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  • 901.
    Wiklund, Martin
    et al.
    KTH, Superseded Departments, Physics.
    Nilsson, S.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Ultrasonic trapping in capillaries for trace-amount biomedical analysis2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 1, p. 421-426Article in journal (Refereed)
    Abstract [en]

    A longitudinal hemispherical standing-wave ultrasonic trap for size-selective separation of microspheres in small-diameter capillaries is described. The trap utilizes the competition between acoustic radiation forces and viscous drag forces on spheres suspended in a liquid inside 20-75-mum-diam fused silica capillaries. Experiments performed on 3.0- and 4.7-mum-diam latex spheres demonstrate the principles of trapping and verify the theoretically calculated size-dependent forces on the spheres. The spheres are detected by the use of laser-induced fluorescence. The goal is to use the trap for separation and ultrahigh-sensitivity detection of trace amounts of proteins and other macromolecules containing two antigenic sites, by binding the target molecule with high specificity to antibody-coated latex spheres.

  • 902.
    Wiklund, Martin
    et al.
    KTH, Superseded Departments, Physics.
    Spegel, P.
    Nilsson, S.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Ultrasonic-trap-enhanced selectivity in capillary electrophoresis2003In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 41, no 4, p. 329-333Article in journal (Refereed)
    Abstract [en]

    We combine ultrasonic trapping and capillary electrophoresis (CE) with the goal to detect ultra-low concentrations of proteins via size-selective separation and enrichment of antibody-coated latex spheres. An 8.5 MHz standing ultrasonic wave is longitudinally coupled into the sub-100-muM diam capillary of the CE system. Competition between acoustic and viscous forces result in inflow separation of mum-diam spheres according to their size. Experiments separating 2.8- and 2.1-mum-diam fluorescent latex particles, which model a protein-specific immunocomplex/free particle mixture, indicate a potential improvement of the concentration limit of detection of 10(4) compared to current CE systems. Theoretical calculations show room for further improvement.

  • 903.
    Wiklund, Martin
    et al.
    KTH, Superseded Departments, Physics.
    Toivonen, J.
    Tirri, M.
    Hanninen, P.
    Hertz, Hans M.
    KTH, Superseded Departments, Physics.
    Ultrasonic enrichment of microspheres for ultrasensitive biomedical analysis in confocal laser-scanning fluorescence detection2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 2, p. 1242-1248Article in journal (Refereed)
    Abstract [en]

    An ultrasonic particle concentrator based on a standing-wave hemispherical resonator is combined with confocal laser-scanning fluorescence detection. The goal is to perform ultrasensitive biomedical analysis by concentration of biologically active microspheres. The standing-wave resonator consists of a 4 MHz focusing ultrasonic transducer combined with the optically transparent plastic bottom of a disposable 96-well microplate platform. The ultrasonic particle concentrator collects suspended microspheres into dense, single-layer aggregates at well-defined positions in the sample vessel of the microplate, and the fluorescence from the aggregates is detected by the confocal laser-scanning system. The biochemical properties of the system are investigated using a microsphere-based human thyroid stimulating hormone assay.

  • 904. Willschutz, H G
    et al.
    Altstadt, E
    Weiss, F P
    Sehgal, Balraj
    KTH, Superseded Departments, Physics.
    Insights from the FOREVER-Programme and the accompanying finite element calculations2004In: ATW. Internationale Zeitschrift für Kernenergie, ISSN 1431-5254, Vol. 49, no 5, p. 345-+Article in journal (Refereed)
    Abstract [en]

    To obtain an improved understanding and knowledge of the melt pool convection thermal loads, the vessel creep, and vessel failure modes occurring during the late phase of a core melt down accident the FOREVER-experiments have been performed at the Royal Institute of Technology, Stockholm. These experiments simulated the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurised vessel scenario. A Finite Element model was developed simulating melt pool convection and calculating the temperature field within the melt pool and within the vessel wall. After performing successful pre- and post-test calculations, a discussion about the lessons learned from the experiments and the analyses led to the idea of providing a vessel support and an external water-flooding device.

