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  • 751.
    Yoluk, Özge
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Experimentell biomolekylär fysik. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Riederer, Erika A.
    Andersson, Magnus
    Klement, Goran
    Trudell, James R.
    Bertaccini, Edward J.
    Howard, Rebecca J.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Contribution of Structural Elements to Activation and Allosteric Modulation in an Anionic Ligand-Gated Ion Channel2014Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 106, nr 2, s. 547A-547AArtikel i tidskrift (Övrigt vetenskapligt)
  • 752. Zackrisson, Erik
    et al.
    Scott, Pat
    Rydberg, Claes-Erik
    Iocco, Fabio
    Edvardsson, Bengt
    Ostlin, Goran
    Sivertsson, Sofia
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Zitrin, Adi
    Broadhurst, Tom
    Gondolo, Paolo
    Finding high-redshift dark stars with the James Webb Space Telescope2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 717, nr 1, s. 257-267Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first stars in the history of the universe are likely to form in the dense central regions of similar to 10(5)-10(6) M-circle dot cold dark matter halos at z approximate to 10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive, and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that all dark stars with masses up to 10(3) M-circle dot are intrinsically too faint to be detected by JWST at z > 6. However, by exploiting foreground galaxy clusters as gravitational telescopes do, certain varieties of cool (T-eff <= 30,000 K) dark stars should be within reach at redshifts up to z approximate to 10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least similar to 1% of the total stellar mass in such objects.

  • 753. Zackrisson, Erik
    et al.
    Scott, Pat
    Rydberg, Claes-Erik
    Iocco, Fabio
    Sivertsson, Sofia
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk partikelfysik.
    Östlin, Göran
    Mellema, Garrelt
    Iliev, Ilian T.
    Shapiro, Paul R.
    Observational constraints on supermassive dark stars2010Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 407, nr 1, s. L74-L78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that such objects may attain masses in the 10(4)-10(7) M-circle dot range and that such supermassive dark stars should be within reach of the upcoming James Webb Space Telescope. Notwithstanding theoretical difficulties with this proposal, we argue here that some of these objects should also be readily detectable with both the Hubble Space Telescope and ground-based 8-10 m class telescopes. Existing survey data already place strong constraints on 10(7) M-circle dot dark stars at z approximate to 10. We show that such objects must be exceedingly rare or short lived to have avoided detection.

  • 754. Zeberg, Hugo
    et al.
    Blomberg, Clas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Arhem, Peter
    Ion Channel Density Regulates Switches between Regular and Fast Spiking in Soma but Not in Axons2010Ingår i: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 6, nr 4, s. e1000753-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The threshold firing frequency of a neuron is a characterizing feature of its dynamical behaviour, in turn determining its role in the oscillatory activity of the brain. Two main types of dynamics have been identified in brain neurons. Type 1 dynamics (regular spiking) shows a continuous relationship between frequency and stimulation current (f-I-stim) and, thus, an arbitrarily low frequency at threshold current; Type 2 (fast spiking) shows a discontinuous f-I-stim relationship and a minimum threshold frequency. In a previous study of a hippocampal neuron model, we demonstrated that its dynamics could be of both Type 1 and Type 2, depending on ion channel density. In the present study we analyse the effect of varying channel density on threshold firing frequency on two well-studied axon membranes, namely the frog myelinated axon and the squid giant axon. Moreover, we analyse the hippocampal neuron model in more detail. The models are all based on voltage-clamp studies, thus comprising experimentally measurable parameters. The choice of analysing effects of channel density modifications is due to their physiological and pharmacological relevance. We show, using bifurcation analysis, that both axon models display exclusively Type 2 dynamics, independently of ion channel density. Nevertheless, both models have a region in the channel-density plane characterized by an N-shaped steady-state current-voltage relationship (a prerequisite for Type 1 dynamics and associated with this type of dynamics in the hippocampal model). In summary, our results suggest that the hippocampal soma and the two axon membranes represent two distinct kinds of membranes; membranes with a channel-density dependent switching between Type 1 and 2 dynamics, and membranes with a channel-density independent dynamics. The difference between the two membrane types suggests functional differences, compatible with a more flexible role of the soma membrane than that of the axon membrane.

  • 755.
    Zhang, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Breaking of a rod induced by wave propagation.2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Rapportens mål är att använda olika metoder för att visualisera hur en spröd stav (där

    sträck och brottgränsen ligger vid samma punkt) kan brytas i  era delar, på grund

    av vågor som fortplantar sig i materialet. Denna process kan exempelvis appliceras i

    vardagliga problemet, om varför en spaghetti oftast bryts i  era delar.

