8,762 research outputs found
Simulation of Chua's Circuit by Means of Interval Analysis
The Chua's circuit is a paradigm for nonlinear scientific studies. It is
usually simulated by means of numerical methods under IEEE 754-2008 standard.
Although the error propagation problem is well known, little attention has been
given to the relationship between this error and inequalities presented in
Chua's circuit model. Taking the average of round mode towards and
, we showed a qualitative change on the dynamics of Chua's circuit.Comment: 6th International Conference on Nonlinear Science and Complexity -
S\~ao Jos\'e dos Campos, 2016, p. 1-
Coherent pressure structures in turbulent channel flow
Most of the studies on pressure fluctuations in wall-bounded turbulent flows
aim at obtaining statistics as power spectra and scaling laws, especially at
the walls. In the present study we study energetic coherent pressure structures
of turbulent channel flows, aiming at a characterization of dominant coherent
structures throughout the channel. Coherent structures are detected using
spectral proper orthogonal decomposition (SPOD) and modeled using resolvent
analysis, similar to related works dealing with velocity fluctuations, but
using pressure fluctuations as the output of interest. The resolvent operator
was considered with and without the Cess eddy viscosity model. Direct numerical
simulations (DNSs) of incompressible turbulent channel flows at friction
Reynolds numbers of approximately 180 and 550 were employed as databases. Three
representative dominant structures emerged from a preliminary spectral
analysis: near-wall, large-scale and spanwise-coherent structures. For
frequency-wavenumber combinations corresponding to these three representative
structures, SPOD results show a strong dominance of the leading mode,
highlighting low-rank behavior of pressure fluctuations. The leading resolvent
mode closely agrees with the first SPOD mode, providing support to studies that
showed better performance of resolvent-based estimators when predicting
pressure fluctuations compared to velocity fluctuations. The dominant
mechanisms of the analyzed modes are seen to be the generation of
quasi-streamwise vortices with pressure fluctuations appearing close to vortex
centers. A study on the individual contributions of the nonlinear terms
(treated as forcing in resolvent analysis) to the pressure output reveals that
each forcing component plays a constructive role to the input-output
formulation, which also helps understanding the weaker role of forcing color in
driving pressure fluctuations.Comment: 24 pages, 23 figure
On fermionic tilde conjugation rules and thermal bosonization. Hot and cold thermofields
A generalization of Ojima tilde conjugation rules is suggested, which reveals
the coherent state properties of thermal vacuum state and is useful for the
thermofield bosonization. The notion of hot and cold thermofields is introduced
to distinguish different thermofield representations giving the correct normal
form of thermofield solution for finite temperature Thirring model with correct
renormalization and anticommutation properties.Comment: 13 page
Self-sustainable bio-methanol & bio-char coproduction from 2nd generation biomass gasification
Methanol is an important intermediate in the synthesis of different chemicals. It is mainly produced by reforming of natural gas in centralized facilities with productive capacities on the order of 109 tons per day. Production of methanol from biomass suffers from the cost and logistics of the transportation of biomass and it has not yet maturated into commercial scale. The techno-economic feasibility of the co-production of bio-methanol and bio-char is assessed through detailed computer simulations using process simulator Aspen HYSYS® together with the gasification simulator GASDS. This work further elaborates the previous results on the bio-methanol production process, presenting particularities and updates on previously reported values. The production model is seen to be valid, with payback times that go from 3 to 6 years according to the capacity of the plant (100 to 1000 kt of biomass per year). Self-sustainability is possible but a 50/50 mix of producing and buying electricity yields the most economic choice. © Copyright 2017, AIDIC Servizi S.r.l
Driven interfaces in disordered media: determination of universality classes from experimental data
While there have been important theoretical advances in understanding the
universality classes of interfaces moving in porous media, the developed tools
cannot be directly applied to experiments. Here we introduce a method that can
identify the universality class from snapshots of the interface profile. We
test the method on discrete models whose universality class is well known, and
use it to identify the universality class of interfaces obtained in experiments
on fluid flow in porous media.Comment: 4 pages, 5 figure
Coulomb and quantum oscillator problems in conical spaces with arbitrary dimensions
The Schr\"odinger equations for the Coulomb and the Harmonic oscillator
potentials are solved in the cosmic-string conical space-time. The spherical
harmonics with angular deficit are introduced.
The algebraic construction of the harmonic oscillator eigenfunctions is
performed through the introduction of non-local ladder operators. By exploiting
the hidden symmetry of the two-dimensional harmonic oscillator the eigenvalues
for the angular momentum operators in three dimensions are reproduced.
A generalization for N-dimensions is performed for both Coulomb and harmonic
oscillator problems in angular deficit space-times.
It is thus established the connection among the states and energies of both
problems in these topologically non-trivial space-times.Comment: 15 page
Uso de marcadores ISSR na caracterização molecular de abacaxizeiro, para uso na produção de polímeros biodegradáveis.
As fibras naturais têm emergido como uma alternativa de baixo custo, pouco peso e com um apelo ambiental superior a outros materiais usados na indústria, substituindo, principalmente as fibras de vidro e gerando um impacto ambiental significativamente menor. A Embrapa Mandioca e Fruticultura possui um total de 670 acessos do gênero Ananas e outras bromeliáceas, sendo considerada a maior coleção de abacaxizeiro e espécies afins do mundo.Em paralelo aconteceram também os seguintes eventos: V Seminário de Pesquisa do Recôncavo da Bahia; V Seminário Estudantil de Pesquisa da UFRB; V Seminário da Pós-Graduação da UFRB; II Seminário Regional de Pesquisa da EBDA; 5ª Jornada Científica da Embrapa Mandioca e Fruticultura; VIII Seminário Estudantil de Pesquisa e Extensão da FAMAM; Semana de Ciência, Tecnologia e Inovação no Agronegócio; Fórum de Gestores de Iniciação Científica e Tecnológica da Bahia; II Simpósio Baiano de Defesa Agropecuária; I Semana de Educação Tutorial da UFRB
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Pipe network model for scaling of dynamic interfaces in porous media
We present a numerical study on the dynamics of imbibition fronts in porous
media using a pipe network model. This model quantitatively reproduces the
anomalous scaling behavior found in imbibition experiments [Phys. Rev. E {\bf
52}, 5166 (1995)]. Using simple scaling arguments, we derive a new identity
among the scaling exponents in agreement with the experimental results.Comment: 13 pages, 3 figures, REVTeX, to appear in Phys. Rev. Let
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