Use of specific Green's functions for solving direct problems involving a heterogeneous rigid frame porous medium slab solicited by acoustic waves

A domain integral method employing a specific Green's function (i.e., incorporating some features of the global problem of wave propagation in an inhomogeneous medium) is developed for solving direct and inverse scattering problems relative to slab-like macroscopically inhomogeneous porous obstacles. It is shown how to numerically solve such problems, involving both spatially-varying density and compressibility, by means of an iterative scheme initialized with a Born approximation. A numerical solution is obtained for a canonical problem involving a two-layer slab.Comment: submitted to Math.Meth.Appl.Sc

Pre-transplant CD45RC expression on blood T cells differentiates patients with cancer and rejection after kidney transplantation

Background Biological biomarkers to stratify cancer risk before kidney transplantation are lacking. Several data support that tumor development and growth is associated with a tolerant immune profile. T cells expressing low levels of CD45RC preferentially secrete regulatory cytokines and contain regulatory T cell subset. In contrast, T cells expressing high levels of CD45RC have been shown to secrete proinflammatory cytokines, to drive alloreactivity and to predict acute rejection (AR) in kidney transplant patients. In the present work, we evaluated whether pre-transplant CD45RClow T cell subset was predictive of post-transplant cancer occurrence. Methods We performed an observational cohort study of 89 consecutive first time kidney transplant patients whose CD45RC T cell expression was determined by flow cytometry before transplantation. Post-transplant events including cancer, AR, and death were assessed retrospectively. Results After a mean follow-up of 11.1±4.1 years, cancer occurred in 25 patients (28.1%) and was associated with a decreased pre-transplant proportion of CD4+CD45RChigh T cells, with a frequency below 51.9% conferring a 3.7-fold increased risk of post-transplant malignancy (HR 3.71 [1.24–11.1], p = 0.019). The sensibility, specificity, negative predictive and positive predictive values of CD4+CD45RChigh<51.9% were 84.0, 54.7, 89.8 and 42.0% respectively. Confirming our previous results, frequency of CD8+CD45RChigh T cells above 52.1% was associated with AR, conferring a 20-fold increased risk (HR 21.7 [2.67–176.2], p = 0.0004). The sensibility, specificity, negative predictive and positive predictive values of CD8+CD45RChigh>52.1% were 94.5, 68.0, 34.7 and 98.6% respectively. Frequency of CD4+CD45RChigh T cells was positively correlated with those of CD8+CD45RChigh (p<0.0001), suggesting that recipients with high AR risk display a low cancer risk. Conclusion High frequency of CD45RChigh T cells was associated with AR, while low frequency was associated with cancer. Thus, CD45RC expression on T cells appears as a double-edged sword biomarker of promising interest to assess both cancer and AR risk before kidney transplantation

Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems

[EN] Perfect, broadband and asymmetric sound absorption is theoretically, numerically and experimentally reported by using subwavelength thickness panels in a transmission problem. The panels are composed of a periodic array of varying crosssection waveguides, each of them being loaded by Helmholtz resonators (HRs) with graded dimensions. The low cut-off frequency of the absorption band is fixed by the resonance frequency of the deepest HR, that reduces drastically the transmission. The preceding HR is designed with a slightly higher resonance frequency with a geometry that allows the impedance matching to the surrounding medium. Therefore, reflection vanishes and the structure is critically coupled. This results in perfect sound absorption at a single frequency. We report perfect absorption at 300¿Hz for a structure whose thickness is 40 times smaller than the wavelength. Moreover, this process is repeated by adding HRs to the waveguide, each of them with a higher resonance frequency than the preceding one. Using this frequency cascade effect, we report quasi-perfect sound absorption over almost two frequency octaves ranging from 300 to 1000¿Hz for a panel composed of 9 resonators with a total thickness of 11¿cm, i.e., 10 times smaller than the wavelength at 300¿Hz.The authors acknowledge fnancial support from the Metaudible Project No. ANR-13-BS09-0003, cofunded by ANR and FRAE.Jimenez, N.; Romero García, V.; Pagneux, V.; Groby, J. (2017). Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems. Scientific Reports. 7(1). doi:10.1038/s41598-017-13706-4S1359571Zheludev, N. I. & Kivshar, Y. S. From metamaterials to metadevices. Nature materials 11, 917–924 (2012).Ding, Y., Liu, Z., Qiu, C. & Shi, J. Metamaterial with simultaneously negative bulk modulus and mass density. Physical review letters 99, 093904 (2007).Christensen, J., Kadic, M., Kraft, O. & Wegener, M. Vibrant times for mechanical metamaterials. Mrs Communications 5, 453–462 (2015).Yang, Z., Mei, J., Yang, M., Chan, N. & Sheng, P. Membrane-type acoustic metamaterial with negative dynamic mass. Phys. Rev. Lett. 101, 204301 (2008).Cummer, S. A., Christensen, J. & Alù, A. Controlling sound with acoustic metamaterials. Nature Reviews Materials 1, 16001 (2016).Landy, N. I., Sajuyigbe, S., Mock, J., Smith, D. & Padilla, W. Perfect metamaterial absorber. Physical review letters 100, 207402 (2008).Watts, C. M., Liu, X. & Padilla, W. J. Metamaterial electromagnetic wave absorbers. Advanced materials 24 (2012).Cui, Y. et al. Plasmonic and metamaterial structures as electromagnetic absorbers. Laser & Photonics Reviews 8, 495–520 (2014).Lee, Y. P., Rhee, J. Y., Yoo, Y. J. & Kim, K. W. Metamaterials for perfect absorption. Springer series in materials science (ISSN 0933-033X 236 (2016).Cui, Y. et al. Ultrabroadband light absorption by a sawtooth anisotropic metamaterial slab. Nano letters 12, 1443–1447 (2012).Ding, F., Cui, Y., Ge, X., Jin, Y. & He, S. Ultra-broadband microwave metamaterial absorber. Applied physics letters 100, 103506 (2012).Mei, J. et al. Dark acoustic metamaterials as super absorbers for low-frequency sound. Nat. Commun. 3, 756 (2012).Ma, G., Yang, M., Xiao, S., Yang, Z. & Sheng, P. Acoustic metasurface with hybrid resonances. Nat. Mater. 13, 873–878 (2014).Romero-García, V. et al. Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators. Sci. Rep. 6, 19519 (2016).Jiang, X. et al. Ultra-broadband absorption by acoustic metamaterials. Applied Physics Letters 105, 243505 (2014).Leclaire, P., Umnova, O., Dupont, T. & Panneton, R. Acoustical properties of air-saturated porous material with periodically distributed dead-end poresa). J. Acoust. Soc. Am. 137, 1772–1782 (2015).Groby, J.-P., Huang, W., Lardeau, A. & Aurégan, Y. The use of slow waves to design simple sound absorbing materials. J. Appl. Phys. 117, 124903 (2015).Groby, J.-P., Pommier, R. & Aurégan, Y. Use of slow sound to design perfect and broadband passive sound absorbing materials. J. Acoust. Soc. Am. 139, 1660–1671 (2016).Li, Y. & Assouar, B. M. Acoustic metasurface-based perfect absorber with deep subwavelength thickness. Appl. Phys. Lett. 108, 063502 (2016).Romero-García, V., Theocharis, G., Richoux, O. & Pagneux, V. Use of complex frequency plane to design broadband and sub-wavelength absorbers. The Journal of the Acoustical Society of America 139, 3395–3403 (2016).Jiménez, N., Huang, W., Romero-García, V., Pagneux, V. & Groby, J.-P. Ultra-thin metamaterial for perfect and quasi-omnidirectional sound absorption. Applied Physics Letters 109, 121902 (2016).Jiménez, N., Romero-García, V., Pagneux, V. & Groby, J.-P. Quasiperfect absorption by subwavelength acoustic panels in transmission using accumulation of resonances due to slow sound. Phys. Rev. B 95, 014205 (2017).Achilleos, V., Theocharis, G., Richoux, O. & Pagneux, V. Non-hermitian acoustic metamaterials: Role of exceptional points in sound absorption. Physical Review B 95, 144303 (2017).Santillán, A. & Bozhevolnyi, S. I. Acoustic transparency and slow sound using detuned acoustic resonators. Phys. Rev. B 84, 064304 (2011).Chong, Y., Ge, L., Cao, H. & Stone, A. D. Coherent perfect absorbers: time-reversed lasers. Physical review letters 105, 053901 (2010).Wan, W. et al. Time-reversed lasing and interferometric control of absorption. Science 331, 889–892 (2011).Groby, J.-P., Duclos, A., Dazel, O., Boeckx, L. & Lauriks, W. Absorption of a rigid frame porous layer with periodic circular inclusions backed by a periodic grating. J. Acoust. Soc. Am. 129, 3035–3046 (2011).Lagarrigue, C., Groby, J., Tournat, V., Dazel, O. & Umnova, O. Absorption of sound by porous layers with embedded periodic arrays of resonant inclusions. J. Acoust. Soc. Am. 134, 4670–4680 (2013).Boutin, C. Acoustics of porous media with inner resonators. J. Acoust. Soc. Am. 134, 4717–4729 (2013).Groby, J.-P. et al. Enhancing the absorption properties of acoustic porous plates by periodically embedding helmholtz resonators. J. Acoust. Soc. Am. 137, 273–280 (2015).Wu, T., Cox, T. & Lam, Y. From a profiled diffuser to an optimized absorber. The Journal of the Acoustical Society of America 108, 643–650 (2000).Yang, M., Chen, S., Fu, C. & Sheng, P. Optimal sound-absorbing structures. Materials Horizons (2017).Yang, J., Lee, J. S. & Kim, Y. Y. Multiple slow waves in metaporous layers for broadband sound absorption. Journal of Physics D: Applied Physics 50, 015301 (2016).Merkel, A., Theocharis, G., Richoux, O., Romero-García, V. & Pagneux, V. Control of acoustic absorption in one-dimensional scattering by resonant scatterers. Appl. Phys. Lett. 107, 244102 (2015).Piper, J. R., Liu, V. & Fan, S. Total absorption by degenerate critical coupling. Appl. Phys. Lett. 104, 251110 (2014).Yang, M. et al. Subwavelength total acoustic absorption with degenerate resonators. Appl. Phys. Lett. 107, 104104 (2015).Jiménez, N. et al. Broadband quasi perfect absorption using chirped multi-layer porous materials. AIP Advances 6, 121605 (2016).Tsakmakidis, K. L., Boardman, A. D. & Hess, O. Trapped rainbow storage of light in metamaterials. Nature 450, 397–401 (2007).Zhu, J. et al. Acoustic rainbow trapping. Scientific reports 3 (2013).Romero-Garcia, V., Picó, R., Cebrecos, A., Sanchez-Morcillo, V. & Staliunas, K. Enhancement of sound in chirped sonic crystals. Applied Physics Letters 102, 091906 (2013).Ni, X. et al. Acoustic rainbow trapping by coiling up space. Scientific reports 4 (2014).Colombi, A., Colquitt, D., Roux, P., Guenneau, S. & Craster, R. V. A seismic metamaterial: The resonant metawedge. Scientific reports 6 (2016).Powell, M. J. A fast algorithm for nonlinearly constrained optimization calculations. In Numerical analysis, 144–157 (Springer, 1978).Stinson, M. R. The propagation of plane sound waves in narrow and wide circular tubes, and generalization to uniform tubes of arbitrary cross-sectional shape. J. Acoust. Soc. Am. 89, 550–558 (1991).Theocharis, G., Richoux, O., García, V. R., Merkel, A. & Tournat, V. Limits of slow sound propagation and transparency in lossy, locally resonant periodic structures. New J. Phys. 16, 093017 (2014).Kergomard, J. & Garcia, A. Simple discontinuities in acoustic waveguides at low frequencies: critical analysis and formulae. J. Sound Vib. 114, 465–479 (1987).Dubos, V. et al. Theory of sound propagation in a duct with a branched tube using modal decomposition. Acta Acustica united with Acustica 85, 153–169 (1999).Mechel, F. P. Formulas of acoustics, 2nd ed. (Springer Science & Business Media, 2008)

