38,239 research outputs found
Phase appearance or disappearance in two-phase flows
This paper is devoted to the treatment of specific numerical problems which
appear when phase appearance or disappearance occurs in models of two-phase
flows. Such models have crucial importance in many industrial areas such as
nuclear power plant safety studies. In this paper, two outstanding problems are
identified: first, the loss of hyperbolicity of the system when a phase appears
or disappears and second, the lack of positivity of standard shock capturing
schemes such as the Roe scheme. After an asymptotic study of the model, this
paper proposes accurate and robust numerical methods adapted to the simulation
of phase appearance or disappearance. Polynomial solvers are developed to avoid
the use of eigenvectors which are needed in usual shock capturing schemes, and
a method based on an adaptive numerical diffusion is designed to treat the
positivity problems. An alternate method, based on the use of the hyperbolic
tangent function instead of a polynomial, is also considered. Numerical results
are presented which demonstrate the efficiency of the proposed solutions
Bifurcations of a large scale circulation in a quasi-bidimensional turbulent flow
We report the experimental study of the bifurcations of a large-scale
circulation that is formed over a turbulent flow generated by a spatially
periodic forcing. After shortly describing how the flow becomes turbulent
through a sequence of symmetry breaking bifurcations, we focus our study on the
transitions that occur within the turbulent regime. They are related to changes
in the shape of the probability density function (PDF) of the amplitude of the
large scale flow. We discuss the nature of these bifurcations and how to model
the shape of the PDF.Comment: 6 pages, 9 figure
Inter edge Tunneling in Quantum Hall Line Junctions
We propose a scenario to understand the puzzling features of the recent
experiment by Kang and coworkers on tunneling between laterally coupled quantum
Hall liquids by modeling the system as a pair of coupled chiral Luttinger
liquid with a point contact tunneling center. We show that for filling factors
the effects of the Coulomb interactions move the system deep into
strong tunneling regime, by reducing the magnitude of the Luttinger parameter
, leading to the appearance of a zero-bias differential conductance peak of
magnitude at zero temperature. The abrupt appearance of the zero
bias peak as the filling factor is increased past a value ,
and its gradual disappearance thereafter can be understood as a crossover
controlled by the main energy scales of this system: the bias voltage , the
crossover scale , and the temperature . The low height of the zero bias
peak observed in the experiment, and its broad finite width,
can be understood naturally within this picture. Also, the abrupt reappearance
of the zero-bias peak for can be explained as an effect caused
by spin reversed electrons, \textit{i. e.} if the 2DEG is assumed to have a
small polarization near . We also predict that as the temperature is
lowered should decrease, and the width of zero-bias peak should become
wider. This picture also predicts the existence of similar zero bias peak in
the spin tunneling conductance near for .Comment: 17 pages, 8 figure
Coronal hole boundaries at small scales: III. EIS and SUMER views
We report on the plasma properties of small-scale transient events identified
in the quiet Sun, coronal holes and their boundaries.
We use spectroscopic co-observations from SUMER/SoHO and EIS/Hinode combined
with high cadence imaging data from XRT/Hinode. We measure Doppler shifts using
single and multiple Gauss fits of transition region and coronal lines as well
as electron densities and temperatures. We combine co-temporal imaging and
spectroscopy to separate brightening expansions from plasma flows. The
transient brightening events in coronal holes and their boundaries were found
to be very dynamical producing high density outflows at large speeds. Most of
these events represent X-ray jets from pre-existing or newly emerging coronal
bright points at X-ray temperatures. The average electron density of the jets
is logNe ~ 8.76 cm^-3 while in the flaring site it is logNe ~ 9.51 cm^-3. The
jet temperatures reach a maximum of 2.5 MK but in the majority of the cases the
temperatures do not exceed 1.6 MK. The footpoints of jets have temperatures of
a maximum of 2.5 MK though in a single event scanned a minute after the flaring
the measured temperature was 12 MK. The jets are produced by multiple
microflaring in the transition region and corona. Chromospheric emission was
only detected in their footpoints and was only associated with downflows. The
Doppler shift measurements in the quiet Sun transient brightenings confirmed
that these events do not produce jet-like phenomena. The plasma flows in these
phenomena remain trapped in closed loops.Comment: 16 pages, accepted for publication in A&
Likelihood-free inference of experimental Neutrino Oscillations using Neural Spline Flows
In machine learning, likelihood-free inference refers to the task of
performing an analysis driven by data instead of an analytical expression. We
discuss the application of Neural Spline Flows, a neural density estimation
algorithm, to the likelihood-free inference problem of the measurement of
neutrino oscillation parameters in Long Baseline neutrino experiments. A method
adapted to physics parameter inference is developed and applied to the case of
the disappearance muon neutrino analysis at the T2K experiment.Comment: 10 pages, 3 figure
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