Electron - positron cascades in multiple-laser optical traps

We present an analytical and numerical study of multiple-laser QED cascades induced with linearly polarised laser pulses. We analyse different polarisation orientations and propose a configuration that maximises the cascade multiplicity and favours the laser absorption. We generalise the analytical estimate for the cascade growth rate previously calculated in the field of two colliding linearly polarised laser pulses and account for multiple laser interaction. The estimate is verified by a comprehensive numerical study of four-laser QED cascades across a range of different laser intensities with QED PIC module of OSIRIS. We show that by using four linearly polarised 30 fs laser pulses, one can convert more than 50 % of the total energy to gamma-rays already at laser intensity $I\simeq10^{24}\ \mathrm{W/cm^2}$. In this configuration, the laser conversion efficiency is higher compared with the case with two colliding lasers

The eigenpairs of a Sylvester-Kac type matrix associated with a simple model for one-dimensional deposition and evaporation

A straightforward model for deposition and evaporation on discrete cells of a finite array of any dimension leads to a matrix equation involving a Sylvester-Kac type matrix. The eigenvalues and eigenvectors of the general matrix are determined for an arbitrary number of cells. A variety of models to which this solution may be applied are discussed.Comment: 7 pages, no figure

Particle Merging Algorithm for PIC Codes

Particle-in-cell merging algorithms aim to resample dynamically the six-dimensional phase space occupied by particles without distorting substantially the physical description of the system. Whereas various approaches have been proposed in previous works, none of them seemed to be able to conserve fully charge, momentum, energy and their associated distributions. We describe here an alternative algorithm based on the coalescence of N massive or massless particles, considered to be close enough in phase space, into two new macro-particles. The local conservation of charge, momentum and energy are ensured by the resolution of a system of scalar equations. Various simulation comparisons have been carried out with and without the merging algorithm, from classical plasma physics problems to extreme scenarios where quantum electrodynamics is taken into account, showing in addition to the conservation of local quantities, the good reproducibility of the particle distributions. In case where the number of particles ought to increase exponentially in the simulation box, the dynamical merging permits a considerable speedup, and significant memory savings that otherwise would make the simulations impossible to perform

Integrated pest management portfolios in UK arable farming: results of a farmer survey.

Farmers are faced with a wide range of pest management (PM) options that can be adopted in isolation or alongside complementary or substitute strategies. This paper presents the results of a survey of UK cereal producers, focusing on the character and diversity of PM strategies currently used by, or available to, farmers. In addition, the survey asked various questions pertaining to agricultural policy participation, attitude towards environmental issues, sources of PM advice and information and the important characteristics of PM technologies. The results indicate that many farmers do make use of a suite of PM techniques, and that their choice of integrated PM (IPM) portfolio appears to be jointly dictated by farm characteristics and government policy. Results also indicate that portfolio choice does affect the number of subsequent insecticide applications per crop. These results help to identify the type of IPM portfolios considered to be adoptable by farmers and highlight the importance of substitution in IPM portfolios. As such, these results will help to direct R&D effort towards the realisation of more sustainable PM approaches and aid the identification of potential portfolio adopters. These findings highlight the opportunity that a revised agri-environmental policy design could generate in terms of enhancing coherent IPM portfolio adoption

Very High Mach Number Electrostatic Shocks in Collisionless Plasmas

The kinetic theory of collisionless electrostatic shocks resulting from the collision of plasma slabs with different temperatures and densities is presented. The theoretical results are confirmed by self-consistent particle-in-cell simulations, revealing the formation and stable propagation of electrostatic shocks with very high Mach numbers ($M \gg 10$), well above the predictions of the classical theories for electrostatic shocks.Comment: 6 pages, submitted to Phys. Rev. Let

Enhanced Detection of Artisanal Small-Scale Mining with Spectral and Textural Segmentation of Landsat Time Series

