1,833 research outputs found
Design study of an entry probe spectro-reflectometer
A wind tunnel was built to simulate the rapid movement of an entry probe through the Jupiter atmosphere. Wind speeds range from 1 to 50 meters per second in a closed system. Wind velocity and temperature probes as well as a cryogenically cooled cold finger can be placed in the 6 inch diameter viewing section. The initial testing of the wind tunnel involved running sectional profiles through the observation port of air currents of 0.1 to 3.0 atmosphere. The velocity profile was very uniform throughout the cross section of the experimental port, with the exception of the wall effects. The deposition of cooled volatiles using the wind tunnel was not performed. However, measurements of the deposition of H2O ice on a cryogenically cooled thickness modulator were made under ambient conditions, namely room temperature and pressure. In the Frost Depositon Test Facility, ice deposition was measured at thicknesses of about a half millimeter and frost was produced whose thickness reflectivity could easily be measured by reflectance spectroscopy
The infrared spectrum of carbon suboxide. Part 1 - Region 1-2.5 microns. Part 2 - Region 2-15 microns. Part 3 - Classification of carbon suboxide vibrational bands
Laboratory tests of infrared spectrum of carbon suboxide, to determine presence in Venus and Mars atmosphere
Comment on "Nucleon elastic form factors and local duality"
We comment on the papers "Nucleon elastic form factors and local duality"
[Phys. Rev. {\bf D62}, 073008 (2000)] and "Experimental verification of
quark-hadron duality" [Phys. Rev. Lett. {\bf 85}, 1186 (2000)]. Our main
comment is that the reconstruction of the proton magnetic form factor, claimed
to be obtained from the inelastic scaling curve thanks to parton-hadron local
duality, is affected by an artifact.Comment: to appear in Phys. Rev.
Fluctuations in viscous fingering
Our experiments on viscous (Saffman-Taylor) fingering in Hele-Shaw channels
reveal finger width fluctuations that were not observed in previous
experiments, which had lower aspect ratios and higher capillary numbers Ca.
These fluctuations intermittently narrow the finger from its expected width.
The magnitude of these fluctuations is described by a power law, Ca^{-0.64},
which holds for all aspect ratios studied up to the onset of tip instabilities.
Further, for large aspect ratios, the mean finger width exhibits a maximum as
Ca is decreased instead of the predicted monotonic increase.Comment: Revised introduction, smoothed transitions in paper body, and added a
few additional minor results. (Figures unchanged.) 4 pages, 3 figures.
Submitted to PRE Rapi
Dual-readout Calorimetry
The RD52 Project at CERN is a pure instrumentation experiment whose goal is
to understand the fundamental limitations to hadronic energy resolution, and
other aspects of energy measurement, in high energy calorimeters. We have found
that dual-readout calorimetry provides heretofore unprecedented information
event-by-event for energy resolution, linearity of response, ease and
robustness of calibration, fidelity of data, and particle identification,
including energy lost to binding energy in nuclear break-up. We believe that
hadronic energy resolutions of {\sigma}/E 1 - 2% are within reach for
dual-readout calorimeters, enabling for the first time comparable measurement
preci- sions on electrons, photons, muons, and quarks (jets). We briefly
describe our current progress and near-term future plans. Complete information
on all aspects of our work is available at the RD52 website
http://highenergy.phys.ttu.edu/dream/.Comment: 10 pages, 10 figures, Snowmass White pape
Hadron detection with a dual-readout fiber calorimeter
In this paper, we describe measurements of the response functions of a
fiber-based dual- readout calorimeter for pions, protons and multiparticle
"jets" with energies in the range from 10 to 180 GeV. The calorimeter uses lead
as absorber material and has a total mass of 1350 kg. It is complemented by
leakage counters made of scintillating plastic, with a total mass of 500 kg.
