A study of the large strain deformation and failure behaviour of mixed biopolymer gels via in situ ESEM

A mixed biopolymer gel, consisting of a protein (gelatin) and polysaccharide (maltodextrin) mixture has been investigated. By controlling the composition it was possible to construct an ‘emulsion-like’ structure, with included spherical particles of one phase (maltodextrin) within a continuous matrix of the second (gelatin). Large strain deformation and failure behaviour of this system has been examined via in situ environmental scanning electron microscopy (ESEM). ESEM has been employed to explore the changes in the structure of the material, whilst allowing the sample to stay hydrated as it was subjected to tensile strain, thereby allowing simultaneous imaging and determination of stress-strain data of the native sample. Ductile behaviour was observed, which has been attributed to the stretching, tearing and fracture of gelatin ligaments and debonding at the interface between the maltodextrin particles and continuous gelatin matrix. Deformation and fracture of the maltodextrin particles during tensile testing was also observed. The interfacial fracture energy of the composite has been calculated following an elastomer composite-debonding model, although there are several limitations to this approach for the mixed gel. It was found in samples tested after different ageing times that the debonding stress and strain was decreasing with ageing leading to a lower interfacial fracture energy. Samples were also tested after successive loading cycles, which resulted in a mechanical strength decrease after each cycle.     

Kinetic Modeling of Large‐Scale Reaction Systems

This review gives a brief account of basic ideas underlying approaches to analysis and modeling of large‐scale reaction systems. The emphasis is on model simplification and mechanism/dimension reduction via heuristic concepts and formal mathematical techniques. Among the key topics discussed are: top‐down and bottom‐up modeling approaches, graph/matrix representation of chemical reactions, mechanistic vs. pathways models, quantitative structure‐reactivity relationships, mathematical reduction of dimensionality, high‐fidelity surrogate models, continuum approximation, lumping of nonlinear kinetics, overall behavior/kinetics of many reactions, effect of pore diffusion, steady state multiplicity and stability. Some common features of dimension reduction methodologies are noted. Areas where further work will be valuable are identified.     

SORPTION DRYING OF SOYBEAN SEEDS WITH SILICA GEL. I. HYDRODYNAMICS OF A FLUIDIZED BED DRYER

ABSTRACT

Fluidization technology has been employed to mix soybean seeds and silica gel particles in aim of sorption drying of particulate agricultural products. The characteristic fluidization velocities, mixing mechanisms and fluidization quality have been studied in a 180 mm I.D. fluidized bed. Two sizes of silica gel particles (SG2 and SG3) were selected, with the mass fractions in the range of 0.33–0.75 to form a static bed with height from 100 to 280 mm (H/D = 0.56–1.56). The results show that the dispersion rate of soybean seeds is increased with addition of either SG2 or SG3, and that the frequency and the span of pressure fluctuations within the bed are increased. It is inferred that the gas–solids contacting is improved with addition of small particles in the bed of large particles. In addition, for practical design and operation of such a fluidized bed of binary mixtures, empirical correlations for characteristic fluidization velocities were developed with a wide application.     

Replication of plastic thin film by microfeature mould in large area hot embossing

Abstract

This study determines the replication property and surface roughness of microfeatures of a Ni mould that combines electroforming and large area hot embossing. The metal mould first uses a 4 in. silicon wafer to fabricate a master using the UV-LIGA method, and then applies the sputtering method to sputter the copper element as the seed layer on the surface of the master. The electroforming method is used to manufacture the Ni mould insert from the master with the seed layer. Finally, this study uses thin film of polymethyl methacrylate (PMMA) material to replicate the microfeatures of Ni mould insert by large area hot embossing. This study shows the replication properties and surface roughness of different microfeature shapes and sizes for the Ni mould insert and moulded PMMA on large area hot embossing. Experimental results show the average error in height of the microfeature is 0·61 μm for the Ni mould insert and moulded PMMA. The average error in surface roughness of the microfeature is 1·63 nm for the Ni mould insert and moulded PMMA. Experimental results show the good replication and surface roughness of moulded PMMA are replicated from the Ni mould insert by large area hot embossing.     

