课程文献中心 更多>>

关键词： 条块力-位移分析法   渐近破坏稳定分析   预测预报  

摘要： 在现行条分法的基础上,建立了一种全新的边坡条块力-位移分析方法。现行条分法中条块底边的力学参数采用极限平衡状态力学参数,即每个条块底边均处于极限平衡状态,这种极限平衡状态对于残余应力是较为适宜的。采用理想弹塑性模型和一种全新的本构模型描述土条块底边力学特性,并以不平衡推力法为例,提出了临界状态条块的确定方法,针对可能的破坏模式进行了分析,并提出了边坡整体破坏各条块的应力和位移的确定方法,计算出相应的稳定系数,如传统强度折减法、综合下滑力-抗滑力法、主推力法、综合位移法和富余位移法稳定系数。通过计算分析论证了理想弹塑性模型在不改变力学参数的情况下是难以描述边坡渐近破坏过程的,而一种全新的本构模型可以描述渐近破坏各条块的力学行为。提出的条块力-位移法可以确定边坡在不同荷载和位移条件下的稳定性,也可以获得边坡的推力变化和滑面移动特征,进而实施边坡的应力、位移和稳定性的初步预测预报。

关键词： 体模   管电流量   管电压   辐射剂量  

摘要： 目的:比较数字乳腺X线摄影曝光模式对乳腺体模图像质量和辐射剂量的影响,为乳腺癌的影像诊断提供依据。方法:将乳腺体模一次成像。自动曝光模式,分别应用低剂量(Dose)、标准(STD)和高对比度(CNT)3种曝光模式;手动曝光模式,固定管电流量32 mAs,分别改变管电压为25、26、27、28、29、30、32、34、36、38和40kV曝光11次;固定管电压29kV,分别改变管电流量为20、32、40、45、56、63、80、100、125、160和200mAs曝光11次。记录各曝光参数下平均腺体剂量(AGD)值,并根据美国放射学会(ACR)评分标准对图像质量进行评价。结果:3种自动曝光模式下,模拟纤维组织的图像质量评分比较差异有统计学意义(P=0.00),模拟钙化和模拟团块的图像质量评分比较差异无统计学意义(P=0.37)。手动曝光模式下,固定管电流量32mAs,改变管电压或固定管电压29kV,改变管电流量曝光,3种模拟病变图像质量评分比较差异均有统计学意义(P=0.00),但3种模拟病变的图像质量评分受管电压或管电流量增加而且引起的变化趋势不同。管电流量或管电压变化对模拟纤维组织的图像评分影响最大,对模拟钙化的图像评分影响最小。自动曝光模式以低剂量模式AGD值最低,高对比度模式AGD最高;手动曝光模式时,AGD随管电压和管电流量增加而增加,均呈正相关关系(R2=0.998,P=0.000;R2=0.979,P=0.000)。结论:数字乳腺X线摄影时,可采用自动曝光的低剂量模式行乳腺癌筛查。使用手动曝光模式行常规临床检查能有效降低辐射剂量。

关键词： 地铁   住房价格   异质性  

摘要： 基于工行—上海财大房地产交易的数据资料,采用半对数形式住房价格特征模型(Hedonic Model),从市区和郊区影响程度的差异性角度检验了地铁的房价溢价效应在城市各区域的异质性特征。研究结果表明,地铁对市区和郊区住房价格的影响程度存在显著差异。在影响范围方面,郊区地铁站点对住房市场的影响范围大于市区地铁站点的影响范围;在影响程度上,郊区地铁站点沿线的房价变化幅度大于市区地铁站点沿线的房价变化幅度;在影响方向上,地铁对房价的影响存在正向和负向影响,靠近站点的区域负向影响更显著,超过一定距离后正向影响更明显;在影响效应的叠加方面,换乘站点比非换乘站点对房价的影响更加显著。

关键词： Structural health monitoring (SHM)   Cable-stayed bridge   Multiscale modeling   Substructuring   Influence line analysis  

