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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.
21

Mechanical Characterization of Patterned Silver Columnar Nanorods with the Atomic Force Microscope.

Kenny, Sean 30 April 2012 (has links)
Patterned silver (Ag) columnar nanorods were prepared by the glancing angle physical vapor deposition method. The Ag columnar nanorods were grown on a Si (100) substrate patterned with posts in a square “lattice” of length 1 μm. An electron beam source was used as the evaporation method, creating the deposition flux which was oriented 85˚ from the substrate normal. A Dimension Icon with NanoScope V controller atomic force microscope was used to measure the spring constant in 10 nm increments along the long axis of five 670 nm long Ag nanorod specimens. The simple beam bending model was used to analyze the data. Unexpected behavior of the spring constant data was observed which prevented a conclusive physically realistic value of the Young’s modulus to be calculated.
22

Přetvárné parametry brněnského téglu z malých deformací v trojosém přístroji / Stiffness anisotropy of Brno Tegel determined by continuous loading in triaxial tests

Mohyla, Tomáš January 2014 (has links)
This Thesis deals with the determination of Young's modulus and Poisson's ratio from the measurement of small strains (10-3 - 10-5 ) in triaxial tests on the overconsolidated Miocene clay from Moravia (Brno Tegel). The tests were performed in a hydraulic triaxial chamber, fitted with submersible local LVDT sensors, which were fixed directly on the sample. The tests were carried out on undisturbed samples of standard height and diameter (76x38 mm). There were three types of tests - isotropic loading probe, axial loading probe and shear test to the failure. The measured data were analyzed and the results were discussed. The research part of the Thesis briefly describes previous works on stiffness of Brno Tegel and also some works on stiffness of similar material to Brno Tegel - London Clay.
23

Flexo electro-optic liquid crystals for phase modulation

Nosheen, Shabeena January 2019 (has links)
Soft matter, self-assembled 3D photonic structures such as blue phase liquid crystals have of great interest to the displays industry and are highly desirable as spatial light modulators because of their polarisation independence and fast switching. However, these types of devices suffer from multistep fabrication conditions and require high threshold voltages. To overcome these limitations, two key points were considered: High flexoelectric liquid crystals are capable of uniform 3D self-assembly, with a wide temperature range but have high threshold voltages, whereas, other classes of high dielectric liquid crystals have fast electro-optic response times with low threshold voltages but show poor 3D self-assembly. In this work, new mixture formulations have been devised having both properties in moderation in order to achieve simple yet stable 3D self-assembled blue phases with fast response times at as low as possible applied fields. Dielectric materials were considered from a commercial source whereas, miscible flexoelectric soft materials were synthesised in-house. These synthesised materials were fully characterised. Then mixtures were formulated in commercial high dielectric hosts to study their miscibility, new mesogenic transitions and electro-optic responses in terms of flexoelectric and dielectric properties. The selected mixtures were further investigated for the rapid growth of blue phases and their compatibility with reactive mesogens to form stable blue phases at room temperature. This new formulation of materials has given rise to mixtures and devices which are inherently easy to fabricate allowing the robust and resilient growth of blue phases under an hour in standard laboratory conditions. Furthermore, polarisation independent electro-optic switching has been characterised at fields < 1V micron m-1. For phase modulation studies of these stabilised blue phase devices, phase shift was measured using a modified Young's slit interferometer. The observed results were very promising, with a full 2.5 pi phase shift observed at a field of 9.25 V micron m-1 when compared to earlier reported devices (which required complicated multistep fabrication processes) giving values of full 1.8 pi phase shifts at 20 V micron m-1.
24

SOBRE LOBOS, MENINAS E FLORESTAS: Literatura infantil/Juvenil e Valores Sociais / ABOUT WOLVES, GIRLS AND FORESTS: Child/Youth Literature and Social Values

