时间关联符合法铀部件质量测量中的几何影响

外中子源注入铀部件后,根据两路探测器间的中子和gamma粒子时间关联符合计数分布可获得铀部件的质量等特性。本文利用粒子蒙特卡罗输运程序,对富集度相同、几何尺寸各异的4块半球壳形状的金属铀部件质量测量实验进行模拟,获得对应粒子的时间关联符合计数分布。然后,根据模拟计算结果,评估几何形状对质量分辨的影响。研究结果表明,4块半球壳金属铀部件的形状对其质量测量的影响不大。     

界面流法计算反应堆六角形燃料组件中子通量密度分布

利用界面流法计算两维六角形轻水堆燃料组件中子通量密度分布。子区内中子源在空间上采用二次分布近似，还考虑了六角形组件周边水隙对组件内中子通量密度的影响。根据提出的模型，编制了TPHEX－E程序，并对一些轻水堆六角形组件问题作了计算，计算结果与蒙特卡罗方法计算结果进行了比较，符合良好。本程序可用于六角形轻水堆燃料组件计算。     

Maximum likelihood-based adaptive differential evolution identification algorithm for multivariable systems in the state-space form

Parameter estimation plays an important role in the field of system control. This article is concerned with the parameter estimation methods for multivariable systems in the state-space form. For the sake of solving the identification complexity caused by a large number of parameters in multivariable systems, we decompose the original multivariable system into some subsystems containing fewer parameters and study identification algorithms to estimate the parameters of each subsystem. By taking the maximum likelihood criterion function as the fitness function of the differential evolution algorithm, we present a maximum likelihood-based differential evolution (ML-DE) algorithm for parameter estimation. To improve the parameter estimation accuracy, we introduce the adaptive mutation factor and the adaptive crossover factor into the ML-DE algorithm and propose a maximum likelihood-based adaptive differential evolution algorithm. The simulation study indicates the efficiency of the proposed algorithms.     

Enhanced mechanical toughness of carbon nanofibrous-coated surface modified Kevlar reinforced polyurethane/epoxy matrix hybrid composites

High-performance Kevlar fiber had extensively been explored to upgraded mechanical properties of the advanced composites. Therefore, this study aimed a challenging work to grow carbon nanofibers onto the Kevlar fiber to improve its fiber-matrix interaction properties. It was successfully done through inexpensive flame deposition as well as modification of matrix with hybrid resin using polyurethane-epoxy mixture. A hand-layup method had been adopted to manufacture the composite laminates. The chemical and surface structures of the prepared laminae were examined by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and the composite's properties were evaluated tensile test, compact tension (CT) fracture test, fractography, and differential scanning calorimetry. The surface modified Kevlar laminae with CNF were used as reinforcing layer in the epoxy and PU/epoxy hybrid resin matrices. CNF-coated heated Kevlar reinforced laminated PU/epoxy hybrid composites (CNF-Kev/PU-Epoxy) showed highest elongation 47% and fracture toughness (11.7 MPa√m) along with good UTS 139 MPa. Therefore, these hybrid nanocomposites developed by simple inexpensive method would be the potential candidates for several advanced applications particularly in defense, automobile, aerospace, and spacecraft applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48802.     

Impact of A134 and E218 Amino Acid Residues of Tropomyosin on Its Flexibility and Function

Tropomyosin (Tpm) is one of the major actin-binding proteins that play a crucial role in the regulation of muscle contraction. The flexibility of the Tpm molecule is believed to be vital for its functioning, although its role and significance are under discussion. We choose two sites of the Tpm molecule that presumably have high flexibility and stabilized them with the A134L or E218L substitutions. Applying differential scanning calorimetry (DSC), molecular dynamics (MD), co-sedimentation, trypsin digestion, and in vitro motility assay, we characterized the properties of Tpm molecules with these substitutions. The A134L mutation prevented proteolysis of Tpm molecule by trypsin, and both substitutions increased the thermal stability of Tpm and its bending stiffness estimated from MD simulation. None of these mutations affected the primary binding of Tpm to F-actin; still, both of them increased the thermal stability of the actin-Tpm complex and maximal sliding velocity of regulated thin filaments in vitro at a saturating Ca²⁺ concentration. However, the mutations differently affected the Ca²⁺ sensitivity of the sliding velocity and pulling force produced by myosin heads. The data suggest that both regions of instability are essential for correct regulation and fine-tuning of Ca²⁺-dependent interaction of myosin heads with F-actin.     

How Far Are We from Prescribing Fasting as Anticancer Medicine?

(1) Background: the present review provides a comprehensive and up-to date overview of the potential exploitation of fasting as an anticancer strategy. The rationale for this concept is that fasting elicits a differential stress response in the setting of unfavorable conditions, empowering the survival of normal cells, while killing cancer cells. (2) Methods: the present narrative review presents the basic aspects of the hormonal, molecular, and cellular response to fasting, focusing on the interrelationship of fasting with oxidative stress. It also presents nonclinical and clinical evidence concerning the implementation of fasting as adjuvant to chemotherapy, highlighting current challenges and future perspectives. (3) Results: there is ample nonclinical evidence indicating that fasting can mitigate the toxicity of chemotherapy and/or increase the efficacy of chemotherapy. The relevant clinical research is encouraging, albeit still in its infancy. The path forward for implementing fasting in oncology is a personalized approach, entailing counteraction of current challenges, including: (i) patient selection; (ii) fasting patterns; (iii) timeline of fasting and refeeding; (iv) validation of biomarkers for assessment of fasting; and (v) establishment of protocols for patients’ monitoring. (4) Conclusion: prescribing fasting as anticancer medicine may not be far away if large randomized clinical trials consolidate its safety and efficacy.     

Relationship of energy to geometry in brittle fracture

Numerous investigators have noticed that there is a relationship between the energy of branching and the energy of initiation during a fracture event in materials that fail in a brittle manner. Usually, this is measured in terms of the stress intensities, i.e., K_B/K_c. The ratio has been reported between 3 and 4, implying a constant value. However, data suggests that it is a constant for a material, but not a universal constant. The fractal dimension of the fracture surface is related to the critical stress intensity factor. It is a measure of the tortuosity of the fracture surface. We show that the K_B/K_C ratio is directly related to the square root of the fractal dimensional increment, indicating a relationship between the energy of crack propagation and the tortuosity of the fracture surface.     

注塑机注射速度的模型预测控制及其仿真

注塑过程具有随机性、非线性以及时变性等特点,常规比例积分微分控制方法很难使注射速度控制达到理想的效果,为此提出了一种基于模型预测的注射速度控制方法。首先介绍了注塑机注塑工作原理,分析了注射速度控制系统,并通过模型预测算法得到当前采样时刻控制量以及下一时刻的控制量。仿真结果表明,基于模型预测的注射速度控制能够很好地跟踪快速变化的速度设定曲线,拥有较好的稳定性和抗干扰性。