1,656 research outputs found
Correlation amplitude and entanglement entropy in random spin chains
Using strong-disorder renormalization group, numerical exact diagonalization,
and quantum Monte Carlo methods, we revisit the random antiferromagnetic XXZ
spin-1/2 chain focusing on the long-length and ground-state behavior of the
average time-independent spin-spin correlation function C(l)=\upsilon
l^{-\eta}. In addition to the well-known universal (disorder-independent)
power-law exponent \eta=2, we find interesting universal features displayed by
the prefactor \upsilon=\upsilon_o/3, if l is odd, and \upsilon=\upsilon_e/3,
otherwise. Although \upsilon_o and \upsilon_e are nonuniversal (disorder
dependent) and distinct in magnitude, the combination \upsilon_o + \upsilon_e =
-1/4 is universal if C is computed along the symmetric (longitudinal) axis. The
origin of the nonuniversalities of the prefactors is discussed in the
renormalization-group framework where a solvable toy model is considered.
Moreover, we relate the average correlation function with the average
entanglement entropy, whose amplitude has been recently shown to be universal.
The nonuniversalities of the prefactors are shown to contribute only to surface
terms of the entropy. Finally, we discuss the experimental relevance of our
results by computing the structure factor whose scaling properties,
interestingly, depend on the correlation prefactors.Comment: v1: 16 pages, 15 figures; v2: 17 pages, improved discussions and
statistics, references added, published versio
Gravity-driven instability in a spherical Hele-Shaw cell
A pair of concentric spheres separated by a small gap form a spherical
Hele-Shaw cell. In this cell an interfacial instability arises when two
immiscible fluids flow. We derive the equation of motion for the interface
perturbation amplitudes, including both pressure and gravity drivings, using a
mode coupling approach. Linear stability analysis shows that mode growth rates
depend upon interface perimeter and gravitational force. Mode coupling analysis
reveals the formation of fingering structures presenting a tendency toward
finger tip-sharpening.Comment: 13 pages, 4 ps figures, RevTex, to appear in Physical Review
Stability analysis of polarized domains
Polarized ferrofluids, lipid monolayers and magnetic bubbles form domains
with deformable boundaries. Stability analysis of these domains depends on a
family of nontrivial integrals. We present a closed form evaluation of these
integrals as a combination of Legendre functions. This result allows exact and
explicit formulae for stability thresholds and growth rates of individual
modes. We also evaluate asymptotic behavior in several interesting limits.Comment: 12 pages, 3 figures, Late
Biot-Savart-like law in electrostatics
The Biot-Savart law is a well-known and powerful theoretical tool used to
calculate magnetic fields due to currents in magnetostatics. We extend the
range of applicability and the formal structure of the Biot-Savart law to
electrostatics by deriving a Biot-Savart-like law suitable for calculating
electric fields. We show that, under certain circumstances, the traditional
Dirichlet problem can be mapped onto a much simpler Biot-Savart-like problem.
We find an integral expression for the electric field due to an arbitrarily
shaped, planar region kept at a fixed electric potential, in an otherwise
grounded plane. As a by-product we present a very simple formula to compute the
field produced in the plane defined by such a region. We illustrate the
usefulness of our approach by calculating the electric field produced by planar
regions of a few nontrivial shapes.Comment: 14 pages, 6 figures, RevTex, accepted for publication in the European
Journal of Physic
Rotating Hele-Shaw cells with ferrofluids
We investigate the flow of two immiscible, viscous fluids in a rotating
Hele-Shaw cell, when one of the fluids is a ferrofluid and an external magnetic
field is applied. The interplay between centrifugal and magnetic forces in
determining the instability of the fluid-fluid interface is analyzed. The
linear stability analysis of the problem shows that a non-uniform, azimuthal
magnetic field, applied tangential to the cell, tends to stabilize the
interface. We verify that maximum growth rate selection of initial patterns is
influenced by the applied field, which tends to decrease the number of
interface ripples. We contrast these results with the situation in which a
uniform magnetic field is applied normally to the plane defined by the rotating
Hele-Shaw cell.Comment: 12 pages, 3 ps figures, RevTe
Radiales time series: 25 years building monitoring and analytical capacities in the Iberian shelf
The RADIALES program has been monitoring shelf waters in Spain for the last 25 years. This is the oldest field program for multidisciplinary marine research addressing long term variability issues at ecosystem level. Core observations include ship-based hydrographic, biogeochemical and plankton observations at monthly frequency in several oceanographic sections along the Iberian shelf. These observations are complemented with buoy and satellite observations and all these data are used to validate hydrographic and ecological models of plankton at local and regional scales. From the first series initiated in the northwestern shelf other programs extended the observations to the Mediterranean and off shelf waters using the same approach. The success of RADIALES extends beyond pure scientific knowledge, as the expertise gathered with the program has been applied to solve multiple environmental issues, from fisheries and pollution to global change. The program is also instrumental for educational purposes, allowing the specialization of students and technicians. Thanks to a basal funding provided by the Instituto Español de OceanografĂa, the program currently obtains more than 60% of its annual budget from competitive calls, as it offers an unique platform for coastal research. Among the results of this program are 400 publications, including peer-review papers, 24 Thesis and 54 scientific reports. The RADIALES data are freely distributed to national and international users as a contribution to the development of cost-effective ocean research and marine servicesIEO (RADIALES
The Saffman-Taylor problem on a sphere
The Saffman-Taylor problem addresses the morphological instability of an
interface separating two immiscible, viscous fluids when they move in a narrow
gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend
the classic Saffman-Taylor situation, by considering the flow between two
curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We
derive the mode-coupling differential equation for the interface perturbation
amplitudes and study both linear and nonlinear flow regimes. The effect of the
spherical cell (positive) spatial curvature on the shape of the interfacial
patterns is investigated. We show that stability properties of the fluid-fluid
interface are sensitive to the curvature of the surface. In particular, it is
found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw
flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.
Regio- and stereo-selectivity in the intramolecular quenching of the excited benzoylthiophene chromophore by tryptophan
Laser flash photolysis studies on the photobehaviour of a series of bichromophoric derivatives bearing benzoylthiophene and tryptophan groups have shown that the efficiency of the intramolecular quenching process depends on both the stereochemistry of the chiral centers and the relative ketone versus tryptophan orientation.Perez Prieto, Julia, [email protected]
Neighborhood properties of complex networks
A concept of neighborhood in complex networks is addressed based on the
criterion of the minimal number os steps to reach other vertices. This amounts
to, starting from a given network , generating a family of networks
such that, the vertices that are steps apart in
the original , are only 1 step apart in . The higher order
networks are generated using Boolean operations among the adjacency matrices
that represent . The families originated by the well known
linear and the Erd\"os-Renyi networks are found to be invariant, in the sense
that the spectra of are the same, up to finite size effects. A further
family originated from small world network is identified
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