A Numerical Simulation of the Boycott Effect

The lattice Boltzmann method has been used to simulate the velocity field induced and the motion of an ensemble of particles during the sedimentation process in inclined tubes. The simulations show the trajectories and flow behavior of individual particles and particle-particle and particle-wall interactions as well as the formation of particle clusters. The global convection motion that was experimentally observed during such processes and tends to enhance the sedimentation process is also reproduced numerically. In addition we have found that smaller intermittent vortices, formed from the wakes of groups of settling particles, also play an important role in the sedimentation process and the final distribution of particles.     

Heat transfer in particulate flows with Direct Numerical Simulation (DNS)

A Direct Numerical Simulation (DNS) method has been developed to solve the heat transfer equations for the computation of thermal convection in particulate flows. This numerical method makes use of a finite difference method in combination with the Immersed Boundary (IB) method for treating the particulate phase. A regular Eulerian grid is used to solve the modified momentum and energy equations for the entire flow region simultaneously. In the region that is occupied by the solid particles, a second particle-based Lagrangian grid is used, which tracks particles, and a force density function or an energy density function is introduced to represent the momentum interaction or thermal interaction between particle and fluid. The numerical methods developed in this paper have been validated extensively by comparing the present simulation results with those obtained by others.     

Geothermal power production from abandoned oil wells

A simulation for the determination of geothermal power production from abandoned oil wells by injecting and retrieving a secondary fluid was performed. The analysis takes into consideration local geothermal gradients and typical well depths and pipe diameters. Isobutane is chosen as the secondary fluid, which is injected in the well at moderate pressures and allowed to heat up and produce vapor. The computational model that was developed takes into account mass, energy, and momentum conservation equations for the well flow, and the simulation helps determine the state of the fluid from injection to retrieval. It is observed that the operation of such systems attains a maximum power that depends on the temperature of the well bottom and the injection pressure. In general, 2–3 MW of electric power may be produced from wells that are typical in the South Texas region.     

Robust treatment of no-slip boundary condition and velocity updating for the lattice-Boltzmann simulation of particulate flows

In the past decade, the lattice-Boltzmann method (LBM) has emerged as a very useful tool in studies for the direct-numerical simulation of particulate flows. The accuracy and robustness of the LBM have been demonstrated by many researchers; however, there are several numerical problems that have not been completely resolved. One of these is the treatment of the no-slip boundary condition on the particle-fluid interface and another is the updating scheme for the particle velocity. The most common used treatment for the solid boundaries largely employs the so-called “bounce-back” method (BBM). [Ladd AJC. Numerical simulations of particulate suspensions via a discretized Boltzmann equation Part I. Theoretical foundation. J Fluid Mech (1994);271:285; Ladd AJC. Numerical simulations of particulate suspensions via a discretized Boltzmann equation Part II. Numerical results. J Fluid Mech (1994);271:311.] This often causes distortions and fluctuations of the particle shape from one time step to another. The immersed boundary method (IBM), which assigns and follows a series of points in the solid region, may be used to ensure the uniformity of particle shapes throughout the computations. To ensure that the IBM points move with the solid particles, a force density function is applied to these points. The simplest way to calculate the force density function is to use a direct-forcing scheme. In this paper, we conduct a complete study on issues related to this scheme and examine the following parameters: the generation of the forcing points; the choice of the number of forcing points and sensitivity of this choice to simulation results; and, the advantages and disadvantages associated with the IBM over the BBM. It was also observed that the commonly used velocity updating schemes cause instabilities when the densities of the fluid and the particles are close. In this paper, we present a simple and very effective velocity updating scheme that does not only facilitate the numerical solutions when the particle to fluid density ratios are close to one, but also works well for particle that are lighter than the fluid.     

Data Mining techniques for the detection of fraudulent financial statements

This paper explores the effectiveness of Data Mining (DM) classification techniques in detecting firms that issue fraudulent financial statements (FFS) and deals with the identification of factors associated to FFS. In accomplishing the task of management fraud detection, auditors could be facilitated in their work by using Data Mining techniques. This study investigates the usefulness of Decision Trees, Neural Networks and Bayesian Belief Networks in the identification of fraudulent financial statements. The input vector is composed of ratios derived from financial statements. The three models are compared in terms of their performances.     

Effect of long‐term dietary administration of oregano and rosemary on the antioxidant status of rat serum,liver, kidney and heart after carbon tetrachloride‐induced oxidative stress

