25,193 research outputs found
The Phase Structure of the Weakly Coupled Lattice Schwinger Model
The weak coupling expansion is applied to the single flavour Schwinger model
with Wilson fermions on a symmetric toroidal lattice of finite extent. We
develop a new analytic method which permits the expression of the partition
function as a product of pure gauge expectation values whose zeroes are the
Lee-Yang zeroes of the model. Application of standard finite-size scaling
techniques to these zeroes recovers previous numerical results for the small
and moderate lattice sizes to which those studies were restricted. Our
techniques, employable for arbitrarily large lattices, reveal the absence of
accumulation of these zeroes on the real hopping parameter axis at constant
weak gauge coupling. The consequence of this previously unobserved behaviour is
the absence of a zero fermion mass phase transition in the Schwinger model with
single flavour Wilson fermions at constant weak gauge coupling.Comment: 8 pages, 2 figures, insert to figure 2 include
The Structure of the Aoki Phase at Weak Coupling
A new method to determine the phase diagram of certain lattice fermionic
field theories in the weakly coupled regime is presented. This method involves
a new type of weak coupling expansion which is multiplicative rather than
additive in nature and allows perturbative calculation of partition function
zeroes. Application of the method to the single flavour Gross-Neveu model gives
a phase diagram consistent with the parity symmetry breaking scenario of Aoki
and provides new quantitative information on the width of the Aoki phase in the
weakly coupled sector.Comment: 9 pages, 1 figure (minor changes) To be published in Phys. Lett.
βCaMKII regulates bidirectional long-term plasticity in cerebellar Purkinje cells by a CaMKII/PP2B switch mechanism
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise statedPeer reviewe
ISM composition through X-ray spectroscopy of LMXBs
The diffuse interstellar medium (ISM) is an integral part of the evolution of
the entire Galaxy. Metals are produced by stars and their abundances are the
direct testimony of the history of stellar evolution. However, the interstellar
dust composition is not well known and the total abundances are yet to be
accurately determined. We probe ISM dust composition, total abundances, and
abundance gradients through the study of interstellar absorption features in
the high-resolution X-ray spectra of Galactic low-mass X-ray binaries (LMXBs).
We use high-quality grating spectra of nine LMXBs taken with XMM-Newton. We
measure the column densities of O, Ne, Mg, and Fe with an empirical model and
estimate the Galactic abundance gradients. The column densities of the neutral
gas species are in agreement with those found in the literature. Solids are a
significant reservoir of metals like oxygen and iron. Respectively, 15-25 % and
65-90 % of the total amount of O I and Fe I is found in dust. The dust amount
and mixture seem to be consistent along all the lines-of-sight (LOS). Our
estimates of abundance gradients and predictions of local interstellar
abundances are in agreement with those measured at longer wavelengths. Our work
shows that X-ray spectroscopy is a very powerful method to probe the ISM. For
instance, on a large scale the ISM appears to be chemically homogeneous showing
similar gas ionization ratios and dust mixtures. The agreement between the
abundances of the ISM and the stellar objects suggests that the local Galaxy is
also chemically homogeneous.Comment: 13 pages, 10 figures, 5 tables, accepted to A&
Gravitational wave background in perfect fluid quantum cosmologies
We discuss the gravitational wave background produced by bouncing models
based on a full quantum evolution of a universe filled with a perfect fluid.
Using an ontological interpretation for the background wave function allows us
to solve the mode equations for the tensorial perturbations, and we find the
spectral index as a function of the fluid equation of state.Comment: 12 pages, 5 figures, to appear in Phys. Rev. D (2006
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
Geometrización del curriculum en la formación del profesorado de matemáticas
Esta comunicación es un documento teórico en el que el autor define la geometrización del currículo en la formación docente en matemáticas, cuando a partir de una cuestión sobre que geometría se debe enseñar en la formación docente y las habilidades de la imaginación, la intuición y la visualización puede ser empleado para la innovación de los planes de estudio. Al comprender cómo un proceso geométrico de la utilización de métodos geométricos como un método para entender y representar visualmente los conceptos matemáticos en diversas áreas, ofrece sugerencias a la enseñanza de los números complejos y matrices
Developing a site-conditions map for seismic hazard Assessment in Portugal
The evaluation of site effects on a broad scale is a critical issue for seismic hazard and risk assessment, land use planning and emergency planning. As characterization of site conditions based on the shear-wave velocity has become increasingly important, several methods have been proposed in the literature to estimate its average over the first thirty meters (Vs30) from more extensively available data. These methods include correlations with geologic-geographic defined units and topographic slope. In this paper we present the first steps towards the development of a site–conditions map for Portugal, based on a regional database of shear-wave velocity data, together with geological, geographic, and lithological information. We computed Vs30 for each database site and classified it according to the corresponding geological-lithological information using maps at the smallest scale available (usually 1:50000). We evaluated the consistency of Vs30 values within generalized-geological classes, and assessed the performance of expedient methodologies proposed in the literature
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