6,497 research outputs found
Comedians without a Cause: The Politics and Aesthetics of Humour in Dutch Cabaret (1966-2020)
Comedians play an important role in society and public debate. While comedians have been considered important cultural critics for quite some time, comedy has acquired a new social and political significance in recent years, with humour taking centre stage in political and social debates around issues of identity, social justice, and freedom of speech. To understand the shifting meanings and political implications of humour within a Dutch context, this PhD thesis examines the political and aesthetic workings of humour in the highly popular Dutch cabaret genre, focusing on cabaret performances from the 1960s to the present. The central questions of the thesis are: how do comedians use humour to deliver social critique, and how does their humour resonate with political ideologies? These questions are answered by adopting a cultural studies approach to humour, which is used to analyse Dutch cabaret performances, and by studying related materials such as reviews and media interviews with comedians. This thesis shows that, from the 1960s onwards, Dutch comedians have been considered âprogressive rebelsâ â politically engaged, subversive, and carrying a left-wing political agenda â but that this image is in need of correction. While we tend to look for progressive political messages in the work of comedians who present themselves as being anti-establishment rebels â such as Youp van ât Hek, Hans Teeuwen, and Theo Maassen â this thesis demonstrates that their transgressive and provocative humour tends to protect social hierarchies and relationships of power. Moreover, it shows that, paradoxically, both the deliberately moderate and nuanced humour of Wim Kan and Claudia de Breij, and the seemingly past-oriented nostalgia of Alex Klaasen, are more radical and progressive than the transgressive humour of van ât Hek, Teeuwen and Maassen. Finally, comedians who present absurdist or deconstructionist forms of humour, such as the early student cabarets, Freek de Jonge, and Micha Wertheim, tend to disassociate themselves from an explicit political engagement. By challenging the dominant image of the Dutch comedian as a âprogressive rebel,â this thesis contributes to a better understanding of humour in the present cultural moment, in which humour is often either not taken seriously, or one-sidedly celebrated as being merely pleasurable, innocent, or progressively liberating. In so doing, this thesis concludes, the âdarkâ and more conservative sides of humour tend to get obscured
'Exarcheia doesn't exist': Authenticity, Resistance and Archival Politics in Athens
My thesis investigates the ways people, materialities and urban spaces interact to form affective ecologies and produce historicity. It focuses on the neighbourhood of Exarcheia, Athensâ contested political topography par excellence, known for its production of radical politics of discontent and resistance to state oppression and eoliberal capitalism. Embracing Exarcheiaâs controversial status within Greek vernacular, media and state discourses, this thesis aims to unpick the neighbourhoodsâ socio-spatial assemblage imbued with affect and formed through the numerous (mis)understandings and (mis)interpretations rooted in its turbulent political history. Drawing on theory on urban spaces, affect, hauntology and archival politics, I argue for Exarcheia as an unwavering archival space composed of affective chronotopes â (in)tangible loci that defy space and temporality. I posit that the interwoven narratives and materialities emerging in my fieldwork are persistently â and perhaps obsessively â reiterating themselves and remaining imprinted on the neighbourhoodâs landscape as an incessant reminder of violent histories that the state often seeks to erase and forget. Through this analysis, I contribute to understandings of place as a primary ethnographic âobjectâ and the ways in which place forms complex interactions and relationships with social actors, shapes their subjectivities, retains and bestows their memories and senses of historicity
GENDERED EMBODIMENT, STABILITY AND CHANGE: WOMENâS WEIGHTLIFTING AS A TOOL FOR RECOVERY FROM EATING DISORDERS
This thesis explores the everyday embodied experiences of women who use amateur weightlifting as a vehicle for recovery from eating disorders. Within online spaces and on social media, women frequently share their experiences of using weightlifting to overcome issues relating to disordered eating, body image, and mental health. In particular, women with a history of eating disorders credit weightlifting to be integral to their recovery journey. However, there is a dearth of research on womenâs experiences with exercise during eating disorder recovery and no research that identifies weightlifting as beneficial to this process. To the contrary, discursive links are drawn between the practices of self-surveillance exercised by both eating disorder sufferers and weightlifters alike. In this regard, engagement with weightlifting during eating disorder recovery may signal the transferal of pathology from one set of behaviours to another. That is, from disordered eating to rigid and self-regulatory exercise routines. This thesis examines how women subjectively navigate and make sense of this pathologisation.
