检索结果-南通市图书馆

Complete characterization of strictly positive real regions and robust strictly positive real synthesis method

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2000年第1期43卷 97-112页

作者：王龙郁文生 Department of Mechanics and Engineering Science Peking University Beijing 100871 China Institute of Automation Chinese Academy of Sciences Beijing 100080 China

The concept of weak strictly positive real regions is introduced, and its properties are discussed . By using the complete discrimination system for polynomials, complete characterization of the (weak) strictly positive real regions for transfer functions in coefficient space is given. A new effective method for robust strictly positive real synthesis is proposed. This method results in necessary and sufficient conditions for low-order stable interval polynomials and segment polynomials, and is also efficient for high-order cases. Numerical examples are provided to illustrate the effectiveness of this method.

关键词： control systems uncertainties strict positive realness robust synthesis weak strictly positive real regions complete discrimination system for polynomials.

Quantifying spatial scale of positive and negative terrains pattern at watershed-scale:Case in soil and water conservation region on Loess Plateau

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2017年第8期14卷 1642-1654页

作者： YANG Feng ZHOU Yi School of Geography and Tourism Shaanxi Normal University

The positive and negative terrains(P-N terrains) widely distributed across China's Loess Plateau constitute the dual structure characteristic of loess landforms. Analysis of loess P-N terrains at the watershed scale can serve to elucidate the structural characteristics and spatial patterns of P-N terrains, which benefits a better understanding of watershed evolution and suitable scales for loess landform research. The Two-Term Local Quadrat Variance Analysis(TTLQV) is calculated as the average of the square of the difference between the block totals of all possible adjacent pairs of block size, which can be used to detect both the scale and the intensity of landscape patches(e.g., plant/animal communities and gully networks). In this study, we determined the latitudinal and longitudinal spatial scale of P-N terrain patterns within 104 uniformly distributed watersheds in our target soil and water conservation region. The results showed that TTLQV is very effective for examining the scale of P-N terrain patterns. There were apparently three types of P-N terrain pattern in latitudinal direction(i.e., Loess Tableland type, Loess Hill type, and Transitional Form between Sand and Loess type), whereas there were both lower and higher values for P-N terrain pattern scales in all loess landforms in the longitudinal direction. The P-N terrain pattern alsoclearly presented anisotropy, suggesting that gully networks in the main direction were well-developed while others were relatively undeveloped. In addition, the relationships between the first scales and controlling factors(i.e., gully density, nibble degree, watershed area, mean watershed slope, NDVI, precipitation, loess thickness, and loess landforms) revealed that the first scales are primarily controlled by watershed area and loess landforms. This may indicate that the current spatial pattern of P-N terrains is characterized by internal force. In selecting suitable study areas in China' Loess Plateau, it is crucial to understand four control variables: the spatial sc

关键词： positive and negative terrains TTLQV Spatial pattern scale Loess landforms Loess Plateau

ON THE GENERALIZED DETERIORATED positive SEMI-DEFINITE AND SKEW-HERMITIAN SPLITTING PRECONDITIONER

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2019年第1期37卷 18-32页

作者： Davod Hezari Vahid Edalatpour Hadi Feyzollahzadeh Davod Khojasteh Salkuyeh Faculty of Mathematical Sciences University of GuilanRashtIran Department of Mathematical and Computer Science Technical Faculty University of BonabBonabIran Facultty of Mathematical Sciences University of Guilan.RashtIvan

For nonsymmetric saddle point problems,Huang et al.in [Numer.Algor.75 (2017), pp.1161-1191]established a generalized variant of the deteriorated positive semi-definite and skew-Hermitian splitting (GVDPSS)preconditioner to expedite the convergence speed of the Krylov subspace iteration methods like the GMRES method.In this paper,some new convergence properties as well as some new numerical results are presented to validate the theoretical results.

关键词： Saddle point problem Preeonditioner Nonsymmetric Symmetric positive definite Krylov subspaee method

Ricci positive Metrics on the Moment-Angle Manifolds

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

Chinese Annals of Mathematics,Series B 2019年第3期40卷 469-480页

作者： Liman CHEN Feifei FAN School of Mathematical Sciences Capital Normal University School of Mathematics Sun Yat-sen University

In this paper, the authors consider the problem of which(generalized) momentangle manifolds admit Ricci positive metrics. For a simple polytope P, the authors can cut off one vertex v of P to get another simple polytope P_v, and prove that if the generalized moment-angle manifold corresponding to P admits a Ricci positive metric, the generalized moment-angle manifold corresponding to P_v also admits a Ricci positive metric. For a special class of polytope called Fano polytopes, the authors prove that the moment-angle manifolds corresponding to Fano polytopes admit Ricci positive metrics. Finally some conjectures on this problem are given.

关键词： Moment-Angle manifolds Simple polytope Cutting off face positive Ricci curvature Fano polytope

Existence and global attractivity of a positive periodic solution of a class of delay differential equation

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 1998年第3期41卷 273-284页

作者：李永昆 Department of Mathematics Yunnan University Kunming China

The existence and the global attractivity of a positive periodic solution of the delay differential equation y·(t)=y(t)F[t, y(t-τ 1(t)),...,y(t-τ n(t))] are studied by using some techniques of the Mawhin coincidence degree theory and the constructing suitable Liapunov functionals. When these results are applied to some special delay bio-mathematics models, some new results are obtained, and many known results are improved.

