Insight into shear‐induced modification for improving processability of polymers: Effect of shear rate on the evolution of entanglement state

Many experimental results have revealed that the re‐entanglement kinetics of disentangled polymers is much slower than that predicted by tube theory. This retarded recovery of fully entangled state is of practical significance that shear‐induced modification may offer a way to improve processability for a polymer by reducing viscosity. This work tried to figure out the shear‐rate dependence variation of viscosity in the view of evolution of entanglement state through disentanglement and re‐entanglement, aiming to provide fundamental insights into application prospect of shear‐induced modification in preparing “in‐pellet” disentangled polymers prior to final processing. High‐density polyethylene was sheared on a parallel‐plate rotational rheometer with a linearly increased shear rate. Results showed that higher shear rate could induce further disentanglement, resulting in a lower viscosity with a reduction rate up to 93.7%, larger molecular weight between entanglements M_e , and longer re‐entanglement time. Additionally, less entanglement would give a larger lamellar thickness of sheared samples after nonisothermal crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 598–606     

Synergistic Effects of Pseudocolor Imaging,Differentiation, and Square and Logarithmic Conversion on Accuracy of Quantification of Chemical Characteristics Using Test Strips and Similar Products

Test strips and similar products are highly feasible tools for the rapid and approximate determination of chemical characteristics. Although the application of both the quantitative observation of coloration and regression modeling has recently enabled these products to become quantitative tools, their precision and accuracy may be further improved. In this study, the pseudocolor imaging of the coloration image, derivative spectrophotometry-like differentiation of the coloration values, and logarithmic conversion of the raw and derivative values were compared in terms of the precision and accuracy of the quantitative determination of corrosiveness, glucose, nitrate, and pH using the products. The best regression models for the determination were provided by the combination of pseudocolor imaging and differentiation (nitrate and pH); pseudocolor imaging, differentiation, and square-conversion (corrosiveness); or all of the techniques (glucose). When compared to the use of the original 10 raw coloration variables of red-green-blue, cyan-magenta-yellow-key black, and L*a*b* color models only, the above combinations improved the normalized mean absolute error from 14.8% to 3.09% (corrosiveness), 6.33% to 3.15% (glucose), 7.46% to 4.56% (nitrate), and 3.22% to 0.94% (pH). These achievements were largely attributed to the combination of multiple variables that have non-linear and nonmonotonic relationships with the chemical characteristics.     

An automated vane shear test tool for environmental monitoring with unmanned ground vehicles

The present work describes the development of a novel robotic vane shear test tool for characterization of soil parameters with high precision and accuracy. The tool automates industrial standards for testing procedures. The proposed system is capable of performing high resolution torque measurements, which are then used to estimate the shear strength of the soil. The design of the instrument and its advantages over traditional manual instruments are discussed, after which error sources, calibration, and test procedures are described. The developed tool was successfully validated against high-end commercial equipment. The built unit was employed for characterizing mine waste in a laboratory setting and also deployed in the field on board an Unmanned Ground Vehicle for remote soil characterization.     

Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region

We performed laboratory experiments on bubbly channel flows using silicone oil, which has a low surface tension and clean interface to bubbles, as a test fluid to evaluate the wall shear stress modification for different regimes of bubble migration status. The channel Reynolds numbers of the flow ranged from 1000 to 5000, covering laminar, transition and turbulent flow regimes. The bubble deformation and swarms were classified as packing, film, foam, dispersed, and stretched states based on visualization of bubbles as a bulk void fraction changed. In the dispersed and film states, the wall shear stress reduced by 9% from that in the single-phase condition; by contrast, the wall shear stress increased in the stretched, packing, and foam states. We carried out statistical analysis of the time-series of the wall shear stress in the transition and turbulent-flow regimes. Variations of the PDF of the shear stress and the higher order moments in the statistic indicated that the injection of bubbles generated pseudo-turbulence in the transition regime and suppressed drag-inducing events in the turbulent regime. Bubble images and measurements of shear stress revealed a correlated wave with a time lag, for which we discuss associated to the bubble dynamics and effective viscosity of the bubble mixture in wall proximity.     

