Journal of Advanced Materials in Engineering (Esteghlal)

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Trigonometric functions are among the most useful functions in the digital signal processing applications. The design introduced in this paper computes the trigonometric functions by means of the systolic arrays. The method for computing these functions for an arbitrary angle, , is the CORDIC algorithm. A simple standard cell is used for the systolic array. Due to the fixed inputs, in some cases, a number of the cells are optimized. The control unit and a read only memory are the essential parts of any CORDIC implementation. The introduced hardware does not use any of these two structures, which makes it a simple and expandable design

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In order to carry out experimental investigations on radial inflow gas turbine, a special test laboratory was designed and constructed at Sharif University of Technology. This laboratory is introduced in the present paper and experimental procedures are elaborated on. Then, some test results are presented and discussed. The trends of performance characterisitics match our expectation and show good agreement with the published research results in this field. Keywords: Radial inflow gas turbine, Experimental, Laboratory, Performance characteristics

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Application of gravity and magnetic separation methods to upgrade low grade Manganese ores from Venaj Mine has been reported elsewhere. This paper discusses the results of flotation tests, as well as combination of flotation and magnetic method to concentrate fine particles (less than 150 microns) of manganese ore. Results obtained from various direct and reverse flotation tests, using different types of reagents, indicated that manganese fines cannot easily be concentrated by flotation. In this investigation, combination of direct flotation and magnetic separation for fine particles (finer than 150 microns) with 8.36% Mn, 34.11% SiO2, 23.05% Fe2O3 yielded a manganese concentrate with 26.78% Mn, 11.64% SiO2, 20.37% Fe2O3 and 56% recovery. Desliming 10-15 micron particles prior to flotation tests improved product quality and the recovery. Keywords: Mineral Processing, Flotation, Manganese, Vanarj Mine

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Overhead transmission lines are influenced by different factors which are mostly electrical and mechanical. These factors can cause problems for lines, distortions in network and outage of line. In designing transmission lines mechanical properties are evaluated after selecting a suitable conductor and clearance with regard to electrical properties. In lines designing, an important mechanical parameter for estimating of phase distance is oscillations. Strong wind or ice fall from conductor surfaces or simultaneous presence of ice and wind may cause different oscillations. These oscillations are classified to aeoliane, galloping, and swing. Aeoliane is of high frequency (5-100Hz) and low amplitude (about a few centimeters), galloping is of low frequency (0.1 to 0.3Hz) and high amplitude (about of span sagging), also swing is of horizontal oscillation. In this paper, the mechanism of conductor galloping oscillation and its different types are described. Also these oscillations are simulated on the typical span by personal computer. Keywords: Galloping, Overhead transmission lines, Single conductors, Modeling

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Dense Silicon nitride was investigated to determine the effect of its microstructural parameters and densification on thermo-mechanical properties and thermal stress resistance to fracture initiation during a hot or cold mechanical and thermal shock testing. The different materials and microstructures were obtained by changing the parameters such as the type of the powder, additive, forming process and sintering condition. Maximum crack growth and thermal shock resistance of dense Si3N4 are achieved after complete conversion of the aàB transformation, and after the change in grain morphology towards elongated grain and the relative crystallization of the second phases have been obtained. The characteristics are obtained by a high a phase content of the starting powder, high Y2O3, and sintering condition of higher temperature (2000ْC), longer soaking times (1h) and load application at the beginning of the thermal cycle. Keywords: Silicon nitride, Thermo- mechanical properties, Thermal shock resistance, Crack propagation resistance

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Hidden Markov Model is a popular statisical method that is used in continious and discrete speech recognition. The probability density function of observation vectors in each state is estimated with discrete density or continious density modeling. The performance (in correct word recognition rate) of continious density is higher than discrete density HMM, but its computation complexity is very high, especially in very large discrete utterance recognition problems. For real time implementation of very large discrete utterance recognition, we must use discrete density HMM (DDHMM). To increase the performance of DDHMM, one usual solution is fuzzy interpolation. In this study, we present a new method named Gaussian interpolation. We implemented and compared the performance of two types of interpolation methods for 1500 Persian speech command words. Results show that precision and flexibility of Gaussian interpolation is better thanthose of the fuzzy interpolation.

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Zinc-Nickel electrodeposits have been widely adopted for surface treatment of automobile steel sheet for high corrosion resistance. In this work the effect of pulse parameters on the Zn-Ni alloy electrodeposits was investigated. The hardness, thickness, corrosion resistance and composition of deposits thus produced were investigated. The surface topography of the deposits was also observed in SEM and results are reported. It has been shown that the thickness of the pulse electrodeposits was almost even. The hardness in the pulse electrodeposits increased by increasing the on-time period and by decreasing the current density. It was also noticed that increasing the on-time period increases the nickel content of the deposit. Pulse electrodposits had fine structure and the structure become finer by reducung the on-time period and pulse frequency. The corrosion dehaviors of the deposits were then investigated. The results showed that the corrosion resistance of the DC electrodeposits improves in their nickel content increases. Pulse electodeposits show the same behavior, but deposits with about 13% nickel show maximum corrosion resistance.

