7,857 research outputs found

    Modelling predicts that heat stress and not drought will limit wheat yield in Europe

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    Global warming is characterised by shifts in weather patterns and increases in extreme weather events. New crop cultivars with specific physiological traits will therefore be required if climate change is not to result in losses of yield and food shortages. However, the intrinsic uncertainty of climate change predictions poses a challenge to plant breeders and crop scientists who have limited time and resources and must select the most appropriate traits for improvement. Modelling is, therefore, a powerful tool to identify future threats to crop production and hence targets for improvement. Wheat is the most important crop in temperate zones, including Europe, and is the staple food crop for many millions of humans and their livestock. However, its production is highly sensitive to environmental conditions, with increased temperature and incidence of drought associated with global warming posing potential threats to yield in Europe. We have therefore predicted the future impacts of these environmental changes on wheat yields using a wheat simulation model combined with climate scenarios based on fifteen global climate models from the IPCC AR4 multi-model ensemble. Despite the lower summer precipitation predicted for Europe, the impact of drought on wheat yields is likely to be smaller than at present, because the warmer conditions will result in earlier maturation before drought becomes severe later in the summer. By contrast, the probability of heat stress around flowering is predicted to increase significantly which is likely to result in considerable yield losses for heat sensitive wheat cultivars commonly grown in north Europe. Breeding strategies should therefore focus on the development of wheat varieties which are tolerant to high temperature around flowering, rather than on developing varieties resistant to drought which may be required for other parts of the world

    Entropy-induced Microphase Separation in Hard Diblock Copolymers

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    Whereas entropy can induce phase behavior that is as rich as seen in energetic systems, microphase separation remains a very rare phenomenon in entropic systems. In this paper, we present a density functional approach to study the possibility of entropy-driven microphase separation in diblock copolymers. Our model system consists of copolymers composed of freely-jointed slender hard rods. The two types of monomeric segments have comparable lengths, but a significantly different diameter, the latter difference providing the driving force for the phase separation. At the same time these systems can also exhibit liquid crystalline phases. We treat this system in the appropriate generalization of the Onsager approximation to chain-like particles. Using a linear stability (bifurcation) analysis, we analytically determine the onset of the microseparated and the nematic phases for long chains. We find that for very long chains the microseparated phase always preempts the nematic. In the limit of infinitely long chains, the correlations within the chain become Gaussian and the approach becomes exact. This allows us to define a Gaussian limit in which the theory strongly simplifies and the competition between microphase separation and liquid crystal formation can be studied essentially analytically. Our main results are phase diagrams as a function of the effective diameter difference, the segment composition and the length ratio of the segments. We also determine the amplitude of the positional order as a function of position along the chain at the onset of the microphase separation instability. Finally, we give suggestions as to how this type of entropy-induced microphase separation could be observed experimentally.Comment: 16 pages, 7 figure

    Values and Governance Systems

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    Cooperative behavior as well as other cultural rules and values are made explicit in organizational units that procure and provide a common service. The common service is procured by a club, which consists of a user-value function, a representation governance, and a budget-allocation function. The common service is provided by a firm, which consists of a value-production function, an implementation governance, and a remuneration function. They extend the concepts of the consumer and the producer in neoclassical theory. The functions mentioned are determined by cooperative games. A governance is represented by a structure of principal-agent relations. The representation governance is a bottom-up hierarchy, empowered by the members of the club. The implementation governance is a top-down hierarchy, empowered by the governor of the firm. The optimal size of the club organization and the firm organization in a competitive environment is determined under certain conditions. This description of a club and a firm allows characterization of some cultural dimensions in the society. For one such cultural dimension, viz. the degree of collectivism in society, the impact on the optimal organization is shown.Governance;cooperation;hierarchy;club;firm;institution;service economy;values;culture;organization

    Vulnerability of horticultural crop production to extreme weather events

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    The potential impact of future extreme weather events on horticultural crops was evaluated. A review was carried out of the sensitivities of a representative set of crops to environmental challenges. It confirmed that a range of environmental factors are capable of causing a significant impact on production, either as yield or quality loss. The most important of these were un-seasonal temperature, water shortage or excess,and storms. Future scenarios were produced by the LARS-WG1, a stochastic weather generator linked with UKCIP02 projections of future climate. For the analyses, 150 years of synthetic weather data were generated for baseline, 2020HI and 2050HI scenarios at defined locations. The output from the weather generator was used in case studies, either to estimate the frequency of a defined set of circumstances known to have impact on cropping, or as inputs to models of crop scheduling or pest phenology or survival. The analyses indicated that episodes of summer drought severe enough to interrupt the continuity of supply of salads and other vegetables will increase while the frequency of autumns with sufficient rainfall to restrict potato lifting will decrease. They also indicated that the scheduling of winter cauliflowers for continuity of supply will require the deployment of varieties with different temperature sensitivities from those in use currently. In the pest insect studies, the number of batches of Agrotis segetum (cutworm) larvae surviving to third instar increased with time, as did the potential number of generations of Plutella xylostella (diamond-back moth) in the growing season, across a range of locations. The study demonstrated the utility of high resolution scenarios in predicting the likelihood of specific weather patterns and their potential effect on horticultural production. Several limitations of the current scenarios and biological models were also identified

    Mixed Quantum/Classical Approach for Description of Molecular Collisions in Astrophysical Environments

