Numerical investigation of blood flow. Part II: In capillaries

In order to understand the normal and pathologic behavior of the human vascular system, detailed knowledge of blood flow and the response of blood vessels is required. In fact the ability to predict the flow hydrodynamics at any site in the vessels can lead to a better understanding of the behavior of blood flow. Simulation can play an important role in understanding the hemodynamic forces. The objective of the present attempt was to simulate the behavior of blood flow in microvessels using computational fluid dynamics (CFD). Numerical analysis is performed using a commercially available CFD package Fluent 6.2 which is based on the finite volume method. A continuum approach is proposed in which fluid structure interaction has been taken into account. Based on limitations imposed by computational resources, a more simplified model based on volume of fluid (VOF) approach is suggested to simulate movements of RBCs in capillaries and also to predict RBCs’ deformation. Three-dimensional incompressible laminar flow fields are obtained by solving continuity and Navier–Stokes equations computationally. It was found that multiphase CFD simulations may give further insight into the dynamic characteristics of blood flow under complex flow conditions.     

A modified method for constructing efficient solutions structure of MOLP

This paper deals with a recently proposed algorithm for obtaining all weak efficient and efficient solutions in a multi objective linear programming (MOLP) problem. The algorithm is based on solving some weighted sum problems, and presents an easy and clear solution structure. We first present an example to show that the algorithm may fail when at least one of these weighted sum problems has not a finite optimal solution. Then, the algorithm is modified to overcome this problem. The modified algorithm determines whether an efficient solution exists for a given MOLP and generates the solution set correctly (if exists) without any change in the complexity.     

Network flow formulation of optimal perimeter sensory coverage problem

In this article, the perimeter detection optimization problem in field surveillance and target tracking are discussed. The detection range of sensors is assumed to be circular or elliptical. Sensors are also assumed to be associated with a cost factor reflecting their operational characteristics and power usage. We show that the problem of optimal sensor selection can be reduced to a network flow problem and can then be solved using any existing classical methodology. This significantly reduces the computational time of sensory selection problem which in many cases needs to be solved in almost real time basis, every time that the dynamics of the field changes. The field dynamics could change due to such events as wind direction change and sensor failures.     

Rapid and enhanced functionalization of MWCNTs in a dielectric barrier discharge plasma in presence of diluted CO<Subscript>2</Subscript>

Multiwalled carbon nanotubes (MWCNTs) have been functionalized in dielectric barrier discharge (DBD) plasma in presence of a mixture of carbon dioxide and a diluent gas at room temperature and atmospheric pressure. He, Ar, and N₂ were examined as the diluent gases. Temperature-programmed desorption was used to investigate the influence of various plasma parameters and type of diluent gas as well as the amount of diluent in the plasma gas. It is found that the quantity of functional groups on the surface of MWCNTs is a maximum when He is used as diluent gas. It also passes through a maximum when He content is 60%. The presence of He improves the reactivity of the plasma, which leads to an increase in the quantity of functional groups. However, high percentages of He decrease the CO₂ content, which in turn decreases the number of functional groups. FTIR and Raman spectroscopy showed the presence of Oxygen-containing functional groups on MWCNTs surfaces.     

Scheduling linear deteriorating jobs to minimize the number of tardy jobs

In this paper a problem of scheduling a single machine under linear deterioration which aims at minimizing the number of tardy jobs is considered. According to our assumption, processing time of each job is dependent on its starting time based on a linear function where all the jobs have the same deterioration rate. It is proved that the problem is NP-hard; hence a branch and bound procedure and a heuristic algorithm with O(n ²) is proposed where the heuristic one is utilized for obtaining the upper bound of the B&B procedure. Computational results for 1,800 sample problems demonstrate that the B&B method can solve problems with 28 jobs quickly and in some other groups larger problems are also solved. Generally, B&B method can optimally solve 85% of the samples which shows high performance of the proposed method. Also it is shown that the average value of the ratio of optimal solution to the heuristic algorithm result with the objective ??(1 ? Ui) is at most 1.11 which is more efficient in comparison to other proposed algorithms in related studies in the literature.     

A comprehensive study of sound pressure in a finite-length fluid-filled multi-walled carbon nanotube

The aim of this paper is to analyze vibrational behavior and the sound wave propagation in the finite-length fluid-filled multi-walled carbon nanotubes (MWCNTs) and to determine the exact sound pressure load effect on it, and compare it to what has been used by the other researchers. For this purpose, the solution of the modified complex Helmholtz equation is derived by considering the non-rigidity of the CNT and the wave reflections at the open ends of the MWCNT. These investigations are very important for potential application of CNT-filled polymeric foam that is used as sound absorber. In this paper, in formulating the sound pressure load exerted on the innermost tube of the finite-length fluid-filled MWCNT, the following points have been studied for the first time: (i) the energy loss in the fluid, which cannot be ignored in the high frequency analysis; (ii) the non-rigidity of the MWCNT through considering finite acoustical impedance for its walls; (iii) the wave reflections at the open ends of the finite-length MWCNT to calculate the sound pressure load term which is coupled with the dynamic equations of motion for the finite-length fluid-filled MWCNT. The results show that ignoring the mentioned points would cause errors in the prediction of the sound pressure load exerted on the finite-length fluid-filled MWCNT.     

Encapsulation of Vitamin B12 by Complex Coacervation of Whey Protein Concentrate–Pectin; Optimization and Characterization

Vitamin B₁₂ (VB₁₂) is one of the essential vitamins for the body, which is sensitive to light, heat, oxidizing agents, and acidic and alkaline substances. Therefore, the encapsulation of VB₁₂ can be one of the ways to protect it against processing and environmental conditions in food. In this work, the influence of pectin concentration (0.5–1% w/v), whey protein concentrate (WPC) level (4–8% w/v) and pH (3–9) on some properties of VB₁₂-loaded pectin–WPC complex carriers was investigated by response surface methodology (RSM). The findings showed that under optimum conditions (1:6.47, pectin:WPC and pH = 6.6), the encapsulation efficiency (EE), stability, viscosity, particle size and solubility of complex carriers were 80.71%, 85.38%, 39.58 mPa·s, 7.07 µm and 65.86%, respectively. Additionally, the formation of complex coacervate was confirmed by Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). In addition, it was revealed that the most important factor in VB₁₂ encapsulation was pH; at a pH < isoelectric point of WPC (pH = 3), in comparison with higher pH values (6 and 9), a stronger complex was formed between pectin and WPC, which led to an increase in EE, lightness parameter, particle size and water activity, as well as a decrease in the zeta-potential and porosity of complex carriers.     

Investigation and Modeling of Temperature Dependence Recovery Behavior of Shape‐Memory Crosslinked Polyethylene

Shape memory was induced in crosslinked low‐density polyethylene by a heating‐stretching‐cooling cycle. The effect of crosslink content on thermal properties and temperature dependence recovery behavior was studied experimentally. The importance of stretching temperature and crosslink content on recovery behavior could be reasonably explained by the observed changes in the thermal properties which were attributed to the differences in crystalline structures and mechanism of crystal formation during the heating‐stretching‐cooling process. A mechanical model was developed to describe qualitatively and quantitatively the temperature dependence recovery behavior of the prepared shape memory crosslinked polyethylene at nonisothermal state under various conditions by driving constitutive equations using a set of model constants. These model constants were determined with the help of a set of optimization codes using a genetic algorithm method. By choosing a suitable set of model constants one can describe with high accuracy the temperature dependence recovery behavior of any shape memory polymer.