Aachen, Techn. Hochsch., Diss., 2004

Techn. Hochsch., Diss., 2005--Aachen.

Transit surveys based on on-board passenger interviews suffer from bias. Most commonly observed is the short trip bias: passengers travelling short distances are underrepresented in survey results. Biased data leads to an incorrect estimation of passenger demand can result in an inequitable allocation of revenues between transport operators. This paper examines how the short trip bias can be mitigated during the data ex-trapolation process. Four methods are examined: A simple extrapolation by boarding counts, three iterative proportional fitting models and an additional weighting concept are tested on simulated survey data. The simulative approach enables the evaluation of the examined methods concerning their effects in reducing short trip bias. A total of eight survey situations with selected parameters variated are simulated to allow conclusions about influencing factors. Results suggest that the most effective method is the weighting approach, followed by the iterative proportional fitting methods. Within the class of the iterative propor-tional fitting methods no significant difference is observed. Furthermore it is observed that the effectiveness of the weighting approach strongly relates to passenger numbers and selection rates. Furthermore an overview on topic related literature is given to examine practical approaches to reduce bias in survey data.

Ein Kernbereich der Informationsvisualisierung ist die effiziente, gleichzeitige Darstellung von Fokus und Kontext. Hierfür wurden verschiedenste Methoden in der Literatur vorgestellt, wenige auch in Nutzertests analysiert. Eine viel versprechende Methode ist die Einbindung der dritten räumlichen Dimension wie sie die perspective wall (Mackinlay et al. 1991) verwendet. Diese wird hier genutzt, um tabellarische Darstellungen zu optimieren. Die Vorteile des semantic zooming für tabellarische Darstellungen wurden bereits von (Reiterer et al. 2005) gezeigt. Hier werden beide Ansätze kombiniert, mit zusätzlich Such- und Filtermöglichkeiten versehen und in einem Nutzertest evaluiert.

Transit surveys based on on-board passenger interviews suffer from bias. Most commonly observed is the short trip bias: passengers travelling short distances are underrepresented in survey results. Biased data leads to an incorrect estimation of passenger demand can result in an inequitable allocation of revenues between transport operators. This paper examines how the short trip bias can be mitigated during the data ex-trapolation process. Four methods are examined: A simple extrapolation by boarding counts, three iterative proportional fitting models and an additional weighting concept are tested on simulated survey data. The simulative approach enables the evaluation of the examined methods concerning their effects in reducing short trip bias. A total of eight survey situations with selected parameters variated are simulated to allow conclusions about influencing factors. Results suggest that the most effective method is the weighting approach, followed by the iterative proportional fitting methods. Within the class of the iterative propor-tional fitting methods no significant difference is observed. Furthermore it is observed