潮湿原煤颗粒在三自由度混联振动筛中筛分效率研究

为研究潮湿难筛分原煤颗粒在两平移一转动三自由度混联振动筛中的筛分效率变化规律,基于三维离散元法,运用EDEM软件模拟潮湿原煤颗粒的筛分过程.自主设计了两平移一转动三自由度混联振动筛,以研究各振动参数对原煤颗粒筛分效率的影响;综合采用动态筛分效率和阻碍粒排出率作为模拟筛分效率的评定指标,得出各自由度振动组合中的最佳激振模式及振动方向对潮湿原煤颗粒在筛面运动的作用;以动态筛分效率为参考值,采用正交实验方法,分析各因素对筛分效率的影响,得出影响因素分别为:外在水分、振动自由度、频率、振幅;用优选的筛分方案进行离散元模拟实验,验证了多维振动有利于潮湿难筛分原煤颗粒的分散、透筛及防堵.     

双弹簧电液激振缸振幅补偿性能的研究

传统的电液激振缸随着激振频率的提高,振动幅值急剧衰减,振幅补偿性能变差。为了解决这一问题,设计了一种双弹簧电液激振缸结构。分析了双弹簧电液激振缸的工作原理,建立了其数学模型和AMESim仿真模型,研究了激振频率、补偿弹簧刚度对其活塞杆位移的影响。结果表明：当激振频率为28 Hz、补偿弹簧刚度为31 N/mm时,激振缸活塞杆的位移增大6.24 mm,相比同一条件下的传统电液激振缸增大了15倍多;在双弹簧电液激振缸的工作过程中,其活塞杆位移振幅存在振荡区和稳定区,稳定区内的振幅大小直接决定了振幅补偿效果的优劣;在补偿弹簧刚度一定的情况下,活塞杆位移振幅不与激振频率呈简单的正相关或负相关关系,而在某一激振频率下谐振现象最明显,能使振幅补偿效果达到最优;激振频率不同,则补偿弹簧最优刚度不同,随着激振频率的提高,补偿弹簧刚度应相应增大。相比于传统的电液激振缸,双弹簧电液激振缸的振动幅值有较大提升,在工程应用中能取得更好的振幅补偿效果。     

随机激振下直线振动筛的振幅分析

振幅是直线振动筛重要工作参数之一,直接影响到振动筛分效率及工作可靠性.考虑激振力幅值大小及方向的随机性,在建立随机模型基础上,研究随机激振参数(偏心块质量矩、激振力方向角、激振频率)对振动筛振幅的影响规律.引入相对均差系数及变差系数,定量描述振动筛振幅的变异规律.结果表明:偏心块质量矩随机对振幅的均值影响很小,但是引起的振幅动态偏离度不容忽视;激振力方向角随机引起振幅的均值变异较大,动态偏离度亦大,是引起振幅变异最敏感的激振参数;当偏心块质量矩、激振力方向角、激振频率同时随机且变差系数达到15%后,振幅变异梯度迅速增大,振幅的均值变异及动态偏离度都很大.振动筛结构在制造与安装过程中随机因素引起的振幅变异必须加以分析与有效控制.     

橡胶隔振器动态特性计算方法的研究

填充橡胶材料的动态特性与预载、激振频率和激振振幅等相关.采用模型叠加方法,建立了用于计算的由填充橡胶材料制造的橡胶隔振器动态特性的弹性-粘弹性-弹塑性模型.其中,弹性模型用于表征橡胶隔振器的弹性部分,粘弹性模型用于表征橡胶隔振器动态特性与激振频率的相关性,弹塑性模型用于表征橡胶隔振器动态特性与激振振幅的相关性.对一试片进行静动态性能实验,得到其静、动刚度和滞后角,由其拟合得到了弹性、粘弹性、弹塑性模型的参数.计算了一动力总成橡胶隔振器的动态特性,并与实验结果进行了对比分析.结果表明.采用的弹性一粘弹性一弹塑性模型可以较好地表征橡胶隔振器动态特性的振幅相关性和频率相关性.其计算方法,可以用于橡胶隔振器动态特性的设计计算.     

川渝地区可控震源道路激振效果分析

川渝地区地形地貌复杂,可控震源在其乡村道路激振时存在激发信号畸变较大及激发能量耗散较大等问题。为了解决该问题,建立了可控震源道路激振模型,构建了可控震源道路激振效果评价体系,开展了川渝地区可控震源乡村道路激振效果研究,分析了可控震源道路激振能量耗散。结果表明：构建的激振效果评价体系能够较为全面地对川渝地区可控震源道路激振效果进行评价;相比碎石土路,可控震源在无缺陷水泥道路激振时传地能量减弱48.31%,地表接触中心点振幅下降77.44%,互作用力振幅下降18.18%,信号畸变增大34.69%,激振效果较差;道路缺陷对激振效果具有明显的减弱影响,圆形孔洞道路缺陷对激振效果的影响尤为突出,其中传地能量减弱54.94%,地表接触中心点振幅下降5.57%,互作用力振幅下降21.16%,信号畸变增大36.17%;川渝地区可控震源道路激振时,平板的结构能量耗散较大,约占系统总耗散能量的90%。研究结果可以为川渝地区可控震源乡村道路激振效果的改善提供理论指导。     

