498 research outputs found
Clinopyroxene growth rates at high pressure. Constraints on magma recharge of the deep reservoir of the Campi Flegrei volcanic district (south Italy)
No full textClinopyroxene growth rates were experimentally determined in a K-basaltic rock from Campi Flegrei Volcanic District (south Italy). The primary objective was to provide constraints on the clinopyroxene crystallization kinetics at high pressure: we carried out a series of experiments at 0.8 GPa, 1030–1250 °C, 1 ≤ H2O ≤ 4 wt.%, with durations of 0.25, 3, 6 and 9 h. Overall, growth rate reaches a maximum value in the shortest experiments (~ 3·10−7 cm·s−1), decreasing to ~ 1·10−8 cm·s−1 in the longest duration runs. Temperature and water content do not seem to significantly affect the growth rate. Moreover, partition coefficients based on the crystal-liquid exchange show that mineral chemistry progressively approaches equilibrium with increasing run duration. Furthermore, to estimate the magma recharge of the deep reservoirs, we combined the determined growth rates with data from thermobarometry and from crystal size distribution analyses of clinopyroxenes in the most primitive scoria clasts of the Campi Flegrei Volcanic District (CFVD). We obtained a minimum residence time of ~ 5 months for the larger clinopyroxene population, and an ascent velocity of ~ 0.5·10−4 m·s−1 for the CFVD K-basaltic magma. The smaller clinopyroxene phenocrysts and microlite populations, however, suggest that the late stage of Procida magma crystallization took place in disequilibrium conditions
Rheology of primitive alkaline basalts: constraints on the pre-eruptive system of Campi Flegrei (Naples, Italy)
No full textThe knowledge of the rheology of magmas at high
pressure and temperature is of fundamental importance to
model their mobility, ascent rate and volcanic activity at
surface. In this study, we determined the viscosity and the
atomic structure of the nominally anhydrous APR16 alkali
basalt representative of the least-evolved magmas of
Phlegrean Volcanic District (Phlegrean Fields, Italy;
Bonechi et al., 2017). The sample is a lithic fragment
belonging to the Solchiaro hydromagmatic tuff of Procida
island, characterized by a porphyritic texture (P.I. 12%
volume) with phenocrysts of olivine (Fo85-80),
occasionally hosting Cr-spinel grains (Cr# ~0.50), and
clinopyroxene (Wo46-48 En46-31 Fs6-23), and a
groundmass made of olivine, clinopyroxene, plagioclase
(An79-52), Ti-magnetite (Usp4.1-4.4). The APR16 has
[Mg/(Mg+Fe)] 0.66, 49 wt% SiO2, 4.4 wt% of total alkali
(Na2O+K2O) and ~12 wt% of CaO. The anhydrous glass
was prepared at Bayerisches Geoinstitut by using a gasmixing
furnace. The rock powder was melted at 1400 °C
for 15 minutes at atmospheric pressure and oxygen
fugacity buffered at Nickel-Nickel Oxide level using a
CO/CO2 gas mixture. The viscosity of glassy APR16 was
determined by the in situ falling sphere technique at P of
0.7-2.5 GPa and T of 1335-1700°C using the Paris-
Edinburgh press available at the 16BMB beamline at the
Advanced Photon Source (Argonne National Lab, Illinois,
USA). The falling velocity of the Pt probing spheres was
measured by X-ray imaging using a high-speed camera
recording 500 frames per second. In addition, analyses of
the melt structure were performed by using multi-angle
energy dispersive X-ray diffraction technique. Preliminary
data show the viscosity being in the range of 0.1-1 Pa·s at
the target P and T. These viscosity values can be used to
model the mobility and ascent velocity of primitive alkali
basalts considered to be parental magmas at Campi Flegrei
with important implications for the volcanic hazard of the
area over time
Kinetic analysis and comparison of models of xylose metabolism by Klebsiella planticola
No full textA model for the degradation of xylose and ethanol production by Klebsiella planticola is proposed and compared with the exponential and Michaelis-Menten approaches. This model is based on the energy system diagrams and it is a simplified version of a previous model developed for the glucose and ethanol kinetics of the yeast Saccharomices cerevisiae. In this model the dynamics of the substrate and of the final product are strictly related by means of the cellular activity. This model shows superior performances with respect to the two alternatives, behaving better along the whole dynamics. (C) 1996 Academic Press, Inc
Clinopyroxene Growth and Dissolution Rates: High-Pressure Investigation on a Primitive Alkaline Basalt from the Campi Flegrei Volcanic District (South Italy)
