349 research outputs found
Does communication enhance pedestrians transport in the dark?
We study the motion of pedestrians through an obscure tunnel where the lack
of visibility hides the exits. Using a lattice model, we explore the effects of
communication on the effective transport properties of the crowd of
pedestrians. More precisely, we study the effect of two thresholds on the
structure of the effective nonlinear diffusion coefficient. One threshold
models pedestrians's communication efficiency in the dark, while the other one
describes the tunnel capacity. Essentially, we note that if the evacuees show a
maximum trust (leading to a fast communication), they tend to quickly find the
exit and hence the collective action tends to prevent the occurrence of
disasters
Sputtering of Oxygen Ice by Low Energy Ions
Naturally occurring ices lie on both interstellar dust grains and on
celestial objects, such as those in the outer solar system. These ices are
continu- ously subjected to irradiation by ions from the solar wind and/or
cosmic rays, which modify their surfaces. As a result, new molecular species
may form which can be sputtered off into space or planetary atmospheres. We
determined the experimental values of sputtering yields for irradiation of
oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2+, N2+ and
O2+) charged ions with 4 keV kinetic energy. In these laboratory experiments,
oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber
at low temperature to simulate the environment of space. The number of
molecules removed by sputtering was observed by measurement of the ice
thickness using laser interferometry. Preliminary mass spectra were taken of
sputtered species and of molecules formed in the ice by temperature programmed
desorption (TPD). We find that the experimental sputtering yields increase
approximately linearly with the projectile ion mass (or momentum squared) for
all ions studied. No difference was found between the sputtering yield for
singly and doubly charged ions of the same atom within the experimental
uncertainty, as expected for a process dominated by momentum transfer. The
experimental sputter yields are in good agreement with values calculated using
a theoretical model except in the case of oxygen ions. Preliminary studies have
shown molecular oxygen as the dominant species sputtered and TPD measurements
indicate ozone formation.Comment: to be published in Surface Science (2015
A mesoscopic lattice model for morphology formation in ternary mixtures with evaporation
We develop a mesoscopic lattice model to study the morphology formation in interacting ternary mixtures with the evaporation of one component. As concrete potential application of our model, we wish to capture morphologies as they are typically arising during the fabrication of organic solar cells. In this context, we consider an evaporating solvent into which two other components are dissolved, as a model for a 2-component coating solution that is drying on a substrate. We propose a 3-spins dynamics to describe the evolution of the three interacting species. As main tool, we use a Monte Carlo Metropolis-based algorithm, with the possibility of varying the system's temperature, mixture composition, interaction strengths, and evaporation kinetics. The main novelty is the structure of the mesoscopic model – a bi-dimensional lattice with periodic boundary conditions, divided into square cells to encode a mesoscopic range interaction among the units. We investigate the effect of the model parameters on the structure of the resulting morphologies. Finally, we compare the results obtained with the mesoscopic model with corresponding ones based on an analogous lattice model with a short range interaction among the units, i.e. when the mesoscopic length scale coincides with the microscopic length scale of the lattice
Free to move or trapped in your group: Mathematical modeling of information overload and coordination in crowded populations
We present modeling strategies that describe the motion and interaction of
groups of pedestrians in obscured spaces. We start off with an approach based
on balance equations in terms of measures and then we exploit the descriptive
power of a probabilistic cellular automaton model. Based on a variation of the
simple symmetric random walk on the square lattice, we test the interplay
between population size and an interpersonal attraction parameter for the
evacuation of confined and darkened spaces. We argue that information overload
and coordination costs associated with information processing in small groups
are two key processes that influence the evacuation rate. Our results show that
substantial computational resources are necessary to compensate for incomplete
information -- the more individuals in (information processing) groups the
higher the exit rate for low population size. For simple social systems, it is
likely that the individual representations are not redundant and large group
sizes ensure that this non--redundant information is actually available to a
substantial number of individuals. For complex social systems information
redundancy makes information evaluation and transfer inefficient and, as such,
group size becomes a drawback rather than a benefit. The effect of group sizes
on outgoing fluxes, evacuation times and wall effects are carefully studied
with a Monte Carlo framework accounting also for the presence of an internal
obstacle
Semi-discrete finite difference multiscale scheme for a concrete corrosion model: approximation estimates and convergence
We propose a semi-discrete finite difference multiscale scheme for a concrete
corrosion model consisting of a system of two-scale reaction-diffusion
equations coupled with an ode. We prove energy and regularity estimates and use
them to get the necessary compactness of the approximation estimates. Finally,
we illustrate numerically the behavior of the two-scale finite difference
approximation of the weak solution.Comment: 22 pages, 1 figure, submitted to Japan Journal of Industrial and
Applied Mathematic
Data Collection Theory in Healthcare Research: The Minimum Dataset in Quantitative Studies.
There is considerable interest in data analytics because of its value in informing decisions in healthcare. Data variables can be derived from routinely collected records or from primary studies. The level of detail for individual variables in quantitative studies is often disregarded. In this work, we aim to present the concept of a minimum dataset for any variable. The most basic level of data collection is the value of a variable. In addition, there may be an indicator of severity and a measure of duration or how long the value has been present. The time course defines how the values for a variable fluctuated over time. The validity or accuracy of the values for a variable is also important to avoid spurious findings. Finally, there may be additional modifiers which drastically change the impact of a variable. In conclusion, the minimum dataset is a framework which can be used for the purposes of study design and appraisal of studies. Not all data requires full consideration of the minimum dataset framework for each variable, but the framework may be important if more detailed results are desired
Identification of a Response Amplitude Operator for Ships
At the European Study Group Mathematics with Industry 2012 in Eindhoven, the Maritime Research Institute Netherlands (MARIN) presented the problem of identifying the response amplitude operator (RAO) for a ship, given input information on the amplitudes of the sea waves and output information on the movement of the ship. We approach the problem from a threefold perspective: a direct least-squares approach, an approach based on truncated Fourier series, and an approach using low-dimensional measures of the RAO. We give a few recommendations for possible further investigations
Exact Cover with light
We suggest a new optical solution for solving the YES/NO version of the Exact
Cover problem by using the massive parallelism of light. The idea is to build
an optical device which can generate all possible solutions of the problem and
then to pick the correct one. In our case the device has a graph-like
representation and the light is traversing it by following the routes given by
the connections between nodes. The nodes are connected by arcs in a special way
which lets us to generate all possible covers (exact or not) of the given set.
For selecting the correct solution we assign to each item, from the set to be
covered, a special integer number. These numbers will actually represent delays
induced to light when it passes through arcs. The solution is represented as a
subray arriving at a certain moment in the destination node. This will tell us
if an exact cover does exist or not.Comment: 20 pages, 4 figures, New Generation Computing, accepted, 200
A Comparative Study of Embedded and Anesthetized Zebrafish in vivo on Myocardiac Calcium Oscillation and Heart Muscle Contraction
The zebrafish (Danio rerio) has been used as a model for studying vertebrate development in the cardiovascular system. In order to monitor heart contraction and cytosolic calcium oscillations, fish were either embedded in methylcellulose or anesthetized with tricaine. Using high-resolution differential interference contrast and calcium imaging microscopy, we here show that dopamine and verapamil alter calcium signaling and muscle contraction in anesthetized zebrafish, but not in embedded zebrafish. In anesthetized fish, dopamine increases the amplitude of cytosolic calcium oscillation with a subsequent increase in heart contraction, whereas verapamil decreases the frequency of calcium oscillation and heart rate. Interestingly, verapamil also increases myocardial contraction. Our data further indicate that verapamil can increase myocardial calcium sensitivity in anesthetized fish. Taken together, our data reinforce in vivo cardiac responses to dopamine and verapamil. Furthermore, effects of dopamine and verapamil on myocardial calcium and contraction are greater in anesthetized than embedded fish. We suggest that while the zebrafish is an excellent model for a cardiovascular imaging study, the cardio-pharmacological profiles are very different between anesthetized and embedded fish
Can multisensorial media improve learner experience?
In recent years, the emerging immersive technologies (e.g. Virtual/Augmented Reality, multisensorial media) bring brand-new multi-dimensional effects such as 3D vision, immersion, vibration,
smell, airflow, etc. to gaming, video entertainment and other aspects of human life. This paper reports results from an European Horizon 2020 research project on the impact of multisensoral media (mulsemedia) on educational learner experience. A mulsemediaenhanced test-bed was developed to perform delivery of video content enhanced with haptic, olfaction and airflow effects. The results of the quality rating and questionnaires show significant improvements in terms of mulsemedia-enhanced teaching
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