589 research outputs found
Theoretical study of ferroelectric potassium nitrate
We present a detailed study of the structural behavior and polarization
reversal mechanism in phase III of KNO, an unusual ferroelectric material
in which the nitrate groups rotate during polarization reversal. This material
was one of several studied in a previous work [O. Di\'eguez and D. Vanderbilt,
Phys. Rev. Lett. {\bf 96}, 056401 (2006)] where methods were described for
computing curves of energy versus electric polarization. In the present work we
extend and systematize the previous first-principles calculations on KNO,
and analyze in detail a two-parameter model in which the energy of the system
is written as a low-order expansion in the polarization and the nitrate group
orientation. We confirm that this model reproduces the first-principles results
for KNO very well and construct its parameter-space phase diagram,
describing regions where unusual triple-well potentials appear. We also present
first-principles calculations of KNO under pressure, finding that its
energy-versus-polarization curves change character by developing a
first-derivative discontinuity at zero polarization.Comment: Replaced with extended versio
Geiger-Mode Avalanche Photodiodes in Particle Detection
It is well known that avalanche photodiodes operated in the Geiger mode above
the breakdown voltage offer a virtually infinite sensitivity and time accuracy
in the picosecond range that can be used for single photon detection. However,
their performance in particle detection remains still unexplored. In this
contribution, we are going to expose the different steps that we have taken in
order to prove the efficiency of Geiger mode avalanche photodiodes in the
aforementioned field. In particular, we will present an array of pixels of
1mmx1mm fabricated with a standard CMOS technology for characterization in a
test beam.Comment: 7 pages, 2 figures, Proceedings of LCWS1
First-principles predictions of low-energy phases of multiferroic BiFeO3
We used first-principles methods to perform a systematic search for
potentially-stable phases of multiferroic BiFeO3. We considered a simulation
cell compatible with the atomic distortions that are most common among
perovskite oxides, and found a large number of local minima of the energy
within 100 meV/f.u. of the ferroelectric ground state. We discuss the variety
of low-symmetry structures discovered, as well as the implications of these
findings as regards current experimental (e.g., on thin films displaying {\em
super-tetragonal} phases) and theoretical (on models for BiFeO3's structural
phase transitions) work on this compound.Comment: 14 pages, 9 figures, accepted in PRB (contains small changes in the
text with respect to the first version
First-principles study of epitaxial strain in perovskites
Using an extension of a first-principles method developed by King-Smith and
Vanderbilt [Phys. Rev. B {\bf 49}, 5828 (1994)], we investigate the effects of
in-plane epitaxial strain on the ground-state structure and polarization of
eight perovskite oxides: BaTiO, SrTiO, CaTiO, KNbO, NaNbO,
PbTiO, PbZrO, and BaZrO. In addition, we investigate the effects of
a nonzero normal stress. The results are shown to be useful in predicting the
structure and polarization of perovskite oxide thin films and superlattices.Comment: 10 page
Ab initio study of the phase diagram of epitaxial BaTiO3
Using a combination of first-principles and effective-Hamiltonian approaches,
we map out the structure of BaTiO3 under epitaxial constraints applicable to
growth on perovskite substrates. We obtain a phase diagram in temperature and
misfit strain that is qualitatively different from that reported by Pertsev et
al. [Phys. Rev. Lett. 80, 1988 (1998)], who based their results on an empirical
thermodynamic potential with parameters fitted at temperatures in the vicinity
of the bulk phase transitions. In particular, we find a region of `r phase' at
low temperature where Pertsev et al. have reported an `ac phase'. We expect our
results to be relevant to thin epitaxial films of BaTiO3 at low temperatures
and experimentally-achievable strains.Comment: 4 pages, with 4 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/od_epi/index.htm
Extern characterisation of iberian pig varieties based in cualitative variables
We are presenting a study of the external charcaterization of nine varieties of the Iberian pig based on seven cualitative external characteritics. We have used a sample of 566 adult individuals (515 females and 51 males) belonging to 28 different farm of the Iberian Pig Breed. The results of the non parametric ANOVA, the canonical discriminant analysis and Mahalanobis distancing have confirmed a clear differentiation among varieties, resulting the Torbiscal and Manchado de Jabugo varieties as the most distanced.Se realiza un estudio de caracterización exteriorista de las distintas variedades del cerdo Ibérico utilizando una muestra formada por un total de 566 individuos (515 hembras y 51 machos) pertenecientes a nueve variedades de la raza Ibérica. Para ello se analizan un total de siete variables cualitativas. Tanto los resultados del análisis de la varianza no paramétrico, el análisis discriminante canónico, como las distancias de Mahanalobis, nos confirman una clara diferenciación de todas las variedades de la raza basada en dichas variables, quedando el Torbiscal y el Manchado de Jabugo como las variedades más destacadas
