Physically-based spectral rendering is becoming increasingly popular in both commercial and academic areas due to its ability to accurately simulate natural phenomena. However, the production of materials defined by their spectral properties is a tedious and expensive process, which makes the utilization of RGB-based assets in spectral renderers a desired feature. To convert RGB values to their spectral representations, a process called spectral uplifting is employed. As the RGB color space is a finite subset of the visible gamut, there exist multiple conversion techniques producing distinct results, which may cause color inconsistencies under various lighting conditions. This thesis proposes a method for constraining the spectral uplifting process. To be specific, pre-defined mappings of RGB values to their spectral representations are preserved and the rest of the RGB gamut is plausibly uplifted. In order to assess its correctness, this technique is then implemented and evaluated in a spectral renderer. The renders uplifted via our method show minimal discrepancies when compared to the original textures.

Dans le cadre de ce travail de thèse plusieurs études seront exposées. La première aborde le problème de la conservation de l'information lors d'un processus d'amplification Brillouin. La seconde s'attache à la réalisation d'un amplificateur Brillouin possédant une large bande passante. Enfin la dernière porte sur la réalisation de lasers Brillouin de très grande cohérence. Une étude expérimentale de la transition entre le générateur Brillouin et l'amplificateur Brillouin dans un régime de saturation est effectuée. Elle met en évidence le transfert d'énergie du générateur vers la sonde amplifiée. Nous avons prouvés que même dans un régime où un générateur est puissant, les qualités spectrales de la sonde amplifiée sont préservées quand la résonance est atteinte. Les qualités de l'amplificateur Brillouin nous amènent dans une seconde partie à tenter d'augmenter sa bande passante car l'étroitesse de la bande de gain est une limite à de nombreuses applications, en particulier dans le domaine des télécommunications. Nous explorons la possibilité de travailler avec une pompe spectralement large et démontrons un élargissement spectral dépassant 10 GHz par l'application d'une pompe originellement large. Nous démontrons un laser monomode, d'une largeur spectrale inférieure au kHz, stable en fréquence et en intensité et dont le seuil est accessible par des diodes lasers DFB commerciales. Le montage est compact, robuste et le coût de revient relativement faible. La cavité peut également être utilisée séparément, c'est-à-dire sans pompe attribuée, pour des applications d'affinement spectral ou de filtrage. Enfin, l'application du dispositif à la caractérisation spectrale de lasers cohérents est démontrée et discutée. / As part of this thesis several studies will be presented. The first presentes the problem of preservation of information in a Brillouin amplification process. The second focuses on the achievement of a Brillouin amplifier with a broad bandwidth. The last part concerns the achievement of Brillouin lasers of high coherence. An experimental study of the transition between Brillouin generator and Brillouin amplifier in a state of saturation is performed. It highlights the transfer of energy from the generator to the probe. We have proven that even in a regime of powerful generator, the spectral qualities of the probe are preserved when the resonance is reached. The qualities of the Brillouin amplifier lead us in a second part to try to increase its bandwidth as narrow band gain is a limitation for many applications, especially in the field of telecommunications. We explore the possibility of working with a large-band pump to achieve broad band amplification. We prove a bandwidth above 10 GHz. We demonstrate a monomode laser, with a spectral width below one kHz, stable in frequency and intensity, in which the threshold is reached by commercial DFB laser diodes. The set-up is compact, robust and cost effective. The cavity can also be used separately, ie without pump assigned, to applications of spectral narrowing or filtering. Finally, the application of the device to spectral characterization of coherent lasers is proved and discussed.

Bidirectional reflectance is a fundamental property used for the analysis of radiative heat transfer. It is a form of reflectivity in which the spectral and directional dependencies of both the beam incident on a surface and the beam reflected from the surface are specified. A new system has been designed expressly for measuring bidirectional reflectance of engineering materials. This apparatus features a unique goniometer design in which the source is fixed, the sample is rotated to change the incident beam directions, and the sensor (which moves with the sample) is rotated about the sample to change the measured reflected beam direction. The system was used to measure the bidirectional reflectance of a surface consisting of flat-white paint on an aluminum substrate. The data for this quasi-diffuse surface were taken over a non-uniform grid. Algorithms are presented for interpolating and reporting values on a uniform grid which is appropriate for use in numerical radiative transfer codes. Bidirectional reflectance data can be used in the form of a look-up table although storage requirements will be large and resolution will be limited by grid resolution. Alternatively, the data can be modeled as continuous functions of the incident beam angle. A simple model of reflectance as the sum of a diffuse and a specular component is described. A second model with a diffuse component and a quasi-specular component is also presented which includes spread in both the polar and azimuthal directions. Both models are continuous and are based on curve fits to the data. / Graduation date: 1994

