凸柱体与摄动体的极值问题

本文证明了由Ｚｏｎｏｉｄ体生成的凸柱体的一个极值性质,并研究了在Ｊｏｈｎ基上的凸摄动体的最大Ｈａｕｓｏｄｏｒｆｆ距离和平均宽度的下界．

第三体摄动分析解的一种表达式

在太阳系中,大行星、小行星和卫星( 包括自然卫星和人造卫星) 等对应的运动问题,都可以处理成受摄二体问题,而摄动源又多为第三体.作为第三体的摄动天体,有的比运动天体离中心天体近,有的则相反,前者称为内摄天体,后者则称为外摄天体.对一个具体的运动天体,可以同时出现这两类摄动天体.但是,只要运动天体与摄动天体的轨道都建立在以中心天体( 质心) 为坐标原点的同一坐标系内,那么在一定条件下( 即除运动天体与摄动天体的轨道有交叉情况外) ,可以构造一种第三体摄动分析解的统一表达式,这种表达式特别有利于了解小行星和自然卫星的运动状况,既可以体现运动天体轨道变化的特征,也便于对共振问题( 包括平运动意义下的轨道共振和慢变量对应的长期共振) 的分析和讨论.在此给出这种表达式的具体形式.

第三体引力摄动的近地轨道卫星相对运动方程

针对受第三体引力摄动的近地轨道卫星,推导了基于参考卫星轨道要素RSV的卫星运动方程、以及卫星的相对运动方程。两组方程均以显式给出,形式简洁且较为精确。基于这两组方程,本文还定性地分析了第三体摄动对卫星(相对)运动的影响。

航摄中如何慢门追摄动体

慢门追摄动体，就是用慢速快门跟踪航摄运动中的物体。 这是一种摄影艺术表现手法，就是有意将快门速度降至30分之一秒以下，跟踪聚焦运动物体，在相机快门开启的瞬间，让镜头移动与被摄主体运动方向和速度保持一致，使运动中的主体清晰定格，前后左右的景物虚化成线条。达到突出主体夸张动势的视觉效果。

行星三体引力摄动对卫星探测器大气制动的影响

考虑行星引力在其卫星探测器大气制动过程中的显著摄动,建立了基于Milankovitch参数的平均轨道动力学模型并对土卫六探测器进行仿真。首先,将轨道参数转换为无奇异的Milankovitch参数,考虑探测卫星的大气阻力、扁率摄动以及行星引力摄动,建立了半解析轨道方程。其次,以土卫六探测器为对象,选择不同的土星初始方位角进行有大气和无大气情况下的数值仿真,并进行比较分析。结果表明,土星初始方位角的选择会引起土卫六大气制动轨道偏心率和近拱点高度在不同范围内震荡,极大地影响大气制动效果。

双球坐标下三体运动的描述

通过求解双球坐标下Ｌａｐｌａｃｅ方程，得到三体问题的引力势分布，并借助于Ｌａｇｒａｎｇｅ函数建立了三体运动的微分方程，其结果具有普遍性．

LOCAM-Ⅱ型高速摄影机在拍摄运动员掷标枪动作中的应用

本文通过对美国红湖有限公司(RED LAKE CORPORATION)的LOCAM—Ⅱ16毫米间歇式高速摄影机的最佳应用参数选择的探讨,试图为有关单位合理使用该机提供一些理论依据,力争做到摄影机的正确使用。同时结合LOCAM—Ⅱ型高速摄影机,介绍了我们协助西安体育学院生物力学专业研究生,在开展对掷标枪过程的生物力学研究时所采用高速摄影法的外场拍摄体会,给出了最佳应用技术参数的选择原则和实用图表。

太阳同步回归轨道的轨道面外运动及在轨数据分析

针对近地太阳同步回归轨道的轨道面外运动,基于在轨遥测数据分析了轨道倾角和降交点地方时的运动变化规律。日月三体摄动对轨道倾角产生了长周期和短周期的运动,基于数据驱动方法进行了不同周期运动的辨识与分解,并与经典的解析解进行了比对。解析解反映的倾角半月周期运动与在轨数据基本一致,可以作为倾角半月周期运动的预报依据。基于轨道面外运动特征,分析了自主轨迹保持任务中虚拟编队构形参数与轨道面外参数的相关性。在精确回归轨道保持时充分考虑了轨道面外运动的特征,降低了自主轨道面外控制的频次。研究结果可以作为轨道面外运动轨迹优化的基础。

