524 research outputs found
Pluripolarity of Graphs of Denjoy Quasianalytic Functions of Several Variables
In this paper we prove pluripolarity of graphs of Denjoy quasianalytic
functions of several variables on the spanning se
Pluricomplex Green and Lempert functions for equally weighted poles
For a domain in , the pluricomplex Green function with
poles is defined as .
When there is only one pole, or two poles in the unit ball, it turns out to be
equal to the Lempert function defined from analytic disks into by . It is known
that we always have . In the more general case where we
allow weighted poles, there is a counterexample to equality due to Carlehed and
Wiegerinck, with equal to the bidisk.
Here we exhibit a counterexample using only four distinct equally weighted
poles in the bidisk. In order to do so, we first define a more general notion
of Lempert function "with multiplicities", analogous to the generalized Green
functions of Lelong and Rashkovskii, then we show how in some examples this can
be realized as a limit of regular Lempert functions when the poles tend to each
other. Finally, from an example where in the case of
multiple poles, we deduce that distinct (but close enough) equally weighted
poles will provide an example of the same inequality. Open questions are
pointed out about the limits of Green and Lempert functions when poles tend to
each other.Comment: 25 page
Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer
We report on the design and commissioning of two silica aerogel Cherenkov
detectors with different refractive indices. In particular, extraordinary
performance in terms of the number of detected photoelectrons was achieved
through an appropriate choice of PMT type and reflector, along with some design
considerations. After four years of operation, the number of detected
photoelectrons was found to be noticeably reduced in both detectors as a result
of contamination, yellowing, of the aerogel material. Along with the details of
the set-up, we illustrate the characteristics of the detectors during different
time periods and the probable causes of the contamination. In particular we
show that the replacement of the contaminated aerogel and parts of the
reflecting material has almost restored the initial performance of the
detectors.Comment: 18 pages, 9 Figures, 4 Tables, 44 Reference
Assimilation of IASI partial tropospheric columns with an Ensemble Kalman Filter over Europe
Partial lower tropospheric ozone columns provided by the IASI (Infrared Atmospheric Sounding Interferometer) instrument have been assimilated into a chemistry-transport model at continental scale (CHIMERE) using an Ensemble Square Root Kalman Filter (EnSRF). Analyses are made for the month of July 2007 over the European domain. Launched in 2006, aboard the MetOp-A satellite, IASI shows high sensitivity for ozone in the free troposphere and low sensitivity at the ground; therefore it is important to evaluate if assimilation of these observations can improve free tropospheric ozone, and possibly surface ozone. The analyses are validated against independent ozone observations from sondes, MOZAIC<sup>1</sup> aircraft and ground based stations (AIRBASE â the European Air quality dataBase) and compared with respect to the free run of CHIMERE. These comparisons show a decrease in error of 6 parts-per-billion (ppb) in the free troposphere over the Frankfurt area, and also a reduction of the root mean square error (respectively bias) at the surface of 19% (33%) for more than 90% of existing ground stations. This provides evidence of the potential of data assimilation of tropospheric IASI columns to better describe the tropospheric ozone distribution, including surface ozone, despite the lower sensitivity. <br><br> The changes in concentration resulting from the observational constraints were quantified and several geophysical explanations for the findings of this study were drawn. The corrections were most pronounced over Italy and the Mediterranean region, we noted an average reduction of 8â9 ppb in the free troposphere with respect to the free run, and still a reduction of 5.5 ppb at ground, likely due to a longer residence time of air masses in this part associated to the general circulation pattern (i.e. dominant western circulation) and to persistent anticyclonic conditions over the Mediterranean basin. This is an important geophysical result, since the ozone burden is large over this area, with impact on the radiative balance and air quality. <br><br><br> <sup>1</sup> Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft (<a href="http://mozaic.aero.obs-mip.fr/web/"target="_blank">http://mozaic.aero.obs-mip.fr/web/</a>)
