16,895 research outputs found
A Single-armed Manta-board as a New Diver-controlled Planing Board and Its Use for Underwater Surveys
Due to inadequacies of previous underwater towing techniques and the special needs of a recent underwater survey, a modified mania-board technique was developed. With this new technique, the diver holds on to the manta-board with one arm; consequently, the board is referred to as a single-armed manta-board (sam-board). The sam-board proved inexpensive and highly maneuverable, allowing the divers to freely collect samples or record information. Through some experimenting with the board and changing some of the variables, such as rope lengths, towing speeds, etc., a highly efficient towing method can be achieved. Preplanning and strict diving safety procedures must, however, be implemented to assure efficiency. This paper presents the materials, guidelines for board construction, equipment, and preplanning and diving safety procedures necessary for the sam-board towing operation
Electrically driven magnetism on a Pd thin film
Using first-principles density functional calculations we demonstrate that
ferromagnetism can be induced and modulated on an otherwise paramagnetic Pd
metal thin-film surface through application of an external electric field. As
free charges are either accumulated or depleted at the Pd surface to screen the
applied electric field there is a corresponding change in the surface density
of states. This change can be made sufficient for the Fermi-level density of
states to satisfy the Stoner criterion, driving a transition locally at the
surface from a paramagnetic state to an itinerant ferromagnetic state above a
critical applied electric field, Ec. Furthermore, due to the second-order
nature of this transition, the surface magnetization of the ferromagnetic state
just above the transition exhibits a substantial dependence on electric field,
as the result of an enhanced magnetoelectric susceptibility. Using a linearized
Stoner model we explain the occurrence of the itinerant ferromagnetism and
demonstrate that the magnetic moment on the Pd surface follows a square-root
variation with electric field consistent with our first-principles
calculations.Comment: 8 pages, 7 figure
Design comparison of cesium and potassium vapor turbine-generator units for space power
Design comparison of cesium and potassium vapor turbogenerator units for space power plant
Physical activity levels of older adults receiving a home care service
Sammenligning av aktivitetsnivå for personer som har hatt hverdagsrehabilitering og vanlige tjenester.The 3 study objectives were to compare the activity levels of older people who had received a restorative home care service with those of people who had received "usual" home care, explore the predictors of physical activity in these 2 groups, and determine whether either group met the minimum recommended activity levels for their age group. A questionnaire was posted to 1,490 clients who had been referred for a home care service between 2006 and 2009. Older people who had received a restorative care service were more active than those who had received usual care (p = .049), but service group did not predict activity levels when other variables were adjusted for in a multiple regression. Younger individuals who were in better physical condition, with good mobility and no diagnosis of depression, were more likely to be active. Investigation of alternatives to the current exercise component of the restorative program is needed
Giant Tunneling Electroresistance Effect Driven by an Electrically Controlled Spin Valve at a Complex Oxide Interface
A giant tunneling electroresistance effect may be achieved in a ferroelectric
tunnel junction by exploiting the magnetoelectric effect at the interface
between a ferroelectric barrier and magnetic La1-xSrxMnO3 electrode. Using
first-principles density functional theory we demonstrate that a few magnetic
monolayers of La1-xSrxMnO3 near the interface act, in response to ferroelectric
polarization reversal, as an atomic scale spin-valve by filtering
spin-dependent current. This effect produces more than an order of magnitude
change in conductance, and thus constitutes a giant resistive switching effect.Comment: 4 pages, 4 figure
A Large Mass of H2 in the Brightest Cluster Galaxy in Zwicky 3146
We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous
(L_{IR}=4e11 L_sun) brightest cluster galaxy (BCG) in the X-ray-luminous
cluster Z3146 (z=0.29). The spectrum shows strong aromatic emission features,
indicating that the dominant source of the infrared luminosity is star
