20,832 research outputs found
Ising model on the Apollonian network with node dependent interactions
This work considers an Ising model on the Apollonian network, where the
exchange constant between two neighboring spins
is a function of the degree of both spins. Using the exact
geometrical construction rule for the network, the thermodynamical and magnetic
properties are evaluated by iterating a system of discrete maps that allows for
very precise results in the thermodynamic limit. The results can be compared to
the predictions of a general framework for spins models on scale-free networks,
where the node distribution , with node dependent
interacting constants. We observe that, by increasing , the critical
behavior of the model changes, from a phase transition at for a
uniform system , to a T=0 phase transition when : in the
thermodynamic limit, the system shows no exactly critical behavior at a finite
temperature. The magnetization and magnetic susceptibility are found to present
non-critical scaling properties.Comment: 6 figures, 12 figure file
Effects of visuospatial tasks on desensitization to emotive memories
Objectives: Vivid and intrusive memories of extreme trauma can disrupt a stepwise approach to
imaginal exposure. Concurrent tasks that load the visuo-spatial sketchpad (VSSP) of working memory
reduce memory vividness during imaginal exposure. Such tasks may help maintain a progressive
exposure protocol while minimizing distress during treatment. The current study tested whether relief
of distress from a competing VSSP load during emotive imagery is at the cost of impaired
desensitization.
Design: This study examined repeated exposure to emotive memories using 18 unselected
undergraduates, using a within-subjects design.
Method: Participants recalled three positive and three negative self-related memories, and rated the
vividness and emotiveness of the image. Participants then received all three conditions (Eye
Movements; Visual Noise; Control) in a counterbalanced order. One positive and one negative
recollection were used for each condition. They then rated the vividness of the image and their
emotional response before proceeding to the next trial. There were 8 trials for each image. At a noninterference
session one week later, participants recalled each image, rating its vividness and their
emotional response.
Results: Consistent with previous research, vividness and distress during imaging were lower during
eye movements than in exposure alone, with passive visual interference giving intermediate results.
A small reduction in emotional responses a week later was of similar size for the three conditions
Analytical approach to directed sandpile models on the Apollonian network
We investigate a set of directed sandpile models on the Apollonian network,
which are inspired on the work by Dhar and Ramaswamy (PRL \textbf{63}, 1659
(1989)) for Euclidian lattices. They are characterized by a single parameter
, that restricts the number of neighbors receiving grains from a toppling
node. Due to the geometry of the network, two and three point correlation
functions are amenable to exact treatment, leading to analytical results for
the avalanche distributions in the limit of an infinite system, for .
The exact recurrence expressions for the correlation functions are numerically
iterated to obtain results for finite size systems, when larger values of
are considered. Finally, a detailed description of the local flux properties is
provided by a multifractal scaling analysis.Comment: 7 pages in two-column format, 10 illustrations, 5 figure
Brief guided imagery and body scanning interventions reduce food cravings
mindfulness cognition food intrusive thoughts acceptance eatingElaborated Intrusion (EI) Theory proposes that cravings occur when involuntary thoughts about food are elaborated; a key part of elaboration is affectively-charged imagery. Craving can be weakened by working memory tasks that block imagery. EI Theory predicts that cravings should also be reduced by preventing involuntary thoughts being elaborated in the first place. Research has found that imagery techniques such as body scanning and guided imagery can reduce the occurrence of food thoughts. This study tested the prediction that these techniques also reduce craving. We asked participants to abstain from food overnight, and then to carry out 10 minutes of body scanning, guided imagery, or a control mind wandering task. They rated their craving at ten points during the task on a single item measure, and before and after the task using the Craving Experience Questionnaire. While craving rose during the task for the mind wandering group, neither the guided imagery nor body scanning group showed an increase. These effects were not detected by the CEQ, suggesting that they are only present during the competing task. As they require no devices or materials and are unobtrusive, brief guided imagery strategies might form useful components of weight loss programmes that attempt to address cravings
Targeted Recovery as an Effective Strategy against Epidemic Spreading
We propose a targeted intervention protocol where recovery is restricted to
individuals that have the least number of infected neighbours. Our recovery
strategy is highly efficient on any kind of network, since epidemic outbreaks
are minimal when compared to the baseline scenario of spontaneous recovery. In
the case of spatially embedded networks, we find that an epidemic stays
strongly spatially confined with a characteristic length scale undergoing a
random walk. We demonstrate numerically and analytically that this dynamics
leads to an epidemic spot with a flat surface structure and a radius that grows
linearly with the spreading rate.Comment: 6 pages, 5 figure
A micromechanical model of collapsing quicksand
The discrete element method constitutes a general class of modeling
techniques to simulate the microscopic behavior (i.e. at the particle scale) of
granular/soil materials. We present a contact dynamics method, accounting for
the cohesive nature of fine powders and soils. A modification of the model
adjusted to capture the essential physical processes underlying the dynamics of
generation and collapse of loose systems is able to simulate "quicksand"
behavior of a collapsing soil material, in particular of a specific type, which
we call "living quicksand". We investigate the penetration behavior of an
object for varying density of the material. We also investigate the dynamics of
the penetration process, by measuring the relation between the driving force
and the resulting velocity of the intruder, leading to a "power law" behavior
with exponent 1/2, i.e. a quadratic velocity dependence of the drag force on
the intruder.Comment: 5 pages, 4 figures, accepted for granular matte
- …