  • 905. Wilson, A. N.
    et al.
    Wadsworth, R.
    Smith, J. F.
    Freeman, S. J.
    Leddy, M. J.
    Chiara, C. J.
    Fossan, D. B.
    LaFosse, D. R.
    Starosta, K.
    Devlin, M.
    Sarantites, D. G.
    Wilson, J. N.
    Carpenter, M. P.
    Davids, C. N.
    Janssens, R. V. F.
    Seweryniak, D.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    High-spin structures and alignment properties in Ce-1262001In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 6305, no 5Article in journal (Refereed)
    Abstract [en]

    Excited states in Ce-126 have been observed with the GAMMASPHERE gamma -ray detector array, used in conjunction with the MICROBALL charged-particle detector. The reaction Zn-64(Zn-64, xpn alpha) (beam energy 260 MeV) was used to populate a wide range of nuclei in the neutron-deficient region with A approximate to 120. Ce-126 was populated via the 2p evaporation channel. The three previously observed bands have been extended to higher spins and some other structures have been identified. The yrast band shows evidence of a delayed neutron alignment occurring at a rotational frequency omega approximate to0.5 MeV/(h) over bar as observed in the neighboring odd-A nucleus Pr-127. One of the two excited bands shows evidence for a similar crossing at a slightly lower frequency and also exhibits a sudden gain in alignment at omega =0.57 MeV/(h) over bar. The third band may involve the coupling of a gamma -vibrational state. All three rotational bands are discussed in terms of standard and extended cranked shell model calculations.

  • 906.
    Wittborn, Jesper
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Canalias, Carlota
    KTH, Superseded Departments, Materials Science and Engineering.
    Rao, K. V.
    KTH, Superseded Departments, Materials Science and Engineering.
    Clemens, Rosalie
    KTH, Superseded Departments, Physics.
    Karlsson, Håkan
    KTH, Superseded Departments, Physics.
    Laurell, Fredrik
    KTH, Superseded Departments, Physics.
    Nanoscale imaging of domains and domain walls in periodically poled ferroelectrics using atomic force microscopy2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 9, p. 1622-1624Article in journal (Refereed)
    Abstract [en]

    We use the inverse piezoelectric effect for high-resolution imaging of artificially produced ferroelectric domains in periodically poled potassium titanium phosphate, KTiOPO4, and lithium niobate, LiNbO3, crystals using a modified atomic force microscope (AFM). By monitoring the vertical as well as the lateral deflection of the AFM tip, details of the domains and the domain walls were obtained at 1 nm resolution. With this approach we determine the domain wall width to be 20-80 nm for KTiOPO4 and about 150 nm for LiNbO3. The above technique is of importance in tailoring ferroelectric crystals for frequency conversion of lasers and studies of domain walls in ferroelectric and its magnetic analogs.

  • 907.
    Wohlert, Jakob
    KTH, Superseded Departments, Physics.
    Electrostatics in lipid membranes: a computer simulation study2004Licentiate thesis, comprehensive summary (Other scientific)
  • 908.
    Wohlert, Jakob
    et al.
    KTH, Superseded Departments, Physics.
    Edholm, Olle
    KTH, Superseded Departments, Physics.
    The Range and Shielding of Dipole-Dipole Interactions in Phospholipid Bilay2004In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 87, p. 2433-Article in journal (Refereed)
  • 909.
    Wolborski, Maciej
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Bakowski, Mietek
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Klamra, Wlodzimierz
    KTH, Superseded Departments, Physics.
    Electrical characterisation of gamma and UV irradiated epitaxial 1.2 kV 4H-SiC PiN diodes2004In: SILICON CARBIDE AND RELATED MATERIALS 2003, PTS 1 AND 2, 2004, Vol. 457-460, p. 1487-1490Conference paper (Refereed)
    Abstract [en]

    Epitaxial 4H-SiC 1.2 kV PiN diodes have been evaluated using IN measurement techniques after exposure to 1, 2, 3.8 and 10 Mrad irradiation from the Co-60 gamma source. After accumulated gamma dose of 10 Mrad the diodes were exposed to UV irradiation. The forward and reverse diode characteristics were measured successively in the temperature range from RT to 350 degrees C. The leakage current increases with gamma irradiation dose up to about 4 Mrads by a factor of 20 compared to the pre-irradiation values. After an accumulated dose of 10 Mrads the leakage current decreases by about one order of magnitude but is still about 2-3 times larger than before irradiation. The decrease in reverse current is accompanied by the appearance of the high noise. The apparent thermal activation energies increase with the gamma irradiation dose and show a relatively large spread in values especially at lower temperatures (150 degrees C to 250 degrees C).

    The UV irradiation has a positive effect on the IN characteristics. The reverse current is lowered by one order of magnitude compared to the pre-irradiation level. The large noise in the leakage current is absent after UV exposure. The low energy level of 0.2 eV appears clearly in the temperature range between 150 degrees C and 250 degrees C after the UV irradiation. The thermal activation energy of 0.91 eV has been determined for the deep energy level in the temperature range from 250 degrees C to 350 degrees C. The values of the thermal activation energies are very consistent between diodes and show less spread as a function of the applied voltage. The Poole-Frenkel dependence with local field enhancement can be fitted to the 0.91 eV level.

