Malek Ashtar University of Technology
Recent publications
Assessing the geometric characteristics of a track is the first step in indicating the results of the laser cladding process. In this research, the effect of three essential process parameters, namely scanning speed, laser power, and powder feed rate, on the geometric characteristics of the Inconel 718 track on the Inconel 738 substrate have been studied. The goal of this research was to obtain the optimal process parameters for Inconel 718 laser cladding. To investigate the impact of process parameters on the geometric characteristics, five levels of laser power, three levels of scanning velocity, and three levels of powder feed rate have been considered, and a full factorial design of experiment has been performed. Consequently, 45 tracks have been cladded, and their geometric characteristics, including penetration depth, wetting angle, track height, track width, and compound characteristics such as dilution, has been investigated. After analyzing the results, the behavior of the geometric characteristics for the same process parameters in other brackets have been predicted via linear regression and genetic optimization via MATLAB software. PαVβFγ is participating in Y=aX+b as a compound variable. The regression process is feasible via accurate estimation of exponents α, β and γ. Therefore, the genetic algorithm was used to reduce the errors of linear regression. It is concluded that all of the process parameters have quantitative and qualitative effects on the geometry of the track. Finally, based on the modeling results, a process map was drawn to predict the impact of process parameters on the track geometry.
The gas discharge for a plasma limiter is simulated at the S-band (2.86 GHz) microwave with 500 kW peak power in three-dimensions. We employed a standard rectangular waveguide WR284 along with metal pins. In this paper, the influence of radius and gap size of pins and also gas type and pressure on the plasma parameters and the limiter operational characteristics are investigated by the finite element method. The wave equation, electron drift–diffusion equation, and particle transfer equation in plasma are used to characterize the interaction between electromagnetic wave and plasma. The optimization parameters include plasma thickness, S21 parameter, response time, insertion loss, and flat leakage. Based on these analyses, the plasma limiter operation is optimized with respect to the pin dimensions, gas type, and pressure. The results show that the optimized parameters for the plasma limiter at S-band are 1 mm pin radius and 4 mm gap between pins. Furthermore, Xe gas at pressure 35 torr has best operation for these pins structure. For these parameters, the plasma limiter is able to switch with a fast response time about 1 ns, to the cutoff operation regime. The proposed plasma limiter could cause a sharp drop in the field amplitude of the incident microwave and reduce the transmitted peak power to 2mW, providing proper protection of the radar system electronic equipment against high power microwave (HPM) threats.
This paper examines the mechanical behavior of carbon nanotube (CNT)/epoxy nanocomposites with and without vacancy defects in the nanotube under uniaxial tension at different loading rates using molecular dynamics (MD) simulation. In order to validate the simulation process, first CNTs and polymer matrix were modeled separately with their behavior and performance investigated, showing the proper agreement of the physical and mechanical properties of the developed models with available studies. In the research process, a method was proposed for controlling the strain rate during loading using Souza-Martinez barostat to control the deformation uniformly. The results revealed that increasing the strain rate (at high rates) had little effect on the mechanical behavior of the isolated CNTs, while enhancing the mechanical properties of the pure polymer. The mechanical behavior of nanocomposite changed at different strain rates, and with elevation of the strain rate, the strength of nanocomposite decreased. Also, the presence of defects affected the form and sensitivity of the mechanical properties of the nanocomposite to the strain rate.
A one pot three component reaction of acenaphthoquinone, barbituric acid/thiobarbituric acid/N,N-dimethyl barbituric acid and arylamines in ethanol for the synthesis of acenaphthoindolopyrimidine derivatives is reported. The reactions take place without a catalyst and gentle conditions. This method is facile and has some benefits such as, readily available starting materials, green solvent, catalyst-free, no column chromatographic purification and good to high yields. Graphical abstract
A new single switch ZVS forward converter with a wide soft‐switching range is proposed here. Compared to the conventional forward converter, the proposed converter uses fewer components and operates under ZVS soft switching. A capacitor, along with both the leakage and magnetizing inductances, provides ZVS soft switching and transformer core reset. To regulate the output voltage against the input voltage and the load variations, an inductor is added to the converter. The inductance of the additional inductor varies with the direct current (DC) of the DC bias winding to regulate the output voltage. Therefore, the duty cycle and the switching frequency are constant in the proposed converter. With the constant duty cycle and the constant switching frequency, the wide ZVS soft switching is achieved. The proposed converter is completely analysed theoretically. The finite element analysis is used to design the additional inductor. By designing an experimental prototype, the theoretical analysis is justified using the experimental results.
