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  • 201.
    Carlström, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Garaud, Julien
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Length scales, collective modes, and type-1.5 regimes in three-band superconductors2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 13, s. 134518-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recent discovery of iron pnictide superconductors has resulted in a rapidly growing interest in multiband models with more than two bands. In this work we specifically focus on the properties of three-band Ginzburg-Landau models which do not have direct counterparts in more studied two-band models. First we derive normal modes and characteristic length scales in the conventional U(1) three-band Ginzburg-Landau model as well as in its time-reversal symmetry-broken counterpart with U(1) x Z(2) symmetry. We show that, in the latter case, the normal modes are mixed phase-density collective excitations. A possibility of the appearance of a massless mode associated with fluctuations of the phase difference is also discussed. Next we show that gradients of densities and phase differences can be inextricably intertwined in vortex excitations in three-band models. This can lead to very long-range attractive intervortex interactions and the appearance of type-1.5 regimes even when the intercomponent Josephson coupling is large. In some cases it also results in the formation of a domainlike structure in the form of a ring of suppressed density around a vortex across which one of the phases shifts by p. We also show that field-induced vortices can lead to a change of broken symmetry from U(1) to U(1) x Z(2) in the system. In the type-1.5 regime, it results in a semi-Meissner state where the system has a macroscopic phase separation in domains with broken U(1) and U(1) x Z(2) symmetries.

  • 202.
    Carlström, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Garaud, Julien
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Semi-Meissner state and nonpairwise intervortex interactions in type-1.5 superconductors2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 13, s. 134515-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate the existence of nonpairwise interaction forces between vortices in multicomponent and layered superconducting systems. That is, in contrast to most common models, the interaction in a group of such vortices is not a universal superposition of Coulomb or Yukawa forces. Next, we consider the properties of vortex clusters in a semi-Meissner state of type-1.5 two-component superconductors. We show that under certain conditions nonpairwise forces can contribute to the formation of very complex vortex states in type-1.5 regimes.

  • 203.
    Cartling, Bo
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    On the implicit acquisition of a context-free grammar by a simple recurrent neural network2008Ingår i: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 71, nr 7-9, s. 1527-1537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The performance of a simple recurrent neural network on the implicit acquisition of a context-free grammar is re-examined and found to be significantly higher than previously reported by Elman. This result is obtained although the previous work employed it multilayer extension of the basic form of simple recurrent network and restricted the complexity of training and test corpora. The high performance is traced to a well-organized internal representation of the grammatical elements, as probed by a principal-component analysis of the hidden-layer activities. From the next-symbol-prediction performance on sentences not present in the training corpus, it capacity of generalization is demonstrated.

  • 204.
    Chen, Tianqi
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Topological edge states in the 1/5-depleted square lattice2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 205.
    Chen, Tianqi
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Topological edge states in the 1/5-depleted square lattice2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 206.
    Chen, Tianqi
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Topological edge states in the 1/5-depleted square lattice2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 207.
    Choubey, S.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Pramanik, D.
    Constraints on sterile neutrino oscillations using DUNE near detector2017Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 764, s. 135-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    DUNE (Deep Underground Neutrino Experiment) is a proposed long-baseline neutrino experiment in the US with a baseline of 1300 km from Fermi National Accelerator Laboratory (Fermilab) to Sanford Underground Research Facility, which will house a 40 kt Liquid Argon Time Projection Chamber (LArTPC) as the far detector. The experiment will also have a fine grained near detector for accurately measuring the initial fluxes. We show that the energy range of the fluxes and baseline of the DUNE near detector is conducive for observing νμ→νe oscillations of Δm2∼ eV2 scale sterile neutrinos, and hence can be effectively used for testing to very high accuracy the reported oscillation signal seen by the LSND and MiniBooNE experiments. We study the sensitivity of the DUNE near detector to sterile neutrino oscillations by varying the baseline, detector fiducial mass and systematic uncertainties. We find that the detector mass and baseline of the currently proposed near detector at DUNE will be able to test the entire LSND parameter region with good precision. The dependence of sensitivity on baseline and detector mass is seen to give interesting results, while dependence on systematic uncertainties is seen to be small.

  • 208.
    Choubey, Sandhya
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Atmospheric neutrinos: Status and prospects2016Ingår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an overview of the current status of neutrino oscillation studies at atmospheric neutrino experiments. While the current data gives some tantalising hints regarding the neutrino mass hierarchy, octant of θ23 and δCP, the hints are not statistically significant. We summarise the sensitivity to these sub-dominant three-generation effects from the next-generation proposed atmospheric neutrino experiments. We next present the prospects of new physics searches such as non-standard interactions, sterile neutrinos and CPT violation studies at these experiments.

  • 209.
    Choubey, Sandhya
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Neutrino oscillations2017Ingår i: Current Science, ISSN 0011-3891, Vol. 112, nr 7, s. 1381-1384Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Neutrinos are massless as proposed in the Standard Model of particle physics. However, neutrino experiments in the last few decades have revealed that neutrinos flavour oscillate, a scenario possible only if they have mass and mixing. Existence of neutrino mass was the first conclusive evidence of physics beyond the Standard Model, and explaining the smallness of the neutrino masses and peculiar mixing angles still remains a challenge for model-builders proposing beyond Standard Model scenarios. We give a brief introduction to the phenomenon of neutrino oscillations and showcase some recent work where we look for physics beyond the three-generation neutrino oscillation paradigm and its impact on future experiments.

