1,017 research outputs found
A NEW METHOD TO COMPUTE FLUIDS SATURATION IN C-H-O-S-SILICATE MELT SYSTEMS
No full textWe developed a method to calculate equilibrium between a
C-O-H-S fluid phase and a silicate melt based on a previous
model for the saturation of H2O-CO2 fluids (Papale, 1999) and
on a thermochemical approach for calculating sulfide and
sulfate solubilities of simple and complex melts. In particular,
this second approach combines the Toop-Samis polymeric
model with the Flood - Grjotheim theoretical treatment of silicate
melts (Ottonello et al., 2001; Moretti, 2002). Moreover,
fugacities in the gaseous phase are computed through the
SUPERFLUID code (Belonoshko et al., 1992). The C-H-O-S
saturation model allows determining the partition of H2O, CO2,
and S between silicate melt and coexisting fluid, and the
composition of the fluid phase in terms of H2O, CO2, SO2, and
H2S, as a function of pressure, temperature, volatile-free liquid
composition, oxygen fugacity, and total amount of volatile
components in the system. For the sake of simplicity, we
assumed that no reduced or oxidized sulfur-saturated solid or
liquid phases nucleate or separate from the liquid-gas system.
Minima in sulfur solubility as a function of oxygen fugacity are
depicted, in good agreement with theory and experiments.
Applications are given for rhyolitic and basaltic melts with
various oxygen fugacities in the range NNO±2, and pressure
from a few hundred MPa to atmospheric. The developed model
accounts for the reciprocal effects of volatiles on their saturation
contents, and the complex relationships between the saturation
surface of a multicomponent fluid and the liquid
composition, volatile abundance, P-T conditions and oxidation
state.
Belonoshko A, Shi PF & Saxena S, Comp. Geosci, 18, 1267-
1269, (1992).
Moretti R, PhD Thesis, University of Pisa
Ottonello G, Moretti R, Marini L& Vetuschi Zuccolini M, Chem.
Geol, 174, 157-179, (2001).
Papale P, Amer. Mineral, 84, 477-492, (1999)
On the saturation surface and oxidation state of C-H-O-S-silicate melt systems
No full textThe equilibrium between a H2O–CO2–SO2–H2S gas phase
and silicate melts is investigated by means of thermochemical
calculations which join homogeneous reactions in the gas
phase and heterogeneous gas–melt saturation modeling based
on classical sub-regular multicomponent mixing and Toop-
Samis polymeric approach. Sulfur in the melt phase is
assumed to be present in two different oxidation states (sulfide
and sulfate ions). The thermodynamic model is an extension
of that presented in Moretti et al. [1] to account for iron
speciation at high pressure with variable dissolved water
contents. The consequences on the equilibrium conditions of
different assumptions on the effective redox buffer in magma
are examined for melts of basaltic and rhyolitic composition,
determining the equilibrium conditions on the basis of i)
constant FeII/FeIII, ii) constant fH2S/fSO2, and iii) constant
relative fO2, expressed as difference in log-units to a solid
buffer. The first two buffers are expected to be effective in
basaltic and andesitic-rhyolitic magmas, respectively,
according to the most abundant reservoir of redox couples.
Furthermore, for each assumed redox buffer the pressure
dependence of phase composition and oxidation state of the
system shows strongly non-linear trends. The largest
compositional differences are shown by sulfur species,
however, the concentrations of H2O and CO2 in the two
phases at equilibrium also show non-negligible dependence on
the redox conditions. For each assumed redox buffer, sulfur
dioxide in the gas phase, and sulfate ions in the liquid phase,
are found to be present in appreciable quantities or represent
the dominating sulfur species. The more reliable redox buffers
represented by constant FeII/FeIII for basalt, and constant
fH2S/fSO2 for rhyolite, show that oxygen fugacity paths
during magma depressurization strongly deviate from those
related to a solid buffer plus or minus a constant.
Results here presented, although not yet accounting for the
separation of S-bearing solid or liquid phases, may furnish
insights on the composition of gases separated from magmas
originated in various geodynamic settings, under different
redox conditions.
Reference
[1] Moretti R., Papale P. and Ottonello G. (2003) In: Volcanic
Degassing (Oppenheimer C., Pyle D. and Barclay J., eds.)
Geol. Soc. London Spec. Publ., 213, 81-101
A model for multicomponent fluid saturation in C-O-H-S-silicate melt systems
No full textThe dissolution behavior of volatile components in magmas is essential to model the
volcanic process from the deep regions of magma generation and storage to the shallow
regions of magma eruption and emplacement.
