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The optical damage of different proton exchanged LiNb[O.sub.3] planar waveguides is studied by measuring the intensity output of a single beam as a function of the intensity input. The role of the different effects is discussed together with the electro-optic properties of the different guides.

La hipertensión asociada al embarazo constituye la primera causa de mortalidad materna actualmente en nuestras instituciones de salud. Con frecuencia, el obstetra se ve enfrentado al manejo de esta complicación médica en medio de un arsenal terapéutico bastante reducido, y con el limitado conocimiento de que se dispone en el momento respecto a su etiología y fisiopatología. Con la intención de salvar parcialmente estos obstáculos se han desarrollado algunos protocolos de clasificación y manejo de esta entidad, los cuales, sin embargo, a pesar de ser útiles, resultan poco funcionales. La presente es una revisión y actualización del tema que incluye además una nueva propuesta de clasificación de estas pacientes por grupos de severidad; los cuales se comportan igualmente como grupos de tratamiento. Nuestro objetivo es que este protocolo facilite el enfoque y manejo terapéutico en las mujeres que padecen esta complicación en el embarazo.

Bi2Te3 is well-known for its utility in thermoelectrical applications and more recently as topological insulator. Its nanostructuration has attracted plenty of attention because of its potential capacity to reduce thermal conductivity. Here, we have grown a composite sample made of a Bi2Te3 nanowires (NWs) array embedded in an alumina matrix. We have then performed scanning thermal microscopy (SThM) in a 3ω configuration to measure its equivalent thermal resistance. Using an effective medium model, we could then estimate the mean composite thermal conductivity as well as the thermal conductivity of the NWs to be, respectively, (λC) = (1.68 ± 0.20) W/mK and (λNW) = (1.37 ± 0.20) W/mK, showing a slight thermal conductivity reduction. Up to now, there have been two main techniques reported in literature to evaluate the thermal conductivity of nanostructures: the use of a thermal microchip to probe a single NW once its matrix has been dissolved or the probing of the whole NWs array embedded in a matrix, obtaining the thermal conductivity of the whole as an effective medium. However, the 3ω-SThM presented here is the only technique able to measure the thermal conductivity of single NWs embedded in a matrix as well as the thermal conductivity of the composite locally. This technique is more versatile and straightforward than other methods to obtain the thermal conductivity of nanostructures. [ABSTRACT FROM AUTHOR]

In view of its central role in many optical waveguide applications, the absolute measurement of the actual light intensity propagating within a planar waveguide has been critically revised. Using prism couplers and proton exchanged LiNbO3 waveguides, several approaches have been experimentally checked and compared. A method is proposed and demonstrated, which combines the measurements of the light power out coupled from the waveguide edge and from the output prism. Reliable power measurements are obtained within a 5% error. A simplified version consists in a previous calibration of the setup in order to measure only the power coming from output coupler. Although inaccuracy rises up to ∼15%, it can be useful in many practical applications because of its simplicity. To assess and compare both methods, they have been applied to the measurement of light-intensity dependences of photovoltaic currents and optical damage thresholds in proton exchanged LiNbO3 guides. [ABSTRACT FROM AUTHOR]

The optical damage of different proton exchanged LiNbO3 planar waveguides has been experimentally studied by measuring the intensity output of a single beam as a function of the intensity input. Parallel measurements of photovoltaic currents (sometimes referred to as photocurrents) have been carried out with the same setup as a function of the input intensity and they have been correlated to the optical damage data. The following proton exchanged phases have been studied and compared with the substrate: α, β1, β2, and reverse proton exchanged (RPE). The greatest intensity thresholds for optical damage, about 2×103 times greater than that of the substrate, have been obtained in RPE guides supporting ordinary polarization and in β1,2 guides which support extraordinary polarization. On the other hand, the lowest photovoltaic currents have been measured in β1,2 phases. As a function of the light intensity, the strong superlinear behavior exhibited by the photovoltaic current in the α phase is almost absent in the others. In addition, it has been experimentally ascertained that a scattering increase produces a decrease of the threshold intensity for optical damage. The role of those different effects is discussed extensively together with the electro-optic properties of the different guides. [ABSTRACT FROM AUTHOR]

