一种低功耗的无线传感器网络MAC协议

在无线传感器网络中,为了避免不必要的能耗而达到延长网络寿命的目的,提出一种低功耗的无线传感器网络MAC协议。此协议在低功率侦听(LPL)基础上进行修改,通过前一次轮询的结果来推测这一次的流量状况,根据流量状况自适应调整侦听睡眠周期结构中相应的占空比,从而降低能耗。通过编程仿真并结合实验,对此模型进行验证,证明了此算法能降低能耗。     

炭分子筛概述

阐述了炭分子筛分离的原理，并分别从其制备原料、制备方法、产品用途等方面综述了近年来炭分子筛的新进展。     

Morphology and properties of blends of polypropylene with ethylene-propylene rubber

Great attention has been paid to the toughening of isotactic polypropylene (PP) in recent years in order to make full use of this plastic. This paper presents the results of our study on the compatibility of PP with ethylene-propylene-diene rubber (EPT), polybutadiene rubber (PB) or styrene-butadiene rubber (SBR) through characterization of the blends' morphology, and on. the morphology and properties of binary blends of PP with EPT (EPT/PP) and ternary blends of PP, EPT, and polyethylene (PE) (EPT/PE/PP). Morphological structure of solution blends and the great improvement in low-temperature impact strength and other properties of the mechanical blends have shown the difference among EPT, PB, and SBR in compatibility with PP, the effectiveness of using EPT as PP's toughening agent, and the effect of EPT on EPT/PP blend as both toughening agent and compatibilizer. Addition of EPT to EPT/PP made interesting changes in morphology but no effect on properties was observed.     

Fabrication and amplification of Rhodamine B‐doped step‐index polymer optical fiber

A step‐index polymer optical fiber (SI POF) containing Rhodamine B in poly(methyl methacrylate) (PMMA) has been fabricated by a preform technique. Fluorescence of different fiber lengths were observed and discussed. A high gain (23 dB) for a SI POF with 60‐cm length, 400‐μm diameter was obtained. The Rhodamine B content of the doped SI POF is 5 ppm‐wt. The signal wavelength providing the highest gain for a 60 cm SI POF is around 630 nm, and the optimum fiber length is about 60 cm at 10 kW launched pump power. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 681–685, 2004     

氧化铝上吸附平衡与动力学的分形特性

在实验测定氧化铝吸附氮气的平衡和动力学过程的基础上 ,由平衡数据得到分形维数 ,对动力学结果分别用欧氏几何和分形几何的动力学模型进行处理 ,比较两种方法得到的扩散系数之间的差别。结果表明 :粉状氧化铝的分形维数为 2 .12 ;采用分形动力学模型得到的扩散系数同欧氏几何扩散模型的结果不一样 ,扩散系数不随浓度的变化而改变 ;而欧氏几何扩散模型中的扩散系数随浓度变化发生改变 ,且变化符合Darken关系     

新型高压密封装置的优化设计

以最低制造成本为优化目标，建立了新型高压密封装置优化设计的数学模型，并给出设计实例。结果表明，采用优化设计可降低制造成本１４．７％。     

Finite-time consensus of multiple second-order dynamic agents without velocity measurements

This article considers the finite-time consensus of multiple second-order dynamic agents without velocity measurements. A feasible protocol under which each agent can only obtain the measurements of its position relative to its neighbours is proposed. By applying the graph theory, Lyapunov theory and the homogeneous domination method, some sufficient conditions for finite-time consensus of second-order multi-agent systems are established under the different kinds of communication topologies. Some examples are presented to illustrate the effectiveness of the theoretical results.     

Sliding mode control for Markov jump linear uncertain systems with partly unknown transition rates

In this paper, based on sliding mode control approach, the robust stabilisation problem for a class of continuous-time Markovian jump linear uncertain systems with partly unknown transition rates is investigated. The transition rate matrix under consideration covers completely known, boundary known and completely unknown elements. By making use of linear matrix inequalities technique, sufficient conditions are presented to derive the linear switching surface and guarantee the stochastic stability of sliding mode dynamics. Then a sliding mode control law is designed to drive the state trajectory of the closed-loop system to the specified linear switching surface in finite time in spite of the existing uncertainties and unknown transition rates. Finally, an example is given to verify the validity of the theoretical results.     

Fisher discrimination based low rank matrix recovery for face recognition

In this paper, we consider the issue of computing low rank (LR) recovery of matrices with sparse errors. Based on the success of low rank matrix recovery in statistical learning, computer vision and signal processing, a novel low rank matrix recovery algorithm with Fisher discrimination regularization (FDLR) is proposed. Standard low rank matrix recovery algorithm decomposes the original matrix into a set of representative basis with a corresponding sparse error for modeling the raw data. Motivated by the Fisher criterion, the proposed FDLR executes low rank matrix recovery in a supervised manner, i.e., taking the with-class scatter and between-class scatter into account when the whole label information are available. The paper shows that the formulated model can be solved by the augmented Lagrange multipliers and provides additional discriminating power over the standard low rank recovery models. The representative bases learned by the proposed method are encouraged to be closer within the same class, and as far as possible between different classes. Meanwhile, the sparse error recovered by FDLR is not discarded as usual, but treated as a feedback in the following classification tasks. Numerical simulations demonstrate that the proposed algorithm achieves the state of the art results.     

A GPU-based parallel method for evolutionary tree construction

Evolutionary trees are widely applied in various applications to show the inferred evolutionary relationships among species or entities. Neighbor-Joining is one solution for data-intensive and time-consuming evolutionary tree construction, with polynomial time complexity. However, its performance becomes poorer with the growth of massive datasets. Graphics Processing Units (GPUs) have brought about new opportunities for these time-consuming applications. Based on its high efficiency, a GPU-based parallel Neighbor-Joining method is proposed, and two efficient parallel mechanisms, data segmentation with asynchronous processing and the minimal chain model with bitonic sort, are put forward to speed up the processing. The experimental results show that an average speedup of 25.1 is achieved and even approximately 30 can be obtained with a sequence dataset ranging from 16,000 to 25,000. Moreover, the proposed parallel mechanisms can be effectively exploited in some other high performance applications.