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  • 201.
    Drake, J R
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brunsell, P R
    KTH, Superseded Departments, Alfvén Laboratory.
    Brzozowski, J H
    KTH, Superseded Departments, Alfvén Laboratory.
    Cecconello, M
    KTH, Superseded Departments, Alfvén Laboratory.
    Gravestijn, R M
    KTH, Superseded Departments, Physics.
    Malmberg, J-A
    KTH, Superseded Departments, Alfvén Laboratory.
    Sallander, E
    KTH, Superseded Departments, Alfvén Laboratory.
    First results from the EXTRAP T2R RFP experiment2001In: Europhysics Conf. Abstracts Vol 25A, 2001, p. 457-460Conference paper (Refereed)
  • 202.
    Edholm, Olle
    et al.
    KTH, Superseded Departments, Physics.
    Blomberg, C.
    Stretched exponentials and barrier distributions2000In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 252, no 02-jan, p. 221-225Article in journal (Refereed)
    Abstract [en]

    Non exponential relaxation in complex macromolecular systems may be the consequence of dispersedness giving rise to different free energy barriers for different molecules. An approximate analytic formula that relates the time derivative of the decaying function to a probability distribution for the barrier is derived. From this, so called stretched exponentials, e(-t beta),are obtained from barrier distributions with width k(B)T/beta in energy and some asymmetry towards low energies. They may be represented as double exponential functions. An exact general formula that relates the Fourier transforms of the barrier height distribution and the time decaying function is also derived. This is gives a much more stable method for the numerical determination of the barrier height distribution than direct inversion of the Laplace transform.

  • 203.
    Edholm, Olle
    et al.
    KTH, Superseded Departments, Physics.
    Nordlander, P.
    Chen, W.
    Ohlsson, P. I.
    Smith, M. L.
    Paul, J.
    The effect of water on the Fe3+/Fe2+ reduction potential of heme2000In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 268, no 3, p. 683-687Article in journal (Refereed)
    Abstract [en]

    Hemeproteins can act as catalysts, oxygen carriers or electron conductors. The ferric/ferrous reduction potential E-m7 of iron in the center of the prosthetic group ranges from negative values for peroxidases to an extreme positive value for cytochrome a, with Hb and Mb in the middle [1]. Proteins exercise their influence on E-m7 in several ways: via substituents at the periphery of the chelate structure, via the proximal ligand, and via interaction with the surrounding medium, amino acid side chains, or polar solvents. Work on recombined proteins and ap-substituted free hemes documented that the first two effects are additive [2]. For the third effect, models of the dielectric media on a molecular level have been successfully applied [3-5]. E-m7 has also been empirically correlated to the degree of heme exposure to water [6-8]. The apoprotein/porphyrin and water/porphyrin interfaces are complementary since water molecules fill any empty space in the crevice and surround any pertinent part of heme outside the protein boundary. The present work links to this idea by a combination of statistical mechanics simulations and quantum mechanical calculations comparing heme in water with heme in an apolar environment. Our results show that polarization of the porphyrin pi-electron cloud by the held from water dipoles influences E-m7 The dominant effect of this and other determinates of iron electron availability is perturbations of delocalized electron density in the porphyrin chelate, reproduced by a model where the prosthetic group is treated as a disc of uniform electron density. The present work is also of interest since the interfacial energy constitutes the main barrier for heme-protein Separation [9-11].

  • 204.
    Ekblad, Ulf
    KTH, Superseded Departments, Physics.
    Earth satellites and air and ground-based activities2004Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis, Earth satellites and detection of air andground based activities by Ulf Ekblad of the Physics departmentat the Royal Institute of Technology (KTH), addresses theproblem of detecting military activities in imagery. Examplesof various techniques are presented. In particular, problemsassociated with "novelties" and "changes" in an image arediscussed and various algorithms presented. The imagery usedincludes satellite imagery, aircraft imagery, and photos offlying aircraft.

    The timely delivery of satellite imagery is limited by thelaws of celestial mechanics. This and other information aspectsof imagery are treated. It is e.g. shown that dozens ofsatellites may be needed if daily observations of a specificsite on Earth are to be conducted from low Earth orbit.

    New findings from bioinformatics and studies of small mammalvisual systems are used. The Intersecting Cortical Model (ICM),which is a reduced variant of the Pulse-Coupled Neural Network(PCNN), is used on various problems among which are changedetection. Still much more could be learnt from biologicalsystems with respect to pre- and post-processing as well asintermediate processing stages.

    Simulated satellite imagery is used for determining theresolution limit for detection of tanks. The necessary pixelsize is shown to be around 6 m under the conditions of thissimulation.

    Difference techniques are also tested on Landsat satelliteimagery with the purpose of detecting underground nuclearexplosions. In particular, it is shown that this can easily bedone with 30 m resolution images, at least in the case studied.Satellite imagery from SPOT is used for detecting undergroundnuclear explosions prior to the detonations, i.e. under certainconditions 10 m resolution images can be used to detectpreparations of underground nuclear explosions. This type ofinformation is important for ensuring the compliance of nucleartest ban treaties. Furthermore, the necessity for havingcomplementary information in order to be able to interpretimages is also shown.

    Keywords: Remote sensing, reconnaissance, sensor,information acquisition, satellite imagery, image processing,image analysis, change detection, pixel difference, neuronnetwork, cortex model, PCNN, ICM, entanglement, Earthobservation, nuclear explosion, SPOT, Landsat, verification,orbit.

