检索结果-南通市图书馆

MULTIPLE TEMPERATURE GAS DYNAMIC EQUATIONS FOR NON-EQUILIBRIUM FLOWS

Journal of Computational Mathematics 2011年第6期29卷 639-660页

作者： kun xu Zhaoli Guo Mathematics Department Hong Kong University of Science and Technology Hong Kong China National Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074 China

In an early approach, a kinetic model with multiple translational temperature [K. xu, H. Liu and J. Jiang, Phys. Fluids 19, 016101 （2007）] to simulate non-equilibrium flows was proposed. In this paper, instead of using three temperatures in the x, y and z-directions, we define the translational temperature as a second-order symmetric tensor. Under the new framework, the differences between the temperature tensor and the pressure tensor will be explicitly pointed out. Based on a multiple stage BGK-type collision model and the Chapman-Enskog expansion, the corresponding macroscopic gas dynamics equations in three-dimensional space will be derived. The zeroth-order expansion gives 10 moment closure equations similar to that of Levermore [C.D. Levermore, J. Stat. Phys 83, pp.1021 （1996）]. The derived gas dynamic equations can be considered as a regularization of the 10 moments equations in the first-order expansion. The new gas dynamic equations have the same structure as the Navier-Stokes equations, but the stress-strain relationship in the Navier-Stokes equations is replaced by an algebraic equation with temperature differences. At the same time, the heat flux, which is absent in Levermore＇s 10 moment closure, is recovered. As a result, both the viscous and the heat conduction terms are unified under a single anisotropic temperature concept. In the continuum flow regime, the new gas dynamic equations automatically recover the standard Navier-Stokes equations. Our gas dynamic equations are natural extensions of the Navier-Stokes equations to the near continuum flow regime and can be used for microfiow computations. Two examples, the force-driven Poiseuille flow and the Couette flow in the transition flow regime, are used to validate the model. Both analytical and numerical results are presented. Theoretically, the Boltzmann equation can be also applied to the current multiple stage gas evolution model to derive generalized macroscopic governing equations in the near co

关键词： Gas-kinetic Model Multiple Translational Temperatures Generalized GasDynamics Equations.

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Analysis of torque transmitting behavior and wheel slip prevention control during regenerative braking for high speed EMU trains

引用

Acta Mechanica Sinica 2016年第2期32卷 244-251页

作者： kun xu Guo-Qing xu Chun-Hua Zheng Shenzhen Institutes of Advanced Technology Chinese Academy of Sciencesand The Chinese University of Hong Kong Shenzhen College of Advanced Technology University of Chinese Academy of Sciences School of Electronics and Information Tongji University

The wheel-rail adhesion control for regenerative braking systems of high speed electric multiple unit trains is crucial to maintaining the stability,improving the adhesion utilization,and achieving deep energy *** remain technical challenges mainly because of the nonlinear,uncertain,and varying features of wheel-rail contact *** research analyzes the torque transmitting behavior during regenerative braking,and proposes a novel methodology to detect the wheel-rail adhesion ***,applications to the wheel slip prevention during braking are investigated,and the optimal slip ratio control scheme is proposed,which is based on a novel optimal reference generation of the slip ratio and a robust sliding mode *** proposed methodology achieves the optimal braking *** simulation results for uncertain slippery rails verify the effectiveness of the proposed methodology.

关键词： High speed electric multiple unit(EMU) train Regenerative braking Wheel-rail adhesion Optimal slip ratio

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A high-order multidimensional gas-kinetic scheme for hydrodynamic equations

引用

Science China(Technological Sciences) 2013年第10期56卷 2370-2384页

作者： LUO Jun xu kun Mathematics Department Hong Kong University of Science and TechnologyClear Water BayKowloon Hong Kong China

This paper concerns the development of high-order multidimensional gas kinetic schemes for the Navier-Stokes *** the current approach,the state-of-the-art WENO-type initial reconstruction and the gas-kinetic evolution model are used in the construction of the *** order to distinguish the physical and numerical requirements to recover a physical solution in a discretized space,two particle collision times will be used in the current high-order gas-kinetic scheme(GKS).Different from the low order gas dynamic model of the Riemann solution in the Godunov type schemes,the current method is based on a high-order multidimensional gas evolution model,where the space and time variation of a gas distribution function along a cell interface from an initial piecewise discontinuous polynomial is fully used in the flux *** high-order flux function becomes a unification of the upwind and central difference *** current study demonstrates that both the high-order initial reconstruction and high-order gas evolution model are important in the design of a high-order numerical ***,for a compact method,the use of a high-order local evolution solution in both space and time may become even more important,because a short stencil and local low order dynamic evolution model,i.e.,the Riemann solution,are contradictory,where valid mechanism for the update of additional degrees of freedom becomes limited.

