171,356 research outputs found
The dehydroxylation of serpentine group minerals
No full textThe thermal transformation, stability field, and reaction kinetics of serpentine minerals (antigorite, chrysotile, and lizardite) have been studied to draw a comprehensive model for their dehydroxylation and recrystallization reactions. In situ X‐ray powder diffraction (XRPD) and kinetic studies were combined with transmission electron microscopy (TEM) observations to describe the mechanisms of dehydroxylation and later high-temperature crystallization. During dehydroxylation, a metastable transition phase with a characteristic peak around 9 Å was observed in antigorite and, to a minor extent, in lizardite. Rietveld refinements confirmed that the 9 Å phase actually possesses a talc-like structure. The appearance of this phase is controlled by structure and kinetic factors.
The kinetic parameters and reaction mechanism for lizardite and antigorite dehydroxylation in air at ambient pressure were calculated using the Avrami models and compared to those of chrysotile. For both lizardite and antigorite, the kinetics of dehydroxylation is controlled by diffusion. Apparent activation energy of the reaction in the temperature range 612–708 °C was 221 and 255 kJ/mol for lizardite and antigorite, respectively. The reaction sequences of chrysotile, lizardite, and antigorite leading to the formation of stable high-temperature products (i.e., forsterite and enstatite) are described taking into account previous topotactic and dissolution-recrystallization models.
Keywords: Main serpentine minerals, dehydroxylation, reaction kinetics, Avrami, metastable phase
Quantitative determination of chrysotile in massive serpentinites using DTA: implications for asbestos determinations
No full textThere is increasing concern about the health hazard of asbestos from natural geologic deposits such as greenstones [natural occurring asbestos (NOA)]. Therefore, quantitative determination of the chrysotile asbestos content within massive serpentinites is a recurrent requirement of recent asbestos-inherent law regulations, due to the possible health hazard associated with the release of chrysotile fibers. Unfortunately, the obtainment of accurate and precise quantitative figures of the actual chrysotile content is strongly complicated by typical serpentinite textures, consisting of fine-to-ultrafine intergrowths of fibrous and non-fibrous serpentine minerals, often difficult to identify by conventional methods, such as X-ray diffraction or microanalytical approaches.
In this paper, we propose a reliable and straightforward method for the quantitative determination of chrysotile asbestos within bulk massive serpentinites, based on thermal analysis data and, specifically, on the distinctive thermal behavior of chrysotile, lizardite, and antigorite during dehydroxylation at 500–800 °C. Deconvolution processing of DTA endothermic signals in the dehydroxylation temperature range revealed good linear correlation between peak area ratios and chrysotile content, for both lizardite + chrysotile and antigorite + chrysotile samples. The DTA correlation curves have been used to determine the chrysotile content in two test serpentinites, revealing surprisingly high-chrysotile content. This novel method is of vast importance as it represents one of the most promising tools for chrysotile quantitative determinations in massive serpentinites, providing unbiased and accurate responses to recent asbestos-related law requirements
Radiative-equilibrium models for Giacobbe et al. (2021), Nature
No full textThis is the repository for the radiative-equilibrium atmospheric models used in:
Five carbon- and nitrogen-bearing species in a hot giant planet atmosphere
by Giacobbe et al. (2021), Nature, DOI: 10.1038/s41586-021-03381-x.
The run_radeq/ folder contains the HD209458b atmospheric models computed under the assumption of radiative and thermochemical equilibrium with the pyratbay code, as described in the methods section of Giacobbe et al. (2021).
The file names indicate the adopted elemental metallicity and C/O abundance ratios, e.g., the "HD209458b_radeq_000.001x-solar_CO-0.10.atm" file corresponds to a metallicity of 0.001 times solar and a C/O ratio of 0.1.
