期刊文献+
共找到1,352篇文章
< 1 2 68 >
每页显示 20 50 100
基于Sentinel-1时序数据的山地冰川表面消融变化研究--以老虎沟12号冰川为例
1
作者 张彦丽 陈刚 +3 位作者 马亚龙 胡嘉正 马宇鹏 张丽萍 《生态学报》 CAS CSCD 北大核心 2024年第4期1389-1403,共15页
冰川是影响气候变化的主要因素,合成孔径雷达(SAR)不仅具有较高空间分辨率和多极化等特点,而且对冰雪融化引起的介电常数变化较为敏感,已成为山地冰川表面消融变化监测的重要数据源。基于Sentinel-1时序数据,提出了一种综合应用多时相... 冰川是影响气候变化的主要因素,合成孔径雷达(SAR)不仅具有较高空间分辨率和多极化等特点,而且对冰雪融化引起的介电常数变化较为敏感,已成为山地冰川表面消融变化监测的重要数据源。基于Sentinel-1时序数据,提出了一种综合应用多时相多极化SAR变化检测算法和Sigmoid函数的冰川表面消融监测方法。以祁连山老虎沟12号冰川为研究区,利用“中心线-圆”方法获得的冰川东、西支64个样区,通过各点2019-2020年124个时相的SAR后向散射系数变化特征确定了7个典型样区及2019和2020年冰川消融期;基于同轨道参考影像与多时相融雪影像对比,分别获得变化监测影像VV和VH极化后向散射系数,对其进行权重组合后提取湿雪像元;通过Sigmoid函数并结合湿雪平均海拔高度提取干雪,从而得到2年冰川消融期内16个时相的冰川表面干湿雪分布。利用2019年09月01日无人机数字正射影像(DOM)以及与Sentinel-1邻近日期5景Sentinel-2影像对提取结果进行精度验证,并结合冰川上气象站点气温和降水数据对误差结果进行深入分析。实验结果表明,该方法能够有效提取冰川表面干、湿雪分布,总体分类精度OA高达96%,Kappa系数高达0.84。老虎沟12号冰川消融期及覆盖各类型消融变化规律存在年际变化:2019年冰川的消融期为5月初至9月中下旬,2020年的消融期为6月中下旬至9月初;2019年从消融季开始,冰川表面干雪面积迅速减小,而湿雪与冰川冰面积在整个消融期均较大,但随着强降雪出现,干雪面积骤然上升,2020年冰川冰和湿雪面积变化明显,冰川冰面积持续增加,湿雪面积持续减小,而干雪面积在高海拔区趋于稳定。 展开更多
关键词 多极化SAR 后向散射系数 多时相多极化变化检测 冰川消融期
下载PDF
MULTI-PERIODIC COLLISIONAL PROCESS BETWEEN INDIAN AND ASIAN CONTINENTS:A CASE OF EASTERN HIMALAYAN SYNTAXIS AND HENGDUAN MOUNTAINS 被引量:6
2
作者 Zhong Dalai 1, Ding Lin 1, Zhang Jinjiang 1, Ji Jianqing 2(1 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2 Department of Geology, Peking University, Beijing 100871, China) 《地学前缘》 EI CAS CSCD 2000年第S1期47-48,共2页
Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between I... Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between Indian and Asian continents during Cenozoic.Based on geometric and kinematic mapping of the major boundary or regional faults (Dongjug—Mainling(1), Anigiao(2) and Jali(3), Guyu(4) faults in EHS, Ailaoshan—Red River(5), Lancangjiang(6), Gaoligong(7), Binlangjiang(8) and Magok(9) faults in WSY) (see Fig.1), especially on abundant geochronological dating of the mylonitic rocks along these faults, and coupled with magmato\|metamorphic sequences of this region, we try to deal with the temporal and spatial relationships of collisional process to answer questions such as: (1) when did collision start ? (2) is thrusting as a initial and dominant deformation mode to absorb the crustal shortening after suturing, or earlier thrusting usually followed by large\|scale strike\|slip faults? (3) are the two structural patterns coeval at times, or do they occur alternatively during deformation history? (4) are the collisional and associate uplift processes a continuous one or periodic? Insight into such questions is crucial for better understanding of the continental deformation and testing the models available or constraining a new one. 展开更多
关键词 COLLISIONAL PROCESS multi\|period TECTONIC events Eastern HIMALAYA
下载PDF
科技金融政策的绿色发展效应评价--基于科技和金融结合试点的准自然实验
3
作者 刘潭 徐璋勇 宋甜甜 《科技管理研究》 2024年第3期56-66,共11页
