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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.
Surface melt on a glacier can perturb the glaciochemical record beyond the natural variability. While the centre of the Greenland ice sheet is usually devoid of surface melt, many high-Arctic and alpine ice cores document frequent summertime melt events. Current hypotheses interpreting melt-affected ice-core chemistry rely on preferential elution of certain major ions. However, the precise nature of chemistry alteration is unknown because it is difficult to distinguish natural variability from melt effects in a perennially melt-affected site. We use eight trace-element snow chemistry records recovered from Summit, Greenland, to study spatial variability and melt effects on insoluble trace chemistry and physical stratigraphy due to artificially introduced meltwater. Differences between non-melt and melt-affected chemistry were significantly greater than the spatial variability in chemistry represented by nearest-neighbour pairs. Melt-perturbed trace elements, particularly rare earth elements, retained their seasonal stratigraphies, suggesting that trace elements may serve as robust chemical indicators for annual layers even in melt-affected study areas. Results suggest trace-element transport via meltwater percolation will deposit eluted material down-pit in refrozen areas below the nearest-surface chemistry peak. In our experiments, snow chemistry analyses are more sensitive to melt perturbations than density changes or unprocessed near-infrared digital imagery.
Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.
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.
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.
Started its regular, daily operational phase in 2011, by the occasion of the Symp264 in the XXVII IAU GA at Rio de Janeiro, the results so far obtained show that the Heliometer of the Observatorio Nacional fulfilled its planed performance of single measurement to the level of few tens of milli-arcsecond, freely pivoting around the heliolatitudes without systematic deviations or error enhancement. We present and discuss the astrometric additions required on ground based astronomic programs. We also discuss instrumental and observations terms, namely the constancy of the basic heliometric angle, against which the measurements are made, and the independence to meteorological and pointing conditions.
Submicron thick niobate films, Na0.5K0.5NbO3 (NKN) and Ag0.9Ta0.42Nb0.58O3-δ (ATN), have been pulsed laser deposited on MgO, Pt80Ir20, and Si substrates for microwave device applications. Strong bi-axial (001)-(011) texture observed in both films on MgO substrates indicates that there are major similarities in the growth mechanisms in these films. The dielectric permittivity ε′ of NKN film increases monotonously with temperature, while that of ATN shows a weak temperature dependence (about 21% of variation) in a wide temperature range from 77 K to 400 K. Measured tunability Δε′/ε′ and dielectric loss tanδ for niobate/MgO interdigital capacitors have been found to be (Δε′/ε′)NKN = 40%, tanδNKN = 1.4-2.3% and (Δε′/ε′)ATN = 4.3%, tanδATN = 0.23-0.25% at 1 MHz under maximum electric field of 100 kV/cm. Microwave spectroscopy studies for NKN/Si varactors show (Δε′/ε′)NKN/Si of 13% and tanδNKN/Si = 1.2-6.6% at 40 GHz @ 200 kV/cm.
We have studied the growth of magnesium oxide using ion-beam assisted deposition (IBAD) to achieve (100) oriented, bi-axially textured films with low mosaic spread, for film thicknesses of 10 nm on silicon substrates. We have refined the process by using reflected high-energy electron diffraction (RHEED) to monitor the growth of IBAD MgO films and found that the diffracted intensity can be used to determine (and ultimately control) final in-plane texture of the film. Here we present results on our work to develop the use of real-time RHEED monitoring to deposit well-oriented IBAD MgO films. The results have been corroborated with extensive grazing-incidence X-ray diffraction (GID). Results of these analyses have allowed us to deposit films on metallic substrates with in-plane mosaic spread less than 7°.
We have used a low temperature magnetic imaging system to determine current pathways in 5 cm long “good” and “bad” regions of a 1-cm-wide YBa2Cu3O7-δ coated conductor. The good and bad regions were identified with 4 point probe measurements taken at 1 cm intervals along the tape length. The current density map from the good region showed the expected edge peaked structure, similar to that seen in previous work on high quality test samples grown on single crystal substrates. The structure was also consistent with theoretical understanding of thin film superconductors where demagnetizing effects are strong. The maps from the bad region showed that the current was primarily confined to the right half of the sample. The left half carried only a small current that reached saturation quickly. Effectively halving the sample width quantitatively explains the critical current measured in that section. Spatially resolved x-ray analysis with 1 mm resolution was used to further characterize the bad section and suggested an abnormally large amount of a-axis YBCO present. This may be the result of non-uniform heating leading to a low deposition temperature in that area.
