一种基于Web的分类体系学习算法

领域分类结构的抽取已成为本体工程和本体学习的关键部分,提出一种新的分类结构学习算法,将Web作为知识获取的语料库,运用迭代方法抽取相关语言学模式,再利用语言学模式抽取分类结构,并采用改进的互信息方法对结果进行评价和过滤,最后通过实验对该分类学习算法的性能进行评价.实验表明：算法具有良好的跨领域性,在准确率和召回率方面也有改善.     

Exploring the Origin of Maximum Entropy States Relevant to Resonant Modes in Modern Chladni Plates

The resonant modes generated from the modern Chladni experiment are systematically confirmed to intimately correspond to the maximum entropy states obtained from the inhomogeneous Helmholtz equation for the square and equilateral triangle plates. To investigate the origin of maximum entropy states, the inhomogeneous Helmholtz equation is modified to consider the point interaction coming from the driving oscillator. The coupling strength associated with the point interaction is characterized by a dimensionless factor α. The δ potential of the point interaction is numerically modelled by a truncated basis with an upper index N. The asymptotic behavior for the upper index N is thoroughly explored to verify that the coupling strength of α = 1.0 can make the theoretical resonant modes agree excellently with the maximum entropy states as N→∞. It is further authenticated that nearly the same resonant modes can be obtained by using a larger coupling strength α when a smaller upper index N is exploited in the calculation.     

Fraunhofer Diffraction Pattern by a Slit Aperture between a Knife Edge and a Metal Cylinder

The Fraunhofer diffraction pattern of an aperture formed between a knife edge and a smooth surface of a turned metal cylinder or half cylinder is different from the diffraction pattern of an ideal slit aperture. The diffraction pattern is simulated by adding the light reflected by the cylinder surface to the pattern formed by a slit, and is measured using a cylinder that has been partly cut away so that it can represent either a full or half cylinder. The theoretical and measured patterns agree well with each other.     

季节因素对气候网络影响研究

气候网络在地球科学领域研究中是一个新的热点,对于分析和揭示气候场的特征及关联结构具有较强优势.已有气候网络的构建一般选取冬季月份的样本数据,而且在研究中忽略了其他季节月份对气候网络的影响.本文研究了季节因素对气候网络的影响,研究发现:气候网络在不同季节的整体特征参数基本保持稳定,但是网络社团结构以及局部节点拓扑连接随季节变化显著.可以利用这一结论来研究不同季节全球遥相关模态变化情况以及局部地区气候特征随季节变化情况.     

不同结构六边形斑图演化过程光谱特性

采用发射光谱法,研究了水电极介质阻挡放电中具有相同对称性的3种不同结构的六边形斑图演化过程的光谱特性。实验结果表明,随着外加电压的增加,放电首先形成六边形点阵斑图,然后是空心六边形斑图,最后是蜂窝六边形斑图。利用氩原子696.5 nm(2P_2→1S_5)谱线的展宽、氩原子763.2 nm(2P_6→1S_5)与772.1 nm(2P_2→1S_3)两条谱线强度比法和氮分子第二正带系(C~3Π_u→B~3Π_g)的发射谱线,研究上述3种斑图的电子密度、电子激发温度及分子振动温度。结果发现,随着外加电压的升高,六边形点阵斑图、空心六边形斑图和蜂窝六边形斑图的电子密度逐渐减小,而电子激发温度和分子振动温度逐渐增加。等离子体状态的改变直接影响着斑图的自组织。     

平顶高斯超短脉冲激光的时间部分相干性对相干合成的影响

 利用准单色光干涉理论,计算了2×2平顶高斯超短脉冲激光在远场的干涉图样,分析了激光的时间部分相干性及其存在束间相位差时对相干合成的影响。计算结果表明,当单路激光输出光束线宽小于100 nm时,理想波前的远场光斑图样和峰值光强基本保持不变,当光束线宽大于100 nm时,干涉减弱衍射效应逐渐增强;光束间存在相位差时,时间部分相干性将破坏远场图样随束间相位差的周期性变化,相位差越大干涉越弱;当超过相干长度时,则为非相干合成,但1/6倍相干长度范围内,仍可视为较理想的相干合成,此时焦斑的斯特列尔比大于0.9,对超短脉冲的相干合成影响可忽略。     

Patterns at the onset of electroconvection in freely suspended smectic films

We report the results of experiments on electrically driven convection that occurs in a thin, freely suspended film of smectic A liquid crystal when an electric field is applied in the plane of the film. Convection in a vortex pattern is found above a well-defined critical voltage. The film behaves as a two-dimensional isotropic liquid: neither its thickness nor the director field are modified by the flow. We present measurements of the critical voltage at the onset of convection in two experimental configurations—one which allows the injection of charges into the film from the electrodes, and one which does not. When injection is present, the critical voltage for the onset of flow increases monotonically with increasing frequency of applied field. With no injection, there is no instability at DC and the critical voltage diverges there. The nature of the flow pattern observed at onset changes with frequency. Below a certain frequency the film flows in vortices that extend over the width of the film; above this frequency the flow is confined to two lines of smaller vortices localized along the electrodes. We present a simple discussion of the mechanisms which drive the convection.     

介质阻挡放电跃变升压模式下靶波斑图研究

在大气压氩气介质阻挡放电中,首次通过跃变外加电压得到了稳定的靶波斑图.实验分别研究了跃变再缓变和直接跃变升压模式下靶波斑图的稳定性和波长选择.研究发现,跃变再缓变升压之后得到的靶波斑图不稳定,其与螺旋波相互转换.在这种转换中,靶波每次出现的时间为几十毫秒.直接跃变升压得到的靶波斑图稳定性明显增强,其稳定时间通常为5 min以上.比较不同升压模式下靶波斑图的波长,发现直接跃变升压模式下波长随电压升高减小较快.综上表明,升压模式对靶波斑图的稳定性和波长都有影响. 关键词： 介质阻挡放电 靶波斑图 跃变升压 缓变升压     

A new tuning procedure for the DTL RF field pattern

The DTL tank is a multi-cell cavity.In a fabricated tank,the measured average axial field E0 for each cell may obviously deviate from the designed value.It is generally thought the deviation is due to the errors in fabrication and assembly.But it is not always true.In this paper,it is shown that the deviation may already exist before fabrication in some cases.It is partly due to the imperfection of the current design procedures.A new design method is introduced to reduce the deviation in the design stage.     

在光敏性三元聚合物混合物中构造 多尺度有序图案

由多组分聚合物混合物所形成的多尺度有序结构能够展现出许多新奇的物理化学性质, 从而使其在材料工程领域具有十分重要的潜 在应用价值. 本文通过计算机模拟, 在光敏性不相容三元混合物体系中创建了多尺度有序结构. 通过调节光照区域和掩膜形状, 获得了棋盘形、箭靶状等十分独特的形貌, 并且这些结构可以在实验上通过在适当的时间淬火而稳定较长的时间. 详细探讨了组分比、掩膜宽度、间距以及光照强度对体系的影响, 从而为实现多尺度长程序花样薄膜的制备提供了一个简便的途径, 同时也为纳米器件的制备提供了一定的指导.