7,491 research outputs found
Pervasive Displays Research: What's Next?
Reports on the 7th ACM International Symposium on Pervasive Displays that took place from June 6-8 in Munich, Germany
The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
Based on data from the ESA Gaia Data Release 2 (DR2) and several
ground-based, multi-band photometry surveys we compiled an all-sky catalogue of
hot subluminous star candidates selected in Gaia DR2 by means of
colour, absolute magnitude and reduced proper motion cuts. We expect the
majority of the candidates to be hot subdwarf stars of spectral type B and O,
followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB
stars, and central stars of planetary nebulae. The contamination by cooler
stars should be about . The catalogue is magnitude limited to Gaia
and covers the whole sky. Except within the Galactic plane
and LMC/SMC regions, we expect the catalogue to be almost complete up to about
. The main purpose of this catalogue is to serve as input
target list for the large-scale photometric and spectroscopic surveys which are
ongoing or scheduled to start in the coming years. In the long run, securing a
statistically significant sample of spectroscopically confirmed hot subluminous
stars is key to advance towards a more detailed understanding of the latest
stages of stellar evolution for single and binary stars.Comment: 13 pages, A&A, accepte
X-Ray Observations of Black Widow Pulsars
We describe the first X-ray observations of five short orbital period ( day), -ray emitting, binary millisecond pulsars. Four of these, PSRs
J0023+0923, J11243653, J1810+1744, and J22561024 are `black-widow'
pulsars, with degenerate companions of mass , three of which
exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing
`redback' with a near Roche-lobe filling 0.2 solar mass non-degenerate
companion. Data were taken using the \textit{Chandra X-Ray Observatory} and
covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and
J22561024, show significant orbital variability while PSR J11243653 shows
marginal orbital variability. The lightcurves for these three pulsars have
X-ray flux minima coinciding with the phases of the radio eclipses. This
phenomenon is consistent with an intrabinary shock emission interpretation for
the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter
and do not demonstrate variability at a level we can detect in these data. All
five spectra are fit with three separate models: a power-law model, a blackbody
model, and a combined model with both power-law and blackbody components. The
preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and
blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135
shows a significant hard X-ray component, with a large number of counts above 2
keV, which is additional evidence for the presence of intrabinary shock
emission and is similar to what has been detected in the low-mass X-ray binary
to millisecond pulsar transition object PSR J1023+0038.Comment: 8 pages, 6 figures, 2 tables, submitted to Ap
The Field White Dwarf Mass Distribution
We revisit the properties and astrophysical implications of the field white
dwarf mass distribution in preparation of Gaia applications. Our study is based
on the two samples with the best established completeness and most precise
atmospheric parameters, the volume-complete survey within 20 pc and the Sloan
Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of
the observed mass distributions with Monte Carlo simulations, but find that it
is difficult to constrain independently the initial mass function (IMF), the
initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the
variation of the Galactic disk vertical scale height as a function of stellar
age, and binary evolution. Each of these input ingredients has a moderate
effect on the predicted mass distributions, and we must also take into account
biases owing to unidentified faint objects (20 pc sample), as well as unknown
masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS
sample). Nevertheless, we find that fixed standard assumptions for the above
parameters result in predicted mean masses that are in good qualitative
agreement with the observed values. It suggests that derived masses for both
studied samples are consistent with our current knowledge of stellar and
Galactic evolution. Our simulations overpredict by 40-50% the number of massive
white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a
Salpeter IMF when we account for all biases. Furthermore, we find no evidence
of a population of double white dwarf mergers in the observed mass
distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA
Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10
We report on the identification of 22 new cool DO-type white dwarfs (WD)
detected in Data Release 10 (DR10) of the Sloan Digital Sky Survey (SDSS).
Among them, we found one more member of the so-called hot-wind DO WDs, which
show ultrahigh excitation absorption lines. Our non-LTE model atmosphere
analyses of these objects and two not previously analyzed hot-wind DO WDs,
revealed effective temperatures and gravities in the ranges Teff=45-80kK and
log g= 7.50-8.75. In eight of the spectra we found traces of C (0.001-0.01, by
mass). Two of these are the coolest DO WDs ever discovered that still show a
considerable amount of C in their atmospheres. This is in strong contradiction
with diffusion calculations, and probably, similar to what is proposed for DB
WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO
WD discovered so far with a mass of 1.07 M_sun if it is an ONe-WD or 1.09 M_sun
if it is a CO-WD. We furthermore present the mass distribution of all known hot
non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7
spectroscopic sample. The mass distribution of DO WDs beyond the wind limit
strongly deviates from the mass distribution of the objects before the wind
limit. We address this phenomenon by applying different evolutionary input
channels. We argue that the DO WD channel may be fed by about 13% by
post-extreme-horizontal branch stars and that PG1159 stars and O(He) stars may
contribute in a similar extent to the non-DA WD channel.Comment: 13 pages, accepted for publication in A&
Fluctuation relation for a L\'evy particle
We study the work fluctuations of a particle subjected to a deterministic
drag force plus a random forcing whose statistics is of the L\'evy type. In the
stationary regime, the probability density of the work is found to have ``fat''
power-law tails which assign a relatively high probability to large
fluctuations compared with the case where the random forcing is Gaussian. These
