检索结果-南通市图书馆

Spectral gap on path spaces with infinite time-interval

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 1999年第6期42卷 600-604页

作者：王凤雨 Department of Mathematics Beijing Normal University Beijing China

Under certain curvature condition, the existence of spectral gap is proved on path spaces with infinite time-interval.

关键词： spectral gap path space Riemannian manifold

Density-functional theory investigation of energy gaps and optical properties of Hg_(1-x)Cd_x Te and In_(1-x)Ga_x As

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2012年第1期21卷 404-408页

作者：郭三栋刘邦贵 Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China

We use a modified Becke-Johnson exchange plus a local density approximation correlation potential within the density functional theory to investigate the electronic structures of Hg1-xCdxTe and In1-xGaxAs with x being 0, 0.25, 0.5, 0.75, and 1. For both of the two series, our calculated energy gaps and dielectric functions （real part 61 and imaginary part 62） are in agreement with the corresponding experimental results with x being between 0 and 1. The calculated zero-frequency refractive index varies greatly with x for Hg1-xCdxTe, but changes little with for In1-xGaxAs, which is consistent with the real parts of their dielectric functions. Therefore, this new approach is satisfactory to describe the electronic structures and the optical properties of the semiconductors.

关键词： semiconductor gap optical property

Effects of hypokalemia on transmural dispersion of ventricular repolarization in left ventricular myocardium

在线全文

学校读者我要写书评

暂无评论

Asian Pacific Journal of Tropical Medicine 2013年第6期6卷 485-488页

作者： Jiang-Hua Zhong Shi-Juan Lu Mo-Shui Chen Zi-Bin Chen Liu Wang Ping-Sheng Wu Department of Cardiology Affiliated South Hospital of South Medical University Department of Cardiology Haikou People's Hospital

Objective:To observe effects of hypokalemia on transmural heterogeneity of ventricular repolarization in left ventricular myocardium of rabbit,and explore the role of hypokalemia in malignant ventricular arrhythmia（MVA）.Methods:A total of 20 rabbits were randomly divided into control group and hypokalemic group.Isolated hearts in the control group were simply perfused with modified Tyrode’s solution,and were perfused with hypokalemic Tyrode’s solution in hypokalemic group.Ventricular fibrillation threshold（VFT）,90%monophasic action potential repolarization duration(APD90) of subepicardial,midmyocardial and subendocardial myocardium,transmural dispersion of repolarization（TDR） and Cx43 protein expression in three layers of myocardium were measured in both groups.Results:VFT in the control group and the hypokalemic group were（13.40±2.95） V,and（7.00±1.49） V,respectively.There was a significant difference between two groups（P90 of three myocardial layers in the hypokalemic group were significantly prolonged than those in the control group（/’90in the hypokalemic group and the control group were（38.10±10\29） ms and（23.7015.68） ms,and TDR were（52.90r 14.55） ms and（36.10±12.44） ms,respectively.△APD90 and TDR in the hypokalemic group were significantly higher than those in the control group(P90 of midmyocardium was more significant in the hypokalemic group.Cx43 protein expression of all three myocardial layers were decreased significantly in the hypokalemic group（P90 was significantly increased {P<0.05).Reduction of Cx43 protein expression was more significant in the midmyocardium.Conclusions:Hypokalemic can increase transmural heterogeneity of Cx43 expression and repolarization in left ventricular myocardium of rabbit,and decrease VFT and can induce MVA more easily.

关键词： Hypokalemia gap junction Repolarization heterogeneity Midmyocardium

Application of the hybrid RANS/LES method on the hydraulic dynamic performance of centrifugal pumps

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

Journal of Hydrodynamics 2019年第3期31卷 637-640页

作者： Zheng-chuan Zhang Hong-xun Chen Zheng Ma Qun Wei Jian-wu He Hui Liu Chao Liu Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200072 China Chinese Ship Scientific Research Center Wuxi 214082 China College of Civil Engineering and Architecture Nanchang University Nanchang 330031 China Shanghai Marine Equipment Research Institute Shanghai 200031 China

The nonlinear hybrid RANS/LES method has been developed considering the simulation efficiency and accuracy to simulate the hydraulic dynamic characteristics of the centrifugal pump. It has been proved that the nonlinear hybrid RANS/LES method could effectively capture the unsteady flow structure and pressure pulsation in 2?D centrifugal pumps. To further investigate the hydraulic dynamic performance of a redesigned 3-D-gap drainage centrifugal pump, the nonlinear hybrid RANS/LES method is employed. Both numerical simulation and experimental results show that the hydraulic performance and pressure pulsation characteristics of the 3-D-gap drainage impeller centrifugal pump are significantly enhanced.

