Valence Values Research Articles

Strong Valence Fluctuation in the Quantum Critical Heavy Fermion Superconductorβ−YbAlB4: A Hard X-Ray Photoemission Study

Electronic structures of the quantum critical superconductor β-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and β-YbAlB4, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show Yb2+ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in β-YbAlB4.

Evaluation of manganese and oxygen content in La0.7Sr0.3MnO3−δ and correlation with the thermodynamic data

In order to understand how the thermodynamic properties are related to the oxygen and manganese content in the Sr-doped lanthanum manganites, nonstoichiometric perovskite phases La0.7Sr0.3MnO3−δ have been investigated by using solid state electrochemical techniques, as well as wet chemical methods. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with solid state electromotive force measurements (EMF). The results were correlated with the average Mn valence values as determined by a chemical method based on two independent iodometric titrations, with amperometric dead-stop end point detection. New features related to the relationship between the average Mn valence, the oxygen nonstoichiometry variation, and the thermodynamic behavior were evidenced.

‘Mister D.J., Cheer Me Up!’: Musical and Textual Features for Automatic Mood Classification

Mass consumption of large collections of digital music asks for efficient and intuitive ways of organization. In this article, a system is presented which recognizes the evoked music mood on the basis of a wide variety of features, closely sticking to real world conditions. A two-dimensional mood model is discussed in which moods resemble binary values for arousal and valence and an easy and thus user-friendly method is presented through which a fuzzy seven-class mood cluster is deducted. The songs of the ‘Twenty Years of MTV Europe Most Wanted’ music database consisting of recorded pop music tracks serve for evaluation of three groups of features: firstly, traditional features such as rhythm and tonal features, zero crossing rate, cepstral, and MPEG-7 Low Level Descriptors for audio content are extracted. Secondly, lyrics, chord sequences, and genre data are obtained from on-line sources. Thirdly, from all these, the high-level features, musical mode, and as a novel feature, the suited ballroom dance style, are created automatically. The features selected are data-driven, and Support Vector Machines are used for classification. Prediction accuracies of 77.4% for arousal and 72.9% for valence as well as 71.8% (including neighbours) for the seven-class cluster model are obtained pre-serving realism in terms of non-prototypical music selection and feature extraction throughout.

Effects of emotion and reward motivation on neural correlates of episodic memory encoding: A PET study

It is known that emotion and reward motivation promote long-term memory formation. It remains unclear, however, how and where emotion and reward are integrated during episodic memory encoding. In the present study, subjects were engaged in intentional encoding of photographs under four different conditions that were made by combining two factors (emotional valence, negative or neutral; and monetary reward value, high or low for subsequent successful recognition) during H 2 15O positron emission tomography (PET) scanning. As for recognition performance, we found significant main effects of emotional valence (negative > neutral) and reward value (high value > low value), without an interaction between the two factors. Imaging data showed that the left amygdala was activated during the encoding conditions of negative pictures relative to neutral pictures, and the left orbitofrontal cortex was activated during the encoding conditions of high reward pictures relative to low reward pictures. In addition, conjunction analysis of these two main effects detected right hippocampal activation. Although we could not find correlations between recognition performance and activity of these three regions, we speculate that the right hippocampus may integrate the effects of emotion (processed in the amygdala) and monetary reward (processed in the orbitofrontal cortex) on episodic memory encoding.

Crystal chemistry of volcanic allanites indicative of naturally induced oxidation-dehydrogenation

