Stress relaxation in network materials: the contribution of the network

Network heterogeneity causes relaxation slow down. A stretched relaxation function describes the variation of stress in time. The stretch exponent has a minimum at the affine-non-affine network transition.

Photocatalytic degradations of JWS-type kinetics

Photocatalytic degradation kinetics of Jurlewicz–Weron–Stanislavsky (JWS) type has been identified. Experimental data are taken from previous published works, and fitted with the JWS relaxation function as well as that of the Havriliak–Negami (HN) model. All experimental data can fit with either model fairly good. From the fitting parameters, the Jonscher indices are calculated and Jonscher diagram is plotted for the chemical kinetics of photocatalytic degradations. This work suggests that material parameters of photocatalysts can be well defined in the sense of fractional calculus.

QUASI-LINEAR VISCOELASTIC MODELLING OF UNCURED PREPREGS UNDER COMPACTION

Reinforcement compaction sometimes referred as consolidation process and is one of the key steps in various composite manufacturing processes such as autoclave and out-of-autoclave processing. The prepregs consist of semi-cured thermoset resin system impregnating the fibers. hence, the prepreg shows strong viscoelastic compaction response, which strongly depends on compaction speed and stress relaxation. modeling of time-dependent response is of utmost importance to understand the behavior of prepregs during different stages of composites manufacturing processes. The quasilinear viscoelastic (QLV) theory has been extensively used for the modeling of viscoelastic response of soft tissues in biomedical applications. In QLV approach, the stress relaxation can be expressed in terms of the nonlinear elastic function and the reduced relaxation function. The constitutive equation can be represented by a convolution integral of the nonlinear strain history, and reduced relaxation function. This study adopted a quasilinear viscoelastic modeling approach to describe the time dependent behavior of uncured-prepregs under compression. The model was modified to account for the compaction behavior of the prepreg under a compressive load. The deformation behavior of the prepreg is usually characterized by the fiber volume fraction, V . In this study, the material used was a 2/2 Twill weave glass prepreg (M26T) supplied by Hexcel® Industries USA. We performed a compaction experiment of the uncured prepreg at room temperature at different displacement rate and subsequent relaxation to describe the viscoelastic behavior of the prepreg. The model parameter calibration was performed using the trust-region-reflective algorithm in matlab to a selected number of test data. The calibrated model was then used to predict the rate dependent compaction and relaxation response of prepregs for different fiber volume fractions and strain rates.

On the stability of a laminated beam with structural damping and Gurt–Pipkin thermal law

In this paper, we investigate the stabilization of a one-dimensional thermoelastic laminated beam with structural damping coupled with a heat equation modeling an expectedly dissipative effect through heat conduction governed by Gurtin–Pipkin thermal law. Under some assumptions on the relaxation function g, we establish the well-posedness of the problem by using Lumer–Phillips theorem. Furthermore, we prove the exponential stability and lack of exponential stability depending on a stability number by using the perturbed energy method and Gearhart–Herbst–Prüss–Huang theorem, respectively.

Physiological and pathological roles of the accommodation response in lower esophageal sphincter relaxation during wet swallows

The preparatory accommodation response of lower esophageal sphincter (LES) before swallowing is one of the mechanisms involved in LES relaxation during wet swallows, however, the physiological and/or pathological roles of LES accommodation remain to be determined in humans. To address this problem, we conducted a prospective observational study of 38 patients with normal high-resolution manometry (HRM) and 23 patients with idiopathic esophagogastric junction outflow obstruction (EGJOO) to assess dry and wet swallows. The LES accommodation measurement was proposed for practical use in evaluating the LES accommodation response. Although swallow-induced LES relaxation was observed in both dry and wet swallows, LES accommodation (6.4, 3.1–11.1 mmHg) was only observed in wet swallows. The extent of LES accommodation was impaired in idiopathic EGJOO (0.6, − 0.6–6 mmHg), and the LES accommodation measurement of patients with idiopathic EGJOO (36.8, 29.5–44.3 mmHg) was significantly higher in comparison to those with normal HRM (23.8, 18–28.6 mmHg). Successful LES relaxation in wet swallowing can be achieved by LES accommodation in combination with swallow-induced LES relaxation. Impaired LES accommodation is characteristic of idiopathic EGJOO. In addition to the IRP value, the LES accommodation measurement may be useful for evaluating the LES relaxation function in clinical practice.

Study on Damage Mechanism and Repair of Vascular Endothelial Cells Based on Ultrasound Technology

Objective. To detect the endothelial function of external iliac artery in rats with different stages of atherosclerosis by high-resolution ultrasound, so as to provide experimental methodological basis for evaluating the function of vascular endothelial cells by ultrasound. Methods. The animals were randomly divided into the control group ( n = 6 ) and the atherosclerosis model group ( n = 15 ). The atherosclerosis group was further divided into 4-week group, 8-week group, and 12-week group, with 5 animals in each group. After separating and grinding rat spleen, the obtained cells were cultured by density gradient centrifugation. After the cells adhered, the morphology of the cells was observed under a microscope and identified by DiI-Ac-LDL and FITC-UEA-I double staining. The activities of LDH and SOD, the contents of MDA and GSH, and the contents of NO in plasma were detected by biochemical methods. Results. The protective effect of rosanilin on brain injury in rats with acute hypobaric hypoxia and its regulation on the expression of pAkt protein; ox-LDL inhibited the proliferation activity of EPCs in a concentration-dependent manner. The expression of KLF2 and S1PR1 in HAEC can be knocked down by small interfering RNA, and knocking down KLF2 can not only downregulate the expression of S1PR1 but also downregulate HAVEN. With the development of atherosclerosis, the endothelium-dependent relaxation function and endothelium-independent relaxation function of the control group and the atherosclerosis model at 4, 8, and 12 weeks were damaged in different degrees and gradually aggravated. Conclusion. Atherosclerosis is a disease with both morphological and functional damage, and vascular endothelial function is damaged in the early stage with corresponding pathological changes. Ultrasound is an effective method to evaluate vascular endothelial function.

Large Time Convergence of the Non-homogeneous Goldstein-Taylor Equation

The Goldstein-Taylor equations can be thought of as a simplified version of a BGK system, where the velocity variable is constricted to a discrete set of values. It is intimately related to turbulent fluid motion and the telegrapher’s equation. A detailed understanding of the large time behaviour of the solutions to these equations has been mostly achieved in the case where the relaxation function, measuring the intensity of the relaxation towards equally distributed velocity densities, is constant. The goal of the presented work is to provide a general method to tackle the question of convergence to equilibrium when the relaxation function is not constant, and to do so as quantitatively as possible. In contrast to the usual modal decomposition of the equations, which is natural when the relaxation function is constant, we define a new Lyapunov functional of pseudodifferential nature, one that is motivated by the modal analysis in the constant case, that is able to deal with full spatial dependency of the relaxation function. The approach we develop is robust enough that one can apply it to multi-velocity Goldstein-Taylor models, and achieve explicit rates of convergence. The convergence rate we find, however, is not optimal, as we show by comparing our result to those found in [8].