179 research outputs found
Investigating transition state resonances in the time domain by means of Bohmian mechanics: The F+HD reaction
In this work, we investigate the existence of transition state resonances on
atom-diatom reactive collisions from a time-dependent perspective, stressing
the role of quantum trajectories as a tool to analyze this phenomenon. As it is
shown, when one focusses on the quantum probability current density, new
dynamical information about the reactive process can be extracted. In order to
detect the effects of the different rotational populations and their
dynamics/coherences, we have considered a reduced two-dimensional dynamics
obtained from the evolution of a full three-dimensional quantum time-dependent
wave packet associated with a particular angle. This reduction procedure
provides us with information about the entanglement between the radial degrees
of freedom (r,R) and the angular one (\gamma), which can be considered as
describing an environment. The combined approach here proposed has been applied
to study the F+HD reaction, for which the FH+D product channel exhibits a
resonance-mediated dynamics.Comment: 12 pages, 9 figure
Loss of coherence in double-slit diffraction experiments
By using optical models based on the theory of partially coherent light, and the quantum decoherence model proposed by Joos and Zeh [Z. Phys. B 59, 223 (1985)], we explore incoherence and decoherence in interference phenomena. The problem chosen to study is that of the double-slit diffraction experiment, a paradigmatic example in quantum mechanics. In particular, we perform an analysis of the experiment carried out with cold neutrons by Zeilinger et al. [Rev. Mod. Phys. 60, 1067 (1988).
Contextuality, decoherence and quantum trajectories
Here we analyze the relationship between quantum contextuality and
decoherence in interference experiments with matter particles by means of a
simple reduced quantum-trajectory model, which attempts to simulate the
behavior of the projections of multi-dimensional, system-plus-environment
Bohmian trajectories onto the subspace of the reduced system. This model allows
us to understand the crossing of the subsystem trajectories as a combined
effect of interference quenching and erasure of ``which-way'' information,
which can be of utility to interpret decoherence effects in many-dimensional
systems where full Bohmian treatments become prohibitive computationally.Comment: 15 pages, 3 figure
Protocolos de conservación de restos pleistocenos de tortuga mediterránea procedentes de la Cova del Rinoceront (Castelldefels, Barcelona)
La Cova del Rinoceront presenta una cronología que abarca desde el Pleistoceno medio a inicios del superior. Este yacimiento presenta una de las colecciones de tortuga mediterránea (Testudo hermanni) fósil más importante de la Península Ibérica. Este conjunto, se caracteriza por la elevada cantidad de restos y su frágil estado de conservación. Los restos se clasifican en función de su estado de preservación para poder definir diferentes metodologías de intervención y garantizar así su rápida estabilización para la investigación
Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories
This paper examines the nature of classical correspondence in the case of
coherent states at the level of quantum trajectories. We first show that for a
harmonic oscillator, the coherent state complex quantum trajectories and the
complex classical trajectories are identical to each other. This congruence in
the complex plane, not restricted to high quantum numbers alone, illustrates
that the harmonic oscillator in a coherent state executes classical motion. The
quantum trajectories are those conceived in a modified de Broglie-Bohm scheme
and we note that identical classical and quantum trajectories for coherent
states are obtained only in the present approach. The study is extended to
Gazeau-Klauder and SUSY quantum mechanics-based coherent states of a particle
in an infinite potential well and that in a symmetric Poschl-Teller (PT)
potential by solving for the trajectories numerically. For the coherent state
of the infinite potential well, almost identical classical and quantum
trajectories are obtained whereas for the PT potential, though classical
trajectories are not regained, a periodic motion results as t --> \infty.Comment: More example
Bohmian mechanics, the quantum-classical correspondence and the classical limit: the case of the square billiard
Square billiards are quantum systems complying with the dynamical
quantum-classical correspondence. Hence an initially localized wavefunction
launched along a classical periodic orbit evolves along that orbit, the
spreading of the quantum amplitude being controlled by the spread of the
corresponding classical statistical distribution. We investigate wavepacket
dynamics and compute the corresponding de Broglie-Bohm trajectories in the
quantum square billiard. We also determine the trajectories and statistical
distribution dynamics for the equivalent classical billiard. Individual Bohmian
trajectories follow the streamlines of the probability flow and are generically
non-classical. This can also hold even for short times, when the wavepacket is
still localized along a classical trajectory. This generic feature of Bohmian
trajectories is expected to hold in the classical limit. We further argue that
in this context decoherence cannot constitute a viable solution in order to
recover classicality.Comment: Figures downgraded to low resolution; To be published in Found. Phys.
