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Pulse Intervals (pulse + interval)

Distribution by Scientific Domains
Life Sciences42%
Medical Sciences28%

Selected Abstracts

Response of Daphnia magna to pulsed exposures of chlorpyrifos,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2000
Rami B. Naddy
Abstract Because aquatic organisms can be exposed to contaminants in an episodic manner, it is necessary to determine whether standard toxicity tests adequately simulate the toxicity of short-lived compounds, such as the organophosphate insecticide chlorpyrifos (CPF). We conducted experiments to evaluate the effect of binary combinations of concentration, duration, and interval of CPF exposures to Daphnia magna. Organisms were monitored for changes in survival and/or reproduction after pulsed exposure to CPF at 0.12, 0.25, 0.5, or 1.0 ,g/L. The exposure duration resulting in a 50% response in survival was 6.5 h at 1.0 ,g/L, 12.2 h at 0.5 ,g/L, and 48 h at 0.25 ,g/L. Daphnids exposed to two 12-h pulses of CPF at 0.5 ,g/L responded similarly (,85% mortality) regardless of the pulse interval (0, 3, 7, 14 d). However, daphnids were able to survive a 12-h exposure of CPF at 0.5 ,g/L if the exposure regime was separated into two 6-h pulses with a minimum interval of 3 d. Further experiments suggested that the interval studies may have been potentially confounded, because organisms exposed on day 3, 7, or 14 seemed more sensitive than those exposed as neonates. Additionally, no latent effects were measured for daphnids that survived the initial exposure. [source]

Microbial community dynamics in nutrient-pulsed chemostats

FEMS MICROBIOLOGY ECOLOGY, Issue 1 2006
Militza Carrero-Colón
Abstract In nature, microbes are subject to nutrient fluxes. As the periodicity of nutrient flux lengthens, different physiological traits may be selected. The competitive exclusion principle stipulates that one organism will dominate these systems; however, interspecies interactions may produce a dynamic microbial community. These issues were investigated in chemostats pulsed with gelatin. Chemostats were run over 30 days with substrate addition continuously or at intervals of 0.5, 1 or 3 days. Growth rates were similar between pulse intervals. Ectoaminopeptidase activity levels remained relatively constant within a pulse interval. Bacterial community structure was monitored using denaturing gradient gel electrophoresis of PCR products of the 16S rRNA gene. There were dynamic changes at all periodicities; however, the pace of these changes decreased over time. Final communities were not identical between different treatments. The structure of persistent vs. active microbial populations was compared by denaturing gradient gel electrophoresis of the PCR and reverse transcriptase-PCR amplicons of 16S rDNA and rRNA templates, respectively. For all the chemostats, the rRNA profiles were not identical to the rDNA profiles for a sample. These experiments demonstrate that complex community dynamics can occur under environmental heterogeneities that are modest relative to those found in natural aquatic habitats. Furthermore, the physiological functionality of these dynamic communities was stable. [source]

Effects of a selective neuropeptide Y Y2 receptor antagonist, BIIE0246, on Y2 receptors at peripheral neuroeffector junctions

BRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2001
Margaret A Smith-White
This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y2 receptor antagonist, on the inhibition of cholinergic neuroeffector transmission in rat heart and guinea-pig trachea and purinergic neuroeffector transmission in guinea-pig vas deferens produced by the NPY Y2 receptor agonist, N-acetyl [Leu28,31] NPY 24-36. In pentobarbitone anaesthetized rats, supramaximal stimulation every 30 s, of the vagus nerve innervating the heart, increased pulse interval by approximately 100 ms. This response was attenuated by intravenous administration of N-acetyl [Leu28,31] NPY 24-36 (10 nmol kg,1). Transmural stimulation of segments of guinea-pig trachea at 1 min intervals with 5 s trains of stimuli at 0.5, 5, 10, 20 and 40 Hz evoked contractions which were reduced in force by N-acetyl [Leu28,31] NPY 24-36 (2 ,M). In guinea-pig vasa deferentia, the amplitude of excitatory junction potentials evoked by trains of 20 stimuli at 1 Hz was reduced in the presence of N-acetyl [Leu28,31] NPY 24-36 (1 ,M). In all preparations BIIE0246 attenuated the inhibitory effect of N-acetyl [Leu28,31] NPY 24-36 but had no effect when applied alone. The findings support the view that the nerve terminals of postganglionic parasympathetic and sympathetic neurones possess neuropeptide Y Y2 receptors which, when activated, reduce neurotransmitter release. British Journal of Pharmacology (2001) 132, 861,868; doi:10.1038/sj.bjp.0703879 [source]

