Sharif Digital Repository

This study aims to optimize, design, and predict the MTMDs performance in SDOF systems using spectral analysis, and then apply their results to MDOF structures. Given the importance of spectral analysis in the design of new engineering structures, achieving a method for designing TMDs based on this theory can be of great importance for structural designers. In this study, several convenient combinations of MTMDs in an SDOF system are first considered to minimize the maximum displacement. For calculating the frequency ratios of dampers, an innovative technique is adopted in which the values of different modal responses obtained from the spectral analysis are approached together. This... 

The product distribution of methanol to hydrocarbons conversion over SAPO-34 and ZSM-5 catalysts was studied using thermodynamic equilibrium and Anderson-Schulz-Flory (ASF) distributions. The equilibrium compositions were calculated using constrained Gibbs free energy minimization. The effect of catalyst type was considered by setting upper limits to product carbon number due to shape selectivity according to zeotype catalyst channel size; that is, n5 for SAPO-34 but n6 for aliphatic and n10 for aromatic compounds over H-ZSM-5 catalyst. The equilibrium selectivity of kinds of paraffin is negligible over SAPO-34 system while that of olefins is very small over H-ZSM-5, both in agreement... 

We proposed a simple method to enhance shielding factor of our previously proposed bi-stage active shield system employed in a SQUID-based magnetocardiography system. The additional proposed design is optimized for canceling the power-line magnetic interference field to provide a calmer magnetic environment for the bi-stage active shield. A 50 Hz cancellation coil is placed around the bi-stage shielding system which includes inner and outer coils designed for compensating low-frequency (0-0.1Hz) and high-frequency (0.1-100Hz) environmental magnetic noise, respectively. In this configuration, a SQUID magnetometer is located at the center of these coils. Considering that the power-line... 

We proposed a simple method to enhance shielding factor of our previously proposed bi-stage active shield system employed in a SQUID-based magnetocardiography system. The additional proposed design is optimized for canceling the power-line magnetic interference field to provide a calmer magnetic environment for the bi-stage active shield. A 50 Hz cancellation coil is placed around the bi-stage shielding system which includes inner and outer coils designed for compensating low-frequency (0-0.1Hz) and high-frequency (0.1-100Hz) environmental magnetic noise, respectively. In this configuration, a SQUID magnetometer is located at the center of these coils. Considering that the power-line... 

Physical and hydraulic properties of new stainless steel spring packing are introduced. The measured hydraulic properties are: dry and wetted packed bed pressure drop, loading and flooding points and the liquid holdups. The appropriate coefficients for predicting the mentioned hydraulic properties from different correlations are also reported. Hydraulic properties for this packing are compared with available packings. In spite of small size, the dry and wetted packed bed pressure drops of spring packing are less than similar Raschig and Protruded rings. The total liquid holdup of this packing is greater than other commercial packings. The big total liquid holdup and physical surface area are... 

A significant segment of system identification literature on civil structures is devoted to response-only identification, simply because lack of measurements of input excitations for civil structures is a fairly common scenario. In recent years, several researchers have successfully adapted a second-order blind identification (SOBI) technique-a method originally developed for "blind source separation" of audio signals-to response-only identification of mechanical and civil structures. However, this development had been confined to fully instrumented classically damped systems. While several approaches have been proposed recently for extending SOBI to non-classically damped systems, they all... 

Cuprous oxide powder was added to WO3 sol as a catalyst and the composite sol was deposited on alumina substrates by spin coating process and annealing at 500 °C for 1 hour. Sensing properties of the pure and doped tungsten oxide samples to H2S gas were analyzed. WO 3-Cu2O (1%) samples showed good sensitivity towards 250 ppb of the gas at 100 °C and 1 ppm at room temperature (25 °C). Crystal structure, morphology and chemical composition of the sample were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX) analyses and X-ray photoelectron spectroscopy (XPS). Based on these data, possible reaction mechanisms of hydrogen sulfide over WO... 

Herein, we propose a method based on the existing second-order blind identification of underdetermined mixtures technique for identifying the modal characteristics - namely, natural frequencies, damping ratio, and real-valued partial mode shapes of all contributing modes - of structures with a limited number of sensors from recorded free/ambient vibration data. In the second-order blind identification approach, second-order statistics of recorded signals are used to recover modal coordinates and mode shapes. Conventional versions of this approach require the number of sensors to be equal to or greater than the number of active modes. In the present study, we first employ a parallel factor... 

The objective of the present work is to compare the performance of the regenerator of pulse tube refrigerators at low and high frequencies. The hydrodynamic and thermal behavior of the regenerator is investigated in this respect. To consider the system performance, a system of conservation equations including two energy equations for the regenerator as a porous media is employed. The present model considers one-dimensional, periodic, unsteady, compressible flow in the regenerator. The conservation equations are transformed by implementing the volumetric average scheme. The method of harmonic approximation is employed to derive an analytical solution. To explore the system performance, net... 

Production and oscillation of sonoluminescence bubbles by laser pulse in the presence of acoustic field in water and different concentrations of sulfuric acid are investigated. In the presence of acoustic field, the laser causes variable speed of sound, surface tension and density; and the host liquid acts as a compressible one and strongly affects the bubble's dynamics equations. The effect of various concentrations of sulfuric acid as a host liquid on the oscillation of bubble radius, bubble wall velocity and bubble interior temperature is studied. Furthermore, the effect of applied frequency on LI-SCBL in the presence of the acoustic field is investigated and an optimum sound wave... 

