Flow and impingement cooling heat transfer along triangular rib-roughened walls

Experiments are performed to study slot air jet impingement cooling flow and the heat transfer along triangular rib-roughened walls. Both flow visualization and local heat transfer measurements along the ribbed wall are made. The effect of different rib protrusions (heights) on the impinging flow and heat transfer along the wall is studied, which is achieved by using different sizes of nozzles. Two different ribbed walls with different rib pitches are selected which have a rib pitch-to-height ratio of 2 and 4, respectively. The widely opened cavity between neighboring ribs make more intense transport of momentum between the wall jet and cavity flow so that recirculation cell in the cavity is hardly observed. This leads to a higher heat transfer around the cavity wall than in the case with rectangular ribs. However, in the region of laminar wall jet, a number of air bubbles enclosing the cavities are formed which prevent penetration of the wall jet into the cavities. This leads to a significant reduction in the heat transfer. The geometric shape of the triangular ribs is more effective in rebounding the wall jet away from the wall than in the case with rectangular ribs. The rebound of the jet away from the wall causes a significant reduction in the heat transfer. A comparison and correlations of the stagnating point Nusselt number under different conditions are presented and discussed. During the experiments, the Reynolds number varies from 2500 to 11,000, the slot width-to-rib height ratio from 1.17 to 6.67, and nozzle-to-plate spacing from 2 to 16.     

Models for tool-path plan optimization in patch-by-patch machining

In this paper, we address the problem of optimizing the tool path plan for patchby-patch machining of parts having multiple surface patches. The tool path plan defines the sequence in which the patches are to be machined and the entry and exit points for the cutting-tool within each patch. Curent CAD/CAM systems require the user to select the tool path plan. When the number of surface patches increases and alternative machining strategies need to be evaluated, it is often difficult for the user to select the optimal tool path plan that minimizes the total time to machine the part. In this paper, we address three cases of this optimization problem, and present models that can be used to incorporate tool path plan evaluation and optimization capabilities in CAD/CAM systems.     

Decision-making in a single-period inventory environment with fuzzy demand

This paper first defines the profitability to be the probability of achieving a target profit under the optimal ordering policy, and introduces a new index (achievable capacity index; I_A) which can briefly analyze the profitability for newsboy-type product with normally distributed demand. Note that since the level of profitability depends on the demand mean μ and the demand standard deviation σ if the related costs, selling price, and target profit are given, the index I_A is a function of μ and σ. Then, we assess level performance which examines if the profitability meets designated requirement. The results can determine whether the product is still desirable to order/manufacture. However, μ and σ are always unknown, and the demand quantity is common to be imprecise, especially for new product. To tackle these problems, a constructive approach combining the vector of fuzzy numbers is introduced to establish the membership function of the fuzzy estimator of I_A. Furthermore, a three-decision testing rule and step-by-step procedure are developed to assess level performance based on fuzzy critical values and fuzzy p-values.     

An optimal design for axial-flow fan blade: theoretical and experimental studies

The technique of inverse design problem (IDP) for optimizing the three-dimensional shape of an axial-flow fan blade based on the desired airflow rate is presented in this work. The desired volume flow rate of air can be obtained from the airflow rate of the existing axialflow fan by multiplying it with a constant which is greater than unity. The geometry of the redesigned fan blade is generated using numerous design variables, which enables the shape of the fan blade to be constructed completely; thus the technique of parameter estimation for the inverse design problem can be used in this study. Results show that with the redesigned optimal fan blade, the airflow rate of fan can be increased, thereby improving the performance of the axial-flow fan. Finally, to verify the validity of this work, the prototypes of the original and optimal axial-flow fan blades are fabricated and fan performance tests are conducted with these blades on the basis of the AMCA-210-99 standard. The algorithm used in the present study can be applied to the blade design problem in any propulsion and power systems.     

A new model for springback prediction in which the Bauschinger effect is considered

Springback prediction is an important issue for the sheet metal forming industry. Most sheet metal elements undergo a complicated cyclical deformation history during the forming process. For an accurate prediction of springback, the Bauschinger effect must be considered to determine accurately the internal stress distribution within the sheet metal after deformation. Based on the foundations for isotropic hardening and kinematic hardening, Mroz multiple surface model, plane strain assumptions, and experimental observations, a new incremental method and hardening model is proposed in this paper. This new model compares well with the experimental results for aluminum sheet metal undergoing multiple-bending processes. As is well known, aluminum is one of the most difficult sheet metals to simulate. The new hardening model proposed in this paper is not only a generic model for springback prediction but also a hardening model for sheet metal forming process simulation.     

氮化硅反应烧结设备PLC自动控制

本文通过对氮化硅反应烧结设备的可编程控制，说明可编程控制技术是材料学科的一个重要应用方向。     

Low gate interface traps AlGaN/GaN HEMTs using a lattice matched ZrZnO transparent gate design

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) using a radio-frequency magnetron sputtered ZrZnO transparent oxide layer as a gate insulator are investigated and compared with traditional GaN HEMTs. A negligible hysteresis voltage shift in the C–V curves is seen, from 0.09 V to 0.36 V, as the thickness of ZrZnO films increases. The composition of ZrZnO at different annealing temperatures is observed using X-ray photoelectron spectroscopy (XPS). The ZrZnO thin film achieves good thermal stability after 600 °C, 700 °C and 800 °C post-deposition annealing (PDA) because of its high binding energy. Based on the interface trap density analysis, D_it has a value of 2.663 × 10¹² cm⁻²/eV for 10-nm-thick ZrZnO-gate HEMTs and demonstrates better interlayer characteristics, which results in a better slopes for the I_ds degradation (5.75 × 10⁻¹ mA/mm K⁻¹) for operation from 77 K to 300 K. The 10-nm-thick ZrZnO-gate device also exhibits a flat and a stable 1/f noise, as V_GS–V_th, and at various operating temperatures. Therefore, ZrZnO has good potential for use as the transparent film for a gate insulator that improves the GaN-based FET threshold voltage and improves the number of surface defects at various operating temperatures.     

实用加解扰系统

介绍一个由４种视频基带加扰模式组成的数字加扰系统，具有很高的保密性。而系统的解扰可以由低成本的模拟解扰器完成。