that the effectiveness of the weighting approach strongly relates to passenger numbers and selection rates. Furthermore an overview on topic related literature is given to examine practical approaches to reduce bias in survey data.:ABBILDUNGSVERZEICHNIS VII TABELLENVERZEICHNIS VII ABKÜRZUNGSVERZEICHNIS VIII SYMBOLVERZEICHNIS IX 1 EINLEITUNG 1 2 ANFORDERUNGEN AN VERKEHRSERHEBUNGEN 5 2.1 Einnahmeaufteilung im SPNV 5 2.2 Aufbau von Verkehrserhebungen 8 2.2.1 Zweistufige Stichprobenziehung 8 2.2.2 Felderhebung: Zählung und Befragung 10 2.2.3 Datenaufbereitung 11 2.2.4 Hochrechnung und Auswertung 11 2.3 Problem der Stichprobenverzerrung 14 2.3.1 Präzision und Genauigkeit 14 2.3.2 Untererfassung von Kurzstreckenfahrern 15 2.3.3 Weitere Verzerrungsursachen 16 3 LITERATURÜBERBLICK: ANSÄTZE ZUR PROBLEMVERMEIDUNG 19 3.1 Hochrechnungsverfahren 19 3.1.1 Iterative Randsummenverfahren (IPF) 19 3.1.2 Gewichtungsverfahren 21 3.2 Weitere Ansätze 24 3.2.1 Platzgruppenverfahren 24 3.2.2 Anpassung der Startlösung des Hochrechnungsverfahrens 25 3.2.3 Veränderung der Auswahlprozedur der Fahrgäste 27 3.2.4 Veränderung des Erhebungsdesigns 28 4 METHODIK 31 4.1 Auswahl der Verfahren 31 4.1.1 Einsteigerhochrechnung 31 4.1.2 Fratarverfahren 32 4.1.3 Durchschnittsfaktormethode 32 4.1.4 MULTI-Verfahren 33 4.1.5 Gewichtungsverfahren von Keppeler und Schulze 34 4.2 Simulationsdaten 36 4.2.1 Fahrtdaten Linie 1 37 4.2.2 Fahrtdaten Linie 2 38 4.2.3 Befragungsszenarien 39 4.3 Gestaltung der IPF-Verfahren 40 4.3.1 Weitere Randbedingungen 40 4.3.2 Abbruchkriterien 42 4.3.3 Bester Iterationsschritt 44 4.3.4 Aufstellung der Startmatrix 44 4.4 Anwendung des Gewichtungsverfahrens 45 5 ERGEBNISSE 49 5.1 Charakteristik der Befragungsstichproben 49 5.2 Aggregierte Ergebnisse 51 5.3 Einfluss der Befragungsquoten 53 5.4 Verteilung der Verkehrsleistung nach Tarif 54 5.5 Konvergenzverhalten 55 6 DISKUSSION 57 6.1 Ergebnisinterpretation 57 6.2 Einordnung und Schlussfolgerungen 59 7 FAZIT UND AUSBLICK 63 EHRENWÖRTLICHE ERKLÄRUNG XVII

We present efficient and globally convergent solvers for several classes of plasticity models. The models in this work are formulated in the primal form as energetic rate-independent systems with an elastic energy potential and a plastic dissipation component. Different hardening rules are considered, as well as different flow rules. The time discretization leads to a sequence of nonsmooth minimization problems. For small strains, the unknowns live in vector spaces while for finite strains we have to deal with manifold-valued quantities. For the latter, a reformulation in tangent space is performed to end up with the same dissipation functional as in the small-strain case. We present the Newton-type TNNMG solver for convex and nonsmooth minimization problems and a newly developed Proximal Newton (PN) method that can also handle nonconvex problems. The PN method generates a sequence of penalized convex, coercive but nonsmooth subproblems. These subproblems are in the form of block-separable small-strain plasticity problems, to which TNNMG can be applied. Global convergence theorems are available for both methods. In several numerical experiments, both the efficiency and the flexibility of the methods for small-strain and finite-strain models are tested.