Quantitative leak test for microholes and microtears in whole gloves and glove pieces

The current leak tests for gloves are qualitative. The developed quantitative leak test uses vacuum pressure to draw measured volumes of water to detect microholes/tears in whole gloves and glove pieces. A modified plastic vacuum desiccator interfaced with a Frazier air permeability tester allowed exposure of disposable unsupported/unlined/powderless Kimtech Blue nitrile to 50 mL of water for glove pieces or to 600 mL within a whole glove at vacua of 8–9 in. (20–23 cm) and 11–12 in. (28–30 cm) water gauge, respectively. Punctures of known dimensions were made before testing in specific glove areas using 21-, 22-, 26-, 30-, and 33-gauge needles (outer/inner diameters in micrometres of 873/514, 794/413, 635/311, 476/127, 318/159 and 238/133, respectively). The length of the punctures varied from 0.13 ± 0.01 to 0.80 ± 0.11 mm. Flow rates of water through the holes/tears ranged from 2.5 ± 0.4 to 106 ± 7 mL/min for glove pieces. For whole gloves, the ranges were from 31 ± 9 to 543 ± 110 mL/min in the palm area; and 0.23 ± 0.06 to 82 ± 18 mL/min in the finger/fingertip area. The method quantified tear lengths as short as 0.13 ± 0.01 mm.     

Direct synthesis of Poly(Ԑ-Caprolactone)-block-poly (glycidyl methacrylate) copolymer and its usage as a potential nano micelles carrier for hydrophobic drugs

Ring-opening (ROP) and enzymatic copolymerization (ECP) are among the most widely used approaches for synthesizing copolymers of polycaprolactone (PCL). It involves multiple-step reactions and the utilization of enzymes that make the process a lot more complicated, time consuming, and expensive. Atom transfer radical polymerization (ATRP) has been adopted to synthesize a novel amphiphilic copolymer in our study. The study presents a method to eliminate the ROP/ECP multiple steps in monomer polymerization thus making the process simpler and smoother. The synthesis of cationic polymer micelles copolymer of PCL-PGMA (polycaprolactone grafted poly glycidyl methacrylate) was carried out using direct functionalization of hydroxy group in crude PCL to achieve a higher degree of functionalization, i.e., 12.8% for macroinitiator. FTIR and ¹H-NMR confirmed the successful synthesis of the copolymer with better control over the molecular weight with a PDI (1.84). DSC and XRD results showed the reduction of crystallinity by 86.81%, making copolymer more compatible for drug delivery application. The synthesized copolymer was further converted to nano-micelles drug carrier having an average size of 96.08 ± 21.22 nm. The drug encapsulation efficiency achieved was 60.0 ± 1.7%, and nano-micelles rendered a slow and controlled release of naproxen with long-term storage stability.     

基于八面体理论的岩石循环加-卸载本构模型及修正

探究岩石的受力特点及破坏特性是研究岩石地下工程安全性的关键,诸多学者都期望能在岩石本构模型的研究上取得突破性进展。在此背景下,提出了一种能够描述循环加-卸载条件下岩石的本构模型。首先,假设岩石的微元强度服从八面体剪应力理论并且微元破坏服从Weibull概率公式,将岩石本构中的损伤变量以及岩石微元强度表达式里包含的损伤因子进行本构变换,得到关于应力、应变等其他表现加-卸载下岩石损伤本构模型的参数,表示出岩石微元强度和损伤变量,再将得到的岩石微元强度和损伤变量代入所提出的岩石本构模型中,并进行等式变换得到一个函数表达式。通过将其与实验数据进行拟合对比分析,得出修正后的拟合参数,将其代入函数式中,得到损伤本构模型的修正式。最后将拟合参数进行必要的敏感性分析,得出各拟合参数的实际物理意义。     

α-Mangostin exhibits antidepressant-like effects mediated by the modification of GABAergic,serotonergic and dopaminergic systems

Abstract

The present study explored the antidepressant-like activity of α-mangostin (α-MG) and the possible mechanism in this process in the tail suspension test (TST) in mice. The results revealed that α-MG (5?mg/kg, i.p.) exhibited markedly antidepressant-like activity, which could be reversed by pretreatment with haloperidol (a non-selective D₂ receptor antagonist), bicuculline (a competitive GABA antagonist), p-chlorophenylalanine (an inhibitor of 5-HT synthesis). Meanwhile, α-MG also effectively increased the brain DA, 5-HT and GABA levels in mice exposed to TST, indicating that the antidepressant-like effect of α-MG might be mediated by the GABAergic, serotonergic and dopaminergic systems.

     

估计感度分布中位数的两阶段优化序贯试验设计方法研究

感度试验在爆炸科学领域有非常广泛的应用,其中位数是含能材料的一个关键性能指标.高效估计感度分布中位数是实际工程应用中的重要问题.文章提出一种两阶段的优化序贯试验设计方法来估计感度分布的中位数,并将正交设计与两阶段优化序贯试验设计方法相结合给出了筛选影响含能材料安定性重要因子的试验设计方法.广泛的模拟比较验证了所提方法在小样本情况下可以获得感度分布中位数的准确估计,并且对模型假设和初始参数猜测具有一定的稳健性.当因子效应不是太小的时候,因子筛选方法可以准确地筛选出有显著影响的因子.