جستجوی مقالات مرتبط با کلیدواژه « Nano » در نشریات گروه « برق »

One of the major challenges facing researchers of tissue engineering is scaffold design with desirable physical and mechanical properties for growth and proliferation of cells and tissue formation. In this paper, firstly, β-tricalcium phosphate (β-TCP) nano powders with particle size of 50-70 nm were synthesized using a simple sol–gel route with calcium nitrate and potassium dihydrogenphosphate as calcium and phosphorus precursors, respectively. Then the porous ceramic scaffold containing 40, 50 and 60wt% of nβ-TCP was prepared by the polyurethane sponge replication method. The scaffolds were coated with P3HB for 30 s and 1 min in order to increase the scaffold’s mechanical properties. XRD, XRF, SEM, TEM and FT-IR were used in order to study the phase and element structure, morphology, particle size and determination of functional groups, respectively. Based on the results of compressive strength and porosimetry tests, the most appropriate type of scaffold is 50 wt% of nβ-TCP immersed for 30 sec in P3HB with 75% porosity in 200-600 μm, with a compressive strength of 1.09 MPa and a compressive modulus of 33MPa, which can be utilized in bone tissue engineering.

In this paper, zinc oxide (ZnO), copper oxide (CuO) and titanium oxide (TiO2) nanoparticles were prepared using sol-gel method. The structural properties of these nanoparticles were characterized using X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). SEM images revealed that the average size of zinc oxide, copper oxide and titanium oxide nanoparticles to be about 37 nm, 86 nm and 50 nm, respectively. Then, nano-composites of metal oxide were produced by Polyvinyl Alcohol (PVA). The antibacterial activity of zinc oxide, copper oxide and titanium oxide nano-composites against human pathogenic bacteria, mainly Escherichia coli HB101 (gram-negative) have been studied using drop test during the time period of 15 minutes, 30 minutes, 1 hour, 2 hours, 12 hours and 24 hours generated reviews.According to the results obtained with the nano-composite zinc oxide nanoparticles exhibit highest antibacterial properties.

Material removal rate and surface roughness are the most important performance measures in nano-finishing processes and these are largely influenced by the process parameters. The optimum combination of process parameters for nano-finishing processes is determined in this paper using a recently proposed optimization algorithm, named as Jaya algorithm. The results show the better performance of the Jaya algorithm over the other approaches attempted by the previous researchers such as genetic algorithm and desirability function approach for the same nano-finishing processes. The results obtained by the Jaya algorithm are useful for the real production systems.

The equal channel angular rolling process was successfully performed on commercial pure copper. After 4 passes of this process, grains with a diameter of about 70- 500 nm were formed. The fatigue test results showed that the ultra-fine grained copper represents a longer lifetime under stress-controlled fatigue. To clarify the formation process of surface damage, morphological changes in the fractured surface were monitored by scanning electron microscopy.

electric eld. In this work, a wire-cylinder corona charger is presented, redesigned, and aerodynamically optimized. An initial 2D axisymmetric geometry of the charger was employed for the simulations using the Computational Fluid Dynamics (CFD) commercial code FLUENT 6.3.26. Through successive attempts, a new geometry was obtained by streamlining the walls to eliminate the undesired vortices produced in the flow eld of the previous ones. The process optimized the charger by minimizing losses and dilutions of the particles. For electrical simulations of the charger, a new numerical algorithm was designed based on the steady-state corona discharge to work with segregated solvers to satisfy governing equations. The algorithm was validated using a one-dimensional semianalytic solution of corona discharge. Tracing particles for the optimized geometry, the percentage of losses was calculated 6%, whereas the loss in the old geometry was more than 30%. The average charge and charge distributions induced on particles were also calculated with evaluation of the residence times in the charger.

BF3/nano-sawdust as a green, inexpensive, natural, biodegradable and readily available biopolymer solid acid catalyst was synthesized and characterized. This catalystwas used successfully for the synthesis of various tri-substituted imidazoles in high yields under solvent free conditions.

