Instituto de Pesquisas Energéticas e Nucleares

Abstract Tropical carbon emissions are largely derived from direct forest clearing processes. Yet, emissions from drought-induced forest fires are, usually, not included in national-level carbon emission inventories. Here we examine Brazilian Amazon drought impacts on fire incidence and associated forest fire carbon emissions over the period 2003–2015. We show that despite a 76% decline in deforestation rates over the past 13 years, fire incidence increased by 36% during the 2015 drought compared to the preceding 12 years. The 2015 drought had the largest ever ratio of active fire counts to deforestation, with active fires occurring over an area of 799,293 km 2 . Gross emissions from forest fires (989 ± 504 Tg CO 2 year −1 ) alone are more than half as great as those from old-growth forest deforestation during drought years. We conclude that carbon emission inventories intended for accounting and developing policies need to take account of substantial forest fire emissions not associated to the deforestation process.

Abstract Here, 10 guidelines are presented for a standardized definition of type I and type II photosensitized oxidation reactions. Because of varied notions of reactions mediated by photosensitizers, a checklist of recommendations is provided for their definitions. Type I and type II photoreactions are oxygen‐dependent and involve unstable species such as the initial formation of radical cation or neutral radicals from the substrates and/or singlet oxygen ( 1 O 2 1 ∆ g ) by energy transfer to molecular oxygen. In addition, superoxide anion radical ( ) can be generated by a charge‐transfer reaction involving O 2 or more likely indirectly as the result of O 2 ‐mediated oxidation of the radical anion of type I photosensitizers. In subsequent reactions, may add and/or reduce a few highly oxidizing radicals that arise from the deprotonation of the radical cations of key biological targets. can also undergo dismutation into H 2 O 2 , the precursor of the highly reactive hydroxyl radical ( ) that may induce delayed oxidation reactions in cells. In the second part, several examples of type I and type II photosensitized oxidation reactions are provided to illustrate the complexity and the diversity of the degradation pathways of mostly relevant biomolecules upon one‐electron oxidation and singlet oxygen reactions.

Measurements of atmospheric CH 4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near‐zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH 4 increased by 8.3 ± 0.6 ppb. CH 4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH 4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH 4 from biomass burning. The most likely drivers of the CH 4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near‐zero CH 4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH 4 hydrates.

Methane retrievals from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument onboard ENVISAT provide important information on atmospheric CH 4 sources, particularly in tropical regions which are poorly monitored by in situ surface observations. Recently, Frankenberg et al. (2008a, 2008b) reported a major revision of SCIAMACHY retrievals due to an update of spectroscopic parameters of water vapor and CH 4 . Here, we analyze the impact of this revision on global and regional CH 4 emissions estimates in 2004, using the TM5‐4DVAR inverse modeling system. Inversions based on the revised SCIAMACHY retrievals yield ∼20% lower tropical emissions compared to the previous retrievals. The new retrievals improve significantly the consistency between observed and assimilated column average mixing ratios and the agreement with independent validation data. Furthermore, the considerable latitudinal and seasonal bias correction of the previous SCIAMACHY retrievals, derived in the TM5‐4DVAR system by simultaneously assimilating high‐accuracy surface measurements, is reduced by a factor of ∼3. The inversions result in significant changes in the spatial patterns of emissions and their seasonality compared to the bottom‐up inventories. Sensitivity tests were done to analyze the robustness of retrieved emissions, revealing some dependence on the applied a priori emission inventories and OH fields. Furthermore, we performed a detailed validation of simulated CH 4 mixing ratios using NOAA ship and aircraft profile samples, as well as stratospheric balloon samples, showing overall good agreement. We use the new SCIAMACHY retrievals for a regional analysis of CH 4 emissions from South America, Africa, and Asia, exploiting the zooming capability of the TM5 model. This allows a more detailed analysis of spatial emission patterns and better comparison with aircraft profiles and independent regional emission estimates available for South America. Large CH 4 emissions are attributed to various wetland regions in tropical South America and Africa, seasonally varying and opposite in phase with CH 4 emissions from biomass burning. India, China and South East Asia are characterized by pronounced emissions from rice paddies peaking in the third quarter of the year, in addition to further anthropogenic emissions throughout the year.

