1,997 research outputs found
Renewal theory of coupled neuronal pools
A theory is provided to analyze the dynamics of delay-coupled pools of spiking neurons based on stability
analysis of stationary firing. Transitions between stable and unstable regimes can be predicted by bifurcation analysis of the underlying integral dynamics. Close to the bifurcation point the network exhibits slowly changingactivities and allows for slow collective phenomena like continuous attractors
Dynamically-Coupled Oscillators -- Cooperative Behavior via Dynamical Interaction --
We propose a theoretical framework to study the cooperative behavior of
dynamically coupled oscillators (DCOs) that possess dynamical interactions.
Then, to understand synchronization phenomena in networks of interneurons which
possess inhibitory interactions, we propose a DCO model with dynamics of
interactions that tend to cause 180-degree phase lags. Employing an approach
developed here, we demonstrate that although our model displays synchronization
at high frequencies, it does not exhibit synchronization at low frequencies
because this dynamical interaction does not cause a phase lag sufficiently
large to cancel the effect of the inhibition. We interpret the disappearance of
synchronization in our model with decreasing frequency as describing the
breakdown of synchronization in the interneuron network of the CA1 area below
the critical frequency of 20 Hz.Comment: 10 pages, 3 figure
GABA-enhanced collective behavior in neuronal axons underlies persistent gamma-frequency oscillations
Gamma (30β80 Hz) oscillations occur in mammalian electroencephalogram in a manner that indicates cognitive relevance. In vitro models of gamma oscillations demonstrate two forms of oscillation: one occurring transiently and driven by discrete afferent input and the second occurring persistently in response to activation of excitatory metabotropic receptors. The mechanism underlying persistent gamma oscillations has been suggested to involve gap-junctional communication between axons of principal neurons, but the precise relationship between this neuronal activity and the gamma oscillation has remained elusive. Here we demonstrate that gamma oscillations coexist with high-frequency oscillations (>90 Hz). High-frequency oscillations can be generated in the axonal plexus even when it is physically isolated from pyramidal cell bodies. They were enhanced in networks by nonsomatic -aminobutyric acid type A (GABAA) receptor activation, were modulated by perisomatic GABAA receptor-mediated synaptic input to principal cells, and provided the phasic input to interneurons required to generate persistent gamma-frequency oscillations. The data suggest that high-frequency oscillations occurred as a consequence of random activity within the axonal plexus. Interneurons provide a mechanism by which this random activity is both amplified and organized into a coherent network rhythm
Astrometric jitter of the sun as a star
The daily variation of the solar photocenter over some 11 years is derived
from the Mount Wilson data reprocessed by Ulrich et al. 2010 to closely match
the surface distribution of solar irradiance. The standard deviations of
astrometric jitter are 0.52 AU and 0.39 AU in the equatorial and the
axial dimensions, respectively. The overall dispersion is strongly correlated
with the solar cycle, reaching AU at the maximum activity in 2000.
The largest short-term deviations from the running average (up to 2.6 AU)
occur when a group of large spots happen to lie on one side with respect to the
center of the disk. The amplitude spectrum of the photocenter variations never
exceeds 0.033 AU for the range of periods 0.6--1.4 yr, corresponding to
the orbital periods of planets in the habitable zone. Astrometric detection of
Earth-like planets around stars as quiet as the Sun is not affected by star
spot noise, but the prospects for more active stars may be limited to giant
planets.Comment: Accepted in Ap
Π ΠΎΠ»Ρ Π΄ΠΈΠ·ΡΡΠ½ΠΊΡΠΈΠ²Π½ΡΡ Π½Π°ΡΡΡΠ΅Π½ΠΈΠΉ Π² ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠΈ, ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ ΠΈ ΡΠ°Π·ΡΡΡΠ΅Π½ΠΈΠΈ Π·Π°Π»Π΅ΠΆΠ΅ΠΉ Π³Π°Π·Π° Π½Π° ΠΠ°Π»ΠΎΡ Π΅ΡΡΠΊΠΎΠΌ Π²Π°Π»Ρ (ΡΠ΅Π²Π΅ΡΠΎ-Π²ΠΎΡΡΠΎΠΊ ΠΠ°ΠΏΠ°Π΄Π½ΠΎ-Π‘ΠΈΠ±ΠΈΡΡΠΊΠΎΠΉ Π½ΠΈΠ·ΠΌΠ΅Π½Π½ΠΎΡΡΠΈ)
High reliable diode laser pump modules are essential for free-space optical telecommunications. Besides the reliability, low mass and small dimensions, radiation-hardness and low power-consumption are requirements to be met for space applications. A diode laser module suited for pumping Nd:YAG lasers for optical intersatellite links has been developed. The module consists of two diode laser bars overlaid by a polarization beam splitter to increase the system's reliability. Each diode laser bar consists of six emitters. If the integrated photodiode detects the failure of one bar, the second, substitute bar is switched on and can fully sustain all module functions. To equalize the beam quality of the diode laser bar, a pair of micro step mirrors is used for each bar. The laser beam is focussed on the entrance of a d=200 Β΅m, NA=0.22 fiber. Both the coupling efficiency and the accuracy of the mounting of the diode laser components have been analyzed by raytracing. Passive cooling has been chosen because liquid chilling systems are unsuitable for space applications. To evaluate the effects of different heat sink materials and to predict the temperature drop over the module, a 3D finite element analysis for the steady-state temperature distribution of the module has been performed. The optical output power of the module described above amounts to 2,8 W with one bar operating derated to 0.5x maximum current, and the whole unit fits in a housing of 78 x 50 x 24 mm. Further developments will lead to a more compact design and a smaller fiber diameter
Imaging the asymmetric dust shell around CI Cam with long baseline optical interferometry
We present the first high angular resolution observation of the B[e]
star/X-ray transient object CI Cam, performed with the two-telescope Infrared
Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T)
and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases
were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was
observed in the near-infrared H and K spectral bands, wavelengths well suited
to measure the size and study the geometry of the hot dust surrounding CI Cam.