Abstract: The effect of photorefractive optical damage on single laser beams in undoped LiNbO3 waveguides has been thoroughly investigated. The experiments have been carried out in soft proton exchanged planar LiNbO3 waveguides covering a wide range of intensities (10–5000W/cm2). Different non-linear behaviours such as self-defocusing, beam break-up and temporal instabilities have been observed as the light intensity increases. X- and Z-cuts have been compared showing similar behaviours at low intensities although at higher intensities they present relevant differences. Some comments on the influence of these results in LiNbO3 devices have been also included. [ABSTRACT FROM AUTHOR]

Geometrical effects on the optical damage in proton exchanged LiNbO3 waveguides are analyzed. Light intensity thresholds and beam profiles at different intensities have been measured for guides prepared on z- and x-cuts. z-cut α-phase proton exchanged guides show a threshold intensity of the same order of magnitude but slightly greater than x-cut. The more important differences between both guides cuts are a clear asymmetry of beam-profile in x-cut guides as opposite to z-cut and the existence of a chaotic evolution at high intensities only found in x-cut guides. The influence of the proton-exchange time on optical damage threshold has been also investigated in z-cut waveguides to compare them with recent reported data on x-cut guides. [ABSTRACT FROM AUTHOR]

The generation of periodically poled structures in waveguides prepared by swift-heavy-ion (SHI) irradiation, i.e. in the electronic stopping power regime, has been achieved following two different strategies. In one of them we have prepared bulk PPLN samples by an applied electrical field, followed by irradiation with F ions at 22 MeV. After the ion irradiation, a waveguide showing a high optical confinement is obtained, preserving the original PPLN structure. The second strategy consisted of electric periodic poling of previously fabricated swift-ion-irradiated waveguides. To our knowledge this method has not been, so far, successful for conventional implanted waveguides. The successful fabrication of PPLN structures on novel waveguides prepared by SHI irradiation offers a promising potential for nonlinear integrated optical devices. [ABSTRACT FROM AUTHOR]

The photorefractive behaviour of a novel type of optical waveguides fabricated in LiNbO3 by swift heavy ion irradiation is investigated. First, the electro-optic coefficient r33 of these guides that is crucial in the photorefractive effect is measured. Second, two complementary aspects of the photorefractive response are studied: (i) recording and light-induced and dark erasure of holographic gratings; (ii) optical beam degradation in single-beam configuration. The main photorefractive parameters, recording and erasing time constants, maximum refractive-index change and optical damage thresholds are determined. [ABSTRACT FROM AUTHOR]

The generation of periodically poled structures in waveguides prepared by swift-heavy-ion (SHI) irradiation, i.e. in the electronic stopping power regime, has been achieved following two different strategies. In one of them we have prepared bulk PPLN samples by an applied electrical field, followed by irradiation with F ions at 22 MeV. After the ion irradiation, a waveguide showing a high optical confinement is obtained, preserving the original PPLN structure. The second strategy consisted of electric periodic poling of previously fabricated swift-ion-irradiated waveguides. To our knowledge this method has not been, so far, successful for conventional implanted waveguides. The successful fabrication of PPLN structures on novel waveguides prepared by SHI irradiation offers a promising potential for nonlinear integrated optical devices. [ABSTRACT FROM AUTHOR]

