Sharif Digital Repository

Green and simple synthesis strategies have gained tremendous popularity for the production of anisotropically-shaped noble metallic nanoparticles. The long-term stability of the produced particles, the short timescale of the target reaction(s), as well as the use of non-toxic chemicals, are pivotal features of a useful green procedure. Herein we describe a simple and convenient wet-chemical approach to synthesize stable, non-toxic and water-soluble small gold nanotriangles (GNTs) and gold nanospheres (GNSs) in one step at room temperature, using Tween 20 and Tween 80, respectively. A high level of purity and monodispersity was obtained for the GNTs, in addition to an excellent colloidal... 

In this article, smoothed particle hydrodynamics method is applied in order to study the free surface flow generated by two-dimensional planing flat plate. For this purpose, a two-dimensional smoothed particle hydrodynamics code is developed and validated by the well-known dam breaking problem. Four trim angles and three different velocities are considered to perform a parametric study to examine their physical effects. The obtained results from smoothed particle hydrodynamics are compared against the corresponding Reynolds-averaged Navier Stokes solutions. It is observed that at lower velocities, there exists a good agreement between the smoothed particle hydrodynamics and Reynolds-averaged... 

Mesoscopic hydrodynamic equations are solved to investigate late-stage evolution of thin liquid films over step topographies. Different geometrical parameters including step height and initial position and configuration of resultant masses of dewetting (droplets) are probed to find their effects on the mass evolution of the system. Our results indicate that increasing the step height and locating the droplets close to the step enhance the dynamics and accelerate smaller droplet collapse  

Mesoscopic hydrodynamic equations are solved to investigate coarsening dynamics of two interacting nanodroplets on chemically patterned substrates. The effects of different parameters such as the surface chemical pattern, the slip length, the profile of the disjoining pressure, the size of the droplets, and the contact angles on the coarsening are studied. Our results reveal that the presence of a chemical heterogeneity can enhance or weaken the coarsening dynamics depending on the pattern type and positions of the droplets on the substrate. Also increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process, and the profile of the... 

Foaming and crystallisation behaviours of compacted glass powders based on a diopside glass-ceramic composition were investigated using the sintering route. The foaming agent was 2 wt.% SiC particles. The effect of PbO on the foaming ability of glasses was investigated. The results showed that the addition of PbO not only improved the foaming ability, by improving the wettability of the glass-SiC particles but also increased the crystallisation temperature and widened the temperature interval between the dilatometric softening point and the onset of crystallisation. The glass-SiC wetting angle was decreased from 85°for the lead-free glass, to 55°for the glass that contains 15 wt.% PbO  

This paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and Casimir force. At the First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained. The dependency of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of casimir force can considerably reduce the stability limits of nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the casimir force applied to the... 

We use three-dimensional molecular dynamics simulation to investigate the driven flow between two parallel plates separated by argon atoms. Our simulations show that fluids in such channels can be continuously driven. Difference in surface wettability can cause a difference in fluid density along the nano channel. To control the nanochannel temperature walls, we use the thermal wall idea, which models the walls using atoms connected to their original positions by enforcing linear spring forces. In this study, we propose a nanochannel system in which, half of the channel has a low surface wettability, while the other half has a higher surface wettability and that the middle part of channel... 

The coupling effect between torsion and bending in nano/micromirrors under the combined effect of capillary force and van der Waals (vdW) force is presented in this paper. At the first, the dimensionless equations governing the statical behavior of the nano/micromirror are obtained using the minimum total potential energy principle. Then the equations governing the pull-in state of the mirror are obtained using the implicit function theorem. The related results show that neglecting bending effect can lead to considerable overestimation in predicting the pull-in limits of the nano/micromirror under combined vdW and capillary forces. It is observed that vdW force reduces the pull-in angle and... 

Porous medium characteristics (e.g., pore geometry and medium heterogeneity) as well as the chemical nature of the co-solvents crucially affect the oil displacement efficiency during solvent flooding processes. In this work, initially saturated models with heavy crude oil were used to perform a series of solvent injection experiments. Several onequarter five-spot micromodels with pre-designed pore geometry were constructed and used. In addition, rock-look-alike flow patterns generated from thin sections of sandstone and dolomite reservoir rocks were etched onto glass plates to form micromodels mimicking the pore geometry and heterogeneity of these rocks. Four different groups of chemicals... 

Low cost dispersed supported cobalt oxide nanocatalysts on activated carbon (AC) were prepared by two different methods: (1) combined impregnation and deposition–precipitation (IMP-DP) and (2) heterogeneous deposition–precipitation (HDP). XRD, TEM, FESEM, BET and Boehm techniques were used for the characterization of the support and the catalysts. Characterization analyses indicated the negative effect of the wet impregnation method on the IMP-DP technique for the preparation of catalysts for the total oxidation of cyclohexane in air. The catalysts prepared by HDP and IMP-DP methods were found to have significant differences in oxidation activity, morphology, particle size, and shape of... 

