1,720,965 research outputs found
Replication Data for Microphone recording of flexural waves for estimation of lake ice thickness
No full textThis dataset is a collection of audio recordings from three frozen lakes that were acquired with the primary purpose of estimating ice thickness using recorded air-coupled flexural waves. The flexural waves were excited by different impulsive artificial sources (hammer strikes, jumping, ice skates) and natural sources (thermal expansion/contraction cracks i.e. icequakes). The flexural wave event characteristics and timings within the audio files are described in the event table.In this study we took an intentionally low-tech approach, aiming to estimate key physical parameters of lake ice using a single, inexpensive microphone. We consider this approach highly relevant to the issue of transport safety and the relatively high number of accidents involving breakthrough failure of thin ice underlines the importance of this topic. We conducted a range of experiments on three frozen lakes in the Tromsø region of Northern Norway and found that the monochromatic air-coupled flexural wave was a robust feature of impulsively excited frozen lakes. Ice thickness was estimated via a closed form solution that only depends on the measured monochromatic frequency of the air-coupled flexural wave and a set of assumed physical parameters for the ice, air and water. We discuss the impact of uncertainty in the assumed parameters on estimated ice thickness and bearing capacity, finding the uncertainty to be quite small, particularly when physical observation of ice type or drilled thickness are available to constrain the assumed Young’s modulus of the ice. Ice thicknesses estimated from air-coupled flexural waves were typically within 5-10% of ice thickness measured in holes drilled in the vicinity of the microphone for both artificial sources including hammer strikes, jumping and tapping with ice skates and natural ice quakes. The thickness estimates were also similarly accurate whether the microphone was resting on the ice, placed on land along the shoreline or handheld. We also showed that it is possible to record the dispersive ice flexural wave using a microphone, particularly when it was resting on the ice surface. Since thickness was constrained by the air-coupled flexural wave, we were able to estimate the propagation distance, corresponding to the horizontal offset between source and microphone, by inversion of the time dispersed arrival of the chirp signal corresponding to the ice flexural wave. We also demonstrated that a microphone can record inharmonic monochromatic overtones of the air-coupled flexural wave, that were linked to the geometry and boundary conditions of the frozen lakes using finite element modal analysis. This study leads us to conclude that a simple microphone can be a powerful tool giving a surprising amount of information on the lake-ice system. Using a microphone to record air-coupled flexural waves appears to be a promising additional tool for evaluation of ice conditions, convenient enough that it could substantially increase the availability of timely and accurate information on ice thickness and thereby contribute to safer travel on floating ice.</p
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
Cracking into Cryoseismology
Get PDFThe cryosphere encompasses the seasonally and perennially frozen parts of the earth and its extent is both sensitive to and impacts upon the global climate through surface energy and moisture fluxes and feedbacks. The dynamics of ice and frozen ground also impact directly on, e.g., construction and maintenance of roads in cold regions or transportation across floating ice sheets. The aim of this thesis was to investigate the extent to which seismic methods can be used to study dynamic processes and longer-term changes in the cryosphere. The thesis is structured around three case studies linking active- and passive-source seismic experiments with numerical models of thermal stress, seismic wave dispersion and propagation. In Paper 1, temporary arrays of geophones with fine spatial sampling demonstrated that high ground-ice content in the near-surface during winter/spring produces a seasonally varying multimodal surface wave dispersion pattern. In Paper 2, the role of thermal stress in triggering frost quakes was further explored using borehole temperature measurements and multi-decadal continuous seismic recordings from the small-aperture Spitsbergen seismic array (SPITS). Thermal contraction cracking within the frozen active layer was shown to be a plausible mechanism contributing to frost quake seismicity. In Paper 3, a multi-annual catalogue of explosive source seismic experiments conducted on first-year sea-ice in Van Mijenfjorden, Svalbard, was used to demonstrate the usefulness of air-coupled flexural waves for estimating the thickness of a floating ice sheet. Viewed as a whole, the case studies developed in this thesis illustrate the ability of seismic methods to record and monitor dynamic processes in the cryosphere over a range of temporal scales. Continuous passive seismic recordings with high-temporal resolution provide a useful complement to other geophysical and remote sensing techniques used for monitoring the dynamics of the cryosphere
Processing and interpretation of the Svyatogor 2016 high-resolution P-Cable 3D seismic dataset. Investigating the dynamics of a sub-seabed gas hydrate system with a potential abiotic methane source
Get PDFA new high-resolution P-Cable 3D seismic dataset was acquired in July 2016 targeting a seafloor pockmark cluster at the northern end of Svyatogor Ridge, offshore west Svalbard. The processing and interpretation of this dataset formed the primary focus of this thesis. The seismic processing sequence was designed to enhance the signal-to-noise ratio of the data while preserving the useful signal bandwidth and was implemented using the RadexPro 2016.3 software package. For example, burst-noise filtering allowed useful signal to be extracted from channels that would otherwise have been discarded, improving the overall trace density of the dataset. The suppression of bubble effects, ghost waves and random noise lead to a significant improvement in the useable bandwidth. In addition, “high-resolution static” correction proved an important means of improving reflector continuity and suppressing acquisition footprint noise caused by tides and streamer depth variations. Considerable effort was also spent on improving the receiver geometry based on a least squares type inversion of direct wave arrivals and produced a noticeable, if subtle, improvement in reflector continuity. This method of assigning geometry also has a potential application in 4D (time-lapse) seismic processing where the small-magnitude but extensive quantitative differences in amplitude, compared to the conventional method of assigning geometry, may become more critical.
Interpretation of the Svyatogor 2016 3D dataset indicates that the gas-hydrate, free-gas system has been relatively stable with respect to leakage and the seafloor pockmarks have been inactive and infilling for some time. However, significant evidence of paleo fluid migration was observed and the continued re-opening of fractures at fault tips or fault-segment junctions may be an important mechanism facilitating focussed, vertical fluid migration. The episodic fluid flow regime is postulated to be driven by 1) gas migration into the system along faults, probably as a dissolved phase 2) gas-hydrate formation at the base of the gas-hydrate stability zone (BGHSZ) produces a hydrate-cemented seal that results in a structurally enhanced trap 3) continued gas migration from depth and recycling of hydrate at the BGHSZ leads to accumulation of a free-gas phase contained beneath the BGHSZ 4) overpressure builds beneath the BGHSZ as gas charge continues eventually resulting in episodic gas release triggered in combination with dynamic stresses from earthquakes. The degree to which free-gas zone overpressure or external tectonic stresses control fault-slip is difficult to differentiate, but free-gas zone overpressures may significantly increase the slip tendency of faults at Svyatogor ridge.
It appears unlikely that the Svyatogor gas-hydrate/free-gas system could have been supplied by in-situ methane production alone. It remains difficult to conclusively rule out the contribution of a thermogenic source, but this would likely be dependent on lateral migration pathways that were not studied in detail in this thesis. However, it does appear plausible that the observed free-gas zone could have been charged by abiotic methane migrating along axial detachment faults during the period of active sedimentation on Svyatogor ridge assuming a similar flux rate to that reported by Cannat et. al. (2010) for the Rainbow hydrothermal field. A small elongated pockmark located above the lateral tip of an underlying fault may be associated with the most recent episode of seabed gas leakage. It is therefore considered the most promising target for future sediment coring aiming to recover gas or hydrate bearing samples for geochemical analysis to potentially resolve the methane source question
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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