Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio

Improved Poly (D,L-lactide) nanoparticles-based formulation for hair follicle targeting

Objective Hair follicles are widely recognized as the preferential target and site of accumulation for nanoparticles after topical application. This feature is of particular importance for hair cosmetics, having the potential to refine the treatment of several hair follicle-related disorders. The aim of this work was to improve the preparation of Poly (D,L-lactide) (PLA) nanoparticles for in vivo follicular target and drug delivery. Methods Envisaging a future industrial scale-up of the process, nanoprecipitation method was used to prepare PLA nanoparticles: the effect of several processing parameters on their properties was examined and the yield of nanoparticles formation determined. Encapsulation efficiencies and in vitro release profiles of lipophilic and hydrophilic model compounds were also assessed. In vitro cytotoxicity and ex vivo penetration studies were performed on a reference skin cell line (NCTC2455, human skin keratinocytes) and porcine skin, respectively. Results Using acetone : ethanol (50 : 50, v/v) as the solvent phase, 0.6% (w/w) of Pluronic® F68 as a surfactant agent and agitation to mix the solvent and non-solvent phases, a monodispersed population of non-cytotoxic spherical nanoparticles of approximately 150 nm was obtained. The yield of nanoparticles for this formulation was roughly 90%. After encapsulation of model compounds, no significant changes were found in the properties of particles and the entrapment efficiencies were above 80%. The release kinetics of dyes from PLA nanoparticles indicate an anomalous transport mechanism (diffusion and polymer degradation) for Nile Red (lipophilic) and a Fickian diffusion of first order for fluorescein 5(6)-isothiocyanate (hydrophilic). Ex vivo skin penetration studies confirmed the presence of nanoparticles along the entire follicular ducts. Conclusions The optimized method allows the preparation of ideal PLA nanoparticles-based formulations for hair follicle targeting. PLA nanoparticles can effectively transport and release lipophilic and hydrophilic compounds into the hair follicles, and the yields obtained are acceptable for industrial purposes.Objectif Les follicules pileux sont largement reconnus comme la cible préférentielle et le site de l'accumulation des nanoparticules après application topique. Cette caractéristique est particulièrement importante pour les produits cosmétiques pour les cheveux, ayant la possibilité d'affiner le traitement de plusieurs troubles des follicules de cheveux. Le but de ce travail était d'améliorer la préparation de nanoparticules poly (D,L-lactide) (PLA) pour une administration folliculaire in vivo ciblée de drogues. Méthodes En envisageant un avenir à l’échelle industrielle du procédé, une méthode de nanoprécipitation a été utilisé pour préparer des nanoparticules de PLA: l'effet de plusieurs paramètres de traitement sur leurs propriétés a été examiné et le rendement de la formation des nanoparticules a été déterminé. Les efficacités d'encapsulation et de profils de libération in vitro de composés modèles lipophiles et hydrophiles ont également été évaluées. La cytotoxicité in vitro et ex vivo des études de pénétration a été effectuée sur une lignée de cellules de peau de référence (NCTC2455, des kératinocytes de peau humaine) et la peau de porc, respectivement. Resultats En utilisant l'acétone : éthanol (50 : 50, v/v) comme phase solvant, 0,6% (p/p) de Pluronic® F68 à titre d'agent tensioactif et l'agitation pour mélanger les phases de solvant et de non-solvant, une population monodispersée des nanoparticules sphériques non cytotoxiques d'environ 150 nm a été obtenue. Le rendement de nanoparticules pour cette formulation était d'environ 90%. Après encapsulation de composés modèles, aucune modification significative n'a été observée dans les propriétés des particules et les efficacités de piégeage ont été supérieures à 80%. La cinétique de libération de colorants de nanoparticules de PLA indique un mécanisme de transport anormal (diffusion et dégradation de polymère) pour le rouge Nil (lipophile) et une diffusion selon Fick de premier ordre pour FITC (hydrophile). Les études de pénétration ex vivo de la peau ont confirmé la présence de nanoparticules sur tous les conduits folliculaires. Conclusions La méthode optimisée permet la préparation de formulations à base de nanoparticules de PLA, idéales pour ciblage du follicule pileux. Les nanoparticules de PLA peuvent effectivement transporter et libérer des composés lipophiles et hydrophiles dans les follicules pileux; les rendements obtenus sont acceptables à des fins industrielles.The authors thank to the FCT Strategic Project PEst-OE/EQB/LA0023/2013 and to the Project “BioHealth – Biotechnology and Bioengineering approaches to improve health quality”, Ref. NORTE- 07-0124-FEDER-000027, co-funded by the Programa Operacional Regional do Norte (ON.2 – O Novo Norte), QREN, FEDER. This work was partly supported by FEDER through POFC–582 COMPETE and by Portuguese funds from FCT– Fundacão Para a Ciência e a Tecnologia through the project PEst-OE/BIA/UI4050/2014. The authors thank C. Botelho for technical assistance

