An efficient nanoscale representative volume element simulation including graded interphase for tensile behavior of epoxy/silica nanocomposites

The behavior of interphase-particle adhesion and interphase region around the nanoparticles can significantly affect the stress distribution and mechanical properties of polymeric nanocomposites. In this study, the elastic modulus of epoxy/silica nanocomposites is analyzed using the finite element method and different mathematical models. A nanoscale representative volume element including graded interphase, homogenous interphase, and no interphase model is implemented. Furthermore, the effect of interfacial adhesion is also considered. The final elastic modulus was clearly affected by the interphase modulus, especially at higher nanoparticle content. Under imperfect interfacial bonding, the existence of an interphase region leads to a slight increase in modulus, and in the absence of that area, the elastic modulus decreases to 3.28 GPa. In perfect bonding models, stress transferred from the matrix to interphase and, then, to nanoparticle, which led to a significant increase in elastic modulus. Unlike the imperfect bonding, the maximum stress was located in the elements along to the loading direction. A maximum 26% increase in elastic modulus for perfect bonding/graded interphase model with 6.54 vol% of nanosilica particles compared to bulk epoxy was achieved. Finally, on comparing the FEM analysis and theoretical results with the experimental data, good agreement between obtained results was found.     

伊朗灌区管理数据库及其说明

伊朗有780万hm2的灌溉土地,在世界排名第五.伊朗国家灌溉排水委员会对全国灌区重要信息设计表格进行了调查,并已经收集了为期7年的相关信息,包括各灌区的14个大类、340个问题.为利用和分析这些数据,开发了一个软件.这个软件可以使用户通过插入新页面来解释各种各样的信息,并能够接受新的信息.也可以通过对数据库的修改加入包含用户要求的新信息表格.也能在某一特定位置粘贴地图.该软件的另一个功能是它能把信息发布到互联网上.     

A High-Rate Li–CO2 Battery Enabled by 2D Medium-Entropy Catalyst

Lithium-air batteries based on CO₂ reactant (Li–CO₂) have recently been of interest because it has been found that reversible Li/CO₂ electrochemistry is feasible. In this study, a new medium-entropy cathode catalyst, (NbTa)_0.5BiS₃, that enables the reversible electrochemistry to operate at high rates is presented. This medium entropy cathode catalyst is combined with an ionic liquid-based electrolyte blend to give a Li–CO₂ battery that operates at high current density of 5000 mA g⁻¹ and capacity of 5000 mAh g⁻¹ for up to 125 cycles, far exceeding reported values in the literature for this type of battery. The higher rate performance is believed to be due to the greater stability of the multi-element (NbTa)_0.5BiS₃ catalyst because of its higher entropy compared to previously used catalysts with a smaller number of elements with lower entropies. Evidence for this comes from computational studies giving very low surface energies (high surface stability) for (NbTa)_0.5BiS₃ and transmission electron microscopystudies showing the structure being retained after cycling. In addition, the calculations indicate that Nb-terminated surface promotes Li–CO₂ electrochemistry resulting in Li₂CO₃ and carbon formation, consistent with the products found in the cell. These results open new direction to design and develop high-performance Li–CO₂ batteries.     

Numerical simulation of secondary clarifier with activated sludge and suction lift removal system: Modified Casson model and sludge withdrawing sensitivity analysis

A computational fluid dynamics model that predicts the sedimentation of activated sludge in a circular secondary clarifier with activated sludge is developed. The axisymmetric single-phase flow is simulated by using a CFD code that has been written with Intel Visual Fortran. First, sludge withdrawing by suction-lift in the near-bottom region of the clarifier is simulated using suction at the bottom of clarifier. The flow and settling processes are simulated using k-e turbulence model on a two-dimensional and orthogonal grid. A convection-dispersion equation that is extended to incorporate the sedimentation of activated sludge in the field of gravity is used. The computational domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. Experimental data provided by Weiss et al. show that the relationship between shear stress and shear rate follows the Casson law for the shear rates lower than 50 s-1. Plastic viscosity of activated sludge is not removed from the concentration diffusion, so using regular non-Newtonian models leads to overestimation of blanket height. Modified Casson model is introduced to overcome the blanket height overestimation problem. Results show that the local sludge distribution in the clarifier has excellent agreement with concentration profile measurements of Weiss et al., for different treatment plant loadings. Alternative sludge withdrawing methods include withdrawing from pipes position at the bottom of clarifier and withdrawing by using sink terms in governing equations are used. Results show that the first withdrawing method gives less error comparing to these withdrawing methods.     

Apoptotic efficacy and antiproliferative potential of silver nanoparticles synthesised from aqueous extract of sumac (Rhus coriaria L.)

