897 research outputs found
Excitation of superconducting qubits from hot non-equilibrium quasiparticles
Superconducting qubits probe environmental defects such as non-equilibrium
quasiparticles, an important source of decoherence. We show that "hot"
non-equilibrium quasiparticles, with energies above the superconducting gap,
affect qubits differently from quasiparticles at the gap, implying qubits can
probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we
predict a non-neligable increase in the qubit excited state probability P_e. By
injecting hot quasiparticles into a qubit, we experimentally measure an
increase of P_e in semi-quantitative agreement with the model and rule out the
typically assumed thermal distribution.Comment: Main paper: 5 pages, 5 figures. Supplement: 1 page, 1 figure, 1
table. Updated to user-prepared accepted version. Key changes: Supplement
added, Introduction rewritten, Figs.2,3,5 revised, Fig.4 adde
Many Body Theory of Charge Transfer in Hyperthermal Atomic Scattering
We use the Newns-Anderson Hamiltonian to describe many-body electronic
processes that occur when hyperthermal alkali atoms scatter off metallic
surfaces. Following Brako and Newns, we expand the electronic many-body
wavefunction in the number of particle-hole pairs (we keep terms up to and
including a single particle-hole pair). We extend their earlier work by
including level crossings, excited neutrals and negative ions. The full set of
equations of motion are integrated numerically, without further approximations,
to obtain the many-body amplitudes as a function of time. The velocity and
work-function dependence of final state quantities such as the distribution of
ion charges and excited atomic occupancies are compared with experiment. In
particular, experiments that scatter alkali ions off clean Cu(001) surfaces in
the energy range 5 to 1600 eV constrain the theory quantitatively. The
neutralization probability of Na ions shows a minimum at intermediate
velocity in agreement with the theory. This behavior contrasts with that of
K, which shows ... (7 figures, not included. Figure requests:
[email protected])Comment: 43 pages, plain TeX, BUP-JBM-
Resonant Photon-Assisted Tunneling Through a Double Quantum Dot: An Electron Pump From Spatial Rabi Oscillations
The time average of the fully nonlinear current through a double quantum dot,
subject to an arbitrary combination of ac and dc voltages, is calculated
exactly using the Keldysh nonequilibrium Green function technique. When driven
on resonance, the system functions as an efficient electron pump due to Rabi
oscillation between the dots. The pumping current is maximum when the coupling
to the leads equals the Rabi frequency.Comment: 6 pages, REVTEX 3.0, 3 postscript figure
Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations
A benchmark ab initio and density functional (DFT) study has been carried out
on the electron affinities of the first- and second-row atoms. The ab initio
study involves basis sets of and quality, extrapolations to
the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and
full CI electron correlation methods. Scalar relativistic and spin-orbit
coupling effects were taken into account. On average, the best ab initio
results agree to better than 0.001 eV with the most recent experimental
results. Correcting for imperfections in the CCSD(T) method improves the mean
absolute error by an order of magnitude, while for accurate results on the
second-row atoms inclusion of relativistic corrections is essential. The latter
are significantly overestimated at the SCF level; for accurate spin-orbit
splitting constants of second-row atoms inclusion of (2s,2p) correlation is
essential. In the DFT calculations it is found that results for the 1st-row
atoms are very sensitive to the exchange functional, while those for second-row
atoms are rather more sensitive to the correlation functional. While the LYP
correlation functional works best for first-row atoms, its PW91 counterpart
appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid)
functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991
correlation) puts in the best overall performance. The best results overall are
obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange
functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with
mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row
atoms. Indications exist that a hybrid of the type mPW1LYP +
mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning
DFT and electron affinities added
Transplant Co-ordination Services in Europe 1989: A Survey by the EDTA Registry
This report contains EDTA Registry data concerning transplant co-ordination services. It is a summary of the results of a special questionnaire mailed in 1989 to all renal transplant centres known to the EDTA Registry in Europe and Mediterranean countries. The response rate to the questionnaire was 86%. A transplant co-ordination service was available in more than 70% of the centres. The larger the transplant activity of a centre, the greater was the likelihood of a co-ordinator service being available. The educational background of the transplant co-ordinator was most commonly that of nurse. More than 70% of the centres had one or two transplant co-ordirtators. A service shared by several centres was fairly common in the United Kingdom and France. The most important duties and activities appeared to be the organisation of transportation of donor teams and organs, giving feedback to the donor hospital's staff, and providing information to the public regarding organ donatio
