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Search Results: 1 - 10 of 352638 matches for " P. D. Buckle "
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A Surface-Gated InSb Quantum Well Single Electron Transistor
J. M. S. Orr,P. D. Buckle,M. Fearn,C. J. Storey,L. Buckle,T. Ashley
Physics , 2007, DOI: 10.1088/1367-2630/9/8/261
Abstract: Single electron charging effects in a surface-gated InSb/AlInSb QW structure are reported. This material, due to its large g-factor and light effective mass, offers considerable advantages over more commonly used materials, such as GaAs, for quantum information processing devices. However, differences in material and device technology result in significant processing challenges. Simple Coulomb blockade and quantised confinement models are considered to explain the observation of conductance oscillations in these structures. The charging energy is found to be comparable with the energy spectrum for single particle states.
High field magneto-transport in high mobility gated InSb/InAlSb quantum well heterostructures
A. M. Gilbertson,W. R. Branford,M. Fearn,L. Buckle,P. D. Buckle,T. Ashley,L. F. Cohen
Physics , 2009, DOI: 10.1103/PhysRevB.79.235333
Abstract: We present high field magneto-transport data from a range of 30nm wide InSb/InAlSb quantum wells. The low temperature carrier mobility of the samples studied ranged from 18.4 to 39.5 m2V-1s-1 with carrier densities between 1.5x1015 and 3.28x1015 m-2. Room temperature mobilities are reported in excess of 6 m2V-1s-1. It is found that the Landau level broadening decreases with carrier density and beating patterns are observed in the magnetoresistance with non-zero node amplitudes in samples with the narrowest broadening despite the presence of a large g-factor. The beating is attributed to Rashba splitting phenomenon and Rashba coupling parameters are extracted from the difference in spin populations for a range of samples and gate biases. The influence of Landau level broadening and spin-dependent scattering rates on the observation of beating in the Shubnikov-de Haas oscillations is investigated by simulations of the magnetoconductance. Data with non-zero beat node amplitudes are accompanied by asymmetric peaks in the Fourier transform, which are successfully reproduced by introducing a spin-dependent broadening in the simulations. It is found that the low-energy (majority) spin up state suffers more scattering than the high-energy (minority) spin down state and that the absence of beating patterns in the majority of (lower density) samples can be attributed to the same effect when the magnitude of the level broadening is large.
Molecular line contamination in the SCUBA-2 450 μm and 850 μm continuum data
E. Drabek,J. Hatchell,P. Friberg,J. Richer,S. Graves,J. V. Buckle,D. Nutter,D. Johnstone,J. Di Francesco
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21140.x
Abstract: Observations of the dust emission using millimetre/submillimetre bolometer arrays can be contaminated by molecular line flux, such as flux from 12CO. As the brightest molecular line in the submillimetre, it is important to quantify the contribution of CO flux to the dust continuum bands. Conversion factors were used to convert molecular line integrated intensities to flux detected by bolometer arrays in mJy per beam. These factors were calculated for 12CO line integrated intensities to the SCUBA-2 850 {\mu}m and 450 {\mu}m bands. The conversion factors were then applied to HARP 12CO 3-2 maps of NGC 1333 in the Perseus complex and NGC 2071 and NGC 2024 in the Orion B molecular cloud complex to quantify the respective 12CO flux contribution to the 850 {\mu}m dust continuum emission. Sources with high molecular line contamination were analysed in further detail for molecular outflows and heating by nearby stars to determine the cause of the 12CO contribution. The majority of sources had a 12CO 3-2 flux contribution under 20 per cent. However, in regions of molecular outflows, the 12CO can dominate the source dust continuum (up to 79 per cent contamination) with 12CO fluxes reaching \sim 68 mJy per beam.
