817 research outputs found
Bosonization on the lattice: the emergence of the higher harmonics
A general and transparent procedure to bosonize fermions placed on a lattice
is presented. Harmonics higher than are shown to appear in the
one-paticle Green function, due to the compact character of real electron
bands. Quantitative estimations of the role of these higher harmonics are made
possible by the bosonization technique presented here.Comment: Pages: 15 (REVTEX 3.0) plus 4 postscript figures appended at the end
of the tex
Stripe Ansatzs from Exactly Solved Models
Using the Boltzmann weights of classical Statistical Mechanics vertex models
we define a new class of Tensor Product Ansatzs for 2D quantum lattice systems,
characterized by a strong anisotropy, which gives rise to stripe like
structures. In the case of the six vertex model we compute exactly, in the
thermodynamic limit, the norm of the ansatz and other observables. Employing
this ansatz we study the phase diagram of a Hamiltonian given by the sum of XXZ
Hamiltonians along the legs coupled by an Ising term. Finally, we suggest a
connection between the six and eight-vertex Anisotropic Tensor Product Ansatzs,
and their associated Hamiltonians, with the smectic stripe phases recently
discussed in the literature.Comment: REVTEX4.b4 file, 10 pages, 2 ps Figures. Revised version to appear in
PR
Efecto de las altas presiones hidrostáticas y el tratamiento térmico tradicional en las características físicoquímicas, microbiológicas y análisis sensorial de una mermelada de aceituna
In the present work the effect of the processing by high hydrostatic pressures (HPP) was assessed as an alternative to the thermal treatment of pasteurization in olive jam. The effects of both treatments on the product after processing were compared and stability during storage under refrigeration was assessed through the characterization of physicochemical, microbiological and sensory aspects. To assess the effect of processing, two HPP treatments (450 and 600MPa) and thermal pasteurization (80 °C for 20 min) were applied, comparing them with the unprocessed product. HPP 600MPa versus the rest of treatments showed a reduction in microorganisms, greater clarity and less browning, and sensory acceptance. The shelf-life of the refrigerated product would indicate the feasibility of the application of the HPP technology for food with similar shelf-life to that obtained with the traditional treatment of pasteurization, but with a better sensory quality.En el presente trabajo se valoró el efecto del procesado por altas presiones hidrostáticas (HPP) como método alternativo al tratamiento térmico de pasteurización en la mermelada de aceitunas. Para ello se comparó el efecto de ambos tratamientos sobre el producto procesado y se evaluó su estabilidad durante el almacenamiento en refrigeración, mediante la caracterización de los aspectos físico-químicos, microbiológicos, y sensoriales. Para evaluar el efecto del procesado, se aplicaron dos tratamientos de HPP (450 y 600MPa) y otro de pasteurización térmica (80 °C durante 20 min), comparándose con el producto no procesado. Las muestras tratadas con HPP 600MPa presentaron, frente al resto de tratamientos una reducción en la presencia de microorganismos, mayor claridad y menor pardeamiento, y una mayor aceptación sensorial. El estudio de la vida útil del producto en refrigeración, indicaría la viabilidad de la aplicación de la tecnología de HPP para obtener alimentos con vida útil similar a la obtenida con el tratamiento tradicional de pasteurización, pero con mejor calidad sensorial
Density Matrix and Renormalization for Classical Lattice Models
We review the variational principle in the density matrix renormalization
group (DMRG) method, which maximizes an approximate partition function within a
restricted degrees of freedom; at zero temperature, DMRG mini- mizes the ground
state energy. The variational principle is applied to two-dimensional (2D)
classical lattice models, where the density matrix is expressed as a product of
corner transfer matrices. (CTMs) DMRG related fields and future directions of
DMRG are briefly discussed.Comment: 21 pages, Latex, 14 figures in postscript files, Proc. of the 1996 El
Escorial Summer School on "Strongly Correlated Magnetic and Superconducting
Systems
Interactions, star formation and extended nebulae in SDSS type 2 quasars at 0.3<~ z <~ 0.6
We present long-slit spectroscopy and imaging data obtained with FORS2 on the
Very Large Telescope of 13 optically selected type 2 quasars at z~0.3-0.6 from
the original sample of Zakamska et al. (2003). The sample is likely to be
affected by different selection biases. We investigate the evidence for: a)
mergers/interactions b) star formation activity in the neighborhood of the
quasars and c) extended emission line regions and their nature. Evidence for
mergers/interactions is found in 5/13 objects. This is a lower limit for our
sample, given the shallowness of most of our continuum images. Although AGN
photoionization cannot be totally discarded, line ratios consistent with
stellar photoionization are found in general in companion galaxies/knots/nuclei
near these same objects. On the contrary, the gas in the neighborhood of the
quasar nucleus shows line ratios inconsistent with HII galaxies and typical of
AGN photoionized nebulae. A natural scenario to explain the observations is
that star formation is ongoing in companion galaxies/knots/nuclei, possibly
triggered by the interactions. These systems are, therefore, composite in their
emission line properties showing a combination of AGN and star formation
features.
