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Krimmel, Mirko. "Top Down Design eines Schubkurbelgetriebes." Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-141781.
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Der von der Firma ibb durch Herrn Mirko Krimmel geplante Vortrag im Rahmen der Saxsim 2014, umfasst die Vorgehensweise zur Entwicklung einer Getriebebaureihe als Top-Down Design.
Dabei werden die Bauteilauslegungen und Festigkeitsberechnungen mit Mathcad nach der FKM-Richtlinie 2012 vorgestellt, sowie die Möglichkeit gezeigt, Mathcad als übergreifendes Steuerelement für das Skelettmodell nutzen zu können.
Weitere Punkte des Vortrags behandeln die Auslegung und Simulation des Gehäuses und der Gesamtbaugruppe mit Creo Simulate 2.0. Anhand der Überprüfung des Verdrehwinkels an der Abtriebsseite infolge von elastischer Verformung der einzelnen Bauteile, zeigen die Stärken des Programms.
Eine parallel zur Entwicklung laufende Simulation mit MDX bestätigte die in Mathcad errechneten Werte und lieferte so gleichzeitig eine Verifizierung der 3D-Daten. Referierende Person ist Herr Mirko Krimmel (interne Konstruktion in Petersberg).
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Benhammouda, B. "Rank-revealing top-down ULV factorizations." Universitätsbibliothek Chemnitz, 1998. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199801313.
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Rank-revealing ULV and URV factorizations are useful tools to determine the rank and to compute bases for null-spaces of a matrix. However, in the practical ULV (resp. URV ) factorization each left (resp. right) null vector is recomputed from its corresponding right (resp. left) null vector via triangular solves. Triangular solves are required at initial factorization, refinement and updating. As a result, algorithms based on these factorizations may be expensive, especially on parallel computers where triangular solves are expensive. In this paper we propose an alternative approach. Our new rank-revealing ULV factorization, which we call ¨top-down¨ ULV factorization ( TDULV -factorization) is based on right null vectors of lower triangular matrices and therefore no triangular solves are required. Right null vectors are easy to estimate accurately using condition estimators such as incremental condition estimator (ICE). The TDULV factorization is shown to be equivalent to the URV factorization with the advantage of circumventing triangular solves.
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Anderson, Giles Mark. "Top-down modulation of visual attention." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1270/.
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This body of work examines the effects of pre-cues on visual search for targets defined by a colour-orientation conjunction. Cueing the identity of targets enhanced the efficiency of search, with stronger effects from cueing the colour of the target compared to cueing its orientation, even though the targets were balanced for search efficiency within both orientation and colour dimensions. The colour advantage remained when the response to the target was task-irrelevant and occurred whether information was presented as visual cues or verbal cues. There was, however, evidence of automatic priming from the physical nature of cue stimuli playing a substantial role in guiding search, particular when based on the cue’s colour. Eye movement data from uncued trials indicated fixations were initially directed to a subset of items with the same colour. Cues were assumed to direct fixations within this colour-grouped array. Colour cueing effects reinforced the parsing of stimuli grouped by colour, while orientation cues enhanced local orientation disparities within the colour groups. The findings suggest that the advantage for colour cueing may be due to a combination of more efficient early segmentation of search items into colour groups and stronger grouping arising within these groups.
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Siegel, Markus. "Top-down Verarbeitung und neuronale Synchronisation." Doctoral thesis, Humboldt-Universität zu Berlin, Medizinische Fakultät - Universitätsklinikum Charité, 2005. http://dx.doi.org/10.18452/15225.
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Wahrnehmung ist kein vollständig durch sensorische Reize determinierter bottom-up Prozeß, sondern wird stark beeinflußt durch von diesen Reizen unabhängige top-down Prozesse wie etwa Aufmerksamkeit oder Erwartungen. Welche neuronalen Mechanismen liegen der Integration von bottom-up und top-down gerichteter Verarbeitung sensorischer Information zu Grunde? Im ersten Teil dieser Arbeit wurde diese Frage an Hand von Simulationen eines neuronales Netzwerks zweier vereinfachter kortikaler Areale untersucht. Dieses Netzwerk berücksichtigt hierbei jüngste zellphysiologische Befunde über die stark asymmetrischen funktionellen Eigenschaften kortikaler Neurone. Das simulierte Netzwerk repliziert zentrale neurophysiologische Befunde: 1) Top-down Signale erhöhen die Feuerraten der Neurone sowohl in einem hierarchisch hohen als auch tiefen kortikalen Areal. 2) Durch selektive top-down Signale wird die Verarbeitung simultaner Reize zu Gunsten eines faszilitierten Reizes moduliert. 3) Durch die reziproke Netzwerkarchitektur kommt es zu einem bidirektionalen Informationsfluß zwischen Arealen. Diese kooperative Verarbeitung bedingt gemeinsam mit einer nichtlinearen somato-dendritischen Interaktion neuronale Salvenentladungen, die ein hohes Signal-Rausch-Verhältnis aufweisen. Das simulierte Netzwerk demonstriert, welche zentrale Rolle die komplexen nichtlinearen Eigenschaften kortikaler Neurone bei der Integration bottom-up und top-down gerichteter Verarbeitung sensorischer Information spielen. Im Mittelpunkt der im zweiten Abschnitt vorgestellten experimentellen Studie steht die hochfrequente Synchronisation neuronaler Aktivität. Das große neurowissenschaftliche Interesse an der zeitlichen Struktur neuronaler Aktivität liegt insbesondere in der kontrovers diskutierten Hypothese eines „Synchronisationscodes“ begründet, gemäß welcher Information nicht nur durch die Feuerraten kortikaler Neurone, sondern auch durch die Synchronisation der Aktionspotentiale einer Neuronenpopulation codiert wird. Finden sich solche Synchronisationsphänomene in wachen, sich unter möglichst natürlichen Bedingungen verhaltenden Tieren wieder? Sind diese Synchronisationen selektiv für Eigenschaften des Reizes? Gelingt es, an Hand eines objektiven Kriteriums ein funktionelles Frequenzband neuronaler Synchronisation zu definieren? Diese Fragestellungen wurden mittels chronischer extrazellulärer Ableitungen im primären visuellen Kortex wacher, sich verhaltender Katzen untersucht: 1) Visuelle Stimulation induziert einen breitbandigen hochfrequenten Anstieg neuronaler Synchronisation. 2) Diese Synchronisation ist selektiv für die Orientierung visueller Reize. 3) Durch Analyse dieser Stimulusselektivität kann ein funktionelles Band neuronaler Synchronisation von etwa 45 Hz bis 120 Hz definiert werden. Diese Untersuchungen an wachen, sich unter vergleichsweise natürlichen Bedingungen verhaltenden Tieren demonstrieren eine überraschend breite Frequenzverteilung neuronaler Synchronisation, die im hochfrequenten Bereich weit über die üblicherweise untersuchten Frequenzbänder hinausreicht. Diese Befunde sprechen gegen die Hypothese hochfrequenter kortikaler Synchronisation als einem schmalbandigen statischen Phänomen.Sensory perception is not purely a bottom-up process determined only by sensory stimuli, but is strongly dependent on top-down factors such as attention or expectations.Which neuronal mechanisms underlie the integration of bottom-up and top-down directed processing of sensory information? In the first part of this study this question was addressed by numerical simulations of a neural network model of two simplified cortical areas. The simulated network takes into account recent findings concerning the pronounced functional asymmetry of cortical neurons.The network replicates several important neurophysiological findings: 1) Top-down signals enhance firing rates in hierarchically high and low cortical areas. 2) The processing of two competing stimuli is biased towards one stimulus by selective top-down signals. 3) The reciprocal network architecture results in a bidirectional flow of information. Together with the implemented non-linear somato-dendritic interaction this leads to neuronal bursting behaviour with a high signal to noise ratio. The simulated network demonstrates the critical role of the complex non-linear properties of cortical neurons for the integration of bottom-up and top-down directed sensory processing. The central question of the second part of this study is the functional role of high-frequency synchronization of neuronal activity. The strong interest in the temporal dynamics of neuronal activity is particularly due to the hypothesis of a “synchronization-code” according to which information is not solely encoded by firing rates but also by the synchronization of neuronal ensembles. Is such synchronization observed in awake animals behaving under natural conditions? Are these synchronizations stimulus selective? Is it possible to define a functional frequency band of synchronization based on an objective criterion? These questions were addressed by chronic extracellular recordings of neuronal activity in primary visual cortex of awake behaving cats: 1) Visual stimulation induces neuronal synchronization in a broad and high frequency range. 2) This synchronization is selective for the orientation of a visual stimulus. 3) By analyzing the stimulus selectivity of synchronization a functional band of neuronal synchronization can be defined from about 45 to 120 Hz. These results from animals behaving under natural conditions show a surprisingly broad spectral distribution of synchronization that extends well beyond typically investigated frequency ranges. These results cast doubt on the hypothesis of cortical high-frequency synchronizations as a spectrally sharp and static phenomenon.
