Change search
Refine search result
123456 1 - 50 of 283
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Becquart, C. S.
    et al.
    Ngayam Happy, R.
    Olsson, P.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe2018In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 500, p. 92-109Article in journal (Refereed)
    Abstract [en]

    The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).

  • 2.
    Abdollahi, S.
    et al.
    Hiroshima Univ, Dept Phys Sci, Higashihiroshima, Hiroshima 7398526, Japan..
    Ajello, M.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Helgason, K.
    KTH. Max Planck Inst Astrophys, Postfach 1317, D-85741 Garching, Germany.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Johannesson, G.
    KTH. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, S.
    KTH, School of Engineering Sciences (SCI), Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;.
    et al.,
    A gamma-ray determination of the Universe's star formation history2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6418, p. 1031-+Article in journal (Refereed)
    Abstract [en]

    The light emitted by all galaxies over the history of the Universe produces the extragalactic background light (EBL) at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for gamma rays via photon-photon interactions, leaving an imprint in the spectra of distant gamma-ray sources. We measured this attenuation using 739 active galaxies and one gamma-ray burst detected by the Fermi Large Area Telescope. This allowed us to reconstruct the evolution of the EBL and determine the star formation history of the Universe over 90% of cosmic time. Our star formation history is consistent with independent measurements from galaxy surveys, peaking at redshift z similar to 2. Upper limits of the EBL at the epoch of reionization suggest a turnover in the abundance of faint galaxies at z similar to 6.

  • 3.
    Li, Liang
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Oskar Klein Centre - AlbaNova, Sverige.
    Wang, Yu
    Shao, Lang
    Wu, Xue-Feng
    Huang, Yong-Feng
    Zhang, Bing
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oskar Klein Centre - AlbaNova, Sverige.
    Yu, Hoi-Fung
    KTH, School of Engineering Sciences (SCI), Physics. Oskar Klein Centre - AlbaNova, Sverige.
    A Large Catalog of Multiwavelength GRB Afterglows. I. Color Evolution and Its Physical Implication2018In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 234, no 2, article id 26Article in journal (Refereed)
    Abstract [en]

    The spectrum of gamma-ray burst (GRB) afterglows can be studied with color indices. Here, we present a large comprehensive catalog of 70 GRBs with multiwavelength optical transient data on which we perform a systematic study to find the temporal evolution of color indices. We categorize them into two samples based on how well the color indices are evaluated. The Golden sample includes 25 bursts mostly observed by GROND, and the Silver sample includes 45 bursts observed by other telescopes. For the Golden sample, we find that 96% of the color indices do not vary over time. However, the color indices do vary during short periods in most bursts. The observed variations are consistent with effects of (i) the cooling frequency crossing the studied energy bands in a wind medium (43%) and in a constant-density medium (30%), (ii) early dust extinction (12%), (iii) transition from reverse-shock to forward-shock emission (5%), or (iv) an emergent SN emission (10%). We also study the evolutionary properties of the mean color indices for different emission episodes. We find that 86% of the color indices in the 70 bursts show constancy between consecutive ones. The color index variations occur mainly during the late GRB-SN bump, the flare, and early reverse-shock emission components. We further perform a statistical analysis of various observational properties and model parameters (spectral index beta(CI)(o), electron spectral indices p(CI), etc.) using color indices. Overall, we conclude that similar to 90% of colors are constant in time and can be accounted for by the simplest external forward-shock model, while the varying color indices call for more detailed modeling.

  • 4. Aaboud, M.
    et al.
    Kastanas, K. A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, B.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, G.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. E.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, J.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    ATLAS Collaboration,
    et.al.,
    A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector2018In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 78, no 3Article in journal (Refereed)
    Abstract [en]

    A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.

  • 5. Aaboud, M
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    A search for resonances decaying into a Higgs boson and a new particle X in the XH -> qqbb final state with the ATLAS detector2018In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 779, p. 24-45Article in journal (Refereed)
    Abstract [en]

    A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle Xis assumed to decay to a pair of light quarks, and the fully hadronic final state XH -> q (q) over bar 'b (b) over bar is analysed. The search considers the regime of high XH resonance masses, where the X and H bosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XH mass versus X mass is scanned for evidence of a signal, over a range of XH resonance mass values between 1 TeV and 4 TeV, and for X particles with masses from 50 GeV to 1000 GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XH and X masses, on the production cross-section of the XH -> q (q) over bar 'b (b) over bar resonance.

  • 6.
    Wallenius, Janne
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Albanova University Centre, 10691 Stockholm, Sweden.
    Bortot, Sara
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Albanova University Centre, 10691 Stockholm, Sweden.
    A small lead-cooled reactor with improved Am-burning and non-proliferation characteristics2018In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 122, p. 193-200Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel approach for transmutation of americium in fast reactors is presented. Using enriched uranium as fissile support, rather than plutonium, it is shown that a minor actinide burning rate of 25 kg/TWhth is possible to achieve in a passively safe, critical lead-cooled reactor. Moreover, the plutonium produced by transmutation of 241Am features up to 38% 238Pu, making it difficult to use for weapons production. 

  • 7.
    Xie, Fei
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden.
    SPHiNX, Collaboration
    A Study of Background Conditions for Sphinx-The Satellite-Borne Gamma-Ray Burst Polarimeter2018In: Galaxies, E-ISSN 2075-4434, Vol. 6, no 2, article id 50Article in journal (Refereed)
    Abstract [en]

    SPHiNX is a proposed satellite-borne gamma-ray burst polarimeter operating in the energy range 50-500 keV. The mission aims to probe the fundamental mechanism responsible for gamma-ray burst prompt emission through polarisation measurements. Optimising the signal-to-background ratio for SPHiNX is an important task during the design phase. The Geant4 Monte Carlo toolkit is used in this work. From the simulation, the total background outside the South Atlantic Anomaly (SAA) is about 323 counts/s, which is dominated by the cosmic X-ray background and albedo gamma rays, which contribute similar to 60% and similar to 35% of the total background, respectively. The background from albedo neutrons and primary and secondary cosmic rays is negligible. The delayed background induced by the SAA-trapped protons is about 190 counts/s when SPHiNX operates in orbit for one year. The resulting total background level of similar to 513 counts/s allows the polarisation of similar to 50 GRBs with minimum detectable polarisation less than 30% to be determined during the two-year mission lifetime.

  • 8.
    Meng, Wang
    KTH, School of Engineering Sciences (SCI), Physics.
    A Study on Characteristics of a Thin Liquid Film Flowing down a Uniformly Heated Plate with Constant Heat Flux2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 9. Mei, Y.
    et al.
    Gong, Shengjie
    KTH. School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
    Gu, H.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    A study on steam-water two phase flow distribution in a rectangular channel with different channel orientations2018In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 99, p. 219-232Article in journal (Refereed)
    Abstract [en]

    Experimental study on steam-water two phase vertical and inclined upward flow (15–90°) was performed in a rectangular channel with cross section of 17 mm × 10 mm under atmospheric pressure to investigate the phase distribution and the average void fraction in the cross section which were obtained from the local void fraction measurement by a conductivity probe. The inlet superficial velocities of the steam and water varied from 0.72 to 3.85 m/s and from 0.11 to 0.3 m/s respectively. A high speed camera was used to identify the flow patterns. Experimental results show that the phase distribution curves are significantly affected by channel orientation and the average void fraction first decreases and then increases with the increase of orientation. Based on the drift-flux model, two parameters, namely, the distribution parameter (C0) and the drift velocity (Ugm) have been studied in detail. Both the distribution parameter and the drift velocity are found to be functions of orientation. The distribution parameter decreases with the increase of orientation while the drift velocity first increases and then decreases with the increase of orientation., Based on the experimental data, an improved drift-flux model is proposed especially for the slug and churn flow, which predicts the void fraction in an inclined channel with good accuracy.

