Brasília, Brazil
Brasília, Brazil

Time filter

Source Type

Miranda V.,University of Chicago | Miranda V.,Capes Foundation | Hu W.,University of Chicago | Adshead P.,University of Illinois at Urbana - Champaign
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The recent BICEP2 B-mode polarization determination of an inflationary tensor-scalar ratio r=0.2-0.05+0.07 is in tension with simple scale-free models of inflation due to a lack of a corresponding low multipole excess in the temperature power spectrum which places a limit of r0.002<0.11 (95% C.L.) on such models. Single-field inflationary models that reconcile these two observations, even those where the tilt runs substantially, introduce a scale into the scalar power spectrum. To cancel the tensor excess, and simultaneously remove the excess already present without tensors, ideally the model should introduce this scale as a relatively sharp transition in the tensor-scalar ratio around the horizon at recombination. We consider models which generate such a step in this quantity and find that they can improve the joint fit to the temperature and polarization data by up to 2ΔlnL≈-14 without changing cosmological parameters. Precision E-mode polarization measurements should be able to test this explanation. © 2014 American Physical Society.


Tudor-Locke C.,Pennington Biomedical Research Center | Schuna Jr. J.M.,Pennington Biomedical Research Center | Frensham L.J.,University of South Australia | Proenca M.,State University Londrina | Proenca M.,CAPES Foundation
International Journal of Obesity | Year: 2014

Emerging evidence supports the feasibility of raising daily energy expenditure (EE) by replacing office work-related sedentary behavior with low-intensity non-exercise physical activity (PA) via workstation alternatives to the traditional office chair and desktop computer-based combinations. The purpose of this review article is to introduce a simple taxonomy to facilitate classification and study of workstation alternatives, catalog the diversity of research undertaken to date related to energy balance, and present and summarize the gaps and opportunities for a research agenda for workstation alternatives moving forward. A PubMed search elicited 57 English language articles published since 2000; additional articles were identified by reviewing reference sections and contacting authors. Selection criteria ultimately focused on use of workstation alternatives during simulated or real work tasks. The EE of sitting on a stability ball or using sit-stand/standing desks is comparable to the traditional seated condition (1.2 kcal min-1). The treadmill and pedal desks (active workstation alternatives) offer the greatest promise in terms of EE (2-4 kcal min-1). Sitting on a stability ball or using sit-stand/standing desks does not impair task performance relative to the traditional seated condition. Some evidence of typing impairment is inconsistently reported with active workstation alternatives; the finer motor skills required for mouse-related tasks may be more affected. Little is known about learning or adaptation with practice. Users are generally accepting of workstation alternatives; however, there is evidence of less than optimal use. Active workstations (that is, treadmill desks and pedal desks) in particular represent a potential strategy for mitigating the diminished EE inherent to contemporary office-based workplaces, but only if they are scalable. The science supporting active workstations is young and heterogeneous; however, this means that there are many knowledge gaps and opportunities for research, including those focused on implementation issues related to optimizing both employers' and workers' uptake. © 2014 Macmillan Publishers Limited All rights reserved.


Benchimol M.,University of East Anglia | Benchimol M.,Capes Foundation | Peres C.A.,University of East Anglia
Journal of Ecology | Year: 2015

Islands formed upstream of mega hydroelectric dams are excellent experimental landscapes to assess the impacts of habitat fragmentation on biodiversity. We examined the effects of plot-, patch- and landscape-scale variables on the patterns of floristic diversity across 34 forest islands that had experienced 26 years of isolation since the creation of the 4437 km2 Balbina Hydroelectric Reservoir of central Brazilian Amazonia. In addition, three undisturbed continuous forest sites in neighbouring mainland areas were also sampled across a comparable elevational gradient. We identified all live trees ≥10 cm DBH at species level within a total of 87 quarter-hectare forest plots and conducted a comprehensive compilation of functional attributes of each tree species. We then examined species-area relationships (SARs) and the additional effects of patch and landscape-scale metrics on patterns of tree assemblage heterogeneity, both in terms of taxonomic and functional diversity. Despite a clearly positive SAR, edge-mediated forest disturbance was the single most important driver of species composition and abundance within islands. Our results suggest that non-random floristic transitions within island plots followed a predictable pattern, with different life-history traits either penalizing or rewarding local persistence of different functional groups. Distance to edges mediated the probability of tree mortality induced by windfalls and episodic surface fires, clearly resulting in faster species turnover and unidirectional changes in guild structure within small islands where light-wooded fast-growing pioneers largely replaced heavy-wooded species of the old-growth flora. Synthesis. Following a simultaneous 26-year post-isolation history, we disentangle the effects of habitat loss and insularization on tree assemblages within a large set of Amazonian 'true' forest islands, of variable sizes, sharing a uniform open-water matrix. Area effects are expressed via a response to edge effects, with trees in smaller islands being more vulnerable to edge-related surface fires and wind-throws. Additionally, forest edge effects can be a powerful driver of non-random floristic transitions across islands within the Balbina archipelago via a process of rapid pioneer proliferation, drastically affecting both the taxonomic and functional composition of insular tree communities. Finally, our results indicate that detrimental effects of forest fragmentation induced by hydroelectric dams are considerably stronger than those of forest patches embedded within a terrestrial vegetation matrix. © 2015 The Authors. Journal of Ecology © 2015 British Ecological Society.