  • 210.
    Choubey, Sandhya
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik. Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad, India.
    Ghosh, Anushree
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Tiwari, D.
    Neutrino physics with non-standard interactions at INO2015Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2015, nr 12, s. 1-22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Abstract: Non-standard neutrino interactions (NSI) involved in neutrino propagation inside Earth matter could potentially alter atmospheric neutrino fluxes. In this work, we look at the impact of these NSI on the signal at the ICAL detector to be built at the India-based Neutrino Observatory (INO). We show how the sensitivity to the neutrino mass hierarchy of ICAL changes in the presence of NSI. The mass hierarchy sensitivity is shown to be rather sensitive to the NSI parameters ϵeμ and ϵeτ , while the dependence on ϵμτ and ϵτ τ is seen to be very mild, once the χ2 is marginalised over oscillation and NSI parameters. If the NSI are large enough, the event spectrum at ICAL is expected to be altered and this can be used to discover new physics. We calculate the lower limit on NSI parameters above which ICAL could discover NSI at a given C.L. from 10 years of data. If NSI were too small, the null signal at ICAL can constrain the NSI parameters. We give upper limits on the NSI parameters at any given C.L. that one is expected to put from 10 years of running of ICAL. Finally, we give C.L. contours in the NSI parameter space that is expected to be still allowed from 10 years of running of the experiment.

  • 211.
    Choubey, Sandhya
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik. Harish-Chandra Research Institute, India .
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Bounds on non-standard neutrino interactions using PINGU2014Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 739, s. 357-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the impact of non-standard neutrino interactions (NSIs) on atmospheric neutrinos using the proposed PINGU experiment. In particular, we focus on the matter NSI parameters epsilon(mu tau) and vertical bar epsilon(tau tau)-epsilon(mu mu)vertical bar that have previously been constrained by the Super-Kamiokande experiment. First, we present approximate analytical formulas for the difference of the muon neutrino survival probability with and without the above-mentioned NSI parameters. Second, we calculate the atmospheric neutrino events at PINGU in the energy range (2-100) GeV, which follow the trend outlined on probability level. Finally, we perform a statistical analysis of PINGU. Using three years of data, we obtain bounds from PINGU given by -0.0043 (-0.0048) < epsilon(mu tau) < 0.0047 (0.0046) and -0.03 (-0.016) < epsilon(tau tau) < 0.017 (0.032) at 90% confidence level for normal (inverted) neutrino mass hierarchy, which improve the Super-Kamiokande bounds by one order of magnitude. In addition, we show the expected allowed contour region in the epsilon-ettplane if NSIs exist in Nature and the result suggests that there is basically no correlation between epsilon(mu tau) and epsilon(tau tau).

  • 212.
    Clementz, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Asymmetric capture of Dirac dark matter in the Sun2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 213.
    Clémentine, Vulliet
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Study Of Non-Standard Interaction Effects On The Solar Neutrino Day-Night Asymmetry2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 214. Collin, A
    et al.
    Lundh, Emil
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Suominen, K A
    Center-of-mass rotation and vortices in an attractive Bose gas2005Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 71, nr 2, s. 023613-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rotational properties of an attractively interacting Bose gas are studied using analytical and numerical methods. We study perturbatively the ground-state phase space for weak interactions, and find that in an anharmonic trap the rotational ground states are vortex or center-of-mass rotational states; the crossover line separating these two phases is calculated. We further show that the Gross-Pitaevskii equation is a valid description of such a gas in the rotating frame and calculate numerically the phase-space structure using this equation. It is found that the transition between vortex and center-of-mass rotation is gradual; furthermore, the perturbative approach is valid only in an exceedingly small portion of phase space. We also present an intuitive picture of the physics involved in terms of correlated successive measurements for the center-of-mass state.

  • 215. Conti, Luca
    et al.
    Renhorn, Jakob
    Gabrielsson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Turesson, Fredrik
    Liin, Sara I.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. Stockholm University, Sweden.
    Elinder, Fredrik
    Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation2016Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikel-id 27562Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Voltage-gated potassium channels open at depolarized membrane voltages. A prolonged depolarization causes a rearrangement of the selectivity filter which terminates the conduction of ions - a process called slow or C-type inactivation. How structural rearrangements in the voltage-sensor domain (VSD) cause alteration in the selectivity filter, and vice versa, are not fully understood. We show that pulling the pore domain of the Shaker potassium channel towards the VSD by a Cd2+ bridge accelerates C-type inactivation. Molecular dynamics simulations show that such pulling widens the selectivity filter and disrupts the K+ coordination, a hallmark for C-type inactivation. An engineered Cd2+ bridge within the VSD also affect C-type inactivation. Conversely, a pore domain mutation affects VSD gating-charge movement. Finally, C-type inactivation is caused by the concerted action of distant amino acid residues in the pore domain. All together, these data suggest a reciprocal communication between the pore domain and the VSD in the extracellular portion of the channel.