Faced with new supply chain challenges, modern companies collaborate with suppliers and consider backup suppliers and circular supplier selection criteria. To resolve this problem, a hybrid approach of DSM clustering and a multi-objective model is developed for the issue of reliable circular supplier selection and order allocation in a circular closed-loop supply chain. The approach considered collaborative costs, circular criteria, shortage, collaboration network reliability, order allocation, competencies, module assignment, capacity, and backup suppliers at the same time and specified the optimal configuration of modules at the early stages of product design. We modeled collaborative costs as a quadratic function. The model maximized suppliers' circularity, skill level, and network reliability. We used the augmented epsilon constraint method to validate the model. The model was evaluated through numerical experiments on real and artificial datasets. The approach was applied to the electro-optical camera. With the implementation of the approach on the artificial network (15 suppliers), the optimal number of modules was equal to four, and the main suppliers = [1, 2, 3, 4, 9, 15], backup suppliers = [3, 4, 8], and optimal orders = [6, 2, 1, 1, 1, 3] were obtained. When it came to the electro-optical camera (10 suppliers), six modules were computed according to experts’ opinions; the main suppliers = [1, 2, 3, 8, 9, 10] and the backup supplier = [4] were achieved. The results demonstrate the applicability and efficiency of the approach and effectively design a main and backup reliable circular supplier network with efficient costs, optimal modules, and backup suppliers. It is suggested that the approach be applied to other products and metaheuristic algorithms be employed to solve large-scale problems.
In this study, the possibility of replacing non-renewable jet engine fuels with biodiesel produced from household waste oils, rapeseed, and Neochloris overabundance microalgae was investigated. To optimize biodiesel production, firstly, the effect of 4 parameters of oil to methanol molar ratio, catalyst weight percentage, temperature, and process time in three levels for household waste and rapeseed oil were investigated using the Taguchi method. The biodiesel production efficiency under the optimal conditions of 1 (w/v)% catalyst, the molar ratio of oil to methanol 1:8 at 65 ℃ for 80 min for waste oil and 40 min for rapeseed oil was 85.83% and 72.7%, respectively. Then, under the optimal conditions (1.1 (w/v/)% catalyst percentage, 1:8 molar ratio of oil to methanol at 65 ℃) obtained by investigating the effect of catalyst percentage and process time as the most impressive parameters on microalgae oil transesterification at three levels by the response surface method, the biodiesel production efficiency of microalgae oil was 86.25%. Gas Chromatography - Mass Spectroscopy (GC-MS) analysis of samples showed a transesterification reaction efficiency of more than 96%. Combustion and qualitative analysis such as flash point, cloud point, pour point, freezing point, viscosity, density, and specific gravity on the produced biodiesels showed that all three biodiesel have the same performance as Jp-4 jet fuel without deposits. Also, Microalgae oil biodiesel with a flash point of 188 ℃, cloud point -of 3℃, pour point -of 8℃, a viscosity of 4.5 mm2/s, a density of 0.882 g/mL, and specific gravity 0.882, calorific value 40.2 (Mj/Kg) had the best performance.
In this study, superhydrophobic surfaces were fabricated on aluminium substrates by chemical etching method and surface modification with perfluorooctyl trichlorosilane (PFTS). The superhydrophobic surface of the aluminium substrate was synthesized by two-step process: first, the roughness on the aluminium surface was created by the chemical etching method. Then, the surface energy of the rough aluminium substrate was reduced by immersion in the PFTS solution. The surface wettability was measured by a droplet contact angle measurement. The morphology and chemical composition of the surface were detected by field emission scanning electron microscope and attenuated total reflection-Fourier transform infrared methods, respectively. The self-cleaning properties of the coated and bare aluminium substrates were investigated. Corrosion behaviour of the samples was evaluated using Tafel polarization and salt spray methods. The contact angle measurement results showed that the surface roughness due to chemical etching reduced the contact angle on the aluminium substrate to 24° and after surface modification, the contact angle increased to 157°. In the Tafel polarization test, after creating a superhydrophobic surface, the corrosion current density and corrosion potential of the aluminium substrate reached from 94.3 to 28.82 (µA cm−2) and −0.695 to −0.68 V, respectively. The superhydrophobic aluminium surface showed self-cleaning effect.