Currently, nanotechnology and nanoparticles (NPs) are recognised due to their extensive applications in medicine and the treatment of certain diseases, including cancer. Silver NPs (AgNPs) synthesised by environmentally friendly method exhibit a high medical potential. This study was conducted to determine the cytotoxic and apoptotic effects of AgNPs synthesised from sumac (Anacardiaceae family) fruit aqueous extract (AgSu/NPs) on human breast cancer cells (MCF‐7). The anti‐proliferative effect of AgSu/NPs was determined by MTT assay. The apoptotic properties of AgSu/NPs were assessed by morphological analysis and acridine orange/propidium iodide (AO/PI) and DAPI staining. The mechanism of apoptosis induction in treated cells was investigated using molecular analysis. Overall results of morphological examination and cytotoxic assay revealed that AgSu/NPs exert a concentration‐dependent inhibitory effect on the viability of MCF‐7 cells (IC50 of ∼10 µmol/48 h). AO/PI staining confirmed the occurrence of apoptosis in cells treated with AgSu/NPs. In addition, molecular analysis demonstrated that the apoptosis in MCF‐7 cells exposed to AgSu/NPs was induced via up‐regulation of Bax and down‐regulation of Bcl‐2. These findings suggested the potential use of AgSu/NP as cytotoxic and pro‐apoptotic efficacy and its possible application in modern medicine for treating certain disorders, such as cancer.Inspec keywords: nanoparticles, silver, nanomedicine, biomedical materials, toxicology, cancer, molecular biophysics, proteins, biochemistry, cellular biophysics, nanofabricationOther keywords: Ag, Bcl‐2 down‐regulation, Bax up‐regulation, MCF‐7 cell viability, concentration‐dependent inhibitory effect, cytotoxic assay, molecular analysis, DAPI staining, acridine orange‐propidium iodide staining, morphological analysis, MTT assay, human breast cancer cells, sumac fruit aqueous extract, Anacardiaceae family, cytotoxic effects, drug delivery function, diseases, Rhus coriaria L, silver nanoparticles, antiproliferative potential, apoptotic efficacy     

Interphase characterization and modeling of tensile modulus in epoxy/silica nanocomposites

The incorporation of second dispersed particulate phases in a polymer matrix enhances its mechanical properties. Because of the high surface to volume ratio of nanoparticles, the molecular structure of the matrix is altered at the nanoparticle/matrix interface and the volume of this perturbed region could be significant. These improved properties are produced by the interfacial interaction of the nanometric domains. In this research, epoxy matrix modified with three different sizes of nanosilica (12, 20, and 40 nm) and the effect of the interphase characteristics on the tensile properties of nanocomposites was investigated. At first, the theoretical values of the elastic modulus using a two-phase mathematical model compared with the experimental data obtained from the nanocomposite samples and values between 8 and 10 nm were estimated for the interphase thickness. Afterward, considering the three-phase model, it takes into account that three different regions for interphase volume fraction, including single particles, polymer trapping, and agglomerated nanoparticles, and an equation for evaluation of interphase volume fraction are defined. Also, the interphase tensile modulus was considered continuously changing from the properties of nanoparticle to the polymer matrix properties. Finally, the overall tensile modulus of nanocomposites, which considers different key parameters including nanoparticle size, values for the interphase thickness (h), and interphase tensile modulus (E_i), were calculated. The results were compared with the experimental ones of other studies and a good agreement was found. The smallest value of h as 6 nm for samples containing 12-nm diameter nanosilica and highest value of h as 8 nm for samples containing 40-nm diameter nanosilica is reported.     

A hybrid variable neighborhood search and simulated annealing algorithm to estimate the three parameters of the Weibull distribution

The Weibull distribution plays an important role in failure distribution modeling of reliability research. While there are three parameters in the general form of this distribution, for simplicity, one of its parameters is usually omitted and as a result, the others are estimated easily. However, due to its more flexibility, when the general form of the Weibull distribution is of interest, the estimation procedure is not an easy task anymore. For example, in the maximum likelihood estimation method, the likelihood function that is formed for a three-parameter Weibull distribution is very hard to maximize. In this paper, a new hybrid methodology based on a variable neighborhood search and a simulated annealing approach is proposed to maximize the likelihood function of a three-parameter Weibull distribution. The performance of the proposed methodology in terms of both the estimation accuracy and the required CPU time is then evaluated and compared to the ones of an existing current method through a wide range of numerical examples in which a sensitivity analysis is performed on the sample size. The results of the comparison study show that while the proposed method provides accurate estimates as well as those of the existing method, it requires significantly less CPU time.     

Numerical study of gas-solid reactive flow in a cylinder

A theoretical model is described for the numerical simulation of unsteady gas-solid reactive flow in packed beds of granular propellants in a tubular geometry. The approach couples continuity, momentum and energy equations in each phase along with porosity and granular stresses. Propellant bed combustion process is neglected, but the mass flow rate due to the combustion is derived using a pressure-based burning rate correlation. As the burning of solid propellant begins, pressure, temperature, density and other gas parameters begin to change rapidly. To catch these changes, a CFD approach with explicit McCormack method is used to solve the coupled system of equations. A moving mesh is used to consider the moving boundary. Pressure history, moving boundary velocity and other parameters of the mixture are obtained and compared with other numerical data.     

Centrifuge study into the effect of liquefaction extent on permanent settlement and seismic response of shallow foundations

Centrifuge experiments were conducted to investigate how the liquefaction extent affects the seismic and post-seismic settlement of shallow foundations resting on saturated sand. Two rigid foundations with different bearing pressures were placed on the ground surface in a model container. Multiple input motions were applied to achieve different extents of soil liquefaction. The results indicate that foundation settlement can be divided into three distinct phases: (I) during shaking, (II) during the time period after shaking has ceased and before soil reconsolidation in the shallowest layers has taken place, and (III) during soil reconsolidation. Contrary to the free-field ground, most of the total settlement of the foundations occurred before soil reconsolidation, i.e., during Phases I and II. The volumetric strain during these phases was not significant as opposed to the shear strain produced by the foundation surcharge. It was demonstrated that foundation settlement is not necessarily proportional to the liquefied depth of the sand. The extent of the liquefaction in the sand medium mostly affected the post-seismic settlement of the foundations, while the co-seismic settlement was relatively the same for both foundations. The response of the foundations was significantly influenced by the liquefaction extent, whereas the foundations did not experience large accelerations when the soil profile was entirely liquefied. However, the foundations tolerated large settlement under severe liquefaction conditions. The results of this study highlight the role of the liquefaction extent on co-seismic and post-seismic settlement as well as the seismic response of shallow foundations.