Metadiffusers : deep-subwavelength sound diffusers

We present deep-subwavelength diffusing surfaces based on acoustic metamaterials, namely metadiffusers. These sound diffusers are rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Strong dispersion is produced in the slits and slow sound conditions are induced. Thus, the effective thickness of the panel is lengthened introducing its quarter wavelength resonance in the deep-subwavelength regime. By tuning the geometry of the metamaterial, the reflection coefficient of the panel can be tailored to obtain either a custom reflection phase, moderate or even perfect absorption. Using these concepts, we present ultra-thin diffusers where the geometry of the metadiffuser has been tuned to obtain surfaces with spatially dependent reflection coefficients having uniform magnitude Fourier transforms. Various designs are presented where, quadratic residue, primitive root and ternary sequence diffusers are mimicked by metadiffusers whose thickness are 1/46 to 1/20 times the design wavelength, i.e., between about a twentieth and a tenth of the thickness of traditional designs. Finally, a broadband metadiffuser panel of 3 cm thick was designed using optimization methods for frequencies ranging from 250 Hz to 2 kHz

The RNA Editing Pattern of cox2 mRNA Is Affected by Point Mutations in Plant Mitochondria

The mitochondrial transcriptome from land plants undergoes hundreds of specific C-to-U changes by RNA editing. These events are important since most of them occur in the coding region of mRNAs. One challenging question is to understand the mechanism of recognition of a selected C residue (editing sites) on the transcript. It has been reported that a short region surrounding the target C forms the cis-recognition elements, but individual residues on it do not play similar roles for the different editing sites. Here, we studied the role of the −1 and +1 nucleotide in wheat cox2 editing site recognition using an in organello approach. We found that four different recognition patterns can be distinguished: (a) +1 dependency, (b) −1 dependency, (c) +1/−1 dependency, and (d) no dependency on nearest neighbor residues. A striking observation was that whereas a 23 nt cis region is necessary for editing, some mutants affect the editing efficiency of unmodified distant sites. As a rule, mutations or pre-edited variants of the transcript have an impact on the complete set of editing targets. When some Cs were changed into Us, the remaining editing sites presented a higher efficiency of C-to-U conversion than in wild type mRNA. Our data suggest that the complex response observed for cox2 mRNA may be a consequence of the fate of the transcript during mitochondrial gene expression

Continuous Symmetries of Difference Equations

Lie group theory was originally created more than 100 years ago as a tool for solving ordinary and partial differential equations. In this article we review the results of a much more recent program: the use of Lie groups to study difference equations. We show that the mismatch between continuous symmetries and discrete equations can be resolved in at least two manners. One is to use generalized symmetries acting on solutions of difference equations, but leaving the lattice invariant. The other is to restrict to point symmetries, but to allow them to also transform the lattice.Comment: Review articl