Thermal Fractionation and isothermal crystallization of polyethylene nanocomposites prepared by in situ polymerization

Nanocomposites of high-density polyethylene (HDPE) and carbon nanotubes (CNT) of different geometries (single wall, double wall, and multiwall; SWNT, DWNT, and MWNT) were prepared by in situ polymerization of ethylene on CNT whose surface had been previously treated with a metallocene catalytic system. In this work, we have studied the effects of applying the successive self-nucleation and annealing thermal fractionation technique (SSA) to the nanocomposites and have also determined the influence of composition and type of CNT on the isothermal crystallization behavior of the HDPE. SSA results indicate that all types of CNT induce the formation of a population of thicker lamellar crystals that melt at higher temperatures as compared to the crystals formed in neat HDPE prepared under the same catalytic and polymerization conditions and subjected to the same SSA treatment. Furthermore, the peculiar morphology induced by the CNT on the HDPE matrix allows the resolution of thermal fractionation to be much better. The isothermal crystallization results indicated that the strong nucleation effect caused by CNT reduced the supercooling needed for crystallization. The interaction between the HDPE chains and the surface of the CNT is probably very strong as judged by the results obtained, even though it is only physical in nature. When the total crystallinity achieved during isothermal crystallization is considered as a function of CNT content, it was found that a competition between nucleation and topological confinement could account for the results. At low CNT content the crystallinity increases (because of the nucleating effect of CNT on HDPE), however, at higher CNT content there is a dramatic reduction in crystallinity reflecting the increased confinement experienced by the HDPE chains at the interfaces which are extremely large in these nanocomposites. Another consequence of these strong interactions is the remarkable decrease in Avrami index as CNT content increases. When the Avrami index reduces to I or lower, nucleation dominates the overall kinetics as a consequence of confinement effects. Wide-angle X-ray experiments were performed at a high-energy synchrotron source and demonstrated that no change in the orthorhombic unit cell of HDPE occurred during crystallization with or without CNT.

Crystallization and stereocomplexation behavior of poly(D- and L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) block copolymers

The thermal properties, crystallization, and morphology of amphiphilic poly(D-lactide)-b-poly(N,N-dimethylamino- 2-ethyl methacrylate) (PDLA-b-PDMAEMA) and poly (L-lactide)-b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PLLA-b-PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA-b-PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk-shape structure and, for high molecular weight samples, the particles displayed unusual star-like shape morphology.

Impegno nero: Italian intellectuals and the African-American struggle

In the aftermath of the Second World War, Italian intellectuals participated in Italy’s reconstruction with an ideological commitment inspired by the African-American struggle for equal rights in the United States. Drawing on the work of many of the leading figures in postwar Italian culture, including Italo Calvino, Giorgio Caproni, Cesare Pavese, and Elio Vittorini, this essay argues that Italian intellectual impegno—defined as the effort to remake Italian culture and to guide Italian social reform—was united with a significant investment in the African-American cause. The author terms this tendency impegno nero and traces its development in the critical reception of African-American writers including W.E.B. DuBois, Langston Hughes, and Richard Wright. Postwar impegno nero is then contrasted with the treatment of African-American themes under Fascism, when commentators had likewise condemned American racism, but had paradoxically linked their laments for the plight of African Americans with defenses of the racial policies of the Fascist regime. Indeed, Fascist colonialism and anti-Semitism were both justified through references to what Fascist intellectuals believed to be America’s greater injustices. After 1945, in contrast, Italian intellectuals advocated an international, interdependent campaign for justice, symbolizing national reforms by projecting them onto an emblematic America. In this way, impegno nero revived and revised the celebrated "myth of America" that had developed in Italy between the world wars. Advancing a new, postwar myth, Italian intellectuals adopted the African-American struggle in order to reinforce their own efforts in the ongoing struggle for justice in Italy.