    Det angrepps punkt som rapporten har på problem, är då att simulera dess rörelse,

    efter att man har släppt en stav från ett jämt böjt läge, där den fria punkten ska motsvara

    ett första brott. Det som kommer då visas att det bildas lokala ökningar av böjningar,

    vilket motsvarar lokala spänningar ökas jämfört med initialt läget.

    Två metoder kommer testas, en lösning med energi perspektiv kommer användas,

    som löses analytisk och numerisk. Den andra metoden, är en mekaniks synsätt, där

    grundläggande mekanik och hållfasthetslära används. Dess fysik och matematik, kommer

    att presenteras i rapporten och dess implementation i MATLAB.

    Resultatet från den mekaniska tillvägagångssätt kan diskuteras, då resultat inte nådde

    upp till förväntan. Resultatet från energiska perspektivet klarar av att visa att vågor

    propagerar, och hur dessa skapar lokala ökningar av spänningar, vilket kan ses som en

    lyckad simulering.

  • 756.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Non-Standard Neutrino Interactions and Non-Unitarity Effects from TeV Seesaw Models2010Ingår i: NEUTRINO FACTORIES, SUPERBEAMS, AND BETA BEAMS / [ed] Goodman MC; Kaplan DM; Sullivan Z, 2010, Vol. 1222, s. 145-149Konferensbidrag (Refereegranskat)
    Abstract [en]

    The motivations and phenomena of seesaw models at the TeV scale are briefly reviewed. We show that nonstandard neutrino interactions and non-unitary effects are two typical features of low-scale scalar and fermionic seesaw models, respectively. For scalar seesaw models, in principle, significant non-standard interaction effects can be accommodated in the type-II seesaw model. As for the low-scale fermionic seesaw models, the inverse seesaw model turns out to be the most natural one, and could be well tested at the future long-baseline neutrino oscillation experiments and the LHC.

  • 757.
    Zhang, He
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Non-standard neutrino interactions in the type-II seesaw model2010Ingår i: TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS (TAUP2009), 2010, Vol. 203Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Within the framework of the type-II seesaw model, we investigate in detail the non-standard neutrino interactions (NSIs). Non-trivial correlations between NSI parameters and neutrino masses and mixing parameters are established. We show that sizable NSIs can be generated as a consequence of a nearly degenerate neutrino mass spectrum. Significant zero distance effects in the near detector of a future neutrino factory, as well as characteristic decays of the doubly charged Higgs at the Large Hadron Collider are discussed.

  • 758.
    Zhang, He
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Zhou, Shun
    The minimal seesaw model at the TeV scale2010Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 685, nr 4-5, s. 297-301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We point out that the minimal seesaw model can provide a natural framework to accommodate tiny neutrino masses, while its experimental testability and notable predictiveness are still maintained. This possibility is based on the Observation that two heavy right-handed Majorana neutrinos in the minimal seesaw model may naturally emerge as a pseudo-Dirac fermion In a specific scenario, we show that the tri-bimaximal neutrino mixing can be produced, and only the inverted neutrino mass hierarchy is allowed The low-energy phenomena, including non-unitarity effects in neutrino oscillations, neutrinoless double-beta decays and rare lepton-flavor-violating decays of charged leptons l(alpha) -> l(beta)gamma, have been explored. The collider signatures of the heavy singlet neutrino are also briefly discussed (C) 2010 Elsevier B.V All rights reserved

  • 759.
    Zhang, Zhigang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Grishini, Alex M.
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Characterization of piezoelectric shear mode inkjet actuator2005Ingår i: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 69, s. 401-+Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Impedance analysis was used to characterize the properties of Piezoelectric Shear Mode Inkjet Actuators. Ceramic actuators poled parallel to the channel walls exhibit good performance. Applying high voltage the actuators can be depolarized at high temperature or even re-poled perpendicular to the channel walls. This limits the drive pulse and the bias voltage below the coercive voltage. The leakage current also has been studied with various conditions. For the ferroelectric ceramic materials, the Schottky barrier also can be measured at definite voltage and temperature ranges, the corresponding Barrier for the Al/PZT contact is 0.98 eV. A pronounced low-temperature dielectric relaxation process was observed between 100-150 K; the relaxation rate fellows the Arrhenius law, the fitted activation energy is 0.194 eV. The resonance frequency increases as decreasing the temperature because of increasing for the stiffness coefficient at low temperature.

