Preface - Personal perspectives in nonlinear science : Looking back, looking forward

Peer reviewedPublisher PD

The Early Triassic magmatism of the Alto ParaguayProvince, Central South America: Paleomagneticand ASM data

Abstract A paleomagnetic studystudywork was carriedout on the Alto Paraguay Province (APP), a belt of alkalinecomplexes that parallel the Paraguay river for morethan 40 km at the border of Brazil and Paraguay. Theprovince is well dated by 40Ar/39Ar method giving ages inthe range 240–250 Ma with a preferred age of 241 Ma. Intrusiverocks are predominant but the stocks may be toppedby lava flows and ignimbrites. Paleomagnetic work onstocks, dikes and flows of the APP identified normal andreversed magnetic components which are carried mainlyby titanomagnetites. The calculated paleomagnetic polelocated at 319ºE 78ºS (α95 = 6º; k = 23) is in agreementwith other South American poles of Permo-Triassic age.Most of the sampling sites showed large variations in rockmagnetization, but similar patterns in the variation of thewithin-site magnetizations, mainly in dikes, suggest geomagneticpolarity transition records. The magnetizationdata along with the anisotropy of magnetic susceptibilitydeterminations suggested that the South and North areasof the province have different evolution characteristics

Resiliently evolving supply-demand networks

Peer reviewedPublisher PD

ELEMENTOS MINERAIS EM MADEIRAS DE EUCALIPTOS E ACÁCIA NEGRA E SUA INFLUÊNCIA NA INDÚSTRIA DE CELULOSE KRAFT BRANQUEADA

No ramo de papel e celulose os efluentes são um dos principais problemas e o consumo de água é crítico. Os circuitos internos estão sendo fechados e as fontes de contaminação precisam ser conhecidas. Uma das fontes de contaminação destes efluentes são os minerais da madeira, matéria-prima neste tipo de indústria. Neste trabalho foi avaliada a quantidade de alumínio, cálcio, cobre, ferro, potássio, magnésio, manganês, sódio, níquel e silício em madeiras de cinco espécies florestais, plantadas na região de Guaíba, RS, compreendendo Acacia mearnsii, Eucalyptus dunnii, Eucalyptus globulus, Eucalyptus grandis, Eucalyptus saligna. As amostras de madeira foram tratadas com digestão ácida e com carbonização em mufla, solubilizando em ácido para serem analisadas por ICP (Inductively Coupled Plasm). Foi observado que a quantidade de elementos é considerável e os principais elementos encontrados foram K, Ca, Na, Al, Mn, e Si. As espécies Eucalyptus grandis e Eucalyptus saligna mostraram melhor crescimento. Por outro lado, Eucalyptus globulus e Eucalyptus dunnii mostraram menor crescimento e maior teor de elementos. Pelo fato dessas espécies introduzirem maiores quantidades de elementos no processo de fabricação, devem conduzir a maiores problemas industriais. A Acacia mearnsii mostrou o menor nível para ferro, manganês e níquel, sendo uma boa opção para uso em branqueamento com oxigênio, ozônio e peróxido. O silício observado estava em baixa quantidade, o que leva a afirmar que há, na prática industrial, muita contaminação da madeira explorada com solo já que se encontram altos valores de sílica nos circuitos de licores. A entrada dos elementos minerais estudados em uma fábrica de celulose via madeira varia de 4 a 6 kg por tonelada de polpa não-branqueada produzida. Cuidados especiais devem ser tomados com as espécies com madeiras mais ricas em cinzas e elementos minerais e mais baixas eficiências nutricionais, como foi o caso de Eucalyptus dunnii e Eucalyptus globulus

