2,568 research outputs found
The family history of children with elective mutism: a research report
The family history was studied in children with elective mutism. The samples comprised a series of N = 38 children with elective mutism and a control group of N = 31 children with a similar behavioural phenotype, i.e., the combination of an emotional disorder and a developmental disorder of articulation or expressive language. Interviews were performed with the respective mothers. There was a clear excess of the personality trait of taciturnity in first-, second-, and third-degree relatives. Although mutism was reported almost exclusively in the group of relatives of children that manifested elective mutism, the differences between the two samples were not significant probably due to low frequencies. Disorders of speech and language were quite common in the relatives of subjects in both samples. Psychiatric disorders were more frequently reported in the families with an electively mute child. The study lends some evidence for the assumption that genetic factors may play a role in the etiology of elective mutis
Long-range epidemic spreading with immunization
We study the phase transition between survival and extinction in an epidemic
process with long-range interactions and immunization. This model can be viewed
as the well-known general epidemic process (GEP) in which nearest-neighbor
interactions are replaced by Levy flights over distances r which are
distributed as P(r) ~ r^(-d-sigma). By extensive numerical simulations we
confirm previous field-theoretical results obtained by Janssen et al. [Eur.
Phys. J. B7, 137 (1999)].Comment: LaTeX, 14 pages, 4 eps figure
Non Sequential Recursive Pair Substitution: Some Rigorous Results
We present rigorous results on some open questions on NSRPS, non sequential
recursive pairs substitution method (see Grassberger in \cite{G}). In
particular, starting from the action of NSRPS on finite strings we define a
corresponding natural action on measures and we prove that the iterated measure
becomes asymptotically Markov. This certify the effectiveness of NSRPS as a
tool for data compression and entropy estimation.Comment: 20 page
Contact processes with long-range interactions
A class of non-local contact processes is introduced and studied using
mean-field approximation and numerical simulations. In these processes
particles are created at a rate which decays algebraically with the distance
from the nearest particle. It is found that the transition into the absorbing
state is continuous and is characterized by continuously varying critical
exponents. This model differs from the previously studied non-local directed
percolation model, where particles are created by unrestricted Levy flights. It
is motivated by recent studies of non-equilibrium wetting indicating that this
type of non-local processes play a role in the unbinding transition. Other
non-local processes which have been suggested to exist within the context of
wetting are considered as well.Comment: Accepted with minor revisions by Journal of Statistical Mechanics:
Theory and experiment
Persistence, extinction and spatio-temporal synchronization of SIRS cellular automata models
Spatially explicit models have been widely used in today's mathematical
ecology and epidemiology to study persistence and extinction of populations as
well as their spatial patterns. Here we extend the earlier work--static
dispersal between neighbouring individuals to mobility of individuals as well
as multi-patches environment. As is commonly found, the basic reproductive
ratio is maximized for the evolutionary stable strategy (ESS) on diseases'
persistence in mean-field theory. This has important implications, as it
implies that for a wide range of parameters that infection rate will tend
maximum. This is opposite with present results obtained in spatial explicit
models that infection rate is limited by upper bound. We observe the emergence
of trade-offs of extinction and persistence on the parameters of the infection
period and infection rate and show the extinction time having a linear
relationship with respect to system size. We further find that the higher
mobility can pronouncedly promote the persistence of spread of epidemics, i.e.,
the phase transition occurs from extinction domain to persistence domain, and
the spirals' wavelength increases as the mobility increasing and ultimately, it
will saturate at a certain value. Furthermore, for multi-patches case, we find
that the lower coupling strength leads to anti-phase oscillation of infected
fraction, while higher coupling strength corresponds to in-phase oscillation.Comment: 12page
Non-equilibrium Phase Transitions with Long-Range Interactions
This review article gives an overview of recent progress in the field of
non-equilibrium phase transitions into absorbing states with long-range
interactions. It focuses on two possible types of long-range interactions. The
first one is to replace nearest-neighbor couplings by unrestricted Levy flights
with a power-law distribution P(r) ~ r^(-d-sigma) controlled by an exponent
sigma. Similarly, the temporal evolution can be modified by introducing waiting
times Dt between subsequent moves which are distributed algebraically as P(Dt)~
(Dt)^(-1-kappa). It turns out that such systems with Levy-distributed
long-range interactions still exhibit a continuous phase transition with
critical exponents varying continuously with sigma and/or kappa in certain
ranges of the parameter space. In a field-theoretical framework such
algebraically distributed long-range interactions can be accounted for by
replacing the differential operators nabla^2 and d/dt with fractional
derivatives nabla^sigma and (d/dt)^kappa. As another possibility, one may
introduce algebraically decaying long-range interactions which cannot exceed
the actual distance to the nearest particle. Such interactions are motivated by
studies of non-equilibrium growth processes and may be interpreted as Levy
flights cut off at the actual distance to the nearest particle. In the
continuum limit such truncated Levy flights can be described to leading order
by terms involving fractional powers of the density field while the
differential operators remain short-ranged.Comment: LaTeX, 39 pages, 13 figures, minor revision
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