1,312 research outputs found
Inflationary and dark energy regimes in 2+1 dimensions
In this work we investigate the behavior of three-dimensional (3D)
cosmological models. The simulation of inflationary and dark-energy-dominated
eras are among the possible results in these 3D formulations; taking as
starting point the results obtained by Cornish and Frankel.
Motivated by those results, we investigate, first, the inflationary case
where we consider a two-constituent cosmological fluid: the scalar field
represents the hypothetical inflaton which is in gravitational interaction with
a matter/radiation contribution. For the description of an old universe, it is
possible to simulate its evolution starting with a matter dominated universe
that faces a decelerated/accelerated transition due to the presence of the
additional constituent (simulated by the scalar field or ruled by an exotic
equation of state) that plays the role of dark energy. We obtain, through
numerical analysis, the evolution in time of the scale factor, the
acceleration, the energy densities, and the hydrostatic pressure of the
constituents. The alternative scalar cosmology proposed by Cornish and Frankel
is also under investigation in this work. In this case an inflationary model
can be constructed when another non-polytropic equation of state (the van der
Waals equation) is used to simulate the behavior of an early 3D universe.Comment: Latex file, plus 9 figures. To appear in General Relativity and
Gravitatio
Energetics and Vibrational States for Hydrogen on Pt(111)
We present a combination of theoretical calculations and experiments for the
low-lying vibrational excitations of H and D atoms adsorbed on the Pt(111)
surface. The vibrational band states are calculated based on the full
three-dimensional adiabatic potential energy surface obtained from first
principles calculations. For coverages less than three quarters of a monolayer,
the observed experimental high-resolution electron peaks at 31 and 68meV are in
excellent agreement with the theoretical transitions between selected bands.
Our results convincingly demonstrate the need to go beyond the local harmonic
oscillator picture to understand the dynamics of this system.Comment: In press at Phys. Rev. Lett - to appear in April 200
Do higher alarm thresholds for arterial blood pressure lead to less perioperative hypotension? A retrospective, observational cohort study
Arterial blood pressure is one of the vital signs monitored mandatory in anaesthetised patients. Even short episodes of intraoperative hypotension are associated with increased risk for postoperative organ dysfunction such as acute kidney injury and myocardial injury. Since there is little evidence whether higher alarm thresholds in patient monitors can help prevent intraoperative hypotension, we analysed the blood pressure data before (group 1) and after (group 2) the implementation of altered hypotension alarm settings. The study was conducted as a retrospective observational cohort study in a large surgical centre with 32 operating theatres. Alarm thresholds for hypotension alarm for mean arterial pressure (MAP) were altered from 60 (before) to 65 mmHg for invasive measurement and 70 mmHg for noninvasive measurement. Blood pressure data from electronic anaesthesia records of 4222 patients (1982 and 2240 in group 1 and 2, respectively) with 406,623 blood pressure values undergoing noncardiac surgery were included. We analysed (A) the proportion of blood pressure measurements below the threshold among all measurements by quasi-binomial regression and (B) whether at least one blood pressure measurement below the threshold occurred by logistic regression. Hypotension was defined as MAPâ<â65 mmHg. There was no significant difference in overall proportions of hypotensive episodes for mean arterial pressure before and after the adjustment of alarm settings (mean proportion of values below 65 mmHg were 6.05% in group 1 and 5.99% in group 2). The risk of ever experiencing a hypotensive episode during anaesthesia was significantly lower in group 2 with an odds ratio of 0.84 (pâ=â0.029). In conclusion, higher alarm thresholds do not generally lead to less hypotensive episodes perioperatively. There was a slight but significant reduction of the occurrence of intraoperative hypotension in the presence of higher thresholds for blood pressure alarms. However, this reduction only seems to be present in patients with very few hypotensive episodes
Spontaneous Polarisation Build up in a Room Temperature Polariton Laser
We observe the build up of strong (~50%) spontaneous vector polarisation in
emission from a GaN-based polariton laser excited by short optical pulses at
room temperature. The Stokes vector of emitted light changes its orientation
randomly from one excitation pulse to another, so that the time-integrated
polarisation remains zero. This behaviour is completely different to any
previous laser. We interpret this observation in terms of the spontaneous
symmetry breaking in a Bose-Einstein condensate of exciton-polaritons
Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off Si and Zr
We report on a new measurement of the beam-normal single spin asymmetry
in the elastic scattering of 570 MeV transversely polarized
electrons off Si and Zr at . The
studied kinematics allow for a comprehensive comparison with former results on
C. No significant mass dependence of the beam-normal single spin
asymmetry is observed in the mass regime from C to Zr.Comment: Submitted for publication to Physics Letters
Welt ohne Bargeld? â VerĂ€nderungen der klassischen Banken- und Bezahlsysteme
Die TAB-Kurzstudie Nr. 2 bietet einen Ăberblick ĂŒber Entwicklungen im Zahlungsverkehr bis einschlieĂlich Februar 2021. Die spezifischen Eigenschaften von Bargeld sowie ausgewĂ€hlter unbarer Zahlungslösungen werden darin genauso in den Blick genommen und miteinander verglichen wie das Zahlungsverhalten in Deutschland, Schweden und China. Eine Betrachtung des sich wandelnden MachtgefĂŒges im Zahlungsverkehr durch das Auftreten neuer Akteure und die Reaktionen traditioneller Kreditinstitute und Zentralbanken hierauf runden die Kurzstudie ab
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