To see the other types of publications on this topic, follow the link: Spatial frequencie.
Dissertations / Theses on the topic 'Spatial frequencie'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Spatial frequencie.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
SILVESTRI, VALENTINA. "AND I’LL SEE YOU IN THE HIGH AND LOW. The ontogenetic origins of sensitivity to facial cues to trustworthiness and emotion." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/379215.
Full textAbstract:
Una componente fondamentale della competenza sociale degli esseri umani è l'abilità di estrarre rapidamente e in modo spontaneo i segnali sociali che provengono dal volto, quali per esempio i tratti emotivi e di affidabilità. Il fatto che le risposte a queste configurazioni facciali siano rapide e automatiche suggerisce come esse derivino dalla pressione evolutiva a rilevare segnali di pericolo per aumentare le possibilità di sopravvivenza. Tuttavia, le origini ontogenetiche di queste abilità sociali sono ancora oggetto di dibattito.
La presente tesi di dottorato si pone l'obiettivo di indagare la natura dell’informazione visiva che media la discriminazione delle emozioni e/o la percezione dell'affidabilità dai volti utilizzando l'approccio del filtraggio spaziale, ossia la rimozione selettiva di bande di frequenze spaziali contenute nell'immagine.
Nello specifico, l’elaborato comprende 5 studi volti a indagare (1) la natura dell'informazione visiva sui cui si basano i giudizi espliciti di affidabilità degli adulti (Studio 1) (2) se la percezione di affidabilità di adulti (Studio 2) e bambini (Studio 3) è generalizzata a volti di un'etnia differente dalla propria e la natura dell'informazione visiva coinvolta, (3) la natura dell'informazione visiva che determina la discriminazione neurale di affidabilità dai volti nei preverbali (Studio 4), e (4) la natura dell'informazione visiva su cui si basa la discriminazione visiva delle emozioni alla nascita (Studio 5a e 5b).
I risultati dello Studio 1 mostrano che sebbene sia le informazioni visive globali, veicolate dalle frequenze spaziali basse, che le informazioni visive locali, veicolate dalle frequenze spaziali alte, sono sufficienti per discriminare tra livelli di affidabilità, l'informazione globale gioca un ruolo cruciale.
Gli Studi 2 e 3 estendono le considerazioni sulla natura dell'informazione visiva coinvolta nella percezione di affidabilità a volti meno presenti nell'ambiente sociale dell'individuo, volti di un'altra etnia. Dunque, l'obiettivo è indagare se la percezione di affidabilità nei bambini (Studio 3) si basa sulle stesse informazioni visive su cui si basa negli adulti (Studio 2) e se la stessa differisca in base all'etnia del volto.
I risultati mostrano che le informazioni visive coinvolte nella percezione di affidabilità dai volti della propria o altrui etnia cambiano in relazione al grado di familiarità del volto durante lo sviluppo.
Nello Studio 4, attraverso un nuovo paradigma di registrazione della risposta neurale, la Fast Periodic Visual Stimulation, viene esplorata l'informazione visiva che i bambini di 6 mesi utilizzano per discriminare tra volti affidabili e inaffidabili. I bambini di 6 mesi discriminano tra volti affidabili e non affidabili sulla base di informazioni visive differenti. Le informazioni locali mediano la discriminazione di volti affidabili mentre la discriminazione di volti non affidabili si basa su informazione visiva locale. I risultati vengono discussi alla luce delle eventuali implicazioni per la comprensione dei meccanismi percettivi e neurali coinvolti nella discriminazione di volti a valenza positiva e negativa.
Lo Studio 5 ha indagato il ruolo dell'informazione visiva nella percezione delle emozioni alla nascita. I neonati a 2 giorni di vita discriminano tra volti felici e impauriti sia quando rimangono solo le frequenze spaziali alte che quando rimangono solo le frequenze spaziali basse. Tuttavia, i neonati preferiscono i volti felici ai volti impauriti solo quando nell’immagine rimangono le frequenze spaziali alte. Dunque, l'informazione visiva presente nell'immagine modula la salienza dei segnali sociali dai volti fin dalle prime ore di vita.
Nel complesso, i risultati suggeriscono che la percezione di affidabilità ed emotiva si basa su una sensibilità adattiva ed evoluzionistica che si raffina nel corso dello sviluppo come risultato dell'esperienza nell'ambiente sociale.One fundamental component of humans' social competence is the ability to rapidly and spontaneously extrapolate facial cues of emotion and trustworthiness - i.e., whether others are likely to approach us friendly or hostilely. The fast and automatic nature of these responses to facial configurations has led to the claim that they derive from evolutionary pressure to detect signals of potential harm, and distinguish between friends or foes to enhance our chances of survival. However, the ontogenetic origins of these fundamental social skills are still debated. To explore this question, the studies reported in this doctoral dissertation investigated the nature of the visual information driving emotion discrimination and/or trustworthiness perception across the life span using the spatial filtering approach - i.e., the selective removal of portions of the spatial frequencies (SF) information contained in the image. Specifically, this doctoral dissertation includes 5 studies aimed at investigating (1) the nature of the visual information on which adults' explicit judgments of trustworthiness are based (Study 1), (2) whether trustworthiness perception in adults (Study 2) and children (Study 3) generalizes across face-race and/or the nature of the visual information on which trustworthiness judgments are based differs for more versus less familiar face categories, (3) the nature of the visual information that triggers neural discrimination of facial cues to trustworthiness in preverbal infants (Study 4), and (4) the nature of the visual information that mediates visual discrimination of emotional facial expressions at birth (Study 5a and 5b). Results of Study 1 showed that, although both global visual cues, conveyed by low-spatial frequency bands, and local visual cues, conveyed by high-spatial frequency bands, are sufficient to discriminate between levels of trustworthiness, the selective removal of global information negatively impacts trustworthiness perception. Study 2 and 3 extended evidence on the nature of visual information involved in trustworthiness perception to faces underrepresented in the individual's social environment, other-race faces, in adults and preschool and school children. Results showed that in the course of development the visual information involved in own- and other-race trustworthiness perception changes. Study 4 used a newly developed Electroencephalographic (EEG) visual discrimination paradigm, the Fast Periodic Visual Stimulation, to investigate which visual information 6-month-old infants use to discriminate between trustworthy and untrustworthy faces. The infants’ brain discriminated between high-trustworthy and low-trustworthy faces based on different types of visual information. Results are discussed for their implications for the understanding of the perceptual/neural mechanisms involved in early discrimination between positive and negative valence faces. Study 5 explored the role of visual information in emotion perception at birth. 2-days-old newborns discriminate between happy and fearful facial expressions with both high and low spatial frequency information but they prefer happy faces when only high spatial frequencies remain. The visual information present in the image modulates the salience of the facial cues to emotions from the first hours of life. Altogether, the evidence gathered from the current studies adds to the existing literature suggesting that emotion and trustworthiness perception are based on an adaptive and evolutionary sensitivity early in life that is refined over the course of development as a result of the quantity and quality of facial experience in the social environment.
2
McSorley, Eugene. "Spatiotemporal integration of spatial frequencies." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4615/.
Full textAbstract:
Spatial frequency processing delays suggest that their integration occurs from coarse to fine. However it may be the case that integration is flexible. The first aim of this thesis was to examine the integration of spatial frequencies and the second was to examine the delays involved in initial spatial frequency processing. A coarse to fine and a fine to coarse presentation order of filtered natural images were shown. The former is judged to be of a higher quality (experiment 1) but neither show any increase in incorrect detection reports of a fullbandwidth image (experiment 2, 3 and 4). When the first three harmonics of a square-wave were shown progressively from coarse to fine and fine to coarse the former leads to more incorrect detection reports of a square-wave (experiment 5) but the latter is favoured in judgements of square-wave resemblance (experiment 6, 8, 9a and 9b), a masking (experiment 10) and a Vernier acuity task (experiment 12). These results suggest that the integration of spatial frequencies is flexible. Despite this, the integration of spatial frequencies must occur from coarse to fine because of the delays involved in the processing of spatial frequencies. In Chapter 6 (experiments 13 - 18) it was found that two widely different spatial frequencies were judged to have simultaneous onset when they were in fact simultaneous. The results of this thesis provided evidence that the integration of spatial frequencies is flexible and dependent upon the information to be derived by any particular processing. The lack of evidence for spatial frequency processing delays suggest that a flexible integration of spatial frequencies may be possible when spatial frequencies are presented simultaneously.
3
Costen, Nicholas Paul. "Spatial frequencies and face recognition." Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU069146.
