1,311 research outputs found
A State Space Framework for Automatic Forecasting Using Exponential Smoothing Methods.
We provide a new approach to automatic business forecasting based on an extended range of exponential smoothing methods. Each method in our taxonomy of exponential smoothing methods can be shown to be equivalent to the forecasts obtained from a state space model. This allows (1) the easy calculation of the likelihood, the AIC and other model selection criteria; (2) the computation of prediction intervals for each method; and (3) random simulation from the underlying state space model. We demonstrate the methods by applying them to the data from the M-competition on the M3-competition.Automatic forecasting, exponential smoothing, prediction intervals, state space models.
Stuffed Rare Earth Pyrochlore Solid Solutions
Synthesis and crystal structures are described for the compounds
Ln2(Ti2-xLnx)O7-x/2, where Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0
to 0.67. Rietveld refinements on X-ray powder diffraction data indicate that in
Tb and Dy titanate pyrochlores, extra Ln3+ cations mix mainly on the Ti4+ site
with little disorder on the original Ln3+ site. For the smaller rare earths
(Ho-Lu), stuffing additional lanthanide ions results in a pyrochlore to defect
fluorite transition, where the Ln3+ and Ti4+ ions become completely randomized
at the maximum (x=0.67). In all of these Ln-Ti-O pyrochlores, the addition of
magnetic Ln3+ in place of nonmagnetic Ti4+ adds edge sharing tetrahedral spin
interactions to a normally corner sharing tetrahedral network of spins. The
increase in spin connectivity in this family of solid solutions represents a
new avenue for investigating geometrical magnetic frustration in the rare earth
titanate pyrochlores.Comment: 25 pages, 7 figures, submitted to J. Solid State Che
Dynamical noncommutativity and Noether theorem in twisted phi^*4 theory
A \star-product is defined via a set of commuting vector fields X_a = e_a^\mu
(x) \partial_\mu, and used in a phi^*4 theory coupled to the e_a^\mu (x)
fields. The \star-product is dynamical, and the vacuum solution phi =0, e_a^\mu
(x)=delta_a^\mu reproduces the usual Moyal product. The action is invariant
under rigid translations and Lorentz rotations, and the conserved
energy-momentum and angular momentum tensors are explicitly derived.Comment: 15 pages LaTeX, minor typos, added reference
The Hamiltonian BRST quantization of a noncommutative nonabelian gauge theory and its Seiberg-Witten map
We consider the Hamiltonian BRST quantization of a noncommutative non abelian
gauge theory. The Seiberg-Witten map of all phase-space variables, including
multipliers, ghosts and their momenta, is given in first order in the
noncommutative parameter . We show that there exists a complete
consistence between the gauge structures of the original and of the mapped
theories, derived in a canonical way, once we appropriately choose the map
solutions.Comment: 10 pages, Latex. Address adde
Kontsevich product and gauge invariance
We analyze the question of gauge invariance in a flat
non-commutative space where the parameter of non-commutativity,
, is a local function satisfying Jacobi identity (and
thereby leading to an associative Kontsevich product). We show that in this
case, both gauge transformations as well as the definitions of covariant
derivatives have to modify so as to have a gauge invariant action. We work out
the gauge invariant actions for the matter fields in the fundamental and the
adjoint representations up to order while we discuss the gauge
invariant Maxwell theory up to order . We show that despite the
modifications in the gauge transformations, the covariant derivative and the
field strength, Seiberg-Witten map continues to hold for this theory. In this
theory, translations do not form a subgroup of the gauge transformations
(unlike in the case when is a constant) which is reflected in
the stress tensor not being conserved.Comment: 7 page
Noncommutativity, generalized uncertainty principle and FRW cosmology
We consider the effects of noncommutativity and the generalized uncertainty
principle on the FRW cosmology with a scalar field. We show that, the
cosmological constant problem and removability of initial curvature singularity
find natural solutions in this scenarios.Comment: 8 pages, to appear in IJT
Divergent effects of static disorder and hole doping in geometrically frustrated b-CaCr2O4
The gallium substituted and calcium deficient variants of geometrically
frustrated b-CaCr2O4, b-CaCr2-2xGa2xO4 (0.02<= x<= 0.25) and b-Ca1-yCr2O4
(0.075<= y<= 0.15), have been investigated by x-ray powder diffraction,
magnetization and specific heat measurements. This allows for a direct
comparison of the effects, in a geometrically frustrated magnet, of the static
disorder that arises from non-magnetic substitution and the dynamic disorder
that arises from hole doping. In both cases, disturbing the Cr3+ lattice
results in a reduction in the degree of magnetic frustration. On substitution
of Ga, which introduces disorder without creating holes, a gradual release of
spins from ordered antiferromagnetic states is observed. In contrast, in the
calcium deficient compounds the introduction of holes induces static
ferrimagnetic ordering and much stronger perturbations of the b-CaCr2O4 host.Comment: 23 pages, 10 figure
Time-Space Noncommutativity in Gravitational Quantum Well scenario
A novel approach to the analysis of the gravitational well problem from a
second quantised description has been discussed. The second quantised formalism
enables us to study the effect of time space noncommutativity in the
gravitational well scenario which is hitherto unavailable in the literature.
The corresponding first quantized theory reveals a leading order perturbation
term of noncommutative origin. Latest experimental findings are used to
estimate an upper bound on the time--space noncommutative parameter. Our
results are found to be consistent with the order of magnitude estimations of
other NC parameters reported earlier.Comment: 7 pages, revTe
Tunneling of massive and charged particles from noncommutative Reissner-Nordstr\"{o}m black hole
Massive charged and uncharged particles tunneling from commutative
Reissner-Nordstrom black hole horizon has been studied with details in
literature. Here, by adopting the coherent state picture of spacetime
noncommutativity, we study tunneling of massive and charged particles from a
noncommutative inspired Reissner-Nordstrom black hole horizon. We show that
Hawking radiation in this case is not purely thermal and there are correlations
between emitted modes. These correlations may provide a solution to the
information loss problem. We also study thermodynamics of noncommutative
horizon in this setup.Comment: 10 pages, 2 figure
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