典型荷载条件下淤泥孔径分布特征核磁共振试验研究

模拟了淤泥地基加固工况对应的几种典型荷载效应,并利用核磁共振测试寻求典型荷载水平和速率下,淤泥孔隙及其孔径分布的变化规律,以探讨淤泥地基典型加固条件下微细观结构的三维响应.结果表明:在一定压力作用下,淤泥中最大孔隙数将会减少,应力水平越高,减少量越大,而当冲击荷载达到更高的某一水平时,淤泥中最大孔隙和最小孔隙所占比例均会减小,孔隙更趋于均匀;约束样品的侧限刚度将会增加淤泥土的总受力水平,进而更易减小大孔隙所占比例;当荷载水平680 kPa时,加载速率是决定相对最大孔隙占总孔隙数比例的关键因素,速率较小会使得该比例增大,速率较大则使得该比例减小,其界限值在0.8 MPa/s与1.6 MPa/s之间;一定的冲击荷载和速率水平下,随着作用次数即总能量的提高,淤泥中的相对大孔隙和最大孔隙部分会明显减少,而当间隔时间较短的作用次数再提高时,上述效应会降低;对于有效减少较大孔隙而言,淤泥受冲击的次数存在某个合适的量值.上述规律有助于从内部本质上寻求和掌握各种静动力排水固结法处理淤泥类软基的微观机理,为其科学设计及施工优化提供了进一步的依据.     

基于模糊理论的土体渗流固结参数识别

基于模糊数学理论,根据埋置在土体内部的超孔隙水压力观测数据,建立了土体固结参数模糊识别数值方法.根据观测点的超孔隙水压力观测数据的统计特性,得到观测数据的隶属度函数.基于待识别土体渗流固结参数的先验信息即约束条件,建立了模糊约束的隶属度函数,进而得到模糊化的目标函数.以信息论方法为基础,研究了观测信息的随机不确定性和荷载的随机不确定性对参数识别结果的影响.研究表明,基于信息论的模糊参数识别方法所得到的参数识别结果同样具有随机不确定性.     

超声场强化超临界CO2萃取除虫菊酯的初步研究

本文以除虫菊花中的除虫菊酯萃取为对象,研究用超临界CO2对其萃取时,施加超声场对萃取物降解及萃取速率的影响.结果表明,在实验范围内施加超声场(200kHz,200W电功率)没有引起超临界CO2流体"空化",从而没有使易分解组分除虫菊酯降解;施加超声场可以提高除虫菊酯的萃取速率,且对萃取速率的影响比用水为共溶剂强,在实验范围内,萃取优化工艺条件为萃取压力(20MPa);施加超声场(200kHz,200W电功率);萃取温度(40℃);添加共溶剂水(0.5ml水/g干花);CO2流量(2.0L·min-1).     

充注率及氦气增压对低温贮箱热分层特性影响

为了揭示低温推进剂贮箱的增压规律和热分层特性,在以液氮为贮存介质的低温流体高效贮存平台上,进行了不同充注率下的贮箱自增压及氦气增压实验。得到充注率分别为35%,50%和65%时的贮箱增压速率分别为7.54 kPa·h~(-1),13.02 kPa·h~(-1)和28.26 kPa·h~(-1).获得了达到相同压力水平时各自充注率对应的温度分布,分析了不同充注率时贮箱温度梯度的变化规律。最后使用常温氦气作为增压气体,将贮箱充注率为50%的贮箱分别增压到180 kPa,380 kPa和580kPa,分析了氦气充注过程及达到不同压力水平时贮箱内温度分布变化规律.     

离子配对动力学不一定遵循Eigen-Tamm机理

Eigen-Tamm模型认为水溶液中的离子对从单水分子桥链离子对到紧密离子对是离子对溶剂化平衡的动力学控制性步骤,两态之间自由能垒最高,相互转化速率最慢. 设计了两类带有单位电荷的离子对模型(2.0:x和x:2.0,固定离子对中的阳离子或阴离子的半径为2 ?,另一个为不同半径的阴阳离子),通过计算离子对不同距离的平均力势来获取自由能曲线,发现2.0:x系列离子对由于溶剂水的作用,从单水分子桥链离子对到紧密离子对转化的自由能垒有明显减低,并不是离子成对动力学平衡中的最慢步骤,与Eigen-Tamm 模型描述存在偏差.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

