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

Germinação de sementes de melancia sob diferentes métodos de tratamento com reguladores vegetais.

A melancia é uma cultura importante para o Brasil pela demanda intensiva de mão-de-obra rural, perfil predominante pela produção familiar e retorno em torno de 85 dias em relação às outras oleráceas. O uso de reguladores de crescimento pode favorecer o desempenho das plântulas, acelerando a velocidade de emergência de sementes de várias espécies. Acredita-se que possam desempenhar um papel importante na regulação de certos aspectos das sementes, além de estarem envolvidas no crescimento de frutos e outros determinados fenômenos fisiológicos. Sementes de melancia cv. Crimson Sweet foram submetidas a dois métodos de tratamento com regulador: a) sementes embebidas: embebição das sementes em regulador por 8 horas; b) substrato embebido em regulador sendo utilizados os reguladores: ácido salicílico (0; 0,5; 5; 25 e 50 ?mol.L-1); putrescina (0; 50; 100; 500 e 1000 ?mol.L-1) e ácido giberélico (0, 50, 100 e 500 ?g.g-1). Para ácido salicílico e putrescina utilizou-se o delineamento experimental inteiramente casualizado em esquema fatorial 2 x 5 (métodos de tratamento x concentrações do regulador), com ácido giberélico foi utilizado esquema fatorial 2 x 4, com quatro repetições de 50 sementes cada. O método mais eficiente com ácido salicílico foi o uso de substrato embebido, juntamente com 0, 25 e 50 ?mol.L-1.A concentração de 1000 ?mol.L-1 de putrescina teve efeito negativo sobre as raízes das plântulas.50 e 100 ?g.g-1deGA3 promoveu maior desenvolvimento da parte aérea das plântulas.500 ?g.g-1 de GA3 teve efeito fitotóxico sobre as sementes e posteriormente sobre as plântulas de melancia

Investigation of the agricultural resources in Sri Lanka

The author has identified the following significant results. Several in-house capabilities were developed. The facilities to prepare color composites of excellent quality were developed, using bulk B/W 70 mm transparencies or 1:1,000,000 positive transparencies. These color composites were studied through optical devices on light tables. A zoom transfer scope was also added, enabling direct transfer of LANDSAT composite data on to base maps

Magnetic monopole and string excitations in a two-dimensional spin ice

We study the magnetic excitations of a square lattice spin-ice recently produced in an artificial form, as an array of nanoscale magnets. Our analysis, based upon the dipolar interaction between the nanomagnetic islands, correctly reproduces the ground-state observed experimentally. In addition, we find magnetic monopole-like excitations effectively interacting by means of the usual Coulombic plus a linear confining potential, the latter being related to a string-like excitation binding the monopoles pairs, what indicates that the fractionalization of magnetic dipoles may not be so easy in two dimensions. These findings contrast this material with the three-dimensional analogue, where such monopoles experience only the Coulombic interaction. We discuss, however, two entropic effects that affect the monopole interactions: firstly, the string configurational entropy may loose the string tension and then, free magnetic monopoles should also be found in lower dimensional spin ices; secondly, in contrast to the string configurational entropy, an entropically driven Coulomb force, which increases with temperature, has the opposite effect of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009

Sensing the impact of COVID-19 restrictions from online reviews: The cases of London and Paris unveiled through text mining

This study aims to understand how the COVID-19 pandemic affected the hotel sector and to identify the current traveler demands. The traveler’s re-views were analyzed based on sentiment analysis and a guest satisfaction model was also proposed, demonstrating a data mining approach within tourism and hospitality research. Given its popularity, TripAdvisor was the chosen platform for collection of hotel reviews in London and Paris. Text data were extracted from reviews made in two time periods, before and during the COVID-19 pan-demic. The sentiment and specific aspects highlighted by travelers were com-pared between each period.info:eu-repo/semantics/acceptedVersio