Water, carbon dioxide, and sulfur compounds are the main volatile components in natural
magmas, constituting in most cases more than 99% of the volcanic gases released
before, during, and after eruption.We have developed a method to calculate the chemical
equilibrium between a fluid phase in the C-O-H-S system and a silicate melt with
composition defined by ten major oxides. The method is based on a previous model
for the saturation of H2O-CO2 fluids [1] and on a sulfur solubility model [2] in silicate
liquids. For the computation of the fugacities of components in fluids with complex
composition we used the SUPERFLUID code [3]. The model allows determining the
partition of H2O, CO2, and S between the silicate liquid and the coexisting fluid, and
the composition of the fluid phase in terms of H2O, CO2, SO2, and H2S, as a function
of pressure, temperature, volatile-free liquid composition, oxygen fugacity, and
total amount of each volatile component in the system. App lications are presented
to several silicate liquids with rhyolitic and basaltic composition, oxygen fugacities
in the range NNO ± 2, and pressure from a few hundred MPa to atmospheric, with
the simplifying assumption that no reduced or oxidized sulfur-saturated solid or liquid
phases nucleate or separate from the liquid-gas system. Results show the well-known
minima in sulfur saturation contents as a function of oxygen fugacity, the reciprocal
effects of volatiles on their saturation contents, and the complex relationships between
saturation surface of a multicomponent fluid, liquid composition, volatile abundance,
P-T conditions, and oxidation state. The method represents therefore a new powerful
tool for the prediction of multicomponent gas-melt equilibria in magmas.
REFERENCES
[1] Papale P. (1999) Am. Mineral., 84, 477-492
[2] Moretti R. and Ottonello G. This issue
[3] Belonoshko A.B., Shi P. and Saxena S,K, (1992) Comp. Geosci., 18, 1267-1269.
Influence of the drying treatment on the performance of V-Nb mixed oxides catalysts synthesised via sol-gel
No full textMixed oxides NbVO5 amorphous catalysts have been synthesised by means of the sol-gel technique using different vanadium oxide to water ratios and gel drying treatments: in particular air-drying at room temperature and microwave heating have been adopted. Successively, the dried materials were calcinated up to 550 C in flowing air. Brunauer-Emmett-Teller (BET) surface area analysis showed that this parameter depends on drying method and on the thermal treatment. Differential thermal analysis (DTA) proved that the crystallisation process of the NbVO5 powders occurred at lower temperature when microwave drying was used. An increase of crystallinity was also recorded by X-ray diffraction (XRD) analysis for samples prepared using a high V/H 2O ratio and dried by microwave heating. These samples also show high reducibility and surface acidity, as demonstrated by temperature programmed reduction (TPR) and temperature programmed desorption (TPD) techniques respectively. An improvement of the catalytic performances for the gel dried by microwave heating in the oxidative dehydrogenation of ethane at 550 C has been observed
Facemasks and Public Health: analysis of bacterial contamination in FFP2 masks: Gaia Papale
No full textBACKGROUND: Facemasks (FM), due to the Covid-19 pandemic, are extensively used and often worn beyond the recommended time. This has led to questions about the negative impact persistent contamination on FMs might have on public health. The study aims to assess the level of contamination reached in a small cohort of subjects after the recommended use (8 h) of FM. METHODS: This descriptive study was carried out between January and April 2022 on 17 people: 9 women and 8 men aged between 25-45 years. These two groups were divided into two micro-groups: women were selected according to their skincare habits (no skincare and skincare with cosmetics). In contrast, men were selected according to the length of their beards (thick or short beard). The FM was worn for 8 h in a controlled office setting, to avoid possible uncontrolled variables. Then, the FM was cut, placed in a tube with a recovery medium and centrifuged. The supernatant was removed and the pellet resuspended. Aliquots were plated on Petri plates and incubated for 48 h at 36 °C to count the Colony Forming Units (CFU). The statistical analysis was conducted using Stata software, performing the Wilcoxon matched-pairs and setting a significance level of p < 0.05. RESULTS: Women had higher FM contamination than men ([Image: see text] = 4960 vs 3130 CFU/ml). Also, we found more colonies ([Image: see text] = 18890 vs 3420 CFU/ml) in the FMs of women without skincare (p = 0.06), while among men, more colonies were reported for those with a thicker beard than for those with a shorter one ([Image: see text] = 3300 vs 2960 CFU/ml). CONCLUSIONS: Extensive FM use increases bacterial contamination exponentially. This could lead to changes in the facial microbiome, inducing skin conditions (such as allergic dermatitis and acne). Facial skin conditions are important public health issues for people wearing FMs daily. In addition, responsible handling of this equipment is essential to avoid the spread of SARS-CoV-2 through contact with these items, which can persist for many days. KEY MESSAGES: • Gender and physical characteristics may influence the level of contamination present on FFP2 face masks. • There is a need to increase community awareness on the proper handling of facemasks, prevent health problems for users, and limit the spread of infection to those around them
The compositional dependence of the saturation surface of H2O+CO2 fluids in silicate melts
