جستجوی مقالات مرتبط با کلیدواژه « ضریب جذب » در نشریات گروه « فنی و مهندسی »

In optoelectronic devices such as photodetectors, solar cells, modulators, filters, etc., the optical absorption coefficient is a key parameter in successful device operation. To this end, in this paper, a dual band absorber, consisting of a metal-graphene-dielectric-metal structure which can operate at communication bands is presented. First of all, the light absorption characteristic has been achieved by finite difference time domain method and then the influences of the thicknesses of top metallic structure, dielectric and substrate layers on the light absorption of the structure have been analyzed. The results revealed that utilizing the graphene monolayer and the plasmonic structure improves the light-graphene interaction and in result, the graphene layer absorption. It is shown that the proposed structure has the light absorption of 95% at the wavelength of 1310nm and the light absorption of 96% at the wavelength of 1675nm. Therefore, this absorber has the ability of operating at two optical communication bands (O-band and U-band) simultaneously.

Nowadays, choosing the right strategy is one of the most important factors in promoting and preventing the loss of company capital. Achieving an integrated system that takes into account the conditions for selecting different strategies, in considering all the effective variables and key factors, is essential for any company. In this paper, using previous studies in the field of technology strategies and corporate behavior, we have attempted to develop a model to provide appropriate technology strategy choices based on key effective components such as appropriability, opportunity, accumulation and implication of knowledge and by integrating technology strategies and corporate behavior. The results of the examination of the balance between basic technologies and Freeman's technology strategies, in a table named of concordance table are extracted and categorized and integrated on the basis of common components with the corporate behavior table. The resulting integrated table, which includes different modes of business environment, is used as the external factor of the company and the absorption coefficient and leakage coefficient are considered as internal factors in the Fuzzy analysis in the FIS system and accordingly the fuzzy model of choosing the appropriate technology strategy of the company is developed. Finally, it is validated using a numerical example of the proposed model.

Today's energy needs are increasing very fast and this is while the energy resources are very limit. In this paper by using numerical methods and investigation absorption coefficient of different colors, the most appropriate color to reduce energy consumption in all seasons has been selected for external wall of a building in Mashhad. Modeling of building has been done and meshed by using Gambit software as a three dimensions model. The simulation of falling solar radiation to building which is the main objective of this study, has been done by Fluent software based on building’s location and in turbulent flow. The results of this research indicate that by selecting the most appropriate color, in total during of the year by 1.5°C temperature decrease in warm days and about 1°C increase in cold days, we have significantly reduce energy consumption in electricity and gas. Finally according to the results of this research and by investigating absorption coefficient of different colors, gray color has been chosen as the most suitable criteria in order to reduce building energy consumption.

Expansive soils are considered as an overall challenge especially for civil engineers. Such soils swell when given an access to water and shrink when they dry out. The most common and economical method for stabilizing these soils is using of the additives that prevent volume changes. Variation, improve and optimize the physical and hydraulic properties of soil with use of additives including zeolite and cement additives have been considered for always. In this study the effect of cement in rang of 3 g/kg and zeolite in range of 4, 8 and 12 g/kg of soil as additives content on physical and hydraulic properties of soil contain percent and pressure swell and sorptivity(S) were investigated. The results showed that the addition of mixture of zeolite and cement into soil in different amounts effect on physical and hydraulic properties of soil in a different way. In general, the addition of a mixture of zeolite and cement helps to reduce percent and pressure swelling of soils in different contents. Combination zeolite and cement with soil decrease sorptivity of specimens. As, the maximum reduction for specimens occurred in application of 8 g/kg zeolite and 3 g/kg of cement.

Solar collectors compared to standard heating systems can provide significant savings in energy consumption. This paper concerns with analyzing the coupled radiative and natural convective heat transfer in solar flat-plate collectors, when the collector cavity is considered as a radiative participating media. First, an appropriate model for analysis of the thermal behavior of the collector is validated using reliable results in the literature. The discrete ordinates method is used for the radiative analysis and thermal analysis of a flat-plat solar collector, with real specifications and by considering water channel under the absorber, in summer solar conditions and for a wide range of air absorption coefficients are performed. According to the results, by increasing the absorption coefficient of the air, the temperature of absorber plate is decreased while the temperature of the air is increased. The effect of the absorption coefficient on the air temperature is higher than the temperature of the absorber plate. Also, by decrease in the absorber temperature, the outlet water temperature, that is approximately equal to the temperature of the absorber plate, is decreased.

