7,194 research outputs found
Efficient Yield Curve Estimation and Forecasting in Brazil
Term Structure of the Interest Rate, Yield Curve, State-Space Model, Kalman Filter.
Two-dimensional quantum spin-1/2 Heisenberg model with competing interactions
We study the quantum spin-1/2 Heisenberg model in two dimensions, interacting
through a nearest-neighbor antiferromagnetic exchange () and a ferromagnetic
dipolar-like interaction (), using double-time Green's function, decoupled
within the random phase approximation (RPA). We obtain the dependence of as a function of frustration parameter , where is the
ferromagnetic (F) transition temperature and is the ratio between the
strengths of the exchange and dipolar interaction (i.e., ). The
transition temperature between the F and paramagnetic phases decreases with
, as expected, but goes to zero at a finite value of this parameter,
namely . At T=0 (quantum phase transition), we
analyze the critical parameter for the general case of an
exchange interaction in the form , where ferromagnetic
and antiferromagnetic phases are present.Comment: 4 pages, 1 figur
Atomistic Simulation of Intrinsic Defects and Trivalent and Tetravalent Ion Doping in Hydroxyapatite
Atomistic simulation techniques have been employed in order to investigate key issues related to intrinsic defects and a variety of dopants from trivalent and tetravalent ions. The most favorable intrinsic defect is determined to be a scheme involving calcium and hydroxyl vacancies. It is found that trivalent ions have an energetic preference for the Ca site, while tetravalent ions can enter P sites. Charge compensation is predicted to occur basically via three schemes. In general, the charge compensation via the formation of calcium vacancies is more favorable. Trivalent dopant ions are more stable than tetravalent dopants
Volume elements and torsion
We reexamine here the issue of consistency of minimal action formulation with
the minimal coupling procedure (MCP) in spaces with torsion. In Riemann-Cartan
spaces, it is known that a proper use of the MCP requires that the trace of the
torsion tensor be a gradient, , and that the modified
volume element be
used in the action formulation of a physical model. We rederive this result
here under considerably weaker assumptions, reinforcing some recent results
about the inadequacy of propagating torsion theories of gravity to explain the
available observational data. The results presented here also open the door to
possible applications of the modified volume element in the geometric theory of
crystalline defects.Comment: Revtex, 8 pages, 1 figure. v2 includes a discussion on
-symmetr
The Shape of Dark Matter Halos: Dependence on Mass, Redshift, Radius, and Formation
Using six high resolution dissipationless simulations with a varying box size
in a flat LCDM universe, we study the mass and redshift dependence of dark
matter halo shapes for M_vir = 9.0e11 - 2.0e14, over the redshift range z=0-3,
and for two values of sigma_8=0.75 and 0.9. Remarkably, we find that the
redshift, mass, and sigma_8 dependence of the mean smallest-to-largest axis
ratio of halos is well described by the simple power-law relation = (0.54
+- 0.02)(M_vir/M_*)^(-0.050 +- 0.003), where s is measured at 0.3 R_vir and the
z and sigma_8 dependences are governed by the characteristic nonlinear mass,
M_*=M_*(z,sigma_8). We find that the scatter about the mean s is well described
by a Gaussian with sigma ~ 0.1, for all masses and redshifts. We compare our
results to a variety of previous works on halo shapes and find that reported
differences between studies are primarily explained by differences in their
methodologies. We address the evolutionary aspects of individual halo shapes by
following the shapes of the halos through ~100 snapshots in time. We determine
the formation scalefactor a_c as defined by Wechsler et al. (2002) and find
that it can be related to the halo shape at z = 0 and its evolution over time.Comment: 18 pages, 21 figures, submitted to MNRA
Fronts and interfaces in bistable extended mappings
We study the interfaces' time evolution in one-dimensional bistable extended
dynamical systems with discrete time. The dynamics is governed by the
competition between a local piece-wise affine bistable mapping and any
couplings given by the convolution with a function of bounded variation. We
prove the existence of travelling wave interfaces, namely fronts, and the
uniqueness of the corresponding selected velocity and shape. This selected
velocity is shown to be the propagating velocity for any interface, to depend
continuously on the couplings and to increase with the symmetry parameter of
the local nonlinearity. We apply the results to several examples including
discrete and continuous couplings, and the planar fronts' dynamics in
multi-dimensional Coupled Map Lattices. We eventually emphasize on the
extension to other kinds of fronts and to a more general class of bistable
extended mappings for which the couplings are allowed to be nonlinear and the
local map to be smooth.Comment: 27 pages, 3 figures, submitted to Nonlinearit
RELAÇÃO Entre a Capacidade Dinâmica e o Desempenho da Firma a Partir de Métricas Contábeis
Este estudo investigou a relação entre a capacidade dinâmica e o desempenho da firma e,
adicionalmente, o efeito moderador dos determinantes do setor, como grau de concentração e
nível de imprevisibilidade, construídos a partir de métricas contidas nas demonstrações
contábeis. Com base no argumento de que as capacidades dinâmicas, sob o enfoque de
processos, são monitoradas por meio dos processos operacionais da firma, que são
evidenciadas pelos índices que compõem ciclos operacional e financeiro, tendo efeitos
peculiares em indústrias distintas. A amostra foi extraída do banco de dados Comdinheiro® e
engloba as empresas de capital aberto listadas na B3. Os dados contábeis foram coletados de
forma trimestral no período de 2010 a 2016. Utilizou-se cinco modelos de regressão linear
múltipla, com interação entre variáveis e combinando modelos aninhados para testar as
hipóteses. Os resultados sugerem a existência de relação inversa entre as capacidades
dinâmicas, quando monitoradas pelos indicadores dinâmicos que compõem os ciclos
operacional e financeiro, e o desempenho da firma. De forma complementar, identificou-se
também um efeito moderador do grau de concentração e do nível de dinamismo do setor nas
relações entre dinâmica operacional e desempenho da firma
Nonsingular solutions of Hitchin's equations for noncompact gauge groups
We consider a general ansatz for solving the 2-dimensional Hitchin's
equations, which arise as dimensional reduction of the 4-dimensional self-dual
Yang-Mills equations, with remarkable integrability properties. We focus on the
case when the gauge group G is given by a real form of SL(2,C). For G=SO(2,1),
the resulting field equations are shown to reduce to either the Liouville,
elliptic sinh-Gordon or elliptic sine-Gordon equations. As opposed to the
compact case, given by G=SU(2), the field equations associated with the
noncompact group SO(2,1) are shown to have smooth real solutions with
nonsingular action densities, which are furthermore localized in some sense. We
conclude by discussing some particular solutions, defined on R^2, S^2 and T^2,
that come out of this ansatz.Comment: 12 pages, 3 figures. To appear in Nonlinearit
Morphology and ultrastructure of the pygidial gland of the Ant Dinoponera Austraus (Hymenoptera, Formicidae)
Determination of zinc in natural waters using a multisyringe flow injection analysis approach coupled with a long liquid waveguide capillary flow cell
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