31,914 research outputs found
Convergence of Particle-Hole Expansions for the Description of Nuclear Correlations
The convergence properties of a multiparticle-multihole (mp-mh) configuration
mixing approach whose purpose is to describe ground state correlations in
nuclei without particle number and Pauli violations is investigated in the case
of an exactly solvable pairing hamiltonian. Two different truncation schemes
are tested by looking at quantities as correlation energies and single-particle
occupation probabilities. Results show that pairing correlations present in
usual superfluid nuclei can be accurately described using up to 6 particle-6
hole excitations, a convergence fast enought for envisaging extensions to fully
microscopic calculations.Comment: 8 pages, 4 figure
Scalar sextet in the 331 model with right-handed neutrinos
A Higgs sextet is introduced in order to generate Dirac and Majorana neutrino
masses in the 331 model with right-handed neutrinos. As will be seen, the
present sextet introduction leads to a rich neutrino mass structure. The
smallness of neutrino masses can be achieved via, for example, a seesaw limit.
The fact that the masses of the charged leptons are not effected by their new
Yukawa couplings to the sextet is convenient for generating small neutrino
masses.Comment: RevTeX4, 5 pages, no figure. To appear in Phys. Rev. D. Misprints
removed (v.2
Origin of conductivity cross over in entangled multi-walled carbon nanotube network filled by iron
A realistic transport model showing the interplay of the hopping transport
between the outer shells of iron filled entangled multi-walled carbon nanotubes
(MWNT) and the diffusive transport through the inner part of the tubes, as a
function of the filling percentage, is developed. This model is based on
low-temperature electrical resistivity and magneto-resistance (MR)
measurements. The conductivity at low temperatures showed a crossover from
Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions
(3D) between the neighboring tubes as the iron weight percentage is increased
from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly
dependent on temperature as well as magnetic field and shows both positive and
negative signs, which are discussed in terms of wave function shrinkage and
quantum interference effects, respectively. A further increase of the iron
percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D
weak localization (WL). This change is ascribed to the formation of long iron
nanowires at the core of the nanotubes, which yields a long dephasing length
(e.g. 30 nm) at the lowest measured temperature. Although the overall transport
in this network is described by a 3D WL model, the weak temperature dependence
of inelastic scattering length expressed as L_phi ~T^-0.3 suggests the
possibility for the presence of one-dimensional channels in the network due to
the formation of long Fe nanowires inside the tubes, which might introduce an
alignment in the random structure.Comment: 29 pages,10 figures, 2 tables, submitted to Phys. Rev.
Out of equilibrium electronic transport properties of a misfit cobaltite thin film
We report on transport measurements in a thin film of the 2D misfit Cobaltite
. Dc magnetoresistance measurements obey the modified
variable range hopping law expected for a soft Coulomb gap. When the sample is
cooled down, we observe large telegraphic-like fluctuations. At low
temperature, these slow fluctuations have non Gaussian statistics, and are
stable under a large magnetic field. These results suggest that the low
temperature state is a glassy electronic state. Resistance relaxation and
memory effects of pure magnetic origin are also observed, but without aging
phenomena. This indicates that these magnetic effects are not glassy-like and
are not directly coupled to the electronic part.Comment: accepted in Phys Rev B, Brief report
SLE_k: correlation functions in the coefficient problem
We apply the method of correlation functions to the coefficient problem in
stochastic geometry. In particular, we give a proof for some universal patterns
conjectured by M. Zinsmeister for the second moments of the Taylor coefficients
for special values of kappa in the whole-plane Schramm-Loewner evolution
(SLE_kappa). We propose to use multi-point correlation functions for the study
of higher moments in coefficient problem. Generalizations related to the
Levy-type processes are also considered. The exact multifractal spectrum of
considered version of the whole-plane SLE_kappa is discussed
Decidable model-checking for a resource logic with production of resources
Several logics for expressing coalitional ability under resource bounds have been proposed and studied in the literature. Previous work has shown that if only consumption of resources is considered or the total amount of resources produced or consumed on any path in the system is bounded, then the model-checking problem for several standard logics, such as Resource-Bounded Coalition Logic (RB-CL) and Resource-Bounded Alternating-Time Temporal Logic (RB-ATL) is decidable. However, for coalition logics with unbounded resource production and consumption, only some undecidability results are known. In this paper, we show that the model-checking problem for RB-ATL with unbounded production and consumption of resources is decidable
Symbolic model checking for one-resource RB±ATL
RB±ATL is an extension of ATL where it is possible to model consumption and production of several resources by a set of agents. The model-checking problem for RB±ATL is known to be decidable. However the only available model-checking algorithm for RB±ATL uses a forward search of the state space, and hence does not have an efficient symbolic implementation. In this paper,
we consider a fragment of RB±ATL, 1RB±ATL, that allows only one resource type. We give a symbolic model-checking algorithm for this fragment of RB±ATL, and evaluate the performance of an MCMAS-based implementation of the algorithm on an example problem that can be scaled to large state spaces
External Control of a Metal-Insulator Transition in GaMnAs Wires
Quantum transport in disordered ferromagnetic (III,Mn)V semiconductors is
studied theoretically. Mesoscopic wires exhibit an Anderson disorder-induced
metal-insulator transition that can be controlled by a weak external magnetic
field. This metal-insulator transition should also occur in other materials
with large anisotropic magneto resistance effects. The transition can be useful
for studies of zero-temperature quantum critical phase transitions and
fundamental material properties.Comment: Major revised final versio
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