مجله مواد مهندسی
پیاپی 4 (2009)

Cochlear implant is an electronic set which is used as a solution to resolve defects in hearing of deaf people. This device bypasses damaged parts of hearing system and transfers audio data directly to the nerves. As a result، it leads to a partial hearing. Despite lots of efforts and improvements to this device، it does not have ideal performance yet and efforts to improve its performance are still being carried out by many researchers. One of the most important challenges is the ability of testing new methods that are introduced by researchers، as implanting the device on patients without considering all the side effects might be dangerous. Computer simulation is a fair solution for this issue. In fact، if the simulation is performed based on a correct and accurate theory then results will be reliable and consistent with reality. This article describes the steps needed for designing and prototyping a sixteen channel Cochlear Implant signal processor using FPGA. It also proposes a computerized test method in order to evaluate its performance.

In this paper، the effect of Ti content and the number of training cycles on the shape memory behavior of TiNi alloys were investigated. For this purpose، four ingots with different composition were caste in VIM furnace and then hot-rolled and annealed. After the investigation of the shape memory effect، in order to study the two-way shape memory effect، all samples were trained in martens tic state. The results show that with increasing Ti content، shape memory effect reduces. Also، it can be seen that with increasing the number of training cycles، two-way shape memory effect increases.

In this work، the structural and electronic properties of orthorhombic LaCrO3 were theoretically investigated. The calculations have been performed using a Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method in the framework of Density Functional Theory (DFT) with various Approximations (GGA96، LDA، LSDA) using Wien2k package. The lattice constant parameters used in this work are a=5. 48A°، b=7. 76 A°، c=5. 15 A° for orthorhombic structure. The structural properties such as lattice constant، bulk modulus (B)، compressibility (kv) and the magnetic moment on the Cr site (µB(Cr)) have been studied in different approximations mentioned above. The calculations have been performed in two cases، (I) considering spin-orbital coupling and (II) neglecting spin-orbital coupling. The obtained results show that using GGA96 with spin effects is in a better agreement with other theoretical approximations. Besides، density of electronic states has been studied in orthorhombic LaCrO3. The results show that، there is a strong covalent band between O-O، Cr-O and La-O.

Zeolites have been considered as potential sorbets for hydrogen storage. So، the adsorption of molecular hydrogen on model zeolites RWY، KFI، and SAS which encompass a range of different pore structures and compositions، has been simulated employing Grand Canonical Monte Carlo (GCMC) procedure for a temperature range of 77-95K and a pressure range of 0–10 bars. The results show that the amount of adsorbed hydrogen can be affected mainly by the available volume and surface area at the same temperature and pressure. The zeolite with larger available volume shows larger adsorption capacity and the highest storage capacity were obtained for zeolite RWY.

In this paper attempt was made to study the simultaneous effects of alumina type، antioxidant wt% and sintering temperature on Permanent Linear Change (PLC) behavior of Alumina-Magnesia-Graphite refractories. Using Box-Behnken experimental design، by taking different weight percentages of brown fused alumina، calcined bauxite and Al-antioxidant into account، 13 compositions and sintering temperatures for different samples were prepared. Three different statistical and econometric models have been proposed to estimate the PLC of all different compositions. In addition، further investigations show that the cubic regression model can significantly estimate and forecast the PLC behavior of all tested and none tested samples. XRD results indicate that the amount of spinel phase has decreased with increasing the addition of brown fused alumina at the expense of calcined bauxite as well as increasing Al-antioxidant wt%.

In this study، the effect of nanoclay particles content on practical properties of wood polymer composite made of polypropylene and wood flour were investigated. For this aim، wood flour were compund with polypropylene at 50% by weight، and nanoclay with 0، 1، 2 and 3% respectivly، also 2% of MAPP was used as the coupling agent in all formulatins. Then samples were made in injection molding، and physical، mechanical، viscoelastic and flammability properties were tested according to ASTM standard. Results indicated flexural strength، tensile strength، flexural modulus، tensile modulus، elongation، storage modulus، loss modulus، char residue and time to ignition incraesd with nanoclay loading. However impact strength، burning rate، heat release rate، total smoke production، water absorption and thickness swelling were decreased by increasing of nanoclay particles content. Also the morphological study with XRD and TEM showed that nanoclay distributed as intercalation structure in polymer matrix، and the d-spacing of layers were increased with increasing of nanoclay particles content.

