Approaching Polymer Dynamics Combining Artificial Neural Networks and Elastically Collective Nonlinear Langevin Equation.

The analysis of structural relaxation dynamics of polymers gives an insight into their mechanical properties, whose characterization is used to qualify a given material for its practical scope. The dynamics are usually expressed in terms of the temperature dependence of the relaxation time, which is only available through time-consuming experimental processes following polymer synthesis. However, it would be advantageous to estimate their dynamics before synthesizing them when designing new materials. In this work, we propose a combined approach of artificial neural networks and the elastically collective nonlinear Langevin equation (ECNLE) to estimate the temperature dependence of the main structural relaxation time of polymers based only on the knowledge of the chemical structure of the corresponding monomer.

Sustained timber yield claims, considerations, and tradeoffs for selectively logged forests.

What is meant by sustainability depends on what is sustained and at what level. Sustainable forest management, for example, requires maintenance of a variety of values not the least of which is sustained timber yields (STYs). For the 1 Bha of the world's forests subjected to selective or partial logging, failure to maintain yields can be hidden by regulatory requirements and questionable auditing practices such as increasing the number of commercial species with each harvest, reducing the minimum size at which trees can be harvested and accepting logs of lower quality. For assertions of STY to be credible, clarity is needed about all these issues, as well as about the associated ecological and economic tradeoffs. Lack of clarity about sustainability heightens risks of unsubstantiated claims and unseen losses. STY is possible but often requires cutting cycles that are longer and logging intensities that are lower than prescribed by law, as well as effective use of low-impact logging practices and application of silvicultural treatments to promote timber stock recovery. These departures from business-as-usual practices will lower profit margins but generally benefit biodiversity and ecosystem services.

Assessing the growth and climate sensitivity of secondary forests in highly deforested Amazonian landscapes.

Tropical forests hold 30% of Earth's terrestrial carbon and at least 60% of its terrestrial biodiversity, but forest loss and degradation are jeopardizing these ecosystems. Although the regrowth of secondary forests has the potential to offset some of the losses of carbon and biodiversity, it remains unclear if secondary regeneration will be affected by climate changes such as higher temperatures and more frequent extreme droughts. We used a data set of 10 repeated forest inventories spanning two decades (1999-2017) to investigate carbon and tree species recovery and how climate and landscape context influence carbon dynamics in an older secondary forest located in one of the oldest post-Columbian agricultural frontiers in the Brazilian Amazon. Carbon accumulation averaged 1.08 Mg·ha-1 ·yr-1 , and species richness was effectively constant over the studied period. Moreover, we provide evidence that secondary forests are vulnerable to drought stress: Carbon balance and growth rates were lower in drier periods. This contrasts with drought responses in primary forests, where changes in carbon dynamics are driven by increased stem mortality. These results highlight an important climate change-vegetation feedback, whereby the increasing dry-season lengths being observed across parts of Amazonia may reduce the effectiveness of secondary forests in sequestering carbon and mitigating climate change. In addition, the current rate of forest regrowth in this region was low compared with previous pan-tropical and Amazonian assessments-our secondary forests reached just 41.1% of the average carbon and 56% of the tree diversity in the nearest primary forests-suggesting that these areas are unlikely to return to their original levels on politically meaningful time scales.

First record of Thaumastocoris peregrinus (Hemiptera, Thaumastocoridae) in Pará state, Brazil

Thaumastocoris peregrinus (Hemiptera, Thaumastocoridae) is a phytophagous pest of eucalyptus plantations. It was introduced in Brazil in 2008, and expanded rapidly due to its adaptive capacity to different climatic conditions. Eucalyptus has been planted in the Brazilian Amazon since the 1980s, being used in silvopastoral systems and for cellulose production. Since its introduction in the southernmost Brazilian state of Rio Grande do Sul, T. peregrinus has expanded its geographical distribution to 117 municipalities in states in the south (Rio Grande do Sul, Santa Catarina and Paraná), southeast (São Paulo, Espirito Santo, Rio de Janeiro and Minas Gerais), mid-west (Mato Grosso do Sul and Goiás) and northeast (Sergipe) of the country. Here we report the first record of T. peregrinus in the Brazilian Amazonian state of Pará. (AU)

Soil changes in a subtropical seasonal forest chronosequences in the south of Brazil / Mudanças no solo em cronossequências da floresta estacional subtropical no sul do Brasil

ABSTRACT:The abandonment of field crops and the vegetation recovery in exhausted soils have been a recently studied subject as a way to assess the forest role on the soil recovering. The aim of this study was assess changes in the chemical(14 variables) and grain size (sand, silt, and clay) soil features in four forests chronosequences grew over abandoned field crops in the edge of the Brazilian Southern plateau, Rio Grande do Sul State. There were selected 25 forests aging from 5 to >100 years old in areas of slopes and highlands where samples of Leptosols and Regosols were collected at 15cm in depth. The Fisher's Discriminant Analysis showed that some variable groups of soils can distinguish significantly the soils under different forest ages. Six chemical features of soil fertility were the best monitoring indicators of areas impacted by agriculture. Changes in soil did not occur in a linear way towards time.

