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  • 51.
    Gustafsson, Peter
    et al.
    Mälardalens högskola, Sweden.
    Jonsson, Gunnar
    Karlstads universitet, Sweden.
    Enghag, Margareta
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education.
    The problem-solving process in physics as observed when engineering students at university level work in groups2013In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 40, no 4, p. 380-399Article in journal (Refereed)
  • 52.
    Hameedi, Alley
    Stockholm University, Faculty of Science, Department of Physics.
    Quantum Random Access Codes & their Applications2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Based on the principles of quantum mechanics, quantum information is a highly interesting and fast emerging field which refers to processing information encoded into the state of a quantum system and the subsequent use of such quantum systems for various information tasks. In this thesis, we have studied the role of single d-level quantum systems (qudits) as a quantum resource in the context of a communication task, commonly known as random access codes (RACs). We investigate the advantage of quantum random access codes (QRACs), employing quantum systems of arbitrary dimensions as means of communication between the parties, in terms of average performances over their classical counterparts. For this purpose, a class of QRACs with dimension d=4 is focused upon. Additionally, these higher dimensional QRACs have also been studied in terms of applications where we consider their potential in generation of true randomness. Furthermore, a parallel implementation of two parallel QRACs (employing qubits) is explored as a resource for test of non-classicality of a physical system.

    Our results obtained show that QRACs outperform their classical counterparts performance wise. Moreover, this advantage over classical resources can be extended further by use of higher dimensional QRACs. The high-level QRACs lead to higher average success probabilities and more generated randomness as compared to classical RACs or QRACs of lower dimensions. Finally, an experimental test of non-classicality is demonstrated which allows for arbitrarily low detection efficiencies and does not invoke extra assumptions as lack of shared randomness between devices.

  • 53.
    Heydari, Hoshang
    Stockholm University, Faculty of Science, Department of Physics.
    Combinatorial and Geometrical Structures of Multipartite Quantum Systems2009In: Mathematical Physics Research Developments / [ed] Morris B. Levy, New York: Nova Science Publishers , 2009, 1, p. 589-604Chapter in book (Other (popular science, discussion, etc.))
  • 54.
    Heydari, Hoshang
    Stockholm University, Faculty of Science, Department of Physics.
    Different classes of quantum gates entanglers2009In: International journal of quantum information, ISSN 0219-7499, Vol. 7, no 1, p. 279-285Article in journal (Refereed)
    Abstract [en]

    We construct quantum gates entanglers for different classes of multipartite states. In particular, we construct entangler operators for W and GHZ classes of multipartite states based on the construction of the concurrence classes. We also discuss in detail these two classes of the quantum gates entanglers for three-partite states.

  • 55.
    Heydari, Hoshang
    Stockholm University, Faculty of Science, Department of Physics.
    Generalized controlled phase quantum gates entanglers2009In: International journal of quantum information, ISSN 0219-7499, Vol. 7, no 6, p. 1211-1216Article in journal (Refereed)
    Abstract [en]

    We construct a generalized controlled phased gate entangler for a multi-qubit state based on the geometrical structure of quantum systems. We also investigate the relation between the generalized controlled phase construction of a quantum gate entangler and graph state for two-qubit and three-qubit states.

  • 56.
    Heydari, Hoshang
    Stockholm University, Faculty of Science, Department of Physics.
    Selective Phase Rotation Quantum Gate Entangler2009In: Open systems & information dynamics, ISSN 1230-1612, E-ISSN 1573-1324, Vol. 16, no 4, p. 407-412Article in journal (Refereed)
    Abstract [en]

    We construct a quantum gate entangler for multi-qubit states based on a selective phase rotation transform. In particular, we establish a relation between the quantum integral transform and the quantum gate entangler in terms of universal controlled gates for multi-qubit states. Our result gives an effective way of constructing topological and geometrical quantum gate entanglers for multipartite quantum systems, which could also lead to a construction of geometrical quantum algorithms.

  • 57.
    Hidvégi, Attila
    Stockholm University, Faculty of Science, Department of Physics.
    FPGA-based Instrumentation for Advanced Physics Experiments2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Modern physical experiments often demand advanced instrumentation based on advances in  technology. This work describes four instrumentation physics projects that are based on modern, high-capacity Field-Programmable Gate Arrays, making use of their versatility, programmability, high bandwidth communication interfaces and signal processing capabilities.

    In the first project, a jet-finding algorithm for the ATLAS detector at the LHC experiment at CERN was developed and implemented, and different verification methods were created to validate the functionality and reliability. The experiment uses a three level trigger system, where the first level uses custom FPGA-based hardware for analysis of collision events in real-time.

    The second project was an advanced timing and triggering distribution system for the new European X-Ray Free Electron Laser (XFEL) facility at DESY in Hamburg. XFEL will enable scientists to study nano structures on the atomic scale. Its laser pulses will have the strongest peak power in the world with extremely short duration and a high repetition rate, which will even allow filming of chemical reactions. The timing system uses modern FPGAs to distribute high-speed signals over optical fibers and to deliver clocks and triggers with high accuracy.

    The third project was a new data acquisition board based on high-speed ADCs combined with high-performance FPGAs, to process data from segmented Ge-detectors in real-time. The aim was to improve system performance by greatly oversampling and filtering the analog signals to achieve greater effective resolution.

    Finally, an innovative solution was developed to replace an aging system used at CERN and Stockholm University to test vital electronics in the Tile Calorimeters of the ATLAS detector system. The new system is entirely based on a commercial FPGA development board, where all necessary custom communication protocols were implemented in firmware to emulate obsolete hardware.

  • 58.
    Huang, Ningdong
    et al.
    Stanford Synchrotron Radiat Lab, Stanford, CA 94309 USA.
    Nordlund, Dennis
    Stanford Synchrotron Radiat Lab, Stanford, CA 94309 USA.
    Huang, Congcong
    Stanford Synchrotron Radiat Lab, Stanford, CA 94309 USA.
    Tyliszczak, Tolek
    LBL, Adv Light Source, Berkeley, CA 94720 USA .
    Weiss, Thomas M.
    Stanford Synchrotron Radiat Lab, Stanford, CA 94309 USA .
    Acremann, Yves
    Stanford Synchrotron Radiat Lab, Stanford, CA 94309 USA .
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Schlesinger, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Microscopic Probing of the Size Dependence in Hydrophobic Solvation2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 7, p. 074507-Article in journal (Refereed)
    Abstract [en]

    A dependence on solute size of the hydrophobic effect has been proposed based on theory and simulations, such that small apolar solutes leave the hydrogen (H-) bonding network in water intact or even strengthened, whereas hydration of larger, nanometer-sized apolar solutes breaks hydrogen bonds and creates a liquid-vapor-like interface around the solutes. Here we report the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in aqueous solutions of amphiphilic tetraalkyl-ammonium (CnH2n+1)4N + (TAA) cations with increased side chain length by probing the H-bonding network in water through O K-edge x-ray absorption spectroscopy and the solute-solute interaction using small angle x-ray scattering. These results open for unique experimental opportunities to investigate hydrophobic effects for a range of important processes in chemistry and biology.

    We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (CnH2n+1)4N+ (R4N+) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 Å, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations.

  • 59.
    Hultqvist, Martha
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Secondary absorbed doses from light ion irradiation in anthropomorphic phantoms representing an adult male and a 10 year old child2010In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 55, no 22, p. 6633-6653Article in journal (Refereed)
    Abstract [en]

    Secondary organ absorbed doses were calculated by Monte Carlo simulations with the SHIELD-HIT07 code coupled with the mathematical anthropomorphic phantoms CHILD-HIT and ADAM-HIT. The simulated irradiations were performed with primary 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 100–400 MeV/u which were directly impinging on the phantoms, i.e. approximating scanned beams, and with a simplified beamline for 12C irradiation. The evaluated absorbed doses to the out-of-field organs were in the range 10−6 to 10−1 mGy per target Gy and with standard deviations 0.5–20%. While the contribution to the organ absorbed doses from secondary neutrons dominated in the ion beams of low atomic number Z, the produced charged fragments and their subsequent charged secondaries of higher generations became increasingly important for the secondary dose delivery as Z of the primary ions increased. As compared to the simulated scanned 12C ion beam, the implementation of a simplified beamline for prostate irradiation with 12C ions resulted in an increase of 2–50 times in the organ absorbed doses depending on the distance from the target volume. Comparison of secondary organ absorbed doses delivered by 1H and 12C beams showed smaller differences when the RBE for local tumor control of the ions was considered and normalization to the RBE-weighted dose to the target was performed.

