3,385 research outputs found
Development of dispersion strengthened nickel-chromium alloy (Ni-Cr-ThO2) sheet for space shuttle vehicles, part 2
Two dispersion strengthened nickel base alloy systems were developed for use at temperatures up to 1204 C(2200 F); TD nickel chromium (TDNiCr) and TD nickel chromium aluminum (TDNiCrA1). They are considered candidate materials for use on the thermal protection systems of the space shuttle and for long term use in aircraft gas turbine engine applications. Improved manufacturing processes were developed for the fabrication of TDNiCr sheet and foil to specifications. Sheet rolling process studies and extrusion studies were made on two aluminum containing alloys: Ni-16%Cr-3.5%A1-2%ThO2 and Ni-16%Cr-5.0%A12%ThO2. Over 1600 kg.(3500 lb.) of plate, sheet, foil, bar and extrusion products were supplied to NASA Centers for technology studies
Surveyor batteries Final engineering report
Design and performance of Surveyor spacecraft silver-zinc main batter
African vegetable diversity in the limelight: project activities by ProNIVA.
Poster presented at Botanical Congress. Hamburg (Germany), 3-7 Sep 200
Numerically improved computational scheme for the optical conductivity tensor in layered systems
The contour integration technique applied to calculate the optical
conductivity tensor at finite temperatures in the case of layered systems
within the framework of the spin-polarized relativistic screened
Korringa-Kohn-Rostoker band structure method is improved from the computational
point of view by applying the Gauss-Konrod quadrature for the integrals along
the different parts of the contour and by designing a cumulative special points
scheme for two-dimensional Brillouin zone integrals corresponding to cubic
systems.Comment: 17 pages, LaTeX + 4 figures (Encapsulated PostScript), submitted to
J. Phys.: Condensed Matter (19 Sept. 2000
Electrical transport properties of bulk NiFe alloys and related spin-valve systems
Within the Kubo-Greenwood formalism we use the fully relativistic,
spin-polarized, screened Korringa-Kohn-Rostoker method together with the
coherent-potential approximation for layered systems to calculate the
resistivity for the permalloy series NiFe. We are able to
reproduce the variation of the resistivity across the entire series; notably
the discontinuous behavior in the vicinity of the structural phase transition
from bcc to fcc. The absolute values for the resistivity are within a factor of
two of the experimental data. Also the giant magnetoresistance of a series of
permalloy-based spin-valve structures is estimated; we are able to reproduce
the trends and values observed on prototypical spin-valve structures.Comment: 6 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to
PR
Non-collinear magnetic structures: a possible cause for current induced switching
Current induced switching in Co/Cu/Co trilayers is described in terms of
ab-initio determined magnetic twisting energies and corresponding sheet
resistances. In viewing the twisting energy as an energy flux the
characteristic time thereof is evaluated by means of the
Landau-Lifshitz-Gilbert equation using ab-initio parameters. The obtained
switching times are in very good agreement with available experimental data. In
terms of the calculated currents, scalar quantities since a classical Ohm's law
is applied, critical currents needed to switch magnetic configurations from
parallel to antiparallel and vice versa can unambiguously be defined. It is
found that the magnetoresistance viewed as a function of the current is
essentially determined by the twisting energy as a function of the relative
angle between the orientations of the magnetization in the magnetic slabs,
which in turn can also explain in particular cases the fact that after having
switched off the current the system remains in the switched magnetic
configuration. For all ab-initio type calculations the fully relativistic
Screened Korringa-Kohn-Rostoker method and the corresponding Kubo-Greenwood
equation in the context of density functional theory are applied.Comment: 20 pages, 4 tables and 15 figures, submitted to PR
Magnetic properties of Quantum Corrals from first principles calculations
We present calculations for electronic and magnetic properties of surface
states confined by a circular quantum corral built of magnetic adatoms (Fe) on
a Cu(111) surface. We show the oscillations of charge and magnetization
densities within the corral and the possibility of the appearance of
spin--polarized states. In order to classify the peaks in the calculated
density of states with orbital quantum numbers we analyzed the problem in terms