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Comandini, Alessio. "Kubernetes su GCP: Un approccio top down." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Nella tesi viene analizzata l'architettura a microservizi e nello specifico la piattaforma kubernetes e le sue topologie di installazione. Successivamente verrà presentata la piattaforma google cloud platform per valutare i servizi che questa offre per il dispiegamento di cluster kubernetes e di applicazioni sopra questo cluster.
Finita la fase di analisi si procederà a mettere in opera un cluster kubernetes e successivamente questo verrà testato attraverso il dispiegamento di una piccola applicazione.
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Ruff, Christian Carl. "Top-down signals in visual selective attention." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1444575/.
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This thesis describes experimental work on the brain mechanisms underlying human visual selective attention, with a focus on top-down activity changes in visual cortex. Using a combination of methods, the experiments addressed related questions concerning the functional significance and putative origins of such activity modulations due to selective attention. More specifically, the experiment described in Chapter 2 shows with TMS-elicited phosphenes that anticipatory selective attention can change excitability of visual cortex in a spatially-specific manner, even when thalamic gating of afferent input is ruled out. The behavioural and fMRI experiments described in Chapter 3 indicate that top-down influences of selective attention are not limited to enhancements of visual target processing, but may also involve anticipatory processes that minimize the impact of visual distractor stimuli. Chapters 4-6 then address questions about potential origins of such top-down activity modulations in visual cortex, using concurrent TMS-fMRI and psychophysics. These experiments show that TMS applied to the right human frontal eye field can causally influence visual cortex activity in a spatially-specific manner (Chapter 4), which has direct functional consequences for visual perception (Chapter 5), and is reliably different from that caused by TMS to the right intra-parietal sulcus (Chapter 6). The data presented in this thesis indicate that visual selective attention may involve top-down signals that bias visual processing towards behaviourally relevant stimuli, at the expense of distracting information present in the scene. Moreover, the experiments provide causal evidence in the human brain that distinct top-down signals can originate in anatomical feedback loops from frontal or parietal areas, and that such regions may have different functional influences on visual processing. These findings provide neural confirmation for some theoretical proposals in the literature on visual selective attention, and they introduce and corroborate new methods that might be of considerable utility for addressing such mechanisms directly.
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Giacaglia, Giuliano Pezzolo. "Integrating bottom-up and top-down information." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91813.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-70).
In this thesis I present a framework for integrating bottom-up and top-down computer vision algorithms. I developed this framework, which I call the Map-Dictionary Pixel framework, because my intuition is that there is a need for tools that make it easier to build computer vision systems that mimic the way human visual systems process information. In particular, we humans humans create models of objects around us, and we use these models, top-down, to interpret, analyze and discern objects in the information that comes bottom-up from the visual world. After introducing my Map-Dictionary Pixel framework, I demonstrate how it empowers computer vision algorithms. I implement two different systems that extract the pixels of the image that correspond to a human. Even though each system uses different sets of algorithms, both use Map-Dictionary Pixel framework as the connecting pipeline. The two implementations demonstrate the utility of the Map-Dictionary Pixel framework and provide an example of how it can be used.
by Giuliano Pezzolo Giacaglia.
M. Eng.
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Limongi, Tirado Roberto. "Linguistic top-down modulation of causal perception /." Available to subscribers only, 2007. http://proquest.umi.com/pqdweb?did=1456283951&sid=6&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Mages, Mark. "Top-Down-Funktionsentwicklung eines Einbiege- und Kreuzenassistenten /." Düsseldorf : VDI-Verl, 2009. http://d-nb.info/992593336/04.
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Mohamed, Abdelhack. "Top-down Modulation in Human Visual Cortex." Kyoto University, 2019. http://hdl.handle.net/2433/242434.
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PETILLI, MARCO ALESSANDRO. "Proactive Top-Down Processes in Visual Search." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199069.
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La letteratura ha indagato il ruolo dei processi top-down e bottom-up nel guidare la ricerca visiva. Recenti studi hanno suggerito un ruolo modulatorio dei processi top-down sulla cattura attentiva. Tuttavia, i risultati sono contraddittori, e il ruolo dei processi top-down non è stato ancora chiaramente stabilito.
In questo lavoro, abbiamo studiato se il controllo top-down fosse reclutato proattivamente quando c’è un’aspettativa di distrattori e abbiamo adottato il paradigma di Distraction Context Manipulation (DCM) per caratterizzare il loro reclutamento nella ricerca visiva. Pertanto, abbiamo combinato un compito di feature search e uno di conjunction search con il DCM (Esp 1-4). In linea con il DCM, i blocchi erano di tre tipi: un blocco Puro senza trial con distrattori, e due blocchi contenenti frequenti trial con distrattori (Mixed Feature e Conjunction). Il compito era individuare il target in ogni trial. Il confronto tra trial senza distrattori nei blocchi misti e nel blocco puro ha permesso di rilevare il reclutamento di processi top-down per l'aspettativa di distrattori.
Inizialmente abbiamo indagato se i processi top-down fossero reclutati nei contesti distraenti e se il loro potenziale reclutamento fosse modulato dal tipo di ricerca (Exp 1). I risultati hanno mostrato un reclutamento proattivo dei processi top-down in caso di aspettativa di distrattori sia nel feature che nel conjunction search. Tale reclutamento è emerso come costo in termini di tempo di risposta nonché come beneficio della sensibilità di detezione del target quando i distrattori erano attesi ma non presentati. Risultati sovrapponibili sono emersi nelle varianti di ricerca visiva covert (Esp 1,3) e overt (Esp 2,4).
Poiché le precedenti esperienze distraenti hanno mostrato di modellare l'aspettativa di distrattori nei trial successivi, abbiamo anche cercato di differenziare il ruolo delle aspettative da quello dell'esperienza nell'attivare i processi top-down. I risultati (Esp 1, 2 e 4) hanno indicato che il costo dovuto all’aspettativa di distrattori si verificava a prescindere che i distrattori fossero o meno presenti nel trial precedente. Tuttavia, l'entità di questo costo era maggiore dopo i trial con distrattori, suggerendo che questi processi non siano basati solo sull'aspettativa, ma siano anche rinforzati dopo un'esperienza distraente. L'esperimento 3 ha cercato di caratterizzare la natura implicita vs esplicita dei processi top-down innescati da esperienze distraenti. I risultati hanno mostrato che i costi e i benefici sui tempi di risposta non cambiano quando l'evento distraente è imprevedibile da quando è predicibile. I processi top-down innescati dalla esperienza distraente non sembrano essere soggetti al controllo esplicito. L'esperimento 4 ha ulteriormente tentato di elucidare i contributi relativi dell'esperienza e delle aspettative. Qui, anche un altro tipo di aspettativa top-down è stata manipolata: la certezza temporale che un evento potenzialmente distraente fosse in arrivo. I risultati hanno indicato un ruolo preponderante delle aspettative top-down mostrando che il costo sui tempi di risposta asseconda il decorso dell'aspettativa temporale di eventi potenzialmente distraenti mentre la prossimità temporale da una precedente esperienza distraente riveste un peso minore. Infine, l’esperimento 4 ha dimostrato che l'aspettativa dei distrattori modula i processi attenzionali. Le analisi EEG hanno indicato che l'aspettativa di distrattori aumenta l'ampiezza della componente occipitale P1 che viene elicitata sia da stimoli di ricerca che neutri, ma questo avviene solo quando viene indotta un'aspettativa temporale di un evento potenzialmente distraente.
