8,590 research outputs found
Process for the leaching of AP from propellant
A method for the recovery of ammonium perchlorate from waste solid rocket propellant is described wherein shredded particles of the propellant are leached with an aqueous leach solution containing a low concentration of surface active agent while stirring the suspension
First comparison of wave observations from CoMP and AIA/SDO
Waves have long been thought to contribute to the heating of the solar corona
and the generation of the solar wind. Recent observations have demonstrated
evidence of quasi-periodic longitudinal disturbances and ubiquitous transverse
wave propagation in many different coronal environments. This paper
investigates signatures of different types of oscillatory behaviour, both above
the solar limb and on-disk, by comparing findings from the Coronal
Multi-channel Polarimeter (CoMP) and the Atmospheric Imaging Assembly (AIA) on
board the Solar Dynamics Observatory (SDO) for the same active region. We study
both transverse and longitudinal motion by comparing and contrasting
time-distance images of parallel and perpendicular cuts along/across active
region fan loops. Comparisons between parallel space-time features in CoMP
Doppler velocity and transverse oscillations in AIA images are made, together
with space-time analysis of propagating quasi-periodic intensity features seen
near the base of loops in AIA. Signatures of transverse motions are observed
along the same magnetic structure using CoMP Doppler velocity
(Vphase=600-750km/s, P=3-6mins) and in AIA/SDO above the limb (P=3-8mins).
Quasi-periodic intensity features (Vphase=100-200km/s, P=6-11mins) also travel
along the base of the same structure. On the disk, signatures of both
transverse and longitudinal intensity features were observed by AIA; both show
similar properties to signatures found along structures anchored in the same
active region three days earlier above the limb. Correlated features are
recovered by space-time analysis of neighbouring tracks over perpendicular
distances of <2.6Mm.Comment: 14 pages, 14 figures, 1 tabl
Twisting type-N vacuum fields with a group
We derive the equations corresponding to twisting type-N vacuum gravitational
fields with one Killing vector and one homothetic Killing vector by using the
same approach as that developed by one of us in order to treat the case with
two non-commuting Killing vectors. We study the case when the homothetic
parameter takes the value -1, which is shown to admit a reduction to a
third-order real ordinary differential equation for this problem, similar to
that previously obtained by one of us when two Killing vectors are present.Comment: LaTeX, 11 pages. To be published in Classical and Quantum Gravit
Vacuum type I spacetimes and aligned Papapetrou fields: symmetries
We analyze type I vacuum solutions admitting an isometry whose Killing
2--form is aligned with a principal bivector of the Weyl tensor, and we show
that these solutions belong to a family of type I metrics which admit a group
of isometries. We give a classification of this family and we study the
Bianchi type for each class. The classes compatible with an aligned Killing
2--form are also determined. The Szekeres-Brans theorem is extended to non
vacuum spacetimes with vanishing Cotton tensor.Comment: 19 pages; a reference adde
An Iterative Approach to Twisting and Diverging, Type N, Vacuum Einstein Equations: A (Third-Order) Resolution of Stephani's `Paradox'
In 1993, a proof was published, within ``Classical and Quantum Gravity,''
that there are no regular solutions to the {\it linearized} version of the
twisting, type-N, vacuum solutions of the Einstein field equations. While this
proof is certainly correct, we show that the conclusions drawn from that fact
were unwarranted, namely that this irregularity caused such solutions not to be
able to truly describe pure gravitational waves. In this article, we resolve
the paradox---since such first-order solutions must always have singular lines
in space for all sufficiently large values of ---by showing that if we
perturbatively iterate the solution up to the third order in small quantities,
there are acceptable regular solutions. That these solutions become flat before
they become non-twisting tells us something interesting concerning the general
behavior of solutions describing gravitational radiation from a bounded source.Comment: 11 pages, a plain TeX file, submitted to ``Classical and Quantum
Gravity'
On the Adoption of Partial Least Squares in Psychological Research: Caveat Emptor
The partial least squares technique (PLS) has been touted as a viable alternative to latent variable structural equation modeling (SEM) for evaluating theoretical models in the differential psychology domain. We bring some balance to the discussion by reviewing the broader methodological literature to highlight: (1) the misleading characterization of PLS as an SEM method; (2) limitations of PLS for global model testing; (3) problems in testing the significance of path coefficients; (4) extremely high false positive rates when using empirical confidence intervals in conjunction with a new "sign change correction" for path coefficients; (5) misconceptions surrounding the supposedly superior ability of PLS to handle small sample sizes and non-normality; and (6) conceptual and statistical problems with formative measurement and the application of PLS to such models. Additionally, we also reanalyze the dataset provided by Willaby et al. (2015; doi:10.1016/j.paid.2014.09.008) to highlight the limitations of PLS. Our broader review and analysis of the available evidence makes it clear that PLS is not useful for statistical estimation and testing
The Galaxy Angular Correlation Functions and Power Spectrum from the Two Micron All Sky Survey
We calculate the angular correlation function of galaxies in the Two Micron
All Sky Survey. We minimize the possible contamination by stars, dust, seeing
and sky brightness by studying their cross correlation with galaxy density, and
limiting the galaxy sample accordingly. We measure the correlation function at
scales between 1-18 arcdegs using a half million galaxies. We find a best fit
power law to the correlation function has a slope of 0.76 and an amplitude of
0.11. However, there are statistically significant oscillations around this
power law. The largest oscillation occurs at about 0.8 degrees, corresponding
to 2.8 h^{-1} Mpc at the median redshift of our survey, as expected in halo
occupation distribution descriptions of galaxy clustering.
We invert the angular correlation function using Singular Value Decomposition
to measure the three-dimensional power spectrum and find that it too is in good
agreement with previous measurements. A dip seen in the power spectrum at small
wavenumber k is statistically consistent with CDM-type power spectra. A fit of
CDM-type power spectra to k < 0.2 h Mpc^{-1} give constraints of
\Gamma_{eff}=0.116 and \sigma_8=0.96. This suggest a K_s-band linear bias of
1.1+/-0.2. This \Gamma_{eff} is different from the WMAP CMB derived value. On
small scales the power-law shape of our power spectrum is shallower than that
derived for the SDSS. These facts together imply a biasing of these different
galaxies that might be nonlinear, that might be either waveband or luminosity
dependent, and that might have a nonlocal origin.Comment: 14 pages, 20 figures, to be published in ApJ January 20th, revision
included two new figures, version with high resolution figures can be found
here http::ww
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