1,721,077 research outputs found
The effect of finite rank perturbations on Jordan chains of linear operators
Full text linkA general result on the structure and dimension of the root subspaces of a linear operator under finite rank perturbations is proved: The increase of dimension from the n-th power of the kernel of the perturbed operator to the (n + 1)-th power differs from the increase of dimension of the corresponding powers of the kernels of the unperturbed operator by at most the rank of the perturbation. This bound is sharp.Fil: Behrndt, Jussi. Technische Universität Graz. Institut für Numerische Mathematik.; AlemaniaFil: Martinez Peria, Francisco Dardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemáticas; ArgentinaFil: Leben,Leslie. Technische Universität Graz. Institut für Numerische Mathematik; AlemaniaFil: Trunk, Carsten. Technische Universität Graz. Institut für Numerische Mathematik; Alemani
Analyticity and Riesz basis property of semigroups associated to damped vibrations
Full text linkSecond order equations of the form z(t)+A0z(t)+D z(t)=0 are considered. Such equations are often used as a model for transverse motions of thin beams in the presence of damping. We derive various properties of the operator matrix A = 0 I −A0 −D associated with the second order problem above. We develop sufficient conditions for analyticity of the associated semigroup and for the existence of a Riesz basis consisting of eigenvectors and associated vectors of A in the phase space
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Spectral Perturbation & Optimization of Matrix Pencils
Full text linkIn this thesis we study the eigenvalues of linear matrix pencils and their behavior under perturbations of the pencil coefficients. In particular we address (i) Possibility of eigenvalue assignment under structured rank-one perturbations; (ii) Distance to nearest pencils with a prescribed set of eigenvalues in norm and gap distance; (iii) Computing nearest matrix pencils with prescribed eigenvalues using structured perturbations. In (i) and (ii) we exploit the connection between matrix pencils and certain subspaces via their Weyr characteristics. This provides a way of lifting perturbation measures for subspaces such as the gap distance to the set of matrix pencils. In (iii) one has to solve a large scale non-convex optimization problem which appears e.g. in optimal redesign of integrated circuits. We show how feasible solutions close to the optimal value can be computed. Finally, this is used to improve the bandwidth of two circuits (two-stage CMOS & μA741).In dieser Arbeit untersuchen wir lineare differentiell-algebraischen Gleichungen (DAEs). Die Lösungen solcher DAEs werden durch Eigenwerte und Hauptvektoren von Matrixbüscheln beschrieben. Hierdurch kann insbesondere das qualitative Verhalten der Lösungen durch eine gezielte Veränderung (oder Störung), hinsichtlich gewisser Robustheits- oder Stabilitätsvorgaben, verbessert werden. Wir untersuchen zunächst das Verhalten der Eigenwerte und Hauptvektoren von Matrixbüscheln unter Störungen niedrigen Ranges. Zur Beschreibung des Störverhaltens nutzen wir einen neuartigen Zugang mit linearen Relationen und einem Zusammenspiel der Segre und Weyr Charakteristiken. Von besonderem Interesse ist dabei das Problem der Eigenwertplatzierbarkeit durch Störungen niedrigen Ranges. Hierbei wird untersucht, ob eine vorgegebene Eigenwertlage durch eine gezielte Veränderung der DAE erreicht werden kann. Durch die Vorgabe der Eigenwertlage wird indirekt das Stabilitätsverhalten der DAE beeinflusst. Vereinfacht gesagt wird in dieser Arbeit gezeigt, dass jede vorgegebene Eigenwertlage durch eine Störung mit Rang eins realisierbar ist. Als Anwendung betrachten wir eine Designoptimierung von Operationsverstärkern, welche in den letzten Jahren in der Arbeitsgruppe um Ralf Sommer (TU Ilmenau & Institut für Mikroelektronik- und Mechatronik-Systeme) entwickelt wurde. Hierbei wurden gezielt Kapazitäten in die Verstärkerschaltung eingefügt, um ihr Übertragungsverhalten nach gewissen Vorgaben zu beeinflussen. Dabei entspricht jede neue Kapazität einer Störung der DAE vom Rang eins. In diesem Kontext sind die Platzierungsergebnisse jedoch nur bedingt geeignet. Hier treten zusätzliche Einschränkungen der erlaubten Modifikationen der DAE auf, da nur sehr wenige Störungen als Kapazitäten in der Schaltung realisiert werden können. Bei der Designoptimierung ist man zudem an kleinstmöglichen Veränderungen der DAE interessiert, um die Produktionskosten des Verstärkers zu minimieren. Daher untersuchen wir im zweiten Teil der Arbeit, wie platzierende Störungen mit kleinstmöglicher Norm sowie mit vorgegebener Struktur bestimmt werden können. Dieses Vorgehen bezeichnen wir als Spektrale Optimierung. Zur Bestimmung einer approximativen Lösung dieses Optimierungsproblems wurde ein Algorithmus entwickelt, welcher dann bei der Designoptimierung von zwei industriellen Verstärkerschaltungen eingesetzt wird
Application of Multi-Parametric Quadratic Programming to Simulation of Deflected Wires in a Wire Saw
No full textOn the Modelling of Thermo-Viscoplasticity of Case-Hardening Steels Over a Wide Temperature Range
No full textThe aim of this work is the development of a thermodynamically consistent fully coupled thermo-viscoplastic material model for metals.The model is based on a split of the free energy into a thermo-elastic, a thermo-plastic and a purely thermal part and covers nonlinear cold-work hardening and thermal softening.Nonlinear temperature dependent effects are accounted for the elastic moduli, the plastic hardening moduli, the thermal expansion, the heat capacity and the heat conductivity.Furthermore, strain rate-dependency of the current yield stress is realized using a temperature dependent nonlinear Perzyna type viscoplastic model based on an associative flow rule.The model and its parameters are fitted against experimental data for case hardening steel 16MnCr5 (1.7131)
On Characteristic Invariants of Matrix Pencils and Linear Relations
No full textThe relationship between linear relations and matrix pencils is investigated. Given a linear relation, we introduce its Weyr characteristic. If the linear relation is the range (or the kernel) representation of a given matrix pencil, we show that there is a correspondence between this characteristic and the Kronecker canonical form of the pencil. This relationship is exploited to obtain estimations on the invariant characteristics of matrix pencils under rank-one perturbations.Fil: Gernandt, Hannes. Technische Universität Berlin; AlemaniaFil: Martinez Peria, Francisco Dardo. Universidad Nacional de la Plata. Facultad de Cs.exactas. Centro de Matematica de la Plata.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto Calderón; ArgentinaFil: Philipp, Friedrich. Technische Universität Ilmenau; AlemaniaFil: Trunk, Carsten Joachim. Technische Universität Ilmenau; Alemani
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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