Sharif Digital Repository

An investigation of the possible performance improvements of thin walled composite beams through the use of the variable stiffness concept with curvilinear fiber is presented. The beams are constructed from a single-cell closed cross section and a number of non-classical effects such as material anisotropy, transverse shear, warping inhibition and nonuniform torsional model are considered in the beam model. The governing equations were derived by means of the extended Hamilton's principle. Also the extended Galerkin's method is used to solve governing equations. Composite beams subjected to different loading with given geometry and material properties are optimized for maximum failure load.... 

In this paper, effect of penicillin addition in enhancing the secretion of glutamic acid by Corynebacterium glutamicum was studied. The proper time of adding penicillin to maximize glutamic acid production was found to drift at repeated trials. In contrast, maximum acid productivity was obtained when penicillin was injected at a proper biomass concentration of about 7.7 gram dry weight per lit (gdw/l). Moreover, rate of consumption of sugar and ammonia through the course of glutamic acid fermentation was monitored. In production phase, these two rates were correlated properly with a ratio of 3.2:1 which is comparable to the theoretical stoichiometric value of 5:1. Therefore, through feeding... 

This paper presents a scalp electroencephalogram (EEG) rhythmic pattern detection scheme based on neural networks. Rhythmic discharges detection is applicable to the majority of seizures seen in newborns, and is listed as detecting 90% of all the seizures. In this approach some features based on various methods are extracted and compared by a modified multilayer neural network in order to find rhythmic discharges. Statistical performance comparison with seizure detection schemes of Gotman et al. and Liu et al. is performed. © 2006 IEEE  

Ring rolling is one of the most significant methods for producing rings with highly precise dimensions and superior qualities such as high strength uniformity, all accomplished without wasting any materials. In this article, we have achieved analytical formulas for calculating the pressure and shear friction over the contact arcs between the rollers and ring in the ring rolling process for the material in general nonlinear hardening property. We have also asserted the best mathematical model to predict friction for rolling processes. The method we use is based on calculating the analytical stress distribution. In other words, by using of Saint-Venan principal the stress components are... 

Recently, the visibility graph has been introduced as a novel method for analyzing time series, which maps a time series to a complex network. In this paper we introduce a new algorithm of visibility, "cross-visibility", which reveals the conjugation of two coupled time series. The correspondence between the two time series is mapped to a network, "the cross-visibility graph", to demonstrate the correlation between them. We have applied the algorithm to several correlated and uncorrelated time series, generated by the linear stationary ARFIMA process, in order to better understand the results of the cross-visibility of empirical series. The comparison between the degree distribution of... 

L-Proline (2%)-TiO2/BiOBr (30%) nanocomposite was synthesized to obtain high photocatalytic performance in the visible light region and infrared radiation(IR) for methylene blue (MB) and congo red (CR) removal from the contaminated wastewater. L-Proline (2%)-TiO2/BiOBr (30%) photocatalyst with strong absorption near IR wavelength and high charge separation ability was fabricated for the first time. X-ray diffraction (XRD), Fourier transform infrared (FTIR), field-emission scanning electron microscope (FESEM)/Energy Dispersive X-ray (EDX), UV–Vis diffuse reflectance spectrum (DRS), photoluminescence (PL) and Brunauer-Emmett-Teller (BET) characterization techniques show that the visible driven... 

In this study, the feasibility of the synthesis of Fe-TiC-Al 2O3 hybrid nanocomposite via mechanical activation followed by carbothermal reduction was investigated. The raw materials including ilmenite, carbon black and aluminum powder were milled in a high energy planetary ball mill. At different time intervals, samples were taken for characterization. After phase evaluation with XRD, some samples were heat treated in an atmosphere controlled tube furnace. Studies proved that increasing the milling time of the raw materials resulted in the formation of more amorphous phase and more active materials. Furthermore, investigations showed that after carbothermal reduction, the synthesized TiC... 

In this paper, the design of an efficient sparse array, used to reconstruct the image from millimeter-wave signals, is presented. The proposed array takes advantage of the sparsity concept of the image in the spatial Fourier domain to reduce the number of array elements such that the beam pattern of the designed array meets the desired beamwidth and sidelobe level. Simulation and measured results confirm the effectiveness of the proposed design on high-quality reconstruction of the image, while 85% reduction in the number of elements is achieved as well as the reduction in scan time and system complexity  

Real-world image classification, which aims to determine the semantic class of un-labeled images, is a challenging task. In this paper, we focus on two challenges of image classification and propose a method to address both of them simultaneously. The first challenge is that representing images by heterogeneous features, such as color, shape and texture, helps to provide better classification accuracy. The second challenge comes from dissimilarities in the visual appearance of images from the same class (intra class variance) and similarities between images from different classes (inter class relationship). In addition to these two challenges, we should note that the feature space of... 

The goal of this paper is to reduce the antenna count in a millimeter (mm)-wave imaging system by proposing both hardware and software solutions. The concept of image sparsity in the transform domain is utilized to present the compressive sensing (CS) formulation for both mono-static and multistatic imaging at mm-wave frequencies. To reduce the complexity of the imaging system and reconstruction process, we introduce 1.5-D array structure, which is a random sparse array with orthogonal element locations. It is shown that the peak signal-to-noise ratio (PSNR) of the reconstructed image obtained by a 1.5-D array with 65% sparsity is very close to the PSNR of a uniform 2-D array for mono-static... 

