Exact analysis of resonance frequency and mode shapes of isotropic and laminated composite cylindrical shells; Part II: Parametric studies

In the second part of this study, the approach developed in Part I is used to analyze parameters which effect the natural frequencies and mode shapes of circular cylindrical shells. Therefore, amplitude ratios are determined analytically for shells of different geometries. The effects of circumferential and longitudinal wave numbers and geometrical parameters are studied on longitudinal, tangential and radial motions. Finally, numerical studies are conducted to investigate the effects of composite laminate parameters on resonance frequencies. Various laminate parameters such as stacking sequence and fiber angle are considered in the study.     

Host (nanopores of zeolite Y)-guest (oxovanadium(IV) tetradentate schiff-base complexes) nanocomposite materials: synthesis,characterization and liquid phase hydroxylation of phenol with hydrogen peroxide

Oxovanadium(IV) tetradentate Schiff-base complexes; [VO(X₂-haacac)] (X = H, Cl, CH₃ and NO₂), X₂-haacac = substituted bis(2-hydroxyanil)acetylacetone; and encapsulated in the nanopores of zeolite NaY; [VO(X₂-haacac)]-NaY; have been synthesized and characterized. The host-guest nanocomposite materials; [VO(X₂-haacac)]-NaY; was characterized by chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET and DRS). The analytical data indicated a composition corresponding to the mononuclear complex of Schiff-base ligand. The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Substitution of the aromatic hydrogen atoms of the Schiff-base ligand by electron withdrawing groups like −Cl, and −NO₂ has two major effects: (1) retention and concentration of the oxovanadium(IV) complex in the zeolite cavities is enhanced (due to the larger size of the substituents) and (2) the electronic and spectral properties of the encapsulated complex are modified. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN has been reported using oxovanadium(IV) Schiff-base complexes encapsulated in zeolite-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, effect of time, volume of solvent and temperature. Under the optimized reaction conditions, [VO((NO₂)₂-haacac)]-NaY has shown the highest conversion of 42.3% after 6 h. All these catalysts are more selective toward catechol formation. Encapsulated oxovanadium(IV) complex is catalytically very efficient as compared to other neat complexes for the hydroxylation of phenol and is stable to be recycled without much deterioration.     

Molecular adsorption on V2O3(0001)/Au(111) surfaces

The adsorption of carbon monoxide (CO), propane (C₃H₈) and propene (C₃H₆) on V₂O₃(0001) films grown on Au(111) was studied by Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopy (XPS). The “oxidized” surface (i.e., as prepared exhibiting V=O termination), the “reduced” surface (i.e., V=O groups being removed by electron irradiation), as well as the oxygen pre-covered reduced surface were investigated. Both TPD and XPS indicate that the oxidized surface has little affinity for CO adsorption, while the reduced surface readily binds CO (CO amount approx. 10 times higher). Accordingly, CO can be used to titrate the presence or absence of vanadyl oxygen (via adsorption on the vanadium atoms) but also of defects like surface oxygen vacancies. For propane and propene, desorption of the parent molecules was the major process, i.e., surface reactions were absent under the applied conditions. When oxygen was pre-adsorbed on the reduced surface, the adsorption properties resembled that of the oxidized surface, i.e., the vanadyl groups were (partially) re-established. TPD and XPS provide a handle to differentiate the binding sites on the V₂O₃ surface. Dedicated to Prof. Konrad Hayek.     

A New Image Analysis Based Method for Measuring Electrospun Nanofiber Diameter

In this paper, a new image analysis based method for electrospun nanofiber diameter measurement has been presented. The method was tested by a simulated image with known characteristics and a real web. Mean (M) and standard deviation (STD) of fiber diameter obtained using this method for the simulated image were 15.02 and 4.80 pixels respectively, compared to the true values of 15.35 and 4.47 pixels. For the real web, applying the method resulted in M and STD of 324 and 50.4 nm which are extremely close to the values of 319 and 42 nm obtained using manual method. The results show that this approach is successful in making fast, accurate automated measurements of electrospun fiber diameters.     

