| 1. |
- Abrahamsson, M. L. A., et al.
(författare)
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Ruthenium-manganese complexes for artificial photosynthesis : Factors controlling intramolecular electron transfer and excited-state quenching reactions
- 2002
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:6, s. 1534-1544
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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)
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First experiments on an evaporative gas turbine pilot power plant : Water circuit chemistry and humidification evaluation
- 2002
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Ingår i: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 124:1, s. 96-102
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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. |
- Baev, A., et al.
(författare)
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Doppler interference in dissociative resonant photoemission
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2
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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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| 4. |
- Barnes, W. L., et al.
(författare)
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Solid-state single photon sources : light collection strategies
- 2002
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 18:2, s. 197-210
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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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| 5. |
- Borg, Andreas, et al.
(författare)
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LIF study of mixing in a model of a vein punctured by a cannula
- 2002
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Ingår i: International Journal of Heat and Fluid Flow. - 0142-727X .- 1879-2278. ; 23:5, s. 664-670
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Tidskriftsartikel (refereegranskat)abstract
- Steady flow and mixing in a model of an "arterialized" vein punctured by a cannula as occurs during hemodialysis has been investigated in vitro. The motivation is that a major cause of vascular access dysfunction is the development of venous stenoses. This phenomenon lacks physiological explanation. However, one may attribute this quick process to the chemical content of the dialyzed blood and its flow near the point of infusion. The interest in mixing of chemical compounds in the dialyzed blood supplied through the cannula is, therefore, genuine due to the clinical impacts of haemodyalysis. We are interested in understanding the mixing of the two streams; namely, the untreated blood through the vein and the treated blood through the cannula. This mixing affects the local pH, which in turn can affect the solubility of several salts used for dialysis. In addition, since the blood contains molecules of widely different diffusivity properties, the local composition of blood near the point of injection is of interest. The hypothesis is that concentration non-uniformities may lead to undesired chemical or bio-chemical reactions leading to the pathological processes in the region around the needle. The mixing of a high Schmidt number substance in the stream entering from the cannula with the base flow in the vein is studied by laser induced fluorescence (LIF). The investigations are performed for a range of typical Reynolds numbers in the cannula and the vein found during hemodialysis. The study shows complicated mixing patterns around the cannula, and that non-uniformities in the blood persist over long distances for the lower flow rates found in vivo. For the higher flow rates, the flow loses its stability and mixing is enhanced. The nature of this instability is shown, and quantitative data of concentration fluctuations are given. We have further considered the effect of rotating the cannula. This leads to a significant change in the mixing process. The significance of the non-uniformities in mixing of solvents in the blood for the development of venous stenoses should be further studied not only in fluid dynamical terms but also in terms of endothelial (cellular) effects. (C) 2002 Published by Elsevier Science Inc.
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| 6. |
- Bäck, Torbjörn, et al.
(författare)
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A TOF-PET system for educational purposes
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 477, s. 82-82
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Tidskriftsartikel (refereegranskat)abstract
- A TOF-PET system has been designed and constructed for educational purposes. The aim of this system is to demonstrate the possibilities of positron emission tomography in general and the time-of-flight method in particular to the students of various courses at the Royal Institute of Technology, Stockholm, Sweden. The set-up consists of 48 small BaF2 crystals coupled to fast photomultipliers placed in a ring geometry. The signals of the photomultipliers are fed into fast constant fraction discriminators (CFD). The outputs of these are directed to a specially designed logic VME unit. which combines the CFD signals of 6 neighbouring channels to one signal by adding a different delay to each channel. The logic circuitry produces a prompt pulse for each event that serves as the start pulse for the 8-channel fast TDC. The delayed pulses act as the stop pulses for the TDC. In a computer. the measured times are converted into information about which the photomultipliers fired with the difference in the time of flight. The set-up is described and the results are presented.
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| 7. |
- Caraeni, Doru, et al.
