15,249 research outputs found
Modeling of the Terminal Velocities of the Dust Ejected Material by the Impact
We compute the distribution of velocities of the particles ejected by the
impact of the projectile released from NASA Deep Impact spacecraft on the
nucleus of comet 9P/Tempel 1 on the successive 20 hours following the
collision. This is performed by the development and use of an ill-conditioned
inverse problem approach, whose main ingredients are a set of observations
taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta
spacecraft, and a set of simple models of the expansion of the dust ejecta
plume for different velocities. Terminal velocities are derived using a maximum
likelihood estimator.
We compare our results with published estimates of the expansion velocity of
the dust cloud. Our approach and models reproduce well the velocity
distribution of the ejected particles. We consider these successful comparisons
of the velocities as an evidence for the appropriateness of the approach. This
analysis provides a more thorough understanding of the properties of the Deep
Impact dust cloud.Comment: Comments: 6 pages, 2 Postscript figures, To appear in the proceedings
of "Deep Impact as a World Observatory Event - Synergies in Space, Time", ed.
Hans Ulrich Kaeufl and Chris Sterken, Springer-Verla
Probabilistic Combination of Noisy Points and Planes for RGB-D Odometry
This work proposes a visual odometry method that combines points and plane
primitives, extracted from a noisy depth camera. Depth measurement uncertainty
is modelled and propagated through the extraction of geometric primitives to
the frame-to-frame motion estimation, where pose is optimized by weighting the
residuals of 3D point and planes matches, according to their uncertainties.
Results on an RGB-D dataset show that the combination of points and planes,
through the proposed method, is able to perform well in poorly textured
environments, where point-based odometry is bound to fail.Comment: Accepted to TAROS 201
Cross-Border Investment, Conflict of Laws, and the Privatization of Securities Law
The rapid acceleration of transnational investing is occurring in an environment in which emerging markets, and foreign interest in these markets, are exploding. The issues involved with cross-border investment, conflict of laws and the privatization of securities law are examined
Evolution and CNO yields of Z=10^-5 stars and possible effects on CEMP production
Our main goals are to get a deeper insight into the evolution and final fates
of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to
investigate their C, N, and O yields. Using the Monash University Stellar
Evolution code we computed and analysed the evolution of stars of metallicity Z
= 10^-5 and masses between 4 and 9 M_sun, from their main sequence until the
late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Our
model stars experience a strong C, N, and O envelope enrichment either due to
the second dredge-up, the dredge-out phenomenon, or the third dredge-up early
during the TP-(S)AGB phase. Their late evolution is therefore similar to that
of higher metallicity objects. When using a standard prescription for the mass
loss rates during the TP-(S)AGB phase, the computed stars lose most of their
envelopes before their cores reach the Chandrasekhar mass, so our standard
models do not predict the occurrence of SNI1/2 for Z = 10^-5 stars. However, we
find that the reduction of only one order of magnitude in the mass-loss rates,
which are particularly uncertain at this metallicity, would prevent the
complete ejection of the envelope, allowing the stars to either explode as an
SNI1/2 or become an electron-capture SN. Our calculations stop due to an
instability near the base of the convective envelope that hampers further
convergence and leaves remnant envelope masses between 0.25 M_sun for our 4
M_sun model and 1.5 M_sun for our 9 M_sun model. We present two sets of C, N,
and O yields derived from our full calculations and computed under two
different assumptions, namely, that the instability causes a practically
instant loss of the remnant envelope or that the stars recover and proceed with
further thermal pulses. Our results have implications for the early chemical
evolution of the Universe.Comment: 12 pages, 13 figures, accepted for publication in A&
Genetic Analyses of Days Open Using a Random Regression Model
The purpose of this study was to investigate the feasibility of using a linear random regression model for the analysis of female fertility as expressed by days open. The analysis provided insight about the kind and amount of variation over the trajectory for age at calving from 24 to 72 mo. Correlations between permanent environmental effects changed from positive to negative values with greater distance between days open in young cows and days open in older cows; r(24,36)=0.88, r(24,72)=-.65. The random regression animal model proved to be a better alternative to a repeatability animal model for prediction of breeding values for days open. Random regression enables breeders to pick the optimum age at calving to select female replacements with enhanced fertility or fewer days open per lactation. Further research is needed to evaluate the advantages of using random regression model on the genetic analysis of days open