of a simple quantum mechanical circular well model. This model is also used to
estimate the behaviour of the magnetization and energy with respect to the
radius of the circular corral. The calculations are performed fully
relativistically using the embedding technique within the
Korringa-Kohn-Rostoker method.Comment: 14 pages, 9 figures, submitted to J. Phys. Cond. Matt. special issue
on 'Theory and Simulation of Nanostructures
Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae: Data and Correlations across Morphological Classes
The morphology of planetary nebulae (PNe) provides an essential tool for
understanding their origin and evolution, as it reflects both the dynamics of
the gas ejected during the TP-AGB phase, and the central star energetics. Here
we study the morphology of 27 Magellanic Cloud planetary nebulae (MCPNe) and
present an analysis of their physical characteristics across morphological
classes. Similar studies have been successfully carried out for galactic PNe,
but were compromised by the uncertainty of individual PN distances. We present
our own HST/FOC images of 15 Magellanic Cloud PNe (MCPNe) acquired through a
narrow-band lambda 5007 [O III] filter. We use the Richardson-Lucy
deconvolution technique on these pre-COSTAR images to achieve post-COSTAR
quality. Three PNe imaged before and after COSTAR confirm the high reliability
of our deconvolution procedure. We derive morphological classes, dimensions,
and surface photometry for all these PNe. We have combined this sample with
HST/PC1 images of 15 MCPNe, three of which are in common with the FOC set,
acquired by Dopita et al. (1996), to obtain the largest MCPN sample ever
examined from the morphological viewpoint. By using the whole database,
supplemented with published data from the literature, we have analyzed the
properties of the MCPNe and compared them to a typical, complete galactic
sample. Morphology of the MCPNe is then correlated with PN density, chemistry,
and evolution.Comment: text file lstanghe_mcpn.tex (LaTex); Figures 2 through 10, Figure 5
is in 3 parts (a,b,c); Figure 1 available by regular mail only; ApJ, in
press, November 10, 199
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Does mode of administration affect health-related quality-of-life outcomes after stroke?
Telephone interviews and postal surveys may be a resource-efficient way of assessing health-related quality-of-life post-stroke, if they produce data equivalent to face-to-face interviews. This study explored whether telephone interviews and postal surveys of the Stroke and Aphasia Quality of Life Scale (SAQOL-39g) yielded similar results to face-to-face interviews. Participants included people with aphasia and comprised two groups: group one (n =22) were 3-6 months post-stroke; group two (n =26) were ≥1 year post-stroke. They completed either a face-to-face and a telephone interview or a face-to-face interview and a postal survey of the SAQOL-39g. Response rates were higher for group two (87%) than for group one (72-77%). There were no significant differences between respondents and non-respondents on demographics, co-morbidities, stroke severity, or communication impairment. Concordance between face-to-face and telephone administrations (.90-.98) was excellent; and very good-excellent between face-to-face and postal administrations (.84-.96), although scores in postal administrations were lower (significant for psychosocial domain and overall SAQOL-39g in group two). These findings suggest that the SAQOL-39g yields similar results in different modes of administration. Researchers and clinicians may employ alternative modes, particularly in the longer term post-stroke, in order to reduce costs or facilitate clients with access difficulties
Limitations of the two-media approach in calculating magneto-optical properties of layered systems
It is shown that in polar geometry and normal incidence the 2x2 matrix
technique - as discussed in detail in a preceeding paper [Phys. Rev. B 65,
144448 (2002)] - accounts correctly for multiple reflections and optical
interferences, and reduces only in the case of a periodic sequence of identical
layers to the Fresnel formula of reflectivity, which in turn is the theoretical
basis of the two-media approach, widely used in the literature to compute
magneto-optical Kerr spectra. As a numerical example ab-initio calculations of
the optical constants for an fcc Pt semi-infinite bulk using the spin-polarized
relativistic screened Korringa-Kohn-Rostoker method show very good agreement
with experimental data.Comment: 16 pages (LaTeX), 4 figures (Encapsulated PostScript), appears in
Phys. Rev. B 66, 1744XX (2002
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