Applied Mechanics and Materials Vols. 380-384

Abstract: The high-precision instruments must be tested to ensure the accuracy and the normal use of the instrument in the application. Traditional detection techniques damage the instrument. So, researching for a technology which has no destruction on high precision instrument is important. This paper puts forward a new ultrasonic nondestructive test technology of precision instruments through empirical mode decomposition method of modern signal processing technology and ultrasonic nondestructive test technology. The first part describes the shortcomings of modern signal processing technology--Fourier and wavelet analysis and the advantage of empirical mode decomposition method. The second part establishes the mathematical model of ultrasonic nondestructive test technology. It also establishes empirical model to enhanced signal and noise ratio using the self-adaptivity of the empirical mode decomposition. It also extracts Intrinsic Mode Function (IMF) of ultrasonic nondestructive test technology using EMD and Hilbert transform signal processing method. Finally, it gets Nonlinear and non-steady-state frequency power spectrum which provides a reliable theoretical basis for the study of nondestructive test technology.

Abstract: The putting forward of Georaster brings a new opportunity for realizing integrated storage of raster data and vector data in Oracle Spatial . This paper analyzed raster images storage and management mechanisms using Georaster model of Oracle spatial, including GeoRester data model,physical storage structure, data block and pyramid strategy. On this basis, the paper demonstrated a typical example of storing and managing raster image data. Through a large number of experiments, the paper pointed out that the Oracle's raster image data loading tool cannot upload large capacity raster image. Aiming at the disadvantage in terms of data capacity, the paper presented a simple yet effective solution, which adopts block processing way, is consistent with "divide and conquer idea, can improve data processing and network transmission speed.

Abstract: Face recognition has received much attention because of its theoretical challenges as well as applications in user identification, surveillance and humancomputer interaction. As a result, numerous methods have been developed for face recognition in the last few decades. Some universally used methods are introduced in this paper. On the same face recognition database, the recognition results are analyzed and compared.

Abstract: The vlf radio wave propagation is usually treated as a waveguide problem. It should be noted that many of the parameters that describe the boundaries of the earth-ionosphere waveguide are not known with great accuracy over all regions and times. In order to know the effect of underwater platform receiving in corresponding region and time, this paper makes use of the waveguide mode theory to predict the propagation effectiveness of vlf radio, offers the service of propagation environment for the system to adjust the variable parameters or abstain from propagation attenuation, makes the system performance matching the channel character and advancing the effects of vlf communication.

Abstract: PC-GOT-PLC is a popular automatic control system. Applied F940GOT and FX2N series PLC to system, without any mitsubishi's special communication board and under a very simple connecting mode, realized their mutual communication; System achieved the efficient, stable and reliable communication under simple attachment without any mitsubishi's special communication board. The communication applied mitsubishi FX series PLC programming interface protocol, no longer need to set up the D8120, simplified the PLC program; Under this protocol and based on VB6.0 development environment,write the serial communication program adapt to FX full series,the program make the PC can read/write the PLC soft equipment and forced ON/OFF directly. In the actual application, No matter accuracy and stability of communication were to achieve requirements of industrial control system.

Abstract: If the reference clock is recovered from the input data ,the data rate must at a low speed. Because there is a large clock jitter when the input data at a high speed .In this paper ,a new method of synchronization has carried out for a wireless communication system .The source of data come from the SDI interface,whose rate is 1.485Gbps.The new mechanism avoid introducing the extra hardware by varying the frames structure.The length of frame is changed by adding difference length of 0 at the tail of the frame.

Abstract: According to the problem that the existing radar signal feature cannot effectively express and analysis its characteristic, a description method of radar emitter signal feature based on improved kernel density estimation is proposed. This improved kernel density estimation algorithm combine the selection of fixed window and variable window's width to achieve the window's width automatic adjustment value between the different estimation points based on the sample distribution. Then the probability density curve using kernel density estimation algorithm as radar emitter signal parameters characteristics stored into database.

Abstract: Stacked Alamouti coding in MIMO wireless communication systems was analyzed through equivalent channel.We derive an upper bound on the portion of the ergodic capacity that the stacked Alamouti scheme can achieve, which is dependent on the ratio of number of transmit antennas to that of receive antennas in the high signal-to-noise ratio regime. As a conclusion, it is shown that the stacked Alamouti scheme can approach the channel capacity as long as the number of transmit antennas is no less than two times that of receive antennas.

Abstract: According to the problem that the existing radar signal recognition method cannot effectively identify the radar signal, a new recognition method based on kernel density estimation is proposed. First using kernel density estimation gets the probability density curve of radar emitter signal parameters, then storing the cures into database as the characteristics, in the end a radar emitter signal recognition algorithm based on template matching is proposed.

Abstract: Low density parity check codes (LDPC) by now is an excellent channel code that approaches Shannons limit. In order to get the effect of random jitter on performance of LDPC, a simulation model is constructed in this paper. Interpolation, filter delay and decimation methods are used to simulate random jitter induced by circuits of the receiver, changing filter delay to control the jitter step length. Thus the bit error rate of LDPC decoder is gotten that shows the sensitivity of LDPC to synchronization jitter. This paper concludes that, complying with channel coding block in DVB-S2, the bit error rate of LDPC decoder goes up on an exponential trend with the effect of random jitter simulation.