6,281 research outputs found
The asymptotic structure of nearly unstable non-negative integer-valued AR(1) models
This paper considers non-negative integer-valued autoregressive processes
where the autoregression parameter is close to unity. We consider the
asymptotics of this `near unit root' situation. The local asymptotic structure
of the likelihood ratios of the model is obtained, showing that the limit
experiment is Poissonian. To illustrate the statistical consequences we discuss
efficient estimation of the autoregression parameter and efficient testing for
a unit root.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ153 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Orbit bifurcations and the scarring of wavefunctions
We extend the semiclassical theory of scarring of quantum eigenfunctions
psi_{n}(q) by classical periodic orbits to include situations where these
orbits undergo generic bifurcations. It is shown that |psi_{n}(q)|^{2},
averaged locally with respect to position q and the energy spectrum E_{n}, has
structure around bifurcating periodic orbits with an amplitude and length-scale
whose hbar-dependence is determined by the bifurcation in question.
Specifically, the amplitude scales as hbar^{alpha} and the length-scale as
hbar^{w}, and values of the scar exponents, alpha and w, are computed for a
variety of generic bifurcations. In each case, the scars are semiclassically
wider than those associated with isolated and unstable periodic orbits;
moreover, their amplitude is at least as large, and in most cases larger. In
this sense, bifurcations may be said to give rise to superscars. The
competition between the contributions from different bifurcations to determine
the moments of the averaged eigenfunction amplitude is analysed. We argue that
there is a resulting universal hbar-scaling in the semiclassical asymptotics of
these moments for irregular states in systems with a mixed phase-space
dynamics. Finally, a number of these predictions are illustrated by numerical
computations for a family of perturbed cat maps.Comment: 24 pages, 6 Postscript figures, corrected some typo
Mecanisme d'obertura dels endocarpis i alliberament de llavors en l'aladern (Rhammus alaternus L.)
Ab initio Molecular Dynamical Investigation of the Finite Temperature Behavior of the Tetrahedral Au and Au Clusters
Density functional molecular dynamics simulations have been carried out to
understand the finite temperature behavior of Au and Au clusters.
Au has been reported to be a unique molecule having tetrahedral
geometry, a large HOMO-LUMO energy gap and an atomic packing similar to that of
the bulk gold (J. Li et al., Science, {\bf 299} 864, 2003). Our results show
that the geometry of Au is exactly identical to that of Au with
one missing corner atom (called as vacancy). Surprisingly, our calculated heat
capacities for this nearly identical pair of gold cluster exhibit dramatic
differences. Au undergoes a clear and distinct solid like to liquid like
transition with a sharp peak in the heat capacity curve around 770 K. On the
other hand, Au has a broad and flat heat capacity curve with continuous
melting transition. This continuous melting transition turns out to be a
consequence of a process involving series of atomic rearrangements along the
surface to fill in the missing corner atom. This results in a restricted
diffusive motion of atoms along the surface of Au between 650 K to 900 K
during which the shape of the ground state geometry is retained. In contrast,
the tetrahedral structure of Au is destroyed around 800 K, and the
cluster is clearly in a liquid like state above 1000 K. Thus, this work clearly
demonstrates that (i) the gold clusters exhibit size sensitive variations in
the heat capacity curves and (ii) the broad and continuous melting transition
in a cluster, a feature which has so far been attributed to the disorder or
absence of symmetry in the system, can also be a consequence of a defect
(absence of a cap atom) in the structure.Comment: 7 figure
Bargaining with Independence of Higher or Irrelevant Claims
This paper studies independence of higher claims and independence of irrelevant claims on the domain of bargaining problems with claims. Independence of higher claims requires that the payoff of an agent does not depend on the higher claim of another agent. Independence of irrelevant claims states that the payoffs should not change when the claims decrease but remain higher than the payoffs. Interestingly, in conjunction with standard axioms from bargaining theory, these properties characterize a new constrained Nash solution, a constrained Kalai-Smorodinsky solution, and a constrained Kalai solution
Efficient Estimation in Semiparametric Time Series: the ACD Model
In this paper we consider efficient estimation in semiparametric ACD models. We consider a suite of model specifications that impose less and less structure. We calculate the corresponding efficiency bounds, discuss the construction of efficient estimators in each case, and study tvide a simulation study that shows the practical gain from using the proposed semiparametric procedures. We find that, although one does not gain as much as theory suggests, these semiparametric procedures definitely outperform more classical procedures. We apply the procedures to model semiparametrically durations observed on the Paris Bourse for the Alcatel stock in July and August 1996.
On quadratic expansions of log likelihoods and a general asymptotic linearity result
Irrespective of the statistical model under study, the derivation of limits,
in the Le Cam sense, of sequences of local experiments (see [7]-[10]) often
follows along very similar lines, essentially involving differentiability in quadratic
mean of square roots of (conditional) densities. This chapter establishes two abstract
and very general results providing sufficient and nearly necessary conditions
for (i) the existence of a quadratic expansion, and (ii) the asymptotic linearity of
local log-likelihood ratios (asymptotic linearity is needed, for instance, when unspecified
model parameters are to be replaced, in some statistic of interest, with
some preliminary estimator). Such results have been established, for locally asymptotically
normal (LAN) models involving independent and identically distributed
observations, by, e.g., [1], [11] and [12]. Similar results are provided here for models
exhibiting serial dependencies which, so far, have been treated on a case-by-case
basis (see [4] and [5] for typical examples) and, in general, under stronger regularity
assumptions. Unlike their i.i.d. counterparts, our results extend beyond the context
of LAN experiments, so that non-stationary unit-root time series and cointegration
models, for instance, also can be handled (see [6])
Soil Geographical Database of Eurasia and the Mediterranean: Instructions Guide for Elaboration at Scale 1:1,000,000
Abstract not availableJRC.H-Institute for environment and sustainability (Ispra
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