A Possible Industrial Solution to Ferment Lignocellulosic Hydrolyzate to Ethanol: Continuous Cultivation with Flocculating Yeast

The cultivation of toxic lignocellulosic hydrolyzates has become a challenging research topic in recent decades. Although several cultivation methods have been proposed, numerous questions have arisen regarding their industrial applications. The current work deals with a solution to this problem which has a good potential application on an industrial scale. A toxic dilute-acid hydrolyzate was continuously cultivated using a high-cell-density flocculating yeast in a single and serial bioreactor which was equipped with a settler to recycle the cells back to the bioreactors. No prior detoxification was necessary to cultivate the hydrolyzates, as the flocks were able to detoxify it in situ. The experiments were successfully carried out at dilution rates up to 0.52 h⁻¹. The cell concentration inside the bioreactors was between 23 and 35 g-DW/L, while the concentration in the effluent of the settlers was 0.32 ± 0.05 g-DW/L. An ethanol yield of 0.42–0.46 g/g-consumed sugar was achieved, and the residual sugar concentration was less than 6% of the initial fermentable sugar (glucose, galactose and mannose) of 35.2 g/L.     

Predicting surface quality of γ-TiAl produced by additive manufacturing process using response surface method

Electron beam melting (EBM) has been found to be a promising technology for producing complex shaped parts from gamma titanium aluminide alloys (γ-TiAl). The parts produced by this process are projected to have dimensions very close to the desired final shapes. However, the surface roughness of the parts produced by EBM is excessively rough. In many applications, it is necessary to improve the quality of manufactured parts using a convenient post process. This paper determines process parameters of end milling when it is used as a post process for the parts produced by EBM. Design of experiments has been used to study the effect of the selected input parameters of end milling (spindle speed, feed rate, depth of cut and coolant type) on the surface roughness of γ-TiAl parts. Response surface methodology is used to develop a predictive model for surface roughness. Effects of the selected milling process are investigated. This paper also optimizes the selected process parameters to minimize the value of the obtained surface roughness.     

A simple approach to solving the kinematics of the 4-UPS/PS (3R1T) parallel manipulator

Journal of Mechanical Science and Technology - This work reports on the position, velocity and acceleration analyses of a four-degrees-of-freedom parallel manipulator, 4-DoF-PM for brevity, which...     

Wire electrical discharge machining of ASP30 tool steel

Wire electrical discharge machining is a non-traditional cutting process for machining of hard and high strength materials. This study analyzed the effects of the main input parameters of wire electrical discharge machining of ASP30 steel (high alloyed Powder metallurgical [PM] high speed steel) as the workpiece on the material removal rate and surface roughness. The input parameters included spraying pressure and electric conductivity coefficient of the dielectric fluid, linear velocity of the wire and wire tension. The machined surface quality was evaluated using SEM pictures. Results indicated that increasing the spraying pressure of dielectric fluid leads to a higher material removal rate and surface roughness and that increasing the wire tension, linear velocity of wire, and electric conductivity of the dielectric fluid decreases the material removal rate and surface roughness.

     

Optimization of triangular microchannel heat sinks using constructal theory

The present paper examines the optimization of triangular microchannel heat sinks. The impact of volume fraction of solid material and pressure drop on the maximum temperature of the microchannel heat sinks are investigated and their optimum operating conditions are compared. From the results, it is seen that increasing the side angle of the triangular microchannel, improves its performance. Furthermore, there is an appropriate agreement between the analytical and numerical results. Finally, the effect of degrees of freedom on the performance of microchannels is investigated. To accomplish this end, the triangular microchannels with the side angle of 60 degree have been chosen as it has the best performance compared to other microchannels. It is observed that the minimized maximum temperatures of optimized microchannel heat sinks with three degrees of freedom are 10% lower than the ones with two degrees of freedom.