19,860 research outputs found
Heights of Special Points on Quaternionic Shimura Varieties
Let be a quaternion algebra over a totally real number field. We give
an explicit formula for heights of special points on the quaternionic Shimura
variety associated with in terms of Faltings heights of CM abelian
varieties. Special points correspond to CM fields and partial CM-types
. We then show that our height is
compatible with the canonical height of a partial CM-type defined by Pila,
Shankar, and Tsimerman. This gives another proof that the height of a partial
CM-type is bounded subpolynomially in terms of the discriminant of .Comment: 30 pages. Comments welcom
Interacting Dark Energy -- constraints and degeneracies
In standard cosmologies, dark energy interacts only gravitationally with dark
matter. There could be a non-gravitational interaction in the dark sector,
leading to changes in the effective DE equation of state, in the redshift
dependence of the DM density and in structure formation. We use CMB, BAO and
SNIa data to constrain a model where the energy transfer in the dark sector is
proportional to the DE density. There are two subclasses, defined by the
vanishing of momentum transfer either in the DM or the DE frame. We conduct a
Markov-Chain Monte-Carlo analysis to obtain best-fit parameters. The background
evolution allows large interaction strengths, and the constraints from CMB
anisotropies are weak. The growth of DM density perturbations is much more
sensitive to the interaction, and can deviate strongly from the standard case.
However, the deviations are degenerate with galaxy bias and thus more difficult
to constrain. Interestingly, the ISW signature is suppressed since the
non-standard background evolution can compensate for high growth rates. We also
discuss the partial degeneracy between interacting DE and modified gravity, and
how this can be broken.Comment: 12 pages, 18 figures. Clarification on instabilities. Accepted by PR
Relativistic corrections and non-Gaussianity in radio continuum surveys
Forthcoming radio continuum surveys will cover large volumes of the
observable Universe and will reach to high redshifts, making them potentially
powerful probes of dark energy, modified gravity and non-Gaussianity. Here we
extend recent works by analyzing the general relativistic (GR) corrections to
the angular power spectrum. These GR corrections to the standard Newtonian
analysis of the power spectrum become significant on scales near and beyond the
Hubble scale at each redshift. We consider the continuum surveys with LOFAR,
WSRT and ASKAP, and examples of continuum surveys with the SKA. We find that
the GR corrections are at most percent-level in LOFAR, WODAN and EMU surveys,
but they can produce changes for high enough sensitivity SKA continuum
surveys. The signal is however dominated by cosmic variance, and
multiple-tracer observations will be needed to overcome this problem. The GR
corrections are suppressed in continuum surveys because of the integration over
redshift -- we expect that GR corrections will be enhanced for future SKA HI
surveys in which the source redshifts will be known. We also provide
predictions for the angular power spectra in the case where the primordial
perturbations have local non-Gaussianity. We find that non-Gaussianity
dominates over GR corrections, and rises above cosmic variance when for SKA continuum surveys.Comment: 8 pages, 6 figures; Version accepted by JCA
Utilizing Distance Metrics on Lineups to Examine What People Read From Data Plots
Graphics play a crucial role in statistical analysis and data mining. This
paper describes metrics developed to assist the use of lineups for making
inferential statements. Lineups embed the plot of the data among a set of null
plots, and engage a human observer to select the plot that is most different
from the rest. If the data plot is selected it corresponds to the rejection of
a null hypothesis. Metrics are calculated in association with lineups, to
measure the quality of the lineup, and help to understand what people see in
the data plots. The null plots represent a finite sample from a null
distribution, and the selected sample potentially affects the ease or
difficulty of a lineup. Distance metrics are designed to describe how close the
true data plot is to the null plots, and how close the null plots are to each
other. The distribution of the distance metrics is studied to learn how well
this matches to what people detect in the plots, the effect of null generating
mechanism and plot choices for particular tasks. The analysis was conducted on
data that has already been collected from Amazon Turk studies conducted with
lineups for studying an array of data analysis tasks.Comment: 28 pages, lots of figure
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Current practice and challenges towards handling uncertainty for effective outcomes in maintenance
The combination of viable heuristic attributes with statistical measurements presents significant challenges in industrial maintenance for complex assets under through-life service contracts. Techniques to obtain and process heuristic attributes raise numerous uncertainties which often go undefined and unmitigated. A holistic view of these uncertainties may improve decision-making capabilities and reduce maintenance costs and turnaround time. It is therefore necessary to identify and rank factors that influence uncertainties originating from challenges in the above context. This, along with an identification of who contributes to such challenges and current practice to handle them, sets the focus for this study.
The influence of 32 categorised factors on uncertainty is assessed through a questionnaire completed by nine experienced maintenance managers from a leading defence company. The pedigree approach is applied to score validity of respondents’ answers according to their experience and job role to normalise scores. Results are discussed in interviews with respondents along with current practice in and ways to improve uncertainty assessment. Scores are weighted through the Analytical Hierarchy Process (AHP) in order to identify the most influential factors on uncertainty in maintenance. The analysis revealed that these include: intellectual property rights (IPR), maintainer performance, quality of information, resistance to change, stakeholder communication and technology integration. These are verified with 40 practitioners from various industrial backgrounds. From the interviews, it is deemed that a holistic view of heuristic and statistical attributes ultimately allows for more accomplished decision-making but requires trade-offs between quality and cost over the asset’s life cycle
Degradation assessment of industrial composites using thermography
Thermographic inspection is a relatively new technique for Non-Destructive Testing (NDT) which has been gathering increasing interest due to its relatively low cost hardware and extremely fast data acquisition properties. This technique is especially promising in the area of rapid automated damage detection and quantification. In collaboration with a major industry partner from the aerospace sector advanced thermography-based NDT software for impact damaged composites is introduced. The software is based on correlation analysis of time-temperature profiles in combination with an image enhancement process. The prototype software is aiming to a) better visualise the damages in a relatively easy-to-use way and b) automatically and quantitatively measure the properties of the degradation. Knowing that degradation properties play an important role in the identification of degradation types, tests and results on specimens which were artificially damaged have been performed and analyzed.EPSR
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