH3COO-]T和[(COO)22-]T，它们的雨量加权平均值各为9.29 μmol•L -1、6.47 μmol•L-1和5.06 μmol•L-1；遵义市区降水中有机酸总浓度为22.28 μmol•L-1，占阴离子总量的9.39 %；遵义市降水中四季的有机酸浓度由高到低分别为：春季>冬季>秋季>夏季。以上结果表明，遵义市的有机酸是降水中的重要组成部分，其浓度存在明显的季节性变化。在一次降雨事件中，有机酸的浓度一般随降雨时间的延长而降低，但在降雨中后期有时会出现上升的现象，表明有机酸主要来自云下淋滤作用，少数情况下来自大气远距离的传输。 (4) 相关性分析发现甲酸和乙酸具有强烈的正相关(r= 0.86)，表明甲酸和乙酸具有共同的来源。有机酸与降水中的主要无机离子NO3-、nss-SO42-、K+、Na+、Ca2+等存在着中度相关，表明有机酸的来源与人为活动有着重要的关系。应用气液平衡的原理，提出了降水中甲酸、乙酸比值(F/A)aq的有机酸来源判定方法。发现遵义降水中的有机酸春季和冬季主要来自人类活动的释放，其中春季主要来自遵义市南郊的工业污染，由南方水汽(占春季总量的54%)将其污染物传输至遵义市中心城区，冬季主要是大量燃煤的燃烧释放；夏季和秋季则主要来自植物的释放，其中秋季中的部分有机酸也受到华中和华东地区(其气团占秋季总量的45%)的远距离影响。而遵义市区的山间盆地地形、高湿度、高静风率和低风速、以尘埃为主的大气污染物和有机酸的短生命周期(几小时~几天)为有机酸来源于当地创造了有利条件。 (5) 根据热力学平衡计算新方法，发现遵义市pH≤5的降水中甲酸和乙酸对自由酸度的贡献分别为14.79% (范围：0.42~91.14%)、3.66% (范围：0.02~31.55%)。对比显示，遵义市的有机酸贡献量低于边远地区，主要由于遵义市降水的低pH值和高无机酸度所致。在春、夏、秋、冬季节，降水中的有机酸对自由酸度的平均贡献值分别为31.95%、26.16%、8.02%、11.17%，表明有机酸酸度有着明显的季节性差异，春季有机酸的高贡献量主要受降水中的有机酸高含量、低水温和高pH值的共同作用，夏季受高pH值的影响，而秋季和冬季的低贡献量主要受降水的低pH值所控制。 (6) 在遵义市的沉降通量中，无机离子的湿沉降通量占所有离子湿沉降总量的94%，并存在明显的季节性变化。SO42-、Ca2+、H+、NH4+、NO3-为最主要的贡献者，分别为90.1、49.8、47.3、26.0和19.2 mmol•m-2•yr-1。对比显示，SO42-、Ca2+、H+的沉降量均属于我国的高值区，而NO3-的沉降量属于我国中值区，NH4+的沉降量属我国低值水平。营养元素总无机氮TIN(TIN= NH4+ -N+ NO3- -N+ NO2- -N)的湿沉降总量为45.7 mmol•m-2•yr-1，其中NH4+和NO3-分别占TIN的57.0%和41.9%，遵义地区高TIN值当地氮肥的施用量和工业NOx的释放量密不可分；营养元素P的沉降量为1.97 mmol•m-2•yr-1，由于P的来源较少，促使P的湿沉降通量较低。有机酸占湿沉降总量的6%，其四季的湿沉降量顺序由高到低依次为：春>秋>冬>夏，这是有机离子的浓度和四季的降雨量共同作用的结果。根据气液平衡理论可知，挥发性有机酸(HCOO-、CH3COO-和CH3CH2COO-)的干沉降量占总沉降量的47.2%，表明遵义市有机酸沉降方式包括干湿沉降两种。因此在研究遵义市的污染物尤其是有机酸类对生态系统和城市建设的影响时，有必要同时收集气样和水样。

Eyes open to stem cells: safety trial may pave the way for cell therapy to treat retinal disease in patients

A clinical trial using human embryonic stem cell (hESC) therapy for an inherited retinal degenerative disease is about to commence. The Advanced Cell Technology (ACT) trial will treat patients with Stargardt's macular dystrophy using transplanted retinal pigment epithelium derived from hESCs. Currently, no effective treatment is available for Stargardt's disease so a stem cell-based therapy that can slow progression of this blinding condition could represent a significant breakthrough. While there are some hurdles to clear, the ACT trial is a fine example of translational research that could eventually pave the way for a range of stem cell therapies for the retina and other tissues.

Human mesenchymal stem cells reduce the severity of acute lung injury in a sheep model of bacterial pneumonia

Background Human bone marrow-derived mesenchymal stem (stromal) cells (hMSCs) improve survival in mouse models of acute respiratory distress syndrome (ARDS) and reduce pulmonary oedema in a perfused human lung preparation injured with Escherichia coli bacteria. We hypothesised that clinical grade hMSCs would reduce the severity of acute lung injury (ALI) and would be safe in a sheep model of ARDS.

Methods Adult sheep (30–40 kg) were surgically prepared. After 5 days of recovery, ALI was induced with cotton smoke insufflation, followed by instillation of live Pseudomonas aeruginosa (2.5×10¹¹ CFU) into both lungs under isoflurane anaesthesia. Following the injury, sheep were ventilated, resuscitated with lactated Ringer's solution and studied for 24 h. The sheep were randomly allocated to receive one of the following treatments intravenously over 1 h in one of the following groups: (1) control, PlasmaLyte A, n=8; (2) lower dose hMSCs, 5×10⁶ hMSCs/kg, n=7; and (3) higher-dose hMSCs, 10×10⁶ hMSCs/kg, n=4.

Results By 24 h, the PaO₂/FiO₂ ratio was significantly improved in both hMSC treatment groups compared with the control group (control group: PaO₂/FiO₂ of 97±15 mm Hg; lower dose: 288±55 mm Hg (p=0.003); higher dose: 327±2 mm Hg (p=0.003)). The median lung water content was lower in the higher-dose hMSC-treated group compared with the control group (higher dose: 5.0 g wet/g dry [IQR 4.9–5.8] vs control: 6.7 g wet/g dry [IQR 6.4–7.5] (p=0.01)). The hMSCs had no adverse effects.

Conclusions Human MSCs were well tolerated and improved oxygenation and decreased pulmonary oedema in a sheep model of severe ARDS.