Applied Mechanics and Materials Vols. 644-650

Abstract: There is not any calibration specification or verification regulation for the milliampere-second meter, a very important instrument for preventive maintenance and calibrating the X-ray machine [1][2], is used to measure the value of the product of tube current and exposure time. To solve the problem that the traditional method can not offer the same standard value in different times, this paper presents a method for calibrating the milliampere-second meter by using a signal generator and a digital meter. It shows that the new method has good repeatability and stability.

Abstract: When laser beam is effected on the material, the surface properties of material can be damaged, and the damage effect is different for the different laser beams. Nevertheless, the distribution of laser intensity is influenced by the proportion of high-frequency phase in wavefront. By researching the propagation character of wavefront phase, the relation of high-frequency phase and laser intensity is given in this paper. The results show that the focal spot increases gradually with the increase of the proportion of high-frequency phase, the peak value of intensity decreases obviously, and the number of side lobe increases observably.

Abstract: The 3D Shape Measuring Technology for physical objects has wide application in fields covering automatic detection, physical object profile modelling, automatic production, computer aided design/manufacturing and quality control, etc. Through the matching relations of several feature points between the partial 3D scanning point cloud data and the space frame, the transformation relations between different coordinate systems can be inferred. As for the inferring of the transformation parameters R and T, the SVD matrix decomposition algorithm has been used to acquire a better precision solution. According to the transformation relation, after registering the partial 3D scanning point cloud data and the space frame, through splicing the partial scanning point cloud data and the space frame data, the detection across the whole field on large-area objects can be realized, which will effectively increase the precision of three-dimensional measuring of large-area objects.

Abstract: Spectral dynamics of femtosecond laser plasma induced on the sea water surface is investigated. Characteristic decay time of continuum and line intensity of Mg II, Ca II and Na I are determined. Electron density that changes from 3.0·10¹⁶ to 2.4·10¹⁵ cm^-3 was provided by usage of three-body recombination coefficient. It is shown that Na detection limit will be least in comparison with Mg and Ca.

Abstract: Coal mine electromechanical equipment plays an important role in the process of producing coal.For the lack of scientific management philosophy and effective management methods, China’s Coal mine electromechanical equipment is now facing severer and severer challenges in its way of moving ahead-shortage of investment, hysteresis of management-hazards emerge in every single seconds in the production of coal mine. These hazards,however,does not merely affect the normal production, but will also increase the risks of accidents.Therefore,in order to improve the management level of electromechanical equipment and optimize the utilization of mechanical and electrical equipment, coal mine managers should pay their attentions to the following three aspects:the importance of coal mining equipment ,the importance of training mechanical and electrical personnels and the importance of accelerating the construction of mechanical and electrical information management system [1].

Abstract: Bed interface material can affect the person's temperature characteristics. This article is based on ergonomics principle and method, paralyzed group for the audience to carry the mattress temperature sensation characteristic experiments. Through the subjective survey, found that paralyzed sponge mattress material local temperature influence the human body, through the objective experiment, it is pointed out that different sponge mattress different effects on human body temperature; correlation between subjective and objective analysis found: Waist temperature on the maximum total thermal comfort; the best waves sponge thermal comfort; consistent with the results of subjective and objective analysis.

Abstract: Space optical communication has become a promising application as a real-time and high-speed data rate in the near future. In this paper consider into account the cut off frequency of the photodetector in the space optical communication. We analyze an appropriate quantum dot infrared photodetector for high speed response. The analysis shows PN junction structure photodiode with the wide as d in the absorption window should be designed carefully to achieve both high sensitivity and high speed.

Abstract: Positioning accuracy of light spot locating algorithms and the stability of the spot are two key factors affect the accuracy in the multi-degree of freedom measurement system based on CCD. Two algorithms of sub-pixel measurement are present. They are threshold gray barycenter algorithm and circle fitting algorithm. The theoretical analysis was carried out with the two algorithms, and the experimental verification was also taken under the laboratory conditions. Experimental results show that the threshold gray barycenter algorithm has a higher locating precision than circle fitting algorithm that the standard deviation in 30 minutes can be under 0.04 pixels. According to CCD pixel size it can be calculated that the light spot locating standard deviation is 0.186μm.

Abstract: Indoor node positioning is a key technology in wireless sensor network but the general indoor nodes positioning algorithm is difficult to meet the precision positioning requirements due to the indoor complex environment such as multilateral positioning algorithm based on RSSI ranging. The weighted multilateral positioning algorithm is proposed based on time reversal ranging to solve the problem. We simulate within 50m*50m area, the experimental results show that the ranging error is less than 1%. The maximum positioning error is less than 0.6m. Compared with general positioning algorithm, it can improve the positioning accuracy greatly in complex environments and has general applicability.

Abstract: Mechanism of hypersonic inlet performance promoting by “virtual cowl” induced by laser energy is introduced, and the physical model of interaction between laser energy and shocks in hypersonic flow field is established. Through comparing results in this paper with the work performed by Macheret et al.(Princeton University) and analyzing effects of laser energy deposited in hypersonic flow, numerical program and the feasibility of model are validated. At Mach 6, with no laser energy addition, air mass capture ratio K_m is 71.87% in this paper, while K_m is 73.17% in the reference. Energy addition module can simulate the formation of shocks induced by laser energy, and the interaction process between laser energy and compression ramp shocks properly. Curves of mass capture ratio K_m agrees well with that of the reference. K_m is a little higher than data in the reference, but the variable trend is consistent with each other when laser power is 1kW. When laser power is 0.5kW, K_m varies a little, and the peak value is 77.36%, which only increases 7.64%, while the value is 7.28% in the reference.