1,875 research outputs found
Variations in mid-ocean ridge CO2 emissions driven by glacial cycles
The geological record shows links between glacial cycles and volcanic
productivity, both subaerially and at mid-ocean ridges. Sea-level-driven
pressure changes could also affect chemical properties of mid-ocean ridge
volcanism. We consider how changing sea-level could alter the CO2 emissions
rate from mid-ocean ridges, on both the segment and global scale. We develop a
simplified transport model for a highly incompatible element through a
homogenous mantle; variations in the melt concentration the emission rate of
the element are created by changes in the depth of first silicate melting. The
model predicts an average global mid-ocean ridge CO2 emissions-rate of 53
Mt/yr, in line with other estimates. We show that falling sea level would cause
an increase in ridge CO2 emissions with a lag of about 100 kyrs after the
causative sea level change. The lag and amplitude of the response are sensitive
to mantle permeability and plate spreading rate. For a reconstructed sea-level
time series of the past million years, we predict variations of up to 12% (7
Mt/yr) in global mid-ocean ridge CO2 emissions. The magnitude and timing of the
predicted variations in CO2 emissions suggests a potential role for ridge
carbon emissions in glacial cycles
Higher physical fitness levels are associated with less language decline in healthy ageing
Healthy ageing is associated with decline in cognitive abilities such as
language. Aerobic fitness has been shown to ameliorate decline in some
cognitive domains, but the potential benefits for language have not been
examined. In a cross-sectional sample, we investigated the relationship between
aerobic fitness and tip-of-the-tongue states. These are among the most frequent
cognitive failures in healthy older adults and occur when a speaker knows a
word but is unable to produce it. We found that healthy older adults indeed
experience more tip-of-the-tongue states than young adults. Importantly, higher
aerobic fitness levels decrease the probability of experiencing
tip-of-the-tongue states in healthy older adults. Fitness-related differences
in word finding abilities are observed over and above effects of age. This is
the first demonstration of a link between aerobic fitness and language
functioning in healthy older adults
Reversible DNA micro-patterning using the fluorous effect
We describe a new method for the immobilisation of DNA into defined patterns with sub-micron resolution, using the fluorous effect. The method is fully reversible via a simple solvent wash, allowing the patterning, regeneration and re-patterning of surfaces with no degradation in binding efficiency following multiple removal/attachment cycles of different DNA sequences
First light for avian embryos: eggshell thickness and pigmentation mediate variation in development and UV exposure in wild bird eggs
Article first published online: 29 JUL 20141. The avian embryo's development is influenced by both the amount and the wavelength of the light that passes through the eggshell. Commercial poultry breeders use light of specific wavelengths to accelerate embryonic growth, yet the effects of the variably patterned eggshells of wild bird species on light transmission and embryonic development remain largely unexplored. 2. Here, we provide the first comparative phylogenetic analysis of light transmission, through a diverse range of bird eggshells (74 British breeding species), in relation to the eggshell's thickness, permeability, pigment concentration and surface reflectance spectrum (colour). 3. The percentage of light transmitted through the eggshell was measured in the spectral range 250–700 nm. Our quantitative analyses confirm anecdotal reports that eggshells filter the light of the externally coloured shell. Specifically, we detected a positive relationship between surface eggshell reflectance (‘brightness’) and the percentage of light transmitted through the eggshell, and this relationship was strongest at wavelengths in the human-visible blue-green region of the spectra (c. 435 nm). 4. We show that less light passes through thicker eggshells with greater total pigment concentrations. By contrast, permeability (measured as water vapour conductance) did not covary significantly with light transmission. Eggs of closed-nesting species let more light pass through, compared with open nesters. 5. We postulate that greater light transmission is required to assist embryonic development under low light exposure. Importantly, this result provides an ecological explanation for the repeated evolution of immaculate, white- or pale-coloured eggshells in species nesting in enclosed spaces. 6. Finally, we detected correlative support for the solar radiation hypothesis, in that eggshells of bird species with a longer incubation period let significantly less of the potentially harmful, ultraviolet (UV) light pass through the eggshell. In summary, we demonstrate suites of avian eggshell properties, including eggshell structure and pigmentation, which are consistent with an evolutionary pressure to both enhance and protect embryonic development.Golo Maurer, Steven J. Portugal, Mark E. Hauber, Ivan Mikšík, Douglas G. D. Russell and Phillip Casse
Influence of extended dynamics on phase transitions in a driven lattice gas
Monte Carlo simulations and dynamical mean-field approximations are performed
to study the phase transition in a driven lattice gas with nearest-neighbor
exclusion on a square lattice. A slight extension of the microscopic dynamics
with allowing the next-nearest-neighbor hops results in dramatic changes.
Instead of the phase separation into high- and low-density regions in the
stationary state the system exhibits a continuous transition belonging to the
Ising universality class for any driving. The relevant features of phase
diagram are reproduced by an improved mean-field analysis.Comment: 3 pages, 3 figure
Variational method and duality in the 2D square Potts model
The ferromagnetic q-state Potts model on a square lattice is analyzed, for
q>4, through an elaborate version of the operatorial variational method. In the
variational approach proposed in the paper, the duality relations are exactly
satisfied, involving at a more fundamental level, a duality relationship
between variational parameters. Besides some exact predictions, the approach is
very effective in the numerical estimates over the whole range of temperature
and can be systematically improved.Comment: 20 pages, 5 EPS figure
Models of competitive learning: complex dynamics, intermittent conversions and oscillatory coarsening
We present two models of competitive learning, which are respectively
interfacial and cooperative learning. This learning is outcome-related, so that
spatially and temporally local environments influence the conversion of a given
site between one of two different types. We focus here on the behavior of the
models at coexistence, which yields new critical behavior and the existence of
a phase involving a novel type of coarsening which is oscillatory in nature.Comment: 23 pages, 11 figures. To appear in Phys. Rev.
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