3,756 research outputs found
The dynamical mass of the young cluster W3 in NGC 7252: Heavy-Weight globular cluster or ultra compact dwarf galaxy ?
We have determined the dynamical mass of the most luminous stellar cluster
known to date, i.e. object W3 in the merger remnant galaxy NGC 7252. The
dynamical mass is estimated from the velocity dispersion measured with the
high-resolution spectrograph UVES on VLT. Our result is the astonishingly high
velocity dispersion of sigma=45 +- 5 km/s. Combined with the large cluster size
R_eff=17.5 +-1.8 pc, this translates into a dynamical virial mass for W3 of 8
+- 2 x 10^7 Msun. This mass is in excellent agreement with the value 7.2 x 10^7
Msun we previously estimated from the cluster luminosity M_V=-16.2 by means of
stellar M/L ratios predicted by Simple Stellar Population models (with a
Salpeter IMF) and confirms the heavy-weight nature of this object. This results
points out that the NGC 7252-type of mergers are able to form stellar systems
with masses up to ~ 10^8 Msun. We find that W3, when evolved to ~ 10 Gyr, lies
far from the typical Milky Way globular clusters, but appears to be also
separated from omegaCen in the Milky Way and G1 in M31, the most massive old
stellar clusters of the Local Group, because it is too extended for a given
mass, and from dwarf elliptical galaxies because it is much more compact for
its mass. Instead the aged W3 is amazingly close to the compact objects named
ultracompact dwarf galaxies (UCDGs) found in the Fornax cluster (Hilker et al.
1999; Drinkwater et al. 2000), and to a miniature version of the compact
elliptical M32. These objects start populating a previously deserted region of
the fundamental plane.Comment: 8 pages, 3 figures, A&A in pres
Symptomatic epiphyseal sprains and stress fractures of the finger phalanges in adolescent sport climbers
The purpose of this study was to document and evaluate patient characteristics, injury mechanisms and clinical outcomes of epiphyseal stress fractures of the finger phalanges in adolescent rock climbers to identify contributing factors to this injury. Twenty-eight climbers with epiphyseal pain treated at our clinic between 2006 and 2018 were included in the study. Sixteen patients completed a questionnaire addressing injury details as well as training regimen before and after the injury. The mean age at the time of injury was 13.7 years (屉1.9 years) with the injury occurring predominantly in male athletes. Middle (58%) and ring (30%) fingers were the most commonly affected sites out of a total of 67 fingers affected; 54% had a radiologically documented epiphyseal fracture (Salter Harris type II/III) while 46% suffered from a symptomatic sprain, which could potentially lead to a stress fracture. Mean time for radiological union of a fracture was 35 weeks. Recovery time for a symptomatic sprain was on average slightly shorter at 24 weeks. All patients were treated conservatively with load reduction for 3-12 months until the symptoms disappeared. Although most patients had a positive outcome when treated correctly, this injury can damage the growth plate when left untreated, resulting in articular surface incongruency (1 severe, 1 moderate, 6 mild) with permanent impairment of the affected finger. Therefore, pain on the dorsal aspect of the proximal interphalangeal joint in adolescent climbers must be assessed carefully
Artificial Brains and Hybrid Minds
The paper develops two related thought experiments exploring variations on an âanimatâ theme. Animats are hybrid devices with both artificial and biological components. Traditionally, âcomponentsâ have been construed in concrete terms, as physical parts or constituent material structures. Many fascinating issues arise within this context of hybrid physical organization. However, within the context of functional/computational theories of mentality, demarcations based purely on material structure are unduly narrow. It is abstract functional structure which does the key work in characterizing the respective âcomponentsâ of thinking systems, while the âstuffâ of material implementation is of secondary importance. Thus the paper extends the received animat paradigm, and investigates some intriguing consequences of expanding the conception of bio-machine hybrids to include abstract functional and semantic structure. In particular, the thought experiments consider cases of mind-machine merger where there is no physical Brain-Machine Interface: indeed, the material human body and brain have been removed from the picture altogether. The first experiment illustrates some intrinsic theoretical difficulties in attempting to replicate the human mind in an alternative material medium, while the second reveals some deep conceptual problems in attempting to create a form of truly Artificial General Intelligence
Structure and thermodynamics of colloid-polymer mixtures: a macromolecular approach
The change of the structure of concentrated colloidal suspensions upon
addition of non-adsorbing polymer is studied within a two-component,
Ornstein-Zernicke based liquid state approach. The polymers' conformational
degrees of freedom are considered and excluded volume is enforced at the
segment level. The polymer correlation hole, depletion layer, and excess
chemical potentials are described in agreement with polymer physics theory in
contrast to models treating the macromolecules as effective spheres. Known
depletion attraction effects are recovered for low particle density, while at
higher densities novel many-body effects emerge which become dominant for large
polymers.Comment: 7 pages, 4 figures; to be published in Europhys. Let
Study of the performance and capability of the new ultra-fast 2 GSample/s FADC data acquisition system of the MAGIC telescope
In February 2007 the MAGIC Air Cherenkov Telescope for gamma-ray astronomy
was fully upgraded with an ultra fast 2 GSamples/s digitization system. Since
the Cherenkov light flashes are very short, a fast readout can minimize the
influence of the background from the light of the night sky. Also, the time
structure of the event is an additional parameter to reduce the background from
unwanted hadronic showers. An overview of the performance of the new system and
its impact on the sensitivity of the MAGIC instrument will be presented.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
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