关键词： 3-D gap drainage blades nonlinear hybrid RANS/LES method pressure pulsation

Novel wide band gap alloyed semiconductors, x(LiGaO_2)_(1/2)-(1-x)ZnO, and fabrication of their thin films

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

Science China(Technological Sciences) 2009年第1期52卷 111-115页

作者： T. OMATA K. TANAKA A. TAZUKE K. NOSE S. OTSUKA-YAO-MATSUO Division of Materials and Manufacturing Science Graduate School of Engineering Osaka University 2-1 Yamada-oka Suita

Oxide semiconductor alloys of x(LiGaO2)1/2-(1-x)ZnO were fabricated by the solid state reaction between β-LiGaO2 and ZnO and rf-magnetron sputtering. For the solid state reaction, the wurtzite-type single phases were obtained in the composition range of x≤0.38. The formation range of the alloys was wider than that of the (Mg1-xZnx)O system, because the β-LiGaO2 possesses a wurtzite-derived structure and approximately the same lattice constants with ZnO. The electrical resistivity and energy band gap of the 0.38(LiGaO2)1/2-0.62ZnO alloyed ceramic were 0.45 Ωcm and 3.7 eV, respectively, at room temperature. For the alloying by sputtering, the films consisting of the wurtzite-type single phase were obtained over the entire composition range of x(LiGaO2)1/2-(1-x)ZnO. The energy band gap was controllable in the range from 3.3 to 5.6 eV. For the as-deposited film fabricated using the 0.4(LiGaO2)1/2- 0.6ZnO alloyed ceramic target, the energy band gap was 3.74 eV, and the electrical resistivity, carrier density and the Hall mobility at room temperature were 3.6 Ωcm, 3.4×1017 cm?3 and 5.6 cm2 V-1 s-1, respectively.

关键词： zinc oxide transparent conductor ultraviolet light band gap engineering oxide electronics

Object-based forest gaps classification using airborne LiDAR data

在线全文

学校读者我要写书评

暂无评论

Journal of Forestry Research 2019年第2期30卷 617-627页

作者： Xuegang Mao Jiyu Hou School of Forestry Northeast Forestry University School of Geographic and Oceanographic Sciences Nanjing University

Object-based classification differentiates forest gaps from canopies at large regional scale by using remote sensing data. To study the segmentation and classification processes of object-based forest gaps classification at a regional scale, we sampled a natural secondary forest in northeast China at Maoershan Experimental Forest Farm.Airborne light detection and ranging(LiDAR; 3.7 points/m2) data were collected as the original data source and the canopy height model(CHM) and topographic dataset were extracted from the LiDAR data. The accuracy of objectbased forest gaps classification depends on previous segmentation. Thus our first step was to define 10 different scale parameters in CHM image segmentation. After image segmentation, the machine learning classification method was used to classify three kinds of object classes, namely,forest gaps, tree canopies, and others. The common support vector machine(SVM) classifier with the radial basis function kernel(RBF) was first adopted to test the effect of classification features(vegetation height features and some typical topographic features) on forest gap classification.Then the different classifiers(KNN, Bayes, decision tree,and SVM with linear kernel) were further adopted to compare the effect of classifiers on machine learning forest gaps classification. Segmentation accuracy and classification accuracy were evaluated by using Mo¨ller's method and confusion metrics, respectively. The scale parameter had a significant effect on object-based forest gap segmentation and classification. Classification accuracies at different scales revealed that there were two optimal scales(10 and 20) that provided similar accuracy, with the scale of 10 yielding slightly greater accuracy than 20. The accuracy of the classification by using combination of height features and SVM classifier with linear kernel was91% at the optimal scale parameter of 10, and it was highest comparing with other classification classifiers, such as SVM RBF(90%), Decision Tree(90%), Bayes(90%),or KNN(87%

