1,554 research outputs found
Aspectos biotecnológicos generales del cultivo de peces marinos de interés comercial
Abstract not availabl
Phase diagram of an extended Agassi model
Background: The Agassi model is an extension of the Lipkin-Meshkov-Glick
model that incorporates the pairing interaction. It is a schematic model that
describes the interplay between particle-hole and pair correlations. It was
proposed in the 1960's by D. Agassi as a model to simulate the properties of
the quadrupole plus pairing model.
Purpose: The aim of this work is to extend a previous study by Davis and
Heiss generalizing the Agassi model and analyze in detail the phase diagram of
the model as well as the different regions with coexistence of several phases.
Method: We solve the model Hamiltonian through the Hartree-Fock-Bogoliubov
(HFB) approximation, introducing two variational parameters that play the role
of order parameters. We also compare the HFB calculations with the exact ones.
Results: We obtain the phase diagram of the model and classify the order of
the different quantum phase transitions appearing in the diagram. The phase
diagram presents broad regions where several phases, up to three, coexist.
Moreover, there is also a line and a point where four and five phases are
degenerated, respectively.
Conclusions: The phase diagram of the extended Agassi model presents a rich
variety of phases. Phase coexistence is present in extended areas of the
parameter space. The model could be an important tool for benchmarking novel
many-body approximations.Comment: Accepted for publication in PR
An extended Agassi model: algebraic structure, phase diagram, and large size limit
The Agassi model is a schematic two-level model that involves pairing and
monopole-monopole interactions. It is, therefore, an extension of the well
known Lipkin-Meshkov-Glick (LMG) model. In this paper we review the algebraic
formulation of an extension of the Agassi model as well as its bosonic
realization through the Schwinger representation. Moreover, a mean-field
approximation for the model is presented and its phase diagram discussed.
Finally, a analysis, with proportional to the degeneracy of each
level, is worked out to obtain the thermodynamic limit of the ground state
energy and some order parameters from the exact Hamiltonian diagonalization for
finite.Comment: Accepted in Physica Scripta. Focus on SSNET 201
Quantum Phase Transitions in the Interacting Boson Model: Integrability, level repulsion and level crossing
We study the quantum phase transition mechanisms that arise in the
Interacting Boson Model. We show that the second-order nature of the phase
transition from U(5) to O(6) may be attributed to quantum integrability,
whereas all the first-order phase transitions of the model are due to level
repulsion with one singular point of level crossing. We propose a model
Hamiltonian with a true first-order phase transition for finite systems due to
level crossings.Comment: Accepted in PR
Scaling Properties of the Lipkin Model at the Critical Point
The influence of Franco Iachello in Physics during the last 50 years and, in
particular, in the use of algebraic methods applied to very different physical
problems has been broad, extense and have permeated most branches of Physics,
from Nuclear and Molecular to Particle and Condensed Matter physics. Apart of
many other contributions, at the beginning of the 2000's he introduced the
concept of critical point symmetry and triggered the study of the many faces of
quantum phase transitions in nuclei and other mesoscopic systems. In this
contribution, we present the analysis of the scaling properties of the Lipkin
model spectrum at the phase transition point and we focus on the differences
between first and second order quantum phase transitions. Moreover, we explain
how the obtained results can be also of application for the interacting boson
model.Comment: Contribution to the proceedings of the meeting Symmetries and Order:
Algebraic Methods in Many Body Systems, in honor of Prof. Francesco Iachell
Fabrication and deposition of copper and copper oxide nanoparticles by laser ablation in open air
The proximity of the “post-antibiotic era”, where infections and minor injuries could be a cause of death, there are urges to seek an alternative for the cure of infectious diseases. Copper nanoparticles and their huge potential as a bactericidal agent could be a solution. In this work, Cu and Cu oxide nanoparticles were synthesized by laser ablation in open air and in argon atmosphere using 532 and 1064 nm radiation generated by nanosecond and picosecond Nd:YVO4 lasers, respectively, to be directly deposited onto Ti substrates. Size, morphology, composition and the crystalline structure of the produced nanoparticles have been studied by the means of field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), the energy dispersive spectroscopy of X-rays (EDS), selected area electron diffraction (SAED) and X-ray diffraction (XRD). The UV-VIS absorbance of the thin layer of nanoparticles was also measured, and the antibacterial capacity of the obtained deposits tested against Staphylococcus aureus. The obtained deposits consisted of porous coatings composed of copper and copper oxide nanoparticles interconnected to form chain-like aggregates. The use of the argon atmosphere contributed to reduce significantly the formation of Cu oxide species. The synthesized and deposited nanoparticles exhibited an inhibitory effect upon S. aureus.Peer ReviewedPostprint (published version
Reproductive and nutritional management on ovarian response and embryo quality on rabbit does
Rabbit does in modern rabbitries are under intensive reproductive rhythms. Females are high milk producers with high energetic expenses due to the extensive overlap between lactation and gestation. This situation leads to a negative energy balance with a mobilization of body fat especially in primiparous rabbit does. Poor body condition and poor health status severely affect the reproductive features (fertility rate and lifespan of the doe as well as ovarian physiology). This paper reviews some reproductive and nutritional approaches used in the last years to improve the reproductive performance of rabbit females, mainly focusing on the influence on ovarian response and embryo quality and with emphasis on epigenetic modifications in pre-implantation embryos and offspring consequences
Aplicación de las tecnologías de la información a la tecnologia ictiológica: el sitio web 'www.ictioterm.es'
Aplicació de les tecnologies de la informació a la terminologia ictiològica: el lloc web www.ictioterm.es. ICTIOTERM és una base de dades que conté informació de tipus
terminològic, lingüístic i biològic sobre més de tres-centes espècies
marines de peixos, mol·luscos, crustacis i altres invertebrats.
En aquest article es descriuen amb detall els continguts del web
www.ictioterm.es, així com la seva estructura d'emmagatzematge
de la informació i les diverses opcions de cerca.Application of Information Technology to Ichthyology Terms: ww.ictioterm.es ICTIOTERM is a database containing terminological, linguistic
and biological information on more than 300 marine
species of fish, molluscs, crustaceans and other invertebrates.
In this paper, we describe the contents of the web site www.ictioterm.es, as well as its information storage structure and
search options.ICTIOTERM es una base de datos que contiene información de
tipo terminológico, lingüístico y biológico sobre más de trescientas
especies marinas de peces, moluscos, crustáceos y otros
invertebrados. En el presente trabajo, se describen de manera
pormenorizada los contenidos del web www.ictioterm.es, así
como su estructura de almacenamiento de la información y sus
diferentes opciones de búsqueda
Two-level interacting boson models beyond the mean field
The phase diagram of two-level boson Hamiltonians, including the Interacting
Boson Model (IBM), is studied beyond the standard mean field approximation
using the Holstein-Primakoff mapping. The limitations of the usual intrinsic
state (mean field) formalism concerning finite-size effects are pointed out.
The analytic results are compared to numerics obtained from exact
diagonalizations. Excitation energies and occupation numbers are studied in
different model space regions (Casten triangle for IBM) and especially at the
critical points.Comment: 14 pages, 13 figure
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