实践十号返回卫星时间同步系统设计与验证

根据返回式卫星的特点,卫星在轨飞行包括两个阶段的时间同步工作模式：1)“返回舱和仪器舱在轨段组合体”时间模式;2)两舱分离后,“仪器舱留轨段”时间模式。因此,如何设计返回式卫星的时间系统,并进行优化使其在不同阶段完成不同任务,是返回式卫星时间系统设计的关键点。返回式卫星时间包括时间产生、时间维护、时间发布及时间传输。返回式卫星时间系统设计就是为了满足时间用户对时间同步精度的需求,通过特定方法和必要手段对星上时间产生、维护和发布机制进行相应的系统设计。针对实践十号返回式科学实验卫星时间同步需求、时间管理模型、时间系统架构以及时间系统的设计进行了说明,并对卫星在整星电测以及在轨运行的验证情况进行说明。     

Prediction of long and short time rheological behavior in soft glassy materials

We present an effective time approach to predict long and short time rheological behavior of soft glassy materials from experiments carried out over practical time scales. Effective time approach takes advantage of relaxation time dependence on aging time that allows time-aging time superposition even when aging occurs over the experimental time scales. Interestingly, experiments on a variety of soft materials demonstrate that the effective time approach successfully predicts superposition for diverse aging regimes ranging from subaging to hyperaging behaviors. This approach can also be used to predict behavior of any response function in molecular as well as spin glasses.     

An advanced time approach for acoustic analogy predictions

This paper deals with a new interpretation of the retarded time approach that is widely used in the prediction of acoustic fields from moving sources.A hierarchical inversion between the emission time and the reception time leads to advanced time approach. This consists in projecting the current status of a source in the observer time domain where the received signal is progressively built.The practical relevance of this methodology lies on two statements: no retarded time equations must be solved; an aerodynamic noise prediction can be processed parallelly to the aerodynamic computation.Theoretically, the advanced time approach differs from the retarded time approach only in one aspect. A signal emitted at a given instant by a point source, moving at subsonic as well as supersonic velocity, is received only one time by an observer moving at subsonic velocity. Consequently, only one value of the advanced time corresponds to a value of the emission time. The advanced time approach is herein applied to a retarded time solution of the Ffowcs Williams and Hawkings equation proposed by Farassat. The noise radiated by elementary acoustic sources in complex motion is then computed and checked against analytical solutions.     

脉冲激光测距时间间隔测量技术

在脉冲激光测距系统中,为提高时间间隔测量的精度,采用插值法进行时间间隔测量。在分析传统的数字计数法测量原理与误差的基础上,重点研究了插值法。其测量对象针对传统数字计数法中待测脉冲上升沿与下一个量化时钟脉冲上升沿之间的时间间隔。测量采用电容充放电技术,把时间间隔加入到一个时间扩展模块(通常为一只高精度的电容),实现时间上的放大,再对放大后的时间进行测量,可提高时间测量的精度。利用该方法得到的时间间隔测量精度可达到100 ps,对应于1.5 cm的测距精度。     

Prandtl–Ishlinskii hysteresis models for complex time dependent hysteresis nonlinearities

We introduce a new class of time dependent hysteresis models by combining the time dependent Prandtl–Ishlinskii model with functional nonlinearities. This combination improves the capability of the time dependent Prandtl–Ishlinskii model to characterize a class of complex time dependent hysteresis nonlinearities in smart actuators. The analytical inversion for the proposed time dependent hysteresis model is also presented in order to extend the inversion algorithm of the inverse time dependent Prandtl–Ishlinskii model for a class of complex time dependent hysteresis nonlinearities.     

Time-Reversed Dynamical Entropy and Irreversibility in Markovian Random Processes

A concept of time-reversed entropy per unit time is introduced in analogy with the entropy per unit time by Shannon, Kolmogorov, and Sinai. This time-reversed entropy per unit time characterizes the dynamical randomness of a stochastic process backward in time, while the standard entropy per unit time characterizes the dynamical randomness forward in time. The difference between the time-reversed and standard entropies per unit time is shown to give the entropy production of Markovian processes in nonequilibrium steady states.     