将科技和金融结合试点视为一项准自然试验,运用多期双重差分模型评估科技金融政策的绿色发展效应。研究发现,科技金融政策能够显著提升试点城市绿色发展水平,并且政策效果随时间推移呈“先增加、后减小”的动态特征。另外,对于等级较高... 将科技和金融结合试点视为一项准自然试验,运用多期双重差分模型评估科技金融政策的绿色发展效应。研究发现,科技金融政策能够显著提升试点城市绿色发展水平,并且政策效果随时间推移呈“先增加、后减小”的动态特征。另外,对于等级较高城市和东部城市,科技金融政策对绿色发展的驱动效应更强。机制分析表明,产业升级、技术创新、政府支持是科技金融政策促进绿色发展的主要路径,其中技术创新的中介效应最为有效。结论启示应进一步完善科技金融政策实施细则,结合各地区情况补充差异化的绿色发展任务。 展开更多
关键词 科技金融 政策评估 绿色发展 多期双重差分模型
下载PDF
DFA-ODENets:面向周期多阶段复杂系统的预测仿真框架 被引量:1
4
作者 李潇睿 宁春宇 +1 位作者 袁兆麟 班晓娟 《工程科学学报》 EI CSCD 北大核心 2024年第1期137-147,共11页
部分复杂系统受内外部因素影响在运行时会呈现出周期性的阶段变化,且在不同阶段具有完全不同的动态特性.因此在使用数据驱动方法解决此类系统的预测和仿真问题时,使用单一结构模型难以准确地学习系统在不同阶段的动态特性.本研究提出了... 部分复杂系统受内外部因素影响在运行时会呈现出周期性的阶段变化,且在不同阶段具有完全不同的动态特性.因此在使用数据驱动方法解决此类系统的预测和仿真问题时,使用单一结构模型难以准确地学习系统在不同阶段的动态特性.本研究提出了基于确定性有限状态机-常微分方程网络的预测仿真框架(DFA-ODENets),以建模周期多阶段系统.该模型由多个ODENet组成,每个ODENet能够从不规则采样的序列数据中学习系统在各个阶段内的动态特性.同时模型集成了基于确定性有限状态自动机思想的阶段转换预测器以实现模型预测时在不同阶段之间自动转换.最后,将DFA-ODENet框架应用于某计算中心制冷系统的预测仿真场景中.模型能够在给定系统运行过程中的服务器负载和环境温度下模拟系统运行过程,并对系统的制冷功率、进气口温度等主要输出变量进行预测.其中,对于制冷系统能耗预测的平均相对误差在5%以内.同时,利用制冷系统仿真模型优化了系统停止制冷时的温度设定值,通过仿真实验表明该优化最高可以节省18%的制冷能耗. 展开更多
关键词 复杂系统建模 周期多阶段系统 神经常微分网络 多输入多输出时间序列预测 制冷系统 能耗优化
下载PDF
Design of multi-band frequency selective surfaces using multi-periodicity combined elements 被引量:1
5
作者 Lu Mingyun Huang Minjie Wu Zhe 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 2009年第4期675-680,共6页
Traditional multi-band frequency selective surface (FSS) approaches are hard to achieve a perfect resonance response in a wide band due to the limit of the onset grating lobe frequency determined by the array. To so... Traditional multi-band frequency selective surface (FSS) approaches are hard to achieve a perfect resonance response in a wide band due to the limit of the onset grating lobe frequency determined by the array. To solve this problem, an approach of combining elements in different period to build a hybrid array is presented. The results of series of numerical simulation show that multi-periodicity combined element FSS, which are designed using this approach, usually have much weaker grating lobes than the traditional FSS. Furthermore, their frequency response can be well predicted through the properties of their member element FSS. A prediction method for estimating the degree of expected grating lobe energy loss in designing multi-band FSS using this approach is provided. 展开更多
关键词 frequency selective surface multi-BAND grating lobe multi-periodicity combined element
下载PDF
含平方阻尼项的Mathieu-Duffing系统混沌与分岔研究
6
作者 解加全 王海军 +4 位作者 师玮 张佳乐 霍逸婷 曹佳琳 高蔷 《振动与冲击》 EI CSCD 北大核心 2024年第7期168-174,195,共8页
旨在研究含平方阻尼项Mathieu-Duffing系统的共振与混沌。利用多尺度法探究系统在参数和受迫联合激励作用下主共振的幅频与相频特性。基于Lyapunov第一方法给出定常解的稳定性条件并判定系统存在的周期解支。依据系统异宿轨道参数方程... 旨在研究含平方阻尼项Mathieu-Duffing系统的共振与混沌。利用多尺度法探究系统在参数和受迫联合激励作用下主共振的幅频与相频特性。基于Lyapunov第一方法给出定常解的稳定性条件并判定系统存在的周期解支。依据系统异宿轨道参数方程推导系统出现异宿轨道横截相交及系统发生混沌的必要条件。根据分岔图、相轨迹图以及Poincare截面研究激励幅值与激励频率对系统进入混沌运动性态的影响,证实激励频率与激励幅值的变化均可导致系统经倍周期分岔进入混沌状态。 展开更多