Mabelini, Ecila Lira de Lima 25 June 2019 (has links)
Esta pesquisa tem como objetivo primeiro investigar as transformações nos textos literários para crianças e jovens, oriundos de mudanças nas relações sociais, e verificar em que medida a literatura infantil e mesmo a juvenil tem exteriorizado no seu universo textual novas maneiras de percepção sobre as narrativas primordiais ou clássicas, consolidadas como tal a partir do século XVII. Na contemporaneidade, sobretudo a partir da segunda metade do século XX no Brasil da releitura do novo texto infantil, observou-se que tais narrativas e seus valores outrora marcados pela presença de uma pedagogia altamente moralizante e excludente, agora reorganizam as estratégias de captação para retomar não só os clássicos ou histórias que caíram no gosto da criança e do jovem, no passado, mas ainda para atualizar narrativas capazes de fazer parecer serem outras, dado o novo arranjo da vestimenta destas novas histórias que intencionam, de modo significativo, evidenciar uma literatura com mais recursos de visualidade e plasticidade, bem como um modo de ser e de estar dessa nova criança e também do jovem num mundo de valores diversos, cujos reflexos corroboram um universo literário de atualizadas prescrições. Assim, tomou-se como corpora as obras Chapeuzinho Amarelo (2006), de Chico Buarque, ilustração de Ziraldo, Chapeuzinho Vermelho (1996), de Charles Perrault, Chapeuzinho Vermelho, dos Grimm (2009), Sapato de salto (2011), de Lygia Bojunga, Antecedentes de uma famosa história (2010), de Carolina Alonso, ilustração de Mariana Massarani, conto publicado em Não era uma vez: contos clássicos recontados coletânea de autores latino-americanos, A outra história de Chapeuzinho Vermelho (2016), de Jean-Claude R. Alphen, ilustrada pelo próprio autor e as intersecções forjadas no texto Preciosidade (1991), de Clarice Lispector, conto publicado em Laços de família. Para tal investigação, foram utilizados como fundamentação teórica elementos dos Estudos Comparados de Literatura, bem como de outras ciências da linguagem afins, além de estudos sobre a gênese e a História da Literatura Infantil e, posteriormente, a Juvenil. Com base em estudos já desenvolvidos sobre essa modalidade de textos, busca-se adentrar mais um pouco nessa floresta ainda vasta de textos que refletem valores humanos e sociais. / This research aims at investigating the transformations in literary texts for children and young people from social relations changes and at verifing the extent to which children\'s and still youth literature has externalized in their textual universe new ways of perception about primordial or classical narratives, consolidated as such from the seventeenth century. In contemporary times, the re-reading of the new children\'s text, especially since the second half of the twentieth century in Brazil, was observed that such narratives and their values were once marked by the presence of a highly moralizing and excluding pedagogy, now reorganize the capture strategies to resume not only the classics or stories that have fallen in the taste of the child and the youth in the past, but still to update narratives capable of making appear to be others, given the new arrangement of the \"clothing\" of these new stories that intend, in a significant way, a literature with more visuality features and plasticity, as well as a way of being of this new child and youth in a world of diverse values, whose reflections corroborate a literary universe of up-to-date prescriptions. Thus, it was taken as corpora the works Chapeuzinho Amarelo (2006), by Chico Buarque and illustrated by Ziraldo, Chapeuzinho Vermelho (1996), by Charles Perrault, Chapeuzinho Vermelho, by Grimm (2009), Sapato de salto (2011), by Lygia Bojunga, Antecedentes de uma famosa história (2010), by Carolina Alonso with illustration by Mariana Massarani, short story published in Não era uma vez: contos clássicos recontados - a collection of latin american authors, A outra história de Chapeuzinho Vermelho (2016), by Jean-Claude R. Alphen, illustrated by the author himself and the intersections forged in the text Preciosidade (1991), by Clarice Lispector, a tale published in Laços de Família. For this investigation, elements of Comparative Literature Studies, as well as other related language sciences and studies on the genesis and History of Children\'s and Juvenile Literature were used as theoretical basis. Based on studies already developed on this modality of texts, it aims at penetrating a little more in the still vast forest of texts that reflect human and social values.
25

