991 resultados para 169-1033A


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The Holocene section in Saanich Inlet, Vancouver Island, British Columbia, is 50-70 m thick. Cores from Saanich Inlet obtained during Leg 169S of the Ocean Drilling Program afford an excellent opportunity to obtain an ultrahigh-resolution paleomagnetic and environmental magnetic record for the Holocene and Late Pleistocene of western Canada. We have used an automated, long-core cryogenic magnetometer to study over 380 m of continuous u-channel samples from ODP Sites 1033 and 1034, the two sites that constitute Leg 169S. Holocene records of paleomagnetic inclination and intensity show excellent intra-site correlation and can be used to fine-tune the lithologic correlation among cores from each site. The Late Pleistocene magnetic records provide a means of intra-site correlation of the otherwise featureless marine clay. Near the Holocene/Late Pleistocene boundary, both sites contain a magnetic intensity feature that is interpreted as a Missoula-type flood event on the Fraser River. The composite Holocene inclination records from the two sites are quite similar and provide a means of comparing current age-models that are based on radiocarbon dating of material from each site. This comparison shows only minor differences in the available age-models. It also provides strong evidence that the sediments of Saanich Inlet represent a reliable record of geomagnetic field behavior.

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Digital image

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Digital image

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High repetition rate passively mode-locked sources are of significant interest due to their potential for applications including optical clocking, optical sampling, communications and others. Due to their short excited state lifetimes mode-locked VECSELs are ideally suited to high repetition rate operation, however fundamentally mode-locked quantum well-based VECSELs have not achieved repetition rates above 10 GHz due to the limitations placed on the cavity geometry by the requirement that the saturable absorber saturates more quickly than the gain. This issue has been overcome by the use of quantum dot-based saturable absorbers with lower saturation fluences leading to repetition rates up to 50 GHz, but sub-picosecond pulses have not been achieved at these repetition rates. We present a passively harmonically mode-locked VECSEL emitting pulses of 265 fs duration at a repetition rate of 169 GHz with an output power of 20 mW. The laser is based around an antiresonant 6 quantum well gain sample and is mode-locked using a semiconductor saturable absorber mirror. Harmonic modelocking is achieved by using an intracavity sapphire etalon. The sapphire then acts as a coupled cavity, setting the repetition rate of the laser while still allowing a tight focus on the saturable absorber. RF spectra of the laser output show no peaks at harmonics of the fundamental repetition rate up to 26 GHz, indicating stable harmonic modelocking. Autocorrelations reveal groups of pulses circulating in the cavity as a result of an increased tendency towards Q-switched modelocking due to the low pulse energies.

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Consultoria de Orçamento e Fiscalização Financeira.

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The purpose of this work is a contribution to the quantitative record of the use of iron by planktonic algae. Preliminary experiments with Chlorella to determine the rate of iron intake in the presence of inorganic sources of iron did not produce the desired result. The crucial point of this work is the investigation of the influence of various external factors on the stability of FeEDTA (FeEDTA = Ferric(III)-compound of ethylene-diamine tetra-acetic acid), since this compound appears to be particularly well-suited as a source of iron for planktonic algae (e.g. TAMIYA et al. 1953). Cultures of Chlorella fusca in a light thermostat were used in experimental research. Methods and results are discussed.

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