Instituto Superior Técnico

About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.

GBTul 2.0 − A second-generation code for the GBT-based buckling and vibration analysis of thin-walled members

Abstract: This paper presents the fundamentals and illustrates the application and potential of the recent 2.0 release of the software G BTul – a computer program developed by the authors and made available as freeware on the website of the Department of Civil Engineering of the University of Lisbon. The program is based on Generalised Beam Theory (GBT), a bar theory accounting for cross-section in-plane and out-of-plane (warping) deformation, and performs linear buckling and undamped free vibration analyses of prismatic thin-walled members. Its domain of application is much wider than that of the previous release (1.0β), making it possible to analyse single or multi-span members (i) with various support conditions, namely those due to discrete bracing systems, (ii) exhibiting arbitrary (open, closed or “mixed”) flat-walled cross-sections and (iii) acted by fairly general loadings, including concentrated and/or distributed transverse forces applied away from the member shear centre axis. After providing a brief overview on the GBT fundamentals, the program capabilities and innovative aspects are addressed, and its application is illustrated by means of a few relevant numerical examples. Moreover, the program Graphical User Interface is described and the procedures and/or options associated with its main commands are mentioned.

Studies on the involvement of the exopolysaccharide produced by cystic fibrosis-associated isolates of the Burkholderia cepacia complex in biofilm formation and in persistence of respiratory infections.

Abstract: Bacteria belonging to the Burkholderia cepacia complex (BCC) are important opportunistic pathogens that lead to respiratory infections in patients with cystic fibrosis (CF). The clinical outcome following colonization with BCC bacteria is highly variable, and so far, unpredictable. A large percentage (80 to 90%) of BCC isolates from CF patients produce the exopolysaccharide (EPS) cepacian, which has been hypothesized to play a role in the colonization and persistence of these bacteria in the CF lung. In this work, we demonstrate that although it is not required for the initiation of biofilm formation, cepacian plays a role in the establishment of thick biofilms. This conclusion was based on a comparison of the abilities of EPS-defective mutants derived from a B. cepacia mucoid CF isolate by random plasposon insertion mutagenesis and the ability of the parental strain to form biofilms. However, the systematic characterization of 108 CF isolates, corresponding to 15 distinct strains, indicated that other strain-dependent factors are also involved in the development of thick, mature biofilms. The isolates examined belonged to the species B. cepacia, B. multivorans, B. cenocepacia, and B. stabilis and were obtained during a 7-year period of surveillance from 21 CF patients receiving care at the major Portuguese CF center. Most of them (90%) were serial isolates from 12 persistently infected patients. In spite of the concept that bacteria growing in biofilms display more resistance to antibiotics and to host phagocyte killing than do planktonically growing cells, no clear correlation could be established between the ability of the various strains examined to produce EPS and/or to form biofilms in vitro and the persistence or virulence of the respiratory infections they caused in different patients.

Hunting down horizon-scale effects with multi-wavelength surveys

Abstract: Next-generation cosmological surveys will probe ever larger volumes of the Universe, including the largest scales, near and beyond the horizon. On these scales, the galaxy power spectrum carries signatures of local primordial non-Gaussianity (PNG) and horizon-scale general relativistic (GR) effects. However, cosmic variance limits the detection of horizon-scale effects. Combining different surveys via the multi-tracer method allows us to reduce the effect down cosmic variance. This method benefits from large bias differences between two tracers of the underlying dark matter distribution, which suggests a multi-wavelength combination of large volume surveys that are planned on a similar timescale. We show that the combination of two contemporaneous surveys, a large neutral hydrogen intensity mapping survey in SKA Phase1 and a Euclid-like photometric survey, will provide unprecedented constraints on PNG as well as detection of the GR effects. We forecast that the error on local PNG will break through the cosmic variance limit on cosmic microwave background surveys and achieve $\sigma(f_{NL})\simeq1.4-0.5$, depending on assumed priors, bias, and sky coverage. GR effects are more robust to changes in the assumed fiducial model, and we forecast that they can be detected with a signal-to-noise of about $14$.

Surface kinetics of N and O atoms in discharges

Abstract: The probability, , of losses of N and O atoms on Pyrex walls was determined from a fit of calculated to measured concentrations [O] and [NO] in a low-pressure glow discharge in , for percentage concentrations The kinetic model used for calculations includes a detailed description of the processes occurring in the discharge bulk and of the surface reactions of O and N atoms It was found that and are functions of the ratio and the wall temperature, The values of were found to increase from about to about as increases from 1% to 90% (corresponding to ) The probability was found to be independent of and to depend only on in the range For , however, depends on , its magnitude increasing by a factor of 2 - 5 as The kinetic model developed here for surface reactions provides closed expressions for and in terms of the rate constants and the activation energies for these reactions It is shown that the behaviour of and is well explained by the model under the following conditions: (i) the main surface processes for the low wall temperatures involved are reversible adsorption followed by surface diffusion of the adatoms to active sites, where they may either be irreversibly adsorbed or recombine; and (ii) there exist two independent systems of active sites, with different reaction probabilities