14,498 research outputs found
Large classical universes emerging from quantum cosmology
It is generally believed that one cannot obtain a large Universe from quantum
cosmological models without an inflationary phase in the classical expanding
era because the typical size of the Universe after leaving the quantum regime
should be around the Planck length, and the standard decelerated classical
expansion after that is not sufficient to enlarge the Universe in the time
available. For instance, in many quantum minisuperspace bouncing models studied
in the literature, solutions where the Universe leave the quantum regime in the
expanding phase with appropriate size have negligible probability amplitude
with respect to solutions leaving this regime around the Planck length. In this
paper, I present a general class of moving gaussian solutions of the
Wheeler-DeWitt equation where the velocity of the wave in minisuperspace along
the scale factor axis, which is the new large parameter introduced in order to
circumvent the abovementioned problem, induces a large acceleration around the
quantum bounce, forcing the Universe to leave the quantum regime sufficiently
big to increase afterwards to the present size, without needing any classical
inflationary phase in between, and with reasonable relative probability
amplitudes with respect to models leaving the quantum regime around the Planck
scale. Furthermore, linear perturbations around this background model are free
of any transplanckian problem.Comment: 8 pages, 1 figur
NUMERICAL AND EXPERIMENTAL ANALYSIS OF THE FLOW OVER A COMMERCIAL VEHICLE - PICKUP
This work presents an ongoing numerical and experimental study of the flow around a pickup vehicle by means of CFD simulations and wind tunnel experiments. The model was based on the light-pickup market in Brazil and it was designed with flat surfaces and sharp edges. One of the objectives of this research was the understanding about the flow pattern around the vehicle, especially in the region behind the cabin and the wake. Another goal was to obtain original data from experimental measurements which could be used on further computational investigations. The experiments were carried out in a low-speed wind tunnel at Reynolds number of 5 x 105. Hot-wire anemometry was used to obtain the velocity profiles. Wall tufts were applied to describe the flow direction and regions of attached/detached and recirculation zones. Acceleration due to the underbody and the shear layer formed on the cabin were well defined, also indicating a region of reverse flow behind the tailgate. The flow visualization allowed the identification of recirculation regions inside the trunk and regions of detached flow. These flow patterns were also reproduced in the CFD simulations resulting satisfactory information to describe the main flow pattern over the pickup vehicle
QED vacuum between an unusual pair of plates
We consider the photon field between an unusual configuration of infinite
parallel plates: a perfectly conducting plate and an
infinitely permeable one . After quantizing the vector potential
in the Coulomb gauge, we obtain explicit expressions for the vacuum expectation
values of field operators of the form and . These field correlators allow us to reobtain the Casimir
effect for this set up and to discuss the light velocity shift caused by the
presence of plates (Scharnhorst effect \cite{Scharnhorst,Barton,BarScharn}) for
both scalar and spinor QED.Comment: Latex, 16 pages, no figure
Concept for a Time-of-Flight Small Angle Neutron Scattering Instrument at the European Spallation Source
A new Small Angle Neutron Scattering instrument is proposed for the European
Spallation Source. The pulsed source requires a time-of-flight analysis of the
gathered neutrons at the detector. The optimal instrument length is found to be
rather large, which allows for a polarizer and a versatile collimation. The
polarizer allows for studying magnetic samples and incoherent background
subtraction. The wide collimation will host VSANS and SESANS options that
increase the resolution of the instrument towards um and tens of um,
respectively. Two 1m2 area detectors will cover a large solid angle
simultaneously. The expected gains for this new instrument will lie in the
range between 20 and 36, depending on the assessment criteria, when compared to
up-to-date reactor based instruments. This will open new perspectives for fast
kinetics, weakly scattering samples, and multi-dimensional contrast variation
studies.Comment: 18 pages, 10 figure
Association Between Sedentary Time and Quality of Life From the Osteoarthritis Initiative: Who Might Benefit Most From Treatment?
