Cs+ conductance in graphene membranes with Ångström-scale pores: the role of pore entrance geometry.

Recently, 2D materials, such as graphene, have been successfully implemented as artificial conduits of molecular sizes. The extreme precision with which these structures can be fabricated provides an unprecedented framework for the development of highly specific and efficient devices. In this work, we study the electrophoretic transport of Cs+ ions in a graphene membrane with effective pore heights of 3.4 Å by conducting molecular dynamics simulations. The entrance of the pore is systematically modified to investigate the effect of pore geometry on ionic conductance. Simulation results suggest a significant correlation between ionic conductance and entrance geometry, with a variation of the conductance up to 100% across the studied cases. To explain the observed correlation, two mechanisms involving an intimate relationship between ion dehydration and edge functional groups are proposed. The present study provides theoretical insights that can aid the design of graphene-based membranes with tunable ionic transport properties.

Quantifying Water Friction in Misaligned Graphene Channels under Ångström Confinements.

Two-dimensional (2D) materials, such as graphene (GE), hold great potential to be employed as the fundamental building blocks of novel nanofluidic devices for a wide range of applications. Recent advances in experimental techniques are materializing such prospects by enabling the assembly of 2D material-based fluidic channels with heights as small as few Ångströms. Here, we conduct molecular dynamics simulations to probe the effect of the relative misalignment between the walls of the GE fluidic channel with Ångströms height on the resistance to water transport through the channel. Two types of misalignments are studied, namely, translational and rotational misalignments. Our results show that the relative misalignment of the GE lattices can lead to a substantial reduction in the friction between water and the channel walls. Moreover, a dependence of the friction on the degree of misalignment and flow direction is found for the cases with translational misalignment. In contrast, the resistance exerted by the channels with rotational misalignment is found to be independent of the rotation angle (θ) for 0° < θ < 60° but always lower than the perfectly aligned case. We associate such lowering of the resistance to water transport to the corrugation and the anisotropy in the corresponding potential energy landscape associated with each degree of misalignment. The findings, therefore, point to an unprecedented possibility of significantly enhancing the water transport in Ångströms height GE channels by engineering the misalignments of the GE channel walls.

On the wetting translucency of hexagonal boron nitride.

When a liquid drop sits on an atomically thin layer of a 2D van der Waals (vdW) solid (like graphene) supported by a hydrophilic material, it is possible that the drop demonstrates an equilibrium contact angle that is influenced by this underlying hydrophilic material and hence is different from that observed on the bulk 2D material (e.g., graphite) surface. Such a behavior is known as the wetting translucency effect. While the wetting translucency effect of graphene has been extensively studied, the wetting translucency of hexagonal boron nitride (hBN) remains largely unexplored despite significant similarities in structural properties between these materials. In this study, we probe the wetting translucency of hBN. For this purpose, we conduct molecular dynamics simulations of water droplets and water films on hBN layers supported on a gold-like hydrophilic substrate. Our results show that for a substrate coated by monolayer hBN ("coated substrate"), depending on the contact distance between underlying substrate and hBN, an increase in the hydrophilicity of the underlying surface causes a monotonic increase in the overall adhesion energy between water and the coated substrate and a monotonic decrease in the contact angle of a drop on the coated substrate. For an increasing number of stacked hBN layers, the wettability of coated substrate becomes independent of the wettability of the underlying solid. Accordingly, our results confirm a distinct wetting translucency nature of hBN very similar to that observed in graphene.

Wettability of nanostructured hexagonal boron nitride surfaces: molecular dynamics insights on the effect of wetting anisotropy.

Nanostructured van der Waals (vdW) layered materials hold great potential for achieving smart surfaces with controllable wettability. Inspired by this possibility, we conduct Molecular Dynamics (MD) simulations of the wetting of nanostructured hexagonal boron nitride (hBN) surfaces. The nanostructure consists of periodically placed nanopillars made of hBN nanoribbons. We demonstrate that the polarity effect of the nanoribbon edges triggers wetting anisotropy of the nanoribbons: the vertical edges of the nanoribbons demonstrate a different wetting behavior as compared to the flat surfaces of the nanoribbons. Depending on the nature of the edge of the nanoribbon (armchair or zigzag), these vertical edges can be more hydrophilic for the zigzag edges or more hydrophobic for the armchair edges than the flat part. Such differences ensure that the nanostructured hBN surfaces become more hydrophilic (hydrophobic) as compared to the flat non-nanostructured hBN surfaces for cases where the edges of the nanoribbon are more hydrophilic (hydrophobic) than the flat part. Overall, the present study develops a most remarkable design space where by introducing nanopillars/nanoribbons on hBN and by merely changing the nature of the edges of these nanopillars, one can ensure atomistically thin coating of hBN with a wide range of wettability.