The purpose of this study is to focus on the relationship between competitive advantage’s criterion of science and technology parks and incubators in order to identify factors with greater efficiency, focus on them, and develop them further in these centers. The key factors affecting the competitive advantage which prepared by our ex-study realized in the form of a DEMATEL questionnaire, and it was drawn up by experts. Questionnaires have been distributed via mail or presence in science and technology parks and experts’ office. The obtained results from the questionnaires on analysis of competitive advantage’s factors were evaluated by using Microsoft Excel, and the results of the review were modeled by yEd graph editor. Eventually, the obtained model was discussed and analyzed. In this research, the effectiveness and influence of each factor of competitive advantage in incubators and science and technology parks on the other factors are studied and the results are presented as chart and graph.
In this research, KO2 pellets as a solid adsorbent have been evaluated for the CO2 adsorption process. The KO2 pellets with advantages in CO2 uptake, besides O2 production, have been considered as air revitalization components, especially for closed respiratory environments in the infrastructure of life support systems (LSS). A unique set of experimental data of a single adsorption equilibrium of CO2 on KO2 pellet adsorbents at concentrations 8500-9500 mg L-1 (as closed atmosphere with a CO2% high value due to respiratory of human) and temperature 298.15 K is reported. Operating parameters such as temperature and humidity are tested experimentally to check the adsorption capacity. The maximum adsorption capacity at a temperature of 20°C and humidity of 70% was 660 and 620 mg g-1, respectively. The kinetic study showed that the CO2 adsorption data correctly are adjusted by the Rate-controlling model with an R2 value of 0.984. The calculated thermodynamic parameters such as entropy (-0.0277 kJ mol-1 K-1), enthalpy (-12.406 kJ mol-1), and Gibbs free energy changes (-4.136 kJ mol-1) indicate the spontaneous and exothermic of the process. Equilibrium adsorption data were placed in the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms. Based on the regression coefficient (R2), the Dubinin-Radushkovich model provides a complete fit with the experimental data (R2 = 0.989). The BET-specific surface area of the KO2 pellets before and after the CO2 adsorption process was about 1.26 and 1.19 m2 g-1, respectively.
By generalising dictionary learning (DL) algorithms to multidimensional (MD) mode and using them in applications where signals are inherently multidimensional, such as in three‐dimensional (3D) inverse synthetic aperture radar (ISAR) imaging, it is possible to achieve much higher speed and less computational complexity. In this study, the formulation of the multidimensional dictionary learning (MDDL) problem is expressed and two algorithms are proposed to solve it. The first one is based on the method of optimum directions (MOD) algorithm for 1D dictionary learning (1DDL), which uses alternating minimisation and gradient projection approach. As the MDDL problem is non‐convex, the second algorithm approximates the non‐convex objective with a new jointly convex function and efficiently solves it. As an application, we use the proposed methods to restore and denoise the ISAR image. Numerical experiments highlight that the proposed algorithms, in addition to reducing the computational complexity and the amount of required memory, also entail less training data for learning the dictionary, and enjoy higher convergence speed in comparison to their one‐dimensional (1D) counterparts. Specifically, convergence speed of MD algorithms, depending on the size of the training data, is up to at least 10.7 times faster than the equivalent 1DDL algorithm. According to the simulation results, the SNR value achieved by the proposed algorithms is higher than the case where we use the 3D‐IFFT for image reconstruction and the case of fixed dictionaries, by approximately 12 and 4 dB, respectively.
