104 research outputs found

    Temperature variability and the yield of annual crops.

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    Abstract Global production of annual crops will be affected by the increases in mean temperatures of 2-4 • C expected towards the end of the 21st century. Within temperate regions, current cultivars of determinate annual crops will mature earlier, and hence yields will decline in response to warmer temperatures. Nevertheless, this negative effect of warmer temperatures should be countered by the increased rate of crop growth at elevated atmospheric CO 2 concentrations, at least when there is sufficient water. Of more importance for the yield of annual seed crops may be changes in the frequency of hot (or cold) temperatures which are associated with warmer mean climates. The objectives of this paper are to review evidence for the importance of variability in temperature for annual crop yields, and to consider how the impacts of these events may be predicted. Evidence is presented for the importance of variability in temperature, independent of any substantial changes in mean seasonal temperature, for the yield of annual crops. Seed yields are particularly sensitive to brief episodes of hot temperatures if these coincide with critical stages of crop development. Hot temperatures at the time of flowering can reduce the potential number of seeds or grains that subsequently contribute to the crop yield. Three research needs are identified in order to provide a framework for predicting the impact of episodes of hot temperatures on the yields of annual crops: reliable seasonal weather forecasts, robust predictions of crop development, and crop simulation models which are able to quantify the effects of brief episodes of hot temperatures on seed yield

    Mechanically stacked four-junction concentrator solar cells

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    Multijunction solar cells can be fabricated by bonding together component cells that are grown separately. Because the component cells are each grown lattice-matched to suitable substrates, this technique allows alloys of different lattice constants to be combined without the structural defects introduced when using metamorphic buffers. Here we present results on the fabrication and performance of four-junction mechanical stacks composed of GaInP/GaAs and GaInAsP/GaInAs tandems, grown on GaAs and InP substrates, respectively. The two tandems were bonded together with a lowindex, transparent epoxy that acts as an omni-directional reflector to the GaAs bandedge luminescence, while simultaneously transmitting nearly all of the sub-bandgap light. As determined by electroluminescence measurements and optical modeling, the GaAs subcell demonstrates a higher internal radiative limit and thus higher subcell voltage, compared with GaAs subcells without enhanced internal optics; all four subcells exhibit excellent material quality. The device was fabricated with four contact terminals so that each tandem can be operated at its maximum power point, which raises the cumulative efficiency and decreases spectral sensitivity. Efficiencies exceeding 38% at one-sun have been demonstrated. Eliminating the series resistance is the key challenge for the concentrator cells. We will discuss the performance of one-sun and concentrator versions of the device, and compare the results to recently fabricated monolithic four-junction cells

    The Top 100 questions for the sustainable intensification of agriculture in India’s rainfed drylands

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    India has the largest area of rainfed dryland agriculture globally, with a variety of distinct types of farming systems producing most of its coarse cereals, food legumes, minor millets, and large amounts of livestock. All these are vital for national and regional food and nutritional security. Yet, the rainfed drylands have been relatively neglected in mainstream agricultural and rural development policy. As a result, significant social-ecological challenges overlap in these landscapes: endemic poverty, malnutrition and land degradation. Sustainable intensification of dryland agriculture is essential for helping to address these challenges, particularly in the context of accelerating climate change. In this paper, we present 100 questions that point to the most important knowledge gaps and research priorities. If addressed, these would facilitate and inform sustainable intensification in Indian rainfed drylands, leading to improved agricultural production and enhanced ecosystem services. The horizon scanning method used to produce these questions brought together experts and practitioners involved in a broad range of disciplines and sectors. This exercise resulted in a consolidated set of questions covering the agricultural drylands, organized into 13 themes. Together, these represent a collective programme for new cross- and multi-disciplinary research on sustainable intensification in the Indian rainfed drylands

    The stellar occultations by the largest satellite of the dwarf planet Haumea, Hi'iaka

