1,028 research outputs found
Shining Light on Modifications of Gravity
Many modifications of gravity introduce new scalar degrees of freedom, and in
such theories matter fields typically couple to an effective metric that
depends on both the true metric of spacetime and on the scalar field and its
derivatives. Scalar field contributions to the effective metric can be
classified as conformal and disformal. Disformal terms introduce gradient
couplings between scalar fields and the energy momentum tensor of other matter
fields, and cannot be constrained by fifth force experiments because the
effects of these terms are trivial around static non-relativistic sources. The
use of high-precision, low-energy photon experiments to search for conformally
coupled scalar fields, called axion-like particles, is well known. In this
article we show that these experiments are also constraining for disformal
scalar field theories, and are particularly important because of the difficulty
of constraining these couplings with other laboratory experiments.Comment: 20 pages, 10 figures. v2: Matches version accepted by JCAP;
additional discussion of the strong coupling scale. Conclusions unchange
Effects of Salinity on Growth, Water Relations and Photosynthetic Rate of Tomatoes Grown in Nutrient Film Technique
Tomato (Lycopersicon esculentum Mill. var Counter) plants were grown under different salinity conditions
using the Nutrient Film Technique (NFT). In the first experiment, plants were exposed to salinities of 2.5 , 5.5
and 8.5 mS cm-l . In the second experiment, plants were exposed to continuous salinity of 2.5 and 8.5 mS cm-l
and altered salinity i. e low to high or vice versa. Leaf and stem dry weight were markedly reduced when plants
were exposed to continuous salinity of 8.5 mS cm-l. Exposure to high salinity at the later stages of growth also
resulted in the reduction of leaf dry weight to a level similar to that of plants exposed to continuous high salinity.
This could be attributed to the restriction in the movement of water within the plants as indicated by the reduction
in plant water uptake and leaf water potential. Photosynthetic rate was not affected although stomatal conductance
and leaf water potential were reduced when plants were exposed to high salinity
Constraining Galileon inflation
In this short paper, we present constraints on the Galileon inflationary model from the CMB bispectrum. We employ a principal-component analysis of the independent degrees of freedom constrained by data and apply this to the WMAP 9-year data to constrain the free parameters of the model. A simple Bayesian comparison establishes that support for the Galileon model from bispectrum data is at best weak
Chronology Protection in Galileon Models and Massive Gravity
Galileon models are a class of effective field theories that have recently
received much attention. They arise in the decoupling limit of theories of
massive gravity, and in some cases they have been treated in their own right as
scalar field theories with a specific nonlinearly realized global symmetry
(Galilean transformation). It is well known that in the presence of a source,
these Galileon theories admit superluminal propagating solutions, implying that
as quantum field theories they must admit a different notion of causality than
standard local Lorentz invariant theories. We show that in these theories it is
easy to construct closed timelike curves (CTCs) within the {\it naive} regime
of validity of the effective field theory. However, on closer inspection we see
that the CTCs could never arise since the Galileon inevitably becomes
infinitely strongly coupled at the onset of the formation of a CTC. This
implies an infinite amount of backreaction, first on the background for the
Galileon field, signaling the break down of the effective field theory, and
subsequently on the spacetime geometry, forbidding the formation of the CTC.
Furthermore the background solution required to create CTCs becomes unstable
with an arbitrarily fast decay time. Thus Galileon theories satisfy a direct
analogue of Hawking's chronology protection conjecture.Comment: 34 pages, no figure
DBI Galileon and Late time acceleration of the universe
We consider 1+3 dimensional maximally symmetric Minkowski brane embedded in a
1+4 dimensional maximally symmetric Minkowski background. The resulting 1+3
dimensional effective field theory is of DBI (Dirac-Born-Infeld) Galileon type.
We use this model to study the late time acceleration of the universe. We study
the deviation of the model from the concordance \Lambda CDM behaviour. Finally
we put constraints on the model parameters using various observational data.Comment: 16 pages, 7 eps figures, Latex Style, new references added, corrected
missing reference
Simple non-mydriatic retinal photography is feasible and demonstrates retinal microvascular dilation in Chronic Obstructive Pulmonary Disease (COPD).
