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

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1.
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2.
  • Algora, A., et al. (författare)
  • Pronounced Shape Change Induced by Quasiparticle Alignment
  • 2000
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 61:3, s. 031303(R)
  • 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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3.
  • Astrom, K. J., et al. (författare)
  • Design of decoupled PI controller for two-by-two systems
  • 2002
  • Ingår i: IEE Proceedings - Control Theory & Applications. - IET. - 1350-2379. ; 149:1, s. 74-81
  • Tidskriftsartikel (refereegranskat)abstract
    • The design of PI controllers for systems with interacting loops is discussed. It is advantageous to deal with the interaction at the loop level, because supervisory control seldom has sufficient bandwidth. A new scheme based on modified scalar PI design and static decoupling is developed, in which the frequency characteristic of the coupling between the lower-level loops is taken into account. This leads to a design method emphasising the trade-off between the individual loop performances and the interaction indices introduced in the paper. The controller is easily implemented, due to its simple configuration based on standard components. A useful observation is that the interaction can be reduced substantially by using set-point weighting. The method is applied to three examples, including a model of a new laboratory system called the quadruple-tank process
4.
  • Back, T., et al. (författare)
  • A TOF-PET system for educational purposes
  • 2002
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 477:03-jan, s. 82-87
  • 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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5.
  • Baev, A., et al. (författare)
  • Doppler interference in dissociative resonant photoemission
  • 2002
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 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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6.
  • 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. ; 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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7.
  • Barnes, WL, et al. (författare)
  • Solid-state single photon sources : light collection strategies
  • 2002
  • Ingår i: European Physical Journal D : Atomic, Molecular and Optical Physics. - 1434-6060. ; 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.
  • Benkestock, K, 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. - Sage Publications. - 1087-0571. ; 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 coorelation 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. Futhermore, 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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9.
  • Berggren, K., et al. (författare)
  • Partitioning of peptides and recombinant protein-peptide fusions in thermoseparating aqueous two-phase systems : effect of peptide primary structure
  • 2000
  • Ingår i: Journal of Chromatography B. - 0378-4347. ; 743:02-jan, s. 295-306
  • Tidskriftsartikel (refereegranskat)abstract
    • Genetic engineering has been used for fusion of peptides, with different length and composition, on a protein to study the effect on partitioning in an aqueous two-phase system. The system was composed of dextran and the thermoseparating ethylene oxide-propylene oxide random copolymer, EO30PO70. Peptides containing tryptophan, proline, arginine or aspartate residues were fused at the C-terminus of the recombinant protein ZZ-cutinase. The aim was to find effective tags for the lipolytic enzyme cutinase for large-scale extraction. The target protein and peptide tags were partitioned separately and then together in the fusion proteins in order to gain increased understanding of the influence of certain amino acid residues on the partitioning. The salt K2SO4 was used to reduce the charge dependent salt effects on partitioning and to evaluate the contribution to the partition coefficient from the hydrophobic-hydrophilic properties of the amino acid residues. The effect of Trp on peptide partitioning was independent of the difference in primary structure for (Trp)n, (Trp-Pro)n, (Ala-Trp-Trp-Pro)n and was only determined by the number of Trp. The effect of the charged residues, Arg and Asp, was dependent on the surrounding residues, i.e. if they were situated next to Trp or not. The partitioning behaviour observed for the peptides was qualitatively and in some cases also quantitatively the same as for the fusion proteins. The effect of the salts sodium perchlorate and triethylammonium phosphate on the partitioning was also studied. The salt effects observed for the peptides were qualitatively similar to the effects observed for the fusion proteins.
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10.
  • Berggren, K., et al. (författare)
  • Peptide fusion tags with tryptophan and charged residues for control of protein partitioning in PEG-potassium phosphate aqueous two-phase systems
  • 2000
  • Ingår i: Bioseparation (Dordrecht). - 0923-179X. ; 9:2, s. 69-80
  • Tidskriftsartikel (refereegranskat)abstract
    • A partition study with peptides and recombinant proteins in poly(ethylene glycol)4000-potassium phosphate aqueous two-phase systems has been performed. The aim was to study to what extent the insertion of charged residues could affect protein partition in addition to the already observed effects of tryptophan residues. The model proteins used are based on a staphylococcal protein A derivative, Z, and modified by the insertion of peptide tags close to the C-terminus. The tags differed with respect to their content of both Trp, negatively (Asp) and positively charged (Lys) amino acid residues. The same partitioning trends were observed for the peptides and fusion proteins. The effect of Trp residues was to direct the partitioning towards the PEG phase. The insertion of two negatively charged (Asp) residues into a Trp(4)-tag enhanced the partition towards the PEG phase even more. The introduction of positively charged (Lys) residues in addition to Trp residues, on the other hand, pulled the peptide or protein towards the potassium phosphate phase. The partitioning of peptides gave a good qualitative picture of the effect of the peptide on partitioning when fused to the protein. The efficiencies of the tags were calculated based on partitioning of tags and fusion proteins, and tag efficiencies generally varied between 60 and 85%.
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  • Resultat 1-10 av 79
  • [1]234567...8Nästa
 
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