Die Arbeit stellt neu entwickelte Röntgenbeugungsmethoden vor, mit deren Hilfe der Verzerrungszustand des Kristallgitters von Halbleiter-Wafern und -Bauteilen im Detail charakterisiert werden kann. Hierzu werden die aussergewöhnlichen Eigenschaften der an modernen Synchrotrons wie der ESRF (Grenoble) verfügbaren Röntgenstrahlung genutzt. <br>Im ersten Teil der Arbeit werden Röntgen-Diffraktometrie und -Topographie zu einer Untersuchungsmethode kombiniert, mit der die makroskopische Krümmung von Halbleiter-Wafern ebenso wie ihre mikroskopische Defektstruktur abgebildet werden kann. Der zweite Teil ist der Untersuchung von epitaktisch gewachsenen und geätzten Oberflächengittern mit Abmessungen im Submikrometer-Bereich gewidmet. Die unterschiedlichen Gitterkonstanten der beteiligten Halbleitermaterialien führen zu einem inhomogenen Verzerrungsfeld in der Probe, das sich im Röntgenbild durch eine charakteristische Verformung des Beugungsmusters in der Umgebung der Bragg-Reflexe äussert. Die Analyse der experimentell gemessenen Beugungsmuster geschieht mit Hilfe eines neu entwickelten Simulationsverfahrens, das Elastizitätstheorie und eine semi-kinematische Röntgenbeugungstheorie miteinander verbindet. Durch quantitativen Vergleich der Simulationsergebnisse mit den Messdaten kann auf den genauen Verlauf des Verzerrungsfeldes in den Proben zurückgeschlossen werden. Dieses Verfahren wird erfolgreich auf verschiedene Halbleiter-Probensysteme angewendet, und schliesslich auch auf die Untersuchung von akustischen Oberflächenwellen in Halbleiterkristallen übertragen. / This thesis presents newly developed X-ray methods which can be used to characterize in detail the state of distortion of the crystal lattice in semiconductor wafers, devices and nanostructures. The methods use the extraordinary properties of the X-rays available from modern synchrotron sources such as the ESRF (Grenoble). <br>In the first part of the thesis, X-ray diffractometry and X-ray topography are combined into a new method, called X-ray rocking curve imaging, which allows to image the macroscopic curvature of semiconductor wafers as well as the underlying microscopic defect structure. The second part of the thesis deals with the investigation of epitaxially grown and subsequently etched semiconductor gratings with lateral periods below the micrometer. The lattice mismatch between the different materials used in heteroepitaxy leads to a non-uniform strain field in the sample, which is reflected in a characteristic distortion of the X-ray diffraction pattern around each Bragg peak. The experimental data are evaluated with the help of a newly developed simulation procedure which combines elasticity theory with a semi-kinematical theory of X-ray diffraction. From a quantitative comparison of measured and simulated data the detailed shape of the strain field in the samples can be deduced. This procedure is used successfully for the structural characterization of different types of semiconductor gratings, and is finally applied also to the investigation of surface acoustic waves in crystals.

Siliziumnanodrähte (SiNWs) bieten aufgrund ihrer exzellenten elektrostatischen Kontrollierbarkeit eine gute Grundlage für die Entwicklung neuartiger Bauelemente, wie rekonfigurierbarer Feldeffekttransistoren (RFETs). Da SiNWs durch die Oxidation gezielt verzerrt werden können und diese Verzerrung die Bandstruktur des Siliziums verändert, bietet der Oxidationsprozess eine Möglichkeit, die Leitungseigenschaften der RFETs zu modulieren und eine symmetrische Transfercharakteristik zu erhalten. Die Untersuchung von SiNWs mit Durchmessern im einstelligen Nanometerbereich bedarf eines atomistischen Ansatzes. In der vorliegenden Arbeit wird mit einem reaktiven Kraftfeld die initiale Phase der Oxidation dünner SiNWs molekulardynamisch simuliert. Gegenstand der Untersuchungen sind die Temperaturabhängigkeit der Oxidation von <110>-SiNWs mit Anfangsradien von 10.2 Å sowie das Oxidationsverhalten von <110>- und <100>-SiNWs mit Anfangsradien von 5.1 Å. Dabei wird neben dem Sauerstoffanteil im Simulationssystem und der radial aufgelösten Dichte auch das radial aufgelöste Verhältnis zwischen Sauerstoff- und Siliziumatomen während der gesamten Simulationsdauer untersucht und ein Zusammenhang zur Dichte festgestellt. Darüber hinaus wird bei 300 K erstmals eine Analyse der Verzerrungsentwicklung während der initialen Oxidationsphase durchgeführt, bei der sich sowohl für <110>-SiNWs als auch für <100>-SiNWs eine tensile Verzerrung im unoxidierten Drahtkern einstellt. Wie eine Analyse der