Sharif Digital Repository

With the proliferation of intermittent renewable energy sources, power systems need to withstand an increasing number of disturbances that may affect system frequency. In this paper, we focus on the effects of high penetration level of wind turbine-generators (WTG) on the power system operational planning from the frequency point of view. Specifically, an exact formulation for the minimum frequency calculation is presented to increase accuracy and speed of analyses. Then, the effect of WTG's frequency response on the power system frequency stability is investigated to compute the maximum acceptable generation outage as a function of penetration level. Finally, as an application to power... 

Coupling of side chain dynamics over long distances is an important component of allostery. Methionine side chains show the largest intrinsic flexibility among methyl-containing residues but the actual degree of conformational averaging depends on the proximity and mobility of neighboring residues. The 13C NMR chemical shifts of the methyl groups of methionine residues located at long distances in the same protein show a similar scaling with respect to the values predicted from the static X-ray structure by quantum methods. This results in a good linear correlation between calculated and observed chemical shifts. The slope is protein dependent and ranges from zero for the highly flexible... 

Gaseous reduction of manganese ores has been studied as it is beneficial for both understanding the common ferromanganese production process and the development of new processes. Thermodynamics, kinetics, and the mechanisms of reduction by methane have been reviewed, supported by thermodynamic calculations from the commercial HSC Chemistry and FactSage software. While there were similarities in reduction process by CO and H2, methane was a more efficient reductant and yielded reduction levels beyond MnO, which was due to the large thermodynamic driving force for carbide formation by metastable methane. The practical aspects of gaseous reduction by methane, such as application of a... 

Oxy-fuel combustion is a modern carbon capture and storage (CCS) technique that improves the combustion process and reduces the environmental penalty of many combustion systems. Evidently, the accurate radiative calculation of oxy-fuel combustion is very important to obtain more improved combustion system designs with less environmental drawbacks. In the present study, a small scale unconfined turbulent bluff-body flame is numerically simulated to calculate the gas radiative properties using three different approaches of ignoring radiation, applying a modified version of the weighted sum of gray gases (WSGG) model, and employing the spectral line based weighted sum of gray gases (SLW) model.... 

Direct drive motors have the excellent ability for precision position control due to their direct connection to load and elimination of the gearbox and pulley backlash. Among the direct drive motors, permanent NdFeB magnet synchronous motors (PMSMs) are the best choice for control systems due to their high efficiency, high power density, good dynamic behaviour, and excellent controllability. This study deals with the design, analysis, and fabrication of a direct drive PMSM for precision position control. To reach this aim, the designed motor should have very low cogging torque and torque ripple to avoid the motor deviation at the target point. To achieve these purposes, at first, a suitable... 

A sustainable eutectic mixture of two fatty acids, i.e. Lauric acid (LA) and Palmitic acid (PA), was produced as Phase Change Materials (PCMs) to control body temperature fluctuations. Based on thermodynamic calculations and related experimental analyses, the mass ratio of the mixture was chosen as LA:PA = 69:31. A core-shell structure was prepared through coaxial electrospinning, so as to prevent the leakage of PCM during phase change from the solid state to liquid one. Nylon 6 covered the core as the shell of the prepared nanofiber. The optimized nanofibers were obtained with the diameter of 152.7 nm. The produced PCM possessed an onset melting temperature of 32.17 °C, which was close to... 

The exponential growth in the semiconductor industry and hence the increase in chip complexity, has led to more power usage and power density in modern processors. On the other hand, most of today's embedded systems are battery-powered, so the power consumption is one of the most critical criteria in these systems. Dynamic Voltage and Frequency Scaling (DVFS) is known as one of the most effective energy-saving methods. In this paper, we propose the optimal DVFS profile to minimize the energy consumption of a battery-based system with uncertain task execution time under deadline constraints using the Calculus of Variations (CoV). The contribution of this work is to analytically calculate the... 

To account for certain essential features of material such as dispersive behaviour and optical branches in dispersion curves, a fundamental departure from classical elasticity to polar theories is required. Among the polar theories, micromorphic elasticity of appropriate grades and anisotropy is capable of capturing these physical phenomena completely. In the mathematical framework of micromorphic elasticity, in addition to the traditional elastic constants, some additional constants are introduced in the pertinent governing equations of motion. A precise evaluation of the numerical values of the aforementioned elastic constants in the realm of the experimentations poses serious... 

Multilayer perceptron (MLP) neural networks have been used extensively for estimation/regression of parameters. Moreover, recent studies have shown that learning algorithms of MLP which are based on Gaussian function are more accurate. In this paper, the mass attenuation coefficient (MAC) of gamma radiation for light-weight materials (e.g. O-8), mid-weight materials (e.g. Al-13), and heavy-weight materials (e.g. Pb-82) is modelled using Gaussian function based regularization of MLP (i.e. Bayesian regularization (BR)) and by a modular estimator. The results are compared with the Reference results. To show better performance of the utilized algorithm, the results of the different supervised... 

A great deal of computational power and time is necessary for simulating highly heterogeneous fractured reservoirs with complex geometry; the efficiency of these computations is a major subject especially in large-scale heterogeneous and fractured reservoirs. So, simulating large scale, complex and fractured reservoirs with both minimum time and maximum accuracy is the scope of current work. The BiCG-Stabilized solver preconditioned by CPR-AAMG has been developed to achieve acceptable results of high efficiency and robustness for large heterogeneous fractured Black-Oil models. The solver's efficiency is demonstrated in an Iranian fractured field model with heterogeneity. As an observation,... 

