307 research outputs found
Travelling waves in a drifting flux lattice
Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type
II superconductor, we derive the equations of motion for the displacement field
of a moving vortex lattice without inertia or pinning. We show that it is
linearly stable and, surprisingly, that it supports wavelike long-wavelength
excitations arising not from inertia or elasticity but from the
strain-dependent mobility of the moving lattice. It should be possible to image
these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling
microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened,
minor textual change
Inertial Mass of a Vortex in Cuprate Superconductors
We present here a calculation of the inertial mass of a moving vortex in
cuprate superconductors. This is a poorly known basic quantity of obvious
interest in vortex dynamics. The motion of a vortex causes a dipolar density
distortion and an associated electric field which is screened. The energy cost
of the density distortion as well as the related screened electric field
contribute to the vortex mass, which is small because of efficient screening.
As a preliminary, we present a discussion and calculation of the vortex mass
using a microscopically derivable phase-only action functional for the far
region which shows that the contribution from the far region is negligible, and
that most of it arises from the (small) core region of the vortex. A
calculation based on a phenomenological Ginzburg-Landau functional is performed
in the core region. Unfortunately such a calculation is unreliable, the reasons
for it are discussed. A credible calculation of the vortex mass thus requires a
fully microscopic, non-coarse grained theory. This is developed, and results
are presented for a s-wave BCS like gap, with parameters appropriate to the
cuprates. The mass, about 0.5 per layer, for magnetic field along the
axis, arises from deformation of quasiparticle states bound in the core, and
screening effects mentioned above. We discuss earlier results, possible
extensions to d-wave symmetry, and observability of effects dependent on the
inertial mass.Comment: 27 pages, Latex, 3 figures available on request, to appear in
Physical Review
Resonant absorption at the vortex-core states in d-wave superconductors
We predict a resonant microwave absorption on collective vortex modes in a
superclean d-wave superconductor. Energies of the collective modes are
multiples of the distance between the exact quantum levels of bound states in
the vortex core at lower temperatures and involve delocalized states for higher
temperatures. We calculate the vortex mass in a d-wave superconductor as a
response to a slow acceleration of the vortex. The universal flux-flow regime
predicted by N. Kopnin and G. Volovik [Phys. Rev. Lett. 79, 1377 (1997)] is
discussed in more detail.Comment: RevTex file, 10 page
Reduced order models for control of fluids using the Eigensystem Realization Algorithm
In feedback flow control, one of the challenges is to develop mathematical
models that describe the fluid physics relevant to the task at hand, while
neglecting irrelevant details of the flow in order to remain computationally
tractable. A number of techniques are presently used to develop such
reduced-order models, such as proper orthogonal decomposition (POD), and
approximate snapshot-based balanced truncation, also known as balanced POD.
Each method has its strengths and weaknesses: for instance, POD models can
behave unpredictably and perform poorly, but they can be computed directly from
experimental data; approximate balanced truncation often produces vastly
superior models to POD, but requires data from adjoint simulations, and thus
cannot be applied to experimental data.
In this paper, we show that using the Eigensystem Realization Algorithm (ERA)
\citep{JuPa-85}, one can theoretically obtain exactly the same reduced order
models as by balanced POD. Moreover, the models can be obtained directly from
experimental data, without the use of adjoint information. The algorithm can
also substantially improve computational efficiency when forming reduced-order
models from simulation data. If adjoint information is available, then balanced
POD has some advantages over ERA: for instance, it produces modes that are
useful for multiple purposes, and the method has been generalized to unstable
systems. We also present a modified ERA procedure that produces modes without
adjoint information, but for this procedure, the resulting models are not
balanced, and do not perform as well in examples. We present a detailed
comparison of the methods, and illustrate them on an example of the flow past
an inclined flat plate at a low Reynolds number.Comment: 22 pages, 7 figure
Elucidating the Mechanistic Role of IL-1R in Late-Stage K-ras Mutant Lung Cancer: Uncovering Therapeutic Potential
https://openworks.mdanderson.org/sumexp23/1088/thumbnail.jp
Bilayers of Chiral Spin States
We study the behavior of two planes of Quantum Heisenberg Antiferromagnet in
the regime in which a Chiral Spin Liquid is stabilized in each plane. The
planes are coupled by an exchange interaction of strength . We show that
in the regime of small (for both ferromagnetic {\it and}
antiferromagnetic coupling), the system dynamically selects an
\underline{antiferromagnetic} ordering of the ground state {\it chiralities} of
the planes. For the case of an antiferromagnetic interaction between the
planes, we find that, at some critical value of the inter-layer
coupling, there is a phase transition to a valence-bond state on the interlayer
links. We derive an effective Landau-Ginzburg theory for this phase transition.
It contains two gauge fields coupled to the order parameter field. We
study the low energy spectrum of each phase. In the condensed phase an
``anti-Higgs-Anderson" mechanism occurs. It effectively restores time-reversal
invariance by rendering massless one of the gauge fields while the other field
locks the chiral degrees of freedom locally. There is no phase transition for
ferromagnetic couplings.Comment: to appear in Phys. Rev. B; shortened version; several typos correcte
Dynamic vortex mass in clean Fermi superfluids and superconductors
We calculate the dynamic vortex mass for clean Fermi superfluids including
both s- and d-wave superconductors as a response to a vortex acceleration.
Assuming a finite quasiparticle mean free time, the vortex mass appears to be a
tensor. The diagonal component dominates in the limit of long mean free time
while the off-diagonal mass takes over in the moderately clean regime.Comment: 4 pages, no figures, typeset using RevTe
Microscopic theory of vortex dynamics in homogeneous superconductors
Vortex dynamics in fermionic superfluids is carefully considered from the
microscopic point of view. Finite temperatures, as well as impurities, are
explicitly incorporated. To enable readers understand the physical
implications, macroscopic demonstrations based on thermodynamics and
fluctuations- dissipation theorems are constructed. For the first time a clear
summary and a critical review of previous results are given.Comment: Presentations are made more straightforward. A detailed presentation
that why the vortex friction is finite when the geometric phase exists, as
required by referees, though I think it is obviou
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