186,856 research outputs found
The 2002-2003 Stromboli eruption
No full textSi tratta del primo DVD della collana del TTC "Formazione e Informazione"Questo documentario mostra i momenti
principali della fase eruttiva 2002-2003 del
Vulcano Stromboli e il lavoro svolto dal
personale dell’INGV nell’ambito del Servizio
Nazionale di Protezione Civile.
Il documentario è stato realizzato da Lilli
Freda e Piergiorgio Scarlato con le immagini
riprese durante l’emergenza; la cronologia
dell’eruzione è stata ricostruita basandosi
sulla loro esperienza personale e sui
comunicati ufficiali INGV.
Il filmato è stato presentato alla comunità
scientifica durante “2004 General Assembly
of International Association of Volcanology
and Chemistry of the Earth’s Interior”
(Pucon, Cile).
This documentary illustrates the topic events
of the 2002-2003 eruptive phase of the
Stromboli Volcano and the work carried out
by the INGV personnel within the Civil
Protection National Service.
The documentary was made by Lilli Freda and
Piergiorgio Scarlato with imagines filmed
during the emergency; the chronology of the
eruption was reconstructed on the basis of
their personal experience and of the official
INGV communications. The movie was shown
to the scientific community during the “2004
General Assembly of International
Association of Volcanology and Chemistry of
the Earth’s Interior” (Pucon, Chile).Published5.8. TTC - Formazione e informazioneope
Selectivity of Metal Ion Binding Specifically Drives the Interaction of a Ni2+-sensor with its operator DNA
No full textTransition metal ions are essential micronutrient for living organisms, being fundamental cofactors of many enzymes that catalyze an enormous variety of biological reactions. At the same time, several metal ions are toxic in their free form for cellular life, demanding a tight regulation of their intracellular trafficking and homeostasis. A paradigmatic example is represented by the human pathogen Helicobacter pylori, which relies on the activity of the nickel-dependent enzymes urease and hydrogenase to survive in the acidic stomach mucosa, where it is responsible of several diseases, such as gastric ulcer and cancer. In this bacterium, homeostasis of essential Ni2+ ions should be tightly controlled to allow growth and colonization. In this processes, NikR, a widespread homo-tetrameric transcription factor controlling the expression of proteins involved in nickel trafficking and/or nickel enzymes, plays a crucial role. The present study investigates the modulation of the interaction between Helicobacter pylori NikR (HpNikR) and DNA, exerted by different concentrations of Ni2+ and/or other metal ions. In particular, the thermodynamic parameters of the interaction between Ni2+, or other divalent metal ions, and HpNikR are determined by using isothermal titration calorimetry (ITC). The metal-dependent capability of HpNikR to bind PureA, the promoter of the urease operon, was determined by using mobility shift assays, DNAse footprinting and ITC. The results provide a congruent description of the factors that determine HpNikR binding to metal ions and DNA and yield clear proofs for activation of HpNikR selectively driven by Ni2+, through a protein conformational rearrangement specifically induced by Ni2+ binding (1-2).
(1) B. Zambelli, M. Bellucci, A. Danielli, V. Scarlato, S. Ciurli; The Ni2+ binding properties of Helicobacter pylori NikR. Chem. Commun., 2007, 35, pp. 3649 - 3651
(2) B. Zambelli, A. Danielli, S. Romagnoli, P. Neyroz, S. Ciurli, V. Scarlato; High-affinity Ni2+ binding selectively promotes binding of Helicobacter pylori NikR to its target urease promoter. J. Mol. Biol., 2008, 383, pp. 1129 - 114
High-speed imaging of Strombolian explosions: The ejection velocity of pyroclasts
No full textExplosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks. Citation: Taddeucci, J., P. Scarlato, A. Capponi, E. Del Bello, C. Cimarelli, D. M. Palladino, and U. Kueppers (2012), High-speed imaging of Strombolian explosions: The ejection velocity of pyroclasts, Geophys. Res. Lett., 39, L02301, doi:10.1029/2011GL050404
Metal ion selectivity and homeostasis: nickel sensing in the human pathogen Helicobacter pylori
No full textHomeostasis of transition metals is crucial for cellular life and is related to the use of metals as cofactors of many enzymes that catalyze an enormous variety of biological reactions. Living organisms elaborated complex and tightly regulated mechanisms to correctly acquire, utilize and allocate metals, neutralizing their harmful potential. In these processes, a fundamental role is played by metal sensor proteins, which are metal-dependent transcription factors that can select, among several intracellular metal ions, the correct metal cofactor, and mediate the specific cellular response by regulating protein expression. Due to the critical function that metal ion homeostasis generally plays in host-pathogen interactions, metal-sensors are considered fundamental virulence factors, because their deletion diminishes or abrogates the survival and colonization of many pathogens. A paradigmatic example is represented by the human pathogen Helicobacter pylori, which relies on the activity of the nickel-dependent enzymes urease and hydrogenase to survive in the acidic stomach mucosa, where it is responsible of several diseases, such as gastric ulcer and cancer. In this bacterium, nickel homeostasis is governed by NikR, a widespread homo-tetrameric transcription factor controlling the expression of proteins involved in nickel trafficking and/or nickel enzymes, in response to different concentrations of intracellular nickel.
