Overall viscoelastic properties of 2D and two-phase periodic composites constituted of elliptical and rectangular heterogeneities

International audienceThis paper presents analytical solutions for the effective rheological viscoelastic properties of 2D periodic structures. The solutions, based on Fourier series analysis, are derived first in the Laplace-Carson (LC) space for different inclusion shapes (rectangle or ellipse) and arrangements. The effective results are obtained in the form of rational functions of the LC transform variable. Two inversion methods are used to find the relaxation behavior. The first one is based on the exact inverse of the LC transform while the second approximates the overall behavior by using a Standard Linear Solid model, which yields very simple analytical formulas for the coefficients entering the constitutive equations. Results of the two methods are compared in the case of an application to real materials

CLASSIFICATION AND ZONING OF WATER QUALITY FOR MAIN RIVERS IN BINH TRI THIEN REGION (CENTRAL VIETNAM) BASED ON WATER QUALITY INDEX

Joint Research on Environmental Science and Technology for the Eart

Elastic properties of two phase composites from optimal Neumann series and structure factors

We consider the problem of finding the effective stiffness tensor \mathbb{C}^e$of periodic heterogeneous martrix-inclusion materials. Given the distribution of the constituents, the cell problem must be solved first and the linear relation between average stress and strain is then established. Estimates can be obtained by making relevant approximation to the ingredients constituting the effective tensor. Although the present contribution concerns the theory of optimally estimating \mathbb{C}^e$ from the microstructure, it is closely related to FFT numerical homogenization methods. By introducing a reference material \mathbb{C}^0$, the heterogeneity effect can be viewed as a distribution of eigenstrains within an homogeneous material. Using the related Green tensor, our problem can be formulated as a Lippmann-Schwinger equation for eigenstrain. The integral equation is the origin of resolution methods based on iteration and Fast Fourier Transform (FFT) techniques (Michel et al., 1999; Bhattacharya and Suquet, 2005). Significant progresses have been made regarding the improvement of convergence rate (Michel et al., 1999; Eyre and Milton, 1999; Milton, 2002; Monchiet and Bonnet, 2012; Brisard and Dormieux, 2010). The study of convergence rate in those works will be extended in the present contribution in the case of new integral equations. The iteration scheme used to solve the Lippmann-Schwinger equation corresponds to the Neumann series summation. The latter can be used to derive exact theoretical relations and estimates. In this paper, we propose a new estimate based on series expansion that works at all contrast ratio, while using the matrix as a reference material. Additionally, we can control and optimize the convergence rate so that the series converges in the quickest way, and therefore produces the best estimates when using a finite sum in the series expansion. A class of integral equations for eigenstrain depending on two parameters \alpha,\beta$ is first derived. The spectral radius and norm of the corresponding operators are bounded by analytical expressions. Different optimization methods are proposed to find the fastest series convergence and the associated estimates. Similarly to the estimations of the effective elasticity tensor using correlation functions, the new method presented in this paper allows to estimate the effective elasticity tensor using the n-$order structure factors, which represent the counterpart in Fourier space of correlation functions. As an example, a direct connection of the effective elasticity tensor to n-$th order structure factors is given in the case of randomly distributed spheres. Numerical applications for cubic arrays and random distribution of spheres yield very good results in comparison with FFT based methods and other results from the literature

Policy Response, Social Media and Science Journalism for the Sustainability of the Public Health System Amid the COVID-19 Outbreak: The Vietnam Lessons