  • 10.
    Bergh, Cathrine
    KTH, School of Engineering Sciences (SCI), Physics.
    A Water Droplet Model as Boundary Condition for Molecular Dynamics Simulations of Solvated Systems2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 11. Nandi, A.
    et al.
    Mandal, S.
    Sreehari, H.
    Radhika, D.
    Das, S.
    Chattopadhyay, I.
    Iyer, Nirmal
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Agrawal, V. K.
    Aktar, R.
    Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass2018In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, no 5, article id 90Article in journal (Refereed)
    Abstract [en]

    We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (∼166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3–150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (m˙ d), sub-Keplerian accretion rate (m˙ h), shock location (rs) and black hole mass (Mbh) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as Ljetobs∼3–6×1037ergs−1 during one of the observed radio flares which indicates that jet power corresponds to 8–16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (∼14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2–7.9 M⊙ with 90% confidence.

  • 12.
    Chauvin, Maxime
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, Stockholm, Sweden.
    Florén, Hans-Gustav
    Friis, Mette
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, Stockholm, SwedenThe Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, Stockholm, Sweden.
    Jackson, Miranda
    KTH, School of Engineering Sciences (SCI), Physics.
    Kamae, Tuneyoshi
    Kataoka, Jun
    Kawano, Takafumi
    Kiss, Mózsi
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mikhalev, Victor
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mizuno, Tsunefumi
    Ohashi, Norie
    Stana, Theodor
    KTH, School of Engineering Sciences (SCI), Physics.
    Tajima, Hiro
    Takahashi, Hiromitsu
    Uchida, Nagomi
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics.
    Accretion geometry of the black-hole binary Cygnus X-1 from X-ray polarimetry2018In: Nature Astronomy, ISSN 2397-3366, Vol. 2, no 8, p. 652-655Article in journal (Refereed)
    Abstract [en]

    Black hole binary (BHB) systems comprise a stellar-mass black hole and a closely orbiting companion star. Matter is transferred from the companion to the black hole, forming an accretion disk, corona and jet structures. The resulting release of gravitational energy leads to the emission of X-rays1. The radiation is affected by special/general relativistic effects, and can serve as a probe for the properties of the black hole and surrounding environment, if the accretion geometry is properly identified. Two competing models describe the disk–corona geometry for the hard spectral state of BHBs, based on spectral and timing measurements2,3. Measuring the polarization of hard X-rays reflected from the disk allows the geometry to be determined. The extent of the corona differs between the two models, affecting the strength of the relativistic effects (such as enhancement of the polarization fraction and rotation of the polarization angle). Here, we report observational results on the linear polarization of hard X-ray emission (19–181 keV) from a BHB, Cygnus X-14, in the hard state. The low polarization fraction, <8.6% (upper limit at a 90% confidence level), and the alignment of the polarization angle with the jet axis show that the dominant emission is not influenced by strong gravity. When considered together with existing spectral and timing data, our result reveals that the accretion corona is either an extended structure, or is located far from the black hole in the hard state of Cygnus X-1.

  • 13.
    Kevrekidis, P. G.
    et al.
    Univ Massachusetts, Dept Math & Stat, Amherst, MA 01003 USA..
    Wang, Wenlong
    KTH, School of Engineering Sciences (SCI), Physics.
    Carretero-Gonzalez, R.
    San Diego State Univ, Nonlinear Dynam Syst Grp, Computat Sci Res Ctr, San Diego, CA 92182 USA.;San Diego State Univ, Dept Math & Stat, San Diego, CA 92182 USA..
    Frantzeskakis, D. J.
    Univ Athens, Dept Phys, Athens 15784, Greece..
    Adiabatic invariant analysis of dark and dark-bright soliton stripes in two-dimensional Bose-Einstein condensates2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 97, no 6, article id 063604Article in journal (Refereed)
    Abstract [en]

    In the present work, we develop an adiabatic invariant approach for the evolution of quasi-one-dimensional (stripe) solitons embedded in a two-dimensional Bose-Einstein condensate. The results of the theory are obtained both for the one-component case of dark soliton stripes, as well as for the considerably more involved case of the two-component dark-bright (alias "filled dark") soliton stripes. In both cases, analytical predictions regarding the stability and dynamics of these structures are obtained. One of our main findings is the determination of the instability modes of the waves as a function of the parameters of the system (such as the trap strength and the chemical potential). Our analytical predictions are favorably compared with results of direct numerical simulations.

  • 14.
    Castin, N.
    et al.
    Studie Ctr Kerneenergie, Ctr Etud Energie Nucl SCK CEN, NMS Unit, Boeretang 200, B-2400 Mol, Belgium..
    Pascuet, M. I.
    Consejo Nacl Invest Cient & Tecn CONICET, Godoy Cruz 2290 C1425FQB CABA, Buenos Aires, DF, Argentina..
    Messina, Luca
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Domain, C.
    EDF R&D, Dept Mat & Mecan Composants, F-77250 Moret Sur Loing, France..
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Pasianot, R. C.
    Consejo Nacl Invest Cient & Tecn CONICET, Godoy Cruz 2290 C1425FQB CABA, Buenos Aires, DF, Argentina.;Comis Nacl Energia Atom CNEA, Gcia Mat, Av Gral Paz 1499, RA-1650 San Martin, Argentina..
    Malerba, L.
    Studie Ctr Kerneenergie, Ctr Etud Energie Nucl SCK CEN, NMS Unit, Boeretang 200, B-2400 Mol, Belgium..
    Advanced atomistic models for radiation damage in Fe-based alloys: Contributions and future perspectives from artificial neural networks2018In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 148, p. 116-130Article in journal (Refereed)
    Abstract [en]

    Machine learning, and more specifically artificial neural networks (ANN), are powerful and flexible numerical tools that can lead to significant improvements in many materials modelling techniques. This paper provides a review of the efforts made so far to describe the effects of irradiation in Fe-based and W-based alloys, in a multiscale modelling framework. ANN were successfully used as innovative parametrization tools in these models, thereby greatly enhancing their physical accuracy and capability to accomplish increasingly challenging goals. In the provided examples, the main goal of ANN is to predict how the chemical complexity of local atomic configurations, and/or specific strain fields, influence the activation energy of selected thermally-activated events. This is most often a more efficient approach with respect to previous computationally heavy methods. In a future perspective, similar schemes can be potentially used to calculate other quantities than activation energies. They can thus transfer atomic-scale properties to higher-scale simulations, providing a proper bridging across scales, and hence contributing to the achievement of accurate and reliable multiscale models.