Validating Regulatory Sensory Processing Disorders Using the Sensory Profile and Child Behavior Checklist (CBCL 1 –5)
The objective was to validate Regulatory Sensory Processing Disorders’ criteria (DC:0-3R, 2005) using empirical data on the presence and severity of sensory modulation deficits and specific psychiatric symptoms in clinical samples. Sixty toddlers who attended a child mental health unit were diagnosed by a clinical team. The
following two groups were created: toddlers with RSPD(N = 14) and those with ‘‘other diagnoses in Axis I/II of the DC:0-3R00(OD3R) (N = 46). Independently of the
clinical process, parents completed the Infant Toddler Sensory Profile (as a checklist for sensory symptoms) and
the Achenbach Behavior Checklist for ages 1/2–5 (CBCL 1/2–5). The scores from the two groups were compared. The results showed the following for the RSPD group: a higher number of affected sensory areas and patterns than in the OD3R group; a higher percentage of sensory deficits in specific sensory categories; and a higher severity of
behavioral symptoms such as withdrawal, inattention, other externalizing problems and pervasive developmental problems in CBCL 1/2–5. The results confirmed our hypotheses by indicating a higher severity of sensory
symptoms and identifying specific behavioral problems in children with RSPD. The results revealed convergent validity between the instruments and the diagnostic criteria
for RSPD and supported the validity of RSPD as a unique diagnosis. The findings also suggested the importance of identifying sensory modulation deficits in order to develop an early intervention to enhance the sensory capacities of children who do not fully satisfy the criteria for some DSM-IV-TR disorders
High dynamic range diamond detector acquisition system for beam wire scanner applications
The CERN Beam Instrumentation group has been working during the last years on the beam wire scanners upgrade to cope up with the increasing requirements of CERN experiments. These devices are used to measure the beam profile by crossing a thin wire through a circulating beam, the resulting secondary particles produced from beam/wire interaction are detected and correlated with the wire position to reconstruct the beam profile. The upgraded secondary particles acquisition electronics will use polycrystalline chemical vapour deposition (pCVD) diamond detectors for particle shower measurements, with low noise acquisitions performed on the tunnel, near the detector. The digital data is transmitted to the surface through an optical link with the GBT protocol. Two integrator ASICs (ICECAL and QIE10) are being characterized and compared for detector readout with the complete acquisition chain prototype. This contribution presents the project status, the QIE10 front-end performance and the first measurements with the complete acquisition system prototype. In addition, diamond detector signals from particle showers generated by an operational beam wire scanner are analysed and compared with an operational system
A linguaxe como medio de violencia simbólica no deporte
[RESUMO] En todas as sociedades machistas a linguaxe ten un papel fundamental na discriminación das mulleres, configurándose como un instrumento de dominación e lexitimador da violencia simbólica. O obxectivo deste estudo foi analizar se as estudantes de Ciencias do Deporte e a Educación Física da Universidade da Coruña reciben frases ao longo da súa carreira deportiva que reflicten a dominación e reprodución dun modelo social discriminatorio. A metodoloxía empregada inscríbese baixo o paradigma cualitativo e feminista, facendo uso da análise de contido como técnica de investigación. Para a recompilación de datos empregouse unha ficha de rexistro anecdótico que se aplicou a corenta alumnas e un grupo de discusión con cinco estudantes. Os resultados permítennos concluír que a linguaxe é un medio máis de violencia simbólica no deporte, que perpetúa un sistema de dominación masculina a través da transmisión dunha visión de inferioridade das mulleres, que menospreza a súa práctica e establece como ideal o deporte masculino. Non se acepta que unha muller poida ser superior a un home en situacións deportivas mixtas e danse casos nos que, a través da linguaxe, se chega a incitar á violencia física e sexual.
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