Resonant interaction between gravitational waves, electromagnetic waves and plasma flows

In magnetized plasmas gravitational and electromagnetic waves may interact coherently and exchange energy between themselves and with plasma flows. We derive the wave interaction equations for these processes in the case of waves propagating perpendicular or parallel to the plasma background magnetic field. In the latter case, the electromagnetic waves are taken to be circularly polarized waves of arbitrary amplitude. We allow for a background drift flow of the plasma components which increases the number of possible evolution scenarios. The interaction equations are solved analytically and the characteristic time scales for conversion between gravitational and electromagnetic waves are found. In particular, it is shown that in the presence of a drift flow there are explosive instabilities resulting in the generation of gravitational and electromagnetic waves. Conversely, we show that energetic waves can interact to accelerate particles and thereby \emph{produce} a drift flow. The relevance of these results for astrophysical and cosmological plasmas is discussed.Comment: 12 pages, 1 figure, typos corrected and numerical example adde

Ecosystem services for intensification of agriculture, with emphasis on increased nitrogen ecological use efficiency

Funding Information: This work was undertaken as part of NUCLEUS, a virtual joint center to deliver enhanced N-use efficiency via an integrated soil?plant systems approach for the United Kingdom and Brazil. This work was funded in Brazil by FAPESP-S?o Paulo Research Foundation (Grant Number 2015/50305-8), FAPEG-Goi?s Research Foundation (Grant Number 2015-10267001479), and FAPEMA-Maranh?o Research Foundation (Grant Number RCUK-02771/16); and in the United Kingdom by the Biotechnology and Biological Sciences Research Council (Grant Number BB/N013201/1) under the Newton Fund scheme.Peer reviewedPublisher PD

Fontes orgânicas de nutrientes em sistemas de produção de batata.

Nos últimos anos, diminuiu muito o número de bataticultores na região da Quarta Colônia, no centro do Estado do Rio Grande do Sul (RS), devido ao elevado risco econômico na produção da batata. A partir de uma demanda da Associação dos Produtores de Batata da Região Central do Rio Grande do Sul (ASBAT), foram instalados experimentos visando a avaliar, técnica e economicamente, fontes orgânicas alternativas à adubação mineral tradicional dos produtores de batata, objetivando diminuir os custos de produção e o impacto do seu cultivo no ambiente. Foram estabelecidas rotações envolvendo culturas comerciais e plantas de cobertura de solo para o cultivo da batata na safra e na safrinha. As fontes de nutrientes foram camas de frango e de suínos e adubo mineral tradicionalmente utilizado pelos bataticultores. Os resultados mostraram que a utilização de fontes orgânicas de nutrientes no cultivo da batata é uma alternativa viável técnica e economicamente. Contudo, sua eficiência pode ser maximizada quando associada com a adubação mineral, especialmente para aumentar a quantidade de nitrogênio disponível desde o início do ciclo da cultura e isso é particularmente importante quando do uso da cama de suínos. A cama de frango, por conter maior quantidade de nutrientes, é uma alternativa melhor do que a cama de suínos, tanto técnica quanto economicamente

Nonlinear coupled Alfv\'{e}n and gravitational waves

In this paper we consider nonlinear interaction between gravitational and electromagnetic waves in a strongly magnetized plasma. More specifically, we investigate the propagation of gravitational waves with the direction of propagation perpendicular to a background magnetic field, and the coupling to compressional Alfv\'{e}n waves. The gravitational waves are considered in the high frequency limit and the plasma is modelled by a multifluid description. We make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell system and derive a wave equation for the coupled gravitational and electromagnetic wave modes. A WKB-approximation is then applied and as a result we obtain the nonlinear Schr\"{o}dinger equation for the slowly varying wave amplitudes. The analysis is extended to 3D wave pulses, and we discuss the applications to radiation generated from pulsar binary mergers. It turns out that the electromagnetic radiation from a binary merger should experience a focusing effect, that in principle could be detected.Comment: 20 pages, revtex4, accepted in PR