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Littérature scientifique sur le sujet « Spatial frequencie »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 19 juillet 2025

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Articles de revues sur le sujet "Spatial frequencie"

Zhang Zhe, 张喆, 郑东晖 Zheng Donghui, 陈磊 Chen Lei та 李金鹏 Li Jinpeng. "低空间频率干涉条纹的载频计算方法". Acta Optica Sinica 44, № 4 (2024): 0412005. http://dx.doi.org/10.3788/aos231718.

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Pankil Butala, Pankil Butala, Hany Elgala Hany Elgala, and Thomas D. C. Little Thomas D. C. Little. "Sample indexed spatial orthogonal frequency division multiplexing." Chinese Optics Letters 12, no. 9 (2014): 090602–90606. http://dx.doi.org/10.3788/col201412.090602.

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ICHIHARA, SHIGERU. "Perceived spatial frequency shift after adaptation to compound gratings of two sinusoidals in phase or 180° out of phase." Japanese Psychological Research 29, no. 1 (1987): 10–16. http://dx.doi.org/10.4992/psycholres1954.29.10.

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Lee, Jeunghoon, Yongsung Park, and Peter Gerstoft. "Generalized frequency-sum beamforming for low frequencies." Journal of the Acoustical Society of America 156, no. 6 (2024): 4037–47. https://doi.org/10.1121/10.0034621.

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For direction-of-arrival (DOA) estimation in the low-frequency range, we improve spatial resolution using generalized frequency-sum (gFS) beamforming with the Qth order frequency-sum autoproduct. The order Q does not exceed the maximum value, determined by the criteria that the sum of frequencies used to create the autoproduct must be less than the array's spatial Nyquist frequency. Unlike other high-resolution beamformers, gFS maintains stable performance even with a single snapshot and is unaffected by the coherence of steering vectors. Rigorous analysis using the multinomial expansion has shown the inapplicability of gFS to multi-DOA scenarios. Simulation and experimental results support that the method is a practical alternative for low-frequency single-DOA estimation with limited data.

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Pohl, M., and R. Börret. "Simulation of mid-spatials from the grinding process." Journal of the European Optical Society-Rapid Publications 11 (2016): 16010. https://doi.org/10.1051/jeos.2016.16010.

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This paper focuses on the simulation of the creation of mid-spatial frequencies (mid-spatials) during the grinding process of optical components. The goal is to simulate this generation process and determine the correlating grinding parameters for mid-spatials. On this base, grinding parameters which lead to less mid-spatials could be determined.

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Stancă Ionut, Rizea Ileana Olguta, Popescu Andreea Caterina, Albu Alice, Rus Mihaela, and Fica Simona. "The importance of cardiac tomography in the evaluation of cardiac changes and coronary atherosclerosis in patients with betathalassemia major." Technium Social Sciences Journal 11 (September 14, 2020): 602–11. http://dx.doi.org/10.47577/tssj.v11i1.1677.

