Mean-preserving interpolation with splines for solar radiation modeling

Interpolation is a fundamental process in solar resource assessment that glues consecutive components of the modeling chain. Most interpolation techniques assume that the interpolating function must go through the interpolation points. However, this assumption does not fit with averaged datasets or variables that must be conserved across interpolation. Here I present a mean-preserving splines method for interpolating one-dimensional data that conserves the interpolated field and is appropriate for averaged datasets. It uses second-order polynomial splines to minimize the fluctuations of the interpolated field, restricts the interpolation results to user-provided limits to prevent unphysical values, deals with periodic boundary conditions in the interpolated field, and can work with non-uniform averaging grids. The validity and performance of the method are illustrated against regular second- and third-order splines using relevant case examples in the solar resource assessment realm.This work was supported by the FEDER 2014–2020 Operative Program, and the Consejería de Economía y Conocimiento of Junta de Andalucía through the research project UMA20-FEDERJA-134, and the Agencia Estatal de Investigación through the research projects PID2019-107455RB-C21 and PID2019-107455RB-C22, Spain. The author is grateful to the scientists and personnel of the Spanish Meteorological Agency and the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center who provided the data used in this study. The University of Málaga/CBUA provided the funding for open access // Funding for open access charge: Universidad de Málaga / CBU

Genetic Algorithm-Based Model Order Reduction of Aeroservoelastic Systems with Consistant States

This paper presents a model order reduction framework to construct linear parameter-varying reduced-order models of flexible aircraft for aeroservoelasticity analysis and control synthesis in broad two-dimensional flight parameter space. Genetic algorithms are used to automatically determine physical states for reduction and to generate reduced-order models at grid points within parameter space while minimizing the trial-and-error process. In addition, balanced truncation for unstable systems is used in conjunction with the congruence transformation technique to achieve locally optimal realization and weak fulfillment of state consistency across the entire parameter space. Therefore, aeroservoelasticity reduced-order models at any flight condition can be obtained simply through model interpolation. The methodology is applied to the pitch-plant model of the X-56A Multi-Use Technology Testbed currently being tested at NASA Armstrong Flight Research Center for flutter suppression and gust load alleviation. The present studies indicate that the reduced-order model with more than 12 reduction in the number of states relative to the original model is able to accurately predict system response among all input-output channels. The genetic-algorithm-guided approach exceeds manual and empirical state selection in terms of efficiency and accuracy. The interpolated aeroservoelasticity reduced order models exhibit smooth pole transition and continuously varying gains along a set of prescribed flight conditions, which verifies consistent state representation obtained by congruence transformation. The present model order reduction framework can be used by control engineers for robust aeroservoelasticity controller synthesis and novel vehicle design

Uniform reconstruction of continuous functions with the RAFU method

[EN] The RAFU (radical functions) method can be used to obtain the uniformreconstruction of a continuous function from its values at some ofthe points of partitions of a closed interval. In this work we willprove that we can reconstruct a continuous function from average samplesof these points, from linear combinations of them and from local averagesamples given by convolution. Uniform error bounds will be established. If these data are unknown but approximate values of them are known, uniform reconstruction will be also possible. Error estimates in these cases will be given. The case of a non-uniform net will be treated. Examples and algorithms will be also shown.Corbacho Cortés, E. (2017). Uniform reconstruction of continuous functions with the RAFU method. Applied General Topology. 18(2):361-375. doi:10.4995/agt.2017.7263SWORD36137518

Biological Dose Accumulation in Image-guided Radiotherapy

Dose accumulation (DA), the computation of the total delivered 3D dose distribution Da of a fractionated radiotherapy treatment using daily patient imaging, is getting established in clinical practice. Although the aim is to estimate the achieved biological outcome of the treatment, the principles of biological effect estimation are currently not followed consistently in the process. In this thesis, the biological effect accumulation approach and total biological dose (bEQD) were derived as a biologically consistent DA workflow. Clinical relevance of bEQD and its dependence on individual workflow aspects were investigated in data from three patient cohorts. It was found that Da systematically underestimates the obtained biological effect, which can be avoided by the use of bEQD. Results showed that this is strongest for late-responding organs at risk (OAR) with low �=� values in dose gradient regions around the target that are prone to organ motion. bEQD to Da deviations occurred locally, in so-called hotspots, showing individual cases of high difference magnitude but only small statistical impact. Hotspots of bEQD - Da deviation around 4 Gy in bladder and rectum were found in patients treated for prostate carcinoma. Hypofractionation increased these deviations strongly up to 8 Gy and also showed clinically relevant deviations in dose-volume analysis. Dose-response correlation in standard fractionation showed only little impact on the DA approaches. Workflow uncertainties are dominated by those from deformable image registration, which are in the same range as the difference between bEQD and Da. bEQD should be considered in the application of treatment adaptation, especially to avoid damage to OARs in individual cases

