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Recent advances in MOS integrated circuit technology have opened new, high-volume applications utilizing epitaxial silicon-on- insulating substrates. To provide good quality heteroepitaxial silicon films for the semiconductor industry, a development program has been established to improve both the crystalline quality and the fabrication techniques for the most promising current substrate, magnesium aluminum spinel.
The role of X-ray diffraction techniques in the investigation of crystal quality, substrate surface quality, and epitaxial film quality are discussed, and results interpreted as the program is traced from crystal growth to epitaxial film analysis.
From a 45ks Chandra observation of V42G Oph we have obtained high-resolution X-ray spectra at moderate signal-to-noise, and a, good quality, uninterrupted lightcurve. The spectra are reasonably fit with a cooling flow model, similar to EX Hya and U Gem. Our analysis of the Chandra and additional X-ray/optical lightcurves reveals a persistent modulation at 4.2 hr from 1988 to 2003, likely the white dwarf spin period indicating an intermediate polar nature for V426 Oph.
On an 11 m firn/ice core from Kongsvegen, Svalbard, we have used dielectric profiling (DEP) to measure electrical properties, and digital photography to measure a core optical stratigraphy (COS) profile. We also used a neutron-scattering probe (NP) to measure a density profile in the borehole from which the core was extracted. The NP- and DEP-derived density profiles were similar, showing large-scale (>30 cm) variation in the gravimetric densities of each core section. Fine-scale features (<10 cm) are well characterized by the COS record and are seen at a slightly lower resolution in both the DEP and NP records, which show increasing smoothing. A combination of the density accuracy of NP and the spatial resolution of COS provides a useful method of evaluating the shallow-density profile of a glacier, improving paleoclimate interpretation, mass-balance measurement and interpretation of radar returns.
We have determined accumulation histories by identifying annual-layer horizons in records obtained by three independent methods: (1) glaciochemical analysis on a core, (2) density profiling in the borehole from which the core was taken, using the neutron-probe (NP) technique, and (3) borehole optical stratigraphy (BOS), again in the same borehole. We also used three different techniques for determining density to convert annual-layer thickness to accumulation: (1) gravimetric measurements on core samples, (2) measurement of density using NP and (3) a simple empirical model based on regional climatology. The result is nine different accumulation time series, three of which are completely independent. The chemical-analysis- and NP-derived accumulation time series are correlated, and the ∼70 year means are in agreement. The BOS-derived accumulation ∼70 year mean is slightly lower, probably due to a combination of the empirical density model’s underestimate of the density profile and the misidentification of sub-annual events in the shallow part of the borehole as annual horizons.
Tidewater glaciers deposit sediment at their terminus, thereby reducing the relative water depth. Reduced water depth can lead to increased glacier stability through decreased rates of iceberg calving, glacier thinning and submarine melting. Here we investigate sedimentation processes at the termini of Kronebreen and Kongsvegen, Svalbard. We mapped the fjord floor bathymetry in August 2009 and calculate sedimentation rates based on our bathymetry and that from a similar study in 2005. A grounding-line fan is developing near the current position of the subglacial stream. An older, abandoned grounding-line fan that likely formed between ∼1987 and 2001 is degrading near the middle of the ice front. Our findings indicate that sediment gravity flows reduce the height of the sediment mound forming at the glacier terminus. The future impact of glacimarine sedimentation processes on glacier stability will depend on the net balance between the observed gravity flows and sediment deposition.
We have made side-by-side measurements in several boreholes at Summit, Greenland, using borehole optical stratigraphy (BOS) and neutron-scattering density logging techniques. The BOS logs show strong positive correlation at shallow depths with neutron-scattering logs taken in the same borehole. This supports the hypothesis that BOS detects changes in density. The positive correlation between returned brightness and density decreases with depth and finally becomes negative. We conclude this inversion of correlation is related to changes in densification regime from grain-boundary sliding to pressure sintering.