关键词 Mathieu-Duffing系统 平方项阻尼 多尺度法 Lyapunov第一方法 倍周期分岔
下载PDF
BIFURCATION IN A NONLINEAR DUFFING SYSTEM WITHMULTI-FREQUENCY EXTERNAL PERIODIC FORCES
7
作者 毕勤胜 陈予恕 吴志强 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 1998年第2期121-128,共8页
By introducing nonlinear frequency, using Floquet theory and referring to the characteristics of the solution when it passes through the transition boundaries, all kinds of bifurcation modes and their transition bound... By introducing nonlinear frequency, using Floquet theory and referring to the characteristics of the solution when it passes through the transition boundaries, all kinds of bifurcation modes and their transition boundaries of Duffing equation with two periodic excitations as well as the possible ways to chaos are studied in this paper. 展开更多
关键词 nonlinear frequency Floquet theory BIFURCATION CHAOS Duffing system with multi-frequency external periodic forces
下载PDF
基于多期超额收益法的工业企业数据资产价值评估研究--以海信家电集团股份有限公司为例
8
作者 朱洁 《现代工业经济和信息化》 2024年第3期183-186,共4页
在多期超额收益法的基础上构建评估模型来对海信家电集团股份有限公司(以下简称:海信家电)数据资产价值进行评估,并提出展望.
关键词 数据资产 价值评估 工业企业 多期超额收益法
下载PDF
Variations of Frost-free Period and Its Impact on Grain Yields in Henan Province during 1961-2013 被引量:4
9
作者 闫军辉 傅辉 +1 位作者 周红升 徐新创 《Agricultural Science & Technology》 CAS 2015年第8期1588-1591,1692,共5页
The aim of this study was to investigate the responses of frost dates to global warming and its influences on grain yields. In this study, based on the frost date series defined by daily minimum ground temperature, th... The aim of this study was to investigate the responses of frost dates to global warming and its influences on grain yields. In this study, based on the frost date series defined by daily minimum ground temperature, the spatial and temporal characteristics of first frost date (FFD), last frost date (LFD) and frost-free period (FFP) were analyzed. The impact of extending FFP on major crop yields was also studied. The results were as follows: FFD showed a significantly delaying trend of 2.2 d/10 y, and LFD presented an advancing trend of 2.4 d/10 y. FFP extended at a rate of 4.5 d/10 y due to the later FFD and earlier LFD. The most obvious trend of FFD was in westem Henan, while the most significant trend of LFD and FFP oc- curred in south central parts of the study area. However, in eestem region, the trends of FFD, LFD and FFP were not so obvious. Major crop yield showed a sig- nificant correlation with frost-free period for Henan during 1961-2013. The yields of grain, rice, wheat, and maize increased by 79.5, 90.0, 79.5 and 70.5 kg/hm2 with FFP extending by one day. 展开更多
关键词 Daily minimum ground temperature Frost-free period Grain yield Henan province 1961-2013
下载PDF
Multi-h CPM信号的有限状态时序机表示 被引量:2
