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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

La soie, "modèle" de polymères naturels fibreux : analyse vibrationnelle et nano/micromécanique, de la fibre au composite / Silk, “pattern” of natural fibrous polymer : vibrationnal and nano/micromechanical analysis from fibre to composite

Wojcieszak, Marine 07 October 2014 (has links)
Les protéines fibreuses (kératine, élastine, collagène, fibroïne…) représentent 1/3 des protéinesconstitutives des mammifères et des oiseaux. Ce sont des protéines qui ont une fonction de protection et/oumécanique. La soie apparait comme le système le plus « simple » car elle est principalement constituée demotifs de répétition à base d’alanine et de glycine, deux petits acides aminés. Certaines soies présentent despropriétés mécaniques comparables ou supérieures à celles des fibres synthétiques et seraient susceptiblesd’être de nouveau largement utilisées dans des applications techniques (par exemple biomédicales) si lavariabilité de leurs propriétés était maîtrisée. Ce travail porte sur la structure des soies grèges ou décreuséesde Bombyx mori (ver à soie domestique), de Nephila madagascariensis (araignée sauvage, fibre sansenveloppe de séricine), de Bombyx mori génétiquement modifié (incluant un gène de Nephila) et sur unesoie recombinante 4RepCT (Escherichia coli). La soie est analysée par spectrométrie Raman (et IRTF) ettraction uni-axiale, ainsi que par le couplage de ces méthodes. L’analyse de la région des bas nombresd’onde en spectroscopie Raman a permis de caractériser des régions ordonnées de 2 à 3 μm de long etdistantes d’environ 60 μm. Il s’agit de la première mise en évidence d’une hétérogénéité de structure de lasoie. Le couplage avec la traction uni-axiale montre une sollicitation de ces régions ordonnées sousdéformation, suggérant une organisation de la soie selon le modèle de Prevorsek, c’est à dire qu’une mêmechaîne macromoléculaire appartient à la fois à des régions amorphes et à des régions ordonnées. L’étudestatistique des propriétés mécaniques de la soie de ver et d’araignée montre une grande distribution, maisune bonne stabilité dans le temps (dizaines d’années). La modification génétique ne procure pasd’amélioration des propriétés mécaniques de la fibre, seulement une légère diminution de la variabilité.Diverses stratégies sont mises en oeuvre pour tenter d’échapper à cette variabilité : production bactérienne,solubilisation de la soie et régénération sous forme de films. Le rôle de l’eau lors de la biosynthèse de lasoie, ainsi que l’effet de divers paramètres (filtration, pH, séchage…) lors de la préparation des films ont étéétudiés. Nous avons pu confirmer que la présence d’agrégats de protéines favorise l’organisation dans lesfilms et 2 types de films ont donc été préparés. Les films les plus amorphes présentent les propriétésmécaniques les plus intéressantes, même si elles n’atteignent de quelques % de celles des fibres. Lafabrication de composites à matrice de soie régénérée renforcée par des fibres de soie permet d’augmenterla résistance et la déformation à rupture. Ces premiers résultats sont encourageants pour le développementde matériaux composites fibres de soie/matrice de soie régénérée. / Fibrous proteins (keratin, elastin, collagen, fibroin ...) make up to one third of the proteins ofmammals and birds. They are structural proteins with a protective and/or mechanical function. Silk appearsto be the ‘simplest’ model because it mainly consists of two small amino acids residues (alanine andglycine). Some silks have comparable or superior mechanical properties compared to those of syntheticfibres and could be used in technical applications (e.g. biomedical) if the variability of their properties canbe controlled. This work focuses on the structure of silks from: Bombyx mori (domestic silkworm)degummed or not, Nephila madagascariensis (wild spider, no sericin coating), GM Bombyx mori (includinga gene of Nephila) a recombinant spider silk 4RepCT (Escherichia Coli). Silk is analyzed by Ramanspectroscopy (and FTIR), uni-axial tensile testing, and also by the coupling of these methods. The analysisof the low wavenumbers region in Raman spectroscopy allowed the characterization of ordered regions of 2to 3 microns separated by about 60 microns. This is the first evidence of the heterogeneous structure ofsilk. Coupling with the uni-axial tensile test shows that these ordered regions are stressed under macroscopicdeformation, suggesting silk organization according to Prevorsek’s model, i.e. that the samemacromolecular chain belongs to both amorphous and ordered regions. The statistical study of themechanical properties of silkworm and spider silks shows great dispersion, but a good stability over time(decades). Genetic modification does not improve the fibres mechanical properties but a slight decrease intheir variability. Various strategies have been investigated to control the variability: bacterial production,solubilization of silk and films regeneration. The role of water in silk biosynthesis, as well as the effect ofvarious parameters (filtration, pH, drying ...) during the preparation of the films were studied. It wasconfirmed that the presence of protein aggregates promotes the organization in film and two types of filmswere prepared. The most amorphous ones have the most interesting mechanical properties, though only afew percent of those from the starting fibres. The fabrication of regenerated silk matrix compositesreinforced by silk fibres increases the strength and strain to failure. These initial results are encouraging forthe development of silk fibres/regenerated silk matrix composite materials.
152

