Obtenção de estirpes de rizóbio eficientes na fixação de nitrogênio para espécies florestais (aproximação 2000).

bitstream/CNPAB-2010/27375/1/doc116.pd

Distinguishing the albedo of exoplanets from stellar activity

Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the observations planned in the context of the CHEOPS mission. As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process.We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure

Simulating different modes of current transfer to thermionic cathodes in a wide range of conditions

Changes in the pattern of steady-state modes of current transfer to thermionic cathodes induced by variations of the cathode geometry and temperature of the cooling fluid are studied numerically. For some combinations of control parameters, only one stable mode in a wide current range exists, which combines features of spot and diffuse modes. This mode, when attached to an elongated protrusion on the cathode surface, may be identified with the so-called super spot mode observed in experiments on low-current arcs. There is also reasonable agreement between the modelling and the experiment on cathodes of high-current arcs operating in the diffuse mode. The conclusions on existence under certain conditions of only one stable mode in a wide current range and of a minimum of the dependence of the temperature of the hottest point of the cathode on the arc current, manifested by this mode, may have industrial importance and admit a straightforward experimental verification.info:eu-repo/semantics/publishedVersio

Non-universal behavior for aperiodic interactions within a mean-field approximation

We study the spin-1/2 Ising model on a Bethe lattice in the mean-field limit, with the interaction constants following two deterministic aperiodic sequences: Fibonacci or period-doubling ones. New algorithms of sequence generation were implemented, which were fundamental in obtaining long sequences and, therefore, precise results. We calculate the exact critical temperature for both sequences, as well as the critical exponent $\beta$, $\gamma$ and $\delta$. For the Fibonacci sequence, the exponents are classical, while for the period-doubling one they depend on the ratio between the two exchange constants. The usual relations between critical exponents are satisfied, within error bars, for the period-doubling sequence. Therefore, we show that mean-field-like procedures may lead to nonclassical critical exponents.Comment: 6 pages, 7 figures, to be published in Phys. Rev.

Influence of asymmetry and nodal planes on high-harmonic generation in heteronuclear molecules

The relation between high-harmonic spectra and the geometry of the molecular orbitals in position and momentum space is investigated. In particular we choose two isoelectronic pairs of homonuclear and heteronuclear molecules, such that the highest occupied molecular orbital of the former exhibit at least one nodal plane. The imprint of such planes is a strong suppression in the harmonic spectra, for particular alignment angles. We are able to identify two distinct types of nodal planes. If the nodal planes are determined by the atomic wavefunctions only, the angle for which the yield is suppressed will remain the same for both types of molecules. In contrast, if they are determined by the linear combination of atomic orbitals at different centers in the molecule, there will be a shift in the angle at which the suppression occurs for the heteronuclear molecules, with regard to their homonuclear counterpart. This shows that, in principle, molecular imaging, which uses the homonuclear molecule as a reference and enables one to observe the wavefunction distortions in its heteronuclear counterpart, is possible.Comment: 14 pages, 7 figures. Figs. 3, 5 and 6 have been simplified in order to comply with the arXiv size requirement

Diversidade de rizóbios em áreas revegetadas após a mineração de bauxita.

A contribuição da diversidade dos rizóbios para manutenção da diversidade e funcionalidade de ecossistemas naturais tem sido pouco estudada. Neste trabalho objetivou-se avaliar a diversidade de rizóbios em áreas revegetadas em diferentes épocas. Utilizou-se siratro e mimosa como plantas-isca e as ferramentas PCR-RFLP, sequencimanto e BOX-PCR. Observou-se que as áreas de maior diversidade foram as revegetadas há mais tempo e as áreas revegetadas com plantio da leguminosa Acacia mangium e, que isolados proximamente relacionados ao gênero Bradyrhizobium foram os mais abundantes

