676 research outputs found
The bipolaron in the strong coupling limit
The bipolaron are two electrons coupled to the elastic deformations of an
ionic crystal. We study this system in the Fr\"{o}hlich approximation. If the
Coulomb repulsion dominates, the lowest energy states are two well separated
polarons. Otherwise the electrons form a bound pair. We prove the validity of
the Pekar-Tomasevich energy functional in the strong coupling limit, yielding
estimates on the coupling parameters for which the binding energy is strictly
positive. Under the condition of a strictly positive binding energy we prove
the existence of a ground state at fixed total momentum , provided is
not too large.Comment: 31 page
Epitaxial ferromagnetic FeSi/Si(111) structures with high-quality hetero-interfaces
To develop silicon-based spintronic devices, we have explored high-quality
ferromagnetic FeSi/silicon (Si) structures. Using low-temperature
molecular beam epitaxy at 130 C, we realize epitaxial growth of
ferromagnetic FeSi layers on Si (111) with keeping an abrupt interface,
and the grown FeSi layer has the ordered phase. Measurements of
magnetic and electrical properties for the FeSi/Si(111) yield a magnetic
moment of ~ 3.16 /f.u. at room temperature and a rectifying
Schottky-diode behavior with the ideality factor of ~ 1.08, respectively.Comment: 3 pages, 3 figure
Momentum operators with a winding gauge potential
Considered is a quantum system of N(?:_ 2) charged particles moving in the plane R2 under the influence of a perpendicular magnetic field. Each particle feels the magnetic field concenrated in the positions of the other particles. The gauge potential which gives this magnetic field is called a winding gauge potential. Properties of the momentum operators with the winding gauge potential are investigated. The momentum operators with the winding gauge potential are represented by the fibre direct integral of Arni's momentum operators [1]. Using this fibre direct integral decomposition, commutation properties of the momentum operators are investigated. A notion of local quantization of the magnetic flux is introduced to characterize the strong commutativity of the momentum operators. Aspects of the representation of the canonical commutation relations (CCR) are discussed. There is an interesting relation between the representation of the CCR with respect to this system and Arni's representation. Some applications of those results are also discussed
Strongry supercommuting serf-adjoint operators
We introduce the notion of strong supercommutativity of self-adjoint operators on a Z2-graded Hilbert space and give some basic properties. We clarify that strong supercommutativity is a unification of strong commutativity and strong anticommutativity. We also establish the theory of super quantization. Applications to supersymmetric quantum field theory and a fermion-boson interaction system are discussed
Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of CoFeSi and FeSi
We study room-temperature generation and detection of pure spin currents
using lateral spin-valve devices with Heusler-compound electrodes, CoFeSi
(CFS) or FeSi (FS). The magnitude of the nonlocal spin-valve (NLSV)
signals is seriously affected by the dispersion of the resistivity peculiarly
observed in the low-temperature grown Heusler compounds with ordered
structures. From the analysis based on the one-dimensional spin diffusion
model, we find that the spin polarization monotonically increases with
decreasing the resistivity, which depends on the structural ordering, for both
CFS and FS electrodes, and verify that CFS has relatively large spin
polarization compared with FS.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. B (Rapid
communication
Development of a dose distribution shifter to fit inside the collimator of a Boron Neutron Capture Therapy irradiation system to treat superficial tumours
The Kansai BNCT Medical Center has a cyclotron based epithermal neutron source for clinical Boron Neutron Capture Therapy. The system accelerates a proton to an energy of 30 MeV which strikes a beryllium target producing fast neutrons which are moderated down to epithermal neutrons for BNCT use. While clinical studies in the past have shown BNCT to be highly effective for malignant melanoma of the skin, to apply BNCT for superficial lesions using this system it is necessary to shift the thermal neutron distribution so that the maximum dose occurs near the surface. A dose distribution shifter was designed to fit inside the collimator to further moderate the neutrons to increase the surface dose and reduce the dose to the underlying normal tissue. Pure polyethylene was selected, and a Monte Carlo simulation was performed to determine the optimum thickness of the polyethylene slab. Compared with the original neutron beam, the shifter increased the thermal neutron flux at the skin by approximately 4 times. The measured and simulated central axis depth distribution and off axis distribution of the thermal neutron flux were found to be in good agreement. Compared with a 2 cm thick water equivalent bolus, a 26% increase in the thermal neutron flux at the surface was obtained, which would reduce the treatment time by approximately 29%. The DDS is a safe, simple and an effective tool for the treatment of superficial tumours for BNCT if an initially fast neutron beam requires moderation to maximise the thermal neutron flux at the tissue surface
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