MI9's escape and evasion mapping programme 1939-1945

Bond, Barbara A. January 2014 (has links)
This thesis examines the programme of mapping produced on silk, and other fabric, by MI9 to facilitate the escape and evasion of British military personnel during World War II. It considers the creation of MI9 in December 1939, the rationale for the new military intelligence branch and the context of the history of military mapping on silk. The map production programme is described, together with its progress and the challenges faced. The various groups of maps are identified and described, together with the source maps on which they were based. This description is developed in nine appendices produced as an integral part of the research to provide a comprehensive carto-bibliography of the 234 individual maps which have been identified. Location details of extant copies in British map collections are also provided. The ingenious methods of smuggling the maps into the camps, with other escape aids, in apparently innocuous leisure items are described. The maps were then copied and reproduced to support the escapes. Coded correspondence with the camps is discussed, and a successful deciphering of some of that correspondence is provided. The implications for the escape and evasion programme were considerable, but so too were the implications of the passage of intelligence from the camps to aid the war effort, a factor apparently largely overlooked in previous studies of the wartime role of the intelligence branches. Three case studies are provided to demonstrate the role and importance of the contribution made by the maps to the escape and evasion programme. The conclusion assesses the significance of this little known episode in British historical cartography of the twentieth century which essentially provides the latest chapter in the story of military mapping on silk, and other fabric, through the ages.
153

Le treuil élasto-capillaire : de la soie d'araignée aux actionneurs intelligents / Elasto-capillary windlass : from spider silk to smart actuators