  • 216. Conti, Luca
    et al.
    Renhorn, Jakob
    Gabrielsson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Turesson, Fredrik
    Liin, Sara
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Elinder, Fredrik
    A Reciprocal Voltage Sensor-To-Pore Coupling in C-Type Inactivation2016Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 110, nr 3, s. 104A-104AArtikel i tidskrift (Övrigt vetenskapligt)
  • 217.
    Contreras, F.-Xabier
    et al.
    Heidelberg University.
    Ernst, Andreas M
    Heidelberg University.
    Haberkant, Per
    Heidelberg University.
    Björkholm, Patrik
    Stockholm University.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Gönen, Başak
    Tischer, Christian
    Heidelberg University.
    Elofsson, Arne
    Stockholm University.
    von Heijne, Gunnar
    Stockholm University.
    Thiele, Christoph
    Heidelberg University.
    Pepperkok, Rainer
    Heidelberg University.
    Wieland, Felix
    Heidelberg University.
    Brügger, Britta
    Heidelberg University.
    Molecular recognition of a single sphingolipid species by a protein's transmembrane domain2012Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 481, nr 7382, s. 525-529Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Functioning and processing of membrane proteins critically depend on the way their transmembrane segments are embedded in the membrane. Sphingolipids are structural components of membranes and can also act as intracellular second messengers. Not much is known of sphingolipids binding to transmembrane domains (TMDs) of proteins within the hydrophobic bilayer, and how this could affect protein function. Here we show a direct and highly specific interaction of exclusively one sphingomyelin species, SM 18, with the TMD of the COPI machinery protein p24 (ref. 2). Strikingly, the interaction depends on both the headgroup and the backbone of the sphingolipid, and on a signature sequence (VXXTLXXIY) within the TMD. Molecular dynamics simulations show a close interaction of SM 18 with the TMD. We suggest a role of SM 18 in regulating the equilibrium between an inactive monomeric and an active oligomeric state of the p24 protein, which in turn regulates COPI-dependent transport. Bioinformatic analyses predict that the signature sequence represents a conserved sphingolipid-binding cavity in a variety of mammalian membrane proteins. Thus, in addition to a function as second messengers, sphingolipids can act as cofactors to regulate the function of transmembrane proteins. Our discovery of an unprecedented specificity of interaction of a TMD with an individual sphingolipid species adds to our understanding of why biological membranes are assembled from such a large variety of different lipids.

  • 218.
    Cordi, Marcus
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    A Study of the Distribution of Firm Sizes Applying Methods of Physics on Team Dynamics2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 219. Cordomi, Arnau
    et al.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Perez, Juan J.
    Effect of different treatments of long-range interactions and sampling conditions in molecular dynamic simulations of rhodopsin embedded in a dipalmitoyl phosphatidylcholine bilayer2007Ingår i: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 28, nr 6, s. 1017-1030Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The present study analyzes the effect of the simulation conditions on the results of molecular dynamics simulations of G-protein coupled receptors (GPCRs) performed with an explicit lipid bilayer. Accordingly, the present work reports the analysis of different simulations of bovine rhodopsin embedded in a dipalmitoyl phosphatidylcholine (DPPC) lipid bilayer using two different sampling conditions and two different approaches for the treatment of long-range electrostatic interactions. Specifically, sampling was carried out either by using the statistical ensembles NVT or NPT (constant number of atoms, a pressure of 1 arm in all directions and fixed temperature), and the electrostatic interactions were treated either by using a twin-cutoff, or the particle mesh Ewald summation method (PME). The results of the present study suggest that the use of the NPT ensemble in combination with the PME method provide more realistic simulations. The use of NPT during the equilibration avoids the need of an a priori estimation of the box dimensions, giving the correct area per lipid. However, once the system is equilibrated, the simulations are irrespective of the sampling conditions used. The use of an electrostatic cutoff induces artifacts on both lipid thickness and the ion distribution, but has no direct effect on the protein and water molecules.

  • 220. Cordomi, Arnau
    et al.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Perez, Juan J.
    Effect of Force Field Parameters on Sodium and Potassium Ion Binding to Dipalmitoyl Phosphatidylcholine Bilayers2009Ingår i: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 5, nr 8, s. 2125-2134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behavior of electrolytes in molecular dynamics simulations of zwitterionic phospholipid bilayers; is very sensitive to the force field parameters used. Here, several 200 ns molecular dynamics of simulations of dipalmitoyl phosphotidylcholine (PC) bilayers in 0.2 M sodium or potassium chloride using various common force field parameters for the cations are presented. All employed parameter sets give a larger number of Na+ ions than K+ ions that bind to the lipid heads, but depending on the parameter choice quite different results are seen. A wide range of coordination numbers for the Na+ and K+ ions is also observed. These findings have been analyzed and compared to published experimental data. Some simulations produce aggregates of potassium chloride, indicating (in accordance with published simulations) that these force fields do not reproduce the delicate balance between salt and solvated ions. The differences between the force fields can be characterized by one single parameter, the electrostatic radius of the ion, which is correlated to sigma(MO) (M represents Na+/K+), the Lennard-Jones radius. When this parameter exceeds a certain threshold, binding to the lipid heads is no longer observed. One would, however, need more accurate experimental data to judge or rank the different force fields precisely. Still, reasons for the poor performance of some of the parameter sets are clearly demonstrated, and a quality control. procedure is provided.

