جستجوی مقالات مرتبط با کلیدواژه "پوسته" در نشریات گروه "فنی و مهندسی"

In this study, zinc oxide (ZnO) nanorods were grown on substrates with and without a seed layer using a hydrothermal process. WO₃ nanoparticles were then coated onto the ZnO nanorods using the spin coating method. Techniques such as XRD, SEM, EDX, and UV-Vis DRS were employed to analyze the phase, microstructure, and photocatalytic properties. The results showed that the morphology of ZnO nanoparticles and nanorods, whether with or without a seed layer, significantly affected their photocatalytic properties. Additionally, the band gap size in the presence of WO₃ influenced the performance of the ZnO/WO₃ core-shell structure. ZnO nanorods with a seed layer exhibited a more uniform and orderly morphology compared to those without. The ZnO/WO₃ nanocomposite also improved dye photodegradation efficiency by enhancing electron-hole separation and reducing recombination. The experiments were designed and analyzed using the Taguchi method, which determined the number of experiments and assessed the effects of pH, time, initial methylene green concentration, and stirring speed on the photocatalytic degradation of methylene green by ZnO nanoparticles, nanorods, and the ZnO/WO₃ catalyst using ANOVA. The findings revealed that the initial methylene green concentration and pH had the most significant impact on the photocatalytic process, with removal rates reaching 70.2% for ZnO nanorods with a seed layer and 82.3% for the ZnO/WO₃ composite.

In this study, the emission of photoelectrons in hydrogen gas is investigated numerically using near scattered fields. The calculations of these fields performed using Mie theory have been for many years a powerful tool for better understanding the scattering of electromagnetic radiation. Whether in single-layered nanosphere or core-shell metallic nanospheres, the oscillating surface charges concentrate close to the poles of the metal surface, which results in both resonance wavelength shifts and intensity modulation. Also, the near fields around the nanoparticles can be spatiotemporally redistributed and may give a great pulses of typical femtosecond oscillators. Harmonic spectra are influenced by incidence beam wavelength, the particle radius, the shell thickness and the distance between the H atom and the nanosphere. Such laser sources opened the door to real-time observation and time-domain control of atomic-scale electron dynamics, ultrafast spectroscopy and photography, and address the expected implications of having the tools to monitor electrons with sub-atomic resolution in both space and time.

Chromium (VI) enters water resources via effluents of metallurgical, chemical pigments, electroplating, and tanning industries. The chromium accumulation in animal and plant tissues can cause serious dangers. In human, chromium (VI) causes damage to liver, kidney, and lung. The aim of this research is the removal of chromium (VI) from water by Fe3O4/CoO nanostructured magnetic adsorbent. In this work, nano magnetic particles of Fe3O4/CoO were synthesized by co-precipitation method and were used for the adsorption of chromium (VI) from water. The Fe3O4/CoO adsorbent was characterized by ICP, XRD, TEM, and VSM methods. Effects of pH on chromium (VI) adsorption on Fe3O4/CoO were studied. The isotherm and kinetics of the adsorption were also studied. TEM images confirmed the formation of the core/shell structure of the nanoparticles. The VSM test showed the magnetic property of the Fe3O4/CoO adsorbent. The experimental data were better fitted to the Freundlich isotherm model. In a batch operation, by using 1.5 g of Fe3O4/CoO adsorbent, 100 mL of chromium (VI) solution with the concentration of 50 mg/L and pH 3, the chromium (VI) removal yield of 89.04% was obtained after 24 hours. The magnetic nanoparticles of Fe3O4/CoO are a good adsorbent to remove chromium (VI) from water with the advantage of easy separation from water by an external magnetic force.

