4,630 research outputs found
Comments on the Chern-Simons photon term in the QED description of graphene
We revisit the Coleman-Hill theorem in the context of reduced planar QED.
Using the global U(1) Ward identity for this non-local but still gauge
invariant theory, we can confirm that the topological piece of the photon
self-energy at zero momentum does not receive further quantum corrections apart
from the potential one-loop contribution, even when considering the Lorentz
non-invariant case due to the Fermi velocity . This is of relevance to
probe possible time parity odd dynamics in a planar sheet of graphene which has
an effective description in terms of -dimensional planar reduced QED.Comment: New section added, published versio
Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal
The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) in Portugal has a long
history of observation of the geomagnetic field, spanning almost 150 yr
since the first geomagnetic measurements in 1866. These long instrumental
geomagnetic records provide very important information about variability of
geomagnetic elements and indices, their trends and cycles, and can be used
to improve our knowledge on the sources that drive variations of the
geomagnetic field: liquid core dynamics (internal) and solar forcing
(external).
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However, during the long life of the Coimbra Observatory, some inevitable
changes in station location, instrument's park and electromagnetic
environment have taken place. These changes affected the quality of the data
collected at COI causing breaks and jumps in the series of geomagnetic field
components and local K index. Clearly, these inhomogeneities, typically
shift-like (step-like) or trend-like, have to be corrected or, at least,
minimized in order for the data to be used in scientific studies or to be
submitted to international databases.
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In this study, the series of local K index and declination of the
geomagnetic field are analysed: the former because it allows direct
application of standard homogenization methods and the latter because it is
the longest continuous series produced at COI. For the homogenization,
visual and statistical tests (e.g. standard normal homogeneity test) have
been applied directly to the local geomagnetic K index series (from 1951 to
2012). The homogenization of the monthly averages of declination (from 1867
to 2012) has been done using visual analysis and statistical tests applied
to the time series of the first differences of declination values, as an
approximation to the first time derivative. This allowed not only
estimating the level of inhomogeneity of the studied series but also
detecting the highly probable homogeneity break points. These points have been
cross-checked with the metadata, and the COI series have been compared with
reference series from the nearest geomagnetic stations and, in the case of
declination series, from the recent geomagnetic field model COV-OBS to set
up the required correction factors. As a result, the homogenized series
measured in COI are considered to be essentially free of artificial shifts
starting from the second half of the 20th century, and ready to be used by
the scientific community
Gruta da figueira brava (Arrabida): Geological setting
Separata do Tomo XXXVIII das Memories da Academia das Ciencias de Lisboa (Classe de Ciencias)The Arrabida Mountain Range is the best example in Portugal of alpine movements.
During Miocene times the Arrabida chain acquired the present structural set
up: overthrusting accidents striking ENE-WSW and N-S or NNE-SSW sinistral
lateral ramps. The main tectonic phases occurred about 17 Ma and somewhat less
than 16 Ma.
The Miocene deposits, mainly biocalcarenites, are middle Burdigalian and
Langhian in age.
During the Pleistocene the sea erosion cut several terrasse levels. Scattered
remnants of conglomerates corresponding to the 12-15 and to 5-8 meters marine
terrasses are ascribed to the last interglacial and to the beginning of the Wiirm glaciation
(= 100000 years, Tyrrhenian II and III). The 5-8 meters terrasse, which is of particular
interest, was deposited in a narrow marine erosion platform; the corresponding
deposits tend to fill the entry of the caves excavated in the sea cliffs during the Upper
Pleistocene such as Lapa de. St" Margarida and Figueira Brava Cave. These holes,
protected by overhanging parts of the cliffs as a sort of ceiling, were good shelters
forman.