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Betathalassemic patients demonstrate an increased rate of extracardiac vascular complications, but very low prevalence for coronary artery disease. Computed tomography (CT) achieves excellent tissue characterization, with high spatial resolution and has developed as a gold standard for noninvasive angiography and calcium score assessment. Methods. We examined 7 patients with major beta-thalassemia and 7 patients who had an indication for cardiac CT for resting ECG changes, without symptoms of angina pectoris. We investigated the coronary atherosclerosis by assessing the coronary artery calcium (CAC) and arterial stifness. Usual tests and echocardiography measurement were performed. Cardiac computed tomography determined left ventricular mass, left ventricular ejection fraction (LVEF), coronary calcium score and coronary anatomy. An analysis of myocardial density was also performed. Artery stiffness was assessed by the cardio ankle vascular index (CAVI). Results. Arterial stiffness index in betathallasemic group was higher than control group, R-CAVI index was 6.21± 0.49 vs 5.65±0.37 and L-CAVI index was 6.21± 0.38 vs 5.71±0.31. The assessment of systolic function by echocardiography and cardiac CT examination in the 2 groups, shows that the LVEF in the betathallasemic group was significantly lower than in the control group, which means that some patients already had cardiomyopathy. LV myocardial mass was significantly higher in the group with beta-thalassemia, which is explained by the appearance of myocardial remodeling. The calcium score in patients with major beta-thalassemia was 0 and 8,5± 5,9 in the control group. Only 3 patients (42,8%) in the control group had a calcium score > 10U. No atherosclerotic lesions were observed in patients with major beta-thalassemia, whereas the control group showed mild coronary atherosclerotic lesions. If myocardial density can be determined, calcium or iron deposits can be detected in the myocardium. In patients with beta-thalassemia, the density of the myocardium was higher, both in the left ventricle (49.29 8.87±HU) and in the septum (56.71± 8.1 HU). Calculation of Pearson’s correlation coefficient revealed a good association between CT and echocardiography, reproducibility of CT was significantly higher on an intra-observer level for LVEF and LV Mass. Conclusions: Patients with β–thalassemia major have a similar calcium score compared to control subjects, but they have an increase in arterial stiffness. However, zero frequencie of coronary heart disease, denotes coronary protection mechanisms in thalassemia, so future research should focus on the anti-atherogenic potential of blood lipids at these patients. The ability of cardiac tomography to detect calcifications and changes in myocardial density should be valued, as it can be a good tool for establishing the diagnosis of cardiomyopathy by iron loading.

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Zhou, Y. X., and C. L. Baker. "Spatial properties of envelope-responsive cells in area 17 and 18 neurons of the cat." Journal of Neurophysiology 75, no. 3 (1996): 1038–50. http://dx.doi.org/10.1152/jn.1996.75.3.1038.

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1. Many neurons in areas 17 and 18 respond to spatial contrast envelope stimuli whose Fourier components fall outside the cell's spatial-frequency-selective range. The spatial properties of such envelope responses are investigated here and compared with responses to conventional luminance-defined gratings to explore the underlying receptive-field mechanism. 2. Three spatial properties of envelope responses are reported more extensively in this paper. First, the envelope responses were selective to the carrier spatial frequency in a narrow range of frequencies higher than a given cell's luminance spatial frequency selective range (luminance passband). Second, a given cell's dependence on envelope spatial frequency often differed from its luminance passband. Last, the optimal carrier spatial frequency did not shift systematically with the envelope spatial frequency, supporting the hypothesis that the carrier and envelope spatial-frequency dependencies were mediated by distinct mechanisms. 3. In contrast to the direction selectivity to the envelope motion in many envelope-responsive cells, no direction preference to carrier motion was found for envelope responses. The direction of carrier motion did not alter the direction selectivity for envelope motion, further supporting the hypothesis that the carrier and envelope temporal properties were mediated by separate mechanisms. 4. The distributions of the optimal carrier and luminance spatial frequencies among envelope-responsive cells were analyzed. The optimal carrier spatial frequencies were randomly distributed from five times the cell's optimal luminance spatial frequency to the upper resolution limit of the X-retinal ganglion cells at the same retinal eccentricity, suggesting that the selective ranges of envelope responses and luminance responses are not strongly correlated over the population of envelope-responsive cells. 5. Our data support a "two-stream" receptive-field model for envelope-responsive cells. One stream is a conventional, spatially linear receptive-field mechanism, mediating luminance responses for the cell; the other mediates envelope responses and consists of a two-stage processing: a set of spatially small and distributed nonlinear neural subunits whose outputs are spatially pooled at the second stage. 6. In conclusion, this study indicates that envelope responses in area 17 and 18 neurons cannot be due to a nonlinearity that is common to all visual stimuli before narrowband spatial-frequency-selective filtering; instead, a specialized processing stream, parallel to the conventional luminance response stream, is needed to supplement the traditional luminance processing stream in these cells. This specialized stream responds to the envelope stimuli and is selective to their carrier and envelope spatial frequencies. The distributions of the optimal luminance and carrier spatial frequencies indicate a rich variety of possible integration between luminance and envelope information.