Different events result in casing distortion of gas turbines. Rubbing between rotating and stationary components, unequal thermal mass between the thick flanges and the thin turbine casing and uneven convection heat transfer coefficient around the casing are main causes of this distortion. Distortion of casing results in compressor efficiency decreases via increase of tip leakage loss. In this study, the effect of natural convection on gas turbine axial flow compressor casing has been investigated. For this purpose, a two-dimensional model, including the shaft, inner casing, outer casing, main gas and fluid between casings has been developed. Transient conjugate heat transfer analysis is conducted by applying different boundary conditions. The results show that the top of casing temperature increases initially to reach a maximum value, then the temperature decreases. On the other side, the temperature of lower part of casing generally decreases over time. According to the casing rate of heating and cooling, natural convection heat transfer causes a significant temperature gradient in the casing at gas turbine shutdown. Also, due to the high value of the Rayleigh number, turbulence in the fluid is high. Although the Rayleigh number increases with increasing the convection heat transfer coefficient in enclosure, the temperature gradient between the upper and lower parts of the casing is reduced locally. To reduce casing distortion practical solutions were presented such as control of the convection coefficient of turbine enclosure, changing of bleed valve logic and improving casing insulation, related to operating conditions.

In this study, ZnO cores were first synthesized by using procedures zinc acetate dehydrate and sodium hydroxide via a co-precipitation method. Then, TiO2 shells were coated on the ZnO nanoparticles by using TTIP through co-precipitation approach to form ZnO/TiO2 core/shell nanocomposites. Structural and elemental studies were performed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Nanostructure morphologies were analyzed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The optical absorption edges and band-gap energies were calculated using UV-vis spectra. Open-aperture z-scan technique was finally used to survey two-photon absorption phenomenon. Obtained results showed an increase in two-photon reverse saturable absorption for the ZnO/TiO2 core/shell nanocomposites compared to pristine ZnO nanoparticles.

Hypothesis: Core-shell nano-fibrous structures obtained from biodegradable and biocompatible polymers such as silk fibroin (SF) have potential applications in drug delivery and tissue engineering. In this work, coaxial electrospinning of silk fibroin as shell and salicylic acid (SA)/polyvinyl alcohol (PVA) blends as core was studied to fabricate core-shell nano-fibrous structures.
Silk fibroin was extracted from cocoon and dissolved in formic acid. An assembled coaxial nozzle was used to fabricate core-shell nanofibers of SF as shell and PVA/salicylic acid as core components, respectively.
Findings: Effects of variation in viscosity and electrical conductivity of the electrospinning solutions on the final nanofibers morphology, diameters and SA release behaviors were studied using Fourier transforms infrared spectroscopy (FTIR), viscometry, electrical conductometry, ultraviolet spectrophotometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Finally, a suitable model for release behaviors of the fabricated core-shell nanofibers was suggested. It was found that the final diameter of fabricated core-shell nanofibers varied from 110 (±22) to 250 (±71) nm and diameter of the core section varied from 40 to 80 nm. The experimental results showed that the shell solution concentration had a significant effect on the final core-shell nanofiber diameter, but increase in the core solution concentration had an insignificant effect on the final nanofibers diameter. It was concluded that the core solution concentration was not the only effective parameter in determining the final diameters of electrospun nanofibers, and the viscosities of shell and core solutions and their electrical conductivities were just as important parameters. According to the results of release profiles, the ratio of the components in core and shell was the effective parameter affecting the profiles of SA released from these structures. The higher PVA concentration in the core increased both the amount of SA and its release rate from fabricated core-shell nanofibers.

This research presents the study on mechanical buckling of thick-walled cylindrical shell made of functionally graded materials with ring supported under uniform axial and lateral loads. The mechanical properties of shell are variable along the thickness direction. First the governing equations on the buckling of the FGM cylindrical shell supported with ring are established based on third-order shear deformation theory. Then the governing characteristic equations were employed, using energy method and by applying the Ritz technique. In the following with solving characteristic equations, the critical load buckling of the FGM thick-walled cylindrical shell supported with axial and lateral loads are calculated. The boundary conditions represented by end conditions of the FGM shell are the following: clamped-clamped and free-free. To verify the validity of the proposed analytical method the results of this research are compared with the results came from using the finite element software. Finally, the effects of the different parameters such as thickness variations, boundary conditions, loading conditions and geometrical parameters of shell and ring on the buckling behavior of FGM thick-walled cylindrical shell are investigated. The results showed that by increasing the FGM volume fraction power in the shell structure, the critical buckling load increases and the location of the ring support has the significant effect on the critical buckling load. The results presented can be used as an important benchmark for researchers to validate their numerical and analytical methods.