The crystal chemistry of volcanic allanites from both the Youngest Toba Tuff (YTT), Sumatra, Indonesia and SK100 volcanic ash beds (SK100-VAB), Niigata, Japan has been examined by electron microprobe analysis (EMPA), Fourier-transform infrared spectroscopic analysis (FTIR), and single-crystal structure analysis. In the FTIR study, based on the Diamond ATR accessory, YTT and SK100- VAB allanites were observed to have different OH contents, respectively: the former has 0.64 wt% H2O (OH: 0.40 apfu.), while the latter has 1.65 wt% H2O (OH: 1.00 apfu.). The crystal structures of these two allanites have been refined to individual R indices (3.64 and 4.25) based on 1350 observed reflections (|Fo| > 4sig|Fo|) measured using a single-crystal diffractometer with MoKα X-radiation. The OH-poor YTT allanite has a shorter b axis, a longer c axis, and larger β value than the relatively OH-rich SK100-VAB one. The bond valence sums of O4 (accepter oxygen for H atom) and O10 (donor oxygen for H atom) are 1.962 and 1.709 v.u. for YTT allanite (valence sum: 3.671 v.u.) and 1.754 and 1.271 v.u. for SK100-VAB one (valence sum: 3.025 v.u.). The difference from the ideal total bond valence value (4.00 v.u.) of O4 and O10 in YTT allanite (0.33 v.u.) is smaller than that in SK100-VAB (0.98 v.u.). These difference values are also broadly consistent with the corresponding differences in OH content between the YTT (OH: 0.40 apfu.) and SK100-VAB allanites (OH: 1.00 apfu.) determined by FTIR- ATR. Chemical analyses, FTIR-ATR and crystal structure refinement of YTT and SK100-VAB allanites yielded the following crystal chemical formula: YTT: (Ca0.83Mn2+ 0.06Fe2+ 0.11)(La0.24Ce0.32Pr0.04Nd0.11Sm0.02Th0.04Ca0.21)(Al0.73Fe3+ 0.19Ti0.08)(Al0.89Fe3+ 0.11)(Fe2+ 0.22Fe3+ 0.62Mg0.16)(SiO4)Si2O7O1.6(OH)0.4, SK100-VAB: (Ca0.81Fe2+ 0.13Mn2+ 0.06)(La0.22Ce0.34Pr0.05Nd0.13Sm0.02Th0.02Ca0.22)(Al0.76Fe3+ 0.19Ti0.05)Al1.00(Fe2+ 0.73Fe3+ 0.17Mg0.10)(Si0.96Al0.04O4)Si2O7O(OH). Therefore, it is concluded that welding of the Youngest Toba Tuff caused the following post-crystallization changes to occur in YTT allanite: oxidation of Fe2+ to Fe3+, release of H2, and the concomitant replacement of OH− by O2−. These oxidation and dehydrogenation processes advanced during the welding to thereby produce oxyallanite. Oxyallanite had been reported only in laboratory studies where it was produced by heating natural allanite. Our report on natural oxyallanite suggests that it may be present in other welded silicic volcanic rocks as well.

An analysis of nonlinear ion transport problem including arbitrary valences of oxidized and reduced species

The nonlocal identification problem related to nonlinear ion transport model including diffusion and migration is studied. Ion transport is assumed to be superposition of diffusion and migration under the influence of an electric field. Mathematical modeling of the experiment leads to an identification problem for a strongly nonlinear parabolic equation with nonlocal additional condition. It is shown that the nonlocal identification problem can be reduced to the initial-boundary value problem for nonlinear parabolic equation. Iteration method for numerical solution of this problem is proposed. Numerical results and their interpretation are presented for wide class of materials, including various values of valences and diffusivities of oxidized and reduced species.

Valency, valence degeneracy, ferroelectricity, and superconductivity

Applications of the oxidation state and valent state systems are discussed with particular emphasis on inorganic solids. Areas addressed include mixed valency, mixed electronic configurations, disproportionation and superconductivity, real charges, valence degeneracy, and stabilization of high oxidation states. The most significant advance to the oxidation state system since its inception is the bond valence approach where every bond between a cation and an anion is assigned a valence value. It is demonstrated that this bond valence approach can be used to understand ferroelectric transitions in oxides whether or not d orbitals are involved. Differences between the oxidation state system and the valent state system are delineated, and examples of common misuse of these systems are discussed.

Unraveling Genuine First Order Bulk Valence Transition and Kondo Resonance Behaviors in YbInCu4by High Energy Photoelectron Spectroscopy

By combining the high resolution hard and soft X-ray photoelectron spectroscopy, the Yb 3d and 4f states in the strongly correlated electron system, YbInCu 4 , are studied. After high accuracy experimental determination of the four unknown physical quantities such as the valence values and thicknesses of the surface and sub-surface regions, genuine behaviors of the Kondo resonance as well as the electronic structures in the bulk and sub-surface are clarified. A clear first order valence transition in the bulk and a gradual valence change in the sub-surface region with temperature are revealed.