The study aims were to (i) identify determinants of Nutrition Facts Panel (NFP) use and (ii) describe the association between NFP use and dietary intake among Latinos with type 2 diabetes.
Baseline cross-sectional data from a clinical trial were used to assess the association between NFP use and dietary intake. Diet was measured using two methods: (i) a diet quality score (the Healthy Eating Index-2010) derived from a single 24 h recall and (ii) dietary pattern (exploratory factor analyses) from an FFQ. Multivariable logistic and non-parametric quantile regressions were conducted, as appropriate.
Hartford County, Connecticut, USA.
Latino adults (n 203), ≥21 years of age, with diagnosed type 2 diabetes, glycosylated Hb≥7 %, and without medical conditions limiting physical activity.
Participants’ education level, diabetes-related knowledge and English speaking were positively associated with NFP use. At the higher percentiles of diet quality score, NFP use was significantly associated with higher diet quality. Similarly, NFP users were more likely to consume a ‘healthy’ dietary pattern (P=0·003) and less likely to consume a ‘fried snack’ pattern (P=0·048) compared with NFP non-users.
The association between reported NFP use and diet quality was positive and significantly stronger among participants who reported consuming a healthier diet. While NFP use was associated with a healthier dietary pattern, not using NFP was associated with a less-healthy, fried snack pattern. Longitudinal studies are needed to understand whether improving NFP use could be an effective intervention to improve diet quality among Latinos with type 2 diabetes.
Mass loss from mountain glaciers contributes to sea-level rise and reduces freshwater availability in glacier-fed river basins, with negative effects on hydropower generation, agriculture and the health of aquatic ecosystems. In this study, we determine the volume of lower Peyto Glacier, Alberta, Canada, from ground-penetrating radar surveys in 2008–10, and compare our volume estimate with previous estimates from 1966 and 1984. The long-term record of mass-balance estimates on Peyto Glacier highlights Peyto’s importance as an ‘index’ glacier for the region. We calculate a mean volume of (3.39 ± 0.30) × 107 m3 for the glacier snout for the period 2008–10. Glacier volume decreased linearly from 1966 to 2010. If this trend persists, the glacier snout will disappear by ~2019 and Peyto Glacier will have retreated by ~1 km. Our results agree with modelling studies, which suggest that Peyto Glacier and other nearby glaciers along the eastern slopes of the Canadian Rocky Mountains will likely lose 80–90% of their present-day volume by 2100.
Accumulation is a key parameter governing the mass balance of the Greenland ice sheet. Several studies have documented the spatial variability of accumulation over wide spatial scales, primarily using point data, remote sensing or modeling. Direct measurements of spatially extensive, detailed profiles of accumulation in Greenland, however, are rare. We used 400 MHz ground-penetrating radar along the 1009 km route of the Greenland Inland Traverse from Thule to Summit during April and May of 2011, to image continuous internal reflecting horizons. We dated these horizons using ice-core chemistry at each end of the traverse. Using density profiles measured along the traverse, we determined the depth to the horizons and the corresponding water-equivalent accumulation rates. The measured accumulation rates vary from ~0.1 m w.e. a–1 in the interior to ~0.7 m w.e. a–1 near the coast, and correspond broadly with existing published model results, though there are some excursions. Comparison of our recent accumulation rates with those collected along a similar route in the 1950s shows a ~10% increase in accumulation rates over the past 52 years along most of the traverse route. This implies that the increased water vapor capacity of warmer air is increasing accumulation in the interior of Greenland.
Young children are particularly vulnerable to malnutrition as nutrition transition progresses. The present study aimed to document the prevalence, coexistence and correlates of nutritional status (stunting, overweight/obesity and anaemia) in Samoan children aged 24–59 months.
A cross-sectional community-based survey. Height and weight were used to determine prevalence of stunting (height-for-age Z-score <−2) and overweight/obesity (BMI-for-age Z-score >+2) based on WHO growth standards. Anaemia was determined using an AimStrip Hemoglobin test system (Hb <110 g/l).
Ten villages on the Samoan island of Upolu.