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Sagi, Dov, and Shaul Hochstein. "Lateral inhibition between spatially adjacent spatial-frequency channels?" Perception & Psychophysics 37, no. 4 (1985): 315–22. http://dx.doi.org/10.3758/bf03211354.

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COHEN, LEON. "Time-Frequency Spatial-Spatial Frequency Representations." Annals of the New York Academy of Sciences 808, no. 1 Nonlinear Sig (1997): 97–115. http://dx.doi.org/10.1111/j.1749-6632.1997.tb51655.x.

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Shi Zhiguo, 石志国, 张洋 Zhang Yang, 王全福 Wang Quanfu та ін. "偏振空间频域成像系统及仿体验证". Chinese Journal of Lasers 50, № 9 (2023): 0907104. http://dx.doi.org/10.3788/cjl221483.

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Thèses sur le sujet "Spatial frequencie"

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.

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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.

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McSorley, Eugene. "Spatiotemporal integration of spatial frequencies." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4615/.

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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.

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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.

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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.

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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.

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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 connues Cannabis 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

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Wiles, Andrew Donald. "Modelling Framework for Radio Frequency Spatial Measurement." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/771.

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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.

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Mudassar, Asloob Ahmad. "Active aperture synthesis using spatial frequency heterodyning." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/158.

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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.

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Shrekenhamer, David. "Dynamic Control of Metamaterials at Terahertz Frequencies." Thesis, Boston College, 2013. http://hdl.handle.net/2345/3152.

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Thesis advisor: Willie J. Padilla Progress 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

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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.

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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

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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.

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Livres sur le sujet "Spatial frequencie"

Pulkki, Ville, Symeon Delikaris-Manias, and Archontis Politis, eds. Parametric Time-Frequency Domain Spatial Audio. John Wiley & Sons, Ltd, 2017. http://dx.doi.org/10.1002/9781119252634.

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Ozin, Linda. Age differences in the shape of spatial frequency filters. National Library of Canada, 1994.

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Simons, Rainee N. Spatial frequency multiplier with active linearly tapered slot antenna array. National Aeronautics and Space Administration, 1994.

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Zahar, Yadh. Eléments d'hydrologie pour l'aménagement: Modélisation spatiale et temporelle des précipitations extrêmes et érosives en Tunisie centrale. Université des lettres, des arts et des sciences humaines, Tunis I, Faculté des lettres de la Manouba, 1997.

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Gold, Jason M. The role of spatial frequency information in the identification of complex visual patterns. National Library of Canada, 1996.

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Chabane, G. The detection of chromatic and achromatic patterns by mechanismsworking in the spatial frequency range. UMIST, 1993.

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G, Schaefer Melvin, Washington (State). Dept. of Transportation., Washington State Transportation Commission. Planning and Programming Service Center., MGS Engineering Consultants Inc, and Oregon Climate Service, eds. Regional precipitation-frequency analysis and spatial mapping of precipitation for 24-hour and 2-hour durations in western Washington. Washington State Dept. of Transportation, 2002.

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Safford, Hugh D. Using fire return interval departure (FRID) analysis to map spatial and temporal changes in fire frequency on national forest lands in California. United States Department of Agriculture, Forest Service, Pacific Southwest Research Station, 2014.

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1953-, Wilson Charles A., United States. Minerals Management Service. Gulf of Mexico OCS Region., and Coastal Marine Institute (Baton Rouge, La.), eds. Seasonal and spatial variation in the biomass and size frequency distribution of the fish associated with oil and gas platforms in the northern Gulf of Mexico. U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 2000.