formation. The most striking feature of the spectrum, however, is the
exceptionally strong molecular hydrogen (H2) emission lines, which seem to be
shock-excited. The line luminosities and inferred warm H2 gas mass (~1e10
M_sun) are 6 times larger than those of NGC 6240, the most H2-luminous galaxy
at z <~ 0.1. Together with the large amount of cold H2 detected previously
(~1e11 M_sun), this indicates that the Z3146 BCG contains disproportionately
large amounts of both warm and cold H2 gas for its infrared luminosity, which
may be related to the intracluster gas cooling process in the cluster core.Comment: 13 pages, 3 figures, 1 table; Accepted for publication in ApJ
Prediction of electrically-induced magnetic reconstruction at the manganite/ferroelectric interface
The control of magnetization via the application of an electric field, known
as magnetoelectric coupling, is among the most fascinating and active research
areas today. In addition to fundamental scientific interest, magnetoelectric
effects may lead to new device concepts for data storage and processing. There
are several known mechanisms for magnetoelectric coupling that include
intrinsic effects in single-phase materials, strain induced coupling in
two-phase composites, and electronically-driven effects at interfaces. Here we
explore a different type of magnetoelectric effect at a
ferromagnetic-ferroelectric interface: magnetic reconstruction induced by
switching of electric polarization. We demonstrate this effect using
first-principles calculations of a La1-xAxMnO3/BaTiO3 (001) interface, where A
is a divalent cation. By choosing the doping level x to be near a transition
between magnetic phases we show that the reversal of the ferroelectric
polarization of BaTiO3 leads to a change in the magnetic order at the interface
from ferromagnetic to antiferromagnetic. This predicted electrically-induced
magnetic reconstruction at the interface represents a substantial interfacial
magnetoelectric effect.Comment: 7 pages, 5 figures, 1 tabl
Elemental Abundance Ratios in Stars of the Outer Galactic Disk. II. Field Red Giants
We summarize a selection process to identify red giants in the direction of
the southern warp of the Galactic disk, employing VI_C photometry and
multi-object spectroscopy. We also present results from follow-up
high-resolution, high-S/N echelle spectroscopy of three field red giants,
finding [Fe/H] values of about -0.5. The field stars, with Galactocentric
distances estimated at 10 to 15 kpc, support the conclusion of Yong, Carney, &
de Almeida (2005) that the Galactic metallicity gradient disappears beyond R_GC
values of 10 to 12 kpc for the older stars and clusters of the outer disk. The
field and cluster stars at such large distances show very similar abundance
patterns, and, in particular, all show enhancements of the "alpha" elements O,
Mg, Si, Ca, and Ti and the r-process element Eu. These results suggest that
Type II supernovae have been significant contributors to star formation in the
outer disk relative to Type Ia supernovae within the past few Gyrs. We also
compare our results with those available for much younger objects. The limited
results for the H II regions and B stars in the outer disk also suggest that
the radial metallicity gradient in the outer disk is shallow or absent. The
much more extensive results for Cepheids confirm these trends, and that the
change in slope of the metallicity gradient may occur at a larger
Galactocentric distance than for the older stars and clusters. However, the
younger stars also show rising alpha element enhancements with increasing R_GC,
at least beyond 12 kpc. These trends are consistent with the idea of a
progressive growth in the size of the Galactic disk with time, and episodic
enrichment by Type II supernovae as part of the disk's growth. [Abridged]Comment: Accepted for publication in A
Nonlinear stabilitty for steady vortex pairs
In this article, we prove nonlinear orbital stability for steadily
translating vortex pairs, a family of nonlinear waves that are exact solutions
of the incompressible, two-dimensional Euler equations. We use an adaptation of
Kelvin's variational principle, maximizing kinetic energy penalised by a
multiple of momentum among mirror-symmetric isovortical rearrangements. This
formulation has the advantage that the functional to be maximized and the
constraint set are both invariant under the flow of the time-dependent Euler
equations, and this observation is used strongly in the analysis. Previous work
on existence yields a wide class of examples to which our result applies.Comment: 25 page
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