  • 205.
    Ekblad, Ulf
    et al.
    KTH, Superseded Departments, Physics.
    Kinser, J M
    Theoretical foundation of the intersecting cortical model and its use for change detection of aircraft, cars, and nuclear explosion tests2004In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 84, no 7, p. 1131-1146Article in journal (Refereed)
    Abstract [en]

    The intersecting cortical model (ICM) is a model based on neural network techniques especially designed for image processing. It was derived from several visual cortex models and is basically the intersection of these models, i.e. the common elements amongst these models. The theoretical foundation of the ICM is given and it is shown how the ICM can be derived as a reduced set of equations of the pulse-coupled neural network based upon models proposed by Eckhorn and Reitboeck. Tests of the ICM are presented: one on a series of images of an aircraft moving in the sky; two on car detection; and one on preparations of underground nuclear explosions. The ICM is shown here, in a few examples, to be useful in imagery change detection: aircraft moving against a homogeneous background without precise geometric matching; car on a road; two cars moving in an urban setting without precise geometric matching; and for a linear structure in a complex background. The ICM can be used when the moving objects are not too small and the background is not too difficult. Changes involving larger linear structures can be detected even if the background is not homogeneous.

  • 206.
    Ekblad, Ulf
    et al.
    KTH, Superseded Departments, Physics.
    Kinser, J. M.
    Atmer, Jenny
    KTH, Superseded Departments, Physics.
    Zetterlund, Nils
    KTH, Superseded Departments, Physics.
    Image information content and extraction techniques2004In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 525, no 1-2, p. 397-401Article in journal (Refereed)
    Abstract [en]

    Methods for detecting changes are discussed. The methods are pixel subtraction, edge segment matching, the dipole method, and the Intersecting Cortical Model (ICM). Image information content and the concept of changes in imagery are also discussed.

  • 207.
    Ekblad, Ulf
    et al.
    KTH, Superseded Departments, Physics.
    Kinser, J. M.
    Atmer, Jenny
    KTH, Superseded Departments, Physics.
    Zetterlund, Nils
    KTH, Superseded Departments, Physics.
    The intersecting cortical model in image processing2004In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 525, no 1-2, p. 392-396Article in journal (Refereed)
    Abstract [en]

    The Intersecting Cortical Model (ICM), or ICM algorithm, is presented. It is a reduced set of equations of the Pulse-Coupled Neural Network (PCNN) model. The ICM algorithm is especially designed for enhancing features without sharp edges or straight lines in images. The ICM is tested on a series of images of an aircraft moving in the sky in order to detect its motion. The ICM algorithm is shown to be useful even when there is a deficiency in reference points. In another test, the ICM is applied to two images taken from a helicopter over a town area.

  • 208.
    Ekenberg, Ulf
    et al.
    KTH, Superseded Departments, Physics.
    Mauritz, O.
    Control of spontaneous spin splitting in an asymmetric quantum well with the use of strain and/or magnetic field2001In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 10, no 03-jan, p. 81-85Article in journal (Refereed)
    Abstract [en]

    Spin-orbit coupling combined with inversion asymmetry gives rise to spin splitting even in the absence of an applied magnetic field. The size of this spin splitting can be controlled by changing the degree of asymmetry using a gate voltage. We present here other less obvious ways of controlling the spontaneous spin splitting in a two-dimensional hole gas, where these effects are particularly large. Applying moderate stress can easily decrease the spin splitting by an order of magnitude. The mechanism is the strain-induced energy shift of the heavy-hole and light-hole subbands, which diminishes the degree of band mixing, which is found to be strongly correlated to the spin splitting. An applied magnetic field causes an additional Zeeman splitting, but we find that a magnetic field of 1T can be sufficient to practically erase the difference between a symmetric quantum well (without subband splitting) and an asymmetric quantum well. We have simulated Shubnikov-de Haas oscillations and found that two periodicities in 1/B can occur even for one filled spin-degenerate hole subband.

  • 209.
    Ekman, Mathias
    KTH, Superseded Departments, Physics.
    Structural and dynamical properties of transistio metal systems2000Doctoral thesis, comprehensive summary (Other scientific)
  • 210.
    Ekstrand, Christian
    KTH, Superseded Departments, Physics.
    Schwinger terms from externalfield problems1999Doctoral thesis, comprehensive summary (Other scientific)
  • 211.
    Ekstrand, Christian
    KTH, Superseded Departments, Physics.
    Schwinger terms in external field problems1997Licentiate thesis, comprehensive summary (Other scientific)
  • 212. Ekvall, K.
    et al.
    van der Meulen, P.
    Dhollande, C.
    Berg, Lars-Erik
    KTH, Superseded Departments, Physics.
    Pommeret, S.
    Naskrecki, R.
    Mialocq, J. C.
    Cross phase modulation artifact in liquid phase transient absorption spectroscopy2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 87, no 5, p. 2340-2352Article in journal (Refereed)
    Abstract [en]

    We present experimental results for the cross phase modulation (xpm) induced transient absorption signal in a 1 mm thick fused silica plate using a white light continuum as a probe. The fused silica plate mimics the entrance window of a commercial flow cell commonly used in liquid-phase transient absorption measurements. The experimental results are compared with those obtained theoretically by numerically solving the set of nonlinear coupled wave equations describing the propagation of the pump and the probe. The simulations allow for the different group velocities of the pump and probe pulses, and include the influence of the first and second order dispersion on the continuum probe. From the calculations the physical origin of the complex oscillatory feature observed around the zero time delay of each wavelength of the (chirped) continuum has been accurately identified. The influence of propagation effects arising from the finite thickness of the sample is discussed in great detail, and the necessity to work with thin samples, preferably free-flowing jets, is emphasized. The good agreement between theory and experiment indicates that the xpm artifact may be useful for characterizing the continuum probe, in particular its chirp.