    General scientific summary. During light ion therapy, the production of nuclear fragments results in a complex secondary radiation field which the organs and normal tissues of the patient are exposed to. In the present work, the absorbed doses to out-of-field organs and the energy distribution of secondary particle fluences in anthropomorphic phantoms have been simulated by the Monte Carlo code SHIELD-HIT07 for brain tumor and prostate irradiation with approximated scanned beams of 1H, 4He, 7Li, 12C and 16O ions in the energy range 100–400 MeV/u, as well as with a simplified beam line for 12C irradiation. The evaluated organ absorbed doses were in the range 10−6 to 10−1 mGy per target Gy. The absorbed dose contribution from secondary neutrons dominated in the ion beams of low atomic number Z, while the produced charged fragments and their subsequent charged secondaries became increasingly important for the secondary dose delivery as Z of the primary ion increased.

  • 60.
    Hultqvist, Martha
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Secondary doses in anthropomorphic phantoms irradiated with light ion beams2009In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 168, no 1, p. 123-127Article in journal (Refereed)
    Abstract [en]

    The mathematical anthropomorphic phantoms EVA-HIT and ADAM-HIT have been used in the Monte Carlo code SHIELD-HIT07 for simulations of lung tumor and prostate irradiation with light ions. Calculations were performed for 1H, 7Li, and 12C beams of energies in the range of 80 to 330 MeV/u. The secondary doses to organs, due to scattered primary ions and secondary particles produced in the phantoms, were studied taking into account the contribution from secondary neutrons, secondary protons, pions, and heavier fragments from helium to calcium. The doses to organs per dose to target (tumor) are of the order of 10-6 to 10-1 mGy Gy-1 and decrease with increasing distance from the target. In general the organ dose per target dose increases with increasing Z of the primary particle; however, for lighter primary ions (Z 3) and for organs close to the target, scattered primary particles show a nonnegligible dose contribution.

  • 61.
    Högås, Marcus
    Stockholm University, Faculty of Science, Department of Physics.
    On the consistency of multigravity theories2016Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    In this thesis a set of recently proposed multigravity theories is analysed. In the special case of bimetric gravity, the theory has been conclusively shown to be ghost-free. On the other hand, for multigravity theories in general, the ghost-issue has not been settled conclusively. Motivated by this fact, the main object of this thesis is to clarify what has been proven so far and what issues that still needs to be addressed. We also provide new calculations and results pointing in the direction that the multigravity theories must be restricted to a set of bimetric Hassan-Rosen couplings in a tree-type structure in order to be consistent. In particular, we prove that for a multivielbein theory of  interacting vielbeins, the Lorentz equations of motion is a set of  Deser-van Nieuwenhuizen conditions if and only if the theory consists of bimetric Hassan-Rosen couplings in a tree-type structure.

  • 62. Iyer, Uma N.
    et al.
    Lebedev, Alexei
    Leites, Dimitry
    Stockholm University, Faculty of Science, Department of Mathematics.
    PROLONGS OF (ORTHO-)ORTHOGONAL LIE (SUPER)ALGEBRAS IN CHARACTERISTIC 22010In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 17, p. 253-309Article in journal (Refereed)
    Abstract [en]

    Cartan described some of the finite dimensional simple Lie algebras and three of the four series of simple infinite dimensional vectorial Lie algebras with polynomial coefficients as prolongs, which now bear his name. The rest of the simple Lie algebras of these two types (finite dimensional and vectorial) are, if the depth of their grading is greater than 1, results of generalized Cartan-Tanaka-Shchepochkina (CTS) prolongs. Here we are looking for new examples of simple finite dimensional modular Lie (super) algebras in characteristic 2 obtained as Cartan prolongs. We consider pairs (an (ortho-)orthogonal Lie (super) algebra or its derived algebra, its irreducible module) and compute the Cartan prolongs of such pairs. The derived algebras of these prolongs are simple Lie (super) algebras. We point out several amazing phenomena in characteristic 2: a supersymmetry of representations of certain Lie algebras, latent or hidden over complex numbers, becomes manifest; the adjoint representation of some simple Lie superalgebras is not irreducible.

  • 63. Iyer, Uma N.
    et al.
    Leites, Dimitry
    Stockholm University, Faculty of Science, Department of Mathematics.
    Messaoudene, Mohamed
    Shchepochkina, Irina
    EXAMPLES OF SIMPLE VECTORIAL LIE ALGEBRAS IN CHARACTERISTIC 22010In: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 17, p. 311-374Article in journal (Refereed)
    Abstract [en]

    The classification of simple finite dimensional modular Lie algebras over algebraically closed fields of characteristic p > 3 (described by the generalized Kostrikin-Shafarevich conjecture) being completed due to Block, Wilson, Premet and Strade (with contributions from other researchers) the next major classification problems are those of simple finite dimensional modular Lie algebras over fields of characteristic 3 and 2. For the latter, the Kochetkov-Leites conjecture involved classification of Lie superalgebras and their inhomogeneous with respect to parity subalgebras, called Volichenko algebras. In characteristic 2, we consider the result of application of the functor forgetting the superstructure to the simple serial vectorial Lie algebras known to us and their Volichenko subalgebras.

  • 64.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    Black holes and trapped surfaces2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The study of black holes is an important part of general relativity. However, the very definition of black holes is not completely satisfactory. Alternative definitions are based on the concept of trapped surfaces. This licentiate thesis is based on work with the aim to better understand the behaviour of such trapped surfaces.

    The standard definition of a black hole and specific examples are reviewed, as well as the definition of trapped surfaces, various horizons related to trapped surfaces, and the trapping boundary. This serves as an introduction to two published papers. The first paper provides an exact model of a marginally trapped tube making a sudden jump outwards as matter is falling into the black hole. The second paper concerns the question of the location of the trapping boundary in the Oppenheimer-Snyder black hole.

  • 65.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    How trapped surfaces jump in 2+1 dimensions2013In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 30, no 6, article id 065022Article in journal (Refereed)
    Abstract [en]

    When a lump of matter falls into a black hole it is expected that a marginally trapped tube when hit moves outwards everywhere, even in regions not yet in causal contact with the infalling matter. But to describe this phenomenon analytically in 3+1 dimensions is difficult since gravitational radiation is emitted. By considering a particle falling into a toy model of a black hole in 2+1 dimensions an exact description of this non-local behaviour of a marginally trapped tube is found.

  • 66.
    Jakobsson, Emma
    Stockholm University, Faculty of Science, Department of Physics.
    Shapes of Spacetimes: Collected tales of black holes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In theory, the existence of black holes is predicted by general relativity. In reality, there is a general consensus that they exist in space; in particular at the center of many galaxies. The theory of black holes has been around for decades, but there are still interesting questions calling for attention. This doctoral thesis and its four contributions touches upon some of these questions.

    One challenging theoretical aspect of black holes lies in their definition, the event horizon. For several reasons, this definition is not satisfactory in many contexts, and alternative horizons based on the concept of trapped surfaces have been suggested to take its place. The question raised in Paper I has to do with the location of such surfaces in a simple model of gravitational collapse, the Oppenheimer-Snyder model.

    A different scenario of gravitational collapse, that of a null shell of dust collapsing in flat spacetime, is the starting point of the original formulation of the Penrose inequality. By a reformulation, this inequality can be turned into a purely geometric relation in Minkowski space. In Paper IV we formulate and prove a (2+1)-dimensional version in anti-de Sitter space.

    The Penrose inequality sometimes goes under the name of the "isoperimetric inequality for black holes". In Paper III a different kind of isoperimetric inequality is discussed (with less rigour), namely that of the volume contained in a black hole with a given area.

    In Paper II, the subject of limits of spacetimes is visualized. Again, (2+1)-dimensional anti-de Sitter space finds its use, as a one parameter family of surfaces, capturing the geometry of charged black hole spacetimes, is embedded in it. Thus different limiting procedures are illustrated.

    Finally, interesting models can be constructed by cutting and gluing in spacetimes, but in doing so one needs to take care, in order to obtain a physically realistic model. With this background as motivation, a study of Lorentzian cones is given.

    Taken together, all of these contributions make up a collection of interesting aspects of black hole geometry, or, shapes of spacetimes.

  • 67.
    Jenei, István Zoltán
    Stockholm University, Faculty of Science, Department of Physics.
    Scanning electron microscopy (SEM) analysis of tribofilms enhanced by fullerene-like nanoparticles2012Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The beneficiary effects of WS2 inorganic fullerene-like nanoparticles in the lubrication industry were shown in recent years. The incorporation of the nanoparticles into lubricants (oils, greases) is however not straightforward.

    When two surfaces are sliding against each other and a lubricant is used, a thin layer (tribofilm) is formed on the contact area, which effects the friction process. Lubricants usually contain several additives. These additives can impair the friction reducing behaviour of the WS2 inorganic fullerene-like nanoparticles. This thesis investigates the effects of several additives in the lubrication process by analysing the tribofilms formed on the worn surfaces using energy-dispersive X-ray spectroscopy in a scanning electron microscope.