This paper presents an overview of the results from the first major mesoscale atmospheric campaign of the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA) Program. The campaign, collocated with a Tropical Rainfall Measuring Mission (TRMM) satellite validation campaigns, was conducted in southwest Rondônia in January and February 1999 during the wet season. Highlights on the interaction between clouds, rain, and the underlying landscape through biospheric processes are presented and discussed.

As part of the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA), a large study of aerosol and trace gas properties was conducted in Amazonia during the dry and wet seasons and for pasture and primary forest sites. Aerosol mass and elemental composition were measured on filters for both fine (d p < 2.0 μm) and coarse (2.0 < d p < 10 μm) modes using polycarbonate filters mounted in stacked filter units (SFU). Measurements with real‐time aerosol and trace gas monitors were made, parallel to the collection of filter samples to obtain high time resolution (1–30 min). Black carbon equivalent (BCE) was determined with a multiwavelength Aethalometer as well as by reflectance in the fine‐mode SFU samples. Elemental carbon as well as total and organic carbon was measured using an R&P 5400 real‐time carbon monitor. PM 10 aerosol mass concentrations were determined with a Tapered Element Oscillating Monitor (TEOM) monitor every 5 min. CO, O 3 , NO, and NO 2 were analyzed with Thermo Environment monitors with trace level capabilities for NO x . A TSI 3010 particle counter measured the total particle number concentration (d p > 10 nm) every minute. A 55‐m tower in a primary forest in Rondônia and a facility built on a pasture site were used to operate the instrumentation for 4 months in the wet season and 3 months in the dry season of 1999. Particle‐Induced X‐Ray Emission (PIXE) was used to measure the concentration of 22 trace elements for fine‐ and coarse‐mode aerosol. During the wet season, very clean atmospheric conditions were observed at both sites. Particle concentration averaged 900 cm −3 , black carbon averaged 250 ng m −3 , and mean fine‐mode mass concentration was 2.9 μg m −3 . In sharp contrast, very high concentrations were observed in the dry season for all the parameters at both sampling sites. Aerosol mass concentrations up to 250 μg m −3 and particle number concentrations of more than 40,000 cm −3 were observed, while the CO peaked at 8 ppm and NO 2 reached 16 ppb. High correlation was observed between BCE, NO 2 , CO, aerosol particle number, mass, aerosol optical thickness, and other properties linked to biomass‐burning emissions. Relatively large concentrations of phosphorus in the coarse‐mode particles were observed, especially at nighttime. The emission of biogenic particulate P could have an effect in the nutrient cycling of this essential and key nutrient, which is present almost exclusively in the form of aerosol particles. Phosphorus is exchanged in the aerosol phase and mostly for coarse‐mode particles and during nighttime.

BACKGROUND AND OBJECTIVES: Low-intensity laser therapy (LILT) has been studied in many fields of dentistry, but to our knowledge, this is the first time that its effects on orthodontic movement velocity in humans are investigated. STUDY DESIGN/PATIENTS AND METHODS: Eleven patients were recruited for this 2-month study. One half of the upper arcade was considered control group (CG) and received mechanical activation of the canine teeth every 30 days. The opposite half received the same mechanical activation and was also irradiated with a diode laser emitting light at 780 nm, during 10 seconds at 20 mW, 5 J/cm2, on 4 days of each month. Data of the biometrical progress of both groups were statistically compared. RESULTS: All patients showed significant higher acceleration of the retraction of canines on the side treated with LILT when compared to the control. CONCLUSIONS: Our findings suggest that LILT does accelerate human teeth movement and could therefore considerably shorten the whole treatment duration.

