检索结果-内蒙古大学图书馆

Random close packing in protein cores

Physical Review E 2016年第3期93卷 032415-032415页

作者： Jennifer C. Gaines W. Wendell Smith Lynne Regan Corey S. O'Hern Program in Computational Biology and Bioinformatics Yale University New Haven Connecticut 06520 USA Integrated Graduate Program in Physical and Engineering Biology (IGPPEB) Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520 USA Department of Molecular Biophysics & Biochemistry Yale University New Haven Connecticut 06520 USA Department of Chemistry Yale University New Haven Connecticut 06520 USA Department of Mechanical Engineering & Materials Science Yale University New Haven Connecticut 06520 USA Department of Applied Physics Yale University New Haven Connecticut 06520 USA

Shortly after the determination of the first protein x-ray crystal structures, researchers analyzed their cores and reported packing fractions ϕ≈0.75, a value that is similar to close packing of equal-sized spheres. A limitation of these analyses was the use of extended atom models, rather than the more physically accurate explicit hydrogen model. The validity of the explicit hydrogen model was proved in our previous studies by its ability to predict the side chain dihedral angle distributions observed in proteins. In contrast, the extended atom model is not able to recapitulate the side chain dihedral angle distributions, and gives rise to large atomic clashes at side chain dihedral angle combinations that are highly probable in protein crystal structures. Here, we employ the explicit hydrogen model to calculate the packing fraction of the cores of over 200 high-resolution protein structures. We find that these protein cores have ϕ≈0.56, which is similar to results obtained from simulations of random packings of individual amino acids. This result provides a deeper understanding of the physical basis of protein structure that will enable predictions of the effects of amino acid mutations to protein cores and interfaces of known structure.

关键词： Protein structure Proteins

来源：评论

学校读者我要写书评

暂无评论

Augmented PD control method for permanent magnet spherical actuators with 3D magnet array 10

Augmented PD control method for permanent magnet spherical a...

引用

10th IEEE Conference on Industrial Electronics and Applications, ICIEA 2015

作者： Yan, Liang Zhu, Bo Jiao, Zongxia Chen, Chin-Yin Chen, Ming School of Automation Science and Electrical Engineering Beihang University Beijing100191 China Research Institute of Beihang University in Shenzhen Shenzhen518000 China Institute of Advanced Manufacturing Technology Ningbo Institute of Material Technology and Engineering Ningbo China School of Mechanical and Aerospace Engineering Nanyang Technological University 50 Nanyang Avenue Singapore

ISBN: (纸本)9781467373173

A permanent magnet spherical actuator (PMSA) with 3D magnet array is proposed in this paper. The application of 3D magnet array improves the output torque significantly. However, as PMSA is a nonlinear and multivariable system, it is very complicate to realize accuracy control. Therefore, an augmented PD algorithm is proposed in this paper. Compared with the simple PD control method, a feedforward term is added into the proposed algorithm to improve the control performance. Euler angles are applied to describe the orientation of rotor. Lagrange equations are utilized to establish the dynamic model of the actuator. As the center of gravity does not coincide with the center of rotor sphere, gravity torque is taken into consideration to enhance the precision of dynamic model. The stability of this algorithm is validated with detailed derivation. Simulation model is formulated in Matlab/Simulink. It proves that the proposed algorithm can make the system track the continuous trajectories in high accuracy. © 2015 IEEE.

关键词： Permanent magnets

来源：评论

学校读者我要写书评

暂无评论

Modeling welding deviation of rotating arc NGW based on support vector machine

Advances in Intelligent Systems and Computing

引用

Advances in Intelligent Systems and Computing 2015年 363卷 459-468页

作者： Li, Wen-Hang Gao, Kai Wu, Jing Wang, Jia-You School of Material Science and Engineering Jiangsu University of Science and Technology Zhenjiang212003 China Department of Mechanical Engineering Aerospace and Biomedical Engineering The University of Tennessee KnoxvilleTN37996-2210 United States

Support Vector Machine (SVM) was employed to describe welding deviation of welding seam tracking in multi-layer single pass, narrow gap rotating arc gas metal arc welding (GMAW). First, work piece was designed and processed to mimic multi-layer single pass welding groove to obtain experimental data under different deviations. Second, for data preprocessing, welding current signal in each rotating circle was divided into 12 parts, and the average value of each part and the difference of the according left-right part were selected and normalization to build an input-output table for predicting the weld deviation. Then, kernel function was selected and its parameters were determined by a grid search method using cross validation approach. The SVM model was built with the train set and was validated with the test set. It showed that the model can meet the criteria of welding seam tracking. In addition, comparison between SVM model and BP neural network model was made and it showed the former has better performance because it adapt to the little sample problem and can avoid the local extreme. © Springer International Publishing Switzerland 2015.

