3,218 research outputs found
Location and Commuting Project â Preliminary Analysis of the Pilot Survey in a Central London Company.
This paper contains preliminary analysis of the data collected during the pilot survey of a Central London company for the Location and Commuting Project. Self-completion questionnaires were distributed to all members of the staff to gather information about their residential and employment histories, together with facts about their characteristics, journey to work trips and the extent to which financial assistance was available to them to help with the cost of housing and travel.
A description of the characteristics of the respondents and their journey to work patterns is followed by analysis of residential and workplace mobility.
Age is found to be an important determinant of both residential and employment mobility with housing tenure and occupational classifications influencing home and job mobility respectively. Analysis of the journey to work trips for recent home movers suggests that the economic constraints of the journey to work may play an important role in locational decisions
Repeatability of fractional flow reserve despite variations in systemic and coronary hemodynamics
Objectives
This study classified and quantified the variation in fractional flow reserve (FFR) due to fluctuations in systemic and coronary hemodynamics during intravenous adenosine infusion.
Background
Although FFR has become a key invasive tool to guide treatment, questions remain regarding its repeatability and stability during intravenous adenosine infusion because of systemic effects that can alter driving pressure and heart rate.
Methods
We reanalyzed data from the VERIFY (VERification of Instantaneous Wave-Free Ratio and Fractional Flow Reserve for the Assessment of Coronary Artery Stenosis Severity in EverydaY Practice) study, which enrolled consecutive patients who were infused with intravenous adenosine at 140 ÎŒg/kg/min and measured FFR twice. Raw phasic pressure tracings from the aorta (Pa) and distal coronary artery (Pd) were transformed into moving averages of Pd/Pa. Visual analysis grouped Pd/Pa curves into patterns of similar response. Quantitative analysis of the Pd/Pa curves identified the âsmart minimumâ FFR using a novel algorithm, which was compared with human core laboratory analysis.
Results
A total of 190 complete pairs came from 206 patients after exclusions. Visual analysis revealed 3 Pd/Pa patterns: âclassicâ (sigmoid) in 57%, âhumpedâ (sigmoid with superimposed bumps of varying height) in 39%, and âunusualâ (no pattern) in 4%. The Pd/Pa pattern repeated itself in 67% of patient pairs. Despite variability of Pd/Pa during the hyperemic period, the âsmart minimumâ FFR demonstrated excellent repeatability (bias â0.001, SD 0.018, paired p = 0.93, r2 = 98.2%, coefficient of variation = 2.5%). Our algorithm produced FFR values not significantly different from human core laboratory analysis (paired p = 0.43 vs. VERIFY; p = 0.34 vs. RESOLVE).
Conclusions
Intravenous adenosine produced 3 general patterns of Pd/Pa response, with associated variability in aortic and coronary pressure and heart rate during the hyperemic period. Nevertheless, FFR â when chosen appropriately â proved to be a highly reproducible value. Therefore, operators can confidently select the âsmart minimumâ FFR for patient care. Our results suggest that this selection process can be automated, yet comparable to human core laboratory analysis
The Casimir Effect for Fermions in One Dimension
We study the Casimir problem for a fermion coupled to a static background
field in one space dimension. We examine the relationship between interactions
and boundary conditions for the Dirac field. In the limit that the background
becomes concentrated at a point (a ``Dirac spike'') and couples strongly, it
implements a confining boundary condition. We compute the Casimir energy for a
masslike background and show that it is finite for a stepwise continuous
background field. However the total Casimir energy diverges for the Dirac
spike. The divergence cannot be removed by standard renormalization methods. We
compute the Casimir energy density of configurations where the background field
consists of one or two sharp spikes and show that the energy density is finite
except at the spikes. Finally we define and compute an interaction energy
density and the force between two Dirac spikes as a function of the strength
and separation of the spikes.Comment: 18 pages, 6 figure
Phasic pressure measurements for coronary and valvular interventions using fluid-filled catheters: Errors, automated correction, and clinical implications.
We sought to develop an automatic method for correcting common errors in phasic pressure tracings for physiology-guided interventions on coronary and valvular stenosis.
Effective coronary and valvular interventions rely on accurate hemodynamic assessment. Phasic (subcycle) indexes remain intrinsic to valvular stenosis and are emerging for coronary stenosis. Errors, corrections, and clinical implications of fluid-filled catheter phasic pressure assessments have not been assessed in the current era of ubiquitous, high-fidelity pressure wire sensors.
We recruited patients undergoing invasive coronary physiology assessment. Phasic aortic pressure signals were recorded simultaneously using a fluid-filled guide catheter and 0.014âł pressure wire before and after standard calibration as well as after pullback. We included additional subjects undergoing hemodynamic assessment before and after transcatheter aortic valve implantation. Using the pressure wire as reference standard, we developed an automatic algorithm to match phasic pressures.
Removing pressure offset and temporal shift produced the largest improvements in root mean square (RMS) error between catheter and pressure wire signals. However, further optimization <1 mmHg RMS error was possible by accounting for differential gain and the oscillatory behavior of the fluid-filled guide. The impact of correction was larger for subcycle (like systole or diastole) versus whole-cycle metrics, indicating a key role for valvular stenosis and emerging coronary pressure ratios.
When calibrating phasic aortic pressure signals using a pressure wire, correction requires these parameters: offset, timing, gain, and oscillations (frequency and damping factor). Automatically eliminating common errors may improve some clinical decisions regarding physiology-based intervention
Nanoindentation modeling of a nanodot-patterned surface on a deformable substrate
AbstractA numerical model was developed to simulate the nanoindentation of a Ni nanodot-patterned surface (NDPS) on a deformable Si substrate. Each contacting nanodot on the Si substrate was treated individually in this model and the interaction among the nanodots was considered through the elastic deformation of the Si substrate. The loadâdeformation relationship for the single-asperity contact between the indenter tip and a nanodot was determined using finite element analysis. A nanoindentation experiment on a Ni NDPS was performed to test the developed model. The simulation and experimental results were found to be in good agreement. The experimentally verified model was used to explore the effects of substrate deformation and surface roughness caused by the Ni nanodots on the nanoindentation behavior. It was found that the effect of the substrate and the effect of roughness must be considered. A detailed study of the substrate deformation shows that the interaction among nanodots, through the substrate, can contribute a considerable portion of the total deformation under a nanodot. The yield strength of the nanodot was found to have a significant effect on the contact deformation, while the elastic modulus was found to have little effect
Supernovae and Positron Annihilation
Radioactive nuclei, especially those created in SN explosion, have long been
suggested to be important contributors of galactic positrons. In this paper we
describe the findings of three independent OSSE/SMM/TGRS studies of positron
annihilation radiation, demonstrating that the three studies are largely in
agreement as to the distribution of galactic annihilation radiation. We then
assess the predicted yields and distributions of SN-synthesized radionuclei,
determining that they are marginally compatible with the findings of the
annihilation radiation studies.Comment: 7 pages, accepted for publication in New Astronomy Reviews (Astronomy
with Radioactivites III
Proton-Induced Background Studies for a Satellite Gamma-Ray Experiment
This work was supported by the National Science Foundation Grant NSF PHY 78-22774 A02 & A03 and by Indiana Universit
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