2,889 research outputs found
Dimerized ground states in spin-S frustrated systems
We study a family of frustrated anti-ferromagnetic spin- systems with a
fully dimerized ground state. This state can be exactly obtained without the
need to include any additional three-body interaction in the model. The
simplest members of the family can be used as a building block to generate more
complex geometries like spin tubes with a fully dimerized ground state. After
present some numerical results about the phase diagram of these systems, we
show that the ground state is robust against the inclusion of weak disorder in
the couplings as well as several kinds of perturbations, allowing to study some
other interesting models as a perturbative expansion of the exact one. A
discussion on how to determine the dimerization region in terms of quantum
information estimators is also presented. Finally, we explore the relation of
these results with a the case of the a 4-leg spin tube which recently was
proposed as the model for the description of the compound
CuClDCSO, delimiting the region of the parameter space
where this model presents dimerization in its ground state.Comment: 10 pages, 9 figure
Phase diagram study of a dimerized spin-S zig-zag ladder
The phase diagram of a frustrated spin- zig-zag ladder is studied through
different numerical and analytical methods. We show that for arbitrary ,
there is a family of Hamiltonians for which a fully-dimerized state is an exact
ground state, being the Majumdar-Ghosh point a particular member of the family.
We show that the system presents a transition between a dimerized phase to a
N\'eel-like phase for , and spiral phases can appear for large . The
phase diagram is characterized by means of a generalization of the usual Mean
Field Approximation (MFA). The novelty in the present implementation is to
consider the strongest coupled sites as the unit cell. The gap and the
excitation spectrum is analyzed through the Random Phase Approximation (RPA).
Also, a perturbative treatment to obtain the critical points is discussed.
Comparisons of the results with numerical methods like DMRG are also presented.Comment: 14 pages, 6 figures. Some typos were corrected, and notation was
clarifie
Construction and evaluation of classifiers for forensic document analysis
In this study we illustrate a statistical approach to questioned document
examination. Specifically, we consider the construction of three classifiers
that predict the writer of a sample document based on categorical data. To
evaluate these classifiers, we use a data set with a large number of writers
and a small number of writing samples per writer. Since the resulting
classifiers were found to have near perfect accuracy using leave-one-out
cross-validation, we propose a novel Bayesian-based cross-validation method for
evaluating the classifiers.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS379 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states
We demonstrate the first experimental violation of a spin-1 Bell inequality.
The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and
Holt formalism. For entangled spin-1 particles the maximum quantum mechanical
prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden
variables. We obtained an experimental value of 2.27 using the
four-photon state generated by pulsed, type-II, stimulated parametric
down-conversion. This is a violation of the spin-1 Bell inequality by more than
13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve
Generalized Pomeranchuk instabilities in graphene
We study the presence of Pomeranchuk instabilities induced by interactions on
a Fermi liquid description of a graphene layer. Using a recently developed
generalization of Pomeranchuk method we present a phase diagram in the space of
fillings versus on-site and nearest neighbors interactions. Interestingly, we
find that for both interactions being repulsive an instability region exists
near the Van Hove filling, in agreement with earlier theoretical work. In
contrast, near half filling, the Fermi liquid behavior appears to be stable, in
agreement with theoretical results and experimental findings using ARPES. The
method allows for a description of the complete phase diagram for arbitrary
filling.Comment: 9 pages, 3 figure
Anharmonic effects in magnetoelastic chains
We describe a new mechanism leading to the formation of rational
magnetization plateau phases, which is mainly due to the anharmonic spin-phonon
coupling. This anharmonicity produces plateaux in the magnetization curve at
unexpected values of the magnetization without explicit magnetic frustration in
the Hamiltonian and without an explicit breaking of the translational symmetry.
These plateau phases are accompanied by magneto-elastic deformations which are
not present in the harmonic case.Comment: 5 pages, 3 figure
Desempenho de genótipos de arroz irrigado em Mato Grosso do Sul.
bitstream/item/65825/1/COT87-2004.pd
Numerical Analysis of Twin Tunnels Lining under Different Seismic Conditions
A large part of this research was done within the Continuum Mechanics and
Structural Analysis Department, Carlos III University of Madrid, Spain, in the framework of Erasmus
grant mobility of 6 months. The authors appreciate the grant from the Erasmus plus Program.The last seismic events showed that tunnel lining may suffer extensive damage. Employing
numerical modeling has a great importance in predicting the seismic performance of tunnels. This
paper tests the tunnel lining of the Zaouit Ait Mellal (ZAM) twin tunnels located between the cities
of Marrakesh and Agadir in Morocco. Dynamic analysis was adopted by FLAC 2D software using
the finite-difference elements. Four soil cross-sections were chosen, with different support devices
installed along the twin tunnels, such as rock bolts and steel ribs. The seismic signals introduced as
input were obtained from three different earthquakes: Al Hoceima 2004 in Morocco, EL Centro 1940
in the USA, and Kobe 1995 in Japan. The numerical results show that the deformation of the tunnel
lining is more noteworthy in the sections using steel ribs compared to those using rock bolts, which
is observed by the large values of relative displacement, reaching 1020 (mm) and 2.29 x 105 (N.m/m)
of maximum bending moment. The analysis indicates that these sections present higher vulnerability
during an earthquake, which should be considered when looking at the overall safety of the tunnel.Erasmus plus Progra
MT-InSAR and Dam Modeling for the Comprehensive Monitoring of an Earth-Fill Dam: The Case of the BenÃnar Dam (AlmerÃa, Spain)
The BenÃnar Dam, located in Southeastern Spain, is an earth-fill dam that has experienced filtration issues since its construction in 1985. Despite the installation of various monitoring systems, the data collected are sparse and inadequate for the dam’s lifetime. The present research integrates Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) and dam modeling to validate the monitoring of this dam, opening the way to enhanced integrated monitoring systems. MT-InSAR was proved to be a reliable and continuous monitoring system for dam deformation, surpassing previously installed systems in terms of precision. MT-InSAR allowed the almost-continuous monitoring of this dam since 1992, combining ERS, Envisat, and Sentinel-1A/B data. Line-of-sight (LOS) velocities of settlement in the crest of the dam evolved from maximums of −6 mm/year (1992–2000), −4 mm/year (2002–2010), and −2 mm/year (2015–2021) with median values of −2.6 and −3.0 mm/year in the first periods (ERS and Envisat) and −1.3 mm/year in the Sentinel 1-A/B period. These results are consistent with the maximum admissible modeled deformation from construction, confirming that settlement was more intense in the dam’s early stages and decreased over time. MT-InSAR was also used to integrate the monitoring of the dam basin, including critical slopes, quarries, and infrastructures, such as roads, tracks, and spillways. This study allows us to conclude that MT-InSAR and dam modeling are important elements for the integrated monitoring systems of embankment dams. This conclusion supports the complete integration of MT-InSAR and 3D modeling into the monitoring systems of embankment dams, as they are a key complement to traditional geotechnical monitoring and can overcome the main limitations of topographical monitoringReMoDams project ESP2017-89344-R
(AEI/FEDER, UE) from the Spanish Ministry of Economy, Industry and CompetitivenessSIAGUA
project PID2021-128123OB-C21PID2021-128123OB-C22MCIN/AEI/10.13039/
501100011033/FEDER,UEPOAIUJA-2023/2024CEACTEMA from University of Jaén (Spain)RNM-282 research group from the Junta de AndalucÃa (Spain
- …