(författare)
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Compact third-order multidimensional upwind scheme for Navier-Stokes simulations
- 2002
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Ingår i: Theoretical and Computational Fluid Dynamics. - : Springer Science and Business Media LLC. - 0935-4964 .- 1432-2250. ; 15:6, s. 373-401
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Tidskriftsartikel (refereegranskat)abstract
- A new compact third-order scheme for the solution of the unsteady Navier-Stokes equations on unstructured grids is proposed. The scheme is a cell-based algorithm, belonging to the class of Multidimensional Upwind schemes, which uses a finite-element reconstruction procedure over the cell to achieve third order (spatial) accuracy. Derivation of the scheme is given. The asymptotic accuracy, for steady/unsteady inviscid or viscous flow situations, is proved using numerical experiments. Those results are compared with the performances of a second-order multidimensional upwind scheme. The new compact high-order discretization proves to have excellent parallel scalability, which makes it well suited for large-scale computations on parallel supercomputers. Our studies show clearly the advantages of the new compact third-order scheme compared with the classical second-order Multidimensional Upwind scheme.
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| 8. |
- Christmansson, M, et al.
(författare)
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A case study of a principally new way of materials kitting - an evaluation of time consumption and physical workload
- 2002
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Ingår i: International Journal of Industrial Ergonomics. - : Elsevier. - 0169-8141. ; 30:1, s. 49-65
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a materials kitting case study, using an alternative method for materials killing: the traditional picker-to-material principle was replaced with a material-to-picker approach. The Study was made in a materials supply workshop of an automobile plant shortly after this kitting process had been introduced. The materials kitting was video recorded and the material pickers' physical exposure was assessed using ambulatory equipment to make an integrated registration of muscular activity, work postures and movements. The material pickers assessed work situations perceived as physically stressful. The materials kitting showed improved productivity as compared with other kitting methods. The study indicated that the work situation offered pickers low levels of physical exposure. The picking work was rather light but involved great repetitiveness in arm movements. The material pickers experienced the work as repetitive and having some physically stressful work situations. The integrated analyses showed: (1) that exposure in picking operations was similar to, but could be distinguished from, other work activities and (2) that picking from one type of storage package, Euro pallets, resulted in higher exposure than picking from plastic containers. More studies are needed on the implications of exposure levels in materials picking.
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| 9. |
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| 10. |
- Collén, Anna, et al.
(författare)
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Extraction of endoglucanase I (Cel7B) fusion proteins from Trichoderma reesei culture filtrate in a poly(ethylene glycol)phosphate aqueous two-phase system
- 2002
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Ingår i: Journal of Chromatography A. - 0021-9673 .- 1873-3778. ; 943:1, s. 55-62
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Tidskriftsartikel (refereegranskat)abstract
- Endoglucanases (EGI) (endo-1,4-beta-D-glucan-4-glucanohydrolase, EC 3.2.1.4, Cel7B) of Trichoderma reesei are industrially important enzymes. Thus, there is a great need for development of a primary recovery method suitable for large-scale utilization. In this study we present a concept applicable for large-scale purification of an EGI fusion protein by one-step extraction in a poly(ethylene glycol) PEG-sodium/potassium phosphate aqueous two-phase system. EGI is a two-module enzyme composed of an N-terminal catalytic module and a C-terminal cellulose binding module (CBM) separated by a glycosylated linker region. Partitioning of six different EGI constructs, containing the C-terminal extensions (WP)(2), (WP)(4) or the amphiphilic protein hydrophobin I (HFB) of T. reesei instead of the CBM were studied to evaluate if any of the fusions could improve the partition coefficient sufficiently to be suitable for large-scale production. All constructs showed improved partitioning in comparison to full length EGI. The (WP)(4) extensions resulted in 26- to 60-fold improvement of partition coefficient. Consequently, a relative minor change in amino acid sequence on the two-module protein EGI improved the partition coefficient significantly in the PEG 4000-sodium/potassium phosphate system. The addition of HFBI to EGI clearly enhanced the partition coefficient (K=1.2) in comparison to full-length EGI (K=0.035). Partitioning of the construct with (WP)(4) fused to the catalytic module and a short sequence of the linker [EGI(core-P5)(WP)(4)] resulted in the highest partition coefficient (K=54) and a yield of 98% in the PEG phase. Gel electrophoresis showed that the construct with the (WP)(4) tag attached after a penta-proline linker could be purified from the other bulk proteins by only a single-step separation in the PEG 4000-sodium/potassium phosphate system. This is a major improvement in comparison with the previously studied model (ethylene oxide-propylene oxide)-dextran system. Hence, this construct will be suitable for further optimization of the extraction of the enzyme in a PEG 4000-sodium/potassium phosphate system from culture filtrate.
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