568 research outputs found
Imaging and manipulating electrons in a 1D quantum dot with Coulomb blockade microscopy
Motivated by the recent experiments by the Westervelt group using a mobile
tip to probe the electronic state of quantum dots formed on a segmented
nanowire, we study the shifts in Coulomb blockade peak positions as a function
of the spatial variation of the tip potential, which can be termed "Coulomb
blockade microscopy". We show that if the tip can be brought sufficiently close
to the nanowire, one can distinguish a high density electronic liquid state
from a Wigner crystal state by microscopy with a weak tip potential. In the
opposite limit of a strongly negative tip potential, the potential depletes the
electronic density under it and divides the quantum wire into two partitions.
There the tip can push individual electrons from one partition to the other,
and the Coulomb blockade micrograph can clearly track such transitions. We show
that this phenomenon can be used to qualitatively estimate the relative
importance of the electron interaction compared to one particle potential and
kinetic energies. Finally, we propose that a weak tip Coulomb blockade
micrograph focusing on the transition between electron number N=0 and N=1
states may be used to experimentally map the one-particle potential landscape
produced by impurities and inhomogeneities.Comment: 4 pages 7 figure
Lanczos algorithm with Matrix Product States for dynamical correlation functions
The density-matrix renormalization group (DMRG) algorithm can be adapted to
the calculation of dynamical correlation functions in various ways which all
represent compromises between computational efficiency and physical accuracy.
In this paper we reconsider the oldest approach based on a suitable
Lanczos-generated approximate basis and implement it using matrix product
states (MPS) for the representation of the basis states. The direct use of
matrix product states combined with an ex-post reorthogonalization method
allows to avoid several shortcomings of the original approach, namely the
multi-targeting and the approximate representation of the Hamiltonian inherent
in earlier Lanczos-method implementations in the DMRG framework, and to deal
with the ghost problem of Lanczos methods, leading to a much better convergence
of the spectral weights and poles. We present results for the dynamic spin
structure factor of the spin-1/2 antiferromagnetic Heisenberg chain. A
comparison to Bethe ansatz results in the thermodynamic limit reveals that the
MPS-based Lanczos approach is much more accurate than earlier approaches at
minor additional numerical cost.Comment: final version 11 pages, 11 figure
What's the evidence that NICE guidance has been implemented? Results from a national evaluation using time series analysis, audit of patients' notes, and interviews
OBJECTIVES: To assess the extent and pattern of implementation of guidance issued by the National Institute for Clinical Excellence (NICE). DESIGN: Interrupted time series analysis, review of case notes, survey, and interviews. SETTING: Acute and primary care trusts in England and Wales. PARTICIPANTS: All primary care prescribing, hospital pharmacies; a random sample of 20 acute trusts, 17 mental health trusts, and 21 primary care trusts; and senior clinicians and managers from five acute trusts. MAIN OUTCOME MEASURES: Rates of prescribing and use of procedures and medical devices relative to evidence based guidance. RESULTS: 6308 usable patient audit forms were returned. Implementation of NICE guidance varied by trust and by topic. Prescribing of some taxanes for cancer (P <0.002) and orlistat for obesity (P <0.001) significantly increased in line with guidance. Prescribing of drugs for Alzheimer’s disease and prophylactic extraction of wisdom teeth showed trends consistent with, but not obviously a consequence of, the guidance. Prescribing practice often did not accord with the details of the guidance. No change was apparent in the use of hearing aids, hip prostheses, implantable cardioverter defibrillators, laparoscopic hernia repair, and laparoscopic colorectal cancer surgery after NICE guidance had been issued. CONCLUSIONS: Implementation of NICE guidance has been variable. Guidance seems more likely to be adopted when there is strong professional support, a stable and convincing evidence base, and no increased or unfunded costs, in organisations that have established good systems for tracking guidance implementation and where the professionals involved are not isolated. Guidance needs to be clear and reflect the clinical context
Evaluation of an integrated sponge - Granular activated carbon fluidized bed bioreactor for treating primary treated sewage effluent
An integrated fluidized bed bioreactor (iFBBR) was designed to incorporate an aerobic sponge FBBR (ASB-FBBR) into an anoxic granular activated carbon FBBR (GAC-FBBR). This iFBBR was operated with and without adding a new starch based flocculant (NSBF) to treat synthetic primary treated sewage effluent (PTSE). The NSBF contains starch based cationic flocculants and trace nutrients. The results indicate that the iFBBR with NSBF addition could remove more than 93% dissolved organic carbon (DOC), 61% total nitrogen (T-N) and 60% total phosphorus (T-P) at just a very short hydraulic retention time of 50min. The optimum frequency of adding NSBF to the iFFBR is four times per day. As a pretreatment to microfiltration, the iFFBR could increase 5L/m2h of critical flux thus reducing the membrane fouling. In addition, better microbial activity was also observed with high DO consumption (>66%) and specific oxygen uptake rate (>35mg O2/gVSSh). © 2010 Elsevier Ltd
