2,506 research outputs found
Which are Better Conditioned Meshes Adaptive, Uniform, Locally Refined or Localised
Adaptive, locally refined and locally adjusted meshes are preferred over
uniform meshes for capturing singular or localised solutions. Roughly speaking,
for a given degree of freedom a solution associated with adaptive, locally
refined and locally adjusted meshes is more accurate than the solution given by
uniform meshes. In this work, we answer the question which meshes are better
conditioned. We found, for approximately same degree of freedom (same size of
matrix), it is easier to solve a system of equations associated with an
adaptive mesh.Comment: 4 Page
Qualitative study in Loop Quantum Cosmology
This work contains a detailed qualitative analysis, in General Relativity and
in Loop Quantum Cosmology, of the dynamics in the associated phase space of a
scalar field minimally coupled with gravity, whose potential mimics the
dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with
the orbits (solutions) of the system, we will see that there are analytic ones,
which lead to the same dynamics as the perfect fluid, and our goal is to check
their stability, depending on the value of the EoS parameter, i.e., to show
whether the other orbits converge or diverge to these analytic solutions at
early and late times.Comment: 12 pages, 7 figures. Version accepted for publication in CQ
Super-Group Field Cosmology
In this paper we construct a model for group field cosmology. The classical
equations of motion for the non-interactive part of this model generate the
Hamiltonian constraint of loop quantum gravity for a homogeneous isotropic
universe filled with a scalar matter field. The interactions represent topology
changing processes that occurs due to joining and splitting of universes. These
universes in the multiverse are assumed to obey both bosonic and fermionic
statistics, and so a supersymmetric multiverse is constructed using superspace
formalism. We also introduce gauge symmetry in this model. The supersymmetry
and gauge symmetry are introduced at the level of third quantized fields, and
not the second quantized ones. This is the first time that supersymmetry has
been discussed at the level of third quantized fields.Comment: 14 pages, 0 figures, accepted for publication in Class. Quant. Gra
The SELF Trial: A self-efficacy based behavioral intervention trial for weight loss maintenance.
The SELF Trial examined the effect of adding individual self‐efficacy (SE) enhancement sessions to standard behavioral weight loss treatment (SBT). Participants were randomly assigned to SBT or SBT plus SE sessions (SBT+SE). Outcome measures were weight loss maintenance, quality of life, intervention adherence, and self‐efficacy at 12 and 18 months. The sample (N = 130) was female (83.08%) with a mean (SD) body mass index of 33.15 (4.11) kg m2. There was a significant time effect for percent weight change (P = 0.002) yet no significant group or group‐by‐time effects. The weight loss for the SBT+SE group was 8.38% (7.48) at 12 months and 8.00% (7.87) at 18 months, with no significant difference between the two time points (P = 0.06). However, weight loss for the SBT group was 6.95% (6.67) at 12 months and 5.96% (7.35) at 18 months, which was significantly different between the two time points (P = 0.005), indicating that the SBT group had significant weight regain. Both groups achieved clinically significant weight loss. The group receiving an intervention targeting enhanced self‐efficacy had greater weight loss maintenance whereas the SBT group demonstrated significant weight regain possibly related to the greater attention provided to the SBT+SE group
Loop Quantum Gravity and the The Planck Regime of Cosmology
The very early universe provides the best arena we currently have to test
quantum gravity theories. The success of the inflationary paradigm in
accounting for the observed inhomogeneities in the cosmic microwave background
already illustrates this point to a certain extent because the paradigm is
based on quantum field theory on the curved cosmological space-times. However,
this analysis excludes the Planck era because the background space-time
satisfies Einstein's equations all the way back to the big bang singularity.