The data for this research comes from longitudinal semi-structured interviews and photo elicitation with 19 women, living in the United Kingdom, who engaged in weightlifting during their eating disorder recovery. In addition, to build up a holistic picture and to explore how this phenomenon also âtakes placeâ online, I conducted a netnography of the overlapping subcultures of female weightlifting and eating disorder recovery on Instagram. Womenâs standpoint theory and interpretative phenomenological analysis are combined to form the underpinning theoretical and analytical tools used to engage with these three rich data sets. Moreover, throughout I draw on an eclectic range of disciplinary perspectives, in order to bring together multiple fields of research and develop novel theoretical frameworks.
In the findings, I argue that womenâs experiences using weightlifting as a tool for recovery from eating disorders manifests in an embodied sense of multiplicity. In this sense, understandings of the body that are often viewed as ontologically distinct (muscularity/thinness/fatness) hang-together at once in the lived experience of a single individual.
I argue that women, particularly those who have previously struggled with an eating disorder, are too readily positioned as vulnerable to media and representation. To theoretically combat these ideas regarding womenâs assumed passivity, I develop the concept of âdigital pruningâ to account for womenâs agency in relation to new media.
I contend that weightlifting offers women in recovery from eating disorders a new framework for approaching eating and exercise. Specifically, weightliftingâs norms and values legitimate occupying a larger body, which gives women in recovery permission to eat and gain-weight in a way that is both culturally sanctioned and health-promoting.
Finally, I explore identity transformation as a specific tenet of recovery from eating disorders. I argue that, on social media, recovery identities are characterised by personal empowerment, resilience, and independence. While offline, quieter and less culturally glorified aspects of recovery (such as relationships of care) are central to womenâs accounts of developing a new sense of self as they transition away from an eating disorder identity.
In summary, this thesis is an examination of the ways in which women strategically navigate pathology in relation to their bodies, social media, food/exercise practices, and identity. I argue that women develop a set of âDIYâ recovery practices that allow them to consciously channel and draw on their negative experiences with eating disorders, to develop new ways of living that serve their overall wellbeing. Weightlifting is integral to this process, as it provides women transitioning out of this difficult phase in their lives with new ways of relating to their bodies and of being in the world. I situate this phenomenon within a neoliberal socio-political climate in which individuals are required to take personal responsibility for their mental health and wellbeing, despite living within conditions which are not conducive to recovery
The Role of Transient Vibration of the Skull on Concussion
Concussion is a traumatic brain injury usually caused by a direct or indirect blow to the head that affects brain function. The maximum mechanical impedance of the brain tissue occurs at 450±50 Hz and may be affected by the skull resonant frequencies. After an impact to the head, vibration resonance of the skull damages the underlying cortex. The skull deforms and vibrates, like a bell for 3 to 5 milliseconds, bruising the cortex. Furthermore, the deceleration forces the frontal and temporal cortex against the skull, eliminating a layer of cerebrospinal fluid. When the skull vibrates, the force spreads directly to the cortex, with no layer of cerebrospinal fluid to reflect the wave or cushion its force. To date, there is few researches investigating the effect of transient vibration of the skull. Therefore, the overall goal of the proposed research is to gain better understanding of the role of transient vibration of the skull on concussion. This goal will be achieved by addressing three research objectives. First, a MRI skull and brain segmentation automatic technique is developed. Due to