772 research outputs found
Modulations of Cortical Power and Connectivity in Alpha and Beta Bands during the Preparation of Reaching Movements
Planning goal-directed movements towards different targets is at the basis of common daily activities (e.g., reaching), involving visual, visuomotor, and sensorimotor brain areas. Alpha (8-13 Hz) and beta (13-30 Hz) oscillations are modulated during movement preparation and are implicated in correct motor functioning. However, how brain regions activate and interact during reaching tasks and how brain rhythms are functionally involved in these interactions is still limitedly explored. Here, alpha and beta brain activity and connectivity during reaching preparation are investigated at EEG-source level, considering a network of task-related cortical areas. Sixty-channel EEG was recorded from 20 healthy participants during a delayed center-out reaching task and projected to the cortex to extract the activity of 8 cortical regions per hemisphere (2 occipital, 2 parietal, 3 peri-central, 1 frontal). Then, we analyzed event-related spectral perturbations and directed connectivity, computed via spectral Granger causality and summarized using graph theory centrality indices (in degree, out degree). Results suggest that alpha and beta oscillations are functionally involved in the preparation of reaching in different ways, with the former mediating the inhibition of the ipsilateral sensorimotor areas and disinhibition of visual areas, and the latter coordinating disinhibition of the contralateral sensorimotor and visuomotor areas
Tanaka Theorem for Inelastic Maxwell Models
We show that the Euclidean Wasserstein distance is contractive for inelastic
homogeneous Boltzmann kinetic equations in the Maxwellian approximation and its
associated Kac-like caricature. This property is as a generalization of the
Tanaka theorem to inelastic interactions. Consequences are drawn on the
asymptotic behavior of solutions in terms only of the Euclidean Wasserstein
distance
99mTc-HMPAO-leukocyte scintigraphy in patients with symptomatic total hip or knee arthroplasty: improved diagnostic accuracy by means of semiquantitative evaluation
Characterization of elderly, stroke and chorea populations using gait variability and stability indexes
The Scintillating Tail of Comet C/2020 F3 (Neowise)
Context. The occultation of a radio source by the plasma tail of a comet can
be used to probe structure and dynamics in the tail. Such occultations are
rare, and the occurrence of scintillation, due to small-scale density
variations in the tail, remains somewhat controversial. Aims. A detailed
observation taken with the Low-Frequency Array (LOFAR) of a serendipitous
occultation of the compact radio source 3C196 by the plasma tail of comet
C/2020 F3 (Neowise) is presented. 3C196 tracked almost perpendicularly behind
the tail, providing a unique profile cut only a short distance downstream from
the cometary nucleus itself. Methods. Interplanetary scintillation (IPS) is
observed as the rapid variation of the intensity received of a compact radio
source due to density variations in the solar wind. IPS in the signal received
from 3C196 was observed for five hours, covering the full transit behind the
plasma tail of comet C/2020 F3 (Neowise) on 16 July 2020, and allowing an
assessment of the solar wind in which the comet and its tail are embedded.
Results. The results reveal a sudden and strong enhancement in scintillation
which is unequivocally attributable to the plasma tail. The strongest
scintillation is associated with the tail boundaries, weaker scintillation is
seen within the tail, and previously-unreported periodic variations in
scintillation are noted, possibly associated with individual filaments of
plasma. Furthermore, contributions from the solar wind and comet tail are
separated to measure a sharp decrease in the velocity of material within the
tail, suggesting a steep velocity shear resulting in strong turbulence along
the tail boundaryComment: Accepted for publication in Astronomy and Astrophysics, 8 pages, 9
figure
LOFAR observations of the quiet solar corona
The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio
emission can only propagate above that radius, , where the local
plasma frequency eqals the observing frequency. The radio interferometer LOw
Frequency ARray (LOFAR) observes in its low band (10 -- 90 MHz) solar radio
emission originating from the middle and upper corona. We present the first
solar aperture synthesis imaging observations in the low band of LOFAR in 12
frequencies each separated by 5 MHz. From each of these radio maps we infer
, and a scale height temperature, . These results can be combined
into coronal density and temperature profiles. We derived radial intensity
profiles from the radio images. We focus on polar directions with simpler,
radial magnetic field structure. Intensity profiles were modeled by ray-tracing
simulations, following wave paths through the refractive solar corona, and
including free-free emission and absorption. We fitted model profiles to
observations with and as fitting parameters. In the low corona,
solar radii, we find high scale height temperatures up to
2.2e6 K, much more than the brightness temperatures usually found there. But if
all values are combined into a density profile, this profile can be
fitted by a hydrostatic model with the same temperature, thereby confirming
this with two independent methods. The density profile deviates from the
hydrostatic model above 1.5 solar radii, indicating the transition into the
solar wind. These results demonstrate what information can be gleaned from
solar low-frequency radio images. The scale height temperatures we find are not
only higher than brightness temperatures, but also than temperatures derived
from coronograph or EUV data. Future observations will provide continuous
frequency coverage, eliminating the need for local hydrostatic density models
Kinetic models with randomly perturbed binary collisions
We introduce a class of Kac-like kinetic equations on the real line, with
general random collisional rules, which include as particular cases models for
wealth redistribution in an agent-based market or models for granular gases
with a background heat bath. Conditions on these collisional rules which
guarantee both the existence and uniqueness of equilibrium profiles and their
main properties are found. We show that the characterization of these
stationary solutions is of independent interest, since the same profiles are
shown to be solutions of different evolution problems, both in the econophysics
context and in the kinetic theory of rarefied gases
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