期刊文献+
共找到2,229篇文章
< 1 2 112 >
每页显示 20 50 100
Limiting Property of the Distribution Function of L^p Function at Endpoints 被引量:1
1
作者 Shaozhen XU Dunyan YAN 《Journal of Mathematical Research with Applications》 CSCD 2016年第2期177-182,共6页
We consider the limiting property of the distribution function of L^p function at endpoints 0 and ∞ and prove that for λ 〉 0 the following two equations limλ→+∞λ^p({x : |f(x)| 〉 λ}) = 0, limλ→0+λ^... We consider the limiting property of the distribution function of L^p function at endpoints 0 and ∞ and prove that for λ 〉 0 the following two equations limλ→+∞λ^p({x : |f(x)| 〉 λ}) = 0, limλ→0+λ^p({x : |f(x)| 〉 λ}) = 0hold for f ∈ L^p(Rn) with 1 ≤ p 〈 ∞. This result is naturally applied to many operators of type(p, q) as well. 展开更多
关键词 Hardy-Littlewood maximal function limiting behavior distribution function
原文传递
THE AUTOMATIC GENERATION OF LIMIT STATE FUNCTION OF HINGED STRUCTURE
2
作者 车维毅 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 1991年第12期1187-1193,共7页
In this paper, the theorem of structure continual variation of truss structure in the analysis of structure reliability is derived, and it is used to generate limit state function automatically. We can avoid repeated ... In this paper, the theorem of structure continual variation of truss structure in the analysis of structure reliability is derived, and it is used to generate limit state function automatically. We can avoid repeated assembly of global stiffness matrix and repeated inverse operations of the matrix caused by constant changes of structure topology. A new criterion of degenerate of the structure into mechanism is introduced. The calculation examples are satisfactory. 展开更多
关键词 hinged structure continual variation theorem limit state function
在线阅读 下载PDF
THE SPHERICAL FUNCTIONS AND THE CENTRAL LIMIT THEOREM ON SU(2,2)/S(U(2)×U(2))
3
作者 杨乔华 张钦 《Acta Mathematica Scientia》 SCIE CSCD 2007年第4期867-874,共8页
Let G = SU(2, 2), K = S(U(2) × U(2)), and for l ∈ Z, let {Tl}l∈z be a one-dimensional K-type and let El be the line bundle over G/K associated to Tl. It is shown that the Tl-spherical function on G is g... Let G = SU(2, 2), K = S(U(2) × U(2)), and for l ∈ Z, let {Tl}l∈z be a one-dimensional K-type and let El be the line bundle over G/K associated to Tl. It is shown that the Tl-spherical function on G is given by the hypergeometric functions of several variables. By applying this result, a central limit theorem for the space G/K is obtained. 展开更多
关键词 Spherical function central limit theorem hypergeometric function
在线阅读 下载PDF
Assessment of the 2 Conventional Physiotherapy Sessions Alone versus One Session Associated to Kabat’s Method in the Rehabilitation of Buruli Ulcer Patients (PUB), with Functional Limitations in the District Hospital of Akonolinga, Cameroon
4
作者 Fred Dikongue Dikongue Faustin Tsatedem Atemkeng +4 位作者 Joseph Fondop Jean Hubert Donfack Alain Djam Nkomo Banga Mbida Mpoame 《Surgical Science》 2023年第6期428-435,共8页
