6,569 research outputs found
Comparison of available measurements of the absolute fluorescence yield
The uncertainty in the absolute value of the fluorescence yield is still one
of the main contributions to the total error in the reconstruction of the
primary energy of ultra-energetic air showers using the fluorescence technique.
A significant number of experimental values of the fluorescence yield have been
published in the last years, however reported results are given very often in
different units (photons/MeV or photons/m) and for different wavelength
intervals. In this work we present a comparison of available results normalized
to its value in photons/MeV for the 337 nm band at 800 hPa and 293 K. The
conversion of photons/m to photons/MeV requires an accurate determination of
the energy deposited by the electrons in the field of view of the experimental
setup. We have calculated the energy deposition for each experiment by means of
a detailed Monte Carlo simulation including when possible the geometrical
details of the particular setup. Our predictions on deposited energy, as well
as on some geometrical factors, have been compared with those reported by the
authors of the corresponding experiments and possible corrections to the
fluorescence yields are proposed.Comment: 29 pages, 5 figures Revised version submitted to Astroparticle
Physic
Improved model for the analysis of air fluorescence induced by electrons
A model recently proposed for the calculation of air-fluorescence yield
excited by electrons is revisited. Improved energy distributions of secondary
electrons and a more realistic Monte Carlo simulation including some additional
processes have allowed us to obtain more accurate results. The model is used to
study in detail the relationship between fluorescence intensity and deposited
energy in a wide range of primary energy (keVs - GeVs). In addition,
predictions on the absolute value of the fluorescence efficiency in the absence
of collisional quenching will be presented and compared with available
experimental data.Comment: Contribution to the 5th Fluorescence Workshop, El Escorial, Madrid,
Spain, September 2007, to appear in Nuclear Instruments and Methods A.
Revised version.- More details on the comparison with experimental dat
Properties of 10 (18)-10 (19)eV EAS at far core distance
The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km
The yield of air fluorescence induced by electrons
The fluorescence yield for dry air and pure nitrogen excited by electrons is
calculated using a combination of well-established molecular properties and
experimental data of the involved cross sections. Particular attention has been
paid to the role of secondary electrons from ionization processes. At high
pressure and high energy, observed fluorescence turns out to be proportional to
the ionization cross section which follows the Born-Bethe law. Predictions on
fluorescence yields in a very wide interval of electron energies (eV - GeV) and
pressures (1 and 1013 hPa) as expected from laboratory measurements are
presented. Experimental results at energies over 1 MeV are in very good
agreement with our calculations for pure nitrogen while discrepancies of about
20% are found for dry air, very likely associated to uncertainties in the
available data on quenching cross sections. The relationship between
fluorescence emission, stopping power and deposited energy is discussed.Comment: 27 pages, 12 figures, 64 references. Accepted in Astroparticle
Physic
Strong Effects of Network Architecture in the Entrainment of Coupled Oscillator Systems
Entrainment of randomly coupled oscillator networks by periodic external
forcing applied to a subset of elements is numerically and analytically
investigated. For a large class of interaction functions, we find that the
entrainment window with a tongue shape becomes exponentially narrow for
networks with higher hierarchical organization. However, the entrainment is
significantly facilitated if the networks are directionally biased, i.e.,
closer to the feedforward networks. Furthermore, we show that the networks with
high entrainment ability can be constructed by evolutionary optimization
processes. The neural network structure of the master clock of the circadian
rhythm in mammals is discussed from the viewpoint of our results.Comment: 15 pages, 11 figures, RevTe
Pair distribution function in a two-dimensional electron gas
We calculate the pair distribution function, , in a two-dimensional
electron gas and derive a simple analytical expression for its value at the
origin as a function of . Our approach is based on solving the
Schr\"{o}dinger equation for the two-electron wave function in an appropriate
effective potential, leading to results that are in good agreement with Quantum
Monte Carlo data and with the most recent numerical calculations of . [C.
Bulutay and B. Tanatar, Phys. Rev. B {\bf 65}, 195116 (2002)] We also show that
the spin-up spin-down correlation function at the origin, , is mainly independent of the degree of spin polarization of
the electronic system.Comment: 5 figures, pair distribution dependence with distance is calculate
Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas
We present an analytical expression for the static many-body local field
factor of a homogeneous two-dimensional electron gas, which
reproduces Diffusion Monte Carlo data and embodies the exact asymptotic
behaviors at both small and large wave number . This allows us to also
provide a closed-form expression for the exchange and correlation kernel
, which represents a key input for density functional studies of
inhomogeneous systems.Comment: 5 pages, 3 figure
Diffractive Contribution to the Elasticity and the Nucleonic Flux in the Atmosphere
We calculate the average elasticity considering non-diffractive and single
diffractive interactions and perform an analysis of the cosmic-ray flux by
means of an analytical solution for the nucleonic diffusion equation. We show
that the diffractive contribution is important for the adequate description of
the nucleonic and hadronic fluxes in the atmosphere.Comment: 10 pages, latex, 2 figures (uuencoded PostScript
A semi-classical over-barrier model for charge exchange between highly charged ions and one-optical electron atoms
Absolute total cross sections for electron capture between slow, highly
charged ions and alkali targets have been recently measured. It is found that
these cross sections follow a scaling law with the projectile charge which is
different from the one previously proposed basing on a classical over-barrier
model (OBM) and verified using rare gases and molecules as targets. In this
paper we develop a "semi-classical" (i.e. including some quantal features) OBM
attempting to recover experimental results. The method is then applied to
ion-hydrogen collisions and compared with the result of a sophisticated
quantum-mechanical calculation. In the former case the accordance is very good,
while in the latter one no so satisfactory results are found. A qualitative
explanation for the discrepancies is attempted.Comment: RevTeX, uses epsf; 6 pages text + 3 EPS figures Journal of Physics B
(scehduled March 2000). This revision corrects fig.
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