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Stanley, David R. Seasonal and spatial variation in the biomass and size frequency distribution of the fish associated with oil and gas platforms in the northern Gulf of Mexico. U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 2000.

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Chapitres de livres sur le sujet "Spatial frequencie"

Heilbronner, Renée, and Steve Barrett. "Spatial Frequencies." In Image Analysis in Earth Sciences. Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-10343-8_19.

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Cristóbal, Gabriel, Salvador Gabarda, and Leon Cohen. "Joint Spatial/Spatial-Frequency Representations." In Optical and Digital Image Processing. Wiley-VCH Verlag GmbH & Co. KGaA, 2011. http://dx.doi.org/10.1002/9783527635245.ch5.

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Swearer, Joan. "Spatial Frequency Analysis." In Encyclopedia of Clinical Neuropsychology. Springer New York, 2011. http://dx.doi.org/10.1007/978-0-387-79948-3_1403.

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Swearer, Joan. "Spatial Frequency Analysis." In Encyclopedia of Clinical Neuropsychology. Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-56782-2_1403-2.

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Swearer, Joan. "Spatial Frequency Analysis." In Encyclopedia of Clinical Neuropsychology. Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-57111-9_1403.

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Martin, Willy. "Variation in lexical frequency." In Distributions spatiales et temporelles, constellations des manuscrits/Spatial and Temporal Distributions, Manuscript Constellations. John Benjamins Publishing Company, 1988. http://dx.doi.org/10.1075/z.37.16mar.

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Griffith, Daniel A., and Jean H. P. Paelinck. "Frequency Distributions for Simulated Spatially Autocorrelated Random Variables." In Non-standard Spatial Statistics and Spatial Econometrics. Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-16043-1_4.

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Saager, Rolf B. "Spatial Frequency Domain Imaging." In Coded Optical Imaging. Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-39062-3_9.

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Söderlind, Gustaf. "Spatial frequencies and iterative methods." In Springer Series in Computational Mathematics. Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-74379-5_27.

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Allard, Denis, Xavier Emery, Céline Lacaux, and Christian Lantuéjoul. "Simulation of Stationary Gaussian Random Fields with a Gneiting Spatio-Temporal Covariance." In Springer Proceedings in Earth and Environmental Sciences. Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-19845-8_4.

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AbstractThe nonseparable Gneiting covariance has become a standard to model spatio-temporal random fields. Its definition relies on a completely monotone function associated with the spatial structure and a conditionally negative semidefinite function associated with the temporal structure. This work addresses the problem of simulating stationary Gaussian random fields with a Gneiting-type covariance. Two algorithms, in which the simulated field is obtained through a combination of cosine waves are presented and illustrated with synthetic examples. In the first algorithm, the temporal frequency is defined on the basis of a temporal random field with stationary Gaussian increments, whereas in the second algorithm the temporal frequency is drawn from the spectral measure of the covariance conditioned to the spatial frequency. Both algorithms perfectly reproduce the correlation structure with minimal computational cost and memory footprint.

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Actes de conférences sur le sujet "Spatial frequencie"

McIntosh, K. A., L. J. Mahoney, K. M. Molvar, O. B. McMahon, M. Rothschild, and E. R. Brown. "Infrared Metallodielectric Photonic Crystals." In Spatial Light Modulators. Optica Publishing Group, 1997. http://dx.doi.org/10.1364/slmo.1997.smc.2.

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During the past several years there has been significant research involving the design, measurement, and theory of periodic dielectric structures that exhibit a photonic bandgap.1 These photonic crystal structures could be useful in many applications that require frequency specific optical modulators or reflectors. As demonstrated recently at microwave frequencies, photonic crystal structures that incorporate metallic scattering centers can exhibit large electromagnetic stop bands.2 The resulting structures are referred to as metallodielectric photonic crystals (MDPCs). We report here progress in developing MDPCs with stop bands in the infrared. Using standard microelectronic techniques we have fabricated arrays of 3-dimensional photonic crystals on silicon substrates. The metallic "atoms" are laid out in a (100)-oriented fee arrangement as seen from the normal to the plane of the substrate. Stop-band characteristics of fabricated IR MDPC samples have been measured using the technique of Fourier-transform spectroscopy. Rejection levels of up to 20 dB are found in the stop bands of some of the structures. IR MDPC results are compared with measurements made on microwave-scale MDPC structures to help in understanding the infrared results.

