Sharif Digital Repository

Enzymatic decolorization of the monoazo dye, acid orange 7 (AO7) by the fungal peroxidase from Coprinus cinereus NBRC 30628 is a complex system, which is greatly affected by temperature, pH, enzyme activity and the concentrations of H2O2 and dye concentration. The study of these factors and investigating the combined interactions between them by applying one-factor-at-a-time (OFAT) method and two other statistical methods including 2-factorial method and response surface methodology (RSM) were aimed in this work. Through OFAT analysis the optimized conditions were a temperature of 25 °C, pH 9.0 with H2O2 concentration of about 3.9 mM and AO7 concentration of 40 mg/l. A complete... 

In this study, a novle robust antistatic waterborne polyurethane (WBPU)-ZrO2 nanoparticle (NP) coating is specially designed using sol-gel process. For this purpose the effective parameters on resin performance and surface resistivity of the synthesized coating investigated and optimized. The WBPU composite containing 6 wt% ZrO2 NPs, dissipates electrostaic charges with surface resistivity of 9.1 × 109 Ω sq−1 and also improves adhesion strength about 30 % compared with neat resin. Moreover, the homogenous distribution of modified ZrO2 NPs provides a surface roughness of 27.0 nm which can avoid the absorption of dust on the surface. Facile fabrication of robust WBPU–ZrO2 coating with... 

While import taxes are easier to levy, there is increasingly more evidence that importers engage in trade tax evasion. The literature uses, trade gap, the difference between reports from the two ends of a trade link, as a proxy for illegal imports. Many papers have found a robust positive correlation between import tax rates and the trade gap. However, like any other tax, importers could avoid paying import duties through legal provisions. Such opportunities are abundant in Iran and could impose a downward bias on the evasion elasticity estimates. Using disaggregated trade reports from 21 partners and Iran Customs Administration from 2004 to 2013, we show three results. First, a... 

This article is focused on a simple approach for determining the natural frequency and mode shape of laminated angle-ply plates with various shapes by rectangular orthotropy. Since the boundary of the domain for all shapes are not natural to the material coordinate axes it seems appropriate to express the plate displacement amplitude in terms of a polynomial and a general shape function multiplication in the x and y coordinates. The boundary conditions considered are clamped and simply supported edges. The effect of the fiber orientation, layer number, and lamination sequence on the natural frequencies of plates is also considered. The natural frequency determinant has been generated using... 

Attitude determination in space missions is of a great importance. Especially, small satellite attitude determination faces two main challenges: a limited number of attitude sensors and weak computational resources. The two aforementioned issues represent the main motivation of this work, where a magnetometer and a rate gyro are employed in a simple and fast algorithm to determine satellite attitude. A part of the attitude is measured with the magnetometer and the other is estimated using the satellite kinematics with optimization. The proposed method solves the optimization problem with an analytical approach based on a closed form relation. Consequently, it does not need an initial time to... 

Auto-Exposure detection is a key feature in digital cameras and smart-phones. The image information can be used to detect scene over and under exposure passively. This paper introduces an effective optimal exposure detection function based on joint probability density function of the pixels in the scene  

Lifetime is the most important concern in wireless sensor networks due to limited battery power of sensor nodes. In this paper, we focus on designing an energy-efficient and energy-aware routing algorithm, LLR, to increase the operational lifetime of multi-hop wireless sensor networks in the presence of unreliable communication links. Our proposed protocol utilizes a parameter, Broadcasting Delay, in each node associated with the hop parameters passed by a route request packet to select long lifetime paths in the network. The key point in Broadcasting Delay formulation is that it includes both node and link specific parameters. We use two different scenarios: either the link layer... 

The reliability of wireless sensor networks (WSNs) depends on both sensing coverage and reliable transmission of collected data provided by the target cluster of sensors in the proximity of the phenomenon to the observer. In this paper, we establish a probabilistic fundamental quantitative notion for performance-critical applications on reliable information transfer and propose a new analytical model to calculate the coverage-oriented reliability of cluster-based WSNs. Here, the packet loss probability is modeled as a function of two main parameters. The first is the probability of link failure when the node's buffer at the end point of the link is full (discarding the packet) or when the... 

A magnetic actuation system is a promising tool for untethered manipulation at the microscale that medical treatment can benefit from. This paper proposes a new magnetic actuation system that comprises of two coaxial coils on a rotary table. A fixed workspace is placed between coils. The proposed system is able to generate magnetic force with desired direction and magnitude in a plane. The conducted simulation and experiment confirm the capability of the proposed system to control the position of the microrobot. © 2019 IEEE  

In recent years, extensive experiments have shown that classical continuum theory cannot predict the behavior of mechanical microstructures with small size. To accurately design and analyze micro- and nano-electro-mechanical systems, size-dependent continuum theories should be used. These theories model micro- and nano-electro-mechanical systems with higher accuracy because they include size-dependent parameters. In this paper, polysilicon nano-beam is modeled using modified couple stress and Eringen's nonlocal elasticity theories. First, partial differential equations governing the vibration of nano-beams are converted to a one D.O.F. differential equations using Galerkin method, resulting... 

