Outstanding spin-orbit-activated interchannel coupling in the Cs and Ba 3d photoemission

Partial 3d5/2 photoionization cross sections of atomic Cs and Ba as well as the asymmetry parameter beta of the angular distribution of the Cs 3d5/2 photoelectrons were investigated near the threshold of the 3d3/2 channel at about 750 eV and 800 eV, respectively. Strong electron correlations, in particular, the spin-orbit activated interchannel coupling between the 3d5/2 and 3d3/2 channels, govern the observed spectra. The most striking effect was found for beta5/2 of Cs with a dramatic increase from beta=1.0 to beta=1.5 in the energy region where the mixing between both channels causes a pronounced minimum in the partial 3d5/2 cross section. This result indicates the decisive influence of the interference term on the asymmetry parameter beta with its dependence on the phase difference between the outgoing p and f waves.     

Etude d'impulsions lumineuses breves par interferometrie a deux ondes

We have studied the evolution of the light transmitted through matter in which an optical breakdown is taking place. With a two-waves interferometer made a birefringent plate between polarizers we get informations about the time correlation function of the fields. With an interferometer made of two identical harmonic generating plates separated by a dispersion medium, we learn about the correlation function of the square of the fields. Both systems act as spectral filters with a notch cosine-shaped centered at the incident frequency. We have also observed a transient angular spreading of the beam not previously emphasized which brings a further complication in the picture.     

Single-ion approach to the susceptibility of an intermediate valence compound paramagnetic Imse

The magnetic properties of an intermediate valence compound are discussed within a single-ion framework. The effects of configuration mixing, crystalline electric fields, and external magnetic fields are included in the hamiltonian. The method incorporates in one single consistent approach both coherent (quantum) and incoherent (thermal) fluctuations. Numerical evaluation of the susceptibility and field dependent magnetization with parameters appropriate for TmSe yields results in good agreement with experiment.     

On the convergence of the Zassenhaus formula

The domain of convergence of the Zassenhaus formula in a Banach algebra is studied. This domain is shown to be strictly larger than the one which was already known.     

Structural and magnetic phase transitions in Pr2NiO4

Neutron powder diffraction and magnetization measurements have been performed in stoichiometric Pr₂NiO₄₊(0), which at room temperature (RT) is orthorhombic (Bmab). Ni²⁺ becomes three dimensionally (3D) antiferromagnetically ordered atT _N 325K, with a propagation vectork=[100], and spins oriented along thea axis (parallel to the propagation vector). The magnetic structure belongs to the _7g (––+)-representation (g _x mode, Shubnikov groupB _pmab') ofBmab, and a magnetic moment of 1.5 _B is measured at 155K. This compound undergoes two different structural phase transitions. First, going down in temperature, Pr₂NiO₄ transforms by a first order phase transition from orthorhombic (Bmab) to tetragonal (P4₂/ncm) atT _c1115K. At high temperature, we can predict a transformation from orthorhombic (Bmab) to tetragonal (I4/mmm) in a continuous way. The extrapolated temperature for this second structural transition isT _c21500±100K. The low temperature structural transformation allows a change in the magnetic structure which forT<T _c1 is better described in the orthorhombic symmetry. Just belowT _c1 the magnetic structure is described by the: _3g (–+)-representation ofPccn(g_xc_yf_z mode, Shubnikov groupPccn), this magnetic phase begins to disappear going down in temperature and at the same time a new magnetic phase grows. This new magnetic structure is described by the _1g ofPccn (c _xg_ya_z mode, Shubnikov groupPccn). Both magnetic structures coexist in a certain temperature range. At 1.5 K thec _xg_ya_z mode represents the total of the magnetic ordering. To reproduce the observed magnetic intensities we are forced to consider that Pr³⁺ is polarized below 40 K, with a magnetic structure which is coupled to the Ni sublattices (i.e. _1g and _3g ). The magnetic moment at low temperature for Pr is about 1.28 _B .     

Characterization of Trimmed NURBS Surface Boundaries Using Topological Criteria

This paper presents an approach based on topology for the determination of characteristics and properties of curves used in the trimming of NURBS surfaces. Through discrete subdivision and topological criteria, a method is presented to determine characteristics of the boundary; such as whether the set of trimming curves forms a set of closed loops, whether trimming curves contain singularities or self intersections, and whether the boundary is simply connected. A surface mesh partitionning the parameter space is used, formed of isoparametric lines in both parametric directions. Topological properties of the cells of this mesh and their intersections with the trimming curves allow to localize the boundary. Topological treatment of this localization allows to define the interior and exterior of the face, and to refine the boundary localization. Singularities and self intersections of the boundary as well as voids in the face are investigated through the study of topological properties of neighbors. As an application, an algorithm for point localization is presented that very rapidly allows to determine whether a given point in parameter space lies inside, on the boundary or outside of the trimmed surface.     

57Fe Mössbauer investigation of the ternary hydride Pd3FeHx

Ordered alloys of Pd₃Fe are shown to readily absorbe hydrogen through electrolytic loading. The resultant ternary hydride phase is observed to retain the fcc structure of Pd₃Fe with approximately the same lattice constant. The ⁵⁷Fe hyperfine field determined by Mössbauer spectroscopy is found to be 30% smaller in the hydride compared to Pd₃Fe. The reduction appears to be associated with a perturbation of the Pd moment by hydrogen. The results suggest the occupation of one type of interstitial site in the structure. The absence of the site in disordered Pd₃Fe would explain the much smaller hydrogen capacity observed for this alloy.