Metafiber transforming arbitrarily structured light.

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for wavefront engineering, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were 3D laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and arbitrary vector field. Our work provides a paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

Liquid crystal doped photopolymer micro-droplets printed by a simple and clean laser-induced forward transfer process.

We print a tunable photopolymer (photopolymer dispersed liquid crystal -PDLC), using the laser-induced direct transfer technique without absorber layer, which was a challenge for this technique given the low absorption and high viscosity of PDLC, and which had not been achieved so far to our knowledge. This makes the LIFT printing process faster and cleaner and achieves a high-quality printed droplet (aspheric profile and low roughness). A femtosecond laser was needed to reach sufficiently peak energies to induce nonlinear absorption and eject the polymer onto a substrate. Only a narrow energy window allows the material to be ejected without spattering.

Laser transfer for circulating tumor cell isolation in liquid biopsy.

75Cancer research has found in the recent years a formidable ally in liquid biopsy, a noninvasive technique that allows the study of circulating tumor cells (CTCs) and biomolecules involved in the dynamics of cancer spread like cell-free nucleid acids or tumor-derived extracellular vesicles. However, single-cell isolation of CTCs with high viability for further genetic, phenotypic, and morphological characterization remains a challenge. We present a new approach for single CTC isolation in enriched blood samples using a liquid laser transfer (LLT) process, adapted from standard laser direct write techniques. In order to completely preserve the cells from direct laser irradiation, we used an ultraviolet laser to produce a blister-actuated laser-induced forward transfer process (BA-LIFT). Using a plasma-treated polyimide layer for blister generation, we completely shield the sample from the incident laser beam. The optical transparency of the polyimide allows direct cell targeting using a simplified optical setup, in which the laser irradiation module, standard imaging, and fluorescence imaging share a common optical path. Peripheral blood mononuclear cells (PBMCs) were identified by fluorescent markers, while target cancer cells remained unstained. As a proof of concept, we were able to isolate single MDA-MB-231 cancer cells using this negative selection process. Unstained target cells were isolated and culture while their DNA was sent for single-cell sequencing (SCS). Our approach appears to be an effective approach to isolate single CTCs, preserving cell characteristics in terms of cell viability and potential for further SCS.

See-through display based on commercial photopolymer: Optimization and shrinkage effects.

Nowadays augmented reality, 3D Image, mixed reality and see-through applications are very attractive technologies due to their great potential. Holographic optical elements can provide interesting solutions for injection and extraction of the image in the waveguides that are part of the see-through devices. We have developed a coupled waveguide system based on slanted transmission gratings recorded in manufactured photopolymers. In this work we optimize our schedule to a commercial photopolymer for this high demanded application. We demonstrate that high diffraction efficiencies can be obtained if we optimize the recording geometry, recording intensity and recording time for this material. In addition, we study the effects of shrinkage in our holographic system. In general shrinkage is an important drawback for holographic applications, nevertheless we demonstrate how shrinkage can help these systems open new possibilities. Lastly, we show how to significantly improve the quality of the guided image.

Adsorption of Pb (II) ions on variable charge oxidic calcined substrates with chemically modified surface.

Background: The paper describes lead ion adsorption on variable charge oxidic calcined substrates with chemically modified surfaces. Amphoteric oxides of iron, aluminum, titanium, and manganese, change their surface electric charge after acid or alkaline treatment, letting cationic or anionic adsorption reactions from aqueous solutions. This property allows using them as adsorbing substrate for heavy metals retention in water treatment systems. Methods: Substrate was prepared by extruding cylindrical strips from a saturate paste of the oxidic lithological material-OLM; dries it up and thermally treated by calcination. The study was performed by triplicated trial, on batch mode, using 2 grams samples of treated with NaOH 0.1N and non-treated substrate. Lead analysis was performed by AAS-GF. Freundlich and Langmuir models were used to fit results. Comparing differential behavior between treated and non-treated substrates showed the variable charge nature of the OLM. Results: Results show L-type isotherms for the adsorption of Pb(II) ions on the activated substrate, suggesting good affinity between Pb(II) ions and OLM's surface. Average value of adsorption capacity ( K) for activated substrate (1791.73±13.06), is around four times greater than the non-activated substrate (491.54±31.97), during the adsorption reaction, 0.35 and 0.26 mmolH + of proton are produced on the activated and non-activated substrate respectively using a 1 mM Pb(II) solution and 72.2 and 15.6 mmolH + using a 10 mM Pb(II) solution. This acidification agrees with the theoretic model of transitional metals chemisorption on amphoteric oxides, present in lithological material used for the preparation of adsorbent substrates, confirming the information given by the L-type isotherms. Conclusions: Results suggest that these variable charge oxidic adsorbent substrate show great potential as an alternative technique for water treatment at small and medium scale using granular filtration system. The easiness and low price make them suitable to apply in rural media where no treating water systems is available.

