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  • 251.
    Fransson, Jonas
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Sandalov, I
    Eriksson, O
    A perfect spin-filter quantum dot system2004Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, nr 16, s. L249-L254Artikel i tidskrift (Refereegranskat)
    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.

  • 252.
    Franzén, Ken Yoshiki
    KTH, Tidigare Institutioner                               , Fysik.
    Formation and fragmentation dynamics of superexcited molecules1998Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 253. Freund, Martin
    et al.
    Ohlsson, Tommy
    KTH, Tidigare Institutioner, Fysik.
    Matter enhanced neutrino oscillations with a realistic earth density profile2000Ingår i: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 15, nr 13, s. 867-874Artikel i tidskrift (Refereegranskat)
    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.

  • 254. Fritioff, K
    et al.
    Sandstrom, J
    Andersson, P
    Hanstorp, D
    Hellberg, F
    Thomas, R
    Larsson, M
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    Collins, G F
    Le Padellec, A
    Pegg, D J
    Gibson, N D
    Danared, H
    Kaillberg, A
    Observation of an excited C-4(2-) ion2004Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 37, nr 11, s. 2241-2246Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports an experimental investigation of the electron impact detachment of C-4(-). We observe structure in the electron impact cross section for detaching a single electron from a C-4(-) cluster anion, which we attribute to the formation and decay of the C-4(2-) dianion. The system is energetically unstable and very rapidly decays via double autodetachment. The energy and width of the resonance were determined to be 8.8(5) eV and 1.4(5) eV, respectively, and the resonance lies 1.5(5) eV above the ground state of the neutral system. The experiment was conducted by merging monoenergetic electron and ion beams in the heavy ion storage ring CRYRING. The detachment channel was monitored by detecting neutral C-4 fragments.

  • 255.
    Fu, Ying
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Jussi, Johnny
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. 1989.
    Qin, Wang
    RISE Acreo AB.
    Brismar, Hjalmar
    KTH, Tidigare Institutioner (före 2005), Fysik. KTH, Centra, Science for Life Laboratory, SciLifeLab. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Liu, Yushen
    College of Physics and Electronic Engineering, China..
    Yang, Xifeng
    College of Physics and Electronic Engineering, China..
    Chen, Yun
    University of Gothenburg, Sweden..
    Endocytic pathway of vascular cell adhesion molecule 1 in human umbilical vein endothelial cell identified in vitro by using functionalized nontoxic fluorescent quantum dots2019Ingår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 297, artikel-id 126702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studies about vascular cell adhesion molecule 1 (VCAM1) in tumor growth, metastasis, and angiogenesis suggest that targeting VCAM1 expression is an attractive strategy for diagnosis and anti-tumor therapy. However, the endocytic pathway of VCAM1 in vascular cells has not been well characterized. In this study we visualize the endocytic pathway of tumor necrosis factor α (TNFα) induced VCAM1 in human umbilical vein endothelial cell (HUVEC) in vitro using 5-carboxyfluorescein labeled VCAM1 binding peptides and fluorescent water-dispersible 3-mercaptopropionic acid (3MPA)-coated CdSe-CdS/Cd0.5Zn0.5S/ZnS core–multishell nontoxic quantum dots (3MPA-QDs) functionalized with VCAM1 binding peptides. Clear key in vitro observations are as follows: (a) 3MPA-QDs functionalized with VCAM1 binding peptides, denoted as VQDs, adhered and aggregated cumulatively to cell membrane around 2 h after VQD deposition to cell culture medium and were found in lysosomes in TNFα-treated HUVECs approximately 24 h after VQD deposition; (b) VQDs remained in TNFα-treated HUVECs for the whole 16 days of the experimental observation period; (c) quite differently, 3MPA-QDs were endocytosed then exocytosed by HUVECs via endosomes in about 24–48 h after 3MPA-QD deposition. Our study suggests that VCAM1 molecules, initially expressed on cell membrane induced by TNFα treatment, are internalized into lysosomes. This provides a novel means to deliver materials to lysosomes such as enzyme replacement therapy. Moreover, our meticulous sensing methodology of devising fluorescent nontoxic QDs advances biosensing technique for studying cellular activities in vitro and in vivo.

  • 256. Fuhse, C
    et al.
    Krebs, H U
    Vitta, S
    Johansson, Göran A.
    KTH, Tidigare Institutioner, Fysik.
    Interface quality and thermal stability of laser-deposited metal/MgO multilayers2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 34, s. 6265-6269Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metal/MgO multilayers (metal of Fe80Ni80Nb20, and Ti) with bilayer periods in the range 1.2-3.0 nm have been prepared by pulsed laser deposition and characterized by both hard and soft-x-ray reflectometry. The interface roughness is found to be less than or equal to 0.5 nm in all the samples and is nearly independent of the total number of deposited bilayers. The interface roughness, however, depends on the absolute thickness of the individual layers and increases from approximate to0.3 nm for a 3.0-nm period to approximate to0.5 nm for a bilayer period of 1.2 nm. The multilayers are found to be highly stable up to temperatures as high as 550 degreesC. The hard-x-ray reflectivity of the multilayers decreases for T > 300 degreesC, whereas the layered structure is stable up to 550 degreesC. The reflectivity in the water window region of soft x rays, lambda = 3.374 nm, was found to be 0.4% at an angle of incidence of approximate to54degrees for multilayers with 60 bilayers at a period of approximate to2.1 nm. (C) 2004 Optical Society of America.

  • 257.
    Gaarder, Andreas
    KTH, Tidigare Institutioner                               , Fysik.
    Time-resolved optical characterisation of defect-rich semiconductors2003Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis explores carrier trapping and recombination indefect-rich semiconductors, and methods for materialcharacterisation. Optimal manufacturing parameters areestablished for materials to be used in the ultrafast devicesneeded for future telecommunication applications. Thesemi-insulating properties and ultrashort carrier lifetimes inthe investigated materials are due to the efficient trapping ofcarriers to centers with their energy levels deep within theband gap of the material. The carrier recombination processesin the investigated materials are studied with time-resolvedphotoluminescence (TRPL) and dynamic transmission (DT)/reflection (DR) measurement techniques. Analysis of several ofthe measurements are performed using computer simulation of theexperiments. The simulations are based on rate equation modelsof the carrier populations in the conduction band, valenceband, and at the deep centers.

    Investigations were made on InP:Fe, GaAs:Fe and GaInP:Feregrown on semiconductor planar lasers and vertical cavitysurface emitting lasers using hydride vapour phase epitaxy. Thecharacterisation was made by TRPL, and by focusing theexcitation beam to a nearly diffraction limited spot size aspatial resolution of about 1 µm was obtained. It wasfound that despite variations in growth velocity and morphologywithin the regrown layers, the semi-insulating properties aremaintained everywhere, even in the critical region close to thelaser mesa where leakage current is most likely to occur.

