14,893 research outputs found
INFORMATION THEORETIC ALTERNATIVES TO TRADITIONAL SIMULTANEOUS EQUATIONS ESTIMATORS IN THE PRESENCE OF HETEROSKEDASTICITY
Finite sampling properties of information theoretic estimators of the simultaneous equations model, including maximum empirical likelihood, maximum empirical exponential likelihood, and maximum log Euclidean likelihood, are examined in the presence of selected forms of heteroskedasticity. Extensive Monte Carlo experiments are used to compare finite sample performance of Wald, Likelihood ratio, and Lagrangian multiplier tests constructed from information theoretic estimators to those from traditional generalized method of moments.Research Methods/ Statistical Methods,
TRUNCATED REGRESSION IN EMPIRICAL ESTIMATION
In this paper we illustrate the use of alternative truncated regression estimators for the general linear model. These include variations of maximum likelihood, Bayesian, and maximum entropy estimators in which the error distributions are doubly truncated. To evaluate the performance of the estimators (e.g., efficiency) for a range of sample sizes, Monte Carlo sampling experiments are performed. We then apply each estimator to a factor demand equation for wheat-by-class.doubly truncated samples, Bayesian regression, maximum entropy, wheat-by-class, Research Methods/ Statistical Methods,
KPD1930+2752 - a candidate Type Ia supernova progenitor
We present spectra of the pulsating sdB star KPD1930+2752 which confirm that
this star is a binary. The radial velocities measured from the H-alpha and
HeI6678 spectral lines vary sinusoidally with the same period (2h 17m) as the
ellipsoidal variability seen by Billeres et al. (2000). The amplitude of the
orbital motion (349.3+-2.7 km/s) combined with the canonical mass for sdB stars
(0.5 solar masses) implies a total mass for the binary of 1.47+-0.01 solar
masses The unseen companion star is almost certainly a white dwarf star. The
binary will merge within about 200 million years due to gravitational wave
radiation. The accretion of helium and other elements heavier than hydrogen
onto the white dwarf which then exceeds the Chandrasekhar mass (1.4 solar
masses) is a viable model for the cause of Type Ia supernovae. KPD1930+2752 is
the first star to be discovered which is a good candidate for the progenitor of
a Type Ia supernova of this type which will merge on an astrophysically
interesting timescale.Comment: Accepted for publication in MNRAS. 4 pages, 2 figures. Added
Institutio
Sub-femtosecond electron bunches created by direct laser acceleration in a laser wakefield accelerator with ionization injection
In this work, we will show through three-dimensional particle-in-cell
simulations that direct laser acceleration in laser a wakefield accelerator can
generate sub-femtosecond electron bunches. Two simulations were done with two
laser pulse durations, such that the shortest laser pulse occupies only a
fraction of the first bubble, whereas the longer pulse fills the entire first
bubble. In the latter case, as the trapped electrons moved forward and
interacted with the high intensity region of the laser pulse, micro-bunching
occurred naturally, producing 0.5 fs electron bunches. This is not observed in
the short pulse simulation.Comment: AAC 201
EMPIRICAL LIKELIHOOD ESTIMATORS OF THE LINEAR SIMULTANEOUS EQUATIONS MODEL
Information theoretic estimators are specified for a system of linear simultaneous equations, including maximum empirical likelihood, maximum empirical exponential likelihood, and maximum log Euclidean likelihood. Monte Carlo experiments are used to compare finite sample performance of these estimators to traditional generalized method of moments.Research Methods/ Statistical Methods,
A STRUCTURAL-EQUATION GME ESTIMATOR
A generalized maximum entropy estimator is developed for the linear simultaneous equations systems model. We provide results on large and small sample properties of the estimator. Empirical results illustrate efficiency advantages of the generalized maximum entropy estimator proposed in this study over traditional estimators (e.g., 2SLS and 3SLS).Research Methods/ Statistical Methods,
The mass ratio distribution of short period double degenerate stars
Short period double degenerates (DDs) are close white dwarf - white dwarf
binary stars which are the result of the evolution of interacting binary stars.
We present the first definitive measurements of the mass ratio for two DDs,
WD0136+768 and WD1204+450, and an improved measurement of the mass ratio for
WD0957-666. We compare the properties of the 6 known DDs with measured mass
ratios to the predictions of various theoretical models. We confirm the result
that standard models for the formation of DDs do not predict sufficient DDs
with mass ratios near 1. We also show that the observed difference in cooling
ages between white dwarfs in DDs is a useful constraint on the initial mass
ratio of the binary. A more careful analysis of the properties of the white
dwarf pair WD1704+481.2 leads us to conclude that the brighter white dwarf is
older than its fainter companion. This is the opposite of the usual case for
DDs and is caused by the more massive white dwarf being smaller and cooling
faster. The mass ratio in the sense (mass of younger star)/(mass of older star)
is then 1.43+-0.06 rather than the value 0.70+-0.03 given previously.Comment: Accepted for publication in MNRA
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