125 research outputs found
Travelling waves in a mixture of gases with bimolecular reversible reactions
Starting from the kinetic approach for a mixture of reacting gases whose
particles interact through elastic scattering and a bimolecular reversible
chemical reaction, the equations that govern the dynamics of the system are
obtained by means of the relevant Boltzmann-like equation. Conservation laws
are considered. Fluid dynamic approximations are used at the Euler level to
obtain a close set of PDEs for six unknown macroscopic fields. The dispersion
relation of the mixture of reacting gases is explicitly derived in the
homogeneous equilibrium state. A set of ODE that governs the propagation of a
plane travelling wave is obtained using the Galilei invariance. After numerical
integration some solutions, including the well-known Maxwellian and the hard
spheres cases, are found for various meaningful interaction laws. The main
macroscopic observables for the gas mixture such as the drift velocity,
temperature, total density, pressure and its chemical composition are shown.Comment: 13 pages, 2 figures, accepted on Physica
Twist operator correlation functions in O(n) loop models
Using conformal field theoretic methods we calculate correlation functions of
geometric observables in the loop representation of the O(n) model at the
critical point. We focus on correlation functions containing twist operators,
combining these with anchored loops, boundaries with SLE processes and with
double SLE processes.
We focus further upon n=0, representing self-avoiding loops, which
corresponds to a logarithmic conformal field theory (LCFT) with c=0. In this
limit the twist operator plays the role of a zero weight indicator operator,
which we verify by comparison with known examples. Using the additional
conditions imposed by the twist operator null-states, we derive a new explicit
result for the probabilities that an SLE_{8/3} wind in various ways about two
points in the upper half plane, e.g. that the SLE passes to the left of both
points.
The collection of c=0 logarithmic CFT operators that we use deriving the
winding probabilities is novel, highlighting a potential incompatibility caused
by the presence of two distinct logarithmic partners to the stress tensor
within the theory. We provide evidence that both partners do appear in the
theory, one in the bulk and one on the boundary and that the incompatibility is
resolved by restrictive bulk-boundary fusion rules.Comment: 18 pages, 8 figure
Effects of Turbulence, Eccentricity Damping, and Migration Rate on the Capture of Planets into Mean Motion Resonance
Pairs of migrating extrasolar planets often lock into mean motion resonance
as they drift inward. This paper studies the convergent migration of giant
planets (driven by a circumstellar disk) and determines the probability that
they are captured into mean motion resonance. The probability that such planets
enter resonance depends on the type of resonance, the migration rate, the
eccentricity damping rate, and the amplitude of the turbulent fluctuations.
This problem is studied both through direct integrations of the full 3-body
problem, and via semi-analytic model equations. In general, the probability of
resonance decreases with increasing migration rate, and with increasing levels
of turbulence, but increases with eccentricity damping. Previous work has shown
that the distributions of orbital elements (eccentricity and semimajor axis)
for observed extrasolar planets can be reproduced by migration models with
multiple planets. However, these results depend on resonance locking, and this
study shows that entry into -- and maintenance of -- mean motion resonance
depends sensitively on migration rate, eccentricity damping, and turbulence.Comment: 43 pages including 14 figures; accepted for publication in The
Astrophysical Journa
Drones and Butterflies : A Low-Cost UAV System for Rapid Detection and Identification of Unconventional Minefields
Aerially-deployed plastic landmines in post-conflict nations present unique detection and disposal challenges. Their small size, randomized distribution during deployment, and low-metal content make these mines more difficult to identify using traditional methods of electromagnetic mine detection. Perhaps the most notorious of these mines is the Sovietera PFM-1 âbutterfly mine,â widely used during the decade-long Soviet-Afghan conflict between 1979 and 1989. Predominantly used by the Soviet forces to block otherwise inaccessible mountain passages, many PFM-1 minefields remain in place due to the high associated costs of access and demining. While the total number of deployed PFM-1 mines in Afghanistan is poorly documented, PFM-1 landmines make up a considerable percentage of the estimated 10 million landmines remaining in place across Afghanistan. Their detection and disposal presents a unique logistical challenge for largely the same reasons that their deployment was rationalized in inaccessible and sparsely populated areas of the country
Percolation Crossing Formulas and Conformal Field Theory
Using conformal field theory, we derive several new crossing formulas at the
two-dimensional percolation point. High-precision simulation confirms these
results. Integrating them gives a unified derivation of Cardy's formula for the
horizontal crossing probability , Watts' formula for the
horizontal-vertical crossing probability , and Cardy's formula for
the expected number of clusters crossing horizontally . The
main step in our approach implies the identification of the derivative of one
primary operator with another. We present operator identities that support this
idea and suggest the presence of additional symmetry in conformal field
theories.Comment: 12 pages, 5 figures. Numerics improved; minor correction
Mixtures in non stable Levy processes
