327 research outputs found
The Semantics of Natural Objects and Tools in the Brain: A Combined Behavioral and MEG Study
Current literature supports the notion that the recognition of objects, when visually pre-sented, is sub-served by neural structures different from those responsible for the semantic processing of their nouns. However, embodiment foresees that processing observed objects and their verbal labels should share similar neural mechanisms. In a combined behavioral and MEG study, we com-pared the modulation of motor responses and cortical rhythms during the processing of graspable natural objects and tools, either verbally or pictorially presented. Our findings demonstrate that conveying meaning to an observed object or processing its noun similarly modulates both motor responses and cortical rhythms; being natural graspable objects and tools differently represented in the brain, they affect in a different manner both behavioral and MEG findings, independent of presentation modality. These results provide experimental evidence that neural substrates responsible for conveying meaning to objects overlap with those where the object is represented, thus supporting an embodied view of semantic processing
Activity-rotation in the dM4 star Gl 729. A possible chromospheric cycle
Recently, new debates about the role of layers of strong shear have emerged
in stellar dynamo theory. Further information on the long-term magnetic
activity of fully convective stars could help determine whether their
underlying dynamo could sustain activity cycles similar to the solar one.
We performed a thorough study of the short- and long-term magnetic activity
of the young active dM4 star Gl 729. First, we analyzed long-cadence
photometry to characterize its transient events (e.g., flares) and global and
surface differential rotation. Then, from the Mount Wilson -indexes derived
from CASLEO spectra and other public observations, we analyzed its long-term
activity between 1998 and 2020 with four different time-domain techniques to
detect cyclic patterns. Finally, we explored the chromospheric activity at
different heights with simultaneous measurements of the H and the Na I
D indexes, and we analyzed their relations with the -Index.
We found that the cumulative flare frequency follows a power-law distribution
with slope for the range to erg. We obtained
days, and we found no evidence of differential
rotation. We also found that this young active star presents a long-term
activity cycle with a length of years; there is less
significant evidence of a shorter cycle of year. The star also shows a
broad activity minimum between 1998 and 2004. We found a correlation between
the S index, on the one hand, and the H the Na I D indexes, on the
other hand, although the saturation level of these last two indexes is not
observed in the Ca lines.
Because the maximum-entropy spot model does not reflect migration between
active longitudes, this activity cycle cannot be explained by a solar-type
dynamo. It is probably caused by an -dynamo
Gravity Field of Ganymede After the Juno Extended Mission
The Juno Extended Mission presented the first opportunity to acquire gravity measurements of Ganymede since the end of the Galileo mission. These new Juno data offered the chance to carry out a joint analysis with the Galileo data set, improving our knowledge of Ganymede's gravity field and shedding new light upon its interior structure. Through reconstruction of Juno's and Galileo's orbit during the Ganymede flybys, the gravity field of the moon was estimated. The results indicate that Ganymede's degree-2 field is compatible with a body in hydrostatic equilibrium within 1−σ and hint at regional gravity anomalies with amplitudes exceeding those inferred by Cassini for Titan. Our explicit treatment of non-hydrostatic effects leads to wider confidence intervals for the derived moment of inertia with respect previous analyses. The higher central value of the derived moment of inertia indicates a lesser degree of Ganymede's differentiation
Gravity field of ganymede after the Juno extended mission
The Juno Extended Mission presented the first opportunity to acquire gravity measurements of Ganymede since the end of the Galileo mission. These new Juno data offered the chance to carry out a joint analysis with the Galileo data set, improving our knowledge of Ganymede's gravity field and shedding new light upon its interior structure. Through reconstruction of Juno's and Galileo's orbit during the Ganymede flybys, the gravity field of the moon was estimated. The results indicate that Ganymede's degree-2 field is compatible with a body in hydrostatic equilibrium within 1-sigma and hint at regional gravity anomalies with amplitudes exceeding those inferred by Cassini for Titan. Our explicit treatment of non-hydrostatic effects leads to wider confidence intervals for the derived moment of inertia with respect previous analyses. The higher central value of the derived moment of inertia indicates a lesser degree of Ganymede's differentiation
Juno spacecraft gravity measurements provide evidence for normal modes of Jupiter
