Modeling and Simulation of Photoelectronic Lambda Bipolar Transistor

Based on the region model of lambda bipolar transistor （ LBT）, a dividing region theory model of PLBT is set up.simulated and verified. Firstly, the principal operations of different kinds of photoelectronic lambda bipolar transistor ,（ PLBT） are characterized by a simple circuit model. Through mathematical analysis of the equivalent circuit, the typical characteristics curve is divided into positive resistance, peak, negative resistance and cutoff regions. Secondly. by analyzing and simulating this model, the ratio of MOSFET width to channel length, threshold voltage and common emitter gain are discovered as the main structure parameters that determine the characteristic curves of PLBT. And peak region width, peak current value, negative resistance value and valley voltage value of PLBT can be changed conveniently according to the actual demands by modifying these parameters. Finally comparisons of the characteristics of the fabricated devices and the simulation results are made, which show that the analytical results are in agreement with the observed devices characteristics.     

Study on the heat transfer of cross flow in vertical upward tubes

INTRODUCTION Cross flow and heat transfer were widely found in oil production and chemical facilities.A detailed study of the hydrodynamic characteristics and heat transfer of cross flow is necessary for optimal design of the system and the development of new measuring techniques.Studies on the heat transfer in sin-gle-phase liquid cross flow were carried out in the past decades.Air or water was often chosen as the working fluid,in these studies commonly focused on fluids flowing across r…     

Characteristics of the dynamic distribution of suspended particles in the flocculation process

Polyaluminium chloride （PAC） synthetic water was selected as a coagulant and kaolin suspension particles as objects to be removed. Online instruments such as the turbidimeter and particle counter were employed to monitor the flocculation process online and collect test data. The aim of the experiments was to study the dynamic distribution characteristics of suspension particles in the flocculation process. The 3D flow field in the reacting vessel was also simulated at different slow stirring speeds. The experiments showed that particle collision and aggregation in the flocculation process is in compliance with the Sutherland cluster aggregation model. This study further indicated that under appropriate hydrodynamic conditions, the distribution of turbulent flow in the reactor could be improved to increase the odds of effective particle collision and restrain the breakup of formed flocs by vortex shearing force. A good flocculation effect could therefore be produced.     

Mechanism of Breakdown in Laminar-Turbulent Transition of Incompressible Boundary Layer on a Flat Plate

Temporal mode direct numerical simulation was done for the process of laminar-turbulent transition in an incompressible boundary layer on a flat plate. The analysis of the results showed that during the breakdown process of laminar-turbulent transition, the modification of the mean flow profile by the disturbances led to a remarkable change in its stability characteristics, manifested in the significant enlargement of the linear unstable zone and the maximum amplification rate, and led to that many more disturbances were excited and enhanced rapidly, correspondingly the turbulent energy also increased rapidly, and the mean flow profiles evolved swiftly from laminar to turbulent. It was also found that if the oblique waves in the initial disturbances did not form symmetrical pairs, the subsequent span-wise mean velocities would, in general, be nonzero due to nonlinear interaction, which would have a great effect on the stability characteristics and also implied that the turbulence obtained by direct numerical simulation might not be fully a random process.     

Investigation of oil-air two-phase mass flow rate measurement using Venturi and void fraction sensor

INTRODUCTION Accurate measurement of multiphase fluids flow rates in the petroleum industry is of great importance. The most reliable measurement technique for multi-phase flow is separating the mixture and using con-ventional devices for measuring single-phase flow. However, in many cases the separation is not practical from both technical and economical points of view. An alternative solution is the multiphase flow me-tering system, usually consisting of a combination of devices for ph…     

CFD Analysis of Gas Distributor in Packed Column——Prediction of Gas Flow and Effect of Tower Intemals Geometry Structure

Computational fluid dynamics (CFD) simulations were carried out on the gas flow patterns of twintangential annular deflector gas distributor in the absence of liquid flow in a packed column (6.4 m in diameter) , and the gas flow field in the column was presented close to reality on the whole. Furthermore, after amelioration of this gas distributor frame, turbulence energy and turbulence energy dissipation rate were both decreased greatly. Simulation results showed that the flow pattern and the distribution of gas flow were strongly affected by the column bottom frame ; the proper column bottom frame could decrease the flow pressure drop greatly. Multifold factors, such as the column bottom geometry structure and distributor structure which affects the distribution capacity, must be considered.     