Elettro, Hervé 24 July 2015 (has links)
Cette thèse a visé à comprendre et à recréer artificiellement un mécanisme d'auto-assemblage présent dans la soie d'araignée. Les gouttes de glue microniques qui existent sur la soie d'araignée dîte de capture servent à fournir à la toile ses propriétés adhésives. Ces gouttes jouent pourtant un autre rôle : elles améliorent grandement les propriétés mécaniques de la soie, et permettent de préserver l'intégrité structurelle de la toile. La localisation de l'instabilité de flambage au sein des gouttes de glue, site de surcompression par les ménisques capillaire, implique que ce système de gouttes sur fibre se comporte sous compression comme un liquide, alors que sous tension il possède un régime solide. Les araignées ont donc trouvé un moyen de créer des hybrides mécaniques liquide-solide.La première partie de ma thèse fut dédiée à la caractérisation d'échantillons naturels, qui a permis dans la seconde partie de construire un système entièrement artificiel qui reproduit la soie d'araignée de capture, grâce à des microfibres flexibles longues de plusieurs centimètres. Une simple goutte de liquide mouillant permet la création efficace d'un système semblable aux échantillons naturels. La caractérisation fine de ces systèmes de gouttes sur fibre enroulables a mené à un très bon accord entre les résultats expérimentaux, les simulations numériques et une analogie avec les transitions de phase, notamment pour des propriétés telles que le seuil d'activation, l'existence d'une hystérésis ou encore la morphologie de l'enroulement. Ces résultats ont permis la conception de techniques non conventionnelles dans des domaines tels que les méta-matériaux et la micro-fabrication. / This PhD work aimed to understand and recreate artificially a self-assembling mechanism involving capillarity and elasticity present in spider silk. The primary function of the micronic glue droplets that exist on spider capture silk is to provide the spider web with adhesive properties. These droplets play yet another role: the dramatic enhancement of silk mechanical properties, as well as the preservation of the integrity of the web structure. The localization of the buckling instability within the glue droplets, site of over-compression due to the capillary meniscii implies that under compression this special drop-on-fibre system behaves like a liquid, whereas under tension it has a classical elastic spring regime. Spiders have thus found a way to create liquid-solid mechanical hybrids.The first part of my thesis aimed to the characterization of natural samples, which allowed in the second part to build a completely artificial system that mimics the natural samples, through fabrication of centimeter-long micronic soft fibres. The simple addition of a wetting liquid droplet made for an effective system with mechanical properties quantitatively close to that of spider capture silk.Fine characterization of the created drop-on-coilable-fibre systems yielded very good agreement between experimental results and predictions from numerical simulations and a analogy with phase transition, especially for properties such as the threshold for activation, the existence of an hysteresis and the coiling morphology. All those results added up to the design of unconventional techniques in field such as metamaterials and micro-fabrication.
154

Silk fibroin biomaterials for skin tissue engineering applications

Hodgkinson, Tom January 2014 (has links)
The limited reparative capacity of the skin and the inadequacy of conventional treatments have necessitated the development of tissue engineered skin substitutes. Several substitutes, including Integra Dermal Regeneration Template, are finding increasingly widespread application in the treatment of acute and chronic wounds. To date, these substitutes are unable to fully recreate the functionality and aesthetics of skin prior to injury. This thesis applied an integrated approach combining solution preparation, material fabrication control and biological testing to investigate electrospun silk fibroin (SF) nano-microfibrous scaffolds as potential biomimetic skin substitutes. Further to this, the improvement of the existing Integra scaffold through the incorporation of hyaluronan (HA) was assessed. Through rheological analysis of regenerated SF solutions under shear and extensional deformation a concentration regime transition at 20 wt% SF was identified. Solutions with relaxation times under 0.001 seconds were found to be unsuitable for electrospinning. The incorporation of poly(ethylene oxide) (PEO) was found to significantly increase solution relaxation times and extensional viscosity, making them much more suitable for electrospinning. Solution viscoelastic properties were shown to directly influence electrospun fibre morphology, with increases in viscosity resulting in increases in fibre diameter under stable spinning conditions. The effects of electrospinning parameters on electrospun fibre morphologies were investigated using SF-PEO blended solutions. Increased electrical field, spinneret height and decreased flow rate were found to decrease fibre diameter. In vitro assessment of the attachment, spreading, proliferation, viability and gene expression of primary human dermal fibroblasts (PHDFs) and bone marrow-derived mesenchymal stem cells (BM-MSCs) was conducted. Both PHDFs and BM-MSCs attached and proliferated with greater rapidity on fibres of the smallest diameters (~250-300 nm) with proliferation decreasing as fibre size increased until fibre diameters reached ~1200 nm. Cells were observed to be spread, with multiple attachments between fibres in scaffolds composed of ~250-300 nm diameter fibres. Cells aligned themselves to single fibres in scaffolds composed of fibres greater than 1 micrometre. HA supplementation to Integra resulted in increased proliferation, viability and migration of PHDFs. In ex vivo cutaneous wound healing models, the invasion of Integra was enhanced when scaffolds were supplemented with HA, with increased matrix deposition observed. Optimal supplementation concentrations for in vitro and ex vivo increases in cell proliferation and migration were at 1.5 – 2 mg ml-1 HA. SF electrospun scaffolds facilitated epithelial migration in ex vivo artificial wounds, with the migratory epidermis more closely resembling the structures observed in vivo. Additional preliminary investigations into the efficacy of a paste-form of Integra, Integra Flowable Wound Matrix (IFWM) were performed ex vivo, with cell invasion comparable to the conventional scaffold format. The potential for the incorporation of viable PHDFs and BM-MSCs was also investigated and keratinocyte migration was enhanced in these scaffolds. The results in this thesis provide valuable optimisation information on the development of SF electrospun scaffolds for skin engineering. Additionally, the supplementation of Integra with HA may provide a simple and effective way to enhance the performance of the scaffold in vivo.
155

