91 research outputs found
Five-loop renormalization-group expansions for the three-dimensional n-vector cubic model and critical exponents for impure Ising systems
The renormalization-group (RG) functions for the three-dimensional n-vector
cubic model are calculated in the five-loop approximation. High-precision
numerical estimates for the asymptotic critical exponents of the
three-dimensional impure Ising systems are extracted from the five-loop RG
series by means of the Pade-Borel-Leroy resummation under n = 0. These
exponents are found to be: \gamma = 1.325 +/- 0.003, \eta = 0.025 +/- 0.01, \nu
= 0.671 +/- 0.005, \alpha = - 0.0125 +/- 0.008, \beta = 0.344 +/- 0.006. For
the correction-to-scaling exponent, the less accurate estimate \omega = 0.32
+/- 0.06 is obtained.Comment: 11 pages, LaTeX, no figures, published versio
Orbital effect of in-plane magnetic field on quantum transport in chaotic lateral dots
We show how the in-plane magnetic field, which breaks time-reversal and
rotational symmetries of the orbital motion of electrons in a heterostructure
due to the momentum-dependent inter-subband mixing, affects weak localisation
correction to conductance of a large-area chaotic lateral quantum dot and
parameteric dependences of universal conductance fluctuations in it.Comment: 4 pages with a figur
Scaling critical behavior of superconductors at zero magnetic field
We consider the scaling behavior in the critical domain of superconductors at
zero external magnetic field. The first part of the paper is concerned with the
Ginzburg-Landau model in the zero magnetic field Meissner phase. We discuss the
scaling behavior of the superfluid density and we give an alternative proof of
Josephson's relation for a charged superfluid. This proof is obtained as a
consequence of an exact renormalization group equation for the photon mass. We
obtain Josephson's relation directly in the form , that
is, we do not need to assume that the hyperscaling relation holds. Next, we
give an interpretation of a recent experiment performed in thin films of
. We argue that the measured mean field like
behavior of the penetration depth exponent is possibly associated with a
non-trivial critical behavior and we predict the exponents and
for the correlation lenght and specific heat, respectively. In the
second part of the paper we discuss the scaling behavior in the continuum dual
Ginzburg-Landau model. After reviewing lattice duality in the Ginzburg-Landau
model, we discuss the continuum dual version by considering a family of
scalings characterized by a parameter introduced such that
, where is the bare mass of the magnetic
induction field. We discuss the difficulties in identifying the renormalized
magnetic induction mass with the photon mass. We show that the only way to have
a critical regime with is having , that
is, with having the scaling behavior of the renormalized photon mass.Comment: RevTex, 15 pages, no figures; the subsection III-C has been removed
due to a mistak
Critical behavior of the two-dimensional N-component Landau-Ginzburg Hamiltonian with cubic anisotropy
We study the two-dimensional N-component Landau-Ginzburg Hamiltonian with
cubic anisotropy. We compute and analyze the fixed-dimension perturbative
expansion of the renormalization-group functions to four loops. The relations
of these models with N-color Ashkin-Teller models, discrete cubic models,
planar model with fourth order anisotropy, and structural phase transition in
adsorbed monolayers are discussed. Our results for N=2 (XY model with cubic
anisotropy) are compatible with the existence of a line of fixed points joining
the Ising and the O(2) fixed points. Along this line the exponent has
the constant value 1/4, while the exponent runs in a continuous and
monotonic way from 1 to (from Ising to O(2)). For N\geq 3 we find a
cubic fixed point in the region , which is marginally stable or
unstable according to the sign of the perturbation. For the physical relevant
case of N=3 we find the exponents and at the cubic
transition.Comment: 14 pages, 9 figure
Critical behavior of magnetic systems with extended impurities in general dimensions
We investigate the critical properties of d-dimensional magnetic systems with
quenched extended defects, correlated in
dimensions (which can be considered as the dimensionality of the
defects) and randomly distributed in the remaining dimensions;
both in the case of fixed dimension d=3 and when the space dimension
continuously changes from the lower critical dimension to the upper one. The
renormalization group calculations are performed in the minimal subtraction
scheme. We analyze the two-loop renormalization group functions for different
fixed values of the parameters . To this end, we apply the
Chisholm-Borel resummation technique and report the numerical values of the
critical exponents for the universality class of this system.Comment: 8 figures. To appear in Phys. Rev.
