666 research outputs found
Extended Palatini action for general relativity and the natural emergence of the cosmological constant
In the Palatini action of general relativity the connection and the metric
are treated as independent dynamical variables. Instead of assuming a relation
between these quantities, the desired relation between them is derived through
the Euler-Lagrange equations of the Palatini action. In this manuscript we
construct an extended Palatini action, where we do not assume any a priori
relationship between the connection, the covariant metric tensor, and the
contravariant metric tensor. Instead we treat these three quantities as
independent dynamical variables. We show that this action reproduces the
standard Einstein field equations depending on a single metric tensor. We
further show that in this formulation the cosmological constant has an
additional theoretical significance. Normally the cosmological constant is
added to the Einstein field equations for the purpose of having general
relativity be consistent with cosmological observations. In the formulation
presented here, the nonvanishing cosmological constant also ensures the
self-consistency of the theory.Comment: in the revised version the original scalar matter action is replaced
with a general matter actio
Scalars, Vectors and Tensors from Metric-Affine Gravity
The metric-affine gravity provides a useful framework for analyzing
gravitational dynamics since it treats metric tensor and affine connection as
fundamentally independent variables. In this work, we show that, a
metric-affine gravity theory composed of the invariants formed from
non-metricity, torsion and curvature tensors can be decomposed into a theory of
scalar, vector and tensor fields. These fields are natural candidates for the
ones needed by various cosmological and other phenomena. Indeed, we show that
the model accommodates TeVeS gravity (relativistic modified gravity theory),
vector inflation, and aether-like models. Detailed analyses of these and other
phenomena can lead to a standard metric-affine gravity model encoding scalars,
vectors and tensors.Comment: 13 p
The reality conditions for the new canonical variables of General Relativity
We examine the constraints and the reality conditions that have to be imposed
in the canonical theory of 4--d gravity formulated in terms of Ashtekar
variables. We find that the polynomial reality conditions are consistent with
the constraints, and make the theory equivalent to Einstein's, as long as the
inverse metric is not degenerate; when it is degenerate, reality conditions
cannot be consistently imposed in general, and the theory describes complex
general relativity.Comment: 11
Evidence for a gene influencing heart rate on chromosome 5p13-14 in a meta-analysis of genome-wide scans from the NHLBI Family Blood Pressure Program
BACKGROUND: Elevated resting heart rate has been shown in multiple studies to be a strong predictor of cardiovascular disease. Previous family studies have shown a significant heritable component to heart rate with several groups conducting genomic linkage scans to identify quantitative trait loci. METHODS: We performed a genome-wide linkage scan to identify quantitative trait loci influencing resting heart rate among 3,282 Caucasians and 3,989 African-Americans in three independent networks comprising the Family Blood Pressure Program (FBPP) using 368 microsatellite markers. Mean heart rate measurements were used in a regression model including covariates for age, body mass index, pack-years, currently drinking alcohol (yes/no), hypertension status and medication usage to create a standardized residual for each gender/ethnic group within each study network. This residual was used in a nonparametric variance component model to generate a LOD score and a corresponding P value for each ethnic group within each study network. P values from each ethnic group and study network were merged using an adjusted Fisher's combining P values method and the resulting P values were converted to LOD scores. The entire analysis was redone after individuals currently taking beta-blocker medication were removed. RESULTS: We identified significant evidence of linkage (LOD = 4.62) to chromosome 10 near 142.78 cM in the Caucasian group of HyperGEN. Between race and network groups we identified a LOD score of 1.86 on chromosome 5 (between 39.99 and 45.34 cM) in African-Americans in the GENOA network and the same region produced a LOD score of 1.12 among Caucasians within a different network (HyperGEN). Combining all network and race groups we identified a LOD score of 1.92 (P = 0.0013) on chromosome 5p13-14. We assessed heterogeneity for this locus between networks and ethnic groups and found significant evidence for low heterogeneity (P ≤ 0.05). CONCLUSION: We found replication (LOD > 1) between ethnic groups and between study networks with low heterogeneity on chromosome 5p13-14 suggesting that a gene in this region influences resting heart rate
