Showing 12 results for Yazdian
Volume 2, Issue 1 (4-2002)
Abstract
This paper presents a new control methodology for active power filters that provide an adaptive online harmonic estimation with partial and selective harmonic reduction schemes, which has been implemented within an integrated controller. The proposed approach is to provide partial and selective reduction of those individual harmonics which exceed the recommended levels as set by regulatory bodies reduces the rating of active power filters thus leading to cost savings. This approach contrasts with existing techniques in which the objective is to reduce all possible harmonic components to zero. Performance evaluation of the proposed technique for harmonic estimation for time-varying non-linear load is carried out when the simulation and experimental results show that the proposed control strategy provides a new alternative for harmonic reduction in power system.
Volume 5, Issue 2 (8-2014)
Abstract
Lovastatin is a potent agent for lowering cholesterol of blood. Since one of the main reasons of mortality in developing countries is cardiovascular disease, which is caused by precipitation of fatty acid (especially cholesterol) in blood vessels; therefore diets containing lovastatin may prevent this type of disease. In this study, Lovastatin, monacolin K or competitive inhibitor of the HMG-CoA reductase (operative enzyme for cholesterol synthesis) was produced by submerged fermentation using Monascus purpureus PTCC5303. Seven chemical and nutritional parameters including maltose, peptone, MgSO4.7H2O, MnSO4.H2O, KH2PO4, thiamin and pH screened using Plackett Burman experimental design for monacolin production. Among different parameters, maltose and MgSO4.7H2O showed significant effect on biomass and monacolin production. The concentration of these agents were optimized using response surface methodology for lovastatin production in the shaker flask. The optimized medium contained 26 g/L maltose, 5 g/L peptone, 0.1 g/L MgSO4.7H2O, MnSO4.H2O 0.5 g/L, 4 g/L KH2PO4, Vitamin B1 0.1 g/L and pH 7. After 10 days of fermentation in the shaker flask with 130 rpm agitation and 30 ºC, we achieved maximum lovastatin production which was 63 mg/l.
Volume 7, Issue 0 (0-2007)
Abstract
This paper investigates the islands formation in initial stages of restoration process in blackout condition and studies the impacts of islands number variation on the process execution. In addition, a method is proposed to determining each island optimal boundaries. Then the effects of transmission lines Thyistor Controlled Series Compensators (TCSC) to facilitate restoration process and improvement of optimal solutions are studied. Energy Not supplied (ENS) index minimization is the objective function and the optimization method is Genetic Algorithm. The test network modeling has been done using a special appropriate chromosome coding. Various operational constraints such as voltage margins in buses, transmission lines capacities and generators loading limits have been considered in optimization process and final solution evaluation. The IEEE-118 bus network has been used as test system to assess the capabilities of the proposed method. Some obtained results have been given in the case study section.
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Volume 8, Issue 1 (0-2008)
Abstract
In this paper, power system restoration in the presence of SVC and TCSC in partial outage conditions is considered and a new method for maximum load restoration using different control variables is presented. Control variables are tap of transformers, generation rescheduling and operating points of FACTS devices. Objective function is restored load (to be maximized) and constraints are voltage magnitudes in buses, carrying load in lines and power generation limits in generators. Also SPA limits in voltage angles in both sides of circuit breakers before closing are considered. With respect to the number of control variables, optimization is done using Genetic Algorithm with IEEE-118bus network as the test system.
Volume 9, Issue 1 (Winter 2018)
Abstract
Aims: Age-Related Macular Degeneration (AMD) is one of the biggest causes of vision loss after 50 years of age in the world. AMD disease destroys the retinal pigment cells. Retinal tissue engineering provides a suitable environment for the growth of retinal pigment epithelium cells using different scaffolds. These scaffolds may cause interior pressure changes in eyes and thus, causes disease of the separation of pigment and retinal epithelial cells. Therefore, the purpose of this study was to simulate gelatin, gelatin-chitosan and poly-caprolactone scaffolds in the retina and compare the pressure gradient and the effect of thickness on the pressure gradient.
Materials & Methods: In the present experimental study, in the first stage, three gelatin, gelatin-chitosan and poly-caprolactone scaffolds were simulated to examine the average scaffold pressure using COMSOL 5.1.1 software and Darcy law. In the next step, a gelatin-chitosan scaffold with thicknesses of 10 and 20 micron was simulated with Darcy law, to examine the effect of thickness on average pressure.
Findings: The output pressure of the gelatin scaffold was calculated as 308.800Pa Which was less than the pressure level of the caroid layer And it was less than the output pressure of other scaffolds. The average pressure of gelatin-chitosan scaffold with thicknesses of 10 and 20 micron was 1997.31 and 2003.13 respectively in the last step.
