A new method for power quality improvement

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A new control method for active power filters in conjunction with a passive filter circuit are presented and analysed in this thesis. A new technique for load modelling is introduced in order to enable the design of compensators to improve the power factor and to reduce harmonic levels in electrical power systems. The principles of analysis, design, operation and control of the new circuit equipped with IGBTs are presented. This enables the compensation of rapidly changing loads and reactive power. A special circuit equipped with IGBTs is able to compensate for the reactive power and harmonic currents of different orders. The important aspect of the present work is based on the compensator control circuit for power factor correction and harmonic elimination, and its application. This new configuration improves the rating of the active power filter, reducing power losses in the switches compared to existing and newly developed active filters. Furthermore, it is very stable in operation and much faster by a factor of 20. The thesis also presents a detailed mathematical modelling of the proposed system with frequency and time domain equations. The frequency response of the proposed system is also discussed. This new proposal has been checked using a dedicated software simulation program, which was specifically developed for this purpose. An experimental set-up has been designed and implemented in order to apply the new method using IGBTs as well as some other devices. This thesis also presents a critical literature survey, which provides a critical overview of previous work relevant to the power quality improvement reactive power compensation and active filtering

Experimental investigation of key assumptions in analytical failure criteria for sheet metal forming

Tearing concerns in sheet metal forming can be predicted based on the strain and stress in the material using analytical models, e.g., the Marciniak Kucyzinski (M-K) model and the Derov et al. model respectively. An assumption to these models is that a thin area of concentrated deformation exists which is referred to as the defect region. Other key assumptions for the models are related to when the material is predicted to fail. For the M-K model, the failure is related to the incremental strain ratio inside and outside the defect region. Similarly, for the Derov et al. model, the failure is related to a critical stress concentration factor, i.e., the ratio of the effective stress inside and outside the defect region. In order to investigate these key assumptions, Marciniak tests with coupled Digital Imaging Correlation (DIC) to measure the strain in the material as well as the size of the defect region were conducted on 1018 steel with eight specimen geometries, which varied the strain path from uniaxial to balanced biaxial. The results show that the parameters investigated to predict failure (i.e., the incremental strain ratio and critical stress concentration factor) were not constant for the various strain paths for both analytical models considered

elastography in primary open-angle glaucoma

Objective: The aim of this study was to compare sonoelastographic findings in the retina-choroid-sclera (RCS) complex and vitreous in glaucomatous and healthy eyes.Methods: For this cross-sectional comparative study, 20 patients with primary open-angle glaucoma and 20 healthy volunteers were recruited. Ultrasound elastography measurements were taken with a sonographic scanner of the RCS complex, anterior vitreous (AV), posterior vitreous (PV), retrobulbar fat tissue (RFT), optic disc (OD) and optic nerve (ON) in each eye.Results: The elasticity index of the RCS complex, RFT, OD, ON, AV and PV was similar in both groups (p > 0.05), although the AV/PV strain ratio in the group of patients with glaucoma was significantly higher (p = 0.04).Conclusion: Glaucoma increases the AV/PV strain ratio. In providing reproducible and consistent values, the real-time elastography (RTE) technique may be helpful in elucidating the mechanisms of glaucoma in some aspects.Advances in knowledge: This study can help to evaluate the elasticity of the RCS complex and vitreous in glaucomatous eyes with RTE

Prediction of Academic Achievement and Happiness in Middle School Students: The Role of Social-Emotional Learning Skills

This study was conducted to test whether social-emotional learning skills are a significant predictor of academic achievement and happiness in middle school students. A total of three different data collection tools were used in the study: A Personal Information Form, The Social-Emotional Learning Skills Scale and The Adolescent Happiness Scale. The study was carried out with 337 middle school students from six different middle schools in Erzurum province. Of these students, 203 (60.2%) were female, and 134 (39.8%) were male. The ages of these students varied between 10 and 14, and the mean age was 12.07 (Sd = 0.93). Descriptive statistics, correlation analysis, and hierarchical regression analysis were employed in the analysis of the data. The findings obtained as a result of the study indicated that there were positive and significant correlations between social-emotional learning skills and academic achievement and happiness. In addition, social-emotional learning skills were a significant predictor of academic achievement and happiness in middle school students. Accordingly, social-emotional learning skills explained 18% of the total variance in academic achievement and 44% of the variance in happiness in middle school students. When all these results are evaluated together, it can be said that promoting the social-emotional learning skills of middle school students will increase academic achievement and happiness

Carrollian Origin of Spacetime Subsystem Symmetry

We propose that models with spacetime dipole symmetry are connected to Lorentz invariant models via the Carrollian limit. In this way, a recently proposed model with spacetime dipole symmetry was readily reproduced together with its conserved charges. We then couple this model to a dynamical Abelian gauge field and Carroll gravity. Our procedure can be applied in arbitrary dimensions and paves the way to construct new models with spacetime dipole symmetry.Comment: 4 pages, v3: title changed, version appeared on PR

Three-dimensional higher-order Schrödinger algebras and Lie algebra expansions

We provide a Lie algebra expansion procedure to construct three-dimensional higher-order Schr\"odinger algebras which relies on a particular subalgebra of the four-dimensional relativistic conformal algebra. In particular, we reproduce the extended Schr\"odinger algebra and provide a new higher-order Schr\"odinger algebra. The structure of this new algebra leads to a discussion on the uniqueness of the higher-order non-relativistic algebras. Especially, we show that the recent d-dimensional symmetry algebra of an action principle for Newtonian gravity is not uniquely defined but can accommodate three discrete parameters. For a particular choice of these parameters, the Bargmann algebra becomes a subalgebra of that extended algebra which allows one to introduce a mass current in a Bargmann-invariant sense to the extended theory.Comment: v3., typos fixed, reference added, version appeared in JHE

Automated Debugging for Arbitrarily Long Executions

One of the most energy-draining and frustrating parts of software development is playing detective with elu-sive bugs. In this paper we argue that automated post-mortem debugging of failures is feasible for real, in-production systems with no runtime recording. We pro-pose reverse execution synthesis (RES), a technique that takes a coredump obtained after a failure and automat-ically computes the suffix of an execution that leads to that coredump. RES provides a way to then play back this suffix in a debugger deterministically, over and over again. We argue that the RES approach could be used to (1) automatically classify bug reports based on their root cause, (2) automatically identify coredumps for which hardware errors (e.g., bad memory), not software bugs are to blame, and (3) ultimately help developers repro-duce the root cause of the failure in order to debug it.