4,599 research outputs found
Strengthening the impact of plant genetic resources through collaborative collection, conservation, characterisation, and evaluation: a tribute to the legacy of Dr Clive Francis
This paper is a tribute to the legacy of Dr Clive Francis, who directly and indirectly collected >14 000 accessions across 60 genera of pasture, forage, and crop species and their wild relatives around the Mediterranean basin, Eastern Africa, and Central and South Asia from 1973 to 2005. This was achieved by a collaborative approach that built strong interactions between disparate organisations (ICARDA, VIR, CLIMA, and Australian genebanks) based on germplasm exchange, conservation and documentation, capacity building, and joint collection. These activities greatly strengthened Australian pasture, forage, and crop genebanks, and led to widespread germplasm utilisation that has waned in the last 5 years, reflecting changing priorities among industry funding bodies and research providers. This situation must be reversed, given the pivotal role genetic resource collections must play to broaden the genetic and adaptive base of plant breeding, to meet the challenge of feeding an increasing population in a depleting resource base. Because the use of germplasm subsets that facilitate phenotyping will stimulate wider utilisation of genetic resources, we discuss the application of core collection and germplasm selection through habitat characterisation/filtering in Australian collections. Both are valid entry points into large collections, but the latter has the advantage of enabling both trait discovery and investigation of plant adaptation, and because it is based on a priori hypothesis testing, it increases understanding even when the trait of interest is not identified
Resilience trinity: safeguarding ecosystem functioning and services across three different time horizons and decision contexts
Ensuring ecosystem resilience is an intuitive approach to safeguard the functioning of ecosystems and hence the future provisioning of ecosystem services (ES). However, resilience is a multi‐faceted concept that is difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resilience. Still, the focus on mechanisms is not specific enough. We suggest a conceptual framework, resilience trinity, to facilitate management based on resilience mechanisms in three distinctive decision contexts and time‐horizons: 1) reactive, when there is an imminent threat to ES resilience and a high pressure to act, 2) adjustive, when the threat is known in general but there is still time to adapt management and 3) provident, when time horizons are very long and the nature of the threats is uncertain, leading to a low willingness to act. Resilience has different interpretations and implications at these different time horizons, which also prevail in different disciplines. Social ecology, ecology and engineering are often implicitly focussing on provident, adjustive or reactive resilience, respectively, but these different notions of resilience and their corresponding social, ecological and economic tradeoffs need to be reconciled. Otherwise, we keep risking unintended consequences of reactive actions, or shying away from provident action because of uncertainties that cannot be reduced. The suggested trinity of time horizons and their decision contexts could help ensuring that longer‐term management actions are not missed while urgent threats to ES are given priority
Physical limits of inference
I show that physical devices that perform observation, prediction, or
recollection share an underlying mathematical structure. I call devices with
that structure "inference devices". I present a set of existence and
impossibility results concerning inference devices. These results hold
independent of the precise physical laws governing our universe. In a limited
sense, the impossibility results establish that Laplace was wrong to claim that
even in a classical, non-chaotic universe the future can be unerringly
predicted, given sufficient knowledge of the present. Alternatively, these
impossibility results can be viewed as a non-quantum mechanical "uncertainty
principle". Next I explore the close connections between the mathematics of
inference devices and of Turing Machines. In particular, the impossibility
results for inference devices are similar to the Halting theorem for TM's.