  • 68.
    Jenei, Zsolt
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Visbeck, Ken
    Lawrence Livermore National Laboratory.
    Cynn, Hyunchae
    Lawrence Livermore National Laboratory.
    Yoo, Choong-Shik
    Washington State University.
    Evans, William
    Lawrence Livermore National Laboratory.
    High temperature experiments using a resistively heated membrane driven diamond anvil cellManuscript (Other academic)
    Abstract [en]

     

    A reliable high-performance heating method using resistive heaters and a membrane driven diamond anvil cell (mDAC) is presented. Two micro-heaters are mounted in a mDAC and use electrical power of less than 150 W to achieve sample temperatures up to 1200 K. For temperature measurement we use two K-type thermocouples mounted near the sample. The approach can be used for in-situ Raman spectroscopy and x-ray diffraction at high pressures and temperatures. A W-Re alloy gasket material permits stable operation of mDAC at high temperature. Using this method, we made an isothermal compression at 900 K to pressures in excess of 100 GPa and isobaric heating at 95 GPa to temperatures in excess of 1000 K. As an example, we present high temperature Raman spectroscopy measurements of nitrogen at high pressures

  • 69.
    Jonsson, Cathrine
    Stockholm University.
    Advances in quantitative emission tomography: development and analysis of methods for validation and correction2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The nuclear medicine imaging techniques SPECT and PET are sensitive tools in mapping various physiological and biochemical processes in vivo. This work was devoted to investigations of methodological and physical properties of the SPECT technique as well as developing methods for validation and correction. Brain imaging was the major focus in this work, but the results are applicable to other examination areas. In the first part regional cerebral blood flow (rCBF) as measured by PET - the golden standard - and by SPECT was compared using a computerised brain atlas. Overall the differences were surprisingly small but revealed an apparent reduced grey-to-white matter ratio for SPECT, mainly due to the lack of scatter correction in SPECT, a lower spatial resolution and a non-linear extraction of the SPECT radiopharmaceutical. Furthermore, the reproducibility of resting state rCBF with SPECT was investigated, imperative information whenever scans are being repeated, as in activation studies, or when comparing an individual scan to a database of scans from healthy individuals. The results indicate that normalised flow data show high intra- and inter-individual reproducibility, expressed as standard deviations, ±1.3% and ±2.9%, respectively. The major error was addressed to the methodology, i.e. the scanning procedure and the atlas adaptation.

    At that stage of the study, using a clinical protocol, without scatter correction and proper attenuation correction there was no possibility to extract quantitative information from the SPECT images. Therefore, in the subsequent work, a phantom concept (the stack phantom) was designed aiming at experimental validation of the SPECT methodology, including effects of photon interactions. Extracting information where the primary (unscattered) photons are separated from the ones undergoing scattering or attenuation before detection, was, until now, only possible using Monte Carlo simulations. The basis of the novel phantom concept is to sample various 3D-activity distributions from a set of 2D samples. The 2D samples are ordinary paper sheets where the cross sectional radioactivity distribution is printed out using radioactive ink. Mounting the samples together with a certain equidistant axial spacing, using either tissue equivalent material or some low-density material, give possibilities to mimick the very same activity distribution clinically (with degrading photon interactions) as well as almost "pure" primary photon images. The phantom concept is very flexible, any activity distribution may be constructed, pathological patterns can easily be introduced and varied. Moreover, correction methods and software evaluation tools may be assessed and validated with the phantom. However, the phantom has not only applicability in research areas - recurrent quality assurance programs can as well make use of dedicated stack phantoms.

    In the last phase of this work a scatter correction algorithm was developed, making use of the stack phantom. The correction was developed using a multi-spectral acquisition system. This allowed for spectral acquisitions in each pixel in the projection images. After correcting for the scatter contribution in the upper half of the photo-peak using the shape of the scatter distribution from the Klein-Nishina cross section the resulting estimate of primary photons was mirrored (folded) over to estimate the primary photons in the lower half of the photo-peak. The scatter correction works in each spectrum and hence corrects for the scatter contribution locally. The correction method was validated both with Monte Carlo simulations and the stack-phantom, both indicating accurate results.

  • 70.
    Khan, Shehryar
    Stockholm University, Faculty of Science, Department of Physics.
    Combined Quantum Mechanical and Molecular Dynamics study of paramagnetic complexes: Towards an understanding of electronic spin relaxation2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The prime objectives of contrast agents in Magnetic Resonance Imaging (MRI) is to accelerate the relaxation rate of the solvent water protons in the surrounding tissue. Paramagnetic relaxation originates from dipole-dipole interactions between the nuclear spins and the fluctuating magnetic field induced by unpaired electrons. Currently Gadolinium(III) chelates are the most widely used contrast agents in MRI, and therefore it is incumbent to extend the fundamental theoretical understanding of parameters that drive the relaxation mechanism in these complexes. In compounds such as Gadolinium(III) complexes with total electron spins higher than 1 (in this case S=7/2) the Zero-Field Splitting (ZFS) plays a significant role in influencing the electron spin dynamics and nuclear spin dynamics. For this purpose, the current research delves into an understanding of the relaxation process, focusing on ZFS in various complexes of interest, using multi-scale modelling by combining quantum, semi-quantum and newtonian methods.

    We compare and contrast Density Function Theory (DFT) with multi-configurational quantum chemical calculation and find that DFT is highly functional dependent and unreliable in accurately reproducing experimental data for the static ZFS. It was found that long-range corrected functionals (in particular LC-BLYP) perform significantly better as compared to other functionals in predicting the magnitude of the static ZFS. We study hydrated Gd(III) and Eu(II) systems to compare and contrast these isoelectronic complexes (both contain 7 unpaired electrons in their valence shell) and through ab-initio molecular dynamics (AIMD) sampling followed by multi-reference quantum chemical calculations, it was established that inclusion of the first shell has a dominant influence (over 90%) on the ZFS. We also studied the complex [Gd(III)(HPDO3A)(H2O)], which is of clinical relevance as a contrast agent for MRI, through post-Hartree-Fock and DFT calculations by utilizing configurations derived from AIMD trajectories. From the fluctuations in the ZFS tensor, we extract a correlation time of the transient ZFS which is on the sub-picosecond time scale, showing a faster decay than experimental data.

  • 71.
    Kimiaei, Shahrokh
    Stockholm University.
    Improvements of SPECT by a new collimator design and simultaneous transmission-emission tomography1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    SPECT (Single Photon Emission Computed Tomography) and planar scintigraphy are the most established and world wide-spread nuclear medicine imaging techniques for clinical use today. SPECT is a tomographic technique that allows 3-D visualization of biochemical processes or physiological flow in the human body by external detection of photons from an administered radiopharmaceutical. However, its ability to depict a "true" activity map depends largely on the imaging properties of the SPECT-system as well as on the methods used for converting the acquired data into values reflecting the activity distribution. Photon attenuation, as well as the contribution of "false" (scattered) events are two of the most disturbing factors for achieving high quantitative accuracy in SPECT. Since these factors are related to the density and composition of the body tissues, it is crucial to have access to individual attenuation maps when high quantitative accuracy is desired.

    Two methods for simultaneous acquisition of emission and transmission data have been developed and analyzed. These methods may either be applied on single-head cameras or on opposed dual-head camera systems. Advantages and disadvantages of various radio-nuclides for use in transmission tomography have been analyzed. Their activity distribution or their scanning speed was of great importance for minimizing the image noise. By careful collimation of the external photon sources for the transmission measurements and by introducing accurate routines of corrections for camera non-uniformity and interferences of photons during simultaneous emission and transmission tomography, accurate attenuation maps can be obtained.

    In the second part of this work, a new collimator was developed in order to reduce the gap between a conventional camera and the convex shape of most body regions. These new collimators are designed planar in one direction and concave in the other which improves the radial spatial resolution and reduces the non-isotropic blur in SPECT. An improved lateral spatial resolution in planar scintigraphy was achieved as well. The impact on imaging quality was investigated by Monte Carlo simulations. The non-isotropic image blurring was reduced by up to 60% for a PC-collimator as compared to that for a conventional collimator. The image noise distribution in SPECT was more uniform but higher than for a planar collimator due to the reduced lateral sensitivity. Simulations of a Hoffman brain phantom showed that the rCBF values achieved with an optimized PC-collimator, were up to 10% higher in the lateral cortex (Brodmann areas 18,19), than those obtained with a planar collimator. Finally, a combination of a planar-concave collimator and a transmission tomography system described may give the same advantages of low noise and reduced requirements on high dynamic range of the camera, as was obtained for photon sources with non-linear activity distributions.

  • 72. Larsson, Johanna
    et al.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Four discourse models of physics teacher education2017Conference paper (Other academic)
    Abstract [en]

    In Sweden, as in many other countries, the education of high-school physics teachers is typically carried out in three different environments; the education department, the physics department and school itself during teaching practice. Trainee physics teachers are in the process of building their professional identity as they move between these three environments. Although much has been written about teacher professional identity (see overview in Beijaard, Meijer, & Verloop, 2004) little is known about how encounters with the potentially disparate notions of “what counts” in these three environments feed into trainee physics teachers’ professional identity work.

