Beating resonance patterns and orthogonal wave propagation due to zero-group-velocity guided elastic waves

Elastic waves in anisotropic media can exhibit a power flux that is not collinear with the wave vector. We show that this has remarkable consequences for the zero-group-velocity (ZGV) resonances that appear in an infinite plate. True ZGV resonances, in the sense that the guided wave's overall power flux vanishes while its wavelength remains finite, are only found when the wave vector is oriented along a principal axis of the material. At other propagation angles, "quasi-ZGV" waves are found for which the power flux is orthogonal to the wave vector. We present original measurements of such a wave field in a single crystal silicon wafer. As a consequence of the nonzero power flux of qZGV waves, time acts as a filter in the wave vector domain that selects precisely the eight plane waves corresponding to true ZGV resonances. This intuitively explains the highly symmetric resonance pattern that emerges naturally on the surface of the plate after a pulsed point source excitation. We showcase a direct measurement of this beating pattern. The developed physical understanding paves the way towards novel designs of surface acoustic wave devices and is of high relevance for ultrasonic nondestructive evaluation.Comment: 10 pages, 9 figure

Generalized Geologic Map for Land-Use Planning: Kenton County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

Generalized Geologic Map for Land-Use Planning: Carroll County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

A signature of quantum gravity at the source of the seeds of cosmic structure?

This article reviews a recent work by a couple of colleagues and myself about the shortcomings of the standard explanations of the quantum origin of cosmic structure in the inflationary scenario, and a proposal to address them. The point it that in the usual accounts the inhomogeneity and anisotropy of our universe seem to emerge from an exactly homogeneous and isotropic initial state through processes that do not break those symmetries. We argued that some novel aspect of physics must be called upon to able to address the problem in a fully satisfactory way. The proposed approach is inspired on Penrose's ideas regarding an quantum gravity induced, real and dynamical collapse of the wave function.Comment: LateX, (jpconference macros), Prepared for the proceedings the Third International Workshop DICE 2006, " Quantum Mechanics between decoherence and Determinism

Generalized Geologic Map for Land-Use Planning: Boone County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

Elastodynamics of a soft strip subject to a large deformation

To produce sounds, we adjust the tension of our vocal cords to shape their properties and control the pitch. This efficient mechanism offers inspiration for designing reconfigurable materials and adaptable soft robots. However, understanding how flexible structures respond to a significant static strain is not straightforward. This complexity also limits the precision of medical imaging when applied to tensioned organs like muscles, tendons, ligaments and blood vessels among others. In this article, we experimentally and theoretically explore the dynamics of a soft strip subject to a substantial static extension, up to 180\%. Our observations reveal a few intriguing effects, such as the resilience of certain vibrational modes to a static deformation. These observations are supported by a model based on the incremental displacement theory. This has promising practical implications for characterizing soft materials but also for scenarios where external actions can be used to tune properties

Generalized Geologic Map for Land-Use Planning: Campbell County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

Generalized Geologic Map for Land-Use Planning: Wolfe County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

Generalized Geologic Map for Land-Use Planning: Gallatin County, Kentucky

This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock

Phenomenological analysis of quantum collapse as source of the seeds of cosmic structure

The standard inflationary version of the origin of the cosmic structure as the result of the quantum fluctuations during the early universe is less than fully satisfactory as has been argued in [A. Perez, H. Sahlmann, and D. Sudarsky, Class. Quantum Grav., 23, 2317, (2006)]. A proposal is made there of a way to address the shortcomings by invoking a process similar to the collapse of the quantum mechanical wave function of the various modes of the inflaton field. This in turn was inspired on the ideas of R. Penrose about the role that quantum gravity might play in bringing about such breakdown of the standard unitary evolution of quantum mechanics. In this paper we study in some detail the two schemes of collapse considered in the original work together with an alternative scheme, which can be considered as "more natural" than the former two. The new scheme, assumes that the collapse follows the correlations indicated in the Wigner functional of the initial state. We end with considerations regarding the degree to which the various schemes can be expected to produce a spectrum that resembles the observed one.Comment: 18 pages, 9 figure