When an applied shear to a fluid results in steep rise in its viscosity, it is referred to as Shear Thickening Fluid (STF). In this study, we investigate rheological response of bimodal against mono-dispersed nano sized silica particles in an STF system. Two sizes of nano-silica particles (50 nm fumed silica and 12 nm colloidal silica) were dispersed in polyethylene glycol in various compositions and were compared with monodispersed STF. Results showed lower critical shear rate for shear thickening in bimodal nanoparticle containing STF than mono-dispersed STF. Higher viscosities were also observed in di erent compositions of bimodal system. Examination of both STF systems under oscillatory stress condition revealed faster response by the bimodal system. Results also indicated that the storage and loss modulus for the bimodal STF system had low critical angular frequency compared to mono-dispersed STF. Study of relaxation time spectrum diagram for the two STFs showed that relaxation time for mono-dispersed STF was faster than that for bimodal STF system.

Design of a sca old with appropriate physical and mechanical properties for tissue engineering is a major challenge. In this research, the e ects of nano-titania (nTiO2) on the physical and mechanical properties of a nano-bioglass (nBG) sca old were evaluated. First, nBG powder with a grain size of 100-110 nm was prepared using the method of melting pure raw material at a temperature of 1400C. Then, a porous ceramic sca old of nBG/nTiO2, with 30 wt% of nBG, containing di erent weight ratios of nano-titania (3, 6 and 9 wt% nTiO2 with a grain size of 35-37 nm), was prepared using the polyurethane sponge replication method. XRD, XRF, SEM, FE-SEM and FTIR were used to study the phase and elemental structures, morphology, particle size, and determination of functional groups, respectively. XRD and XRF results showed that the type of produced bioglass was 45S5. he results of XRD and FT-IR showed that the best temperature to produce a bioglass sca old was 600C, because, at this temperature, the crystal was obtained, and the main sign of the obtained crystal was the presence of Na2Ca2Si3O9 crystal. The mechanical strength and modulus of the sca old improved by adding nTiO2 to the nBG sca old. The results showed that the sca olds have 80-88% porosity at the range of 200- 600 m; a compressive strength of 0.04-0.16 MPa, and a compressive modulus of 4-13.33 MPa, illustrating that they could be good candidates for bone tissue engineering.

Undoped and copper doped nickel oxide films, prepared onto glass substrate by spray pyrolysis method, were studied from various physical view points including: morphological, structural, optical, electrical and thermo-electrical properties. The XRD patterns show the nano-sized grains have cubic polycrystalline nature (with no additional related Cu-content phase) and the data analysis revealed while the crystallite sizes are decreased (13-10.5 nm) the dislocation density are increased (5.92×10-3 - 9.07×10-3 nm-2) with increments in the doping density. The electrical and thermo-electrical data (Seebeck effect) confirmed more substitutions of Cu ions with Ni2+ ions and in turn more p-type conductivity in samples with higher doping. Optical measurements showed the direct and indirect band gaps of the transparent conductive layers are decreased. These variations are in good agreement with the variations of the crystallite sizes and carrier densities of the samples

A facile and environmentally benign procedure for the synthesis of pyranopyrazoles and biscoumarin derivatives، using non-toxic and magnetically separable catalyst in water as green solvent، is reported.

A novel micro/nano-porous superabsorbent hydrogel was synthesized via graft copolymerization of acrylamide (AAm) onto salep (a polysaccharide mixture) and gelatin (a protein) hybrid backbone, after hydrolysis of this system. The Taguchi method was applied for the experiments and standard 18 orthogonal arrays (OA) with seven factors and three levels for each factor proposed trial conditions. Considering the results of 18 trials according to analysis of variance (ANOVA), optimum conditions were suggested. In addition, swelling kinetics, swelling in various organic solvents, the absorbency under load (AUL) and On-Off switching behavior were investigated. Also, the hydrogel formation was confirmed by Fourier transform infrared spectroscopy (FTIR). Surface morphology of the synthesized hydrogels was assessed by scanning electron microscope (SEM) and showed micro/nano-porous structure. Also, the surface area and total pore volume of the optimized hydrogel were measured by Brunauer-Emmett-Teller (BET) technique.

