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.     

Formulation of elastic modulus of concrete using linear genetic programming

This paper proposes a novel approach for the formulation of elastic modulus of both normal-strength concrete (NSC) and high-strength concrete (HSC) using a variant of genetic programming (GP), namely linear genetic programming (LGP). LGP-based models relate the modulus of elasticity of NSC and HSC to the compressive strength, as similarly presented in several codes of practice. The models are developed based on experimental results collected from the literature. A subsequent parametric analysis is further carried out to evaluate the sensitivity of the elastic modulus to the compressive strength variations. The results demonstrate that the proposed formulas can predict the elastic modulus with an acceptable degree of accuracy. The LGP results are found to be more accurate than those obtained using the buildings codes and various solutions reported in the literature. The LGP-based formulas are quite simple and straightforward and can be used reliably for routine design practice.     

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.     

A new expression for spherical aerosol drag in slip flow regime

A 3D simulation study for an incompressible slip flow around a spherical aerosol particle was performed. The full Navier–Stokes equations were solved and the velocity jump at the gas–particle interface was treated numerically by imposition of the slip boundary condition. Analytical solution to the Stokesian slip flow past a spherical particle was used as a benchmark for code verification, and excellent agreement was achieved. The simulation results showed that in addition to the Knudsen number, the Reynolds number affects the slip correction factor. Thus, the Cunningham-based slip corrections must be augmented by the inclusion of the effect of Reynolds number for application to Lagrangian tracking of fine particles. A new expression for the slip correction factor as a function of both Knudsen number and Reynolds number was developed. The particle total drag coefficient was also correlated against Re and Kn over the range of gas–particle relative speeds yielding the incompressible slip flow from the Stokesian regime up to the threshold of compressibility. Inclusion of gas slip on the particle surface enhances the accuracy of particle drag force prediction up to 40.9% in the range of 0.01<Kn<0.1 and 0.125<Re<20 compared to the no-slip continuum drag values.     

The Three Integrated Phases of Left Atrial Macrophysiology and Their Interactions

Our understanding of the left atrium is growing, although there are many aspects that are still poorly understood. The left atrium size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes and of different cardiovascular disorders, such as, but not limited to, atrial fibrillation, congestive heart failure, mitral regurgitation and stroke. Left atrial function has been conventionally divided into three integrated phases: reservoir, conduit and booster-pump. The highly dynamic left atrium and its response to the stretch and secretion of atrial neuropeptides leaves the left atrium far from being a simple transport chamber. The aim of this review is to provide an understanding of the left atrial physiology and its relation to disorders within the heart.     

A Self-Sustaining Hydrogels with Autonomous Supply of Nutrients and Bioactive Domains for 3D Cell Culture

Photo-crosslinkable platelet lysate (PL)-based hydrogels have been proven to support human-derived cell cultures owing to their high content of bioactive molecules, such as cytokines and growth factors. As a unique self-maintained and biocompatible 3D scaffold, the recently reported self-feeding hydrogels with enzyme-empowered degradation capacity have shown high biological performance in vitro and in vivo. To take advantage of all features of both PL and self-feeding hydrogels, here UV responsive laminaran-methacrylate (LamMA) and PL-methacrylate (PLMA) derivatives plus glucoamylase (GA), which significantly improve the overall features of a 3D system, is coupled. This self-sustaining hybrid hydrogel emerges as a unique scaffold due to the sustained delivery of glucose produced via enzymatic degradation of laminaran while granting the release of growth factors through the presence of PL. This biomaterial is applied to fabricate high-throughput freestanding microgels with controlled geometric shapes. Furthermore, this multicomponent hybrid hydrogel is successfully implemented as the first reported glucose supplier bioink to manufacture intricate and precisely defined cell-laden structures using a support matrix. Finally, such hydrogels are utilized as a proof of concept to serve as 3D in vitro cancer models, with the aim of recapitulating the tumor microenvironment.     

Reliable fragility functions for seismic collapse assessment of reinforced concrete special moment resisting frame structures under near‐fault ground motions

A collapse fragility function shows how the probability of collapse of a structure increases with increasing ground motion intensity measure (IM). To have a more reliable fragility function, an IM should be applied that is efficient and sufficient with respect to ground motion parameters such as magnitude (M) and source‐to‐site distance (R). Typically, pulse‐like near‐fault ground motions are known by the presence of a velocity pulse, and the period of this pulse (T_p) affects the structural response. The present study investigates the application of different scalar and vector‐valued IMs to obtain reliable seismic collapse fragility functions for reinforced concrete special moment resisting frames (RC SMRFs) under near‐fault ground motions. The efficiency and sufficiency of the IMs as the desirable features of an optimal IM are investigated, and it is shown that seismic collapse assessments by using most of the IMs are biased with respect to T_p. The results show that (Sa(T₁), Sa(T₁)/DSI) has high efficiency and sufficiency with respect to M, R, T_p, and scale factor for collapse capacity prediction of RC SMRFs. Moreover, the multiobjective particle swarm optimization algorithm is applied to improve the efficiency and sufficiency of some advanced scalar IMs, and an optimal scalar IM is proposed.     

An intrinsic kinetic model for liquid-phase photocatalytic hydrogen production

A kinetic study was accomplished to describe the photocatalytic production of hydrogen in liquid phase. A reaction mechanism and a kinetic model were proposed to predict the rate of hydrogen production, which is a function of light intensity, catalyst loading, substrate concentration, and time. To assess the capability of the proposed model, glycerol and ethanol were selected as representative hydrogen sources (substrates). The experimental data performed under different operating conditions, based on Box–Behnken experimental design, were used to train the developed kinetic model, optimize the parameters using genetic algorithms and check its accuracy. The analysis confirms the validity of the model under different operating conditions. In addition, the ability of the model to predict the rate of hydrogen production for other substrates, photocatalysts, and operating conditions was confirmed by comparing model predictions with experimental data from literature.     

Evaluation of interfacial layer properties in the polystyrene/silica nanocomposite

Processing conditions and final mechanical properties of polymer nanocomposites are affected by their interfacial layers behavior. However, it is impossible to determine directly the properties of these layers by dynamic rheometry tests. In this work, the interfacial layers properties are evaluated for polystyrene containing silica nanoparticles by the concept of glass‐transition temperature shift. The samples were prepared via solution‐mixing method and dynamic rheometry was used to determine the viscoelastic behavior of filled polymers in the melt state. This initial step showed that addition of silica particles increased the glass‐transition temperature. By preference, decrease in the filler particle size lead to a drastic increase in the glass‐transition temperature and interfacial layer volume fraction due to relatively high surface area of the small filler particles. Then, in the next step, the viscoelastic properties of interfacial layer have been evaluated on the basis of the properties of neat polystyrene using temperature‐frequency superposition law. For this purpose, the shift factor was calculated from the glass‐transition temperature of the sample with maximum filler content. Finally, the effect of immobilized interfacial layer on the viscoelastic properties of the polymer nanocomposite samples has been estimated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011