Multiproduct firms and product differentiation : a survey

We start the survey by reviewing the implications of horizontal and vertical product differentiation on market structure under the assumption of single-product firms. Then, we analyse the main results of the multi-product firm models, both when variants are assumed differentiated in vertical attributes only and when variants are assumed differentiated in two dimensions (vertical and horizontal). Finally, we review the empirical literature about discrete-choice models of product differentiation

Applying Deweyan Principles to Global Citizenship Education in a Rural Context

Abstract Global citizenship education (GCE) helps students conceptualize citizenship beyond national boundaries so they are capable of action in dealing with global issues like human rights and environmental sustainability. However, very little literature exists to assist rural teachers in implementing GCE as they face specific challenges due to the context of their schools. This paper identifies challenges rural educators encounter, such as conservative communities and geographic isolation, and details a Deweyan approach to GCE as a means to overcome these challenges. Specifically, we apply Dewey’s democratic and social learning theories to reconceptualize GCE around student, family, and community life to foster a more relevant curriculum that utilizes students’ experiences (Dewey, 1897, 1902, 1938, 1916/2008). It emphasizes the utmost respect for local customs and culture by using them as sources of content for the curriculum while simultaneously extending citizenship thoughts and actions to the global arena.

Biodiversity and food web structure influence short-term accumulation of sediment organic matter in an experimental seagrass system

We tested the effects of grazer diversity and food chain length on the quantity and quality of accumulated sediment organic matter (SOM) in experimental eelgrass (Zostera marina) mesocosms. By use of a factorial manipulation of crustacean grazer species richness and predator presence, we examined the effects of epibenthic consumers on SOM composition by using stable carbon isotopes (delta C-13) and lipid biomarker compounds. Grazer species composition strongly influenced nearly all measures of SOM quantity and quality. In particular, increased densities of the grazing amphipod, Gammarus mucronatus, decreased accumulation of benthic microalgae (chlorophyll a) and the relative abundance of polyunsaturated fatty acids (FA, a proxy for labile algal organic matter) and branched FA (a proxy for bacterial biomass). On average, increasing grazer species richness decreased SOM quantity (percentage of total organic carbon). Increasing food chain length by addition of predatory blue crabs (Callinectes sapidus) resulted in a trophic cascade, increasing algal biomass and accumulation of algal organic matter in sediments, and enhancing the quality of SOM. Concomitantly, the relative proportion of bacterial branched FA increased. The identity and number of epibenthic consumers strongly influence accumulation and composition of SOM and the pathways by which it is processed, and these responses are not easily predictable from bulk measurements (delta C-13, percentage of total organic carbon) alone

Radionuclide and biomarker proxies of past ocean circulation and productivity in the Arabian Sea

We present new excess Pa-231/Th-230 activity ratios and lipid biomarker results from northeastern Arabian Sea sediments (core 93KL) spanning the past 50 ka in an effort to constrain further the relationship between climate at low and high latitudes. Pa-231/Th-230 activity ratios are maintained at values significantly higher than the water-column production ratio of 0.093. Average Pa-231/Th-230 activity ratios are lower during the last glacial period than during the Holocene. The lowest Pa-231/Th-230 activity ratios coincide with the timing of Heinrich Events 1-5. Profiles of lipid biomarker fluxes and Pa-231/Th-230 activity ratios from 32 to 12 ka show similar patterns, suggesting that Pa-231 is more efficiently scavenged relative to Th-230 at times when diatoms make up a proportionally larger part of the primary biomass signal. In the Holocene, high Pa-231/Th-230 activity ratios may indicate enhanced Pa-231 export from the southern to the northern Indian Ocean via intensified thermohaline circulation

A 28-ka history of sea surface temperature, primary productivity and planktonic community variability in the western Arabian Sea

