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Search Results: 1 - 10 of 208489 matches for " L. 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.
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.
The JCMT dense gas survey of the Perseus Molecular Cloud
S. L. Walker-Smith,J. S. Richer,J. V. Buckle,J. Hatchell,E. Drabek-Maunder
Physics , 2014, DOI: 10.1093/mnras/stu512
Abstract: We present the results of a large-scale survey of the very dense gas in the Perseus molecular cloud using HCO+ and HCN (J = 4 - 3) transitions. We have used this emission to trace the structure and kinematics of gas found in pre- and protostellar cores, as well as in outflows. We compare the HCO+/HCN data, highlighting regions where there is a marked discrepancy in the spectra of the two emission lines. We use the HCO+ to identify positively protostellar outflows and their driving sources, and present a statistical analysis of the outflow properties that we derive from this tracer. We find that the relations we calculate between the HCO+ outflow driving force and the Menv and Lbol of the driving source are comparable to those obtained from similar outflow analyses using 12CO, indicating that the two molecules give reliable estimates of outflow properties. We also compare the HCO+ and the HCN in the outflows, and find that the HCN traces only the most energetic outflows, the majority of which are driven by young Class 0 sources. We analyse the abundances of HCN and HCO+ in the particular case of the IRAS 2A outflows, and find that the HCN is much more enhanced than the HCO+ in the outflow lobes. We suggest that this is indicative of shock-enhancement of HCN along the length of the outflow; this process is not so evident for HCO+, which is largely confined to the outflow base.
The structure and kinematics of dense gas in NGC 2068
S. L. Walker-Smith,J. S. Richer,J. V. Buckle,R. J. Smith,J. S. Greaves,I. A. Bonnell
Physics , 2012, DOI: 10.1093/mnras/sts582
Abstract: We have carried out a survey of the NGC 2068 region in the Orion B molecular cloud using HARP on the JCMT, in the 13CO and C18O (J = 3-2) and H13CO+ (J = 4-3) lines. We used 13CO to map the outflows in the region, and matched them with previously defined SCUBA cores. We decomposed the C18O and H13CO+ into Gaussian clumps, finding 26 and 8 clumps respectively. The average deconvolved radii of these clumps is 6200 +/- 2000 AU and 3600 +/- 900 AU for C18O and H13CO+ respectively. We have also calculated virial and gas masses for these clumps, and hence determined how bound they are. We find that the C18O clumps are more bound than the H13CO+ clumps (average gas mass to virial mass ratio of 4.9 compared to 1.4). We measure clump internal velocity dispersions of 0.28 +/- 0.02 kms-1 and 0.27 +/- 0.04 kms-1 for C18O and H13CO+ respectively, although the H13CO+ values are heavily weighted by a majority of the clumps being protostellar, and hence having intrinsically greater linewidths. We suggest that the starless clumps correspond to local turbulence minima, and we find that our clumps are consistent with formation by gravoturbulent fragmentation. We also calculate inter-clump velocity dispersions of 0.39 +/- 0.05 kms-1 and 0.28 +/- 0.08 kms-1 for C18O and H13CO+ respectively. The velocity dispersions (both internal and external) for our clumps match results from numerical simulations of decaying turbulence in a molecular cloud. However, there is still insufficient evidence to conclusively determine the type of turbulence and timescale of star formation, due to the small size of our sample.
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.
The X-Ray Crystal Structure of Escherichia coli Succinic Semialdehyde Dehydrogenase; Structural Insights into NADP+/Enzyme Interactions
Christopher G. Langendorf,Trevor L. G. Key,Gustavo Fenalti,Wan-Ting Kan,Ashley M. Buckle,Tom Caradoc-Davies,Kellie L. Tuck,Ruby H. P. Law,James C. Whisstock
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0009280
Abstract: In mammals succinic semialdehyde dehydrogenase (SSADH) plays an essential role in the metabolism of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) to succinic acid (SA). Deficiency of SSADH in humans results in elevated levels of GABA and γ-Hydroxybutyric acid (GHB), which leads to psychomotor retardation, muscular hypotonia, non-progressive ataxia and seizures. In Escherichia coli, two genetically distinct forms of SSADHs had been described that are essential for preventing accumulation of toxic levels of succinic semialdehyde (SSA) in cells.
Aerial Measurement of Radioxenon Concentration off the West Coast of Vancouver Island following the Fukushima Reactor Accident
L. E. Sinclair,H. C. J. Seywerd,R. Fortin,J. M. Carson,P. R. B. Saull,M. J. Coyle,R. A. Van Brabant,J. L. Buckle,S. M. Desjardins,R. M. Hall
Physics , 2011, DOI: 10.1016/j.jenvrad.2011.06.008
Abstract: In response to the Fukushima nuclear reactor accident, on March 20th, 2011, Natural Resources Canada conducted aerial radiation surveys over water just off of the west coast of Vancouver Island. Dose-rate levels were found to be consistent with background radiation, however a clear signal due to Xe-133 was observed. Methods to extract Xe-133 count rates from the measured spectra, and to determine the corresponding Xe-133 volumetric concentration, were developed. The measurements indicate that Xe-133 concentrations on average lie in the range of 30 to 70 Bq/m3.
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.
Efficient Antifouling Surface for Quantitative Surface Plasmon Resonance Based Biosensor Analysis
Claude Nogues, Hervé Leh, Joseph Lautru, Olivier Delelis, Malcolm Buckle
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044287
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 refractive to analysis due to the prevalent high degree of non-specific binding. In this manuscript we explore the dynamic process of the formation of self-assembled monolayers and optimize physical and chemical properties thus reducing considerably non-specific binding while maintaining the integrity of the immobilized biomolecules. As a result, analysis of specific binding of analytes to immobilized target molecules is significantly facilitated.
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