    A TRPLand DT/DR study of Be-doped low-temperature-grown GaAshas also been undertaken to investigate the effects ofannealing and Be concentration on the ultrafast carriertrapping properties of this material. The electron trappingtimes in this material vary from tens of femtoseconds up to afew picoseconds, depending on the Be doping and annealingconditions. Optimal fabrication parameters are presented foruse in ultrafast optoelectronic devices. TRPLand DR was used tocharacterise implanted and annealed InP and In- GaAs for use infuture Tbit/s telecommunication applications. Optimalfabrication parameters are presented also for thesematerials.

    Carrier dynamics in aligned InAs/GaAs quantum dots grown ondislocationinduced patterns was studied with TRPL. Shortcarrier lifetimes in the dots indicate effective nonradiativerecombination through point traps near the dots. A proposal onthe nature of the carrier traps is given.

  • 258. Gadea, A.
    et al.
    de Angelis, G.
    Farnea, E.
    Marginean, N.
    Nyberg, J.
    Wyss, Ramon
    KTH, Tidigare Institutioner                               , Fysik.
    et al,
    Spectroscopy of heavy N=Z nuclei with GASP and EUROBALL2003Ingår i: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 34, nr 4, s. 2429-2438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coupling of big Ge-arrays like EUROBALL or GASP with ancillary detectors for the study of the structure properties of very exotic nuclei, far from the stability valley, has given outstanding results in the last years. A large fraction of the experiments performed with both arrays has been devoted to study both proton-rich and neutron-rich nuclei populated using stable beams provided by the LNL Legnaro and MeS Strasbourg accelerators. Nuclei lying close to the N = Z line are of particular interest being a laboratory where collective excitations as well as fundamental properties of the nuclear force can be tested, like isospin symmetry and isospin breaking terms, proton neutron pairing, dripline effects and coherent neutron and proton contributions to the nuclear excitations. Some of this properties are more evident (degree of isospin mixing) or can be only observed (collective effects) in heavy N = Z nuclei. In this contribution we present the experimental results obtained by our collaboration along and in the vicinity of N = Z line.

  • 259.
    Gador, Niklas
    KTH, Tidigare Institutioner, Fysik.
    Curve-crossing quantum wavepacket dynamics - Experiment and theory2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, I present experimental and theoretical workon quantum wavepacket dynamics in potential curve-crossings,using gas-phase Rb2 as working media. Particularly, we havefocused on curve-crossing cases with intermediate strengthcoupling, which leads to complicated wavepacket motion withe.g. large splittings and interference. Previous experiments onsuch systems are scarce.

    Experimentally, femto-second pump-probe spectroscopy wasperformed using two independent optical parametric amplifiers.A near-effusive Rb2molecular beam source was developed to produce astable, high density and collision-free beam. Pump-probefluorescence was detected using an optical assembly designedfor good collection efficiency.

    Theoretically, analysis of experimental data was aided byquantum dynamical calculations. The used numerical simulationprogram is powerful in its ability to include any number ofstates with coupling elements, together with a fully timepropagated pump pulse-molecule interaction. It was furtherdeveloped to include molecular rotation as a centrifugalcorrection term to the potential curves, and to do statisticalthermal averaging to permit direct comparison withexperiment.

    Our work on the Rb2A-state system is a pioneering femto-secondexperimental curve-crossing study of a system of twointermediately coupled bound electronic states. The wavepacketfragments, following different roads, meet and interfere attheir return to the crossing. Thus, new results on theinterference properties of wavepacket dynamics in such a systemwere obtained, such as the existence of two hybrid diabatic/adiabatic trajectories, robust towards thermal averaging.Further, we show that certain scanning possibility existbetween relative contents of these two trajectories at elevatedtemperature by scanning the pump wavelength. The systemrepresents a quantum matter-wave close analogue to an opticalpulsed Michelson interferometer. The dynamics of the A-statesystem was also investigated by anisotropy measurements. Thehigh degree of signal to noise ratio obtained, revealed a newtype of small oscillatory structure, which the analysis showsoriginates from coupling between all degrees of freedom of theRb2molecule, namely electronic, vibrational androtational motion.

    The results of the work on the higher lying D-state systemconsist of the determination of a parallel excitationmechanism, where two wavepackets are simultaneously created intwo different electronic states. Further analysis showed thattheir future dynamics proceed essentially independently. Oneperforms adiabatic dynamics in a single‘shelf-shaped’state, while the other goes throughcurve-crossings of somewhat weaker coupling strength thanintermediate. We propose the shape of the final, unknown,pump-probe states, guided by the quantum dynamical simulationstogether with the experimental data.

  • 260.
    Gador, Niklas
    KTH, Tidigare Institutioner                               , Fysik.
    Experimental studies of dynamics in gas-phase diatomic molecules. From lifetime-measurements of BaF tofemtosecond pump-probe spectroscopy of Rb2.2002Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 261.
    Gador, Niklas
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Zhang, Bo
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, H O
    Hansson, T
    Dynamical interference structures in fully coupled bound-bound state quantum wave-packet dynamics2004Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, nr 3, s. 033418-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The quantum wave-packet dynamics in a bound-bound state system at intermediate coupling strength, the A and b states in the Rb-2 molecule coupled by spin-orbit interaction, was studied by ultrafast pump-probe molecular beam spectrocopy and quantum dynamical calculations. It was shown that even at elevated molecular temperatures the experimentally observed traces are characterized by dynamical interference structures of mesobatic, i.e., diabatic-adiabatic hybrid, kind. Two types of mesobatic motion were discerned: bistable, which occurs in both bound-unbound and bound-bound systems, and astable, which is particular to bound-bound systems at intermediate coupling strength. Contrary to previous expectations, the signatures of the quantum interference structures in pump-probe delay traces were found to be robust toward averaging over initial quantum states. It was shown that the spectral variations observed while tuning the pump pulse wavelength is a quantum matter-wave relative of the fringes observed in a pulsed optical Michelson interferometer.

  • 262.
    Ganchenkova, Marija
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Kuznetsov, A Y
    Nieminen, R M
    Electronic structure of the phosphorus-vacancy complex in silicon: A resonant-bond model2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 11, s. 115204-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using first-principles calculations, the electronic structure of the phosphorus-vacancy pair in silicon has been studied. Detailed analysis of the atomic displacement fields associated with the atomic structure optimization after the defect formation indicates a strong dependence of the character and magnitude of relaxation both on the supercell size and the E-center charge state. Our simulation results strongly suggest that the E-center structure is of the resonant-bond type with a strong localization of an electron pair at the phosphorus atom. The energy level splitting for shared electrons in a vacancy due to the appearance of the resonance distortion is discussed, as well as the nature of and the reasons for the level occupation.

