9,339 research outputs found
Synergistic relationships among remote-sensing and geophysical media: Geological and hydrological applications
The synergistic relationships among LANDSAT imagery, Skylab photographs, and aerial photographs were useful for establishing areas of near surface bedrock. Lineaments were located on LANDSAT imagery and aerial photographs during 1978 and near surface water tables were to be located during 1980. Both of these subjects can be identified by remote sensing methods more reliably than individual outcrops, which are small and occur in a wide variety of environments with a wide range of responses. Bedrock outcrops themselves could not be resolved by any of the data sources used, nor did any combination of data sources specifically identify rock at the ground surface. The data sources could not simply be combined mathematically to produce a visual image of probable areas of near surface bedrock. Outcrops and near surface bedrock had to be verified visually at the site. Despite these drawbacks, a procedure for locating areas of near surface bedrock within which actual surface outcrops may occur was developed
PCA of PCA: Principal Component Analysis of Partial Covering Absorption in NGC 1365
We analyse 400 ks of XMM-Newton data on the active galactic nucleus NGC 1365
using principal component analysis (PCA) to identify model independent spectral
components. We find two significant components and demonstrate that they are
qualitatively different from those found in MCG?6-30-15 using the same method.
As the variability in NGC 1365 is known to be due to changes in the parameters
of a partial covering neutral absorber, this shows that the same mechanism
cannot be the driver of variability in MCG-6-30-15. By examining intervals
where the spectrum shows relatively low absorption we separate the effects of
intrinsic source variability, including signatures of relativistic reflection,
from variations in the intervening absorption. We simulate the principal
components produced by different physical variations, and show that PCA
provides a clear distinction between absorption and reflection as the drivers
of variability in AGN spectra. The simulations are shown to reproduce the PCA
spectra of both NGC 1365 and MCG-6-30-15, and further demonstrate that the
dominant cause of spectral variability in these two sources requires a
qualitatively different mechanism.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
Behavior of Proteins at Interfaces
The adsorption and conformational changes of three plasma
proteins, (bovine) serum albumin, .y-globulin and fibrinogen, on
several (bio)polymer surfaces are reported. A theory is developed
which invokes reversible adsorption of the proteins in the initial
stages and a time dependent conformational change of adsorbed
protein leading to essentially irreversible long-term adsorption.
In each case experimental evidence indicates that there .is a time-
dependent decrease in structural order. It is postulated that the
protein unfolds to optimize surface bonding, thus inducing the
c;hemistry of the protein/water interface by bonding at the protein/
/polymer interface. Cell binding studies support the concept that
the plasma proteins unfold to optimize the polymer/protein interaction
Remarks on the structure constants of the Verlinde algebra associated to
The structure constants of the Verlinde
algebra as functions of either vanish or can be expressed after a change
of variable as the weight function of an irreducible representation of .
We give a similar formula in the case.Comment: 5 pages, AmsTeX, 1 figure available on reques
Disentangling the Complex Broadband X-ray Spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku
We present results from a coordinated -+ observation of
the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source,
with strong contributions from relativistic reflection from the inner accretion
disk, neutral absorption and further reprocessing by more distant material, and
ionised absorption from an outflow. We undertake a detailed spectral analysis
combining the broadband coverage provided by -+ with a
multi-epoch approach incorporating archival observations performed by
- and . Our focus is on characterising the reflection from
the inner accretion disk, which previous works have suggested may dominate the
AGN emission, and constraining the black hole spin. Using lamppost disk
reflection models, we find that the results for the inner disk are largely
insensitive to assumptions regarding the geometry of the distant reprocessor
and the precise form of the illuminating X-ray continuum. However, these
results do depend on the treatment of the iron abundance of the distant
absorber/reprocessor. The multi-epoch data favour a scenario in which the AGN
is chemically homogeneous, and we find that a rapidly rotating black hole is
preferred, with , but a slowly-rotating black hole is not
strongly excluded. In addition to the results for the inner disk, we also find
that both the neutral and ionised absorbers vary from epoch to epoch, implying
that both have some degree of inhomogeneity in their structure.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Revealing the X-ray Variability of AGN with Principal Component Analysis
We analyse a sample of 26 active galactic nuclei with deep XMM-Newton
observations, using principal component analysis (PCA) to find model
independent spectra of the different variable components. In total, we identify
at least 12 qualitatively different patterns of spectral variability, involving
several different mechanisms, including five sources which show evidence of
variable relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, NGC 3516
and Mrk 766) and three which show evidence of varying partial covering neutral
absorption (NGC 4395, NGC 1365, and NGC 4151). In over half of the sources
studied, the variability is dominated by changes in a power law continuum, both
in terms of changes in flux and power law index, which could be produced by
propagating fluctuations within the corona. Simulations are used to find unique
predictions for different physical models, and we then attempt to qualitatively
match the results from the simulations to the behaviour observed in the real
data. We are able to explain a large proportion of the variability in these
sources using simple models of spectral variability, but more complex models
may be needed for the remainder. We have begun the process of building up a
library of different principal components, so that spectral variability in AGN
can quickly be matched to physical processes. We show that PCA can be an
extremely powerful tool for distinguishing different patterns of variability in
AGN, and that it can be used effectively on the large amounts of high-quality
archival data available from the current generation of X-ray telescopes.Comment: 25 pages, 27 figures, accepted to MNRAS. Analysis code available on
request to lead author. Edit: Rogue table remove
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