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A special class of the knapsack problem is called the separable nonlinear knapsack problem. This problem has received considerable attention recently because of its numerous applications. Dynamic programming is one of the basic approaches for solving this problem. Unfortunately, the size of state-pace will dramatically increase and cause the dimensionality problem. In this paper, an efficient algorithm is developed to find surrogate multipliers in each stage of dynamic programming in order to transform the original problem to a single constraint problem called surrogate problem. The upper and lower bounds obtained by solving the surrogate problem can eliminate a large number of state variables in dynamic programming and extremely reduce the duality gap according to our computational results.

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In this paper, the Radiation Transfer Equation(RTE) for a non-gray gas between two large parallel planes has been solved and the temperature distribution obtained. With the RTE, solution heat fluxes are also determined. Since and are two components of most combustion products, the problem has been solved for these two gases. The results were, whenever possible, compared with data reported elsewhere. Since the simulation of exact absorbing bands has been used, it can be claimed to be relatively close to exact solution. From the results otained, it can be maintained that treating, the above mentioned gases as a gray gas could cause considerable errors in the determination of temperature distribution and heat fluxes. The error would be more for water vapour than for carbon dioxide.

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Artificial Neural Networks are information processing systems. Over the past several years, these algorithms have received much attention for their applications in pattern completing, pattern matching and classification and also for their use as a tool in various areas of problem solving. In this work, an Artificial Neural Network model is presented for predicting the tensile properties of cotton-covered nylon core yarns. Multilayer Feedforward network with Back Propagation learning algorithm was used to study the relationship and mapping among the process parameters, i.e. count of sheath part, count of core part, applying pretension to the core part, inserted twist to the core spun-yarn as well as tensile properties, i.e. breaking strength and breaking elongation. The results show that ANN is an effective method for the prediction of the tensile properties of these yarns. This is due to the fact that in each case, standard deviation of prediction error for test and train data was less than that obtained from the expreiments.

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A physical model of gabion overflow dams was studied to determine the velocity profile and Reynolds shear stress. Physical tests were done under two different conditions of dam crest, overflow dams with impermeable and with permeable crests. Instantaneous velocity components over dam crest were measured by an ADV (Acoustic Doppler Velocimeter) instrument. This instrument is capable of measuring instantaneous velocity components with frequencies up to 25 Hz. Average velocity components and bed shear stress were extracted from ADV measurements. The results of this research show the effect of crest permeability on velocity and Reynolds shear stress. The magnitude of Reynolds shear stresses, horizontal velocity components, and absolute value of vertical velocity components under the permeable scenario are bigger than those of the impermeable scenario. Velocity distribution over the dam crest is different from the universal logarithmic profile.

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A systolic serial multiplier for unsigned numbers is presented which operates without zero words inserted between successive data words, outputs the full product and has only one clock cycle latency. The multiplier is based on a modified serial/parallel scheme with two adjacent multiplier cells. Systolic concept is a well-known means of intensive computational task through replication of functional units and their repetitive use. Digital signal processing applications often involve high-speed sequential data. Bit-serial processing in particular can result in efficient communications, both within and between VLSI chips because of the reduced number of interconnections required. Serial input multipliers have received considerable attention, particularly for hardwired VLSI algorithms used in signal processing application, due to their minimal chip area required for interconnections. Bit-serial architectures are often used in parallel systems with high connectivity to reduce the wiring down to a reasonable level. The conventional add-shift technique for multiplication, which uses a minimum number of gates, is inexpensive to implement, but too slow to achieve the desired result. Iterative array multipliers are needed to satisfy the high speed requirement of systems. With the advantage of high scale integration, the hardware is not regarded as a major obstacle in implementation.

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In this paper, two suboptimum detectors are proposed for coherent radar signal detection in K-distributed clutter. Assuming certain values for several initial moments of clutter amplitude, the characteristic function of the clutter amplitude is approximated by a limited series. Using the Pade approximation, it is then converted to a rational fraction. Thus, the pdf of the clutter amplitude is obtained as a sum of simple exponential functions. Using such a pdf, we develop the suboptimum detectors PGLR and PAALR, which are simplified forms of the GLR and AALR. Computer simulations show that the suggested detectors have appropriate performance compared to OLD, GLR and AALR detectors.

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This paper presents a nonlinear mixed-integer programming model to minimize the stoppage cost of mixed-model assembly lines. Nowadays, most manufacturing firms employ this type of line due to the increasing varieties of products in their attempts to quickly respond to diversified customer demands. Advancement of new technologies, competitiveness, diversification of products, and large customer demand have encouraged practitioners to use different methods of improving production lines. Minimizing line stoppage is regarded as a main factor in determining the sequence of processing products. Line stoppage results in idleness of operators and machines, reduced throughput, increased overhead costs, and decreased overall productivity. Due to the complexity of the model proposed, which belongs to a class of NP-hard problems, a meta-heuristic method based on a genetic algorithm (GA) is proposed to obtain near-optimal solutions in reasonable time, especially for large-scale problems. To show the efficiency of the proposed GA, the computational results are compared with those obtained by the Lingo software.