With the advance of the Wiirm glaciation the sea level was progressively going
down. About 30000 years ago, the 5-8 meters platform and the caves dug in the cliffs
were elevated as related to an extensive coastal plain. The sea level was ca. 60 meters
below the present level (Miskovski, 1987). The human communities found in these
territories an excellent hunting ground. The Santa Margarida and Figueira Brava
caves were thus natural shelters. A large number of remnants of their occupation are
preserved such as shells, animal bones, a few Neanderthal remnants as well as lithic
and bone implements. 14C (and U series) dating indicate an age about 30000 years for
level 2 where archaeologic remnants were exploited
Double non-perturbative gluon exchange: an update on the soft Pomeron contribution to pp scattering
We employ a set of recent, theoretically motivated, fits to non-perturbative
unquenched gluon propagators to check in how far double gluon exchange can be
used to describe the soft sector of pp scattering data (total and differential
cross section). In particular, we use the refined Gribov--Zwanziger gluon
propagator (as arising from dealing with the Gribov gauge fixing ambiguity) and
the massive Cornwall-type gluon propagator (as motivated from Dyson-Schwinger
equations) in conjunction with a perturbative quark-gluon vertex, next to a
model based on the non-perturbative quark-gluon Maris-Tandy vertex, popular
from Bethe-Salpeter descriptions of hadronic bound states. We compare the cross
sections arising from these models with "older" ISR and more recent TOTEM and
ATLAS data. The lower the value of total energy \sqrt{s}, the better the
results appear to be.Comment: 14 pages, 8 .pdf figures. To appear in Phys.Rev.
Effect of the Gribov horizon on the Polyakov loop and vice versa
We consider finite temperature SU(2) gauge theory in the continuum
formulation, which necessitates the choice of a gauge fixing. Choosing the
Landau gauge, the existing gauge copies are taken into account by means of the
Gribov-Zwanziger (GZ) quantization scheme, which entails the introduction of a
dynamical mass scale (Gribov mass) directly influencing the Green functions of
the theory. Here, we determine simultaneously the Polyakov loop (vacuum
expectation value) and Gribov mass in terms of temperature, by minimizing the
vacuum energy w.r.t. the Polyakov loop parameter and solving the Gribov gap
equation. Inspired by the Casimir energy-style of computation, we illustrate
the usage of Zeta function regularization in finite temperature calculations.
Our main result is that the Gribov mass directly feels the deconfinement
transition, visible from a cusp occurring at the same temperature where the
Polyakov loop becomes nonzero. In this exploratory work we mainly restrict
ourselves to the original Gribov-Zwanziger quantization procedure in order to
illustrate the approach and the potential direct link between the vacuum
structure of the theory (dynamical mass scales) and (de)confinement. We also
present a first look at the critical temperature obtained from the Refined
Gribov-Zwanziger approach. Finally, a particular problem for the pressure at
low temperatures is reported.Comment: 19 pages, 8 .pdf figures. v2: extended section 3 + extra references;
version accepted for publication in EPJ
Mathematical circus clown tricks
The Mathematical Circus project was created in 2011 by the LUDUS association with the main goal of promoting the interest and motivation for learning mathematics. The Mathematical Circus team performs mathematical magic shows where complementary skills are merged to produce a high intervention capacity within a wide geographical range in Portugal. Some tricks are performed by a mathematical clown, a unique
character in the circus world, who brings together the usual foolish characteristics of a clown and the rigorous mathematical knowledge. In this paper we will describe and explain some of the tricks of the Mathematical Circus repertoire involving the clown.info:eu-repo/semantics/publishedVersio
Questões acerca do coping: a propósito do estudo de adaptação do Brief Cope
O objectivo do presente estudo é investigar as propriedades psicométricas
da versão reduzida do questionário de coping desenvolvido por Carver a partir da
versão longa do mesmo questionário e, simultaneamente, discutir alguns aspectos de
coping que se colocam no virar do século. Participaram no estudo 364 indivÃduos,
41,5% do sexo masculino, com caracterÃsticas idênticas aos participantes do estudo de
Carver. O questionário Brief COPE foi submetido a tratamentos estatÃsticos idênticos
ao original e os resultados encontrados são também idênticos à versão original. A
versão encontrada em português é uma boa adaptação da versão original que sugere a
sua utilidade em estudos no Campo da saúde? ------ ABTRACT ------ The primary purpose of the present paper is to identify the
psychometric properties of the short form of the COPE scale named Brief-COPE.
Participants are 364 individuals, 41.5% males, with similar characteristics of the
participants in Carver’s study. The translation of the Brief-COPE followed standard
procedures (translation, back translation, reconciliation, cultural equivalence
verification of translation, identification of content validity, cognitive debriefing).
Statistical procedures followed the original model. Portuguese version that emerges
from the present study shows similar patterns to the original version. The Portuguese
version proposed seems to be a good adaptation of the original one, and a useful
instrument to be used in health psychology
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