关键词： Forest gap Scale segmentation Classification feature LiDAR CHM Object based Machine learning

Analytical theory for shape stiffness

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2000年第4期43卷 337-343页

作者：张进之 Central Iron and Steel Research Institute Beijing 100081 China

The shape stiffness of mill m is defined as the crosswise rigidity of the unit width of steel plate, that is, m = k/b. By differentiating the steel plate crown equation in the vector model of steel plate shape, a new concise equation for the shape stiffness, kc = m + q, is obtained. Furthermore, by combining the calculation equation for steel plate crown derived from Castigliano’s theorem, an analytical calculation equation for the shape rigidity of rolled steel plate is derived. The correctness and practicability of the theory for the shape stiffness are demonstrated by comparing the results from the numerical calculation with the practical data of a rolling mill.

关键词： crosswise rigidity of mill shape stiffness of mill shape stiffness of rolled piece roll gap rigidity.

Causes of maize density loss in farmers’ fields in Northeast China

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2019年第8期18卷 1680-1689页

作者： ZHAO Ying-jie XING Sen ZHANG Qing-song ZHANG Fu-suo MA Wen-qi Key Laboratory of Plant-Soil Interactions Ministry of Education Beijing 100193 P.R.China College of Resources and Environmental Sciences China Agricultural University Beijing 100193 P.R.China College of Resources and Environmental Science Hebei Agricultural University Baoding 071001 P.R.China

Increasing plant density is an effective and important way to reduce maize yield gaps in Northeast China. However, the fact is that a significant plant density gap exists between optimum plant density and actual plant density in farmers’ fields.To quantify the density gap between planned planting density and final harvest plant density(HPD), we studied 60 farmers’ fields on three types of soil for three crop seasons from 2015 to 2017 by measuring their plant-plant distance, actual seedlings density(ASD), final HPD and yield. We also explored the potential causes of density loss by digging the places where the seedlings were missing for two consecutive years in 2016–2017. Results show that the three-year average HPD in farmers’ fields was 59 699 plants ha^–1, which was significantly lower than the planned density, including both the machine setting density(MSD;67 962 plants ha^–1) and theoretical plant density(TPD;67 467 plants ha^–1). No significant difference was found in HPD between years and soil types. However, for MSD and TPD, the average value in 2015 was significantly higher than that in 2016 and 2017. No significant difference between soil types was observed. Furthermore,the results from 2016 till 2017 indicated that a lack of seeds in the soil, a failure to germinate due to low-quality seeds,and a lack of seedlings breaking out of the soil due to environmental problems explained approximately 60.88, 10.33 and 28.80% of density loss, respectively. According to our survey, 63% of farmers did not know their own TPD and HPD, and 54% of farmers did not know the density loss. Therefore, we argue that farmers’ limited knowledge of density and density loss is an urgent problem that needs to be solved in maize production. These observations will be useful for determining best management practices for maize production and for providing helpful suggestions for machine improvement.

关键词： plant density maize production density loss density gap farmers’ fields

A theoretical study of the long-range-disorder mixed-spin antiferromagnet L_2BaNiO_5

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2006年第5期49卷 576-587页

作者： ZHANG Lin KONG Hongyan Nonlinear Research Institute Department of PhysicsBaoji University of Arts and ScienceBaoji 721007China Nonlinear Research InstituteDepartment of PhysicsBaoji University of Arts and ScienceBaoji 721007China

In this paper, we introduce a quasi-one-dimensional S = 1 antiferromagnet Heisenberg model, and some physical properties of antiferromagnet L2BaNiO5 without antiferromagnet long-range-order above the Néel temperature are analyzed based on the frame of two-time Green’s function theory. In a high temperature region, we calculate the correlation functions, and obtain excitation spectrum along Ni chains and the Haldane gap in this spectrum versus temperature. We find that the short-range correlation still exists at high temperature, which leads to the existence of Haldane gap in excitation spectrum. The increment of excitation energy in the spectrum along the Ni chain is found to be induced by the AF interaction between spins of rare-earth and Ni ions. Additionally, we also find that Haldane gap goes up with temperature increasing.

关键词： Heisenberg model two-time Green's-function method Haldane gap antiferromagnetic long-range order