12,214 research outputs found
Aerospace lubrication technology transfer to industrial applications
Difficulties encountered in entering industrial markets with an aerospace lubrication and coating technology are discussed along with the technical, financial, and managerial solutions that evolved
Pupil remapping for high contrast astronomy: results from an optical testbed
The direct imaging and characterization of Earth-like planets is among the
most sought-after prizes in contemporary astrophysics, however current optical
instrumentation delivers insufficient dynamic range to overcome the vast
contrast differential between the planet and its host star. New opportunities
are offered by coherent single mode fibers, whose technological development has
been motivated by the needs of the telecom industry in the near infrared. This
paper presents a new vision for an instrument using coherent waveguides to
remap the pupil geometry of the telescope. It would (i) inject the full pupil
of the telescope into an array of single mode fibers, (ii) rearrange the pupil
so fringes can be accurately measured, and (iii) permit image reconstruction so
that atmospheric blurring can be totally removed. Here we present a laboratory
experiment whose goal was to validate the theoretical concepts underpinning our
proposed method. We successfully confirmed that we can retrieve the image of a
simulated astrophysical object (in this case a binary star) though a pupil
remapping instrument using single mode fibers.Comment: Accepted in Optics Expres
The molecular and dusty composition of Betelgeuse's inner circumstellar environment
The study of the atmosphere of red supergiant stars in general and of
Betelgeuse (alpha Orionis) in particular is of prime importance to understand
dust formation and how mass is lost to the interstellar medium in evolved
massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the
atmosphere of Betelgeuse has been proposed to account for the near- and
mid-infrared spectroscopic observations of Betelgeuse. The goal is to further
test this hypothesis and to identify some of the molecules in this MOLsphere.
We report on measurements taken with the mid-infrared two-telescope beam
combiner of the VLTI, MIDI, operated between 7.5 and 13.5 m. The data are
compared to a simple geometric model of a photosphere surrounded by a warm
absorbing and emitting shell. Physical characteristics of the shell are
derived: size, temperature and optical depth. The chemical constituents are
determined with an analysis consistent with available infrared spectra and
interferometric data. We are able to account for the measured optical depth of
the shell in the N band, the ISO-SWS spectrum and K and L band interferometric
data with a shell whose inner and outer radii are given by the above range and
with the following species: H2O, SiO and Al2O3. These results confirm the
MOLsphere model. We bring evidence for more constituents and for the presence
of species participating in the formation of dust grains in the atmosphere of
the star, i.e. well below the distance at which the dust shell is detected. We
believe these results bring key elements to the understanding of mass loss in
Betelgeuse and red supergiants in general and bring support to the dust-driven
scenario.Comment: 11 pages, 10 figures, accepted for publication in A&
A Slow-Release Nitrogen Fertilizer: Ammonium-Loaded Clinoptilolite
Crops grown in sandy soils require frequent irrigation. As a result, nitrogen (N) fertilizers. such as ammonium sulfate((NH4)2SO4), are leached from the rooting zone of crops. This loss of N increases N fertilizer use and the potential for nitrate (NO3-) contamination of water. Ammonium-loaded clinoptilolite (NH4+-Cp) may reduce this N leaching, increase N fertilizer use-efficiency, and prevent NO3- contamination of water while sustaining normal crop growth.
