13,511 research outputs found
Representation of transport: A Rural Destination Analysis
Moscovici’s social representations perspective is applied to a study of transport in a
rural destination. The principles are demonstrated using empirical data from a questionnaire
survey, developed following in-depth qualitative research. The data analysis strategy was
founded on inductive reasoning, by employing cluster analysis and correspondence analysis.
A social representations analysis demonstrates how individuals draw on socially accepted
explanations of transport where they have little or no direct knowledge or experience of
the actual transport modes (notably the alternatives to the car). By so doing, ideas are further
perpetuated. Importantly there is ambiguity surrounding responsibility to take positive action
yet a key to addressing transport issues is acknowledgement of responsibility. Keywords: social
representations, transport, rural destinations
Estimating past exposure to arsenic from drinking water from both residential and occupational sources
The limits of filopodium stability
Filopodia are long, finger-like membrane tubes supported by cytoskeletal
filaments. Their shape is determined by the stiffness of the actin filament
bundles found inside them and by the interplay between the surface tension and
bending rigidity of the membrane. Although one might expect the Euler buckling
instability to limit the length of filopodia, we show through simple energetic
considerations that this is in general not the case. By further analyzing the
statics of filaments inside membrane tubes, and through computer simulations
that capture membrane and filament fluctuations, we show under which conditions
filopodia of arbitrary lengths are stable. We discuss several in vitro
experiments where this kind of stability has already been observed.
Furthermore, we predict that the filaments in long, stable filopodia adopt a
helical shape
Generalized Wilson Chain for solving multichannel quantum impurity problems
The Numerical Renormalization Group is used to solve quantum impurity
problems, which describe magnetic impurities in metals, nanodevices, and
correlated materials within DMFT. Here we present a simple generalization of
the Wilson Chain, which improves the scaling of computational cost with the
number of channels/bands, bringing new problems within reach. The method is
applied to calculate the t-matrix of the three-channel Kondo model at T=0,
which shows universal crossovers near non-Fermi liquid critical points. A
non-integrable three-impurity problem with three bands is also studied,
revealing a rich phase diagram and novel screening/overscreening mechanisms.Comment: 5 pages + 5 pages supplementary materia
Investigations on the Role of Thyroxine in the Development of Hepatomas in Hypophysectomized Rats and Pituitary Dwarf Mice
IT has been shown that the susceptibility of epithelial tissues to powerful chemical carcinogens is not a constant entity determined solely by the genetic constitution but varies according to the endocrine status of the experimental animal. The importance of the endocrine status is easily demonstrated when the liver is the target organ of the carcinogen, because the difference between the response of the intact and that of the hypophysectomized (Griffin, Rinfret and Corsigilia, 1953) or thyroidectomized (Bielschowsky and Hall, 1953) rat to hepatoma inducing agents is of an order of magnitude sufficient to make statistical treatment of results superfluous. After ablation of these glands the liver is refractory to azo dyes as well as to aminofluorene and its derivatives. How this effect comes about is still problematical; neither has the role of individual hormones been elucidated, nor is it certain whether the hormonal requirements necessary for the development of liver tumours are the same for all agents (O'Neal, Hoffman, Dodge and Griffin, 1958; Dodge, O'Neal, Chang and Griffin, 1961). The experiments presented in this paper were designed to enquire once more into the role of the thyroid hormone in the pathogenesis of hepatomas. It was expected that findings obtained in hypophysectomized rats and in pituitary dwarf mice would be more amenable to interpretation than those obtained in intact or thyroidectomized rats and allow a sharper distinction between direct and indirect effects of the thyroid hormone to be made
Nestling diet, secondary sexual traits and fitness in the zebra finch
We examined the effect of nestling diet quality on a suite of physiological, morphological and life-history
traits in adult male zebra finches,Taeniopygia guttata. Compared with birds reared on a supplemented diet,
nestlings reared on a seed-only diet showed a reduced rate of growth and reduced cell-mediated immune function as measured by an in vivo response to aT lymphocyte-dependent mitogen. There were no differences between birds reared on the two diets in any of the following adult traits: body size, primary sexual traits (testes mass, numbers of stored sperm, sperm function, velocity and morphology), secondary sexual traits (beak colour and song rate), serological traits or immunological traits. The only differences we detected were a lower body mass and a greater proportion of individuals with plumage abnormalities among those reared on a seed-only diet (this latter effect was transient). The fact that male zebra finches reared on a seed-only diet were, as adults, virtually indistinguishable from those reared on a supple-