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Billock, Vincent A., and Thomas H. Harding. "Spatio-temporal tuning of temporal frequency mechanisms." In OSA Annual Meeting. Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thaa7.

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Billock and Harding (ARVO, 1991) derived three temporal frequency mechanisms responsible for the independent detection of temporal modulated 4 c/deg gratings. Here we extend this approach to a wide range of spatial frequencies. We measured binocular spatio–temporal contrast sensitivity in thirty young (18–35 yr) observers. The stimuli were presented at 100 cd/m2 and were embedded in an extended surround of the same luminance and chromaticity. Spatial frequency ranged from 0.5 to 22.6 c/deg in steps of an octave. Temporal frequency ranged from 0.25 to 32 Hz in steps of 0.5 octave. For each spatial frequency, a temporal frequency contrast sensitivity correlation matrix was computed. These matrices were factor analyzed and solutions for 1–4 factors were varimax-rotated to obtain easily interpretable structures. Our criteria for the discernment of mechanisms were the variance accounted for by each factor and the meaningfulness of the derived tuning. Based on these criteria we found evidence for three broadband temporal frequency mechanisms: (1) a high temporal frequency mechanism with a maximum near 8 Hz and a spatial frequency range of 0.5 to 5.7 c/deg; (2) an intermediate temporal frequency mechanism with a peak near 2 Hz and a spatial frequency range of 0.5 to 4 c/deg; (3) a low temporal frequency mechanism, with a peak between 0 and 0.5 Hz at spatial frequencies > 2 c/deg.

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Vicari, L. "Dielectric Behavior Of Polymer Dispersed Liquid Crystals." In Spatial Light Modulators. Optica Publishing Group, 1997. http://dx.doi.org/10.1364/slmo.1997.stue.1.

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A Polymer Dispersed Liquid Crystal (PDLC) is a dispersion of liquid crystal microdroplets in a polymeric binder. Droplets are randomly oriented anisotropic spheres and, if their size is close to visible light wavelength, produce a strong light scattering so that the sample is translucent. Light scattering is due to the refractive index mismatch between droplets and surrounding polymer, and can be controlled by changing the droplets effective refractive index: this can be achieved in different manners, but usually it is easily obtained applying an external, low frequency, electric field. Possible applications range from large scale flexible displays to windows with controlled transparency or thermal sensors.In recent papers we have presented detailed experimental and theoretical studies of the behavior of a PDLC sample when a light beam impinges on it. Here we study the frequency dependence of light transmittance in a PDLC sample. To this aim we use a mathematical model assuming the liquid crystal dielectric permittivities ε|| and ε⊥ to be the most important parameters for the applied field frequency dependence of light transmittance. Theoretical results show a sudden decrease of the transmitted intensity increasing the frequency of the applied voltage. We present also preliminary experimental results confirming this behavior.

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Burbeck, Christina A. "Pattern adaptation in detection and discrimination." In OSA Annual Meeting. Optica Publishing Group, 1987. http://dx.doi.org/10.1364/oam.1987.wt8.

