7,193 research outputs found
Matter Lagrangians Coupled with Connections
We shall here consider extended theories of gravitation in the metric-affine
formalism with matter coupled directly to the connection. A sufficiently
general procedure will be exhibited to solve the resulting field equation
associated to the connection. As special cases one has the no-coupling case
(which is standard in f(R) literature) as well as the cases already analyzed in
ref.[1].Comment: Refs adde
First Order Extended Gravity and the Dark Side of the Universe: the General Theory
General Relativity is not the definitive theory of Gravitation due to several
shortcomings which are coming out both from theoretical and experimental
viewpoints. At large scales (astrophysical and cosmological scales) the
attempts to match it with the today observational data lead to invoke Dark
Energy and Dark Matter as the bulk components of the cosmic fluid. Since no
final evidence, at fundamental level, exists for such ingredients, it is clear
that General Relativity presents shortcomings at infrared scales. On the other
hand, the attempts to formulate theories more general than the Einstein one
give rise to mathematical difficulties that need workarounds which, in turn,
generate problems from the interpretative viewpoint. We present here a
completely new approach to the mathematical objects in terms of which a theory
of Gravitation may be written in a first-order `a la Palatini formalism, and
introduce the concept of Dark Metric which could completely bypass the
introduction of disturbing concepts as Dark Energy and Dark Matter.Comment: Proceedings of the Conference "The Invisible Universe" Paris, June
29-July 3, 2009 10 page
Covariant Lagrangian Formulation of Chern-Simons and BF Theories
We investigate the covariant formulation of Chern-Simons theories in a
general odd dimension which can be obtained by introducing a vacuum connection
field as a reference. Field equations, Noether currents and superpotentials are
computed so that results are easily compared with the well-known results in
dimension 3. Finally we use this covariant formulation of Chern-Simons theories
to investigate their relation with topological BF theories.Comment: 23 pages, refs. adde
P-273WHICH TYPE OF VIDEO-ASSISTED THORACOSCOPIC SURGERY LOBECTOMY SHOULD BE THE FIRST TO BE TAUGHT?
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New Cases of Universality Theorem for Gravitational Theories
The "Universality Theorem" for gravity shows that f(R) theories (in their
metric-affine formulation) in vacuum are dynamically equivalent to vacuum
Einstein equations with suitable cosmological constants. This holds true for a
generic (i.e. except sporadic degenerate cases) analytic function f(R) and
standard gravity without cosmological constant is reproduced if f is the
identity function (i.e. f(R)=R). The theorem is here extended introducing in
dimension 4 a 1-parameter family of invariants R' inspired by the
Barbero-Immirzi formulation of GR (which in the Euclidean sector includes also
selfdual formulation). It will be proven that f(R') theories so defined are
dynamically equivalent to the corresponding metric-affine f(R) theory. In
particular for the function f(R)=R the standard equivalence between GR and
Holst Lagrangian is obtained.Comment: 10 pages, few typos correcte
From Dark Energy and Dark Matter to Dark Metric
It is nowadays clear that General Relativity cannot be the definitive theory
of Gravitation due to several shortcomings that come out both from theoretical
and experimental viewpoints. At large scales (astrophysical and cosmological)
the attempts to match it with the latest observational data lead to invoke Dark
Energy and Dark Matter as the bulk components of the cosmic fluid. Since no
final evidence, at fundamental level, exists for such ingredients, it is clear
that General Relativity presents shortcomings at infrared scales. On the other
hand, the attempts to formulate more general theories than Einstein's one give
rise to mathematical difficulties that need workarounds that, in turn, generate
problems from the interpretative viewpoint. We present here a completely new
approach to the mathematical objects in terms of which a theory of Gravitation
may be written in a first-order (a' la Palatini) formalism, and introduce the
concept of Dark Metric which could completely bypass the introduction of
disturbing concepts as Dark Energy and Dark Matter
Rapid tranquillisation for agitated patients in emergency psychiatric rooms: a randomised trial of midazolam versus haloperidol plus promethazine
OBJECTIVE: To compare two widely used drug treatments for people with aggression or agitation due to mental illness.
DESIGN: Pragmatic, randomised clinical trial.
SETTING: Three psychiatric emergency rooms in Rio de Janeiro, Brazil.
SUBJECTS: 301 aggressive or agitated people.
INTERVENTIONS: Open treatment with intramuscular midazolam or intramuscular haloperidol plus promethazine.
MAIN OUTCOME MEASURES: Patients tranquil or sedated at 20 minutes. Secondary outcomes: patients tranquil or asleep by 40, 60, and 120 minutes; restrained or given extra drugs within 2 hours; severe adverse events; another episode of agitation or aggression; needing extra visits from doctor during first 24 hours; overall antipsychotic load in first 24 hours; and not discharged by two weeks
Diphoton Signals for Large Extra Dimensions at the Tevatron and CERN LHC
We analyze the potentiality of hadron colliders to search for large extra dimensions via the production of photon pairs. The virtual exchange of Kaluza--Klein gravitons can significantly enhance this processes provided the quantum gravity scale () is in the TeV range. We studied in detail the subprocesses and taking into account the complete Standard Model and graviton contributions as well as the unitarity constraints. We show that the Tevatron Run II will be able to probe up to 1.5--1.9 TeV at 2 level, while the LHC can extend this search to 5.3--6.7 TeV, depending on the number of extra dimensions
High Flow Nasal Cannulae in preterm infants
Despite of improved survival of premature infants, the incidence of long term pulmonary complications, mostly associated with ventilation-induced lung injury, remains high. Non invasive ventilation (NIV) is able to reduce the adverse effects of mechanical ventilation. Although nasal continuous positive airway pressure (NCPAP) is an effective mode of NIV, traumatic nasal complications and intolerance of the nasal interface are common. Recently high flow nasal cannula (HFNC) is emerging as an efficient, better tolerated form of NIV, allowing better access to the baby's face, which may improve nursing, feeding and bonding. The aim of this review is to discuss the available evidence of effectiveness and safety of HFNC in preterm newborns with respiratory distress syndrome (RDS). It is known that distending pressure generated by HFNC increases with increasing flow rate and decreasing infant size and varies according to the amount of leaks by nose and mouth. The effects of HFNC on lung mechanics, its clinical efficacy and safety are still insufficiently investigated. In conclusion, there is a growing evidence of the feasibility of HFNC as an alternative mode of NIV. However, further larger randomized trials are required, before being able to recommend HFNC in the treatment of moderate respiratory distress of preterm infants
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