1,720,958 research outputs found
Numerical modelling of stress generation and microfracturing of vesicle walls in glassy rocks
No full textIn the absence of stress-concentrating flaws such as microfractures, vesicular glassy materials can withstand gas pressures within vesicles in excess of 100 MPa; however, vesicles within such materials are known to decrepitate explosively at much lower internal gas pressures, both in natural systems and in the laboratory. Here we present a model that quantitatively predicts the generation of microfractures in vesicle walls during cooling. Cooling of gas-bearing vesicles in glassy rock has little effect on water solubility in the glass, but leads to a rapid decrease in gas pressure in the vesicles. The drop in pressure causes disequilibrium between the water in the glass and in the vesicle. Dehydration of the glass in a diffusive boundary layer around the vesicle leads to elastic shrinkage. The resulting strain generates large tensile tangential stresses which can exceed the strength of the glass, causing microfracturing. Such microfractures present a possible means by which glassy rock surrounding vesicles could be weakened enough to permit explosive decrepitation at low pore vapor pressures. The results have implications wherever hydrous vesicular glasses are formed. For example rocks formed in shallow subvolcanic intrusions or vent plugs may spontaneously disintegrate with explosive emission of vapor; glassy submarine lavas spontaneously decrepitate upon dredging from the ocean floor (''popping rock''); vesicular glasses produced in laboratory experiments investigating vapor-melt phase equilibria have been observed to contain abundant fractures surrounding vesicles and to dehydrate at anomalously high rates
Near Infrared spectroscopic determination of water species in glasses of the system MAlSi3O8 (M= Li, Na, K): an interlaboratory study
No full texthe near-infrared absorption bands at 5200 cm-1, assigned to molecular water, and at 4500 cm-1, assigned to hydroxyl groups bonded to network forming cations, were used to specify concentrations of water species in glasses of alkali feldspar composition MAlSi3O8 (M = Li, Na, K). To allow an accurate quantitative evaluation of the water species in hydrous glasses, we have determined the composition dependence of the density and the linear and integral extinction coefficients of the glasses. For each feldspar composition, 8-28 samples with various amounts of water have been synthesized. All samples were quenched isobarically to avoid desorption of water during cooling, Water contents of the glasses were analyzed by Karl-Fischer titration. Spectra of the same sample collected by four different FTIR micro spectrometers vary by up to 10% relative in peak intensities. The differences are attributed to the specific measurement conditions (e.g., magnification of the objectives, spectral ranges of the systems, characteristics of the detectors) applied in the laboratories. However, an unambiguous explanation of the differences is not possible due to the complexity of FTIR spectroscopy. In order to reduce the uncertainty in determination of water species and total water by FTIR spectroscopy a calibration of spectrometers against a reference system should be performed. For evaluation of linear and integral molar extinction coefficients we have chosen the FTIR spectrometer Bruker(R) IFS88 of Hannover as the reference system. All spectroscopic data were recalculated on the basis of this spectrometer. For compositions of the system MAlSi(3)O(8) the extinction coefficients are strongly dependent on the alkali cation and vary non-linearly along the binary joins of the system. The extinction coefficients of both the 4500- and the 5200-cm-1 bands are significantly lower for a strong peralkaline glass than for glasses with feldspar compositions. This is attributed to strong H bonding of water species to adjacent non-bridging oxygens in the peralkaline glass, Probably, for the peralkaline composition only a part of the water species contribute to the NIR absorption bands. Variation of species concentration for glasses of the system MAlSi3O8 with same water content are attributed to differences in the fictive temperature of the glass which depends on cooling rate, water content and anhydrous composition of glass
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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