Determination of avocado and mango fruit properties by ultrasonic technique

A nondestructive ultrasonic measurement system was developed for the assessment of some transmission parameters which might have quantitative relations with the maturity, firmness and other quality-related properties of avocado and mango fruits. The system utilizes a set of low-frequency probes arranged to measure the ultrasonic signal transmitted and received over a short distance across the peel. The attenuation of the ultrasonic waves, transmitted through the peel and the attached fruit tissue, changes as a result of the progressive ripening and softening of the fruit during the fruiting season and in the course of storage. The present study quantitatively addressed the linkage between the ultrasonic attenuation and the physiological parameters of the flesh of the fruits. Results were obtained in the time and frequency domain, and the data set was analyzed statistically to identify the relations between the major physiological indices and the ultrasonic parameters. Quantitative relations were developed to describe the linkage between ultrasonic parameters and the maturity, firmness and other quality-related properties in mango and avocado fruits.     

A direct method for acoustic impedance measurement based on the measurement of electrical impedance of acoustic transmitter

A simple and straight forward method for acoustic impedance measurement is presented and evaluated. In this method a speaker is used as the signal source. The relationship between the electrical impedance of the speaker and its acoustical load is developed and studied. It is shown that the electrical current and voltage of the speaker relate to the acoustical pressure and volume velocity. The mechanical and acoustical impedances are therefore easily derived by measuring the electrical current and voltage of the circuit. The proposed method yield itself to the automatic computer measurement and can be used for the field and in situ measurements.Comparison of the measurement data with those from other methods proves the applicability and accuracy of the proposed method.     

基于自适应加窗spline曲线拟合的拉曼光谱去基线方法

拉曼光谱是一种无损快速检测技术,可以提供材料的定性和定量信息,因而在医药、化工等诸多领域得到了广泛的应用。但是,由于样品荧光背景噪声的影响,造成拉曼光谱信号出现基线漂移现象,这给拉曼光谱的特征峰识别和拉曼成像带来十分严重的影响。目前,改进实验方法和数值处理是解决该问题的两种重要手段。改进实验方法上,有偏振调制法和高频调制法等,但存在实验设备复杂,检测技术难度大等缺点;数值处理上,有多项式拟合和小波变换等,但容易出现欠拟合和过拟合等现象。本文在不改换高精密设备的前提下,针对传统基线校正的方法进行了改进,提出一种基于自适应加窗spline曲线拟合的拉曼光谱去基线方法。首先,基于谱峰识别算法和初始搜索步长求得谷值的最优搜索间距,并利用谱谷识别算法完成谷值曲线的拟合;其次,利用最优搜索间距和谱峰识别算法,求得谷值曲线峰值位置,并在该位置处对称添加自适应矩形窗函数去除峰值,重新划分整个区间,拟合谷值曲线;再次,逐点比较拟合曲线与原拉曼光谱信号,取较小值,拟合曲线;最后,重复加窗去除峰值操作,直至自适应窗函数宽度低于阈值,完成拉曼光谱信号的基线拟合。在实验中,选用乙酸丁酯、聚甲基丙烯酸甲酯(polymethyl methacrylate, PMMA)作为实验样品,利用该方法对其拉曼光谱信号进行了基线校正,观察并比较该方法和传统方法的校正结果。实验结果表明,该方法能够有效地消除拉曼光谱信号的基线漂移,较好的保留一些较弱的拉曼特征峰,且不易出现欠拟合和过拟合的现象,获得了良好的基线校正效果,为进一步分析光谱数据和实现拉曼成像提供准确可靠的信息。     

Energy loss and plasmon excitation during electron emission in the proximity of a solid surface

We study the interaction with bulk and surface modes of electrons emitted in the proximity of a solid surface. We analyze the modifications in the energy loss, and in bulk and surface plasmon excitations, taking into account the effects due to the sudden creation of the electron and residual atomic hole, and the finite distance to the surface. The process is described using the dielectric function formulation and the specular reflection model. We derive expressions for the electrostatic potential in the medium and in vacuum, which include all the terms due to bulk and surface modes. The effect of each term in the energy loss rate and in the average number of plasmon excitations is discussed. The results illustrate in detail the different spatial dependences of the electron and ion interactions with the bulk and surface perturbations, through the relevant range of distances for studies of electron emission in the proximity of solid surfaces.     

