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Investigation of the bond coat interface topography effect on lifetime, microstructure and mechanical properties of air-plasma sprayed thermal barrier coatings
No full textThe effect of bond coat/thermal barrier coating (BC/TBC) interface topography on the lifetime of air-plasma sprayed (APS) TBCs was comprehensively investigated in the present work. A quantitative description of the interface topography was achieved by utilising multiple surface texture parameters obtained from confocal microscopy, including a newly formulated parameter, denominated as total thresholded summit area, Ssth. Thermal cycling fatigue (TCF) testing showed a clear correlation between the TBC lifetime and the interface topography, especially for the novel Ssth parameter. The topographical and microstructural analysis revealed that deposition of a TBC over tortuous BC topographies leads to a highly curved TBC splat morphology, which in turn affected the crack path configuration. Mechanical testing of as-deposited and heat-treated specimens evidenced that the aforementioned microstructural changes promoted a reduced local and global elastic moduli, effectively linking the more compliant TBC microstructures with more beneficial fracture mechanics behaviours and higher TCF lifetimes
Fast Approximate Bayesian Contextual Cold Start Learning (FAB-COST)
No full textCold-start is a notoriously difficult problem which can occur in recommendation systems, and arises when there is insufficient information to draw inferences for users or items. To address this challenge, we propose a contextual bandit algorithm that we call the Fast Approximate Bayesian Contextual Cold Start Learning algorithm (FAB-COST), which is designed to provide improved accuracy compared to the traditionally used Laplace approximation in the logistic contextual bandit, while controlling both algorithmic complexity and computational cost. To this end, FAB-COST uses a combination of two moment projection variational methods: Expectation Propagation (EP), which performs well at the cold start, but becomes slow as the amount of data increases; and Assumed Density Filtering (ADF), which has slower growth of computational cost with data size but requires more data to obtain an acceptable level of accuracy. By switching from EP to ADF when the dataset becomes large, we are able to exploit their complementary strengths. Here, we present the empirical justification for FAB-COST, and systematically compare it to other approaches on simulated data. In a benchmark against the Laplace approximation on real data consisting of around 31, 000 impressions from autotrader.co.uk, we demonstrate an increase in number of user clicks of over 16%. On the basis of our results, we argue that FAB-COST is likely to be an attractive approach to cold-start recommendation systems in a variety of contexts
Low voltage organic transistors with water-processed gum arabic dielectric
No full text— In this communication, low voltage organic thin film transistors (OTFTs) using water-processed gum arabic (GA) as the gate dielectric are reported. The fabricated OTFTs operate at 3 V with a field-effect mobility in the saturation regime µsat = 0.6 cm2V-1s-1, threshold voltage Vth = -0.35 V, subthreshold swing SS = 350 mV/dec, and on/off current ratio ION/OFF > 102. The characterization of metal-insulator-metal (MIM) capacitors shows that the studied GA displays high dielectric constant at 1 kHz (k ~ 30) and that the leakage current density through the prepared (1250 ± 14) nm thick GA films is around 10-7 A/cm2 at ±3 V. As a result, gum arabic emerges as a promising gate dielectric for low voltage OTFTs especially when the requirements of eco-friendly manufacturing are considered
Synergistic Effects of a Novel Method of Preparing Graphene/Polyvinyl Alcohol to Modify Cementitious Material
No full textThis paper presents a new method of improving mechanical and physical properties of a composite cementitious material, by a one-step combined modification using graphene and polyvinyl alcohol (PVA) to overcome limitations of other modification methods by polymer and nanomaterials. The complementary and combined effect of graphene and PVA can solve key problems such as high cost, low production of graphene and poor dispersion of graphene in the cementitious matrix. The proposed method of graphene/PVA aqueous dispersions by shear exfoliation has high stability and can directly replace water in cement casting. The exfoliation and dispersion mechanisms of graphene by PVA aqueous solution are revealed by molecular dynamics simulation. Compared to plain cement, the graphene/PVA modified cementitious material has up to 71.1% higher compressive strength, 106.5% higher flexural strength and 75.8% increase in thermal conductivity, whilst PVA-modified cement has only 0.8% increase in compressive strength and 36.2% increment in flexural strength
Automated cortical auditory response detection strategy
No full textObjectiveThis study describes a new automated strategy to determine the detection status of an electrophysiological response. DesignResponse, noise and signal-to-noise ratio of the cortical auditory evoked potential (CAEP) were characterized. Detection rules were defined: when to start testing, when to conduct subsequent statistical tests using residual noise as an objective criterion, and when to stop testing. Study sampleSimulations were run to determine optimal parameters on a large combined CAEP data set collected in 45 normal-hearing adults and 17 adults with hearing loss.ResultsThe proposed strategy to detect CAEPs is fully automated. The first statistical test is conducted when the residual noise level is equal to or smaller than 5.1 µV. The succeeding Hotelling’s T2 statistical tests are conducted using pre-defined residual noise levels criteria ranging from 5.1 to 1.2 µV. A rule was introduced allowing to stop testing before the maximum number of recorded epochs is reached, depending on a minimum p-value criterion.ConclusionThe proposed framework can be applied to systems which involves detection of electrophysiological responses in biological systems containing background noise. The proposed detection algorithm which optimize sensitivity, specificity, and recording time has the potential to be in clinical setting.<br/
