The Dynamic Formation of Prominence Condensations

We present simulations of a model for the formation of a prominence condensation in a coronal loop. The key idea behind the model is that the spatial localization of loop heating near the chromosphere leads to a catastrophic cooling in the corona (Antiochos & Klimchuk 1991). Using a new adaptive grid code, we simulate the complete growth of a condensation, and find that after approx. 5,000 s it reaches a quasi-steady state. We show that the size and the growth time of the condensation are in good agreement with data, and discuss the implications of the model for coronal heating and SOHO/TRACE observations.Comment: Astrophysical Journal latex file, 20 pages, 7 b-w figures (gif files

Optimization of DC-DC Converters via Geometric Programming

The paper presents a new methodology for optimizing the design of DC-DC converters. The magnitudes that we take into account are efficiency, ripples, bandwidth, and RHP zero placement. We apply a geometric programming approach, because the variables are positives and the constraints can be expressed in a posynomial form. This approach has all the advantages of convex optimization. We apply the proposed methodology to a boost converter. The paper also describes the optimum designs of a buck converter and a synchronous buck converter, and the method can be easily extended to other converters. The last example allows us to compare the efficiency and bandwidth between these optimal-designed topologies

Variação da qualidade do solo em áreas submetidas a sistemas de manejo de base ecológica.

bitstream/item/145137/1/Boletim-228.pd

Eficiência energética do processo top-down na produção de nanofibrilas de celulose.

O presente estudo tem por objetivo produzir nanofibrilas de celulose vegetal com polpa kraft marrom por meio de pré-tratamento enzimático e posteriormente mecânico, com o intuito de redução no consumo energético. Para isso, as amostras de polpas de celulose foram previamente desestruturadas através da saturação em água e desmembradas em um desfibrador mecânico. Após, armazenadas sob refrigeração a 5°C. Para o pré-tratamento enzimático utilizou-se a enzima comercial Cellic Ctec-2, em porcentagens que variaram de 0,01 a 0,1% por meio de hidrólise controlada com pH neutro e temperatura ambiente durante uma hora, sendo que as amostras com quantidade de 0,01% sofreram hidrólise por diferentes períodos (1 e 2 horas). Após o tempo de hidrólise, a polpa foi processada em um moinho de discos, o qual possui medidor de energia. As polpas sofreram passagens em ciclos pelo moinho, até o ponto de se transformarem em um gel viscoso. Para estacionar a ação enzimática o conteúdo foi aquecido à 85°C. Os géis foram armazenados em resfriamento de 5°C. O processo foi caracterizado pelo gasto energético medido a cada amostra com suas testemunhas, além de ser medido o rendimento de cada gel produzido. De acordo com os resultados, foi observado que o processo combinado apresentou-se viável para a produção de nanofibrilas, pois este, diminui o tempo e gasto energético do processo. A polpa marrom mesmo sem ter passado por processos de deslignificação, mostrou-se promissora na produção das nanofibrilas de celulose vegetal

Making Climate Change Mitigation and Adaptability Real in Africa with Conservation Agriculture

In this report, the authors have gathered essential information on how the agricultural sector can respond to climate change through Conservation Agriculture (CA). This document aims to serve as a basis for decision-making based on science and agricultural experimentation in Africa

Ranking protected areas in the Azores using standardised sampling of soil epigean arthropods

Copyright © Springer 2005.Nineteen areas in seven of the nine Azorean islands were evaluated for species diversity and rarity based on soil epigean arthropods. Fifteen out of the 19 study areas are managed as Natural Forest Reserves and the remaining four were included due to their importance as indigenous forest cover. Four of the 19 areas are not included in the European Conservation network, NATURA 2000. Two sampling replicates were run per study area, and a total of 191 species were collected; 43 of those species (23%) are endemic to the archipelago and 12 have yet to be described. To produce an unbiased multiple-criteria index (importance value for conservation, IV-C) incorporating diversity and rarity based indices, an iterative partial multiple regression analysis was performed. In addition, an irreplaceability index and the complementarity method (using both optimisation and heuristic methods) were used for priority-reserves analyses. It was concluded that at least one well-managed reserve per island is absolutely necessary to have a good fraction of the endemic arthropods preserved. We found that for presence/absence data the suboptimal complementarity algorithm provides solutions as good as the optimal algorithm. For abundance data, optimal solutions indicate that most reserves are needed if we want that at least 50% of endemic arthropod populations are represented in a minimum set of reserves. Consistently, two of the four areas not included in the NATURA 2000 framework were considered of high priority, indicating that vascular plants and bird species used to determine NATURA 2000 sites are not good surrogates of arthropod diversity in the Azores. The most irreplaceable reserves are those located in older islands, which indicates that geological history plays an important role in explaining faunal diversity of arthropods in the Azores. Based both on the uniqueness of species composition and high species richness, conservation efforts should be focused on the unmanaged Pico Alto region in the archipelago’s oldest island, Santa Maria

A Millennium Scale Sunspot Number Reconstruction: Evidence For an Unusually Active Sun Since the 1940's

The extension of the sunspot number series backward in time is of considerable interest for dynamo theory, solar, stellar, and climate research. We have used records of the Be-10 concentration in polar ice to reconstruct the average sunspot activity level for the period between the year 850 to the pr esent. Our method uses physical models for processes connecting the Be-10 concentration with the sunspot number. The reconstruction shows reliably that the period of high solar activity during the last 60 years is unique throughout the past 1150 years. This nearly triples the time interval for which such a statement could be made previouslyComment: 4 pages, LaTeX, revtex4 macros; Phys. Rev. Let., in pres