摘要： Structural health monitoring (SHM) systems have been installed in many long-span bridges to assess bridge performance and safety. However, the number of sensors in a SHM system is always limited;therefore, not all of the bridge components can be directly monitored. To facilitate an effective assessment of stress-related bridge performance and safety, a multiscale finite-element (FE) model with detailed geometry and affordable computation time is needed. This paper presents the details of establishing a multiscale model for the Stonecutters Bridge in Hong Kong, which is a cable-stayed bridge with a 1,018-m main span. The twin-box deck of the bridge is modeled with shell elements in detailed geometry such that all stress responses in the bridge deck can be directly computed;other bridge components are modeled using either beam or truss elements. Each segment of the girder is then condensed into a superelement with the substructuring method in order to reduce the number of degrees of freedom. A sensitivity-based model updating is also performed to update the multiscale model with the measured modal frequencies. The comparison between the simulation and test results shows that updating with only modal frequencies can ensure consistency in the dynamic properties between the model and the bridge. Nevertheless, the accuracy in the static displacements and stress responses from the influence line analysis may not be improved by the standard updating process. This indicates a need for multiscale updating techniques that take into account both the dynamic properties and local responses of the multiscale model. (C) 2014 American Society of Civil Engineers.

关键词： glucose uptake   proliferation   viability   trophoblast cells   xanthohumol  

摘要： In this study, we aimed to investigate modulation of glucose uptake by the HTR-8/SVneo human first-trimester extravillous trophoblast cell line by a series of compounds and to study its consequences upon cell proliferation, viability and migration. We observed that uptake of H-3-deoxy-D-glucose (H-3-DG;10 nM) was time-dependent, saturable, inhibited by cytochalasin B (50 and 100 mu M), phloretin (0.5 mM) and phloridzin (1 mM), insulin-insensitive and sodium-independent. In the short term (30 min), neither 5-HT (100-1000 mu M), melatonin (10 nM) nor the drugs of abuse ethanol (100 mu M), nicotine (100 mu M), cocaine (25 mu M), amphetamine (10-25 mu M) and 3,4-methylene-dioxy-N-methamphetamine (10 mu M) affected 3H-DG uptake, while dexamethasone (100-1000 mu M), fluoxetine (100-300 mu M), quercetin, epigallocatechin-3-gallate (30-1000 mu M), xanthohumol (XH) and resveratrol (1-500 mu M) decreased it. XH was the most potent inhibitor [IC50 = 3.55 (1.37-9.20) mu M] of H-3-DG uptake, behaving as a non-competitive inhibitor of 3H-DG uptake, both after short-and long-term (24 h) treatment. The effect of XH(5 mu M;24 h) upon H-3-DG uptake involved mammalian target of rapamycin, tyrosine kinases and c-Jun N-terminal kinases intracellular pathways. Moreover, XH appeared to decrease cellular uptake of lactate due to inhibition of the monocarboxylate transporter 1. Additionally, XH (24 h;5 mu M) decreased cell viability, proliferation, culture growth and migration. The effects of XH upon cell viability and culture growth, but not the antimigratory effect, were mimicked by low extracellular glucose conditions and reversed by high extracellular glucose conditions. We thus suggest that XH, by inhibiting glucose cellular uptake and impairing HTR-8/SVneo cell viability and proliferation, may have a deleterious impact in the process of placentation.

关键词： Capacitance  

摘要： In this paper we have done performance comparison of double gate tunnel FET (DGTFET) and sandwich tunnel barrier FET (STBFET i.e., line tunnel FET) with temperature variation. It is noticed that the OFF state current of STBFET shows more variations with increased temperature than DGTFET counterparts. The impact of temperature variations at transconductance is approximately four orders of magnitude higher than the DGTFET. The Miller capacitance component CGD dominates in DGTFET whereas CGS dominates in STBFET. Copyright © 2015 American Scientific Publishers.

关键词： Sun   polarization   particle beams  

摘要： During our spectropolarimetric observations of the 2B/4.8X flare on July 23, 2002, with the Large Solar Vacuum Telescope (LSVT), we detected impact linear polarization in the southern ribbon. The maximum polarization exceeded 10%. On the whole, the polarization was observed only for similar to 6 min out of almost 2 h of observations of this flare. At this time, the H alpha line profiles had a deep central self-reversal. We have compared the LSVT observations with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data, where the locations of gamma-ray emission were obtained for the first time. A careful comparison has revealed that the effects in the H alpha line were observed in a region < 10aEuro(3) located between two X-ray sources in the southern ribbon. According to the RHESSI data, a gamma-ray source attributable to a beam of high-energy (similar to 1 MeV) electrons was observed at the same place. The events in the corona and the upper chromosphere also coincide in time with the observed effects in the H alpha line. The two X-ray sources are assumed to represent a common footpoint of the southern foot of the loop bifurcated due to the precipitation of high-energy electrons. It is suggested that the penetration of these electrons into the dense layers of the chromosphere could lead to impact polarization and a decrease of the H alpha line intensity in the southern ribbon of the flare, in contrast to the northern ribbon where a typical hard X-ray source with an energy similar to 20-120 keV was observed;there were no self-reversal at the H alpha line center and polarization.

