小波收缩中统一阈值函数及其偏差、方差与风险分析

该文建立了小波阈值消噪的统一阈值函数,推导了统一阈值函数的偏差、方差、风险的明确关系式.利用这些公式研究了参数不同时(以u=1,2,为例)统一阈值函数估计的偏差、方差、风险与阈值以及小波系数的关系,得到了小波统一阈值函数消噪估计的性能,对小波消噪在工程中应用有重要的理论指导意义.     

Potential of low-voltage organic transistors with high on-state drain current for temperature sensor development

Organic transistors with high on-state drain current at gate and drain voltages of −2 V fabricated on polyethylene naphthalate foils were investigated for sensor development. Two aspects were studied: (a) the ability of such transistors to raise the sensitivity of a temperature sensor and (b) the bias stress stability of the transistors subjected to square voltage pulses that turned them on and off repeatedly. To demonstrate the first aspect, the voltage-amplifying ability of the organic transistor was used to increase the response to the temperature, ordinarily achieved with a thermistor. To achieve voltage amplification, the transistor must have on-state drain current of at least 20 μA at gate and drain voltages of −2 V. Two transistors with on-state drain current of ~60 and ~120 μA were tested, leading to voltage gain of −2.8 and −4.9 V/V, respectively, thus increasing the sensitivity of the temperature sensor by a factor of up to 5. To study the second aspect, the same square voltage pulses were concurrently applied to the gate and drain electrodes, causing the transistor to turn on and off repeatedly. The turn-on and turn-off voltages were −2 and 0 V respectively and four different pulse periods were used: T of 5, 20, 40 and 60 s. For each T, 1000 pulses with turn-on time of 1 s and varying turn-off times were applied to the transistors, leading to the aggregate net stress time of 1000 s in all cases. The changes in the on-state drain current, threshold voltage, and field-effect mobility depended on T, in spite of the net stress time being the same. The reduction in the on-state drain current did not exceed 17%, stabilization was also observed after about 500 cycles in some cases, and the maximum drop occurred for medium T, thus making T = 60 s a favorable condition for sensor operation.     

基于有偏场的光栅图像模糊聚类分割算法

针对有偏场环境下带有光栅的散焦图像分割问题,提出了一种新的基于有偏场估计的模糊聚类分割算法。通过建立依赖于有偏场的模糊聚类目标函数,导出了基于灰度以及邻域灰度均值的聚类中心、模糊聚类函数以及有偏场估计的迭代算法;并在该算法生成的初始分割基础上,利用膨胀算子对分类结果进行细化。该方法较好地处理了传统模糊聚类对有偏场下光栅图像分割精度下降的问题。实验结果表明,基于有偏场的模糊聚类算法能有效分割光栅图像,其分割精度优于传统模糊聚类和阈值法。     

High operational stability of solution-processed organic field-effect transistors with top-gate configuration

Electrical characteristics of top-gate field-effect transistors based on a wide range of solution-processed organic semiconductors are systematically investigated. The top-gate field-effect transistors based on different organic semiconductors—from an amorphous polymer semiconductor to a polycrystalline molecular semiconductor—exhibit higher operational stability compared with bottom-gate organic field-effect transistors reported in literature, in spite of significant difference in field-effect mobility. The correlation between charge transport and operational stability is discussed to gain insight into high operational stability of top-gate organic field-effect transistors.     

因特网拥塞控制的公平性研究综述

将网络拥塞控制的公平性研究划分为在同质流网络中的公平性和在异质流网络中的公平性两个方面,公平性研究在两类网络中均有重大的意义.依此划分,分别介绍了近年来拥塞控制公平性研究的重要进展.同质流网络中公平性研究主要是围绕解决TCP流的RTT歧视这一问题而展开和深入的;异质流网络中公平性研究主要是围绕保护正当行为流的问题而不断推进的,目前的研究热点是对用户公平的AQM算法.最后对拥塞控制公平性研究领域未来有价值的研究问题给出了预测,并阐述了对这几个问题的理解.     