超弹性球体入水过程空泡演化及球体变形实验

超弹性材料是工程实际中常用的材料,具有很强的非线性力学性能.将超弹性材料应用于入水问题是一个新的跨学科研究方向.与传统的刚性球体入水现象不同,超弹性球体入水后极易发生变形.为了探究该大变形的入水流固耦合问题,本文采用高速摄像方法,对超弹性球体垂直入水问题开展实验研究.基于实验结果,对比分析了球体材料属性和入水冲击条件对入水空泡流动及球体变形行为的影响.实验结果表明,超弹性球体入水后产生嵌套空泡现象的条件是需要足够大的入水冲击条件和小的材料剪切模量.嵌套空泡产生和保持的时间与球体的剪切模量和直径有关.超弹性球体的入水位移及其形成空泡的长度随入水冲击速度和剪切模量的增大而增大,却随球体直径的增大而减小.入水冲击速度的增加只会加剧球体的变形程度,而不影响嵌套空泡的产生时刻.同时,本文对球体的变形行为随弗劳德数和剪切模量与水动力之比的变化特性进行了描述与研究.     

新建高焓激波风洞Ma=8飞行模拟条件的实现与超燃实验

针对高Mach数超燃冲压发动机实验能力空缺问题,基于航天十一院新建的FD-21高能脉冲风洞,进行了Ma=8超燃飞行条件的模拟能力设计与调试,获得了总焓2.9 MJ/kg、总压11.01 MPa实验条件,实现了Ma=8、高度31 km飞行条件的风洞模拟.在此基础上,研发了匹配的氢燃料供应及喷注时序控制系统,设计了超燃冲压发动机模型,开展了超燃冲压发动机模型自由射流应用性风洞实验,获得了氢气燃料与空气、氮气超声速气流耦合流动作用下的实验模型壁面压力数据.在当量比近似一致条件下,空气来流对应的燃烧室壁面压力明显高于氮气来流情况,表明氢气在1 ms有效实验时间内完成了与超声速空气来流的混合、点火与燃烧,获得燃烧释热特性,确认了在FD-21高能脉冲风洞开展高Mach数超燃实验是切实可行的,为后续研究奠定了良好的基础.      

大电流冲击条件下高温超导线圈热稳定边界的数值求解

不同于低温超导体,在高温超导线圈中,一定体积内的热积累是造成失超的较主要原因.因此,在遭遇大电流冲击时,线圈仍有可能保持稳定.在本文中,我们通过数值求解,作出了在大电流冲击条件下高温超导线圈的热稳定边界.求解结果表明,存在分别对应两种热积累情况的热稳定边界.为安全起见,应用在高温超导电力设备中的线圈应采取热稳定化路线设计.     

α铁冲击相变的离散元方法

利用离散元方法结合基于无扩散相变的两相模型、热力学相容的自由能函数与有限速率相变动力学方程,模拟α铁的冲击相变过程.得到铁的相边界、冲击Hugoniot关系及自由面速度剖面,并对不同冲击压力下加卸载过程的波系传播和相互作用过程进行分析,获得了加卸载波速特征.     

Electrical and optical characteristics of the radio frequency surface dielectric barrier discharge plasma actuation

Electrical characteristics and optical emission spectrum of the radio frequency(RF) surface dielectric barrier discharge(SDBD) plasma actuation are investigated experimentally in this paper. Influences of operating pressure, duty cycle and load power on the discharge are analyzed. When the operating pressure reaches 30 kPa, the discharge energy calculated from the Charge–Voltage(Q–V) Lissajous figure increases significantly, while the effective capacitance decreases remarkably. As the duty cycle of the applied voltage increases, the voltage–current waveforms, the area of Q–V loop and the capacity show no distinct changes. Below 40 W, effective capacitance increases with the increase of load power, but it almost remains unchanged when load power is between 40 W and 95 W. The relative intensity I_(391.4)~peak/I_(380.5)~peak changes little as the operating pressure varies from 4 kPa to 100 kPa, while it rises evidently with the pressure below 4 kPa, which indicates that the RF discharge mode shifts from filamentary discharge to glow discharge at around 4 kPa. With the increase of load power, the relative intensity I_(391.4)~peak/I_(380.5)~peak rises evidently. Additionally, the relative intensity I_(371.1)~peak/I_(380.5)~peak is insensitive to the pressure,the duty cycle, and the load power.     

