621 research outputs found
Nonperturbative renomalization group for Einstein gravity with matter
we investigate the exact renormalization group (RG) in Einstein gravity
coupled to N-component scalar field, working in the effective average action
formalism and background field method. The truncated evolution equation is
obtained for the Newtonian and cosmological constants. We have shown that
screening or antiscreening behaviour of the gravitational coupling depends
cricially on the choice of scalar-gravitational and the number of scalar
fields.Comment: 7 pages, LaTeX, a few typos correcte
Gauge Dependence of the Effective Average Action in Einstein Gravity
We study the gauge dependence of the effective average action Gamma_k and
Newtonian gravitational constant using the RG equation for Gamma_k. Then we
truncate the space of action functionals to get a solution of this equation. We
solve the truncated evolution equation for the Einstein gravity in the De
Sitter background for a general gauge parameter alpha and obtain a system of
equations for the cosmological and the Newtonian constants. Analyzing the
running of the gravitational constant we find that the Newtonian constant
depends strongly on the gauge parameter. This leads to the appearance of
antiscreening and screening behavior of the quantum gravity. The resolution of
the gauge dependence problem is suggested. For physical gauges like the
Landau-De Witt gauge the Newtonian constant shows an antiscreening.Comment: 19 pages, LaTeX, 1 figure, misprints correcte
Development of sampling efficiency and internal noise in motion detection and discrimination in school-aged children
AbstractThe aim of this study was to use an equivalent noise paradigm to investigate the development and maturation of motion perception, and how the underlying limitations of sampling efficiency and internal noise effect motion detection and direction discrimination in school-aged children (5–14years) and adults. Contrast energy thresholds of a 2c/deg sinusoidal grating drifting at 1.0 or 6.0Hz were measured as a function of added dynamic noise in three tasks: detection of a drifting grating; detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Compared to the ideal observer, in both children and adults, the performance for all tasks was limited by reduced sampling efficiency and internal noise. However, the thresholds for discrimination of motion direction and detection of moving gratings show very different developmental profiles. Motion direction discrimination continues to improve after the age of 14years due to an increase in sampling efficiency that differs with speed. Motion detection and summation were already mature at the age of 5years, and internal noise was the same for all tasks. These findings were confirmed in a 1-year follow-up study on a group of children from the initial study. The results support suggestions that the detection of a moving pattern and discriminating motion direction are processed by different systems that may develop at different rates
Unified mechanism of local drivers in a percolation model of atrial fibrillation
The mechanisms of atrial fibrillation (AF) are poorly understood, resulting in disappointing success rates of ablative treatment. Different mechanisms defined largely by different atrial activation patterns have been proposed and, arguably, this dispute has slowed the progress of AF research. Recent clinical evidence suggests a unifying mechanism of local drivers based on sustained re-entrant circuits in the complex atrial architecture. Here, we present a percolation inspired computational model showing spontaneous emergence of AF that strongly supports, and gives a theoretical explanation for, the clinically observed diversity of activation. We show that the difference in surface activation patterns is a direct consequence of the thickness of the discrete network of heart muscle cells through which electrical signals percolate to reach the imaged surface. The model naturally follows the clinical spectrum of AF spanning sinus rhythm, paroxysmal and persistent AF as the decoupling of myocardial cells results in the lattice approaching the percolation threshold. This allows the model to make the novel prediction that for paroxysmal AF, re-entrant circuits emerge near the endocardium, but in persistent AF they emerge deeper in the bulk of the atrial wall. If experimentally verified, this may go towards explaining the lowering ablation success rate as AF becomes more persistent
Effective Average Action in N=1 Super-Yang-Mills Theory
For N=1 Super-Yang-Mills theory we generalize the effective average action
Gamma_k in a manifest supersymmetric way using the superspace formalism. The
exact evolution equation for Gamma_k is derived and, introducing as an
application a simple truncation, the standard one-loop beta-function of N=1 SYM
theory is obtained.Comment: 17 pages, LaTeX, some remarks added, misprints corrected, to appear
in Phys. Rev.
Is Quantum Einstein Gravity Nonperturbatively Renormalizable?