    In this paper we try to capture the different ways the educational practice of teacher education is valued in the discourse of teacher educators. We use the concept of discourse models (Gee, 2005). Our research questions are as follows:

    1. What is signalled as valued (and not valued) by members of the three environments physics teachers meet during their training (school, education department, physics department)?

    2. What discourse models can be identified from these value statements? 

    We carried out semi-structured interviews with instructors from the three environments. Our analysis involved iterative coding of the interview transcripts (Bogdan & Biklen, 1992) to construct discourse models. We identify four competing discourse models and discuss the ways in which these models can be seen to be at work, dictating how educational practice is valued.

  • 73. Larsson, Johanna
    et al.
    Airey, John
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education. Uppsala University, Sweden.
    Lundqvist, Eva
    How does the culture of physics affect physics teacher education?2017Conference paper (Other academic)
    Abstract [en]

    In this paper we ask how the culture of physics may affect physics teacher education. Our interest is motivated by the pessimistic description of the status of physics teacher education in the US reported by the Task Force on Teacher Education in Physics (T-TEP) (2012). We present the results of an empirical study that examines the culture of physics in Sweden. The main finding is what we call the physics expert model. This was the dominant framing that physicists and physics teachers used in our interviews to talk about physics teacher education. The goal of the physics expert model is to create future physicists, something that is clearly at odds with the purpose of physics teacher education (which is to create future physics teachers). We discuss the implications of the dominance of the physics expert model and suggest that our results offer an important explanatory interpretation of the chronic problems of physics teacher training described in the T-TEP report.

  • 74.
    Laura, Antonovic
    Stockholm University, Faculty of Science, Department of Physics.
    Radiobiological end-points for the theoretical evaluation of the effectiveness of carbon ions and photons in treating tumours with dynamic hypoxia2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Tumours are characterised by unorganised vasculature, which often results in hypoxic regions. Hypoxia is a common cause for photon radiotherapy (RT) treatment failure, as hypoxic cells require up to 2-3 times higher doses compared to well-oxygenated cells for the same effect in terms of cell kill. The increase in dose that would be required to treat the tumours of cancer patients is limited by the radiation sensitivity of surrounding normal tissues. Using carbon ions instead of photons, the radiation dose can be conformed to the tumour to a much higher degree, resulting in an improved sparing of normal tissues. In addition, carbon ions have a much higher radiobiological effectiveness near the end of their range, which is positioned in the tumour. Also, the radiation modes of action leading to cell death when carbon ions interact with living tissues, are less sensitive to the oxygen status compared with the action modes of photons.

    The focus of this thesis lies in the development of models for the computation of the cell surviving fraction and tumour control probability (TCP) in hypoxic tumours after photon and carbon ion RT. The impact of fractionation was evaluated with regard to possible spatial changes in oxygenation, both for stereotactic body RT and for carbon ion RT. The feasibility of a method to determine and deliver the optimal photon dose for achieving a high TCP according to spatial variations in radiation sensitivity was evaluated in a treatment planning study. The radiobiological models were finally used for the theoretical quantification of the gain in using carbon ions instead of photons.

    The results show that there are great possibilities to increase the number of positive outcomes of radiation treatment of tumours if the key influential factors are taken into account, such as level and distribution of hypoxia, radiation quality and choice of fractionation schedule.

  • 75. Lee, Sungmin
    et al.
    Holme, Petter
    Stockholm University, Faculty of Social Sciences, Department of Sociology.
    Wu, Zhi-Xi
    Cooperation, structure, and hierarchy in multiadaptive games2011In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 84, no 6, p. 61148-Article in journal (Refereed)
    Abstract [en]

    Game-theoretical models where the rules of the game and the interaction structure both coevolve with the game dynamics-multiadaptive games-capture very flexible situations where cooperation among selfish agents can emerge. In this work, we will discuss a multiadaptive model presented in a recent Letter [Phys. Rev. Lett. 106, 028702 (2011)] as well as generalizations of it. The model captures a nonequilibrium situation where social unrest increases the incentive to cooperate and, simultaneously, agents are partly free to influence with whom they interact. First, we investigate the details of how feedback from the behavior of agents determines the emergence of cooperation and hierarchical contact structures. We also study the stability of the system to different types of noise, and find that different regions of parameter space show very different response. Some types of noise can destroy an all-cooperator (C) state. If, on the other hand, hubs are stable, then so is the all-C state. Finally, we investigate the dependence of the ratio between the time scales of strategy updates and the evolution of the interaction structure. We find that a comparatively fast strategy dynamics is a prerequisite for the emergence of cooperation.

  • 76.
    Liljequist, David
    Stockholm University, Faculty of Science, Department of Physics.
    Limits of validity of trajectory simulation: correlation of the error with density of scatterers and particle wavelength2009In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 267, p. 3409-3419Article in journal (Refereed)
    Abstract [en]

    To a first approximation, the elastic scattering of long wavelength particles in amorphous matter may be modelled as scattering in a volume filled with a density n of N point scatterers in random positions. For not too large N (up to about 2×103), the error in trajectory simulation (classical transport theory) due to the neglect of interference effects can then be determined in detail by means of a comparison with an exact quantum calculation of the plural or multiple scattering process. A relative error RE is defined and calculated for the scattering in different directions as well as for the distribution of scattering events inside the volume. A very strong correlation is found between the relative error and the ratio λ/dnn, where λ is the wavelength of the incident particle and dnn=n-1/3 is an average distance between nearest neighbour scatterers. For scattering in a volume of dimensions large compared to the particle wavelength, present calculations suggest that the correlation can be described as REa·(λ/dnn)b, where the parameters a<0.05 and b2 depend on the s-wave phaseshift δ0 in the scattering process. The condition for validity of trajectory simulation, defined in terms of a limit of validity L (maximum acceptable relative error), may thus be written λ/dnn<ξ, where ξ=(L/a)1/b1. For λ/dnn<1, the relative error is generally less than 5%, and trajectory simulation may be regarded as valid with at least 95% accuracy. In the exact quantum calculation, two features of pronounced quantum character are observed in the distribution of scattering events: oscillations due to quantum interference in finite volumes, and, for small negative δ0, randomly localized peaks due to proximity resonance.

  • 77.
    Lindblom, Emely
    Stockholm University, Faculty of Science, Department of Physics.
    Searching for the optimal radiotherapy treatment time, dose and fractionation - the role of hypoxia and reoxygenation: A modelling study2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The search for the optimal choice of treatment time, dose and fractionation regimen is one of the major challenges in radiation therapy. Several aspects of the radiation response of tumours and normal tissues give different indications of how the parameters defining a fractionation schedule should be altered relative to each other which often results in contradictory conclusions. For example, the increased sensitivity to fractionation in late-reacting as opposed to early-reacting tissues indicates that a large number of fractions is beneficial, while the issue of accelerated repopulation of tumour cells starting at about three weeks into a radiotherapy treatment would suggest as short overall treatment time as possible. Another tumour-to-normal tissue differential relevant to the sensitivity as well as the fractionation and overall treatment time is the issue of tumour hypoxia and reoxygenation.

    The tumour oxygenation is one of the most influential factors impacting on the outcome of many types of treatment modalities. Hypoxic cells are up to three times as resistant to radiation as well oxygenated cells, presenting a significant obstacle to overcome in radiotherapy as solid tumours often contain hypoxic areas as a result of their poorly functioning vasculature. Furthermore, the oxygenation is highly dynamic, with changes being observed both from fraction to fraction and over a time period of weeks as a result of fast and slow reoxygenation of acute and chronic hypoxia. With an increasing number of patients treated with hypofractionated stereotactic body radiotherapy (SBRT), the clinical implications of a substantially reduced number of fractions and hence also treatment time thus have to be evaluated with respect to the oxygenation status of the tumour.

    The perhaps most promising tool available for the type of study aiming at determining the optimal SBRT approach with respect to fractionation is radiobiological modelling. With clinically-derived tissue-specific radiobiological parameters and well-established survival models, in silico modelling offers a wide range of opportunities to test various hypotheses with respect to time, dose, fractionation and details of the tumour microenvironment. Any type of radiobiological modelling study intended to provide a realistic representation of a clinical tumour should therefore take into account details of both the spatial and temporal tumour oxygenation.

    This thesis, consisting of papers I-III and a summary, presents the results of three-dimensional radiobiological modelling of the response of tumours with heterogeneous oxygenation to various radiation qualities, fractionation schemes, oxygenation levels and dynamics using different survival models. The results of this work indicate that hypoxia and its dynamics play a major role in the outcome of both photon and carbon ion radiotherapy, and that neglecting the oxygenation status of tumours treated with SBRT may compromise the treatment outcome substantially. Continued to include clinical studies on the impact of hypoxia on the treatment outcome in lung cancer patients treated with SBRT, this project will hopefully advance the evolution towards routinely incorporating functional imaging of hypoxia into treatment planning. This is ultimately expected to result in increased levels of local control with more patients being cured from their cancer.