bonesâ weak magnetic resonance signal, MRI scans struggle with differentiating bone tissue from other structures. One of the most important components for a successful segmentation is high-quality ground truth labels. Therefore, we introduce a deep learning framework for skull segmentation purpose where the ground truth labels are created from CT imaging using the standard tessellation language (STL). Furthermore, the brain region will be important for a future work, thus, we explore a new initialization concept of the convolutional neural network (CNN) by orthogonal moments to improve brain segmentation in MRI. Second, the creation of a novel 2D and 3D Automatic Method to Align the Facial Skeleton is introduced. An important aspect for further impact analysis is the ability to precisely simulate the same point of impact on multiple bone models. To perform this task, the skull must be precisely aligned in all anatomical planes. Therefore, we introduce a 2D/3D technique to align the facial skeleton that was initially developed for automatically calculating the craniofacial symmetry midline. In the 2D version, the entire concept of using cephalometric landmarks and manual image grid alignment to construct the training dataset was introduced. Then, this concept was extended to a 3D version where coronal and transverse planes are aligned using CNN approach. As the alignment in the sagittal plane is still undefined, a new alignment based on these techniques will be created to align the sagittal plane using Frankfort plane as a framework. Finally, the resonant frequencies of multiple skulls are assessed to determine how the skull resonant frequency vibrations propagate into the brain tissue. After applying material properties and mesh to the skull, modal analysis is performed to assess the skull natural frequencies. Finally, theories will be raised regarding the relation between the skull geometry, such as shape and thickness, and vibration with brain tissue injury, which may result in concussive injury
Contribution of non-canonical DNA G-quadruplex structures to premature ageing
Previous studies have identified Cockayne Syndrome B (CSB) as a helicase that can resolve non-canonical DNA structures, called G-quadruplexes (G4s). The aim of this study is to investigate the properties of CSB as a G4-binder and -resolvase, and examine the correlation between the G4-helicase activity of CSB and premature ageing phenotype observed in CSB-deficient cells. Accordingly, the recombinant CSB full-length protein (FL) and its helicase- âlike" domain (HD) were respectively expressed from insect and bacterial cells, and their resolvase and binding activities were tested over a large panel of DNA substrates. Native gel analysis and biophysical characterisations revealed that ribosomal DNA (rDNA) sequences, that typically act as CSB substrate, can form intermolecular G4s. We discovered that intermolecular G4s were strongly bound by CSB with picomolar affinity, whilst negligible binding to intramolecular G4s was observed. In vitro and cellular data demonstrated that G4-ligands can compete with CSB for binding to intermolecular rDNA G4, which results in CSB being displaced off the nucleoli of cells upon treatment with G4-ligands. Immunostaining with the selective G4-antibody BG4 revealed a lack of BG4-staining in the nucleoli of CSB-deficient cells after exogenous expression of recombinant CSB, further corroborating the hypothesis that CSB can bind intermolecular rDNA G4s in the nucleoli and compete with BG4 for the binding of such DNA-substrate. The work presented in this thesis allowed us to observe that (I) intermolecular G4s are likely to form from long-range distant rDNA sequences within the nucleoli of cells, and (II) CSB specifically binds and resolves these structures. Our results provide the first evidence of an endogenous protein that specifically interacts with intermolecular G4s, suggesting potential biological significance of these structures. The biological relevance of intermolecular rDNA G4s could be key in rare genetic disorders like Cockayne Syndrome, where senescence and premature ageing is observed when CSB is functionally mutated.Open Acces
II tĂŒĂŒpi kollageeni neoepitoop C2C uriinis kui pĂ”lve osteoartriidi diagnoosimise ja kulu prognoosimise biomarker