  • 263. Garcia, FC
    et al.
    Fokine, Mikael
    KTH, Tidigare Institutioner                               , Fysik.
    Margulis, Walter
    KTH, Tidigare Institutioner                               , Fysik.
    Kashyap, Raman
    Mach-Zehnder interferometer using single standard telecommunication optical fibre2001Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 37, nr 24, s. 1440-1442Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is demonstrated that a single, short-length, standard telecommunications optical fibre can function as an interferometer when subjected to hydroxyl-flooding. The interferometer is based on the mode beating effect arising from the induced-refractive index change.

  • 264.
    García, Emilio Melero
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Álvarez Ruiz, Jesús
    KTH, Tidigare Institutioner, Fysik.
    Erman, Peter
    KTH, Tidigare Institutioner, Fysik.
    Kivimäki, Antti Eerik
    KTH, Tidigare Institutioner, Fysik.
    Rachlew-Källne, Elisabeth
    KTH, Tidigare Institutioner, Fysik.
    Rius Riu, Jaume
    KTH, Tidigare Institutioner, Fysik.
    Stankiewicz, Marek
    KTH, Tidigare Institutioner, Fysik.
    Veseth, V.
    Neutral dissociation of superexcited states in nitric oxide2003Ingår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 293, nr 1, s. 65-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Near-infrared dispersed fluorescence measurements of 13 different atomic multiplets of neutral atomic fragments from photon induced neutral dissociation processes in NO are reported. For excitation of the molecules narrow band synchrotron photons of energy 17.2-25.8 eV were used. Neither Rydberg series nor other molecular states in NO known so far can account for the collected data. From ab initio calculations we try to obtain more information regarding the NO precursor states, and the mechanism behind the observed neutral dissociation.

  • 265. Garibaldi, F.
    et al.
    Cisbani, E.
    Cusanno, F.
    Colilli, S.
    Fratoni, R.
    Giuliani, F.
    Gricia, M.
    Iodice, M.
    Lucentini, M.
    Santavenere, F.
    Urciuoli, G. M.
    De Cataldo, G.
    De Leo, R.
    Lagamba, L.
    Marrone, S.
    Nappi, E.
    Coluzza, C.
    Peskov, Vladimir
    KTH, Tidigare Institutioner, Fysik.
    Pani, R.
    Pellegrini, R.
    Cinti, M. N.
    A PET scanner employing CsI films as photocathode2004Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 525, nr 1-2, s. 263-267Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Medical imaging is a fundamental tool in the diagnosis, treatments, and monitoring of disease processes as cancer. Detectors of large area and high Field Of View are necessary to scan the whole body in a reasonable time. Relatively large area photodetectors are necessary even for imaging of small mice and rats with high sensitivities and spatial resolutions, generally obtained by using pinhole or multipinhole collimators. Standard PET scanners, with scintillators coupled to photomultipliers, have generally a limited detector area due to the high costs of both scintillators and photomultipliers. In this respect, the replacement of photomultipliers with gaseous photodetectors represents a possible solution of the problem and brings the additional advantage to provide devices with sensitive areas free from dead regions. In this paper we report on a PET scanner equipped with a multiwire proportional chamber with a CsI thin film as photoconverter. A similar approach has already been successfully pursued in nuclear and particle physics experiments. A prototype of such a PET detector has been designed and built, and will be tested soon. Possible solutions for increasing the photoelectron number, and thus the detector performance, are presented.

  • 266. Gauthier, Y.
    et al.
    Baudoing-Savois, R.
    Rundgren, J.
    Hammar, M.
    KTH, Tidigare Institutioner, Fysik.
    Göthelid, M.
    Reconstruction of the Pt50Ni50(100) surface: a LEED and STM study1995Ingår i: Surface Science, ISSN 00396028 (ISSN), Vol. 327, nr 1-2, s. 100-120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of the Pt50Ni50(100) surface was investigated by low energy electron diffraction (LEED) and scanning tunnelling spectroscopy (STM). Superstructures corresponding to 12 × 1 and 19 × 1 reconstructions were observed in the LEED pattern, and these reconstructions were identified with atomic resolution by STM. The reconstructed surface layer has a quasi-hexagonal atomic mesh with almost (111) atomic density and is divided into terraces and domains the size of which can be more than a thousand ångströms. The domains are corrugated with protrusions made up by 5 × 1 subunits of the quasi-hexagonal mesh and with valleys containing depressed atoms or 2 × 1 subunits. The 12 × 1 and 19 × 1 periodicities are determined by the sequence of valleys; depending on the thermal treatment, one or the other dominates but both generally coexist on the terrace. Owing to the complexity of the structure, LEED calculations were performed for a simplified model with surface atoms situated in a planar net and uniform quasi-hexagonal meshes. We find that in both reconstructions the two surface layers are significantly enriched with platinum. The top layer enrichment is consistent with previous Auger measurements. © 1995.

  • 267. Geppert, W D
    et al.
    Ehlerding, A
    Hellberg, F
    Semaniak, J
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    Kaminska, M
    Al-Khalili, A
    Zhaunerchyk, V
    Thomas, R
    Af Ugglas, M
    Kallberg, A
    Simonsson, A
    Larsson, M
    Dissociative recombination of nitrile ions: DCCCN+ and DCCCND+2004Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 613, nr 2, s. 1302-1309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of DCCCN+ and DCCCND+ using the CRYRING ion storage ring. In the case of DCCCN+ the dissociation yielding D + C3N and those leading to two fragments containing a pair of heavy atoms dominate, whereas pathways producing a fragment with three heavy atoms play only a minor role. Conversely, for DCCCND+, only those channels preserving the carbon chain or producing two fragments with a pair of heavy atoms each are detected. The cross sections of the reactions are very similar and can be fitted to the expressions sigma = (2.9 +/- 0.5) x 10(-15)E(eV)(-1.05 +/- 0.02) cm(2) and sigma = (2.3 +/- 0.4) x 10(-15)E(eV)(-1.10 +/- 0.02) cm(2) for DCCCN+ and DCCCND+, respectively. From these data, thermal reaction rates of k(T) = (1.5 +/- 0.3) x 10(-6)(T/300 K)(-0.60 +/- 0.02) cm(3) s(-1) and k(T) = (1.5 +/- 0.3) x 10(-6)(T/300 K)(-0.58 +/- 0.02) cm(3) s(-1) were calculated for DCCCN+ and DCCCND+, respectively. These rates and branching ratios are compared with those hitherto used in astrophysical models.

  • 268. Geppert, W D
    et al.
    Hellberg, F
    Ehlerding, A
    Semaniak, J
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    Kaminska, M
    Zhaunerchyk, V
    Al-Khalili, A
    af Ugglas, M
    Thomas, R
    Kallberg, A
    Larsson, M
    Dissociative recombination of (SO2+)-O-18: Evidence for three-body breakup2004Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 610, nr 2, s. 1228-1233Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of (SO2+)-O-18 using the CRYRING ion storage ring. The branching ratio of the (SO2+)-O-18 + e(-)-->(SO)-O-18+O-18 channel amounts to 61%, while the three-body breakup (SO2+)-O-18 + e(-)-->S+2(18)O accounts for the remaining 39% of the total reaction. The cross section of the reaction could be fitted by the expression sigma=(1.2+/-0.4)x10(-15) E-0.96+/-0.02 cm(2), which leads to a thermal reaction rate of k(T)=(4.6+/-0.2)x10(-7)(T/300 K)(-0.52+/-0.02) cm(3) mol(-1) s(-1).