In the present study, the modulation of the interaction between Helicobacter pylori NikR (HpNikR) and DNA, exerted by different concentrations of Ni2+ and/or other metal ions, is investigated. In particular, the thermodynamic parameters of the interaction between Ni2+, or other divalent metal ions, and HpNikR are determined by using isothermal titration calorimetry (ITC). The metal ion-dependent capability of HpNikR to bind PureA, the promoter of the urease operon, was investigated by using mobility shift assays, DNAse footprinting and ITC. The results provide a congruent description of the parameters that determine HpNikR binding to metal ions and DNA and yield clear proofs for activation of HpNikR selectively driven by Ni2+, through a protein conformational rearrangement specifically induced by Ni2+ binding (1-2). A general scheme (see Figure) for the nickel selective HpNikR–DNA interaction is proposed.
(1) B. Zambelli, M. Bellucci, A. Danielli, V. Scarlato, S. Ciurli
The Ni2+ binding properties of Helicobacter pylori NikR
Chem. Commun., 2007, 35, pp. 3649 - 3651
(2) B. Zambelli, A. Danielli, S. Romagnoli, P. Neyroz, S. Ciurli, V. Scarlato
High-affinity Ni2+ binding selectively promotes binding of Helicobacter pylori NikR to its target urease promoter
J. Mol. Biol., 2008, 383, pp. 1129 - 114
Modeling clinopyroxene and plagioclase growth kinetics at Mt. Etna and Stromboli: a time-integrated, polybaric and polythermal perspective
No full textBasaltic volcanoes (e.g., Mt. Etna, Stromboli, Hawaii, etc.) are characterized by a range of effusive to explosive activities with variable intensity, which can pose different type of threats to local populations. Challenges in modern volcanology and petrology involve the attempt to constrain pre-eruptive magmatic processes, which provide the basis for volcanic hazard assessment. Although the recent literature has reported constant advancements in this respect, several key questions remain unanswered. Understanding how magma is stored, migrates and feeds eruption is not a trivial task, requiring for renewed improvements over the years. In this context, both textural maturation and compositional variability of minerals crystallizing in basaltic systems represent valuable sources of information to quantify the physio-chemical conditions experienced by magmas upon the effect of changing and complex plumbing system dynamics.
This study aims to provide new insights on the solidification behavior of mafic alkaline magmas erupted at Mt. Etna and Stromboli (Italy). Such open conduit volcanoes are characterized by the ubiquitous stability of clinopyroxene from mantle depths to shallow crustal levels. More evolved magmas are also saturated with plagioclase, especially at lower temperatures, melt-water contents, and pressures. Thus, clinopyroxene and plagioclase crystals represent powerful recorders of the intricate ascent dynamics explored by mafic alkaline magmas during their ascent paths towards the surface. By focusing on textural and chemical features of natural/synthetic clinopyroxene, plagioclase and coexisting glasses, I have provided new tools for interpreting polythermal-polybaric changes of magmas, together with several guidelines and a secure methodology to model pre- and syn-eruptive conditions. The temporal evolution of Etnean and Strombolian magmas has been also tracked via timescale modeling to better constrain the cooling-decompression paths of magmas rising and accelerating through the vertically extended, highly dynamic plumbing systems.
In the first part of this PhD thesis, I have experimentally explored the role of supersaturation and relaxation phenomena on clinopyroxene nucleation and growth processes, which affect the final crystal cargo of variably undercooled magmas. A certain degree of undercooling is pivotal to promote the growth and textural maturation of crystals. With increasing crystallization time, however, the crystal growth rate decreases as the system approaches to near-equilibrium conditions that minimize the effect of melt supersaturation. By quantifying the textural features of synthetic and natural crystals it has been possible to parameterize clinopyroxene growth kinetics under a broad range of isothermal-isobaric, decompression, and cooling conditions representative of crystallization scenarios typically encountered in open-conduit volcanoes. This model parameterization has been combined with the textural analysis of natural clinopyroxene crystals erupted during lava fountain events at Mt. Etna allowing to unlock timescale of growth for microphenocryst and microlite populations. The retrieved temporal information has been used to develop a new conceptual model for the timescale of magma dynamics recorded by the (dis)equilibrium textural evolution of clinopyroxene and for the rapid acceleration of magma ascending within the volcanic conduit, immediately before eruption at the vent.