VĂ€itekirja elektrooniline versioon ei sisalda publikatsiooneOsteoartriit (OA) on sagedasim liigeshaigus, tabades ligi poolt miljardit inimest maailmas. PĂ”lv on ĂŒks peamisi kahjustuskohti. Haiguse kaasaegse kĂ€sitluse jĂ€rgi arenevad kahjustused molekulaarsetest muutustest kuni kudede (kĂ”hr, luu, sĂŒnoviaalkest, menisk, sidemed) struktuuri muutusteni. OA on aastate jooksul ebaĂŒhtlase kiirusega sĂŒvenev haigus, mille puhul stabiilsemad perioodid vahelduvad kiiremate muutustega, kulgedes varajases jĂ€rgus haigustunnusteta. SeetĂ”ttu pakuvad kudede ainevahetuse muutusi peegeldavad molekulaarsed markerid varajast hoiatust koekahjustuse tekkest, vĂ”imalust hinnata haiguse kulgu ning tulevikus ka ravivastust. Kuna II tĂŒĂŒpi kollageen (Kol2) on kĂ”hre peamine struktuurne komponent, on OA hindamiseks loodud mitmeid Kol2 lammutamist mÔÔtvaid teste. KĂ€esolevas uurimuses hindasime OA uue biomarkeri, uC2C kasutusvĂ”imalusi pĂ”lve OA (pOA) korral. uC2C on Kol2 lĂ”hustumise neoepitoop C2C uriinis. VĂ”rdlesime uC2C vÀÀrtusi röntgenleiu, kĂ”hre otsese vaatlusleiu ja patsiendi kliinilise seisundiga, kasutades erinevaid statistilisi mudeleid. Selgus, et uC2C on sobiv kandidaat pOA varajase diagnostilise testi arendamiseks. C2C sisaldus tĂ”useb juba haiguse varajases jĂ€rgus ja on seotud haiguse mitme pĂ”hiprotsessiga: kĂ”hre lammutamise ja luukasviste tekkega pĂ”lveliigese eri osades. uC2C on hea progressioonimarker naistel: uC2C kĂ”rgem algvÀÀrtus ennustab naistel vĂ€ga hĂ€sti (>90%) pOA teket vĂ”i sĂŒvenemist jĂ€rgneva 3 aasta jooksul. uC2C tase on kĂ”rgem suuremate röntgenmuutuste korral, seega uC2C tase on seotud pOA raskusastmega. uC2C vÀÀrtused on suurimad kOA lĂ”ppjĂ€rgus olevatel haigetel, kes jĂ”uavad liigeseasenduseni suhteliselt noorelt (50â70 a vanuses). PĂ€rast pĂ”lveliigese asendamist vĂ”ib C2C eritumine uriiniga vĂ€heneda, suureneda vĂ”i jÀÀda muutumatuks. Seega ei peata liigeseasendus paljudel juhtudel Kol2 lammutamist organismis ja OA on sĂŒsteemsem haigus, kui on seni arvatud. uC2C nĂ€ib olevat naistel vĂ”rreldes meestega parem pOA biomarker.Osteoarthritis (OA) is the most common joint disease, affecting about half a billion people worldwide. The knee is one of the main sites of impairment. According to the new approach to the disease, the alterations develop from the molecular level to structural changes in tissues (cartilage, bone, synovium, meniscus, ligaments). OA is a disease with an alternating course, with no signs of disease at an early stage. Therefore, molecular markers that reflect changes in tissue metabolism provide an early warning of tissue damage, an opportunity to assess the course of the disease, and a response to future treatment. Because type II collagen (Col2) is a major structural component of cartilage, several tests have been developed to measure Col2 degradation. In the current study, we evaluated the potential use of a new OA biomarker, C2C, in knee OA (kOA). uC2C is a Col2 cleavage neoepitope in urine. We compared uC2C values with X-ray findings, direct visual assessment of cartilage, and clinical status using different statistical models. uC2C is a good candidate for the development of an early diagnostic test for kOA. The level of uC2C is increased in the early stages of kOA and is related to several main processes of kOA: the cartilage lesions and the osteophytes in distinct knee compartments. uC2C is a good marker of progression in womenâa higher baseline uC2C is an excellent predictor (> 90%) of the initiation or worsening of kOA over the next 3 years. uC2C is higher in higher X-ray grades, so uC2C levels are associated with the severity of kOA. uC2C values are highest in patients with end-stage kOA who reach joint replacement at a relatively young age (50-70 years). After knee replacement, urinary excretion of C2C may decrease, increase, or remain unchanged. Thus, in many cases, joint replacement does not stop the breakdown of Col2 in the body, and OA is a more systemic disease than previously thought. uC2C appears to be a better biomarker of pOA in women than in men.https://www.ester.ee/record=b550707
Characterisation of the unfolded protein response in prostate cancer, and investigation of the ATF6 interactome using a modified mammalian expression system.