  • 269. Geppert, W D
    et al.
    Thomas, R
    Ehlerding, A
    Hellberg, F
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    af Ugglas, M
    Larsson, M
    Dissociative recombination of C3H4+: preferential formation of the C3H3 radical2004Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 237, nr 1, s. 25-32Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of C3H4+ using the CRYRING ion storage ring. The pre-eminent channel involves the production of C3H3 and H, whereas processes involving rupture of carbon-carbon bonds are clearly disfavoured. The cross section of the reaction could be fitted to the expression sigma = 5.5 +/- 0.2 x 10(-15) E-1.01+/-0.02, which leads to a thermal reaction rate of k(T) = 2.95 +/- 0.1 x 10(-6) (T/300)(-0.67+/-0.02) cm(3) s(-1).

  • 270. Geppert, W D
    et al.
    Thomas, R
    Ehlerding, A
    Semaniak, J
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    af Ugglas, M
    Djuric, N
    Paal, A
    Larsson, M
    Extraordinary branching ratios in astrophysically important dissociative recombination reactions2004Ingår i: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 127, s. 425-437Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios of the dissociative recombination reactions of the astrophysically relevant ions DCO+, N2H+ and DOCO+ ( as substitute for HOCO+) have been measured using the CRYRING storage ring at the Manne Siegbahn Laboratory at the University of Stockholm, Sweden. For DCO+, the channel leading to D and CO was by far the most important one ( branching ratio 0.88), only small contributions of the CD+O and OD+C product pathways ( branching ratios 0.06 each) were recorded. In the case of N2H+ the surprising result of a break-up of the N-N bond to N and NH ( branching ratio 0.64) was found with the branching ratio of the N-2+H product channel therefore displaying a branching ratio of only 0.36. In the case of DOCO+, the three-body break-up into D+O+CO dominated ( branching ratio 0.68), whereas the contribution of the CO2+H channel was only minute (0.05). The remaining share ( branching ratio 0.27) was taken by the pathway leading to OH+CO. For the dissociative recombination of N2H+ and DOCO+ also absolute reaction cross sections were obtained in the collisional energy range between 0 and 1 eV. From these cross sections it was possible to work out the thermal rate constants, which were found to be k(T) = 1.0 +/- 0.1 x 10(-7) (T/300 K)(-0.51 +/- 0.02) cm(3) s(-1) and k(T) = 1.2 +/- 0.1 x 10(-6) (T/300 K)(-0.64 +/- 0.02) cm(3) s(-1) for N2H+ and DOCO+, respectively.

  • 271. Geppert, W D
    et al.
    Thomas, R
    Hellberg, F
    Ehlerding, A
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    af Ugglas, M
    Larsson, M
    Dissociative recombination of N2OD+2004Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, nr 13, s. 3415-3419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of N2OD+ using the CRYRING ion storage ring. The most dominating pathways were found to be those eading to N-2 + OD (46%) and the three-body break-up producing N-2 + O + D (40%). The production of N2O is not observed. The cross section of the reaction could be fitted to the expression sigma = 1.25 +/- 0.25 x 10(-15)(E/eV)(-1.24+/-0.02), which leads to a thermal reaction rate of k(T) = 1.4 +/- 0.1 x 10(-6)(T/300)(-0.74+/-0.02) cm(3) s(-1). The findings are compared with those of the related dissociative recombination of DOCO+ as well as with earlier flowing afterglow measurements.

  • 272. Geppert, W. D.
    et al.
    Thomas, R.
    Semaniak, J.
    Ehlerding, A.
    Millar, T. J.
    Osterdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    Ugglas, M. A.
    Djuric, N.
    Paal, A.
    Larsson, M.
    Dissociative recombination of N2H+: Evidence for fracture of the N-N bond2004Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 609, nr 1, s. 459-464Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of N2H+ using the CRYRING ion storage ring. It has been found that the channel N2H+ + e(-) --> N-2 + H accounts for only 36% of the total reaction and that the branching into the other exoergic pathway, N2H+ + e(-) --> NH + N, consequently amounts to 64%. The cross section of the reaction could be fitted by the expression sigma = (2.4 +/- 0.4) x 10(-16) E-1.04 +/- 0.02 cm(2), which leads to a thermal reaction rate of k(T) = (1.0 +/- 0.2) x 10(-7)(T/300)(-0.51 +/- 0.02) cm(3) s(-1), in favorable agreement with previous flowing afterglow Langmuir probe measurements at room temperature, although our temperature dependence is very different. The implications of these measurements for the chemistry of interstellar clouds are discussed. A standard model calculation for a dark cloud predicts a slight increase of N2H+ in the dark clouds but a five- to sevenfold increase of the NH concentration as steady state is reached.

  • 273.
    Gharibi, Arash Gholam
    KTH, Tidigare Institutioner                               , Fysik.
    A study of the cosmic muon charge ratio at the top of the atmosphere2000Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 274.
    Ghorbani, Shaban Reza
    KTH, Tidigare Institutioner                               , Fysik.
    Structural and Electrical Transport Properties of Doped Nd-123 Superconductors2003Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    It is generally believed that one of the key parameterscontrolling the normal state and superconducting properties ofhigh temperature superconductors is the charge carrierconcentrationpin the CuO2planes.By changing the non-isovalent dopingconcentration on the RE site as well as the oxygen content in(RE)Ba2Cu3O7−δ, an excellent tool is obtained tovary the hole concentration over a wide range from theunderdoped up to the overdoped regime.In the present thesis thefocus is on the doping effects on the structural and normalstate electrical properties in Nd-123 doped with Ca, La, Pr,Ca-Pr, and Ca-Th.T he effects of doping have been investigatedby X-ray and neutron powder diffraction, and by measurements ofthe resistivity, thermoelectric powerS, and Hall coefficient RH.T he thermoelectric power is a powerful tool forstudies of high temperature superconductivity and is highlysensitive to details of the electronic band structure.Sas a function of temperature has been analyzed in twodifferent two band models.The parameters of these models arerelated to charactristic features of the electron bands and asemiempirical physical description of the doping dependence ofSis obtained.So me important results are following:

    (i)The valence of Pr in the RE-123 family.Results from thestructural investigations, the critical temperature Tc, and thethermoelectric power indicated a valence +4 at low dopingconcentration, which is in agreement with results of chargeneutral doping in the RE-123 family.(ii)Hole localization. The results of bond valence sum (BVS)calculations from neutron diffraction data showed that holelocalization on the Pr+4site was the main reason for the decrease of thehole concentration p.Differ ent types of localization wereinferred by S measurements for Ca-Th and Ca-Pr dopings.(iii)Competition between added charge and disorder. Theresults of RH measurements indicated that Ca doping introduceddisorder in the CuO2planes in addition to added charge.This could bethe main reason for the observed small decrease of thebandwidth of the density of states in the description of aphenomenological narrow band model.(iv) Empirical parabolic relation between γ and p.S data were analyzed and well described by a two-band modelwith an additional linear T term, γT.An empiricalparabolic relation for γ as a function of holeconcentration has been found.

