Free vibration analysis of beams by using a third-order shear deformation theory

In this study, free vibration of beams with different boundary conditions is analysed within the framework of the third-order shear deformation theory. The boundary conditions of beams are satisfied using Lagrange multipliers. To apply the Lagrange’s equations, trial functions denoting the deflections and the rotations of the cross-section of the beam are expressed in polynomial form. Using Lagrange’s equations, the problem is reduced to the solution of a system of algebraic equations. The first six eigenvalues of the considered beams are calculated for different thickness-to-length ratios. The results are compared with the previous results based on Timoshenko and Euler-Bernoulli beam theories.     

Electrochemical and morphological assessments of inhibition level of 8-hydroxylquinoline for AA2024-T4 alloy in 3.5% NaCl solution

The corrosion inhibition of AA2024-T4 in 3.5% NaCl solution by 8-hydroxylquinoline (8-HQ) was investigated by potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy and dynamic electrochemical impedance spectroscopy. Experimental results were supported with scanning electron microscopy (SEM), atomic force microscopy and Fourier transform-infrared (FTIR) spectroscopy analysis. It was found that 8-HQ molecules adsorbed on the alloy surface and protected it against corrosion. SEM, energy dispersive spectroscopy, and FTIR results confirm the adsorption of 8-HQ molecules on AA2024-T4. The inhibition efficiency of 8-HQ is found to increase with increase in concentration and the highest concentration studied (0.05 M) offered corrosion inhibition efficiency of 84%. PDP results show that 8-HQ acts as mixed type inhibitor in the studied medium.     

Regional bit allocation with visual attention and distortion sensitivity

This paper proposes a regional rate allocation method for enhancing the perceived quality in image compression. Bit allocation to image regions should be performed by considering the viewer’s attention and distortion sensitivity maps in order to address subjective quality concerns. The paper first proposes an exponential model for the relation between the viewer’s fixation duration and perceived information. The human visual system is more sensitive to the distortion around edges than the distortion in complex textured regions. Therefore, a novel distortion sensitivity method is also proposed that distinguishes true edges from complex textures without using edge detectors or gradient magnitude thresholds. The estimates for the visual attention level and the distortion sensitivity level are jointly used to modify the distortion contribution of each codeblock for determining its quantization parameter. The experiments validate the improved perceptual quality of decoded images due to the integrated use of the visual distortion sensitivity and the visual attention level in bit allocation. Moreover, the proposed bit allocation method is experimentally shown to yield a substantially higher subjective evaluation score than the other well-known bit allocation methods based on post-compression rate-distortion optimization, saliency maps, foveation of fixations and foveated just-noticeable-difference maps.

     

Young children’s computer skills development from kindergarten to third grade

This investigation explores young children’s computer skills development from kindergarten to third grade using the Early Childhood Longitudinal Study–Kindergarten (ECLS–K) dataset. The sample size of the study was 8642 children. Latent growth curve modeling analysis was used as an analytical tool to examine the development of children’s computer skills using LISREL software version 8.80. Results indicated, not surprisingly, that the availability of a computer at home and a high socio-economic status were statistically significant predictors of children’s baseline computer skills in kindergarten. The availability of computers in kindergarten, however, was a statistically significant predictor of the development of children’s computer skills from kindergarten to third grade. Although there was no difference between girls and boys in their baseline computer skills in kindergarten, the rate of development in computer skills was higher for girls than boys. Results suggest that the availability of an adequate level of computers in kindergarten classrooms can help close the initial gap in children’s computer skills due to socio-economic status and lack of computer access prior to entering school. Supplying kindergarten classrooms with adequate computers could positively contribute to children’s long-term development of computer skills.     