Prostate cancer (PCa) cells grow in an environment which is known to cause endoplasmic reticulum (ER) stress. This activates a process called the unfolded protein response (UPR) which PCa utilises in order to survive and adapt to the adverse environmental conditions. Using interdisciplinary approaches and tissue culture models representing different stages of PCa, this project investigated the link between the UPR and the key oncogenic driver of PCa, the androgen receptor. It has been observed that hormone responsive PCa utilises all three UPR arms in order to promote ER homeostasis and cell survival. The importance of the UPR during the progression of PCa to the castrate resistant stage was also assessed. Interestingly, UPR signalling was inactivated in castrate-resistant models of PCa, and the cells were instead dependent on the ER-associated degradation (ERAD) pathway in order to resolve the stress and survive. These findings have identified potential UPR vulnerabilities that can be targeted to prevent disease progression.
Little is known about the structure and interaction partners of the UPR sensor ATF6, as protein expression has been shown to be problematic. To resolve this issue a stable tetracycline-inducible HEK293S GnTI(-) cell line for the expression of ATF6 was generated and mass spectrometry performed to characterise the ATF6 interactome. Sixty novel interaction partners of ATF6 were identified, most of which are associated with the cytoskeleton, such as Spectrin ÎČ-II and p195, which were validated by immunoblotting. It is hoped that the use of this modified expression system will provide an advantage in the process of expression, solubilisation and structure determination of ATF6 and of other membrane proteins
Multifunctional Lightweight Structures of Silicon Carbide Nanowires
Silicon carbide (SiC) as a type of ceramic material possesses unique properties such as high hardness, good high temperature strength, and excellent oxidation resistance. However, the intrinsic shortcomings of ceramic-based materials, such as high brittleness, low recoverable compressibility, and low fatigue resistance, prevent their utilisations as structural or functional components. To overcome these issues, highly porous lightweight and flexible SiC ceramics constructed by nanowires are promising alternatives for advanced engineering applications. The aim of this thesis is therefore to fabricate highly porous lightweight and flexible SiC nanowire structures by three novel approaches: (1) in-situ chemical-blowing; (2) melamine foam-based replica template; (3) electrospinning and explore their properties towards different applications.
The overview, including the aims and objectives of this thesis is outlined in Chapter 1. The existing knowledge about lightweight SiCNW structures including crystallography, synthesis approaches, physical properties (mechanical strength, thermal conductivity, high temperature stability), and well-developed energy and environment-related applications (piezoresistive sensors, catalyst support, absorbers, and filters) is documented in Chapter 2. The generic information of the starting materials, synthesis techniques, equipment, and method used for the fabrication of 3D SiCNW structures, characterisation of their microstructural features, and evaluation of the various aspects of their multifunctionalities is descripted in Chapter 3. To identify suitable techniques to assemble SiC nanowires (SiCNWs) into 3D architectures, Chapter 4 provides a selection of advanced manufacturing approaches for lightweight SiCNW structures with easy and precise control of the overall shape and growth of SiCNWs. Followed with the demonstration of the exciting properties of the as-obtained three SiCNW structures including mechanical properties, thermal insulation performance, thermo-oxidation resistance, and fire-retardance in Chapter 5. Finally, based on their own characteristics, the applications of the SiCNW structures such as piezoresistive sensors, catalyst support, and efficient absorbents for oil and organic solvents are present in Chapter 6. A guidance in the manufacturing of advanced ceramic nanowire structures with desired microstructures and properties tailored for specific applications will be eventually provided.
I first demonstrated the creation of SiCNW sponges by a facile template/catalyst-free sugar-blowing technique, by reacting SiO2 with sustainable kitchen sugar, using NH4Cl as a blowing agent. The as-grown, highly porous SiCNW sponges exhibited a core-shell structure, the core part with a density of 115-125 mg cm-3 was comprised of short and tangled SiC whiskers with SiC flakes embedded, while the shell layer with an ultralow density of ~25 mg cm-3 consisted of numerous smooth SiCNWs. These sponges exhibited a compressive modulus of ~389 kPa, recoverability under cyclic compression loading for 100 cycles at a strain of 20% and a thermal conductivity of 42-92 mW m-1K-1.