Modified regional self‐interaction corrected time‐dependent density functional theory for core excited‐state calculations

A modified regional self-interaction correction (mRSIC) method is proposed for obtaining accurate core-excitation energies in time-dependent density functional theory (TDDFT) calculations. The mRSIC method is an improvement of the RSIC method (Tsuneda et al. J Comput Chem 2003, 24, 1592). It takes into account the energy contributions from 2s and higher atomic orbitals that the RSIC method neglects. Furthermore, mRSIC improves the poor description for the nuclear-electron cusp of Gaussian basis functions. The mRSIC method was combined with a long-range correction (LC) scheme, which has been proved to give accurate valence-, Rydberg-, and charge transfer (CT)-excitation energies. In so doing, it dramatically improved the accuracy of the calculated core-excitation energies and did not affect the already accurate values of valence-, Rydberg-, and CT-excitation energies produced by the LC functionals. These results mean that the combined scheme is accurate for all excitation energy forms.

Characterization of polysulfone hollow-fiber ultrafiltration membrane and its cleaning efficiency by streaming potential and flux method

Polysulfone (PS) hollow-fiber ultrafiltration membrane was characterized combined with flux and streaming potential in single electrolyte solutions. The effects of trans-membrane pressure, electrolyte concentration, ion valence and pH value of electrolyte solution on the streaming potential (SP) of the membrane were investigated. The zeta potential and surface charge density of the membrane were calculated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory. The results indicate that the valence and concentration of cation have a greater influence on the SP and surface charge density of PS membrane than those of anion, and the pH value of electrolyte solution has great effects on the SP and zeta potential of the membrane surface. Both the absolute value of the streaming potential and water flux of the adsorbed membrane decrease, compared with those of the clean membrane. The streaming potential and flux of the cleaned membrane can be completely recovered by cleaning with the mass fraction of 0.8% EDTA at pH=10.

Effect of pressure on thermopower and electrical resistivity of YbMn2Ge2

The thermopower S and electrical resistivity ρ of YbMn2 Ge2 were measured under pressures up to 2 GPa in the temperature range from 1.5 to 300 K. The magnetic transition temperature increases with increasing pressure, having maximum at Pc ≈ 1.3 GPa, and decreases with increasing pressure above P > 1.3 GPa. The temperature dependences of S and ρ change their features at critical pressure Pc ≈ 1.3 GPa, where reported that the mean Yb valence value changes from +2.4 to +2.8 at room-temperature. The pressure dependences of S and ρ at 4.2 and 300 K show the abrupt changes at the critical pressure, which indicate the changes of the electronic state near the Fermi level and the magnetic structure of Mn 3d electron.

Atomic-resolution imaging of oxidation states in manganites

Aberration corrected electron optics allows routine acquisition of high spatial resolution spectroscopic images in the scanning transmission electron microscope, which is important when trying to understand the physics of transition-metal oxides such as manganites. The physical properties of these perovskites are intimately related to the occupancies of the partially filled $3d$ bands, which define their oxidation state. In this work, we review procedures to obtain this electronic property in ${\text{La}}_{x}{\text{Ca}}_{1\ensuremath{-}x}{\text{MnO}}_{3}$ from atomic-column-resolved electron energy-loss spectra measured in the aberration corrected scanning transmission electron microscope. In bulk samples, several features of both the average $\text{Mn}\text{ }{L}_{2,3}$ edge and the $\text{O}\text{ }K$ edge fine structure change linearly with Mn nominal valence. These linear correlations are extracted and used as a calibration to quantify oxidation states from atomic resolution spectroscopic images. In such images, the same fine-structure features exhibit further changes, commensurate with the underlying atomic lattice. Mn valence values calculated from those images show unexpected oscillations. The combination of experiment with density-functional theory and dynamical scattering simulations allows detailed interpretation of these maps, distinguishing dynamical scattering effects from actual changes in electronic properties related to the local atomic structure. Specifically, in ${\text{LaMnO}}_{3}$, the two nonequivalent O sites can be distinguished by these methods.

