An analytical model for probing ion dynamics in clays with broadband dielectric spectroscopy

A simple two-state model is proposed to explicitly derive the ionic contribution to the frequency-dependent dielectric permittivity of clay. This model is based on a separation of time scales and accounts for two possible solvation modes (inner/outer-sphere complexes) for ions in the interlayer spacing and a possible chemical exchange between both forms. The influence on the permittivity of thermodynamic (distribution constant K(d)) and dynamic (diffusion coefficient, chemical relaxation rate) parameters is discussed. In turn, this model is used to analyze experimental data obtained with Na-montmorillonite for two relative humidities. The values of the parameters extracted from these measurements, and their variation with water content, show that the proposed model is at least reasonable.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

Broadband dielectric and resistivity spectroscopy of WO(3) x H(2)O in the range of 10(3)-10(10) Hz: particle size effect

The interest in studying the electrical properties of WO(3) x H(2)O powders is made absolutely necessary because their infrared modulation properties depend on their morphologies and electronic populations. Broadband dielectric and resistivity spectra of WO(3) x H(2)O powders were recorded in a frequency range of 10(3)-10(10) Hz at temperatures varying between 200 and 300 K. Complex resistivity and permittivity diagrams have permitted thermal behavior of both dc-conductivity and permittivity to be obtained. A dielectric relaxation is found, attributed to water molecules motions. The role of the powder morphology has been investigated on two types of compounds: the first one being constituted by nanometric particles and the second by micrometric particles. Strong differences are observed in the thermal behaviors of the dc-conductivities (activation energies). Particle size effect is evidenced, giving rise to stronger electron localization on the nanometric particles. The permittivity values and the dynamical behavior of the structural water are also influenced by the particle size effect. A strong interaction between moving polarons and water molecules has been determined.     

Electrochromic Variation of the Infrared Emissivity in Tungsten Oxide Compounds

The so-called plastic technology first developed for the Li-based batteries leads to a new flexible infrared modulator. Orthorhombic monohydrated tungsten oxide (o-WO³ · H₂O) is used as the active insertion element in the LiCoO₂/o-WO³ · H₂O system. To prevent its degradation under air moisture, the device is protected with hermetic plastic and a window. Measurements of the reflectivity values indicate a very good contrast between the bleached and colored states for the first insertion (about 50% contrast in the 2.5–15 μm range), but the contrast between the inserted and de-inserted states is only about 30%. Optical properties follow quite well Drude mechanism.     

Defects,phase transitions and dynamical disorder in superionic protonic conductors H3OUO2PO4 · 3H2O and CsHSO4

Specific properties of the hydrogen bond and protons appear to be responsible for the formation of the quasi-liquid state of conducting ions and the resulting superionic behaviour. This state is reached by successive phase transitions involving the mobile species and their interactions with a more or less rigid framework. H₃OUO₂PO₄ · 3H₂O (HUP) and CsHSO₄ can be considered as models of wet and dry superionic conduction, respectively. Interactions between static effects and dynamical disorder as well as the coupling between sublattices are discussed in relation to results obtained by calorimetry, impedance spectroscopy (up to 10 GHz), vibrational spectroscopy and quasi-elastic neutron scattering.