Full textAbstract:
If face images are degraded by spatial quantisation there is a non-linear acceleration of the decline of recognition accuracy as block-size increases, suggesting recognition requires a critical minimum range of object spatial frequencies. These may define the facial configuration, reflecting the structural properties allowing differentiation of faces. Experiment 1 measured speed and accuracy of recognition of six fronto-parallel faces shown with 11, 21 and 42 pixels/face, produced by quantisation, a Fourier low-pass filter and Gaussian blurring. Performance declined with image quality in a significant, non-linear manner, but faster for the quantised images. Experiment 2 found some of this additional decline was due to frequency-domain masking. Experiment 3 compared recognition for quantised, Fourier low-pass and high-pass versions, recognition was only impaired when the frequency limit exceeded the range 4.5-12.5 cycles/face. Experiment 4 found this was not due to contrast differences. Experiments 5, 6 and 7 used octave band-pass filters centred on 4.14, 9.67 and 22.15 cycles/face, varying view-point for both sequential matching and recognition. The spatial frequency effect was not found for matching, but was for recognition. Experiment 8 also measured recognition of band-passed images, presented with octave bands centred on 2.46-50.15 cycles/face and at 0-90 degrees from fronto-parallel. Spatial frequency effects were found at all angles, with best performance for semi-profile images and 11.10 cycles/face. Experiment 9 replicated this, with perceptually equal contrasts and the outer facial contour removed. Modeling showed this reflected a single spatial-frequency channel two octaves wide, centred on 9 cycles/face. Experiment 10 measured response time for successive matching of faces across a size-disparity, finding an asymmetrical effect.
4
Jeantet, Coline. "Evaluation du traitement visuel précoce des visages chez les usagers de cannabis : étude par potentiels évoqués." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0329/document.
Full textAbstract:
Le cannabis est la drogue illégale la plus consommée actuellement en France. Le Δ9-tétrahydrocannabinol (Δ9-THC), en tant qu’excocannabinoïde, a un impact sur le système visuel via le système endocannabinoïde. Physiologiquement, parmi les deux voies majoritairement responsables de la transmission de l’information visuelle aux stades les plus précoces, la voie magnocellulaire pourrait être la plus sensible à l’effet du Δ9-THC. La perception des visages, stimuli complexes, nécessite le traitement précoce d’informations de bas niveaux : les fréquences spatiales. Or, les différentes gammes de fréquences spatiales, séparables en gamme de basses (BFS) et de hautes fréquences spatiales (HFS) seraient respectivement transmises de manière privilégiée par les voies magnocellulaire et parvocellulaire. Par ailleurs, la littérature fait état d’anomalies du traitement magnocellulaire dans la schizophrénie, une pathologie dont le risque accroît avec l’usage de cannabis. Ainsi, par le concours d’études chez des usagers de cannabis, des personnes souffrant de schizophrénie et des volontaires sains, notre recherche devait permettre d’évaluer l’impact de l’usage de cannabis sur les processus sensoriels et perceptifs en jeu dans le traitement des visages. Grâce à la mesure des composantes des potentiels évoqués P100 et N170 en réponse aux différentes gammes de fréquences spatiales contenues dans les visages, nous validons dans une première étude la méthodologie utilisée, confirmant notamment la sensibilité de la composante P100 aux BFS et de la N170 aux HFS. Une deuxième étude utilisant la même méthodologie suggère une altération du traitement des informations de BFS chez les consommateurs de cannabis, mesurable par une altération de l’étape perceptive d’intégration des informations de bas niveau associée à la N170. Une troisième étude portant sur des patients souffrant de schizophrénie retrouve une altération du traitement des BFS au cours des étapes précoces (composantes P100 et N170) et permet d’interpréter les résultats observés chez les usagers de cannabis sur la base d’une pathologie dont les dysfonctions visuelles sont mieux connuesCannabis is currently the most consumed illegal drug in France. The Δ9-tetrahydrocannabinol (Δ9-THC), as an exocannabinoid impacts the human visual system through the endocannabinoid system. Among the two main pathways responsible for early visual transmission, the magnocellular pathway might be the most affected by Δ9-THC. As they are complex stimuli, visual perception of faces requires the early processing of spatial frequencies, which are a type of low level information. The extreme ranges of spatial frequencies, qualified as low spatial frequencies (LSF) and high spatial frequencies (HSF), would be mainly transmitted, respectively by magnocellular and parvocellular pathways. In addition, literature already provides evidence towards magnocellular pathway impairments in schizophrenia, a pathology which incidence is known to increase with cannabis use. Hence, from studies with cannabis regular users, patients suffering from schizophrenia, and healthy controls, our research aimed at assessing the impact of regular cannabis use on early visual processes of face perception. Considering the P100 and N170 event-related potential (ERP) components in response to specific ranges of spatial frequencies available in our face stimuli, our first study tested and validated the methodology. As expected, healthy participants showed a stronger sensibility in response to LSF stimuli on the P100 and to the HSF stimuli on the N170. Using the same methodology, the second study suggests a LSF processing alteration in cannabis users, as reflected by the N170 ERP component. Our last study was conducted on patients suffering from schizophrenia and confirmed an alteration of LSF processing on both the P100 and the N170. On the basis of a pathology presenting well documented visual deficits, this last observation allows us to propose an interpretation of cannabis users’ data
5
Wiles, Andrew Donald. "Modelling Framework for Radio Frequency Spatial Measurement." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/771.
Full textAbstract:
The main crux of this thesis was to produce a model that was capable of simulating the theoretical performance of different configurations for a spatial measurement system using radio frequency technology. It has been important to study new modalities of spatial measurement since spatial measurement systems are an enabling technology that have allowed for the creation of better medical procedures and techniques, provided valuable data for motion capture in animation and biomechanics, and have improved the quality of manufacturing processes in many industries. However, there has been room for improvement in the functional design and accuracy of spatial measurement systems that will enhance current applications and further develop new applications in medicine, research and industry. In this thesis, a modelling framework for the investigation of spatial measurement based on radio frequency signals was developed. The simulation framework was designed for the purpose of investigating different position determination algorithms and sensor geomatries. A finite element model using the FEMLAB partial differential equation modelling tool was created for a time-domain model of electromagnetic wave propagation in order to simulate the radio frequency signals travelling from a transmitting source antenna to a set of receiving antenna sensors. Electronic line signals were obtained using a simple receiving infinitesimal dipole model and input into a time difference of arrival localization algorithm. The finite element model results were validated against a set of analytical solutions for the free space case. The accuracy of the localization algorithm was measured against a set of possible applications for a potential radio frequency spatial measurement system design.
It was concluded that the simulation framework was successful should one significant deficiency be corrected in future research endeavours. A phase error was observed in the signals extracted at the receiving antenna locations. This phase error, which can be up to 40°, was attributed to the zeroth order finite elements implemented in the finite element model. This phase error can be corrected in the future if higher order vector elements are introduced into future versions of FEMLAB or via the development of custom finite element analysis software but were not implemented in this thesis due to time constraints. Other improvements were also suggested for future work.
6
Mudassar, Asloob Ahmad. "Active aperture synthesis using spatial frequency heterodyning." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/158.
Full text
7
Elias, Bartholomew. "Cross-modal facilitation of spatial frequency discriminations through auditory frequency cue presentations." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/28611.
Full text
8
Shrekenhamer, David. "Dynamic Control of Metamaterials at Terahertz Frequencies." Thesis, Boston College, 2013. http://hdl.handle.net/2345/3152.
Full textAbstract:
Thesis advisor: Willie J. PadillaProgress in the field of metamaterials has started coming to a point where the field may finally begin to emerge as a viable solution to many electromagnetic challenges facing the community. No where is that more true then at terahertz frequencies where there lies an immense opportunity for growth. The development of mature technologies within this region of the electromagnetic spectrum would provide a valuable resource to become available for a multitude of applications. In order to achieve this, the necessary first steps of identifying viable materials and paths to integrate these with metamaterials will need to be completed. In this dissertation, we examine several different paths to achieve dynamic metamaterial electromagnetic response at terahertz frequencies, and demonstrate several paths to package these devices into imaging systems. In Chapter 1, we introduce the basic theory and design principles of metamaterials. We also describe the experimental techniques involved in the study of terahertz metamaterials. Chapter 2 presents a computational and experimental study investigating the integration of high electron mobility transistors with metamaterials allowing for high speed modulation of incident terahertz radiation. In Chapters 3 and 4, we investigate several different paths to create tunable terahertz metamaterial absorbers. Chapter 3 presents an investigation where we encapsulate a metametarial absorber unit cell with liquid crystals. We study both computationally and experimentally the tuning mechanism of the absorber as the liquid crystal refractive index is controlled as a function of the applied electric field strength and modulation frequency. In Chapter 4, we form a doped semiconducting metamaterial spatial light modulator with multi-color super-pixels composed of arrays of electronically controlled terahertz metamaterial absorbers. We computationally and experimentally study the independent tunability of each pixel in the spatial array and demonstrate high speed modulation. Chapter 5 introduces a multiplex imaging approach by using a terahertz spatial light modulator to enable terahertz imaging with a single pixel detector. We demonstrate the capability for high speed image acquisition, currently only limited by the commerical software used to reconfigure the spatial masks. We also configure the system to capture high fidelity images of varying complexity. In Chapter 6, we show how a metamaterial absorber can be implemented into a detector focal plane array for high sensitivity, low mutual coupling, and broad angle performance. Finally, we summarize in Chapter 7 the achievments of the research presented and highlight the direction of future work
Thesis (PhD) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
9
Foster, Collin David. "Spatial parameter estimation using measured frequency response functions." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314556.