  • 910.
    Xiao, Ying
    KTH, Superseded Departments, Physics.
    Basic studies of advanced magneto-optic media and MAMMOS- modulated magnetically amplified M-O system1998Doctoral thesis, comprehensive summary (Other scientific)
  • 911. Xu, F. R.
    et al.
    Satula, W.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Quadrupole pairing interaction and signature inversion2000In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 669, no 02-jan, p. 119-134Article in journal (Refereed)
    Abstract [en]

    The signature inversion in the pi h(11/2) x vh(11/2) rotational bands of the odd-odd Cs and La isotopes and the pi h(11/2) x vi(13/2) bands of the odd-odd Tb, Ho and Tm nuclei is investigated using pairing and deformation self-consistent mean-field calculations, The model can rather satisfactorily account for the anomalous signature splitting provided that spin assignments in some of the bands are revised. Our calculations show that signature inversion can appear already at axially symmetric shapes. It is found that this is due to the contribution of the (lambda mu) = (22) component of the quadrupole-pairing interaction to the mean-field potential.

  • 912. Xu, F. R.
    et al.
    Walker, P. M.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Limit to high-spin isomerism in hafnium isotopes2000In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 6201, no 1Article in journal (Refereed)
    Abstract [en]

    Configuration-constrained nuclear shape calculations are used to show that reinforcing neutron and proton orbital structures create exceptional conditions for the formation of multiquasiparticle isomers in neutron-rich hafnium isotopes, with axially symmetric, prolate shapes. Highly excited, long-lived states are predicted. However, at angular momenta close to 40 (h) over bar, orbital alignment effects for collective oblate rotation lend to a deep potential minimum that competes energetically with the prolate multiquasiparticle states.

  • 913. Xu, F. R.
    et al.
    Walker, P. M.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Oblate stability of A approximate to 110 nuclei near the r-process path2002In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 65, no 2Article in journal (Refereed)
    Abstract [en]

    Even-even A approximate to 110 nuclei approaching the astrophysical r-process path have been investigated using both the cranked and the configuration-constrained shell models. The calculations show that, with increasing neutron number in the Zgreater than or equal to40 nuclides, nuclear shapes evolve from prolate, through triaxial to oblate deformations. In contrast to other regions of the nuclear chart, pronounced oblate shapes dominate the collective rotation from ground states to very high spins (Isimilar to40), when Ngreater than or equal to70. The stability of the oblate shapes is due to the simultaneous upper-shell neutron and proton Fermi surfaces, reinforced by the rotation alignment behavior of both nucleon types. Configuration-constrained calculations predict the coexistence of well-deformed prolate and oblate multiquasiparticle (isomeric) states.

  • 914. Xu, F. R.
    et al.
    Zhao, E. G.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Walker, P. M.
    Enhanced stability of superheavy nuclei due to high-spin isomerism2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 25, p. 252501-Article in journal (Refereed)
    Abstract [en]

    Configuration-constrained calculations of potential-energy surfaces in even-even superheavy nuclei reveal systematically the existence at low excitation energies of multiquasiparticle states with deformed axially symmetric shapes and large angular momenta. These results indicate the prevalence of long-lived, multiquasiparticle isomers. In a quantal system, the ground state is usually more stable than the excited states. In contrast, in superheavy nuclei the multiquasiparticle excitations decrease the probability for both fission and alpha decay, implying enhanced stability. Hence, the systematic occurrence of multiquasiparticle isomers may become crucial for future production and study of even heavier nuclei. The energies of multiquasiparticle states and their alpha decays are calculated and compared to available data.

  • 915. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments, Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Evaluation of the Darcy's law performance for two-fluid flow hydrodynamics in a particle debris bed using a lattice-Boltzmann model2000In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 36, no 4, p. 295-304Article in journal (Refereed)
    Abstract [en]

    In the present paper, multiphase flow dynamics in a porous medium are analyzed by employing the lattice-Boltzmann modeling approach. A two-dimensional formulation of a lattice-Boltzmann model, using a D2Q9 scheme, is used. Results of the FlowLab code simulation for single phase flow in porous media and for two-phase flow in a channel are compared with analytical solutions. Excellent agreement is obtained. Additionally, fluid-fluid interaction and fluid-solid interaction (wettability) are modeled and examined. Calculations are performed to simulate two-fluid dynamics in porous media, in a wide range of physical parameters of porous media and flowing fluids. It is shown that the model is capable of determining the minimum body force needed for the nonwetting fluid to percolate through the porous medium. Dependence of the force on the pore size, and geometry, as well as on the saturation of the nonwetting fluid is predicted by the model. In these simulations, the results obtained for the relative permeability coefficients indicate the validity of the reciprocity for the two coupling terms in the modified Darcy's law equations. Implication of the simulation results on two-fluid flow hydrodynamics in a decay-heated particle debris bed is discussed.

