预应力混凝土框架次弯矩简化计算方法探讨

对于单跨预应力混凝土框架梁和多跨预应力混凝土框架的内跨梁,通过位移法证明了用一定矢高的单波抛物线代替实际预应力筋进行次弯矩的计算,方法简单,结果准确。对于多跨预应力混凝土框架的边跨梁,由于预应力筋布置形式与内跨不同,采用与单跨梁相同的简化方法进行计算,结果可能会有较大误差,建议按实际预应力筋形状计算。     

大型预应力U型薄壳渡槽施工过程仿真分析

针对预应力U型薄壳渡槽的施工问题,采用单元“生和死”的技术及“时程”分析的方法进行了仿真计算,得出了预应力U型薄壳渡槽在张拉纵、环向预应力锚索、装配横杆、造槽机移位过跨等受载过程中槽身混凝土的力学行为变化规律.在上述一系列的施工过程中,施加预压应力效果较好,采用造槽机施工对槽身损伤小,为渡槽的设计和施工提供了依据.     

预应力多跨混凝土连续板桥在老龙口水利枢纽中的应用评价

文章就预应力多跨混凝土连续板桥在老龙口水利枢纽中的实际应用,通过对河道平槽流量的推求和建桥后桥址处河道过流能力的计算分析,确认该结构形式对河道过平槽流量无大影响。     

近距离煤层煤柱下应力分布和巷道支护技术

针对和尚嘴煤业近距离煤层煤柱下掘进巷道变形大的问题,在介绍地质力学特征的基础上,采用数值模拟分析上部煤层不同方式采动后,采空区和煤柱在下部煤层的应力分布情况。分析煤柱下巷道变形特点和支护要点,结合高预应力强力锚杆支护理论,提出合理的锚网与锚索联合支护设计,现场试验效果明显。     

预应力混凝土旧吊车梁疲劳及承载性能评估

某机械制造厂有预应力混凝土旧吊车梁数十根.为检验这批旧吊车梁能否继续使用,对两根锈蚀程度较严重的吊车梁进行疲劳强度试验和静力荷载试验.试验结果表明:在2×106次疲劳荷载下,旧吊车梁仍处于弹性工作阶段;在静力荷载作用下,旧吊车梁承载力满足正常工作要求且具有良好的延性,达到破坏荷载时端部的预应力锚具状态完好.     

肉品风味的研究综述

肉是人类必需物质蛋白质、脂肪、维生素等的重要来源.本文简单介绍了肉品中所含有的风味物质的种类、风味物质的形成以及影响肉品风味的因素.     

A comparative study for the quantitative determination of soluble solids content,pH and firmness of pears by Vis/NIR spectroscopy

Visible and near infrared (Vis/NIR) spectroscopy was investigated to determine the soluble solids content (SSC), pH and firmness of different varieties of pears. Two-hundred forty samples (80 for each variety) were selected as sample set. Two-hundred ten pear samples (70 for each variety) were selected randomly for the calibration set, and the remaining 30 samples (10 for each variety) for the validation set. Partial least squares (PLS) and least squares-support vector machine (LS-SVM) with different spectral preprocessing techniques were implemented for calibration models. Different wavelength regions including Vis, NIR and Vis/NIR were compared. It indicated that Vis/NIR (400–1800 nm) was optimal for PLS and LS-SVM models. Then, LS-SVM models were developed with a grid search technique and RBF kernel function. All LS-SVM models outperformed PLS models. Next, effective wavelengths (EWs) were selected according to regression coefficients. The EW-LS-SVM models were developed and a good prediction precision and stability was achieved compared with PLS and LV-LS-SVM models. The correlation coefficient of prediction (r_p), root mean square error of prediction (RMSEP) and bias for the best prediction by EW-LS-SVM were 0.9164, 0.2506 and −0.0476 for SSC, 0.8809, 0.0579 and −0.0025 for pH, whereas 0.8912, 0.6247 and −0.2713 for firmness, respectively. The overall results indicated that the regression coefficient was an effective way for the selection of effective wavelengths. LS-SVM was superior to the conventional linear PLS method in predicting SSC, pH and firmness in pears. Therefore, non-linear models may be a better alternative to monitor internal quality of fruits. And the EW-LS-SVM could be very helpful for development of portable instrument or real-time monitoring of the quality of pears.     

Field effect surface passivation of SiO2/Si interfaces by heat treatment with high-pressure H2O vapor

We investigated a simple field effect passivation of the silicon surfaces using the high-pressure H₂O vapor heating. Heat treatment with 2.1×10⁶ Pa H₂O vapor at 260°C for 3 h reduced the surface recombination velocity from 405 cm/s (before the heat treatment) to 38 cm/s for the thermally evaporated SiO_x film/Si. Additional deposition of 140 nm-SiO_x films (x<2) with a high density of fixed positive charges on the SiO₂/Si samples further decreased the surface recombination velocity to 22 cm/s. We also demonstrated the field effect passivation for n-type silicon wafer coated with thermally grown SiO₂. Additional deposition of 210 nm SiO_x films on both the front and rear surfaces increased the effective lifetime from 1.4 to 4.6 ms. Combination of thermal evaporation of SiO_x film and the heat treatment with high-pressure H₂O vapor is effective for low-temperature passivation of the silicon surface.     

Determination of effective moisture diffusivity and assessment of quality attributes of banana slices during drying

The influence of drying temperatures on the moisture diffusivity and quality attributes of the dried banana slices in terms of volatile compound, shrinkage, color, texture and microstructure were studied. Bananas with peel color index of 5 corresponding to yellow color with green tip were sliced into 3 mm thickness, dipped into ascorbic acid solution and dried at four temperatures of 70, 80, 90 and 100 °C. Drying rate of banana slices can be divided into two sub-drying periods, first and second falling rate periods. The effective diffusivity estimated by the optimization technique was found to decrease sharply with moisture content in the first falling rate period and changed slightly in the second falling rate period. High-temperature drying seems to provide lower loss of volatile compounds in the dried sample. Moreover, the dried banana was very porous, resulting in remarkably lower hardness value than that obtained from the low-temperature drying whilst the crispiness was not significantly different amongst the samples obtained at various drying temperatures. Although the textural property could be improved at high temperature, the product color was brown as manifested by the low L- and hue values in particular at the drying temperature of 100 °C.     

Determination of pesticide residues in food matrices using the QuEChERS methodology

The determination of pesticide residues in food matrices is a formidable challenge mainly because of the small quantities of analytes and large amounts of interfering substances which can be co-extracted with analytes and, in most cases, adversely affect the results of an analysis. However, safety concerns require that pesticides of the wide range of chemical properties (including acidic, basic and neutral) should be monitored. Because of the wide variety of food matrices, the sample must initially be cleaned up before final analysis. That is why the analytical chemist is faced with the need to devise new methodologies for determining such residues to be determined in a single analytical run. To accomplish the goal, QuEChERS methodology has been developed. It is a streamlined and effective extraction and cleanup approach for the analysis of diverse analyte residues in food matrices. So far, there have been achieved promising results by liquid or gas chromatography analysis, including pesticides, but also acrylamide, pharmaceuticals and veterinary drugs.