1,721,296 research outputs found
On the generalisation of the Brewster law
Full text linkIn classical photoelasticity of transparent isotropic materials, the Brewster law states that the difference in principal refraction index (birefringence) is propor- tional to the difference in principal stress. Here we show that such a relation can be generalized to anisotropic crystals only for the high-symmetry classes of the cubic group and for a specific plane stress, also for the high-symmetry classes of the trigonal, tetragonal, and hexagonal groups. No further generalizations are possible
Some approximate relations in the photoelasticity of strongly-anisotropic crystals
Full text linkThe knowledge of the principal refractive indeces and their dependence on the applied stress are the starting point for any experimental analysis of transparent crys- tals. Since for strongly-anisotropic crystals and general state of stress an explicit analytical solution can be difficult to obtain, then we need some approximated solu- tions. Here we propose a coherent approximation procedure which generalizes results already obtained and give a simple example of application
On twinning and domain switching in ferroelectric Pb(Zr1-x Tx )O3. Part I: twins and domain walls
No full textWe study the electromechanical behavior of lead zirconate titanate ferroelectric ceramics (PZT), by means of a three-dimensional continuum model for deformable ferroelectric bodies in their polar phase characterized by spontaneous polarization and strain. Spontaneous polarization and strain organize into a domain structure which minimizes electrostatic and elastic energies and which can be modified by the application of electromechanical loads. Such process, which is called ''domain switching'', is associated with electrical and mechanical hysteresis and can be studied as a minimization problem for a functional which reminds the micromagnetic energy of deformable ferromagnetics. In this paper, which is the first of two, we deal with the electromechanical model and related constitutive assumptions, as well as with the analysis of domain structure in PZT. In particular, following the discover of a new monoclinic phase in PZT carried by Noheda and co-workers, we analyze twinning between spontaneous strain at the various phase boundaries and show that both non-generic, non-conventional twins and finely-twinned laminates are possible, and also that the presence of a monoclinic phase may explain PZT exceptional properties
Existence, Decay Time and Light Yield for a Reaction-Diffusion-Drift Equation in the Continuum Physics of Scintillators
No full textA scintillator is a material which converts incoming ionizing energy into visible light. This conversion process, which is a strongly nonlinear one, can be described by a Reaction-Diffusion-Drift equation we obtain from a model of continua with microstructure endowed with a suitable thermodynamics. For such an equation it can be show the global existence of renormalizable and weak solutions, and the solutions exponential decay estimates can be given; moreover we give also a mathematical definition for the light yield which is a measure of scintillation efficiency
On the photoelastic constants for anisotropic stressed crystals
No full textThe need for high-quality and high-performance crystals for high-energy physics (e.g. scintillators) and biomedical applications require a good knowledge of their mechanical and optical properties, amongst the others. This is a mandatory step in many quality control process aimed at the improvement of the technological processes for crystals growth. Following the first analysis already done for Tetragonal crystals, in this paper we study the elasto-optic behavior of optically biaxial (Monoclinic and Orthorhombic groups) and uniaxial crystals (Trigonal and Hexagonal groups). We evaluate the photoelastic constants, the optic angle and the optic plane associated to various states of stress, in terms of the components of the Piezo-Optic tensor
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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