Optimal FIR filter design

The design of Finite Impulse Response (FIR) digital filters that considers both phase and magnitude specifications is investigated. This dissertation is divided into two parts. In Part I we present our implementation of an algorithm for the design of minimum phase filters. In Part II we investigate the design of FIR filters in the complex domain and develop a new powerful design method for digital FIR filters with arbitrary specification of magnitude and phase;Part I considers the design of minimum-phase filters. The method presented uses direct factorization of the transfer function of a companion Parks-McClellan linear-phase filter of twice the length of the desired minimum-phase filter. The minimum-phase filter is derived with excision of half the zeros of the companion linear-phase filter. The zeros of the prototype filter are found using Laguerre\u27s method. We will present our implementation of the design method, and describe some practical aspects and problems associated with the design of minimum-phase filters;Part II investigates the design of optimal Chebychev FIR filters in the complex domain. The design of FIR filters with arbitrary specification of magnitude and phase is formulated into a problem of complex approximation. The method developed is capable of designing filters with real or complex coefficients. Complex impulse response designs are an extension of the real coefficient case based on a proper selection of the approximating basis functions;The minimax criterion is used and the complex Chebychev approximation is posed as a minimization problem in linear optimization. The primal problem is converted to its dual and is solved using an efficient, quadratically convergent algorithm developed by Tang (14). The relaxation of the linear-phase constraint results in a reduction of the number of coefficients compared to linear-phase designs. Linear-phase filters are a special case of our filter design approach. We examine the design of frequency selective filters with or without the conjugate symmetry, the design of one-sided, two-sided, narrowband and fullband Hilbert Transformers and differentiators

Manufacturing of integrated cooling channels by Directed Energy Deposition for hot stamping tools with ball burnished surfaces

Hot stamping tools require cooling channels, preferably with a high positioning flexibility. Conventionally, these are machined. This represents a disadvantage because of the limited accessibility for milling tools and the low flexibility. By means of the Directed Energy Deposition (DED) process, a flexible design of the cooling channels is possible. Different geometries of cooling channels can be manufactured by DED in order to control the heat balance in the hot stamping tool. In this context an agreement between the additive producibility and the surface fraction of the cooling channels, which contributes to the effective heat at the tool surface, is important. Experimental and numerical analyses demonstrate that a possible configuration in this field is the drop shaped cooling channel. To reduce the surface roughness after the DED process, the tool surfaces are ball burnished subsequently. The resulting roughness and the waviness of the tool surface are reduced but not leveled completely. Texturing of the surface can be applied to in fluence the material flow in the hot stamping process which is implemented by DED. The combination of the described methods allows for manufacturing hot stamping tools with near-surface cooling channels and a global or local adjustment of the surface properties of the tools.Presshärtewerkzeuge erfordern Kühlkanäle, vorzugsweise mit einer hohen Positionierungsflexibilität. Diese werden üblicherweise gefräst. Dies stellt aufgrund der eingeschränkten Zugänglichkeit für Fräswerkzeuge und der geringen Flexibilität einen Nachteil dar. Mit Hilfe des Laserpulverauftragsschweißens (LPA) ist eine flexible Gestaltung der Kühlkanäle möglich. Mittels LPA können unterschiedliche Kühlkanalgeometrien hergestellt werden, um den Wärmehaushalt im Presshärtewerkzeug zu steuern. In diesem Zusammenhang ist eine Abstimmung zwischen der additiven Herstellbarkeit und dem Oberflächenanteil der Kühlkanäle, der zur effektiven Wärme an der Werkzeugoberfläche beiträgt, wichtig. Experimentelle und numerische Analysen zeigen, dass eine mögliche Konfiguration in diesem Bereich der tropfenförmige Kühlkanal ist. Um die Oberflächenrauheit nach dem LPA-Prozess zu reduzieren, werden die Werkzeugoberflächen anschließend glattgewalzt. Die resultierende Rauheit und die Welligkeit der Werkzeugoberfläche werden reduziert, aber nicht vollständig eingeebnet. Die Texturierung der Oberfläche, welche durch das LPA-Verfahren realisiert wird, kann zur Beeinflussung des Werkstoffflusses im Presshärteprozess eingesetzt werden. Die Kombination der beschriebenen Verfahren ermöglicht die Herstellung von Presshärtewerkzeugen mit oberflächennahen Kühlkanälen und eine globale oder lokale Einstellung der Oberflächeneigenschaften der Werkzeuge

Group Spike and Slab Variational Bayes

We introduce Group Spike-and-slab Variational Bayes (GSVB), a scalable method for group sparse regression. A fast co-ordinate ascent variational inference (CAVI) algorithm is developed for several common model families including Gaussian, Binomial and Poisson. Theoretical guarantees for our proposed approach are provided by deriving contraction rates for the variational posterior in grouped linear regression. Through extensive numerical studies, we demonstrate that GSVB provides state-of-the-art performance, offering a computationally inexpensive substitute to MCMC, whilst performing comparably or better than existing MAP methods. Additionally, we analyze three real world datasets wherein we highlight the practical utility of our method, demonstrating that GSVB provides parsimonious models with excellent predictive performance, variable selection and uncertainty quantification.Comment: 66 pages, 5 figures, 7 table