Zero-field spin-splitting and spin lifetime in n-InSb/In1-xAlxSb asymmetric quantum well heterostructures
A. M. Gilbertson,M. Fearn,J. H. Jefferson,B. N. Murdin,P. D. Buckle,L. F. Cohen
Physics , 2008, DOI: 10.1103/PhysRevB.77.165335
Abstract: The spin-orbit (SO) coupling parameters for lowest conduction subband due to structural (SIA) and bulk (BIA) inversion asymmetry are calculated for a range of carrier densities in [001]-grown delta-doped n-type InSb/In1-xAlxSb asymmetric quantum wells using the established 8 band k.p formalism [PRB 59,8 R5312 (1999)]. We present calculations for conditions of zero bias at 10 K. It is shown that both the SIA and BIA parameters scale approximately linearly with carrier density, and exhibit a marked dependence on well width when alloy composition is adjusted to allow maximum upper barrier height for a given well width. In contrast to other material systems the BIA contribution to spin splitting is found to be of significant and comparable value to the SIA mechanism in these structures. We calculate the spin lifetime for spins oriented along [11-0] based on D'yakonov-Perel mechanism using both the theory of Averkiev et al. [J. Phys.:Condens. Matter 14 (2002)] and also the rate of precession of spins about the effective magnetic field, taking into account all three SO couplings, showing good agreement.Spin lifeime for this direction is largest in the narrow wells over the range of moderate carrier densities considered, which is attributed to the reduced magnitude of the k-cubic BIA parameter in narrow wells. The inherently large BIA induced SO coupling in these systems is shown to have considerable effect on the spin lifetime, which exhibits significant reduction in the maximum spin lifetime compared to previous studies which consider systems with relatively weak BIA induced SO coupling. The relaxation rate of spins oriented in the [001] direction is dominated by the k-linear SIA and BIA coupling parameters and at least an order of magnitude greater than in the [11-0] direction.
Room temperature ballistic transport in InSb quantum well nanodevices
A. M. Gilbertson,A. Kormanyos,P. D. Buckle,M. Fearn,T. Ashley,C. J. Lambert,S. A. Solin,L. F. Cohen
Physics , 2011, DOI: 10.1063/1.3668107
Abstract: We report the room temperature observation of significant ballistic electron transport in shallow etched four-terminal mesoscopic devices fabricated on an InSb/AlInSb quantum well (QW) heterostructure with a crucial partitioned growth-buffer scheme. Ballistic electron transport is evidenced by a negative bend resistance signature which is quite clearly observed at 295 K and at current densities in excess of 10$^{6}$ A/cm$^{2}$. This demonstrates unequivocally that by using effective growth and processing strategies, room temperature ballistic effects can be exploited in InSb/AlInSb QWs at practical device dimensions.
Characterisation of Peptide Microarrays for Studying Antibody-Antigen Binding Using Surface Plasmon Resonance Imagery
Claude Nogues,Hervé Leh,Christopher G. Langendorf,Ruby H. P. Law,Ashley M. Buckle,Malcolm Buckle
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012152
Abstract: Non-specific binding to biosensor surfaces is a major obstacle to quantitative analysis of selective retention of analytes at immobilized target molecules. Although a range of chemical antifouling monolayers has been developed to address this problem, many macromolecular interactions still remain refractory to analysis due to the prevalent high degree of non-specific binding. We describe how we use the dynamic process of the formation of self assembling monolayers and optimise physical and chemical properties thus reducing considerably non-specific binding and allowing analysis of specific binding of analytes to immobilized target molecules.
Radio continuum observations of Class I protostellar disks in Taurus: constraining the greybody tail at centimetre wavelengths
Anna M. M. Scaife,Jane V. Buckle,Rachael E. Ainsworth,Matthew Davies,Thomas M. O. Franzen,Keith J. B. Grainge,Michael P. Hobson,Natasha Hurley-Walker,Anthony N. Lasenby,Malak Olamaie,Yvette C. Perrott,Guy G. Pooley,Tom P. Ray,John S. Richer,Carmen Rodriguez-Gonzalvez,Richard D. E. Saunders,Michel P. Schammel,Paul F. Scott,Timothy Shimwell,David Titterington,Elizabeth Waldram
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.20254.x
Abstract: We present deep 1.8 cm (16 GHz) radio continuum imaging of seven young stellar objects in the Taurus molecular cloud. These objects have previously been extensively studied in the sub-mm to NIR range and their SEDs modelled to provide reliable physical and geometrical parametres.We use this new data to constrain the properties of the long-wavelength tail of the greybody spectrum, which is expected to be dominated by emission from large dust grains in the protostellar disk. We find spectra consistent with the opacity indices expected for such a population, with an average opacity index of beta = 0.26+/-0.22 indicating grain growth within the disks. We use spectra fitted jointly to radio and sub-mm data to separate the contributions from thermal dust and radio emission at 1.8 cm and derive disk masses directly from the cm-wave dust contribution. We find that disk masses derived from these flux densities under assumptions consistent with the literature are systematically higher than those calculated from sub-mm data, and meet the criteria for giant planet formation in a number of cases.