partiellen radialen Verteilungsfunktion zeigt, kommt es zu dieser Verzerrung, weil während der Oxidation die Grundstruktur des Siliziums im Oxid erhalten bleibt, durch die Einlagerung des Sauerstoffs allerdings der Bindungsabstand erhöht wird. Dieser erhöhte Bindungsabstand wird durch Bindungen zu Siliziumatomen im Oxid auch Siliziumatomen im unoxidierten Kern aufgezwungen.:Inhaltsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Abkürzungsverzeichnis Symbolverzeichnis 1. Einleitung 2. Theoretische Grundlagen 2.1. Molekulardynamik 2.2. Siliziumnanodrähte 2.3. Verzerrung und Verspannung 3. Modellsystem 3.1. Ausgangsstruktur 3.2. Vorrelaxation 3.3. Ablauf der Oxidation 4. Untersuchungsmethoden 4.1. Sauerstofffluenz, Oxidationsgrad und Oxidationsrate 4.2. Massendichte und Siliziumanteil 4.3. Radiale Verteilungsfunktion 4.4. Verzerrung 4.4.1. <110>-Draht 4.4.2. <100>-Draht 5. Ergebnisse und Diskussion 5.1. Festlegung des Einsetzintervalls 5.2. Temperaturvariation 5.2.1. Oxidationsgrad 5.2.2. Siliziumanteil 5.2.3. Massendichte 5.2.4. Radiale Verteilungsfunktion 5.3. Radius- und Orientierungsvariation 5.4. Verzerrung 6. Zusammenfassung und Ausblick 6.1. Zusammenfassung 6.2. Ausblick A. Festlegung des Einsetzintervalls Literaturverzeichnis

BACKGROUND.One group of theories aiming at providing a framework explaining the etiology, maintenance and phenomenology of anxiety disorders is classified as cognitive models of anxiety. These approaches assume that distortions in specific levels of information processing are relevant for the onset and maintenance of the disorder. A detailed knowledge about the nature of these distortions would have important implications for the therapy of anxiety, as the implementation of confrontative or cognitive elements precisely fitting the distortions might enhance efficacy. Still, these models and related empirical evidence provide conflicting assumptions about the nature of disorder-linked processing distortions. Many cognitive models of anxiety (e.g., Fox, Russo, &amp;amp; Dutton, 2002; Mathews &amp;amp; Mackintosh, 1998; Williams, Watts, MacLeod, &amp;amp; Mathews, 1997) postulate that anxiety-linked biases of attention imply hypervigilance to threat and distractibility from other stimuli in the presence of feared materials. This is convincingly confirmed by various experimentalclinical studies assessing attention for threat in anxious participants compared to non-anxious controls (for a review, seeMathews &amp;amp;MacLeod, 2005). In contrast, assumptions concerning anxiety-linked biased memory for threat are less convincing; based on the shared tendency for avoidance of deeper elaboration in anxiety disorders, some models predict memory biases only for implicit memory tasks (Williams et al., 1997) or even disclaim the relevance of memory in anxiety at all (e.g., Mogg, Bradley, Miles, &amp;amp; Dixon, 2004). Other theories restrict the possibility of measuring disorder-specific memory biases to tasks that require merely perceptual encoding of the materials instead of verbal-conceptual memory (e.g., Fox et al., 2002; Mathews &amp;amp;Mackintosh, 1998). On the one hand, none of these models has integrated all the inconsistencies in empirical data on the topic. On the other hand, the numerous empirical studies on memory in anxiety that have been conducted with varying materials, anxiety disorders, encoding and retrieval conditions do not allow final conclusions about the prerequisites for finding memory biases (for a review, see MacLeod &amp;amp; Mathews, 2004). A more detailed investigation of the complete spectrum of memory for threat utilizing carefully controlled variations of depth of encoding and materials is needed. In view of these inconsistencies, it is all the more surprising that one important part of this spectrum has so far remained completely uninvestigated: visual working memory (VWM). No study has ever differentially addressed VWM for threat in anxious vs. nonanxious participants and none of the cognitive models of anxiety provides any predictions concerning this stage of information processing. Research on cognitive biases in anxiety has thus far only addressed the two extremes of the processing continuum: attention and longer-term memory. In between, a gap remains, the bridging of which might bring us closer to defining the prerequisites of memory biases in anxiety. As empirical research has provided substantial and coherent knowledge concerning attention in anxiety, and as attention and VWM are so closely linked (see, for instance, Cowan, 1995), the thorough investigation of VWM may