Nel complesso, i risultati suggeriscono che sia nel feature che nel conjunction search l’attenzione è modulata in maniera proattiva per meglio affrontare le aspettative rispetto alle richieste del compito formate sulle precedenti esperienze.Literature has long investigated the contributions of top-down and bottom-up processes in guiding search behavior. Recent findings suggest a modulatory role of top-down processes on attentional capture. However, results are contradictory, and whether and how top-down processes intervene has not been clearly established yet. Here, we approached the issue from the perspective of proactive top-down processes of distractor expectation and leveraged the Distractor Context Manipulation (DCM) paradigm to help characterizing their recruitment in visual search. Thus, we combined a feature search (i.e., search for a high-contrast target among no-contrast distractors) and a conjunction search (i.e., search for a high-contrast target among high-contrast distractors) with the DCM paradigm (Exp 1-4). Accordingly, blocks of trials were of three types: a Pure block containing no distractor-present trials, and two blocks containing frequent distractor-present trials (i.e., Mixed Feature and Mixed Conjunction). Subjects were instructed to look for the target on each trial. The comparison of distractor-absent trials of Mixed vs Pure blocks allowed detecting proactive top-down processes of distractor expectation. First, we investigated whether proactive top-down processes were recruited in distracting contexts of visual search and whether their potential recruitment was modulated by the type of search (Exp 1). Results attested for a proactive recruitment of top-down processes of distractor expectation in both feature and conjunction search. Such recruitment entailed a response time (RT) cost as well as a beneficial enhancement of the detection sensitivity (d’) to the target when distractors were expected, yet not presented. Overlapping results emerged in covert (Exp 1, 3) and overt (Exp 2, 4) variants of visual search. Since previous distracting experience shaped distractor expectation, we, also, sought to disentangle the role of expectation and experience in the activation of top-down processes. Results (Exp 2, 4) showed that the distractor expectation cost occurred regardless of whether or not distractors occurred in the immediately preceding trial. However, the magnitude of the cost was larger after distracting trials suggesting that these processes do not rely only on tonic expectation-based mechanisms but they are also contingently reinstated after a distracting experience occurred. Experiment 3 tried to characterize the implicit vs explicit nature of top-down mechanisms triggered by distracting experience. Results showed that RT-costs and d'-benefits did not change when distraction occurrence was unpredictable and when it was predictable. Therefore, top-down control setting triggered by recent distracting experience seems to be not subjected to explicit control. Experiment 4 further investigated the role of experience and expectations in order to disentangle their relative contributions. Here, also another type of top-down expectation was manipulated: the temporal certainty of incoming potentially distracting event. Results indicated a preponderant role of top-down expectations by showing that RT-costs followed the time course of temporal expectation of incoming potentially distracting events while temporal recency from a previous distracting experience had a smaller weight. Finally, Experiment 4 explored the EEG correlates of distractor expectation. An enhancement of the occipital P1 amplitude was elicited by both search and neutral stimuli but only when a temporal expectation of a potentially distracting event was induced indicating that distractor expectation modulates visual attentional processes in lower sensory areas. Overall, results suggested that in both feature and conjunction search preparatory top-down processes are proactively enrolled to face with expected task demands based on previous distracting experiences. These results help characterizing how top-down mechanisms intervene in different types of visual search.
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Meitinger, Karl-Heinz. "Top-Down-Entwicklung von aktiven Sicherheitssystemen für Kreuzungen /." Düsseldorf : VDI-Verl, 2009. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017617877&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Buffett, Scott. "Investigating iterative deepening in top-down automated reasoning." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ38363.pdf.
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Goschy, Harriet-Rosita. "Top-down shielding from distraction in visual attention." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-171000.
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The present work examines top-down shielding from distraction in visual attention; that is, under which circumstances can the intentions and goals of an observer counteract the bottom-up salience of irrelevant distractors. Several factors of influence will be considered: First, prior experience with distractors, i.e. did observers previously acquire an effective distractor shielding strategy; second, intra- vs. cross-dimensionality of distractors, i.e. are irrelevant distractors defined in the same feature dimension (e.g., shape, color) as the target or in a different feature dimension; third, time, i.e. how effective is distractor shielding early vs. later in processing; and finally, the incentive for effective distractor shielding.
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Park, Chi-youn 1981. "Recognition of English vowels using top-down method." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28538.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 69-70).
Many recognizers use bottom-up methods for recognizing each phoneme or feature, and use the cues and the context to find the most appropriate words or sentences. But humans recognize words not just through bottom-up processing, but also top-down. In many cases of listening, one can usually predict what will come based on the preceding context, or one can determine what has been pronounced by listening to the following sounds. Therefore, if some cues to a word are given, it would be possible to refine the recognition by using the top-down method. This thesis deals with the improvement of the performance of recognition by using the top-down method. And most of the work will be concentrated on the problem of vowel recognition, when the adjacent consonants are known.
by Park Chi-youn.
S.M.
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Singer, Amy M. (Amy Michelle). "Top-down design of digital signal processing systems." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/40000.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (leaves 45-46).
by Amy M. Singer.
M.Eng.
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Morton, Dennis P. (Dennis Paul). "Hardware modeling and top-down design using VHDL." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/39962.
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Sakellaridou, Irini. "A top-down analytic approach to architectural composition." Thesis, University College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504524.
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This thesis is an exercise in theory with an empirical exercise. It deals with the traditional architectural ideas of 'composition' and 'parti', and applies a formal analytic approach to them. It takes a top-down approach to the notion of 'composition', which tries to reflect the way architects think, and looks at the 'parti' as the deep structure of the building, which is abstract, global, and capable of many realisations. As a case study, 19 houses of Mario Botta are analysed. The purpose of the empirical exercise is to explore how far it is possible to produce an analytic construction of the notion of 'parti'. It asks: are there formal top-down themes which underly the composition of the houses and have to do with their relational structure? After the description of the houses a formal analysis of the identified themes takes place. These formal top-down themes are defined as rules. A distinction is made between the nature of the rule, the degree of its realisation and the domains (mass, elevations, plan) of its realisation. Formal analysis, thus, measures properties of the mass, the elevations and the plan. What analysis shows is that the interrelations of the rules define the 'parti'. Three phases are identified in the development of the 'parti' of the houses which show an evolution of it from combinations to structure. A distinction between a short and a long genotype for order is thus made, as well as a distinction between the intension and the extension of the rule seen as a relation. In the last part the thesis explores what these findings suggest towards theory building as well as implications for further research by addressing the notion of relation and by defining two different types of interrelations.
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Santhana, Krishnan Archanaa. "Top-down Approach To Securing Intermittent Embedded Systems." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/105128.
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The conventional computing techniques are based on the assumption of a near constant source of input power. While this assumption is reasonable for high-end devices such as servers and mobile phones, it does not always hold in embedded devices. An increasing number of Internet of Things (IoTs) is powered by intermittent power supplies which harvest energy from ambient resources, such as vibrations. While the energy harvesters provide energy autonomy, they introduce uncertainty in input power. Intermittent computing techniques were proposed as a coping mechanism to ensure forward progress even with frequent power loss. They utilize non-volatile memory to store a snapshot of the system state as a checkpoint. The conventional security mechanisms do not always hold in intermittent computing. This research takes a top-down approach to design secure intermittent systems. To that end, we identify security threats, design a secure intermittent system, optimize its performance, and evaluate our design using embedded benchmarks. First, we identify vulnerabilities that arise from checkpoints and demonstrates potential attacks that exploit the same. Then, we identify the minimum security requirements for protecting intermittent computing and propose a generic protocol to satisfy the same. We then propose different security levels to configure checkpoint security based on application needs.
