20,746 research outputs found
Synchronizations in small-world networks of spiking neurons: Diffusive versus sigmoid couplings
By using a semi-analytical dynamical mean-field approximation previously
proposed by the author [H. Hasegawa, Phys. Rev. E, {\bf 70}, 066107 (2004)], we
have studied the synchronization of stochastic, small-world (SW) networks of
FitzHugh-Nagumo neurons with diffusive couplings. The difference and similarity
between results for {\it diffusive} and {\it sigmoid} couplings have been
discussed. It has been shown that with introducing the weak heterogeneity to
regular networks, the synchronization may be slightly increased for diffusive
couplings, while it is decreased for sigmoid couplings. This increase in the
synchronization for diffusive couplings is shown to be due to their local,
negative feedback contributions, but not due to the shorten average distance in
SW networks. Synchronization of SW networks depends not only on their structure
but also on the type of couplings.Comment: 17 pages, 8 figures, accepted in Phys. Rev. E with some change
Classical small systems coupled to finite baths
We have studied the properties of a classical -body system coupled to a
bath containing -body harmonic oscillators, employing an model
which is different from most of the existing models with . We have
performed simulations for -oscillator systems, solving
first-order differential equations with and , in order to calculate the time-dependent energy exchange between the
system and the bath. The calculated energy in the system rapidly changes while
its envelope has a much slower time dependence. Detailed calculations of the
stationary energy distribution of the system (: an energy per
particle in the system) have shown that its properties are mainly determined by
but weakly depend on . The calculated is analyzed with the
use of the and - distributions: the latter is derived with
the superstatistical approach (SSA) and microcanonical approach (MCA) to the
nonextensive statistics, where stands for the entropic index. Based on
analyses of our simulation results, a critical comparison is made between the
SSA and MCA. Simulations have been performed also for the -body ideal-gas
system. The effect of the coupling between oscillators in the bath has been
examined by additional () models which include baths consisting of
coupled linear chains with periodic and fixed-end boundary conditions.Comment: 30 pages, 16 figures; the final version accepted in Phys. Rev.
NMR Knight shifts and linewidths in the Ni‐Pd‐P and Ni‐Pt‐P metallic glasses: Composition and temperature dependences
NMR Knight shift and linewidth measurements are reported for the ^(31)P nuclei in the metallic glasses (Ni_(0.50)Pd_(0.50))100−_xP_x (where x=16 to 26.5) and (Ni_yPd_(1−y))_(80)P_(20) (where y=0.20 to 0.80), and both the ^(31)P and 195Pt nuclei in the metallic glass (Ni_yPt_(1−y))_(75)P_(25) (where y=0.20 to 0.68). The results are discussed in terms of the amorphous structure, electronic structure, and stability of transition metal + metalloid metallic glasses
Fast accretion of small planetesimals by protoplanetary cores
We explore the dynamics of small planetesimals coexisting with massive
protoplanetary cores in a gaseous nebula. Gas drag strongly affects the motion
of small bodies leading to the decay of their eccentricities and inclinations,
which are excited by the gravity of protoplanetary cores. Drag acting on larger
( km), high velocity planetesimals causes a mere reduction of their
average random velocity. By contrast, drag qualitatively changes the dynamics
of smaller ( km), low velocity objects: (1) small planetesimals
sediment towards the midplane of the nebula forming vertically thin subdisk;
(2) their random velocities rapidly decay between successive passages of the
cores and, as a result, encounters with cores typically occur at the minimum
relative velocity allowed by the shear in the disk. This leads to a drastic
increase in the accretion rate of small planetesimals by the protoplanetary
cores, allowing cores to grow faster than expected in the simple oligarchic
picture, provided that the population of small planetesimals contains more than
roughly 1% of the solid mass in the nebula. Fragmentation of larger
planetesimals ( km) in energetic collisions triggered by the
gravitational scattering by cores can easily channel this amount of material
into small bodies on reasonable timescales ( Myr in the outer Solar
System), providing a means for the rapid growth (within several Myr at 30 AU)
of rather massive protoplanetary cores. Effects of inelastic collisions between
planetesimals and presence of multiple protoplanetary cores are discussed.Comment: 17 pages, 8 figures, additional clarifications, 1 more figure and
table adde
Quasi Markovian behavior in mixing maps
We consider the time dependent probability distribution of a coarse grained
observable Y whose evolution is governed by a discrete time map. If the map is
mixing, the time dependent one-step transition probabilities converge in the
long time limit to yield an ergodic stochastic matrix. The stationary
distribution of this matrix is identical to the asymptotic distribution of Y
under the exact dynamics. The nth time iterate of the baker map is explicitly
computed and used to compare the time evolution of the occupation probabilities
with those of the approximating Markov chain. The convergence is found to be at
least exponentially fast for all rectangular partitions with Lebesgue measure.
In particular, uniform rectangles form a Markov partition for which we find
exact agreement.Comment: 16 pages, 1 figure, uses elsart.sty, to be published in Physica D
Special Issue on Predictability: Quantifying Uncertainty in Models of Complex
Phenomen
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