Sharif Digital Repository

Using solid-state power amplifiers for next generation of weather radars becomes feasible by pulse compression techniques. In this study a 1.5 kW solid-state power amplifier (transmitter) for C-band weather radars is designed and fabricated by GaN high electron mobility transistor (HEMT) technology. An experimental setup based on heterodyne receiver with 16-bit digitiser is developed to investigate the behavior of the power amplifier under different cooling methods and back-off points. Several measurements with shaped LFM pulse show an approximately identical pulse to pulse (P2P) stability for 3 dB compression, P1dB and 2 dB back-off points while the best sidelobe level (SLL) is achieved for... 

The hydrodynamics of two immiscible fluids in a rectangular Hele-Shaw cell under the influence of a magnetic field is studied, both theoretically and numerically. A linear stability analysis is conducted to determine the effect of magnetic fields on the formation of viscous fingers. As a result, an analytical solution is found to calculate the growth rate of perturbations. For numerical simulation of the two-phase flow, the interfacial tension is treated as a body force using the continuum surface force model and the interface tracking is performed by the volume of fluid method. The variations of the width and growth rate of fingers in an unstable displacement versus Hartmann number, a... 

Significant increase of static power in nano-CMOS era and, subsequently, the end of Dennard scaling has put a Power Wall to further integration of CMOS technology in Field-Programmable Gate Arrays (FPGAs). An efficient solution to cope with this obstacle is power gating inactive fractions of a single die, resulting in Dark Silicon. Previous studies employing power gating on SRAM-based FPGAs have primarily focused on using large-input Look-up Tables (LUTs). The architectures proposed in such studies inherently suffer from poor logic utilization which limits the benefits of power gating techniques. This paper proposes a Power-Efficient Architecture for FPGAs (PEAF) based on combination of... 

These days, considering the importance of reliability in industries, utilities’ role for preparing high levels of reliability becomes more important. This can be done by adding numbers of switches and Tie switches which impose high expenses to system. These expenditures should be provided by customers. Level of reliability in different points of network is different. So customers which pay more, receive higher level of reliability. If a customer raises its payment, utility change the location of switches in order to raise level of reliability of that customer. all customers change their payment and then utility fixes the switches at a point that all customers reach their favorable... 

Beside the major objective of providing congestion control, achieving predictable queuing delay, maximizing link utilization, and robustness are the main objectives of an active queue management (AQM) controller. This paper proposes an improved queue dynamic model while incorporating the packet drop probability as well. By applying the improved model, a new compensated PID AQM controller is developed for Transmission Control Protocol/Internet Protocol (TCP/IP) networks. The non-minimum phase characteristic caused by Padé approximation of the network delay restricts the direct application of control methods because of the unstable internal dynamics. In this paper, a parameter-varying dynamic... 

When the network suffers from congestion, the core or edge routers signal the incidence of congestion through the active queue management (AQM) to the sources. The time-varying nature of the network dynamics and the complex process of retuning the current AQM algorithms for different operating points necessitate the development of a new AQM algorithm. Since the non-minimum phase characteristics of the network dynamics restrict direct application of the proportional-integral-derivative (PID) controller, we propose a compensated PID controller based on a new control strategy addressing the phase-lag and restrictions caused by the delay. Based on the unstable internal dynamics caused by the... 

With the emerging nanoscale CMOS technology, Multiple Event Transients (METs) originated from radiation strikes are expected to become more frequent than Single Event Transients (SETs). In this paper, a fast and accurate layout- based Soft Error Rate (SER) estimation technique with consideration of both SET and MET fault models is pro- posed. Unlike previous techniques in which the adjacent MET sites are obtained from logic-level netlist, we perform a comprehensive layout analysis to extract MET adjacent cells. It is shown that layout-based technique is the only effective solution for identification of adjacent cells as netlist-based techniques significantly underestimate the overall SER.... 

While the transistor density continues to grow exponentially in Field-Programmable Gate Arrays (FPGAs), the increased leakage current of CMOS transistors act as a power wall for the aggressive integration of transistors in a single die. One recently trend to alleviate the power wall in FPGAs is to turn off inactive regions of the silicon die, referred to as dark silicon. This paper presents a reconfigurable architecture to enable effective fine-grained power gating of unused Logic Blocks (LBs) in FPGAs. In the proposed architecture, the traditional soft logic is replaced with Mega Cells (MCs), each consists of a set of complementary Generic Reconfigurable Hard Logic (GRHL) and a conventional... 

Abstract A desired circulatory flow in flat-plate closed-loop pulsating heat pipes (FP-CLPHPs), which may ameliorate electronic thermal management, was achieved by using the new idea of interconnecting channels (ICs) to decrease flow resistance in one direction and increase the total heat transfer of fluid. In order to experimentally investigate the effects of the IC, two aluminum flat-plate thermal spreaders - one with ICs (IC-FP-CLPHP) and one without them - were fabricated. The FP-CLPHPs were charged with ethanol as working fluid with filling ratios of 35%, 50%, 65%, and 80% by volume. Performance of interconnecting channels in different heat inputs was explored, and the results... 