  • 78.
    Lindbäck, Elias
    Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI). Stockholm University, Faculty of Science, Department of Physics.
    "Imaging with CBCT and 4D-CT of objects moving with respiratory motions"2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    AB S TRACT

    purpose

    : To further investigate the effects of respiratory motions

    on CBCT imaging, as well as 4D-CT examinations, with a future goal

    of using obtained results to implement new methods for individual

    margins and daily matching procedures into routine clinical practice.

    background

    : Since the implementation of CBCT combined with

    modern accelerators, a higher degree of accuracy has been made possible

    in RT. However, due to the slow gantry speed of linear accelerators,

    the imaging procedure of CBCT is a slow process which is

    thereby degraded by internal motion such as respiration.

    material and methods

    : Attain patient specific respiratory motion

    patterns from CBCT projection data of previous examinations.

    Utilize this data to perform simulations for both CBCT and 4D-CT

    using a steering system which allows for arbitrary motion patterns in

    the longitudinal direction.

    results

    : Various imaging with CBCT showed that the resulting

    images during respiratory motion, can be described by the Probability

    Density Function of the motion for as long as it does not cause related

    distortions. This also meant that convolution could be implemented

    as a model to estimate the CBCT images during oscillation, knowing

    the object and motion pattern.

    The 4D-CT examinations using the steering system showed that

    irregular motion patterns were less accurately described than regular

    patterns, making the actual motion an important feature to combine

    together with the measured amplitude.

    conclusions

    : It was made clear that CBCT images can be described

    by the PDF, and thus can be seen as a Color Intensity Projection

    of the object position. Also it has been shown that the projection

    data of CBCT images contains valuable information about the respiratory

    motion of the patient.

    Another conclusion is that with the help of fiducials, the position

    of the target within the respiratory cycle can be determined relative

    to the 4D-CT examination, enabling further input data as to the daily

    matching procedure, proper applied margins as well as dose to the

    OAR.

  • 79.
    Marcks von Würtemberg, Klas
    Stockholm University, Faculty of Science, Department of Physics.
    Monte Carlo simulation of low energy electrons and positrons in liquid water2003Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An advanced simulation code, LEEPS (Low Energy Electron Positron Simulation), has been adapted to simulation of electrons and positrons in liquid water for energies down to 50 eV. Different scattering parameters and results from simulations are compared with existing data in the literature.

      Several programs including a subroutine package for simulation of secondary electrons created in binary like collisions have been developed in purpose of charting different characteristics of the energy deposition.

      A toy model for DNA damage is presented as an example of how LEEPS possibly can be used for future investigation of cellular damage due to radiation.

     

  • 80.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental investigations of model catalytic surface reactions on metal and metal oxide surfaces2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the development of renewable energies catalysis plays an important role, for example in the production of H2 gas that drives fuel cells, or in the decomposition of annoying by-products of renewable energy production. Most catalysts and catalytic processes currently used in the industry have their roots in macroscopic empirical investigations and trial and error-based optimization. In order to be able to design novel catalytic processes more efficiently, detailed understanding of the catalyst-reactant interaction and the dynamics of the microscopic reaction steps is needed. The present thesis aims to contribute to the fundamental understanding of catalyst reactant systems by means of experiments using model systems in Ultra High Vacuum. For this purpose, several surface science techniques were employed such as vibrational sum-frequency generation (SFG), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and femtochemistry.

    In the present thesis the results of three different projects are presented. The first concerns the adsorption and decomposition of naphthalene on Ni(111). Using scanning tunnelling microscopy (STM) and density functional theory (DFT) we identify the adsorption energy and geometry of the naphthalene molecule. Using SFG and TPD we investigate the temperature dependent breakdown of the naphthalene molecule and identify geometrical changes of the adsorbate as an intermediate step in the decomposition reaction. Additionally, we observe poisoning of the surface due to graphene growth using both STM and XPS and explore the possible effect of co-adsorption with oxygen on the reaction pathway and the poisoning of the catalyst.

    The second section concerns the adsorption and decomposition of ethanol and methanol on cuprous oxide (Cu2O). Using mainly XPS and SFG we show that ethanol adsorbs dissociatively on Cu2O(100) and (111) and that methanol adsorbs dissociatively on the (100) but molecularly on the (111) surface. Furthermore, we identify intermediate surface species and products of the temperature dependent dehydrogenation of both alcohols and show that the (111) surface is the more effective catalyst for decomposition.

    The third section explores the physics of non-thermal excitation methods and discusses CO oxidation on ruthenium (0001) induced by an optical laser and by X-rays from a free electron laser. Based on these femtochemistry experiments we discuss in particular the energy transfer both for direct excitation and for substrate mediated excitations. We show that we were able to control the branching ratios of competing mechanisms and understand the role of non-thermal electrons in the mechanisms of optical laser excitation. Furthermore, we show that it is possible to induce CO oxidation by direct X-ray core hole excitation and can rationalize the relaxation process that leads to CO oxidation.

  • 81. Mijovilovich, Ana
    et al.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Mangold, S.
    Janousch, M.
    Susini, J.
    Salome, M.
    de Groot, Frank M.F.
    Weckhuysen, Bert M.
    The Interpretation of Sulfur K-edge XANES spectra: A case Study on Thiophene and Aliphatic Sulfur Compounds2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, p. 2750-2756Article in journal (Refereed)
    Abstract [en]

    Sulfur K-edge XANES has been measured for three sulfur model compounds, dibenzothiophene, dibenzothiophene sulfone, and aliphatic sulfur (DL-methionine). The spectra have been simulated with Density Functional Theory (DFT) using a number of methods, including the half core hole approximation. Dipole transition elements were calculated and the transitions were convoluted with linearly increasing Gaussian functions in the first 20 eV of the near edge region. In the case of dibenzothiophene, relaxation of the first excited states in the presence of the core-hole gave a further improvement. The theoretical results reproduce well the features of the spectra and give insight in the relation between geometric structure and molecular orbitals. Though DL-methionine and dibenzothiophene show a similar sharp rise of the white line, their molecular levels are quite different, pointing out the difficulties in finding useful “fingerprints” in the spectra for specific compounds.

  • 82.
    Mondlane, Gracinda
    Stockholm University, Faculty of Science, Department of Physics.
    A comparative treatment planning study of radiotherapy of clinical liver- and stomach-cancer cases with either photon or proton beams2014Independent thesis Advanced level (degree of Master (Two Years)), 300 HE creditsStudent thesis
    Abstract [en]

    There has been an increasing interest in proton beam therapy (PBT) in recent years related to the advantageous depth-dose characteristics of proton beams compared to what is achievable with standard external photon beam radiotherapy (RT). With PBT, improved target dose conformity can be achieved together with a reduction in the dose to the organs at risk (OARs). This can for certain cases lead to an increased tumour control probability (TCP) at the same time as the probabilities for normal tissue complications (NTCP) and radiation-induced secondary cancers are reduced. However, there are challenges with PBT, in the form of uncertainties in the dose delivery to the patient, due to different influencing factors. These perturbing factors are contributing to the uncertainties during different steps in the RT flow process, from the treatment planning to the irradiation.

    In the present work, a comparative treatment planning study of PBT and photon RT for a few clinical liver- and stomach-cancer cases were performed with the aim of determining possible advantages of PBT. The treatment planning comparisons were performed by means of dosimetric evaluations and by use of tissue response models. The later included the calculation of TCP and NTCP as well as the assessment of risk of radiation-induced secondary cancer for the two compared RT techniques. A total of eleven patients previously treated with RT at Karolinska University Hospital were included in the study. Three of these patients had been treated for liver cancer and eight for stomach cancer. The photon plans which had been used in the real treatments at the hospital were taken as reference plans. The treatment planning for the liver cancer cases had been performed on conventional CT images, but 4D-CT images were used for target definition to account for the target motion.  Three distinct CT images were used in the planning of the stomach cancer cases, the original CT image study on which the photon plans had been done and two CT image studies with artificially changed physical density for some of the internal organs to simulate different possible fillings of the stomach. The extra- or reduced gas filling was drawn on the CT slices by the radiation oncologist to estimate two worst-case scenarios for changes in density within the irradiated volume.

    The results indicate an improved target dose conformity, dose homogeneity and sparing of OARs for the PBT plans compared to the photon RT plans for the two clinical cases studied. The sparing of the OARs was also observed in the form of decreased NTCP for the PBT plans. The PBT plans showed to be worse than the photon plans when some structures were replaced by air and water. In the case of extra air there was a shift of the higher doses beyond the distal edge of the planned proton range which caused both an increase of the irradiated volumes of sensitive normal tissues and of the maximum doses to the OARs. In the case of extra water in the stomach, the maximum range of the protons was reduced causing target underdosage.  The calculations of probabilities for radiation-induced secondary malignancies indicated a reduced risk for all the OARs with the proton plans for the liver cancer cases. For the stomach cancer cases, reduced risks were obtained for induction of cancer in the liver but an increased risk was calculated for the bowel(-)PTV, with the proton- compared to the photon-plans. The results of the calculations of risk for radiation-induced cancer in the kidneys were inconclusive. The assessment of risk of secondary cancer for other organs, not delineated in this work (to obtain the whole body risk), is needed in order to obtain more comprehensive and clinically useful results.