Stepped planing hulls enable the feasibility of running at relatively low Drag-Lift ratio by means of achieving more optimal trim angle at high speeds. Currently, there is no precise method to analyze these hulls over the full range of operating speeds. In this study, a three-dimensional computational fluid dynamics (CFD) model using volume of fluid (VOF) approach is presented for examining the characteristics of a planing hull having one transverse step. A procedure is presented to transform a series of fixed-position simulations into a free to heave and pitch simulation. Resistance, lift, running draft, dynamic trim angle, and wetted area are compared with available experimental data and... 

Hydro collapsible soils are of kinds of problematic soils which show high shear strength at low degrees of saturation but due to wetting, their Meta stable structure collapses and will be subjected to large deformation. In this study by applying isotropic triaxial loadings to undisturbed samples, mechanical behavior of a highly collapsible loessial soil has been assessed. During tests, matric suction of the samples was controlled as well as the mean net stress, and the variation of the degree of saturation was monitored continuously. Two types of stress paths were conducted on the samples namely "Isotropic induced collapse" under applying constant matric suctions and "wetting induced... 

In this work, a newly formulated sulfonate-based surfactant and two other commercial sulfate-based surfactants with the capability of tolerating harsh underground reservoir conditions, such as high-saline formation water and high temperature, were prepared. Sodium metaborate as an effective alkali compound was also used to provide alkali-surfactant combination. Interfacial tension (IFT) measurements as well as wettability examinations for different salinities and mixture conditions were performed for an extended range of the chemical concentrations. The wettability tests including both contact angle measurements and Amott cell tests were performed on saturated Berea sandstone plug samples... 

This paper describes results of an advanced suction controlled triaxial test device on a loessial soil in an attempt to define the constitutive relationship between suction stress and matric suction (suction stress characteristic curve) for highly collapsible soils. Due to the presence of void spaces with different degrees of collapse potential within the soil matrix, the collapse phenomenon in loess is believed to be a continuous-stepwise reduction in volume rather than a sudden drop during wetting. Due to this unique volume change behavior, the definition of the suction stress characteristic curve for loess may require a soil-specific experimental testing approach capable of making precise... 

Silver nanostructures are very important agents in biomedical research, because of its unique activity against unfavorable processes in bioscience. In the current study, reagent-free facile preparation of silver nanoparticles (average diameter: 72 nm) and silver nanoparticles/ nanorods hybrid was reported via wet chemical synthesis method. Kappa-carrageenan (kC), a hydrophilic biopolymer with sulphate groups on its backbone, as capping agent was used in the reaction medium. Silver nanoparticles and silver nanoparticles/ nanorods formation was confirmed by SEM images. Further investigations were carried out using DLS data and GPC analysis  

In this work, the silver particle absorption and antibacterial activity of cotton fabric when modified by low temperature plasma were investigated. The modification consisted of plasma pre-functionalization followed by one-step wet treatment with silver nitrate solution. Oxygen and nitrogen were used as the working gases in the system, and the results were compared. The results showed that nitrogen plasma-treated samples can absorb more silver particles than oxygen-treated samples, and thus the antibacterial activity of the samples in this case, which was analyzed by the counting bacteria test, was increased considerably  

In this paper, a numerical model is developed for the fully coupled analysis of deforming porous media containing weak discontinuities which interact with the flow of two immiscible, compressible wetting and non-wetting pore fluids. The governing equations involving the coupled solid skeleton deformation and two-phase fluid flow in partially saturated porous media are derived within the framework of the generalized Biot theory. The solid phase displacement, the wetting phase pressure and the capillary pressure are taken as the primary variables of the three-phase formulation. The other variables are incorporated into the model via the experimentally determined functions that specify the... 

The small-strain shear modulus Gmax is a key material parameter in modeling the behavior of soils subjected to dynamic loading. Recent experimental results indicate that seasonal weather interaction with near-surface soils causes Gmax to change by up to an order of magnitude in some climates, with a hysteretic response upon drying and wetting. The increase in Gmax during drying and the stiffer response during subsequent wetting have been postulated to be due to plastic hardening during drying. To further understand this behavior, a series of isotropic compression tests were performed on compacted silt specimens at different values of matric suction to evaluate changes in the preconsolidation... 

A literature review of laboratory and field scale studies on low salinity water (LSW) injection showed that the salinity and composition of injected water can have a significant impact on oil recovery. Historically, extensive research has been completed to understand the mechanisms and factors affecting LSW injection. However, although numerous mechanisms have been proposed to describe the interactions in the target process, none have been widely accepted. In this study, waterflooding tests were used to investigate the advantages, disadvantages, and effect of LSW injection. In laboratory tests, two different brines and crude oil of one of Iran's southern reservoirs were used to assess the... 

A very simple and well-controlled procedure was employed to prepare CdS nanoparticle/few-layer MoS2 nanosheet/Indium tin oxide (ITO) thin film heterostructures. To tune and fabricate the CdS/MoS2(t)/ITO thin films with various surface topographies, first electrophoretic deposition (EPD) was used to deposit MoS2 nanosheets on the ITO substrate under an optimized applied potential difference (8 V) for different deposition times (t) of 30, 60, 120 and 240 s. Then, CdS nanoparticles were deposited via a successive ion layer adsorption and reaction (SILAR) technique. The highest photo-current density of 285 μA cm-2 was measured for the CdS/MoS2(60 s)/ITO sample, which was about 2.3 times higher...