Estimating NAA in cortical gray matter with applications for measuring changes due to aging

N-acetylaspartic acid (NAA), a prominent peak in the proton spectrum, is an amino acid thought to be present almost exclusively in neurons and their dendritic and axonal extensions. While 1H MRS studies are showing promise in identifying NAA deficits in different patient groups, unwanted lipid signal from subcutaneous fat surrounding the skull, and necessarily large voxels have limited investigators' ability to assess NAA in cortical gray matter. Here we report a technique developed to derive estimates of NAA signal from cortical gray matter. This approach uses an inversion recovery imaging pulse sequence with a long TE to suppress lipid signal from the scalp and information from concurrently obtained structural MR images to determine the CSF, white and gray matter composition of each spectroscopic voxel. A regression analysis is then used to estimate what NAA levels would be in "pure" white and gray matter voxels. This technique has been applied to demonstrate reduced NAA gray/white levels in the brains of five healthy older compared with five healthy younger women.     

Dark adaptaion processes in the amphibian rod

Rod dark adaptation in the amphibian retina appears to be due to three processes: 1. background adaptation, occurring immediately after the extinction of an adapting or bleaching light, 2. intermediate adaptation, that frequently lasts 30 min or more and 3. opsin adaptation, which in the isolated retina where regeneration of rhodopsin is insignificant, is observed a a permanent loss of sensitivity after the completion of intermediate adaptation. Intermediate adaptation is characterized by a linear relation between log threshold and the amount of "retinal" present, a similar relation is obtained between log threshold and the amount of rhodopsin bleached in opsin adaptation. These adaptation processes are discussed in terms of a model of the rod outer segment.     

The crack growth resistance of thin steel sheets under eccentric tension

The stable crack growth in thin steel sheets is the topic of this paper. The crack opening was observed using a videoextensometry system, allowing the crack extension determination. J_R-curve and δ_R-curve were established from obtained data. The ductile tearing properties of different thin sheets of steel were determined, including the impact of the specimen orientation, from test performed on compact tension specimens loaded under two conditions. The effect of the material, the rolling direction, and loading rate on the crack growth resistance of thin steel sheets was analyzed. In addition to the crack growth resistance, J-integral values for crack initiation were also estimated. The relation between J _i and J_0.2 was assessed using the basic mathematical and statistical methods. This relation was described by a linear regression model.     

前沿道路的研究与应用

从介绍现有前沿道路的几种基本类型出发,着重对其运营及安全进行了对比分析,并阐述了前沿道路实施的基本原则,指出为了降低公路主线车道的事故发生频率和严重性,适当采用前沿道路对此具有重要意义.     

基于神经网络的损伤构件及损伤程度识别

确定损伤构件及其损伤程度是分阶段损伤识别的最后一步,同时又是进一步制定结构安全运行决策的前提和基础。研究了在确定了结构损伤区域的条件下,应用反向传播(BP)神经网络同时实现对具体损伤构件及其损伤程度识别的方法。探讨了针对上述神经网络训练数据的构造和训练策略。应用提出的方法对汲水门斜拉桥桥面结构进行了损伤识别仿真模拟。基于模态参数对损伤的灵敏度分析,选取了12个自振频率和损伤区域附近的6个振型分量作为构造网络输入的基本数据。网络的输出向量同时指示了损伤构件及其损伤程度。就模拟的10种损伤情况,当损伤程度达到60%以上时,有9种实现了正确的构件识别,半数以上给出了可以接受的损伤程度描述。     

NANO-BEARING： THE DESIGN OF A NEW TYPE OF AIR BEARING WITH FLEXURE STRUCTURE

A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to provide 3D damping to absorb shocks from all directions. Two designs are presented: one has 12 T-shape slots in the radian direction while the other has 8 spiral slots in the radian direction. Both designs have flexure mountings on the axial directions. Based on the finite element analysis (FEA), the new bearing can reduce the vibration (displacement) by as much as 8.37% and hence, can better protect the shafts.     

Protective action of capsaicin and chilli on haemorrhagic shock-induced gastric mucosal injury in the rat

Chilli and its pungent ingredient, capsaicin, have been shown to protect against experimental gastric mucosal injury induced by various necrotizing agents such as ethanol and aspirin and stress. We investigated the effect of capsaicin and long-term ingestion of chilli on haemorrhagic shock-induced gastric mucosal injury in the rat. Anaesthetized male Sprague-Dawley rats were subjected to haemorrhagic shock by withdrawing blood to reduce the mean arterial blood pressure to 30-40 mmHg with subsequent reinfusion of shed blood. This resulted in gastric mucosal injury with readily identifiable haemorrhagic lesions. Capsaicin (5 mg) administered prior to, but not after, haemorrhagic shock, significantly reduced the gastric mucosal injury in intact animals. Sensory ablation with capsaicin pretreatment (125 mg/kg bodyweight) abolished the gastroprotective effect afforded by capsaicin. Similarly, 4 week intake of chilli powder (360 mg daily) reduced the gastric mucosal injury in intact, but not in capsaicin-desensitized rats. Capsaicin and long-term chilli intake protected against haemorrhagic shock-induced gastric mucosal injury and the protection may be mediated by capsaicin-sensitive afferent neurons. Our studies are of potential significance in the context of stress ulcer disease in the human.     

地震激励邻接高层建筑的随机最优控制

采用控制设备联接相邻的高层建筑以降低其地震响应是一个切实有效的方法。基于随机动态规划原理与随机平均法,提出耦合相邻高层建筑的随机最优控制方法。先建立任意层数并在任意层高处控制联接的耦合结构的缩聚模型,再运用随机平均法导出关于模态能量的oIt随机微分方程,应用随机动态规划原理建立动态规划方程,由此可确定最优控制律。将结构的响应控制化为模态能量控制,缩减控制系统的维数。用高斯随机过程模拟地震激励,可计及其功率谱特性。数值结果表明该耦合结构随机最优控制方法的有效性。