Mother–child pairs (n 305) recruited using convenience sampling.
Moderate or severe stunting was apparent in 20·3 % of children, 16·1 % were overweight/obese and 34·1 % were anaemic. Among the overweight/obese children, 28·6 % were also stunted and 42·9 % anaemic, indicating dual burden of malnutrition. Stunting was significantly less likely among girls (OR=0·41; 95 % CI 0·21, 0·79, P<0·01) than boys. Overweight/obesity was associated with higher family socio-economic status and decreased sugar intake (OR per 10 g/d=0·89, 95 % CI 0·80, 0·99, P=0·032). The odds of anaemia decreased with age and anaemia was more likely in children with an anaemic mother (OR=2·20; 95 % CI 1·22, 3·98, P=0·007). No child, maternal or household characteristic was associated with more than one of the nutritional status outcomes, highlighting the need for condition-specific interventions in this age group.
The observed prevalences of stunting, overweight/obesity and anaemia suggest that it is critical to invest in nutrition and develop health programmes targeting early childhood growth and development in Samoa.
We have obtained HST/STIS time series observations of active, very low mass stars of spectral types M7-M9. The observations comprise 15 consecutive exposures on each of the stars VB 8, VB 10, and LHS 2065. Emission is present in several transition region lines including Si IV, C IV and He II. The emission appears to be variable between exposures, but is always observed. A strong flare was observed in one exposure on VB 10. Our results suggest that active, very low-mass stars maintain a persistent quiescent chromosphere and transition region that is similar to those observed in active, earlier type M dwarfs. This contradicts the currently popular idea that very low mass stars exhibit only relatively strong flares and no quiescent emission.
Determining the process(es) by which brown dwarfs form is key to understanding their intrinsic nature. If their origins are within circumstellar disks they are akin to giant planets. If, on the other hand, they coalesce from molecular cloud cores, then they share a common lineage with low mass stars. These two mechanisms can be distinguished by investigation of young (< 10 Myr) substellar objects. If brown dwarfs are small failed stars, we expect to find very low mass analogs of the Classical T Tauris, with primordial magnetic fields from the molecular cloud collapse. Accretion onto these objects leads to characteristic magnetic activity signatures such as chromospheric and coronal emission resulting in an ultraviolet excess continuum.
The Orion OB1b association (m-M = 7.9, 2 Myr) provides a laboratory for following the strength and occurrence of the accretion process as a function of mass. Studies of the substellar mass function within the sigma Orionis cluster at the southern end of the association indicate that brown dwarfs are common. Based on model isochrones and the SDSS M dwarf sequence we expect the 95% completeness limit of the “Orion” scans to correspond to 0.1 and 0.03 solar masses for the u and g bands.
We report on a large, multi-wavelength campaign to observe variability across the electromagnetic spectrum in the M dwarf flare star EV Lacertae, in 2001 September. The campaign involved X-ray (Chandra ACIS-S+HETG), UV (HST/STIS), and optical (McDonald) spectra, as well as optical photometry and multi-frequency radio (VLA) observations. EV Lac demonstrated both frequent and extreme variability during the course of the two day intensive recordings. Dispersed X-ray spectra confirm the metal underabundance seen in other active stars. The increase in continuum fluxes at short X-ray wavelengths during flare intervals compared to quiescent intervals signals the creation of high temperature plasma, a signature of the flare process. Multi-wavelength comparisons reveal interesting trends: X-ray flare frequencies are within the range predicted by optical observations, yet there is no correspondence between X-ray flares and optical flares in our data. Two UV flares occur during the rise stages of X-ray flares; a major radio flare is accompanied by a large optical flare, which has no apparent counterpart in the X-ray. The results give conflicting evidence for the applicability of the Neupert effect interpretation in stellar coronae.
