圆柱壳仅受轴向均匀外压的总稳定性分析

环肋圆柱壳存在异常特性。在异常特性区间内,其总失稳临界压力取决于仅受轴向均匀外压环肋圆柱壳的失稳临界压力。通过理论计算,揭示了环肋圆柱壳仅受轴向均于外压的失稳性质与光圆柱壳几乎一致。纵横加筋圆柱壳仅受轴向均匀外压下的失稳临界压力随肋骨尺寸或纵骨尺寸的增加而增大,随舱室长度的减小呈现先增大后减小再增大的反复递增规律。提高环肋圆柱壳在异常特性区间的失稳临界压力的有效方法是增设纵骨。

大型潜艇总稳定性计算中出现异常特性的研究

本文通过两个实艇计算对比,阐明大型潜艇在总稳定性计算中会出现异常特性,归纳了异常后的变化规律,指出原有计算公式应作相应的改变。研究指出纵向刚度不足是出现异常的原因,分析了为什么纵向刚度不足会导致异常,确定了异常出现的判据,计算并绘制了异常区域的界限曲线。三个钛合金模型试验验证了异常特性的客观存在。

股总动脉斑块稳定性和颈动脉斑块最大厚度对缺血性脑血管疾病的预测价值

目的:探讨股总动脉斑块稳定性和颈动脉斑块最大厚度对缺血性脑血管疾病(ICVD)的预测价值。方法:选取颈动脉粥样硬化患者80例,根据ICVD的发生情况将患者分为ICVD组(19例)与非ICVD组(61例)。收集两组患者临床资料。超声检查测量颈动脉斑块最大厚度,行股总动脉斑块易损评分,并评估股总动脉斑块稳定性。采用Logistic回归分析发生ICVD的影响因素。绘制受试者工作特征(ROC)曲线分析股总动脉斑块易损评分和颈动脉斑块最大厚度对ICVD的预测价值。结果:年龄、高血压、高血脂、Essen卒中风险评分量表(ESRS)、股总动脉斑块易损评分及颈动脉斑块最大厚度与ICVD有关(均P<0.05)。ESRS评分、股总动脉斑块易损评分以及颈动脉斑块最大厚度为发生ICVD的独立影响因素(均P<0.05)。股总动脉斑块易损评分、颈动脉斑块最大厚度预测ICVD的曲线下面积(AUC)分别为0.794、0.745,而两者联合预测的AUC(0.874)更高(均P<0.05)。结论:股总动脉斑块易损评分和颈动脉斑块最大厚度是发生ICVD的影响因素,两者联合对ICVD的预测价值较高。

股总动脉粥样硬化斑块稳定性、颈动脉内中膜厚度联合血清sdLDL-C检测对脑卒中复发的预测效能

目的探讨脑卒中患者股总动脉粥样硬化斑块稳定性、颈动脉内中膜厚度(IMT)联合血清小而密低密度脂蛋白胆固醇(sdLDL-C)预测脑卒中复发的效能。方法选取111例脑卒中患者,根据出院后3个月内脑卒中是否复发,将患者分为复发组20例和未复发组91例。比较两组出院时的股总动脉斑块易损评分、颈动脉IMT、sdLDL-C、90 d复发风险评估量表(RRE-90)评分,采用Pearson分析RRE-90评分与股总动脉斑块易损评分、颈动脉IMT、血清sdLDL-C的相关性,采用偏相关性分析脑卒中复发的相关影响因素,采用受试者工作特征曲线(ROC)及ROC下面积(AUC)分析股总动脉斑块易损评分、颈动脉IMT、血清sdLDL-C预测脑卒中复发风险的效能。结果复发组出院时的RRE-90评分、股总动脉斑块易损评分、颈动脉IMT、血清sdLDL-C均高于未复发组(P均<0.05);RRE-90评分与股总动脉斑块易损评分、颈动脉IMT、血清sdLDL-C呈正相关(r分别为0.816、0.857、0.749,P均<0.05);股总动脉斑块易损评分、颈动脉IMT、血清sdLDL-C预测复发的AUC依次为0.815、0.821、0.750,各指标联合预测复发的AUC最大为0.916,预测复发敏感度为80.00%、特异度为87.91%。结论脑卒中患者股总动脉粥样硬化斑块稳定性、颈动脉IMT、血清sdLDL-C与脑卒中复发相关,三者联合对脑卒中复发具有良好的预测价值。