A more comprehensive work, focusing on plagioclase textural and compositional features, characterized the second part of my PhD thesis with the aim to identify disparate aspects of plagioclase growth scenarios. Following the same approach discussed above, timescale of plagioclase crystallization from mafic alkaline magmas has been parameterized as a function of growth rate by integrating experimental (i.e., isothermal-isobaric, decompression, and cooling experiments) and natural textural data from literature. Timescales of eruptive processes at Mt. Etna and Stromboli volcanoes have been quantified by considering phenocryst/microphenocryst and microlite crystals growing during lava flow and explosive eruptions. Statistical methodologies have been employed to assess the correlation between plagioclase growth rate and other system parameters governing the crystallization process. Special attention has been paid to disambiguate the role of temperature and melt-H2O content on plagioclase chemical zoning patterns at Stromboli and Mt. Etna. By using plagioclase components and major cation substitution mechanisms, I have refined and readapted equilibrium, thermometric, and hygrometric models for future investigations
The autoregulatory HspR repressor protein governs chaperone gene transcription in Helicobacter pylori
No full textIn the present study, we provide evidence that the groESL, hrcA-grpE-dnaK and cbpA-hspR-orf operons encoding the major chaperones of the human gastric pathogen Helicobacter pylori are transcribed by the vegetative sigma factor σ80 and are regulated negatively by the transcriptional repressor HspR. In vitro studies with purified recombinant HspR protein established that the protein represses transcription by binding to large DNA regions centred around the transcription initiation site in the case of the P(cbp) promoter, and around -85 and -120 in the case of the P(gro) and P(hrc) promoters respectively. All three binding sites contain DNA motifs with some similarity to the HAIR sequence identified as a consensus for the HspR protein of Streptomyces. In contrast to the situation in Streptomyces, in which transcription of HspR-regulated genes is induced in response to heat shock, transcription of the HspR-dependent genes in H. pylori is not inducible by thermal stimuli. Transcription of the groESL and cbpA-hspR-orf operons is induced by osmotic shock, while transcription of the hrcA-grpE-dnaK operon, although HspR dependent, is not affected by salt treatment. The possibility that HspR could constitute a global transcriptional regulator for diverse cellular functions with implications for pathogenesis is discussed
Parameterizing the Dynamics of Strombolian Eruptions through High-Speed Video Analysis
No full textStrombolian explosive activity is generally characterized by a series of short, mild explosions caused by the bursting of large individual gas pockets at the magma free surface; however individual explosions at Stromboli Volcano (Italy) show how these events can be complex and heterogeneous. A new method to study the dynamics of Strombolian eruptions is proposed here, based on the acquisition and elaboration of high-speed videos at Stromboli Volcano. The analysis of high-speed videos of Strombolian explosions reveals previously unreported processes, including pre- and post- explosion crater floor deformation and multiple jet pulses within a single explosion, different explosive styles at individual vents, deformation and fragmentation of in-flight scoria clasts. Video frame elaboration allows us to measure the mass flux, velocity and exit angle of ejecta. In addition, particle velocity trends, in the light of shock tube fragmentation/ejection experiments, may provide information on the source depth of single explosion pulses. These results should be useful for future researches and may help describe quantitatively the dynamics and energetics of Strombolian eruptions, with implications on related hazard assessment
Water diffusion in natural potassic melt. In Volcanic Degassing: experiments, models, observations and impacts
No full textWater diffusion experiments were performed on a trachytic melt from the Agnano-Monte Spina explosive eruption (Phlegrean Fields, South Italy). Experiments were run in a piston cylinder apparatus at 1 GPa pressure, at temperatures from 1373 to 1673 K and for durations of 0 to 255 s, using the diffusion-couple technique. Water concentration profiles were measured by Fourier transform infrared spectrometry. Water diffusion coefficients at different temperatures and water concentrations were calculated from the total water profiles, using the Boltzmann-Matano technique.
Over the investigated range of temperatures and water concentrations, the diffusivity of water in potassic melts (Dwater), m2/s can be described by Arrhenius equations that can be generalized for water concentrations between 0.25 and 2 wt% as follows: Formula where CH2O is the water concentration in wt%, R is 8.3145 (J K−1 mol.−1) and T is the temperature in Kelvin. Water diffusivities in trachytic melts were compared with water diffusivities in rhyolitic and basaltic melts. The activation energies for water diffusivity in trachyte and basalt are comparable, and higher than the haplogranitic melt. This results in a convergence of water diffusion coefficients in all melts at lower (magmatic) temperatures
The 2011–2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system
No full textMt. Etna activity from January 2011 to April 2012 was characterized by 24 short-lasting (few to several hours) eruptions from the New South East summit crater. Despite the violence of the no appreciable geophysical signals were recorded during this period, except for an increase in the seismic tremors just minutes/hours before the occurrence of the paroxysm. This type represents a significant shift from the mainly effusive eruptions of 2004, 2006, 2008/2009 and from the lateral rift-related event of 2001 and 2002/2003.
