4,731 research outputs found
Adolescent Experiences With Intrauterine Devices: A Qualitative Study
PURPOSE: The purpose of this study was to improve understanding of adolescents\u27 reasons for choosing an intrauterine device (IUD) and to explore experiences that led to continuation or discontinuation of the levonorgestrel intrauterine system (LNG-IUS) and the copper IUD (copper IUD). METHODS: We conducted focus groups (FGs) with adolescents and young women who were current or former IUD users stratified by IUD type and 12-month IUD continuation or discontinuation. All subjects were participants from the Contraceptive CHOICE Project. FG data were supplemented with in-depth interviews (IDIs). Data collection was continued until thematic saturation was reached. Transcripts were independently coded by two researchers, and interrater reliability was calculated using a Kappa coefficient. Analysis followed a standard text-analysis approach. RESULTS: Thirteen FGs and seven IDIs were conducted with 43 young women. Effectiveness, duration of use, convenience, and potential bleeding changes emerged as themes for both choosing and continuing IUDs. Some women chose the LNG-IUS to achieve amenorrhea, whereas copper IUD users wanted a nonhormonal method and continued menses. Copper IUD users cited expulsion and bleeding irregularities as reasons for discontinuation, whereas LNG-IUS users reported bleeding irregularities and continued pain as reasons for removal. IUD users noted an adjustment period of weeks to months in which side effects were present before lessening. CONCLUSIONS: Effectiveness, duration of use, convenience, and potential changes in bleeding patterns drove adolescents\u27 choice and continuation of an IUD. Bleeding changes and pain contributed to IUD discontinuation. Discussion of effectiveness, duration and convenience, and anticipatory guidance regarding post-insertion side effects may be important in counseling young women about IUDs
Gas-to-Dust mass ratios in local galaxies over a 2 dex metallicity range
This paper analyses the behaviour of the gas-to-dust mass ratio (G/D) of
local Universe galaxies over a large metallicity range. We combine three
samples: the Dwarf Galaxy Survey, the KINGFISH survey and a subsample from
Galametz et al. (2011) totalling 126 galaxies, covering a 2 dex metallicity
range, with 30% of the sample with 12+log(O/H) < 8.0. The dust masses are
homogeneously determined with a semi-empirical dust model, including submm
constraints. The atomic and molecular gas masses are compiled from the
literature. Two XCO are used to estimate molecular gas masses: the Galactic
XCO, and a XCO depending on the metallicity (as Z^{-2}). Correlations with
morphological types, stellar masses, star formation rates and specific star
formation rates are discussed. The trend between G/D and metallicity is
empirically modelled using power-laws (slope of -1 and free) and a broken
power-law. We compare the evolution of the G/D with predictions from chemical
evolution models. We find that out of the five tested galactic parameters,
metallicity is the galactic property driving the observed G/D. The G/D versus
metallicity relation cannot be represented by a power-law with a slope of -1
over the whole metallicity range. The observed trend is steeper for
metallicities lower than ~ 8.0. A large scatter is observed in the G/D for a
given metallicity, with a dispersion of 0.37 dex in metallicity bins of ~0.1
dex. The broken power-law reproduces best the observed G/D and provides
estimates of the G/D that are accurate to a factor of 1.6. The good agreement
of the G/D and its scatter with the three tested chemical evolution models
shows that the scatter is intrinsic to galactic properties, reflecting the
different star formation histories, dust destruction efficiencies, dust grain
size distributions and chemical compositions across the sample. (abriged)Comment: 23 pages, 12 figures, accepted in Astronomy & Astrophysic
Non-standard grain properties, dark gas reservoir, and extended submillimeter excess, probed by Herschel in the Large Magellanic Cloud
Context. Herschel provides crucial constraints on the IR SEDs of galaxies, allowing unprecedented accuracy on the dust mass estimates. However, these estimates rely on non-linear models and poorly-known optical properties.
Aims. In this paper, we perform detailed modelling of the Spitzer and Herschel observations of the LMC, in order to: (i) systematically study the uncertainties and biases affecting dust mass estimates; and to (ii) explore the peculiar ISM properties of the LMC.
Methods. To achieve these goals, we have modelled the spatially resolved SEDs with two alternate grain compositions, to study the impact of different submillimetre opacities on the dust mass. We have rigorously propagated the observational errors (noise and calibration) through the entire fitting process, in order to derive consistent parameter uncertainties.