Conclusion: The gelatin scaffold produces a moderate lower pressure than the gelatin-chitosan scaffold and poly-caprolactone in the retina and it is more suitable than other scaffolds. In the simulation of gelatin-chitosan scaffold, increasing the thickness causes increased pressure and retinal impairment.
Volume 9, Issue 2 (Spring 2018)
Abstract
Aims: The effect of crude oil pollutants on water and soil pollution and ecological changes has resulted in several studies on the identification and removal of these pollutants. The biological methods have been highly regarded for controlling this type of pollution due to their optimal performance. The aim of this study was the comparative assessment of crude oil biodegradation by Acinetobacter Calcoaceticus RAG-1 in the presence and absence of biofunctional magnetic nanoparticles.
Materials and Methods: In this laboratory research, the amount of degradation of N-decane and Hexadecane were studied, as indices of normal paraffins in crude oil pollutions, by Acinetobacter Calcoaceticus RAG-1 in the optimal conditions, which Emulsan produced. Also, the effect of magnetic nanoparticles of iron oxide coated with two layers of Decanoic acid on the degradation was investigated separately. The independent t-test was performed to examine the significance of the model parameters and the two-way ANOVA was used to examine the goodness of fit. The experiment was done with a fractional factorial design. For statistical analysis of the results, Minitab V.16 software was used.
Findings: The biodegradation of N-decane and Hexadecane were obtained 85% and 86%, respectively, after 60 days. The presence of nanoparticles also led to an improvement in the biodegradation process and an increase of 91% and 89%, respectively.
Conclusion: Acinetobacter Calcoaceticus RAG- succeeds in eliminating paraffinic compounds from crude oil with medium chain length. The effect of presence of nanoparticle in the biodegradation of N-decane is greater than that of Hexadecane.
Volume 9, Issue 2 (Spring 2018)
Abstract
Aims: Today, crude oil is one of the main sources of energy. The combustion of sulfur-containing compounds in fossil fuels leads to the production of sulfur oxides that has adverse effects to human health and the environment. At the moment, the current method for removal of sulfur is Hydrodesulfurization. The aim of this study was to investigate the effect of magnetic nanoparticles and modified carbon nanotubes as nano-adsorbent on improving the biodesulfurization activity of microorganisms (Rhodococcus erythropolis IGTS8).
Materials and Methods: In the current experimental study, the nanoparticles were synthesized by chemical co-precipitation and the carbon nanotubes were initially carboxylated. Multi-layer carbon nanotubes were mixed with 95% sulfuric acid and 52% nitric acid (volume ratio 1:3) and, then, modified by polyethylene glycol. In order to characterize nanoparticles and carbon nanotubes, scanning transmission electron microscopy (STEM), X-ray diffraction, magnetic surveys, analysis of arch Raman, and fourier-transform infrared spectroscopy (FTIR) were conducted.
Findings: The size of nanoparticles was estimated to be 7-8nm and modified carbon nanotubes showed the highest solubility as well as stability in deionized water for two weeks. The growth of microorganisms in the presence of magnetic nanoparticles and carbon nanotubes compared to their absence increased by 40% and 8%, respectively. Moreover the desulfurization activity of microorganisms in the presence of magnetic nanoparticles and carbon nanotubes showed a significant increase compared to their absence.
Conclusion: Nanoparticles with adsorption of sulfur compounds increase their availability for microorganisms.
Volume 10, Issue 2 (Spring 2019)
Abstract
Biosurfactants are surface tension reducing compounds produced by a wide range of microorganisms. These compounds are caused to facilitate the absorption insoluble substrate by microbial cells. The aim of this study was to investigate the effects of nanoparticles of Fe/SDS on the biosurfactant production by Pseudomonas aeruginosa in culture is molasses.
For this purpose were used different concentrations of nanoparticles 1, 500 and 1000 mg/L. As a result the concentration of 1mg /L of Fe/SDS nanoparticles has the best effect on the growth of bacteria and biosurfactant production. This concentration increased 23.21% cell growth and 20.73% biosurfactant production compared with control samples. By increasing the concentration of nanoparticles reduced growth rate and biosurfactant production was observed. This indicates that the nanoparticles having negative effects of higher concentrations.
The results showed that low concentrations of nanoparticles Fe/SDS has positive effects on bacterial biosurfactant production and therefore a good alternative to chemical surfactants for use in the petroleum industry.
Volume 10, Issue 4 (Fall 2019)
Abstract
Aims: Curcumin is a natural molecule that due to its various curative effects including antibacterial properties, it can be used as a medicine, albeit after reducing its disadvantages. The aim of the present study is to develop a method for preparation of nanoparticles of curcumin using PAA, PVA, and PEI polymers with a view to improve its stability, increasing bioavailability and aqueous solubility as well as study its effectiveness against methicillin-resistant to Staphylococcus aureus.