We analyze the Levy processes produced by means of two interconnected classes
of non stable, infinitely divisible distribution: the Variance Gamma and the
Student laws. While the Variance Gamma family is closed under convolution, the
Student one is not: this makes its time evolution more complicated. We prove
that -- at least for one particular type of Student processes suggested by
recent empirical results, and for integral times -- the distribution of the
process is a mixture of other types of Student distributions, randomized by
means of a new probability distribution. The mixture is such that along the
time the asymptotic behavior of the probability density functions always
coincide with that of the generating Student law. We put forward the conjecture
that this can be a general feature of the Student processes. We finally analyze
the Ornstein--Uhlenbeck process driven by our Levy noises and show a few
simulation of it.Comment: 28 pages, 3 figures, to be published in J. Phys. A: Math. Ge
Solutions of the Maxwell equations and photon wave functions
Properties of six-component electromagnetic field solutions of a matrix form
of the Maxwell equations, analogous to the four-component solutions of the
Dirac equation, are described. It is shown that the six-component equation,
including sources, is invariant under Lorentz transformations. Complete sets of
eigenfunctions of the Hamiltonian for the electromagnetic fields, which may be
interpreted as photon wave functions, are given both for plane waves and for
angular-momentum eigenstates. Rotationally invariant projection operators are
used to identify transverse or longitudinal electric and magnetic fields. For
plane waves, the velocity transformed transverse wave functions are also
transverse, and the velocity transformed longitudinal wave functions include
both longitudinal and transverse components. A suitable sum over these
eigenfunctions provides a Green function for the matrix Maxwell equation, which
can be expressed in the same covariant form as the Green function for the Dirac
equation. Radiation from a dipole source and from a Dirac atomic transition
current are calculated to illustrate applications of the Maxwell Green
function.Comment: 75 pages; typo corrected, slight text chang
Propagation and Structure of Planar Streamer Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.
In the present long paper, you find the physics of the model and the
interfacial approach further explained. As a first ingredient of this approach,
we here analyze planar fronts, their profile and velocity. We encounter a
selection problem, recall some knowledge about such problems and apply it to
planar streamer fronts. We make analytical predictions on the selected front
profile and velocity and confirm them numerically.
(abbreviated abstract)Comment: 23 pages, revtex, 14 ps file
The high-precision, charge-dependent Bonn nucleon-nucleon potential (CD-Bonn)
We present a charge-dependent nucleon-nucleon (NN) potential that fits the
world proton-proton data below 350 MeV available in the year of 2000 with a
chi^2 per datum of 1.01 for 2932 data and the corresponding neutron-proton data
with chi^2/datum = 1.02 for 3058 data. This reproduction of the NN data is more
accurate than by any phase-shift analysis and any other NN potential. The
charge-dependence of the present potential (that has been dubbed `CD-Bonn') is
based upon the predictions by the Bonn Full Model for charge-symmetry and
charge-independence breaking in all partial waves with J <= 4. The potential is
represented in terms of the covariant Feynman amplitudes for one-boson exchange
which are nonlocal. Therefore, the off-shell behavior of the CD-Bonn potential
differs in a characteristic and well-founded way from commonly used local
potentials and leads to larger binding energies in nuclear few- and many-body
systems, where underbinding is a persistent problem.Comment: 69 pages (RevTex) including 20 tables and 9 figures (ps files
Comparing Methods to Constrain Future European Climate Projections Using a Consistent Framework
Political decisions, adaptation planning, and impact assessments need reliable estimates of future climate change and related uncertainties. To provide these estimates, different approaches to constrain, filter, or weight climate model projections into probabilistic distributions have been proposed. However, an assessment of multiple such methods to, for example, expose cases of agreement or disagreement, is often hindered by a lack of coordination, with methods focusing on a variety of variables, time periods, regions, or model pools. Here, a consistent framework is developed to allow a quantitative comparison of eight different methods; focus is given to summer temperature and precipitation change in three spatial regimes in Europe in 2041â60 relative to 1995â2014. The analysis draws on projections from several large ensembles, the CMIP5 multimodel ensemble, and perturbed physics ensembles, all using the high-emission scenario RCP8.5. The methodsâ key features are summarized, assumptions are discussed, and resulting constrained distributions are presented. Method agreement is found to be dependent on the investigated region but is generally higher for median changes than for the uncertainty ranges. This study, therefore, highlights the importance of providing clear context about how different methods affect the assessed uncertaintyâin particular, the upper and lower percentiles that are of interest to risk-averse stakeholders. The comparison also exposes cases in which diverse lines of evidence lead to diverging constraints; additional work is needed to understand how the underlying differences between methods lead to such disagreements and to provide clear guidance to users.ISSN:0894-8755ISSN:1520-044
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