Better than expected or as bad as you thought? The neurocognitive development of probabilistic feedback processing

Learning from feedback lies at the foundation of adaptive behavior. Two prior neuroimaging studies have suggested that there are qualitative differences in how children and adults use feedback by demonstrating that dorsolateral prefrontal cortex (DLPFC) and parietal cortex were more active after negative feedback for adults, but after positive feedback for children. In the current study we used functional magnetic resonance imaging (fMRI) to test whether this difference is related to valence or informative value of the feedback by examining neural responses to negative and positive feedback while applying probabilistic rules. In total, 67 healthy volunteers between ages 8 and 22 participated in the study (8–11 years, n = 18; 13–16 years, n = 27; 18–22 years, n = 22). Behavioral comparisons showed that all participants were able to learn probabilistic rules equally well. DLPFC and dorsal anterior cingulate cortex were more active in younger children following positive feedback and in adults following negative feedback, but only when exploring alternative rules, not when applying the most advantageous rules. These findings suggest that developmental differences in neural responses to feedback are not related to valence per se, but that there is an age-related change in processing learning signals with different informative value.

An analysis of nonlinear ion transport model including diffusion and migration

The nonlocal identification problem related to nonlinear ion transport model including diffusion and migration is studied. Ion transport is assumed to be superposition of diffusion and migration under the influence of an electric field. Mathematical modeling of the experiment leads to an identification problem for a strongly nonlinear parabolic equation with nonlocal additional condition. Uniqueness of the nonlinear direct problem solution, and its continuity with respect to the total charge function is proved. An existence of a quasisolution of the identification problem is proved in the class of derived admissible coefficients. The nonlinear finite difference approximation of this problem, with an appropriate iteration algorithm, is derived. Numerical solutions of the identification problem are presented for various values of valences and diffusivities of oxidized and reduced oxidized species. The obtained results permits one to derive behaviour of the concentration and total charge depending on physical parameters.

Electronic structures of Al-based transition metal compounds and effective valence of transition elements

Abstract Electronic structures of Al-TM (transition metal) compounds with rather simple B2, L12 and A15 structures are studied. Focusing on the energy bands, which are not hybridized strongly with the TM-d bands, we estimate the number of electrons occupying the states below the gap induced by periodic potentials and hence obtain the average number of valence electrons per atom e/a. Although the values of e/a obtained for the different structures are scattered in spite of combination of the same chemical species, these values are obtained if one assumes similar negative values for effective valence of TM. Roles of the interference effect opening the gap in the nearly-free-electron bands are discussed.

Applying quantum-chemical methods to interpretation of the antiradical activity in a series of hydroxy derivatives of cinnamic acid

Reactivity indices of a series of cinnamic acid derivatives with respect to active oxygen species have been investigated by semi-empirical quantum-chemical methods (PM3, AM1). A new characteristic, the total unsaturation index, is proposed and is determined using the values of bond orders, binding numbers, and valences of carbon atoms in the analyzed structures. On the basis of the quantum-chemical analysis data and the results of a pharmacological activity prognosis for the virtual structures (using the PASS program package), some new potentially active cinnamic acid hydroxy derivatives have been synthesized.

A bond-valence investigation of two series of isostructural lanthanide compounds

Since the days of Pauling it has been tacitly assumed that the valence, which is distributed between the bonds to neighbouring atoms, is the stoichiometric valence, (stoich)V, which has integer values. It is shown here that this is not true. Instead, bond-valence sums (BVS) calculated for lanthanide (Ln) atoms of a series of garnet-type compounds Ln(3)(III)Te(2)(VI)Li(3)(I)O(12) deviate significantly from (stoich)V. Values of (BVS)(Ln) of this series, plotted versus the element number Z(Ln), show the same irregular sequence as: (i) the third ionization potentials of Ln atoms, (ii) the valence values previously calculated with quantum-chemical methods for lanthanide metals and sulfides, and (iii) the experimental efficiencies of the reactions between Ln(I) and SF(6) in the gas phase. This indicates that in the Ln(3)Te(2)Li(3)O(12) series the BVS values of the Ln atoms, which are ;rattling' in rather large and rigid voids of the structure, reflect the electronic structure of Ln. It is, therefore, concluded that BVS represent a non-integer valence, which is based on the electronic structure of bonded atoms, rather than (stoich)V. For this non-integer valence the term ;structural valence' and the symbol (struct)V have been proposed. In another series of lanthanide chelates the (BVS)(Ln) values deviate even more from (stoich)V(Ln) = 3 v.u. than in the garnet-type series. In the chelates the Ln atoms are ;squeezed' in rather small voids so that the electronic effects of Ln acting on (BVS)(Ln) are overridden by stronger steric effects exerted by the organic ligands.