Uranium series radionuclides and organic biomarkers, which represent major groups of planktonic organisms, were measured in western Arabian Sea sediments that span the past 28 ka. Variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity, sea surface temperature (SST), and planktonic community structure were investigated. The average alkenone-derived SST for the last glacial period was similar to 3 degrees C lower than that measured for the Holocene. Prior to the deglacial, the lowest SSTs coincide with the highest measured fluxes of organic biomarkers, which represent primarily a planktonic suite of diatoms, coccolithophorids, dinoflagellates, and zooplankton. We propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing, cold SSTs and enhanced primary productivity. In contrast, postdeglacial (\u3c 17 ka) SSTs are warmer during times in which biomarker fluxes are high. Associated with this transition is a planktonic community structure change, in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and Holocene than the average ratio during the last glacial period. We suggest that this temporal transition represents a shift from a winter northeast monsoon-dominated (pre-17 ka) to a summer southwest monsoon-dominated (post-17 ka) wind system

Effects of northbound long-haul international air travel on sleep quantity and subjective jet lag and wellness in professional Australian soccer players

© 2015 Human Kinetics, Inc. The current study examined the effects of 10-h northbound air travel across 1 time zone on sleep quantity, together with subjective jet lag and wellness ratings, in 16 male professional Australian football (soccer) players. Player wellness was measured throughout the week before (home training week) and the week of (away travel week) travel from Australia to Japan for a preseason tour. Sleep quantity and subjective jet lag were measured 2 d before (Pre 1 and 2), the day of, and for 5 d after travel (Post 1-5). Sleep duration was significantly reduced during the night before travel (Pre 1; 4.9 [4.2-5.6] h) and night of competition (Post 2; 4.2 [3.7-4.7] h) compared with every other night (P 0.90). Moreover, compared with the day before travel, subjective jet lag was significantly greater for the 5 d after travel (P 0.90), and player wellness was significantly lower 1 d postmatch (Post 3) than at all other time points (P 0.90). Results from the current study suggest that sleep disruption, as a result of an early travel departure time (8 PM) and evening match (7:30 PM), and fatigue induced by competition had a greater effect on wellness ratings than long-haul air travel with a minimal time-zone change. Furthermore, subjective jet lag may have been misinterpreted as fatigue from sleep disruption and competition, especially by the less experienced players. Therefore, northbound air travel across 1 time zone from Australia to Asia appears to have negligible effects on player preparedness for subsequent training and competition

Workload profiles prior to injury in professional soccer players

© 2017, © 2017 Informa UK Limited, trading as Taylor & Francis Group. This study examined if a particular profile of internal and external workload existed prior to injury. Forty-five professional soccer players were monitored over two seasons. For each non-contact injury, a profile of workload variables was determined for 4 weeks and expressed as (i) an absolute, (ii) week-to-week change and (iii) relative to the player’s season mean. Variables included exposure, session rating of perceived exertion (s-RPE) workload, total distance, low-, high-, very-high-speed running distance, mean speed, bodyload, monotony and strain. Acute:chronic workload ratio was also calculated and sensitivity of the relative workload was tested. Absolute and relative exposure and s-RPE workload were greater in all 3 weeks compared to the injury week (P  0.05). Acute:chronic workload ratio for s-RPE was significantly greater than acute:chronic workload ratio for very-high-speed running (P = 0.04). A workload threshold of 114% of a player’s season mean reported low sensitivity and specificity for exposure (25.6[20.2–33.5]% and 73.9[22.6–28.2]%,) and s-RPE workload (16.3[12.6–24.9]% and 79.9[20.3–26.1]%, respectively). No specific load profile existed, although high-sustained exposure and s-RPE were evident for the 3 weeks prior to injury. Consequently, load prescription should be aware of sustained high workloads

Probing deeper into the risks of slips, trips and falls for an ageing rail passenger population: applying a systems approach

In this study, the authors report the findings from a study of the contributory factors leading to slips, trips and falls (STFs) amongst elderly passengers at train stations and how these are likely to change in the future over the medium to long term (the period 2035–2050). Their data draws on: stakeholder interviews with rail personnel and elderly passengers; a set of station observations carried out across the UK; and, a survey of the views of station managers. The findings point to a set of 22 contributory factors covering aspects of organisational, station environment and passenger (individual) influence on STFs. Amongst the factors which most concern station managers at the present and over the next few decades are: rushing behaviour on train platforms; the consumption of alcohol by passengers; aspects of station design (e.g. flooring); and, training for station staff as regard the risks of STFs. The authors summarise their findings in the form of a systems model which highlights priorities with regard to STFs in terms of all of the stakeholders taking part in the study. A final section discusses a set of issues which might form the basis for a future agenda for research and practice in this area