593 research outputs found
Monte Carlo simulation method for Laughlin-like states in a disk geometry
We discuss an alternative accurate Monte Carlo method to calculate the
ground-state energy and related quantities for Laughlin states of the
fractional quantum Hall effect in a disk geometry. This alternative approach
allows us to obtain accurate bulk regime (thermodynamic limit) values for
various quantities from Monte Carlo simulations with a small number of
particles (much smaller than that needed with standard Monte Carlo approaches).Comment: 13 pages, 6 figures, 2 table
Second Generation of Composite Fermions in the Hamiltonian Theory
In the framework of a recently developed model of interacting composite
fermions restricted to a single level, we calculate the activation gaps of a
second generation of spin-polarized composite fermions. These composite
particles consist each of a composite fermion of the first generation and a
vortex-like excitation and may be responsible for the recently observed
fractional quantum Hall states at unusual filling factors such as
nu=4/11,5/13,5/17, and 6/17. Because the gaps of composite fermions of the
second generation are found to be more than one order of magnitude smaller than
those of the first generation, these states are less visible than the usual
states observed at filling factors nu=p/(2ps+1). Their stability is discussed
in the context of a pseudopotential expansion of the composite-fermion
interaction potential.Comment: 5 pages, 3 figures; after publication in PRB, we have realized that a
factor was missing in one of the expressions; the erroneous results are now
corrected; an erratum has been sent to PR
Microfabricated Chemical Analysis Systems for Environmental Applications
Recent contributions to the design, development, and fabrication of microtechnological devices for chemical analysis are summarized. The discussion includes microdisk-electrode arrays for voltammetric analysis of trace metals, and micro total-analysis systems for coulometric nanotitrations
of different analytes
Excitation gaps in fractional quantum Hall states: An exact diagonalization study
We compute energy gaps for spin-polarized fractional quantum Hall states in
the lowest Landau level at filling fractions nu=1/3, 2/5,3/7 and 4/9 using
exact diagonalization of systems with up to 16 particles and extrapolation to
the infinite system-size limit. The gaps calculated for a pure Coulomb
interaction and ignoring finite width effects, disorder and LL mixing agree
with predictions of composite fermion theory provided the logarithmic
corrections to the effective mass are included. This is in contrast with
previous estimates, which, as we show, overestimated the gaps at nu=2/5 and 3/7
by around 15%. We also study the reduction of the gaps as a result of the
non-zero width of the 2D layer. We show that these effects are accurately
accounted for using either Gaussian or z*Gaussian' (zG) trial wavefunctions,
which we show are significantly better variational wavefunctions than the
Fang-Howard wavefunction. For quantum well parameters typical of
heterostructure samples, we find gap reductions of around 20%. The experimental
gaps, after accounting heuristically for disorder,are still around 40% smaller
than the computed gaps. However, for the case of tetracene layers
inmetal-insulator-semiconductor (MIS) devices we find that the measured
activation gaps are close to those we compute. We discuss possible reasons why
the difference between computed and measured activation gaps is larger in GaAs
heterostructures than in MIS devices. Finally, we present new calculations
using systems with up to 18 electrons of the gap at nu=5/2 including width
corrections.Comment: 18 pages, 17 figure
Quasi-Particle Tunneling in Anti-Pfaffian Quantum Hall State
We study tunneling phenomena at the edge of the anti-Pfaffian quantum Hall
state at the filling factor . The edge current in a single
point-contact is considered. We focus on nonlinear behavior of two-terminal
conductance with the increase in negative split-gate voltage. Expecting the
appearance of the intermediate conductance plateau we calculate the value of
its conductance by using the renormalization group (RG) analysis. Further, we
show that non-perturbative quasi-particle tunneling is effectively described as
perturbative electron tunneling by the instanton method. The two-terminals
conductance is written as a function of the gate voltage. The obtained results
enable us to distinguish the anti-Pfaffian state from the Pfaffian state
experimentally.Comment: 5 pages, 4 figure
Light intensity enhancement by diffracting structures in solar cells
A simplified three-dimensional study is presented of the light confinement, that is, of the enhancement of the Poynting vector of the electromagnetic radiation of the light inside a solar cell absorbing the light weakly when diffracting structures are used. The model is based on the theory of periodic radiation arrays and is easily applied to one- and two-dimensional diffraction gratings. Realistically wide illumination bundles are considered. The extended nature of illumination severely limits the enhancement capabilities of diffraction structures. Results are compared to those of the more widely used Lambertian light confinement
Quasi-particle behavior of composite fermions in the half-filled Landau level
We calculate the effect of infrared fluctuations of the Chern-Simons gauge
field on the single-particle Green's function of composite fermions in the
half-filled Landau level via higher-dimensional bosonization on a curved Fermi
surface. We find that composite fermions remain well-defined quasi-particles,
with an effective mass given by the mean-field value, but with anomalously
large damping and a spectral function that contains considerable weight away
from the quasi-particle peak.Comment: reference added; accepted for publication in Phys. Rev. Let
Patient satisfaction with anaesthesia care: development of a psychometric questionnaire and benchmarking among six hospitals in Switzerland and Austriaâ âĄ
Background. We describe the development and comparison of a psychometric questionnaire on patient satisfaction with anaesthesia care among six hospitals. Methods. We used a rigorous protocol: generation of items, construction of the pilot questionnaire, pilot study, statistical analysis (construct validity, factor analysis, reliability analysis), compilation of the final questionnaire, main study, repeated analysis of construct validity and reliability. We compared the mean total problem score and the scores for the dimensions: âInformation/Involvement in decisionâmaking', and âContinuity of personal care by anaesthetist'. The influence of potential confounding variables was tested (multiple linear regression). Results. The average problem score from all hospitals was 18.6%. Most problems are mentioned in the dimensions âInformation/Involvement in decisionâmaking' (mean problem score: 30.9%) and âContinuity of personal care by anaesthetist' (mean problem score: 32.2%). The overall assessment of the quality of anaesthesia care was good to excellent in 98.7% of cases. The most important dimension was âInformation/Involvement in decisionâmaking'. The mean total problem score was significantly lower for two hospitals than the total mean for all hospitals (significantly higher at two hospitals) (P<0.05). Amongst the confounding variables considered, age, sex, subjective state of health, type of anaesthesia and level of education had an influence on the total problem score and the two dimensions mentioned. There were only marginal differences with and without the influence of the confounding variables for the different hospitals. Conclusions. A psychometric questionnaire on patient satisfaction with anaesthesia care must cover areas such as patient information, involvement in decisionâmaking, and contact with the anaesthetist. The assessment using summed scores for dimensions is more informative than a global summed rating. There were significant differences between hospitals. Moreover, the high problem scores indicate a great potential for improvement at all hospitals. Br J Anaesth 2002; 89: 863-7
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