Vietnam, with a geographical proximity and a high volume of trade with China, was the first country to record an outbreak of the new Coronavirus disease (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 or SARS-CoV-2. While the country was expected to have a high risk of transmission, as of April 4, 2020—in comparison to attempts to contain the disease around the world—responses from Vietnam are being seen as prompt and effective in protecting the interests of its citizens, with 239 confirmed cases and no fatalities. This study analyzes the situation in terms of Vietnam’s policy response, social media and science journalism. A self-made web crawl engine was used to scan and collect official media news related to COVID-19 between the beginning of January and April 4, yielding a comprehensive dataset of 14,952 news items. The findings shed light on how Vietnam—despite being under-resourced—has demonstrated political readiness to combat the emerging pandemic since the earliest days. Timely communication on any developments of the outbreak from the government and the media, combined with up-to-date research on the new virus by the Vietnamese science community, have altogether provided reliable sources of information. By emphasizing the need for immediate and genuine cooperation between government, civil society and private individuals, the case study offers valuable lessons for other nations concerning not only the concurrent fight against the COVID-19 pandemic but also the overall responses to a public health crisis

Physical therapy for sleep apnea: a smartphone application for home-based physical therapy for patients with obstructive sleep apnea

PurposeIn this study, we described “PT for Sleep Apnea”, a smartphone application for home-based physical therapy of patients with Obstructive Sleep Apnea (OSA).MethodsThe application was created in a joint program between the University of Medicine and Pharmacy at Ho Chi Minh City (UMP), Vietnam, and National Cheng Kung University (NCKU), Taiwan. Exercises maneuvers were derived from the exercise program previously published by the partner group at National Cheng Kung University. They included exercises for upper airway and respiratory muscle training and general endurance training.ResultsThe application provides video and in-text tutorials for users to follow at home and a schedule function to assist the user in organizing the training program, which may improve the efficacy of home-based physical therapy in patients with Obstructive Sleep Apnea.ConclusionIn the future, our group plans to conduct a user study and randomized-controlled trials to investigate whether our application can benefit patients with OSA

Properties of water confined in hydroxyapatite nanopores as derived from molecular dynamics simulations

Bone tissue is characterized by nanopores inside the collagen-apatite matrix where fluid can exist and flow. The description of the fluid flow within the bone has however mostly relied on a macroscopic continuum mechanical treatment of the system, and, for this reason, the role of these nanopores has been largely overlooked. However, neglecting the nanoscopic behaviour of fluid within the bone volume could result in large errors in the overall description of the dynamics of fluid. In this work, we have investigated the nanoscopic origin of fluid motion by conducting atomistic molecular dynamics simulations of water confined between two parallel surfaces of hydroxyapatite (HAP), which is the main mineral phase of mammalian bone. The polarizable core–shell interatomic potential model used in this work to simulate the HAP–water system has been extensively assessed with respect to ab initio calculations and experimental data. The structural (pair distribution functions), dynamical (self-diffusion coefficients) and transport (shear viscosity coefficients) properties of confined water have been computed as a function of the size of the nanopore and the temperature of the system. Analysis of the results shows that the dynamical and transport properties of water are significantly affected by the confinement, which is explained in terms of the layering of water on the surface of HAP as a consequence of the molecular interactions between the water molecules and the calcium and phosphate ions at the surface. Using molecular dynamics simulations, we have also computed the slip length of water on the surface of HAP, the value of which has never been reported before

Antioxidant and in vitro antidiabetic activities of Peperomia pellucida (L.) Kunth extract

Peperomia pellucida (L.) is commonly used as a herbal plant. Its effectiveness in treating inflammatory diseases, digestive disorders, and cancer in tropical and subtropical countries was introduced, especially in field of folk medicine. However, this plant species has not been studied widely in Vietnam, especially for its biological activities. This study was done to determine the antioxidant capacity of P. pellucida by using in vitro and in vivo methods, as well as its inhibitory ability to α-amylase enzyme activity. The total polyphenolic and flavonoid contents of P. pellucida extract were reported to be 359.91±0.77 mg GAE/g and 200.28±1.23 mg QE/g extract, respectively. The results showed the in vitro antioxidant activity of P. pellucida extract in four methods, including DPPH, and ABTS.+, RP and TAC, had EC50 values of 730.34 μg/mL, 84.33 μg/mL, 95.28 μg/mL, respectively, and Abs0.5 value of 114.73 μg/mL. Under H2O2-induced oxidative stress, fruit flies that were raised in the feed medium supplemented with a concentration of 1 mg/mL of P. pellucida extract showed their average survival time, 50% survival time, and 10% survival time at 1.6 times, 1.8 times, and 1.62 times, respectively, higher than those of the control treatment. The ability to inhibit the α-amylase activity in P. pellucida extract was determined with an EC50 value of 115.32±2.65 μg/mL compared with the commercial drug of 18.67±0, 01 μg/mL. The research results showed that P. pellucida is a potential species in the study of natural compounds with antioxidant and antidiabetic activities