No full textWith the aim to investigate the influence of time, temperature, water content and pressure on clinopyroxene growth and dissolution rate, we performed crystallization and dissolution experiments on a K-basaltic rock from Procida island (Campi Flegrei Volcanic District, south Italy). Crystallization experiments were performed at anhydrous and hydrous (1 ≤ H2O ≤ 4 wt.%) conditions, pressure of 0.8 GPa, temperature between 1030 °C and 1250 °C and dwell time between 0.25 and 9 hours. Crystallization experiments show that time is the factor that most affects the growth rate compared to temperature and water content. Clinopyroxene growth rate, indeed, varies from 10-7 to 10-8 cm/s and it reaches the maximum value in the shortest experiments (0.25 h) while it decreases increasing time (9 h). Comparing our high-pressure growth rates with the low-pressure ones available in literature related to clinopyroxene, it was possible to note that pressure does no affect the growth rate. Indeed, all the considered growth rates show similar values that vary from 10-5 to 10-9 cm/s regardless of pressure but as a function of time. Moreover, partition coefficients based on the crystal-liquid exchange demonstrate that the chemistry of minerals progressively approaches to equilibrium from the shortest to long-lasting experiments, putting forward the latter as representative of the ideal condition of crystallization in a deep magmatic reservoir. Short experiments, instead, could be representative of ascent mechanisms in disequilibrium conditions and quick times. Dissolution experiments, instead, were carried out at high pressure (0.8-2 GPa), superliquidus temperatures and different dwell times by using the seeding technique. Preliminary results show that clinopyroxene dissolution rate varies from 10-2 to 10-7 cm/s, highlighting an influence of temperature and time with respect to pressure
Influence of pre-existing nuclei on the crystallization kinetics of primitive alkaline magmas: insights on the deep feeding system of the campi flegrei Volcanic district
No full textAiming to evaluate the influence of pre-existing nuclei on the clinopyroxene crystallization kinetics, time-series experiments were performed using both natural and vitrified starting materials. Experiments were carried out at pressure of 0.8 GPa, temperatures between 1220 and 1250 °C, and dwell times ranging from 0.16 to 12 h. Clinopyroxene growth rates of the runs performed using the natural starting material containing pre-existing nuclei (~2 × 10−7 to ~6 × 10−8 cm∙s−1) are higher than those of the runs performed using the vitrified one (~3 × 10−7 to ~2 × 10−8 cm∙s−1). In both cases the growth rates decrease with increasing time. Conversely, clinopyroxene nucleation rates are lower in the experiments performed using the natural powder (102 and 10 mm−3 s−1) compared to those performed with the glassy starting material (105 and 103 mm−3∙s−1). The nucleation rates tend to decrease increasing dwell time in all the series up to ~3 h, after which it remains nearly constant. Finally, the combination of the obtained clinopyroxene growth rates with the crystal size analysis of natural clinopyroxenes, allowed to estimate the magma ascent rate and the recharge rate of the Campi Flegrei Volcanic District deep reservoir
Modelling interpretation of the kinetics of metabolic processes
No full textIn vivo NMR spectroscopy and sugars selectively enriched with C-13 were used to follow the step-by-step metabolic kinetics of microorganisms. A new modelling approach is discussed for the analysis of microbial dynamics. It is based on structurally non linear compartmental models and on the dynamics of the substrate and product. This combined approach was tested with the fermentation of sugars by bacteria and yeasts. The models were fitted with experimental data to obtain the values of the kinetic constants related to the investigated metabolic path
In My New Home: The Daily Lives of People Living in Public Houses after a Long Period of Homelessness
No full textHomelessness refers to a loss of social relationships and a condition of isolation and stigma that affects a person's well-being. Although the literature has revealed the crucial role of a home in a person's well-being, few studies have explored the daily lives of people who transition from homeless services to an independent home. People who experience homelessness are at risk of remaining connected to homeless services even after finding a home. This study aimed to explore the daily lives of people who have obtained public housing, focusing on their daily relationships and the places they frequent. Data were collected through interviews with quantitative and qualitative measures involving 14 people with a history of homelessness who had obtained a public house in a medium-sized Italian city. Several themes concerning social relationships and places were identified. Regarding social relationships, people experience loneliness or a connection with the community and homeless services. They spend their time alone at home or around the city. The implications of the results are discussed with respect to practice and research on homelessness
