Impaction of spray droplets on leaves: influence of formulation and leaf character on shatter, bounce and adhesion

This paper combines experimental data with simple mathematical models to investigate the influence of spray formulation type and leaf character (wettability) on shatter, bounce and adhesion of droplets impacting with cotton, rice and wheat leaves. Impaction criteria that allow for different angles of the leaf surface and the droplet impact trajectory are presented; their predictions are based on whether combinations of droplet size and velocity lie above or below bounce and shatter boundaries. In the experimental component, real leaves are used, with all their inherent natural variability. Further, commercial agricultural spray nozzles are employed, resulting in a range of droplet characteristics. Given this natural variability, there is broad agreement between the data and predictions. As predicted, the shatter of droplets was found to increase as droplet size and velocity increased, and the surface became harder to wet. Bouncing of droplets occurred most frequently on hard to wet surfaces with high surface tension mixtures. On the other hand, a number of small droplets with low impact velocity were observed to bounce when predicted to lie well within the adhering regime. We believe this discrepancy between the predictions and experimental data could be due to air layer effects that were not taken into account in the current bounce equations. Other discrepancies between experiment and theory are thought to be due to the current assumption of a dry impact surface, whereas, in practice, the leaf surfaces became increasingly covered with fluid throughout the spray test runs.Comment: 19 pages, 6 figures, accepted for publication by Experiments in Fluid

High porosity metallic glass foam: A powder metallurgy route

A powder metallurgy route to the fabrication of metallic glass foam is introduced. The method involves consolidating metallic glass powder blended with blowing agent particulates to produce expandable precursors, capable of yielding foams with porosities as high as 86%. The foams are found to inherit the strength of the parent metallic glass and to be able to deform heavily toward full densification absorbing high amounts of energy

Modelling the Architecture of Plants: Some Concepts and Potential Applications

The reactions of plant parts at a particular position in the canopy to local environmental conditions depend on local growth processes. Consequently, differences in photosynthesis due to variation in light intensity or the distribution of materials such as sprays that are applied are not easily addressed by conventional crop models that usually treat the canopy as an homogenous mass. To adequately address these issues, factors such as the structure of the canopy and its function as an exchange medium (for water and gases) and for capturing light need to be considered. The rate of extension of stems and leaves and distribution of leaves (including their angle of inclination) and branches in the space between plants (plant architecture) has been researched extensively, but until recently, these processes had not been included in crop models. As well as the leaves and branches of the plants of interest, e.g. crop plants, the space between plants may be occupied by other desirable plants or weeds. Also, the architecture of the canopy is determined by conditions in the canopy, but the canopy itself affects the physical and chemical environment in it, and other organisms that inhabit it e.g. pest organisms. Early plant architectural models focussed on the structure of the canopy, but more recently architectural models have also included processes of plant development, and can be applied to roots as well as canopies. In this paper we focus on modelling the architecture and function of above ground plant structures, and potential applications in crop management, with emphasis on maize and sweet corn

Electrical expression of spin accumulation in ferromagnet/semiconductor structures

We treat the spin injection and extraction via a ferromagnetic metal/semiconductor Schottky barrier as a quantum scattering problem. This enables the theory to explain a number of phenomena involving spin-dependent current through the Schottky barrier, especially the counter-intuitive spin polarization direction in the semiconductor due to current extraction seen in recent experiments. A possible explanation of this phenomenon involves taking into account the spin-dependent inelastic scattering via the bound states in the interface region. The quantum-mechanical treatment of spin transport through the interface is coupled with the semiclassical description of transport in the adjoining media, in which we take into account the in-plane spin diffusion along the interface in the planar geometry used in experiments. The theory forms the basis of the calculation of spin-dependent current flow in multi-terminal systems, consisting of a semiconductor channel with many ferromagnetic contacts attached, in which the spin accumulation created by spin injection/extraction can be efficiently sensed by electrical means. A three-terminal system can be used as a magnetic memory cell with the bit of information encoded in the magnetization of one of the contacts. Using five terminals we construct a reprogrammable logic gate, in which the logic inputs and the functionality are encoded in magnetizations of the four terminals, while the current out of the fifth one gives a result of the operation.Comment: A review to appear in Mod. Phys. Lett.

