Sum rules in x-ray resonant Raman scattering: recovering the Co ground state information in CoFe2O4 as a test case

We present an approach to x-ray resonant Raman scattering suitable for sum-rule analysis. In magnetic systems it gives ground state information as represented by an expansion in coupled multipoles of orbital and spin moments. The experiment is based on the angular dependence of the integrated peak intensities. In 3d transition elements one obtains information up to order 4 from the channel 2p(6)3d(n)-->2p(5)3d(n+1)-->2p(6)3s(1)3d(n+1). By combining these results with L(2,3) absorption dichroism, we show quantitatively the atomiclike properties of cobalt in CoFe2O4 up to high-order multipoles.     

Electron correlation effects in the valence band photoemission spectra of cooper dichloride

He I, He II and Al Kα photoemission measurements of the valence band of CuCl₂ are reported. The presence of the 3d⁸-like satellite indicates the strong correlation effects in the final state and the breakdown of the one-particle model. It is shown that the reduction of the satellite intensity in the valence band compared with the core hole emission is caused by the delocalization of the photo-hole. The satellite intensity in resonance with the super-Coster-Kronig decay is calculated.     

An improvement of fixed point algorithms by using a good triangulation

We consider measures for triangulations ofR ⁿ. A new measure is introduced based on the ratio of the length of the sides and the content of the subsimplices of the triangulation. In a subclass of triangulations, which is appropriate for computing fixed points using simplicial subdivisions, the optimal one according to this measure is calculated and some of its properties are given. It is proved that for the average directional density this triangulation is optimal (within the subclass) asn goes to infinity. Furthermore, we compare the measures of the optimal triangulation with those of other triangulations. We also propose a new triangulation of the affine hull of the unit simplex. Finally, we report some computational experience that confirms the theoretical results.     

Optimal balanced control for call centers

In this paper we study the optimal assignment of tasks to agents in a call center. For this type of problem, typically, no single deterministic and stationary (i.e., state independent and easily implementable) policy yields the optimal control, and mixed strategies are used. Other than finding the optimal mixed strategy, we propose to optimize the performance over the set of ??balanced?? deterministic periodic non-stationary policies. We provide a stochastic approximation algorithm that allows to find the optimal balanced policy by means of Monte Carlo simulation. As illustrated by numerical examples, the optimal balanced policy outperforms the optimal mixed strategy.     

Polarized X-ray absorption study of Bi2Sr2CuO6 and Bi2Sr2CaCu2O8

Polarization dependent X-ray absorption measurements on single crystal Bi₂Sr₂CuO₆ (T _c =9 K) and Bi₂Sr₂CaCu₂O₈ (T _c =80 K) with one and two CuO₂ layers, respectively, show no energy shift of the Cu 2p main peak, and no relation between the amount of 3d(m=0, ±1) character and the critical temperatureT _c . At grazing incidence a structure in Bi₂Sr₂CaCu₂O₈ is found at 937 eV, which can be ascribed to a composite state of Cu 3d(z ²), Cu 4s ando–2p(z).     

On the existence and approximation of zeroes

In this paper we consider the problem of finding zeroes of a continuous functionf from a convex, compact subsetU of ℝ ⁿ to ℝ ⁿ . In the first part of the paper it is proved thatf has a computable zero iff:C ⁿ →ℝ ⁿ satisfies the nonparallel condition for any two antipodal points on bdC ⁿ, i.e. if for anyx∈bdC ⁿ ,f(x)≠αf(−x), α≥0, holds. Therefore we describe a simplicial algorithm to approximate such a zero. It is shown that generally the degree of the approximate zero depends on the number of reflection steps made by the algorithm, i.e. the number of times the algorithm switches from a face τ on bdC ⁿ to the face −τ. Therefore the index of a terminal simplex σ is defined which equals the local Brouwer degree of the function if σ is full-dimensional. In the second part of the paper the algorithm is used to generate possibly several approximate zeroes off. Two sucessive solutions may have both the same or opposite degrees, again depending on the number of reflection steps. By extendingf:U→ℝ ⁿ to a function g from a cube containingU to ℝ ⁿ , the procedure can be applied to any continuous functionf without having any information about the global and local Brouwer degrees a priori.     

Angle-dependent Ni2+ X-ray magnetic linear dichroism: interfacial coupling revisited

Using x-ray magnetic linear dichroism (XMLD) for magnetometry requires detailed knowledge of its dependence on the relative orientation of polarization, magnetic moments, and crystallographic axes. We show that Ni2+ L(2,3) XMLD in cubic lattices has to be described as a linear combination of two fundamental spectra--not one as previously assumed. The spectra are calculated using atomic multiplet theory and the angular dependence is derived from crystal field symmetry. Applying our results to Co/NiO(001) interfaces, we find perpendicular coupling between Ni and Co moments.     

Element-specific magnetocrystalline anisotropy energy studied by transverse magnetic circular X-ray dichroism

The magnetocrystalline anisotropy energy in 3d transition metal systems is related to the spin-subband orbital moments and the magnetic dipole operator which accounts for the spin-flip excitations. Magnetic circular X-ray dichroism measurements in a transverse geometry, where the light helicity is perpendicular to the magnetization direction, make it feasible to determine the easy-axis of magnetization.