Global Mission Sensitivity Study for Phased MissionSystem with Analysis of Variance Method

A comprehensive mission sensitivity analysis index based on Sobol's index called global mission sensitivity( GMS) was proposed in this paper which focused on analyzing the mission sensitivity of components of phased mission systems( PMS). The simulation strategy of GMS based on a Petri net and Monte Carlo method was presented which had broad applicability. Finally,the GMS and Birnbaum's sensitivity of components in a PMS example were compared. The GMS of component is demonstrated to be more adaptable to reflect the component mission sensitivity when the rated reliability parameters of components cannot be obtained, and components have state dependency or the system is subjected to common cause failure.

Inversion of 3-D crustal p-wave velocity structure in Ningxia and its neighborhood by using direct, reflected and refracted waves

In this paper, simultaneous inversions for hypocentres and three-dimensional (3-D) crustral P-wave velocitystructure of Ningxia and its neighborhood are performed, by using the data of direct P wave, reflected Pm andrefracted Pn phases from the Moho discontinuity. The number of arrival-time applied to the inversion is 11 816total, which are recorded by the Seismic Station Network of Ningxia from 1 107 local natural earthquakes happened since 1970. The LSQR algorithm with damping that has been developed in recent years to solve the largescale sparse matrix is adopted. At different steps of iterative computing process, weighting is made on the actionsof each earthquake at first and on each ray further, to aim at the inhomogeneous features of spatial distribution ofearthquake and ray. Numerical analogue and computational results of actual multi-group data and different iterative control processes, show that under a certain residual standard, there is obvious trade-off on the assignment oftravel-time residuals between medium parameters and earthquakes parameters (especially the origin time anddepth of earthquake), so the obtained solution is related to the selected initial values of medium parameters tosome extent, but there are the basically same variation features on different results in the almost same area. That isthe solution of surface layer has a close relation to the strata and landform. In Yinchuan basin there is obvious lowvelocity feature. and it coincides with the results of a man-made earthquake section crossing the region, tomographic patterns show that there are many low velocity regions in middle-lower crust, and it seems to have someconnections between the positions of historical strong earthquakes and the low velocity region or the anomalousvariations of velocity gradient.

Approximate Method for Reliability Assessment of Complex Phased Mission Systems

Phased-mission systems (PMSs) have wide applications in engineering practices, such as manmade satellites. Certain critical parts in the system, such as cold standby, hot standby and functional standby, are designed in redundancy architecture to achieve high reliability performance. State-space models such as Markov process have been used extensively in previous studies for reliability evaluation of PMSs with dynamic behaviors. The most popular way to deal with the dynamic behaviors is Markov process, but it is well known that Markov process is limited to exponential distribution. In practice, however, the lifetime of most machinery products can follow non-exponential distributions like the Weibull distribution which cannot be handled by the Markov process. In order to solve this kind of problem, we present a semi-Markov model combined with an approximation algorithm to analyze PMS reliability subjected to non-exponential failures. Furthermore, the accuracy of the approximation algorithm is investigated by comparing to an accurate solution, and a typical PMS (attitude and orbit control system) is analyzed to demonstrate the implementation of the method. © 2017, Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg.

Optically pumped terahertz sources

High-power terahertz(THz) generation in the frequency range of 0.1-10 THz has been a fast-developing research area ever since the beginning of the THz boom two decades ago, enabling new technological breakthroughs in spectroscopy, communication, imaging,etc. By using optical(laser) pumping methods with near-or mid-infrared(IR) lasers, flexible and practical THz sources covering the whole THz range can be realized to overcome the shortage of electronic THz sources and now they are playing important roles in THz science and technology. This paper overviews various optically pumped THz sources, including femtosecond laser based ultrafast broadband THz generation, monochromatic widely tunable THz generation, single-mode on-chip THz source from photomixing, and the traditional powerful THz gas lasers. Full descriptions from basic principles to the latest progress are presented and their advantages and disadvantages are discussed as well. It is expected that this review gives a comprehensive reference to researchers in this area and additionally helps newcomers to quickly gain understanding of optically pumped THz sources.