Effect of an external electric field on capillary filling of water in hydrophilic silica nanochannels.

Development of functional nanofluidic devices requires understanding the fundamentals of capillary driven flow in nanochannels. In this context, we conduct molecular dynamics simulations of water capillary imbibition in silica nanoslits under externally applied electric (E) fields with strengths between 0 and 1 V nm-1. For increasing E-fields, we observe a systematic lowering in the meniscus contact angle and a decrease in the corresponding water filling rates. These results contrast markedly the classical Washburn-Bosanquet's equation which predicts an increase in filling rates for lower water contact angles. Our study provides evidence that the observed decrease in water filling rates can be attributed to the interplay between two underlying mechanisms, a reduced fluidity of interfacial water and a systematic alignment of the water molecules in the bulk as a response to the particular strength of the applied E-field. Therefore, during water capillary filling a constant E-field applied in the direction parallel to the water imbibition leads to a lower than expected filling rate caused by a viscosity increase in the bulk and an altered solid-liquid friction on the channel walls. These coupled mechanisms governing capillarity under the action of applied E-fields could be manipulated for controlling imbibition of polar liquid solutions in nanofluidic devices.

Slip divergence of water flow in graphene nanochannels: the role of chirality.

Graphene has attracted considerable attention due to its characteristics as a 2D material and its fascinating properties, providing a potential building block for nanofabrication. In nanochannels the solid-liquid interface plays a non-negligible role in determining the fluid dynamics. Therefore, for an optimal design of nanofluidic devices, a comprehensive understanding of the slippage in a water flow confined between graphene walls is important. In nanoconfinement, experimental and computational studies have found the slip length to increase nonlinearly when the shear rate is larger than a critical value. Here, by conducting molecular dynamics simulations, we study the influence of the graphene crystallographic orientation on the slip boundary conditions inside a nanoslit channel. The flow in channels with heights of 2.0, 2.4 and 2.8 nm is driven parallel to the zig-zag and arm-chair crystallographic directions. We extract flow rates, velocity profiles, slip velocities and slip lengths. The slip velocity displays a linear relationship to the shear stress up to a critical value, which is not size dependent. Moreover, the slip length is found to be shear stress dependent above a critical shear stress value of 0.4 MPa. Furthermore, our results indicate that after this critical shear stress is reached, the flow rates are significantly influenced (up to 10%) by the particular orientation of the graphene topology.

Epidemiología de dermatosis pediátricas: experiencia de 30 años en Antofagasta, Chile / Epidemiology of pediatric dermatoses: experience of 30 years in Antofagasta, Chile

Introducción: La consulta por dermatología pediátrica es prevalente en dermatología general, por lo que estudiamos su importancia relativa y los motivos de consulta, en un periodo de 30 años en Antofagasta, Chile. Material y método: Se analizó el principal motivo de consulta en los menores de 15 años en una consulta dermatológica privada en 3 décadas, de 1984 a 2013. Se consideró diagnóstico, género, edad, previsión y se estudiaron las diferencias epidemiológicas entre las décadas en estudio. Resultados: El 26,6% de la consulta fue por dermatología pediátrica (15.742 pacientes). Los 10 principales motivos de consulta fueron prurigo insectario, dermatitis atópica, verrugas, escabiosis, impétigo, acné, estigmas atópicos, hemangioma, tiña y nevus melanocítico. Según décadas en estudio, la dermatitis atópica pasó del tercer al primer lugar en el periodo. Asimismo, disminuyeron escabiosis e impétigo y aumentaron acné y nevus melanocítico. Discusión: La dermatitis atópica ha llegado a ser el principal motivo de consulta dermatológica pediátrica en gran parte del mundo, especialmente en países desarrollados. Igualmente, la disminución de enfermedades bacterianas y parasitarias también es propia de países en desarrollo. Conclusiones: El volumen de consulta dermatológica pediátrica es importante, por lo que debe considerarse cuidadosamente en el currículo formativo del dermatólogo. Asimismo, los cambios epidemiológicos demostrados sugieren que nuestro país ha mutado a una epidemiología de país desarrollado.