The economics of enhanced landfill mining: private and societal performance drivers

This paper addresses the economics of Enhanced Landfill Mining (ELFM) both from a private point of view as well as from a society perspective. The private potential is assessed using a case study for which an investment model is developed to identify the impact of a broad range of parameters on the profitability of ELFM. We found that especially variations in Waste-to-Energy (WtE efficiency, electricity price, CO2-price, WtE investment and operational costs) and ELFM support explain the variation in economic profitability measured by the Internal Rate of Return. To overcome site-specific parameters we also evaluated the regional ELFM potential for the densely populated and industrial region of Flanders (north of Belgium). The total number of potential ELFM sites was estimated using a 5-step procedure and a simulation tool was developed to trade-off private costs and benefits. The analysis shows that there is a substantial economic potential for ELFM projects on the wider regional level. Furthermore, this paper also reviews the costs and benefits from a broader perspective. The carbon footprint of the case study was mapped in order to assess the project’s net impact in terms of greenhouse gas emissions. Also the impacts of nature restoration, soil remediation, resource scarcity and reduced import dependence were valued so that they can be used in future social cost-benefit analysis. Given the complex trade-off between economic, social and environmental issues of ELFM projects, we conclude that further refinement of the methodological framework and the development of the integrated decision tools supporting private and public actors, are necessary.

Why children differ in motivation to learn: insights from 13,000 twins from 6 countries

Little is known about why people differ in their levels of academic motivation. This study explored the etiology of individual differences in enjoyment and self-perceived ability for several school subjects in nearly 13,000 twins aged 9 to 16 from 6 countries. The results showed a striking consistency across ages, school subjects, and cultures. Contrary to common belief, enjoyment of learning and children’s perceptions of their competence were no less heritable than cognitive ability. Genetic factors explained approximately 40% of the variance and all of the observed twins’ similarity in academic motivation. Shared environmental factors, such as home or classroom, did not contribute to the twin’s similarity in academic motivation. Environmental influences stemmed entirely from individual specific experiences.

Assimetria de informação no mercado de seguro de automóveis

Neste trabalho, estudaremos as possibilidades de existência de assimetria de informação relevante no mercado de seguros de automóveis brasileiro. Mais especificamente, estudaremos a relação entre o nsco empírico dos segurados, supostamente uma informação assimétrica, e sua demanda por cobertura. Utilizando uma extensa e detalhada base de dados, obtida junto a Superintendência de Seguros Privados (SUSEP), implementamos os principais testes econométricos existentes na literatura (paramétricas e semi­ paramétricas) para verificar a existência de assimetria de informação relevante no mercado de seguros de automóveis brasileiro. Inicialmente, replicamos os testes propostos por Chiappori e Salanié (2000) e Dionne, Gouriéroux e Vanasse (2001) e obtivemos o mesmo resultado: ausência de dependência condicional entre cobertura con­ tratada e risco empírico. Porém, constatamos que este resultado não é robusto a alterações marginais na metodologia de teste. Em seguida, estudamos uma característica peculiar dos contratos brasileiros: a não-monotonicidade das coberturas. Veremos que segurados mais arriscados terão incentivos em demandar contratos com franquias maiores (e, portanto, com menores coberturas). Após exaustivos testes, constatamos que tal característica inverte, de fato, o sinal da correlação entre cobertura e risco. Por fim, testamos se os prêmios dos contratos de seguro são funções lineares da cobertura. Constatamos que sim. Com isso, concluímos que as seguradoras não utilizam o par prêmio/ cobertura para separar os segurados de acordo com seu nsco (tal como prevê os modelos que consideram a existência de seleção adversa nesse mercado). Os resultados obtidos neste trabalho sugerem que, no mínimo, não devemos ignorar a possibilidade de existência de assimetria de informação relevante no mercado segurador brasileiro. Sendo assim, sugerimos que o apreçamento do risco nos contratos de seguro não deva se valer apenas de ferramentas atuariais, tal como é feito atualmente, mas deve considerar também os incentivos implícitos que os contratos de seguro exercem sobre o comportamento (arriscado) dos segurados.

