1,399 research outputs found
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
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
Activation of TLR3 in keratinocytes increases expression of genes involved in formation of the epidermis, lipid accumulation, and epidermal organelles.
Injury to the skin, and the subsequent release of noncoding double-stranded RNA (dsRNA) from necrotic keratinocytes, has been identified as an endogenous activator of Toll-like receptor 3 (TLR3). As changes in keratinocyte growth and differentiation follow injury, we hypothesized that TLR3 might trigger some elements of the barrier repair program in keratinocytes. dsRNA was observed to induce TLR3-dependent increases in human keratinocyte mRNA abundance for ABCA12 (ATP-binding cassette, sub-family A, member 12), glucocerebrosidase, acid sphingomyelinase, and transglutaminase 1. Additionally, treatment with dsRNA resulted in increases in sphingomyelin and morphologic changes including increased epidermal lipid staining by Oil Red O and TLR3-dependent increases in lamellar bodies and keratohyalin granules. These observations show that dsRNA can stimulate some events in keratinocytes that are important for skin barrier repair and maintenance
Multimodal transition and excitability of a neural oscillator
We analyze the response of the Morris-Lecar model to a periodic train of
short current pulses in the period-amplitude plane. For a wide parameter range
encompassing both class 2 and class 3 behavior in Hodgkin's classification
there is a multimodal transition between the set of odd modes and the set of
all modes. It is located between the 2:1 and 3:1 locked-in regions. It is the
same dynamic instability as the one discovered earlier in the Hodgkin-Huxley
model and observed experimentally in squid giant axons. It appears
simultaneously with the bistability of the states 2:1 and 3:1 in the
perithreshold regime. These results imply that the multimodal transition may be
a universal property of resonant neurons
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