液压衬套动态特性实测分析及集总参数模型研究

以轴、径向型两种结构形式液压衬套为研究对象,测试分析液压衬套动态特性及与激振频率、激振振幅关系,分别建立轴向型、径向型液压衬套动态特性分析的集总参数模型,计算激振振幅一定时液压衬套动刚度及滞后角与激振频率关系曲线。计算结果与实验值吻合较好,验证集总参数模型的正确性。基于所建集总参数模型,计算分析惯性通道数量及尺寸对液压衬套性能优化设计影响。     

风速对水线及斜拉索振动的影响

斜拉桥拉索的风雨激振是特定风速及降雨条件下的低频、大幅度振动,为研究风速对斜拉索风雨激振的影响,将两自由度滑移理论模型与Comsol软件相结合,大幅提高了计算效率,通过数值计算得到了不同风速下的水线运动规律、拉索气动力变化规律及其振动响应。结果表明:斜拉索发生风雨激振时,横风向振幅约为顺风向振幅的两倍;只有当风速处于特定风速范围内时,斜拉索才会发生明显的风雨激振现象,此时上水线振荡频率及气动力变化频率均接近拉索自振频率,水线与拉索间的共振是风雨激振的主要原因之一。     

采用粘弹性分数导数模型的橡胶隔振器动态特性的建模及应用

橡胶隔振器的动态特性与激振振幅及激振频率相关。给出一个可以表征橡胶隔振器动态特性与激振振幅及激振频率相关性的模型,其中,用摩擦力模型表征其动态特性与振幅的相关性,用分数导数粘弹性模型表征其动态特性与频率的相关性。计算分析了所建立的模型与目前广泛采用的两种描述橡胶隔振器动态特性模型(基于Maxwell的模型和粘性阻尼模型)在表征其与激振振幅及激振频率的相关性;使用分数导数和Kelvin-Voigt模型时,计算分析了一个含有橡胶隔振器的单自由度振动系统的自由振动和阶跃激励的时域响应。计算结果表明:采用分数导数模型能更加准确地描述橡胶隔振器的动态特性,建立的模型可以用于含有橡胶隔振器的振动系统的动态特性分析。     

基于AFSA-SimpleMKL对振动筛建模及筛机优化

针对目前振动筛筛分性能差及筛分理论不完善,亟待建立筛机参数与筛分效率间综合数学模型来指导振动筛的设计.基于离散单元法(Discrete Element Method,DEM)的筛分仿真实验解决筛分过程的复杂性和筛分数据难获得等问题,用可调参数的振动筛对仿真实验进行验证.筛分效率与筛分参数之间的数学关系是一个复杂的非线性问题,由于传统的回归算法对筛分数学模型预测精度低,利用能有效解决小样本问题和基于统计学理论的简单多核支持向量机(Simple Multiple Kernel Learning,SimpleMKL)对仿真实验获得的数据建立回归模型.但其模型是多极值且不可微分的多参数大规模计算问题,借用鲁棒性强和全局收敛性好的人工鱼群优化算法(Artificial Fish Swarm Algorithm,AFSA)对由SimpleMKL建立的筛分回归模型进行参数寻优,得出筛机振动和结构参数:振幅为2.5mm,振动频率为22Hz,振动方向角为50°,筛孔大小为0.9mm,筛丝直径为0.4mm,筛面倾角为21.6°.提高了振动筛的筛分效率,为振动筛的设计和制造提供了新思路.     

大跨度缆索承重桥并列索尾流激振研究

近距离并列索(并列吊索和并列斜拉索)在大跨度缆索承重桥中应用广泛,下游索常会发生尾流致涡激共振、尾流驰振和尾流颤振等尾流激振。以间距为4 D(D为圆柱直径)的串列和错列双圆柱的尾流致涡激共振和尾流驰振为研究对象,在风攻角为0°~20°的条件下,主要通过风洞试验研究了下游圆柱发生尾流激振的起振条件、振动幅度和运动轨迹,研究了提高结构阻尼比的减振效果,讨论了尾流驰振的雷诺数效应,结合静止双圆柱绕流场的大涡模拟结果对尾流干扰机理进行了探讨。研究表明:在某些风攻角下,下游圆柱的尾流致涡激共振振幅远大于单圆柱涡激共振振幅;在0°以外的其他风攻角下,下游圆柱均发生大幅尾流驰振,但小攻角(5°和10°)与大攻角(20°)下的尾流驰振现象有明显差别,很可能存在不同的流场激励机理;风攻角为15°时,下游圆柱的尾流驰振有明显的雷诺数效应,其动力响应特性与经典驰振不同,下游圆柱起振后的振幅和运动轨迹随雷诺数(风速)的增大呈现复杂的变化形态;提高结构阻尼比可有效抑制下游圆柱的尾流致涡激共振,但对尾流驰振的减振效果不佳。     

