Spherically symmetric dissipative anisotropic fluids: A general study

The full set of equations governing the evolution of self--gravitating spherically symmetric dissipative fluids with anisotropic stresses is deployed and used to carry out a general study on the behaviour of such systems, in the context of general relativity. Emphasis is given to the link between the Weyl tensor, the shear tensor, the anisotropy of the pressure and the density inhomogeneity. In particular we provide the general, necessary and sufficient, condition for the vanishing of the spatial gradients of energy density, which in turn suggests a possible definition of a gravitational arrow of time. Some solutions are also exhibited to illustrate the discussion.Comment: 28 pages Latex. To appear in Phys.Rev.

Remittance micro-worlds and migrant infrastructure: circulations, disruptions, and the movement of money

Remittances are increasingly central to development discourses in Africa. The development sector seeks to leverage transnational migration and rapid innovations in financial technologies (fintech), to make remittance systems cheaper for end-users and less risky for states and companies. Critical scholarship, however, questions the techno-fix tendency, calling for grounded research on the intersections between remittances, technologies, and everyday life in African cities and beyond. Building on this work, we deploy the concepts of “micro-worlds” and “migrant infrastructure” to make sense of the complex networks of actors, practices, regulations, and materialities that shape remittance worlds. To ground the work, we narrate two vignettes of remittance service providers who operate in Cape Town, South Africa, serving the Congolese diaspora community. We showcase the important role of logistics companies in the “informal” provision of remittance services and the rise of fintech companies operating in the remittance space. These vignettes give substance to the messy and relational dynamics of remittance micro-worlds. This relationality allows us to see how remittances are circulations, not unidirectional flows; how they are not split between formal and informal, but in fact intersect in blurry ways; how digital technologies are central to the story of migrant infrastructures; and how migrants themselves are compositional of these networks. In doing so, we tell a more relational story about how remittance systems are constituted and configured

A global spectral library to characterize the world's soil

Soil provides ecosystem services, supports human health and habitation, stores carbon and regulates emissions of greenhouse gases. Unprecedented pressures on soil from degradation and urbanization are threatening agro-ecological balances and food security. It is important that we learn more about soil to sustainably manage and preserve it for future generations. To this end, we developed and analyzed a global soil visible-near infrared (vis-NIR) spectral library. It is currently the largest and most diverse database of its kind. We show that the information encoded in the spectra can describe soil composition and be associated to land cover and its global geographic distribution, which acts as a surrogate for global climate variability. We also show the usefulness of the global spectra for predicting soil attributes such as soil organic and inorganic carbon, clay, silt, sand and iron contents, cation exchange capacity, and pH. Using wavelets to treat the spectra, which were recorded in different laboratories using different spectrometers and methods, helped to improve the spectroscopic modelling. We found that modelling a diverse set of spectra with a machine learning algorithm can find the local relationships in the data to produce accurate predictions of soil properties. The spectroscopic models that we derived are parsimonious and robust, and using them we derived a harmonized global soil attribute dataset, which might serve to facilitate research on soil at the global scale. This spectroscopic approach should help to deal with the shortage of data on soil to better understand it and to meet the growing demand for information to assess and monitor soil at scales ranging from regional to global. New contributions to the library are encouraged so that this work and our collaboration might progress to develop a dynamic and easily updatable database with better global coverage. We hope that this work will reinvigorate our community's discussion towards larger, more coordinated collaborations. We also hope that use of the database will deepen our understanding of soil so that we might sustainably manage it and extend the research outcomes of the soil, earth and environmental sciences towards applications that we have not yet dreamed of

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

Avaliação de danos de insetos e de severidade de oídio em genótipos de soja Evaluation of insect damage and powdery mildew severity in soybean genotypes

Avaliou-se o desempenho de 24 linhagens de soja do programa de melhoramento do Instituto Agronômico (IAC) em experimentos de campo em relação ao ataque de insetos e à incidência de oídio. Três experimentos, um para cada ciclo (precoce, semiprecoce e médio) foram instalados nas unidades experimentais de Assis (anos agrícolas 2001/2002 e 2002/2003) e de Ribeirão Preto (2001/2002). Para os três experimentos, o delineamento utilizado foi o de blocos ao acaso, com dez tratamentos e seis repetições. As injúrias foliares causadas por lagartas de Anticarsia gemmatalis Hübner foram estimadas visualmente, atribuindo-se uma porcentagem de desfolha à parcela inteira. Os danos de percevejos [Piezodorus guildinii (West.) e Euschistus heros (F.)] foram avaliados através da porcentagem de retenção foliar atribuída à parcela inteira e por meio da massa de grãos comerciáveis. A severidade de oídio (Microsphaera diffusa Cke. Pk.) foi estimada mediante escala de notas de 1 a 5, de acordo com a intensidade dos sintomas. Considerando-se os resultados das duas localidades, entre o germoplasma de ciclo precoce destaca-se a linhagem IAC 98-4307, com baixa retenção foliar e maior produtividade em presença de percevejos. No grupo de ciclo semiprecoce, observa-se que na linhagem IAC 98-2814 não há retenção foliar, porém, maior produtividade, caracterizando-se como resistente a percevejos, embora seja o genótipo mais desfolhado por lagartas e com maiores sintomas de oídio. Entre os genótipos de ciclo médio, IAC 98-2856 tem produtividade superior em presença de altas ou baixas infestações de percevejos, indicando possuir resistência do tipo tolerância, embora apresente retenção foliar sob baixa pressão de percevejos.<br>Performance of 24 soybean lines from the breeding program of Instituto Agronômico (IAC) was evaluated under field conditions, as to attack of insects and incidence of powdery mildew. Three experiments, one for each maturity group (early-110, intermediate-120, and late-135 days), were carried out at the Experimental Station of Assis (2001/2002 and 2002/2003 growing seasons) and Experimental Station of Ribeirão Preto (2001/2002), both located in the State of São Paulo, Brazil. For all experiments, with ten treatments and six replicates, in randomized block design was adopted. Defoliation damage caused by Anticarsia gemmatalis Hübn. caterpillars was estimated visually, by the percentage of eaten leaf area (PAFC). Stink bugs [Piezodorus guildiniii (West.) and Euschistus heros (F.)] damage was evaluated by two criteria: percentage of foliar retention (PRF) and yield. The severity of powdery mildew (Microsphaera diffusa Cke. Pk.) was evaluated using a scale from 1 (no symptom) to 5 (more than 50% of leaves with symptoms). Considering the results of both locations, among the early maturity genotypes (110 days), the line IAC 98-4307 could be distinguished for the higher grain yield and low PRF under stink bug infestations. Regarding the genotypes of 120-day maturity group, the line IAC 98-2814 does not show foliar retention and presents higher grain yield, proving to be resistant to stink bugs; however this line is the most defoliated by caterpillars and presents more intense powdery mildew symptoms. Among the genotypes of 135-day maturity group, higher grain yield was observed in IAC 98-2856 under high or low stink bugs infestations, indicating tolerance to these insects, although it shows foliar retention under low stink bug infestation