Improved Hardness of Approximation for Stackelberg Shortest-Path Pricing

We consider the Stackelberg shortest-path pricing problem, which is defined as follows. Given a graph G with fixed-cost and pricable edges and two distinct vertices s and t, we may assign prices to the pricable edges. Based on the predefined fixed costs and our prices, a customer purchases a cheapest s-t-path in G and we receive payment equal to the sum of prices of pricable edges belonging to the path. Our goal is to find prices maximizing the payment received from the customer. While Stackelberg shortest-path pricing was known to be APX-hard before, we provide the first explicit approximation threshold and prove hardness of approximation within 2−o(1). We also argue that the nicely structured type of instance resulting from our reduction captures most of the challenges we face in dealing with the problem in general and, in particular, we show that the gap between the revenue of an optimal pricing and the only known general upper bound can still be logarithmically large

Optical Propagation and Communication

Contains research objectives and summary of research on four research projects.National Aeronautics and Space Administration (Grant NGR 22-009-013)U.S. Navy - Office of Naval Research (Contract N00014-76-C-0605)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Science Foundation (Grant ENG74-00131-AO2)U. S. Air Force - Electronic Systems Division (Contract F19628-76-C-0054)National Science Foundation (Grant ENG74-03996-A1

Optical Propagation and Communication

Contains research objectives and reports on two research projects.National Science Foundation (Grant ENG78-21603)U.S. Army Research Office - Durham (Contract DAAG29-80-C-0010)Joint Services Electronics Program (Contract DAAG29-78-C-0020

Caractérisation des sédiments des retenues pour la prévision des risques écotoxicologiques liés aux vidanges

L'acumulation de sédiments dans les retenues de barrages hydro-électriques nécessite de procéder à des opérations régulières de désenvasement indispensables à leur bon fonctionnement.Ces opérations de vidange ont le plus souvent un effet destructeur sur la faune et la flore aquatique.Cet effet destructeur est principalement lié à une diminution de la concentration en oxygène dissous et une augmentation de la teneur en matières en suspension.La méthodologie présentée a pour but d'estimer préalablement à toute vidange les risques écotoxicologlques correspondant à une telle opération. Elle implique d'une part la description et l'analyse physico-chimique des sédiments en place, d'autre part la mesure en laboratoire de la consommation en oxygène dissous des matériaux remis en suspension au cours du temps.La fiabilité d'une telle procédure a été montrée en particulier à l'occasion de vidanges de retenues situées sur le cours de l'Isère.Le protocole est décrit précisément de façon à pouvoir guider les exploitants de retenues à l'occasion des opérations de vidange qu'ils dirigent.Sediment silting up in hydroelectric dams Implies regular draining operations in order to prevent disfunction of the dams.These operations often lead to drastic lethal affects on aquatic fauna and flora.A toxicological study has clearly shown two main factors responsible for acute toxicological effects : dissolved oxygen deficit and suspended solids increase.These effects have been quantified by experimental tests on Brown trout fry (Salmo trutta fario) the results of which are summarized.The second step consisted in the prediction of water quality evolution downstream during dam draining operation, regarding both factors suspected, in order to assess ecotoxicological hazard.The proposed methodology based on a sedimentological study made in Grangent dam, located on river Loire and immediately downstream of St. Etienne urban area, and in St. Hilaire dam situated on the river Isère downstream partIt consists in sampling cored sediments and in measuring dissolved oxygen kinetic by mixing sediments with water In a reactor.The sample conservation as carried out in jar glasses kept at 4 °C.Results are reproducible as long as residual dissolved oxygen concentration is higher than 3 mg/l. If this condition is respected, oxygen consumption is strictly dependent on suspended sediment concentration.An increase in test water temperature makes the oxygen consumption rise.In accordance with these results, recommendations for dissolved oxygen measures are about 5 g/l suspended sediment concentration, with an experimental temperature reaching the temperature observed during dam draining.The variability of the results for different samples depends on the dam studied. Surface tore samples collected in St. Hilaire dam consume dissolved oxygen faster than the same bottom tore samples.However, in Grangent dam, only one surface core sample collected near the dam construction has clearly shown reducing properties. The difference between two dam sediments is very important : Grangent dam sediment have, on average, dissolved oxygen consumption three more times higher than St. Hilaire in the same duration.Taking into account dissolved oxygen kinetics by mixed sediments, and a simple aeration model using water and sediment deposits from downstream dam, may expert both suspended sediment and oxygen consumption evolution.Hazardous mortality of trout fario fry in downstream dam are quickly graphically visualized.Dam draining operator may so assess, for different suspended sediment land the harmful exposition to fish at any distance from it.This knowledge allows him to plan more strictly floodgate working : pointly dissolved oxygen continuous measurement on downstream dam is sufficient to give a mark related to model hazard assessment.The model reliability has been demonstrated by the examination of data collected during St. Hilaire dam draining operation

