968 research outputs found
Domestication for Conservation of an Endangered Species: The Case of the Wollemi Pine
A small population of tall slender conifers was discovered in 1994 in a deep rainforest canyon of the Wollemi National Park, New SouthWales, Australia. The living trees closely resembled fossils that were more than 65 million years old, and this ‘living fossil’ was recognised as a third extant genus in the Araucariaceae (Araucaria, Agathis and now Wollemia). The species was named the Wollemi pine (W. nobilis). Extensive searches uncovered very few populations, with the total number of adult trees being less than 100. Ex situ collections were quickly established in Sydney as part of the Wollemi Pine Recovery Plan. The majority of the ex situ population was later transferred to our custom-built facility in Queensland for commercial multiplication. Domestication has relied very heavily on the species’ amenability to vegetative propagation because seed collection from the natural populations is dangerous, expensive, and undesirable for conservation reasons. Early propagation success was poor, with only about 25% of cuttings producing roots. However, small increases in propagation success have a very large impact on a domestication program because plant production can be modelled on an exponential curve where each rooted cutting develops into a mother plant that, in turn, provides more rooted cuttings. An extensive research program elevated rooting percentages to greater than 80% and also provided in vitro methods for plant multiplication. These successes have enabled international release of the Wollemi pine as a new and attractive species for ornamental horticulture
Substitution in a sense
The Reference Principle (RP) states that co-referring expressions are everywhere intersubstitutable salva congruitate. On first glance, (RP) looks like a truism, but a truism with some bite: (RP) transforms difficult philosophical questions about co-reference into easy grammatical questions about substitutability. This has led a number of philosophers to think that we can use (RP) to make short work of certain longstanding metaphysical debates. For example, it has been suggested that all we need to do to show that the predicate ‘( ) is a horse’ does not refer to a property is point out that ‘( ) is a horse’ and ‘the property of being a horse’ are not everywhere intersubstitutable salva congruitate. However, when we understand ‘substitution’ in the simplest and most straightforward way, (RP) is no truism; in fact, natural languages are full of counterexamples to the principle. In this paper, I introduce a new notion of substitution, and then develop and argue for a version of (RP) that is immune to these counterexamples. Along the way I touch on the following topics: the relation between argument forms and their natural language instances; the reification of sense; the difference between terms and predicates; and the relation between reference and disquotation. I end by arguing that my new version of (RP) cannot be used to settle metaphysical debates quite as easily as some philosophers would like
Perturbative framework for the pi(+)pi(-) atom
The perturbative framework is developed for the calculation of the pi(+)pi(-)
atom characteristics on the basis of the field-theoretical Bethe-Salpeter
approach. A closed expression for the first-order correction to the pi(+)pi(-)
atom lifetime has been obtained.Comment: 8 pages, LaTeX-fil
Massively parallel landscape-evolution modelling using general purpose graphical processing units
As our expectations of what computer systems can do and our ability to capture data improves, the desire to perform ever more computationally intensive tasks increases. Often these tasks, comprising vast numbers of repeated computations, are highly interdependent on each other – a closely coupled problem. The process of Landscape-Evolution Modelling is an example of such a problem. In order to produce realistic models it is necessary to process landscapes containing millions of data points over time periods extending up to millions of years. This leads to non-tractable execution times, often in the order of years. Researchers therefore seek multiple orders of magnitude reduction in the execution time of these models. The massively parallel programming environment offered through General Purpose Graphical Processing Units offers the potential for multiple orders of magnitude speedup in code execution times. In this paper we demonstrate how the time dominant parts of a Landscape-Evolution Model can be recoded for a massively parallel architecture providing two orders of magnitude reduction in execution time
Combining simulation modeling and stable isotope analyses to reconstruct the last known movements of one of Nature’s giants
The spatial ecology of rare, migratory oceanic animals is difficult to study directly. Where incremental tissues are available, their chemical composition can provide valuable indirect observations of movement and diet. Interpreting the chemical record in incremental tissues can be highly uncertain, however, as multiple mechanisms interact to produce the observed data. Simulation modeling is one approach for considering alternative hypotheses in ecology and can be used to consider the relative likelihood of obtaining an observed record under different combinations of ecological and environmental processes. Here we show how a simulation modeling approach can help to infer movement behaviour based on stable carbon isotope profiles measured in incremental baleen tissues of a blue whale (Balaenoptera musculus). The life history of this particular specimen, which stranded in 1891 in the UK, was selected as a case study due to its cultural significance as part of a permanent display at the Natural History Museum, London. We specifically tested whether measured variations in stable isotope compositions across the analysed baleen plate were more consistent with residency or latitudinal migrations. The measured isotopic record was most closely reproduced with a period of residency in sub-tropical waters for at least a full year followed by three repeated annual migrations between sub-tropical and high latitude regions. The latitudinal migration cycle was interrupted in the year prior to stranding, potentially implying pregnancy and weaning, but isotopic data alone cannot test this hypothesis. Simulation methods can help reveal movement information coded in the biochemical compositions of incremental tissues such as those archived in historic collections, and provides context and inferences that are useful for retrospective studies of animal movement, especially where other sources of individual movement data are sparse or challenging to validate.© 2019 Trueman et al.
