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- Holliger, K, et al.
(författare)
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Stochastic analysis of sonic logs from the upper crystalline crust: Methodology
- 1996
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 264:1-4, s. 341-356
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Tidskriftsartikel (refereegranskat)abstract
- To relate local fluctuations observed in sonic logs to small-scale velocity fabric along boreholes, both filtering effects and noise introduced by the logging procedure must be taken into account. Sonic log velocities are represented as a time series consisting of a large-scale deterministic and a small-scale stochastic component. The deterministic trend, approximated by a low-order polynomial best-fit, contains information on the average velocity structure, whereas the small-scale stochastic variations consist of noise plus in situ velocity variations convolved with the logging system response. The velocity fluctuations of the sonic data considered here are zero-mean and have quasi-Gaussian probability density functions. Therefore, they are well characterised by their second statistical moment, i.e. their autocovariance function. Tests on synthetic data indicate that the autocovariance function corresponding to this data model may be used to extract information on the second-order statistics of the in situ velocity variations along the borehole and to constrain the level of white noise in sonic logs. Ignoring the presence of filtering effects and noise in sonic logs may result in seriously flawed estimates of the second-order statistics of the actual velocity structure. Assuming a von Kármán autocovariance function for the in situ velocity variations, this model provides a good match to the autocovariance functions of sonic log data from the Siljan Ring (Sweden) and Sudbury areas (Canada). Although differing significantly in their noise content, these two data sets yield similar results for the small-scale velocity structure, which is modelled as a bandlimited self-affine time series. For the Siljan Ring borehole we found a close relation between small-scale variations of the borehole diameter as determined from caliper logs and the level of uncorrelated noise present in the sonic log data.
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- Kimblad, P O, et al.
(författare)
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Prostanoid release after lung transplantation
- 1996
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Ingår i: The Journal of Heart and Lung Transplantation. - 1557-3117. ; 15:10, s. 999-1004
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Increased pulmonary vascular resistance is frequently seen after lung transplantation. Thromboxane A2 is a potent vasoconstrictor of pulmonary arteries. Thromboxane-elicited vasoconstriction can ben counteracted by prostacyclin. The effects of lung transplantation on the biosynthesis of these substances were investigated. METHODS: Pulmonary artery flush perfusion with a low-potassium dextran glucose solution was performed in six donor pigs. After a 24-hour storage period, the left lung was transplanted into a recipient, followed by right pneumonectomy, making the recipient's survival entirely dependent on the transplanted lung. A sham operation (bilateral thoracotomy, right pneumonectomy) ws done in six pigs. the urine contents of the stable thromboxane A2 metabolite 2,3-dinor-thromboxane B2 and the stable prostacyclin metabolite 2,3-dinor-6-keto-protaglandin F1 alpha were measured with a gas chromatography-mass spectrometry method. RESULTS: One to four hours after reperfusion, thromboxane A2 production reached its maximum in both groups: it ws fivefold the basal value in the transplanted group, but only twofold in the sham-operated group, the difference being significant (p < 0.005). Twenty to twenty-four hours after reperfusion, thromboxane A2 production had stabilized at about twofold the basal value in both the transplanted and in the sham-operated group. Four to eight hours after reperfusion, prostacyclin production reached 15 times the basal value in the transplanted group and twofold in the sham-operated group, the difference being significant (p < 0.05). Twenty to twenty-four hours after reperfusion, prostacyclin production was 18-fold the basal value in the transplanted group and sevenfold in the sham-operated group. No correlation was found between the thromboxane or prostacyclin production and the pulmonary vascular resistance or the mean pulmonary arterial pressure. CONCLUSIONS: The thromboxane A2 production increased fivefold after lung transplantation, with a concomitant 15-fold increase in prostacyclin synthesis, which might have counteracted the vasoconstrictor effect of thromboxane.
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- Roth, Michael, et al.
(författare)
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Guided waves in near-surface seismic surveys
- 1998
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 25:7, s. 1071-1074
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Tidskriftsartikel (refereegranskat)
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