  • 221. Cordomi, Arnau
    et al.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Perez, Juan J.
    Effect of ions on a dipalmitoyl phosphatidylcholine bilayer. A molecular dynamics simulation study2008Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, nr 5, s. 1397-1408Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of physiological concentrations of different chlorides on the structure of a dipalmitoyl phosphatidylcholine (DPPC) bilayer has been investigated through atomistic molecular dynamics simulations. These calculations provide support to the concept that Li+, Na+, Ca2+, Mg2+, Sr2+, Ba2+, and Ac3+, but not K+, bind to the lipid-head oxygens. Ion binding exhibits an influence on lipid order, area per lipid, orientation of the lipid head dipole, the charge distribution in the system, and therefore the electrostatic potential across the head-group region of the bilayer. These structural effects are sensitive to the specific characteristics of each cation, i.e., radius, charge, and coordination properties. These results provide evidence aimed at shedding some light into the apparent contradictions among different studies reported recently regarding the ordering effect of ions on zwitterionic phosphatidylcholine lipid bilayers.

  • 222. Cortés-Pérez, O.
    et al.
    Ordoñez-Romero, C. L.
    Ortega-Martínez, R.
    Kolokoltsev, O. V.
    Grishin, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Difracción de Bragg de ondas ópticas guiadas por ondas de dipolo de spin en guías de onda ferromagnéticas de doble capa2008Ingår i: Revista Mexicana de Fisica, ISSN 0035-001X, Vol. 54, nr 5, s. 376-381Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The peculiarities of the Bragg diffraction of optical guided waves (OGWs) by spin-dipole waves (SDWs) in a new ferrite heterostructure, based on Bi3Fe5O12(BIG) thin film deposited on a standard YIG/GGG (a Yttrium Iron Garnet thin film over a Galium Gadolinum Garnet substrate) sample, is presented. It is shown that the efficiency of waveguide magnetooptic interaction between OGWs and SDWs in BIG/YIG/GGG can be 4-14 times larger than in the standard YIG/GGG waveguide, even in the case when the interacting waves are localized in YIG waveguide layer.

  • 223. Cricchio, F.
    et al.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Burakovsky, L.
    Preston, D. L.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    High-pressure melting of lead2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting curve of the hexagonal close-packed (hcp) phase of lead (Pb) has been determined over a wide pressure range using both ab initio molecular dynamics (AIMD) simulations and classical molecular dynamics (CMD) employing an effective pair potential. The AIMD simulations are based on a density functional theory (DFT) in the generalized gradient approximation (GGA). The Pb melting curve, constructed using a well-established theoretical scheme, is in excellent agreement with the AIMD results. Our calculated equation of state (EOS) of hcp Pb is in excellent agreement with experimental data up to 40 GPa. Our melting curve agrees very well with melting temperatures obtained in both shock-wave and diamond-anvil cell (DAC) experiments, but at higher pressures our curve lies between the two data sets.

  • 224.
    Crona, Daniel
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Summ, Benjamin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Classical Yang-Mills theory and simulations of a toy model in (1+1) dimensions2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Modellen som beskriver modern partikelfysik är känd som standardmodellen och bygger på Yang-Mills teori, vilken även används i andra sammanhang inom teoretisk fysik. I denna rapport undersöks klassisk Yang-Mills teori och dess koppling till klassisk elektrodynamik. 

    Teorin introduceras som en generalisering av elektrodynamik samt reduceras till ett specialfall som tolkas fysikaliskt. Genom numeriska simuleringar undersöks dynamiken i Yang-Mills teori och jämförs med elektrodynamiken.

    De erhållna resultaten pekar på att Yang-Mills teori kan ge upphov till mycket mer komplex dynamik än klassisk elektrodynamik. Vidare ges det betraktade specialfallet av teorin en tolkning som elektrodynamik med extra frihetsgrader.

  • 225.
    Dalarsson, Nils
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Maksimovic, M.
    Jaksic, Z.
    A simplified analytical approach to calculation of the electromagnetic behavior of left-handed metamaterials with a graded refractive index profile2007Ingår i: SCIENCE OF SINTERING, ISSN 0350-820X, Vol. 39, nr 2, s. 185-191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated the spectral properties of a new class of nanostructured artificial composite materials with tailored electromagnetic response, i.e. negative refractive index materials, also known as "left-handed" metamaterials. We analyzed structures incorporating both ordinary positive index media and negative refractive index metamaterials where the interface may be graded to art arbitrary degree. Utilizing a modified version of the Rosen-Morse function, we derived analytical expressions for the field intensity and spectral reflection and transmission through a graded interface between positive and negative index materials. We compared our results to numerical solutions obtained using the transfer matrix technique.

  • 226.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Model for diffusion at the microcanonical superheating limit from atomistic computer simulations2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 6, s. 064102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The diffusion statistics of atoms in a crystal close to the critical superheating temperature was studied in detail using molecular dynamics and Monte Carlo simulations. We present a continuous random-walk model for diffusion of atoms hopping through thermal vacancies. The results obtained from our model suggest that the limit of superheating is precisely the temperature for which dynamic percolation happens at the time scale of a single individual jump. A possible connection between the critical superheating limit and the maximization of the Shannon entropy associated with the distribution of jumps is suggested. As a practical application of our results, we show that an extrapolation of the critical superheating temperature (and therefore an estimation of the melting point) can be performed using only the dynamical properties of the solid state.

