42,496 research outputs found
Near Infrared Spectroscopy Describes Physiologic Payback Associated With Excess Postexercise Oxygen Consumption in Healthy Controls and Children With Complex Congenital Heart Disease
Exercise creates a physiologic burden with recovery from such effort crucial to adaptation. Excess postexercise oxygen consumption (EPOC) refers to the body’s increased metabolic need after work. This investigation was designed to determine the role of near infrared spectroscopy (NIRS) in the description of exercise recovery in healthy controls (NL) and children with congenital heart disease (CHD). Subjects were recruited with exercise testing performed to exhaustion. Exercise time (EXT), heart rate (HR), and oxygen consumption (VO2) were measured. Four-site NIRS (brain, kidney, deltoid, and vastus lateralis) were measured during exercise and into recovery to establish trends. Fifty individuals were recruited for each group (NL = 26 boys and 24 girls; CHD = 33 boys and 17 girls). Significant differences existed between EXT, VO2, and peak HR (P \u3c 0.01). NIRS values were examined at four distinct intervals: rest, peak work, and 2 and 5 min after exercise. Significant cerebral hyperemia was seen in children with CHD post exercise when compared to normal individuals in whom redistribution patterns were directed to somatic muscles. These identified trends support an immediate compensation of organ systems to re-establish homeostasis in peripheral beds through enhanced perfusion. Noninvasive NIRS monitoring helps delineate patterns of redistribution associated with EPOC in healthy adolescents and children with CHD
Role of spatial coherence in polarization tomography
We analyze an experimental setup in which a quasi-monochromatic spatially
coherent beam of light is used to probe a paraxial optical scatterer. We
discuss the effect of the spatial coherence of the probe beam on the Mueller
matrix representing the scatterer. We show that according to the degree of
spatial coherence of the beam, the \emph{same} scattering system can be
represented by \emph{different} Mueller matrices. This result should serve as a
warning for experimentalists.Comment: 3 pages, 1 figur
Irrigation management research in Sri Lanka: A review of selected literature. Occasional paper. Occasional paper
Irrigation management / Research / Irrigation systems / Rehabilitation / Financing / Resource management / Policy / Farmer participation / Farmer-agency interactions / Sri Lanka
Two Modes of Solid State Nucleation - Ferrites, Martensites and Isothermal Transformation Curves
When a crystalline solid such as iron is cooled across a structural
transition, its final microstructure depends sensitively on the cooling rate.
For instance, an adiabatic cooling across the transition results in an
equilibrium `ferrite', while a rapid cooling gives rise to a metastable twinned
`martensite'. There exists no theoretical framework to understand the dynamics
and conditions under which both these microstructures obtain. Existing theories
of martensite dynamics describe this transformation in terms of elastic strain,
without any explanation for the occurence of the ferrite. Here we provide
evidence for the crucial role played by non-elastic variables, {\it viz.},
dynamically generated interfacial defects. A molecular dynamics (MD) simulation
of a model 2-dimensional (2d) solid-state transformation reveals two distinct
modes of nucleation depending on the temperature of quench. At high
temperatures, defects generated at the nucleation front relax quickly giving
rise to an isotropically growing `ferrite'. At low temperatures, the defects
relax extremely slowly, forcing a coordinated motion of atoms along specific
directions. This results in a twinned critical nucleus which grows rapidly at
speeds comparable to that of sound. Based on our MD results, we propose a
solid-state nucleation theory involving the elastic strain and non-elastic
defects, which successfully describes the transformation to both a ferrite and
a martensite. Our work provides useful insights on how to formulate a general
dynamics of solid state transformations.Comment: 3 pages, 4 B/W + 2 color figure
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