三维位势问题的梯度边界积分方程的新解法

三维位势问题的边界元分析中,关于坐标变量的边界位势梯度的计算是一个困难的问题. 已有一些方法着手解决这个问题,然而,这些方法需要复杂的理论推导和大量的数值计算. 本文提出求解一般边界位势梯度边界积分方程的辅助边值问题法. 该方法构造了与原边界值问题具有相同解域的辅助边值问题,该辅助边值问题具有已知解,因此通过求解此辅助边值问题,可获得梯度边界积分方程对应的系统矩阵,然后将此系统矩阵应用于求解原边值问题,求解过程非常简单,只需求解一个线性系统即可获得原边值问题的解. 值得注意的是,在求解原边值问题时,不再需要重新计算系统矩阵,因此辅助边值问题法的效率并不很差. 辅助边值问题法避免了强奇异积分的计算,具有数学理论简单、程序设计容易、计算精度高等优点,为坐标变量梯度边界积分方程的求解提供了一个新的途径. 3个标准的数值算例验证了方法的有效性.      

群集建筑中大跨裙摆屋盖风荷载特性的数值模拟研究

以苏州太平金融大厦为工程背景,针对其大跨裙摆屋盖的风荷载作用,首先采用RNG k-ε模型模拟分析了其平均风压分布规律,以及风向变化对屋盖表面风荷载体型系数的影响;其次,引入干扰因子IF,探讨了周边建筑对大跨裙摆屋盖风荷载的气动干扰作用。结果表明:0°风向下,走廊上方屋盖两侧区域出现“上吸下顶”的叠加作用;90°风向下屋盖北侧飘带末端区域受到狭道风效应出现正压集中现象;风向变化对大跨裙摆屋盖的风荷载体型系数分布影响较大;且周围建筑物对大跨裙摆屋盖的气动干扰效应明显,主要表现为风压“遮挡效应”,而局部区域表现为风压“放大效应”。     

4-氯查尔酮缩氨基硫脲微环境效应的紫外-可见光谱研究

合成了新化合物4-氯查尔酮缩氨基硫脲(CCT)并进行了表征;探讨了溶剂极性、溶液的酸度、β-CD及不同离子存在的微环境对CCT的紫外-可见吸收光谱的影响。     

生物组织电穿孔中的热效应研究

本文对生物组织电穿孔中的热效应问题进行了计算研究。结果表明生物组织电穿孔过程中,选用不当的脉冲电压参数,会对组织造成严重的热损伤。若采用相同的烧伤阈值来描述热损伤范围,则相同电脉冲参数条件下在体组织比离体组织受到的热损伤更大。     

Polarization-enhanced bulk photovoltaic effect of BiFeO3 epitaxial film under standard solar illumination

In this Letter, we report the polarization-enhanced bulk photovoltaic effect (BPV) in pristine BiFeO₃ (BFO) epitaxial film under standard 1 sun AM 1.5 G illumination. High-quality epitaxial BFO films are grown on (001)-oriented niobium doped-SrTiO₃ substrates by pulsed laser deposition. The best BFO film based photovoltaic device achieves a power conversion efficiency of 0.0062% under standard illumination. Besides, it is found that the number of bipolar pulses plays a key role in improving the short-circuit current density and open-circuit voltage. These results are beneficial for further understanding of physical origin of the photovoltaic properties in ferroelectric oxides.     

塞曼效应仿真实验平台

塞曼效应实验是学生了解原子具有磁矩和空间取向量子化现象的重要实验,至今塞曼效应仍是研究能级结构的重要方法之一.为了能够让学生更加清楚地了解塞曼效应实验的基本原理和操作规程,针对教学中的重点和难点,运用flash软件制作出塞曼效应仿真实验.该程序可全程高度仿真实验过程,具有界面友好、易于操作、无需安装等优点.为实验教学提供了一种新的辅助方式.     