One of the most vital aspects of the orthopedic implant field has been the development of multifunctional coatings that improve bone-implant contact while simultaneously preventing bacterial infection. The present study investigates the fabrication and characterization of multifunctional polysaccharides, including carboxymethyl cellulose (CMCn) and carboxymethyl chitosan nanofibers (CMCHn), as a novel implant coating on titania nanotube arrays (T). Field emission scanning electron microscopy (FESEM) images revealed a nanofibrous morphology with a narrow diameter for CMCn and CMCHn, similar to extracellular matrix nanostructures. Compared to the T surface, the roughness of CMCn and CMCHn... 

In this paper, a sparsity-aware target localization method in multiple-input-multiple-output (MIMO) radars by utilizing time difference of arrival (TDOA) measurements is proposed. This method provides a maximum likelihood (ML) estimator for target position by employing compressive sensing techniques. Also, for fast convergence and mitigating the mismatch problem due to grid discretization, we address a block-based search coupled with an adaptive dictionary learning technique. The Cramer-Rao lower bound for this model is derived as a benchmark. Simulations results are included to verify the localization performance  

We investigate both pure and mixed states Floquet dynamical quantum phase transition (DQPT) in the periodically time-dependent extended XY model. We exactly show that the proposed Floquet Hamiltonian of interacting spins can be expressed as a sum of noninteracting quasispins imposed by an effective time dependent magnetic field (Schwinger-Rabi model). The calculated Chern number indicates that there is a topological transition from the nonadiabatic to adiabatic regime. In the adiabatic regime, the quasispins trace the time dependent effective magnetic field and then oscillate between spin up and down states. While in the nonadiabatic regime, the quasispins cannot follow the time dependent... 

Out-of-time-order correlators (OTOCs) progressively play an important role in different fields of physics, particularly in the nonequilibrium quantum many-body systems. In this paper, we show that OTOCs can be used to probe the Floquet dynamical quantum phase transitions (FDQPTs). We investigate the OTOCs of two exactly solvable Floquet spin models, namely, Floquet XY chain and synchronized Floquet XY model. We show that the border of driving frequency range, over which the Floquet XY model shows FDQPT, is signaled by the global minimum of the infinite-temperature time averaged OTOC. Moreover, our results manifest that OTOCs decay algebraically in the long time, for which the decay exponent... 

In this paper, a new approach based on hybrid Particle Swarm-Based- Simulated Annealing Optimization (PSO-B-SA) for solving thermal unit commitment (UC) problems is proposed. The PSO-B-SA presented in this paper solves the two sub-problems simultaneously and independently; unit-scheduled problem that determines on/off status of units and the economic dispatch problem for production amount of generating units. Problem formulation of UC is defined as minimization of total objective function while satisfying all the associated constraints such as minimum up and down time, production limits and the required demand and spinning reserve. Simulation results show that the proposed approach can... 

We prove that every negatively associated sequence of Bernoulli random variables with “summable covariances” has a trivial tail σ-field. A corollary of this result is the tail triviality of strongly Rayleigh processes. This is a generalization of a result due to Lyons, which establishes tail triviality for discrete determinantal processes. We also study the tail behavior of negatively associated Gaussian and Gaussian threshold processes. We show that these processes are tail trivial though, in general, they do not satisfy the summable covariances property. Furthermore, we construct negatively associated Gaussian threshold vectors that are not strongly Rayleigh. This identifies a natural... 

In this study, free vibration analysis of moderately thick symmetrically laminated general trapezoidal plates with various combinations of boundary conditions is investigated. The governing partial differential equations and boundary conditions for trapezoidal plate are obtained using first order shear deformation theory (FSDT) together with proper transformation from Cartesian system into trapezoidal coordinates. Generalized differential quadrature (GDQ) method is then employed to obtain solutions for the governing equations. Results of the GDQ method are compared and validated with available results in the literature which show accuracy and fast rate of convergence of the method. Effect of... 

This study evaluates the effects of carbon, nitrogen, and sulfur dopants on the photocatalytic activity of TiO2 for degradation of oxytetracycline (OTC) and chemical oxygen demand (COD) removal from licorice extraction plant wastewater (LEPW). Three novel visible-light-responsive nanostructures, including L-Histidine-TiO2, L-Methionine-TiO2 and L-Asparagine-TiO2, were successfully synthesized. The results showed that the modification of TiO2 with these three amino acids made the catalyst active in the visible light region and reduced the recombination rate of e−/h+ pairs according to PL analysis. The photodegradation efficiency of L-Histidine (2 wt.%)-TiO2 was 100% and 94% for OTC and COD,... 

This paper deals with the nonlinear free vibration analysis of in-plane bi-directional functionally graded (IBFG) rectangular plate with porosities which are resting on Winkler-Pasternak elastic foundations. The material properties of the IBFG plate are assumed to be graded along the length and width of the plate according to the power-law distribution, as well as, even and uneven types are taken into account for porosity distributions. Equations of motion are developed by means of Hamilton's principle and von Karman nonlinearity strain-displacement relations based on classical plate theory (CPT). Afterward, the time-dependent nonlinear equations are derived by applying the Galerkin... 

An inexpensive silicon rubber-based chip was constructed by fabricating a triangle-shaped microcanal with a 135 μm width and 234 μm depth by laser ablation technique. The fabricated groove was sealed by a thin glass cover while two pieces of stainless-steel tubing were connected to each side of the canal. Then, a thin polyaniline film was synthesized on the walls of the canal by chemical oxidation using a syringe pump to deliver the relevant reagents. The microfluidic system was eventually connected to a gas chromatography-mass spectrometry. To evaluate the capability of the constructed microfluidic system, it was implemented to the analysis of submilliliter volumes of environmental samples...