We realize configurable intermittent security to optimize our generic secure intermittent computing protocol to reduce the overhead of introducing security to intermittent computing. Finally, we study the role of application in intermittent computing and study the various factors that affect the forward progress of applications in secure intermittent systems. This research highlights that power loss is a threat vector even in embedded devices, establishes the foundation for security in intermittent computing.Doctor of Philosophy
The embedded systems are present in every aspect of life. They are available in watches, mobile phones, tablets, servers, health aids, home security, and other everyday useful technology. To meet the demand for powering up a rising number of embedded devices, energy harvesters emerged as a solution to provide an autonomous solution to power on low-power devices. With energy autonomy, came energy scarcity that introduced intermittent computing, where embedded systems operate intermittently because of lack of constant input power. The intermittent systems store snapshots of their progress as checkpoints in non-volatile memory and restore the checkpoints to resume progress. On the whole, the intermittent system is an emerging area of research that is being deployed in critical locations such as bridge health monitoring. This research is focused on securing intermittent systems comprehensively. We perform a top-down analysis to identify threats, mitigate them, optimize the mitigation techniques, and evaluate the implementation to arrive at secure intermittent systems. We identify security vulnerabilities that arise from checkpoints to demonstrate the weakness in intermittent systems. To mitigate the identified vulnerabilities, we propose secure intermittent solutions to protect intermittent systems using a generic protocol. Based on the implementation of the generic protocol and its performance, we propose several optimizations based on the needs of the application to securing intermittent systems. And finally, we benchmark the security properties using two-way relation between security and application in intermittent systems. With this research, we create a foundation for designing secure intermittent systems.
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Johansson, Lucas. "Improving asset readability in top-down VR games." Thesis, Luleå tekniska universitet, Institutionen för konst, kommunikation och lärande, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-63864.
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With this work I wanted to examine how to improve readability of battlefields in top-down gamesfor VR by increasing the visual distinction between units. I analyzed three successful PC gameswithin the genre and created three different user tests to come up with my results and conclusions.The results from my VR test is compared to my non-VR tests to see what one has to do to reachthe same level of readability or better in VR. It turns out you need to put more time in to yourassets for improving readability in VR than without VR on a non-stereo display.
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Meitinger, Karl-Heinz. "Top-down-Entwicklung von aktiven Sicherheitssystemen für Kreuzungen." Düsseldorf VDI-Verl, 2008. http://d-nb.info/994851790/04.
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Namubiru, Evelyn Lwanga. "Coping with top-down institutional changes in forestry." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3342198.
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Thesis (Ph.D.)--Indiana University, School of Public and Environmental Affairs and the Dept. of Political Science, 2008.Title from PDF t.p. (viewed on Oct. 6, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 0760. Adviser: Elinor Ostrom.
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Louchet, Hadrien. "Top-down analysis of high-capacity fiber-optic transmission." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981530613.
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Lüdecke, André. "Simulationsgestützte Verfahren für den Top-Down-Entwurf heterogener Systeme." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970523009.
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Vaurette, Francois. "Fabrication top-down, caractérisation et applications de nanofils silicium." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2008. http://tel.archives-ouvertes.fr/tel-00342294.
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Cette thèse porte sur l'étude de nanofils silicium réalisés par approche top-down. Elle s'inscrit dans le contexte de la miniaturisation des composants et la compréhension du transport dans les systèmes 1D.Deux voies de fabrication sont envisagées : la lithographie par AFM (Microscope à Force Atomique) et la lithographie électronique. Cette dernière étant plus reproductible, les dispositifs finaux sont fabriqués par cette technique, à partir d'un substrat SOI et plusieurs étapes de gravure et métallisation.
L'étude des nanofils par mesures I(V) nous permet de mettre en évidence une zone déplétée à l'interface Si/SiO2 natif. Grâce à l'utilisation de nanofils de largeurs et de longueurs différentes, nous sommes capables de déterminer la largeur de la zone déplétée, la densité d'états d'interface ainsi que le niveau de dopage des nanofils. L'évolution de la résistance des nanofils avec la température est également étudiée et montre une dépendance associée à la diffusion des phonons de surface.
Trois applications sont ensuite décrites : un décodeur, un commutateur de courant et un capteur biologique. En effet, la gravure locale des nanofils conduit à une modulation de la bande de conduction, rendant possible la réalisation d'un décodeur. D'autre part, la fabrication de croix à base de nanofils et de grilles latérales à proximité des croix qui contrôlent le passage du courant dans les différentes branches permet de former un commutateur de courant. Enfin, grâce au rapport important de la surface par rapport au volume des nanofils et leur bonne fonctionnalisation chimique, ceux-ci sont utilisés pour détecter électriquement des interactions biologiques (détection de l'ovalbumine).
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Kloninger, Paul. "Top - Down Design eines universellen Kegelrollenlagermodells in Pro/MECHANICA." Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-68438.
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In dieser Präsentation wird das universelle FE-Modell eines Kegelrollenlagers vorgestellt. Mittels eines Pro/ENGINEER-Layouts, basierend auf dem Top-Down Designkonzept, kann automatisch innerhalb einer kurzen Bearbeitungszeit ein geprüftes und lauffähiges FE-Modell eines Kegelrollenlagers abgeleitet werden. Dieses Modell kann z.B. in großen Getriebemodellen eingebaut werden, um eine quasistatische Betrachtung mit korrekten Lagersteifigkeiten zu ermöglichen.
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Burke, Madeline Jane. "Top-down and bottom-up approaches to tissue engineering." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720837.
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Chandra, Naveen. "A top-down approach to delta-sigma modulator design /." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32955.
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This work presents the use of a new design methodology for the creation of analog integrated circuit components featuring optimization with Matlab and Simulink. This procedure allows circuit design to take place at the highest level of abstraction, and has the added advantage that designs can be implemented with currently used, and widely available tools. It results in building block requirements being specified prior to the undertaking of transistor level simulations, thereby saving much valued design time.Also presented are the issues behind the design of an audio-band, single bit switched capacitor delta-sigma modulator with 16 bits of performance. This begins with the filtering function design, continues with the realization in a low voltage standard CMOS process, and concludes with experimental measurements to gauge performance. The creation of the modulator was carried out using the proposed top-down design methodology, and its experimental performance is used to help validate the procedure.
In addition, the design and fabrication of a multibit DeltaSigma modulator including a novel internal DAC was carried out. The multibit DAC is based on encoding DC levels into digital PDM bitstreams, which are then decoded by a single analog filter. The use of a single filtering path reduces mismatch effects in the DAC. The functionality, performance, and limitations are explored by examining the experimental results of a 2.5 V, audio-band, 2nd order, 3-bit DeltaSigma modulator in a 0.25 mum CMOS process.
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Za'bah, Nor Farahidah. "Top-down fabrication of silicon nanowire using optical lithography." Thesis, University of Newcastle Upon Tyne, 2012. http://hdl.handle.net/10443/1423.
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A nanowire is a thin wire with a cross section conveniently measured in nanometres (nm). It has a large surface area to volume ration which allows it to have more exposure to the environment. Therefore, it is highly desirable to be implemented as a biosensor as it would exhibit a characteristic of being ultra-sensitive and highly selective to a wide range of biological and chemical species.
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Li, Da-Hai. "Top-down and step-wise refinement of protocol specifications." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47093.
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Skogsholm, Lauren. "Distractibility, Impulsivity, and Activation of Top-down Control Resources." Thesis, Boston College, 2011. http://hdl.handle.net/2345/1977.