    Key words:high temperature superconductors, criticaltemperature, resistivity, thermoelectric power, Hallcoefficient, X-ray diffraction, Neutron diffraction, NdBa2Cu3O7−δ, hole concentration,substitution.

  • 275.
    Ghorbani, Shaban Reza
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Lundqvist, Pieter
    KTH, Tidigare Institutioner, Fysik.
    Valldor, M.
    Arrheniuslaboratoriet, Stockholms Universitet.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Thermoelectric power and resistivity of Nd1-xCaxBa2Cu3Oy and Nd1-xLaxBa2Cu3Oy2000Ingår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 339, nr 4, s. 245-252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structural and transport properties of Nd1-xCaxBa2Cu3Oy (x = 0.0, 0.03, 0.06, and 0.10) and Nd1-xLax- Ba2Cu3Oy. (x nominally 0.0, 0.05, 0.10, and 0.15) have been studied by X-ray powder diffraction, electrical resistivity, and thermoelectric power measurements. In both series, the a- and b-axis lattice parameters decrease with increasing doping while the c-axis lattice parameter increases. The transport properties suggest improved metallic behaviour with increasing Ca doping in contrast to La doping. An anomalous sharp peak in the thermoelectric power close to T-c was observed, which depended on the doping content. We analysed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained.

  • 276. Glowacz, S.
    et al.
    Satula, Wojtek
    KTH, Tidigare Institutioner                               , Fysik.
    Wyss, Ramon
    KTH, Tidigare Institutioner                               , Fysik.
    Cranking in isospace2004Ingår i: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 19, nr 1, s. 33-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The response of isovector and isoscalar pair fields to generalized rotation in isospace is studied. Analytical expressions for constant gap solutions for different limiting cases of the model are derived. In particular, the connections between gauge angles among pairing gaps and the position of the iso-cranking axis are investigated in N = Z nuclei. The two domains of collective and noncollective rotation in space are generalized to isospace. The amplitudes for pair-transfer of T = 0 and T = 1 pairs are calculated. It is shown that the structure of the T = 0 state in odd-odd nuclei prevents any enhancement of pair transfer also in the presence of strong isoscalar pairing correlations. The energy differences of the T = 0 and T = 1 excitations in odd-odd nuclei are qualitatively reproduced by Total-Routhian-Surface calculations.

  • 277. Gono, Y.
    et al.
    Odahara, A.
    Fukuchi, T.
    Ideguchi, E.
    Kishida, T.
    Kubo, T.
    Watanabe, H.
    Motomura, S.
    Saito, K.
    Kashiyama, O.
    Morikawa, T.
    Cederwall, Bo
    KTH, Tidigare Institutioner                               , Fysik.
    Zhang, Y. H.
    Zhou, X. H.
    Ishihara, M.
    Sagawa, H.
    Systematics of high-spin isomers in N=83 isotones and a high-spin isomer beam2002Ingår i: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 13, nr 02-jan, s. 5-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Isomers in N = 83 isotones of Z = 60 66 were studied systematically. Their spins and parities arc,49/2(+) and 27(+) for odd and odd-odd nuclei, respectively. Nearly constant excitation energies of these isomers indicated a decrease of a Z = 64 shell gap energy as Z decreases from 64 to 60 within the framework of a deformed independent-particle model (DIPM). Their configurations are [v(f(tau/2)h(9/2)i(13/2)), pi(h(11/2))(2)](49/2+) and [v(f(7/2)h(9/2)i(13/2)), pi(h(11/2))(2)(d(5/2))(-1)](27+) for odd and odd-odd nuclei, respectively. The shape of the yrast status changes suddenly at spin 49/2(odd) and 27(odd-odd) from a near spherical to an oblate shape. Transitions from isomers are highly hindered because of the shape changes. They may be categorized to be shape isomers. The development of a secondary beam produced by using these high-spin isomers is also described.

  • 278. Gorska, M
    et al.
    Lipoglavsek, M
    Grawe, H
    Nyberg, J
    Atac, A
    Axelsson, A
    Bark, R
    Blomqvist, J
    KTH, Tidigare Institutioner, Fysik.
    Cederkäll, Joakim
    KTH, Tidigare Institutioner, Fysik.
    Cederwall, Bo
    KTH, Tidigare Institutioner, Fysik.
    DeAngelis, G
    Fahlander, C
    Johnson, A
    KTH, Tidigare Institutioner, Fysik.
    Leoni, S
    Likar, A
    Matiuzzi, M
    Mitarai, S
    Norlin, L O
    KTH, Tidigare Institutioner, Fysik.
    Palacz, M
    Persson, J
    Roth, H A
    Schubart, R
    Seweryniak, D
    Shizuma, T
    Skeppstedt, O
    Sletten, G
    Walters, W B
    Weiszflog, M
    Spectroscopy of the T-z=1 nuclei close to Sn-1001997Ingår i: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 28, nr 1-2, s. 303-307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The two nuclei Cd-98 and Sn-102, closest neighbours of Sn-100, have been studied with a recoil catcher setup, following the reactions: Ni-58(Ti-46, alpha 2n)Cd-98 and Ni-58(Cr-50, alpha 2n)Sn-102. Long lived isomeric states were measured in Cd-98 I-pi = (8+), t(1/2) = 0.48(8) mu s and in Sn-102 I-pi = (6(+)) with t(1/2) = 1.0(6) mu s. The proposed experimental level schemes of the isomeric decay are presented and compared to the shell model predictions.

  • 279. Gosch, M.
    et al.
    Serov, A.
    Anhut, T.
    Lasser, T.
    Rochas, A.
    Besse, P. A.
    Popovic, R. S.
    Blom, Hans
    KTH, Tidigare Institutioner, Fysik.
    Rigler, R.
    Parallel single molecule detection with a fully integrated single-photon 2X2 CMOS detector array2004Ingår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 9, nr 5, s. 913-921Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present parallel single molecule detection (SMD) and fluorescence correlation spectroscopy (FCS) experiments with a fully integrated complementary metal oxide semiconductor (CMOS) single-photon 2 X 2 detector array. Multifocal excitation is achieved with a diffractive optical element (DOE). Special emphasis is placed on parallelization of the total system. The performance of the novel single-photon CMOS detector is investigated and compared to a state-of-the-art single-photon detecting module [having an actively quenched avalanche photodiode (APD)] by measurements on free diffusing molecules at different concentrations. Despite the order of magnitude lower detection efficiency of the CMOS detector compared to the state-of-the-art single-photon detecting module, we achieve single molecule sensitivity and reliably determine molecule concentrations. In addition, the CMOS detector performance for the determination of the fraction of slowly diffusing molecules in a primer solution (two-component analysis) is demonstrated. The potential of this new technique for high-throughput confocal-detection-based systems is discussed.

