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21.
The effects of noise on neuronal dynamical systems are of much current interest. Here, we investigate noise-induced changes
in the rhythmic firing activity of single Hodgkin–Huxley neurons. With additive input current, there is, in the absence of
noise, a critical mean value μ = μ
c above which sustained periodic firing occurs. With initial conditions as resting values, for a range of values of the mean
μ near the critical value, we have found that the firing rate is greatly reduced by noise, even of quite small amplitudes.
Furthermore, the firing rate may undergo a pronounced minimum as the noise increases. This behavior has the opposite character
to stochastic resonance and coherence resonance. We found that these phenomena occurred even when the initial conditions were
chosen randomly or when the noise was switched on at a random time, indicating the robustness of the results. We also examined
the effects of conductance-based noise on Hodgkin–Huxley neurons and obtained similar results, leading to the conclusion that
the phenomena occur across a wide range of neuronal dynamical systems. Further, these phenomena will occur in diverse applications
where a stable limit cycle coexists with a stable focus. 相似文献
22.
F. L. Boschke E. Lamla W. Jost H. Elsässer H. Haffner W. Funke R. Tschesche S. Hünig Th. Wieland O. Prokop P. Läuger G. Pfleiderer E. Macher G. Drews G. Siebert H. W. Raudonat H. Autrum H. Sioli B. Frenzel K. Esser D. H. Welte H. -U. Schmincke K. Strobach M. Schidlowski 《Die Naturwissenschaften》1970,57(8):400-404
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Hiroaki Naoe Shuichi Hasegawa Jost Heintzenberg Kikuo Okada Akihiro Uchiyama Yuji Zaizen Eriko Kobayashi Akihiro Yamazaki 《Atmospheric environment (Oxford, England : 1994)》2009,43(6):1296-1301
The state of mixture of light-absorbing carbonaceous particles was investigated in relation to light absorption properties using electron microscopic examinations, black carbon (BC) analyses of quartz filter by thermal/optical reflectance (TOR) method, measurements with two continuous light-absorbing photometers at a suburban site of Tsukuba, about 60 km northeast of Tokyo. The volume fraction of water-soluble material (?) in individual particles is important for assessing particulate light-absorbing and/or scattering of atmospheric aerosols. The values of ? in BC particles were evaluated by electron micrographs before and after dialysis (extraction) of water-soluble material. The mass absorption coefficient (MAC in units of m2 g?1) tended to increase with increasing the average ? in BC particles with the radius range of 0.05–0.5 μm. Thus, our results indicate that coatings of water-soluble material around BC particles can enhance the absorption of solar radiation. Moreover, the single scattering albedo (SSA) will increase because a large amount of coating material will scatter more light. 相似文献
25.
Silvan U. Goldenberg Jost Borcherding Martina Heynen 《Behavioral ecology and sociobiology》2014,68(6):989-998
Group size, predation risk and habituation are key drivers of behaviour and evolution in gregarious prey animals. However, the extent to which they interact in shaping behaviour is only partially understood. We analyzed their combined effects on boldness and vigilance behaviour in juvenile perch (Perca fluviatilis) by observing individuals in groups of one, two, three and five faced with four different levels of predation risk in a repeated measures design. The perch showed an asymptotic increase in boldness with increasing group size and the highest per capita vigilance in groups of two. With increasing predation risk, individuals reduced boldness and intensified vigilance. The interaction between group size and predation risk influenced vigilance but not boldness. In this context, individuals in groups of two elevated their vigilance compared to individuals in larger groups only when at higher risk of predation. Further, as only group size, they significantly reduced vigilance at the highest level of risk. With increasing habituation, solitary individuals became considerably bolder. Also, predation risk affected boldness only in the more habituated situation. Hence, repeated measures may be essential to correctly interpret certain relationships in behaviour. Our results suggest that perch may adjust boldness behaviour to group size and predation risk independently. This is rather unexpected since in theory, natural selection would strongly favour an interactive adjustment. Finally, vigilance might be particularly effective in groups of two due to the intense monitoring and detailed response to changing levels of risk. 相似文献
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Challet M Fourcassié V Blanco S Fournier R Theraulaz G Jost C 《Die Naturwissenschaften》2005,92(8):367-370
Environmental heterogeneities can change animal movement in two different manners. First, they can modify movement characteristics
(move lengths or turning angles), in which case the movement remains of the diffusive kind. Second, they can bias displacement
towards a particular direction in which case it becomes non-diffusive. We propose in this paper a simple method that only
requires computing the mean length of a sample of trajectories in some bounded area to distinguish between these two kinds
of movement. We show through simulations that the method allows to detect the presence of heterogeneities that orient animal
movement. We apply it to experimental trajectories of Messor sancta ants engaged in corpse aggregation to show that their displacement is oriented at the contact of the formed corpse piles
and that their trajectories become non-diffusive. 相似文献
30.
The Science of Nature - 相似文献