tails lead to a strong violation of existing fluctuation theorems, as the ratio
of the probabilities of positive and negative work fluctuations of equal
magnitude behaves in a non-monotonic way. Possible experiments that could probe
these features are proposed.Comment: 5 pages, 2 figures, RevTeX4; v2: minor corrections and references
added; v3: typos corrected, new conclusion, close to published versio
The population of hot subdwarf stars studied with Gaia I. The catalogue of known hot subdwarf stars
In preparation for the upcoming all-sky data releases of the Gaia mission we
compiled a catalogue of known hot subdwarf stars and candidates drawn from the
literature and yet unpublished databases. The catalogue contains 5613 unique
sources and provides multi-band photometry from the ultraviolet to the far
infrared, ground based proper motions, classifications based on spectroscopy
and colours, published atmospheric parameters, radial velocities and light
curve variability information. Using several different techniques we removed
outliers and misclassified objects. By matching this catalogue with astrometric
and photometric data from the Gaia mission, we will develop selection criteria
to construct a homogeneous, magnitude-limited all-sky catalogue of hot subdwarf
stars based on Gaia data.Comment: 11 pages, A&A accepte
Tidal dwarf galaxies as a test of fundamental physics
Within the cold dark matter (CDM) framework tidal dwarf galaxies (TDGs)
cannot contain dark matter, so the recent results by Bournaud et al. (2007)
that 3 rotating TDGs do show significant evidence for being dark matter
dominated is inconsistent with the current concordance cosmological theory
unless yet another dark matter component is postulated. We confirm that the TDG
rotation curves are consistent with Newtonian dynamics only if either an
additional dark matter component is postulated, or if all 3 TDGs happen to be
viewed nearly edge-on, which is unlikely given the geometry of the tidal
debris. We also find that the observed rotation curves are very naturally
explained without any free parameters within the modified Newtonian dynamics
(MOND) framework if inclinations are adopted as derived by Bournaud et al. We
explore different inclination angles and two different assumptions about the
external field effect. The results do not change significantly, and we conclude
therefore that Newtonian dynamics has severe problems while MOND does
exceedingly well in explaining the observed rotation curves of the 3 TDGs
studied by Bournaud et al.Comment: Accepted for publication in A&A Letters, 5 pages, 3 figure
Systematic review of platelet-rich plasma use in androgenetic alopecia compared with minoxidil\uae, finasteride\uae, and adult stem cell-based therapy
The number of articles evaluating platelet-rich plasma (PRP) efficacy in androgenic alopecia (AGA) have exponentially increased during the last decade. A systematic review on this field was performed by assessing in the selected studies the local injections of PRP compared to any control for AGA. The protocol was developed in accordance with the Preferred Reporting for Items for Systematic Reviews and Meta-Analyses-Protocols (PRISMA-P) guidelines. A multistep search of the PubMed, MEDLINE, Embase, PreMEDLINE, Ebase, CINAHL, PsycINFO, Clinicaltrials.gov, Scopus database, and Cochrane databases was performed to identify studies on hair loss treatment with platelet-rich plasma. Of the 163 articles initially identified, 123 articles focusing on AGA were selected and, consequently, only 12 clinical trials were analyzed. The studies included had to match predetermined criteria according to the PICOS (patients, intervention, comparator, outcomes, and study design) approach. In total, 84% of the studies reported a positive effect of PRP for AGA treatment. Among them, 50% of the studies demonstrated a statistically significant improvement using objective measures and 34% of the studies showed hair density and hair thickness improvement, although no p values or statistical analysis was described. In total, 17% of the studies reported greater improvement in lower-grade AGA, while 8% noted increased improvement in higher-grade AGA. Only 17% of the studies reported that PRP was not effective in treating AGA. The information analyzed highlights the positive effects of PRP on AGA, without major side effects and thus it be may considered as a safe and effective alternative procedure to treat hair loss compared with Minoxidil\uae and Finasteride\uae
Systematic review: Adipose-derived mesenchymal stem cells, platelet-rich plasma and biomaterials as new regenerative strategies in chronic skin wounds and soft tissue defects
The number of clinical trials evaluating adipose-derived mesenchymal stem cells (AD-MSCs), platelet-rich plasma (PRP), and biomaterials efficacy in regenerative plastic surgery has ex-ponentially increased during the last ten years. AD-MSCs are easily accessible from various fat depots and show intrinsic plasticity in giving rise to cell types involved in wound healing and angiogenesis. AD-MSCs have been used in the treatment of soft tissue defects and chronic wounds, employed in conjunction with a fat grafting technique or with dermal substitute scaffolds and platelet-rich plasma. In this systematic review, an overview of the current knowledge on this topic has been provided, based on existing studies and the authors\u2019 experience. A multistep search of the PubMed, MEDLINE, Embase, PreMEDLINE, Ebase, CINAHL, PsycINFO, Clinicaltrials.gov, Scopus data-base, and Cochrane databases has been performed to identify papers on AD-MSCs, PRP, and bio-materials used in soft tissue defects and chronic wounds. Of the 2136 articles initially identified, 422 articles focusing on regenerative strategies in wound healing were selected and, consequently, only 278 articles apparently related to AD-MSC, PRP, and biomaterials were initially assessed for eligibility. Of these, 85 articles were excluded as pre-clinical, experimental, and in vitro studies. For the above-mentioned reasons, 193 articles were selected; of this amount, 121 letters, expert opinions, commentary, and editorials were removed. The remaining 72 articles, strictly regarding the use of AD-MSCs, PRP, and biomaterials in chronic skin wounds and soft tissue defects, were analyzed. The studies included had to match predetermined criteria according to the patients, intervention, comparator, outcomes, and study design (PICOS) approach. The information analyzed highlights the safety and efficacy of AD-MSCs, PRP, and biomaterials on soft tissue defects and chronic wounds, without major side effects
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