人工电离层洞形态调制及其对短波传播的影响

本文在电离层中性气体点源扩散近似解的基础上,给出了多源释放动力学模型.分析了释放物质、释放高度、释放模式和释放量等因素对人工电离层洞形态调制的影响,并利用电离层短波三维数字射线追踪技术,对不同调制电离层洞的电波传播效应进行了数值模拟和分析. 关键词： 化学物质释放 人工电离层洞 形态调制 电波传播效应     

Ultrasonically assisted evaluation of the impact of atherosclerotic plaque on the pulse pressure wave propagation: a clinical feasibility study

The purpose of this work was to evaluate ultrasound modality as a non-invasive tool for determination of impact of the degree of the atherosclerotic plaque located in human internal carotid arteries on the values of the parameters of the pulse wave. Specifically, the applicability of the method to such arteries as brachial, common, and internal carotid was examined. The method developed is based on analysis of two characteristic parameters: the value of the mean reflection coefficient modulus |Γ|_a of the blood pressure wave and time delay Δt between the forward (travelling) and backward (reflected) blood pressure waves. The blood pressure wave was determined from ultrasound measurements of the artery’s inner (internal) diameter, using the custom made wall tracking system (WTS) operating at 6.75 MHz. Clinical data were obtained from the carotid arteries measurements of 70 human subjects. These included the control group of 30 healthy individuals along with the patients diagnosed with the stenosis of the internal carotid artery (ICA) ranging from 20% to 99% or with the ICA occlusion. The results indicate that with increasing level of stenosis of the ICA the value of the mean reflection coefficient measured in the common carotid artery, significantly increases from |Γ|_a = 0.45 for healthy individuals to |Γ|_a = 0.61 for patients with stenosis level of 90-99%, or ICA occlusion. Similarly, the time delay Δt decreases from 52 ms to 25 ms for the respective groups. The method described holds promise that it might be clinically useful as a non-invasive tool for localization of distal severe artery narrowing, which can assist in identifying early stages of atherosclerosis especially in regions, which are inaccessible for the ultrasound probe (e.g. carotid sinus or middle cerebral artery).     

A modified tonality and its application to objective evaluation of laser printers noise

Noise in a laser printer is affected by many components, such as spring force, spring constant, and friction coefficient. Objective evaluation of pick up noise is difficult because of background noises, such as operating sound. In particular, pick up noise generated between the friction pad and paper in the process of printing has become an essential aspect of quality evaluation. However, the existing criteria for evaluating pick-up noise have solely relied on subjective human judgments; therefore, there is a need to objectify these criteria. In this paper, the noise index for determining the existence of pick-up noise is established using a modified tonality at just noticeable sound level limit. The study has investigated factors that cause pick-up noise and suggests the substitution of printer components that determine spring constants, spring force, and the quality of friction pads. The proposed noise index is successfully applied to classifying the pick-up noise and mitigating the noise through the optimized design combination of laser printer components.     

基于离散元方法的颗粒材料缓冲性能及影响因素分析

在冲击荷载作用下, 颗粒材料通过颗粒间的摩擦及非弹性碰撞可有效进行能量耗散实现缓冲作用. 本文采用离散元方法对冲击载荷下颗粒材料的缓冲过程进行数值分析, 研究不同厚度下颗粒材料的缓冲性能. 计算结果表明: 颗粒层厚度H是影响颗粒材料缓冲性能的关键因素, 并存在一个临界厚度H_c. 当H < H_c时, 冲击力随H的增加而降低; 当H > H_c时, 冲击力对H的变化不敏感并趋于稳定值. 此外, 在不同颗粒摩擦系数和初始密集度下对缓冲过程的离散元分析表明, 光滑和疏松颗粒材料具有更好的缓冲性能. 最后, 对颗粒材料在冲击过程中的力链结构和底板的压力分布进行了讨论, 以揭示颗粒材料缓冲性能的内在机理.     

毛发的形态结构及其拉伸性能

比较4类毛发的形态结构,测量7种毛发的直径、伸长率及杨氏弹性模量.实验表明鳞片状毛发具有优良的拉伸性能,毛发的不同形态结构在很大程度上影响其拉伸性能.     

Theory of surface tension and its application to simple fluids

We consider a liquid-vapor interface in thermal equilibrium. The tangential component of the pressure tensor is supposed to depend explicitly upon the position and the density profile. Under this hypothesis the mechanical definition of surface tension becomes a finite summation ofN+1 terms related directly to the local compressibility. When the inhomogeneous compressibility equation is considered, the theory provides a microscopic expression of the surface tension coefficient. A calculation for argon near the critical point is done; the agreement with experiment is satisfactory.     

分光仪调整中干涉现象的分析与应用

描述了在分光仪调整实验中观察到的干涉条纹现象,并且当转动平行平板玻璃时,该干涉条纹有粗细疏密变化.本文从理论上分析了产生干涉条纹及干涉条纹疏密粗细变化的原因.在已知平行平板玻璃的厚度和光的波长的情况下,可应用该现象测量平行平板玻璃折射率,给出了折射率的计算方法,对结果进行了数据处理及误差分析.     