Artisanal small-scale mines (ASMs) in the Amazon Rainforest are an important cause of deforestation, forest degradation, biodiversity loss, sedimentation in rivers, and mercury emissions. Satellite image data are widely used in environmental decision-making to monitor changes in the land surface, but ASMs are difficult to map from space. ASMs are small, irregularly shaped, unevenly distributed, and confused (spectrally) with other land clearance types. To address this issue, we developed a reliable and efficient ASM detection method for the Tapajós River Basin of Brazil—an important gold mining region of the Amazon Rainforest. We enhanced detection in three key ways. First, we used the time-series segmentation (LandTrendr) Google Earth Engine (GEE) Application Programming Interface to map the pixel-wise trajectory of natural vegetation disturbance and recovery on an annual basis with a 2000 to 2019 Landsat image time series. Second, we segmented 26 textural features in addition to 5 spectral features to account for the high spatial heterogeneity in ASM pixels. Third, we trained and tested a Random Forest model to detect ASMs after eliminating irrelevant and redundant features with the Variable Selection Using Random Forests “ensemble of ensembles” technique. The out-of-bag error and overall accuracy of the final Random Forest was 3.73 and 92.6%, which are comparable to studies mapping large industrial mines with the normalized difference vegetation index (NDVI) and LandTrendr. The most important feature in our study was NDVI, followed by textural features in the near and shortwave infrared. Our work paves the way for future ASM regulation through large area monitoring from space with free and open-source GEE and operational satellites. Studies with sufficient computational resources can improve ASM monitoring with advanced sensors consisting of spectral narrow bands (Sentinel-2, Environmental Mapping and Analysis Program, PRecursore IperSpettrale della Missione Applicativa) and deep learning

Upwelling in the Humboldt Coastal Current near Valparaiso, Chile

In December, 1975, an upwelling study was conducted at Punta Curaumilla near Valparaiso, Chile. Previous work (Silva, 1973) had indicated a zone of relatively intense upwelling around this point of land. In the present study , a bathythermograph survey confirmed the presence of the intensification, identified as a tongue of cool water extending seaward and equatorward of the point. Following Arthur\u27s (1965) scale analysis it is suggested that the acceleration of relative vorticity past the point of land is responsible for intensification...

A fine is a more effective financial deterrent when framed retributively and extracted publicly

Introducing monetary fines to decrease an undesired behavior can sometimes have the counterintuitive effect of increasing the prevalence of the behavior being targeted. Such findings raise important social psychological questions in relation to both the way in which financial penalties are framed and the social contexts in which they are administered. In a field experiment ( Study 1), we informed participants who had signed up for an experiment that they would be fined if they arrived late. This fine was presented as either compensatory or retributive in nature and as being administered either privately or publicly. We then observed participants' subsequent arrival time. In accordance with our hypotheses, participants' punctuality was only improved (relative to a no-fine control) in response to retributive rather than compensatory fines and when told that fines would be administered publicly rather than privately. In Study 2 we used a scenario method to demonstrate that the greater efficacy of retributively framed fines can be attributed to their presence being less likely to undermine the perceived immorality of transgression than is the case for compensatory fines. We propose a material promotion-moral prevention (MPMP) theory to account for our findings and consider its practical implications for the use of financial disincentives to encourage cooperative behavior through public policy in domains such as climate change.</p

Partners in biodiversity science and policy

The development of standards, data sharing, and initiatives like the Global Biodiversity Information Facility and others have advanced research in many fields, including in conservation of biodiversity. Global assessments of extinction risk to species have been completed by IUCN for multiple taxa. The IUCN global assessments have had a major impact on conservation science and practice as well as biodiversity funding mechanisms though the Global Environment Facility, the World Bank, and the Critical Ecosystem Partnership Fund (CEPF). A signature of the assessments is a process of sustained interaction between conservation organizations and the research and academic community, effectively integrating science and policy on global scale. The model relies on several critical components: openness of the conservation community to scientific input and debate, engagement of the scientific community, conservation organization mediated data collation, and data sharing with ease of access. This model can be applied to other challenges to conserve biodiversity and assess how biodiversity loss affects the well-being of societies across the world. The recognition of the importance of biodiversity in meeting the Millennium Development Goals and the recognition of the failure to meet the 2010 Biodiversity Target illustrate the gap between what needs to be achieved and our current trajectory