4,045 research outputs found
Sparsity and Parallel Acquisition: Optimal Uniform and Nonuniform Recovery Guarantees
The problem of multiple sensors simultaneously acquiring measurements of a
single object can be found in many applications. In this paper, we present the
optimal recovery guarantees for the recovery of compressible signals from
multi-sensor measurements using compressed sensing. In the first half of the
paper, we present both uniform and nonuniform recovery guarantees for the
conventional sparse signal model in a so-called distinct sensing scenario. In
the second half, using the so-called sparse and distributed signal model, we
present nonuniform recovery guarantees which effectively broaden the class of
sensing scenarios for which optimal recovery is possible, including to the
so-called identical sampling scenario. To verify our recovery guarantees we
provide several numerical results including phase transition curves and
numerically-computed bounds.Comment: 13 pages and 3 figure
Dynamics of Order Parameter in Photoexcited Peierls Chain
The photoexcited dynamics of order parameter in Peierls chain is investigated
by using a microscopic quantum theory in the limit where the hot electrons may
establish themselves into a quasi-equilibrium state described by an effective
temperature. The optical phonon mode responsible for the Peierls instability is
coupled to the electron subsystem, and its dynamic equation is derived in terms
of the density matrix technique. Recovery dynamics of the order parameter is
obtained, which reveals a number of interesting features including the change
of oscillation frequency and amplitude at phase transition temperature and the
photo-induced switching of order parameter.Comment: 5 pages, 3 figure
Synthesis of octa-tailed calix[4]resorcinarenes and characterization of Langmuir-Blodgett films on these compounds.
This project was focused on synthesis of octa-tailed calix[4]resorcinarenes functionalized with pendant alpha-(diethyl acetamide) or alpha-(methyl acetate), preparation of Langmuir films and Langmuir-Blodgett films of the calix[4]resorcinarenes, and characterization of these compounds in solution and the Langmuir-Blodgett films. The octa-tailed calix[4]resorcinarene was synthesized by the cyclooligomerization of resorcinol and alpha,alpha-dihexyl acetaldehyde under acid-catalyzed conditions. The functionalized octa-tailed calix[4]resorcinarenes were obtained by substitution reaction with 2-bromo-NN-diethylacetamide or methyl bromoacetate under basic conditions. Langmuir films of the octa-tailed resorcin[4]arenes and their amide and ester derivatives were fabricated at the air/water interface. (Abstract shortened by UMI.)Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1999 .C44. Source: Masters Abstracts International, Volume: 39-02, page: 0513. Adviser: P. Datton. Thesis (M.Sc.)--University of Windsor (Canada), 1999
An hourglass model for the flare of HST-1 in M87
To explain the multi-wavelength light curves (from radio to X-ray) of HST-1
in the M87 jet, we propose an hourglass model that is a modified two-zone
system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or
Laval nozzle-shaped layer connected by two revolving exponential surfaces
surrounding a fast spine, through which plasma blobs flow. Based on the
conservation of magnetic flux, the magnetic field changes along the axis of the
hourglass. We adopt the result of TG08---the high-energy emission from GeV to
TeV can be produced through inverse Compton by the two-zone system, and the
photons from radio to X-ray are mainly radiated by the fast inner zone system.
Here, we only discuss the light curves of the fast inner blob from radio to
X-ray. When a compressible blob travels down the axis of the first bulb in the
hourglass, because of magnetic flux conservation, its cross section experiences
an adiabatic compression process, which results in particle acceleration and
the brightening of HST-1. When the blob moves into the second bulb of the
hourglass, because of magnetic flux conservation, the dimming of the knot
occurs along with an adiabatic expansion of its cross section. A similar broken
exponential function could fit the TeV peaks in M87, which may imply a
correlation between the TeV flares of M87 and the light curves from radio to
X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1
verifies our prediction based on the model fit to the main peak of the VLA 15
GHz radio light curve.Comment: 14 pages, 2 figures, accepted for publication in A
Anderson Impurity in Helical Metal
We use a trial wave function to study the spin-1/2 Kondo effect of a helical
metal on the surface of a three-dimensional topological insulator. While the
impurity spin is quenched by conduction electrons, the spin-spin correlation of
the conduction electron and impurity is strongly anisotropic in both spin and
spatial spaces. As a result of strong spin-orbit coupling, the out-of-plane
component of the impurity spin is found to be fully screened by the orbital
angular momentum of the conduction electrons.Comment: The published versio
Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas
The dynamics of magnetization coupled to an electron gas via s-d exchange
interaction is investigated by using density matrix technique. Our theory shows
that non-equilibrium spin accumulation induces a spin torque and the electron
bath leads to a damping of the magnetization. For the two-dimensional
magnetization thin film coupled to the electron gas with Rashba spin-orbit
coupling, the result for the spin-orbit torques is consistent with the previous
semi-classical theory. Our theory predicts a damping of the magnetization,
which is absent in the semi-classical theory. The magnitude of the damping due
to the electron bath is comparable to the intrinsic Gilbert damping and may be
important in describing the magnetization dynamics of the system.Comment: 7 pages, 2 figure
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