Non-linear Changes (non-linear + change)

Distribution by Scientific Domains

Selected Abstracts

The influence of pool length on local turbulence production and energy slope: a flume experiment

Douglas M. Thompson
Abstract The in,uence of pool length on the strength of turbulence generated by vortex shedding was investigated in a 6 m long recirculating ,ume. The experiment utilized a 38% constriction of ,ow and an average channel-bed slope of 0007. The base geometry for the intermediate-length pool experiment originated from a highly simpli,ed, 010 scale model of a forced pool from North Saint Vrain Creek, Colorado. Discharge in the ,ume was 316 l/s, which corresponds to a discharge in the prototype channel of 10 m3/s. Three shorter and four longer pool lengths also were created with a ,xed bed to determine changes in turbulence intensities and energy slope with pool elongation. Three-dimensional velocities were measured with an acoustic Doppler velocimeter at 31,40 different 06-depth and near-bed locations downstream of the rectangular constriction. The average velocity and root mean square (RMS) of the absolute magnitude of velocity at both depths are signi,cantly related to the distance from the constriction in most pool locations downstream of the constriction. In many locations, pool elongation results in a non-linear change in turbulence intensities and average velocity. Based on the overall ,ow pattern, the strongest turbulence occurs in the center of the pool along the shear zone between the jet and recirculating eddy. The lateral location of this shear zone is sensitive to changes in pool length. Energy slope also was sensitive to pool length due to a combination of greater length of the pool and greater head loss with shorter pools. The results indicate some form of hydraulic optimization is possible with pools adjusting their length to adjust the location and strength of turbulent intensities in the center of pools, and lower their rate of energy dissipation. Copyright 2004 John Wiley & Sons, Ltd. [source]

Interactive effects of distance and matrix on the movements of a peatland dragonfly

ECOGRAPHY, Issue 5 2009
Krista S. Chin
We conducted a mark,release,recapture survey of a peatland dragonfly (Leucorrhinia hudsonica) in each of two years (2002; 2003) in a harvested forest landscape in western Newfoundland, Canada. The odds of an individual male moving between peatlands was influenced by both the distance between peatlands and the type of intervening habitat (the matrix). Specifically, at meso scales (>700,m) there was a positive effect of the amount of cut matrix between peatlands on the odds of moving, but at fine scales (<700,m) there was the opposite effect; proportionally fewer individuals moved between peatlands. The odds of moving out of a peatland decreased as the surface area of water in the peatland increased. Multi-state mark,recapture models showed that the daily probability of a male moving between any two peatlands was 1.9% in 2002 and 6.9% in 2003 (n=1527 and 1280 marked individuals). The results suggest that additional empirical studies that directly measure patterns of movement with respect to landscape structure at multiple spatial scales in other taxa and situations are needed in order to uncover other possible non-linear changes in behavior. [source]

Effects of food limitation and emigration on self-thinning in experimental minnow cohorts

J. B. Dunham
Summary 1.,The theory of food-regulated self-thinning (FST) for mobile animals predicts population density (N) to be an inverse function of mean body mass (W) scaled to an exponent (b), such that N = k W,b, where k is a constant. FST also predicts energy requirements (or energy flow) to remain constant over time (termed energetic equivalence) as losses to cohorts (e.g. emigration and mortality) are balanced by increased growth of surviving individuals. 2.,To test these predictions, we analysed the dynamics of six experimental minnow cohorts. Replicate populations of fish were held under identical conditions with a constant and limited supply of food over a 126-day period. Half of the cohorts were open to emigration, and half were closed so that fish could only be lost through starvation mortality. 3.,Patterns of self-thinning indicated non-linear changes in population density and energy flow in relation to changes in mean body mass and time, respectively. Non-linear patterns of self-thinning were probably due to a delayed growth response to changes in population density effected through mortality and/or emigration. Contrary to results of similar experiments on other fish, emigration did not have a significant influence on the pattern of self-thinning. 4.,These results may be attributed to trophic interactions within cohorts and the importance of social behaviour to cohort dynamics. Both population density and energy flow in our experimental populations appeared to cycle, with episodes of starvation and mortality alternating with food recovery and weight gain, as predicted by recent models of stepwise die-off and stunted growth in animal cohorts. 5.,Most of the support for FST in mobile animals comes from observational data on mean body mass and population density. Potentially important mechanisms, including the manner in which individuals are lost or retained in populations, are usually not investigated directly. Such tests of FST can only provide equivocal support. Detailed observational study and controlled experiments are needed to understand casual mechanisms. [source]

Structural complexity and land-surface energy exchange along a gradient from arctic tundra to boreal forest

C. Thompson
Abstract: Question: Current climate changes in the Alaskan Arctic, which are characterized by increases in temperature and length of growing season, could alter vegetation structure, especially through increases in shrub cover or the movement of treeline. These changes in vegetation structure have consequences for the climate system. What is the relationship between structural complexity and partitioning of surface energy along a gradient from tundra through shrub tundra to closed canopy forest? Location: Arctic tundra-boreal forest transition in the Alaskan Arctic. Methods: Along this gradient of increasing canopy complexity, we measured key vegetation characteristics, including community composition, biomass, cover, height, leaf area index and stem area index. We relate these vegetation characteristics to albedo and the partitioning of net radiation into ground, latent, and sensible heating fluxes. Results: Canopy complexity increased along the sequence from tundra to forest due to the addition of new plant functional types. This led to non-linear changes in biomass, cover, and height in the understory. The increased canopy complexity resulted in reduced ground heat fluxes, relatively conserved latent heat fluxes and increased sensible heat fluxes. The localized warming associated with increased sensible heating over more complex canopies may amplify regional warming, causing further vegetation change in the Alaskan Arctic. [source]

Changes in extracellular K+ concentration modulate contractility of rat and rabbit cardiac myocytes via the inward rectifier K+ current IK1

Ron Bouchard
The mechanisms underlying the inotropic effect of reductions in [K+]o were studied using recordings of membrane potential, membrane current, cell shortening and [Ca2+]i in single, isolated cardiac myocytes. Three types of mammalian myocytes were chosen, based on differences in the current density and intrinsic voltage dependence of the inwardly rectifying background K+ current IK1 in each cell type. Rabbit ventricular myocytes had a relatively large IK1 with a prominent negative slope conductance whereas rabbit atrial cells expressed much smaller IK1, with little or no negative slope conductance. IK1 in rat ventricle was intermediate in both current density and slope conductance. Action potential duration is relatively short in both rabbit atrial and rat ventricular myocytes, and consequently both cell types spend much of the duty cycle at or near the resting membrane potential. Rapid increases or decreases of [K+]o elicited significantly different inotropic effects in rat and rabbit atrial and ventricular myocytes. Voltage-clamp and current-clamp experiments showed that the effects on cell shortening and [Ca2+]i following changes in [K+]o were primarily the result of the effects of alterations in IK1, which changed resting membrane potential and action potential waveform. This in turn differentially altered the balance of Ca2+ efflux via the sarcolemmal Na+,Ca2+ exchanger, Ca2+ influx via voltage-dependant Ca2+ channels and sarcoplasmic reticulum (SR) Ca2+ release in each cell type. These results support the hypothesis that the inotropic effect of alterations of [K+]o in the heart is due to significant non-linear changes in the current,voltage relation for IK1 and the resulting modulation of the resting membrane potential and action potential waveform. [source]