Review of river fisheries valuation in Central and South America

Unlike Africa and Asia, where a large part of the population are heavily dependent upon fishing for their livelihoods, fishing for a living in the interior of Central and South America (CSA) remains a marginal occupation for all but the most isolated of families. As such, the economics and management of fisheries on the continent have received little attention from within the continent and the rest of the world. This study shows that while a number of studies have been carried out on fishing in the region, they tend to be limited in their geographical focus and time scale. Although fishing of freshwater species may appear to be comparatively insignificant in the region, the rivers of CSA are very important. This report attempts to analyze the literature available on CSA river fisheries and attempts to draw out an economic value of these fisheries. It is divided into a number of sections. First, the authors describe the major river basins on the continent, characterize their fisheries, and place freshwater fisheries in CSA into a global context. Second, the authors provide a review of valuation techniques for fisheries and use this analytical framework to review the principal literature on freshwater fisheries in the region. Then they turn their attention to the economic impact of dams and water abstraction schemes, reviewing the available literature to ascertain how/if economic values are computed for the impact on fisheries. Finally, they offer some conclusions and recommendations on the direction for future studies of freshwater fisheries in CSA

The Potential of Freeform Construction Processes

The level of automation technology and processes control found in modern day construction lags significantly behind other industries such as automotive and aerospace. The construction industry has health and safety issues and still uses traditional methods of procurement. These problems are compounded by diminishing skills in the labour force. Methods of production must change if these issues are to be resolved and Freeform Construction is a collection of processes that could have potential impact. This paper outlines some of the major issues facing construction and sets a context with examples of digital fabrication in construction. Freeform Construction is defined and potential applications are presented and related to application scale. The viability of two potential applications are investigated in terms of cost.Mechanical Engineerin

Extremely Anisotropic Scintillations

A small number of quasars exhibit interstellar scintillation on time-scales less than an hour; their scintillation patterns are all known to be anisotropic. Here we consider a totally anisotropic model in which the scintillation pattern is effectively one-dimensional. For the persistent rapid scintillators J1819+3845 and PKS1257-326 we show that this model offers a good description of the two-station time-delay measurements and the annual cycle in the scintillation time-scale. Generalising the model to finite anisotropy yields a better match to the data but the improvement is not significant and the two additional parameters which are required to describe this model are not justified by the existing data. The extreme anisotropy we infer for the scintillation patterns must be attributed to the scattering medium rather than a highly elongated source. For J1819+3845 the totally anisotropic model predicts that the particular radio flux variations seen between mid July and late August should repeat between late August and mid November, and then again between mid November and late December as the Earth twice changes its direction of motion across the scintillation pattern. If this effect can be observed then the minor-axis velocity component of the screen and the orientation of that axis can both be precisely determined. In reality the axis ratio is finite, albeit large, and spatial decorrelation of the flux pattern along the major axis may be observable via differences in the pairwise fluxes within this overlap region; in this case we can also constrain both the major-axis velocity component of the screen and the magnitude of the anisotropy.Comment: 5 pages, 4 figures, MNRAS submitte

Asymmetry of jets, lobe size and spectral index in radio galaxies and quasars

We investigate the correlations between spectral index, jet side and extent of the radio lobes for a sample of nearby FRII radio galaxies. In Dennett-Thorpe et al. (1997) we studied a sample of quasars and found that the high surface brightness regions had flatter spectra on the jet side (explicable as a result of Doppler beaming) whilst the extended regions had spectral asymmetries dependent on lobe length. Unified schemes predict that asymmetries due to beaming will be much smaller in narrow-line radio galaxies than in quasars: we therefore investigate in a similar manner, a sample of radio galaxies with detected jets. We find that spectral asymmetries in these objects are uncorrelated with jet sidedness at all brightness levels, but depend on relative lobe volume. Our results are not in conflict with unified schemes, but suggest that the differences between the two samples are due primarily to power or redshift, rather than to orientation. We also show directly that hotspot spectra steepen as a function of radio power or redshift. Whilst a shift in observed frequency due to the redshift may account for some of the steepening, it cannot account for all of it, and a dependence on radio power is required.Comment: accepted for publication in MNRAS, 10 pages; typos/minor correctio

Magnetic properties of microtektites Semiannual status report, 1 Jan. - 31 Jun. 1969

Magnetic susceptibility, magnetization, and Curie constants for normal and bottle-green microtektites found in deep-sea sediment core

Pentagonal puckering in a sheet of amorphous graphene

Ordered graphene has been extensively studied. In this paper we undertake a first density functional study of it topologically disordered analogues of graphene, in the form of a random network, consisting predominantly of hexagonal rings, but also including pentagons and heptagons. After some preliminaries with crystalline material, we relax various random network models and find that the presence of carbon pentagons induce local curvature, thus breaking the initial planar symmetry, in some analogy with the case of fullerenes. Using density functional theory to calculate the total energy, we find that while the planar state is locally stable, there is a puckered state that has lower energy. The scale of the puckering is consistent with that expected with local maxima and minima associated with pentagons surrounded by larger rings; forming local "buckyball domes"

Breaking internal waves and turbulent dissipation

We explore what might be discovered about the breaking of progressive internal waves and the consequent mixing by following some of the methodologies and techniques used to study surface wave breaking. It is suggested that breaking is most likely to occur in wave groups, where the wave field is locally amplified. In a stratified fluid of uniform buoyancy frequency, N, the breaking regions of internal wave groups extend in approximately horizontal directions. Two classes of breaking, “convective overturn” and “shear instability,” are possible in progressive internal waves propagating in uniform stratification with no mean shear. Convective overturning and associated static instability occur at all wave frequencies, but only if the wave slope, s = am, exceeds unity, where a is the wave amplitude and m is the vertical wavenumber. Self-induced shear instability may take place in waves with slopes s \u3c 1, and therefore less than the slopes required for convective overturn, but only when a wave-related Richardson number is sufficiently small; to achieve this, the wave frequency must be close to the inertial frequency. Equations are derived to express the energy dissipated in breaking or the strength of breaking in terms of the characteristics of a breaking wave. A particular measure of breaking analogous to that used to quantify surface wave breaking is ΛI(cb)dcb, the mean area of the fronts of breaking regions, projected onto the vertical and per unit volume, that are produced by internal breakers traveling at speeds between cb and cb + dcb. Estimates are made of the values of ΛI required to sustain a vertical eddy diffusion coefficient of Kρ = 10–5 m2 s–1 through the breaking of internal waves of typical amplitude by convective overturn (with s \u3e 1) and by the self-induced shear instability of near-inertial waves when s \u3c 1. Values of ΛI are of order 1.0 × 10–2 m–1 (i.e., a vertical surface area of about 10 cm × 10 cm in each cubic meter). The predictions are tested by using them to find the fraction of the water column in which turbulence occurs and by comparing the predicted values with existing observations. Additional theoretical studies and laboratory experiments are required to test the proposed analytical relations. Existing sea-going measurement techniques are reviewed and further observations are suggested to advance the understanding of breaking internal waves