provide important clues for models of anxiety. Is anxiety related to VWM biases favoring the processing of threatening information, or does the avoidance presumed by cognitive models of anxiety already begin at this stage? RESEARCH AIMS. To investigate the relevance of biased VWM in anxiety, the present research focused in eight experiments on the following main research questions: (1) Is threat preferably stored in VWM in anxious individuals? (2) Does threat preference occur at the cost of the storage of other items, or is extra storage capacity provided? (3) Would the appearance of threat interrupt ongoing encoding of non-threatening items? (4) Does prioritized encoding of threat in anxiety occur strategically or automatically? (5) Are disorder-specific VWM biases also materials-specific? (6) Are VWM biases in anxiety modifiable through cognitive-behavioral therapy? METHODS. In Experiments 1-4, a spatial-sequential cueing paradigm was used. A subset of real-object display items was successively cued on each trial by a sudden change of the picture background for 150 ms each. After the cueing, one of the display pictures was hidden and probed for a memory test. On most trials, a cued item was tested, and memory accuracy was determined depending on the item’s position within the cue string and depending on its valence. In some cases, memory for an uncued item was tested. Experiment 1 and 2 were directed at discovering whether spider fearfuls and non-anxious controls would differ with respect to the accuracy in memorizing cued spiders and uncued spiders and, thus, reveal disorder-specific biases of VWM. In addition, the question whether the presence of a spider image is related to costs for the memorization of other images was tested. Experiment 3 addressed whether any disorder-specific VWM biases found earlier were specific to the feared spiders. Therefore, the critical stimuli here were a snake and a spider. Participants were spider fearfuls and non-anxious controls, both without snake anxiety. In Experiment 4, it was tested whether disorder-specific biases found in Experiment 1 and 2 were modifiable through cognitive-behavioral treatment. The critical stimulus was a spider image. Spider fearfuls were tested three times. Half of them received a cognitive-behavioral intervention after the first test, the other half only after the second test. In two additional experiments, VWM was assessed with a change-detection paradigm. The main aim was to clarify whether disorder-specific effects found in the previous experiments were associated with automatic or with strategic selective encoding of threatening materials, and whether any group differences in spider change detection were materials-specific to spiders, but not to snakes. In Experiment 5, several images were presented simultaneously in a study display for either 100 or 500 milliseconds. After a short interruption, a test display was presented including either the same items as the first one or one changed item. Participants’ accuracy in determining whether displays were the same or different was measured depending on the valence of the changed item, set size, and presentation time of the display. There were trials with and without spiders. If a change was made, it could involve either a non-spider or a spider item. Of specific interest was the condition in which a spider image was presented initially, but not in the test phase, as noticing this specific change would require storage of that image in VWM. Would group differences be particularly pronounced in the shorter encoding condition suggesting automatic encoding of threat, or would they occur in the longer encoding condition, suggesting strategic encoding of spiders? In Experiment 6, change detection accuracy for spiders vs. snakes was tested. The participants in both experiments were spider fearfuls vs. controls, but those of Experiment 6 were additionally required to lack snake anxiety. Moreover, a temporal VWM paradigm - an attentional blink task - was applied to assess whether a biased encoding of spider images in spider fearfuls would occur at the expense of non-threatening items undergoing concurrent processing, and whether this effect was specific to spiders, but not to snakes. Series of real-object pictures were presented at rates of 80 ms at the display center. The observer’s task was to identify and report the two target pictures indicated by a brighter background. In Experiment 7, the first target always depicted a neutral item. The valence of the second target was varied - either negative depicting a