Marine-terminating outlet glaciers discharge most of the Greenland ice sheet's mass through frontal ablation and meltwater runoff. While calving can be estimated by in situ and remote sensing observations, submarine melting and subglacial meltwater transport are more challenging to quantify. Here we investigate the subglacial hydrology of Rink Isbræ, a fast-flowing West Greenland tidewater glacier, using time-lapse photography, modeled runoff estimates and daily satellite imagery from 2007 to 2011. We find that sediment plumes appear episodically at four distinct locations across the terminus, and last between 2 h and 17 d. This suggests short-term variability in discharge and the existence of persistent pathways. The seasonal onset of sediment plumes occurs before supraglacial lake drainages, shortly after the onset of runoff, and only after the wintertime ice mélange has begun disintegrating. Plumes were also visible after the cessation of runoff (23 ± 5 d), which is indicative of subglacial storage. The lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage. Subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front.
Coronal mass ejections are the most spectacular form of solar activity and they play a key role in driving space weather at the Earth. These eruptions are associated with active regions and occur throughout an active region's entire lifetime. All coronal mass ejection models invoke the presence of a twisted magnetic field configuration known as a magnetic flux rope either before or after eruption onset. The observational identification of magnetic flux ropes in the solar atmosphere using remote sensing data represents a challenging task, but theoretical models have led to the understanding that there are signatures that reveal their presence. The range of coronal mass ejection models are helping build a more complete picture of both the trigger and drivers of these eruptions.
We present observations of an “EIT wave” associated with an X-class flare from 2012 July 6, the propagation of which was severely restricted by the magnetic structure of the solar corona surrounding the erupting active region. The “EIT wave” was observed by both SDO and STEREO-A, allowing a three-dimensional examination of how the propagation of the disturbance was affected both by a neighbouring coronal hole and a trans-equatorial loop system. In addition, the eruption was observed at the limb by the ground-based CoMP instrument, allowing the Doppler motion associated with the eruption and resulting coronal loop oscillation to be investigated in detail. This combination of data-sets provides a unique insight into the three-dimensional evolution of the “EIT wave” and its effects on the surrounding corona.
A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5-m GREGOR telescope, using a 0.1 nm Ca II H interference filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show that the ribbon is a part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. A 140 second long time series of Ca II H images was reconstructed by means of the Multi-Frame Blind Deconvolution method, giving the respective spatial and temporal resolutions of 0”.1 and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary but three move along the ribbon with speeds of 7–11 km s−1. Two of them move in the opposite direction and exhibit highly correlated intensity changes, providing evidence for the presence of slipping reconnection at small spatial scales.
The proper characterisation of stellar winds is essential for the study of propagation of eruptive events (flares, coronal mass ejections) and the study of space weather events on exoplanets. Here, we quantitatively investigate the nature of the stellar winds surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive the wind properties at the position of the hot-Jupiters’ orbits (temperature, velocity, magnetic field intensity and pressure). We show that the exoplanets studied here are immersed in a local stellar wind that is much denser than the local conditions encountered around the solar system planets (e.g., 5 orders of magnitude denser than the conditions experienced by the Earth). The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (2 to 3 orders of magnitude larger than the interplanetary medium surrounding the Earth). The characterisation of the host star's wind is also crucial for the study of how the wind interacts with exoplanets. For example, we compute the exoplanetary radio emission that is released in the wind-exoplanet interaction. For the hot-Jupiters studied here, we find radio fluxes ranging from 0.02 to 0.13 mJy. These fluxes could become orders of magnitude higher when stellar eruptions impact exoplanets, increasing the potential of detecting exoplanetary radio emission.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a new instrument currently undergoing commissioning at the 3.5 m telescope of the Calar Alto Observatory. It has been constructed by a consortium of eleven Spanish and German institutions. The scientific goal of the project is a 600-night radial-velocity survey targeting 300 M dwarfs with sufficient precision to detect terrestrial planets in their habitable zones. The CARMENES instrument consists of two separate échelle spectrographs covering the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a long-term radial velocity precision of 1 m s−1. The wavelength calibration will be done with Th-Ne and U-Ne emission line lamps, and with Fabry-Pérot etalons.
We review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.