(2009)
Thrombolysis with tissue plasminogen activator in acute myocardial infarction: no additional benefit from immediate percutaneous coronary angioplasty
A randomised trial of 367 patients with acute myocardial infarction was performed to determine whether an invasive strategy combining thrombolysis with recombinant tissue-type plasminogen activator (rTPA), heparin, and acetylsalicylic acid, and immediate percutaneous transluminal coronary angioplasty (PTCA) would be superior to a noninvasive strategy with the same medical treatment but without immediate angiography and PTCA. Intravenous infusion of 100 mg rTPA was started within 5 h after onset of symptoms (median 156 min). Angiography was performed 6-165 min later in 180 out of 183 patients allocated to the invasive strategy; 184 patients were allocated to the non-invasive strategy. Immediate PTCA reduced the percentage stenosis of the infarc
The British Influence in the Birth of Spanish Sport
Sports started to gain relevance in Spain around the end of the nineteenth century and the beginning of the twentieth century as a leisure and health option of the upper classes imported from Britain. Its early development was intertwined with the spread of other kinds of physical activities with much more tradition on the continent: gymnastics and physical education. First played by the ruling classes – aristocracy and high bourgeoisie – sports permeated towards petty bourgeoisie and middle classes in urban areas such as Madrid, Barcelona, San Sebastián and Santander. This pattern meant that the expansion of sports was unavoidably tied to the degree of industrialisation and cultural modernisation of the country. Since 1910, and mainly during the 1920s, sport grew in popularity as a spectacle and, toa much lesser degree, as a practice among the Spanish population
<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7.
Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release.
Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue.
Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼0.3 mas should be added to the parallax uncertainties. For the subset of ∼94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼0.03 mag over the magnitude range 5 to 20.7.
Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data
Sex differences between women and men with COPD: A new analysis of the 3CIA study
Background: There is partial evidence that COPD is expressed differently in women than in men, namely on symptoms, pulmonary function, exacerbations, comorbidities or prognosis. There is a need to improve the characterization of COPD in females.
Methods: We obtained and pooled data of 17 139 patients from 22 COPD cohorts and analysed the clinical differences by sex, establishing the relationship between these characteristics in women and the prognosis and severity of the disease. Comparisons were established with standard statistics and survival analysis, including crude and multivariate Cox-regression analysis.
Results: Overall, 5355 (31.2%) women were compared with men with COPD. Women were younger, had lower pack-years, greater FEV1%, lower BMI and a greater number of exacerbations (all p < 0.05). On symptoms, women reported more dyspnea, equal cough but less expectoration (p < 0.001). There were no differences in the BODE index score in women (2.4) versus men (2.4) (p = 0.5), but the distribution of all BODE components was highly variable by sex within different thresholds of BODE. On prognosis, 5-year survival was higher in COPD females (86.9%) than in males (76.3%), p < 0.001, in all patients and within each of the specific comorbidities that we assessed. The crude and adjusted RR and 95% C.I. for death in males was 1.82 (1.69–1.96) and 1.73 (1.50–2.00), respectively.
Conclusions: COPD in women has some characteristic traits expressed differently than compared to men, mainly with more dyspnea and COPD exacerbations and less phlegm, among others, although long-term survival appears better in female COPD patients
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