Super-resonances in a dielectric mesoscale sphere immersed in water: effects in extreme field localization of acoustic wave

We predict acoustic super resonance modes with a field-intensity enhancement several tens of thousands of times higher (order of magnitude: 104 -10 5) with the support of dielectric mesoscale spheres submerged in water, by means of numerical simulations. The super resonances are related to the internal dispersion in specific values of both Mie and particle material parameters, being responsible for the generation of giant fields within the particles and near its surface. Taking into account the analogy between electromagnetic and acoustic waves, this phenomenon is valid in the electromagnetic (optical) wave band.Rubio Michavila, C.; Minin, IV.; Minin, OV.; Uris Martínez, A. (2019). Super-resonances in a dielectric mesoscale sphere immersed in water: effects in extreme field localization of acoustic wave. Acoustical Society of America. 1-7. https://doi.org/10.1121/2.0001139S1

The formation and disintegration of magnetic bright points observed by Sunrise/IMaX

The evolution of the physical parameters of magnetic bright points (MBPs) located in the quiet Sun (mainly in the interwork) during their lifetime is studied. First we concentrate on the detailed description of the magnetic field evolution of three MBPs. This reveals that individual features follow different, generally complex, and rather dynamic scenarios of evolution. Next we apply statistical methods on roughly 200 observed MBP evolutionary tracks. MBPs are found to be formed by the strengthening of an equipartition field patch, which initially exhibits a moderate downflow. During the evolution, strong downdrafts with an average velocity of 2.4 km/s set in. These flows, taken together with the concurrent strengthening of the field, suggest that we are witnessing the occurrence of convective collapses in these features, although only 30% of them reach kG field strengths. This fraction might turn out to be larger when the new 4 m class solar telescopes are operational as observations of MBPs with current state of the art instrumentation could still be suffering from resolution limitations. Finally, when the bright point disappears (although the magnetic field often continues to exist) the magnetic field strength has dropped to the equipartition level and is generally somewhat weaker than at the beginning of the MBP's evolution. Noteworthy is that in about 10% of the cases we observe in the vicinity of the downflows small-scale strong (exceeding 2 km/s) intergranular upflows related spatially and temporally to these downflows.Comment: 19 pages, 13 figures; final version published in "The Astrophysical Journal

Enhancement of pupil-masked wavelength-scale gas-filled flat acoustic lens based on anomaly apodization effect

[EN] In this letter, the improvement in focus by the use of a pupil mask produced in an acoustic mesoscale cuboid particle ¿lled with CO2 is reported. Thereby, the result shows that the pupil mask increases the sound intensity and also increases the resolution (or a reduction of the full width at half maximum, FWHM) in focus compared to the non-masked one. These results are important because they con¿rm the effect of abnormal amplitude apodization for a one-wavelength dimension acoustic lens and demonstrate that it is possible to improve sound focusing of a cuboid gas-¿lled lens with one wavelength dimension. This is the smallest size of an acoustic lens ever considered in this type of literature, with side dimensions of the cube equal to one wavelength and a diameter to focus ratio of 2.5, the sound ampli¿cation in focus is 5.4 dB at 4125 Hz, with the resolution near to the diffraction limit.This work has been supported by TEC2015-70939-R (MINECO/FEDER). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2019). Enhancement of pupil-masked wavelength-scale gas-filled flat acoustic lens based on anomaly apodization effect. Physics Letters A. 383:396-399. https://doi.org/10.1016/j.physleta.2018.11.014S39639938

Sound focusing of a wavelength-scale gas-filled flat lens

[EN] The capability of focusing of a novel acoustic lens based on a mesoscale acoustic cuboid particle filled with CO2 gas is analysed. This flat lens is able to focus sound in the same way that conventional curved acoustic lenses do. It is shown that the sound speed inside the cuboid is the responsible for this effect. By changing the percentage of CO2, the sound speed inside the cube changes and, therefore, the focusing properties change as well. The focusing effect is numerically investigated and experimentally validated. The results obtained allow the design of new flat low cost acoustic lenses with wavelength-scale dimensions for different applications.This work has been supported by TEC2015-70939-R (MINECO/FEDER). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program. IVM and OVM would like to thank Dr RUBEN PICO VILA for useful discussions.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2018). Sound focusing of a wavelength-scale gas-filled flat lens. EPL (Europhysics Letters). 123(6):64002-1-64002-4. https://doi.org/10.1209/0295-5075/123/64002S64002-164002-4123

