Gorji M.A.,University of Mazandaran
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016
In this paper, inspired by the ultraviolet deformation of the Friedmann–Lemaître–Robertson–Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as ΛCDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from weff=0 to weff=−2. Interestingly and nontrivially, the unstable de Sitter phase with weff=−1 is corresponding to Ωm=Ωd=0.5 and the universe crosses the phantom divide from the quintessence phase with weff>−1 and Ωm>Ωd to the phantom phase with weff<−1 and Ωm<Ωd which shows that the model is observationally viable. The results show that the universe finally ends up in a big rip singularity for a finite time proportional to the inverse of the minimum of the Hubble parameter. Moreover, we consider the dynamical stability of the model and we show that the universe starts from the matter dominated era at the past attractor with weff=0 and ends up in a future attractor at the big rip with weff=−2. © 2016 The Author
Sadeghi J.,University of Mazandaran |
Pourhassan B.,I.H.U. |
Pourasadollah F.,University of Mazandaran
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013
In this work, we follow Kim and Yamada [JHEP 1107 (2011) 120] and utilize AdS in light-cone frame to derive thermodynamical properties of two kinds of Schrödinger black holes with hyperscaling violation. In that case, we show entropy and temperature are depend on θ. In θ = 0 we see our results are agree with the work of Kim and Yamada. We also construct R-charged black hole with hyperscaling violation and obtain thermodynamical properties. © 2013 Elsevier B.V.
Hatami M.,Esfarayen University |
Hatami M.,University of Mazandaran |
Ganji D.D.,University of Mazandaran
Energy Conversion and Management | Year: 2014
In this study, heat transfer of a fin shaped microchannel heat sink (MCHS) cooled by Cu-water nanofluid is investigated and temperature distribution in solid section (fin) and fluid section (Cu-water) are obtained by porous media approach and least square method and the results are compared with numerical procedure. The effective thermal conductivity and viscosity of nanofluid are calculated by the Parsher and Brinkman models respectively and MCHS is considered as a porous medium proposed by Kim and Kim. Modified Darcy equation is applied to the fluid and porous medium for heat transfer between fluid and solid sections. In addition, to deal with nanofluid heat transfer, a model based on Brownian-motion of nanoparticles is used. The effects of the nanoparticles volume fraction, porosity, Darcy number, microchannel dimensions, etc. on temperature distribution, velocity and Nusselt number are considered. As an outcome, by increasing the nanoparticles volume fraction, Brownian motion of the particles which carries heat and distributes it to the surroundings increases, and consequently difference between coolant and wall temperature will become less. Also, the optimum point for MCHS design is calculated by minimizing the friction factor which obtained channel aspect ratio (αs) is 2.45. © 2013 Elsevier Ltd. All rights reserved.
Kafashi S.,University of Mazandaran
International Journal of Advanced Manufacturing Technology | Year: 2011
Process planning is an essential component for linking design and manufacturing process. Setup planning and operation sequencing are two most important functions in the implementation of CAD/CAPP/CAM integration. Many researches solved these two problems separately. Considering the fact that the two functions are complementary, it is necessary to integrate them more tightly so that performance of a manufacturing system can be improved economically and competitively. This paper presents a generative system and genetic algorithm (GA) approach to process plan the given part. The proposed approach and optimization methodology analysis constraints such as TAD∈(tool approach direction), tolerance relation between features and feature precedence relations to generate all possible setups and operations using workshop resource database. Tolerance relation analysis has a significant impact in setup planning for obtaining the part accuracy. Based on technological constraints, the GA algorithm approach, which adopts the feature-based representation, simultaneously optimizes the setup plan and sequence of operations using cost indices. Case studies show that the developed system can generate satisfactory results in optimizing the integrated setup planning and operation sequencing in feasible condition. © 2011 Springer-Verlag London Limited.
Khodadoust S.,University of Mazandaran |
Hadjmohammadi M.,University of Mazandaran
Analytica Chimica Acta | Year: 2011
A rapid and simple method for the extraction and preconcentration of N-methylcarbamates (NMCs) (carbofuran, carbaryl and promecarb) in water samples using dispersive liquid-liquid microextraction (DLLME) using chemometrics was developed. Influence variables such as volume of extracting (CHCl3) and dispersing solvents (ACN), pH and ionic strength, extraction time and centrifugation time and speed were screened in a 27-4 Plackett-Burman design was investigated. The significant variables were optimized by using a central composite design (CCD) combined with desirability function (DF). At optimum conditions values of variables set as 126μL chloroform, 1.5mL acetonitrile, 1min extraction time, 10min centrifugation at 4000rpmmin-1, natural pH, 4.7% (w/v) NaCl, the separation was reached in less than 14min using a C18 column and an isocratic binary mobile phase (acetonitrile: water (50:50, v/v)) with flow rate of 1.0mLmin-1. At optimum conditions method has linear response over 0.001-10μgmL-1 with detection limit between 0.0001 and 0.0005μgmL-1 with relative standard deviations (RSDs) in the range 2.18-5.06% (n=6). © 2011 Elsevier B.V.
