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Sökning: LAR1:lu > Kungliga Tekniska Högskolan > Refereegranskat > (2000-2004)

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1.
  • Abrahamsson, M. L. A., et al. (författare)
  • Ruthenium-manganese complexes for artificial photosynthesis : Factors controlling intramolecular electron transfer and excited-state quenching reactions
  • 2002
  • Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:6, s. 1534-1544
  • Tidskriftsartikel (refereegranskat)abstract
    • Continuing our work toward a system mimicking the electron-transfer steps from manganese to P-680(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 X 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximate to 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium (III) electrontransfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.
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2.
  • Agren, N. D., et al. (författare)
  • First experiments on an evaporative gas turbine pilot power plant : Water circuit chemistry and humidification evaluation
  • 2002
  • Ingår i: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 124:1, s. 96-102
  • Tidskriftsartikel (refereegranskat)abstract
    • The evaporative gas turbine (EvGT), also known as the humid air turbine (HAT) cycle, is a novel advanced gas turbine cycle that has attracted considerable interest for the last decade. This high-efficiency cycle shows the potential to be competitive with Diesel engines or combined cycles in small and intermediate scale plants for power production and/or cogeneration. A 0.6 MW natural gas-fired EvGT pilot plant has been constructed by a Swedish national research group in cooperation between universities and industry. The plant is located at the Lund Institute of Technology, Lund, Sweden. The pilot plant uses a humidification tower with metallic packing in which heated water from the flue gas economizer is brought into direct counter current contact with the pressurized air from the compressor This gives an efficient heat recovery and thereby a thermodynamically sound cycle. As the hot sections in high-temperature gas turbines are sensitive to particles and alkali compounds, water quality issues need to be carefully considered. As such, apart from evaluating the thermodynamic and part-load performance characteristics of the plant, and verifying the operation of the high-pressure humidifier, much attention is focused on the water chemistry issues associated with the recovery and reuse of condensate water from the flue gas. A water treatment system has been designed and integrated into the pilot plant. This paper presents the first water quality results from the plant. The experimental results show that the condensate contains low levels of alkali and calcium, around 2 mg/l Sigma(K,Na,Ca), probably originating from the unfiltered compressor intake, About 14 mg/l NO2- +NO3- comes from condensate absorption of flue gas NOx. Some Cu is noted, 16 mg/l, which originates from copper corrosion of the condenser tubes. After CO2 stripping, condensate filtration and a mixed bed ion exchanger the condensate is of suitable quality for reuse as humidification water The need,for large quantities of demineralized water has by manY authors been identified as a drawback for the evaporative cycle. However, by cooling the humid flue gas, the recovery, of condensed water cuts the need of water feed. A self-supporting water circuit can be achieved, with no need for any net addition of water to the system. In the pilot plant, this was achieved by cooling the flue gas to around 35degreesC.
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3.
  • Algora, A., et al. (författare)
  • Pronounced Shape Change Induced by Quasiparticle Alignment
  • 2000
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813 .- 1089-490X. ; 61:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Mean lifetimes of high-spin states of Kr-74 have been determined using the Doppler-shift attenuation method. The high-spin states were studied using the Ca-40(Ca-40, alpha 2p) reaction at a beam energy of 160 MeV with the GASP gamma-ray spectrometer. The ground-state band and negative parity side band show the presence of three different configurations in terms of transitional quadrupole deformations. A dramatic shape change was found along the ground-state band after the S-band crossing. The deduced quadrupole deformation changes are well reproduced by cranked Woods-Saxon Strutinsky calculations.
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4.
  • Baev, A., et al. (författare)
  • Doppler interference in dissociative resonant photoemission
  • 2002
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.
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5.
  • Baev, A., et al. (författare)
  • Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission
  • 2003
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:2
  • Tidskriftsartikel (refereegranskat)abstract
    • An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
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6.
  • Bai, Xue-Song, et al. (författare)
  • Laminar flamelet structure at low and vanishing scalar dissipation rate
  • 2000
  • Ingår i: Combustion and Flame. - 0010-2180 .- 1556-2921. ; 120:3, s. 285-300
  • Tidskriftsartikel (refereegranskat)abstract
    • The laminar flamelet structures of methane/air, propane/air, and hydrogen/air nonpremixed combustion at low and vanishing scalar dissipation rates are investigated, by numerical calculations of a system of conservation equations in a counterflow diffusion flame configuration, together with a transport equation defining the mixture fraction and scalar dissipation rate. The chemical reaction mechanisms consist of 82 elementary reactions up to C-3 species. In the limit of vanishing scalar dissipation rate, two types of structures are shown to appear. In one structure fuel and oxygen are consumed in a thin layer located near the stoichiometric mixture fraction, Z(st), where the temperature and the major products reach their peaks. This is similar to the so-called Burke-Schumann single layer flame sheet structure. One example is the hydrogen/air diffusion flame. The second structure consists of multilayers. Fuel and oxygen are consumed at different locations. Oxygen is consumed at Z(l) (near Z(st)), where the temperature and the major products reach their peaks. Fuel is consumed at Z(r) (> Z(st)). Between Z(l) and Z(r) some intermediate and radical species are found in high concentrations. Hydrocarbon/air nonpremixed flames are of this type. It is shown that for methane/air diffusion flames, some chemical reactions which are negligible at large scalar dissipation rate near flame quenching conditions, play essential roles for the existence of the multilayer structure. Examples of such reactions are, CH4 --> CH3 + H, H2O + O-2 --> HO2 + OH, H2O + M --> H + OH + M and CHO + H-2 --> O + H. The sensitivity of the species distributions in the flamelet to the scalar dissipation rate varies for different species. The most sensitive species are the intermediates and radicals at the fuel-rich side. At low scalar dissipation rate the radiative heat transfer can significantly move the fuel consumption layer to the oxygen consumption layer, increase the oxygen leakage to fuel side, and even quench the flame. Differential diffusion modifies the species and temperature profiles in the flamelet, but does not affect the multilayer nature of the flamelet. This result is used to successfully explain the high CO emissions in a turbulent methane/air diffusion flame.
