Concentration dependence of upconversion emission from Er:YAG fibers.

Fibers of Er:YAG have been grown using the laser-heated pedestal growth method. Fibers with Er concentrations ranging from 0.5 to 10 mol. % have been produced and excitation at 965 nm has been used to produce intense upconversion emission at green and red wavelengths. The dependence of ground state absorption and upconversion emission on dopant concentration has been studied and shown to exhibit lower levels of self-absorption than previously reported. At Er concentrations of 5 mol. % and above; however, the variation of upconversion emission intensity with pump power deviates from theoretical predictions, exhibiting saturation behavior consistent with concentration quenching.

Functional convergence of microbes associated with temperate marine sponges.

Most marine sponges establish a persistent association with a wide array of phylogenetically and physiologically diverse microbes. To date, the role of these symbiotic microbial communities in the metabolism and nutrient cycles of the sponge-microbe consortium remains largely unknown. We identified and quantified the microbial communities associated with three common Mediterranean sponge species, Dysidea avara, Agelas oroides and Chondrosia reniformis (Demospongiae) that cohabitate coralligenous community. For each sponge we quantified the uptake and release of dissolved organic carbon (DOC) and nitrogen (DON), inorganic nitrogen and phosphate. Low microbial abundance and no evidence for DOC uptake or nitrification were found for D. avara. In contrast A. oroides and C. reniformis showed high microbial abundance (30% and 70% of their tissue occupied by microbes respectively) and both species exhibited high nitrification and high DOC and NH(4) (+) uptake. Surprisingly, these unique metabolic pathways were mediated in each sponge species by a different, and host specific, microbial community. The functional convergence of microbial consortia found in these two sympatric sponge species, suggest that these metabolic processes may be of special relevance to the success of the holobiont.

High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy.

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.

High-concentration Er:YAG single-crystal fibers grown by laser-heated pedestal growth technique.

High-concentration Er:YAG single-crystal fibers have been grown using the laser-heated pedestal growth technique. Instability in the melt and concomitant opacity of fibers were observed at source concentrations higher than 15 mol.%. Spectroscopic examination shows that broadening of the linewidth of the 4I(13/2) → 4I(15/2) transition is strongly dependent on Er³âº concentration.

Experimental systems implementation of a hybrid optical-digital correlator.

A high-speed hybrid optical-digital correlator system was designed, constructed, modeled, and demonstrated experimentally. This correlator is capable of operation at approximately 3000 correlations/s. The input scene is digitized at a resolution of 512 x 512 pixels and the phase information of the two-dimensional fast Fourier transform calculated and displayed in the correlator filter plane at normal video frame rates. High-fidelity reference template images are stored in a phase-conjugating optical memory placed at the nominal input plane of the correlator and reconstructed with a high-speed acousto-optic scanner; this allows for cross correlation of the entire reference data set with the input scene within one frame period. A high-speed CCD camera is used to capture the correlation-plane image, and rapid correlation-plane processing is achieved with a parallel processing architecture.

Graded-index characteristics in single-crystal fibers.

Single-crystal fibers of Ti(3+):Al(2)O (3)have been grown by the laser-heated pedestal growth technique and shown to exhibit radial refractive-index gradients. A refractive-index increase of approximately 12% in the fiber core with respect to the fiber sidewalls has been measured. The index profile can be fitted with a parabolic model. Postgrowth treatment of Cr(3+):Gd(3)Sc (2)Al (3)O(12)fibers has been shown to produce a uniform cladding region with a graded-index core. The core index is some 12.5% larger than the cladding region, with an index profile shape that is approximately parabolic in nature.

Compact phase-conjugating correlator: simulation and experimental analysis.

A simulation and experimental investigation of a recently proposed, compact, phase-conjugating correlator is undertaken. The effects of noise and other distortions in the input image and in the correlator filter plane are considered. As with other phase-only designs, the phase-conjugating correlator is sensitive to distortion of the input image while being robust in the presence of filter-plane distortions; this robustness is enhanced by the phase-conjugating property of the design.

High-speed, acousto-optically addressed optical memory.

A page-oriented, angle-multiplexed volume holographic optical-memory recording system has been constructed. This memory is addressed by the use of an acousto-optic deflector with a random-access time of 16 µs per page. This enables data transfer rates of 5.28 Gbits/s when pages of binary data are being stored. The reconstruction quality of images stored as memory pages is assessed with the quality achieved with the acousto-optic device compared with that achieved with the original recording optics.

