Post-buckling behavior of a fixed arch for variable geometry structures

The behavior of a bistable strut for variable geometry structures was investigated in this paper. A fixed shallow arch subjected to a central concentrated load was used to study the equilibrium path of the bistable strut. Based on a nonlinear strain–displacement relationship, the critical loads for both the symmetric snap-through and asymmetric bifurcation buckling modes were obtained. Moreover, the principal of virtual work was also used to establish the post-buckling differential equilibrium equations of the arch in the horizontal and vertical directions. Therefore, the whole mechanical behavior before and after the buckling of fixed arches is investigated.     

Characterization of a new chiral antiferroelectric liquid crystal with a lateral bromo substituent

In this paper we present the characterization of a new chiral mesogen with a lateral bromo substituent. The identification of the various smectic phases is achieved by texture observation, miscibility studies and DSC. The optic and electro-optic properties are also investigated. The real part of the complex dielectric permittivity as a function of the temperature was also measured in the planar geometry for thin samples. The dielectric behaviour will be qualitatively discussed on the simple assumption of different anchorings. These results point out the importance of anchoring conditions in relation to the macroscopic properties observed in very thin cells of antiferroelectric liquid crystals.     

Detecting extensional viscosity of polypropylene melt using the Rheotens test: A comparison between standard and steady state test modes

The Rheotens test was used to determine the extensional viscosity of a polypropylene (PP) melt at three different extrusion velocities and using two capillaries with different length-to-diameter ratios. Results showed that, in the standard Rheotens test, the extensional viscosity curves determined under different testing conditions exhibit an obvious difference, especially under low extensional strain rates. This is attributed to the pre-orientation of macromolecular chains taking place in the capillary. Hence, a steady state Rheotens test was tentatively proposed. It was demonstrated that the extensional viscosity curves determined under most of the testing conditions by this test mode almost overlap, which is attributed to the fact that the pre-orientation of chains relaxes sufficiently near the capillary exit. This implies that equivalent extensional viscosities can be obtained under a wider range of extrusion velocities and capillary length-to-diameter ratios. Moreover, the equivalent extensional viscosities determined in the steady state Rheotens test exhibit good agreement with the extrapolated extensional viscosity curve determined using the Cogswell convergent flow method.     

Apparent viscosity characteristics and prediction model of an unstable oil-in-water or water-in-oil dispersion system

A series of theoretical analysis and experimental measurements were done to analyze the characteristic of the apparent viscosity of oil-water unstable mixtures which display the similar distributions as the mixtures in pipeline flow. Based on the experimental results, it can be concluded that the unstable oil-water dispersed mixtures are always show the characteristic of non-Newtonian fluid. The shear rate has a great influence on the apparent viscosity, particular for the water-in-oil mixtures. The effect of dispersed phase volume fraction on the apparent viscosity of the unstable mixtures displays the similar rules as the stable emulsions. Also, the influences of the dispersed phase distribution and viscosity on the apparent viscosity were studied through the corresponded experiments systematically. Furthermore, a new kind of prediction model was obtained in the present study. The unstable and non-Newtonian fluid characteristics of oil-water two-phase dispersed mixtures were considered in this model to improve their range of application and the prediction accuracy. Moreover, this kind of apparent viscosity prediction model was validated by using the experimental data from some other literatures including different kinds of oils such as white oil and crude oil, and the average deviation was always less than 9% which was a great accuracy of apparent viscosity prediction.     

Use of the bootstrap and permutation methods for a more robust variable importance in the projection metric for partial least squares regression

Bio-pharmaceutical manufacturing is a multifaceted and complex process wherein the manufacture of a single batch hundreds of processing variables and raw materials are monitored. In these processes, identifying the candidate variables responsible for any changes in process performance can prove to be extremely challenging. Within this context, partial least squares (PLS) has proven to be an important tool in helping determine the root cause for changes in biological performance, such as cellular growth or viral propagation. In spite of the positive impact PLS has had in helping understand bio-pharmaceutical process data, the high variability in measured response (Y) and predictor variables (X), and weak relationship between X and Y, has at times made root cause determination for process changes difficult. Our goal is to demonstrate how the use of bootstrapping, in conjunction with permutation tests, can provide avenues for improving the selection of variables responsible for manufacturing process changes via the variable importance in the projection (PLS-VIP) statistic. Although applied uniquely to the PLS-VIP in this article, the generality of the aforementioned methods can be used to improve other variable selection methods, in addition to increasing confidence around other estimates obtained from a PLS model.     

