Thermodynamic modeling of the NbeB system

In the present work, the Nb–B binary system was thermodynamically optimized. The stable phases in this system are BCC (niobium), Nb3B2, NbB, Nb3B4, Nb5B6, NbB2, B (boron) and liquid L. The borides Nb3B2, NbB, Nb3B4 and Nb5B6 and the B (boron) were modeled as stoichiometric phases and the liquid L, BCC (niobium) and NbB2 as solutions, using the sublattices model, with their excess terms described by the Redlich–Kister polynomials. The Gibbs energy coefficients were optimized based on the experimental values of enthalpy of formation, low temperature specific heat, liquidus temperatures and temperatures of invariant transformations. The calculated Nb–B diagram reproduces well the experimental values from the literature

Superliga Inconel-718: Caracterização microestrutural e validação da base de dados termodinâmicos

Neste trabalho foi realizada a validação da base de dados para superligas à base de níquel através da comparação de dados termodinâmicos calculados e caracterização microestrutural da superliga Inconel 718. O material adquirido no estado bruto de fusão foi tratado termicamente inicialmente para solubilização das fases secundárias na matriz seguido de tratamento na temperatura de 700 °C durante os períodos de 500, 1000 e 2000 horas com objetivo deixar a microestrutura do material próxima a condição de equilíbrio termodinâmico. Os cálculos termodinâmicos em equilíbrio mostraram que na superliga Inconel 718 as fases predominantes são gama duas linhas (γ’’) e gama linha (γ’). Com aumento do tempo de tratamento térmico o cálculo prevê a dissolução da fase γ’’ na fase delta (δ), além da presença do carbeto MC em menor quantidade. Com os resultados obtidos por meio das análises utilizando o MEV e a comparação com os cálculos termodinâmicos conclui-se que a base de dados pode ser utilizada como ferramenta auxiliar no desenvolvimento de novas ligas à base de níquel e seus processos de fabricação

Proteomic characterization of vanA-containing Enterococcus recovered from Seagulls at the Berlengas Natural Reserve, W Portugal

<p>Abstract</p> <p>Background</p> <p>Enterococci have emerged as the third most common cause of nosocomial infections, requiring bactericidal antimicrobial therapy. Although vancomycin resistance is a major problem in clinics and has emerged in an important extend in farm animals, few studies have examined it in wild animals. To determine the prevalence of <it>van</it>A-containing <it>Enterococcus </it>strains among faecal samples of Seagulls (<it>Larus cachinnans</it>) of Berlengas Natural Reserve of Portugal, we developed a proteomic approach integrated with genomic data. The purpose was to detect the maximum number of proteins that vary in different enterococci species which are thought to be connected in some, as yet unknown, way to antibiotic resistance.</p> <p>Results</p> <p>From the 57 seagull samples, 54 faecal samples showed the presence of <it>Enterococcus </it>isolates (94.7%). For the enterococci, <it>E. faecium </it>was the most prevalent species in seagulls (50%), followed by <it>E. faecalis </it>and <it>E. durans </it>(10.4%), and <it>E. hirae </it>(6.3%). <it>VanA-containing </it>enterococcal strains were detected in 10.5% of the 57 seagull faecal samples studied. Four of the <it>vanA</it>-containing enterococci were identified as <it>E. faecium </it>and two as <it>E. durans</it>. The <it>tet</it>(M) gene was found in all five tetracycline-resistant <it>vanA </it>strains. The <it>erm</it>(B) gene was demonstrated in all six erythromycin-resistant <it>vanA </it>strains. The <it>hyl </it>virulence gene was detected in all four <it>van</it>A-containing <it>E. faecium </it>isolates in this study, and two of them harboured the <it>pur</it>K1 allele. In addition these strains also showed ampicillin and ciprofoxacin resistance. The whole-cell proteomic profile of <it>van</it>A-containing <it>Enterococcus </it>strains was applied to evaluate the discriminatory power of this technique for their identification. The major differences among species-specific profiles were found in the positions corresponding to 97-45 kDa. Sixty individualized protein <it>spots </it>for each <it>vanA </it>isolate was identified and suitable for peptide mass fingerprinting measures by spectrometry measuring (MALDI/TOF MS) and their identification through bioinformatic databases query. The proteins were classified in different groups according to their biological function: protein biosynthesis, ATP synthesis, glycolysis, conjugation and antibiotic resistance. Taking into account the origin of these strains and its relation to infectious processes in humans and animals, it is important to explore the proteome of new strains which might serve as protein biomarkers for biological activity.</p> <p>Conclusions</p> <p>The comprehensive description of proteins isolated from vancomycin-resistant <it>Enterococcus faecium </it>and <it>E. durans </it>may provide new targets for development of antimicrobial agents. This knowledge may help to identify new biomarkers of antibiotic resistance and virulence factors.</p

Maquete dos sistemas binários Nb-B, Cr-Nb e Cr-B no triângulo de Gibbs como um produto didático de apoio ao estudo do sistema ternário Nb-Cr-B e ensino de diagramas de fase ternários.

