360 research outputs found
New analytic models of traversable wormholes
The analytic solution of the general relativity equations for spherically
symmetric wormholes are given. We investigate the special case of a
"traversable" wormhole i.e., one allowing the signal to pass through it. The
energy-momentum tensor of wormhole matter is represented as a superposition of
a spherically symmetric magnetic field and dust matter with negative matter
density. The dynamics of the model are investigated. We discuss both the
solution of the equation with a Lambda-term and without it. Superposing enough
dust matter, a magnetic field, and a Lambda-term can produce a static solution,
which turns out to be a spherical Multiverse model with an infinite number of
wormholes connected spherical universes. Corresponding solution can be static
and dynamic.Comment: 15 pages, 2 figure
Automated Calculation of Thermal Rate Coefficients using Ring Polymer Molecular Dynamics and Machine-Learning Interatomic Potentials with Active Learning
We propose a methodology for fully automated calculation of thermal rate
coefficients of gas phase chemical reactions, which is based on combining the
ring polymer molecular dynamics (RPMD) with the machine-learning interatomic
potentials actively learning on-the-fly. Based on the original computational
procedure implemented in the RPMDrate code, our methodology gradually and
automatically constructs the potential energy surfaces (PESs) from scratch with
the data set points being selected and accumulated during the RPMDrate
simulation. Such an approach ensures that our final machine-learning model
provides reliable description of the PES which avoids artifacts during
exploration of the phase space by RPMD trajectories. We tested our methodology
on two representative thermally activated chemical reactions studied recently
by RPMDrate at temperatures within the interval of 300--1000~K. The
corresponding PESs were generated by fitting to only a few thousands
automatically generated structures (less than 5000) while the RPMD rate
coefficients retained the deviation from the reference values within the
typical convergence error of RPMDrate. In future, we plan to apply our
methodology to chemical reactions which proceed via complex-formation thus
providing a completely general tool for calculating RPMD thermal rate
coefficients for any polyatomic gas phase chemical reaction
Symbolic representation and classification of integrable systems
This is a review paper of recent results in the perturbative symmetry
approach in the symbolic representation
Creation of a homogeneous plasma column by means of hohlraum radiation for ion-stopping measurements
In this work, we present the results of two-dimensional
radiation-hydrodynamics simulations of a hohlraum target whose outgoing
radiation is used to produce a homogeneously ionized carbon plasma for ion-beam
stopping measurements. The cylindrical hohlraum with gold walls is heated by a
frequency-doubled ( ) long laser pulse
with the total energy of . At the laser spot, the peak matter
and radiation temperatures of, respectively, and are observed. X-rays from the hohlraum heat the attached
carbon foam with a mean density of to a temperature of
. The simulation shows that the carbon ionization degree () and its column density stay relatively stable (within variations
of about ) long enough to conduct the ion-stopping measurements. Also,
it is found that a special attention should be paid to the shock wave, emerging
from the X-ray heated copper support plate, which at later times may
significantly distort the carbon column density traversed by the fast ions.Comment: 12 pages, 12 figure
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