3,240 research outputs found
Analysis of ultrasonic transducers with fractal architecture
Ultrasonic transducers composed of a periodic piezoelectric composite are generally accepted as the design of choice in many applications. Their architecture is normally very regular and this is due to manufacturing constraints rather than performance optimisation. Many of these manufacturing restrictions no longer hold due to new production methods such as computer controlled, laser cutting, and so there is now freedom to investigate new types of geometry. In this paper, the plane wave expansion model is utilised to investigate the behaviour of a transducer with a self-similar architecture. The Cantor set is utilised to design a 2-2 conguration, and a 1-3 conguration is investigated with a Sierpinski Carpet geometry
Hypervelocity Stars from the Andromeda Galaxy
Hypervelocity stars (HVSs) discovered in the Milky Way (MW) halo are thought
to be ejected from near the massive black hole (MBH) at the galactic centre. In
this paper we investigate the spatial and velocity distributions of the HVSs
which are expected to be similarly produced in the Andromeda galaxy (M31). We
consider three different HVS production mechanisms: (i) the disruption of
stellar binaries by the galactocentric MBH; (ii) the ejection of stars by an
in-spiraling intermediate mass black hole; and (iii) the scattering of stars
off a cluster of stellar-mass black holes orbiting around the MBH. While the
first two mechanisms would produce large numbers of HVSs in M31, we show that
the third mechanism would not be effective in M31. We numerically calculate
1.2*10^6 trajectories of HVSs from M31 within a simple model of the Local Group
and hence infer the current distribution of these stars. Gravitational focusing
of the HVSs by the MW and the diffuse Local Group medium leads to high
densities of low mass (~ solar mass) M31 HVSs near the MW. Within the
virialized MW halo, we expect there to be of order 1000 HVSs for the first
mechanism and a few hundred HVSs for the second mechanism; many of these stars
should have distinctively large approach velocities (< -500 km/s). In addition,
we predict ~5 hypervelocity RGB stars within the M31 halo which could be
identified observationally. Future MW astrometric surveys or searches for
distant giants could thus find HVSs from M31.Comment: 14 pages, 6 figures, changed to match version accepted by MNRA
Nuclear alpha-clustering, superdeformation, and molecular resonances
Nuclear alpha-clustering has been the subject of intense study since the
advent of heavy-ion accelerators. Looking back for more than 40 years we are
able today to see the connection between quasimolecular resonances in heavy-ion
collisions and extremely deformed states in light nuclei. For example
superdeformed bands have been recently discovered in light N=Z nuclei such as
Ar, Ca, Cr, and Ni by -ray spectroscopy.
The search for strongly deformed shapes in N=Z nuclei is also the domain of
charged-particle spectroscopy, and our experimental group at IReS Strasbourg
has studied a number of these nuclei with the charged particle multidetector
array {\sc Icare} at the {\sc Vivitron} Tandem facility in a systematical
manner. Recently the search for -decays in Mg has been
undertaken in a range of excitation energies where previously nuclear molecular
resonances were found in C+C collisions. The breakup reaction
MgC has been investigated at E(Mg) = 130 MeV, an
energy which corresponds to the appropriate excitation energy in Mg for
which the C+C resonance could be related to the breakup
resonance. Very exclusive data were collected with the Binary Reaction
Spectrometer in coincidence with {\sc Euroball IV} installed at the {\sc
Vivitron}.Comment: 10 pages, 4 eps figures included. Invited Talk 10th Nuclear Physics
Workshop Marie and Pierre Curie, Kazimierz Dolny Poland, Sep. 24-28, 2003; To
be published in International Journal of Modern Physics
Massive open star clusters using the VVV survey III: A young massive cluster at the far edge of the Galactic bar
Context: Young massive clusters are key to map the Milky Way's structure, and
near-IR large area sky surveys have contributed strongly to the discovery of
new obscured massive stellar clusters.
Aims: We present the third article in a series of papers focused on young and
massive clusters discovered in the VVV survey. This article is dedicated to the
physical characterization of VVV CL086, using part of its OB-stellar
population.
Methods: We physically characterized the cluster using near-infrared
photometry from ESO public survey VVV images, using the VVV-SkZ pipeline, and
near-infrared -band spectroscopy, following the methodology presented in the
first article of the series.
Results: Individual distances for two observed stars indicate that the
cluster is located at the far edge of the Galactic bar. These stars, which are
probable cluster members from the statistically field-star decontaminated CMD,
have spectral types between O9 and B0V. According to our analysis, this young
cluster ( Myr age Myr) is located at a distance of
kpc, and we estimate a lower limit for the cluster total mass of
. It is likely that the cluster
contains even earlier and more massive stars.Comment: Accepted for publication as a Letter in A&
Longitudinal stability of genetic and environmental influences on the association between diurnal preference and sleep quality in young adult twins and siblings
Overlapping genetic influences have been implicated in diurnal preference and subjective sleep quality. Our overall aim was to examine overlapping concurrent and longitudinal genetic and environmental effects on diurnal preference and sleep quality over ~5 years. Behavioural genetic analyses were performed on data from the longitudinal British G1219 study of young adult twins and non-twin siblings. 1556 twins and siblings provided data on diurnal preference (Morningness-Eveningness Questionnaire) and sleep quality (Pittsburgh Sleep Quality Index) at time 1 (mean age=20.30 years, SD=1.76; 62% female); and 862 participated at time 2 (mean age=25.30 years, SD=1.81; 66% female). Preference for eveningness was associated with poorer sleep quality at both time-points (r=.25[95% confidence intervals, (CI)=.20-.30], and r=.21[CI=.15-.28]). There was substantial overlap in the genetic influences on diurnal preference and sleep quality individually, across time (genetic correlations [rA’s]: .64[95% CI = .59-.67] and .48[95% CI = .42-.53]). There were moderate genetic correlations between diurnal preference and sleep quality concurrently and longitudinally (rAs=.29-.60). Non-shared environmental overlap was substantially smaller for all cross-phenotype associations (non-shared environmental correlations [rE’s]=-.02-.08). All concurrent and longitudinal associations within and between phenotypes were largely accounted for by genetic factors (explaining between 60%-100% of the associations). All shared environmental effects were non-significant. Non-shared environmental influences played a smaller role on the associations between phenotypes (explaining between -.06%-40% of the associations). These results suggest that to some extent similar genes contribute to the stability of diurnal preference and sleep quality throughout young adulthood, but also that different genes play a part over this relatively short time-frame. While there was evidence of genetic overlap between phenotypes concurrently and longitudinally, the possible emergence of new genetic factors (or decline of previously associated factors) suggests that molecular genetic studies focussing on young adults should consider more tightly specified age-groups, given that genetic effects may be time-specific
Shot-noise-limited spin measurements in a pulsed molecular beam
Heavy diatomic molecules have been identified as good candidates for use in
electron electric dipole moment (eEDM) searches. Suitable molecular species can
be produced in pulsed beams, but with a total flux and/or temporal evolution
that varies significantly from pulse to pulse. These variations can degrade the
experimental sensitivity to changes in spin precession phase of an electri-
cally polarized state, which is the observable of interest for an eEDM
measurement. We present two methods for measurement of the phase that provide
immunity to beam temporal variations, and make it possible to reach
shot-noise-limited sensitivity. Each method employs rapid projection of the
spin state onto both components of an orthonormal basis. We demonstrate both
methods using the eEDM-sensitive H state of thorium monoxide (ThO), and use one
of them to measure the magnetic moment of this state with increased accuracy
relative to previous determinations.Comment: 12 pages, 6 figure
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