Homography estimation from a single-point correspondence using template matching and particle swarm optimization.

Existing feature-based methods for homography estimation require several point correspondences in two images of a planar scene captured from different perspectives. These methods are sensitive to outliers, and their effectiveness depends strongly on the number and accuracy of the specified points. This work presents an iterative method for homography estimation that requires only a single-point correspondence. The homography parameters are estimated by solving a search problem using particle swarm optimization, by maximizing a match score between a projective transformed fragment of the input image using the estimated homography and a matched filter constructed from the reference image, while minimizing the reprojection error. The proposed method can estimate accurately a homography from a single-point correspondence, in contrast to existing methods, which require at least four points. The effectiveness of the proposed method is tested and discussed in terms of objective measures by processing several synthetic and experimental projective transformed images.

Precise-Integration Time-Domain Formulation for Optical Periodic Media.

A numerical formulation based on the precise-integration time-domain (PITD) method for simulating periodic media is extended for overcoming the Courant-Friedrich-Levy (CFL) limit on the time-step size in a finite-difference time-domain (FDTD) simulation. In this new method, the periodic boundary conditions are implemented, permitting the simulation of a wide range of periodic optical media, i.e., gratings, or thin-film filters. Furthermore, the complete tensorial derivation for the permittivity also allows simulating anisotropic periodic media. Numerical results demonstrate that PITD is reliable and even considering anisotropic media can be competitive compared to traditional FDTD solutions. Furthermore, the maximum allowable time-step size has been demonstrated to be much larger than that of the CFL limit of the FDTD method, being a valuable tool in cases in which the steady-state requires a large number of time-steps.

El Valor Agregado de la Realidad Virtual en Tratamientos de Rehabilitación Muscular. Revisión de Literatura / The Added Value of Virtual Reality in Muscle Rehabilitation Treatments. A Literature Review / O Valor Agregado da Realidade Virtual nos Tratamentos de Reabilitação Muscular. Revisão de Literatura

Resumen La realidad virtual (RV) constituye una herramienta alternativa para la rehabilitación de distintas lesiones del cuerpo humano. Este artículo identifica los principales aportes de la RV en tratamientos de rehabilitación muscular reportados en la literatura. Según las investigaciones analizadas, se evidenció que, a diferencia de los tratamientos convencionales para la rehabilitación muscular, los realizados con RV incrementaron el nivel de motivación de los pacientes para culminar con éxito, gracias al ambiente interactivo que la RV ofrece. Así mismo, de acuerdo con los estudios revisados, los pacientes manifestaron disminución de dolor durante y después de las terapias.

Abstract Virtual reality (VR) is an alternative tool for the rehabilitation of various injuries of the human body. This paper identified the main contributions of RV in muscle rehabilitation treatments reported in the literature. According to the analyzed research, it was shown that, unlike conventional treatments for muscle rehabilitation, those performed with RV increased the level of motivation of patients to successfully complete them, thanks to the interactive environment that VR offers. Likewise, according to the reviewed studies, the patients manifested decreased pain during and after therapies.