企业间水污染物排放权交易价格竞争博弈

基于不完全信息条件下的贝叶斯博弈模型,建立了水污染物排放权交易市场中交易企业关于排放权交易价格谈判的博弈模型。分别从买卖方交易企业效用最大化的角度确定了双方的最优报价策略。研究表明:排污权交易双方的真实报价有利于促成排污权的成功交易,且有助于交易双方实现帕累托效率优化。     

Search Concentration,Bias, and Parochialism: A Comparative Study of Google,Baidu, and Jike's Search Results From China

Do search engines drive Web traffic to well‐established sites leading to a high degree of search results concentration? Do search engines favor their own content while demoting others? How parochial or cosmopolitan are search engines in directing traffic to sites beyond users' national borders? This study explores these issues by empirically comparing search results of Baidu, Google, and Jike from mainland China obtained in August 2011 and August 2012. It finds that search engines in China, particularly Baidu, tend to drive traffic to well‐established sites. Baidu's results also raise serious doubts over its impartiality. Rather than making users' search experiences more cosmopolitan, tuned to the larger world around them, search engines rarely direct Chinese users to content beyond national borders.     

引入偏置的矩阵分解推荐算法研究

由于矩阵分解良好的可扩展性和较高的预测精度,在推荐算法的应用中都有出色的表现。本文在基础的矩阵分解模型上先后加入全局偏置和时间偏置,以提高预测准确度和推荐质量。以个性化推荐系统为对象,在MovieLens数据集上的实验表明,两种方法在一定程度上提高了算法的准确度。     

Frame of reference and adaptation to directional bias in a video-controlled reaching task

The present study (N=56) investigated spatio-temporal accuracy of horizontal reaching movements controlled visually through a vertical video monitor. Direct vision of the hand was precluded and the direction of hand trajectory, as perceived on the video screen, was varied by changing the angle of the camera. The orientation of the visual scene displayed on the fronto-parallel plane was thus congruent (0° condition) or non-congruent (directional bias of 15°, 30° or 45° counterclockwise) according to the horizontal working space. The goal of this study was to determine whether local learning of a directional bias can be transferred to other locations in the working space, but taking into account the magnitude of the directional bias (15°, 30° or 45°), and the position of the successive objectives (targets at different distances (TDD) or different azimuths (TDA)). Analysis of the spatial accuracy of pointing movements showed that when introducing a directional bias, terminal angular error was linearly related to the amount of angular perturbation (around 30%). Seven trials were, on average, necessary to eliminate this terminal error, whatever the magnitude of the directional bias and the position of the successive targets. When changing the location of the spatial objective, transfer of adaptation was achieved in the TDD condition but remained partial in the TDA condition. Furthermore, initial orientation of the trajectory suggested that some participants used a hand-centred frame of reference whereas others used an external one to specify movement vector. The adaptation process differed as a function of the frame of reference used, but only in the TDA condition. Adaptation for participants using a hand-centred frame of reference was more concerned with changes in the shape of the trajectory, whereas participants using an external frame of reference adapted their movement by up-dating the initial direction of hand trajectory. As a whole, these findings suggest that the processes involved in remote visual control of hand movement are complex with the result that tasks requiring video-controlled manipulation like video-controlled surgery require specific spatial abilities in actors and consequential plasticity of their visuo-motor system, in particular concerning the selection of the frame of reference for action.     

Predicting growth rates and growth boundary of Listeria monocytogenes — An international validation study with focus on processed and ready-to-eat meat and seafood

The performance of six predictive models for Listeria monocytogenes was evaluated using 1014 growth responses of the pathogen in meat, seafood, poultry and dairy products. The performance of the growth models was closely related to their complexity i.e. the number of environmental parameters they take into account. The most complex model included the effect of nine environmental parameters and it performed better than the other less complex models both for prediction of maximum specific growth rates (µ_max values) and for the growth boundary of L. monocytogenes. For this model bias and accuracy factors for growth rate predictions were 1.0 and 1.5, respectively, and 89% of the growth/no-growth responses were correctly predicted. The performance of three other models, including the effect of five to seven environmental parameters, was considered acceptable with bias factors of 1.2 to 1.3. These models all included the effect of acetic acid/diacetate and lactic acid, one of the models also included the effect of CO₂ and nitrite but none of these models included the effect of smoke components. Less complex models that did not include the effect of acetic acid/diacetate and lactic acid were unable to accurately predict growth responses of L. monocytogenes in the wide range of food evaluated in the present study. When complexity of L. monocytogenes growth models matches the complexity of foods of interest, i.e. the number of hurdles to microbial growth, then predicted growth responses of the pathogen can be accurate. The successfully validated models are useful for assessment and management of L. monocytogenes in processed and ready-to-eat (RTE) foods.