1,036 research outputs found
Polarization singularities in the clear sky
Ideas from singularity theory provide a simple account of the pattern of polarization directions in daylight. The singularities (two near the Sun and two near the anti-Sun) are points in the sky where the polarization line pattern has index +1/2 and the intensity of polarization is zero. The singularities are caused by multiple scattering that splits into two each of the unstable index +1 singularities at the Sun and anti-Sun, which occur in the single-dipole scattering (Rayleigh) theory. The polarization lines are contours of an elliptic integral. For the intensity of polarization (unnormalized degree), it is necessary to incorporate the strong depolarizing effect of multiple scattering near the horizon. Singularity theory is compared with new digital images of sky polarization, and gives an excellent description of the pattern of polarization directions. For the intensity of polarization, the theory can reproduce not only the zeros but also subtle variations in the polarization maxima
Achieving More Freedom by Farm Tenancy Improvement
Some studies have shown that share tenants use about the same farming practices as cash tenants and owner operators. Other studies show that share tenants have lost most of the freedom and incentive to develop, improve and conserve the land and buildings they lease. This situation raises these questions: (1) What are the freedoms provided by ownership? Why are they important? (2) What are the alternative ways these freedoms can be provided? (3) What are the problems of share rent leasing? (4) What are the problems and possibilities of fixed or flexible cash rent leasing? (5) What research is suggested by this review of farm ownership and tenancy problems? The purpose of this circular is to answer these and related questions. Most evidence to support answers is drawn from many studies made during the past 30 years. Some of the more important sources are listed at the end for readers who want further information
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
Numerical study of scars in a chaotic billiard
We study numerically the scaling properties of scars in stadium billiard.
Using the semiclassical criterion, we have searched systematically the scars of
the same type through a very wide range, from ground state to as high as the 1
millionth state. We have analyzed the integrated probability density along the
periodic orbit. The numerical results confirm that the average intensity of
certain types of scars is independent of rather than scales with
. Our findings confirm the theoretical predictions of Robnik
(1989).Comment: 7 pages in Revtex 3.1, 5 PS figures available upon request. To appear
in Phys. Rev. E, Vol. 55, No. 5, 199
Casimir Effects: An Optical Approach I. Foundations and Examples
We present the foundations of a new approach to the Casimir effect based on
classical ray optics. We show that a very useful approximation to the Casimir
force between arbitrarily shaped smooth conductors can be obtained from
knowledge of the paths of light rays that originate at points between these
bodies and close on themselves. Although an approximation, the optical method
is exact for flat bodies, and is surprisingly accurate and versatile. In this
paper we present a self-contained derivation of our approximation, discuss its
range of validity and possible improvements, and work out three examples in
detail. The results are in excellent agreement with recent precise numerical
analysis for the experimentally interesting configuration of a sphere opposite
an infinite plane.Comment: Minor corrections. Submitted to Nucl. Phys.
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Preliminary technology report for Southern Sector bioremediation
This project was designed to demonstrate the potential of intrinsic bioremediation and phytoremediation in the Southern Sector of the A/M-Area at the Savannah River Site. A subsurface plume of trichloroethylene (TCE) and perchloroethylene (PCE) is present in the Lost Lake aquifer upgradient of the study site and is predicted to impact the area at some point in the future. The surface area along the Lost lake aquifer seep line where the plume is estimated to emerge was identified. Ten sites along the seep line were selected for biological, chemical, and contaminant treatability analyses. A survey was undertaken in this area to to quantify the microbial and plant population known to be capable of remediating TCE and PCE. The current groundwater quality upgradient and downgradient of the zone of influence was determined. No TCE or PCE was found in the soils or surface water from the area tested at this time. A TCE biodegradation treatability test was done on soil from the 10 selected locations. From an initial exposure of 25 ppm of TCE, eight of the samples biodegraded up to 99.9 percent of all the compound within 6 weeks. This biodegradation of TCE appears to be combination of aerobic and anaerobic microbial activity as intermediates that were detected in the treatability test include vinyl chloride (VC) and the dichloroethenes (DCE) 1,2-cis-dichloroethylene and 1,1-dichloroethylene. The TCE biological treatability studies were combines with microbiological and chemical analyses. The soils were found through immunological analysis with direct fluorescent antibodies (DFA) and microbiological analysis with direct fluorescent antibodies (DFA) and microbiological analysis to have a microbial population of methanotrophic bacteria that utilize the enzyme methane monooxygenase (MMO) and cometabolize TCE
Elementary Professional Development within a âPracticalâ Action Research Effort to Improve Student Literacy
The purpose of this inquiry was to support and augment the action research efforts of elementary teachers who were attempting to enhance literacy outcomes in their respective classrooms. Included are elementary teacher insights, university-based facilitator views, and principal perspectives that together complete a picture of our professional development efforts. Together the data provide an overview of an action research effort, wherein praxis was noted as a necessary element to assume âpracticalâ investigative roles. Praxis herein is the deliberate, informed, planned, and systematic action which is the critical underpinning of all action research efforts. The action in this case was directed towards improvement and implementation of an instructional initiative. This outcome brings with it an immense level of significance in that all educators seek to improve educational outcomes personally, professionally, and politically; therefore a report such as this may be viewed as an essential tool to refine educational practice
Chaos and Quantum-Classical Correspondence via Phase Space Distribution Functions
Quantum-classical correspondence in conservative chaotic Hamiltonian systems
is examined using a uniform structure measure for quantal and classical phase
space distribution functions. The similarities and differences between quantum
and classical time-evolving distribution functions are exposed by both
analytical and numerical means. The quantum-classical correspondence of
low-order statistical moments is also studied. The results shed considerable
light on quantum-classical correspondence.Comment: 16 pages, 5 figures, to appear in Physical Review
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