Core-Shell Type Polymer Microspheres Prepared from Diblock Copolymer Films

In the first part of this article, the preparation method for core-shell type polymer microspheres from diblock copolymer films is reviewed. The core-shell type polymer microspheres were obtained from the crosslinking reaction in spherical microdomains formed by diblock copolymer film. In the second section, the solution and solid properties of core-shell type microspheres are reviewed. The micelle of core-shell type microsphere moved like pseudolatex. Its solubility depended strongly on that of shell segments. Finally, the miscibility behaviors of binary core-shell type microsphere blends are reported briefly.     

The effect of cyber-friends on loneliness and social anxiety: Differences between high and low self-evaluated physical attractiveness groups

This study examined the causal relationships between the number of cyber-friends participants had and their social anxiety or loneliness. We predicted that participants who gave low self-evaluations of physical attractiveness would be able to lower their social anxiety or reduce their loneliness through Internet-based interpersonal relationships. Also, such effects would be more prominent if the cyber-friends were of the opposite sex. A two-wave panel study was conducted with 178 Japanese undergraduate students (63 men and 115 women; mean age was 20.29). Results showed that for those who gave a low evaluation of their physical attractiveness, having a large number of cyber-friends lowered their social anxiety and reduced the loneliness felt in friendships. These effects differed by gender of the cyber-friends. In particular, for those who gave a low evaluation of their physical attractiveness, having a large number of cyber-friends of the same sex had a positive effect on social anxiety. In contrast, cyber-friends of the opposite sex had no effect on social anxiety, but had a complex effect upon loneliness. Namely, while a large number of cyber-friends of the opposite sex reduced the loneliness felt in friendships, it also heightened the loneliness felt in family relationships. Implications of these results for further research and practice are provided.     

Synthesis of non-equilibrium phases in immiscible metals mechanically mixed by high pressure torsion

The structural changes in mechanically mixed metals of immiscible combinations of elements caused by bulk mechanical alloying (MA) through the use of high pressure torsion (HPT) were investigated in Ag–Ni and Nb–Zr systems. There was no alloying between Ag and Ni on atomic scale even after 100 rotations of HPT. On the other hand, the β-Zr phase started to appear after HPT 2 rotations in the Nb–Zr system, even though β-Zr is a high temperature phase. Further, Nb and Zr were completely mixed to form a bcc structured single phase after HPT 100 rotations. The sequence of alloying in the Nb–Zr system during HPT was discussed. These results clearly suggest that non-equilibrium phases can form in the Nb–Zr system by bulk MA by the use of HPT.     

Compositional SOS and beyond: a coalgebraic view of open systems

In this paper we address the issue of providing a structured coalgebra presentation of transition systems with algebraic structure on states determined by an equational specification Γ. More precisely, we aim at representing such systems as coalgebras for an endofunctor on the category of Γ-algebras. The systems we consider are specified by using arbitrary SOS rules, which in general do not guarantee that bisimilarity is a congruence. We first show that the structured coalgebra representation works only for systems where transitions out of complex states can˜be derived from transitions out of corresponding component states. This decomposition property of transitions indeed ensures that bisimilarity is a congruence. For a system not satisfying this requirement, next we propose a closure construction which adds context transitions, i.e., transitions that spontaneously embed a state into a bigger context or vice versa. The notion of bisimulation for the enriched system coincides with the notion of dynamic bisimilarity for the original one, i.e., with the coarsest bisimulation which is a congruence. This is sufficient to ensure that the structured coalgebra representation works for the systems obtained as result of the closure construction.     

A mathematical model study of the influence of degree of mixing and powder particle size variation on the homogenization kinetics of compacted blends of powders

The rates of diffusional homogenization of compacted blends of powders are sometimes less than predictions based upon mathematical diffusion models. Discrepancies between model calculations and experimental data are most apparent during the later stages of homogenization and are generally ascribed to the effects of nonuniform particle mixing and variations in particle size which are not treated by the models. The present mathematical model study (using both numerical and analytical techniques) was undertaken as a means of estimating the magnitudes of the effects of mixing and particle size variations on homogenization rates. A one-dimensional model (“stacked plates”) was employed wherein two solute-rich plates of the same size or different sizes could be positioned at various locations within a distance element. The remaining spaces were assumed to be filled with solvent-rich plates. An isomorphous alloy system was considered. Thus, the model was a one-dimensional, two-plate analog of the distribution of solute-rich particles in a continuous matrix of very fine solvent-rich particles. The effects of variations in solute-rich plate positions (degree of mixing) and of unequal solute-rich plate thicknesses (size distributions) were both shown to influence homogenization significantly. It is concluded that the variations in the local environments of the solute-rich particles in a compacted powder blend can result in decreases in the rate of diffusional homogenization that are of the magnitude of the departures of actual experimental data from predictions of models which assume uniform mixing of solute-rich particles of constant size.     

