5,100 research outputs found

    Accurate determination of crystal structures based on averaged local bond order parameters

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    Local bond order parameters based on spherical harmonics, also known as Steinhardt order parameters, are often used to determine crystal structures in molecular simulations. Here we propose a modification of this method in which the complex bond order vectors are averaged over the first neighbor shell of a given particle and the particle itself. As demonstrated using soft particle systems, this averaging procedure considerably improves the accuracy with which different crystal structures can be distinguished

    Energy deposition studies for the High-Luminosity Large Hadron Collider inner triplet magnets

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    A detailed model of the High Luminosity LHC inner triplet region with new large-aperture Nb3Sn magnets, field maps, corrector packages, and segmented tungsten inner absorbers was built and implemented into the FLUKA and MARS15 codes. In the optimized configuration, the peak power density averaged over the magnet inner cable width is safely below the quench limit. For the integrated luminosity of 3000 fb-1, the peak dose in the innermost magnet insulator ranges from 20 to 35 MGy. Dynamic heat loads to the triplet magnet cold mass are calculated to evaluate the cryogenic capability. In general, FLUKA and MARS results are in a very good agreement.Comment: 24 p

    Energy Deposition Studies for the Hi-Lumi LHC Inner Triplet Magnets

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    A detailed model of the High Luminosity LHC inner triplet region with new large-aperture Nb3Sn magnets, field maps, corrector packages, and segmented tungsten inner absorbers was built and implemented into the FLUKA and MARS15 codes. In the optimized configuration, the peak power density averaged over the magnet inner cable width is safely below the quench limit. For the integrated luminosity of 3000 fb -1, the peak dose in the innermost magnet insulator ranges from 20 to 35 MGy. Dynamic heat loads to the triplet magnet cold mass are calculated to evaluate the cryogenic capability. In general, FLUKA and MARS results are in a very good agreement.Comment: 4 pp. Presented paper at the 5th International Particle Accelerator Conference, June 15 -20, 2014, Dresden, German

    Direct determination of vibrational density of states change on ligand binding to a protein

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    The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium

    Diffusive Josephson junctions made out of multiwalled carbon nanotubes

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    We have investigated electrical transport in diffusive multiwalled carbon nanotubes (MWNT) contacted using superconducting leads made of Ti/Al/Ti sandwich structure. We measure proximity-induced supercurrents up to Icm = 1.3 nA and find tunability by the gate voltage due to variation of the Thouless energy via the diffusion constant that is controlled by scattering in the MWNT. The modeling of these results by long, diffusive SNS junctions, supplemented with phase diffusion effects is discussed: the agreement between theory and experiments is tested especially on the basis of the temperature dependence of the Josephson coupling energy. In order to prove conclusively that the diffusive model works for MWNT proximity junctions, we propose an improved measurement scheme that is based on the kinetic inductance of superconducting junctions.Peer reviewe

    Equilibrium free energies from fast-switching trajectories with large time steps

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    Jarzynski's identity for the free energy difference between two equilibrium states can be viewed as a special case of a more general procedure based on phase space mappings. Solving a system's equation of motion by approximate means generates a mapping that is perfectly valid for this purpose, regardless of how closely the solution mimics true time evolution. We exploit this fact, using crudely dynamical trajectories to compute free energy differences that are in principle exact. Numerical simulations show that Newton's equation can be discretized to low order over very large time steps (limited only by the computer's ability to represent resulting values of dynamical variables) without sacrificing thermodynamic accuracy. For computing the reversible work required to move a particle through a dense liquid, these calculations are more efficient than conventional fast switching simulations by more than an order of magnitude. We also explore consequences of the phase space mapping perspective for systems at equilibrium, deriving an exact expression for the statistics of energy fluctuations in simulated conservative systems

    MODELLING OF BINARY RADIO TRANSMISSION CHANNELS

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    Tuning of structure inversion asymmetry by the δ\delta-doping position in (001)-grown GaAs quantum wells

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    Structure and bulk inversion asymmetry in doped (001)-grown GaAs quantum wells is investigated by applying the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry (SIA) can be tailored by variation of the delta-doping layer position. Symmetrically-doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position we grow samples with almost equal degrees of structure and bulk inversion asymmetry.Comment: 4 pages 2 figure

    Test Results on the Silicon Pixel Detector for the TTF-FEL Beam Trajectory Monitor

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    Test measurements on the silicon pixel detector for the beam trajectory monitor at the free electron laser of the TESLA test facility are presented. To determine the electronic noise of detector and read-out and to calibrate the signal amplitude of different pixels the 6 keV photons of the manganese K line are used. Two different methods determine the spatial accuracy of the detector: In one setup a laser beam is focused to a straight line and moved across the pixel structure. In the other the detector is scanned using a low-intensity electron beam of an electron microscope. Both methods show that the symmetry axis of the detector defines a straight line within 0.4 microns. The sensitivity of the detector to low energy X-rays is measured using a vacuum ultraviolet beam at the synchrotron light source HASYLAB. Additionally, the electron microscope is used to study the radiation hardness of the detector.Comment: 14 pages (Latex), 13 figures (Postscript), submitted to Nuclear Instruments and Methods

    Spin precession and alternating spin polarization in spin-3/2 hole systems

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    The spin density matrix for spin-3/2 hole systems can be decomposed into a sequence of multipoles which has important higher-order contributions beyond the ones known for electron systems [R. Winkler, Phys. Rev. B \textbf{70}, 125301 (2004)]. We show here that the hole spin polarization and the higher-order multipoles can precess due to the spin-orbit coupling in the valence band, yet in the absence of external or effective magnetic fields. Hole spin precession is important in the context of spin relaxation and offers the possibility of new device applications. We discuss this precession in the context of recent experiments and suggest a related experimental setup in which hole spin precession gives rise to an alternating spin polarization.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
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