About the thermal stability and pore elimination in the ordered hexagonal mesoporous silica SBA-15

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Superconducting State of a Disk with a Pentagonal/Hexagonal Trench/Barrier

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb, Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Local classification of singular hexagonal 3-webs with holomorphic Chern connection form and infinitesimal symmetries

Implicit ODE, cubic in derivative, generically has no infinitesimal symmetries even at regular points with distinct roots. Cartan showed that at regular points, ODEs with hexagonal 3-web of solutions have symmetry algebras of the maximal possible dimension 3. At singular points such a web can lose all its symmetries. In this paper we study hexagonal 3-webs having at least one infinitesimal symmetry at singular points. In particular, we establish sufficient conditions for the existence of non-trivial symmetries and show that under natural assumptions such a symmetry is semi-simple, i.e. is a scaling in some coordinates. Using the obtained results, we provide a complete classification of hexagonal singular 3-web germs in the complex plane, satisfying the following two conditions: 1) the Chern connection form is holomorphic at the singular point, 2) the web admits at least one infinitesimal symmetry at this point. As a by-product, a classification of hexagonal weighted homogeneous 3-webs is obtained.

Construção de códigos esféricos através do reticulado hexagonal

Códigos esféricos n-dimensionais gerados por grupos comutativos em dimensão par, n = 2m, podem ser determinados pelo quociente de reticulados m-dimensionais, quando os vetores que geram o sub-reticulado são mutuamente ortogonais [4]. Apresentamos a construção de sub-reticulados nestas condições, a partir do reticulado hexagonal, A2. Comparamos a distância mínima do código esfé- rico construído através do quociente destes reticulados com o limitante da distância mínima estabelecido em [5].

Multifunction hexagonal liquid-crystal containing modified surface TiO2 nanoparticles and terpinen-4-ol for controlled release

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Study of La2-xCaxCuO4 perovskites for the low temperature water gas shift reaction

The effects of small fractions of calcium (x = 0, 0.05, 0.1, 0.15, and 0.20) on the structure and the catalytic properties of La2-xCaxCuO4 peroviskites have been investigated. The samples have been synthesized using the co-precipitation method. Perovskite-type oxides were characterized by XRD, TPR, XPS, XANES, SEM, and TEM. Catalytic tests for the water gas shift reaction (WGSR) were carried out in a tubular reactor at 290 degrees C. All samples showed a well-defined perovskite structure with surface areas between 6 and 18 m(2) g(-1). The partial substitution of La by Ca enhanced the stability of the perovskites and increased their reduction temperature. All catalysts were actives for WGSR, and the best catalytic performance was obtained for the La1.85Ca0.15CuO4 catalyst, but the samples with 5 and 10% of Ca had the best TOF values for reaction. These results can be associated to promoter effect of calcium, the high surface area, and the reducible species Cu-0 and Cu1+. (C) 2011 Elsevier B.V. All rights reserved.

Fe valence fluctuations and magnetoelastic coupling in Pb-based multiferroics perovskites

Lead-based multiferroics perovskites with nominal compositions Pb(Fe1/2Nb1/2)O3 and Pb(Fe2/3W1/3)O3 were synthesized following a two-stage method. Magnetic proprieties were investigated and correlated to anelastic proprieties, measured by the conventional pulse-echo method. The discussions are focused in the region around 250 K, where magnetoelectroelastic instabilities have been observed. X-ray absorption nearedge structure (XANES) study further indicates that the edge position varies with temperature revealing a fluctuation on the valence of iron ions with the temperature, which can be related to a variation in anelastic and magnetic proprieties.

Darstellung und Untersuchung von Materialien mit negativem Magnetowiderstand

Mit dem System KCo2-xCuxS2 wurde ein neues magnetoresistives System gefunden. Der negative Magnetowiderstand ist mit der Größenordnung von 10 % in 8 Tesla bei 4 K klein im Vergleich zu Mangan-Perowskiten, jedoch eindeutig intrinsisch.Die magnetische Struktur des Thiospinells Fe0.5Cu0.5Cr2S4 konnte durch Neutronenbeugung, Mößbauer-Spektroskopie sowie begleitende Bandstrukturrechnungen aufgeklärt werden. Ein negativen Magnetowiderstand von 5,5 % nahe der Curie-Temperatur in Magnetfeldern von 8 Tesla bei der isostrukturellen eisenreichen Verbindung Fe0.75Cu0.25Cr2S4 wurde gefunden.Die intermetallischen Verbindungen des Gadoliniums weisen alle hohe negative Magnetowiderstände bei TC auf. Sowohl bei GdAl2 als auch bei GdPdP und GdPtP werden Widerstandsabsenkungen in 8 Tesla beobachtet, die bei ~1,5 TC 4 % erreichen und bis zu Temperaturen von 5 K über 6 % liegen. Während der Transportmechanismus in GdAl2 offenbar auf einer direkten Gd-Gd Wechselwirkung beruht, ist bei GdPdP und GdPtP bei tiefen Temperaturen ein nicht eindeutiges Verhalten beobachtbar. Ein Einfluss von Fremdphasen kann jedoch ausgeschlossen werden.Unter den metallreichen Phosphiden hexagonaler Struktur zeigt Fe2P große negative MR-Effekte von 7 % schon bei Raumtemperatur in hohen Feldern. Nahe der ferromagnetischen Ordnung reagiert die Verbindung auf äußere Felder bei niedrigen Feldstärken von weniger als 2 Tesla mit einer Erhöhung der Leitfähigkeit um 10 bis 11 %.

Cubic and hexagonal InGaAsN dilute arsenides by unintentional homogeneous incorporation of As into InGaN

Arsenic alloying is observed for epitaxial layers nominally intended to be In0.75Ga0.25N. Voids form beneath their interfaces with GaAs substrates, acting as sources of Ga + As out-diffusion into the growing epilayers. As a result, heteroepitaxial single-phase quaternary InxGa1-xAsyN1-y, films are formed with x similar to 0.55 and 0.05 menor que y menor que 0,10. While an undoped epilayer retains the wurtzite structure, a Mn-doped sample showed randomly spaced dopant segregations, which, together with a slightly higher As concentration, led to a transformation from the hexagonal to the twinned cubic phase.