Full text
10
Méred, Mohamed Chakib. "Théorie chromatique de l'effet Lau : Application au codage de fréquences spatiales et de densités en fausse couleur." Besançon, 1986. http://www.theses.fr/1986BESA2022.
Full textAbstract:
Role du codage en fausse couleur dans l'analyse visuelle de l'information. Tour d'horizon comparatif des différentes méthodes de codage optiques. Codage en fausse couleur base sur l'effet lau. Théorie chromatique de l'effet lau et sa génération
11
Freeman, Tyler E. "Investigating the role of spatial frequency bands in drawing." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2291.
Full text
12
Mungara, Ratheesh Kumar. "System-level performance of interference-aware spatial frequency reuse." Doctoral thesis, Universitat Pompeu Fabra, 2016. http://hdl.handle.net/10803/400869.
Full textAbstract:
Spatial frequency reuse is a long-established approach for enhancing the capacity of wireless systems through increased spectral efficiency (bits per second per unit bandwidth). The future 5th generation of wireless systems is expected to incorporate various forms of frequency reuse. This includes multiple-input multiple-output (MIMO) communication enabling frequency reuse across antennas, device-to-device (D2D)-based densification allowing spectrum reuse across direct communication links, and full duplexing utilizing the same spectrum for communication in the transmit and receive directions.
This dissertation aims at determining the performance limits of emerging wireless systems underpinned by dense spatial frequency reuse and interference suppression, and to glean key system design insights. Stochastic geometry is the toolbox invoked to conduct the analysis, with network locations modeled as points of a Poisson process. A new framework is developed by introducing a Gaussian fit to the interference and variable degrees of spatial averaging, which enable more meaningful results and compact expressions compared to those of existing analyses.
Within this framework, we first consider MIMO spatial multiplexing and interference alignment (IA). The former scheme utilizes all available spatial dimensions for signaling and the latter minimizes interference at the expense of knowing the instantaneous fading states at both transmitters and receivers and of a reduction in spatial signaling dimensions. Despite the intense work on IA and spatial multiplexing, there is limited work aimed at understanding their engineering tradeoff in the context of practically relevant cellular settings such as propagation losses, fading dynamics due to user mobility and imperfect knowledge of the fading states. We have studied this problem in depth through both system- and link-level analyses. Even under perfect knowledge of the fading, IA is seen to be beneficial over spatial multiplexing only in very specific and relatively infrequent network situations, and IA loses all its advantages at vehicular speeds when the fading knowledge is imperfect.
Second, we focus on ITLinQ and FlashLinQ, the two principal channelization schemes proposed to date for controlling the interference in D2D networks. An analytical characterization of ITLinQ scheme is provided, opening the door to optimizing its controllable parameters. It is shown that both channelization schemes outperform the unchannelized baseline, with a slight edge for ITLinQ. On the most unfavorable network geometries, ITLinQ yields multiple-fold improvements in spectral efficiency with respect to an unchannelized network.
Finally, we introduce full-duplex transceivers in cellular networks and characterize the impact of increased interference on their performance. It is established through analysis and complemented by simulations on a Vodafone LTE field test network that additional user-to-user interference only has a minor impact while base-to-base interference would render full-duplex operation unfeasible in dense microcellular networks without any interference management.
In summary, MIMO spatial multiplexing and D2D-based densification are seen to play a vital role in improving wireless system capacity while IA and full duplexing are found to be ineffective.La reutilització de la freqüència espacial és l’aproximació més acceptada per tal de millorar la capacitat dels sistemes wireless mitjançant l'increment de l'eficiència espectral (bits per segon per unitat d'ample de banda). S'espera que la futura cinquena generació de sistemes wireless incorpori diverses formes de reutilització de freqüència. Això inclou la comunicació multi-input multi-output (MIMO) que permet la reutilització a través d'antenes, densificació dispositiu-a-dispositiu (D2D) que permet reutilitzar l'espectre a través d’enllaços de comunicació directa, així com un full-dúplex emprant el mateix espectre per a la comunicació en la transmissió i recepció de direccions. Aquest treball pretén determinar els límits de rendiment dels sistemes wireless emergents, basats en una densa reutilització de la freqüència espacial i en la supressió d'interferències, així com espigolar coneixement clau per al disseny de sistemes d'aquest tipus. La geometria estocàstica és l'eina que s'aplicarà a l'anàlisi que es durà a terme, modelitzant les localitzacions dins la xarxa com a punts d'un procés de Poisson. La introducció d'un ajust Gaussià a la interferència, conjuntament amb la consideració de nivells variables d'expectació espacial, han permès definir un nou marc matemàtic que fa possible unes expressions més compactes i uns resultats més significatius en comparació amb els anàlisis existents. Dins d'aquest marc, en primer lloc es prenen en consideració la multiplexació MIMO i l'aliniament d'interferència (IA, en les seves sigles en anglès). El primer esquema empra totes les dimensions espacials disponibles per a la senyalització i el segon minimitza la interferència a costa de conèixer els estats de esvaïment instantani dels transmissors i receptors, i d'una reducció en les dimensions de senyalització espacial. Malgrat l'intens treball en l'IA i la multiplexació espacial, s'ha prestat escassa atenció a tractar de comprendre el seu balanç d’enginyeria en el context d'xarxes cel.lulars de rellevància pràctica, com els de propagació de pèrdues, o les dinàmiques de esvaïment degudes a la mobilitat de l'usuari i al coneixement imperfecte dels estats de esvaïment. En aquest treball s'ha estudiat en profunditat aquest problema a través d'anàlisis tant a nivell dels enllaços com del sistema. Fins i tot en condicions de coneixement perfecte del esvaïment, l'IA resulta beneficiós sobre la multiplexació només en situacions de xarxa molt específiques i relativament infreqüents, mentre que perd tots els seus avantatges a velocitats vehiculars quan el coneixement del esvaïment és imperfecte. En segon lloc, el treball es centra en el ITLinQ i el FlashLinQ, els dos principals esquemes de canalització proposats fins al moment per controlar la interferència en xarxes D2D. S'ofereix una caracterització analítica de l'esquema ITLinQ, obrint així la porta a l'optimització dels seus paràmetres controlables. Es mostra que tots dos esquemes de canalització aconsegueixen millors resultats que l'esquema no canalitzat, amb un lleuger avantatge per al ITLinQ. Considerant la geometria de xarxa més desfavorable, el ITLinQ produeix millores múltiples en l'eficiència espectral en comparació amb la xarxa no canalitzada. Finalment, el treball introdueix els transreceptors full-dúplex en xarxes cel.lulars i caracteritza l'impacte de la interferència incrementada en el seu funcionament. A través d'anàlisis i de simulacions complementàries en una xarxa de test de Vodafone LTE, s'estableix que la interferència d'usuari a usuari té un impacte poc significatiu mentre que la interferència de base a base faria inviable l'operació full-dúplex en xarxes microcell.lulars sense gestió de les interferències. En resum, aquest tesis doctoral aporta evidència de que el multiplexat MIMO i la densificació basada en D2D juguen un paper vital en la millora de la capacitat dels sistemes wireless mentre que el IA i el full-dúplex resulten inefectius.
13
Friedrich, J. O. "Frequency and spatial selectivity in nuclear magnetic resonance spectroscopy." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234964.
Full text
14
Cleary, Robert. "Spatial frequency selective processes in short range motion perception." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237562.
Full text
15
Zheng, Xiao. "Mid-spatial frequency control for automated functional surface processing." Thesis, University of Huddersfield, 2018. http://eprints.hud.ac.uk/id/eprint/34723/.
Full textAbstract:
Functional surfaces interact with surrounding substances, such as another solid, a liquid, gas, acoustic or electromagnetic waves etc., in order to achieve a required effect. Surfaces are increasingly required with complex forms and ever-increasing precision, can be very challenging to make. In particular, mid-spatial frequency (MSF) ripples are difficult to avoid for various reasons, but especially the changing misfit between a polishing tool as it moves across a complex workpiece surface. Current surface processing techniques are limited in their ability effectively to control or remove MSF errors for the reasons: i) lack of the ability to conform to the complex working surfaces, including grinding and lapping; ii) low material removal rate, such as Magnetorheological finishing and fluid jet polishing; iii) high cost (typically for ion beam figuring); iv) constrains for the size of the workpiece, such as stressed lap polishing and stressed mirror polishing. This thesis reports on the development of enhanced techniques, both to understand the formation of MSF errors on aspherical surfaces, and to mitigate them, increasing overall production efficiency. This has been achieved by: 1) Development of a novel stressed mirror technique providing a universal platform for aspheric experiments. 2) Results and analysis of kinetic simulations to understand the working mechanism of the non-Newtonian material under different stress conditions. 3) Developing a non-Newtonian tool, used in a novel way, to manage misfit between an aspherical workpiece and the tool surface. Peak-to-valley MSF error on an off-axis aspheric part better than 10 nm has been achieved. 4) Using bonded diamond pads, with various diamond sizes in a ‘grolishing’ (hybrid between grinding and polishing) procedure to achieve extremely high material removal rates (up to 267 mm3 /min), and control MSF errors 10 nm peak-to-valley, on flat and spherical surfaces. 5) Providing an aspherical surface after grolishing by a 3-microns diamond pad, with texture of sufficiently quality to be measured directly by an interferometer, which usually be achieved only after polishing.
16
Payne, Joseph Allen. "Spatial structure of very low frequency modulated ionospheric currents /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
17
Lingner, Andrea. "The Processing of Low-Frequency Spatial Cues – A Behavioral Approach." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-123605.
Full text
18
Collin, Charles Alain. "Effects of spatial frequency overlap on face and object recognition." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36896.
Full textAbstract:
There has recently been much interest in how limitations in spatial frequency range affect face and object perception. This work has mainly focussed on determining which bands of frequencies are most useful for visual recognition. However, a fundamental question not yet addressed is how spatial frequency overlap (i.e., the range of spatial frequencies shared by two images) affects complex image recognition. Aside from the basic theoretical interest this question holds, it also bears on research about effects of display format (e.g., line-drawings, Mooney faces, etc.) and studies examining the nature of mnemonic representations of faces and objects. Examining the effects of spatial frequency overlap on face and object recognition is the main goal of this thesis.A second question that is examined concerns the effect of calibration of stimuli on recognition of spatially filtered images. Past studies using non-calibrated presentation methods have inadvertently introduced aberrant frequency content to their stimuli. The effect this has on recognition performance has not been examined, leading to doubts about the comparability of older and newer studies. Examining the impact of calibration on recognition is an ancillary goal of this dissertation.
Seven experiments examining the above questions are reported here. Results suggest that spatial frequency overlap had a strong effect on face recognition and a lesser effect on object recognition. Indeed, contrary to much previous research it was found that the band of frequencies occupied by a face image had little effect on recognition, but that small variations in overlap had significant effects. This suggests that the overlap factor is important in understanding various phenomena in visual recognition. Overlap effects likely contribute to the apparent superiority of certain spatial bands for different recognition tasks, and to the inferiority of line drawings in face recognition. Results concerning the mnemonic representation of faces and objects suggest that these are both encoded in a format that retains spatial frequency information, and do not support certain proposed fundamental differences in how these two stimulus classes are stored. Data on calibration generally shows non-calibration having little impact on visual recognition, suggesting moderate confidence in results of older studies.
19
Barr, J. M. "A study of visual detection latency using spatial frequency stimuli." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376874.
Full text
20
Taylor, Neil Thomas. "A study of spatial and frequency compounding in sonar imaging." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/288.
Full text
21
Wang, Shan. "Recognition of facial expressions of pain using spatial frequency information." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715254.
Full textAbstract:
Individuals’ pain experiences can be communicated both verbally and non-verbally. Facial expressions are a primary non-verbal channel of pain communication, and so need to be clearly and unambiguously recognised and differentiated from other non-noxious emotional expressions. It is known that we are able to identify others’ pain from their facial expressions in an accurate and efficient manner, even under challenging visual conditions. However, little is known about how facial expressions are processed by observers, and what information is actually used, to make the identification of pain possible. To account for this, the current thesis considered facial expressions as a type of visual stimulus and investigated possible mechanisms that underpin the recognition of pain expressions from the perspective of perceptual information analysis. Spatial frequency (SF) information is a type of fundamental perceptual information that encodes different characteristics of a visual display. For a facial expression, low-SF information conveys the large-scale facial configuration and structural changes, whereas high-SF information depicts the fine details of facial features. In order to understand how we recognise pain expressions in terms of SF analysis, a series of experiments were conducted within this thesis to primarily investigate the role of low-SF and high-SF information in the recognition of pain expressions (Experiment 1–4), and the temporal feature of low-SF and high-SF information processing in pain recognition (Experiment 5–7). Data of this thesis revealed that although pain expressions could be recognised with either low-SF or high-SF information available, low-SF information plays a prominent role that leads to more accurate judgements (Experiment 1) and is preferentially perceived by observers (Experiment 2–4). Moreover, the processing of low-SF information shows a temporal advantage over high-SF information (Experiment 5). Pain expressions presented with low-SF information only was decoded more rapidly than those presented with high-SF (Experiment 6), and the asynchrony between low-SF and high-SF processing originated from a very early stage of information extraction (Experiment 7). Therefore, the decoding of low-SF pain expressions is not only faster in duration but also precedes the decoding of high-SF pain. Altogether, these findings suggest that when we differentiate facial expressions of pain from non-noxious emotions, the coarse low-SF information plays a key role by providing a preliminary understanding of the overall quality of pain expressions rapidly, and the fine-detailed high-SF information is integrated at a later stage and plays a trivial role. More interestingly, this pattern was found not only for the recognition of pain expressions, but also the core emotions investigated, which suggests that expressions of pain and core emotions share similar visual perceptual properties. This thesis provides a visuoperceptual account of how we recognise facial expressions of pain and suggests that in addition to analysing a series of facial action units the recognition of pain expressions is also a visual perceptual process that relies heavily on the perceptual information analysis. Limitations that were associated with the research contained within this thesis were acknowledged, suggesting directions for future research.
22
Gray, Thomas S. M. (Thomas L. ). Massachusetts Institute of Technology. "Minimizing high spatial frequency residual in active space telescope mirrors." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45217.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 141-143).
The trend in future space telescopes is towards large apertures and lightweight, rib-stiffened, and actively controlled deformable mirrors. These mirror architectures permit the development of segmented and deployed primary mirrors that lead to tremendous advancement in space telescope performance. Rib-stiffened and discretely actuated deformable mirrors have been shown to effectively mitigate common low order disturbances, but they are inevitably plagued by the "correction limit," or the extent to which the actuators can correct for a given shape disturbance. Improving the correctability of deformable mirrors requires understanding the origins of the correction limit, and optimizing the mirror design accordingly. This thesis details efforts to evaluate the mirror correction limit and the three predominant high spatial frequency mirror surface residual components: actuation-induced dimpling, manufacturing-induced print-through, and disturbance-induced uncorrectable error. The methods for simulating each effect are discussed, and an objective function is developed to quantify the effects of these residual components to gage the performance of each mirror design. A gradient descent algorithm is combined with the parametric capability of the Modular Optical Space Telescope (MOST) modeling tool to allow rapid trade space navigation and optimization of the mirror design across variations in mirror areal density, f-number, structural mass fractions, and rib aspect ratio. These optimization routines yield more advanced design heuristics that improve upon the simplified design techniques that are typical in industry. By forming the heuristics in terms of minimum machinable rib thickness, these new design relationships produce mirrors that satisfy manufacturing constraints and minimize uncorrectable high spatial frequency error.
by Thomas Gray.
S.M.
23
Webb, Richard Davis 1957. "Spatial frequency based closed-loop control of sheet metal forming." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14827.
Full text
24
Haines, Ross. "Simultaneous reconstruction of spatial frequency fields and field sample locations." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:aa35073d-003b-4939-bf0e-8348243871b7.
Full textAbstract:
Classically, spatial smoothing methods such as kriging estimate smooth interpolating fields for features measured at well-located points. In this thesis, we make a simultaneous reconstruction of interpolating spatial fields and measurement locations. We give models, and sample-based Bayesian inference, for estimating locations of dialect samples on a map of England. The method exploits dialect-based spellings to locate these samples. The data are feature vectors extracted from written dialect samples. Just a fraction of the feature vectors ('anchors') have an associated spatial location. When coupled to a prior for the smoothly varying feature field, and the anchor texts, the unlocated feature vectors are jointly informative of their own location and the feature fields. The dataset is large, but sparse, since a given word has a large number of variant spellings which may appear in just a few documents. We report an analysis including Bayesian model fitting and validation on a large and representative subset of the data. The thesis has two main aims - to provide statistical tools for the linguists who collected the data, and to meet the computational and inferential challenge of simultaneously locating large numbers of feature vectors. The results presented in this thesis show that we have largely succeeded in meeting these challenges.
25
Poplawski, Jaroslaw. "Very low frequency - Magnetic spatial position detection range and map." Thesis, University of Ballarat, 2008. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/40771.
Full textAbstract:
Automated positioning systems designed to measure three-dimensional locations of objects are of paramount importance to flexible manufacturing applications. These systems should perform in an industrial environment, withstanding obstacles of solid objects and must be immune from external influences including changes in atmospheric conditions and surrounding noise. Automated positioning systems should also be free of mechanical contact and able to perform without having to establish a line-of-sight with the measured object. In this thesis, a novel design is proposed for the spatial measurement of the six degrees of freedom industrial robots and autonomous vehicles. Not only does the proposed system comply with the above characteristics, but it is also capable of achieving better resolutions than CCD cameras, easier to implement, safer than laser devices and more accurate than ultrasound systems.[...]Doctor of Philosophy
26
Poplawski, Jaroslaw. "Very low frequency - Magnetic spatial position detection range and map." University of Ballarat, 2008. http://archimedes.ballarat.edu.au:8080/vital/access/HandleResolver/1959.17/15472.
Full textAbstract:
Automated positioning systems designed to measure three-dimensional locations of objects are of paramount importance to flexible manufacturing applications. These systems should perform in an industrial environment, withstanding obstacles of solid objects and must be immune from external influences including changes in atmospheric conditions and surrounding noise. Automated positioning systems should also be free of mechanical contact and able to perform without having to establish a line-of-sight with the measured object. In this thesis, a novel design is proposed for the spatial measurement of the six degrees of freedom industrial robots and autonomous vehicles. Not only does the proposed system comply with the above characteristics, but it is also capable of achieving better resolutions than CCD cameras, easier to implement, safer than laser devices and more accurate than ultrasound systems.[...]Doctor of Philosophy in Engineering
27
Huang, Ben. "Removing Textured Artifacts from Digital Photos Using Spatial Frequency Filtering." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/148.
Full textAbstract:
An abstract of the thesis of Ben Huang for the Master of Science in Electric and Computer Science presented [August 12nd, 2010]. Title: Removing textured artifacts from digital photos by using spatial frequency filtering Virtually all image processing is now done with digital images. These images, captured with digital cameras, can be readily processed with various types of editing software to serve a multitude of personal and commercial purposes. But not all images are directly captured and even of those that are directly captured many are not of sufficiently high quality. Digital images are also acquired by scanning old paper images. The result is often a digital image of poor quality. Textured artifacts on some old paper pictures were designed to help protect pictures from discoloration. However, after scanning, these textured artifacts exhibit annoying textured noise in the digital image, highly degrading the visual definition of images on electronic screens. This kind of image noise is academically called global periodic noise. It is in a spurious and repetitive pattern that exists consistently throughout the image. There does not appear to be any commercial graphic software with a tool box to directly resolve this global periodic noise. Even Photoshop, considered to be the most powerful and authoritative graphic software, does not have an effective function to reduce textured noise. This thesis addresses this problem by proposing the use of an alternative graphic filter to what is currently available. To achieve the best image quality in photographic editing, spatial frequency domain filtering is utilized instead of spatial domain filtering. In frequency domain images, the consistent periodicity of the textured noise leads to well defined spikes in the frequency transform of the noisy image. When the noise spikes are at a sufficient distance from the image spectrum, they can be removed by reducing their frequency amplitudes. The filtered spectrum may then yield a noise reduced image through inverse frequency transforming. This thesis proposes a method to reduce periodic noise in the spatial frequency domain; summarizes the difference between DFT and DCT, FFT and fast DCT in image processing applications; uses fast DCT as the frequency transform to solve the problem in order to improve both computational load and filtered image quality; and develops software that can be implemented as a plug in for large graphic software to remove textured artifacts from digital images.
28
Kauffmann, Louise. "Mécanismes et bases cérébrales du traitement des fréquences spatiales lors de la catégorisation de scènes visuelles." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAS047/document.
Full textAbstract:
L'analyse visuelle de scènes débute par l'extraction en parallèle de l'information à différentes fréquences spatiales, en suivant un mode de traitement par défaut « coarse-to-fine ». L'analyse rapide de l'information grossière (« coarse ») en basses fréquences spatiales fournirait un aperçu global de la scène, qui serait ensuite affiné par l'analyse des détails de la scène (« fine ») en hautes fréquences spatiales. L'objectif de cette thèse a été de préciser les bases cérébrales du traitement des fréquences spatiales lors de la catégorisation de scènes. A travers deux études comportementales, nous avons tout d'abord montré qu'une analyse « coarse-to-fine » est plus avantageuse pour la catégorisation rapide de scènes, et ce, indépendamment de la valeur de contraste de luminance associée aux différentes fréquences spatiales (Expériences 1 et 2). Des études en IRMf nous ont par la suite permis de mettre en évidence l'implication d'un large réseau cérébral lors de l'analyse « coarse-to-fine » des scènes, incluant les aires visuelles primaires et occipito-temporales, mais également le cortex frontal inférieur (Expérience 3). Une analyse de la connectivité a révélé que lors de cette analyse, le cortex frontal inférieur exercerait une influence « top-down » sur le cortex visuel primaire et les gyri fusiforme et parahippocampique au sein du cortex occipito-temporal. Ces résultats soulignent le rôle du cortex visuel primaire comme région intégrative, codant à la fois les afférences rétino-thalamiques et les influences « top-down » de régions supérieures. Nous avons également observé que le gyrus frontal inférieur et le gyrus fusiforme participaient activement à l'intégration de l'information sémantique contenue dans les basses et hautes fréquences spatiales d'une scène (Expérience 4). Enfin, nous avons spécifiquement étudié le traitement des fréquences spatiales au sein de régions occipito-temporales sélectives aux scènes : la « parahippocampal place area » (PPA), le cortex retrosplenial et l'« occipital place area ». Nous avons montré que ces trois régions participent de façon distincte au traitement des fréquences spatiales dans les scènes (Expérience 5) et qu'une stratégie d'analyse « coarse-to-fine » serait privilégiée par la PPA (Expérience 6). Les résultats de ces travaux nous permettent de conforter et de préciser les modèles actuels de la catégorisation visuelle de scènes basés sur un traitement fréquentiel de l'information visuelleVisual analysis begins with the parallel extraction of different attributes at different spatial frequencies following a predominantly coarse-to-fine default processing sequence. Rapid processing of low spatial frequency information would permit a coarse parsing of the visual input, prior to the detailed analysis of fine information in high spatial frequencies. Our aim was to further address the neural bases of spatial frequency processing during scene categorization. We first demonstrated in two behavioral studies that a coarse-to-fine processing is indeed an advantageous strategy for rapid scene categorization, and is independent of the luminance contrast values associated with the different spatial frequencies (Experiments 1 and 2). In two fMRI studies, we showed first the involvement of a large cerebral network during coarse-to-fine processing of scenes, including early visual and occipito-temporal areas, but also the inferior frontal cortex. Effective connectivity analysis revealed that the inferior frontal gyrus exerts top-down influence on the early visual cortex as well as on the parahippocampal and fusiform gyri in the occipito-temporal cortex (Experiment 3). These results highlight the role of the primary visual cortex in integrating top-down influences from frontal areas to retino-thalamic incoming signals. We also evidenced that the inferior frontal and fusiform gyri actively participate to the integration of the semantic information contained in low and high spatial frequency (Experiment 4). Finally, we specifically investigated the spatial frequency processing of scenes within scene-selective areas of the occipito-temporal cortex: the parahippocampal place area (PPA), the retrosplenial cortex, and the occipital place area. We demonstrated that these regions participate differently in the spatial frequency processing of scenes (Experiment 5) and that a coarse-to-fine processing is favored within the PPA (Experiment 6). Overall, results allow us to refine current model of visual scene categorization based on a spatial frequency analysis
29
Masud, Salwa Fatima. "The role of high-frequency envelope cues for spatial hearing in rooms." Thesis, Boston University, 2014. https://hdl.handle.net/2144/21215.
Full textAbstract:
Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Perception of sound laterality (left-right angle) is mediated by both interaural time differences (ITD) and interaural level differences (ILD). Previous localization studies in anechoic settings consistently show that low-frequency ITDs dominate perception of source laterality. However, reverberant energy differentially degrades ITDs and ILDs; the effects of room reflections on the perceptual weight given to ITDs and ILDs are not well understood. Here, we tested the hypothesis that high-frequency envelope ITD cues are important for spatial judgments in reverberant rooms by measuring the perceived laterality of high-pass, low-pass and broadband sounds. Results show that when ILD cues and ITD envelope cues are both available, reverberant energy has the smallest effect on localization of high-pass stimuli. When ILD cues are set to zero, localization of high-pass stimuli with strong envelopes (i.e. click trains and speech tokens) is also minimally affected by reverberant energy; however, as envelope modulation is reduced, subjects show increasing localization bias, responding towards the center. Moreover, for stimuli with strong envelopes, subjects with better modulation detection sensitivity are affected less by the addition of reverberant energy. These results suggest that, in contrast to in anechoic space, high-frequency envelope ITD cues influence localization in reverberant settings.
2031-01-01
30
Munding-Minier, Dashiel. "La dynamique spatio-temporelle de la production des mots : études par magnétoencéphalographie." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM3061/document.