The AZ algorithm for least squares systems with a known incomplete generalized inverse
No full textWe introduce an algorithm for the least squares solution of a rectangular linear system Ax = b, in which A may be arbitrarily ill-conditioned. We assume that a complementary matrix Z is known such that A − AZ∗A is numerically low rank. Loosely speaking, Z∗ acts like a generalized inverse of A up to a numerically low rank error. We give several examples of (A, Z) combinations in function approximation, where we can achieve high-order approximations in a number of nonstandard settings: the approximation of functions on domains with irregular shapes, weighted least squares problems with highly skewed weights, and the spectral approximation of functions with localized singularities. The algorithm is most efficient when A and Z∗ have fast matrix-vector multiplication and when the numerical rank of A − AZ∗A is small
The Leviathan of Rationality: Using Film to Develop Creativity and Imagination in Management Learning and Education
No full textDogma is an ever-present danger to reason and rationality. In times of climate emergency and the dawn of a new geological era known as the Anthropocene dogma becomes particularly disabling and dangerous for business and management. However, recent research findings in the study of creativity and imagination in management learning and education provide some promising ways of responding. This essay draws on techniques in experiential learning andcontributes to the call for ‘disciplined imagination’ (Weick, 1989) to explore what can be learnt from the study of film for stimulating classroom creativity. The paper is devoted to a close analysis of Leviathan (2013), an experiential and avant-garde contemporary masterpiece in ethnographic filmmaking. We find that existing approaches to creativity need to be supplemented with greater attention to the technological apparatus of cinema and its affective materialities. Drawing on the work of Gilles Deleuze the essay shows that cinema can producewhat we call an ‘event of thought’. These events of thought require the generation of original concepts and we propose ‘becoming Go-Pro’ to best harness the affects and heightened existential awareness stimulated by Leviathan. With this concept we produce findings that challenge prevailing concepts of reason and rationality in management studies
Platinum Group Metal-free Oxygen Reduction Electroctatalysts Employed in Neutral Electrolytes for Bio-electrochemical Reactors Applications
No full textThe oxygen reduction reaction is one ofthe limiting stepsin microbial fuel cellperformance. M-N-C catalysts (M as transition metal) represent the best compromise of optimal cost, electrocatalytic activity and durability. The Fe-based catalysts were shown to be the best compared to Co-, Mn-, Ni-based catalysts. The addition of the second transition metal such as Mn was shown to increase the selectivity of the reaction and reduce peroxide production. The use of different N-C precursors resulted in diverse surface chemistry that directly affects the performance. Generally, surface chemistry plays a critical role in the electrocatalytic activity. Integration of the catalyst in the air-breathing cathode is also discussed with a performance that is enhanced by: i) increasedcatalyst loading; ii) the addition of graphene to structure
An undergraduate laboratory experiment to determine the critical point of SF6 using light scattering at selected wavelengths.
No full textMolecules and atoms that are normally gaseous at room temperature and pressure will liquefy or solidify as their temperature reduces or their pressure increases. In the apparatus detailed here a commercial cell contains pressurised SF6 so that it exists in both gaseous and liquid states, with the density of both being similar at room temperature. The critical point on the phase diagram can then be investigated, by elevating the temperature of the cell so the densities of liquid and gas equalize. Under these conditions light passing through the cell is highly scattered by density fluctuations in the fluid. By measuring the transmitted light as a function of both temperature and wavelength, the critical exponent can be derived and the effects of light scattering with wavelength investigated
Chatter Stability of Machining Operations
No full textThis paper reviews the dynamics of machining and chatter stability research since the first stability laws were introduced by Tlusty and Tobias in the 1950s. The paper aims to introduce the fundamentals of dynamic machining and chatter stability, as well as the state of the art and research challenges, to readers who are new to the area. First, the unified dynamic models of mode coupling and regenerative chatter are introduced. The chatter stability laws in both the frequency and time domains are presented. The dynamic models of intermittent cutting, such as milling, are presented and their stability solutions are derived by considering the time-periodic behavior. The complexities contributed by highly intermittent cutting, which leads to additional stability pockets, and the contribution of the tool’s flank face to process damping are explained. The stability of parallel machining operations is explained. The design of variable pitch and serrated cutting tools to suppress chatter is presented. The paper concludes with current challenges in chatter stability of machining which remains to be the main obstacle in increasing the productivity and quality of manufactured parts