Differential Effects of p38, MAPK, PI3K or Rho Kinase Inhibitors on Bacterial Phagocytosis and Efferocytosis by Macrophages in COPD

Pulmonary inflammation and bacterial colonization are central to the pathogenesis of chronic obstructive pulmonary disease (COPD). Defects in macrophage phagocytosis of both bacteria and apoptotic cells contribute to the COPD phenotype. Small molecule inhibitors with anti-inflammatory activity against p38 mitogen activated protein kinases (MAPKs), phosphatidyl-inositol-3 kinase (PI3K) and Rho kinase (ROCK) are being investigated as novel therapeutics in COPD. Concerns exist, however, about off-target effects. We investigated the effect of p38 MAPK inhibitors (VX745 and SCIO469), specific inhibitors of PI3K α (NVS-P13K-2), δ (NVS-P13K-3) or γ (NVS-P13K-5) and a ROCK inhibitor PF4950834 on macrophage phagocytosis, early intracellular killing of bacteria and efferocytosis of apoptotic neutrophils. Alveolar macrophages (AM) obtained from broncho-alveolar lavage (BAL) or monocyte-derived macrophages (MDM) from COPD patients (GOLD stage II/III) enrolled from a well characterized clinical cohort (MRC COPD-MAP consortium) or from healthy ex-smoker controls were studied. Both COPD AM and MDM exhibited lower levels of bacterial phagocytosis (using Streptococcus pneumoniae and non-typeable Haemophilus influenzae) and efferocytosis than healthy controls. None of the inhibitors altered bacterial internalization or early intracellular bacterial killing in AM or MDM. Conversely PF4950834, but not other inhibitors, enhanced efferocytosis in COPD AM and MDM. These results suggest none of these inhibitors are likely to exacerbate phagocytosis-related defects in COPD, while confirming ROCK inhibitors can enhance efferocytosis in COPD

Stress concentration and surface instability of anisotropic solids with slightly wavy boundary

International audienceThis paper presents a first order perturbation analysis of stress concentration and surface morphology instability of elastically anisotropic solids. The boundary of the solids under consideration is periodic along two orthogonal directions. The magnitude of the undulation is sufficiently small so that a half-space model can be used for simplification. We derive expressions for the stress concentration factors and the critical wavelength of the perturbation in terms of the remote stresses, surface energy anisotropy and the elastic anisotropy of the solid. Numerical applications to cubic materials using Barnett-Lothe integrals are also given. (C) 2011 Elsevier Ltd. All rights reserved

A numerical-analytical coupling computational method for homogenization of effective thermal conductivity of periodic composites

International audienceBackground : In the framework of periodic homogenization, the conduction problem can be formulated as an integral equation whose solution can be represented by a eumann series. From the theory, many efficient computational methods and analytical estimations have been proposed to compute the effective conductivity of composites.Methods: We combine a Fast Fourier Transform (FFT) numerical method based on the Neumann series and analytical estimation based on the integral equation to solve the problem. Specifically, the analytical approximation is used to estimate the remainder of the series.Results: From some numerical examples, the coupling method has shown to improve significantly the original FFT iteration scheme and results are also superior to the analytical estimation.Conclusions: We have proposed a new efficient computation method to determine the effective conductivity of composites. This method combines the advantages of the FFT methods and the analytical estimation based on integral equation