2,074 research outputs found
âWalking ... just walkingâ: how children and young peopleâs everyday pedestrian practices matter
In this paper we consider the importance of âwalking⊠just walkingâ for many children and young peopleâs everyday lives. We will show how, in our research with 175 9-16-year-olds living in new urban developments in south-east England, some particular (daily, taken-for-granted, ostensibly aimless) forms of walking were central to the lives, experiences and friendships of most children and young people. The main body of the paper highlights key characteristics of these walking practices, and their constitutive role in these children and young peopleâs social and cultural geography. Over the course of the paper we will argue that âeveryday pedestrian practicesâ (after Middleton 2010, 2011) like these require us to think critically about two bodies of geographical and social scientific research. On one hand, we will argue that the large body of research on childrenâs spatial range and independent mobility could be conceptually enlivened and extended to acknowledge bodily, social, sociotechnical and habitual practices. On the other hand, we will suggest that the empirical details of such practices should prompt critical reflection upon the wonderfully rich, multidisciplinary vein of conceptualisation latterly termed ânew walking studiesâ (Lorimer 2011). Indeed, in conclusion we shall argue that the theoretical vivacity of walking studies, and the concerns of more applied empirical approaches such as work on childrenâs independent mobility, could productively be interrelated. In so doing we open out a wider challenge to social and cultural geographers, to expedite this kind of interrelation in other research contexts
Intra-Specific Difference in the Effect of Salinity on Physiological Performance in European Perch (<i>Perca fluviatilis</i>) and Its Ecological Importance for Fish in Estuaries
Changes in environmental salinity challenge fish homeostasis and may affect physiological performance, such as swimming capacity and metabolism, which are important for foraging, migration, and escaping predators in the wild. The effects of salinity stress on physiological performance are largely species specific, but may also depend on intra-specific differences in physiological capabilities of sub-populations. We measured critical swimming speed (U
crit
) and metabolic rates during swimming and at rest at salinities of 0 and 10 in European perch (
Perca fluviatilis
) from a low salinity tolerance population (LSTP) and a high salinity tolerance population (HSTP). U
crit
of LSTP was significantly reduced at a salinity of 10 yet was unaffected by salinity change in HSTP. We did not detect a significant cost of osmoregulation, which should theoretically be apparent from the metabolic rates during swimming and at rest at a salinity of 0 compared to at a salinity of 10 (iso-osmotic). Maximum metabolic rates were also not affected by salinity, indicating a modest tradeoff between respiration and osmoregulation (osmo-respiratory compromise). Intra-specific differences in effects of salinity on physiological performance are important for fish species to maintain ecological compatibility in estuarine environments, yet render these sub-populations vulnerable to fisheries. The findings of the present study are therefore valuable knowledge in conservation and management of estuarine fish populations
An Index to Assess the Sensitivity of Gulf of Mexico Species to Changes in Estuarine Salinity Regimes
An index of biological sensitivity to changes in freshwater inflow was developed for 44 species in 22 Gulf of Mexico estuaries for adult and juvenile life stages of fishes and macroinvertebrates. The BioSalinity Index (BSI) provides an innovative approach to quantify estuary-specific sensitivity of organisms to changes in estuarine salinity regimes based upon our knowledge of species salinity habitat preferences, the availability of this preferred habitat, and the relative abundance and distribution of species in time and space. We found that a significant difference exists between adult and juvenile life stage sensitivity, with juveniles exhibiting a lower sensitivity to salinity changes than adults, and that a considerable disparity exists in species-specific sensitivities among Gulf estuaries. Likewise, when the full complement of 44 species-level BSIs are averaged, marked differences in assemblage-wide sensitivity are evident across estuaries. The availability of preferred salinity habitat had a greater influence on the BSI for estuarine species than did their relative abundance and temporal distribution. The BSI was applied by members of a 1995 Gulf of Mexico freshwater inflow workshop to identify a subset of estuaries which appear more sensitive to freshwater inflow changes and are candidates for further study
An assessment of chemical contaminants in the marine sediments of southwest Puerto Rico
This report summarizes the results of a characterization
of chemical contaminants in the sediments in southwest
Puerto Rico. The report is part of a project to integrate
various analytical specialties to assess linkages between
chemical contaminants and the condition of coral reefs. In this phase of the project, over 120 chemical contaminants were analyzed in sediments collected, including a number of organic (e.g., hydrocarbons), inorganic (e.g., metals), and biological (bacterial) compounds/analytes. The report also provides a preliminary analysis of the association between
sediment contaminants and coral species richness.
Overall, the levels of chemical contaminants in the study area between Guanica Bay and the town of La Parguera were fairly low. At most of the sites sampled, particularly
adjacent to the town of La Parguera, concentrations of
organic and inorganic contaminants were below the median values from NOAAâs National Status and Trends Program, which monitors the Nationâs coastal and estuarine waters for chemical contaminants. Elevated levels of a number of contaminant classes were seen at the two sites sampled within Guanica Bay.
