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

Strong disorder renormalization group study of aperiodic quantum Ising chains

We employ an adaptation of a strong-disorder renormalization-group technique in order to analyze the ferro-paramagnetic quantum phase transition of Ising chains with aperiodic but deterministic couplings under the action of a transverse field. In the presence of marginal or relevant geometric fluctuations induced by aperiodicity, for which the critical behavior is expected to depart from the Onsager universality class, we derive analytical and asymptotically exact expressions for various critical exponents (including the correlation-length and the magnetization exponents, which are not easily obtainable by other methods), and shed light onto the nature of the ground state structures in the neighborhood of the critical point. The main results obtained by this approach are confirmed by finite-size scaling analyses of numerical calculations based on the free-fermion method

On the role of shield wires in mitigating lightning-induced overvoltages in overhead lines. Part II: Simulation results for practical configurations

In the companion Part I, the theory relevant to the role of shield wires in mitigating lightning-induced overvoltages in overhead lines has been analyzed and clarified. A more consistent meaning has been assigned to the concept of Shielding Factor by introducing two innovations compared to the current literature: the first one concerning the distinction between internal and external parameters, and the other one concerning the point along the line where to assess the mitigation effect. Thanks to this new approach, uncertainties seen in the literature have been sorted out, and the Shielding Factor has been shown to be a parameter which can be precisely quantified. However, our new contribution was applied to a schematic (unrealistic) configuration: a line with a shield wire grounded at only one point. This Part II is precisely devoted to confirming the results obtained in Part I, by applying the proposed approach to more realistic and practical line configurations, namely a line with multi-grounded shield wire, and a line equipped with laterals too

Potencial de rochas silicáticas no fornecimento de nutrientes para milheto. 1. Macronutrientes.

Realizaram-se experimentos com o objetivo de avaliar o efeito residual de diferentes doses e fontes de potássio no acúmulo de macronutrientes na parte aérea do milheto. Foram implantados dois ensaios em casa de vegetação na Embrapa Semi-Árido, em Petrolina-PE: um em Argissolo Acinzentado, de rextura arenosa, e outro em Vertissolo, de textura argilosa. As variáveis em estudo foram três fontes de K (Biotita-Xisto, Brecha Piroclástica e Cloreto de Potássio comercial), três doses de K2O (50, 100 e 150 mg dm-3) e quatro tratamentos adicionais (testemunha absoluta, testemunha mais demais nutrientes, 50 mg dm-3 de K2O nas formas de Biotita-Xisto e de Brecha Piroclástica). Cada ensaio constituiu-se de um fatorial (3 x 3) + 4, disposto no delineamento inteiramente casualizado, com quatro repetições. As unidades experimentais consistiram de vasos plásticos com 3 dm3 de solo. Todas as unidades experimentais, com exceção dos tratamentos testemunha absoluta e adicionais com as duas rochas teste, receberam uma adubação básica e uniforme com macro e micronutrientes, definida em função dos resultados de análise de solo. No Argissolo Acinzentado, ambas as rochas silicáticas proporcionaram baixas quantidades de K e dos demais nutrientes às plantas de milheto. A biotita-xista forneceu maior conteúdo de S às plantas. No Vertissolo, as rochas silicáticas não foram eficientes no fornecimento de nutrientes ao milheto

Propagation of Light in Photonic Crystal Fibre Devices

We describe a semi-analytical approach for three-dimensional analysis of photonic crystal fibre devices. The approach relies on modal transmission-line theory. We offer two examples illustrating the utilization of this approach in photonic crystal fibres: the verification of the coupling action in a photonic crystal fibre coupler and the modal reflectivity in a photonic crystal fibre distributed Bragg reflector.Comment: 15 pages including 7 figures. Accepted for J. Opt. A: Pure Appl. Op

On the role of shield wires in mitigating lightning-induced overvoltages in overhead lines. Part I: a critical review and a new analysis

The ability of shield wires installed in overhead lines to mitigate lightning-induced overvoltages has been extensively investigated. Unfortunately, these studies came to different results, sometimes contradicting each other: some authors found that shield wires produce a significant overvoltage reduction, while others found the reduction negligible; conflicting results also pertain to the role played by the various parameters involved, such as the relative height of the shield wires compared to the phase conductors. This paper aims to clarify this topic. The paper is organized in two parts: Part I, which starts from the analysis of the theory behind the mitigation effect, is devoted to establishing a more solid base to the topic. Two fundamental improvements are proposed: the first one is the distinction between internal and external of the parameters involved: current literature makes an indiscriminate grouping of all of them; the second one is concerned with the point along the line where the mitigation effect needs to be assessed. Thanks to this new approach, we show that this effect can be precisely quantified. The analysis in this Part I is limited to the basic case of a single grounding point of the shield wire, which represents an unrealistic case. Part II is devoted to completing the study, by applying the proposed approach to more realistic and practical cases

Potencial de rochas silicáticas no fornecimento de nutrientes para milheto. 2. Micronutrientes.

