Self-esteem development from age 14 to 30 years: A longitudinal study.

We examined the development of self-esteem in adolescence and young adulthood. Data came from the Young Adults section of the National Longitudinal Survey of Youth, which includes 8 assessments across a 14-year period of a national probability sample of 7,100 individuals age 14 to 30 years. Latent growth curve analyses indicated that self-esteem increases during adolescence and continues to increase more slowly in young adulthood. Women and men did not differ in their self-esteem trajectories. In adolescence, Hispanics had lower self-esteem than Blacks and Whites, but the self-esteem of Hispanics subsequently increased more strongly, so that at age 30 Blacks and Hispanics had higher self-esteem than Whites. At each age, emotionally stable, extraverted, and conscientious individuals experienced higher self-esteem than emotionally unstable, introverted, and less conscientious individuals. Moreover, at each age, high sense of mastery, low risk taking, and better health predicted higher self-esteem. Finally, the results suggest that normative increase in sense of mastery accounts for a large proportion of the normative increase in self-esteem. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Artificial neural network investigation of hardness and fracture toughness of hydroxylapatite

Hardness and fracture toughness of hydroxylapatite were investigated by artificial neural network (ANN). Hardness and fracture toughness of hydroxylapatite were predicted by using its sintering temperature, sintering time, relative density, and grain size with ANN. It was found that prediction results of its hardness and fracture toughness closely matched with the experimental results.     

The adsorption behavior of cesium on poly(N-isopropylacrylamide/itaconic acid) copolymeric hydrogels

In this study, N-isopropylacrylamide/itaconic acid (NIPAAm/IA) hydrogels prepared by irradiating with γ radiation were used in experiments on cesium ion adsorption. The cesium ion adsorption capacity of the hydrogels was investigated as a function of Cs⁺ concentration, pH and temperature. The adsorption behavior of cesium was evaluated by using the radiotracer method. The adsorption isotherm models were applied to the experimental data, and it was seen that Freundlich isotherm explained the adsorption better than Langmuir isotherm. Two simplified kinetic models including pseudo-first-order and pseudo-second-order equation were selected to follow the adsorption processes. The Cs⁺ adsorption could be best described by the pseudo-first-order equation. The thermodynamic parameters including ΔG°, ΔH° and ΔS° for adsorption processes of Cs⁺ on the hydrogel were also calculated, and the negative ΔH° and ΔG° confirmed that the adsorption process was exothermic and spontaneous.     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part I. The Effects of Loading Rate,Test Temperature,Fiber Sizing and Global Strain Level

The effects of loading rate, fiber sizing, test temperature and global strain level on the adhesion strength between carbon fibers and a thermosetting epoxy (Epon 815) are studied using the single fiber fragmentation test procedure. Analytical methodology describing the viscoelastic behavior observed is also presented. The possibility of rate-temperature-interphase thickness superposition for the interfacial strength function is illustrated based on the analytical models discussed. Experimental data are discussed using Weibull statistics and also presented in the form of percent relative frequency histograms for the fiber fragments in a collective fashion. The use of histograms allows for interpretation of the skewness in the data population.     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part III. The Effects of Postcure

A novel method for tailoring the interphase of carbon fiber-polymer composites by resistive electric heating is presented. The single-fiber fragmentation test is used to investigate the adhesion and fracture properties of the interphase. Electric resistive heating is shown to increase adhesion and toughness at the interphase region. In analyzing the results, the strength and fracture energy of the interphase are related to the thermal postcure conditions created by resistive electric heating. For this purpose, a difference analysis method is used to obtain a numerical solution for the heat conduction problem in the single-fiber test specimen and the temperature distributions are determined. Improvements obtained by using resistive electric heating of the carbon fiber are compared with those obtained by postcuring of the whole sample via convective thermal postcuring. The results obtained using these two different postcure methods seem to be similar.     

CHARACTERIZATION OF THE STRUCTURAL FEATURES OF OXIDIZED BEYPAZARI LIGNITE USING DECONVOLUTED SOLID STATE 13C NMR SPECTRA

ABSTRACT

The solid state ¹³C NMR method have been used to investigate the structural changes occurred in Beypazari lignite while oxidizing at 150°C in a dynamic air atmosphere. Least squares curve fitting techniques have been used to resolve the overlapping bands in the 0-220 ppm region of the 13_c NMR spectra. Measurements of the relative intensities of the functional groups observed in the oxidized coals were used to follow the progress of air oxidation. Oxidation reactions seemed to decrease the total intensities of both aliphatics and aromatics, though the reduction in aliphatics was more pronounced. The relative intensities of the total aliphatics decreased from 1.0 to 0.9 and 0.6 in the original and lignites oxidized for 12 and 312 hours, respectively. The relative intensities of Ar-C-C in the 130-148 ppm region for the same set of samples were 1.0, 0.9 and 0.8. The least-squares bands resolved in the carbonyl region were at 175 ppm and 190 ppm in the original lignite; at 180 ppm (carboxylic acids), 195 ppm (meta substituted ketones) 210 ppm (di orto substituted ketones) in the lignite oxidized for 12 hours and at 170 ppm (esters), 180 ppm, 200 ppm (aldehydes) and 210 ppm in the lignite oxidized for 312 hr. Carbonyl intensity increased from 1.0 in the original lignite to 2.3 and 3.3 in the oxidized lignites. The intensity of aromatic ethers increased from 1.0 in the original lignite to 1.9 and 1.6 for the oxidized samples. The mechanism of oxidation ether. Aldehydes are easily oxidized to carboxylic acids in the presence of air by the free radical formation of a peroxy acid. The carboxylic acid formed by disproportionation reactions between the peroxy acid and aldehydes might combine with phenols to produce esters as it was observed in the present work. The presence of high free radical concentration in the oxidation atmosphere probably caused to abstract hydrogen atoms from the aromatic structures thus degrading aromatics to produce hydroperoxides which acted later as it was described above. The gradual degradation of aromatic structures observed in the present study indicated that the oxidation reactions of the aromatic rings should less probable when compared to the oxidation of aliphatic structures.     

Polystyrene Suspension Polymerization: The Effect of Polymerization Parameters on Particle Size and Distribution

Effects of polymerization parameters are studied to better understand interactions between parameters in stirred-tank polymerization reactors and to derive a regression model correlating polymer particle size and particle-size distribution with agitator speed, agitator diameter, tricalcium phosphate, dodecyl benzene sodium sulfonate concentrations, and mass cycle period. The derived equations give way to prediction of the polymerization conditions in order to obtain desired particle size and particle-size distributions which covers particle sizes between 0.3 and 5 mm. The roles of some other parameters and limiting agitation parameters are also investigated.     

Increasing single-lap joint strength by adherend curvature-induced residual stresses

Single-lap joint (SLJ) geometry is the most widely used type of adhesive joint geometry. In this joint, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. To this end, we exploited elastic spring-back capability of (steel) metal adherends by initially forming curved segments of varying arc lengths and radii at overlap ends. These adherends with curved-end sections were then bonded in single-lap configuration, simply by applying sufficient bonding pressure to elastically flatten the curved segments to result in typically flat overlap sections subsequent to adhesive cure and the removal of bonding pressure. Since the elastic adherend overlap ends tend to revert back to their initial curved form, they exert compressive residual stresses on the adhesive layer in the overlap end regions. We determined that the compressive residual stresses induced in this fashion considerably increased the load capacity of SLJs subjected to tension.