基于氧化石墨烯的长周期光纤光栅的全光控制

实验验证了一种通过将氧化石墨烯分散液沉积在长周期光纤光栅的全光控制的相关研究。通过外加的垂直泵浦光的作用,氧化石墨烯吸收泵浦光产生热量,改变长周期光纤光栅的包层模式的相位差,由于热膨胀的作用改变了氧化石墨烯所覆盖部分的光栅周期,使得谐振谱发生了移动,其最大调制深度可达10.6 dB,谐振谱最大可红移12.8 nm。通过实验发现,沉积相同浓度氧化石墨烯分散液的次数影响实验结果,通过在相同光栅的相同位置分别沉积三次,发现沉积三次可以在光纤表面获得更加均匀的氧化石墨烯膜,进行了时间响应的测试,其中沉积三次后的长周期光纤光栅的响应速度可达0.61 ms,沉积多次氧化石墨烯分散液可以在光纤表面沉积得更加平整均匀,从而获得更大的导热性能。     

Hydrodynamic and Thermodynamic Nonequilibrium Effects around Shock Waves: Based on a Discrete Boltzmann Method

A shock wave that is characterized by sharp physical gradients always draws the medium out of equilibrium. In this work, both hydrodynamic and thermodynamic nonequilibrium effects around the shock wave are investigated using a discrete Boltzmann model. Via Chapman–Enskog analysis, the local equilibrium and nonequilibrium velocity distribution functions in one-, two-, and three-dimensional velocity space are recovered across the shock wave. Besides, the absolute and relative deviation degrees are defined in order to describe the departure of the fluid system from the equilibrium state. The local and global nonequilibrium effects, nonorganized energy, and nonorganized energy flux are also investigated. Moreover, the impacts of the relaxation frequency, Mach number, thermal conductivity, viscosity, and the specific heat ratio on the nonequilibrium behaviours around shock waves are studied. This work is helpful for a deeper understanding of the fine structures of shock wave and nonequilibrium statistical mechanics.     

Inactivation of foodborne pathogens based on synergistic effects of ultrasound and natural compounds during fresh produce washing

Ultrasound has potential to be used for disinfection, and its antimicrobial effectiveness can be enhanced in presence of natural compounds. In this study, we compared the antimicrobial effects of ultrasound at 20 kHz (US 20 kHz) or 1 MHz (US 1 MHz) in combination with carvacrol, citral, cinnamic acid, geraniol, gallic acid, lactic acid, or limonene against E. coli K12 and Listeria innocua at a constant power density in water. Compared to the cumulative effect of the individual treatments, the combined treatment of US 1 MHz and 10 mM citral generated >1.5 log CFU/mL additional inactivation of E. coli K12. Similarly, combined treatments of US 1 MHz and 2 mM carvacrol (30 min), US 20 kHz and 2 mM carvacrol, 10 mM citral, or 5 mM geraniol (15 min) generated >0.5–2.0 log CFU/mL additional inactivation in L. innocua. The synergistic effect of citral, as a presentative compound, and US 20 kHz treatment was determined to be a result of enhanced dispersion of insoluble citral droplets in combination with physical impact on bacterial membrane structures, whereas the inactivation by US 1 MHz was likely due to generation of oxidative stress within the bacteria. Combined ultrasound and citral treatments improved the bacterial inactivation in simulated wash water in presence of organic matter or during washing of inoculated blueberries but only additive antimicrobial effects were observed. Findings in this study will be useful to enhance fresh produce safety and shelf-life and design other alternative ultrasound based sanitation processes.     

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

Orthorhombic La_0.7-xEu_xCa_0.3MnO₃ samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm³ prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (T_C) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around T_C reaches the maximum (|ΔS_max|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔS_max| values are about 5.88, 4.93, and 4.71 J/kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔS_max| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around T_C have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La_0.7Ca_0.3MnO₃ materials for magnetic refrigeration below room temperature.