基于光谱指数的蜜橘成熟度评价模型研究

本文探索了基于光谱指数的蜜橘成熟度快速无损评价方法及模型。以2016年9~11月份6个不同采收期的300个蜜橘作为实验样品,采集重量、横纵径、叶绿素、色差、可溶性固形物(SSC)、酸度(TA)、近红外光谱等数据。通过对比分析上述各参数的平均值和偏差,筛选出叶绿素、叶绿素/SSC、叶绿素/固酸比作为蜜橘成熟度评价指标。利用光谱变异系数分析光谱的特征,筛选出649、724、672、1 100 nm 4个特征波长,通过特征波长线性组合方法以及相关性分析,得出最佳光谱指数。接着,以225个样品为建模集、75个样品为预测集,在成熟度评价指标与光谱指数间进行多元线性回归(MLR)分析。对比发现,以叶绿素为成熟度评价指标的评价模型的预测结果最准确,建模和预测相关系数分别达到0.98和0.96,建模均方根误差(RMSEC)和预测均方根误差(RMSEP)分别为0.49和0.59,建模和预测偏差分别为-6.1×10-8和-0.014。实验结果表明,利用光谱指数能便捷、准确地评定蜜橘成熟度,为后续开发低成本测量成熟度的仪器提供了理论依据。     

Grain orientation and magnetic evaluation of the hot forged Bi-Sr-Ca-Cu-O system

The Bi-Sr-Ca-Cu-O superconductor (BSCC) shows strong anisotropy in its physical and mechanical properties. Therefore, superconducting properties may be changed with the degree of grain orientation. In this paper, we describe the process of hot forging in the Bi-Sr-Ca-Cu-O system. In the hot forging temperature range of 770 ～ 820°C, highly dense samples have been obtained under the applied pressure of 200 ～ 300 kg/cm². Critical current density J_c is increasing with increase of grain orientation. Grain orientation is usually checked by X-ray analysis. However, it is found that the BSCC compound has a different value of grain orientation in the surface and inside the samples. Magnetic evaluation is effective for checking grain orientation in bulk samples.     

盐水-水的小孔周期性泄流实验与分析

通过对盐水-水小孔周期性泄流的实验研究,对孔径为1.32 mm的8种不同孔长进行测量,得出周期正比于孔长的1.1±0.1次方,同时对孔径为1.32 mm孔长为113.00 mm条件下的内筒液面跟踪记录得出实验曲线为指数形式,与理论分析符合得较好.     

泄漏Lamb波在固井质量评价中的应用

轻质水泥在油气田固井中的广泛应用使得传统声阻抗测井方式难以准确地对固井水泥胶结质量作出评价。本文基于弯曲型Lamb波传播特征对层状介质胶结质量较为敏感的特点,首先对套管井建立合适的层状介质模型,计算了层状介质的平面波反射系数,从反射系数的角度探讨了在套管井内激发弯曲型Lamb波的条件。然后依据该条件并结合声波角谱理论计算了稳态有限宽脉冲束入射时在套管井内产生的弯曲型Lamb波泄漏波的时间波列信号。通过对泄漏波波列信号的分析,得到了弯曲型Lamb波与套管井水泥胶结质量间的关系。研究表明,入射声波在满足一定条件下可以在套管内激发弯曲型Lamb波,其传播时的衰减率与套管水泥胶结质量以及水泥的声学参数均相关,当水泥为轻质水泥或者普通水泥时,其衰减率随着套管水泥间水层厚度的增加而减小,当水泥为快水泥时,其衰减率随着水层厚度的减小而增加,但当水层厚度减为零即套管水泥胶结良好情况下,其衰减率转而变小。     

Morphological Change of Aggregates of Polystyrene-block-poly (2-vinyl pyridine)/HAuCl4 Complexes in Solution

The self-assembly of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)/HAuCl₄ complexes in solutions is described. A morphological change from spheres to aggregated spheres, and then to vesicles, all of which contain Au precursor within the micellar corona or vesicle shell, can be prepared from an identical diblock copolymer by controlling the solvent selectivity. The possible mechanisms leading to the morphological transitions are also discussed. This may be a simple, facile route for preparation of a desired gold-containing aggregate.     