10
作者 钟声 张健 +2 位作者 杨春 王鹏 刘璐 《华南理工大学学报(自然科学版)》 EI CAS CSCD 北大核心 2013年第1期52-57,69,共7页
为获得多指数连续相位调制(Multi-h CPM)信号更为简洁的脉冲幅度调制(PAM)分解形式,提出了一种用有限状态时序机表示Multi-h CPM信号的新算法.该算法利用调制指数循环周期变化的特性,通过基本波形分解算法,将Multi-h CPM信号表示为周期... 为获得多指数连续相位调制(Multi-h CPM)信号更为简洁的脉冲幅度调制(PAM)分解形式,提出了一种用有限状态时序机表示Multi-h CPM信号的新算法.该算法利用调制指数循环周期变化的特性,通过基本波形分解算法,将Multi-h CPM信号表示为周期时不变的有限状态时序机和周期时不变的PAM调制器的级联结构;然后通过限定输入符号进制数为偶数,将时序机的状态转移过程描述成一个可约的、周期平稳的、非齐次Markov链.文中采用该算法对不同调制指数下的状态转移过程进行算例验证,并给出了算法的最佳接收机模型和仿真结果.与传统的PAM最优检测算法相比,文中算法的检测性能可达到理论值,而网格状态数仅为PAM最优检测算法的一半. 展开更多
关键词 多指数连续相位调制 BD分解 周期时不变 有限状态时序机 PAM调制器 MARKOV链
下载PDF
数字经济,营商环境与企业家精神--基于“智慧城市”的准自然实验 被引量:7
11
作者 王治 陈曦 《科学决策》 2023年第6期92-116,共25页
文章以2010-2019年中国285个地级市为样本,借助智慧城市设立的“准自然实验”,分析数字经济对企业家精神的影响。首先对中国城市营商环境进行评价,并结合面板门槛回归、中介效应模型等方法,检验了数字经济对企业家精神成长的影响效应及... 文章以2010-2019年中国285个地级市为样本,借助智慧城市设立的“准自然实验”,分析数字经济对企业家精神的影响。首先对中国城市营商环境进行评价,并结合面板门槛回归、中介效应模型等方法,检验了数字经济对企业家精神成长的影响效应及理论机制。结果表明,通过直接和间接两种路径,数字经济显著地提升了城市企业家精神,营商环境对企业家精神的影响呈边际递增效应。异质性分析发现,相较于南方城市,数字经济对北方城市企业家精神的正向影响更为明显;相较于直辖市和副省级城市,数字经济对外围城市企业家精神的促进效果更为明显。 展开更多
关键词 数字经济 营商环境 企业家精神 多期DID 面板门槛回归
下载PDF
拉伸-扭转-弯曲作用下系泊缆索的应力响应 被引量:1
12
作者 张若瑜 陈六合 +2 位作者 赵文斌 何鑫 赵同岩 《中国海洋平台》 2023年第2期69-76,共8页
考虑6×19多股系泊缆索编制特点,研究缆索受到拉伸-扭转-弯曲共同作用下的应力响应。推导多股系泊缆索的螺旋线方程和不同层股丝接触点轴向距离,建立仿真模型中的代表性体积元素,推导该体积元素下的周期性边界条件,简化多股系泊缆... 考虑6×19多股系泊缆索编制特点,研究缆索受到拉伸-扭转-弯曲共同作用下的应力响应。推导多股系泊缆索的螺旋线方程和不同层股丝接触点轴向距离,建立仿真模型中的代表性体积元素,推导该体积元素下的周期性边界条件,简化多股系泊缆索仿真模型,进一步优化应变和曲率加载方式,优化仿真模型加载形式。在有限元软件ANSYS中进行仿真分析,同时与解析模型进行对照。结果表明,所选取的代表性体积元素和周期性边界条件计算可靠,应力与曲率半径为非线性负相关关系,应变与应力为线性正相关关系,不同应变下曲率半径对应力的影响主要体现在最大应力数值以及位置,对应力-应变关系影响较小。 展开更多
关键词 多股系泊缆索 拉伸-扭转-弯曲共同作用 代表性体积元素 周期性边界条件
下载PDF
绿色金融政策是否促进了环境质量提升?---基于多期DID的实证研究
13
作者 贤成毅 章德花 《武汉商学院学报》 2023年第2期21-29,共9页
基于2005-2020年全国30个省市的面板数据对环境质量指数进行测算,采用多期双重差分模型对绿色金融政策的实施情况进行剖析,探讨绿色金融政策对环境质量的实际影响情况,并探讨绿色金融政策与产业结构升级和技术创新之间的交互作用。研究... 基于2005-2020年全国30个省市的面板数据对环境质量指数进行测算,采用多期双重差分模型对绿色金融政策的实施情况进行剖析,探讨绿色金融政策对环境质量的实际影响情况,并探讨绿色金融政策与产业结构升级和技术创新之间的交互作用。研究结果表明,绿色金融政策的实施显著的提升了环境质量,且可通过产业结构升级与技术创新两个传导机制促进环境质量的提升;对区域异质性进行研究发现,绿色金融政策对环境质量的提升效应存在区域异质性,其中东部地区的效应最为明显,而中部地区和西部地区的效应不明显。基于此,金融机构需继续构建丰富直达实体的多层次绿色金融市场体系,加快绿色金融产品和服务的创新,促进绿色技术创新;建立健全对环境信息的披露制度,减少信息不对称。 展开更多
关键词 绿色金融政策 环境质量 产业结构升级 技术创新 多期DID
下载PDF
Periodic oscillation and fine structure of wedge-induced oblique detonation waves 被引量:11
14
作者 Ming-Yue Gui Bao-Chun Fan Gang Dong 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2011年第6期922-928,共7页
An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30 turning angle is simulated numerically using Euler equation and one-step rection model.The fifth-order WENO scheme is adopted to captur... An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30 turning angle is simulated numerically using Euler equation and one-step rection model.The fifth-order WENO scheme is adopted to capture the shock wave.The numerical results