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Previous findings indicate that detection and discrimination of sine wave gratings do not occur at a common site. The effects of pattern adaptation are fundamentally different for detection and discrimination,1 and frequency discrimination is based on the object spatial frequencies, whereas contrast detection thresholds are based on the retinal spatial frequencies.2 These findings raise the question: are the effects of pattern adaptation on frequency discrimination3 tied to the object spatial frequencies or to the retinal spatial frequencies? We were unable to replicate Regan and Beverley's results. However, we were able to replicate the well-known perceived spatial frequency shift, which also entails spatial frequency comparisons, and found that it depends on the retinal (not object) spatial frequencies of the test and adapt gratings. Finally, we show that the perceived spatial frequency shift predicts that frequency discrimination thresholds should be altered by pattern adaptation but that the primary predicted effect should be enhancement of frequency discrimination sensitivity at the adapting frequency and not dimunition of frequency discrimination sensitivity away from the adapting frequency as Regan and Beverley reported.

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Rohaly, Ann Marie, and Hugh R. Wilson. "Coarse disparity processing does not shift fine scale processing." In OSA Annual Meeting. Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.wm7.

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Several stereomatching algorithms posit that processing on coarse (low spatial frequency) scales constrains processing on fine (high spatial frequency) scales by shifting the disparity range over which fine mechanisms operate. To test this hypothesis, we measured stereoacuity and stereo increment thresholds for high spatial frequency test stimuli in the presence of low spatial frequencies. If high spatial frequency mechanisms are always shifted to an optimal range for disparity processing, as proposed in the coarse-to-fine models, stereo increment thresholds for high frequencies in the presence of low frequencies should be constant, regardless of base disparity. In contrast, we find that in the presence of low spatial frequencies, increment thresholds for high spatial frequencies increase with base disparity as do increment thresholds for high frequencies alone. As a further test of whether information on coarse scales enhances processing on fine scales, diplopia thresholds were measured. In the presence of low frequencies, fusion ranges for high frequencies are severely reduced.

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Chan, Hoover, Christopher W. Tyler, and Lei Liu. "Asymmetries in the perception of luminance increments and decrements at low contrasts." In OSA Annual Meeting. Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thaa6.

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Studies of luminance increments and decrements have typically used transient pulses of localized stimuli. We employed two new paradigms to examine increment/decrement response asymmetries in grating stimuli presented with a smooth spatio–temporal envelope. For the first paradigm, we studied apparent width of the light and dark bars making up sinusoidal gratings as a function of contrast. In contrast ranges close to threshold, the light bars appeared up the three times wider than the dark bars, with a peak at contrast of ~3%. Similar asymmetries were seen over a range of spatial frequencies. For the second paradigm, the gratings were generated as only luminance increment bars from the grey background (or only luminance decrement bars). We found asymmetries in the response to increments and decrements than varied as a function of spatial frequency of the test grating. At low spatial frequencies, the visual system was more sensitive to decrements. At intermediate spatial frequencies, sensitivity was higher for increments than for decrements by a factor of ~2. Sensitivity to both become the same at high spatial frequencies.

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McCourt, Mark E. "Spatial-frequency tuning, contrast tuning, and spatial summation of suprathreshold lateral spatial interactions: grating induction and contrast–contrast." In OSA Annual Meeting. Optica Publishing Group, 1993. http://dx.doi.org/10.1364/oam.1993.wrr.3.

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Two supra-threshold lateral interactions, the grating-induction effect,1 and the contrast–contrast effect,2,3 were compared regarding their dependence upon inducing grating spatial frequency, inducing and “victim” grating contrast, and inducing grating extent. Both effects cause “victim” gratings to be matched non-veridically. The respective magnitude of the effects was measured in common units which indexed the veridicality of contrast matches across a wide range (-0.9 to 0.9) of “victim” grating contrast. Grating induction had a low-pass, and contrast-contrast had a high-pass spatial frequency response, crossing over at ca. 1 c/d. Maximal grating induction strength exceeded that of contrast–contrast for 5 of 6 observers. Observers demonstrating strong grating induction tended to show weak contrast-contrast magnitudes, and vice versa. When inducing contrast was 0.75, the departures from veridical matching varied with “victim” grating contrast. For low frequencies (0.03125-0.125 c/d) grating induction produced a skewed unimodal departure from veridical matching, peaking at “victim” grating contrasts of 0.5. The pattern became bimodal at higher spatial frequencies (0.25-2.0 c/d) peaking at “victim” contrasts of ca. -0.3 and 0.5. Contrast–contrast caused symmetrical departures from veridicality which were consistent across spatial frequency, peaking at “victim” contrasts of ca. ±0.5. Both grating induction and contrast–contrast magnitudes decreased with reductions in inducing grating height, implying spatially extended mechanisms. With increasing inducing grating spatial frequency, however, the summation space-constant for grating induction decreased, whereas it increased for contrast–contrast.

