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 $T\neq 0$, 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 $N$-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 $N$% -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