养分添加和降水变化对荒漠草原地上和地下生物量稳定性的影响

为明确荒漠草原生态系统功能和稳定性对水分和养分资源可利用性改变的响应,阐明荒漠草原生物量稳定性的影响机制及途径,本研究在宁夏荒漠草原开展了为期5年的养分添加和降水变化野外控制试验(2018-2022年),试验包括9个处理:对照(Cont)、N添加(N)、NPK添加(NPK)、减少50%降水(Cont–50%)、增加50%降水(Cont+50%)、N添加+减少50%降水(N–50%)、N添加+增加50%降水(N+50%)、NPK添加+减少50%降水(NPK–50%)和NPK添加+增加50%降水(NPK+50%)。通过测定地上、地下生物量及物种多样性,分析了物种异步性、物种多样性、生物量稳定性及生物量稳定性的影响因素。结果表明:(1)养分添加和降水变化显著影响荒漠草原植物群落生物量,NPK+50%处理增加了地上生物量(156.28%)、地下生物量(51.95%)及总生物量(75.67%),而Cont–50%处理降低了地上生物量(45.59%)、地下生物量(25.09%)及总生物量(31.41%);(2)除NPK+50%处理外,其他处理的地上生物量、地下生物量和总生物量稳定性均显著低于对照处理。NPK+50%处理降低了地上生物量稳定性(31.90%),但增加了地下和总生物量稳定性(33.48%和12.38%);(3)养分添加和降水变化显著影响物种多样性(物种丰富度和Shannon-Wiener多样性指数)和物种异步性,其交互作用对物种异步性有显著影响;(4)降水变化通过降低物种异步性进而降低地上生物量稳定性和总生物量稳定性。地上生物量稳定性对总生物量稳定性无显著的直接效应,而地下生物量稳定性对总生物量稳定性具有显著正效应。综上所述,养分添加和降水变化降低荒漠草原生物量稳定性,物种异步性(互补效应)是荒漠草原生物量稳定性的主要影响机制。在荒漠草原地区地下生物量稳定性对总生物量稳定性的贡献大于地上生物量稳定性,因此,在探究植物群落稳定性对养分添加和降水变化的响应模式及其机制时,不能仅局限于植物地上部分的研究,也要充分考虑植物地下部分的变化和响应。

各向均匀外压力作用下环肋圆柱壳的稳定特性

各向均匀外压力作用下的环肋圆柱壳，在总稳定方面会出现异常特性，例如，其稳定性不能正常地随其刚度的增加而增大。本文根据环肋圆柱壳在三种外力状态下（仅受轴向均匀外压，仅受横向均匀外压和各向均匀外压），总稳定性随几何参数变化的规律，从理论上详细说明了异常特性的实质是仅受轴向外压的特性，最后用模型实验结果证明理论分析与研究的正确性。

广州城轨DP 700型架桥机结构创新

对广州城轨DP700型架桥机上所采用的桌形截面单主梁结构进行介绍,阐述这种新型结构的工作原理、构造细节、力学特性及其功能实现方式,导出在架桥机纵移过孔过程中,桌形截面单主梁结构处于大悬臂状态下侧向总稳定性的计算理论和方法。

节段拼装型架桥机桌形截面单主梁结构的创立与应用

介绍了广州城轨DP700型架桥机上所采用的桌形截面单主梁结构的创立与应用,阐述了这种新型结构的工作原理、构造细节、力学特性及其功能实现方式,导出了在架桥机纵移过孔过程中,桌形截面单主梁结构处于大悬臂状态下侧向总稳定性的计算理论和方法。

Soil organic carbon contents, aggregate stability,and humic acid composition in different alpine grasslands in Qinghai-Tibet Plateau

Alpine grassland soils on Qinghai-Tibet Plateau store approximately 33.5 Pg of organic carbon(C) at 0–0.75 m depth and play an important role in the global carbon cycle.We investigated soil organic C(SOC),water-soluble organic C(WSOC),easily oxidizable organic C(EOC),humic C fractions,aggregate-associated C,aggregate stability,and humic acid(HA) composition along an east-west transect across Qinghai-Tibet Plateau,and explored their spatial patterns and controlling factors.The contents of SOC,WSOC,EOC,humic C fractions and aggregate-associated C,the proportions of macroaggregates(2-0.25) and micro-aggregates(0.25-0.053 mm),and the aggregate stability indices all increased in the order alpine desert < alpine steppe < alpine meadow.The alkyl C,O-alkyl C,and aliphatic C/aromatic C ratio of HA increased as alpine desert < alpine meadow < alpine steppe,and the trends were reverse for the aromatic C and HB/HI ratio.Mean annual precipitation and aboveground biomass weresignificantly correlated with the contents of SOC and its fractions,the proportions of macro- and microaggregates,and the aggregate stability indices along this transect.Among all these C fractions,SOC content and aggregate stability were more closely associated with humic C and silt and clay sized C in comparison with WSOC,EOC,and macro- and microaggregate C.The results suggested that alpine meadow soils containing higher SOC exhibited high soil aggregation and aggregate stability.Mean annual precipitation should be the main climate factor controlling the spatial patterns of SOC,soil aggregation,and aggregate stability in this region.The resistant and stable C fractions rather than labile C fractions are the major determinant of SOC stocks and aggregate stability.

