Sharif Digital Repository

Chemical bioreactions are an important aspect of many recent microfluidic devices, and their applications in biomedical science have been growing worldwide. Droplet-based microreactors are among the attractive types of unit operations, which utilize droplets for enhancement in both mixing and chemical reactions. In the present study, a finite-volume-method (FVM) numerical investigation is conducted based on the volume-of-fluid (VOF) applying for the droplet-based flows. This multiphase computational modeling is used for the study of the chemical reaction and mixing phenomenon inside a serpentine microchannel and explores the effects of the aspect ratio (i.e., AR = height/width) of... 

In this paper, a multiplate nonlocal shear model and molecular dynamic simulations are presented to investigate the effects of interlayer shear and nonlocality on the natural frequencies of multilayer graphene sheets (MLGSs). From one aspect in the optimal design of such structures, the interaction between graphene layers, which can significantly vary the static and dynamic behavior due to lack of solidity of layers stack, should be considered. On the other hand, it is requied that the nonlocality phenomenon which has an effective role in the mechanical analysis of nanostructures is taken into account. To this aim, the equation of motion along with corresponding boundary conditions is... 

Biogenic amines (BAs) are known as substantial indicators of the quality and safety of food. Developing rapid and visual detection methods capable of simultaneously monitoring BAs is highly desired due to their harmful effects on human health. In the present study, we have designed a multicolor sensor array consisting of two types of gold nanostructures (i.e., gold nanorods (AuNRs) and gold nanospheres (AuNSs)) for the discrimination and determination of critical BAs (i.e., spermine (SM), tryptamine (TT), ethylenediamine (EA), tyramine (TR), spermidine (SD), and histamine (HT)). The design principle of the probe was based on the metallization of silver ions on the surface of AuNRs and AuNSs... 

This study deals with the geometrically non-linear vibration analysis of concrete shallow funicular shells of rectangular plan with four clamped edges under impulse loads. The shape of a concrete funicular shell is such that the shell is subjected to pure compression under its dead weight. Following the existing method presented for the linear vibration analysis, the geometrically non-linear vibration analysis is considered through the use of non-linear shallow shells theory. Each displacement component is expanded in a double Fourier series and the kinetic energy, the elastic strain energy and the virtual work done by external forces are calculated in terms of the displacement components.... 

This study investigates the various effects of Soil-Structure Interaction (SSI) on the seismic behavior of steel frames with Steel Plate Shear Wall (SPSW) lateral resisting systems. Nine steel frames with various aspect ratios are studied under multiple seismic hazard levels. The SPSWs are modeled based on the strip model concept, and the Soil-Structure Systems are simulated using the substructure method. The soil beneath the structure is considered as a homogeneous elastic half-space. The Endurance Time method is exploited for nonlinear dynamic analysis of the fixed-base structures and soil-structure systems. Results indicate that use of fixed-base models leads to the significant... 

The water desalination process using nanoporous single-layer graphene membranes is simulated through classical molecular dynamics. The effect of nanopores shapes on the capacity of the membrane for filtration of water is investigated. According to the results, the geometry of the nanopores considerably affects the performance of the membrane and can completely change the water flow rate and salt rejection. The results reveal that the effective area of the nanopores plays a critical role and for a better understanding of the impact of this parameter, aspect ratio and the equal diameter of noncircular pores based on different methods such as equal area, equal perimeter, and hydraulic diameter... 

Experimental and numerical study regarding the uniaxial tensile test and the forming limit diagram are addressed in this paper for AL2024 with the face-centered cube structure. First, representation of a grain structure can be obtained directly by mapping metallographic observations via scanning electron microscopy approach. Artificial grain microstructures produced by Voronoi Tessellation method are employed in the model using VGRAIN software. By resorting to the finite element software (ABAQUS) capabilities, the constitutive equations of the crystal plasticity were utilized and implemented as a user subroutine material UMAT code. The hardening parameters were calibrated by a trial and... 

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. Concern has been raised about the identity of the author “David Ross” as the listed institution has denied the affiliation of a person with this name. Further inquiry revealed that the names of the co-authors were added to the revised version of the article without notifying the handling Editor, which is contrary to the journal policy on changes to authorship. Also, the co-authors were not able to provide a reasonable description of their contribution to the article.... 

Prediction of the anti-plane moduli of solids consisting of a given distribution of unidirectionally aligned elliptic multi-coated fibers with interfacial damage is the focus of this paper. The fibers and their coating layers may be in the order of nano or micro scales. All the constituent phases of the composite are supposed to be described in terms of couple stress elasticity. Accordingly, the bounds for the overall shear moduli of the aforementioned composites are provided by employing the principles of minimum potential and complementary energies. Certain subtleties associated with the elliptic multi-coated fibers for three cases of pure sliding (completely damaged), imperfect (partially... 

Particle size and shape of iron ore concentrate are effective parameters in the production of quality green pellets. In this research, the effect of particle morphology on green pellet quality was studied. It was concluded that pellet quality improved with increasing specific surface area. Drop number and green compression strength of pellets ground by HPGR were found to be superior over those ground in the ball mill. The chief reasons were related to particle shape and the fraction of fine particles. Smaller particle size results in a higher order of bonding between particles and therefore the formation of a stronger system. Also, the rougher and less circular shape of particles resulted in... 