Today, with the increasing damages of explosion, it is of great significance to assess the performance of structures against such damages that established by explosive load. Accidental explosions exert great and intense dynamic forces to surrounding structures. Recently, composite shells have been used in structures to protect them against explosion which is due to its high resistance to volume ratio, flexibility and resistance to shock forces. Thus, it is essential to assess how structures protected by such materials behave against these forces. In this paper, we have used Abaqus software to analyze data pertaining the behavior of composite shells against explosive loads. We assessed the various parameters affecting the behavior of CRFP and E-Glass Epoxy and how they were affected by explosive load. Some of the parameters assessed include loading, curving rate, number of layers and size of interior angle. In practice, it is necessary to include openings in the composite shell, thus it is important to evaluate the effect of these openings on the behavior of the composite shell. The survey showed that use of the opening has fallen down shift. The reason for this phenomenon is reduction of area that effected by explosive load in composite shell

In this paper, the thermos-electro mechanical behavior of piezoelectric laminate shell has been studied by isogeometric analysis. Isogeometric analysis (IGA) is based on geometry generation technique, such as nurbs and splines. In Isogeometric analysis, same basis functions employed for geometry and approximation of the unknown field, unlike finite element method. In this paper, the analysis of composite shell structure is based on first-order shear deformation theory (Mindlin-Reissner), therefore each control point has five degrees of freedom, three displacement degrees of freedom and two rotations. For modeling of the electric field, we assume the variation of electric potential is linear through the thickness of piezo electric layers. The current work is validated though solving typical examples. For the Scordelis-Lo-Roof, maximum error is 0.066% that take place at the midpoint of free edge and for clamped shell maximum error is 0.039%. In other case studies, the goal is to achieve desired shape deformation by applying voltage. First by increasing the voltage on laminate shell under uniform load, the out of plane deformation has been eliminate. In continue, for control of thermal distortion, the symmetric and antisymmetric composite shell exposed to temperature gradient. By applying the voltage with same or opposite polarity, thermal twist or thermal bending has been compensated.

In this paper, SnO2/ZnO core - shell nanocomposites were synthesized via sonochemical processing. To achieve this, ZnO nanoparticles were prepared by ultrasonic method. In the next stage, the core-shell nanocomposites in the presence of ZnO particles (prepared in the previous step) and adding precursor SnCl4.5H2O was prepared by ultrasonic. After synthesizing the nanocomposites, their properties were studied by XRD, TG-DTA and TEM analyses. The synthesized SnO2/ZnO core - shell nanocomposites have amorphous structure that can be changed to crystalline structure after calcination at 650 C for 1 hour. Also, the gas sensing characteristics of SnO2/ZnO core- shell nanocomposite was studied. For evaluating the gas sensing properties, the synthesized particles were prepared by pressing the powder into pills and gas sensing test was performed with respect to the various gases such as methanol, CO, and H2. Due to the unique properties of the core - shell semiconductor particles in the mechanism of charge separation, the gas sensing properties of core - shell particles are higher than those of pure oxides.

Due to high strength and stiffness in comparison with their weights، laminated composite materials are widely used in many structures such as aerospace. Therefore to predict their mechanical response، the understanding of their failure mechanisms is very important. The delamination between composite layers and adhesive joints is one of the main damage modes of these materials. In this research، the cohesive zone model is used to predict the damage evaluation of composite wing adhesive joints. The advantage of this method is the modeling of delamination growth without any requirements to the presence of initial crack and remeshing. Moreover to predict the probable damage in composite layers the Ladeveze progressive damage model has been implemented in Abaqus using user defined code (Umat) and also the importance of considering the intralaminar failure on the acceleration in damage initiation and propagation in adhesively bonded joints have been evaluated. The results verify the proper accuracy of implemented method. Furthermore، the results of solid cohesive elements showed to be more accurate in predicting damage initiation and evaluation in comparison to shell elements. Finally effects of adhesive properties such as thickness and quality of bonding in load capability of wing structure have been investigated.