RESUMO:O abandono de terras agrícolas e a recuperação da vegetação e dos solos exauridos têm sido um tema recentemente investigado como forma de avaliar o papel da floresta na recuperação do solo. O objetivo deste estudo foi verificar as mudanças nas propriedades químicas (14 variáveis) e granulométricos (areia, silte e argila) em quatro cronossequências florestais originadas após o cultivo agrícola no rebordo do Planalto Meridional, sul do Brasil. Foram selecionadas 25 florestas com idades variando de 5 a >100 anos, localizadas em áreas de encostas e patamares onde amostras de Neossolos Litólicos e Regolíticos Eutróficos foram coletados a 15cm de profundidade. A análise discriminante de Fisher demonstrou que alguns grupos de variáveis dos solos podem distinguir significativamente os solos sob as diferentes idades florestais. Seis atributos químicos relacionados com a fertilidade do solo poderiam ser considerados os melhores indicadores de monitoramento das áreas impactadas pela agricultura. As mudanças no solo não ocorreram de forma linear ao longo do tempo.

AFM based dielectric spectroscopy: extended frequency range through excitation of cantilever higher eigenmodes.

In the last years, a new AFM based dielectric spectroscopy approach has been developed for measuring the dielectric relaxation of materials at the nanoscale, the so called nanoDielectric Spectroscopy (nDS). In spite of the effort done so far, some experimental aspects of this technique remain still unclear. In particular, one of these aspects is the possibility of extending the experimental frequency range, to date limited at high frequencies by the resonance frequency of the AFM cantilever as a main factor. In order to overcome this limitation, the electrical excitation of cantilever higher eigenmodes for measuring the dielectric relaxation is here explored. Thus, in this work we present a detailed experimental analysis of the electrical excitation of the cantilever second eigenmode. Based on this analysis we show that the experimental frequency range of the AFM based dielectric spectroscopy can be extended by nearly two decades with a good signal-to-noise ratio. By using the combination of first and second cantilever eigenmodes we study dissipation processes on well known PVAc based polymeric samples. Both, relaxation spectra and images with molecular dynamics contrast were thus obtained over this broader frequency range.

Determining concentration depth profiles in fluorinated networks by means of electric force microscopy.

By means of electric force microscopy, composition depth profiles were measured with nanometric resolution for a series of fluorinated networks. By mapping the dielectric permittivity along a line going from the surface to the bulk, we were able to experimentally access to the fluorine concentration profile. Obtained data show composition gradient lengths ranging from 30 nm to 80 nm in the near surface area for samples containing from 0.5 to 5 wt. % F, respectively. In contrast, no gradients of concentration were detected in bulk. This method has several advantages over other techniques because it allows profiling directly on a sectional cut of the sample. By combining the obtained results with x-ray photoelectron spectroscopy measurements, we were also able to quantify F/C ratio as a function of depth with nanoscale resolution.

High pressure dynamics of polymer/plasticizer mixtures.

Plasticizers are usually added to polymers to give them the desired flexibility and processability by changing the dynamical properties of the polymer chains. It is therefore important to give a quantitative description about how the dynamic behavior of a given polymer is modified by the incorporation of a second component. We analyze in this work, by means of dielectric spectroscopy, the dynamics of poly(vinyl acetate)/diethyl phthalate mixtures, at different concentrations, over a broad range of frequency, pressure, and temperature. The dynamics of these particular mixtures show only one main relaxation process contrarily to what is observed in athermal miscible polymer mixtures. From the dielectric spectra the maximum relaxation time as a function of pressure and temperature was obtained and analyzed. We studied the pressure dependence of the glass transition temperature as well as the fragility of both the neat components and the mixtures at different concentrations (on the rich polymer range). Finally, the experimental data were rationalized within the framework of an Adam-Gibbs (AG) based approach recently developed [G. A. Schwartz et al., J. Chem. Phys. 127, 154907 (2007)]. The model, originally developed for athermal blends, is here modified to take into account the non-negligible interaction between polymer and plasticizer. We found that the temperature-pressure dependence of the alpha-relaxation time is very well described by this AG extended model.