关键词： isochrones   golden hour   ambulance deployment   small towns  

摘要： It is well known that excessive rescue times after traffic accidents negatively affect the health of those injured. There is a need to quantitatively measure the impact of unexpected events like ambulance availability, weather, floating population and congestion in those rescue times. A family of indicators based on isochrones is disguised and proposed to understand the risk of the whole population as the probability of not being assisted on time. Indicators of health risk for local towns are also defined. The indicators are calculated using a simulation model and visualized in web format. The framework of analysis is validated using avila (Spain) and the problem of the optimal deployment of ambulances as a test-bench.

关键词： broiler   camosine   gender   L-histidine   meat quality  

摘要： The aim of the investigation was to determine influence of L-histidine dietary supplementation (P1 0.0%, P2 0.1%, P3 0.2% and P4 0.3%), hybrid line (Cobb 500 and Hubbard Classic) and gender on meat quality and carnosine concentration in chicken breast and thigh muscles. The research was carried out on 184 one day old broiler chickens as 4 X 2 X 2 factorial design. Chicken live weight, carcass weight, dressing percentage, absolute and relative shares of main body parts in the carcass, pHi, pHu, colour, drip loss, cooking loss and share force of breast muscle, and carnosine concentration in breast and thigh muscles were determined. L-histidine dietary supplementation significantly affected live weight, carcass weight, weight of drumsticks and thighs, backs and wings, share of back and the CIE a* value (P<0.05), as well as the content of carnosine in breast muscle (P=0.003). Hybrid line influenced relative shares of main body parts in the carcasses, except for wings, and the CIE a* value of breast muscle (P<0.001). Chicken gender affected live weight of chickens, carcass weight, as well as weight of main parts (P<0.001), except for breast. The results of the investigation showed that dietary L-histidine significantly increased carnosine content in broiler breast muscle. Cobb 500 female chickens of the P4 group had higher carnosine concentrations in breast muscle by 156.61 and male chickens by 150.49 mu g/g of tissue than the control group. Cobb 500 broiler chickens deposited more carnosine in meat than Hubbard Classic broilers.

关键词： Heterogeneity   Microclimate   Paramo   Plant-plant interactions   Secondary succession   Species richness   Tree establishment  

摘要： QuestionsDo local plant-plant interactions and facilitation play an important role in vegetation dynamics after disturbance in the high tropical Andes? In particular, does the dominant shrub Baccharis prunifolia have an effect on microclimate and local vegetation structure within old-fields at the upper forest line? Does distance from the border of the surrounding forests also influence community structure within fallow plots? Is there an interaction between facilitation and edge effects on vegetation regeneration? LocationGavidia Valley, Sierra Nevada de Merida, Venezuela. MethodsPlant cover, species richness and community structure were compared in circular micro-plots placed under the canopy of *** shrubs and in open areas (12 micro-plots in each case) both near and far from the forest border within two 10-12yr successional plots at 3400m a.s.l. (a total of 96 micro-plots). Additionally, topsoil temperature was monitored for 1mo in the four situations under study. ResultsAverage and maximum temperature and temperature amplitudes were lower under the canopy of *** shrubs than in open areas;this effect being more marked far from the forest edge. Species richness, vegetation cover and the density of dominant forest trees were higher under the shrubs' canopy than in the inter-shrub spaces. The proximity to the edge of the surrounding forest also had a positive effect on species richness, with no significant interaction with the local sampling situation (under shrub vs outside). ConclusionsOur results suggest that both facilitation and edge effects influence the effectiveness of vegetation regeneration within old-fields in the high tropical Andes. Consequently, these processes should be considered for interpreting vegetation dynamics in environmental change scenarios at the tropical mountain tree line and for the design of ecological restoration strategies in these high-diversity ecotones, which have been subjected to large-scale anthropogenic transf