  • 227.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    An atomistic model for homogeneous meltingManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The diffusion statistics of atoms in a crystal close to the critical superheating temperature wasstudied in detail using molecular dynamics (MD) and Monte Carlo (MC) simulations. We present ageneral dynamic percolation model for diffusion of atoms hopping through thermal vacancies. Theresults obtained from our model suggest that the limit of superheating is precisely the temperaturefor which dynamic percolation happens at the time scale of a single individual jump. We show thatthis prediction of the critical superheating temperature can give an estimate of the melting pointusing only the dynamical properties of the solid state.

  • 228.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Rosengren, Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    van Duin, Adri
    Johansson, Börje
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Molecular dynamics simulation of zirconia melting2010Ingår i: Central European Journal of Physics, ISSN 1895-1082, E-ISSN 1644-3608, Vol. 8, nr 5, s. 789-797Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.

  • 229.
    Davis, Sergio
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Skorodumova, Natalia
    van Duin, Adri
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    High-pressure melting curve of hydrogen2008Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, s. 194508-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.

  • 230.
    de Woul, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Fermions in two dimensions and exactly solvable models2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This Ph.D. thesis in mathematical physics concerns systems of interacting fermions with strong correlations. For these systems the physical properties can only be described in terms of the collective behavior of the fermions. Moreover, they are often characterized by a close competition between fermion localization versus delocalization, which can result in complex and exotic physical phenomena.

    Strongly correlated fermion systems are usually modelled by many-body Hamiltonians for which the kinetic- and interaction energy have the same order of magnitude. This makes them challenging to study as the application of conventional computational methods, like mean field- or perturbation theory, often gives unreliable results. Of particular interest are Hubbard-type models, which provide minimal descriptions of strongly correlated fermions. The research of this thesis focuses on such models defined on two-dimensional square lattices. One motivation for this is the so-called high-Tc problem of the cuprate superconductors.

    A main hypothesis is that there exists an underlying Fermi surface with nearly flat parts, i.e. regions where the surface is straight. It is shown that a particular continuum limit of the lattice system leads to an effective model amenable to computations. This limit is partial in that it only involves fermion degrees of freedom near the flat parts. The result is an effective quantum field theory that is analyzed using constructive bosonization methods. Various exactly solvable models of interacting fermions in two spatial dimensions are also derived and studied.

  • 231.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Hoppe, Jens
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Lundholm, Douglas
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Partial Hamiltonian reduction of relativistic extended objects in light-cone gauge2011Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 1, s. 031-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elimination of the non-transversal field in the standard light-cone formulation of higher-dimensional extended objects is formulated as a Hamiltonian reduction.

  • 232.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Hoppe, Jens
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Lundholm, Douglas
    Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark.
    Sundin, Martin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    A dynamical symmetry for supermembranes2011Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 3, nr 134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A dynamical symmetry for supersymmetric extended objects is given.

  • 233.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Exact Solution of a 2D Interacting Fermion Model2012Ingår i: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 314, nr 1, s. 1-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study an exactly solvable quantum field theory (QFT) model describing interacting fermions in 2+1 dimensions. This model is motivated by physical arguments suggesting that it provides an effective description of spinless fermions on a square lattice with local hopping and density-density interactions if, close to half filling, the system develops a partial energy gap. The necessary regularization of the QFT model is based on this proposed relation to lattice fermions. We use bosonization methods to diagonalize the Hamiltonian and to compute all correlation functions. We also discuss how, after appropriate multiplicative renormalizations, all short- and long distance cutoffs can be removed. In particular, we prove that the renormalized two-point functions have algebraic decay with non-trivial exponents depending on the interaction strengths, which is a hallmark of Luttinger-liquid behavior.

  • 234.
    De Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Fermions in two dimensions, bosonization, and exactly solvable models2012Ingår i: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 26, nr 22, s. 1244005-Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    We discuss interacting fermion models in two dimensions, and, in particular, such that can be solved exactly by bosonization. One solvable model of this kind was proposed by Mattis as an effective description of fermions on a square lattice. We review recent work on a specific relation between a variant of Mattis' model and such a lattice fermion system, as well as the exact solution of this model. The background for this work includes well-established results for one-dimensional systems and the high-T c problem. We also mention exactly solvable extensions of Mattis' model.

  • 235.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Gauge invariance, correlated fermions, and Meissner effect in 2+1 dimensionsArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    We present a 2+1 dimensional quantum gauge theory model with correlated fermions that is exactly solvable by bosonization. This model gives an effective description of partially gapped fermions on a square lattice that have density-density interactions and are coupled to photons. We show that the photons in this model are massive due to gauge-invariant normal-ordering, similarly as in the Schwinger model. Moreover, the exact excitation spectrum of the model has two gapped and one gapless mode. We also compute the magnetic field induced by an external current and show that there is a Meissner effect. We find that the transverse photons have significant effects on the low-energy properties of the model even if the fermion-photon coupling is small.

  • 236.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Gauge Invariance, Correlated Fermions, and Photon Mass in 2+1 Dimensions2014Ingår i: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 154, nr 3, s. 877-894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a 2+1 dimensional quantum gauge theory with correlated fermions that is exactly solvable by bosonization. This model describes a system of Luttinger liquids propagating on two sets of equidistant lines forming a grid embedded in two dimensional continuum space; this system has two dimensional character due to density-density interactions and due to a coupling to dynamical photons propagating in the continuous embedding space. We argue that this model gives an effective description of partially gapped fermions on a square lattice that have density-density interactions and are coupled to photons. Our results include the following: after non-trivial renormalizations of the coupling parameters, the model remains well-defined in the quantum field theory limit as the grid of lines becomes a continuum; the photons in this model are massive due to gauge-invariant normal-ordering, similarly as in the Schwinger model; the exact excitation spectrum of the model has two gapped and one gapless mode.

