Vesicle shrinkage in hydrous phonolitic melt during cooling.

The ascent of hydrous magma prior to volcanic eruptions is largely driven by the formation of H2O vesicles and their subsequent growth upon further decompression. Porosity controls buoyancy as well as vesicle coalescence and percolation, and is important when identifying the differences between equilibrium or disequilibrium degassing from textural analysis of eruptive products. Decompression experiments are routinely used to simulate magma ascent. Samples exposed to high temperature (T) and pressure (P) are decompressed and rapidly cooled to ambient T for analysis. During cooling, fluid vesicles may shrink due to decrease of the molar volume of H2O and by resorption of H2O back into the melt driven by solubility increase with decreasing T at P < 300 MPa. Here, we quantify the extent to which vesicles shrink during cooling, using a series of decompression experiments with hydrous phonolitic melt (5.3-3.3 wt% H2O, T between 1323 and 1373 K, decompressed from 200 to 110-20 MPa). Most samples degassed at near-equilibrium conditions during decompression. However, the porosities of quenched samples are significantly lower than expected equilibrium porosities prior to cooling. At a cooling rate of 44 K·s-1, the fictive temperature T f, where vesicle shrinkage stops, is up to 200 K above the glass transition temperature (T g), Furthermore, decreasing cooling rate enhances vesicles shrinkage. We assess the implications of these findings on previous experimental degassing studies using phonolitic melt, and highlight the importance of correctly interpreting experimental porosity data, before any comparison to natural volcanic ejecta can be attempted.

In situ observation of the percolation threshold in multiphase magma analogues.

Magmas vesiculate during ascent, producing complex interconnected pore networks, which can act as outgassing pathways and then deflate or compact to volcanic plugs. Similarly, in-conduit fragmentation events during dome-forming eruptions create open systems transiently, before welding causes pore sealing. The percolation threshold is the first-order transition between closed- and open-system degassing dynamics. Here, we use time-resolved, synchrotron-source X-ray tomography to image synthetic magmas that go through cycles of opening and closing, to constrain the percolation threshold Φ C at a range of melt crystallinity, viscosity and overpressure pertinent to shallow magma ascent. During vesiculation, we observed different percolative regimes for the same initial bulk crystallinity depending on melt viscosity and gas overpressure. At high viscosity (> 106 Pa s) and high overpressure (~ 1-4 MPa), we found that a brittle-viscous regime dominates in which brittle rupture allows system-spanning coalescence at a low percolation threshold (Φ C ~0.17) via the formation of fracture-like bubble chains. Percolation was followed by outgassing and bubble collapse causing densification and isolation of the bubble network, resulting in a hysteresis in the evolution of connectivity with porosity. At low melt viscosity and overpressure, we observed a viscous regime with much higher percolation threshold (Φ C > 0.37) due to spherical bubble growth and lower degree of crystal connection. Finally, our results also show that sintering of crystal-free and crystal-bearing magma analogues is characterised by low percolation thresholds (Φ C = 0.04 - 0.10). We conclude that the presence of crystals lowers the percolation threshold during vesiculation and may promote outgassing in shallow, crystal-rich magma at initial stages of Vulcanian and Strombolian eruptions.

Employing temporal self-similarity across the entire time domain in computed tomography reconstruction.

There are many cases where one needs to limit the X-ray dose, or the number of projections, or both, for high frame rate (fast) imaging. Normally, it improves temporal resolution but reduces the spatial resolution of the reconstructed data. Fortunately, the redundancy of information in the temporal domain can be employed to improve spatial resolution. In this paper, we propose a novel regularizer for iterative reconstruction of time-lapse computed tomography. The non-local penalty term is driven by the available prior information and employs all available temporal data to improve the spatial resolution of each individual time frame. A high-resolution prior image from the same or a different imaging modality is used to enhance edges which remain stationary throughout the acquisition time while dynamic features tend to be regularized spatially. Effective computational performance together with robust improvement in spatial and temporal resolution makes the proposed method a competitive tool to state-of-the-art techniques.

Protection of pregnant swine by vaccination against Leptospira infection.

The protection conferred on pregnant gilts by 2 commercially available leptospira interrogans serovars pomona and tarassovi bacterins was evaluated. Gilts vaccinated either 3, 6 or 12 months prior to natural challenge with L. interrogans serovar pomona had significantly lower abortion rates (2% vs 69%) and foetal mortality rates (14% vs 57%) than unvaccinated controls. One vaccine was significantly superior to the other and contained approximately twice the number of L. interrogans serovar pomona organisms per vaccine dose. Neither vaccine protected against renal colonisation but vaccination reduced urinary excretion of leptospires. Both vaccines reduced agglutinating antibody response to infection, as measured by the microscopic agglutination (MA) test. This may prevent the detection of a carrier animal by serology. Foetal pigs did not develop specific MA titres. Cultural methods were not reliable in making a diagnosis of foetal infection. Histopathology of foetal liver and kidneys helped in making a diagnosis of foetal infection.

Experimental Sarcoptes scabiei infestation in pigs: (1) pathogenesis.

Animals were experimentally infested with Sarcoptes scabiei var suis at weekly intervals between birth and five weeks of age. Excoriations were observed on the luminal surface of the ear seven days after the initial infestation. Encrusted lesions developed in the ears of all pigs between the third and eighth weeks but spontaneously regressed and disappeared by the 14th week. A generalised pruritus, accompanied by focal erythematous skin lesions developed in a majority of pigs between seven and 11 weeks of age. The presence of pruritus was associated with an eosinophilia and histological changes in the skin which were consistent with an allergic reaction. The results are discussed in relation to their diagnostic significance and their importance in the control and eradication of the disease.

Experimental sarcoptes scabiei infestation in pigs: (2) Effects on production.

A study on the development and effect of experimental Sarcoptes scabiei var suis infestations in growing pigs is described. Pigs were infested at either weekly or fortnightly intervals throughout each experimental and individual growth rates and feed conversion ratios were determined. The animals were fed diets which contained either optimal or sub-optimal levels of protein. They were housed either intensively or extensively. In all experiments the majority of infested animals developed a generalised hypersensitivity to sarcoptes mites and performed significantly less efficiently than non-infested littermates. Mean growth rates were depressed from 9.2 to 12.5 per cent and feed conversion efficiencies by a similar margin. Well fed, intensively housed pigs developed a more severe hypersensitivity reaction than poorly fed, extensively housed pigs.

Trichlorfon toxicity in pigs.

A field outbreak of suspected poisoning is recorded from feed medicated with the organophosphorus insecticide trichlorfon. A controlled experiment showed that toxicity could occur when trichlorfon was fed from 3-5 days at levels greater than that recommended. Signs recorded were inappetence, muscle tremor, ataxia and deaths. Attention is drawn to conditions which could result in overdosage and toxicity when used on the farm.

Leptospiral titres in pigs after vaccination.

Two groups of 8 pigs were vaccinated and given a booster vaccination 6 weeks later each with a commercial dual L. pomona and L. tarassovi killed vaccine. Serum from bloods collected before and up to 30 weeks after vaccination had agglutinating antibodies only after the 0ooster vaccination and then only with 1 vaccine. Titres persisted less than 8 weeks when tested against L. pomona but up to 16 weeks when tested against L. tarassovi at the 1:300 dilution and up to 20 weeks at the 1:100 dilution.