4,908 research outputs found
Numerical study of the temperature and porosity effects on the fracture propagation in a 2D network of elastic bonds
This article reports results concerning the fracture of a 2d triangular
lattice of atoms linked by springs. The lattice is submitted to controlled
strain tests and the influence of both porosity and temperature on failure is
investigated. The porosity is found on one hand to decrease the stiffness of
the material but on the other hand it increases the deformation sustained prior
to failure. Temperature is shown to control the ductility due to the presence
of cavities that grow and merge. The rough surfaces resulting from the
propagation of the crack exhibit self-affine properties with a roughness
exponent over a range of length scales which increases
with temperature. Large cavities also have rough walls which are found to be
fractal with a dimension, , which evolves with the distance from the crack
tip. For large distances, is found to be close to 1.5, and close to 1.0 for
cavities just before their coalescence with the main crack
Testing Option Pricing with the Edgeworth Expansion
There is a well developed framework, the Black-Scholes theory, for the
pricing of contracts based on the future prices of certain assets, called
options. This theory assumes that the probability distribution of the returns
of the underlying asset is a gaussian distribution. However, it is observed in
the market that this hypothesis is flawed, leading to the introduction of a
fudge factor, the so-called volatility smile. Therefore, it would be
interesting to explore extensions of the Black-Scholes theory to non-gaussian
distributions. In this contribution we provide an explicit formula for the
price of an option when the distributions of the returns of the underlying
asset is parametrized by an Edgeworth expansion, which allows for the
introduction of higher independent moments of the probability distribution,
namely skewness and kurtosis. We test our formula with options in the brazilian
and american markets, showing that the volatility smile can be reduced. We also
check whether our approach leads to more efficient hedging strategies of these
instruments.Comment: 9 pages, 3 figure. Contribution to the International Workshop on
Trends and Perspectives on Extensive and Non-Extensive Statistical Mechanics,
November 19-21, 2003, Angra dos Reis, Brazi
More statistical properties of order books and price impact
We investigate present some new statistical properties of order books. We
analyse data from the Nasdaq and investigate (a) the statistics of incoming
limit order prices, (b) the shape of the average order book, and (c) the
typical life time of a limit order as a function of the distance from the best
price. We also determine the `price impact' function using French and British
stocks, and find a logarithmic, rather than a power-law, dependence of the
price response on the volume. The weak time dependence of the response function
shows that the impact is, surprisingly, quasi-permanent, and suggests that
trading itself is interpreted by the market as new information.Comment: Proceedings of the Bali conference of Econophysics, to appear in
Physica
On the Adam-Gibbs-Wolynes scenario for the viscosity increase in glasses
We reformulate the interpretation of the mean-field glass transition scenario
for finite dimensional systems, proposed by Wolynes and collaborators.
This allows us to establish clearly a temperature dependent length xi* above
which the mean-field glass transition picture has to be modified. We argue in
favor of the mosaic state introduced by Wolynes and collaborators, which leads
to the Adam-Gibbs relation between the viscosity and configurational entropy of
glass forming liquids.
Our argument is a mixture of thermodynamics and kinetics, partly inspired by
the Random Energy
Model: small clusters of particles are thermodynamically frozen in low energy
states, whereas large clusters are kinetically frozen by large activation
energies. The relevant relaxation time is that of the smallest `liquid'
clusters. Some physical consequences are discussed.Comment: 8 page
Economics need a scientific revolution
I argue that the current financial crisis highlights the crucial need of a
change of mindset in economics and financial engineering, that should move away
from dogmatic axioms and focus more on data, orders of magnitudes, and
plausible, albeit non rigorous, arguments.Comment: An edited version of this essay appeared in Natur
The demise of constant price impact functions and single-time step models of speculation
Constant and symmetric price impact functions, most commonly used in
agent-based market modelling, are shown to give rise to paradoxical and
inconsistent outcomes in the simplest case of arbitrage exploitation when
open-hold-close actions are considered. The solution of the paradox lies in the
non-constant nature of real-life price impact functions. A simple model that
includes explicit position opening, holding, and closing is briefly introduced
and its information ecology discussed, shedding new light on the relevance of
the Minority Game to the study of financial markets.Comment: 10 pages, 2 figures. Proceedings of APFA5 conferenc
Econophysics: Still fringe after 30 years?
Some personal reflections on the past and future of "econophysics", to appear
in Europhysics NewsComment: 5 pages + references, 1 figur
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