  • 237.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Partial continuum limit of the 2D Hubbard modelArtikel i tidskrift (Övrigt vetenskapligt)
  • 238.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Partially Gapped Fermions in 2D2010Ingår i: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 139, nr 6, s. 1033-1065Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We compute mean field phase diagrams of two closely related interacting fermion models in two spatial dimensions (2D). The first is the so-called 2D t-t'-V model describing spinless fermions on a square lattice with local hopping and density-density interactions. The second is the so-called 2D Luttinger model that provides an effective description of the 2D t-t'-V model and in which parts of the fermion degrees of freedom are treated exactly by bosonization. In mean field theory, both models have a charge-density-wave (CDW) instability making them gapped at half-filling. The 2D t-t'-V model has a significant parameter regime away from half-filling where neither the CDW nor the normal state are thermodynamically stable. We show that the 2D Luttinger model allows to obtain more detailed information about this mixed region. In particular, we find in the 2D Luttinger model a partially gapped phase that, as we argue, can be described by an exactly solvable model.

  • 239.
    de Woul, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Establishing analogies between the physics of extra dimensions and carbon nanotubes2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 714, nr 1, s. 44-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We point out a conceptual analogy between the physics of extra spatial dimensions and the physics of carbon nanotubes which arises for principle reasons, although the corresponding energy scales are at least ten orders of magnitude apart. For low energies, one can apply the Kaluza-Klein description to both types of systems, leading to two completely different but consistent interpretations of the underlying physics. In particular, we discuss in detail the Kaluza-Klein description of armchair and zig-zag carbon nanotubes. Furthermore, we describe how certain experimental results for carbon nanotubes could be re-interpreted in terms of the Kaluza-Klein description. Finally, we present ideas for new measurements that could allow to probe concepts of models with extra spatial dimensions in table-top experiments, providing further links between condensed matter and particle physics.

  • 240. Dewaele, A.
    et al.
    Belonoshko, Anatoly B.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Garbarino, G.
    Occelli, F.
    Bouvier, P.
    Hanfland, M.
    Mezouar, M.
    High-pressure high-temperature equation of state of KCl and KBr2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, nr 21, s. 214105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equation of state of KCl and KBr, compressed in a helium pressure medium in a diamond-anvil cell, has been measured by x-ray diffraction in the B1 and B2 phases up to 165 GPa at 298 K. The P-V-T of B2 KCl and B2 KBr has been calculated by ab initio molecular dynamics in a wide compression range and up to 7000 K. The thermal pressure exhibits a linear behavior with temperature and remains low under high compression. The experimental P-V points and the thermal pressure calculated by molecular dynamics have been used to set up a high-pressure high-temperature equation of state of B2 KCl and B2 KBr. With these equations of state, B2 KCl and B2 KBr can be used as pressure markers in laser-heated diamond-anvil-cell experiments.

  • 241.
    Di Bari, Pasquale
    et al.
    University of Southampton.
    King, Stephen
    University of Southampton.
    Luhn, Christoph
    University of Southampton.
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Schmidt-May, Angnis
    Max-Planck-Institut fuer Kernphysik.
    Radiative Inflation and Dark Energy2011Ingår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a model based on radiative symmetry breaking that combines inflation with dark energy and is consistent with the Wilkinson Microwave Anisotropy Probe 7-year regions. The radiative inflationary potential leads to the prediction of a spectral index 0.955 less than or similar to n(S) less than or similar to 0.967 and a tensor to scalar ratio 0.142 less than or similar to r less than or similar to 0.186, both consistent with current data but testable by the Planck experiment. The radiative symmetry breaking close to the Planck scale gives rise to a pseudo Nambu-Goldstone boson with a gravitationally suppressed mass which can naturally play the role of a quintessence field responsible for dark energy. Finally, we present a possible extra dimensional scenario in which our model could be realized.

  • 242. Di Iura, A.
    et al.
    Herrero-Garcia, Juan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Meloni, D.
    Phenomenology of SU(5) low-energy realizations: The diphoton excess and Higgs flavor violation2016Ingår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 911, s. 388-424Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We discuss different SU(5) low-energy realizations and illustrate their use with the diphoton excess and Higgs flavor violation, which require new physics at the TeV scale. In particular, we study two scenarios for a 750 GeV resonance: in the first one the resonance belongs to the adjoint of SU(5), being either an SU(2)L singlet or a triplet, while in the second case the signal is due to the CP-even and CP-odd states of a new SU(2)L Higgs doublet belonging to a 45H or a 70H representations, giving rise to a two-Higgs doublet model at low energies. We study the fine-tuning needed for the desired members of the multiplets to be light enough, while having the rest at the GUT scale. In these scenarios, the production and decay into photons of the new resonance are mediated by the leptoquarks (LQ) present in these large SU(5) representations. We analyze the phenomenology of such scenarios, focusing on the most relevant predictions that can help to disentangle the different models, like decays into gauge bosons, Standard Model (SM) fermions and LQs pair production. In the case of the 45H (the Georgi–Jarlskog model), we also study the possibility to have Higgs flavor violation. We find that Bs mixing limits (in addition to τ→μγ) always imply that Br(h→τμ,bs)≲10−5.

