2,621 research outputs found
Comment on "Order parameter of A-like 3He phase in aerogel"
We argue that the inhomogeneous A-phase in aerogel is energetically more
preferable than the "robust" phase suggested by I. A. Fomin, JETP Lett. 77, 240
(2003); cond-mat/0302117 and cond-mat/0401639.Comment: 2 page
Bidimensionality of Geometric Intersection Graphs
Let B be a finite collection of geometric (not necessarily convex) bodies in
the plane. Clearly, this class of geometric objects naturally generalizes the
class of disks, lines, ellipsoids, and even convex polygons. We consider
geometric intersection graphs GB where each body of the collection B is
represented by a vertex, and two vertices of GB are adjacent if the
intersection of the corresponding bodies is non-empty. For such graph classes
and under natural restrictions on their maximum degree or subgraph exclusion,
we prove that the relation between their treewidth and the maximum size of a
grid minor is linear. These combinatorial results vastly extend the
applicability of all the meta-algorithmic results of the bidimensionality
theory to geometrically defined graph classes
A New World Average Value for the Neutron Lifetime
The analysis of the data on measurements of the neutron lifetime is
presented. A new most accurate result of the measurement of neutron lifetime
[Phys. Lett. B 605 (2005) 72] 878.5 +/- 0.8 s differs from the world average
value [Phys. Lett. B 667 (2008) 1] 885.7 +/- 0.8 s by 6.5 standard deviations.
In this connection the analysis and Monte Carlo simulation of experiments
[Phys. Lett. B 483 (2000) 15] and [Phys. Rev. Lett. 63 (1989) 593] is carried
out. Systematic errors of about -6 s are found in each of the experiments. The
summary table for the neutron lifetime measurements after corrections and
additions is given. A new world average value for the neutron lifetime 879.9
+/- 0.9 s is presented.Comment: 27 pages, 13 figures; Fig.13 update
Towards Field Theory in Spaces with Multivolume Junctions
We consider a spacetime formed by several pieces having common timelike
boundary which plays the role of a junction between them. We establish junction
conditions for fields of various spin and derive the resulting laws of wave
propagation through the junction, which turn out to be quite similar for fields
of all spins. As an application, we consider the case of multivolume junctions
in four-dimensional spacetime that may arise in the context of the theory of
quantum creation of a closed universe on the background of a big mother
universe. The theory developed can also be applied to braneworld models and to
the superstring theory.Comment: 20 pages, 3 figures, revtex; published versio
Photoluminescence of tetrahedral quantum-dot quantum wells
Taking into account the tetrahedral shape of a quantum dot quantum well
(QDQW) when describing excitonic states, phonon modes and the exciton-phonon
interaction in the structure, we obtain within a non-adiabatic approach a
quantitative interpretation of the photoluminescence (PL) spectrum of a single
CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW
is bright, in contrast to the dark ground state for a spherical QDQW.Comment: 4 pages, 2 figure
Inversion of Sequence of Diffusion and Density Anomalies in Core-Softened Systems
In this paper we present a simulation study of water-like anomalies in
core-softened system introduced in our previous publications. We investigate
the anomalous regions for a system with the same functional form of the
potential but with different parameters and show that the order of the region
of anomalous diffusion and the region of density anomaly is inverted with
increasing the width of the repulsive shoulder.Comment: 8 pages, 10 figure
Core-Softened System With Attraction: Trajectory Dependence of Anomalous Behavior
In the present article we carry out a molecular dynamics study of the
core-softened system and show that the existence of the water-like anomalies in
this system depends on the trajectory in space along which the
behavior of the system is studied. For example, diffusion and structural
anomalies are visible along isotherms as a function of density, but disappears
along the isochores and isobars as a function of temperature. On the other
hand, the diffusion anomaly may be seen along adiabats as a function of
temperature, density and pressure. It should be noted that it may be no
signature of a particular anomaly along a particular trajectory, but the
anomalous region for that particular anomaly can be defined when all possible
trajectories in the same space are examined (for example, signature of
diffusion anomaly is evident through the crossing of different isochors.
However, there is no signature of diffusion anomaly along a particular
isochor). We also analyze the applicability of the Rosenfeld entropy scaling
relations to this system in the regions with the water-like anomalies. It is
shown that the validity of the Rosenfeld scaling relation for the diffusion
coefficient also depends on the trajectory in the space along which
the kinetic coefficients and the excess entropy are calculated.Comment: 16 pages, 21 figures. arXiv admin note: this contains much of the
content of arXiv:1010.416
Optical spectra of quantum dots: effects of non-adiabaticity
It is shown that in many cases an adequate description of optical spectra of
semiconductor quantum dots requires a treatment beyond the commonly used
adiabatic approximation. We have developed a theory of phonon-assisted optical
transitions in semiconductor quantum dots, which takes into account
non-adiabaticity of the exciton-phonon system. Effects of non-adiabaticity lead
to a mixing of different exciton and phonon states that provides a key to the
understanding of surprisingly high intensities of phonon satellites observed in
photoluminescence spectra of quantum dots. A breakdown of the adiabatic
approximation gives an explanation also for discrepancies between the serial
law, observed in multi-phonon optical spectra of some quantum dots, and the
Franck-Condon progression, prescribed by the adiabatic approach.Comment: 4 pages, 3 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected],
[email protected]
Stable vortex-antivortex molecules in mesoscopic superconducting triangles
A thermodynamically stable vortex-antivortex pattern has been revealed in
mesoscopic type I superconducting triangles, contrary to type II
superconductors where similar patterns are unstable. The stable
vortex-antivortex "molecule" appears due to the interplay between two factors:
a repulsive vortex-antivortex interaction in type I superconductors and the
vortex confinement in the triangle.Comment: 5 pages, 4 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected]
Generalized van der Waals theory of liquid-liquid phase transitions
In the framework of the thermodynamic perturbation theory for fluids we study
how the phase diagram of an isotropic repulsive soft-core attractive potential,
where a liquid-liquid phase transition exists in addition to the standard
gas-liquid phase transition, changes by varying the parameters of the
potential. We show that existence of the liquid-liquid transition is determined
by the interplay of the parameters of the potential and the structure of a
reference liquid.Comment: 5 pages, 6 figure
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