Realizaram-se experimentos com o objetivo de avaliar o efeito residual de diferentes doses e fontes de potássio no acúmulo de micronutrientes na parte aérea do milheto. Foram implantados dois ensaios em casa de vegetação na Embrapa Semi-Árido, em Petrolina-PE: um em Argissolo Acinzentado, de textura arenosa/média, e outro em vertissolo, de textura argilosa. As variáveis em estudo foram três fontes de K (Biotita-Xisto, Brecha Piroclástica e Cloreto de Potássio comercial), três doses de K2O (50, 100 e 150 mg dm-3) e quatro tratamentos adicionais (testemunha absoluta, testemuha mais demais nutrientes, 50 mg dm-3 de K2O nas formas de Biotita-Xisto e de Brecha Piroclástica). Cada ensaio constituiu-se de um fatorial (3 x 3) + 4, disposto no delineamento inteiramente casualizado, com quatro repetições. As unidades experimentais consistiram de vasos plásticos com 3 dm3 de solo. Todas as unidades experimentais, com exceção dos tratamentos testemunha absoluta e adicionais com as duas rochas teste, receberam uma adubação básica e uniforme com macro e micronutrientes, definida em função dos resultados da análise de solo. A aplicação das rochas silicáticas e do cloreto de potássio não afetou o conteúdo de micronutrientes na parte aérea do milheto em ambos os ensaios

Equation level matching: An extension of the method of matched asymptotic expansion for problems of wave propagation

We introduce an alternative to the method of matched asymptotic expansions. In the "traditional" implementation, approximate solutions, valid in different (but overlapping) regions are matched by using "intermediate" variables. Here we propose to match at the level of the equations involved, via a "uniform expansion" whose equations enfold those of the approximations to be matched. This has the advantage that one does not need to explicitly solve the asymptotic equations to do the matching, which can be quite impossible for some problems. In addition, it allows matching to proceed in certain wave situations where the traditional approach fails because the time behaviors differ (e.g., one of the expansions does not include dissipation). On the other hand, this approach does not provide the fairly explicit approximations resulting from standard matching. In fact, this is not even its aim, which to produce the "simplest" set of equations that capture the behavior

Organic melon response to natural phosphates in sequential culture in the São Francisco River Valley.

The application of solublle fertilizers, chemically treated, is not permitted in organic agriculture. This work aimed to evaluate the bahavior of melon crop cultivated with natural phosfhate in sud-middle of the São Francisco River Valley

Potencial de rochas silicáticas potássicas no fornecimento de macronutrientes para soja.

Com o objetivo de avaliar o potencial de suprimento de macronutrientes para soja resultante da aplicação de duas rochas silicáticas como fonte de potássio, quando comparadas com o fertilizante comercial (KCI), foram instalados dois exoerimentos em casa de vegetação na Embrapa Semi-Árido, em Petrolina-PE. Avaliaram-se duas rochas silicáticas (Biotita-Xisto e Brecha Piroclástica), três doses de K2O (50, 100 e 150 mg/dm3) e quatro tratamentos adicionais (testemunha absoluta, testemunha mais demais nutrientes, 50 mg/dm3 de K2O nas formas de Biotita-Xisto e de Brecha Piroclástica). Foram escolhidos dois solos que apresentavam baixo teor de potássio disponível ou baixa saturação de potássio, sendo um argissolo Acinzentado e um Vertissolo. Cada ensaio constituiu-se de um fatorial (3 x 3) + 4, disposto no delineamento inteiramente casualizado, com quatro repetições. As unidades experimentais consistiram de vasos plásticos com 3 dm3 de solo. No Argissolo Acinzentado, o KCI proporcionou maior conteúdo de K às plantas de soja. No Vertissolo as rochas silicáticas foram mais eficientes que o Cloreto de Potássio quanto ao conteúdo de K nas plantas. A Brecha Piroclástica foi capaz de proporcionar maior conteúdo de N no Argissolo e maior conteúdo de K, Ca, Mg e S às plantas de soja cultivadas no Vertissolo, quando não houve adubação de nivelamento com macro e micronutrientes