365 research outputs found
Superfluidity of a perfect quantum crystal
In recent years, experimental data were published which point to the
possibility of the existence of superfluidity in solid helium. To investigate
this phenomenon theoretically we employ a hierarchy of equations for reduced
density matrices which describes a quantum system that is in thermodynamic
equilibrium below the Bose-Einstein condensation point, the hierarchy being
obtained earlier by the author. It is shown that the hierarchy admits solutions
relevant to a perfect crystal (immobile) in which there is a frictionless flow
of atoms, which testifies to the possibility of superfluidity in ideal solids.
The solutions are studied with the help of the bifurcation method and some
their peculiarities are found out. Various physical aspects of the problem,
among them experimental ones, are discussed as well.Comment: 24 pages with 2 figures, version accepted for publication in
Eur.Phys.J.
Fast Diffusion Process in Quenched hcp Dilute Solid He-He Mixture
The study of phase structure of dilute He - He solid mixture of
different quality is performed by spin echo NMR technique. The diffusion
coefficient is determined for each coexistent phase. Two diffusion processes
are observed in rapidly quenched (non-equilibrium) hcp samples: the first
process has a diffusion coefficient corresponding to hcp phase, the second one
has huge diffusion coefficient corresponding to liquid phase. That is evidence
of liquid-like inclusions formation during fast crystal growing. It is
established that these inclusions disappear in equilibrium crystals after
careful annealing.Comment: 7 pages, 3 figures, QFS200
Borcherds symmetries in M-theory
It is well known but rather mysterious that root spaces of the Lie
groups appear in the second integral cohomology of regular, complex, compact,
del Pezzo surfaces. The corresponding groups act on the scalar fields (0-forms)
of toroidal compactifications of M theory. Their Borel subgroups are actually
subgroups of supergroups of finite dimension over the Grassmann algebra of
differential forms on spacetime that have been shown to preserve the
self-duality equation obeyed by all bosonic form-fields of the theory. We show
here that the corresponding duality superalgebras are nothing but Borcherds
superalgebras truncated by the above choice of Grassmann coefficients. The full
Borcherds' root lattices are the second integral cohomology of the del Pezzo
surfaces. Our choice of simple roots uses the anti-canonical form and its known
orthogonal complement. Another result is the determination of del Pezzo
surfaces associated to other string and field theory models. Dimensional
reduction on corresponds to blow-up of points in general position
with respect to each other. All theories of the Magic triangle that reduce to
the sigma model in three dimensions correspond to singular del Pezzo
surfaces with (normal) singularity at a point. The case of type I and
heterotic theories if one drops their gauge sector corresponds to non-normal
(singular along a curve) del Pezzo's. We comment on previous encounters with
Borcherds algebras at the end of the paper.Comment: 30 pages. Besides expository improvements, we exclude by hand real
fermionic simple roots when they would naively aris
The Partition Function of the Two-Dimensional Black Hole Conformal Field Theory
We compute the partition function of the conformal field theory on the
two-dimensional euclidean black hole background using path-integral techniques.
We show that the resulting spectrum is consistent with the algebraic
expectations for the SL(2,R)/U(1) coset conformal field theory construction. In
particular, we find confirmation for the bound on the spin of the discrete
representations and we determine the density of the continuous representations.
We point out the relevance of the partition function to all string theory
backgrounds that include an SL(2,R)/U(1) coset factor.Comment: 17 pages, references added and typos correcte
Parity Violating Measurements of Neutron Densities
Parity violating electron nucleus scattering is a clean and powerful tool for
measuring the spatial distributions of neutrons in nuclei with unprecedented
accuracy. Parity violation arises from the interference of electromagnetic and
weak neutral amplitudes, and the of the Standard Model couples primarily
to neutrons at low . The data can be interpreted with as much confidence
as electromagnetic scattering. After briefly reviewing the present theoretical
and experimental knowledge of neutron densities, we discuss possible parity
violation measurements, their theoretical interpretation, and applications. The
experiments are feasible at existing facilities. We show that theoretical
corrections are either small or well understood, which makes the interpretation
clean. The quantitative relationship to atomic parity nonconservation
observables is examined, and we show that the electron scattering asymmetries
can be directly applied to atomic PNC because the observables have
approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.