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Abraham, N. B., L. M. Hoffer, and G. L. Lippi. "Phase and Frequency Dynamics in a Bidirectional Ring Laser." In Optical Bistability. Optica Publishing Group, 1988. http://dx.doi.org/10.1364/obi.1988.wc.4.

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Homogeneously broadened bidirectional ring lasers show alternation of the lasing direction induced dynamically by a long-lived population grating and slight detuning of the laser cavity from the atomic resonance1. We show that the mode switching is accompanied by abrupt jumps by pi in the total relative phase of the system2. Our analysis reveals that the carrier frequencies of the two modes are not equal even though the two unidirectional steady state solutions have the same frequency2. When one mode dominates and the other is suppressed, the dominant mode has the steady state frequency. However, a mode growing in strength has a frequency closer to the atomic resonance while a mode falling in strength has a frequency further from the atomic resonance. The dynamically induced mode-pulling and mode-pushing can be as much as 25 % of the steady state frequency detuning. The shifting frequencies of the modes indicate that the standing wave interference pattern rotates in the laser ring cavity, alternately moving clockwise and counterclockwise with nearly equal and constant speeds. The longitudinal spatial hole-burning pattern consequently also rotates in the ring tending to wash out the population grating and keeping it from developing an amplitude of much more than one percent of the spatially averaged population inversion.

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Klein, Stanley A., and Brent Beutter. "Hermite functions maximize the spacespatial frequency uncertainty of Gaborlike functions." In OSA Annual Meeting. Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.ww3.

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Wavelets that are localized both in space and in spatial frequency are useful for vision modeling and image processing. For example, in image compression one would like localization in spatial frequency so that the small spatial filters are insensitive to low spatial frequencies to which the visual system is highly sensitive. One would also like spatially localized filters to reduce interference between adjacent features. Several investigators, including Gabor, asked what particular wavelet shape minimizes the joint space-spatial frequency uncertainty (the Heisenberg uncertainty). Consider the class of functions that are an nth-order polynomial times a Gaussian. Gabor proved that the nth-order Hermite polynomial produced the extremum of the Heisenberg uncertainty. He believed that the extremum he found was the minimum. We found that Gabor was partly right and partly wrong. A Hermite polynomial when multiplied by a Gaussian is indeed an extremum of the Heisenberg uncertainty for the class functions that are an nth-order polynomial times a Gaussian. The problem is that it maximizes rather than minimizes the uncertainty.

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HASHIMOTO, Nobuyuki. "High-resolution LCTV-SLM and its application to holography." In Spatial Light Modulators. Optica Publishing Group, 1997. http://dx.doi.org/10.1364/slmo.1997.stua.2.

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The MIM active matrix liquid crystal device with pixel pitch of 30 μm has been developed and its holographic display characteristics and application to 3D holography have been studied. In the system, a CCD camera reads holographic fringes with quite low career spatial frequency and the fringes are transferred and displayed on the SLM. We use the spatial filtering technique to reduce 0 th. order diffracted light on reconstruction. Recent results of polarization filtering to remove 0 th. order light and of 3M pixel LCDs using MIM technology are presented.

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Rapports d'organisations sur le sujet "Spatial frequencie"

Fitzgerald, T. J. Spatial and frequency coherence of oblique, one-hop, high-frequency paths. Office of Scientific and Technical Information (OSTI), 1995. http://dx.doi.org/10.2172/114649.