Universal field equations for metric-affine theories of gravity
We show that almost all metric--affine theories of gravity yield Einstein
equations with a non--null cosmological constant . Under certain
circumstances and for any dimension, it is also possible to incorporate a Weyl
vector field and therefore the presence of an anisotropy. The viability
of these field equations is discussed in view of recent astrophysical
observations.Comment: 13 pages. This is a copy of the published paper. We are posting it
here because of the increasing interest in f(R) theories of gravit
Algebraic analysis of a model of two-dimensional gravity
An algebraic analysis of the Hamiltonian formulation of the model
two-dimensional gravity is performed. The crucial fact is an exact coincidence
of the Poisson brackets algebra of the secondary constraints of this
Hamiltonian formulation with the SO(2,1)-algebra. The eigenvectors of the
canonical Hamiltonian are obtained and explicitly written in closed
form.Comment: 21 pages, to appear in General Relativity and Gravitatio
Validation protocols for blood pressure measuring devices: the impact of the European Society of Hypertension International Protocol and the development of a Universal Standard
In the last three decades protocols for the validation of blood pressure measuring devices have been developed by the US Association for the Advancement of Medical Instrumentation, the British Hypertension Society, the German Hypertension League, the European Society of Hypertension Working Group on blood pressure Monitoring and the International Organization for Standardization. The European Society of Hypertension International Protocol required much smaller sample size than the other protocols, aiming to reduce the time, resources and cost of validation studies and thereby increase the number of validated devices. Given its specifications, the European Society of Hypertension International Protocol was adequate for ‘high- and low-accuracy’ devices, yet assessment of ‘moderate accuracy’ devices had high uncertainty with resultant high rate of device failure. Thus, devices validated using the European Society of Hypertension International Protocol should be considered to be as accurate as those validated with the previous Association for the Advancement of Medical Instrumentation or British Hypertension Society protocols. However, the European Society of Hypertension International Protocol did not allow subgroup evaluation (arm sizes, special populations, etc). The mission of the European Society of Hypertension International Protocol to promote the concept of validation has been well achieved, as almost double studies have been published using it than all the other protocols together. However, the maintenance of different validation protocols is confusing and therefore experts from the Association for the Advancement of Medical Instrumentation, European Society of Hypertension International Protocol and International Organization for Standardization have now developed the AAMI/ESH/ISO Universal Standard (ISO 81060-2:2018) as the recommended 21st-century procedure for worldwide application. The European Society of Hypertension Working Group has published a practical guide for using the Universal Standard. It is in the interests of all scientific bodies to propagate the Universal Standard and ensure its wide implementation
The Hamiltonian of Einstein affine-metric formulation of General Relativity
It is shown that the Hamiltonian of the Einstein affine-metric (first order)
formulation of General Relativity (GR) leads to a constraint structure that
allows the restoration of its unique gauge invariance, four-diffeomorphism,
without the need of any field dependent redefinition of gauge parameters as is
the case for the second order formulation. In the second order formulation of
ADM gravity the need for such a redefinition is the result of the non-canonical
change of variables [arXiv: 0809.0097]. For the first order formulation, the
necessity of such a redefinition "to correspond to diffeomorphism invariance"
(reported by Ghalati [arXiv: 0901.3344]) is just an artifact of using the
Henneaux-Teitelboim-Zanelli ansatz [Nucl. Phys. B 332 (1990) 169], which is
sensitive to the choice of linear combination of tertiary constraints. This
ansatz cannot be used as an algorithm for finding a gauge invariance, which is
a unique property of a physical system, and it should not be affected by
different choices of linear combinations of non-primary first class
constraints. The algorithm of Castellani [Ann. Phys. 143 (1982) 357] is free
from such a deficiency and it leads directly to four-diffeomorphism invariance
for first, as well as for second order Hamiltonian formulations of GR. The
