154 research outputs found
Guiding optical flows by photonic crystal slabs made of dielectric cylinders
We investigate the electromagnetic propagation in two-dimensional photonic
crystals, formed by parallel dielectric cylinders embedded a uniform medium.
The frequency band structure is computed using the standard plane-wave
expansion method, while the propagation and scattering of the electromagnetic
waves are calculated by the multiple scattering theory. It is shown that within
partial bandgaps, the waves tend to bend away from the forbidden directions.
Such a property may render novel applications in manipulating optical flows. In
addition, the relevance with the imaging by flat photonic crystal slabs will
also be discussed.Comment: 5 pages, 5 figure
Sonic crystal lenses that obey Lensmaker's formula
This paper presents a theoretical study of the phenomenon of acoustic imaging
by sonic crystals, which are made of two-dimensional regular arrays of rigid
cylinders placed in parallel in air. The scattering of acoustic waves is
computed using the standard multiple scattering theory, and the band structures
are computed by the plane-wave expansion method. It is shown that properly
arranged arrays not only can behave as acoustic lenses, but also the focusing
effect can be well described by Lensmaker's formula. Possible applications are
also discussed.Comment: 4 pages, 5 figure
Theoretical analysis of acoustic stop bands in two-dimensional periodic scattering arrays
This paper presents a theoretical analysis of the recently reported
observation of acoustic stop bands in two-dimensional scattering arrays
(Robertson and Rudy, J. Acoust. Soc. Am. {\bf 104}, 694, 1998). A
self-consistent wave scattering theory, incorporating all orders of multiple
scattering, is used to obtain the wave transmission. The band structures for
the regular arrays of cylinders are computed using the plane wave expansion
method. The theoretical results compare favorably with the experimental data.Comment: 18 pages, 4 page
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Bandgaps in the propagation and scattering of surface water waves over cylindrical steps
Here we investigate the propagation and scattering of surface water waves by
arrays of bottom-mounted cylindrical steps. Both periodic and random
arrangements of the steps are considered. The wave transmission through the
arrays is computed using the multiple scattering method based upon a recently
derived formulation. For the periodic case, the results are compared to the
band structure calculation. We demonstrate that complete band gaps can be
obtained in such a system. Furthermore, we show that the randomization of the
location of the steps can significantly reduce the transmission of water waves.
Comparison with other systems is also discussed.Comment: 4 pages, 3 figure
Manifestation of photonic band structure in small clusters of spherical particles
We study the formation of the photonic band structure in small clusters of
dielectric spheres. The first signs of the band structure, an attribute of an
infinite crystal, can appear for clusters of 5 particles. Density of resonant
states of a cluster of 32 spheres may exhibit a well defined structure similar
to the density of electromagnetic states of the infinite photonic crystal. The
resonant mode structure of finite-size aggregates is shown to be insensitive to
random displacements of particles off the perfect lattice positions as large as
half-radius of the particle. The results were obtained by an efficient
numerical method, which relates the density of resonant states to the the
scattering coefficients of the electromagnetic scattering problem. Generalized
multisphere Mie (GMM) solution was used to obtain scattering matrix elements.
These results are important to miniature photonic crystal design as well as
understanding of light localization in dense random media.Comment: 4 pages, 2 figure
Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals
Motivated by a recent experiment on acoustic lenses, we perform numerical
calculations based on a multiple scattering technique to investigate the
focusing of acoustic waves with sonic crystals formed by rigid cylinders in
air. The focusing effects for crystals of various shapes are examined. The
dependance of the focusing length on the filling factor is also studied. It is
observed that both the shape and filling factor play a crucial role in
controlling the focusing. Furthermore, the robustness of the focusing against
disorders is studied. The results show that the sensitivity of the focusing
behavior depends on the strength of positional disorders. The theoretical
results compare favorably with the experimental observations, reported by
Cervera, et al. (Phys. Rev. Lett. 88, 023902 (2002)).Comment: 8 figure
Anisotropic mass density by two-dimensional acoustic metamaterials