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Thesis advisor: Elizabeth KensingerThesis advisor: Katherine Mickley Steinmetz
Distractibility and impulsivity have long been thought of as two separate psychological processes; however, there is currently evidence that suggests otherwise. The aim of this study was to gain a better understanding on the behavioral level of the interaction between these two traits. I proposed a model in which some individuals have a higher than average threshold for activation of the top-down cognitive control resources that are important for directing and maintaining attention as well as for regulating impulsive behaviors. To test the strength of this model I used an experimental paradigm that combined two different types of tasks—a spatial working memory task and a delay discounting of a primary reward (juice) task. Participants were administered the Conners’ Adult ADHD Rating Scale in order to be classified in terms of their trait distractibility and trait impulsivity subscale scores. The results suggest that there is indeed an association between the traits of distractibility and impulsivity, and that they may be linked by a common mechanism involving a variable threshold of activation of top-down control resources to regulate these behaviors
Thesis (BS) — Boston College, 2011
Submitted to: Boston College. College of Arts and Sciences
Discipline: College Honors Program
Discipline: Psychology
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Best, Maisy Jane. "Top-down and bottom-up influences on response inhibition." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/24650.
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Following exposure to consistent stimulus–stop mappings, response inhibition can become automatised with practice. What is learned is less clear, even though this has important theoretical and practical implications. The main contribution of this thesis is to investigate how stimulus-stop associations are acquired and the conditions under which they influence behaviour. To this end, this thesis addressed several outstanding issues concerning the associative architecture of stop learning, the role of expectancies, and the specificity of learning in inhibition tasks. Experiments 1-4 provide evidence that participants can acquire direct associations between specific stimuli and the stop goal without mediation via a single representation of the stop signal. However, these experiments also suggest that the influence of stimulus-stop associations on behaviour depends on top-down attentional settings: if participants begin to ignore the stop-associated stimuli, the effects of stop learning are diminished or eliminated entirely. Across eight experiments, this thesis provides evidence that participants generate expectancies during stop learning that are consistent with the stimulus-stop contingencies in play. However, Experiments 5-6 indicate that there may be some differences in the relationships between stimulus-stop expectancies and task performance under instructed and uninstructed conditions; stimulus-stop associations that are acquired via task instructions or via task practice have similar effects on behaviour, but seem to differ in how they trigger response slowing for the stop-associated items. Experiments 7-8 investigated the role of signal detection processes during the acquisition of stimulus-stop associations. To distinguish between stimulus-stop learning and stimulus-signal learning, the contingencies between specific stimuli and the stop goal and the contingencies between specific stimuli and the spatial location of the stop signal were independently manipulated. Although these experiments showed evidence of stop/go (goal) learning, there was no evidence that participants acquired the stimulus-signal associations. Across four experiments, this thesis investigated the specificity of stop learning. Experiments 9-10 compared the effects of training on behavioural performance in inhibition (go/no-go) and non-inhibition (two-choice) tasks. The results of these experiments revealed that learning in inhibition and non-inhibition tasks could arise through similar associative mechanisms, but suggest that the effects of training in these tasks could also depend on top-down response settings and general non-associative processes. Experiments 11-12 investigated the neural specificity of stop learning. These experiments also revealed similar effects of training across the go/no-go and two-choice tasks adding weight to the claim that training in inhibition tasks primarily influences task-general processes. Combined, the overall conclusion of this thesis is that bottom-up control can influence response inhibition but what is learned depends on top-down factors. It is therefore important to consider bottom-up factors and top-down factors as dependent, rather than independent, influences on response inhibition.
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Burkholder, Derek A. "Top Down Control in a Relatively Pristine Seagrass Ecosystem." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/799.
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The loss of large-bodied herbivores and/or top predators has been associated with large-scale changes in terrestrial, freshwater, and marine ecosystems around the world. Understanding the consequences of these declines has been hampered by a lack of studies in relatively pristine systems. To fill this gap, I investigated the dynamics of the relatively pristine seagrass ecosystem of Shark Bay, Australia. I began by examining the seagrass species distributions, stoichiometry, and patterns of nutrient limitation across the whole of Shark Bay. Large areas were N-limited, P-limited, or limited by factors other than nutrients. Phosphorus-limitation was centered in areas of restricted water exchange with the ocean. Nutrient content of seagrasses varied seasonally, but the strength of seasonal responses were species-specific. Using a cafeteria-style experiment, I found that fast-growing seagrass species, which had higher nutrient content experienced higher rates of herbivory than slow-growing species that are dominant in the bay but have low nutrient content. Although removal rates correlated well with nutrient content at a broad scale, within fast-growing species removal rates were not closely tied to N or P content. Using a combination of stable isotope analysis and animal borne video, I found that green turtles (Chelonia mydas) – one of the most abundant large-bodied herbivores in Shark Bay – appear to assimilate little energy from seagrasses at the population level. There was, however, evidence of individual specialization in turtle diets with some individuals foraging largely on seagrasses and others feeding primarily on macroalgae and gelatinous macroplankton. Finally, I used exclusion cages, to examine whether predation-sensitive habitat shifts by megagrazers (green turtles, dugongs) transmitted a behavior-mediated trophic cascade (BMTC) between sharks and seagrasses. In general, data were consistent with predictions of a behavior-mediated trophic cascade. Megaherbivore impacts on seagrasses were large only in the microhabitat where megaherbivores congregate to reduce predation risk. My study highlights the importance of large herbivores in structuring seagrass communities and, more generally, suggests that roving top predators likely are important in structuring communities - and possibly ecosystems - through non-consumptive pathways.
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VIJAY, VIKAS. "A TOP-DOWN METHODOLOGY FOR SYNTHESIS OF RF CIRCUITS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100584283.
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Vaurette, François. "Fabrication top-down, caractérisation et applications de nanofils silicium." Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10009/document.
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Cette thèse porte sur l'étude de nanofils silicium réalisés par approche top-down. Elle s'inscrit dans le contexte de la miniaturisation des composants et la compréhension du transport dans les systèmes 1D. Deux voies de fabrication sont envisagées: la lithographie par AFM (Microscope à Force Atomique) et la lithographie électronique. Cette dernière étant plus reproductible, les dispositifs finaux sont fabriqués par cette technique, à partir d'un substrat SOI et plusieurs étapes de gravure et métallisation. L'étude des nanofils par mesures l(V) nous permet de mettre en évidence une zone déplétée à l'interface Si/SiO2 natif. Grâce à l'utilisation de nanofils de largeurs et de longueurs différentes, nous sommes capables de déterminer la largeur de la zone déplétée, la densité d'états d'interface ainsi que le niveau de dopage des nanofils. L'évolution de la résistance des nanofils avec la température est également étudiée et montre une dépendance associée à la diffusion des phonons de surface. Trois applications sont ensuite décrites : un décodeur, un commutateur de courant et un capteur biologique. En effet, la gravure locale des nanofils conduit à une modulation de la bande de conduction, rendant possible la réalisation d'un décodeur. D'autre part, la fabrication de croix à base de nanofils et de grilles latérales à proximité des croix qui contrôlent le passage du courant dans les différentes branches permet de former un commutateur de courant. Enfin, grâce au rapport important de la surface par rapport au volume des nanofils et leur bonne fonctionnalisation chimiques, ceux-ci sont utilisés pour détecter électriquement des interactions biologiques (détection de l'ovalbumine)This work focuses on the study of silicon nanowires made by a top-down approach. The context of the study is the miniaturisation of the components and the understanding of the transport in 1D systems. Two fabrication approaches are studied : AFM lithography (Atomic Force Microscope) and e-beam lithography. The latter being more reproducible, the final devices are fabricated by this technique using a SOI substrate and multiple steps of etching and metallization.Transport characterization of the Si nanowires allows us to highlight a depleted area at the interface Si/native SiO2. Using nanowires with different widths and lengths, we can determine the depletion width, the surface state density as well as the doping level of the nanowires. The evolution of the nanowires resistance with temperature is also investigated, showing a dependence associated with surface phonons scattering. In the last chapter, three applications are described : a decoder, a current switch and a biosensor. The use of a local etching allows the modulation of the conduction band of the nanowires, opening the way to build a decoder using two local gates. Crossbar structures, where lateral gates which can derive the current in the di_erent branches, lead to the fabrication of a current switch. Finally, thanks to the large surface to volume ratio in these structures, the nanowires are used to detect electrically the interactions between molecules (ovalbumine detection)
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Itti, Laurent Koch Christof. "Models of bottom-up and top-down visual attention /." Diss., Pasadena, Calif. : California Institute of Technology, 2000. http://resolver.caltech.edu/CaltechETD:etd-12022005-103530.
