196 research outputs found
How Well Do We Know the Orbits of the Outer Planets?
This paper deals with the problem of astrometric determination of the orbital
elements of the outer planets, in particular by assessing the ability of
astrometric observations to detect perturbations of the sort expected from the
Pioneer effect or other small perturbations to gravity. We also show that while
using simplified models of the dynamics can lead to some insights, one must be
careful to not over-simplify the issues involved lest one be misled by the
analysis onto false paths. Specifically, we show that the current ephemeris of
Pluto does not preclude the existence of the Pioneer effect. We show that the
orbit of Pluto is simply not well enough characterized at present to make such
an assertion. A number of misunderstandings related to these topics have now
propagated through the literature and have been used as a basis for drawing
conclusions about the dynamics of the solar system. Thus, the objective of this
paper is to address these issues. Finally, we offer some comments dealing with
the complex topic of model selection and comparison.Comment: Accepted for publication in the Ap
Multi-fractional analysis of molecular diffusion in polymer multilayers by FRAP: a new simulation-based approach
Comprehensive analysis of the multifractional molecular diffusion provides a deeper understanding of the diffusion phenomenon in the fields of material science, molecular and cell biology, advanced biomaterials, etc. Fluorescence recovery after photobleaching (FRAP) is commonly employed to probe the molecular diffusion. Despite FRAP being a very popular method, it is not easy to assess multifractional molecular diffusion due to limited possibilities of approaches for analysis. Here we present a novel simulation-optimization-based approach (S-approach) that significantly broadens possibilities of the analysis. In the S-approach, possible fluorescence recovery scenarios are primarily simulated and afterward compared with a real measurement while optimizing parameters of a model until a sufficient match is achieved. This makes it possible to reveal multifractional molecular diffusion. Fluorescent latex particles of different size and fluorescein isothiocyanate in an aqueous medium were utilized as test systems. Finally, the S-approach has been used to evaluate diffusion of cytochrome c loaded into multilayers made of hyaluronan and polylysine. Software for evaluation of multifractional molecular diffusion by S-approach has been developed aiming to offer maximal versatility and user-friendly way for analysis
The Shearing HI Spiral Pattern of NGC 1365
The Tremaine-Weinberg equations are solved for a pattern speed that is
allowed to vary with radius. The solution method transforms an integral
equation for the pattern speed to a least squares problem with well established
procedures for statistical analysis. The method applied to the HI spiral
pattern of the barred, grand-design galaxy NGC 1365 produced convincing
evidence for a radial dependence in the pattern speed. The pattern speed
behaves approximately as 1/r, and is very similar to the material speed. There
are no clear indications of corotation or Lindblad resonances. Tests show that
the results are not selection biased, and that the method is not measuring the
material speed. Other methods of solving the Tremaine-Weinberg equations for
shearing patterns were found to produce results in agreement with those
obtained using the current method. Previous estimates that relied on the
assumptions of the density-wave interpretation of spiral structure are
inconsistent with the results obtained using the current method. The results
are consistent with spiral structure theories that allow for shearing patterns,
and contradict fundamental assumptions in the density-wave interpretation that
are often used for finding spiral arm pattern speeds. The spiral pattern is
winding on a characteristic timescale of ~ 500 Myrs.Comment: Accepted for publication in The Astrophysical Journa
Accounting for Calibration Uncertainties in X-ray Analysis: Effective Areas in Spectral Fitting
While considerable advance has been made to account for statistical
uncertainties in astronomical analyses, systematic instrumental uncertainties
have been generally ignored. This can be crucial to a proper interpretation of
analysis results because instrumental calibration uncertainty is a form of
systematic uncertainty. Ignoring it can underestimate error bars and introduce
bias into the fitted values of model parameters. Accounting for such
uncertainties currently requires extensive case-specific simulations if using
existing analysis packages. Here we present general statistical methods that
incorporate calibration uncertainties into spectral analysis of high-energy
data. We first present a method based on multiple imputation that can be
applied with any fitting method, but is necessarily approximate. We then
describe a more exact Bayesian approach that works in conjunction with a Markov
chain Monte Carlo based fitting. We explore methods for improving computational
efficiency, and in particular detail a method of summarizing calibration
uncertainties with a principal component analysis of samples of plausible
calibration files. This method is implemented using recently codified Chandra
effective area uncertainties for low-resolution spectral analysis and is
verified using both simulated and actual Chandra data. Our procedure for
incorporating effective area uncertainty is easily generalized to other types
of calibration uncertainties.Comment: 61 pages double spaced, 8 figures, accepted for publication in Ap
A physically meaningful method for the comparison of potential energy functions
In the study of the conformational behavior of complex systems, such as
proteins, several related statistical measures are commonly used to compare two
different potential energy functions. Among them, the Pearson's correlation
coefficient r has no units and allows only semi-quantitative statements to be
made. Those that do have units of energy and whose value may be compared to a
physically relevant scale, such as the root mean square deviation (RMSD), the
mean error of the energies (ER), the standard deviation of the error (SDER) or
the mean absolute error (AER), overestimate the distance between potentials.