Resumo Nos últimos anos, a realidade virtual (VR) se estabeleceu como uma ferramenta alternativa para a reabilitação das diferentes lesões que o corpo humano pode sofrer. O objetivo desta revisão sistemática é identificar as principais contribuições evidenciadas em pesquisas anteriores sobre o assunto, que serviram de base para a formulação deste artigo. Para avaliação da literatura, foi realizada uma consulta preliminar nas principais bases de dados, a partir da qual foram obtidos resultados que permitiram dimensionar a contribuição do VD na recuperação de lesões musculares. De acordo com a amostra, ficou evidente que, diferentemente dos tratamentos convencionais para reabilitação muscular, aqueles realizados com o VD aumentavam o nível de motivação dos pacientes para concluir com sucesso o tratamento, portanto a adesão a todas as terapias era mais alto, isso graças ao ambiente interativo que o RV consegue oferecer. Por outro lado, de acordo com os estudos revisados, os pacientes manifestaram diminuição da dor durante e após a realização de diferentes terapias implementadas em cada investigação.

Wastewater collection system failures in a capital city: analysis and sustainable prevention.

An analysis of failures in a capital city's wastewater collection system was carried out and recommendations were made for sustainable preventive measures based on a risk of failure assessment. Most failures in sewer lines were associated with blockage caused by sediment accumulation and clogging from fats, oils and/or grease dumped by restaurants along several streets, combined with poor or nonexistent maintenance of the lines. Sewer lines in streets with higher risk levels due to multiple food establishments along those streets experienced most of the failures. Sustainability of the proposed maintenance was evidenced since it reduces costs and exposure to harmful substances and hazardous conditions as well as minimizing environmental impacts.

Unitary matrix approach for a precise voltage dependent characterization of reflective liquid crystal devices by average Stokes polarimetry.

Precise characterization of parallel-aligned liquid crystal on silicon microdisplays has an important impact in many advanced photonics applications. We show liquid crystal on silicon (LCoS) modeled as a non-absorbent reciprocal device. Combined with time-average Stokes polarimetry, LCoS enables us to demonstrate robust measurements across the whole applied voltage range for the retardance and its flicker, and also as a novelty for the director orientation. We obtain that the director orientation changes across the voltage range, especially at larger applied voltages. This is a small effect, but it may provide a deeper insight into the internal dynamics in the liquid crystal layer, and in sensitive phase-only applications will produce a coupling between amplitude and phase.

Accurate, Efficient and Rigorous Numerical Analysis of 3D H-PDLC Gratings.

This work presents recent results derived from the rigorous modelling of holographic polymer-dispersed liquid crystal (H-PDLC) gratings. More precisely, the diffractive properties of transmission gratings are the focus of this research. This work extends previous analysis performed by the authors but includes new features and approaches. More precisely, full 3D numerical modelling was carried out in all analyses. Each H-PDLC sample was generated randomly by a set of ellipsoid geometry-based LC droplets. The liquid crystal (LC) director inside each droplet was computed by the minimisation of the Frank elastic free energy as a function of the applied electric field. The analysis carried out considered the effects of Frank elastic constants K11, K22 and K33; the anchoring strength W0; and even the saddle-splay constant K24. The external electric field induced an orientation of the LC director, modifying the optical anisotropy of the optical media. This effect was analysed using the 3D split-field finite-difference time-domain (SF-FDTD) method. In order to reduce the computational costs due to a full 3D tensorial analysis, a highly optimised method for high-performance computing solutions (HPC) was developed. The influences of the anchoring and voltage on the diffraction efficiencies were investigated, showing the potential of this approach.

Phase-Shift Optimization in AA/PVA Photopolymers by High-Frequency Pulsed Laser.

Photopolymers can be used to fabricate different holographic optical elements, although maximization of the phase-shift in photopolymers has been a challenge for the last few decades. Different material compositions and irradiation conditions have been studied in order to achieve it. One of the main conclusions has been that with continuous laser exposure better results are achieved. However, our results show for the first time that higher phase-shift can be achieved using a pulsed laser. The study has been conducted with crosslinked acrylamide-based photopolymers exposed with a pulsed laser (532 nm). The increment of the phase-shift between the pulsed laser and continuous laser exposure is 17%, achieving a maximum phase-shift of 3π radians and a refractive index shift of 0.0084 at the zero spatial frequency limit, where monomer diffusion does not take place. This allows this photopolymer to be used in large-scale manufacturing.