目标天体极轨道卫星的轨道寿命

星际探测器轨道的特征与探测目的密切相关 ,对目标天体两极地区进行探测显然采用的是极轨道 (或接近极轨道 )。对于这类卫星 (或称轨道器 ) ,如果轨道半长径较大 ,则会因第三体摄动导致轨道偏心率增大 ,使其近星距减小到等于目标天体的赤道半径而落到该天体上 ,结束其运动寿命 ,即使目标天体不存在大气 (如月球等 )亦会如此。

0D-1D coupling model and 3D fluid-structure interaction model based on coronary CT angiography for displaying hemodynamic characteristics of coronary artery stenosis

Objective To observe value of 0D-1D coupling model and 3D fluid-structure interaction(FSI)model based on coronary CT angiography(CCTA)for displaying hemodynamic characteristics of coronary artery stenosis.Methods Based on CCTA data of the stenosed left anterior descending branch(LAD)in a patient with coronary heart disease,an 0D-1D coupling model and 3D FSI model were built,respectively.Then hemodynamic characteristic indexes,including the pressure,flow velocity and wall shear stress(WSS)were obtained in every 0.01 s during 1 s at 5 sampling points(i.e.sampling point 1—5)using these 2 models,respectively,and the consistencies of the results between models were evaluated with Spearman correlation coefficient r s.Results The time consuming for construction of 0D-1D coupling model and 3D FSI model was 0.033 min and 704 min,respectively.Both models showed basically distribution of the pressure,flow velocity and WSS of the stenosed LAD.For more details,the pressure at the stenosed segment of LAD and the proximal segment of stenosis were both higher,which gradually decreased at the distal segment of stenosis,and the flow velocity at the proximal segment of stenosis was in a relatively slow and uniform condition,with significantly increased flow velocity and WSS at the stenosed segment.Compared with 3D FSI model,0D-1D vascular coupling model was relatively unrefined and lack of distal flow lines when displaying blood flow velocity.For sampling point 2 at the stenosed segment of LAD,no significant consistency for pressure between 2 models was found(P=0.118),but strong consistency for the flow velocity and WSS(r s=0.730,0.807,both P<0.05).The consistencies of pressure,flow velocity and WSS between 2 models at the proximal and distal segment of stenosis,i.e.1,3—5 sampling points were week to moderate(r s=0.237—0.669,all P<0.05).Conclusion 0D-1D coupling model exhibited outstanding computational efficiency and might provide relatively reasonable results,while 3D FSI model showed higher accuracy for details and streamline when simulating LAD stenosis.

大面质比空间碎片在太阳光压和引力作用下的轨道演化

分析了较高轨道(a>10000 km)大面质比空间碎片的轨道动力学演化问题.重点讨论了位于地球同步轨道的空间碎片轨道演化问题,并给出轨道偏心率随时间演化的表达式.通过进一步分析得出,倾角大于63°26′的GTO轨道空间碎片,仅在J_2和第三体摄动影响下,会出现轨道偏心率升高;而对于大面质比空间碎片,在J_2项和太阳光压同时作用下,当近地点指向的角变率与太阳平黄经变化率接近时,会出现长期共振现象,导致轨道偏心率升高,近地点降低.分析还得出,轨道演化过程中,偏心率的最大值与初始轨道近地点的指向有关.

地球静止轨道CW方程建模误差分析

针对地球静止轨道的小倾角、小偏心率的特点,本文在瞬时密切轨道坐标系推导分析了CW方程的各类误差要素,包括地球非球形摄动、三体引力等环境误差,以及线性化误差、非圆轨道相关误差等。采用误差线性化方法结合CW方程解析解得到了J_(2)、偏心率相关误差项的解析表达式。数值计算表明:地球静止轨道下CW方程的误差项要素较多,与相对运动构型的尺寸、漂移特性等均相关。二次项误差、偏心率相关误差、J_(2)项相关误差量级相当,是地球静止轨道CW方程的主要误差源,同时呈现出常数和低频波动相结合的误差形式,分析结果可作为地球静止轨道高精度相对导航和制导设计的理论依据。

Analysis of the One Dimensional Steady State Semiconductor Multijunction Device Model with the Avalanche Effect *

In this paper we consider the stationary multijunction device model with the avalanche effect. Using the singular perturbation method, an approximation to the current voltage curve is obtained. The cause and the condition for the occurrence of saturation current is analyzed. Especially, it is pointed that the avalanche effect is responsible for the blowing up of the saturation current. We prove the existence of multiple steady state solution when the ionization rate is relatively small. Finally, some numerical examples are presented to show the reliability of the theoretical results.