Population genetic inference of demographic processes in the African Wild Silk Moth, Gonometa postica (Lasiocampidae)

Delport, Wayne 07 November 2006 (has links)
The African Wild Silk moths (Gonometa spp., Lasiocampidae) are species that are presently of particular economic interest in southern Africa. Both Gonometa postica and G. rufobrunnea, two species of African Wild Silk moth native to southern Africa, have been shown to possess a silk fibre of exceptional quality. A small-scale cottage industry utilizing the silk of Gonometa species currently exists in southern Africa, yet a consistent complaint is the lack of supply of cocoons. The Gonometa species in southern Africa have been shown to exhibit large inter-annual population fluctuations. However, it is uncertain whether eruptions are only the result of local populations experiencing ideal conditions or whether current eruptions are initiated by dispersal of individuals from eruptive populations in previous generations. A second observation, regarding eruptions, is that they are patchily distributed at both the local (within outbreaks) and regional scale (across southern Africa). In this thesis I have studied population eruptions through distribution analysis of three years of presence/absence data, and through spatial and temporal population genetic analysis. The analysis of population genetic data allows the inference of population demographic parameters such as population size fluctuations and migrations. In particular, the use of microsatellite markers allows a high-resolution analysis of the connectivity of populations, and provides signal of population size fluctuations. I utilise both mitochondrial DNA control region sequences and polymorphic microsatellite loci to make inferences of population processes in G. postica, using a combination of both analytical and simulation model analysis approaches. The results, in general, indicate that dispersal of moths across South Africa is extensive. These results are further considered in light of the effects of population size fluctuations on spatial genetic pattern, where the potential exists for unstable population demography to influence the inference of dispersal from population genetic data. The population genetic analyses presented here allow the inference of the extent of a local population/outbreak, and the degree of movement between local populations. Given that a large-scale population dynamics project based on G. postica is currently under development, the results determine the geographical extent at which the population dynamics study should be conducted. Furthermore, the population genetics data generated will contribute to the construction of a population dynamics model, including abiotic and biotic variables, which will allow a better understanding of eruptions in this species. / Thesis (PhD (Genetics))--University of Pretoria, 2006. / Genetics / unrestricted
156

Manufacture, analysis and conservation strategies for historic tapestries

Duffus, Philippa January 2013 (has links)
This project aimed to address the lack of research into the mechanical properties and degradation mechanisms for historical tapestries at the fabric level and understand how effective conservation support strategies can be in the preservation of these artifacts. The research incorporated a large range of techniques from diverse disciplines including weaving, ageing, computer modeling, biochemistry and conservation science. The successful manufacture and ageing of relevant samples provided an excellent opportunity to include testing of historical samples for comparison. Tensile testing of all samples provided a valuable insight into the characteristics of degraded historical samples compared to artificially aged samples. Although individual ageing processes – including UV ageing, Relative Humidity (RH) – thermal cycling and mechanical strain ageing produced a reduction in strength, the historical samples showed a far greater loss of strength due to the combination of all types of ageing in addition to handling and pollution damage. A proteomic analysis of the wool fibres resulted in a greater understanding of the degradative “dark” wool ageing process which suggests that wool yellowing and tendering can be produced not just through photo-chemical reaction. Additionally, the chemical analysis laid an important foundation for future research into linking chemical mechanisms of damage with mechanical loss of strength. Analysis using electron paramagnetic resonance spectroscopy (EPR) provided an insight into the free radical chemistry of a range of wool/wool samples. It was observed that the light aged samples produced thiyl radicals whereas thioperoxy radicals were seen in the heat-humidity aged samples. This implies separate chemical reactions occur to produce degradation in the different ageing regimes. EPR analysis of some historical samples produced a carbon-based radical peak linked to a soot calibration signal. Further research on historical samples found phenolic radicals, possibly linked to the complex dye chemistry. Further research needs to be undertaken to fully clarify these findings. A world-wide questionnaire to textile conservators has provided a useful resource in terms of a survey of methods and materials used across the world – including technical data as well as more “ethical” motivations for conservation. The results of this survey were used along with the physical data collated in the mechanical testing as information inputted into a finite element model (FEA) to undertake the digital modeling of a tapestry hanging under its own weight. Although more research is needed to fully develop this model, a preliminary investigation has been established which can be used in future research as a tool for textile conservators across the world.
157