BACKGROUND: This study was performed on female Wistar rats allocated to eight groups of six animals each. Groups 1 and 2 were fed the basal diet, groups 3 and 4 were fed the basal diet supplemented with ground oregano at 20 g kg^?1 level, groups 5 and 6 were fed the basal diet supplemented with ground rosemary at 20 g kg^?1 level, while groups 7 and 8 were fed the basal diet supplemented with both oregano and rosemary, each at 20 g kg^?1 level. Following 6 weeks feeding, groups 2, 4, 6 and 8 were injected with CCl₄ at 1 mL kg^?1 body weight, and 6 h thereafter all animals were sacrificed. RESULTS: Administration of CCl₄ to the control rats enhanced (P < 0.05) aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) activities, decreased cholesterol and triglycerides content in serum, increased (P < 0.05) lipid peroxidation and decreased (P < 0.05) the ABTS radical cation, the hydroxyl anion radical, the superoxide anion radical, and the hydrogen peroxide scavenging activities in all tested tissues, as compared to the control. Feeding oregano, rosemary or both before CCl₄ treatment resulted in decline (P < 0.05) of the increase in AST, ALT and ALP activities, increase (P < 0.05) of cholesterol and triglycerides in serum, decrease (P < 0.05) of lipid peroxidation, and increase (P < 0.05) of the ABTS radical cation, hydroxyl anion radical, superoxide anion radical and hydrogen peroxide scavenging activity. CONCLUSION: The results of this study suggest that long‐term dietary administration of oregano and rosemary has the potential to quench free radicals and alleviate CCl₄‐induced oxidative stress in rats. Copyright © 2009 Society of Chemical Industry     

The symbolic operator representation applied to the derivation of solutions of unsteady heat diffusion problems

The method of the Symbolic Operator Representation, first introduced by Lord Rayleigh in the solution of the wave equation, is applied to the unsteady heat conduction problem. The general equations for the temperature field around particle of arbitrary shape are expressed in terms of a symbolic operator Ξ Hence, the analytical solution for the temperature field around a sphere and for the rate of heat transfer from a spherical particle are obtained, when the temperature of the particle is a time-dependent function. As an example for the use of this method, analytic solution is derived in an explicit form for the case of a linear field around the spherical particle. The solutions obtained by this method are exact.     

Analytical determination of the ultimate strength of sandwich beams

An analytical determination of the ultimate strength of a typical GRP/PVC sandwich beam has been performed. These beams represent common building practise in marine applications. Equations describing the behaviour of a sandwich panel under beam loading and various failure modes have been developed. The method has been applied to predict the ultimate load for a simple supported sandwich beam. The critical loads have been compared with those from the experimental investigation of a typical bulkhead-to-hull GRP/PVC sandwich T-joint under pull out forces.     

Fluid-Particle Interactions and Resuspension in Simple Shear Flow

The lattice Boltzmann method (LBM) is used to simulate the particle resuspension process in a two-dimensional simple shear flow. At first, the lift force on a single disk-shaped particle attached at the channel wall is computed. It is found that when the particle is allowed to freely move in the viscous fluid, the resulting lift force is smaller than that when the particle is constrained to be stationary. The bulk properties of fluids with particles suspended under various concentrations are numerically calculated. The results agree reasonably well with analytical results by Batchelor when the volume fraction is lower than 50%. The resuspension process of a group of particles (up to 500) is simulated at different particle-to-fluid density ratios. It is found that the height and shape of particle bed depend on the particle density ratio and flow conditions. Interactions of groups of particles as well as the final shape of the bedform of the particles were studied during this resuspension process. Finally, the pressure distribution and flow above the bedform of particles was examined. The results obtained agree well with those observed in naturally occurring bedforms of sediments.     

Effect of acid tolerance response (ATR) on attachment of Listeria monocytogenes Scott A to stainless steel under extended exposure to acid or/and salt stress and resistance of sessile cells to subsequent strong acid challenge

The aim of this study was to investigate the potential effect of adaptive stationary phase acid tolerance response (ATR) of Listeria monocytogenes Scott A cells on their attachment to stainless steel (SS) under low pH or/and high salt conditions and on the subsequent resistance of sessile cells to strong acid challenge. Nonadapted or acid-adapted stationary-phase L. monocytogenes cells were used to inoculate (ca. 10? CFU/ml) Brain Heart (BH) broth (pH 7.4, 0.5% w/v NaCl) in test tubes containing vertically placed SS coupons (used as abiotic substrates for bacterial attachment). Incubation was carried out at 16 °C for up to 15 days, without any nutrient refreshment. L. monocytogenes cells, prepared as described above, were also exposed to low pH (4.5; adjusted with HCl) or/and high salt (5.5% w/v NaCl) stresses, during attachment. On the 5th, 10th and 15th day of incubation, cells attached to SS coupons were detached (through bead vortexing) and enumerated (by agar plating). Results revealed that ATR significantly (p<0.05) affected bacterial attachment, when the latter took place under moderate acidic conditions (pH 4.5, 0.5 or 5.5% w/v NaCl), with the acid-adapted cells adhering slightly more than the nonadapted ones. Regardless of acidity/salinity conditions during attachment, ATR also enhanced the resistance of sessile cells to subsequent lethal acid challenge (exposure to pH 2 for 6 min; pH adjusted with either hydrochloric or lactic acid). The trend observed with viable count data agreed well with conductance measurements, used to indirectly quantify remaining attached bacteria (following the strong acid challenge) via their metabolic activity. To sum, this study demonstrates that acid adaptation of L. monocytogenes cells during their planktonic growth enhances their subsequent attachment to SS under extended exposure (at 16 °C for up to 15 days) to mild acidic conditions (pH 4.5), while it also improves the resistance of sessile cells to extreme acid treatment (pH 2). Therefore, the ATR of bacterial cells should be carefully considered when applying acidic decontamination strategies to eradicate L. monocytogenes attached to food processing equipment.