Numerical Simulation of Steady Mixed Convection Around Two Heated Circular Cylinders in a Square Enclosure

In this paper, a numerical study has been carried out to investigate the steady-state mixed convection around two heated horizontal cylinders in a square two-dimensional enclosure. The cylinders are located at the middle of the enclosure height and the walls of the cavity are adiabatic. Streamlines and isotherms are produced and the effects of cylinder diameter, Reynolds number, and Richardson number on the heat transfer characteristics are numerically analyzed. The average Nusselt number over the surface of cylinders and average nondimensional temperature in the enclosure are also presented. The results show that both heat transfer rates from the heated cylinders and the dimensionless fluid temperature in the enclosure increase with increasing Richardson number and cylinder diameter. However, the trend of average Nusselt number and nondimensional temperature variation is completely opposite when Reynolds number increases. In addition, by increasing the cylinders diameter and Richardson number, the left cylinder is less affected by the inlet flow than right one.     

Stress analysis in a cracked strip

The stress fields in a strip containing climb and glide edge dislocations are obtained utilizing a complex Fourier transform. The dislocation solutions are then employed to perform integral equations for the analysis of a strip weakened by multiple cracks with any configuration and arrangement. The integral equations are solved numerically for the dislocation density on the cracked surfaces. The stress-intensity factors for two straight cracks compared favorably with the results rendered in literature. Three new examples are solved to demonstrate the applicability of the procedure.     

A possibilistic programming approach for the location problem of multiple cross-docks and vehicle routing scheduling under uncertainty

This article considers the design of cross-docking systems under uncertainty in a model that consists of two phases: (1) a strategic-based decision-making process for selecting the location of cross-docks to operate, and (2) an operational-based decision-making process for vehicle routing scheduling with multiple cross-docks. This logistic system contains three echelons, namely suppliers, cross-docks and retailers, in an uncertain environment. In the first phase, a new multi-period cross-dock location model is introduced to determine the minimum number of cross-docks among a set of location sites so that each retailer demand should be met. Then, in the second phase, a new vehicle routing scheduling model with multiple cross-docks is formulated in which each vehicle is able to pickup from or deliver to more than one supplier or retailer, and the pickup and delivery routes start and end at the corresponding cross-dock. This article is the first attempt to introduce an integrated model for cross-docking systems design under a fuzzy environment. To solve the presented two-phase mixed-integer programming (MIP) model, a new fuzzy mathematical programming-based possibilistic approach is used. Furthermore, experimental tests are carried out to demonstrate the effectiveness of the presented model. The computational results reveal the applicability and suitability of the developed fuzzy possibilistic two-phase model in a variety of problems in the domain of cross-docking systems.     

General method of simulating radiation fields using measured boundary values

A general methodology integrating the Fresnell, Snell, and Beer-Lambert laws for modeling the radiant distribution in a medium is presented. The model considers refraction/reflection through/from the body of the UV lamp and sleeve, as well as the reflections from other sources, such as the reactor body. The measured boundary conditions are applied to realistically simulate the fluence/irradiance rate around the radiant source, in particular, in the zone closest to the radiant source. Different low-pressure UV lamps were tested under different operating conditions using photodiodes and a radiometer. The experimentally measured irradiance rate was in a very good agreement with the simulation results of the presented model.     

Occult hepatitis B infection in a hemodialysis population in Guilan province, northern Iran

Hemodialysis (HD) patients are vulnerable to transfusion-transmitted infections such as hepatitis B virus (HBV). HBV infection with undetectable hepatitis B surface antigens (HBsAg) is described as occult HBV and can lead to serious complications. The aim of this study was to evaluate the prevalence of occult HBV and concomitant factors in HD patients. Using a cross-sectional design, clinical and epidemiological data were obtained from May to September 2009 in 11 different HD units in Guilan province in northern Iran. After serological testing for HBV surface antigens in 514 HD patients using a third-generation enzyme-linked immunosorbent assay kit (Diapro, Milano, Italy), HBsAg-negative patients were tested for HBV DNA using a Qiagen PCR kit (Artus Qiagen GmbH, Hilden, Germany). After omission of seven HBsAg-positive patients, 507 patients were included in the study, 280 (55.2%) of whom were male and 227 (44.8%) were female. Patients ranged in age from 16 to 66 years (mean 53.2 years). No HBV DNA was detected in HBsAg-negative patients. Some 59 patients (11.6%) were anti-hepatitis C virus positive and 32 (6.3%) were hepatitis C virus positive according to polymerase chain reaction. The study results indicate that occult HBV infection is not a significant health problem in HD patients in Guilan province.     