Abordagem cross-cultural para comitês organizadores de jogos: caso dos XV Jogos Pan-americanos Rio 2007

O escopo teórico de Gestão Internacional atualmente atinge tantos locais quanto pessoas ao redor do planeta e pode se expandir para atender também a um conjunto mais amplo de empresas que somente as multinacionais. Com o objetivo de analisar os desafios cross-culturais e os conflitos que permearam o Comitê Organizador dos XV Jogos Pan-americanos Rio 2007, este estudo equipara Comitês Organizadores de Jogos a subsidiárias com mandato global. A partir de uma metodologia de inspiração interpretativista cultural defendendo o papel do contexto local por uma abordagem crítica, analisa o sistema de ação cultural brasileiro e contrapõe teorias clássicas da abordagem cross-cultural com uma visão qualitativa de base sócio-antropológica. Foram realizadas entrevistas semiestruturadas com ex-funcionários do Comitê Rio 2007 tanto brasileiros quanto estrangeiros e consultores que apoiaram a realização dos Jogos. Várias questões foram levantadas que apóiam a influência de características comportamentais culturais brasileiras como o paternalismo, a lealdade às pessoas, a flexibilidade, e evitar conflitos nas relações pessoais e organizacionais. Ao mesmo tempo, foi possível identificar três possíveis causas de conflitos entre os atores principais das narrativas (os consultores, o Comitê Organizador Rio2007 e o governo): (1) a diferença no nível de experiência /conhecimento explícito e tácito, (2) a desconfiança, e (3) o orgulho; e o esforço de comunicação foi identificado como possível solução. Por fim, foi possível visualizar traços das teorias clássicas cross-culturais dentro do estudo, mas foi reforçada a crítica de que é impossível isolar a cultura e o contexto local como variáveis contingenciais, muito menos ignorá-los.

A fotografia em Las babas del diablo e em Blow-Up : marca de indecisões

Esta dissertação é um estudo sobre o conto Las babas del diablo, de Julio Cortázar, e do filme Blow-Up, de Michelangelo Antonioni. Entre as inúmeras portas de entrada para abordar essas duas obras, optamos por explorá-las pelo caminho da fotografia, que é, a um só tempo, eixo temático ficcional do conto e do filme e também mola propulsora para um debate teórico sobre o fotográfico. Inserida em uma perspectiva comparatista, lançamos mão da intertextualidade e da interdisciplinaridade, conceitos fundamentais da Literatura Comparada. Nesse sentido, abordamos inicialmente as relações de produtividade entre os próprios textos e, depois, entre textos e imagens. Posteriormente, aproveitando uma proposta de Cortázar de comparar a fotografia com o conto, passamos a explorar a fotografia no seu âmbito teórico. Dois autores são basilares nesse ponto do trabalho: Roland Barthes e Philippe Dubois. O primeiro, na obra A câmara clara, coloca-se como mediador de toda análise sobre a fotografia, procedendo, dentro de uma perspectiva teórica, de forma semelhante aos personagens de Las babas del diablo e de Blow-Up, estes no mundo da ficção. Já Dubois, em O ato fotográfico, debate algumas das propostas de Barthes e faz um apanhado histórico bastante produtivo na medida em que aborda as três percepções da fotografia desde sua invenção até os dias atuais. Ao alçarmos a fotografia como mediadora teórica principal do corpus deste trabalho, realizamos um novo recorte, detendo-nos naqueles eixos levantados por Dubois e por Barthes que, na leitura de Las babas del diablo e de Blow-Up, nos pareceram exigir uma exploração mais produtiva. Nesse momento, estarão presentes questões relacionadas tanto à fotografia em si quanto às relações que ela estabelece com o fotógrafo e com aquele que a observa, sempre levando em conta as tentativas de tradução da imagem fotográfica para o texto e para o filme.

Effects on school enrollment and performance of a conditional transfers program in Mexico

We study the effects of a conditional transfers program on school enrollment and performance in Mexico. We provide a theoretical framework for analyzing the dynamic educational decision and process inc1uding the endogeneity and uncertainty of performance (passing grades) and the effect of a conditional cash transfer program for children enrolled at school. Careful identification of the program impact on this model is studied. This framework is used to study the Mexican social program Progresa in which a randomized experiment has been implemented and allows us to identify the effect of the conditional cash transfer program on enrollment and performance at school. Using the mIes of the conditional program, we can explain the different incentive effects provided. We also derive the formal identifying assumptions needed to provide consistent estimates of the average treatment effects on enrollment and performance at school. We estimate empirically these effects and find that Progresa had always a positive impact on school continuation whereas for performance it had a positive impact at primary school but a negative one at secondary school, a possible consequence of disincentives due to the program termination after the third year of secondary school.

