4,812 research outputs found
Notes on implementation of sparsely distributed memory
The Sparsely Distributed Memory (SDM) developed by Kanerva is an unconventional memory design with very interesting and desirable properties. The memory works in a manner that is closely related to modern theories of human memory. The SDM model is discussed in terms of its implementation in hardware. Two appendices discuss the unconventional approaches of the SDM: Appendix A treats a resistive circuit for fast, parallel address decoding; and Appendix B treats a systolic array for high throughput read and write operations
Existence and Stability of Steady Fronts in Bistable CML
We prove the existence and we study the stability of the kink-like fixed
points in a simple Coupled Map Lattice for which the local dynamics has two
stable fixed points. The condition for the existence allows us to define a
critical value of the coupling parameter where a (multi) generalized
saddle-node bifurcation occurs and destroys these solutions. An extension of
the results to other CML's in the same class is also displayed. Finally, we
emphasize the property of spatial chaos for small coupling.Comment: 18 pages, uuencoded PostScript file, J. Stat. Phys. (In press
Explicitly solvable cases of one-dimensional quantum chaos
We identify a set of quantum graphs with unique and precisely defined
spectral properties called {\it regular quantum graphs}. Although chaotic in
their classical limit with positive topological entropy, regular quantum graphs
are explicitly solvable. The proof is constructive: we present exact periodic
orbit expansions for individual energy levels, thus obtaining an analytical
solution for the spectrum of regular quantum graphs that is complete, explicit
and exact
-NMR of Isolated Li Implanted into a Thin Copper Film
Depth-controlled -NMR was used to study highly spin-polarized Li
in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive
Knight Shifts and spin relaxation data show that Li occupies two sites at
low temperatures, assigned to be the substitutional () and octahedral ()
interstitial sites. Between 50 to 100 K, there is a site change from to
. The temperature dependence of the Knight shifts and spin-lattice
relaxation rates at high temperatures, i.e. when all the Li are in the
site, is consistent with the Korringa Law for a simple metal.Comment: Accepted for publication in Phys. Rev.
Initialization and Readout of Spin Chains for Quantum Information Transport
Linear chains of spins acting as quantum wires are a promising approach to
achieve scalable quantum information processors. Nuclear spins in apatite
crystals provide an ideal test-bed for the experimental study of quantum
information transport, as they closely emulate a one-dimensional spin chain.
Nuclear Magnetic Resonance techniques can be used to drive the spin chain
dynamics and probe the accompanying transport mechanisms. Here we demonstrate
initialization and readout capabilities in these spin chains, even in the
absence of single-spin addressability. These control schemes enable preparing
desired states for quantum information transport and probing their evolution
under the transport Hamiltonian. We further optimize the control schemes by a
detailed analysis of F NMR lineshape
A quasi-diagonal approach to the estimation of Lyapunov spectra for spatio-temporal systems from multivariate time series
We describe methods of estimating the entire Lyapunov spectrum of a spatially
extended system from multivariate time-series observations. Provided that the
coupling in the system is short range, the Jacobian has a banded structure and
can be estimated using spatially localised reconstructions in low embedding
dimensions. This circumvents the ``curse of dimensionality'' that prevents the
accurate reconstruction of high-dimensional dynamics from observed time series.
The technique is illustrated using coupled map lattices as prototype models for
spatio-temporal chaos and is found to work even when the coupling is not
strictly local but only exponentially decaying.Comment: 13 pages, LaTeX (RevTeX), 13 Postscript figs, to be submitted to
Phys.Rev.
Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance
Low energy -detected nuclear magnetic resonance (-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power , and a field
extrapolated to T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
D-Branes and Fluxes in Supersymmetric Quantum Mechanics
Type 0A string theory in the (2,4k) superconformal minimal model backgrounds,
with background ZZ D-branes or R-R fluxes can be formulated non-perturbatively.
The branes and fluxes have a description as threshold bound states in an
associated one-dimensional quantum mechanics which has a supersymmetric
structure, familiar from studies of the generalized KdV system. The relevant
bound state wavefunctions in this problem have unusual asymptotics (they are
not normalizable in general, and break supersymmetry) which are consistent with
the underlying description in terms of open and closed string sectors. The
overall organization of the physics is very pleasing: The physics of the closed
strings in the background of branes or fluxes is captured by the generalized
KdV system and non-perturbative string equations obtained by reduction of that
system (the hierarchy of equations found by Dalley, Johnson, Morris and
Watterstam). Meanwhile, the bound states wavefunctions, which describe the
physics of the ZZ D-brane (or flux) background in interaction with probe FZZT
D-branes, are captured by the generalized mKdV system, and non-perturbative
string equations obtained by reduction of that system (the Painleve II hierachy
found by Periwal and Shevitz in this context).Comment: 41 pages, LaTe
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