CdSe (Core) and CdSe/ZnS (Core/Shell) nanocrystals were produced using a green synthesis method by using phosphine- free precursor materials. The optical properties of the produced nanocrystals were investigated using UV- Vis absorption and PL emission spectra, and the average size of the nanocrystals was estimated optically using the absorption data. Size and morphology of the nanocrystals were also investigated using Williamson- Hall analysis and the TEM images. Our results show good agreement among the mentioned three different methods. Thus, size of CdSe nanocrystals was estimated within the 5.5-8.5 nm range. It was shown by X-ray diffraction method that CdSe nanocrystals, with zinc-blende structure, are formed. With increasing the growth time and decreasing the temperature, a red-shift was observed in both absorption and emission edges, which indicates an increase in the size of the grown nanocrystals. After core/shelling the nanocrystals, red-shifts of ~ 10 nm and ~ 30-40 nm were observed in the absorption and emission spectra of the grown nanocrystals, respectively. Accordingly, in our method it was possible to obtain CdSe nanocrystals, with justified green emission, without using octadecene.

D‌e‌s‌i‌g‌n o‌f e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌s i‌s o‌n‌e o‌f t‌h‌e m‌o‌s‌t p‌o‌w‌e‌r‌f‌u‌l t‌o‌o‌l‌s i‌n i‌m‌p‌r‌o‌v‌i‌n‌g m‌a‌n‌u‌f‌a‌c‌t‌u‌r‌i‌n‌g p‌r‌o‌c‌e‌s‌s‌e‌s t‌h‌a‌t a‌r‌e b‌e‌g‌u‌n b‌y d‌e‌t‌e‌r‌m‌i‌n‌i‌n‌g a t‌e‌s‌t a‌n‌d s‌e‌l‌e‌c‌t‌i‌n‌g p‌r‌o‌c‌e‌s‌s f‌a‌c‌t‌o‌r‌s. O‌n‌e p‌r‌a‌c‌t‌i‌c‌a‌l t‌e‌c‌h‌n‌i‌q‌u‌e w‌h‌i‌c‌h u‌s‌e‌d f‌o‌r m‌o‌d‌e‌l‌i‌n‌g a‌n‌d p‌r‌o‌b‌l‌e‌m s‌o‌l‌v‌i‌n‌g i‌s r‌e‌s‌p‌o‌n‌s‌e s‌u‌r‌f‌a‌c‌e m‌e‌t‌h‌o‌d‌o‌l‌o‌g‌y (R‌S‌M).I‌n t‌h‌i‌s s‌t‌u‌d‌y, D‌e‌s‌i‌g‌n o‌f e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌s h‌a‌s b‌e‌e‌n u‌s‌e‌d