Convex Hull of Arithmetic Automata

Arithmetic automata recognize infinite words of digits denoting decompositions of real and integer vectors. These automata are known expressive and efficient enough to represent the whole set of solutions of complex linear constraints combining both integral and real variables. In this paper, the closed convex hull of arithmetic automata is proved rational polyhedral. Moreover an algorithm computing the linear constraints defining these convex set is provided. Such an algorithm is useful for effectively extracting geometrical properties of the whole set of solutions of complex constraints symbolically represented by arithmetic automata

Evaluating Marketing Channel Options for Small-Scale Fruit and Vegetable Producers: Case Study Evidence from Central New York

An investigation of the relative costs and benefits of marketing channels used by typical small-scale diversified vegetable crop producers is conducted. Using case study evidence from four small farms in Central New York, this study compares the performance of wholesale and direct marketing channels, including how the factors of risk, owner and paid labor, price, lifestyle preferences, and sales volume interact to impact optimal market channel selection. Given the highly perishable nature of the crops grown, along with the risks and potential sales volume of particular channels, a combination of different marketing channels is needed to maximize overall firm performance. Accordingly, a ranking system is developed to summarize the major firm-specific factors across channels and to prioritize those channels with the greatest opportunity for success based on individual firm preferences.Marketing channel, small-scale, fruit and vegetable producers, case study, Agribusiness, Crop Production/Industries, Financial Economics,

Mountain trail formation and the active walker model

We extend the active walker model to address the formation of paths on gradients, which have been observed to have a zigzag form. Our extension includes a new rule which prohibits direct descent or ascent on steep inclines, simulating aversion to falling. Further augmentation of the model stops walkers from changing direction very rapidly as that would likely lead to a fall. The extended model predicts paths with qualitatively similar forms to the observed trails, but only if the terms suppressing sudden direction changes are included. The need to include terms into the model that stop rapid direction change when simulating mountain trails indicates that a similar rule should also be included in the standard active walker model.Comment: Introduction improved. Analysis of discretization errors added. Calculations from alternative scheme include

A review of the localities and flora of the lower Permian Karoo strata at Vereeniging, South Africa

Main articleThe Vereeniging fossil floras are particularly well known and often referred to, as it is among them that attached glossopteridophyte fructifications were first recorded. No recent review of the localities, flora and age of the deposits is available. The history of collecting and description of fossil plants from Vereeniging dates from 1879. Ten localities have been recorded to date, the most important of which are the three Leeukuil quarries from which a diverse flora has been collected and described over the past thirty years. Two of the localities are considered to fall within the Lower Ecca and the remaining eight within a restricted section of the Middle Ecca coal measures. The older flora is poorly known and is represented only by the genera Gangamopteris and Noeggerathiopsis. The younger flora is fairly comprehensively known and includes some 23 genera and 33 species of plants.Non

Mise en place d’un laboratoire naturel sur le mont Covey Hill (Québec, Canada)

Le mont Covey Hill héberge des populations de salamandres rares et menacées dont les habitats sont maintenus en partie par\ud l’eau souterraine. Des travaux de recherche multidisciplinaires (UQAM, U. McGill, U. Montréal, IRBV, Centre Brace, SCABRIC et\ud ministères) ont permis de comprendre l’hydrologie ainsi que la répartition et les caractéristiques des habitats de salamandres. Ces projets ont contribué à la mise en place de stations de suivi écologique à long terme et de stations hydrométriques permanentes. En tant que propriétaire de terrains dédiés à la conservation, Conservation de la Nature assure la coordination de ces initiatives. Le mont Covey Hill est aujourd’hui un Laboratoire naturel unique au Québec, dédié à la compréhension intégrée et à long terme d’un écosystème fragile. Cet article a pour objectif de présenter le Laboratoire naturel par une description des recherches en cours et à venir

Trifluoromethylation of carbonyl groups in aromatic poly(ether ketone)s: formation of strongly polar yet surface-hydrophobic poly(arylenenecarbinol)s

Fluoride-catalyzed reactions of trimethyl(trifluoromethyl)silane with a range of aromatic poly(ether ketone)s, both amorphous and semi-crystalline, proceed quantitatively in THF to yield soluble, amorphous polymers in which the carbon-silicon bond of CF3SiMe3 has added across the carbonyl-oxygen double bond of each carbonyl group. When the starting poly(ether ketone) is amorphous and soluble in THF the reaction is fairly rapid (hours), but is much slower (days) when the starting polymer is semi-crystalline, with only low solubility in THF. Quantitative desilylation of the resulting polymers is achieved by reaction with excess fluoride ion, affording poly(arylene-trifluoromethylcarbinol)s. These extremely polar polymers are readily soluble in protic solvents such as methanol or ethanol, to give solutions from which tough, coherent films may be cast by evaporation in air. Despite the evidently high polarity of the bulk polymers, the surfaces of cast films are relatively hydrophobic, with static water contact angles of ~ 90°. Surface analyses by XPS are consistent with enrichment of the polymer-air interface in CF3 groups