Radiocarbon age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 119 (2014): 1630–1651, doi:10.1002/2014JG002688.Continued warming of the Arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon (OC), thereby accentuating global warming. However, it is unclear if recent warming has raised the current rates of permafrost OC release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing. Here we use a time series of radiocarbon age-offsets (14C) between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost OC release over the last 14,500 years. The lake traps and archives OC imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age-offsets. Today, the age-offset (2 ka; thousand of calibrated years before A.D. 1950) and the depositional rate of ancient OC from the watershed into the lake are relatively low and similar to those during the Younger Dryas cold interval (occurring 12.9–11.7 ka). In contrast, age-offsets were higher (3.0–5.0 ka) when summer air temperatures were warmer than present during the Holocene Thermal Maximum (11.7–9.0 ka) and Bølling-Allerød periods (14.5–12.9 ka). During these warm times, permafrost thaw contributed to ancient OC depositional rates that were ~10 times greater than today. Although permafrost OC was vulnerable to climate warming in the past, we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release. As a result, the temperature threshold to trigger widespread permafrost OC release is higher than during previous warming events.National Science Foundation. Grant Number: ARC-09021692015-02-2

Spatial distribution of global runoff and its storage in river channels

The present dissertation attempts to improve our current understanding of some of the key elements of the surface runoff and its horizontal transfers in rivers. The dissertation presents an intensive analysis of the uncertainties in water balance calculations and the impact of uncertainties in the input data and the formulation of the water balance calculations on the runoff estimate. A simple technique is presented to combine observed river discharge and simulated runoff to derive accurate estimates of the spatially distributed runoff. Such composite runoff estimates are valuable for numerous earth science and water resource studies. The dissertation also discusses the representation of river networks for flow simulations. The performance of simulated river networks is analyzed with respect to resolution which provides guidance for the design of simulated river networks. New relationships are developed between river discharge and the riverbed geometry. These relationships provide the basis for the design of flow routing schemes incorporating the complete hydraulic dynamics of the riverine flow in the flow simulations. The dissertation demonstrates the use the composite runoff in a simulated river network context and the application of the relationships relating river discharge to flow properties to estimate the volume and surface of waters stored in rivers. The estimates agree well with previous estimates published in the scientific literature, but provide more insight into the spatial distribution of river water storage

A Markov Random Field Based Approach to 3D Mosaicing and Registration Applied to Ultrasound Simulation

A novel Markov Random Field (MRF) based method for the mosaicing of 3D ultrasound volumes is presented in this dissertation. The motivation for this work is the production of training volumes for an affordable ultrasound simulator, which offers a low-cost/portable training solution for new users of diagnostic ultrasound, by providing the scanning experience essential for developing the necessary psycho-motor skills. It also has the potential for introducing ultrasound instruction into medical education curriculums. The interest in ultrasound training stems in part from the widespread adoption of point-of-care scanners, i.e. low cost portable ultrasound scanning systems in the medical community. This work develops a novel approach for producing 3D composite image volumes and validates the approach using clinically acquired fetal images from the obstetrics department at the University of Massachusetts Medical School (UMMS). Results using the Visible Human Female dataset as well as an abdominal trauma phantom are also presented. The process is broken down into five distinct steps, which include individual 3D volume acquisition, rigid registration, calculation of a mosaicing function, group-wise non-rigid registration, and finally blending. Each of these steps, common in medical image processing, has been investigated in the context of ultrasound mosaicing and has resulted in improved algorithms. Rigid and non-rigid registration methods are analyzed in a probabilistic framework and their sensitivity to ultrasound shadowing artifacts is studied. The group-wise non-rigid registration problem is initially formulated as a maximum likelihood estimation, where the joint probability density function is comprised of the partially overlapping ultrasound image volumes. This expression is simplified using a block-matching methodology and the resulting discrete registration energy is shown to be equivalent to a Markov Random Field. Graph based methods common in computer vision are then used for optimization, resulting in a set of transformations that bring the overlapping volumes into alignment. This optimization is parallelized using a fusion approach, where the registration problem is divided into 8 independent sub-problems whose solutions are fused together at the end of each iteration. This method provided a speedup factor of 3.91 over the single threaded approach with no noticeable reduction in accuracy during our simulations. Furthermore, the registration problem is simplified by introducing a mosaicing function, which partitions the composite volume into regions filled with data from unique partially overlapping source volumes. This mosaicing functions attempts to minimize intensity and gradient differences between adjacent sources in the composite volume. Experimental results to demonstrate the performance of the group-wise registration algorithm are also presented. This algorithm is initially tested on deformed abdominal image volumes generated using a finite element model of the Visible Human Female to show the accuracy of its calculated displacement fields. In addition, the algorithm is evaluated using real ultrasound data from an abdominal phantom. Finally, composite obstetrics image volumes are constructed using clinical scans of pregnant subjects, where fetal movement makes registration/mosaicing especially difficult. Our solution to blending, which is the final step of the mosaicing process, is also discussed. The trainee will have a better experience if the volume boundaries are visually seamless, and this usually requires some blending prior to stitching. Also, regions of the volume where no data was collected during scanning should have an ultrasound-like appearance before being displayed in the simulator. This ensures the trainee\u27s visual experience isn\u27t degraded by unrealistic images. A discrete Poisson approach has been adapted to accomplish these tasks. Following this, we will describe how a 4D fetal heart image volume can be constructed from swept 2D ultrasound. A 4D probe, such as the Philips X6-1 xMATRIX Array, would make this task simpler as it can acquire 3D ultrasound volumes of the fetal heart in real-time; However, probes such as these aren\u27t widespread yet. Once the theory has been introduced, we will describe the clinical component of this dissertation. For the purpose of acquiring actual clinical ultrasound data, from which training datasets were produced, 11 pregnant subjects were scanned by experienced sonographers at the UMMS following an approved IRB protocol. First, we will discuss the software/hardware configuration that was used to conduct these scans, which included some custom mechanical design. With the data collected using this arrangement we generated seamless 3D fetal mosaics, that is, the training datasets, loaded them into our ultrasound training simulator, and then subsequently had them evaluated by the sonographers at the UMMS for accuracy. These mosaics were constructed from the raw scan data using the techniques previously introduced. Specific training objectives were established based on the input from our collaborators in the obstetrics sonography group. Important fetal measurements are reviewed, which form the basis for training in obstetrics ultrasound. Finally clinical images demonstrating the sonographer making fetal measurements in practice, which were acquired directly by the Philips iU22 ultrasound machine from one of our 11 subjects, are compared with screenshots of corresponding images produced by our simulator

