Effect of Size and Initial Water Content on the Effective Diffusion Coefficient during Convective Drying of Sweet Potato Cut into Cubic and Cylindrical Shapes

In this article, we investigated the influence of size and initial water content on the effective diffusion coefficient of sweet potatoes samples cut into cubic and cylindrical shapes. The sizes of the cubic samples are 0.5, 1, 1.5, 1.75, 2, 2.5 and 3 cm edge with a respective initial water content of 2.7, 3.76, 3.48, 2.68, 3.28, 2.17 and 2.29 kg/kgms. For cylindrical samples, the radius is set at 0.5 cm and sample heights are 1, 1.5, 2, 2.5, 3, 3.5 and 4 cm with respective water contents of 2.2, 3.19, 2.85, 2.1, 2.17, 2.39 and 2.03 kg/kgms. The effective diffusion coefficients of cubic samples are of the order of 10−10 and 10−9 m2∙s−1 grew with sample edge. As for the cylindrical samples, the effective diffusion coefficients were of the order of 10−9 m2∙s−1 and there was no linear correlation between cylinder height and their effective diffusion coefficient. As for the examination of the initial water content on the effective diffusion coefficient, it turned out that the initial water content had no influence on the effective diffusion coefficient of the sweet potato samples.

ASYMPTOTIC HOMOGENIZATION IN A PARABOLIC SEMILINEAR PROBLEM WITH PERIODIC COEFFICIENTS AND INTEGRABLE INITIAL DATA

In this paper, we study the large time behavior of solutions of the parabolic semilinear equation δtu-div（a（x）△↓u） = -｜u｜^αu in （0,∞） × R^N, where α 〉 0 is constant and a∈ Cb^1（R^N） is a symmetric periodic matrix satisfying some ellipticity assumptions.Considering an integrable initial data u0 and α ∈ （2/N, 3/N）, we prove that the large time behavior of solutions is given by the solution U（t, x） of the homogenized linear problem δtU-div（a^h△↓U）=0,U（0） = C, where a^h is the homogenized matrix of a（x）, C is a positive constant and δ is the Dirac measure at 0.

INITIAL-OBLIQUE DERIVATIVE PROBLEMS FOR NONLINEAR PARABOLIC SYSTEMS WITH MEASURABLE COEFFICIENTS

This paper deals with some initial-oblique derivative boundary value problems for nonlinear nondivergent parabolic systems of several second order equations with measurable coefficients in multiply connected domains. Firstly, a priori estimates of solutions for the initial-boundary value problems are given, and then by using the above estimates of solutions and the Leray-Schauder theorem, the existence and uniqueness of solutions for the problems are proved.

Reflection of Plane Waves from a Free Surface of an Initially Stressed Transversely Isotropic Dissipative Medium

The governing equations of a transversely isotropic dissipative medium are solved analytically to obtain the speeds of plane waves. The appropriate solutions satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflection coefficients of reflected quasi-P (qP) and quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter. The impact of initial stress parameter on the reflection coefficients is observed significantly.

Reflection of Plane Waves from Free Surface of an Initially Stressed Rotating Orthotropic Dissipative Solid Half-Space

The governing equations of an initially stressed rotating orthotropic dissipative medium are solved analytically to obtain the velocity equation which indicates the existence of two quasi-planar waves. The appropriate particular solutions in the half-space satisfy the required boundary conditions at the stress-free surface to obtain the expressions of the reflec-tion coefficients of the reflected quasi-P (qP) and reflected quasi-SV (qSV) waves in closed form for the incidence of qP and qSV waves. A particular model is chosen for numerical computation of these reflection coefficients for a certain range of the angle of incidence. The numerical values of these reflection coefficients are shown graphically against the angle of incidence for different values of initial stress parameter and rotation parameter. The impact of initial stress and rotation parameters on the reflection coefficients is observed significantly.