The effect of visual sexual content on the event-related potential

In the present study we investigated the effect of emotional valence and arousal value of non-erotic visual stimuli on event-related potentials. We also directly compared the effects of erotic and non-erotic stimuli of comparable valence and arousal levels. Sixteen sexually functional heterosexual males rated 150 computer screen pictures, selected from the International Affective Picture System, representing five stimulus types differing along dimensions of emotional valence and arousal, and erotic vs. non-erotic content. A positive deflection of the ERP between 300 and 500ms after stimulus onset (P300) was found to be sensitive to stimulus differences, with positive valence and high arousal resulting in larger P300. Furthermore, the positive slow wave (PSW) between 500 and 750ms revealed additive effects of valence and arousal value. High arousal and positive valence of the stimuli resulted in larger PSW. Importantly, an interaction effect was absent here. In addition, sexual content led to a larger P300 and PSW than expected on the basis of a mere additive contribution of high arousal and positive valence.

Retrospective Voting and Electoral Volatility: A Nordic Perspective

This article examines why people vote for the same party, switch parties or move from voting to non‐voting at consecutive elections. By using post‐election survey data from Iceland, Finland, Norway and Sweden in the beginning of the 2000s, the main aim is to model the impact of retrospective evaluations of party performance while controlling for theoretically relevant variables. The results of the multinomial regression analyses confirm that dissatisfaction with the performance of a party correlates strongly with party defection, and that the relationship is not weakened with the inclusion of variables for general dissatisfaction with the political system and its actors, standard background factors and political variables. This suggests that many voters are concerned with valence issues and value the overall competence of politicians and parties when they are making a decision whom to vote for.

Crystal structure, electrical conductivity, thermal expansion and compatibility studies of Co-substituted lanthanum strontium manganite system

La 0.76Sr 0.19Mn 1− x Co x O 3± δ , LSMCo x (0 ≤ x ≤ 1) perovskite oxides were synthesized by conventional ceramic route. The effect of Co substitution for Mn on the crystal structure, electrical conductivity and thermal expansion properties was investigated. XRD indicated rhombohedral symmetry for the studied compositions at 1673 K. The lattice parameters so determined showed significant reduction in cell volume, which is attributed to smaller ionic radii of Co 3+ ions. The results of electrical conductivity data indicated that the conductivity mechanism is by thermally activated hopping of small polarons between localized states corresponding to Mn or Mn and Co sites of different valence value. The conductivity decreases at all temperatures up to 40 mol% Co substitution while the energy of activation increases. This is possibly due to an increase in Jahn–Teller distortion, at an extent higher than the increase of the concentration of charge carriers. Thermal expansion coefficient values in the series increase with increasing Co content which has been explained on the basis of the changes in the spin states of the Co ions and the consequent changes in the ionic size with temperature. Solution route synthesis produces fine-size particles with better properties, consequently one composition from the above having enhanced requisite properties, viz. La 0.76Sr 0.19Mn 0.8Co 0.2O 3± δ was synthesized by sol–gel route. The sol–gel synthesized compound had crystallite size of ∼30 nm at 1173 K obtained using Scherrer's equation. Thus the potential of these compounds as cathodes for solid oxide fuel cells (SOFCs) have been evaluated. As Ce 0.8RE 0.2O 2− δ (RE = Sm, Gd) are being investigated for their use as electrolytes in SOFCs, their mechanical compatibility as well as chemical compatibility with the potential cathode material from the above LSMCo x series was also studied.