Electron energy-loss spectroscopy at incommensurately modulated crystalline and glassy Ba2TiGe2O8

Based on cluster molecular orbital calculations, high-energy resolution (ΔE?～ 0.4?eV) Ti–L_2,3 electron energy loss near-edge structures of single-crystalline and glassy Ba₂TiGe₂O₈ are interpreted. The finding that the Ti–L_2,3 near-edge structure of the Ba₂TiGe₂O₈ single crystal possesses less pronounced peaks than the glass under identical experimental conditions can be attributed to distinct distortions of the titanium environment caused by the very strong one-dimensional structural modulation hosted by the Ba₂TiGe₂O₈ crystal lattice. As lattice periodicity is absent in the glass, the titanium environment is more regular in the vitreous surroundings. Moreover, the modulation in crystalline Ba₂TiGe₂O₈ is responsible for the virtually indiscernible O–K near-edge structures of the glassy and crystalline samples.     

From sum rules to RPA: 2. 3He droplets

We investigate the excitation spectra of closed-shell ³He droplets using a flexible formulation of the RPA which has been presented in preceeding papers. The calculations are based on an energy functional which thorougly employs finite-range interactions. We compare the results for different stages in a hierarchy of approximations to the full RPA. We furthermore discuss the consequences of taking the zero-range limit of the present energy functional, i.e. of using Skyrme-type interactions.     

Toroidal,compression, and vortical dipole strengths in 144-154Sm: Skyrme-RPA exploration of the deformation effect

All transfer reactions and radiative capture nuclear-astrophysical reactions at low energies measured so far are analysed using a reaction theory that contains overlap functions between the wave functions of the target and residual nuclei. These overlaps are assumed to have an asymptotic form determined by the separation energy of the transferred (or radiative captured) cluster and such an assumption is incorporated into all reaction codes. We point out that although this asymptotic form is dominant for the majority of the transfer reactions and the nuclear-astrophysical radiative capture reactions, for some cases the overlap function has anomalous asymptotic behavior. This behavior originates from virtual decays of the complex nucleus into intermediate channels and, mathematically, is generated by contributions from the singularities of the triangle Feynman diagram and the generalised triangle diagram containing a loop. In the present work, these contributions are investigated in detail and expressions are derived for the strengths of the anomalous terms taking spin variables and the Coulomb effects into account. We present specific examples of nuclear vertices with anomalous asymptotics and discuss their application for peripheral nuclear processes.     

Time-asymptotic boson states from infinite mean field quantum systems coupled to the boson gas

By means of cocycle techniques in a recent paper, the global dynamics of mean field-boson couplings has been studied. Here, by restricting to the bosonic system the infinite time limit (t ) for very general initial states, one obtains time-asymptotic states on the bosonicC ^*-Weyl algebra, in which one partially rediscovers the collective ordering of the infinite mean field lattice.     

Tracking X‐ray‐derived redox changes in crystals of a methylamine dehydrogenase/amicyanin complex using single‐crystal UV/Vis microspectrophotometry

X‐ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X‐ray‐derived redox changes in trapped oxidative half‐reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single‐crystal UV/Vis microspectrophotometer was installed on‐line at the BioCARS beamline 14‐BM‐C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X‐ray exposure permitted the creation of a general multi‐crystal data collection strategy to generate true structures of each redox intermediate.     

The low temperature magnetic phase diagram of EuxSr1−xTiO3

Specific heat and magnetization measurements demonstrate that the antiferromagnetic (AFM) phase transition at T _N  = 5.7 K of EuTiO₃ is rapidly suppressed with Sr doping in Eu _x Sr_1?x TiO₃. Close to x = 0.25, T _N  = 0 K and AFM order vanishes. Above this critical concentration a finite transition temperature to an AFM phase is observed. The exchange couplings are derived as a function of x and the corresponding low temperature phase diagram is presented.     

A Preisach-based hysteresis model for magnetic and ferroelectric hysteresis

In this paper we present a model for hysteretic nonlinearities with non-local memories. This model can be applied to describe hysteretic material behavior. Common applications are ferromagnetic or ferroelectric materials. Our model consists of an analytic function and a Preisach operator. We define a continuous Preisach weight function and introduce a method for the identification of the model parameters. The model parameters are customized to a set of symmetric hysteresis curves. We verify our model for a soft magnetic material, a hard magnetic material and the ferroelectric behavior of some piezoelectric material. After that, non-symmetric curves like the virgin curve are predicted very well by the model. It is especially useful, if forced magnetization or polarization, that appears beyond technical saturation, come into account.     

A proof of the bounded graph conjecture

Summary An infinite graph is called bounded if for every labelling of its vertices with natural numbers there exists a sequence of natural numbers which eventually exceeds the labelling along any ray in the graph. We prove an old conjecture of Halin, which characterizes the bounded graphs in terms of four forbidden topological subgraphs.Oblatum 17-IV-1991 & 25-X-1991