Experimental investigation on the development characteristics of initial electrons in a gas pressurized closing switch under DC voltage

As one of the most important elements in linear transformer driver(LTD) based systems, the gas pressurized closing switches are required to operate with a very low prefire probability during the DC-charging process to ensure reliable operation and stable output of the whole pulsed power system. The most direct and effective way to control the prefire probability is to select a suitable working coefficient. The study of the development characteristics of the initially generated electrons is useful for optimizing the working coefficient and improving the prefire characteristic of the switches. In this paper an ultraviolet pulsed laser is used to generate initial electrons inside the gap volume. A current measuring system is used to measure the time-dependent current generated by the growth of the initial electrons so as to study the development characteristics of the electrons under different working coefficients. Experimental results show that the development characteristics of the initial electrons are influenced obviously by the working coefficient. With the increase of the working coefficient, the development degree of the electrons increases consequently. At the same times, there is a threshold of working coefficient which produces the effect of ionization on electrons. The range of the threshold has a slow growth but remains close to 65% with the gas pressure increase. When the working coefficient increases further, γ processes are starting to be generated inside the gap volume. In addition, an optimal working coefficient beneficial for improving the prefire characteristic is indicated and further tested.

Effect of Rotation, Magnetic Field and Initial Stresses on Propagation of Plane Waves in Transversely Isotropic Dissipative Half Space

The problem regarding the reflection of plane waves in a transversely isotropic dissipative medium is considered, in which we are studying about the reflection of incidence waves in initially stressed dissipative half space. After solving the governing equations, we find the two complex quasi-P (qP) and quasi-SV (qSV) waves. The occurrence of reflected waves is studied to calculate the reflection coefficient and the energy partition of incidence wave at the plane boundary of the dissipative medium. Numerical example is considered for the reflection coefficient and the partition of incident energy, in which we study about the effect of rotation, initial stresses and magnetic field.

The Mathematical Modelling for Studying the Influence of the Initial Stresses and Relaxation Times on Reflection and Refraction Waves in Piezothermoelastic Half-Space

The present paper concentrates on the study of reflection and refraction phenomena of waves in pyroelectric and piezo-electric media under initial stresses and two relaxation times influence by apply suitable conditions. The generalized theories of linear piezo-thermoelasticity have been employed to investigate the problem. In two-dimensional model of transversely isotropic piezothermoelastic medium, there are four types of plane waves quasi-longitudinal (qP), quasi-transverse (qSV), thermal wave (T-mode), and potential electric waves (φ-mode) The amplitude ratios of reflection and refraction waves have been obtained. Finally, the results in each case are presented graphically.

Stress concentration coefficients of optimized cope-hole welded detail

The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings.In addition,local finite element models of this welded detail were established using finite element software ANSYS.The influences of different factors such as plate thickness,plate gap and initial geometric imperfections on the stress concentration coefficient(SCC) were discussed.The experimental results indicate that the fatigue life of three specimens for this welded detail is 736,000,1,044,200 and 1,920,300 times,respectively.The web thickness,the filler plate thickness and the initial geometric imperfection have relatively less effect on the SCCs of this welded detail.However,cope-hole radius is influential on the SCCs of the web and the weld.The SCC of weld is significantly affected by the weld size and plate gap,but the SCCs of other parts of the welded detail are hardly affected by the plate gap.

THE CALCULATION OF INITIAL SHOCK WAVE IN ROCK WITH UNCOUPLING CHARGE BLASTING

According to the structure of explosive charge in rock blasting, a physical model has been set up in this paper. Based on the model, a methodology for calculating initial shock wave of uncoupling charge has been given. The pressure p3 has been calculated when high explosives act on granite, limestone, marble and shaIe respectively. Some important conclusions are also gained by the analysis of results.

混凝土暴露试验的稳定时长与试验分析方法

混凝土自然暴露试验通常用于研究混凝土的氯离子扩散系数,但需要选择合适的分析方法,并确定稳定暴露时长。为此,首先系统研究混凝土的氯离子瞬时扩散和平均扩散理论,明确扩散方程中不同参数的时变特性,揭示了瞬时扩散解析解在分析混凝土中氯离子扩散过程和浓度分布时与平均扩散解析解等价。然后,引入随机数模拟混凝土取样误差,利用蒙特卡洛法分析氯盐环境下混凝土暴露时长、取样误差以及不同回归分析方法对扩散系数计算结果的影响,研究表明瞬时扩散解用于混凝土自然暴露试验分析时容易受到参数迭代初值的影响,导致初始扩散系数计算结果不稳定,而平均扩散解可以避免该问题,因而平均扩散解更适合于混凝土自然暴露试验数据的回归分析。在此基础上,研究确定了不同取样误差下的混凝土稳定暴露时长。最后,通过工程实例分析验证了回归分析方法以及稳定暴露时长在氯盐环境下混凝土自然暴露试验数据分析中的合理性和必要性。