Benchimol M.,University of East Anglia | Benchimol M.,Capes Foundation | Peres C.A.,University of East Anglia
Diversity and Distributions | Year: 2013

Aim: We conducted the first comprehensive quantitative review on the effects of habitat fragmentation on Neotropical primates to examine how both patch disturbance and landscape variables modulate species-area relationships (SARs) and species persistence in fragmented forest landscapes. Location: Neotropical forests, from Mexico to Argentina. Methods: We use species occupancy data from 705 forest fragments and 55 adjacent continuous forests nested within 61 landscapes, which we compiled from 96 studies reporting data on patch-scale species composition and patch size/location. Presence-absence data on 19 species functional groups and an index of hunting pressure and matrix type were assigned to each forest patch. We adopted a multilevel analysis, examining SARs and patterns of species retention coupled with the additive effects of hunting pressure and landscape connectivity both across all forest patches and 728 sites nested within 38 landscapes containing four or more sites. Results: We uncovered a consistent effect of patch area in explaining primate species richness. Over and above area effects, however, SARs were strongly modulated by levels of hunting pressure at the landscape scale in predicting species occurrence and aggregate assemblage biomass. Matrix type was also a good predictor of both extant species richness and aggregate biomass when only non-hunted sites were considered, with patches in more permeable matrices containing more species. Main conclusions: Although the importance of patch area in predicting species persistence is undeniable, we found that SARs were clearly affected by within-patch human exploitation of increasingly isolated primate populations. Both expanding the number of forest reserves and enforcing protection within nominal protected areas are therefore required to ensure the long-term persistence of full primate assemblages. We highlight the importance of considering multiple anthropogenic effects in assessing the synergistic effects of land use to explain patterns of species persistence in fragmented tropical forest landscapes. © 2013 John Wiley & Sons Ltd.


Barcellos-de-Souza P.,University of Florence | Barcellos-de-Souza P.,CAPES Foundation | Gori V.,Childrens Hospital Meyer | Bambi F.,Childrens Hospital Meyer | Chiarugi P.,University of Florence
Biochimica et Biophysica Acta - Reviews on Cancer | Year: 2013

Tumor progression is a multistep phenomenon in which tumor-associated stromal cells perform an intricate cross-talk with tumor cells, supplying appropriate signals that may promote tumor aggressiveness. Among several cell types that constitute the tumor stroma, the discovery that bone marrow-derived mesenchymal stem cells (BM-MSC) have a strong tropism for tumors has achieved notoriety in recent years. Not only are the BM-MSC recruited, but they can also engraft at tumor sites and transdifferentiate into cells such as activated fibroblasts, perivascular cells and macrophages, which will perform a key role in tumor progression. Whether the BM-MSC and their derived cells promote or suppress the tumor progression is a controversial issue. Recently, it has been proposed that proinflammatory stimuli can be decisive in driving BM-MSC polarization into cells with either tumor-supportive or tumor-repressive phenotypes (MSC1/MSC2). These considerations are extremely important both to an understanding of tumor biology and to the putative use of BM-MSC as "magic bullets" against tumors. In this review, we discuss the role of BM-MSC in many steps in tumor progression, focusing on the factors that attract BM-MSC to tumors, BM-MSC differentiation ability, the role of BM-MSC in tumor support or inhibition, the immunomodulation promoted by BM-MSC and metastatic niche formation by these cells. © 2013 Elsevier B.V.


