625 research outputs found
Multi-field DBI inflation: introducing bulk forms and revisiting the gravitational wave constraints
We study multi-field Dirac-Born-Infeld (DBI) inflation models, taking into
account the NS-NS and R-R bulk fields present in generic flux
compactifications. We compute the second-order action, which governs the
behaviour of linear cosmological perturbations, as well as the third-order
action, which can be used to calculate non-Gaussianities in these models.
Remarkably, for scalar-type perturbations, we show that the contributions due
to the various form fields exactly cancel in both the second- and third-order
actions. Primordial perturbations and their non-Gaussianities are therefore
unaffected by the presence of form fields and our previous results are
unmodified. We also study vector-type perturbations associated with the U(1)
gauge field confined on the D3-brane, and discuss whether their quantum
fluctuations can be amplified. Finally, we revisit the gravitational wave
constraints on DBI inflation and show that an ultra-violet DBI multi-field
scenario is still compatible with data, in contrast with the single field case,
provided there is a transfer from entropy into adiabatic perturbations.Comment: 22 page
Initial Investigation on the Impact of In Situ Hydrogen Plasma Exposure to the Interface Between Molecular Beam Epitaxially Grown P-Ga<sub>0.7</sub>In<sub>0.3</sub>Sb (100) and Thermal Atomic Layer Deposited (ALD) Al<sub>2</sub>O<sub>3</sub>
This work presents, to the best of the authors knowledge, the first experimental findings on the impact of in situ H<sub>2</sub> plasma exposure to the electrical properties of the interface between p-type Ga<sub>0.7</sub>In<sub>0.3</sub>Sb and atomic layer deposited Al<sub>2</sub>O<sub>3</sub>. The effects of trimethyl aluminium (TMA) exposure prior to Al<sub>2</sub>O<sub>3</sub> deposition, and of a post gate metal forming gas anneal (FGA) are also investigated. The control sample, which was subjected to an ex situ HCl clean prior to ALD only, demonstrated a capacitance modulation of 36.29 % before FGA. This degraded for samples exposed to the H<sub>2</sub> plasma for all plasma powers investigated. TMA exposure offered no improvement, and significantly increased the frequency dispersion in accumulation for all samples. A post gate metal FGA at 350 °C for 15 minutes was found to substantially improve the interface quality, with the capacitance modulation, frequency dispersion in accumulation and dC/dV improving by as much as 190 %, 91 %, and 170 % respectively
A new monolithic approach for mid-IR focal plane arrays
Antimonide-based photodetectors have recently been grown on a GaAs substrate by molecular beam epitaxy (MBE) and reported to have comparable performance to the devices grown on more expensive InSb and GaSb substrates. We demonstrated that GaAs, in addition to providing a cost saving substrate for antimonide-based semiconductor growth, can be used as a functional material to fabricate transistors and realize addressing circuits for the heterogeneously grown photodetectors. Based on co-integration of a GaAs MESFET with an InSb photodiode, we recently reported the first demonstration of a switchable and mid-IR sensible photo-pixel on a GaAs substrate that is suitable for large-scale integration into a focal plane array. In this work we report on the fabrication steps that we had to develop to deliver the integrated photo-pixel. Various highly controllable etch processes, both wet and dry etch based, were established for distinct material layers. Moreover, in order to avoid thermally-induced damage to the InSb detectors, a low temperature annealed Ohmic contact was used, and the processing temperature never exceeded 180 °C. Furthermore, since there is a considerable etch step (> 6 Όm) that metal must straddle in order to interconnect the fabricated devices, we developed an intermediate step using polyimide to provide a smoothing section between the lower MESFET and upper photodiode regions of the device. This heterogeneous technology creates great potential to realize a new type of monolithic focal plane array of addressable pixels for imaging in the medium wavelength infrared range without the need for flip-chip bonding to a CMOS readout chip
Multispectral mid-infrared light emitting diodes on a GaAs substrate
We have designed, simulated, and experimentally demonstrated four-colour mid-infrared (mid-IR) Light Emitting Diodes (LEDs) integrated monolithically into a vertical structure on a semi-insulating GaAs substrate. In order to finely control the peak wavelength of the emitted mid-IR light, quantum well (QW) structures based on AlInSb/InSb/AlInSb are employed. The completed device structure consists of three p-QW-n diodes with different well widths stacked on top of one bulk AlInSb p-i-n diode. The epitaxial layers comprising the device are designed in such a way that one contact layer is shared between two LEDs. The design of the heterostructure realising the multispectral LEDs was aided by numerical modelling, and good agreement is observed between the simulated and experimental results. Electro-Luminescence measurements, carried out at room temperature, confirm that the emission of each LED peaks at a different wavelength. Peak wavelengths of 3.40âÎŒm, 3.50âÎŒm, 3.95âÎŒm, and 4.18âÎŒm are observed in the bulk, 2ânm, 4ânm, and 6ânm quantum well LEDs, respectively. Under zero bias, Fourier Transform Infrared photo-response measurements indicate that these fabricated diodes can also be operated as mid-IR photodetectors with an extended cut-off wavelength up to 4.6âÎŒm
Australian co-operation with the national agricultural research project - Project Completion Report 1990
This Project Completion Report (PCR) has been written to meet the project monitoring requirements of AIDAB.
