23,458 research outputs found
Singularity theory study of overdetermination in models for L-H transitions
Two dynamical models that have been proposed to describe transitions between
low and high confinement states (L-H transitions) in confined plasmas are
analysed using singularity theory and stability theory. It is shown that the
stationary-state bifurcation sets have qualitative properties identical to
standard normal forms for the pitchfork and transcritical bifurcations. The
analysis yields the codimension of the highest-order singularities, from which
we find that the unperturbed systems are overdetermined bifurcation problems
and derive appropriate universal unfoldings. Questions of mutual equivalence
and the character of the state transitions are addressed.Comment: Latex (Revtex) source + 13 small postscript figures. Revised versio
A simple solution of sound transmission through an elastic wall to a rectangular enclosure, including wall damping and air viscosity effects
A simple solution to the problem of the acoustical coupling between a rectangular structure, its air content, and an external noise source is presented. This solution is a mathematical expression for the normalized acoustic pressure inside the structure. Numerical results for the sound-pressure response for a specified set of parameters are also presented
Bifurcation in electrostatic resistive drift wave turbulence
The Hasegawa-Wakatani equations, coupling plasma density and electrostatic
potential through an approximation to the physics of parallel electron motions,
are a simple model that describes resistive drift wave turbulence. We present
numerical analyses of bifurcation phenomena in the model that provide new
insights into the interactions between turbulence and zonal flows in the
tokamak plasma edge region. The simulation results show a regime where, after
an initial transient, drift wave turbulence is suppressed through zonal flow
generation. As a parameter controlling the strength of the turbulence is tuned,
this zonal flow dominated state is rapidly destroyed and a turbulence-dominated
state re-emerges. The transition is explained in terms of the Kelvin-Helmholtz
stability of zonal flows. This is the first observation of an upshift of
turbulence onset in the resistive drift wave system, which is analogous to the
well-known Dimits shift in turbulence driven by ion temperature gradients.Comment: 21 pages, 11 figure
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
The geology of the Newbury Mining District
Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mining Engineering and Metallurgy, 1905.Accompanied by maps in a folder.by William Gilbert Ball - Charles Horace Clapp.B.S
Blow-up of the hyperbolic Burgers equation
The memory effects on microscopic kinetic systems have been sometimes
modelled by means of the introduction of second order time derivatives in the
macroscopic hydrodynamic equations. One prototypical example is the hyperbolic
modification of the Burgers equation, that has been introduced to clarify the
interplay of hyperbolicity and nonlinear hydrodynamic evolution. Previous
studies suggested the finite time blow-up of this equation, and here we present
a rigorous proof of this fact
Agency workers and zero hours : the story of hidden exploitation
This report highlights the extent and experiences of workers on temporary agency and zero-hours contracts.Using interviews with the workers themselves and data from the Annual Population Surveys it examines the impacts of hidden exploitation. It makes a number of recommendations to tackle the harsh and imposed regimes of temporary agency work and zero-hours contracts
Stability for Borell-Brascamp-Lieb inequalities
We study stability issues for the so-called Borell-Brascamp-Lieb
inequalities, proving that when near equality is realized, the involved
functions must be -close to be -concave and to coincide up to
homotheties of their graphs.Comment: to appear in GAFA Seminar Note
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