Time-course of formation of volatile reductive metabolites of halothane in humans and an animal model.

The time-course of the formation of 2-chloro-1,1,1-trifluoroethane (CTF) and 2-chloro-1-1-difluoroethylene (CDF), two recently identified volatile reductive metabolites of halothane, has been studied in four patients receiving 1% halothane with 99% oxygen. The concentrations of CTF and CDF in end-expired breath increased with time and reached a plateau after approximately 60 min from commencing administration. A similar time-course and plateau was seen when Fischer 344 rats were anaesthetized with halothane 1% in oxygen. However, there was an eight-fold and 12-fold increase in CTF and CDF concentrations respectively when halothane 1% was administered under conditions of mild hypoxia (oxygen 14% inspired) to rats pretreated with phenobarbitone (this results in a marked increase in serum alanine aminotransferase (ALT) and necrotic damage in the vicinity of the central veins of the liver). It is suggested that breath concentrations of CDF and CTF provide a sensitive method of monitoring the reductive metabolism of halothane.

Hepatotoxicity and halothane metabolism in an animal model with application for human toxicity.

Centrilobular necrosis and a ten-fold elevation in serum alanine amino-transferase (ALT) consistently followed 2 hours of 1% halothane anaesthesia in an animal model. Conditional factors were the presence of enzyme induction and moderate hypoxia (14% oxygen), indicating an association between reductive metabolism and hepatotoxicity. Under these conditions there was at least a four-fold increase in reductive metabolites detected in the exhaled air. In clinical studies, reductive metabolites were also detected in the exhaled air of all patients examined, even after halothane anaesthesia with 100% oxygen. The amounts of reductive metabolites were comparable in man and the model, following equivalent halothane doses. It appears that a model with a similar route and rate of halothane biotransformation to man has been identified. The lesion of halothane hepatotoxicity in this model appears to be similar to that reported in man - centrilobular hepatic necrosis.

Volatile metabolites and decomposition products of halothane in man.

The presence of two volatile halothane metabolites, 2-chloro-1,1,1-trifluoroethane (CF3CH2Cl) and 2-chloro-1,1-difluoroethylene (CF2CHCl), and a metabolite-decomposition product, 2-bromo-2-chloro-1,1-difluoroethylene (CF2CBrCl), were identified by gas chromatography-mass spectrometry in exhaled gases of 16 patients anesthetized with halothane in nonrebreathing, semiclosed and totally closed anesthesia circuits. No significant differences in concentrations of CF3CH2Cl and CF2CHCl were found relative to the anesthesia circuits used. CF2CBrCl could not be identified in the expired gases of patients anesthetized with a nonrebreathing circuit (Bain), but was present in gases recovered from both semiclosed and totally closed circuits. Under totally closed-circuit rebreathing conditions, the concentration of CF2CBrCl increased to 4-5 ppm, indicating significant breakdown of halothane by the soda lime. Possible pathways for formation of the two metabolites and the metabolite-decomposition product are presented, as well as clinical implications of these findings.

Metabolism of enflurane in man following a second exposure.

A second administration of one half MAC enflurane for two hours one week following a previous identical exposure caused no increase in urinary inorganic Fluoride excretion (UFV). At this dosage of 1 MAC hour, which is equivalent to use as a supplement, UFV did not sub-anaesthetic doses of enflurane are administered at this time interval there appears to be no increased risk of nephrotoxicity. This study also provides strong support for the concept that drug metabolism is very reproducible within individuals but there is considerable variation between individuals. Since the subjects in this study were all of similar age, and drug free, the results are in keeping with recent twin studies which indicate that individual differences in drug metabolism are largely determined on a genetic basis.

BLUE-GREEN ALGAE FROM BERMUDA WATERS: ECOLOGICALLY SELECTED VARIATIONS OF A SINGLE SPECIES.

Three strains were isolated from Bermuda waters as unialgal cultures. Although identical in cell shape, cell size, and general growth features, marked differences in pigmentation, filament length, and sheath thickness were noted. These differences are explained as being due to differences in physical conditions of the areas of isolation of the 3 strains. It is concluded that the 3 strains are ecologically selected mutants of the single species, Schizothrix calcicola.