287 research outputs found
Dispersion Theory and the Low Energy Constants for Neutral Pion Photoproduction
The relativistic amplitudes of pion photoproduction are evaluated by
dispersion relations at t=const. The imaginary parts of the amplitudes are
taken from the MAID model covering the absorption spectrum up to center-of-mass
energies W = 2.2 GeV. For sub-threshold kinematics the amplitudes are expanded
in powers of the two independent variables \nu and t related to energy and
momentum transfer. Subtracting the loop corrections from this power series
allows one to determine the counter terms of covariant baryon chiral
perturbation theory. The proposed continuation of the amplitudes into the
unphysical region provides a unique framework to derive the low-energy
constants to any given order as well as an estimate of the higher order terms
by global properties of the absorption spectrum.Comment: 13 pages, 6 figures, 5 table
Ensemble evaluation of hydrological model hypotheses
It is demonstrated for the first time how model parameter, structural and data uncertainties can be accounted for explicitly and simultaneously within the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. As an example application, 72 variants of a single soil moisture accounting store are tested as simplified hypotheses of runoff generation at six experimental grassland field-scale lysimeters through model rejection and a novel diagnostic scheme. The fields, designed as replicates, exhibit different hydrological behaviors which yield different model performances. For fields with low initial discharge levels at the beginning of events, the conceptual stores considered reach their limit of applicability. Conversely, one of the fields yielding more discharge than the others, but having larger data gaps, allows for greater flexibility in the choice of model structures. As a model learning exercise, the study points to a “leaking” of the fields not evident from previous field experiments. It is discussed how understanding observational uncertainties and incorporating these into model diagnostics can help appreciate the scale of model structural error
Modified Hagedorn formula including temperature fluctuation - Estimation of temperatures at RHIC experiments -
We have systematically estimated the possible temperatures obtained from an
analysis of recent data on distributions observed at RHIC experiments.
Using the fact that observed distributions cannot be described by the
original Hagedorn formula in the whole range of transverse momenta (in
particular above 6 GeV/c), we propose a modified Hagedorn formula including
temperature fluctuation. We show that by using it we can fit
distributions in the whole range and can estimate consistently the relevant
temperatures, including their fluctuations.Comment: Some misprints corrected, references updated. To be published in Eur.
Phys. J. C (2006
Phase properties of the superposition of squeezed and displaced number states
We show that a nonlinear asymmetric directional coupler composed of a linear
waveguide and a nonlinear waveguide operating by nondegenerate parametric
amplification is an effective source of single-mode squeezed light. This is has
been demonstrated, under certain conditions and for specific modes, for
incident coherent beams in terms of the quasiprobability functions,
photon-number distribution and phase distribution.Comment: 17 pages, 4 figure
Osvrti na publikacije
The World Urban Database and Access Portal Tools (WUDAPT) is a community initiative to collect worldwide data on urban form (i.e., morphology, materials) and function (i.e., use and metabolism). This is achieved through crowdsourcing, which we define here as the collection of data by a bounded crowd, composed of students. In this process, training data for the classification of urban structures into Local Climate Zones (LCZ) are obtained, which are, like most volunteered geographic information initiatives, of unknown quality. In this study, we investigated the quality of 94 crowdsourced training datasets for ten cities, generated by 119 students from six universities. The results showed large discrepancies and the resulting LCZ maps were mostly of poor to moderate quality. This was due to general difficulties in the human interpretation of the (urban) landscape and in the understanding of the LCZ scheme. However, the quality of the LCZ maps improved with the number of training data revisions. As evidence for the wisdom of the crowd, improvements of up to 20% in overall accuracy were found when multiple training datasets were used together to create a single LCZ map. This improvement was greatest for small training datasets, saturating at about ten to fifteen sets
Generation of squeezed light in a nonlinear asymmetric directional coupler
We show that a nonlinear asymmetric directional coupler composed of a linear
waveguide and a nonlinear waveguide operating by nondegenerate parametric
amplification is an effective source of single-mode squeezed light. This is has
been demonstrated, under certain conditions and for specific modes, for
incident coherent beams in terms of the quasiprobability functions,
photon-number distribution and phase distribution.Comment: 19 pages, 5 figure
- …