114 research outputs found
Econometric Modeling and Analysis of Residential Water Demand Based on Unbalanced Panel Data
This paper develops an econometric methodology devised to analyze a sample of time unbalanced panel data on residential water consumption in the French island La Reunion with the purpose to bring out the main determinants of household water consumption and estimate the importance of water consumption by uses. For this purpose, we specify a daily panel econometric model and derive, by performing a time aggregation, a general linear regression model accounting for water consumption data recorded on periods of any calendar date and time length. To esti-mate efficiently the parameters of this model we develop a feasible two step generalized least square method. Using the principle of best linear unbiased prediction, we finally develop an approach allowing to consistently break down the volume of water consumption recorded on household water bills by uses, namely by enforcing this estimated decomposition to add up to the observed total. The application of this methodology to a sample of 437 unbalanced panel observations shows the scope of this approach for the empirical analysis of actual data.econometric modeling; water consumption; panel data
Growth Of AlN Crystals On AlN/SiC Seeds By AlN Powder Sublimation In Nitrogen Atmosphere
AlN single crystals were grown on AlN/SiC seeds by sublimation of AlN powder in TaC crucibles in a nitrogen atmosphere. The seeds were produced by metallorganic chemical vapor deposition (MOCVD) of AlN on SiC crystals. The influence of growth temperature, growth time and source-toseed distance on the crystallinity and the crystal growth rate were investigated. Crystals were grown in an RF heated sublimation reactor at growth temperatures ranging from 1800-2000 °C, at a pressure of 600 Torr, nitrogen flow-rate of 100 sccm and source-to-seed distances of 10 and 35 mm. At 1870 °C and a source-to-seed distance of 35 mm, isolated crystals were observed with few instances of coalescence. At 1930 °C, a source-to-seed distance of 10 mm and longer growth times (~30 hrs), crystal coalescence was achieved. Above 1930 °C, the decomposition of SiC was evidently affecting the growth morphology and resulted in growth of polycrystalline AlN. After an initial nucleation period, the observed growth rates (10-30 μm/hr) were in close agreement with predictions of a growth model that assumed gas-phase diffusion controlled growth. Optical and electron microscope observations revealed step-flow growth, while X-ray diffraction results showed the single crystal nature of the grown material. Single crystalline AlN was grown over surface areas of 200-300 mm2 and was transparent and essentially colorless
Deflection of Slow Light by Magneto-Optically Controlled Atomic Media
We present a semi-classical theory for light deflection by a coherent
-type three-level atomic medium in an inhomogeneous magnetic field or
an inhomogeneous control laser. When the atomic energy levels (or the Rabi
coupling by the control laser) are position-dependent due to the Zeeman effect
by the inhomogeneous magnetic field (or the inhomogeneity of the control field
profile), the spatial dependence of the refraction index of the atomic medium
will result in an observable deflection of slow signal light when the
electromagnetically induced transparency happens to avoid medium absorption.