Acoustical hooks: A new subwavelength self-bending beam

[EN] In this work, we report the first experimental observation of a new type of near-field curved acoustic beam confirmed by simulations. This new curved acoustical beam is generated by asymmetric distribution of the vortices in a polymer Janus particle (particle with broken symmetry) immersed in water. The origin of the vortices is in the conversion of an incident longitudinal wave mode to a shear wave in a solid and then back to a longitudinal wave in the water and has unique features, the radius of curvature of acoustical hook is less than the wavelength. Indeed, it is the smallest radius of curvature ever recorded for any acoustical beams. These results may be potentially useful when an object, located in the path of the beam, must be avoided. It could also have potential applications in particle manipulations.This work has been supported by Spanish Ministry of Science, Innovation and Universities (grant No. RTI2018-100792-B-I00). The research was partially supported by the Russian Foundation for Basic Research (Grant No. 20-57-S52001) and by Tomsk Polytechnic University Competitiveness Enhancement Program. D.T.-S. acknowledges financial support from MICINN BES-2016-07713 project.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2020). Acoustical hooks: A new subwavelength self-bending beam. Results in Physics. 16:1-5. https://doi.org/10.1016/j.rinp.2019.102921S151

Ultrasonic focusing with mesoscale polymer cuboid

[EN] In this paper, we demonstrate that, contrary to what the Geometrical Optics laws dictate, a flat polymer mesoscale cuboid immersed in water with no need of negative refraction can focus sound. Two main polymers were considered and lens parameters compared: PMMA and Rexolite®. It was concluded that Rexolite® is preferable for acoustic jet formation. The nature of the formation of the foci along the longitudinal axis, that is to say along the wave propagation axis, is numerically and experimentally demonstrated. In addition, the conditions under which a cubic particles lens of this type forms a single localized region with a sub-diffraction transverse size (approximately 0.44 wavelength) are determined. The comparisons of the acoustic wave pressures and the focal distance between the Finite Element Method based numerical results and the experimental results show fair agreement.This work has been supported by Spanish Ministry of Science, Innovation and Universities (grant No. RTI2018-100792-B-I00). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program.Tarrazó-Serrano, D.; Rubio Michavila, C.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2020). Ultrasonic focusing with mesoscale polymer cuboid. Ultrasonics. 106:1-5. https://doi.org/10.1016/j.ultras.2020.1061431510

Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries

Full Stokes filter-polarimeters are key instruments for investigating the rapid evolution of magnetic structures on the solar surface. To this end, the image quality is routinely improved using a-posteriori image reconstruction methods. We analyze the robustness of circular polarization asymmetries to phase-diversity image reconstruction techniques. We use snapshots of magneto-hydrodynamical simulations carried out with different initial conditions to synthesize spectra of the magnetically sensitive Fe I line at 5250.2 A. We degrade the synthetic profiles spatially and spectrally to simulate observations with the IMaX full Stokes filter-polarimeter. We also simulate the focused/defocused pairs of images used by the phase-diversity algorithm for reconstruction and the polarimetric modulation scheme. We assume that standard optimization methods are able to infer the projection of the wavefront on the Zernike polynomials with 10% precision. We also consider the less favorable case of 25% precision. We obtain reconstructed monochromatic modulated images that are later demodulated and compared with the original maps. Although asymmetries are often difficult to define in the quiet Sun due to the complexity of the Stokes V profiles, we show how asymmetries are degraded with spatial and spectral smearing. The results indicate that, although image reconstruction techniques reduce the spatial smearing, they can modify the asymmetries of the profiles, mainly caused by the appearance of spatially-correlated noise.Comment: 10 pages, accepted for publication in A&