Reversible post-breakdown conduction in aluminum oxide-polymer capacitors

Aluminum/Al2O3/polymer/metal capacitors submitted to a low-power constant current stress undergo dielectric breakdown. The post-breakdown conduction is metastable, and over time the capacitors recover their original insulating properties. The decay of the conduction with time follows a power law (1/t)(alpha). The magnitude of the exponent alpha can be raised by application of an electric field and lowered to practically zero by optical excitation of the polyspirofluorene polymer. The metastable conduction is attributed to formation of metastable pairs of oppositely charged defects across the oxide-polymer interface, and the self-healing is related to resistive switching. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4802485

Interactions between glycerol, PEG-200 and (NH4)2 SO4 in the stability of heterologous cutinase

Cutinases (EC 3.1.1.74)are versatile enzymes that have hydrolytic activity on various esters [1]. The spacial structure and the catalytic site of the enzymes can be protected by chemical additives to promove the stability of the activity [2, 3]. The goal of this work was to improve the stability of a recombinant cutinase produced by Escherichia coli

Tensor-Based Methods for Blind Spatial Signature Estimation in Multidimensional Sensor Arrays

The estimation of spatial signatures and spatial frequencies is crucial for several practical applications such as radar, sonar, and wireless communications. In this paper, we propose two generalized iterative estimation algorithms to the case in which a multidimensional (R-D) sensor array is used at the receiver. The first tensor-based algorithm is an R-D blind spatial signature estimator that operates in scenarios where the source’s covariance matrix is nondiagonal and unknown. The second tensor-based algorithm is formulated for the case in which the sources are uncorrelated and exploits the dual-symmetry of the covariance tensor. Additionally, a new tensor-based formulation is proposed for an L-shaped array configuration. Simulation results show that our proposed schemes outperform the state-of-the-art matrix-based and tensor-based techniques

Processo de sobremoldação de vedante numa tampa plástica

O objeto da presente patente é o processo de sobremoldação de uma tampa Plástica com vedante incorporado, na qual é injetado o material de maior dureza sobre o De menor dureza. Este processo de sobremoldação é aplicado somente em bi-injecção (utilização de dois materiais ou mais), em tampas plásticas rígidas para embalagens de Forma redonda ou outras. A solução adotada passou por proteger o vedante (3) do fluxo (9) do material da tampa (2) de modo a evitar que este cause deformações no vedante (3) Durante o processo de enchimento. A forma de orientação precisa do fluxo (9) do sobre o Material de menor dureza (3) evita a deformação deste ultimo recorrendo aos diferenciais De pressão conjugados com a velocidade. Desta forma é possível injetar sobre um Material de menor dureza (3), um material de maior dureza (2)

Lithium fluoride injection layers can form quasi-Ohmic contacts for both holes and electrons

Thin LiF interlayers are typically used in organic light-emitting diodes to enhance the electron injection. Here, we show that the effective work function of a contact with a LiF interlayer can be either raised or lowered depending on the history of the applied bias. Formation of quasi-Ohmic contacts for both electrons and holes is demonstrated by electroluminescence from symmetric LiF/polymer/LiF diodes in both bias polarities. The origin of the dynamic switching is charging of electrically induced Frenkel defects. The current density-electroluminescence-voltage characteristics can qualitatively be explained. The interpretation is corroborated by unipolar memristive switching and by bias dependent reflection measurements. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License