Measurement of the Electric Form Factor of the Neutron at Q^2=0.5 and 1.0 (GeV/c)^2
The electric form factor of the neutron was determined from measurements of
the \vec{d}(\vec{e},e' n)p reaction for quasielastic kinematics. Polarized
electrons were scattered off a polarized deuterated ammonia target in which the
deuteron polarization was perpendicular to the momentum transfer. The scattered
electrons were detected in a magnetic spectrometer in coincidence with neutrons
in a large solid angle detector. We find G_E^n = 0.0526 +/- 0.0033 (stat) +/-
0.0026 (sys) and 0.0454 +/- 0.0054 +/- 0.0037 at Q^2 = 0.5 and 1.0 (GeV/c)^2,
respectively.Comment: 5 pages, 2 figures, as publishe
Cross Section Measurement of Charged Pion Photoproduction from Hydrogen and Deuterium
We have measured the differential cross section for the gamma n --> pi- p and
gamma p --> pi+ n reactions at center of mass angle of 90 degree in the photon
energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at photon
energies greater than 3.3 GeV exhibit a global scaling behavior for both pi-
and pi+ photoproduction, consistent with the constituent counting rule and the
existing pi+ photoproduction data. Possible oscillations around the scaling
value are suggested by these new data The data show enhancement in the scaled
cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio
of exclusive pi- to pi+ photoproduction at high energy is consistent with the
prediction based on one-hard-gluon-exchange diagrams
Cross Section Measurements of Charged Pion Photoproduction in Hydrogen and Deuterium from 1.1 to 5.5 GeV
The differential cross section for the gamma +n --> pi- + p and the gamma + p
--> pi+ n processes were measured at Jefferson Lab. The photon energies ranged
from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4
GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The
pi- and pi+ photoproduction data both exhibit a global scaling behavior at high
energies and high transverse momenta, consistent with the constituent counting
rule prediction and the existing pi+ data. The data suggest possible
substructure of the scaling behavior, which might be oscillations around the
scaling value. The data show an enhancement in the scaled cross section at
center-of-mass energy near 2.2 GeV. The differential cross section ratios at
high energies and high transverse momenta can be described by calculations
based on one-hard-gluon-exchange diagrams.Comment: 18 pages, 19 figure
Low Q^2 measurements of the proton form factor ratio
We present an updated extraction of the proton electromagnetic form factor
ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial
distribution of the proton, and precise measurements can be used to constrain
models of the proton. An improved selection of the elastic events and reduced
background contributions yielded a small systematic reduction in the ratio mu_p
G_E/G_M compared to the original analysis.Comment: 12 pages, 5 figures, archival paper for proton form factor extraction
from Jefferson Lab "LEDEX" experimen
Measurements of the Electric Form Factor of the Neutron up to Q2=3.4 GeV2 using the Reaction He3(e,e'n)pp
The electric form factor of the neutron was determined from studies of the
reaction He3(e,e'n)pp in quasi-elastic kinematics in Hall A at Jefferson Lab.
Longitudinally polarized electrons were scattered off a polarized target in
which the nuclear polarization was oriented perpendicular to the momentum
transfer. The scattered electrons were detected in a magnetic spectrometer in
coincidence with neutrons that were registered in a large-solid-angle detector.
More than doubling the Q2-range over which it is known, we find GEn = 0.0225
+/- 0.0017 (stat) +/- 0.0024 (syst), 0.0200 +/- 0.0023 +/- 0.0018, and 0.0142
+/- 0.0019 +/- 0.0013 for Q2 = 1.72, 2.48, and 3.41 GeV2, respectively.Comment: submitted to PR
Proton Spin Structure in the Resonance Region
We have examined the spin structure of the proton in the region of the
nucleon resonances (1.085 GeV < W < 1.910 GeV) at an average four momentum
transfer of Q^2 = 1.3 GeV^2. Using the Jefferson Lab polarized electron beam, a
spectrometer, and a polarized solid target, we measured the asymmetries
A_parallel and A_perp to high precision, and extracted the asymmetries A_1 and
A_2, and the spin structure functions g_1 and g_2. We found a notably non-zero
A_perp, significant contributions from higher-twist effects, and only weak
support for polarized quark--hadron duality.Comment: 6 pages, 4 figures, REVTeX4, similar to PRL submission, plots
colorized and appenix added, v3: minor edit, matches PR
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