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Patterns in radar-detected internal layers in glaciers and ice streams can be tracked hundreds of kilometers downstream. We use distinctive patterns to delineate flowbands of Thwaites Glacier in the Amundsen Sea sector of West Antarctica. Flowbands contain information for the past century to millennium, the approximate time for ice to flow through the study region. GPS-detected flow directions (acquired in 2007/08) agree within uncertainty (~4°) with the radar-detected flowlines, indicating that the flow direction has not changed significantly in recent centuries. In contrast, InSAR-detected directions (from 1996) differ from the radar- and GPS-detected flowlines in all but the middle tributary, indicating caution is needed when using InSAR velocities to define flow directions. There is agreement between all three datasets in the middle tributary. We use two radar-detected flowlines to define a 95 km long flowband and perform a flux balance analysis using InSAR-derived velocities, radar-detected ice thickness, and estimates of the accumulation rate. Inferred thinning of 0.49 ± 0.34 m a–1 is consistent with satellite altimetry measurements, but has higher uncertainty due mainly to the velocity uncertainty. The uncertainty is underestimated because InSAR velocities often differ from GPS velocities by more than the stated uncertainties.
Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.
Southern range extensions of the tropical Australian heterobranch sea slug fauna may be symptomatic of climate change, particularly in south-eastern Australia, a recognized climate change hot-spot. In the Solitary Islands Marine Park, northern New South Wales, the presence of biogeographic mixing means that the southern coastal distribution limit of several tropical marine species and the northern limit of some temperate species overlap. During a year-long series of monthly surveys of sea slug communities on intertidal rocky shores, we observed four species beyond their previously recorded range – Colpodaspis thompsoni, Elysia pusilla, Phidiana bourailli and Herviella claror. The southern migration of species is an anticipated response to warming seas and we note an apparent extension of the southern limit for these taxa.
It has long been recognised that the Neolithic spread across Europe via two separate routes, one along the Mediterranean coasts, the other following the axis of the major rivers. But did these two streams have a common point of origin in south-west Asia, at least with regard to the principal plant and animals species that were involved? This study of barley DNA shows that the domesticated barley grown in Neolithic Europe falls into three separate types (groups A, B and C), each of which may have had a separate centre of origin in south-west Asia. Barley was relatively rarely cultivated by the early Linearbandkeramik farmers of Central and Northern Europe, but became more common during the fifth and fourth millennia BC. The analysis reported here indicates that a genetic variety of barley more suitable for northern growing conditions was introduced from south-west Asia at this period. It also suggests that the barley grown in south-eastern Europe at the very beginning of the Neolithic may have arrived there by different routes from two separate centres of domestication in south-west Asia. The multiple domestications that this pattern reveals imply that domestication may have been more a co-evolutionary process between plants and people than an intentional human action.
We have determined the influence of the severity of retinopathy of prematurity (ROP) on development at 3 years of age in infants <29 weeks gestation from a population-based cohort. Primary analysis of surviving infants born <29 weeks gestational age (GA) from 1998 to 2001 in New South Wales and the Australian Capital Territory were grouped according to stage of ROP. Infants with periventricular leukomalacia, Grade III or IV intraventricular haemorrhage, hydrocephalus, major congenital abnormalities, Stage 4 or 5 ROP, cerebral palsy or a severe hearing impairment were excluded. Infants with Stage 3 ROP were matched for GA, birthweight and gender to those with no ROP, Stage 1 and Stage 2 ROP. The four groups were then compared for their 3-year-old developmental outcome, using the Griffiths Mental Development Scale. Development was also compared for those infants with Stage 3 ROP who were either treated or not treated with laser therapy. A secondary multivariate regression analysis on developmental outcome was performed with all infants included in the analysis. In neurologically comparable groups and in the multivariate analysis, there was no association between ROP and developmental outcome. There was also no difference in the Griffiths assessment at 3 years between those who were or were not treated for severe ROP. Neither severity of ROP nor treatment for severe ROP were related to developmental outcome at 3 years of age in a large population-based cohort of infants born <29 weeks gestation.
The latest deep ultra-violet (DUV) photomask technology requires macroscopic properties such as optical transmission, reflectance, and chemical reactivity to be precisely controlled. Therefore, a fundamental understanding of the relationship between atomic bonding and nanometer scale property variation is required. Thin films of Cr-OC-N are compositionally graded to produce specific attenuation and phase shift of optical radiation. A combination of techniques was used to relate the local atomic bonding to macroscopic properties. Sputtered neutral mass spectroscopy was used to resolve local composition, and variable angle spectroscopic ellipsometry was used to determine local optical properties (on nm scale) that are then related to local composition. Core level shifts in X-ray photoelectron spectroscopy characterize changes in the Cr environment associated with changes in composition. A model is suggested in which bonding at the atomic level is controlled within different 10-100 nm sized regions which can be combined to produce arbitrary optical properties.
Majority carrier transport measurements were made across the potential barriers at (100) twist boundaries in silicon. The bicrystals were prepared by hot-pressing single crystals of lightly doped float-zone material, under ultra-high vacuum conditions. The current - voltage measurements were analyzed using combined drift-diffusion and thermionic emission transport mechanisms, and incorporating some inhomogeneity in the charge distribution at the boundary. Evidence has been found for a small, Nd = 3 × 1010 cm−2, density of mono-energetic defect states near midgap, in bicrystals characterized by a variety of misorientation angles. This density is too small to result from the intrinsic structure of the boundary. In addition, no dependence was found on misorientation angle.