Introduction: Consultation for pediatric dermatology is prevalent in general dermatology, that's why we studied the relative importance and motives of children's consultation in a period of 30 years in Antofagasta, Chile. Material and method: We analyzed the main motive of consultation in children under 15 years of age at a private dermatological clinic in 3 decades, from 1984 to 2013. Diagnosis, gender, age and social security system were considered and we studied the epidemiological differences between the decades in review. Results: 26,6% of the consultation was for pediatric dermatology (15.742 patients). The 10 main reasons for consultation were papular urticaria, atopic dermatitis, wart, scabies, impetigo, acne, atopic stigma, hemangioma, tinea and melanocytic nevus. According to decades under study, atopic dermatitis went from third to first place in the period. Likewise, scabies and impetigo diminished and acne and melanocytic nevus increased. Discussion: atopic dermatitis has become the main reason for pediatric dermatological consultation largely in the world, especially in developed countries. Similarly, the decline in bacterial and parasitic diseases is characteristic of developing countries. Conclusion: The volume of pediatric dermatological consultation is important, so it should be carefully considered in the training curriculum of the dermatologist. Likewise, the epidemiological changes demonstrated suggest that our country has mutated to a developed country epidemiology. Capsule Summary: Pediatric dermatology consultation is prevalent at a global level and atopic dermatitis is its main reason. In our investigation, both premises are fulfilled, important information that is partly extrapolable to guide public policies in dermatological formation and resource distribution.

Wall embedded electrodes to modify electroosmotic flow in silica nanoslits.

Electroosmotic flow in a silica slit channel with nonuniform surface charge density is investigated. In nanoconfinement, the electrical double layer occupies a non-negligible fraction of the system. Therefore, modifying the charge density on specific locations on the channel wall surface allows effective manipulation of the electroosmotic flow rates. In the present study, extensive (160 ns) nonequilibrium molecular dynamics simulations are conducted to investigate the ability of controlling the electroosmotic flow control in a nanoslit by patterning the surface potential. The mechanism to modify the surface charge consists of a set of charged electrodes embedded within one of the channel walls. The presence of the embedded electrodes results in the redistribution of ions in the electrolyte solution and in the alteration of the electroosmotic flow throughout the nanochannel. Indeed, the results reveal significant changes in the electroosmotic driving force and velocity profiles including local flow reversal. This study provides physical insight into the direct manipulation of the electrokinetic flow in nanoslits.

Angioma en penacho / Tufted angioma

El Angioma en Penacho es un raro tumor vascular de la infancia, que comparte características con el hemangioendotelioma kaposiforme, teniendo ambos posibilidad de desarrollar Síndrome de Kasabach-Merrit. Presentamos una paciente portadora de un angioma en penacho desde el nacimiento, que hemos seguido por 13 años: clínicamente, con estudios de imágenes y biopsias. El caso presenta similitudes con la literatura, con algunas interesantes peculiaridades en su evolución. Consideramos que por el comportamiento clínico e histológico, el Angioma en Penacho es parte de la misma enfermedad que el Hemangioendotelioma Kaposiforme.

Tufted angioma is a rare vascular tumor of childhood that shares features with the Kaposiform hemangioendothelioma, having both tumors the possibility of developing Kasabach-Merrit phenomenon. We report the case of a patient with a tufted angioma since birth, which we have followed for 13 years: clinically, with imaging studies and biopsies. The case presents similarities with literature, with some interesting peculiarities in its evolution. We consider that because of the clinical and histological behavior, Tufted angioma is a part of the same disease that Kaposiform hemangioendothelioma.

Sarcoma de Kaposi: a propósito de una revisión clinicopatológica / Kaposi's sarcoma: a propose of a clinic-pathological review

Desde la aparición de la enfermedad del Sida, se ha profundizado el estudio sobre sarcoma de kaposi (SK) debido a la asociación de esta neoplasia con la infección por el virus VIH. Sin embargo, debe recordarse que existen también otras formas de sarcoma de kaposi no asociadas al Sida. Ultimamente se ha investigado la patogenia del SK y se han postulado varias teorías que explicarían el origen de esta enfermedad. En el presente trabajo, se analizan las características clínicas, histológicas, junto a la etiología de esta neoplasia, así como su tratamiento; además, se incluye el análisis del diagnóstico histológico realizado de los casos biopsiados en nuestro Departamento desde 1979 a 1994