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Jajliardo, Adam Paul. "Development of specification criteria to mitigate top-down cracking." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000706.
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Del, Pero Luca. "Top-Down Bayesian Modeling and Inference for Indoor Scenes." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/297040.
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People can understand the content of an image without effort. We can easily identify the objects in it, and figure out where they are in the 3D world. Automating these abilities is critical for many applications, like robotics, autonomous driving and surveillance. Unfortunately, despite recent advancements, fully automated vision systems for image understanding do not exist. In this work, we present progress restricted to the domain of images of indoor scenes, such as bedrooms and kitchens. These environments typically have the "Manhattan" property that most surfaces are parallel to three principal ones. Further, the 3D geometry of a room and the objects within it can be approximated with simple geometric primitives, such as 3D blocks. Our goal is to reconstruct the 3D geometry of an indoor environment while also understanding its semantic meaning, by identifying the objects in the scene, such as beds and couches. We separately model the 3D geometry, the camera, and an image likelihood, to provide a generative statistical model for image data. Our representation captures the rich structure of an indoor scene, by explicitly modeling the contextual relationships among its elements, such as the typical size of objects and their arrangement in the room, and simple physical constraints, such as 3D objects do not intersect. This ensures that the predicted image interpretation will be globally coherent geometrically and semantically, which allows tackling the ambiguities caused by projecting a 3D scene onto an image, such as occlusions and foreshortening. We fit this model to images using MCMC sampling. Our inference method combines bottom-up evidence from the data and top-down knowledge from the 3D world, in order to explore the vast output space efficiently. Comprehensive evaluation confirms our intuition that global inference of the entire scene is more effective than estimating its individual elements independently. Further, our experiments show that our approach is competitive and often exceeds the results of state-of-the-art methods.
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Larsson, Therese, and Louise Pettersson. "Perspektiv på goodwill : En studie om användningen av teoretiska begrepp i praktiken." Thesis, Karlstads universitet, Avdelningen för företagsekonomi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-31524.
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Det finns två typer av goodwill, den första typen är internt upparbetad goodwill och den andra typen är goodwill som uppkommer vid förvärv av företag. Fokus i denna uppsats kommer att ligga på den förvärvade goodwill, som kan upplevas som en svart låda då det kan vara oklart vad posten faktiskt består av. Förvärvad goodwill kan definieras på olika sätt av företagen, i den akademiska världen har främst två perspektiv identifierats, top-downperspektivet och bottom-upperspektivet. Ur den första synvinkeln ses goodwill som en restpost och ur den andra synvinkeln kan goodwill ses som en summa av de komponenter som posten består av. Genom att betrakta dessa perspektiv är tanken att få en inblick i hur företagen väljer att redovisa sin goodwill. Det kan vara lättare sagt än gjort, teori och praktik går inte alltid hand i hand. Det finns ett glapp mellan hur praktiker jobbar med goodwill och teoretikers åsikt om posten. Varför det finns meningsskiljaktigheter växer successivt fram under studiens gång. Det finns än så länge bara ett fåtal studier som behandlar själva begreppet goodwill och dess olika perspektiv samt hur företagen ser på goodwill. För att försöka bidra till ökad förståelse på detta område, har vi i denna uppsats undersökt om teorin och praktiken kommit varandra närmare. Det främsta syftet med studien är att ta reda på om företag inom bemanningsbranschen definierar sin goodwill olika i sina årsredovisningar. För att undersöka detta på ett begripligt sätt har tre professionella respondenter intervjuats i ett försök att klargöra komplexiteten av posten. Slutsatsen är att det inte går att identifiera vilket perspektiv som används i en årsredovisning på grund av att dessa är väldigt standardiserade, vilket gör att det blir svårt för intressenten att utläsa särskilt mycket information om goodwillposten. Det alternativ som kändes mest relevant att använda och som skulle hjälpa oss att kunna få klarhet i vår frågeställning, var att vända sig till en urvalsgrupp av representanter på området. Den analys som efterföljde resulterade i att vi kunde konstatera att samtliga svarande på det praktiska området såg goodwillposten mer eller mindre som en restpost. Ingen värdering eller starkare reflektion gjordes kring det andra teoretiska perspektivet. Sammanfattningsvis vågar vi påstå att det inte skett någon märkbar förändring som gjort att teori och praktik närmat sig varandra.There is two ways to understand goodwill. Number one, internally generated goodwill and number two, acquired purchase goodwill. The main topic for this research is acquired purchase goodwill. Many people believe that goodwill is a sort of black box. It is unclear what goodwill actually is. There is no limit on how you can define acquired purchase goodwill. In academia we talk about two perspectives, top-down perspective and bottom-up perspective. The first perspective sees goodwill as a residual and the second perspective sees goodwill as a sum of its components. When you put on these two glasses, the idea is that you may be able to see how businesses account for their goodwill. It is easier said than done, many times theory and practice does not get along. There is a big space between the theories on how you work with goodwill in the reality. Only a few have studied the definition of goodwill. Because of that we really wanted to investigate this phenomenon. We have analyzed if the gap between theory and reality has been reduced. The purpose of this study is to investigate if the staffing companies define goodwill different in their annual reports. The tool we have used is to interview professional accountants to get their opinion. The conclusion is that the annual report is quite standardized which means it is difficult to understand what goodwill actually is. Everybody we interviewed have the same opinion, that goodwill is a residual. They made no reflections or additions on that subject. In summary, we know now that after our study, no big change has been made between theory and practice.
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BAUTISTA, DE LA TORRE ARACELI. "ANÁLISIS Y PROPUESTA DE MEJORA PARA LA INFRAESTRUCTURA DE LA RED INALÁMBRICA, BASADA EN LA METODOLOGÍA DEL TOP/DOWN, EN EL CAMPUS UNIVERSITARIO “EL CERRILLO”." Tesis de Licenciatura, Universidad Autónoma del Estado de México, 2014. http://hdl.handle.net/20.500.11799/66069.
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Este proyecto estudia la estructura de la red inalámbrica en el Campus Universitario “El Cerrillo” de la Universidad Autónoma del Estado de México, identificando las necesidades y la problemática a la que se enfrentan los usuarios de esta red. Está basado en el análisis sistemático y metodológico del diseño de redes que nos orienta en un enfoque diferente al que tradicionalmente se utiliza en la elaboración de un proyecto.
Algunas instalaciones requieren mantenimiento y actualización, ya que tienen bastantes años y sus equipos se están volviendo obsoletos, de ahí la importancia de proponer mejoras a la infraestructura de la red inalámbrica para asegurar una mejor conectividad o mejor desempeño en el Campus.
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Naureen, Shagufta. "Top-down Fabrication Technologies for High Quality III-V Nanostructures." Doctoral thesis, KTH, Halvledarmaterial, HMA, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-117766.