  • 213.
    Ekvall, Karin
    KTH, Superseded Departments, Physics.
    Time resolved laser spectroscopy2000Doctoral thesis, comprehensive summary (Other scientific)
  • 214.
    El-Ansary, Sameh
    et al.
    Distributed Systems Lab, SICS-Swedish Institute of Computer Science.
    Aurell, Erik
    KTH, Superseded Departments, Physics.
    Brand, Per
    Distributed Systems Lab, SICS-Swedish Institute of Computer Science.
    Haridi, Seif
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Experience with a physics-style approach for the study of self properties in structured overlay networks2004In: SELF-STAR: International Workshop on Self-* Properties in Complex Information Systems, May 2004, Bertinoro, Italy, 2004Conference paper (Other academic)
    Abstract [en]

    This paper gives a brief summary of our experience in applying a physics-style approach for analyzing the behavior of structured overlay networks that deploy self-organization and self-repair policies. Such systems are not always simple to model analytically and simulation of scales of interest can be prohibitive. Physicists deal with scale by characterizing a system using intensive variables, i.e. variables that are size independent. The approach proved its substantial usefulness when applied to satisfiability theory and it is the hope that it can be as useful in the field of large-scale distributed systems. We report here our finding of one simple self-organization-related intensive variable, and a more complex self-repair-related intensive variable.

  • 215.
    El-Ansary, Sameh
    et al.
    Distributed Systems Laboratory, SICS Swedish Institute of Computer Science.
    Krishnamurthy, Supriya
    Distributed Systems Laboratory, SICS Swedish Institute of Computer Science.
    Aurell, Erik
    KTH, Superseded Departments, Physics.
    Haridi, Seif
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An Analytical Study of Consistency and Performance of DHTs under Churn2004Report (Other academic)
    Abstract [en]

    In this paper, we present a complete analytical study of dynamic membership (aka churn) in structured peer-to-peer networks. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. We demonstrate that this methodology is infact also well suited to describing structured overlay networks by an application to the Chord system. For any rate of churn and stabilization rates, and any system size, we accurately account for the functional form of: the distribution of inter-node distances, the probability of network disconnection, the fraction of failed or incorrect successor and finger pointers and show how we can use these quantities to predict both the performance and consistency of lookups under churn. Additionally, we also discuss how churn may actually be of different 'types' and the implications this will have for structured overlays in general. All theoretical predictions match simulation results to a high extent. The analysis includes details that are applicable to a generic structured overlay deploying a ring as well as Chord-specific details that can act as guidelines for analyzing other systems.

  • 216. Ellmann, A
    et al.
    Schef, P
    Lundin, P
    Royen, P
    Mannervik, S
    Fritioff, K
    Andersson, P
    Hanstorp, D
    Fischer, C F
    Österdahl, Fabian
    KTH, Superseded Departments, Physics.
    Pegg, D J
    Gibson, N D
    Danared, H
    Kallberg, A
    Radiative lifetime of a bound excited state of Te-2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 25, p. 253002-Article in journal (Refereed)
    Abstract [en]

    We report on the first experimental study of the lifetime of a bound excited state of a negative ion. A new experimental technique was developed and used to measure the radiative lifetime of the 5p(5) P-2(1/2) level of Te-. The experiment was performed in a magnetic storage ring, where a laser beam was applied along one of the straight sections. In the experiment the population of the excited J=1/2 level was probed each time the Te- ions passed through the laser field. A decay curve was built up by sampling the population of the excited level of the Te- ions as a function of time after injection into the ring. A multiconfiguration Dirac-Hartree-Fock calculation was performed in conjunction with the experiment. The calculation yielded a radiative lifetime of 0.45 s, in excellent agreement with the measured value of 0.42(5) s.

  • 217. Eriksson, F.
    et al.
    Johansson, G. A.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Birch, J.
    Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition2002In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 41, no 11, p. 2903-2909Article in journal (Refereed)
    Abstract [en]

    Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second orders, with multilayer periods of 1.692 and 3.381 nm, and layer thickness ratios of 0,471 and 0.237, respectively. At-wavelength soft-x-ray reflectivity measurements were carried out using a reflectometer with a compact soft-x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9 to 113 eV) and flux, in order to stimulate the adatom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required, Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the required ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low-energy (9 eV) Ar ions yielded the most favorable growth condition, limiting the intermixing with a subsistent good surface flatness.

  • 218. Eriksson, F.
    et al.
    Johansson, G. A.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Gullikson, E. M.
    Kreissig, U.
    Birch, J.
    14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window2003In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 28, no 24, p. 2494-2496Article in journal (Refereed)
    Abstract [en]

    Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5degrees measured at the wavelength A = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of similar to1.6 X 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Se sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.

  • 219.
    Eriksson, Marcus
    et al.
    KTH, Superseded Departments, Physics.
    Cahalan, James E.
    Argonne National Laboratory, Reactor Analysis and Engineering Division.
    Inherent Shutdown Capabilities in Accelerator-driven Systems2002In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 29, no 14, p. 1689-1706Article in journal (Refereed)
    Abstract [en]

    The applicability for inherent shutdown mechanisms in accelerator-driven systems (ADS) has been investigated. We study the role of reactivity feedbacks. The benefits, in terms of dynamics performance, for enhancing the Doppler effect are examined. Given the performance characteristics of source-driven systems, it is necessary to manage the neutron source in order to achieve inherent shutdown. The shutdown system must be capable of halting the external source before excessive temperatures are obtained. We evaluate methods, based on the analysis of unprotected accidents, to accomplish such means. Pre-concepted designs for self-actuated shutdown of the external source suggested. We investigate time responses and evaluate methods to improve the performance of the safety system. It is shown that maximum beam output must be limited by fundamental means in order to protect against accident initiators that appear to be achievable in source driven systems. Utilizing an appropriate burnup control strategy plays a key role in that effort.

