1,721,012 research outputs found
The formation of talc during the dehydroxylation reaction of serpentine minerals
No full textThe occurrence of talc which may form during the dehydroxylation reaction of the serpentine minerals antigorite, lizardite and chrysotile has been studied. Several experiments were carried out both
ex situ and in situ in order to better understand the conditions of formation of this phase. Talc is
observed as a metastable phase only during the dehydroxylation reaction of antigorite and, to a lesser extent, of lizardite. On the other hand, talc formation was not observed during the dehydroxylation reaction of chrysotile because of its corrugated unstable cylindrical lattice that readily prompts the formation of forsterite
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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
Familial hypercholesterolemia: A complex genetic disease with variable phenotypes
No full textFamilial hypercholesterolemia (FH) is the most frequent genetic disease and is characterized by elevation of LDL-cholesterol that accumulates in tissues leading to premature atherosclerosis and sometime tendon xanthomas. Main causes of FH are pathogenic variants in the genes encoding the LDL receptor (LDLR), its ligand - the apolipoprotein B (APOB) - or Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9). Rarer causes include variants in genes encoding apolipoprotein E (APOE) and the signal-transducing adaptor family member 1 (STAP1). Genetics of FH is extremely complicated by 1. high heterogeneity, 2. presence of variant clusters and 3. phenotypic variability. In fact, a great variability was observed among patients with the same genetic status: an overlap of LDL-cholesterol levels was observed between heterozygous patients (HeFH) and homozygous FH patients, as well as some HeFH showed a normal lipid profile. A correct pathogenicity evaluation is the first step to correctly define the genetic status helping to identify the variants which really cause the FH. Several phenotypic differences were observed among HeFH patients carrying different variant types (null or defective) or variants in different affected genes. Patients with a null variant in LDLR gene showed higher LDL-cholesterol levels and higher risk for coronary artery disease than patients with a defective variant. Pathogenic variants in several lipid-related genes causing different dyslipidemias were found among FH patients acting as both modifying factors (worsening the phenotype) and confounding factors (needing a differential diagnosis to be discriminated from FH). This review aims at depicting the complex genetic basis of FH
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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