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7.
  • Barnes, W. L., et al. (författare)
  • Solid-state single photon sources : light collection strategies
  • 2002
  • Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 18:2, s. 197-210
  • Tidskriftsartikel (refereegranskat)abstract
    • We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics, in which the pathways by which the source may emit a photon are restricted, thus channeling emission into one desired mode. Second are those where we try to reshape the free space modes into a target mode in an optimal way, by means of refraction, without fundamentally altering the way in which the source emits. Respectively, we examine a variety of microcavities and solid immersion lenses. Whilst we find that the micropillar microcavities offer the highest collection efficiency (similar to70%), choosing this approach may not always be appropriate due to other constraints. Details of the different approaches, their merits and drawbacks are discussed in detail.
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8.
  • Bengtsson, Göran, et al. (författare)
  • Irregular walks and loops combines in small-scale movement of a soil insect : implications for dispersal biology
  • 2004
  • Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 231:2, s. 299-306
  • Tidskriftsartikel (refereegranskat)abstract
    • Analysis of small-scale movement patterns of animals we may help to understand and predict movement at a larger scale, such as dispersal, which is a key parameter in spatial population dynamics. We have chosen to study the movement of a soil-dwelling Collembola, Protaphorura armata, in an experimental system consisting of a clay surface with or without physical obstacles. A combination of video recordings, descriptive statistics, and walking simulations was used to evaluate the movement pattern. Individuals were found to link periods of irregular walk with those of looping in ahomogeneous environment as well as in one structured to heterogeneity by physical obstacles. The number of loops varied between 0 and 44 per hour from one individual to another and some individuals preferred to make loops by turning right and others by turning left. P. armata spent less time at the boundary of small obstacles compared to large, presumably because of a lower probability to track the steepness of the curvature as the individual walks along a highly curved surface. Food deprived P. armata had amore winding movement and made more circular loops than those that were well fed. The observed looping behaviour is interpreted in the context of systematic search strategies and compared with similar movement patterns found in other species.
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9.
  • Benkestock, Kurt, et al. (författare)
  • Automated Nano-Electrospray Mass Spectrometry for Protein-Ligand Screening by Noncovalent Interaction Applied to Human H-FABP and A-FABP
  • 2003
  • Ingår i: Journal of Biomolecular Screening. - : Elsevier BV. - 1087-0571 .- 1552-454X. ; 8:3, s. 247-256
  • Tidskriftsartikel (refereegranskat)abstract
    • A method for ligand screening by automated nano-electrospray ionization mass spectrometry (nano-ESI/MS) is described. The core of the system consisted of a chip-based platform for automated sample delivery from a 96-well plate and subsequent analysis based on noncovalent interactions. Human fatty acid binding protein, H-FABP (heart) and A-FABP (adipose), with small potential ligands was analyzed. The technique has been compared with a previously reported method based on nuclear magnetic resonance (NMR), and excellent correlation with the found hits was obtained. In the current MS screening method, the cycle time per sample was 1.1 min, which is approximately 50 times faster than NMR for single compounds and approximately 5 times faster for compound mixtures. High reproducibility was achieved, and the protein consumption was in the range of 88 to 100 picomoles per sample. Furthermore, a novel protocol for preparation of A-FABP without the natural ligand is presented. The described screening approach is suitable for ligand screening very early in the drug discovery process before conventional high-throughput screens (HTS) are developed and/or used as a secondary screening for ligands identified by HTS.
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10.
  • Berg, K. E., et al. (författare)
  • Covalently linked ruthenium(II)-manganese(II) complexes : Distance dependence of quenching and electron transfer
  • 2001
  • Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; 2001:4, s. 1019-1029
  • Tidskriftsartikel (refereegranskat)abstract
    • Continuing our development of artificial models for photosystem II in green plants, a series of compounds have been prepared in which a RU(bpy)(3)(2+) photosensitizer is covalently Linked to a manganese(II) electron donor. In addition to a trispicolylamine Ligand, two other manganese Ligands, dipicolylamine and aminodiacetic acid, have been introduced in order to study Ligands that are appropriate for the construction of manganese dimers with open coordination sites for the binding of water. Coordination equilibria of the manganese ions were monitored by EPR. The interactions between the ruthenium and manganese moieties were probed by flash photolysis, cyclic voltammetry and steady-state and time-resolved emission measurements. The quenching of the Ru-II excited state by Mn-II was found to be rapid in complexes with short Ru-Mn distances. Nevertheless, each Run species could be photo-oxidized by bimolecular quenching with methylviologen, and the subsequent electron transfer from Mn-II to Ru-III could be monitored.
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