  • 916. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments, Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Numerical investigation of boiling regime transition mechanism by a Lattice-Boltzmann model2001In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 204, no 1-3, p. 143-153Article in journal (Refereed)
    Abstract [en]

    A numerical study has been performed to investigate the hydrodynamic aspects of the pool boilingon horizontal-, vertical- and downward-facing surfaces. The FlowLab code, which is based on a Lattice-Boltzmann (LB) model of two-phase flows, is employed. Macroscopic properties, such as surface tension (a) and contact angle (beta), are implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model is found to express a linear relation between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The simulation results on bubble departure diameter appear to have the same parametric dependence as the empirical correlation. Hydrodynamic aspects of two-phase flow regime transition mechanism are investigated for different surface-coolant configurations. Results of the LB simulation clearly demonstrate that not only the bubble nucleation site density (related, e.g. to the heater surface condition and heat fluxes), but also the surface position have a profound effect on the flow regime (pool boiling) characteristics. The results of the LB simulation of hydrodynamics of two-phase flow on the horizontal surface provide the pictures quite similar to the experimental observation for saturated pool boiling. Two mechanisms of flow (boiling) regime transition on the vertical surface are predicted for the local bubble coalescence at bubble generation site and the downstream bubble coalescence. On the downward-facing surfaces, friction between bubbles and the surface wall is found to significantly enlarge the bubble size prior the bubble slip upwards. This behavior is responsible for the earlier bubble coalescence, and therefore, lowers the maximum heat removal rate, in a similar regime of nucleate boiling on a downward-facing surface.

  • 917. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments, Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Numerical investigation of bubble coalescence characteristics under nucleate boiling condition by a lattice-Boltzmann model2000In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 39, no 1, p. 1-17Article in journal (Refereed)
    Abstract [en]

    A numerical study was performed to investigate the characteristics of bubble growth, detachment and coalescence on vertical, horizontal, and inclined downward-facing surfaces. The FlowLab code, which is based on a lattice-Boltzmann model of two-phase flows, was employed. Macroscopic properties, such as surface tension (sigma) and contact angle (beta), were implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model predicted a linear relationship between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The simulation results on bubble departure diameter appear to have the same parametric dependence as the empirical correlation. Hydrodynamic aspects of bubble coalescence are investigated by simulating the growth and detachment behavior of multiple bubbles generated on horizontal, vertical, and inclined downward-facing surfaces. For the case of horizontal surface, three distinct. regimes of bubble coalescence were represented in the lattice-Boltzmann simulation: lateral coalescence of bubbles situated on the surface; vertical coalescence of bubbles detached in a sequence from a site; and lateral coalescence of bubbles, detached from the surface. Multiple coalescence was predicted on the vertical surface as the bubble detached from a lower elevation merges with the bubble forming on a higher site. The bubble behavior on the inclined downward-facing surface was represented quite similar to that in the nucleate boiling regime on a downward facing surface.

  • 918. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments, Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Numerical investigation of bubble growth and detachment by the lattice-Boltzmann method2001In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 44, no 1, p. 195-206Article in journal (Refereed)
    Abstract [en]

    A numerical study has been performed to investigate the characteristics of bubble growth on, and detachment from, an orifice. The FlowLab code, which is based on a lattice-Boltzmann model of two-phase flows, was employed. Macroscopic properties, such as surface tension (a) and contact angle (beta), were implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model was found to possess a linear relation between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The separate effects of the body force (gravity), gas injection rate, surface tension, and wettability were analyzed for both horizontal and vertical surfaces. It is shown that results of the lattice-Boltzmann modeling exhibit correct parametric dependencies of the departure diameter of bubbles generated on the horizontal surface on the above factors as previously established in experiments. For the case of bubble growth and departure on the vertical surface, the different effects of hydrodynamic parameters, except gas generation rate, were predicted.