基于小样本数据的储层渗透率预测方法

针对Timur/Coates和SDR公式计算储层渗透率处理步骤繁琐的缺点,设计了一个实现非线性回归的单隐层前馈神经网络(single hidden layer feedforward neural network,SLFNN),该网络包含一个具有非线性激活函数的隐含层、两个线性全连接层和一个dropout层。为了防止学习过程中陷于局部最优和小样本数据集造成的过拟合,使用了Adam优化器、ReLU激活函数、何恺明均匀分布权重初始化方法和余弦退火热重启学习率调整算法。以某油田A~D四口生产井不同层位上的测井和岩心构成的小样本数据作为训练集和验证集,采用5折交叉验证方法,确定了隐含层神经元个数、初始学习率和dropout层神经元失活概率。最后以同区块E井数据作为测试集,使用4种模型(SLFNN、随机森林回归、支持向量回归和极端梯度提升回归)分别对渗透率进行了预测和对比。实验结果表明,在测试集下SLFNN模型的平均绝对误差(MAE)和决定系数(R 2)均比其他3种模型的优,说明SLFNN模型对储层渗透率的预测是有效的。

半导体桥火工品的防静电与防射频设计

为提高半导体桥(SCB)火工品的防静电与防射频的双防能力,将静电加固器件瞬态电压抑制(TVS)二极管和射频加固器件负温度系数(NTC)热敏电阻同时集成入SCB火工品的结构中,并研究了上述组合器件对SCB火工品发火性能和抗电磁性能的影响规律。结果表明:集成防护器件后,SCB火工品的安全电流从1.2 A升至1.5 A;抗静电性能满足500 pF/500Ω/25 kV条件下不发火;在22μF/16 V的电容发火条件下,集成SCB火工品的平均爆发时间较SCB火工品增加了1.77μs。因此,该组合型防护器件可以在不改变SCB发火性能的基础上有效提高SCB的抗静电和抗射频的能力。

不同分子分型年轻乳腺癌患者的MRI特征性表现

目的分析不同分子分型年轻乳腺癌患者MRI特征性表现。方法选择新疆医科大学附属肿瘤医院2013年4月—2020年12月406例经病理证实的乳腺癌患者,其中年轻组乳腺癌190例(<40岁),中老年组乳腺癌216例(≥40岁),术前均接受MRI检查。对比2组患者MRI特征性表现,并比较不同分子分型年轻乳腺癌患者MRI特征及组织学分级。结果与中老年组乳腺癌患者比较,年轻组乳腺癌患者MRI更易表现为边缘清晰、不均匀强化,早期强化率(IER)更高,表观弥散系数(ADC)值更低(P均<0.05)。年轻组乳腺癌患者中,三阴性型IER明显高于Luminal A型(P<0.05);Luminal B型ADC值高于HER-2过表达型、三阴性型(P<0.05);HER-2过表达型、三阴性型组织学分级以Ⅲ级为主,Luminal A型、Luminal B型组织学分级以Ⅱ级为主(P<0.05)。结论年轻乳腺癌MRI表现有一定特征性,可为其临床治疗方案制定及预后评估提供参考。

基于降阶投影的初始渗流场反演方法

为了解决传统基于降阶模型的参数反演方法的高耗时问题,提出了一种改进的降阶反演方法(IterROM),用于执行快速参数反演任务。不同于传统降阶反演方法先训练后反演的流程,该方法将参数反演与降阶模型训练紧密融合,使用训练中的降阶模型代替原始模型进行参数反演,同时将反演结果应用于降阶模型的训练。该方法在参数反演阶段使用观测资料和后验误差共同组成目标函数,并使用降阶模型解与全阶模型解的最大节点误差作为迭代终止精度。经过某工程初始渗流场反演模型的测试,发现IterROM相比传统方法精度高、计算成本低,可用于快速执行初始渗流场的反演任务。

过硫酸铵对煤的吸附解吸性影响研究

探讨了过硫酸铵对煤储层的解吸常数、临界解吸压力、含气饱和度、瓦斯放散初速度及坚固性系数等参数的影响,为过硫酸铵作为破胶剂在煤储层压裂中的应用提供了基础数据。分别对过硫酸铵处理前后的10组煤样进行等温吸附、瓦斯放散初速度及坚固性系数测试,结果表明:过硫酸铵能够有效地降低中高阶煤储层极限吸附量,提高其临界解吸压力和含气饱和度,有利于煤层气的产出;能够一定程度上加快煤层气在常压下的解吸,提高煤层气产出效率;煤样经过硫酸铵处理后,f值全面下降,且总体呈现原始f值越大,其降幅越大的趋势。

