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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 152 (1998), S. 193-211 
    ISSN: 1420-9136
    Keywords: Key words: Volcanic domain, subterrenean porous-permeable horizon, thermo-mechanical solitary shock waves.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —This work is a further development of the modern thermo-poro-elasticity theory which has recently been applied to understand how fluid-rock coupling dynamics related to unrest episodes in volcanic domains can both determine, and occur with, ground deformation and rock fracturing processes. In particular by reformulating the energy equation, one of the two nonlinear heat-like equations upon which the thermo-poroelasticity theory is based, it is shown here how fluid thermal expansivity may influence fluid migration during its movement through subsurface volcanic porous-per meable horizons. With these new considerations it is found that a recent theory in which fluid-rock coupling dynamics is interpreted in terms of thermal and mechanical solitary shock wave propagation remains valid. However, the natural time scale of the propagating wave is reduced and consequently Darcy’s velocity is increased as a result of fluid thermal expansivity.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 125 (1987), S. 883-917 
    ISSN: 1420-9136
    Keywords: Campi Flegrei ; Volcanic earthquakes ; Attenuation ; Source parameters ; Moment tensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Microearthquake digital data collected at Campi Flegrei during the recent (1982–1985) ground uplift episode have been analyzed in order to infer source and medium seismic properties. The main results obtained from these analyses are: 1. Hypocenter distribution and the size of the seismic zone do not change with time and do not depend on the ground uplift rate. Events occurred clustered in time with no simple causal relations between the cluster occurrences and their energy. 2. Anelastic attenuation does not depend strongly on frequency, showing a constant pattern at high frequencies. The observed values of low and high frequency attenuation, due to the short source receiver distances, do not seriously affect the spectral content of signals radiated by the sources. 3. A constant Brune stress drop pattern (∼4–5 bars) as a function of seismic moment is observed. This indicates that the manner of fracturing is almost independent on magnitude of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic processes in a prefractured medium can explain the observed small stress drop values. 4. Focal mechanisms from moment tensor estimates show that radiation patterns are mostly well interpreted in terms of double couple source models. 5. The scaling of peak ground motion parameters (A max andV max vs seismic moment) can be explained by an ω2 source model (constant stress drop) multiplied by an exponential function with a small decay parameter, which takes into account the measured attenuation. These results support the hypothesis of earthquakes generated by simple shear fractures along prefractured structures as a response to changes in the stress field due to the ground deformation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1420-9136
    Keywords: Q ; code waves ; volcanic earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Digital recordings of three component microearthquake codas from shallow seismic events in the volcanic region of Campi Flegrei — Southern Italy — were used with an automatic technique to calculate the attenuation factorQ c (codaQ) in the hypothesis of singleS toS backscattering. Results show the same value ofQ for each of the three components. This result is interpreted as due to isotropicS wave radiation pattern. A check of the coda method was performed using a single station method based on simple assumptions on the direct SH wave spectrum. Single stationQ was averaged over the stations and over the earthquakes. Results show that the two methods lead to comparable results. A frequency dependence quite different from that evaluated in active tectonic regions was found for coda attenuation, comparable to other volcanic areas throughout the world. This is interpreted as due to the presence of magma that affects anelasticity and scattering.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0738
    Keywords: Key words: Manganese neurotoxicity – Oxidative stress – GSH – Ascorbic acid – Uric acid – Striatum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. In 6-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), uric acid and glutathione (GSH) were determined by HPLC in the striatum and striatal synaptosomes after subchronic oral exposure to MnCl2 50 – 100 – 150 mg/kg. Mn significantly decreased levels of DA and GSH and increased levels of DHAA and uric acid both in the striatum and synaptosomes. In synaptosomes, individual total Mn doses/rat were directly correlated with individual DOPAC/DA ratio values (r = +0.647), uric acid (r = +0.532) and DHAA levels (r = +0.889) and inversely correlated with DA (r = –0.757) and GSH levels (r = –0.608). In turn, GSH levels were inversely correlated with uric acid (r = –0.451) and DHAA levels (r = –0.460). In conclusion, the response of striatal cellular defense mechanisms (increase in AA oxidation, decrease in GSH levels) correlated well with changes in markers of dopaminergic system activity and increase in uric acid levels. The latter provides evidence of an Mn-induced oxidative stress mediated by xanthine oxidase.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 47 (1987), S. 25-42 
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2013
    Keywords: Proximal tubule ; Atrial natriuretic peptide ; Micropuncture ; Tubule suspension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Infusion of ANP has been shown to increase the urinary excretion of sodium and water. However it is still controversial in which tubular segment sodium reabsorption is inhibited. To clarify this problem we have performed in vivo and in vitro studies to examine the direct effect of ANP on rat proximal tubules. The in vivo effect of ANP has been tested by using the micropuncture technique and in particular the shrinking droplet method that allows each investigated tubule to serve as its own control. Addition of either low (10−9 M) or high (2×10−6 M) concentrations of ANP to the luminal perfusate resulted in no significant change in isotonic fluid reabsorption (J v). The same holds when the proximal tubules were perfused on both the tubular and peritubular side, with modified Ringer solution containing 10−9 M ANP. To examine possible in vitro effects of ANP we prepared highly purified proximal tubule suspension derived from rat renal cortex and monitored oxygen consumption (QO2) that is tightly coupled to sodium transport in this segment. Synthetic ANP, either at low (10−9 M) or at high (10−6 M) concentrations, did not affect basal rate of tubular respiration. Moreover the peptide hormone (10−9 M) did not inhibit nystatin stimulated and ouabain sensitive QO2. These results indicate that the enhancement of renal sodium excretion induced by ANP is not related to a direct inhibition of sodium transport in the proximal tubule.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of volcanology 47 (1984), S. 219-224 
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Digital recordings of microearthquake codas from shallow seismic events in the Phlegraean Fields region (south-central Italy) were used to calculate the attenuation factor Qc. A quite unusual frequency dependence was found for the coda attenuation comparable to Hawaii pattern of Qc. This is interpreted as due to the presence of magma that increases the amount of anelasticity. Amount of scattering at Phlegraean Fields was estimated through the « turbidity » coefficient (Dainty model), that shows a high degree of scattering due to inhomogeneities as compared to Hawaii. Probably this is due to the greater crustal thickness of Phlegraean Fields with respect to Hawaii that produces more scattering.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of volcanology 47 (1984), S. 201-207 
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A preliminary statistical analysis of the space-time distribution of small seismic events in the volcanic area of Phlegraean Fields, south-central Italy, was done on the basis of a catalogue of earthquakes recorded by the local seismic stations in the period January 1, December 31, 1983. The non-random character of the sequence has been tested by matching the observed time-dstribution of seismic events with the theoretical Poisson process. A clustered occurrence of seismic events seems to be the main cause of the departure from a Poisson process as the inter-arrival times distribution clearly shows. Furthermore, the non-random behaviour of the events space-time distribution mainly due to quiescient and clustered recursive seismic phases could be studied by using the method proposed byVon Seggern et al. (1981). The analysis and the space-time diagrams confirm the swarm-type character of the entire seismic sequence.
    Type of Medium: Electronic Resource
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