Microbial community dynamics in nutrient-pulsed chemostats

FEMS MICROBIOLOGY ECOLOGY, Issue 1 2006
Militza Carrero-Colón
Abstract In nature, microbes are subject to nutrient fluxes. As the periodicity of nutrient flux lengthens, different physiological traits may be selected. The competitive exclusion principle stipulates that one organism will dominate these systems; however, interspecies interactions may produce a dynamic microbial community. These issues were investigated in chemostats pulsed with gelatin. Chemostats were run over 30 days with substrate addition continuously or at intervals of 0.5, 1 or 3 days. Growth rates were similar between pulse intervals. Ectoaminopeptidase activity levels remained relatively constant within a pulse interval. Bacterial community structure was monitored using denaturing gradient gel electrophoresis of PCR products of the 16S rRNA gene. There were dynamic changes at all periodicities; however, the pace of these changes decreased over time. Final communities were not identical between different treatments. The structure of persistent vs. active microbial populations was compared by denaturing gradient gel electrophoresis of the PCR and reverse transcriptase-PCR amplicons of 16S rDNA and rRNA templates, respectively. For all the chemostats, the rRNA profiles were not identical to the rDNA profiles for a sample. These experiments demonstrate that complex community dynamics can occur under environmental heterogeneities that are modest relative to those found in natural aquatic habitats. Furthermore, the physiological functionality of these dynamic communities was stable. [source]

Radio-transmitted electromyogram signals as indicators of swimming speed in lake trout and brown trout

JOURNAL OF FISH BIOLOGY, Issue 3 2000
E. B. Thorstad
Swimming speed and average electromyogram (EMG) pulse intervals were highly correlated in individual lake trout Salvelinus namaycush (r2=0·52,0·89) and brown trout Salmo trutta (r2=0·45,0·96). High correlations were found also for pooled data in both lake trout (r2=0·90) and brown trout of the Emĺ stock (r2=0·96) and Lćrdal stock (r2=0·96). The linear relationship between swimming speed and average EMG pulse intervals differed significantly among lake trout and the brown trout stocks. This successful calibration of EMGs to swimming speed opens the possibility of recording swimming speed of free swimming lake trout and brown trout in situ. EMGs can also be calibrated to oxygen consumption to record energy expenditure. [source]

Intense pulsed light (IPL): A review

LASERS IN SURGERY AND MEDICINE, Issue 2 2010
Philipp Babilas MD
Abstract Background Intense pulsed light (IPL) devices use flashlamps and bandpass filters to emit polychromatic incoherent high-intensity pulsed light of determined wavelength spectrum, fluence, and pulse duration. Similar to lasers, the basic principle of IPL devices is a more or less selective thermal damage of the target. The combination of prescribed wavelengths, fluences, pulse durations, and pulse intervals facilitates the treatment of a wide spectrum of skin conditions. Objective To summarize the physics of IPL, to provide guidance for the practical use of IPL devices, and to discuss the current literature on IPL in the treatment of unwanted hair growth, vascular lesions, pigmented lesions, acne vulgaris, and photodamaged skin and as a light source for PDT and skin rejuvenation. Methods A systematic search of several electronic databases, including Medline and PubMed and the authors experience on intense pulsed light. Results Numerous trials show the effectiveness and compatibility of IPL devices. Conclusion Most comparative trials attest IPLs similar effectiveness to lasers (level of evidence: 2b to 4, depending on the indication). However, large controlled and blinded comparative trials with an extended follow-up period are necessary. Lasers Surg. Med. 42:93,104, 2010. © 2009 Wiley-Liss, Inc. [source]