  • 243. Diaz-Mendez, Rogelio
    et al.
    Mezzacapo, Fabio
    Lechner, Wolfgang
    Cinti, Fabio
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Pupillo, Guido
    Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors2017Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 118, nr 6, artikel-id 067001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an "effective polydispersity" induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of "type-1.5" superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.

  • 244.
    Dizdarevic, Goran
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Sallmen, Karl
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Studies of relativistic quantum mechanics - The fundamentals of the Dirac equation and an analytical solution to hydrogen-like atoms2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    År 1928 lyckades den enastående vetenskapsmannen Paul Dirac härleda en ekvation som var fullt hållbar inom både kvantmekanik och speciella relativitetsteorin. I detta kandidatexamensarbete har vi studerat de grundläggande principerna inom relativistisk kvantmekanik såsom härledningen av Dirac ekvationen som den ursprungligen gjordes av Paul Dirac. Vidare har vi undersökt den analytiska lösningen för väteliknande atomer. Detta följdes upp av en numerisk analys av energi spektrum, radiella delens utmärkande drag och korrektions termer med hjälp av program skrivna i Python och MATLAB. Slutligen har vi granskat implikationer och tillämpningar av Dirac hamiltonianen och dess möjligheter att beskriva guld atomens attribut.

    Vi fann att de relativistiska bidragen ökar med ungefär Z2 för stora värden på Z. Vidare drog vi slutsatsen att Dirac hamiltonianen är av stor betydelse för en noggrann beskrivningav de kemiska och fysiska egenskaperna av guld atomen. Vi färdigställde sedan beräkningar av den radiella lösningen till Coulumb potentialen och för en fri partikel.

  • 245.
    Dizdarevic, Peda
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Mathematical analysis and simulation of Shor's algorithm and the quantum Fourier transfrom.2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 246.
    Dizdarevic, Peda
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Ahlström, Marcus
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Mathematical Analysis and Simulation of Shor’s Algorithm and the Quantum Fourier Transform2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In 1994, Peter Shor presented an algorithm for integer factorization that used exponentially

    less operations than the most efficient known algorithm. His algorithm requires

    the use of a quantum computer, a theoretical computational device using quantum mechanical

    effects not utilized in contemporary computers. In this paper we have analysed

    the mathematics behind Shor’s algorithm and the quantum circuits on which it operates.

    We have also studied the Quantum Fourier Transform, a central component of Shor’s

    Algorithm. Furthermore we have written a program in C++ to simulate a quantum circuit

    performing Shor’s algorithm and the quantum Fourier transform. We were able to

    understand the critical parts of Shor’s algorithm that contribute with the great increase

    in efficiency compared to classical algorithms.

  • 247. Duerr, Michael
    et al.
    Lindner, Manfred
    Merle, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    On the quantitative impact of the Schechter-Valle theorem2011Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 6, s. 091-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We evaluate the Schechter-Valle (Black Box) theorem quantitatively by considering the most general Lorentz invariant Lagrangian consisting of point-like operators for neutrinoless double beta decay. It is well known that the Black Box operators induce Majorana neutrino masses at four-loop level. This warrants the statement that an observation of neutrinoless double beta decay guarantees the Majorana nature of neutrinos. We calculate these radiatively generated masses and find that they are many orders of magnitude smaller than the observed neutrino masses and splittings. Thus, some lepton number violating New Physics (which may at tree-level not be related to neutrino masses) may induce Black Box operators which can explain an observed rate of neutrinoless double beta decay. Although these operators guarantee finite Majorana neutrino masses, the smallness of the Black Box contributions implies that other neutrino mass terms (Dirac or Majorana) must exist. If neutrino masses have a significant Majorana contribution then this will become the dominant part of the Black Box operator. However, neutrinos might also be predominantly Dirac particles, while other lepton number violating New Physics dominates neutrinoless double beta decay. Translating an observed rate of neutrinoless double beta decay into neutrino masses would then be completely misleading. Although the principal statement of the Schechter-Valle theorem remains valid, we conclude that the Black Box diagram itself generates radiatively only mass terms which are many orders of magnitude too small to explain neutrino masses. Therefore, other operators must give the leading contributions to neutrino masses, which could be of Dirac or Majorana nature.