The Python script "fig_radeq_atmospheres.py" reproduces the extended data figures showing the radiative-equilibrium atmospheric models of Giacobbe et al. (2021), which are also provided in the plots/ folder
HIGH TEMPERATURE REACTIONS OF SERPENTINE GROUP MINERALS
No full textSerpentine minerals are important components of the oceanic crust and play a chief role in lithosphere dynamics; for this reason, their structural and mineralogical modification with temperature have major implications(e.g.,Ulmer and Trommsdorff 1995; Escartin et al. 2001;). Despite the huge amount of work devoted to the temperature-induced dehydroxylation and recrystallization reactions of serpentine minerals in air at ambient pressure, several issues are still open to debate: the nature and stability of amorphous dehydroxylate phases, thenature and stability field of talc- and chlorite-like phases possibly appearing during the reaction path, possible topotactic relationships between the serpentine and newly formed phases forsterite and enstatite, the nature of the pyroxene phase, and a comprehensive model based on kinetic parameters is still missing. The thermaltransformation, stability field, and reaction kinetics of serpentine minerals antigorite, chrysotile, and lizardite havebeen studied to draw a comprehensive model for their dehydroxylation and recrystallization reactions. In situ Xray powder diffraction (XRPD) and kinetic studies were combined with transmission electron microscopy (TEM)observations to describe the mechanisms of dehydroxylation and later high-temperature crystallization.It was found that the three serpentine polymorphs decompose at different temperatures. Chrysotile is stable upto 750 C, lizardite up to 775 C and antigorite decomposes at 800 C. During dehydroxylation, a metastable transition phase with a characteristic peak around 9 Å was observed in antigorite and, to a minor extent, in lizardite (Gualtieri et al. 2012). Rietveld refinements confirmed that the 9 Å phase actually possesses a talc-like structure. It was found that when the heating rate is fast (that is > 30 C/min), the talc-like phase is not observed.When the heating rate is slower (< 30 C/min), the talc-like phase is observed. Regardless the rate of heating,talc is never observed in chrysotile indicating both a crystal chemical (thermodynamic) and kinetic control of the reaction. The kinetic parameters and reaction mechanism for lizardite and antigorite dehydroxylation in air at ambient pressure were calculated using the Avrami models and compared to those of chrysotile. For both lizardite and antigorite, the kinetics of dehydroxylation is controlled by diffusion. Apparent activation energy of the reaction in the temperature range 612–708 C was 184, 221 and 255 kJ/mol for chrysotile, lizardite and antigorite,respectively. The reaction sequences of chrysotile, lizardite, and antigorite leading to the formation of stable high-temperature products (i.e. forsterite and enstatite) are described taking into account previous topotactic and dissolution-recrystallization models
Flexibility of action verbs processing in Parkinson’s disease
No full textObjective: This study aims to investigate action language processing abilities in Parkinson's disease (PD) compared to healthy controls (HCs), specifically examining whether the involvement of motor systems is influenced by task context. By focusing on implicit versus explicit task demands, the study evaluates how semantic processing differs in PD and whether these differences align with a flexible embodied cognition framework.Methods: The study analyzed the performance of participants on two tasks: an explicit task (semantic judgment task, SJ) and an implicit task (letter detection task, LD). PD outpatients (n = 31, mean age 64.58 years) referred to the Parkinson and Movement Disorders Unit of ICS Maugeri Hermitage were enrolled, along with a group of healthy controls (n = 31, mean age 64.19 years). Performance was measured through reaction times (RTs) and accuracy scores (Acc) during the processing of action verbs and abstract verbs.Results: PD patients exhibited slower RTs and lower accuracy when processing action verbs compared to abstract verbs, but only during the SJ task. Slower RTs in the SJ task were predicted by language and executive functioning (semantic fluency) and disease progression (Hoehn and Yahr stages) for both action and abstract verbs. In the LD task, slower RTs were predicted by executive functioning for action verbs and attention (measured by Trail Making Test Part B and Stroop task) for abstract verbs.Conclusions: The findings suggest a context-dependent involvement of the motor system in action language processing, supporting a flexible, embodied approach to conceptual semantic processing rather than an automatic one
Quasi-periodicity in relative quasi-periodic tori
No full textAt variance from the cases of relative equilibria and relative periodic orbits
of dynamical systems with symmetry, the dynamics in relative quasi-periodic
tori (namely, subsets of the phase space that project to an invariant torus of
the reduced system on which the flow is quasi-periodic) is not yet completely
understood. Even in the simplest situation of a free action of a compact and
abelian connected group, the dynamics in a relative quasi-periodic torus is not
necessarily quasi-periodic. It is known that quasi-periodicity of the unreduced
dynamics is related to the reducibility of the reconstruction equation, and
sufficient conditions for it are virtually known only in a perturbation context.