Prevalence and risk factors of inappropriate use of intravenous and urinary catheters in surgical and medical patients
Background: Previously, the RICAT (Reduction of Inappropriate use of intravenous and urinary CATheters) study had been conducted by ourselves to reduce inappropriate use of intravenous and urinary catheters in medical wards to prevent healthcare-associated infections. Aim: To compare surgical and medical wards, and to determine risk factors for inappropriate catheter u
The nature of the silicaphilic fluorescence of PDMPO
PDMPO (2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-vis and fluorescence spectroscopy supported by computational data, (SPARC, molecular dynamics simulations, density functional theory calculations), dynamic light scattering and zeta potential measurements to understand the PDMPO–silica interaction. From absorption data, PDMPO exhibited a pKa of 4.20 for PDMPOH22+ to PDMPOH+ . Fluorescence emission measurements revealed large shifts in excited state pKa* values with different behaviour when bound to silica (pKa* of 10.4). PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH+* and dielectric constant (4.8–80). Additional chromatic effects were attributed to changes in solvent accessible surface area. Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3–5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification
Coordinated analysis of age, sex, and education effects on change in MMSE scores
Objectives. We describe and compare the expected performance trajectories of older adults on the Mini-Mental Status Examination (MMSE) across six independent studies from four countries in the context of a collaborative network of longitudinal studies of aging. A coordinated analysis approach is used to compare patterns of change conditional on sample composition differences related to age, sex, and education. Such coordination accelerates evaluation of particular hypotheses. In particular, we focus on the effect of educational attainment on cognitive decline.Method. Regular and Tobit mixed models were fit to MMSE scores from each study separately. The effects of age, sex, and education were examined based on more than one centering point.Results. Findings were relatively consistent across studies. On average, MMSE scores were lower for older individuals and declined over time. Education predicted MMSE score, but, with two exceptions, was not associated with decline in MMSE over time.Conclusion. A straightforward association between educational attainment and rate of cognitive decline was not supported. Thoughtful consideration is needed when synthesizing evidence across studies, as methodologies adopted and sample characteristics, such as educational attainment, invariably differ. © 2012 The Author
Critical properties of two-dimensional Josephson junction arrays with zero-point quantum fluctuations
We present results from an extensive analytic and numerical study of a
two-dimensional model of a square array of ultrasmall Josephson junctions. We
include the ultrasmall self and mutual capacitances of the junctions, for the
same parameter ranges as those produced in the experiments. The model
Hamiltonian studied includes the Josephson, , as well as the charging,
, energies between superconducting islands. The corresponding quantum
partition function is expressed in different calculationally convenient ways
within its path-integral representation. The phase diagram is analytically
studied using a WKB renormalization group (WKB-RG) plus a self-consistent
harmonic approximation (SCHA) analysis, together with non-perturbative quantum
Monte Carlo simulations. Most of the results presented here pertain to the
superconductor to normal (S-N) region, although some results for the insulating
to normal (I-N) region are also included. We find very good agreement between
the WKB-RG and QMC results when compared to the experimental data. To fit the
data, we only used the experimentally determined capacitances as fitting
parameters. The WKB-RG analysis in the S-N region predicts a low temperature
instability i.e. a Quantum Induced Transition (QUIT). We carefully simulations
and carry out a finite size analysis of as a function of the
magnitude of imaginary time axis . We find that for some relatively
large values of (, the
limit does appear to give a {\it non-zero} , while
for , . We use the SCHA to analytically understand
the dependence of the QMC results with good agreement between them.
Finally, we also carried out a WKB-RG analysis in the I-N region and found no
evidence of a low temperature QUIT, up to lowest order in Comment: 39 pages, 18 postscript figures, to appear in Phys. Rev.
- …