6,497 research outputs found
Anderson Localization in Disordered Vibrating Rods
We study, both experimentally and numerically, the Anderson localization
phenomenon in torsional waves of a disordered elastic rod, which consists of a
cylinder with randomly spaced notches. We find that the normal-mode wave
amplitudes are exponentially localized as occurs in disordered solids. The
localization length is measured using these wave amplitudes and it is shown to
decrease as a function of frequency. The normal-mode spectrum is also measured
as well as computed, so its level statistics can be analyzed. Fitting the
nearest-neighbor spacing distribution a level repulsion parameter is defined
that also varies with frequency. The localization length can then be expressed
as a function of the repulsion parameter. There exists a range in which the
localization length is a linear function of the repulsion parameter, which is
consistent with Random Matrix Theory. However, at low values of the repulsion
parameter the linear dependence does not hold.Comment: 10 pages, 6 figure
Contribution of exclusive channels to the leading order HVP of the muon
We evaluate the contributions of
exclusive channels to the dispersion integral of the leading order HVP of the
muon anomalous magnetic moment. These channels are included in some way in
previous evaluations of the and
contributions to , where the vector resonances (decaying
into ) are assumed to be on-shell. Since the separation of
resonance and background contributions in a given observable is, in general, a
model-dependent procedure, here we use pseudoscalar mesons and the photon as
the and states of the -matrix, such that the cross section contains the
interferences among different contributing to the amplitudes. We find , where
uncertainties stem mainly from vector meson dominance model parameters.
Improved experimental studies of these exclusive channels in the whole range
below 2 GeV would reduce model-dependency
Exact relativistic models of thin disks around static black holes in a magnetic field
The exact superposition of a central static black hole with surrounding thin
disk in presence of a magnetic field is investigated. We consider two models of
disk, one of infinite extension based on a Kuzmin-Chazy-Curzon metric and other
finite based on the first Morgan-Morgan disk. We also analyze a simple model of
active galactic nuclei consisting of black hole, a Kuzmin-Chazy-Curzon disk and
two rods representing jets, in presence of magnetic field. To explain the
stability of the disks we consider the matter of the disk made of two
pressureless streams of counterrotating charged particles (counterrotating
model) moving along electrogeodesic. Using the Rayleigh criterion we derivate
for circular orbits the stability conditions of the particles of the streams.
The influence of the magnetic field on the matter properties of the disk and on
its stability are also analyzed.Comment: 17 pages, 14 figures. arXiv admin note: text overlap with
arXiv:gr-qc/0409109 by other author
Quantum Interference in Single Molecule Electronic Systems
We present a general analytical formula and an ab initio study of quantum
interference in multi-branch molecules. Ab initio calculations are used to
investigate quantum interference in a benzene-1,2-dithiolate (BDT) molecule
sandwiched between gold electrodes and through oligoynes of various lengths. We
show that when a point charge is located in the plane of a BDT molecule and its
position varied, the electrical conductance exhibits a clear interference
effect, whereas when the charge approaches a BDT molecule along a line normal
to the plane of the molecule and passing through the centre of the phenyl ring,
interference effects are negligible. In the case of olygoynes, quantum
interference leads to the appearance of a critical energy , at which the
electron transmission coefficient of chains with even or odd numbers of
atoms is independent of length. To illustrate the underlying physics, we derive
a general analytical formula for electron transport through multi-branch
structures and demonstrate the versatility of the formula by comparing it with
the above ab-initio simulations. We also employ the analytical formula to
investigate the current inside the molecule and demonstrate that large counter
currents can occur within a ring-like molecule such as BDT, when the point
charge is located in the plane of the molecule. The formula can be used to
describe quantum interference and Fano resonances in structures with branches
containing arbitrary elastic scattering regions connected to nodal sites.Comment: 12 pages, 11 figure
Wannier-Stark ladders in one-dimensional elastic systems
The optical analogues of Bloch oscillations and their associated
Wannier-Stark ladders have been recently analyzed. In this paper we propose an
elastic realization of these ladders, employing for this purpose the torsional
vibrations of specially designed one-dimensional elastic systems. We have
measured, for the first time, the ladder wave amplitudes, which are not
directly accessible either in the quantum mechanical or optical cases. The wave
amplitudes are spatially localized and coincide rather well with theoretically
predicted amplitudes. The rods we analyze can be used to localize different
frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let
SVtL: System Verification through Logic: tool support for verifying sliced hierarchical statecharts
SVtL is the core of a slicing-based verification environment for UML statechart models. We present an overview of the SVtL software architecture. Special attention is paid to the slicing approach. Slicing reduces the complexity of the verification approach, based on removing pieces of the model that are not of interest during verification. In [18] a slicing algorithm has been proposed for statecharts, but it was not able to handle orthogonal regions efficiently. We optimize this algorithm by removing false dependencies, relying on the broadcasting mechanism between different parts of the statechart model
Using late-time optical and near-infrared spectra to constrain Type Ia supernova explosion properties
The late-time spectra of Type Ia supernovae (SNe Ia) are powerful probes of
the underlying physics of their explosions. We investigate the late-time
optical and near-infrared spectra of seven SNe Ia obtained at the VLT with
XShooter at 200 d after explosion. At these epochs, the inner Fe-rich ejecta
can be studied. We use a line-fitting analysis to determine the relative line
fluxes, velocity shifts, and line widths of prominent features contributing to
the spectra ([Fe II], [Ni II], and [Co III]). By focussing on [Fe II] and [Ni
II] emission lines in the ~7000-7500 \AA\ region of the spectrum, we find that
the ratio of stable [Ni II] to mainly radioactively-produced [Fe II] for most
SNe Ia in the sample is consistent with Chandrasekhar-mass delayed-detonation
explosion models, as well as sub-Chandrasekhar mass explosions that have
metallicity values above solar. The mean measured Ni/Fe abundance of our sample
is consistent with the solar value. The more highly ionised [Co III] emission
lines are found to be more centrally located in the ejecta and have broader
lines than the [Fe II] and [Ni II] features. Our analysis also strengthens
previous results that SNe Ia with higher Si II velocities at maximum light
preferentially display blueshifted [Fe II] 7155 \AA\ lines at late times. Our
combined results lead us to speculate that the majority of normal SN Ia
explosions produce ejecta distributions that deviate significantly from
spherical symmetry.Comment: 17 pages, 12 figure, accepted for publication in MNRA
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