Sharif Digital Repository

The most important goal of studying an extensive air shower is to find the energy, mass and arrival direction of its primary cosmic ray. In order to find these parameters, the core position and arrival direction of the shower should be determined. In this paper, a new method for finding core location has been introduced that utilizes trigger time information of particle detectors. We have also developed a simple technique to reconstruct the arrival direction. Our method is not based upon density-sensitive detectors which are sensitive to the number of crossing particles and is also independent of lateral distribution models. This model has been developed and examined by the analysis of... 

In this paper, a simple method for detection of multiple edge cracks in Euler-Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm. The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each... 

A simple method for synthesis of novel organogels based on multiwalled carbon nanotubes (MWCNTs) is reported. Three classes of organogels were synthesized by crosslinking polymerization of dodecyl methacrylate with various weight percentages of 1,4-butanediol dimethacrylate, vinyl-group-modified MWCNTs or pristine MWCNTs in the presence of 2,2-azoisobutyronitrile as initiator. In this reaction, the carbon nanotubes (CNTs) served simultaneously as an adsorbent, a comonomer and a crosslinking agent. The oil-absorbent containing CNTs showed much higher swelling capacity in oil and organic solvents compared with that without CNTs. Therefore, CNT-based organogels can be introduced as a promising... 

In an electronic warfare environment, an electronic support system receives signals emitted by different radars. One of the key tasks in an electronic support system is detection of Pulse Repetition Interval Modulation for these signals. In this paper we present a new robust and yet simple method for detection of complex PRI Modulation. Simulation results show that the proposed method is more robust against noise (spurious and missing pulses) and unwanted jitter than previous methods  

Nano-sized particles of manganese oxides have been prepared by a very simple and cheap process using a decomposing aqueous solution of manganese nitrate at 100 °C. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the manganese oxide. The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(iv) ammonium nitrate and hydrogen peroxide, respectively  

A simple method has been demonstrated to grow silver nanoparticles on the surface of cellulose fibers. The preparation is based on photo-activation of surface by ultraviolet (UV) photons, followed by chemical reduction of silver nitrate. It is found that the concentration of silver nitrate in the solution is not a determining factor, while UV intensity affects the rate of initial growth and determines the final concentration of the loaded silver. We explain the phenomena based on a model including the number of reducing sites on the surface of cellulose fibers activated by UV photons, and a release mechanism that causes a slow rate of dissolution of silver back into the solution  

Brain is the most complicated organ of body. It controls the activity of all other organs. Understanding its function and its language could give us a direct communication pathway for connecting with injured motor organ and it could be the core of functional repairing. Neurons are the vertices of a vast network that generates the brain signals. Neuronal recordings capture brain activity signatures. The processing of these signals can help to translate brain's language. Usually it follows three main stages: spike detection and extraction, spike sorting, and intention extraction from the encoded signal. In this work, we introduce an original idea based on Hidden Markov Models (HMM) which helps... 

In almost all of the currently working circuits, especially in analog circuits implementing signal processing applications, basic arithmetic operations such as multiplication, addition, subtraction and division are performed on values which are represented by voltages or currents. However, in this paper, we propose a new and simple method for performing analog arithmetic operations which in this scheme, signals are represented and stored through a memristance of the newly found circuit element, i.e. memristor, instead of voltage or current. Some of these operators such as divider and multiplier are much simpler and faster than their equivalent voltage-based circuits and they require less... 

A new method to evaluate the steady state performance of a three-phase self excited induction generator based on conductance minimization is proposed. It can be simply used to take series compensation into account. Among the priorities of this method are the absence of convergence problem and flexibility. Simple methods to find the frequency and magnetizing reactance have been proposed. Simulation results show the efficiency of this method  

Friction plays an important role in metal forming operations. Therefore, many techniques are developed for evaluation of friction in large deformation processes. Among them the "Barrel Compression Test" (BCT) is a very simple method that quantitatively evaluates the constant friction factor, m, simply by compressing a cylindrical specimen. BCT was analyzed by Avitzur [B. Avitzur, Metal Forming Processes and Analysis, McGraw-Hill, 1968] using the upper bound theory. Ebrahimi et al. [R. Ebrahimi, A. Najafizadeh, J. Mater. Process. Technol. 152 (2004) 136-143] suggested a method in order to make Avitzur's mathematical results applicable. However, they made an assumption in their work which... 