Modeling degradation and failure of Ni-Cr-Al overlay coatings

Degradation of an Ni-16at.%Cr-25at.%Al-0.06at.%Zr overlay coating on an Ni-22at.%Cr substrate was examined after oxidation accompanied by thermal cycling. Concentration-distance profiles were measured in the coating and substrate after various numbers of 1 h cycles at 1150°C. A numerical model was developed to simulate coating degradation by simultaneously oxidation and coating- substrate interdiffusion. The validity of the model was confirmed by comparison of predicted and measured concentration—distance profiles. The ability of the model to identify critical system parameters was demonstrated for the case of the initial aluminum and chromium content of the coating and substrate.     

A mathematical model for internal oxidation

A mathematical model for internal oxidation kinetics was developed using numerical methods (finite difference) and computer techniques. The flexibility of the model permitted analysis of semi-infinite and finite situations with planar, cylindrical, and spherical geometries for systems with various amounts of local solute enrichment. Graphical results are presented for subscale thickness as a function of time and local enrichment as a function of position in the subscale. The model is also applied to internal oxidation with a discontinuous change in surface oxygen concentration; a graphical solution encompassing a wide range of possible experimental conditions is presented. The use of the model in analyzing nonisothermal internal oxidation problems is demonstrated.     

Deformation behavior of continuous-fiber metal-matrix composite materials

The deformation behavior of continuous-fiber, metal-matrix composites was studied in terms ofin situ deformation behavior of the matrix and the fibers. X-ray diffraction techniques were employed to monitor the stress-strain behavior of the composite components (matrix and fibers) as a function of total composite stress-strain behavior. This experimental technique provided a unique approach to the study of metal-matrix composites since the deformation response of the components could be measuredin situ while the composite was under load. Furthermore, the influence of residual stress, component mechanical properties, and stress interactions between the matrix and the fibers could be incorporated into the analysis of composite deformation behavior. The study was conducted on composites of 2024 aluminum reinforced with tungsten fibers, and composites of 2024 aluminum reinforced with boron fibers. Composites were tested on a specially-designed, tensile device which served as a diffractometer specimen holder such that diffraction experiments could be performed while the specimen was incrementally deformed in uniaxial tension. Experimental results indicated that, except for the residual stress effects, the composites exhibited rule-of-mixture s behavior in the stage I, II, and in deformation regions. Measurements obtained perpendicular to the fiber and tensile axis during the tensile tests indicated that negligible stresses were developed as a result of Poisson’s ratio differences between the matrix and the fibers. Composite yield behavior was significantly influenced by residual stresses present in the individual components. Residual stresses parallel to the fiber axis could be included in the rule-of-mixtures analysis by considering the amount of prestrain which was present in each component. Formerly, Graduate Student, Department of Metallurgical Engineering, Drexel University, Philadelphia, Pa. This paper is based on a thesis submitted by H. P. CHESKIS to the Graduate Faculty in Materials Engineering at Drexel University in partial fulfillment of the requirements of the degree of Doctor of Philosophy.     

Effects of growth mechanism on solution kinetics

The solution kinetics of second phases were studied as a function of various initial conditions resulting from either diffusion-controlled growth or interface-reaction-controlled growth prior to solution treatment. Calculations of solution kinetics based upon a planar, finite-geometry model were carried out using numerical methods and computer techniques. It was shown that second-phase particles formed by diffusion-controlled growth and existing in a matrix containing concentration gradients exhibit dissolution kinetics that differ markedly from those of particles formed by interface-reaction-controlled growth. An experimental analysis designed to use solution kinetics measurements to obtain the mechanism of growth of second phases is discussed. The effects of linear-gradient assumptions that have been used in an existing, closed-form, infinite-geometry model are evaluated. Formerly, Graduate Student in the Department of Metallurgical Engineering, Drexel University, Philadelphia, Pa.