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited
New 26P(p,{\gamma})27S thermonuclear reaction rate and its astrophysical implication in rp-process
Accurate nuclear reaction rates for 26P(p,{\gamma})27S are pivotal for a
comprehensive understanding of rp-process nucleosynthesis path in the region of
proton-rich sulfur and phosphorus isotopes. However, large uncertainties still
exist in the current rate of 26P(p,{\gamma})27S because of the lack of the
nuclear mass and the energy level structure information of 27S. We reevaluate
this reaction rate using the experimentally constrained 27S mass, together with
the shell-model predicted level structure. It is found that the
26P(p,{\gamma})27S reaction rate is dominated by a direct-capture (DC) reaction
mechanism despite the presence of three resonances at E = 1.104, 1.597, 1.777
MeV above the proton threshold in 27S. The new rate is overall smaller than the
other previous rates from Hauser-Feshbach statistical model by at least one
order of magnitude in the temperature range of X-ray burst interest. In
addition, we consistently update the photodisintegration rate using the new 27S
mass. The influence of new rates of forward and reverse reaction in the
abundances of isotopes produced in rp-process is explored by post-processing
nucleosynthesis calculations. The final abundance ratio of 27S/26P obtained
using the new rates is only 10% of that from the old rate. The abundance flow
calculations show the reaction path 26P(p,{\gamma})27S(\b{eta}+,{\nu})27P is
not as important as thought previously for producing 27P. The adoption of the
new reaction rates for 26P(p,{\gamma})27S only reduces the final production of
aluminum by 7.1%, and has no discernible impact on the yield of other elements
The analytical singlet QCD contributions into the -annihilation Adler function and the generalized Crewther relations
The generalized Crewther relations in the channels of the non-singlet and
vector quark currents are considered. They follow from the double application
of the operator product expansion approach to the same axial
vector-vector-vector triangle amplitude in two regions, adjoining to the angle
sides (or ). We assume that the generalized Crewther relations
in these two kinematic regimes result in the existence of the same perturbation
expression for two products of the coefficient functions of annihilation and
deep-inelastic scattering processes in the non-singlet and vector channels.
Taking into account the 4-th order result for and the perturbative
effects of the violation of the conformal symmetry in the generalized Crewther
relation, we obtain the analytical contribution to the singlet
correction to the -function. Its a-posteriori comparison with the
recent result of direct diagram-by-diagram evaluation of the singlet 4-th order
corrections to - function demonstrates the coincidence of the
predicted and obtained -contributions to the singlet term. They can
be obtained in the conformal invariant limit from the original Crewther
relation. On the contrary to previous belief, the appearance of -terms
in perturbative series in gauge models does not contradict to the property of
conformal symmetry and can be considered as ragular feature. The Banks-Zaks
motivated relation between our predicted and obtained 4-th order corrections is
mentioned. This confirms Baikov-Chetyrkin-Kuhn expectation that the generalized
Crewther relation in the channel of vector currents receives additional singlet
contribution, which in this order of perturbation theory is proportional to the
first coefficient of the QCD -function.Comment: Concrete new foundations explained, abstract updated, presentation
improved, 2 references added, extra acknowledgements added. This work is
dedicated to K. G. Chetyrkin on the occasion of his 60th anniversary, to be
published in Jetp. Lett supposedly in vol.94, issue 1
Hadronic Atoms and Effective Interactions
We examine the problem of hadronic atom energy shifts using the technique of
effective interactions and demonstrate equivalence with the conventional
quantum mechanical approach.Comment: 22 page latex file with 2 figure
Tuning gastropod locomotion: Modeling the influence of mucus rheology on the cost of crawling
Common gastropods such as snails crawl on a solid substrate by propagating
muscular waves of shear stress on a viscoelastic mucus. Producing the mucus
accounts for the largest component in the gastropod's energy budget, more than
twenty times the amount of mechanical work used in crawling. Using a simple
mechanical model, we show that the shear-thinning properties of the mucus favor
a decrease in the amount of mucus necessary for crawling, thereby decreasing
the overall energetic cost of locomotion.Comment: Corrected typo
Separable potential model for interactions at low energies
The effective separable meson-baryon potentials are constructed to match the
equivalent chiral amplitudes up to the second order in external meson momenta.
We fit the model parameters (low energy constants) to the threshold and low
energy data. In the process, the -proton bound state problem is
solved exactly in the momentum space and the 1s level characteristics of the
kaonic hydrogen are computed simultaneously with the available low energy
cross sections. The model is also used to describe the
mass spectrum and the energy dependence of the amplitude.Comment: 31 pages, v2 - added corrections to make it compatible with the
published versio
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