2,150 research outputs found
Surface term for the capillary condensation transitions in a slit geometry
It is shown that a bare simple fluid model (SFM) proposed some years ago for
studying adsorption between two semi-infinite solid walls can be improved by
modifying the surface term in the grand potential for the film phase. Such a
correction substantially improves the agreement between the predictions for
phase transitions provided by that SFM and results obtained from calculations
carried out for He with the density-functional method at zero temperature.
The corrective term depends on the strength of the adsorption potential and
observables of bulk helium.Comment: 4 pages, 1 table and 5 figure
Perceptive and Expressive Skills in Language Learning
Perceptive and Expressive Skills in Language Learnin
Effects of Squark Processes on the Axino CDM Abundance
We investigate the role of an effective dimension-4 axino-quark-squark
coupling in the thermal processes producing stable cold axino relics in the
early Universe. We find that, while the induced squark and quark scattering
processes are always negligible, squark decays become important in the case of
low reheat temperature and large gluino mass. The effect can tighten the bounds
on the scenario from the requirement that cold dark matter axinos do not
overclose the Universe.Comment: 20 pages, 9 figures, uses JHEP3.cl
Liouville theory and uniformization of four-punctured sphere
Few years ago Zamolodchikov and Zamolodchikov proposed an expression for the
4-point classical Liouville action in terms of the 3-point actions and the
classical conformal block. In this paper we develop a method of calculating the
uniformizing map and the uniformizing group from the classical Liouville action
on n-punctured sphere and discuss the consequences of Zamolodchikovs conjecture
for an explicit construction of the uniformizing map and the uniformizing group
for the sphere with four punctures.Comment: 17 pages, no figure
Treatment of coronary chronic total occlusion by transradial approach: Current trends and expert recommendations
The aim of this review is to highlight the technical details and the scientific data on percutaneous coronary interventions (PCIs) in chronic total occlusion (CTO) performed by transradial approach (TRA). Transfemoral approach (TFA) is commonly regarded as the standard for CTO PCI, but there is a growing number of CTO recanalization procedures performed by TRA. We discuss the relevant technical details to approach a CTO by transradial access, especially the compatibility of various CTO recanalization techniques with specific guiding catheter sizes. Randomized prospective trials in this field are lacking and only data from observational studies are available. We can conclude that transradial access for CTO PCI is feasible and could be very useful in selected patients. In our opinion, transradial access in CTO PCIs should be limited to operators and centers highly experienced in CTO recanaliza¬tion and in TRA
On the twin paradox in static spacetimes: I. Schwarzschild metric
Motivated by a conjecture put forward by Abramowicz and Bajtlik we reconsider
the twin paradox in static spacetimes. According to a well known theorem in
Lorentzian geometry the longest timelike worldline between two given points is
the unique geodesic line without points conjugate to the initial point on the
segment joining the two points. We calculate the proper times for static twins,
for twins moving on a circular orbit (if it is a geodesic) around a centre of
symmetry and for twins travelling on outgoing and ingoing radial timelike
geodesics. We show that the twins on the radial geodesic worldlines are always
the oldest ones and we explicitly find the conjugate points (if they exist)
outside the relevant segments. As it is of its own mathematical interest, we
find general Jacobi vector fields on the geodesic lines under consideration. In
the first part of the work we investigate Schwarzschild geometry.Comment: 18 pages, paper accepted for publication in Gen. Rel. Gra
Geometry of Non-Hausdorff Spaces and Its Significance for Physics
Hausdorff relation, topologically identifying points in a given space,
belongs to elementary tools of modern mathematics. We show that if subtle
enough mathematical methods are used to analyze this relation, the conclusions
may be far-reaching and illuminating. Examples of situations in which the
Hausdorff relation is of the total type, i.e., when it identifies all points of
the considered space, are the space of Penrose tilings and space-times of some
cosmological models with strong curvature singularities. With every Hausdorff
relation a groupoid can be associated, and a convolutive algebra defined on it
allows one to analyze the space that otherwise would remain intractable. The
regular representation of this algebra in a bundle of Hilbert spaces leads to a
von Neumann algebra of random operators. In this way, a probabilistic
description (in a generalized sense) naturally takes over when the concept of
point looses its meaning. In this situation counterparts of the position and
momentum operators can be defined, and they satisfy a commutation relation
which, in the suitable limiting case, reproduces the Heisenberg indeterminacy
relation. It should be emphasized that this is neither an additional assumption
nor an effect of a quantization process, but simply the consequence of a purely
geometric analysis.Comment: 13 LaTex pages, no figure
Ground state energy of the modified Nambu-Goto string
We calculate, using zeta function regularization method, semiclassical energy
of the Nambu-Goto string supplemented with the boundary, Gauss-Bonnet term in
the action and discuss the tachyonic ground state problem.Comment: 10 pages, LaTeX, 2 figure
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