Acoustical Properties of Mud Sediments
Abstract : Goals include the development of models and methods that explain observed material and acoustic properties of different physical types of shallow-ocean mud sediments. Other goals are to assess prior data relating to the acoustic properties of mud and to provide guidance in the development and interpretation of experiments. A related goal is to construct models that will guide inversion techniques for inferring properties of mud sediments, for estimating accuracy of results, and for use in applications. These goals are science relevant to resolving long-term Naval problems of transmission loss and array response in shallow water over mud sediments and of acoustic detection, localization, and classification of objects buried in mud. Develop analytical fundamental-physics models for geoacoustic properties that show their dependence on mud parameters. Properties include material density, porosity, and compressional and shear sound speeds and attenuations, with focus on depth and frequency dependence. Estimate the accuracy of physical mud parameters that is required for acoustic data comparisons and for making predictions in applications. Use modeling results to provide methodologies for inversion methods in order to determine parameters and profiles in mud sediments.
Geoacoustic modeling for acoustic propagation in mud ocean-bottom sediments
This paper reviews research developed since 2007 at BU and RPI, with leadership by the late W.M. Carey, on acoustic properties of mud. Marine mud consists primarily of small clay mineral platelets, which are comprised of crystalline layers and usually carry charge because of isomorphous substitution. Because of resulting electrical forces, the physical nature of mud is considerably different from sand sediments. In particular, as platelets settle under gravity, electrical forces repel face-to-face contact while strong van der Waals forces permit edge-to-face attachment. This platelet aggregation results in card-house structures, for which a tentative quantitative model has been analyzed (J.O. Fayton, RPI Ph.D. thesis). The model preserves basic physics of platelet interactions and leads to low shear wave speed predictions that are consistent with observations. However, because compressional sound speed is independent of the electrostatic interactions, accurate sound speed estimates are available from the ...
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.