3,399 research outputs found
A simple method of obtaining concentration depth-profiles from X-ray diffraction
The construction of composition profiles from X-ray intensity bands was investigated. The intensity band-to-composition profile transformation utilizes a solution which can be easily evaluated. The technique can be applied to thin films and thick speciments for which the variation of lattice parameters, linear absorption coefficient, and reflectivity with composition are known. A deconvolution scheme with corrections for the instrumental broadening and ak-alfadoublet is discussed
An X-ray diffraction study of titanium oxidation
Titanium specimens of commercial purity were exposed at 1100 to 1400 F to laboratory air for times up to 100 hours. The extent of substrate contamination by interstitial oxygen was was determined by a new X-ray diffraction analysis involving transformation of X-ray diffraction intensity bands. The oxygen solid-solubility at the oxide-metal interfaces and its variation with time at temperature were also determined. Diffusion coefficients are deduced from the oxygen depth profiles
Analytical estimation of the dynamic apertures of circular accelerators
By considering delta function sextupole, octupole, and decapole perturbations
and using difference action-angle variable equations, we find some useful
analytical formulae for the estimation of the dynamic apertures of circular
accelerators due to single sextupole, single octupole, single decapole (single
2 pole in general). Their combined effects are derived based on the Chirikov
criterion of the onset of stochastic motions. Comparisons with numerical
simulations are made, and the agreement is quite satisfactory. These formulae
have been applied to determine the beam-beam limited dynamic aperture in a
circular collider.Comment: 24 pages, 23 figure
Medium-induced color flow softens hadronization
Medium-induced parton energy loss, resulting from gluon exchanges between the
QCD matter and partonic projectiles, is expected to underly the strong
suppression of jets and high- hadron spectra observed in
ultra-relativistic heavy ion collisions. Here, we present the first
color-differential calculation of parton energy loss. We find that color
exchange between medium and projectile enhances the invariant mass of energetic
color singlet clusters in the parton shower by a parametrically large factor
proportional to the square root of the projectile energy. This effect is seen
in more than half of the most energetic color-singlet fragments of
medium-modified parton branchings. Applying a standard cluster hadronization
model, we find that it leads to a characteristic additional softening of
hadronic spectra. A fair description of the nuclear modification factor
measured at the LHC may then be obtained for relatively low momentum transfers
from the medium
Commensurate Nb2Zr5O15: Accessible Within the Field Nb2ZrxO2x+5 After All
Doped niobium zirconium oxides are applied in field-effect transistors and as special-purpose coatings. Whereas their material properties are sufficiently known, their crystal structures remain widely uncharacterized. Herein, we report on the comparably mild sol–gel synthesis of Nb2Zr5O15 and the elucidation of its commensurately modulated structure via neutron diffraction. We describe the structure using the most appropriate superspace as well as the convenient supercell approach. It is part of an α-PbO2-homeotypic field with the formula Nb2ZrxO2x+5, which has previously been reported only for x ≥ 5.1, and is closely related to the structure of Hf3Ta2O11. The results, supported by X-ray diffraction and additional synthesis experiments, are contextualized within the existing literature. Via the sol–gel route, metastable Nb–Zr–O compounds and their heavier congeners are accessible that shed light on possible structures of these commercially utilized materials.DFG, 198634447, SPP 1613: Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische KonzepteTU Berlin, Open-Access-Mittel - 201
Bose-Einstein Final State Symmetrization for Event Generators of Heavy Ion Collisions
We discuss algorithms which allow to calculate identical two-particle
correlations from numerical simulations of relativistic heavy ion collisions. A
toy model is used to illustrate their properties.Comment: Talk given at CRIS'98 (Catania, June 8-12, 1998), to appear in
"CRIS'98: Measuring the size of things in the Universe: HBT interferometry
and heavy ion physics", (S. Costa et al., eds.), World Scientific, Singapore,
1998. (10 pages Latex, 1 eps-figure, extended version of conference
proceedings, Fig1 a,b added and corresponding discussion enlarged
Bose-Einstein Correlations in a Space-Time Approach to e+ e- Annihilation into Hadrons
A new treatment of Bose-Einstein correlations is incorporated in a space-time
parton-shower model for e+ e- annihilation into hadrons. Two alternative
afterburners are discussed, and we use a simple calculable model to demonstrate
that they reproduce successfully the size of the hadron emission region. One of
the afterburners is used to calculate two-pion correlations in e+ e- -> Z^0 ->
hadrons and e+ e- -> W+ W- -> hadrons. Results are shown with and without
resonance decays, for correlations along and transverse to the thrust jet axis
in these two classes of events.Comment: 30 pages, Latex, 8 figure
Jet quenching via jet collimation
The strong modifications of dijet properties in heavy ion collisions measured
by ATLAS and CMS provide important constraints on the dynamical mechanisms
underlying jet quenching. In this work, we show that the transport of soft
gluons away from the jet cone - jet collimation - can account for the observed
dijet asymmetry with values of that lie in the expected order of
magnitude. Further, we show that the energy loss attained through this
mechanism results in a very mild distortion of the azimuthal angle dijet
distribution.Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conferenc
Oxidation and emittance of superalloys in heat shield applications
Recently developed superalloys that form alumina coatings have a high potential for heat shield applications for advanced aerospace vehicles at temperatures above 1095C. Both INCOLOY alloy MA 956 (of the Inco Alloys International, Inc.), an iron-base oxide-dispersion-strengthened alloy, and CABOT alloy No. 214 (of the Cabot Corporation), an alumina-forming nickel-chromium alloy, have good oxidation resistance and good elevated temperature strength. The oxidation resistance of both alloys has been attributed to the formation of a thin alumina layer (alpha-Al2O3) at the surface. Emittance and oxidation data were obtained for simulated Space Shuttle reentry conditions using a hypersonic arc-heated wind tunnel. The surface oxides and substrate alloys were characterized using X-ray diffraction and scanning and transmission electron microscopy with an energy-dispersive X-ray analysis unit. The mass loss and emittance characteristics of the two alloys are discussed
Multi-layer light-weight protective coating and method for application
A thin, light-weight, multi-layer coating is provided for protecting metals and their alloys from environmental attack at high temperatures. A reaction barrier is applied to the metal substrate and a diffusion barrier is then applied to the reaction barrier. A sealant layer may also be applied to the diffusion barrier if desired. The reaction barrier is either non-reactive or passivating with respect to the metal substrate and the diffusion barrier. The diffusion barrier is either non-reactive or passivating with respect to the reaction barrier and the sealant layer. The sealant layer is immiscible with the diffusion barrier and has a softening point below the expected use temperature of the metal
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