Buruli ulcer (BU) is a chronic, indolent necrotizing disease of the skin and underlying tissues caused by Mycobacterium ulcerans, which may result in functional disability. This disease is the third most frequent infe... Buruli ulcer (BU) is a chronic, indolent necrotizing disease of the skin and underlying tissues caused by Mycobacterium ulcerans, which may result in functional disability. This disease is the third most frequent infection after leprosy and tuberculosis caused by a mycobacterium. The main objective of this study was to determine comparative effectiveness of conventional physiotherapy alone to its association with Kabat’s method in the management of post-Buruli ulcer functional limitations. This was an interventional randomized, comparative and prospective study. It took place at the district hospital of Akonolinga from the 12<sup>th</sup> June to 12<sup>th</sup> September 2016. The study was included, post-Buruli ulcer patients who matched the eligibility criteria, were under treatment in the physiotherapy unit, and who accepted to participate in our study. A questionnaire on the socio-demographic profile of participants, the ulcer localization, the limitation stage, previous medical history and functional mobility assessment scale was administered to the subjects before and after the intervention which lasted for twelve weeks. We had 2 groups: the case group received association of Kabat technique to conventional physiotherapy and the control group received conventional physiotherapy alone. We had 22 patients, 11 patients for the experimental group, 11 patients for the control group. The mean age was 26.18 years, 54.5% of female participation, 68.2% of leg localization, 59.1% patients with severe limitations of functional mobility, and preference for traditional medication 95.5%. After evaluation of efficiency, we concluded that there was no statistically significant difference between the two treatment protocols. Further studies with larger sample size are recommended. 展开更多
关键词 Buruli Ulcer functional limitations PHYSIOTHERAPY Kabat Technique
暂未订购
A Class of Strong Limit Theorems and Moment Generating Function Method 被引量:1
5
作者 Wen Hart LI Gao Rong LI Nan Bin CAO 《Journal of Mathematical Research with Applications》 CSCD 2012年第1期76-82,共7页
In virtue of the notion of likelihood ratio and moment generating function, the limit properties of the sequences of absolutely continuous random variables are studied, and a class of strong limit theorems represented... In virtue of the notion of likelihood ratio and moment generating function, the limit properties of the sequences of absolutely continuous random variables are studied, and a class of strong limit theorems represented by inequalities with random bounds are obtained. 展开更多
关键词 likelihood ratio strong limit theorem moment generating function.
原文传递
PADE APPROXIMANTS AS LIMITS OF RATIONAL FUNCTIONS OF BEST APPROXIMATION IN ORLICZ SPACE
6
作者 Li Jialiang Central China Normal University, China Department of Mathematics Central Normal University 《Analysis in Theory and Applications》 1994年第2期74-82,共9页
In this paper, we prove that the best rational approximation of a given analytic function in Orlicz space L~*(G), where G = {|z|≤∈}, converges to the Pade approximants of the function as the measure of G approaches ... In this paper, we prove that the best rational approximation of a given analytic function in Orlicz space L~*(G), where G = {|z|≤∈}, converges to the Pade approximants of the function as the measure of G approaches zero. 展开更多