Impacts of long-term ridge culture on aggregate stability in purple paddy soil of Sichuan basin

Ridge culture is a special conservation tillage method, but the long-term influence of this tillage system on soil aggregate-size stability in paddy fields is largely unknown in southwest of China. The paper is to evaluate soil aggregate stability and to determine the relationship between soil organic carbon (SOC) and soil aggregate stability. Soil samples at 0 cm-20 cm layer were adopted from a long-term (16 a) field experiment including conventional tillage: plain culture, summer rice crop and winter upland crop under drained conditions (PUR-r); and conservation tillage: ridge culture without tillage, summer rice and winter fallow with floodwater layer annually (NTR-f), winter upland crop under drained conditions (NTR-r), and wide ridge culture without tillage, summer rice crop and winter upland crop under conditions (NTRw-r), respectively. Different pretreatments, such as slaking in fast wetting, wetting and subsequent slaking, were applied to simulate the breakdown mechanisms of aggregates in paddy soil. The results show that soil particles contents were mainly consisted of silt (0.050 mm to 1.000 mm) in fraction of 42.9% to 51.2%, sand (0.050 mm to 0.001 mm) in fraction of 28.0% to 31.8%, and clay (<0.001 mm) in fraction of 17.9% to 25.4%. The amount of aggregate-size was greatly observed in fraction of 2.000 mm-6.720 mm under ridge culture in paddy soil (more than 50$) under slaking and wetting pretreatment. The proportion of soil macro-aggregates (>0.250 mm) in conservation tillage was greatly higher than that in conventional tillage under subsequent fast slaking treatment. Minimal differences of aggregate stability between slaking in fast wetting and wetting were observed, while significant differences were found between ridge culture and plain culture. The aggregate stability under slaking treatment ranked in the order of NTR-r>NTRw-r> NTR-f > PUR-r, while under wetting was NTRw-r > NTR-r > NTR-f >PUR-r. There was a positive correlation between the aggregate stability and SOC concentration under wetting, and a low correlation was observed under slaking pretreatment. Soil exposure with tillage and lack of rice/rape-seed stubble inputs caused declines in aggregation and organic carbon, both of which make soil susceptible to water erosion. Adoption of ridge culture with no-tillage integrated with crop rotation and stubble mulch significantly altered soil organic concentration. It was a valuable conservation practice for soil aggregation and soil organic carbon sequestration on paddy soil.

Uncovering the Connections Among Sustainability, Governance and GDP

This paper examines the connections among sustain- ability, governance and GDP, using the data from 123 countries. Sustainability is found to be related with GDP in two contradic- tory ways. On the one hand, growth in GDP strengthens a nation’s ability to maintain favorable environmental conditions into the future. On the other hand, GDP growth is built on more consump- tion of natural resources, and therefore generates a larger “foot- print” on the Earth. Governance plays a key role in sustainable development. However, it is not helping to reduce our footprint on the Earth. In fact, good governance is linked to a larger footprint. This reflects our materialist value and human impulse. When a society prefers the comfort and well-being of human beings to the welfare of its environment, democratic governance might be used as an effective tool against nature.

Labour Productivity and the Chaotic Economic Growth Model： G7

Chaos theory is used to prove that erratic and chaotic fluctuations can indeed arise in completely deterministic models. Chaos theory reveals structure in aperiodic, dynamic systems. The number of nonlinear business cycle models use chaos theory to explain complex motion of the economy. Almost three years after the crisis, the G7 countries continue to be challenged with economic volatility. The global economy has slowed. Growth in the United States has weakened. In Europe, economic instability is generated by the financial and economic imbalances. Europe is gripped with financial strains from the sovereign debt crisis in the euro area periphery. How these G7 economies confront their fiscal challenges will profoundly affect their economic stability. The basic aim of this paper is to provide a relatively simple chaotic economic growth model that is capable of generating stable equilibria, cycles, or chaos. This paper looks in more detail at the GDP growth stability issues in each of the G7 countries in the period 1990-2012 （Retrieved from http：//www, imf.org）. A key hypothesis of this work is based on the idea that the coefficient π =[p（s_p-i-n/pb-p_mb_m）] plays a crucial role in explaining local stability of the gross domestic product growth, where, p---the coefficient of labour productivity; p.,--the coefficient of the marginal labour productivity, sp-private saving rate;i--investment rate; b-percent of the gross domestic product which belongs to budget deficit; bm-marginal budget deficit coefficient; n-net capital outflow rate.