  • 280.
    Goshtasbi Rad, Mohammad
    KTH, Tidigare Institutioner                               , Fysik.
    Electronic Structure and Reactions at some Tetrahedral Semiconductor Surfaces2000Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 281.
    Gravestijn, Bob
    KTH, Tidigare Institutioner                               , Fysik.
    Importance of radial profiles in spectroscopic diagnostics applied to the EXTRAP-T2R reversed-field pinch2003Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The determination of the plasma confinement propertiesdemand data as the electron temperature, the ionic and electrondensity profiles and the radiative emissivity profiles. Thefocus of this thesis is the importance of radial profiles inspectroscopic diagnostics applied to the EXTRAP-T2Rreversed-field pinch.

    EXTRAP-T2R is a resistive shell reversed-field pinch with amagnetic field shell penetration time much longer than therelaxation cycle time scale. Significant improvements inconfinement properties derived by quantitative plasmaspectroscopy in the vacuum ultraviolet are observed compared tothe previous device EXTRAP-T2. The low level of magneticturbulence and the good magnetic surfaces in the edge regionexplain this observed improvement. A current profile controlexperiment reduces the stochastic transport, which is connectedto the dynamo, and improves the confinement in EXTRAP-T2R evenmore.

    A comparison of the electron temperature estimated by usinga ratio of line intensities from the same ionization stage ofoxygen and the Thomson scattering system shows that thedifference is explained by the different spatial dependence ofthe excited state populations and the corresponding emissivityof these spectral lines. A collisional radiative model givesestimates for radial profiles of impurities which are notmeasured in EXTRAP-T2R. The estimated profiles can in turn beused to determine the radial profile of the effective ioncharge, the emissivity and finally the radiative power. Asinput, the model uses radial profiles.

    Neutral hydrogen is predominantly present in the boundaryregion of the plasma. Spectroscopic investigations in this areashow very asymmetric spectral lines of hydrogen due to themovement of atoms. The velocity of the hydrogen atoms dependson the type of plasma-wall interaction and their measurementhelps to identify the different interaction processes. Theexistence of hydrogen molecules in the edge complicates theinterpretation of the line shapes and on the determination ofthe particle confinement time.

    Keywords:Reversed-field pinch, EXTRAP-T2R, quantitativeplasma spectroscopy, VUV spectroscopy, line-integrated electrontemperature, oxygen, profiles, confinement properties, powerbalance, hydrogen, particle confinement time.

  • 282.
    Gravestijn, Bob
    KTH, Tidigare Institutioner                               , Fysik.
    Spectroscopic diagnistic of fusion plasma at the reversed-field pinch EXTRAP-T2R2002Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 283.
    Gravestijn, Robert
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Drake, James R.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Hedqvist, Anders
    KTH, Tidigare Institutioner, Fysik.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner, Fysik.
    Comparison of confinement in resistive-shell reversed-field pinch devices with two different magnetic shell penetration times2004Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 46, nr 1, s. 11-22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A loop voltage is required to sustain the reversed-field pinch (RFP) equilibrium. The configuration is characterized by redistribution of magnetic helicity but with the condition that the total helicity is maintained constant. The magnetic field shell penetration time, tau(s), has a critical role in the stability and performance of the RFP Confinement in the EXTRAP device has been studied with two values of tau(s), first (EXTRAP-T2) with tau(s), of the order of the typical relaxation cycle timescale and then (EXTRAP-T2R) with tau(s), much longer than the relaxation cycle timescale, but still much shorter than the pulse length. Plasma parameters show significant improvements in confinement in EXTRAP-T2R. The typical loop voltage required to sustain comparable electron poloidal beta values is a factor of 3 lower in the EXTRAP-T2R device. The improvement is attributed to reduced magnetic turbulence.

  • 284. Grehk, T. M.
    et al.
    Göthelid, Mats
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Bjorkqvist, M.
    Le Lay, G.
    Karlsson, Ulf O.
    KTH, Tidigare Institutioner                               , Fysik.
    Li-induced phase transition from the Ge(111)3X1: Li surface reconstruction to the Ge(111)root 3X root 3 : Li lithium germanide2000Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, nr 7, s. 4963-4967Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated the Li-induced phase transition from the Ge(111)3X1:Li to the Ge(111)root 3X root 3:Li reconstruction with photoemission. The Ge(111)3X1:Li reconstruction can be described as parallel rows of Ge atoms separated by single rows of Li atoms. The Ge(111)root 3X root 3:Li reconstruction, on the other hands, has to be described in terms of a Li-germanide phase extending over at least two atomic layers.

  • 285.
    Grigelionis, Gintautas
    KTH, Tidigare Institutioner                               , Fysik.
    Application of the cluster-variation method to ordering in two-dimensionallatticesystems1997Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 286.
    Grimvall, Göran
    KTH, Tidigare Institutioner, Fysik.
    Socrates, Fermi, and the second law of thermodynamics2004Ingår i: American Journal of Physics, ISSN 0002-9505, E-ISSN 1943-2909, Vol. 72, nr 9, s. 1145-1146Artikel i tidskrift (Övrigt vetenskapligt)
  • 287.
    Grivel, Jean-Claude
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Eltsev, Yuri
    KTH, Tidigare Institutioner, Fysik.
    Andersson, Magnus
    KTH, Tidigare Institutioner, Fysik.
    Rapp, Östen
    KTH, Tidigare Institutioner, Fysik.
    Erb, Andreas
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Walker, Eric
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    Flükiger, René
    Dept. de la Matière Condensée, University of Geneva, Geneva.
    First-order melting transition observed from resistivity measurements in ultra-pure YBa2Cu3O7-delta single crystals with high twin boundary density1999Ingår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 322, nr 3-4, s. 203-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    R(T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa2Cu3O7-delta single crystals, under a magnetic field B oriented parallel to the twin boundary planes (B parallel to c). The characteristic feature attributed to the flux line lattice melting transition has been observed in the overdoped case for B greater than or equal to 5 T. The first-order transition was not found in the optimally doped sample, even when B was tilted with respect to the c-axis. Differences between these samples are discussed.

  • 288. Gromov, A.
    et al.
    Korenivski, Vladislav
    KTH, Tidigare Institutioner                               , Fysik.
    Electromagnetic analysis of layered magnetic/conductor structures2000Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 33, nr 7, s. 773-779Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is described for calculating the impedance of conductor structures comprised of ferromagnetic and non-magnetic layers of arbitrary cross sectional shape with transverse dimensions which are small compared to the conductors length. The method is exemplified on a conductor of axial symmetry enclosed in a high permeability film of uniaxial anisotropy along the conductor axis. To find the impedance the full boundary value problem for the vector potential is solved, allowing driving and eddy currents in both the conductor and the magnetic film, and taking into account the dynamics of the magnetization governed by the Landau-Lifshitz equations. The results obtained are used to model the giant magneto impedance effect in ferromagnetically coated wires.