关键词 RATIONAL MATH PADE APPROXIMANTS AS limitS OF RATIONAL functionS OF BEST APPROXIMATION IN ORLICZ SPACE AS
在线阅读 下载PDF
The Ill-Posedness of Derivative Interpolation and Regularized Derivative Interpolation for Non-Bandlimited Functions
7
作者 Weidong Chen 《Applied Mathematics》 2022年第1期87-100,共14页
In this paper, the ill-posedness of derivative interpolation is discussed, and a regularized derivative interpolation for non-bandlimited signals is presented. The convergence of the regularized derivative interpolati... In this paper, the ill-posedness of derivative interpolation is discussed, and a regularized derivative interpolation for non-bandlimited signals is presented. The convergence of the regularized derivative interpolation is studied. The numerical results are given and compared with derivative interpolation using the Tikhonov regularization method. The regularized derivative interpolation in this paper is more accurate in computation. 展开更多
关键词 Nonband-limited function Derivative Interpolation ILL-POSEDNESS REGULARIZATION
在线阅读 下载PDF
THE INTEGRAL AS A FUNCTION OF THE UPPER LIMIT AND AN ANALYTICAL SOLUTION TO PLANE STRAIN DRAWING AND EXTRUSION
8
作者 赵德文 赵志业 张强 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 1990年第8期759-765,共7页
A kinematically admissible velocity field which is different from Avitzur's is established in Cartesian Coordinates. An upper-bound analytical solution to strip drawing andextrusion is obtained by using the integr... A kinematically admissible velocity field which is different from Avitzur's is established in Cartesian Coordinates. An upper-bound analytical solution to strip drawing andextrusion is obtained by using the integral as a function of the upper limit in this paper. 展开更多
关键词 THE INTEGRAL AS A function OF THE UPPER limit AND AN ANALYTICAL SOLUTION TO PLANE STRAIN DRAWING AND EXTRUSION
在线阅读 下载PDF
Right prefrontal cortex is activated for perceiving postural limits: a functional near-infrared spectroscopy study
9
作者 Noriyuki Kamata Yoshimi Matsuo +2 位作者 Ayako Matsuya Satoru Inoue Kazuo Abe 《Health》 2009年第3期239-243,共5页
The purpose of this study was to investigate neuronal mechanisms active during the percep-tion of forward postural limits in a standing po-sition and to specify fall-related brain activity using optical functional nea... The purpose of this study was to investigate neuronal mechanisms active during the percep-tion of forward postural limits in a standing po-sition and to specify fall-related brain activity using optical functional near-infrared spectros-copy. The study group included six right-handed, healthy female volunteers (range: 19, 20 years). The optical imaging device comprised 16 opto-des designed to provide 24-channel recording of changes in hemoglobin oxygenation. We meas-ured the changes of oxygenated hemoglobin levels in the frontal region when subjects per-ceived reachability in a standing position. Com- pared with those in other regions, the oxygen-ated hemoglobin levels in the right frontal region compatible with the right prefrontal cortex sig-nificantly increased. This result suggests that brain activities in the right prefrontal cortex are related to perception of reachability. Overesti-mation of postural limits has been reported as one of the risk factor for falling. This overesti-mation might be induced by dysfunction in the prefrontal cortex, resulting in a failure to inhibit a motor program that would have caused a loss of balance in reaching. Activation of the right prefrontal cortex may be a key factor for pre-venting accidental falls in the elderly and in pa-tients with neurological disorders. 展开更多
