5,110 research outputs found
Neutron-activation analysis applied to copper ores and artifacts
Neutron activation analysis is used for quantitative identification of trace metals in copper. Establishing a unique fingerprint of impurities in Michigan copper would enable identification of artifacts made from this copper
Evolution and Magnitudes of Candidate Planet Nine
The recently renewed interest in a possible additional major body in the
outer solar system prompted us to study the thermodynamic evolution of such an
object. We assumed that it is a smaller version of Uranus and Neptune. We
modeled the temporal evolution of the radius, temperature, intrinsic
luminosity, and the blackbody spectrum of distant ice giant planets. The aim is
also to provide estimates of the magnitudes in different bands to assess
whether the object might be detectable. Simulations of the cooling and
contraction were conducted for ice giants with masses of 5, 10, 20, and 50
Mearth that are located at 280, 700, and 1120 AU from the Sun. The core
composition, the fraction of H/He, the efficiency of energy transport, and the
initial luminosity were varied. The atmospheric opacity was set to 1, 50, and
100 times solar metallicity. We find for a nominal 10 Mearth planet at 700 AU
at the current age of the solar system an effective temperature of 47 K, much
higher than the equilibrium temperature of about 10 K, a radius of 3.7 Rearth,
and an intrinsic luminosity of 0.006 Ljupiter. It has estimated apparent
magnitudes of Johnson V, R, I, L, N, Q of 21.7, 21.4, 21.0, 20.1, 19.9, and
10.7, and WISE W1-W4 magnitudes of 20.1, 20.1, 18.6, and 10.2. The Q and W4
band and other observations longward of about 13 microns pick up the intrinsic
flux. If candidate Planet 9 has a significant H/He layer and an efficient
energy transport in the interior, then its luminosity is dominated by the
intrinsic contribution, making it a self-luminous planet. At a likely position
on its orbit near aphelion, we estimate for a mass of 5, 10, 20, and 50 Mearth
a V magnitude from the reflected light of 24.3, 23.7, 23.3, and 22.6 and a Q
magnitude from the intrinsic radiation of 14.6, 11.7, 9.2, and 5.8. The latter
would probably have been detected by past surveys.Comment: 6 pages, 3 figures, accepted to A&
Accelerated Parameter Estimation with DALE
We consider methods for improving the estimation of constraints on a
high-dimensional parameter space with a computationally expensive likelihood
function. In such cases Markov chain Monte Carlo (MCMC) can take a long time to
converge and concentrates on finding the maxima rather than the often-desired
confidence contours for accurate error estimation. We employ DALE (Direct
Analysis of Limits via the Exterior of ) for determining confidence
contours by minimizing a cost function parametrized to incentivize points in
parameter space which are both on the confidence limit and far from previously
sampled points. We compare DALE to the nested sampling algorithm
implemented in MultiNest on a toy likelihood function that is highly
non-Gaussian and non-linear in the mapping between parameter values and
. We find that in high-dimensional cases DALE finds the same
confidence limit as MultiNest using roughly an order of magnitude fewer
evaluations of the likelihood function. DALE is open-source and available
at https://github.com/danielsf/Dalex.git
Measuring dark energy properties with 3D cosmic shear
We present parameter estimation forecasts for present and future 3D cosmic
shear surveys. We demonstrate that, in conjunction with results from cosmic
microwave background (CMB) experiments, the properties of dark energy can be
estimated with very high precision with large-scale, fully 3D weak lensing
surveys. In particular, a 5-band, 10,000 square degree ground-based survey to a
median redshift of zm=0.7 could achieve 1- marginal statistical errors,
in combination with the constraints expected from the CMB Planck Surveyor, of
w0=0.108 and wa=0.099 where we parameterize w by
w(a)=w0+wa(1-a) where a is the scale factor. Such a survey is achievable with a
wide-field camera on a 4 metre class telescope. The error on the value of w at
an intermediate pivot redshift of z=0.368 is constrained to
w(z=0.368)=0.0175. We compare and combine the 3D weak lensing
constraints with the cosmological and dark energy parameters measured from
planned Baryon Acoustic Oscillation (BAO) and supernova Type Ia experiments,
and find that 3D weak lensing significantly improves the marginalized errors. A
combination of 3D weak lensing, CMB and BAO experiments could achieve
w0=0.037 and wa=0.099. Fully 3D weak shear analysis avoids the
loss of information inherent in tomographic binning, and we show that the
sensitivity to systematic errors is much less. In conjunction with the fact
that the physics of lensing is very soundly based, this analysis demonstrates
that deep, wide-angle 3D weak lensing surveys are extremely promising for
measuring dark energy properties.Comment: 18 pages, 16 figures. Accepted to MNRAS. Figures now in grayscale.
Further discussions on non-Gaussianity and photometric redshift errors. Some
references adde
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