19,711 research outputs found

    Application of Multichannel Active Vibration Control in a Multistage Gear Transmission System

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    Gears are the most important parts of rotating machinery and power transmission devices. When gears are engaged in meshing transmission, vibration will occur due to factors such as gear machining errors, meshing rigidity, and meshing impact. The traditional FxLMS algorithm, as a common active vibration algorithm, has been widely studied and applied in gear transmission system active vibration control in recent years. However, it is difficult to achieve good performance in convergence speed and convergence precision at the same time. This paper proposes a variable-step-size multichannel FxLMS algorithm based on the sampling function, which accelerates the convergence speed in the initial stage of iteration, improves the convergence accuracy in the steady-state adaptive stage, and makes the modified algorithm more robust. Simulations verify the effectiveness of the algorithm. An experimental platform for active vibration control of the secondary gear transmission system is built. A piezoelectric actuator is installed on an additional gear shaft to form an active structure and equipped with a signal acquisition system and a control system; the proposed variable-step-size multichannel FxLMS algorithm is experimentally verified. The experimental results show that the proposed multichannel variable-step-size FxLMS algorithm has more accurate convergence accuracy than the traditional FxLMS algorithm, and the convergence accuracy can be increased up to 123%

    Metaphors of London fog, smoke and mist in Victorian and Edwardian Art and Literature

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    Julian Wolfreys has argued that after 1850 writers employed stock images of the city without allowing them to transform their texts. This thesis argues, on the contrary, that metaphorical uses of London fog were complex and subtle during the Victorian and Edwardian periods, at least until 1914. Fog represented, in particular, formlessness and the dissolution of boundaries. Examining the idea of fog in literature, verse, newspaper accounts and journal articles, as well as in the visual arts, as part of a common discourse about London and the state of its inhabitants, this thesis charts how the metaphorical appropriation of this idea changed over time. Four of Dickens's novels are used to track his use of fog as part of a discourse of the natural and unnatural in individual and society, identifying it with London in progressively more negative terms. Visual representations of fog by Constable, Turner, Whistler, Monet, Markino, O'Connor, Roberts and Wyllie and Coburn showed an increasing readiness to engage with this discourse. Social tensions in the city in the 1880s were articulated in art as well as in fiction. Authors like Hay and Barr showed the destruction of London by its fog because of its inhabitants' supposed degeneracy. As the social threat receded, apocalyptic scenarios gave way to a more optimistic view in the work of Owen and others. Henry James used fog as a metaphorical representation of the boundaries of gendered behaviour in public, and the problems faced by women who crossed them. The dissertation also examines fog and individual transgression, in novels and short stories by Lowndes, Stevenson, Conan Doyle and Joseph Conrad. After 1914, fog was no more than a crude signifier of Victorian London in literature, film and, later, television, deployed as a cliche instead of the subtle metaphorical idea discussed in this thesis

    Underwater optical wireless communications in turbulent conditions: from simulation to experimentation

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    Underwater optical wireless communication (UOWC) is a technology that aims to apply high speed optical wireless communication (OWC) techniques to the underwater channel. UOWC has the potential to provide high speed links over relatively short distances as part of a hybrid underwater network, along with radio frequency (RF) and underwater acoustic communications (UAC) technologies. However, there are some difficulties involved in developing a reliable UOWC link, namely, the complexity of the channel. The main focus throughout this thesis is to develop a greater understanding of the effects of the UOWC channel, especially underwater turbulence. This understanding is developed from basic theory through to simulation and experimental studies in order to gain a holistic understanding of turbulence in the UOWC channel. This thesis first presents a method of modelling optical underwater turbulence through simulation that allows it to be examined in conjunction with absorption and scattering. In a stationary channel, this turbulence induced scattering is shown to cause and increase both spatial and temporal spreading at the receiver plane. It is also demonstrated using the technique presented that the relative impact of turbulence on a received signal is lower in a highly scattering channel, showing an in-built resilience of these channels. Received intensity distributions are presented confirming that fluctuations in received power from this method follow the commonly used Log-Normal fading model. The impact of turbulence - as measured using this new modelling framework - on link performance, in terms of maximum achievable data rate and bit error rate is equally investigated. Following that, experimental studies comparing both the relative impact of turbulence induced scattering on coherent and non-coherent light propagating through water and the relative impact of turbulence in different water conditions are presented. It is shown that the scintillation index increases with increasing temperature inhomogeneity in the underwater channel. These results indicate that a light beam from a non-coherent source has a greater resilience to temperature inhomogeneity induced turbulence effect in an underwater channel. These results will help researchers in simulating realistic channel conditions when modelling a light emitting diode (LED) based intensity modulation with direct detection (IM/DD) UOWC link. Finally, a comparison of different modulation schemes in still and turbulent water conditions is presented. Using an underwater channel emulator, it is shown that pulse position modulation (PPM) and subcarrier intensity modulation (SIM) have an inherent resilience to turbulence induced fading with SIM achieving higher data rates under all conditions. The signal processing technique termed pair-wise coding (PWC) is applied to SIM in underwater optical wireless communications for the first time. The performance of PWC is compared with the, state-of-the-art, bit and power loading optimisation algorithm. Using PWC, a maximum data rate of 5.2 Gbps is achieved in still water conditions