mented diet, despite having reduced growth and immune function as nestlings, demonstrates that they
subsequently compensated through the di¡erential allocation of resources. Our results indicate that differ-
ential allocation is costly in terms of fitness since birds reared on a seed-only diet experienced a significantly greater mortality rate than those reared on a supplemented diet. This in turn suggests the existence of a trade-of between the development of traits important for reproduction, such as primary and secondary sexual traits and longevity
A genome-wide investigation of the worldwide invader Sargassum muticum shows high success albeit (almost) no genetic diversity
Twenty years of genetic studies of marine invaders have shown that successful invaders are often characterized by native and introduced populations displaying similar levels of genetic diversity. This pattern is presumably due to high propagule pressure and repeated introductions. The opposite pattern is reported in this study of the brown seaweed, Sargassum muticum, an emblematic species for circumglobal invasions. Albeit demonstrating polymorphism in the native range, microsatellites failed to detect any genetic variation over 1,269 individuals sampled from 46 locations over the Pacific-Atlantic introduction range. Single-nucleotide polymorphisms (SNPs) obtained from ddRAD sequencing revealed some genetic variation, but confirmed severe founder events in both the Pacific and Atlantic introduction ranges. Our study thus exemplifies the need for extreme caution in interpreting neutral genetic diversity as a proxy for invasive potential. Our results confirm a previously hypothesized transoceanic secondary introduction from NE Pacific to Europe. However, the SNP panel unexpectedly revealed two additional distinct genetic origins of introductions. Also, conversely to scenarios based on historical records, southern rather than northern NE Pacific populations could have seeded most of the European populations. Finally, the most recently introduced populations showed the lowest selfing rates, suggesting higher levels of recombination might be beneficial at the early stage of the introduction process (i.e., facilitating evolutionary novelties), whereas uniparental reproduction might be favored later in sustainably established populations (i.e., sustaining local adaptation).Agence Nationale de la Recherche - ANR-10-BTBR-04; European Regional Development Fund; Fundacao para a Ciencia e a Tecnologia - SFRH/BPD/107878/2015, UID/Multi/04326/2016, UID/Multi/04326/2019; Brittany Region;info:eu-repo/semantics/publishedVersio
Exoplanet atmospheres with EChO: spectral retrievals using EChOSim
We demonstrate the effectiveness of the Exoplanet Characterisation
Observatory mission concept for constraining the atmospheric properties of hot
and warm gas giants and super Earths. Synthetic primary and secondary transit
spectra for a range of planets are passed through EChOSim (Waldmann & Pascale
2014) to obtain the expected level of noise for different observational
scenarios; these are then used as inputs for the NEMESIS atmospheric retrieval
code and the retrieved atmospheric properties (temperature structure,
composition and cloud properties) compared with the known input values,
following the method of Barstow et al. (2013a). To correctly retrieve the
temperature structure and composition of the atmosphere to within 2 {\sigma},
we find that we require: a single transit or eclipse of a hot Jupiter orbiting
a sun-like (G2) star at 35 pc to constrain the terminator and dayside
atmospheres; 20 transits or eclipses of a warm Jupiter orbiting a similar star;
10 transits/eclipses of a hot Neptune orbiting an M dwarf at 6 pc; and 30
transits or eclipses of a GJ1214b-like planet.Comment: 13 pages, 15 figures, 1 table. Accepted by Experimental Astronomy.
The final publication will shortly be available at Springer via
http://dx.doi.org/10.1007/s10686-014-9397-
A polynomial training algorithm for calculating perceptrons of optimal stability
Recomi (REpeated COrrelation Matrix Inversion) is a polynomially fast
algorithm for searching optimally stable solutions of the perceptron learning
problem. For random unbiased and biased patterns it is shown that the algorithm
is able to find optimal solutions, if any exist, in at worst O(N^4) floating
point operations. Even beyond the critical storage capacity alpha_c the
algorithm is able to find locally stable solutions (with negative stability) at
the same speed. There are no divergent time scales in the learning process. A
full proof of convergence cannot yet be given, only major constituents of a
proof are shown.Comment: 11 pages, Latex, 4 EPS figure
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