303 research outputs found
Auto-tail dependence coefficients for stationary solutions of linear stochastic recurrence equations and for GARCH(1,1)
We examine the auto-dependence structure of strictly stationary solutions of linear stochastic recurrence equations and of strictly stationary GARCH(1, 1) processes from the point of view of ordinary and generalized tail dependence coefficients. Since such processes can easily be of infinite variance, a substitute for the usual auto-correlation function is needed
Evaporation of buffer gas-thermalized anions out of a multipole rf ion trap
We identify plain evaporation of ions as the fundamental loss mechanism out
of a multipole ion trap. Using thermalized negative Cl- ions we find that the
evaporative loss rate is proportional to a Boltzmann factor. This thermodynamic
description sheds new light on the dynamics of particles in time-varying
confining potentials. It specifically allows us to extract the effective depth
of the ion trap as the activation energy for evaporation. As a function of the
rf amplitude we find two distinct regimes related to the stability of motion of
the trapped ions. For low amplitudes the entire trap allows for stable motion
and the trap depth increases with the rf field. For larger rf amplitudes,
however, rapid energy transfer from the field to the ion motion can occur at
large trap radii, which leads to a reduction of the effective trapping volume.
In this regime the trap depth decreases again with increasing rf amplitude. We
give an analytical parameterization of the trap depth for various multipole
traps that allows predictions of the most favorable trapping conditions.Comment: Phys. Rev. Lett., in pres
On logarithmically optimal exact simulation of max-stable and related random fields on a compact set
Weak convergence of Vervaat and Vervaat Error processes of long-range dependent sequences
Following Cs\"{o}rg\H{o}, Szyszkowicz and Wang (Ann. Statist. {\bf 34},
(2006), 1013--1044) we consider a long range dependent linear sequence. We
prove weak convergence of the uniform Vervaat and the uniform Vervaat error
processes, extending their results to distributions with unbounded support and
removing normality assumption
Is network traffic approximated by stable Levy motion or fractional Brownian motion?
Cumulative broadband network traffic is often thought to be well modeled by fractional Brownian motion (FBM). However, some traffic measurements do not show an agreement with the Gaussian marginal distribution assumption. We show that if connection rates are modest relative to heavy tailed connection length distribution tails, then stable Levy motion is a sensible approximation to cumulative traffic over a time period. If connection rates are large relative to heavy tailed connection length distribution tails, then FBM is the appropriate approximation. The results are framed as limit theorems for a sequence of cumulative input processes whose connection rates are varying in such a way as to remove or induce long range dependence
Formation of ultracold LiCs molecules
We present the first observation of ultracold LiCs molecules. The molecules
are formed in a two-species magneto-optical trap and detected by two-photon
ionization and time-of-flight mass spectrometry. The production rate
coefficient is found to be in the range 10^{-18}\unit{cm^3s^{-1}} to
10^{-16}\unit{cm^3s^{-1}}, at least an order of magnitude smaller than for
other heteronuclear diatomic molecules directly formed in a magneto-optical
trap.Comment: 8 pages, 2 figure
A planar multipole ion trap
We report on the realisation of a chip-based multipole ion trap manufactured
using micro-electromechanical systems (MEMS) technology. It provides ion
confinement in an almost field-free volume between two planes of radiofrequency
electrodes, deposited on glass substrates, which allows for optical access to
the trap. An analytical model of the effective trapping potential is presented
and compared with numerical calculations. Stable trapping of argon ions is
achieved and a lifetime of 16s is measured. Electrostatic charging of the chip
surfaces is studied and found to agree with a numerical estimate
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Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation
High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected
Gaussian risk models with financial constraints
In this paper, we investigate Gaussian risk models which include financial elements, such as inflation and interest rates. For some general models for inflation and interest rates, we obtain an asymptotic expansion of the finite-time ruin probability for Gaussian risk models. Furthermore, we derive an approximation of the conditional ruin time by an exponential random variable as the initial capital tends to infinity
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