8,932 research outputs found
Group Importance Sampling for Particle Filtering and MCMC
Bayesian methods and their implementations by means of sophisticated Monte
Carlo techniques have become very popular in signal processing over the last
years. Importance Sampling (IS) is a well-known Monte Carlo technique that
approximates integrals involving a posterior distribution by means of weighted
samples. In this work, we study the assignation of a single weighted sample
which compresses the information contained in a population of weighted samples.
Part of the theory that we present as Group Importance Sampling (GIS) has been
employed implicitly in different works in the literature. The provided analysis
yields several theoretical and practical consequences. For instance, we discuss
the application of GIS into the Sequential Importance Resampling framework and
show that Independent Multiple Try Metropolis schemes can be interpreted as a
standard Metropolis-Hastings algorithm, following the GIS approach. We also
introduce two novel Markov Chain Monte Carlo (MCMC) techniques based on GIS.
The first one, named Group Metropolis Sampling method, produces a Markov chain
of sets of weighted samples. All these sets are then employed for obtaining a
unique global estimator. The second one is the Distributed Particle
Metropolis-Hastings technique, where different parallel particle filters are
jointly used to drive an MCMC algorithm. Different resampled trajectories are
compared and then tested with a proper acceptance probability. The novel
schemes are tested in different numerical experiments such as learning the
hyperparameters of Gaussian Processes, two localization problems in a wireless
sensor network (with synthetic and real data) and the tracking of vegetation
parameters given satellite observations, where they are compared with several
benchmark Monte Carlo techniques. Three illustrative Matlab demos are also
provided.Comment: To appear in Digital Signal Processing. Related Matlab demos are
provided at https://github.com/lukafree/GIS.gi
Feynman-Hellmann theorem for resonances and the quest for QCD exotica
The generalization of the Feynman-Hellmann theorem for resonance states in
quantum field theory is derived. On the basis of this theorem, a criterion is
proposed to study the possible exotic nature of certain hadronic states
emerging in QCD. It is shown that this proposal is supported by explicit
calculations in Chiral Perturbation Theory and by large- arguments.
Analyzing recent lattice data on the quark mass dependence in the pseudoscalar,
vector meson, baryon octet and baryon decuplet sectors, we conclude that, as
expected, these are predominately quark-model states, albeit the corrections
are non-negligible.Comment: 26 pages, 2 figure
Extracting the sigma-term from low-energy pion-nucleon scattering
We present an extraction of the pion-nucleon () scattering lengths
from low-energy scattering, by fitting a representation based on
Roy-Steiner equations to the low-energy data base. We show that the resulting
values confirm the scattering-length determination from pionic atoms, and
discuss the stability of the fit results regarding electromagnetic corrections
and experimental normalization uncertainties in detail. Our results provide
further evidence for a large -term, MeV,
in agreement with, albeit less precise than, the determination from pionic
atoms.Comment: 17 pages, 3 figures; journal versio
High-precision determination of the pion-nucleon -term from Roy-Steiner equations
We present a determination of the pion-nucleon () -term
based on the Cheng-Dashen low-energy theorem (LET), taking
advantage of the recent high-precision data from pionic atoms to pin down the
scattering lengths as well as of constraints from analyticity,
unitarity, and crossing symmetry in the form of Roy-Steiner equations to
perform the extrapolation to the Cheng-Dashen point in a reliable manner. With
isospin-violating corrections included both in the scattering lengths and the
LET, we obtain MeV MeV,
where the first error refers to uncertainties in the amplitude and the
second to the LET. Consequences for the scalar nucleon couplings relevant for
the direct detection of dark matter are discussed.Comment: 6 pages, 1 figure; title changed by journal, version to be published
in PR
Matching pion-nucleon Roy-Steiner equations to chiral perturbation theory
We match the results for the subthreshold parameters of pion-nucleon
scattering obtained from a solution of Roy-Steiner equations to chiral
perturbation theory up to next-to-next-to-next-to-leading order, to extract the
pertinent low-energy constants including a comprehensive analysis of systematic
uncertainties and correlations. We study the convergence of the chiral series
by investigating the chiral expansion of threshold parameters up to the same
order and discuss the role of the \Delta(1232) resonance in this context.
Results for the low-energy constants are also presented in the counting scheme
usually applied in chiral nuclear effective field theory, where they serve as
crucial input to determine the long-range part of the nucleon-nucleon potential
as well as three-nucleon forces.Comment: 6 pages, 4 tables; version to appear in PR
Extracting the sigma-term from low-energy pion-nucleon scattering
We present an extraction of the pion-nucleon () scattering lengths
from low-energy scattering, by fitting a representation based on
Roy-Steiner equations to the low-energy data base. We show that the resulting
values confirm the scattering-length determination from pionic atoms, and
discuss the stability of the fit results regarding electromagnetic corrections
and experimental normalization uncertainties in detail. Our results provide
further evidence for a large -term, MeV,
in agreement with, albeit less precise than, the determination from pionic
atoms.Comment: 17 pages, 3 figures; journal versio
Meet the HENRYs: A hybrid focus group study of conspicuous luxury consumption in the social media context
Social media has created different dimension of consumers for luxury products, specifically the aspirational consumer who wishes to own a product, but for economic reasons cannot. In other words aspirational consumers use luxury brands to create value for themselves using social media to conspicuously consume without purchase. Aspirational consumers are mostly found among HENRYs (high earners, not rich yet). Studies around conspicuous consumption of luxury products as a result of digital technology influence are fragmented. However, in-depth understanding of HENRYs’ consumer behaviour in the pre-experience (before actual purchase) stage is important. Using hybrid of online and face-to-face focus group data, this study maps HENRYs’ consumer journeys that reflects the role of social media in conspicuous consumption of luxury brands. We found that most of HENRYs purchase luxury for status and in the context of social media it becomes even more rationale to demonstrate own luxury possessions via creating own social media content - most HENRYs are narcissist. Social media represents an immediate environment of luxury conspicuous consumption where HENRYs are aspired to purchase luxury by mostly user-generated content and are driven to produce own social media content as evidence of luxury purchasing and possessions – to satisfy own narcissistic ambitions
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