  • 15. Cui, J. P.
    et al.
    Zhang, Y. L.
    Zhang, S.
    Wang, Y. Z.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    alpha-decay half-lives of superheavy nuclei2018In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 97, no 1, article id 014316Article in journal (Refereed)
    Abstract [en]

    The alpha-decay half-lives of superheavy nuclei (SHN) with Z >= 104 are investigated by employing the effective liquid drop model (ELDM). By comparison between the calculated half-lives and the experimental ones, it is shown that the ELDM is a successful model to reproduce the experimental half-lives of SHN. Within the ELDM the alpha-decay half-lives of Z = 118-120 isotopes are predicted by inputting the alpha-decay energy (Q(alpha)) values extracted from the newest Weizsacker-Skyrme-4 (WS4) model, the finite-range droplet model (FRDM), the Kourra-Tachibaba-Uno-Yamada (KTUY) formula, and the Hartree-Fock-Bogoliubovmean field with the D1S Gogny force (GHFB). It is found that the shell effects at N = 178 and 184 are evident by analyzing the Q(alpha) values and half-lives versus the neutron number N. Because the WS4 Q(alpha) values have the smallest rms deviation, the predicted alpha-decay half-lives could be more accurate than the ones of other models, which will be helpful for future experiments.

  • 16.
    Ramirez Alvarez, André
    KTH, School of Engineering Sciences (SCI), Physics.
    Alternative Calculation of Real Price Changes2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 17.
    Manickam, Louis
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    An Experimental Study on Melt Fragmentation, Oxidation and Steam Explosion during Fuel Coolant Interactions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nordic type boiling water reactors (BWRs) adopt reactor cavity flooding as a severe accident mitigation strategy (SAMS) to achieve core melt fragmentation and long-term cooling of decay heat generating core debris. The qualification of this SAMS needs to address two main severe accident issues: debris bed coolability and steam explosion. 

     

    Since the coolability of a debris bed is determined by the bed’s  properties including debris particle’s size distribution and morphology as well as the bed’s configuration and inhomogeneity, it is important to investigate the mechanisms of melt jet breakup and resulting fragmentation in water which affect debris bed’s properties. Hence, the first part of this thesis is concerned with characterization of melt jet breakup and resulting debris particles.  A series of jet breakup experiments have been conducted in small scale with simulant binary oxide melt mixtures of WO3-Bi2O3, WO3-ZrO2 and Wood's metal. The experiments reveal significant influence of melt superheat, water subcooling, melt jet diameter and material properties on debris size and morphology. Specifically, transition in debris size and morphology is found to occur at a specific water subcooling range. The difference in debris properties at varied melt release conditions is attributed to the competition between liquid melt hydrodynamic fragmentation and thermomechanical fracture of quenched particles.

     

    The second part of this thesis work is dedicated to provide a new understanding of steam explosion (SE) with the support of small-scale experiments at the level of droplets. Self- and externally-triggered SE experiments are conducted with simulant binary oxide melt mixtures in the temperature range of 1100 to 1500°C. The dynamics of steam explosion process is recorded using a sophisticated simultaneous visualization system of videography and X-ray radiography. Further, the influence of melt composition on steam explosion is summoned.  The results reveal that a droplet of eutectic composition is more explosive than a droplet of non-eutectic composition since latter may form a mushy zone which thereby limits the amount of melt actively participating in a steam explosion. To reduce the temperature difference between simulant melt and corium, investigation was extended to perform high temperature (˃2000°C) melt experiments. For this purpose, steam explosion of a molten Al2O3 droplet was investigated, and the experimental results confirmed that Al2O3 melt can undergo spontaneously triggered steam explosion at a high melt superheat and high subcooling. Within the context the effects of melt superheat and water subcooling were obtained.

     

    The third part of this thesis is concerned with the oxidation of metallic melt representing unmixable metallic liquid of molten corium, which interactions with water can be spatially and chronologically separated from the oxidic corium FCI. The objective of the study  is to provide new insights into the characteristics of oxidation of Zr droplet falling in a water pool through a series of small-scale experiments. The dynamics of droplet and bubbles were recorded by high-speed cameras, and the spatial distributions of the elements in the quenched droplet (debris) were acquired by Energy- Dispersive X-Ray Spectroscopy (EDS). The results have shown noticeable influence of generated hydrogen and oxidation heat on droplet behavior and cooling rate. Water subcooling had significant influence on oxidation kinetics, and the oxygen content of the solidified particle increased with decreasing subcooling. Incomplete oxidation of Zr happened before melt crystallization and cooling down in all experiments.  

  • 18.
    Manickam, Louis
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. KTH.
    Qiang, Guo
    KTH, School of Engineering Sciences (SCI).
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI).
    Bechta, Sevostian
    An experimental study on the intense intense heat transfer and phase change during melt and water interactions2018In: Experimental heat transfer, ISSN 0891-6152, E-ISSN 1521-0480Article in journal (Refereed)
  • 19. Spirzewski, M.
    et al.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Warsaw University of Technology, Poland.
    An improved phenomenological model of annular two-phase flow with high-accuracy dryout prediction capability2018In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 331, p. 176-185Article in journal (Refereed)
    Abstract [en]

    This paper presents a new phenomenological model of annular two-phase flow with dryout prediction capability, implemented in the CATHARE-3 system code. The model comprises existing correlations for entrainment and deposition rates and a new equation to determine the initial entrained fraction (IEF) of the liquid phase at the onset of annular two-phase flow. The proposed new model allows for a significant reduction of mean error variations with pressure and mass flux, when compared with measured dryout in pipes with internal diameter from 8 to 14.9 mm, system pressure from 3 to 10 MPa, mass flux from 500 to 6000 kg/m2s, test section length from 1 to 7 m, inlet subcooling form 10 to 100 K, and critical heat flux from 0.15 to 3.90 MW/m2. It has been also shown that, at certain conditions, the phenomenological model is unable to provide an accurate prediction, irrespective of the chosen value for the IEF parameter. Such behavior is thoroughly investigated in this paper and seldom addressed in the literature, even though it sets limits on the applicability of the model to dryout predictions.

  • 20.
    Bergagio, Mattia
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Li, Haipeng
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Warsaw University of Technology, Poland.
    An iterative finite-element algorithm for solving two-dimensional nonlinear inverse heat conduction problems2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 126, p. 281-292Article in journal (Refereed)
    Abstract [en]

    It is often useful to determine temperature and heat flux in multidimensional solid domains of arbitrary shape with inaccessible boundaries. In this study, an effective algorithm for solving boundary inverse heat conduction problems (IHCPs) is implemented: transient temperatures on inaccessible boundaries are estimated from redundant simulated measurements on accessible boundaries. A nonlinear heat equation is considered, where some of the material properties are dependent on temperature. The IHCP is reformulated as an optimization problem. The resulting functional is iteratively minimized using a conjugate gradient method together with an adjoint (dual) problem approach. The associated partial differential equations are solved using the finite-element package FEniCS. Tikhonov regularization is introduced to mitigate the ill-posedness of the IHCP. The accuracy of the implemented algorithm is assessed by comparing the solutions to the IHCP with the correct temperature values, on the inaccessible boundaries. The robustness of our method is tested by adding Gaussian noise to the initial conditions and redundant boundary data in the inverse problem formulation. A mesh independence study is performed.