  • 220.
    Eriksson, Marcus
    et al.
    KTH, Superseded Departments, Physics.
    Piaszczyk, Christopher M.
    Reliability Assessment of the LANSCE Accelerator System1999In: Proceedings of the Workshop on Utilisation and Reliability of High Power Proton Accelerators: 13-15 October 1998, Mito, Japan, 1999, p. 183-Conference paper (Other academic)
  • 221.
    Eriksson, Marcus
    et al.
    KTH, Superseded Departments, Physics.
    Wallenius, Janne
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Cahalan, James E.
    Argonne National Laboratory.
    Tucek, Kamil
    KTH, Superseded Departments, Physics.
    Gudowski, Waclaw
    KTH, Superseded Departments, Physics.
    Safety Analysis of Na and Pb-Bi Coolants in Response to Beam Instabilities2003In: UTILISATION AND RELIABILITY OF HIGH POWER PROTON ACCELERATORS, WORKSHOP PROCEEDINGS, 2003, p. 227-236Conference paper (Refereed)
    Abstract [en]

    A comparative safety study has been performed on sodium vs. lead/bismuth as coolant for accelerator-driven systems. Transient studies are performed for a beam overpower event. We examine a fuel type of recent interest in the research on minor actinide burners, i.e. uranium-free oxide fuel. A strong positive void coefficient is calculated for both sodium and lead/bismuth. This is attributed to the high fraction of americium in the fuel. It is shown that the lead/bismuth-cooled reactor features twice the grace time with respect to fuel or cladding damage compared to the sodium-cooled reactor of comparable core size and power rating. This accounts to the difference in void reactivity contribution and to the low boiling point of sodium. For improved safety features the general objective is to reduce the coolant void reactivity effect. An important safety issue is the high void worth that could possibly drive the system to prompt criticality.

  • 222. Eriksson, Ulf
    et al.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Arrangement relating to an X-ray imaging apparatus for adjusting a number of settings when performing recurrent mammography using recorded settings from recent X-rays2000Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    f a patient has been examined before and the relevant data have been stored in the database (21), the system is activated by entering the patient identity through an input device (20) and a main control unit (15) controls sub-control units (16-19) according to the data, to position an X-ray source (11) at the correct height and to position pedals (13) at the correct height to enclose a breast. The pedals are moved by a motor (19) to compress the breast. AN Independent claim is included for a method of adjusting settings of an X-ray device.

  • 223. Erman, P.
    et al.
    Karawajczyk, A.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Riu, J. R. I.
    Stankiewicz, M.
    Franzen, K. Y.
    Moen, A. W.
    Veseth, L.
    Non Franck-Condon effects in photoionization of molecular oxygen2000In: Physica scripta. T, ISSN 0281-1847, Vol. 62, no 4, p. 294-300Article in journal (Refereed)
    Abstract [en]

    We present a theoretical and experimental analysis of non Franck-Condon effects in photoionization to the b (4)Sigma(g)(-), state of O-2(+). Experimentally, by dispersing the synchrotron radiation induced O-2(+) b (4)Sigma(g)(-) a (IIu)-I-4 fluorescence we derive the b (4)Sigma(g)(-), State vibrational branching ratios in the excitation energy range 21-34 eV. The vibrational branching ratios reveal features in the region 21-28 eV indicating strong non Franck-Condon effects. The experimental results have been analysed by computing ab initio the vibrational population branching ratios using a many-body perturbation method. Additionally the autoionizing neutral states existing in this energy region have been studied. We have computed the energies of the valence states up to an energy of 30 eV their transition moments for excitations from the ground state, and autoionization rates. Our calculations show, that strong non Franck-Condon effects recorded in the branching ratio spectrum (below 25 eV) are actually caused by the narrow 3 sigma(g) --> sigma(u) shape resonance, and its coupling to the 1 pi(u) --> pi(g) channel.

  • 224.
    Ersmark, Tore
    et al.
    KTH, Superseded Departments, Physics.
    Carlson, Per
    KTH, Superseded Departments, Physics.
    Daly, E
    Fuglesang, C
    Gudowska, I
    Lund-Jensen, Bengt
    KTH, Superseded Departments, Physics.
    Nartallo, R
    Nieminen, P
    Pearce, Mark
    KTH, Superseded Departments, Physics.
    Santin, G
    Sobolevsky, N
    Status of the DESIRE project: Geant4 physics validation studies and first results from columbus/ISS radiation simulations2004In: IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORD, 2004, p. 1540-1544Conference paper (Other academic)
    Abstract [en]

    The DESIRE (Dose Estimation by Simulation of the ISS Radiation Environment) project aimes to accurately calculate radiation fluxes and doses to astronauts inside the European Columbus module of the International Space Station using Geant4. Firstly physics benchmark studies have been performed and comparisons made to experimental data and other particle transport programs. This will be followed by a detailed evaluation of the incident radiation fields on the ISS and culminate with the geometry modelling and full-scale flux and dose simulations for the Columbus. Geant4 validation studies are presented here. These concern the angle and energy distribution of particles leaving irradiated targets and of energy depositions in the targets. Comparisons are made between simulations using different Geant4 physics models, experimental data and other particle transport programs. Geant4 using the "Binary Cascade" model for inelastic nucleon reactions performs very well in these comparisons but some issues with other models remain to be resolved if these models are to be used for space radiation shielding applications. Results of Geant4 simulations of the transport of relevant radiation field components through the hull of the Columbus/ISS are also presented.

