3,522 research outputs found
Application of the coherent state formalism to multiply excited states
A general expression is obtained for the matrix element of an m-body operator
between coherent states constructed from multiple orthogonal coherent boson
species. This allows the coherent state formalism to be applied to states
possessing an arbitrarily large number of intrinsic excitation quanta. For
illustration, the formalism is applied to the two-dimensional vibron model
[U(3) model], to calculate the energies of all excited states in the large-N
limit.Comment: LaTeX (iopart); 10 pages; to be published in J. Phys.
A data infrastructure for the assessment of health care performance: Lessons from the BRIDGE-health project
The integration of different administrative data sources from a number of European countries has been shown useful in the assessment of unwarranted variations in health care performance. This essay describes the procedures used to set up a data infrastructure (e.g., data access and exchange, definition of the minimum common wealth of data required, and the development of the relational logic data model) and, the methods to produce trustworthy healthcare performance measurements (e.g., ontologies standardisation and quality assurance analysis). The paper ends providing some hints on how to use these lessons in an eventual European infrastructure on public health research and monitoring. Although the relational data infrastructure developed has been proven accurate, effective to compare health system performance across different countries, and efficient enough to deal with hundred of millions of episodes, the logic data model might not be responsive if the European infrastructure aims at including electronic health records and carrying out multi-cohort multi-intervention comparative effectiveness research. The deployment of a distributed infrastructure based on semantic interoperability, where individual data remain in-country and open-access scripts for data management and analysis travel around the hubs composing the infrastructure, might be a sensible way forward
Calibration of the INCA model in a Mediterranean forested catchment: the effect of hydrological inter-annual variability in an intermittent stream
International audienceMediterranean regions are characterised by a stream hydrology with a marked seasonal pattern and high inter-annual variability. Accordingly, soil N processes and leaching of solutes in Mediterranean regions also show a marked seasonality, occurring in pulses as soils re-wet following rain. The Integrated Nitrogen Catchment model (INCA) was applied to Fuirosos, a Mediterranean catchment located in NE Spain using hydrological data and streamwater nitrate and ammonium concentrations collected from 1999 to 2002. This study tested the model under Mediterranean climate conditions and assessed the effect of the high inter-annual variability on the ability of INCA to simulate discharge and N fluxes. The model was calibrated for the whole three-year period and the n coefficients of determinion (r2) between simulated and observed data were 0.54 and 0.1 for discharge and nitrate temporal dynamics, respectively. Ammonium dynamics were simulated poorly and the linear regression between observed and simulated data was not significant statistically. To assess the effect of inter-annual variability on INCA simulations, the calibration process was run separately for two contrasting hydrological years: a dry year with a total rainfall of 525 mm and a wet year with a total of 871 mm. The coefficients of determination for the correlation between observed and simulated discharge for these two periods were 0.67 (p2 = 0.13 p2 = 0.56 p Keywords: environmental modelling, intermittent stream, Mediterranean climate, Fuirosos, hydrology, nitrat
Two-neutron halo nuclei in one dimension: dineutron correlation and breakup reaction
We propose a simple schematic model for two-neutron halo nuclei. In this
model, the two valence neutrons move in a one-dimensional mean field,
interacting with each other via a density-dependent contact interaction. We
first investigate the ground state properties, and demonstrate that the
dineutron correlation can be realized with this simple model due to the
admixture of even- and odd-parity single-particle states. We then solve the
time-dependent two-particle Schr\"odinger equation under the influence of a
time-dependent one-body external field, in order to discuss the effect of
dineutron correlation on nuclear breakup processes. The time evolution of
two-particle density shows that the dineutron correlation enhances the total
breakup probability, especially for the two-neutron breakup process, in which
both the valence neutrons are promoted to continuum scattering states. We find
that the interaction between the two particles definitely favours a spatial
correlation of the two outgoing particles, which are mainly emitted in the same
direction.Comment: 17 pages, 11 figure
Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems
Muon spin rotation and relaxation (SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materialsComment: 24 pages, 15 figures, submitted to J. Phys.: Condens. Matte
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