Spectral Energy Distribution Modeling of Markarian 501 through a non-linear least square minimization

So far the Spectral Energy Distribution (SED) of Active Galactic Nuclei (AGN), in particular blazars, have been obtained in a heuristics way. This is mainly due to both the many free parameters of the emission model and the severe lack of simultaneous multi-frequency data. This leads to non-rigorous and possibly biased analyses, and makes it difficult to compare results coming from different analyses. However, recent simultaneous multi-frequency campaigns are providing long-term broad-band coverages of source activity, and large multi-frequency data sets are becoming available. So emission model fitting may be attempted with better profit now. The main aim of this thesis is to develop a statistical approach that fits AGN SEDs in a rigorous way. Such an approach consists in a Chi squared -minimization, based on the Levenberg-Marquardt algorithm, that returns the most likely values of the SED parameters, plus a method devised to obtain the related uncertaintes. The whole minimization process is implemented in a C++ code. However, this approach may reveal unexpected features of the Chi squared-manifold that might affect convergence, due to spurious correlations between model parameters and/or inadequacy of the currently available datasets. For these reasons, a statistical analysis will be carried out on the solutions obtained from several minimizations, each starting from different points of the parameter space. This approach is applied to different activity states of the blazar Markarian 501, in a Synchrotron Self Compton (SSC) framework. In particular, starting from available observations of this source taken with the ground-based Major Atmospheric Gamma-ray Imaging Cherenkov telescopes (MAGIC) in 2011, 7 multi-frequency datasets were obtained. Based on multi-frequency and simultaneity requirements, all datasets include also data provided by the Swift UVOT, Swift XRT, and Fermi LAT orbiting telescopes. The SED modelling of each dataset will be performed through a non-linear Chi squared-minimization in order to obtain the most likely values of the parameters describing the SSC model. Finally, it is worth remarking that this approach is not only a rigorous statistical method to find the most likely source parameters for different scenarios, but it also represents a powerful tool to efficiently discriminate between different emission models

Predicting glacier accumulation area distributions

A mass balance model based on energy balance at the terrain surface was developed and used to predict glacier accumulation areas in the Jotunheimen, Norway. Spatially distributed melt modelling used local climate and energy balance surfaces to drive predictions, derived from regional climate and topographic data. Predictions had a temporal resolution of 1 month and a spatial resolution of 100 m, which were able to simulate observed glacier accumulation area distributions. Data were stored and manipulated within a GIS and spatial trends and patterns within the data were explored. These trends guided the design of a suite of geomorphologically and climatologically significant variables which were used to simulate the observed spatial organisation of climatic variables, specifically temperature, precipitation and wind speed and direction. DEM quality was found as a critical factor in minimising error propagation. A new method of removing spatially and spectrally organised DEM error is presented using a fast Fourier transformation. This was successfully employed to remove error within the DEM minimising error propagation into model predictions. With no parameter fitting the modeled spatial distribution of snowcover showed good agreement with observed distributions. Topographic maps and a Landsat ETM+ image are used to validate the predictions and identify areas of over or under prediction. Topographically constrained glaciers are most effectively simulated, where aspect, gradient and altitude impose dominant controls on accumulation. Reflections on the causes of over or under prediction are presented and future research directions to address these are outlined. Sensitivity of snow accumulation to climatic and radiative variables was assessed. Results showed the mass balance of accumulation areas is most sensitive to air temperature and cloud cover parameterisations. The model was applied to reconstruct snow accumulation at the last glacial maximum and under IPCC warming scenarios to assess the sensitivity of melt to changing environmental conditions, which showed pronounced sensitivity to summer temperatures Low data requirements: regional climate and elevation data identify the model as a powerful tool for predicting the onset, duration and rate of melt for any geographical area

Space programs summary no. 37-45, volume IV FOR the period April 1, 1967 to May 31, 1967. Supporting research and advanced development

Space exploration projects on systems, guidance and control, environmental simulation, space sciences, propulsion, telecommunications, and engineering mechanic

Aeronautical Engineering: A continuing bibliography with indexes (supplement 161)

This bibliography lists 375 reports, articles and other documents introduced into the NASA scientific and technical information system in April 1983

An Insulating Glass Knowledge Base

This report will discuss issues relevant to Insulating Glass (IG) durability performance by presenting the observations and developed conclusions in a logical sequential format. This concluding effort discusses Phase II activities and focuses on beginning to quantifying IG durability issues while continuing the approach presented in the Phase I activities (Appendix 1) which discuss a qualitative assessment of durability issues. Phase II developed a focus around two specific IG design classes previously presented in Phase I of this project. The typical box spacer and thermoplastic spacer design including their Failure Modes and Effect Analysis (FMEA) and Fault Tree diagrams were chosen to address two currently used IG design options with varying components and failure modes. The system failures occur due to failures of components or their interfaces. Efforts to begin quantifying the durability issues focused on the development and delivery of an included computer based IG durability simulation program. The focus/effort to deliver the foundation for a comprehensive IG durability simulation tool is necessary to address advancements needed to meet current and future building envelope energy performance goals. This need is based upon the current lack of IG field failure data and the lengthy field observation time necessary for this data collection. Ultimately, the simulation program is intended to be used by designers throughout the current and future industry supply chain. Its use is intended to advance IG durability as expectations grow around energy conservation and with the growth of embedded technologies as required to meet energy needs. In addition the tool has the immediate benefit of providing insight for research and improvement prioritization. Included in the simulation model presentation are elements and/or methods to address IG materials, design, process, quality, induced stress (environmental and other factors), validation, etc. In addition, acquired data is presented in support of project and model assumptions. Finally, current and suggested testing protocol and procedure for future model validation and IG physical testing are discussed

Space programs summary no. 37-62, volume 3 for the period 1 February - 31 March 1970. Supporting research and advanced development

Spacecraft communication, equipment, guidance, construction materials, propulsion, and related researc