The Juno spacecraft has been collecting data to shed light on the planet’s origin and characterize its interior structure. The onboard gravity science experiment based on X-band and Ka-band dual-frequency Doppler tracking precisely measured Jupiter’s zonal gravitational field. Here, we analyze 22 Juno’s gravity passes to investigate the gravity field. Our analysis provides evidence of new gravity field features, which perturb its otherwise axially symmetric structure with a time-variable component. We show that normal modes of the planet could explain the anomalous signatures present in the Doppler data better than other alternative explanations, such as localized density anomalies and non-axisymmetric components of the static gravity field. We explain Juno data by p-modes having an amplitude spectrum with a peak radial velocity of 10–50 cm/s at 900–1200 μHz (compatible with ground-based observations) and provide upper bounds on lower frequency f-modes (radial velocity smaller than 1 cm/s). The new Juno results could open the possibility of exploring the interior structure of the gas giants through measurements of the time-variable gravity or with onboard instrumentation devoted to the observation of normal modes, which could drive spacecraft operations of future missions
The spectroscopic binary system Gl 375. I. Orbital parameters and chromospheric activity
We study the spectroscopic binary system Gl 375. We employ medium resolution
echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory
CASLEO and photometric observations obtained from the ASAS database. We
separate the composite spectra into those corresponding to both components. The
separated spectra allow us to confirm that the spectral types of both
components are similar (dMe3.5) and to obtain precise measurements of the
orbital period (P = 1.87844 days), minimum masses (M_1 sin^3 i = 0.35 M_sun and
M_2 sin^3 i =0.33 M_sun) and other orbital parameters. The photometric
observations exhibit a sinusoidal variation with the same period as the orbital
period. We interpret this as signs of active regions carried along with
rotation in a tidally synchronized system, and study the evolution of the
amplitude of the modulation in longer timescales. Together with the mean
magnitude, the modulation exhibits a roughly cyclic variation with a period of
around 800 days. This periodicity is also found in the flux of the Ca II K
lines of both components, which seem to be in phase. The periodic changes in
the three observables are interpreted as a sign of a stellar activity cycle.
Both components appear to be in phase, which implies that they are magnetically
connected. The measured cycle of approximately 2.2 years (800 days) is
consistent with previous determinations of activity cycles in similar stars.Comment: 10 pages, including 11 figures and 3 tables. Accepted for publication
in Astronomy & Astrophysic
Radio Occultation Measurements of Europa's Ionosphere From Juno's Close Flyby
On 29 September 2022 the Juno spacecraft flew within 354 km of Europa's surface while several instruments probed the moon's surroundings. During the close flyby, radio occultations were performed by collecting single-frequency Doppler measurements. These investigations are essential to the study of Europa's ionosphere and represent the first repeat sampling of any set of conditions since the Galileo era. Ingress measurements resulted in a marginal detection with a peak ionospheric density of 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude. A more significant detection emerged on egress, with a peak density of 6,000 ± 3,000 cm−3 (3σ) at 320 km altitude. Comparison with Galileo measurements reveals a consistent picture of Europa's ionosphere, and confirms its dependence on illumination conditions and position within Jupiter's magnetosphere. However, the overall lower densities measured by Juno suggest a dependence on time of observation, with implications for the structure of the neutral atmosphere
Habitable Zones of Host Stars During the Post-MS Phase
A star will become brighter and brighter with stellar evolution, and the
distance of its habitable zone will become farther and farther. Some planets
outside the habitable zone of a host star during the main sequence phase may
enter the habitable zone of the host star during other evolutionary phases. A
terrestrial planet within the habitable zone of its host star is generally
thought to be suited to life existence. Furthermore, a rocky moon around a
giant planet may be also suited to life survive, provided that the planet-moon
system is within the habitable zone of its host star. Using Eggleton's code and
the boundary flux of habitable zone, we calculate the habitable zone of our
Solar after the main sequence phase. It is found that Mars' orbit and Jupiter's
orbit will enter the habitable zone of Solar during the subgiant branch phase
and the red giant branch phase, respectively. And the orbit of Saturn will
enter the habitable zone of Solar during the He-burning phase for about 137
million years. Life is unlikely at any time on Saturn, as it is a giant gaseous
planet. However, Titan, the rocky moon of Saturn, may be suitable for
biological evolution and become another Earth during that time. For low-mass
stars, there are similar habitable zones during the He-burning phase as our
Solar, because there are similar core masses and luminosities for these stars
during that phase.Comment: 6 pages, 7 figures. Accepted by Ap & S
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