711 research outputs found
Characterizing the morphology of the debris disk around the low-mass star GSC 07396-00759
Context. Debris disks have commonly been studied around intermediate-mass
stars. Their intense radiation fields are believed to efficiently remove the
small dust grains that are constantly replenished by collisions. For lower-mass
stars, in particular M-stars, the dust removal mechanism needs to be further
investigated given the much weaker radiation field produced by these objects.
Aims. We present new polarimetric observations of the nearly edge-on disk
around the pre-main sequence M-type star GSC 07396-00759, taken with VLT/SPHERE
IRDIS, with the aim to better understand the morphology of the disk, its dust
properties, and the star-disk interaction via the stellar mass-loss rate.
Methods. We model our observations to characterize the location and properties
of the dust grains using the Henyey-Greenstein approximation of the polarized
phase function and evaluate the strength of the stellar winds. Results. We find
that the observations are best described by an extended and highly inclined
disk (i\approx 84.3\,^{\circ}\pm0.3) with a dust distribution centered at a
radius au. The polarized phase function is best
reproduced by an anisotropic scattering factor and small
micron-sized dust grains with sizes m. We furthermore
discuss some of the caveats of the approach and a degeneracy between the grain
size and the porosity. Conclusions. Even though the radius of the disk may be
over-estimated, our results suggest that using a given scattering theory might
not be sufficient to fully explain key aspects such as the shape of the phase
function, or the dust grain size. With the caveats in mind, we find that the
average mass-loss rate of GSC 07396-00759 can be up to 500 times stronger than
that of the Sun, supporting the idea that stellar winds from low-mass stars can
evacuate small dust grains from the disk
Recommended from our members
ALMA observations of the η Corvi debris disc: Inward scattering of CO-rich exocomets by a chain of 3-30 Mâ planets?
While most of the known debris discs present cold dust at tens of astronomical unit (au), a few young systems exhibit hot dust analogous to the Zodiacal dust. η Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here, we present ALMA observations of η Corvi with a resolution of 1.2 arcsec (~22 au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152 au and radial full width at half-maximum of 46 au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4Ï detection of CO at ~20 au. CO could be released in situ from icy planetesimals being passed in when crossing the H2O or CO2 ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100 au, with a mass of 3-30Mâ and an eccentricity < 0.08. Such a planet would be able to clear its chaotic zone on a time-scale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust.ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. MCW, LM, AB and QK acknowledge the support of the European Union through ERC grant number 279973. LM also acknowledges support by STFC through a graduate studentship. The work of OP is supported by the Royal Society Dorothy Hodgkin Fellowship. GMK is supported by the Royal Society as a Royal Society University Research Fellow
Exercise Training in Pregnancy for obese women (ETIP): study protocol for a randomised controlled trial
<p/> <p>Background</p> <p>Both maternal pre-pregnancy obesity and excessive gestational weight gain are increasing in prevalence and associated with a number of adverse pregnancy outcomes for both mother and child. Observational studies regarding physical activity in pregnancy have found reduced weight gain in active mothers, as well as reduced risk of adverse pregnancy outcomes. There is however a lack of high quality, randomized controlled trials on the effects of regular exercise training in pregnancy, especially those with a pre-pregnancy body mass index (BMI) at or above 30 kg/m<sup>2</sup>.</p> <p>Methods</p> <p>We are conducting a randomised, controlled trial in Norway with two parallel arms; one intervention group and one control group. We will enroll 150 previously sedentary, pregnant women with a pre-pregnancy BMI at or above 30 kg/m<sup>2</sup>. The intervention group will meet for organized exercise training three times per week, starting in gestation week 14 (range 12-16). The control group will get standard antenatal care. The main outcome measure will be weight gain from baseline to delivery. Among the secondary outcome measures are changes in exercise capacity, endothelial function, physical activity level, body composition, serum markers of cardiovascular risk, incontinence, lumbopelvic pain and cardiac function from baseline to gestation week 37 (range 36-38). Offspring outcome measures include anthropometric variables at birth, Apgar score, as well as serum markers of inflammation and metabolism in cord blood.</p> <p>Discussion</p> <p>The results of this trial will provide knowledge about effects of regular exercise training in previously sedentary, obese pregnant women. If the program proves effective in reducing gestational weight gain and adverse pregnancy outcomes, such programs should be considered as part of routine pregnancy care for obese women.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov: <a href="http://www.clinicaltrials.gov/ct2/show/NCT01243554">NCT01243554</a></p
HIV Risks and Seroprevalence Among Mexican American Injection Drug Users in California