A basis for the representation, manufacturing tool path generation and scanning measurement of smooth freeform surfaces

Freeform surfaces find wide application, particularly in optics, from unique single-surface science programmes to mobile phone lenses manufactured in billions. This thesis presents research into the mathematical and algorithmic basis for the generation and measurement of smooth freeform surfaces. Two globally significant cases are reported: 1) research in this thesis created prototype segments for the world’s largest telescope; 2) research in this thesis made surfaces underpinning the redefinition of one of the seven SI base units – the kelvin - and also what will be the newly (and permanently) defined value for the Boltzmann constant. Theresearchdemonstratestwounderlyingphilosophiesofprecisionengineering, the critical roles of determinism and of precision measurement in precise manufacturing. The thesis presents methods, and reports their implementation, for the manufacture of freeform surfaces through a comprehensive strategy for tool path generation using minimum axis-count ultra-precision machine tools. In the context of freeform surface machining, the advantages of deterministic motion performance of three-axis machines are brought to bear through a novel treatment of the mathematics of variable contact point geometry. This is applied to ultra-precision diamond turning and ultra-precision large optics grinding with the Cranfield Box machine. New techniques in freeform surface representation, tool path generation, freeform tool shape representation and error compensation are presented. A comprehensive technique for very high spatial resolution CMM areal scanning of freeform surfaces is presented, with a new treatment of contact error removal, achieving interferometer-equivalent surface representation, with 1,000,000+ points and sub-200 nm rms noise without the use of any low-pass filtering

Forecasting Instability Indicators in the Horn of Africa Region

The forecasting of state failure and the associated indicators has been a topic of great interest to a number of different agencies. USAID, CENTCOM, the World Bank, the Center for Army Analyses, and others have all examined the subject based on their own specific objectives. Whether the goal is denying terrorists space in which to operate, deciding how to pre-position materials in anticipation of unrest, stabilizing foreign markets and trade, or preventing or mitigating humanitarian disasters, man made or otherwise, this topic has been of interest for over a decade. The Horn of Africa has been one of the least stable regions in the world over the past three decades, and a continual source of humanitarian crises as well as terrorist activity. Some of the initial modeling of instability was done in response to crises in the Horn of Africa, but research is ongoing. Current models forecasting instability suffer from lack of lead time, subjective predictions, and lack of specificity. The models demonstrated in this study provide 4 year forecasts of battle deaths per capita, refugees per capita, genocide, and undernourishment for Djibouti, Ethiopia, Eritrea, Kenya, Somalia, Sudan, and Yemen. This thesis used principal component analysis, canonical correlation, ordinary least squares regression, logistic regression, and discriminant analysis to develop models of each instability indicator using 54 variables covering 32 years of observations. The key variables within each model are identified, and the accuracy of each model is compared with current models