LiNbO 3 is a distinguished multifunctional material where ferroelectric domain engineering is of paramount importance. This degree of freedom of the spontaneous polarization remarkably enhances the applicability of LiNbO 3 , for instance, in photonics. In this work, we report the first method for all-optical domain inversion of LiNbO 3 crystals using continuous-wave visible light. While we focus mainly on iron-doped LiNbO 3 , the applicability of the method is also showcased in undoped congruent LiNbO 3 . The technique is simple, cheap, and readily accessible. It relies on ubiquitous elements: a light source with low/moderate intensity, basic optics, and a conductive surrounding medium, e.g., water. Light-induced domain inversion is unequivocally demonstrated and characterized by combination of several experimental techniques: selective chemical etching, surface topography profilometry, pyroelectric trapping of charged microparticles, scanning electron microscopy, and 3D Čerenkov microscopy. The influence of light intensity, exposure time, laser spot size, and surrounding medium is thoroughly studied. To explain all-optical domain inversion, we propose a novel physical mechanism based on an anomalous interplay between the bulk photovoltaic effect and external electrostatic screening. Overall, our all-optical method offers straightforward implementation of LiNbO 3 ferroelectric domain engineering, potentially sparking new research endeavors aimed at novel optoelectronic applications of photovoltaic LiNbO 3 platforms., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The resistance of an ordered 3D-Bi 2 Te 3 nanowire nanonetwork was studied at low temperatures. Below 50 K the increase in resistance was found to be compatible with the Anderson model for localization, considering that conduction takes place in individual parallel channels across the whole sample. Angle-dependent magnetoresistance measurements showed a distinctive weak antilocalization characteristic with a double feature that we could associate with transport along two perpendicular directions, dictated by the spatial arrangement of the nanowires. The coherence length obtained from the Hikami-Larkin-Nagaoka model was about 700 nm across transversal nanowires, which corresponded to approximately 10 nanowire junctions. Along the individual nanowires, the coherence length was greatly reduced to about 100 nm. The observed localization effects could be the reason for the enhancement of the Seebeck coefficient observed in the 3D-Bi 2 Te 3 nanowire nanonetwork compared to individual nanowires.

The 1D nanowire arrays and 3D nanowire networks of topological insulators and metals have been fabricated by template-assisted deposition of Bi 2 Te 3 and Ni inside anodic aluminum oxide (AAO) templates, respectively. Despite the different origins of the plasmon capabilities of the two materials, the results indicate that the optical response is determined by plasmon resonances, whose position depends on the nanowire interactions and material properties. Due to the thermoelectric properties of Bi 2 Te 3 nanowires, these plasmon resonances could be used to develop new ways of enhancing thermal gradients and their associated thermoelectric power.

Recently, polymers have been attracted great attention because of their thermoelectric materials' excellent mechanical properties, specifically their cost-effectiveness and scalability at the industrial level. In this study, the electropolymerization conditions (applied potential and deposition time) of PEDOT films were investigated to improve their thermoelectric properties. The morphology and Raman spectroscopy of the PEDOT films were analyzed according to their applied potential and deposition time. The best thermoelectric properties were found in films grown at 1.3 V for 10 min, with an electrical conductivity of 158 ± 8 S/cm, a Seebeck coefficient of 33 ± 1 µV/K, and a power factor of 17 ± 2 µW/K·m 2 . This power factor value is three times higher than the value reported in the literature for electropolymerized PEDOT films in acetonitrile using lithium perchlorate as a counter-ion. The thermal conductivity was found to be (1.3 ± 0.3) × 10 -1 W/m·K. The highest figure of merit obtained at room temperature was (3.9 ± 1.0) × 10 -2 using lithium perchlorate as a counter-ion. In addition, three-dimensional (3D) PEDOT nanonetworks were electropolymerized inside 3D anodic aluminum oxide (3D AAO), obtaining lower values in their thermoelectric properties.