The objective of the study was to evaluate the effects of nucleation agent particle size on the properties of lithium disilicate glass ceramics for dentistry applications. In order to achieve this aim، the TiO2-ZrO2-Li2O-CaO-Al2O3-SiO2 system was investigated by incorporation of P2O5 and Nb2O5 as nucleation agent. Raw materials were melted and glass heat treated at different temperatures ranging from 500-900ºC to produce glass-ceramic with the lithium disilicate major crystalline phase. In the end، flexural strength and micro hardness of the samples were studied. Then، the size of P2O5 particles was changed to the size of nano particles and the effects of nucleation agent particle size on the properties of the glass-ceramics were discussed. The change of nucleation agent particle size to nano size resulted in decreasing the nucleation temperature، the changing morphology of Li2Si2O5 crystals from needle-shaped to spherical-like، the increasing volume fraction of the lithium disilicate major crystalline phase، the decreasing volume fraction of the minor and middle phases and the optimizing of mechanical properties. In the next step، Nb2O5 was used as a nucleating agent. The changing of nucleation agent resulted in the changing kind of crystalline phases and microstructure and the changing of crystallization mechanism from volume to surface. In this step، due to the crystalline phase''s directional crystallization and coarsening، many cracks were observed in these samples. By using the nucleating agent Nb2O5، the major crystalline phase became spodumene

Tungsten carbide-10wt% cobalt powders with particle size of 0/5micron were milled by high energy planetary ball mill at different balls to powder weight ratios (BPRs). The powders characterizations were studied by SEM، TEM and XRD. The best results were found at BPR equal to 15. In this ratio، the crystallite and particle size of WC decreased to 39 nm. In order to reduce the WC grain growth during the sintering process، tantalum carbide was added as a WC grain growth inhibitor during sintering. The prepared powders were compacted at 200 MPa and sintered at 1370-1450 ˚C during 1 hour. Then the mechanical and micro structural properties of the samples were determined. At optimum sintering temperature، the inhibition of WC grains growth is improved and the hardness increases from 1490 to 1615 HV30.

Cu-20%Vol Al2O3 matal matrix nano composite powder has been synthesized by using of high energy planetrary fast milling. Due to high exothermic reaction between CuO and Al powders، direct mixing of powders could not be done therefore، to solve this problem، Cu (Al) solid solution powder has been prepared to prevent against explosion in the milling chamber. It has to be mentioned that the mechanical alloying of Cu and Al (14% At.) with atomic ratio of 6:1 for 50 hours، cause to formation of Cu (Al) solid solution powder. After that CuO powder will be added to the powder mixture and milling will be continued to produce relevant composite after 100 hours. During this process، Al will be extracted from the Cu structure and with reaction by oxygen، will produce Alumina. In the other hand، Cu. (Al) solid solution turns back to the pure Cu. Presence of alumina particles (5~30 nm) have been demonstrated by TEM micrographs.

Researches show that properties of semiconductor materials such as electrical، optical and sensor properties can be improved in the nano scale. Among the semiconductor materials، zinc oxide with excellent electronic properties has been considered extremely. The application and properties of zinc oxide nanoparticles relate to their size and morphology. Therefore، many researches have been made on the synthesis of zinc oxide nanoparticles with different morphologies. In this paper، zinc oxide nanoparticles have been synthesized at different temperatures from 2- Methoxy Ethanol via chemical bath deposition. The results show that the average size of the nanoparticles is 30- 50 nm and changing the synthesis temperature causes to morphological transformation.

In this paper، SNO/ZNO nano-composites have been synthesized via chemical bath deposition، CBD and the effect of synthesize temperature on the particles size and their morphology has been studied. The obtained results show that with increasing the synthesize temperature، the particles size of nano-composite decreases and their morphology changes from plate with width and length median of 58 to 260nm for samples synthesized at 25˚C to sphere with doiameter median of 58 and 50nm for samples synthesized at 50 and 75˚C، respectively. Also، at low temperature the content of SNO nano-particles is lower than that of ZNO. In this research، the type of obtained phases، phase''s percent، particles size، morphology and specific surface area were determined by XRD، XRF، Tem، SEM and BET، respectively.