Sharif Digital Repository

Thermal conductivity, thermal dispersion, and structural effects in resin transfer molding (RTM) process are studied numerically. The injection part of the RTM process is modeled as a transport of resin flow through a fibrous porous medium in a long rectangular channel. The fluid flow is modeled using the Darcy-Brinkman-Forchheimer model and the heat transfer process using the energy equation based on local thermal equilibrium assumption. Both isotropic and anisotropic heat transfer in porous media are investigated. The governing equations are solved numerically for the isotropic heat transfer case and analytically for the anisotropic case. The numerical results are fitted to the available... 

Numerical investigation on the application of nanofluids in Micro-Pin-Fin Heat Sinks (MPFHSs) has been presented in this paper. To investigate flow and heat transfer behavior in MPFHS the three-dimensional steady Navier-Stokes and energy equations were discretized using a finite volume approach and have been solved iteratively, using the SIMPLE algorithm. DI-water is used as a base coolant fluid while the nanoparticles used in the present study are CuO nanoparticles with mean diameters of 28.6 and 29 nm and Al 2O 3 nanoparticles with mean diameters of 38.4 and 47 nm. The results show that (i) a significant enhancement of heat transfer in the MPFHS due to suspension of CuO orAl 2O 3... 

The recently reported UNIversal QUAsiChemical Segment Activity coefficient (UNIQUAC-SAC) model [developed by Haghtalab and Yousefi Seyf Ind. Eng. Chem. Res. 2015, 54, 8611] provides a practical thermodynamic framework to be used in VLE, LLE, and SLE calculations. The UNIQUAC-SAC model has the advantage of being independent of area (q) and volume (r) structural parameters used in the combinatorial part. While the UNIFAC or UNIFAC-DMD could not apply to the 47% (44 of 94) of the studied molecules because of the undefined groups. Here, the numbers of solvents with identified segment numbers were extended from 82 to 130 with a slight refinement to the previous values. The model parameters... 

The perturbed chain-statistical associating fluid theory equation of state (PC-SAFT EoS) is one of the state-of-the-art thermodynamic models used in the phase equilibrium calculation of associating mixtures, in particular, in the pharmaceutical industry. Accordingly, parametrization of the PC-SAFT EoS for approved solvents reviewed for use in pharmaceutical process design by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) was done in the present study. First, the PeC-SAFT EoS model parameters for 41 pure solvents were regressed (of 62 solvents). The available high-quality binary vapor-liquid equilibrium (VLE)... 

In future smart grids, energy storage systems (EESs) and demand response (DR) are expected to have an important role in balancing load changes arising from life-style of consumers and varying output of some renewable energy resources. However, activating DR and installing ESSs need huge investment forcing system owner to justify their effectiveness prior to any implementation. This paper presents a model to find the optimal capacity of EESs in distribution systems with demand responding to electricity price changes. The model aims at maximizing system owner profit by lessening total electricity provision costs. The model is formulated as a mixed integer non-linear programming problem. Due to... 

The non-randomness two-liquid (NRTL) activity coefficient model and its variants are widely used in phase equilibria calculations. In the present study, the number of main groups of the NRTL-FAC (GC-NRTL) model (Fluid Phase Equilibria, 541:113088, 2021), was extended from 50 to 66 (including 125 subgroups). 160 molecules containing 3318 binary vapor–liquid-equilibrium (VLE) data sets (54,689 data points) were used in the extension of the model. That is, the main groups including DOH, ACRY, ClC = C, COO, ACCN, NCO, Anhydrides, ACCHO, ACCOOH, OCCOH, Lactames, Lactones, Peroxides, CF3H, CF3Cl, and CF4 were added to the main group list of the GC-NRTL model. In addition, the temperature... 

In future smart grids, energy storage systems (EESs) are expected to play an indispensable role in balancing continuous load changes arising from customers' life-style as well as varying output of intermittent energy resources. This, however, needs significant investment that should be justified prior to their implementation. This paper presents a model to find the optimal capacity for ESSs in distribution systems. The model aims at maximizing system owner profit by reducing total electricity procurement costs. The model is formulated as a mixed integer non-linear programming problem. Due to the complexity and large size of the problem, a decouplebased method is proposed wherein optimal... 

The distributed nature and complexity of computer networks and various services provided via them, makes the networks vulnerable to numerous attacks. The TCP/IP presumptions which are based on using this protocol to provide a simple, open communication infrastructure in an academic and collaborative environment, causes this protocol lack of built-in mechanisms for authentication, integrity and privacy. Even though in the last few years a more systematic approach to TCP/IP network security problem has been followed, a formal approach to this problem is lacking. In this paper, we propose using Description Logics as a formal model which could be used to analyze TCP/IP networks against attacks.... 

