Ratcheting of granular materials

We investigate the quasi-static mechanical response of soils under cyclic loading using a discrete model of randomly generated convex polygons. This response exhibits a sequence of regimes, each one characterized by a linear accumulation of plastic deformation with the number of cycles. At the grain level, a quasi-periodic ratchet-like behavior is observed at the contacts, which excludes the existence of an elastic regime. The study of this slow dynamics allows to explore the role of friction in the permanent deformation of unbound granular materials supporting railroads and streets.Comment: Changed content Submitted to Physical Review Letter

Examining the Personal and Institutional Determinants of Research Productivity in Hospitality and Tourism Management

The transition toward a post-capitalist knowledge-oriented economy has resulted in an increasingly competitive academic environment, where the success of faculty is dependent on their research productivity. This study examines the personal and institutional determinants of the quantity and quality of the research productivity of hospitality and tourism management faculty in US institutions. A survey of 98 faculty found that a different set of determinants impact the quantity and quality aspects of research productivity. Also, institutional determinants were found to play a larger role, indicating the need for administrators to strive for a culture that is supportive of and an infrastructure that is conducive to their faculty’s research success. The authors use the field of hospitality and tourism management as a case study to develop a holistic and cohesive framework for knowledge worker productivity that can guide the evaluation, hiring, and development of researchers

Navigation/traffic control satellite mission study. Volume 3 - System concepts

Satellite network for air traffic control, solar flare warning, and collision avoidanc

Infrastructure: A technology battlefield in the 21st century

A major part of technological advancement has involved the development of complex infrastructure systems, including electric power generation, transmission, and distribution networks; oil and gas pipeline systems; highway and rail networks; and telecommunication networks. Dependence on these infrastructure systems renders them attractive targets for conflict in the twenty-first century. Hostile governments, domestic and international terrorists, criminals, and mentally distressed individuals will inevitably find some part of the infrastructure an easy target for theft, for making political statements, for disruption of strategic activities, or for making a nuisance. The current situation regarding the vulnerability of the infrastructure can be summarized in three major points: (1) our dependence on technology has made our infrastructure more important and vital to our everyday lives, this in turn, makes us much more vulnerable to disruption in any infrastructure system; (2) technologies available for attacking infrastructure systems have changed substantially and have become much easier to obtain and use, easy accessibility to information on how to disrupt or destroy various infrastructure components means that almost anyone can be involved in this destructive process; (3) technologies for defending infrastructure systems and preventing damage have not kept pace with the capability for destroying such systems. A brief review of these points will illustrate the significance of infrastructure and the growing dangers to its various elements

Cyclic-routing of Unmanned Aerial Vehicles

© 2019 Various missions carried out by Unmanned Aerial Vehicles (UAVs) are concerned with permanent monitoring of a predefined set of ground targets under relative deadline constraints, i.e., the targets have to be revisited ‘indefinitely’ and there is an upper bound on the time between two consecutive successful scans of each target. A solution to the problem is a set of routes—one for each UAV—that jointly satisfy these constraints. Our goal is to find a solution with the least number of UAVs. We show that the decision version of the problem (given k, is there a solution with k UAVs?) is PSPACE-complete. On the practical side, we propose a portfolio approach that combines the strengths of constraint solving and model checking. We present an empirical evaluation of the different solution methods on several hundred randomly generated instances

Evolution of habitat and environment of red deer (Cervus elaphus) during the Lateglacial and early Holocene in eastern France using stable isotope composition ( d13C, d15N, d18O) of archaeological bones.

International audienceRed deer (Cervus elaphus) is a flexible species that survived the significant climatic and environmental change toward warming temperature and forested landscape of the Late-glacial to early Holocene transition (ca. 17–6 ka cal BP). To investigate the conditions of ethological adaptation of red deer at that time, isotopic analysis of carbon, nitrogen, sulfur in collagen (δ13Ccoll, δ15Ncoll, δ34Scoll) and of oxygen in phosphate (δ18Op) were performed on red deer from archaeological sites of the French Jura and the western Alps. Fifty out of eighty two samples benefited from direct AMS radiocarbon dating, which confirmed the few number of red deer record during the cold Younger Dryas oscillation (ca. 12.8–11.6 ka cal BP) in Western Europe. The French Jura red deer showed a significant decrease in their δ13Ccoll values and increase in their δ15Ncoll values in the early Holocene compared to the Late-glacial, which is most likely due to the change in environment from open areas with low pedogenic activity to warm dense forests with increasing soil maturity. In contrast, the stable δ13Ccoll and δ15Ncoll values over time in the western Alps were thought to indicate a change to higher altitude for the red deer habitat in this mountainous region. A decrease of the δ18Op values between the Late-glacial and the early Holocene was observed in the western Alps red deer, in contrast to the expected increase with rising temperature which was indeed confirmed for the French Jura red deer. The multi-isotope results pointed to open areas home range at higher altitude for the Alps red deer in the Holocene compared to the previous period. The similarity of the δ34Scoll patterns with those of the δ15Ncoll suggested the primarily influence of soil activity on the 34S abundances recorded by red deer in a purely terrestrial context. Red deer of the French Jura on one hand and of the western Alps on the other hand showed different adaptive response to the global warming of the early Holocene, with an ethological change in the first case and a change in home range in the second case

I RAPPORTI ECONOMICO-FINANZIARI TRA ITALIA E REPUBBLICA DI SAN MARINO

Circadian clocks coordinate 24-hr rhythms of behavior and physiology. In mammals, a master clock residing in the suprachiasmatic nucleus (SCN) is reset by the light-dark cycle, while timed food intake is a potent synchronizer of peripheral clocks such as the liver. Alterations in food intake rhythms can uncouple peripheral clocks from the SCN, resulting in internal desynchrony, which promotes obesity and metabolic disorders. Pancreas-derived hormones such as insulin and glucagon have been implicated in signaling mealtime to peripheral clocks. In this study, we identify a novel, more direct pathway of food-driven liver clock resetting involving oxyntomodulin (OXM). In mice, food intake stimulates OXM secretion from the gut, which resets liver transcription rhythms via induction of the core clock genes Per1 and 2. Inhibition of OXM signaling blocks food-mediated resetting of hepatocyte clocks. These data reveal a direct link between gastric filling with food and circadian rhythm phasing in metabolic tissues