Improving rail wear and RCF performance using laser cladding

Laser cladding has been considered as a method for improving the wear and RCF performance of standard grade rail. This paper presents results of small scale tests carried out to assess the wear and RCF performance of rail which had been laser clad. Using the laser cladding process premium metals can be deposited on to the working surface of standard rail with the aim of enhancing the wear and RCF life of the rail. Various laser clad samples were tested using a twin-disc method. The candidate metals were clad on to standard R260 grade rail discs and were tested against a disc of standard wheel material. During the tests, wear rates and RCF initiation were monitored and compared to those of a standard rail disc. Six candidate cladding materials were chosen for this test: A multi-phase Manganese Steel Variant (MMV), Martensitic Stainless Steel (MSS), TWIP Steel, NiCrBSi, Stellite 12 and Stellite 6. The MSS, Stellite 6, and Stellite 12 samples showed reduced wear rates relative to the standard R260 Grade rail discs, and also produced a reduction in wheel steel wear. The RCF initiation resistance of all of the candidate materials was superior compared to the R260 Grade material

Laser cladding of rail; the effects of depositing material on lower rail grades

This paper presents a study comparing the wear performance of laser clad rails. A grade of martensitic stainless steel (MSS) was deposited on two substrate materials: The European standard grade rail steel R260, and a lower grade rail steel R200. A twin-disc method has been used to simulate the contact of wheel and rail under closely controlled conditions. Although cladding on a lesser grade of rail has an effect on the hardness and wear performance of the clad layer (due to dilution), the resulting wear performance of the clad layer assessed using this approach is still vastly improved over R260 material alone

Density-dependent, central-place foraging in a grazing herbivore: competition and tradeoffs in time allocation near water

Optimal foraging theory addresses one of the core challenges of ecology: predicting the distribution and abundance of species. Tests of hypotheses of optimal foraging, however, often focus on a single conceptual model rather than drawing upon the collective body of theory, precluding generalization. Here we demonstrate links between two established theoretical frameworks predicting animal movements and resource use: central-place foraging and density-dependent habitat selection. Our goal is to better understand how the nature of critical, centrally placed resources like water (or minerals, breathing holes, breeding sites, etc.) might govern selection for food (energy) resources obtained elsewhere - a common situation for animals living in natural conditions. We empirically test our predictions using movement data from a large herbivore distributed along a gradient of water availability (feral horses, Sable Island, Canada, 2008–2013). Horses occupying western Sable Island obtain freshwater at ponds while in the east horses must drink at self-excavated wells (holes). We studied the implications of differential access to water (time needed for a horse to obtain water) on selection for vegetation associations. Consistent with predictions of density-dependent habitat selection, horses were reduced to using poorer-quality habitat (heathland) more than expected close to water (where densities were relatively high), but were free to select for higher-quality grasslands farther from water. Importantly, central-place foraging was clearly influenced by the type of water-source used (ponds vs. holes, the latter with greater time constraints on access). Horses with more freedom to travel (those using ponds) selected for grasslands at greater distances and continued to select grasslands at higher densities, whereas horses using water holes showed very strong density-dependence in how habitat could be selected. Knowledge of more than one theoretical framework may be required to explain observed variation in foraging behavior of animals where multiple constraints simultaneously influence resource selection

Too much of a good thing:Sea ice extent may have forced emperor penguins into refugia during the last glacial maximum

The relationship between population structure and demographic history is critical to understanding microevolution and for predicting the resilience of species to environmental change. Using mitochondrial DNA from extant colonies and radiocarbon-dated subfossils, we present the first microevolutionary analysis of emperor penguins (Aptenodytes forsteri) and show their population trends throughout the last glacial maximum (LGM, 19.5–16 kya) and during the subsequent period of warming and sea ice retreat. We found evidence for three mitochondrial clades within emperor penguins, suggesting that they were isolated within three glacial refugia during the LGM. One of these clades has remained largely isolated within the Ross Sea, while the two other clades have intermixed around the coast of Antarctica from Adélie Land to the Weddell Sea. The differentiation of the Ross Sea population has been preserved despite rapid population growth and opportunities for migration. Low effective population sizes during the LGM, followed by a rapid expansion around the beginning of the Holocene, suggest that an optimum set of sea ice conditions exist for emperor penguins, corresponding to available foraging area

A temperate former West Antarctic ice sheet suggested by an extensive zone of bed channels

Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the icesheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods

Autonomous vehicle decision-making: Should we be bio-inspired?

© Springer International Publishing AG 2017. On our crowded roads, drivers must compete for space but cooperate to avoid occupying the same space at the same time. Decision-making is strategic and requires mutual understanding of other’s choices. Fully autonomous vehicles (AVs) will need risk management software to make these types strategic decisions without human arbitration. Accidents will occur, and what constitutes rational and ‘safe’ decisions will be scrutinized by the legal system. It is far from clear how AV-Human and AV-AV interactions should be managed. Game Theory provides a framework for analyzing mutual ‘games’ with 2 or more players. It assumes that players mutually optimize their outcomes according to Nash equilibria (NE), but do humans follow Nash equilibria in Human-Human interactions? We implemented simple two-player competitive games to see whether people played rationally according to Nash equilibria. On each of 100 trials, each player was instructed to maximise their reward by pressing one of three buttons labelled “4”, “6”, and “12”, without knowing the other players choice. If players pressed different buttons, they received a reward of 4, 6, or 12 points accordingly. If players pressed the same button, the reward was reduced depending on the game type. Results showed that players did not follow NE, but played a probabilistic game that included the “4” button, even though pressing this button is always suboptimal. We suggest that this may be an evolutionary strategy, but it clearly shows that people do not follow the ‘rational’ Nash strategy. It seems that AV-human interactions will be probabilistic. In AV-AV interactions, software may be playing itself, and may also require probabilistic optimal evolutionary-type strategies. We doubt that the full implications of autonomous decision-making have been fully worked out. Whether probabilistic decisions will tolerated legally and actuarially is doubtful. One way to avoid them would be to allow regulated AV-AV communications, and force software decisions to be deterministic according to some protocol. However, AV-Human interactions seem likely to remain problematic