We show that specially designed two-dimensional arrangements of full elastic cylinders embedded in a nonviscous fluid or gas define ( in the homogenization limit) a new class of acoustic metamaterials characterized by a dynamical effective mass density that is anisotropic. Here, analytic expressions for the dynamical mass density and the effective sound velocity tensors are derived in the long wavelength limit. Both show an explicit dependence on the lattice filling fraction, the elastic properties of cylinders relative to the background, their positions in the unit cell, and their multiple scattering interactions. Several examples of these metamaterials are reported and discussed.Torrent Martí, D.; Sánchez-Dehesa Moreno-Cid, J. (2008). Anisotropic mass density by two-dimensional acoustic metamaterials. New Journal of Physics. 10. doi:10.1088/1367-2630/10/2/023004S10Sánchez-Pérez, J. V., Caballero, D., Mártinez-Sala, R., Rubio, C., Sánchez-Dehesa, J., Meseguer, F., … Gálvez, F. (1998). Sound Attenuation by a Two-Dimensional Array of Rigid Cylinders. Physical Review Letters, 80(24), 5325-5328. doi:10.1103/physrevlett.80.5325Cervera, F., Sanchis, L., Sánchez-Pérez, J. V., Martínez-Sala, R., Rubio, C., Meseguer, F., … Sánchez-Dehesa, J. (2001). Refractive Acoustic Devices for Airborne Sound. Physical Review Letters, 88(2). doi:10.1103/physrevlett.88.023902Krokhin, A. A., Arriaga, J., & Gumen, L. N. (2003). Speed of Sound in Periodic Elastic Composites. Physical Review Letters, 91(26). doi:10.1103/physrevlett.91.264302Sanchis, L., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2003). Acoustic interferometers based on two-dimensional arrays of rigid cylinders in air. Physical Review B, 67(3). doi:10.1103/physrevb.67.035422Gupta, B. C., & Ye, Z. (2003). Theoretical analysis of the focusing of acoustic waves by two-dimensional sonic crystals. Physical Review E, 67(3). doi:10.1103/physreve.67.036603Garcia, N., Nieto-Vesperinas, M., Ponizovskaya, E. V., & Torres, M. (2003). Theory for tailoring sonic devices: Diffraction dominates over refraction. Physical Review E, 67(4). doi:10.1103/physreve.67.046606Li, J., & Chan, C. T. (2004). Double-negative acoustic metamaterial. Physical Review E, 70(5). doi:10.1103/physreve.70.055602Håkansson, A., Sánchez-Dehesa, J., Cervera, F., Meseguer, F., Sanchis, L., & Llinares, J. (2005). Comment on «Theory of tailoring sonic devices: Diffraction dominates over refraction». Physical Review E, 71(1). doi:10.1103/physreve.71.018601Hou, Z., Wu, F., Fu, X., & Liu, Y. (2005). Effective elastic parameters of the two-dimensional phononic crystal. Physical Review E, 71(3). doi:10.1103/physreve.71.037604Mei, J., Liu, Z., Wen, W., & Sheng, P. (2006). Effective Mass Density of Fluid-Solid Composites. Physical Review Letters, 96(2). doi:10.1103/physrevlett.96.024301Torrent, D., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2006). Homogenization of Two-Dimensional Clusters of Rigid Rods in Air. Physical Review Letters, 96(20). doi:10.1103/physrevlett.96.204302Torrent, D., & Sánchez-Dehesa, J. (2006). Effective parameters of clusters of cylinders embedded in a nonviscous fluid or gas. Physical Review B, 74(22). doi:10.1103/physrevb.74.224305Li, S., George, T. F., Chen, L.-S., Sun, X., & Kuo, C.-H. (2006). Disorder effect on the focus image of sonic crystals in air. Physical Review E, 73(5). doi:10.1103/physreve.73.056615Torrent, D., Sánchez-Dehesa, J., & Cervera, F. (2007). Evidence of two-dimensional magic clusters in the scattering of sound. Physical Review B, 75(24). doi:10.1103/physrevb.75.241404Torrent, D., & Sánchez-Dehesa, J. (2007). Acoustic metamaterials for new two-dimensional sonic devices. New Journal of Physics, 9(9), 323-323. doi:10.1088/1367-2630/9/9/323Berryman, J. G. (1992). Single‐scattering approximations for coefficients in Biot’s equations of poroelasticity. The Journal of the Acoustical Society of America, 91(2), 551-571. doi:10.1121/1.402518Cummer, S. A., & Schurig, D. (2007). One path to acoustic cloaking. New Journal of Physics, 9(3), 45-45. doi:10.1088/1367-2630/9/3/045Leonhardt, U. (2006). Optical Conformal Mapping. Science, 312(5781), 1777-1780. doi:10.1126/science.1126493Pendry, J. B. (2006). Controlling Electromagnetic Fields. Science, 312(5781), 1780-1782. doi:10.1126/science.1125907Twersky, V. (1952). Multiple Scattering of Radiation by an Arbitrary Configuration of Parallel Cylinders. The Journal of the Acoustical Society of America, 24(1), 42-46. doi:10.1121/1.1906845Chen, Y.-Y., & Ye, Z. (2001). Acoustic Attenuation by Two-Dimensional Arrays of Rigid Cylinders. Physical Review Letters, 87(18). doi:10.1103/physrevlett.87.184301Waterman, P. C. (1969). New Formulation of Acoustic Scattering. The Journal of the Acoustical Society of America, 45(6), 1417-1429. doi:10.1121/1.1911619Faran, J. J. (1951). Sound Scattering by Solid Cylinders and Spheres. 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Solitary osteochondroma of the twelfth rib with intraspinal extension and cord compression in a middle-aged patient
<p>Abstract</p> <p>Background</p> <p>Osteochondroma is a disease of growing bone and thus typically presents in younger patients. It has rarely been described in middle-aged and elderly patients. Data on the occurrence of osteochondroma show that the reported incidence of costal osteochondroma is very low. Moreover, costal osteochondroma arising at the costovertebral junction with neural foraminal extension and spinal cord compression is extremely rare.</p> <p>Case presentation</p> <p>This study reports the case of a 58-year-old patient with a solitary osteochondroma of the 12th rib with intraspinal extension and spinal cord compression. The clinical history, plain radiographs, computed tomography (CT), magnetic resonance imaging, and pathologic findings of the reported patient have been reviewed. The relevant medical literature has also been reviewed. The patient was treated with surgery for complete tumour excision to avoid tumour recurrence. After surgery, the patient's symptoms improved. An additional CT scan obtained at 1 year after surgery did not show any evidence of recurrence.</p> <p>Conclusions</p> <p>This patient is the oldest patient reported to have this rare form of costal osteochondroma. The age of the patient and the erosion of the adjacent bones raised clinical suspicion of malignancy; therefore, surgical management involved complete tumour excision with thoracolumbar fixation and fusion.</p
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