  • 21.
    Galushin, Sergey
    et al.
    employer.
    Kudinov, Pavel
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Analysis of the Effect of Severe Accident Scenario on the Vessel Lower Head Failure in Nordic BWR using MELCOR code2018Conference paper (Refereed)
  • 22.
    Aaboud, M.
    et al.
    Univ Mohamed Premier, Fac Sci, Oujda, Morocco.;LPTPM, Oujda, Morocco..
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Lawrence Berkeley Natl Lab, Phys Div, Berkeley, CA USA.;Univ Calif Berkeley, Berkeley, CA 94720 USA.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Angular analysis of B-d(0) -> K* mu(+)mu(-) decays in pp collisions at root s=8 TeV with the ATLAS detector2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 10, article id 047Article in journal (Refereed)
    Abstract [en]

    An angular analysis of the decay B-d(0) -> K*mu(+)mu(-) is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb(-1) of integrated luminosity collected during 2012 at centre-of-mass energy of root s = 8TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.

  • 23. Lu, D.
    et al.
    Peña, A.
    Segonds, P.
    Debray, J.
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Canalias, Carlota
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Physics.
    Boulanger, B.
    Angular quasi-phase-matching in a sphere of PPRKTP2018In: Optics InfoBase Conference Papers, Optical Society of America, 2018Conference paper (Refereed)
    Abstract [en]

    we report the first measurements of angular quasi-phase-matching directions of secondharmonic generation performed in the periodically-poled Rb-doped KTiOPO4 biaxial crystal cut as a sphere.

  • 24.
    Pozo, Oscar
    et al.
    Inst Ciencia Mat Madrid, Madrid 28049, Spain.;CSIC, Madrid 28049, Spain..
    Ferreiros, Yago
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Vozmediano, Maria A. H.
    Inst Ciencia Mat Madrid, Madrid 28049, Spain.;CSIC, Madrid 28049, Spain..
    Anisotropic fixed points in Dirac and Weyl semimetals2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 11, article id 115122Article in journal (Refereed)
    Abstract [en]

    The effective low energy description of interacting Dirac and Weyl semimetals is that of massless quantum electrodynamics with several Lorentz breaking material parameters. We perform a renormalization group analysis of Coulomb interaction in anisotropic Dirac and Weyl semimetals and show that the anisotropy persists in the material systems at the infrared fixed point. In addition, a tilt of the fermion cones breaking inversion symmetry induces a magnetoelectric term in the electrodynamics of the material whose magnitude runs to match that of the electronic tilt at the fixed point.

  • 25.
    Ludovico Benfenati, Andrea
    KTH, School of Engineering Sciences (SCI), Physics.
    Anisotropic Three-Component Superconductors2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 26.
    Kööp, Kaspar
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Application of a system thermal-hydraulics code to development of validation process for coupled STH-CFD codes2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Generation IV reactors are designed to provide sustainable energy generation, minimize waste production and excel in safety. Due to lack of operational experience, ever evolving design and stringent safety requirements, these novel reactors have to rely heavily on simulations.

    Best estimate one-dimensional (1D) system thermal-hydraulics (STH) codes, originally intended for simulating water-cooled reactor systems with high coolant mass flow rates, are unable to capture complex three-dimensional (3D) phenomena in liquid metal cooled pool-type reactors. Computational fluid dynamics (CFD) codes are capable of resolving the 3D effects, however applying these methods with high resolution for the whole primary system results in prohibiting computational cost.

    At the same time, there are system components where flow can, with reasonable accuracy, be approximated with 1D models (e.g. core channels, some heat exchangers, etc.). One of the proposed solutions in order to achieve adequate accuracy and affordable computational efficiency in modelling of a Generation IV reactor is to divide the primary system into 1D and 3D regions and apply coupled STH and CFD codes on the respective sub-domains.

    Successful validation is a prerequisite for application of both, standalone and coupled STH and CFD codes in design and safety analysis of Generation IV systems. In this work we develop and apply different aspects of code validation methodology with an emphasis on (i) STH code analysis in support of validation experiment design (facility and test conditions), (ii) calibration of uncertain code input parameters and validation of standalone STH code, (iii) development of an approach to couple STH and CFD codes.

    A considerable part of the thesis work is related to the development of a loop-type, 3 leg, liquid metal experimental facility TALL-3D for code validation. Particular focus was on identification of test conditions featuring complex feedbacks between 1D-3D phenomena, which can be challenging for the codes. Standalone STH code (RELAP5) was validated against experimental data. The domain of natural circulation instabilities in TALL-3D operation parameters was discovered using a validated STH code and global optimum search algorithms. Then existence of growing natural circulation oscillations was experimentally confirmed. An international benchmark was initiated in the framework of EU SESAME project based on the obtained experimental data.

    Simulations were performed to define dimensions and location of a new test section for coolant solidification experiments that would also enhance possibilities for studying natural circulation instabilities in the future tests.

    An approach to automated input calibration and code validation is developed in order to minimize possible “user effect” in case of multiple uncertain input parameters (UIPs) and system response quantities (SRQs). These methods were applied extensively in the development of RELAP5 input models and identification of the natural circulation instability regions.

    Domain overlapping approach to coupling of RELAP5 and Star-CCM+ codes was proposed and resulted in considerable improvement of the predictive capabilities in comparison to standalone RELAP5.

  • 27.
    Bujila, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Karolinska Univ Hosp, Med Radiat Phys & Nucl Med, Stockholm, Sweden.
    Kull, Love
    Sunderby Hosp, Dept Radiat Phys, Lulea, Sweden..
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Andersson, Jonas
    Umea Univ, Dept Radiat Sci, Umea, Sweden..
    Applying three different methods of measuring CTDIfree air to the extended CTDI formalism for wide-beam scanners (IEC 60601-2-44): A comparative study2018In: Journal of Applied Clinical Medical Physics, ISSN 1526-9914, E-ISSN 1526-9914, Vol. 19, no 4, p. 281-289Article in journal (Refereed)
    Abstract [en]

    Purpose: The weighted CT dose index (CTDIw) has been extended for a nominal total collimation width (nT) greater than 40 mm and relies on measurements of CTDfree air. The purpose of this work was to compare three methods of measuring CTDIfree air and subsequent calculations of CTDIw to investigate their clinical appropriateness. Methods: The CTDIfree air, for multiple nTs up to 160 mm, was calculated from (1) high-resolution air kerma profiles from a step-and-shoot translation of a liquid ionization chamber (LIC) (considered to be a dosimetric reference), (2) pencil ionization chamber (PIC) measurements at multiple contiguous positions, and (3) air kerma profiles obtained through the continuous translation of a solid-state detector. The resulting CTDIfree air was used to calculate the CTDIw, per the extended formalism, and compared. Results: The LIC indicated that a 40 mm nT should not be excluded from the extension of the CTDIw formalism. The solid-state detector differed by as much as 8% compared to the LIC. The PIC was the most straightforward method and gave equivalent results to the LIC. Conclusions: The CTDIw calculated with the latest CTDI formalism will differ most for 160 mm nTs (e.g., whole-organ perfusion or coronary CT angiography) compared to the previous CTDI formalism. Inaccuracies in the measurement of CTDIfree air will subsequently manifest themselves as erroneous calculations of the CTDIw, for nTs greater than 40 mm, with the latest CTDI formalism. The PIC was found to be the most clinically feasible method and was validated against the LIC.