ISIC_WSM: Generating Weak Segmentation Maps for the ISIC archive
No full textRecognizing skin cancer in time could greatly increase patients' chances of recovery. For this reason, in recent years, numerous decision support systems have been proposed to help dermatologists in this diagnosis. These systems are generally based on Convolutional Neural Networks and are used for both segmentation and classification of lesions. Although their main goal is to correctly recognize the lesions' type, the preliminary segmentation step has been shown to increase the performance of the classifier. In fact, this is not surprising because physicians also use information on the shape of the lesion to make a diagnosis. Thanks to the ISIC archive, a huge number of skin lesion images, along with the corresponding metadata (type, position, dimension, etc.), are publicly available to train a deep neural network, but, unfortunately, only a small fraction of them are labeled for segmentation. To overcome this limitation, in this paper, a weak supervised approach is proposed to extract the segmentation label maps from the entire ISIC archive. Moreover, to demonstrate the quality of the proposed approach, the generated supervisions were first compared with those available in ISIC and, then, used to train a segmentation network, whose performance was evaluated against that obtained using only the small set of ISIC label maps. To foster reproducibility and to promote future research in lesion segmentation and classification, the generated ISIC Weak Segmentation Map (ISIC_WSM) dataset has been released. As far as we know, this is the first dataset that contains segmentation supervisions for clinical images of skin lesions. (c) 2022 Elsevier B.V. All rights reserved
The Olive Tree, a source of antioxidant compounds
No full textProducts from Olea europaea L. i.e. leaves, olive oil and pomace are promising sources of bioactive compounds. In
leaves, antioxidant compounds show a concentration dependence on the vegetative cycle of the trees, higher antioxidant concentration
coinciding with seasonal vegetative changes. Olive oil, but particularly pomances are a rich source of health-giving
effect compounds more specifically polyphenolic antioxidants. Many of these compounds may be of interest for pharmaceutical,
cosmetic and food industry, especially because both pomance and leaves are currently considered waste of the olive oil
production
Analytical composition of flours through thermogravimetric and rheological combined methods
No full textThe suitability of thermogravimetric analysis (TGA) and rheology for predicting analytical composition of flour was verified. The percentage weight loss of flour samples in different temperature ranges and their analytical composition determined following the American Association of Cereal Chemists (AACC) approved methods were correlated. The moisture content determined by AACC method showed a strong correlation with the weight loss of dried samples in the temperature range 30 – 125°C. Similarly, the weight loss of fully swollen samples, determined by TGA in the temperature range of 30 – 125°C, perfectly correlated with the water-Solvent Retention Capacity (w-SRC) determined by standard method (AACC). The weight loss in the range 200 – 400°C revealed a good correlation with the starch content, while the weight loss in the range 400 – 600°C correlated with the gluten content. Finally, the so-called residue at 600°C (usually attributable to mineral content) correlated with the ash content (AACC standard method). The rheological parameters (G', G'' and tan δ) also showed a strong correlation with the analytical composition of analyzed flours. A perfect correlation was observed between the mineral content and the elastic modulus, as well as between both G' and G'' and the starch content. As the resilience of dough samples strongly depends on the relative amount of gliadins and glutenins, a strong correlation between the Gli/Glu ratio and tan δ was also found
- …