Uma maquete tridimensional para os sistemas binários Nb-B, Cr-Nb e Cr-B num triângulo de Gibbs foi desenvolvida visando à utilização de uma ferramenta didática para facilitar o estudo de diagramas de fases ternários e a necessidade de atender a demanda estabelecida para conclusão do curso de “mestrado profissional” envolvendo a apresentação de um produto. O sistema Nb-Cr-B é o foco da dissertação apresentada ao Curso de Mestrado Profissional em Materiais do UniFOA intitulada “Contribuição ao Desenvolvimento de Materiais Estruturais para Aplicações em Altas Temperaturas: Avaliação Experimental das Relações de Fases do Sistema NB-Cr-B na Região Nb – Cr – CrB – Nb3B4”. Esta maquete é constituída dos três subsistemas binários Nb-B, Cr-Nb e CrB, que permitem a construção do sistema ternário correspondente. Durante o desenvolvimento do trabalho de pesquisa do sistema ternário, foi identificada a necessidade de uma ferramenta tridimensional para facilitar o entendimento das relações de equilíbrio de fases deste sistema. A metodologia consistiu na reprodução dos subsistemas binários Nb-B, Cr-Nb e Cr-B em arame e fixação dos mesmos em uma base de acrílico contendo a representação gráfica do triângulo de Gibbs

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Recently, a new ternary phase was discovered in the Ti-Si-B system, located near the Ti6Si2B composition. The present study concerns the preparation of titanium alloys that contain such phase mixed with &#945;-titanium and other intermetallic phases. High-purity powders were initially processed in a planetary ball-mill under argon atmosphere with Ti-18Si-6B and Ti-7.5Si-22.5B at. (%) initial compositions. Variation of parameters such as rotary speed, time, and ball diameters were adopted. The as-milled powders were pressureless sintered and hot pressed. Both the as-milled and sintered materials were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Sintered samples have presented equilibrium structures formed mainly by the &#945;-Ti+Ti6Si2B+Ti5Si3+TiB phases. Silicon and boron peaks disappear throughout the milling processes, as observed in the powder diffraction data. Furthermore, an iron contamination of up to 10 at. (%) is measured by X-ray spectroscopy analysis on some regions of the sintered samples. Density, hardness and tribological results for these two compositions are also presented here

Avaliação de Microdureza de Ligas Hf–Si–B

O avanço tecnológico tem gerado demanda crescente por materiais que possam ser utilizados sob alta temperatura, o que inclui ligas intermetálicas MR–Si–B (MR = metal refratário) com estruturas multifásicas, que podem ser aplicados também em ambientes oxidantes. Assim, este trabalho teve por objetivo estudar a microdureza de ligas do sistema Hf–Si–B na seção isotérmica a 1600ºC, na região rica em Hf. Ligas Hf–Si–B foram produzidas com lâminas de Hf (min. 99,8%), Si (min. 99,998%) e B (min. 99,5%), em forno a arco e tratadas termicamente a 1600 ºC sob atmosfera de argônio. As relações de fases nessas ligas foram previamente identificadas por difração de raios-X e por contraste, em imagens obtidas via microscopia eletrônica de varredura no modo elétrons retroespalhados. As ligas tiveram sua dureza analisada pelo método Vickers (microdureza) com carga de 0,2 kgf e tempo de aplicação de 20 s. Os resultados, obtidos da média aritmética de cinco medições realizadas para cada liga, mostram que as ligas estudadas apresentam elevada dureza

Boron site preference in ternary Ta and Nb boron suicides

X-ray single crystal (XSC) and neutron powder diffraction data (NPD) were used to elucidate boron site preference for five ternary phases. Ta3Si1-xBx (x=0.112(4)) crystallizes with the Ti3P-type (space group P4(2)/n) with B-atoms sharing the 8g site with Si atoms. Ta5Si3-x (x=0.03(1); Cr5B3- type) crystallizes with space group 14/mcm, exhibiting a small amount of vacancies on the 4 alpha site. Both, Ta-5(Si1-xBx)(3), X=0.568(3), and Nb-5(Si1-xBx)(3), x=0.59(2), are part of solid solutions of M5Si3 with Cr5B3-type into the ternary M-Si-B systems (M=Nb or Ta) with B replacing Si on the 8h site. The D8(8)-phase in the Nb-Si-B system crystallizes with the Ti5Ga4-type revealing the formula Nb5Si3B1-x (x=0.292(3)) with B partially filling the voids in the 2b site of the Mn5Si3 parent type. (C) 2012 Elsevier Inc. All rights reserved.Higher Education Commission of Pakistan (HEC)Austrian OEADFAPESP (Sao Paulo, Brazil)FAPESP (Sao Paulo, Brazil) [97/06348-4]European Commission [RII3-CT-2003-505925]European Commissio

Rarity of monodominance in hyperdiverse Amazonian forests.

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors