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  • 251.
    Edholm, Olle
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Tjörnhammar, Richard
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Waheed, Qaiser
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Cholesterol/Phospholipid Bilayer Phase Diagrams from Coarse Grained Simulations2013Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, nr 2, s. 590A-590AArtikel i tidskrift (Övrigt vetenskapligt)
  • 252.
    Edström, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Three and four-body intervortex forces in the Ginzburg-Landau model of single- and multicomponent superconductivity2013Ingår i: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 487, s. 19-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A systematic numerical study of non-pairwise vortex interaction forces in the Ginzburg-Landau model for single-and multicomponent superconductivity is presented. The interactions are obtained by highly accurate numerical free energy minimization. In particular a three-body interaction is defined as the difference between the total interaction and sum of pairwise interactions in a system of three vortices and such interactions are studied for single and two-component type-1, type-2, and type-1.5 superconductors. In the investigated regimes, the three-body inter action is found to be short-range repulsive but long-range attractive in the type-1 case, zero in the critical kappa (Bogomoln'y) case, attractive in the type-2 case and repulsive in the type-1.5 case. Some systems of four vortices are also studied and results indicate that four-body forces are of substantially less significance than the three-body interactions.

  • 253. Elber, R.
    et al.
    Ruymgaart, A. P.
    Hess, Berk
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    SHAKE parallelization2011Ingår i: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 200, nr 1, s. 211-223Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    SHAKE is a widely used algorithm to impose general holonomic constraints during molecular simulations. By imposing constraints on stiff degrees of freedom that require integration with small time steps (without the constraints) we are able to calculate trajectories with time steps larger by approximately a factor of two. The larger time step makes it possible to run longer simulations. Another approach to extend the scope of Molecular Dynamics is parallelization. Parallelization speeds up the calculation of the forces between the atoms and makes it possible to compute longer trajectories with better statistics for thermodynamic and kinetic averages. A combination of SHAKE and parallelism is therefore highly desired. Unfortunately, the most widely used SHAKE algorithm (of bond relaxation) is inappropriate for parallelization and alternatives are needed. The alternatives must minimize communication, lead to good load balancing, and offer significantly better performance than the bond relaxation approach. The algorithm should also scale with the number of processors. We describe the theory behind different implementations of constrained dynamics on parallel systems, and their implementation on common architectures.

  • 254.
    Ergül, Adem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Lidmar, Jack
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Johansson, Jan
    Azizoglu, Yagiz
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Schaeffer, David
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Localizing quantum phase slips in one-dimensional Josephson junction chains2013Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 15, s. 095014-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We studied quantum phase-slip (QPS) phenomena in long one-dimensional Josephson junction series arrays with tunable Josephson coupling. These chains were fabricated with as many as 2888 junctions, where one sample had a separately tunable link in the middle of the chain. Measurements were made of the zero-bias resistance, R-0, as well as current-voltage characteristics (IVC). The finite R-0 is explained by QPS and shows an exponential dependence on root E-J/E-C with a distinct change in the exponent at R-0 = R-Q = h/4e(2). When R-0 > R-Q, the IVC clearly shows a remnant of the Coulomb blockade, which evolves to a zero-current state with a sharp critical voltage as E-J is tuned to a smaller value. The zero-current state below the critical voltage is due to coherent QPSs and we show that these are enhanced when the central link is weaker than all other links. Above the critical voltage, a negative, differential resistance is observed, which nearly restores the zero-current state.

  • 255.
    Ergül, Adem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Schaeffer, David
    KTH.
    Lindblom, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Haviland, David B.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Lidmar, Jack
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Johansson, Jan
    Phase sticking in one-dimensional Josephson junction chains2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, nr 10, s. 104501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, E-J >> E-C. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, I-chain at high bias. Our experiments showed that I-chain is not only voltage-independent but it is also practically temperature-independent up to T = 0.7T(C). We have successfully model the transport properties in these chains using a capacitively shunted junction model with nonlinear damping.

  • 256. Eriksson, Jens
    et al.
    Eriksson, Olaspers Sara
    Maudsdotter, Lisa
    Palm, Oskar
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Engman, Jakob
    Sarkissian, Tim
    Aro, Helena
    Wallin, Mats
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Jonsson, Ann-Beth
    Characterization of motility and piliation in pathogenic Neisseria2015Ingår i: BMC Microbiology, ISSN 1471-2180, E-ISSN 1471-2180, Vol. 15, artikel-id 92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: The type IV pili (Tfp) of pathogenic Neisseria (i. e., N. gonorrhoeae and N. meningitidis) are essential for twitching motility. Tfp retraction, which is dependent on the ATPase PilT, generates the forces that move bacteria over surfaces. Neisseria motility has mainly been studied in N. gonorrhoeae whereas the motility of N. meningitidis has not yet been characterized. Results: In this work, we analyzed bacterial motility and monitored Tfp retraction using live- cell imaging of freely moving bacteria. We observed that N. meningitidis moved over surfaces at an approximate speed of 1.6 mu m/s, whereas N. gonorrhoeae moved with a lower speed (1.0 mu/s). An alignment of the meningococcal and gonococcal pilT promoters revealed a conserved single base pair variation in the -10 promoter element that influence PilT expression. By tracking mutants with altered pilT expression or pilE sequence, we concluded that the difference in motility speed was independent of both. Live-cell imaging using total internal reflection fluorescence microscopy demonstrated that N. gonorrhoeae more often moved with fewer visible retracting filaments when compared to N. meningitidis. Correspondingly, meningococci also displayed a higher level of piliation in transmission electron microscopy. Nevertheless, motile gonococci that had the same number of filaments as N. meningitidis still moved with a lower speed. Conclusions: These data reveal differences in both speed and piliation between the pathogenic Neisseria species during twitching motility, suggesting a difference in Tfp-dynamics.

  • 257. Facey, Jody-Ann
    et al.
    Venner, Laura
    Hyde, Michael
    Pouya, Iman
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik.
    Howard, Rebecca
    Polar substitutions in the ion-conducting pore of GLIC alter gating and alcohol modulation2014Ingår i: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 28, nr 1, s. 1061.9-Artikel i tidskrift (Övrigt vetenskapligt)
  • 258.
    Falkman, Patrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Efficient reduction over threads2011Självständigt arbete på grundnivå (högskoleexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The increasing number of cores in both desktops and servers leads to a demand for efficient parallel algorithms. This project focuses on the fundamental collective operation reduce, which merges several arrays into one by applying a binary operation element wise. Several reduce algorithms are evaluated in terms of performance and scalability and a novel algorithm is introduced that takes advantage of shared memory and exploits load imbalance. To do so, the concept of dynamic pair generation is introduced which implies constructing a binary reduce tree dynamically based on the order of thread arrival, where pairs are formed in a lock-free manner. We conclude that the dynamic algorithm, given enough spread in the arriving times, can outperform the reference algorithms for some or all array sizes.

  • 259. Fjelstad, Jens
    et al.
    Månsson, Teresia
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    New symmetries of the chiral Potts model2012Ingår i: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 45, nr 15, s. 155208-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a hitherto unknown spectrum generating algebra, consisting of two coupled Temperley-Lieb algebras, is found in the three-state chiral Potts model. From this, we can construct new Onsager integrable models. One realization is in terms of a staggered isotropic XY spin chain. Further we investigate the importance of the algebra for the existence of mutually commuting conserved charges. This leads us to a natural generalization of the boost operator, which generates the charges.

  • 260. Forger, M
    et al.
    Paufler, Cornelius
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Matematisk fysik.
    Romer, H
    Hamiltonian multivector fields and Poisson forms in multisymplectic field theory2005Ingår i: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 46, nr 11, s. 112903-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a general classification of Hamiltonian multivector fields and of Poisson forms on the extended multiphase space appearing in the geometric formulation of first order classical field theories. This is a prerequisite for computing explicit expressions for the Poisson bracket between two Poisson forms.

  • 261.
    Fors, Rickard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Khartsev, Sergiy
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Grishin, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Non-volatile giant resistance switching in metal-insulator-manganite junctions2005Ingår i: Materials and Processes for Nonvolatile Memories / [ed] Claverie, A; Tsoukalas, D; King, TJ; Slaughter, JM, WARRENDALE: MATERIALS RESEARCH SOCIETY , 2005, Vol. 830, s. 379-384Konferensbidrag (Refereegranskat)
    Abstract [en]

    Heteroepitaxial CeO2(80nm)/L0.67Ca0.33MnO3(400nm) film structures have been pulsed laser deposited on LaAlO3(001) single crystals to fabricate two terminal resistance switching devices. Ag/CeO2/L0.67Ca0.33MnO3 junctions exhibit reproducible switching between a high resistance state (FIRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 10(5). Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime.

  • 262.
    Forsblom, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Atomistic simulations of lattice defects2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Mechanical properties of solids are governed by crystal imperfections. Computational materials science is largely concerned with the modelling of such defects, e.g. their formation, migration, and interaction energies. Atomistic simulations of systems containing lattice defects are inherently difficult because of the generally complicated geometrical structure of the defects, the need for large simulation cells, etc.

    In this thesis, the role of lattice defects in the mechanism behind homogeneous melting is demonstrated. Also, a generic calculational scheme for studying atomic vibrations close to extended defects (applied to a dislocation) has been considered. Furthermore, heat capacities in the solid and liquid phases of aluminium have been calculated, as well as various thermophysical defect properties.

    The work was carried out using classical atomistic simulations, mainly molecular dynamics, of aluminium and copper. The interatomic forces were modelled with effective interactions of the embedded-atom type.

    The main results of this thesis are the following:

    • The thermal fluctuation initiating melting is an aggregate typically with 6-7 interstitials and 3-4 vacancies.

    • In the initial stage of melting, no signs of a shear modulus melting mechanism, or the presence of line-like defects (dislocations), can be seen.

    • The typical time interval from when melting initiates to the time at which the liquid phase is fully developed is of the order of 1000τ, where the period τ corresponds to the maximum vibrational frequency in the solid.

    • The solid-liquid boundary advances at a pace comparable to that of thermal transport by vibrating atoms in the crystal at high temperatures.

    • The seemingly small anharmonic effect in the heat capacity of aluminium is caused by a partial cancellation of the low-order term linear in the temperature and anharmonic terms of higher order in the temperature.

    • The core region of an edge dislocation in face-centred cubic aluminium has compressed and expanded regions. The excess volume associated with the dislocation core is small, about 6 percent of the atomic volume, as a result of a partial cancellation between the volume changes of the compressed and expanded regions.

    • The compressed and expanded regions of the edge dislocation core give negative and positive contributions, respectively, to the excess vibrational entropy. The overall effect is a positive vibrational excess entropy of the dislocation core which is about 2kB per atomic repeat length along the dislocation core.

    • The atomic vibrations near the dislocation core are modelled by considering an atomic cluster with about 500-1000 atoms containing the core of dislocation, embedded in a large discrete, but relaxed, lattice of about 23 000 atoms. An atomic region that is four atomic layers thick and about 18 atomic diameters long in the direction parallel to the Burgers vector, accounts for most of the excess entropy.

    • The constant-pressure heat capacity of aluminium shows a minimum as a function of temperature in the liquid phase.

  • 263.
    Forsblom, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Grimvall, Göran
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Heat capacity of liquid Al: Molecular dynamics simulations2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 13, s. 132204-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The heat capacities at constant pressure, c(P), at constant volume and at fixed volume, and the isothermal bulk modulus, are calculated for liquid Al over a wide range of temperatures using molecular dynamics simulations with interactions due to Ercolessi and Adams and Mei and Davenport. c(P) has only a weak temperature dependence, with a shallow minimum that results from the opposing effects of a gradual loss of shear resistance and thermal expansion.

  • 264.
    Forsblom, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Grimvall, Göran
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Homogeneous melting of superheated crystals: Molecular dynamics simulations2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 5, s. 054107-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The homogeneous melting mechanism in a superheated fcc lattice is studied through molecular dynamics simulations, usually for about 20 000 atoms, with the Ercolessi and Adams interaction that represents aluminum. The periodic boundary conditions for the simulation cell suppress the usual surface-initiated melting at T-m=939 K, and the solid-to-liquid transition takes place at the temperature T-s=1.3T(m). By logging the position of each atom at every time step in the simulation, we can follow the melting process in detail at the atomic level. Thermal fluctuations close to T-s create interstitial-vacancy pairs, which occasionally separate into mobile interstitials and almost immobile vacancies. There is an attraction between two interstitials, with a calculated maximum interaction energy of about 0.7 eV. When three to four migrating interstitials have come close enough to form a bound aggregate of point defects, and a few thermally created interstitial-vacancy pairs have been added to the aggregate, such a defect configuration usually continues to grow irreversibly to the liquid state. For 20 000 atoms in the simulation cell, the growth process takes about 10(2)tau to be completed, where tau is the period of a typical atomic vibration in the solid phase. This melting mechanism involves fewer atoms in its crucial initial phase than has been suggested in other melting models. The elastic shear moduli c(44) and c(')=(c(11)-c(12))/2 were calculated as a function of temperature and were shown to be finite at the onset of melting.

  • 265.
    Forsblom, Mattias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    Grimvall, Göran
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Materialteori.
    How superheated crystals melt2005Ingår i: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 4, nr 5, s. 388-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The melting of superheated crystalline solids through the penetration of intense radiation within at a temperature above the equilibrium melting temperature was investigated. The atomistic simulations, relevant for aluminum, was used to show that the thermal fluctuation initiating melting is an aggregate typically with 6-7 interstitials and 3-4 vacancies. Vacancy-interstital pairs were created through thermal fluctuation and interstitial-vacancy pairs were created close to the interstitial aggregate. It was found that when a defect aggregate contains more than about 10 point defects, it usually grows rapidly and irreversibly.

  • 266.
    Forsman, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Thorén, Per Anders
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    AC Behaviour of Josephson Junctions in Series2011Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 267.
    Forstén, Andreas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Letzner, Josephine
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    On the Use of Formations in Land Warfare: a statistical analysis2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Om bruket av formationer vid krigföring på land. 

    Rapporten behandlar militära formationer och försöker ge svar på frågan om hur geometrin hos dessa påverkar ett slag. Undersökningen har i huvudsak gjorts med en modell baserad på Markovkedjor. Denna metod kompletterades sedan med simuleringar i Unity 3D. Speciell fokus har lagts vid överflyglingsmanövern och jämförelser har gjorts med rekommendationer från officiella källor inom militären. De erhållna slutsatserna pekar mot att geometrin är av icke försumbar betydelse.

  • 268. Friedland, S.
    et al.
    Krop, E.
    Lundow, Per Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Markstrom, K.
    On the Validations of the Asymptotic Matching Conjectures2008Ingår i: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 133, nr 3, s. 513-533Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we review the asymptotic matching conjectures for r-regular bipartite graphs, and their connections in estimating the monomer-dimer entropies in d-dimensional integer lattice and Bethe lattices. We prove new rigorous upper and lower bounds for the monomer-dimer entropies, which support these conjectures. We describe a general construction of infinite families of r-regular tori graphs and give algorithms for computing the monomer-dimer entropy of density p, for any p is an element of[0,1], for these graphs. Finally we use tori graphs to test the asymptotic matching conjectures for certain infinite r-regular bipartite graphs.

  • 269.
    Friedland, Shmuel
    et al.
    Department of Mathematics, Statistics and Computer Science, University of Illinois at Chicago.
    Lundow, Per Håkan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Markström, Klas
    Department of Mathematics and Mathematical Statistics, Umeå University.
    The 1-Vertex Transfer Matrix and Accurate Estimation of Channel Capacity2010Ingår i: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 56, nr 8, s. 3692-3699Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The notion of a 1-vertex transfer matrix for multidimensional codes is introduced. It is shown that the capacity of such codes, or the topological entropy, can be expressed as the limit of the logarithm of spectral radii of 1-vertex transfer matrices. Storage and computations using the 1-vertex transfer matrix are much smaller than storage and computations needed for the standard transfer matrix. The method is applied to estimate the first 15 digits of the entropy of the 2-D (0, 1) run length limited channel. A large-scale computation of eigenvalues for the (0, 1) run length limited channel in 2-D and 3-D have been carried out. This was done in order to be able to compare the computational cost of the new method with the standard transfer matrix and have rigorous bounds to compare the estimates with. This in turn leads to improvements on the best previous lower and upper bounds for these channels.

  • 270. Fritzsch, H.
    et al.
    Zhou, Shun
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Neutrino mixing angles from texture zeros of the lepton mass matrices2013Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 718, nr 4-5, s. 1457-1464Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Taking into account the latest neutrino oscillation data, we study texture zeros of the lepton mass matrices. Assuming the Dirac neutrino mass matrix MD, the charged-lepton mass matrix Ml and the mass matrix of heavy right-handed Majorana neutrinos MR to have three texture zeros, we show that the observed neutrino mixing angles can naturally be obtained. The phenomenological implications for the neutrino mass spectrum, the CP-violating phases, the tritium beta decay and the neutrinoless double-beta decay are explored.

  • 271.
    Fu, Jie
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Developing semi-empirical ab initio based potentials in materials modeling2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Ab initiocalculation based on density function theory (DFT) is an accu-rate and efficient method for modelling material properties. It is performedby solving the Shrödinger equations with a few assumptions to obtain thephysical properties of the system. It is very computational demanding whendealing with large systems or long-time simulations. Developing empiricalpotentials on the basis ofab initiocalculations on smaller systems is a possi-ble way to solve this problem. The empirical potentials will benefit from theaccuracy ofab initiosimulations and can facilitate applications to large sys-tems and long-time simulations. In this thesis, we have performed two studiesregarding fitting empirical potentials: one is fitting an empirical Sutton-Chenpotential based onab initiosimulations for iron under extreme conditionsand the other one is fitting an improved Finnis-Sinclair potential for ternaryV-Ti-Cr alloy.In the first part, we focus on fitting a Sutton-Chen potential for solid Feunder the Earth’s inner core condition. Based onab initiomolecular dynam-ics (MD) simulation results, the Sutton-Chen potential is fitted to energies ofthe configurations obtained fromab initioMD simulations at the pressure of360 GPa and temperature of 6000 K. The method applied for the fitting isthe Particle Swarm Optimization (PSO) algorithm. The Sutton-Chen poten-tial can reproduce theab initioenergies with an error of 6.2 meV/atom. Setas the same withab initioMD simulations, classical MD using Sutton-Chenpotential can obtain the consistent results with those fromab initioMD sim-ulations at the pressure of 360 GPa and temperature of 6000 K. In order toexplore the size effect on the results, we extend the classical MD to large-sizesystems (from 1024 atoms to 65536 atoms). We also extend the temperaturerange to see the temperature effect on the results.In the second part, we develop an improved Finnis-Sinclair (IFS) potentialfor ternary V-Ti-Cr alloys. The interaction parameters of V-V, Ti-Ti andCr-Cr are fitted to the experimental lattice constants, cohesive energies andelastic constants. The binary alloy potential parameters are obtained byconstructing 3 binary alloy models (V15Ti, V15Cr, V8Ti8) and fitting to theirtheoretical lattice constants, cohesive energies and elastic constants. Finally,the IFS potential is successfully used to calculate mechanical properties andthe monovacancy formation energy in V-Ti-Cr alloy. It is also applied toinvestigate the composition effect on the mechanical properties of ternaryV-Ti-Cr alloys.

  • 272.
    Fu, Jie
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Improved Finnis-Sinclair potential for V-Ti-Cr ternary alloysManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We have developed an improved Finnis-Sinclair (IFS) potential for vanadium-rich body-centred cubic V–Ti–Cr random alloys. An extra exponential term is added to the original Finnis-Sinclair potential to enhance the repulsive interactions between atoms. IFS potential is fitted to experimental and theoretical lattice constants, cohesive energies, and elastic constants of the pure metals (V, Ti, and Cr) and binary alloys (V15Ti, V15Cr and Ti8Cr8). The experimental lattice constants, cohesive energies, and elastic constants of pure metals and binary alloys are well reproduced by the IFS potential. The good agreement of the predicted V mono-vacancy and self-interstitial formation energies with available experimental and theoretical data further confirms the accuracy of our IFS potential. The elastic properties and the influence of one vacancy on them are investigated for two technologically relevant alloys, V–4Ti–4Cr and V–5Ti–5Cr, using the IFS potential. The predicted results for the vacancy formation energies indicate that it is energetically easy to produce a Ti vacancy, but hard to generate a Cr vacancy in the considered alloys. Finally, this work also provides a reference method to fit empirical potentials for other ternary alloys.

  • 273.
    Full, Peter
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Percolation and Universality2013Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis a detailed discussion of the topic percolation theory in squared lattices in

    two dimensions will be conducted. To support this discussion numerical calculations will

    be done. For the data analysis and simulations the Hoshen-Kopelman-Algorithm [2] will

    be used. All concepts deduced will nally lead to the determination of the conductance's

    exponent

    t in random resistor networks. Using Derrida's transfer matrix program to

    calculate the conductivity of random resistors in two and three dimensions [11] and

    the nite-size scaling approach were used. In two dimensions

    t= = 0:955 0:006 was

    obtained. Were

    is the exponent of the correlation length in innite lattices. This

    value is in excellent agreement with Derrida (

    t= = 0:960:02, [11]) and slightly smaller

    than Sahimi (

    t= = 0:97480:001, [21]). In three dimensions the same approach yielded

    t=

    = 2:155 0:012 which some what smaller than the value found by Sahimi t= =

    2

    :27 0:20 [21] and Gingold and Lobb t= = 2:276 0:012 [25].

  • 274.
    Gabrielsson, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Liin, Sara
    Elinder, Fredrik
    Lindahl, Erik
    Binding Structure & Dynamics for Toxins Modifying the Gating Mechanism of Kv Channels2014Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, nr 2, s. 738A-738AArtikel i tidskrift (Övrigt vetenskapligt)
  • 275. Galteland, Peder Notto
    et al.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Sudbo, Asle
    Fluctuation effects in rotating Bose-Einstein condensates with broken SU(2) and U(1) x U(1) symmetries in the presence of intercomponent density-density interactions2015Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 91, nr 1, s. 013605-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermal fluctuations and melting transitions for rotating single-component superfluids have been intensively studied and are well understood. In contrast, the thermal effects on vortex states for two-component superfluids with density-density interaction, which have a much richer variety of vortex ground states, have been much less studied. Here, we investigate the thermal effects on vortex matter in superfluids with U(1) x U(1) broken symmetries and intercomponent density-density interactions, as well as the case with a larger SU(2) broken symmetry obtainable from the [U(1) x U(1)]-symmetric case by tuning scattering lengths. In the former case we find that, in addition to first-order melting transitions, the system exhibits thermally driven phase transitions between square and hexagonal lattices. Our main result, however, concerns the case where the condensate exhibits SU(2) symmetry, and where vortices are not topological. At finite temperature, the system exhibits effects which do not have a counterpart in single-component systems. Namely, it has a state where thermally averaged quantities show no regular vortex lattice, yet the system retains superfluid coherence along the axis of rotation. In such a state, the thermal fluctuations result in transitions between different (nearly) degenerate vortex states without undergoing a melting transition. Our results apply to multicomponent Bose-Einstein condensates, and we suggest how to detect some of these unusual effects experimentally in such systems.

  • 276. Galteland, Peder Notto
    et al.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Sudbo, Asle
    Thermal remixing of phase-separated states in two-component bosonic condensates2015Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, artikel-id 103040Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a two-component interacting bosonic condensate with dominating intra-species repulsive density-density interactions. We study the phase diagram of the system at finite temperature with rotation, using large-scale Monte Carlo simulations of a two-component Ginzburg-Landau model of the system. In the presence of rotation, the system features a competition between long-range vortex-vortex interactions and short-range density-density interactions. This leads to a rotation-driven 'mixing' phase transition in a spatially inhomogeneous state with a broken U(1) symmetry. Thermal fluctuations in this state lead to nematic two-component sheets of vortex liquids. At sufficiently strong inter-component interaction, we find that the superfluid and Z(2) phase transitions split. This results in the formation of an intermediate state which breaks only Z(2) symmetry. It represents two phase separated normal fluids with a difference in their densities.

  • 277. Ganguly, Pritam
    et al.
    Schravendijk, Pim
    Hess, Berk
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. Technische Universität Darmstadt, Germany; Stockholm University, Sweden .
    van der Vegt, Nico F. A.
    Ion Pairing in Aqueous Electrolyte Solutions with Biologically Relevant Anions2011Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, nr 13, s. 3734-3739Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed molecular simulations to study ion pairing in aqueous solutions. Our results indicate that ion specific interactions of Li+, Na+, and K+ with the dimethyl phosphate anion are solvent-mediated. The same mechanism applies to carboxylate ions, as has been illustrated in earlier simulations of aqueous alkali acetate solutions. Contact ion pairs play only a minor role or no role at all in determining the solution structure and ion specific thermodynamics of these systems. On the basis of the Kirkwood Buff theory of solution we furthermore show that the well-known reversal of the Hofmeister series of salt activity coefficients, comparing chloride or bromide with dimethyl phosphate or acetate, is caused by changing from a contact pairing mechanism in the former system to a solvent-mediated interaction mechanism in the latter system.

  • 278.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Agterberg, Daniel F.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Vortex coalescence and type-1.5 superconductivity in Sr2RuO42012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 6, s. 060513-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently vortex coalescence was reported in superconducting Sr2RuO4 by several experimental groups for fields applied along the c axis. We argue that Sr2RuO4 is a type-1.5 superconductor with long-range attractive, short-range repulsive intervortex interaction. The type-1.5 behavior stems from an interplay of the two orbital degrees of freedom describing this chiral superconductor together with the multiband nature of the superconductivity. These multiple degrees of freedom give rise to multiple coherence lengths, some larger and some smaller than the magnetic field penetration length, resulting in nonmonotonic intervortex forces.

  • 279.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Domain walls and their experimental signatures in s + i s superconductors2014Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, nr 1, s. 017003-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arguments were recently advanced that hole-doped Ba1-xKxFe2As2 exhibits the s+is state at certain doping. Spontaneous breaking of time-reversal symmetry in the s+is state dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in the s+is state. We find that in this state the domain walls can have a dipolelike magnetic signature (in contrast to the uniform magnetic signature of domain walls p+ip superconductors). We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm the s+is state.

  • 280.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Properties of skyrmions and multi-quanta vortices in chiral p-wave superconductors2015Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikel-id 17540Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chiral p-wave superconducting state supports a rich spectrum of topological excitations different from those in conventional superconducting states. Besides domain walls separating different chiral states, chiral p-wave state supports both singular and coreless vortices also interpreted as skyrmions. Here, we present a numerical study of the energetic properties of isolated singular and coreless vortex states as functions of anisotropy and magnetic field penetration length. In a given chiral state, single quantum vortices with opposite winding have different energies and thus only one kind is energetically favoured. We find that with the appropriate sign of the phase winding, two-quanta (coreless) vortices are always energetically preferred over two isolated single quanta (singular) vortices. We also report solutions carrying more flux quanta. However those are typically more energetically expensive/metastable as compared to those carrying two flux quanta.

  • 281.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Skyrmionic state and stable half-quantum vortices in chiral p-wave superconductors2012Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 6, s. 060514-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observability of half-quantum vortices and skyrmions in p-wave superconductors is an outstanding open question. Under the most common conditions, fractional flux vortices are not thermodynamically stable in bulk samples. Here we show that in chiral p-wave superconductors, there is a regime where, in contrast, lattices of integer-flux vortices are not thermodynamically stable. Instead, skyrmions made of spatially separated half-quantum vortices are the topological defects produced by an applied external field.

  • 282.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Topological defects in mixtures of superconducting condensates with different charges2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 21, s. 214507-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the topological defects in phenomenological models describing mixtures of charged condensates with commensurate electric charges. Such situations are expected to appear for example in liquid metallic deuterium. This is modeled by a multicomponent Ginzburg-Landau theory where the condensates are coupled to the same gauge field by different coupling constants whose ratio is a rational number. We also briefly discuss the case where electric charges are incommensurate. Flux quantization and finiteness of the energy per unit length dictate that the different condensates have different winding and thus different number of (fractional) vortices. Competing attractive and repulsive interactions lead to molecule-like bound states between fractional vortices. Such bound states have finite energy and carry integer flux quanta. These can be characterized by the CP1 topological invariant that motivates their denomination as skyrmions.

  • 283.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Vortex chains due to nonpairwise interactions and field-induced phase transitions between states with different broken symmetry in superconductors with competing order parameters2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 1, s. 014510-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study superconductors with two order components and phase separation driven by intercomponent densitydensity interaction, focusing on the phase where only one condensate has nonzero ground-state density and a competing order parameter exists only in vortex cores. We demonstrate there that multibody intervortex interactions can be strongly nonpairwise, leading to some unusual vortex patterns in an external field, such as vortex pairs and vortex chains. We demonstrate that in an external magnetic field such a system undergoes a field-driven phase transition from (broken) U(1) to (broken) U(1) x U(1) symmetries when a subdominant order parameter in the vortex cores acquires global coherence. Observation of these characteristic ordering patterns in surface probes may signal the presence of a subdominant condensate in the vortex core.

  • 284.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    Vortex matter in U(1)xU(1)xZ(2) phase-separated superconducting condensates2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 21, s. 214524-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the properties of vortex solutions and magnetic response of two-component U(1)xU(1)xZ(2) superconductors, with phase separation driven by intercomponent density-density interaction. Such a theory can be viewed arising from the breakdown of SU(2) symmetry by a biquadratic interaction between the components of the field. Depending on the symmetry-breaking term, there are two ground-state phases: one where both components of the doublet are equal (the miscible phase) and one where only one component assumes a nonzero vacuum expectation value (the immiscible state). In the latter phase, the spectrum of topological excitations contains both domain walls and vortices. We show the existence of another kind of excitation that has properties of both topological excitations at the same time. This kind of excitation combines vorticity together with a circular domain wall, interpolating between inequivalent broken states, that shows up as a ring of localized magnetic flux. Asymptotically, this resembles a vortex carrying multiple flux quanta, but because the magnetic field is localized at a given distance from the center this looks like a pipe. The isolated multiquanta pipelike vortices can be either stable or metastable, even if the system is not type 1. We discuss the response of such a system to an externally applied magnetic field. Also we discuss magnetic response of SU(2) superconductor.

  • 285.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Bojesen, Troels Arnfred
    Sudbo, Asle
    Lattices of double-quanta vortices and chirality inversion in p(x) + i p(y) superconductors2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, artikel-id 104509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the magnetization processes of a standard Ginzburg-Landau model for chiral p-wave superconducting states in an applied magnetic field. We find that the phase diagram is dominated by triangular lattices of doubly quantized vortices. Only in close vicinity to the upper critical field the lattice starts to dissociate into a structure of single-quanta vortices. The degeneracy between states with opposite chirality is broken in a nonzero field. If the magnetization starts with an energetically unfavorable chirality, the process of chirality inversion induced by the external magnetic field results in the formation of a sequence of metastable states with characteristic magnetic signatures that can be probed by standard experimental techniques.

  • 286. Garaud, Julien
    et al.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Topological Solitons in Three-Band Superconductors with Broken Time Reversal Symmetry2011Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 19, s. 197001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that three-band superconductors with broken time reversal symmetry allow magnetic flux-carrying stable topological solitons. They can be induced by fluctuations or quenching the system through a phase transition. It can provide an experimental signature of the time reversal symmetry breakdown.

  • 287.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Carlström, Johan
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Speight, Martin
    Chiral CP2 skyrmions in three-band superconductors2013Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, nr 1, s. 014507-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that under certain conditions, three-component superconductors (and, in particular, three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, characterized by a CP2 topological invariant, in models for three-component superconductors with broken time-reversal symmetry. We term these topological defects "chiral GL((3)) skyrmions," where "chiral" refers to the fact that due to broken time-reversal symmetry, these defects come in inequivalent left-and right-handed versions. In certain cases, these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations, these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time-reversal symmetry in three-band superconductors or in Josephson-coupled bilayers of s(+/-) and s-wave superconductors.

  • 288.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik. Department of Physics, University of Massachusetts, Amherst, MA 01003, United States.
    Radu, Eugen
    Volkov, Mikhail S.
    Stable Cosmic Vortons2013Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, nr 17, s. 171602-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present solutions in the gauged U(1) x U(1) model of Witten describing vortons-spinning flux loops stabilized against contraction by the centrifugal force. Vortons were heuristically described many years ago; however, the corresponding field theory solutions were not obtained and so the stability issue remained open. We construct explicitly a family of stationary vortons characterized by their charge and angular momentum. Most of them are unstable and break in pieces when perturbed. However, thick vortons with a small radius preserve their form in the 3 + 1 nonlinear dynamical evolution. This gives the first ever evidence of stable vortons and impacts several branches of physics where they could potentially exist. These range from cosmology, since vortons could perhaps contribute to dark matter, to QCD and condensed matter physics.

  • 289.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Sellin, Karl A. H.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Jäykkä, Juha
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Skyrmions induced by dissipationless drag in U(1)xU(1) superconductors2014Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 10, s. 104508-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rather generically, multicomponent superconductors and superfluids have intercomponent current-current interaction. We show that in superconductors with substantially strong intercomponent drag interaction, the topological defects which form in an external field are characterized by a skyrmionic topological charge. We then demonstrate that they can be distinguished from ordinary vortex matter by a very characteristic magnetization process due to the dipolar nature of inter-skyrmion forces. The results provide an experimental signature to confirm or rule out the formation p-wave state with reduced spin stiffness in p-wave superconductors.

  • 290.
    Garaud, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Silaev, Mihail
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
    Thermoelectric Signatures of Time-Reversal Symmetry Breaking States in Multiband Superconductors2016Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, nr 9, artikel-id 097002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that superconductors with broken time-reversal symmetry have very specific magnetic and electric responses to inhomogeneous heating. A local heating of such superconductors induces a magnetic field with a profile that is sensitive to the presence of domain walls and crystalline anisotropy of superconducting states. A nonstationary heating process produces an electric field and a charge imbalance in different bands. These effects can be measured and used to distinguish s + is and s + id superconducting states in the candidate materials such as Ba1-xKxFe2As2.

  • 291. Garbrecht, Björn
    et al.
    Konstandin, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Hybrid inflation exit through tunneling2007Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 1, s. 033-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For hybrid inflationary potentials, we derive the tunneling rate from field configurations along the flat direction towards the waterfall regime. This process competes with the classically rolling evolution of the scalar fields and needs to be strongly subdominant for phenomenologically viable models. Tunneling may exclude models with a mass scale below 10(12) GeV, but can be suppressed by small values of the coupling constants. We find that tunneling is negligible for those models, which do not require fine tuning in order to cancel radiative corrections, in particular for GUT-scale SUSY inflation. In contrast, electroweak scale hybrid inflation is not viable, unless the inflaton-waterfall field coupling is smaller than approximately 10(-11).

