Nonlinear stability of the ensemble Kalman filter with adaptive covariance inflation

The Ensemble Kalman filter and Ensemble square root filters are data assimilation methods used to combine high dimensional nonlinear models with observed data. These methods have proved to be indispensable tools in science and engineering as they allow computationally cheap, low dimensional ensemble state approximation for extremely high dimensional turbulent forecast models. From a theoretical perspective, these methods are poorly understood, with the exception of a recently established but still incomplete nonlinear stability theory. Moreover, recent numerical and theoretical studies of catastrophic filter divergence have indicated that stability is a genuine mathematical concern and can not be taken for granted in implementation. In this article we propose a simple modification of ensemble based methods which resolves these stability issues entirely. The method involves a new type of adaptive covariance inflation, which comes with minimal additional cost. We develop a complete nonlinear stability theory for the adaptive method, yielding Lyapunov functions and geometric ergodicity under weak assumptions. We present numerical evidence which suggests the adaptive methods have improved accuracy over standard methods and completely eliminate catastrophic filter divergence. This enhanced stability allows for the use of extremely cheap, unstable forecast integrators, which would otherwise lead to widespread filter malfunction.Comment: 34 pages. 4 figure

The effect of divided attention on inadvertent plagiarism for young and older adults

Older adults inadvertently plagiarize more than young adults (McCabe, Smith, & Parks, 2007). One current explanation proposes that this effect can be understood in terms of age-related declines in working and episodic memory (McCabe et al., 2007). The current study tested this hypothesis by placing groups of young and older adult participants under divided attention while performing within the typical experimental paradigm. Results indicated that for some measures, dividing the attention of young adults equated their performance to older adults with full attention. For other measures, older adults still produced more errors. Except for false recall, regression analyses revealed that episodic and working memory accounted for age-related variance in these plagiarism errors. The current findings provide tenuous support for the McCabe et al. (2007) hypothesis and suggest other factors may be at play.M.S.Committee Chair: Smith, Anderson; Committee Member: Hertzog, Christopher; Committee Member: Rogers, Wend

Students pay the price: Doctoral candidates are targeted by contract cheating websites

Aim/Purpose This paper analyses the textual features of contract cheating websites that offer thesis writing services for doctoral students and considers implications for practice. Background Contract cheating is an increasing challenge for higher education institutions, governments and societies worldwide. However, relatively little is known about the prevalence of online thesis writing services and the ways in which these companies attract doctoral students as customers. Methodology This study has a three-step textual analysis methodological approach: firstly, identifying contract cheating websites that target doctoral students; secondly, applying a top-down thematic approach to the literature to identify potential vulnerabilities; and, thirdly, using these themes in a textual analysis to interrogate the language used on these websites. Contribution Much of the current research into contract cheating has focused on coursework students. This study builds on the small sub-field of scholarship that has investigated contract cheating in a research writing context, and in contradistinction to previous studies, analyses the persuasive language features used by online contract cheating websites in the context of commonly reported doctoral student challenges. This is a novel approach not yet explored in the literature. Findings The analysis reveals that contract cheating websites include specific language to appeal to doctoral students\u27 vulnerabilities across four common themes: \u27balancing work and personal life\u27, \u27the complexity of doctoral academic writing\u27, \u27self-efficacy\u27 and \u27academic career progression\u27. Recommendations The themes present in this study highlight the critical role thesis supervisors can for Practitioners play in supporting doctoral students\u27 thesis writing progression, as well as the value of peer learning groups in building self-efficacy. The limited research literature into contract cheating in a doctoral context also suggests a need for increased training and awareness-raising programs for supervisors, thesis examiners and new graduate students. Recommendations Future studies that further investigate the prevalence of these themes across a for Researchers broader scope of websites and countries will provide greater insights into the extent to which these websites are a global threat to vulnerable doctoral students. Impact on Society The paper provides a foundation for researchers and graduate schools to raise greater awareness of contract cheating amongst doctoral students and, in so doing, combats the reputational risks it can have on universities and the potential safety risks for the general public. Future Research Semi-structured interviews and focus groups with doctoral students and supervisors that explore their awareness of contract cheating for thesis writing and their ability to identify research writing that has been completed by a third-party

Residential home heating: The potential for air source heat pump technologies as an alternative to solid and liquid fuels

AbstractInternational commitments on greenhouse gases, renewables and air quality warrant consideration of alternative residential heating technologies. The residential sector in Ireland accounts for approximately 25% of primary energy demand with roughly half of primary home heating fuelled by oil and 11% by solid fuels. Displacing oil and solid fuel usage with air source heat pump (ASHP) technology could offer household cost savings, reductions in emissions, and reduced health impacts. An economic analysis estimates that 60% of homes using oil, have the potential to deliver savings in the region of €600 per annum when considering both running and annualised capital costs. Scenario analysis estimates that a grant of €2400 could increase the potential market uptake of oil users by up to 17% points, whilst a higher oil price, similar to 2013, could further increase uptake from heating oil users by 24% points. Under a combined oil-price and grant scenario, CO2 emissions reduce by over 4 million tonnes per annum and residential PM2.5 and NOX emissions from oil and peat reduce close to zero. Corresponding health and environmental benefits are estimated in the region of €100m per annum. Sensitivity analyses are presented assessing the impact of alternate discount rates and technology performance. This research confirms the potential for ASHP technology and identifies and informs policy design considerations with regard to oil price trends, access to capital, targeting of grants, and addressing transactions costs

Advantages of 3D time-of-flight range imaging cameras in machine vision applications

Machine vision using image processing of traditional intensity images is in wide spread use. In many situations environmental conditions or object colours or shades cannot be controlled, leading to difficulties in correctly processing the images and requiring complicated processing algorithms. Many of these complications can be avoided by using range image data, instead of intensity data. This is because range image data represents the physical properties of object location and shape, practically independently of object colour or shading. The advantages of range image processing are presented, along with three example applications that show how robust machine vision results can be obtained with relatively simple range image processing in real-time applications

Production of ethyl acetate from pyrolysis of lignin model compound guaiacylglycerol-β-guaiacyl using TGA-MS

Due to the complex chemical structure of lignin, the fundamental chemistry underlying its pyrolysis behaviour is poorly understood. A detailed knowledge of this chemistry would allow for the construction of detailed predictive chemical kinetic models, which could be used to maximise the efficiency of the pyrolysis process. Lignin is comprised of three monolignols, guaiacyl, p-hydroxyphenyl and syringyl. These are joined together by aryl ether linkages of which β-O-4 is the most common, representing approximately 50% of the linkages found in lignin.[1] In this study, pyrolysis (20oC/minute heating rate) was carried out on a lignin model compound, guaiacylglycerol-β-guaiacyl ether (GGE). GGE is composed of two guaiacyl subunits connected by a β-O-4 linkage, making it broadly representative of the lignin motif and as such an important lignin model compound. A detailed understanding of the thermal degradation of GGE under pyrolysis conditions will provide valuable information of the role of the β-O-4 linkage in lignin. Please click Additional Files below to see the full abstract