Owing to the development of smart grids technologies, including renewable energy resources and integrated demand response, the traditional distribution network undergoes systemic improvements and has become an active system. To meet such changes in technology, the smart distribution grid is highly dependent on communication infrastructures. Although this strong reliance can make the distribution network susceptible to cyber threats, there has been inadequate attention to the distribution network cyber-security. An intruder can disrupt communication and effectively target the distribution management system core functions, leaving the distribution grid susceptible to loss of stability... 

Due to non-linear factors such as the rate capacity and the recovery effect, the shape of the battery discharge curve plays a significant role in the overall lifetime of the batteries. Accordingly, this paper proposes a simple heuristic battery-aware speed scheduling policy for periodic and non-periodic real-time tasks in Dynamic Voltage Scaling (DVS) systems with non-negligible leakage/static power. A set of comprehensive analysis has been conducted to compare the battery efficiency of the proposed policies with an optimal solution, which could be derived via the Calculus of Variations (CoV). These evaluations have taken into account both periodic and non-periodic tasks in DVS-based... 

In the present study, we employ all-atom molecular dynamics simulations to investigate the dynamic behaviors and structural properties of the native and modified cellulose chains in the bulk, aqueous, and organic media. Particular attention has been directed to the role of different hydrophobic and hydrophilic functional groups as linear and branched aliphatic and also cyclic pendent groups on the solubility and packing of the cellulose chain. The various properties related to density profile, mean squared displacement, intramolecular entropy, radius of gyration, and radial distribution function were calculated. The results showed that the chain tendency toward crystallinity decreased when... 

We consider a demand response program in which a block of apartments receive a discount from their electricity supplier if they ensure that their aggregate load from air conditioning does not exceed a predetermined threshold. The goal of the participants is to obtain the discount, while ensuring that their individual temperature preferences are also satisfied. As such, the apartments need to collectively optimise their use of air conditioning so as to satisfy these constraints and minimise their costs. Given an optimal cooling profile that secures the discount, the problem that the apartments face then is to divide the total discounted cost in a fair way. To achieve this, we take a... 

Multisensor arrays employing various sensing principles are a rapidly developing field of research as they allow simple and inexpensive quantification of various parameters in complex samples. Quantitative analysis with such systems is based on multivariate regression techniques, and deriving of traditional analytical figures of merit (e.g., sensitivity, selectivity, limit of detection, and limit of quantitation) for such systems is not obvious and straightforward. Nevertheless, it is absolutely needed for further development of the multisensor research field and for introducing these instruments into the general context of analytical chemistry. Here, we report on the protocol for... 

Multi-turn resolvers are employed in the applications that high reliability; high accuracy and absolute position measurement are required, simultaneously. They are basically consisted of two individual resolvers in a common frame. In this paper a novel sinusoidal air-gap length multi-turn resolver is proposed. The rotor shape and the winding configuration are designed to achieve single-speed and multi-speed operations using a single rotor and a single stator core. Furthermore, some constraints are laid down and discussed in such a way that the performance of two resolvers has no interference with each other. All the mathematical calculations are validated using time stepping finite element... 

In this work, after formulating the weakly nonlocal micromorphic equations of motion for non-Bravais crystals with general anisotropy, specialization to diamond structures is made. A critical dilemma is the determination of the elastic moduli tensor appearing in the equations of motion. From the equivalency of these equations with the pertinent equations obtained in the context of lattice dynamics, the expressions of the components of the elastic moduli tensors in terms of the atomic force constants are derived analytically. Subsequently, the atomic force constants are calculated via ab initio density functional perturbation theory (DFPT) with high precision. As a benchmark for the accuracy... 

The corrosion inhibition of glycine-based dithiocarbamates with benzyl (BDTC) and propyl (PDTC) groups were investigated for cold rolled carbon steel (CRS) in 0.5 M HCl, indicating that the compounds as mixed type inhibitors significantly reduced the corrosion rate of the CRS due to the formation of a stable protective film on the metal surface. As confirmed by ATR-FTIR, SEM, AFM, XPS and theoretical studies, chemically adsorbed BDTC molecule is a better corrosion inhibitor with higher corrosion efficiency of about 98% at room temperature and a better thermal stability attributed to the Fe-S and Fe-N bindings, and in addition, to the presence of the benzene ring in the molecular structure. ©... 

Using a tight-binding approach and first-principles calculations combined with the nonequilibrium Green’s function method, the thermal spin transport in a zigzag molybdenum disulfide (MoS 2) nanoribbon in the proximity of a ferromagnetic insulator that induces a local exchange magnetic field in the center of the nanoribbon is investigated. It is found that a pure spin current and perfect spin Seebeck effect with zero charge current can be generated by applying a thermal gradient and local exchange magnetic field without a bias voltage near room temperature. Furthermore, it is shown that this nanoscale device can act as a spin Seebeck diode for the control of thermal and spin information in... 

The fault-tolerant capability is a prerequisite for electrical safety-critical applications. In this regard, multi-phase induction motors are well-known actuators used to provide this feature. Compared to conventional three-phase machines with distributed windings, induction machines having concentrated windings could be more fault-tolerant because of increasing the number of phases. In addition, concentrated windings have shorter end-winding and less required copper weight which makes it a lower cost solution compared to distributed windings. However, concentrated windings adversely increase the distortion of the air gap flux density which affects motor performances. In this paper, a...