The effects of science,technology, society and environment （STSE） education on students＇ career planning

The leakages in secondary level education brought forward the necessity to restructure the educational system so as to address the social and individual needs and meet the requirements of Turkey; therefore, a ＂reformation＂ study became an obligation. The formal education in Turkey starts at the age of 6, when the individual is shaped within the system. Determination of the characteristics of an ideal future citizen of a country should be apprehended at all levels of education and individuals should attain these appreciated characteristics. The reformed science education programs in Turkey aim to guide the individuals to be scientifically and technologically literate. Through enabling an individual, who is in a technological media, to attain the required knowledge, skills and attitudes, the individual should have the ＂science and technology literacy and creative thinking＂ skills. Individuals should recognize the technological environment they live in as well as the dimensions and facilities of technology, and should be aware of the fact that they could make use of these opportunities. In the light of this aim, this study involves the teaching of ＂separating mixtures＂ to 9th grade students in relation with science, technology, society and environment and the examination of its possible effects on students＇ achievement as well as their career choices. The Chemistry Achievement Test and the Career Choice Questionnaire were administered as pre- and post-test to serve as data collection tools. The study concluded that chemistry education in relation with science, technology, society and environment would lead students to choosing different fields for their future careers by changing their perspectives towards science. A significant increase in students＇ chemistry achievement levels was also observed.     

Analysis of the Characteristics of Project Financing

Project financing is independent on the sponsors credit or tangible assets, but in the project’s expected reliable, stable cash flow and future earnings as the fund source, and mainly to the project entity assets as a debt security financing. It will be of great theoretical and practical significance by conducting a detailed research on related concept and characteristics.     

The Analysis of Comparison Between English and Chinese Animal Idioms

Idioms are essence of a language and a kind of special and fixed phrases or short sentences in the long period of language use.Because animals have been considered as people’s best friends for hundreds of years,people adopt different species of animals as metaphors to express all their emotions.However,due to the different national characteristics between English and Chinese,such as geographical conditions and tradition so in most cases easterners and westerners have different attitudes and understanding towards same animals,of course,some animal idioms have the same meaning.     

Dependence patterns associated with the fundamental diagram： a copula function approach

Randomness plays a major role in the interpretation of many interesting traffic flow phenomena, such as hysteresis, capacity drop and spontaneous breakdown. The analysis of the uncertainty and reliability of traffic systems is directly associated with their random characteristics. Therefore, it is beneficial to understand the distributional properties of traffic variables. This paper focuses on the dependence relation between traffic flow density and traffic speed, which constitute the fundamental diagram （FD）. The traditional model of the FD is obtained essentially through curve fitting. We use the copula function as the basic toolkit and provide a novel approach for identifying the distributional patterns associated with the FD. In particular, we construct a rule-of-thumb nonparametric copula function, which in general avoids the mis-specification risk of parametric approaches and is more efficient in practice. By applying our construction to loop detector data on a freeway, we identify the dependence patterns existing in traffic data. We find that similar modes exist among traffic states of low, moderate or high traffic densities. Our findings also suggest that highway traffic speed and traffic flow density as a bivariate distribution is skewed and highly heterogeneous.     

Equivalent thickness of materials of fused silica and stainless steel in the flow of microtubes

The deviation of flow characteristics from the predictions of the conventional theory for microtubes was attributed to the change of fluid viscosity resulted from the interactions between the molecules on solid wall and in fluid. The degree of this departure is dependent on the microtubes materials. A concept of equivalent thickness with which conventional theory can be used to predict the flow in microtubes without modifying the fluid viscosity was put forward. The values of equivalent thickness for fused silica and stainless steel materials were determined as 1.8 μm and 1.5 μm, respectively, by repeated numerical simulation.     

