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1.
Using the sequential decay process e<'+>e<'->→ J/ψ→ΛΛ, Λ→pπ<'->,Λ→pπ<'+> as an example, the procedure for deducing the full angular distribution is illustrated by adopting both the Jacob-Wick and Jackson conventions in the helicity formalism. To make sure that the final physical result is free of phase conventions, we point out that the coefficients that relate the angular momentum states in different coordinate systems of reference frames have to be taken into account properly in the procedure. The fact that those coefficients are constants suggests that the Jackson convention is favorable in dealing with the processes with sequential decays.  相似文献   

2.
We look at the dynamics of a Brownian particle with internal degrees of freedom and conformation dependent damping. Inhomogeneous damping apparently makes the problem a stochastic process with multiplicative noise. We derive the equilibrium distribution of such a system on the basis of a single postulate that the stochastic forces on the system produces no drift. Based on this postulate, we generalize the expression of the stochastic force for the equilibrium of such systems. The equilibrium probability distribution obtained deviates from the exact canonical form, although, the equipartition of energy remains intact when the internal degrees of freedom are integrated out. We also show a crucial local balance of the rate of average energy inflow and outflow as a consequence of the equilibrium probability distribution.  相似文献   

3.
考虑交通出行惯例的双向行人流模型研究   总被引:1,自引:0,他引:1       下载免费PDF全文
杨凌霄  赵小梅  高自友  郑建风 《物理学报》2011,60(10):100501-100501
推广了Baek等人最近提出的一个双向行人流模型,提出了两种改进策略,并从行人平均速度-密度关系、行人空间分布密度和位置分布等方面进行了数值分析. 研究发现,引入的两个新策略不仅可以提高行人流的平均速度,而且可以提高道路系统(尤其是道路中央区域)利用率,减轻拥堵状况,有效避免严重堵塞的发生. 改进的策略对行人的心理特点和行为特性等方面考虑更加全面,而且可以较好地模拟高密度的双向行人流. 关键词: 元胞自动机模型 双向行人流 交通惯例  相似文献   

4.
于惠存  曹祥玉  高军  杨欢欢  韩江枫  朱学文  李桐 《物理学报》2018,67(22):224101-224101
将超材料设计思想与微电机系统(micro-electro-mechanical system,MEMS)技术相结合,提出了一种宽带可重构反射型极化旋转表面.该结构由上层方形金属贴片、中间介质层、金属底板以及连接贴片与底板的金属通孔构成,通过在电流短路点处加载MEMS开关,使其具有电可调特性.仿真结果表明,当MEMS开关导通时,该结构能在7.78 GHz–14.10 GHz频带内将入射的线极化波转化为正交极化波并反射;当MEMS开关断开时,入射波则以同极化全反射.加工了实际的样品并进行了测试,结果与仿真符合较好.该结构具有结构简单易加工、器件个数少、工作频带宽、损耗低等优点,在电磁波动态调控中具有潜在应用价值.  相似文献   

5.
The Metre Convention was signed on May 20, 1875 with the mission “to assure the international unification and perfection of the metric system” (today the International System of Units SI). The Convention continues to fulfill this mission, notably with the redefinition of the SI at the 26th General Conference on Weights and Measures in November 2018. A key role in the drawing up of the Convention was played by Wilhelm Foerster, at the time Director of the German Weights and Measures Service and Director of the Berlin Observatory. Foerster and Adolph Hirsch, Director of the Neuchatel Observatory, were the principal architects of the Convention and both contributed very much to the early years of its operation, Foerster as President of the International Committee for Weights and Measures and Hirsch as Secretary. In this article, the origin of the Convention, the creation of the International Bureau of Weights and Measures established at Sevres, and the many contributions of Wilhelm Foerster are outlined.  相似文献   

6.
The change in the reading on a distant Earth clock from the point of view of a traveling twin who instantaneously reverses direction is calculated by considering the behavior of the Earth clock during the turnaround, performing an integral, and taking a limit.  相似文献   

7.
利用Gel'fand基和对相因子约定的分析,编写了一个计算SU(3)Clebsch-Gordan(C-G)系数的Mathematica软件。其计算结果与广义Condon-Shortley相因子约定下的结果一致。  相似文献   

8.
大功率脉冲TEA CO2激光器的放电腔在不同工作气压和不同配气比例条件下对激光器输出能量和电光转换效率均有较大影响,因此,通过充气压力从30kPa到60kPa的改变和配气比例CO2:N2=1:1到CO2:N2=1:4的变化,可以改变激光器的输出能量,提高激光器电光转换效率。实验结果表明:当CO2:N2的配气比例为1:3时,激光器输出的电光转换效率存在最佳点。在最佳配气比例CO2:N2:He=3:9:28,总气压40kPa和注入激励电能保持不变的情况下,激光器单脉冲放电时的输出能量为24.6J;激光器高重复频率放电运转时的电光转换效率达16.4%。激光器的最高放电频率可以达到500Hz并且连续稳定运行工作。  相似文献   

9.
Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.  相似文献   

10.
A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.  相似文献   

11.
Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·104 Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.  相似文献   

12.
The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.  相似文献   

13.
14.
A multi-conjugate adaptive optics (MCAO) can offer a possibility of widening field of view (FOV) characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle's expressions of two deformable mirrors (DMs) MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.  相似文献   

15.
Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.  相似文献   

16.
17.
We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.  相似文献   

18.
Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.  相似文献   

19.
A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.  相似文献   

20.
Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.  相似文献   

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