Stability of differential equations with piecewise constant argument via discrete equations

Lyapunov stability for a class of differential equation with piecewise constant argument (EPCA) is considered by means of the stability of a discrete equation. Applications to some nonlinear autonomous equations are given improving some linear known cases.

Stability results for impulsive functional differential equations with infinite delay

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

Thermal stability of the martensitic transformation of Cu-Al-Ni-Mn-Ti

The development of new shape memory alloys with high martensitic transformation temperature increases the potential for applications. The development and use of these new alloys depends on the stability of the structure during cycling at high temperatures. If it is possible to guarantee that on alloys keeps the structure during cycling, then the alloy can be used because of the shape memory properties. The aim of this work is to obtain a kinetic model of the forward and backward martensitic transformation of two Cu-Al-Ni-Mn-Ti alloys. Differential scanning calorimetry has been performed in order to establish the kinetic stability of the martensite and the beta transformation. (c) 2006 Elsevier B.V. All rights reserved.

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity. (C) 2005 Elsevier Ltd. All rights reserved.

Electrochemical stability and corrosion resistance of Ti-Mo alloys for biomedical applications

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

Dependence on composition of electronic properties and stability of Pt-Fe/C catalysts for oxygen reduction

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

Pd-based catalysts: Influence of the second metal on their stability and oxygen reduction activity

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

Structural aspects, thermal behavior, and stability of a self-assembled supramolecular polymer derived from flunixin-meglumine supramolecular adducts

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Thermal decomposition and stability in a series of heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X=Cl, Br, I)

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

Fermentation, losses, and aerobic stability of sugarcane silages treated with chemical or bacterial additives

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

THERMAL REGIME AND STABILITY OF JURUMIRIM RESERVOIR (PARANAPANEMA RIVER, SAO-PAULO, BRAZIL)

Thermal regime and stability in Jurumirim Reservoir (São Paulo, Brazil) were studied for a year. Isothermy and thermal stratification were observed from June to September and from October to March, respectively. The annual heat budget was 14.0 Kcal . cm-2 and average heat gain per day was 67.2 cal . cm-2 . day-1. Maximum stability and wind work reached 324.2 and 3,037.5 g . cm . cm-2, respectively. According to thermal structure and heat content, Jurumirim Reservoir was classified as a warm tropical monomictic lake.

Electrochemical stability of SnO2-based coated Ti electrodes

The electrochemical behavior of SnO2-SbOx, based electrodes, with and without the addition of RuO2, was studied by cyclic voltammetry, service life measurements and electrochemical impedance spectroscopy in 0.5 M H2SO4 the physical characteristics of these materials were investigated using SEM, EDX and XRD. The resulting cyclic voltammograms obtained using SnO2-SbOx, and SnO2-SbOx-RuO2(x), x = 30, 5, 1 and 0.4 % showed that the OER overpotential decreased with the addition of RuO2. In the repetitive triangular potential voltammetry applied to the SnO2 electrode without and with RuO2 (1%), a higher anodic current is observed during the first potential scan; it is explained in terms of the oxidation of the Ti substrate. The addition of 1% RuO2 increased the service life from 8 to 20 hours at 10 mAcm(-2), while at 50 mAcm(-2) this increase was from 1 to 8 hours. AC Impedance diagrams obtained for the Ti/SnO2-SbOx and Ti/SnO2-SbOx-RuO2 electrodes at the rest potential and at a potential in the OER region can be explained by a single equivalent circuit containing two elements in series. The results showed that the charge transfer resistance and the resistance of the oxide film are lower in the oxide film containing RuO2. Surface analysis of Ti/SnO2-SbOx, revealed that it is relatively porous and formed by clusters of small particles. The Ti/SnO2-SbOx-RuO2 (1%) film is more compact, though. XRD analysis showed that a Sn1-xTixO2 oxide is formed on the Ti/SnO2-SbOx with 1% and without RuO2 electrodes.

Investigations on the stability of plasma modified silicone surfaces

In this work it was investigated the effect of the exposure to different plasmas on the wettability of silicone samples. We have observed that oxygen. argon, and hydrogen glow discharges are quite effective in reducing the water contact angle of such polymer. However, indifferently to efficiency of the treatment, practically all the modified surfaces recovered great part of their original hydrophobicity. We have investigated this hydrophobic recovery using surface energy measurements and theoretical simulations based on the exponential decay of the population of polar groups on the surface. According to our results such recovery can be attributed to the decrease of polar species at the interface water-polymer surface.

Existence and stability of new nanoreactors: Highly swollen hexagonal liquid crystals

We report the preparation of direct hexagonal liquid crystals, constituted of oil-swollen cylinders arranged on a triangular lattice in water. The volume ratio of oil over water, rho, can be as large as 3.8. From the lattice parameter measured by small-angle X-ray scattering, we show that all the oil is indeed incorporated into the cylinders, thus allowing the diameter of the cylinders to be controlled over one decade range, provided that the ionic strength of the aqueous medium and rho are varied concomitantly. These hexagonal swollen liquid crystals (SLCs) have been first reported with sodium dodecyl sulfate as anionic surfactant, cyclohexane as solvent, 1-pentanol as co-surfactant, and sodium chloride as salt (Ramos, L.; Fabre, P. Langmuir 1997, 13, 13). The stability of these liquid crystals is investigated when the pH of the aqueous medium or the chemical nature of the components (salt and surfactant) is changed. We demonstrate that the range of stability is quite extended, rendering swollen hexagonal phases potentially useful for the fabrication of nanomaterials. As illustrations, we finally show that gelation of inorganic particles in the continuous aqueous medium of a SLC and polymerization within the oil-swollen cylinders of a SLC can be conducted without disrupting the hexagonal order of the system.