关键词： WENO reconstruction gas-kinetic schemes Euler Navier-Stokes high-order methods

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Contrastive Self-supervised Representation Learning Using Synthetic Data

引用

International Journal of Automation and computing 2021年第4期18卷 556-567页

作者： Dong-Yu She kun xu Beijing National Research Center for Information Science and Technology Department of Computer Science and TechnologyTsinghua UniversityBeijing 100084China

Learning discriminative representations with deep neural networks often relies on massive labeled data, which is expensive and difficult to obtain in many real scenarios. As an alternative, self-supervised learning that leverages input itself as supervision is strongly preferred for its soaring performance on visual representation learning. This paper introduces a contrastive self-supervised framework for learning generalizable representations on the synthetic data that can be obtained easily with complete ***, we propose to optimize a contrastive learning task and a physical property prediction task simultaneously. Given the synthetic scene, the first task aims to maximize agreement between a pair of synthetic images generated by our proposed view sampling module, while the second task aims to predict three physical property maps, i.e., depth, instance contour maps, and surface normal maps. In addition, a feature-level domain adaptation technique with adversarial training is applied to reduce the domain difference between the realistic and the synthetic data. Experiments demonstrate that our proposed method achieves state-of-the-art performance on several visual recognition datasets.

关键词： Self-supervised learning contrastive learning synthetic image convolutional neural network representation learning

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

单纯疱疹病毒1型脑炎临床特点及预后影响因素分析

引用

中国现代神经疾病杂志 2024年第4期24卷 224-229页

作者：徐坤榕王晓娟张弥兰薛红飞徐佳佳李玮河南省人民医院郑州大学人民医院神经内科450003

目的分析单纯疱疹病毒1型(HSV-1)脑炎的临床特点及预后影响因素。方法纳入2018年1月至2023年9月河南省人民医院诊断与治疗的51例HSV-1脑炎患者,记录其临床资料、实验室和影像学检查结果。采用改良Rankin量表(mRS)评估患者预后及脑损伤... 详细信息

目的分析单纯疱疹病毒1型(HSV-1)脑炎的临床特点及预后影响因素。方法纳入2018年1月至2023年9月河南省人民医院诊断与治疗的51例HSV-1脑炎患者,记录其临床资料、实验室和影像学检查结果。采用改良Rankin量表(mRS)评估患者预后及脑损伤后神经功能恢复情况,单因素和多因素逐步法Logistic回归分析筛查HSV-1脑炎预后不良的危险因素。结果共51例患者主要症状为发热、头痛;血清学检查可见血常规白细胞计数增加(14例),中性粒细胞计数增加(14例),淋巴细胞计数减少(8例),血清钠水平降低(17例);腰椎穿刺脑脊液压力升高(18例),白细胞计数增加(28例),蛋白定量升高(32例),葡萄糖水平升高(15例);有48例患者进行头部MRI检查,43例(89.58%)MRI显示有明显的脑区受累,其中35例(72.92%)MRI阳性病例均表现为典型的HSV-1脑炎单侧或双侧颞叶、额叶受累,软脑膜强化影增多8例(16.67%)。出院后6个月内有66.67%(34/51)患者完全康复,21.57%(11/51)遗留后遗症,病死率为11.76%(6/51);34例(66.67%)患者预后良好,17例(33.33%)患者预后不良。多因素Logistic回归分析显示,年龄增大(OR=1.090,95%CI:1.020~1.200;P=0.023)和脑脊液葡萄糖水平升高(OR=23.800,95%CI:23.800~1250.000;P=0.030)是HSV-1脑炎患者预后不良的危险因素。结论年龄增大和脑脊液葡萄糖水平升高是HSV-1脑炎患者预后不良的危险因素。临床实践中须掌握HSV-1脑炎的临床特点,做到早发现、早诊断、早治疗。

关键词：脑炎单纯疱疹预后危险因素 Logistic模型

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Semantic segmentation of high-resolution images

引用

Science China(Information Sciences) 2017年第12期60卷 256-261页

作者： Juhong WANG Bin LIU kun xu Department of Computer Science and Technology Tsinghua University

Image semantic segmentation is a research topic that has emerged recently. Although existing approaches have achieved satisfactory accuracy, they are limited to handling low-resolution images owing to their large memory consumption. In this paper, we present a semantic segmentation method for high-resolution images. First, we downsample the input image to a lower resolution and then obtain a low-resolution semantic segmentation image using state-of-the-art methods. Next, we use joint bilateral upsampling to upsample the low-resolution solution and obtain a high-resolution semantic segmentation image. To modify joint bilateral upsampling to handle discrete semantic segmentation data, we propose using voting instead of interpolation in filtering computation. Compared to state-of-the-art methods, our method significantly reduces memory cost without reducing result quality.