Kiani F.,University of Mazandaran |
Nozari K.,University of Mazandaran
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014
We study a new type of the modified teleparallel gravity of the form F(T,Θ) in which T, the torsion scalar, is coupled with T, the trace of the stress-energy tensor. In a perturbational approach, we study the stability of the solutions and as a special case we find a condition for stability of the de Sitter phase. Then we adopt a suitable form for F(T,Θ) that realizes a stable de Sitter solution so that the stability condition creates a specific constraint on the parametric space of the model. Finally, the energy conditions in the framework of F(T,Θ) gravity is investigated. © 2013 The Authors. Published by Elsevier B.V.
Kiani K.,University of Mazandaran
Journal of Physics and Chemistry of Solids | Year: 2014
The vibration and instability of a single-walled carbon nanotube (SWCNT) under a general magnetic field are of particular interest to researchers. Using nonlocal Rayleigh beam theory and Maxwell's equations, the dimensionless governing equations pertinent to the free vibration of a SWCNT due to a general magnetic field were derived. The effects of the longitudinal and transverse magnetic fields on the longitudinal and flexural frequencies as well as their corresponding phase velocities were addressed and are discussed below. The critical transverse magnetic field (CTMF) associated with the lateral buckling of the SWCNT was obtained. The obtained results reveal that the CTMF increases with the longitudinally induced magnetic field. Further, its value decreases as the effect of the small-scale parameter increases. © 2013 Elsevier Ltd. All rights reserved.
Azizi T.,University of Mazandaran
International Journal of Theoretical Physics | Year: 2013
We study wormhole solutions in the framework of f(R,T) gravity where R is the scalar curvature, and T is the trace of the stress-energy tensor of the matter. We have obtained the shape function of the wormhole by specifying an equation of state for the matter field and imposing the flaring out condition at the throat. We show that in this modified gravity scenario, the matter threading the wormhole may satisfy the energy conditions, so it is the effective stress-energy that is responsible for violation of the null energy condition. © 2013 Springer Science+Business Media New York.
Rezaee Jordehi A.,University of Mazandaran
International Journal of Electrical Power and Energy Systems | Year: 2015
In electric power systems, finding optimal location and setting of flexible AC transmission system (FACTS) devices represents a difficult optimisation problem. This is due to its discrete, multi-objective, multi-modal and constrained nature. Finding near-global solutions in such a problem is very demanding. Brainstorm optimisation algorithm (BSOA) is a novel promising heuristic optimisation algorithm inspired by brainstorming process in human beings. In this paper, BSOA is employed to find optimal location and setting of FACTS devices. Static var compensators (SVC's) and thyristor controlled series compensators (TCSC's) are used as FACTS devices. FACTS allocation problem is formulated as a multi-objective problem whose objectives are voltage profile enhancement, overload minimisation and loss minimisation. The results of applying BSOA to FACTS allocation problem in IEEE 57 bus system demonstrate its high efficacy in solving this problem both with TCSC and SVC units. BSOA leads to better voltage profile and lower losses than particle swarm optimisation (PSO), genetic algorithm (GA), differential evolution (DE), simulated annealing (SA), hybrid of genetic algorithm and pattern search (GA-PS), backtracking search algorithm (BSA), gravitational search algorithm (GSA) and asexual reproduction optimisation (ARO). The findings of this research can be used by power system decision makers in order to establish a better voltage profile and lower voltage deviations during contingencies. © 2015 Elsevier Ltd. All rights reserved.
Fatemi M.H.,University of Mazandaran |
Izadiyan P.,University of Mazandaran
Chemosphere | Year: 2011
Cytotoxicity of a diverse set of 227 ionic liquids (taken from UFT/Merck Ionic Liquids Biological Effects Database) containing 94 imidazolium, 53 pyridinium, 23 pyrrolidinium, 22 ammonium, 15 piperidinium, 10 morpholinium, 5 phosphanium, and 5 quinolinium cations in combination with 25 different types of anions to Leukemia Rat Cell Line (IPC-81) was estimated from their structural parameters using quantitative structure - toxicity relationship " QSTR" methodology. Linear and nonlinear models were developed using genetic algorithm (GA), multiple linear regressions (MLR) and multilayer perceptron neural network (MLP NN) approaches. Robustness and reliability of the constructed models were evaluated through internal and external validation methods. Furthermore, chemical applicability domain was determined via leverage approach. In this work, it was revealed that the cationic moieties make the major contribution to cytotoxicity and the anionic parts play a secondary role in cytotoxicity of the ionic liquids studied here. Structural information represented in this work, can be used for a rational design of safer ILs. © 2011 Elsevier Ltd.