188 research outputs found
Eclipsing Binaries in Open Clusters
Detached eclipsing binaries are very useful objects for calibrating
theoretical stellar models and checking their predictions. Detached eclipsing
binaries in open clusters are particularly important because of the additional
constraints on their age and chemical composition from their membership of the
cluster. I compile a list containing absolute parameters of well-studied
eclipsing binaries in open clusters, and present new observational data on the
B-type systems V1481 Cyg and V2263 Cyg which are members of the young open
cluster NGC 7128.Comment: 4 pages, 2 colour figures. Poster presentation for IAUS 240 (Binary
Stars as Critical Tools and Tests in Contemporary Astrophysics), Prague,
August 2006. The poster itself can be dowloaded in ppt and pdf versions from
http://www.astro.keele.ac.uk/~jkt/pubs.htm
Fearless versus Fearful Speculative Financial Bubbles
Using a recently introduced rational expectation model of bubbles, based on
the interplay between stochasticity and positive feedbacks of prices on returns
and volatility, we develop a new methodology to test how this model classifies
9 time series that have been previously considered as bubbles ending in
crashes. The model predicts the existence of two anomalous behaviors occurring
simultaneously: (i) super-exponential price growth and (ii) volatility growth,
that we refer to as the ``fearful singular bubble'' regime. Out of the 9 time
series, we find that 5 pass our tests and can be characterized as ``fearful
singular bubbles.'' The 4 other cases are the information technology Nasdaq
bubble and three bubbles of the Hang Seng index ending in crashes in 1987, 1994
and 1997. According to our analysis, these four bubbles have developed with
essentially no significant increase of their volatility. This paper thus
proposes that speculative bubbles ending in crashes form two groups hitherto
unrecognized, namely those accompanied by increasing volatility (reflecting
increasing risk perception) and those without change of volatility (reflecting
an absence of risk perception).Comment: 12 pages + 9 figures + 9 table
Towards Landslide Predictions: Two Case Studies
In a previous work [Helmstetter, 2003], we have proposed a simple physical
model to explain the accelerating displacements preceding some catastrophic
landslides, based on a slider-block model with a state and velocity dependent
friction law. This model predicts two regimes of sliding, stable and unstable
leading to a critical finite-time singularity. This model was calibrated
quantitatively to the displacement and velocity data preceding two landslides,
Vaiont (Italian Alps) and La Clapi\`ere (French Alps), showing that the former
(resp. later) landslide is in the unstable (resp. stable) sliding regime. Here,
we test the predictive skills of the state-and-velocity-dependent model on
these two landslides, using a variety of techniques. For the Vaiont landslide,
our model provides good predictions of the critical time of failure up to 20
days before the collapse. Tests are also presented on the predictability of the
time of the change of regime for la Clapi\`ere landslide.Comment: 30 pages with 12 eps figure
Criticality and finite size effects in a simple realistic model of stock market
We discuss a simple model based on the Minority Game which reproduces the
main stylized facts of anomalous fluctuations in finance. We present the
analytic solution of the model in the thermodynamic limit and show that
stylized facts arise only close to a line of critical points with non-trivial
properties. By a simple argument, we show that, in Minority Games, the
emergence of critical fluctuations close to the phase transition is governed by
the interplay between the signal to noise ratio and the system size. These
results provide a clear and consistent picture of financial markets as critical
systems.Comment: 4 pages, 4 figure
Failure time in the fiber-bundle model with thermal noise and disorder
The average time for the onset of macroscopic fractures is analytically and
numerically investigated in the fiber-bundle model with quenched disorder and
thermal noise under a constant load. We find an implicit exact expression for
the failure time in the low-temperature limit that is accurately confirmed by
direct simulations. The effect of the disorder is to lower the energy barrier.Comment: 11 pages, 6 figures; accepted for publication in Phys. Rev.
On the Temperature Dependence of the Lifetime of Thermally Isolated Metastable Clusters
The temperature dependence of the lifetime of the thermally isolated
metastable N8 cubane up to its decay into N2 molecules has been calculated by
the molecular dynamics method. It has been demonstrated that this dependence
significantly deviates from the Arrhenius law. The applicability of the finite
heat bath theory to the description of thermally isolated atomic clusters has
been proved using statistical analysis of the results obtained.Comment: 14 pages, 4 figure
Using an Observational Framework to investigate adult language input to young children in a naturalistic environment
The correlation between the communicative intent of parents, in terms of their expectation of a response and the response patterns of young children aged 23—25 months during parent—child interactions, was investigated. An Observational Framework was used to code these parameters in interactions between 36 children and their mothers. The children were assigned by cluster analysis to `advanced', `typical' and `delayed' language groups and their responses were coded with respect to the degree of correctness or appropriateness within the interaction. Differences in both the parental response expectations and the children's response patterns across the three clusters are discussed
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
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