Journal of Advanced Materials in Engineering (Esteghlal)

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The useful and efficient method of Finite Element (FEM) has a drawback for dynamic analysis of complex structures, especially in the medium and high frequency range. To overcome this fundamental difficulty, application of Statistical Energy Analysis (SEA) and power flow technique has been suggested. As the SEA is based on the average response of structure and statistical properties of its resonant modes, SEA is found to be effective in cases like high modal density, high modal overlap and in short wave length. In these cases, the average response is found to be both real and an acceptable value, contrary to the FEM which is not accurate enough. In this study, the fundamental difficulties of FEM in the high frequency range are explained and then the advantages and applications of SEA and power flow technique are presented. Moreover, a description of SEA basis, fundamental concepts of General Energy Method (GEM) are explained and formulated to be used in the longitudinal and transversal vibrations of beams. Finally, by satisfying the energy boundary conditions, the energy flow analysis of rods and beams with elastic support and under harmonic excitation are investigated.

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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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Routing is one of the basic parts of a message passing multiprocessor system. The routing procedure has a great impact on the efficiency of a system. Neural algorithms that are currently in use for computer networks require a large number of neurons. If a specific topology of a multiprocessor network is considered, the number of neurons can be reduced. In this paper a new recurrent neural network and its energy function is introduced. This network requires a significantly smaller number of neurons compared to its counterparts. Also presented is the performance of this neural network. Keywords: Routing, Multicomputer systems, Recurrent neural networks, Mesh interconnection networks.

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Fabrication of an integrated circuit with smaller area, besides reducing the cost of manufacturing, usually causes a reduction in the power dissipation and propagation delay. Using the static CMOS technology to fabricate a circuit that realizes a specific logic function and occupies a minimum space, it must be implemented with continuous diffusion runs. Therefore, at the design stage, an Eulerian path should be found for the logic function. Every discontinuity causes an increase in the area as well as a reduction in the clock rate and performance. The realization of a logic function using the static CMOS technology is done through different methods, most of which are based on the Uehara's method. In this paper, an algorithm is suggested that finds the Eulerian path and allows the implementation of the circuit with continuity in the diffusion region that results in minimum area. In a case where there is no Eulerian path, the possible sub-paths are found. In addition, the algorithm gives information that helps the layout generation. Keywords: VLSI, Uehara's method, Static CMOS, Continous diffusion, Standard cell.

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A variety of methods are used for speaker adaptation in speech recognition. In some techniques, such as MAP estimation, only the models with available training data are updated. Hence, large amounts of training data are required in order to have significant recognition improvements. In some others, such as MLLR, where several general transformations are applied to model clusters, the results are desirable for small training data, but with increasing training data, the performance improvement reaches the saturation lvel. In this paper, a new approach is introduced that makes use of the advantages of both mentioned techniques to improve the recognition rate. Here, the models with available training data are trained using MAP while for those with insufficient training data, appropriate prior parameters for MAP estimation are found using MLLR. This technique has yielded better performance in comparison to either MAP or MLLR, in a system based on FARSDAT speech corpus.

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: The CIECAM97s and its revision, as a colour appearance model, were applied for a series of fabrics with different colours and depths to explain their colour appearance coordinates in similar viewing conditions. The results show that due to some modifications which expand the scale, the modified model has improved capadilities in calculating chroma. Besides, the calculations were simpler for the revised version of CIECAM97s model while the results from the two models were the same.

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In this paper, the equation of motion of an elastic 2 DoF wing model has been derived using Lagrange's method. The aerodynamic loads on the wing were calculated via the Strip-Theory and the effect of compressibility was included. Wing deflections due to bending and twist motions were determined using the Assume-Mode method. The aeroelastic equations were solved numerically using the V-g method. The results obtained for different types of wings were in good agreement with experimental data.

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An intensive experimental investigation was conducted to study the effect of vertical tail, single and twin (with different cant angles) on the flow field and the corresponding aerodynamic forces and moments of a model of a fighter A/C. Aerodynamic forces under different flight conditions and different vertical tail settings were measured in a supersonic wind tunnel. Furthermore, effects of vertical tail on the model wake at subsonic speed were investigated. In addition to the force and pressure measurements, schlieren system was used to visualize the shock formation and movement oat various locations on the model. The results show existence of a pair of symmetric vortices for the model equipped with a 22 degree vertical tail cant angle. The vortices burst symmetrically at moderate angle of attack. The drag coefficient increases with increasing cant angle at low to moderate alpha and decreases when alpha is further increased.

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In this study, ZrB2-HfB2 composite was produced by pressureless sintering method. MoSi2 B4C and SiC particles were used as reinforcement. ZrB2 powder was milled in planetary ball mill apparatus and then reinforcement particles were added to the milled powder. The composite powders were then CIPed and sintered at 2100oC and 2150oC. Scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDS), flexural test, and resonance frequency method were used to compare the added particle effects on mechanical properties and pressureless sintering behavior of ZrB2-HfB2 composite. The analysis showed that the ZrB2-HfB2-MoSi2-SiCnano composite displays the largest gain in flexural strength. Furthermore, increasing the sintering temperature leads to an increase in flexural strength of samples.

