262 research outputs found
Nonequilibrium mesoscopic transport: a genealogy
Models of nonequilibrium quantum transport underpin all modern electronic
devices, from the largest scales to the smallest. Past simplifications such as
coarse graining and bulk self-averaging served well to understand electronic
materials. Such particular notions become inapplicable at mesoscopic
dimensions, edging towards the truly quantum regime. Nevertheless a unifying
thread continues to run through transport physics, animating the design of
small-scale electronic technology: microscopic conservation and nonequilibrium
dissipation. These fundamentals are inherent in quantum transport and gain even
greater and more explicit experimental meaning in the passage to atomic-sized
devices. We review their genesis, their theoretical context, and their
governing role in the electronic response of meso- and nanoscopic systems.Comment: 21p
Thermodynamics of perfect fluids from scalar field theory
The low-energy dynamics of relativistic continuous media is given by a
shift-symmetric effective theory of four scalar fields. These scalars describe
the embedding in spacetime of the medium and play the role of St\"uckelberg
fields for spontaneously broken spatial and time translations. Perfect fluids
are selected imposing a stronger symmetry group or reducing the field content
to a single scalar. We explore the relation between the field theory
description of perfect fluids to thermodynamics. By drawing the correspondence
between the allowed operators at leading order in derivatives and the
thermodynamic variables, we find that a complete thermodynamic picture requires
the four Stuckelberg fields. We show that thermodynamic stability plus the
null-energy condition imply dynamical stability. We also argue that a
consistent thermodynamic interpretation is not possible if any of the shift
symmetries is explicitly broken.Comment: 25 pages, 1 figure. Few typos corrected. Accepted for publication in
PR
Grushin problems and control theory: Formulation and examples
In this paper we give a new formulation of an abstract control problem in
terms of a Grushin problem, so that we will reformulate all notions of
controllability, observability and stability in a new form that gives readers
an easy interpretation of these notions
Anelastic sensitivity kernels with parsimonious storage for adjoint tomography and full waveform inversion
We introduce a technique to compute exact anelastic sensitivity kernels in
the time domain using parsimonious disk storage. The method is based on a
reordering of the time loop of time-domain forward/adjoint wave propagation
solvers combined with the use of a memory buffer. It avoids instabilities that
occur when time-reversing dissipative wave propagation simulations. The total
number of required time steps is unchanged compared to usual acoustic or
elastic approaches. The cost is reduced by a factor of 4/3 compared to the case
in which anelasticity is partially accounted for by accommodating the effects
of physical dispersion. We validate our technique by performing a test in which
we compare the sensitivity kernel to the exact kernel obtained by
saving the entire forward calculation. This benchmark confirms that our
approach is also exact. We illustrate the importance of including full
attenuation in the calculation of sensitivity kernels by showing significant
differences with physical-dispersion-only kernels
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