Implications from protein uptake kinetics onto dextran-grafted Sepharose FF coupled with ion exchange and affinity ligands

Our previous studies have reported the presence of "chain delivery" effects of protein adsorption onto ion exchangers with polymer-grafted ion-exchange groups, such as dextran-grafted and poly(ethylenimine)-modified Sepharose gels. However, it is unclear if the "chain delivery" occurs on affinity adsorption with specific interactions. This work is designed to address this issue. A dextran-grafted Sepharose gel was prepared, and then the matrix was modified using diethylaminoethyl, a typical ion-exchange group, or octapeptide(FYCHWQDE), an affinity ligand for human immunoglobulin G(h Ig G) to prepare ion-exchange or affinity adsorbents, respectively.Results of h Ig G adsorption showed that the uptake rate represented by the effective diffusivity of h Ig G onto the dextran-grafted ion exchangers was obviously enhanced by the dextran grafting, indicating the presence of"chain delivery" of the bound proteins on the charged groups on the dextran chains. By contrast, the effective diffusivity of h Ig G changed little as ligand density increased on the dextran-grafted FYCHWQDE adsorbents.Their adsorption capacities decreased and effective diffusivities were not accelerated by the dextran grafting.Thus, this work clarified that grafted dextran could not accelerate h Ig G uptake rate on the affinity resins, or in other words, chain delivery did not occur on the specific interaction-based affinity adsorption.

Ontogenetic changes in feeding and food preferences of the dog conch Laevistrombus canarium Linnaeus 1758 (Mollusca： Gastropoda) from Merambong shoal, Malaysia

Laevistrombus canarium is one of the marine gastropod mollusks that have high commercial value, particularly in the aquaculture sector in Malaysia. This study was conducted to determine the feeding and food items of L. canarium at different ontogenetic stages （juveniles, sub-adults and adults） from Merambong shoals, Malaysia. Field observations on feeding activity were conducted, followed by detailed laboratory analysis on the stomach content. Five-minutes observations on randomly selected individuals were conducted at the field sampling site and their feeding activities were recorded with reference to age stage. Various shell sizes from each ontogenetic stage were randomly collected and quickly anaesthetized with ice and preserved in 10% formalin before being transported to the laboratory for stomach content analyses. Field observations showed that L. canarium mainly grazed on epiphytes occurring on seagrass （46.67%）, followed by sediment surface （40%） and epiphytes occurring on macroalgae （13.33%）. Stomach content analyses showed a significant difference （P〈0.05） in gastro-somatic index （Gasi） between the juveniles （0.39±0.05）, sub-adults （0.68±0.09） and adults （0.70±0.05） （P〈0.05）. Food items found in the conch stomach include diatoms, detritus, foraminifera, seagrass and macroalgae fragments, sand particles and shell fragments. The Index of Relative Importance （%IRI） indicates three main types of food dominated the three ontogenetic stages namely diatoms, sand particles and detritus. However, no significant difference （P〉0.05） was detected between the three main food items （diatoms, sand particles and detritus） among the ontogenetic stages. Therefore, feeding activity revealed the role of the dog conch in the marine food network. While, classification of the types of food consumed by L. canarium through stomach content analysis determines the particular position of the gastropod in the food chain. Further studies are needed to provide a better insight between trophic relationships ofL. eanarium with marine ecosystem.

