106 research outputs found
Time-resolved extinction rates of stochastic populations
Extinction of a long-lived isolated stochastic population can be described as
an exponentially slow decay of quasi-stationary probability distribution of the
population size. We address extinction of a population in a two-population
system in the case when the population turnover -- renewal and removal -- is
much slower than all other processes. In this case there is a time scale
separation in the system which enables one to introduce a short-time
quasi-stationary extinction rate W_1 and a long-time quasi-stationary
extinction rate W_2, and develop a time-dependent theory of the transition
between the two rates. It is shown that W_1 and W_2 coincide with the
extinction rates when the population turnover is absent, and present but very
slow, respectively. The exponentially large disparity between the two rates
reflects fragility of the extinction rate in the population dynamics without
turnover.Comment: 8 pages, 4 figure
Highly Radiating Charged Particles in a Strong Electromagnetic Field
We consider highly radiating ultra-relativistic electrons in a strong
external electromagnetic field. High intensity radiative losses and consequent
-pair production, appearing in the frame of quantum electrodynamics,
determine indirectly mass operator of electrons in the strong field. We
calculate a leading term of the mass operator at asymptotically high energies
of electrons in a strong constant field. We do not use any perturbation theory
based on a low ratio of this mass operator to the electron mass , but only
the original small parameter of quantum electrodynamics, the fine structure
constant, . The analogous %but less nontrivial result is obtained for
the polarization operator for photon propagator. These results resolve at least
partially a very long-lasted controversy originating from traditional and
straightforward application of perturbative approaches for description of
highly radiating ultra-relativistic charged particles in a very strong
electromagnetic fields.Comment: 5 page
On the new and old physics in the interaction of a radiating electron with the extreme electromagnetic field
We show that an all-optical configuration of the laser-electron collision in
the configuration based on 10~PW-class lasers presents a viable
platform for reaching the range of parameters where a perturbative QED in
strong external electromagnetic field breaks. This case is contingently
referred to as a case of the nonperturbative QED; and this range of parameters
is the intriguing goal from an experimental point of view because of a possible
manifestation of a new physics of the interaction of a highly radiating
particle with a strong electromagnetic field. We show that the strong field
region can be reached by the electrons having the initial energy higher than 50
GeV. Our theoretical considerations are in agreement with three-dimensional
particle-in-cell simulations. While increasing of the electron energy raises
the number of electrons experiencing the strong field region, the observable
signature of photon emission radiative correction in the strong field is
expected to fade out when the electron energy surpasses the optimal value. This
threshold of electron energy is identified and the parameters for achieving the
nonperturbative limit of QED are provided.Comment: 6 pages, 2 figure
Scaling and self-similarity in an unforced flow of inviscid fluid trapped inside a viscous fluid in a Hele-Shaw cell
We investigate quasi-two-dimensional relaxation, by surface tension, of a
long straight stripe of inviscid fluid trapped inside a viscous fluid in a
Hele-Shaw cell. Combining analytical and numerical solutions, we describe the
emergence of a self-similar dumbbell shape and find non-trivial dynamic
exponents that characterize scaling behavior of the dumbbell dimensions.Comment: 4 pages, 5 figures, to appear in PR
Laser-heater assisted plasma channel formation in capillary discharge waveguides
A method of creating plasma channels with controllable depth and transverse
profile for the guiding of short, high power laser pulses for efficient
electron acceleration is proposed. The plasma channel produced by the
hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser
pulse, which heats the electrons near the capillary axis. This interaction
creates a deeper plasma channel within the capillary discharge that evolves on
a ns-time scale, allowing laser beams with smaller spot sizes than would
otherwise be possible in the unmodified capillary discharge.Comment: 5 pages, 3 figure
Optimisation of Thin Plastic Foil Targets for Production of Laser-Generated Protons in the GeV Range
In order to realistically simulate the interaction of a femtosecond laser
pulse with a nanometre-thick target it is necessary to consider a target
preplasma formation due to the nanosecond long amplified-spontaneous-emission
pedestal and/or prepulse. The relatively long interaction time dictated that
hydrodynamic simulations should be employed to predict the target particles'
number density distributions prior the arrival of the main laser pulse. By
using the output of the hydrodynamic simulations as input into particle-in-cell
simulations, a detailed understanding of the complete laser-foil interaction is
achieved. Once the laser pulse interacts with the preplasma it deposits a
fraction of its energy on the target, before it is either reflected from the
critical density surface or transmitted through an underdense plasma channel. A
fraction of hot electrons is ejected from the target leaving the foil in a net
positive potential, which in turn results in proton and heavy ion ejection. In
this work protons reaching ~25 MeV are predicted for a laser of ~40 TW peak
power and ~600 MeV are expected from a ~4 PW laser system.Comment: 17 pages, 21 figure
Logarithmically Slow Expansion of Hot Bubbles in Gases
We report logarithmically slow expansion of hot bubbles in gases in the
process of cooling. A model problem first solved, when the temperature has
compact support. Then temperature profile decaying exponentially at large
distances is considered. The periphery of the bubble is shown to remain
essentially static ("glassy") in the process of cooling until it is taken over
by a logarithmically slowly expanding "core". An analytical solution to the
problem is obtained by matched asymptotic expansion. This problem gives an
example of how logarithmic corrections enter dynamic scaling.Comment: 4 pages, 1 figur
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