7,222 research outputs found
Spinning Q-balls in the complex signum-Gordon model
Rotational excitations of compact Q-balls in the complex signum-Gordon model
in 2+1 dimensions are investigated. We find that almost all such spinning
Q-balls have the form of a ring of strictly finite width. In the limit of large
angular momentum M_z their energy is proportional to |M_z|^(1/5).Comment: 10 page
Axion Dark Matter and Cosmological Parameters
We observe that photon cooling after big bang nucleosynthesis (BBN) but
before recombination can remove the conflict between the observed and
theoretically predicted value of the primordial abundance of Li. Such
cooling is ordinarily difficult to achieve. However, the recent realization
that dark matter axions form a Bose-Einstein condensate (BEC) provides a
possible mechanism, because the much colder axions may reach thermal contact
with the photons. This proposal predicts a high effective number of neutrinos
as measured by the cosmic microwave anisotropy spectrum.Comment: 4 pages, one figure. Version to appear in Phys. Rev. Lett.,
incorporating useful comments by the referees and emphasizing that photon
cooling by axion BEC is a possibility, not a certaint
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells is studied
via the fully microscopic kinetic spin Bloch equation approach where all the
scatterings, such as the electron-impurity, electron-phonon, electron-electron
Coulomb, electron-hole Coulomb, electron-hole exchange (the Bir-Aronov-Pikus
mechanism) and the - exchange scatterings, are explicitly included. The
Elliot-Yafet mechanism is also incorporated. From this approach, we study the
spin relaxation in both -type and -type Ga(Mn)As quantum wells. For
-type Ga(Mn)As quantum wells where most Mn ions take the interstitial
positions, we find that the spin relaxation is always dominated by the DP
mechanism in metallic region. Interestingly, the Mn concentration dependence of
the spin relaxation time is nonmonotonic and exhibits a peak. This behavior is
because that the momentum scattering and the inhomogeneous broadening have
different density dependences in the non-degenerate and degenerate regimes. For
-type Ga(Mn)As quantum wells, we find that Mn concentration dependence of
the spin relaxation time is also nonmonotonic and shows a peak. Differently,
this behavior is because that the - exchange scattering (or the
Bir-Aronov-Pikus) mechanism dominates the spin relaxation in the high Mn
concentration regime at low (or high) temperature, whereas the DP mechanism
determines the spin relaxation in the low Mn concentration regime. The
Elliot-Yafet mechanism also contributes the spin relaxation at intermediate
temperature. The spin relaxation time due to the DP mechanism increases with Mn
concentration due to motional narrowing, whereas those due to the spin-flip
mechanisms decrease with Mn concentration, which thus leads to the formation of
the peak.... (The remaining is omitted due to the space limit)Comment: 12 pages, 8 figures, Phys. Rev. B 79, 2009, in pres
Extreme laser pulses for possible development of boron fusion power reactors for clean and lasting energy
Extreme laser pulses driving non-equilibrium processes in high density
plasmas permit an increase of the fusion of hydrogen with the boron isotope 11
by nine orders of magnitude of the energy gains above the classical values.
This is the result of initiating the reaction by non-thermal ultrahigh
acceleration of plasma blocks by the nonlinear (ponderomotive) force of the
laser field, in addition to the avalanche reaction that has now been
experimentally and theoretically manifested. The design of a very compact
fusion power reactor is scheduled to produce then environmentally fully clean
and inexhaustible generation of energy at profitably low costs. The reaction
within a volume of cubic millimetres during a nanosecond can only be used for
controlled power generation.Comment: 10 pages, 5 fugure
Compact Q-balls and Q-shells in a scalar electrodynamics
We investigate spherically symmetric non topological solitons in
electrodynamics with a scalar field self interaction U ~|\psi| taken from the
complex signum-Gordon model. We find Q-balls for small absolute values of the
total electric charge Q, and Q-shells when |Q| is large enough. In both cases
the charge density exactly vanishes outside certain compact region in the three
dimensional space. The dependence of the total energy E of small Q-balls on the
total electric charge has the form E ~ |Q|^(5/6), while in the case of very
large Q-shells E ~ |Q|^(7/6).Comment: 21 pages, 7 figure
Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields
The drift and diffusion of a cloud of ions in a fluid are distorted by an
inhomogeneous electric field. If the electric field carries the center of the
distribution in a straight line and the field configuration is suitably
symmetric, the distortion can be calculated analytically. We examine the
specific examples of fields with cylindrical and spherical symmetry in detail
assuming the ion distributions to be of a generally Gaussian form. The effects
of differing diffusion coefficients in the transverse and longitudinal
directions are included
Mean first passage times for bond formation for a Brownian particle in linear shear flow above a wall
Motivated by cell adhesion in hydrodynamic flow, here we study bond formation
between a spherical Brownian particle in linear shear flow carrying receptors
for ligands covering the boundary wall. We derive the appropriate Langevin
equation which includes multiplicative noise due to position-dependent mobility
functions resulting from the Stokes equation. We present a numerical scheme
which allows to simulate it with high accuracy for all model parameters,
including shear rate and three parameters describing receptor geometry
(distance, size and height of the receptor patches). In the case of homogeneous
coating, the mean first passage time problem can be solved exactly. In the case
of position-resolved receptor-ligand binding, we identify different scaling
regimes and discuss their biological relevance.Comment: final version after minor revision
The Expansion in Width for Domain Walls in Nematic Liquid Crystals in External Magnetic Field
The improved expansion in width is applied to curved domain walls in uniaxial
nematic liquid crystals in external magnetic field. In the present paper we
concentrate on the case of equal elastic constants. We obtain approximate form
of the director field up to second order in magnetic coherence length.Comment: 18 pages, Latex 2.09, no figure
Static deformation of heavy spring due to gravity and centrifugal force
The static equilibrium deformation of a heavy spring due to its own weight is
calculated for two cases. First for a spring hanging in a constant
gravitational field, then for a spring which is at rest in a rotating system
where it is stretched by the centrifugal force. Two different models are
considered. First a discrete model assuming a finite number of point masses
connected by springs of negligible weight. Then the continuum limit of this
model. In the second case the differential equation for the deformation is
obtained by demanding that the potential energy is minimized. In this way a
simple application of the variational calculus is obtained.Comment: 11 pages, 2 figure
Generic Subsequence Matching Framework: Modularity, Flexibility, Efficiency
Subsequence matching has appeared to be an ideal approach for solving many
problems related to the fields of data mining and similarity retrieval. It has
been shown that almost any data class (audio, image, biometrics, signals) is or
can be represented by some kind of time series or string of symbols, which can
be seen as an input for various subsequence matching approaches. The variety of
data types, specific tasks and their partial or full solutions is so wide that
the choice, implementation and parametrization of a suitable solution for a
given task might be complicated and time-consuming; a possibly fruitful
combination of fragments from different research areas may not be obvious nor
easy to realize. The leading authors of this field also mention the
implementation bias that makes difficult a proper comparison of competing
approaches. Therefore we present a new generic Subsequence Matching Framework
(SMF) that tries to overcome the aforementioned problems by a uniform frame
that simplifies and speeds up the design, development and evaluation of
subsequence matching related systems. We identify several relatively separate
subtasks solved differently over the literature and SMF enables to combine them
in straightforward manner achieving new quality and efficiency. This framework
can be used in many application domains and its components can be reused
effectively. Its strictly modular architecture and openness enables also
involvement of efficient solutions from different fields, for instance
efficient metric-based indexes. This is an extended version of a paper
published on DEXA 2012.Comment: This is an extended version of a paper published on DEXA 201
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