The use of metallic nanostructures in the fabrication of bioelectrodes ( e.g. , neural implants) is gaining attention nowadays. Nanostructures provide increased surface area that might benefit the performance of bioelectrodes. However, there is a need for comprehensive studies that assess electrochemical performance of nanostructured surfaces in physiological and relevant working conditions. Here, we introduce a versatile scalable fabrication method based on magnetron sputtering to develop analogous metallic nanocolumnar structures (NCs) and thin films (TFs) from Ti, Au, and Pt. We show that NCs contribute significantly to reduce the impedance of metallic surfaces. Charge storage capacity of Pt NCs is remarkably higher than that of Pt TFs and that of the other metals in both morphologies. Circuit simulations of the electrode/electrolyte interface show that the signal delivered in voltage-controlled systems is less filtered when nanocolumns are used. In a current-controlled system, simulation shows that NCs provide safer stimulation conditions compared to TFs. We have assessed the durability of NCs and TFs for potential use in vivo by reactive accelerated aging test, mimicking one-year in vivo implantation. Although each metal/morphology reveals a unique response to aging, NCs show overall more stable electrochemical properties compared to TFs in spite of their porous structure.

3D interconnected nanowire scaffoldings are shown to increase the thermoelectric efficiency in comparison to similar diameter 1D nanowires and films grown under similar electrodeposition conditions. Bi 2 Te 3 3D nanonetworks offer a reduction in thermal conductivity (κ T ) while preserving the high electrical conductivity of the films. The reduction in κ T is modeled using the hydrodynamic heat transport equation, and it can be understood as a heat viscosity effect due to the 3D nanostructuration. In addition, the Seebeck coefficient is twice that of nanowires and films, and up to 50% higher than in a single crystal. This increase is interpreted as a nonequilibrium effect that the geometry of the structure induces on the distribution function of the phonons, producing an enhanced phonon drag. These thermoelectric metamaterials have higher performance and are fabricated with large areas by a cost-effective method, which makes them suitable for up-scale production., Competing Interests: The authors declare no competing financial interest., (© 2021 American Chemical Society.)

Evidence suggests that aging-related dysfunctions of adipose tissue and metabolic disturbances increase the risk of diabetes and metabolic syndrome (MtbS), eventually leading to cognitive impairment and dementia. However, the neuroprotective role of adipocytokines in this process has not been specifically investigated. The present study aims to identify metabolic alterations that may prevent adipocytokines from exerting their neuroprotective action in normal ageing. We hypothesize that neuroprotection may occur under insulin resistance (IR) conditions as long as there are no other metabolic alterations that indirectly impair the action of adipocytokines, such as hyperglycemia. This hypothesis was tested in 239 cognitively normal older adults (149 females) aged 52 to 87 years (67.4 ± 5.9 yr). We assessed whether the homeostasis model assessment-estimated insulin resistance (HOMA-IR) and the presence of different components of MtbS moderated the association of plasma adipocytokines (i.e., adiponectin, leptin and the adiponectin to leptin [Ad/L] ratio) with cognitive functioning and cortical thickness. The results showed that HOMA-IR, circulating triglyceride and glucose levels moderated the neuroprotective effect of adipocytokines. In particular, elevated triglyceride levels reduced the beneficial effect of Ad/L ratio on cognitive functioning in insulin-sensitive individuals; whereas under high IR conditions, it was elevated glucose levels that weakened the association of the Ad/L ratio with cognitive functioning and with cortical thickness of prefrontal regions. Taken together, these findings suggest that the neuroprotective action of adipocytokines is conditioned not only by whether cognitively normal older adults are insulin-sensitive or not, but also by the circulating levels of triglycerides and glucose, respectively.

