551 research outputs found
Quantifying farm sustainability through the lens of ecological theory
The achievements of the Green Revolution in meeting the nutritional needs of a growing global population have been won at the expense of unintended consequences for the environment. Some of these negative impacts are now threatening the sustainability of food production through the loss of pollinators and natural enemies of crop pests, the evolution of pesticide resistance, declining soil health and vulnerability to climate change. In the search for farming systems that are sustainable both agronomically and environmentally, alternative approaches have been proposed variously called âagroecologicalâ, âconservation agricultureâ, âregenerativeâ and âsustainable intensificationâ. While the widespread recognition of the need for more sustainable farming is to be welcomed, this has created etymological confusion that has the potential to become a barrier to transformation. There is a need, therefore, for objective criteria to evaluate alternative farming systems and to quantify farm sustainability against multiple outcomes. To help meet this challenge, we reviewed the ecological theories that explain variance in regulating and supporting ecosystem services delivered by biological communities in farmland to identify guiding principles for management change. For each theory, we identified associated system metrics that could be used as proxies for agroecosystem function. We identified five principles derived from ecological theory: (i) provide key habitats for ecosystem service providers; (ii) increase crop and non-crop habitat diversity; (iii) increase edge density: (iv) increase nutrient-use efficiency; and (v) avoid extremes of disturbance. By making published knowledge the foundation of the choice of associated metrics, our aim was to establish a broad consensus for their use in sustainability assessment frameworks. Further analysis of their association with farm-scale data on biological communities and/or ecosystem service delivery would provide additional validation for their selection and support for the underpinning theories
Hyperentangled States
We investigate a new class of entangled states, which we call
'hyperentangled',that have EPR correlations identical to those in the vacuum
state of a relativistic quantum field. We show that whenever hyperentangled
states exist in any quantum theory, they are dense in its state space. We also
give prescriptions for constructing hyperentangled states that involve an
arbitrarily large collection of systems.Comment: 23 pages, LaTeX, Submitted to Physical Review
This elusive objective existence
Zurek's existential interpretation of quantum mechanics suffers from three
classical prejudices, including the belief that space and time are
intrinsically and infinitely differentiated. They compel him to relativize the
concept of objective existence in two ways. The elimination of these prejudices
makes it possible to recognize the quantum formalism's ontological implications
- the relative and contingent reality of spatiotemporal distinctions and the
extrinsic and finite spatiotemporal differentiation of the physical world -
which in turn makes it possible to arrive at an unqualified objective
existence. Contrary to a widespread misconception, viewing the quantum
formalism as being fundamentally a probability algorithm does not imply that
quantum mechanics is concerned with states of knowledge rather than states of
Nature. On the contrary, it makes possible a complete and strongly objective
description of the physical world that requires no reference to observers. What
objectively exists, in a sense that requires no qualification, is the
trajectories of macroscopic objects, whose fuzziness is empirically irrelevant,
the properties and values of whose possession these trajectories provide
indelible records, and the fuzzy and temporally undifferentiated states of
affairs that obtain between measurements and are described by counterfactual
probability assignments.Comment: To appear in IJQI; 21 pages, LaTe
The Free Will Theorem
On the basis of three physical axioms, we prove that if the choice of a
particular type of spin 1 experiment is not a function of the information
accessible to the experimenters, then its outcome is equally not a function of
the information accessible to the particles. We show that this result is
robust, and deduce that neither hidden variable theories nor mechanisms of the
GRW type for wave function collapse can be made relativistic. We also establish
the consistency of our axioms and discuss the philosophical implications.Comment: 31 pages, 6figure
Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces
Electron-hole excitations in the surface bands of GaAs(110) are analyzed
using constrained density-functional theory calculations. The results show that
Frenkel-type autolocalized excitons are formed. The excitons induce a local
surface unrelaxation which results in a strong exciton-exciton attraction and
makes complexes of two or three electron-hole pairs more favorable than
separate excitons. In such microscopic exciton "droplets" the
electron density is mainly concentrated in the dangling orbital of a surface Ga
atom whereas the holes are distributed over the bonds of this atom to its As
neighbors thus weakening the bonding to the substrate. This finding suggests
the microscopic mechanism of a laser-induced emission of neutral Ga atoms from
GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from:
[email protected]
Chapter F of the International Code of Nomenclature for algae, fungi, and plants as approved by the 11th International Mycological Congress, San Juan, Puerto Rico, July 2018
A revised version of Chapter F of the International Code of Nomenclature for algae, fungi, and plants is presented, incorporating amendments approved by the Fungal Nomenclature Session of the 11th International Mycological Congress held in San Juan, Puerto Rico in July 2018. The process leading to the amendments is outlined. Key changes in the San Juan Chapter F are (1) removal of option to use a colon to indicate the sanctioned status of a name, (2) introduction of correctability for incorrectly cited identifiers of names and typifications, and (3) introduction of option to use name identifiers in place of author citations. Examples have been added to aid the interpretation of new Articles and Recommendations, and Examples have also been added to the existing Art. F.3.7 concerning the protection extended to new combinations based on sanctioned names or basionyms of sanctioned names (which has been re-worded), and to Art. F.3.9 concerning typification of names accepted in the sanctioning works
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The influence of landscape composition and configuration on crop yield resilience
1. Sustainable agriculture aims to produce sufficient food while minimizing environmental damage. To achieve this, we need to understand the role of agricultural landscapes in providing diverse ecosystem services and how these affect crop production and resilience, that is, maintaining yields despite environmental perturbation.