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    An efficient and accurate mixed quantum/classical theory approach for computational treatment of inelastic scattering is extended to describe collision of an atom with a general asymmetric-top rotor polyatomic molecule. Quantum mechanics, employed to describe transitions between the internal states of the molecule, and classical mechanics, employed for description of scattering of the atom, are used in a self-consistent manner. Such calculations for rotational excitation of HCOOCH3 in collisions with He produce accurate results at scattering energies above 15 cm–1, although resonances near threshold, below 5 cm–1, cannot be reproduced. Importantly, the method remains computationally affordable at high scattering energies (here up to 1000 cm–1), which enables calculations for larger molecules and at higher collision energies than was possible previously with the standard full-quantum approach. Theoretical prediction of inelastic cross sections for a number of complex organic molecules observed in space becomes feasible using this new computational tool

    Weak localization, Aharonov-Bohm oscillations and decoherence in arrays of quantum dots

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    Combining scattering matrix theory with non-linear σ\sigma-model and Keldysh technique we develop a unified theoretical approach enabling one to non-perturbatively study the effect of electron-electron interactions on weak localization and Aharonov-Bohm oscillations in arbitrary arrays of quantum dots. Our model embraces (i) weakly disordered conductors (ii) strongly disordered conductors and (iii) metallic quantum dots. In all these cases at T0T \to 0 the electron decoherence time is found to saturate to a finite value determined by the universal formula which agrees quantitatively with numerous experimental results. Our analysis provides overwhelming evidence in favor of electron-electron interactions as a universal mechanism for zero temperature electron decoherence in disordered conductors.Comment: 19 pages, 13 figures, invited paper, published in a special issue of Fiz. Nizk. Temp. (Kharkov) dedicated to Prof. Igor Kuli

    A new signature for color octet pseudoscalars at the LHC

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    Color octet (pseudo)scalars, if they exist, will be copiously produced at the CERN Large Hadron Collider (LHC). However, their detection can become a very challenging task. In particular, if their decay into a pair of top quarks is kinematically forbidden, the main decay channel would be into two jets, with a very large background. In this Brief Report we explore the possibility of using anomaly-induced decays of the color octet pseudoscalars into gauge bosons to find them at the LHC.Comment: 4 pages, 2 figures. New references adde

    Построение информационных отношений в сфере майнинга, криптовалюты и криптоактивов на примере Кыргызской Республики

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    The subject of the research is the study of mining, cryptocurrency, crypto assets in the legislation of the Kyrgyz Republic. Relevance. The relevance of the article is due to the presence of gaps in the field of mining, cryptocurrency, crypto assets in the legislation of the Kyrgyz Republic. The objectives of the article are to analyze the areas of mining, cryptocurrency, crypto assets and identify legal problems, as well as make proposals for improving the national legislation of the Kyrgyz Republic. Methodology. The authors use scientific methods: general methods (analysis, synthesis, induction, deduction, comparison); special methods (legal, comparative legal).Main results. Problems were identified, such as: lack of legal status of crypto assets, cryptocurrencies; lack of legal status of a cryptocurrency exchange operator; the system of risk management in the field of cryptocurrency is not indicated; lack of detailed study of the legal status of mining; subjects of mining, mining objects, classification of mining, standards for conducting financial transactions are not defined; lack of understanding of the nature of cryptocurrencies, crypto assets and virtual assets; lack of licensing and permitting activities in the field of mining, cryptocurrency, crypto assets; the absence of the category of mining, cryptocurrencies, crypto assets in the State Classifier of Economic Activities; lack of legal status of blockchain in the format of a regulatory legal act and etc. Relevant proposals were given: to finalize and adopt a single regulatory legal act (in the form of a law) in the field of crypto assets, cryptocurrencies, since they are interconnected; establish the legal status of a cryptocurrency exchange operator and introduce licensing and permitting activities (obtaining a license from the National Bank of the Kyrgyz Republic); develop and adopt a regulatory legal act (in the form of a law) on mining, with a detailed designation of what mining is, its classification, mining object, mining subjects; understand the nature of cryptocurrencies, crypto assets, virtual assets and understand what they can be attributed to, in particular, to money, a product, a medium of exchange, a universal service or other activity; Enshrine in civil law the concepts of cryptocurrency, crypto assets, virtual assets, including the rights and obligations arising from them; add to the Law of the Kyrgyz Republic "On licensing and permitting activities of the system in the Kyrgyz Republic" paragraph 61 of Article 15 - the activity of mining, cryptocurrency, crypto assets; add a category to the State Classifier of Economic Activities - mining, cryptocurrencies, crypto assets; form a working group at the level of the Cabinet of Ministers of the Kyrgyz Republic to study blockchain technology with areas of application, both in the private sector and in the public sector, including smart contracts and etc.Conclusion. Introduce legal regulators in the field of mining, cryptocurrency, crypto assets in the Kyrgyz Republic in order to avoid possible legal gaps that can lead to negative consequences in relation to the state, ranging from various shadow schemes in the economy that can slow down the digital transformation of the country.Вопросы развития майнинга, криптовалюты, криптоактивов рассматриваются на примере Кыргызской Республики. Актуальность статьи обусловлена существованием пробелов в законодательстве Кыргызской Республики по данным направлениям. Цели статьи – провести анализ сфер майнинга, криптовалюты, криптоактивов и выявить правовые проблемы, а также дать предложения по совершенствованию национального законодательства Кыргызской Республики. Сделан вывод о необходимости правового регулирования отношений в области майнинга, криптовалюты, криптоактивов в Кыргызской Республике для преодоления правовых пробелов, способствующих развитию теневых схем в экономике и препятствующих общей цифровой трансформации
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