2,466 research outputs found
Particle Dispersion on Rapidly Folding Random Hetero-Polymers
We investigate the dynamics of a particle moving randomly along a disordered
hetero-polymer subjected to rapid conformational changes which induce
superdiffusive motion in chemical coordinates. We study the antagonistic
interplay between the enhanced diffusion and the quenched disorder. The
dispersion speed exhibits universal behavior independent of the folding
statistics. On the other hand it is strongly affected by the structure of the
disordered potential. The results may serve as a reference point for a number
of translocation phenomena observed in biological cells, such as protein
dynamics on DNA strands.Comment: 4 pages, 4 figure
Shannon entropy of brain functional complex networks under the influence of the psychedelic Ayahuasca
The entropic brain hypothesis holds that the key facts concerning
psychedelics are partially explained in terms of increased entropy of the
brain's functional connectivity. Ayahuasca is a psychedelic beverage of
Amazonian indigenous origin with legal status in Brazil in religious and
scientific settings. In this context, we use tools and concepts from the theory
of complex networks to analyze resting state fMRI data of the brains of human
subjects under two distinct conditions: (i) under ordinary waking state and
(ii) in an altered state of consciousness induced by ingestion of Ayahuasca. We
report an increase in the Shannon entropy of the degree distribution of the
networks subsequent to Ayahuasca ingestion. We also find increased local and
decreased global network integration. Our results are broadly consistent with
the entropic brain hypothesis. Finally, we discuss our findings in the context
of descriptions of "mind-expansion" frequently seen in self-reports of users of
psychedelic drugs.Comment: 27 pages, 6 figure
Characterization of the Noise in Secondary Ion Mass Spectrometry Depth Profiles
The noise in the depth profiles of secondary ion mass spectrometry (SIMS) is
studied using different samples under various experimental conditions. Despite
the noise contributions from various parts of the dynamic SIMS process, its
overall character agrees very well with the Poissonian rather than the Gaussian
distribution in all circumstances. The Poissonian relation between the measured
mean-square error (MSE) and mean can be used to describe our data in the range
of four orders. The departure from this relation at high counts is analyzed and
found to be due to the saturation of the channeltron used. Once saturated, the
detector was found to exhibit hysteresis between rising and falling input flux
and output counts.Comment: 14 pages, 4 postscript figures, to appear on J. Appl. Phy
School screening program: update of the prevalence of overweight and obesity between 1996 and 2017
Within the School Screening Program, around 16 school nurses measure selected health indicators every year, including weight, height and selected other lifestyles variables in all ~5800 students in the C2, P4, S1 and S4 grades in all schools.
• Overweight and obesity are defined along standard age and sex specific criteria by the International Obesity Task Force (IOTF).
• In 2017, weight and height were measured in 3351 students from 5760 eligible students, a participation rate of only 58%. The disappointingly low participation rate in 2017, and in recent years in general, seems to be partially related to the fact that school nurses often cannot run the school program because of concurrent duties in health centers. This issue should be addressed urgently if the screening program is to be sustained in 2018.
• The prevalence of overweight or obesity in children aged 9-16 years (P4, S1 and S4) increased by more than two times, between 1998 and 2017, from 9.3% to 26.4% in boys and from 12.9% in 1998 to 28.5% in girls. The current levels are extremely high by international comparison. The steep linear increase over time, including in recent years, underlies a major public health problem
Long-Range Navigation on Complex Networks using L\'evy Random Walks
We introduce a strategy of navigation in undirected networks, including
regular, random, and complex networks, that is inspired by L\'evy random walks,
generalizing previous navigation rules. We obtained exact expressions for the
stationary probability distribution, the occupation probability, the mean first
passage time, and the average time to reach a node on the network. We found
that the long-range navigation using the L\'evy random walk strategy, compared
with the normal random walk strategy, is more efficient at reducing the time to
cover the network. The dynamical effect of using the L\'evy walk strategy is to
transform a large-world network into a small world. Our exact results provide a
general framework that connects two important fields: L\'evy navigation
strategies and dynamics on complex networks.Comment: 6 pages, 3 figure
First passages in bounded domains: When is the mean first passage time meaningful?