Full textAbstract:
Cette thèse porte sur l'utilisation de la magnétoencéphalographie (MEG) comme outil d'étude de la dynamique des réponses corticales durant la production de mots. Les données empiriques accumulées dans la littérature sont évaluées au regard des modèles psycho- et neuro-linguistiques de la production des mots et du langage. Nous réalisons une exploration de l'évolution des modèles psycho-linguistiques et effectuons en ce sens une revue de la littérature MEG. Les forces et limites de la technique et des données empiriques existantes sont considérées et utilisées pour établir un protocole de dénomination d'images qui soit compatible avec la MEG. Nous développons ensuite une étude empirique réalisée en MEG, en utilisant une manipulation visuo-sémantique pour explorer la dynamique des réponses corticales. Cette étude démontre une large réponse bi-hémisphérique avec des différences inter-conditions précoces (~100ms) dans la BA8 et des différences dans le gyrus cingulaire antérieur, le cortex médial temporal antérieur droit à 207ms et dans la jonction temporo-pariétale à 233ms après apparition du stimulus. Des différences entre les conditions apparaissent tardivement dans le cuneus droit et suggèrent également un traitement visuel en cours. Nos résultats questionnent le timing estimé pour les traitements phonologiques et sémantiques suggérés par les modèles sériels actuels de production du langage. A la lumière de la revue de la littérature et de l'étude empirique conduite, nous évaluons les modèles existants et discutons des directions potentielles pour les recherches futuresThis thesis concerns the use of magnetoencephalography [MEG] as a tool for investigating the dynamics of the cortical response during word production. The evidence gathered is considered in the context of existing psycho- and neuro-linguistic models of word and speech production. An exploration of the evolution of psycholinguistic models is performed, motivating a review of the MEG literature. The strengths and limitations of the technique and existing evidence are considered, and used to guide the design of a picture naming protocol compatible with MEG. An empirical MEG study is then developed and implemented using a visuo-semantic manipulation to explore the dynamics of the cortical response. This study demonstrates a broad, bi-hemispheric response with early (~100ms) between-conditions differences in bilateral BA8 and anterior cingulate cortex, in right anterior medial temporal cortex at 207ms, and a difference in right temporo-parietal junction at 233ms post stimulus. Late between conditions differences in the right cuneus also suggest ongoing visual processing. Our findings question the timing estimated for semantic and phonological processing suggested by current serial models of speech processing. In the light of the review and empirical study, a contextual evaluation of existing models is performed and potential future avenues of investigation are discussed
31
Cepeda, Miguel D. "Effects of spatial separation on across-frequency grouping in narrowband speech." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12067.
Full textAbstract:
Thesis (M.S.)--Boston UniversityUnderstanding how we perceive speech in the face of competing sound sources coming from a variety of directions is an important goal in psychoacoustics. In everyday situations, noisy interference can obscure the content of a conversation and require listeners to integrate speech information across different frequency regions. Two studies will be explained that investigate the effects of spatial separation on the grouping of two spectrally separated, narrow bands of target speech with a variety of filler stimuli centered in between these bands. Target sentences taken from the IEEE corpus were broken into two 3/4-octave bands with the lowest centered around 370 Hz and the highest centered around 6kHz. The first study explored the spatial influences of spectral restoration. The primary experiment measured speech intelligibility of the speech bands (presented diotically) with a single band of noise between 700 Hz and 3 kHz used as the filler and then with the same noise band modulated by the target speech envelope as the filler. These fillers were presented diotically as well as with an ITD of 600 s leading to the left ear. Performance was worse for the unmodulated noise condition when the filler was separated spatially from the speech bands. Across-frequency grouping was not observed with the modulated noise conditions. The second study explored the effect of attention on intelligibility of speech bands presented from the left with related fillers. The filler objects used in this study were dual bands of vocoded or narrowband speech presented either from left or right. The fillers were derived from either the same target speech token (matched) or an independent sentence (conflicting). In a key experimental block, listeners were instructed to attend to the target speech on the left while either conflicting bands or, infrequently, matched bands were presented on the right. The infrequently presented matching trials were physically identical to trials in another block where listeners were instructed to attend to both ears. Results showed that splitting the target and filler across the ears degraded intelligibility, however, directed spatial attention had no effect on performance. These results demonstrate that speech elements group together strongly, overcoming spatial attention, even for degraded speech.
32
Callegary, James Briggs. "Spatial sensitivity of low-induction-number frequency-domain electromagnetic-induction instruments." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/282901.
Full textAbstract:
Numerical simulations were used to study spatial averaging in low-induction-number frequency-domain electromagnetic induction (LIN FEM) instruments. Local ( LS) and cumulative (CS) sensitivity were used to analyze three different aspects of LIN FEM spatial sensitivity. LS is the variation in a measured property given a small change at a given location of the property of interest. CS contours are derived from LS and reveal the shape and the fraction of total instrument sensitivity enclosed within the contours. The first study re-evaluated the asymptotic approach to LIN FEM spatial sensitivity. Using this approach, LIN FEM measurements have often been assumed to represent electrical conductivity (sigma) at discreet depths that do not vary with the sigma of the ground. This assumption was tested using simulations of electromagnetic fields in environments with homogeneous and layered sigma distributions. When the induction number was greater than 0.01, the 1-D vertical CS distribution and the depth of investigation varied up to 20% over the range of sigma simulated. As sigma increased, CS contours and depth of investigation decreased in depth. In the second study a small perturbation approach was used to calculate CS distributions so that each distribution is unique to a given LS distribution. CS was summed from regions of high to low LS, and retained information on the magnitude and location of LS. As sigma increased, CS became focused around the highest LS values. The maximum reduction in depth of investigation was about 40% at the highest sigma investigated. In the final study, a series of small, electrically conductive perturbations was simulated in a three-dimensional, homogeneous environment. Three-dimensional LS varied markedly with a large difference between horizontal (HMD) and vertical (VMD) orientations of the transmitter and receiver dipoles. In some regions, the calculated magnetic field intensity with the perturbation was less than that calculated for the host without the perturbation. This occurred for both VMD and HMD orientations of the transmitter. CS contours were highly complex. One dimensional, vertical LS curves extracted from the three-dimensional data were very different from curves from infinite layer simulations.
33
Senesi, Matteo. "Frequency steerable acoustic transducers." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44819.
Full textAbstract:
Structural health monitoring (SHM) is an active research area devoted to the assessment of the structural integrity of critical components of aerospace, civil and mechanical systems. Guided wave methods have been proposed for SHM of plate-like structures using permanently attached piezoelectric transducers, which generate and sense waves to evaluate the presence of damage. Effective interrogation of structural health is often facilitated by sensors and actuators with the ability to perform directional scanning.
In this research, the novel class of Frequency Steerable Acoustic Transducers (FSATs) is proposed for directional generation/sensing of guided waves. The FSATs are characterized by a spatial arrangement of the piezoelectric material which leads to frequency-dependent directionality. The resulting FSATs can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels.
Because there is no need for individual control of transducer elements, hardware and power requirements are drastically reduced so that cost and hardware limitations of traditional phased arrays can be partially overcome. The FSATs can be also good candidates for remote sensing and actuation applications, due to their hardware simplicity and robustness.
Validation of the proposed concepts first employs numerical methods. Next, the prototyping of the FSATs allows an experimental investigation confirming the analytical and numerical predictions. Imaging algorithm based on frequency warping is also proposed to enhance results representation.
34
Kim, Youngtae. "Spatial resolution limits for the reconstruction of acoustic source distribution by inverse techniques." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274706.
Full text
35
Kramer, Michael L. "Collinearity and Surround Size Effects on Spatial Discrimination Tasks." Miami University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=miami1154716341.
Full text
36
Ayalew, Tibebu Bekele. "Physical basis of the power-law spatial scaling structure of peak discharges." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1537.
Full textAbstract:
Key theoretical and empirical results from the past two decades have established that peak discharges exhibit power-law, or scaling, relation with drainage area across multiple scales of time and space. This relationship takes the form Q(A)= $#945;AΘ where Q is peak discharge, A is the drainage area, Θ is the flood scaling exponent, and α is the intercept. Motivated by seminal empirical studies that show that the flood scaling parameters α and Θ change from one rainfall-runoff event to another, this dissertation explores how certain rainfall and catchment physical properties control the flood scaling exponent and intercept at the rainfall-runoff event scale using a combination of extensive numerical simulation experiments and analysis of observational data from the Iowa River basin, Iowa. Results show that Θ generally decreases with increasing values of rainfall intensity, runoff coefficient, and hillslope overland flow velocity, whereas its value generally increases with increasing rainfall duration. Moreover, while the flood scaling intercept is primarily controlled by the excess rainfall intensity, it increases with increasing runoff coefficient and hillslope overland flow velocity. Results also show that the temporal intermittency structure of rainfall has a significant effect on the scaling structure of peak discharges. These results highlight the fact that the flood scaling parameters are able to be estimated from the aforementioned catchment rainfall and physical variables, which can be measured either directly or indirectly using in situ or remote sensing techniques. The dissertation also proposes and demonstrates a new flood forecasting framework that is based on the scaling theory of floods. The results of the study mark a step forward to provide a physically meaningful framework for regionalization of flood frequencies and hence to solve the long standing hydrologic problem of flood prediction in ungauged basins.
37
Kim, Yong Sang. "Effects of luminance, color, and spatial frequency variations on perceived image quality." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40190.