Materials & Methods: In order to synthesize polymeric nanoparticles including curcumin with the nano-precipitation method, optimizing the effective concentration of polymer, curcumin, and water were determined by using the Response Surface Method (RSM). Synthesized nanoparticles were characterized by Scanning Electron Microscope (SEM), Dynamic Light Scattering (DLS) and zeta potential measurement methods. Furthermore, minimal concentration inhibitory of synthesized nanoparticles against the Staphylococcus aureus resistant to methicillin was measured.
Findings: The created nanoparticles were round, discrete and smooth in surface morphology and the average particle size for PAA, PVA, and PEI were 149±7nm, 175±8nm, and 184±9nm respectively. The minimum inhibitory concentration for PAA, PVA and PEI nanoparticles against the Staphylococcus aureus were 0.480±0.024, 0.390±0.019 and 0.340±0.017mg/ml. The concentration of solvent, polymer, and curcumin was important to obtain small size particles.
Conclusion: The results indicated that the water solubility of curcumin significantly improved by particle size reduction up to the nano range. The inhibitory property of curcumin nanoparticles has greatly increased due to the smaller particle size and their increased penetration into the bacteria and nanoparticles loaded with curcumin could be a promising drug carrier for the treatment of cancer, infections and other diseases.
Volume 11, Issue 2 (Spring 2020)
Abstract
The combustion of fossil fuels containing sulfur results in the release of sulfur dioxide into the atmosphere and environmental pollution. Hence, the researchers focused on the biological desulfurization method. Dibenzothiophene is used as the model molecule to study the ability of the desulfurization of microorganisms. The most suitable sources of carbon, nitrogen and sulfur concentration optimized by response surface method to obtain the highest cell growth and biological desulfurization activity. The performance of iron nanoparticles on the growth and biodesulfurization activity of thermophilic bacterium Bacillus thermoamylovorans strain EAMYO was investigated. Characterization of starch-modified iron nanoparticles was performed by TEM, SEM. The images of TEM and SEM of starch / Iron nanoparticles showed that the Fe3O4 and Fe0 nanoparticles were 20 and 30 nm, respectively. The investigating the growth of microorganism in the presence of iron nanoparticles showed that these nanoparticles not only did not have a toxic effect on microorganism growth, but also increased the growth of microorganism in 96 h (OD 660 = 1.864, 1.896 respectively in the presence of nanoparticles Fe0 and Fe3O4), while the highest rate of growth in the absence of nanoparticles in 96 h (OD660 = 1.51). Also, the activity of desulfurization in the presence of starch/Fe0 nanoparticles and starch/Fe3O4 / starch increased by 26.52% and 10.75%, respectively, compared to the cells without the coating of iron nanoparticles.
Volume 12, Issue 1 (12-2020)
Abstract
Biosurfactants are produced by microorganisms. Surfactin is one of the main lipopeptide biosurfactants produced by different species of Bacillus subtilis. This study aims to analyze the effect of starch-coated Fe0and Fe3+nanoparticles on the biosurfactant production of Bacillus subtilis. Out of 70 soil samples, 20 Bacillus were isolated and genome sequenced by biochemical methods and 16S rRNA gene. Quantitative and qualitative screening methods were used to isolate and detect biosurfactant production. For the aim of this study, 61 and 63 (Bacillus subtilis subsp. Inaquosorum) were selected. Then, hemolytic activity, surfactant production and reduction of surface tension in Minimal Salt Medium containing Fe0 and Fe3+ nanoparticles were examined after 48h, 72h and 96h of culture. The binding of the nanoparticles to the surfactant was confirmed by SEM. Strain 61 was the best bacterium and Fe3+ was the best nanoparticle and it was cultured. The results were compared with the results of non-nanoparticle bioreactor. Surfactin from strain 61 culture in the Fe3+ nanoparticle bioreactor after 72 hours of growth showed higher production than the same strain culture after 72 hours without Fe3+, if continuing the research, this strain can be commercialized in the future.
Volume 14, Issue 4 (1-2015)
Abstract
In this paper, a new configuration for delta conversion UPS is proposed, which could help the system for better utilization of the UPS inverters. In this configuration, parallel and series inverters of the conventional delta conversion UPS, under the grid fault conditions, are connected in parallel which help to share the load power and this results in utilizing the series inverter during fault mode. Therefore, using this configuration not only decreases the total capacity of the UPS inverters, but also decreases the system total cost. In the proposed configuration, two inverters have the same sizes and specifications which results in the system modularity that simplifies its implementation and maintenance and reduces the manufacturing and life cycle cost of the UPS system. In addition, the proposed configuration increases the system reliability. To illustrate proper operation of the proposed configuration, some simulations are carried out under the different conditions. The given simulation results validate appropriate operation of the proposed configuration.
