archives@tulane.edu / This dissertation explores the dielectric Huygens metasurface system. High index dielectric discs in a low index medium act as optical nanoantennas and support electric and magnetic dipole resonant modes. The two resonances are separately tunable, allowing both their absolute and relative spectral locations to be controlled. Spectrally overlapping resonances enable high transmissivity with optical phase controllable by the diameter of the nanoantenna elements, providing a critical building block for the development of gradient phased arrays. Conversely, spectrally separated resonances result in a reflectance peak with tunable shape and depth, a useful feature for sensing applications. The dissertation is divided into four key chapters. Chapter 2 concerns the development of highly efficient gradient Huygens metasurfaces. Design rules are introduced to mitigate the effects of inter-element coupling, and gradient metasurfaces are computationally demonstrated in the ultraviolet, visible, and infrared spectrums, and experimentally demonstrated for infrared light. Chapter 3 investigates the use of these metasurfaces to sense changes in the refractive index of fluids. A computational analysis is shown, demonstrating broad customizability of sensor performance. Detection of salt and CaCl2 in water is demonstrated experimentally. Chapter 4 explores the potential of Huygens metasurfaces for dynamic tunability. Various methods and materials are discussed. Progress towards tunable metasurfaces utilizing vanadium dioxide (VO2) nanoantennas is highlighted. Chapter 5 describes a unique interferometric measurement tool designed for the characterization of dynamic and ultra-thin materials and metasurfaces. In summary, we explore the unique physics of highly resonant Huygens metasurfaces and pursue their use in a number of promising applications. / 1 / Adam Ollanik

Certains microorganismes sont capables de communiquer en utilisant des molécules et d’utiliser ce système pour réguler des comportements en fonction de la densité cellulaire. Ce système de communication, appelé quorum sensing (QS), régule des comportements bactériens, tels que la virulence et la formation de biofilm. Les molécules signal les plus étudiées sont les acyle-homosérine lactones (AHLs). Les enzymes qui sont capables de dégrader ces molécules peuvent couper la communication bactérienne, et se comportent ainsi comme des inhibiteurs de virulence et de biofilm. Ce phénomène, appelé quorum quenching (QQ), est une approche prometteuse pour le contrôle bactérien sans les tuer, ainsi que pour le développement de nouvelles thérapies contre les bactéries résistantes aux antibiotiques. Les travaux menés durant ma thèse ont permis d’isoler et de caractériser biochimiquement, enzymatiquement et structuralement de nouvelles lactonases provenant d’organismes thermophiles, capables d’inhiber le QS. J’ai résolu les structures de trois lactonases et en complexe avec différents types de lactones. Ces données ont révélées l’extrême polyvalence des sites actifs de ces enzymes, et ont permis d’identifier les résidus potentiellement impliqués dans la spécificité de substrat de ces enzymes. Ces résultats serviront de bases aux futurs projets d’ingénierie visant à changer la spécificité de ces enzymes. Enfin, mes travaux de caractérisation sur ces lactonases très stables ont permis de les utiliser hors du laboratoire et de démontrer l’importance de la signalisation bactérienne dans des processus biologiques complexes tels que la formation de biofilm et la bio-corrosion. / Numerous microorganisms are able to communicate using molecules and use this signaling system to coordinate behaviors in a cell-density-dependent manner. This communication system, dubbed quorum sensing (QS), regulates bacterial behaviors such as biofilm formation. The most popular system utilizes acyl homoserine lactones (AHLs) as signals. Enzymes that can degrade these signaling molecules can effectively disrupt bacterial signaling, and thereby behave as potent biofilm and virulence inhibitors. Therefore, the inhibition of QS, termed quorum quenching (QQ) by these enzymes is a promising approach to control microbes without killing them and develop therapies on multidrugs resistant strains. During this thesis, I have isolated and characterized biochemically, enzymatically and structurally novel lactonases from thermophilic sources. I have determined the structures of three lactonases in complex with different types of lactones. This enabled me to elucidate their catalytic mechanisms, as well as the unique binding modes of structurally different lactones. These data revealed the extreme catalytic versatility of the active sites of these enzymes, and allowed for the determination of residues possibly involved in substrate specificity. These data, in combination with structural data obtained on improved lactonase mutants, will serve as a foundation to guide future engineering studies aiming at altering lactonases’ specificity. Lastly, isolation and characterization work on these thermostable lactonases allowed to demonstrate the importance of bacterial signaling in complex biological processes, in the field, including biofilm formation and biocorrosion.