  • 28.
    Burgess, J. Michael
    et al.
    KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Engineering Sciences (SCI), Physics. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..
    Yu, Hoi-Fung
    Max Planck Inst Extraterr Phys, D-85748 Garching, Germany..
    Greiner, Jochen
    Max Planck Inst Extraterr Phys, D-85748 Garching, Germany..
    Mortlock, Daniel J.
    Imperial Coll London, Stat Sect, Dept Math, London SW7 2AZ, England.;Imperial Coll London, Blackett Lab, Astrophys Grp, Prince Consort Rd, London SW7 2AZ, England.;Stockholm Univ, Dept Astron, AlbaNova, SE-10691 Stockholm, Sweden..
    Awakening the BALROG: BAyesian Location Reconstruction Of GRBs2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 2, p. 1427-1444Article in journal (Refereed)
    Abstract [en]

    The accurate spatial location of gamma-ray bursts (GRBs) is crucial for both accurately characterizing their spectra and follow-up observations by other instruments. The Fermi Gamma-ray Burst Monitor (GBM) has the largest field of view for detecting GRBs as it views the entire unocculted sky, but as a non-imaging instrument it relies on the relative count rates observed in each of its 14 detectors to localize transients. Improving its ability to accurately locate GRBs and other transients is vital to the paradigm of multimessenger astronomy, including the electromagnetic follow-up of gravitational wave signals. Here we present the BAyesian Location Reconstruction Of GRBs (BALROG) method for localizing and characterizing GBM transients. Our approach eliminates the systematics of previous approaches by simultaneously fitting for the location and spectrum of a source. It also correctly incorporates the uncertainties in the location of a transient into the spectral parameters and produces reliable positional uncertainties for both well-localized sources and those for which the GBM data cannot effectively constrain the position. While computationally expensive, BALROG can be implemented to enable quick follow-up of all GBM transient signals. Also, we identify possible response problems that require attention and caution when using standard, public GBM detector response matrices. Finally, we examine the effects of including the uncertainty in location on the spectral parameters of GRB080916C. We find that spectral parameters change and no extra components are required when these effects are included in contrast to when we use a fixed location. This finding has the potential to alter both the GRB spectral catalogues and the reported spectral composition of some well-known GRBs.

  • 29.
    Boucenna, Sofiane M.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Shafi, Qaisar
    Univ Delaware, Bartol Res Inst, Newark, DE 19716 USA..
    Axion inflation, proton decay, and leptogenesis in SU (5) x U(1)(PQ)2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 97, no 7, article id 075012Article in journal (Refereed)
    Abstract [en]

    We implement inflation in a nonsupersymmetric SU(5) model based on a nonminimal coupling of the axion field to gravity. The isocurvature fluctuations are adequately suppressed, axions comprise the dark matter, proton lifetime estimates are of order 8 x 10(34)-3 x 10(35) yr, and the observed baryon asymmetry arises via nonthermal leptogenesis. The presence of low-scale colored scalars ensures unification of the Standard Model gauge couplings and also helps in stabilizing the electroweak vacuum.

  • 30.
    Yu, Hoi-Fung
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Hui, Chung Yue
    Chungnam Natl Univ, Dept Astron & Space Sci, Daejeon 34134, South Korea..
    Kong, Albert K. H.
    Natl Tsing Hua Univ, Inst Astron, Hsinchu, Taiwan..
    Takata, Jumpei
    Huazhong Univ Sci & Technol, Inst Particle Phys & Astron, Wuhan, Hubei, Peoples R China..
    Bayesian Inference on the Radio-quietness of Gamma-ray Pulsars2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 857, no 2Article in journal (Refereed)
    Abstract [en]

    For the first time we demonstrate using a robust Bayesian approach to analyze the populations of radio-quiet (RQ) and radio-loud (RL) gamma-ray pulsars. We quantify their differences and obtain their distributions of the radiocone opening half-angle d and the magnetic inclination angle a by Bayesian inference. In contrast to the conventional frequentist point estimations that might be non-representative when the distribution is highly skewed or multi-modal, which is often the case when data points are scarce, Bayesian statistics displays the complete posterior distribution that the uncertainties can be readily obtained regardless of the skewness and modality. We found that the spin period, the magnetic field strength at the light cylinder, the spin-down power, the gamma-rayto-X-ray flux ratio, and the spectral curvature significance of the two groups of pulsars exhibit significant differences at the 99% level. Using Bayesian inference, we are able to infer the values and uncertainties of d and a from the distribution of RQ and RL pulsars. We found that d is between 10 degrees and 35 degrees and the distribution of a is skewed toward large values.

  • 31.
    Radhika, D.
    et al.
    Dayananda Sagar Univ, Dept Phys, Bangalore 560068, Karnataka, India..
    Sreehari, H.
    ISRO Satellite Ctr, Space Astron Grp, SSIF ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India.;Indian Inst Sci, Bangalore 560012, Karnataka, India..
    Nandi, A.
    ISRO Satellite Ctr, Space Astron Grp, SSIF ISITE Campus,Outer Ring Rd, Bangalore 560037, Karnataka, India..
    Iyer, Nirmal
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Albanova Univ Ctr, KTH PAP, S-10691 Stockholm, Sweden..
    Mandal, S.
    Indian Inst Space Sci & Technol, Thiruvananthapuram, Kerala, India..
    Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: SWIFT and NuSTAR results2018In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, no 9, article id 189Article in journal (Refereed)
    Abstract [en]

    We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical 'q'-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along-with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the -class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5-79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of with 90% confidence, which is consistent with earlier findings.

  • 32.
    Berggren, Karl
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Cascaded systems analysis of shift-variant image quality in slit-scanning breast tomosynthesis2018In: Medical PhysicsArticle in journal (Refereed)
  • 33.
    Berggren, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Philips Mammog Solut, S-16440 Kista, Sweden..
    Cederström, Björn
    Philips Mammog Solut, S-16440 Kista, Sweden..
    Lundqvist, Mats
    Philips Mammog Solut, S-16440 Kista, Sweden..
    Fredenberg, Erik
    Philips Res, S-16440 Kista, Sweden..
    Cascaded systems analysis of shift-variant image quality in slit-scanning breast tomosynthesis2018In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, no 10, p. 4392-4401Article in journal (Refereed)
    Abstract [en]

    PurposeDigital breast tomosynthesis (DBT) is becoming an important part of breast cancer screening and diagnosis. Compared to two-dimensional mammography, tomosynthesis introduces limited three-dimensional (3D) resolution, but maintains high in-plane resolution, low dose, and allows for similar clinical protocols. The scanning motion and oblique projections of tomosynthesis acquisitions introduce shift-variance to the image quality, in addition to effects such as source blurring and geometric magnification. Shift-variant detector response caused by oblique incidence has been extensively studied previously and is most easily mitigated by letting the source and detector move in sync. In addition, conical reconstruction grids, that is, a grid aligned with the central tomosynthesis projection, have been proposed to compensate for magnification effects. This paper introduces a shift-variant cascaded systems model for tomosynthesis and validates it against measurements. As an example, the model was used to investigate the shift-variance of a tomosynthesis system. MethodsThe shift-variant cascaded systems model was validated on a slit-scanning photon-counting DBT system, with synchronous source-detector movement, using simple back-projection in a conical reconstruction volume. The modulation transfer function (MTF), normalized noise-power spectrum (NNPS), and detective quantum efficiency (DQE) were used as figures of merit. Simulations were performed for single points while measurements were done over a finite volume, assuming local shift invariance. To investigate the full extent of shift-variance, 80 locations across the volume were simulated, and the MTF and DQE at 2.5lp/mm were calculated as a function of position. ResultsThe simulated metrics generally agreed well with their corresponding measurements. The frequency at 50% MTF along the scan direction showed a relatively small variation, ranging from 2.1 to 2.4lp/mm for the different locations. The frequency at 50% MTF along the chest-mammilla direction showed a larger variation, ranging from 2.9 to 3.8lp/mm. All points exhibited a similarly shaped NNPS but the noise magnitude varied with slice height. The zero-frequency DQE in reconstructed slices was lower than that of the projections, an effect likely caused by noise-aliasing increasing the zero-frequency noise. ConclusionsA shift-variant cascaded systems model has been developed for slit-scanning tomosynthesis using simple back-projection. The model was successfully validated against measurements. Even though the study was performed on a slit-scanning system, several parts of the framework can be applied and extended to other tomosynthesis geometries. The conical reconstruction grid has low variation in image quality in the scan direction where the 3D information is acquired, but source and geometric magnification still dominate in the slit direction, causing a larger variation in image quality. We conclude that image quality is close to shift-invariant in the scan direction, but not in the height and chest-mammilla directions, and we recommend that small measurement volumes are used when measuring image quality in these directions to minimize the effects of shift variance.

