Making waves round a structured cloak: lattices, negative refraction and fringes

Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic and electromagnetic waves. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularized cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularized cloak, a Young’s double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly, in the low-frequency regime

Ultrasonic scattering from spherically orthotropic shells

Concerns over the detectability of embrittlement in high strength alloys has led to studying a simple anisotropic shell model [1] for grain boundaries decorated by precipitates, or otherwise enriched by segregated inhomogenieties. In this model the shell is presumed to be “spherically orthotropic,” having five independent elastic constants and symmetry about the origin of a spherical coordinate system. This structure is analogous to transversely isotropic materials in a Cartesian coordinate system. By studying ultrasonic scattering from such shells (embedded in an isotropic host, and surrounding an isotropic core), we hope to learn whether their presence could be detected, and differentiated from scattering due to the inherent anisotropy of single metal crystals [2,3]

Relating Intensity of Soil Redistribution to Land Use Changes in Abandoned Pyrenean Fields Using Fallout Caesium-137

39 Pags.- 3 Tabls.- 6 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-145XFallout caesium-137 has been used to trace soil redistribution in abandoned fields located in the Central Spanish Pyrenees. A total of 28 fields with different lengths, slope angles and time since abandonment were selected on a representative south-facing slope of the Estarrún valley. The local reference inventory and the magnitude and spatial distribution of 137Cs inventories within these fields were documented and used as a basis for assessing patterns of soil redistribution. The local reference inventory was estimated to be 4,500 Bqm−2. Within the fields, the average 137Cs inventory at the top of the slope was 3,920 Bqm−2, and accumulation of soil at the bottom of the slopes was demonstrated by an average 137Cs inventory of 5,320 Bqm−2. Deviations from the reference inventory were highest for fields with the longest slopes that had been abandoned for less than 30 years. Here, increases in the 137Cs inventory, relative to the reference inventory, in excess of 20% were found at the bottom of the slopes. Considering all the fields and all geomorphic positions within the fields, the greatest 137Cs losses and gains were found in the fields with the longest duration of abandonment, indicating more intense soil redistribution. Irrespective of the timing of abandonment, the ranges of 137Cs inventories in the fields were found to be proportional to the water erosion index. The 137Cs technique demonstrated that patterns of sediment redistribution were closely related to the topographic and physiographic characteristics of the slopes.The work reported received financial support from CICYT project CGL2014-52986-R. This support is gratefully acknowledged.Peer reviewe

Spectral caustic rendering of a homogeneous caustic object based on wavelength clustering and eye sensitivity

In the real world, the index of refraction of a refractive object (caustic object) varies across the wavelengths. Therefore, in physically based caustic rendering, we need to take into account spectral information. However, this may lead to prohibitive running time. In response, we propose a two-step acceleration scheme for spectral caustic rendering. Our acceleration scheme takes into account information across visible wavelengths of the scene, that is, the index of refraction (IOR) (caustic object), light power (light), and material reflectance (surface). To process visible wavelengths effectively, firstly we cluster the wavelengths which have similar first refraction (air to caustic object) directions. In this way, all the wavelengths in a cluster can be represented by one light ray during rendering. Secondly, by considering the surrounding objects (their material reflectance from and visible surface area of the caustic objects) and light power, we compute the refinement amount of each wavelength cluster. Our accelerated algorithm can produce photorealistic rendering results close to their reference images (which are generated by rendering every 1 nm of visible wavelengths) with a significant acceleration magnitude. Computational experiment results and comparative analyses are reported in the paper.Accepted versio