753 research outputs found
Adatoms and nanoengineering of carbon
We present a new and general mechanism for inter-conversion of carbon
structures via a catalytic exchange process, which operates under conditions of
Frenkel pair generation. The mechanism typically lowers reaction barriers by a
factor of four compared to equivilent uncatalysed reactions. We examine the
relevance of this mechanism for fullerene growth, carbon onions and nanotubes,
and dislocations in irradiated graphite.Comment: 3 Figures, 5 Page letter accepted for publication in Chemical Physics
Letter
Semantic-based policy engineering for autonomic systems
This paper presents some important directions in the use of ontology-based semantics in achieving the vision of Autonomic Communications. We examine the requirements of Autonomic Communication with a focus on the demanding needs of ubiquitous computing environments, with an emphasis on the requirements shared with Autonomic Computing. We observe that ontologies provide a strong mechanism for addressing the heterogeneity in user task requirements, managed resources, services and context. We then present two complimentary approaches that exploit ontology-based knowledge in support of autonomic communications: service-oriented models for policy engineering and dynamic semantic queries using content-based networks. The paper concludes with a discussion of the major research challenges such approaches raise
Compositional tuning of ferromagnetism in Ga1-xMnxP
We report the magnetic and transport properties of Ga1-xMnxP synthesized via
ion implantation followed by pulsed laser melting over a range of x, namely
0.018 to 0.042. Like Ga1-xMnxAs, Ga1-xMnxP displays a monotonic increase of the
ferromagnetic Curie temperature with x associated with the hole-mediated
ferromagnetic phase while thermal annealing above 300 C leads to a quenching of
ferromagnetism that is accompanied by a reduction of the substitutional
fraction of Mn. However, contrary to observations in Ga1-xMnxAs, Ga1-xMnxP is
non-metallic over the entire composition range. At the lower temperatures over
which the films are ferromagnetic, hole transport occurs via hopping conduction
in a Mn-derived band; at higher temperatures it arises from holes in the
valence band which are thermally excited across an energy gap that shrinks with
x.Comment: To be published in Solid State Communication
Impact of infection control interventions on rates of Staphylococcus aureus bacteraemia in National Health Service acute hospitals, East Midlands, UK, using interrupted time-series analysis
Background: Reducing healthcare-associated infection (HCAI) is a UK national priority. Multiple national and regional interventions aimed at reduction have been implemented in National Health Service acute hospitals, but assessment of their effectiveness is methodologically challenging.
Aim: To assess the effectiveness of national and regional interventions undertaken between 2004 and 2008 on rates of meticillin-resistant Staphylococcus aureus (MRSA) and meticillin-sensitive Staphylococcus aureus (MSSA) bacteraemia within acute hospitals in the East Midlands, using interrupted time-series analysis.
Methods: We used segmented regression to compare rates of MRSA and MSSA bacteraemia in the pre-intervention, implementation, and post-intervention phases for combined intervention packages in eight acute hospitals.
Findings: Most of the change in MSSA and MRSA rates occurred during the implementation phase. During this phase, there were significant downward trends in MRSA rates for seven of eight acute hospital groups; in four, this was a steeper quarter-on-quarter decline compared with the pre-intervention phase, and, in one, an upward trend in the pre-intervention phase was reversed. Regarding MSSA, there was a significant positive effect in four hospital groups: one upward trend during the pre-intervention phase was reversed, two upward trends plateaued, and in one hospital group an indeterminate trend decreased significantly. However, there were significant increasing trends in quarterly MSSA rates in four hospital groups during the implementation or post-intervention periods. Conclusion The impact of interventions varied by hospital group but the overall results suggest that national and regional campaigns had a beneficial impact on MRSA and MSSA bacteraemia within the East Midlands
Graphene based superconducting quantum point contacts
We investigate the Josephson effect in the graphene nanoribbons of length
smaller than the superconducting coherence length and an arbitrary width .