Spin Effects in Two Quark System and Mixed States
Based on the numeric solution of a system of coupled channels for vector
mesons (- and -waves mixing) and for tensor mesons (- and -waves
mixing) mass spectrum and wave functions of a family of vector mesons
in triplet states are obtained. The calculations are performed using
a well known Cornell potential with a mixed Lorentz-structure of the
confinement term. The spin-dependent part of the potential is taken from the
Breit-Fermi approach. The effect of singular terms of potential is considered
in the framework of the perturbation theory and by a configuration interaction
approach (CIA), modified for a system of coupled equations. It is shown that
even a small contribution of the -wave to be very important at the
calculation of certain characteristics of the meson states.Comment: 12 pages, LaTe
Is It Rational to Assume that Infants Imitate Rationally? A Theoretical Analysis and Critique
It has been suggested that preverbal infants evaluate the efficiency of others' actions (by applying a principle of rational action) and that they imitate others' actions rationally. The present contribution presents a conceptual analysis of the claim that preverbal infants imitate rationally. It shows that this ability rests on at least three assumptions: that infants are able to perceive others' action capabilities, that infants reason about and conceptually represent their own bodies, and that infants are able to think counterfactually. It is argued that none of these three abilities is in place during infancy. Furthermore, it is shown that the idea of a principle of rational action suffers from two fallacies. As a consequence, is it suggested that it is not rational to assume that infants imitate rationally. Copyright (C) 2012 S. Karger AG, Base
Thickness-dependent Electrochromic Properties of Amorphous Tungsten Trioxide Thin Films
Tungsten Trioxide (WO3) thin films were grown by thermal evaporation method to study the effect of
film’s thickness on its electrochromic (EC) properties. The WO3 thin films of different thicknesses were
grown on Indium Tin Oxide (ITO) coated glass and soda lime (bare) glass substrate held at room temperature.
The surface composition of the thin films was investigated using X-ray photoelectron spectroscopy
measurement, which showed the oxygen to tungsten atomic composition ratio to be nearly 2.97. The EC
properties of the thin films were examined using electrochemical techniques. Cyclic-voltammetery shows
the diffusion coefficient (D) of the intercalated H+ ion in the WO3 thin film increases with the film’s thickness.
It turns out that the ‘thicker’ film exhibits better coloration efficiency (CE) as compared to the ‘thinner’
film. The coloration time was found to be independent of film thickness; however, the bleaching time
increases as the film thickness increases
Thickness-dependent electrochromic properties of amorphous tungsten trioxide thin films
Tungsten Trioxide (WO3) thin films were grown by thermal evaporation method to study the effect of
film’s thickness on its electrochromic (EC) properties. The WO3thin films of different thicknesses
were grown on Indium Tin Oxide (ITO) coated glass and soda lime (bare) glass substrate held at room
temperature. The surface composition of the thin films was investigated using X-ray photoelectron
spectroscopy measurement, which showed the oxygen to tungsten atomic composition ratio to be
nearly 2.97. The EC properties of the thin films were examined using electrochemical techniques.
Cyclic-voltammetery shows the diffusion coefficient (D) of the intercalated H+ ion in the WO3 thin film
increases with the film’s thickness. It turns out that the ‘thicker’ film exhibits better coloration
efficiency (CE) as compared to the ‘thinner’ film. The coloration time was found to be independent of
film thickness; however, the bleaching time increases as the film thickness increases
Thickness-dependent electrochromic properties of amorphous tungsten trioxide thin films
Tungsten Trioxide (WO3) thin films were grown by thermal evaporation method to study the effect of
film’s thickness on its electrochromic (EC) properties. The WO3thin films of different thicknesses
were grown on Indium Tin Oxide (ITO) coated glass and soda lime (bare) glass substrate held at room
temperature. The surface composition of the thin films was investigated using X-ray photoelectron
spectroscopy measurement, which showed the oxygen to tungsten atomic composition ratio to be
nearly 2.97. The EC properties of the thin films were examined using electrochemical techniques.
Cyclic-voltammetery shows the diffusion coefficient (D) of the intercalated H+ ion in the WO3 thin film
increases with the film’s thickness. It turns out that the ‘thicker’ film exhibits better coloration
efficiency (CE) as compared to the ‘thinner’ film. The coloration time was found to be independent of
film thickness; however, the bleaching time increases as the film thickness increases
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