109,800 research outputs found
The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets
There is no universally acknowledged criterion to distinguish brown dwarfs
from planets. Numerous studies have used or suggested a definition based on an
object's mass, taking the ~13-Jupiter mass (M_J) limit for the ignition of
deuterium. Here, we investigate various deuterium-burning masses for a range of
models. We find that, while 13 M_J is generally a reasonable rule of thumb, the
deuterium fusion mass depends on the helium abundance, the initial deuterium
abundance, the metallicity of the model, and on what fraction of an object's
initial deuterium abundance must combust in order for the object to qualify as
having burned deuterium. Even though, for most proto-brown dwarf conditions,
50% of the initial deuterium will burn if the object's mass is ~(13.0 +/-
0.8)M_J, the full range of possibilities is significantly broader. For models
ranging from zero-metallicity to more than three times solar metallicity, the
deuterium burning mass ranges from ~11.0 M_J (for 3-times solar metallicity,
10% of initial deuterium burned) to ~16.3 M_J (for zero metallicity, 90% of
initial deuterium burned).Comment: "Models" section expanded, references added, accepted by Ap
Cosmological Deuterium Production in Non-Standard Scenarios
It is widely believed that the cosmic baryon density may be obtained by
inferring deuterium abundances in low-metallicity quasar absorption line
systems. The implicit assumptions which enter this argument are critically
assessed. In particular, the production of deuterium in non-standard Big Bang
nucleosynthesis scenarios, the putative production of deuterium in
astrophysical environments, and the possible destruction of deuterium via
non-standard chemical evolution are discussed.Comment: 11 pages, article based on a talk presented at "Deuterium in the
Universe", Meudon, June 2001, to be published in Planetary and Space Scienc
On the deuterium abundance and the importance of stellar mass loss in the interstellar and intergalactic medium
We quantify the gas-phase abundance of deuterium and fractional contribution
of stellar mass loss to the gas in cosmological zoom-in simulations from the
Feedback In Realistic Environments project. At low metallicity, our simulations
confirm that the deuterium abundance is very close to the primordial value. The
chemical evolution of the deuterium abundance that we derive here agrees
quantitatively with analytical chemical evolution models. We furthermore find
that the relation between the deuterium and oxygen abundance exhibits very
little scatter. We compare our simulations to existing high-redshift
observations in order to determine a primordial deuterium fraction of 2.549 +/-
0.033 x 10^-5 and stress that future observations at higher metallicity can
also be used to constrain this value. At fixed metallicity, the deuterium
fraction decreases slightly with decreasing redshift, due to the increased
importance of mass loss from intermediate-mass stars. We find that the
evolution of the average deuterium fraction in a galaxy correlates with its
star formation history. Our simulations are consistent with observations of the
Milky Way's interstellar medium: the deuterium fraction at the solar circle is
85-92 per cent of the primordial deuterium fraction. We use our simulations to
make predictions for future observations. In particular, the deuterium
abundance is lower at smaller galactocentric radii and in higher mass galaxies,
showing that stellar mass loss is more important for fuelling star formation in
these regimes (and can even dominate). Gas accreting onto galaxies has a
deuterium fraction above that of the galaxies' interstellar medium, but below
the primordial fraction, because it is a mix of gas accreting from the
intergalactic medium and gas previously ejected or stripped from galaxies.Comment: Accepted for publication in MNRAS. Revised version: expanded
discussion and added Figure 2 (residual dependence on iron abundance
The Impact of Deuterated CMOS processing on Gate Oxide Reliability
In recent literature, a controversy has arisen over the question whether deuterium improves the stability of the MOS gate dielectric. In particular, the influence of deuterium incorporation on the bulk oxide quality is not clear. In this letter, deuterium or hydrogen is introduced during either the gate oxidation, postoxidation anneal, and/or the postmetal anneal (PMA). The oxide bulk degradation was evaluated using charge-to-breakdown and stress-induced leakage current; and the oxide interface degradation using hot-carrier degradation and low-frequency noise. The obtained results show that the oxide bulk does not benefit from the presence of deuterium, regardless of the stage of deuterium introduction, or the gate oxide thickness. The oxide interface is more stable only when deuterium is introduced in the PMA
Enhanced anti-deuteron Dark Matter signal and the implications of PAMELA
We show that the jet structure of DM annihilation or decay products enhances
the anti-deuterium production rate by orders of magnitude compared to the
previous computations done assuming a spherically symmetric coalescence model.
In particular, in the limit of heavy DM, M >> m_p, we get a constant rather
than 1/M^2 suppressed anti-deuterium production rate. Therefore, a detectable
anti-deuterium signal is compatible with the lack of an excess in the
anti-proton PAMELA flux. Most importantly, cosmic anti-deuterium searches
become sensitive to the annihilations or decays of heavy DM, suggesting to
extend the experimental anti-deuterium searches above the O(1) GeV scale.Comment: 13 pages, 7 figures. Final versio
Evolution of dispersion in the cosmic deuterium abundance
Deuterium is created during Big Bang Nucleosynthesis, and, in contrast to the
other light stable nuclei, can only be destroyed thereafter by fusion in
stellar interiors. In this paper we study the cosmic evolution of the deuterium
abundance in the interstellar medium and its dispersion using realistic galaxy
evolution models. We find that models that reproduce the observed metal
abundance are compatible with observations of the deuterium abundance in the
local ISM and z ~ 3 absorption line systems. In particular, we reproduce the
low astration factor which we attribute to a low global star formation
efficiency. We calculate the dispersion in deuterium abundance arising from
different structure formation histories in different parts of the Universe. Our
model also predicts an extremely tight correlation between deuterium and metal
abundances which could be used to measure the primordial deuterium abundance.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letters.
Figures rearranged to match published versio
Field desorption ion source development for neutron generators
A new approach to deuterium ion sources for deuterium-tritium neutron
generators is being developed. The source is based upon the field desorption of
deuterium from the surfaces of metal tips. Field desorption studies of
microfabricated field emitter tip arrays have been conducted for the first
time. Maximum fields of 30 V/nm have been applied to the array tip surfaces to
date, although achieving fields of 20 V/nm to possibly 25 V/nm is more typical.
Both the desorption of atomic deuterium ions and the gas phase field ionization
of molecular deuterium has been observed at fields of roughly 20 V/nm and 20-30
V/nm, respectively, at room temperature. The desorption of common surface
adsorbates, such as hydrogen, carbon, water, and carbon monoxide is observed at
fields exceeding ~10 V/nm. In vacuo heating of the arrays to temperatures of
the order of 800 C can be effective in removing many of the surface
contaminants observed
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