MEMS-based Mechanical Characterization of Micrometer-sized Biomaterials

Kim, Keekyoung 24 September 2009 (has links)
The mechanical properties of biomaterials play important roles in performing their specialized functions: synthesizing, storing, and transporting biomolecules; maintaining internal structures; and responding to external environments. Besides biological cells, there are also many other biomaterials that are highly deformable and have a diameter between 1μm and 100μm, comparable to that of most biological cells. For example, many polymeric microcapsules for drug delivery use are spherical particles of micrometers size. In order to mechanically characterize individual micrometer-sized biomaterials, the capability of capturing high-resolution and low-magnitude force feedback is required. This research focuses on the development of micro devices and experimental techniques for quantifying the mechanical properties of alginate-chitosan microcapsules. The micro devices include microelectromechanical systems (MEMS) capacitive force sensors and force-feedback microgrippers, capable of measuring sub-μN forces. Employing the MEMS devices, systems were constructed to perform the micro-scale compression testing of microcapsules. The force sensors are capable of resolving forces up to 110μN with a resolution of 33.2nN along two independent axes. The force sensors were applied to characterizing the mechanical properties of hydrogel microparticles without assembling additional end-effectors. The microcapsules were immobilized by a PDMS holding device and compressed between the sensor probe and holding device. Young's modulus values of individual microcapsules with 1%, 2%, and 3% chitosan coating were determined through the micro-scale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate buffered saline (PBS). The Young's modulus values were also correlated to protein release rates. Instead of compressing the microcapsule against the wall of the holding device, a force-feedback MEMS microgripper with the capability of directly compressing the microcapsule between two gripping arms has been used for characterizing both the elastic and viscoelastic properties of the microcapsules during micromanipulation. The single-chip microgripper integrates an electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5nN) and the other for gripping force measurements (force resolution: 19.9nN). Through nanoNewton force measurements, closed-loop force control, and visual tracking, the system quantified the Young's modulus values and viscoelastic parameters of alginate microcapsules, demonstrating an easy-to-operate, accurate compression testing technique for characterizing soft, micrometer-sized biomaterials.
26

Breaking Glass: Exploring the Relationship Between Kinetic Energy and Radial Fracturing in Plate Glass

Hulman, Andrea 23 April 2012 (has links)
When glass breaks from the impact of an object, it exhibits a distinctive shattering pattern comprised of two different regions. This pattern was investigated using experimental impacts and predicted using Young’s Modulus. Results were not as expected, and it is likely that there exists error in some measurements. Further investigation of this topic is recommended.
27

MEMS-based Mechanical Characterization of Micrometer-sized Biomaterials

Kim, Keekyoung 24 September 2009 (has links)
The mechanical properties of biomaterials play important roles in performing their specialized functions: synthesizing, storing, and transporting biomolecules; maintaining internal structures; and responding to external environments. Besides biological cells, there are also many other biomaterials that are highly deformable and have a diameter between 1μm and 100μm, comparable to that of most biological cells. For example, many polymeric microcapsules for drug delivery use are spherical particles of micrometers size. In order to mechanically characterize individual micrometer-sized biomaterials, the capability of capturing high-resolution and low-magnitude force feedback is required. This research focuses on the development of micro devices and experimental techniques for quantifying the mechanical properties of alginate-chitosan microcapsules. The micro devices include microelectromechanical systems (MEMS) capacitive force sensors and force-feedback microgrippers, capable of measuring sub-μN forces. Employing the MEMS devices, systems were constructed to perform the micro-scale compression testing of microcapsules. The force sensors are capable of resolving forces up to 110μN with a resolution of 33.2nN along two independent axes. The force sensors were applied to characterizing the mechanical properties of hydrogel microparticles without assembling additional end-effectors. The microcapsules were immobilized by a PDMS holding device and compressed between the sensor probe and holding device. Young's modulus values of individual microcapsules with 1%, 2%, and 3% chitosan coating were determined through the micro-scale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate buffered saline (PBS). The Young's modulus values were also correlated to protein release rates. Instead of compressing the microcapsule against the wall of the holding device, a force-feedback MEMS microgripper with the capability of directly compressing the microcapsule between two gripping arms has been used for characterizing both the elastic and viscoelastic properties of the microcapsules during micromanipulation. The single-chip microgripper integrates an electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5nN) and the other for gripping force measurements (force resolution: 19.9nN). Through nanoNewton force measurements, closed-loop force control, and visual tracking, the system quantified the Young's modulus values and viscoelastic parameters of alginate microcapsules, demonstrating an easy-to-operate, accurate compression testing technique for characterizing soft, micrometer-sized biomaterials.
28