We provide a different, though equivalent, approach to this subject, based on
the hypothesis of the existence of commuting, group-invariant lifts of a set
of generators of the reduced torus. Under this hypothesis, which is shown
to be equivalent to the reducibility of the reconstruction equation, we give a
complete description of the structure of the relative quasi-periodic torus, which
is a principal torus bundle whose fibers are tori of a dimension which exceeds
that of the reduced torus by at most the rank of the group. The construction
can always be done in such a way that these tori have minimal dimension and
carry ergodic flow
Disability manager
No full textIl Disability Manager è una figura professionale qualificata, destinata a promuovere soluzioni tecnico-organizzative all’interno di enti e aziende pubbliche e private, per agevolare l’inserimento delle persone con disabilità nel mondo del lavoro attraverso politiche finalizzate a garantire l’autonomia e l’inclusione. Queste tendono a rimuovere barriere fisiche, sociali, culturali, economiche, istituzionali e, a tal fine, è indispensabile il dialogo costante con gli interlocutori interni ed esterni (operatori sanitari, professionisti sociali, psicologi). Il Disability Manager è pertanto responsabile del processo di inclusione delle persone con disabilità nell’ambiente di lavoro, garantendo loro gli accomodamenti ragionevoli. Questi sono soluzioni tecniche e organizzative personalizzate, definite attraverso un dialogo tra il Disability Manager e l’interessato, necessarie per esercitare un diritto o una libertà altrimenti esclusi
Structural and spectroscopic characterization of anorthite synthesized from secondary raw materials
No full textRecycling of secondary raw materials is a priority of waste handling in the countries of the
European community. A virtual secondary raw material of great importance is the product of
the thermal transformation of cement – asbestos. This work illustrates the study of calcination
products obtained starting from the product of the thermal transformation of cement-asbestos
at 1200 °C, added to primary raw materials (kaolin, aluminum hydroxide) and boric acid as
mineralizing agent. The calcination has been conducted at 1200 °C for 1 hour. The
crystallization kinetics has been monitored using in situ high temperature X-ray powder
diffraction. The microscopic characterization of the final product of calcination has been
conducted with SEM and TEM imaging supported by X-ray microanalysis. The structure
refinement was conducted on the powder sample using the Rietveld method. The results are
compared with the spectroscopic characterization including Mössbauer and UV-Vis
spectroscopies. The final product of the calcination is essentially anorthite (about 89 wt%)
with minor spinel (11 wt%). All experimental data converge to support the hypothesis that
the anorthite is stoichiometric, and the small amounts of iron detected (1.32 wt%) is Fe3+
hosted in the structure of spinel
Figure 2 in The point on Opaliopsis atlantis (Gastropoda: Epitoniidae) distribution: new data from the Mediterranean and implications
No full textFigure 2. (A-F) Opaliopsis atlantis: (A-C) Shell from Station CWR145POP'95RAN10, height 9.0 mm. (D-F) Shell from Station BEL145POP'95FRAN1, heigh 8.4 mm.Published as part of Giacobbe, Salvatore & Renda, Walter, 2020, The point on Opaliopsis atlantis (Gastropoda: Epitoniidae) distribution: new data from the Mediterranean and implications, pp. 1-7 in Papéis Avulsos de Zoologia 60 on page 3, DOI: 10.11606/1807-0205/2020.60.59, http://zenodo.org/record/498388
- …