关键词 POSTURAL limits FALLS functional NEAR-INFRARED Spectroscopy (fNIRS) PREFRONTAL CORTEX (PFC)
暂未订购
Iterative and adjusting method for computing stream function and velocity potential in limited domains and convergence analysis
10
作者 黎爱兵 张立凤 +1 位作者 臧增亮 张云 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 2012年第6期687-700,共14页
The stream function and the velocity potential can be easily computed by solving the Poisson equations in a unique way for the global domain. Because of the var- ious assumptions for handling the boundary conditions, ... The stream function and the velocity potential can be easily computed by solving the Poisson equations in a unique way for the global domain. Because of the var- ious assumptions for handling the boundary conditions, the solution is not unique when a limited domain is concerned. Therefore, it is very important to reduce or eliminate the effects caused by the uncertain boundary condition. In this paper, an iterative and ad- justing method based on the Endlich iteration method is presented to compute the stream function and the velocity potential in limited domains. This method does not need an explicitly specifying boundary condition when used to obtain the effective solution, and it is proved to be successful in decomposing and reconstructing the horizontal wind field with very small errors. The convergence of the method depends on the relative value for the distances of grids in two different directions and the value of the adjusting factor. It is shown that applying the method in Arakawa grids and irregular domains can obtain the accurate vorticity and divergence and accurately decompose and reconstruct the original wind field. Hence, the iterative and adjusting method is accurate and reliable. 展开更多
关键词 limited domain stream function velocity potential iteration and adjust-ment CONVERGENCE
在线阅读 下载PDF
基于ICF的智力残疾儿童言语功能障碍和沟通活动受限特征与康复干预 被引量:1
11
作者 易玲 周静 +3 位作者 陈雪芬 陈川帆 陈科伊 董慧繁 《中国康复理论与实践》 北大核心 2025年第4期398-405,共8页
目的系统分析智力残疾儿童言语和沟通障碍的特点,设计整体性的康复方案。方法运用《国际功能、残疾和健康分类》(ICF)的理论和方法,从身体功能和结构、活动和参与、环境因素等多个维度对智力残疾儿童的言语和沟通功能障碍特征进行深入... 目的系统分析智力残疾儿童言语和沟通障碍的特点,设计整体性的康复方案。方法运用《国际功能、残疾和健康分类》(ICF)的理论和方法,从身体功能和结构、活动和参与、环境因素等多个维度对智力残疾儿童的言语和沟通功能障碍特征进行深入分析。在言语康复和特殊教育情境下实施综合干预方法。结果在身体功能和结构方面,言语功能障碍常常表现为语言的心理功能、发音功能、言语的流畅性和节律功能等障碍。在活动和参与层面,表现为沟通障碍,包括说话、倾听、对话以及人际互动等方面可能存在障碍或困难。环境因素,如家庭支持、同伴态度、专业服务以及辅助沟通技术的可及性,对智力残疾儿童的言语功能和沟通功能的发展有重要的影响。本研究基于ICF架构提出了儿童的言语功能和沟通活动功能的系统性评估方法,强调从整体视角理解智力残疾儿童的言语功能障碍和沟通活动障碍,注重沟通活动功能对智力残疾儿童的学习和日常生活的影响。在言语康复治疗和教育康复情境下,针对智力残疾儿童的言语障碍和沟通活动障碍的特点,设计个别化的干预方法,注重培养儿童的功能性沟通技能,并将其融入到日常生活和教育活动中。辅助和替代沟通技术、自然情境下的语言干预、视觉支持以及同伴介导等干预均是有效的康复措施。结论本研究运用ICF架构和方法,对智力残疾儿童的言语功能和沟通活动功能进行了系统分析,从身体功能和结构、活动和参与以及环境因素3个层面,系统探讨了智力残疾儿童的言语功能和沟通活动功能的特征,并且提出了在言语康复治疗和教育康复情景下,推动智力残疾儿童言语功能和沟通活动功能发展的系统性方法,包括设计个别化干预方法、辅助技术应用、视觉辅助支持以及同伴介导等措施。 展开更多