  • 225.
    Ersmark, Tore
    et al.
    KTH, Superseded Departments, Physics.
    Carlson, Per
    KTH, Superseded Departments, Physics.
    Daly, E.
    Fuglesang, C.
    Gudowska, I.
    Lund-Jensen, Bengt
    KTH, Superseded Departments, Physics.
    Nartallo, R.
    Nieminen, P.
    Pearce, Mark
    KTH, Superseded Departments, Physics.
    Santin, G.
    Sobolevsky, N.
    Status of the DESIRE project: Geant4 physics validation studies and first results from columbus/ISS radiation simulations2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 4, p. 1378-1384Article in journal (Refereed)
    Abstract [en]

    The Dose Estimation by Simulation of the ISS Radiation Environment (DESIRE) project aims to accurately calculate radiation fluxes and doses to astronauts inside the European Columbus module of the International Space Station using Geant4. Since Geant4 has not been previously used for this type of application it needs to be validated. This will be followed by a detailed evaluation of the incident radiation fields on ISS and culminate with the geometry modeling and full-scale flux and dose simulations for Columbus. Geant4 validation studies and comparisons to other tools are presented. These concern the angle and energy distributions of particles leaving irradiated targets and of energy depositions in the targets. Comparisons are made between simulations using different Geant4 physics models, experimental data, and other particle transport programs. Geant4 using the Binary Cascade model for inelastic nucleon reactions performs very well in these comparisons, but some issues with other models remain to be resolved if they are to be used for space radiation shielding applications. Results of Geant4 simulations of the transport of some relevant radiation field components through the hull of a simplified model of Columbus are also presented.

  • 226.
    Evekull, D.
    et al.
    Acreo AB, Kista.
    Johansson, Sandra
    KTH, Superseded Departments, Physics.
    Bjurshagen, Stefan
    Acreo AB, Kista.
    Olson, M.
    Acreo AB, Kista.
    Koch, R.
    Acreo AB, Kista.
    Laurell, Fredirk
    KTH, Superseded Departments, Physics.
    Polymer encapsulated miniature Nd:YAG lasers2003In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 39, no 20, p. 1446-1448Article in journal (Refereed)
    Abstract [en]

    A continuation of the previously introduced microstructured silicon carrier concept for diode-pumped solid-state lasers is presented, using novel heat-conducting polymers as a carrier. The most prominent features of the silicon carrier concept are maintained, adding to the mass production possibilities of the inexpensive polymers. The first experiments, using a continuous wave Nd:YAG microchip laser, have given an output power of 2 W at 1064 nm, showing the potential of this new approach.

  • 227.
    Evekull, D.
    et al.
    Acreo AB, Kista.
    Rydholm, J.
    Cobolt AB, Stockholm.
    Bjurshagen, Stefan
    KTH, Superseded Departments, Physics.
    Bäcklin, L.
    Acreo AB, Kista.
    Kindlundh, M.
    Acreo AB, Kista.
    Kjellberg, L.
    Acreo AB, Kista.
    Koch, R.
    Acreo AB, Kista.
    Olson, M.
    Acreo AB, Kista.
    High power Q-switched Nd:YAG laser mounted in a silicon microbench2004In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 36, no 5, p. 383-385Article in journal (Refereed)
    Abstract [en]

    A high-power Q-switched Nd:YAG/Cr:YAG laser mounted in a silicon microbench is presented. It reaches an average output power well above 2 W and the pulse width is in the order of 1.4 ns. The use of microstructure silicon carriers provides efficient thermal control, compact integration and alignment of active and passive optical components.

  • 228. Fahlander, C.
    et al.
    Palacz, M.
    Rudolph, D.
    Sohler, D.
    Blomqvist, J.
    Lagergren, K.
    Norlin, L. O.
    Nyberg, J.
    Cederwall, Bo
    KTH, Superseded Departments, Physics.
    Johnson, Arne
    KTH, Superseded Departments, Physics.
    Kerek, A.
    Klamra, Wlodzimierz
    KTH, Superseded Departments, Physics.
    Wolinska, M.
    et al,
    Excited states in Sn-103: Neutron single-particle energies with respect to Sn-1002001In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 6302, no 2Article in journal (Refereed)
    Abstract [en]

    Gamma-ray lines from Sn-103 have been identified for the first time using EUROBALL and ancillary detectors. The level scheme of Sn-103 has been established by means of particle-gated gamma gamma coincidences. The energy spacing between the g(7/2) and d(5/2) neutron single-particle orbitals is determined from the excited states in Sn-103.

  • 229. Feve, J. P.
    et al.
    Pacaud, O.
    Boulanger, B.
    Menaert, B.
    Hellstrom, J.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Widely and continuously tunable optical parametric oscillator based on a cylindrical periodically poled KTiOPO4 crystal2001In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 26, no 23, p. 1882-1884Article in journal (Refereed)
    Abstract [en]

    We report on what is to our knowledge the first realization of a quasi-phase-matched optical parametric oscillator (OPO) based on a crystal with a cylindrical shape. The main reason for interest in this device is its broad, continuous tuning. In experiments with a 1064-nm pump, the signal tuning range was equal to 525 nn (1515-2040 nm), and the corresponding idler was continuously tuned over 1340 nn (2220-3560 nm). The angular tuning was 26 degrees, with only a minor variation of the OPO threshold over the entire tuning range.

  • 230. Fischer, S. M.
    et al.
    Lister, C. J.
    Balamuth, D. P.
    Bauer, R.
    Becker, J. A.
    Bernstein, L. A.
    Carpenter, M. P.
    Durell, J.
    Fotiades, N.
    Freeman, S. J.
    Garrett, P. E.
    Hausladen, P. A.
    Janssens, R. V. F.
    Jenkins, D.
    Leddy, M.
    Ressler, J.
    Schwartz, J.
    Svelnys, D.
    Sarantites, D. G.
    Seweryniak, D.
    Varley, B. J.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Alignment delays in the N = Z nuclei Kr-72, Sr-76, and Zr-802001In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 8713, no 13Article in journal (Refereed)
    Abstract [en]

    The ground state rotational bands of the N = Z nuclei Kr-72, Sr-76, and Zr-80 have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. Kr-72 shows the most marked effect. It has been widely suggested that these delayed alignments arise from np-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation.