  • 919.
    Yu, Zhiming
    KTH, Superseded Departments, Physics.
    Metastable growth of diamond1998Doctoral thesis, comprehensive summary (Other scientific)
  • 920.
    Zetterlund, Nils
    et al.
    KTH, Superseded Departments, Physics.
    Lindblad, Thomas
    KTH, Superseded Departments, Physics.
    Ekblad, Ulf
    KTH, Superseded Departments, Physics.
    The minimum risk angle for automatic target recognition using the intersecting cortical model2004In: Proc. Seventh Int. Conf. Inf. Fusion, 2004, p. 1014-1021Conference paper (Refereed)
    Abstract [en]

    While kids easily find 3-D objects like animals in a scene (e.g. a photograph), this is still not the case for algorithms running on von Neumann computers or neural network chips. The present investigation has two goals: Finding "signatures" of the object in the scene and trying to find out at which observation angle the chance of correct identification is the best. By signatures we mean a vector of reasonable size (say 50 elements). Clearly a cow looks different from the back or from the side. A car is probably more easily identified viewed from the front than it is from above. For a plane it may be the other way around. Thus if we define a general but compact "signature" of the object, it will surely depend on the viewing angle. The problem of finding the most optimal viewing angle is dealt with in this paper.

  • 921. Zhang, B.
    et al.
    Berg, Lars-Erik
    KTH, Superseded Departments, Physics.
    Hansson, T.
    Wavepacket dynamics and predissociation of the D-1 Pi(u) state of Rb-22000In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 325, no 06-maj, p. 577-583Article in journal (Refereed)
    Abstract [en]

    We present the first experimental investigation of the real-time dynamics of predissociation in a diatomic molecule involving more than two electronic states - the predissociation of the D(1)Pi(u) state of Rb-2. Our results show that the state is strongly predissociated, tau approximate to 5 ps, above a sharp energy threshold. We propose that mainly the (1)(3)Delta(u) state causes the fast predissociation and that the fine-structure components of the products are mixed by coupling among molecular states at large internuclear distances. Furthermore, an outward-inward asymmetry of the wavepacket signal is attributed to autoionisation of the wavepacket evolving in the probe (Rydberg) state.

  • 922.
    Zhang, Bo
    KTH, Superseded Departments, Physics.
    Experimental studies of molecular quantum dynamics2000Licentiate thesis, comprehensive summary (Other scientific)
  • 923.
    Zhang, Bo
    KTH, Superseded Departments, Physics.
    Experimental Studies of Quantum Dynamics and Coherent Control in Homonuclear Alkali Diatomic Molecules2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The main theme covered in this thesis is experimentalstudies of quantum dynamics and coherent control in homonuclearalkali diatomic molecules by ultrafast laser spectroscopy iththe implementation of pump-probe techniques.

    A series of experiments have been performed on the Rb2molecules in a molecular beam as well as in a thermal oven. Thereal-time molecular quantum dynamics of the predissociatingelectronically excited D(3)1Πu state of Rb2, which couples to/intersects several otherneighbouring states, is investigated using wavepackets. Thepredissociation of the D state, explored by this wavepacketmethod, arises from two independent states, the (4)3Σu+and (1)3u, for which the second corresponds to a much fasterdecay channel above a sharp energy threshold around 430 nm. Thelifetime of the D state above the energy threshold is obtained,τ ≈ 5 ps, by measuring the decay time of thewavepacket in a thermal oven. Further experimentalinvestigation performed in a molecular beam together withquantum calculations of wavepacket dynamics on the D state haveexplored new probe channels of wavepacket evolution: theD′(3)1Σu+ channel, which exhibits vibrational motionin a shelf state and the (4)3Σu+ channel, where direct build-up of thewavefunction is observed due to its spin-orbit oupling to the Dstate.

    The real-time quantum dynamics of wavepackets confined totwo bound states, A1Σu+(0u+) and b3Πu(0u+), have been studied by experiment andcalculations. It is shown that these two states are fullycoupled by spin-orbit interaction, characterised by itsintermediate strength. The intermediate character of thedynamics is established by complicated wavepacket oscillationatterns and a value of 75 cm-1is estimated for the coupling strength at thestate crossing.

    The experiments on the Li2molecule are performed by coherent control ofrovibrational molecular wavepackets. First, the Deutsch-Jozsaalgorithm is experimentally demonstrated for three-qubitfunctions using a pure coherent superposition of Li2rovibrational eigenstates. The function’scharacter, either constant or balanced, is evaluated by firstimprinting the function, using a phase-tailored femtosecond(fs) pulse, on a coherent superposition of the molecularstates, and then projecting the superposition onto an ionicfinal state using a second fs pulse at a specific delay time.Furthermore, an amplitude-tailored fs pulse is used to exciteselected rovibrational eigenstates and collision induceddephasing of the wavepacket signal, due to Li2-Ar collisions, is studied experimentally. Theintensities of quantum beats decaying with the delay time aremeasured under various pressures and the collisional crosssections are calculated for each well-defined rovibrationalquantum beat, which set the upper limitsfor ure dephasingcross sections.

