Formation of beta-nickel hydroxide plate-like structures under mild conditions and their optical properties

Nanostructural beta-nickel hydroxide (beta-Ni(OH)(2)) plates were prepared using the microwave hydrothermal (MH) method at a low temperature and short reaction times. An ammonia solution was employed as the coordinating agent, which reacts with [Ni(H(2)O)(6)](2+) to control the growth of beta-Ni(OH)(2) nuclei. A trigonal beta-Ni(OH)(2) single phase was observed by X-ray diffraction (XRD) analyses, and the crystal cell was constructed with structural parameters and atomic coordinates obtained from Rietveld refinement. Field emission scanning electron microscopy (FE-SEM) images revealed that the samples consisted of hexagonal-shaped nanoplates with a different particle size distribution. Broad absorption bands assigned as transitions of Ni(2+) in oxygen octahedral sites were revealed by UV-vis spectra. Photoluminescence (PL) properties observed with a maximum peak centered in the blue-green region were attributed to different defects, which were produced during the nucleation process. We present a growth process scheme of the beta-Ni(OH)(2) nanoplates. (C) 2011 Elsevier Inc. All rights reserved.

Horo-tight spheres in hyperbolic space

We study horo-tight immersions of manifolds into hyperbolic spaces. The main result gives several characterizations of horo-tightness of spheres, answering a question proposed by Cecil and Ryan. For instance, we prove that a sphere is horo-tight if and only if it is tight in the hyperbolic sense. For codimension bigger than one, it follows that horo-tight spheres in hyperbolic space are metric spheres. We also prove that horo-tight hyperspheres are characterized by the property that both of its total absolute horospherical curvatures attend their minimum value. We also introduce the notion of weak horo-tightness: an immersion is weak horo-tight if only one of its total absolute curvature attends its minimum. We prove a characterization theorem for weak horo-tight hyperspheres.

REIDEMEISTER TORSION AND ANALYTIC TORSION OF SPHERES

We provide a simple topological derivation of a formula for the Reidemeister and the analytic torsion of spheres.

Homotopy type of gauge groups of quaternionic line bundles over spheres

Let P be a principal S(3)-bundle over a sphere S(n), with n >= 4. Let G(p) be the gauge group of P. The homotopy type of G(p) when n - 4 was studied by A. Kono in [A. Kono, A note on the homotopy type of certain gauge groups, Proc. Roy. Soc. Edinburgh Sect. A 117 (1991) 295-297]. In this paper we extend his result anti we study the homotopy type of the gauge group of these bundles for all n <= 25. (C) 2008 Elsevier B.V. All rights reserved.

Single-step chemical synthesis of ferrite hollow nanospheres

We report a single-step chemical synthesis of iron oxide hollow nanospheres with 9.3 nm in diameter. The sample presents a narrow particle diameter distribution and chemical homogeneity. The hollow nature of the particles is confirmed by HRTEM and HAADF STEM analysis. Electron and x-ray diffraction show that the outer material component is constituted by 2 nm ferrite crystals. Mossbauer data provide further evidence for the formation of iron oxide with high structural disorder, magnetically ordered at 4.2 K and superparamagnetism at room temperature. An unusual magnetic behavior under an applied field is reported, which can be explained by the large fraction of atoms existing at both inner and outer surfaces.

UNIT VECTOR FIELDS ON ANTIPODALLY PUNCTURED SPHERES: BIG INDEX, BIG VOLUME

We establish in this paper a lower bound for the volume of a unit vector field (v) over right arrow defined ou S(n) \ {+/-x}, n = 2,3. This lower bound is related to the sum of the absolute values of the indices of (v) over right arrow at x and -x.