spider, positive, or neutral. Participants varied with respect to their spider anxiety. In Experiment 8, spider fearfuls and non-anxious controls, both without snake anxiety, were tested. The experiment was nearly the same as the previous one, but two negative target types were tested: disorder-relevant spiders and negative but not feared snakes. Of specific interest was whether the appearance of a threatening target would reduce the report probability of the earlier attended target, indicating the interruption of its VWM encoding in favor of the threat item. RESULTS. (1) Both anxious and non-anxious controls, showed VWM advantages for negative materials such as spider or snake images. (2) In addition, there were disorderspecific VWM biases: some effects were larger in spider fearfuls than in non-anxious controls and some effects occurred exclusively in spider fearfuls. (3) Group differences and, thus, disorder-specificity were particularly pronounced under competitive circumstances, that is, under the condition of numerous stimuli competing for processing resources: when only little orientation time was allowed, when only little time was provided for selecting and encoding items from a crowd, and when VWMfor the critical item required reflexive instead of voluntary attention. (4) Pronounced memory for task-relevant, voluntarily attended spiders was related to difficulties in disengaging attention from these items in the fearful group, reflected in reduced memory accuracy for the item following it. (5) Disorder-specific VWM biases seem to be based on attentional biases to threatening materials resulting in a very quick, automatic memory consolidation. However, this preferential encoding was not at the cost of neutral materials currently undergoing encoding processes. (6) All disorder-specific VWM biases occured only with fear-related materials, not with other negative materials. (7) Automatic and highly disorder-specific fear-related VWM biases – but not strategic VWM biases occuring in both groups - were modifiable through cognitive-behavioral intervention. CONCLUSIONS. This work provides additional information about informationprocessing distortions related to specific anxiety. With the experimental investigation of biased VWM, this work has been performed to fill a gap within research on cognitive biases in anxiety. Moreover, this dissertation contributes to cognitive theories of anxiety by proposing several recommendations for refinements of current theoretical approaches. Most important, it was suggested to extend existing models by a more detailed consideration of attention and memory. In view of numerous previous empirical studies on the topic and the conclusions of this dissertation, a differentiation of the attentional engagement and disengagement component appears inevitable. Even more important, in view of the data presented here predictions concerning VWM for threatening materials need to be taken into account. In addition, suggestions are provided for the differential consideration of biases occuring from prepotent threat value of negative stimuli vs. individual threat value. A proposal for a cognitive model of anxiety extended by all these aspects is provided to serve as an invitation of further research in the investigation of the nature of memory biases in anxiety disorders. REFERENCES: Cowan, N. (1995). Attention and Memory. An integrated framework.New York: Oxford University Press. Fox, E., Russo, R., &amp;amp; Dutton, K. (2002). Attentional bias for threat: Evidence for delayed disengagement from emotional faces. Cognition and Emotion, 16, 355-379. MacLeod, C., &amp;amp; Mathews, A. (2004). Selective memory effects in anxiety disorders: An overview of research findings and their implications. In D. Reisberg &amp;amp; P. Hertel (eds.), Memory and Emotion. Oxford: Oxford University Press. Mathews, A., &amp;amp; Mackintosh, B. (1998). A cognitive model of selective processing in anxiety. Cognitive Therapy and Research, 22 (6), 539-560. Mathews, A., &amp;amp; MacLeod, C. (2005). Cognitive vulnerability to emotional disorders. Annual Review of Clinical Psychology, 1, 167-195.Mathews, Mogg, May, &amp;amp; Eysenck (1989). Mogg, K., Bradley, B.P., Miles, F., &amp;amp; Dixon, R. (2004). Time course of attentional bias for threat scenes: Testing the vigilance avoidance hypothesis. Cognition and Emotion, 18(5), 689-700. Williams, J.M.G., Watts, F.N., MacLeod, C., &amp;amp; Mathews, A. (1997). Cognitive psychology and emotional disorders. Chichester: John Wiley.

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