Effect of Fluid Flow on Tissue-Engineered Cartilage in a Novel Bioreactor

Gemmiti, Christopher V. 10 November 2006 (has links)
Due to its relative avascularity, low cellularity and lack of an undifferentiated cell reservoir, articular cartilage has a limited capacity for self-repair when damaged through trauma or disease. Articular cartilage impairment and the resultant reduced joint function affects millions of people at a substantial cost. In the U.S. alone, over 20 million adults are afflicted with osteoarthritis, costing more than $65 billion per year in health care and lost wages. Surgical techniques have been developed to address small, focal lesions, but more critical sized defects remain without a viable solution. Tissue engineering strategies produce cartilage-like constructs in vitro containing living cells in the hope of replacing damaged cartilage and restoring joint function. However, these constructs lack both sufficient integration into the surrounding tissue following implantation and the mechanical properties capable of withstanding the demanding and complex in vivo loading environment. Our central hypothesis is that exposure of engineered cartilage to fluid-induced shear stress increases the collagen content and mechanical properties (tensile and compressive). The overall objective of this project is to modulate the matrix composition and mechanical properties of engineered cartilage to be more like native tissue using a novel bioreactor. Improving the matrix components and mechanical stability of the tissue to be more similar to that of native tissue may aid in integration into a defect in vivo. The central hypothesis was proven in that shear stress potently altered the matrix composition, gene expression and mechanical properties of both thick and thin engineered cartilage. Modulation was found to be highly dependent on shear stress magnitude, duration, and waveform and affected different matrix constituents and mechanical properties in disparate ways. Our overall objective was satisfied on the basis that the bioreactor created stronger engineered tissues, but with the caveat that the tissues showed an increase in presence of type I collagen. Such an effect would be undesirable for articular cartilage engineered tissues, but could be very beneficial in fibrocartilaginous tissues such as that found in the temporomandibular joint. In conclusion, the novel bioreactor system provides a flexible platform technology for the study of three-dimensional engineered tissues, not just articular cartilage.
29

A comparative membrane surface analysis between two human hepatocarcinoma cell lines ( SK-HEP-1 and Hep G2 cells ) using Atomic Force Microscope

Li, I-Ting 03 September 2010 (has links)
Atomic force microscopy (AFM) can be used to acquire high-resolution topographical images of surfaces, but has the additional capability of detecting the local nanometer scale mechanical properties. For these reasons, it becomes a standard research tool in the surface science recently. In this paper, we used AFM to measure the several properties of two different human hepatocellular carcinoma cell lines, Hep G2 ( known as well differentiated and more highly carcinomatous hepatoma cell lines ) and SK-HEP-1 ( known as poorly differentiated and more lightly carcinomatous hepatoma cell lines ) cells fixed on the glass substrate, which including the surface morphology and the relationship between the cantilever deflections and loading forces ( force curve ). Considered the heterogeneous characteristics of the cell surface, the preferred experimental method is to make pixel-by-pixel force curves in a designated area ( force map ) , both adhesion forces and elasticity associated with different locations on the cell surfaces will be obtained. Finally, we use Hertzian model to calculate Young's modulus of Hep G2 and SK-HEP-1 respectively. Based on these results, we can understand the surface properties of two human hepatocarcinoma cell lines with different differentiated stage. The results showed the difference of the morphology, height, cell migration, degree of cell aggregation, roughness, elasticity, adhesive force of two cells. SK-HEP-1 cell has the wide distance of the folds, better cell migration, homogeneous properties of elasticity. It can be assumed that the SK-HEP-1 cells have a dense network structure of actin filaments under the cell membrane like branches (branched networks); Hep G2 cell has the narrow distance of the folds, poor cell migration, heterogeneous properties of elasticity. It can be assumed that the Hep G2 cells have the individual actin filaments and cross-linked network structure of actin filaments under the cell membrane. The above results can be speculated that the elastic properties of the membrane surface will be influenced of actin filaments.
30

The investigation of mechanical properties of ZrCu/Zr/ZrCu amorphous¡Ðcrystalline¡@nanolaminates with inclined interface by molecular statics simulation

Feng, Yu-ting 23 July 2012 (has links)
In this study, the mechanical properties of Cu-Zr binary bulk metallic glasses (BMG) were investigated at the nano-scale. The stable amorphous structures and corresponding energies of BMG structures are performed by density functional theory (DFT) calculation as reference data. This study will combine the Force-Matching (FM) method and Basin-Hopping (BH) method to develop a new method for fitting the Cu-Zr Tight-binding (TB) potential parameters. Moreover, the Bulk modulus, Shear modulus, Young's modulus and Poisson ratio of Cu46Zr54, Cu50Zr50 and Cu64Zr36 structures are calculated with the fitting TB parameters. In addition, the compression process of BMG materials is simulated by the Molecular Statics. The stress and strain are obtained to investigate the deformation mechanism of CuZr/Zr/CuZr nanolaminates at 0 and 45 inclined degree. Finally, we investigate the angle in the deformation process under different strain in the shear band, shear transformation zones (STZs) and force caused by the slip of the atomic distribution of TFMGs layer.

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