关键词： Support vector machines

来源：评论

学校读者我要写书评

暂无评论

A review and preliminary experiment on application of infrared thermography in welding

Advances in Intelligent Systems and Computing

引用

Advances in Intelligent Systems and Computing 2015年 363卷 351-359页

作者： Hu, Chao Chen, Xi-Zhang School of Material Science and Engineering Jiangsu University Zhenjiang212013 China School of Mechanical and Electrical Engineering Wen Zhou University Wenzhou325035 China

Infrared thermography, as a convenient, non-contact, non-destructive and real-time detection method, has especially advantages for the welding technology because fusion welding always company with high temperature history. The aim of this publication is to review the state-of-the-art of instrumentation and methodology in the application of infrared thermography for welding, especially focusing on the welding quality control. Researches show that infrared thermography can be used to inspect weld joints and monitor the welding process, seam tracking, control the penetration depth and improve the quality of welds. The author also did some research and obtained some valuable results. Preliminary experiments are also carried out to acquire real time IR image and temperature profile in order to analyze the weld geometry and detect the welding defects. © Springer International Publishing Switzerland 2015.

关键词： Thermography (imaging)

来源：评论

学校读者我要写书评

暂无评论

Interaction between spinnable multi-wall carbon nanotube webs

引用

Journal of Experimental Nanoscience 2015年第15期10卷 1180-1193页

作者： Khandoker, Noman noman.khandoker@curtin.edu.my Ibrahim, Raafat Hawkins, Stephen C. Huynh, Chi P. Department of Mechanical Engineering Faculty of Engineering and Science School of Engineering & Science Curtin University Sarawak CDT 250 Miri Sarawak 98009 Malaysia Department of Mechanical and Aerospace Engineering Monash University Clayton Melbourne Victoria Australia School of Mechanical and Aerospace Engineering Queen''s University Belfast United Kingdom Department of Materials Engineering Monash University Clayton Melbourne Victoria Australia CSIRO Material Science and Engineering (CMSE) Bayview Avenue Clayton Melbourne Victoria Australia

This paper presents the results on interaction behaviour between spinnable multiwall carbon nanotube bundles. Spinnable carbon nanotube webs were used as test specimens. mechanical peel tests were performed to investigate the effect of average orientation angles on interactions between nanotube bundles. Thus, in the absence of any binding agents, the effect of orientation directions on Van Der Waals forces between the nanotube bundles was revealed. The experimental results obtained from this study are consistent with theoretical calculations from published literature. It was found that the interaction force of the spinnable nanotube bundles is inversely related to their average orientation angle. It is shown that the force for parallel nanotube bundles at 0[°] angle is higher than the force for crossed nanotube bundles at 90[°] angle. [ABSTRACT FROM AUTHOR]

关键词： peel test spinnable carbon nanotube Van der Waals force

来源：评论

学校读者我要写书评

暂无评论

Multiphase phase field theory for temperature- and stress-induced phase transformations

引用

Physical Review B 2015年第17期91卷 174109-174109页

作者： Valery I. Levitas Arunabha M. Roy Iowa State University Departments of Aerospace Engineering Mechanical Engineering and Material Science and Engineering Ames Iowa 50011 USA Iowa State University Department of Aerospace Engineering Ames Iowa 50011 USA

Thermodynamic Ginzburg-Landau potential for temperature- and stress-induced phase transformations (PTs) between n phases is developed. It describes each of the PTs with a single order parameter without an explicit constraint equation, which allows one to use an analytical solution to calibrate each interface energy, width, and mobility; reproduces the desired PT criteria via instability conditions; introduces interface stresses; and allows for a controlling presence of the third phase at the interface between the two other phases. A finite-element approach is developed and utilized to solve the problem of nanostructure formation for multivariant martensitic PTs. Results are in a quantitative agreement with the experiment. The developed approach is applicable to various PTs between multiple solid and liquid phases and grain evolution and can be extended for diffusive, electric, and magnetic PTs.

关键词： THERMODYNAMICS NANOSTRUCTURED materials FINITE element method MARTENSITIC structure MICROSTRUCTURE

来源：评论

学校读者我要写书评

暂无评论

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

引用

Physical Review B 2016年第22期94卷 224108-224108页

作者： Martin Zelený Ladislav Straka Alexei Sozinov Oleg Heczko Institute of Materials Science and Engineering NETME Centre Faculty of Mechanical Engineering Brno University of Technology Technická 2896/2 CZ-616 69 Brno Czech Republic Central European Institute of Technology CEITEC MU Masaryk University Kamenice 753/5 CZ-625 00 Brno Czech Republic Institute of Physics Academy of Sciences of the Czech Republic Na Slovance 1999/2 CZ-182 21 Prague Czech Republic Material Physics Laboratory Lappeenranta University of Technology Laitaatsillantie 3 FI-57170 Savonlinna Finland

The ab initio electronic structure calculations of the Ni2MnGa alloy indicate that the orthorhombic 4O structure exhibits the lowest energy compared to all known martensitic structures. The 4O structure is formed by nanotwin double layers, i.e., oppositely oriented nanotwins consisting of two (101) lattice planes of nonmodulated martensitic structure. It exhibits the lowest occupation of density of states at the Fermi level. The total energy 1.98 meV/atom below the energy of nonmodulated martensite is achieved within structural relaxation by shifting Mn and Ga atoms at the nanotwin boundaries. The same atomic shift can also be found in other martensitic nanotwinned or modulated structures such as 10M and 14M, which indicates the importance of the nanotwin double layer for the stability of these structures. Our discovery shows that the nanotwinning or modulation is a natural property of low-temperature martensitic phases in Ni-Mn-Ga alloys.