This thesis presents the musical composition Elucide, scored for a chamber ensemble of ten players. The work builds upon concepts and compositional methods that are central to the spectral approach to composition, established by such composers as Gérard Grisey, Tristan Murail, and Hugues Dufourt. This musical genre is characterized by a focus on the acoustic properties of sound, a concern that is typically reflected both in rich and colourful musical textures, as well as in the conceptual foundations of compositional processes. It is often the case that spectral composers will refer to computer analyses of acoustic phenomena during the pre-compositional stages of a work’s development, using these data to generate the piece’s raw materials and to inform structural decisions. Although the spectral approach is rooted in the perceptual appreciation of sonic phenomena, the manner in which analysis data are obtained and applied can encourage a range of listening postures, potentially leading the listener towards both perceptually- and semantically-oriented hearings. Furthermore, this music displays varying symbolic facets stemming from the poetic idea of a musical composition unfolding from the internal structure of sonic materials. The interplay of these dynamics raises a number of issues that are inherent in the compositional application of spectral information; this thesis first examines the spectral endeavor from a philosophical perspective, and then goes on to demonstrate the ways in which Elucide develops from and comments upon these issues. In order to explicitly engage these dynamics in a musical composition, I developed a set of software tools using the graphical programming environment "OpenMusic". These tools provided raw musical materials that were employed at various levels during the compositional process. While the early stages of the work aim to draw aural connections between the overtone structures of source sounds and musical structures, individual spectral elements are progressively divorced from their acoustic origins and woven into musical semantic patterns over the course of the piece. In its elucidation of the relationships between perceptual phenomena and musical semantics, therefore, Elucide represents a broader exploration of the mechanisms by which the human mind finds meaning in sensory information.

This thesis presents the musical composition Elucide, scored for a chamber ensemble of ten players. The work builds upon concepts and compositional methods that are central to the spectral approach to composition, established by such composers as Gérard Grisey, Tristan Murail, and Hugues Dufourt. This musical genre is characterized by a focus on the acoustic properties of sound, a concern that is typically reflected both in rich and colourful musical textures, as well as in the conceptual foundations of compositional processes. It is often the case that spectral composers will refer to computer analyses of acoustic phenomena during the pre-compositional stages of a work’s development, using these data to generate the piece’s raw materials and to inform structural decisions. Although the spectral approach is rooted in the perceptual appreciation of sonic phenomena, the manner in which analysis data are obtained and applied can encourage a range of listening postures, potentially leading the listener towards both perceptually- and semantically-oriented hearings. Furthermore, this music displays varying symbolic facets stemming from the poetic idea of a musical composition unfolding from the internal structure of sonic materials. The interplay of these dynamics raises a number of issues that are inherent in the compositional application of spectral information; this thesis first examines the spectral endeavor from a philosophical perspective, and then goes on to demonstrate the ways in which Elucide develops from and comments upon these issues. In order to explicitly engage these dynamics in a musical composition, I developed a set of software tools using the graphical programming environment "OpenMusic". These tools provided raw musical materials that were employed at various levels during the compositional process. While the early stages of the work aim to draw aural connections between the overtone structures of source sounds and musical structures, individual spectral elements are progressively divorced from their acoustic origins and woven into musical semantic patterns over the course of the piece. In its elucidation of the relationships between perceptual phenomena and musical semantics, therefore, Elucide represents a broader exploration of the mechanisms by which the human mind finds meaning in sensory information.

This thesis presents the musical composition Elucide, scored for a chamber ensemble of ten players. The work builds upon concepts and compositional methods that are central to the spectral approach to composition, established by such composers as Gérard Grisey, Tristan Murail, and Hugues Dufourt. This musical genre is characterized by a focus on the acoustic properties of sound, a concern that is typically reflected both in rich and colourful musical textures, as well as in the conceptual foundations of compositional processes. It is often the case that spectral composers will refer to computer analyses of acoustic phenomena during the pre-compositional stages of a work’s development, using these data to generate the piece’s raw materials and to inform structural decisions. Although the spectral approach is rooted in the perceptual appreciation of sonic phenomena, the manner in which analysis data are obtained and applied can encourage a range of listening postures, potentially leading the listener towards both perceptually- and semantically-oriented hearings. Furthermore, this music displays varying symbolic facets stemming from the poetic idea of a musical composition unfolding from the internal structure of sonic materials. The interplay of these dynamics raises a number of issues that are inherent in the compositional application of spectral information; this thesis first examines the spectral endeavor from a philosophical perspective, and then goes on to demonstrate the ways in which Elucide develops from and comments upon these issues. In order to explicitly engage these dynamics in a musical composition, I developed a set of software tools using the graphical programming environment "OpenMusic". These tools provided raw musical materials that were employed at various levels during the compositional process. While the early stages of the work aim to draw aural connections between the overtone structures of source sounds and musical structures, individual spectral elements are progressively divorced from their acoustic origins and woven into musical semantic patterns over the course of the piece. In its elucidation of the relationships between perceptual phenomena and musical semantics, therefore, Elucide represents a broader exploration of the mechanisms by which the human mind finds meaning in sensory information. / Arts, Faculty of / Music, School of / Graduate

The main subsect of this thesis is the theory of Lifshits-Krein spectral shift function in semifinite von Neumann algebras and its connection with the theory of spectral flow. Main results are an analogue of the Krein trace formula for semifinite von Neumann algebras, the semifinite analogue of the Birman-Solomyak spectral averaging formula, a connection between the spectral shift function and the spectral flow and a Lidskii type formula for Dixmier traces. In particular, it is established that in the case of operators with compact resolvent, the spectral shift function and the spectral flow are identical notions.

Thesis (M.S.)--Naval Postgraduate School, 1977. / Includes bibliographical references (leaves 88-90).

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