Materials Literature
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A surface of thin square polytetrafluoroethylene (PTFE) samples (1 × 1 × 0.2 cm3) was irradiated with Ar+ at 1 keV with varying ion dose from 5 × 1014 to 1 × 1017 ions/cm2 with and without an oxygen environment. The irradiated surface of the samples was examined by scanning electron microscopy (SEM) for surface textur…
The performance of magnetostrictive Terfenol-D is highly dependent on the state of the material and in particular on the mechanical prestress. This paper presents an experimental investigation of the effect of prestress on the dynamic performance of a Terfenol-D transducer. The effects of both prestress and magnetic b…
Thermal characteristics of ethylene—vinylacetate (EVA) copolymers having vinylacetate contents ranging from 5 to 40 w/w % are studied by differential scanning calorimetry. It is first shown that EVA copolymers having a vinylacetate content lower than 30 w/w % obey the Flory and Burfield theories of copolymer crystalli…
Molecularly designed surfaces formed by chemisorption of alkanethiols on ultrathin films of gold permit control of both the azimuthal and polar orientations of supported nematic liquid crystals (LCs). These surfaces, when patterned, form simple and versatile templates for the fabrication of complex optical structures…
The electronic structures of Sr_{14-x}Ca_{x}Cu24O41 are calculated within the local density approximation. Around the Fermi energy there exist quasi-one-dimensional bands originated from the ladder and chain layers. The nearest-neighbor inter-ladder hoppings are estimated to be 5--20% of the intra-ladder ones. Possibl…
Environmentally benign chemical synthesis is a central thrust in the current U.S. research arena. Production of polymers contributes to pollution during synthesis and after use. Thus, the synthesis of a biodegradable plastic by “green” technology could have a real impact. Indeed, such a polymer produced by microorgani…
We studied interplay between kinetic roughening and phase ordering in 1+1 dimensional single-step solid-on-solid growth model with two kinds of particles and Ising-like interaction. Evolution of both geometrical and compositional properties was investigated by Monte Carlo simulations for various strengths of coupling.…
This paper describes recent results of AF-sponsored research in the thermal stability of high temperature fuels. At temperatures of 550 °C (1000 °F) and above, both thermal -oxidative and pyrolytic deposition are important. A brief discussion of deposition characteristics and mitigation measures is presented.
Results of quantum chemical calculations for the and F centres in cubic and orthorhombic phases of a perovskite ferroelectric are presented and analysed in the light of existing experimental literature. It is shown that one (two) electrons of the and F centres, respectively, are considerably delocalized, even in the g…
For a composite consisting of magnetostrictive particles dispersed in a nonmagnetostrictive matrix, a simple, approximate model for the effective magnetostriction, defined as the ratio of the magnetostriction of the composite to that of the magnetostrictive component, is described. The predictions of the model compare…
A team led by Solar Turbines Incorporated is conducting a three phase program under the sponsorship of the United States Department of Energy, Office of Industrial Technologies, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section components wi…
A probabilistic design code is being developed for high energy disks and rotors used in aircraft gas turbine engines. This code is intended to augment, not replace, the current safe-life approach to the design of these critical components. While the code will ultimately be applicable to a range of disk alloys, initial…
According to band theory, an ideal undoped $(n,n)$ carbon nanotube is metallic. We show that the electron-electron interaction causes it to become Mott insulating with a spin gap. More interestingly, upon doping it develops superconducting fluctuations.
We report the observation of both metallic and semiconducting behavior in epitaxial thin films of the metallic oxide CaRuO3 deposited under identical conditions. X-ray diffraction studies showed that while semiconducting films with enlarged unit cells were obtained on single-crystal (100) SrTiO3 substrates, metallic f…
In low temperature studies of ultrapure erbium (and dysprosium) we have discovered unusual thermal effects at the first order magnetic transformation of erbium $(\ensuremath{\cong}19\mathrm{K})$. These include (1) superheating (i.e., the metal is colder after heat has been added to it than before the heat pulse), (2)…
The classic Peierls theory of dislocations is critically examined and shown to contain a number of inconsistencies. For narrow core dislocations, as in Si, the classic theory leads to gross overestimation of the barrier to dislocation motion. We present a new, semidiscrete theory which corrects the inconsistencies of…
We present an effective medium theory in order to analyze the reported optical properties of aligned carbon nanotube films [W. A. de Heer et al., Science 268, 845 (1995)]. This methodology is based on photonic band structure calculations and allows treatment of complex media consisting of particles that interact stron…
We studied three distorted perovskite manganites, ${\mathrm{Pr}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_{3}$ and ${\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ with $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ and 0.55 by the neutron diffraction technique. Two samples with $x\phanto…
We have observed an insulator-to-metal (I-M) transition triggered by the photocarrier injection into the charge-ordered (CO) state of a perovskite manganite crystal, ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$. The photocurrent is a highly nonlinear function of applied electric field and of light intens…
In this Letter we present a coherent description of the optical properties of a unique type of nanoparticle, metal-coated dielectric nanoparticles. These structures occur naturally in the form of Au-coated ${\mathrm{Au}}_{2}\mathrm{S}$ nanoparticles. During the course of nanoparticle growth, the plasmon-related absorp…