Exact-Diagonalization Studies of Inelastic Light Scattering in Self-Assembled Quantum Dots
We report exact diagonalization studies of inelastic light scattering in
few-electron quantum dots under the strong confinement regime characteristic of
self-assembled dots. We apply the orthodox (second-order) theory for scattering
due to electronic excitations, leaving for the future the consideration of
higher-order effects in the formalism (phonons, for example), which seem
relevant in the theoretical description of available experiments. Our numerical
results stress the dominance of monopole peaks in Raman spectra and the
breakdown of selection rules in open-shell dots. The dependence of these
spectra on the number of electrons in the dot and the incident photon energy is
explicitly shown. Qualitative comparisons are made with recent experimental
results.Comment: 11 pages, 11 figure
Cost effectiveness analysis of larval therapy for leg ulcers
Objective: To assess the cost effectiveness of larval therapy compared with hydrogel in the management of leg ulcers. Design: Cost effectiveness and cost utility analyses carried out alongside a pragmatic multicentre, randomised, open trial with equal randomisation. Population: Intention to treat population comprising 267 patients with a venous or mixed venous and arterial ulcers with at least 25% coverage of slough or necrotic tissue. Interventions: Patients were randomly allocated to debridement with bagged larvae, loose larvae, or hydrogel. Main outcome measure: The time horizon was 12 months and costs were estimated from the UK National Health Service perspective. Cost effectiveness outcomes are expressed in terms of incremental costs per ulcer-free day (cost effectiveness analysis) and incremental costs per quality adjusted life years (cost utility analysis). Results: The larvae arms were pooled for the main analysis. Treatment with larval therapy cost, on average, 96.70 pound ((sic)109.61; $140.57) more per participant per year (95% confidence interval -491.9 pound to 685.8) pound than treatment with hydrogel. Participants treated with larval therapy healed, on average, 2.42 days before those in the hydrogel arm (95% confidence interval -0.95 to 31. 91 days) and had a slightly better health related quality of life, as the annual difference in QALYs was 0.011 (95% confidence interval -0.067 to 0.071). However, none of these differences was statistically significant. The incremental cost effectiveness ratio for the base case analysis was estimated at 8826 pound per QALY gained and 40 pound per ulcer-free day. Considerable uncertainty surrounds the outcome estimates. Conclusions: Debridement of sloughy or necrotic leg ulcers with larval therapy is likely to produce similar health benefits and have similar costs to treatment with hydrogel. Trial registration: Current Controlled Trials ISRCTN55114812 and National Research Register N0484123692
Inelastic effects in electron transport studied with wave packet propagation
A time-dependent approach is used to explore inelastic effects during
electron transport through few-level systems. We study a tight-binding chain
with one and two sites connected to vibrations. This simple but transparent
model gives insight about inelastic effects, their meaning and the
approximations currently used to treat them. Our time-dependent approach allows
us to trace back the time sequence of vibrational excitation and electronic
interference, the ibrationally introduced time delay and the electronic phase
shift. We explore a full range of parameters going from weak to strong
electron-vibration coupling, from tunneling to contact, from one-vibration
description to the need of including all vibrations for a correct description
of inelastic effects in transport. We explore the validity of single-site
resonant models as well as its extension to more sites via molecular orbitals
and the conditions under which multi-orbital, multi-vibrational descriptions
cannot be simplified. We explain the physical meaning of the spectral features
in the second derivative of the electron current with respect to the bias
voltage. This permits us to nuance the meaning of the energy value of dips and
peaks. Finally, we show that finite-band effects lead to electron
back-scattering off the molecular vibrations in the regime of high-conductance,
although the drop in conductance at the vibrational threshold is rather due to
the rapid variation of the vibronic density of states.Comment: 38 pages, 14 figure
Accurate evaluation of the Green's function of disordered graphenes
An accurate simulation of Green's function and self-energy function of
non-interacting electrons in disordered graphenes are performed. Fundamental
physical quantities such as the elastic relaxation time {\tau}e, the phase
velocity vp, and the group velocity vg are evaluated. New features around the
Dirac point are revealed, showing hints that multi-scattering induced
hybridization of Bloch states plays an important role in the vicinity of the
Dirac point.Comment: 4 figure
Top Arc Seam Weld Shear Strength and Stiffness for Sheet-to-sheet Connections
The North American Specification for the Design of Cold-Formed Steel Structural Members does not provide specific design guidance for sheet-to-sheet top arc seam welds in shear. A collaborative industry study has developed design guidance for both strength and stiffness of the connection to facilitate analytical evaluation of floor and roof diaphragm assemblies and wall assemblies. The test program was performed per AISI S905 and addressed material ductility, weld length, sheet thickness and the distribution of the force being transferred by the weld connection
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