Guerin W.,CNRS Non-Linear Institute of Nice | Araujo M.O.,CNRS Non-Linear Institute of Nice | Araujo M.O.,CAPES Foundation | Kaiser R.,CNRS Non-Linear Institute of Nice
Physical Review Letters | Year: 2016

Since Dicke's seminal paper on coherence in spontaneous radiation by atomic ensembles, superradiance has been extensively studied. Subradiance, on the contrary, has remained elusive, mainly because subradiant states are weakly coupled to the environment and are very sensitive to nonradiative decoherence processes. Here, we report the experimental observation of subradiance in an extended and dilute cold-atom sample containing a large number of particles. We use a far detuned laser to avoid multiple scattering and observe the temporal decay after a sudden switch-off of the laser beam. After the fast decay of most of the fluorescence, we detect a very slow decay, with time constants as long as 100 times the natural lifetime of the excited state of individual atoms. This subradiant time constant scales linearly with the cooperativity parameter, corresponding to the on-resonance optical depth of the sample, and is independent of the laser detuning, as expected from a coupled-dipole model. © 2016 American Physical Society.


Goulart E.,CAPES Foundation | Goulart E.,University of Cambridge
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

It is shown that the causal structure associated to stringlike solutions of the Faddeev-Niemi model is described by an effective metric. Remarkably, the surfaces characterizing the causal replacement depend on the energy momentum tensor of the background soliton and carry implicitly a topological invariant π3(S2). As a consequence, it follows that the preimage curves in R3 nontrivially define directions where the cones remain unchanged. We expect that these early results may be of importance in understanding time dependent solutions (collisions/scatterings) numerically or analytically. © 2015 American Physical Society.


Adshead P.,University of Chicago | Hu W.,University of Chicago | Miranda V.,University of Chicago | Miranda V.,Capes Foundation
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We develop an integral form for the bispectrum in general single-field inflation whose domain of validity includes models of inflation where the background evolution is not constrained to be slowly varying everywhere. Our integral form preserves the squeezed-limit consistency relation, allows for fast evaluation of the bispectrum for all triangle configurations expediting the efficient comparison of slow-roll violating models with data, and provides complete and compact slow-roll expressions correct to first order in slow-roll parameters. Motivated by the recent Planck results, we consider as an example a sharp step in the warped-brane tension of Dirac-Born-Infeld inflation and provide analytic solutions for the peak of the resulting bispectrum. For the step in the warp that reproduces the oscillations in the power spectrum favored by the Planck data, the corresponding equilateral bispectrum is both extremely large and highly scale dependent. The bispectrum serves as a means of distinguishing such a model from alternative scenarios that generate otherwise indistinguishable power spectra, such as a step in the potential in canonical single-field inflation. © 2013 American Physical Society.


Nunes R.C.,Autonomous University of Barcelona | Nunes R.C.,CAPES Foundation | Pavon D.,Autonomous University of Barcelona
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Recent determinations of the equation of state of dark energy hint that this may well be of the phantom type, i.e., wde<-1. If confirmed by future experiments, this would strongly point to the existence of fields that violate the dominant energy condition, which are known to present serious theoretical difficulties. This paper presents an alternative to this possibility, namely, that the measured equation of state, wde, is in reality an effective one, the equation of state of the quantum vacuum, wΛ=-1, plus the negative equation of state, wc, associated to the production of particles by the gravitational field acting on the vacuum. To illustrate this, three phenomenological models are proposed and constrained with recent observational data. © 2015 American Physical Society.


Miranda V.,University of Chicago | Miranda V.,Capes Foundation | Hu W.,University of Chicago
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We extend and improve the modeling and analysis of large-amplitude, sharp inflationary steps for second order corrections required by the precision of the Planck cosmic microwave background power spectrum and for arbitrary Dirac-Born-Infeld sound speed. With two parameters, the amplitude and frequency of the resulting oscillations, step models improve the fit by Δχ2=-11.4. Evidence for oscillations damping before the Planck beam scale is weak: damping only improves the fit to Δχ2=-14.0 for one extra parameter, if step and cosmological parameters are jointly fit, in contrast to analyses which fix the latter. Likewise, further including the sound speed as a parameter only marginally improves the fit to Δχ2=-15.2 but has interesting implications for the lowest multipole temperature and polarization anisotropy. Since chance features in the noise can mimic these oscillatory features, we discuss tests from polarization power spectra, lensing reconstruction and squeezed and equilateral bispectra that should soon verify or falsify their primordial origin. © 2014 American Physical Society.

Loading CAPES Foundation collaborators
Loading CAPES Foundation collaborators