BACKGROUND: Chronic Obstructive Pulmonary Disease (COPD) is associated with an increased risk of myocardial infarction and stroke but it remains unclear how to identify microvascular changes in this population. OBJECTIVES: We hypothesized that simple non-mydriatic retinal photography is feasible and can be used to assess microvascular damage in COPD. METHODS: Novel Vascular Manifestations of COPD was a prospective study comparing smokers with and without COPD, matched for age. Non-mydriatic, retinal fundus photographs were assessed using semi-automated software. RESULTS: Retinal images from 24 COPD and 22 control participants were compared. Cases were of similar age to controls (65.2 vs. 63.1 years, p = 0.38), had significantly lower Forced Expiratory Volume in one second (FEV1) (53.4 vs 100.1% predicted; p < 0.001) and smoked more than controls (41.7 vs. 29.6 pack years; p = 0.04). COPD participants had wider mean arteriolar (155.6 ±15 uM vs. controls [142.2 ± 12 uM]; p = 0.002) and venular diameters (216.8 ±20.7 uM vs. [201.3± 19.1 uM]; p = 0.012). Differences in retinal vessel caliber were independent of confounders, odds ratios (OR) = 1.08 (95% confidence intervals [CI] = 1.02, 1.13; p = 0.007) and OR = 1.05 (CI = 1.01, 1.09; p = 0.011) per uM increase in arteriolar and venular diameter respectively. FEV1 remained significantly associated with retinal vessel dilatation r = -0.39 (p = 0.02). CONCLUSIONS: Non-mydriatic retinal imaging is easily facilitated. We found significant arteriole and venous dilation in COPD compared to age-matched smokers without COPD associated with lung function independent of standard cardiovascular risk factors. Retinal microvascular changes are known to be strongly associated with future vascular events and retinal photography offers potential to identify this risk. TRIAL REGISTRATION: clinicaltrials.gov NCT02060292
Spinning Black Holes with Axion Hair
In this work we construct and analyse non-perturbative stationary and
axially-symmetric black hole solutions in General Relativity coupled to an
electromagnetic and an axion field. The axion field is coupled to the
electromagnetic field, which leads to hairy solutions in the presence of an
electric charge and rotation. We investigate the existence and characteristics
of these solutions for different values of the spin, charge and coupling
constant. Our analysis shows the presence of violations of the Kerr-Newman
bound, solutions with large positive and negative values of the gyromagnetic
ratio, and the existence of multiple branches of solutions with distinct
properties, demonstrating that black hole uniqueness does not hold in this
scenario. The code used in this study is publicly available, providing a
valuable tool for further research on this model.Comment: 17 pages, 10 figure
Growth Histories in Bimetric Massive Gravity
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity
for general homogeneous and isotropic backgrounds. In the de Sitter
approximation, we obtain decoupled sets of massless and massive scalar
gravitational fluctuations. Matter perturbations then evolve like in Einstein
gravity. We perturb the future de Sitter regime by the ratio of matter to dark
energy, producing quasi-de Sitter space. In this more general setting the
massive and massless fluctuations mix. We argue that in the quasi-de Sitter
regime, the growth of structure in bimetric gravity differs from that of
Einstein gravity.Comment: 28 pages + appendix, 11 figure
Discrete Razumikhin-type technique and stability of the Euler-Maruyama method to stochastic functional differential equations
A discrete stochastic Razumikhin-type theorem is established to investigate whether the Euler--Maruyama (EM) scheme can reproduce the moment exponential stability of exact solutions of stochastic functional differential equations (SFDEs). In addition, the Chebyshev inequality and the Borel-Cantelli lemma are applied to show the almost sure stability of the EM approximate solutions of SFDEs. To show our idea clearly, these results are used to discuss stability of numerical solutions of two classes of special SFDEs, including stochastic delay differential equations (SDDEs) with variable delay and stochastically perturbed equations
The 'top 100' drugs and classes in England An updated 'starter formulary' for trainee prescribers.
AIMS: Prescribing is a complex skill required of doctors and, increasingly, other healthcare professionals. Use of a personal formulary can help to develop this skill. In 2006-9, we developed a core list of the 100 most commonly prescribed drugs. Our aim in the present study was to update this 'starter formulary' to ensure its continued relevance for prescriber training. METHODS: We analysed large contemporary primary and secondary care datasets to identify the most frequently prescribed medicinal products. Items were classified into natural groups, broadly following their British National Formulary classification. The resulting drug groups were included in the core list if they comprised ≥0.1% prescriptions in both settings or ≥0.2-0.3% prescriptions in one setting. Drugs from emergency guidelines that did not qualify by prescribing frequency completed the list. RESULTS: Over 1 billion primary care items and approximately 1.8 million secondary care prescriptions were analysed. The updated list comprises 81 drug groups commonly prescribed in both settings; 6 from primary care; 7 from secondary care; and 6 from emergency guidelines. 88% of the formulary was unchanged. Notable changes include entry of newer anti-epileptics and dipeptidyl peptidase-4 inhibitors and exit of phenytoin and thiazolidinediones. CONCLUSIONS: The relative stability of the core drug list over 9 years and the current update ensure that learning based on this list remains relevant to practice. Trainee prescribers may be encouraged to use this 'starter formulary' to develop a sound basis of prescribing knowledge and skills that they can subsequently apply more widely
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