Riveting is one of the major joining methods used in assembly, and the robotic riveting has been gradually introduced into aircraft industry. In this paper, a method is presented for modeling and ...simulation of percussive robotic riveting. In percussive riveting, vibration always exists. When an impact force is employed, a forced vibration will be induced. If it resonates with a robot natural frequency, the vibration will cause damage to the robot. The main content of this paper is divided into three parts. Firstly, a robot dynamic model is established to compute the driving torque for each joint. Secondly, vibration responses under impact are analyzed for the percussive riveting process. Thirdly, the effect of riveting on robot vibration is studied over the robot workspace. The purpose of this paper is to discuss the suitable regions for riveting where the robot vibration is very minimal. It is shown that based on the presented method an appropriate trajectory can be planned for robotic riveting.
We present here a brief summary of a National Natural Science Foundation Major Project entitled ＂Theoretical study of the low-lying electronic excited state for molecular aggregates＂. The project ...focuses on theoretical investigation of the electronic structures and dynamic processes upon photo-and electric-excitation for molecules and aggregates. We aim to develop reliable methodology to predict the optoelectronic properties of molecular materials related to the electronic excitations and to apply in the experiments. We identify two essential scientific challenges： （i） nature of intramolecular and intermolecular electronic excited states; （ii） theoretical description of the dynamic processes of the coupled motion of electronic excitations and nucleus. We propose the following four subjects of research： （i） linear scaling time-dependent density-functional theory and its application to open shell system; （ii） computational method development of electronic excited state for molecular aggregates; （iii） theoretical investigation of the time evolution of the excited state dynamics; （iv） methods to predict the optoelectronic properties starting from electronic excited state investigation for organic materials and experimental verifications.
A direct drive actuator （DDA） with direct drive valves （DDVs） as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor ...（TRVCM） used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet （PM） Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization （PSO） method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis （FEA）. A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems.
The reliability of the integrated circuits (ICs) has become one of the greatest challenges with the increasing complexity of the electromagnetic environment. On this basis, an explicit difference in ...the damage location is observed in the high-power microwave (HPM) radiated CMOS inverters. The detailed damage mechanism analysis is performed. The analysis shows that the overcurrent-dominant failure and the latch-up-dominant failure are induced in positive and negative half radiation cycle respectively, resulting in the damage location discrepancy. The depletion region current <inline-formula> <tex-math notation="LaTeX">I_{\textrm {SS}} </tex-math></inline-formula> and the body current <inline-formula> <tex-math notation="LaTeX">I_{\textrm {body}} </tex-math></inline-formula> are derived from the established theoretical charge transport model. TCAD simulations demonstrate the junctional-overcurrent and latch-up process, empirical formula is obtained to explain the damage mechanism and predict the thermal damage location. The damage dependency on interference characteristics is discussed for further understanding. Corresponding experiments are performed using the six-integrated-inverters chip. The results support the theoretical charge transport model well.
The monostatic radar cross section are used widely in radar applications. The numerical algorithms such as integral equation can be used for accurate simulation of monostatic radar cross section. ...However, the simulation of monostatic radar cross section is much more time consuming than bistatic radar cross section, if an iterative solver is used. In this paper we propose a scheme based on the adaptive cross approximation (ACA) and singular value decomposition (SVD) which can reduce the simulation time of monostatic radar cross section simulation using integral equation method.
This work describes a study of elemental abundances for 30 metal-poor stars whose chemical abundances provide excellent information for setting constraints on models of neutron-capture processes. ...Based on the abundances of main r- and weak r-process stars, the abundance patterns of main r-process and weak r-process are obtained. The two r-process component coefficients are defined to determine the relative contributions from individual neutron-capture process to abundances of metal-poor stars. Based on the component coefficients, we find that metal-poor stars BD+4 2621 and HD 4306 are also weak r-process stars, which means that the abundance pattern produced by weak r-process is stable. All metal-poor star abundances contain the contributions of both main r-process and weak r-process. The elements produced by weak r-process have increased along with Fe over the polluted history. Most of the metal-poor star abundances do not follow the pattern observed in solar system, but there is a small fraction that do. For the low-Sr/Fe star BD-18 5550 (Sr/Fe\(\lesssim-1\)), neutron-capture element abundances can be explained by the mixture of two r-process components. Since lighter elements in this star cannot be fitted by the two components, the abundance pattern of P-component is estimated from those abundances.
Nowadays integration of electronic platforms has been a new research area, in which the radar and communication integration system is becoming a hot topic. Aiming to solve the incompatibility of ...signal design between the radar and communication applications, and followed by the principle of signal energy sharing, a radar and communication integration system based on random stepped frequency waveform is proposed. The transmission information is modulated on the carrier frequency, which accomplished the communication function without affecting the imaging radar performance. The radar imaging is mainly accomplished using Compressed Sensing theory. Simulations and analysis prove its feasibility.
According to the basic principle of linear antenna array's beam forming, an imaging method for moving target based on sparse array single input multiple output (SIMO) radar with multiple carrier ...frequencies is proposed in this paper. By launching large bandwidth signal, the target's two-dimensional image of the same resolution can be obtained with fewer array elements. Combined with the thought of minimal redundant array in spatial spectrum estimation, the range of antenna's working frequency is effectively narrowed by increasing just few elements. The validity of the method is verified by simulations.
Aim： To investigate the mechanism underlying the increase of hepatoma cell proliferation by hepatitis B virus X protein （HBx）. Methods： HepG2, H7402 and HepG2.2.15 cells, which constitutively ...replicated hepatitis B virus were used. The effects of HBx on hepatoma cell proliferation were examined using 5-ethynyl-2-deoxyuridine （EdU） incorporation assay and MTT assay. The expression level of MEKK2 was measured using RT-PCR, Western blot and luciferase reporter gene assay. The activity of activator protein 1 （AP- 1） was detected using luciferase reporter gene assay. The phosphorylation levels of JNK and c-Jun were measured using Western blot. The expression levels of HBx and MEKK2 in 11 clinical hepatocellular carcinoma （HCC） tissues were measured using real time PCR and Western blot. In addition, the expression of MEKK2 in 95 clinical HCC tissues was examined using immunohistochemistry. Results： HBx significantly enhanced HepG2-X cell proliferation. In HepG2-X, H7402-X and HepG2.2.15 ceils, the expression level of MEKK2 was remarkably increased. In HepG2.2.15 cells, HBx was found to activate JNK and AP-1, which were the downstream effectors of MEKK2 in HepG2-X and HepG2.2.15 cells. In 11 clinical HCC tissues, both HBx and MEKK2 expression levels were remarkably increased, as compared to those in the corresponding peritumor tissues. In 95 clinical HCC tissues, the rate of detection of MEKK2 was 85.3%. Conclusion： HBx promotes hepatoma cell proliferation via upregulating MEKK2, which may be involved in hepatocarcinogenesis.
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