distinct role of primary first class constraints, the effect of considering
different linear combinations of constraints, the canonical transformations of
phase-space variables, and their interplay are discussed in some detail for
Hamiltonians of the second and first order formulations of metric GR. The first
order formulation of Einstein-Cartan theory, which is the classical background
of Loop Quantum Gravity, is also discussed.Comment: 74 page
Gravitation, electromagnetism and cosmological constant in purely affine gravity
The Ferraris-Kijowski purely affine Lagrangian for the electromagnetic field,
that has the form of the Maxwell Lagrangian with the metric tensor replaced by
the symmetrized Ricci tensor, is dynamically equivalent to the metric
Einstein-Maxwell Lagrangian, except the zero-field limit, for which the metric
tensor is not well-defined. This feature indicates that, for the
Ferraris-Kijowski model to be physical, there must exist a background field
that depends on the Ricci tensor. The simplest possibility, supported by recent
astronomical observations, is the cosmological constant, generated in the
purely affine formulation of gravity by the Eddington Lagrangian. In this paper
we combine the electromagnetic field and the cosmological constant in the
purely affine formulation. We show that the sum of the two affine (Eddington
and Ferraris-Kijowski) Lagrangians is dynamically inequivalent to the sum of
the analogous (CDM and Einstein-Maxwell) Lagrangians in the
metric-affine/metric formulation. We also show that such a construction is
valid, like the affine Einstein-Born-Infeld formulation, only for weak
electromagnetic fields, on the order of the magnetic field in outer space of
the Solar System. Therefore the purely affine formulation that combines
gravity, electromagnetism and cosmological constant cannot be a simple sum of
affine terms corresponding separately to these fields. A quite complicated form
of the affine equivalent of the metric Einstein-Maxwell- Lagrangian
suggests that Nature can be described by a simpler affine Lagrangian, leading
to modifications of the Einstein-Maxwell-CDM theory for
electromagnetic fields that contribute to the spacetime curvature on the same
order as the cosmological constant.Comment: 17 pages, extended and combined with gr-qc/0612193; published versio
Blood pressure control and treatment adherence in hypertensive patients with metabolic syndrome: protocol of a randomized controlled study based on home blood pressure telemonitoring vs. conventional management and assessment of psychological determinants of adherence (TELEBPMET Study).
BACKGROUND: Inadequate blood pressure control and poor adherence to treatment remain among the major limitations in the management of hypertensive patients, particularly of those at high risk of cardiovascular events. Preliminary evidence suggests that home blood pressure telemonitoring (HBPT) might help increasing the chance of achieving blood pressure targets and improve patient's therapeutic adherence. However, all these potential advantages of HBPT have not yet been fully investigated.
METHODS/DESIGN: The purpose of this open label, parallel group, randomized, controlled study is to assess whether, in patients with high cardiovascular risk (treated or untreated essential arterial hypertension--both in the office and in ambulatory conditions over 24 h--and metabolic syndrome), long-term (48 weeks) blood pressure control is more effective when based on HBPT and on the feedback to patients by their doctor between visits, or when based exclusively on blood pressure determination during quarterly office visits (conventional management (CM)). A total of 252 patients will be enrolled and randomized to usual care (n = 84) or HBPT (n = 168). The primary study endpoint will be the rate of subjects achieving normal daytime ambulatory blood pressure targets (< 135/85 mmHg) 24 weeks and 48 weeks after randomization. In addition, the study will assess the psychological determinants of adherence and persistence to drug therapy, through specific psychological tests administered during the course of the study. Other secondary study endpoints will be related to the impact of HBPT on additional clinical and economic outcomes (number of additional medical visits, direct costs of patient management, number of antihypertensive drugs prescribed, level of cardiovascular risk, degree of target organ damage and rate of cardiovascular events, regression of the metabolic syndrome).
DISCUSSION: The TELEBPMET Study will show whether HBPT is effective in improving blood pressure control and related medical and economic outcomes in hypertensive patients with metabolic syndrome. It will also provide a comprehensive understanding of the psychological determinants of medication adherence and blood pressure control of these patients
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