Using techniques from loop quantum gravity, the paradigm has now been extended
to a self-consistent theory from the Planck regime to the onset of inflation,
covering some 11 orders of magnitude in curvature. In addition, for a narrow
window of initial conditions, there are departures from the standard paradigm,
with novel effects, such as a modification of the consistency relation
involving the scalar and tensor power spectra and a new source for
non-Gaussianities. Thus, the genesis of the large scale structure of the
universe can be traced back to quantum gravity fluctuations \emph{in the Planck
regime}. This report provides a bird's eye view of these developments for the
general relativity community.Comment: 23 pages, 4 figures. Plenary talk at the Conference: Relativity and
Gravitation: 100 Years after Einstein in Prague. To appear in the Proceedings
to be published by Edition Open Access. Summarizes results that appeared in
journal articles [2-13
Lattice loop quantum cosmology: scalar perturbations
We study the scalar modes of linear perturbations in loop quantum cosmology.
This is done on a lattice where each cell is taken to be homogeneous and
isotropic and can be quantized via standard homogeneous loop quantum cosmology
techniques. The appropriate interactions between nearby cells are included in
the Hamiltonian in order to obtain the correct physics. It is shown that the
quantum theory is anomaly-free: the scalar and diffeomorphism constraint
operators weakly commute with the Hamiltonian. Finally, the effective theory
encoding the leading order quantum gravity corrections is derived and is shown
to give the same holonomy-corrected effective equations that have been obtained
in previous studies.Comment: 32 pages, v2: Minor change
Numerical loop quantum cosmology: an overview
A brief review of various numerical techniques used in loop quantum cosmology
and results is presented. These include the way extensive numerical simulations
shed insights on the resolution of classical singularities, resulting in the
key prediction of the bounce at the Planck scale in different models, and the
numerical methods used to analyze the properties of the quantum difference
operator and the von Neumann stability issues. Using the quantization of a
massless scalar field in an isotropic spacetime as a template, an attempt is
made to highlight the complementarity of different methods to gain
understanding of the new physics emerging from the quantum theory. Open
directions which need to be explored with more refined numerical methods are
discussed.Comment: 33 Pages, 4 figures. Invited contribution to appear in Classical and
Quantum Gravity special issue on Non-Astrophysical Numerical Relativit
A complete parameterisation of the relative humidity and wavelength dependence of the refractive index of hygroscopic inorganic aerosol particles
Calculations of aerosol radiative forcing require knowledge of
wavelength-dependent aerosol optical properties, such as single-scattering
albedo. These aerosol optical properties can be calculated using Mie theory
from knowledge of the key microphysical properties of particle size and
refractive index, assuming that atmospheric particles are well-approximated
to be spherical and homogeneous. We provide refractive index determinations
for aqueous aerosol particles containing the key atmospherically relevant
inorganic solutes of NaCl, NaNO3, (NH4)2SO4,
NH4HSO4 and Na2SO4, reporting the refractive index
variation with both wavelength (400–650 nm) and relative humidity (from
100 % to the efflorescence value of the salt). The accurate and precise
retrieval of refractive index is performed using single-particle cavity
ring-down spectroscopy. This approach involves probing a single aerosol
particle confined in a Bessel laser beam optical trap through a combination
of extinction measurements using cavity ring-down spectroscopy and elastic
light-scattering measurements. Further, we assess the accuracy of these
refractive index measurements, comparing our data with previously reported
data sets from different measurement techniques but at a single wavelength.
Finally, we provide a Cauchy dispersion model that parameterises refractive
index measurements in terms of both wavelength and relative humidity. Our
parameterisations should provide useful information to researchers requiring
an accurate and comprehensive treatment of the wavelength and relative
humidity dependence of refractive index for the inorganic component of
atmospheric aerosol
Building the ACS Exams Anchoring Concept Content Map for Undergraduate Chemistry
The ability to coherently assess content knowledge throughout an entire undergraduate career represents a significant advantage for programmatic assessment strategies. Chemistry, as a discipline, has an unusual tool in this regard because of the nationally standardized exams from the ACS Exams Institute. These exams are norm-referenced and allow chemistry departments to make comparisons between the performance of their own students relative to national samples; however, currently there appears to be no systematic means for noting students’ content knowledge growth over a four-year degree. The Exams Institute is undertaking the task of organizing content along an anchoring concept or “big ideas” framework to facilitate this type of analysis
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