A Space-Time Reverberation Model for Moving Target Detection

In recent years,moving target detection methods based on low-rank and sparse matrix decomposition have been developed,and they have achieved good results.However,there is not enough interpretation to support the assumption that there is a high correlation among the reverberations after each transmitting pulse.In order to explain the correlation of reverberations,a new reverberation model is proposed from the perspective of scattering cells in this paper.The scattering cells are the subarea divided from the detection area.The energy fluctuation of a scattering cell with time and the influence of the neighboring cells are considered.Key parameters of the model were analyzed by numerical analysis,and the applicability of the model was verified by experimental analysis.The results showed that the model can be used for several simulations to evaluate the performance of moving target detection methods.

Controlling cooperativity of a metastable open system coupled weakly to a noisy environment

The notion of cooperativity comprises a specific characteristic of a multipartite system concerning its ability to demonstrate a sigmoidal-type response of varying sensitivities to input stimuli in transitions between states under controlled conditions.From a statistical physics viewpoint,in this work we attempt to describe the cooperativity by the stability of a metastable open system with respect to irreversibility.To treat the evolution of a system weakly coupled to the environment in a kinetic framework,we consider two fluctuating energy levels of different dimensionalities,initial population of one level,reversible transitions of population between the levels,and irreversible depopulation of another level.An average is made over level fluctuations and environment vibrations so that an inter-level transition rate can be obtained accounting for the influences of external control on level position and dimensionality.It is found that the cooperativity of the two-level system is bounded approximately between 0.736 and unity,with the lower bound indicating worsening system stability.

Nanoscale fluctuation of stacking fault energy strengthens multi-principal element alloys

Chemical randomness and the associated energy fluctuation are essential features of multi-principal ele-ment alloys(MPEAs).Due to these features,nanoscale stacking fault energy(SFE)fluctuation is a natural and independent contribution to strengthening MPEAs.However,existing models for conventional alloys(i.e.,alloys with one principal element)cannot be applied to MPEAs.The extreme values of SFEs required by such models are unknown for MPEAs,which need to calculate the nanoscale volume relevant to the SFE fluctuation.In the present work,we developed an analytic model to evaluate the strengthening ef-fect through the SFE fluctuation,profuse in MPEAs.The model has no adjustable parameters,and all parameters can be determined from experiments and ab initio calculations.This model explains available experimental observations and provides insightful guidance for designing new MPEAs based on the SFE fluctuation.It generally applies to MPEAs in random states and with chemical short-range order.

Novel correction method for X-ray beam energy fluctuation of high energy DR system with a linear detector

A high energy digital radiography （DR） testing system has generated diverse scientific and technological interest in the field of industrial non-destructive testing. However, due to the limitations of manufac-turing technology for accelerators, an energy fluctuation of the X-ray beam exists and leads to bright and dark streak artifacts in the DR image. Here we report the utilization of a new software-based method to correct the fluctuation artifacts. The correction method is performed using a high pass filtering operation to extract the high frequency information that reflects the X-ray beam energy fluctuation, and then subtracting it from the original image. Our experimental results show that this method is able to rule out the artifacts effectively and is readily implemented on a practical scanning system.

Energy Fluctuation of Ideal Fermi Gas Trapped under Generic Power Law Potential U=Σ_(i=1)~d c_i|x_i/a_i|^(n_i) in d Dimensions

Energy fluctuation of ideal Fermi gas trapped under generic power law potential U=Σ_(i=1)~d c_i|x_i/a_i|^(n_i) has been calculated in arbitrary dimensions.Energy fluctuation is scrutinized further in the degenerate limit μ>>K_B T with the help of Sommerfeld expansion.The dependence of energy fluctuation on dimensionality and power law potential is studied in detail.Most importantly our general result can not only exactly reproduce the recently published result regarding free and harmonically trapped ideal Fermi gas in d =3 but also can describe the outcome for any power law potential in arbitrary dimension.

Velocity profiles and energy fluctuations in simple shear granular flows

Rheology analysis of granular flows is important for predicting geophysical hazards and designing industrial processes. Using a discrete element method, we simulate simple shear flows in 3D under a constant confining pressure of 10 kPa. The inertial number proposed by the GDR MiDi group in France is adopted to distinguish rheology regimes, Both translational and angular velocity profiles are investigated, and both fluid-like and solid-like behavior modes are observed in the flows. The maximum angular velocity occurs near the localized deformation area. We also investigate the energy characteristics of the flows and find that at very small shearing speed, the mean kinetic energy density ek is close to zero, while the mean elastic energy density ec is much greater. At large shearing speed, ek increases. The fluctuating parts of the two types of energy increase with increasing shear speed. Thus, the mean energy density ratio ek/ec can be used in addition to the inertial number to distinguish flow regimes. These results provide insights from energetics into the rheological properties of granular flows.

Experimental investigations of a prototype reversible pump turbine in generating mode with water head variations

Influences of water head variations on the performances of a prototype reversible pump turbine are experimentally studied in generating mode within a wide range of load conditions(from 25% to 96% of the rated power). The pressure fluctuations of the reversible pump turbine at three different water heads(with non-dimensional values being 0.48, 0.71 and 0.90) are measured and compared based on the pressure data recorded in the whole flow passage of the turbine. Furthermore, effects of monitoring points and load variations on the impeller-induced unstable behavior(e.g. blade passing frequency and its harmonics) are quantitatively discussed. Our findings reveal that water head variations play a significant role on the pressure fluctuations and their propagation mechanisms inside the reversible pump turbine.

Simulation studies on laser pulse stability for Dalian coherent light source

Dalian Coherent Light Source will use a 300 MeV LINAC to produce fully coherent photon pulses in the wavelength range between 150–50 nm by high gain harmonic generation free electron laser（FEL） scheme. To generate stable FEL pulses, a stringent tolerance budget is required for the LINAC output parameters, such as the mean beam energy stability, electron bunch arrival time jitter, peak current variation and the transverse beam position ofset. In order to provide guidance for the design of the Dalian Coherent Light Source, in this paper, the sensitivity of FEL pulse energy fluctuation to various error sources of the electron bunch was performed using intensive start-to-end FEL simulations.