Formation mechanism and size prediction of bubble in opposite-flowing T-shaped microchannel

Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.     

Control of pinhole defects formation in semi-flexible coaxial cable by vertical tin-plating process

Holistic tin-plating on the outer conductor is one of the key processes in the manufacture of semi-flexible coaxial cable, which is widely applied to the third generation (3G) mobile communication system. However, in the traditional horizontal tin-plating process, disadvantages such as the pinhole defects and low productivity effect cannot be avoided. In this paper, a vertical tin-plating process was proposed to reduce the pinhole defects and improve the tincoating quality. Compared with the traditional horizontal tin-plating process, the immersion length was reduced from 300-400 mm to 10-100 mm and the tin-plating time was reduced from 7 s to 3 s in the proposed method. The experimental results indicate that immersion length and time are key parameters for the tin-plating quality. With this new tin-plating process, the experimental results show that the pinhole defects can be eliminated effectively by controlling the immersion depth below 100 mm and tin-plating time at 3 s. The thickness of tin-coating increased from not more than 5 μm to 12.3 μm with the proposed vertical tin-plating process. Meanwhile, the thickness of the intermetallic compounds (IMCs) layer between the tin-coating and copper wires was reduced from 3.26 μm to 0.62 μm if the immersion time decreased from 30 s to 1 s. Besides, a self-developed flux, which possesses a boiling point or decomposed temperature of active components over 300℃, exhibits a better efficiency in reducing the pinhole formation.     

Numerical study on viscosity reduction in mining heavy oil by circulating hot water

Viscosity reduction is an important process in mining heavy oil.To predict the temperature variation and viscosity variation of heavy oil in flow direction,computational fluid dynamics(CFD) was adopted to simulate the process of heat transfer and flow in this paper.Moreover,an objective function,namely viscosity reduction efficiency,was established to analyze the effect of viscosity reduction.The results indicate that circulating hot water can reduce viscosity significantly,and that the effect of viscosity reduction depends on the inlet temperature and inlet volumetric flow rate of hot water.There is a maximum temperature of heavy oil in flow direction.With the inlet volumetric flow rate of 2.0m3/h and the inlet temperatures of 60,℃,70,℃ and 80,℃,viscosity reduction efficiencies are 94.6%,96.7% and 97.3%,respectively.With the inlet temperature of 70,℃ and the volumetric flow rates of 1.5m3 /h,2.0 m3/h and 2.5m3/h,viscosity reduction efficiencies are 94.4%,96.7% and 97.2%,respectively.     

Comparison of high order aberration after conventional and customized ablation in myopic LASIK in different eyes of the same patient

Purpose: To verify whether there exists any difference in higher order aberrations after undergoing myopic LASIK (laser in situ keratomileusis) with conventional ablation and customized ablation in different eyes of the same patient. Methods: This was a prospective randomized study of 54 myopic eyes (27 patients) that underwent LASIK using the Nidek EC-5000 ex-cimer laser system (Nidek, Gamagori, Japan). Topography-guided customized aspheric treatment zone (CATz) was used in the first eye of the patient (study group) and the other eye of the same patient was operated on with conventional ablation (control group). Higher order aberrations [root-mean-square (RMS) in the 5-mm zone] of both groups were observed with the Nidek OPD-Scan aberrometer before and 3 months after LASIK. Preoperative mean refractive error was similar between two eyes of the same patient (t=?0.577, P>0.05). Results: Preoperatively, higher order aberrations (RMS in the 5-mm zone) in the CATz ablation and conventional groups were (0.3600±0.0341) μm and (0.2680±0.1421) μm, respectively. This difference was not statistically significant (t=1.292, P>0.05). Three months after LASIK, higher order aberrations (RMS in 5-mm zone) in the CATz ablation and conventional groups were (0.3627±0.1510) μm and (0.3991±0.1582) μm, respectively. No statistically significant difference was noted between pre- and postoperative higher order aberrations in the CATz group (t=?0.047, P>0.05). However, a statistically significant increase in higher order aberrations was observed after conventional ablation (t=?5.261, P<0.05). A statistically sig-nificant difference was noted in the increase of higher order aberrations after LASIK between groups (t=?2.050, P=0.045). Con-clusion: LASIK with conventional ablation and topography-guided CATz ablation resulted in the same BSCVA (best specta-cle-corrected visual acuity) 3 month after LASIK. Higher order aberrations were increased, but the increase of higher order ab-errations after customized ablation treatment was less than that after conventional ablation.     