Influence of temporal averaging in the performance of a rotating retarder imaging Stokes polarimeter.

We study the optimum operating conditions for a rotating retarder fixed polarizer (RRFP) when the measurements are not quasi-instantaneous but time-averaged. We obtain the optimum retardance and retarder orientations as a function of the integrated angle interval. We also study how the increase in the number of time-averaged measurements leads to a better equally weighted variance (EWV) value, and thus, to a better performance of the polarimeter in terms of noise amplification for the case of additive noise. Two different analyzers configurations are studied in this work: uniformly spaced retarder angles and when measurements are taken at optimum angles (non-uniformly spaced angles). We also consider the case of polychromatic illumination. We discuss the best measurement conditions in terms of the signal-to-noise ratio depending on whether there is a fixed or a limited amount of photons per measurement.

Complex Diffractive Optical Elements Stored in Photopolymers.

We study the recording of complex diffractive elements, such as achromatic lenses, fork gratings or axicons. Using a 3-D diffusion model, previously validated, we are able to predict the behavior of photopolymer during recording. The experimental recording of these complex elements is possible thanks to a new generation spatial light modulator capable of generating periodic and aperiodic profiles. Both experimental and theoretical are analyzed and compared. The results show not only the good response of theoretical model to predict the behavior of the materials, but also the viability of photopolymers to store these kind of elements.

Thermal Effects in the Ablation of Bovine Cortical Bone with Pulsed Laser Sources.

Lasers have advantages as bone surgical tools over mechanical methods, but two goals should be achieved to assure its use: Similar ablation rates to those obtained with mechanical tools (1 mm3/s at least) and to avoid thermal damage, a condition that can prevent proper bone healing. We present results of cow femoral bone with a 355 nm nanosecond (ns) and a 1064 nm picosecond (ps) pulsed laser sources that allow us to discuss the influence on the process of pulse duration and the selective ablation through high energy absorption (as bone highly absorbs 355 nm radiation). The treated samples were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The evaluation of the thermal effects produced in the samples shows clear differences between both laser sources: On one hand, the ns laser allows reaching high ablation rates (around 1 mm3/s); Raman spectra show no signal of bone carbonization, but unavoidable thermal effects in the form of melted and solidified material have been observed by electron microscopy in the samples treated with this laser. On the other hand, ablation without any sign of thermal effects is obtained using the ps laser, but with lower ablation rates, (around 0.15 mm3/s).

Estudio de estabilidad acelerado en café verde: una aproximación sensorial / Accelerated stability test in green coffee: A sensory approach / Estudo da estabilidade acelerada em café verde: uma abordagem sensorial

Resumen Introducción: el café verde es un producto del mercado mundial cuyo precio es determinado por sus características sensoriales en taza; sin embargo, estos atributos cambian durante el almacenamiento, convirtiendo esta etapa de la cadena productiva en una etapa crucial para garantizar la calidad del producto. Objetivo: en este trabajo se buscó determinar el impacto de diversos factores de almacenamiento en la calidad sensorial y física del café verde colombiano, bajo condiciones de estabilidad acelerada y natural. Materiales y métodos: cerezas maduras de café de la misma cosecha fueron procesadas en paralelo por dos métodos postcosecha para obtener café lavado y semilavado, después se sometieron a diferentes tratamientos de almacenamiento. Resultados: el café verde almacenado en condiciones ambientales presentó notas propias de reposo, la densidad y los parámetros del color cambiaron de diferente manera en los dos tipos de café. El comportamiento del café verde en almacenamiento acelerado varió en función de los métodos de beneficio; en el café lavado, el almacenamiento con humedad afecto los atributos sensoriales y alteró la densidad, el % HR y los parámetros de color L* y b*; en el café semilavado, el oxígeno fue el factor de mayor impacto, afectando también la densidad y el color. Conclusiones: diferentes métodos de beneficio de café no solo dan lugar a diferencias en los perfiles de la calidad sensorial, sino que también condicionan el comportamiento del grano de café verde durante el almacenamiento.