We find considerable evidence supporting the conjecture that four-dimensional
Quantum Einstein Gravity is ``asymptotically safe'' in Weinberg's sense. This
would mean that the theory is likely to be nonperturbatively renormalizable and
thus could be considered a fundamental (rather than merely effective) theory
which is mathematically consistent and predictive down to arbitrarily small
length scales. For a truncated version of the exact flow equation of the
effective average action we establish the existence of a non-Gaussian
renormalization group fixed point which is suitable for the construction of a
nonperturbative infinite cutoff-limit. The truncation ansatz includes the
Einstein-Hilbert action and a higher derivative term.Comment: 18 pages, latex, 3 figure
Searches for solar-influenced radioactive decay anomalies using Spacecraft RTGs
Experiments showing a seasonal variation of the nuclear decay rates of a
number of different nuclei, and decay anomalies apparently related to solar
flares and solar rotation, have suggested that the Sun may somehow be
influencing nuclear decay processes. Recently, Cooper searched for such an
effect in Pu nuclei contained in the radioisotope thermoelectric
generators (RTGs) on board the Cassini spacecraft. In this paper we modify and
extend Cooper's analysis to obtain constraints on anomalous decays of
Pu over a wider range of models, but these limits cannot be applied to
other nuclei if the anomaly is composition-dependent. We also show that it may
require very high sensitivity for terrestrial experiments to discriminate among
some models if such a decay anomaly exists, motivating the consideration of
future spacecraft experiments which would require less precision.Comment: 8 pages, 4 figures (to appear in Astroparticle Physics
Phase transitions in two dimensions - the case of Sn adsorbed on Ge(111) surfaces
Accurate atomic coordinates of the room-temperature (root3xroot3)R30degree
and low-temperature (3x3) phases of 1/3 ML Sn on Ge(111) have been established
by grazing-incidence x-ray diffraction with synchrotron radiation. The Sn atoms
are located solely at T4-sites in the (root3xroot3)R30degree structure. In the
low temperature phase one of the three Sn atoms per (3x3) unit cell is
displaced outwards by 0.26 +/- 0.04 A relative to the other two. This
displacement is accompanied by an increase in the first to second double-layer
spacing in the Ge substrate.Comment: RevTeX, 5 pages including 2 figure
Changing dietary patterns is necessary to improve the sustainability of Western diets from a One Health perspective
Western diets are associated with multiple environmental impacts and risks to human health. European countries are gradually taking action towards the Farm to Fork Strategy, embracing a Life Cycle Assessment (LCA) perspective to promote the sustainability of food production and consumption. Although LCA enables the comprehensive assessment of environmental impacts, diet-related human health and animal welfare impacts are often underrepresented. This study proposes integrating additional indicators into LCA to evaluate the sustainability of diets under the One Health (OH) approach, which holistically considers interlinked complex health issues between humans, animals and the environment. Human health loss is estimated according to risk factors for non-communicable diseases; while animal welfare is measured as animal life years suffered, loss of animal lives and loss of morally-adjusted animal lives. The extended LCA framework is applied to men and women's reference diets in the German federal state of North Rhine-Westphalia (NRW); compared to three optimized dietary scenarios under nutritional constraints: 1) the national dietary guidelines, 2) a vegan diet (VD) and 3) a Mediterranean diet (MD). Men's reference diet causes greater impacts than women's across OH dimensions due to the higher food consumption, especially of ready-to-eat meals, sausages, meat, and sweetened and alcoholic beverages. Both reference diets are associated with risk factors for cardiovascular diseases, diabetes, stroke and neoplasms. Besides meat, consumption of honey, fish and seafood has the greatest impact on animal welfare, because of the high number of individuals involved. Alternative diets improve the sustainability of food consumption in NRW, although trade-offs arise: MD worsens animal suffering due to the higher fish intake; water use increases in both VD and MD due the higher intake of nuts and vegetables. Results highlight the importance of including animal welfare and human health indicators in LCA to better elucidate the potential impacts of diets characterized by the high intake of animal products, from a OH perspective
Corrigendum to “Changing dietary patterns is necessary to improve the sustainability of Western diets from a One Health perspective” [Sci. Total Environ. 811 (2022)/151437]
- …