1,616 research outputs found
Spatial Resolution with Time-and-Polarization-Resolved Acoustic Microscopy
Spatial resolution is an important factor in ultrasonic materials characterization. Scanning acoustic microscopy [1–2] has proved to be a useful tool for materials evaluation with micrometer-scale spatial resolution. Point-focus-beam (PFB) acoustic microscopy has high spatial resolution and is often used to produce images as well as to probe material inhomogeneity. However, a disadvantage of the PFB technique lies in its insensitivity to material anisotropy. In contrast, line-focus-beam (LFB) acoustic microscopy can provide a directional ultrasonic velocity measurement and is employed for characterization of anisotropic materials [3–5]. But the LFB technique, with its unidirectional spatial resolution, is generally incapable of producing images, and is therefore disadvantageous for probing inhomogeneous materials. In response to this need, a variety of lens designs [6–9] in acoustic microscopy have been proposed for measuring materials, which are both inhomogeneous and anisotropic
Covariance and Fisher information in quantum mechanics
Variance and Fisher information are ingredients of the Cramer-Rao inequality.
We regard Fisher information as a Riemannian metric on a quantum statistical
manifold and choose monotonicity under coarse graining as the fundamental
property of variance and Fisher information. In this approach we show that
there is a kind of dual one-to-one correspondence between the candidates of the
two concepts. We emphasis that Fisher informations are obtained from relative
entropies as contrast functions on the state space and argue that the scalar
curvature might be interpreted as an uncertainty density on a statistical
manifold.Comment: LATE
Expansion of the Gibbs potential for quantum many-body systems: General formalism with applications to the spin glass and the weakly non-ideal Bose gas
For general quantum systems the power expansion of the Gibbs potential and
consequently the power expansion of the self energy is derived in terms of the
interaction strength. Employing a generalization of the projector technique a
compact representation of the general terms of the expansion results. The
general aspects of the approach are discussed with special emphasis on the
effects characteristic for quantum systems. The expansion is systematic and
leads directly to contributions beyond mean-field of all thermodynamic
quantities. These features are explicitly demonstrated and illustrated for two
non-trivial systems, the infinite range quantum spin glass and the weakly
interacting Bose gas. The Onsager terms of both systems are calculated, which
represent the first beyond mean-field contributions. For the spin glass new
TAP-like equations are presented and discussed in the paramagnetic region. The
investigation of the Bose gas leads to a beyond mean-field thermodynamic
description. At the Bose-Einstein condensation temperature complete agreement
is found with the results presented recently by alternative techniques.Comment: 17 pages, 0 figures; revised version accepted by Phys Rev
Nuclear Shape Fluctuations in Fermi-Liquid Drop Model
Within the nuclear Fermi-liquid drop model, quantum and thermal fluctuations
are considered by use of the Landau-Vlasov-Langevin equation. The spectral
correlation function of the nuclear surface fluctuations is evaluated in a
simple model of an incompressible and irrotational Fermi liquid. The dependence
of the spectral correlation function on the dynamical Fermi-surface distortion
is established. The temperature at which the eigenvibrations become overdamped
is calculated. It is shown that, for realistic values of the relaxation time
parameter and in the high temperature regime, there is a particular eigenmode
of the Fermi liquid drop where the restoring force is exclusively due to the
dynamical Fermi-surface distortion.Comment: 23 pages, revtex, file and 3 figures, accepted for publication in
Nuclear Physics
Effective Feedback to Improve Primary Care Prescribing Safety (EFIPPS) a pragmatic three-arm cluster randomised trial:designing the intervention (ClinicalTrials.gov registration NCT01602705)
Peer reviewedPublisher PD
Density-operator approaches to transport through interacting quantum dots: Simplifications in fourth-order perturbation theory
Various theoretical methods address transport effects in quantum dots beyond
single-electron tunneling while accounting for the strong interactions in such
systems. In this paper we report a detailed comparison between three prominent
approaches to quantum transport: the fourth-order Bloch-Redfield quantum master
equation (BR), the real-time diagrammatic technique (RT), and the scattering
rate approach based on the T-matrix (TM). Central to the BR and RT is the
generalized master equation for the reduced density matrix. We demonstrate the
exact equivalence of these two techniques. By accounting for coherences
(nondiagonal elements of the density matrix) between nonsecular states, we show
how contributions to the transport kernels can be grouped in a physically
meaningful way. This not only significantly reduces the numerical cost of
evaluating the kernels but also yields expressions similar to those obtained in
the TM approach, allowing for a detailed comparison. However, in the TM
approach an ad hoc regularization procedure is required to cure spurious
divergences in the expressions for the transition rates in the stationary
(zero-frequency) limit. We show that these problems derive from incomplete
cancellation of reducible contributions and do not occur in the BR and RT
techniques, resulting in well-behaved expressions in the latter two cases.
