Theoretical Analysis and Simulation of BJFET Obstructive Characteristics

A new bipolar junction field-effect transistor (BJFET) was described. The theoretical analysis and computer simulation of BJFET obstructive characteristic are achieved. The gate bias voltage affects the BJFET obstructive voltage greatly. The BJFET obstructive characteristic is relevant to structure parameters of channel width W and channel length L. The decrease-bias-voltage operation can weaken the device obstructive characteristic. The forward turn in device forward obstructive region can also affect the BJFET obstructive characteristic. BJFET has a good high temperature obstructive characteristic and can be applying to high temperature status as high voltage switch devices.

Morphological Studies on the Infraciliature of a Planktonic Ciliate,Tintinnopsis brasiliensis(Ciliophora:Tintinina)

A poorly-described marine planktonic ciliate, Tintinnopsis brasiliensis Kofoid ＆ Campbell, 1929, collected from the Taiping Cape of Qingdao, China, was morphologically investigated based on permanent preparation after protargol impregnation and was compared with other related congeners. According to the infraciliature, three ciliary groups can be recognized, which reveals a very stable structure among specimens and denotes that the pattern of infraciliature is, apart from the features of the lorica, a highly reliable criterion for species identification.

Zonal disintegration phenomenon in enclosing rock mass surrounding deep tunnels—mechanism and discussion of characteristic parameters

The mechanism of the zonal disintegration phenomenon(ZDP) was realized based on the analysis of the stressedstrained state of the rock mass in the vicinity of the maximum stress zone, which resides in the creep instability failure of rock mass due to the development of a plastic zone and transfer of the maximum stress zone within the rock mass.Some characteristic parameters of the ZDP are discussed theoretically.In first instance, the analytical critical depth condition for the occurrence of ZDP was obtained, which depends on the characteristics and stress concentration coefficient of the rock mass.Secondly, based on creep theory, the expression of the outer radius of the undisturbed zones in the deep rock mass was obtained with the use of an improved Burgers rheological model, which indicated that the radius depends on the characteristics of the rock mass and the depth of excavation and increases quasi-linearly with the rise of creep compliance of the rock mass.Finally, the formula for the distance of the most remote fissured zone away from the working periphery was derived, which increases logarithmically with the increase in the ratio of the in-situ stress and ultimate strength of rock mass.The distances between fissured zones are discussed in qualitative terms.

Vibration-based feature extraction of determining dynamic characteristic for engine block low vibration design

In order to maintain vibration performances within the limits of the design, a vibration-based feature extraction method for dynamic characteristic using empirical mode decomposition （EMD） and wavelet analysis was proposed. The proposed method was verified experimentally and numerically by implementing the scheme on engine block. In the implementation process, the following steps were identified to be important： 1） EMD technique in order to solve the feature extraction of vibration signals; 2） Vibration measurement for the purpose of confirming the structural weak regions of engine block in experiment; 3） Finite element modeling for the purpose of determining dynamic characteristic in time region and frequency region to affirm the comparability of response character corresponding to improvement schemes; 4） Adopting a feature index oflMF for structural improvement based on EMD and wavelet analysis. The obtained results show that IMF of signal is more sensitive to response character corresponding to improvement schemes. Finally, examination of the results confirms that the proposed vibration-based feature extraction method is very robust, and focuses on the relative merits of modification and full-scale structural optimization of engine, together with the creation of new low-vibration designs.

Multi-dimensional and Multi-threshold Airframe Damage Region Division Method Based on Correlation Optimization

In order to obtain the image of airframe damage region and provide the input data for aircraft intelligent maintenance,a multi-dimensional and multi-threshold airframe damage region division method based on correlation optimization is proposed.On the basis of airframe damage feature analysis,the multi-dimensional feature entropy is defined to realize the full fusion of multiple feature information of the image,and the division method is extended to multi-threshold to refine the damage division and reduce the impact of the damage adjacent region’s morphological changes on the division.Through the correlation parameter optimization algorithm,the problem of low efficiency of multi-dimensional multi-threshold division method is solved.Finally,the proposed method is compared and verified by instances of airframe damage image.The results show that compared with the traditional threshold division method,the damage region divided by the proposed method is complete and accurate,and the boundary is clear and coherent,which can effectively reduce the interference of many factors such as uneven luminance,chromaticity deviation,dirt attachment,image compression,and so on.The correlation optimization algorithm has high efficiency and stable convergence,and can meet the requirements of aircraft intelligent maintenance.

Numerical investigation on the thermal protection mechanism for blunt body with forward-facing cavity

Numerical experiments are carried out using the standard hypersonic ballistic-type model(HB-2) to investigate the effect of forward-facing cavity on the aerodynamic heating. A general concept is proposed which utilizes the flow disturbances generated passively in the nosed subsonic region to weaken the detached shock wave. Several aspects are mainly studied, including shock shape and standoff distance, surface heat flux and pressure, flowfield feature and cooling mechanism. The numerical results indicate that shock strength and standoff distance increase with an increase in the L/D ratio of the cavity. Interestingly, a bulge structure of the detached shock associated with a deep cavity is observed for the first time. Local surface heat flux and pressure around the concave nose are much lower respectively than those at the stagnation point of the baseline model. In addition, both surface heat and pressure reductions are proportional to the L/D ratio. A negative heating phenomenon may occur in the vicinity of a sharp lip or on the base wall of a deep cavity. If the L/D ratio exceeds 0.7, the detached shock appears as a self-sustained oscillation which can be referred to as the cooling mechanism.