11,883 research outputs found
Semiparametric estimation of a panel data proportional hazards model with fixed effects
This paper considers a panel duration model that has a proportional hazards specification
with fixed effects. The paper shows how to estimate the baseline and integrated
baseline hazard functions without assuming that they belong to known, finitedimensional
families of functions. Existing estimators assume that the baseline hazard
function belongs to a known parametric family. Therefore, the estimators presented here
are more general than existing ones. This paper also presents a method for estimating
the parametric part of the proportional hazards model with dependent right censoring,
under which the partial likelihood estimator is inconsistent. The paper presents some
Monte Carlo evidence on the small sample performance of the new estimators
Nonparametric estimation of an additive quantile regression model
This paper is concerned with estimating the additive components of a nonparametric
additive quantile regression model. We develop an estimator that is asymptotically
normally distributed with a rate of convergence in probability of n^{-r/(2+10)} when the
additive components are r-times continuously differentiable for some r\geq2. This result
holds regardless of the dimension of the covariates and, therefore, the new estimator
has no curse of dimensionality. In addition, the estimator has an oracle property and is
easily extended to a generalized additive quantile regression model with a link function.
The numerical performance and usefulness of the estimator are illustrated by Monte
Carlo experiments and an empirical example
Finite element-integral simulation of static and flight fan noise radiation from the JT15D turbofan engine
An iterative finite element integral technique is used to predict the sound field radiated from the JT15D turbofan inlet. The sound field is divided into two regions: the sound field within and near the inlet which is computed using the finite element method and the radiation field beyond the inlet which is calculated using an integral solution technique. The velocity potential formulation of the acoustic wave equation was employed in the program. For some single mode JT15D data, the theory and experiment are in good agreement for the far field radiation pattern as well as suppressor attenuation. Also, the computer program is used to simulate flight effects that cannot be performed on a ground static test stand
Comments on Black Holes in String Theory
A very brief review is given of some of the developments leading to our
current understanding of black holes in string theory. This is followed by a
discussion of two possible misconceptions in this subject - one involving the
stability of small black holes and the other involving scale radius duality.
Finally, I describe some recent results concerning quasinormal modes of black
holes in anti de Sitter spacetime, and their implications for strongly coupled
conformal field theories (in various dimensions).Comment: 13 pages. Talk given at Strings '99, Potsdam, German
Electroweak Measurements of Neutron Densities in CREX and PREX at JLab, USA
Measurement of the parity-violating electron scattering asymmetry is an
established technique at Jefferson Lab and provides a new opportunity to
measure the weak charge distribution and hence pin down the neutron radius in
nuclei in a relatively clean and model-independent way. This is because the Z
boson of the weak interaction couples primarily to neutrons. We will describe
the PREX and CREX experiments on Pb and Ca respectively;
these are both doubly-magic nuclei whose first excited state can be
discriminated by the high resolution spectrometers at JLab. The heavier lead
nucleus, with a neutron excess, provides an interpretation of the neutron skin
thickness in terms of properties of bulk neutron matter. For the lighter
Ca nucleus, which is also rich in neutrons, microscopic nuclear theory
calculations are feasible and are sensitive to poorly constrained 3-neutron
forces.Comment: A contribution to the upcoming EPJA Special Volume on Nuclear
Symmetry Energ
Charge-conjugation violating neutrino interactions in supernovae
The well known charge conjugation violating interactions in the Standard
Model increase neutrino- and decrease anti-neutrino- nucleon cross sections.
This impacts neutrino transport in core collapse supernovae through "recoil"
corrections of order the neutrino energy over the nucleon mass . All
corrections to neutrino transport deep inside a protoneutron star are
calculated from angular integrals of the Boltzmann equation. We find these
corrections significantly modify neutrino currents at high temperatures. This
produces a large mu and tau number for the protoneutron star and can change the
ratio of neutrons to protons. In addition, the relative size of neutrino mean
free paths changes. At high temperatures, the electron anti-neutrino mean free
path becomes {\it longer} than that for mu or tau neutrinos.Comment: 14 pages, 2 included ps figures, subm. to Phys. Rev.
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