Secondly, I reported the fabrication of SiCNW scaffolds with tuneable microstructures, densities, and therefore properties, by regulating the solid loading content in the reticulated melamine foam (MF) template. The resulting samples exhibited high strength (modulus up to ~167.3 kPa), good recoverability (11% residual strain and 72% maximum stress after 100 compressive cycles at a Δ = 20%), and low thermal conductivity of 32-54 mW m-1K-1.
Finally, I successfully created 3D SiCNW aerogels by using a Mille crĂȘpe stacking and sintering of the electrospun PAN/SiO2 fibres for the first time. The resulting aerogels made of interconnected SiCNWs displayed an ultralight density of 29 mg cm-3, excellent compressive recoverability and fatigue resistance. Meanwhile, the SiCNW aerogels exhibited a thermal conductivity of 24 mW m-1K-1, even lower than that of the air, suggesting its superinsulation capability. Benefitting from intrinsic properties of SiC, experimental results have shown that all the as-obtained SiCNW structures exhibited good thermal insulation performance, exceptional high-temperature stability, fire-retardance, and temperature-invariant elasticity.
Furthermore, I have explored the best-suited functional applications for each SiCNW structure. The SiCNW sponges and aerogels with better compressive recoverability and mechanical stability exhibited interesting electromechanical sensing capability. The sponge-based sensor exhibited a gauge factor up to 87 and stable wide-range compression-resistance responses. Whilst the aerogel-based strain sensor with higher recoverable strains presented stable sensing behaviour at different strains, frequencies, elevated temperatures over 200 °C and excellent repeatability over 2000 cycles.
Owing to the cellular structure with the co-existence of SiC nanowires and struts, good interconnectivity, and competent mechanical strength and stability, the SiCNW scaffolds demonstrated the exclusive suitability as excellent support for MOF-derived TiO2-C catalyst, with ~35% enhanced in-situ loading of the catalyst, enabling a superior photocatalytic performance and good repeatability for at least 3 cycles.
I further examined the SiCNW structures as organic solvent/oil absorbent. They exhibited rapid absorption of various organic solvents and oils. Typically, the SiCNW aerogels possess the highest absorption capacity of 32-86 g g-1, as well as robust recoverability. Meanwhile, the absorbed content can be easily removed by squeezing, distillation, and combustion, while the SiCNW structures remain unchanged. These features have shown that the SiCNW structures are promising for applications for the potential removal of chemical spills and oil leakage, with the advantage of easy recycling.
All these remarkable findings will not only provide an important opportunity to advance the understanding of lightweight SiCNWs structures and make original contributions to utilise them as multifunctional devices, but also bring us the new ways to reshape the manufacturing of porous ceramics for future energy and environment-related applications
Improved methods for characterising acoustoplasticity
The benefits of high-power ultrasonics to industrial metal forming processes have long been demonstrated in uniaxial mechanical tests. The astonishing reductions in flow stress observed have been linked to changes to surface friction and to an interaction of the excitation with the mechanisms of plastic deformation in metals. Many advanced techniques and material models have been brought to bear on the problem of the underlying physics of acoustoplasticity, and yet all rely fundamentally on accurate force and extension data. The effects of inertia and inhomogeneity in the loading distribution on the specimen have been largely ignored, and yet are incompatible with commonly used instrumentation.
This thesis reports investigations which address the error introduced into force measurement in mechanical testing by ultrasonic excitation. After reviewing experimental mechanics techniques, it was found that the piezoelectric force transducer retained its central role in defining true flow stress reduction. An inertia-based barrier to vibration was introduced between the force transducer and test machine crosshead, to impose the rigid boundary condition desired to ensure the force transducer coincided with a displacement node. Lumped-parameter modelling indicated that the dynamic response of the piezoelectric force transducerâs structure could significantly distort the amplitude of an oscillatory force measurand. Either amplification or attenuation could result depending on the proximity of excitation frequency to natural frequency of the force transducerâs first longitudinal mode. Simple impulse experiments provided the natural frequency of the force transducer in the free-free condition, a parameter used in later finite element (FE) modelling of the ultrasonic tensile test structure.