Adam-Gibbs based model to describe the single component dynamics in miscible polymer blends under hydrostatic pressure.

We present in this work a new model to describe the component segmental dynamics in miscible polymers blends as a function of pressure, temperature, and composition. The model is based on a combination of the Adam-Gibbs (AG) theory and the concept of the chain connectivity. In this paper we have extended our previous approach [D. Cangialosi et al. J. Chem. Phys. 123, 144908 (2005)] to include the effects of pressure in the component dynamics of miscible polymer blends. The resulting model has been tested on poly(vinyl methyl ether) (PVME)/polystyrene (PS) blends at different concentrations and in the temperature range where the system is in equilibrium. The results show an excellent agreement between the experimental and calculated relaxation times using only one fitting parameter. Once this parameter is known the model allows calculating the size of the relevant length scale where the segmental relaxation of the dielectrically active component takes place, i.e., the so called cooperative rearrangement region (CRR) in the AG framework. Thus the size of the CRR for PVME in the blends with PS has been determined as well as its dependence with pressure, temperature, and concentration.

Describing the component dynamics in miscible polymer blends: towards a fully predictive model.

We have recently proposed [D. Cangialosi et al., J. Chem. Phys. 123, 144908 (2005)] an extension of the Adam-Gibbs [J. Chem. Phys. 43, 139 (1965)] theory, combined with the concept of self-concentration, to describe the temperature dependence of the relaxation time for the component segmental dynamics in miscible polymer blends. Thus, we were able to obtain the dynamics of each component in the blend starting from the knowledge of the dynamic and thermodynamic data of the pure polymers, with a single fitting parameter (alpha) which had to be obtained from the fitting of the experimental data. In the present work we demonstrate that this model is also suitable to describe the polymer segmental dynamics in concentrated polymer solutions. From this result we have developed a new route for determining the value of the alpha parameter associated with any given polymer. Once this value is known for the two components of a possible polymer blend, our model for polymer blends dynamics becomes fully predictive.

Morfometria de Papilioninae (Lepidoptera, Papilionidae) ocorrentes em quatro localidades do Rio Grande do Sul, Brasil. I. Comparações com a massa corporal / Morphometrics of Papilioninae (Lepidoptera, Papilionidae) occurring in four localities of Rio Grande do Sul, Brazil. I. Comparisons with body mass

A análise da relação entre a asa e partes do corpo em Lepidoptera podem revelar uma conexão entre a estrutura e a função. Este estudo investigou relações entre o tamanho do corpo de papilionídeos e suas partes, importantes para entender como a forma e o tamanho são determinados, e como eles estão adaptados aos ambientes bióticos e abióticos. Fêmeas são mais pesadas que machos (acima de 1,75 g). Em habitat diferentes, o tórax e o abdômen das fêmeas é maior em 100 por cento das 11 espécies analisadas, a massa total 92 por cento, e a massa de asas 75 por cento. Espécies cujas fêmeas tiveram a maior massa também mostraram maior deslocamento e dispersão nas suas áreas de vida. Em habitats mais perturbados pelo homem ou com menor cobertura vegetal, o aumento no tamanho do tórax é significativamente maior que o das asas, tanto para os machos como para as fêmeas. Nos machos, o aumento de abdômen não é significativamente maior que o das asas, em todos os locais investigados. Porém, nas fêmeas o aumento do abdômen é significativo em todas os locais. A análise de agrupamento mostra dois grandes grupos caracterizados por espécies com tamanhos e proporções semelhantes. Um grupo com espécies que ocupam ambientes com umidade alta, e outro (mais heterogêneo) que ocupa habitats alterados pela ação do homem. O primeiro mostra duas subdivisões distinguidas pelo tipo de exibição que machos apresentam às fêmeas.

Relaxation dynamics of a polymer in a 2D confinement.

The molecular dynamics of oligomeric poly(propylene glycol) (PPG) liquids (MW=1000, 2000, and 4000 g/mol) confined in a two-dimensional layer-structured Na-vermiculite clay has been studied by broadband dielectric spectroscopy. The alpha-relaxation and the normal mode relaxation processes were studied for all samples in bulk and confinement. The most prominent experimental observation was that for the normal mode process: the relaxation rate in the clay is drastically shifted to lower frequencies compared to that of the bulk material. This slowing down is probably caused by the strongly reduced number of accessible chain conformations in two dimensions. Also the temperature dependence of the relaxation time for the normal mode process is strongly affected by the confinement. In contrast, for the alpha-relaxation of the confined polymers we observed only a slight increase of the relaxation rate at high temperatures compared to the corresponding bulk samples, and a decrease of its relaxation strength relative to the beta relaxation. Thus, the glass transition is unaffected by the 2D confinement, suggesting that the underlying phenomena responsible for the glass transition is the same as in bulk. Moreover, in the clay the intensity of the normal mode is stronger than that of the alpha-process, in contrast to the bulk samples where the opposite behavior is observed.