  • 248. Edgecock, T. R.
    et al.
    Caretta, O.
    Davenne, T.
    Densam, C.
    Fitton, M.
    Kelliher, D.
    Loveridge, P.
    Machida, S.
    Prior, C.
    Rogers, C.
    Rooney, M.
    Thomason, J.
    Wilcox, D.
    Wildner, E.
    Efthymiopoulos, I.
    Garoby, R.
    Gilardoni, S.
    Hansen, C.
    Benedetto, E.
    Jensen, E.
    Kosmicki, A.
    Martini, M.
    Osborne, J.
    Prior, G.
    Stora, T.
    Mendonca, T. Melo
    Vlachoudis, V.
    Waaijer, C.
    Cupial, P.
    Chance, A.
    Longhin, A.
    Payet, J.
    Zito, M.
    Baussan, E.
    Bobeth, C.
    Bouquerel, E.
    Dracos, M.
    Gaudiot, G.
    Lepers, B.
    Osswald, F.
    Poussot, P.
    Vassilopoulos, N.
    Wurtz, J.
    Zeter, V.
    Bielski, J.
    Kozien, M.
    Lacny, L.
    Skoczen, B.
    Szybinski, B.
    Ustrycka, A.
    Wroblewski, A.
    Marie-Jeanne, M.
    Balint, P.
    Fourel, C.
    Giraud, J.
    Jacob, J.
    Lamy, T.
    Latrasse, L.
    Sortais, P.
    Thuillier, T.
    Mitrofanov, S.
    Loiselet, M.
    Keutgen, Th
    Delbar, Th
    Debray, F.
    Trophine, C.
    Veys, S.
    Daversin, C.
    Zorin, V.
    Izotov, I.
    Skalyga, V.
    Burt, G.
    Dexter, A. C.
    Kravchuk, V. L.
    Marchi, T.
    Cinausero, M.
    Gramegna, F.
    De Angelis, G.
    Prete, G.
    Collazuol, G.
    Laveder, M.
    Mazzocco, M.
    Mezzetto, M.
    Signorini, C.
    Vardaci, E.
    Di Nitto, A.
    Brondi, A.
    La Rana, G.
    Migliozzi, P.
    Moro, R.
    Palladino, V.
    Gelli, N.
    Berkovits, D.
    Hass, M.
    Hirsh, T. Y.
    Schaumann, M.
    Stahl, A.
    Wehner, J.
    Bross, A.
    Kopp, J.
    Neuffer, D.
    Wands, R.
    Bayes, R.
    Laing, A.
    Soler, P.
    Agarwalla, S. K.
    Cervera Villanueva, A.
    Donini, A.
    Ghosh, T.
    Gomez Cadenas, J. J.
    Hernandez, P.
    Martin-Albo, J.
    Mena, O.
    Burguet-Castell, J.
    Agostino, L.
    Buizza-Avanzini, M.
    Marafini, M.
    Patzak, T.
    Tonazzo, A.
    Duchesneau, D.
    Mosca, L.
    Bogomilov, M.
    Karadzhov, Y.
    Matev, R.
    Tsenov, R.
    Akhmedov, E.
    Blennow, M.
    Lindner, M.
    Schwetz, T.
    Fernandez Martinez, E.
    Maltoni, M.
    Menendez, J.
    Giunti, C.
    Gonzalez Garcia, M. C.
    Salvado, J.
    Coloma, P.
    Huber, P.
    Li, T.
    Pavon, J. Lopez
    Orme, C.
    Pascoli, S.
    Meloni, D.
    Tang, J.
    Winter, W.
    Ohlsson, Tommy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Scotto-Lavina, L.
    Terranova, F.
    Bonesini, M.
    Tortora, L.
    Alekou, A.
    Aslaninejad, M.
    Bontoiu, C.
    Kurup, A.
    Jenner, L. J.
    Long, K.
    Pasternak, J.
    Pozimski, J.
    Back, J. J.
    Harrison, P.
    Beard, K.
    Bogacz, A.
    Berg, J. S.
    Stratakis, D.
    Witte, H.
    Snopok, P.
    Bliss, N.
    Cordwell, M.
    Moss, A.
    Pattalwar, S.
    Apollonio, M.
    High intensity neutrino oscillation facilities in Europe2013Ingår i: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402, Vol. 16, nr 2, s. 021002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Frejus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of mu(+) and mu(-) beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He-6 and Ne-18, also stored in a ring. The far detector is also the MEMPHYS detector in the Frejus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.

  • 249.
    Edholm, Olle
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Time and length scales in lipid bilayer simulations2008Ingår i: Computational Modeling Of Membrane Bilayers / [ed] Feller, SE, 2008, Vol. 60, s. 91-110Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Time and length scales for different kinds of local and collective motions in lipid bilayers that may be probed in molecular dynamics simulations are discussed. The possibility to determine parameters in continuum models using simulation techniques is discussed. Agreements and discrepancies between simulations and experimental data are presented and discussed. The chapter covers large scale undulations and peristaltic thickness fluctuations, hydrocarbon chain reorientation motion, lipid lateral diffusion and motion of the entire monolayers with respect to each other and with respect to the water.

  • 250.
    Edholm, Olle
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Nagle, J. F.
    Areas of molecules in membranes consisting of mixtures2005Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 89, nr 3, s. 1827-1832Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The question has arisen in recent literature: how to partition the total area in simulations of membranes consisting of more than one kind of molecule into average areas for each kind of molecule. Several definitions have been proposed, each of which has arbitrary features. When applied to mixtures of cholesterol and DPPC, these definitions give different results. This note recalls that physical chemistry provides a canonical way to de. ne molecular area, in analogy to the definition of partial-specific volume. Results for partial-specific area are obtained from simulations of DPPC/cholesterol bilayers and compared to the results from the other recent definitions. The partial-specific-area formalism dramatically demonstrates the condensing effect of cholesterol and this leads to the introduction of a specific model that accounts for the area of mixtures of cholesterol and lipid over the entire range of cholesterol concentrations.

2345678 201 - 250 av 764
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