t‌o s‌u‌r‌v‌e‌y t‌h‌e e‌f‌f‌e‌c‌t o‌f t‌h‌r‌e‌e c‌o‌n‌t‌r‌o‌l‌l‌a‌b‌l‌e i‌n‌p‌u‌t f‌a‌c‌t‌o‌r‌s (i.e., E‌q c‌a‌r‌b‌o‌n, p‌e‌r‌d‌u‌r‌a‌b‌i‌l‌i‌t‌y t‌i‌m‌e a‌n‌d o‌x‌y‌g‌e‌n) o‌n r‌e‌s‌p‌o‌n‌s‌e v‌a‌r‌i‌a‌b‌l‌e (i.e., t‌h‌e O‌x‌i‌d‌e s‌c‌a‌l‌e c‌o‌n‌s‌i‌s‌t‌s o‌f p‌r‌e‌h‌e‌a‌t‌i‌n‌g f‌u‌r‌n‌a‌c‌e).S‌i‌n‌c‌e a‌l‌l c‌o‌m‌b‌i‌n‌a‌t‌i‌o‌n‌s o‌f s‌t‌e‌e‌l a‌r‌e e‌f‌f‌e‌c‌t‌i‌v‌e i‌n t‌h‌e o‌x‌i‌d‌a‌t‌i‌o‌n, b‌a‌s‌e‌d o‌n t‌h‌e d‌e‌f‌i‌n‌i‌t‌i‌o‌n A‌m‌e‌r‌i‌c‌a‌n S‌o‌c‌i‌e‌t‌y o‌f M‌a‌t‌e‌r‌i‌a‌l‌s, c‌a‌r‌b‌o‌n e‌q‌u‌i‌v‌a‌l‌e‌n‌t w‌a‌s u‌s‌e‌d w‌h‌i‌c‌h a‌c‌t‌u‌a‌l‌l‌y c‌o‌n‌t‌a‌i‌n‌s c‌a‌r‌b‌o‌n, m‌a‌n‌g‌a‌n‌e‌s‌e, c‌h‌r‌o‌m‌i‌u‌m, s‌i‌l‌i‌c‌o‌n, m‌o‌l‌y‌b‌d‌e‌n‌u‌m, v‌a‌n‌a‌d‌i‌u‌m, c‌o‌p‌p‌e‌r, a‌n‌d n‌i‌c‌k‌e‌l T‌h‌i‌s p‌a‌p‌e‌r h‌a‌s b‌e‌e‌n s‌t‌u‌d‌i‌e‌d t‌h‌e e‌f‌f‌e‌c‌t o‌f t‌h‌r‌e‌e i‌n‌p‌u‌t f‌a‌c‌t‌o‌r‌s: c‌a‌r‌b‌o‌n e‌q‌u‌i‌v‌a‌l‌e‌n‌t i‌n p‌e‌r‌c‌e‌n‌t‌s, t‌i‌m‌e i‌n m‌i‌n‌u‌t‌e‌s a‌n‌d t‌h‌e r‌a‌t‌i‌o o‌f o‌x‌y‌g‌e‌n/g‌a‌s o‌n q‌u‌a‌l‌i‌t‌y o‌f t‌h‌e p‌r‌o‌d‌u‌c‌t. T‌h‌e e‌x‌p‌e‌r‌i‌m‌e‌n‌t w‌a‌s d‌o‌n‌e b‌y 23 f‌a‌c‌t‌o‌r p‌l‌a‌n a‌n‌d 5 c‌e‌n‌t‌e‌r p‌o‌i‌n‌t, 6 p‌i‌v‌o‌t‌a‌l p‌o‌i‌n‌t‌s a‌n‌d 95 c‌o‌n‌f‌i‌d‌e‌n‌c‌e l‌e‌v‌e‌l. A‌f‌t‌e‌r e‌x‌a‌m‌i‌n‌a‌t‌i‌o‌n o‌f t‌h‌e f‌a‌c‌t‌o‌r‌s a‌n‌d t‌h‌e r‌e‌c‌o‌g‌n‌i‌t‌i‌o‌n o‌f t‌h‌e e‌f‌f‌e‌c‌t‌i‌v‌e f‌a‌c‌t‌o‌r‌s, a‌c‌c‌o‌r‌d‌i‌n‌g t‌o a‌p‌p‌l‌i‌c‌a‌t‌i‌o‌n o‌f r‌e‌s‌p‌o‌n‌s‌e s‌u‌r‌f‌a‌c‌e m‌e‌t‌h‌o‌d‌o‌l‌o‌g‌y, t‌h‌e r‌e‌l‌a‌t‌i‌o‌n‌s‌h‌i‌p b‌e‌t‌w‌e‌e‌n t‌h‌e r‌e‌l‌a‌t‌e‌d v‌a‌r‌i‌a‌b‌l‌e‌s o‌f t‌h‌e e‌f‌f‌e‌c‌t‌i‌v‌e i‌n‌p‌u‌t f‌a‌c‌t‌o‌r‌s a‌n‌d t‌h‌e r‌e‌s‌p‌o‌n‌s‌e s‌u‌r‌f‌a‌c‌e v‌a‌r‌i‌a‌b‌l‌e i‌s d‌e‌t‌e‌r‌m‌i‌n‌e‌d u‌s‌i‌n‌g r‌e‌g‌r‌e‌s‌s‌i‌o‌n m‌o‌d‌e‌l. F‌i‌n‌a‌l‌l‌y, t‌h‌e o‌p‌t‌i‌m‌u‌m v‌a‌l‌u‌e o‌f e‌a‌c‌h v‌a‌r‌i‌a‌b‌l‌e i‌n t‌h‌e r‌e‌g‌r‌e‌s‌s‌i‌o‌n m‌o‌d‌e‌l‌s i‌s o‌b‌t‌a‌i‌n‌e‌d b‌y g‌o‌a‌l p‌r‌o‌g‌r‌a‌m‌m‌i‌n‌g m‌e‌t‌h‌o‌d.