  • 34.
    Twengström, William
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Persson, Jonas
    Szekely, Laszlo
    Hertz, Hans
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Cellular-resolution 3D virtual histology of human coronary arteries using x-ray phase tomography2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 11014Article in journal (Refereed)
    Abstract [en]

    High-spatial-resolution histology of coronary artery autopsy samples play an important role for understanding heart disease such as myocardial infarction. Unfortunately, classical histology is often destructive, has thick slicing, requires extensive sample preparation, and is time-consuming. X-ray micro-CT provides fast nondestructive 3D imaging but absorption contrast is often insufficient, especially for observing soft-tissue features with high resolution. Here we show that propagation-based x-ray phase-contrast tomography has the resolution and contrast to image clinically relevant soft-tissue features in intact coronary artery autopsy samples with cellular resolution. We observe microscopic lipid-rich plaques, individual adipose cells, ensembles of few foam cells, and the thin fibrous cap. The method relies on a small-spot laboratory x-ray microfocus source, and provides high-spatial resolution in all three dimensions, fast data acquisition, minimum sample distortion and requires no sample preparation.

  • 35.
    Nakane, Takanori
    et al.
    MRC Lab Mol Biol, Cambridge, England..
    Kimanius, Dari
    Lindahl, Erik
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences (SCI), Physics.
    Scheres, Sjors H. W.
    MRC Lab Mol Biol, Cambridge, England..
    Characterisation of molecular motions in cryo-EM single-particle data by multi-body refinement in RELION2018In: eLIFE, E-ISSN 2050-084X, Vol. 7, article id e36861Article in journal (Refereed)
    Abstract [en]

    Macromolecular complexes that exhibit continuous forms of structural flexibility pose a challenge for many existing tools in cryo-EM single-particle analysis. We describe a new tool, called multi-body refinement, which models flexible complexes as a user-defined number of rigid bodies that move independently from each other. Using separate focused refinements with iteratively improved partial signal subtraction, the new tool generates improved reconstructions for each of the defined bodies in a fully automated manner. Moreover, using principal component analysis on the relative orientations of the bodies over all particle images in the data set, we generate movies that describe the most important motions in the data. Our results on two test cases, a cytoplasmic ribosome from Plasmodium falciparum, and the spliceosomal B-complex from yeast, illustrate how multi-body refinement can be useful to gain unique insights into the structure and dynamics of large and flexible macromolecular complexes.

  • 36.
    Giono, G.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Olentsenko, G.
    KTH, School of Engineering Sciences (SCI), Physics.
    Ivchenko, N.
    KTH, School of Engineering Sciences (SCI), Physics.
    Christensen, O. M.
    Chalmers Univ Technol, Gothenburg, Sweden..
    Gumbel, J.
    Stockholm Univ, MISU, Stockholm, Sweden..
    Frisk, U.
    Omnisys Instruments AB, Gothenburg, Sweden..
    Hammar, A.
    Omnisys Instruments AB, Gothenburg, Sweden..
    Davies, I.
    Teledyne E2V, Chelmsford, England..
    Megner, L.
    Stockholm Univ, MISU, Stockholm, Sweden..
    Characterisation of the analogue read-out chain for the CCDs onboard the Mesospheric Airglow/Aerosol Tomography and Spectroscopy (MATS)2018In: SPACE TELESCOPES AND INSTRUMENTATION 2018: OPTICAL, INFRARED, AND MILLIMETER WAVE / [ed] Lystrup, M MacEwen, HA Fazio, GG, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 106984YConference paper (Refereed)
    Abstract [en]

    The MATS satellite aims at observing airglow and noctilucent clouds in the mesosphere. The main instrument consists of a six channels limb imager in the near-ultraviolet and near-infrared. A high signal-to-noise ratio is required for detecting these mesospheric phenomena: 100 and 500 for ultraviolet and infrared, respectively. This is achieved by an optical design minimizing stray-light, but also with a dedicated design of the read-out analogue chain for the CCD on each channel. The requirements and expected light level on the imaging channels are briefly discussed before focusing on the CCD read-out analogue chain, for which the design and performances are presented.

  • 37.
    Berggren, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Philips Mammorgaphy Solutions.
    Cederström, Björn
    Philips Mammography Solutions.
    Lundqvist, Mats
    Philips Mammography Solutions.
    Fredenberg, Erik
    Philips Research.
    Characterization of photon-counting multislit breast tomosynthesis2018In: Medical Physics, E-ISSN 2473-4209Article in journal (Refereed)
    Abstract [en]

    Purpose: It has been shown that breast tomosynthesis may improve sensitivity and specificity compared to two-dimensional mammography, resulting in increased detection-rate of cancers or lowered call-back rates. The purpose of this study is to characterize a spectral photon-counting multislit breast tomosynthesis system that is able to do single-scan spectral imaging with multiple collimated x-ray beams. The system differs in many aspects compared to conventional tomosynthesis using energyintegrating flat-panel detectors. Methods: The investigated system was a prototype consisting of a dual-threshold photon-counting detector with 21 collimated line detectors scanning across the compressed breast. A review of the system is done in terms of detector, acquisition geometry, and reconstruction methods. Three reconstruction methods were used, simple back-projection, filtered back-projection and an iterative algebraic reconstruction technique. The image quality was evaluated by measuring the modulation transfer-function (MTF), normalized noise-power spectrum, detective quantum-efficiency (DQE), and artifact spread-function (ASF) on reconstructed spectral tomosynthesis images for a total-energy bin (defined by a low-energy threshold calibrated to remove electronic noise) and for a high-energy bin (with a threshold calibrated to split the spectrum in roughly equal parts). Acquisition was performed using a 29 kVp W/Al x-ray spectrum at a 0.24 mGy exposure. Results: The difference in MTF between the two energy bins was negligible, that is, there was no energy dependence on resolution. The MTF dropped to 50% at 1.5 lp/mm to 2.3 lp/mm in the scan direction and 2.4 lp/mm to 3.3 lp/mm in the slit direction, depending on the reconstruction method. The full width at half maximum of the ASF was found to range from 13.8 mm to 18.0 mm for the different reconstruction methods. The zero-frequency DQE of the system was found to be 0.72. The fraction of counts in the high-energy bin was measured to be 59% of the total detected spectrum. Scantimes ranged from 4 s to 16.5 s depending on voltage and current settings. Conclusions: The characterized system generates spectral tomosynthesis images with a dual-energy photon-counting detector. Measurements show a high DQE, enabling high image quality at a low dose, which is beneficial for low-dose applications such as screening. The single-scan spectral images open up for applications such as quantitative material decomposition and contrast-enhanced tomosynthesis. 

