邻近隧道的岩质深基坑开挖影响研究

目前基坑开挖对邻近隧道的影响研究主要集中于软土地层,在土岩组合地层当中研究较少。以重庆临江门开挖深度近30 m、邻近隧道的岩质深基坑工程为例,运用数值模拟方法与工程现场监测成果对基坑开挖所造成的影响进行分析研究。研究结果表明：岩质基坑变形总体较小,支护桩加分阶预留岩墙作为围护体系比较有效,支护结构变形主要集中于土层部分;有邻近隧道时,拱圈所对应支护桩弯矩比无隧道时要大,直墙段所对应支护桩弯矩比无隧道时要小;由于受连续介质及隧道几何形态的影响,隧道会改变位移场传递的方向,并且竖直方向改变大于水平方向,隧道主要表现为横向变形。衬砌拱顶、左拱脚、左墙中的弯矩明显增加,隧道具有明显的偏压效应。     

iPP/EBR合金的结晶和相形态EI北大核心

通过偏光显微镜(POM)、动态力学分析(DMA)、差示扫描量热(DSC)和扫描电镜(SEM)对等规聚丙烯/聚乙丁烯(iPP/EBR)合金的结晶和相形态进行了研究。结果表明,iPP和EBR在合金中是分别结晶的,组分EBR嵌入了iPP球晶;当EBR含量小于50%(质量分数,下同)时,合金中本体相iPP和分散相EBR处于相分离状态;而当EBR含量达到50%后,合金中还有EBR/iPP共存相。文中还提出了合金的相结构模型。     

在弗吉尼亚州的人井修复

本文简要介绍了在弗吉尼亚州进行人井修复和修复质量检测情况。     

Winter-time climatic control on dissolved organic carbon export and surface water chemistry in an Adirondack forested watershed

Although most of forested watersheds in temperate and boreal regions are snow-covered for a substantial portion of the year, responses of biogeochemical processes under the snow pack to climatic fluctuations are poorly understood. We investigated responses of dissolved organic carbon (DOC) and surface water chemistry in stream and lake discharge waters draining the Arbutus Lake Watershed in the Adirondacks of New York State to climatic fluctuations during the snow-covered months from December through April. Interannual variability in stream discharge corresponded to changes in air temperature and snow pack depth across the winter months. Concentrations of DOC in stream water draining a subcatchment showed immediate positive responses to rising temperatures and subsequent increases in runoff during most snowmelt events. Increases in DOC concentrations usually coincided with decreases in pH and increases in total aluminum (Al) concentrations, while the correlations between concentrations of DOC and SO4(2-) or base cations were negative. Although changes in air temperature, snow pack depth, and runoff were all significantly correlated with stream water concentrations of major solutes, stepwise linear regression found that runoff was the best predictor of solute concentrations. Results of stepwise linear regression with long-term monthly monitoring data collected at the lake outlet showed weaker but still consistent climatic effects on interannual variations in concentrations of DOC and other solutes. Over the 17 winter periods from December 1983 through April 2000, changes in seasonal average concentrations of DOC, H+, and Al in lake discharge generally corresponded to interannual variations in temperature, precipitation, and runoff, while SO4(2-) and base cations displayed an opposite trend. The results suggest that snowmelt-mediated DOC responses to temperature fluctuations during the winter months might offset increases in the surface water pH caused by decreasing acidic deposition and pose a potential hazard of Al toxicity in surface waters.     

An application system for automation of constant-time radio frequency electron paramagnetic resonance imaging

A Windows based application system for data collection, Fourier reconstruction and analysis of pure phase encoded constant-time radio frequency electron paramagnetic resonance (EPR) images, is described. The graphical user interface (GUI) of the system was written in MATLAB version 5.0, using its built-in GUI utilities. Design considerations of the application system included speed, flexibility and user-friendly data display and analysis. To maximize the speed of image data collection, MATLAB's built-in C interface system, MEX was not used for data collection. Instead, MATLAB programs call the C programs from the DOS prompt directly, based on the data collection parameters entered through the GUI. Computational procedures included various digital signal-processing steps such as filtering, interpolation etc. for the Fourier reconstruction of 2D, and 3D EPR images from the pure phase encoded data. Examples of 2D images illustrating the performance of the system are presented. Although the application system has been developed for the specific purpose of EPR imaging, it can easily be adapted to other areas such as magnetic resonance microscopy as well.     

