5,145 research outputs found
Photoassociation spectra and the validity of the dipole approximation for weakly bound dimers
Photoassociation (PA) of ultracold metastable helium to the 2s2p manifold is
theoretically investigated using a non-perturbative close-coupled treatment in
which the laser coupling is evaluated without assuming the dipole
approximation. The results are compared with our previous study [Cocks and
Whittingham, Phys. Rev. A 80, 023417 (2009)] that makes use of the dipole
approximation. The approximation is found to strongly affect the PA spectra
because the photoassociated levels are weakly bound, and a similar impact is
predicted to occur in other systems of a weakly bound nature. The inclusion or
not of the approximation does not affect the resonance positions or widths,
however significant differences are observed in the background of the spectra
and the maximum laser intensity at which resonances are discernable. Couplings
not satisfying the dipole selection rule |J-1| <= J' <= |J+1| do not lead to
observable resonances.Comment: 5 pages, 2 figures; Minor textual revision
Exotic solutions in string theory
Solutions of classical string theory, correspondent to the world sheets,
mapped in Minkowsky space with a fold, are considered. Typical processes for
them are creation of strings from vacuum, their recombination and annihilation.
These solutions violate positiveness of square of mass and Regge condition. In
quantum string theory these solutions correspond to physical states |DDF>+|sp>
with non-zero spurious component.Comment: accepted in Il Nuovo Cimento A for publication in 199
Viscous tilting and production of vorticity in homogeneous turbulence
Viscous depletion of vorticity is an essential and well known property of turbulent flows, balancing, in the mean, the net vorticity production associated with the vortex stretching mechanism. In this letter, we, however, demonstrate that viscous effects are not restricted to a mere destruction process, but play a more complex role in vorticity dynamics that is as important as vortex stretching. Based on the results from three dimensional particle tracking velocimetry experiments and direct numerical simulation of homogeneous and quasi-isotropic turbulence, we show that the viscous term in the vorticity equation can also locally induce production of vorticity and changes of the orientation of the vorticity vector (viscous tilting)
Dispersion Characteristics of Spin-Electromagnetic Waves in Planar Multiferroic Structures with Coplanar Transmission Line
Introduction. The distinctive feature of a coplanar transmission line with thin ferrite and ferroelectric films is the absence of undesirable irregularities in dispersion for relatively low frequencies when the wavelength approaches the thickness of ferroelectric layer, in contrast to the open ferrite-ferroelectric wave-guiding structure without metallization.Aim. The purpose of this paper is twofold: (i) to develop a theory of the wave spectra in the multiferroic structures based on the coplanar lines; (ii) using this theory to find ways to enhance the electric tuning range.Materials and methods. The dispersion relation for spin-electromagnetic waves was derived through analytical solution of the full set of the Maxwell's equations utilizing a method of approximate boundary conditions.Results. A theory of spin-electromagnetic wave spectrum has been developed for the thin-film ferrite-ferroelectric structure based on a coplanar transmission line. According to this theory, dispersion characteristics of the spin-electromagnetic waves were described and analyzed for different parameters of the structure. The obtained results show that the investigated structure demonstrates a dual electric and magnetic field tunability of wave spectra. Its efficiency increases with an increase in the thicknesses of the ferrite and ferroelectric films and with a decrease in the width of the central metal strip.Conclusion. The distinctive features of the proposed coplanar waveguides are the thin-film planar topology and dual tunability of the wave spectra. All these advantages make the proposed structures perspective for development of new microwave devices.Introduction. The distinctive feature of a coplanar transmission line with thin ferrite and ferroelectric films is the absence of undesirable irregularities in dispersion for relatively low frequencies when the wavelength approaches the thickness of ferroelectric layer, in contrast to the open ferrite-ferroelectric wave-guiding structure without metallization.Aim. The purpose of this paper is twofold: (i) to develop a theory of the wave spectra in the multiferroic structures based on the coplanar lines; (ii) using this theory to find ways to enhance the electric tuning range.Materials and methods. The dispersion relation for spin-electromagnetic waves was derived through analytical solution of the full set of the Maxwell's equations utilizing a method of approximate boundary conditions.Results. A theory of spin-electromagnetic wave spectrum has been developed for the thin-film ferrite-ferroelectric structure based on a coplanar transmission line. According to this theory, dispersion characteristics of the spin-electromagnetic waves were described and analyzed for different parameters of the structure. The obtained results show that the investigated structure demonstrates a dual electric and magnetic field tunability of wave spectra. Its efficiency increases with an increase in the thicknesses of the ferrite and ferroelectric films and with a decrease in the width of the central metal strip.Conclusion. The distinctive features of the proposed coplanar waveguides are the thin-film planar topology and dual tunability of the wave spectra. All these advantages make the proposed structures perspective for development of new microwave devices
Relativistic Coulomb problem for particles with arbitrary half-integer spin
Using relativistic tensor-bispinorial equations proposed in hep-th/0412213 we
solve the Kepler problem for a charged particle with arbitrary half-integer
spin interacting with the Coulomb potential.Comment: Misprints are correcte
Superconductivity and magnetic order in the non-centrosymmetric Half Heusler compound ErPdBi
We report superconductivity at K and magnetic order at K in the semi-metallic noncentrosymmetric Half Heusler compound ErPdBi.
The upper critical field, , has an unusual quasi-linear temperature
variation and reaches a value of 1.6 T for . Magnetic order is
found below and is suppressed at T for . Since , the interaction of superconductivity and magnetism
is expected to give rise to a complex ground state. Moreover, electronic
structure calculations show ErPdBi has a topologically nontrivial band
inversion and thus may serve as a new platform to study the interplay of
topological states, superconductivity and magnetic order.Comment: 6 pages, 5 figures; accepted for publication in Europhysics Letter
New characterization based symmetry tests
Two new symmetry tests, of integral and Kolmogorov type, based on the
characterization by squares of linear statistics are proposed.
The test statistics are related to the family of degenerate U-statistics.
Their asymptotic properties are explored. The maximal eigenvalue, needed for
the derivation of their logarithmic tail behavior, was calculated or
approximated using techniques from the theory of linear operators and the
perturbation theory.
The quality of the tests is assessed using the approximate Bahadur efficiency
as well as the simulated powers. The tests are shown to be comparable with some
recent and classical tests of symmetry
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