Sharif Digital Repository

In this paper, size dependent static behavior of micro and nano cantilevers actuated by a static electric field including deflection and pull-in instability, is analyzed implementing nonlocal theory. Euler-bernoulli assumptions are made to model the relation between deflection of the beam and bending moment. Differential form of the constitutive equation of nonlocal theory is used to find the revised equation for bending moment and substituting in the equilibrium equation of electrostatically actuated beams final nonlinear ordinary differential equation is arrived. Also the boundary conditions for solving the equation are revised and to analyze the size effect better governing equation is... 

The dynamic pull-in voltage as a criterion for the system stability is one of the most important effects considered with the dynamics of microstructures. In this study effect of microbeam electrical resistivity on the pull-in voltage of an electrostatically actuated microbeam is investigated. Assuming Euler-Bernoulli theory for the microbeam, two coupled nonlinear partial differential equations are derived for the beam deflection and voltage. The one parameter Galerkin method is implemented to transform the equations to a set of nonlinear coupled ordinary differential equations. Obtained equations are solved implementing the differential quadrature method (DQM). Variation of dynamic pull-in... 

In this study vibration amplitude, frequency and damping of a microbeam is controlled using a RLC block containing a capacitor, resistor and inductor in series with the microbeam. Applying this method all of the considerable characteristics of the oscillatory system can be determined and controlled with no change in the geometrical and physical characteristics of the microbeam. Euler-Bernoulli assumptions are made for the microbeam and the electrical current through the microbeam is computed by considering the microbeam deflection and its voltage. Considering the RLC block, the voltage difference between the microbeam and the substrate is calculated. Two coupled nonlinear partial... 

Nonlinear vibration of a microbeam actuated by a suddenly applied voltage with considering the effect of voltage distribution on the beam due to electrical resistivity of beam is investigated. Homotopy perturbation method is implemented to solve the coupled nonlinear partial differential equations of motion. The vibration frequency variation and damping at various resistivities is studied. Considering resistivity, effect of applied voltage and beam length on the frequency shift and damping ratio is analyzed. Findings indicate there exists a jump in frequency shift and damping ratio at a critical resistivity. Variation of critical resistivity with respect to modulus of elasticity and beam... 

Some tetra substituted derivatives of 2,2′ and 4,4′ bithiazoles have been synthesized and characterized in various solvents  

We report here a newly and facile synthesis of the phospholipids@gold nanoflowers (AuNFs) from intact cells as a new biomimetic organic-inorganic hybrid. The most appealing feature of this nanostructure is its dual-absorbing peak in near infrared (NIR) and visible region of spectra, which makes them a potential light-sensitive agent for reactive oxygen species (ROS)-induced apoptosis. Here, in contrast to previous studies, proposed nanostructures are synthesized in a one-pot reaction using phospholipids present in living cell membranes (as a donor cell) with detectable micro process of AuNF formation. The properties of the resulting AuNFs were evaluated through transmission electron... 

This paper presents an effective control scheme in dc microgrids to precisely share the load current oscillatory and dc components among distributed generation (DG) units. The proposed control strategy includes current and voltage control blocks. The current control block consists of oscillatory and dc current-sharing units. The main idea of the proposed method is to share the load current oscillatory and dc components among the DG units based on their rated power, by assigning appropriate output impedance values and droop coefficients to each DG unit. The voltage control block is a multiloop voltage control unit employed to control the microgrid voltage. The detailed model of the proposed... 

Zeolitic imidazole frameworks (ZIFs) provide an exciting platform to design and fabricate non-precious-metal carbon-based catalysts for oxygen reduction/evolution reaction (ORR/OER). Herein, we elaborately design a facile enzyme-assisted synthetic strategy that enables to tailor the ZIFs precursors into structural stable decussation shape, which derived Co nanoislands grafted on decussate N-doped carbon nanoleaves (D-Co@NC) can well retain the interpenetrating nanostructure. Benefiting from the combined advantages of compositions and interpenetrating nanostructures, D-Co@NC possesses 5.2 times higher exposed electrochemical active area than the conventional dodecahedral one, thus endowing... 

The adhesion and mechanical properties of hydrogels used for vascular wound repair often deteriorate dramatically on wet surfaces, resulting in ineffective repair. In this work, a poly(N-isopropyl acrylamide-co-dopamine methacrylamide) nanogel with dopamine groups was synthesized and introduced into a polyacrylamide (PAAm) hydrogel to produce temperature-responsive hydrogels, which greatly improved mechanical and adhesive properties of PAAm hydrogels. Nanogel-reinforced PAAm (NR-PAAm hydrogel) can adhere to the surface of various solid materials and biological tissues through special physical interactions, which exhibited different mechanical and adhesion properties as temperature changes... 

