1,721,739 research outputs found
Field examples and numerical modelling of oversteps and bends along normal faults in cross-section
No full textSurface Wave FWI on Complex Models - The Robustness of the Inversion to Assumptions and Forward Modeling Approximations
No full textFull waveform inversion (FWI) of surface waves with genetic algorithm (GA) is able to invert complex near surface models even in the case where very limited a-priori information is available, but it requires long computing time. One way to reduce the computing time is to make assumptions on the subsurface and to simplify the forward modelling. By using a few complex near surface models, with velocity inversions, lateral velocity variations and with an irregular topographic surface, we discuss how the following issues affect the inversion results in terms of either the data misfit or the model misfit: 1) fixing the compressional wave velocities and densities to the estimated shear wave velocities according to empirical equations, instead of inverting them; 2) neglecting attenuation in the forward modelling; 3) performing 2D forward modelling and applying a 3D to 2D correction to the observed data. Although these approximations degrade model prediction, yet the main features of the shear wave models can be retrieved. Instead, the data prediction is always satisfactory, showing again that theoretical approximations in the forward modelling affect more the model misfit than the data misfit
Two-grid Full Waveform Rayleigh Wave Inversion by Means of Genetic Algorithm with Frequency Marching
No full textWe present a 2D elastic full waveform inversion (FWI) of Rayleigh waves (RW) with a genetic algorithm (GA) as the optimization tool and with a finite difference code as the forward modeling engine. To limit the computing time required by GA, we implement the RW FWI, making use of a two-grid parametrization of the subsurface model, one fine grid and one coarse grid, and of frequency marching during the evolution of the GA optimization. Forward modeling is performed on the fine grid to avoid numerical dispersion, while the GA inverts for the unknown velocities and densities at the nodes of the coarse grid. The coarser the grid the less the unknowns to be inverted for, at the expense of the final model resolution. Frequency marching also speeds up convergence because it has the ability of rejecting unrealistic models at the initial generations of the GA. Due to the very band-limited nature of RW, we suggest to start frequency marching from near the peak frequency of RW. Synthetic examples reproducing velocity inversions, lateral velocity variations and varying elevations show the feasibility of the proposed RW FWI, without any a-priori information and with shear-wave and
compressional-wave velocities and densities as unknowns
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
Bi-direction quasi-travelling wave piezoelectric rotary motor with single vibrator
No full textIn this paper, a cylindrical piezoelectric quasi-travelling wave motor, which used only a single vibrator to generate bidirectional rotations by changing the driving signal frequencies, was presented. The stator of the proposed motor consists of a metal tube and one piece of piezo-plate bonded onto the tube. Because of the asymmetric structure design, the single piezo-plate can excite two degenerated bending modes at one resonant frequency for generating rotation; while it can also excite a torsion mode and a bending vibration at another resonant frequency for generating reverse rotation. The prototype motor, whose stator was 6 mm in diameter and 26 mm in length, can rotate anticlockwise at a driving frequency of similar to 51 kHz and clockwise at a driving frequency of similar to 58 kHz. The motor achieved a maximum speed of 606 rev min(-1) and a stall torque of 1.08 mN m under a driving voltage of 116Vp-p. This research has provided a design way for piezo-motor miniaturisation
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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