关键词 智力残疾 儿童 言语功能障碍 沟通活动受限 国际功能、残疾和健康分类
暂未订购
生境隔离作用对喀斯特季节性雨林群落树种空间格局的影响 被引量:1
12
作者 李冬兴 向悟生 +6 位作者 丁涛 王登惠 农正权 龙继凤 郭屹立 李先琨 王斌 《广西植物》 北大核心 2025年第6期991-1005,共15页
森林群落内强烈生境异质性可能会驱动不同树种间形成空间隔离,从而塑造出与局域复杂生境相适应的群落树种空间结构。该文以广西喀斯特季节性雨林中具有不同生境异质性强烈程度的3个典型森林群落1 hm^(2)样地为研究对象,通过分析主要树... 森林群落内强烈生境异质性可能会驱动不同树种间形成空间隔离,从而塑造出与局域复杂生境相适应的群落树种空间结构。该文以广西喀斯特季节性雨林中具有不同生境异质性强烈程度的3个典型森林群落1 hm^(2)样地为研究对象,通过分析主要树种的种内空间分布格局和种间关联格局来量化群落树种空间结构,检测其对喀斯特局域生境隔离作用的响应规律。结果表明:(1)3个森林群落树种的空间分布格局整体上以中小尺度聚集分布为主,在较小尺度(0~13 m)上聚集分布比例为85%,在中尺度(13~30 m)上逐步降低至60%,在较大尺度(>30 m)上降低至20%以下;随着生境异质性强烈程度的增加,群落内中小尺度种内聚集分布的比例逐步增加,平均值分别为63.1%、89.5%、94.4%。(2)3个森林群落树种的种间关联格局整体上以空间隔离和部分重叠为主;在小尺度(0~3 m)上二者共占50%,在中小尺度(3~20 m)上占70%,在较大尺度(>20 m)上逐步降低至40%;随着生境异质性强烈程度增加,群落中小尺度种间空间隔离和部分重叠的比例逐步增加,平均值分别为60.4%、70.2%、83.7%。综上结果表明,强烈的局域喀斯特生境异质性会增加群落树种的种内聚集分布强度,提高群落不同树种之间产生空间隔离的概率,说明局域复杂生境的隔离作用是塑造喀斯特森林群落树种空间结构的重要因素。该研究强调,在喀斯特石漠化区域进行植被生态恢复时,需充分评估不同地段生境条件,并参考相应原生境森林群落来配置树种及其空间组合。 展开更多
关键词 种间关联 空间隔离 生境异质性 扩散限制 双关联函数
在线阅读 下载PDF
Inverse Limit of Spaces of Upper Semicontinuous Functions
13
作者 张德学 《Northeastern Mathematical Journal》 CSCD 2001年第1期49-52,共4页
Given a compact Hausdorff space X, U(X) denotes the compact Hausdorff space of all the upper semicontinuous functions from X to the unit interval with the dual lim inf topology. Then U is an endofunctor o... Given a compact Hausdorff space X, U(X) denotes the compact Hausdorff space of all the upper semicontinuous functions from X to the unit interval with the dual lim inf topology. Then U is an endofunctor on compact Hausdorff space. It is proved in this note that this functor preserves inverse limits. 展开更多
关键词 upper semicontinuous function continuous lattice lim inf convergence inverse limit
在线阅读 下载PDF
LIMITING WEAK-TYPE BEHAVIORS FOR CERTAIN LITTLEWOOD-PALEY FUNCTIONS 被引量:2
14
作者 Xianming HOU Huoxiong WU 《Acta Mathematica Scientia》 SCIE CSCD 2019年第1期11-25,共15页
In this paper, we establish the following limiting weak-type behaviors of Littlewood-Paley g-function g_φ: for nonnegative function f∈ L^1(R^n),■and ■where f_t(x) =t^(-n)f(t^(-1) x) for t > 0. Meanwhile, the co... In this paper, we establish the following limiting weak-type behaviors of Littlewood-Paley g-function g_φ: for nonnegative function f∈ L^1(R^n),■and ■where f_t(x) =t^(-n)f(t^(-1) x) for t > 0. Meanwhile, the corresponding results for Marcinkiewicz integral and its fractional version with kernels satisfying L_α~q-Dini condition are also given. 展开更多
关键词 limitING BEHAVIORS weak-type bounds LITTLEWOOD-PALEY g-functions Marcinkiewicz integrals L_α~q -Dini conditions
在线阅读 下载PDF
Effect of Intermittent Pneumatic Compression on Functional Level and Quality of Life in Community-Dwelling Older Adults with Limited Ambulation Due to Leg Pain: A Randomized Controlled Trial
15
作者 Weerasinghe Mudiyanselage Sujeewa Weerasinghe Thunpaththu Mudiyanselage Upul Sanjeewa Thunpaththu +4 位作者 Weerasinghe Mudiyanselage Sandali Anjana Weerasinghe Weerasinghe Mudiyanselage Shalindu Thushen Weerasinghe Pahala Walpola Gamarallage Shirani Walpola Dissanayaka Mudiyanselage Tharanga Padmini Dissanayaka Angelo Karunaratne 《Health》 2021年第10期1145-1169,共25页