show that with the compression of the wedge wall the detonation wave front structure is divided into three sections:the ZND model-like strcuture,single-sided triple point structure and dual-headed triple point strucuture.The first structure is the smooth straight,and the second has the characteristic of the triple points propagating dowanstream only with the same velocity,while the dual-headed triple point structure is very complicated.The detonation waves facing upstream and downstream propagate with different velocities,in which the periodic collisions of the triple points cause the oscillation of the detonation wave front.This oscillation process has temporal and spatial periodicity.In addition,the triple point trace are recorded to obtain different cell structures in three sections. 展开更多
关键词 Oblique detonation wave Wedge - periodic oscillation Fine structure
下载PDF
Multi-features Based Approach for Moving Shadow Detection 被引量:4
15
作者 周宁 周曼丽 +1 位作者 许毅平 方宝红 《Journal of Donghua University(English Edition)》 EI CAS 2004年第6期76-80,共5页
In the video-based surveillance application, moving shadows can affect the correct localization and detection of moving objects. This paper aims to present a method for shadow detection and suppression used for moving... In the video-based surveillance application, moving shadows can affect the correct localization and detection of moving objects. This paper aims to present a method for shadow detection and suppression used for moving visual object detection. The major novelty of the shadow suppression is the integration of several features including photometric invariant color feature, motion edge feature, and spatial feature etc. By modifying process for false shadow detected, the averaging detection rate of moving object reaches above 90% in the test of Hall-Monitor sequence. 展开更多
关键词 MOVING SHADOW detection multi - features MOVING OBJECT DETECTION
下载PDF
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) 被引量:40
16
作者 Xiang-Qun Cui Yong-Heng Zhao +52 位作者 Yao-Quan Chu Guo-Ping Li Qi Li Li-Ping Zhang Hong-Jun Su Zheng-Qiu Yao Ya-Nan Wang Xiao-Zheng Xing Xin-Nan Li Yong-Tian Zhu Gang Wang Bo-Zhong Gu A-Li Luo Xin-Qi Xu Zhen-Chao Zhang Gen-Rong Liu Hao-Tong Zhang De-Hua Yang Shu-Yun Cao Hai-Yuan Chen Jian-Jun Chen Kun-Xin Chen Ying Chen Jia-Ru Chu Lei Feng Xue-Fei Gong Yong-Hui Hou Hong-Zhuan Hu Ning-Sheng Hu Zhong-Wen Hu Lei Jia Fang-Hua Jiang Xiang Jiang Zi-Bo Jiang Ge Jin Ai-Hua Li Yan Li Ye-Ping Li Guan-QunLiu Zhi-Gang Liu Huo-Ming Shi Zheng-Hong Tang Qing-Sheng Tao Xiang-Yan Yuan Chao Zhai Jing Zhang Yan-Xia Zhang Yong Zhang Ming Zhao Fang Zhou Guo-Hua Zhou Jie Zhu Si-Cheng Zou 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2012年第9期1197-1242,共46页