Extended emission line regions (EELRs) have been found in 7/13 objects,
although this fraction might be higher if a complete spatial coverage around
the quasars was performed. The sizes vary between few and up to 64 kpc. In
general, the EELRs apparently consist of an extended nebula associated with the
quasar. In at least one case the EELR is associated with ionized tidal
features.Comment: Accepted for publication in MNRAS. 19 pages, 30 figure
Diodos orgánicos emisores de luz: estrategias para la optimización de dispositivos y la obtención de un oled blanco
III Encuentro sobre Nanociencia y Nanotecnología de Investigadores y Tecnólogos Andaluce
Magnetization plateaux in dimerized spin ladder arrays
We investigate the ground state magnetization plateaux appearing in spin 1/2
two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and
dimerized zig-zag interchain couplings. Using both Abelian bosonization and
Lanczos methods we find that the system yields rather unusual plateaux and
exhibits massive and massless phases for specific choices or ``tuning'' of
exchange interactions. The relevance of this behavior in the study of
NH_4CuCl_3 is discussed.Comment: 9 pages, RevTeX, 11 postscript figure
Seguimiento del Grado en Geología (Facultad de Ciencias, Universidad de Alicante, curso 2015-16)
La Facultad de Ciencias de la Universidad de Alicante ha constituido una red de trabajo formada por los profesores coordinadores de semestre del Grado en Geología, así como por los coordinadores responsables de la titulación. Los objetivos de esta red son: Asegurar la ejecución efectiva de las enseñanzas conforme al contenido del plan de estudios del título verificado; detectar posibles deficiencias en su implementación, proponiendo recomendaciones y sugerencias de mejora; y evidenciar los progresos en el desarrollo del Sistema de Garantía Interno de Calidad (SGIC) tanto en lo relativo a la revisión de la aplicación del plan de estudios como a la propuesta de acciones para mejorar su diseño en la implantación. El método de trabajo se basa en reuniones en las que los miembros de la red plantearán y debatirán los parámetros e indicadores de seguimiento de la red. Cada coordinador llevará a cabo una investigación individualizada del semestre del que es responsable en coordinación con los miembros de su comisión. Asimismo, se participará en la elaboración de los informes de autoevaluación del título
Influence of the electric field on the latent heat of the ferroelectric phase transition in KDP
The specific heat, heat flux (DTA trace) and dielectric constant of KDP
ferroelectric crystal have been measured simultaneously for various electric
fields with a conduction calorimeter. The specific heat presents a strong
anomaly but these simultaneous measurements allow us to evaluate the latent
heat accurately. Latent heat decreases with field and the value of critical
electric field --that where latent heat disappears-- is estimated to be
(0.44\pm0.03) kV/cm. Incidentally, we have measured simultaneously the
dielectric permittivity which suggests that latent heat is developed as domains
are growing.Comment: 7 pages, 6 figures, ReVTeX, twocolumn format, to appear in J. Phys.
Cond. Matte
- …