  • 292.
    Gavrilyuk, Sergey
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Gelmukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Miron, V.
    Kimberg, P.
    Morin, C.
    Nicolas, N.
    Kosugi, S.
    May which-path detection trigger vibrational anisotropy of resonant Auger scattering?Manuskript (preprint) (Övrigt vetenskapligt)
  • 293. Gavryushkin, P. N.
    et al.
    Popov, Z. I.
    Litasov, K. D.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Gavryushkin, A.
    Stability of B2-type FeS at Earth's inner core pressures2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 16, s. 8435-8440Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density functional theory, we investigated how substituting sulfur atoms for iron atoms affects the structure and energy of the body centered cubic and hexagonal close-packed iron phases at 350 GPa and at 0 K. We conclude that formation of random (Fe,S) solid solutions is energetically favorable in all intermediate compositions, although the random low-symmetry substitutions cause structural distortion. The (Fe,S) solid solution is nearly as favorable as the mechanical mixture of Fe-hcp and FeS-B2. This finding, in combination with dynamical stability, defines the B2 structure as a strong candidate for the sulfur-bearing phase of the Earth's inner core.

  • 294. Ghosh, M.
    et al.
    Goswami, S.
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Can the hint of δCP from T2K also indicate the hierarchy and octant?2016Ingår i: Springer Proceedings in Physics, Springer, 2016, s. 339-344Konferensbidrag (Refereegranskat)
    Abstract [en]

    The T2K neutrino data has already given a hint for the best-fit value of the leptonic CP phase δCP as −90◦. In this paper we ask the question that if this hint is confirmed by the subsequent neutrino and anti-neutrino runs of T2K, then can it also give any information about the other two remaining unknown oscillation parameters—the neutrino mass hierarchy and octant of θ23. We find that if T2K runs in only neutrino mode with its full targeted exposure, then δCP = −90◦ would indicate the true hierarchy as normal and the true octant as higher. On the other hand if T2K runs in equal neutrino and anti-neutrino mode then the true hierarchy can be confirmed as normal but the octant will remain undetermined. We have also studied the effect of anti-neutrino runs on CP sensitivity of T2K.

  • 295. Ghosh, M.
    et al.
    Goswami, S.
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik. Physical Research Laboratory, Navrangpura, Ahmedabad, India.
    Maximizing the DUNE early physics output with current experiments2016Ingår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 76, nr 3, artikel-id 114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The deep underground neutrino experiment (DUNE) is a proposed next generation superbeam experiment at Fermilab. Its aims include measuring the unknown neutrino oscillation parameters—the neutrino mass hierarchy, the octant of the mixing angle θ23, and the CP-violating phase δCP. The current and upcoming experiments T2K, NOνA, and ICAL@INO will also be collecting data for the same measurements. In this paper, we explore the sensitivity reach of DUNE in combination with these other experiments. We evaluate the least exposure required by DUNE to determine the above three unknown parameters with reasonable confidence. We find that for each case, the inclusion of data from T2K, NOνA, and ICAL@INO help to achieve the same sensitivity with a reduced exposure from DUNE thereby helping to economize the configuration. Further, we quantify the effect of the proposed near detector on systematic errors and study the consequent improvement in sensitivity. We also examine the role played by the second oscillation cycle in furthering the physics reach of DUNE. Finally, we present an optimization study of the neutrino–antineutrino running of DUNE.

  • 296. Ghosh, Monojit
    et al.
    Ghoshal, Pomita
    Goswami, Srubabati
    Nath, Newton
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    New look at the degeneracies in the neutrino oscillation parameters, and their resolution by T2K, NO nu A and ICAL2016Ingår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 93, nr 1, artikel-id 013013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The three major unknown neutrino oscillation parameters at the present juncture are the mass hierarchy, the octant of the mixing angle theta(23) and the CP phase delta(CP). It is well known that the presence of hierarchy-delta(CP) and octant degeneracies affects the unambiguous determination of these parameters. In this paper, we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy -theta(23) - delta(CP) degeneracy. This is best depicted as contours in the test (theta(23) - delta(CP)) plane for different representative true values of parameters. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of delta(CP). These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if theta(13) is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of delta(CP). We identify which of these eight different degenerate solutions can occur in the test (theta(23) - delta(CP)) parameter space, taking the long-baseline experiment NO nu A running in the neutrino mode as an example. The inclusion of the NO nu A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy-right octant solutions to a large extent. The remaining wrong-hierarchy solutions can be removed by combining NO nu A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the 2 sigma level by the combined data set, for the true parameter space considered in the study.

  • 297. Ghosh, Monojit
    et al.
    Ghoshal, Pomita
    Goswami, Srubabati
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Evidence for leptonic CP phase from NO nu A, T2K and ICAL2016Ingår i: Pramana (Bangalore), ISSN 0304-4289, E-ISSN 0973-7111, Vol. 86, nr 2, s. 387-393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phenomenon of neutrino oscillation is now well understood from the solar, atmospheric, reactor and accelerator neutrino experiments. This oscillation is characterized by a unitary PMNS matrix which is parametrized by three mixing angles (oee integral (12), oee integral (23) and oee integral (13)) and one phase (delta (CP)) known as the leptonic CP phase. Neutrino oscillation also involves two mass squared differences: the solar mass square difference () and the atmospheric mass square difference (). Though there is already significant amount of information about the three mixing angles, the CP phase is still unknown. Apart from the CP phase, one should also know what is the true nature of the neutrino mass hierarchy, i.e., normal (m (3)> m (1): NH) or inverted (m (1)> m (3): IH) and what is the true octant of oee integral (23), i.e., lower (oee integral (23)< 45(a similar to): LO) or higher (oee integral (23)> 45(a similar to): HO). The long-baseline experiments (LBL) have CP sensitivity coming from the appearance channel (). On the other hand, atmospheric neutrinos are known to have negligible CP sensitivity. In this work, we study the synergy between the LBL experiment NO nu A, T2K and the atmospheric neutrino experiment ICAL@INO for obtaining the first hint of CP violation in the lepton sector. We find that due to the lack of knowledge of hierarchy and octant, CP sensitivity of NO nu A/T2K is poorer for some parameter ranges. Addition of ICAL data to T2K and NO nu A can exclude these spurious wrong-hierarchy and /or wrong-octant solutions and cause a significant increase in the range of delta (CP) values for which a hint of CP violation can be achieved. Similarly, the precision with which delta (CP) can be measured also improves with the inclusion of ICAL data.

