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Only A Few Days (only a + few_day)
Selected AbstractsTransport and settlement of organic matter in small streamsFRESHWATER BIOLOGY, Issue 2 2010TRENT M. HOOVER Summary 1.,After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (,flexible' red alder leaves and three ,stiff' particle types , Douglas-fir needles, red cedar fronds and Douglas-fir branch pieces). 2.,Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas-fir needles and red cedar fronds, which all reached constant still-water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3.,We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ,riffle' than a slow, deep ,pool'. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4.,These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second-order coastal stream. 5.,When the experimental channel and in-stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams. [source] Strong seasonal disequilibrium measured between the oxygen isotope signals of leaf and soil CO2 exchangeGLOBAL CHANGE BIOLOGY, Issue 11 2010LISA WINGATE Abstract The oxygen isotope composition (,18O) of atmospheric CO2 is among a very limited number of tools available to constrain estimates of the biospheric gross CO2 fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber-based field measurements of total CO2 and CO18O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the ,18O signals of foliage and soil CO2 exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the ,18O signatures of net CO2 fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the ,18O of CO2 exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation. [source] Sensory neuropathy in the prodromal phase of hepatitis A and review of the literatureJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 7 2000Shamsul Islam Abstract We report an unrecognized clinical presentation of hepatitis A with unilateral peripheral acute sensory loss in the prodromal phase of the illness. Although rare, focal neurological signs are known to occur in hepatitis A before, during and after the icteric phase; a pure peripheral sensory neuropathy is distinctly uncommon. Possible lesions could include radiculopathy of the lower thoraco,lumbo,sacral dorsal nerve roots or a partial transverse myelitis of Brown-Séquad like distribution. The signs and symptoms lasted only a few days and the patient had an uneventful recovery. [source] Mathematical modeling of the circadian rhythm of key neuroendocrine,immune system players in rheumatoid arthritis: A systems biology approachARTHRITIS & RHEUMATISM, Issue 9 2009Michael Meyer-Hermann Objective Healthy subjects and patients with rheumatoid arthritis (RA) exhibit circadian rhythms of the neuroendocrine,immune system. Understanding circadian dynamics is complex due to the nonlinear behavior of the neuroendocrine,immune network. This study was undertaken to seek and test a mathematical model for studying this network. Methods We established a quantitative computational model to simulate nonlinear interactions between key factors in the neuroendocrine,immune system, such as plasma tumor necrosis factor (TNF), plasma cortisol (and adrenal cholesterol store), and plasma noradrenaline (NA) (and presynaptic NA store). Results The model was nicely fitted with measured reference data on healthy subjects and RA patients. Although the individual circadian pacemakers of cortisol, NA, and TNF were installed without a phase shift, the relative phase shift between these factors evolved as a consequence of the modeled network interactions. Combined long-term and short-term TNF increase (the "RA model") increased cortisol plasma levels for only a few days, and cholesterol stores started to become markedly depleted. This nicely demonstrated the phenomenon of inadequate cortisol secretion relative to plasma TNF levels, as a consequence of adrenal deficiency. Using the RA model, treatment with glucocorticoids between midnight and 2:00 AM was found to have the strongest inhibitory effect on TNF secretion, which supports recent studies on RA therapy. Long-term reduction of TNF levels by simulation of anti-TNF therapy normalized cholesterol stores under "RA" conditions. Conclusion These first in silico studies of the neuroendocrine,immune system in rheumatology demonstrate that computational biology in medicine, making use of large collections of experimental data, supports understanding of the pathophysiology of complex nonlinear systems. [source] | |||||||||||||