Centre-to-limb properties of small, photospheric quiet Sun jets

Strongly Doppler-shifted Stokes $V$ profiles have been detected in the quiet Sun with the IMaX instrument on-board the SUNRISE stratospheric balloon-borne telescope. High velocities are required in order to produce such signals, hence these events have been interpreted as jets, although other sources are also possible. We aim to characterize the variation of the main properties of these events (occurrence rate, lifetime, size and velocities) with their position on the solar disk between disk centre and the solar limb. These events have been identified in Sunrise/IMaX data according to the same objective criteria at all available positions on the solar disk. Their properties were determined using standard techniques. Our study yielded a number of new insights into this phenomenon. Most importantly, the number density of these events is independent of the heliocentric angle, i.e. the investigated supersonic flows are nearly isotropically distributed. Size and lifetime are also nearly independent of the heliocentric angle, while their intensity contrast increases towards the solar limb. The Stokes $V$ jets are associated with upflow velocities deduced from Stokes $I$, which are stronger towards the limb. Their intensity decreases with time, while their line-of-sight (LOS) velocity does not display a clear temporal evolution. Their association with linear polarization signals decreases towards the limb. The density of events appears to be independent of heliocentric angle, establishing that they are directed nearly randomly. If these events are jets triggered by magnetic reconnection between emerging magnetic flux and the ambient field, then our results suggest that there is no preferred geometry for the reconnection process.Comment: 9 pages, 9 figure

Cylindrical 3D printed confgurable ultrasonic lens for subwavelength focusing enhancement

[EN] In this study, we report the characteristics of acoustic jets obtained through a mesoscale (radius less than 5 wavelengths) ABS cylinder made with a 3D printer. We have analyzed the influence of cylinder size on the characteristic parameters of an acoustic jet, such as maximum acoustic intensity at focus, Full Width at Half Maximum and length of Acoustic Jet. FWHM below 0.5 wavelength in AJ was experimentally obtained. It has been observed that there are two operating regimes depending on the cylinder radius: the resonant and the non-resonant. In the resonant regime, the excitation of Whispering Gallery Modes results in optimal parameter values of the acoustic jet. However, as it is a resonant regime, any minimal variation in cylinder size, working frequency or refractive index would make resonance disappear. In non-resonant mode, a phononic crystal has been embedded inside the cylinder and the characteristic parameters of the acoustic jet have been studied. These have been observed to improve. Finally, we have shown that curved acoustic jets can be obtained with the ABS cylinder with a phononic crystal embedded inside.This work has been supported by Spanish Ministry of Science, Innovation and Universities (Grant No. RTI2018100792-B-I00). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program. D. T.-S. acknowledges financial support from Ministerio de Ciencia, Innovacion y Universidades de Espana through Grant BES-2016-077133.Castiñeira Ibáñez, S.; Tarrazó-Serrano, D.; Uris Martínez, A.; Rubio Michavila, C.; Minin, OV.; Minin, IV. (2020). Cylindrical 3D printed confgurable ultrasonic lens for subwavelength focusing enhancement. Scientific Reports. 10(1):1-8. https://doi.org/10.1038/s41598-020-77165-0S18101Chen, Z., Taflove, A. & Backman, V. Photonic nanojet enhancement of backscattering of light by nanoparticles: A potential novel visible-light ultramicroscopy technique. Opt. 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Characterization of novel microsphere chain fiber optic tips for potential use in ophthalmic laser surgery. J. Biomed. Opt. 17, 068004. https://doi.org/10.1117/1.JBO.17.6.068004 (2012).Chen, Z., Taflove, A. & Backman, V. Highly efficient optical coupling and transport phenomena in chains of dielectric microspheres. Opt. Lett. 31, 389. https://doi.org/10.1364/OL.31.000389 (2006).Mendes, M. J., Tobías, I., Martí, A. & Luque, A. Light concentration in the near-field of dielectric spheroidal particles with mesoscopic sizes. Opt. Express 19, 16207. https://doi.org/10.1364/OE.19.016207 (2011).Bonakdar, A. et al. Deep-UV microsphere projection lithography. Opt. Lett. 40, 2537. https://doi.org/10.1364/OPEX.12.0012140 (2015).Lee, S. & Li, L. Rapid super-resolution imaging of sub-surface nanostructures beyond diffraction limit by high refractive index microsphere optical nanoscopy. Opt. Commun. 334, 253–257. https://doi.org/10.1016/j.optcom.2014.08.048 (2015).Minin, I. V. & Minin, O. V. Terahertz artificial dielectric cuboid lens on substrate for super-resolution images. Opt. Quant. Electron. 49, 326. https://doi.org/10.1364/OPEX.12.0012142 (2017).Pacheco-Peña, V., Minin, I. V., Minin, O. V. & Beruete, M. Comprehensive analysis of photonic nanojets in 3D dielectric cuboids excited by surface plasmons. Ann. Phys. 528, 684–692. https://doi.org/10.1364/OPEX.12.0012143 (2016).Minin, O. V. & Minin, I. V. Acoustojet: Acoustic analogue of photonic jet phenomenon based on penetrable 3D particle. Opt. Quant. Electron. 49, 54. https://doi.org/10.1007/s11082-017-0893-y (2017).Lopes, J. H. et al. Focusing acoustic beams with a ball-shaped lens beyond the diffraction limit. Phys. Rev. Appl. 8, 024013. https://doi.org/10.1103/PhysRevApplied.8.024013 (2017).Minin, I. & Minin, O. Mesoscale Acoustical Cylindrical Superlens. In MATEC Web of Conferences, Vol. 155, 01029 (eds. 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Diagnóstico: cáncer. ¿Queremos conocer la verdad?