In this article a simple method is reported for the promotion of the synthesis of imidazo[1,2-a]pyrimidine-3-carbonitriles and 1,2,4-triazolo[4,3-a]pyrimidines derivatives via three component one-pot condensation of various aromatic aldehydes, malononitrile and 2-aminobenzimidazole or 3-amino-1,2,4-triazole using TiO2-[bip]-NH2⁺ C(NO2)3⁻ as a new efficient nano-catalyst. All the products which were obtained under mild and solvent-free conditions were identified with the comparison of their physical properties and spectral data with the authentic samples. The structure of the prepared catalyst was characterized using Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray analysis (EDX), field emission scanning electron microscopy (FESEM), thermo gravimetric analysis (TGA) and X-ray diffraction (XRD). The significant features of this procedure are short reaction times, high yields of the products, ease of separation of the products and easy preparation of the catalyst. Also the catalyst can be recycled and reutilized for several cycles in the studied reactions.
Graphitic carbon nitride (g-CN) is a promising metal-free catalyst for environmental remediation. However, its practical applications have been limited due to insufficient solar-light responsivity. Hetero-element doping and the construction of heterostructures, comprised of g-CN and other band-matched semiconductors could be considered to overcome these drawbacks. In the present work, a series of 2D/3D heterostructures comprised of a few layers of boron-doped g-CN (B-CN) anchored on sea urchin-like Bi2S3 (BS) particles ([email protected]) were successfully synthesized. The catalytic performances of [email protected] composites were assessed for the photo-reduction of Cr(VI) and in-situ generation of H2O2 under solar-light illumination. A binary composite containing 10 wt% of B-CN ([email protected]) achieved a photo-reduction of Cr(VI) with a rate of 86.77% during 150 min, which was 3.41- and 2.04-fold higher than those of pure BS and B-CN, respectively. Interestingly, BS particles not only acted as an excellent co-catalyst to broaden the optical window from UV–vis to near-infrared (NIR), but also provided a large active surface area, enhancing migration of charge-carriers between heterointerface, suppressing charge recombination, and thus improving the photocatalytic activities of [email protected] composites. Density functional theory calculations were performed to confirm that N atoms were appropriately replaced with boron atoms in the carbon nitride framework. Replacing nitrogen with boron was found to be beneficial in tuning the energy band levels of B-CN. Moreover, [email protected] had greater photocatalytic activity for H2O2 generation, which was 4.93 and 2.15 times higher than that of bare BS and B-CN, respectively. The charge-carrier transport pathway and possible photocatalytic mechanisms using were systematically studied using ultraviolet photoelectron spectroscopy and electron spin resonance analyses, respectively. These findings showed heterostructure strategy could be a breakthrough for developing new photocatalysts with both visible- and NIR-light responsiveness to address the current environmental and energy issues.
The optimum rotor blade planform of a fixed-pitch quadrotor required to minimize power, maximize rotor thrust, maximize lift-to-drag ratio, and maximize agility in a slalom flight, using a numerical optimization technique, is investigated in two cases. The procedure is performed by Central Composite Design Data (CCD) and inverse flight dynamic simulation program coupled with desirability optimization approach implemented in the process of blade optimization. Therefore, the optimum blade planform parameters (i.e., root chord, taper ratio, taper offset, and blade twist) affected quadrotor performance in different gross weights and flight speeds are calculated. Also, the main effects and the interaction of parameters on quadrotor performance are studied. The CCD data were computed using an inverse simulation program previously validated by flight test data of a typical quadrotor. The results of optimization in case 1 are appropriate, but case 2 shows that the rotor with a tapered blade lowers the power coefficient by 65% and enhances the lift-to-drag ratio (forward flight efficiency) and roll attitude quickness up to 11% and 30%, respectively. Consequently, a satisfactory planform improvement relative to the reference blade planform with VR-12 cross-section is quite evident and it can be appropriate for advanced blade design.
