Epitaxial gallium arsenide wafers

The preparation of GaAs epitaxial layers by a vapor transport process using AsCl3, Ga and H2 was pursued to provide epitaxial wafers suitable for the fabrication of transferred electron oscillators and amplifiers operating in the subcritical region. Both n-n(+) structures, and n(++)-n-n(+) sandwich structures were grown using n(+) (Si-doped) GaAs substrates. Process variables such as the input AsCl3 concentration, gallium temperature, and substrate temperature and temperature gradient and their effects on properties are presented and discussed

Studies on microfungi from litter and soil in relation to the ecology of lignin decomposition

The studies reported here on microfungi from litter and soil involved: 1) The behaviour of microfungi in pure culture towards lignin related-phenolic acids. 2) The chemistry and microbiology of Scots Pine litter in relation to lignin decomposition. 3) The decomposition of ferulic acid by mixed populations of microorganisms. Ferulic acid incorporated into agar could be inhibitory or stimulatory to the spore germination and germ hyphal growth of microfungi depending upon its concentration and the fungal species. Within a certain concentration range, the total growth potential of some Angiosperm leaf saprophytes was depressed relative to control whereas there was an increase in the case of conifer needle litter saprophytes and some common soil fungi. Other phenolic acids produced similar patterns of results but the differential effects were generally less marked. The ability of litter and soil microfungi to utilise ferulic acid as a sole carbon source was defined from the decomposition of the substrate after inoculating culture solution with spores. The pattern in the ability to decompose ferulic acid was not related to the effects of this compound on germination on agar or in the liquid medium. Dothichiza pityophila and Fusicoccum bacillare were isolated as the principal primary saprophytes of Scots Pine needle litter while the widespread primary saprophytes of Angiosperm leaf litters, including Aureobasidium pullulans were absent, confirming and reinforcing the results of previous European work. The use of Infra-red spectroscopy of finely divided, but unextracted, Pine needles and humus to follow the course of the decomposition of the litter permitted an evaluation of the role of soil-inhabiting fungi in this process. Burial of litter needles in a deciduous woodland soil or in a field soil led to colonisation by several soil fungi not characteristic of Pine litter, notably Gliocladium roseum and an Actinomycete of genus Nocardia. These two species were able to colonise the needle interior in the presence of needle saprophytes surviving in buried needles whereas Trichoderma viride remained restricted to the needle surface by prior- colonisation. Finally, experiments are described in which Pine needle and soil material from the burial experiments and samples of two other soils of contrasting ligninolytic characteristics were used as inoculum for the decomposition of ferulic acid, the results of these experiments relating to known microbiological and chemical properties of the soils. The importance of phenolic acids released during lignin decomposition in the fungal colonisation of substrates in litter and soil is discussed, and some conclusions are made regarding the validity of phenolic acids as 'lignin model compounds'

A new nickel-base wrought superalloy for applications up to 1033 K (1400 F)

Alloy was melted from high purity raw materials and cast ingots extruded at 1422 K. Material was hot rolled to 0.013 m diameter bar stock. Partial solution heat-treatment followed by aging produced structure of fine gamma prime precipitate reinforcing gamma matrix containing coarser blocky gamma prime particles. Alloy can be processed by powder metallurgy

High-temperature optically activated GaAs power switching for aircraft digital electronic control

Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas

Molecular clouds in the centers of galaxies: Constraints from HCN and CO-13 line emission

We have searched for HCN J=1-0 line emission in the centers of 12 galaxies and have detected it in 10 of them. We have obtained complementary data on J=1-0 and 2-1 transitions of CO-12 and CO-13 in these systems. The ratio of integrated intensities, I(CO 1-0)/I(HCN 1-0) = 25 +/- 11 for this sample. We find that HCN emission of this strength can be produced under conditions of subthermal excitation. In combination with the line ratios in CO and CO-13, HCN puts constraints on the mean conditions of molecular clouds and on the mix of cloud types within the projected beam

Influence of temperature dependent inelastic scattering on the superconducting proximity effect

We have measured the differential resistance of mesoscopic gold wires of different lengths connected to an aluminum superconductor as a function of temperature and voltage. Our experimental results differ substantially from theoretical predictions which assume an infinite temperature independent gap in the superconductor. In addition to taking into account the temperature dependence of the gap, we must also introduce a temperature dependent inelastic scattering length in order to fit our data

Tunneling Anomaly in Superconductor above Paramagnetic Limit

We study the tunneling density of states (DoS) in the superconducting systems driven by Zeeman splitting E_Z into the paramagnetic phase. We show that, even though the BCS gap disappears, superconducting fluctuations cause a strong DoS singularity in the vicinity of energies -E^* for electrons polarized along the magnetic field and E^* for the opposite polarization. The position of the singularity E^*=(1/2) (E_Z + \sqrt{E_Z^2- \Delta^2}) (where \Delta is BCS gap at E_Z=0) is universal. We found analytically the shape of the DoS for different dimensionality of the system. For ultrasmall grains the singularity has the form of the hard gap, while in higher dimensions it appears as a significant though finite dip. Our results are consistent with recent experiments in superconducting films.Comment: 4 pages, 2 .eps figures include

New nickel-base wrought superalloy with applications up to 1253 K (1800 F)

Alloy possesses combination of high tensile strength at low and intermediate temperatures to 1033 K with good rupture strength at high temperatures to 1255 K. Alloy has promise for turbine disk application in future gas turbine engines and for wrought integrally bladed turbine wheel; thickness and weight of disk portion of wheel could be reduced

Patient-reported outcome assessment of inflammatory arthritis patient experience with intravenously administered biologic therapy

Objective: To evaluate patient perspectives regarding utilization of intravenous (IV) therapy for inflammatory arthritis (IA). Methods: This was a single-center, non-interventional, patient questionnaire-based study of adult IA patients currently receiving IV biologics. At a single visit, patients completed the questionnaire comprising 30 questions centered on their experience receiving an intravenously administered therapy to treat their IA. The questionnaire included questions on patient demographics, disease characteristics, and previous biologic treatment for IA (subcutaneous [SC] and IV). Patients rated their level of agreement with statements regarding satisfaction with current IV biologic therapy and potential advantages and disadvantages of IV biologic therapy using a 5-point Likert scale (1= strongly disagree, 5= strongly agree). Results: One hundred patients were enrolled and completed the survey; 66% were female and the mean age was 58 years. Before IV treatment, 97% of patients received information regarding therapy options. Ninety patients ranked their satisfaction with current IV therapy as 4 or 5. The proportion of patients with an “extremely favorable” perception of IV therapy increased from 33% to 71% following initiation of their current medication. Thirty-one patients had previously received SC therapies to treat their IA. Conclusion: These results demonstrated an overall favorable perception of IV therapy among this patient population. Patients previously treated with SC therapy also had a positive shift in the perception of IV therapy after initiating IV therapy. Patients’ perception and preference for treatment options should be highly considered by the treating physician during or as part of a shared decision-making process. © 2017 Gaylis et al