High-Frequency EPR and ENDOR Spectroscopy on Semiconductor Quantum Dots

It is shown that high-frequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy are excellent tools for the investigation of the electronic properties of semiconductor quantum dots (QDs). The great attractions of these techniques are that, in contrast to optical methods, they allow the identification of the dopants and provide information about the spatial distribution of the electronic wave function. This latter aspect is particularly attractive because it allows for a quantitative measurement of the effect of confinement on the shape and properties of the wave function. In this contribution EPR and ENDOR results are presented on doped ZnO QDs. Shallow donors (SDs), related to interstitial Li and Na and substitutional Al atoms, have been identified in this material by pulsed high-frequency EPR and ENDOR spectroscopy. The shallow character of the wave function of the donors is evidenced by the multitude of ENDOR transitions of the 67Zn nuclear spins and by the hyperfine interaction of the 7Li, 23Na and 27Al nuclear spins that are much smaller than for atomic lithium, sodium and aluminium. The EPR signal of an exchange-coupled pair consisting of a shallow donor and a deep Na-related acceptor has been identified in ZnO nanocrystals with radii smaller than 1.5 nm. From ENDOR experiments it is concluded that the deep Na-related acceptor is located at the interface of the ZnO core and the Zn(OH)2 capping layer, while the shallow donor is in the ZnO core. The spatial distribution of the electronic wave function of a shallow donor in ZnO semiconductor QDs has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine interactions as monitored by ENDOR spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles. In addition, the effect of confinement on the g-factor of SDs in ZnO as well as in CdS QDs is observed. Finally, it is shown that an almost complete dynamic nuclear polarization (DNP) of the 67Zn nuclear spins in the core of ZnO QDs and of the 1H nuclear spins in the Zn(OH)2 capping layer can be obtained. This DNP is achieved by saturating the EPR transition of SDs present in the QDs with resonant high-frequency microwaves at low temperatures. This nuclear polarization manifests itself as a hole and an antihole in the EPR absorption line of the SD in the QDs and a shift of the hole (antihole). The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with nuclear magnetic resonance techniques

Structure and function in flow networks

Peer reviewedPublisher PD

THE USE OF VIRTUAL REALITY AS AN INFORMATION TOOL ON EXTERNALITIES OF ENERGY SOURCES

Almost daily communication vehicles make some reference to the need to combat the indiscriminated use of fossil fuels and to use less polluting energy sources. In this scenario, nuclear energy should be presented as an option but this is still covered by many myths. Thus, to inform the youth public about the characteristics of the main sources that compose the brazilian energy matrix it is necessary to promote the transfer of knowledge and to demystify the nuclear sector in playful and responsible way

Fitofármaco, fitoterápico, plantas medicinais: o reducionismo e a complexidade na produção do conhecimento científico

Esse estudo tem por objetivo discutir como a forma de produção do conhecimento científico pode determinar a maneira do homem conhecer, lidar e apropriar-se da natureza, especificamente, em relação ao conhecimento associado ao estudo das plantas medicinais e seus derivados. Visando fornecer subsídios para a compreensão do que norteia os pesquisadores que buscam o entendimento sobre as plantas medicinais a partir de uma abordagem complexa, algumas questões de caráter epistemológico são formuladas e discutidas à luz dos referenciais teóricos construídos por Morin6 e Latour7

Site selection process for new nuclear power plants-a method to support decision making and improving public participation

The Brazilian Energy Plan (PNE 2030) that guides the Government in formulating its strategy for expanding energy supply by 2030 highlights the need for the Brazilian electrical system have more than 4,000 MW from nuclear sources by 2025. Therefore, the Government presented a proposal to build four more nuclear power plants with capacity of 1,000 MW each, at first, two in the Northeast and two in Southeast. The selection and site assessment are key parts of the installation process of a nuclear plant and may significantly affect the cost, public acceptance and safety of the facility during its entire life cycle. The result of this initial stage, it can even seriously affect program success. Wrong decisions in the process of site selection may also require a financial commitment to higher planned in a later phase of the project, besides causing extensive and expensive downtime. Select the location where these units will be built is not a trivial process, because involves the consideration of multiple criteria and judgments in addition to obtaining, organizing and managing a diverse range of data, both qualitative and quantitative, to assist in decision making and ensure that the site selected is the most appropriate in relation to safety and technical, economic and environmental feasibility. This paper presents an overview of the site selection process and its stages, the criteria involved in each step, the tools to support decision making that can be used and the difficulties in applying a formal process of decision making. Also discussed are ways to make the process more transparent and democratic, increasing public involvement as a way to improve acceptance and reduce opposition from various sectors of society, trying to minimize the expense and time involved in the implementation of undertakings of this kind