  • 298. Ghosh, Monojit
    et al.
    Goswami, Srubabati
    Physical Research Laboratory India, Ahmedabad, India .
    Raut, Sushant K.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Implications of delta(CP) =-90 degrees towards determining hierarchy and octant at T2K and T2K-II2017Ingår i: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 32, nr 6, artikel-id 1750034Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The T2K experiment has provided the first hint for the best-fit value for the leptonic CP phase delta(CP) similar to -90 degrees from neutrino data. This is now corroborated by the NO nu A neutrino runs. We study the implications for neutrino mass hierarchy and octant of theta(23) in the context of this data assuming that the true value of delta(CP) in nature is -90 degrees. Based on simple arguments on degeneracies in the probabilities, we show that a clear signal of delta(CP) = -90 degrees coming from T2K neutrino (antineutrino) data is only possible if the true hierarchy is normal and the true octant is higher (lower). Thus, if the T2K neutrino and antineutrino data are fitted separately and both give the true value of delta(CP) = -90 degrees, this will imply that nature has chosen the true hierarchy to be normal and theta(23) approximate to 45 degrees. However, we find that the combined fit of neutrino and antineutrino data will still point to true hierarchy as normal but the octant of theta(23) will remain undetermined. We do our analysis for both, the current projected exposure (7.8 x 10(21) pot) and planned extended exposure (20 x 10(21) pot). We also present the CP discovery potential of T2K emphasizing on the role of antineutrinos. We find that one of the main contributions of the antineutrino data is to remove the degenerate solutions with the wrong octant. Thus, the antineutrino run plays a more significant role for those hierarchy-octant combinations for which this degeneracy is present. If this degeneracy is absent, then only neutrino run gives a better result for fixed theta(13). However, if we marginalize over theta(13) then, sensitivity corresponding to mixed run can be better than pure neutrino run.

  • 299. Gianti, Eleonora
    et al.
    Delemotte, Lucie
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Klein, Michael L.
    Carnevale, Vincenzo
    On the role of water density fluctuations in the inhibition of a proton channel2016Ingår i: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, ISSN 0027-8424, Vol. 113, nr 52, s. E8359-E8368Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hv1 is a transmembrane four-helix bundle that transports protons in a voltage-controlled manner. Its crucial role in many pathological conditions, including cancer and ischemic brain damage, makes Hv1 a promising drug target. Starting from the recently solved crystal structure of Hv1, we used structural modeling and molecular dynamics simulations to characterize the channel's most relevant conformations along the activation cycle. We then performed computational docking of known Hv1 inhibitors, 2-guanidinobenzimidazole (2GBI) and analogs. Although salt-bridge patterns and electrostatic potential profiles are well-defined and distinctive features of activated versus nonactivated states, the water distribution along the channel lumen is dynamic and reflects a conformational heterogeneity inherent to each state. In fact, pore waters assemble into intermittent hydrogen-bonded clusters that are replaced by the inhibitor moieties upon ligand binding. The entropic gain resulting from releasing these conformationally restrained waters to the bulk solvent is likely a major contributor to the binding free energy. Accordingly, we mapped the water density fluctuations inside the pore of the channel and identified the regions of maximum fluctuation within putative binding sites. Two sites appear as outstanding: One is the already known binding pocket of 2GBI, which is accessible to ligands from the intracellular side; the other is a site located at the exit of the proton permeation pathway. Our analysis of the waters confined in the hydrophobic cavities of Hv1 suggests a general strategy for drug discovery that can be applied to any ion channel.

  • 300. Gingras, M. J. P.
    et al.
    Henelius, Patrik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Collective phenomena in the LiHo xY 1-xF 4 quantum ising magnet: Recent progress and open questions2011Ingår i: Journal of Physics: Conference Series, ISSN 1742-6588, Vol. 320, s. 012001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In LiHo xY 1-xF 4, the magnetic Holmium Ho 3+ ions behave as effective Ising spins that can point parallel or antiparallel to the crystalline c-axis. The predominant inter-Ho 3+ interaction is dipolar, while the Y 3+ ions are non-magnetic. The application of a magnetic field B x transverse to the c-axis Ising direction leads to quantum spin-flip fluctuations, making this material a rare physical realization of the celebrated transverse field Ising model. The problems of classical and transverse-field-induced quantum phase transitions in LiHo xY 1-xF 4 in the dipolar ferromagnetic (x = 1), diluted ferromagnetic (0.25 ≤∼ x &lt; 1) and highly diluted x ≤∼ 0.25 dipolar spin glass regimes have attracted much experimental and theoretical interest over the past twenty-five years. Two questions have received particular attention: (i) is there an antiglass (quantum disordered) phase at low Ho 3+ concentration and (ii) what is the mechanism responsible for the fast B x-induced destruction of the ferromagnetic (0.25 ≤∼ x &lt; 1) and spin glass (x ≤∼ 0.25) phases? This paper reviews some of the recent theoretical and experimental progress in our understanding of the collective phenomena at play in LiHo xY 1-xF 4, in both zero and nonzero B x.

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