单体结构对紫外光固化氧阻聚影响的研究

利用光量热仪(UV-DSC)对单体TMPTA以及不同乙氧基化的TMPTA单体进行了紫外光固化实验。通过比较空气气氛和氮气气氛下光固化速率增长最快时的时间t_amax的差异来评价光固化初期氧阻聚的大小。考察了单体中乙氧基上的α-H的数量以及单体的流动特性对氧阻聚的影响。结果表明,提高单体中乙氧基的数量能减小光固化过程中的氧阻聚,氧阻聚的大小与单体中α-H的数量以及单体的黏度有关.     

疏水基含量和微嵌段长度对缔合聚合物溶液弹性的影响

研究了疏水基含量和微嵌段长度对缔合聚合物,聚(丙烯酰胺-丙烯酸钠-十六烷基二甲基烯丙基氯化铵)[P(AM-NaAA-C16DMAAC)],弹性行为的影响规律。研究结果表明,对于结构类似且具有相近零剪切粘度的缔合聚合物,疏水基含量越高,聚合物分子链间形成稠密网络结构的疏水缔合能力越强,其第一法向应力差N1越大,N1出现拐点处对应剪切速率越小,缔合聚合物溶液弹性越好;并且缔合聚合物溶液的弹性随着疏水微嵌段长度的增加先增加后降低,存在最佳微嵌段长度。因此,可以通过调整分子结构有效改变缔合聚合物溶液的弹性行为。     

Kinetic phenomena in non-crystalline materials studied by thermal analysis

The structural relaxation and viscosity behavior of Ge₃₈S₆₂ glass has been studied by thermomechanical analysis. The relaxation response to any thermal history is well described by the Tool-Naraynaswamy-Moynihan model. The apparent activation energy of structural relaxation is very close to the activation energy of viscous flow (Eη=478±12 kJ mol^-1). However, the activation energy of crystal growth obtained by optical microscopy is about one half of this value. Similar result has been obtained from isothermal DSC measurement (Ea=220±20 kJ mol^-1). The kinetic analysis of these data reveals interface controlled crystal growth with zero nucleation rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoresponsive gels based on ABA triblock copolymers: Does the asymmetry matter?

The aim of this study was to investigate the effect of the asymmetry of the triblock copolymers on their thermoresponsive self‐assembly behavior. To this end, nine ABA‐type triblock copolymers with n‐butyl methacrylate and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) consisting of the A and the B blocks, respectively, were synthesized. Polymers of three different DMAEMA contents (50, 60, and 70 wt %) were synthesized while varying the length ratio of the two hydrophobic A blocks. Specifically, one symmetric ABA triblock copolymer and two asymmetric ABA′ triblock copolymers with the length of the second A block to be twice or four times bigger than the length of the first A block (AB2A and AB4A triblock copolymer) were synthesized for each DMAEMA composition. Three statistical copolymers were also synthesized for comparison. The thermoresponsive behavior of the copolymers was studied and it was found that the cloud point and rheological properties of the polymers were strongly affected by the architecture (statistical vs. block) and less strongly by the DMAEMA composition and the asymmetry of the polymers. Nevertheless, interestingly the asymmetry of the ABA triblock copolymers did influence the thermoresponsive behavior with the more symmetric polymers presenting a sol–gel transition at lower temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2850–2859.     

Acoustical Studies of Some Schiff Bases in 1,4-Dioxane and Dimethylformamide at 318.15 K

From experimental data of density,viscosity and ultrasonic velocity,the various acoustical properties,such asspecific impedance(Z),isentropic compressibility(к_s),Rao's molar sound function(R_m),the van der Waals con-stant(b),molar compressibility(W),intermolecular free length(L_f),relaxation strength(r),internal pressure(π),free volume(V_f),solvation number(S_n)etc.,were calculated for three Schiff bases in 1,4-dioxane and dimethylfor-mamide(DMF)at 318.15 K.The results are interpreted in terms of molecular interactions occurring in the solu-tions.