23,230 research outputs found

    A Reanalysis of Small Scale Velocity Dispersion in the CfA1 Survey

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    The velocity dispersion of galaxies on scales of r1h1r\sim1h^{-1} Mpc, σ12(r)\sigma_{12}(r), may be estimated from the anisotropy of the galaxy-galaxy correlation function in redshift space. We present a reanalysis of the CfA1 survey, correct an error in the original analysis of Davis and Peebles (1983), and find that σ12(r)\sigma_{12}(r) is extremely sensitive to the details of how corrections for infall into the Virgo cluster are applied. We conclude that a robust value of σ12\sigma_{12} cannot be obtained from this survey. We also discuss results from other redshift surveys, including the effect of removing clusters.Comment: 12 pages, uuencoded(latex file + 2 Postscript figures), uses aas macro

    Multiple wavemode scanning for near and far-side defect characterisation

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    The combination of ultrasonic inspections using different wavemodes can give more information than is available with single mode inspection. In this work, the response of shear and Rayleigh waves to surface-breaking defects propagating on the near-side and far-side of a sample is investigated. The directivity of shear waves generated by a racetrack coil electromagnetic acoustic transducer (EMAT) is identified and used to set an ideal separation for a pair of transmit-receive EMATs. Defects are indicated by a reduction in the transmitted Rayleigh wave amplitude, and by blocking of the shear wave. Used together, these can identify features in the bulk wave behaviour which are due to near-face surface-breaking defects, and give a full picture of both surfaces. By using a combination of the two wavemodes, the angle of propagation and length of any near-side defects can additionally be identified. A scanning method for samples is proposed

    Lamb wave near field enhancements for surface breaking defects in plates

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    Near field surface wave ultrasonic enhancements have previously been used to detect surface breaking defects in thick samples using Rayleigh waves. Here, we present analogous surface wave enhancements for Lamb waves propagating in plates. By tracking frequency intensities in selected regions of time-frequency representations, we observe frequency enhancement in the near field, due to constructive interference of the incident wave mode with those reflected and mode converted at the defect. This is explained using two test models; a square based notch and an opening crack, which are used to predict the contribution to the out-of-plane displacement from the reflected and mode converted waves. This method has the potential to provide a reliable method for the near field identification and characterisation of surface breaking defects in plates

    Interpretation at the controller's edge: designing graphical user interfaces for the digital publication of the excavations at Gabii (Italy)

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    This paper discusses the authors’ approach to designing an interface for the Gabii Project’s digital volumes that attempts to fuse elements of traditional synthetic publications and site reports with rich digital datasets. Archaeology, and classical archaeology in particular, has long engaged with questions of the formation and lived experience of towns and cities. Such studies might draw on evidence of local topography, the arrangement of the built environment, and the placement of architectural details, monuments and inscriptions (e.g. Johnson and Millett 2012). Fundamental to the continued development of these studies is the growing body of evidence emerging from new excavations. Digital techniques for recording evidence “on the ground,” notably SFM (structure from motion aka close range photogrammetry) for the creation of detailed 3D models and for scene-level modeling in 3D have advanced rapidly in recent years. These parallel developments have opened the door for approaches to the study of the creation and experience of urban space driven by a combination of scene-level reconstruction models (van Roode et al. 2012, Paliou et al. 2011, Paliou 2013) explicitly combined with detailed SFM or scanning based 3D models representing stratigraphic evidence. It is essential to understand the subtle but crucial impact of the design of the user interface on the interpretation of these models. In this paper we focus on the impact of design choices for the user interface, and make connections between design choices and the broader discourse in archaeological theory surrounding the practice of the creation and consumption of archaeological knowledge. As a case in point we take the prototype interface being developed within the Gabii Project for the publication of the Tincu House. In discussing our own evolving practices in engagement with the archaeological record created at Gabii, we highlight some of the challenges of undertaking theoretically-situated user interface design, and their implications for the publication and study of archaeological materials

    Investigating the Magnitude and Range of the Urban Heat Island within Gettysburg, Pennsylvania

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    Cities experience UHIs due to the thermal properties (albedo, thermal emittance, radiative flux, and heat capacity) of human-made substances and urban geometry. This study investigated the existence of an urban heat island (UHI) in Gettysburg, Pennsylvania. The goal of this project was to assess whether a small-scale city like Gettysburg demonstrates an UHI effect and, if present, the extent and magnitude of the UHI. We hypothesized that (1) temperatures within the city are significantly higher than the surrounding area, (2) the magnitude of the UHI will diminish as distance from the city center increases, and (3) the UHI will not extend further than 0.5 miles outside the city center. Air temperatures were collected using digital thermometers over four weeks along two different transects that each extended one mile from the center square of Gettysburg. Our results show that Gettysburg, despite its small size, has an UHI. A linear regression model shows that there is a strong correlation between temperature and distance from the center square. The magnitude of the UHI lessens with increasing distance from the center of town. The first two hypotheses were supported while the hypothesis that the UHI will be localized was not. Statistically analyses show that the temperature change remains significant past 0.5 miles. The results of this study demonstrate that even a small-scale city like Gettysburg create a UHI
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