No full textThe volatile saturation surface in H2O-CO2-silicate melt systems is modeled by applying thermodynamic equilibrium between gaseous and liquid volatile components. The whole database of existing saturation data in the C-O-H-silicate liquid systems has allowed us to re-calibrate a previously developed fully multicomponent H2O-CO2 saturation model [Papale, P., 1999. Modeling of the solubility of a two-component H2O + CO2 fluid in silicate liquid. Am. Mineral., 84, 477-492]. The new database nearly doubles the previous one, greatly improving the performances of the whole model, which now adopts a significantly lower number of model parameters with respect to the previous calibration. The multicomponent H2O + CO2 saturation model is fully non-ideal, the only assumption being that the excess Gibbs free energy of the silicate mixture can be represented by an expansion of first-order symmetric interaction terms. No a-priori assumption is made on the P-T dependence of the volatile-oxide interaction terms, meaning that no assumption is made on the partial molar volume and enthalpy of the dissolved volatiles. The whole treatment is evaluated by restrictive statistical algorithms, which confirm the model validity on an extended database. The model allows to investigate extensively the dependence of the complex volatile saturation surface on composition. In order to explore the non-linear behaviors implicit in the physics of the dissolution process, the model is employed in a series of calculations aimed at illustrating some of the compositional features of the volatile saturation surface in both one-component and two-component volatile conditions. The results show compositional-dependent minima and maxima, some of which are known from the experiments. Non-ideal behavior is enhanced in two-component fluid phase conditions and pressures above a few hundreds MPa, where calculated isobaric H2O-CO2 saturation curves reveal the possible existence of a maximum in CO2 saturation at non-zero H2O contents. Due to the compositional dependence of the volatile saturation surface, it is outlined the important role played by redox conditions, especially in iron-rich melt systems like basalts
Volatile solubility and melt reactivity in the C-H-O-S-silicate liquid system: the role of redox variables
No full textretinal involvement in pigment dispersion syndrome
No full textRetinal involvement has been documented in a number of patients with pigment dispersion syndrome, which also appears to be associated with a higher than normal risk of retinal detachment. We studied 24 patients with this syndrome to determine the prevalence of lattice degeneration and other retinal disorders associated with a predisposition to detachment. Lattice degeneration was found in 8 of 24 patients examined, with a prevalence that is significantly higher than that reported for normal subjects. Four eyes presented areas of retinoschisis and only one displayed a rhegmatogenous detachment. A father and son (both myopes) were found to have similar lattice lesions in the same retinal quadrants. These findings suggest that pigment dispersion syndrome may be associated with developmental anomalies that are not restricted to the anterior chamber but involve other portions of the bulb as well
Structure and Microrheology of Complex Polymer Solutions: from Genome Organization to Active-Passive Mixtures
No full textPolymers are intriguing physical systems whose complex properties are at the heart of how viscoelastic substances, materials which under strain manifest a behavior which is intermediate between a liquid and a solid, work. Understanding the properties of these materials is the main goal of the theoretical and computational tools of Polymer Physics. A particularly important, yet not fully understood, class of polymer materials is represented by concentrated solutions and melts of unknotted and unconcatenated ring polymers: in fact, at odds with the more familiar case of linear polymers which tend to become highly mixed and mutually penetrating, the presence of mutual avoidance and topological constraints (entanglements) between ring polymers force these chains to remain “territorial”, i.e. each chain is virtually unmixed from the rest of the others. Because of this feature, solutions of ring polymers display unique material properties, in particular single chains tend to crumple into highly branched conformations and feature marked corrugated surfaces. Recently, it has been suggested that the spatial configurations of ring polymers in solution can be used as model systems for the organization of chromosome conformations during interphase, i.e. inside the nuclei of eukaryotic cells. This surprising analogy is built upon the claim that chromosomes undergo slow relaxation inside the nucleus which results in the spontaneous formation of so-called territories, regions of the nucleus which have a profound impact on crucial cellular functions such as gene expression and gene regulation. In this Thesis, we explore the analogy between ring polymers in solution, their large-scale crumpled 3d structure and interphase chromosomes by employing a combination of the theory of polymer solutions and numerical simulations. In more detail, we investigate primarily the following aspects: (a) the formation of ordered domains on a simple Ising-like toy model for crumpled polymers; (b) The analysis of the viscoelastic properties of model chromosome conformations whose stochastic motion is restricted by the presence of external constraints; (c) The discussion of the viscoelastic properties of solutions of active vs. non- active rings, where ”active” means that polymers are driven out-of-equilibrium by pumping energy inside the system
Silica-polyethylene glycol hybrids synthesized by sol-gel: Biocompatibility improvement of titanium implants by coating
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