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Field and microcosm observations of methanogenic phenolic compound degradation indicate that Monod kinetics governs the substrate disappearance but overestimates the observed biomass. In this paper we present modeling results from an ongoing multidisciplinary study of methanogenic biodegradation of phenolic compounds in a sand and gravel aquifer contaminated by chemicals and wastes used in wood treatment. Field disappearance rates of four phenols match those determined in batch microcosm studies previously performed by E.M. Godsy and coworkers. The degradation process appears to be at steady-state because even after a sustained influx over several decades, the contaminants still are disappearing in transport downgradient. The existence of a steady-state degradation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no net growth. This may be due to the oligotrophic nature of the biomass population in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate due to hostile conditions or predation. 相似文献
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ter Hofstede HM Goerlitz HR Montealegre-Z F Robert D Holderied MW 《Die Naturwissenschaften》2011,98(12):1057-1061
Ears evolved in many groups of moths to detect the echolocation calls of predatory bats. Although the neurophysiology of bat
detection has been intensively studied in moths for decades, the relationship between sound-induced movement of the noctuid
tympanic membrane and action potentials in the auditory sensory cells (A1 and A2) has received little attention. Using laser
Doppler vibrometry, we measured the velocity and displacement of the tympanum in response to pure tone pulses for moths that
were intact or prepared for neural recording. When recording from the auditory nerve, the displacement of the tympanum at
the neural threshold remained constant across frequencies, whereas velocity varied with frequency. This suggests that the
key biophysical parameter for triggering action potentials in the sensory cells of noctuid moths is tympanum displacement,
not velocity. The validity of studies on the neurophysiology of moth hearing rests on the assumption that the dissection and
recording procedures do not affect the biomechanics of the ear. There were no consistent differences in tympanal velocity
or displacement when moths were intact or prepared for neural recordings for sound levels close to neural threshold, indicating
that this and other neurophysiological studies provide good estimates of what intact moths hear at threshold. 相似文献
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