15,117 research outputs found
Rings associated to coverings of finite p-groups
In general the endomorphisms of a non-abelian group do not form a ring under
the operations of addition and composition of functions. Several papers have
dealt with the ring of functions defined on a group which are endomorphisms
when restricted to the elements of a cover of the group by abelian subgroups.
We give an algorithm which allows us to determine the elements of the ring of
functions of a finite -group which arises in this manner when the elements
of the cover are required to be either cyclic or elementary abelian of rank
. This enables us to determine the actual structure of such a ring as a
subdirect product. A key part of the argument is the construction of a graph
whose vertices are the subgroups of order and whose edges are determined by
the covering.Comment: 11 pages. No figures. To appear Turkish Journal of Mathematic
Evidence for Photoionization Driven Broad Absorption Line Variability
We present a qualitative analysis of the variability of quasar broad
absorption lines using the large multi-epoch spectroscopic dataset of the Sloan
Digital Sky Survey Data Release 10. We confirm that variations of absorption
lines are highly coordinated among different components of the same ion or the
same absorption component of different ions for C IV, Si IV and N V.
Furthermore, we show that the equivalent widths of the lines decrease or
increase statistically when the continuum brightens or dims. This is further
supported by the synchronized variations of emission and absorption line
equivalent width, when the well established intrinsic Baldwin effect for
emission lines is taken into account. We find that the emergence of an
absorption component is usually accompanying with dimming of the continuum
while the disappearance of an absorption line component with brightening of the
continuum. This suggests that the emergence or disappearance of a C IV
absorption component is only the extreme case, when the ionic column density is
very sensitive to continuum variations or the continuum variability amplitude
is larger. These results support the idea that absorption line variability is
driven mainly by changes in the gas ionization in response to continuum
variations, that the line-absorbing gas is highly ionized, and in some extreme
cases, too highly ionized to be detected in UV absorption lines. Due to
uncertainties in the spectroscopic flux calibration, we cannot quantify the
fraction of quasars with asynchronized continuum and absorption line
variations.Comment: 41 pages, 15 figures, accepted to Ap
Atmospheric turbulence profiling with SLODAR using multiple adaptive optics wavefront sensors
The slope detection and ranging (SLODAR) method recovers atmospheric turbulence profiles from time averaged spatial cross correlations of wavefront slopes measured by Shack-Hartmann wavefront sensors. The Palomar multiple guide star unit (MGSU) was set up to test tomographic multiple guide star adaptive optics and provided an ideal test bed for SLODAR turbulence altitude profiling. We present the data reduction methods and SLODAR results from MGSU observations made in 2006. Wind profiling is also performed using delayed wavefront cross correlations along with SLODAR analysis. The wind profiling analysis is shown to improve the height resolution of the SLODAR method and in addition gives the wind velocities of the turbulent layers
Study of eddy current probes
The recognition of materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques
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