Sharif Digital Repository

A brass vortextube is used to carry out a series of experiments. The main objective of the present research is to investigate the separation performances of a vortex tube (VT) for a hydrocarbon mixture. Examination is also applied to study the effects of nozzle intakes number and cold fraction on the gas species separation at specific inlet pressure 236.37 kPa in a VT with two gas mixtures (LPG as a hydrocarbon mixture and LPG-N2). A two-dimensional computational fluid dynamic (CFD) model simulation of a VT is presented. CFD code after validation is also applied to investigate the role of cold fraction and nozzle intakes number on the gas species separation. The highly rotating flow field... 

A brass vortex tube with changeable parts is used to obtain the optimum nozzle intake numbers and diameter. The effects of inlet pressure and CF (cold fraction) are also investigated. Results illustrate that increasing the number of nozzles causes a temperature drop and the optimum nozzle diameter corresponds to quarter of vortex tube diameter. The distance between cold end orifice and nozzle intakes is investigated in this work and it is found that for a better performance, this distance should be decreased. A series of experiments conducted to investigate the CF effect on VT performance and an optimum amount for this parameter is found. A two-dimensional computational fluid dynamics... 

In this paper, the optimal sampling strategies (uniform or nonuniform) and distortion tradeoffs for stationary bandlimited periodic signals are studied. We justify and use both the average and variance of distortion as the performance criteria. To compute the optimal distortion, one needs to find the optimal sampling locations, as well as the optimal pre-sampling filter. A complete characterization of the optimal distortion for the rates lower than half the Landau rate is provided. It is shown that nonuniform sampling outperforms uniform sampling. In addition, this nonuniform sampling is robust with respect to missing samples. Next, for the rates higher than half the Landau rate, we find... 

In this paper, the optimal sampling strategies (uniform or nonuniform) and distortion tradeoffs for Gaussian bandlimited periodic signals with additive white Gaussian noise are studied. Our emphasis is on characterizing the optimal sampling locations as well as the optimal pre-sampling filter to minimize the reconstruction distortion. We first show that to achieve the optimal distortion, no pre-sampling filter is necessary for any arbitrary sampling rate. Then, we provide a complete characterization of optimal distortion for low and high sampling rates (with respect to the signal bandwidth). We also provide bounds on the reconstruction distortion for rates in the intermediate region. It is... 

In this paper, the optimal sampling strategies (uniform or nonuniform) and distortion tradeoffs for Gaussian bandlimited periodic signals with additive white Gaussian noise are studied. Our emphasis is on characterizing the optimal sampling locations as well as the optimal presampling filter to minimize the reconstruction distortion. We first show that to achieve the optimal distortion, no presampling filter is necessary for any arbitrary sampling rate. Then, we provide a complete characterization of optimal distortion for low and high sampling rates (with respect to the signal bandwidth). We also provide bounds on the reconstruction distortion for rates in the intermediate region. It is... 

Small islands around the world face various hazards such as sea-water level rise, hurricanes, human activities over pressure, environmental degradation, and pollution. Resiliency is a critical feature that has to be maintained in these sensitive and vulnerable areas. This paper focuses on the importance of Integrated Coastal Management (ICM) in increasing the level of resiliency in small islands. Integrated Coastal Zone Management (ICZM) has been recommended for practice by United Nations 1992 Rio Conference resolution to conserve the valuable natural resources of the coastal areas around the globe and improve their deteriorating environmental conditions. Integrated coastal management plan... 

The problem of finding the optimal node density for reconstructing a stochastic signal from its noisy samples in sensor networks is considered. The signal could be nonstationary and nonbandlimited. A weight is assigned to each location that indicates the relative importance of the signal at that location. It is shown that when the number of samples is very large, the optimal density of the samples at each location is proportional to the square root of the weight associated to that location  

Let (Formula presented.) be a graph of order (Formula presented.) and size (Formula presented.). Suppose that (Formula presented.) is a function such that (Formula presented.). In this paper we provide a criterion for (Formula presented.)-choosability of (Formula presented.). Using this criterion, it is shown that the choice number of the complete (Formula presented.)-partite graph (Formula presented.) is (Formula presented.), which is a well-known result due to Erdös, Rubin and Taylor. Among other results we study the (Formula presented.)-choosability of the complete (Formula presented.)-partite graphs with part sizes at most (Formula presented.), when (Formula presented.), for every vertex... 

TiO2 nanorods have been successfully grown into a track-etched polycarbonate (PC) membrane by a particulate sol-electrophoretic deposition from an aqueous medium. The prepared sols had a narrow particle size distribution around 17 nm and excellent stability against aging, with zeta potentials in the range of 47-50 mV at pH 2. It was found that TiO2 nanorods were grown from dilute aqueous sol with a low, 0.1-M concentration. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversion of titanium isopropoxide was obtained by hydrolysis, resulting in the formation of TiO2 particles. X-ray diffraction (XRD) results revealed that TiO2 nanorods dried at 100 °C were a... 

Inverse design in external flow regimes usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this research, a novel iterative inverse design method is developed for inviscid subsonic and transonic external flow regimes. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a 2D inviscid analysis code. The Euler equations are solved for a physical domain of which some unknown boundaries are iteratively modified via BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called... 

