6,633 research outputs found
A comprehensive Maximum Likelihood analysis of the structural properties of faint Milky Way satellites
We derive the structural parameters of the recently discovered very low
luminosity Milky Way satellites through a Maximum Likelihood algorithm applied
to SDSS data. For each satellite, even when only a few tens of stars are
available down to the SDSS flux limit, the algorithm yields robust estimates
and errors for the centroid, position angle, ellipticity, exponential
half-light radius and number of member stars. This latter parameter is then
used in conjunction with stellar population models of the satellites to derive
their absolute magnitudes and stellar masses, accounting for `CMD shot-noise'.
We find that faint systems are somewhat more elliptical than initially found
and ascribe that to the previous use of smoothed maps which can be dominated by
the smoothing kernel. As a result, the faintest half of the Milky Way dwarf
galaxies (M_V>-7.5) is significantly (4-sigma) flatter (e=0.47+/-0.03) than its
brightest half (M_V<-7.5, e=0.32+/-0.02). From our best models, we also
investigate whether the seemingly distorted shape of the satellites, often
taken to be a sign of tidal distortion, can be quantified. We find that, except
for tentative evidence of distortion in CVnI and UMaII, these can be completely
accounted for by Poisson scatter in the sparsely sampled systems. We consider
three scenarios that could explain the rather elongated shape of faint
satellites: rotation supported systems, stars following the shape of more
triaxial dark matter subhalos, or elongation due to tidal interaction with the
Milky Way. Although none of these is entirely satisfactory, the last one
appears the least problematic, but warrants much deeper observations to track
evidence of such tidal interaction.Comment: 20 pages, 11 figures, ApJ in press; some typos corrected, magnitude
of BooII corrected (thanks go to Shane Walsh for spotting the erroneous
original value
Larmor diffraction measurement of the temperature dependence of lattice constants in CuGeO3
International audienceBy using the neutron Larmor diffractionmethod and a setup based on the improvedneutron resonant spin echooption ZETA recently installed on the three-axis spectrometer IN22 (CRG beam line at the ILL), we have determined the precise relative evolution of the inter- and intra-chain lattice constants of the paradigmatic spin-Peierls compound CuGeO3 as a function of temperature. Our results are consistent with previous results obtained by conventional high-resolution diffraction. This method also allows to retrieve independently the sample mosaicities, as well as the widths of various lattice-spacings distributions, thus offering an evaluation of the intrinsic sample quality. In spite of the good definition of the spin-Peierls transition at T_{SP}=14.1(1) K in our sample, we observe a large distribution of lattice constants (\Delta d/d ~ 3 10^{- 3}), while the mosaicity of the sample appears to be quite reasonable (\le 20 minutes)
Magnetic chirality of the spin triplet in the spin-ladder compound Sr14Cu24O41 as seen via polarized inelastic neutron scattering
International audienceWe report the direct observation by polarized inelastic neutron scattering experiments at low fields (3.5 T) of the splitting of the spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr14Cu24O41. By conveniently choosing the magnetic field configuration and by making use of the spin chirality of the excitations, the splitting can be observed at relatively low fields. In this way, resonant excitations can be separated from the remainder of magnetic and phonon excitations at high temperatures. In Sr14Cu24O41, the 32-meV gapped mode vanishes above ∼200 K, close to the hole-crystal melting temperature previously observed by resonant x-ray and neutron diffraction
Self-organized transition to coherent activity in disordered media
Synchronized oscillations are of critical functional importance in many
biological systems. We show that such oscillations can arise without
centralized coordination in a disordered system of electrically coupled
excitable and passive cells. Increasing the coupling strength results in waves
that lead to coherent periodic activity, exhibiting cluster, local and global
synchronization under different conditions. Our results may explain the
self-organized transition in a pregnant uterus from transient, localized
activity initially to system-wide coherent excitations just before delivery.Comment: 5 pages, 4 figure
High Tc Josephson nanoJunctions made by ion irradiation : characteristics and reproducibility
Reproducible High Tc Josephson junctions have been made in a rather simple
two-step process using ion irradiation. A microbridge 1 to 5 micrometers wide
is firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7 film through
a gold mask such as the unprotected part becomes insulating. A lower Tc part is
then defined within the bridge by irradiating with a much lower dose through a
20 nm wide narrow slit opened in a standard electronic photoresist. These
planar junctions, whose settings can be finely tuned, exhibit reproducible and
nearly ideal Josephson characteristics. Non hysteretic Resistively Shunted
Junction (RSJ) like behavior is observed, together with sinc Fraunhofer
patterns for rectangular junctions. The IcRn product varies with temperature ;
it can reach a few mV. The typical resistance ranges from 0.1 to a few ohms,
and the critical current density can be as high as 30 kA/cm2. The dispersion in
characteristics is very low, in the 5% to 10% range. Such nanojunctions have
been used to make microSQUIDs (Superconducting Quantum Interference Device)
operating at Liquid Nitrogen (LN2) temperature. They exhibit a very small
asymmetry, a good sensitivity and a rather low noise. The process is easily
scalable to make rather complex Josephson circuits.Comment: 4 pages, 5 figures, Applied Superconductivity Conference Seattle 200
Estimating the number of people living with dementia at different stages of the condition in India: a Delphi process
Introduction: Numerous studies have previously estimated the dementia prevalence in India. However, as these estimates use different methodologies and sampling strategies, generating definitive prevalence estimates can be difficult. Methods: A Delphi process involving eight clinical and academic experts provided prevalence estimates of dementia within India, split by sex and age. The experts were also asked to estimate the number of people potentially living at different stages of the condition. A priori criteria were used to ascertain the point in which consensus was achieved. Results: Our consensus estimates generated a dementia prevalence of 2.8% (95% CI = 1.9 to 3.6) for those aged 60 years and above in India. Consensus was achieved across age and sex prevalence estimates, with the exception of one (females aged 60-64). Our experts estimated that 42.9% of people living with dementia in India had a mild severity. Conclusions: The findings indicate that there could be approximately 3.9 million people living with dementia in India, of which 1.7 million could be living with dementia of mild severity. Such estimates can better help researchers and policy makers to estimate the true cost and impact of dementia in India and can inform resource allocation decisions
Macroscopic Quantum Coherence of the Spin Triplet in the Spin-Ladder Compound Sr14Cu24O41
International audienceWe report the direct observation by inelastic neutron scattering experiments of a spin triplet of magnetic excitations in the response associated with the ladders in the composite cuprate Sr14Cu24O41. This appears as a peak at q_{Q1D}=\pi and energy \Delta_1=32.5 meV, and we conjecture that all the triplets making up this conspicuous peak have the same phase and therefore interpret it as the signature of the occurrence of quantum coherence along the ladder direction between entangled spin pairs. From the comparison with previous neutron and x-ray data, we conclude that the temperature evolution of this mode is driven by the crystallization of holes into a charge density wave in the ladder sublattic
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