We find that in contrast to an ordinary superconducting quantum point contact
(SQPC) the critical supercurrent is not quantized for the nanoribbons
with smooth and armchair edges. For a low concentration of the carriers
decreases monotonically with lowering and tends to a constant minimum for
a narrow nanoribbon with . The minimum is zero for the
smooth edges but for the armchair edges. At higher
concentrations of the carriers this monotonic variation acquires a series of
peaks. Further analysis of the current-phase relation and the Josephson
coupling strength in terms of and the concentration of carriers
revels significant differences with those of an ordinary SQPC. On the other
hand for a zigzag nanoribbon we find that, similar to an ordinary SQPC,
is quantized but to the half-integer values .Comment: 8 pages, 5 figure
High-field magnetization study of the S = 1/2 antiferromagnetic Heisenberg chain [PM Cu(NO)(HO)] with a field-induced gap
We present a high-field magnetization study of the = 1/2
antiferromagnetic Heisenberg chain [PM Cu(NO)(HO)]. For
this material, as result of the Dzyaloshinskii-Moriya interaction and a
staggered tensor, the ground state is characterized by an anisotropic
field-induced spin excitation gap and a staggered magnetization. Our data
reveal the qualitatively different behavior in the directions of maximum and
zero spin excitation gap. The data are analyzed via exact diagonalization of a
linear spin chain with up to 20 sites and on basis of the Bethe ansatz
equations, respectively. For both directions we find very good agreement
between experimental data and theoretical calculations. We extract the magnetic
coupling strength along the chain direction to 36.3(5) K and determine
the field dependence of the staggered magnetization component .Comment: 5 pages, 2 figures (minor changes to manuscript and figures
Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors
It is predicted that certain atomically ordered interfaces between some
ferromagnetic metals (F) and semiconductors (S) should act as ideal spin
filters that transmit electrons only from the majority spin bands or only from
the minority spin bands of the F to the S at the Fermi energy, even for F with
both majority and minority bands at the Fermi level. Criteria for determining
which combinations of F, S and interface should be ideal spin filters are
formulated. The criteria depend only on the bulk band structures of the S and F
and on the translational symmetries of the S, F and interface. Several examples
of systems that meet these criteria to a high degree of precision are
identified. Disordered interfaces between F and S are also studied and it is
found that intermixing between the S and F can result in interfaces with spin
anti-filtering properties, the transmitted electrons being much less spin
polarized than those in the ferromagnetic metal at the Fermi energy. A patent
application based on this work has been commenced by Simon Fraser University.Comment: RevTeX, 12 pages, 5 figure
Design, development and testing of multi-functional non-linear ultrasonic instrumentation for the detection of defects and damage in CFRP materials and structures
Copyright © 2013 Elsevier. NOTICE: this is the authorâs version of a work that was accepted for publication in Composites Science and Technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Composites Science and Technology Vol. 87 (2013), DOI: 10.1016/j.compscitech.2013.07.014A multi-functional non-linear ultrasonic testing approach is presented for in situ and ex-situ detection of a variety of defects (e.g. micro-cracking, delamination and disbonding) induced by various damage mechanisms (stress, impact, heat) in CFRP materials and structures. Such multi-functionality is provided via programmable and re-configurable instrumentation that incorporates a wide range of non-linear ultrasonic testing regimes, including harmonic and overtone generation, inter-modulation product generation, resonant frequency shift and pulse-inversion techniques. The capabilities of this multi-functional approach to defect detection are demonstrated by examining CFRP samples subjected to various forms of damage, specifically stress, impact and heat induced damage. We show that the multi-functional non-linear approach is well-suited to the detection of such forms of damage and that the pulse-inversion technique, largely âignoredâ in the CFRP literature, potentially provides a powerful, but as yet un-tapped, simple and effective route to the defect and damage detection
Assessment of the Noise Reduction Potential of Advanced Subsonic Transport Concepts for NASA's Environmentally Responsible Aviation Project
Aircraft system noise is predicted for a portfolio of NASA advanced concepts with 2025 entry-into-service technology assumptions. The subsonic transport concepts include tube-and-wing configurations with engines mounted under the wing, over the wing nacelle integration, and a double deck fuselage with engines at a mid-fuselage location. Also included are hybrid wing body aircraft with engines upstream of the fuselage trailing edge. Both advanced direct drive engines and geared turbofan engines are modeled. Recent acoustic experimental information was utilized in the prediction for several key technologies. The 301-passenger class hybrid wing body with geared ultra high bypass engines is assessed at 40.3 EPNLdB cumulative below the Stage 4 certification level. Other hybrid wing body and unconventional tube-and-wing configurations reach levels of 33 EPNLdB or more below the certification level. Many factors contribute to the system level result; however, the hybrid wing body in the 301-passenger class, as compared to a tubeand- wing with conventional engine under wing installation, has 11.9 EPNLdB of noise reduction due to replacing reflection with acoustic shielding of engine noise sources. Therefore, the propulsion airframe aeroacoustic interaction effects clearly differentiate the unconventional configurations that approach levels close to or exceed the 42 EPNLdB goal
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