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III-V nanostructures have attracted substantial research effort due to their interesting physical properties and their applications in new generation of ultrafast and high efficiency nanoscale electronic and photonic components. The advances in nanofabrication methods including growth/synthesis have opened up new possibilities of realizing one dimensional (1D) nanostructures as building blocks of future nanoscale devices. For processing of semiconductor nanostructure devices, simplicity, cost effectiveness, and device efficiency are key factors. A number of methods are being pursued to fabricate high quality III-V nanopillar/nanowires, quantum dots and nano disks. Further, high optical quality nanostructures in these materials together with precise control of shapes, sizes and array geometries make them attractive for a wide range of optoelectronic/photonic devices. This thesis work is focused on top-down approaches for fabrication of high optical quality nanostructures in III-V materials. Dense and uniform arrays of nanopillars are fabricated by dry etching using self-assembly of colloidal SiO2 particles for masking. The physico-chemistry of etching and the effect of etch-mask parameters are investigated to control the shape, aspect ratios and spatial coverage of the nanopillar arrays. The optimization of etch parameters and the utilization of erosion of etch masks is evaluated to obtain desired pillar shapes from cylindrical to conical. Using this fabrication method, high quality nanopillar arrays were realized in several InP-based and GaAs-based structures, including quantum wells and multilayer heterostructures. Optical properties of these pillars are investigated using different optical spectroscopic techniques. These nanopillars, single and in arrays, show excellent photoluminescence (PL) at room temperature and the measured PL line-widths are comparable to the as-grown wafer, indicating the high quality of the fabricated nanostructures. The substrate-free InP nanopillars have carrier life times similar to reference epitaxial layers, yet an another indicator of high material quality. InGaAs layer, beneath the pillars is shown to provide several useful functions. It effectively blocks the PL from the InP substrate, serves as a sacrificial layer for generation of free pillars, and as a “detector” in cathodoluminescence (CL) measurements. Diffusion lengths independently determined by time resolved photoluminescence (TRPL) and CL measurements are consistent, and carrier feeding to low bandgap InGaAs layer is evidenced by CL data. Total reflectivity measurements show that nanopillar arrays provide broadband antireflection making them good candidates for photovoltaic applications. A novel post etch, sulfur-oleylamine (S-OA) based chemical process is developed to etch III-V materials with monolayer precision, in an inverse epitaxial manner along with simultaneous surface passivation. The process is applied to push the limits of top-down fabrication and InP-based high optical quality nanowires with aspect ratios more than 50, and nanostructures with new topologies (nanowire meshes and in-plane wires) are demonstrated. The optimized process technique is used to fabricate nanopillars in InP-based multilayers (InP/InGaAsP/InP and InP/InGaAs/InP). Such multilayer nanopillars are not only attractive for broad-band absorption in solar cells, but are also ideal to generate high optical quality nanodisks of these materials. Finally, the utility of a soft stamping technique to transfer free nanopillars/wires and nanodisks onto Si substrate is demonstrated. These nanostructures transferred onto Si with controlled densities, from low to high, could provide a new route for material integration on Si.QC 20130205
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Lawson, Helen Sarah. "Educators' responses to key top-down citizenship education related initiatives." Thesis, Manchester Metropolitan University, 2014. http://e-space.mmu.ac.uk/332147/.
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Introduction: In 2001, the year before citizenship education became a statutory subject in England there were disturbances and violence ‘involving large numbers of people from different cultural backgrounds’ (The Cantle Report, 2001). That same year the attacks on the Twin Towers rocked the world and in 2005 so-called ‘home-grown’ extremists bombed London killing 52 people. Reports were commissioned to explore the reasons behind these events and to suggest recommended ways forward. Concerns were raised about intuitional racism, internal security, a lack of a sense of Britishness and extremism. All prompted an education response. From 2002 teachers had to cope with more and more education initiatives and directives which addressed key issues and concerns, with citizenship education in particular being seen as playing a key role in bringing about the necessary societal change. The aims of this research are to show how teachers, student teachers and tutors say they are responding to the many top-down initiatives related to citizenship education, and reveal the mechanisms that impact on the ways in which educators say they are responding to the top-down initiatives related to citizenship education. Methodology: The research uses a qualitative research design which is underpinned by critical realism. Critical realism helped to provide the necessary methodological framework to reveal the generative mechanisms which might be working to influence educators’ responses (tendencies) to top-down initiatives; and how and why these tendencies occur in some settings but not others. The empirical research has been generated over a ten year period and I employed a variety of data collection tools including questionnaires; semi-structured interview; focus group and participant observation. Findings: The number of top-down initiatives that have been introduced by the government has seen some very different responses from educators. Some educators are able to interlace different agendas and weave varied themes together in creative ways as a means of addressing different demands. For others the initiatives seem to be source of pressure which sets up a tendency to interpret the initiatives as something more, something additional that has to be managed, particularly in the case where educators are having to address different priorities such as raising or maintaining results. This in turn helps to create further sets of tendencies and tensions with some educators employing teaching and learning processes which are incompatible with citizenship education. Conclusion: While there are a number of mechanisms which seem to be particularly significant to tendency generation including school context and appropriate training, highly significant mechanisms for generating educators’ responses are personal commitment and motivation, and the ability to think creatively. It is possible that, through appropriate training, educators can acquire skills in creative and critical thinking. However the passion and motivation to teach citizenship education is much harder to impart. The majority of educators who were committed to citizenship, and in particular those committed to teaching for diversity and dialogue, had had some kind of personal experience which had not only provoked commitment but also provided a personal resource for educators to draw on in the classroom, which in turn helped to increase educators’ confidence to address potentially highly controversial issues. The potential for innovative educator training to capture and transmit the feelings that personal experience can inspire is thus an area that would benefit from further research.
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Krol, Magdalena E. "The role and mechanisms of top-down optimisation of perception." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/the-role-and-mechanisms-of-topdown-optimisation-of-perception(19b58dfe-67ce-48df-a6b8-5d1299afc493).html.
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According to the predictive coding approach to perception, the brain uses predictions based on previous experience to optimise perception, by allocating more computational resources to important or unexpected stimuli. Overall, predictions allow faster and more accurate recognition, but occasionally, when the prediction is incorrect, it may lead to a misperception. The aim of this thesis was to investigate the influence of top - down processes on perceptual decisions. I utilised misperceptions as a signature of those top - down influences and Signal Detection Theory to assess their size, type and direction. I used Electroencephalography to determine the stage of information processing at which different types of predictions influence sensory processing.The empirical studies are clustered around Topic 1: Influence of Predictions on Perception, Topic 2: Types of Predictions and Topic 3: Value as Modulator of Perception.Studies clustered in Topic 1 analysed and quantified the influence of predictions on perceptual decisions and showed that misperceptions can be triggered by wrong predictions only in very specific circumstances. In particular, misperceptions occurred only if there was some degree of correspondence between the wrong prediction and the sensory input. Otherwise, predictions were easily rejected, increasing the overall accuracy. I also demonstrated that misperceptions were most likely to happen in a window on the continuum of input quality where the stimulus - related uncertainty was highest. Topic 2 comprised experiments investigating different types of predictions and their interaction. Behavioural (but not EEG) results revealed interference between passive and active expectations. The early event related (ERP) components N1 and P2, as well as the P300, were all modulated by expectations. Expected events either increased or decreased the P300 amplitude, depending on whether the expected item was predictable and thus ignored, or awaited and thus flagged for further processing. This suggests that P300 might be an index of top - down resource allocation. Experiments within Topic 3 studied the influence of values, as examples of executive processes, on perceptual decisions, using either natural or acquired high - value stimuli. The results suggested that the process of recognition is adjusted in a top - down manner to account for the cost and benefit values related to different outcomes. The trade - off between processing time and accuracy is not fixed, but can be adjusted to optimise recognition in the task at hand. Furthermore, value can change the focus of perception, resulting in different elements of the sensory input being amplified or ignored. Overall, these results showed that misperceptions are 'intelligent mistakes' - a by - product of a top-down, prediction - based optimisation strategy that decreases the computational load, while increasing accuracy and improving the allocation of computational resources.
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Butler, Joe. "Top-down and exogenous effects on covert and overt orienting." Thesis, Bangor University, 2015. https://research.bangor.ac.uk/portal/en/theses/topdown-and-exogenous-effects-on-covert-and-overt-orienting(88a8f964-f569-444a-ad9d-803c36609366).html.