Background and Purpose: Walking difficulties are defined as any reduction in speed, balance, or change of gait, causing limited ambulation. These difficulties are a common problem in older adults and may greatly affec... Background and Purpose: Walking difficulties are defined as any reduction in speed, balance, or change of gait, causing limited ambulation. These difficulties are a common problem in older adults and may greatly affect their quality of life (QOL) and restrict their personal independence and participation. This study aimed to determine the effect of intermittent pneumatic compression (IPC) on lower leg pain, walking capacity, functional mobility, ankle range of motion (AROM), and QOL of community-dwelling older people with walking difficulties. Methods: In this randomized controlled trial, 34 eligible participants with self-reported lower limb pain and limited ambulation were randomized either to the intermittent pneumatic compression intervention group (IPCIG) or static compression control group (SCCG). The IPCIG and SCCG were trained to receive IPC and SC respectively for both lower legs and instructed to continue the application independently at home for 15 minutes per session, 2 sessions a day, 7 days per week for 4 weeks independently at the home. Outcome measures of lower leg pain, AROM, walking capacity, and functional mobility were assessed at baseline and at the first, second, third, and fourth weeks after randomization. Quality of life was assessed at baseline and immediately after the intervention. Results and Discussion: IPCIG showed a more significant improvement compared to the SCCG at the post-interventional stage for QOL and all the subscales. The findings show that “80% improved QOL” is 53% higher with the application of IPC than with SC for 4 weeks. The IPCIG showed a more significant improvement in the 6-minute walk test (6 MWT) at the third and fourth weeks compared to the SCCG. A pairwise comparison of mean values of 6 MWT over 4 weeks within the IPCIG showed a significant difference between all the weeks. Pairwise comparisons between groups at each time point showed that the IPCIG showed a more significant improvement in the timed up and go (TUG) test at the third and fourth weeks compared to the SCCG. Pairwise comparison of mean values of TUG test within the IPCIG showed a significant difference over 4 weeks, except between the second and third weeks, fourth week, and third and fourth weeks. The IPCIG showed a more significant improvement in lower leg pain between all weeks except the first week compared to the SCCG. Pairwise comparison of mean values of lower leg pain over 4 weeks within the IPCIG showed a significant difference among all weekly outcomes except between 1 and 2 weeks. The IPCIG showed a more significant improvement in left and right ankle dorsiflexion ROM at the third and fourth weeks compared to the SCCG. Conclusions: The IPC was effective in reducing lower leg pain and increasing the AROM and improving the walking capacity, functional mobility level, and QOL of community-dwelling older people with walking disabilities. Walking disability in old age is a common condition requiring physical therapy. Intermittent pneumatic compression can be used as a physical therapy modality for this patient group. 展开更多
