1,720,971 research outputs found
CRYSTAL-CHEMISTRY AND INTRACRYSTALLINE RELATIONSHIPS OF ORTHO-PYROXENE IN A SUITE OF HIGH-PRESSURE ULTRAMAFIC NODULES FROM THE NEWER VOLCANICS OF VICTORIA, AUSTRALIA
No full textA suite of orthopyroxenes from spinel lherzolite xenoliths associated with basanites occurring in the Victorian (Australia) post-Pliocene 'Newer Volcanics' province was investigated by means of a crystal chemical methodology which provides accurate site occupancy and site configuration parameters.
The M1 configuration is essentially constrained by Al(IV) rather than Fe2+. In addition, Fe3+, Cr3+ and Ti4+ are confined to M1 (Molin, 1989) and Al(IV) to TB. M2 is controlled by Fe(M2)2+ half arrow right over half arrow left constrained by (Fe2+ + Ca)M2 > 0.14 atoms per formula unit (p.fu.). Cation substitution in TB and M2 constrains the sum of the volumes of the respective polyhedra V(TB) + V(M2) to remain essentially constant. Therefore, M2 favours the retention of the large Fe2+ up to melting-point, causing nonideality of this iron-depleted orthopyroxene. As a consequence, the investigated orthopyroxene can be considered an ultimate Fe2+ carrier during partial mantle melting
Kinetics of Fe2+-Mg order-disorder in orthopyroxene: experimental studies and applications to cooling rates of rochs
No full textWe determined the forward rate constant (K+)
for the Fe2+–Mg order–disorder between the M2 and
M1 sites of orthopyroxene (OPx), which is described by
the homogeneous reaction Fe2+ (M2) + Mg(M1) M
Mg(M2) + Fe2+ (M1), by both ordering and disordering
experiments at isothermal condition and also by
continuous cooling experiments. The rate constant was
determined as a function of temperature in the range of
550–750C, oxygen fugacity between quartz–fayalite–
iron and Ni–NiO buffers, and at compositions of 16 and
50 mol% ferrosilite component. The K+ value derived
from disordering experiment was found to be larger than
that derived from ordering experiment at 550C, while at
T>580C, these two values are essentially the same. The
fO2 dependence of the rate constant can be described by
the relation K+ a (fO2)n with n=5.5–6.5, which is
compatible with the theoretically expected relation. The
Arrhenius relation at the WI buffer condition is given by
lnðCoKþÞ 1⁄4
41511 12600XFe
T ðKÞ
þ 28:26
þ 5:27 XFe; min1
where Co represents the total number of M2 + M1 sites
occupied by Fe2+ and Mg per unit volume of the crystal.
The above relation can be used to calculate the cooling
rates of natural OPx crystals around the closure temperature
(Tc) of Fe–Mg ordering, which are usually below
300C for slowly cooled rocks. We determined the
Fe–Mg ordering states of several OPx crystals ( Fs50)
from the Central Gneissic Complex (Khtada Lake),
British Columbia, which yields Tc 290C. Numerical
simulation of the change of Fe2+-Mg ordering in OPx as
a function of temperature using the above expression of
rate constant and a non-linear cooling model yields
quenched values of ordering states that are in agreement
with the observed values for cooling rates of 11–17C/
Myr below 300C. The inferred cooling rate is in
agreement with the available geochronological constraints
Fe2+-Mg order-disorder in orthopyroxene: equilibrium fractionation between the octahedral sites and thermodynamic analysis
No full textThe equilibrium intracrystalline distribution coefficient, k*(D), of Fe* (i.e. Fe2+ + Mn) and Mg between the M1 and M2 sites of three natural nearly binary Fe2+-Mg orthopyroxene crystals (FS14 FS15 and Fs(49)) were determined by annealing experiments at several temperatures between 550 and 1000 degrees C and single crystal X-ray structure refinements. In addition, the X-ray data of an orthopyroxene crystal (Fs(23)) which were collected earlier by Molin et al. (1991) between 700 and 1000 degrees C, were re-refined. The data were processed through two different refinement programs (SHELXL-93 and RFINE90) using both unit and individual weights and also both ionic and atomic scattering factors. The calculated site occupancies were found to agree within their estimated standard errors. However, the use of ionic scattering factors led to significantly better goodness of fit and agreement index, and smaller standard deviations of the site occupancies than those obtained from the use of atomic scattering factors. Furthermore, the weighted refinements yielded significantly smaller standard deviations of the site occupancies than the unweighted refinements even when the same set of reflections was used in the two procedures. The site occupancy data from this study were combined with selected published data to develop expressions of k*(D) as a function of temperature and composition. Calculation of the excess configurational entropy, Delta S-XS, suggests that orthopyroxene should be treated as a two parameter symmetric solution instead of as a "simple mixture" The calculated Delta S-XS values and the excess Gibbs free energy of mixing suggested by available cation exchange data lead to a slightly negative enthalpy of mixing in the orthopyroxene solid solution
Mechatronic Handling Solution for a Robotized Pizza-Chef Assistant
No full textIn the Industry 4.0 context, advanced mechatronic solutions are more and more adopted also outside the manufacturing field, e.g. food. Being pizza one of the most spread foods worldwide and since not all the tasks for preparing it need the dexterity of a pizza-chef, e.g. topping, an autonomous collaborative robot helping the pizza-chef would represent a possible and effective support solution. However, a crucial aspect in handling the ingredients for topping is the selection of a proper end-effector. Indeed, foodstuff is usually characterized by non-uniform shapes and dimensions as well as it is soft and/or fragile. As first step for conceiving and testing an intelligent (collaborative) robotic pizza topping system, this paper firstly investigates the commercially available low-cost grippers able to deal with foodstuff. Starting from this analysis, a versatile ad-hoc designed gripper able to handle most of the ingredient typically used for topping pizzas has been designed and tested
Orthopyroxene from the Serra de Magé meteorite: structure refinement and estimation of C2/c pyroxene contributions to apparent Pbca diffraction violations
No full text
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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