8,298 research outputs found
A fundamental measure theory for the sticky hard sphere fluid
We construct a density functional theory (DFT) for the sticky hard sphere
(SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the
hard sphere fluid [Phys. Rev. Lett. {\bf 63}, 980 (1989)], is based on a set of
weighted densities and an exact result from scaled particle theory (SPT). It is
demonstrated that the excess free energy density of the inhomogeneous SHS fluid
is uniquely defined when (a) it is solely a function of the
weighted densities from Kierlik and Rosinberg's version of FMT [Phys. Rev. A
{\bf 42}, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c)
it yields any given direct correlation function (DCF) from the class of
generalized Percus-Yevick closures introduced by Gazzillo and Giacometti [J.
Chem. Phys. {\bf 120}, 4742 (2004)]. The resulting DFT is shown to be in very
good agreement with simulation data. In particular, this FMT yields the correct
contact value of the density profiles with no adjustable parameters. Rather
than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT
produces them. Interestingly, although equivalent to Kierlik and Rosinberg's
FMT in the case of hard spheres, the set of weighted densities used for
Rosenfeld's original FMT is insufficient for constructing a DFT which yields
the SHS DCF.Comment: 11 pages, 3 figure
Liquidity measures and cost of trading in an illiquid market
We provide the first in-depth study of trading on the Ukrainian stock exchange, using trade-by-trade data. Although Ukraine has some large listed companies, the market is quite illiquid. We study the efficiency of five liquidity measures in the market. The proportion of no-trading days is the most reliable of the five, while turnover, which is widely used in the literature, is a poor measure. On trading cost, trades in all size categories are executed within the quoted spread, as in other dealership markets, with medium-sized trades being the cheapest. The cost of sales is higher than the cost of purchases under all market conditions
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Thermal extraction of volatiles from the lunar regolith simulant NU-LHT-2M: preparations for in-situ analyses on the Moon
The present work describes the end-to-end demonstration of enriching the lunar highland regolith simulant NU-LHT-2M with loosely adsorbed water, releasing this and other volatile compounds by thermal treatment in high-vacuum, and identifying the released volatile species through mass spectrometry. This demonstration was performed to characterise how different sample conditions will affect the in-situ measurements performed by the ProSPA gas analysis instrument that is to operate at the lunar south pole on board the Russian Luna-27 lander. A laboratory breadboard was set up that allows testing of variable parameter combinations, such as different initial water contents, particle sizes, quantities, and bulk densities of the sample, as well as different heating rates. Three distinct temperature-dependent phases of outgassing were identified. Between -50 °C and 300 °C loosely adsorbed volatiles, mainly water in a mass fraction of around 0.1 % to 0.2 %, were released from the samples. Above that the samples showed mineral decomposition which led to the release of trapped water, carbon dioxide, and hydrogen sulfide. It was shown that the gas pressure produced by outgassing of the volatile species in a continuously pumped system is noticeably higher if the sample is larger, contains smaller particles, or if a higher heating rate is applied
Relativistic photoelectron spectra in the ionization of atoms by elliptically polarized light
Relativistic tunnel ionization of atoms by intense, elliptically polarized
light is considered. The relativistic version of the Landau-Dykhne formula is
employed. The general analytical expression is obtained for the relativistic
photoelectron spectra. The most probable angle of electron emission, the
angular distribution near this angle, the position of the maximum and the width
of the energy spectrum are calculated. In the weak field limit we obtain the
familiar non-relativistic results. For the case of circular polarization our
analytical results are in agreement with recent derivations of Krainov [V.P.
Krainov, J. Phys. B, {\bf 32}, 1607 (1999)].Comment: 8 pages, 2 figures, accepted for publication in Journal of Physics
Relativistic semiclassical approach in strong-field nonlinear photoionization
Nonlinear relativistic ionization phenomena induced by a strong laser
radiation with elliptically polarization are considered. The starting point is
the classical relativistic action for a free electron moving in the
electromagnetic field created by a strong laser beam. The application of the
relativistic action to the classical barrier-suppression ionization is briefly
discussed. Further the relativistic version of the Landau-Dykhne formula is
employed to consider the semiclassical sub-barrier ionization. Simple
analytical expressions have been found for: (i) the rates of the strong-field
nonlinear ionization including relativistic initial and final state effects;
(ii) the most probable value of the components of the photoelectron final state
momentum; (iii) the most probable direction of photoelectron emission and (iv)
the distribution of the photoelectron momentum near its maximum value.Comment: 13 pages, 3 figures, to be published in Phys. Rev.
Occurence of elliptical fractal patterns in multi-bit bandpass sigma delta modulators
It has been established that the class of bandpass sigma delta modulators (SDMs) with single
bit quantizers could exhibit state space dynamics represented by elliptic or fractal patterns
confined within trapezoidal regions. In this letter, we find that elliptical fractal patterns may
also occur in bandpass SDMs with multibit quantizers, even for the case when the saturation
regions of the multibit quantizers are not activated and a large number of bits are used for the
implementation of the quantizers. Moreover, the fractal pattern may occur for low bit quantizers,
and the visual appearance of the phase portraits between the infinite state machine and the finite
state machine with high bit quantizers is different. These phenomena are different from those
previously reported for the digital filter with two’s complement arithmetic. Furthermore, some
interesting phenomena are found. A bit change of the quantizer can result in a dramatic change
in the fractal patterns. When the trajectories of the corresponding linear systems converge to a
fixed point, the regions of the elliptical fractal patterns diminish in size as the number of bits
of the quantizers increases
Formation of an Icosahedral Structure during the Freezing of Gold Nanoclusters: Surface-Induced Mechanism
The freezing behavior of gold nanoclusters was studied by employing molecular
dynamics simulations based on a semi-empirical embedded-atom method.
Investigations of the gold nanoclusters revealed that, just after freezing,
ordered nano-surfaces with a fivefold symmetry were formed with interior atoms
remaining in the disordered state. Further lowering of temperatures induced
nano-crystallization of the interior atoms that proceeded from the surface
towards the core region, finally leading to an icosahedral structure. These
dynamic processes explain why the icosahedral cluster structure is dominantly
formed in spite of its energetic metastability.Comment: 9 pages, 4 figures(including 14 eps-files
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Accessing and assessing lunar resources with PROSPECT
PROSPECT is a package in development by ESA to assess the in-situ resource potential of lunar regolith. PROSPECT will: obtain sub-surface regolith samples, extract volatiles, identify chemical species, quantify abundances, and characterize isotopes
Spintessence: a possible candidate as a driver of the late time cosmic acceleration
In this paper, it is shown completely analytically that a spintessence model
can very well serve the purpose of providing an early deceleration and the
present day acceleration.Comment: 5 pages, no figure. Accepted for publication in Astrophysics and
Space Scienc
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