6,742 research outputs found
Cellular Automata Model of Macroevolution
In this paper I describe a cellular automaton model of a multi-species
ecosystem, suitable for the study of emergent properties of macroevolution.
Unlike majority of ecological models, the number of coexisting species is not
fixed. Starting from one common ancestor they appear by "mutations" of existent
species, and then survive or extinct depending on the balance of local
ecological interactions. Monte-Carlo numerical simulations show that this model
is able to qualitatively reproduce phenomena that have been observed in other
models and in nature.Comment: 8 pages, 3 figures, Fourteenth National Conference on Application of
Mathematics in Biology and Medicine, Leszno 2008 (POLAND
Multichannel Kondo impurities in superconductors
We discuss the effect of multichannel Kondo impurities on superconductivity.
In the strong coupling regime such impurities are pairbreakers, in contrast to
the ordinary Kondo effect. Measurements of -suppression may help in
identifying impurities displaying this more exotic exchange coupling to the
conduction band.Comment: 3 pages, 4 figures, uuencoded compressed postscript file, submitted
to SCES'94 (Amsterdam
On Magnetic Impurities in Gapless Fermi Systems
In ordinary metals, antiferromagnetic exchange between conduction electrons
and a magnetic impurity leads to screening of the impurity spin below the Kondo
temperature, . In systems such as semimetals, small-gap semiconductors and
unconventional superconductors, a reduction in available conduction states near
the chemical potential can greatly depress . The behavior of an Anderson
impurity in a model with a power-law density of states, , , for , where , is
studied using the non-crossing approximation. The transition from the Kondo
singlet to the magnetic ground state can be seen in the behavior of the
impurity magnetic susceptibility . The product saturates at a
finite value at low temperature for coupling smaller than the critical one. For
sufficiently large coupling , as , indicating complete
screening of the impurity spin.Comment: 4 pages + 2 postscript figures, uses RevTeX, psfig.sty, submitted to
the European Conference "Physics of Magnetism", Poznan, June 199
Multimodal transition and stochastic antiresonance in squid giant axons
The experimental data of N. Takahashi, Y. Hanyu, T. Musha, R. Kubo, and G.
Matsumoto, Physica D \textbf{43}, 318 (1990), on the response of squid giant
axons stimulated by periodic sequence of short current pulses is interpreted
within the Hodgkin-Huxley model. The minimum of the firing rate as a function
of the stimulus amplitude in the high-frequency regime is due to the
multimodal transition. Below this singular point only odd multiples of the
driving period remain and the system is highly sensitive to noise. The
coefficient of variation has a maximum and the firing rate has a minimum as a
function of the noise intensity which is an indication of the stochastic
coherence antiresonance. The model calculations reproduce the frequency of
occurrence of the most common modes in the vicinity of the transition. A linear
relation of output frequency vs. for above the transition is also
confirmed.Comment: 5 pages, 9 figure
Interpolated-DFT-Based Fast and Accurate Amplitude and Phase Estimation for the Control of Power
The quality of energy produced in renewable energy systems has to be at the
high level specified by respective standards and directives. The estimation
accuracy of grid signal parameters is one of the most important factors
affecting this quality. This paper presents a method for a very fast and
accurate amplitude and phase grid signal estimation using the Fast Fourier
Transform procedure and maximum decay sidelobes windows. The most important
features of the method are the elimination of the impact associated with the
conjugate's component on the results and the straightforward implementation.
Moreover, the measurement time is very short - even far less than one period of
the grid signal. The influence of harmonics on the results is reduced by using
a bandpass prefilter. Even using a 40 dB FIR prefilter for the grid signal with
THD = 38%, SNR = 53 dB and a 20-30% slow decay exponential drift the maximum
error of the amplitude estimation is approximately 1% and approximately 0.085
rad of the phase estimation in a real-time DSP system for 512 samples. The
errors are smaller by several orders of magnitude for more accurate prefilters.Comment: in Metrology and Measurement Systems, 201
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