Pushing fillings in right-angled Artin groups

We construct "pushing maps" on the cube complexes that model right-angled Artin groups (RAAGs) in order to study filling problems in certain subsets of these cube complexes. We use radial pushing to obtain upper bounds on higher divergence functions, finding that the k-dimensional divergence of a RAAG is bounded by r^{2k+2}. These divergence functions, previously defined for Hadamard manifolds to measure isoperimetric properties "at infinity," are defined here as a family of quasi-isometry invariants of groups; thus, these results give new information about the QI classification of RAAGs. By pushing along the height gradient, we also show that the k-th order Dehn function of a Bestvina-Brady group is bounded by V^{(2k+2)/k}. We construct a class of RAAGs called "orthoplex groups" which show that each of these upper bounds is sharp.Comment: The result on the Dehn function at infinity in mapping class groups has been moved to the note "Filling loops at infinity in the mapping class group.

Filling loops at infinity in the mapping class group

We study the Dehn function at infinity in the mapping class group, finding a polynomial upper bound of degree four. This is the same upper bound that holds for arbitrary right-angled Artin groups.Comment: 7 pages, 2 figures; this note presents a result which was contained in an earlier version of "Pushing fillings in right-angled Artin groups" (arXiv:1004.4253) but is independent of the techniques in that pape

Spatial judgment in Parkinson's disease: Contributions of attentional and executive dysfunction

Spatial judgment is impaired in Parkinson's disease (PD), with previous research suggesting that disruptions in attention and executive function are likely contributors. If judgment of center places demands on frontal systems, performance on tests of attention/executive function may correlate with extent of bias in PD, and attentional disturbance may predict inconsistency in spatial judgment. The relation of spatial judgment to attention/executive function may differ for those with left-side versus right-side motor onset (LPD, RPD), reflecting effects of attentional lateralization. We assessed 42 RPD, 37 LPD, and 67 healthy control participants with a Landmark task (LM) in which a cursor moved horizontally from the right (right-LM) or left (left-LM). The task was to judge the center of the line. Participants also performed neuropsychological tests of attention and executive function. LM group differences were found on left-LM only, with both PD subgroups biased leftward of the control group (RPD p < .05; LPD p < .01; no RPD-LPD difference). For left-LM trials, extent of bias significantly correlated with performance on the cognitive tasks for PD but not for the control group. PD showed greater variability in perceived center than the control group; this variability correlated with performance on the cognitive tasks. The correlations between performance on the test of spatial judgment and the tests of attention/executive function suggest that frontal-based attentional dysfunction affects dynamic spatial judgment, both in extent of spatial bias and in consistency of response as indexed by intertrial variability. (PsycINFO Database Record (c) 2019 APA, all rights reserved).R01 NS067128 - NINDS NIH HHS; R21 NS043730 - NINDS NIH HHS; National Institute of Neurological Disorders and Stroke; American Parkinson's Disease Association; Massachusetts ChapterAccepted manuscrip

Tell Khaiber: An administrative centre of the Sealand period

Excavations at Tell Khaiber in southern Iraq by the Ur Region Archaeological Project have revealed a substantial building (hereafter the Public Building) dating to the mid-second millennium b.c. The results are significant for the light they shed on Babylonian provincial administration, particularly of food production, for revealing a previously unknown type of fortified monumental building, and for producing a dated archive, in context, of the little-understood Sealand Dynasty. The project also represents a return of British field archaeology to long-neglected Babylonia, in collaboration with Iraq's State Board for Antiquities and Heritage. Comments on the historical background and physical location of Tell Khaiber are followed by discussion of the form and function of the Public Building. Preliminary analysis of the associated archive provides insights into the social milieu of the time. Aspects of the material culture, including pottery, are also discussed

Pricing Perishables with Uncertain Demand, Substitutes, and Consumer Heterogeneity

Within the marketing window for perishables such as food products, demand uncertainty is complicated by price sensitivity and propensity to postpone purchase that is heterogeneous across consumers. These features pose substantial challenges to retailers when pricing multiple products over time and across consumer segments. Getting the dynamic profile of prices right has implications for performance of vertical food chains ranging from revenues to food waste. This paper proposes an approach to dynamic pricing that is demonstrated to improve performance within this setting

Pricing Perishables

 A key feature of food products is their perishability. Within the short marketing window that characterizes most food and ag products, demand is typically highly stochastic and difficult to predict. This combination of features poses substantial challenges to retailers when pricing products and has implications for performance that ripples through vertical food chains. For many food products, processing to forms that can be preserved and held in inventory has traditionally been used as a means of coping with these conditions, despite its high costs and ancillary risks introduced such as change in product attributes and deterioration. This paper presents an alternative ERM strategy that focuses on dynamic pricing to control the rate of sale for perishable products. The paper considers a retailer that has market power to price and supplies perishable products to a market with substitute products and demand originating from heterogeneous consumers. Perishability implies a finite horizon for the marketing of the products over which demand across market segments of consumers is both dynamic and stochastic. Faced with uncertainty, we suppose the firm has limited information about the stochastic properties of demand and must choose a pricing strategy that projects over the market horizon. This price trajectory represents a key control mechanism to cope with uncertainty of both the perishability of the product and of demand

Out of Africa: a typology for analysing open educational resources initiatives

This paper describes how a typology was developed and used between 2008 and 2010 to investigate three different open educational resources (OER) initiatives in Sub Saharan Africa (SSA). The typology was first developed by careful scrutiny of the many OER and OER-related initiatives both globally and in Sub Saharan Africa. The typology was then both tested and further developed and refined by applying it to the TESSA, Thutong Portal and Rip-Mix-Learn initiatives. The typology uses four main categories – creation, organisation, dissemination and utilisation – and 18 sub categories to examine and analyse each initiative, with each sub category having a number of properties and possible dimensions. This typology was used to distinguish one type of OER initiative from another while grounding each in a wider context. As there are different levels of categorisation the typology is simple at the highest level, with just four elements, for use by practitioners; but is detailed enough at other levels to enable researchers to generate research questions. Furthermore the typology is flexible enough to evolve over time as it is applied to more and more OER initiatives both within and outside Africa and also as existing initiatives change and develop over time and while new initiatives emerge