一种双段多层长周期光纤光栅光谱特性研究

长周期光纤光栅(LPFG)传感器具有非常广泛的应用价值,而有效解决物理量交叉敏感问题是其实用化的关键。基于LPFG对包层外介质折射率和厚度的敏感性,提出一种双段多层折射率横向分布结构的新型LPFG传感器的设计,并利用耦合模理论和传输矩阵方法分析了镀膜材料折射率、膜层厚度和镀层长度对新型LPFG传感器光谱特性的影响。软件仿真结果证明,这种LPFG由于结构设计上的特殊性,将使LPFG的谐振峰发生分裂,即一个透射峰分裂为两个。由于两个分裂峰对应力和温度的灵敏度不同,利用该结构的LPFG作为传感器,可以实现温度、应力等物理量的同步测量,从而解决LPFG传感器的交叉敏感问题。     

水下目标回波与混响的时频形态特征域盲分离

水下沉底或掩埋目标识别受海底混响干扰严重,并且目标回波与混响在时-频域上均存在混叠,增大了对目标回波与混响的分离难度。根据目标回波与混响的产生机理差异,将图像形态学与时频分析相结合的盲分离算法用于目标回波与混响的分离。推导了目标几何声散射成分与混响在Wigner-Ville时频面的形态特征表达式,利用图像形态学滤波去除Wigner-Ville时频面中的混响及刚性亮点之间交叉项,在时频形态特征域获取解混矩阵,实现了目标回波和混响的分离。仿真与实验数据处理结果表明,结合图像形态学的时频域盲分离算法提高了目标回波信号的信混比。     

儿童发育性髋关节脱位的磁共振形态学定量

发育性髋关节脱位（developmental dysplasia of the hip,DDH）作为一类常见的、严重威胁儿童健康成长的髋关节疾病会严重影响到儿童的肢体发育和生活质量,其早诊断、早治疗非常重要.磁共振成像（magnetic resonance imaging,MRI）技术可提供丰富的有关髋关节发育情况的形态学信息.目前,基于磁共振图像的DDH临床诊断主要凭借医生的肉眼观测,对医生要求甚高,而且无法定量判断DDH病情.本文提出了一种针对儿童DDH磁共振图像的形态学定量评估方法,通过对DDH病理改变密切相关的形态学参数的自动测定,完成形态学参数的定量评估,为临床提供辅助的量化参考.该方法包括磁共振图像预处理、股骨及盆骨分割、髋关节三维模型重建,以及结合了厚度搜索、三维霍夫变换和最小二乘拟合等算法实现的中心边缘角（center-edge angle,CEA）、髋臼角（acetabular index,AI）和股骨颈前倾角（femoral neck anteversion,FNA）等重要指标的自动测量.儿童DDH形态学定量评估方法的建立对儿童DDH的筛查、诊断和确诊患儿手术方案的制定,以及术后的动态随访,都具有重要参考价值.     

标准图像发生器及在图像板性能评价中的应用

本文介绍了一种标准图像信号发生器的原理、结构和特点。该发生器采用先进的数字合成技术，融合了ＥＰＬＤ编程技术、ＥＰＲＯＭ技术和高速、高精度１２ｂｉｔＤ／Ａ转换器，配以高性能视频放大和高阶模拟低通滤波器，产生的信号波形失真小、信噪比高。可生成正弦波、方波、三角波、线性波及直流等多种标准图像信号。并介绍了将该系统应用于图像板性能评价的具体方法。实际分析了一种图像板的时域和频域特性，主要包括线性度、Ａ／Ｄ转换精度和调制传递函数等。给出了被测图像板的调制传递函数曲线     

一种改进的高性能Lorenz系统构造及其应用

Lorenz系统是一种最具有代表性、典型性的混沌模型之一, 一直被众多学者深入研究和广泛应用.为了获取结构和动力学行为更为复杂的混沌吸引子, 不断改善Lorenz系统已成为混沌动力系统研究中的重要课题之一. 为此, 本文提出了一个具有复杂系统动力学行为的改进的Lorenz系统, 并将其用于图像信息安全保护. 在现有各种改进的Lorenz系统的基础上, 首先通过增加Lorenz系统的控制参数和改变非线性项相结合的方法构造出一种新的Lorenz 混沌系统; 其次采用微分动力系统方法深入研究该系统并获得与Lorenz系统、Bao系统、Tee系统和Y系统等具有相似的耗散性、对称性、稳定性, 以及更加复杂的混沌特性和动力学行为, 同时分析该系统所产生随机序列具有良好的相关性和复杂性; 最后将其所产生的离散伪随机序列用于图像置乱和扩散加密, 通过对图像加密结果的相邻像素相关性分析、灰度空间相关特性不确定性分析、抗差分攻击以及密钥敏感性测试, 表明本文所构造的改进的Lorenz系统应用于图像加密能获得相对较高的安全性.     

一种新的混沌映射散列函数构造方法及应用

提出了一种基于混沌映射和乘同余法构建单向散列函数的算法. 该算法通过乘同余法生成伪随机序列作为系统的初始值, 把明文信息的美国标准信息交换码(ASCII码) 归一化后作为混沌映射的初始值, 经过可变步长的混沌数字量化后, 提取出128 bit的散列值. 理论分析和仿真结果表明: 该算法具有较好的不可逆性、 抗碰撞性、 防伪造性、 初值敏感性以及较高地运行速度.