A new characteristic-based method is developed and used for solving the mixed and forced convection problems. The nano-fluid flow with heat transfer is simulated with a novel characteristic-based scheme in closed domains with different aspect ratios. For this purpose, a FORTRAN code has been written and developed. Water as a pure fluid and water-titanium dioxide as a nano-fluid were considered. The governing equations are solved by the finite volume utilizing a characteristic-based scheme for the convective fluxes. The simulation is done at Grashof numbers from 100 to 104, Reynolds numbers from 100 to 1000, and volume fractions of nano-particles from 0% to 10%. Streamlines, isotherms,... 

In recent years, thin silver nanowires (Ag NWs) with diameters smaller than 150 nm have been synthesized by implementation of NaCl or FeCl3 as reaction promoters and high molecular weight polyvinylpyrrolidone (PVP) as the capping agent. However, the yield of Ag NWs still remains low, mostly due to the insufficient aspect ratio (AR) of the synthesized nanostructures and the production of Ag nanoparticles, which is an undesirable by product. This study proposes a modified technique to alleviate the problem by using a mixture of FeCl3/CuCl2 as the reaction promoter and two different types of PVP with molecular weight of 360 k and 40 k as the capping agents. The appropriate mixtures of... 

Resistive pulse sensing (RPS) has proved to be a viable method for the detection and characterization of micro and nano particles. Modern fabrication methods have introduced different nanopore geometries for resistive pulse sensors. In this paper, we have numerically studied the effects of membrane thickness and the pore's cone angle, as the main geometrical parameters, on the sensing performance of the nanopores used for nanoparticle detection in the resistive pulse sensing method. To compare the sensing performance, three resistive pulse quality parameters were investigated-sensitivity, pulse duration and pulse amplitude. The thorough investigation on the relations between the geometrical... 

In the present study, based on 12-unknown higher order shear deformation theory (HSDT), buckling and vibration analysis of FG-CNTRC rectangular plate are investigated for various types of temperature distribution and boundary conditions. Implementing Hamilton’s principle, the equations of motion are derived and solved by adopting the Navier solution for the simply supported boundary conditions and DQM method for other boundary conditions. Validation is carried out by comparing the numerical results with those obtained in the open literature. Also, a detailed parametric analysis is carried out to illuminate the influence of different system parameters such as CNT distributions, CNT volume... 

In this paper, a new approach for multi-objective robust optimization of flutter velocity and maximum displacement of the wing tip are investigated. The wing is under the influence of bending–torsion coupling and its design variables have different levels of uncertainty. In designing and optimizing wings with a high aspect ratio, the optimization process can be done in such a way to increase the flutter velocity, but this can increase the amplitude of the wing tip displacement to a point that leads to the wings damage and structural failure. Therefore, single-objective design optimization may lead to infeasible designs. Thus, for multi-objective optimization, modeling is based on the... 

In this work, the optical responses of Fe3O4@Au and Fe3O4@Ag are comprehensively investigated using the discrete dipole approximation. It is found that the resonance wavelength and absorption efficiency strongly depend on the composition of the core and shell, geometry of the nanoparticles, core to particle volume ratio, core radius and shell thickness. The strongest impact is due to the shell material, the shape of the nanoparticles and their combination. When the composition of the shell is changed from gold to silver, instead of one fundamental resonance peak the absorption spectrum shows two, corresponding to the bonding plasmon mode at the nanoparticle-environment interface and... 

Background and objective: In this study, the effect of the second excitation frequency mode under different conditions on the fluid streaming and its microparticles displacement is investigated. Methods: For this purpose, some variable parameters such as the particle diameter, microchannel aspect ratio, and applied frequency modes have been selected to study. The resulted acoustic streaming was scrutinized to understand the physics of the problem under different geometrical and input conditions. Finally, the effect of the increasing the microparticle size and aspect ratio of the microchannel, simultaneously, has been evaluated. Results: The results demonstrated that increasing the... 

In this study, the effects of geometry and operating conditions upon the thermal and hydraulic performance of Finned Microchannel Heat Sink (FMCHS) were investigated. Water and aluminum were considered as fluid and solid for the computational domain (30 mm × 0.8 mm × 0.8 mm). The Microchannel (MC) was supposed to have 0.65 mm height with an aspect ratio of 0.5. CFD analysis was applied for the assessments of four-types of micro-fins (i.e., conical, pyramidal, cylindrical and cubical). In order to evaluate the effects of height, diameter, the spacing of fins and Reynolds number on the overall performance of FMCHS, central composite design at five levels was used to generate design points.... 

The behavior of low-speed liquid jets emerging from rectangular orifices into a quiescent air is studied numerically. After ejection, the rectangular cross-section transforms into an elliptical form along the jet and while axis-switching includes elliptical cross-sections only, the rectangular shape never establishes again. The optimum wavenumber, corresponding to the most dominant wave, is found to be greater in orifices with higher aspect ratios and, as a result, breakup length of the jet will be shorter. The breakup length decreases exponentially with the initial amplitude of disturbances. Moreover, it is observed that the form of final breakup leads to elimination of the satellite... 

Numerical simulations are performed to provide an in-depth insight into the effect of instabilities on liquid jets discharging from elliptical orifices. The axis-switching phenomenon and breakup are simulated and characterized under the effect of disturbances imposed at the nozzle exit. The simulations are based on the volume of fluid approach and an adaptive meshing. A range of orifice aspect ratios from 1 to 4 at the Rayleigh breakup regime is considered. The evolution of the jet cross section and axis switching under the influence of disturbances is compared with that of nonperturbed elliptical jets. It is found that the axis-switching repetition and breakup length exponentially decrease...