检索结果-南通市图书馆

Relaxor ferroelectric behavior of BaBi_(4)ti_(4)O_(15) aurivillius ceramic

在线全文

学校读者我要写书评

暂无评论

Journal of Advanced Dielectrics 2013年第2期3卷 52-58页

作者： t.Badapanda R.K.Harichandan A.Mishra S.Anwar Department of Physics C.V.Raman College of Engineering BhubaneswarOdisha 752054India Department of Physics Centurion University of Technology&Management BhubaneswarOdisha 751020India Colloids&Materials Chemistry Institute of Minerals and Materials Technology BhubaneswarOdisha 751013India

Aurivillius type compound BaBi_(4)ti_(4)O_(15)(BBt)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius *** scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius *** temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the *** diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic *** dielectric relaxation obeyed the VogelFulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve *** temperature dependence of dielectric constant at temperatures much higher and lower than tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower *** other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.

关键词： Aurivillius compound diffuse phase transition relaxor ferroelectric P-E loop

Scaling Leaf Measurements to Estimate Whole Canopy Gas Exchanges of Cotton

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

American Journal of Plant Sciences 2016年第14期7卷 1952-1963页

作者： Dennis C. Gitz III Jeffrey t. Baker Robert J. Lascano Wind Erosion and Water Conservation Unit Cropping Systems Research Laboratory USDA-ARS1 Lubbock TX USA

Diurnal leaf and canopy gas exchanges of well-watered field grown cotton were measured. Our objective was to scale leaf-level values of transpiration and net assimilation to the whole canopy level using estimates of canopy leaf area. Single leaf gas exchange measurements were made with two portable photosynthesis systems and canopy measurements with four open Canopy Evapo-transpiration and Assimilation (CEtA) chamber systems. Canopy leaf area was measured at the end of the experiment and estimated during gas exchange by fitting values to a growth curve. Leaf level measurements were arithmetically scaled to estimate canopy level gas exchange based on canopy leaf area and then compared to the measured values. Scaled values of single leaf transpiration were very similar to canopy transpiration measurements, although both whole canopy transpiration and assimilation were overestimated around mid-day. We conclude that canopy cotton transpiration of well-watered field grown plants could be estimated within 5% throughout the day by scaling leaf level measurements to the whole canopy using measured canopy leaf area. Estimating canopy assimilation from leaf level measurements remains problematic.

关键词： Cotton Gossypium hirsutum Scaling Assimilation transpiration Drought Stress

通过航空POLDER数据估计地表二向性反射分布函数(英文)

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

遥感学报 1997年第S1期1卷 26-32页

作者： Y.Kawata K.takemata t.Yonekura

研究中，通过选择目标区的ＰＯＬＤＥＲ图象数据来估计目标的二向性反射分布函数，其主要结果可简述如下：１）我们发展了一种大气纠正算法，它适用于源自ＰＯＬＤＥＲ传感器的图象数据格式。通过这种算法，将连续的不同视角的ＰＯＬＤ... 详细信息

研究中，通过选择目标区的ＰＯＬＤＥＲ图象数据来估计目标的二向性反射分布函数，其主要结果可简述如下：１）我们发展了一种大气纠正算法，它适用于源自ＰＯＬＤＥＲ传感器的图象数据格式。通过这种算法，将连续的不同视角的ＰＯＬＤＥＲ陆地图象转化为一系列表面反照率图象，该过程考虑了多次散射。２）然后，选定２１个目标区，包括河流、水塘、城市、道路、森林等，其光谱二向性反射分布函数通过连续的反照率图象来估计。研究发现，水表面的二向性反射分布函数５５０ｎｍ，６５０ｎｍ，８５０ｎｍ处呈现朗伯体特征，同时发现有植被覆盖地表的二向性反射分布函数在５５０ｎｍ和６５０ｎｍ处大致为各向同性，而在８５０ｎｍ处则表现为各向异性。该文给出了所有靶区按经验二向性反射分布函数的拟合参数值。

关键词： POLDER 二向性反射分布函数(BRDF) 大气纠正多次散射

A Precise Model for Simulation of temperature Distribution in Power Modules

在线全文

学校读者我要写书评

暂无评论

Journal of Semiconductors 2001年第5期22卷 548-553页

作者：耿莉陈治明 R.Kruemmer t.Reimann J.Petzoldt 西安理工大学应用电子学系 Department of Electronics technical University of Ilmenau

the interaction between the active chips mounted and the same base plate is considered as a thermoelectrical coupling *** approach to coupling effect analysis of a multi-chip system is presented with IGBt as a *** element method is used to evaluate the temperature distribution in power *** precise electrothermal model is obtained by fitting the curve of transient thermal impedance with a finite series of exponential terms,in which,the thermal-coupling effect among chips is considered as a prediction of the highest transient temperature of the *** model can be used in many thermal monitoring *** ANSYS and PSPICE si- mulation software have been employed,and the simulation results agree with the experimental ones very well.