Variational Bayes for high-dimensional proportional hazards models with applications within gene expression

Few Bayesian methods for analyzing high-dimensional sparse survival data provide scalable variable selection, effect estimation and uncertainty quantification. Such methods often either sacrifice uncertainty quantification by computing maximum a posteriori estimates, or quantify the uncertainty at high (unscalable) computational expense. We bridge this gap and develop an interpretable and scalable Bayesian proportional hazards model for prediction and variable selection, referred to as SVB. Our method, based on a mean-field variational approximation, overcomes the high computational cost of MCMC whilst retaining useful features, providing a posterior distribution for the parameters and offering a natural mechanism for variable selection via posterior inclusion probabilities. The performance of our proposed method is assessed via extensive simulations and compared against other state-of-the-art Bayesian variable selection methods, demonstrating comparable or better performance. Finally, we demonstrate how the proposed method can be used for variable selection on two transcriptomic datasets with censored survival outcomes, and how the uncertainty quantification offered by our method can be used to provide an interpretable assessment of patient risk.Comment: Published in Bioinformatic

Signal Structure of the Starlink Ku-Band Downlink

We develop a technique for blind signal identification of the Starlink downlink signal in the 10.7 to 12.7 GHz band and present a detailed picture of the signal's structure. Importantly, the signal characterization offered herein includes the exact values of synchronization sequences embedded in the signal that can be exploited to produce pseudorange measurements. Such an understanding of the signal is essential to emerging efforts that seek to dual-purpose Starlink signals for positioning, navigation, and timing, despite their being designed solely for broadband Internet provision

Low-loss multimode interference couplers for terahertz waves

The terahertz (THz) frequency region of the electromagnetic spectrum is located between the traditional microwave spectrum and the optical frequencies, and offers a significant scientific and technological potential in many fields, such as in sensing, in imaging and in spectroscopy. Waveguiding in this intermediate spectral region is a major challenge. Amongst the various THz waveguides suggested, metal-clad plasmonic waveguides and specifically hollow core structures, coated with insulating material are the most promising low-loss waveguides used in both active and passive devices. Optical power splitters are important components in the design of optoelectronic systems and optical communication networks such as Mach-Zehnder Interferometric switches, polarization splitter and polarization scramblers. Several designs for the implementation of the 3dB power splitters have been proposed in the past, such as the directional coupler-based approach, the Y-junction-based devices and the MMI-based approach. In the present paper a novel MMI-based 3dB THz wave splitter is implemented using Gold/polystyrene (PS) coated hollow glass rectangular waveguides. The H-field FEM based full-vector formulation is used here to calculate the complex propagation characteristics of the waveguide structure and the finite element beam propagation method (FE-BPM) and finite difference time domain (FDTD) approach to demonstrate the performance of the proposed 3dB splitter

Development and implementation of a combined discrete and finite element multibody dynamics simulation environment

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (p. [195]-198) and index.Some engineering applications and physical phenomena involve multiple bodies that undergo large displacements involving collisions between the bodies. Considering the difficulties and cost associated when conducting physical experiments of such systems, there is a demand for numerical simulation capabilities. The discrete element methods (DEM) are numerical techniques that have been specifically developed to facilitate simulations of distinct bodies that interact with each other through contact forces. In DEM the simulated bodies are typically assumed to be infinitely rigid. However, there are multibody systems for which it is useful to take into account the deformability of the simulated bodies. The objective of this research is to incorporate deformability in DEM, enabling the evaluation of the stress and strain distributions within simulated bodies during simulation. In order to achieve this goal, an Updated Lagrangian (UL) Finite Element (FE) formulation and an explicit time integration scheme have been employed together with some simplifiying assumptions to linearize this highly nonlinear contact problem and obtain solutions with realistic computational cost. An object-oriented extendable computational tool has been built specifically to allow us to simulate multiple distinct bodies that interact through contact forces allowing selected bodies to be deformable. Database technology has also been utilized in order to efficiently handle the huge amounts of computed results.by Petros Komodromos.Ph.D

Femtosecond and UV inscribed grating characterization in photonic crystal fibres:optimization for sensing applications

Photonic crystal fibres (PCF) and more commonly microstructure fibres, remain interesting and novel fibre types and when suitably designed can prove to be "ideal" for sensing applications, as the different geometrical arrangement of the air holes alters their optical wave-guiding properties, whilst also providing tailored dispersion characteristics. This impacts the performance of grating structures, which offer wavelength encoded sensing information. We undertake a study on different air hole geometries and proceed with characterization of fibre Bragg and long period gratings, FBG and LPG, respectively that have been inscribed (using either a femtosecond or ultraviolet laser system) within different designs of microstructured fibre that are of interest for sensing applications

Application of seismic isolation as a performance-based earthquake-resistant design method

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995.Includes bibliographical references (p. 129-131).by Petros I. Komodromos.M.S