https://cjemt.ausmt.ac.ir/ Caspian Journal of Engineering Modern Technologies en daily 1 Sat, 01 Jun 2024 00:00:00 +0330 Sat, 01 Jun 2024 00:00:00 +0330 https://cjemt.ausmt.ac.ir/article_196684.html In this paper we propose a model to evaluate the dispersion relationship of Carbon Nanotubes. The model is based on the application to band-structure calculation of both of them the tight-binding approximation and the theory of Linear Combination of Atomic Orbitals (LCAO), obtaining a reduction of computational time compared to other methods proposed in literature, without losing in accuracy. https://cjemt.ausmt.ac.ir/article_196686.html Chitin and its valuable derivative chitosan offer a set of unique properties: biocompatibility, biodegradability for harmless products, non-toxicity, physiological inertness, etc. The main resources exploited are two marine crustaceans; shrimp and crab. In the present study, our aim is to produce chitin and chitosan and compare their properties with commercial properties. Due to the possibility of industrial and mass production, pre-purification methods were used to produce standard chitin and chitosan. In this regard, after the treatment of the shrimp, their shells were further cleaned and facilitated for the processes of demineralization, deproteinization, and deacetylation. Deproteinization was done with 1 M of sodium hydroxide and demineralized with 1%, 2%, 3%, 4% and 5% of hydrochloric acid, respectively. The novelty of this work is comparing different concentrations of HCl to choose the best concentration for the production of chitin and chitosan. This method showed the high purity of chitin and chitosan with less than 1% protein residue along with high molecular weight and high crystallinity. The produced chitin and chitosan were characterized by FTIR and XRD analyses. It was found that the surface morphology of chitin increases with increasing acid concentration. According to our study, the best degree of deacetylation (%DD) was 88.76 %. This modified approach has the potential for large-scale production due to ease of operation and reduced environmental issues. https://cjemt.ausmt.ac.ir/article_196685.html Photonic BandGap (PBG) crystals are able to overcome the typical integration limits of traditional optical circuits, allowing a scale of integration similar to the electronic ULSI. According to their geometrical characteristics, photonic crystals inhibit the light propagation in one or more directions, depending on the working frequency: if so, a band gap exists, i.e. a frequency range in which the wave cannot propagate.  Moreover, the introduction of defects inside the periodical structure of a photonic crystal determines the forming of photonic states located in the gap. In this paper, after a brief description of operation principle of photonic crystals, we present a review of the most important photonic crystals devices, describing, in particular, the main steps required to model and design resonant cavities and particle accelerators. https://cjemt.ausmt.ac.ir/article_196682.html A nano-engineered superhydrophobic coating was fabricated using a two-step and low-cost method employing a liquid oxy-acetylene flame spray mechanism on mild A516 steel. Oxygen and acetylene were used as flammable gases. Nanostructured coating is obtained by flame spraying aluminum nitrate solved in ethanol on the substrate. To lower the surface energy, Perfluorodecyltriethoxysilane [PFDTES] and silicone elastomer were used. Results revealed that the wettability of the surface strongly depends on the precursor concentration so that at 3.5% concentration of aluminum nitrate in ethanol, maximum contact angle [157°] occurs. The distance between the substrate and nozzle is another key parameter to control and it directly affects the contact angle. Sandpaper abrasion test showed outstanding mechanical durability so that the coating maintained in hydrophobicity range under the load of 100 grams of weight and moving 10 cm on sandpaper 1000 grit for 8 cycles. The parameters affecting the process were thoroughly analyzed according to the applied liquid flame spray mechanism and the appropriate performance range of each was obtained that According to the experiments, the precursor flowrate and the distance between the substrate and nozzle should be repectively 0.9-1.9 ml/min and 14-22 cm. https://cjemt.ausmt.ac.ir/article_196687.html In this review we first examine the main issues of nanotechnology. In particular, in the broad scenario of nanoscale devices, we present a detailed study of Carbon Nanotubes (CNTs), which arouse a growing interest for their unique properties and their versatility. We study and characterize the electronic properties of carbon nanotubes through the determination of the relationship between structure and electronic characteristics of CNTs. https://cjemt.ausmt.ac.ir/article_196683.html We present a theoretical study of electromagnetic defect states localized at a defect layer with left-handed (LH) material between two symmetric semi-infinite one-dimensional photonic crystals (1DPCs) composed of right-handed (RH) materials. We consider magnetic permeability and electric permittivity of LH layer being dispersive. An analytical direct matching procedure within the Kronig-Penney model was applied to analyze the dispersion properties of the localized defect states. It is shown that the dispersive LH layer act as an effective tool to tune the type of defect modes from backward to forward and vice versa and it plays an important role on the localization of them, when the frequency and the parameters of the defect layer vary. Also, we show that when the LH layers are chosen dispersive, three types of dispersion:  positive, zero, and negative dispersion of defect waves are obtained in a wide range of radiation angle and frequency, which is depending on the physical and optical parameters of the defect layer. https://cjemt.ausmt.ac.ir/article_213515.html    In this paper we present a comparison among I-V models of CNTFETs proposed in literature in order to determine the model more easily implementable in simulation software for electronic circuit design. In particular we have compared the CNTFET model, already proposed by us, with Deng-Wong’s and Koswatta’s models. Our model, already structured to implement in simulator software, has been modified to characterize the I-V characteristics of CNTFETs below threshold, because the other examined models consider the behaviour of device in sub-threshold regime. In spite of other models, our model seems to allow an easier implementation in the computer aided design of the most common analogue and digital circuits, showing a good agreement between the experimental and simulated characteristics, with processing times practically instant. https://cjemt.ausmt.ac.ir/article_213516.html A model of Waveguide Photonic Band Gap (WPBG) structures, based on Leaky Mode Propagation (LMP) method, has been developed to perform a complete analysis of the electromagnetic (e.m.) wave propagation including the radiation loss for a structure of finite extension. The model allows to determine the mode propagation constants, electromagnetic harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided power and total losses. Moreover, the mode amplitude attenuation constant, radiated power, the angle of radiation and radiation efficiency both in the cover and substrate, for both TE and TM modes, can be determined. https://cjemt.ausmt.ac.ir/article_213517.html The aim of this paper is to propose a procedure to analyze the behavior of Carbon NanoTube Field Effect Transistors (CNTFETs) operating in sub-threshold region for ultra-low power applications, through the design of a SRAM cell, in which we use a CNTFET model, already proposed by us. The proposed technique allows to obtain easily static, dynamic and transient analysis, in order to determine the optimal operating condition.  All simulations are carried out using the software Advanced Design System (ADS), which is compatible with the Verilog-A programming language.