2,698 research outputs found
Constructions of Coupling Processes for L\'evy Processes
We construct optimal Markov couplings of L\'{e}vy processes, whose L\'evy
(jump) measure has an absolutely continuous component. The construction is
based on properties of subordinate Brownian motions and the coupling of
Brownian motions by reflection.Comment: 16 page
Detecting independence of random vectors: generalized distance covariance and Gaussian covariance
Distance covariance is a quantity to measure the dependence of two random
vectors. We show that the original concept introduced and developed by
Sz\'{e}kely, Rizzo and Bakirov can be embedded into a more general framework
based on symmetric L\'{e}vy measures and the corresponding real-valued
continuous negative definite functions. The L\'{e}vy measures replace the
weight functions used in the original definition of distance covariance. All
essential properties of distance covariance are preserved in this new
framework. From a practical point of view this allows less restrictive moment
conditions on the underlying random variables and one can use other distance
functions than Euclidean distance, e.g. Minkowski distance. Most importantly,
it serves as the basic building block for distance multivariance, a quantity to
measure and estimate dependence of multiple random vectors, which is introduced
in a follow-up paper [Distance Multivariance: New dependence measures for
random vectors (submitted). Revised version of arXiv: 1711.07775v1] to the
present article.Comment: Published at https://doi.org/10.15559/18-VMSTA116 in the Modern
Stochastics: Theory and Applications (https://www.i-journals.org/vtxpp/VMSTA)
by VTeX (http://www.vtex.lt/
Real-Time Description of the Electronic Dynamics for a Molecule close to a Plasmonic Nanoparticle
The optical properties of molecules close to plasmonic nanostructures greatly
differ from their isolated molecule counterparts. To theoretically investigate
such systems in a Quantum Chemistry perspective, one has to take into account
that the plasmonic nanostructure (e.g., a metal nanoparticle - NP) is often too
large to be treated atomistically. Therefore, a multiscale description, where
the molecule is treated by an ab initio approach and the metal NP by a lower
level description, is needed. Here we present an extension of one such
multiscale model [Corni, S.; Tomasi, J. {\it J. Chem. Phys.} {\bf 2001}, {\it
114}, 3739] originally inspired by the Polarizable Continuum Model, to a
real-time description of the electronic dynamics of the molecule and of the NP.
In particular, we adopt a Time-Dependent Configuration Interaction (TD CI)
approach for the molecule, the metal NP is described as a continuous dielectric
of complex shape characterized by a Drude-Lorentz dielectric function and the
molecule- NP electromagnetic coupling is treated by an equation-of-motion (EOM)
extension of the quasi-static Boundary Element Method (BEM). The model includes
the effects of both the mutual molecule- NP time-dependent polarization and the
modification of the probing electromagnetic field due to the plasmonic
resonances of the NP. Finally, such an approach is applied to the investigation
of the light absorption of a model chromophore, LiCN, in the presence of a
metal NP of complex shape.Comment: This is the final peer-reviewed manuscript accepted for publication
of an open access article published under an ACS AuthorChoice License, which
permits copying and redistribution of the article or any adaptations for
non-commercial purposes. Link to the original article:
http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b1108
Gender gap in the ERASMUS mobility program
Studying abroad has become very popular among students. The ERASMUS mobility
program is one of the largest international student exchange programs in the
world, which has supported already more than three million participants since
1987. We analyzed the mobility pattern within this program in 2011-12 and found
a gender gap across countries and subject areas. Namely, for almost all
participating countries, female students are over-represented in the ERASMUS
program when compared to the entire population of tertiary students. The same
tendency is observed across different subject areas. We also found a gender
asymmetry in the geographical distribution of hosting institutions, with a bias
of male students in Scandinavian countries. However, a detailed analysis
reveals that this latter asymmetry is rather driven by subject and consistent
with the distribution of gender ratios among subject areas
Clout, Activists and Budget: The Road to Presidency
Political campaigns involve, in the simplest case, two competing campaign
groups which try to obtain a majority of votes. We propose a novel mathematical
framework to study political campaign dynamics on social networks whose
constituents are either political activists or persuadable individuals.
Activists are convinced and do not change their opinion and they are able to
move around in the social network to motivate persuadable individuals to vote
according to their opinion. We describe the influence of the complex interplay
between the number of activists, political clout, budgets, and campaign costs
on the campaign result. We also identify situations where the choice of one
campaign group to send a certain number of activists already pre-determines
their victory. Moreover, we show that a candidate's advantage in terms of
political clout can overcome a substantial budget disadvantage or a lower
number of activists, as illustrated by the US presidential election 2016.Comment: 23 pages, 10 figure
Electrostatic fluctuations in cavities within polar liquids and thermodynamics of polar solvation
We present the results of numerical simulations of fluctuations of the
electrostatic potential and electric field inside cavities created in the fluid
of dipolar hard spheres. We found that the thermodynamics of polar solvation
dramatically changes its regime when the cavity size becomes about 4-5 times
larger than the size of the liquid particle. The range of small cavities can be
reasonably understood within the framework of current solvation models. On the
contrary, the regime of large cavities is characterized by a significant
softening of the cavity interface resulting in a decay of the fluctuation
variances with the cavity size much faster than anticipated by both the
continuum electrostatics and microscopic theories. For instance, the variance
of potential decays with the cavity size approximately as
instead of the scaling expected from standard electrostatics. Our
results suggest that cores of non-polar molecular assemblies in polar liquids
lose solvation strength much faster than is traditionally anticipated.Comment: 10 pp, 10 fig
Modeling the Emission Processes in Blazars
Blazars are the most violent steady/recurrent sources of high-energy
gamma-ray emission in the known Universe. They are prominent emitters of
electromagnetic radiation throughout the entire electromagnetic spectrum. The
observable radiation most likely originates in a relativistic jet oriented at a
small angle with respect to the line of sight. This review starts out with a
general overview of the phenomenology of blazars, including results from a
recent multiwavelength observing campaign on 3C279. Subsequently, issues of
modeling broadband spectra will be discussed. Spectral information alone is not
sufficient to distinguish between competing models and to constrain essential
parameters, in particular related to the primary particle acceleration and
radiation mechanisms in the jet. Short-term spectral variability information
may help to break such model degeneracies, which will require snap-shot
spectral information on intraday time scales, which may soon be achievable for
many blazars even in the gamma-ray regime with the upcoming GLAST mission and
current advances in Atmospheric Cherenkov Telescope technology. In addition to
pure leptonic and hadronic models of gamma-ray emission from blazars,
leptonic/hadronic hybrid models are reviewed, and the recently developed
hadronic synchrotron mirror model for TeV gamma-ray flares which are not
accompanied by simultaneous X-ray flares (``orphan TeV flares'') is revisited.Comment: Invited Review at "The Multimessenger Approach to Gamma-Ray Sources",
Barcelona, Spain, July 2006; submitted to Astrophysics and Space Science. 10
pages, including 6 eps figures. Uses Springer's ApSS macro
- …