264 research outputs found
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Simultaneous coupling of phototaxis and electrotaxis in Volvox algae
In nature, living creatures are affected by several stimuli simultaneously. The response of living creatures to stimuli is called taxis. In order to reveal the principles of taxis behavior in response to complex stimuli, we simultaneously applied photostimulation and electric stimulation perpendicularly to a Volvox algae solution. The probability distribution of the swimming direction showed that a large population of swimming cells moved in a direction that was the result of the composition of phototaxis and electrotaxis. More surprisingly, we uncovered the coupling of signs of taxis, i.e., coupling of phototaxis and electrotaxis induced positive electrotaxis, which did not emerge in the single stimulation experiments. We qualitatively explained the coupling of taxis based on the polarization of the swimming cells induced by the simultaneous photo- and electric stimulation
Modelling of self-driven particles: foraging ants and pedestrians
Models for the behavior of ants and pedestrians are studied in an unified way
in this paper. Each ant follows pheromone put by preceding ants, hence creating
a trail on the ground, while pedestrians also try to follow others in a crowd
for efficient and safe walking. These following behaviors are incorporated in
our stochastic models by using only local update rules for computational
efficiency. It is demonstrated that the ant trail model shows an unusual
non-monotonic dependence of the average speed of the ants on their density,
which can be well analyzed by the zero-range process. We also show that this
anomalous behavior is clearly observed in an experiment of multiple robots.
Next, the relation between the ant trail model and the floor field model for
studying evacuation dynamics of pedestrians is discussed. The latter is
regarded as a two-dimensional generalization of the ant trail model, where the
pheromone is replaced by footprints.Comment: 15 pages, 11 Postscript figures, uses elsart.cl
Long Term X-Ray Spectral Variation of the Wolf-Rayet Binary WR 102-1 in the Galactic bulge: evidence for wind distortion in the binary
WR~102-1 was detected by Suzaku as a conspicuous point source in the 6.7 keV
intensity map of the central region of the Milky Way. The source was suggested
as a possible Wolf-Rayet binary based on its X-ray and infrared spectral
characteristics. The iron line emission is expected to originate in the
Wolf-Rayet star's dynamic stellar-wind when colliding the companion's mild
stellar wind. Here, we report the result of a long-term X-ray monitoring of
WR~102-1 since 1998 using archival data of ASCA, XMM-Newton, Chandra, Suzaku,
and Swift to reveal variations of the iron K-emission line and the
circumstellar absorption. Consequently, we have detected significant redshifts
of the iron K-emission line from the XMM-Newton observation in March 2003 and
the Suzaku observation in September 2006. Furthermore, when the red-shift was
observed, which suggests that the Wolf-Rayet star was in front of the companion
star, the circumstellar absorption values were smaller than other periods.
These results appear contrary to the expectation if the Wolf-Rayet's stellar
wind is spherically symmetric, but may be understood if the Wolf-Rayet star's
stellar wind is significantly distorted due to the rapid orbital motion near
the periastron.Comment: 6 pages, 4 figure
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Effect of pair interactions on transition probabilities between inactive and active states: achieving collective behaviour via pair interactions in social insects
To understand the evolution of well-organized social behaviour, we must first understand the mechanism by which collective behaviour establishes. In this study, the mechanisms of collective behaviour in a colony of social insects were studied in terms of the transition probability between active and inactive states, which is linked to mutual interactions. The active and inactive states of the social insects were statistically extracted from the velocity profiles. From the duration distributions of the two states, we found that 1) the durations of active and inactive states follow an exponential law, and 2) pair interactions increase the transition probability from inactive to active states. The regulation of the transition probability by paired interactions suggests that such interactions control the populations of active and inactive workers in the colony
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Adaptation-induced collective dynamics of a single-cell protozoan
We investigate the behavior of a single-cell protozoan in a narrow tubular ring. This environment forces them to swim under a one-dimensional periodic boundary condition. Above a critical density, single-cell protozoa aggregate spontaneously without external stimulation. The high-density zone of swimming cells exhibits a characteristic collective dynamics including translation and boundary fluctuation. We analyzed the velocity distribution and turn rate of swimming cells and found that the regulation of the turing rate leads to a stable aggregation and that acceleration of velocity triggers instability of aggregation. These two opposing effects may help to explain the spontaneous dynamics of collective behavior. We also propose a stochastic model for the mechanism underlying the collective behavior of swimming cells
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