72,367 research outputs found
boosting in kernel regression
In this paper, we investigate the theoretical and empirical properties of
boosting with kernel regression estimates as weak learners. We show that
each step of boosting reduces the bias of the estimate by two orders of
magnitude, while it does not deteriorate the order of the variance. We
illustrate the theoretical findings by some simulated examples. Also, we
demonstrate that boosting is superior to the use of higher-order kernels,
which is a well-known method of reducing the bias of the kernel estimate.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ160 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Relativistic r-modes in Slowly Rotating Neutron Stars: Numerical Analysis in the Cowling Approximation
We investigate the properties of relativistic -modes of slowly rotating
neutron stars by using a relativistic version of the Cowling approximation. In
our formalism, we take into account the influence of the Coriolis like force on
the stellar oscillations, but ignore the effects of the centrifugal like force.
For three neutron star models, we calculated the fundamental -modes with
and 3. We found that the oscillation frequency of the
fundamental -mode is in a good approximation given by , where is defined in the corotating frame at the
spatial infinity, and is the angular frequency of rotation of the
star. The proportional coefficient is only weakly dependent on
, but it strongly depends on the relativistic parameter ,
where and are the mass and the radius of the star. All the fundamental
-modes with computed in this study are discrete modes with distinct
regular eigenfunctions, and they all fall in the continuous part of the
frequency spectrum associated with Kojima's equation (Kojima 1998). These
relativistic -modes are obtained by including the effects of rotation higher
than the first order of so that the buoyant force plays a role, the
situation of which is quite similar to that for the Newtonian -modes.Comment: 22 pages, 8 figures, accepted for publication in Ap
R-Modes on Rapidly Rotating, Relativistic Stars: I. Do Type-I Bursts Excite Modes in the Neutron-Star Ocean?
During a Type-I burst, the turbulent deflagation front may excite waves in
the neutron star ocean and upper atmosphere with frequencies,
Hz. These waves may be observed as highly coherent flux oscillations during the
burst. The frequencies of these waves changes as the upper layers of the
neutron star cool which accounts for the small variation in the observed QPO
frequencies. In principle several modes could be excited but the fundamental
buoyant mode exhibits significantly larger variability for a given
excitation than all of the other modes. An analysis of modes in the burning
layers themselves and the underlying ocean shows that it is unlikely these
modes can account for the observed burst oscillations. On the other hand,
photospheric modes which reside in a cooler portion of the neutron star
atmosphere may provide an excellent explanation for the observed oscillations.Comment: 18 pages, 1 figure, substantial changes and additions to reflect
version to appear in Ap
Effect of Plasma Irradiation on films
The effect of plasma irradiation is studied systematically on a 4H polytype
(002) oriented stoichiometric film having compressive residual
stress. Plasma irradiation was found to change the orientation to (110) of the
film at certain moderate irradiation distances. A linear decrease in grain size
and residual stress was observed with decreasing irradiation distance (or
increasing ion energy) consistent with both structural and morphological
observations. The direct optical energy gap was found to increase
linearly at the rate with the compressive stress. The
combined data of present compressive stress and from earlier reported tensile
stress show a consistent trend of change with stress. The
iodine-iodine distance in the unit cell could be responsible for the observed
change in with stress.Comment: 13 pages and 10 fi
Vacuum as a less hostile environment to entanglement
We derive sufficient conditions for infinite-dimensional systems whose
entanglement is not completely lost in a finite time during its decoherence by
a passive interaction with local vacuum environments. The sufficient conditions
allow us to clarify a class of bipartite entangled states which preserve their
entanglement or, in other words, are tolerant against decoherence in a vacuum.
We also discuss such a class for entangled qubits.Comment: Replaced by the published versio
Quantum Phase Transitions of Hard-Core Bosons in Background Potentials
We study the zero temperature phase diagram of hard core bosons in two
dimensions subjected to three types of background potentials: staggered,
uniform, and random. In all three cases there is a quantum phase transition
from a superfluid (at small potential) to a normal phase (at large potential),
but with different universality classes. As expected, the staggered case
belongs to the XY universality, while the uniform potential induces a mean
field transition. The disorder driven transition is clearly different from
both; in particular, we find z~1.4, \nu~1, and \beta~0.6.Comment: 4 pages (6 figures); published version-- 2 references added, minor
clarification
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