关键词： delay differential equation logistic equation positive periodic solution global attractivity Fredholm mapping.

Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning

在线全文

学校读者我要写书评

暂无评论

Science China Earth Sciences 2006年第2期49卷 212-224页

作者： Krehbiel Paul New Mexico Institute of Mining and Technology Socorro New Mexico 87801 USA

The three-dimension spatiotemporal development characteristics of positive cloud-to- ground (CG) lightning discharges have been analyzed by using the data measured by the lightning mapping array system with high time and space resolution. The results indicate that a positive CG lightning discharge can be divided into three stages based on the characteristics of its development. The first stage is discharge process in cloud with a long duration preceding the return stroke. This process with an average of 370 ms propagated at velocity of 105 m/s and produced intensive radiation with a magnitude equal to that of the negative leader. During this stage, the lightning channels de-veloped horizontally in the positive charge region with few branches as the negative polarity break-down. During the stage after the return stroke of the positive CG lightning, the lightning channels propagated at velocity of 2 times faster than that before the return stroke. This stage involved lots of positive fast impulses and corresponded to the continuing current process producing less and dis-persed radiation points and more intensive radiation powers. During the final stage of the positive CG lightning, the lightning channels developed at velocity equal to that before the return stroke and the radiation points appeared mainly at the ends of channel. The spatiotemporal development character-istics of the positive CG lightning are very different from that of the negative CG lightning. All of the radiation points of the positive CG lightning appeared in the positive charge region of cloud. Little or no radiation was detected during the positive leader just before the return stroke. The duration of the positive CG lightning was an average of 730 ms. The positive CG lightning discharges with lasting time of 500―600 ms were 43%. 90% of the positive CG lightning discharges involved one return stroke, the most return stroke number being four. The current of the return stroke was an average of 36.5 kA with maximum and minimum values of 70 kA and

关键词： positive CG lightning, radiation characteristics, bidirectional leader.

Axillary lymph node management in breast cancer with positive sentinel lymph node biopsy

在线全文

学校读者我要写书评

暂无评论

World Journal of Clinical Oncology 2015年第1期6卷 1-6页

作者： Ioannis A Voutsadakis Silvana Spadafora Division of Medical Oncology Department of Internal Medicine Sault Area Hospital Sault Ste. Marie Ontario ON P6B 0A8 Canada Division of Clinical Sciences Northern Ontario School of Medicine Sudbury Ontario ON P0M Canada

The surgical treatment of localized breast cancer has become progressively less aggressive over the years.The management of the axillary lymph nodes has been modified by the introduction of sentinel lymph node biopsy. Axillary dissection can be avoided in patients with sentinel lymph node negative biopsies. Based on randomized trials data, it has been proposed that no lymph node dissection should be carried out even in certain patients with sentinel lymph node positive biopsies. This commentary discusses the basis of such recommendations and cautions against a general omission of lymph node dissection in breast cancer patients with positive sentinel lymph node biopsies. Instead, an individualized approach based on axillary tumor burden and biology of the cancer should be considered.

关键词： Tumor sub-types Micro-metastatic Node positive Breast cancer Axillary lymph node dissection Macro-metastatic Axillary recurrence

A positive AND MONOTONE NUMERICAL SCHEME FOR VOLTERRA-RENEWAL EQUATIONS WITH SPACE FLUXES

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 Computational Mathematics 2019年第1期37卷 33-47页

作者： Mario Annunziato Eleonora Messina Dipartimento di Matematica Universita degli Studi di Salerno Via G.Paolo II 132.84084 Fisciano (SA)Italy Dipartimento di Matematica e Applicazioni "R.Caccioppoli" Universita degli Studi di Napoli "Federico II"Via CintiaMonte S.Angelo80126 NapoliItaly

We study a numerical method for solving a system of Volterra-renewal integral equations with space fluxes,that represents the Chapman-Kohnogorov equation for a class of piecewise deterministic stochastic processes.The solution of this equation is related to the time dependent distribution function of the stochastic process and it is a non-negative and non-decreasing function of the space.Based on the Bernstein polynomials,we build up and prove a non-negative and non-decreasing numerical method to solve that equation, with quadratic convergence order in space.

关键词： Volterra renewal Piecewise deterministic process Monotone positive numerical scheme Bernstein polynomials

ON SHRINKING GRADIENT RICCI SOLITONS WITH positive RICCI CURVATURE AND SMALL WEYL TENSOR

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

Acta Mathematica Scientia 2019年第5期39卷 1235-1239页

作者：张珠洪陈志伟 School of Mathematical Sciences South China Normal University Guangzhou 510631 China Department of Applied Mathematics National Sun Yat-sen University Kaohsiung China

We show that closed shrinking gradient Ricci solitons with positive Ricci curvature and sufficiently pinched Weyl tensor are Einstein. When Weyl tensor vanishes, this has been proved before but our proof here is much ... 详细信息

关键词： shrinking gradient Ricci solitons positive Ricci curvature pinched Weyl tensor