1,654 research outputs found
Dephasing via stochastic absorption: A case study in Aharonov-Bohm oscillations
The Aharonov-Bohm ring has been the mainstay of mesoscopic physics research
since its inception. In this paper we have dwelt on the problem of dephasing of
AB oscillations using a phenomenological model based on stochastic absorption.
To calculate the conductance in the presence of inelastic scattering we have
used the method due to Brouwer and Beenakker. We have shown that conductance is
symmetric under flux reversal and visibility of AB oscillations decay to zero
as a function of the incoherence parameter thus signalling dephasing in the
system. Some comments are made on the relative merits of stochastic absorption
with respect to optical potential model, which have been used to mimic
dephasing.Comment: 4 pages, 4 figures Minor corrections made and journal reference adde
Plastic hinge relocation in reinforced concrete beams using Cu-Al-Mn SMA bars
costs. The use of Ni-Ti superelastic shape memory alloy (SMA) constitutes a considerable portion of this research. Cu-Al-Mn superelastic SMA has been recently developed to eliminate the high cost of Ni-Ti SMA, as well as, to have better machining characteristics. This paper explores the use of Cu-Al-Mn SMA bars to relocate the plastic hinge of concrete beams through an experimental–numerical study. The cyclic performance of four beams was examined. The first was reinforced with steel bars and the remaining three were reinforced with combination of SMA and steel bars. The location of the SMA bars was different for each of the examined beams. The beams were loaded such that the moment diagram is zero at midspan and maximum at the ends to simulate the expected seismic moments. Results of the experimental–numerical investigation confirmed the recentering capability of SMA RC beams. Relocating the plastic hinge, by placing Cu-Al-Mn SMA bars away from the beam ends, improved the strength, rigidity, and energy dissipation
Treating latent TB in primary care: a survey of enablers and barriers among UK General Practitioners.
BACKGROUND: Treating latent tuberculosis infection (LTBI) is an important public health intervention. In the UK, LTBI treatment is delivered in secondary care. Treating LTBI in the community would move care closer to home and could increase uptake and treatment completion rates. However, healthcare providers' views about the feasibility of this in the UK are unknown. This is the first study to investigate perceived barriers and enablers to primary care-based LTBI treatment among UK general practitioners (GPs). METHODS: A national survey amongst 140 randomly sampled UK GPs practising in areas of high TB incidence was performed. GPs' experience and perceived confidence, barriers and enablers of primary care-based LTBI treatment were explored and multivariable logistic regression was used to determine whether these were associated with a GP's willingness to deliver LTBI treatment. RESULTS: One hundred and twelve (80 %) GPs responded. Ninety-three (83 %; 95 % CI 75 %-89 %) GPs said they would be willing to deliver LTBI treatment in primary care, if key perceived barriers were addressed during service development. The major perceived barriers to delivering primary care-based LTBI treatment were insufficient experience among GPs of screening and treating LTBI, lack of timely specialist support and lack of allied healthcare staff. In addition, GPs felt that appropriate resourcing was key to the successful and sustainable delivery of the service. GPs who reported previous experience of screening or treatment of patients with active or latent TB were almost ten times more likely to be willing to deliver LTBI treatment in primary care compared to GPs with no experience (OR: 9.98; 95 % CI 1.22-81.51). CONCLUSIONS: UK GPs support primary care-based LTBI treatment, provided they are given appropriate training, specialist support, staffing and financing
Aharonov-Bohm oscillations and spin transport in a mesoscopic ring with a magnetic impurity
We present a detailed analysis of the Aharonov-Bohm (AB) interference
oscillations manifested through transmission of an electron in a mesoscopic
ring with a magnetic impurity atom inserted in one of its arms. The spin
polarization transport is also studied. The electron interacts with the
impurity through the exchange interaction leading to exchange spin-flip
scattering. Transmission in the spin-flipped and spin-unflipped channels are
explicitly calculated. We show that the entanglement between electron and
spin-flipper states lead to a reduction of AB oscillations in spite of absence
of any inelastic scattering. The spin-conductance (related to spin-polarized
transmission coefficient) is asymmetric in the flux reversal as opposed to the
two probe conductance which is symmetric under flux reversal. We point out
certain limitations of this model in regard to the general notion of dephasing
in quantum mechanics.Comment: 6 pages RevTeX, 9 eps figures included, enlarged version of
cond-mat/000741
Comparison between the two models of dephasing in mesoscopic systems
In mesoscopic systems to study the role of inelastic scattering on the phase
coherent motion of electrons two phenomenological models have been proposed. In
the first one, due to B\"uttiker, one adds a voltage probe into the system (or
in the scattering matrix). The second model invokes the complex (or optical)
potential in the system Hamiltonian. Studying a simple geometry of a metallic
loop in the presence of Aharonov-Bohm magnetic flux, we show that the two probe
conductance is symmetric in the reversal of the magnetic field in B\"uttiker's
approach. Whereas the two probe conductance within the complex potential model
is asymmetric in the magnetic flux reversal contrary to the expected behavior.Comment: 11 pages RevTex, 4 figures inculded, Communicated to PR
Spin Polarization at Semiconductor Point Contacts in Absence of Magnetic Field
Semiconductor point contacts can be a useful tool for producing
spin-polarized currents in the presence of spin-orbit (SO) interaction. Neither
magnetic fields nor magnetic materials are required. By numerical studies, we
show that (i) the conductance is quantized in units of 2e^2/h unless the SO
interaction is too strong, (ii) the current is spin-polarized in the transverse
direction, and (iii) a spin polarization of more than 50% can be realized with
experimentally accessible values of the SO interaction strength. The
spin-polarization ratio is determined by the adiabaticity of the transition
between subbands of different spins during the transport through the point
contacts.Comment: 4 pages, 4 figures; minor changes, published in J. Phys. Soc. Jp
Spin Transport in Two Dimensional Hopping Systems
A two dimensional hopping system with Rashba spin-orbit interaction is
considered. Our main interest is concerned with the evolution of the spin
degree of freedom of the electrons. We derive the rate equations governing the
evolution of the charge density and spin polarization of this system in the
Markovian limit in one-particle approximation. If only two-site hopping events
are taken into account, the evolution of the charge density and of the spin
polarization is found to be decoupled. A critical electric field is found,
above which oscillations are superimposed on the temporal decay of the total
polarization. A coupling between charge density and spin polarization occurs on
the level of three-site hopping events. The coupling terms are identified as
the anomalous Hall effect and the recently proposed spin Hall effect. Thus, an
unpolarized charge current through a sheet of finite width leads to a
transversal spin accumulation in our model system.Comment: 15 pages, 3 figure
Effect of quantum entanglement on Aharonov-Bohm oscillations, spin-polarized transport and current magnification effect
We present a simple model of transmission across a metallic mesoscopic ring.
In one of its arm an electron interacts with a single magnetic impurity via an
exchange coupling. We show that entanglement between electron and spin impurity
states leads to reduction of Aharonov-Bohm oscillations in the transmission
coefficient. The spin-conductance is asymmetric in the flux reversal as opposed
to the two probe electrical conductance which is symmetric. In the same model
in contradiction to the naive expectation of a current magnification effect, we
observe enhancement as well as the suppression of this effect depending on the
system parameters. The limitations of this model to the general notion of
dephasing or decoherence in quantum systems are pointed out.Comment: Talk presented at the International Discussion Meeting on Mesoscopic
and Disordered systems, December, 2000, at IISc Bangalore 17 pages, 8figure
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