Solution to causality paradox upon total reflection

A dispute about the existence of an additional time (named as the Goos-H?nchen time) associated with the Goos-H?nchen shift in total reflection has recently arisen. At the same time, an inconsistency between the optical ray model and the electromagnetic theory also appears in the optical planar waveguide. By analyzing light propagation in an optical planar waveguide with both the zigzag-ray model and the electromagnetic theory, this paper shows that the Goos-H?nchen time really exists, and the total time delay upon total reflection upon an ideal nonabsorbing plasma mirror is the sum of the group-delay time and the Goos-H?nchen time. The causality paradox of total reflection of a TM wave upon an ideal nonabsorbing plasma mirror is also solved taking into consideration the negative Goos-H?nchen shift. Finally, the expression of the group velocity of the guided mode in optical planar waveguide was obtained, which clearly shows that the time delay upon total reflection is the sum of the group-delay time and the Goos-H?nchen time at given any time.     

聚龙一号主开关导通时刻对负载电流的影响

利用FCM-PTS程序与负载动力学程序耦合模拟研究了聚龙一号装置中主开关导通时刻对Z箍缩实验中负载电流峰值和上升时间的影响。结果表明,虽然聚龙一号装置上下支路三平板传输线的单向传输时间相差20 ns,但是当上下支路主开关导通时刻的时间差为22 ns时,负载电流的峰值最大,上升时间最短。将上下支路主开关导通时刻的时间差设置为20 ns和22 ns时,主开关导通时刻10 ns的抖动导致负载电流峰值损失最大值分别为163 kA和136 kA,上升时间最多分别延长2.4 ns和2.9 ns。     

量子体系中的时域压缩-频域展宽正、逆效应及其非经典性

本文利用全量子理论,对连续能谱量子体系和分立能谱量子体系中的时域压缩-频域展宽以及频域压缩-时域展宽效应进行了详细研究.在文献17构造时间算符的基础上给出频率算符ω∧的定义,根据时间算符t∧与频率算符ω∧之间的对易关系并利用Cauchy-Schwartz不等式导出t∧和ω∧所满足的测不准关系式.给出时域压缩和频域压缩的定义,并对时域/频域上的最小测不准态、压缩最小测不准态和压缩态等进行了详细讨论,指出了时域压缩和频域压缩的非经典性质.给出时域上的拟量子产生算符τ∧+(t)、拟量子湮没算符τ∧(t)和拟量子数算符N∧τ(t)的定义,首次建立了时域量子化的形式理论,并由此进一步提出了时域量子化的基本观点.     

Silex-I飞秒激光装置X射线探测系统时间特性北大核心CSCD

在Silex-Ⅰ飞秒激光装置上,利用32fs、800nm的激光辐照平面金靶,产生小于1ps的X射线脉冲,作为δ脉冲X射线源,研究XRD探测器的时间响应特性,并且探索X射线条纹相机时间分辨和分幅相机曝光时间的X射线标定方法。实验给出了XRD探测器的时间响应特性。解决了条纹相机和分幅相机触发晃动问题,给出了条纹相机时间分辨和分幅相机曝光时间的X射线标定方法,初步给出条纹相机时间分辨和分幅相机曝光时间。     

Slow-time acceleration for modeling multiple-time-scale problems

The numerical simulation of a system exhibiting a broad range of time scales can be very expensive because the time discretization will in general need to resolve the smallest time scale, and the simulation will have to extend over many times the longest time scale. However, it is common that not all the time scales are of interest for a particular problem. When the long time scales are of primary interest, a number of techniques are available to eliminate the unwanted short time scales from consideration. When the short time scales are of primary interest, a technique for mitigating the consequences of anomalously long time scales is needed. The “slow-time acceleration” technique presented here has been developed to address this problem. In the slow-time acceleration technique, a modified evolution equation is developed in which the longest time scale is much shorter than that of the original system, and which has the same multi-time scale asymptotic structure as the original system. As an example, this approach is applied to the numerical simulation of solid-propellant rockets in which the long time scale is associated with the regression of the burning propellant.     

Transmission time of a particle in the reflectionless Sech-squared potential: Quantum clock approach

We investigate the time for a particle to pass through the reflectionless Sech-squared potential. Using the Salecker-Wigner and Peres quantum clock an average transmission time of a Gaussian wave packet representing the particle is explicitly evaluated in terms of average momentum and travel distance. The average transmission time is shown to be shorter than the time of free-particle motion and very close to the classical time for wave packets with well-localized momentum states. Since the clock measures the duration of scattering process the average transmission time can be interpreted as the average dwell time.     