High Resolution Image Download MS PowerPoint Slide Silica nanoparticles (SiO 2 NPs) from renewable sources can be used in very different materials, such as paints, membranes for fuel cells, Li-ion batteries, adsorbents, catalysts, and so on. Brazil is the world’s largest producer of sugarcane and generates huge amounts of sugarcane waste ash (SWA), which is a Si-rich source. This study investigates a method to produce highly pure SiO 2 NPs from SWA. The SiO 2 NPs were characterized by inductively coupled plasma optical emission spectroscopy, scanning and transmission electron microscopy (TEM), X-ray diffraction analyses, specific surface area and pore distribution, UV and Fourier transform infrared spectroscopy, and thermogravimetric analyses and applied as an adsorbent material in the removal of acid orange 8 (AO8) dye from aqueous solution. The SiO 2 content was 88.68 and 99.08 wt % for SWA and SiO 2 NPs, respectively. TEM images of SWA and SiO 2 NPs exhibit drastic alterations of the material size ranging from several micrometers to less than 20 nm. The SiO 2 NPs showed a specific surface area of 131 m 2 g –1 and adsorption capacity of around 230 mg g –1 for acid orange 8 dye. Furthermore, the recycling of the SiO 2 NPs adsorbent after AO8 adsorption was very satisfactory, with reuse for up to five cycles being possible. The results indicate that it was possible to obtain highly pure silica in a nanosize from the waste material and produce an adsorbent with high adsorption capacity and the possibility of reuse.

The effect of glass dosage (0.001 g ml(-1) to 0.015 g ml(-1)) on the in vitro dynamic dissolution behavior of melt-derived 45S5 and sol-gel-derived 58S bioactive glasses, in simulated body fluid (SBF) at 37 degrees C, was evaluated. These glasses differ significantly in texture, especially the specific surface area and porosity, as a result of differences in manufacturing route. The concentrations of elements (Si, Ca, P, and Na) leached from the glasses into the dissolution medium, from 1 to 22 h, were evaluated with the use of induced coupled plasma analysis (ICP). The reacted powders were analyzed with the use of FTIR to observe the formation of a hydroxycarbonate apatite layer on the surface. The results show that the rate of HCA formation on both gel- and melt-derived bioactive glass powders in vitro depends on the concentration of the powders in solution. This result must be taken into account when carrying out in vitro cell-culture studies to simulate conditions in vivo and in experiments using extracts of the bioactive glass powders.

We have performed a detailed characterization of the magnetic properties of Ni nanoparticles embedded in a ${\mathrm{SiO}}_{2}$ amorphous matrix. A modified sol-gel method was employed which resulted in Ni particles with average radius $\ensuremath{\sim}3\mathrm{nm},$ as inferred by TEM analysis. Above the blocking temperature ${T}_{B}\ensuremath{\approx}20\mathrm{K}$ for the most diluted sample, magnetization data show the expected scaling of the ${M/M}_{S}$ vs $H/T$ curves for superparamagnetic particles. The hysteresis loops were found to be symmetric about zero field axis with no shift via exchange bias, suggesting that Ni particles are free from an oxide layer. For $T<{T}_{B}$ the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles, as suggested by the temperature dependence of the coercivity field that obeys the relation ${H}_{C}{(T)=H}_{C0}[1\ensuremath{-}{(T/T}_{B}{)}^{1/2}]$ below ${T}_{B}$ with ${H}_{C0}\ensuremath{\sim}780\mathrm{Oe}.$ The obtained values of ${H}_{C0},$ considering the temperature dependence of the magnetic anisotropy constant, are discussed within the scenario of isolated randomly oriented and noninteracting single-domain particles.

At a nano-level, optical properties of gold are unique and gave birth to an emerging platform of nanogold-based systems for diverse applications, because gold nanoparticle properties are tunable as a function of size and shape. Within the available techniques for the synthesis of gold nanoparticles, the radiolytic synthesis allows proper control of the nucleation process without the need for reducing agents, in a single step, combined or not with simultaneous sterilization. This review details and summarizes the use of radiation technologies for the synthesis and preparation of gold nanoparticles concerning fundamental aspects, mechanism, current pathways for synthesis and radiation sources, as well as briefly outlines final applications and some toxicity aspects related to nanogold-based systems.

