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1.
  • Abdalla, M. A., et al. (författare)
  • A CMOS APS for dental X-ray imaging using scintillating sensors
  • 2001
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 460:1, s. 197-203
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present an integrating CMOS Active Pixel Sensor (APS) circuit to be used with scintillator type X-ray sensors for intra oral dental X-ray imaging systems. Different pixel architectures were constructed to explore their performance characteristics and to study the feasibility of the development of such systems using the CMOS technology. A prototype 64×80 pixel array has been implemented in a CMOS 0.8 μm double poly n-well process with a pixel pitch of 50 μm. A spectral sensitivity measurement for the different pixels topologies, as well as measured X-ray direct absorption in the different APSs are presented. A measurement of the output signal showed a good linearity over a wide dynamic range. This chip showed that the very low sensitivity of the CMOS APSs to direct X-ray exposure adds a great advantage to the various CMOS advantages over CCD-based imaging systems.
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2.
  • Abdalla, M. A., et al. (författare)
  • An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier
  • 2001
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 466:1, s. 232-236
  • Tidskriftsartikel (refereegranskat)abstract
    • We present in this paper an integrating CMOS Active Pixel Sensor (APS) circuit coated with scintillator type sensors for intra-oral dental X-ray imaging systems. The photosensing element in the pixel is formed by the p-diffusion on the n-well diode. The advantage of this photosensor is its very low direct absorption of X-rays compared to the other available photosensing elements in the CMOS pixel. The pixel features an integrating capacitor in the feedback loop of a preamplifier of a finite gain in order to increase the optical sensitivity. To verify the effectiveness of this in-pixel preamplification, a prototype 32 x 80 element CMOS active pixel array was implemented in a 0.8 mum CMOS double poly, n-well process with a pixel pitch of 50 mum. Measured results confirmed the improved optical sensitivity performance of the APS. Various measurements on device performance are presented.
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3.
  • Aboelfotoh, M O, et al. (författare)
  • Schottky-barrier behavior of metals on n- and p-type 6H-SiC
  • 2003
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 67:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The Schottky-barrier height of a number of metals (Ti, Ni, Cu, and Au) on n- and p-type Si-terminated 6H-SiC has been measured in the temperature range 150-500 K. It is found that the barrier height to n-type 6H-SiC does not exhibit a temperature dependence, while for p-type 6H-SiC the change in the barrier height with temperature follows very closely the change in the indirect energy gap in 6H-SiC. These results are inconsistent with models of Schottky-barrier formation based on the concept of a charge neutrality level. Furthermore, the present results cannot be reconciled with a defect pinning mechanism, contrary to the conclusions of earlier studies on III-V compound semiconductors. We suggest that chemical bonding at the metal-semiconductor interface plays an important role in determining the Schottky-barrier height.
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4.
  • Amon, B., et al. (författare)
  • From First-Order Logic to Automated Word Generation for Lyee
  • 2003
  • Ingår i: Knowledge-Based Systems. - 0950-7051. ; 16:7/8, s. 249-262
  • Tidskriftsartikel (refereegranskat)abstract
    • A conceptual schema can be viewed as a language to describe the phenomena in a system to be modelled, i.e. a set of derivation rules and integrity constraints as well as a set of event-rules describing the behaviour of an object system. In this paper, we investigate the relationship between the Lyee software requirements concepts with various constructs in conceptual modelling. Within our work we choose the Unified Modelling Language (UML) as a modelling notation for explaining conceptual models. The result obtained models a fully expressive set of UML and First Order Logic constructs mapped into Lyee concepts.
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5.
  • Anderson, Mattias, et al. (författare)
  • Total Synthesis of Capsaicin Analogues from Lignin-Derived Compounds by Combined Heterogeneous Metal, Organocatalytic and Enzymatic Cascades in One Pot
  • 2014
  • Ingår i: Advanced Synthesis and Catalysis. - 1615-4150. ; 356:9, s. 2113-2118
  • Tidskriftsartikel (refereegranskat)abstract
    • The total synthesis of capsaicin analogues was performed in one pot, starting from compounds that can be derived from lignin. Heterogeneous palladium nanoparticles were used to oxidise alcohols to aldehydes, which were further converted to amines by an enzyme cascade system, including an amine transaminase. It was shown that the palladium catalyst and the enzyme cascade system could be successfully combined in the same pot for conversion of alcohols to amines without any purification of intermediates. The intermediate vanillyl-amine, prepared with the enzyme cascade system, could be further converted to capsaicin analogues without any purification using either fatty acids and a lipase, or Schotten-Baumann conditions, in the same pot. An aldol compound (a simple lignin model) could also be used as starting material for the synthesis of capsaicin analogues. Using l-alanine as organocatalyst, vanillin could be obtained by a retro-aldol reaction. This could be combined with the enzyme cascade system to convert the aldol compound to vanillylamine in a one-step one-pot reaction.
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6.