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effecti... The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5°). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror’s surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67m×6.05 m) and active Schmidt mirror (5.74m×4.40 m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480 000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multiwaveband properties in celestial objects. 展开更多
关键词 techniques: wide field telescope - active optics - multi fiber - spectroscopy survey - data reduction
下载PDF
Periodic Packing Mode for Trickle-Bed Reactors: Experiments and Modeling 被引量:2
17
作者 刘国柱 米镇涛 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2004年第3期372-378,共7页
A periodic packing mode of trickle-bed reactor (TBR) for the gas limited reaction was proposed. Hy-drogenation of 2-ethylanthraquinone over Pd/Al2O3 in a laboratory-scale TBR was taken as a test reaction for determini... A periodic packing mode of trickle-bed reactor (TBR) for the gas limited reaction was proposed. Hy-drogenation of 2-ethylanthraquinone over Pd/Al2O3 in a laboratory-scale TBR was taken as a test reaction for determining whether the periodic packing mode is advantageous. The effects of operating conditions and packing type on TBR performance were experimentally examined to demonstrate the cause-effect relationships. A mathe-matic model of TBR considering axial dispersion and fractional wetting was developed to quantitatively illuminate the reason of performance enhancement. 展开更多
关键词 trickle-bed reactor periodic packing mode MODELING HYDROGENATION 2- ethylanthraquinone
下载PDF
PW-CFRP弹性性能预测及三维钻削仿真
18
作者 周强 陈燕 +5 位作者 王晓宇 张川川 陈雪梅 刘元吉 陈清良 勾江洋 《金刚石与磨料磨具工程》 CAS 北大核心 2023年第5期592-603,共12页
平纹编织结构碳纤维增强树脂基复合材料(plain-woven carbon fiber-reinforced plastic,PW-CFRP)展现出高损伤容限特性,在航空航天领域应用广泛。针对PW-CFRP钻削仿真中由于其材料弹性性能变化导致单一尺度钻削仿真难以体现实际钻削力... 平纹编织结构碳纤维增强树脂基复合材料(plain-woven carbon fiber-reinforced plastic,PW-CFRP)展现出高损伤容限特性,在航空航天领域应用广泛。针对PW-CFRP钻削仿真中由于其材料弹性性能变化导致单一尺度钻削仿真难以体现实际钻削力的问题,研究其弹性性能预测及多尺度三维钻削仿真。基于周期性边界条件的弹性性能参数预测模型,利用预测的材料弹性性能参数,采用多尺度有限元方法,仿真PWCFRP的三维钻削并开展试验验证。研究结果表明:基于周期边界条件的有限元法能准确预测编织复合材料的弹性常数;在剪切载荷下,其编织单胞的边界面均由平面变成曲面,发生凸凹翘曲变形;基于刚度预测模型基础的PW-CFRP三维钻削仿真模型能够准确预测制孔过程中的轴向力、扭矩;在相同工艺参数下,制孔轴向力和扭矩的仿真预测与试验结果相对误差分别为14.2%和8.5%。 展开更多
关键词 CFRP 周期性边界条件 多尺度分析 弹性常数 钻削仿真
下载PDF
A Comparative Study of Acute Hemodynamic Effects of Multi -site Cardiac Pacing in patients with cardiac function NYHA class ⅠtoⅡ without bundle branch block 被引量:2
19
作者 朱参战 崔长琮 +5 位作者 张全发 薛小临 刘维维 刘引会 《South China Journal of Cardiology》 CAS 2001年第2期101-105,共5页
