24,032 research outputs found
Improved estimators for dispersion models with dispersion covariates
In this paper we discuss improved estimators for the regression and the
dispersion parameters in an extended class of dispersion models (J{\o}rgensen,
1996). This class extends the regular dispersion models by letting the
dispersion parameter vary throughout the observations, and contains the
dispersion models as particular case. General formulae for the second-order
bias are obtained explicitly in dispersion models with dispersion covariates,
which generalize previous results by Botter and Cordeiro (1998), Cordeiro and
McCullagh (1991), Cordeiro and Vasconcellos (1999), and Paula (1992). The
practical use of the formulae is that we can derive closed-form expressions for
the second-order biases of the maximum likelihood estimators of the regression
and dispersion parameters when the information matrix has a closed-form.
Various expressions for the second-order biases are given for special models.
The formulae have advantages for numerical purposes because they require only a
supplementary weighted linear regression. We also compare these bias-corrected
estimators with two different estimators which are also bias-free to the
second-order that are based on bootstrap methods. These estimators are compared
by simulation
Statistical multifragmentation model with discretized energy and the generalized Fermi breakup. I. Formulation of the model
The Generalized Fermi Breakup recently demonstrated to be formally equivalent
to the Statistical Multifragmentation Model, if the contribution of excited
states are included in the state densities of the former, is implemented. Since
this treatment requires the application of the Statistical Multifragmentation
Model repeatedly on the hot fragments until they have decayed to their ground
states, it becomes extremely computational demanding, making its application to
the systems of interest extremely difficult. Based on exact recursion formulae
previously developed by Chase and Mekjian to calculate the statistical weights
very efficiently, we present an implementation which is efficient enough to
allow it to be applied to large systems at high excitation energies. Comparison
with the GEMINI++ sequential decay code shows that the predictions obtained
with our treatment are fairly similar to those obtained with this more
traditional model.Comment: 8 pages, 6 figure
Avaliação de cultivares de tomateiro estaqueado nos Tabuleiros Costeiros do Piauí.
bitstream/item/72599/1/CPAMN-PESQ.-AND.-4-90.pd
Inclusive Breakup Theory of Three-Body Halos
We present a recently developed theory for the inclusive breakup of
three-fragment projectiles within a four-body spectator model
\cite{CarPLB2017}, for the treatment of the elastic and inclusive non-elastic
break up reactions involving weakly bound three-cluster nuclei in
/ collisions. The four-body theory is an extension of the
three-body approaches developed in the 80's by Ichimura, Autern and Vincent
(IAV) \cite{IAV1985}, Udagawa and Tamura (UT) \cite{UT1981} and Hussein and
McVoy (HM) \cite{HM1985}. We expect that experimentalists shall be encouraged
to search for more information about the system in the elastic
breakup cross section and that also further developments and extensions of the
surrogate method will be pursued, based on the inclusive non-elastic breakup
part of the spectrum.Comment: 8 pages, 3 figures, Contribution to the Proceedings of Fusion17:
"International Conference on Heavy-Ion Collisions at Near-Barrier Energies",
20-24 February 2017 Hobart, Tasmania, Australi
Vortex rectification effects in films with periodic asymmetric pinning
We study the transport of vortices excited by an ac current in an Al film
with an array of nanoengineered asymmetric antidots. The vortex response to the
ac current is investigated by detailed measurements of the voltage output as a
function of ac current amplitude, magnetic field and temperature. The
measurements revealed pronounced voltage rectification effects which are mainly
characterized by the two critical depinning forces of the asymmetric potential.
The shape of the net dc voltage as a function of the excitation amplitude
indicates that our vortex ratchet behaves in a way very different from standard
overdamped models. Rather, as demonstrated by the observed output signal, the
repinning force, necessary to stop vortex motion, is considerably smaller than
the depinning force, resembling the behavior of the so-called inertia ratchets.
Calculations based on an underdamped ratchet model provide a very good fit to
the experimental data.Comment: 5 pages, 4 figure
- …