Flexible joints control: A minimum-time feed-forward technique

The paper proposes a linear programming approach to the feed-forward minimum-time control of flexible joints. Taking into account both input and output constraints, the optimal bang–bang control is computed by discretizing a continuous-time joint model and by solving a sequence of linear programming feasibility problems. The resulting joint motion is a smooth rest-to-rest motion without oscillations. Theoretical analysis is presented and proof of convergence is given. Experimental results illustrate the proposed open-loop technique. Comparisons are made with inversion-based techniques.     

Dual-Current Pump Module for Transient Improvement of Step-Down DC–DC Converters

This paper presents a novel dual-current pump module (DCPM) to improve the transient response of dc-dc converters. The DCPM operates only during transient to provide two additional current injections for step-up load and current drains for step-down load. Due to the two current pump paths, the current stress on the switches of the DCPM is also reduced. The measurement results show that the DCPM can enhance the dynamic recovery time of the buck dc-dc converter by more than an order.     

Integration of a-Si:H solar cell with novel twist nematic liquid crystal cell for adjustable brightness and enhanced power characteristics

This study improves the output power and brightness characteristics of a translucent hydrogenated amorphous silicon (a-Si:H) solar cell by integrating the solar cell with a novel twist nematic (TN) liquid crystal (LC) cell incorporating a sub-wavelength metal grating polarization beam splitter (PBS). Although conventional TN-LC cells are widely used to adjust the brightness in many display applications, the sheet polarizers used in such cells decay when exposed to ultraviolet (UV) rays and have a low light efficiency. Accordingly, in this study, a sub-wavelength metal grating PBS is used to replace not only the sheet polarizers in the conventional TN-LC cell but also the upper and lower alignment layers and transparent electrodes. Therefore, a translucent a-Si:H solar cell integrating with the novel TN-LC cell with the sub-wavelength metal grating PBS could improve power efficiency and durability in UV ray environment. The experimental results show that the transmittance gap between the “on” and “off” states of the enhanced translucent a-Si:H solar cell/novel TN-LC cell is of the order of 26.6% (i.e. 4.3-30.9%) for incident light with a wavelength of 800 nm, 6.3% (i.e. 10.8-17.1%) for an incident wavelength of 400 nm and 2.7% (i.e. 0-2.7%) for an incident wavelength of 510 nm. Moreover, it is shown that the novel TN-LC cell increases the maximum electrical power developed by the translucent a-Si:H solar cell and improves its power conversion efficiency by 0.209% in the “off” state and 0.417% in the “on” state. As a result, the proposed device represents an ideal solution for building-integrated photovoltaic (BIPV) systems, automobile industry applications and many other adjustable brightness photovoltaic applications.     

A multiple circular path convolution neural network system for detection of mammographic masses

A multiple circular path convolution neural network (MCPCNN) architecture specifically designed for the analysis of tumor and tumor-like structures has been constructed. We first divided each suspected tumor area into sectors and computed the defined mass features for each sector independently. These sector features were used on the input layer and were coordinated by convolution kernels of different sizes that propagated signals to the second layer in the neural network system. The convolution kernels were trained, as required, by presenting the training cases to the neural network. In this study, randomly selected mammograms were processed by a dual morphological enhancement technique. Radiodense areas were isolated and were delineated using a region growing algorithm. The boundary of each region of interest was then divided into 36 sectors using 36 equi-angular dividers radiated from the center of the region. A total of 144 Breast Imaging-Reporting and Data System-based features (i.e., four features per sector for 36 sectors) were computed as input values for the evaluation of this newly invented neural network system. The overall performance was 0.78-0.80 for the areas (Az) under the receiver operating characteristic curves using the conventional feed-forward neural network in the detection of mammographic masses. The performance was markedly improved with Az values ranging from 0.84 to 0.89 using the MCPCNN. This paper does not intend to claim the best mass detection system. Instead it reports a potentially better neural network structure for analyzing a set of the mass features defined by an investigator.     

Simulation of the effects of space charge and Schottky barriers on ferroelectric thin film capacitor using Landau Khalatnikov theory

The role of space charge induced in a ferroelectric thin film and the presence of Schottky barriers at the two electrode/film interfaces are studied by numerical simulation using Landau-Khalatnikov theory. In this work, the whole film is considered as the stacking of dipolar layers, each of which contains multilayers of perovskite cells. In the presence of a local electric field, the double-well thermodynamic potential of each layer is modified in an asymmetric manner. The local electric field distribution is determined both by the space charge and the boundary conditions imposed by the Schottky barrier heights. Asymmetric and skewed hysteresis loops are generated     

Building blocks for a two-frequency laser lidar-radar: a preliminary study

A new principle of lidar-radar is theoretically and experimentally investigated. The proposed architecture is based on the use of an rf modulation of the emitted light beam and a direct detection of the backscattered intensity. Use of a radar-processing chain allows one to obtain range and Doppler measurements with the advantages of lidar spatial resolution. We calculate the maximum range of this device, taking into account different possible improvements. In particular, we show that use of a pulsed two-frequency laser and a spatially multimode optical preamplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility of both range and Doppler measurements. The building blocks of this lidar-radar are tested experimentally: The radar processing of an rf-modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. In addition, signal-to-noise ratio improvement by optical pre-amplification is demonstrated at 1.06 microm. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits two-frequency pulses with tunable pulse duration (from 18 to 240 ns) and beat frequency (from 0 to 2.65 GHz) to be obtained.     

Human Motion Planning Based on Recursive Dynamics and Optimal Control Techniques

This paper presents an efficient optimal control and recursive dynamics-based computer animation system for simulating and controlling themotion of articulated figures. A quasi-Newton nonlinear programmingtechnique (super-linear convergence) is implemented to solve minimumtorque-based human motion-planning problems. The explicit analyticalgradients needed in the dynamics are derived using a matrix exponentialformulation and Lie algebra. Cubic spline functions are used to make thesearch space for an optimal solution finite. Based on our formulations,our method is well conditioned and robust, in addition to beingcomputationally efficient. To better illustrate the efficiency of ourmethod, we present results of natural looking and physically correcthuman motions for a variety of human motion tasks involving open andclosed loop kinematic chains.     

WiMax与TDD-HSDPA的性能分析与比较

随着无线Internet用户的急剧增长和数据业务的快速增加，对下代无线网络系统提出了越来越高的要求。各运营商更是积极地部署各种宽带无线接入（BWA）技术；第三代无线移动通信技术（3G）就是其中的备选方案之一。同时，随着无限局域网（WLAN）802.11的成功商用，IEEE802.16以及对应的无线城域网（WMAN）空口也成为宽带无线接入技术的有利可选方案。在本文中，我们将对这两种技术提供详细的性能分析和比较。     

Robust H/sub /spl infin// control for fuzzy systems with Frobenius norm-bounded uncertainties

In this paper, we investigate the problem of robust H/sub /spl infin// performance and stabilization for a class of uncertain fuzzy systems with Frobenius norm-bounded parameter uncertainties in all system matrices. Both continuous- and discrete-time uncertain fuzzy systems are considered under a unified treatment called bounded real lemma for fuzzy systems. Unlike the bounded real lemma in the linear theory of robust H/sub /spl infin// control where necessary and sufficient conditions were obtained, only sufficient condition based on Lyapunov method is shown. Furthermore, connection between robust H/sub /spl infin// problems involving uncertainty and standard uncertainty-free H/sub /spl infin// problems is established via matrix algebra. As for controller synthesis, a state feedback fuzzy control law is designed via relaxed linear matrix inequality (LMI) formulations.