ObjetivoConocer los deseos de información y otras actitudes ante el diagnóstico de cáncerDiseñoEstudio descriptivo transversaEmplazamientoCentros de Salud de Irún, Oñati y Asteasu en GipuzkoaParticipantesDe las citaciones a las 19 consultas durante marzo-mayo del 2002 se obtuvo una muestra aleatoria, prospectiva y sistemática, estratificada por cupos (n=725). Se administró una encuestamodificada de Fernández Díaz en la que se recogieron los datos personales y 8preguntas con respuestas cerradas: aspectos de comunicación (5 ítems) y actitudes relacionadas con la muerte (3 ítems)ResultadosEl 81,3% (IC del 95%, 78,4- 84,1) quiere conocer su diagnóstico. El 68,9% (IC del 95%, 65,5–72,2) elige al médico para comunicarlo. De éstos, el 36,6%, al especialista, y el 26,6%, al médicode familia. Si el afectado es un familiar, el 46,6% (IC del 95%, 42,9–50,2) se lo dirían siempre, sólo si él lo pregunta el 38,6% (ICdel 95%, 35–42,1) y nunca el 9,6% (IC del 95%, 7,4–11,7). El 49,3% (IC del 95%,45,6–52,9) preferiría morir en casa. Para el 44% (IC del 95%, 40,3–47,6) el dolor es el mayor temorConclusionesLa mayoría de la población quiere que se le informe de su diagnóstico, sin que el hábitat urbano o rural o la experiencia de haber tenido familiares con cáncer modifique la opinión. Si el afectadode cáncer es un familiar, son muy pocos los partidarios de no decírselo nunca. Eligen almédico para transmitir la información,prefieren morir en casa y el dolor es lamayor preocupaciónObjectivesTo find people's desire for information and their other attitudes when faced with a cancer diagnosisDesignTransversal, descriptive studySettingIrun, Oñati and Asteasu Health Centres, Gipuzkoa, SpainParticipantsFrom the appointments for 19 clinics in March-May 2002, a randomised, prospective and systematic sample, stratified by lists, was extracted (n=725). A modified Fernández Díaz questionnaire was administered. It had personal details and 8questions with closed replies on aspects of communication (5) and attitudes to death (3Results81.3% (95% CI, 78.4–84.1) wanted to know their diagnosis. 68.9% (95% CI, 65.5- 72.2) chose the doctor to tell them. Of these, 6.6% chose the specialist and 26.6%, thegeneral practitioner. If the person affected was a family member, 46.6% (95% CI, 42.9–50.2) would always tell the person; 38.6% (95% CI, 35–42.1), only if the person asked; and 9.6%, never (95% CI, 7.4–11.7). 49.3% (95% CI, 45.6–52.9) would prefer to die at home. The greatest fear for 44% (95% CI, 40.3–47.6) waspainConclusionsMost people want to be informed of their diagnosis. Neither an urban or rural environment nor having had family members with cancer affects their view. If the personaffected by cancer is a family member, very few people favour not telling him/her at all. Sufferers want the doctor to tell them the information, prefer to die at home and pain is what worries them mos