Moreover, their precise statistical meaning is far from clear. In this article,
a new measure of the distance between potential energy functions is defined
which overcomes the aforementioned difficulties. In addition, its precise
physical meaning is discussed, the important issue of its additivity is
investigated and some possible applications are proposed. Finally, two of these
applications are illustrated with practical examples: the study of the van der
Waals energy, as implemented in CHARMM, in the Trp-Cage protein (PDB code 1L2Y)
and the comparison of different levels of the theory in the ab initio study of
the Ramachandran map of the model peptide HCO-L-Ala-NH2.Comment: 30 pages, 7 figures, LaTeX, BibTeX. v2: A misspelling in the author's
name has been corrected. v3: A new application of the method has been added
at the end of section 9 and minor modifications have also been made in other
sections. v4: Journal reference and minor corrections adde
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Assessing the spatial spread–skill of ensemble flood maps with remote-sensing observations
An ensemble of forecast flood inundation maps has the potential to represent the uncertainty in the flood forecast and provide a location-specific likelihood of flooding. Ensemble flood map forecasts provide probabilistic information to flood forecasters, flood risk managers and insurers and will ultimately benefit people living in flood-prone areas. Spatial verification of the ensemble flood map forecast against remotely observed flooding is important to understand both the skill of the ensemble forecast and the uncertainty represented in the variation or spread of the individual ensemble-member flood maps. In atmospheric sciences, a scale-selective approach has been used to evaluate a convective precipitation ensemble forecast. This determines a skilful scale (agreement scale) of ensemble performance by locally computing a skill metric across a range of length scales. By extending this approach through a new application, we evaluate the spatial predictability and the spatial spread–skill of an ensemble flood forecast across a domain of interest. The spatial spread–skill method computes an agreement scale at every grid cell between each unique pair of ensemble flood maps (ensemble spatial spread) and between each ensemble flood map with a SAR-derived flood map (ensemble spatial skill; SAR: synthetic aperture radar). These two are compared to produce the final spatial spread–skill performance. These methods are applied to the August 2017 flood event on the Brahmaputra River in the Assam region of India. Both the spatial skill and spread–skill relationship vary with location and can be linked to the physical characteristics of the flooding event such as the location of heavy precipitation. During monitoring of flood inundation accuracy in operational forecasting systems, validation and mapping of the spatial spread–skill relationship would allow better quantification of forecast systematic biases and uncertainties. This would be particularly useful for ungauged catchments where forecast streamflows are uncalibrated and would enable targeted model improvements to be made across different parts of the forecast chain
Improving urban flood mapping by merging Synthetic Aperture Radar-derived flood footprints with flood hazard maps
Remotely sensed flood extents obtained in near real-time can be used for emergency flood incident management and as observations for assimilation into flood forecasting models. High resolution Synthetic Aperture Radar (SAR) sensors have the potential to detect flood extents in urban areas through cloud during both day- and night-time. This paper considers a method for detecting flooding in urban areas by merging near real-time SAR flood extents with model-derived flood hazard maps. This allows a two-way symbiosis, whereby currently available SAR urban flood extent improves future model flood predictions, while flood hazard maps obtained after the SAR overpass improve the SAR estimate of the urban flood extent. The method estimates urban flooding using SAR backscatter only in rural areas adjacent to the urban ones. It was compared to an existing method using SAR returns in both the rural and urban areas. The method using SAR solely in rural areas gave an average flood detection accuracy of 94% and a false positive rate of 9% in the urban areas, and was more accurate than the existing method
The roared-at boys? Repertory casting and gender politics in the RSC's 2014 Swan season
This essay interrogates the loading of the “Roaring Girls” season by asking what it means to “roar” in both the early modern period and twenty-first century, unpacking the terms on which the women of these productions are empowered or undermined through their treatment by their male counterparts. Performed alongside the 2014 “Midsummer Mischief” new writing season, the plays reposition “roaring” as challenging male-centred modes of representation. Drawing on Marvin Carlson's influential work on “ghosting”, this essay addresses these questions through investigation of the practices and implications of ensemble casting. With Arden of Faversham, The Roaring Girl and The White Devil sharing a single ensemble, the iterated roles of actors across the ensemble become key to understanding the season's overall strategies for presenting and interrogating misogyny. The recycling of actors’ bodies throws into relief the individual roles of the main “roaring girls”, framing and articulating the role of mischievous disruption within the company's work
Antarctic Peninsula mesoscale cyclone variability and climatic impacts influenced by the SAM
The frequency of mesoscale cyclones in the Western Antarctic Peninsula (WAP) region during 1991-94 is correlated with the Southern Hemisphere Annular Mode (SAM) index, most strongly during winter and spring. Also, during periods of positive SAM index polarity there is a shift in the storm tracks to favor more east-bound trajectories, consistent with strengthening of circumpolar westerlies. The presence of mesoscale cyclones is associated with positive near-surface-air temperature anomalies in the WAP region year-round, largest during winter
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