A method for estimating the microscopic probability rate of phonon-assisted energy transfer between rare-earth $(3+)$ ions in solids was developed based on Dexter's theory for phonon-assisted energy transfer. The proposed method in this paper enables one to calculate the overlap integral from fundamental cross-section spectra of nonresonant energy transfer involving a multiphonon generation in both donor and acceptor sites. A translation of the donor emission spectrum towards the acceptor absorption scaled with the $N$-phonon emission probability represents the $m$-phonon emission band which performs the energy transfer to the acceptor. A nonvanishing overlap integral ${10}^{\ensuremath{-}2}--{10}^{\ensuremath{-}3}$ times smaller than for the resonant case is found. A multiphonon generation probability assisting the energy transfer was considered due to a combined mechanism of creation and annihilation of phonons. The participation of each phonon in the process was determined. This method was used to investigate the ${\mathrm{Tm}}^{3+}{(}^{3}{F}_{4})\ensuremath{\rightarrow}{\mathrm{Ho}}^{3+}{(}^{5}{I}_{7}),{\mathrm{Er}}^{3+}{(}^{4}{I}_{13/2})\ensuremath{\rightarrow}[{\mathrm{Ho}}^{3+}{(}^{5}{I}_{7}),{\mathrm{Tm}}^{3+}{(}^{3}{F}_{4})]$ direct energy transfers in ${\mathrm{LiYF}}_{4}$ crystals, as well the back transfers.

This study presents the manufacture of highly porous hydroxyapatite by a novel technique that employs the foaming of suspensions prior to the in situ polymerization of organic monomers contained in the compositions. This method produces strong gelled bodies with up to 90% porosity that can withstand machining in the green state. Complex-shaped components can be obtained if the process comprises casting in one of the processing steps. The organic additives are eliminated at temperatures above 300 degrees C, and sintering is carried out for consolidation of the ceramic matrix. Spherical interconnected cells with sizes ranging from 20 to 1000 micrometer characterize the porous structure, depending on the specimen density. Cytotoxicity tests were conducted on extracts from sintered HA foams based on a quantitative method of cell colony formation and the determination of cell death after indirect contact of the porous material with mammalian cells. This in vitro test of biological evaluation revealed that the original purity of the biomedical-grade hydroxyapatite powder was affected neither through processing nor by the employed reagents.

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)3(H2O)2] and [Tb(acac)3(H2O)3] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln3+–β-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand–Ln3+ intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the 5D4 emitting level of the Tb3+ ion to the excited triplet state T1 of the tta ligand coordinated to the Eu3+ ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Abstract. We estimated the isoprene and monoterpene source strengths of a pristine tropical forest north of Manaus in the central Amazon Basin using three different micrometeorological flux measurement approaches. During the early dry season campaign of the Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001), a tower-based surface layer gradient (SLG) technique was applied simultaneously with a relaxed eddy accumulation (REA) system. Airborne measurements of vertical profiles within and above the convective boundary layer (CBL) were used to estimate fluxes on a landscape scale by application of the mixed layer gradient (MLG) technique. The mean daytime fluxes of organic carbon measured by REA were 2.1 mg C m−2 h−1 for isoprene, 0.20 mg C m−2 h−1 for α-pinene, and 0.39 mg C m−2 h−1 for the sum of monoterpenes. These values are in reasonable agreement with fluxes determined with the SLG approach, which exhibited a higher scatter, as expected for the complex terrain investigated. The observed VOC fluxes are in good agreement with simulations using a single-column chemistry and climate model (SCM). In contrast, the model-derived mixing ratios of VOCs were by far higher than observed, indicating that chemical processes may not be adequately represented in the model. The observed vertical gradients of isoprene and its primary degradation products methyl vinyl ketone (MVK) and methacrolein (MACR) suggest that the oxidation capacity in the tropical CBL is much higher than previously assumed. A simple chemical kinetics model was used to infer OH radical concentrations from the vertical gradients of (MVK+MACR)/isoprene. The estimated range of OH concentrations during the daytime was 3–8×106 molecules cm−3, i.e., an order of magnitude higher than is estimated for the tropical CBL by current state-of-the-art atmospheric chemistry and transport models. The remarkably high OH concentrations were also supported by results of a simple budget analysis, based on the flux-to-lifetime relationship of isoprene within the CBL. Furthermore, VOC fluxes determined with the airborne MLG approach were only in reasonable agreement with those of the tower-based REA and SLG approaches after correction for chemical decay by OH radicals, applying a best estimate OH concentration of 5.5×106 molecules cm−3. The SCM model calculations support relatively high OH concentration estimates after specifically being constrained by the mixing ratios of chemical constituents observed during the campaign. The relevance of the VOC fluxes for the local carbon budget of the tropical rainforest site during the measurements campaign was assessed by comparison with the concurrent CO2 fluxes, estimated by three different methods (eddy correlation, Lagrangian dispersion, and mass budget approach). Depending on the CO2 flux estimate, 1–6% or more of the carbon gained by net ecosystem productivity appeared to be re-emitted through VOC emissions.