The 2011-2012 activity thus represent a unique opportunity to investigate the effects of chemical-physical variables (P-T-fO2) on the crystallization and fractionation processes occurring Etna open conduit feeding system. We investigated the petrographic and geochemical features of lava and scoria clasts from 10 paroxysmal events. Whole rock compositions plot inside the field with the typical etnean intraplate chondrite-normalized trace element distribution, characterized by positive U, Th and La and negative Rb, K, Nb anomalies.
MELTs and mass balance fractional crystallization modelling suggest that most of the eruptive events were fed by magma differentiating along the conduit and by a deep basic magma during the 4/3/2012 event.
Olivine (Ol), clinopyroxene (Cpx) and plagioclase (Plg) crystal-melt equilibrium conditions were checked before applying thermo-barometric, oxy-fugacity and hygrometer equations by the composition of phenocrysts with those of whole rock, glass and reconstructed composition of the basic magma. Results show that the erupted products are made up of a mixture of phenocrysts
in equilibrium with the whole rock or disequilibrated toward more basic or more evolved compositions.
Thermobarometric calculations indicate that ol is the first phase on the liquidus (~1270°C, up to 1200 MPa). Cpx crystallizes from 1200°C, at 700 Mpa in most basic melt (4/3/2012), to 100 Mpa. Plg nucleation is constrained by the dissolved amount of H2O in the melt and mostly occur above 250 Mpa. Hygrometer determinations indicate that basic magma contains up to H2O.
The overall dataset suggests that the feeding system of 2011-2012 eruptive events was vertically extended without any significant ponding zone. The conduit is periodically filled with basic magma at +2 DFMQ average oxidation condition. The H2O degassing in the shallower portion of the magmatic column (P < 200 Mpa) induce a vertical differentiation. In the deeper the magmatic column at P > 300 MPa, the femic geochemical signature is preserved due to the low undercooling degree. The intermediate portion (300-200 Mpa) is repeatedly pushed H2O exsolution depth which promotes the plagioclase saturation and nucleation. In the shallower portion (< 200 Mpa) the efficient H2O exsolution result in a strong undercooling and promote massive plg nucleation and differentiation
The 2011–2012 paroxysmal eruptions at Mt. Etna volcano. Insights on the vertically zoned plumbing system
No full textThe activity ofMt. Etna volcano from January 2011 to April 2012 was characterized by 24 paroxysmal, short-duration
(from a few to several hours) eruptions at the New South-East summit crater. Despite the violence of the
activity, no appreciable geophysical signals were recorded during this period, except for an increase in seismic
tremors just minutes/hours before the occurrence of the paroxysm. This type of activity represents a significant
shift from the mainly effusive eruptions of 2004, 2006, and 2008/2009, as well as from the lateral rift-related
events of 2001 and 2002/2003.
The 2011–2012 paroxysmal activity thus represents an important opportunity to better understand the effects of
different magmatic parameters (i.e., P-T-fO2) and magmatic H2O content on the crystallization and fractionation
processes. To this aim the petrographic and geochemical features of lava and scoria clasts from 10 paroxysmal
events have been investigated. Fractional crystallization modelling indicates that most of the eruptions are related
to magmas rising along the vertically-developed feeding systemof the volcano, accompanied by one main recharge
of a more primitive, deep-seated magma feeding the 4/3/2012 event. Olivine-, clinopyroxene-, and
plagioclase-melt equilibria and thermobarometric calculations were performed in order to estimate the crystallization
conditions of magmas. These calculations reveal that the erupted products contain different phenocryst
populations in equilibrium with a spectrum of primitive to more evolved magma compositions. On the basis of
crystal composition, crystal-melt equilibriumconditions and thermobarometric estimations, four main magmatic
facies have been recognized: F1, 1600 MPa at 1270 °C (Ol Fo88); F2, 800 MPa to 600MPa at 1178 °C to 1151 °C
(Ol Fo84–78); F3, 450 MPa to 250 MPa at 1139 °C to 1118 °C (Ol Fo79–74); F4, b250 MPa at b1120 °C (Ol Fo75–70).
The overall geochemistry and thermobarometric data allowus to characterize the central feeding systemas continuous
and vertically zoned. During the 2011–2012 activity the studied 30/7/11, 29/8/11, 8/9/11, 18/3/11 and
24/4/12 events were fed by magma residing at F3 and F4 facies. Mafic magma influx from deeper F2 facies occurred
18/2/11 and 20/8/11,with a major recharge event before the 4/3/12 eruption. The primitive magma is testified
by rare olivine crystals equilibrated at the F1 facies, located at crust-mantle boundary depth and close to
liquidus temperature
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