Do dielectric bilayer metasurfaces behave as a stack of decoupled single-layer metasurfaces?

Flat optics or metasurfaces have opened new frontiers in wavefront shaping and its applications. Polarization optics is one prominent area which has greatly benefited from the shape-birefringence of metasurfaces. However, flat optics comprising a single layer of meta-atoms can only perform a subset of polarization transformations, constrained by a symmetric Jones matrix. This limitation can be tackled using metasurfaces composed of bilayer meta-atoms but exhausting all possible combinations of geometries to build a bilayer metasurface library is a very daunting task. Consequently, bilayer metasurfaces have been widely treated as a cascade (product) of two decoupled single-layer metasurfaces. Here, we test the validity of this assumption for dielectric metasurfaces by considering a metasurface made of titanium dioxide on fused silica substrate at a design wavelength of 532 nm. We explore regions in the design space where the coupling between the top and bottom layers can be neglected, i.e., producing a far-field response which approximates that of two decoupled single-layer metasurfaces. We complement this picture with the near-field analysis to explore the underlying physics in regions where both layers are strongly coupled. We also show the generality of our analysis by applying it to silicon metasurfaces at telecom wavelengths. Our unified approach allows the designer to efficiently build a multi-layer dielectric metasurface, either in transmission or reflection, by only running one full-wave simulation for a single-layer metasurface.

Ginecomastia: Consideraciones médicas y quirúrgicas en cirugía general / Gynecomastia: Medical and surgical considerations in general surgery

La ginecomastia, definida como el crecimiento del tejido glandular mamario en los hombres, aparece desde la etapa neonatal hasta la senil, puede ser unilateral o bilateral, y es de causa multifactorial, incluyendo aquellos pacientes asociados al uso de medicamentos, donde predomina un desbalance en la relación testosterona­estrógeno. Relativamente, la idiopática es la más frecuente. La mayoría involucionan espontáneamente, las neonatales por perdida del influjo transplacentario en las primeras semanas, y las puberales entre 12 a 24 meses. Se presenta como un aumento del tamaño mamario, asintomático o con hipersensibilidad por inflamación durante el crecimiento del tejido fibroglandular mamario, con una repercusión psicológica enorme, sobre todo en la etapa de la adolescencia. El estudio y manejo es interdisciplinario y se ofrece de acuerdo con las condiciones y la etiología. Aquellos pacientes púberes en quienes no involuciona reciben tratamientos médicos, o tratamientos quirúrgicos cuando falla la terapéutica o hay presión social, e incluso radioterapia en casos donde desarrollan ginecomastia con hipersensibilidad al tratamiento hormonal del cáncer de próstata

Gynecomastia, defined as the growth of breast glandular tissue in men, appears from the neonatal to senile stage, can be unilateral or bilateral, and is of multifactorial cause, including those patients associated with the use of medications, where an imbalance in the testosterone ­ estrogen ratio. Relatively, idiopathic is the most common. Most regress spontaneously, neonatals due to loss of transplacental influx in the first weeks, and pubertal ones between 12 to 24 months. It presents as an increase in breast size, asymptomatic or with hypersensitivity due to inflammation during the growth of the mammary fibroglandular tissue, with an enormous psychological repercussion, especially in adolescence. The study and management is interdisciplinary and offered according to conditions and etiology. Those pubertal patients in whom it does not regress receive medical treatments, or surgical treatments when therapy fails or there is social pressure, and even radiotherapy in cases where they develop gynecomastia with hypersensitivity to hormonal treatment of prostate cancer

Vólvulo de la vesícula biliar / Gallbladder volvulus

El vólvulo, o torsión de la vesícula biliar, es una enfermedad de la sexta a la octava décadas de la vida, condición excepcional por su poca frecuencia y síntomas atípicos. Dado que tiende a confundirse con la colecistitis de origen no litiásico, su diagnóstico suele ser intraoperatorio y puede llegar a causar complicaciones graves, como la gangrena y la sepsis biliar e incluso la muerte. Pese a que hace 120 años se hizo el primer reporte de caso, en la actualidad se notifican cada vez más casos en la población añosa. En este artículo se presentan dos casos clínicos de vólvulo de la vesícula biliar y se hace una revisión de la literatura

Volvulus, or torsion of the gallbladder, is a disease of the sixth to eighth decades of life, an exceptional condition due to its infrequent and atypical symptoms.Since it tends to be confused with non-lithiasic cholecystitis, its diagnosis is usually intraoperative and can lead to serious complications such as gangrene and biliary sepsis, even death.Although the first case was reported 120 years ago, more cases are reported in the elderly population.In this article, two clinical cases of gallbladder volvulus are presented and a review of the literature is made