Furthermore, one can define an analog of Universal TM's (UTM's) for inference
devices. I call those analogs "strong inference devices". I use strong
inference devices to define the "inference complexity" of an inference task,
which is the analog of the Kolmogorov complexity of computing a string. However
no universe can contain more than one strong inference device. So whereas the
Kolmogorov complexity of a string is arbitrary up to specification of the UTM,
there is no such arbitrariness in the inference complexity of an inference
task. I end by discussing the philosophical implications of these results,
e.g., for whether the universe "is" a computer.Comment: 43 pages, updated version of Physica D version, which originally
appeared in 2007 CNLS conference on unconventional computatio
Quantum Entanglement and Order Parameter in a Paired Finite Fermi System
We study the pairing correlations in a finite Fermi system from quantum
entanglement point of view. We investigate the relation between the order
parameter, which has been introduced recently to describe both finite and
infinite superconductors, and the concurrence. For a proper definition of the
concurrence, we argue that a possible generalization of spin flip
transformation is time reversal operation. While for a system with indefinite
number of particles concurrence is a good measure of entanglement, for a finite
system it does not distinguish between normal and superconducting states. We
propose that the expectation value of the radial operator for the total
pseudospin can be used to identify entanglement of pairing.Comment: submitted to Solid State Communications (the Festschrift in the honor
of Prof. Salim Ciraci's 60th birthday
Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations
In this concept paper, the development of strategies for the integration of
first-principles methods with crystallographic database mining for the
discovery and design of novel ferroelectric materials is discussed, drawing on
the results and experience derived from exploratory investigations on three
different systems: (1) the double perovskite Sr(SbMn)O as a
candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite
SbO; and (3) ferroelectric semiconductors with formula
P(S,Se). A variety of avenues for further research and
investigation are suggested, including automated structure type classification,
low-symmetry improper ferroelectrics, and high-throughput first-principles
searches for additional representatives of structural families with desirable
functional properties.Comment: 13 pages, 5 figures, 4 table
Habitable Climates: The Influence of Eccentricity
In the outer regions of the habitable zone, the risk of transitioning into a
globally frozen "snowball" state poses a threat to the habitability of planets
with the capacity to host water-based life. We use a one-dimensional energy
balance climate model (EBM) to examine how obliquity, spin rate, orbital
eccentricity, and ocean coverage might influence the onset of such a snowball
state. For an exoplanet, these parameters may be strikingly different from the
values observed for Earth. Since, for constant semimajor axis, the annual mean
stellar irradiation scales with (1-e^2)^(-1/2), one might expect the greatest
habitable semimajor axis (for fixed atmospheric composition) to scale as
(1-e^2)^(-1/4). We find that this standard ansatz provides a reasonable lower
bound on the outer boundary of the habitable zone, but the influence of
obliquity and ocean fraction can be profound in the context of planets on
eccentric orbits. For planets with eccentricity 0.5, our EBM suggests that the
greatest habitable semimajor axis can vary by more than 0.8 AU (78%!) depending
on obliquity, with higher obliquity worlds generally more stable against
snowball transitions. One might also expect that the long winter at an
eccentric planet's apoastron would render it more susceptible to global
freezing. Our models suggest that this is not a significant risk for Earth-like
planets around Sun-like stars since such planets are buffered by the thermal
inertia provided by oceans covering at least 10% of their surface. Since
planets on eccentric orbits spend much of their year particularly far from the
star, such worlds might turn out to be especially good targets for direct
observations with missions such as TPF-Darwin. Nevertheless, the extreme
temperature variations achieved on highly eccentric exo-Earths raise questions
about the adaptability of life to marginally or transiently habitable
conditions.Comment: References added, text and figures updated, accepted by Ap
Black hole and holographic dark energy
We discuss the connection between black hole and holographic dark energy. We
examine the issue of the equation of state (EOS) for holographic energy density
as a candidate for the dark energy carefully. This is closely related to the
EOS for black hole, because the holographic dark energy comes from the black
hole energy density. In order to derive the EOS of a black hole, we may use its
dual (quantum) systems. Finally, a regular black hole without the singularity
is introduced to describe an accelerating universe inside the cosmological
horizon. Inspired by this, we show that the holographic energy density with the
cosmological horizon as the IR cutoff leads to the dark energy-dominated
universe with .Comment: 11pages, 1 figure, version to appear in PL
Exile Vol. VI No. 2
EDITORIAL 4-5
Clearing in the Forest (woodcut) by Raymond Berger 6
Haiku (poems) by Jean Ludwig 7
Four in Another Punchbowl (story) 8-15
Untitled (etching) by Patricia Wagenhals 16
Staggering Sky (poem) by Robert Canary 16
Song (poem) by Christine Condit 17
Quadrangle (poem) by James Gallant 18-19
P Stands for Pole (story) by Lee Cullen 20-30
The Beachcomber (poem) by William Bennett 31
Harvest in Kansas (poem) by James Gallant 32
Awarded the semi-annual EXILE-Denison Bookstore Writing Prize: P Stands for Pole by Lee Cullen 20-3
Instability of holographic dark energy models
We investigate the difference between holographic dark energy, Chaplygin gas,
and tachyon model with constant potential. For this purpose, we examine their
squared speeds of sound which are evaluated to zeroth order in perturbation
theory and hence depends only on time. We find that the squared speed for
holographic dark energy is always negative when choosing the future event
horizon as the IR cutoff, while those for Chaplygin gas and tachyon are
non-negative. This means that the perfect fluid for holographic dark energy is
classically unstable. Hence the holographic interpretation for Chaplygin gas
and tachyon is problematic.Comment: 11 pages, 4 eps figures, to appear in PL
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