75,075 research outputs found
Robust Feature Detection and Local Classification for Surfaces Based on Moment Analysis
The stable local classification of discrete surfaces with respect to features such as edges and corners or concave and convex regions, respectively, is as quite difficult as well as indispensable for many surface processing applications. Usually, the feature detection is done via a local curvature analysis. If concerned with large triangular and irregular grids, e.g., generated via a marching cube algorithm, the detectors are tedious to treat and a robust classification is hard to achieve. Here, a local classification method on surfaces is presented which avoids the evaluation of discretized curvature quantities. Moreover, it provides an indicator for smoothness of a given discrete surface and comes together with a built-in multiscale. The proposed classification tool is based on local zero and first moments on the discrete surface. The corresponding integral quantities are stable to compute and they give less noisy results compared to discrete curvature quantities. The stencil width for the integration of the moments turns out to be the scale parameter. Prospective surface processing applications are the segmentation on surfaces, surface comparison, and matching and surface modeling. Here, a method for feature preserving fairing of surfaces is discussed to underline the applicability of the presented approach.
Quantum limits on phase-preserving linear amplifiers
The purpose of a phase-preserving linear amplifier is to make a small signal
larger, regardless of its phase, so that it can be perceived by instruments
incapable of resolving the original signal, while sacrificing as little as
possible in signal-to-noise. Quantum mechanics limits how well this can be
done: a high-gain linear amplifier must degrade the signal-to-noise; the noise
added by the amplifier, when referred to the input, must be at least half a
quantum at the operating frequency. This well-known quantum limit only
constrains the second moments of the added noise. Here we derive the quantum
constraints on the entire distribution of added noise: we show that any
phase-preserving linear amplifier is equivalent to a parametric amplifier with
a physical state for the ancillary mode; the noise added to the amplified field
mode is distributed according to the Wigner function of the ancilla state.Comment: 37 pages, 6 figure
A Couplet from Flavored Dark Matter
We show that a couplet, a pair of closely spaced photon lines, in the X-ray
spectrum is a distinctive feature of lepton flavored dark matter models for
which the mass spectrum is dictated by Minimal Flavor Violation. In such a
scenario, mass splittings between different dark matter flavors are determined
by Standard Model Yukawa couplings and can naturally be small, allowing all
three flavors to be long-lived and contribute to the observed abundance. Then,
in the presence of a tiny source of flavor violation, heavier dark matter
flavors can decay via a dipole transition on cosmological timescales, giving
rise to three photon lines. The ratios of the line energies are completely
determined in terms of the charged lepton masses, and constitute a firm
prediction of this framework. For dark matter masses of order the weak scale,
the couplet lies in the keV-MeV region, with a much weaker line in the eV-keV
region. This scenario constitutes a potential explanation for the recent claim
of the observation of a 3.5 keV line. The next generation of X-ray telescopes
may have the necessary resolution to resolve the double line structure of such
a couplet.Comment: 17 pages, 4 figures, 1 haik
Probability flux as a method for detecting scaling
We introduce a new method for detecting scaling in time series. The method
uses the properties of the probability flux for stochastic self-affine
processes and is called the probability flux analysis (PFA). The advantages of
this method are: 1) it is independent of the finiteness of the moments of the
self-affine process; 2) it does not require a binning procedure for numerical
evaluation of the the probability density function. These properties make the
method particularly efficient for heavy tailed distributions in which the
variance is not finite, for example, in Levy alpha-stable processes. This
utility is established using a comparison with the diffusion entropy (DE)
method
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