302 research outputs found
Centaur 1939
Digitised by the Faculty of the Veterinary Scienc
An earthworm-like modular soft robot for locomotion in multi-terrain environments
Robotic locomotion in subterranean environments is still unsolved, and it requires innovative designs and strategies to overcome the challenges of burrowing and moving in unstructured conditions with high pressure and friction at depths of a few centimeters. Inspired by antagonistic muscle contractions and constant volume coelomic chambers observed in earthworms, we designed and developed a modular soft robot based on a peristaltic soft actuator (PSA). The PSA demonstrates two active configurations from a neutral state by switching the input source between positive and negative pressure. PSA generates a longitudinal force for axial penetration and a radial force for anchorage, through bidirectional deformation of the central bellows-like structure, which demonstrates its versatility and ease of control. The performance of PSA depends on the amount and type of fluid confined in an elastomer chamber, generating different forces and displacements. The assembled robot with five PSA modules enabled to perform peristaltic locomotion in different media. The role of friction was also investigated during experimental locomotion tests by attaching passive scales like earthworm setae to the ventral side of the robot. This study proposes a new method for developing a peristaltic earthworm-like soft robot and provides a better understanding of locomotion in different environments
Water maser variability over 20 years in a large sample of star-forming regions: the complete database
Context. Water vapor emission at 22 GHz from masers associated with
star-forming regions is highly variable. Aims. We present a database of up to
20 years of monitoring of a sample of 43 masers within star-forming regions.
The sample covers a large range of luminosities of the associated IRAS source
and is representative of the entire population of H2O masers of this type. The
database forms a good starting point for any further study of H2O maser
variability. Methods. The observations were obtained with the Medicina 32-m
radiotelescope, at a rate of 4-5 observations per year. Results. To provide a
database that can be easily accessed through the web, we give for each source:
plots of the calibrated spectra, the velocity-time-flux density plot, the light
curve of the integrated flux, the lower and upper envelopes of the maser
emission, the mean spectrum, and the rate of the maser occurrence as a function
of velocity. Figures for just one source are given in the text for
representative purposes. Figures for all the sources are given in electronic
form in the on-line appendix. A discussion of the main properties of the H2O
variability in our sample will be presented in a forthcoming paper.Comment: 11 pages, 9 figures, to be published in Astronomy and Astrophysics;
all plots in appendix (not included) can be downloaded from
http://www.arcetri.astro.it/~starform/water_maser_v2.html or
http://www.ira.inaf.it/papers/masers/water_maser_v2.htm
A project for polarimetric observations in single dish with Medicina and Noto 32 m antennas
A project with multidisciplinary characteristics, aimed to implement the possibility of polarimetric measurements in single dish at the VLBI stations of Medicina and Noto, is presented. The project will open a new window on many
astrophysical items that may be approached using the already existing instrumentation and facilities of the two Italian radioastronomical stations. We report here some scientific backgrounds, together with some technical evaluations, on which the feasibility of the project is based
Stranger to Familiar: Wild Strepsirhines Manage Xenophobia by Playing
The power of play in limiting xenophobia is a well-known phenomenon in humans. Yet, the evidence in social animals remains meager. Here, we aim to determine whether play promotes social tolerance toward strangers in one of the most basal group of primates, the strepsirhines. We observed two groups of wild lemurs (Propithecus verreauxi, Verreaux's sifaka) during the mating season. Data were also collected on nine visiting, outgroup males. We compared the distribution of play, grooming, and aggressive interactions across three conditions: OUT (resident/outgroup interactions), IN (resident/resident interactions in presence of outgroups) and BL-IN (baseline of resident/resident interactions in absence of outgroups). Play frequency between males was higher in OUT than in IN and BL-IN conditions; whereas, grooming was more frequent in IN than in OUT and BL-IN conditions. Aggression rates between resident and outgroup males were significantly higher than those between residents. However, aggressions between resident and outgroup males significantly decreased after the first play session and became comparable with resident-resident aggression levels. The presence of strangers in a well-established group implies the onset of novel social circumstances, which sifaka males cope with by two different tactics: grooming with ingroup males and playing with outgroup ones. The grooming peak, concurrently with the visit of outgroups, probably represents a social shield adopted by resident males to make their pre-existing affiliation more evident to the stranger “audience”. Being mostly restricted to unfamiliar males, adult play in sifaka appears to have a role in managing new social situations more than in maintaining old relationships. In particular, our results indicate not only that play is the interface between strangers but also that it has a specific function in reducing xenophobia. In conclusion, play appears to be an ice-breaker mechanism in the critical process that “upgrades” an individual from stranger to familiar
Monitoring water masers in star-forming regions
An overview is given of the analysis of more than a decade of H2O maser data
from our monitoring program. We find the maser emission to generally depend on
the luminosity of the YSO as well as on the geometry of the SFR. There appears
to be a threshold luminosity of a few times 10**4 Lsol above and below which we
find different maser characteristics.Comment: 9 pages, 1 table, 11 figures. Accepted for publ. in Ap&SpSci.
