346 research outputs found

    Trapping of electrons in metal oxide-polymer memory diodes in the initial stage of electroforming

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    Metal oxide-polymer diodes require electroforming before they act as nonvolatile resistive switching memory diodes. Here we investigate the early stages of the electroforming process in Al/Al2O3 /polyspirofluorene /Ba/Al diodes using quasistatic capacitance-voltage measurements. In the initial stage, electrons are injected into the polymer and then deeply trapped near the polyspirofluorene-Al2O3 interface. For bias voltages below 6 V, the number of trapped electrons is found to be CoxideV/q with Coxide as the geometrical capacitance of the oxide layer. This implies a density of traps for the electrons at the polymer-metal oxide interface larger than 31017 m−2

    Nitisinone Arrests but Does Not Reverse Ochronosis in Alkaptonuric Mice.

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    Alkaptonuria (AKU) is an ultrarare autosomal recessive disorder resulting from a deficiency of homogentisate 1,2 dioxygenase (HGD), an enzyme involved in the catabolism of phenylalanine and tyrosine. Loss of HGD function prevents metabolism of homogentisic acid (HGA), leading to increased levels of plasma HGA and urinary excretion. Excess HGA becomes deposited in collagenous tissues and subsequently undergoes polymerisation, principally in the cartilages of loaded joints, in a process known as ochronosis. This results in an early-onset, devastating osteoarthropathy for which there is currently no effective treatment. We recently described the natural history of ochronosis in a murine model of AKU, demonstrating that deposition of ochronotic pigment begins very early in life and accumulates with age. Using this model, we were able to show that lifetime treatment with nitisinone, a potential therapy for AKU, was able to completely prevent deposition of ochronotic pigment. However, although nitisinone has been shown to inhibit ochronotic deposition, whether it can also facilitate removal of existing pigment has not yet been examined. We describe here that midlife administration of nitisinone to AKU mice arrests further deposition of ochronotic pigment in the tibiofemoral joint, but does not result in the clearance of existing pigment. We also demonstrate the dose-dependent response of plasma HGA to nitisinone, highlighting its efficacy for personalised medicine, where dosage can be tailored to the individual AKU patient

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

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    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

    Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

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    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron-hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10(25)/m(3). The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics. (C) 2014 Author(s)

    Introductory clifford analysis

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    In this chapter an introduction is given to Clifford analysis and the underlying Clifford algebras. The functions under consideration are defined on Euclidean space and take values in the universal real or complex Clifford algebra, the structure and properties of which are also recalled in detail. The function theory is centered around the notion of a monogenic function, which is a null solution of a generalized Cauchy–Riemann operator, which is rotation invariant and factorizes the Laplace operator. In this way, Clifford analysis may be considered as both a generalization to higher dimension of the theory of holomorphic functions in the complex plane and a refinement of classical harmonic analysis. A notion of monogenicity may also be associated with the vectorial part of the Cauchy–Riemann operator, which is called the Dirac operator; some attention is paid to the intimate relation between both notions. Since a product of monogenic functions is, in general, no longer monogenic, it is crucial to possess some tools for generating monogenic functions: such tools are provided by Fueter’s theorem on one hand and the Cauchy–Kovalevskaya extension theorem on the other hand. A corner stone in this function theory is the Cauchy integral formula for representation of a monogenic function in the interior of its domain of monogenicity. Starting from this representation formula and related integral formulae, it is possible to consider integral transforms such as Cauchy, Hilbert, and Radon transforms, which are important both within the theoretical framework and in view of possible applications

    España. Mapas generales. 1834 (1827). 1:2525250

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    Escala gráfica, además en : '30 lieues marines de 25 au degré ; 20 lieues portugaises de 17 1/2 au degré'. Coordenadas : E05 00'-E22 50'/N44 30'-N35 00'. Meridiano de FerroInserta leyenda con los signos de las materias del map

    New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean

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    Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of 208Pb/207Pb vs. εNd, 208Pb/207Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and εNd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5 μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean
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