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In recent years, many different plans have been considered to use the nuclear energy gained from inertial confinement fusion (ICF) as attempts to obtain high energy efficiencies. In conventional ICF methods, a small amount (about mg) of the deuterium–tritium compound is confined in a small spherical chamber of a few millimeters in radius and compressed by laser or heavy ion beams with powers in the order of W. The consequent plasma froming at the center of the chamber is an essential issue for fusion. The hydrodynamical instabilities during the fuel compression process arising in the conventional ICF technique leads to a decline in energy efficiency. The new plans for reducing instabilities involve compression of the fuel chamber in two stages using laser or ion beams. In the first stage, fuel is preheated by laser or ion and in the second phase, relativistic electrons are constructed by -W laser phases in the fuel. This heating method has come to be known as a fast “ignition method”. More recently, cylindrical rather than spherical fuel chambers with magnetic control in the plasma domain have been also considered. In this work, fast ignition method in cylindrical fuel chambers will be investigated and transportation of the relativistic electrons will be calculated using MCNP code and the Fokker–Planck program. Furthermore, the transfer rate of relativistic electron energy to the fuel will be calculated. Our calculations show that the fast ignition method and cylindrical chambers guarantee a higher energy efficiency than the one-step ignition and that it can be considered an appropriate substitute for the current ICF techniques.

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In this paper, bare spot defects in hot-dip galvanized sheets were studied in terms of the microstructure and their influence on the corrosion and mechanical properties. Surface characteristics and microstructural features were examined by scanning electron microscopy equipped with energy dispersive spectroscopy microanalysis system. The results showed that the major cause of the bare spots was the lack of wetability of the sheet surface due to contamination, improper heat treatment or chemical composition. Corrosion resistance was evaluated by standard salt spray test. Mechanical properties were examined by tensile testing. The time to red rust was much shorter on the bare spots as compared to other regions, but it appeared that bare spot defects had no significant effect on the mechanical properties of the galvanized steel sheets.

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Recently, high – K materials such as Al2O3 and TiO2 films have been studied to replace ultra thin gate silicon dioxide film. In the present work, these films were grown on the top of Si(100) surface at different temperatures and under ultra high vacuum conditions. The obtained results showed that Al2O3 has a structure better than that of TiO2 and thus can be used as a good gate dielectric for future MISFET (Metal – Insulator- Semiconductor- Field – Effect- Transistors) devices.

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In this paper, preparation and characterization of a-SiNx thin films deposited by LPCVD method from free radicals of TCS and NH3 gaseous system were investigated. These radicals are made by passing each of the precursor gases separately over Pt-Ir/Al2O3 catalyst at the temperature of 600 ᐤC. Kinetics of this process was investigated at different total pressures, NH3/TCS flow rate ratios and temperatures. Surface topography and chemical concentrations were studied by Ellipsometry, XXPS, AFM and ADP. Our analyses of the performed experiments indicated that at the temperatures between 730 ᐤC and 830 ᐤC, the growth rate of thin films follows an Arrhenius behavior with activation energy of 166.3 KJ.mol-1. The measured H2 contamination in a-SiNx thin films is 1.05 at%, which is 17 times lower than the corresponding contamination in the films produced by PECVD and 3.4 times lower than the contamination in the LPCVD thin films with SiH4 or DCS and NH3. The created surface topography of the prepared films is smooth and uniform.

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In some applications such as morphing technology, high strain and anisotropic behavior are considered a good advantage. The corrugated composite sheets due to their special geometries have a potential of high deflection under axial loading. In this research, to investigate the strain and anisotropic behavior of corrugated composite sheets some glass/epoxy samples with Quasi-sinusoidal, trapezoidal, rectangular and triangular geometries were manufactured and put to tension and flexural tests in the longitudinal and transverse directions of corrugation. Then, in order to determine anisotropic behavior of corrugated sheets two concepts were introduced: tensile anisotropic and flexural anisotropic criteria based on which anisotropic magnitude was investigated theoretically and experimentally. This research used Yokozeki’s theoretical model for quasi-sinusoidal geometry and his model for trapezoidal, rectangular and triangular geometries. Experimental results showed that corrugated sheets have a strain more than 90%. In the corrugated samples, the strain magnitude was dependent on amplitude and pitch of elements in other words, it was dependent on the number of elements per length unit. Generally, the Quasi-sinusoidal corrugated sheets have a high strain (more than 50%). Experimental results of trapezoidal sheets showed that amplitude of the elements is one of the most important parameters in the ultimate strain. Generally, increasing the amplitude leads to the growth of the ultimate strain