Thermal noise is one of the most important limiting factors on the performance of switched-capacitor (SC) circuit due to the aliasing effect of wide-band thermal noise. In this paper a new simple method for estimating the effect of thermal noise is presented. In the proposed technique only the discrete sampled noise is considered. HSPICE simulator and analytical analysis are used to estimate the sampled noise specification on each clock state. Next, using difference equations of the circuit, time domain simulation is done by MATLAB. Based on this method, a SC integrator is analyzed and results compared to the measured noise response  

In this study main reactive power calculation methods are evaluated and compared. Furthermore, a novel simple method that can be used for calculation of reactive power in electric arc furnace (EAF) plants is proposed. The focus here is on their application in the control system of static VAr compensators (SVCs). SVC can compensate only the fundamental harmonic component. So the reactive power signal used in the control system should be sensitive only to the main harmonic component. In addition, the reactive power calculation should be fast enough that SVC can follow the quick changes of the load to mitigate the flicker efficiently. To compare various reactive power calculation methods and to... 

Multi-phase flows, particularly two-phase flows, are widely used in the industries, hence in order to predict flow regime, pressure drop, heat transfer, and phase change, two-phase flows should be studied more precisely. In the petroleum industry, separation of phases such as water from petroleum is done using rotational flow and vortices; thus, the evolution of the vortex in two-phase flow should be considered. One method of separation requires the flow to enter a long tube in a free vortex. Investigating this requires sufficient knowledge of free vortex flow in a tube. The present study examined the evolution of tube-constrained two-phase free vortex using computational fluid dynamics. The... 

A simple method for synthesis of NaxWO3 nanorods and nanobelts on sputtered tungsten films by using sodium in soda lime substrate as the catalyst was reported for the first time. After thermally post annealing thin films in a temperature range of 600-750 °C in N2 ambient for 80 min, crystalline NaxWO3 nanorods and nanobelts with [001] direction were formed depending on the annealing temperature. Experimental results reveal that the annealing temperature at 700 °C is the optimum temperature for the growth of sodium-doped tungsten oxide nanorods with maximum density on the surface. According to scanning electron microscopic observations, the synthesized nanorods are ∼50 nm in width and a few... 

The planar-adaptive routing algorithm is a simple method to enhance wormhole routing algorithms for fault-tolerance in meshes but it cannot handle faults on the boundaries of mesh without excessive loss of performance. In this paper, we show that this algorithm can further be improved using a flag bit introduced for guiding misrouted messages. So, the proposed algorithm can be used to route messages when fault regions touch the boundaries of the mesh. We also show that our scheme does not lead to diminish the performance of the network and only three virtual channels per physical channels are sufficient for tolerating multiple boundary faulty regions. © 2008 Springer-Verlag Berlin Heidelberg... 

Multiple target detection in conventional PCL (Passive Coherent Location) radar systems by means of Ambiguity Function Processing and without any powerful algorithm is impossible. Presented Gradual Clean Algorithm (GCA) is a new and simple method, which could provide the perfect detection in noisy environment and heavy clutter condition up to SNR=-15 dB and SCR=-100 dB (clutter is assumed as a distributed target with large RCS). Determining the number of real targets and keeping the false alarm probability approximately constant are the presented algorithm capabilities  

Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

Dynamic analyses are necessary problems in offshore jacket structures design and assessment. These analyses have various applications in recognition of dynamic behavior, fatigue analysis, damage detection, etc. Natural frequencies and mode shapes, as inherent vibrational features of a structure, are key parameters in referred analyses. These parameters are mainly affected by mass and stiffness matrices and slightly by damping. Therefore, it is more important to estimate the stiffness matrix of a structure accurately, especially in stiff structures such as offshore jacket platforms. In many cases, the stiffness of levels is required. For example, it can be useful in the construction of an... 

Thermal noise is one of the most important challenges in analogue integrated circuits design. This problem is more crucial in switched-capacitor (SC) filters due to the aliasing effect of wide-band thermal noise. In this article, a new simple method is proposed for estimating the power spectrum density of output thermal noise in SC filters, which have acceptable accuracy and short running time. In the proposed method, first using HSPICE simulator, accurate value of accumulated sampled noise on sampler capacitors in each clock state is achieved. Next, using difference equations of the SC filter, frequency response of the SC filter is shaped by time domain analysis. Based on the proposed... 

In this paper a novel soft switching isolated buck rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the value of switching power loss in each state transition is investigated. The switching power loss of the converter is decreased by using zero current switching (ZCS) method. The operation modes of the converter are explained and analyzed. By using an auxiliary circuit with a simple method of energy recovery, the current is diverted away from the main power switches before they are turned off; so, switching losses in the converter are reduced. In this topology, the power transformer has only the...