Results. First, we show that using the integrated SED leads to underestimating the dust mass by ≃50% compared to the value obtained with sufficient spatial resolution, for the region we studied. This might be the case, in general, for unresolved galaxies. Second, we show that Milky Way type grains produce higher gas-to-dust mass ratios than what seems possible according to the element abundances in the LMC. A spatial analysis shows that this dilemma is the result of an exceptional property: the grains of the LMC have on average a larger intrinsic submm opacity (emissivity index β ≃ 1.7 and opacity κ_(abs)(160 μm) = 1.6 m^2 kg^(-1)) than those of the Galaxy. By studying the spatial distribution of the gas-to-dust mass ratio, we are able to constrain the fraction of unseen gas mass between ≃10, and ≃100% and show that it is not sufficient to explain the gas-to-dust mass ratio obtained with Milky Way type grains. Finally, we confirm the detection of a 500 μm extended emission excess with an average relative amplitude of ≃15%, varying up to 40%. This excess anticorrelates well with the dust mass surface density. Although we do not know the origin of this excess, we show that it is unlikely the result of very cold dust, or CMB fluctuations
Accelerator Testing of the General Antiparticle Spectrometer, a Novel Approach to Indirect Dark Matter Detection
We report on recent accelerator testing of a prototype general antiparticle
spectrometer (GAPS). GAPS is a novel approach for indirect dark matter searches
that exploits the antideuterons produced in neutralino-neutralino
annihilations. GAPS captures these antideuterons into a target with the
subsequent formation of exotic atoms. These exotic atoms decay with the
emission of X-rays of precisely defined energy and a correlated pion signature
from nuclear annihilation. This signature uniquely characterizes the
antideuterons. Preliminary analysis of data from a prototype GAPS in an
antiproton beam at the KEK accelerator in Japan has confirmed the
multi-X-ray/pion star topology and indicated X-ray yields consistent with prior
expectations. Moreover our success in utilizing solid rather than gas targets
represents a significant simplification over our original approach and offers
potential gains in sensitivity through reduced dead mass in the target area.Comment: 18 pages, 9 figures, submitted to JCA
The dust properties and physical conditions of the interstellar medium in the LMC massive star forming complex N11
We combine Spitzer and Herschel data of the star-forming region N11 in the
Large Magellanic Cloud to produce detailed maps of the dust properties in the
complex and study their variations with the ISM conditions. We also compare
APEX/LABOCA 870um observations with our model predictions in order to decompose
the 870um emission into dust and non-dust (free-free emission and CO(3-2) line)
contributions. We find that in N11, the 870um can be fully accounted for by
these 3 components. The dust surface density map of N11 is combined with HI and
CO observations to study local variations in the gas-to-dust mass ratios. Our
analysis leads to values lower than those expected from the LMC low-metallicity
as well as to a decrease of the gas-to-dust mass ratio with the dust surface
density. We explore potential hypotheses that could explain the low observed
gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas
or of optically thick HI or variations in the dust abundance in the dense
regions). We finally decompose the local SEDs using a Principal Component
Analysis (i.e. with no a priori assumption on the dust composition in the
complex). Our results lead to a promising decomposition of the local SEDs in
various dust components (hot, warm, cold) coherent with that expected for the
region. Further analysis on a larger sample of galaxies will follow in order to
understand how unique this decomposition is or how it evolves from one
environment to another.Comment: 24 pages, 16 figures, accepted for publication in MNRA
Terahertz bandwidth RF spectrum analysis of femtosecond pulses using a chalcogenide chip
We report the first demonstration of the use of an RF spectrum
analyser with multi-terahertz bandwidth to measure the properties of
femtosecond optical pulses. A low distortion and broad measurement
bandwidth of 2.78 THz (nearly two orders of magnitude greater than
conventional opto-electronic analyzers) was achieved by using a 6 cm long
As2S3 chalcogenide waveguide designed for high Kerr nonlinearity and near
zero dispersion. Measurements of pulses as short as 260 fs produced from a
soliton-effect compressor reveal features not evident from the pulse’s
optical spectrum. We also applied an inverse Fourier transform numerically
to the captured data to re-construct a time-domain waveform that resembled
pulse measurement obtained from intensity autocorrelation
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