    Theorising Christian Anarchism A Political Commentary on the Gospel

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    This thesis argues that there is a tradition in political theology and in political theory that deserves to be called "Christian anarchism." The various thinkers that contribute to this tradition have never before been considered to be part of a theoretical movement or tradition, and the originality of this thesis is to weave these thinkers together and present a generic theory of Christian anarchism. . Taken together, thinkers like Tolstoy, Ellul, Elliott and Andrews put forward a comprehensive exegesis of Jesus' teaching and example as implying a critique of the state and a vision of a stateless society. Based on this understanding of the Gospel, they accuse both the state and the church of contradicting, betraying and corrupting the essence of Christianity. Some Christian anarchists - Eller in particular - even see Romans 13 and the "render unto Caesar" passage as not discrediting but indeed confirming their interpretation, and although more activist Christian anarchists sometimes disagree on the potential role of civil disobedience, they do all stress that what matters above all is obedience to God Moreover, they all call for the "true" church to lead the Christian anarchist revolution by example, despite the very demanding sacrifices which this involves. They point to numerous examples of similar witness ever since the early church, and themselves strive to emulate such examples in their own lives - the Catholic Worker movement being perhaps the most notable example in this regard Thus, Christian anarchist thinkers' critique of the current order and appeal to follow God's radical commandments echoes the voices of the prophets of old, calling society to return to God's covenant. By weaving their scattered voices together - by theorising Christian anarchism - this thesis provides a political commentary on the Gospel which contributes as much to political theory as it does to political theology

    Response of saline reservoir to different phaseCOâ‚‚-brine: experimental tests and image-based modelling

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    Geological CO₂ storage in saline rocks is a promising method for meeting the target of net zero emission and minimizing the anthropogenic CO₂ emitted into the earth’s atmosphere. Storage of CO₂ in saline rocks triggers CO₂-brine-rock interaction that alters the properties of the rock. Properties of rocks are very crucial for the integrity and efficiency of the storage process. Changes in properties of the reservoir rocks due to CO₂-brine-rock interaction must be well predicted, as some changes can reduce the storage integrity of the reservoir. Considering the thermodynamics, phase behavior, solubility of CO₂ in brine, and the variable pressure-temperature conditions of the reservoir, there will be undissolved CO₂ in a CO₂ storage reservoir alongside the brine for a long time, and there is a potential for phase evolution of the undissolved CO₂. The phase of CO₂ influence the CO₂-brine-rock interaction, different phaseCO₂-brine have a unique effect on the properties of the reservoir rocks, Therefore, this study evaluates the effect of four different phaseCO₂-brine reservoir states on the properties of reservoir rocks using experimental and image-based approach. Samples were saturated with the different phaseCO₂-brine, then subjected to reservoir conditions in a triaxial compression test. The representative element volume (REV)/representative element area (REA) for the rock samples was determined from processed digital images, and rock properties were evaluated using digital rock physics and rock image analysis techniques. This research has evaluated the effect of different phaseCO₂-brine on deformation rate and deformation behavior, bulk modulus, compressibility, strength, and stiffness as well as porosity and permeability of sample reservoir rocks. Changes in pore geometry properties, porosity, and permeability of the rocks in CO₂ storage conditions with different phaseCO₂-brine have been evaluated using digital rock physics techniques. Microscopic rock image analysis has been applied to provide evidence of changes in micro-fabric, the topology of minerals, and elemental composition of minerals in saline rocks resulting from different phaseCO₂-br that can exist in a saline CO₂ storage reservoir. It was seen that the properties of the reservoir that are most affected by the scCO₂-br state of the reservoir include secondary fatigue rate, bulk modulus, shear strength, change in the topology of minerals after saturation as well as change in shape and flatness of pore surfaces. The properties of the reservoir that is most affected by the gCO₂-br state of the reservoir include primary fatigue rate, change in permeability due to stress, change in porosity due to stress, and change topology of minerals due to stress. For all samples, the roundness and smoothness of grains as well as smoothness of pores increased after compression while the roundness of pores decreased. Change in elemental composition in rock minerals in CO₂-brine-rock interaction was seen to depend on the reactivity of the mineral with CO₂ and/or brine and the presence of brine accelerates such change. Carbon, oxygen, and silicon can be used as index minerals for elemental changes in a CO₂-brine-rock system. The result of this work can be applied to predicting the effect the different possible phases of CO₂ will have on the deformation, geomechanics indices, and storage integrity of giant CO₂ storage fields such as Sleipner, In Salah, etc

    A subpopulation of Talin 1 resides in the nucleus and regulates gene expression

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    Talin 1 (TLN1) is best known for its role at focal adhesions, where it activates β-integrin receptors and transmits mechanical stimuli to the actin cytoskeleton. Interestingly, the localization of TLN1 is not restricted to the focal adhesions, but its function in other cellular compartments remains poorly understood. By utilizing both biochemical and confocal microscopy analyses, we show that TLN1 localizes to the nucleus and that it strongly interacts with the chromatin. Importantly, depletion of endogenous TLN1 results in extensive changes in the gene expression profile of human breast epithelial cells. To determine the impact of nuclear TLN1 on gene regulation, we expressed a TLN1 fusion protein containing a nuclear localization signal. Our results reve aled that nuclear TLN1 regulates a specific subset of the TLN1-dependent genes. Taken together, we show that apart from localizing at the plasma membrane and cytoplasm, TLN1 also resides in the nucleus where it functions in the regulation of gene expression
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