Prediction of time required for onset of convection in a porous medium saturated with oil and a layer of gas underlying the oil

The onset of convection for a viscous oil confined in a cylindrical porous medium and contacted with a gas to diffuse into it from below is investigated experimentally and theoretically. Two experiments are carried out, both at a specific reservoir temperature and pressure, starting with the medium saturated with the oil and bringing the gas into contact with it from the base. In the first experiment, the setup is arranged horizontally in order to determine the diffusion coefficient of gas in the absence of convection. In the second experiment, the setup is vertical to investigate the onset of convection. The pressure is maintained constant during both experiments and the volume of gas dissolving in oil is measured vs. time. The dissolved gas data obtained from the vertical experiment show a sharp slope change at the onset of convection. The observed onset time is in excellent agreement with the value obtained by means of an instability theory developed in this study.     

The use of a fuzzy multi-objective linear programming for solving a multi-objective single-machine scheduling problem

This paper develops a fuzzy multi-objective linear programming (FMOLP) model for solving a multi-objective single-machine scheduling problem. The proposed model attempts to minimize the total weighted tardiness and makespan simultaneously. In this problem, a proposed FMOLP method is applied with respect to the overall acceptable degree of the decision maker (DM) satisfaction. A number of numerical examples are solved to show the effectiveness of the proposed approach. The related results are compared with the Wang and Liang's approach. These computational results show that the proposed FMOLP model achieves lower objective functions and higher satisfaction degrees.     

Evaluation of antibacterial property of hydroxyapatite and zirconium oxide‐modificated magnetic nanoparticles against Staphylococcus aureus and Escherichia coli

In the first section of this research, superparamagnetic nanoparticles (NPs) (Fe₃ O₄) modified with hydroxyapatite (HAP) and zirconium oxide (ZrO₂) and thereby Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs were synthesised through co‐precipitation method. Then Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs characterised with various techniques such as X‐ray photoelectron spectroscopy, X‐ray diffraction, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer–Emmett–Teller, Fourier transform infrared, and vibrating sample magnetometer. Observed results confirmed the successful synthesis of desired NPs. In the second section, the antibacterial activity of synthesised magnetic NPs (MNPs) was investigated. This investigation performed with multiple microbial cultivations on the two bacteria; Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Obtained results proved that although both MNPs have good antibacterial properties, however, Fe₃ O₄ /HAP NP has greater antibacterial performance than the other. Based on minimum inhibitory concentration and minimum bactericidal concentration evaluations, S. aureus bacteria are more sensitive to both NPs. These nanocomposites combine the advantages of MNP and antibacterial effects, with distinctive merits including easy preparation, high inactivation capacity, and easy isolation from sample solutions by the application of an external magnetic field.Inspec keywords: nanocomposites, X‐ray chemical analysis, microorganisms, magnetic particles, scanning electron microscopy, precipitation (physical chemistry), nanomagnetics, X‐ray diffraction, X‐ray photoelectron spectra, nanoparticles, superparamagnetism, iron compounds, antibacterial activity, biomedical materials, nanomedicine, calcium compounds, nanofabrication, Fourier transform infrared spectra, magnetometers, zirconium compoundsOther keywords: antibacterial effects, antibacterial property, superparamagnetic nanoparticles, X‐ray photoelectron spectroscopy, X‐ray diffraction, X‐ray analysis, antibacterial activity, bactericidal concentration, S. aureus bacteria, Staphylococcus aureus, Escherichia coli, hydroxyapatite, coprecipitation method, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer‐Emmett‐Teller method, Fourier transform infrared spectroscopy, vibrating sample magnetometer, microbial cultivations, nanocomposites