Percursos para novas imagens: a produção audiovisual por não videntes

The purpose is to write a reflection on the audiovisual production by the visually impaired. The starting point for this research was a documentary video production workshop offered by the Instituto de Educação e Reabilitação de Cegos do Rio Grande do Norte - IERC / RN, with the participation of blind people with low vision and sighted employees of the institution. The research approach follows the precepts of complex thinking, where work is woven into the network, along with the researched. The theoretical framework is based on the theory of French sociologist Edgar Morin, and other important thinkers for this work, namely: Erving Goffman, Paulo Freire, Michel Foucault, Edward Said, Jacques Aumont, Phillpe Dubois, as well as scholars who think and theorize about his own condition and conduct discussions on the issue of blindness: Francisco Jose de Lima, Evgen Bavcar Jacques Lusseyran and Joana Belarmino. The research was formulated based on the statement in the interest of respondents to understand and produce visual images using video as a tool. In this sense, the methodology adopted approaches of action research in constructing the text and dialogue with the participation of those involved in the project. The technique of gathering the information was based on ethnographic description describing the dynamics of the workshop, the relationships between participants, relationship to the other that sees and the manner of operation of equipment. The main focus is the relationship based on dialogue of information, attitudes and ways of knowing from experience and capacity developed and obstacles for blind people to produce visual images using other benchmarks, such as touch, smell and time dimension and space, and add references that give new meaning to the guidelines based on visuality of ministering to the workshop. It is also held to discuss aspects related to the concept of image with sociological reflection about the audiovisual production made by blind people socially constructed and perpetuated by what Edgar Morin called cultural imprinting. Thus we attempted to walk the route with its obstacles and achievements in the production of new images that were seen

Referenciação anáforica: um estudo de produções textuais no ensino fundamental

Esta pesquisa trata da referenciação ocorrida pelas anáforas diretas e indire-tas em produções textuais de alunos do Ensino Fundamental. Como elemento pri-mordial de nossas investigações, ancoramo-nos na referenciação e estudos da aná-fora no âmbito da Lingüística Textual como fazem Mondada e Dubois (2003); KOCH (2003) e Marcuschi (2005). De acordo com estudos já realizados e envolvidos com a temática, defendemos a noção de referenciação como sendo um processo de cons-trução de sentidos que se realiza no discurso, isto é, em atividades interativas entre os sujeitos exigindo, portanto, uma ação colaborativa entre os interlocutores. Nesse aspecto, a interação precisa existir, visto que os referentes de um termo anafórico nem sempre se encontram na superfície textual; muitas vezes, são construídos a partir de uma representação ou modelo mental disponível na memória discursiva. Nessa perspectiva, procuramos analisar o processo de referenciação construído a partir de anáforas diretas e indiretas identificando as estratégias utilizadas em textos produzidos em situações de sala de aula. Dizemos que a anáfora direta, de modo geral, é definida pela relação de correferencialidade estabelecida entre o anafórico e seu antecedente, enquanto a anáfora indireta é vista como uma estratégia referenci-al de associação, sem referente explícito, tendo que se esforçar para estabelecer a continuidade referencial no texto e para isso utiliza-se da ativação (referenciação mental) de elementos novos e não de uma reativação de referentes já conhecidos, o que constitui um processo de referenciação implícita. Para alcançarmos nosso obje-tivo, utilizamos como subsídio teórico, o processo de informação na memória cogni-tiva, a referência e estudos da anáfora no âmbito da Lingüística Textual. O corpus deste trabalho constitui-se de sessenta textos escritos por alunos de 7ª série (atual 8º ano), dentre os quais analisamos o processo de referenciação ocasionado pelas anáforas diretas e indiretas em doze desses textos. Considerando os dados analisa-dos, dentre os tipos de anáforas estudados, constatamos que houve preponderância no uso das anáforas diretas, destacando-se entre elas a anáfora direta correferencial co-significativa, com maior manifestação no uso das retomadas diretas por pronomi-nalização

Hyperfine interaction in Zn-Al layered double hydroxides intercalated with conducting polymers

