Defective and Clustered Choosability of Sparse Graphs

An (improper) graph colouring has "defect" $d$ if each monochromatic subgraph has maximum degree at most $d$, and has "clustering" $c$ if each monochromatic component has at most $c$ vertices. This paper studies defective and clustered list-colourings for graphs with given maximum average degree. We prove that every graph with maximum average degree less than $\frac{2d+2}{d+2} k$ is $k$-choosable with defect $d$. This improves upon a similar result by Havet and Sereni [J. Graph Theory, 2006]. For clustered choosability of graphs with maximum average degree $m$, no $(1-\epsilon)m$ bound on the number of colours was previously known. The above result with $d=1$ solves this problem. It implies that every graph with maximum average degree $m$ is $\lfloor{\frac{3}{4}m+1}\rfloor$-choosable with clustering 2. This extends a result of Kopreski and Yu [Discrete Math., 2017] to the setting of choosability. We then prove two results about clustered choosability that explore the trade-off between the number of colours and the clustering. In particular, we prove that every graph with maximum average degree $m$ is $\lfloor{\frac{7}{10}m+1}\rfloor$-choosable with clustering $9$, and is $\lfloor{\frac{2}{3}m+1}\rfloor$-choosable with clustering $O(m)$. As an example, the later result implies that every biplanar graph is 8-choosable with bounded clustering. This is the best known result for the clustered version of the earth-moon problem. The results extend to the setting where we only consider the maximum average degree of subgraphs with at least some number of vertices. Several applications are presented

Comparison between different approaches for the evaluation of the hot spot structural stress in welded pressure vessel components

Fatigue cracks in welds often occur at the toe of a weld where stresses are difficult to calculate at the design stage. To circumvent this problem the ASME Boiler and PV code Section VIII Division 2 Part 5 [1] uses the structural stress normal to the expected crack to predict fatigue life using elastic analysis and as welded fatigue curves. The European Unfired Pressure Vessel Code [2] uses a similar approach. The structural stress excludes the notch stress at the weld toe itself. The predicted fatigue life has a strong dependency on the calculated value of structural stress. This emphasizes the importance of having a unique and robust way of extracting the structural stress from elastic finite element results. Different methods are available for the computation of the structural hotspotstress at welded joints. These are based on the extrapolation of surface stresses close to the weld toe, on the linearisation of stresses in the through-thickness direction or on the equilibrium of nodal forces. This paper takes a critical view on the various methods and investigates the effects of the mesh quality on the value of the structural stress. T-shaped welded plates under bending are considered as a means for illustration

The effect of articulation and word-meaning on gait and balance in people with Parkinson’s disease

Performing two tasks simultaneously is ubiquitous in everyday life, and the resulting interference may degrade performance on one or both of the tasks. This is potentially important, as diminished performance of a postural task places an individual at a greater risk for falling, especially in a movement impaired population such as individuals with Parkinson’s disease (PD). Many secondary tasks have been shown to reduce the performance of gait and balance, but to date only one study has investigated the effects of a verbal secondary task that systematically controls articulatory, cognitive, and linguistic demands. Previous research suggested that these components have independent effects on gait and balance within a sample of healthy young adults. The purpose of the present study was to replicate this previous research, within a sample of healthy older adults (n=20) and a sample of individuals with PD (n=20), and to evaluate the effects of individual differences in information processing speed, on dual-task interference. Results suggested that oral-motor movement significantly affected parameters of gait and balance, with men displaying significantly more dual-task interference than women. The addition of speech and lexicality to the secondary task did not significantly increase interference during the gait or balance protocol. Results also indicated that dual-task interference is directly related to individual differences in information processing speed, a finding that supports the capacity-sharing model of dual task interference

Swan-plant interactions in a chalk river catchment

Plants are of fundamental importance to the structure, functioning and service provision of many ecosystems. However, herbivores can have negative ecological and socioeconomic effects on plant communities through consumption, trampling and alteration of nutrient cycles. In this thesis I address a particular herbivore-plant interaction: the grazing of plants in chalk river catchments, principally the submerged macrophyte water crowfoot (Ranunculus penicillatus ssp. pseudofluitans (Syne) S.D. Webster) and terrestrial pasture grass species, by flocks of non-breeding mute swans (Cygnus olor Gmelin, 1789). This research was carried out over two years in the River Frome catchment (Dorset, UK). Based on a meta-analysis of previous waterfowl grazing studies I show that waterfowl biomass density (kg ha-1) rather than individual density (ind. ha-1) is a better predictor of reductions in plant standing crop. Most studies to date have analysed such reductions using only individual densities, despite large between-taxa variation in waterfowl body mass, diet and intake rates. I quantified the abundance, species richness, evenness, flowering and dominance of the chalk river aquatic plant community in relation to biotic and abiotic factors during the growth-, peak-, and recession-phases of the growth cycle. The relative importance of herbivory, riparian shading, water temperature and distance downstream varied between different phases of the plant growth cycle, highlighting the importance of seasonal patterns in regulation of plant community structure. The River Frome swan population varied seasonally, being highest in the winter. The population was dominated by non-breeding adults and juveniles that lived in flocks. These flocks exhibited strong seasonal habitat switches between terrestrial pasture in winter and spring, and river in summer and autumn. I provided evidence that this switch was linked to the seasonal decrease in water velocity between spring and summer, which reduced the metabolic costs of river feeding and increased the relative profitability of aquatic food resources. I used a mathematical population model and an individual-based behavioural model respectively to explore two management options for the alleviation of the swan grazing conflict in chalk rivers: population control and habitat alterations. Population control measures, such as clutch manipulations, fertility control, culling or translocations, were predicted to be unsuccessful except at impractically high levels of management effort, due to the effects of immigration and high survival rates in offsetting removed eggs or individuals. Habitat alterations, in particular the narrowing of river channels to cause a local increase in water velocity and thus swan foraging costs, are more promising management options as they require lower management effort, are less ethically controversial, and address the fundamental reason why swans select their food resources, the rate of net energy gain (‘profitability’)

