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991.
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994.
众所周知, 风场分解与重构最有效的方法就是引入速度势和流函数, 其一般通过求解两个Poisson 方程得到. 由于速度势和流函数在边界上的耦合性质,有限区域风场分解是不唯一的, 这对风场分解带来了很大困难. 本文采用变分伴随结合正则化方法来克服风场分解的不唯一性, 其核心是把速度势和流函数的边值作为控制变量来反演. 目标泛函由两部分组成, 一是衡量重构风场误差大小的观测项; 二是保证风场分解问题适定的正则化项, 其目的在于寻求具有气象意义的稳定正则化解. 数值试验结果表明, 在正确选取正则化参数后, 利用变分伴随结合正则化方法进行有限区域风场分解与重构是有效可行的. 相似文献
995.
We have precisely derived a “rigorous instantaneous formulation“ for transitions between two bound states when the bound states are well-described by instantaneous Bethe-Salpeter (BS) equation (i.e. the kernel of the equation is instantaneous“occasionally“). The obtained rigorous instantaneous formulation, in fact, is expressed as an operator sandwiched by two “reduced BS wave functions“ properly, while the reduced BS wave functions appearing in the formulation are the rigorous solutions of the instantaneous BS equation, and they may relate to Schr(o)dinger wave functions straightforwardly. We also show that the rigorous instantaneous formulation is gauge-invariant with respect to the Uem(1) transformation precisely, if the concerned transitions are radiative. Some applications of the formulation are outlined. 相似文献
996.
An attempt is made to study the interaction Hamiltonian,H
int =Gψ
2(x)U(φ(x)) in the Bethe-Salpeter framework for the confined states of theψ particles interactingvia the exchange of theU field, whereU(φ) = cos (gφ). An approximate solution of the eigenvalue problem is obtained in the instantaneous approximation by projecting the Wick-rotated
Bethe-Salpeter equation onto the surface of a four-dimensional sphere and employing Hecke’s theorem in the weak-binding limit.
We find that the spectrum of energies for the confined states,E =2m+B (B is the binding energy), is characterized byE ∼n
6, wheren is the principal quantum number. 相似文献
997.
腹部撞击伤时血流压力的变化对肝脏损伤的作用 总被引:1,自引:0,他引:1
在撞击载荷对动物下腹部撞击致伤、并测量了动物胸、腹主动脉和肝门静脉等主干血管内血流压力变化的基础上,分析和讨论了腹部撞击伤时血流压力的急剧升高及其传播对肝脏损伤的作用和程度。 相似文献
998.
土壤的加速侵蚀已成为当前全球性环境灾害之一.对土壤侵蚀及其预防、控制的研究引起了人们的普遍关注.本文通过对国外文献的广泛调研,系统地分析与评价了有关土壤风力侵蚀的研究进展. 相似文献
999.
I.IntroductionWindvelocitiesaroundbuildingsandwind-inducedpressuresonbuildingsurfaceareimportantparametersforbuildingdisign.Withtherapidadvanceofcomputertechnology,ithasbecomepossibletoevaluatethethree-dimensionalwind-turbulentflow'sbyusingnumericalsimulationtechniques.Atpresent.awidevarietyofnumericalapproacheshavebeendevelopedanddifferenttypesofturbulencemodellinghavebeenappliedforthepredictionofwindflowphenomena.Amongtheseapproaches,thenumericalsimulationbasedonthesteadyReynold'saveragedN… 相似文献
1000.
This paper deals with the identification of the wind profile along a flight trajectory by means of a two-dimensional kinematic approach. In this approach, the wind velocity components are computed as the difference between the inertial velocity components and the airspeed components. The airspeed profile is obtained from flight measurements. The inertial velocity profile is obtained by integration of the measured inertial acceleration. The accelerometer biases and the impact values of the inertial velocity components are determined by matching the computed flight trajectory with the measured flight trajectory, available from the digital flight data recorder and air traffic control radar. This leads to a least-square problem, which is solved analytically for both the continuous formulation and the discrete formulation. Key to the precision of the identification process is the proper selection of the integration time. Because the measured data are noise-corrupted, unstable identification occurs if the integration time is too short. On the other hand, if the integration time is too long, the hypothesis of two-dimensional motion (flight trajectory nearly contained in a vertical plane) breaks down. Application of the 2D-kinematic approach to the case of Flight Delta 191 shows that stable identification takes place for integration times in the range τ = 120 to 180 sec before impact. The results of the 2D-kinematic approach are close to those of the 3D-kinematic approach (Ref. 1), particularly in terms of the inertial velocity components at impact (within 1 fps) and the maximum wind velocity differences (within 2 fps). The 2D-kinematic approach is applicable to the analysis of wind-shear accidents in take-off or landing, especially for the case of older-generation, shorter-range aircraft which do not carry the extensive instrumentation of newer-generation, longer-range aircraft. 相似文献