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Due to numerous bottlenecks, the human brain is unable to consciously process all data available at the retina. To overcome these constraints, evolution has developed a system that breaks down retinal information into fragments and subsequently analyses them according to current goals and expectations. This biasing system is frequently referred to as attention. Yet despite a long history of itself having been the focus of analysis, there are a number of questions about attention that are clearly unanswered by the literature. Therefore, we wanted to address three problems highlighted by our literature review. Specifically, we wanted learn, (I) Are the effects of probabilistic expectations, when instructed either by spatial blocking of the target location or through a central cue, on response latencies the product of a ballistic, attentional process, or the product of an information theoretical decision-making process? (II) Can the inhibitory aspects of spatial attention be pre-deployed by using a central cue to manipulate prior expectations of where a task-irrelevant distractor is likely to appear? (III) What is the relationship between attention and eye movements?We investigated this last question by way of testing healthy participants on covert and overt versions of the behavioural paradigms designed to address questions I and II, and then in a neuropsychology patient who presented with hypometric saccades, we investigated if eye movements and attention can be dissociated. Experiments 1-4, showed that the effects of target probability - when either spatially manipulated or instructed through a central cue - can neither be fully accounted for by attentional accounts or information theoretical accounts. Additionally, the outcome of target probability is context dependent. That is, outcomes depend on how target probability was instructed. Experiment 5 showed that spatial inhibition cannot be endogenously deployed using central cues. Although we found that distractor suppression takes place when targets are invalidly cued, suggesting distractor suppression takes place during reorienting. Experiments 6-7 showed that attentional orienting can be preserved in the presence of oculomotor impairment, indicating eye movements and attention can be structurally dissociated. Whereas the results of experiments 1-5 are consistent with claims that covert and overt orienting are similarly affected by expectations due to a common attentional process. We conclude that expectations influence a mechanism common to overt and covert responses, but ultimately, both processes are distinct. In the discussion chapter, we discuss a number of future avenues of research,including how electrophysiology could be used to further understand the phenomena presented here. Overall, the contribution of this body of research is to illustrate that the relationship between top-down expectations and exogenous effects is extremely complicated, and are, currently, inadequately captured by present models of attention.
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Sock, Ching Low. "Giving centre stage to top-down inhibitory mechanisms for selective attention." Doctoral thesis, Universitat Pompeu Fabra, 2020. http://hdl.handle.net/10803/670753.
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Selective attention determines the sensory signals that are processed at higher levels at the expense of others and is biased by higher-order brain regions which anticipate task-relevant stimuli and increase neural sensitivity to them in the sensory cortex. Often, this is thought to occur through excitation of selected neurons, but some studies have suggested that it is not the full description of the process. Increasingly, evidence has pointed to an alternative, top-down inhibitory biasing mechanism. Here, we investigated such an inhibitory model of attention. We first showed how sensitivity to stimulus features known to be task-irrelevant are reduced through top-down suppression. Secondly, we demonstrated a biologically grounded spiking model’s ability to modulate information processing and benchmarked it to physiology. Lastly, we explored the interaction between the excitatory and inhibitory models of top-down attention in a foraging agent. Our results support the inhibitory model of top-down attention as a biological attentional mechanism and show how it fits into the current zeitgeist of top-down attentional mechanisms.L’atenció selectiva determina els senyals sensorials que es processen a nivells superiors a costa dels altres. Està esbiaixada per regions cerebrals d’ordre superior que anticipen estímuls rellevants per a la tasca i augmenten la sensibilitat neuronal a l’escorça sensorial. Sovint, es creu que això es produeix mitjançant l'excitació de neurones seleccionades, però alguns estudis han suggerit que no és la descripció completa del procés. Cada vegada més, l’evidència apunta cap a un mecanisme alternatiu de polarització inhibitiva de dalt a baix. Aquí hem investigat, aleshores, un model d’atenció inhibitori. Primer, vam demostrar com es redueix la sensibilitat a les funcions d’estímul irrellevants per tasques mitjançant la supressió de dalt a baix. En segon lloc, vam demostrar la capacitat d’un model d’espiga basat en la biologia per modular el processament de la informació i l’hem comparat amb la fisiologia. Per últim, hem explorat la interacció entre els models excitadors i inhibidors d’atenció de dalt a baix en un agent de cerca d’aliments. Els nostres resultats donen suport al model inhibitori de l’atenció de dalt a baix com a mecanisme d’atenció biològica i mostren com s’adapta al ‘zeitgeist’ actual dels mecanismes d’atenció de dalt a baix.
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Kondo, Michio. "TOP-DOWN AND BOTTOM-UP FORCES STRUCTURING BIOLOGICAL COMMUNITIES : THEORETICAL CONSIDERATIONS." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150859.
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Laurinen, P. (Perttu). "A top-down approach for creating and implementing data mining solutions." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514281268.
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Abstract
The information age is characterized by ever-growing amounts of data surrounding us. By reproducing this data into usable knowledge we can start moving toward the knowledge age. Data mining is the science of transforming measurable information into usable knowledge. During the data mining process, the measurements pass through a chain of sophisticated transformations in order to acquire knowledge. Furthermore, in some applications the results are implemented as software solutions so that they can be continuously utilized. It is evident that the quality and amount of the knowledge formed is highly dependent on the transformations and the process applied. This thesis presents an application independent concept that can be used for managing the data mining process and implementing the acquired results as software applications.
The developed concept is divided into two parts – solution formation and solution implementation. The first part presents a systematic way for finding a data mining solution from a set of measurement data. The developed approach allows for easier application of a variety of algorithms to the data, manages the work chain, and differentiates between the data mining tasks. The method is based on storage of the data between the main stages of the data mining process, where the different stages of the process are defined on the basis of the type of algorithms applied to the data. The efficiency of the process is demonstrated with a case study presenting new solutions for resistance spot welding quality control.
The second part of the concept presents a component-based data mining application framework, called Smart Archive, designed for implementing the solution. The framework provides functionality that is common to most data mining applications and is especially suitable for implementing applications that process continuously acquired measurements. The work also proposes an efficient algorithm for utilizing cumulative measurement data in the history component of the framework. Using the framework, it is possible to build high-quality data mining applications with shorter development times by configuring the framework to process application-specific data. The efficiency of the framework is illustrated using a case study presenting the results and implementation principles of an application developed for predicting steel slab temperatures in a hot strip mill.
In conclusion, this thesis presents a concept that proposes solutions for two fundamental issues of data mining, the creation of a working data mining solution from a set of measurement data and the implementation of it as a stand-alone application.
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Clarke, Stephen E. "Top-down control of sensory focus in bursty pyramidal cell populations." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36826.
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Through a series of original research articles, this thesis describes the role of neural
network feedback in top-down control of bursty ON and OFF type electrosensory
neurons while processing motion toward (looming) and away (receding) from the
body. Neural codes for motion reversal in weakly electric fish are not simply evoked
by bottom-up sensory input and amplified by feedback; instead, positive feedback
loops must synthesize a directionally invariant representation of motion reversal that
is distributed across both the ON and OFF pyramidal cell populations. Through
balanced excitatory and inhibitory feedback, the system establishes an optimal distance for motion estimation (a sensory focus) that is maintained by the animal during a motion tracking behaviour. Remarkably, this sensory focus is size, direction and speed-invariant. The speed invariance likely derives from the speed invariance of
the electrosensory afferent response, a consequence of timescale-free spike frequency adaptation. Since natural swimming movements are associated with tail-bending that cause spatially diffuse sensory noise, we demonstrate that spatially localized motion processing by the ON and OFF neurons co-occurs with cancellation of the distraction; this supports the circuit's role as a robust `sensory searchlight' mechanism for spatial attention. A simple algorithm for motion tracking is discussed, as well as potential generalizations of the described coding principles to more complex mammalian circuits.
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Boddington, Steven Paul. "Education from the top down, a biography of W. H. Swift." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ34739.pdf.
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Ma, Chuan. "A computational approach to top-down hierarchical supervisory control of DES." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0004/MQ45611.pdf.
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