Analysis of phonon-induced spin relaxation processes in silicon

We study all of the leading-order contributions to spin relaxation of \textit{conduction} electrons in silicon due to the electron-phonon interaction. Using group theory, $k\cdot p$ perturbation method and rigid-ion model, we derive an extensive set of matrix element expressions for all of the important spin-flip transitions in the multi-valley conduction band. The scattering angle has an explicit dependence on the electron wavevectors, phonon polarization, valley position and spin orientation of the electron. Comparison of the derived analytical expressions with results of empirical pseudopotential and adiabatic band charge models shows excellent agreement.Comment: 30 pages,10 figure

Response of carbon fluxes to water relations in a savanna ecosystem in South Africa

International audienceThe principal mechanisms that connect carbon fluxes with water relations in savanna ecosystems were studied by using eddy covariance in a savanna ecosystem at Kruger National Park, South Africa. Since the annual drought and rewetting cycle is a major factor influencing the function of savanna ecosystems, this work focused on the close inter-connection between water relations and carbon fluxes. Data from a nine-month measuring campaign lasting from the early wet season to the late dry season were used. Total ecosystem respiration showed highest values at the onset of the growing season, a slightly lower plateau during the main part of the growing season and a continuous decrease during the transition towards the dry season. The regulation of canopy conductance was changed in two ways: changes due to phenology during the course of the growing season and short-term acclimation to soil water conditions. The most constant parameter was water use efficiency that was influenced by VPD during the day but the VPD response curve of water usage did change only slightly during the course of the growing season and decreased by about 30% during the transition from wet to dry season. The regulation of canopy conductance and photosynthetic capacity were closely related. This observation meets recent leaf-level findings that stomatal closure triggers down-regulation of Rubisco during drought. Our results may show the effects of these processes on the ecosystem scale

Spin transport theory in ferromagnet/semiconductor systems with non-collinear magnetization configurations

We present a comprehensive theory of spin transport in a non-degenerate semiconductor that is in contact with multiple ferromagnetic terminals. The spin dynamics in the semiconductor is studied during a perturbation of a general, non-collinear magnetization configuration and a method is shown to identify the various configurations from current signals. The conventional Landauer-B\"{u}ttiker description for spin transport across Schottky contacts is generalized by the use of a non-linearized I-V relation, and it is extended by taking into account non-coherent transport mechanisms. The theory is used to analyze a three terminal lateral structure where a significant difference in the spin accumulation profile is found when comparing the results of this model with the conventional model.Comment: 17 pages, 10 figure

Halogens in seaweeds : Biological and Environmental Significance

Acknowledgments: We are grateful to the Kuwait Institute for Scientific Research (KISR) for PhD 1129 funding for Hanan Al-Adilah and to the European Commission for a Marie Curie International In- 1130 coming Fellowship (Horizon 2020 Research and Innovation Programme of the European Union un- 1131 der the Marie Skłodowska-Curie grant agreement No 839151) to Puja Kumari. We would equally 1132 like to thank the UK Natural Environment Research Council for their support to FCK (program 1133 Oceans 2025 – WP 4.5 and grants NE/D521522/1 and NE/J023094/1) and LJC (grant NE/N009983/1). 1134 This work also received support from the Marine Alliance for Science and Technology for Scotland 1135 pooling initiative. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and 1136 contributing institutions. MCF, FCK and HAA thank the Lorentz Center (funded by the Netherlands 1137 Organization for Scientific Research, NWO, and the University of Leiden) for the organization of 1138 the workshop ‘IODINE: Biogeochemical Cycle of Iodine and Human Health’ (Oct. 4-6, 2017) which 1139 partly inspired this review. LJC acknowledges funding from the European Research Council (ERC) 1140 under the European Union’s Horizon 2020 programme (project O3-SML; grant agreement no. 1141 833290).Peer reviewedPublisher PD

Short-Term Dry Season Forage Monitoring in Rangelands and Savannas of West Africa

Dry season plant biomass is critical for livestock production and hence livelihoods in rangeland communities. We have developed a cloud-based application that employs remote sensing data to provide weekly spatially explicit information on plant vegetation cover in West Africa during the dry season (typically October-June). In this paper, we discuss the data analysis steps and results that drive the application. Linear spectral mixture analysis is used to derive endmember samples of basic landcover primitives (active/green vegetation, non-active vegetation, and bare soil) from very high-resolution imagery that spans the spatiotemporal spectrum from wet/peak-green to dry/dormant conditions in Senegal. These samples are used to train and evaluate ensemble tree models for predicting proportional cover of the same land cover primitives at 500m scale, using MODIS derived NDVI, shortwave infra-red bands 3 and 2 (SWIR3 and SWIR2), and total 15-day antecedent precipitation as predictors. Our trained models can predict the fractional cover of green vegetation, non-green vegetation and bare soil across space and time with cross-validation root-mean square errors of 12%, 15% and 9% respectively. With a weekly cadence and low latency (~2-3 weeks), the tool can also provide timely information to support local decision making in the management of critical rangeland resources