Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2.

Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A2CoO2Cu2Se2 materials could operate in the intermediate temperature region.

Neural correlates of inhibitory control and visual processing in youths with attention deficit hyperactivity disorder: a counting Stroop functional MRI study.

BACKGROUND: Despite evidence of inhibitory control and visual processing impairment in attention deficit hyperactivity disorder (ADHD), knowledge about its corresponding alterations in the brain is still evolving. The current study used counting Stroop functional MRI and the Cambridge Neuropsychological Test Automated Battery (CANTAB) to investigate if brain activation of inhibitory control and visual processing would differ in youths with ADHD relative to neurotypical youths. METHOD: We assessed 25 youths with ADHD [mean age 10.9 (s.d.=2.2) years] and 23 age-, gender- and IQ-matched neurotypical youths [mean age 11.2 (s.d.=2.9) years]. The participants were assessed by using the Wechsler Intelligence Scale for Children, third edition, and two tests from the CANTAB: rapid visual information processing (RVP) and pattern recognition memory (PRM) outside the scanner. RESULTS: Youths with ADHD showed more activation than neurotypical youths in the right inferior frontal gyrus [Brodmann area (BA) 45] and anterior cingulate cortex, which were correlated with poorer performance on the RVP test in the CANTAB. In contrast, youths with ADHD showed less activation than neurotypical youths in the left superior parietal lobule (BA 5/7), which was correlated with the percentage of correct responses on the PRM test in the CANTAB. CONCLUSIONS: Our findings suggest that youths with ADHD might need more inhibitory control to suppress interference between number and meaning and may involve less visual processing to process the numbers in the counting Stroop task than neurotypical youths.

Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study.

Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra.

The processing of coreference for reduced expressions in discourse integration.

Three reading-time experiments in Chinese are reported that test contrasting views of how pronominal coreference is achieved. On the one hand, studies of reading time and eye tracking suggest that reduced expressions, such as the pronoun he, serve as critical links to integrate separate utterances into a coherent model of discourse. On the other hand, probe-word recognition studies indicate that full anaphoric expressions, such as a repeated name, are more readily interpreted than reduced expressions due to their rich lexical information, which provides effective cues to match the representation of the appropriate referent in memory. The results indicate that the ease of integrating the critical referent into a model of discourse is a function of the congruence of lexical, semantic, and discourse features conveyed by a syntactically prominent reduced expression within linguistic input. This pattern supports the view that a reduced expression is interpreted on-line and indeed plays a critical role in promoting discourse coherence by facilitating the semantic integration of separate utterances.

Encoding operation and transcoding as the major loci of the frequency effect.

The present study used a lexical naming task as well as a regular naming task and a lexical decision task for locating the frequency effects in lexical decision and naming. The naming of Chinese characters in the lexical naming task (pseudocharacters also presented as in the lexical decision task) involves decision processes, while they are absent in the regular naming task. Since naming a Chinese character necessarily involves lexical access, a decision component of the frequency effect in lexical decision can be isolated. This procedure will not work for alphabetic orthographies, because sublexical processes underestimate the frequency effect in the regular naming task. As a consequence, not only can a prelexical component of the frequency effect in lexical decision be estimated, but a postlexical component of the frequency effect in naming can be estimated.

Variation of geosmin content in Anabaena cells and its relation to nitrogen utilization.

The addition of the proper amount of ammonium to the culture medium containing nitrate as nitrogen source enhanced the growth rate of Anabaena viguieri. The amount of geosmin produced by these cells varied with the concentrations of ammonium added. A negative correlation between the amount of geosmin produced and of the growth rate of cells was revealed. This was also found in cells grown on various forms of nitrogen sources. Without supply of any nitrogen compound, this organism is capable of fixing gaseous nitrogen, and under these conditions the cells grew relatively slowly. However, they produced more geosmin (per unit protein mass) than cells grown in the presence of combined nitrogen. The isolation of heterocysts, in which nitrogen was fixed, showed that these cells produced higher amounts of geosmin than vegetative cells. The possible relation of nitrogen assimilation to the production of geosmin in the cells was discussed.