BACKGROUND: Progressive peri-implant bone losses, which are accompanied by inflammatory lesions in the soft tissues, are referred to as peri-implantitis. The aim of this study was to compare the effects of photodynamic therapy (PDT) and conventional technique on microbial reduction in ligature-induced peri-implantitis in dogs. METHODS: Eighteen third premolars from nine Labrador retriever dogs were extracted and the implants were submerged. After osseointegration, peri-implantitis was induced. After 4 months, ligature was removed and natural bacterial plaque was allowed to form for another 4 months. The animals were then randomly divided into two groups. In the conventional group, they were treated using mucoperiosteal flaps for scaling the implant surface and chlorexidine (conventional) irrigation. In the PDT group, only mucoperiosteal scaling was carried out before photodynamic therapy. Inside the peri-implant pocket, a paste-based azulene photosensitizer was placed and then a GaAlAs low-power laser (lambda=660 nm, P=40 mW, E=7.2 J for 3 minutes) was used. Microbiological samples were obtained before and immediately after treatment. Before treatment, one implant was removed and analyzed by scanning electron microscopy to validate the contamination. RESULTS: The results of this study showed that Prevotella sp., Fusobacterium sp., and S. Beta-haemolyticus were significantly reduced for both groups. After treatment, no significant differences were observed between the groups. CONCLUSION: These findings suggest that photodynamic therapy is a non-invasive method that could be used to reduce microorganisms in peri-implantitis.

The aerosol characterization experiment performed within the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia–Smoke, Aerosols, Clouds, Rainfall and Climate (LBA‐SMOCC) field experiment carried out in Rondônia, Brazil, in the period from September to November 2002 provides a unique data set of size‐resolved chemical composition of boundary layer aerosol over the Amazon Basin from the intense biomass‐burning period to the onset of the wet season. Three main periods were clearly distinguished on the basis of the PM 10 concentration trend during the experiment: (1) dry period, with average PM 10 well above 50 μ g m −3 ; (2) transition period, during which the 24‐hour‐averaged PM 10 never exceeded 40 μ g m −3 and never dropped below 10 μ g m −3 ; (3) and wet period, characterized by 48‐hour‐averaged concentrations of PM 10 below 12 μ g m −3 and sometimes as low as 2 μ g m −3 . The trend of PM 10 reflects that of CO concentration and can be directly linked to the decreasing intensity of the biomass‐burning activities from September through November, because of the progressive onset of the wet season. Two prominent aerosol modes, in the submicron and supermicron size ranges, were detected throughout the experiment. Dry period size distributions are dominated by the fine mode, while the fine and coarse modes show almost the same concentrations during the wet period. The supermicron fraction of the aerosol is composed mainly of primary particles of crustal or biological origin, whereas submicron particles are produced in high concentrations only during the biomass‐burning periods and are mainly composed of organic material, mostly water‐soluble, and ∼10% of soluble inorganic salts, with sulphate as the major anion. Size‐resolved average aerosol chemical compositions are reported for the dry, transition, and wet periods. However, significant variations in the aerosol composition and concentrations were observed within each period, which can be classified into two categories: (1) diurnal oscillations, caused by the diurnal cycle of the boundary layer and the different combustion phase active during day (flaming) or night (smouldering); and (2) day‐to‐day variations, due to alternating phases of relatively wet and dry conditions. In a second part of the study, three subperiods representative of the conditions occurring in the dry, transition, and wet periods were isolated to follow the evolution of the aerosol chemical composition as a function of changes in rainfall rate and in the strength of the sources of particulate matter. The chemical data set provided by the SMOCC field experiment will be useful to characterize the aerosol hygroscopic properties and the ability of the particles to act as cloud condensation nuclei.

