Browsing by Issue Date, starting with "1996"
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- All-fibre interrogation technique for fibre Bragg sensors using a biconical fibre filterPublication . Lobo Ribeiro, Antonio B.; Ferreira, L. A.; Tsvetkov, M.; Santos, J. L.A passive self-referencing all-fibre technique for Bragg wavelength shift detection using a biconical fibre filter is described. This filter, basically a tapered depressed-cladding fibre, exhibits a periodic spectral power dependence which permits direct tracking of wavelength shifts in a 20nm unambiguous range. Dynamic strain resolution of 1.5 μstrain/√Hz has been achieved.
- Fecundity, spore recruitment and size in Gelidium sesquipedale (Gelidiales,Rhodophyta)Publication . Santos, R.; Duarte, PedroGelidium sesquipedale fecundity was quantified by counting tetrasporangial sori and cystocarps per meter squared and by estimating the number of spores contained inside them . These were obtained by regression on a size metric of reproductive structures . Tetrasporangial sori length and cystocarp thickness were the best estimators of spore number. To assess spore recruitment, 12 pottery tiles were fixed to the bottom, and the appearance of small fronds was monitored. No clear seasonal pattern of reproduction was found . Tetraspore production peaked in March 1990 with 10.4 x 106 spores m-2, whereas the carpospore peak was lower, 4.9 x 10 5 spores m-2 in July 1989. Recruitment followed tetraspore peaks . The probability of a G. sesquipedale tetraspore making the transition to a recruit was 4.7 x 10-5. Frond length was significantly related to tetrasporangial sori number, while cystocarp number was only related to frond branching order. Minimum size for reproduction was 6.9 cm for gametophytes and 5.4 cm for tetrasporophytes; very rarely were cystocarpic fronds smaller than 9 cm, while tetrasporic fronds were often longer than 15 cm . Cystocarpic fronds were significantly shorter and had more branches than tetrasporic fronds .
- Prospecting for coalbed methane: preliminary investigation into the possibilities in SpainPublication . Lemos de Sousa, M. J.; Pinheiro, H. J.The fundamental objetive of this study resides in investigating the potential suitability of spanish coalfields to prospecting natural gas from coal in-situ (Coalbed Methane-CBM). The study was based not only on a literature survey and supplemented by onsite visits and investigations, but also on inhouse research activities. Tree selecting criteria have been defined: 1.1. Existing resources: a figure of 20MT of coal was estrablished as the minimum in-situ tonnage worth considering. This limit is comprised of the sum of "very probable" and " probable" resources. 1.2. Coal rank: in agreement with the generally accepted principle that the most significant amount of gas produced by coal corresponds to a coalification level of Rr> 1.2% (ca VM (daf) < 30&), only coalfields reporting such values were selected. 1.3 Geological and Structural considerations such as: 1.3.1 Identification of stratigraphic units, their sedimentary conditions including the presence of coal-bearing units with sufficient seams (frequency) with thickness that will potentially permit their in-situ exploration and exploitation for natural gas. 1.3.2 Structural regime compatible with the retention of gas by the coal beds and adjacent host rocks. 2. On the basis of currently available information, and on applying the abovementioned criteria to spanish coalfields, the following ones have been identified as potentially the most suitable for coalbed methane prospecting (in decreasing order of importance): • Ciñera-Matallana and Cerredo-Villablino, considered to have equivalent potential • La Pernía-Barruelo • Central Asturian Coalfield, South region • El Bierzo.
- Simultaneous measurement of displacement and temperature using a low finesse cavity and a fiber Bragg gratingPublication . Ferreira, L.A.; Lobo Ribeiro, Antonio B.; Santos, J.L.; Farahi, F.An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.
- Time-and-spatial-multiplexing tree topology for fiber-optic Bragg-grating sensors with interferometric wavelength-shift detectionPublication . Lobo Ribeiro, Antonio B.; Rao, Y. J.; Zhang, L.; Bennion, I.; Jackson, D. A.A combined time-and-spatial-division-multiplexed tree topology with eight fiber-optic Bragg-grating sensors operating at the 830-nm wavelength was constructed and tested for both quasistatic and periodic strain and temperature measurements. The system uses a interferometric wavelength-shift discriminator and incorporates a reference channel for thermal drift compensation in the output. Dynamic sensor sensitivity, as determined by primary noise sources, is evaluated, and numerical results are presented and compared with experimental results.