1,720,987 research outputs found
The uncertainty of estimating the thickness of soft sediments with the HVSR method: A computational point of view on weak lateral variations
No full textThe use of the ratio of microtremor spectra, as computed by the Nakamura’s technique, was recently proved successful for the evaluating the thickness of sedimentary covers laying over both shallow and deep rocky bedrocks thus enabling bedrock mapping. The experimental success of such application and its experimental uncertainties are today reported in many publications. To map bedrock, two approaches exist. The first is to assume a constant shear wave velocity profile of the sediments. The second, and most preferable, is Ibs-von Seht and Wohlenberg’s, based on correlating Nakamura’s curves main peak and wells information. In the latter approach, the main sources of uncertainty addressed by authors, despite the lack of formal proof, comprise local deviations of the subsurface from the assumed model. I first discuss the reliability of the simplified constant velocity approach showing its limitations. As a second task, I evaluate the uncertainty of the Ibs-von Seht and Wohlenberg’s approach with focus on local subsurface variations. Since experimental basis is well established, I entirely focus my investigation on numerical simulations to evaluate to what extent local subsurface deviations from the assumed model may affect the outcome of a bedrock mapping survey. Further, the present investigation strategy suggests that modeling and inversion, through the investigation of the parameters space around the reference model, may reveal a very convenient tool when lateral variations are suspected to exist or when the number of available wells is not sufficient to obtain an accurate frequency-depth regression
Expeditious seismic methods for noninvasive diagnostics of the dynamic characteristics of the subsoil in urban centers using Rayleigh waves: The case of the city of Ferrara
No full textThe HVSR technique from array data, speeding up mapping of paleo-surfaces and buried remains. The case of the Bronze-Age site of Pilastri (Italy)
No full textIn the framework of a geophysical survey at the “Pilastri Terramara“ Middle Bronze Age archeological site (Northern Italy), which aimed at using cost-effective approaches to investigate a 12.000 m2 portion of land, we verified that in this site the most commonly used GPR, magnetometry and ERT geophysical methods were hampered by specific unfavorable conditions. Since the main purpose of the survey was to obtain information on ancient walking surfaces, we speculated that compaction, caused by the trampling of human activity over centuries, increased both density and seismic velocity of these paleo-surfaces. Assuming that such compacted layers still lie embedded in the shallow subsurface we successfully used the Horizontal-to-Vertical Spectral Ratio of microtremors, popular as HVSR, as a mapping tool. HVSR technique is seldom used in archaeological studies. The curve obtained by this method shows peaks and features that can be associated to the elastic impedance contrasts of a layered subsurface. Results from a previous single-station HVSR survey carried out on the whole area and consisted of 67 measurement points, allowed to obtain an indication about acoustic impedance contrasts and to spot few anomalies. The preliminary, yet promising result however, needed further acquisitions in order to achieve a better spatial sampling. We then tested microtremors acquisition using a linear array of seismic prospection geophones (4.5 Hz proper frequency) which have a worse response with respect the short period sensor used in single-station configuration. Yet the use of the array allowed for a comparable mapping of both paleo-surfaces and anomalies and data collection was performed at 24 locations simultaneously, so greatly accelerating the field work. In the following the two approaches are compared and an anomaly is highlighted which was located outside the hypothesized Bronze Age settlement area. Once excavated, such feature revealed to be a layer of roman age remains. Further, we show our best GPR section over the same anomaly. An indication was present in the GPR section but this became clear only afterward
Geometric seismic-wave inversion by the boundary element method
No full textSurface-wave methods are widely used in earth sciences and engineering for the geometric characterization of geological bodies and tectonic structures of the subsurface. These techniques exploit the dispersive nature of Rayleigh waves to indirectly estimate shear wave velocity profiles from surface-wave measurements; however, they are limited to parallel-layered geometries. To overcome such limitations, we present a new class of geometric inverse models for a full waveform inversion (FWI) based on the boundary element method (BEM). The proposed approach enables an effective identification of two dimensional (2D) subsurface geometries by directly estimating the shape of laterally varying interfaces from raw measurements. It thus aims at filling the gap between the standard simplistic parallellayered-based inversion and that of more complex three-dimensional (3D) geometries based on finite element methods (FEMs). Numerical tests on synthetic data unveil the effectiveness of the inverse algorithm, and its applicability to field measurements is finally presented
Exploring the paleolithic cave of Fumane (Italy): Geophysical methods as planning tool for archaeology
No full textGeophysical techniques are seldom used for the investigation of paleolithic archeological sites, mostly due to their sedimentary nature and the almost complete absence of architectural remains that can result in clear geophysical anomalies. The Fumane cave (Italy) is considered one of the most important sites in Europe. Recent investigations and studies carried out by the archaeological group of the Dep. Of Humanities (University of Ferrara) with the enrollment of the Department of Engineering of the same University allowed for the reconstruction of the 3D model of the Fumane Cave. This offered an opportunity for the applied geophysics group of the same university to assess the capability of Electrical Resistivity Tomography to retrieve subsurface information of archaeological interest. As primary goals, the study aimed at the creation of a three-dimensional resistivity model of the subsurface, to infer the nature of the sedimentary infill, so enabling a better understanding of the depositional processes involved in the formation of this important archaeological deposit and at the same time, for planning long-term field-investigations and to locate areas interesting for excavation. Moreover a Ground penetrating radar and a Nakamura survey were attempted in an integrate approach to test whether the combined methodologies could provide further insight about the subsurface. With respect to previous work, we present new and improved results both on ERT, GPR and HVSR. In particular, the HVSR test was accomplished to gain information about the maximum thickness of the deposit and to see if other impedance contrast discontinuities are present as was anticipated by previous archaeological studies
Directionally paired principal component analysis for bivariate estimation problems
No full textWe propose Directionally Paired Principal Component Analysis (DP-PCA), a novel linear dimension-reduction model for estimating coupled yet partially observable variable sets. Unlike partial least squares methods (e.g., partial least squares regression and canonical correlation analysis) that maximize correlation/covariance between the two datasets, our DP-PCA directly minimizes, either conditionally or unconditionally, the reconstruction and prediction errors for the observable and unobservable part, respectively. We demonstrate the optimality of the proposed DP-PCA approach, we compare and evaluate relevant linear cross-decomposition methods with data reconstruction and prediction experiments on synthetic Gaussian data, multi-target regression datasets, and a single-channel image dataset. Results show that when only a single pair of bases is allowed, the conditional DP-PCA achieves the lowest reconstruction error on the observable part and the total variable sets as a whole; meanwhile, the unconditional DP-PCA reaches the lowest prediction errors on the unobservable part. When an extra budget is allowed for the observable part's PCA basis, one can reach an optimal solution using a combined method: standard PCA for the observable part and unconditional DP-PCA for the unobservable part
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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