Objective To compare the acute hemodynamic effects of five different pacing modes in patients with cardiac function NYHA class Ⅰ to Ⅱ without bundle branch block (BBB). Methods This study included 12 patients (SSS ... Objective To compare the acute hemodynamic effects of five different pacing modes in patients with cardiac function NYHA class Ⅰ to Ⅱ without bundle branch block (BBB). Methods This study included 12 patients (SSS 7, Ⅲ°AVB 5) undergoing pacemaker implantation. Right ventricular apex (RVA), right ventricular outflow tract (RVOT), right ventricular bifocal (RV-Bi), left ventricular base (LVB) and bi -ventricular (Bi-Ⅴ) pacing at 60 -80 ppm were done in VVI mode prior to implantation of DDD pacemaker. The cardiac index (CI), mean pulmonary artery pressure (mPAP) and pulmonary capillary wedge pressure (PCWP) were measured with Swan - Ganz thermodilution catheter after 5 minutes of each pacing mode. Results (1) Comparing to pacing at RVA (CI: 2. 41± 0. 38 L/min per m2, PCWP: 16. 7 ±3.3 mmHg), the CI increased and the PCWP decreased significantly in pacing at RVOT(CI: 2. 63 ± 0.46, PCWP: 13. 8±2. 3), LVB(CI: 2. 78±0.52, PCWP: 14. 4±3.1), RV-Bi(CI: 2. 83±0.57, PCWP: 12. 8± 2. 5) and Bi -Ⅴ pacing (CI: 2. 94± 0.60, PCWP: 12. 7±2. 5), P < 0. 01, respectively. (2) The CI of RV-Bi and Bi-Ⅴ pacing was higher than that of RVOT and LVB pacing, the PCWP was lower, P < 0. 05, respectively. (3) There was no significant difference between RV - Bi pacing and Bi-Ⅴ pacing in CI and PCWP. Conclusion There is no significant difference between RV - Bi pacing and Bi -V pacing in the acute hemodynamic effects; however,dual - site pacing is much better than single site pacing in that aspect for patients with cardiac function NYHA class Ⅰ to Ⅱ without BBB. Among single site pacing, the RVOT and LVB pacing is better than RVA pacing in cardiac function. 展开更多
关键词 multi - site cardiac pacingHemodynamics
下载PDF
Multi-Objective Production Planning Using Lexicographic Procedure
20
作者 Mohamad Sayed Al-Ashhab Taiser Attia Shadi Mohammad Munshi 《American Journal of Operations Research》 2017年第3期174-186,共13页
This paper presents a multi-objective production planning model for a factory operating under a multi-product, and multi-period environment using the lexicographic (pre-emptive) procedure. The model objectives are to ... This paper presents a multi-objective production planning model for a factory operating under a multi-product, and multi-period environment using the lexicographic (pre-emptive) procedure. The model objectives are to maximize the profit, minimize the total cost, and maximize the Overall Service Level (OSL) of the customers. The system consists of three potential suppliers that serve the factory to serve three customers/distributors. The performance of the developed model is illustrated using a verification example. Discussion of the results proved the efficacy of the model. Also, the effect of the deviation percentages on the different objectives is discussed. 展开更多
关键词 multi-OBJECTIVE Production PLANNING GOAL PROGRAMMING multi-Products and multi-periods
下载PDF
上一页 1 2 68 下一页 到第
使用帮助 返回顶部