22,660 research outputs found
In situ performance measurements of the mitre photovoltaic array
A data acquisition system was developed to provide more accurate and consistent measurement of the degradation of solar arrays. A technique was developed for in-situ measurement of photovoltaic panels of sufficient quality to permit evaluation of electrical performance over extended periods of several years
On the Integrability and Chaos of an N=2 Maxwell-Chern-Simons-Higgs Mechanical Model
We apply different integrability analysis procedures to a reduced (spatially
homogeneous) mechanical system derived from an off-shell non-minimally coupled
N=2 Maxwell-Chern-Simons-Higgs model that presents BPS topological vortex
excitations, numerically obtained with an ansatz adopted in a special -
critical coupling - parametric regime. As a counterpart of the regularity
associated to the static soliton-like solution, we investigate the possibility
of chaotic dynamics in the evolution of the spatially homogeneous reduced
system, descendant from the full N=2 model under consideration. The originally
rich content of symmetries and interactions, N=2 susy and non-minimal coupling,
singles out the proposed model as an interesting framework for the
investigation of the role played by (super-)symmetries and parametric domains
in the triggering/control of chaotic behavior in gauge systems.
After writing down effective Lagrangian and Hamiltonian functions, and
establishing the corresponding canonical Hamilton equations, we apply global
integrability Noether point symmetries and Painleveproperty criteria to both
the general and the critical coupling regimes. As a non-integrable character is
detected by the pair of analytical criteria applied, we perform suitable
numerical simulations, as we seek for chaotic patterns in the system evolution.
Finally, we present some Comments on the results and perspectives for further
investigations and forthcoming communications.Comment: 18 pages, 5 figure
Excitonic Instabilities and Insulating States in Bilayer Graphene
The competing ground states of bilayer graphene are studied by applying
renormalization group techniques to a bilayer honeycomb lattice with nearest
neighbor hopping. In the absence of interactions, the Fermi surface of this
model at half-filling consists of two nodal points with momenta ,
, where the conduction band and valence band touch each other,
yielding a semi-metal. Since near these two points the energy dispersion is
quadratic with perfect particle-hole symmetry, excitonic instabilities are
inevitable if inter-band interactions are present. Using a perturbative
renormalization group analysis up to the one-loop level, we find different
competing ordered ground states, including ferromagnetism, superconductivity,
spin and charge density wave states with ordering vector
, and excitonic insulator states. In
addition, two states with valley symmetry breaking are found in the excitonic
insulating and ferromagnetic phases. This analysis strongly suggests that the
ground state of bilayer graphene should be gapped, and with the exception of
superconductivity, all other possible ground states are insulating.Comment: 17 pages, 6 figures, 2 Tables, Added reference
Field-induced charge transport at the surface of pentacene single crystals: a method to study charge dynamics of 2D electron systems in organic crystals
A method has been developed to inject mobile charges at the surface of
organic molecular crystals, and the DC transport of field-induced holes has
been measured at the surface of pentacene single crystals. To minimize damage
to the soft and fragile surface, the crystals are attached to a pre-fabricated
substrate which incorporates a gate dielectric (SiO_2) and four probe pads. The
surface mobility of the pentacene crystals ranges from 0.1 to 0.5 cm^2/Vs and
is nearly temperature-independent above ~150 K, while it becomes thermally
activated at lower temperatures when the induced charges become localized.
Ruling out the influence of electric contacts and crystal grain boundaries, the
results contribute to the microscopic understanding of trapping and detrapping
mechanisms in organic molecular crystals.Comment: 14 pages, 4 figures. Submitted to J. Appl. Phy
Neutrino magnetohydrodynamics
A new neutrino magnetohydrodynamics (NMHD) model is formulated, where the
effects of the charged weak current on the electron-ion magnetohydrodynamic
fluid are taken into account. The model incorporates in a systematic way the
role of the Fermi neutrino weak force in magnetized plasmas. A fast
neutrino-driven short wavelengths instability associated with the magnetosonic
wave is derived. Such an instability should play a central role in strongly
magnetized plasma as occurs in supernovae, where dense neutrino beams also
exist. In addition, in the case of nonlinear or high frequency waves, the
neutrino coupling is shown to be responsible for breaking the frozen-in
magnetic field lines condition even in infinite conductivity plasmas.
Simplified and ideal NMHD assumptions were adopted and analyzed in detail
Chiral density waves in quark matter within the Nambu--Jona-Lasinio model in an external magnetic field
A possibility of formation of static dual scalar and pseudoscalar density
wave condensates in dense quark matter is considered for the
Nambu--Jona-Lasinio model in an external magnetic field. Within a mean-field
approximation, the effective potential of the theory is obtained and its minima
are numerically studied; a phase diagram of the system is constructed. It is
shown that the presence of a magnetic field favors the formation of spatially
inhomogeneous condensate configurations at low temperatures and arbitrary
non-zero values of the chemical potential.Comment: 13 pages, 4 figure
Entanglement, fidelity and topological entropy in a quantum phase transition to topological order
We present a numerical study of a quantum phase transition from a
spin-polarized to a topologically ordered phase in a system of spin-1/2
particles on a torus. We demonstrate that this non-symmetry-breaking
topological quantum phase transition (TOQPT) is of second order. The transition
is analyzed via the ground state energy and fidelity, block entanglement,
Wilson loops, and the recently proposed topological entropy. Only the
topological entropy distinguishes the TOQPT from a standard QPT, and
remarkably, does so already for small system sizes. Thus the topological
entropy serves as a proper order parameter. We demonstrate that our conclusions
are robust under the addition of random perturbations, not only in the
topological phase, but also in the spin polarized phase and even at the
critical point.Comment: replaced with published versio
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