Glass transition and relaxation processes in supercooled water.

Many of water's peculiar physical properties are still not well understood, and one of the most important unresolved questions is its glass transition related dynamics. The consensus has been to accept a glass transition temperature (T(g)) around 136 K, but this value has been questioned and reassigned to about 165 K. We find evidence that the dielectric relaxation process of confined water that has been associated with the long accepted T(g) of water (130-140 K) must be a local process which is not related to the actual glass transition. Rather, our data indicate a glass transition at 160-165 K for bulk water and about 175 K for confined water (depending on the confining system).

Evidence for a stress hypothesis: hemiparasitism effect on the colonization of Alchornea castaneaefolia A. Juss.uphorbiaceae) by Galling Insects

Stressed plants are generally more attacked by galling insects. In this study we investigated the relationship between population abundance and species richness of galling insects on the tree Alchornea castaneaefolia A. JUSS. (Euphorbiaceae), submited to stress induced by the hemiparasite Psittacanthus sp. (Loranthaceae) in the Amazon, Brazil. Branches of A. castaneaefolia attacked by the hemiparasite were more heavily infested by galling insects than non-attacked branches. The field observations partially corroborate the hypothesis that there would be an optimal level of host-plant stress for galling insect establishment.

Plantas estressadas geralmente são mais atacadas por insetos galhadores. Neste estudo investigamos a relação entre abundância populacional e a riqueza de espécies de insetos galhadores na árvore Alchornea castaneaefolia A. JUSS. (Euphorbiaceae), submetida ao estresse induzido pela hemiparasita Psittacanthus sp. (Loranthaceae) na Amazônia, Brasil. Galhos de A. castaneaefolia atacados pela hemiparasita foram mais fortemente infestados por insetos galhadores do que os galhos não atacados. As observações de campo corroboram parcilmente a hipótese de que haveria um nível ótimo de estresse da planta hospedeira para o estabelecimento de insetos galhadores.

Diversidade de quinze espécies de borboletas (lepidoptera, papilionidae) em sete comunidades de Santa Maria, RS / Diversity of fifteen species of butterflies (lepidoptera, papilionidae) in seven communities of Santa Maria, RS, Brazil

O trabalho compara a diversidade estimada para sete áreas de Santa Maria, RS, com diferentes níveis de antropização, com base na abundância, similaridade e constância de 15 espécies de papilionídeos. O estudo foi realizado de Setembro de 1994 a Março de 1995, e de Novembro de 1995 a Fevereiro de 1996. As capturas foram efetuadas em intervalos médios de trinta dias, utilizando rede entomológica convencional, durante intervalos médios de 4 horas. As borboletas foram transportadas em envelopes glicinados, individualizados e etiquetados, para o laboratório do Departamento de Biologia da UFSM. Os dados sugerem que a cobertura vegetal desempenha uma função importante na distribuição e abundância dessas borboletas, e os mecanismos que agem em escalas geográficas mais amplas podem ser diferentes daqueles que atuam em escalas menores. Habitats, como capões e ambientes urbanos, representam locais favoráveis onde as borboletas podem usar esses ambientes complexos, exibindo uma norma de reação que minimiza a competição e a ação de inimigos naturais.

The research has as objective to compare the esteemed diversity for seven of Santa Maria's counties, RS, Brazil, with different urbane levels, based on the study of abundance, similarity and steadiness among 15 Papilionidae species, from September 1994 to March 1995 and November 1995 to February 1996. Captures were performed in intervals of thirty days, using entomological net, during intervals of 4 hours average. The butterflies were transported in glassine envelopes, individualized, properly labeled to the Laboratory at UFSM Biology Department. The results suggest that the canopy carries out an important function in the distribution and abundance of those butterflies. The mechanisms that act in wider geographical scales can be different from those that act in smaller scales. Coppices and urban landscapes can represent locals, where butterflies can use these complex environments exhibiting a reaction norm that minimizes competition and natural enemies' actions use these complex environments exhibiting a reaction norm that minimizes competition and natural enemies' actions.