加载速率对焊接接头断裂行为的影响

在不同温度、不同加载速率下，对典型建筑结构用钢及其焊缝进行拉伸试验，测试其基本力学性能。采用能综合考虑加载速率及高加载速率下材料温度变化的R参量，确定本构关系。通过断裂力学试验，测试不同温度及加载速率下供试钢材及其焊接接头的断裂韧度值。随加载速率的增大，断裂韧度降低，但存在有较大的分散性。不同加载速率下裂纹尖端应力场数值分析结果表明，裂纹尖端最大主应力随加载速率的增大而升高。最后基于局部法，研究不同加载速率下母材及接头的断裂行为。局部断裂参量－－威布尔应力不受温度、加载速率的影响，可有效地描述材料的断裂行为。     

MPEG-2传送流监测和分析原理

介绍了MPEG-2传送流监测和分析仪的研究背景和对传送流进行测试的框架,并提出了分析仪的实现方法。     

本地传输网建设方案浅析

通过对本地传输网的网络特点、结构、分层以及技术要求等各方面的分析,对合理确定本地传输网络的建设方案,以及确定合理方案的方法进行了论述。     

基于点密集度的非线性流形学习算法

提出一种样本点密集度的非线性流形学习算法.该算法提出了一个有效的数据点密集参数,能够很好地对非均匀数据的低维嵌入进行约束,其嵌效结果明显优于LLE算法.在人工和人脸数据集上的实验结果表明,新算法产生了较好的嵌入及分类结果.     

Integrating Lo cal Binary Patterns into Normalized Moment of Inertia for Up dating Tracking Templates

This paper presents an e?cient visual tracking framework which is robust to rotation, scale vari-ation and occlusion. The target template is characterized by Local binary patterns (LBP), which exhibit invariance to rotation. The LBP features are then integrated into the Normalized moment of inertia (NMI) to decide whether the template requires update. This procedure enables an adaptive tem plate m atching strategy which addresses the tracking failures arising from scale variations. Kalman fil-tering is exploited for predicting the tra jectory of the tar-get when it is occluded. The matching e?ciency is achieved by applying a locally pyramid searching scheme. Experi-m ental results validate the e?ciency and effectiveness of our tracking framework.     

Adaptive and optimal difference operators in image processing

Differential operators are essential in many image processing applications. Previous work has shown how to compute derivatives more accurately by examining the image locally, and by applying a difference operator which is optimal for each pixel neighborhood. The proposed technique avoids the explicit computation of fitting functions, and replaces the function fitting process by a function classification process using a filter bank of feature detection templates. Both the feature detectors and the optimal difference operators have a specific shape and an associated cost, defined by a rigid mathematical structure, which can be described by Gröbner bases. This paper introduces a cost criterion to select the operator of the best approximating function class and the most appropriate template size so that the difference operator can be locally adapted to the digitized function. We describe how to obtain discrete approximates for commonly used differential operators, and illustrate how image processing applications can benefit from the adaptive selection procedure for the operators by means of two example applications: tangent computation for digitized object boundaries and the Laplacian of Gaussian edge detector.     

Detection and mapping of long-term land degradation using local net production scaling: Application to Zimbabwe

Degradation of vegetation and soils in drylands, sometimes called desertification, is thought to be a serious threat to the sustainability of human habitation, but maps of the extent and severity of degradation at country and global scales do not exist. Degraded land, by definition, has suffered a change relative to its previous condition set by its climate, soil properties, topography and expectations of land managers. The local net production scaling (LNS) method, tested here in Zimbabwe, estimates potential production in homogeneous land capability classes and models the actual productivity using remotely-sensed observations. The difference between the potential and actual productivities provides a map of the location and severity of degradation. Six years of 250 m resolution MODIS data were used to estimate actual net production in Zimbabwe and calculate the LNS using three land capability classifications. The LNS maps agreed with known areas of degradation and with an independent degradation map. The principal source of error arose because of inhomogeneity of some land capability classes caused by, for example, the inclusion of local hot-spots of high production and differences in precipitation caused by local topography. Agriculture and other management can affect the degradation estimates and careful inspection of the LNS maps is essential to verify and identify the local causes of degradation. The Zimbabwe study found that approximately 16% of the country was at its potential production and the total loss in productivity due to degradation was estimated to be 17.6 Tg Cyr^− 1, that is 13% of the entire national potential. Since the locations of degraded land were unrelated to natural environmental factors such as rainfall and soils, it is clear that the degradation has been caused by human land use, concentrated in the heavily-utilized, communal areas.     

Stigma and barriers to care in soldiers postcombat.

The present study examined the effects of leadership and unit cohesion on mental health stigma and perceived barriers to care. A sample of 680 soldiers from combat support units were surveyed 3 months after their return from combat operations in Iraq. The survey included scales on psychological symptoms and perceptions of leader behaviors and unit cohesion, as well as items assessing stigma and barriers to care. The sample was used to test the independent and interactive effects of leadership and unit cohesion on soldiers’ perceptions of stigma and barriers to care. Analyses yielded significant interaction effects between leadership and cohesion in predicting stigma and barriers to care, while controlling for the effects of mental health symptoms. Soldiers who rated their leaders more highly and who reported higher unit cohesion also reported lower scores on both stigma and perceived barriers to care. Thus, positive leadership and unit cohesion can reduce perceptions of stigma and barriers to care, even after accounting for the relationship between mental health symptoms and these outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of constraints on lattice re-orientation and strain in polycrystal plasticity simulations

Employing a rate-dependent crystal plasticity model implemented in a novel and fast algorithm, two instantiations of an OFHC copper microstructure have been simulated by FE modelling to 11% tensile engineering strain with two different sets of boundary conditions. Analysis of lattice rotations, strain distributions and global stress–strain response show the effect of changing from free to periodic boundary conditions to be a perturbation of a response dictated by the microstructure. Average lattice rotation for each crystallographic grain has been found to be in fair agreement with Taylor-constraint simulations while fine scale element-resolved analysis shows large deviations from this prediction. Locally resolved analysis shows the existence of large domains dominated by slip on only a few slip systems. The modelling results are discussed in the light of recent experimental advances with respect to 2- and 3-dimensional characterization and analysis methods.     

网络教室的建立、管理及维护

本文通过基本的局域网组网技术、“赛思多媒体网络教室”和shutdown命令,实现了现代化的计算机机房教学和管理要求。