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排序方式: 共有1585条查询结果,搜索用时 31 毫秒
981.
Jia Li 《Journal of Difference Equations and Applications》2013,19(4):649-666
We investigate dynamics of mosquito population models under two assumptions, respectively, and then formulate simple discrete-time compartmental susceptible-exposed-infective-recovered models for the malaria transmission based on the mosquito population models. We show that the mosquito population models either have robust dynamics or exhibit period-doubling bifurcation depending on the model assumptions. We derive a formula for the reproductive number of infection for the malaria model, which determines the stability of the infection-free fixed point. We then determine the existence of endemic fixed points for the malaria models. Using numerical simulations, we demonstrate that the dynamical characteristics of the mosquito populations, such as the global stability of the endemic fixed point and the appearance of a period-doubling bifurcation, are reflected in the dynamics of the malaria transmission. 相似文献
982.
Infinite Leslie matrices, introduced by Demetrius 40 years ago, are mathematical models of age-structured populations defined by a countable infinite number of age classes. This article is concerned with determining solutions of the discrete dynamical system in finite time. We address this problem by appealing to the concept of kneading matrices and kneading determinants. Our analysis is applicable not only to populations models, but also to models of self-reproducing machines and self-reproducing computer programs. The dynamics of these systems can also be described in terms of infinite Leslie matrices. 相似文献
983.
High-angle double-crystal X-ray diffractometry (HADOX) has been applied to measure the intensity around three reciprocal lattice points: 400, 040 and 004 of SrTiO3. Each point splits into two in the tetragonal phase according to the appearance of three kinds of domains; the temperature dependence of the intensity of component peaks at these points was measured under identical conditions. The results show that the domain population varies with temperature in a range of about 20 K below the transition. It is found, however, that the total intensities of 400 and 004 of the tetragonal phase are constant; this is observed by summing up the relevant intensity at the three reciprocal lattice points. 相似文献
984.
David W. Podlesak Gabriel J. Bowen Shannon O'Grady Thure E. Cerling James R. Ehleringer 《Isotopes in environmental and health studies》2013,49(2):259-279
An understanding of the factors influencing the isotopic composition of body water is important to determine the isotopic composition of tissues that are used to reconstruct movement patterns of humans. The δ2H and δ18O values of body water (δ2Hbw and δ18Obw) are related to the δ2H and δ18O values of drinking water (δ2Hdw and δ18Odw), but clearly distinct because of other factors including the composition of food. Here, we develop a mechanistic geographical information system (GIS) model to produce spatial projections of δ2Hbw and δ18Obw values for the USA. We investigate the influence of gender, food, and drinking water on the predicted values by comparing them with the published values. The strongest influence on the predicted values was related to the source of δ2Hdw and δ18Odw values. We combine the model with equations that describe the rate of turnover to produce estimates for the time required for a non-resident to reach an isotopic equilibrium with a resident population. 相似文献
985.
This article is concerned with the optimal control problem of age-structured population dynamics for the spread of universally fatal diseases. The existence and uniqueness of solution of the system, which consists of a group of partial differential equations with nonlocal boundary conditions, is proved. The Dubovitskii and Milyutin functional analytical approach is adopted in the investigation of the Pontryagin maximum principle of the system. The necessary condition is presented for the optimal control problem in fixed final horizon case. Finally, a remark on how to utilize the obtained results is also made. 相似文献
986.
Using the three-state model and time-dependent wavepacket method, the influence of the parameters of the intense femtosecond laser field on the wavepacket dynamic process of the double-minimum potential state 51Σ+ and the population of the ground and diabatic electronic states of NaLi are investigated. The calculations show that different femtosecond laser parameters result in different influences on the evolution of the wavepacket and the population of NaLi. With increasing laser intensity and wavelength the diabatic coupling strength between A and B states first strengthens and then weakens. The population interchanges between A and B states when the laser pulse disappears. The above results provide the suggestions and useful information for one to achieve quantum manipulation of the molecule in an experiment. 相似文献
987.
由于激光雷达光轴夹角的存在和光束质量分布的非均匀性, 导致理论回波信号与实际回波信号有较大差别, 需要对其进行校正. 基于数学推导和软件仿真, 给出了激光雷达重叠因子的数学表达式, 分析了光轴夹角导致的系统重叠因子在全程探测空间的变化情况; 分析了光束分布为高斯分布和均匀分布时的重叠因子变化情况; 对激光雷达的距离校正信号和Klett算法公式进行了重叠因子修正, 最后在对激光雷达系统参数标定的基础上, 在重叠区域利用修正的Klett公式对其所测得到的回波信号进行了修正, 在探测盲区利用斜率法修正距离校正信号, 进而得到了符合理论与实际情况的激光雷达在全程上校正的消光系数曲线.
关键词:
激光雷达
标定
重叠因子
消光系数 相似文献
988.
989.
《Journal of Coordination Chemistry》2012,65(1-4):327-340
Abstract The thermochromic phase transition of bis(N,N-diethylethylenediamine) copper(II) perchlorate has been studied by adiabatic calorimetry in the 12–359 K temperature range. A large heat capacity anomaly was observed at 317.64 K with a long heat-capacity tail extending down to ~200 K. The enthalpy and entropy of the phase transition were found to be δtrs H = 17.43 kJ mol?1 and δtrs S = 55.21 J K?1 mol?1, respectively. Together with a calorimetric study of a homologous thermochromic complex, bis(N,N-diethylethylenediamine)copper(II) tetrafluoroborate (J. Phys. Chem. Solids, 55, 99 (1994)), the nature of the present thermochromic phase transition is well described by a puckering motion of the copper-ligand chelate rings and a change in the ligand-field strength estimated on the basis of the angular overlap model. The correlation between structures, electronic spectra and thermal properties is discussed. 相似文献
990.
在3A"势能面上,在散射能为14~20 kcal/mol的范国内,运用准经典轨线方法对O+DCl→ OD+Cl进行了动力学研究.我们发现积分散射截面随着散射能的增加而增大,产物OD的振动分布发生了很强的粒子数的反转现象,且振动激发较弱、转动激发较强.后向散射居于主导地位,碰撞能的变化对产物转动取向的影响不大. 相似文献