319 research outputs found
Scaling theory of temporal correlations and size dependent fluctuations in the traded value of stocks
Records of the traded value f_i(t) of stocks display fluctuation scaling, a
proportionality between the standard deviation sigma(i) and the average :
sigma(i) ~ f(i)^alpha, with a strong time scale dependence alpha(dt). The
non-trivial (i.e., neither 0.5 nor 1) value of alpha may have different origins
and provides information about the microscopic dynamics. We present a set of
recently discovered stylized facts, and then show their connection to such
behavior. The functional form alpha(dt) originates from two aspects of the
dynamics: Stocks of larger companies both tend to be traded in larger packages,
and also display stronger correlations of traded value.Comment: 8 pages, 7 figures, 1 table, accepted to Phys. Rev.
THE GENERAL SPATIAL SYSTEM OF ROCKY ENVIRONMENT FOR BUILDING PURPOSES
The paper summarizes and methodizes the necessary civil engineering knowledge for
the consideration of interaction between the construction and its rocky environment planned
from the point of view of both the construction and the earth's crust region. The rocky environment
of the construction has been formed under natural conditions. This determines its properties.
Models constructed by the selection of earth's crust elements of uniform properties and
by carrying out the necessary and possible generalizations serve to eyaluate the interactions
Dynamic asset trees and Black Monday
The minimum spanning tree, based on the concept of ultrametricity, is
constructed from the correlation matrix of stock returns. The dynamics of this
asset tree can be characterised by its normalised length and the mean
occupation layer, as measured from an appropriately chosen centre called the
`central node'. We show how the tree length shrinks during a stock market
crisis, Black Monday in this case, and how a strong reconfiguration takes
place, resulting in topological shrinking of the tree.Comment: 6 pages, 3 eps figues. Elsevier style. Will appear in Physica A as
part of the Bali conference proceedings, in pres
Bound states in the 3d Ising model and implications for QCD at finite temperature and density
We study the spectrum of bound states of the three dimensional Ising model in
the (h,beta) plane near the critical point. We show the existence of an
unbinding line, defined as the boundary of the region where bound states exist.
Numerical evidence suggests that this line coincides with the beta=beta_c axis.
When the 3D Ising model is considered as an effective description of hot QCD at
finite density, we conjecture the correspondence between the unbinding line and
the line that separates the quark-gluon plasma phase from the superconducting
phase. The bound states of the Ising model are conjectured to correspond to the
diquarks of the latter phase of QCD.Comment: Lattice2001(hightemp
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Piling and avalanches of magnetized particles
We performed computer simulations based on a two-dimensional Distinct Element
Method to study granular systems of magnetized spherical particles. We measured
the angle of repose and the surface roughness of particle piles, and we studied
the effect of magnetization on avalanching. We report linear dependence of both
angle of repose and surface roughness on the ratio of the magnetic dipole
interaction and the gravitational force (\emph{interparticle force ratio}).
There is a difference in avalanche formation at small and at large
interparticle force ratios. The transition is at . For
the particles forming the avalanches leave the system in a quasi-continuous
granular flow (\emph{granular regime}), while for the avalanches are
formed by long particle clusters (\emph{correlated regime}). The transition is
not sharp. We give plausible estimates for based on stability criteria.Comment: 9 pages, 7 figure
Force indeterminacy in the jammed state of hard disks
Granular packings of hard discs are investigated by means of contact dynamics
which is an appropriate technique to explore the allowed force-realizations in
the space of contact forces. Configurations are generated for given values of
the friction coefficient, and then an ensemble of equilibrium forces is found
for fixed contacts. We study the force fluctuations within this ensemble. In
the limit of zero friction the fluctuations vanish in accordance with the
isostaticity of the packing. The magnitude of the fluctuations has a
non-monotonous friction dependence. The increase for small friction can be
attributed to the opening of the angle of the Coulomb cone, while the decrease
as friction increases is due to the reduction of connectivity of the
contact-network, leading to local, independent clusters of indeterminacy. We
discuss the relevance of indeterminacy to packings of deformable particles and
to the mechanical response properties.Comment: 4 pages, 3 figures. Minor changes, journal reference adde
Avalanche statistics of sand heaps
Large scale computer simulations are presented to investigate the avalanche
statistics of sand piles using molecular dynamics. We could show that different
methods of measurement lead to contradicting conclusions, presumably due to
avalanches not reaching the end of the experimental table.Comment: 6 pages, 4 figure
Two-dimensional array of magnetic particles: The role of an interaction cutoff
Based on theoretical results and simulations, in two-dimensional arrangements
of a dense dipolar particle system, there are two relevant local dipole
arrangements: (1) a ferromagnetic state with dipoles organized in a triangular
lattice, and (2) an anti-ferromagnetic state with dipoles organized in a square
lattice. In order to accelerate simulation algorithms we search for the
possibility of cutting off the interaction potential. Simulations on a dipolar
two-line system lead to the observation that the ferromagnetic state is much
more sensitive to the interaction cutoff than the corresponding
anti-ferromagnetic state. For (measured in particle diameters)
there is no substantial change in the energetical balance of the ferromagnetic
and anti-ferromagnetic state and the ferromagnetic state slightly dominates
over the anti-ferromagnetic state, while the situation is changed rapidly for
lower interaction cutoff values, leading to the disappearance of the
ferromagnetic ground state. We studied the effect of bending ferromagnetic and
anti-ferromagnetic two-line systems and we observed that the cutoff has a major
impact on the energetical balance of the ferromagnetic and anti-ferromagnetic
state for . Based on our results we argue that is a
reasonable choice for dipole-dipole interaction cutoff in two-dimensional
dipolar hard sphere systems, if one is interested in local ordering.Comment: 8 page
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