  • 231. Fisun, V. V.
    et al.
    Balkashin, O. P.
    Najdyuk, Y. G.
    Bashlakov, D. L.
    Yanson, I. K.
    Korenivski, Vladislav
    KTH, Superseded Departments, Physics.
    Shekhter, R.
    Features in nonlinear electroconductivity of nanocontacts on the base of ferromagnetic metals (Co and Fe)2004In: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 26, no 11, p. 1439-1446Article in journal (Refereed)
    Abstract [en]

    For normal metal-ferromagnet (N-F) point contacts, a step-like change of the resistance is observed at reaching of the current density similar to 10(9) A/cm(2). This is observed only for the case, when electron flow is directed from the normal metal to the ferromagnetic one, and is connected with magnetization reversal in the microconstriction at high transport-current density. Increasing of a magnetic field leads to the shift of observed peculiarity into the higher-current region that testifies its magnetic origin. As shown, the observed effect, which is widely studied in the recent time in N-F sandwiches, has more common character and requires the presence only N-F boundary and high-current density. The increasing of the amplitude of the resistance peculiarity is observed at electromagnetic radiation with a frequency of 3.10(9) Hz that testifies stimulating influence of the HF-radiation on the dynamics of precessing spins in the contacts at issue.

  • 232.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Formation of thermally stable chemical composition gratings in optical fibers2002In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 19, no 8, p. 1759-1765Article in journal (Refereed)
    Abstract [en]

    Experimental results and a discussion of possible chemical pathways in the formation of thermally stable chemical composition gratings in optical fibers are presented. Gratings are formed through high-temperature treatment of UV-exposed hydrogen-loaded fibers. The final refractive-index modulation is ascribed to variations in fluorine concentration attained by periodically increased diffusion of fluorine. The mechanism behind this increase is the formation of mobile hydrogen fluoride from chemical reactions of fluorine and UV-induced hydroxyl, which occur with the spatial periodicity of the UV pattern. A hydroxyl-assisted increase in fluorine diffusion has been verified by time-of-flight secondary-ion mass spectroscopy. Formation of ultrastable grating by periodic variation of oxygen concentration through diffusion of molecular water is also discussed.

  • 233.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Growth dynamics of chemical composition gratings in flourine-doped silica optical fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, p. 1974-1976Article in journal (Refereed)
    Abstract [en]

    The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700 degrees C, before development at a fixed temperature of 1000 degrees C. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 degrees C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.

  • 234.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    High temperature miniature oven with low thermal gradient for processing fiber Bragg gratings2001In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 72, no 8, p. 3458-3461Article in journal (Refereed)
    Abstract [en]

    A miniature oven for processing fiber Bragg gratings in excess of 1000 degreesC has been projected and evaluated. The dimensions and the design of the oven allow rapid insertion and removal of the fiber during heating and minimizes mechanical degradation of the fiber. The 22 mm long oven has a flat zone at 1000 degreesC of 16 mm with a temperature variation of less than 2% and 20 mm with a temperature variation of 10%. The long term stability (hours) is +/- 20 degreesC measured at the center of the oven at 1000 degreesC. Rapid heating is possible, and heating optical fibers to 1000 degreesC shows a delay of approximately 400 ms before the core reaches thermal equilibrium.

  • 235.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Thermal stability of chemical composition gratings in fluorine-germanium-doped silica fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 12, p. 1016-1018Article in journal (Refereed)
    Abstract [en]

    A model based on diffusion of dopants in a periodic structure has been applied to describe thermal decay of chemical composition gratings in fluorine-germanium-doped silica fibers. The good agreement between previously reported values and the diffusion coefficients derived here from experiments and models in the 1000 - 1200 degreesC temperature range indicate that fluorine diffusion is the main mechanism of grating decay. Experimental results also indicate that the presence of phosphorous significantly increases the decay rate of chemical composition gratings.

  • 236.
    Fokine, Michael
    et al.
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Large increase in photosensitivity through massive hydroxyl formation2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 5, p. 302-304Article in journal (Refereed)
    Abstract [en]

    We report a large increase in photosensitivity of germanium-doped silicate fibers by rapid heat treatment of hydrogen-loaded fibers at 1000 degrees C before exposure of the fibers to 242-nm radiation. The increase in photosensitivity is compared with thermally induced absorption caused by introduction of massive amounts of hydroxyl species. The absorption loss was measured to be 0.02 dB/cm mol.% OH at 1.55 mu m. Strong gratings (Delta n > 1 x 10(-4)) in germanium-free phosphorous-doped fibers in the presence of 242-nm radiation have also been manufactured by this technique.

  • 237.
    Fokine, Mikael
    et al.
    KTH, Superseded Departments, Physics.
    Nilsson, Lars-Erik
    Claesson, Åke
    Berlemont, D
    Kjellberg, L
    Krummenacher, L
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Integrated fiber Mach-Zehnder interferometer for electro-optic switching2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 18, p. 1643-1645Article in journal (Refereed)
    Abstract [en]

    Molten alloys under high pressure were used to obtain fibers with long internal electrodes that are solid at room temperature. An integrated Mach-Zehnder interferometer was constructed from a twin-core twin-hole fiber that permitted application of an electric field preferentially to one of the cores. Good stability and a switching voltage of 1.4 kV were measured with a 1-m-long fiber device with a quadratic voltage dependence.

  • 238.
    Forsblom, Mattias
    KTH, Superseded Departments, Physics.
    Simulation of lattice defacts im metals2002Licentiate thesis, comprehensive summary (Other scientific)
  • 239.
    Forsblom, Mattias
    et al.
    KTH, Superseded Departments, Physics.
    Sandberg, Nils
    KTH, Superseded Departments, Physics.
    Grimvall, Göran
    KTH, Superseded Departments, Physics.
    Anharmonic effects in the heat capacity of Al2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 16, p. 165106-1-165106-6Article in journal (Refereed)
    Abstract [en]

    The vibrational heat capacity of aluminum at fixed volume is studied in molecular dynamics and Monte Carlo simulations, using effective interactions due to Ercolessi and Adams, Mishin , and Mei and Davenport. When experimental data are reduced to represent the classical vibrational heat capacity at fixed volume, the result is within about +/-2 % of 3k(B)/atom up to the melting temperature of Al, thus suggesting small anharmonic effects. Our simulations of the heat capacity are in good agreement with experiments, but also show that anharmonic effects are in fact large, with a cancellation between the low-order linear term in the temperature T and higher-order terms.

