Short-range charge-order in RRNiO3_{3} perovskites (RR=Pr,Nd,Eu) probed by X-ray absorption spectroscopy

The short-range organization around Ni atoms in orthorhombic $R$NiO$_{3}$ ($R$=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni K-edge x-ray absorption spectroscopy. Our results demonstrate that two different Ni sites, with different average Ni-O bond lengths, coexist in those orthorhombic compounds and that important modifications in the Ni nearest neighbors environment take place across the metal-insulator transition. We report evidences for the existence of short-range charge-order in the insulating state, as found in the monoclinic compounds. Moreover, our results suggest that the two different Ni sites coexists even in the metallic state. The coexistence of two different Ni sites, independently on the $R$ ion, provides a common ground to describe these compounds and shed new light in the understanding of the phonon-assisted conduction mechanism and unusual antiferromagnetism present in all $R$NiO$_{3}$ compounds.Comment: 4 pages, 3 figures, accepted PRB - Brief Report Dec.200

Spin-orbit induced mixed-spin ground state in RRNiO3_3 perovskites probed by XAS: new insight into the metal to insulator transition

We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L$_{3}$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$ perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200

Differences in decision-making behavior between elite and amateur team-handball players in a near-game test situation

Athletic features distinguishing experts from non-experts in team sports are relevant for performance analyses, talent identification and successful training. In this respect, perceptual-cognitive factors like decision making have been proposed to be important predictor of talent but, however, assessing decision making in team sports remains a challenging endeavor. In particular, it is now known that decisions expressed by verbal reports or micro-movements in the laboratory differ from those actually made in on-field situations in play. To address this point, our study compared elite and amateur players' decision-making behavior in a near-game test environment including sport-specific sensorimotor responses. Team-handball players (N = 44) were asked to respond as quickly as possible to representative, temporally occluded attack sequences in a team-handball specific defense environment on a contact plate system. Specifically, participants had to choose and perform the most appropriate out of four prespecified, defense response actions. The frequency of responses and decision time were used as dependent variables representing decision-making behavior. We found that elite players responded significantly more often with offensive responses (p < 0.05, odds ratios: 2.76-3.00) in left-handed attack sequences. Decision time decreased with increasing visual information, but no expertise effect was found. We suppose that expertise-related knowledge and processing of kinematic information led to distinct decision-making behavior between elite and amateur players, evoked in a domain-specific and near-game test setting. Results also indicate that the quality of a decision might be of higher relevance than the required time to decide. Findings illustrate application opportunities in the context of performance analyses and talent identification processes

Performance of soil-matrix composite reinforced with recycled shredded fibers from waste tires

Abstract Some experimental results concerning the performance of fiber-reinforced soil composites made of soil and shredded fibers from waste tires are presented. The composite mixtures were prepared with fiber addition of 0, 15, 30, and 45 wt%. After molding, the specimens were oven-dried and tested for unconfined compressive strength and water immersion durability. The results showed an improvement in durability with the addition of fiber. The results also indicated good compressive strength performance for the composites with a fiber content of 15 and 30 wt%. The 30 wt% fiber addiction was the best choice because of the environmental sustainability appeal to solid waste reduction

Inhibition of DNA replication fork progression and mutagenic potential of 1, N6-ethenoadenine and 8-oxoguanine in human cell extracts