Batch growth of Salmonella typhimurium LT2: stoichiometry and factors leading to cessation of growth

Salmonella typhimurium LT2 was grown in batch culture (trypticase soy broth, with 0.3%(w/v) yeast extract, 1% (w/v) glucose and 0.5% (w/v/) NaCl, 20 degrees C) at a range of initial pH (4.4, 4.8, 5.0 and 7.0). The consumption of oxygen and glucose was found to be independent of initial pH, and stoichiometric with growth. Mean yield coefficients of 6.9 x 10(-15) and 15.5 x 10(-15) mol oxygen/cell were estimated. Calculation of the instantaneous state of carbon during the cultivation showed stoichiometric conversion of glucose into biomass, carbon dioxide and organic acids. The concentration of the undissociated form of the primary acidic product (acetic acid) was shown to be the factor limiting growth.     

Prediction of pork carcass composition based on cross-sectional region analysis of dual energy X-ray absorptiometry (DXA) scans

Dual energy X-ray absorptiometry (DXA) was used to measure pork carcass composition by performing a total scan of the right half of 262 pork carcasses (42.7±5.2 kg). The DXA scans were analyzed for percentage fat in the entire half-carcass as well as the shoulder, ham, loin, and side regions. In addition, a total of 14 cross-sections (57.6 mm wide) were analyzed: six in the shoulder/thoracic region, three in the loin region, and five in the ham region. Relative to the DXA measurement of total fat content, the coefficient of determination (R(2)) for a single cross-sectional slice ranged from 0.908 to 0.976. Relative to chemical analysis, a single slice from the ham region predicted the percentage of fat or lean in the half-carcass with an R(2) of 0.81 and a standard error of the estimate of 2.04. Prediction equations were used to analyze a separate group of 65 half-carcasses. These results indicate that carcass fat and lean percentages can be measured by performing a single-pass cross-sectional scan that would be compatible with on-line processing.     

Enhancement of G protein-coupled signaling by DHA phospholipids

The effect of phospholipid acyl chain and cholesterol composition on G protein-coupled signaling was studied in native rod outer segment (ROS) disk and reconstituted membranes by measuring several steps in the visual transduction pathway. The cholesterol content of disk membranes was varied from 4 to 38 mol% cholesterol with methyl-β-cyclodextrin. The visual signal transduction system [rhodopsin, G protein (G_t), and phosphodiesterase (PDE)] was reconstituted with membranes containing various levels of phospholipid acyl chain unsaturation, with and without cholesterol. ROS membranes from rats raised on n−3 fatty acid-deficient and-adequate diets were also studied. The ability of rhodopsin to form the active metarhodopsin II conformation and bind G_t was diminished by a reduction in the level of DHA (22∶6n−3) acyl chains or an increase in membrane cholesterol. DHA acyl chain containing phospholipids minimized the inhibitory effects of cholesterol on the rate of rhodopsin-G_t coupling. The activity of PDE, which is a measure of the integrated signal response, was reduced in membranes lacking or deficient in DHA acyl chains. PDE activity in membranes containing docosapentaenoic acid (DPA, 22∶5n−6) acyl chains, which replace DHA in n−3 fatty acid deficiency, was 50% lower than in DHA-containing membranes. Our results indicate that efficient and rapid propagation of G protein-coupled signaling is optimized by DHA phospholipid acyl chains.     

A new disease-burden method for estimating the impact of outdoor air quality on human health

Urban air quality is a serious problem, with an estimated 40 million people in Europe exposed to exceedences of existing WHO air-quality guidelines, with prospects of further declines in air quality due to projected growth in motor vehicle traffic. Air-quality management strategies, underpinned by legislation are attempting to combat this problem. To support such strategies, assessment of the costs and benefits of remedial measures is required, including an assessment of the impact of urban air quality on human health. This paper describes a disease burden estimation approach, developed to assess 'health gain' from recreational water quality improvement, and its application to urban air quality and incidence of respiratory disease. The method represents an improvement over existing disease-burden estimation techniques applied to air quality, in that by considering the probability density function of pollutant concentrations, improved estimates of exposure and hence disease burden, and also 'health gain' from air-quality improvement, are possible. Estimations of mortality advanced by fine particulate matter (PM10) are presented for five UK cities. Implications of the method for disease burden and air-quality standards are discussed. The utility of integrating the disease-burden assessment model with linked dynamic models of land-use, vehicle movement and pollutant dispersion, as a means to identify remedial strategic planning initiatives, is highlighted.