Testing the Freeze/Thaw Cycles in Lime Mortar

2nd Historic Mortars Conference - HMC 2010 and RILEM TC 203-RHM Final Workshop, Prague, September 2010The purpose of this study is to evaluate the behaviour of lime mortars in cold climates, namely by the effect of freeze/thaw cycles. Twelve compositions of mortars were prepared by varying the type of binder (air lime, hydraulic lime and air lime plus cement) and the grain size distribution of the sand and by including an air entraining agent. Tests, including the open porosity, mechanical strength and resistance to freeze/thaw cycles, were conducted in order to evaluate the performance of lime mortars in cold climates. The analysis of results allowed the determination of relevant conclusions about the influence of the grain size of aggregate, the use of an air entraining agent and the behaviour of mortars with different types of binder to be drawn. The open porosity depends mainly on the granulometry of sands while the mechanical strength is correlated with the binder type. These two characteristics have a great influence on the strength of mortar during freeze/thaw cycles and consequently on their performance in cold climates

Low redshift constraints on energy-momentum-powered gravity models

There has been recent interest in the cosmological consequences of energy-momentum-powered gravity models, in which the matter side of Einstein's equations is modified by the addition of a term proportional to some power, $n$, of the energy-momentum tensor, in addition to the canonical linear term. In this work we treat these models as phenomenological extensions of the standard $\Lambda$CDM, containing both matter and a cosmological constant. We also quantitatively constrain the additional model parameters using low redshift background cosmology data that are specifically from Type Ia supernovas and Hubble parameter measurements. We start by studying specific cases of these models with fixed values of $n,$ which lead to an analytic expression for the Friedmann equation; we discuss both their current constraints and how the models may be further constrained by future observations of Type Ia supernovas for WFIRST complemented by measurements of the redshift drift by the ELT. We then consider and constrain a more extended parameter space, allowing $n$ to be a free parameter and considering scenarios with and without a cosmological constant. These models do not solve the cosmological constant problem per se. Nonetheless these models can phenomenologically lead to a recent accelerating universe without a cosmological constant at the cost of having a preferred matter density of around $\Omega_M\sim0.4$ instead of the usual $\Omega_M\sim0.3$. Finally we also briefly constrain scenarios without a cosmological constant, where the single component has a constant equation of state which needs not be that of matter; we provide an illustrative comparison of this model with a more standard dynamical dark energy model with a constant equation of state.Comment: 13+2 pages, 12+1 figures; A&A (in press

Internova e-learning platform in an entrepreneurial context

Currently, there is still an opposition of teachers to the implementation of new technologies in an educational context. Although several studies point out the relevance of the use of information and communication technologies in pedagogical practices, providing educational contexts more focused on learning practices and fostering more active and autonomous professionals. In this context, this article emphasizes the purpose of using Information and Communication Technologies (ICT), as well as virtual learning environments, in the higher education system, to support the teaching-learning processes. In this article, a state of the art was carried out, in order to demonstrate some advantages of the teaching-learning process, the teacher's and student behaviour profiles and its role in relation to the use of new technologies. The objective of this study was to analyse the impact of using a digital platform on the teaching-learning process in an educational context. An e-learning digital platform, INTERNOVA, developed within the scope of the INTERNOVAMARKET-FOOD project (0437_internovamarket-food_1_E - Internovamarket accelerator program to increase the competitiveness of the food sector in Galicia-Northern), within the curricular unit of Food Safety and Certification of the Master in Food Engineering's curriculum. In order to assess the impact of the training course on the students' learning outcomes, a survey was applied to master's students and Food Engineering research fellows (participants). The same survey was applied before the training and after it in order to compare both results. At the end of each training course, another survey was addressed to all the participants asking about the organization, quality and the easiness of the platform. The results obtained show that the students had no difficulties in using the platform, having revealed that they would like to continue using it more frequently. The data obtained are an evidence of the participants' learning improvement and their involvement in the learning process through the INTERNOVA platform. With this work, it can be concluded that the ICT applied to a curricular program can be a very important support in the teaching-learning process. In this context, it is important to recommend well-designed curricular programs so that teachers can improve their teaching practices, enhancing students' digital skills, and thus contributing to the development of more active and autonomous professionals. © Proceedings of the 14th IADIS International Conference e-Learning 2020, EL 2020 - Part of the 14th Multi Conference on Computer Science and Information Systems, MCCSIS 2020. All rights reserved.This work was supported by INTERREG V-A Espanha-Portugal (POCTEP) 2014-2020 (0437_INTERNOVAMARKET-FOOD_1_E) under the development of the project entitled “INTERNOVAMARKET-FOOD – Programa acelerador para aumentar a competitividade do sector alimentar da Galiza-Norte de Portugal”info:eu-repo/semantics/publishedVersio