纵向单裂隙分布位置对洞室围岩失稳特征影响试验研究

为研究纵向裂隙分布位置对洞室围岩失稳特征的影响规律,通过无预制裂隙洞室模型及含不同位置预制裂隙洞室模型双轴加载试验,结合数字图像技术(DIC)对比分析了洞室模型宏观力学参数及破坏模式。试验结果表明,随侧压力系数(λ)增大,洞室模型峰值强度和峰值应变呈先增大后减小趋势,在λ=1时达到最大值,弹性模量与之相反,呈先减小后增大趋势;从破坏模式来看,λ<1时,洞室破坏模式主要由张拉破坏逐渐转为拉剪复合破坏,裂隙位于拱顶,底板破坏明显,而裂隙位于直墙和底脚处,拱顶及底脚均破坏严重,随λ增大,λ≥1时,模型破坏以张拉裂纹为主,相比其他两个位置的裂隙,裂隙位于直墙,洞室稳定性最差;在相同λ下,高应变集中区会随裂隙位置改变而发生转移,但高应变区主要集中在预制裂隙端及洞室两底脚处。

基于数字孪生技术与时间变异系数的SIM卡初始信息聚合算法

为了扩展SIM卡移动终端的空口带宽,提升SIM的通信速率,提出基于数字孪生技术与时间变异系数的SIM卡初始信息聚合算法。利用数字孪生技术获取SIM卡中包含初始信息的孪生数据,构建SIM卡的虚拟组件,时序排列初始信息,分析时间变异系数,确定与划分待聚合的初始信息,计算各网格单元内的密度阈值函数,构建评价函数,获取最佳聚合系数,完成SIM卡初始信息聚合。实验结果表明:上行通信速率和下行通信速率均提升至90Mbps,SIM卡初始信息的聚合效果良好。可以有效拓宽移动通信终端的空口带宽,增强通信信号强度。

冷冻砂型对铸铁合金凝固行为及组织性能影响规律研究

采用冷冻砂型铸造铸铁合金,界面换热系数是反映冷冻砂型与铸铁合金换热程度的重要参数,对于分析铸铁合金组织性能具有重要意义。研究测定了合金的界面接触温度随时间的变化规律,在此基础上分析了界面换热特征,获得了界面换热系数随初始界面温度变化的函数式,同时分析了冷冻砂型中铸件凝固的铸态微观组织及力学性能。结果表明:界面换热系数随着冷冻砂型初始温度的增加而降低,随含水率的减少而升高。当含水率为6%(质量分数,下同)时,在-35℃、-30℃、-25℃初始冷冻温度条件下,铸型铸件界面换热系数峰值分别是195663W/(m^(2)·K)、147933W/(m^(2)·K)、120836W/(m^(2)·K);当含水率为5%时,在-35℃、-30℃、-25℃初始冷冻温度条件下,铸型铸件界面换热系数峰值分别是209257W/(m^(2)·K)、176878W/(m^(2)·K)、134472W/(m^(2)·K)。相同含水率下初始冷冻温度越低,珠光体晶粒越细,石墨化程度越高,抗拉强度也越高。

基于三参数模型的方钢管柱-H型梁单向螺栓端板连接节点承载力研究

单向螺栓可较好地解决封闭截面内使用普通螺栓带来的施工不便和焊缝连接易发生脆性断裂等问题。为探索方钢管柱与H型梁单向螺栓端板连接节点的承载性能和影响因素,分别对梁柱平齐式端板连接节点和梁柱外伸式端板连接节点进行静力加载试验。试验通过校准有限元模型,发现两组数据吻合度较高,对此通过改变方钢管柱、H型梁和端板的截面参数与单向螺栓的直径建立了有限元模型进行承载力分析。研究结果表明:梁高度、柱壁厚度和螺栓直径对梁柱平齐式端板连接节点和梁柱外伸式端板连接节点的初始刚度和极限弯矩都有较大影响;梁柱外伸式端板连接节点的初始刚度和极限弯矩还受端板的宽度和厚度的影响。最后基于三参数模型拟合出初始刚度、极限弯矩和形状系数的近似公式,为此类节点在工程中的应用提供了参考。