2,439 research outputs found
On understanding the figures of merit for detection and measurement of x-ray polarization
The prospects for accomplishing X-ray polarization measurements appear to
have grown in recent years after a more than 35-year hiatus. Unfortunately,
this long hiatus has brought with it some confusion over the statistical
uncertainties associated with polarization measurements of astronomical
sources. The heart of this confusion stems from a misunderstanding (or
potential misunderstanding) of a standard figure of merit-the minimum
detectable polarization (MDP)-that one of us introduced many years ago. We
review the relevant statistics, and quantify the differences between the MDP
and the uncertainty of an actual polarization measurement. We discuss the
implications for future missions.Comment: 5 pages, 2 figures, to be presented at SPIE conference 7732 (paper
13), corrected typo
Measuring x-ray polarization in the presence of systematic effects: Known background
The prospects for accomplishing x-ray polarization measurements of
astronomical sources have grown in recent years, after a hiatus of more than 37
years. Unfortunately, accompanying this long hiatus has been some confusion
over the statistical uncertainties associated with x-ray polarization
measurements of these sources. We have initiated a program to perform the
detailed calculations that will offer insights into the uncertainties
associated with x-ray polarization measurements. Here we describe a
mathematical formalism for determining the 1- and 2-parameter errors in the
magnitude and position angle of x-ray (linear) polarization in the presence of
a (polarized or unpolarized) background. We further review relevant
statistics-including clearly distinguishing between the Minimum Detectable
Polarization (MDP) and the accuracy of a polarization measurement.Comment: 12 pages, 4 figures, for SPIE conference proceeding
Universal Plug-n-Play Sensor Integration for Advanced Navigation
This research investigates the potential for Plug-n-Play sensor integration for navigation and other applications. Specifically, the requirements of such a system are outlined and attempts are made to achieve them using two separate systems: one using Robot Operating System (ROS) as middleware and the other using more traditional software design patterns. The end result is not so much a deliverable in terms of software, but more of a feasibility analysis comparing the two approaches
The Simplicial Characterisation of TS networks: Theory and applications
We use the visibility algorithm to construct the time series networks
obtained from the time series of different dynamical regimes of the logistic
map. We define the simplicial characterisers of networks which can analyse the
simplicial structure at both the global and local levels. These characterisers
are used to analyse the TS networks obtained in different dynamical regimes of
the logisitic map. It is seen that the simplicial characterisers are able to
distinguish between distinct dynamical regimes. We also apply the simplicial
characterisers to time series networks constructed from fMRI data, where the
preliminary results indicate that the characterisers are able to differentiate
between distinct TS networks.Comment: 11 pages, 2 figures, 4 tables. Accepted for publication in
Proceedings of the 4th International Conference on Applications in Nonlinear
Dynamics (ICAND 2016
Methods of optimizing X-ray optical prescriptions for wide-field applications
We are working on the development of a method for optimizing wide-field X-ray
telescope mirror prescriptions, including polynomial coefficients, mirror shell
relative displacements, and (assuming 4 focal plane detectors) detector
placement along the optical axis and detector tilt. With our methods, we hope
to reduce number of Monte-Carlo ray traces required to search the
multi-dimensional design parameter space, and to lessen the complexity of
finding the optimum design parameters in that space. Regarding higher order
polynomial terms as small perturbations of an underlying Wolter I optic design,
we begin by using the results of Monte-Carlo ray traces to devise trial
analytic functions, for an individual Wolter I mirror shell, that can be used
to represent the spatial resolution on an arbitrary focal surface. We then
introduce a notation and tools for Monte-Carlo ray tracing of a polynomial
mirror shell prescription which permits the polynomial coefficients to remain
symbolic. In principle, given a set of parameters defining the underlying
Wolter I optics, a single set of Monte-Carlo ray traces are then sufficient to
determine the polymonial coefficients through the solution of a large set of
linear equations in the symbolic coefficients. We describe the present status
of this development effort.Comment: 14 pages, to be presented at SPIE conference 7732 (paper 93
Matrilines in Neolithic cattle from Orkney, Scotland reveals complex husbandry patterns of ancestry
mtDNA, isotopic and archaeozoological analyses of cattle teeth and bones from the Late Neolithic site of Links of Noltland, Orkney, Scotland revealed these animals followed similar grazing regimes but displayed diverse genetic origins and included one cattle skull that carried an aurochs (wild cattle) genetic haplotype. Morphometric analyses indicate the presence of some cattle larger than published dimensions of Neolithic domestic cattle. Several explanations for these finding are possible but may be the evidence of a complex pattern of domestic cattle introductions into Neolithic Orkney and interbreeding between domestic and wild cattle
Calculation of the persistence length of a flexible polymer chain with short range self-repulsion
For a self-repelling polymer chain consisting of n segments we calculate the
persistence length L(j,n), defined as the projection of the end-to-end vector
on the direction of the j`th segment. This quantity shows some pronounced
variation along the chain. Using the renormalization group and
epsilon-expansion we establish the scaling form and calculate the scaling
function to order epsilon^2. Asymptotically the simple result L(j,n) ~
const(j(n-j)/n)^(2nu-1) emerges for dimension d=3. Also outside the excluded
volume limit L(j,n) is found to behave very similar to the swelling factor of a
chain of length j(n-j)/n. We carry through simulations which are found to be in
good accord with our analytical results. For d=2 both our and previous
simulations as well as theoretical arguments suggest the existence of
logarithmic anomalies.Comment: 28 pages, 8 figures, changed conten
Measurements with the Chandra X-Ray Observatory's flight contamination monitor
NASA's Chandra X-ray Observatory includes a Flight Contamination Monitor
(FCM), a system of 16 radioactive calibration sources mounted to the inside of
the Observatory's forward contamination cover. The purpose of the FCM is to
verify the ground-to-orbit transfer of the Chandra flux scale, through
comparison of data acquired during the ground calibration with those obtained
in orbit, immediately prior to opening the Observatory's sun-shade door. Here
we report results of these measurements, which place limits on the change in
mirror--detector system response and, hence, on any accumulation of molecular
contamination on the mirrors' iridium-coated surfaces.Comment: 7pages,8figures,for SPIE 4012, paper 7
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