Materials Literature
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Nous examinons le comportement de solutions diluées de « bâtons durs », en présence de diverses perturbations extérieures : a) Près d'une paroi plane agissant de façon purement stérique (pas d'adsorption), la concentration en monomères est réduite sur une distance L (L, longueur des bâtons). Nous évaluons le profil de…
The properties and morphology of the cholesteric « blue » phase (BP) are discussed in terms of the « quasicrystalline » (QC) hypothesis, which states that the BP is ordered with three-dimensional translational periodicity. The lattice parameter of the « crystalline » BP is comparable to optical wavelengths, giving ris…
Liquid‐crystalline Heterocycloalkanes. I. Synthesis and Properties of Substituted 1,3‐Dioxanes The synthesis of 2,5‐disubstituted 1,3‐dioxanes is described, their melting and clearing points and their physical properties (dielectric anisotropy, viscosity, transition enthalpies, optical birefringence) are investigated.…
The optical absorption, emission, and excitation spectra for the Eu 5+ ion in the alkali halides have been investigated at room temperature. It was found that the magnitude of the 10Dq splitting of the 4f 6 5d configuration into its t 2g and e g components caused by the cubic crystalline field follows the spectrochemi…
Yeast enolase as prepared by current procedures is inherently chemically homogeneous, though deamidation and partial denaturation can produce electrophoretically distinct forms. A true isozyme of the enzyme exists but does not survive the purification procedure. The chemical sequence for both has been established. The…
Dielectric and light scattering spectroscopy are the most sensitive methods for the direct observation of low-frequency excitations in incommensurate phases. In several cases they have been successfully used for the observation of amplitudon and phason modqs. Whereas the amplitudon below the normal-incommensurate tran…
Measurements we have made of electric permittivities have revealed new pre-transitional effects in nematics with cyano end groups. These effects have been found to be related to the discontinuity in the mean permittivity at TNI observed for these nematics and they have been attributed to pre-transitional changes in th…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics of doping and degradation of polyacetylene by oxygenJ. M. Pochan, D. F. Pochan, H. Rommelmann, and H. W. GibsonCite this: Macromolecules 1981, 14, 1, 110–114Publication Date (Print):January 1, 1981Publication History Published online1 May 2002Published inissue 1 Jan…
The tunneling of the Wannier exciton from its metastable free state to the stable self-trapped state is described in the context of the multi-phonon nonradiative transition. The escape path through the adiabatic potential barrier is determined by a variational method: the tunneling is assumed to occur along a trial in…
X-ray diffuse scattering studies of one dimensional conductors (TMTSF) 2ReO4 and (TMTSF)2NO3 reveal the formation of low temperature superstructures which might involve an ordering of the counter ions ReO-4 and NO-3. The superstructure reflections are characterized by wave vectors q = (1/2, 1/2, 1/2) for the perrhenat…
The x-ray-diffraction spectra of ${\mathrm{Ba}}_{2}$Na${\mathrm{Nb}}_{5}$${\mathrm{O}}_{15}$ have been investigated by means of a precession camera between room temperature and 500\ifmmode^\circ\else\textdegree\fi{}C, across the orthorhombic-tetragonal transition near ${T}_{\mathrm{I}}=300$\ifmmode^\circ\else\textdegr…
Raman scattering and optical-depolarization measurements have been employed in investigations of the ferroelectric phase transition in $\mathrm{K}{\mathrm{Ta}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{x}{\mathrm{O}}_{3}$ in the limit $x<~0.05$. The critical niobium concentration for which ${T}_{c}\ensuremath{\approx}0$ K w…
Order in the orientations of bond angles in bulk smectic liquid crystals is investigated. A simple model which couples in-plane bond orientations to a tilt degree of freedom is solved in the mean-field approximation. In addition to the usual smetic-$A$ and smetic-$C$ phases, there is an untilted hexatic phase, with lo…
A method for the determination of carbon in soils and soil extracts is described. It involves the dry combustion of samples in a standard tube furnace and the direct titrimetric determination of the evolved carbon dioxide as carbonic acid in a sodium hydroxide trap. Liquid samples are dried onto a siliceous earth bed…
A weak electrolyte model for the mixed‐alkali effect on electrical conductivity and ionic mobility in glass was developed for the dilute foreign alkali region. The basic assumptions are (a) that alkali transport in single‐alkali glasses is due to a small concentration of mobile species and (A) adding small amounts of…
When homothallic cells of Schizosaccharomyces pombe were plated on agar sporulation medium, a few residual divisions were usually observed before induction of conjugation and sporulation. Four cells resulting from the last two residual divisions were usually lined; the "four-lined-cell" formed. Each four-lined-cell co…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSupermolecular structure and thermodynamic properties of linear and branched polyethylenes under rapid crystallization conditionsL. Mandelkern, M. Glotin, and R. A. BensonCite this: Macromolecules 1981, 14, 1, 22–34Publication Date (Print):January 1, 1981Publication History…
Experimental results are reported which show for the first time a transfer inside pairs of ions after their selective excitation by a pulsed laser. This transfer is studied in Pr3+ : LaF3 by monitoring the time dependence of an up-conversion fluorescence. The results show that two mechanisms must be considered, depend…
In a binary isobaric diagram there appears an intermediate smectic phase between a monomolecular smectic A phase and a bimolecular one. By means of several techniques evidence is given for this new mesophase with a liquid-like short range ordering. Some considerations about the long range structure of this novel fluid…
The discotic liquid crystalline mesophase of p-n-hexa-hexyloxytriphenylene was studied using deuterium NMR spectroscopy. Spectra of two selectively deuterated isotopic species were recorded : (i) in which all aromatic positions were substituted, and (ii) in which the substitution was made in the α-carbon side-chains.…