流场可视化的便携式烟风洞装置

文章介绍了一种整体长度为0.64m,重约为4kg,轻巧、便携的烟风洞装置的特点.该装置有着良好的烟气发生装置和烟气流动质量,方便的燃油补充机构和试件磁力固定结构,是流体力学学科中一种较完美的教学工具.轻巧的结构使得这种烟风洞装置可以很方便地携入教室用于教学演示.各种研究对象在风洞中的绕流情况可以很好地用高质量的数字照片显示出来,这些照片如圆柱绕流,平面叶栅的流线分布,都能较好地反映了流体力学流动基本规律;同时,通过对一个模型汽车所进行的流体力学数值计算（FLUENT）与实验对比,其结果显示出它们的流动状态吻合较好,说明这种便携式烟风洞的良好性能.     

Numerical investigation of confined swirling gas-solid two phase jet

This paper presents ak-ε-k _p multi-fluid model for simulating confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two-phase flow of 30 μm, 45 μm, 60 μm diameter particles respectively yielded results fitting well with published experimental data. Project is supported by Zheijiana Provincial Natural Science Foundation (No. 598017)     

PbMoO4声光器件换能器五层镀层厚度和带宽的确定

利用换能器等效电路网络分析法,计算36°Y切LN/PM声光器件换能器的五层电极结构随归一化频率f/f0变化的声能损耗TL,按照声光器件的布拉格带宽要求选择了换能器各镀层的材料并确定了其厚度和带宽.     

Unsteady flow structure of an airfoil in ground effect

Particle image velocimetry （PIV） experimental results of wake flow structure of a NACA0012 airfoil with small attack angle mounted above water surface are introduced.The experiment was carried out in a small-scale wind-wave tunnel.The diameter of wind-wave tunnel test section is 1.7 m （long） × 0.4 m （width） × 0.4 m （height）.The flow fields around the airfoil were measured under four diffierent conditions by varying the distance between the airfoil and the water surface.The attack angle of the airfoil was kept 10- during the experiment.For each experimental condition,the time series of particle images was captured to calculate continuous evolution of the velocity fields.The velocity fields were ensemble averaged to get the statistic parameters such as mean velocity and vorticity.Typical instantaneous velocity fields for each case are introduced to show the basic flow structure of wind surface flow separation.The aerodynamic loads acting on the airfoil are analyzed qualitatively according to the mean vorticity distribution in the flow field based on the theory of vorticity aerodynamics.The results indicate that the flow structures and drag/lift force of the airfoil alter remarkably with the changing distance between the airfoil and water surface.     

均布载荷作用下悬臂不可压饱和多孔梁的非线性变形

Nonlinear bending of cantilever incompressible poroelastic beams subjected to a uniform load is investigated with the constraint that fluid flow is only in the axial direction. The governing equations for large deflection of the poroelastic beam are derived from theory of incompressible saturated porous media. Then, nonlinear responses of a cantilever beam with impermeable fixed end and permeable free end are examined with the Galerkin truncation method. The deflections and bending moments of the poroelastie beam and the equivalent couples of the pore fluid pressures are shown in figures. The differences of the results between the large deflection and the small deflection theories are analyzed. It is shown that the results of the large deflection theory are smaller than those of the small deflection theory, and the time needed to approach their stationary states for the large deflection theory is shorter than that for the small deflection theory.