717 research outputs found

    Theoretical consideration of pits recording and etching processes in chalcogenide vitreous semiconductors

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    We propose theoretical consideration and computer modeling of information pit recording and etching processes in chalcogenide vitreous semiconductors. We demonstrate how to record and develop information pits with the necessary shape and sizes in chalcogenide photoresists using gaussian laser beam and selective etching. It has been shown that phototransformed region cross-section could be almost trapezoidal or parabolic depending on the photoresist material optical absorption, recording beam power, exposure, etchant selectivity and etching time. After illumination, the spatial distribution of photo-transformed material fraction was calculated using the Kolmogorov-Awrami equation. Analyzing obtained results, we derived a rather simple approximate analytical expression for the dependence of the photo-transformed region width and depth on the recording gaussian beam power, radius and exposure time. Then the selective etching process was simulated numerically. The obtained results quantitatively describes the characteristics of pits recorded by the gaussian laser beam in thin layers of As40S60 chalcogenide semiconductor.Comment: 14 pages, 1 scheme, 9 figure

    Selective Preparation of a Heteroleptic Cyclometallated Ruthenium Complex Capable of Undergoing Photosubstitution of a Bidentate Ligand

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    Cyclometallated ruthenium complexes typically exhibit red‐shifted absorption bands and lower photolability compared to their polypyridyl analogues. They also have lower symmetry, which sometimes makes their synthesis challenging. In this work, the coordination of four N,S bidentate ligands, 3‐(methylthio)propylamine (mtpa), 2‐(methylthio)ethylamine (mtea), 2‐(methylthio)ethyl‐2‐pyridine (mtep), and 2‐(methylthio)methylpyridine (mtmp), to the cyclometallated precursor [Ru(bpy)(phpy)(CH3CN)2]+ (bpy=2,2â€Č‐bipyridine, Hphpy=2‐phenylpyridine) has been investigated, furnishing the corresponding heteroleptic complexes [Ru(bpy)(phpy)(N,S)]PF6 ([2]PF6–[5]PF6, respectively). The stereoselectivity of the synthesis strongly depended on the size of the ring formed by the Ru‐coordinated N,S ligand, with [2]PF6 and [4]PF6 being formed stereoselectively, but [3]PF6 and [5]PF6 being obtained as mixtures of inseparable isomers. The exact stereochemistry of the air‐stable complex [4]PF6 was established by a combination of DFT, 2D NMR, and single‐crystal X‐ray crystallographic studies. Finally, [4]PF6 was found to be photosubstitutionally active under irradiation with green light in acetonitrile, which makes it the first cyclometallated ruthenium complex capable of undergoing selective photosubstitution of a bidentate ligand.Metals in Catalysis, Biomimetics & Inorganic Material

    On the algebraic K-theory of the complex K-theory spectrum

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    Let p>3 be a prime, let ku be the connective complex K-theory spectrum, and let K(ku) be the algebraic K-theory spectrum of ku. We study the p-primary homotopy type of the spectrum K(ku) by computing its mod (p,v_1) homotopy groups. We show that up to a finite summand, these groups form a finitely generated free module over a polynomial algebra F_p[b], where b is a class of degree 2p+2 defined as a higher Bott element.Comment: Revised and expanded version, 42 pages

    Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry

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    In semiconductor heterostructures, bulk and structural inversion asymmetry and spin-orbit coupling induce a k-dependent spin splitting of valence and conduction subbands, which can be viewed as being caused by momentum-dependent crystal magnetic fields. This paper studies the influence of these effective magnetic fields on the intersubband spin dynamics in an asymmetric n-type GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin plasmons using linear response theory. The so-called D'yakonov-Perel' decoherence mechanism is inactive for collective intersubband excitations, i.e., crystal magnetic fields do not lead to decoherence of spin plasmons. Instead, we predict that the main signature of bulk and structural inversion asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting of the spin plasmon dispersion. The importance of many-body effects is pointed out, and conditions for experimental observation with inelastic light scattering are discussed.Comment: 8 pages, 6 figure

    Intersubband spin-density excitations in quantum wells with Rashba spin splitting

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    In inversion-asymmetric semiconductors, spin-orbit coupling induces a k-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDEs) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDEs in the conduction band of quantum wells with subbands that may be non-parabolic and spin-split due to bulk or structural inversion asymmetry (Rashba effect). As an example, we consider a 40 nm GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction subbands. We find a coupling and wavevector-dependent splitting of the longitudinal and transverse SDEs. However, decoherence of the SDEs is not determined by subband spin splitting, due to collective effects arising from dynamical exchange and correlation.Comment: 10 pages, 4 figure

    Effect of short-term versus long-term grassland management and seasonal variation in organic and conventional dairy farming on the composition of bulk tank milk

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    Bulk tank milk from 28 dairy farms was sampled every second month for 2 yr to assess the effects of grassland management, production system and season on milk fatty acid (FA) composition, concentrations of fat-soluble vitamins, Se, and milk sensory quality. Grassland management varied in terms of time since establishment. Short-term grassland management (SG) was defined as establishment or reseeding every fourth year or more often, and long-term grassland management (LG) was defined as less frequent establishment or reseeding. Fourteen organic (ORG) dairy farms with either short-term or long-term grassland management were paired with 14 conventional (CON) farms with respect to grassland management. Within ORG farms, SG farms differed from LG farms in herbage botanical composition, but not in concentrate FA concentrations, dry matter intake, or milk yield. Within CON farms, herbage composition, concentrate FA concentrations, dry matter intake, and milk yield showed no or insignificant variations. The ORG farms differed from CON farms in herbage botanical composition, concentrate FA concentrations, concentrate intake, and milk yield. Compared with ORG-LG farms, ORG-SG farms produced milk fat with higher proportions of C10:0 and C12:0 associated with higher herbage proportions of legumes (Fabaceae) and lower proportions of other dicotyledon families. Compared with milk from CON farms, milk fat from ORG farms had higher proportions of most saturated FA and all n-3 FA, but lower proportions of C18:0 and C18:1 cis-9 associated with higher forage proportion and differences in concentrations of FA in concentrates. Compared with the outdoor-feeding periods, the indoor feeding periods yielded milk fat with higher proportions of most short-chain and medium-chain FA and lower proportions of most C18-FA associated with grazing and higher forage proportions. Milk concentrations of α-tocopherol and ÎČ-carotene were lower during the grazing periods. Inclusion of fishmeal in organic concentrates may explain higher Se concentrations in organically produced milk. Milk sensory quality was not affected in this study. In conclusion, grassland management had minor effects on milk composition, and differences between ORG farms and CON farms may be explained by differences in concentrate intake and concentrate FA concentrations. Milk produced on ORG farms versus CON farms and milk produced during the outdoor versus indoor feeding periods had potential health benefits due to FA composition. In contrast, the higher milk-fat proportions of saturated FA in milk from ORG farms may be perceived as negative for human health

    Magnetic Field Amplification in Galaxy Clusters and its Simulation

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    We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
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