182 research outputs found
Thermal Detection of Turbulent and Laminar Dissipation in Vortex Front Motion
We report on direct measurements of the energy dissipated in the spin-up of
the superfluid component of 3He-B. A vortex-free sample is prepared in a
cylindrical container, where the normal component rotates at constant angular
velocity. At a temperature of 0.20Tc, seed vortices are injected into the
system using the shear-flow instability at the interface between 3He-B and
3He-A. These vortices interact and create a turbulent burst, which sets a
propagating vortex front into motion. In the following process, the free energy
stored in the initial vortex-free state is dissipated leading to the emission
of thermal excitations, which we observe with a bolometric measurement. We find
that the turbulent front contains less than the equilibrium number of vortices
and that the superfluid behind the front is partially decoupled from the
reference frame of the container. The final equilibrium state is approached in
the form of a slow laminar spin-up as demonstrated by the slowly decaying tail
of the thermal signal.Comment: 12 pages, 5 figures, to appear in Journal of Low Temperature Physic
Vortex phase diagram in trapped Bose-Einstein condensation
The vortex phase diagram in the external rotation frequency versus
temperature is calculated for dilute Bose-Einstein condensed gases. It is
determined within the Bogoliubov-Popov theory for a finite temperature where
the condensate and non-condensate fractions are treated in an equal footing.
The temperature dependences of various thermodynamic instability lines for the
vortex nucleation are computed to construct the phase diagram. Experiments are
proposed to resolve a recent controversy on the vortex creation problem
associated with the quantized vortex observation in Rb atom gases.Comment: 11 pages, 8 figure
Complex zeros of real ergodic eigenfunctions
We determine the limit distribution (as ) of complex
zeros for holomorphic continuations \phi_{\lambda}^{\C} to Grauert tubes of
real eigenfunctions of the Laplacian on a real analytic compact Riemannian
manifold with ergodic geodesic flow. If is an
ergodic sequence of eigenfunctions, we prove the weak limit formula
\frac{1}{\lambda_j} [Z_{\phi_{j_k}^{\C}}] \to \frac{i}{\pi} \bar{\partial}
{\partial} |\xi|_g, where [Z_{\phi_{j_k}^{\C}}] is the current of
integration over the complex zeros and where is with respect
to the adapted complex structure of Lempert-Sz\"oke and Guillemin-Stenzel.Comment: Added some examples and references. Also added a new Corollary, and
corrected some typo
Relativistic description of electron scattering on the deuteron
Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.Comment: (19 pages in revtex + 15 figures not included, available upon
request.) report THU-93-10
Neutrino Quasielastic Scattering on Nuclear Targets: Parametrizing Transverse Enhancement (Meson Exchange Currents)
We present a parametrization of the observed enhancement in the transverse
electron quasielastic (QE) response function for nucleons bound in carbon as a
function of the square of the four momentum transfer () in terms of a
correction to the magnetic form factors of bound nucleons. The parametrization
should also be applicable to the transverse cross section in neutrino
scattering. If the transverse enhancement originates from meson exchange
currents (MEC), then it is theoretically expected that any enhancement in the
longitudinal or axial contributions is small. We present the predictions of the
"Transverse Enhancement" model (which is based on electron scattering data
only) for the differential and total QE cross sections
for nucleons bound in carbon. The dependence of the transverse
enhancement is observed to resolve much of the long standing discrepancy in the
QE total cross sections and differential distributions between low energy and
high energy neutrino experiments on nuclear targets.Comment: Revised Version- July 21, 2011: 17 pages, 20 Figures. To be published
in Eur. Phys. J.
eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV
Differential cross sections for the reaction gamma p -> eta-prime p have been
measured with the CLAS spectrometer and a tagged photon beam with energies from
1.527 to 2.227 GeV. The results reported here possess much greater accuracy
than previous measurements. Analyses of these data indicate for the first time
the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710)
resonances, known to couple strongly to the eta N channel in photoproduction on
the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure
Measurement of the Deuteron Structure Function F2 in the Resonance Region and Evaluation of Its Moments
Inclusive electron scattering off the deuteron has been measured to extract
the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer
(CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement
covers the entire resonance region from the quasi-elastic peak up to the
invariant mass of the final-state hadronic system W~2.7 GeV with four-momentum
transfers Q2 from 0.4 to 6 (GeV/c)^2. These data are complementary to previous
measurements of the proton structure function F2 and cover a similar
two-dimensional region of Q2 and Bjorken variable x. Determination of the
deuteron F2 over a large x interval including the quasi-elastic peak as a
function of Q2, together with the other world data, permit a direct evaluation
of the structure function moments for the first time. By fitting the Q2
evolution of these moments with an OPE-based twist expansion we have obtained a
separation of the leading twist and higher twist terms. The observed Q2
behaviour of the higher twist contribution suggests a partial cancellation of
different higher twists entering into the expansion with opposite signs. This
cancellation, found also in the proton moments, is a manifestation of the
"duality" phenomenon in the F2 structure function
First measurement of direct photoproduction on the proton
We report on the results of the first measurement of exclusive
meson photoproduction on protons for GeV and GeV. Data were collected with the CLAS detector at the Thomas
Jefferson National Accelerator Facility. The resonance was detected via its
decay in the channel by performing a partial wave analysis of the
reaction . Clear evidence of the meson
was found in the interference between and waves at GeV. The -wave differential cross section integrated in the mass range of
the was found to be a factor of 50 smaller than the cross section
for the meson. This is the first time the meson has been
measured in a photoproduction experiment
Developing a predictive modelling capacity for a climate change-vulnerable blanket bog habitat: Assessing 1961-1990 baseline relationships
Aim: Understanding the spatial distribution of high priority habitats and
developing predictive models using climate and environmental variables to
replicate these distributions are desirable conservation goals. The aim of this
study was to model and elucidate the contributions of climate and topography to
the distribution of a priority blanket bog habitat in Ireland, and to examine how
this might inform the development of a climate change predictive capacity for
peat-lands in Ireland.
Methods: Ten climatic and two topographic variables were recorded for grid
cells with a spatial resolution of 1010 km, covering 87% of the mainland
land surface of Ireland. Presence-absence data were matched to these variables
and generalised linear models (GLMs) fitted to identify the main climatic and
terrain predictor variables for occurrence of the habitat. Candidate predictor
variables were screened for collinearity, and the accuracy of the final fitted GLM
was evaluated using fourfold cross-validation based on the area under the curve
(AUC) derived from a receiver operating characteristic (ROC) plot. The GLM
predicted habitat occurrence probability maps were mapped against the actual
distributions using GIS techniques.
Results: Despite the apparent parsimony of the initial GLM using only climatic
variables, further testing indicated collinearity among temperature and precipitation
variables for example. Subsequent elimination of the collinear variables and
inclusion of elevation data produced an excellent performance based on the AUC
scores of the final GLM. Mean annual temperature and total mean annual
precipitation in combination with elevation range were the most powerful
explanatory variable group among those explored for the presence of blanket
bog habitat.
Main conclusions: The results confirm that this habitat distribution in general
can be modelled well using the non-collinear climatic and terrain variables tested
at the grid resolution used. Mapping the GLM-predicted distribution to the
observed distribution produced useful results in replicating the projected
occurrence of the habitat distribution over an extensive area. The methods
developed will usefully inform future climate change predictive modelling for
Irelan
Irish cardiac society - Proceedings of annual general meeting held 20th & 21st November 1992 in Dublin Castle
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