The main characteristic of sound propagation in shallow waters in that graph of sound speed is almost constant or it has a downward fracture. Therefore, the sound propagation is shallow waters areas is that each beam emitted from the sound source during the propagation time is constantly reflected from the seabed reflectivity of the seabed is more important than the reflectivity of the surface of the sea.
Is this paper, the characteristics of geographical environment in the Persian Gulf and HORMUZ strait and the way of sound propagation in these areas has been explained. The effect of heat, cold, salinity and water flow on the speed will also be evaluated. The Persian Gulf and its coastal areas with less than 200 meters is a type of shallow waters environments.

In this paper، an inverse analysis is performed for estimation of temperature-dependent absorption coefficient in a twodimensional absorbing، emitting and isotropically scattering medium. The finite volume method has been adopted as the numerical technique. The S method is employed to solve the radiative transfer equation. The inverse problem is solved by using a combined method of genetic algorithm and conjugate gradient. The accuracy of the presented method for solving the inverse radiation problem is checked by using four examples. The effect of the measurement errors on the accuracy of the inverse analysis is also investigated. The results show that the algorithm can estimate the unknown absorption coefficient when the measurement errors are neglected. Also it is found that increasing the measurement error decreases the accuracy of estimation of temperature-dependent absorption coefficient.

In this article, we study the position of sonar and the possibility of using it in small high speed boats. First, the subject is studied from different aspects and the problem of sonar designing in these boats are stated. Then, two designs were proposed that it is possible to beapplicable. Finally, by the primary calculations, the optimization of 37.7 decibel in sonar equation is proved between the first and second design. Also, for the proposed design to be applicable, hydrodynamic calculations were presented, too.

In this study، after preparation of Li2O-Al2O3-SiO2-TiO2 base glass containing Cr2O3 dopant using casting method، the effect of different amount of dopant on spectroscopic and optical properties of glass has been investigated. Due to the spectroscopic، optical and structural properties of glasses، UV-Vis and FTIR spectrophotometers have been utilized. Hence، optical parameters such as absorption coefficient، extinction coefficient، Fermi energy level، optical band gap and Urbach energy have been calculated. According to results of calculations، augment of dopant to 1. 5% leads to the reduction of molar volume، optical band gap، Fermi energy، Urbach energy and enhancement of density. The mentioned changes could be attributed to the role of Cr3+ as the network modifier.

The sample used in the photo/dark measurement was fabricated in the sandwich Al/Polyamide/TiOPc/Oxadiazole/ITO/Glass. Nanostructure Titanium Oxide Phthalocyanine with the average particle size about 25 nm (TiOPc) is used as Charge Generation Material (CGM). Photoreceptor absorption spectra shows that there are some peaks at wavelengths 282,402,578 and 762 nm and there is no absorption in the region of 402-578 nm. Photo/dark induced discharge curve shows 67% contrast is achieved at 345 ms.

Thermophysical properties, electrical contact resistance (ECR) and corrosion performance are considered as critical properties of coatings, which are utilized in the satellite manufacturing industry. Chromate conversion coatings (CCCs) for Al alloys are among these coatings.In this study, CCCs were applied on Alclad AA7075-T6 Al Alloy by means of a chromating solution having chemical composition very near to the commercial chromating solution of Alodine 1200S. Influence of coating time on the coatings thermophysical properties including coefficients of solar absorption or Absorptivity (αs) and thermal emission or Emissivity (εT) as well as their ECR values were investigated. The εT was measured directly by Emmisometer device, while αs was determined indirectly by Reflectometer equipment. In coating time from 30 up to 180 seconds αs and εT values were measured in the ranges of 0.7-0.94 and 0.06-0.22, respectively. The results were revealed that different εT and αs as well as desired ECR values according to the specifications of satellite industry are obtainable by control of coating parameters such as coating time. In addition, base on the results of surface coating morphology evaluating conducted by SEM and AFM, it was concluded that developed coatings were formed in nanocrystalized structures.