Sharif Digital Repository

Memristor devices have attracted tremendous interest due to different applications ranging from nonvolatile data storage to neuromorphic computing units. Exploring the role of surface roughness of the bottom electrode (BE)/active layer interface provides useful guidelines for the optimization of the memristor switching performance. This study focuses on the effect of surface roughness of the BE electrode on the switching characteristics of Au/TiO2/Au three-layer memristor devices. An optimized wet-etching treatment condition was found to modify the surface roughness of the Au BE where the measurement results indicate that the roughness of the Au BE is affected by both duration time and... 

Nanostructured materials have attracted much attention in recent decades. Nowadays, there are numerous nanomaterials with several applications. The ultrasonic spray pyrolysis method is a cost-effective and adaptable technique based on an aerosol process for synthesizing nanoparticles and depositing thin films. The technique is capable of synthesizing metal, oxide, and composite nanomaterials with precisely controllable morphologies and chemical compositions using metal salts in aqueous solvents. More importantly, it is popular, as evident from the growing number of studies being conducted on the technique. Here, we review studies conducted on basic principles and applications of the... 

Microbial desalination cell (MDC) is a new bio-electrochemical technique which converts chemical energy into electrical energy, and at the same time desalinates water and treats wastewater. In this study, MDC performance and water biofouling conditions were tested as an efficient pretreatment desalination process of reverse osmosis (RO). The experiments were designed in a three-chamber reactor to compare the performance of batch and continuous fed modes, using bio-cathode and synthetic wastewater in four different hydraulic retention times and 17 and 35 g/L NaCl concentrations. According to the results, maximum salt removal of about 52.3% was obtained in the continuously fed MDC at 35 g/L... 

Laboratory investigation on the influence of solute concentration on the soil water-retention curve (SWRC) and volumetric behaviour of expansive soils has received much attention in recent years due to increasing environmental pollution. However, most studies only considered applying wetting or drying path with almost no attention to hydraulic hysteresis. Furthermore, these studies have focused on examining expansive soils and only marginal effort has been devoted to collapsible soils. Therefore, the main objective of this study is to systematically explore the SWRC and shrinkage characteristics of an artificially made collapsible soil at various molar concentrations. The tests were... 

In addition to enhancement of the results near the point of application of a concentrated load in the vicinity of nano-size defects, capturing surface effects in small structures, in the framework of second strain gradient elasticity is of particular interest. In this framework, sixteen additional material constants are revealed, incorporating the role of atomic structures of the elastic solid. In this work, the analytical formulations of these constants corresponding to fee metals are given in terms of the parameters of Sutton-Chen interatomic potential function. The constants for ten fcc metals are computed and tabulized. Moreover, the exact closed-form solution of the bending of a... 

In this paper, a size-dependent Timoshenko beam is developed on the basis of the couple stress theory. The couple stress theory is a non-classic continuum theory capable of capturing the small-scale size effects on the mechanical behavior of structures, while the classical continuum theory is unable to predict the mechanical behavior accurately when the characteristic size of structures is close to the material length scale parameter. The governing differential equations of motion are derived for the couple-stress Timoshenko beam using the principles of linear and angular momentum. Then, the general form of boundary conditions and generally valid closed-form analytical solutions are obtained... 

A highly efficient polybutylene terephthalate (PBT)-based nanocomposite containing nickel oxide nanoparticles was synthesized by electrospinning technique and used as a fiber coating for solid phase microextraction. The influential morphological parameters and capability of the prepared nanocomposite including the NiO content, the coating time, the PBT concentration and applied voltage were considered for optimization. The applicability of the synthesized fiber coating was examined by headspace solid phase micro extraction and gas chromatography mass spectrometry detection of some volatile organic compounds in aqueous samples. Among the synthesized nanocomposites and pristine PBT nanofibers,... 

The flux behavior during the industrial cross-flow ultrafiltration of apple juice in a batch process was modeled using a combination of the fouling and concentration polarization models. It was observed that the major flux reduction was at the beginning and at the end of operation due to fouling and increasing solute concentration in the feed tank, respectively. The fouling phenomenon was analyzed by classical and empirical models and it was shown that the empirical one has the best correlation within less than 0.3% error for each experiment. The most significant advantage of this model is its ability to predict a steady flux, while other models predict zero flux at infinite time, which is... 

Stochastic parameters of self-agglomerated metallic nanoparticles on a dielectric film surface were studied using atomic force microscopy (AFM) analysis. In this regard, the rough surfaces including the nanoparticles were analyzed and characterized using structure function, roughness exponent and power spectrum density of the AFM profiles and their gradients, for different metal concentrations and heat treatment temperatures. The diffusion parameters, such as activation energy, of the nanoparticles initially accumulated on the surface into a porous and aqueous silica thin film were obtained using the AFM spectral analysis of the profiles and their gradients. It was found that the tip... 

In this work, a mathematical model was developed to simulate the urinary concentration mechanism. A 3-D geometry was derived based on the detail physiological pictures of rat kidney. The approximate region of each tubule was obtained from the volume distribution of structures based on Walter Pfaller's monograph and Layton's region-based model. Mass and momentum balances were applied to solve for the change in solutes concentration and osmolality. The osmolality of short and long descending nephrons at the end of the outer medulla was obtained to be 530 mOsmol/kgH2O and 802 mOsmol/kgH2O, respectively, which were in acceptable agreement with experimental data. The fluid osmolality of the short... 

Clay liners are widely used as porous membrane barriers to control solute transport and to prevent the leakage of leachate both in horizontal and vertical flow scenarios, such as the isolated base and ramps of sanitary landfills. Despite the primary importance of saturated hydraulic conductivity in a reliable simulation of fluid flow through clay barriers, there is no model to predict hydraulic conductivity of clayey soils permeated with saline aqueous solutions because most of the current models were developed for pure water. Therefore, the main motivation behind this study is to derive semi-empirical models for simulating the hydraulic conductivity of clayey soils in the presence of...