Two-Dimensional Riemann Problems:Transonic Shock Waves and Free Boundary Problems

We are concerned with global solutions of multidimensional(M-D)Riemann problems for nonlinear hyperbolic systems of conservation laws,focusing on their global configurations and structures.We present some recent developments in the rigorous analysis of two-dimensional(2-D)Riemann problems involving transonic shock waves through several prototypes of hyperbolic systems of conservation laws and discuss some further M-D Riemann problems and related problems for nonlinear partial differential equations.In particular,we present four different 2-D Riemann problems through these prototypes of hyperbolic systems and show how these Riemann problems can be reformulated/solved as free boundary problems with transonic shock waves as free boundaries for the corresponding nonlinear conservation laws of mixed elliptic-hyperbolic type and related nonlinear partial differential equations.

Survey on research and development of on-orbit active debris removal methods

Space debris is growing dramatically with the rapid pace of human exploration of space,which seriously threatens the safety of artificial spacecraft in orbit.Therefore,the active debris removal(ADR)is important.This review aims to review the ADR methods and to advance related research in the future.The current research and development status are clearly demonstrated by mapping knowledge domain and charts.In this paper,the latest research results are classified and summarized in detail from two aspects of space debris capture and removal.The scheme comparison and evaluation of all ADR methods are performed,and the applicable scopes of various methods are summarized.Each ADR method is scored using a cobweb evaluation model based on six indicators.Future development of ADR is discussed to promote further research interest.

Efcient autofocus method for sequential automatic capturing of high-magnification microscopic images

This letter presents an autofocus （AF） method to position a high-magnification microscope lens that automatically captures hundreds of images from a single moving slide. These images are taken by a mobile clinic unit in a rural location, and are later automatically processed and revised by a remote specialist. This process requires high focus precision to enable image processing techniques to achieve proper results. Low focusing times are also required for the system to be operative. We propose a novel method that combines two focus measures with an adapted searching scheme to cope with both constraints.

Kiwifruit recognition at nighttime using artificial lighting based on machine vision

Most researches involved so far in kiwifruit harvesting robot suggest the scenario of harvesting in daytime for taking advantage of sunlight.A robot operating at nighttime can overcome the problem of low work efficiency and would help to minimize fruit damage.In addition,artificial lights can be used to ensure constant illumination instead of the variable natural sunlight for image capturing.This paper aims to study the kiwifruit recognition at nighttime using artificial lighting based on machine vision.Firstly,an RGB camera was placed underneath the canopy so that clusters of kiwifruits could be included in the images.Next,the images were segmented using an R-G color model.Finally,a group of image processing conventional methods,such as Canny operator were applied to detect the fruits.The image processing results showed that this capturing method could reduce the background noise and overcome any target overlapping.The experimental results showed that the optimal artificial lighting ranged approximately between 30-50 lx.The developed algorithm detected 88.3%of the fruits successfully.

ASSESSMENT OF A CENTRAL DIFFERENCE FINITE VOLUME SCHEME FOR MODELING OF CAVITATING FLOWS USING PRECONDITIONED MULTIPHASE EULER EQUATIONS

A numerical treatment for the prediction of cavitating flows is presented and assessed. The algorithm uses the preconditioned multiphase Euler equations with appropriate mass transfer terms. A central difference finite volume scheme with suitable dissipation terms to account for density jumps across the cavity interface is shown to yield an effective method for solving the multiphase Euler equations. The Euler equations are utilized herein for the cavitation modeling, because some certain characteristics of cavitating flows can be obtained using the solution of this system of equations with relative low computational effort. In addition, the Euler equations are appropriate for the assessment of the numerical method used, because of the sensitivity of the solution to the numerical instabilities. For this reason, a sensitivity study is conducted to evaluate the effects of various parameters, such as numerical dissipation coefficients and grid size, on the accuracy and performance of the solution. The computations are performed for steady cavitating flows around the NACA 0012 and NACA 66 （MOD） hydrofoils and also an axisymmetric hemispherical fore-body under different conditions and the results are compared with the available numerical and experimental data. The solution procedure presented is shown to be accurate and efficient for predicting steady sheet- and super-cavitation for 2D/axisymmetric geometries.

Thermally stimulated properties in ZnSe：Tb and ZnSe：(Mn, Tb) phosphors

Thermoluminescence studies were performed of ZnSe：Tb and ZnSe：（Mn, Tb） phosphors. A method of preparation for ZnSe phosphors doped with Tb and（Mn, Tb） has been discussed. The thermoluminescence（TL）properties of these phosphors have been studied from 100 to 370 K temperature after exciting by UV radiation（365 nm）at three uniform heating rates 0.4, 0.6 and 0.9 K/s. The trapping parameters like trap depth, lifetime of electrons and capture cross-section have also been determined using various methods.