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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4594-4599 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on polymer light-emitting electrochemical cells (LECs) with frozen p-i-n junctions. The dynamic p-i-n junction in polymer LECs is stabilized by lowering the temperature below the glass transition temperature of the ion-transport polymer. Detailed studies have shown that the frozen p-i-n junction in LECs based on the luminescent polymer poly[5-(2′ethylhexyloxy)-2-methoxy-1,4-phenylene vinylene] and polyethylene oxide containing lithium triflate (PEO:LiCF3SO3) is stable at temperatures up to 200 K. Frozen-junction LECs offer a number of advantages; they exhibit unipolar light emission, balanced injection, fast response, high brightness, low operating voltage, and insensitivity to electrode materials and film thickness. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7020-7029 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of molecular dynamics simulations of a water supported monolayer of F(CF2)6(CH2)6OC6H4COOH. A grazing incidence x-ray diffraction study of this system showed, unexpectedly, the absence of any strongly ordered condensed phase. We find that the monolayer has a partially ordered structure with a range of order intermediate between that typically found in monolayers of, e.g., arachidic acid, and that expected for a two-dimensional liquid. The calculated width of the first order diffraction peak is about ten times larger than for arachidic acid, yet is ten times smaller than expected for a two-dimensional liquid. We argue that monolayers with intermediate order represent a different class of systems that those heretofore studied, and that these systems may have some unusual properties.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2785-2800 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the evaluation of the structure factor for polymer chains near an interface when illuminated with evanescent light. The evanescent light is generated when there is total internal reflection of light at an interface between two dielectric media. We begin with a general virial expansion for the scattering intensity in powers of the polymer surface concentration to define the nature of the extrapolation to the infinite dilution limit, and to thereby extract the structure factor in that limit. The scattering per unit surface area is a function of the chain surface concentration when the polymers are attached to the surface, and a function of the bulk polymer concentration when the chains are distributed throughout the solution. The single chain scattering function is evaluated for Gaussian chains interacting with an impenetrable interface and either terminally anchored to the surface or free to move throughout the solution. The structure factors are obtained for the independent in-plane and out-of-plane scattering geometries, which provide information, respectively, about the chain dimensions parallel and perpendicular to the interface. The dependence of the evanescent wave scattering on such parameters as the scattering angle and the polymer-surface interaction parameter is explained on the basis of the exponential decay of the evanescent wave intensity away from the interface.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3469-3478 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method for studying the properties of adsorbed polymer molecules is proposed. If polymer molecules are adsorbed on the low refractive index side of an interface between two transparent dielectric media, they can scatter the evanescent radiation generated by total internal reflection of light incident on the interface from the high refractive index medium. Analysis of the angular distribution of the scattered light yields information about the mean extension of the polymer perpendicular to the interface and its mean extension parallel to the interface. As an example, the theory is illustrated for the case of rods, anchored at one end to the interface, and with uniform angular distribution in the half space of the low refractive index medium. Both analytical and numerical analyses are presented.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 901-903 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Certain porous-silicon (PS) films exhibit well-resolved Fabry–Pérot fringes in their optical reflection spectra due to thin-film interference. The fringes shift to higher wavelengths when the PS is exposed to vapors from organic solvents, as a result of an increase in the average refractive index of the PS layer. If a small diode laser is used as the light source, the shift of the Fabry–Pérot fringes upon analyte adsorption results in a change in the reflected light intensity, which correlates with the concentration of the analyte (ethanol) in an air stream. Based on this principle, a PS vapor sensor has been demonstrated with a detection limit of 500 ppb and a dynamic range of nearly five orders of magnitude. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1293-1295 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The p-i-n junction in a polymer light-emitting electrochemical cell (LEC) is stabilized by cooling the device below the glass transition temperature of the ion-transport polymer. LECs with frozen p-i-n junctions exhibit typical light emitting diode (LED) behavior including diode rectification, unipolar light emission (same polarity as that used for generating the junction), and fast response. The freezeout of ion motion allows polymer LECs to be driven at bias voltages well beyond the electrochemical stability window, and thereby extends the potential applications of polymer LECs to high pixel density, column-row addressable displays. © 1997 American Institute of Physics.
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  • 7
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Under phosphate-limiting conditions, some bacteria replace their membrane phospholipids by lipids not containing any phosphorus. One of these phosphorus-free lipids is an ornithine-containing lipid (OL) that is widespread among eubacteria. In earlier work, we had identified a gene (olsA) required for OL biosynthesis that probably encodes an O-acyltransferase using acyl-acyl carrier protein (acyl-AcpP) as an acyl donor and that converts lyso-ornithine lipid into OL. We now report on a second gene (olsB) required for OL biosynthesis that is needed for the incorporation of radiolabelled ornithine into OL. Overexpression of OlsB in an olsA-deficient mutant of Sinorhizobium (Rhizobium) meliloti leads to the transient accumulation of lyso-ornithine lipid, the biosynthetic intermediate of OL biosynthesis. Overexpression of OlsB in Escherichia coli is sufficient to cause the in vivo formation of lyso-ornithine lipid in this organism and is the cause for a 3-hydroxyacyl-AcpP-dependent acyltransferase activity forming lyso-ornithine lipid from ornithine. These results demonstrate that OlsB is required for the first step of OL biosynthesis, in which ornithine is N-acylated with a 3-hydroxy-fatty acyl residue in order to obtain lyso-ornithine lipid. OL formation in a wild-type S. meliloti is increased upon growth under phosphate-limiting conditions. Expression of OlsB from a broad host range vector leads to the constitutive formation of relatively high amounts of OL (12–14% of total membrane lipids) independently of whether strains are grown in the presence of low or high concentrations of phosphate, suggesting that in S. meliloti the formation of OlsB is usually limiting for the amount of OL formed in this organism. Open reading frames homologous to OlsA and OlsB were identified in many eubacteria and although in S. meliloti the olsB and olsA gene are 14 kb apart, in numerous other bacteria they form an operon.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 45 (2002), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Phospholipids are the membrane-forming constituents in all living organisms. In addition to phosphorus-containing lipids, the membranes of numerous bacteria contain significant amounts of phosphorus-free polar lipids, often derived from amino acids. Although lipids derived from the amino acid ornithine are widespread among bacteria, their biosynthesis is unknown. Here, we describe the isolation of mutants of Sinorhizobium meliloti deficient in the biosynthesis of ornithine-derived lipids (OL). Complementation of such mutants with a sinorhi-zobial cosmid gene bank, subcloning of the complementing fragment and sequencing of the subclone led to the identification of a gene (olsA) coding for a presumptive acyltransferase. Amplification of this gene and its expression in OL-deficient mutant backgrounds of S. meliloti demonstrates that it is required for OL biosynthesis. An OL-deficient mutant of S. meliloti disrupted in olsA shows wild type-like growth behaviour and is capable of inducing nitrogen-fixing nodules on legume hosts. A lyso-ornithine lipid-dependent acyltransferase activity forming OL requires acyl-AcpP as the acyl donor and expression of the olsA gene.
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  • 10
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Parkinson disease is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic-ubiquitinated inclusions (Lewy bodies). Mutations in α-synuclein (A53T, A30P) and parkin cause familial Parkinson disease. Both these proteins are ...
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