星载激光雷达云和气溶胶分类反演算法研究

激光探测对于获取云和气溶胶的垂直廓线,研究大气中云和气溶胶的垂直分布特征以及对全球气候变化的影响意义重大。而星载大气激光雷达云气溶胶分类算法的研究,对于激光雷达数据的参数反演及应用极为重要。针对激光条件下探测的云和气溶胶特有的光学信息和空间分布,结合概率统计与机器学习算法,提出了一种对于云/气溶胶、云相态及气溶胶子类型识别的分类算法,实现了星载激光雷达的大气特征层快速、有效分类。算法采用中国地区2016年CALIOP的观测数据作为样本数据,主要由三部分组成：（1）基于激光探测的云和气溶胶层不同的光学特性以及地理空间分布特征,分别构建了云和气溶胶的γ₅₃₂,χ,δ,Z和lat的五维概率密度函数,以此为基础构建云气溶胶的分类置信函数,并基于此实现了云和气溶胶类型的反演;（2）选取支持向量机(SVM)作为随机朝向冰晶粒子(ROI)和水云分类的算法模型基础,结合云层的γ₅₃₂,χ,δ Z和云顶温度T的概率密度函数构建ROI,水平朝向冰晶粒子(HOI)和水云的分类置信函数以修正SVM误分的特征层以及筛选出水云中少部分的HOI冰云,获得云相态的分类结果;（3）以各气溶胶子类型的光学以及空间分布特性为基础,采用决策树策略的气溶胶子类型识别算法实现了对气溶胶子类型的区分,完成气溶胶子类型的识别。利用现有CALIOP观测结果作为样本数据构建分类数据库,避免了对于地面以及航测数据的依赖,而机器学习则大大简化了算法的实现过程,使得云气溶胶分类更加高效。算法结果与正交极化云气溶胶激光雷达垂直特征层分布数据(CALIPSO VFM)产品对比分析：云层有98.51%一致性,气溶胶有88.43%的一致性,且白天比夜间一致性高。对于云相态分类,可以有效区分出水云和冰云,其中二者水云一致性高达93.44%。在气溶胶子类型反演结果中,可以准确识别出大多数气溶胶特征层子类型。霾、沙尘以及晴空三种典型情况下的反演结果均与CALIOP VFM产品数据具有较好的一致性。其中,霾天的大部分煤烟型以及污染型（污染沙尘以及污染大陆）气溶胶反演结果与VFM具有较好的一致性。沙尘天也能够获得较好的沙尘以及污染沙尘的结果。晴空为数不多的气溶胶层也取得了较为一致的结果。对于实现的星载大气激光雷达特征层分类算法,针对CALIOP激光测量的云气溶胶层的分类进行了重要的改进,在保证一定精度的基础上,简化了算法,提高了数据处理的效率,在下一步工作中,将分别构建不同时段和季节的分类模型以及提高两种不同偏振特性的冰云和气溶胶子类型的分类精度。     