Abstract Introduction: Green coffee i s a product of the world market whose price is determined by its sensory characteristics in the cup; however, these attributes change during storage, turning this stage of the production chain into a crucial stage to guarantee product quality. Objective: In the present work we sought to determine the impact of various storage factors on the sensory and physical quality of Colombian green coffee, under conditions of accelerated and natural stability. Materials and methods: Mature coffee cherries from the same harvest were processed in parallel by two post-harvest methods to obtain washed and semi-washed coffee, and then they were subjected to different storage treatments. Results: It was found that green coffee stored under environmental conditions had the characteristic notes of rest; in addition, density and color parameters changed differently in the two types of coffee. The behavior of green coffee in accelerated storage treatments varied according to the processing methods. For the case of washed coffee, storage with humidity negatively affected sensory attributes and also altered density, the RH % and color parameters L* and b*; for the semi-washed coffee, oxygen was the factor that promoted the greatest sensory changes, also affecting density and color. Conclusions: Different coffee post-harvest processes not only give rise to differences in the profiles of sensory quality but also condition the behavior of green coffee bean during storage.

Resumo Introdução: O café verde é um produto do mercado mundial cuj o preço é determinado pelas suas características sensoriais na xícara; no entanto, estes atributos mudam durante o armazenamento, tornando esta etapa da cadeia produtiva em uma etapa crucial para garantir a qualidade do produto. Objetivo: em este trabalho se procura determinar o impacto de diversos fatores de armazenamento na qualidade sensorial e física do café verde colombiano, sob condições de estabilidade acelerada e natural. Materiais e métodos: cerejas maduras do café da mesma colheita foram processadas em paralelo pelos métodos pós-colheita para obter café lavado e semi-lavado, despois someteram-se a diferentes tratamentos de armazenamento. Resultados: o café verde armazenado em condições ambientais apresentou notas próprias de repouso, a densidade e os parâmetros da color mudaram de diferente maneira nos dois tipos de café. O comportamento do café verde em armazenamento acelerado variou em função dos métodos de benefício; no café lavado, o armazenamento com umidade afetou os atributos sensoriais e alterou a densidade, o %HR e os parâmetros da color L* e b*; no café semi-lavado, o oxigénio foi o fator de maior impacto, afetando também a densidade e a color. Conclusões: diferentes processos de pós-colheita do café não só produziriam diferenças nos perfis de qualidade sensorial, mas também condicionam o comportamento do grão de café verde durante o armazenamento.

Combining average molecular tilt and flicker for management of depolarized light in parallel-aligned liquid crystal devices for broadband and wide-angle illumination.

We demonstrate a complete semiphysical and analytical model describing the angular and wavelength dependencies not only of retardance, but also its flicker, in parallel aligned liquid crystal (PA-LC) devices. It relies on the fitting of the molecules' equivalent tilt angle as a function of applied voltage. The wide range of calculations it offers without requiring extensive characterization makes the model unique. We focus on PA-LCoS application as a polarization state generator across the visible spectrum and for a wide range of incidence angles. This approach offers novel capabilities for managing arbitrary states of both full and partial polarization. To highlight the richness of situations with PA-LCoS devices, we provide results for two different digital addressing sequences producing different levels of flicker.

Simplified physical modeling of parallel-aligned liquid crystal devices at highly non-linear tilt angle profiles.

In recent works, we demonstrated the accuracy and physical relevance of a highly simplified reverse-engineering analytical model for a parallel-aligned liquid crystal on silicon devices (PA-LCoS). Both experimental measurements and computational simulations applying the rigorous split-field finite difference time domain (SF-FDTD) technique led to this conclusion in the low applied voltages range. In this paper, we develop a complete rigorous validation covering the full range of possible applied voltages, including highly non-linear liquid crystal (LC) tilt angle profiles. We demonstrate the applicability of the model for spectral and angular retardation calculations, of interest in spatial light modulation applications. We also show that our analytical model enables the calculation of the retardance for novel PA-LC devices as a function of the LC compound and cell gap, becoming an appealing alternative to the usual numerical approaches for PA-LC devices design.