1,071 research outputs found
Phase transitions in Bose-Fermi-Hubbard model in the heavy fermion limit: Hard-core boson approach
Phase transitions are investigated in the Bose-Fermi-Hubbard model in the
mean field and hard-core boson approximations for the case of infinitely small
fermion transfer and repulsive on-site boson-fermion interaction. The behavior
of the Bose-Einstein condensate order parameter and grand canonical potential
is analyzed as functions of the chemical potential of bosons at zero
temperature. The possibility of change of order of the phase transition to the
superfluid phase in the regime of fixed values of the chemical potentials of
Bose- and Fermi-particles is established. The relevant phase diagrams are
built.Comment: 20 pages, 15 figure
Spherically symmetric black holes in minimally modified self-dual gravity
We discuss spherically symmetric black holes in the modified self-dual theory
of gravity recently studied by Krasnov, obtained adding a Weyl-curvature
dependent `cosmological term' to the Plebanski lagrangian for general
relativity. This type of modified gravity admits two different types of
singularities: one is a true singularity for the theory where the fundamental
fields of the theory, as well as the (auxiliary) spacetime metric, become
singular, and the other one is a milder "non-metric singularity" where the
metric description of the spacetime breaks down but the fundamental fields
themselves are regular. We first generalise this modified self-dual gravity to
include Maxwell's field and then study basic features of spherically symmetric,
charged black holes, with particular focus on whether these two types of
singularities are hidden or naked. We restrict our attention to minimal forms
of the modification, and find that the theory exhibits `screening' effects of
the electric charge (or `anti-screening', depending upon the sign of the
modification term), in the sense that it leads to the possibility of charging
the black hole more (or less) than it would be possible in general relativity
without exposing a naked singularity. We also find that for any (even
arbitrarily large) value of charge, true singularities of the theory appear to
be either achronal (non-timelike) covered by the hypersurface of a harmless
non-metric singularity, or simply hidden inside at least one Killing horizon.Comment: 42 pages, many colour figures. v2: discussion of the conformal
ambiguity improved, references added. v3: amended to match published versio
Research of the system of loose material automated precision batching
The imitating model of the system of loose material automated batching, including the robust system of engine control of auger feeder has been considered. The model is described in space of conditions by means of the programming language MATLAB, the interface of S-functions and the Simulink environment. The Kalman filter is used for noise filtration in the channel of measurement. Graphic representation of modeling results proves adequacy of the imitating batching model, the efficiency of the method of regulator parameter retuning and expediency of using the algorithm of measured signal filtration. A weight error at parametrical indignations influence on the worm feeder engine without retuning regulator parameters amounts to 0,3 kg (+3 %) at the set 10 kg, and with retuning regulator parameters amounts 0,01 kg (+0,1 %)
A Lattice Model of Intercalation
The thermodynamics of the lattice model of intercalation of ions in crystals
is considered in the mean field approximation. Pseudospin formalism is used for
the description of interaction of electrons with ions and the possibility of
hopping of intercalated ions between different positions is taken into account.
Phase diagrams are built. It is shown that the effective interaction between
intercalated ions can lead to phase separation or to appearance of modulated
phase (it depends on filling of the electron energy band). At high values of
the parameter of ion transfer the ionic subsystem can pass to the
superfluid-like state
COSMOS 2044. Experiment K-7-19. Pineal physiology in microgravity: Relation to rat gonadal function
It is now known that the pineal organ can interact with many endocrine and nonendocrine tissues in a regulatory fashion. Given its key role in the regulation of melatonin synthesis, its high concentration, and that its levels may persist longer than the more rapidly changing melatonin, it was felt that serotonin might give a more accurate assessment of the effects of microgravity on pineal function following recovery of animals from flight. Five-hydroxyindole acetic acid (5-HIAA), a major metabolite of serotonin metabolism, was also measured. One of the most interesting concomitants to spaceflight and exposure to microgravity has been the disturbing alteration in calcium metabolism and resulting skeletal effects. Given the link between exposure to microgravity and perturbation of calcium metabolism and the fact that the pineal is apparently one of the only soft tissues to calcify, pineal calcium content was examined following spaceflight
Interlayer tunneling spectroscopy of BiSrCaCuO: a look from inside on the doping phase diagram of high superconductors
A systematic, doping dependent interlayer tunneling spectroscopy of Bi2212
high superconductor is presented. An improved resolution made it possible
to simultaneously trace the superconducting gap (SG) and the normal state
pseudo-gap (PG) in a close vicinity of and to analyze closing of the PG
at . The obtained doping phase diagram exhibits a critical doping point
for appearance of the PG and a characteristic crossing of the SG and the PG
close to the optimal doping. This points towards coexistence of two different
and competing order parameters in Bi2212. Experimental data indicate that the
SG can form a combined (large) gap with the PG at and that the
interlayer tunneling becomes progressively incoherent with decreasing doping.Comment: 5 pages, 5 figure
Holography for the Lorentz Group Racah Coefficients
A known realization of the Lorentz group Racah coefficients is given by an
integral of a product of 6 ``propagators'' over 4 copies of the hyperbolic
space. These are ``bulk-to-bulk'' propagators in that they are functions of two
points in the hyperbolic space. It is known that the bulk-to-bulk propagator
can be constructed out of two bulk-to-boundary ones. We point out that there is
another way to obtain the same object. Namely, one can use two bulk-to-boundary
and one boundary-to-boundary propagator. Starting from this construction and
carrying out the bulk integrals we obtain a realization of the Racah
coefficients that is ``holographic'' in the sense that it only involves
boundary objects. This holographic realization admits a geometric
interpretation in terms of an ``extended'' tetrahedron.Comment: 12 pages, 2 figures; v2: minor changes; v3: "extended" tetrahedron
interpretation adde
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