4,216 research outputs found
Melting of Charge/Orbital Ordered States in NdSrMnO: Temperature and Magnetic Field Dependent Optical Studies
We investigated the temperature ( 15 290 K) and the magnetic
field ( 0 17 T) dependent optical conductivity spectra of a
charge/orbital ordered manganite, NdSrMnO. With variation
of and , large spectral weight changes were observed up to 4.0 eV. These
spectral weight changes could be explained using the polaron picture.
Interestingly, our results suggested that some local ordered state might remain
above the charge ordering temperature, and that the charge/orbital melted state
at a high magnetic field (i.e. at 17 T and 4.2 K) should be a three
dimensional ferromagnetic metal. We also investigated the first order phase
transition from the charge/orbital ordered state to ferromagnetic metallic
state using the - and % -dependent dielectric constants . In
the charge/orbital ordered insulating state, was positive and
. With increasing and , was
increased up to the insulator-metal phase boundaries. And then,
abruptly changed into negative and , which was
consistent with typical responses of a metal. Through the analysis of using an effective medium approximation, we found that the melting
of charge/orbital ordered states should occur through the percolation of
ferromagnetic metal domains.Comment: submitted to Phys. Rev.
Miscibility in a degenerate fermionic mixture induced by linear coupling
We consider a one-dimensional mean-field-hydrodynamic model of a
two-component degenerate Fermi gas in an external trap, each component
representing a spin state of the same atom. We demonstrate that the
interconversion between them (linear coupling), imposed by a resonant
electromagnetic wave, transforms the immiscible binary gas into a miscible
state, if the coupling constant, , exceeds a critical value, . The effect is predicted in a variational approximation, and
confirmed by numerical solutions. Unlike the recently studied model of a binary
BEC with the linear coupling, the components in the immiscible phase of the
binary fermion mixture never fill two separated domains with a wall between
them, but rather form anti-locked ( -phase-shifted) density waves.
Another difference from the bosonic mixture is spontaneous breaking of symmetry
between the two components in terms of numbers of atoms in them, and
. The latter effect is characterized by the parameter (only is a conserved quantity), the
onset of miscibility at meaning a transition
to . At , features damped
oscillations as a function of . We also briefly consider an asymmetric
model, with a chemical-potential difference between the two components.Comment: 9 pages, 12 figures, PRA (in press
Can Network Analysis Techniques help to Predict Design Dependencies? An Initial Study
The degree of dependencies among the modules of a software system is a key
attribute to characterize its design structure and its ability to evolve over
time. Several design problems are often correlated with undesired dependencies
among modules. Being able to anticipate those problems is important for
developers, so they can plan early for maintenance and refactoring efforts.
However, existing tools are limited to detecting undesired dependencies once
they appeared in the system. In this work, we investigate whether module
dependencies can be predicted (before they actually appear). Since the module
structure can be regarded as a network, i.e, a dependency graph, we leverage on
network features to analyze the dynamics of such a structure. In particular, we
apply link prediction techniques for this task. We conducted an evaluation on
two Java projects across several versions, using link prediction and machine
learning techniques, and assessed their performance for identifying new
dependencies from a project version to the next one. The results, although
preliminary, show that the link prediction approach is feasible for package
dependencies. Also, this work opens opportunities for further development of
software-specific strategies for dependency prediction.Comment: Accepted at ICSA 201
Exclusive Production of Neutral Vector Mesons at the Electron-Proton Collider HERA
The first five years of operation of the multi-purpose experiments ZEUS and
H1 at the electron-proton storage ring facility HERA have opened a new era in
the study of vector-meson production in high-energy photon-proton interactions.
The high center-of-mass energy available at this unique accelerator complex
allows investigations in hitherto unexplored kinematic regions, providing
answers to long-standing questions concerning the energy-dependence of the rho,
omega, phi, and J/psi production cross sections. The excellent angular
acceptance of these detectors, combined with that of specialized tagging
detectors at small production angles, has permitted measurements of elastic and
inelastic production processes for both quasi-real photons and those of
virtuality exceeding the squared mass of the vector meson. This report provides
a quantitative picture of the present status of these studies, comparing them
to the extensive measurements in this field at lower energies and summarizing
topical developments in theoretical work motivated by the new data.Comment: This replacement serves to correct an error in Eq. 3.41. An improved
version of this review will appear in book form as Nr. 140 in the series
Springer Tracts in Modern Physics on 6.October. 90 pages including 34 figure
Geometric properties of two-dimensional coarsening with weak disorder
The domain morphology of weakly disordered ferromagnets, quenched from the
high-temperature phase to the low-temperature phase, is studied using numerical
simulations. We find that the geometrical properties of the coarsening domain
structure, e.g., the distributions of hull enclosed areas and domain perimeter
lengths, are described by a scaling phenomenology in which the growing domain
scale R(t) is the only relevant parameter. Furthermore, the scaling functions
have forms identical to those of the corresponding pure system, extending the
'super-universality' property previously noted for the pair correlation
function.Comment: 6 pages, 6 figure
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