Dynamics of Changes in Viscoelastic Properties of a Tofu During Frying

The viscoelastic properties of a tofu were characterized using the stress relaxation test after deep-fat frying at 147–172°C for 0 to 5 minutes. The results were expressed with a model with two Maxwell elements and a residual spring in parallel. Each elastic modulus and relaxation time followed zero order reaction kinetics. The Arrhenius temperature dependency was applied for the modeling of reaction rate constant, k. The activation energies for the viscoelastic properties were 1.00 × 10⁵ ? 1.49 × 10⁵ J/mol. There was a good agreement between the measured and computed data (R² = 0.976 ? 0.988).     

Enthalpic Relaxation of Vital and Protease-Treated Wheat Gluten

Commercially available vital wheat gluten was purified with α-amylase and treated with protease in a one-step process. The supernatant of the protease-treated gluten was freeze dried, quench cooled, and aged for 2 weeks and analyzed using differential scanning calorimetry, sodium dodecyl sulfate poly-acrylamide gel electrophoresis, reverse phase high performance liquid chromatography, size exclusion high performance liquid chromatography, capillary zone electrophoresis, and dynamic mechanical analysis. The differential scanning calorimetry profile of the aged (un-purified or un-modified) gluten sample exhibited enthalpic relaxation beneath its glass transition (Tg) indicating molecular relaxation. Samples treated with 0.006 g protease/g gluten showed Tg at 49.11°C with ΔCp = 0.12 (J/°C g). Higher protease levels and longer aging time caused high Tg temperature, ΔCp, and ΔH of enthalpic relaxation. The size exclusion high performance liquid chromatography profile of the protease-treated gluten clearly showed differences in molecular size between the supernatant and the precipitate, while reverse phase high performance liquid chromatography profiles signified more hydrophilic gluten molecules than the control. The small difference in gluten molecular size after protease treatments (0.024 g protease versus 0.032 g) appeared to have a significant effect on the enthalpic relaxation, where the two treatments showed different degrees of enthalpic relation. The capillary zone electrophoresis data confirmed the insignificant difference between 0.024 and 0.032 g protease/g gluten regarding the size to charge ratio. The molecular interactions for protease-treated gluten were much weaker than vital gluten, as indicated by much weaker network and sensitivity to temperature, especially above Tg. The weaker network was evidenced by higher G″ versus G′, which explained the fluid like behavior of the protease-treated gluten.     

The role of geometry on the viscoelastic materials properties: tensile and stress relaxation of the yarn

The time-dependent mechanical behavior of textiles has particular importance. One of such behaviors is stress relaxation. When strain is applied constantly, there is a decreased stress with time in viscoelastic materials, which is called stress relaxation. The aim of this study is to investigate the effect of knot’s geometry (surgeon, square and eight) and the number of knots on the tensile and stress relaxation properties of the polyester yarn. Significant differences were observed for the tensile characteristics of the yarn in the presence of the knot. Generally, the knotted yarns demonstrated lower tensile stress and strain at failure. Moreover, the results revealed that the stress relaxation behavior of the yarn is affected by the number of knots and their geometry. The yarn without knot exhibited the highest stress relaxation percent while the yarn with the surgeon’s knot displayed the least stress relaxation percent. On the other hand, increasing the number of knots led to a decrease in the percentage of yarn stress relaxation.     

一致K-（Fb，ρ）-凸多目标半无限规划的Wolfe型对偶性

利用K-方向导数和K-次微分,定义了一致K-（Fb,ρ）-凸,一致K-（Fb,ρ）-伪凸和一致K-（Fb,ρ）-拟凸等一些非光滑非凸函数,并研究了涉及此类广义凸性的一类非光滑多目标半无限规划的Wolfe型对偶性．     

建筑用PTFE膜材应力松弛和徐变性能研究

对建筑用PTFE(聚四氟乙烯)膜材进行单轴应力松弛和徐变试验,得到松弛模量和蠕变柔量随时间的变化曲线,然后采用广义线性黏弹性模型、分数阶模型和分指数模型分别进行数值模拟,再比较各模型预测精度.结果表明:各类模型模拟短期的松弛模量和蠕变柔量有较好的精度;随时间增长,广义线性黏弹性模型模拟的松弛模量和蠕变柔量偏离试验值,长期预测精度较差;分数阶模型对长期松弛模量和蠕变柔量预测精度较好;分指数模型可预测长期的经向蠕变柔量,但对长期松弛模量和纬向蠕变柔量的预测精度不高.     

盾构隧道弹性密封垫松弛性能检测研究

介绍了盾构隧道弹性密封垫松弛性能检测现状,并基于密封垫的闭合压缩试验装置,研制出一套密封垫松弛应力检测装置。该装置通过在夹具间放置垫片模拟不同开张量,并通过在密封垫间放置传感器,得到密封垫接触面的压力值,能够更加准确地反映密封垫的松弛性能,为隧道工程长期可靠的防水性能提供保障。     

一种用于计算机辅助产物设计中基于BP-NN优化问题的求解方法

Because of the powerful mapping ability, back propagation neural network (BP-NN) has been employed in computer-aided product design (CAPD) to establish the property prediction model. The backward problem in CAPD is to search for the appropriate structure or composition of the product with desired property, which is an optimization problem. In this paper, a global optimization method of using the a BB algorithm to solve the backward problem is presented. In particular, a convex lower bounding function is constructed for the objective function formulated with BP-NN model, and the calculation of the key parameter a is implemented by recurring to the interval Hessian matrix of the objective function. Two case studies involving the design of dopamine β-hydroxylase (DβH) inhibitors and linear low density polyethylene (LLDPE) nano composites are investigated using the proposed method.     

态势标绘中态势图的生成研究

态势图是多传感器数据融合中态势估计和威胁估计中态势标绘必需的部件,本文简要介绍了态势图的基本结构,引入了椭圆包络线生成态势图的方法。着重介绍了椭圆包络线生成的基本算法,同时给出了两种基于面积的优化算法。试验和实用结果证明,这种方法是正确可行的,它也可以应用于军事领域外的许多领域。     

不确定性结构特征值上下界的估计方法

用凸模型理论描述了结构参数的不确定性 ,提出了一种用于估计含不确定性参数结构特征值的上下界的新方法 ,并以框架结构特征值的算例验证了所提理论的有效性。     

Mechanical relaxation processes of wood in the low-temperature range

The dynamic viscoelastic properties of untreated and chemically modified wood specimens were determined in the temperature range 123 to 293 K and at constant frequencies. Absolutely dry wood specimens exhibited one relaxation process labeled γ at around 180 K, being attributed to the motions of methylol groups in the amorphous region of the wood constituents. The changes in the γ process due to the chemical modifications were explained by the reduction in the original γ loss peak due to the decrease of methylol groups, and an additional relaxation induced by the other groups introduced. With moisture adsorption, an additional relaxation labeled β was induced at 220–240 K. It appeared only when the wood adsorbed moisture irrespective of chemical modifications, and its characteristics were not affected by the formaldehyde and PEG treatments involving the remarkable changes in the mobility of amorphous molecules. These results suggested that the dominant mechanism of β relaxation was not the segmental motions of the main chain, but the motion of the adsorbed water molecules. The positive activation entropy of the β relaxation was interpreted to reflect rearrangement of the adsorption sites required for the rotation of the adsorbed water molecules. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3338–3347, 2001