Today, unmanned vehicles get involved in challenging missions like search and rescue, surveillance, recognition, border patrolling, and other information-gathering roles. These vehicles prevent humans from being in dangerous situations, and their cost of production is lower than manned vehicles. Many researchers in past decades have studied the problem of tracking maneuvering targets based on noisy sensor measurements. The key to successfully tracking a target is to extract useful information from observations about the target state. Indeed, a proper model of the target dynamic and sensor observation will facilitate the extraction of this information, significantly. The filters used for estimation are the base model because there is knowledge of the target motion model. The purpose of this paper is to investigate and compare the capability of different dynamic models in tracking a high-maneuverability target using a 3D space by using a visual sensor. The goal is to test 10 different dynamic models with several different random processes and filters to find the most suitable model for tracking an aerial target. Sensor failure and model processing error have been selected as the two main criteria in measuring the performance of these models. We have introduced the best dynamic model based on the behavior of these models against these defects.
In order to balance the contradiction between safety and performance of energetic compounds, a novel approach known as cocrystallization has been widely utilized. In this work, a novel cocrystal of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and ammonium perchlorate (AP) was successfully synthesized and characterized. The SEM images, PXRD spectra, and FT-IR spectrum confirmed the varied crystal structure of the cocrystal in comparison to the raw materials. In addition, the density of the cocrystal was measured to be 1.90⁻³, and the detonation velocity and detonation pressure were calculated to be (8.53) km.s⁻¹ and (35.21) GPa, respectively.
Improving the properties of hydroxyl-terminated polybutadiene (HTPB) has always been one of the important topics for researchers in the propellant field. In this research work, a prepolymer from blend of HTPB and polyethylene glycol (PEG) is prepared with isophorone diisocyanate (IPDI). This prepolymer is mixed with glycerol for the synthesis of polyurethane (PU) elastomer. The compatibility of n-butyl nitroxyethylnitramine (n-BuNENA) as an energetic plasticizer with a non-energetic PU matrix was investigated. The properties of HTPB-PEG blend elastomer prepared with n-BuNENA plasticizer were compared with elastomers made by HTPB. The results of SEM analysis showed that incorporation of PEG improved the compatibility of plasticizer with PU matrices. DSC, FTIR spectroscopy and tensile analysis revealed that the phase separation degree and crystallinity in PEG-based PU were much higher than HTPB elastomer. It was determined by TGA results that the n-BuNENA plasticizer reduced the thermal stability of PU. Mechanical studies also indicated that the incorporation of PEG increases the modulus and tensile strength while the addition of plasticizer decreases the modulus and enhances the tensile strength and elongation.
In the present work, a new aqueous sol–gel procedure has been used for producing hard transparent organic–inorganic nanohybrid coatings on polycarbonate (PC) substrate for improving its optical and mechanical properties. Sol-gel thins films were prepared by mixing Si and Al aqueous precursors and applied them on the cold plasma treated PC substrate. TEOS, GPTMS and aluminum tri sec-butoxide were used as main precursors. In order to improve the adhesion strength onto polymer, PC substrates were treated by Dielectric Barrier Discharge (DBD) system being conducted at atmosphere pressure in open air. The effects of sol ratios, curing temperature and aging time on the prepared coatings properties were investigated. Chemical, structural, morphological, optical and mechanical characteristics of the samples were studied by ATR-FTIR, EDS, XRD, FE-SEM, TEM, UV/vis spectroscopy, pencil hardness and eraser scratch methods. The obtained results indicated that the water contact angle of PC (73.24°) decreased to 6.32° by 45 second plasma treatment due to added functional groups on the treated surfaces. All of the films showed higher optical transmittance (89%) than the raw PC (86%) that was stemmed from the lower refractive index of the prepared films. Films indicated good adhesion onto the plasma treated substrates (5B). The pencil hardness of the PC substrate (4B) improved to 3H (8 pencil grade increment) with just a single layer coating (about 200 nm thickness) due to the preparation of new hard structures of interlocked Si and Al atoms.
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673 members
Valiollah Babaeipour
  • Faculty of Chemistry and Chemical Engineering
Masood Barekat
  • Material Engineering
Seied Mahdi Pourmortazavi
  • Department of Chemistry
Akbar Eshaghi
  • Department of Materials Engineering
Mahdi Karbasian
  • Department of Industrial Engineering (1)
Lavizan , 15875-1774, Tehran, Tehran, Iran
Head of institution
Dr. A. Shafaghat