光谱仪动态采样时间特性的研究

在实时传输的光谱仪数据采样中,通常存在采样时间间隔不等的现象,这使得实时传输光谱仪在一些特殊场合的应用受到较大的限制,如在预测能力更强,检测精度更高的动态光谱分析法中。而恰恰在动态光谱法等时间分辨光谱分析中对光谱信号的采样定时特性要求更高,时间间隔不等会直接影响光谱分析的结果,得到失真的结论。同时与一般采样所不同的是,光谱仪是一定时间的积分采样,这无形中增加了对光谱仪定时采样特性研究的难度。因此,巧妙地利用锯齿波的幅值与时间存在一线性编码的关系,对某一型号的光谱仪进行采样时间及采样时间间隔的测试与分析,测试表明采样时间与积分时间的设置相关,同时时间间隔与积分时间也息息相关,进一步探究了该型号光谱仪在不同积分时间下采样时间间隔波动的范围。研究对注重光谱时间特性的分析法提供积分时间选取的参考依据,同时也提出了一种评估动态时间特性的方法,有利于光谱的动态特性的评估与应用。     

Quantum speed limits for Bell-diagonal states

The lower bounds of the evolution time between two distinguishable states of a system, defined as quantum speed limit time, can characterize the maximal speed of quantum computers and communication channels. We study the quantum speed limit time between the composite quantum states and their target states in the presence of nondissipative decoherence.For the initial states with maximally mixed marginals, we obtain the exact expressions of the quantum speed limit time which mainly depend on the parameters of the initial states and the decoherence channels. Furthermore, by calculating the quantum speed limit time for the time-dependent states started from a class of initial states, we discover that the quantum speed limit time gradually decreases in time, and the decay rate of the quantum speed limit time would show a sudden change at a certain critical time. Interestingly, at the same critical time, the composite system dynamics would exhibit a sudden transition from classical decoherence to quantum decoherence.     

Crystal growth by dynamic gradient reversal techniques - II. General comments on selection

The difference of the admittable time between growth time and dissolution time (delay time) within one period has been deduced. The general course of the growth parameters with time in gradient reversal methods is given. The general influence of experimental parameters on the selection effect is discussed.     

集合种群的延时效应

用简化的延时率函数模型对集合种群的稳定性和平均灭绝时间进行研究.对集合种群的定态概率分布函数和平均首通时间的分析和计算,发现：1)延迟时间增大将使集合种群在斑块中占有率减小;2) 随延迟时间增大,集合种群的灭绝时间将会减小. 关键词： 集合种群 延时效应 灭绝时间     

光折变晶体多重全息存储衍射效率均匀性的研究

推导出了全息多重存储时间递减曝光法各幅图象写入时间的解析表达式,研究了时间递减法和循环曝光法单次曝光时间、总曝光时间以及循环次数随存储图象的幅数之间的变化关系,结果表明时间递减法不但对记录系统的要求较低,而且也可获得相当均匀的衍射效率.     

百kJ级储能型Marx发生器建立时间及抖动

针对"闪光二号"百kJ级储能型Marx发生器,设计了研究其建立时间和抖动的实验方案,根据发生器开关击穿模式的不同,分别研究了典型排的建立时间和抖动与Marx发生器建立时间和抖动之间的关系,研究了开关工作系数与Marx发生器及其典型排建立时间的关系。对Marx发生器建立时间、发生器第一排和第二排建立时间的实验测量表明:Marx发生器第一排建立时间对整个发生器的贡献大于60%,前两排建立时间对整个发生器的贡献大于73%;Marx发生器建立时间抖动主要来源于发生器第一排建立时间抖动,第一排建立时间和抖动则主要来自于气体火花开关的击穿时延抖动。根据实验结果,分析了影响建立时间抖动的主要因素,提出了减小建立时间抖动的措施。     

再论时域的量子化及其物理本质

本文在提出时域吸收过程、时域辐射过程和时域无辐射跃迁过程等概念的基础上,进一步揭示出时域量子化的本质含义.对时间不可逆性问题进行了详细论证,并在给出“时间量子”t与光子能量ε_t之间的关系式t=h/ε_t(式中h为普朗克常量)的同时,进一步提出了时域量子化的新观点.利用t=h/ε_t这一关系对超快科学研究领域中的新时间尺度(诸如超短激光脉冲的脉宽压缩、阿秒界限的突破等)问题进行了详细讨论.最后,在对时空对称性以及时空对称结构等问题进行详细分析的基础上,进一步提出了量子时空观和量子化时空结构的基本观点.