Preparação e caracterização de membranas obtidas a partir de blendas de fibroína de seda e poli(álcool vinílico) / Preparation and characterization of membranes obtained by silk fibroin and poly(vinyl alcohol)

Marcelo Henrique Kravicz 10 June 2013 (has links)
A fibroína da seda (SF) é uma proteína fibrosa, com caráter hidrofóbico, produzida pelo bicho-da-seda (Bombyx mori L.), cuja produção e armazenamento ocorre em glândulas especializadas antes do processo de fiação em fibras. Recentemente, soluções de fibroína de seda regenerada (RSF) têm sido utilizadas para formar diferentes materiais tais como géis, membranas, filmes e esponjas, para aplicações médicas (Medicina Regenerativa) e em sistemas de liberação de fármacos. Neste trabalho, procuramos estudar o comportamento da solução RSF 2% com adição de 0,25, 0,5 e 1% de PVA (polímero sintético e hidrofílico) por meio de ensaios de reologia dos géis obtidos (SF:PVA), e caracterização das membranas obtidas por meio da secagem em moldes dos géis. Os ensaios de reologia mostraram uma inversão de módulos, com transição de caráter elástico (G\') para viscoso (G\") para SF1 a 3%, entre 230 e 900% de deformação (\'gama\'); transição de caráter viscoso para elástico para as blendas SF:PVA 0,5 e 1% em ensaio de frequência (\'ômega\'). Com o aumento de temperatura, todas as blendas mantiveram seus comportamentos elástico (SF:PVA 0,25%) e viscoso (SF:PVA 0,5 e 1%) até 49 - 51°C, com transição líquido-gel; o aumento dos módulos G\' e G\"com o resfriamento das amostras ocorreu em todas as blendas. As membranas obtidas das blendas SF:PVA tiveram maior absorção de tampão fosfato salino (PBS) após 5 min de ensaio, no qual a blenda SF:PVA apresentou maiores valores de absorção. A caracterização das membranas por FT-IR ATR e DRX mostrou que ocorreu uma transição de conformação aleatória e hélice \'alfa\' para folha \'beta\', para todas as membranas, indicando que a adição do PVA nas blendas promoveu transições silk I para silk II. Deslocamentos de modo vibracional de 1.637/cm (amida I) para 1.616/cm (amida I) com modo centrado em 1.512/cm (amida II) foram vistos em todas as blendas no FT-IR ATR, e difratogramas apresentaram picos característicos às estruturas silk I (2\'teta\' = 10,12º, 2\'teta\' = 12,2° e 2\'teta\' = 28,2º) e silk II (2\'teta\' = 20 - 21 °1). TGA e DSC mostraram uma interação entre as cadeias de RSF c PVA, pela presença de uma temperatura única ele transição vítrea (Tg) entre RSF e PVA. Imagens AFM das blendas mostraram a presença de estruturas nanofibrilares, em formato de ilhas compactas e ramos, confirmando a transição da fase amorfa de SF 2% para hélice \'alfa\' e folha \'beta\', com a adição do PVA. / Silk fibroin (SF) is a fibrous hydrophobic protein produced by silkworms (Bombyx mori L.), which production and storage occur into specialized glands previously fiber formation. Lately, regenerated silk fibroin (RSF) solutions have been used to produce different materials such as gels, membranes, films and sponges, for medical applications and drug delivery systems. In this study, the RSF with 0.25, 0.5 anel 1% PVA (synthetic and hydrophilic polymer) blends were characterized by rheological tests of the gels (SF:PVA), also membranes produced by casting process were characterized as well. Rheological tests showed moduli inversion with elastic to viscous behavior transition for SF 1 to 3%, between 230 anel 900% of strain (\'gama\'); a transition fram viscous to elastic behavior to SF:PVA 0.5 to 1% blends into frequency sweep tests was observed. With the temperature increment, all blends have kept their viscous anel elastic behavior until 49 - 51°C, and a liquid-gel transition occurred in the SF:PVA 0.5 and 1% blends, as well as all moduli have increased with the cooling stage of the samples. All membranes had the highest buffer absorption after 5 min of test, in which SF:PVA 0.5% blend presented high absorption values. FT-IR spectra and XRD diffractograms showed a transition from random and \'alfa\'-helix to \'beta\'-sheet, for all blends, indicating that PVA addition promotes silk I to silk II transition. Modal shifts were observed from 1.637/cm (amide I) to 1.616/cm (amide I) with a central mode in 1.512/cm (amide II) in all blends in the FT-IR ATR spectra. XRD diffractograms showed characteristic peaks of silk I structures (2\'teta\' = 10,12°, 2\'teta\' = 12,2° e 2\'teta\' = 28,2°) and silk II structures (2\'teta\' = 20 - 21 °1). TGA and DSC studies showed the possibility of interaction between SF and PVA chains by acquirement of mobility at once, at an intermediate temperature between SF anel PVA glass transition (Tg). AFM images exhibited different phases for all membranes, with the presence of nanofibers, wires, rods and branch islands, suggesting the formation of more organized structures, such as and \'alfa\'-helix and \'beta\'-sheet, with PVA addition.
158