Des bactéries utilisent un système de communication, quorum sensing (QS), qui leur permet de synchroniser leur comportement proportionnellement à la densité de population. Des bactéries pathogènes utilisent le QS pour coordonner leur virulence et la formation de biofilm. Bloquer le QS, quorum quenching (QQ), constitue donc une piste pour étendre l'arsenal thérapeutique antibactérien. Durant cette thèse, SsoPox, une lactonase hyperstable hydrolysant les acyl homosérine lactones (AHL) impliquées dans le QS de bactéries à Gram négative pathogènes comme P. aeruginosa, a été étudiée. Son utilisation dans des pansements contre les infections à P. aeruginosa a été évaluée. La résistance aux contraintes industrielles liées aux procédés de fabrication des pansements a été évaluée. SsoPox s'est montrée résistante à la chaleur, aux solvants organiques, au stockage à température ambiante et à la stérilisation. L’efficacité de l’enzyme a été montrée sur 2 souches modèles et 51 isolats cliniques de P. aeruginosa. SsoPox a été plus efficace que 2 inhibiteurs du QS. L’efficacité de l’enzyme est aussi conservée après immobilisation. Une étude phénotypique et moléculaire du QQ enzymatique de P. aeruginosa a été réalisée entre SsoPox et une autre lactonase GcL ayant un spectre d'action distinct sur les AHL. In vitro, il a été mis en évidence des impacts différents entre les 2 enzymes sur les facteurs de virulence et le biofilm. In vivo, il a été montré que seul SsoPox réduit la virulence de P. aeruginosa. L’expression des gènes du QS et le protéome ont confirmé des différences entre GcL et SsoPox. Ainsi SsoPox semble constituer un bon candidat pour le développement de pansements innovants. / Bacteria use a communication system, or quorum sensing (QS), to synchronize group behaviors according to population density. Some pathogens use QS to coordinate virulence and biofilm formation. Interfering with QS, or quorum quenching, represents a target to extent antibacterial drug resources. Along this PhD project, SsoPox, a hyperstable lactonase, hydrolyzing acyl homoserine lactones (AHL) involved in the QS of Gram-negative pathogen bacteria like Pseudomonas aeruginosa was studied. SsoPox was studied and characterized for its use in wound dressing against P. aeruginosa infection. The enzyme resistance to industrial constraints encountered during wound dressings manufacturing processes was estimated. SsoPox demonstrated a high tolerance to heat, organic solvents, ambient temperature storage and to sterilization processes. The enzyme efficiency was shown on 2 model strains and 51 clinical isolates of P. aeruginosa. SsoPox was also more efficient than 2 well characterized QS inhibitors. The enzyme kept its efficiency even when immobilized. A last part was dedicated to phenotypical and molecular study of enzymatic QQ of P. aeruginosa. SsoPox and another lactonase GcL, having distinct AHL specificities, were compared. In vitro experiments highlighted different impacts between the enzymes on virulence factors and biofilm. An in vivo study showed that SsoPox, unlike GcL, was able to reduce P. aeruginosa virulence. QS gene expression and proteome study confirmed distinct impacts between each enzyme treatment s. Thus, SsoPox seems to be a prime candidate for development of innovative medical devices.

Thesis (M.S.)--Tufts University, 2002. / Submitted to the Dept. of Mechanical Engineering. Includes bibliographical references (leaves 122-123).

No description available.