近红外光谱通用模型在农产品及食品检测中的研究进展

我国人口基数大,农产品和食品的需求量多。农产品和食品的质量与安全与人们的日常生活息息相关。如何实现使用无损、快速、环境友好型、高通量的检测方法对农产品和食品的品质进行检测,是当代社会的发展需要。传统的检测分析方法存在着耗时耗力、检测的样品不能再次出售、产生次品漏检的现象等缺点。近红外光谱分析技术作为一种快速无损的检测手段,逐渐被一些学者以及相关行业人员所重视。然而,近红外光谱分析方法大多数只针对于单一物料建立数学模型。对于数量庞大且种类众多的农产品和食品而言,如不同地域、不同年份、不同温度、不同加工方法、不同成分组成甚至是不同品种,这种相对传统的近红外分析方法无疑会增加建模的工作量。随着计算机技术、光谱仪硬件、化学计量学以及互联网技术的发展,相关学者已经开始着手于近红外光谱通用模型的研究与开发来解决这一问题,即建立一个近红外通用模型,能够对多种物料的同一指标或多种指标进行检测。相比于传统的近红外光谱模型,通用模型具有建模成本低、工作量小等优点,特别使近红外光谱技术在农产品和食品领域中应用以及推广方面具有重要的意义。针对近红外光谱通用模型在农产品和食品检测中的研究进行综述,通过比较传统模...     

垂直振动床中的能量传递与耗散

本文采用数值方法分析了一维垂直振动床内颗粒动能/温度、能量耗散以及体积分数的分布规律.离散元模拟结果表明:当床底做低频、小振幅振动时,床层内颗粒整体随床底上下运动,沿床高方向颗粒动能逐渐增加;对于高频振动,床层内的颗粒做无规则的运动,沿床高方向颗粒动能逐渐降低.在不同振动频率(高频、低频)下体积分数、能量耗散也表现出不同的分布规律.将离散元模拟结果与动力学理论计算值对比,当系统做高频振动时,两模型所得结果基本吻合;而对于低频、小振幅振动,所得结果存在较大差异.由于低频、小振幅振动时床内颗粒并非做无规则运动,动力学理论的适用性需进一步完善.     

Mechanism of microweld formation and breakage during Cu-Cu wire bonding investigated by molecular dynamics simulation

Currently,wire bonding is the most popular first-level interconnection technology used between the die and package terminals,but even with its long-term and excessive usage,the mechanism of wire bonding has not been completely evaluated.Therefore,fundamental research is still needed.In this study,the mechanism of microweld formation and breakage during Cu-Cu wire bonding was investigated by using molecular dynamics simulation.The contact model for the nanoindentation process between the wire and substrate was developed to simulate the contact process of the Cu wire and Cu substrate.Elastic contact and plastic instability were investigated through the loading and unloading processes.Moreover,the evolution of the indentation morphology and distributions of the atomic stress were also investigated.It was shown that the loading and unloading curves do not coincide,and the unloading curve exhibited hysteresis.For the substrate,in the loading process,the main force changed from attractive to repulsive.The maximum von Mises stress increased and shifted from the center toward the edge of the contact area.During the unloading process,the main force changed from repulsive to attractive.The Mises stress reduced first and then increased.Stress concentration occurs around dislocations in the middle area of the Cu wire.     

传声器次声段灵敏度校准的误差机理研究*

次声波广泛存在于自然界与人类活动中,由于次声波具有穿透能力强、衰减小等特点,隔离和消除十分困难,对次声的监测防护与利用成为人们关注的焦点。次声波的定量研究依托传声器的测量实现,对传声器的灵敏度原级校准是保证测量精度的前提。该文基于活塞发生器校准原理下的压力泄漏与热传导耦合衰减模型,在COMSOL多物理场仿真软件中对校准腔和传声器后腔内的声场特征进行了数值仿真。创新性地提出了模型比较法,准确量化了次声段校准核心的泄漏、热传导独立与耦合修正量,验证并揭示了声压泄漏与热传导损失的幅值与相位变化机理。进一步地对传声器的次声段灵敏度校准过程进行了联合数值模拟,仿真结果表明,内外均压校准声场下传声器灵敏度的幅相频响应存在明显差异,但与校准腔内的泄漏与热传导效应无关。基于搭建的活塞发生器原级校准平台对传声器系统进行了原级校准,通过实验手段初步揭示了内外均压校准机制下传声器幅值灵敏度与相位灵敏度的显著差异。     