In this research, a site selection method for wind-compressed air energy storage (wind-CAES) power plants was developed and Iran was selected as a case study for modeling. The parameters delineated criteria for potential wind development localities for wind-CAES power plant sites. One important consequence of this research was the identification of the wind energy potential for wind-CAES sites. The theoretical wind energy potential of Iran of greater than 50 W/m2 was identified from a wind atlas of Iran. The model produced factor maps by considering the boundary conditions of the input data and created geo-databases from the outputs maps. The main factor maps were electrical grids and... 

Titanium nitride/graphene nanocomposite as an anode material of lithium ion batteries has been fabricated through the reaction of TiCl4 and NaN3 in supercritical benzene medium followed by ammonia treating at 1000 °C for 10 h. The synthesized TiN/G nanocomposite depicts rate-dependent behavior in such a way that it shows specific capacity of 115 mAh g−1 when is cycled at higher rate (1.6 C) while it shows 76 mAh g−1 when is cycled initially at lower rate (0.2 C) and is subsequently subjected to higher rate (1.6 C). Moreover, TiN/G anode demonstrates capacity retention of 112%, 100%, and 70% after 250 cycles at charge/discharge rates of 1.6, 0.7, and 0.2 C, respectively. This unusual behavior... 

In this research, a new approach for extraction and determination of polycyclic aromatic hydrocarbons from sea and rain water samples was developed by implementing a superhydrophobic substrate and consuming the least amount of solvent. This version of solvent–supported microextraction enabled us to perform the procedure in the immersion mode with the slightest troubles arising from water leakage into the gas chromatography. The superhydrophobic property leads to the fixation of extracting solvent on the substrate surface during water sampling. To prepare a superhydrophobic substrate, a piece of melamine foam was coated by tannic acid and silica nanoparticles using methyltrimethoxysilane and... 

Results are presented from a numerical study examining the flow of a viscous, incompressible fluid through a random packing of non-overlapping spheres at moderate Reynolds numbers, spanning a wide range of flow conditions for porous media. By using a laminar model including inertial terms and assuming rough walls, numerical solutions of the Navier-Stokes equations in three-dimensional porous packed beds resulted in dimensionless pressure drops in excellent agreement with those reported in a previous study. This observation suggests that no transition to turbulence could occur in the range of the Reynolds number studied. For flows in the Forchheimer regime, numerical results are presented of... 

We study queues with impatient customers and Processor Sharing (PS) discipline as well as other variants of PS discipline, namely, Discriminatory Processor Sharing (DPS) and Generalized Processor Sharing (GPS) disciplines, where customers have deadlines until the end of service (DES). Customers arrive according to a state-dependent Poisson process and have general impatience. Customers have exponential service times with state-dependent service rates. Analytical methods based on simple Markov chains are given for the performance analysis of such queues. The principal measures of performance are the steady-state probability of missing deadline and the steady-state probability of blocking.... 

We study queues with impatient customers and Processor Sharing (PS) discipline as well as other variants of PS discipline, namely, Discriminatory Processor Sharing (DPS) and Generalized Processor Sharing (GPS) disciplines, where customers have deadlines until the end of service (DES). Customers arrive according to a state-dependent Poisson process and have general impatience. Customers have exponential service times with state-dependent service rates. Analytical methods based on simple Markov chains are given for the performance analysis of such queues. The principal measures of performance are the steady-state probability of missing deadline and the steady-state probability of blocking.... 

In this study, dynamic response of a micro- and nanobeams under electrostatic actuation is investigated using strain gradient theory. To solve the governing sixth-order partial differential equation, mode shapes and natural frequencies of beam using Euler–Bernoulli and strain gradient theories are derived and then compared with classical theory. Galerkin projection is utilized to convert the partial differential equation to ordinary differential equations representing the system mode shapes. Accuracy of proposed one degree of freedom model is verified by comparing the dynamic response of the electrostatically actuated micro-beam with analogue equation and differential quadrature methods.... 

Data aggregation is a very important method to conserve energy by eliminating the inherent redundancy of raw data in dense WSNs. Although structured approaches are particularly useful for data gathering applications, they incur high maintenance overhead in dynamic scenarios for event-based applications. Moreover, a WSN should be capable of timely fulfilling its mission without losing important information in event-critical applications. In this paper, we focus on designing a structure-free Real-time data AGgregation protocol, RAG, using two mechanisms for temporal and spatial convergence of packets - Judiciously Waiting policy and Real-time Data-aware Anycasting policy. Using extensive... 

Prior to the design and fabrication of MEMS/NEMS devices, analysis of static and dynamic behaviors of these systems is necessary. In the present study, the nonlinear dynamic behavior of micro- and nano-mechanical resonators is investigated and classified based on the resonator’s physical parameters for first time. The Galerkin method is used to convert the distributed-parameter model to a nonlinear ordinary differential equation where mid-plane stretching, axial stress, DC electrostatic and AC harmonic voltages are taken into account. To obtain the analytical frequency response of the micro resonator near its primary resonance, the second order multiple scales method is applied to the... 

Prior to the design and fabrication of MEMS/NEMS devices, analysis of static and dynamic behaviors of these systems is necessary. In the present study, the nonlinear dynamic behavior of micro- and nano-mechanical resonators is investigated and classified based on the resonator’s physical parameters for first time. The Galerkin method is used to convert the distributed-parameter model to a nonlinear ordinary differential equation where mid-plane stretching, axial stress, DC electrostatic and AC harmonic voltages are taken into account. To obtain the analytical frequency response of the micro resonator near its primary resonance, the second order multiple scales method is applied to the...