The effects of these leakage counters on the calorimeter performance are
studied as well. In a separate section, we investigate and compare different
methods to measure the energy resolution of a calorimeter. Using only the
signals provided by the calorimeter, we demonstrate that our dual-readout
calorimeter, calibrated with electrons, is able to reconstruct the energy of
proton and pion beam particles to within a few percent at all energies. The
fractional widths of the signal distributions for these particles (sigma/E)
scale with the beam energy as 30%/sqrt(E), without any additional contributing
terms
Recalculation of Proton Compton Scattering in Perturbative QCD
At very high energy and wide angles, Compton scattering on the proton (gamma
p -> gamma p) is described by perturbative QCD. The perturbative QCD
calculation has been performed several times previously, at leading twist and
at leading order in alpha_s, with mutually inconsistent results, even when the
same light-cone distribution amplitudes have been employed. We have
recalculated the helicity amplitudes for this process, using contour
deformations to evaluate the singular integrals over the light-cone momentum
fractions. We do not obtain complete agreement with any previous result. Our
results are closest to those of the most recent previous computation, differing
significantly for just one of the three independent helicity amplitudes, and
only for backward scattering angles. We present results for the unpolarized
cross section, and for three different polarization asymmetries. We compare the
perturbative QCD predictions for these observables with those of the handbag
and diquark models. In order to reduce uncertainties associated with alpha_s
and the three-quark wave function normalization, we have normalized the Compton
cross section using the proton elastic form factor. The theoretical predictions
for this ratio are about an order of magnitude below existing experimental
data.Comment: Latex, 23 pages, 13 figures. Checked numerical integration one more
way; added results for one more proton distribution amplitude; a few other
minor changes. Version to appear in Phys. Rev.
Electro-Magnetic Nucleon Form Factors and their Spectral Functions in Soliton Models
It is demonstrated that in simple soliton models essential features of the
electro-magnetic nucleon form factors observed over three orders of magnitude
in momentum transfer are naturally reproduced. The analysis shows that
three basic ingredients are required: an extended object, partial coupling to
vector mesons, and relativistic recoil corrections. We use for the extended
object the standard skyrmion, one vector meson propagator for both isospin
channels, and the relativistic boost to the Breit frame. Continuation to
timelike leads to quite stable results for the spectral functions in the
regime from the 2- or 3-pion threshold to about two rho masses. Especially the
onset of the continuous part of the spectral functions at threshold can be
reliably determined and there are strong analogies to the results imposed on
dispersion theoretic approaches by the unitarity constraint.Comment: 24 pages, (RevTeX), 5 PS-figures; Data points in fig.2 and
corresponding references added. Final version, to be published in Z.Physik
New empirical fits to the proton electromagnetic form factors
Recent measurements of the ratio of the elastic electromagnetic form factors
of the proton, G_Ep/G_Mp, using the polarization transfer technique at
Jefferson Lab show that this ratio decreases dramatically with increasing Q^2,
in contradiction to previous measurements using the Rosenbluth separation
technique. Using this new high quality data as a constraint, we have reanalyzed
most of the world e-p elastic cross section data. In this paper, we present a
new empirical fit to the reanalyzed data for the proton elastic magnetic form
factor in the region 0 < Q^2 < 30 GeV^2. As well, we present an empirical fit
to the proton electromagnetic form factor ratio, G_Ep/G_Mp, which is valid in
the region 0.1 < Q^2 < 6 GeV^2
Nucleon and pion electromagnetic form factors in a light-front constituent quark model
Nucleon and pion electromagnetic form factors are evaluated in the spacelike
region within a light-front constituent quark model, where eigenfunctions of a
mass operator, reproducing a large set of hadron energy levels, are adopted and
quark form factors are considered in the one-body current. The hadron form
factors are sharply affected by the high momentum tail generated in the wave
function by the one-gluon-exchange interaction. Useful information on the
electromagnetic structure of light constituent quarks can be obtained from the
comparison with nucleon and pion experimental data.Comment: 9 pages, latex, 4 figures available as separate .uu fil
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