Simulation Video Games as Learning Tools: An Examination of Instructor Guided Reflection on Cognitive Outcomes

Simulation video games potentially offer students the opportunity to participate in activities designed to bring about higher order thinking. Gee (2005b, 2007) elucidates that without the guidance of instructors, humans involved in a simulation experience have a high probability of finding creative but spurious patterns and generalizations that send learners down miseducative paths. The focus of this study is an examination of the function of instructor guided reflection and prior participant interest and exposure to video games in promoting affective and cognitive learning during participant use of single and multiplayer simulation video games in the classroom. One hundred twenty- eight students enrolled in World History classes at a suburban high school located in the Southeastern United States participated in this research study. Participants completed a survey of their interest and prior exposure to video games, played a tutorial of the simulation video game, played a single player or multiplayer version of the game with or without instructor guided reflection, and completed a posttest of reasoning and knowledge ability. The researcher used independent samples t tests, analysis of variance, and descriptive statistical analysis in combination with qualitative methods outlined by Miles and Huberman (1994) to analyze the data. Thomas (2003) described the mixed methodology used to analyze and interpret the data in this research study. Quantitative analysis of the data revealed that participants who engaged in both reflection and multiplayer groups scored significantly higher on posttest of reasoning ability at the .05 level. Furthermore, qualitative analysis revealed that participants in the multiplayer and reflection treatment groups were more likely to be engaged in the lesson, participate in more cognitive discussions, and made more connections to the large context of the lesson. Participants with a high level of prior interest in video games scored significantly higher on a posttest of reasoning ability at the .05 level of significance and were more likely to participate actively during the lesson. The findings from this study suggest the need for teaching educators to utilize reflective and collaborative practices in the incorporation of digital technology in the classroom

STS-40 descent BET products: Development and results

Descent Best Estimate Trajectory (BET) Data were generated for the final Orbiter Experiments Flight, STS-40. This report discusses the actual development of these post-flight products: the inertial BET, the Extended BET, and the Aerodynamic BET. Summary results are also included. The inertial BET was determined based on processing Tracking and Data Relay Satellite (TDRSS) coherent Doppler data in conjunction with observations from eleven C-band stations, to include data from the Kwajalein Atoll and the usual California coastal radars, as well as data from five cinetheodolite cameras in the vicinity of the runways at EAFB. The anchor epoch utilized for the trajectory reconstruction was 53,904 Greenwich Mean Time (GMT) seconds which corresponds to an altitude at epoch of approximately 708 kft. Atmospheric data to enable development of an Extended BET for this mission were upsurped from the JSC operational post-flight BET. These data were evaluated based on Space Shuttle-derived considerations as well as model comparisons. The Aerodynamic BET includes configuration information, final mass properties, and both flight-determined and predicted aerodynamic performance estimates. The predicted data were based on the final pre-operational databook, updated to include flight determined incrementals based on an earlier ensemble of flights. Aerodynamic performance comparisons are presented and correlated versus statistical results based on twenty-two previous missions

Two-Person Zero-Sum Games for Network Interdiction

Operations Research, Volume 43, Issue 2 (Mar. - Apr., 1995), 243-251. The article of record as published may be located at http://dx.doi.org/10.1287/opre.43.2.243.A single evader attempts to traverse a path between two nodes in a network while a single interdictor attempts to detect the evader by setting up an inspection point along one of the network arcs. For each arc there is a known probability of detection if the evader traverses that arc that the interdictor is inspecting. The evader must determine a probabilistic "path-selection" strategy which minimizes the probability of detection. The interdictor represents, in a simplified form, U.S. and allied forces attempting to interdict drugs and precursor chemicals as they are moved through river, road, and air routes in Latin America and the Caribbean. We show that the basic scenario is a two-person zero-sum game that might require the enumeration of an exponential number of paths, but then show that optimal strategies can be found using network flow techniques of polynomial complexity. To enhance realism, we also solve problems with unknown origins and destinations, multiple interdictors or evaders, and other generalizations

“We Just Need the Developer to Develop”: Entrepreneurialism, Financialization and Urban Redevelopment in Lexington, Kentucky

Since the 1980s US city governments have increased their use of more speculative means of financing economic redevelopment. This has involved experimenting with a variety of financial and taxation instruments as a way of growing their economies and redeveloping their built environments. This very general tendency, of course, masks how some cities have done well through the use of these instruments while others have not. The work to date has tended to pivot around a “winner-loser dichotomy”, which emphasises either the capacity of US cities to be able to experiment and speculate through the use of one financial instrument or another or their failings with these instruments, resulting in bankruptcy and fiscal crisis. This paper presents a case study of Lexington, Kentucky and using archival research and interviews we argue that speculative financial instruments are harder to choreograph for some cities than for others. We draw particular attention to US cities beyond those that tend to be over-represented in the metro-centric academic literature. This argument has conceptual significance. Building theory out of the experiences of US cities such as Lexington, Kentucky turns attention to the work required by city governments as they seek to finance the redevelopment of their downtowns. We make the case for a continued appreciation of the messy politics around the use of financial instruments, and its indeterminate, open and unpredictable nature in an era of fragile and uncertain entrepreneurial US urban policy-making