Because the ACNARP Project was part of a larger joint WB/IFAD project known as the National Agricultural Research Project (NARP), a summary of ACNARP and its progress and achievements, cannot be divorced from NARP. The report should therefore be read within the context that ACNARP alone has not been responsible for all the developments and achievements listed. Achievements in relation to some of the project objectives have been the result of Thai inputs, often with advice from ACNARP, rather than being able to be attributed solely to ACNARP. There were also some objectives and components of the larger WB/IFAD NARP Project, for which there were no corresponding specific ACNARP inputs
Enzymatic investigations into extra-helical and terminal structures of collagen
The presence of 0.1 - 0.2 moles of free N-terminal groups per 100.000 g. of soluble collagen was demonstrated, and it was proposed that this arises as a result of either tissue catabolism or an incomplete asking of N-terminal residues. Liberation of carbohydrate from collagen by the action of alpha-amylase, without a concomitant release of significant amounts of extra N-terminal residues, precluded the involvement of bexose as a masking factor for alpha-amino groups; although linkage of carbohydrate to E amino groups or histidine residues, is still a possibility. All of the E lysyl amino groups of collagen were demonstrated to be effectively free for substitution by the reagent 1 Fluoro 2:4 dinitrobenzene, with the reservation that one or two residues way be covalently bonded at the E amino group and so not available to F.D.H.B. The presence of free lysine in hydrolyses of D.N.P. peptides obtained by collagenase digestion of collagen, and subsequent dinitrophenyletion, was shown to be probably due to this. As more free lysine was found in analyses of material from insoluble collagen than of material from soluble collagen, it was concluded that the free lysine probably has been involved mainly in intermolecular crosslinking. Further evidence for covalently linked E-lysyl groups came from investigations on polar peptides obtained by electrophoretic separation of the collagenase-liberated peptides. It was suggested that these linkages may be involved in intermolecular crosslinking, but were not involved in intermolecular crosslinking of the type proposed by Bornstein et. Al. (1965)
Primordial fluctuations and non-Gaussianities in multi-field DBI inflation
We study Dirac-Born-Infeld (DBI) inflation models with multiple scalar
fields. We show that the adiabatic and entropy modes propagate with a common
effective sound speed and are thus amplified at the sound horizon crossing. In
the small sound speed limit, we find that the amplitude of the entropy modes is
much higher than that of the adiabatic modes. We show that this could strongly
affect the observable curvature power spectrum as well as the amplitude of
non-Gaussianities, although their shape remains as in the single-field DBI
case.Comment: 4 page
Integration techniques of pHEMTs and planar Gunn diodes on GaAs substrates
This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation (fmax). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 ÎŒm anode-to-cathode separation (LAC) presented oscillations at 87.6 GHz with maximum power of oscillation equal to -40 dBm
Design and development of information systems for the geosciences: An application to the Middle East
Publisher's version archived with permission from publisher.
http://www.gulfpetrolink.net/publication/geoarabia.htmAs our understanding grows of how the Earth functions as a complex system of myriad
interrelated mechanisms, it becomes clear that a revolutionary and novel approach is
needed to study and understand it. In order to take advantage of an ever-growing
number of observations and large data sets and to employ them efficiently in
multidisciplinary studies aimed at solving earth system science problems, we are
developing a comprehensive Solid Earth Information System (SEIS). The complex
nature of the solid earth sciences raises serious challenges for geoscientists in their
quest to understand the nature and the dynamic mechanisms at work in the planet.
SEIS forms a first step in developing a broader and more comprehensive information
system for earth system sciences designed for the needs of the geoscientists of the 21st
century. In a way, SEIS is a step towards the Digital Earth. Application of SEIS to the
complex tectonics of the Middle East shows that information systems are crucial in
multidisciplinary research studies and open new avenues in research efforts. SEIS
includes an Internet module that provides open access to anyone interested.
Researchers as well as educators and students can access this knowledge and
information system at http://atlas.geo.cornell.edu
- âŠ