Latinos in the United States are an ethnically diverse group disproportionately affected by HIV/AIDS. We describe HIV seroprevalence, HIV risk behaviors and utilization of health services among Mexican American injection drug users (IDUs) in California (n = 286) and compare them to White (n = 830) and African American (n = 314) IDUs. Study participants were recruited from syringe exchange programs (n = 24) in California. HIV seroprevalence among Mexican Americans (0.5%) was dramatically lower than Whites (5%) and African Americans (8%). Mexican Americans reported fewer sex-related risks than Whites and African Americans though injection-related risks remained high. Compared to Whites, Mexican Americans were more likely to participate in drug treatment during a 6 month period (AOR 1.5, 95% CI 1.1, 2.0) but less likely to receive any health care (AOR 0.6, 95% CI 0.5, 0.8). Exploring cultural and structural factors among Mexican American IDUs may offer new insights into how to maintain low rates of HIV seroprevalence and reduce barriers to health care utilization
The effect of high tibial osteotomy on the results of total knee arthroplasty: a matched case control study
BACKGROUND: We performed a matched case control study to assess the effect of prior high tibia valgus producing osteotomy on results and complications of total knee arthroplasty (TKA). METHODS: From 1996 until 2003 356 patients underwent all cemented primary total knee replacement in our institution. Twelve patients with a history of 14 HTO were identified and matched to a control group of 12 patients with 14 primary TKA without previous HTO. The match was made for gender, age, date of surgery, body mass index, aetiology and type of prosthesis. Clinical and radiographic outcome were evaluated after a median duration of follow-up of 3.7 years (minimum, 2.3 years). The SPSS program was used for statistical analyses. RESULTS: The index group had more perioperative blood loss and exposure difficulties with one tibial tuberosity osteotomy and three patients with lateral retinacular releases. No such procedures were needed in the control group. Mid-term HSS, KSS and WOMAC scores were less favourable for the index group, but these differences were not significant. The tibial slope of patients with prior HTO was significantly decreased after this procedure. The tibial posterior inclination angle was corrected during knee replacement but posterior inclination was significantly less compared to the control group. No deep infection or knee component loosening were seen in the group with prior HTO. CONCLUSION: We conclude that TKA after HTO seems to be technically more demanding than a primary knee arthroplasty, but clinical outcome was almost identical to a matched group that had no HTO previously
Observation of a J^PC = 1-+ exotic resonance in diffractive dissociation of 190 GeV/c pi- into pi- pi- pi+
The COMPASS experiment at the CERN SPS has studied the diffractive
dissociation of negative pions into the pi- pi- pi+ final state using a 190
GeV/c pion beam hitting a lead target. A partial wave analysis has been
performed on a sample of 420000 events taken at values of the squared
4-momentum transfer t' between 0.1 and 1 GeV^2/c^2. The well-known resonances
a1(1260), a2(1320), and pi2(1670) are clearly observed. In addition, the data
show a significant natural parity exchange production of a resonance with
spin-exotic quantum numbers J^PC = 1-+ at 1.66 GeV/c^2 decaying to rho pi. The
resonant nature of this wave is evident from the mass-dependent phase
differences to the J^PC = 2-+ and 1++ waves. From a mass-dependent fit a
resonance mass of 1660 +- 10+0-64 MeV/c^2 and a width of 269+-21+42-64 MeV/c^2
is deduced.Comment: 7 page, 3 figures; version 2 gives some more details, data unchanged;
version 3 updated authors, text shortened, data unchange
Measurement of the branching fraction and CP content for the decay B(0) -> D(*+)D(*-)
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APS.We report a measurement of the branching fraction of the decay B0âD*+D*- and of the CP-odd component of its final state using the BABAR detector. With data corresponding to an integrated luminosity of 20.4ââfb-1 collected at the ΄(4S) resonance during 1999â2000, we have reconstructed 38 candidate signal events in the mode B0âD*+D*- with an estimated background of 6.2±0.5 events. From these events, we determine the branching fraction to be B(B0âD*+D*-)=[8.3±1.6(stat)±1.2(syst)]Ă10-4. The measured CP-odd fraction of the final state is 0.22±0.18(stat)±0.03(syst).This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A.P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Measurement of D-s(+) and D-s(*+) production in B meson decays and from continuum e(+)e(-) annihilation at âs=10.6 GeV
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APSNew measurements of Ds+ and Ds*+ meson production rates from B decays and from qqÌ
continuum events near the ΄(4S) resonance are presented. Using 20.8 fb-1 of data on the ΄(4S) resonance and 2.6 fb-1 off-resonance, we find the inclusive branching fractions B(BâDs+X)=(10.93±0.19±0.58±2.73)% and B(BâDs*+X)=(7.9±0.8±0.7±2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+âÏÏ+ branching fraction uncertainty. The production cross sections Ï(e+e-âDs+X)ĂB(Ds+âÏÏ+)=7.55±0.20±0.34pb and Ï(e+e-âDs*±X)ĂB(Ds+âÏÏ+)=5.8±0.7±0.5pb are measured at center-of-mass energies about 40 MeV below the ΄(4S) mass. The branching fractions ÎŁB(BâDs(*)+D(*))=(5.07±0.14±0.30±1.27)% and ÎŁB(BâDs*+D(*))=(4.1±0.2±0.4±1.0)% are determined from the Ds(*)+ momentum spectra. The mass difference m(Ds+)-m(D+)=98.4±0.1±0.3MeV/c2 is also measured.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the Swiss NSF, A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Effective Rheology of Bubbles Moving in a Capillary Tube
We calculate the average volumetric flux versus pressure drop of bubbles
moving in a single capillary tube with varying diameter, finding a square-root
relation from mapping the flow equations onto that of a driven overdamped
pendulum. The calculation is based on a derivation of the equation of motion of
a bubble train from considering the capillary forces and the entropy production
associated with the viscous flow. We also calculate the configurational
probability of the positions of the bubbles.Comment: 4 pages, 1 figur
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
- âŠ