DSpace Coleção:
https://localhost:443/handle/123456789/552
20200218T17:34:06ZHidden momentum and the AbrahamMinkowski debate.
https://localhost:443/handle/123456789/11488
Título: Hidden momentum and the AbrahamMinkowski debate.
Autor(es): Saldanha, Pablo Lima; Oliveira Filho, Juvenil Siqueira de
Resumo: We use an extended version of electrodynamics, which admits the existence of magnetic charges and currents,
to discuss how different models for electric and magnetic dipoles do or do not carry hidden momentum under
the influence of external electromagnetic fields. Based on that, we discuss how the models adopted for the
electric and magnetic dipoles from the particles that compose a material medium influence the expression for
the electromagnetic part of the light momentum in the medium.We show that Abraham expression is compatible
with electric dipoles formed by electric charges and magnetic dipoles formed by magnetic charges, while
Minkowski expression is compatible with electric dipoles formed by magnetic currents and magnetic dipoles
formed by electric currents. The expression ε0E × B, on the other hand, is shown to be compatible with electric
dipoles formed by electric charges and magnetic dipoles formed by electric currents, which are much more
natural models. So this expression has an interesting interpretation in the AbrahamMinkowski debate about the
momentum of light in a medium: It is the expression compatible with the nonexistence of magnetic charges. We
also provide a simple justification of why Abraham and Minkowski momenta can be associated with the kinetic
and canonical momentum of light, respectively.20170101T00:00:00ZRealization of rectangular artificial spin ice and direct observation of high energy topology.
https://localhost:443/handle/123456789/11350
Título: Realization of rectangular artificial spin ice and direct observation of high energy topology.
Autor(es): Ribeiro, Igor Renato Bueno; Nascimento, F. S.; Ferreira Júnior, Silvio da Costa; Melo, Winder Alexander de Moura; Costa, C. A. R.; Borme, J.; Freitas, P. P.; Wysin, G. M.; Araujo, Clodoaldo Irineu Levartoski de; Pereira, Amanda Raimundi
Resumo: In this work, we have constructed and experimentally investigated frustrated arrays of dipoles forming
twodimensional artificial spin ices with different lattice parameters (rectangular arrays with horizontal
and vertical lattice spacings denoted by a and b respectively). Arrays with three different aspect ratios
γ = a/b = 2, 3 and 4 are studied. Theoretical calculations of lowenergy demagnetized configurations
for these same parameters are also presented. Experimental data for demagnetized samples confirm
most of the theoretical results. However, the highest energy topology (doublycharged monopoles) does
not emerge in our theoretical model, while they are seen in experiments for large enough γ. Our results
also insinuate that the string tension connecting two magnetic monopoles in a pair vanishes in rectangular
lattices with a critical ratio γ = γc = 3, supporting previous theoretical predictions.20170101T00:00:00ZMathematical modelling for the transmission of dengue : symmetry and travelling wave analysis.
https://localhost:443/handle/123456789/10317
Título: Mathematical modelling for the transmission of dengue : symmetry and travelling wave analysis.
Autor(es): Bacani, Felipo; Dimas, Stylianos; Freire, Igor Leite; Maidana, Norberto Anibal; Torrisi, Mariano
Resumo: In this paper we propose some mathematical models for the transmission of dengue using a system of reaction–diffusion equations. The mosquitoes are divided into infected, uninfected and aquatic subpopulations, while the humans, which are divided into susceptible, infected and recovered, are considered homogeneously distributed in space with a constant total population. We find Lie point symmetries of the models and we study theirs temporal dynamics, which provides us the regions of stability and instability, depending on the values of the basic offspring and the basic reproduction numbers. Also, we calculate the possible values of the wave speed for the mosquitoes invasion and dengue spread and compare them with those found in the literature.20180101T00:00:00ZTorsion functions and the Cheeger problem : a fractional approach.
https://localhost:443/handle/123456789/9844
Título: Torsion functions and the Cheeger problem : a fractional approach.
Autor(es): Bueno, Hamilton Prado; Ercole, Grey; Macedo, Shirley da Silva; Pereira, Gilberto A.
Resumo: Let Ω be a Lipschitz bounded domain of ℝN, N ≥ 2. The fractional Cheeger constant hs(Ω),
0 < s < 1, is defined by
hs(Ω) = inf
E⊂Ω
Ps(E)
E
, where Ps(E) = ∫
ℝN
∫
ℝN
χE(x) − χE(y)
x − y
N+s
dx dy,
with χE denoting the characteristic function of the smooth subdomain E. The main purpose of this paper is
to show that
lim
p→1
+
ϕ
s
p

1−p
L∞(Ω)
= hs(Ω) = lim
p→1
+
ϕ
s
p

1−p
L
1(Ω)
,
where ϕ
s
p
is the fractional (s, p)torsion function of Ω, that is, the solution of the Dirichlet problem for the
fractional pLaplacian: −(∆)
s
p u = 1 in Ω, u = 0 in ℝN \ Ω. For this, we derive suitable bounds for the first
eigenvalue λ
s
1,p
(Ω) of the fractional pLaplacian operator in terms of ϕ
s
p
. We also show that ϕ
s
p minimizes the
(s, p)Gagliardo seminorm in ℝN, among the functions normalized by the L
1
norm.20160101T00:00:00Z