Enzymatic Post-Translational Halogenation for Adding Functionality to Biomaterials

Compean, Alexander L. 24 August 2021 (has links)
No description available.
159

Biological and bioinspired photonic materials: From butterfly wings and silk fibers to radiative-cooling textiles and object-recognition smart glass

Tsai, Cheng-Chia January 2022 (has links)
Biological organisms, organs and tissues have evolved through natural selection diverse functional and structural traits to accomplish complex tasks. For example, small insects with tiny thermal capacitance have developed tailored spectral properties and behavioral tactics to mitigate rapid changes of body temperatures caused by environmental electromagnetic radiations; neural networks in the brain, through changing the efficacy of synapses, can recognize hidden patterns and correlations in raw data, cluster and classify them, and continuously learn and improve over time. These biological systems are a rich source of bio-inspiration for developing solutions to address engineering challenges. My thesis work focuses on the intersection between photonics and biology and explores three unique biological systems and their technological implications. Beginning with the investigation of butterfly wings, we observed that the wings contain a matrix of living structures, including mechanical and thermal sensory neural cells, hemocytes, pheromone producing organs, , and even “wing hearts”, and that these living structures carry out their specific functions over the entire life span of butterflies but are vulnerable to sustained high temperatures. We discovered that butterflies have evolved heterogeneously thickened wing cuticles and special nanostructured wing scales to locally enhance thermal emissivity so that the regions of the wings containing living structures can better dissipate heat through thermal radiation. Furthermore, we discovered that butterfly wings almost always possess enhanced reflectivity in the near-infrared, which can significantly reduce heating caused by solar radiation. This enhanced near-infrared reflectivity is found to originate from optical scattering at the porous wing scales, especially pale-colored scales underneath the surface layer of colorful ones. Besides these structural adaptations, our bioassays showed that butterflies utilize a number of behavioral strategies to avoid overheating or overcooling of their wings. We found that butterflies can use their wings as a fast and sensitive temperature monitor to detect the direction and strength of sunlight or artificial light applied onto the wings; as such, they can adapt the most suitable postures to minimize overheating of the wings if the illumination is too strong and to warm up the wings when ambident temperatures are insufficient for taking flight. Drawing inspiration from the multi-layered wing scales, which impart coloration to the wings while maintaining their high near-infrared reflectivity, we developed a double-layered, radiative-cooling coating that is able to minimize solar heating while still stay colorful. The second part of my thesis work explored nanostructured fibers and textiles as a novel solution for radiative cooling. The work was motivated by our discovery that the silk fibers produced by the caterpillars of the Madagascan moon moth (Argema mittrei) contain a high density of filamentary air voids, which enable individual fibers of the moth to strongly reflect light over the solar spectrum. This, in combination with natural polymers’ intrinsic high mid-infrared emissivity, provides the cocoons of the moth with remarkable passive radiative-cooling properties. We developed fabrication platforms to produce synthetic fibers with filamentary air voids by modifying both wet spinning and melt extrusion techniques. The melt extrusion approach, in particular, is implemented in an industry-scale fiber extrusion