Large quantum nonlinear dynamic susceptibility of single-molecule magnets

The nonlinear dynamical response of Mn12 single-molecule magnets is experimentally found to be very large, quite insensitive to the spin-lattice coupling constant, and displaying peaks reversed with respect to classical superparamagnets. It is shown that these features are caused by the strong field dependence of the relaxation rate due to the detuning of energy levels between which tunneling takes place. The nonlinear susceptibility technique, previously overlooked, is thus proposed as a privileged probe to ascertain the occurrence of quantum effects in mesoscopic magnetic systems.     

Strong local homogeneity and coset spaces

We prove that for every homogeneous and strongly locally homogeneous separable metrizable space there is a metrizable compactification of such that, among other things, for all there is a homeomorphism such that . This implies that is a coset space of some separable metrizable topological group .

     

On an internal property of absolute retracts,II

Let X be a (metrizable) space. A mixer for X is, roughly speaking, a map μ:X³→X such that μ(x, x, y) = μ(x, y, x) = μ(y, x, x) = x for all x, y ∈ X. We show that each AR has a mixer and that a finite dimensional path connected space with a mixer is an AR. Our main result is that each separable space with a mixer and having an open cover by sets contractible within the whole space, is LEC.     

The reduced measure algebra and a K1-space which is not K0

The reduced measure algebra is used to construct, under CH, a hereditarily Lindelöf separable K₁-space X which is not a K₀-space.     

Studies on copolymers of vinyl chloride with diethyl fumarate,isobutylene and vinyl bromide,as models of PVC with chain irregularities—II The influence of copolymerization on the tacticity of PVC sequences: The influence f copolymerization on the tacticity of PVC sequences

Copolymers of vinyl chloride (> 90%) with diethyl fumarate, isobutylene and vinyl bromide, prepared at temperatures between +25 and ?30°, were used to determine the influence of the copolymerization on the tacticity of polyvinyl chloride sequences in the copolymers. The tacticity appeared to decrease in proportion as the comonomer content increases, this effect being different for the three kinds of copolymers. The results are discussed by taking into consideration the comonomer volume, the Arrhenius plots and the sequence distribution in copolymers after calculation of the number of alternances per 100 monomer units.     

Aloe vera–eluting collagen I microgels: physicochemical characterization and in vitro biological performance

Microgels absorb and retain high amounts of solvents, especially water. Because of their size, and association, the release kinetics of active molecules from microgels is easier to control than in hydrogels. Collagen I is one of the most extensively investigated biomaterials, although the key process parameters to produce microgels must be understood well before they can be used in veterinary and human medicine. Emulsification-gelation is widely used to obtain microgels because of its ease of handling and high yields. The concentration of the biomaterial and the homogenization method are among the critical parameters in this method. In this work, we produced cytocompatible collagen I microgels by emulsification-gelation and evaluated the effect of three different concentrations and homogenization methods on their physicochemical, mechanical, and biological properties. As proof of concept, microgels were loaded with an Aloe vera extract and the loading efficiency and the polyphenol release kinetics, as well as their properties assessed. When the same homogenization method (e.g. magnetic stirring) was used, the size of the microgels decreased with an increase of collagen I concentration, and the size distribution increased. In addition, the size and size distribution of microgels prepared with the same collagen I concentration were smaller when produced by high-energy homogenization methods (shear stress and ultrasound) than with a low-energy one (magnetic stirring). Collagen I concentration and the homogenization method also influenced the zeta-potential, the enzymatic degradation, and the encapsulation efficiency of the microgels. Overall, we show that the size of these microgels can be fine-tuned by the collagen I concentration and the homogenization method. Moreover, the integration of microgels of different sizes into the same carrier platform will pave the way for the combination of active compounds with different release kinetics.     

Homogeneous spaces and transitive actions by Polish groups

We prove that for every homogeneous and strongly locally homogeneous Polish space X there is a Polish group admitting a transitive action on X. We also construct an example of a homogeneous Polish space which is not a coset space and on which no separable metrizable topological group acts transitively.     

Infrared spectroscopy of the Nd3+ ion in Nd2BaCuO5 and Nd2BaZnO5

Absorption spectra of the Nd³⁺ ion in the Nd₂BaCuO₅ and Nd₂BaZnO₅ ternary oxides were measured within broad spectral (1500–17000 cm^?1) and temperature (4.2–200 K) intervals. The positions and widths of the Stark sublevels were determined. The exchange splittings of the Nd³⁺ Kramers doublets in several multiplets were found for the magnetically ordered state of Nd₂BaCuO₅ (T _N =7.5 K).     

Subbase characterizations of subspaces of compact trees

In this paper we apply the methods of supercompactifications and normal subbases to characterize subspaces of compact treelike spaces. This characterization is related to the subbase characterizations of ordered spaces, of trees and of normally supercompact spaces described in [5, 1, 9, 10, 14].