High-throughput single-molecule DNA screening based on electrophoresis

In electrophoresis, the migration velocity is used for sizing DNA and proteins or for distinguishing molecules based on charge and hydrodynamic radius. Many protein and DNA assays relevant to disease diagnosis are based on such separations. However, standard protocols are not only slow (minutes to hours) but also insensitive (many molecules in a detectable band). We successfully demonstrated a high-throughput imaging approach that allows determination of the individual electrophoretic mobilities of many molecules at a time. Each measurement only requires a few milliseconds to complete. This opens up the possibility of screening single copies of DNA or proteins within single biological cells for disease markers without performing polymerase chain reaction or other biological amplification. The purpose is not to separate the DNA molecules but to identify each one on the basis of the measured electrophoretic mobility. We developed three different procedures to measure the individual molecular mobilities. The results correlate well with capillary electrophoresis (CE) experiments for the same samples (2-49 kb dsDNA) under identical separation conditions. The implication is that any electrophoresis protocols from slab gels to CE should be adaptable to single-molecule screening for disease diagnosis.     

Sequential screening procedure based on individual misclassification error

A one-sided sequential screening procedure based on the Individual Misclassification Error (IME) is developed. The generalized formulas for any Sequential Screening Procedure (SQSP) with r stages are derived under the assumption of a multivariate normal distribution. Total Inspection Cost (TIC), Average Outgoing Quality (AOQ) and Producer's Risk (PR) are used as the criteria for selecting the optimal allocation. An example with four screening variables allocated into single-stage, double-stage and triple-stage sequential screening procedures (SSP, DSP and TSP) is illustrated using the derived generalized formulas to search for the best allocation.     

Automated microfluidic screening assay platform based on DropLab

This paper describes DropLab, an automated microfluidic platform for programming droplet-based reactions and screening in the nanoliter range. DropLab can meter liquids with picoliter-scale precision, mix multiple components sequentially to assemble composite droplets, and perform screening reactions and assays in linear or two-dimensional droplet array with extremely low sample and reagent consumptions. A novel droplet generation approach based on the droplet assembling strategy was developed to produce multicomponent droplets in the nanoliter to picoliter range with high controllability on the size and composition of each droplet. The DropLab system was built using a short capillary with a tapered tip, a syringe pump with picoliter precision, and an automated liquid presenting system. The tapered capillary was used for precise liquid metering and mixing, droplet assembling, and droplet array storage. Two different liquid presenting systems were developed based on the slotted-vial array design and multiwell plate design to automatically present various samples, reagents, and oil to the capillary. Using the tapered-tip capillary and the picoliter-scale precision syringe pump, the minimum unit of the droplet volume in the present system reached ~20 pL. Without the need of complex microchannel networks, various droplets with different size (20 pL-25 nL), composition, and sequence were automatically assembled, aiming to multiple screening targets by simply adjusting the types, volumes, and mixing ratios of aspirated liquids on demand. The utility of DropLab was demonstrated in enzyme inhibition assays, protein crystallization screening, and identification of trace reducible carbohydrates.     

数字加网技术

介绍了数字加网技术的研究现状,阐述了数字调幅和调频加网以及混合加网的原理及算法,并对其特点进行了分析.在此基础上,指出了数字加网技术应用中存在的问题,并对数字加网的未来进行了展望.     

并联运动振动筛的筛分特性研究

并联振动筛具有良好的筛分效果,其研究已成为振动筛研究的热点.为便于对其进行优化控制,需对其筛分特性进行深入研究.通过考察并联振动筛的结构及其工作过程,得到了筛分特性曲线,分别用参数回归法和最小二乘法确定其特性参数,由此建立筛分模型.将理论计算结果与实验结果对照,经误差分析可知,最大误差为084%,平均误差为026%.所得模型精度高,构建方便有效.     

Influence of screening on calculations on the total energy of calcium oxide

A unified formulation of a method which conserves the pseudopotential norm and the electron density functional is used to calculate the total energy and the equilibrium atomic volume of calcium oxide. Various methods of screening the pseudopotential are considered as a fitting procedure. Pis’ma Zh. Tekh. Fiz. 25, 64–68 (April 12, 1999)     

The effect of electrostatic screening on a nanometer scale electrometer

We investigate the effect of electrostatic screening on a nanoscale silicon MOSFET electrometer. We find that screening by the lightly doped p-type substrate, on which the MOSFET is fabricated, significantly affects the sensitivity of the device. We are able to tune the rate and magnitude of the screening effect by varying the temperature and the voltages applied to the device, respectively. We show that despite this screening effect, the electrometer is still very sensitive to its electrostatic environment, even at room temperature.