Climate Change Impacts on Southern Ross Sea Phytoplankton Composition, Productivity, and Export

The Ross Sea, a highly productive region of the Southern Ocean, is expected to experience warming during the next century along with reduced summer sea ice concentrations and shallower mixed layers. This study investigates how these climatic changes may alter phytoplankton assemblage composition, primary productivity, and export. Glider measurements are used to force a one-dimensional biogeochemical model, which includes diatoms and both solitary and colonial forms of Phaeocystis antarctica. Model performance is evaluated with glider observations, and experiments are conducted using projections of physical drivers for mid-21st and late-21st century. These scenarios reveal a 5% increase in primary productivity by midcentury and 14% by late-century and a proportional increase in carbon export, which remains approximately 18% of primary production. In addition, scenario results indicate diatom biomass increases while P. antarctica biomass decreases in the first half of the 21st century. In the second half of the century, diatom biomass remains relatively constant and P. antarctica biomass increases. Additional scenarios examining the independent contributions of expected future changes (temperature, mixed layer depth, irradiance, and surface iron inputs from melting ice) demonstrate that earlier availability of low light due to reduction of sea ice early in the growing season is the primary driver of productivity increases over the next century; shallower mixed layer depths additionally contribute to changes of assemblage composition and export. This study further demonstrates how glider data can be effectively used to facilitate model development and simulation, and inform interpretation of biogeochemical observations in the context of climate change

Remote sensing reveals Antarctic green snow algae as important terrestrial carbon sink

Abstract: We present the first estimate of green snow algae community biomass and distribution along the Antarctic Peninsula. Sentinel 2 imagery supported by two field campaigns revealed 1679 snow algae blooms, seasonally covering 1.95 × 106 m2 and equating to 1.3 × 103 tonnes total dry biomass. Ecosystem range is limited to areas with average positive summer temperatures, and distribution strongly influenced by marine nutrient inputs, with 60% of blooms less than 5 km from a penguin colony. A warming Antarctica may lose a majority of the 62% of blooms occupying small, low-lying islands with no high ground for range expansion. However, bloom area and elevation were observed to increase at lower latitudes, suggesting that parallel expansion of bloom area on larger landmasses, close to bird or seal colonies, is likely. This increase is predicted to outweigh biomass lost from small islands, resulting in a net increase in snow algae extent and biomass as the Peninsula warms

Full-scale testing of laser clad railway track; case study - testing for wear, bend fatigue and insulated block joint lipping integrity

This paper reports on a series of tests which were carried out on full-scale sections of rail that had been treated by laser cladding aiming to create a layer (~1-2mm) of high performance material on the rail head. Experiments were designed to measure wear, lipping of insulated block joints (IBJs) and bending fatigue of clad samples. The wear rate of the clad samples was between 78- 89% lower than that of the standard R260 reference sample. Cladding of either side of an insulated block joint greatly improves its lipping resistance and allows it to withstand approximately 3 times the energy input into the contact compared to a standard un-clad IBJ. A section of rail clad with martensitic stainless steel was subject to bend fatigue testing and ran out to 5,000,000 cycles at a stress range of 350 MPa matching the performance of an unclad R260 rail. Although there is no standard for the bend testing of laser clad rail this performance exceeds the performance requirements of the NR/SP/TRK111 standard which governs the bend testing of flash but welded rail

Collective Animal Behavior from Bayesian Estimation and Probability Matching

Animals living in groups make movement decisions that depend, among other factors, on social interactions with other group members. Our present understanding of social rules in animal collectives is based on empirical fits to observations and we lack first-principles approaches that allow their derivation. Here we show that patterns of collective decisions can be derived from the basic ability of animals to make probabilistic estimations in the presence of uncertainty. We build a decision-making model with two stages: Bayesian estimation and probabilistic matching.
In the first stage, each animal makes a Bayesian estimation of which behavior is best to perform taking into account personal information about the environment and social information collected by observing the behaviors of other animals. In the probability matching stage, each animal chooses a behavior with a probability given by the Bayesian estimation that this behavior is the most appropriate one. This model derives very simple rules of interaction in animal collectives that depend only on two types of reliability parameters, one that each animal assigns to the other animals and another given by the quality of the non-social information. We test our model by obtaining theoretically a rich set of observed collective patterns of decisions in three-spined sticklebacks, Gasterosteus aculeatus, a shoaling fish species. The quantitative link shown between probabilistic estimation and collective rules of behavior allows a better contact with other fields such as foraging, mate selection, neurobiology and psychology, and gives predictions for experiments directly testing the relationship between estimation and collective behavior