  • 289.
    Gromov, Andrey
    KTH, Tidigare Institutioner                               , Fysik.
    Dynamic response of ferromagnetic-nonmagnetic layered structures1999Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 290.
    Gromov, Andrey
    KTH, Tidigare Institutioner                               , Fysik.
    Impedance of Soft Magnetic Multilayers: Application to GHz Thin Film Inductors2001Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A theoretical approach to calculating impedance of metallicmagnetic/conductor layered structures is developed. Thefrequency range considered extends to the ferromagneticresonance region of soft magnetic films (of the order of 1GHz). The analysis includes the effects of screening of thehigh frequency fields by eddy currents as well as the dynamicsand relaxation of the magnetization of the ferromagneticsub-system. Analytical expressions for the impedance as afunction of frequency and material parameters and geometry ofmagnetic sandwich stripes are obtained. Two maincross-sectional layouts are considered: amagnetic/conductor/magnetic sandwich stripe with and withoutflux closure at the edges along the stripe length - with andwithout the magnetic film enclosing the conductor strip. Theimportance of good magnetic flux closure for achieving largespecific inductance gains and high efficiency at GHzfrequencies is emphasized.

    The theoretical results obtained were used to design andanalyze magneticfilm inductors produced using iron nitridealloy films. Patterned sandwiches, consisting of two Fe-N filmsenclosing a conductor film made of Cu, were fabricated onoxidized Si substrates using lift-off lithography. Theinductors exhibited a 2-fold specific inductance enhancement at1 GHz. The magnetic contribution to the total flux in thenarrow devices was less then predicted theoretically, which wasattributed to hardening of the magnetic material at the edgesof the strip leading to incomplete flux closure. Material anddesign issues important for further improving the performanceof the devices are discussed.

  • 291. Grosse, H.
    et al.
    Langmann, Edwin
    KTH, Tidigare Institutioner                               , Fysik.
    Chiral Schwinger models without gauge anomalies2000Ingår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 587, nr 03-jan, s. 568-584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We find a large class of quantum gauge models with massless fermions where the coupling to the gauge fields is not chirally symmetric and which nevertheless do not suffer from gauge anomalies. To be specific we study two dimensional Abelian models in the Hamiltonian framework which can be constructed and solved by standard techniques. The general model describes Np photon fields and NF flavors of Dirac fermions with 2N(F)N(P) different coupling constants, i.e., the chiral component of each fermion can he coupled to the gauge fields differently We construct these models and find conditions so that no gauge anomaly appears. If these conditions hold it is possible to construct and solve the model explicitly, so that gauge- and Lorentz invariance are manifest.

  • 292. Grosse, Harald
    et al.
    Langmann, Edwin
    KTH, Tidigare Institutioner, Fysik.
    Paufler, Cornelius
    KTH, Tidigare Institutioner, Fysik.
    Exact solution of a 1D quantum many-body system with momentum-dependent interactions2004Ingår i: Journal of Physics A: Mathematical and General, ISSN 0305-4470, E-ISSN 1361-6447, Vol. 37, nr 16, s. 4579-4592Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We discuss a ID quantum many-body model of distinguishable particles with local, momentum-dependent two-body interactions. We show that the restriction of this model to fermions corresponds to the non-relativistic limit of the massive Thirring model. This fermion model can be solved exactly by a mapping to the 1D boson gas with inverse coupling constant. We provide evidence that this mapping is the non-relativistic limit of the duality between the massive Thirring model and the quantum sine-Gordon model. We show that the generalized model with distinguishable particles remains exactly solvable by the (coordinate) Bethe ansatz. Our solution provides a generalization of the above mentioned boson-fermion duality to particles with arbitrary exchange statistics characterized by any irreducible representation of the permutation group.

  • 293.
    Gubaidullin, Askar
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Sehgal, Balraj
    KTH, Tidigare Institutioner, Fysik.
    Numerical analysis of natural convection and mixing in two-fluid stratified pools with internal heat sources2004Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 126, nr 4, s. 600-610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The heat transport in two-layer fluid systems has been investigated numerically for slice-type semicircular pools with internal heat sources. The fixed interface model has been applied to study natural convection in the system of the immiscible fluids. The double-diffusion model has been employed to describe the heat transfer and mixing for the miscible fluids. The numerical results are compared to data measured in the SIMECO experiments. Based on the numerical simulations, the effect of the ratio of the fluid properties has been quantified. The results are of interest for the corium melt coolability in a postulated severe accident scenario in a light water reactor.

  • 294.
    Gudowski, Waclaw
    KTH, Tidigare Institutioner                               , Fysik.
    Transmutation of isotopes - Ecological and energy production aspects2000Ingår i: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 31, nr 1, s. 107-122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes principles of Accelerator-Driven Transmutation of Nuclear Wastes (ATW) and gives some flavour of the most important topics which are today under investigations in many countries. Pin assessment of the potential impact of ATW on a future of nuclear energy is also given. Nuclear reactors based on self-sustained fission reactions - after spectacular development in fifties and sixties, that resulted in deployment of over 400 power reactors - are wrestling today more with public acceptance than with irresolvable technological problems. In a whole spectrum of reasons which resulted in today's opposition against nuclear power few of them are very relevant for the nuclear physics community and they arose from the fact that development of nuclear power had been handed over to the nuclear engineers and technicians with some generically unresolved problems, which should have been solved properly by nuclear scientists. In a certain degree of simplification one can say, that most of the problems originate from very specific features of a fission phenomenon: self-sustained chain reaction in fissile materials and very strong radioactivity of fission products and very long half-life of some of the fission and activation products. And just this enormous concentration of radioactive fission products in the reactor core is the main problem of managing nuclear reactors: it requires unconditional guarantee for the reactor core integrity in order to avoid radioactive contamination of the environment; it creates problems to handle decay heat in the reactor core and finally it makes handling and/or disposal of spent fuel almost a philosophical issue, due to unimaginable long time scales of radioactive decay of some isotopes. A lot can be done to improve the design of conventional nuclear reactors (like Light Water Reactors); new, better reactors can be designed but it seems today very improbable to expect any radical change in the public perception of conventional nuclear power. In this context a lot of hopes and expectations have been expressed for novel systems called Accelerator-Driven Systems, Accelerator-Driven Transmutation of Waste or just Hybrid Reactors. All these names are used for description of the same nuclear system combining a powerful particle accelerator with a subcritical reactor. A careful analysis of possible environmental impact of ATW together with limitation of this technology is presented also in this paper.