    Keywords:Ultrafast laser spectroscopy, pump-probetechnique, predissociation, wavepacket, pin-orbit interaction,coherent control, (pure) dephasing

  • 924. Zhaunerchyk, V
    et al.
    Ehlerding, A
    Geppert, W D
    Hellberg, F
    Thomas, R D
    Larsson, M
    Viggiano, A A
    Arnold, S T
    Österdahl, Fabian
    KTH, Superseded Departments, Physics.
    Hlavenka, P
    Dissociative recombination study of Na+(D2O) in a storage ring2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 21, p. 10483-10488Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination of Na+(D2O) ion has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The cross section has been measured as a function of center-of-mass energy ranging from 1 meV to 0.1 eV and found to have an E-1.37 dependence. The rate coefficient has been deduced to be (2.3+/-0.32)x10(-7)(T-e/300)(-0.95+/-0.01) cm(3) s(-1) for T-e=50-1000 K. The branching ratios have been measured at 0 eV. Of the four energetically accessible dissociation channels, three channels are found to occur although the channel that breaks the weak Na+-D2O bond is by far dominant.

  • 925.
    Álvarez Ruiz, Jesús
    KTH, Superseded Departments, Physics.
    Photon induced fluorescence studies of molecules using synchrotron radiation2003Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This Licentiate thesis presents research accomplished at theSection of Atomic and Molecular Physics at the Royal Instituteof Technology in Stockholm using photon induced fluorescencespectroscopy (PIFS) during the last two years.

    The main results presented are summarized:

    - Neutral photodissociation in CO was observed aftersynchrotron photon excitation in the range 19-26 eV bycollecting dispersed fluorescence from excited neutral C atoms.Follow-up ab initio calculations point out CO Rydberg seriesconverging to the CO+ C and D states as precursors.

    - The branching ratio between N2 + (B-X)(v’=1,v’’=2) and (v’=0,v’’=1)transitions in the 20-46 eV energy range reveals strongnon-Franck-Condon effects. Ab initio calculations indicate thatthe autoionization of certain superexcited states areresponsible for some of the structures present in the branchingratio curve, confirming the important role of non-Rydbergdoubly excited resonant states (NRDERS) in de-excitationprocesses above the ionization potential.

    - Photon induced neutral dissociation processes in NO arereported. Neither Rydberg series nor other molecular states inNO known so far can account for the collected data. From abinitio calculations more information regarding the NO precursorstates and the mechanism behind the observed neutraldissociation were obtained.

    - The details of a new experimental set-up for gas phasefluorescence measurements using synchrotron radiation aredescribed. It is able to perform simultaneous measurements ofdispersed and total fluorescence in the visible range. Thefirst results obtained with this set-up are presented,concerning fluorescence after excitation of the N2 molecules inthe N 1s edge.

    These four studies conform the set of papers enclosed in theLicentiate thesis.

    Finally a pre-study to further apply PIFS to speciespreviously excited by microwave discharge is included as futureplans.

  • 926.
    Álvarez Ruiz, Jesús
    KTH, Superseded Departments, Physics.
    Synchrotron radiation induced fluorescence spectroscopy of gas phase molecules2004Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    A new experimental set-up for gas phase fluorescence studies using synchrotron radiation has been designed and constructed to perform simultaneously total and dispersed fluorescence measurements.

    Neutral photodissociation of CO has been investigated after excitation with 19-26 eV photons. Fluorescence from 3p 3P, 3p 3S and 3p 1D excited states in carbon was recorded and interpreted by ab initio calculations. The population and dissociation of states belonging to the C and D Rydberg series in CO seem to explain the production of the observed triplet states but not the 3p 1D state.

    Neutral photodissociation of NO is reported in the 17-26 eV energy range. No known molecular states can account for the collected data. New information regarding the precursor states of the observed neutral dissociation is provided by ab initio calculations.

    Autoionization of superexcited states in molecular nitrogen is evidenced by strong deviations of the Franck-Condon ratio in the fluorescence of the N2+ B state. Ab initio calculations predict the existence of autoionizing-excited states that may account for some of the observed structures in the 20-46 eV energy range.

    Selective molecular fluorescence from the npó1Óu+ and npð 1Ðu (n=3-7) Rydberg levels to the E,F 1Óg+ state in H2 was recorded and rotationally analyzed. Vibrational levels of the E,F 1Óg+ state (vEF =0,1,3,6-10) are determined. The predissociation of npð 1Ð+ levels is observed in agreement with the literature.

    Fragmentation of SF6 was investigated after excitation with 25–80 eV photons. Dispersed fluorescence measurements reveal the emission of S, S+, F and F+ excited atoms. These fragments are produced after single, double and triple excitations as well as direct ionizations and shake-ups in SF6.