Full textAbstract:
The primary objective of this dissertation was to investigate the effects of varying levels of luminance, color, and spatial frequency content on the perceived image quality of a soft-copy color image. A secondary objective was to test the robustness of selected image quality metrics (MTFA, SQRI, and ICS) to the color variations as measured by the change in correlations between the perceived quality ratings and the values of the image quality metrics. To accomplish these objectives, a color image was selected and its luminance, color, and spatial frequency components were attenuated systematically using image processing software. With the manipulated images, an experiment was conducted in which subjects were asked to rate, on a 0.0 - 9.0 continuous scale, the perceived quality of a displayed image in comparison to the original image. Results of the statistical analysis of the collected data were characterized by the highly significant main effects and interaction effects. However, the magnitudes of the interactions were small.
The effect of the luminance component on perceived quality was found to be dominant and consistent across all the levels of the other two variables. As the luminance increased, the perceived quality increased at a decreasing rate. The luminance main effect was modeled well (R2 = 0.9968) by the second-order polynomial of the luminance attenuation level, or, equivalently, by the relative amount of the luminance contained in the image. The range of variation of perceived quality produced by the six luminance levels was about five units on a 0.0 - 9.0 continuous scale. It was concluded that perceived quality of the color image was determined primarily by the luminance component of the image.
The effect of color on perceived quality was found to be smaller than expected. The range of variation in perceived quality produced by the six color levels was only a little over one unit on a 0.0 - 9.0 continuous scale. Perceived qualities increased at a decreasing rate as the level of color increased. However, the slope of the curve representing the color effect was smaller than that of the luminance effect The main effect of color was modeled well (R2 = 0.9972) by the second-order polynomial of the color attenuation level, or, equivalently, by the relative amount of color contained in the image. Based on the findings of the color effect, two different roles of color in image perception are suggested. At extremely low luminance, color acts primarily as a facilitator of the luminance by providing more cues on the content of the image. At sufficiently high luminance, the increased perceived quality stems from the aesthetic characteristics of the color.
Both highpass and lowpass filtering, on the average, caused about 1.5 units of degradation as compared to the unfiltered image in perceived image quality on a 0.0 - 9.0 continuous scale. The perceived quality of the unfiltered image was greater than that of the filtered images across all the levels of luminance and color attenuation except at a low luminance level. There was no significant difference between the perceived qualities of the highpass and lowpass filtered images.
The R2 of the second-order polynomial for image qUality metrics (MTFA, SQRI, and ICS) and the mean perceived qualities did not vary across the color variations in the image manipulations. That is, these image quality metrics were robust to the color variations when the relationship between the quality metric values and the actual perceived qualities was represented by the second-order polynomial. However, with the first-order model, the R2 increased as the color level increased. The SQRI yielded higher R2 values than did the MTFA and ICS metrics when the first-order model was used. Also, the range of variation of R2 for the SQRI was smaller than that for the other two metrics. Therefore, it appears that the robustness of an image quality metric to the color variation is affected by the degree of non-linearity correction in the metric if the robustness is tested in the context of the straight-line relationship.Ph. D.
38
Gu, Xun. "Measuring Ultracomplex Supercontinuum Pulses and Spatio-Temporal Distortions." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5082.
Full textAbstract:
This thesis contains two components of research: studies of supercontinuum pulses generated in the novel microstructure fiber, and research on spatio-temporal coupling in ultrafast laser beams.
One of the most exciting developments in optics in recent years has been the invention of the microstructure optical fiber. By controlling the structural parameters of these novel fibers in design and manufacturing, their dispersion profile can be freely tailored, opening up a huge application base. One particularly interesting effect in the microstructure fiber is the generation of ultrabroadband supercontinuum with only nJ-level Ti:sapphire
oscillator pulse pump. This supercontinuum is arguably the most complicated ultrafast pulse ever generated, with its huge time-bandwidth product (> 1000 from a 16-cm-long fiber). Although many applications have been demonstrated or envisioned with this continuum, its generation is a very complicated process that is poorly understood, and the characteristics of the continuum pulses are not clearly known. In this work, we make a full-intensity-and-phase measurement of the continuum pulses using cross-correlation frequency-resolved optical gating (XFROG). The results reveal surprising unstable fine spectral structure in the continuum pulses, which is confirmed by single-shot measurements. Our study on the coherence of the continuum, on the other hand, shows that the spectral phase of the supercontinuum is fairly stable. Numerical simulations are carried out whose results are in good agreement with experiments.
The second component of this thesis is the study of spatio-temporal coupling in ultrafast beams. We propose two definitions of spatial chirp, point out their respective physical meanings, and derive their relationship. On the common perception of the equivalence between pulse-front tilt and angular dispersion, we show that the equivalence only holds for plane waves. We establish a generalized theory of ultrafast laser beams with first-order spatio-temporal couplings, and discover a new pulse-front tilt effect associated with the combination of spatial chirp and temporal chirp. For the measurement of spatio-temporal distortions, the effects of such distortions in the input beam to a GRENOUILLE trace are carefully studied. An algorithm is proposed and tested to retrieve information about the distortions from the GRENOUILLE trace.
39
McCormick, Jackson C. "Spatial and temporal ionospheric monitoring using broadband sferic measurements." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54469.
Full textAbstract:
The objective of this thesis is to use radio emissions from lightning, known as `radio atmospherics' or `sferics', to study the temporal and spatial variation of the lower ionosphere, a layer of ionized atmosphere beginning at $\sim$70 km altitude (D-region). Very Low Frequency (VLF, 3$-$30kHz) radio waves are a useful diagnostic for lower ionospheric monitoring due to their reflection from this region and global propagation. Traditionally, the lower ionosphere has been sensed using single-frequency VLF transmitters allowing for analysis of a single propagation path, as there are only a small number of transmitters.
A lightning stroke, however, releases an intense amount of impulsive broadband VLF radio energy in the form of a sferic, which propagates through the Earth-ionosphere waveguide. Lightning is globally distributed and very frequent, so a sferic is therefore also a useful diagnostic of the D-region. This is true both for ambient or quiet conditions, and for ionospheric perturbations such as solar flare x-ray bursts. Lightning strokes effectively act as separate VLF transmitting sources. As such, they uniquely provide the ability to add a spatial component to ionospheric remote sensing, in addition to their broadband signature which cannot be achieved with man-made transmitters.
We describe the methods of processing in detail. As an example, we analyze a solar flare during which time there is a significant change in magnitude and frequency content of sferics. This disturbance varies with distance from the source, as well as time. We describe the methods of processing in detail, and show results at Palmer Station, Antarctica for both a quiet and active solar day.
40
Palmer, Chris M. "Topographic and laminar models for the development and organisation of spatial frequency and orientation in V1." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4114.
Full textAbstract:
Over the past several decades, experimental studies of the organisation of spatial frequency (SF) preference in mammalian visual cortex (V1) have reported a wide variety of conflicting results. A consensus now appears to be emerging that in the superficial layers SF is mapped continuously across the cortical surface. However, other evidence suggests that SF may differ systematically with cortical depth, at least in layer 4, where the magnocellular (M) and parvocellular (P) pathway afferents terminate in different sublaminae. It is not yet clear whether the topographic organisation for SF observed in the superficial layers is maintained throughout the input layers as well, or whether there is a switch from a laminar to a topographic organisation along the vertical dimension in V1. I present results from two alternative self-organising computational models of V1 that receive natural image inputs through multiple SF channels in the LGN, differing in whether they develop laminar or topographic organisation in layer 4. Both models lead to topographic organisation for orientation (OR) and SF preference in upper layers, consistent with current experimental evidence. The results suggest that in either case separate sub-populations of neurons are required to obtain a wide range of SF preference from Hebbian learning of natural images. These models show that a laminar organisation for SF preference can coexist with a topographic, columnar organisation for orientation, and that the columnar organisation for orientation is dependent upon inter-laminar feedback. These results help clarify and explain the wide range of SF results reported in previous studies.
41
Shorrock, Heather. "Optical, neural and perceptual basis of blur sensitivity and the effect of text detail in myopes and emmetropes." Thesis, Anglia Ruskin University, 2013. http://arro.anglia.ac.uk/305407/.
