广义神经传播方程的整体吸引子

使用Galerkin方法,结合Sobolev空间理论和不等式技巧,给出了广义神经传播方程解的存在唯一性定理,然后利用吸引子存在性定理,采用半群方法证明了方程整体吸引子的存在性.     

Condensed Mode Cooling of Ethylene Polymerization in Fluidized Bed Reactors

This review gives an overview of the evolution of the technology of condensed mode cooling, primarily for the case of ethylene polymerization on supported catalysts in fluidized bed reactors. It is well known that this mode of heat removal is quite effective in allowing polyolefin manufacturers to increase significantly production rates. What is perhaps less well understood are all of the issues that, in addition to the effect of the latent heat of vaporization of injected liquid components, also have an impact on the rate of production and behavior of the reactor. However, the liquid components injected into the reactor can vaporize rapidly under full‐scale conditions, leaving behind several heavy components (with respect to ethylene) that have numerous effects on how the particles behave, on the reaction rate, and on fluidization, fouling, and other parameters related to reactor and process performance.     

A conjugated alkyne functional bicyclic polybenzoxazine with superior heat resistance

A difunctional benzoxazine (coPh‐apa) with a conjugated alkyne group is synthesized by the oxidative coupling reaction from a monocycle‐benzoxazine (Ph‐apa) containing an alkyne group. A model compound, 1,4‐diphenylbutadiyne (coPa), is used to study the curing reaction process of coPh‐apa by DSC, Fourier transform infrared spectroscopy, and ¹³C NMR, and the results suggest that the conjugated alkyne groups are involved in the crosslinking reaction via the trimerization reaction of the conjugated alkynyl groups and the Diels–Alder reaction. Furthermore, thermal properties of the polybenzoxazine are studied by dynamic thermomechanical analysis and thermogravimetric analysis. A glass‐transition temperature (T_gs) of as high as 412 °C and a char yield of 75.6% at 800 °C under nitrogen are obtained with the aid of the conjugated alkyne groups. Its excellent heat resistance dominates most thermosetting resins and will serve for heat shields. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1587–1592     

Transient transition behaviors of fractional-order simplest chaotic circuit with bi-stable locally-active memristor and its ARM-based implementation

This paper proposes a fractional-order simplest chaotic system using a bi-stable locally-active memristor. The characteristics of the memristor and transient transition behaviors of the proposed system are analyzed, and this circuit is implemented digitally using ARM-based MCU. Firstly, the mathematical model of the memristor is designed, which is nonvolatile, locally-active and bi-stable. Secondly, the asymptotical stability of the fractional-order memristive chaotic system is investigated and some sufficient conditions of the stability are obtained. Thirdly, complex dynamics of the novel system are analyzed using phase diagram, Lyapunov exponential spectrum, bifurcation diagram, basin of attractor, and coexisting bifurcation, coexisting attractors are observed. All of these results indicate that this simple system contains the abundant dynamic characteristics. Moreover, transient transition behaviors of the system are analyzed, and it is found that the behaviors of transient chaotic and transient period transition alternately occur. Finally, the hardware implementation of the fractional-order bi-stable locally-active memristive chaotic system using ARM-based STM32F750 is carried out to verify the numerical simulation results.     

大尺寸电阻加热式碳化硅晶体生长热场设计与优化

大尺寸低缺陷碳化硅(SiC)单晶体是功率器件和射频(RF)器件的重要基础材料,物理气相传输(physical vapor transport, PVT)法是目前生长大尺寸SiC单晶体的主要方法。获得大尺寸高品质晶体的核心是通过调节组分、温度、压力实现气相组分在晶体生长界面均匀定向结晶,同时尽可能减小晶体的热应力。本文对电阻加热式8英寸(1英寸=2.54 cm)碳化硅大尺寸晶体生长系统展开热场设计研究。首先建立描述碳化硅原料受热分解热质输运及其多孔结构演变、系统热输运的物理和数学模型,进而使用数值模拟方法研究加热器位置、加热器功率和辐射孔径对温度分布的影响及其规律,并优化热场结构。数值模拟结果显示,通过优化散热孔形状、保温棉的结构等设计参数,电阻加热式大尺寸晶体生长系统在晶锭厚度变化、多孔介质原料消耗的情况下均能达到较低的晶体横向温度梯度和较高的纵向温度梯度。     

Correlating Charge-Carrier Dynamics with Efficiency in Quantum-Dot Solar Cells: Can Excitonics Lead to Highly Efficient Devices?

