On the centralization of the circumcentered-reflection method

This paper is devoted to deriving the first circumcenter iteration scheme that does not employ a product space reformulation for finding a point in the intersection of two closed convex sets. We introduce a so-called centralized version of the circumcentered-reflection method (CRM). Developed with the aim of accelerating classical projection algorithms, CRM is successful for tracking a common point of a finite number of affine sets. In the case of general convex sets, CRM was shown to possibly diverge if Pierra's product space reformulation is not used. In this work, we prove that there exists an easily reachable region consisting of what we refer to as centralized points, where pure circumcenter steps possess properties yielding convergence. The resulting algorithm is called centralized CRM (cCRM). In addition to having global convergence, cCRM converges linearly under an error bound condition, and superlinearly if the two target sets are so that their intersection have nonempty interior and their boundaries are locally differentiable manifolds. We also run numerical experiments with successful results.Comment: 29 pages with 7 figure

Agropastoral Systems an Alternative to Revert Pasture Degradation in the Cerrados of Brazil: Preliminary Results

A long term experiment was set to test the hypothesis that agropastoral systems could improve crop and animal production, being more profitable and sustainable relative to economical, biological and environmental aspects, than continuous and traditional crop and grazing pasture systems. Five farming systems are being tested: two traditional (continuous soybean annual cropping and continuous pasture cropping) and three agropastoral systems (two combinations of four by four years of rotational crop-pasture systems and one by three years of crop-pasture rotation). Animal production in continuous pasture cropping measured as liveweight gain/ha (LWG) are declining along the years in the sub-treatment without fertilizer maintenance. After five cycles of animal performance evaluation, average yields were 397 as compared to 444 kg of LWG/ha, in fertilized pasture. Agropastoral systems, in the other hand, have shown promising results of LWG, either in the one by three or in the four by four cropping combination, with animal production ranking from 547 to 789 kg of LWG/ha/year. Soil fertility in agropastoral systems increased substantially

Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifcations to forest expansion, but generally lacked high resoltiuon proxies to measure these efects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profles confrm that in spite of climatic fuctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifcations were linked to demographic changes, the efects of which are still visible today

O eucalipto em sistemas de integração lavoura-pecuária-floresta (ILPF) na Amazônia.

PT-BR: A pecuária na Amazônia, intensificada a partir de 1960, sem planejamento e manejo adequados, causou danos ambientais pelo desmatamento, baixo nível tecnológico e explora¬ção intensiva das pastagens, o que contribuiu para a degradação de milhões de hectares na região. Atualmente, a intensificação sustentável na recuperação de pastagens degradadas da região Amazônica mediante implantação de sistemas integrados de produção agropecuária é a principal ação de modernização e possibilita aumentar e diversificar a produção por meio da uti¬lização sustentável dos recursos naturais. Nos últimos anos foi estabelecida na Amazônia, pela Embrapa e seus parceiros, a estratégia de implantação de Unidades de Referência Tecnológicas (URT) com os sistemas de integração lavoura-pecuária-floresta (ILPF), para divulgar resultados de pesquisa aos produtores e à rede de Assistência Técnica e Extensão Rural (Ater), a fim de incentivar e ampliar a adoção de sistemas integrados de produção agropecuária. As experiências com sistemas de ILPF realizadas nos estados do Acre, Amapá, Amazonas, Mato Grosso, Pará, Rondônia e Roraima apresentam resultados promissores. Atualmente existem mais de 20 URTs com ILPF em toda a região Amazônica, a qual permite a geração e divulgação de resultados técnicos e científicos aos produtores e à rede de assistência técnica e extensão rural, visando oferecer tecnologias e conhecimentos necessários à implantação desses sistemas. A ILPF, como estratégia de produção, ocupa uma área superior a 1,5 milhão de hectares na região Amazônica, onde a integração lavoura-pecuária (ILP) é a modalidade predominante, ou seja, superior a 90% da área. As modalidades que contemplam o componente florestal, em sua maioria, são adotadas por pequenos e médios produtores, visando ao bem-estar animal e, quando possível, à explo¬ração comercial da madeira e de produtos não madeireiros. As experiências na Amazônia com o eucalipto em sistemas integrados de produção agropecuária são promissoras. O eucalipto é a principal espécie florestal utilizada nos sistemas ILPF para reincorporar ao processo produtivo grandes extensões de áreas degradadas da Amazônia. | EN-US: Livestock production in the Amazon has intensified since the 1960s, but with inadequate planning and management. As such, deforestation, low-levels of technology, and intensive exploitation of pastures have contributed to the degradation of millions of hectares of forest in the region. Currently, the main development strategy in the Amazon is the implementation of integrated agricultural production systems to achieve sustainable intensification in the recovery of degraded pastures. These systems enable an increase in, and diversification of, production through sustainable natural resource use. In recent years, Embrapa and its partners have established a strategy to implement Technical Reference Units (URT) with integrated crop-livestock-forest (ICLF) systems in the Amazon. The goal of the URTs is to disseminate research results to producers and the vast network of Technical Assistance and Rural Extension workers (Ater) and encourage and expand the adoption of integrated agricultural production systems. The experiences with ICLF in the states of Acre, Amapá, Amazonas, Mato Grosso, Pará, Rondônia, and Roraima show promising results. Currently, there are more than 20 URTs with ICLF throughout the Amazon that offer the technologies and knowledge necessary to implement these systems. As a production strategy, ICLF occupy an area of more than 1.5 million hectares in the Amazon, where crop-livestock integration (ICLF) is the most common and corresponds to more than 90% of the area. Systems that integrate a forest component are mostly used by small- and medium-scale producers, aiming to improve animal welfare and, when possible, the commercial exploitation of wood and non-timber forest products. Eucalyptus is the main forest species used in ICLF systems to reincorporate large areas of degraded land into the production process, and the experiences in the Amazon with eucalyptus in integrated agricultural production systems are showing promise

