9,132 research outputs found
Phase Synchronization in Railway Timetables
Timetable construction belongs to the most important optimization problems in
public transport. Finding optimal or near-optimal timetables under the
subsidiary conditions of minimizing travel times and other criteria is a
targeted contribution to the functioning of public transport. In addition to
efficiency (given, e.g., by minimal average travel times), a significant
feature of a timetable is its robustness against delay propagation. Here we
study the balance of efficiency and robustness in long-distance railway
timetables (in particular the current long-distance railway timetable in
Germany) from the perspective of synchronization, exploiting the fact that a
major part of the trains run nearly periodically. We find that synchronization
is highest at intermediate-sized stations. We argue that this synchronization
perspective opens a new avenue towards an understanding of railway timetables
by representing them as spatio-temporal phase patterns. Robustness and
efficiency can then be viewed as properties of this phase pattern
A superfluid hydrodynamic model for the enhanced moments of inertia of molecules in liquid 4He
We present a superfluid hydrodynamic model for the increase in moment of
inertia, , of molecules rotating in liquid He. The static
inhomogeneous He density around each molecule (calculated using the Orsay-Paris
liquid He density functional) is assumed to adiabatically follow the
rotation of the molecule. We find that the values created by the
viscousless and irrotational flow are in good agreement with the observed
increases for several molecules [ OCS, (HCN), HCCCN, and HCCCH ]. For
HCN and HCCH, our model substantially overestimates . This is likely
to result from a (partial) breakdown of the adiabatic following approximation.Comment: 4 pages, 1 eps figure, corrected version of published paper. Erratum
has been submitted for change
Anomalous Aharonov--Bohm gap oscillations in carbon nanotubes
The gap oscillations caused by a magnetic flux penetrating a carbon nanotube
represent one of the most spectacular observation of the Aharonov-Bohm effect
at the nano--scale. Our understanding of this effect is, however, based on the
assumption that the electrons are strictly confined on the tube surface, on
trajectories that are not modified by curvature effects. Using an ab-initio
approach based on Density Functional Theory we show that this assumption fails
at the nano-scale inducing important corrections to the physics of the
Aharonov-Bohm effect. Curvature effects and electronic density spilled out of
the nanotube surface are shown to break the periodicity of the gap
oscillations. We predict the key phenomenological features of this anomalous
Aharonov-Bohm effect in semi-conductive and metallic tubes and the existence of
a large metallic phase in the low flux regime of Multi-walled nanotubes, also
suggesting possible experiments to validate our results.Comment: 7 figure
Vibrational properties of amorphous silicon from tight-binding O(N) calculation
We present an O(N) algorithm to study the vibrational properties of amorphous
silicon within the framework of tight-binding approach. The dynamical matrix
elements have been evaluated numerically in the harmonic approximation
exploiting the short-range nature of the density matrix to calculate the
vibrational density of states which is then compared with the same obtained
from a standard O() algorithm. For the purpose of illustration, an
1000-atom model is studied to calculate the localization properties of the
vibrational eigenstates using the participation numbers calculation.Comment: 5 pages including 5 ps figures; added a figure and a few references;
accepted in Phys. Rev.
Crossover critical behavior of Ga1-xMnxAs
The critical behavior of Ga1-xMnxAs in a close vicinity of the Curie
temperature was experimentally studied by using the thermal diffusivity
measurements. Taking into account that the inverse of the thermal diffusivity
has the same critical behavior as the specific heat, the critical exponent
{\alpha} for the samples investigated has been determined. With approaching
close to the critical temperature, the crossover from the mean-field-like to
the Ising-like critical behavior has been observed. From the crossover behavior
the values of the Ginzburg number and the exchange interaction length in
Ga1-xMnxAs with different concentrations of Mn were determined.Comment: 17 pages, 5 figure
On the Universal Tachyon and Geometrical Tachyon
We study properties of non-BPS D(p+1)-brane in the background of k
NS5-branes, with one transverse direction compactified on a circle, from the
point of view of Dirac-Born-Infeld action. We present the analysis of two
different embedding of non-BPS D(p+1)-brane in given background and study the
classical solutions of given world-volume theory. We argue for the
configuration of a non-BPS D(p+1)-brane which allows us to find solutions of
the equations of motion that give unified descriptions of G and U-type branes.Comment: 24 pages, minor change
Directed Ising type dynamic preroughening transition in one dimensional interfaces
We present a realization of directed Ising (DI) type dynamic absorbing state
phase transitions in the context of one-dimensional interfaces, such as the
relaxation of a step on a vicinal surface. Under the restriction that particle
deposition and evaporation can only take place near existing kinks, the
interface relaxes into one of three steady states: rough, perfectly ordered
flat (OF) without kinks, or disordered flat (DOF) with randomly placed kinks
but in perfect up-down alternating order. A DI type dynamic preroughening
transition takes place between the OF and DOF phases. At this critical point
the asymptotic time evolution is controlled not only by the DI exponents but
also by the initial condition. Information about the correlations in the
initial state persists and changes the critical exponents.Comment: 12 pages, 10 figure
Does hardcore interaction change absorbing type critical phenomena?
It has been generally believed that hardcore interaction is irrelevant to
absorbing type critical phenomena because the particle density is so low near
an absorbing phase transition. We study the effect of hardcore interaction on
the N species branching annihilating random walks with two offspring and report
that hardcore interaction drastically changes the absorbing type critical
phenomena in a nontrivial way. Through Langevin equation type approach, we
predict analytically the values of the scaling exponents, in one dimension for all N > 1. Direct numerical
simulations confirm our prediction. When the diffusion coefficients for
different species are not identical, and vary
continuously with the ratios between the coefficients.Comment: 4 pages, 1 figur
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