Comparative mutagenesis of 1,N6-ethenoadenine (εA) and 8-oxoguanine (8-oxoG), two endogenous DNA lesions that are also formed by exogenous DNA damaging agents, have been evaluated in HeLa and xeroderma pigmentosum variant (XPV) cell extracts. Two-dimensional gel electrophoresis of the duplex M13mp2SV vector containing these lesions established that there was significant inhibition of replication fork movement past εA, whereas 8-oxoG caused only minor stalling of fork progression. In extracts of HeLa cells, εA was weakly mutagenic inducing all three base substitutions in approximately equal frequency, whereas 8-oxoG was 10-fold more mutagenic inducing primarily G→T transversions. These data suggest that 8-oxoG is a miscoding lesion that presents a minimal, if any, block to DNA replication in human cells. We hypothesized that bypass of εA proceeded principally by an error-free mechanism in which the undamaged strand was used as a template, since this lesion strongly blocked fork progression. To examine this, we determined the sequence of replication products derived from templates in which a G was placed across from the εA. Consistent with our hypothesis, 93% of the progeny were derived from replication of the undamaged strand. When translesion synthesis occurred, εA→T mutations increased 3-fold in products derived from the mismatched εA: G construct compared with those derived from the εA: T construct. More efficient repair of εA in the εA: T construct may have been responsible for lower mutation frequency. Primer extension studies with purified pol η have shown that this polymerase is highly error-prone when bypassing εA. To examine if pol η is the primary mutagenic translesion polymerase in human cells, we determined the lesion bypass characteristics of extracts derived from XPV cells, which lack this polymerase. The εA: T construct induced εA→G and εA→C mutant frequencies that were approximately the same as those observed using the HeLa extracts. However, εA→T events were increased 5-fold relative to HeLa extracts. These data support a model in which pol η-mediated translesion synthesis past this adduct is error-free in the context of semiconservative replication in the presence of fidelity factors such as PCNA

A combined XAS and XRD Study of the High-Pressure Behaviour of GaAsO4 Berlinite

Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments have been carried out on GaAsO4 (berlinite structure) at high pressure and room temperature. XAS measurements indicate four-fold to six-fold coordination changes for both cations. The two local coordination transformations occur at different rates but appear to be coupled. A reversible transition to a high pressure crystalline form occurs around 8 GPa. At a pressure of about 12 GPa, the system mainly consists of octahedral gallium atoms and a mixture of arsenic in four-fold and six-fold coordinations. A second transition to a highly disordered material with both cations in six-fold coordination occurs at higher pressures and is irreversible.Comment: 8 pages, 5 figures, LaTeX2

Momentum-resolved charge excitations in high-Tc cuprates studied by resonant inelastic x-ray scattering

We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of high-Tc cuprates. Momentum-resolved charge excitations in the CuO2 plane are examined from parent Mott insulators to carrier-doped superconductors. The Mott gap excitation in undoped insulators is found to commonly show a larger dispersion along the [pi,pi] direction than the [pi,0] direction. On the other hand, the resonance condition displays material dependence. Upon hole doping, the dispersion of the Mott gap excitation becomes weaker and an intraband excitation appears as a continuum intensity below the gap at the same time. In the case of electron doping, the Mott gap excitation is prominent at the zone center and a dispersive intraband excitation is observed at finite momentum transfer

On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x

We have compared the ground-state energy of several observed or proposed " 2 \sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS), with those of "chain superstructures" (CS) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The model Hamiltonian contains i) the Madelung energy, ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and iii) covalency effects based on known results for $t-J$ models in one and two dimensions. The optimum distribution of charge is determined minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure, and long-range Coulomb interactions, are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb in Phys. Rev.

Concerning Order and Disorder in the Ensemble of Cu-O Chain Fragments in Oxygen Deficient Planes of Y-Ba-Cu-O

In connection with numerous X-ray and neutron investigations of some high temperature superconductors (YBa$_2$Cu$_3$O$_{6+x}$ and related compounds) a non-trivial part of the structure factor, coming from partly disordered Cu-O-$\dots$-O-Cu chain fragments, situated within basal planes, CuO$_x$, can be a subject of theoretical interest. Closely connected to such a diffusive part of the structure factor are the correlation lengths, which are also available in neutron and X-ray diffraction studies and depend on a degree of oxygen disorder in a basal plane. The quantitative measure of such a disorder can be associated with temperature of a sample anneal, $T_q$, at which oxygen in a basal plane remains frozen-in high temperature equilibrium after a fast quench of a sample to room or lower temperature. The structure factor evolution with $x$ is vizualized in figures after the numerical calculations. The theoretical approach employed in the paper has been developed for the orthorhombic state of YBCO.Comment: Revtex, 27 pages, 14 PostScript figures upon request, ITP/GU/94/0