Cassava brown streak disease and the sustainability of a clean seed system

One method of reducing disease in crops is the dissemination of disease-free planting material from a multiplication site to growers. This study assesses the validity and sustainability of this method for cassava brown streak disease, a threat to cassava crops across East Africa. Using mathematical modelling, the effects of different environmental and control conditions on pathogen spread were determined in a single-field multiplication site. High disease pressure, through large vector populations and disease in the surrounding area, combined with poor roguing practice, resulted in unsuccessful disease suppression. However, fields may produce sufficiently clean material for replanting if these factors can be overcome. Assessing the sustainability of a low-pressure system over multiple harvests, well-managed fields were found to maintain low disease levels, although producing sufficient cuttings may prove challenging. Replanting fields from the previous harvest does not lead to degeneration of planting material, only cutting numbers, and the importation of new clean material is not necessarily required. It is recommended that multiplication sites are only established in areas of low disease pressure and vector population density, and the importance of training in field management is emphasized. Cultivars displaying strong foliar symptoms are to be encouraged, as these allow for effective roguing, resulting in negative selection against the disease and reducing its spread. Finally, efforts to increase plant multiplication rates, the number of cuttings that can be obtained from each plant, have a significant impact on the sustainability of sites, as this represents the primary limiting factor to success

Concentration of atomic hydrogen diffused into silicon in the temperature range 900–1300 °C

Boron-doped Czochralski silicon samples with [B]~1017 cm−3 have been heated at various temperatures in the range 800–1300 °C in an atmosphere of hydrogen and then quenched. The concentration of [H-B] pairs was measured by infrared localized vibrational mode spectroscopy. It was concluded that the solubility of atomic hydrogen is greater than [Hs] = 5.6 × 1018 exp( − 0.95 eV/kT)cm−3 at the temperatures investigated

Disturbance of primary producer communities disrupts the thermal limits of the associated aquatic fauna

Environmental fluctuation forms a framework of variability within which species have evolved. Environmental fluctuation includes predictability, such as diel cycles of aquatic oxygen fluctuation driven by primary producers. Oxygen availability and fluctuation shape the physiological responses of aquatic animals to warming, so that, in theory, oxygen fluctuation could influence their thermal ecology. We describe annual oxygen variability in agricultural drainage channels and show that disruption of oxygen fluctuation through dredging of plants reduces the thermal tolerance of freshwater animals. We compared the temperature responses of snails, amphipods, leeches and mussels exposed to either natural oxygen fluctuation or constant oxygen in situ under different acclimation periods. Oxygen saturation in channel water ranged from c. 0 % saturation at night to >300 % during the day. Temperature showed normal seasonal variation and was almost synchronous with daily oxygen fluctuation. A dredging event in 2020 dramatically reduced dissolved oxygen variability and the correlation between oxygen and temperature was lost. The tolerance of invertebrates to thermal stress was significantly lower when natural fluctuation in oxygen availability was reduced and decoupled from temperature. This highlights the importance of natural cycles of variability and the need to include finer scale effects, including indirect biological effects, in modelling the ecosystem-level consequences of climate change. Furthermore, restoration and management of primary producers in aquatic habitats could be important to improve the thermal protection of aquatic invertebrates and their resistance to environmental variation imposed by climate change

Parasite species richness and its effect on persistence in food webs

Parasitic species are likely to have a significant effect on the stability of ecosystems. However, little is known of the nature of this effect, with debate over whether it is positive or negative. In previous work it was observed that a mixture of interaction types increases the local stability of a network. Following this, we investigate the consequences for species persistence of replacing host species with parasitic species. We consider systems with varying mixtures of mutualistic and antagonistic interactions, showing that the effect of parasitic interactions on a system depends on both the interaction types present and the levels of parasitism considered. Higher levels of mutualism make a system vulnerable to destabilisation on the addition of parasite species. However, for systems with antagonistic interactions, persistence in the system decreases primarily due to the failure of parasite species to persist. This increases with increasing proportions of parasite species, leading to a peak number of parasite species able to persist. Increasing parasite species richness does not have as significant an effect on host species richness as we might expect; although parasites have an important role to play in ecological networks, their effect on persistence is seen primarily through their own self-limitation

Towards accurate partial volume correction in (99m}^Tc oncology SPECT: perturbation for case-specific resolution estimation