  • 83.
    Mondlane, Gracinda
    Stockholm University, Faculty of Science, Department of Physics.
    Comparative study of Radiation Therapy of Targets in the Upper Abdomen with Photon- or Scanned Proton-beams2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recently, there has been an increase in the number of proton beam therapy (PBT) centers operating worldwide. For certain cases, proton beams have been shown to provide dosimetric and radiobiological advantages when used for cancer treatment, compared to the regular photon-beam based treatments. Under ideal circumstances, the dose given to the tissues surrounding a target can be reduced with PBT. The risk for side effects following treatment is then expected to decrease. Until present, mainly stationary targets, e.g. targets in the brain, have been treated with PBT. There is currently a growing interest to treat also target volumes in other parts of the body with PBT. However, there are sources of uncertainties, which must be more carefully considered when PBT is used, especially for PBT carried out with scanned proton beams. PBT is more sensitive to anatomical changes, e.g. organ motion or a variable gas content in the intestines, which requires that special precautions are taken prior to treating new tumour sites. In photon beam radiotherapy (RT) of moving targets, the main consequence of organ motion is the loss of sharpness of the dose gradients (dose smearing). When scanned proton beams are used, dose deformation caused by the fluctuations in the proton beam range, due to varying tissue heterogeneities (e.g., the ribs moving in and out of the beam path) and the so-called interplay effect, can be expected to impact the dose distributions in addition to the dose smearing. The dosimetric uncertainties, if not accounted for, may cause the planned and accurately calculated dose distribution to be distorted, compromising the main goal of RT of achieving the maximal local disease control while accepting certain risks for normal tissue complications.

    Currently there is a lack of clinical follow-up data regarding the outcome of PBT for different tumour sites, in particular for extra-cranial tumour sites in moving organs. On the other hand, the use of photon beams for this kind of cancer treatment is well-stablished. A treatment planning comparison between RT carried out with photons and with protons may provide guidelines for when PBT could be more suitable. New clinical applications of particle beams in cancer therapy can also be transferred from photon-beam treatments, for which there is a vast clinical experience. The evaluation of the different uncertainties influencing RT of different tumour sites carried out with photon- and with proton-beams, will hopefully create an understanding for the feasibility of treating cancers with scanned proton beams instead of photon beams. The comparison of two distinct RT modalities is normally performed by studying the dosimetric values obtained from the dose volume histograms (DVH). However, in dosimetric evaluations, the outcome of the treatments in terms of local disease control and healthy tissue toxicity are not estimated. In this regard, radiobiological models can be an indispensable tool for the prediction of the outcome of cancer treatments performed with different types of ionising radiation. In this thesis, different factors that should be taken into consideration in PBT, for treatments influenced by organ motion and density heterogeneities, were studied and their importance quantified.

    This thesis consists of three published articles (Articles I, II and III). In these reports, the dosimetric and biological evaluations of photon-beam and scanned proton-beam RT were performed and the results obtained were compared. The studies were made for two tumour sites influenced by organ motion and density changes, gastric cancer (GC) and liver metastases. For the GC cases, the impact of changes in tissue density, resulting from variable gas content (which can be observed inter-fractionally), was also studied. In this thesis, both conventional fractionations (implemented in the planning for GC treatments) and hypofractionated regimens (implemented in the planning for the liver metastases cases) were considered. In this work, it was found that proton therapy provided the possibility to reduce the irradiations of the normal tissue located near the target volumes, compared to photon beam RT. However, the effects of density changes were found to be more pronounced in the plans for PBT. Furthermore, with proton beams, the reduction of the integral dose given to the OARs resulted in reduced risks of treatment-induced secondary malignancies.

  • 84.
    Mondlane, Gracinda
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universidade Eduardo Mondlane, Mozambique.
    Gubanski, Michael
    Lind, Pehr A.
    Ureba, Ana
    Stockholm University, Faculty of Science, Department of Physics.
    Siegbahn, Albert
    Stockholm University, Faculty of Science, Department of Physics.
    Comparative study of the calculated risk of radiation-induced cancer after photon- and proton-beam based radiosurgery of liver metastases2017In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 42, p. 263-270Article in journal (Refereed)
    Abstract [en]

    Introduction

    The potential of proton therapy to improve the sparing of the healthy tissue has been demonstrated in several studies. However, even small doses delivered to the organs at risk (OAR) may induce long-term detriments after radiotherapy. In this study, we investigated the possibility to reduce the risk of radiation-induced secondary cancers with intensity modulated proton therapy (IMPT), when used for radiosurgery of liver metastases.

    Material and methods

    Ten patients, previously treated for liver metastases with photon-beam based stereotactic body radiation therapy (SBRT) were retrospectively planned for radiosurgery with IMPT. A treatment plan comparison was then performed in terms of calculated risk of radiation-induced secondary cancer. The risks were estimated using two distinct models (Dasu et al., 2005; Schneider et al., 2005, 2009). The plans were compared pairwise with a two-sided Wilcoxon signed-rank test with a significance level of 0.05.

    Results

    Reduced risks for induction of fatal and other types of cancers were estimated for the IMPT plans (p < 0.05) with the Dasu et al. model. Using the Schneider et al. model, lower risks for carcinomainduction with IMPT were estimated for the skin, lungs, healthy part of the liver, esophagus and the remaining part of the body (p < 0.05). The risk of observing sarcomas in the bone was also reduced with IMPT (p < 0.05).

    Conclusion

    The findings of this study indicate that the risks of radiation-induced secondary cancers after radiosurgery of liver metastases may be reduced, if IMPT is used instead of photon-beam based SBRT.

  • 85.
    Mondlane, Gracinda
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Eduardo Mondlane University, Mozambique .
    Ureba, Ana
    Stockholm University, Faculty of Science, Department of Physics.
    Gubanski, Michael
    Lind, Pehr A.
    Siegbahn, Albert
    Estimation of Risk of Normal-tissue Toxicity Following Gastric Cancer Radiotherapy with Photon- or Scanned Proton-beams2018In: Anticancer Research, ISSN 0250-7005, E-ISSN 1791-7530, Vol. 38, no 5, p. 2619-2625Article in journal (Refereed)
    Abstract [en]

    Background/Aim: Gastric cancer (GC) radiotherapy involves irradiation of large tumour volumes located in the proximities of critical structures. The advantageous dose distributions produced by scanned-proton beams could reduce the irradiated volumes of the organs at risk (OARs). However, treatment-induced side-effects may still appear. The aim of this study was to estimate the normal tissue complication probability (NTCP) following proton therapy of GC, compared to photon radiotherapy. Patients and Methods: Eight GC patients, previously treated with volumetric-modulated arc therapy (VMAT), were retrospectively planned with scanned proton beams carried out with the single-field uniform-dose (SFUD) method. A beam-specific planning target volume was used for spot positioning and a clinical target volume (CTV) based robust optimisation was performed considering setup- and range-uncertainties. The dosimetric and NTCP values obtained with the VMAT and SFUD plans were compared. Results: With SFUD, lower or similar dose-volume values were obtained for OARs, compared to VMAT. NTCP values of 0% were determined with the VMAT and SFUD plans for all OARs (p>0.05), except for the left kidney (p<0.05), for which lower toxicity was estimated with SFUD. Conclusion: The NTCP reduction, determined for the left kidney with SFUD, can be of clinical relevance for preserving renal function after radiotherapy of GC.

  • 86.
    Mondlane, Gracinda
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universidade Eduardo Mondlane, Mozambique.
    Ureba, Ana
    Gubanski, Michael
    Lind, Pehr A.
    Siegbahn, Albert
    Estimation of the risk for radiation-induced liver disease following photon- or proton-beam radiosurgery of liver metastases2018In: Radiation Oncology, ISSN 1748-717X, E-ISSN 1748-717X, Vol. 13, article id 206Article in journal (Refereed)
    Abstract [en]

    Background: Radiotherapy of liver metastases is commonly being performed with photon-beam based stereotactic body radiation therapy (SBRT). The high risk for radiation-induced liver disease (RILD) is a limiting factor in these treatments. The use of proton-beam based SBRT could potentially improve the sparing of the healthy part of the liver. The aim of this study was to use estimations of normal tissue complication probability (NTCP) to identify liver-metastases patients that could benefit from being treated with intensity-modulated proton therapy (IMPT), based on the reduction of the risk for RILD.