Full textAbstract:
Retinal blur experienced by myopes during near work has been linked to myopia development and progression. Whether poor responses to blur signals are due to poor perceptual blur sensitivity (subjective depth of focus), poor neural accommodation responses (objective depth of focus) to blur or optical differences such as higher order aberrations making blur detection difficult is yet unclear. This study investigates whether myopes respond to blur differently compared to emmetropes and whether filtering spatial frequencies in reading text influence accommodation responses. Accommodative functions were investigated using spatial frequency filtered text targets of two different sizes (N10 and N20). Monocular objective depth of focus (DOF), accommodative microfluctuations, and dynamic accommodation were measured. Subjective DOF after cycloplegia was also recorded with the same targets. Higher order aberration measurements explored optical contributions to blur. Peripheral refraction and accommodative lag were also measured to consider how in combination they might increase peripheral retinal blur for near tasks. Results showed that myopes demonstrated larger subjective DOF. Subjective DOF was larger when viewing the peak text spatial frequency in both refractive error groups. The optimum focus was more myopic for text peak spatial frequencies. Levels of spherical aberration were correlated with the point of optimum focus. Objective DOF and accommodative microfluctuations were larger in myopes when viewing the peak text spatial frequencies. Dynamic accommodation showed that while myopes were not poorer at initiating accommodation responses they had longer positive response times. Accommodative lag, although not different in myopes, increases the peripheral hyperopic blur experienced for near tasks. Conclusion: Myopes were poorer at using retinal blur cues to refine accommodation responses especially when viewing peak text spatial frequencies. Larger positive response times, DOF and accommodative microfluctuations in myopes resulted in accommodative error and hyperopic blur for near tasks. Spherical aberration, previously thought to provide a myopigenic stimulus, was not different between refractive groups and is unlikely to be large enough to enhance DOF during naturalistic viewing. Blur adaptation studies might consider using peak text spatial frequencies as adaptation targets to reduce accommodation differences in myopes and emmetropes. Optical treatment strategies aimed at correcting peripheral refraction to control myopia should consider the combined effect of accommodative lag which increases levels of hyperopic peripheral blur experienced by myopes.
42
Shorrock, Heather. "Optical, neural and perceptual basis of blur sensitivity and the effect of text detail in myopes and emmetropes." Thesis, Anglia Ruskin University, 2013. https://arro.anglia.ac.uk/id/eprint/305407/1/Heather%20Shorrock%20-%20PhD%20Thesis.pdf.
Full textAbstract:
Retinal blur experienced by myopes during near work has been linked to myopia development and progression. Whether poor responses to blur signals are due to poor perceptual blur sensitivity (subjective depth of focus), poor neural accommodation responses (objective depth of focus) to blur or optical differences such as higher order aberrations making blur detection difficult is yet unclear. This study investigates whether myopes respond to blur differently compared to emmetropes and whether filtering spatial frequencies in reading text influence accommodation responses.
Accommodative functions were investigated using spatial frequency filtered text targets of two different sizes (N10 and N20). Monocular objective depth of focus (DOF), accommodative microfluctuations, and dynamic accommodation were measured. Subjective DOF after cycloplegia was also recorded with the same targets. Higher order aberration measurements explored optical contributions to blur. Peripheral refraction and accommodative lag were also measured to consider how in combination they might increase peripheral retinal blur for near tasks.
Results showed that myopes demonstrated larger subjective DOF. Subjective DOF was larger when viewing the peak text spatial frequency in both refractive error groups. The optimum focus was more myopic for text peak spatial frequencies. Levels of spherical aberration were correlated with the point of optimum focus. Objective DOF and accommodative microfluctuations were larger in myopes when viewing the peak text spatial frequencies. Dynamic accommodation showed that while myopes were not poorer at initiating accommodation responses they had longer positive response times. Accommodative lag, although not different in myopes, increases the peripheral hyperopic blur experienced for near tasks.
Conclusion: Myopes were poorer at using retinal blur cues to refine accommodation responses especially when viewing peak text spatial frequencies. Larger positive response times, DOF and accommodative microfluctuations in myopes resulted in accommodative error and hyperopic blur for near tasks. Spherical aberration, previously thought to provide a myopigenic stimulus, was not different between refractive groups and is unlikely to be large enough to enhance DOF during naturalistic viewing.
Blur adaptation studies might consider using peak text spatial frequencies as adaptation targets to reduce accommodation differences in myopes and emmetropes.
Optical treatment strategies aimed at correcting peripheral refraction to control myopia should consider the combined effect of accommodative lag which increases levels of hyperopic peripheral blur experienced by myopes.
43
Persanyi, Mary Wylie. "Individual differences in spatial frequency-dependent visible persistence: The role of temporal summation." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1057952547.
Full text
44
Herold, F. W., and J. A. Kaiser. "ELIMINATION OF SIDELOBE RESPONSE." International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/607377.
Full textAbstract:
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, CaliforniaConventional phased arrays nominally sum the signals received by the elements prior to detection. By multiplying rather than summing signals received from pairs of elements, i.e., interferometer pairs, a set of Spatial Frequencies (SFs) is obtained. Obtaining the SFs requires employment of a multiple local oscillator technique. When summed, these spatial frequencies produce a single lobed (voltage) radiation pattern which, when passed through a biased detector, removes all sidelobes from the response at a small loss of desired signal power.
45
Lee, Stan S. "Disparity contingent high spatial frequency constraints on the upper velocity limit of stereopsis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60961.pdf.
Full text
46
Kuo, Yun-Ching. "Determination of image quality for added noise as a function of spatial frequency /." Online version of thesis, 1989. http://hdl.handle.net/1850/11527.
Full text
47
Carvajal, Alexander. "Temporal and spatial dependency of high frequency wave collisions in rat somatosensory cortex." Online access for everyone, 2008. http://www.dissertations.wsu.edu/Thesis/Summer2008/A_Carvajal_062208.pdf.
Full text
48
Lalonde, Jasmin. "Task-dependent transfer of perceptual to memory representations during delayed spatial frequency discrimination." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33911.
Full textAbstract:
Discrimination thresholds were obtained during a delayed spatial frequency discrimination task. In Experiment 1, we found that presentation of a mask 3 s before onset of a reference Gabor patch caused selective interference in a subsequent discrimination task. However, a 10 s interval abolished this masking effect. In Experiment 2, the mask was associated with a second spatial frequency discrimination task so that a representation of the mask had to be coded into short-term perceptual memory. The presence of this second discrimination task now caused similar interference effects on the primary discrimination task at both the 3 s and 10 s ISI conditions. The different results from these two experiments are best explained by a two-step perceptual memory mechanism. The results also provide further insight into the conditions under which stimulus representations are shared between the perceptual and memory domains.
49
Adams, Agur S. "Source localization in a cognitive radio environment consisting of frequency and spatial mobility." Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/10719.
Full textAbstract:
Cognitive radio presents a unique challenge to source localization in that the radio has the ability to adapt to the environment, thus rendering current localization techniques ineffective due to a shifting combination of spatial, frequency, and temporal parameters. For any localization scheme to be effective, it must be able to adapt over time as a cognitive radio adapts to its surroundings. In this thesis an extended semi range-based localization scheme is proposed to accomplish this task. The proposed scheme estimates the position of a cognitive radio using the collaborative spectrum sensing results of a wireless radio frequency sensor network in a cognitive radio environment. The central idea behind the proposed scheme is to exploit the relationships between spatial, frequency, and temporal parameters of the environment to solve for the position of the cognitive radio. The proposed scheme is modeled in the MATLAB programming language, and its efficacy is demonstrated through simulation. It is shown that over time the proposed scheme is capable of estimating the frequency band of operation and the location of a cognitive radio, and is thus capable of accounting for both frequency and spatial mobility inherent in the cognitive radio environment.
50
Zhao, Yong 1980. "Ultra-high precision scanning beam interference lithography and its application : spatial frequency multiplication." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44756.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 135-138).
Scanning beam interference lithography (SBIL) is a technique developed at MIT in 2003. The SBIL system, referred to as the Nanoruler, could fabricate grating patterns with around ten-nanometer phase repeatability. There were many factors which limit its precision and thus limit its utility for applications which require more precise phase control. In this thesis the main sources of error impairing the Nanoruler's patterning precision, which include thermal error of the environmental enclosure and the measurement error of a critical mirror in the stage interferometry system, have been identified. A digital PI-lead compensation controller has been designed to improve the air temperature stability of the environmental enclosure. A digital low-pass filter is utilized to reduce high spatial-frequency noise in the stage mirror non-flatness measurement. A factor that causes another kind of the mirror measurement error, which is an apparent location-dependent mirror non-flatness measurement, has been determined. A corresponding solution is developed to reduce this kind of error. Afterwards, as an application of ultra-high precision patterning, multiple-exposure SBIL is utilized to multiply the spatial frequency of patterns over large areas. The high nonlinearity of photo resists and the excellent pattern repeatability of the Nanoruler enable higher line densities to be achieved by applying a nonlinear process (development) between exposures of the Nanoruler. A phase control technique for accurately overlaying interference lithography exposures has been developed. Accurate phase control over large areas during spatial frequency multiplication by utilizing a surrounding alignment grating has been achieved. Three key factors- the angle, period, and phase of the alignment grating- have been accurately measured and utilized to position subsequent patterns with respect to previous patterns.
(cont.) Some factors that can dramatically diminish the accuracy of phase control, such as particle-induced substrate distortion and nonlinear distortion of the alignment grating, have also been considered and minimized in order to improve the accuracy of phase control. For spatial frequency doubling with a 574 nm principal pitch, we achieved overlay phase errors with a mean of -1.0 nm ± 2.8nm(la) between overlaid grating patterns over a 25 x 32.5 mm2 area. Utilizing the same technique, we fabricated 50 nm-pitch gratings with spatial frequency quadrupling starting from a principal pitch of 200 nm.
by Yong Zhao.
Ph.D.