某核电厂主蒸汽及主给水管道横向限制件设计优化

针对国内某核电厂主蒸汽及主给水横向限制件力学工况及设计功能,依据已发生的主蒸汽管道横向限制件螺栓断裂失效问题及核电用高强度螺栓断裂报告,通过分析横向限制件的载荷状态和受力特点,发现应力腐蚀的根本原因是螺栓受到的剪切力过大,依据限制件应力分析报告和对土建结构作用载荷计算分析完成主蒸汽及主给水管道横向限制件的设计优化,论述增设抗剪件是其中一项主要优化及其他优化,并对设计优化经济效益进行分析。

核电主蒸汽超级管道限制件焊接变形控制

核电主蒸汽超级管道限制件(P295GH、P280GH)由于焊接尺寸控制严格,国内首次制造,文中针对核电主蒸汽超级管道限制件的焊接变形进行研究,通过设计相应的防变形工装和制造模拟件实现了限制件焊接变形控制。

甩击限制件设计安装浅析

通过对核电站核岛主蒸汽和主给水管道甩击限制件的设计分析,结合工程设计安装实践,阐述其设计原理和方法,论述施工操作要点,明确了设计过程中的关键控制点。通过验证表明,采用典型的屈服型甩击限制件按其在弹性区的性状进行设计是合理的。

核电主蒸汽超级管道限制件的焊接研究

文中主要对核电主蒸汽超级管道限制件(P295GH、P280GH)焊接材料选用、焊条电弧焊方法研究,找出实现此产品国内制造的先例。

五脚正装限制件注射模设计

分析了五脚正装限制件的功能要求、结构特点和成型工艺,阐述了成型收缩率的确定、1模8腔的型腔排布与浇注系统布置的设计方案,重点介绍了定、动模大镶块设计、主要成型型芯的设计要点和模具工作过程。针对塑件特点,采用一分为二的哈夫结构形式,使得模具制造难度大幅降低,并借助哈夫型芯相拼微间隙进行有效排气,在很大程度上提高了塑件的合格品率,保证了塑件质量;经实际生产验证,塑件的尺寸精度高,注射成型工艺过程稳定可靠,可满足大批量生产的需求。

航空发动机寿命限制件工作边界系统级分析模型

针对提高航空发动机系统安全性的迫切需求,以发动机本质特征和探索性研究成果为依据,分析了寿命限制件工作边界系统级分析模型(systematic model for engine life limited parts operating boundary analysis,SMELLIPOBA)的必要属性及各属性对应的技术基础,总结了相关技术基础领域的研究进展,介绍了SMELLI-POBA的发展现状,展望了这一领域未来研究方向.得出如下结论:满足适航性设计需求的SMELLIPOBA需具备耦合性、动态性、不确定性、学科交叉、多尺度等属性,未来SMELLIPOBA的发展仍将以上述属性为主线.

无侧限试件制作设备的改进

对现有无侧限试件制作过程和试验设备进行了研究,并对试验设备进行了改良,以达到降低操作劳动强度,节约设备成本的目的,通过平行试验,使改良后的设备对试验数据没有影响,从而促进无侧限试件制作设备的改进。

业绩型股权激励、行权限制与企业创新

心理学家认为基于绩效的财务激励损害企业创造力,本文证实绩效薪酬制度对企业创新的影响取决于其结构,结构合理的绩效薪酬制度也能够促进企业创新。具体而言,本文利用中国上市公司2006-2014年股权激励计划的详细数据,研究业绩型股权激励及其行权限制特征对企业创新活动的影响。本文发现,整体而言,业绩型股权激励有助于激发企业创新。相对于非股权激励公司,股权激励公司的研发投入和专利申请数量分别高4 0%和4 6.2%。更重要的是,股权激励对企业创新活动的促进作用受到股权激励计划行权限制特征的影响。行权时间限制能够提升股权激励效应,股权激励久期增加一年能相应增加15%的研发投入和18.3%的专利申请数量;但行权业绩考核会抑制企业创新,经行业调整的R O E目标增加一个标准差会使企业研发投入下降5%,专利申请数量下降8.39%。这些发现说明,管理层对短期业绩的关注是绩效薪酬损害企业创新活力的主要原因。

Epigenetics and neural stem cell commitment

Neural stem cell is presently the research hotspot in neuroscience. Recent progress indicates that epigenetic modulation is closely related to the self-renewal and differentiation of neural stem cell. Epigenetics refer to the study of mitotical/meiotical heritage changes in gene function that cannot be explained by changes in the DNA sequence. Major epigenetic mechanisms include DNA methylation, histone modification, chromatin remodeling, genomic imprinting, and non-coding RNA. In this review, we focus on the new insights into the epigenetic mechanism for neural stem cells fate.