We used 10 years of English wheat yield data to derive three metrics of resilience (relative yield across the time series, yield stability around a moving average and resistance to an extreme weather event) at 10 km Ă 10 km resolution. We used remotely sensed maps to calculate measures of landscape structure, including composition (proportions of different land cover types) and configuration (metrics of connectivity and proximity), known to affect ecosystem service delivery (e.g. control of pests by beneficial invertebrates). We then used an informationâtheoretic approach to identify the bestâfitting combination of landscape structure predictors for each resilience metric, using a potential yield model to account for the effects of climate and soils.
Relative yield showed a strongly positive relationship with the area of arable land. For yield stability, this relationship was evident but alongside other landscape structure variables in the bestâfitting model. No relationship with arable land was evident for resistance.
Yield stability showed a strongly positive effect of proximity to semiânatural habitats. For resistance, the bestâfitting model included positive relationships with the cover of semiânatural habitats and proximity to semiânatural grasslands.
Synthesis and applications. Landscapes with the highest relative wheat yields did not show the highest yield stability or resistance to extreme events. As resilience metrics were derived from shorter portions of the time series, the importance of semiânatural habitats compared to arable land increased. This is probably driven by the complex interplay between landscape structure, agricultural management and ecosystem services. These results demonstrate that measuring relative yield over time may be insufficient to capture the full effect that nonâarable components of the landscape, and the ecosystem services they deliver, have on other aspects of resilience, and that there are clear tradeâoffs in managing agricultural landscapes to maximize different aspects of crop yield resilience
Resilience of UK crop yields to compound climate change
Recent extreme weather events have had severe impacts on UK crop yields, and so there is concern that a greater frequency of extremes could affect crop production in a changing climate. Here we investigate the impacts of future climate change on wheat, the most widely grown cereal crop globally, in a temperate country with currently favourable wheat-growing conditions. Historically, following the plateau of UK wheat yields since the 1990s, we find there has been a recent significant increase in wheat yield volatility, which is only partially explained by seasonal metrics of temperature and precipitation across key wheat growth stages (foundation, construction and production). We find climate impacts on wheat yields are strongest in years with compound weather extremes across multiple growth stages (e.g. frost and heavy rainfall). To assess how these conditions might evolve in the future, we analyse the latest 2.2âkm UK Climate Projections (UKCP Local): on average, the foundation growth stage (broadly 1 October to 9 April) is likely to become warmer and wetter, while the construction (10 April to 10 June) and production (11 June to 26 July) stages are likely to become warmer and slightly drier. Statistical wheat yield projections, obtained by driving the regression model with UKCP Local simulations of precipitation and temperature for the UK's three main wheat-growing regions, indicate continued growth of crop yields in the coming decades. Significantly warmer projected winter night temperatures offset the negative impacts of increasing rainfall during the foundation stage, while warmer day temperatures and drier conditions are generally beneficial to yields in the production stage. This work suggests that on average, at the regional scale, climate change is likely to have more positive impacts on UK wheat yields than previously considered. Against this background of positive change, however, our work illustrates that wheat farming in the UK is likely to move outside of the climatic envelope that it has previously experienced, increasing the risk of unseen weather conditions such as intense local thunderstorms or prolonged droughts, which are beyond the scope of this paper
Renormalization group analysis of the QCD quark potential to order v^2
A one-loop renormalization group analysis of the order v^2 relativistic
corrections to the static QCD potential is presented. The velocity
renormalization group is used to simultaneously sum ln(m/mv) and ln(m/mv^2)
terms. The results are compared to previous calculations in the literature.Comment: 13 pages. important change: running of soft Lagrangian include
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