Search

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) passed national acceptance and is taking pilot cycle of 'Shared-Risk' observations. The 19-beam receiver covering 1.05-1.45 GHz was used for most of these observations. The electronics gain fluctuation of the system is better than 1\% over 3.5 hours, enabling enough stability for observations. Pointing accuracy, aperture efficiency and system temperature are three key parameters of FAST. The measured standard deviation of pointing accuracy is 7.9$''$, which satisfies the initial design of FAST. When zenith angle is less than 26.4$^\circ$, the aperture efficiency and system temperature around 1.4 GHz are $\sim$ 0.63 and less than 24 K for central beam, respectively. The measured value of these two parameters are better than designed value of 0.6 and 25 K, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward N672 and polarization observations toward 3C286. The performance allows FAST to take sensitive observations in various scientific goals, from studies of pulsar to galaxy evolution., 29 pages, 28 figures, accepted by Research in Astronomy and Astrophysics

Sol-gel-processed silica films doped with Disperse Red 1(DR1) were prepared at 80°C aging temperature and 120°C baking temperature with corona poling to obtain stable and large electro-optic (EO) coefficient and film strength. A large EO coefficient of γ33 = 56 pm/V was measured for the film of 0.5-μm thickness at the wavelength of 1300 nm, and the value was unvaried at room temperature. Moreover, an external EO probe tip using the film was fabricated for the first time, and a signal voltage level corresponding to the EO signal was calibrated successfully.

Conventional algorithms to estimate lateral load transfer for single vehicle are not so completely applicable for articulated vehicles, so an improved algorithm to estimate dynamic lateral load transfer for tractor-semi trailer is presented. Considering the influence of related factors such as saddle, the algorithm lies in systematic analysis for dynamic lateral load transfer of tractor-semi trailer. Based on dynamics model with 6-DOF vehicles, the wheels’ vertical load is estimated and the related models are verified by a practical simulation platform for tractor-semi trailer, TruckSim. The results show that roll stiffness and roll height of saddle have a large effect on lateral load transfer, the improved algorithm is more accurate to analyze the change of wheels’ vertical load and the estimated value is increased about 20%, so the deficiency of conventional algorithms in adaptability and accuracy is solved.

Vibration signals are the important information for system failures. Forecasting the trend of vibration signals is an important content of condition monitoring and fault diagnosis. A novel time series analysis is presented to analyze and forecast nonlinear random vibration signals. Mathematical models are established to describe vibration signals. First, the non-stationary vibration signals acquired in the field are transformed to stationary time series. Second, the time series models are constructed from the selected reference signals, and nonlinear least square method is used to estimate the model's parameters. Then, the vibration signals are forecasted using the models. The application results show that the models can simulate time series of vibration signals quite well with good accuracy and meet the need of forecasting.

Curved section is divided into pre-decelerating area, decelerating area and accelerating area according to human-vehicle operation state. The characteristics and formation process of respective dangerous area of the three areas were analyzed based on the changes in vehicles' speed and acceleration as well as drivers' psychophysical indicators. The results show that in the pre-decelerating area, dangerous driving areas are distributed near the beginning of the curved section, in spotty manner, which area will become the driver's subjective safety dangerous area since a psychophysical mutation may occur to the driver in this area. In the decelerating area, dangerous driving area is distributed in belt shape, on most section of such area the psychophysical reaction of the driver will continuously remain at a high level, resulting in a high incidence of vehicles being out of control or running off the road. In the accelerating area, dangerous driving area is distributed in short belt shape, in which area another more dramatic change will happen to the drivers psychophysical reaction, the vehicle is more likely to collide with the vehicle driving in opposite direction at the initial stage of accelerating.

In order to analyze the influence of saddle parameters on driving stability of tractor semi-trailer, the steering stability was investigated in the typical operating conditions under the time-domain simulation based on the dynamics model. Then, the paper analyzed the match and the estimation of the effects of parameter variations, these analyses got better values for the design reference. The results show that the changing of saddle parameters effect on the vehicle performance insensitively, their values do not need have very high precision.

In collisions with trucks, there is a high risk for car occupants to sustain severe or fatal injuries. The intelligent rear under-run protection system, as a very important part to prevent under-run accidents and decrease loss, its dynamic deformation and stress distribution mostly lie on the characteristic of energy absorber and keeping directional stability of the rear vehicle during collision. In this paper, based on the related actuality in China and abroad, an intelligent rear under-run protection system with integrated function is presented and the key structure is systematically given. Then taking a car as an example, the whole process of under-run collision is simulated and analyzed by applying nonlinear FE program. Simultaneously, the time histories of collision force of the key support structure and velocity variation are presented. All of these can be worth using as references in related fields.

Gesture segmentation is the first and the most critical step in sign language recognition. In this paper a method of gesture segmentation from the video image sequence based on monocular vision is presented by skin color and motion cues. Firstly, determine the background images and capture the gesture images with a sampling interval of 10 frames. Then with the difference method, the movement region of hand gestures is detected, meanwhile, through the analysis of the skin color information, the skin color region of hand gestures is obtained. After that, the initial gesture region can be gained by the AND operation on the movement region and the skin color region. Last but not least, gestures are separated from video image sequence reliably and completely using the mathematical morphology method. The experimental results indicate that the technique is capable of segmenting the gestures quite effectively.

This work presents a detailed study of deep and shallow level defects in nitrogen implanted n-type GaAs. Deep-level transient spectroscopy (DLTS) measurements show four electron traps and one hole trap in 140 keV nitrogen implanted GaAs after a dose of 1×1013cm-2 and a thermal annealing at 800℃ for 30 min: E1(0.111) ,E2(0.234) ,E3(0.415) ,E4(0.669) ,and H(0.545). Meanwhile,only E4 and H(0.545) defects are observed in 10 keV nitrogen-implanted GaAs after a dose of 5×1014cm-2 and the same annealing treatment. It oncluded that E2 and E3 correspond to the damages due to the high-energy implantation, E4 may be complex of intrinsic defect and implantation damage, H(0.545)is a nitrogen-related deep-level and may contribute to the free-carrier compensation in the nitrogen-implanted n-type GaAs.

Behavior of gold in the Si/SiO2 interface region has been investigated using deep level transient spectroscopy (DLTS) in the MOS structures made on p-type silicon wafers with orientation. The results are as follows. A new defect, Au-Hit(0.445), has been observed at the interface, which is the incorporation of gold atom by the interaction with the interface defect, Hit(0.494). A continuous spectrum of the interface states related to gold has also been measured in the lower half of Si band gap, which are acceptors, and the physical mechanism of the positive shift of the flat band voltage of the MOS structure caused by gold doping ean be explained in terms of these gap states. The profile of the gold donors in the silicon near the interface has been obtained, which is not monotonically increase towards the surface but exhibits a maximum at 0.37μm from the surface.