The present study provides an inverse solution and analysis on a new approach for Electrical Impedance Tomography (EIT) process as block method in EIT. In this method, it is assumed that all of the panicles of each block have the same electrical properties (electrical conductivities). This technique is used to enhance image resolution and also to improve reconstruction algorithm. Although this method has been developed for 3D objects, in this study it is assumed that the subject has a (two-dimensional) rectangular shape and is made of fixed size blocks. By considering the previous conditions and computing relationship among currents, voltages and electrical impedances of blocks, the required... 

With continuous technology downscaling, the rate of radiation induced soft errors is rapidly increasing. Fast and accurate soft error vulnerability analysis in early design stages plays an important role in cost-effective reliability improvement. However, existing solutions are suitable for either regular (a.k.a address-based such as memory hierarchy) or irregular (random logic such as functional units and control logic) structures, failing to provide an accurate system-level analysis. In this paper, we propose a hybrid approach integrating architecture-level and logic-level techniques to accurately estimate the vulnerability of all regular and irregular structures within a microprocessor.... 

In this article, the flow field around NACA0024 airfoil with step at lower and upper surfaces is experimentally investigated. For this purpose, particle image velocimetry technique based on the instantaneous flow structures is used to investigate the flow field around the airfoil at different times. All the experimental measurements in current study are conducted at very low Reynolds number condition based on the chord of the airfoil (Re=2000) and at angles of attack at 0° and 5° where the flow around airfoils is separated. The differences between vortical structures, mean streamlines, sizes of the wake regions, and vortex shedding of the stepped airfoils compared to unmodified airfoil are... 

The authors regret that the first author's last name was left out of the published version of the article. The author's full name should have appeared as above. © 2021 Elsevier Ltd  

Switched Reluctance Motors (SRMs) are widely used in high-speed and low voltage applications because of their attractive features such as robustness and simplicity. No winding on the rotor of this type of motors allows reaching high speed which is desired for many applications. Drive circuits of SRMs also play an important role in their performance and operation. In this paper, a new bifilar drive circuit for this type of motors has been proposed. This novel configuration has been tested and investigated by PSIM software. Results show that the new bifilar drive circuit highly reduces the voltage stresses on semiconductor switches, and also considerably reduces the switching losses which are... 

This paper presents a dry mechanochemical process to produce hydroxyapatite (HAp) nanoparticles. Two distinct chemical reactions are introduced to prepare HAp powders using milling process. Structural and morphological properties of the obtained materials are studied by X-ray diffraction and transmission electron microscopy. The results reveal that the single crystal HAp nanoparticles have been successfully produced in metallic and polymeric vials through two different experimental procedures. Tempered chrome steel and polyamide-6 materials are adopted as the metallic and polymeric vials respectively. Nanoellipse, nanorod and nanosphere powders are obtained in these experimental procedures.... 

In this research work, different devices made of glutaraldehyde cross-linked chitosan hydrogels loaded by amoxicillin, have been prepared using freeze-drying method. Effects of system parameters such as cross-linker concentration, pH, and gel structure on the morphology and release behavior of devices have been investigated using standard methods. Morphological studies were performed using SEM instrument and controlled releases are followed via spectrophotometeric method. Reaction of glutaraldehyde with chitosan has been studied using FTIR instrument. SEM micrographs have shown that with increasing cross-linker percentage in hydrogel, pore sizes increased where pore size distribution... 

Regarding the increasing number of electrical devices in the smart homes that leads to increase in total electricity consumption and cost, it is essential to use energy management methods to reduce the electricity cost. However, this can cause resident's dissatisfaction. Hence, it is important to define a method in which cost and dissatisfaction be optimized simultaneously. Among different services, an electric vehicle is the one that can be used as an energy storage system, so it can reduce the daily cost despite of increasing the total energy consumption. In this paper, we study the effect of the EV on the cost and dissatisfaction in our proposed method. © 2018 IEEE  

Application of Probabilistic Safety Assessment (PSA) to a Uranium hexafluoride (UF 6) production process is presented in this paper. The process is constituted from three main units: UF 4 conversion to UF 6, condensation of produced UF 6 gas and tail gas treatment. Radioactive gas is present in all parts of the process and occurrence of high pressure or high temperature in the process equipments may lead to radioactive release to workplace and environment. The work is mainly based on PSA experience in nuclear power plants. Accordingly for the process, eight group of Initiating Events (IE) that lead to UF 6 gas release have been identified using HAZOP study. For each IE, based on related... 

In self-controlling hyperthermia therapy, once the desired temperature is reached, the heat generation ceases and overheating is prevented. In order to design a system that generates sufficient heat without thermal ablation of surrounding healthy tissue, a good understanding of temperature distribution and its change with time is imperative. This study is conducted to extend our understanding about the heat generation and transfer, temperature distribution and temperature rise pattern in the tumor and surrounding tissue during self-controlling magnetic hyperthermia. A model consisting of two concentric spheres that represents the tumor and its surrounding tissue is considered and temperature... 

This study investigates the aerodynamic loads and energy losses of a typical 600 kW wind turbine with S816 airfoil blade under two different icing conditions. Three sections at different radial positions were considered to estimate the icing effect along the blade. Ice accretion simulations in wet and dry regimes were carried out using the NASA LEWICE 3.2 computer program. The airflow simulations were performed with CFD method and SST k -ω turbulence model. The results of these simulations, including streamlines, surface pressure, skin friction, lift, and drag coefficients, were inspected for both clean and iced airfoils. In the case of wet iced airfoil, a separation bubble was created in...