Anodic porous alumina, -AAO- (also known as nanoporous alumina, nanohole alumina arrays, -NAA- or nanoporous anodized alumina platforms, -NAAP-) has opened new opportunities in a wide range of fields, and is used as an advanced photonic structure for applications in structural coloration and advanced optical biosensing based on the ordered nanoporous structure obtained and as a template to grow nanowires or nanotubes of different materials giving rise to metamaterials with tailored properties. Therefore, understanding the structure of nanoporous anodic alumina templates and knowing how they are fabricated provide a tool for the further design of structures based on them, such as 3D nanoporous structures developed recently. In this work, we review the latest developments related to nanoporous alumina, which is currently a very active field, to provide a solid and thorough reference for all interested experts, both in academia and industry, on these nanostructured and highly useful structures. We present an overview of theories on the formation of pores and self-ordering in alumina, paying special attention to those presented in recent years, and different nanostructures that have been developed recently. Therefore, a wide variety of architectures, ranging from ordered nanoporous structures to diameter changing pores, branched pores, and 3D nanostructures will be discussed. Next, some of the most relevant results using different nanostructured morphologies as templates for the growth of different materials with novel properties and reduced dimensionality in magnetism, thermoelectricity, etc. will be summarised, showing how these structures have influenced the state of the art in a wide variety of fields. Finally, a review on how these anodic aluminium membranes are used as platforms for different applications combined with optical techniques, together with principles behind these applications will be presented, in addition to a hint on the future applications of these versatile nanomaterials. In summary, this review is focused on the most recent developments, without neglecting the basis and older studies that have led the way to these findings. Thus, it gives an updated state-of-the-art review that should be useful not only for experts in the field, but also for non-specialists, helping them to gain a broad understanding of the importance of anodic porous alumina, and most probably, endow them with new ideas for its use in fields of interest or even developing the anodization technique.

Aging is associated with an increasing dysfunction of key brain homeostasis mechanisms and represents the main risk factor across most neurodegenerative disorders. However, the degree of dysregulation and the affectation of specific pathways set apart normal aging from neurodegenerative disorders. In particular, the neuronal metabolism of catecholaminergic neurotransmitters appears to be a specifically sensitive pathway that is affected in different neurodegenerations. In humans, catecholaminergic neurons are characterized by an age-related accumulation of neuromelanin (NM), rendering the soma of the neurons black. This intracellular NM appears to serve as a very efficient quencher for toxic molecules. However, when a neuron degenerates, NM is released together with its load (many undegraded cellular components, transition metals, lipids, xenobiotics) contributing to initiate and worsen an eventual immune response, exacerbating the oxidative stress, ultimately leading to the neurodegenerative process. This review focuses on the analysis of the role of NM in normal aging and neurodegeneration related to its capabilities as an antioxidant and scavenging of harmful molecules, versus its involvement in oxidative stress and aberrant immune response, depending on NM saturation state and its extracellular release.

Background: The older population has been especially affected by the severe acute respiratory syndrome coronavirus 2 pandemic (COVID-19)., Objective: The aim of the study was to explore the incidence, severity, mortality rate, clinical features, and risk factors of symptoms of COVID-19 in home-dwelling older people, and its association with type of residence, cognitive deterioration, and neurodegenerative diseases., Methods: Data about symptoms of COVID-19 were collected through a telephone survey in the cohort of 913 older volunteers of the Vallecas Project, aged 75-90 years, most of them (902) home-dwelling, in Madrid, Spain. The association of demographic and anthropometric measures, genetic polymorphisms, comorbidities, life habits, type of residence, and frailty surrogates were explored as potential risk factors for the incidence, severity, and mortality of COVID-19 in the older population., Findings: Sixty-two cases reported symptoms compatible with COVID-19; 6 of them had died, 4 in their home and 2 in the nursing home. Moderate/severe cases were significantly older and more frequently males. The APOE ε4 allele was associated with the presence of symptoms of COVID-19. Higher systolic blood pressure, more intense smoking habit, more alcohol intake, lower consumption of coffee and tea, and cognitive impairment were associated with disease severity., Conclusions: The estimated incidence of symptomatic COVID-19 in this older cohort of Madrid was 6.8%, with an overall mortality rate of 0.7% (18.2% in those living in a nursing home) and a fatality rate of 9.9%. Our exploratory study indicates that life habits, other clinical conditions and, the ε4 variant of the APOE gene are associated with the presence and clinical severity of coronavirus infection., (© 2021 S. Karger AG, Basel.)