Synthesis of core–shell-type styrene acrylic latexes with low NMA content and their application in pigment printing pastes

In this paper, novel core–shell polymers comprising styrene (St) and butyl acrylate (BA) in both core and shell layers of the polymer particles have been synthesized and employed in pigment printing pastes which were applied on 100% cotton and 65% cotton/35% polyester (PET) fabrics. The aim was to reduce the NMA content and the formation of free formaldehyde from pigment printing pastes by employing newly synthesized core-/shell-type polymers. After five washing cycles, the synthesized core-/shell-type polymer including 1% NMA in the core and 1% NMA in the shell with T _g values +30°C and ?20°C, respectively, with lowest total NMA content (1.03%) yielded the best result and showed closest ΔE values to the commercially available polymer including 4% NMA. Dry and wet rubbing fastness results showed no significant changes in the absence of NMA when compared with NMA containing samples. The penetration degree of the pigment pastes of the corresponding polymers was relatively higher on 100% cotton fabric for both red- and blue-colored pigments. A negligible decrease in color strength has been observed for all polymers when colored in red.     

Circularly polarized slot antenna array with sequentially rotated feed network for broadband application

This article presents a novel circularly polarized sequentially rotated slot antenna array (CPSSAA) designed to operate at a frequency of 5.5 GHz. This antenna is suitable for communication applications such as WLAN/WiMAX. Method of feeding is based on sequential rotation with seven quarter‐wavelength transformers. In this case, the elements with 200 Ω impedance could be replaced by other elements with different input impedance. Reducing the elements input impedance, maximum power can be transferred to the elements. Because the lower losses in transmission line occur in presence of lower impedance, the 3 dB axial‐ratio bandwidth of the CPSSAA extends to ～1.3 GHz. The CPSSAA was designed to operate over the frequency range between 4.5 and 6.4 GHz corresponding to an impedance bandwidth of 34.86% for VSWR < 2. Acceptable agreement between the simulation and measured results validates the proposed design. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:358–363, 2015.     

Development of a new highly conductive and thermomechanically stable complex membrane based on sulfonated polyimide/ionic liquid for high temperature anhydrous fuel cells

The paper deals with the synthesis and characterization of a new type of acid doped highly conductive complex membrane based on sulfonated polyimide (sPI) and ionic liquid (IL) for high temperature anhydrous fuel cells. For this purpose, 2,4-diaminobenzene sulfonic acid (2,4-DABSA) is reacted with benzophenontetracarboxylic dianhydride (BTDA) to yield sulfonated poly(amic acid) (sPAA) intermediate. Subsequently, IL is added into sPAA to form an interaction between sulfonic acid and imidazolium group of IL followed by acid doping. The ionic conductivity of acid doped sPI/IL complex polymer membrane is higher than that of IL containing composite membranes reported in the literature (5.59 × 10⁻² S cm⁻¹ at 180 °C). Furthermore, dynamic mechanical analysis (DMA) results of acid doped sPI/IL complex membrane show that the mechanical strength of the complex product is slightly changed until 350 °C due to the formation of ionic interactions between sulfonic acid groups of sPI and imidazolium groups of IL. Consequently, the ionic interaction not only provides high ionic conductivity with excellent thermomechanical properties (the storage module of 0.91 GPa at 300 °C) but also results in a positive effect in long term conductivity stability by blocking IL migration through the membrane.     

Adsorption studies of aqueous basic dye solutions using sepiolite

Sepiolite, low cost, locally available and natural mineral was studied as an adsorbent for the removal of Basic Astrazon yellow 7GL from aqueous solutions and batch contact tests. The kinetics of the adsorption process was tested for the pseudo-first order, pseudo-second order reaction and intra-particle diffusion models. The rate constants of adsorption for all these kinetic models were calculated. Good correlation coefficients were obtained for the pseudo-second order kinetic model. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were applied to the experimental equilibrium data by changing temperature. The isotherm constants were determined by using the linear regression of these models. The monolayer coverage capacities of sepiolite for basic dye were found to be in the range of 62.5-88.5 mg/g at different temperatures. Thermodynamic studies showed that the reaction for dye uptake by sepiolite is endothermic in nature. Based on the optimum parameters sepiolite was also used as adsorbent for raw wastewater treatment and found as efficient as dye color removal.