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In this paper, the effect of Equal Channel Angular Pressing (ECAP) process on the structure and mechanical properties of AM30 magnesium alloy was studied. The results showed a considerable effect of ECAP process on creating an ultrafine grain size structure. Scanning Electron Microscope indicated that the grain size dropped from 20.4 µm in the extruded form to 7.2 µm in the first pass and 3.9 µm in fourth pass. The fourth pass presented higher ductility and lower yield stress in comparison with the extruded case. This behavior can be explained based on higher rate of texture softening versus the effects of the grain refinement on strength. The hardness test on the samples cross-section showed an increase in hardness and a uniform strain distribution at higher ECAP passes.

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In this study, AlN whiskers were prepared in a tube furnace at 1000˚C for 1h with 500 nitrogen gas flow. Al powders with particle size of 3 μm and 45 μm and NH4Cl were used as raw materials. SEM, TEM and XRD analysis were used to characterize AlN whiskers. The results showed that the diameters of AlN whiskers would range from 140 nm to 340 nm if different amounts of NH4Cl and 3 μm Al powder were used. In the case of using NH4Cl more than 40wt%, pure AlN without any unreacted Al was formed as the final product. Using NH4Cl and Al with particle size of 45 μm led to AlN whiskers with 630 nm to 870 nm in diameter. By adding 50%wt NH4Cl, pure AlN was formed. The diameter of the whiskers was increased by increasing NH4Cl content in starting materials (about 200 nm). Also, an increase in the diameter of AlN whisker resulted from coarse Al powder. By adding NH4Cl to Al, thermodynamically spontaneous cholororination - nitridation reactions were increased in vapor phase and whiskers and pure AlN powder were produced.

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The aim of this investigation was to produce Ti47Al48Mn5 intermetallic compounds with different microstructures in order to study their oxidation behavior. The reason for selecting manganese as an alloying element was to enhance the toughness of the compound. Ti47Al48Mn5 alloys were obtained through mechanical alloying, cold pressing and heat treatment. XRD results showed that milling of the elemental powder mixture for 30 hours causes the formation of Al and Mn in Ti solid solution, while by increasing milling time up to 50 hours, amorphization of powder mixture occurs. To obtain duplex and fully lamellar microstructures, the mechanically alloyed powders were cold pressed and then heat treated at 1100 °C and 1400 °C in argon atmosphere for 50 hours, respectively. The results of the oxidation test at 1000 °C revealed that the different microstructures of Ti47Al48Mn5 alloy investigated in this study have little effect on the oxidation resistance, and similar oxidation mechanisms existed for the two microstructures.

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In the present research NdFeB thin films coupled with buffer and capping layer of W were formed on Si/SiO₂ substrate by means of RF magnetron sputtering. The system was annealed at vaccum at different temperatures of 450, 500, 550,. 600 and 650 °C Phase analysis was carried out by XRD and it was found that NdFeB was formed without the formation of any kind of secondary phase. The cross sectional and grain size of the thin films were measured by scanning electron microscopy. Morphological studies were performed by atomic force microscopy. Magnetic properties of thin films including coercivity, saturation of magnetization and hysteresis area were evcaluated by vibrating sample magnetometer. It was found that by annealing at 400 °C the amorphous layer was formed.The highest intensity of peaks was formed at 550 °C and with an increase in temperature the intensity was declined. The grain size was increased by temperature and had an impact on the coercivity. With an increase of temperature up to 600 °C, perpendicular coercivity was increased and then by further increase of temperatute, coercivity was reduced. Based on the obtained data the temperature of 600 °C was selected as the optimum annealing temperature for reaching enhanced structural and magnetic feature.

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In this study, iron powder (~45 μm) with the  minimum purity of 99% was insulated by the 1 to 4 wt% sodium silicate insulator (SiO₂.3Na₂O solution in 40 wt% water) and the 0.5 wt% zinc stearate. Insulated powders were pressed in a die with  a toroidal shape at the pressure of 320 MPa. The effects of insulator percentage and annealing temperature on the magnetic permeability, core loss tangent, and the total loss were investigated. The results indicated that the sodium silicate insulator could be suitable for insulating iron powders used in iron powder cores for high frequencies up to 1000 kHz. Also, this insulator could be stable against heat up to 450 °C.

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In this study, the synthesis of nano-porous calcium magnesium silicate was performed and studied to improve drug properties and drug release. This synthesis was carried out by using the tetraethyl ortho silicate precursor (TEOS) and the Cetyltrimethyl ammonium bromide surfactant (CTAB) in a sol-gel alkaline environment; and the product was heat treated at 600° C and 800° C temperatures. The purpose of this study is to investigate the effect of the calcination temperature on the potential for ibuprofen release by the production produced compound. The product was studied using X-ray diffraction patterns (XRD), Nitrogen adsorption / desorption, Fourier-transform infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV) and Transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The results of Nitrogen absorption-desorption assay showed a surface area of 42-140 m² /g The drug release after 240 hours showed that the calcite sample had a lower release at 600 ° C, temperature that which was is due to the smaller size of the cavities and the more surface area, as compared tothan the other specimens. Also, calcium and magnesium elements increased  the loading capacity, and createcreating a suitable substrate for for the slower drug release. Overall, This this study showed that nano-porous magnesium silicate calcium has had  the ability to load and release the ibuprofen and can could be, therefore, used as a modern drug delivery system in the bone tissue engineering field.
 

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