The analysis of the visibility data over an 8 year period from soon after the
1998 outburst to 2006 shows that the dust visibility has not changed over the
years. The visibility data shows that CI Cam is elongated which confirms the
disc-shape of the circumstellar environment and totally rules out the
hypothesis of a spherical dust shell. Closure phase measurements show direct
evidence of asymmetries in the circumstellar environment of CI Cam and we
conclude that the dust surrounding CI Cam lies in an inhomogeneous disc seen at
an angle. The near-infrared dust emission appears as an elliptical skewed
Gaussian ring with a major axis a = 7.58 +/- 0.24 mas, an axis ratio r = 0.39
+/- 0.03 and a position angle theta = 35 +/- 2 deg.Comment: 9 pages, 5 figures, accepted MNRA
Genetically altered AMPA-type glutamate receptor kinetics in interneurons disrupt long-range synchrony of gamma oscillation
Gamma oscillations synchronized between distant neuronal populations may be critical for binding together brain regions devoted to common processing tasks. Network modeling predicts that such synchrony depends in part on the fast time course of excitatory postsynaptic potentials (EPSPs) in interneurons, and that even moderate slowing of this time course will disrupt synchrony. We generated mice with slowed interneuron EPSPs by gene targeting, in which the gene encoding the 67-kDa form of glutamic acid decarboxylase (GAD67) was altered to drive expression of the Ξ±-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunit GluR-B. GluR-B is a determinant of the relatively slow EPSPs in excitatory neurons and is normally expressed at low levels in Ξ³-aminobutyric acid (GABA)ergic interneurons, but at high levels in the GAD-GluR-B mice. In both wild-type and GAD-GluR-B mice, tetanic stimuli evoked gamma oscillations that were indistinguishable in local field potential recordings. Remarkably, however, oscillation synchrony between spatially separated sites was severely disrupted in the mutant, in association with changes in interneuron firing patterns. The congruence between mouse and model suggests that the rapid time course of AMPA receptor-mediated EPSPs in interneurons might serve to allow gamma oscillations to synchronize over distance
ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π°ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ Ρ ΡΠΎΠΌΠΎ-ΠΎΠ»ΠΎΠ²ΡΠ½Π½ΡΡ ΠΊΠ°ΡΠ°Π»ΠΈΠ·Π°ΡΠΎΡΠΎΠ² Π΄Π»Ρ ΠΎΠΊΠΈΡΠ»Π΅Π½ΠΈΡ SO2 Π² SO3
Π¦Π΅Π»ΡΡ Π½Π°ΡΡΠΎΡΡΠ΅ΠΉ ΡΠ°Π±ΠΎΡΡ ΡΠ²Π»ΡΠ΅ΡΡΡ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π°ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΊΠ°ΡΠ°Π»ΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ Cr[2]O[3]+SnO[2] Π² ΡΠΈΡΠΎΠΊΠΈΡ
ΠΏΡΠ΅Π΄Π΅Π»Π°Ρ
ΡΠΎΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΠΉ ΠΌΠ΅ΠΆΠ΄Ρ Π΄Π²ΡΠΌΡ Π΅Π΅ ΠΈΡΡ
ΠΎΠ΄Π½ΡΠΌΠΈ ΠΊΠΎΠΌΠΏΠΎΠ½Π΅Π½ΡΠ°ΠΌΠΈ
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