Joint Genetic Analysis of Conception and Maintenance of Pregnancy in Dairy Cattle Using a Linear-Threshold Model
A joint analysis of days open and calving success was implemented to further enhance the identification of cows with greater genetic merit for reproductive performance. Calving success is a categorical trait with similar genetic variation as days open and is analyzed jointly with days open to make effective use of the positive genetic correlation between these two traits. The joint analysis can identify cows with greater genetic merit for conception at an earlier stage of lactation and greater success at maintenance of pregnancy. The joint analysis also enhances the reliability of detecting true genetic differences between cows for fertility because it makes more effective use of all data
Reversible Fluorination of Graphene: towards a Two-Dimensional Wide Bandgap Semiconductor
We report the synthesis and evidence of graphene fluoride, a two-dimensional
wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits
hexagonal crystalline order and strongly insulating behavior with resistance
exceeding 10 G at room temperature. Electron transport in graphene
fluoride is well described by variable-range hopping in two dimensions due to
the presence of localized states in the band gap. Graphene obtained through the
reduction of graphene fluoride is highly conductive, exhibiting a resistivity
of less than 100 k at room temperature. Our approach provides a new
path to reversibly engineer the band structure and conductivity of graphene for
electronic and optical applications.Comment: 7 pages, 5 figures, revtex, to appear in PR
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Factors influencing the relationship between fluoride in drinking water and dental fluorosis: a ten-year systematic review and meta-analysis
The relationship between naturally fluoridated groundwater and dental fluorosis has received large attention from researchers around the world. Despite recognition that several factors influence this relationship, there is a lack of systematic studies analyzing the heterogeneity of these results. To fill such a gap, this study performs a systematic review and meta-analysis to understand which factors influence this relationship and how. Selected studies were sampled between 2007 and 2017 from Web of Science, PubMed, Google Scholar and Scopus using keywords and Boolean operators. Results of the systematic review show that dental fluorosis affects individuals of all ages, with the highest prevalence below 11, while the impact of other factors (gender, environmental conditions, diet and dental caries) was inconclusive. Meta-regression analysis, based on information collected through systematic review, indicates that both fluoride in drinking water and temperature influence dental fluorosis significantly and that these studies might be affected by publication bias. Findings show that fluoride negatively affects people's health in less developed countries. The conclusions discuss policy tools and technological innovations that could reduce fluoride levels below that of the WHO (<1.5 mg/L)
Ion dynamics in a linear radio-frequency trap with a single cooling laser
We analyse the possibility of cooling ions with a single laser beam, due to
the coupling between the three components of their motion induced by the
Coulomb interaction. For this purpose, we numerically study the dynamics of ion
clouds of up to 140 particles, trapped in a linear quadrupole potential and
cooled with a laser beam propagating in the radial plane. We use Molecular
Dynamics simulations and model the laser cooling by a stochastic process. For
each component of the motion, we systematically study the dependence of the
temperature with the anisotropy of the trapping potential. Results obtained
using the full radio-frequency (rf) potential are compared to those of the
corresponding pseudo-potential. In the rf case, the rotation symmetry of the
potential has to be broken to keep ions inside the trap. Then, as for the
pseudo-potential case, we show that the efficiency of the Coulomb coupling to
thermalize the components of motion depends on the geometrical configuration of
the cloud. Coulomb coupling appears to be not efficient when the ions organise
as a line or a pancake and the three components of motion reach the same
temperature only if the cloud extends in three dimensions
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