2,024 research outputs found
Stability of the Bragg glass phase in a layered geometry
We study the stability of the dislocation-free Bragg glass phase in a layered
geometry consisting of coupled parallel planes of d=1+1 vortex lines lying
within each plane, in the presence of impurity disorder. Using renormalization
group, replica variational calculations and physical arguments we show that at
temperatures the 3D Bragg glass phase is always stable for weak
disorder. It undergoes a weakly first order transition into a decoupled 2D
vortex glass upon increase of disorder.Comment: RevTeX. Submitted to EP
Cross-Over between universality classes in a magnetically disordered metallic wire
In this article we present numerical results of conduction in a disordered
quasi-1D wire in the possible presence of magnetic impurities. Our analysis
leads us to the study of universal properties in different conduction regimes
such as the localized and metallic ones. In particular, we analyse the
cross-over between universality classes occurring when the strength of magnetic
disorder is increased. For this purpose, we use a numerical Landauer approach,
and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27
pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427
No quasi-long-range order in strongly disordered vortex glasses: a rigorous proof
The paper contains a rigorous proof of the absence of quasi-long-range order
in the random-field O(N) model for strong disorder in the space of an arbitrary
dimensionality. This result implies that quasi-long-range order inherent to the
Bragg glass phase of the vortex system in disordered superconductors is absent
as the disorder or external magnetic field is strong.Comment: 3 pages, Revte
Non-Universal Quasi-Long Range Order in the Glassy Phase of Impure Superconductors
The structural correlation functions of a weakly disordered Abrikosov lattice
are calculated for the first time in a systematic RG-expansion in d=4-\epsilon
dimensions. It is shown, that in the asymptotic limit the Abrikosov lattice
exhibits still quasi long range translational order described by a
non-universal exponent \bar\eta_{\bf G} which depends on the ratio of the
renormalized elastic constants \kappa =\tilde c_{66}/\tilde c_{11} of the flux
line (FL) lattice. Our calculations show clearly three distinct scaling regimes
corresponding to the Larkin, the manifold and the asymptotic Bragg glass
regime. On a wide range of intermediate length scales the FL displacement
correlation function increases as a power law with twice of the manifold
roughness exponent \zeta_{rm}(\kappa), which is also non-universal. Our
results, in particular the \kappa-dependence of the exponents, are in variance
with those of the variational treatment with replica symmetry breaking which
allows in principle an experimental discrimination between the two approaches.Comment: 4 pages, 3 figure
Glass phases of flux lattices in layered superconductors
We study a flux lattice which is parallel to superconducting layers, allowing
for dislocations and for disorder of both short wavelength and long wavelength.
We find that the long wavelength disorder has a significant effect on the phase
diagram -- it produces a first order transition within the Bragg glass phase
and leads to melting at strong disorder. This then allows a Friedel scenario of
2D superconductivity.Comment: 5 pages, 1 eps figure, Revte
Continuous atom laser with Bose-Einstein condensates involving three-body interactions
We demonstrate, through numerical simulations, the emission of a coherent
continuous matter wave of constant amplitude from a Bose-Einstein Condensate in
a shallow optical dipole trap. The process is achieved by spatial control of
the variations of the scattering length along the trapping axis, including
elastic three body interactions due to dipole interactions. In our approach,
the outcoupling mechanism are atomic interactions and thus, the trap remains
unaltered. We calculate analytically the parameters for the experimental
implementation of this CW atom laser.Comment: 11 pages, 4 figure
Absence of Two-Dimensional Bragg Glasses
The stability to dislocations of the elastic phase, or ``Bragg glass'', of a
randomly pinned elastic medium in two dimensions is studied using the
minimum-cost-flow algorithm for a disordered fully-packed loop model. The
elastic phase is found to be unstable to dislocations due to the quenched
disorder. The energetics of dislocations are discussed within the framework of
renormalization group predictions as well as in terms of a domain wall picture.Comment: 5 pages, REVTEX, 3 figures included. Further information can be
obtained from [email protected]
Domain regime in two-dimensional disordered vortex matter
A detailed numerical study of the real space configuration of vortices in
disordered superconductors using 2D London-Langevin model is presented. The
magnetic field is varied between 0 and for various pinning
strengths . For weak pinning, an inhomogeneous disordered vortex matter
is observed, in which the topologically ordered vortex lattice survives in
large domains. The majority of the dislocations in this state are confined to
the grain boundaries/domain walls. Such quasi-ordered configurations are
observed in the intermediate fields, and we refer it as the domain regime (DR).
The DR is distinct from the low-field and the high-fields amorphous regimes
which are characterized by a homogeneous distribution of defects over the
entire system. Analysis of the real space configuration suggests domain wall
roughening as a possible mechanism for the crossover from the DR to the
high-field amorphous regime. The DR also shows a sharp crossover to the high
temperature vortex liquid phase. The domain size distribution and the roughness
exponent of the lattice in the DR are also calculated. The results are compared
with some of the recent Bitter decoration experiments.Comment: 9 pages, 9 figure
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Spherical correlation as a similarity measure for 3D radiation patterns of musical instruments
This work is part of an artistic-research residency where composer Aaron Einbond seeks to apply audio descriptor analysis and corpus-based synthesis techniques to the spatial manipulation of instrumental radiation patterns for projection with a compact spherical loudspeaker array. Starting from a database of 3D directivity patterns of orchestral instruments, measured with spherical microphone arrays in anechoic conditions, we wish to derive spatial descriptors in order to classify the corpus. This paper investigates the use of spherical cross-correlation as a similarity measure between radiation patterns. Considering two directivity patterns f and g as bandlimited, square integrable functions on the 2-sphere, their correlation can be computed from their spherical harmonic spectra via a spatial inverse discrete Fourier transform. The magnitudes of these Fourier coefficients provide a rotation-invariant representation of the functions on the sphere. One can therefore search for the transformation matrix m, in the 3D rotation group SO(3), which maximizes the cross-correlation, i.e. which offers the optimal spherical shape matching between f and g. The mathematical foundations of these tools are well established in the literature ; however, their practical use in the field of acoustics remains limited and challenging. In this study, we apply these techniques to both simulated and measured radiation data, attempting to answer a number of practical questions : How does the similarity measure behave when f and g are not rotated cousins ? How can we adapt the cross-correlation formalism established for complex-valued harmonics to real-valued harmonics, as the latter are predominantly used in the field of Ambisonics ? Can we compute the correlation of spherical spectra of different bandwidths ? What is the impact of the finite sampling distribution used for integration on the SO(3) space? How do we normalize the cross-correlation function ? And most importantly, is the cross-correlation an efficient measure for the classification of 3D radiation patterns
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