Enhanced Thermoelectric Power and Electronic Correlations in RuSe2_2

We report the electronic structure, electric and thermal transport properties of Ru$_{1-x}$Ir$_{x}$Se$_2$ ($x \leq 0.2$). RuSe$_2$ is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe$_2$ exceeds -200 $\mu$V/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru$_{0.8}$Ir$_{0.2}$Se$_{2}$ shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb$_{2}$.Comment: 6 pages, 4 figure

Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

The search for durable dyes led several past civilizations to develop artificial pigments. Maya Blue (MB), manufactured in pre-Columbian Mesoamerica, is one of the best known examples of an organic-inorganic hybrid material. Its durability is due to the unique association of indigo molecule and palygorskite, a particular fibrous clay occurring in Yucatan. Despite 50 years of sustained interest, the microscopic structure of MB and its relation to the durability remain open questions. Combining new thermogravimetric and synchrotron X-ray diffraction analyses, we show that indigo molecules can diffuse into the channel of the palygorskite during the heating process, replacing zeolitic water and stabilizing the room temperature phases of the clay

Dynamic Study of N'N-dimethylparanitroaniline encapsulated in Silicalite-1 matrix using neutron spin-echo spectroscopy

International audienceThe present work focuses on the dynamic studies of N'N-dimethyl- paranitroaniline (dmpNA) encapsulated in silicalite zeolite. Quasielastic neutron scattering (QENS) experiments are carried out using neutron spin-echo technique. Polarisation of the scattered neutron beam is measured at carefully chosen values of Q=0.35, 0.9, 1.1 and 1.45 A -1 at xed T=298 K and at xed Q=0.9 A -1 at 150, 200, 250 and 298 K. This gives insight into the motion and the related activation energy of the guest dmpNA molecule. The quasielastic signal observed in the present system within the time range considered is due to fast local rotational motions of protons of the end methyl groups. The results are in good agreement with the dynamics of methyl group rotations reported in the literature by back- scattering QENS technique

X-ray diffraction studies of the effects of N incorporation in amorphous CNx, materials

The effects of nitrogen incorporation on the atomic-scale structure of amorphous CNx samples have been studied for 0, 5, 20, and 30 at. % N concentration, by x-ray diffraction. Significant differences in the structure are observed on the incorporation of only 5 at. % N, and the changes in structure continue as further N is added. From the experimental data, we are able to obtain directly the average bond distances and then calculate the average bond angles for each of the samples. The average first neighbor distance shows a gradual decrease from 1.55 Angstrom for 0 at. % N, to 1.44 Angstrom for 30 at. % N, and a similar trend is observed in the position of the second neighbor peak. This gives a corresponding increase in the average bond angle from 108 degrees to 114 degrees. The results show an increase in the fraction of sp(2) bonded carbon atoms with increasing N concentration, and there is evidence for the presence of significant numbers of C=N and C=N bonds. These results are also consistent with stress, hardness, and optical gap measurements for these samples. (C) 1998 American Institute of Physics. [S0021-8979(98)03907-3]

Association of indigo with zeolites for improved colour stabilization

International audienceThe durability of an organic colour and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidising conditions, using Raman and UV-visible spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high colour stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment

Історична наука в УРСР як предмет дослідження в англо-американській історіографії

У статті відтворено образ історичної науки в УРСР у працях англо-американських учених другої половини ХХ – початку ХХІ ст. Вивчено еволюцію ролі та функцій трьох основних акторів історіографічного процесу в Радянському Союзі – влади, істориків та пересічних громадян. Визначено сталі та змінні компоненти у загальній схемі їх взаємодії.In the article the image of historical science in the Ukrainian SSR in the works of the Anglo-American researchers published during the second half of the twentieth and the beginning of the twenty-first centuries is reconstructed. The modification of roles and functions of three main actors in Soviet historiographical process – power, historians and average citizens – is examined. The invariable and change components in the general pattern of its interaction are defined

Revisiting Maya Blue and Designing Hybrid Pigments by Archaeomimetism

Maya Blue is actually one of the best known examples of an organic-inorganic hybrid material. Yet despite 50 years of sustained interest, its microscopic structure and its relation to durability remain open questions. We address the issue by archaeomimetism: engineering an archaeoinspired pigment, satisfactorily reproducing the colour and chemical stability of Maya Blue. By comparing and contrasting ancient pigment and the new analogue, we deduce a new explanation for this durability