Estimation of fretting fatigue life using a multiaxial stress-based critical distance methodology

This work presents a methodology for life estimation of mechanical couplings subjected to fretting fatigue. In this approach, a stress-based multiaxial fatigue parameter is evaluated at a critical distance below the contact surface. The fatigue parameter is based on an improved formulation of the Modified Wöhler Curve Method, in which the shear stress amplitude is measured via the Maximum Rectangular Hull method. To apply the Theory of Critical Distances in the medium-cycle fatigue regime, the critical distance is assumed to depend on the number of cycles to failure. Available fretting fatigue data, conducted on a cylinder-plane contact configuration made of Al alloy 4% Cu, were used to assess the methodology. Most of the life estimates were within an error band given by a factor of 2

Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe(2)O(4)) thin films have been deposited on Si (001) substrates, with different substrate ternperatures (Td,p = 25 degrees C - 600 degrees C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength lambda = 248 nm). The oxygen pressure during deposition was 2 x 10(-2) mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture ofa CoFe(2)O(4) phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for Tdep = 600 degrees C the films were composed mainly by polycrystalline CoFe(2)O(4). The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (H(exch)) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe(2)O(4) phase on the magnetic properties of the thin films.This work has been financially supported by the Portuguese Foundation for Science and Technology (FCT), through the project POCI/CTM/60181/2004

Caracterização das Distribuições pelas Propriedades dos Estimadores de Bayes

Neste trabalho reapresentamos os resultados obtidos por Kagan e Karpov [1,2], mostrando que: para a construção do Estimador Linear Bayseano a condição necessária e suficiente é que, a priori, a distribuição dos erros sejam normais

Optimizing the choice of microsatellite markers for fingerprinting eucalyptus

In this study we have analyzed the information provided by 17 publicly available Eucalyptus microsatellite (SSR) markers (Brondani et al. 1998, 2002; Jones et al. 2002; Steane et al. 2001) in the context of genetic identification within a sample of 140 individuals from an elite collection (denoted hereafter base) of RAIZ genetic improvement population

Comparative measurements of carbon dioxide fluxes from two nearby towers in a central Amazonian rainforest: the Manaus LBA site

Forests around Manaus have staged the oldest and the longest forest-atmosphere CO2 exchange studies made anywhere in the Amazon. Since July 1999 the exchange of CO2, water, and energy, as well as weather variables, have been measured almost continuously over two forests, 11 km apart, in the Cuieiras reserve near Manaus, Brazil. This paper presents the sites and climatology of the region based upon the new data sets. The landscape consists of plateaus dissected by often waterlogged valleys, and the two sites differ in terms of the relative areas of those two landscape components represented in the tower footprints. The radiation and wind climate was similar to both towers. Generally, both the long-wave and short-wave radiation input was less in the wet than in the dry season. The energy balance closure was imperfect (on average 80%) in both towers, with little variation in energy partitioning between the wet and dry seasons; likely a result of anomalously high rainfall in the 1999 dry season. Fluxes of CO2 also showed little seasonal variation except for a slightly shorter daytime uptake duration and somewhat lower respiratory fluxes in the dry season. The net effect is one of lower daily net ecosystem exchange (NEE) in the dry season. The tower, which has less waterlogged valley areas in its footprint, measured a higher overall CO2 uptake rate. We found that on first sight, NEE is underestimated during calm nights, as was observed in many other tower sites before. However, a closer inspection of the diurnal variation of CO2 storage fluxes and NEE suggests that at least part of the nighttime deficits is recovered from either lateral influx of CO2 from valleys or outgassing of soil storage. Therefore there is a high uncertainty in the magnitude of nocturnal NEE, and consequently preliminary estimates of annual carbon uptake reflecting this range from 1 to 8 T ha-1 y-1, with an even higher upper range for the less waterlogged area. The high uptake rates are clearly unsustainable and call for further investigations into the integral carbon balance of Amazon landscapes

Validation of spallation neutron production and propagation within Geant4

Using simulations to understand backgrounds from muon-induced neutrons is important in designing next-generation low-background underground experiments. Validation of relevant physics within the Geant4 simulation package has been completed by comparing to data from two recent experiments. Verification focused on the production and propagation of neutrons at energies important to underground experiments. Discrepancies were observed between experimental data and the simulation. Techniques were explored to correct for these discrepancies.Comment: 12 pages, 6 figures, 5 tables, submitted to NIM A. 6 Aug 200

BIOCHEMICAL DIFFERENTIATION AMONG S. aureus, S. Intermedius AND S. hyicus ISOLATED FROM BOVINES WITH SUBCLINICAL MASTITIS

