Systematic Approach to IMM Mixing for Unequal Dimension States

The interacting multiple model (IMM) estimator outperforms fixed model filters, e.g. the Kalman filter, in scenarios where the targets have periods of disparate behavior. Key to the good performance and low complexity is the mode mixing. Here we propose a systematic approach to mode mixing when the modes have states of different dimensions. The proposed approach is general and encompasses previously suggested solutions. Different mixing approaches are compared, and the proposed methodology is shown to perform very well

Subleading Regge limit from a soft anomalous dimension

Wilson lines capture important features of scattering amplitudes, for example soft effects relevant for infrared divergences, and the Regge limit. Beyond the leading power approximation, corrections to the eikonal picture have to be taken into account. In this paper, we study such corrections in a model of massive scattering amplitudes in N = 4 super Yang-Mills, in the planar limit, where the mass is generated through a Higgs mechanism. Using known three-loop analytic expressions for the scattering amplitude, we find that the first power suppressed term has a very simple form, equal to a single power law. We propose that its exponent is governed by the anomalous dimension of a Wilson loop with a scalar inserted at the cusp, and we provide perturbative evidence for this proposal. We also analyze other limits of the amplitude and conjecture an exact formula for a total cross-section at high energies.Comment: 19 pages, several appendices, many figure

School tracking, social segregation and educational opportunity: evidence from Belgium

Educational tracking is a very controversial issue in education. The tracking debate is about the virtues of uniformity and vertical differentiation in the curriculum and teaching. The pro-tracking group claims that curriculum and teaching better aimed at children's varied interest and skills will foster learning efficacy. The anti-tracking group claims that tracking systems are inefficient and unfair because they hinder learning and distribute learning inequitably. In this paper we provide a detailed within-country analysis of a specific educational system with a long history of early educational tracking between schools, namely the Flemish secondary school system in Belgium. This is interesting place to look because it provides a remarkable mix of excellence and inequality. Indeed the Flemish school system is repeatedly one of the best performer in the international harmonized PISA tests in math, science and reading; whereas it produces some of the most unequal distributions of learning between schools and students. Combining evidence from the PISA 2006 data set at the student and school level with recent statistical methods, we show first the dramatic impact of tracking on social segregation; and then, the impact of social segregation on equality of educational opportunity (adequately measured). It is shown that tracking, via social segregation, has a major effect on inequality of opportunity. Children of different economic classes will have different access to knowledge.tracking, ability grouping, educational performance, social segregation, inequality, PISA

Multiple model based state estimation and trajectory control for micro aerial vehicles

This thesis proposes the design of a multiple model state estimation and control scheme for micro aerial vehicles (MAVs) to cope with different flight conditions such as aggressive flights, hovering flights, and flights under high external disturbances. The work is divided into two main parts. The first part of this thesis presents the design of an interacting multiple model (IMM) filter for visual-inertial navigation (VIN) of MAVs. VIN of MAVs in practice typically uses a single system model for its state estimator design. However, MAVs can operate in different scenarios requiring changes to the estimator model. This thesis proposes the use of a conventional VIN and a drag force VIN in an error-state IMM filtering framework to address the need for multiple models in the estimator. We use an epipolar geometry constraint for the design of the measurement model for both filters to realize computationally efficient state updates. Observability of the proposed modifications to VIN filters (drag force model, and epipolar measurement model) are analyzed, and observability-based consistency rules are derived for the two filters of the IMM. Monte Carlo numerical simulations validate the performance of the observability constrained IMM, which improved the accuracy and consistency of the VINS for changing flight conditions and external wind disturbance scenarios. Experimental validation is performed using the EuRoC dataset to evaluate the performance of the proposed IMM filter design

Ablative response of a silica phenolic to simulated liquid propellant rocket engine operating conditions

Ablative response of silica phenolic to simulated liquid propellant rocket engine operating condition

Scattering processes and resonances from lattice QCD

The vast majority of hadrons observed in nature are not stable under the strong interaction, rather they are resonances whose existence is deduced from enhancements in the energy dependence of scattering amplitudes. The study of hadron resonances offers a window into the workings of quantum chromodynamics (QCD) in the low-energy non-perturbative region, and in addition, many probes of the limits of the electroweak sector of the Standard Model consider processes which feature hadron resonances. From a theoretical standpoint, this is a challenging field: the same dynamics that binds quarks and gluons into hadron resonances also controls their decay into lighter hadrons, so a complete approach to QCD is required. Presently, lattice QCD is the only available tool that provides the required non-perturbative evaluation of hadron observables. In this article, we review progress in the study of few-hadron reactions in which resonances and bound-states appear using lattice QCD techniques. We describe the leading approach which takes advantage of the periodic finite spatial volume used in lattice QCD calculations to extract scattering amplitudes from the discrete spectrum of QCD eigenstates in a box. We explain how from explicit lattice QCD calculations, one can rigorously garner information about a variety of resonance properties, including their masses, widths, decay couplings, and form factors. The challenges which currently limit the field are discussed along with the steps being taken to resolve them

Representing and Constructing. Psychometrics from the perspectives of measurement theory and concept formation.

Social scientific measurement is much desired and much criticized. In this dissertation I evaluate one of the main approaches to social scientific measurement that has nevertheless been virtually ignored by philosophers – the psychometric approach. Psychometric measures are typically used to measure unobservable attributes such as intelligence and personality. They typically take the form of questionnaires or tests and are validated by statistical tests of properties such as reliability and model-fit. My thesis is two-fold. In the first, more critical part, I argue that psychometric instruments normally fail to fulfil plausible criteria for adequate measurement. To make this argument, I define and defend a conception of quantitative representation necessary for measurement. My definition is grounded in the Representational Theory of Measurement but avoids the main critiques this theory has faced. I then show that the typical psychometric process of measure validation fails to produce evidence of such quantitative representation. The upshot is that although a quantitative interpretation of psychometric data is common, it is largely unwarranted. In the second part, I argue that psychometric instruments are nonetheless apt for various other purposes. This argument hinges on a new outlook on how concepts should be formed for psychometric purposes. Philosophers have traditionally thought that concepts should cohere with intuitions and/or pick out so-called natural kinds, while many psychometricians argue that concepts should pick out real as opposed to constructed attributes. I argue that, when it comes to social scientific measurement, it is much more important to focus on the usefulness of the concept, where usefulness can take on different meanings in different contexts. Building on the defended outlook on concept formation, I show what useful functions psychometric instruments can serve even when they fail at quantitative representation.I thank the following institutions for funding my PhD research: Arts and Humanities Research Council, the British Society for the Philosophy of Science, Cambridge Trust and Newnham College