36 research outputs found
Slow Learning Deaf Children
The hearing impaired child is educationally handicapped because of his lack of achieving language through the ordinary channel â hearing. He would be given half a chance if that were his only problem. The deaf child who is further handicapped by a learning disability delays his educational achievement even beyond that of a singly-handicapped deaf child because he is not only limited by his means of acquiring language but also limited in the amount and number of language and language principles he is able to learn. This is the slow learning deaf child; he is doubly handicapped in his struggle to learn â to learn language, reading, speech, lipreading, and content areas. He is the child who has been neglected and overlooked for many years in educational history because he does not differ from the normal enough to be noticed. But he is calling teachers to his attention and is being heard by more educators and administrators
Surface Tension in Kac Glass Models
In this paper we study a distance-dependent surface tension, defined as the
free-energy cost to put metastable states at a given distance. This will be
done in the framework of a disordered microscopic model with Kac interactions
that can be solved in the mean-field limit.Comment: 13 pages, 6 figure
Role of the Tracy-Widom distribution in the finite-size fluctuations of the critical temperature of the Sherrington-Kirkpatrick spin glass
We investigate the finite-size fluctuations due to quenched disorder of the
critical temperature of the Sherrington-Kirkpatrick spin glass. In order to
accomplish this task, we perform a finite-size analysis of the spectrum of the
susceptibility matrix obtained via the Plefka expansion. By exploiting results
from random matrix theory, we obtain that the fluctuations of the critical
temperature are described by the Tracy-Widom distribution with a non-trivial
scaling exponent 2/3
Numerical simulations of liquids with amorphous boundary conditions
It has recently become clear that simulations under amorphpous boundary
conditions (ABCs) can provide valuable information on the dynamics and
thermodynamics of disordered systems with no obvious ordered parameter. In
particular, they allow to detect a correlation length that is not measurable
with standard correlation functions. Here we explain what exactly is meant by
ABCs, discuss their relation with point-to-set correlations and briefly
describe some recent results obtained with this technique.Comment: Presented at STATPHYS 2
3D simulations of RS Oph: from accretion to nova blast
RS Ophiuchi is a recurrent nova with a period of about 22 years, consisting
of a wind accreting binary system with a white dwarf (WD) very close to the
Chandrasekhar limit and a red giant star (RG). The system is considered a prime
candidate to evolve into an SNIa. We present a 3D hydrodynamic simulation of
the quiescent accretion and the subsequent explosive phase. The computed
circumstellar mass distribution in the quiescent phase is highly structured
with a mass enhancement in the orbital plane of about a factor of 2 as compared
to the poleward directions. The simulated nova remnant evolves aspherically,
propagating faster toward the poles. The shock velocities derived from the
simulations are in agreement with those derived from observations. For v_RG =
20 km/s and for nearly isothermal flows, we derive a mass transfer rate to the
WD of 10% of the mass loss of the RG. For an RG mass loss of 10^{-7} solar
masses per year, we found the orbit of the system to decay by 3% per million
years. With the derived mass transfer rate, multi-cycle nova models provide a
qualitatively correct recurrence time, amplitude, and fastness of the nova. Our
simulations provide, along with the observations and nova models, the third
ingredient for a deeper understanding of the recurrent novae of the RS Oph
type. In combination with recent multi-cycle nova models, our results suggests
that the WD in RS Oph will increase in mass. Several speculative outcomes then
seem plausible. The WD may reach the Chandrasekhar limit and explode as an SN
Ia. Alternatively, the mass loss of the RG could result in a smaller Roche
volume, a common envelope phase, and a narrow WD+WD system. Angular momentum
loss due to graviational wave emission could trigger the merger of the two WDs
and - perhaps - an SN Ia via the double degenerate scenario.Comment: Accepted by Astronomy & Astrophysics Letters, 4 pages, 5 figures;
Version with high resolution figures and movie can be found at
http://www.astro.phys.ethz.ch/staff/folini/private/research/rsoph/rsoph.htm
Finite-size scaling analysis of the distributions of pseudo-critical temperatures in spin glasses
Using the results of large scale numerical simulations we study the
probability distribution of the pseudo critical temperature for the
three-dimensional Edwards-Anderson Ising spin glass and for the fully connected
Sherrington-Kirkpatrick model. We find that the behavior of our data is nicely
described by straightforward finite-size scaling relations.Comment: 23 pages, 9 figures. Version accepted for publication in J. Stat.
Mec
On the concentration of large deviations for fat tailed distributions, with application to financial data
Large deviations for fat tailed distributions, i.e. those that decay slower
than exponential, are not only relatively likely, but they also occur in a
rather peculiar way where a finite fraction of the whole sample deviation is
concentrated on a single variable. The regime of large deviations is separated
from the regime of typical fluctuations by a phase transition where the
symmetry between the points in the sample is spontaneously broken. For
stochastic processes with a fat tailed microscopic noise, this implies that
while typical realizations are well described by a diffusion process with
continuous sample paths, large deviation paths are typically discontinuous. For
eigenvalues of random matrices with fat tailed distributed elements, a large
deviation where the trace of the matrix is anomalously large concentrates on
just a single eigenvalue, whereas in the thin tailed world the large deviation
affects the whole distribution. These results find a natural application to
finance. Since the price dynamics of financial stocks is characterized by fat
tailed increments, large fluctuations of stock prices are expected to be
realized by discrete jumps. Interestingly, we find that large excursions of
prices are more likely realized by continuous drifts rather than by
discontinuous jumps. Indeed, auto-correlations suppress the concentration of
large deviations. Financial covariance matrices also exhibit an anomalously
large eigenvalue, the market mode, as compared to the prediction of random
matrix theory. We show that this is explained by a large deviation with excess
covariance rather than by one with excess volatility.Comment: 38 pages, 12 figure
A fresh look at the unstable simulations of Bondi-Hoyle-Lyttleton accretion
The instability of Bondi-Hoyle-Lyttleton accretion, observed in numerical
simulations, is analyzed through known physical mechanisms and possible
numerical artefacts. The mechanisms of the longitudinal and transverse
instabilities, established within the accretion line model, are clarified. They
cannot account for the instability of BHL accretion at moderate Mach number
when the pressure forces within the shock cone are taken into account. The
advective-acoustic instability is considered in the context of BHL accretion
when the shock is detached from the accretor. This mechanism naturally explains
the stability of the flow when the shock is weak, and the instability when the
accretor is small. In particular, it is a robust proof of the instability of 3D
accretion when gamma=5/3 if the accretor is small enough, even for moderate
shock strength (M sim 3). The numerical artefacts that may be present in
existing numerical simulations are reviewed, with particular attention paid to
the advection of entropy/vorticity perturbations and the artificial acoustic
feedback from the accretor boundary condition. Several numerical tests are
proposed to test these mechanisms.Comment: 15 pages, 5 figures, accepted for publication in A&