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Material Leads (material + lead)

Distribution by Scientific Domains
Polymers and Materials Science40%

Selected Abstracts

Structural and photooxidation studies of poly(styrene oxide) prepared with Maghnite-H+ as cationic catalyst

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Aïcha Hachemaoui
Abstract The nature of irregularities and end-groups in poly(styrene oxide) samples prepared using Maghnite-H+ as a cationic catalyst were studied by 1H- and 13C-NMR at 200 MHz. Head-to-head (H-H) and tail-to-tail (T-T) irregularities are detected in all the samples studied. Secondary hydroxyl terminal groups are identified in polymers prepared with Maghnite-H+. Poly(styrene oxide) was found to undergo chain scission by aging at 25°C. It was confirmed that oxidation of this type of polymers results from the important sensitivity of the polyether soft segment to oxidative degradation. For this reason, the scissions due to the oxidation of the material lead to notable quantities of low molecular weight photoproducts. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified by MALDI-TOF-MS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Conductive nanodots on the surface of irradiated CaF2

PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2008
Tino Roll
Abstract CaF2(111) single crystal surfaces have been irradiated with fast heavy ions under oblique angles resulting in chains of nanosized hillocks. In order to characterize these nanodots with respect to their conductivity we have applied non-contact atomic force microscopy using a magnetic tip. Measurements in ultra high vacuum as well as under ambient conditions reveal a clearly enhanced electromagnetic interaction between the magnetic tip and the nanodots. The dissipated energy per cycle is comparable to the value found for metals, indicating that the interaction of the ion with the target material leads to the creation of metallic Ca nanodots on the surface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Affective spaces, melancholic objects: ruination and the production of anthropological knowledge,

THE JOURNAL OF THE ROYAL ANTHROPOLOGICAL INSTITUTE, Issue 1 2009
Yael Navaro-Yashin
This article critically engages with recent theoretical writings on affect and non-human agency by way of studying the emotive energies discharged by properties and objects appropriated during war from members of the so-called ,enemy' community. The ethnographic material comes from long-term fieldwork in Northern Cyprus, focusing on how it feels to live with the objects and within the ruins left behind by the other, now displaced, community. I study Turkish-Cypriots' relations to houses, land, and objects that they appropriated from the Greek-Cypriots during the war of 1974 and the subsequent partition of Cyprus. My ethnographic material leads me to reflect critically on the object-centred philosophy of Actor Network Theory and on the affective turn in the human sciences after the work of Gilles Deleuze. With the metaphor of ,ruination', I study what goes amiss in scholarly declarations of theoretical turns or shifts. Instead, proposing an anthropologically engaged theory of affect through an ethnographic reflection on spatial and material melancholia, I argue that ethnography, in its most productive moments, is trans-paradigmatic. Retaining what has been ruined as still needful of consideration, I suggest an approach which merges theories of affect and subjectivity as well as of language and materiality. Résumé L'article examine sous un angle critique les écrits théoriques récents sur l'affect et l'agency non humaine pour étudier les énergies émotives libérées par les biens et objets confisqués lors d'un conflit armé aux membres de la communauté dite «ennemie». Le matériel ethnographique provient d'un travail de terrain de longue durée dans le Nord de Chypre, qui portait sur le ressenti de ceux qui vivent avec ces objets, dans les ruines laissées par l'autre communauté désormais déplacée. L'auteure étudie les relations des Chypriotes turcs avec les maisons, les terres et les objets qu'ils se sont appropriés sur les Chypriotes grecs lors de la guerre de 1974 et de la partition de Chypre. Le matériel ethnographique la conduit à une réflexion critique sur la philosophie centrée sur les objets de la théorie de l'acteur-réseau et sur le tournant affectif des sciences humaines à la suite des travaux de Gilles Deleuze. Par la métaphore de la «ruine», l'auteur sonde ce qui ne va pas dans les proclamations académiques de tournants théoriques et de changements paradigmatiques. En lieu et place, elle propose une théorie de l'affect engagée dans l'anthropologie, par une réflexion ethnographique sur la mélancolie spatiale et matérielle, et affirme que l'ethnographie, dans ses moments les plus productifs, est trans-paradigmatique. En gardant ce qui est «ruiné» comme digne encore de considération, l'auteure suggère une approche qui concilie les théories de l'affect et de la subjectivité et du langage et de la matérialité. [source]

Assembly of Pure Silver-Tungsten-Oxide Frameworks from Nanostructured Solution Processable Clusters and Their Evolution into Materials with a Metallic Component

ADVANCED MATERIALS, Issue 38 2010
Thomas McGlone
Silver-Tungsten-Oxide Frameworks: Isomerically pure forms of the unique isopolyoxotungstate system are incorporated into highly connected framework materials using Ag(I) as a linking unit. Thermal treatment of the materials leads to the formation of silver microparticles embedded in a tungsten oxide matrix. This novel synthetic approach promises to create a new class of nanostructured tungsten-silver-oxides with exciting physical properties, as well as exemplifies the potential for new frameworks based upon solution processable POM clusters. [source]

A geometrically and materially non-linear piezoelectric three-dimensional-beam finite element formulation including warping effects

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2008
A. Butz
Abstract This paper is concerned with a three-dimensional piezoelectric beam formulation and its finite element implementation. The developed model considers geometrically and materially non-linear effects. An eccentric beam formulation is derived based on the Timoshenko kinematics. The kinematic assumptions are extended by three additional warping functions of the cross section. These functions follow from torsion and piezoelectrically induced shear deformations. The presented beam formulation incorporates large displacements and finite rotations and allows the investigation of stability problems. The finite element model has two nodes with nine mechanical and five electrical degrees of freedom. It provides an accurate approximation of the electric potential, which is assumed to be linear in the direction of the beam axis and quadratic within the cross section. The mechanical degrees of freedom are three displacements, three rotations and three scaling factors for the warping functions. The latter are computed in a preprocess by solving a two-dimensional in-plane equilibrium condition with the finite element method. The gained warping patterns are considered within the integration through the cross section of the beam formulation. With respect to material non-linearities, which arise in ferroelectric materials, the scalar Preisach model is embedded in the formulation. This model is a mathematical model for the general description of hysteresis phenomena. Its application to piezoelectric materials leads to a phenomenological model for ferroelectric hysteresis effects. Here, the polarization direction is assumed to be constant, which leads to unidirectional constitutive equations. Some examples demonstrate the capability of the proposed model. Copyright © 2008 John Wiley & Sons, Ltd. [source]