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Patterson, Frederick R., and Joseph F. Chandler. Effect of Acceleration Frequency on Spatial Orientation Mechanisms. Defense Technical Information Center, 2010. http://dx.doi.org/10.21236/ada529816.

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Mathew, Sonu, Srinivas S. Pulugurtha, and Sarvani Duvvuri. Modeling and Predicting Geospatial Teen Crash Frequency. Mineta Transportation Institute, 2022. http://dx.doi.org/10.31979/mti.2022.2119.

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This research project 1) evaluates the effect of road network, demographic, and land use characteristics on road crashes involving teen drivers, and, 2) develops and compares the predictability of local and global regression models in estimating teen crash frequency. The team considered data for 201 spatially distributed road segments in Mecklenburg County, North Carolina, USA for the evaluation and obtained data related to teen crashes from the Highway Safety Information System (HSIS) database. The team extracted demographic and land use characteristics using two different buffer widths (0.25 miles and 0.5 miles) at each selected road segment, with the number of crashes on each road segment used as the dependent variable. The generalized linear models with negative binomial distribution (GLM-based NB model) as well as the geographically weighted negative binomial regression (GWNBR) and geographically weighted negative binomial regression model with global dispersion (GWNBRg) were developed and compared. This research relied on data for 147 geographically distributed road segments for modeling and data for 49 segments for validation. The annual average daily traffic (AADT), light commercial land use, light industrial land use, number of household units, and number of pupils enrolled in public or private high schools are significant explanatory variables influencing the teen crash frequency. Both methods have good predictive capabilities and can be used to estimate the teen crash frequency. However, the GWNBR and GWNBRg better capture the spatial dependency and spatial heterogeneity among road teen crashes and the associated risk factors.

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Maimone, Mark W., and Steven A. Shafer. Modeling Foreshortening in Stereo Vision Using Local Spatial Frequency. Defense Technical Information Center, 1995. http://dx.doi.org/10.21236/ada292246.

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Huang, Ben. Removing Textured Artifacts from Digital Photos Using Spatial Frequency Filtering. Portland State University Library, 2000. http://dx.doi.org/10.15760/etd.148.

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Nguyen, H. T., J. A. Britten, R. D. Boyd, B. D. Shore, and M. D. Perry. Ultrahigh spatial-frequency, high-contrast periodic structures produced by interference lithography. Office of Scientific and Technical Information (OSTI), 1996. http://dx.doi.org/10.2172/489588.

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Yamano, Takashi, Murali Krishna Gumma, Pranay Panjala, et al. Applying Spatial Analysis to Assess Crop Damage: A Case Study of the Pakistan 2022 Floods. Asian Development Bank, 2024. http://dx.doi.org/10.22617/wps240225-2.

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Climate change is expected to increase the frequency and magnitude of extreme weather events in Pakistan. During and immediately after such events many locations are inaccessible, yet the government needs evidence-based data to help plan effective responses. This paper uses spatial analysis and spectral mapping to assess the agricultural damage from the 2022 floods in Pakistan. Spatial analysis could be a vital tool in assessing and verifying damage from disaster events. The paper emphasizes the need to build spatial analysis capacities in provincial crop reporting services and the Ministry of National Food Security and Research.

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D'Spain, Gerald L. Mid-Frequency Ambient Noise Spatial Structure and Implications for Passive Signal Processing. Defense Technical Information Center, 2005. http://dx.doi.org/10.21236/ada438283.

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Amin, Moeness. Classification and Discrimination of Sources with Time-Varying Frequency and Spatial Spectra. Defense Technical Information Center, 2002. http://dx.doi.org/10.21236/ada406349.

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Marcotte, D. Spatial estimation of frequency distribution of acid rain data using Bigaussian kriging. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1990. http://dx.doi.org/10.4095/128070.

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