272 research outputs found
Characterisation of an Electrostatic Vibration Harvester
Harvesting energy from ambient vibration is proposed as an alternative to
storage based power supplies for autonomous systems. The system presented
converts the mechanical energy of a vibration into electrical energy by means
of a variable capacitor, which is polarized by an electret. A lumped element
model is used to study the generator and design a prototype. The device has
been micromachined in silicon, based on a two-wafer process. The prototype was
successfully tested, both using an external polarization source and an
electret.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Motion-Based Generators for Industrial Applications
Scaling down of electronic systems has generated a large interest in the
research on miniature energy sources. In this paper a closer look is given to
the use of vibration based scavengers in industrial environments, where waste
energy is abundantly available as engine related vibrations or large amplitude
motions. The modeling of mechanical generators resulted in the design and
realization of two prototypes, based on electromagnetic and electrostatic
conversion of energy. Although the prototypes are not yet optimized against
size and efficiency, a power of 0.3 mW has been generated in a 5 Hz motion with
a 0.5 meter amplitude.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Long-term spectroscopic monitoring of the Luminous Blue Variable HD160529
We have spectroscopically monitored the galactic Luminous Blue Variable HD
160529 and obtained an extensive high-resolution data set that covers the years
1991 to 2002. During this period, the star evolved from an extended photometric
minimum phase towards a new visual maximum. In several observing seasons, we
covered up to four months with almost daily spectra. Our spectra typically
cover most of the visual spectral range with a high spectral resolution (about
20,000 or more). This allows us to investigate the variability in many lines
and on many time scales from days to years. We find a correlation between the
photospheric HeI lines and the brightness of the star, both on a time scale of
months and on a time scale of years. The short-term variations are smaller and
do not follow the long-term trend, strongly suggesting different physical
mechanisms. Metal lines also show both short-term and long-term variations in
strength and also a long-term trend in radial velocity. Most of the
line-profile variations can be attributed to changing strengths of lines.
Propagating features in the line profiles are rarely observed. We find that the
mass-loss rate of HD 160529 is almost independent of temperature, i.e. visual
brightness.Comment: 14 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
An X-ray investigation of the NGC 346 field in the SMC (3): XMM-Newton data
We present new XMM-Newton results on the field around the NGC346 star cluster
in the SMC. This continues and extends previously published work on Chandra
observations of the same field. The two XMM-Newton observations were obtained,
respectively, six months before and six months after the previously published
Chandra data. Of the 51 X-ray sources detected with XMM-Newton, 29 were already
detected with Chandra. Comparing the properties of these X-ray sources in each
of our three datasets has enabled us to investigate their variability on times
scales of a year. Changes in the flux levels and/or spectral properties were
observed for 21 of these sources. In addition, we discovered long-term
variations in the X-ray properties of the peculiar system HD5980, a luminous
blue variable star, that is likely to be a colliding wind binary system, which
displayed the largest luminosity during the first XMM-Newton observation.Comment: 19 pages, 5 figures (in gif), accepted by ApJ, also available from
http://vela.astro.ulg.ac.be/Preprints/P89/index.htm
Electrostatic microgenerators
Accepted versio
Outbursts of EX Hydrae: mass-transfer events or disc instabilities?
We present the 45-yr record of EX Hya's lightcurve and discuss the
characteristics of its 15 observed outbursts. We then concentrate on the 1998
outburst, reporting the first outburst X-ray observations. We discover an X-ray
beat-cycle modulation, indicating that an enhanced accretion stream couples
directly with the magnetosphere in outburst, confirming our previous
prediction. Optical eclipse profiles late in outburst show that the visible
light is dominated by an enhanced mass-transfer stream overflowing the
accretion disc. We are uncertain whether the enhanced mass transfer is
triggered by a disc instability, or by some other cause. While in outburst, EX
Hya shows some of the characteristics of SW Sex stars.Comment: To appear in MNRAS (8 pages; 9 figs
Galactic Twins of the Ring Nebula Around SN1987A and a Possible LBV-like Phase for Sk-69 202
Some core-collapse supernovae show clear signs of interaction with dense
circumstellar material that often appears to be non-spherical. Circumstellar
nebulae around supernova progenitors provide clues to the origin of that
asymmetry in immediate pre-supernova evolution. Here I discuss outstanding
questions about the formation of the ring nebula around SN1987A and some
implications of similar ring nebulae around Galactic B supergiants. Several
clues hint that SN1987A's nebula may have been ejected in an LBV-like event,
rather than through interacting winds in a transition from a red supergiant to
a blue supergiant.Comment: 2 pages, to appear in procedings of "Massive stars: fundamental
parameters and circumstellar interactions", conference in honor of Virpi
Niemela's 70th birthda
A Second Look at String-Inspired Models for Proton-Proton Scattering via Pomeron Exchange
We re-examine a string dual model for elastic proton-proton scattering via
Pomeron exchange. We argue that the method of "Reggeizing" a propagator to take
into account an entire trajectory of exchanged particles can be generalized, in
particular by modifying the value of the mass-shell parameter in the model. We
then fit the generalized model to scattering data at large s and small t. The
fitting results are inconclusive, but suggest that a better fit might be
obtained by allowing the mass-shell to vary. The model fits the data equally
well (roughly) for a wide range of values of the mass-shell parameter, but the
other fitting parameters (the slope and intercept of the Regge trajectory, and
the coupling constant and dipole mass from the proton-proton-glueball coupling)
are then inconsistent with what we expect. On the other hand, using the
traditional method of Reggeization generates a weaker fit, but the other
parameters obtain more physically reasonable values. In analyzing the fitting
results, we also found that our model is more consistent with the sqrt(s) =
1800 GeV coming from the E710 experiment than that coming from the CDF
experiment, and that our model has the greatest discrepancy with the data in
the range 0.5 GeV^2 < |t| < 0.6 GeV^2, suggesting that the transition from soft
Pomeron to hard Pomeron may occur closer to t = -0.5 GeV^2 rather than t = -0.6
GeV^2 as previously thought.Comment: 16 pages, 7 figures, 2 table
- …