3,268 research outputs found
Power systems research at MSFC
Power systems research reviews at Marshall Space Flight Cente
Weak turbulence theory of the non-linear evolution of the ion ring distribution
The nonlinear evolution of an ion ring instability in a low-beta
magnetospheric plasma is considered. The evolution of the two-dimensional ring
distribution is essentially quasilinear. Ignoring nonlinear processes the
time-scale for the quasilinear evolution is the same as for the linear
instability 1/t_ql gamma_l. However, when nonlinear processes become important,
a new time scale becomes relevant to the wave saturation mechanism. Induced
nonlinear scattering of the lower-hybrid waves by plasma electrons is the
dominant nonlinearity relevant for plasmas in the inner magnetosphere and
typically occurs on the timescale 1/t_ql w(M/m)W/nT, where W is the wave energy
density, nT is the thermal energy density of the background plasma, and M/m is
the ion to electron mass ratio, which has the consequence that the wave
amplitude saturates at a low level, and the timescale for quasilinear
relaxation is extended by orders of magnitude
Unexpected Magnetism of Small Silver Clusters
The ground-state electronic, structural, and magnetic properties of small
silver clusters, Ag (2n22), have been studied using a linear
combination of atomic Gaussian-type orbitals within the density functional
theory. The results show that the silver atoms, which are diamagnetic in bulk
environment, can be magnetic when they are grouped together in clusters. The
Ag cluster with icosahedral symmetry has the highest magnetic moment per
atom among the studied silver clusters. The cluster symmetry and the reduced
coordination number specific of small clusters reveal as a fundamental factor
for the onset of the magnetism.Comment: 4 pages, 4 figure
Late-Type Stars in M31. I.: A Photometric Study of AGB Stars and Metallicity Gradients.
We have imaged five 7\arcmin \x 7\arcmin\ fields in M31 spanning
galactocentric radii from 4 to 32 kpc along the SW-major axis. The fields were
observed through two broad-band (\V\ and \I) and two narrow-band (\CN\ and
\TiO) filters. The broad-band data were used to construct \IvsVI\
color-magnitude diagrams (CMDs) and, in some of our fields, we found
significant numbers of stars in the Cepheid instability strip. A distance
modulus for the Cepheids in the middle field was found that agreed well with
other values in the literature values. The width of the giant branch (GB) in
the \IvsVI\ CMD of all 5 fields was investigated, and we show that in four of
the fields a likely explanation for the GB width is a combination of {\it both}
metallicity and mass variations. Using the broad-band data, the asymptotic
giant branch (AGB) luminosity functions (LFs) were measured in the five fields,
and we show that differences exist between these LFs. We speculate on how the
different star forming histories in the fields may lead to the observed AGB LFs
and GB widths. Using the narrow-band data along with the broad-band data we
separated the AGB stars into carbon-rich (C) and oxygen-rich (M) types. The
carbon stars LFs were used to obtain an estimate for the distance modulus of
M31 which agrees with the value derived from Cepheids. The ratio of C- to
M-stars (C/M) is believed to be an indicator of gaseous chemical abundance at
the time of formation of these stars. We show that the C/M ratio increases
smoothly with galactocentric distance, suggesting an inverse correlation with
metallicity. This is the first demonstration of this effect within a single
extragalactic system. We find that differences in the width of the GB and the
AGB LFs do not significantly affect the C/M ratio. We consider the effect of
the increasing C/M ratio on the ISM in M31, and cite evidence in favor of a
model where the grain composition in M31 is a function of galactocentric
distance.Comment: UUencoded compressed postscript, 3 Figs. available on request.
(Contact [email protected]
Problematising international placements as a site of intercultural learning
This paper theorises some of the learning outcomes of a three-year project concerning student learning in international social work placements in Malaysia. The problematic issue of promoting cultural and intercultural competence through such placements is examined, where overlapping hegemonies are discussed in terms of isomorphism of social work models, that of the nation state, together with those relating to professional values and knowledge, and the tyrannies of received ideas. A critical discussion of cultural competence as the rationale for international placements is discussed in terms of the development of the graduating social worker as a self-reflexive practitioner. The development of sustainable international partnerships able to support student placement and the issue of non-symmetrical reciprocation, typical of wide socio-economic differentials across global regions, is additionally discussed
Enabling the new economic actor: data protection, the digital economy, and the Databox
This paper offers a sociological perspective on data protection regulation and its relevance to design. From this perspective, proposed regulation in Europe and the USA seeks to create a new economic actor—the consumer as personal data trader—through new legal frameworks that shift the locus of agency and control in data processing towards the individual consumer or “data subject”. The sociological perspective on proposed data regulation recognises the reflexive relationship between law and the social order, and the commensurate needs to balance the demand for compliance with the design of computational tools that enable this new economic actor. We present the Databox model as a means of providing data protection and allowing the individual to exploit personal data to become an active player in the emerging data economy.The authors acknowledge the support of the EPSRC, Grants EP/M001636/1, EP/M02315X/1, EP/N028260/1, and EU FP7 Grant 611001.This is the final version of the article. It first appeared from [PUBLISHER] via http://dx.doi.org/10.1007/s00779-016-0939-
Carbon Stars and other Luminous Stellar Populations in M33
The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its
proximity and almost face-on inclination means that it projects over a large
area on the sky, making it an ideal candidate for wide-field CCD mosaic
imaging. Photometry was obtained for more than 10^6 stars covering a 74' x 56'
field centered on M33. Main sequence (MS), supergiant branch (SGB), red giant
branch (RGB) and asymptotic giant branch (AGB) populations are identified and
classified based on broad-band V and I photometry. Narrow-band filters are used
to measure spectral features allowing the AGB population to be further divided
into C and M-star types. The galactic structure of M33 is examined using star
counts, colour-colour and colour-magnitude selected stellar populations. We use
the C to M-star ratio to investigate the metallicity gradient in the disk of
M33. The C/M-star ratio is found to increase and then flatten with increasing
galactocentric radius in agreement with viscous disk formation models. The
C-star luminosity function is found to be similar to M31 and the SMC,
suggesting that C-stars should be useful distance indicators. The ``spectacular
arcs of carbon stars'' in M33 postulated recently by Block et al. (2004) are
found in our work to be simply an extension of M33's disk.Comment: 20 pages, 20 figures. Accepted for publication in The Astronomical
Journa
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