34,537 research outputs found
A new method for the determination of thin film porosity
Internal reflection spectroscopy may be used to determine presence of water in thin film pores. Presence of water in such pores is function of relative humidity and pore size. Thus, one can determine pore size by controlling humidity. Fluids with surface tension different from that of water can be used to detect pores
Experimental study of pop-in behavior of surface flaw-type cracks Final report
Growth behavior of surface-flaw type cracks in titanium alloy
Magnetic fields from inflation: the transition to the radiation era
We compute the contribution to the scalar metric perturbations from
large-scale magnetic fields which are generated during inflation. We show that
apart from the usual passive and compensated modes, the magnetic fields also
contribute to the constant mode from inflation. This is different from the
causal (post inflationary) generation of magnetic fields where such a mode is
absent and it might lead to significant, non-Gaussian CMB anisotropies.Comment: 19 pages, no figures. v2: Substantially revised version with
different conclusions. v3: one reference added, matches version accepted for
publication in PR
Multilevel Double Loop Monte Carlo and Stochastic Collocation Methods with Importance Sampling for Bayesian Optimal Experimental Design
An optimal experimental set-up maximizes the value of data for statistical
inferences and predictions. The efficiency of strategies for finding optimal
experimental set-ups is particularly important for experiments that are
time-consuming or expensive to perform. For instance, in the situation when the
experiments are modeled by Partial Differential Equations (PDEs), multilevel
methods have been proven to dramatically reduce the computational complexity of
their single-level counterparts when estimating expected values. For a setting
where PDEs can model experiments, we propose two multilevel methods for
estimating a popular design criterion known as the expected information gain in
simulation-based Bayesian optimal experimental design. The expected information
gain criterion is of a nested expectation form, and only a handful of
multilevel methods have been proposed for problems of such form. We propose a
Multilevel Double Loop Monte Carlo (MLDLMC), which is a multilevel strategy
with Double Loop Monte Carlo (DLMC), and a Multilevel Double Loop Stochastic
Collocation (MLDLSC), which performs a high-dimensional integration by
deterministic quadrature on sparse grids. For both methods, the Laplace
approximation is used for importance sampling that significantly reduces the
computational work of estimating inner expectations. The optimal values of the
method parameters are determined by minimizing the average computational work,
subject to satisfying the desired error tolerance. The computational
efficiencies of the methods are demonstrated by estimating the expected
information gain for Bayesian inference of the fiber orientation in composite
laminate materials from an electrical impedance tomography experiment. MLDLSC
performs better than MLDLMC when the regularity of the quantity of interest,
with respect to the additive noise and the unknown parameters, can be
exploited
Measuring cosmic magnetic fields by rotation measure-galaxy cross-correlations in cosmological simulations
Using cosmological MHD simulations of the magnetic field in galaxy clusters
and filaments we evaluate the possibility to infer the magnetic field strength
in filaments by measuring cross-correlation functions between Faraday Rotation
Measures (RM) and the galaxy density field. We also test the reliability of
recent estimates considering the problem of data quality and Galactic
foreground (GF) removal in current datasets. Besides the two self-consistent
simulations of cosmological magnetic fields based on primordial seed fields and
galactic outflows analyzed here, we also explore a larger range of models
scaling up the resulting magnetic fields of one of the simulations. We find
that, if an unnormalized estimator for the cross-correlation functions and a GF
removal procedure is used, the detectability of the cosmological signal is only
possible for future instruments (e.g. SKA and ASKAP). However, mapping of the
observed RM signal to the underlying magnetization of the Universe (both in
space and time) is an extremely challenging task which is limited by the
ambiguities of our model parameters, as well as to the weak response of the RM
signal in low density environments. Therefore, we conclude that current data
cannot constrain the amplitude and distribution of magnetic fields within the
large scale structure and a detailed theoretical understanding of the build up
and distribution of magnetic fields within the Universe will be needed for the
interpretation of future observations.Comment: 11 pages, 11 figures, comparation between RM data and simulations in
fig. 8, submited to MNRAS
The radio-infrared correlation in galaxies
The radio-infrared correlation was explained as a direct and linear
relationship between star formation and IR emission. However, one fact making
the IR-star formation linkage less obvious is that the IR emission consists of
at least two emission components, cold dust and warm dust. The cold dust
emission may not be directly linked to the young stellar population.
Furthermore, understanding the origin of the radio-IR correlation requires to
discriminate between the two main components of the radio continuum emission,
free-free and synchrotron emission. Here, we present a multi-scale study of the
correlation of IR with both the thermal and non-thermal (synchrotron)
components of the radio continuum emission from the nearby galaxies M33 and
M31.Comment: To appear in Highlights of Astronomy, Volume 15, XXVIIth IAU General
Assembly, August 200
Miss Appropriation: Why Do We Keep Talking About Her?
In this short opinion piece, I add to the discussion of Native American cultural misappropriation, particularly in the area of fashion design, and discuss why I believe it is such a popular topic in contemporary mainstream media
Transverse electric scattering widths for strips-Fourier transform technique
A technique which is based on Fourier transformations is introduced for predicting scattering widths. For a strip it is shown that explicit determination of the linear current density is not necessary for bistatic or monostatic scattering width calculations. Comparisons of the predictions of the technique are made with the integral equation technique predictions, which do not require explicit evaluations of linear current densities
Modeling 3-D objects with planar surfaces for prediction of electromagnetic scattering
Electromagnetic scattering analysis of objects at resonance is difficult because low frequency techniques are slow and computer intensive, and high frequency techniques may not be reliable. A new technique for predicting the electromagnetic backscatter from electrically conducting objects at resonance is studied. This technique is based on modeling three dimensional objects as a combination of flat plates where some of the plates are blocking the scattering from others. A cube is analyzed as a simple example. The preliminary results compare well with the Geometrical Theory of Diffraction and with measured data
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