Topological representation for monadic implication algebras

In this paper, every monadic implication algebra is represented as a union of a unique family of monadic filters of a suitable monadic Boolean algebra. Inspired by this representation, we introduce the notion of a monadic implication space, we give a topological representation for monadic implication algebras and we prove a dual equivalence between the category of monadic implication algebras and the category of monadic implication spaces.      

Metrics in the sphere of a C*-module

Given a unital C*-algebra and a right C*-module over , we consider the problem of finding short smooth curves in the sphere = {x ∈ : 〈x, x〉 = 1}. Curves in are measured considering the Finsler metric which consists of the norm of at each tangent space of . The initial value problem is solved, for the case when is a von Neumann algebra and is selfdual: for any element x ₀ ∈ and any tangent vector ν at x ₀, there exists a curve γ(t) = e ^tZ (x ₀), Z ∈ , Z* = −Z and ∥Z∥ ≤ π, such that γ(0) = x ₀ and (0) = ν, which is minimizing along its path for t ∈ [0, 1]. The existence of such Z is linked to the extension problem of selfadjoint operators. Such minimal curves need not be unique. Also we consider the boundary value problem: given x ₀, x ₁ ∈ , find a curve of minimal length which joins them. We give several partial answers to this question. For instance, let us denote by f ₀ the selfadjoint projection I − x ₀ ⊗ x ₀, if the algebra f ₀ f ₀ is finite dimensional, then there exists a curve γ joining x ₀ and x ₁, which is minimizing along its path.      

Inference for a truncated positive normal distribution

The main object of this paper is to study an extension of the half normal distribution defined by adding a positive truncation to it. The new model is more flexible than the half-normal distribution and contains the half normal distribution as a special case. Properties of this distribution, such as moments, hazard function and entropy are studied and parameters estimation is dealt with by using moments and maximum likelihood. A real data application indicates good fit performance of the new model when compared to other competitors in literatures.     

Study on the formation during the production of lead-free piezoceramics at the morphotropic phase boundary

Because of the environmental concerns, the manufacture of ceramics based on lead titanate zirconate [Pb(Zr_1−xTi_x)O₃−PZT] has been condemned because of the lead toxicity. In this context, the electromechanical properties of sodium, potassium and lithium niobate [(Na_0.5−x/2K_0.5−x/2Li_x)NbO₃−NKLN] at the morphotropic phase boundary granted these materials the position of most suitable candidate to replace PZT. However, the production of these ceramics is rather critical mainly because of a natural tendency of forming secondary phases. To help with the studies of the synthesis of this lead-free piezoceramic, this work presents an evaluation of the crystallization of the (Na_0.47K_0.47Li_0.06)NbO₃ phase by solid-state reactions. TG-DTA, XRD, dilatometric and ferroelectric hysteresis analyses indicated that a secondary phase (K₃Li₂Nb₅O₁₅) crystallizes at temperatures above 850 C and also during the sintering of the powders compacts at 1080 C. To prevent the formation of this phase, the addition of Na₂Nb₂O₆.nH₂O microfibers obtained through a microwave hydrothermal synthesis was performed in the sintering process. After to this addition, the suppression of the K₃Li₂Nb₅O₁₅ phase occurred and an increase of the NKLN electrical properties was then obtained.     

High-quality epitaxial LaNiO3 thin films on SrTiO3(100) and LaAlO3(100)

LaNiO₃ thin films have been deposited by pulsed laser deposition on SrTiO₃(100) and LaAlO₃(100) substrates. The processing conditions have been investigated in order to optimize electrical resistivity, crystal quality, and surface morphology. Excellent properties are achieved at moderate substrate temperature and relatively low oxygen pressure, without the need for annealing. Thickness exerts an important influence on electrical transport, as the electrical resistivity increases quickly in films thicker than a few tens of nanometer. The surface of the films on LaAlO₃ is very flat in all the studied thickness range, but the films on SrTiO₃ develop a pattern of boundaries and even cracks as the thickness is higher. Below the critical thickness, high-quality epitaxial films with very smooth surface and low electrical resistivity are obtained under the optimum conditions of substrate temperature and oxygen pressure. The optimum processing conditions are different depending on the substrate, and control is especially critical in films deposited on SrTiO₃.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

A manganese(II) coordination polymer with a 3D porous structure: Synthesis,structure, and spectroscopic and magnetic behaviour

A manganese(II) complex with N,N′-bis(carboxymethyl)dithiooxamide (H₄GLYDTO), [Mn(H₂GLYDTO)(H₂O)₂]_n, has been synthesized and characterized by elemental analysis and thermogravimetric analysis, as well as by infrared, electronic and EPR spectroscopy and magnetic susceptibility measurements. The crystal and molecular structure of this complex was determined by single-crystal X-ray structure analysis. The compound shows a 3D porous framework with alternate left- and right-handed helical channels where the manganese(II) ions have an octahedral environment. Variable temperature magnetic measurements reveal the existence of very weak antiferromagnetic interactions through the syn-anti carboxylate bridge, with an exchange parameter of J/k = −0.12 K.     

Direct evidence for block-by-block growth in high-temperature superconductor ultrathin films

Charge neutrality and stoichiometry impose severe restrictions on the mechanisms of epitaxial growth of complex oxides. The fundamental question arises of what is the minimum growth unit when sample thickness is reduced beyond the size of the unit cell. We have investigated the growth mechanism of YBa2Cu3O7 cuprate superconductor, using a consistent approach based on the growth of noninteger numbers of YBa2Cu3O7 layers in YBa(2)Cu(3)O(7)/PrBa(2)Cu3O7 superlattices. Ex situ chemical and structural analysis evidence a 2D block-by-block mechanism in which the minimum growth units are complete unit cell blocks, growing coherently over large lateral distances.     

Magnetic properties of Co nanoparticles in zirconia matrix

Granular films composed of nanometric Co particles embedded in an insulating ZrO₂ matrix were prepared by pulsed laser deposition in a wide range of Co volume concentrations (0.06<x_v<0.42). High-resolution electron microscopy (HREM) shows very sharp interfaces between the crystalline particles and the amorphous matrix, with no evidence of intermixing. The mean particles size and width of the distribution determined by fitting the low-field magnetic susceptibility and magnetization curves in the paramagnetic regime to a distribution of Langevin functions are in agreement with the parameters extracted from direct TEM observations. Ferromagnetic correlations between Co particles are evident in the field-cooled state when increasing Co concentration. The effective anisotropy constant estimated from magnetic measurements is about two orders of magnitude larger than the bulk value, and decreases as particle size increases.