A three-phase dual active bridge (DAB) converter is designed and constructed as the DC/DC stage of a 50 kW fast charger station. Recently introduced 300A SiC power modules and drivers are utilized in the converter to obtain a high efficiency. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as over-current, gate under-voltage, or gate overvoltage. In such case the module operates as a leg with two diodes until an external hardware signal resets the driver. The aim of this paper is to provide analysis, simulation and experiments for a three-phase... 

Least squares estimation is a widely-used technique for range-based source localization, which obtains the most probable position of mobile station. These methods cannot provide desirable accuracy in the case with a non line of sight (NLOS) path between mobile station and base stations. To circumvent this drawback, many algorithms have been proposed to identify and mitigate this error; however, they have a large run-time overhead. On the other hand, new positioning systems utilize a large set of base stations, and a practical algorithm should be fast enough to deal with them. In this paper, we propose a novel algorithm based on subspace method to identify and eliminate the NLOS error.... 

Power electronics is becoming an underpinning technology for modern power systems. Power converters are increasingly used in various applications implying different levels of importance in power systems. Hence, optimal decision-making for manufacturing, control, operation and maintenance of them requires understanding of their importance in the power systems. Furthermore, identifying the converters importance may be beneficial for simplifying the system-level reliability modeling in a large Power Electronic based Power Systems (PEPSs). Thereby, a Failure Mode, Effects and Criticality Analysis (FMECA) approach is proposed in this paper in order to figure out the importance of converters in... 

The land-sliding forces applied to buried pipelines depend on the ground condition, types of loading and pipelines features. This paper intends to numerically investigate the effect of ground condition on pipelines. The loading type and pipeline features are kept constant. The pipeline which is positioned at mid-length of the slope, is made of steel and intersects the slope at the angle of 90o. The slope material specifications are determined based on geotechnical reports andthe harmonic loading simulates a 7.5 magnitude earthquake. The descending trend of slope displacement in sandy clay, loose to medium sand, cemented sand and medium to hard clayare shown by numerical calculations. But,... 

In this article, indium doped ZnO nanoparticles (alloy nanoparticles) were investigated as inhibitors against algae growth on adobe mud and earthen artworks for surface preservation from destruction caused by micro-organisms under humid conditions, through surface modification and activation run off. Nanoparticles (NPs) were fabricated by physical vapor deposition (PVD) growth mechanism. The fabricated NPs were approximately 20 nm in size. The Chlorella vulgaris and Scenedesmus quadricauda were tested by application of indium doped ZnO nanoparticles (In/ZnO NPs) as inhibitors. As concentrations of NPs increased, the negative impacts of NPs on the algal growth were enhanced and physical... 

The land-sliding forces applied to buried pipelines depend on the ground condition, types of loading and pipelines features. This paper intends to numerically investigate the effect of ground condition on pipelines. The loading type and pipeline features are kept constant. The pipeline which is positioned at mid-length of the slope, is made of steel and intersects the slope at the angle of 90o. The slope material specifications are determined based on geotechnical reports andthe harmonic loading simulates a 7.5 magnitude earthquake. The descending trend of slope displacement in sandy clay, loose to medium sand, cemented sand and medium to hard clayare shown by numerical calculations. But,... 

Technology scaling has exacerbated the aging impact on the performance and reliability of integrated circuits. By entering into nanotechnology era in recent years, the power density per unit of area has increased, which leads to a higher chip temperature. Aging in a chip is originated from multiple phenomena; all of them are intensified by increased temperature. Several circuit- and architecture-level schemes tried to mitigate the aging in the literature. However, these schemes are not sufficient for multi-core systems due to their unawareness of the unique constraints and features of these platforms. In this paper, we propose a system-level aging mitigation method, so-called Adaptive Task... 

5G networks are going to support a variety of vertical services, with a diverse set of key performance indicators (KPIs), by using enabling technologies such as software-defined networking and network function virtualization. It is the responsibility of the network operator to efficiently allocate the available resources to the service requests in such a way to honor KPI requirements, while accounting for the limited quantity of available resources and their cost. A critical challenge is that requests may be highly varying over time, requiring a solution that accounts for their dynamic generation and termination. With this motivation, we seek to make joint decisions for request admission,... 

Technology scaling has exacerbated the aging impact on the performance and reliability of integrated circuits. By entering into nanotechnology era in recent years, the power density per unit of area has increased, which leads to a higher chip temperature. Aging in a chip is originated from multiple phenomena; all of them are intensified by increased temperature. Several circuit- and architecture-level schemes tried to mitigate the aging in the literature. However, these schemes are not sufficient for multi-core systems due to their unawareness of the unique constraints and features of these platforms. In this paper, we propose a system-level aging mitigation method, so-called Adaptive Task... 

Let (Formula presented.) be a graph of order (Formula presented.) and size (Formula presented.). Suppose that (Formula presented.) is a function such that (Formula presented.). In this paper we provide a criterion for (Formula presented.)-choosability of (Formula presented.). Using this criterion, it is shown that the choice number of the complete (Formula presented.)-partite graph (Formula presented.) is (Formula presented.), which is a well-known result due to Erdös, Rubin and Taylor. Among other results we study the (Formula presented.)-choosability of the complete (Formula presented.)-partite graphs with part sizes at most (Formula presented.), when (Formula presented.), for every vertex...