Unsplittable coverings in the plane

A system of sets forms an {\em $m$-fold covering} of a set $X$ if every point of $X$ belongs to at least $m$ of its members. A $1$-fold covering is called a {\em covering}. The problem of splitting multiple coverings into several coverings was motivated by classical density estimates for {\em sphere packings} as well as by the {\em planar sensor cover problem}. It has been the prevailing conjecture for 35 years (settled in many special cases) that for every plane convex body $C$, there exists a constant $m=m(C)$ such that every $m$-fold covering of the plane with translates of $C$ splits into $2$ coverings. In the present paper, it is proved that this conjecture is false for the unit disk. The proof can be generalized to construct, for every $m$, an unsplittable $m$-fold covering of the plane with translates of any open convex body $C$ which has a smooth boundary with everywhere {\em positive curvature}. Somewhat surprisingly, {\em unbounded} open convex sets $C$ do not misbehave, they satisfy the conjecture: every $3$-fold covering of any region of the plane by translates of such a set $C$ splits into two coverings. To establish this result, we prove a general coloring theorem for hypergraphs of a special type: {\em shift-chains}. We also show that there is a constant $c>0$ such that, for any positive integer $m$, every $m$-fold covering of a region with unit disks splits into two coverings, provided that every point is covered by {\em at most} $c2^{m/2}$ sets

Reconciling Taking the Indian out of the Nurse

Currently, we are faced with an important equity gap and opportunity for nursing in higher education related to Indigenous Peoples and health. While Westernized higher education often marginalizes Indigenous Peoples, there is an important opportunity to respectfully engage with Indigenous Knowledges. Furthermore, broadening perspectives beyond a dominant Westernized worldview has the potential to advance higher education for Indigenous and non-Indigenous learners alike. We are concerned that ongoing assimilation of Indigenous learners poses a profound risk of social injustice that is contrary to the aim of higher education. In our effort to reconcile nursing education in this context, we offer this discussion paper of scholarly and grey literature interwoven with story work by Indigenous nursing students regarding their undergraduate experiences in the academy. Two significant interrelated gaps/opportunities are revealed: enactment of cultural safety and respectful engagement with Indigenous Knowledges. Action strategies include heart-mind knowledge connection, contextual learning, and two-way teaching and learning. It is our hope that this discussion will inspire critical conversations and meaningful action for educators to reconcile higher education and address structural racism. While reconciliation may be viewed as a duty in higher education and society, we further recognize it as a natural fit within the caring ethos of nursing. Résumé Nous sommes confrontés à d’importantes inégalités relativement à la santé des Autochtones et aux possibilités d’enseignement supérieur en sciences infirmières pour eux. Alors que l’enseignement supérieur occidentalisé marginalise souvent les peuples autochtones, il a une occasion de faire respectueusement appel à leurs Connaissances. S’ouvrir aux perspectives au-delà de la vision du monde occidentalisée dominante pourrait faire progresser l’enseignement supérieur pour les étudiants autochtones et non autochtones. Nous craignons que l’assimilation en cours des étudiants autochtones constitue un signe important d’injustice sociale contraire à l’objectif de l’enseignement supérieur. Dans un esprit de conciliation de la formation en sciences infirmières, nous proposons ce texte de discussion appuyé de publications universitaires, de la littérature grise et de récits d’étudiantes autochtones en sciences infirmières sur leur parcours universitaire au premier cycle. Deux importantes lacunes/possibilités étroitement inter-reliées ont été mises au jour : la mise en œuvre de la sécurité culturelle et le recours respectueux aux Connaissances Autochtones. Les stratégies d’action préconisées portent notamment sur l’ouverture cœur/esprit aux connaissances, l’apprentissage contextuel ainsi que l’enseignement et l’apprentissage bidirectionnels. Nous espérons que cette discussion inspirera d’importantes conversations et des actions significatives chez les enseignants en vue de rapprocher l’enseignement supérieur et de lutter contre le racisme structurel. Bien que la réconciliation puisse être considérée comme un devoir dans le domaine de l’enseignement supérieur et dans la société, nous reconnaissons également qu’il s’agit d’une adéquation naturelle au sein de la philosophie du soin en sciences infirmières

Analysis of cold worked holes for structural life extension

Cold working holes for improved fatigue life of fastener holes are widely used on aircraft. This paper presents methods used by the authors to determine the percent of cold working to be applied and to analyze fatigue crack growth of cold worked fastener holes. An elastic, perfectly-plastic analysis of a thick-walled tube is used to determine the stress field during the cold working process and the residual stress field after the process is completed. The results of the elastic/plastic analysis are used to determine the amount of cold working to apply to a hole. The residual stress field is then used to perform damage tolerance analysis of a crack growing out of a cold worked fastener hole. This analysis method is easily implemented in existing crack growth computer codes so that the cold worked holes can be used to extend the structural life of aircraft. Analytical results are compared to test data where appropriate