洱海上覆水DOM荧光特征及对富营养化的指示意义

湖泊溶解性有机物（DOM）组成特征对水质具有重要的影响,研究上覆水DOM组成特征对指示湖泊富营养化现状具有重要意义。采用荧光光谱区域体积积分分析法（FRI）定量分析洱海上覆水DOM组分时空变化,以及DOM组分与水质因子间的关系,对比分析不同来源入湖水体、不同富营养化程度高原湖泊上覆水DOM组分荧光特征。结果表明,洱海上覆水体DOM主要以类腐殖酸为主,其次为类富里酸,洱海DOM总量及类腐殖酸组分中部较高,色氨酸和络氨酸等类蛋白质DOM南部较高,类富里酸DOM北部较高。藻华易发期（10月）类蛋白质和类富里酸DOM较低,类腐殖酸DOM显著增加,DOM生物源降低,DOM生物活性降低。洱海沉积物内源释放和入湖河流主要影响上覆水中类腐殖酸DOM,湿沉降主要增加类蛋白质DOM。在湖泊贫营养阶段类富里酸DOM对水质影响较大,在富营养阶段类腐殖酸DOM对水质影响较大。随着湖泊富营养化程度的加剧,上覆水类蛋白质和类富里酸DOM所占比例呈下降趋势,微生物降解产物和类腐殖酸DOM所占比例呈增加趋势。DOM荧光组分占比变化对湖泊富营养化具有指示作用。     

线偏振拉盖尔-高斯光束的远场发散特性

利用稳相法和矢量结构理论, 导出了线偏振拉盖尔-高斯光束的矢量结构项TE项和TM项在远场的解析表达式. 进而利用TE项和TM项的远场能流分布, 给出了TE项和TM项的功率占总功率比例的度量式,同时还给出了线偏振拉盖尔-高斯光束、TE项和TM项三者远场发散角的解析式以及三者远场发散角间的关系式. 所得到的公式不仅适用于傍轴情形,而且还适用于非傍轴情形. 通过数值计算, 分析了TE项和TM项在远场的功率占总功率的比例与参数f和模数间的依赖关系;还分析了拉盖尔-高斯光束、TE项和TM项的远场发散角随参数f、模数和线偏振角的变化关系.这一研究从矢量结构本性揭示了线偏振拉盖尔-高斯光束的远场发散特性, 丰富了对其传输特性的认识.     

ICP法和原子吸收光谱法测定褐马鸡羽毛中的10种元素

珍稀濒危鸟类-褐马鸡是中国特有的野生鸟类,是国家一级重点保护动物。采用ICP法和原子吸收光谱法对来自芦芽山、庞泉沟国家自然保护区的野生褐马鸡和太原市动物园圈养褐马鸡羽毛中Mo,Zn,Ni,Fe,Mn,Cr,Cu,K,Pb和Cd等10种元素的含量进行了测定,并对这3个不同地理分布区的样品中10种元素的含量进行了比较。结果表明,在所有羽毛样品中Fe元素含量最高,Mo和Cr含量较低,Cd未检出。动物园饲养的褐马鸡羽毛中除K和Cu外,其余八种元素的含量均低于芦芽山和庞泉沟国家自然保护区野生的褐马鸡羽毛中的含量。生境的不同对褐马鸡机体微量元素有一定影响,野生环境更有利于它们的生长发育。     

可控聚焦型减速场能量分析器的设计分析

基于之前减速电场能量分析的设计与实验,针对实验中出现的绝缘性不好、能量分辨率不高等问题,对原结构进行了改进与仿真分析,以更好地实现行波管电子枪电子注及注波互作用后电子注参数的精确测量和分析,为行波管的设计、性能改进和研制提供参考。该可控聚焦型减速场能量分析器结构将高压圆筒与减速栅网进行电气绝缘隔离,并在二者之间设置一个可控的小电压,产生的第二个静电透镜对发散的电子注产生加速会聚的作用,以削弱在第一个透镜聚焦作用的薄弱区域空间电荷效应及电子注发射角等因素对注发散的影响,调整粒子轨迹倾斜度和分辨率。同时,整体结构在不影响测试精度的情况下向小型化和轻型化发展。应用CST粒子工作室对不同粒子界面处粒子分布及整体场结构进行模拟,然后用Matlab软件进行数据处理并导出关键参数。着重分析结构性能的优化和提升在分辨率及半峰值全宽度等参数上的体现。结果表明该能量分析器适用于几keV到10keV的强流电子注的测量。     

