202 research outputs found
Locally Perturbed Random Walks with Unbounded Jumps
In \cite{SzT}, D. Sz\'asz and A. Telcs have shown that for the diffusively
scaled, simple symmetric random walk, weak convergence to the Brownian motion
holds even in the case of local impurities if . The extension of their
result to finite range random walks is straightforward. Here, however, we are
interested in the situation when the random walk has unbounded range.
Concretely we generalize the statement of \cite{SzT} to unbounded random walks
whose jump distribution belongs to the domain of attraction of the normal law.
We do this first: for diffusively scaled random walks on having finite variance; and second: for random walks with distribution
belonging to the non-normal domain of attraction of the normal law. This result
can be applied to random walks with tail behavior analogous to that of the
infinite horizon Lorentz-process; these, in particular, have infinite variance,
and convergence to Brownian motion holds with the superdiffusive scaling.Comment: 16 page
A mechanical model of normal and anomalous diffusion
The overdamped dynamics of a charged particle driven by an uniform electric
field through a random sequence of scatterers in one dimension is investigated.
Analytic expressions of the mean velocity and of the velocity power spectrum
are presented. These show that above a threshold value of the field normal
diffusion is superimposed to ballistic motion. The diffusion constant can be
given explicitly. At the threshold field the transition between conduction and
localization is accompanied by an anomalous diffusion. Our results exemplify
that, even in the absence of time-dependent stochastic forces, a purely
mechanical model equipped with a quenched disorder can exhibit normal as well
as anomalous diffusion, the latter emerging as a critical property.Comment: 16 pages, no figure
Chaos in cylindrical stadium billiards via a generic nonlinear mechanism
We describe conditions under which higher-dimensional billiard models in
bounded, convex regions are fully chaotic, generalizing the Bunimovich stadium
to dimensions above two. An example is a three-dimensional stadium bounded by a
cylinder and several planes; the combination of these elements may give rise to
defocusing, allowing large chaotic regions in phase space. By studying families
of marginally-stable periodic orbits that populate the residual part of phase
space, we identify conditions under which a nonlinear instability mechanism
arises in their vicinity. For particular geometries, this mechanism rather
induces stable nonlinear oscillations, including in the form of
whispering-gallery modes.Comment: 4 pages, 4 figure
On the changes of the electronic structure of early-transition-metal-systems at hydrogenation
The hydrogenation effect on Sc, Y, La, Cd and Eu has been investigated by XPS. The stability, the charge transfer as well as the microscopic behaviours of the processes have been discussed
Macroscopic collectivity on microscopic base in living systems
The collective phenomena in living systems is discussed on the dynamic frustration
basis.
The frustrated connection is introduced on all the organising levels of the living
phenomenon:
· for water states (proton migration),
· for proteins and protein-structures (metabolic charge transfer),
· for cells (membrane states and ordering),
· for tissues (social signals),
· for organs and organism (overall transport problems).
It is shown, that the cancer-genesis is tightly connected with the failure of the
collectivity in the system. The relevant mechanisms of the collectivity is analised in
details for the better understanding the malignant tumor development
CLOSE-PACKED FRANK-KASPER COORDINATION AND HIGH CRITICAL TEMPERATURE SUPERCONDUCTIVITY
It has been proposed that a relation exists between close packed Frank-Kasper co-ordination in the layers containing Cu-O planes and high-Tc superconductivity. The origin of the superconductivity in perovskite-type materials is attributed in part to a three dimensional nesting of the Fermi-surface with the boundary of Jones-zone, causing 'partially-gapped' Fermi surface and to a gliding charge density wave arising from a three-dimensional 'breathing' of
distorted perovskite structures associated with close-packed seeking symmetry
Weak integrability breaking and level spacing distribution
Recently it was suggested that certain perturbations of integrable spin
chains lead to a weak breaking of integrability in the sense that integrability
is preserved at the first order in the coupling. Here we examine this claim
using level spacing distribution. We find that the volume dependent crossover
between integrable and chaotic level spacing statistics which marks the onset
of quantum chaotic behaviour, is markedly different for weak vs. strong
breaking of integrability. In particular, for the gapless case we find that the
crossover coupling as a function of the volume scales with a law
for weak breaking as opposed to the law previously found for the strong
case.Comment: 15 pages, 12 figures. v2: references added. v3: text thoroughly
revised, presentation clarified and improved, main results and conclusions
unchange
On the protection of the isolation at the fabrication of all niobium josepshson-junctions
The protection mechanism of thin gold layer for preparation of all-niobium devices is
discussed. A suggestion on the electronic origin of protection is presented
Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point
defects in semiconductors is a key resource for both initializing nuclear
quantum memories and producing nuclear hyperpolarization. DNP is therefore an
important process in the field of quantum-information processing,
sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based
spintronics. DNP based on optical pumping of point defects has been
demonstrated by using the electron spin of nitrogen-vacancy (NV) center in
diamond, and more recently, by using divacancy and related defect spins in
hexagonal silicon carbide (SiC). Here, we describe a general model for these
optical DNP processes that allows the effects of many microscopic processes to
be integrated. Applying this theory, we gain a deeper insight into dynamic
nuclear spin polarization and the physics of diamond and SiC defects. Our
results are in good agreement with experimental observations and provide a
detailed and unified understanding. In particular, our findings show that the
defects' electron spin coherence times and excited state lifetimes are crucial
factors in the entire DNP process
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