The potential of NH4+-Cp as a N fertilizer was assessed in three leaching experiments without plants and two leaching experiments with plants. Pots containing rounded quartz sand were amended with (NH4)2SO4 and one of three NH4+-Cp size fractions: small (
Finally, in two leaching studies, pots containing the sandy soil were planted with sweet corn and grown for 35 d and 42 d, respectively. No differences were found among N sources in corn relative growth rates, leaf area ratios, and net assimilation rates, even though the corn plants that were fertilized with NH4+-Cp assimilated significantly more N than the (NH4)2SO4-fertilized plants. The pots fertilized with NH5+-Cp leached
In the greenhouse, NH4+-Cp is a slow-release fertilizer that will reduce N leaching while maintaining normal plant growth. However, field studies are needed to confirm the suitability of NH4+-Cp as a slow-release fertilizer under field conditions
Two-body anticorrelation in a harmonically trapped ideal Bose gas
We predict the existence of a dip below unity in the second-order coherence
function of a partially condensed ideal Bose gas in harmonic confinement,
signaling the anticorrelation of density fluctuations in the sample. The dip in
the second-order coherence function is revealed in a canonical-ensemble
calculation, corresponding to a system with fixed total number of particles. In
a grand-canonical ensemble description, this dip is obscured by the
occupation-number fluctuation catastrophe of the ideal Bose gas. The
anticorrelation is most pronounced in highly anisotropic trap geometries
containing small particle numbers. We explain the fundamental physical
mechanism which underlies this phenomenon, and its relevance to experiments on
interacting Bose gases.Comment: 10 pages, 5 figures. v2: Minor changes and corrections to figures and
text. To appear in PR
Critical Rotation of an Annular Superfluid Bose Gas
We analyze the excitation spectrum of a superfluid Bose-Einstein condensate
rotating in a ring trap. We identify two important branches of the spectrum
related to outer and inner edge surface modes that lead to the instability of
the superfluid. Depending on the initial circulation of the annular condensate,
either the outer or the inner modes become first unstable. This instability is
crucially related to the superfluid nature of the rotating gas. In particular
we point out the existence of a maximal circulation above which the superflow
decays spontaneously, which cannot be explained by invoking the average speed
of sound.Comment: 5 pages, 5 figures, PRA Rapid Com
Performance of astrometric detection of a hotspot orbiting on the innermost stable circular orbit of the galactic centre black hole
The galactic central black hole Sgr A* exhibits outbursts of radiation in the
near infrared (so-called IR flares). One model of these events consists in a
hotspot orbiting on the innermost stable circular orbit (ISCO) of the hole.
These outbursts can be used as a probe of the central gravitational potential.
One main scientific goal of the second generation VLTI instrument GRAVITY is to
observe these flares astrometrically. Here, the astrometric precision of
GRAVITY is investigated in imaging mode, which consists in analysing the image
computed from the interferometric data. The capability of the instrument to put
in light the motion of a hotspot orbiting on the ISCO of our central black hole
is then discussed.
We find that GRAVITY's astrometric precision for a single star in imaging
mode is smaller than the Schwarzschild radius of Sgr A*. The instrument can
also demonstrate that a body orbiting on the last stable orbit of the black
hole is indeed moving. It yields a typical size of the orbit, if the source is
as bright as m_K=14.
These results show that GRAVITY allows one to study the close environment of
Sgr A*. Having access to the ISCO of the central massive black hole probably
allows constraining general relativity in its strong regime. Moreover, if the
hotspot model is appropriate, the black hole spin can be constrained.Comment: 13 pages, 11 figures ; accepted by MNRA
The K giant star Arcturus: the hybrid nature of its infrared spectrum
We study infrared spectrum of Arcturus to clarify the nature of the cool
component of its atmosphere, referred to as the CO-mosphere, with the use of
the IR spectral atlas by Hinkle et al.(1995). The nature of CO lines shows an
abrupt change at logW/nu = -4.75, and the lines stronger than this limit can no
longer be analyzed by the classical line-formation theory. A more simple
manifestation of this fact is that the curves-of-growth (CG) of CO lines show
an unpredictable upturn at logW/nu = -4.75. Similar unusual behaviors of
empirical CG are confirmed in other red (super)giant stars, and it looks as if
the CG is a hybrid of at least two components of different origins. Although
strong lines of the CO fundamentals observed in Arcturus show strengthening
compared with the predicted photospheric spectrum, the weaker lines show slight
weakening, and we interpret these results as due to absorption/emission by the
molecular clouds formed in the extended atmosphere. Now do clouds exist in
stellar atmospheres? It is by no means easy to answer this question by
spectroscopic observations alone, but we find several arguments in favor of
such a possibility in Arcturus by analyzing the CO lines. In cooler
(super)giant stars in which CO lines show similar unusual behaviors as in
Arcturus, the presence of molecular clouds in the outer atmospheres was
demonstrated by direct observations with spatial interferometry. We suggest
that the formation of molecular clouds is a general feature in cool luminous
stars from early K to late M (super)giant stars.Comment: 18 pages, 15 Postscript figures, 1 Table in electronic form, Accepted
for publication in Astronomy and Astrophysic
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