关键词： Martensitic phase transition Crystal structures Shape-memory materials First-principles calculations

来源：评论

学校读者我要写书评

暂无评论

Ion transport and surface kinetics in oxygen ion conducting nanocrystalline oxide thin films 228

Ion transport and surface kinetics in oxygen ion conducting ...

引用

Symposium on Ionic Conducting Oxide Thin Films - 228th ECS Meeting

作者： Bae, J. An, J. Kim, Y.B. Gür, T.M. Prinz, F.B. Department of Mechanical Convergence Engineering Hanyang University Seoul133-791 Korea Republic of Program Seoul National University of Science and Technology Seoul139-743 Korea Republic of Institute of Nano Science and Technology Hanyang University Seoul133-791 Korea Republic of Department of Materials Science and Engineering Stanford University StanfordCA94305 United States Department of Mechanical Engineering Stanford University StanfordCA94305 United States

ISBN: (纸本)9781607685395

Nanocrystalline materials often exhibit extraordinary electrical and electrochemical properties related to high density of grain boundaries. In this regard, we have investigated grain boundary structure and grain boundary's role for ionic transport and surface kinetics using atomic simulations, electrochemical analysis and spectroscopic/spectrometric experiments. Thereby, it was found that the segregation of dopants and vacancies near grain boundaries facilitates oxygen exchange while impeding cross-boundary ionic transport. © The Electrochemical Society.

关键词： Grain boundaries

来源：评论

学校读者我要写书评

暂无评论

Design of a Unit Cell Facility for Studies of the Prismatic VHTR Lower Plenum 16

Design of a Unit Cell Facility for Studies of the Prismatic ...

引用

16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2015

作者： Landfried, D. Tyler Kristo, Paul Kimber, Mark University of Pittsburgh 3700 O'Hara St PittsburghPA15213 United States Department of Mechanical Engineering and Material Science University of Pittsburgh 3700 O'Hara St PittsburghPA15213 United States

ISBN: (纸本)9781510811843

One proposed design for a Generation IV reactor is the very high temperature gas reactor, which uses helium as the primary coolant due to its advantageous properties as an inert gas. One area of concern for the VHTR is the lower plenum, where temperature differences as high as 300-400 K can cause hot streaking. The lower plenum consists of a series of structural posts and an array of coolant jets which lead to a singular outlet from the reactor core. The objective of this study is to present the design for an experimental facility where insight can be gained into flow physics within the VHTR lower plenum. To study the lower plenum mixing behavior, an experimental setup including a test section herein called the 'unit cell' is designed. The unit cell consists of six hexagonally arranged jets directing their flow into the test section and subsequently traveling through a hexagonal array of seven support posts, all in the presence of a cross flow. Temperature profiles are captured via multiple thermocouples embedded in each post. With the 6 jets whose outlets are on the top face of the test section, along with the cross flow at the inlet of the test section, the unit cell is capable of experimentally simulating notable post and jet configurations found in the lower plenum. With the radial temperature profiles, the thermal fluctuations and flow behavior on these posts can be studied. The present work focuses on the scaling and design of the unit cell facility. This facility will be used to provide high quality experimental data for future validation studies as well aid to achieve more comprehensive understanding of the loading conditions which cause the thermal stresses experienced by the structural support posts in the lower plenum of the VHTR.

关键词： Coolants

来源：评论

学校读者我要写书评

暂无评论

Lightweight Custom Composite Prosthetic Components Using an Additive Manufacturing-based Molding Technique

Lightweight Custom Composite Prosthetic Components Using an ...

引用

Annual International Conference of the IEEE engineering in Medicine and Biology Society

作者： Michael T. Leddy Joseph T. Belter Kevin D. Gemmell Aaron M. Dollar the department of Mechanical Engineering and Material Science Yale University New Haven CT 06511 USA

ISBN: (纸本)9781424492695

Additive manufacturing techniques are becoming more prominent and cost-effective as 3D printing becomes higher quality and more inexpensive. The idea of 3D printed prosthetics components promises affordable, customizable devices, but these systems currently have major shortcomings in durability and function. In this paper, we propose a fabrication method for custom composite prostheses utilizing additive manufacturing, allowing for customizability, as well the durability of professional prosthetics. The manufacturing process is completed using 3D printed molds in a multi-stage molding system, which creates a custom finger or palm with a lightweight epoxy foam core, a durable composite outer shell, and soft urethane gripping surfaces. The composite material was compared to 3D printed and aluminum materials using a three-point bending test to compare stiffness, as well as gravimetric measurements to compare weight. The composite finger demonstrates the largest stiffness with the lowest weight compared to other tested fingers, as well as having customizability and lower cost, proving to potentially be a substantial benefit to the development of upper-limb prostheses.

关键词： 3D development upper-limb prostheses customizability Printing, Three-Dimensional Three Dimensions Composites Prosthesis Customs Forming techniques Customization Lightweight Fingers Durability Additive manufacturing Moulds dies stiffness

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：