68,740 research outputs found
Core-valence correlations for atoms with open shells
We present an efficient method of inclusion of the core-valence correlations
into the configuration interaction (CI) calculations. These correlations take
place in the core area where the potential of external electrons is
approximately constant. A constant potential does not change the core electron
wave functions and Green's functions. Therefore, all operators describing
interaction of valence electrons and core electrons (the core part of
the Hartree-Fock Hamiltonian
, the correlation potential and
the screening of interaction between valence electrons by the core electrons
) may be calculated with all
valence electrons removed. This allows one to avoid subtraction diagrams
which make accurate inclusion of the core-valence correlations for
prohibitively complicated. Then the CI Hamiltonian for valence electrons is
calculated using orbitals in complete potential (the mean field
produced by all electrons); + are added to the CI
Hamiltonian to account for the core-valence correlations. We calculate
and using many-body perturbation theory in which
dominating classes of diagrams are included in all orders.
We use neutral Xe I and all positive ions up to Xe VIII as a testing ground.
We found that the core electron density for all these systems is practically
the same. Therefore, we use the same and to build
the CI Hamiltonian in all these systems (). Good agreement
with experiment for energy levels and Land\'{e} factors is demonstrated for all
cases from Xe I to Xe VIII.Comment: 13 pages, 5 figure
Interelectronic-interaction effect on the transition probability in high-Z He-like ions
The interelectronic-interaction effect on the transition probabilities in
high-Z He-like ions is investigated within a systematic quantum electrodynamic
approach. The calculation formulas for the interelectronic-interaction
corrections of first order in 1/Z are derived using the two-time Green function
method. These formulas are employed for numerical evaluations of the magnetic
transition probabilities in heliumlike ions. The results of the calculations
are compared with experimental values and previous calculations
Electron-impact excitation of X 1Sigma<sub>g</sub><sup>+</sup>(v[double-prime]=0) to the a[double-prime] 1Sigma<sub>g</sub><sup>+</sup>, b 1Piu, c3 1Piu, o3 1Piu, b[prime] 1Sigma<sub>u</sub><sup>+</sup>, c<sub>4</sub><sup>[prime]</sup> 1Sigma<sub>u</sub><sup>+</sup>, G 3Piu, and F 3Piu states of molecular nitrogen
Measurements of differential cross sections (DCSs) for electron-impact excitation of the a[double-prime] 1Sigmag+, b 1Piu, c3 1Piu, o3 1Piu, b[prime] 1Sigmau+, c4[prime] 1Sigmau+, G 3Piu, and F 3Piu states in N2 from the X 1Sigmag+(v[double-prime]=0) ground level are presented. The DCSs were obtained from energy-loss spectra in the region of 12 to 13.82 eV measured at incident energies of 17.5, 20, 30, 50, and 100 eV and for scattering angles ranging from 2° to 130°. The analysis of the spectra follows a different algorithm from that employed in a previous study of N2 for the valence states [Khakoo et al. Phys. Rev. A 71, 062703 (2005)], since the 1Piu and 1Sigmau+ states form strongly interacting Rydberg-valence series. The results are compared with existing data
Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium
Experiments with acoustic waves guided along the mechanically free surface of
an unconsolidated granular packed structure provide information on the
elasticity of granular media at very low pressures that are naturally
controlled by the gravitational acceleration and the depth beneath the surface.
Comparison of the determined dispersion relations for guided surface acoustic
modes with a theoretical model reveals the dependencies of the elastic moduli
of the granular medium on pressure. The experiments confirm recent theoretical
predictions that relaxation of the disordered granular packing through
non-affine motion leads to a peculiar scaling of shear rigidity with pressure
near the jamming transition corresponding to zero pressure. Unexpectedly, and
in disagreement with the most of the available theories, the bulk modulus
depends on pressure in a very similar way to the shear modulus
String Theory and Water Waves
We uncover a remarkable role that an infinite hierarchy of non-linear
differential equations plays in organizing and connecting certain {hat c}<1
string theories non-perturbatively. We are able to embed the type 0A and 0B
(A,A) minimal string theories into this single framework. The string theories
arise as special limits of a rich system of equations underpinned by an
integrable system known as the dispersive water wave hierarchy. We observe that
there are several other string-like limits of the system, and conjecture that
some of them are type IIA and IIB (A,D) minimal string backgrounds. We explain
how these and several string-like special points arise and are connected. In
some cases, the framework endows the theories with a non-perturbative
definition for the first time. Notably, we discover that the Painleve IV
equation plays a key role in organizing the string theory physics, joining its
siblings, Painleve I and II, whose roles have previously been identified in
this minimal string context.Comment: 49 pages, 4 figure
Electron spin resonance investigation of Mn^{2+} ions and their dynamics in manganese doped SrTiO_3
Using electron spin resonance, lattice position and dynamic properties of
Mn2+ ions were studied in 0.5 and 2 % manganese doped SrTiO3 ceramics prepared
by conventional mixed oxide method. The measurements showed that Mn2+ ions
substitute preferably up to 97 % for Sr if the ceramics is prepared with a
deficit of Sr ions. Motional narrowing of the Mn2+ ESR spectrum was observed
when temperature increases from 120 K to 240-250 K that was explained as a
manifestation of off-center position of this ion at the Sr site. From the
analysis of the ESR spectra the activation energy Ea = 86 mV and frequency
factor 1/?0 ? (2-10)x10^(-14) 1/s for jumping of the impurity between
symmetrical off-center positions were determined. Both values are in agreement
with those derived previously from dielectric relaxation. This proves the
origin of dielectric anomalies in SrTiO3:Mn as those produced by the
reorientation dynamics of Mn2+ dipoles.Comment: 16 pages, 6 figure
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