关键词： power electronics IGBt module thermal simulation thermal coupling

在线全文

学校读者我要写书评

暂无评论

半导体量子阱材料的调制光谱研究

Journal of Semiconductors 1991年第3期12卷 150-155页

作者：钱士雄袁述吴建耀李郁芬 t.G.Andersson 复旦大学物理系上海200433 Department of physics Chalmeers University of TechnologyGoteborgSweden

我们采用光调制透射方法从In_xGa_(1-x)As/GaAs单量子阱样品测量了调制透射谱,得到了InGaAs量子阱中激子的清晰的调制结构.由电场调制原理对调制透射谱进行拟合,得到了激子的跃迁能量.结果与其他测量以及理论计算结果有较好的一致.

关键词： InGaAs/GaAs 量子阱调制光谱

在线全文

学校读者我要写书评

暂无评论

逆向蒙特卡罗模拟在无序体系中的应用

中国科学：物理学、力学、天文学 2023年第3期53卷 142-159页

作者：江明辉于素波赖本聪张富祥马东 DOVE Martin t. 李工燕山大学亚稳材料制备技术与科学国家重点实验室秦皇岛066004 松山湖材料实验室东莞523000 四川大学计算机学院成都610065 School of Physical and Chemical Sciences Queen Mary University of LondonLondon E14NSUK 东莞理工学院机械系东莞523000

晶体学只能够给出有关晶体平均原子结构的信息,而结合逆向蒙特卡罗(Reverse Monte Carlo,RMC)模拟的全散射方法将同时包含原子的平均结构和局部尺度上原子间距、键角以及结构多面体的取向和形变等方面的信息,这也是RMC方法一个独特的优... 详细信息

晶体学只能够给出有关晶体平均原子结构的信息,而结合逆向蒙特卡罗(Reverse Monte Carlo,RMC)模拟的全散射方法将同时包含原子的平均结构和局部尺度上原子间距、键角以及结构多面体的取向和形变等方面的信息,这也是RMC方法一个独特的优势.近年来,借助第三代同步辐射加速器和散裂中子源,RMC方法在实验和理论上都有了较快的发展,同时数据质量高,保证了该方法在材料的局域波动和无序的精细结构研究中的适用性.本文从RMC基本原理和分析方法两个方面介绍了无序体系中的逆向蒙特卡罗方法,同时给出了一系列有助于理解的RMC模型实例.最后,对RMC方法的发展进行了展望.近年来我国对大科学装置的投入迅速增长,相信RMC方法搭载第四代高能量光源,必将在我国新材料的设计与开发中发挥重要的作用.

关键词： RMC 约束条件多数据拟合原子对分布函数近邻分析

在线全文

学校读者我要写书评

暂无评论

苹果果实日灼预测预报计算机模型

植物保护学报 2004年第1期31卷 69-73页

作者：张建光刘玉芳孙建设 Larry S Jerry t 河北农业大学园艺学院保定071001 美国华盛顿州立大学乔木果树研究与推广中心威纳奇华盛顿州98801

为了及时准确地预测预报苹果果实日灼发生的时间,提高预防措施的效果,特研制了本计算机模型。通过对树上活体果实表面温度进行生长季全程连续监测,同步对比相应的气象资料,研究了主要气象因子(包括气温、日照、风速和相对湿度)与果实表... 详细信息

