Palatini Variational Principle for an Extended Einstein-Hilbert Action

We consider a Palatini variation on a generalized Einstein-Hilbert action. We find that the Hilbert constraint, that the connection equals the Christoffel symbol, arises only as a special case of this general action, while for particular values of the coefficients of this generalized action, the connection is completely unconstrained. We discuss the relationship between this situation and that usually encountered in the Palatini formulation.Comment: 14 pages, LaTe

GEANT4 : a simulation toolkit

Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 2

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory is a second generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and epsf style files. For additional information about SNO see http://www.sno.phy.queensu.ca . This version has some new reference

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

PREVENTION OF LETHAL YELLOWING IN THE EASTERN CARIBBEAN

Lethal yellowing (LY) is a fast-spreading disease which destroys coconut and other palms. Once limited to the Greater Antilles except for Puerto Rico, it has crossed ocean barriers of 14 5 km or greater to invade new areas and thus should be considered a threat to Puerto Rico and the Lesser Antilles. The American palm cixiid (Myndus crudus Van Duzee), which is the known vector of LY, has not been reported in Puerto Rico nor in the Lesser Antilles north of Trinidad. Otherwise, environmental conditions appear to be conducive to the spread of LY, were it introduced into these islands. Principles and techniques which could lessen the risk of introduction and spread of LY in the eastern Caribbean are discussed

EVALUATION OF SIX SPECIES OF GRASSES AS BREEDING HOSTS OF MYNDUS CRUDUS, A VECTOR OF LETHAL YELLOWING OF PALMS.

Nymphs of Myndus crudus Van Duzee (Homoptera : Cixiidae), a vector of lethal yellowing (LY) of palms, develop in the root zones of grasses. Management of grasses under coconuts is a potential method of suppressing populations of this insect vector. To identify grasses unfavorable as hosts of M. crudus, six species of grasses grown in containers were exposed to field collected adult M. crudus. Host suitability was measured by the relative degree of colonization of the roots of these grasses by immatures, compared torootsof Stenotaphrumsecundatum (Wait.) Kuntze, a know host of M. crudus immatures. Of the grasses tested. Hyparrhenia rufa (Nees) Stapf, proved to be the poorest breeding host of this insect, and may prove useful as a potential ground cover in coconut plantations to reduce the incidence of the vector and thus the spread of LY. ----- Les nymphes de Myndus crudus Van Duzee, un vecteur du jaunissement létal du palmier se développent dans les racines des herbes. Le contrôle des herbages poussant sous les cocotiers est une méthode potentielle pour supprimer les populations de cet insecte vecteur. Pour identifier les herbes mauvais hôtes de M. crudus, six espèces d'herbes, cultivées en containers, ont été exposées à des adultes de M. crudus récoltés sur le terrain. La qualité d'hôtes des espèces testées a été mesurée par le degré relatif de colonisation des racines de ces herbes comparé aux racines de Steriotphrum secundatum, un hôte connu de M. crudus. Parmi les herbes testées, Hyparrhenia rufa (Nees) Stapf, s'est montrée l'hôte le plus médiocre de cet insecte et s'avère donc intéressante comme plante de couverture en cocoteraie pour réduire l'impact du vecteur et en conséquence la dispersion du J.L

Prospects for Control of the Vector of Lethal Yellowing on Small Coconut Farms

Recent experimental evidence has implicated a planthopper, Myndus crudus Van Duzee, as the vector of lethal yellowing (LY). It may be inferred from experimental results that chemical control of LY would not be practical on small coconut farms. The fact that the immature forms of M. crudus utilize grasses as hosts may be a key to controlling this insect. The potential use of ground covers that are unattractive to M. crudus is discussed