Organic-inorganic hybrid materials based on the assembly between inorganic 2D host structure and polymer have received considerable attention in the last few years. This emerging class of materials presents several applications according to their structural and functional properties. Particularly, among others, layered double hydroxides (LDHs) provide the opportunity of preparing new organically modified 2D nanocomposites. Pyrrole carboxylic acid derivatives, namely 4-(lH-pyrrol-1-yl)benzoate, 3-(pyrrol-i-yl)-propanoate,7-(pyrrol-1-yl)-heptanoate, and aniline carboxylic acid derivative, namely 3-aminobenzoic acid, have been intercalated in LDHs of intralamellar composition Zn2Al(OH)(6). The LDHs were synthesized by the co-precipitation method at constant pH followed by hydrothermal treatment for 72 h. The materials were characterized by powder X-ray diffraction patterns (PXRD), transmission electron microscopy (TEM) thermogravimetric analysis (TGA), and electron spin resonance (ESR). The basal spacing found by the PXRD technique gives evidence of the formation of bilayers of the intercalated anions. ESR spectra present a typical signal with a superhyperfine structure with 6 + 1 lines (g = 2.005 +/- 0.0004), which is assigned to the interaction between a carboxylate radical from the guest molecules and a nearby aluminium nucleus (I = 5/2) from the host structure. Additionally, the ESR data suggest that the monomers are connected to each other in limited number after thermal treatment. (c) 2007 Elsevier Ltd. All rights reserved.

Neuroimaging in dementias

Purpose of reviewTo critically review data on the use of neuroimaging tools in the clinical diagnostic investigation of dementias.Recent findingsFor many years, the use of neuroimaging tools in the evaluation of dementias has been restricted to excluding neurosurgical lesions that may account for the cognitive decline. However, modern neuroimaging extends beyond this traditional role of excluding other conditions and has a key role in the clinical investigation of Alzheimer's disease and of other degenerative cortical dementias. MRI, PET with fluorodeoxyglucose, and single-photon emission computed tomography are topographic markers of neural damage and enable the identification of specific lesional patterns that characterize Alzheimer's disease and other cortical dementias. More recently, PET amyloid markers have enabled the in-vivo assessment of amyloid load, a key feature in the physiopathology of Alzheimer's disease.SummaryThe combined use of neuroimaging examinations with clinical, neuropsychological, and cerebrospinal fluid markers can improve the specificity of the diagnosis of Alzheimer's disease, even at early stages of the disease. In the following years, progress in research will provide standardized and validated imaging markers of Alzheimer's disease and other dementias, which may increase their application in clinical settings.

New layered double hydroxides intercalated with substituted pyrroles. 2. 3-(Pyrrol-1-yl)-propanoate and 7-(pyrrol-1-yl)-heptanoate LDHs

We report the synthesis and characterization of organic-inorganic hybrid materials: Zn-2-Al-LDHs (layered double hydroxides) containing 3-(1H-pyrrol-1-yl)-propanoate and 7-(1H-pyrrol-l-yl)-heptanoate as the interlayer anions. The LDHs were synthesized by the co-precipitation method at constant pH followed by hydrothermal treatment for 72 h. The materials were characterized by PXRD, C-13 CP-MAS NMR, TGA, and ESR. The basal spacing found by PXRD technique is coincident with the formation of bilayers of the intercalated anions. The solid state C-13 NMR showed that the interlayered anions remain identical after intercalation. ESR data suggest that the monomers connect each other in a limited number of guests when a thermal treatment is applied. The inorganic LDH sheets delay the temperature of degradation of the monomers. (c) 2006 Elsevier Ltd. All rights reserved.

Modifications induced by acetylacetone in properties of sol-gel derived Y3Al5O12:Tb3+ - I: Structural and morphological organizations

Acetylacetone has been used as a chemical modifier for the synthesis of undoped and Tb3+-doped Y3Al5O12 powders. A systematic investigation concerning its influence on the structural and morphological properties of amorphous and crystallized samples has been carried out. These properties have been comparatively studied by means of X-ray diffraction, infrared spectroscopy, SEM, XAS and SAXS. 27Al NMR and EPR experiments have been performed to complete the study. The combined results have evidenced that acetylacetone promotes organic groups departure during calcination, entailing a better structural organization at lower temperatures compared with unmodified powders. Structuration has been proven to occur at short-scale range until a 600°C heating treatment before being extended by coalescence at higher temperatures. Finally, the presence of acac ligands on the alkoxides leads to a monomer-cluster aggregation process, and thus to a more open network. © 2010 The Royal Society of Chemistry.