  • 295.
    Gudowski, Waclaw
    KTH, Tidigare Institutioner                               , Fysik.
    Transmutation of nuclear waste2000Ingår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 663, s. 169C-182CArtikel i tidskrift (Refereegranskat)
  • 296.
    Gudowski, Waclaw
    et al.
    KTH, Tidigare Institutioner                               , Fysik.
    Arzhanov, Vasily
    Broeders, C.
    Broeders, I.
    Cetnar, J.
    Cummings, R.
    Ericsson, M.
    Fogelberg, B.
    Gaudard, C.
    Koning, A.
    Landeyro, P.
    Magill, J.
    Pazsit, I.
    Peerani, P.
    Phlippen, P.
    Piontek, M.
    Ramstrom, E.
    Ravetto, P.
    Ritter, G.
    Shubin, Y.
    Soubiale, S.
    Toccoli, C.
    Valade, M.
    Wallenius, Janne
    KTH, Tidigare Institutioner                               , Fysik.
    Youinou, G.
    Review of the European project - Impact of Accelerator-Based Technologies on Nuclear Fission Safety (IABAT)2001Ingår i: Progress in nuclear energy (New series), ISSN 0149-1970, E-ISSN 1878-4224, Vol. 38, nr 1-2, s. 135-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The IABAT project - Impact of Accelerator Based Technologies on Nuclear Fission Safety - started in 1996 in the frame of 4(th) Framework Programme of the European Union, R&D specific programme Nuclear fission safety 1994-1998, area A.2 Exploring innovative approaches/Fuel cycle concepts, as one of the first common European activities in ADS. The project was completed October 31, 1999. The overall objective of the IABAT project has been a preliminary assessment of the potential of Accelerator-Driven Systems (ADS) for transmutation of nuclear waste and for nuclear energy production with minimum waste generation. Moreover, more specific topics related to nuclear data and code development for ADS have been studied in more detail. Four ADSs have been studied for different fuel/coolant combinations: liquid metal coolant and solid fuel, liquid metal coolant and dispersed fuel, and fast and thermal molten salt systems. Target studies comprised multiple target solutions and radiation damage problems in a target environment. In a tool development part of the project a methodology of subcriticality monitoring has been developed based on Feynman-alpha and Rossi-alpha methods. Moreover, a new Monte-Carlo burnup code taking full advantage of continuous neutron cross-section data has been developed and benchmarked. Impact on the risk from high-level waste repositories fi om radiotoxicity reduction using ADS has been assessed giving no crystal-clear benefits of ADS for repository radiotoxicity reduction but concluding some important prerequisites for effective transmutation. In proliferation studies important differences between critical reactors and ADS have been underlined and non-proliferation measures have been proposed. In assessment of accelerator technology costing models have been created that allow the circular and linear accelerator options to be compared and the effect of parameter variations examined. The calculations reported show that cyclotron systems would be more economical, due mainly to the advantage of the cost of RF power supplies. However, the accelerator community regards with skepticism the possibility of transporting and extracting more than a 10mA beam current from a 1GeV cyclotron and therefore technical factors may limit the application of cyclotrons. Finally, this review summarizes development of nuclear data in the energy region between 20 Mev and 150 MeV. Neutron and proton transport data files for Fe, Ni, Pb, Th, U-238 and Pu-239 have been created. The high-energy part of the data files consists completely of results from model calculations, which are benchmarked against the available experimental data. Although there is obviously future work left regarding fine-tuning of several parts of the data files, the representation of nuclear reaction information up to 150 MeV is already better than can be attained with intranuclear cascade codes.

  • 297. Gueorguieva, E.
    et al.
    Schück, C.
    Minkova, A.
    Vieu, C.
    Hannachi, F.
    Kaci, M.
    Porquet, M. G.
    Wyss, Ramon
    KTH, Tidigare Institutioner                               , Fysik.
    Dionisi, J. S.
    Korichi, A.
    Lopez-Martens, A.
    High-spin states in Au-191: Evidence for triaxial shape?2003Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 68, nr 5, s. 543081-5430814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The level scheme of Au-191 was considerably extended to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the Orsay electron spectrometer. Several bands that appear as strongly coupled were associated with low- Omega configurations in Au-191 . Using total routhian surface and cranked shell model calculations it was shown that these bands have a rotation-aligned nature and are most likely generated by the nonaxiallity of the nucleus induced by the odd proton. The predictions for the presence of such bands in Au-191 and in the oblate nuclei in the Pt-Au-Hg region found excellent agreement with the experimental data, as well as the predictions for their alignments and band-crossing frequencies in Au-191 .

  • 298. Gueorguieva, E.
    et al.
    Schück, C.
    Minkova, A.
    Vieu, C.
    Kaci, M.
    Hannachi, F.
    Wyss, Ramon
    KTH, Tidigare Institutioner, Fysik.
    Dionisio, J. S.
    Korichi, A.
    Lopez-Martens, A.
    Sets of rotation-aligned bands indicating nonaxiality in Au-1902004Ingår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 69, nr 4, s. 044320-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The level scheme of Au-190 was extended up to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the electron- gamma spectrometer of Orsay. Several sets of rotation-aligned bands were found and associated with high- j, low- K configurations. According to the total Routhian surface and cranked shell model calculations these bands are caused by the nonaxiality of the nuclear deformation (gammaless than or equal to-70degrees). Furthermore, very good agreement was obtained between the experimental data and the theoretical predictions for the properties of these bands, such as alignments, band-crossing frequencies, and signature inversion, thus supporting the suggested nonaxial shapes.

  • 299. Gulacsi, M.
    et al.
    McCulloch, I. P.
    Juozapavicius, Ausrius
    KTH, Tidigare Institutioner, Fysik.
    Rosengren, Anders
    KTH, Tidigare Institutioner, Fysik.
    Magnetism in the dilute Kondo lattice model2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The one-dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is vertified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the f spins are diluted. For the incommensurate case, short-range antiferromagnetic correlations are found to dominate at low doping, which distinguishes the dilute Kondo lattice model from the standard Kondo lattice model.

  • 300. Göthelid, M.
    et al.
    Grehk, T. M.
    Hammar, M.
    KTH, Tidigare Institutioner, Fysik.
    Karlsson, U. O.
    Flodström, S. A.
    Adatom and rest-atom contributions in Ge(111)c(2×8) and Ge(111)-Sn(7×7) core-level spectra1993Ingår i: Physical Review B, ISSN 01631829 (ISSN), Vol. 48, nr 3, s. 2012-2015Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have identified the adatom contribution in the Ge 3d core-level spectra from the clean Ge(111)c(2×8) surface, shifted 0.17 eV to higher binding energy compared to the bulk. This adatom component vanishes in the Ge(111)-Sn(7×7) surface core-level spectra where Sn occupies the adatom site. Moreover we report the observation of an earlier proposed difference between the rest atoms in the c(2×8) structure, and also a shift to lower binding energy for the rest atoms in both structures studied. © 1993 The American Physical Society.

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