Measuring and modeling the speed of human navigation

Navigation, the goal-related movement through space and time to reach a destination, is a fundamental human activity. Geographers, physiologists, anthropologists, and psychologists have long been interested in the spatial and temporal aspects of navigation speed. Hikers, search and rescue teams, firefighters, the military, and others navigate on foot, and their success depends on understanding how the dynamics of foot-based navigation affect individual capabilities. This research modeled the speed of movement of humans engaged in navigation in wooded environments with varied terrain. Movement models were developed using spatiotemporal analysis of multiple subjects’ trajectories. Speed estimates were collected via satellite positioning from 200 subjects engaged in foot-based navigation. Trajectory data were merged with land-cover data to analyze human navigation over varying slopes and terrain. Generalizing these characteristics provided a model of navigational speed of movement from an origin to a destination along an unknown route. Tobler’s hiking function and Naismith’s rule were used in an analysis of the trajectory data. The model created from this study was shown to outperform those classic human movement speed estimators by predicting route completion time within 10% accuracy (M = 11.1min, 95% CI [9.8, 12.4] min). These models help explain the human dynamics of navigation.]     

Post‐glacial biota from the inner part of southwest Joseph Bonaparte Gulf

Seventeen vibrocores from the inner part of Joseph Bonaparte Gulf off northwestern Australia penetrate a range of marine and marginal‐marine sediments deposited in the post‐glacial transgression and highstand. Ranging from gravelly sand to fine silt, these sediments contain a diverse fossil biota dominated by molluscs and bryozoans, but also including ostracods and foraminifers. Minor components include solitary corals, echinoids, soft coral and sponge spicules, wood debris and bone fragments. The biota can be divided into five major marine or marginal‐marine environments (intertidal, lagoonal, estuarine, strandline and shelf) and one terrestrial (riverine) environment. The intertidal environment contains four sub‐assemblages (mangroves, salt marsh, mud flat and sand flat) and the shelf environment six sub‐assemblages (hard substrate inner shelf, sandy substrate inner shelf, muddy substrate inner shelf, epiphytic, inshore and oceanic). The most useful organisms for palaeoenvironmental reconstruction are bryozoans for differentiating various shallow‐marine substrates, and foraminifers and ostracods for defining water depths, euryhaline, freshwater and oceanic influences. Palynomorphs were the only microfossils capable of providing control on terrestrial environments. The scarcity of marine plankton and the dominance of terrestrial palynomorphs in these marine sediments provides a salutary warning of the dangers of relying on plant microfossils alone when no independent environmental data are available to test the interpretation. The mollusc and bryozoan biota in the inner part of Joseph Bonaparte Gulf superficially resembles the bryomol assemblage of cool‐water shelves. This biotic assemblage is the result of turbidity rather than water temperature. The turbidity suppresses the photosynthetic, zooxanthellate and hermatypic organisms allowing molluscs, bryozoans and other apparently cool‐water biotic elements to dominate.     

Precipitation trends using in-situ and gridded datasets

Six in situ precipitation time series of varying time periods in the northwestern region and the Global Precipitation Climatology Centre (GPCC) v6 0.5° monthly dataset (1901–2010) were statistically examined for monotonic trends in Trinidad. The Pettit test was used to investigate the abrupt changes in the mean while the Mann–Kendall test was employed to assess the monotonic trends. It was found that three in situ stations and the six grids experienced abrupt changes in the rainfall patterns and that there was an apparent shift in the seasons. In addition, for five out of the six in situ stations no monotonic change was detected in the monthly, seasonal, and annual rainfall patterns. Gradual decreases were detected in the calculated weighted area average for five stations, the GPCCv6 dataset and St. Ann’s time series. The GPCCv6 data indicated that the dry season in the southern Trinidad is becoming drier. Results also suggested that the range between the greatest and lowest recorded rainfall values for some months have increased while others decreased. The gridded dataset appears to give a good representation of the dry season (January to May) rainfall compared with the wet season (June to December) and was found to be negatively biased for the north-western region but may not necessarily be so for the entire island. The results suggested that in the north-western region mirco-climates may exist. It is recommended that further investigations are needed using in situ data.     