Epitaxially grown oxides of both SrTiO3 (STO) and YBa2Cu3O7-δ (YBCO) have been removed from their growth substrate and transferred for integration into other circuits (microwave devices) and onto other substrate material (glass). The enabling element in the separation process is the high selectivity of etching between YBCO and other oxide materials. Thus, a thin layer of YBCO is used as the sacrificial layer in the structure, allowing rapid etchant ingress under the device structures and separation from the growth substrate. Initial demonstrations of microwave device tuning using a lifted-off STO layer is detailed.
The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (CMR) is investigated by comparing the physical properties of magnetoresistive manganites and cobaltites. The samples studied in this work include epitaxial films and ceramics of manganites with both A- and B-site substitution, (La0.7Ca0.3MnO3, LaMn0.7 Ni0.3O3, LaMnO.5Ni0.5O3), as well as epitaxial films and ceramics of cobaltites (La0.5Ca0.5CoO3). The structural, chemical, electrical transport, magnetic, optical properties and tunneling spectroscopy are studied. Based on our experimental results, we conclude that both double-exchange interaction and strong electron-phonon coupling due to the Jahn-Teller effect are essential to the occurrence of CMR.
Spinel Fe3O4 contains two sites for iron: tetrahedrally coordinated sites containing Fe3+ ions and octahedrally coordinated sites containing a mixture of Fe2+ and Fe3+ ions. Scanning tunneling microscopy performed on the (001) surface of Fe3O4, grown epitaxially on MgO, shows localized charge density at the tetrahedral sites. The images show that the p(1×1) surface reconstruction (also observed during molecular beam epitaxy of Fe3O4) is produced by a displacement of the two tetrahedrally coordinated Fe ions on the unit cell surface from their bulk positions toward each other. The octahedral Fe ions are imaged as extended rows of charge density, with no resolution of atom-size features along the rows. This slight corrugation of electron charge density along the octahedral sites is consistent with the original conjectures explaining the high electrical conductivity in bulk Fe3O4: electrons move by hopping between the Fe3+ and Fe2+ atoms along the octahedral rows of Fe ions.
The recent experimental results obtained for c-axis oriented YBaCuO thin films deposited at the optimized conditions for the microwave applications are presented and discussed. The emphasis is on the study of the relationship between oxygen profiles, crystallographic structure and electrical and physical properties of the films formed in situ at the same and optimized conditions of sample deposition and further submitted to the different conditions of sample cooling. The studies of the oxygen depth concentration profiles and of the oxygen contents are carried out using the recently developed Nuclear Reaction Analysis (NRA). These results are correlated, on one hand, with the measurements of the atomic composition and structure by RBS, XRD and TEM and, on the other hand, by the measurements of the electrical and physical properties Tc, Jc and microwave surface resistance Rs. All results are consistent with the idea that the fully oxygenated films are formed during in situ growth at T∼ 700°C. For T< 300°C, the oxygen interface transfer coefficient is very small and the oxygen content is practically preserved. However a large room temperature oxidation (corrosion like) takes place in the presence of water vapor. The fundamental and applied consequences of these findings for the mechanism of thin films growth and for the properties of the films in the presence of cathodic plasma or laser plume are analysed.
The structure of epitaxial BaTiO3 thin films prepared by hydrothermal synthesis on (001) SrTiO3 substrates was studied by transmission electron microscopy (TEM). The growth evolution was followed from initial island formation, through island impingement and fusion. Plan view and cross-section imaging demonstrated that the films grew by an unusual islanding mechanism. Electron diffraction showed the islands and the fully formed film are single crystal with mosaic character and in all cases strain relaxed. Cross-section TEM of the early growth films showed a several monolayer thick interfacial layer and the film/substrate region had no misfit dislocations. In the fully formed films, this interfacial layer was not observed, however a clear misfit dislocation network was observed. Defects analysis shows that the misfit dislocations have pure edge character with <100> Une directions, and <010> Burgers vectors (parallel to the film/substrate interface).