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    Two stellar occultations by the largest satellite of the dwarf planet Haumea, Hi'iaka, were predicted to happen on April, 6th and 16th, 2021. Additional high accuracy astrometric analysis was carried out in order to refine the prediction for April 6th, using several telescopes in the 1.2-m to 2-m range, with the final shadow path crossing North Africa. We successfully detected the first event from TRAPPIST-North telescope at Oukaïmeden Observatory (Morocco). Although it was recorded from only one site, this first detection allowed us to improve the prediction for the second that crossed North America from East to West. We had a good success recording six positive detections and several negative detections that constrain the shape and size of the body. The light curves obtained from the different observatories provide the time at which the star disappears and reappears, which are translated into chords (the projected lines on the sky-plane as observed from each location). Additionally, we carried out a campaign to study Hi'iaka's rotational light-curve, studying the residuals of Haumea's rotational light-curve to a four-order Fourier fit. We obtained the rotational phases at the times of the occultations, which is critical for the analysis of the occultations, given that Hi'iaka is clearly non-spherical. Our preliminary results show that Hi'iaka indeed has a triaxial shape with a larger effective diameter than what has been published so far. The preliminary results and their implications will be discussed in this talk

    Recurrent De Novo Dominant Mutations in SLC2SA4 Cause Severe Early-Onset Mitochondrial Disease and Loss of Mitochondrial DNA Copy Number

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    Mutations in SLC25A4 encoding the mitochondrial ADP/ATP carrier AAC1 are well-recognized causes of mitochondrial disease. Several heterozygous SLC25A4 mutations cause adult-onset autosomal-dominant progressive external ophthalmoplegia associated with multiple mitochondrial DNA deletions, whereas recessive SLC25A4 mutations cause childhood-onset mitochondrial myopathy and cardiomyopathy. Here, we describe the identification by whole-exome sequencing of seven probands harboring dominant, de novo SLC25A4 mutations. All affected individuals presented at birth, were ventilator dependent and, where tested, revealed severe combined mitochondria' respiratory chain deficiencies associated with a marked loss of mitochondria' DNA copy number in skeletal muscle. Strikingly, an identical c.239G>A (p.Arg80His) mutation was present in four of the seven subjects, and the other three case subjects harbored the same c.703C>G (p.Arg235Gly) mutation. Analysis of skeletal muscle revealed a marked decrease of AAC1 protein levels and loss of respiratory chain complexes containing mitochondria' DNA-encoded subunits. We show that both recombinant AAC1 mutant proteins are severely impaired in ADP/ATP transport, affecting most likely the substrate binding and mechanics of the carrier, respectively. This highly reduced capacity for transport probably affects mitochondria' DNA maintenance and in turn respiration, causing a severe energy crisis. The confirmation of the pathogenicity of these de novo SLC25A4 mutations highlights a third distinct clinical phenotype associated with mutation of this gene and demonstrates that early-onset mitochondria' disease can be caused by recurrent de novo mutations, which has significant implications for the application and analysis of whole-exome sequencing data in mitochondrial disease.Peer reviewe

    In-situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory

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    The IceCube Neutrino Observatory instruments about 1 km3 of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. A unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. Birefringent light propagation has been examined as a possible explanation for this effect. The predictions of a first-principles birefringence model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties do not only include the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube LED calibration data, the theory and parametrization of the birefringence effect, the fitting procedures of these parameterizations to experimental data as well as the inferred crystal properties.</p

    TXS 0506+056 with Updated IceCube Data

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    Past results from the IceCube Collaboration have suggested that the blazar TXS 0506+056 is a potential source of astrophysical neutrinos. However, in the years since there have been numerous updates to event processing and reconstruction, as well as improvements to the statistical methods used to search for astrophysical neutrino sources. These improvements in combination with additional years of data have resulted in the identification of NGC 1068 as a second neutrino source candidate. This talk will re-examine time-dependent neutrino emission from TXS 0506+056 using the most recent northern-sky data sample that was used in the analysis of NGC 1068. The results of using this updated data sample to obtain a significance and flux fit for the 2014 TXS 0506+056 "untriggered" neutrino flare are reported

    Conditional normalizing flows for IceCube event reconstruction

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