Our theoretical approach based on Fermat's principle in geometrical optics not
only provides a consistent explanation for the most recent experiment in a
straightforward way, but also predicts the new effects for the slow signal
light deflection by the atomic media in an inhomogeneous off-resonant control
laser field.Comment: 4 pages, 3 figure
Highly charged ion X-rays from Electron-Cyclotron Resonance Ion Sources
Radiation from the highly-charged ions contained in the plasma of
Electron-Cyclotron Resonance Ion Sources constitutes a very bright source of
X-rays. Because the ions have a relatively low kinetic energy ( eV)
transitions can be very narrow, containing only small Doppler broadening. We
describe preliminary accurate measurements of two and three-electron ions with
Z=16--18. We show how these measurement can test sensitively many-body
relativistic calculations or can be used as X-ray standards for precise
measurements of X-ray transitions in exotic atoms
Production and decay of Sulphur excited species in a ECRIS plasma
The most important processes for the creation of S12+ to S14+ ions excited
states from the ground configurations of S9+ to S14+ ions in an electron
cyclotron resonance ion source, leading to the emission of K X-ray lines, are
studied. Theoretical values for inner-shell excitation and ionization cross
sections, including double KL and triple KLL ionization, transition
probabilities and energies for the deexcitation processes, are calculated in
the framework of the multi-configuration Dirac-Fock method. With reasonable
assumptions about the electron energy distribution, a theoretical K
X-ray spectrum is obtained, which is compared to recent experimental data
Pionic Deuterium
The strong interaction shift and broadening in pionic deuterium have been
remeasured with high statistics by means of the (3p-1s) X-ray transition using
the cyclotron trap and a high-resolution crystal spectrometer. Preliminary
results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV
for the width, which yields precise values for the pion-deuteron scattering
length and the threshold parameter for pion production.Comment: Conf. Proc. Few Body 19 (FB19), August 31 - September 5, 2009, Bonn,
Germany 9 pages, 13 figure
Precision determination of the dpi -> NN transition strength at threshold
An unusual but effective way to determine at threshold the dpi -> NN
transition strength is to exploit the hadronic ground-state broadening in
pionic deuterium, accessible by x-ray spectroscopy. The broadening is dominated
by the true absorption channel dpi- -> nn, which is related to s-wave pion
production pp -> dpi+ by charge symmetry and detailed balance. Using the exotic
atom circumvents the problem of Coulomb corrections to the cross section as
necessary in the production experiments. Our dedicated measurement finds
(1171+23/-49) meV for the broadening yielding (252+5/-11) \mub.Comment: 4 pages, 2 figures, 1 tabl
Phonon pressure coefficients and deformation potentials of wurtzite AlN determined by uniaxial pressure-dependent Raman measurements
© 2014 American Physical Society. We studied bulk crystals of wurtzite AlN by means of uniaxial pressure-dependent Raman measurements. As a result, we derive the phonon pressure coefficients and deformation potentials for all zone center optical phonon modes. For the A1 and E1 modes, we further experimentally determined the uniaxial pressure dependence of their longitudinal optical-transverse optical (LO-TO) splittings. Our experimental approach delivers new insight into the large variance among previously reported phonon deformation potentials, which are predominantly based on heteroepitaxial growth of AlN and the ball-on-ring technique. Additionally, the measured phonon pressure coefficients are compared to their theoretical counterparts obtained by density functional theory implemented in the siesta package. Generally, we observe a good agreement between the calculated and measured phonon pressure coefficients but some particular Raman modes exhibit significant discrepancies similar to the case of wurtzite GaN and ZnO, clearly motivating the presented uniaxial pressure-dependent Raman measurements on bulk AlN crystals
A vacuum double-crystal spectrometer for reference-free highly charged ions X-ray spectroscopy
We have built a vacuum double crystal spectrometer, which coupled to an
electron-cyclotron resonance ion source, allows to measure low-energy x-ray
transitions in highly-charged ions with accuracies of the order of a few parts
per million. We describe in detail the instrument and its performances.
Furthermore, we present a few spectra of transitions in Ar, Ar
and Ar. We have developed an ab initio simulation code that allows us
to obtain accurate line profiles. It can reproduce experimental spectra with
unprecedented accuracy. The quality of the profiles allows the direct
determination of line width.Comment: 21 pages; Version
Resonant nonlinear magneto-optical effects in atoms
In this article, we review the history, current status, physical mechanisms,
experimental methods, and applications of nonlinear magneto-optical effects in
atomic vapors. We begin by describing the pioneering work of Macaluso and
Corbino over a century ago on linear magneto-optical effects (in which the
properties of the medium do not depend on the light power) in the vicinity of
atomic resonances, and contrast these effects with various nonlinear
magneto-optical phenomena that have been studied both theoretically and
experimentally since the late 1960s. In recent years, the field of nonlinear
magneto-optics has experienced a revival of interest that has led to a number
of developments, including the observation of ultra-narrow (1-Hz)
magneto-optical resonances, applications in sensitive magnetometry, nonlinear
magneto-optical tomography, and the possibility of a search for parity- and
time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002,
Figure added, typos corrected, text edited for clarit
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