Magnetic polystyrene nanocapsules with core-shell morphology obtained by emulsifier-free miniemulsion polymerization

Nanocapsules containing hexadecane and Fe₃O₄ magnetic nanoparticles as core materials and polystyrene as shell were produced in a new method through emulsifier-free miniemulsion polymerization using 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50) as a water-soluble initiator. The effect of some parameters such as the amounts of Fe₃O₄ and initiator on morphology of resulting nanocapsules was studied. Transmission electron microscopy showed that the products had latex particles having a size range of about 300–1300 nanometer and both magnetic nanocapsules with core-shell morphology and solid particles. The phase transition temperature and phase transition heat of the produced capsules were determined by differential scanning calorimetric analyses. Thermal properties of the latex were compared with those of magneticparticles-free latex and with those of latex free of both magnetic particles and hexadecane. Thermogravimetric analysis was also used to confirm the encapsulation and to determine the amounts of hexadecane and Fe₃O₄ within the capsules.     

The influence of the type of loading on the asymptotic behavior of slender elastic rings

We study the influence of the type of loading on the asymptotic behavior of linearly elastic, isotropic and homogeneous slender circular rings. By using formal asymptotic expansions, we obtain three families of models depending on the properties of the loads. If the loads expend work in inextensional displacements, then we find the classical model where the leading term of the energy corresponds to the bending-torsion energy of inextensional displacements. If the loads do no work in inextensional displacements, the model must be refined and we obtain two other types of models. In these other models, which depend on the type of loading, the leading term of the energy contains additional terms such as, for the second class, an extension energy due to the circumferential stretching of the ring, and even, for the third class, specific load-dependent contributions. This classification is illustrated in several examples.     

Dimensionality Effects on the Mixed Spin-1/2 and Spin-2 Blume-Capel Model: Renormalization Group Theory

We have used the real-space Migdal-Kadanoff renormalization group technique on d-dimensional hypercubic lattice to study the mixed spin-1/2 and spin-2 Blume-Capel model. First, we indicate a critical dimension d_C ≈?2.05, above and below which different topologies of phase diagrams occur. The phase diagrams have been plotted in the (crystal field, temperature) plane around d_C, in which there is a second-order phase transition. Moreover, using the variation of the free energy at low temperatures, we have established the ground-state phase diagrams in the (?/J, C/J) plane for d?<?d_C and d?≥?d_C. In particular, we have seen the appearance of two first-order transitions at very low temperatures by the use of the free energy and its isotherm derivative. A detailed analysis of fixed points and flow diagrams indicates that there is no tricritical point.

     

On toric locally conformally Kähler manifolds

We study compact toric strict locally conformally Kähler manifolds. We show that the Kodaira dimension of the underlying complex manifold is \(-\infty \), and that the only compact complex surfaces admitting toric strict locally conformally Kähler metrics are the diagonal Hopf surfaces. We also show that every toric Vaisman manifold has lcK rank 1 and is isomorphic to the mapping torus of an automorphism of a toric compact Sasakian manifold.     

Positron annihilation lifetime study of PTFE/silica composites

Positron annihilation lifetime spectroscopy (PALS) was used to study the microstructure of PTFE/silica composites. The positron lifetimes (τ_n) and intensities (I_n) of PTFE and the composites (30-62% silica) were measured at room temperature as a function of specimen thickness. Four lifetime components were found in PTFE and the composites. The longer lifetime components, τ₃ = 1.4 ns and τ₄ = 4.4 - 4.1 ns, were interpreted to be due to the presence of two different sized free volume cavity distributions within the PTFE/silica composites. A strong silica concentration dependence was found in the bulk intensities (I_3b and I_4b). The I_3b value increased from 13.0% in PTFE to 28.2% in the 62% composite, while the I_4b value decreased from 17.5% in PTFE to 4.5% in the 62% composite. The smaller-void size, free volume fraction (τ₃I_3b) values increased linearly between 0 and 100% silica concentration, while the larger void size, free volume fraction (τ₄I_4b) values decreased nonlinearly with silica concentration. Since silica has a long lifetime component (τ₃ = 1.6 ns), this behavior is ascribed to silica particles occupying the large free volume cavities (370 ų) in the PTFE/silica composites. © 1996 John Wiley & Sons, Inc.     

Constrained extremum problems with infinite dimensional image. Selection and saddle point

The paper deals with Image Space Analysis for constrained extremum problems having infinite dimensional image. It is shown that the introduction of selection for point- to-set maps and of quasi-multipliers allows one to establish sufficient optimality conditions for problems, where the classic ones fail.      

Constrained Extremum Problems with Infinite-Dimensional Image: Selection and Necessary Conditions

This paper deals with image space analysis for constrained extremum problems having an infinite-dimensional image. It is shown that the introduction of selection for point-to-set maps and of quasi multipliers allows one to establish optimality conditions for problems where the classical approach fails.