A general analytical framework was established to investigate the scale-related variabilities in remote sensing. The variabilities were studied first by investigating canopy structure, canopy interaction with light, relation between spectral reflectance and plant phenological parameters. The variabilities simulated by the plant model were compared with the actual spectral data acquired by ground spectroradiometer and satellite sensors. The theoretical relation between orthogonal-basedtransform and Kahunen-Lo6ve transform was investigated in the vector space. The role of spectral indices in identifying the status of phenological parameters was briefly studied. The radiometric corrections of the remotely sensed data were carefully controlled to avoid the unwanted noise introduced by typical resampling/correction procedures from commercial operation. The non-linearity and sensor response corrections were applied to the spectral data as necessary. Variability analysis was conducted to illustrate the complexities of spectral variability embedded in the remotely sensed data. The information extraction in spatial frequency domain was investigated with emphasis in Fourier domain feature extraction. The Radon transform was introduced as the potential tool to enhance the spatial information of the Fourier transformed image. The adequacy of entropy and fractal dimension as image information measures was proved. A functional link between entropy and fractal dimension was established. The image information content was extracted using various first and second order statistics, entropy, and fractal dimension. Results were presented for different remote sensors based on the full image information content and specific agricultural ground features. The quality of spatial resampling algorithms was tested by investigating the capability to maintain image information in the resampled image. Finally, two applications utilizing this analytical framework were presented to show its potential in land-use classification and multiscale data fusion. / Graduation date: 1993

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Richard C. Olsen, David M. Task. Includes bibliographical references (p. 141-142). Also available online.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Richard C. Olsen, Alan A. Ross. Includes bibliographical references (p. 127-129). Also available online.

Using the remote sensing data, this study aims to enhance our understanding of land surface features, including ecosystem distribution in association with topographic controls and climatic controls, vegetation disturbance due to natural hazards, and surface temperature changes with consideration of the influence of urbanization. In this study, the Global Inventory Monitoring and Modeling System (GIMMS) Normalized Difference Vegetation Index (NDVI) data sets from 1982 to 2006 were used to explore vegetation variation. A data mining method, Exhaustive Chi-squared Automatic Interaction Detector algorithm, was successfully applied to investigate the topographic influences on vegetation distribution in China. The study revealed that elevation is a predominant factor for controlling vegetation distribution among different topographic attributes (slope, aspect, Compound Topographic Index (CTI) and distance to the nearest river). Further, the study results indicated that solar radiation is the limited factor for plant growth in majority of the Northern Hemisphere in summer, and temperature is the main limitation for other seasons. Partial correlation coefficient (PCC) method was adopted to investigate the complex relationships of NDVI with weather variables (i.e., temperature, precipitation and solar radiation) and key climate indices (such as, El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Arctic Oscillation (AO), and Antarctic Oscillation (AAO)). The study indicated that AO is the most significant index in affecting the temperatures in spring and winter in the Northern Hemisphere. This study enhanced the understanding of vegetation responds to asymmetric daytime (Tmax) and nighttime (Tmin) warming in different seasons. The result revealed that asymmetric warming of Tmax and Tmin may influence vegetation photosynthesis and respiration in the plant growth in different periods across biomes. In spring and autumn, vegetation in boreal and wet temperate regions of the Northern Hemisphere is positively correlated with Tmax and negatively correlated with Tmin, whereas, in dry regions the NDVI is always negatively correlated with Tmax and positively correlated with Tmin. In summer, the NDVI is negatively correlated with Tmax in many dry regions. In addition, this study developed a new index, Continued Vegetation Decrease Index (CVDI), to detect vegetation disturbance due to extreme natural hazards (such as, earthquake, wildfire, ice storms and so on). Using the Wenchuan earthquake occurred in Sichuan China on 12 May 2008 as an example, this study confirmed that the CVDI method can effectively identify the regions with severe vegetation damage, and it is expected that the newly-developed index can be used for detecting vegetation disturbance in other regions of the world. Finally, using the remote sensing data (land use data and surface temperature data) and weather station data, this study developed a new method to evaluate the urbanization influence on the temperature recorded at weather stations. The results revealed that the weather stations with most fast increase temperature are not in developed countries, but in developing countries. The results also imply that the global warming trend may be overestimated due to the under-estimation of urbanization influence on temperature increase. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

<p>The Richtersveld falls within the succulent karoo and dester biomes. This studu made use of remote sensing technologies in order to investigate possible vegetation cover changes that have taken place over time, and which have manifested through a combination of threats to the region. Te aims of the study were adressed using three key questions that sought to gainan understanding of the relationship between vegetation response and moisture, in order to interpret teporal and spatial vegetyation cover changes. A spartially and temporarily representative remotely sensed dataset was used together with techniques that are repeatable and able to quantify change with a limited human bias.</p>