3,691 research outputs found
Do the recent severe droughts in the Amazonia have the same period of length?
We propose a new measure based on drought period length to assess the
temporal difference between the recent two severe droughts of 2005 and 2010 in
the Amazonia. The sensitivity of the measure is demonstrated by disclosing the
distinct spatial responding mechanisms of the Northeastern and Southwestern
Amazon (NA, SA) to the surrounding sea surface temperature (SST) variabilities.
The Pacific and Atlantic oceans have different roles on the precipitation
patterns in Amazonia. More specifically, the very dry periods in the NA are
influenced by El Ni\~no events, while the very dry periods in the SA are
affected by the anomalously warming of the SST in the North Atlantic. We show
convincingly that the drought 2005 hit SA, which is caused by the North
Atlantic only. There are two phases in the drought 2010: (i) it was started in
the NA in August 2009 affected by the El Ni\~no event, and (ii) later shifted
the center of action to SA resulted from anomalously high SST in North
Atlantic, which further intensifies the impacts on the spatial coverage.Comment: 5 figure
A skyrmion-based spin-torque nano-oscillator
A model for a spin-torque nano-oscillator based on the self-sustained
oscillation of a magnetic skyrmion is presented. The system involves a circular
nanopillar geometry comprising an ultrathin film free magnetic layer with a
strong Dzyaloshinkii-Moriya interaction and a polariser layer with a
vortex-like spin configuration. It is shown that spin-transfer torques due to
current flow perpendicular to the film plane leads to skyrmion gyration that
arises from a competition between geometric confinement due to boundary edges
and the vortex-like polarisation of the spin torques. A phenomenology for such
oscillations is developed and quantitative analysis using micromagnetics
simulations is presented. It is also shown that weak disorder due to random
anisotropy variations does not influence the main characteristics of the
steady-state gyration.Comment: 15 pages, 6 figure
Avaliação de sistema de produção alternativo de milho em monocultivo.
O sistema de produção preconizado apresenta sérias limitações à obtenção de ganhos de produtividade da cultura, mesmo nas áreas de solos mais férteis, por apresentar poucas alternativas tecnológicas. Face impirismo que lhe é peculiar, o cultivo do milho em Porto Velho constitui-se num desafio ao produtor e uma atividade de alto risco. A tecnologia disponível pela pesquisa poderá melhorar o desempenho técnico e econômico da cultura, imprimindo algumas mudanças ao sistema proposto para as demais áreas do Estado. Com a finalidade de viabilizar a produção de milho em Porto Velho, algumas inferências foram feitas ao modelo preconizado, buscando novas opções de escolha ao produtor e menor margem de riscos econômicos.bitstream/item/57012/1/PA-1555-0001.pd
Hubbard-model description of the high-energy spin-spectral-weight distribution in La(2)CuO(4)
The spectral-weight distribution in recent neutron scattering experiments on
the parent compound LaCuO (LCO), which are limited in energy range to
about 450\,meV, is studied in the framework of the Hubbard model on the square
lattice with effective nearest-neighbor transfer integral and on-site
repulsion . Our study combines a number of numerical and theoretical
approaches, including, in addition to standard treatments, density matrix
renormalization group calculations for Hubbard cylinders and a suitable spinon
approach for the spin excitations. Our results confirm that the
magnitude suitable to LCO corresponds to intermediate values smaller than
the bandwidth , which we estimate to be eV for
. This confirms the unsuitability of the conventional linear
spin-wave theory. Our theoretical studies provide evidence for the occurrence
of ground-state d-wave spinon pairing in the half-filled Hubbard model on the
square lattice. This pairing applies only to the rotated-electron spin degrees
of freedom, but it could play a role in a possible electron d-wave pairing
formation upon hole doping. We find that the higher-energy spin spectral weight
extends to about 566 meV and is located at and near the momentum .
The continuum weight energy-integrated intensity vanishes or is extremely small
at momentum . This behavior of this intensity is consistent with that
of the spin waves observed in recent high-energy neutron scattering
experiments, which are damped at the momentum . We suggest that future
LCO neutron scattering experiments scan the energies between 450 meV and 566
meV and momenta around .Comment: 23 pages, 5 figure
Single side damage simulations and detection in beam-like structures
Beam-like structures are the most common components in real engineering, while single side damage is often encountered. In this study, a numerical analysis of single side damage in a free-free beam is analysed with three different finite element models; namely solid, shell and beam models for demonstrating their performance in simulating real structures. Similar to experiment, damage is introduced into one side of the beam, and natural frequencies are extracted from the simulations and compared with experimental and analytical results. Mode shapes are also analysed with modal assurance criterion. The results from simulations reveal a good performance of the three models in extracting natural frequencies, and solid model performs better than shell while shell model performs better than beam model under intact state. For damaged states, the natural frequencies captured from solid model show more sensitivity to damage severity than shell model and shell model performs similar to the beam model in distinguishing damage. The main contribution of this paper is to perform a comparison between three finite element models and experimental data as well as analytical solutions. The finite element results show a relatively well performanc
The Importance of Information and Participation Principles in Environmental Law in Brazil
This article explores the two different kinds of uncertainty, ‘hard’ uncertainty (unknown unknowns) and ‘soft’ uncertainty (known unknowns), in the context of environmental law decision making. First, the authors argue that these different categories should not be treated the same when facing decisions under uncertainty. To deal with these different uncertainties, a tiered risk analysis process is called for, using participatory techniques to turn hard uncertainty into (more manageable) soft uncertainty as well as to increase the legitimacy of environmental decision making, even in cases of hard uncertainty. This methodology can and should apply to all instances of domestic, transnational and international environmental law making. This article applies this conceptual platform to analyze how participatory techniques can be factored in to manage uncertainty by reference to two domestic systems – American and Brazilian environmental law – as well as to international (environmental) law. The authors conclude that managing uncertainty in the environmental decision-making process is a procedural justice tool to promote more balanced and equitable outcomes
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