  • 38.
    Bhagwat, A.
    et al.
    UM DAE Ctr Excellence Basic Sci, Mumbai 400098, Maharashtra, India.;AlbaNova Univ Ctr, Dept Nucl Phys, KTH Royal Inst Technol, S-10691 Stockholm, Sweden..
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Cluster emission from superheavy nuclei2018In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 54, no 11, article id 200Article in journal (Refereed)
    Abstract [en]

    The process leading to cluster emission from superheavy nuclei in the range 100 122 has been systematically investigated. This topic is of importance because it opens up the possibility of identifying superheavy elements through deposition of clusters in the detection system. In this paper we evaluate the cluster decay half lives by considering the cluster as a particle. The motion of this particle in the field induced by the daughter nucleus is determined by solving the corresponding Schrodinger equation imposing outgoing boundary conditions (Gamow state). The corresponding Wood-Saxon potential is fitted to obtain the energies provided by a mass formula that has been established recently to have a very high degree of precision. The resulting expression for the decay width is exact, i.e. no approximation besides the assumption of a preformed cluster is introduced. It is found that the heavy cluster emission probability in the superheavy region is much smaller than the corresponding a emission probability.

  • 39.
    Acuner, Zeynep
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Clustering of gamma-ray burst types in the Fermi GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 475, no 2, p. 1708-1724Article in journal (Refereed)
    Abstract [en]

    Many different physical processes have been suggested to explain the prompt gamma-ray emission in gamma-ray bursts (GRBs). Although there are examples of both bursts with photospheric and synchrotron emission origins, these distinct spectral appearances have not been generalized to large samples of GRBs. Here, we search for signatures of the different emission mechanisms in the full Fermi Gamma-ray Space Telescope/GBM (Gamma-ray Burst Monitor) catalogue. We use Gaussian Mixture Models to cluster bursts according to their parameters from the Band function (alpha, beta, and E-pk) as well as their fluence and T-90. We find five distinct clusters. We further argue that these clusters can be divided into bursts of photospheric origin (2/3 of all bursts, divided into three clusters) and bursts of synchrotron origin (1/3 of all bursts, divided into two clusters). For instance, the cluster that contains predominantly short bursts is consistent of photospheric emission origin. We discuss several reasons that can determine which cluster a burst belongs to: jet dissipation pattern and/or the jet content, or viewing angle.

  • 40. Aaboud, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Woods, N.
    et al.,
    Combination of inclusive and differential t(t)over-bar charge asymmetry measurements using ATLAS and CMS data at root S =7 and 8 TeV2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 4, article id 033Article in journal (Refereed)
    Abstract [en]

    This paper presents combinations of inclusive and differential measurements of the charge asymmetry (A(C)) in top quark pair (t(t)over-bar) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb(-1) for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are A(C)(LHC7) = 0.005 +/- 0.007 (stat) +/- 0.006 (syst) at 7 TeV and A(C)(LHC8) = 0.0055 +/- 0.0023 (stat) +/- 0.0025 (syst) at 8 TeV. These values, as well as the combination of A(C )measurements as a function of the invariant mass of the t(t)over-bar system at 8 TeV, are consistent with the respective standard model predictions.

  • 41. Aaboud, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    et al.,
    Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36 fb(-1) of proton-proton collision data at root s=13 TeV with the ATLAS detector2018In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 98, no 5, article id 052008Article in journal (Refereed)
    Abstract [en]

    Searches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as dirffiffiffiectly into leptons, are presented using a data sample corresponding to 36.1 fb(-1) of pp collisions at root s = 13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the qqqq, vvqq, evqq, eeqq, evev, eevv, evee, eeee, qqbb, vvbb, evbb, and eebb final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic ev and ee final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV.

  • 42.
    Aaboud, M.
    et al.
    Univ Mohamed Premier, Fac Sci, Oujda, Morocco.;LPTPM, Oujda, Morocco..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    et. al,
    Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at root s=13 TeV with the ATLAS Detector2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 21, article id 211801Article in journal (Refereed)
    Abstract [en]

    A combination of the searches for pair-produced vectorlike partners of the top and bottom quarks in various decay channels (T -> Zt/Wb/Ht, B -> Zb/Wt/Hb) is performed using 36.1 fb(-1) of pp collision data at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the standard model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross section for a range of vectorlike quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vectorlike quarks decay to standard model particles. A singlet T is excluded for masses below 1.31 TeV and a singlet B is excluded for masses below 1.22 TeV. Assuming a weak isospin (T, B) doublet and vertical bar V-Tb vertical bar << vertical bar V-tB vertical bar, T and B masses below 1.37 TeV are excluded.

  • 43. Aaboud, M.
    et al.
    Kastanas, Konstatinos A.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    Combined measurement of differential and total cross sections in the H → γγ and the H → ZZ⁎ → 4ℓ decay channels at s=13 TeV with the ATLAS detector2018In: Vol. 786, p. 114-133Article in journal (Refereed)
    Abstract [en]

    A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb−1 of 13 TeV proton–proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H→γγ and H→ZZ⁎→4ℓ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0−5.9 +6.0 (stat.) −3.3 +4.0 (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.

  • 44.
    Mishchenko, Yulia
    KTH, School of Engineering Sciences (SCI), Physics.
    Composite UN-UO2 fuels2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 45.
    Harpole, Tyler J.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Delemotte, Lucie
    KTH, School of Engineering Sciences (SCI), Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Conformational landscapes of membrane proteins delineated by enhanced sampling molecular dynamics simulations2018In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1860, no 4, p. 909-926Article, review/survey (Refereed)
    Abstract [en]

    The expansion of computational power, better parameterization of force fields, and the development of novel algorithms to enhance the sampling of the free energy landscapes of proteins have allowed molecular dynamics (MD) simulations to become an indispensable tool to understand the function of biomolecules. The temporal and spatial resolution of MD simulations allows for the study of a vast number of processes of interest. Here, we review the computational efforts to uncover the conformational free energy landscapes of a subset of membrane proteins: ion channels, transporters and G-protein coupled receptors. We focus on the various enhanced sampling techniques used to study these questions, how the conclusions come together to build a coherent picture, and the relationship between simulation outcomes and experimental observables.