We study the first passage statistics to adsorbing boundaries of a Brownian
motion in bounded two-dimensional domains of different shapes and
configurations of the adsorbing and reflecting boundaries. From extensive
numerical analysis we obtain the probability P(\omega) distribution of the
random variable \omega=\tau_1/(\tau_1+\tau_2), which is a measure for how
similar the first passage times \tau_1 and \tau_2 are of two independent
realisations of a Brownian walk starting at the same location. We construct a
chart for each domain, determining whether P(\omega) represents a unimodal,
bell-shaped form, or a bimodal, M-shaped behaviour. While in the former case
the mean first passage time (MFPT) is a valid characteristic of the first
passage behaviour, in the latter case it is an insufficient measure for the
process. Strikingly we find a distinct turnover between the two modes of
P(\omega), characteristic for the domain shape and the respective location of
absorbing and reflective boundaries. Our results demonstrate that large
fluctuations of the first passage times may occur frequently in two-dimensional
domains, rendering quite vague the general use of the MFPT as a robust measure
of the actual behaviour even in bounded domains, in which all moments of the
first passage distribution exist.Comment: 9 pages, 6 figure
Spontaneous symmetry breaking in amnestically induced persistence
We investigate a recently proposed non-Markovian random walk model
characterized by loss of memories of the recent past and amnestically induced
persistence. We report numerical and analytical results showing the complete
phase diagram, consisting of 4 phases, for this system: (i) classical
nonpersistence, (ii) classical persistence (iii) log-periodic nonpersistence
and (iv) log-periodic persistence driven by negative feedback. The first two
phases possess continuous scale invariance symmetry, however log-periodicity
breaks this symmetry. Instead, log-periodic motion satisfies discrete scale
invariance symmetry, with complex rather than real fractal dimensions. We find
for log-periodic persistence evidence not only of statistical but also of
geometric self-similarity.Comment: 4 pages, 2 color fig
Amnestically induced persistence in random walks
We study how the Hurst exponent depends on the fraction of the
total time remembered by non-Markovian random walkers that recall only the
distant past. We find that otherwise nonpersistent random walkers switch to
persistent behavior when inflicted with significant memory loss. Such memory
losses induce the probability density function of the walker's position to
undergo a transition from Gaussian to non-Gaussian. We interpret these findings
of persistence in terms of a breakdown of self-regulation mechanisms and
discuss their possible relevance to some of the burdensome behavioral and
psychological symptoms of Alzheimer's disease and other dementias.Comment: 4 pages, 3 figs, subm. to Phys. Rev. Let
Analyzing the House Fly's Exploratory Behavior with Autoregression Methods
This paper presents a detailed characterization of the trajectory of a single
housefly with free range of a square cage. The trajectory of the fly was
recorded and transformed into a time series, which was fully analyzed using an
autoregressive model, which describes a stationary time series by a linear
regression of prior state values with the white noise. The main discovery was
that the fly switched styles of motion from a low dimensional regular pattern
to a higher dimensional disordered pattern. This discovered exploratory
behavior is, irrespective of the presence of food, characterized by anomalous
diffusion.Comment: 20 pages, 9 figures, 1 table, full pape
QCD Strings as Constrained Grassmannian Sigma Model:
We present calculations for the effective action of string world sheet in R3
and R4 utilizing its correspondence with the constrained Grassmannian sigma
model. Minimal surfaces describe the dynamics of open strings while harmonic
surfaces describe that of closed strings. The one-loop effective action for
these are calculated with instanton and anti-instanton background, reprsenting
N-string interactions at the tree level. The effective action is found to be
the partition function of a classical modified Coulomb gas in the confining
phase, with a dynamically generated mass gap.Comment: 22 pages, Preprint: SFU HEP-116-9
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