    Photoabsorption and fluorescence yield have been measured in SF5CF3 using 10-30eV photons. The photoabsorption spectrum can be explained in terms of its similarities to those of the SF6 and CF4 molecules. The dispersed and un-dispersed fluorescence resemble those of the CF3X family. Several features suggest the migration of an F atom across the S-C bond that fragments the molecule producing excited CF4.

    Doubly excited states of H2 have been investigated in the range of 26-60 eV by monitoring Balmer á emission. The experimental data show the already known emission correlated with the fragmentation of the Q1 and Q2 states, and new features which could be attributed to dissociative photoionization and higher lying doubly excited states Qn (n>2) of the hydrogen molecule

  • 927.
    Álvarez Ruiz, Jesús
    et al.
    KTH, Superseded Departments, Physics.
    Erman, Peter
    KTH, Superseded Departments, Physics.
    Rachlew-Källne, Elisabeth
    KTH, Superseded Departments, Physics.
    Rius Riu, Jaume
    KTH, Superseded Departments, Physics.
    Stankiewicz, Marek
    KTH, Superseded Departments, Physics.
    Veseth, V.
    Neutral dissociation of superexcited states in carbon monoxide2002In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 35, no 13, p. 2975-2983Article in journal (Refereed)
    Abstract [en]

    Neutral photodissociation of CO has been investigated using synchrotron light in the range 19-26 eV by observing dispersed fluorescence from excited neutral C atoms. Follow-up ab initio calculations support the observed neutral carbon excitation functions, which to a large extent are associated with the CO Rydberg - series converging to the CO+ C and D states.

  • 928.
    Ågren, Peter
    KTH, Superseded Departments, Physics.
    Charging effects in small capacitance Josephson junction circuits2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis describes fabrication, measurements and analysisof two different Josephson junction circuits; the Cooper pairtransistor (CPT) and the one dimensional Josephson junctionarray (JJA). All experiments are conducted in a dilutionrefrigerator with a base temperature of 15{30 mK.In the experiments on CPTs the maximum supercurrent,called the switch- ing current, is measured versus the gatecharge. The importance of filtering of the measurement leads inorder to suppress quasi-particle excitations and to get2e-periodic switching currents is demonstrated. Normal metalgold leads close to the CPTs are introduced to further reducethe effect of quasi-particles. To prove that switching currentis 2e-periodic, magnetic fields and increased temperatures areused to induce a transition to e-periodicity. CPTs where eachJosephson junction is replaced by a Superconducting QuantumInterference de- vice (SQUID) have also been fabricated andmeasured. The SQUIDs make it possible to tune the effectiveJosephson energy with an external magnetic field. The measuredswitching current is tunable in magnitude and 2e-periodic. Theswitching currents are compared with theory. Good agreementbetween the- ory and experiments is found using a model of theCPT in an electrodynamic environment with a high effectivetemperature.The JJAs are also fabricated with a SQUID geometry toenable tuning of the effective Josephson energy. The currentvoltage characteristics (IVCs) of the measured JJAs exhibit aCoulomb blockade of Cooper pair tunneling which is tunable withmagnetic field and periodic with the ux quanta. The IVCs of theJJA show a region of negative differential resistance, alsocalled back- bending. This is interpreted as evidence of Blochoscillations in the JJAs. Two different models are discussed toexplain the measured IVC.The thesis ends by presenting a theoretical proposal ona Josephson junction charge qubit, called the array-qubit. Thearray-qubit consists of an array with N SQUIDs and N +1islands. The two basis states of the qubit corresponds to anexcess Cooper pair on either island 1 or N +1. These two statesare coupled through an Nth-order tunneling process which makesit possible to effectively suppress the Josephson coupling.This facilitate a long relaxation time so that the state of thequbit can be read with a slow detector.

  • 929.
    Ågren, Peter
    KTH, Superseded Departments, Physics.
    Cooper pair transport and Coulomb blockade in one dimensional Josephson arrays2000Licentiate thesis, comprehensive summary (Other scientific)
  • 930.
    Ågren, Peter
    et al.
    KTH, Superseded Departments, Physics.
    Walter, Jochen
    KTH, School of Engineering Sciences (SCI), Physics.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Switching Current of a Cooper Pair Transistor with Tunable Josephson Junctions2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 1, p. 14510-Article in journal (Refereed)
    Abstract [en]

    We investigate the switching current of a Cooper pair transistor with tunable Josephson energy. The junctions are fabricated in a superconducting quantum interference device (SQUID) geometry which allows for an in situ tunable effective Josephson energy by application of a magnetic field. We find a 2e-periodic switching current versus gate charge. As the magnetic field is increased the switching current stays 2e-periodic but the magnitude is suppressed. At a magnetic field of half a flux quantum through the SQUID's the switching current is minimum. We can theoretically model the experimental data by assuming a switching current which is proportional to the ideal critical current squarred. We show that such a dependence is expected in the limit where the effect of thermal fluctuations on the system is strong.

