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Ice cliffs have been identified as a reason for higher ablation rates on debris-covered glaciers than are implied by the insulation effects of the debris. This study aims to improve our understanding of cliff backwasting, and the role of radiative fluxes in particular. An energy-balance model is forced with new data gathered in May and October 2013 on Lirung Glacier, Nepalese Himalaya. Observations show substantial variability in melt between cliffs, between locations on any cliff and between seasons. Using a high-resolution digital elevation model we calculate longwave fluxes incident to the cliff from surrounding terrain and include the effect of local shading on shortwave radiation. This is an advance over previous studies, that made simplified assumptions on cliff geometry and radiative fluxes. Measured melt rates varied between 3.25 and 8.6 cm d−1 in May and 0.18 and 1.34 cm d−1 in October. Model results reproduce the strong variability in space and time, suggesting considerable differences in radiative fluxes over one cliff. In October the model fails to reproduce stake readings, probably due to the lack of a refreezing component. Disregarding local topography can lead to overestimation of melt at the point scale by up to ∼9%.
Active Trypanosoma cruzi transmission persists in the Gran Chaco region, which is considered hyperendemic for Chagas disease. Understanding domestic and sylvatic transmission cycles and therefore the relationship between vectors and mammalian hosts is crucial to designing and implementing improved effective control strategies. Here we describe the species of triatomine vectors and the sylvatic mammal reservoirs of T. cruzi, in different localities of the Paraguayan and Bolivian Chaco. We identify the T. cruzi genotypes discrete typing units (DTUs) and provide a map of their geographical distribution. A total of 1044 triatomines and 138 sylvatic mammals were captured. Five per cent of the triatomines were microscopically positive for T. cruzi (55 Triatoma infestans from Paraguay and one sylvatic Triatoma guasayana from Bolivia) and 17 animals (12·3%) comprising eight of 28 (28·5%) Dasypus novemcinctus, four of 27 (14·8%) Euphractus sexcinctus, three of 64 (4·7%) Chaetophractus spp. and two of 14 (14·3%) Didelphis albiventris. The most common DTU infecting domestic triatomine bugs was TcV (64%), followed by TcVI (28%), TcII (6·5%) and TcIII (1·5%). TcIII was overwhelmingly associated with armadillo species. We confirm the primary role of T. infestans in domestic transmission, armadillo species as the principal sylvatic hosts of TcIII, and consider the potential risk of TcIII as an agent of Chagas disease in the Chaco.
Mastoid surgery carried out to treat chronic otitis media can lead to improvement in objective and subjective measures post-operatively. This study investigated the subjective change in quality of life using the Glasgow Benefit Inventory relative to the type of mastoid surgery undertaken.
A retrospective multicentre postal survey of 157 patients who underwent mastoid surgery from 2008 to 2012 was conducted.
Eighty-three questionnaire responses were received from patients who underwent surgery at one of three different hospitals (a response rate of 53 per cent). Fifty-seven per cent of patients had a Glasgow Benefit Inventory score of 0, indicating no change in quality of life post-operatively. Thirty-five per cent scored over 50, indicating significant improvement. The only significant difference found was that women fared worse after surgery than men.
The choice of mastoid surgery technique should be determined by clinical need and surgeon preference. There is no improvement in quality of life for most patients following mastoid surgery.
The gut microbiota plays an important role in the development of the immune and gastrointestinal systems of infants. In the present study, we investigated whether increased salmon consumption during pregnancy, maternal weight gain during pregnancy or mode of infant feeding alter the markers of gut immune defence and inflammation. Women (n 123) who rarely ate oily fish were randomly assigned to continue consuming their habitual diet or to consume two 150 g portions of farmed salmon per week from 20 weeks of pregnancy to delivery. Faecal samples were collected from the mothers (n 75) at 38 weeks of gestation and from their infants (n 38) on days 7, 14, 28 and 84 post-partum. Fluorescence in situ hybridisation was used to determine faecal microbiota composition and ELISA to measure faecal secretory IgA (sIgA) and calprotectin concentrations. There was no effect of salmon consumption on maternal faecal microbiota or on maternal or infant faecal sIgA and calprotectin concentrations. The degree of weight gain influenced maternal faecal microbiota, and the mode of infant feeding influenced infant faecal microbiota. Faecal samples collected from infants in the salmon group tended to have lower bacterial counts of the Atopobium cluster compared with those collected from infants in the control group (P= 0·097). This difference was significant in the formula-fed infants (P< 0·05), but not in the exclusively breast-fed infants. In conclusion, the impact of oily fish consumption during pregnancy on maternal and infant gut microbiota composition is limited, but significant differences are associated with maternal weight gain during pregnancy and mode of infant feeding.