关键词 Intermittent Pneumatic Compression functional Level Quality of Life Older Adults limited Ambulation Leg Pain
暂未订购
新工科背景下数学与机械设计基础融合教学实践
16
作者 张彩霞 李世利 +1 位作者 安会明 赵莉 《陇东学院学报》 2025年第5期123-127,共5页
“新工科”建设需要探索专业分割转向跨界交叉融合,优质的课堂教学是“新工科”建设基础。为了建设优质的机械设计基础课堂教学,通过“三角函数”的理论与机械设计基础课程中机构运动简图的融合,实现“数形结合”的教学方式;借助“函数... “新工科”建设需要探索专业分割转向跨界交叉融合,优质的课堂教学是“新工科”建设基础。为了建设优质的机械设计基础课堂教学,通过“三角函数”的理论与机械设计基础课程中机构运动简图的融合,实现“数形结合”的教学方式;借助“函数的极限”思维与机械设计基础教学方法的融合,构建出了相关知识点的系统教学方法。教学实践表明,数学与机械设计基础的有机融合,有效提升学生对基础知识的应用技能,培养学生的创新思维能力。 展开更多
关键词 三角函数 函数的极限 机械设计基础 教学融合
在线阅读 下载PDF
局域与区域过程对生物多样性的影响:群落构建的饱和与开放
17
作者 韩博平 王璐 +2 位作者 刘振元 周婷婷 黄琦 《水生生物学报》 北大核心 2025年第1期29-40,共12页
自MacArthur和Wilson建立岛屿生物地理学的平衡模型以来,以生物多样性为核心的群落生态学进入了范式转变的阶段,从更为广阔的视角重新审视群落构建这一决定生物多样性的核心机制。与经典群落生态学不同,新范式的群落生态学将局域群落视... 自MacArthur和Wilson建立岛屿生物地理学的平衡模型以来,以生物多样性为核心的群落生态学进入了范式转变的阶段,从更为广阔的视角重新审视群落构建这一决定生物多样性的核心机制。与经典群落生态学不同,新范式的群落生态学将局域群落视为一个开放的单元,认为区域群落和集合群落内部的物种扩散与迁移是平衡局域群落中物种灭绝的关键力量。局域群落的物种组成与多样性是局域过程与区域过程共同作用的产物,局域过程包括生物过滤和非生物过滤,而区域过程包含了影响物种形成的地理、历史和进化过程。局域过程与区域过程在局域群落构建中的相对重要性具有时空依赖性。文章回顾了半个世纪以来群落生态学研究范式的变化,从群落构建、物种库与群落饱和性等概念入手,系统地介绍了基于局域-区域物种丰富度关系分析区域与局域过程相对重要性的方法及其局限性,并介绍了克服这些局限性的辅助分析方法。物种库是生物地理学的基础概念,物种库的物种数量与组成记录了地理与区域尺度上历史上发生的生态与进化过程,物种库为表述区域过程的作用提供了可定量化的变量。局域群落是区域物种库所有物种的子集,局域群落构建是这一子集形成的过程与机制。局域-区域物种丰富度关系是用于比较群落构建中区域与局域过程的相对重要性的直观方法,这种关系的非线性反映了群落的饱和性。由于这种关系受到空间尺度、环境条件和群落中物种特性的影响,在判读群落是否饱和时需要结合其他理论与经验方法。对于物种均处于同一营养级的群落而言,当局域尺度足够小时,容易检测到群落的饱和性。而对于包括多个营养级的群落,局域-区域物种丰富度关系的解读需要考虑跨营养级的相互作用。环境选择与种间相互作用都是通过性状实现的,实际观测的局域群落与随机群落的功能多样性比较可以辅助判断局域过程的性质与强度。准确定义物种库是理解局域群落构建与生物多样性维持机制的前提,同时应考虑物种库的大小与功能属性,这将促进我们对群落结构与生物多样性格局的理解与认识。 展开更多
关键词 物种库 区域群落 扩散限制 环境过滤 物种库功能多样性
在线阅读 下载PDF
一种水电机组调速系统稳定性分析方法及超低频振荡抑制
18
作者 汪芳宗 余坤 李默 《中国电机工程学报》 北大核心 2025年第10期3858-3864,I0024,共8页
水电机组调速系统包含死区以及限幅环节,是一个典型的非光滑动力系统,也是一个线性切换系统。若控制参数设置不合理,切换系统将产生切换振荡现象。水电机组调速系统已多次出现与调速死区及限幅相关的超低频频率振荡问题。目前,为分析水... 水电机组调速系统包含死区以及限幅环节,是一个典型的非光滑动力系统,也是一个线性切换系统。若控制参数设置不合理,切换系统将产生切换振荡现象。水电机组调速系统已多次出现与调速死区及限幅相关的超低频频率振荡问题。目前,为分析水电机组调速系统的稳定性,主要采用描述函数法,但描述函数法是一种频域工程近似方法,在实际应用中需满足一定的前提条件。为解决超低频振荡问题,该文提出一种基于时域状态空间的稳定性分析新方法,并给出相应的理论证明。该方法既可用于一般光滑动力系统的稳定性分析,也可应用于间断微分系统。将该方法应用于水电机组调速系统的稳定性分析及控制参数的优化设计,可以彻底避免超低频振荡现象。算例结果验证该方法的有效性。 展开更多
关键词 水电机组 调速系统 线性切换系统 超低频振荡 极限环 描述函数法 Filippov方法
原文传递
基于深度置信网络的旋转机械在线故障诊断
19
作者 郭俊杰 郭正红 《计算机测量与控制》 2025年第1期60-68,共9页
针对现有旋转机械在线故障诊断算法所存在的数据遍历耗时长,检测准确率低,故障分类准确率低等不足,提出一种基于深度置信网络的故障诊断算法;先基于受限的玻尔兹曼机搭建深度置信网络框架,利用数据标签在输入层和后端的受限玻尔兹曼机... 针对现有旋转机械在线故障诊断算法所存在的数据遍历耗时长,检测准确率低,故障分类准确率低等不足,提出一种基于深度置信网络的故障诊断算法;先基于受限的玻尔兹曼机搭建深度置信网络框架,利用数据标签在输入层和后端的受限玻尔兹曼机之间建立联系;然后利用k-means算法压缩聚类处理数据集降低数据集的规模和复杂度;最后在不同故障特征的分类诊断方面,引入加入核函数的SVM分类算法,提升对不同机械故障类型的分类精度;实验结果显示,提出的旋转机械故障在线诊断方案的迭代效率高,数据遍历耗时少,训练集和测试集F1指标的分别为97.9%和97.4%,优于传统故障诊断算法。 展开更多
关键词 深度置信网络 改进K-MEANS算法 受限的玻尔兹曼机 核函数 SVM
在线阅读 下载PDF
显著性理论下消费者受内外影响时软件公司免费策略研究
20
作者 赵娜 陈飔佳 +1 位作者 吴浩 李扬 《运筹与管理》 北大核心 2025年第5期193-200,I0072-I0083,共20页
消费者选择软件产品时,受个体偏好与网络外部性影响。基于显著性理论,采用统一参数刻画不同群体对产品属性的内在偏好异质性,将其划分为价格敏感型与质量敏感型,进而构建融合网络外部性的效用函数。通过求解不同市场结构下的均衡状态,... 消费者选择软件产品时,受个体偏好与网络外部性影响。基于显著性理论,采用统一参数刻画不同群体对产品属性的内在偏好异质性,将其划分为价格敏感型与质量敏感型,进而构建融合网络外部性的效用函数。通过求解不同市场结构下的均衡状态,探讨软件公司面向异质用户群体的最优免费策略。模型证明:随网络外部性强度递增,当消费者单位认知增量低于产品初始感知质量时,企业最优策略演化路径为时间限免→无免费→功能限免;当单位认知增量超过初始感知质量时,演化路径则为时间限免→功能限免。 展开更多
关键词 显著性理论 网络外部性 时间限免策略 功能限免策略
在线阅读 下载PDF
上一页 1 2 112 下一页 到第
使用帮助 返回顶部