Influence of pavement frictional properties on braking distance

In order to study the relationship between pavement friction management criteria and braking distance requirements of road geometric design, an approach for determining the braking distance considering pavement frictional properties is proposed. A finite element model （FEM） of a rolling tire under steady state is established based on theoretical hydrodynamics and mechanics principles, in which factors, including tire type, water film thickness, pavement surface properties, and vehicle speed, are considered. With the FEM, braking distances under different operating conditions are calculated. Furthermore, the allowable water film thickness is determined by comparing braking distances calculated with friction management criteria and that required by road geometric design. The results show that the braking distance is affected by the above operating conditions. As a result, it is necessary to maintain consistency between geometric design braking distance requirements and pavement friction management to achieve safe road operations.

A Novel Polysilicon and Oxide Sandwich Deep Trench with Field Limiting Ring for RF Power Transistors

A vertical sandwich deep trench with a field limiting ring is proposed to improve the breakdown voltage of power devices and high voltage devices.Simulation result shows that nearly 100% breakdown voltage of the plane junction can be realized.

Compact Modeling for Inversion Charge in Nanoscale DG-MOSFETs

A compact model for the integrated inversion charge density Qi in double-gate （DG-） MOSFETs is developed. For nanoscale applications,quantum confinement of the inversion carriers must be taken into account. Based on the previous work of Ge, we establish an expression for the surface potential with respect to Qi, and form an implicit equation, from which Qi can be solved. Results predicted by our model are compared to published data as well as results from Schred,a popular 1D numerical solver that solves the Poisson＇s and Schr6dinger equa- tions self-consistently. Good agreement is obtained for a wide range of silicon layer thickness,confirming the supe- riority of this model over previous work in this field.

Manufacturing of ultra-large plate forgings by unfolding and flattening of thick cylinders

Ultra-large plate forgings are foundation of heavy machinery,but many parts of the type cannot be made by conventional technologies due to the characters of extreme manufacturing in terms of size and quality requirements.This paper introduced a systematically method called cylinder unfolding method(CUM)for producing large plate forgings,by using a serial of operations including“splitting”,“unfolding”,and“flattening”of a thick cylinder obtained from saddle forging.The technological route of CUM was presented in detail with an example of plate forging with the horizontal sizes of 6100 mm and thickness of 300 mm.The deformation features of saddle forging for fabricating transitional cylinders were analyzed,and then the subsequent handling steps including splitting,unfolding and flattening of the cylinder,as well as the auxiliary processing,were addressed.The practice proved that CUM can provide an efficient way for manufacturing ultra-large plate forgings and meet the strict requirements in geometry and mechanical performance,without highly increasing the investments of forming equipment and tooling.

The effect of acute exercise on cognitive performance in children with and without ADHD

Background： Attention deficit hyperactivity disorder （ADHD） is a common childhood disorder that affects approximately 11% of children in the United States. Research supports that a single session of exercise benefits cognitive performance by children, and a limited number of studies have demonstrated that these effects can also be realized by children with ADHD. The purpose of this study was to examine the effect of acute exercise on cognitive performance by children with and without ADHD. Methods： Children with and without ADHD were asked to perform cognitive tasks on 2 days following treatment conditions that were assigned in a random, counterbalanced order. The treatment conditions consisted of a 30-min control condition on 1 day and a moderate intensity exercise condition on the other day. Results： Exercise significantly benefited performance on all three conditions of the Stroop Task, but did not significantly affect performance on the Tower of London or the Trail Making Test. Conclusion： children with and without ADHD realize benefits in speed of processing and inhibitory control in response to a session of acute exercise, but do not experience benefits in planning or set shifting.

Origin of Symmetry Breaking and Confinement in Conducting Polymers with Ring Structures

A model to describe the main features of conjugated polymers with ring structures, such as polythiophene and polypyrrole, is constructed. It is shown that the origin of the symmetry breaking and confinement of a soliton and anti-soliton pair is branch hopping in the polymer rings.