BACKGROUND: Currently, there is no consensus on the optimal partial volume correction (PVC) algorithm for oncology imaging. Several existing PVC methods require knowledge of the reconstructed resolution, usually as the point spread function (PSF)-often assumed to be spatially invariant. However, this is not the case for SPECT imaging. This work aimed to assess the accuracy of SPECT quantification when PVC is applied using a case-specific PSF. METHODS: Simulations of SPECT [Formula: see text]Tc imaging were performed for a range of activity distributions, including those replicating typical clinical oncology studies. Gaussian PSFs in reconstructed images were estimated using perturbation with a small point source. Estimates of the PSF were made in situations which could be encountered in a patient study, including; different positions in the field of view, different lesion shapes, sizes and contrasts, noise-free and noisy data. Ground truth images were convolved with the perturbation-estimated PSF, and with a PSF reflecting the resolution at the centre of the field of view. Both were compared with reconstructed images and the root-mean-square error calculated to assess the accuracy of the estimated PSF. PVC was applied using Single Target Correction, incorporating the perturbation-estimated PSF. Corrected regional mean values were assessed for quantitative accuracy. RESULTS: Perturbation-estimated PSF values demonstrated dependence on the position in the Field of View and the number of OSEM iterations. A lower root mean squared error was observed when convolution of the ground truth image was performed with the perturbation-estimated PSF, compared with convolution using a different PSF. Regional mean values following PVC using the perturbation-estimated PSF were more accurate than uncorrected data, or data corrected with PVC using an unsuitable PSF. This was the case for both simple and anthropomorphic phantoms. For the simple phantom, regional mean values were within 0.7% of the ground truth values. Accuracy improved after 5 or more OSEM iterations (10 subsets). For the anthropomorphic phantoms, post-correction regional mean values were within 1.6% of the ground truth values for noise-free uniform lesions. CONCLUSION: Perturbation using a simulated point source could potentially improve quantitative SPECT accuracy via the application of PVC, provided that sufficient reconstruction iterations are used

Mathematical models of drug-resistant tuberculosis lack bacterial heterogeneity: A systematic review

Drug-resistant tuberculosis (DR-TB) threatens progress in the control of TB. Mathematical models are increasingly being used to guide public health decisions on managing both antimicrobial resistance (AMR) and TB. It is important to consider bacterial heterogeneity in models as it can have consequences for predictions of resistance prevalence, which may affect decision-making. We conducted a systematic review of published mathematical models to determine the modelling landscape and to explore methods for including bacterial heterogeneity. Our first objective was to identify and analyse the general characteristics of mathematical models of DR-mycobacteria, including M. tuberculosis. The second objective was to analyse methods of including bacterial heterogeneity in these models. We had different definitions of heterogeneity depending on the model level. For between-host models of mycobacterium, heterogeneity was defined as any model where bacteria of the same resistance level were further differentiated. For bacterial population models, heterogeneity was defined as having multiple distinct resistant populations. The search was conducted following PRISMA guidelines in five databases, with studies included if they were mechanistic or simulation models of DR-mycobacteria. We identified 195 studies modelling DR-mycobacteria, with most being dynamic transmission models of non-treatment intervention impact in M. tuberculosis (n = 58). Studies were set in a limited number of specific countries, and 44% of models (n = 85) included only a single level of “multidrug-resistance (MDR)”. Only 23 models (8 between-host) included any bacterial heterogeneity. Most of these also captured multiple antibiotic-resistant classes (n = 17), but six models included heterogeneity in bacterial populations resistant to a single antibiotic. Heterogeneity was usually represented by different fitness values for bacteria resistant to the same antibiotic (61%, n = 14). A large and growing body of mathematical models of DR-mycobacterium is being used to explore intervention impact to support policy as well as theoretical explorations of resistance dynamics. However, the majority lack bacterial heterogeneity, suggesting that important evolutionary effects may be missed

Manipulating Ferroelectric Domains in Nanostructures Under Electron Beams

Freestanding BaTiO3 nanodots exhibit domain structures characterized by distinct quadrants of ferroelastic 90{\deg} domains in transmission electron microscopy (TEM) observations. These differ significantly from flux-closure domain patterns in the same systems imaged by piezoresponse force microscopy. Based upon a series of phase field simulations of BaTiO3 nanodots, we suggest that the TEM patterns result from a radial electric field arising from electron beam charging of the nanodot. For sufficiently large charging, this converts flux-closure domain patterns to quadrant patterns with radial net polarizations. Not only does this explain the puzzling patterns that have been observed in TEM studies of ferroelectric nanodots, but also suggests how to manipulate ferroelectric domain patterns via electron beams.Comment: 5 pages, 6 figure

Disturbance of primary producer communities disrupts the thermal limits of the associated aquatic fauna

Environmental fluctuation forms a framework of variability within which species have evolved. Environmental fluctuation includes predictability, such as diel cycles of aquatic oxygen fluctuation driven by primary producers. Oxygen availability and fluctuation shape the physiological responses of aquatic animals to warming, so that, in theory, oxygen fluctuation could influence their thermal ecology. We describe annual oxygen variability in agricultural drainage channels and show that disruption of oxygen fluctuation through dredging of plants reduces the thermal tolerance of freshwater animals. We compared the temperature responses of snails, amphipods, leeches and mussels exposed to either natural oxygen fluctuation or constant oxygen in situ under different acclimation periods. Oxygen saturation in channel water ranged from c. 0 % saturation at night to >300 % during the day. Temperature showed normal seasonal variation and was almost synchronous with daily oxygen fluctuation. A dredging event in 2020 dramatically reduced dissolved oxygen variability and the correlation between oxygen and temperature was lost. The tolerance of invertebrates to thermal stress was significantly lower when natural fluctuation in oxygen availability was reduced and decoupled from temperature. This highlights the importance of natural cycles of variability and the need to include finer scale effects, including indirect biological effects, in modelling the ecosystem-level consequences of climate change. Furthermore, restoration and management of primary producers in aquatic habitats could be important to improve the thermal protection of aquatic invertebrates and their resistance to environmental variation imposed by climate change