关键词： image semantic segmentation high-resolution images joint bilateral upsampling

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

A gas-kinetic theory based multidimensional high-order method for the compressible Navier–Stokes solutions

引用

Acta Mechanica Sinica 2017年第4期33卷 733-741页

作者： Xiaodong Ren kun xu Wei Shyy Key Laboratory for Thermal Science and Power Engineeringof Ministry of Education Department of Thermal Engineering Tsinghua University Beijing 100084 China Department of Mathematics School of Science The Hong Kong University of Science and Technology Hong KongChina Department of Mechanical and Aerospace Engineering School of Engineering The Hong Kong University of Scienceand Technology Hong Kong China

This paper presents a gas-kinetic theory based multidimensional high-order method for the compressible Naiver–Stokes solutions. In our previous study, a spatially and temporally dependent third-order flux scheme with the use of a third-order gas distribution function is ***, the third-order flux scheme is quite complicated and less robust than the second-order scheme. In order to reduce its complexity and improve its robustness, the secondorder flux scheme is adopted instead in this paper, while the temporal order of method is maintained by using a two stage temporal discretization. In addition, its CPU cost is relatively lower than the previous scheme. Several test cases in two and three dimensions, containing high Mach number compressible flows and low speed high Reynolds number laminar flows, are presented to demonstrate the method capacity.

关键词： compressible Stokes Navier Reynolds discretization laminar robustness spatially dimensions instead

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Dynamics and Wheel's Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

引用

Chinese Journal of Mechanical Engineering 2012年第5期25卷 1060-1067页

作者： DING Xilun LI Kejia xu kun School of Mechanical Engineering and Automation Beihang UniversityBeijing 100191China

The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS- Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS- Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified, Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.

关键词： wheel-legged robot dynamics slip ratio change of height nonholonomic constraints

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

深层套管开窗技术在渤海S井的应用

引用

化工设计通讯 2024年第7期50卷 27-29页

作者：马宏伟徐鲲中海石油(中国)有限公司天津分公司天津300451

为满足地质油藏对地层的评价需求,同时节省钻井工期,勘探井的侧钻比例、侧钻深度也随之逐年增加[1-4]。以S井Φ244.47 mm套管一趟式开窗作业为例,将从侧钻点优选、作业准备、开窗作业程序、裸眼钻进等方面对渤海油田深层套管开窗技术及... 详细信息

为满足地质油藏对地层的评价需求,同时节省钻井工期,勘探井的侧钻比例、侧钻深度也随之逐年增加[1-4]。以S井Φ244.47 mm套管一趟式开窗作业为例,将从侧钻点优选、作业准备、开窗作业程序、裸眼钻进等方面对渤海油田深层套管开窗技术及关键点进行阐述,针对深井、超深井在开窗作业程序阶段提出在井口摆好斜向器导斜面方位,下钻全程锁紧转盘,再使用陀螺复测确认的方式可以大大节省时间,为后续深层套管开窗作业提供技术指导。

关键词：侧钻比例侧钻深度一趟式开窗深层套管开窗技术关键点

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A Survey of Image Synthesis and Editing with Generative Adversarial Networks

引用

Tsinghua Science and Technology 2017年第6期22卷 660-674页

作者： Xian Wu kun xu Peter Hall TNList and the Department of Computer Science and Technology Tsinghua UniversityBeijing 100084China the Department of Computer Science University of BathBathUK

This paper presents a survey of image synthesis and editing with Generative Adversarial Networks（GANs）. GANs consist of two deep networks, a generator and a discriminator, which are trained in a competitive way. Due to the power of deep networks and the competitive training manner, GANs are capable of producing reasonable and realistic images, and have shown great capability in many image synthesis and editing *** paper surveys recent GAN papers regarding topics including, but not limited to, texture synthesis, image inpainting, image-to-image translation, and image editing.

关键词： image synthesis image editing constrained image synthesis generative adversarial networks imageto-image translation

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

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

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

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

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

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：