663 research outputs found
The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)
An X-ray structure determination of the title compound shows that the co-ordination about the cobalt atom is approximately trigonal bipyramidal; n.m.r. data indicate that the complex is non-rigid in solution
Role of Layering Oscillations at Liquid Metal Surfaces in Bulk Recrystallization and Surface Melting
The contrasting melting behavior of different surface orientations in metals
can be explained in terms of a repulsive or attractive effective interaction
between the solid-liquid and the liquid-vapor interface. We show how a crucial
part of this interaction originates from the layering effects near the liquid
metal surface. Its sign depends on the relative tuning of layering oscillations
to the crystal interplanar spacing, thus explaining the orientational
dependence. Molecular dynamics recrystallization simulations of Au surfaces
provide direct and quantitative evidence of this phenomenon.Comment: 10 pages (RevTeX) plus 3 figures (PostScript
Measurements of the Cerenkov light emitted by a TeO2 crystal
Bolometers have proven to be good instruments to search for rare processes
because of their excellent energy resolution and their extremely low intrinsic
background. In this kind of detectors, the capability of discriminating alpha
particles from electrons represents an important aspect for the background
reduction. One possibility for obtaining such a discrimination is provided by
the detection of the Cerenkov light which, at the low energies of the natural
radioactivity, is only emitted by electrons. In this paper, the results of the
analysis of the light emitted by a TeO2 crystal at room temperature when
transversed by a cosmic ray are reported. Light is promptly emitted after the
particle crossing and a clear evidence of its directionality is also found.
These results represent a strong indication that Cerenkov light is the main, if
not even the only, component of the light signal in a TeO2 crystal. They open
the possibility to make large improvements in the performance of experiments
based on this kind of material
Measurements and optimization of the light yield of a TeO crystal
Bolometers have proven to be good instruments to search for rare processes
because of their excellent energy resolution and their extremely low intrinsic
background. In this kind of detectors, the capability of discriminating alpha
particles from electrons represents an important aspect for the background
reduction. One possibility for obtaining such a discrimination is provided by
the detection of the Cherenkov light which, at the low energies of the natural
radioactivity, is only emitted by electrons. This paper describes the method
developed to evaluate the amount of light produced by a crystal of TeO when
hit by a 511 keV photon. The experimental measurements and the results of a
detailed simulation of the crystal and the readout system are shown and
compared. A light yield of about 52 Cherenkov photons per deposited MeV was
measured. The effect of wrapping the crystal with a PTFE layer, with the aim of
maximizing the light collection, is also presented
Recent discoveries of supersoft X-ray sources in M 31
Classical novae (CNe) have recently been reported to represent the major
class of supersoft X-ray sources (SSSs) in the central area of our neighbouring
galaxy M 31. This paper presents a review of results from recent X-ray
observations of M 31 with XMM-Newton and Chandra. We carried out a dedicated
optical and X-ray monitoring program of CNe and SSSs in the central area of M
31. We discovered the first SSSs in M 31 globular clusters (GCs) and their
connection to the very first discovered CN in a M 31 GC. This result may have
an impact on the CN rate in GCs. Furthermore, in our optical and X-ray
monitoring data we discovered the CN M31N 2007-11a, which shows a very short
SSS phase of 29 - 52 days. Short SSS states (durations < 100 days) of CNe
indicate massive white dwarfs (WDs) that are candidate progenitors of
supernovae type Ia. In the case of M31N 2007-11a, the optical and X-ray light
curves suggest a binary containing a WD with M_WD > 1.0 M_sun. Finally, we
present the discovery of the SSS counterpart of the CN M31N 2006-04a. The X-ray
light curve of M31N 2006-04a shows short-time variability, which might indicate
an orbital period of about 2 hours.Comment: 4 pages, 1 figure; Proc. of workshop "Supersoft X-ray Sources - New
Developments", ESAC, May 2009; accepted for publication in Astronomische
Nachrichte
Symbolic Melodic Similarity: State of the Art and Future Challenges
Fostered by the introduction of the Music Information Retrieval Evaluation eXchange (MIREX) competition, the number of systems which calculate Symbolic Melodic Similarity has recently increased considerably. In order to understand the state of the art, we provide a comparative analysis of existing algorithms. The analysis is based on eight criteria that help characterising the systems, and highlighting strengths and weaknesses. We also propose a taxonomy which classifies algorithms based on their approach. Both taxonomy and criteria are fruitfully exploited for providing input for new forthcoming research in the area
BZ Cam during its 1999/2000 optical low state
We report optical observations of the VY Scl star BZ Cam during its previous
optical low state in 1999/2000. We find drastic variations in the line
profiles. Narrow-band imaging observations show that its nebula extends farther
than previously known and seems to be composed of two components. We determine
the [OIII] line intensity of BZ Cam's nebula to 4.8 * 10^-13 erg/cm^2/s. We
discover a proper motion of BZ Cam of 25+-2 mas/yr which together with the
systemic radial velocity yields a space velocity of 125 km/s. We re-interpret
the nebula as being photo-ionized by hypothesized transient, luminous,
supersoft X-ray emission during optical low states, and shaped by the
transverse motion of BZ Cam.Comment: 8 pages with aa.sty, 8 figures, to appear in A&
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