Anomalous dimensions and phase transitions in superconductors
The anomalous scaling in the Ginzburg-Landau model for the superconducting
phase transition is studied. It is argued that the negative sign of the
exponent is a consequence of a special singular behavior in momentum space. The
negative sign of comes from the divergence of the critical correlation
function at finite distances. This behavior implies the existence of a Lifshitz
point in the phase diagram. The anomalous scaling of the vector potential is
also discussed. It is shown that the anomalous dimension of the vector
potential has important consequences for the critical dynamics in
superconductors. The frequency-dependent conductivity is shown to obey the
scaling . The prediction is
obtained from existing Monte Carlo data.Comment: RevTex, 20 pages, no figures; small changes; version accepted in PR
New methodology for describing the equilibrium beach profile applied ti teh Valencia's beachs
[EN] Nuevo metodo de determinación de la profundidad de cierre del prfil de playa y su aplicación para ajustar el volumen de arenas de aportación en alimentaciones artificialesAragones, L.; Serra Peris, JC.; Villacampa, Y.; Saval, JM.; Tinoco, H. (2016). New methodology for describing the equilibrium beach profile applied ti teh Valencia's beachs. Geomorphology. 259:1-11. doi:10.1016/j.geomorph.2015.06.049S11125
Evolução quaternária, distribuição de partículas nos solos e ambientes de sedimentação em manguezais do estado de São Paulo
RELATIONSHIPS BETWEEN SHALE CONTENT AND GRAIN-SIZE PARAMETERS IN THE SAFANIYA SANDSTONE RESERVOIR, NE SAUDI ARABIA
The grain-size distribution of a sediment is controlled by the hydrodynamics of the depositional environment. There is a relationship between the petrophysical properties of a reservoir rock, such as porosity and permeability, and the grain-sie distribution. Therefore, the grain-size distribution is important in interpreting both the depositional environment and the petrophysical properties of a sedimentary rock. Determination of the grain-size parameters from gamma-ray and/or other shale-indicator well logs may be possible if the necessary correlations are established
Automated early detection of diabetic retinopathy
Purpose To compare the performance of automated diabetic retinopathy (DR) detection, using the algorithm that won the 2009 Retinopathy Online Challenge Competition in 2009, the Challenge2009, against that of the one currently used in EyeCheck, a large computer-aided early DR detection project. Design Evaluation of diagnostic test or technology. Participants Fundus photographic sets, consisting of 2 fundus images from each eye, were evaluated from 16 670 patient visits of 16 670 people with diabetes who had not previously been diagnosed with DR. Methods The fundus photographic set from each visit was analyzed by a single retinal expert; 793 of the 16 670 sets were classified as containing more than minimal DR (threshold for referral). The outcomes of the 2 algorithmic detectors were applied separately to the dataset and were compared by standard statistical measures. Main Outcome Measures The area under the receiver operating characteristic curve (AUC), a measure of the sensitivity and specificity of DR detection. Results Agreement was high, and examination results indicating more than minimal DR were detected with an AUC of 0.839 by the EyeCheck algorithm and an AUC of 0.821 for the Challenge2009 algorithm, a statistically nonsignificant difference (z-score, 1.91). If either of the algorithms detected DR in combination, the AUC for detection was 0.86, the same as the theoretically expected maximum. At 90% sensitivity, the specificity of the EyeCheck algorithm was 47.7% and that of the Challenge2009 algorithm was 43.6%. Conclusions Diabetic retinopathy detection algorithms seem to be maturing, and further improvements in detection performance cannot be differentiated from best clinical practices, because the performance of competitive algorithm development now has reached the human intrareader variability limit. Additional validation studies on larger, well-defined, but more diverse populations of patients with diabetes are needed urgently, anticipating cost-effective early detection of DR in millions of people with diabetes to triage those patients who need further care at a time when they have early rather than advanced DR. Financial Disclosure(s) Proprietary or commercial disclosure may be found after the references
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