Controlled graphitization has become known as a practical method for improvement of wear resistance and machining properties in steels. In this paper, the effect of heat treatment on microstructure of CK45 steel has been investigated. Austenitising was carried out at 920 °C for 5 h. Besides, isothermal transformation was conducted at 750 °C in the time range of 1-20 h. In this work, full potential carbon resource was tried to be used around samples as a factor to prevent the burning of the limited carbon in steel and also to increase the percentage of sample surface carbon in order to improve wear capability and machining. The microstructure of the steel considerably changes by this heat... 

To synthesize a novel biopolymer-based superabsorbent hydrogel, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was grafted onto kappa-carrageenan (KC) backbones. The graft copolymerization reaction was carried out in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator, N,N,N',N'-tetramethyl ethylenediamine (TMEDA) as an accelerator, and N,N'-methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for KC-g-AMPS formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The affecting variables on swelling capacity, i.e., the initiator, the crosslinker, and the monomer concentration, as well as reaction temperature,... 

Synthesis of polyvinyl pyrrolidone (PVP) coated ultrasmall Gd2O3 nanoparticles (NPs) with enhanced T1-weighted signal intensity and r2/r1 ratio close to unity is performed by a microwave-assisted polyol process. PVP coated Gd2O3NPs with spherical shape and uniform size of 2.5 ± 0.5 nm have been synthesized below 5 min and structure and morphology confirmed by HRTEM, XRD and FTIR. The longitudinal (r1) and transversal relaxation (r2) of Gd2O3NPs is measured by a 3 T MRI scanner. The results showed considerable increasing of relaxivity for Gd2O3NPs in... 

This paper proposes a high performance voltage tracking and current sharing among parallel connected inverters by applying optimal control and minimizing the cost function. The control system forces the voltage of load to track the voltage reference, and the current of all inverters becomes equal. Therefore, both current sharing and voltage tracking are obtained. In addition, the smallest input energy and simplicity in control circuit are the other advantages of the suggested method. To show the performance of the proposed control scheme, the simulations with two-modular practical systems are performed and the results are provided. The results indicate that the control objectives are... 

An analytical model is proposed to study the effect of particle size on melting enthalpy and entropy of metallic nanoparticles (NPs). The Mott's and Regel's equations for melting entropy in the combination of core average coordination number (CAC) and surface average coordination number (SAC) of freestanding NPs are considered. Clusters of icosahedral (IC), body centered cubic (BCC), and body centered tetragonal (BCT) structure without any vacancies and defects are modeled. Using the variable coordination number made this model to be in good agreement with experimental and molecular dynamic (MD) results of different crystal structures. The model predicts melting entropy and enthalpy of... 

Adaptive Noise Cancellation (ANC) is a well-known technique for background noise reduction in automobile and vehicular environments. The noise fields in automobile and other vehicle interior obey the diffuse noise field model closely. On the other hand, the ANC does not provide sufficient noise reduction in the diffuse noise fields. In this paper, a new multistage post-filter is designed for ANC as a solution to diffuse noise conditions. The designed post-filter is a single channel Linear Prediction (LP) based speech enhancement system. The LP is performed by an adaptive lattice filter and attempts to extract speech components by using intermediate ANC signals. The post-filter has no... 

Modeling and analysis of information system vulnerabilities helps us to predict possible attacks to networks using the network configuration and vulnerabilities information. As a fact, exploiting most of vulnerabilities result in access rights alteration. In this paper, we propose a new vulnerability analysis method based on the Take-Grant protection model. We extend the initial Take-Grant model to address the notion of vulnerabilities and introduce the vulnerabilities rewriting rules to specify how the protection state of the system can be changed by exploiting vulnerabilities. Our analysis is based on a bounded polynomial algorithm, which generates the closure of the Take-Grant graph... 

In this paper, for the first time, we present a small signal circuit model of quantum dot laser considering two photon modes, i.e., ground and first excited states lasing. By using the presented model, effect of temperature variations on modulation response of quantum dot laser is investigated. Simulation results of modulation response are in agreement with the numerical and experimental results reported by other researchers  

Enzymatic decolorization of reactive blue 221 (RB221) using laccase was investigated in a dual-chamber microbial fuel cell (MFC). Suspended laccase was used in the cathode chamber in the absence of any mediators in order to decolorize RB221 and also improve oxygen reduction reaction in the cathode. Molasses was utilized as low cost and high strength energy source in the anode chamber. The capability of MFC for simultaneous molasses and dye removal was investigated. A decolorization efficiency of 87% was achieved in the cathode chamber and 84% COD removal for molasses was observed in the anode chamber. Laccase could catalyze the removal of RB221 and had positive effect on MFC performance as...