Experimental Modal Analysis (EMA) was used to investigate the dynamic response of the ultrasonic tensile test structure, and to map the mode shape of the first longitudinal mode, the mode utilised in ultrasonic tensile testing. A finite element model was constructed of the test apparatus, and subsequently solved in an eigenvalue analysis to extract the natural frequency and mode shape of the first longitudinal mode. When the numerically predicted waveform was compared with that found from EMA, a significant difference was discovered between the horn and specimen. The compliance of the joint was adjusted until the simulated mode shape converged on its experimental counterpart.
Once experimentally calibrated, the FE model was used to predict the force experienced by the force transducer for increasing values of vibration amplitude. Comparison with experimental force measurements found good agreement. Of greatest importance to the investigation of flow stress, the FE model predicted the indicated value from the force transducer to be 1.91 times greater than the measurand at the specimen-force transducer interface.
Strain gauges were attached to the gauge section of the specimen in the ultrasonic tensile test apparatus, and the vibration varied over a range of amplitudes. By converting the oscillatory strain measurement into force on the specimen cross-section, the loading experienced by the specimen at the strain gauge location was compared to force measurements made simultaneously by the piezoelectric force transducer. The ratio of force amplitude from the force transducer over the force amplitude calculated from the specimen strain measurement was found to vary from 3.13 to 3.50, with a mean of 3.32. Repeating the experiment within the FE model calculated an amplitude ratio of 3.33, constant over all vibration amplitudes. This value was used to develop a correction factor to extrapolate force on the specimen from piezoelectric force transducer measurement. The correction was applied to an ultrasonic tensile test on a soft aluminium. Though the mean stress was reduced during the periods of excitation, no real reduction in flow stress was observed, which is consistent with the theory of stress superposition.
The evolution of plastic deformation was studied over the gauge section of an ultrasonically excited specimen, using an optical metrology system adapted for use on the ultrasonic tensile test. To eliminate oscillatory motion from images, a high-speed strobe lit the specimen in bursts of light synchronised with the ultrasonic excitation. Digital Image Correlation was used to process the image sequence to find strain and strain rate across the whole face of the specimen gauge length. It was observed that the application of ultrasonic excitation disrupted the usual distribution of plastic deformation along the specimen length, focussing deformation towards the location of peak stress amplitude. Again, observations were consistent with the theory of stress superposition.
This thesis demonstrates how the dynamic response of the structure of the specimen and force transducer in an ultrasonic tensile test can significantly distort the force measurement, crucial for accurately identifying a real reduction in flow stress. This has implications for studies of acoustoplasticity aiming at determining underlying physical mechanisms. It is found that, when the effect of inertia is accounted for, the theory of stress superposition is sufficient to explain the stress-strain relationship observed
Stability, Electronic Structure, and Nonlinear Optical Properties in Clusters and Materials: A Synergistic Experimental-Computational Analysis
The main objective of Chemistry as a science is an understanding of how and why certain atoms are bonded together and what effects these bonds cause. Modern computational chemistry offers a wide range of tools that greatly assist the exploration of vast chemical space replacing expensive trial-and-error experimental approaches. Computational chemistry may serve to characterize newly synthesized compounds and provide atomic scale insights inaccessible to experimentalistsâ vision. Moreover, predictive power of computational chemistry may be used as a guidance for future experiments and for the rational design of new compounds with desired properties.
This dissertation demonstrates the capabilities of joint experimental and theoretical approaches in the characterization of atomic clusters. Bonding and stability analysis in such systems is crucial for understanding the relations between various atomic-scale changes and resulting alterations in chemical properties. This work also makes use of predictive power of modern theoretical methods to probe new chemical species with peculiar electronic properties. A common thread through the projects presented here has been a rationalization of size-and composition-dependent properties of chemical systems based on the analysis of their electronic structure. An essential part of this dissertation is the deciphering of electronic structure via chemical bonding analysis which helps explain various properties in a chemically intuitive manner
- âŠ