Refereed contribution to "Dense Molecular Gas around Protostars and in
Galactic Nuclei", European Workshop 2004 on Astronomical Molecules. Eds. Y.
Hagiwara, W.A. Baan, H.J. van Langeveld
VLA Observations of H2O Masers in the Class 0 Protostar S106 FIR: Evidence for a 10 AU-Scale Accelerating Jet-like Flow
We conducted VLA observations at 0".06 resolution of the 22 GHz water masers
toward the Class 0 source S106 FIR (d=600 pc; 15" west of S106-IRS4) on two
epochs separated by ~3 months. Two compact clusters of the maser spots were
found in the center of the submillimeter core of S106 FIR. The separation of
the clusters was ~80 mas (48 AU) along P. A. = 70 degrees and the size of each
cluster was ~20 mas x 10 mas. The western cluster, which had three maser
components, was 7.0 km/s redshifted with respect to the ambient cloud velocity.
Each component was composed of a few spatially localized maser spots and was
aligned on a line connecting the clusters. We found relative proper motions of
the components with ~30 mas/yr (18 AU/yr) along the line. In addition, a series
of single-dish observations show that the maser components drifted with a
radial acceleration of ~1 km/s/yr.
These facts indicate that the masers could be excited by a 10 AU-scale
jet-like accelerating flow ejected from an assumed protostar located between
the two clusters. The outflow size traced by the masers was 50 AU x 5 AU after
correction for an inclination angle of 10 degrees which was derived from the
relative proper motions and radial velocities of the maser components. The
three-dimensional outflow velocity ranged from 40 to 70 km/s assuming symmetric
motions for the blue and red components. Since no distinct CO molecular
outflows have been detected so far, we suggest that S106 FIR is an extremely
young protostar observed just after the onset of outflowing activity.Comment: 24 pages, 6 figures, No. 5 color. Accepted, Astrophysical Journa
New signposts of massive star formation in the S235A-B region
We report on new aspects of the star-forming region S235AB revealed through
high-resolution observations at radio and mid-infrared wavelengths. Using the
Very Large Array, we carried out sensitive observations of S235AB in the cm
continuum (6, 3.6, 1.3, and 0.7) and in the 22 GHz water maser line. These were
complemented with Spitzer Space Telescope Infrared Array Camera archive data to
clarify the correspondence between radio and IR sources. We made also use of
newly presented data from the Medicina water maser patrol, started in 1987, to
study the variability of the water masers found in the region. S235A is a
classical HII region whose structure is now well resolved. To the south, no
radio continuum emission is detected either from the compact molecular core or
from the jet-like structure observed at 3.3 mm, suggesting emission from dust
in both cases. We find two new compact radio continuum sources (VLA-1 and
VLA-2) and three separate maser spots. VLA-1 coincides with one of the maser
spots and with a previously identified IR source (M1). VLA-2 lies towards S235B
and represents the first radio detection from this peculiar nebula that may
represent an ionized wind from a more evolved star. The two other maser spots
coincide with an elongated structure previously observed within the molecular
core in the C34S line. This structure is perpendicular to a bipolar molecular
outflow observed in HCO+(1-0) and may trace the associated equatorial disk. The
Spitzer images reveal a red object towards the molecular core. This is the most
viable candidate for the embedded source originating the outflow and maser
phenomenology. The picture emerging from these and previous data shows the
extreme complexity of a small (< 0.5 pc) star-forming region where widely
different stages of stellar evolution are present.Comment: 15 pages, 16 figures, to be published in Astronomy & Astrophysic
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