The electronic structure of delta plutonium (δ-Pu) and plutonium compounds is investigated using photoelectron spectroscopy (PES). Results for δ-Pu show a small component of the valence electronic structure which might reasonably be associated with a 5f6 configuration. PES results for PuTe are used as an indication for the 5f6 configuration due to the presence of atomic multiplet structure. Temperature dependent PES data on δ-Pu indicate a narrow peak centered 20 meV below the Fermi energy and 100 meV wide. The first PES data for PuCoIn5 indicate a 5f electronic structure more localized than the 5fs in the closely related PuCoGa5. There is support from the PES data for a description of Pu materials with an electronic configuration of 5f5 with some admixture of 5f6 as well as a localized/delocalized 5f5 description.
Rapid thermal chemical vapor deposition (RTCVD) oxides formed using TEOS and oxygen (O2) are compared with RTCVD oxides formed using silane (SiH4) and nitrous oxide (N2O). These oxides were deposited under varying pressure and gas composition to investigate the film step coverage and electrical properties. Cross-sectional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used in determining the oxide step coverage. Excellent oxide conformality, greater than 90 %, was achieved with SiH4 and N2O over a wide range of aspect ratios. The average breakdown field obtained for the SiH4/N2O oxides is approximately 13 MV/cm, which is greater than values measured for oxides formed by conventional dry thermal process. Oxides deposited using TEOS typically have an average breakdown field of about 8 MV/cm. We conclude that the SiH4/N2O oxide process for the deposition of SiO2 films in a RTCVD reactor is a very promising candidate for sidewall spacer formation in advanced device applications.
Rapid thermal chemical vapor deposition (RTCVD) has been investigated as an alternative to low pressure chemical vapor deposition (LPCVD) for formation of sidewall spacer dielectric. Silane (SiH 4 ) and tetraethylorthosilicate (TEOS) were chosen as the silicon gas sources in these studies. Reasonable deposition rates were obtained for RTCVD oxides, oxynitrides and nitrides for use in thin sidewall spacer application. Refractive index and etch rate measurements suggest that oxides deposited with a 2 % flow rate ratio of SiH 4 /N2O and annealed at 900 °C for 10 seconds produces films with excellent structural quality. Refractive index and wet etch rate both exhibit a linear dependence with the gas flow ratio. An increase in deposition pressure decreased the refractive index while increasing the etch rate. Oxide and oxynitride dielectrics formed using SiH 4 had a much superior step coverage over a wide range of aspect ratios than TEOS dielectrics. Dit and breakdown fields for oxides and oxynitrides with 3 atomic % nitrogen were comparable to that of thermal oxide indicating their good electrical quality. The results reported suggest that RTCVD sidewall spacers are a promising candidate for use in future MOSFET devices.
Gtain boundaries and twin boundaries in commercial Cd1−xZnxTe, which is prepared by a high-pressure Bridgeman technique, have been investigated with transmission electron microscopy, scanning electron microscopy, infrared-light microscopy and visible-light microscopy. Boundaries inside these materials were found to be decorated with Te precipitates. The shape and local density of the precipitates were found to depend on the particular boundary. For precipitates that decorate grain boundaries, their microstructure was found to consist of a single, saucer-shaped grain of hexagonal Te (space group P3,2 1). Analysis of a Te precipate by selected-area diffraction revealed the Te to be aligned with the surrounding Cd1−xZnxTe grains. This alignment was found to match the (111) Cd1−xZxTe planes with the (0 111) planes of hexagonal Te. Crystallographic alignments between the Cd1−xZnxTe grains were also observed for a high-angle grain boundary. The structures of the grain boundaries and the Te/Cd1−xZnxTe interface are discussed.
