73 research outputs found
Profiles of electrostatic potential across the water-vapor, ice-vapor and ice-water interfaces
Ice-water, water-vapor interfaces and ice surface are studied by molecular
dynamics simulations with the SPC/E model of water molecules having the purpose
to estimate the profiles of electrostatic potential across the interfaces. We
have proposed a methodology for calculating the profiles of electrostatic
potential based on a trial particle, which showed good agreement for the case
of electrostatic potential profile of the water-vapor interface of TIP4P model
calculated in another way. The measured profile of electrostatic potential for
the pure ice-water interface decreases towards the liquid bulk region, which is
in agreement with simulations of preferential direction of motion of Li
and F solute ions at the liquid side of the ice-water interface. These
results are discussed in connection with the Workman-Reynolds effect.Comment: 7 pages, 5 figure
NATO Workshop on Ionic Soft Matter
On 14-17 April 2004 the NATO Advanced Research Workshop (ARW) on Ionic Soft Matter convened in the beautiful and historic city of Lviv. This was only the second NATO ARW to be held in Ukraine at that time
Construction of the free energy landscape by the density functional theory
On the basis of the density functional theory, we give a clear definition of
the free energy landscape. To show the usefulness of the definition, we
construct the free energy landscape for rearrangement of atoms in an FCC
crystal of hard spheres. In this description, the cooperatively rearranging
region (CRR) is clealy related to the hard spheres involved in the saddle
between two adjacent basins. A new concept of the simultaneously rearranging
region (SRR) emerges naturally as spheres defined by the difference between two
adjacent basins. We show that the SRR and the CRR can be determined explicitly
from the free energylandscape.Comment: 11 pages, 3 figures, submitted to J. Chem. Phy
Heterogeneities in Supercooled liquids: A Density Functional Study
A metastable state, characterized by a low degree of mass localization is
identified using Density Functional Theory. This free energy minimum, located
through the proper evaluation of the competing terms in the free energy
functional, is independent of the specific form of the DFT used. Computer
simulation results on particle motion indicate that this heterogeneous state
corresponds to the supercooled state.Comment: 10 pages, 6 figure
Density functional formalism in the canonical ensemble
Density functional theory, when applied to systems with , is based
on the grand canonical extension of the Hohenberg-Kohn-Sham theorem due to
Mermin (HKSM theorem). While a straightforward canonical ensemble
generalization fails, work in nanopore systems could certainly benefit from
such extension. We show that, if the asymptotic behaviour of the canonical
distribution functions is taken into account, the HKSM theorem can be extended
to the canonical ensemble. We generate -modified correlation and
distribution functions hierarchies and prove that, if they are employed, either
a modified external field or the density profiles can be indistinctly used as
independent variables. We also write down the % -modified free energy
functional and prove that its minimum is reached when the equilibrium values of
the new hierarchy are used. This completes the extension of the HKSM theorem.Comment: revtex, to be submitted to Phys. Rev. Let
Density-functional theory of freezing of vortex-liquid in quasi two-dimensional superconductors
We present a theory of vortex liquid-to-solid transition in homogeneous quasi
2D superconductors. The free energy is written as a functional l of density of
zeroes of the fluctuating order parameter. The transition is weakly first-order
and well below the Hc2(T) line. Transition temperature, discontinuities of the
average Abrikosov ratio and of the average superfluid density, the Debay-Waller
factor and the latent heat are in good agreement with Monte Carlo simulations.
The density is only weakly modulated in the "vortex-solid" phase, consistent
with the density-wave behavior.Comment: 12 pages and 1 figure available upon request, LaTex Version 2.09,
submitted to Phys. Rev. Let
Search for corannulene (C20H10) in the Red Rectangle
Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers
of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any
specific interstellar PAH is still missing. For polar PAHs, pure rotational
transitions can be used as fingerprints for identification. Combining dedicated
experiments, detailed simulations and observations, we explored the mm domain
to search for specific rotational transitions of corannulene (C20H10). We
performed high-resolution spectroscopic measurements and a simulation of the
emission spectrum of UV-excited C20H10 in the environment of the Red Rectangle,
calculating its synthetic rotational spectrum. Based on these results, we
conducted a first observational campaign at the IRAM 30m telescope towards this
source to search for several high-J rotational transitions of (C20H10). The
laboratory detection of the J = 112 <- 111 transition of corannulene showed
that no centrifugal splitting is present up to this line. Observations with the
IRAM 30m telescope towards the Red Rectangle do not show any corannulene
emission at any of the observed frequencies, down to a rms noise level of Tmb =
8 mK for the J =135 -> 134 transition at 137.615 GHz. Comparing the noise level
with the synthetic spectrum, we are able to estimate an upper limit to the
fraction of carbon locked in corannulene of about 1.0x10(-5) relative to the
total abundance of carbon in PAHs. The sensitivity achieved shows that radio
spectroscopy can be a powerful tool to search for polar PAHs. We compare this
upper limit with models for the PAH size distribution, emphasising that small
PAHs are much less abundant than predicted. We show that this cannot be
explained by destruction but is more likely related to the chemistry of their
formation in the environment of the Red Rectangle.Comment: 8 pages, 7 figures, 2 tables, accepted for publication in MNRA
A probability-conserving cross-section biasing mechanism for variance reduction in Monte Carlo particle transport calculations
In Monte Carlo particle transport codes, it is often important to adjust
reaction cross sections to reduce the variance of calculations of relatively
rare events, in a technique known as non-analogous Monte Carlo. We present the
theory and sample code for a Geant4 process which allows the cross section of a
G4VDiscreteProcess to be scaled, while adjusting track weights so as to
mitigate the effects of altered primary beam depletion induced by the cross
section change. This makes it possible to increase the cross section of nuclear
reactions by factors exceeding 10^4 (in appropriate cases), without distorting
the results of energy deposition calculations or coincidence rates. The
procedure is also valid for bias factors less than unity, which is useful, for
example, in problems that involve computation of particle penetration deep into
a target, such as occurs in atmospheric showers or in shielding
Basics of Bose-Einstein Condensation
The review is devoted to the elucidation of the basic problems arising in the
theoretical investigation of systems with Bose-Einstein condensate.
Understanding these challenging problems is necessary for the correct
description of Bose-condensed systems. The principal problems considered in the
review are as follows: (i) What is the relation between Bose-Einstein
condensation and global gauge symmetry breaking? (ii) How to resolve the
Hohenberg-Martin dilemma of conserving versus gapless theories? (iii) How to
describe Bose-condensed systems in strong spatially random potentials? (iv)
Whether thermodynamically anomalous fluctuations in Bose systems are
admissible? (v) How to create nonground-state condensates? Detailed answers to
these questions are given in the review. As examples of nonequilibrium
condensates, three cases are described: coherent modes, turbulent superfluids,
and heterophase fluids.Comment: Review articl
- …