  • 240. Forsblom, Mattias
    et al.
    Sandberg, Nils
    KTH, Superseded Departments, Physics.
    Grimvall, Göran
    Energies and vibrational entrpoies of stacking faults and dislocation in Al and CuArticle in journal (Other academic)
  • 241.
    Forsblom, Mattias
    et al.
    KTH, Superseded Departments, Physics.
    Sandberg, Nils
    KTH, Superseded Departments, Physics.
    Grimvall, Göran
    KTH, Superseded Departments, Physics.
    Vibrational entropy of dislocations in Al2004In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 84, no 6, p. 521-532Article in journal (Refereed)
    Abstract [en]

    The region nearest to a lattice defect must be described by an atomistic model, while a continuum model suffices further away from the defect. We study such a separation into two regions for an edge dislocation. In particular we focus on the excess defect energy and vibrational entropy, when the dislocation core is described by a cluster of about 500-100 atoms, embedded in a large discrete and relaxed, but static, lattice. The interaction between the atoms is given by a potential of the embedded-atom model type referring to Al. The dynamic matrix of the vibrations in the cluster is fully diagonalized. The excess entropy DeltaS near the core has positive and negative contributions, depending on the sign of the local strain. Typically, DeltaS/k(B) approximate to 2 per atomic repeat length along the dislocation core in fcc Al. In the elastic continuum region far from the dislocation core the excess entropy shows the same logarithmic divergence as the elastic energy. Although the work refers to a specific material and defect type, the results are of a generic nature.

  • 242.
    Fragemann, Anna
    KTH, Superseded Departments, Physics.
    Quasi-Phasematched nonlinear processes in KTiOPO4 isomorphs2003Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis explores the use of nonlinear crystals from theKTiOPO4(KTP) family with the aim to extend the possibleapplications for laser sources and to gain more knowledge aboutthe material’s benefits and limits. The work focussed onoptical parametric oscillators (OPOs) and optical parametricamplifiers (OPAs), which employ second order nonlinearprocesses. Both devices transfer energy from a laser beam at aparticular wavelength to a different wavelength, which istuneable. In OPOs two new beams at different wavelengths aregenerated, whereas in OPAs an existing weak beam is amplified.The essential part of these devices, which enables theoccurrence of the energy conversion, is a nonlinear crystal. Inthis work the ferroelectric crystals KTP and RbTiOPO4(RTP) have been utilized.

    By modifying the material’s structure,quasi-phasematching can be obtained, which is a crucialrequirement for achieving efficient energy conversion betweenthe incident and the generated waves. The fabrication ofquasi-phasematched crystals is dependent on the controlledreversion of the material’s spontaneous polarisation,which is accomplished by periodic electric field poling.

    Nanosecond pulses of more than 200 kW were generated in the“eye-safe”region by employing a double pass OPA.Small signal gains exceeding 75 dB were obtained for anessentially diffraction limited beamwithout spectralbroadening of the seed. By subsequent signal coupling intofibres substantial broadening was accomplished. A systematicmeasurement series of several RTP crystals allowed us toaccurately determine the wavelength and temperature dispersionof the refractive index, which are two essential requirementsfor further employment of this material. The OPOs based on RTPwere widely tuneable by controlling the temperature. It wasalso concluded that RTP behaves similar to KTP in parametricdevices, thus being a material, which can sustain high powers,possesses large nonlinear coefficients and can operate in abroad wavelength region.Efficient Raman oscillation concurrent with parametricoscillation was observed and analysed in several KTP samples.This gave further insight into the processes taking placeinside the material when performing as a frequency converter,if the generated idler lies in the absorption band.This thesis also covers the investigation of afemtosecond optical parametric chirped pulse amplifier.Temporally stretched seed pulses were amplified to 85 µJ,resulting in a gain above 60 dB, and subsequent recompressionresulted in 270 fs pulses.

    Keywords:nonlinear optics, KTiOPO4, optical parametric oscillator, optical parametricamplifier, RbTiOPO4, quasi-phasematching, electric field poling,stimulated Raman scattering.

  • 243.
    Fragemann, Anna
    et al.
    KTH, Superseded Departments, Physics.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Karlsson, Gunnar
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    High-peak power nanosecond optical parametric amplifier with periodically poled KTP2003In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 11, no 11, p. 1297-1302Article in journal (Refereed)
    Abstract [en]

    A two-stage optical parametric amplifier generating 5 ns 208 kW peak power pulses in the spectral region at 1.535 mum in a diffraction-limited beam was realized in a single periodically poled KTP crystal. The maximum small-signal gain for the two stages reached 75dB and the total conversion efficiency was 30%. An analysis of the small-signal gain dependence on the M-2 of the pump beam is presented for the collinear and noncollinear OPA. Efficient spectral broadening of the signal was demonstrated in short pieces of single-mode telecommunication fiber.

  • 244.
    Fragemann, Anna
    et al.
    KTH, Superseded Departments, Physics.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Second-order nonlinearities in the domain walls of periodically poled KTiOPO42004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 3, p. 375-377Article in journal (Refereed)
    Abstract [en]

    The domain wall regions in periodically poled KTiOPO4 crystals were examined and found to give rise to phasematched second harmonic generation in the Cerenkov directions. This phenomenon is caused by the nonlinear coefficients d(11) and d(12), which are not present in single domain regions, but are nonzero at and close to domain walls. The appearance of these nonlinearities is attributed to strain, produced by the domain inversion process and results in the creation of a dc piezoelectric field.