The photovoltaic performance of quantum-dot solar cells strongly depends on the charge-carrier relaxation and recombination processes, which need to be modulated in a favorable way to obtain maximum efficiency. Recently, significant efforts have been devoted to investigate the carrier dynamics of nanocrystal sensitizers, both in solution and deposited on TiO₂ photoanodes, with the aim to correlate the excitonics with solar-energy conversion efficiency. This Minireview summarizes some proof of the concepts that efficiency can be directly correlated to the exciton dynamics of quantum-dot solar cells. The presented findings are based on CdSeS alloy, CdSe/CdS core/shell, Au/CdSe nanohybrids, and Mn-doped CdZnSSe nanocrystals, where the favourable excitonic processes are optimized to enhance the efficiency. Future prospects and limitations are addressed as well.     

Effect of rotation in magneto-thermoelastic transversely isotropic hollow cylinder with three-phase-lag model

This article deals with the various heat source responses in a transversely isotropic hollow cylinder under the purview of three-phase-lag (TPL) generalized thermoelasticity theory. In presence of magnetic field and due to the rotating behavior of the cylinder, the governing equations are redefined for generalized thermoelasticity with thermal time delay. In order to obtain the stress, displacement and temperature field, the field functions are expressed in terms of modified Bessel functions in Laplace transformed domain. When the outer radius of hollow cylinder tends to infinity, the corresponding results are discussed. Finally an appropriate Laplace transform inversion technique is adopted.     

Proton conductivity study on three CS/IL@fle-MOF membranes

The low-cost, high specific surface area and porosity, controlled pore size, and chemical properties of metal–organic framework (MOF) materials have attracted much attention in the exploration of proton conduction. The method of chemically modifying MOF structures or introducing conductive medium into the holes can effectively improve the proton conductivities of the materials. Here, the structural tunability of ionic liquid (IL) and flexible MOF (fle-MOF) materials are matched to give full play to the conductivity of IL, the framework support, and the microporous effect of MOFs, which achieves the synergistic effect of performance and expands the temperature range of proton transfer. Three kinds of CS/IL@fle-MOF membranes were prepared by combining three fle-MOFs with 1-carboxymethyl-3-methylimidazole (CMMIM) in different proportions to obtain 15 pieces of membranes. The comparative analyses show that CS/IL@fle-MOF membranes have excellent proton conduction performance at a wider temperature range (263–353 K) and lower relative humidity (75% RH). Among them, the proton conductivities of CS/CMMIM@MIL-88A-25% and CS/CMMIM@MIL-88B-125% are up to 1.33 and 1.42 S cm⁻¹ at 75% RH and 353 K, respectively; whereas those of CS/CMMIM@MIL-53(Fe)-75% and CS/CMMIM@MIL-88B-125% reach up to 2.1 × 10⁻³ and 1.28 × 10⁻³ S cm⁻¹ at 75% RH and 263 K, respectively. The E_a of CS/CMMIM@fle-MOFs is in the range of 0.1–0.5 eV, suggesting that the proton transport follows predominantly the typical Grotthuss transfer mechanism. The results of this study indicate that the CS/CMMIM@fle-MOF membranes combinations offer great potential for the design of composite porous proton-conducting materials.     

超临界压力CO2在水平圆管内流动传热数值分析

采用SST k-w低雷诺数湍流模型对加热条件下超临界压力CO2在内径di=22.14 mm,加热长度Lh=2440 mm水平圆管内三维稳态流动与传热特性进行了数值计算.通过超临界CO2在水平圆管内的流动传热实验数据验证了数值模型的可靠性和准确性.首先,研究了超临界压力CO2在水平圆管内的流动传热特点,基于超临界CO2在类临界温度Tpc处发生类液-类气“相变”的假设,揭示了水平圆管顶母线和底母线区域不同的流动传热行为.然后,分析了热流密度qw和质量流速G对水平圆管内超临界压力CO2流动换热的影响,通过获取流体域内的物性分布、速度分布和湍流分布等详细信息,重点解释了不同热流密度qw和质量流速G下顶母线内壁温度Tw,i分布产生差异的传热机理,分析结果确定了类气膜厚度d、类气膜性质、轴向速度u和湍动能k是影响顶母线壁温分布差异的主要因素.研究结果可以为超临界压力CO2换热装置的优化设计和安全运行提供理论指导.