We demonstrate that non-normal incidence ion bombardment applied during thin film growth has a pronounced alignment effect on crystallographic orientation. Restricted fiber texture is achieved in Nb films deposited at room temperature onto amorphous silica substrates with simultaneous 200 eV Ar+ ion bombardment at 20 degrees from glancing angle. Xray pole figure measurements and transmission electron diffraction show that the alignment direction is a channeling direction for the incident ions between (110) planes. The degree of alignment increases linearly with the fraction resputtered by the ion beam. Recommendations are given for optimizing this ion beam orientation effect.
It is well established from studies of bicrystals that the properties of a grain boundary depend on the atomic structure of the boundary. However, constitutive relations for the properties of polycrystalline materials do not currently take into account this boundary-toboundary variability. Instead, such relations depend on a single length scale, typically the average grain diameter. We extend the traditional viewpoint by proposing that boundaries may be divided into two distinct categories, depending on their misorientation angle. The relevant length scale in constitutive relations for polycrystals is then the average cluster size, where clusters consist of grains connected by boundaries in the same misorientation category. A brief discussion of this additional length scale and how it may be reflected in various constitutive relations for physical and mechanical properties of polycrystals is given.
A preliminary survey of the dislocation structures of grain boundaries in Bridgman grownpolycrystalline GaAs suggests that many of the phenomena observed in grain boundaries inface centered cubic metals, silicon and germanium also occur in boundaries of a polar semiconductor. Our experiments show that low angle grain boundaries are comprised of crystal lattice dislocations and deviations from coincidence orientations are accommodated bysecondary dislocations; specifically, in twins, the a-fringe technique reveals that there are multiple structures where the different domains are separated by partial grain boundary dislocations.
The feasibility of studying dynamical changes in nickel thin films on ion-implanted silicon thin films by cross-sectional transmission electron microscopy (XTEM) with intermittent annealings in N2 ambient up to 850 °C is demonstrated. Interactions of nickel thin films with oxidation induced stacking faults, fluorine bubbles and process-induced defects in ion implanted silicon are provided as examples. The technique may be applied to clarify a number of important issues encountered in the study of the reactions and diffusion of thin films and obtain informations otherwise unattainable.
The structure of the Au segregated Ni(110)-0.8%Au surface has been studied by scanning tunneling microscopy. The segregated Au layer forms a (7×4) structure with a c(2×4) subunit. At various coverages of Au overlayer, commensurate and incommensurate Au structures were observed. At a coverage of I monolayer, islands and facets assciated with incommensurate Au atoms were observed.
Electron scattering and diffraction in X-ray photoemission spectroscopy (XPS) have been used to characterize GaAs(001) and InP(001) chemically etched surfaces. 6a(3d),As(3d), In(4d) and P(2p) photoelectrons have been observed as a function of polar angles for the two [1–10] and  azimuths For kinetic energy range of these photoelectrons the experimental results have been correctly predicted by the single-scattering cluster model with spherical-wave corrections.
The problems of quantitative measurements in XPS have been discussed in relation with the diffraction phenomena.
Silicon vapor phase epitaxial growth with SiH2Cl2 is theoretically studied. The optimized geometries and total energigs of the species, generated from SiH2Cl2, are calculated by using ab initio molecular orbital method. As the intgraction between silicon surface and SiCl2 the charge transfer is considered. Based on the computational result that SiCl2 - has the lower total energy than SiCl2, a new adsorption mechanism, named, charge transfer adsorption, is p~oposed. By using this charge transfer adsorption followed by the surface reaction at the hollow bridge site, the epitaxial growths on the silicon (001), (111), and (110) surfaces are discussed.
The epitaxy of CaF2 on Si(111) is characterized on an atomic scale using various photoelectron spectroscopy techniques. We find both F and Ca bonding to Si with Ca forming most of the interface bonds. The bonding orbital is found at 1.5 eV below the valence band maximum of Si. It consists of the Si3p-like dangling bond orbital and the 4s electron of Ca1+. Ca has changed its oxidation state at the interface from Ca2+ to Ca1+, which is demonstrated by the multiplet structure of the Ca 2p absorption edge. The electronic properties of the CaF2 interface layer are altered dramatically relative to bulk material, with the band gap shrinking from 12 eV to about 2 eV. Such strong effects raise prospects for creating new materials in the vicinity of an interface.
High resolution electron microscope studies were undertaken of the epitaxy and oxidation of thin layers (<30Å) of vapor deposited Cu on single crystal Au films. The metal/metal and oxide/metal orientation relationships were analyzed for both the diffraction and imaging modes, before and after the Cu oxidation was significant. For the oxide overlayers two cases were studied: (111) Cu which transforms into three (110) variants of Cu2O, each rotated by 120° and (110) Cu transforming to a layered (211) oxide overgrowth. A lateral displacement of the surface top layer of Cu atoms was found for the (110) orientation of Cu2O. The (211) orientation of Cu2O had two structural variants of surface ordering rotated by 90° relative to the underlying metal. One of these cases directly exhibits a 3.01Å × 7.39Å supercell structure characteristic of a 0.58Å atomic step height of the (211) planar layers perpendicular to the surface.
The bonding at the interface between CaF2 and Si(111) has been investigated using core-level photoemission spectroscopy. The results are discussed in terms of various structural models of the interface. The stable interface has a depletion of fluorine from the interface resulting in strong Si - Ca bonding.
The initial stage of Ge overgrowth on CaF2/Si structures was controlled by electron beam (e-beam) exposure through a room-temperature-deposited thin Ge layer on CaF2. It was found that the island growth of Ge was prevented in the e-beam exposed region and the crystalline quality and the surface flat-ness of the Ge film were much improved. From several experimental results, a growth model that e-beam dissociates the surface F atoms of CaF2 and improves the wettability between Ge and CaF2 is proposed.