  • 931.
    Ågren, Peter
    et al.
    KTH, Superseded Departments, Physics.
    Walter, Jochen
    KTH, School of Engineering Sciences (SCI), Physics.
    Schöllmann, Volker
    KTH, School of Engineering Sciences (SCI), Physics.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Switching Currents and Quasi-Particle Poisoning in the Superconducting Single Electron Transistor2002In: INTERNATIONAL WORKSHOP ON SUPERCONDUCTING NANO-ELECTRONICS DEVICES, 2002, p. 25-31Conference paper (Refereed)
  • 932.
    Åkermark, Torbjörn
    KTH, Superseded Departments, Physics.
    Molecular or atomic oxygen as the transported species in oxidation of silicon2000In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 147, no 5, p. 1882-1887Article in journal (Refereed)
    Abstract [en]

    There is a general belief that the oxidation of silicon is due to the transport of molecular oxygen through the growing oxide. However, several recent experimental results have shown that atomic oxygen is also a possible candidate fur the transported species. This paper discusses which of these two candidates is the most likely transported species, considering both traditional arguments and these based on more recent experimental results. This discussion shows that the experimental results traditionally used as arguments for molecular oxygen being the transported species are equally valid for atomic oxygen as the transported species. However more recent experimental results strongly support atomic oxygen, not molecular oxygen, as the transported species. The conclusion is that atomic oxygen is the more likely candidate For the transported species in the oxidation of silicon.

  • 933. Åslund, M.
    et al.
    Cederström, Björn
    KTH, Superseded Departments, Physics.
    Lundqvist, M.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Scatter rejection in scanned multi-slit digital mammography2004In: Proceedings of SPIE - The International Society for Optical Engineering, 2004, no 1, p. 478-487Conference paper (Refereed)
    Abstract [en]

    Measurements and Monte Carlo simulations were used to investigate the scatter properties of a scanned multi-slit digital mammography system. Scatter to primary ratio (S/P) in the center of the image field was calculated for different thickness of breast equivalent material and different tube potentials. The simulated model also varied the angular acceptance, the number of slits and the distance between the slits of a dedicated scatter rejection device. In addition to the expected scatter from the breast equivalent material, scatter within the detector contributes to the S/P-ratio. The main part of the scatter is identified as coming from this process. Measured total 5/P-ratios below 3% are reported for breast range 3-8 cm. The scatter-DQE is used as figure-of-merit for comparison to other imaging geometries and scatter rejection schemes.

  • 934.
    Öhberg, Patrik
    KTH, Superseded Departments, Physics.
    Studies of inhomogeneous Bose-Einstein condensates1998Doctoral thesis, comprehensive summary (Other scientific)
  • 935. Öjekull, J.
    et al.
    Andersson, P. U.
    Någård, M. B.
    Pettersson, J. B. C.
    Derkatch, Alik
    Neau, A.
    Rosén, S.
    Thomas, R.
    Larsson, M.
    Österdahl, Fabian
    KTH, Superseded Departments, Physics.
    Semaniak, J.
    Danared, Håkan
    Källberg, A.
    af Ugglas, M.
    Markovic, N.
    Dissociative recombination of NH4+ and ND4+ ions: Storage ring experiments and ab initio molecular dynamics2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 16, p. 7391-7399Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.

  • 936. Östling, J.
    et al.
    Brahme, A.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Iacobaeus, C.
    Peskov, Vladimir
    KTH, Superseded Departments, Physics.
    A radiation-tolerant electronic readout system for portal imaging2004In: 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. 308-312Article in journal (Refereed)
    Abstract [en]

    A new electronic portal imaging device, EPID, is under development at the Karolinska Institutet and the Royal Institute of Technology. Due to considerable demands on radiation tolerance in the radiotherapy environment, a dedicated electronic readout system has been designed. The most interesting aspect of the readout system is that it allows to read out similar to 1000 pixels in parallel, with all electronics placed outside the radiation beam-making the detector more radiation resistant. In this work we are presenting the function of a small prototype (6 x 100 pixels) of the electronic readout board that has been tested. Tests were made with continuous X-rays (10-60 keV) and with alpha particles. The results show that, without using an optimised gas mixture and with an early prototype only, the electronic readout system still works very well.

16171819 901 - 936 of 936
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