Biochar chemistry in a weathered tropical soil: kinetics of phosphorus sorption.

The phosphorus (P) chemistry of biochar (BC)-amended soils is poorly understood. This statement is based on the lack of published research attempting a comprehensive characterization of biochar?s influence on P sorption. Therefore, this study addressed the kinetic limitations of these processes. This was accomplished using a fast pyrolysis biochar made from a mix of waste materials applied to a highly weathered Latossolo Vermelho distrofico (Oxisol) from São Paulo, Brazil. Standard method (batch method) was used. The sorption kinetic studies indicated that P sorption in both cases, soil (S) and soil-biochar (SBC), had a relatively fast initial reaction between 0 to 5 min. This may have happened because adding biochar to the soil decreased P sorption capacity compared to the mineral soil alone. Presumably, this is a result of: (i) Inorganic phosphorus desorbed from biochar was resorbed onto the mineral soil; (ii) charcoal particles physically covered P sorption locations on soil; or (iii) the pH increased when BC was added SBC and the soil surface became more negatively charged, thus increasing anion repulsion and decreasing P sorption

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide

Widespread reforestation before European influence on Amazonia

An estimated 90-95% of indigenous people in Amazonia died following European Contact. This population collapse is postulated to have caused decreases in atmospheric CO2 concentrations at c. 1610 CE, as a result of a wave of land abandonment in the wake of disease, slavery and warfare, whereby the attendant reversion to forest significantly increased terrestrial carbon sequestration. Based on 39 Amazonian fossil pollen records, we show that there was no synchronous reforestation event associated with such an atmospheric CO2 response following European arrival in Amazonia. Instead, we find that, at most sites, land abandonment and forest regrowth began c. 300 - 600 years before European arrival. Pre-European pandemics, social strife or environmental change may have contributed to these early site abandonments and ecological shifts

Pigment epithelium-derived factor protects retinal ganglion cells

BACKGROUND: Retinal ganglion cells (RGCs) are responsible for the transmission of visual signals to the brain. Progressive death of RGCs occurs in glaucoma and several other retinal diseases, which can lead to visual impairment and blindness. Pigment epithelium-derived factor (PEDF) is a potent antiangiogenic, neurotrophic and neuroprotective protein that can protect neurons from a variety of pathologic insults. We tested the effects of PEDF on the survival of cultured adult rat RGCs in the presence of glaucoma-like insults, including cytotoxicity induced by glutamate or withdrawal of trophic factors. RESULTS: Cultured adult rat RGCs exposed to glutamate for 3 days showed signs of cytotoxicity and death. The toxic effect of glutamate was concentration-dependent (EC(50 )= 31 μM). In the presence of 100 μM glutamate, RGC number decreased to 55 ± 4% of control (mean ± SEM, n = 76; P < 0.001). The glutamate effect was completely eliminated by MK801, an NMDA receptor antagonist. Trophic factor withdrawal also caused a similar loss of RGCs (54 ± 4%, n = 60, P < 0.001). PEDF protected against both insults with EC(50 )values of 13.6 ng/mL (glutamate) and 3.4 ng/mL (trophic factor withdrawal), respectively. At 100 ng/mL, PEDF completely protected the cells from both insults. Inhibitors of the nuclear factor κB (NFκB) and extracellular signal-regulated kinases 1/2 (ERK1/2) significantly reduced the protective effects of PEDF. CONCLUSION: We demonstrated that PEDF potently and efficaciously protected adult rat RGCs from glutamate- and trophic factor withdrawal-mediated cytotoxicity, via the activation of the NFκB and ERK1/2 pathways. The neuroprotective effect of PEDF represents a novel approach for potential treatment of retinopathies, such as glaucoma