Objective To investigate the relationship between sedentary behavior and quality-adjusted life years (QALYs) among participants in the Osteoarthritis Initiative. Design Longitudinal, observational design. Setting Osteoarthritis Initiative cohort. Participants
Individuals (N=1794) from a prospective, multicenter longitudinal cohort were classified into quantile groups based on average daily sedentary time (most sedentary, quartile 1 [Q1] ≥11.6h; 10.7h≤ Q2 Interventions Not applicable. Main Outcome Measures Individual QALYs were estimated over 2 years from the area under the curve of health-related utility scores derived from the Medical Outcomes Study 12-Item Short-Form Health Survey versus time. The relationship between baseline sedentary behavior and median 2-year QALYs was estimated using quantile regression adjusted for socioeconomic factors and body mass index. Results Lower QALYs over 2 years were more frequently found among the most sedentary (Q1, median 1.59), and QALYs increased as time spent in baseline sedentary behavior decreased (median QALYs for Q2, 1.64; Q3, 1.65; Q4, 1.65). The relationship of sedentary time and median QALY change was only significant for the most sedentary Q1 group, where an additional hour of sedentary behavior significantly reduced QALYs by −.072 (95% confidence interval, −.121 to −.020). Conclusions Our findings suggest that individuals with the most extreme sedentary profiles may be vulnerable to additional losses of quality of life if they become more sedentary. Targeting these individuals to decrease sedentary behavior has the potential to be cost-effective
Quantum Stephani exact cosmological solutions and the selection of time variable
We study perfect fluid Stephani quantum cosmological model. In the present
work the Schutz's variational formalism which recovers the notion of time is
applied. This gives rise to Wheeler-DeWitt equation for the scale factor. We
use the eigenfunctions in order to construct wave packets for each case. We
study the time-dependent behavior of the expectation value of the scale factor,
using many-worlds and deBroglie-Bohm interpretations of quantum mechanics.Comment: 19 pages, 7 figure
Possible Stellar Metallicity Enhancements from the Accretion of Planets
A number of recently discovered extrasolar planet candidates have
surprisingly small orbits, which may indicate that considerable orbital
migration takes place in protoplanetary systems. A natural consequence of
orbital migration is for a series of planets to be accreted, destroyed, and
then thoroughly mixed into the convective envelope of the central star. We
study the ramifications of planet accretion for the final main sequence
metallicity of the star. If maximum disk lifetimes are on the order of 10 Myr,
stars with masses near 1 solar mass are predicted to have virtually no
metallicity enhancement. On the other hand, early F and late A type stars with
masses of 1.5--2.0 solar masses can experience significant metallicity
enhancements due to their considerably smaller convection zones during the
first 10 Myr of pre-main-sequence evolution. We show that the metallicities of
an aggregate of unevolved F stars are consistent with an average star accreting
about 2 Jupiter-mass planets from a protoplanetary disk having a 10 Myr
dispersal time.Comment: 14 pages, AAS LaTeX, 3 figures, accepted to ApJ Letter
Widening the perspectives for legume consumption: the case of bioactive non-nutrients
Legume grains have provided essential nutrients in human diets for centuries, being excellent sources of proteins, carbohydrates, fatty acids, and fibers. They also contain several non-nutrients that historically have been connotated as toxic but that in recent years have been shown to have interesting bioactive properties. The discussion on the role of bioactive non-nutrients is becoming more important due to increasing science-based evidence on their potential antioxidant, hypoglycemic, hypolipidemic, and anticarcinogenic properties. At a time when legume-based products consumption is being strongly promoted by national governments and health authorities, there is a need to clearly define the recommended levels of such non-nutrients in human diets. However, there is insufficient data determining the ideal amount of non-nutrients in legume grains, which will exert the most positive health benefits. This is aligned with insufficient studies that clearly demonstrate if the positive health effects are due to the presence of specific non-nutrients or a result of a dietary balance. In fact, rather than looking directly at the individual food components, most nutritional epidemiology studies relate disease risk with the food and dietary patterns. The purpose of this perspective paper is to explore different types of non-nutrients present in legume grains, discuss the current evidence on their health benefits, and provide awareness for the need for more studies to define a recommended amount of each compound to identify the best approaches, either to enhance or reduce their levels.info:eu-repo/semantics/publishedVersio
Quantum Cosmology in Scalar-Tensor Theories With Non Minimal Coupling
Quantization in the minisuperspace of non minimal scalar-tensor theories
leads to a partial differential equation which is non separable. Through a
conformal transformation we can recast the Wheeler-DeWitt equation in an
integrable form, which corresponds to the minimal coupling case, whose general
solution is known. Performing the inverse conformal transformation in the
solution so found, we can construct the corresponding one in the original
frame. This procedure can also be employed with the bohmian trajectories. In
this way, we can study the classical limit of some solutions of this quantum
model. While the classical limit of these solutions occurs for small scale
factors in the Einstein's frame, it happens for small values of the scalar
field non minimally coupled to gravity in the Jordan's frame, which includes
large scale factors.Comment: latex, 18 page
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