8,392 research outputs found
The enigmatic He-sdB pulsator LS IV14116: new insights from the VLT
The intermediate Helium subdwarf B star LS IV14116 is a unique
object showing extremely peculiar atmospheric abundances as well as long-period
pulsations that cannot be explained in terms of the usual opacity mechanism.
One hypothesis invoked was that a strong magnetic field may be responsible. We
discredit this possibility on the basis of FORS2 spectro-polarimetry, which
allows us to rule out a mean longitudinal magnetic field down to 300 G.
Using the same data, we derive the atmospheric parameters for LS
IV14116 to be = 35,150111 K, =
5.880.02 and = 0.620.01. The high
surface gravity in particular is at odds with the theory that LS
IV14116 has not yet settled onto the Helium Main Sequence, and that
the pulsations are excited by an mechanism acting on the
Helium-burning shells present after the main Helium flash.
Archival UVES spectroscopy reveals LS IV14116 to have a radial
velocity of 149.12.1 km/s. Running a full kinematic analysis, we find that
it is on a retrograde orbit around the Galactic centre, with a Galactic radial
velocity component =13.238.28 km/s and a Galactic rotational velocity
component =55.5622.13 km/s. This implies that LS IV14116
belongs to the halo population, an intriguing discovery.Comment: accepted for publication in A&
HRTEM study of a new non-stoichiometric BaTiO(3-δ) structure
BaTiO3-based multilayer ceramic capacitors (MLCCs) with Ni internal electrodes are co-fired in
reducing atmospheres to avoid oxidation of the electrode. Although dielectric materials are doped by
acceptor, donor and amphoteric dopants to minimize the oxygen vacancy content, there is still a
large concentration of oxygen vacancies that are accommodated in the BaTiO3 active layers. In
general, ABO3 perovskites demonstrates a strong ability to accommodate the oxygen vacancies and
maintain a regular pseudo-cubic structure. Oxygen deficient barium titanate can be transformed to a
hexagonal polymorph (h-BT) at high temperatures1,2. In this paper, we report the new modulated and
long range ordered structures of non-stoichiometric BaTiO3-δ that are observed in the electrically
degraded Ni-BaTiO3 MLCCs at low temperature
Paper Session I-A - Starlab Overview
Stariab, a test bed designed to be flown on NASA\u27s Space Shuttle, will be used to conduct a series of acquisition, tracking, and pointing (ATP) experiments that are relevant to the Strategic Defense Initiative (SDI) Mission. In the primary experiment, Stariab will acquire, track, and precisely point a laser beam at an instrumented 4-stage booster rocket known as Starbird. Simultaneously, booster plume data will be collected at a variety of wavelengths and at resolutions never before achieved in space. Stariab will also be used to demonstrate advanced adaptive optics techniques using a booster plume source, rapid optical retargeting, and laser communications from space to below the ocean\u27s surface. In addition, Stariab will be used to collect data on earthspace backgrounds and on adaptive optics systems used to compensate for atmospheric turbulence
Dissolved nitrogen in the sea water of the Northeast Pacific with notes on the total carbon dioxide and the dissolved oxygen
This paper deals with a study and discussion of the distribution of dissolved nitrogen in sea water and its relation to the dissolved oxygen and the total carbon dioxide. Previous studies have been made by Buch (1), Knudsen (8, 9), Petterson (11), Jacobsen (7), Hamburg (6), Dittmar (3) and recently by Rakestraw and Emmel (13., 14). Fox (4) published data showing the variation in the concentration of dissolved nitrogen in equilibrium with the nitrogen of the atmosphere at standard pressure for different temperatures and for different concentrations of sea water. Using these data it is possible to calculate the percent of saturation of the dissolved nitrogen in sea water at a given temperature and chlorinity, the pressure of the gaseous nitrogen being equivalent to that of the gas in air at standard pressur
Entropy-Area Relations in Field Theory
We consider the contribution to the entropy from fields in the background of
a curved time-independent metric. To account for the curvature of space, we
postulate a position-dependent UV cutoff. We argue that a UV cutoff on energy
naturally implies an IR cutoff on distance. With this procedure, we calculate
the scalar contribution in a background anti-de Sitter space, the exterior of a
black hole, and de Sitter space. In all cases, we find results that can be
simply interpreted in terms of local energy and proper volume, yielding insight
into the apparent reduced dimensionality of systems with gravity.Comment: 20 pages, 1 figur
Remote sensing of the Martian surface
Researchers investigated the physical properties of the Martian surface as inferred from a combination of orbiting and earth-based remote sensing observations and in-situ observations. This approach provides the most detailed and self-consistent view of the global and regional nature of the surface. Results focus on the areas of modeling the diurnal variation of the surface temperature of Mars, incorporating the effects of atmospheric radiation, with implications for the interpretation of surface thermal inertia; modeling the thermal emission from particulate surfaces, with application to observations of the surfaces of the Earth, Moon, and Mars; modeling the reflectance spectrum of Mars in an effort to understand the role of particle size in the difference between the bright and dark regions; and determining the slope properties of different terrestrial surfaces and comparing them with planetary slopes derived from radar observations
Momentum space topology of fermion zero modes on brane
We discuss fermion zero modes within the 3+1 brain -- the domain wall between
the two vacua in 4+1 spacetime. We do not assume relativistic invariance in 4+1
spacetime, or any special form of the 4+1 action. The only input is that the
fermions in bulk are fully gapped and are described by nontrivial
momentum-space topology. Then the 3+1 wall between such vacua contains chiral
3+1 fermions. The bosonic collective modes in the wall form the gauge and
gravitational fields. In principle, this universality class of fermionic vacua
can contain all the ingredients of the Standard Model and gravity.Comment: LaTeX file, 8 pages, no figures, version accepted in JETP Letter
Conformal smectics and their many metrics
We establish that equally spaced smectic configurations enjoy an infinite-dimensional conformal symmetry and show that there is a natural map between them and null hypersurfaces in maximally symmetric spacetimes. By choosing the appropriate conformal factor it is possible to restore additional symmetries of focal structures only found before for smectics on flat substrates
Bright matter wave solitons in Bose-Einstein condensates
We review recent experimental and theoretical work on the creation
of bright matter wave solitons in Bose–Einstein condensates. In two recent experiments,
solitons are formed from Bose–Einstein condensates of 7Li by utilizing
a Feshbach resonance to switch from repulsive to attractive interactions.
The solitons are made to propagate in a one-dimensional potential formed by a
focused laser beam. For repulsive interactions, the wavepacket undergoes dispersivewavepacket
spreading, while for attractive interactions, localized solitons are
formed. In our experiment, a multi-soliton train containing up to ten solitons is
observed to propagate without spreading for a duration of 2 s. Adjacent solitons
are found to interact repulsively, in agreement with a calculation based on the
nonlinear Schr¨odinger equation assuming that the soliton train is formed with an
alternating phase structure. The origin of this phase structure is not entirely clear
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
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