Skins related-morphing technology، are studied with relation to their mechanical and thermal properties. Morphing wings are those wings that can undergo self-change in shape and geometry. Although، engineers present different configurations for self-changing wings but there are not much studies on skin materials in this wings. A suitable material in morphing skins has to be elastic and flexible and capable of fast recovery to its initial condition. Also، it should be resistant against different environmental conditions، chemicals and abrasive agents، and sufficient hardness number of its structure to tolerate the aerodynamic loads. According to the above notes، the commercial materials are selected to meet the necessary requirements and include thermoplastic polyurethane، elastomeric copolymer، shape memory polymers and woven materials. First، history of different configurations of morphing wings is described and it is concluded that different configurations and shapes must not include hard materials as morphing wings.

Electrospinning is a novel and efficient method by which fibers with nanoscale diameters are produced in a simple and sophisticated manner. In fact، this technique is the most popular route for producing nanofibers in variety of profiles including core/shell، porous and hollow nanofibers. Amongst numerous profiles، the hollow nanofibers due to higher specific area compared to normal nanofiber have found extensive applications in different areas such as sensors، solar cells، fuel cells، catalysts and also drug delivery. The current paper attempts to present a comprehensive review on different approaches for producing hollow nanofibers based on electrospinning with no nozzle and equipped with one needle and coaxial needle. In the final part، a specific attention has been paid on conductive hollow nanofibers. Furthermore، the classified information regarding various characterization techniques including microscopy and spectroscopy is reported for detail investigation on hollow nanofiber. Diverse applications of hollow nanofiber based on appropriate studies are also presented.

In this paper, ZnO/Cu2O nanostructures were synthesized via molten salt and hydrothermal method. At the first step, the ZnO hierarchical nanostructures were successfullyprepared bymolten salt method at 200 oC without any calcination and post treatment. The hierarchical star-like structures were used as core due to higher light absorption. Secondly, Cu2O nanoparticles were formed on the arms surfaces of ZnO star-like particles via facile hydrothermal method. X ray diffraction, UV-Vis spectrum analyses were used to characterize the phases and optical behavior of core-shell structures. Microstructures of core-shell particles were also analyzed by scanning electron microscopy. Based on the result, the higher light absorption of core-shell structure made them as a good candidate to apply in photoelectrochemical cells.

Inorganic-organic hybrid coatings with TiO2-SiO2 core/shell nanoparticles were prepared in order to develop the self-cleaning and corrosion resistant coatings. As proved in XRD test, the anatase TiO2 nanoparticles were prepared by sol-gel method in two different thermal conditions namely high temperature and low temperature process. The size and the shape of the particles in amorphous TiO2 sol and the thickness of SiO2 layer on the anatase nanoparticles revealed a core/shell structure by transmission electron microscopy. The photocatalytic activities of the coatings using the prepared TiO2-SiO2 nanoparticles were investigated via the decomposition of methylene blue (MB) under UV-radiation and compared with those samples prepared using commercial TiO2, i.e. P25 Degussa. It was found that the photocatalytic activity of the coatings was significantly attributed to the crystallinity and the particle size of anatase nanoparticles. To find out the effect of photocatalytic activity on the corrosion resistance, the nanocomposites coatings were exposed under UV for 1080 h. The Tafel curves of the samples showed lower corrosion resistance for the coatings of higher photocatalytic activity. J. Color Sci. Tech. 7(2013), 151-164©. Institute for Color Science and Technology.

This article is devoted to the simultaneous optimization of shape and topology of shell structures. The optimum shape is obtained together with the optimum layout for the reinforcement layers at the both sides of the shell surface. To solve this problem the finite element method is employed. It is assumed that each element is comprised of a porous media with microscopic rectangular voids where the density of the material in each element is a function of the geometric parameters of the voids. These parameters are also considered as the design variables of the topology optimization problem. The geometry of the shell structure is defined by using Non-Uniform Rational B-Splines (NURBS) technique and the control points of the NURBS’ surfaces are considered as the design variables of the shape optimization problem. For solution the Method of Moving Asymptotes (MMA) is employed. To demonstrate the efficiency of the method a few examples are presented and the results are discussed.