Dissipative Kerr solitons in optical microresonators with Raman effect and third-order dispersion

Using the mean-field normalized Lugiato–Lefever equation, we theoretically investigate the dynamics of cavity soliton and comb generation in the presence of Raman effect and the third-order dispersion. Both of them can induce the temporal drift and frequency shift. Based on the moment analysis method, we analytically obtain the temporal and frequency shift,and the results agree with the direct numerical simulation. Finally, the compensation and enhancement of the soliton spectral between the Raman-induced self-frequency shift and soliton recoil are predicted. Our results pave the way for further understanding the soliton dynamics and spectral characteristics, and providing an effective route to manipulate frequency comb.     

Creep and shrinkage effect on the dynamic analysis of reinforced concrete slab-and-beam structures

In this paper, a solution to the dynamic problem of reinforced concrete slab-and-beam structures including creep and shrinkage effects is presented. The adopted model takes into account the resulting in-plane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to the combined response of the system. The analysis consists of isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The influence on creep and shrinkage effects of the time between the casting and the loading of the plate and the beams is taken into account. A lumped mass matrix is constructed from the tributary mass areas to the nodal mass points and a stiffness matrix is computed using the solution of the corresponding static problem. Both free and forced vibrations are considered and numerical examples of practical interest are presented. The discrepancy between the eigenvalues obtained using the present analysis, which better approximates to the actual response of the plate-beam system and the corresponding ones which ignore the in-plane forces and deformations requires the adopted model.     

Interactions Between an Ionic Liquid and Silica,Silica and Silica,and Rubber and Silica and Their Effects on the Properties of Styrene-Butadiene Rubber Composites

An investigation of the effect of an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMI), on the properties of silica reinforced styrene-butadiene rubber (SBR), aimed to correlate the interactions between the ionic liquid and silica, silica and silica, and silica and rubber with the macro-properties and microstructure of SBR and SBR/silica vulcanizates is described. The interaction between the ionic liquid and silica was characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), the interaction between silica and silica was characterized by a rubber processing analyzer (RPA), and the interaction between rubber and silica was characterized by the bound rubber content. The FTIR analysis revealed that BMI can react with the hydroxyl groups on the surface of silica, improving the compatibility between the rubber and silica. The RPA and bound rubber testing indicated that the interactions between silica and silica particles were weakened and the interaction between silica and rubber increased with the incorporation of BMI into the SBR rubber. The bound rubber content showed a maximum with a BMI content of 3 phr. At the same time, the dispersion of silica in SBR was improved with the incorporation of BMI. With the increase of BMI content, the curing rate was greatly improved and the crosslink density increased. BMI also increased the tensile strength and abrasion resistance of the SBR vulcanizates. Most important, the BMI significantly improved the dynamic properties of the rubber composites, especially the wet-skid resistance and rolling resistance. However, excessive BMI (beyond 3 phr) acted as a plasticizer and was detrimental to the mechanical properties, resulting in a decrease of tensile strength and abrasion resistance.     

