28,631 research outputs found
Dynamic polarizabilities and related properties of clock states of ytterbium atom
We carry out relativistic many-body calculations of the static and dynamic
dipole polarizabilities of the ground 6s^2 ^1S_0 and the first excited states of Yb. With these polarizabilities, we compute several
properties of Yb relevant to optical lattice clocks operating on the 6s^2
^1S_0 - 6s6p ^3P^o_0 transition. We determine (i) the first four {\em magic}
wavelengths of the laser field for which the frequency of the clock transition
is insensitive to the laser intensity. While the first magic wavelength is
known, we predict the second, the third and the forth magic wavelengths to be
551 nm, 465 nm, and 413 nm. (ii) We reevaluate the effect of black-body
radiation on the frequency of the clock transition, the resulting clock shift
at being Hz. (iii) We compute long-range
interatomic van der Waals coefficients (in a.u.) C_6(6s^2 ^1S_0 +6s^2 ^1S_0) =
1909(160), C_6(6s^2 ^1S_0 + 6s6p ^3P_0) =2709(338) , and . Finally, we determine the atom-wall interaction
coefficients (in a.u.), C_3 (6s^2 ^1S_0) =3.34 and .
We also address and resolve a disagreement between previous calculations of the
static polarizability of the ground state.Comment: 11 pages, 1 figur
Pre-K-Edge Structure on Anomalous X-Ray Scattering in LaMnO3
We study the pre-K-edge structure of the resonant X-ray scattering for
forbidden reflections (anomalous scattering) in LaMnO3, using the band
calculation based on the local density approximation. We find a two-peak
structure with an intensity approximately 1/100 of that of the main peak. This
originates from a mixing of 4p states of Mn to 3d states of neighboring Mn
sites. The effect is enhanced by an interference with the tail of the main
peak. The effect of the quadrupole transition is found to be one order of
magnitude smaller than that of the dipole transition, modifying slightly the
azimuthal-angle dependence.Comment: 4 pages, 5 figures, submitted to J. Phys. Soc. Jp
Proximity-driven source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor voltage-biased Josephson junction
We theoretically investigate an opportunity to implement a source of highly
spin-polarized ac current on the basis of superconductor/weak
ferromagnet/superconductor (SFS) voltage-biased junction in the regime of
essential proximity effect and calculate the current flowing through the probe
electrode tunnel coupled to the ferromagnetic interlayer region. It is shown
that while the polarization of the dc current component is generally small in
case of weak exchange field of the ferromagnet, there is an ac component of the
current in the system. This ac current is highly spin-polarized and entirely
originated from the non-equilibrium proximity effect in the interlayer. The
frequency of the current is controlled by the voltage applied to SFS junction.
We discuss a possibility to obtain a source of coherent ac currents with a
certain phase shift between them by tunnel coupling two probe electrodes at
different locations of the interlayer region.Comment: 8 pages, 5 figure
Atomistic Simulations of Metallic Cluster Coalescence
A new computational method is introduced to investigate the stresses developed in the island-coalescence stage of polycrystalline film formation during deposition. The method uses molecular dynamics to examine the behavior of clusters of atoms both in free space and on substrates. Continuum treatments used in previous models may not be applicable at small length scales or low dimensionality. In atomistic simulations, the effects of surface diffusion, bond straining and defect formation can be directly studied. TEM experiments will be used to evaluate the validity of the simulation model.Singapore-MIT Alliance (SMA
The oscillation effects on thermalization of the neutrinos in the universe with low reheating temperature
We study how the oscillations of the neutrinos affect their thermalization
process during the reheating period with temperature O(1) MeV in the early
universe. We follow the evolution of the neutrino density matrices and
investigate how the predictions of big bang nucleosynthesis vary with the
reheating temperature. For the reheating temperature of several MeV, we find
that including the oscillations makes different predictions, especially for
He abundance. Also, the effects on the lower bound of the reheating
temperature from cosmological observations are discussed.Comment: 24 pages, 8 figures; references and explanatory comments added,
conclusion unchange
Metallic Cluster Coalescence: Molecular Dynamics Simulations of Boundary Formation
During the evaporative deposition of polycrystalline thin films, the development of a tensile stress at small film thicknesses is associated with island coalescence. Several continuum models exist to describe the magnitude of this tensile stress but the coalescence stress becomes significant at small enough thicknesses to draw the continuum models into question. For nanometer-sized islands, we perform atomistic simulations of island coalescence to determine if the atomistic methods and continuum models are mutually consistent. The additional detail provided by the atomistic simulations allows for study of the kinetics of island coalescence and the treatment of different crystallographic orientations. We find that the atomistic simulations are consistent with the continuum models. We also note that the atomistic simulations predict extremely fast coalescence times and include the possibility of island rotations during coalescence.Singapore-MIT Alliance (SMA
A magnetic nozzle calculation of the force on a plasma
The measured axial force imparted from a magnetically expanding current-free plasma has been shown recently [Takahashi, Phys. Rev. Lett. 107, 235001 (2011)] to equal the axial force on that plasma calculated by a two-dimensional fluid model. Here, we calculate the same axial force on the plasma by a quasi one-dimensional model of a magnetic nozzle. The quasi one-dimensional magnetic nozzle model provides us with an estimate of the force on the plasma that is similar to that found by the more accurate two-dimensional model.This research has been partially supported by the Israel
Science Foundation (Grants 864/07 and 765/11)
Exact solution of a one-dimensional continuum percolation model
I consider a one dimensional system of particles which interact through a
hard core of diameter \si and can connect to each other if they are closer
than a distance . The mean cluster size increases as a function of the
density until it diverges at some critical density, the percolation
threshold. This system can be mapped onto an off-lattice generalization of the
Potts model which I have called the Potts fluid, and in this way, the mean
cluster size, pair connectedness and percolation probability can be calculated
exactly. The mean cluster size is S = 2 \exp[ \rho (d -\si)/(1 - \rho \si)] -
1 and diverges only at the close packing density \rho_{cp} = 1 / \si . This
is confirmed by the behavior of the percolation probability. These results
should help in judging the effectiveness of approximations or simulation
methods before they are applied to higher dimensions.Comment: 21 pages, Late
Spin wave dispersion in La2CuO4
We calculate the antiferromagnetic spin wave dispersion in the half-filled
Hubbard model for a two-dimensional square lattice and find it to be in
excellent agreement with recent high-resolution inelastic neutron scattering
performed on La2CuO4 [Phys. Rev. Lett. 86, 5377 (2001)].Comment: typos correcte
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