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Serpens region
Anna M. M. Scaife,Jennifer Hatchell,Rachael E. Ainsworth,Jane V. Buckle,Matthew Davies,Thomas M. O. Franzen,Keith J. B. Grainge,Michael P. Hobson,Natasha Hurley-Walker,Anthony N. Lasenby,Malak Olamaie,Yvette C. Perrott,Guy G. Pooley,John S. Richer,Carmen Rodriguez-Gonzalvez,Richard D. E. Saunders,Michel P. Schammel,Paul F. Scott,Timothy Shimwell,David Titterington,Elizabeth Waldram
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19957.x
Abstract: We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Serpens molecular cloud by the Spitzer c2d programme at a wavelength of 1.8cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). These observations have a resolution of ~30arcsec and an average sensitivity of 19microJy/beam. The targets are predominantly Class I sources, and we find the detection rate for Class I objects in this sample to be low (18%) compared to that of Class 0 objects (67%), consistent with previous works. For detected objects we examine correlations of radio luminosity with bolometric luminosity and envelope mass and find that these data support correlations found by previous samples, but do not show any indiction of the evolutionary divide hinted at by similar data from the Perseus molecular cloud when comparing radio luminosity with envelope mass. We conclude that envelope mass provides a better indicator for radio luminosity than bolometric luminosity, based on the distribution of deviations from the two correlations. Combining these new data with archival 3.6cm flux densities we also examine the spectral indices of these objects and find an average spectral index of 0.53+/-1.14, consistent with the canonical value for a partially optically thick spherical or collimated stellar wind. However, we caution that possible inter-epoch variability limits the usefulness of this value, and such variability is supported by our identification of a possible flare in the radio history of Serpens SMM 1.
Effects of Live Load on Seismic Response of Bridges: A Preliminary Study
Wibowo H.,Sanford D.M.,Buckle I.G.,Sanders D.H.
Civil Engineering Dimension , 2012,
Abstract: Although live load is well known to have a dynamic effect on bridge response in addition to its self-weight, the significance of these effects on seismic response is unclear. In addition, most bridge design specifications have few requirements concerning the inclusion of live load in their seismic design provisions. The main objective of this study is therefore to investigate and obtain insight into the effect of vehicle-bridge interaction during earthquake shaking. The study consists of both experimental and analytical investigations. This paper focuses on the experimental work, which includes shake table testing of a 2/5-scale model of a horizontally curved steel girder bridge loaded with a series of representative vehicles. Preliminary experimental results show that the presence of the live load had a clear beneficial effect on performance for small amplitude motions, but that this improvement diminished with increasing amplitude of shaking. Parameters used to measure performance include column displacements, abutment shear forces, abutment uplift, and concrete spalling.
AMI radio continuum observations of young stellar objects with known outflows
AMI Consortium,:,Rachael E. Ainsworth,Anna M. M. Scaife,Tom P. Ray,Jane V. Buckle,Matthew Davies,Thomas M. O. Franzen,Keith J. B. Grainge,Michael P. Hobson,Natasha Hurley-Walker,Anthony N. Lasenby,Malak Olamaie,Yvette C. Perrott,Guy G. Pooley,John S. Richer,Carmen Rodriguez-Gonzalvez,Michel P. Schammel,Paul F. Scott,Timothy Shimwell,Richard D. E. Saunders,David Titterington,Elizabeth Waldram
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20935.x
Abstract: We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (Td) according to evolutionary class; (2) allowing Td to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with free-free emission. We find an average spectral index in both Td scenarios consistent with free-free emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass, and outflow force and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, beta. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1.
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