  • 760.
    Åkerblom, Karl
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Investigations of Single Longitudinal Mode and Frequency Stabilityin Standing Wave and Unidirectional Cavity Lasers2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 761. Århem, P.
    et al.
    Klement, G.
    Blomberg, Clas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Channel density regulation of firing patterns in a cortical neuron model2006Ingår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 90, nr 12, s. 4392-4404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modifying the density and distribution of ion channels in a neuron (by natural up- and downregulation or by pharmacological intervention or by spontaneous mutations) changes its activity pattern. In this investigation we analyzed how the impulse patterns are regulated by the density of voltage-gated channels in a neuron model based on voltage-clamp measurements of hippocampal interneurons. At least three distinct oscillatory patterns, associated with three distinct regions in the Na-K channel density plane, were found. A stability analysis showed that the different regions are characterized by saddle-node, double-orbit, and Hopf-bifurcation threshold dynamics, respectively. Single, strongly graded action potentials occur in an area outside the oscillatory regions, but less graded action potentials occur together with repetitive. ring over a considerable range of channel densities. The relationship found here between channel densities and oscillatory behavior may partly explain the difference between the principal spiking patterns previously described for crab axons (class 1 and 2) and cortical neurons ( regular. ring and fast spiking).

  • 762. Århem, Peter
    et al.
    Blomberg, Clas
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Teoretisk biologisk fysik.
    Ion channel density and threshold dynamics of repetitive firing in a cortical neuron model2007Ingår i: Biosystems (Amsterdam. Print), ISSN 0303-2647, E-ISSN 1872-8324, Vol. 89, nr 1-3, s. 117-125Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modifying the density and distribution of ion channels in a neuron (by natural up- and down-regulation, by pharmacological intervention or by spontaneous mutations) changes its activity pattern. In the present investigation, we analyze how the impulse patterns are regulated by the density of voltage-gated channels in a model neuron, based on voltage clamp measurements of hippocampal interneurons. At least three distinct oscillatory patterns, associated with three distinct regions in the Na-K channel density plane, were found. A stability analysis showed that the different regions are characterized by saddle-node, double-orbit, and Hopf bifurcation threshold dynamics, respectively. Single strongly graded action potentials occur in an area outside the oscillatory regions, but less graded action potentials occur together with repetitive firing over a considerable range of channel densities. The presently found relationship between channel densities and oscillatory behavior may be relevance for understanding principal spiking patterns of cortical neurons (regular firing and fast spiking). It may also be of relevance for understanding the action of pharmacological compounds on brain oscillatory activity.

  • 763. Åström, J.A.
    et al.
    Carter, A.
    Hetherington, J.
    Ioakimidis, K.
    Lindahl, Erik
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Beräkningsbiofysik. KTH, Centra, Science for Life Laboratory, SciLifeLab.
    Mozdzynski, G.
    Nash, R. W.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Signell, A.
    Westerholm, J.
    Preparing scientific application software for exascale computing2013Ingår i: Applied Parallel and Scientific Computing: 11th International Conference, PARA 2012, Helsinki, Finland, June 10-13, 2012, Revised Selected Papers / [ed] Pekka Manninen, Per Öster, Springer, 2013, s. 27-42Konferensbidrag (Refereegranskat)
    Abstract [en]

    Many of the most widely used scientifc application software of today were developed largely during a time when the typical amount of compute cores was calculated in tens or hundreds. Within a not too distant future the number of cores will be calculated in at least hundreds of thousands or even millions. A European collaboration group CRESTA has recently been working on a set of renowned scientific software to investigate and develop these codes towards the realm of exascale computing. The codes are ELMFIRE, GROMACS, IFS, HemeLB, NEK5000, and OpenFOAM. This paper contains a summary of the strategies for their development towards exascale and results achieved during the first year of the collaboration project.

  • 764.
    Örd, Teet
    et al.
    Univ Tartu, Inst Phys, W Ostwaldi Str 1, EE-50411 Tartu, Estonia..
    Rago, Ullike
    Univ Tartu, Inst Phys, W Ostwaldi Str 1, EE-50411 Tartu, Estonia..
    Vargunin, Artjom
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik. Univ Tartu, Inst Phys, W Ostwaldi Str 1, EE-50411 Tartu, Estonia.
    Litak, Grzegorz
    Lublin Univ Technol, Fac Mech Engn, Nadbystrzycka 36, PL-20618 Lublin, Poland.;AGH Univ Sci & Technol, Dept Proc Control, Mickiewicza 30, PL-30059 Krakow, Poland..
    Strong temperature effect on the sizes of the Cooper pairs in a two-band superconductor2018Ingår i: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 91, nr 1, artikel-id 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the temperature dependencies of the mean sizes of the Cooper pairs in a two-band BCS-type s-wave superconductivity model with coupling cut-off in the momentum space. It is found that, in contrast to single-band systems, the size of Cooper pairs in the weaker superconductivity band can significantly decrease with a temperature increase due to an interband proximity effect. The relevant spatial behaviour of the wave functions of the Cooper pairs is analyzed. The results also indicate a possibility that the size of Cooper pairs in two-band systems may increase with an increase in temperature.

13141516 751 - 764 av 764
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