This paper focuses on a theoretical analysis of an AFM based nano-manipulation in liquid environment. To achievethis goal, major forces in liquid environment were reviewed and the of manipulation processes was modelled by introducing the effect of intermolecular forces and hydrodynamic forces. Dynamic behaviour of pushing a gold nanoparticle of 50-nm radius on a silicon substrate at a velocity of 100 nm/s was investigated. A virtual reality user interface was also implemented and evaluated in liquid environment so that the users can get a senseof forces. The results show that, in comparison to air, the required forces and time are increased by 2 and 6.5%, for sliding and 2 and 4.3% for rolling in liquid environment. Furthermore for various submerged lengths of the cantilever in water, forces and time value are varied 8 and 10.5% respectively.Based on the simulation a result, sliding occurs in nominal values and critical forces and manipulation time in liquid environment increases over the values. For biologicalmanipulation purposes liquid environment is superior in comparison to air and the obtained results are verified by existing experimental.

Simulation of manipulation is a basic tool for accurate and controllable displacement of bodies and particles at micro and nano scale. The atomic force microscope (AFM) system has become a useful tool for direct measurements of micro and nano structural parameters and unraveling the intermolecular forces at nanoscale level with atomic-resolution characterization. Friction forces are one of the parts of surface properties which play an important role in manipulation of nanoparticles. In order to gain more precise manipulation, different friction models have been developed one of which is LuGre model. In this paper sensitivity of manipulation of nanoparticle has been analyzed to dimensional and environmental parameters based on LuGre friction model using Sobol method. In previous work sensitivity analysis has been performed using graphical sensitivity analysis; hence the importance percentages of parameters are not clear but Sobol method, which is a statistical model, solves this problem. Results show that cantilever thickness is the most effective dimensional parameter on critical force value while cantilever length and width are less important. Environmental parameters such as cantilever elasticity modulus, substrate velocity and adhesion, respectively, take next orders.

Pull-in instability of Boron Nitride Nano-Beam (BNNB) under the combined electrostatic and Casimir force as nano-switch is presented. Using Euler-Bernoulli Beam (EBB) theory, nonlocal piezoelasticity theory, von Karman geometric nonlinearity and virtual work principle, the nonlinear governing di erential equations are obtained. The equations are discretized by two types of numerical methods, namely the Modi ed Adomian Decomposition (MAD) method and Di erential Quadrature Method (DQM). Analysis of lower pull-in voltage values is considered for nano-switches with di erent boundary conditions. The detailed parametric study is considered, focusing on the remarkable eff ects of nonlocal parameter, beam length, boundary condition, geometrical aspect ratio and gap distance on the behavior of the pull-in instability voltage. The obtained results of DQM and MAD are compared with published relevant study. This work is hoped to be useful in designing and manufacturing of Nano-Electro-Mechanical Systems (NEMS) in advanced applications such as high-tech devices and nano-transistors with great applications in computer industry.

We present a micro/nano-machining process to introduce nanostructured poly-silicon layer on the gate region of the pH-sensitive field effect transistors. Decoration of the gate of the field effect transistors by nanostructures plays an important role to improve the sensitivity of the pH-sensitive FETs. Electron beam lithography was exploited to realize the poly-Si nanopillars on the gate surface. Comparison between different micro and nanostructures demonstrates the potential of nanopillars to be utilized on the gate of this device rather than micro-conical structures (different size and shapes) and vertically carbon nanotubes. A high sensitivity of 500 mV/pH has been achieved, through the incorporation of silicon based nanopillars.

Nowadays, designing a reliable controller for an Atomic Force Microscope (AFM) during the manipulation process is a main issue, since the tip can jump over the target nanoparticle and, thus, the process can fail. This study aims to design a Sliding Mode Controller (SMC) as a robust chattering-free controller to push nano-particles on the substrate. The first control purpose is positioning the micro cantilever tip at a desired trajectory by the control input force, which can be exerted on the micro cantilever in the Y direction by an actuator located at its base. The second control target is the micro-positioning stage in X, Y directions. The simulation results indicate that not only are the proposed controllers robust to external disturbances and nonlinearities, such as deflection of the AFM tip, but are chattering free SMC laws that are able to make the desired variable state to track a specified trajectory during a nano-scale manipulation.

Nano- TiCl4.SiO2 is an efficient, readily available and reusable catalyst for the synthesis of 1, 2, 4, 5-tetrasubstituted imidazoles using benzil, aromatic aldehyde and an amine in the presence of ammonium acetate. The one-pot procedure is very simple with good to excellent yields.