On the impact noise generation due to a wheel passing over rail joints

Impacts occur when a railway wheel encounters discontinuities such as rail joints. A model is presented in which the wheel/rail impacts due to rail joints are simulated in the time domain. The impact forces are transformed into the frequency domain and converted into the form of an equivalent roughness input. Using Track-Wheel Interaction Noise Software (TWINS) and the equivalent roughness input, the impact noise radiation is predicted for different rail joints and at various train speeds. It is found that the impact noise radiation due to rail joints is related to the train speed, the joint geometry and the static wheel load. The overall impact noise level from a single joint increases with the speed V at a rate of roughly .     

Short-term changes in delta(13)C and delta(15)N signatures of water discharged from grazed grasslands

The composition of dissolved organic matter (DOM) in a soil is the product of a variety of soil processes. Changes in the composition of DOM in water discharged from soil should, therefore, give an important insight into modifications in these soil processes. We hypothesise that these processes in soils, under different grassland management regimes, would be affected to different extents by the short-term disturbance of a storm event and that evidence of this could be detected in delta(13)C and delta(15)N signatures in drainage and surface runoff waters. During a storm event we collected discharge waters from 1 ha grassland lysimeters, with or without artificial drainage, which received contrasting fertiliser inputs, and delta(13)C and delta(15)N signatures were determined. Changes in (13)C enrichment during the storm event were clearly identifiable, as were differences between plots for (13)C and (15)N, illustrating that this technique has potential to be a useful tool for identifying and investigating short- and long-term changes in soil organic matter dynamics. Copyright 1999 John Wiley & Sons, Ltd.     

X波段高功率负载的优化设计与测试

利用三维电磁场仿真软件CST进行了圆形水室水负载的仿真设计，先后设计的两种不同规格的负载驻波比分别为1.032 5和1.055 3，在50 MW的峰值功率下，峰值场强分别为21.16 MV/m和17.57 MV/m；并探究了陶瓷片和水的介电性质对驻波比的影响；测试驻波比分别为1.058 2和1.076 3。对一种圆筒水负载进行了优化设计，结果表明其具有很高的功率耐受水平。最后设计了一种不锈钢干负载，对其吸收齿结构和长度进行了优化，使其更利于加工。使用ANSYS对干负载结构进行了热应力分析，结果显示，最高温度和最大应力分别为83.478 ℃和63.917 MPa，最大形变为0.072 971 mm。     

Hydrostatic high pressure applied to food sterilization III: Application to spices and spice mixtures

Abstract

The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography.     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

Generation of ultraharmonics in surfactant based ultrasound contrast agents: use and advantages.

A unique distinction between surfactant stabilized ultrasound contrast agent ST68 and water (or tissue), is the enhanced ability of the agent to generate non-linear frequencies such as sub-harmonics (f0/2), higher harmonics (2fo, 3fo, 4fo,...), and ultraharmonics (3f0/2, Sf0/2, 7f0/2,...), when insonated with fundamental frequency f0. Currently, second harmonics (2f0) have been predominantly researched, to exploit the diagnostic benefits of the contrast-specific non-linear imaging. However, we found that at normal imaging pressures (100 kPa-1 MPa), ST68 agent-generated second harmonic enhancements dropped to approximately 8 dB at 100 kPa and approximately 2 dB at 1 MPa. Moreover, at these pressures water (or tissue) produced strong second harmonics due to non-linear propagation. Ultraharmonics and sub-harmonics on the other hand, were generated only by the agent, and were not produced due to the non-linear propagation of ultrasound in either water or tissue. Additionally, ultraharmonic (3f0/2) enhancements of approximately 23 dB at 100 kPa, approximately 35 dB at 0.5 MPa and approximately 41dB at 1.1 MPa for ST68-PFC, offer much greater signal to noise ratio than higher harmonics.     

Spherically symmetric static inhomogeneous cosmological models

Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum) energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third of the combined value of radiation pressure and density.     

船载光电转台设计及特定环境下可行性分析

结合船载光电转台的技术要求,通过pro/E软件设计舰载光电转台的机械结构。根据转台的表面材料,运用ABAQUS软件对其在海洋的等价静力风载、极端温度场和海浪振动3种特殊环境下进行表面变形分析,校验结构的应力和应变,确保满足船载光电转台的设计精度要求;得到在等价静力风载作用下,光电转台的最大应力点大小为255 MPa,小于钢的屈服强度355 MPa;在温差作用下最大应力点分别为174.8 MPa、247.1 MPa,均小于铝合金的屈服强度274 MPa;在海浪振动作用下,1~5阶振型的最大形变位置均不在转轴附近。