Control of Fundamental Frequency in Dysphonic Patients During Phonation and Speech

PurposeThe pitch-shift reflex (PSR) is the adaptation of the fundamental frequency during phonation and speech and describes the auditory feedback control. Speakers without voice and speech disorders mostly show a compensation of the pitch change in the auditory feedback and adapt their fundamental frequency to the opposite direction. Dysphonic patients often display problems with the auditory perception and control of their voice during therapy. Our study focuses on the auditory and kinesthetic control mechanisms of patients with muscle tension dysphonia (MTD) and speakers without voice and speech problems. Main purpose of the study is the analysis of the functionality of the control mechanisms within phonation and speech between patients with MTD and normal speakers.MethodSixty-one healthy subjects (17 male, 44 female) and 22 patients with MTD (7 male, 15 female) participated following two paradigms including a sustained phonation (vowel /a/) and speech ([‘mama]). Within both paradigms the fundamental frequency of the auditory feedback was increased synthetically. For the analysis of the PSR the electroencephalogram, electroglottography, the voice signal, and the high-speed endoscopy data were recorded simultaneously. The PSR in the electroencephalogram was detected via the N100 and the mismatch negativity. Statistical tests were applied for the detection of the PSR in the physiological response within the electroglottography, voice, and high-speed endoscopy signals. The results were compared between both groups.ResultsNo differences were found between the controls and patients with MTD regarding latency and magnitude of the perception of the pitch shift in both paradigms, but for the magnitude of the behavioral response. Differences also could be found for both groups between the “no pitch” and “pitch” condition of the two paradigms regarding vocal fold dynamics and voice quality. Patients with MTD showed more vibrational irregularities during the PSR than the controls, especially regarding the symmetry of vocal fold dynamics.ConclusionPatients with MTD seem to have a disturbed interaction between the auditory and kinesthetic feedback inducing the execution of an overriding behavioral response.     

基于双树复小波变换的遥感图像去云雾系统设计

在研究双树复小波变换原理的基础上,结合遥感图像中云雾和景物的频率差异,提出一种去云雾方法。设计并建立了去云雾处理硬件系统,介绍系统组成和系统开发步骤,叙述摄像头驱动程序、视频信号输出程序、人机交互界面等的设计方法,采用设计的系统开展图像采集和去云雾处理,给出并分析处理效果。实验结果表明,当分解层数、分界数和权重取默认值时,该文算法的图像处理的熵达到7.61,优于小波阈值法和同态滤波法。设计的系统去云雾处理能力和自适应性强。     

The effective torque on patchy spheres nearby a flat substrate induced by infinitely thin rods with adsorptive ends

The system studied here is the mixture of infinitely thin rods and a patchy sphere nearby a flat substrate. The adsorption between the rod ends and the patch can induce an effective torque on the sphere, which are studied by the Monte Carlo method. At the proper patch angle, the effective torque makes the patchy surface face away from the substrate, and the effective interaction between the bare surface and the substrate is attractive at the same time. The effective torque strengthens with the approach between the sphere and the substrate, while first strengthens and then weakens with the increase of the included angle between the axis of the patch and the normal of the substrate. The relationships between the effective torque and the adsorptive strength, the patch angle and the diameter of the sphere have also been studied. The effective torque discussed here may play a role in the biological lock-and-key mechanism and be used to adjust the two-dimensional self-assembly of the colloidal particles with the anisotropic surface.     

A new approach with piecewise-constant arguments to approximate and numerical solutions of oscillatory problems

This paper is devoted to the development of a novel approximate and numerical method for the solutions of linear and non-linear oscillatory systems, which are common in engineering dynamics. The original physical information included in the governing equations of motion is mostly transferred into the approximate and numerical solutions. Therefore, the approximate and numerical solutions generated by the present method reflect more accurately the characteristics of the motion of the systems. Furthermore, the solutions derived are continuous everywhere with good accuracy and convergence in comparing with Runge-Kutta method. An approximate solution is developed for a linear oscillatory problem and compared with its corresponding exact solution. A non-linear oscillatory problem is also solved numerically and compared with the solutions of Runge-Kutta method. Both the graphical and numerical comparisons are provided in the paper. The accuracy of the approximate and numerical solutions can be controlled as desired by the number of terms in the Taylor series and the value of a single parameter used in the present work. Formulae for numerical computation in solving various linear and non-linear oscillatory problems by the new approach are provided in the paper.