    Methods: Ten liver metastases patients, previously treated with photon-beam based SBRT, were retrospectively planned with IMPT. A CTV-based robust optimisation (accounting for setup and range uncertainties), combined with a PTV-based conventional optimisation, was performed. A robustness criterion was defined for the CTV (V95% > 98% for at least 10 of the 12 simulated scenarios). The NTCP was estimated for different endpoints using the Lyman-Kutcher-Burman model. The ΔNTCP (NTCPIMPT − NTCPSBRT) for RILD was registered for each patient. The patients for which the NTCP (RILD) < 5% were also identified. A generic relative biological effectiveness of 1.1 was assumed for the proton beams.

    Results: For all patients, the objectives set for the PTV and the robustness criterion set for the CTV were fulfilled with the IMPT plans. An improved sparing of the healthy part of the liver, right kidney, lungs, spinal cord and the skin was achieved with the IMPT plans, compared to the SBRT plans. Mean liver doses larger than the threshold value of 32 Gy led to NTCP values for RILD exceeding 5% (7 patients with SBRT and 3 patients with the IMPT plans). ΔNTCP values (RILD) ranging between − 98% and − 17% (7 patients) and between 0 and 2% (3 patients), were calculated.

    Conclusions: In this study, liver metastases patients that could benefit from being treated with IMPT, based on the NTCP reductions, were identified. The clinical implementation of such a model-based approach to select liver metastases patients to proton therapy needs to be made with caution while considering the uncertainties involved in the NTCP estimations.

  • 87.
    Morå, Knut Dundas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harmonizing discovery thresholds and reporting two-sided confidence intervals: a modified Feldman & Cousins methodManuscript (preprint) (Other academic)
    Abstract [en]

    When searching for new physics effects, collaborations will often wish to publish upper limits and intervals with a lower confidence level than the threshold they would set to claim an excess or a discovery. However, confidence intervals are typically constructed to provide constant coverage, or probability to contain the true value, with possible overcoverage if the random parameter is discrete. In particular, that means that the confidence interval will contain the 0-signal case with the same frequency as the confidence level. This paper details a modification to the Feldman-Cousins method to allow a different, higher excess reporting significance than the interval confidence level.

  • 88. Negi, Devendra
    et al.
    Spiegelberg, Jakob
    Muto, Shunsuke
    Thersleff, Thomas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ohtsuka, Masahiro
    Schönström, Linus
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tatsumi, Kazuyoshi
    Rusz, Ján
    Proposal for Measuring Magnetism with Patterned Apertures in a Transmission Electron Microscope2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 3, article id 037201Article in journal (Refereed)
    Abstract [en]

    We propose a magnetic measurement method utilizing a patterned post-sample aperture in a transmission electron microscope. While utilizing electron magnetic circular dichroism, the method circumvents previous needs to shape the electron probe to an electron vortex beam or astigmatic beam. The method can be implemented in standard scanning transmission electron microscopes by replacing the spectrometer entrance aperture with a specially shaped aperture, hereafter called ventilator aperture. The proposed setup is expected to work across the whole range of beam sizes -- from wide parallel beams down to atomic resolution magnetic spectrum imaging.

  • 89. Nielsen, Steffen
    et al.
    Bassler, Niels
    Stockholm University, Faculty of Science, Department of Physics.
    Grzanka, Leszek
    Swakon, Jan
    Olko, Pawel
    Andreassen, Christian Nicolaj
    Overgaard, Jens
    Alsner, Jan
    Singers Sørensen, Brita
    Differential gene expression in primary fibroblasts induced by proton and cobalt-60 beam irradiation2017In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 56, no 11, p. 1406-1412Article in journal (Refereed)
    Abstract [en]

    Introduction: Proton beam therapy delivers a more conformal dose distribution than conventional radiotherapy, thus improving normal tissue sparring. Increasing linear energy transfer (LET) along the proton track increases the relative biological effectiveness (RBE) near the distal edge of the Spread-out Bragg peak (SOBP). The severity of normal tissue side effects following photon beam radiotherapy vary considerably between patients.

    Aim: The dual study aim was to identify gene expression patterns specific to radiation type and proton beam position, and to assess whether individual radiation sensitivity influences gene expression levels in fibroblast cultures irradiated in vitro.

    Methods: The study includes 30 primary fibroblast cell cultures from patients previously classified as either radiosensitive or radioresistant. Cells were irradiated at three different positions in the proton beam profile: entrance, mid-SOBP and at the SOBP distal edge. Dose was delivered in three fractions × 3.5 Gy(RBE) (RBE 1.1). Cobalt-60 (Co-60) irradiation was used as reference. Real-time qPCR was performed to determine gene expression levels for 17 genes associated with inflammation response, fibrosis and angiogenesis.

    Results: Differences in median gene expression levels were observed for multiple genes such as IL6, IL8 and CXCL12. Median IL6 expression was 30%, 24% and 47% lower in entrance, mid-SOBP and SOBP distal edge groups than in Co-60 irradiated cells. No genes were found to be oppositely regulated by different radiation qualities. Radiosensitive patient samples had the strongest regulation of gene expression; irrespective of radiation type.

    Conclusions: Our findings indicate that the increased LET at the SOBP distal edge position did not generally lead to increased transcriptive response in primary fibroblast cultures. Inflammatory factors were generally less extensively upregulated by proton irradiation compared with Co-60 photon irradiation. These effects may possibly influence the development of normal tissue damage in patients treated with proton beam therapy.

  • 90.
    Nyberg, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Dynamical Spin Systems2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As of today, there is still no general theory that can be applied to understand the dynamics innon-equilibrium systems and usually one has to turn to approximations and simulations in orderto extract any information out of a system. In fact, there are only a few known examples, such asthe asymmetric simple exclusion process and a family of related models where analytical resultshave been proven successful.

    In this thesis we will start by studying the dynamics in three different classical spin systems.The common factor in all of them is that we consider quenches to low temperatures. Before thequench takes place the system is in equilibrium at a high temperature, usually taken to be atinfinity. For systems in one dimension, this process can be described in terms of domains evolvingtowards a new equilibrium configuration. The approach of elucidating the dynamics starts with themaster equation. This can however be exactly solved only in a very few cases. One approximationthat can be made in the context of quenches is the independent interval approximation (IIA),which captures the main features of the dynamics. The IIA is proven to be exact when domainsonly monotonically increase its length and never split up. But even in those cases where it is notexact it gives the main qualitative behavior of the system in the asymptotic limit.

    The three spin models studied, all have exactly determinable steady states (which in fact areequilibrium configurations in two of the cases). In this thesis, we introduce a new spin model,in which the dynamics is truly irreversible and the steady state is not exactly determinable. Wecall it the Modified East model. Using the IIA and a generating function approach we are able tofind some analytical properties of the system. These results agree well with simulations at hightemperatures, surprisingly, since the IIA is only exact at very low temperatures. We have not beenable to verify analytical predictions with simulations in the limit of zero temperature but we canargue that it should still be a good match.

  • 91.
    Olenius, Tinja
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Pichelstorfer, Lukas
    Stolzenburg, Dominik
    Winkler, Paul M.
    Lehtinen, Kari E. J.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Robust metric for quantifying the importance of stochastic effects on nanoparticle growth2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 14160Article in journal (Refereed)
    Abstract [en]

    Comprehensive representation of nanoparticle dynamics is necessary for understanding nucleation and growth phenomena. This is critical in atmospheric physics, as airborne particles formed from vapors have significant but highly uncertain effects on climate. While the vapor-particle mass exchange driving particle growth can be described by a macroscopic, continuous substance for large enough particles, the growth dynamics of the smallest nanoparticles involve stochastic fluctuations in particle size due to discrete molecular collision and decay processes. To date, there have been no generalizable methods for quantifying the particle size regime where the discrete effects become negligible and condensation models can be applied. By discrete simulations of sub-10 nm particle populations, we demonstrate the importance of stochastic effects in the nanometer size range. We derive a novel, theory-based, simple and robust metric for identifying the exact sizes where these effects cannot be omitted for arbitrary molecular systems. The presented metric, based on examining the second- and first-order derivatives of the particle size distribution function, is directly applicable to experimental size distribution data. This tool enables quantifying the onset of condensational growth without prior information on the properties of the vapors and particles, thus allowing robust experimental resolving of nanoparticle formation physics.

  • 92. Paardekooper, Sijme-Jan
    et al.
    Mellema, Garrelt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Halting type I planet migration in non-isothermal disks2006In: Astronomy and Astrophysics, Vol. 459, no 1, p. L17-L20Article in journal (Refereed)
    Abstract [en]

    Aims: We investigate the effect of including a proper energy balance on the interaction of a low-mass planet with a protoplanetary disk.

    Methods: We use a three-dimensional version of the RODEO method to perform hydrodynamical simulations including the energy equation. Radiation is included in the flux-limited diffusion approach.

