3,758 research outputs found
Nonparametric estimation of a convex bathtub-shaped hazard function
In this paper, we study the nonparametric maximum likelihood estimator (MLE)
of a convex hazard function. We show that the MLE is consistent and converges
at a local rate of at points where the true hazard function is
positive and strictly convex. Moreover, we establish the pointwise asymptotic
distribution theory of our estimator under these same assumptions. One notable
feature of the nonparametric MLE studied here is that no arbitrary choice of
tuning parameter (or complicated data-adaptive selection of the tuning
parameter) is required.Comment: Published in at http://dx.doi.org/10.3150/09-BEJ202 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Estimation of a discrete monotone distribution
We study and compare three estimators of a discrete monotone distribution:
(a) the (raw) empirical estimator; (b) the "method of rearrangements"
estimator; and (c) the maximum likelihood estimator. We show that the maximum
likelihood estimator strictly dominates both the rearrangement and empirical
estimators in cases when the distribution has intervals of constancy. For
example, when the distribution is uniform on , the asymptotic
risk of the method of rearrangements estimator (in squared norm) is
, while the asymptotic risk of the MLE is of order .
For strictly decreasing distributions, the estimators are asymptotically
equivalent.Comment: 39 pages. See also
http://www.stat.washington.edu/www/research/reports/2009/
http://www.stat.washington.edu/jaw/RESEARCH/PAPERS/available.htm
Non-equilibrium dynamics and phase transitions
We study the poles of the retarded Green's functions of strongly coupled
field theories exhibiting a variety of phase structures from a crossover up to
a first order phase transition. These theories are modeled by a dual
gravitational description. The poles of the holographic Green's functions
appear at the frequencies of the quasinormal modes of the dual black hole
background. We establish that near the transition, in all cases considered, the
applicability of a hydrodynamic description breaks down already at lower
momenta than in the conformal case. We establish the appearance of the spinodal
region in the case of the first order phase transition at temperatures for
which the speed of sound squared is negative. An estimate of the preferential
scale attained by the unstable modes is also given. We additionally observe a
novel diffusive regime for sound modes for a range of wavelengths.Comment: 5 pages, 4 figures. Some points are clarified. Typos corrtecte
Heavy Quark Production at the TESLA Collider and its Sensitivity to the Gluon Content in Photon
Heavy quark production is studied at the high energy linear e^+e^- collider
(LC) TESLA both in its nominal and Photon Collider (PC) mode. Leading order
cross-sections are calculated for the production of heavy quarks, e^+e^- ->
e^+e^- Q\bar{Q}X, at high transverse momenta. The sensitivity of this process
to the gluon content in the photon is studied.Comment: 16 pages, Latex, 10 ps figures, uses epsfig.sty. IFT 2001/3
Conformal defects in supergravity - backreacted Dirac delta sources
We construct numerically gravitational duals of theories deformed by
localized Dirac delta sources for scalar operators both at zero and at finite
temperature. We find that requiring that the backreacted geometry preserves the
original scale invariance of the source uniquely determines the potential for
the scalar field to be the one found in a certain Kaluza-Klein compactification
of supergravity. This result is obtained using an efficient perturbative
expansion of the backreacted background at zero temperature and is confirmed by
a direct numerical computation. Numerical solutions at finite temperatures are
obtained and a detailed discussion of the numerical approach to the treatment
of the Dirac delta sources is presented. The physics of defect configurations
is illustrated with a calculation of entanglement entropy.Comment: 23 pages, 12 figure
Quasinormal modes and the phase structure of strongly coupled matter
We investigate the poles of the retarded Green's functions of strongly
coupled field theories exhibiting a variety of phase structures from a
crossover up to different first order phase transitions. These theories are
modeled by a dual gravitational description. The poles of the holographic
Green's functions appear at the frequencies of the quasinormal modes of the
dual black hole background. We focus on quantifying linearized level dynamical
response of the system in the critical region of phase diagram. Generically
non-hydrodynamic degrees of freedom are important for the low energy physics in
the vicinity of a phase transition. For a model with linear confinement in the
meson spectrum we find degeneracy of hydrodynamic and non-hydrodynamic modes
close to the minimal black hole temperature, and we establish a region of
temperatures with unstable non-hydrodynamic modes in a branch of black hole
solutions.Comment: 33 pages, 14 figure
Extended range harmonic filter
Two types of filters, leaky-wall and open-guide, are combined into single component. Combination gives 10 db or greater additional attenuation to fourth and higher harmonics, at expense of increasing loss of fundamental frequency by perhaps 0.05 to 0.08 db. Filter is applicable to all high power microwave transmitters, but is especially desirable for satellite transmitters
Cascaded half-harmonic generation of femtosecond frequency combs in mid-IR
For the growing demand of frequency combs in mid-infrared (mid-IR), known as
the "molecular fingerprint" region of the spectrum [1], down conversion of
near-IR frequency combs through half- harmonic generation offers numerous
benefits including high conversion efficiency and intrinsic phase and frequency
locking to the near-IR pump [2]. Hence cascaded half-harmonic generation
promises a simple path towards extending the wavelength coverage of stable
frequency combs. Here, we report a two-octave down-conversion of a frequency
comb around 1 {\mu}m through cascaded half-harmonic generation with ~64%
efficiency in the first stage, and ~18% in the second stage. We obtain
broadband intrinsically-frequency-locked frequency combs with ~50-fs pulses at
~2 {\mu}m and ~110-fs pulses at ~4 {\mu}m. These results indicate the
effectiveness of half-harmonic generation as a universal tool for efficient
phase- and frequency-locked down-conversion, which can be beneficial for
numerous applications requiring long-wavelength coherent sources
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