  • 245.
    Fragemann, Anna
    et al.
    KTH, Superseded Departments, Physics.
    Pasiskevicius, Valdas
    KTH, Superseded Departments, Physics.
    Nordborg, Jenni
    KTH, Superseded Departments, Physics.
    Hellström, Jonas
    KTH, Superseded Departments, Physics.
    Karlsson, Håkan
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Frequency converters from visible to mid-infrared with periodically poled RbTiOPO42003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 15, p. 3090-3092Article in journal (Refereed)
    Abstract [en]

    Electric-field poling has been used to fabricate quasi-phase-matched frequency converters in RbTiOPO4. A more accurate Sellmeier equation has been obtained for wavelengths between 0.43 and 3.4 mum. The dispersion of the thermo-optic coefficient for n(z) refractive index has been derived in the near- to mid-infrared spectral region. The nonlinear performance of periodically poled RbTiOPO4 obtained in the infrared optical parametric devices is comparable to that of periodically poled KTiOPO4.

  • 246. Francke, T
    et al.
    Peskov, Vladimir
    KTH, Superseded Departments, Physics.
    Rodionov, I
    Fonte, P
    High rate (up to 10(5) Hz/cm(2)), high position resolution (30 mu m) photosensitive RPCs2004In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 533, no 1-2, p. 163-168Article in journal (Refereed)
    Abstract [en]

    In many applications there is a need for high position resolution VUV and UV imagers. For these applications we have developed and successfully tested 1D and 2D VUV imaging detectors based on microgap RPCs. Two versions of these detectors were extensively tested: one filled with photosensitive vapours and the other one with the GaAs cathode coated by a 400 nm thick CsI layer. The main feature of these detectors is the high position resolution-30 mum in digital form. Additionally, it is spark-protected and can operate at high counting rates (up to 10(5) Hz/cm(2)). In this study the results in application for these detectors for spectroscopy are presented.

  • 247.
    Fransson, Jonas
    et al.
    KTH, Superseded Departments, Physics.
    Eriksson, O.
    Sandalov, I.
    Transport through quasi-degenerate states in coupled quantum dots2004In: Photonics and Nanostructures - Fundamentals and Applications, ISSN 1569-4410, Vol. 2, no 1, p. 11-21Article in journal (Refereed)
    Abstract [en]

    By means of a general method for treating mesoscopic systems with strong internal correlations, transport properties through a set of quasi-degenerate transitions in the interacting region, or active element (AE), are considered. It is shown that the behaviour of the AE drastically changes as the couplings to the contacts are varied from the strong to the weak coupling limit. These changes strongly influence the transport properties of the system, from a single increase of the current to a staircase form with unequally large steps. In the present study, kinematic interactions, non-equilibrium populations numbers and dependence on the bias voltage has been included in the treatment of the local properties of the AE. Analytical results for the equilibrium situation are presented as well as a derivation of the corresponding non-equilibrium quantities. Results from self-consistent numerical calculations of the considered case are presented.

  • 248.
    Fransson, Jonas
    et al.
    KTH, Superseded Departments, Physics.
    Sandalov, I
    Eriksson, O
    A perfect spin-filter quantum dot system2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 16, p. L249-L254Article in journal (Refereed)
    Abstract [en]

    The discovery of a novel effect in the transport through a QD spin-dependently coupled to magnetic contacts is reported. For a finite range of source-drain voltages the spin projections of the current cancel exactly, resulting in a completely suppressed output current. The spin down current behaves as one normally expects whereas the spin up current becomes negative. As the source-drain voltage is increased the spin up current eventually becomes positive. Thus, tuning the source-drain voltage such that the spin up current vanishes will result in a perfect spin filter.

  • 249.
    Franzén, Ken Yoshiki
    KTH, Superseded Departments, Physics.
    Formation and fragmentation dynamics of superexcited molecules1998Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    A series of experimental studies on superexcited smallmolecules have been performed giving new information on theformation and fragmentation dynamics of small superexcitedmolecules. Highly monochromatized synchrotron radiation hasbeen applied in the 5-30 eV energy region, corresponding tovalence shell excitation, and in the 60-600 eV region,corresponding to core shell excitation, to reach these neutralstates above the ionization potential.

    The superexcited states in the irradiated N2and CO and molecules have been probed in thevalence excitation region by detecting dispersed fluorescencewith vibrational resolution emitted from subsequently producedfragments using a liquid nitrogen cooled CCD detector togetherwith a grating spectrometer. The measurements have resulted inthe discovery of non-Rydberg doubly excited resonances. Thesestates are reached directly by simultaneous promotion of twovalence electrons to in space close lying orbitals or viapotential curve crossings. The experimental results have beencomparedwith the results from extensive calculations.

    A time-of-flight mass spectrometer has been built and usedto measure branching ratios and kinetic energy distributions ofionic fragments produced from molecules in core excited valenceand Rydberg states. The measurements have been performed on CO,OCS and CS2molecules using different coincidence and angularresolved techniques. The results include new information on thegeometry and fragmentation dynamics of these highly excitedmolecules. Monte Carlo simulations have been performed tointerpret some of the data suggesting new models for thefragmentation dynamics. Strong evidences for state and siteselectivity in the fragmentation dynamics of core excitedmolecules have been obtained.

  • 250. Freund, Martin
    et al.
    Ohlsson, Tommy
    KTH, Superseded Departments, Physics.
    Matter enhanced neutrino oscillations with a realistic earth density profile2000In: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 15, no 13, p. 867-874Article in journal (Refereed)
    Abstract [en]

    We have investigated matter enhanced neutrino oscillations with a mantle-core-mantle step function and a realistic Earth matter density profile in both a two- and a three-neutrino scenario. We found that the realistic Earth matter density profile can be well approximated with the mantle-core-mantle step function and that there could be an influence on the oscillation channel nu(mu) --> nu(tau) due to resonant enhancement of one of the mixing angles.

2345678 201 - 250 of 938
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