The Importance of Regional,System-Wide and Local Spatial Scales in Structuring Temperate Estuarine Fish Communities

An extensive literature base worldwide demonstrates how spatial differences in estuarine fish assemblages are related to those in the environment at (bio)regional, estuary-wide or local (within-estuary) scales. Few studies, however, have examined all three scales, and those including more than one have often focused at the level of individual environmental variables rather than scales as a whole. This study has identified those spatial scales of environmental differences, across regional, estuary-wide and local levels, that are most important in structuring ichthyofaunal composition throughout south-western Australian estuaries. It is the first to adopt this approach for temperate microtidal waters. To achieve this, we have employed a novel approach to the BIOENV routine in PRIMER v6 and a modified global BEST test in an alpha version of PRIMER v7. A combination of all three scales best matched the pattern of ichthyofaunal differences across the study area (ρ?=?0.59; P?=?0.001), with estuary-wide and regional scales accounting for about twice the variability of local scales. A shade plot analysis showed these broader-scale ichthyofaunal differences were driven by a greater diversity of marine and estuarine species in the permanently-open west coast estuaries and higher numbers of several small estuarine species in the periodically-open south coast estuaries. When interaction effects were explored, strong but contrasting influences of local environmental scales were revealed within each region and estuary type. A quantitative decision tree for predicting the fish fauna at any nearshore estuarine site in south-western Australia has also been produced. The estuarine management implications of the above findings are highlighted.     

The rise of corporate retailing and the impacts on small-scale retailing: the survival strategies of Kirana stores and informal street vendors in Durgapur,India

In many developing world economies in recent years, the state has been seen to encourage neoliberal economic expansion policies. This has involved both large-scale foreign corporations and sometimes large-scale domestic corporations. Many studies have discussed the new landscapes of economic hardship and the impacts on small businesses. The aim of this paper is to argue that the impacts on small traders are in fact more complex and varied than usually appears in the literature. The research was conducted in the industrial city of Durgapur in the Bardhaman district of West Bengal, India. First it is argued that the impact has been greatest on the ‘kirana’ owners, operating small convenience type stores with legalized trading arrangements and fixed premises. On the other hand, the street vendors (often unlicensed and having no fixed premises) seem not to be affected in terms of customer loss and indeed could be seen to be doing well against the backcloth of neoliberal expansion. In fact we argue that the growth in the number of street vendors provides as much of a threat to future livelihoods for traditional kirana owners as the growth of large corporations itself.     

Competitive accretion in embedded stellar clusters

We investigate the physics of gas accretion in young stellar clusters. Accretion in clusters is a dynamic phenomenon as both the stars and the gas respond to the same gravitational potential. Accretion rates are highly non-uniform with stars nearer the centre of the cluster, where gas densities are higher, accreting more than others. This competitive accretion naturally results in both initial mass segregation and a spectrum of stellar masses. Accretion in gas-dominated clusters is well modelled using a tidal-lobe radius instead of the commonly used Bondi–Hoyle accretion radius. This works as both the stellar and gas velocities are under the influence of the same gravitational potential and are thus comparable. The low relative velocity which results means that R _tidal< R _BH in these systems. In contrast, when the stars dominate the potential and are virialized, R _BH< R _tidal and Bondi–Hoyle accretion is a better fit to the accretion rates.     

Modeling North American Freshwater Runoff through the Last Glacial Cycle

The Northern Hemisphere ice sheets decayed rapidly during deglacial phases of the ice-age cycle, producing meltwater fluxes that may have been of sufficient magnitude to perturb oceanic circulation. The continental record of ice-sheet history is more obscured during the growth and advance of the last great ice sheets, ca. 120,000–20,000 yr B.P., but ice cores tell of high-amplitude, millennial-scale climate fluctuations that prevailed throughout this period. These climatic excursions would have provoked significant fluctuation of ice-sheet margins and runoff variability whenever ice sheets extended to mid-latitudes, giving a complex pattern of freshwater delivery to the oceans. A model of continental surface hydrology is coupled with an ice-dynamics model simulating the last glacial cycle in North America. Meltwater discharged from ice sheets is either channeled down continental drainage pathways or stored temporarily in large systems of proglacial lakes that border the retreating ice-sheet margin. The coupled treatment provides quantitative estimates of the spatial and temporal patterns of freshwater flux to the continental margins. Results imply an intensified surface hydrological environment when ice sheets are present, despite a net decrease in precipitation during glacial periods. Diminished continental evaporation and high levels of meltwater production combine to give mid-latitude runoff values that are highly variable through the glacial cycle, but are two to three times in excess of modern river fluxes; drainage to the North Atlantic via the St. Lawrence, Hudson, and Mississippi River catchments averages 0.356 Sv for the period 60,000–10,000 yr B.P., compared to 0.122 Sv for the past 10,000 yr. High-amplitude meltwater pulses to the Gulf of Mexico, North Atlantic, and North Pacific occur throughout the glacial period, with ice-sheet geometry controlling intricate patterns of freshwater routing variability. Runoff from North America is staged in the final deglaciation, with a stepped sequence of pulses through the Mississippi, St. Lawrence, Arctic, and Hudson Strait drainages.