  • Andersson, Fredrik (författare)
  • 1. Asymmetric aldol and alkylation reactions using pyrrolidine-based chiral auxiliaries 2. Syntheses of pine sawfly pheromone precursors and structurally related compounds
  • 2002
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • This thesis describes the syntheses of the 1-propionylatedauxiliaries (S)-(− )-2-(pyrrolidin-2-yl)propan-2-ol and (S)-(− )-2-(1-methoxy-1-methylethyl)pyrrolidine andtheir use in asymmetric aldol and alkylation reactions. Thesynthesis of 1-propionylated (2S,4R) 2-{4-[(tert-butyldimethylsilyl)oxy]pyrrolidin-2-yl}propan-2-olis also described. The effects on the stereoselectivity, byvariations of solvent, temperature, Lewis acids as additive aswell as the amount of additive are studied. None of thepropionylated auxiliaries exhibited remarkable selectivity foreither diastereomer in aldol reactions with benzaldehyde. Bestresults were obtained with SnCl2as additive giving asyn:antiratio up to 73:27, and Cp2ZrCl2and Cp2TiCl2giving a reversedsyn:antiratio up to 27:73 for the former auxiliary. Highselectivity for onesynand oneantidiastereomer were obtained with TMS-Cl as anadditive. The latter propionylated auxiliary was less selectivethan the former. Reversal insyn/antiselectivity was observed when Cp2ZrCl2and Cp2TiCl2was used with asyn:antiratio = 68:32 and 33:67. In alkylation reactions,the former propionylated auxiliary showed lower and similarselectivity with benzyl bromide andn-butyl iodide, compared with the literature. Enhancedselectivity was obtained in the benzylation reactions (78% and84% diastereomeric excess), with LiCl and Cp2ZrCl2as additives. Cp2ZrCl2and Cp2TiCl2resulted in lower selectivity in butylationreactions. High selectivity was obtained for the latterpropionylated auxiliary and with a reversal in selectivity,compared with the former. Benzylation reactions resulted in82-98% diastereomeric excess, with the highest selectivity ofCp2ZrCl2as additive. In butylation reactions the use ofLiCl resulted in highest diastereomeric excess (94%).The second part of the thesis describes the syntheses ofcompounds related to sex pheromones of pine sawflies. (2S,6R)-(− )-2,6-Dimethyl-1-octanol, a building blockin the synthesis of the sex pheromone of the pine sawflyMicrodiprion pallipesin high stereoisomeric purity wasprepared from the optically pure (S)-citronellal. Lipase-catalysed (Amano PS and Im-CRL)kinetic separations, based on selective acylation andesterification of (2R/S,6R)-2,6-dimethyl-1-octanol and the corresponding acidwere the key steps in this sequence. The alcohol precursors tosex pheromones ofDiprion nipponica,Macrodiprion nemoralisandMicrodiprion pallipeswere synthesised as racemicmixtures in moderate yields. Stereoisomeric mixtures of severalmethyl-branched long-chain 2-alkanols, structurally related tosex pheromone alcohol precursors of pine sawfly species, werealso synthesised in moderate yields. The key reaction in thesyntheses was the ring opening of&#947-butyrolactonesusing different alkyl lithiums as nucleophiles.Keywords: Chiral auxiliary, Stereoselectivity, Lewisacid, Aldol, Alkylation, Sex pheromone, Pine sawfly, Lipase,Synthesis, Diprion nipponica, Macrodiprion nemoralis,Microdiprion pallipes
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7.
  • Andersson, J, et al. (författare)
  • Ageing of Flexographic Printed Model Cellulose Surfaces and Determination of the Mechanisms Behind Ageing
  • 2009
  • Ingår i: Pulp & paper Canada. - 0316-4004. ; 110:6, s. 34-38
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of storage conditions on the ink detachment efficiency of water-based flexographic ink printed onto model cellulose surfaces and handsheets was investigated. It was shown that UV light, elevated temperatures, longer storage time, increasing surface roughness, and increasing surface hydrophobicity all had a negative effect on ink detachment. It was also shown that the ink's chemical and structural characteristics changed when stored at elevated temperatures. No chemical or structural changes could be observed for the ink when stored under UV light.
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8.
  • Andersson, Kerstin, et al. (författare)
  • Effects of biological treatment on the chemical structure of dissolved lignin-related substances in effluent from thermomechanical pulping
  • 2008
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631. ; 23:2, s. 164-171
  • Tidskriftsartikel (refereegranskat)abstract
    • Effluent from a TMP-based pulp and paper mill was collected at the inlet and outlet of the mill's biological treatment plant and fractionated by sorption on XAD-8 resin and MTBE precipitation. Fractionation indicated that the refractory dissolved organic material in biologically treated effluent was mainly composed of lignin-related substances. Characterisation of the lignin-related substances by chromatographic and spectrometric methods confirmed the similarities of the isolated material and milled wood lignin. Fractionation and characterisation of alkali-extracted material from solids (biosludge) in biologically treated effluent found evidence of lignin-related material. Results indicated that biological treatment had altered the chemical structure and molar-mass distribution of dissolved lignin-related substances.
9.
  • Andreasson, B., et al. (författare)
  • Determination of fibre pore structure : influence of salt, pH and conventional wet strength resins
  • 2005
  • Ingår i: Cellulose (London). - 0969-0239. ; 12:3, s. 253-265
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.
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10.
  • Andreasson, B., et al. (författare)
  • The porous structure of pulp fibres with different yields and its influence on paper strength
  • 2003
  • Ingår i: Cellulose (London). - 0969-0239. ; 10:2, s. 111-123
  • Tidskriftsartikel (refereegranskat)abstract
    • The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of H-2 in fibres saturated with (H2O)-H-2. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/ lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.
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