    Results: The sign of the torque is sensitive to the ability of the disk to radiate away the energy generated in the immediate surroundings of the planet. In the case of high opacity, corresponding to the dense inner regions of protoplanetary disks, migration is directed outward, instead of the usual inward migration that was found in locally isothermal disks. For low values of the opacity we recover inward migration and show that torques originating in the coorbital region are responsible for the change in migration direction.

  • 93.
    Pidokrajt, Narit
    Stockholm University, Faculty of Science, Department of Physics.
    Information geometries in black hole physics2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis we aim to develop new perspectives on the statistical mechanics of black holes using an information geometric approach (Ruppeiner and Weinhold geometry). The Ruppeiner metric is defined as a Hessian matrix on a Gibbs surface, and provides a geometric description of thermodynamic systems in equilibrium. This Ruppeiner geometry exhibits physically suggestive features; a flat Ruppeiner metric for systems with no interactions i.e. the ideal gas, and curvature singularities signaling critical behavior(s) of the system. We construct a flatness theorem based on the scaling property of the black holes, which proves to be useful in many cases. Another thermodynamic geometry known as the Weinhold geometry is defined as the Hessian of internal energy and is conformally related to the Ruppeiner metric with the system’s temperature as a conformal factor.

     We investigate a number of black hole families in various gravity theories. Our findings are briefly summarized as follows: the Reissner-Nordström type, the Einstein-Maxwell-dilaton andBTZ black holes have flat Ruppeiner metrics that can be represented by a unique state space diagram. We conjecture that the state space diagram encodes extremality properties of the black hole solution. The Kerr type black holes have curved Ruppeiner metrics whose curvature singularities are meaningful in five dimensions and higher, signifying the onset of thermodynamic instabilities of the black hole in higher dimensions. All the three-parameter black hole families in our study have non-flat Ruppeiner and Weinhold metrics and their associated curvature singularities occur in the extremal limits. We also study two-dimensional black hole families whose thermodynamic geometries are dependent on parameters that determine the thermodynamics of the black hole in question. The tidal charged black hole which arises in the braneworld gravity is studied. Despite its similarity to the Reissner-Nordström type, its thermodynamic geometries are distinctive.

  • 94.
    Pidokrajt, Narit
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gergely, Laszlo
    Szeged University, Hungary.
    Winitzki, Sergei
    Munich University, Germany.
    Thermodynamics of tidal charged black holesManuscript (preprint) (Other academic)
    Abstract [en]

    We study the thermodynamics of tidal charged black holes in four dimensions. Such black holes are spherically symmetric vacuum solutions of the effective Einstein equations on the brane and are characterized by the mass m and (generalizing their general relativistic counterparts) by a second parameter, the tidal charge q. The latter is an imprint of the Weyl curvature of the 5-dimensional space-time, in which the brane is embedded. The heat capacity of the tidal charged black hole diverges on a set of measure zero of the parameter space. However, there is no phase transition at those points, similarly to the Reissner-Nordstr\"om black hole. We investigate the thermodynamic geometry of such black holes by deriving the Weinhold and the Ruppeiner metrics. Whereas the Weinhold metric is flat, the Ruppeiner metric has a positive Ricci curvature, which is in sharp contrast with the Reissner-Nordstr\"om black hole, the general relativistic analogue of the tidal charged metric. The state space is conformal to the right half of the interior of the future light cone in a Minkowski plane. We find two constraints on the possible 5-dimensional extensions of the tidal-charged black hole: First, we conjecture that the 5-dimensional black object should have the same entropy as its 4-dimensional section studied here, modulo corrections which are small for large black holes. Second, for constant m any quasi-stationary evolution of the tidal charged black hole leads to a decrease of q, contributing towards the localization of gravity on the brane. This represents an important constraint on the evolution of the 5-dimensional space-time.

  • 95.
    Pidokrajt, Narit
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Åman, Jan E.
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Ingemar
    Stockholm University, Faculty of Science, Department of Physics.
    Geometry of black hole thermodynamics2003In: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 35, no 10, p. 1733-1743Article in journal (Refereed)
    Abstract [en]

    The Hessian of the entropy function can be thought of as a metric tensor on the state space. In the context of thermodynamical fluctuation theory Ruppeiner has argued that the Riemannian geometry of this metric gives insight into the underlying statistical mechanical system; the claim is supported by numerous examples. We study this geometry for some families of black holes. It is flat for the BTZ and Reissner-Nordstrom black holes, while curvature singularities occur for the Reissner-Nordstrom-anti-de Sitter and Kerr black holes.

  • 96.
    Pidokrajt, Narit
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Åman, Jan E.
    Stockholm University, Faculty of Science, Department of Physics.
    Ward, John
    University of Victoria, Dept. of Physics and Astronomy.
    On Geometro-thermodynamics of dilaton black holes2008In: EAS Publications Series, ISSN 1638-1963, Vol. 30, p. 279-283Article in journal (Refereed)
    Abstract [en]

    In this talk we present the latest results from our ongoing project on geometro-thermodynamics (also known as information geometry of thermodynamics or Ruppeiner geometry) of dilaton BHs in 4D in both Einstein and string frames and a dyonic dilaton BH and at the end we report very briefly results from this approach to the 2D dilaton BHs.

  • 97. Pollmann, Friederike
    et al.
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Eden, Carsten
    Olbers, Dirk
    Resolving the horizontal direction of internal tide generation2019In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 864, p. 381-407Article in journal (Refereed)
    Abstract [en]

    The mixing induced by breaking internal gravity waves is an important contributor to the ocean's energy budget, shaping, inter alia, nutrient supply, water mass transformation and the large-scale overturning circulation. Much of the energy input into the internal wave field is supplied by the conversion of barotropic tides at rough bottom topography, which hence needs to be described realistically in internal gravity wave models and mixing parametrisations based thereon. A new semi-analytical method to describe this internal wave forcing, calculating not only the total conversion but also the direction of this energy flux, is presented. It is based on linear theory for variable stratification and finite depth, that is, it computes the energy flux into the different vertical modes for two-dimensional, subcritical, small-amplitude topography and small tidal excursion. A practical advantage over earlier semi-analytical approaches is that the new one gives a positive definite conversion field. Sensitivity studies using both idealised and realistic topography allow the identification of suitable numerical parameter settings and corroborate the accuracy of the method. This motivates the application to the global ocean in order to better account for the geographical distribution of diapycnal mixing induced by low-mode internal gravity waves, which can propagate over large distances before breaking. The first results highlight the significant differences of energy flux magnitudes with direction, confirming the relevance of this more detailed approach for energetically consistent mixing parametrisations in ocean models. The method used here should be applicable to any physical system that is described by the standard wave equation with a very wide field of sources.

  • 98.
    Polyakov, Eugeniy
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Vorontsov-Velyaminov, Pavel
    St.Petersburg State University.
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stochastic positive P-representation in problems of quantum statistics. Simulation of one-dimensional Bose-gas with delta-repulsion2009In: Vychislitel'nye Metody i Programirovaniye [Numerical methods and programming], ISSN 0507-5386, Vol. 10, p. 223-247Article in journal (Other academic)
    Abstract [en]

    A method of stochastic positive P-representation for the computer simulation of thermal equilibrium and dynamical properties of many-particle quantum systems with interactions is proposed and thoroughly analyzed. The testing procedure of the method includes the evaluation of spatial correlation functions for the one-dimensional Bose-gas with delta-repulsion between particles, both in the state of thermal equilibrium and in the dynamical evolution from a given initial state. This work was supported by the Russian Foundation for Basic Research (project number 08–02–00041) and by the Royal Swedish Academy of Sciences.

     

  • 99.
    Rosquist, Kjell
    Stockholm University, Faculty of Science, Department of Physics.
    A dielectric analogue model of the Kerr equatorial plane2008In: Proceedings of the eleventh Marcel Grossmann meeting: On recent developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories, 2008, p. 1475-1478Conference paper (Refereed)
    Abstract [en]

    An optical analogue solution of the Kerr equatorial plane is given. To find the solution a special notation for calculations with two different metrics has been used. The possibility of extending the solution to the complete Kerr geometry is also discussed.

  • 100.
    Rosquist, Kjell
    Stockholm University, Faculty of Science, Department of Physics.
    A link between general relativity and quantum mechanics2008In: The eleventh Marcel Grossmann meeting: On recent developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories, 2008, p. 2634-2638Conference paper (Refereed)
    Abstract [en]

    For a number of reasons including having a Dirac g-factor g = 2, the most probable approximation for the exterior gravitational and electromagnetic field of the electron is the Kerr-Newman solution to the Einstein-Maxwell equations. It is shown that the Kerr-Newman solution when used as the exterior Einstein-Maxwell field for the electron gives rise to a standard statistical measuring uncertainty in the position of the particle. The size of the uncertainty is the Compton wavelength. The uncertainty therefore coincides with that which is usually inferred for the electron in the context of relativistic quantum mechanics.

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