Staphylococcus aureus é, entre as espécies de estafilococos, a mais relacionada a infecções em animais e humanos, bem como a doenças de origem alimentar. Entretanto, S. intermedius e S. hyicus, duas espécies com características morfológicas muito similares a S. aureus, também podem causar doenças, bem como produzir enterotoxinas em alimentos, tornando importante a diferenciação entre essas três espécies de estafilococos. O objetivo deste trabalho foi avaliar a eficiência de oito técnicas bioquímicas com relação à sua capacidade para distinguir entre S. aureus, S. intermedius e S. hyicus. Para isso, 65 cepas, previamente identificadas em nível de espécie através de técnicas moleculares, foram submetidas aos testes de produção de pigmentos carotenóides, atividade hemolítica em ágar sangue, produção de b- galactosidase, produção de acetoína, atividade lipolítica em polisorbato, fermentação aeróbica da maltose, fermentação anaeróbica do manitol e crescimento em ágar Baird-Paker e ágar P suplementados com acriflavina. Verificou-se que os testes de sensibilidade a acriflavina e de produção de b- galactosidase apresentaram bom poder discriminatório, demonstrando serem os melhores testes bioquímicos para a diferenciação entre essas três espécies de estafilococos. Abstract Among staphylococcus species, Staphylococcus aureus is the one mostly related to animal and human infections, as well as food diseases. However, S. intermedius and S. hyicus, two species with very similar morphological characteristics to S. aureus, can also cause diseases as well as produce enterotoxins in food, what makes important the differentiation of these three species. The aim of this work was to study the efficiency of eight biochemical techniques regarding their capacity to distinguish among S. aureus, S. intermedius and S. hyicus. For that purpose, sixty five strains, previously identified at species level through molecular techniques, were submitted to the tests of carotenoid pigments production, hemolytic activity in blood agar, b- galactosidase production, acetoin production, lipolytic activity in polysorbate, maltose aerobic fermentation, manitol anaerobic fermentation and growth in Baird-Parker and P agar supplemented with acriflavine. It was verified that tests of sensitivity to acriflavine and b-galactosidase production display good distinguishing properties, constituting as a whole, the best biochemical tests for the identification of these three staphylococcus species

A Multiaxial Stress-Based Critical Distance Methodology To Estimate Fretting Fatigue Life

This work presents a methodology for fretting fatigue life estimation based on the evaluation of a multiaxial fatigue parameter at a critical distance below the contact surface. The fatigue parameter is defined using the Modified Wöhler Curve Method together with a measure of shear stress amplitude based on the Maximum Rectangular Hull concept. To apply the approach in the medium-cycle fatigue regime, the critical distance is assumed to depend on the fatigue life. Available fretting fatigue experiments conducted on a cylinder-on-flat contact configuration made of Al-4%Cu alloy were used to evaluate the methodology. Most of the fatigue life estimates were within factor-of-two boundaries

Molecular estimates of similarity in Eucalyptus globulus

The base populations used in most forest tree genetic improvement programs usually lack detailed pedigree information. Molecular markers, such as microsatellites (SSR), can be used to estimate individuals’ pairwise relatedness, which is based on the probabilities’ ratios of the identity in state between the individuals compared and the reference unrelated population These estimates can be very useful to infer the level of relationship among sub-populations of elite material and/or for the design of controlled crosses between putatively unrelated parents. Using 113 putatively unrelated individuals - genotyped with 18 SSR - self, full-sib, half-sib and unrelated were simulated, and four pairwise similarity coefficients were tested: Queller & Goodnight 1989; Li et al. 1993; Ritland 1996, and Lynch & Ritland 1999. The Lynch & Ritland (1999) coefficient was selected (Figure 1), for it displayed a better adjustment with the expected level of relatedness and narrower standard errors (SE). SE were calculated through Monte- Carlo techniques, to avoid unequal sample size bias, by using 105 simulations for each relatedness group. To illustrate the usefulness of molecular estimates of similarity in genetic improvement programs, a clustering (UPGMA) based on the pairwise Lynch & Ritland (1999) coefficient (LR) values was performed to infer about the putative relationship among individuals of the subgroups of E. globulus elite individuals. From that analysis at least two pairs might be related and a PCA analysis confirmed the clustering results

A novel niobium (oxy)nitride-BaCe0.7Zr0.1Y0.2O3-δ composite electrode for Proton Ceramic Membrane Reactors (PCMRs)

The necessity to accelerate green and low carbon technologies, to mitigate the pending energetic crisis, potentiates the urgent search for alternative energy transfer methods. In this regard, Proton Ceramic Membrane Reactors (PCMRs) have shown great potential as a clean alternative for both energy production and the electrochemical synthesis of a wide range of chemical products. One of the most important is that of ammonia, where recent literature has demonstrated the potential use of PCMRs to either synthesize this chemical product or to use it as a fuel, and where suitable new electrodes must be developed. Hence, this work investigates the use of niobium (oxy)nitride (NbNxOy) in combination with proton ceramic conducting materials, as a new category of composite electrode for PCMRs applications. To achieve this goal, firstly, the chemical compatibility of the NbNxOy phase with the well-known proton conducting perovskite, yttrium-doped barium cerate (BaCe0.9Y0.1O3-δ, BCY10), was assessed. By X-ray powder diffraction, BaCe0.7Zr0.1Y0.2O3-δ (BCZY712) was shown to be chemically stable with the NbNxOy phase, surviving up to 850 °C, thus, facilitating the production of an electrolyte supported composite electrode film based on BCZY712-NbNxOy (40–60 vol%). Thermogravimetric experiments combined with X-ray diffraction were also made to assess the thermal stability of the NbNxOy material in both N2 and 2 % H2/N2 atmospheres, revealing that NbNxOy decomposes into its parent oxide in N2, while retaining the pure (oxy)nitride phase in the more reducing conditions. The polarization behavior of the BCZY712-NbNxOy composite electrode was evaluated by electrochemical impedance spectroscopy under different gaseous conditions of H2/N2 and NH3 atmospheres. The overall electrode mechanism was tentatively explained by three main steps, including i) proton incorporation/water release or adsorption/desorption of water, ii) gaseous hydrogen adsorption/desorption, and iii) interfacial transfer reaction of either protons or oxygen-ion vacancies. To the best of our knowledge, this is the first work that reports a detailed chemical compatibility study of niobium (oxy)nitride with a protonic ceramic matrix, while also outlining a detailed electrode mechanism under prospective conditions of hydrogenation/de‑hydrogenation of ammonia.publishe