Salsa dance and Zumba fitness: Acute responses during community-based classes

Background： Research interest in both partnered Latin dance and non-partnered Latin-themed aerobic dance has increased in recent years, likely a result of the gaining popularity of these types of instructor-led group classes among the mainstream dance and fitness audiences; however, the efficacy of these activities for the purposes of health promotion currently remains unclear. The purpose of this study was to simultaneously assess the physiological responses and psychological experiences during salsa dance and Zumba fitness in a community sample of physically inactive women. Methods： Twenty-four participants, aged 22-56 years, visited the laboratory to perform a graded exercise test for determination of maximal oxygen uptake and maximal heart rate. The participants then attended 2 partnered salsa dance and 2 non-partnered Zumba fitness classes each in a counterbalanced order over a 2-week period. The 1-h classes were taught by certified instructors in established venues in the Royal Borough of Kingston and the surrounding communities of London, UK. Physiological data were collected using a wrist-worn ActiGraph wGT3X＋ acceler- ometer with accompanying heart rate monitor and were processed using previously validated dance-specific techniques. Psychological experiences were measured via the Subjective Exercise Experiences Scale. Results： There was a significantly higher （p 〈 0.001） total time spent in moderate-to-vigorous physical activity （51.2± 3.1 vs. 32.6 ±5.9 min）, total energy expenditure （411±66 vs. 210 ± 46 kcal）, and total step count （6773 ± 556 vs. 4108 ±781 steps） during Zumba fitness when compared to salsa dance. Significant pre- to post-class improvements in positive well-being （p 〈 0.01, partial 7/2 = 0.4l） and psychological distress （p 〈 0.001, partial 02 = 0.72） were simultaneously observed for both salsa dance and Zumba fitness. Conclusion： The acute responses to classes of partnered Latin dance and non-partnered Latin-themed aerobic dance suggest that in physically inactive women participation is indeed efficacious in terms of community-based physical activity and psychosocial health promotion.

Extension of Tao-Mason Equation of State to Heavy n-Alkanes

In our previous paper we extended the Tao and Mason equation of state (TM EOS) to refrigerant fluids, using the speed of sound data. This is a continuation for evaluating TM EOS in predicting PVT properties of heavy n-alkanes. Liquid density of long-chain n-alkane systems from C 9 to C 20 have been calculated using an analytical equation of state based on the statistical-mechanical perturbation theory. The second virial coefficients of these n-alkanes are scarce and there is no accurate potential energy function for their theoretical calculation. In this work the second virial coefficients are calculated using a corresponding state correlation based on surface tension and liquid density at the freezing point. The deviation of calculated densities of these alkanes is within 0.5% from experimental data. The densities of n-alkanes obtained from the TM EOS are compared with those calculated from Ihm-Song-Mason equation of state and the corresponding-states liquid densities (COSTALD). Our results are in favor of the preference of the TM EOS over other two equations of state.

（2＋1）-Dimensional Electron Acoustic Solitary Waves in an Unmagnetized Collisionless Plasma with Vortex-Like Hot Electrons

In this paper, （2＋1）-dimensional electron acoustic waves （EAW） in an unmagnetized collisionless plasma have been studied by the linearized method and the reductive perturbation technique, respectively. The dispersion relation and a modified Kadomtsev-Petviashvili （KP） equation have been obtained for the EAW in the plasma considering a cold electron fluid and a vortex-like hot electrons. It is found from some numerical results that the parameter β（the ratio of the free hot electron temperature to the hot trapped electron temperature） effects on the amplitude and the Width of the electron acoustic solitary waves （EASW）. It can be indicated that the free hot electron temperature and the hot trapped electron temperature have very important effect on the characters of the propagation for the EASW.

Solution to the MHD flow over a non-linear stretching sheet by homotopy perturbation method

In this study,by means of homotopy perturbation method(HPM) an approximate solution of the magnetohydrodynamic(MHD) boundary layer flow is obtained.The main feature of the HPM is that it deforms a difficult problem into a set of problems which are easier to solve.HPM produces analytical expressions for the solution to nonlinear differential equations.The obtained analytic solution is in the form of an infinite power series.In this work,the analytical solution obtained by using only two terms from HPM solution.Comparisons with the exact solution and the solution obtained by the Pade approximants and shooting method show the high accuracy,simplicity and efficiency of this method.

Dynamics of Front Driven by Convection Field in Bistable Media

The front dynamics driven by a convection field in a model of FitzHugh-Nagumo type is studied both analytieMly and numerically. Saddle-node bifurcation induced by the convection field is found by using a singular perturbation analysis of front solutions. Convection field accelerates the B1och front propagating opposite the direction of convection field, but inhibits the Bloch front propagating along the direction of convection field. In addition convection field drives Ising front to travel opposite the direction of convection field.