An initial analysis of modeled PAH (hydrocarbon) data and coral species richness (reef building species) indicated a strong negative correlation between the presence of PAHs in the sediments and coral species richness. Additional work is needed to assess possible reasons for this observed pattern. (PDF contains 126 pages)
Low-Loss Plasmonic Dielectric Nanoresonators
Material losses in metals are a central bottleneck in plasmonics for many applications. Here we propose and theoretically demonstrate that metal losses can be successfully mitigated with dielectric particles on metallic films, giving rise to hybrid dielectric-metal resonances. In the far field, they yield strong and efficient scattering, beyond even the theoretical limits of all-metal and all-dielectric structures. In the near field, they offer high Purcell factor (>5000), high quantum efficiency (>90%), and highly directional emission at visible and infrared wavelengths. Their quality factors can be readily tailored from plasmonic-like (âŒ10) to dielectric-like (âŒ103), with wide control over the individual resonant coupling to photon, plasmon, and dissipative channels. Compared with conventional plasmonic nanostructures, such resonances show robustness against detrimental nonlocal effects and provide higher field enhancement at extreme nanoscopic sizes and spacings. These hybrid resonances equip plasmonics with high efficiency, which has been the predominant goal since the fieldâs inception. Keywords: light scattering; nanoantennas; Nanoparticles; nonlocality; radiative efficiency; spontaneous emissionUnited States. Army Research Office (Contract W911NF-13-D-0001)National Science Foundation (U.S.) (Grant DMR-1419807)United States. Department of Energy (Grant DE-SC0001299
Quasicrystalline Weyl points and dense Fermi-Bragg arcs
We introduce a general mechanism for obtaining Weyl points in a stack of 2D
quasicrystals, which can be extended to any stack of aperiodic layers. We do so
by driving a topological phase transition with the vertical crystal-momentum as
the tuning parameter, which leads to gap closures at the critical points
sourcing Berry curvature. To illustrate, we use a simple 3D generalization of
the Qi-Wu-Zhang model defined on a Penrose quasicrystal. The presence of Weyl
points is established via the local Chern marker, projected band structure and
density of states. Interestingly, we uncover an analogue of Fermi arcs in the
quasicrystalline setting, which we deem Fermi-Bragg arcs, densely distributed
lines connecting the band degeneracies and indexed by the Bragg peaks.
Signatures of such surface states in quantum oscillations and the prospect of a
fully quasicrystalline Weyl system are also discussed. The flexibility of our
proposal brings new opportunities for realizing other gapless topological
phases in aperiodic systems, paving the way for a significantly expanded role
for topological band theory.Comment: 6 pages, 3 figure
Positivity of Spin Foam Amplitudes
The amplitude for a spin foam in the Barrett-Crane model of Riemannian
quantum gravity is given as a product over its vertices, edges and faces, with
one factor of the Riemannian 10j symbols appearing for each vertex, and simpler
factors for the edges and faces. We prove that these amplitudes are always
nonnegative for closed spin foams. As a corollary, all open spin foams going
between a fixed pair of spin networks have real amplitudes of the same sign.
This means one can use the Metropolis algorithm to compute expectation values
of observables in the Riemannian Barrett-Crane model, as in statistical
mechanics, even though this theory is based on a real-time (e^{iS}) rather than
imaginary-time (e^{-S}) path integral. Our proof uses the fact that when the
Riemannian 10j symbols are nonzero, their sign is positive or negative
depending on whether the sum of the ten spins is an integer or half-integer.
For the product of 10j symbols appearing in the amplitude for a closed spin
foam, these signs cancel. We conclude with some numerical evidence suggesting
that the Lorentzian 10j symbols are always nonnegative, which would imply
similar results for the Lorentzian Barrett-Crane model.Comment: 15 pages LaTeX. v3: Final version, with updated conclusions and other
minor changes. To appear in Classical and Quantum Gravity. v4: corrects # of
samples in Lorentzian tabl
A habitat-use model to determine essential fish habitat for juvenile brown shrimp (Farfantepenaeus aztecus) in Galveston Bay, Texas
A density prediction model for juvenile brown shrimp (Farfantepenaeus aztecus) was developed by using three bottom types, five salinity zones, and four seasons to quantify patterns of habitat use in Galveston Bay, Texas. Sixteen years of quantitative density data were used. Bottom types were vegetated marsh edge, submerged aquatic vegetation, and shallow nonvegetated bottom. Multiple regression was used to develop density estimates, and the resultant formula was then coupled with a geographical information system (GIS) to provide a spatial mosaic (map) of predicted habitat use. Results indicated that juvenile brown shrimp (0.50. These results indicate that this model may have a broader geographic application and is a plausible approach in refining current EFH designations for all Gulf of Mexico estuaries with similar geomorphological and hydrological characteristics
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