The Application of Neural Networks in the Prediction of Spring-back in an L-Shaped Bend

The purpose of this work is to establish an effective prediction of the spring-back of material during the processing of an L-shaped bend. FEM-simulation of an L-shaped bend is carried out for various thicknesses of material, various punch-round-radii and die-round-radii. The spring-back depends on the shape of the bend-die and the mechanical properties of the material. The results of spring-back from FEM-simulation are then input to a neural network to establish a model for the L-shaped bend variables. The neural network is composed of a number of functional nodes. Once the L-shaped bend para-meters (material thickness, punch-round-radius and die-round-radius) are given, the bend processing performance (spring-back) can be accurately predicted by this developed network. A simulation annealing (SA) optimisation algorithm with a performance index to obtain a perfect L-shape can search for the optimal bend processing parameters. A satisfactory result was achieved based on a demonstration of simulation and on practical experience, showing that this is a new and feasible approach for use in the control of spring-back of materials.     

Plane wave reflection and refraction involving a finitely conducting medium

In this work the structure of electromagnetic field in a lossy conducting medium is studied in detail. The meaning of the complex angle of refraction is explained in terms of real parameters involved in this problem. The concepts are illustrated with a wave refracting from air into pure water at a frequency of 95 GHz and an incidence angle of 60/spl deg/. The approach is similar to that used to derive refraction in many electromagnetic textbooks, such as Stratton (J. A. Stratton, 1941), which has been cited in many of the textbooks published since. Our results agree with his for the real angle of the equiphase surface of the refracted fields, but we explore further subjects, including the instantaneous and time-averaged Pointing vectors.     

复杂变断面锻件辊锻成形的金属流动

本文针对复杂变断面锻件在辊锻成形过程中的变形特征及金属流动规律,通过辊锻成形理论并结合实例进行了分析,对不均匀变形:变形过程中断面各部分金属相互牵制及相互转移,断面各部位变形的导前与滞后、辊锻件在变形过程中的稳定条件、影响金属填充的各因素等问题进行了理论分析与探讨,并提出了相应的技术措施。     

A method that preserves circulation during preparation of the pectoralis major myocutaneous flap in head and neck reconstruction

The present article describes a method that preserves circulation during the preparation of the pectoralis major myocutaneous flap used in head and neck reconstruction. The major disadvantage of this flap is its poor circulation and consequent partial necrosis. To solve this problem, we analyzed the circulation and hemodynamics of the pectoralis major myocutaneous flap (the perforator of the anterior intercostal branch located about 1 to 2 cm medial to the areola in the fourth intercostal space is important), evaluated the safe donor sites in the chest wall for a skin island (the perforator is included on the skin island's central axis), improved the surgical procedure for elevating flaps (for preventing perforator injuries), and devised a means to transfer flaps, thereby increasing the range of the flaps (the transfer route is under the clavicle). Using this technique, head and neck reconstruction was performed on 62 patients. The diagnosis included oral cancer (21), oropharyngeal carcinoma (10), parotid carcinoma (10), hypopharyngeal carcinoma (9), and other head and neck malignant tumors (12). Of these, partial or marginal necrosis of the flap caused by circulatory problems was detected in three patients (5 percent). Using our method, the problems associated with inadequate circulation in the pectoralis major myocutaneous flap were greatly alleviated, thus reconfirming the usefulness of this flap in head and neck reconstruction.     

Image Segmentation Using Some Piecewise Constant Level Set Methods with MBO Type of Projection

In this work, we are trying to propose fast algorithms for Mumford-Shah image segmentation using some recently proposed piecewise constant level set methods (PCLSM). Two variants of the PCLSM will be considered in this work. The first variant, which we call the binary level set method, needs a level set function which only takes values ±1 to identify the regions. The second variant only needs to use one piecewise constant level set function to identify arbitrary number of regions. For the Mumford-Shah image segmentation model with these new level set methods, one needs to minimize some smooth energy functionals under some constrains. A penalty method will be used to deal with the constraint. AOS (additive operator splitting) and MOS (multiplicative operator splitting) schemes will be used to solve the Euler-Lagrange equations for the minimization problems. By doing this, we obtain some algorithms which are essentially applying the MBO scheme for our segmentation models. Advantages and disadvantages are discussed for the proposed schemes. We acknowledge support from the Norwegian Research Council and IMS of the National University of Singapore.     

UHF频段射频识别读写器的设计

结合ISO18000-6c的RFID系统标准,提出其读写器的设计方案。阐述了读写器的硬件设计,介绍了射频发送与接收单元的电路结构,并运用混频器直接下变频的方式对915 MHz信号进行解调,简化了解调电路。仿真测试结果说明该设计方案可满足实际RFID应用系统的需要。     

遗传算法在边坡稳定系数计算中的应用

边坡稳定性的关键问题是确定最危险滑动面(潜在最危险滑动面)和边坡的稳定系数。国内外一般是采用先假定边坡滑移模式,然后近似确定最危险滑动面,再求近似的边坡稳定系数的方法来分析边坡的稳定性,但假设的边坡滑移模式难以反映边坡滑移的实际状态。因此本文探索利用遗传算法搜索最危险滑动面,并得到最小稳定系数及对应的最危险滑动面曲线,取得了较好的效果。     

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.     

Statistical correlations between two-dimensional images and three-dimensional structures in natural scenes

In spite of the recent surge in the popularity of statistical approaches to vision, the joint statistics of coregistered range and light-intensity images have gone relatively unexplored. We investigate statistical correlations between images and the surface shapes that produced them. We determine which linear properties of range images can be best predicted from simple computations on intensity information, and we determine those properties of intensity images that best predict range information. We find that significant (up to p = 0.45) and potentially exploitable correlations exist between linear properties of range and intensity images, and we explore the structure of these correlations.     

Simulation analysis of conduction block in unmyelinated axons induced by high-frequency biphasic electrical currents

Nerve conduction block induced by high-frequency biphasic electrical currents is analyzed using a lumped circuit model of the unmyelinated axon based on Hodgkin-Huxley equations. Axons of different diameters (5-20 microm) can not be blocked completely when the stimulation frequency is between 2 kHz and 4 kHz. However, when the stimulation frequency is above 4 kHz, all axons can be blocked. At high-frequency a higher stimulation intensity is needed to block nerve conduction. The larger diameter axon has a lower threshold intensity for conduction block. The stimulation waveform in which the pulsewidth changes with frequency is more effective in blocking nerve conduction than the waveform in which the pulsewidth is fixed. The activation of potassium channels, rather than inactivation of sodium channels, is the possible mechanism underlying the nerve conduction block of the unmyelinated axon. This simulation study further increases our understanding of axonal conduction block induced by high-frequency biphasic currents, and can guide future animal experiments as well as optimize stimulation waveforms that might be used for electrical nerve block in clinical applications.