Forty-five selected samples from two different sequences, and from different sites spread over the Parana Basin have been analysed for major and trace elements and Sr isotope ratios. Results demonstrate the existence of two geochemically and isotopically distinct groups, namely a high phosphorus and titanium (HPT) and a low phosphorus and titanium (LPT) group. HPT rocks are relatively rich in LIL elements and have more homogeneous and markedly lower isotopic Sr ratios than LPT rocks. Since no relationship between the two groups was found, they may derive from different mantle sources, the HPT source being more enriched in most incompatible trace elements except Th, U and Rb than the LPT one. The LPT group, comprising basalts to rhyodacites, displays a large range in Sr isotopic ratios. This is interpreted as a result of a fractional crystallization process occurring at high crustal levels associated with assimilation of crustal material.

Abstract. Sub-micrometer atmospheric aerosol particles were studied in the Amazon region, 125 km northeast of Manaus, Brazil (-1°55.2'S, 59°28.1'W). The measurements were performed during the wet-to-dry transition period, 4-28 July 2001 as part of the LBA (Large-Scale Biosphere Atmosphere Experiment in Amazonia) CLAIRE-2001 (Cooperative LBA Airborne Regional Experiment) experiment. The number size distribution was measured with two parallel differential mobility analyzers, the hygroscopic growth at 90% RH with a Hygroscopic Tandem Mobility Analyzer (H-TDMA) and the concentrations of cloud condensation nuclei (CCN) with a cloud condensation nuclei counter. A model was developed that uses the H-TDMA data to predict the number of soluble molecules or ions in the individual particles and the corresponding minimum particle diameter for activation into a cloud droplet at a certain supersaturation. Integrating the number size distribution above this diameter, CCN concentrations were predicted with a time resolution of 10 min and compared to the measured concentrations. During the study period, three different air masses were identified and compared: clean background, air influenced by aged biomass burning, and moderately polluted air from recent local biomass burning. For the clean period 2001, similar number size distributions and hygroscopic behavior were observed as during the wet season at the same site in 1998, with mostly internally mixed particles of low diameter growth factor (~1.3 taken from dry to 90% RH). During the periods influenced by biomass burning the hygroscopic growth changed slightly, but the largest difference was seen in the number size distribution. The CCN model was found to be successful in predicting the measured CCN concentrations, typically within 25%. A sensitivity study showed relatively small dependence on the assumption of which model salt that was used to predict CCN concentrations from H-TDMA data. One strength of using H-TDMA data to predict CCN concentrations is that the model can also take into account soluble organic compounds, insofar as they go into solution at 90% RH. Another advantage is the higher time resolution compared to using size-resolved chemical composition data.

Abstract Potassium–argon dating, field relations, geochemical and strontium-isotope compositions are reported for the island of Pantelleria (Strait of Sicily, Italy). These data support the following model for the genesis and evolution through time of the volcanic system: the peralkaline rocks originated from mantle-derived parental magmas; the trachytic magma differentiated in a low pressure magma chamber by crystal–liquid fractionation. This process led to a chemically zoned magma chamber tapped at different levels by successive eruptions. During low-pressure differentiation the 87 Sr/ 86 Sr ratios of some of the most evolved Sr-poor rhyolitic magmas increased from 0.703 up to 0.708 by contamination with crustal material. The chemical variation displayed by the products of each of the defined eruptive cycles in the last 50000 years suggests an open system behaviour of the magma chamber which is episodically refilled by more mafic parent magma, differentiated at high rate and episodically erupted.