Self-assembly of C60 containing poly(methyl methacrylate) in ethyl acetate/decalin mixtures solvent

[60]Fullerene (C₆₀) was mono-substituted with well-defined poly(methyl methacrylate) (PMMA-b-C₆₀) using the atom transfer radical polymerization (ATRP) technique. The self-assembly behaviors of PMMA-b-C₆₀ in ethyl acetate (EA) and decalin mixtures were studied using laser light scattering (LLS) and transmission electron microscopy (TEM). Homogeneous solutions of PMMA-b-C₆₀ can be obtained in the solvent mixtures containing more than 40 wt% EA, where the molar ratio of decalin to EA is close to 1. For each solvent mixture, unimers coexist with micelles and large aggregates. The sizes of PMMA-b-C₆₀ micelles and aggregates are independent of polymer concentration, confirming that they are produced via the closed association mechanism. For the various solvent mixtures, the weight-averaged molecular weights, M_w of the PMMA-b-C₆₀ aggregates range from 4.1×10⁷ to 12.5×10⁷ g/mol. The hydrodynamic radii of the large aggregate, R_h, vary from 90 to 136 nm, while the z-averaged radii of gyration, R_g, range from 210 to 311 nm. The R_g/R_h value for each solvent mixture is ∼2.3, which is independent of decalin contents in the mixed solvents. The morphological study using the transmission electron microscope suggests that the large aggregates are composed of porous large compound micelles (LCM) in solution.     

Similar simulation study on the deformation and failure of surrounding rock of a large section chamber group under dynamic loading

Large and super-large section chamber groups in coal mines are frequently affected by dynamic loads resulting from production activities such as roadway driving and blasting. The stability of the surrounding rock is poor, and it is difficult to control. In this paper, a similar simulation test was used to study the deformation and evolution laws of the surrounding rock of a triangle-shaped chamber group under different dynamic loads. The results showed that under dynamic loading, the vertical stress of the surrounding rock of the chamber group increased in an oscillatory form. The maximum stress concentration coefficient reached 4.09. The damage degree of the roof was greater than that of the two sides. The deformation of the roof was approximately 1.2 times that of the two sides. For the chamber closer to the power source, the stress oscillation amplitude of the surrounding rock was larger, and the failure was more serious. The force of the anchorage structure showed a phased increasing characteristic; additionally, the force of the anchorage structure on the adjacent side of the chambers was greater than that on the other side. This study reveals the deformation and failure evolution laws of the surrounding rock of large section chamber groups under dynamic loading.     

基于线上线下混合式大班翻转的单片机教学改革

在电子行业迅速发展的背景下,单片机课程对学生的作用越来越重要,然而学生对单片机课程不容易学会并且没兴趣,导致学生掌握的课程内容跟不上时代发展的步伐.提出了线上线下混合式大班翻转的教学改革思路,将线上自主学习和线下翻转教学相结合,学生通过网络平台自主学习基本理论;知识延伸部分以翻转课堂的形式在多媒体教室进行.使学生有针对...     

Fully Developed Turbulence of Power-Law Fluids in Circular Pipe Based on Large Eddy Simulation

幂律流体圆管湍流的大涡模拟

王淑彦^1,2, 李淼¹, 王树青³, 李好婷¹, 陈羽佳¹, 马一玫¹, 孙启冀¹

（1.东北石油大学 石油工程学院, 黑龙江 大庆 163318;

2.提高采收率教育部重点实验室（东北石油大学）, 黑龙江 大庆 163318;

3.中国石油大庆油田股份有限公司第四采油厂, 黑龙江 大庆 163511）

摘 要：本文采用动态亚格子模型,对幂律流体在圆管内的充分发展湍流流动进行了大涡模拟（LES）,得到了不同幂律指数下的湍流流动信息。文中分析了平均轴向速度、脉动速度均方根和雷诺应力等随着幂律指数增加的变化趋势,得出随着幂律指数的增加对数区的平均轴向速度减小,脉动速度均方根和雷诺应力的值增大,模拟结果表明剪切稀化流体比剪切稠化流体的非牛顿特征更明显。同时对湍流流动的高阶统计量（偏斜因子和平坦因子）进行了分析,结果表明随着幂律指数的减小,轴向脉动的偏斜因子和平坦因子在近壁面区增大,随着幂律指数的减小轴向脉动的间歇性和非对称性更强。不同幂律指数下的湍流流动变化明显,进一步说明了幂律指数对幂律流体的湍流流动有重要影响。模拟结果与直接数值模拟结果吻合较好,证实了大涡模拟可以用来预测较大雷诺数情况下幂律流体流动的湍流特性。

关键词：大涡模拟;幂律流体;充分发展湍流

     

水辅助注塑大直径介质导管制品的冷却分析

采用数学分析方法，通过假设、简化分析模型，用数学模型来表述物理模型，确定了水辅助注塑(VAIM)大直径介质导臂制品的冷却时间，并运用算例和国外试验的结果进行验证。结果发现：水辅助注射成型新工艺可以更加显著地缩短注塑周期，降低制件壁厚，允许制件有更大的实际直径。因此，VAIM技术可用来高效率地生产大直径、高质量、薄壁的介质导臂。     

Compensation excavation method control for large deformation disaster of mountain soft rock tunnelOA

In recent years, the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China. It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling. Hence, the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation. It uses supportive...