machine for high-throughput, high-yield production. The fabricated nanostructured fibers reproduce the prominent solar reflectivity of the Madagascan moon moth silk fibers and possess high emissivity due to the variety of chemical bonds in the synthetic polymers used. The melt-extruded fibers were twisted into yarns, which were subsequently woven and knitted into fabrics. The finished fabric samples were demonstrated to perform as effective radiative cooling devices compared to conventional white fabrics. Lastly, inspired by how neural networks in the brain form the basis of learning and motivated by how artificial neural networks are implemented in computers, we develop a novel platform of optical neural computing, a smart glass, for object recognition. Our optical neural network takes advantage of strong light-matter interactions with sub-wavelength resolutions in metasurfaces to emulate the layered computations in a biological or artificial neural network. In the simplest implementation of a single-layer smart glass, a metasurface was trained to provide 2D phase modulations that can transform the complex optical wave scattered from an input object into a characteristic intensity distribution pattern on the output plane corresponding to the identity of the object. We experimentally demonstrated the recognition of handwritten numerical digits and letters with different fonts with high accuracies using the smart glass and explored the capability of a polarization-multiplexing smart glass based on birefringent metasurfaces for performing distinct recognition tasks at orthogonal incident polarizations. This optical neural computing platform represents a new paradigm of computation operating at the speed of light with no power consumption and this physical-wave-based computation guarantees data security beyond digital encryption.
160

Promoting digital authoritarianism : A study of China’s Digital Silk Road

Wahlberg Scott, Andrea January 2021 (has links)
China’s influence is increasing steadily in all corners of the world. One of China’s foreign policy goals is to become a technological superpower by 2025. An important part of that goal is the Digital Silk Road (DSR), a sub-project to China’s massive infrastructure project, the Belt and Road Initiative. The DSR is on one hand contributing to positive technological developments, especially in developing countries. But on the other hand, it has gotten substantial criticism for being a front for spreading China’s digital authoritarian model and for giving authoritarian regimes the tools to effectively repress citizens and violate human rights. The aim of this study is twofold. The first aim is to examine and map out how China might be promoting autocracy through the DSR, this will contribute to a deeper empirical understanding. The second aim is to give a theoretical contribution by categorizing autocracy promotion and testing the value of active and passive autocracy promotion in relation to China and the DSR. To conduct the analysis, I will draw on literature about autocracy promotion and digital authoritarianism. The existing literature is divided on whether or not China is promoting autocracy, and I will thus be arguing that technological advances, and the DSR, makes it problematic to claim that China is not engaged in autocracy promotion. Therefore, I seek to contribute to the existing literature. The results show that China is in fact involved in autocracy promotion through the different DSR projects. It also shows that China’s support, in some cases, have been crucial in providing authoritarian regimes with repressive technologies. The results also indicate that promoting autocracy might not be an outspoken goal or strategy from China, but rather an unintended consequence when trying to reach domestic political and economic goals.

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