We introduce a new annealing procedure to prepare well defined surfaces of SrTiO3 single crystal and bicrystal substrates. Annealing SrTiO3 (001) substrates in oxygen and then in ultra high vacuum produces a uniformly TiO2-terminated, atomically flat and ordered SrTiO3 (001) surfaces, as revealed by Auger electron spectroscopy, low energy electron diffraction, and high resolution scanning tunneling microscopy. Applying this annealing procedure to slightly off-cut (∼1.2°) SrTiO3 (001) surfaces has a strong influence on the resulting step structure. Particular annealing procedures can be used to tailor the structure and morphology of the surface and of bicrystal boundaries down to the atomic level. For example, steps of SrTiO3 (001) surfaces can be adjusted to a height of one, two, or multiple times the unit-cell size of STO (aSTO=0.3905 nm). Atomically flat SrTiO3 (001) substrates were used for deposition of SmBa2Cu3O7-δ (SBCO) thin films. The thickness (in a range from 10 nm to 200 nm) dependency of the surface morphology of SmBa2Cu3O7-δ films was investigated with UHV-STM. No spiral growth was observed. Surfaces of all films exhibit stacks of flat terraces which are frequently separated by steps, smaller than the c-axis length cSBCO of SBCO (cSBCO=1.17 nm).
We have investigated the structural and compositional changes that are induced by the segregation of substrate Mg to the surface of 1μm-thick Fe3O4 films on MgO(001). The thin films have been grown with plasma-assisted MBE, and characterization with RHEED (reflection high-energy electron diffraction), x-ray diffraction (XRD), and Superconducting Quantum Interference Device (SQUID) magnetometry show slightly strained, single-crystalline Fe3O4 films. For the surface studies, we have combined Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). Initial and final surface characterization employed X-ray Photoelectron Spectroscopy (XPS) and Ion Scattering Spec-troscopy (ISS) respectively. The surfaces of the MBE-grown samples are flat and show a (√2 × √2)R45° reconstruction with respect to the Fe3O4 surface unit cell. We observe the onset of Mg segregation to the surface at around 700 K, with long, narrow extensions of terraces being observed growing along the  and  directions. Upon prolonged heating at 800 K, massive Mg segregation to the surface is observed. Heating in an oxygen atmosphere induces a 1×4 surface reconstruction, and results in extremely long (≈ 1000 Å), wide terraces.
The relationship between structural distortions and resistivity in pulsed laser deposited La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3MnO3 (LSMO) thin films was investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and resistivity measurements. The growth defects inherent to annealed films were characterized, and then additional defects were introduced by radiation damage. Epitaxially grown films on (100) LaA1O3 substrates exhibited three primary types of growth defects: interface strain, column boundary mismatch, and column rotation. High resolution TEM measurements show well-ordered regions of film that offer low resistance paths for current flow around growth defects. A series of annealed samples were irradiated with 6 Mev Si+3 ions to produce 0.006 to 0.024 displacements per atom (dpa) in LCMO films, and 0.028 to 0.14 dpa in LSMO films. The peak resistance temperature (Tp) was found to depend strongly on defect concentration, varying from 235K ± 15K for the unirradiated LCMO films to 95K for 0.018 dpa. At 0.024 dpa, the LCMO film was insulating at all temperatures. LSMO films showed a downward shift in Tp from 300K for an unirradiated film to 250K for 0.028 dpa, and complete insulating behavior for 0.14 dpa.
Epitaxial PbTiO3 and Bi4Ti3O12 thin films have been grown on (100) SrTiO3 and (100) LaAlO3 substrates by reactive molecular beam epitaxy (MBE). Titanium is supplied to the film in the form of shuttered bursts each containing a one monolayer dose of titanium atoms for the growth of PbTi03 and three monolayers for the growth of Bi4Ti3O12. Lead, bismuth, and ozone are continuously supplied to the surface of the depositing film. Growth of phase pure, c-axis oriented epitaxial films with bulk lattice constants is achieved using an overpressure of these volatile species. With the proper choice of substrate temperature (600 – 650 °C) and ozone background pressure (PO3 = 2×10−5 Torr), the excess of the volatile metals and ozone desorb from the surface of the depositing film leaving a phase-pure stoichiometric crystal. The smooth PbTiO3 surface morphology revealed by atomic force microscopy (AFM) suggests that the PbTiO3 films grow in a layer-by-layer fashion. In contrast the Bi4Ti3O12 films contain islands which evolve either continuously or around screw dislocations via a spiral-type growth mechanism.