Additionally, we show that a standard regularization procedure of the TM rates
employed in the literature does not correctly reproduce the BR and RT
expressions. All the results apply to general quantum dot models and we present
explicit rules for the simplified calculation of the zero-frequency kernels.
Although we focus on fourth-order perturbation theory only, the results and
implications generalize to higher orders. We illustrate our findings for the
single impurity Anderson model with finite Coulomb interaction in a magnetic
field.Comment: 29 pages, 12 figures; revised published versio
Diffusion in multiscale spacetimes
We study diffusion processes in anomalous spacetimes regarded as models of
quantum geometry. Several types of diffusion equation and their solutions are
presented and the associated stochastic processes are identified. These results
are partly based on the literature in probability and percolation theory but
their physical interpretation here is different since they apply to quantum
spacetime itself. The case of multiscale (in particular, multifractal)
spacetimes is then considered through a number of examples and the most general
spectral-dimension profile of multifractional spaces is constructed.Comment: 23 pages, 5 figures. v2: discussion improved, typos corrected,
references adde
Constraints on Gamma-ray Emission from the Galactic Plane at 300 TeV
We describe a new search for diffuse ultrahigh energy gamma-ray emission
associated with molecular clouds in the galactic disk. The Chicago Air Shower
Array (CASA), operating in coincidence with the Michigan muon array (MIA), has
recorded over 2.2 x 10^{9} air showers from April 4, 1990 to October 7, 1995.
We search for gamma rays based upon the muon content of air showers arriving
from the direction of the galactic plane. We find no significant evidence for
diffuse gamma-ray emission, and we set an upper limit on the ratio of gamma
rays to normal hadronic cosmic rays at less than 2.4 x 10^{-5} at 310 TeV (90%
confidence limit) from the galactic plane region: (50 degrees < l < 200
degrees); -5 degrees < b < 5 degrees). This limit places a strong constraint on
models for emission from molecular clouds in the galaxy. We rule out
significant spectral hardening in the outer galaxy, and conclude that emission
from the plane at these energies is likely to be dominated by the decay of
neutral pions resulting from cosmic rays interactions with passive target gas
molecules.Comment: Astrophysical Journal, submitted, 11 pages, AASTeX Latex, 3
Postscript figure
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
Patient-specific instrumentation does not improve radiographic alignment or clinical outcomes after total knee arthroplasty: A meta-analysis
Background and purpose: Patient-specific instrumentation (PSI) for total knee arthroplasty (TKA) has been introduced to improve alignment and reduce outliers, increase efficiency, and reduce operation time. In order to improve our understanding of the outcomes of patient-specific instrumentation, we conducted a meta-analysis.
Patients and methods: We identified randomized and quasi-randomized controlled trials (RCTs) comparing patient-specific and conventional instrumentation in TKA. Weighted mean differences and risk ratios were determined for radiographic accuracy, operation time, hospital stay, blood loss, number of surgical trays required, and patient-reported outcome measures.
Results: 21 RCTs involving 1,587 TKAs were included. Patient-specific instrumentation resulted in slightly more accurate hip-knee-ankle axis (0.3°), coronal femoral alignment (0.3°, femoral flexion (0.9°), tibial slope (0.7°), and femoral component rotation (0.5°). The risk ratio of a coronal plane outlier (\u3e 3° deviation of chosen target) for the tibial component was statistically significantly increased in the PSI group (RR = 1.64). No significance was found for other radiographic measures. Operation time, blood loss, and transfusion rate were similar. Hospital stay was significantly shortened, by approximately 8 h, and the number of surgical trays used decreased by 4 in the PSI group. Knee Society scores and Oxford knee scores were similar.
Interpretation: Patient-specific instrumentation does not result in clinically meaningful improvement in alignment, fewer outliers, or better early patient-reported outcome measures. Efficiency is improved by reducing the number of trays used, but PSI does not reduce operation time
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