A phase frequency detector (PFD) with a very low dead zone is proposed which is based on a configuration adaptable to both CMOS or carbon nano-tube transistors (CNTFETs). In the first step the proposed configuration is designed using CMOS transistors, and then CNTFETs are substituted to improve the speed and reduce the propagation delay. The proposed PFD in addition to very low dead zone, has low power consumption and high frequency range of operation, which are achieved as a result of the elimination of the reset path. The simulation results based on 32 nm technology for CNTFET and 180 nm technology for CMOS, illustrate that CNTFET-based proposed circuit dissipates 2 µW and has frequency of... 

In this paper, bulk and suspension free radical polymerization of styrene in batch reactor has been modelled. This research contains two parts. In the first part, the derivation of a mathematical model from kinetics of reactions was performed. The solution of this mathematical model required roughly 10000-50000 stiff-differential equations to be solved simultaneously. However, the number of equations were reduced to only five non-stiff differential equations and six algebraic equations using moment model and quasi-steady-state assumption. Due to an enormous increase in viscosity during polymerization, the system translates into diffusion-controlled state, which causes gel and glassy effects.... 

In this study, the effects of an exercise therapy comprising yoga exercises and medial-thrust gait (YogaMT) on lower-extremity kinetics, pain, and function in patients with medial knee osteoarthritis were investigated. Fifty-nine patients were randomly allocated to three treatment groups: (a) the YogaMT group practiced yoga exercises and medial thrust gait, (b) the knee-strengthening group performed quadriceps-and hamstring-strengthening exercises, and (c) the treadmill walking group practiced normal treadmill walking in 12 supervised sessions. The adduction and flexion moments of the hip, knee, and ankle; pain intensity; and 2-min walking test were assessed before and after treatment and at... 

BACKGROUND: Medial thrust (MT) gait is a nonsurgical approach for reducing the knee adduction moment (KAM) in patients with knee osteoarthritis. However, its usefulness is indeterminate due to scarcity of research about changes in lower extremity kinetics and the ground reaction force (GRF) which have been investigated in this study. MATERIALS AND METHODS: Twenty patients (6 males, 14 females, age: 56.2±6.2 years) with medial knee osteo-arthritis participated in this cross-sectional study. A 12-camera motion analysis system and two force plates recorded kinematic and GRF data while participants walked barefoot along a 12m path with 1) their regular gait pattern and 2) MT gait pattern. The... 

A graph G is called an Mr(k)-graph if G has no k-list assignment to its vertices with exactly r vertex colorings. We characterize all A 3(2)-graphs. More precisely, it is shown that a connected graph G is an A3(2)-graph if and only if each block of G is a complete graph with at least three vertices  

A series of experiments were carried out to investigate unsteady behavior of the flow field as well as the boundary layer of an airfoil oscillating in plunging-type motion in a subsonic wind tunnel. The measurements involved surface-mounted hot films complimented with surface pressure. In addition, wind tunnel wall pressure distribution was acquired to furnish a baseline for the wall interference corrections. The airfoil is the section of a 660-kW wind turbine blade. The experiments were conducted at a Reynolds number of 0.42 million, and over two reduced frequencies of k = 0.06 and 0.085, at prestall, nearstall, and poststall regions. The unsteady aerodynamic loads were calculated from the... 

In this study, the prospects of energy efficiency potential, clean development mechanism (CDM) and carbon income up to and beyond 2012 are investigated in the petrochemical industries of Iran as a major oil-producing country. This paper is to address four questions of: (1) the GHGs emission in Iranian petrochemical complexes, (2) the most energy-consuming processes, (3) units with the highest energy efficiency potentials and (4) potentials of CDM or similar carbon projects based on post-2012 scenarios. The petrochemical processes are investigated in two categories of non-polymeric and polymeric productions. Based on capital expenditure, economic saving, simple payback period, CO2 equivalent... 

In the present research, the introduction of multi-walled carbon nanotubes (MWCNTs) into the hydroxyapatite (HA) matrix and dip coating of nanocomposite on titanium alloy (Ti-6Al-4V) plate was conducted in order to improve the performance of the HA-coated implant via the sol-gel method. The structural characterization and electron microscopy results confirmed well crystallized HA-MWCNT coating and homogenous dispersion of carbon nanotubes in the ceramic matrix at temperatures as low as 500 C. The evaluation of the mechanical properties of HA and HA/MWCNT composite coatings with different weight percentages of MWCNTs showed that the addition of low concentrations of MWCNTs (0.5 and 1 wt.%)... 

This paper describes a simple and low-cost test strip for on-site monitoring of methiocarb insecticide. Hydrophilic filter paper soaked in agarose solution was bounded by hydrophobic solid wax and then was coated with unmodified gold nanoparticles (AuNPs). AuNPs aggregation caused by methiocarb served as colorimetric response. We demonstrated detection capability of methiocarb both in solution- and substrate-based sensor. A good linear relationship was obtained between the colorimetric response and the concentration of methiocarb ranging from 20 to 80 ng mL -1 with a limit of detection of 5 ng mL -1. Excellent selectivity toward methiocarb was observed among various pesticides and cationic... 

One of the most critical issues in manufacturing systems is the operator management. In this paper, the operator assignment problem is studied within a cellular manufacturing system. The most important novelty of this research is the consideration of operator learning and forgetting effects simultaneously. The skill level of an operator can be increased/decreased based on the time spent on a machine. Moreover, the issues related to operators like hiring, firing, and salaries are considered in the proposed model. The parameters are considered to be uncertain in this model, and a robust optimization approach is developed to handle it. Using this approach, the model solution remains feasible...