As an important precursor of crystalline phases, amorphous calcium carbonate (ACC), especially ultrasmall ACC clusters, have been attracting great interest in fundamental research, materials chemistry, as well as industrial applications. However, it is still challenging to synthesize stable ACC clusters in water that can be isolated and concentrated without severe aggregation. Herein, we report a facile dialysis method for producing colloidally stable ACC clusters that are well dispersed in water with the protection of specific polycarboxylic acids, which could be also easily deprotected by small-molecule acids like sodium citrate. Inherent proto-calcite short-range order is found to be... 

As an important precursor of crystalline phases, amorphous calcium carbonate (ACC), especially ultrasmall ACC clusters, have been attracting great interest in fundamental research, materials chemistry, as well as industrial applications. However, it is still challenging to synthesize stable ACC clusters in water that can be isolated and concentrated without severe aggregation. Herein, we report a facile dialysis method for producing colloidally stable ACC clusters that are well dispersed in water with the protection of specific polycarboxylic acids, which could be also easily deprotected by small-molecule acids like sodium citrate. Inherent proto-calcite short-range order is found to be... 

We study the asymmetric primordial fluctuations in a model of inflation in which translational invariance is broken by a domain wall. We calculate the corrections to the power spectrum of curvature perturbations; they are anisotropic and contain dipole, quadrupole, and higher multipoles with non-trivial scale-dependent amplitudes. Inspired by observations of these multipole asymmetries in terms of two-point correlations and variance in real space, we demonstrate that this model can explain the observed anomalous power asymmetry of the cosmic microwave background (CMB) sky, including its characteristic feature that the dipole dominates over higher multipoles. We test the viability of the... 

To investigate the gas–solid flow pattern of a combustor-style fluid catalytic cracking regenerator, a laboratory-scale regenerator was designed. In scaling down from an actual regenerator, large-diameter hydrodynamic effects were taken into consideration. These considerations are the novelties of the present study. Applying the Eulerian–Eulerian approach, a three-dimensional computational fluid dynamics (CFD) model of the regenerator was developed. Using this model, various aspects of the hydrodynamic behavior that are potentially effective in catalyst regeneration were investigated. The CFD simulation results show that at various sections the gas–solid flow patterns exhibit different... 

Pesticides are widely used to increase agricultural productivity, however, weak adhesion and deposition lead to low efficient utilization. Herein, we prepare a nanopesticide formulation (tebuconazole nanopesticides) which is leaf-adhesive, and water-dispersed via a rapid nanoparticle precipitation method, flash nanoprecipitation, using temperature-responsive copolymers poly-(2-(dimethylamino)ethylmethylacrylate)-b-poly(ε-caprolactone) as the carrier. Compared with commercial suspensions, the encapsulation by the polymer improves the deposition of TEB, and the contact angle on foliage is lowered by 40.0°. Due to the small size and strong van der Waals interactions, the anti-washing efficiency... 

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative... 

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative... 

As a problem, generally, energy security components do not interfere with the calculation of the optimal energy supply situation. Energy security indices so-called ‘passive indices’ cannot illustrate comprehensive optimal situation. In this paper, we are looking to find a solution to make a framework of the impact of energy security on energy supply in order to obtain comprehensive analysis of the economic optimal point. Method is based on the competition of energy costs to meet demand during the study period. Threats that have been addressed in the energy security are seen as risky and stochastic parameters in the model. The nature of these parameters is of uncertainty type, therefore,... 

Background: In nuclear medicine application often it is required to use computational methods for evaluation of organ absorbed dose. Monte Carlo simulation and phantoms have been used in many works before. The shape, size and volume in organs are varied, and this variation will produce error in dose calculation if no correction is applied. Materials and Methods: A computational framework for constructing individual phantom for dosimetry was performed on five liver CT scan data sets of Japanese normal individuals. The Zubal phantom was used as an original phantom to be adjusted by each individual data set. This registration was done by Spherical Harmonics (SH) and Thin-Plate Spline methods.... 

Although the role of individual ingredients of hot mix asphalt (HMA) such as asphalt binder and aggregates on its performance is readily recognized, there is only limited understanding about the interactions between these components and the properties of binder-aggregate interface. In order to study the interactions between asphalt binder and mineral aggregates, an interfacial test method was developed and its effectiveness was evaluated. Interfacial interactions were evaluated by testing thin films of an asphalt binder interfaced with the surface of aggregates under two different modes of loading in shear: sinusoidal oscillation and monotonically increasing. An Interaction Parameter (IP)... 

Approximate solutions for vibrations of flexible beam-type appendages subjected to tip mass are studied while uniform and exponential profiles for arm deployment are simulated. Applying an equivalent dynamical system and following Lagrangian approach, the equations of motion of the system are derived as nonlinear ordinary differential equations (ODEs) (with time-varying coefficients), in which the effect of the tip mass can be considered as some nonlinearity added to the 'no tip mass' case dynamics. The approximate closed-form solutions are obtained through a novel methodology using a computer algorithm, in which the solutions of the 'no tip mass' case are expanded by imposing quadratic...