  • 46. Guidoboni, G.
    et al.
    Stephenson, E. J.
    Wronska, A.
    Bagdasarian, Z.
    Bsaisou, J.
    Chekmenev, S.
    Ciullo, G.
    Dymov, S.
    Eversmann, D.
    Gaisser, M.
    Gebel, R.
    Hejny, V.
    Hempelmann, N.
    Hinder, F.
    Kacharava, A.
    Keshelashvili, I.
    Kulessa, P.
    Lenisa, P.
    Lehrach, A.
    Lorentz, B.
    Maanen, P.
    Maier, R.
    Mchedlishvili, D.
    Mey, S.
    Nass, A.
    Pesce, A.
    Orlov, Y.
    Pretz, J.
    Prasuhn, D.
    Rathmann, F.
    Rosenthal, M.
    Saleev, A.
    Semertzidis, Y. K.
    Senichev, Y.
    Shmakova, V.
    Stockhorst, H.
    Stroeher, H.
    Talman, R.
    Thörngren Engblom, Pia
    KTH, School of Engineering Sciences (SCI), Physics.
    Trinkel, F.
    Valdau, Yu.
    Weidemann, C.
    Wuestner, P.
    Zurek, M.
    Zyuzin, D.
    Connection between zero chromaticity and long in-plane polarization lifetime in a magnetic storage ring2018In: Physical Review Accelerators and Beams, ISSN 2469-9888, Vol. 21, no 2, article id 024201Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97-GeV/c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbontarget polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting.

  • 47.
    Li, Liang
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Chinese Acad Sci, Purple Mt Observ, Nanjing 210008, Jiangsu, Peoples R China.;Stockholm Univ, AlbaNova, Dept Phys, SE-10691 Stockholm, Sweden.
    Wu, Xue-Feng
    Chinese Acad Sci, Purple Mt Observ, Nanjing 210008, Jiangsu, Peoples R China..
    Lei, Wei-Hua
    Huazhong Univ Sci & Technol, Sch Phys, Wuhan 430074, Hubei, Peoples R China..
    Dai, Zi-Gao
    Nanjing Univ, Sch Astron & Space Sci, Nanjing 210093, Jiangsu, Peoples R China..
    Lian, En-Wei
    Guanxi Univ, GXU NAOC Ctr Astrophys & Space Sci, Dept Phys, Nanning 530004, Peoples R China..
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Constraining the Type of Central Engine of GRBs with Swift Data2018In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 236, no 2, article id 26Article in journal (Refereed)
    Abstract [en]

    The central engine of gamma-ray bursts (GRBs) is poorly constrained. There exist two main candidates: a fast-rotating black hole and a rapidly spinning magnetar. Furthermore, X-ray plateaus are widely accepted to be the energy injection into the external shock. In this paper, we systematically analyze the Swift/XRT light curves of 101 GRBs having plateau phases and known redshifts (before 2017 May). Since a maximum energy budget (similar to 2 x 10(52) erg) exists for magnetars but not for black holes, this provides a good clue to identifying the type of GRB central engine. We calculate the isotropic kinetic energy E-K,(iso) and the isotropic X-ray energy release E-X,E-iso for individual GRBs. We identify three categories based on how likely a black hole harbors a central engine: "Gold" (9 out of 101; both E-X,E-iso and E-K,E-iso exceed the energy budget), "Silver" (69 out of 101; E-X,E-iso less than the limit but E-K,E-iso greater than the limit), and "Bronze" (23 out of 101; the energies are not above the limit). We then derive and test the black hole parameters with the Blandford-Znajek mechanism, and find that the observations of the black hole candidate ("Gold" + "Silver") samples are consistent with the expectations of the black hole model. Furthermore, we also test the magnetar candidate ("Bronze") sample with the magnetar model, and find that the magnetar surface magnetic field (B-p) and initial spin period (P-0) fall into reasonable ranges. Our analysis indicates that if the magnetar wind is isotropic, a magnetar central engine is possible for 20% of the analyzed GRBs. For most GRBs, a black hole is most likely operating.

  • 48.
    Chauvin, Maxime
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Florén, H. -G
    Friis, M.
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Jackson, M.
    KTH, School of Engineering Sciences (SCI), Physics. Present address: School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, UK.
    Kamae, T.
    Kataoka, J.
    Kawano, T.
    Kiss, M.
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Mikhalev, V.
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Mizuno, T.
    Ohashi, N.
    Stana, T.
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Tajima, H.
    Takahashi, H.
    Uchida, N.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, 106 91, Stockholm, Sweden.
    Correction: Shedding new light on the crab with polarized X-rays (Scientific Reports DOI: 10.1038/s41598-017-07390-7)2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 7975Article in journal (Refereed)
    Abstract [en]

    This Article contains a typographical error in the legend of Figure 2. "Gaussian 1, 2 and 3& #x1D70E;" should read: "Gaussian 1, 2 and 3σ". 

  • 49.
    Grönberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Sjölin, Martin
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Count statistics and pileup correction for nonparalyzable photon counting detectors with finite pulse length2018In: Medical Imaging 2018: Physics Of Medical Imaging / [ed] Lo, JY Schmidt, TG Chen, GH, SPIE - International Society for Optical Engineering, 2018, article id UNSP 105730ZConference paper (Refereed)
    Abstract [en]

    Photon counting detectors are expected to be the next big step in the development of medical computed tomography. Accurate modeling of the behavior of photon counting detectors in the high count rate regime is therefore important for detector performance evaluations and the development of accurate image reconstruction methods. The commonly used ideal nonparalyzable detector model is based on the assumption that photon interactions are converted to pulses with zero extent in time, which is too simplistic to accurately predict the behavior of photon counting detectors in both low and high count rate regimes. In this work we develop a statistical count model for a nonparalyzable detector with finite pulse length and use it to derive the asymptotic mean and variance of the output count distribution using tools from renewal theory. We use the statistical moments of the distribution to construct an estimator of the true number of counts for pileup correction. We con firm the accuracy of the model and evaluate the pileup correction using Monte Carlo simulations. The results show that image quality is preserved for surprisingly high count rates.

  • 50.
    Grönberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Sjölin, Martin
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Count statistics of nonparalyzable photon-counting detectors with nonzero pulse length2018In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, no 8, p. 3800-3811Article in journal (Refereed)
    Abstract [en]

    PurposePhoton-counting detectors are expected to be the next big step in the development of medical computed tomography (CT). Accurate modeling of the behavior of photon-counting detectors in both low and high count rate regimes is important for accurate image reconstruction and detector performance evaluations. The commonly used ideal nonparalyzable (delta pulse) model is built on crude assumptions that make it unsuitable for predicting the behavior of photon-counting detectors at high count rates. The aim of this work is to present an analytical count statistics model that better describes the behavior of photon-counting detectors with nonzero pulse length. MethodsAn analytical statistical count distribution model for nonparalyzable detectors with nonzero pulse length is derived using tools from statistical analysis. To validate the model, a nonparalyzable photon-counting detector is simulated using Monte Carlo methods and compared against. Image performance metrics are computed using the Fisher information metric and a comparison between the proposed model, approximations of the proposed model, and those made by the ideal nonparalyzable model is presented and analyzed. ResultsIt is shown that the presented model agrees well with the results from the Monte Carlo simulation and is stable for varying x-ray beam qualities. It is also shown that a simple Gaussian approximation of the distribution can be used to accurately model the behavior and performance of nonparalyzable detectors with nonzero pulse length. Furthermore, the comparison of performance metrics show that the proposed model predicts a very different behavior than the ideal nonparalyzable detector model, suggesting that the proposed model can fill an important gap in the understanding of pileup effects. ConclusionsAn analytical model for the count statistics of a nonparalyzable photon-counting detector with nonzero pulse length is presented. The model agrees well with results obtained from Monte Carlo simulations and can be used to improve, speed up and simplify modeling of photon-counting detectors.

123456 1 - 50 of 283
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf