61 research outputs found
The Effect of absorbing sites on the one-dimensional cellular automaton traffic flow with open boundaries
The effect of the absorbing sites with an absorbing rate β0 , in both one absorbing site (one way out) and two absorbing sites (two ways out) in a road, on the traffic flow phase transition is investigated using numerical simulations in the one-dimensional cellular automaton traffic flow model with open boundaries using parallel dynamics. It is found that the behavior of density and current depends strongly on the value of β0 , the position of the way(s) out from the entering and the distance between the ways out. Indeed, in the case of one way out, there exist a critical position of the way out ic1 below which the current is constant for β0 β0c2 When the way out is located at a position greater than i c2 , the current increases with β0 for β0 β0c2 . In the later case the density undergoes two successive first order transitions; from high density to maximal current phase at β0 =β0c1 and from intermediate density to the low one at β0 =β0c2 . In the case of two ways out located respectively at the positions i1 and i2, the two successive transitions occur only when the distance i2 - i1 seating the two ways is smaller than a critical distance dc , otherwise the traffic flow increases with β0, passes through a maximum at β0 =βmax and decreases for any value of β0 greater than βmax. The values of β0c1, β0c2, ic1, ic2 and dc depend on the injecting rate α, the extracting rate β and the position(s) of the way(s) out in the road. Moreover ic1 and ic2 , depend on the size of the system. Phase diagrams in the (α, β0 ), ( β, β0 ) and (i1 ,β0 ) planes are established. It is found that the transitions between Free traffic, Congested traffic and maximal current phase are first order.The effect of the absorbing sites with an absorbing rate β0 , in both one absorbing site (one way out) and two absorbing sites (two ways out) in a road, on the traffic flow phase transition is investigated using numerical simulations in the one-dimensional cellular automaton traffic flow model with open boundaries using parallel dynamics. It is found that the behavior of density and current depends strongly on the value of β0 , the position of the way(s) out from the entering and the distance between the ways out. Indeed, in the case of one way out, there exist a critical position of the way out ic1 below which the current is constant for β0 β0c2 When the way out is located at a position greater than i c2 , the current increases with β0 for β0 β0c2 . In the later case the density undergoes two successive first order transitions; from high density to maximal current phase at β0 =β0c1 and from intermediate density to the low one at β0 =β0c2 . In the case of two ways out located respectively at the positions i1 and i2, the two successive transitions occur only when the distance i2 - i1 seating the two ways is smaller than a critical distance dc , otherwise the traffic flow increases with β0, passes through a maximum at β0 =βmax and decreases for any value of β0 greater than βmax. The values of β0c1, β0c2, ic1, ic2 and dc depend on the injecting rate α, the extracting rate β and the position(s) of the way(s) out in the road. Moreover ic1 and ic2 , depend on the size of the system. Phase diagrams in the (α, β0 ), ( β, β0 ) and (i1 ,β0 ) planes are established. It is found that the transitions between Free traffic, Congested traffic and maximal current phase are first order
Vesicle dynamics in confined steady and harmonically modulated Poiseuille flows
We present a numerical study of the time-dependent motion of a
two-dimensional vesicle in a channel under an imposed flow. In a Poiseuille
flow the shape of the vesicle depends on the flow strength, the mechanical
properties of the membrane, and the width of the channel as reported in the
past. This study is focused on the centered snaking (CSn) shape, where the
vesicle shows an oscillatory motion like a swimmer flagella even though the
flow is stationary. We quantify this behavior by the amplitude and frequency of
the oscillations of the vesicle's center of mass. We observe regions in
parameter space, where the CSn coexists with the parachute or the unconfined
slipper. The influence of an amplitude modulation of the imposed flow on the
dynamics and shape of the snaking vesicle is also investigated. For large
modulation amplitudes transitions to static shapes are observed. A smaller
modulation amplitude induces a modulation in amplitude and frequency of the
center of mass of the snaking vesicle. In a certain parameter range we find
that the center of mass oscillates with a constant envelope indicating the
presence of at least two stable states.Comment: 10 pages, 7 figure
BB84 with Both Several Cloning and Intercept-resend Attacks
The goal of the protocol QKD BB84 is to allow a transmitter and a receiver which uses a quantum channel to exchange their keys and to detect the presence of eavesdropping attacks. In the present research, we investigate the effect of several eavesdroppers with both intercept-resend and cloning attacks. We will propose the different possible cases of the positioning of the eavesdroppers and their strategies of attacks; also we will calculate the mutual information for each case. The explicit expressions of the mutual information and quantum error clearly show that the security of the exchanged information depends on the numbers of the eavesdroppers and their attacks parameters on the quantum channel
Erythrocyte-erythrocyte aggregation dynamics under shear flow
Red blood cells (RBCs) -- erythrocytes -- suspended in plasma tend to
aggregate and form rouleaux. During aggregation the first stage consists in the
formation of RBC doublets [Blood cells, molecules, and diseases 25, 339
(1999)]. While aggregates are normally dissociated by moderate flow stresses,
under some pathological conditions the aggregation becomes irreversible, which
leads to high blood viscosity and vessel occlusion. We perform here
two-dimensional simulations to study the doublet dynamics under shear flow in
different conditions and its impact on rheology. We sum up our results on the
dynamics of doublet in a rich phase diagram in the parameter space (flow
strength, adhesion energy) showing four different types of doublet
configurations and dynamics. We find that membrane tank-treading plays an
important role in doublet disaggregation, in agreement with experiments on
RBCs. A remarkable feature found here is that when a single cell performs
tumbling (by increasing vesicle internal viscosity) the doublet formed due to
adhesion (even very weak) remains stable even under a very strong shear rate.
It is seen in this regime that an increase of shear rate induces an adaptation
of the doublet conformation allowing the aggregate to resist cell-cell
detachment. We show that the normalized effective viscosity of doublet
suspension increases significantly with the adhesion energy, a fact which
should affect blood perfusion in microcirculation.Comment: 14page
Predicting optimal hematocrit in silico
Optimal hematocrit maximizes oxygen transport. In healthy humans, the
average hematocrit is in the range of 40-45, but it can significantly
change in blood pathologies such as severe anemia (low ) and polycythemia
(high ). Whether the hematocrit level in humans corresponds to the optimal
one is a long standing physiological question. Here, using numerical
simulations with the Lattice Boltzmann method and two mechanical models of the
red blood cell (RBC) we predict the optimal hematocrit, and explore how
altering the mechanical properties of RBCs affects . We develop a
simplified analytical theory that accounts for results obtained from numerical
simulations and provides insight into the physical mechanisms determining
. Our numerical and analytical models can easily be modified to
incorporate a wide range of mechanical properties of RBCs as well as other soft
particles thereby providing means for the rational design of blood substitutes.
Our work lays the foundations for systematic theoretical study of the optimal
hematocrit and its link with pathological RBCs associated with various diseases
(e.g. sickle cell anemia, diabetes mellitus, malaria, elliptocytosis)
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