Progress on mid-infrared photodetectors fabricated by the liquid phase epitaxial growth of GaInAsSb, InAsSbP, and AlGaAsSb on GaSb and InAs substrates is reported. GaInAsSb p/n and p-i-n detectors, InAsSbP p/n detectors and AlGaAsSb/GaInAsSb avalanche photodiode (APD) structures were fabricated. Preliminary results indicate that these devices can have higher detectivity with lower cooling requirements than commercially available detectors in the same wavelength range. Infrared p/n junction detectors made from GaInAsSb and InAsSbP showed cut-off wavelengths of 2.3.μm and 2.8. μm respectively. Room temperature background noiselimited detectivity (D*BLIP) of 4 × 1010 cmHz1/2/W for GaInAsSb detectors and 4 × 108 cmHz1/2/W for InAsSbP was measured. Room-temperature avalanche multiplication gain of 20 was measured on AlGaAsSb/GaInAsSb avalanche photodiodes.
Spectral ellipsometry (SE) was applied to in situ composition control of Hg1−xCdxTe grown by molecular beam epitaxy (MBE), and the impact of surface topography of the Hg1−xCdxTe layers on the accuracy of SE was investigated. Of particular importance is the presence of surface defects, such as voids in MBE- Hg1−xCdxTe layers. While dislocations do not have any significant impact on the dielectric functions, the experimental data in this work show that MBE- Hg1−xCdxTe samples having the same composition, but different void densities, have different effective dielectric functions.
We are developing modular arrays of CdZnTe radiation detectors for high-resolution nuclear medicine imaging. Each detector is delineated into a 64×64 array of pixels; the pixel pitch is 380 ptm. Each pixel is connected to a corresponding pad on a multiplexer readout circuit. The imaging system is controlled by a personal computer. We obtained images of standard nuclear medicine phantoms in which the spatial resolution of approximately 1.5 mm was limited by the collimator that was used. Significant improvements in spatial resolution should be possible with different collimator designs. These results are promising for high-resolution nuclear medicine imaging.
A CdZnTe strip detector large area array (∼ 60 cm2 with 36 detectors) with capabilities for high resolution imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. The detector array also has applications in nuclear medical imaging. Two dimensional orthogonal strip detectors with 100 gm pitch have been fabricated and tested. Details for the array design, fabrication and evaluation of the detectors will be presented.
Single crystals of ZnSe, with varying amounts of Cr doping have been studied using Raman and photoluminescence(PL) spectroscopy. The Cr-doped samples show the existence of a coupling mechanism of longitudinal optical(LO) phonons of ZnSe with hole-plasmons. The dependence of intensity ratio of LO and transverse optical(TO) mode on temperature and excitation wavelength, has been attributed to the interaction of the field of LO phonons with the surface electric field in the depletion layer. The interaction of discreet phonons with the electronic continuum of conduction band in ZnSe is responsible for the shift of Raman peaks. The large electron capture cross-section of deep-level Cr2+ and Cr1+ impurities is inhibitive for the observation of band-to-band PL transition at ∼2.7eV in ZnSe:Cr.
We have demonstrated 4-μm InAs/InGaSb/AlSb interband cascade lasers with optical output power close to 0.5 W per facet with 1-μs pulses at 1 kHz repetition rate. At 10% duty cycle, an average output power ∼20 mW was realized. External and internal quantum efficiencies exceeding 200% have been achieved at 80 K.
We report the first observations of electroluminescence (EL) and lasing in laser structures with high Al-content (x=0.64, Eg=1.474 eV) cladding layers and a narrow-gap InGaAsSb active layer (Eg=0.326 eV at T=77K). The structures are LPE-grown lattice-matched to GaSb substrate. Band energy diagrams of the laser structures had strongly asymmetric band offsets. The heterojunction between high Al-content layer and InGaAsSb narrow-gap active layer has a type II broken-gap alignment at 300K. In this laser structure spontaneous emission was obtained at λ=3.8μm at T=77K and λ=4.25 μm at T=300K. Full width at half maximum (FWHM) of emission band was 34 meV. Emission intensity decreased by a factor of 30 from T=77K to 300K. Lasing with single dominant mode was achieved at λ=3.774 μm (T=80K) in pulsed mode. Threshold current as low as 60 mA and characteristic temperature T0=26K were obtained at T=80–120K.
The optical spectra of PbTe:In,Ga samples were studied in the Far Infrared region at temperatures T=11 K–3 50K. Anomalous behavior of the temperature dependence of the plasma frequency at 65K–80K was observed for the first time. This is explained by means of a model of localized changes in the lead telluride lattice structure near impurity centers.