328 research outputs found
Inhomogeneous cosmologies with Q-matter and varying
Starting from the inhomogeneous shear--free Nariai metric we show, by solving
the Einstein--Klein--Gordon field equations, how a self--interacting scalar
field plus a material fluid, a variable cosmological term and a heat flux can
drive the universe to its currently observed state of homogeneous accelerated
expansion. A quintessence scenario where power-law inflation takes place for a
string-motivated potential in the late--time dominated field regime is
proposed.Comment: 11 pages, Revtex. To be published in Physical Review
Ghost Condensation and a Consistent Infrared Modification of Gravity
We propose a theoretically consistent modification of gravity in the
infrared, which is compatible with all current experimental observations. This
is an analog of Higgs mechanism in general relativity, and can be thought of as
arising from ghost condensation--a background where a scalar field \phi has a
constant velocity, = M^2. The ghost condensate is a new kind of
fluid that can fill the universe, which has the same equation of state, \rho =
-p, as a cosmological constant, and can hence drive de Sitter expansion of the
universe. However, unlike a cosmological constant, it is a physical fluid with
a physical scalar excitation, which can be described by a systematic effective
field theory at low energies. The excitation has an unusual low-energy
dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it
gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin
dependent force. In the ghost condensate, the energy that gravitates is not the
same as the particle physics energy, leading to the possibility of both sources
that can gravitate and antigravitate. The Newtonian potential is modified with
an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time
scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking
cosmological problems, including inflation, dark matter and dark energy.Comment: 42 pages, LaTeX 2
Diffeomorphism Invariance in the Hamiltonian formulation of General Relativity
It is shown that when the Einstein-Hilbert Lagrangian is considered without
any non-covariant modifications or change of variables, its Hamiltonian
formulation leads to results consistent with principles of General Relativity.
The first-class constraints of such a Hamiltonian formulation, with the metric
tensor taken as a canonical variable, allow one to derive the generator of
gauge transformations, which directly leads to diffeomorphism invariance. The
given Hamiltonian formulation preserves general covariance of the
transformations derivable from it. This characteristic should be used as the
crucial consistency requirement that must be met by any Hamiltonian formulation
of General Relativity.Comment: 13 page
Pollen season is reflected on symptom load for grass and birch pollen-induced allergic rhinitis in different geographic areas—An EAACI Task Force Report
Background: The effectiveness of allergen immunotherapy (AIT) in seasonal allergic rhinitis (AR) depends on the definition of pollen exposure intensity or time period. We recently evaluated pollen and symptom data from Germany to examine the new definitions of the European Academy of Allergy and Clinical Immunology (EAACI) on pollen season and peak pollen period start and end. Now, we aim to confirm the feasibility of these definitions to properly mirror symptom loads for grass and birch pollen-induced allergic rhinitis in other European geographical areas such as Austria, Finland and France, and therefore their suitability for AIT and clinical practice support. Methods: Data from twenty-three pollen monitoring stations from three countries in Europe and for 3 years (2014-2016) were used to investigate the correlation between birch and grass pollen concentrations during the birch and grass pollen season defined via the EAACI criteria, and total nasal symptom and medication scores as reported with the aid of the patient's hay-fever diary (PHD). In addition, we conducted a statistical analysis, together with a graphical investigation, to reveal correlations and dependencies between the studied parameters. Results: The analysis demonstrated that the definitions of pollen season as well as peak pollen period start and end as proposed by the EAACI are correlated to pollen-induced symptom loads reported by PHD users during birch and grass pollen season. A statistically significant correlation (slightly higher for birch) has been found between the Total Nasal Symptom and Medication Score (TNSMS) and the pollen concentration levels. Moreover, the maximum symptom levels occurred mostly within the peak pollen periods (PPP) following the EAACI criteria. Conclusions: Based on our analyses, we confirm the validity of the EAACI definitions on pollen season for both birch and grass and for a variety of geographical locations for the four European countrie
Anomalous Hall effect in Fe/Cu bilayers
The scaling of anomalous Hall resistivity on the longitudinal resistivity has
been intensively studied in the different magnetic systems, including
multilayers and granular films, to examine which mechanism, skew scattering or
side-jump, dominates. The basis of the scaling law is that both the
resistivities are due to the electron scattering at the imperfections in the
materials. By studying of anomalous Hall effect (AHE) in the simple Fe/Cu
bilayers, we demonstrate that the measured anomalous Hall effect should not
follow the scaling laws derived from skew scattering or side-jump mechanism due
to the short-circuit and shunting effects of the non-magnetic layers.Comment: 12 pages, 4 figures;
http://www.springerlink.com/content/1718722u75j24587
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
Collapsing shear-free perfect fluid spheres with heat flow
A global view is given upon the study of collapsing shear-free perfect fluid
spheres with heat flow. We apply a compact formalism, which simplifies the
isotropy condition and the condition for conformal flatness. This formalism
also presents the simplest possible version of the main junction condition,
demonstrated explicitly for conformally flat and geodesic solutions. It gives
the right functions to disentangle this condition into well known differential
equations like those of Abel, Riccati, Bernoulli and the linear one. It yields
an alternative derivation of the general solution with functionally dependent
metric components. We bring together the results for static and time- dependent
models to describe six generating functions of the general solution to the
isotropy equation. Their common features and relations between them are
elucidated. A general formula for separable solutions is given, incorporating
collapse to a black hole or to a naked singularity.Comment: 26 page
Black Hole Thermodynamics and Statistical Mechanics
We have known for more than thirty years that black holes behave as
thermodynamic systems, radiating as black bodies with characteristic
temperatures and entropies. This behavior is not only interesting in its own
right; it could also, through a statistical mechanical description, cast light
on some of the deep problems of quantizing gravity. In these lectures, I review
what we currently know about black hole thermodynamics and statistical
mechanics, suggest a rather speculative "universal" characterization of the
underlying states, and describe some key open questions.Comment: 35 pages, Springer macros; for the Proceedings of the 4th Aegean
Summer School on Black Hole
ARIA 2016: Care pathways implementing emerging technologies for predictive medicine in rhinitis and asthma across the life cycle
The Allergic Rhinitis and its Impact on Asthma (ARIA) initiative commenced during a World Health Organization workshop in 1999. The initial goals were (1) to propose a new allergic rhinitis classification, (2) to promote the concept of multi-morbidity in asthma a
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