2,559 research outputs found
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
The arginine deiminase pathway in the wine lactic acid bacteria Lactobacillus hilgardii X1B: structural and functional study of the arcABC genes
The genes implicated in the catabolism of the amino acid arginine by Lactobacillus hilgardiiX1Bwere investigated to assess the potential for
formation of ethyl carbamate precursors in wine. L. hilgardii X1B can use arginine via the arginine deiminase pathway. The complete
nucleotide sequence of the arc genes involved in this pathway has been determined. They are clustered in an operon-like structure in the order
arcABC. No evidence was found for the presence of a homologue of the arcD gene, coding for the arginine/ornithine antiporter. The arc genes
have been expressed in Escherichia coli resulting in arginine deiminase (ArcA), ornithine carbamoyltransferase (ArcB) and carbamate kinase
(ArcC) activities. The results indicate the need for caution in the selection of lactic acid bacteria for conducting malolactic fermentation in wine
since arginine degradation could result in high amounts of ethyl carbamate.This work was supported by grant VIN00-016 from the
Instituto Nacional de Investigación y Tecnología Agraria y
Alimentaria (INIA) and Consejo de Investigaciones de la
Universidad Nacional de Tucumán (CIUNT). M.E. Arena was
a recipient of a Contrato UNT-Proyecto FOMEC 1214 from
the Programa de Reforma de la Educación Superior. The
nucleotide sequence of the arcABC gene cluster has been
deposited in the EMBL/GenBank/DDBJ databases under
accession number AJ421514.Peer reviewe
Satellite design optimization for differential lift and drag applications
Utilizing differential atmospheric forces in the Very Low Earth Orbits (VLEO)
regime for the control of the relative motion within a satellite formation is a
promising option as any thrusting device has tremendous effects on the mission
capacity due to the limited weight and size restrictions of small satellites.
One possible approach to increase the available control forces is to reduce the
mass of the respective satellites as well as to increase the available surface
area. However, satellites of these characteristics suffer from rapid orbital
decay and consequently have a reduced service lifetime. Therefore, achieving
higher control forces is in contradiction to achieving a minimum orbital decay
of the satellites, which currently represents one of the biggest challenges in
the VLEO regime. In this work, the geometry of a given reference satellite, a
3UCubeSat, is optimized under the consideration of different surface material
properties for differential lift and drag control applications while
simultaneously ensuring a sustained VLEO operation. Notably, not only the
consideration of sustainability but also the optimization with regard to
differential lift is new in literature. It was shown that the advantageous
geometries strongly depend on the type of gas-surface interaction and thus, two
different final designs, one for each extreme type, are presented. In both
cases, improvements in all relevant parameters could be achieved solely via
geometry adaptions
Розробка алгоритму суспільних екологічних слухань при проектуванні підприємств з виробництва полімерів
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 α-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 γ-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
First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae star MWC 325
We present the first N-band nulling plus K- and L-band V2 observations of a
young stellar object, MWC325, taken with the 85 m baseline Keck Interferometer.
The Keck nuller was designed for the study of faint dust signatures associated
with debris disks, but it also has a unique capability for studying the
temperature and density distribution of denser disks found around young stellar
objects. Interferometric observations of MWC 325 at K, L and N encompass a
factor of five in spectral range and thus, especially when spectrally dispersed
within each band, enable characterization of the structure of the inner disk
regions where planets form. Fitting our observations with geometric models such
as a uniform disk or a Gaussian disk show that the apparent size increases
monotonically with wavelength in the 2-12 um wavelength region, confirming the
widely held assumption based on radiative transfer models, now with spatially
resolved measurements over broad wavelength range, that disks are extended with
a temperature gradient. The effective size is a factor of about 1.3 and 2
larger in the L-band and N-band, respectively, compared to that in the K-band.
The existing interferometric measurements and the spectral energy distribution
can be reproduced by a flat disk or a weakly-shadowed nearly flat-disk model,
with only slight flaring in the outer regions of the disk, consisting of
representative "sub-micron" (0.1 um) and "micron" (2 um) grains of a 50:50
ratio of silicate and graphite. This is marked contrast with the disks
previously found in other Herbig Ae/Be stars suggesting a wide variety in the
disk properties among Herbig Ae/Be stars.Comment: Accepted for publication in the Ap
Measuring and improving data quality of media collections for professional tasks
htmlabstractCarrying out research tasks on data collections is hampered, or even made impossible, by data quality issues of different types, such as incompleteness or inconsistency, and severity. We identify research tasks carried out by professional users of data collections that are hampered by inherent quality issues. We investigate what types of issues exist and how they influence these research tasks. To measure the quality perceived by professional users, we develop a quality metric. This allows us to measure the suitability of the data quality for a chosen user task. For a chosen task, we study how the data quality can be improved using crowdsourcing. We validate our quality metric by investigating whether professionals perform better on the chosen research task
Characterization of the anticipated synchronization regime in the coupled FitzHugh--Nagumo model for neurons
We characterize numerically the regime of anticipated synchronization in the
coupled FitzHugh-Nagumo model for neurons. We consider two neurons, coupled
unidirectionally (in a master-slave configuration), subject to the same random
external forcing and with a recurrent inhibitory delayed connection in the
slave neuron. We show that the scheme leads to anticipated synchronization, a
regime in which the slave neuron fires the same train of pulses as the master
neuron, but earlier in time. We characterize the synchronization in the
parameter space (coupling strength, anticipation time) and introduce several
quantities to measure the degree of synchronization.Comment: 8 pages. Proceedings of the conference on "Stochastic Systems: From
Randomness to"Complexit
Starspot Jitter in Photometry, Astrometry and Radial Velocity Measurements
Analytical relations are derived for the amplitude of astrometric,
photometric and radial velocity perturbations caused by a single rotating spot.
The relative power of the star spot jitter is estimated and compared with the
available data for Ceti and HD 166435, as well as with numerical
simulations for Ceti and the Sun. A Sun-like star inclined at
i=90\degr at 10 pc is predicted to have a RMS jitter of 0.087 \uas in its
astrometric position along the equator, and 0.38 m s in radial
velocities. If the presence of spots due to stellar activity is the ultimate
limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like
planets in habitable zones is about an order of magnitude higher that the
sensitivity of prospective ultra-precise radial velocity observations of nearby
stars.Comment: accepted in ApJ Letters, Nov. 200
Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models
We present K'-band observations of five Mira stars with the IOTA
interferometer. The interferograms were obtained with the FLUOR fiber optics
beam combiner, which provides high-accuracy visibility measurements in spite of
time-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU
Her, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters
11.7mas, 10.9mas, 8.4mas, 8.1mas, and 7.9mas (+/- 0.3mas), respectively.
Simultaneous photometric observations yielded the bolometric fluxes. The
derived angular Rosseland radii and the bolometric fluxes allowed the
determination of effective temperatures. For instance, the effective
temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland
radius for R Aql of (250 +100/-60) Rsun was derived from the angular Rosseland
radius of 5.5mas +/- 0.2mas and the HIPPARCOS parallax of 4.73mas +/- 1.19mas.
The observations were compared with theoretical Mira star models of Bessel et
al. (1996) and Hofmann et al. (1998). The effective temperatures of the M-type
Miras and the linear radius of R Aql indicate fundamental mode pulsation.Comment: 12 pages, 4 postscript figure
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