VIV analysis of pipelines under complex span conditions

Spans occur when a pipeline is laid on a rough undulating seabed or when upheaval buckling occurs due to constrained thermal expansion. This not only results in static and dynamic loads on the flowline at span sections,but also generates vortex induced vibration (VIV),which can lead to fatigue issues. The phenomenon,if not predicted and controlled properly,will negatively affect pipeline integrity,leading to expensive remediation and intervention work. Span analysis can be complicated by:long span lengths,a large number of spans caused by a rough seabed,and multi-span interactions. In addition,the complexity can be more onerous and challenging when soil uncertainty,concrete degradation and unknown residual lay tension are considered in the analysis. This paper describes the latest developments and a'state-of-the-art' finite element analysis program that has been developed to simulate the span response of a flowline under complex boundary and loading conditions. Both VIV and direct wave loading are captured in the analysis and the results are sequentially used for the ultimate limit state (ULS) check and fatigue life calculation.

Effect of Limiting Access to Drinking Water on Carcass Characteristics, Meat Quality and Kidneys of Rabbits

Feed restriction is a common practice to reduce post weaning digestive disorders in rabbits and to get carcasses with less fat. Hydric restriction is commonly used to induce feed restriction in growing rabbits. Two hydric restriction times （2 h and 4 h per day, continuously） were used in our trial carried in good sanitary conditions. Thirty six rabbits were divided at weaning （28 days） into three groups： R2 with restricted access to drinking water from 35 days to 80 days age of 2 h per day （from 8 a.m. to 10 a.m.）, R4： access to drinking water 4 h per day （from 8 a.m. to 12 a.m.） and T （control group） with unlimited access to drinking water. Six animals from each group were slaughtered at 80 days of age. Carcass measurements and meat quality were studied. Histological study for kidneys was carried out. Relative weight of gastrointestinal tract increases with the degree of restriction： 16.5, 18.4 and 18.9 for T, R4 and R2, respectively （P 〈 0.05）. Perirenal fat was lower in restricted groups but differences were not statically significant. Scapular fat decreases of 2/3 or 1/3 respectively with limiting access to drinking water of 2 h or 4 h per day. Compared to control group （T）, meat of restricted groups contains more water： 70.3%, 70% and 69.3% respectively for R4, R2 and T （P 〈 0.01）. The same tendency was observed for proteins： 19.2%, 19.3% and 17.7% for groups R2, R4 and T. Fat decreases in meat of restricted animals： 8.4%, 8.2% and 8.1% respectively for T, R4 and R2 （P 〈 0.05）. Water restriction induced decrease of carcass and meat adiposity. There were no differences between pH post mortem and pH ultimate （after 24 h） between the three groups. Hydric restriction does not effect on kidney histology.

Research on temperature rise of hoisting machine disk brake

A mathematical model and finite element model for analysis of temperature rise of the hoisting machine brake sys- tem was constructed, limit conditions were defined, and the law of temperature rise of brake shoes during emergent brake course was analyzed and calculated by using finite element software. By analyzing the calculation results, the law of tempera- ture change of surface of brake disk and shoes during the braking process was found. The law of brake shoes surface tempera- ture distribution and the law of temperature change along with thickness of brake shoes at brake time 0.5 s, 1.0 s and 1.5 s was analyzed. A hoisting machine emergent braking test was carried out. Finally, the author concluded that velocity rebound in the process of hoisting machine emergent brake is due to decreased friction coefficient caused by the temperature rise of the brake shoes surface.

Continuous FEM simulation of multi-pass plate hot rolling suitable for plate shape analysis

In order to continuously simulate multi-pass plate rolling process,a 3-D elastic hollow-roll model was proposed and an auto mesh-refining module with data passing was developed and integrated with FE software,Marc.The hollow-roll model has equivalent stiffness of bending resistance and deformation to the real solid and much less meshes,so the computational time is greatly reduced.Based on these,the factors influencing plate profile,such as the roll-bending force,initial crown,thermal crown and heat transfer during rolling and inter-pass cooling can be taken into account in the simulation.The auto mesh-refining module with data passing can automatically refine and re-number elements and transfer the nodal and elemental results to the new meshes.Furthermore,the 3-D modeling routine is parametrically developed and can be run independently of Marc pre-processing program.A seven-pass industrial hot rolling process was continuously simulated to validate the accuracy of model.By comparison of the calculated results with the industrial measured data,the rolling force,temperature and plate profile are in good accordance with the measured ones.

Analysis and optimization of assembly variations for non-rigid parts

Traditional variation analysis methods are not applicable to non-rigid assemblies due to possible part deformation during the assembly process. This paper presents the use of finite element methods to simulate assembly deformation. The relationship between the parts’ variation and the variation of the key points in final assembly for quality control is set up by calculating the spring back deformation after assembly. Moreover, the optimization method for non-rigid assembly variations based on finite element analysis is presented. The optimal objective is to reduce the manufacturing cost. The approach is implemented by using ANSYS and MATLAB. The test example shows that the proposed method is effective and applicable.