为了及时准确地预测预报苹果果实日灼发生的时间,提高预防措施的效果,特研制了本计算机模型。通过对树上活体果实表面温度进行生长季全程连续监测,同步对比相应的气象资料,研究了主要气象因子(包括气温、日照、风速和相对湿度)与果实表面温度的相关性,确定了上述气象要素与果实表面温度变化的多元回归方程。此外,通过比较研究不同品种、果实发育期以及树势对果实日灼敏感性的差异,确定了不同品种果实日灼阈值温度以及这些因子在影响果实日灼中的效应参数。将模型预测值与田间果实温度实测值进行对比,验证该模型预报结果符合率达85.22％。近两年该模型已开始在美国华盛顿州果园试用。通过在本模型的用户界面下拉菜单中选择品种、月份和树势,并在相应位置输入当日11:00～14:00平均日照、气温、风速和相对湿度数值,即可得到当日是否发生果实日灼的预测预报结果。

关键词：苹果果实日灼预测预报计算机模型生理性病害气象因子果实表面温度

Review of Soil Water Retention Characteristic (SWRC) Models between Saturation and Oven Dryness

在线全文

学校读者我要写书评

暂无评论

Open Journal of Modern Hydrology 2014年第4期4卷 173-182页

作者： Vitalis K. too Christian t. Omuto Elijah K. Biamah John P. Obiero Department of Environmental and Biosystems Engineering University of Nairobi Nairobi Kenya

Soil water retention characteristic is the key soil property used in many applications in the fields of irrigation, hydrology, geotechnical engineering and soil science in general. Since the advent of digital soil mapping and digital soil assessment paradigms, there has been an upsurge of development of soil inference models and the need to increase accurate application of soil mapping products. All soils can be partially saturated with water and also near oven dryness. therefore, constitutive models for soils should ideally represent the soil behaviour over entire range. this paper reviewed commonly used SWRC models. In order to stem potential for biasness, the models were grouped into three categories depending on the number of fitting parameters, namely, five-parameter, four-parameter and three-parameter categories. the evaluation used correlation and residual standard error statistics to choose the best overall performing model and in each category. Its results serve as a guide for selecting the models to be preferred for fitting SWRC in case there are limitations to the number of suction potential levels in the measured data.

关键词： Water Retention Hydraulic Parameters Models

Estimation of exponential growth rate and basic reproduction number of the coronavirus disease 2019 (COVID-19)in Africa

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

Infectious Diseases of Poverty 2020年第4期9卷 60-65页

作者： Salihu S.Musa Shi Zhao Maggie H.Wang Abdurrazaq G.Habib Umar t.Mustapha Daihai He Department of Applied Mathematics Hong Kong Polytechnic UniversityHong KongChina Department of Mathematics Kano University of Science and TechnologyWudilNigeria JC School of Public Health and Primary Care Chinese University of Hong KongHong KongChina Shenzhen Research Institute of Chinese University of Hong Kong ShenzhenChina Collage of Health Sciences Bayero UnuversityKanoNigeria Department of Mathematics Federal University DutseDutseNigeria

Background:Since the first case of coronavirus disease 2019(COVID-19)in Africa was detected on February 14,2020,the cumulative confirmations reached 15207 including 831 deaths by April 13,*** has been described as one of the most vulnerable region with the COVID-19 infection during the initial phase of the outbreak,due to the fact that Africa is a great commercial partner of China and some other EU and American *** result in large volume of travels by traders to the region more frequently and causing African countries face even bigger health threat during the COVID-19 ***,the fact that the control and management of COVID-19 pandemic rely heavily on a country's health care system,and on average Africa has poor health care system which make it more vulnerable indicating a need for timely intervention to curtail the *** this paper,we estimate the exponential growth rate and basic reproduction number(R0)of COVID-19 in Africa to show the potential of the virus to spread,and reveal the importance of sustaining stringent health measures to control the disease in ***:We analyzed the initial phase of the epidemic of COVID-19 in Africa between 1 March and 13 April 2020,by using the simple exponential growth *** examined the publicly available materials published by the WHO situation report to show the potential of COVID-19 to spread without sustaining strict health *** Poisson likelihood framework is adopted for data fitting and parameter *** modelled the distribution of COVID-19 generation interval(GI)as Gamma distributions with a mean of 4.7 days and standard deviation of 2.9 days estimated from previous work,and compute the basic reproduction ***:We estimated the exponential growth rate as 0.22 per day(95%CI:0.20-0.24),and the basic reproduction number,R0,as 2.37(95%CI:2.22-2.51)based on the assumption that the exponential growth starting from 1 March *** an R0 at 2.37,we quantif

关键词： COVID-19 Reproduction number Pandemic Statistical modelling