Uma nova proposta para evitar sintering de nanopartículas em catálise

Sintering is a process whereby nanoparticles increase their size and reduce their number under high temperatures. Since catalytic activity depends on the number of active sites, and those lie on the surface of nanoparticles, the most detrimental consequence of sintering for catalysis is the loss of surface area, which reduces the number of active sites. Sintering is the main cause of catalyst deactivation and the current prevention strategies demand specific synthesis methods, modification of the chemical properties of the nanoparticles or nanostructuring of supports. A new proposal for the prevention of sintering of nanoparticles, easily reproducible, is presented and applied to Cu nanoparticles supported on MgO. A combination of XRD, in situ EXAFS and TEM shows the prevention of sintering of Cu nanoparticles under H2 atmosphere at 300◦C. In situ timeresolved XANES and XPS techniques were used to investigate the possibility of catalyst poisoning due to the strategy employed. The results show no evidence of poisoned species. Furthermore, by modelling the system with Monte Carlo simulations, it was possible to reproduce sintering prevention and to propose a possible mechanism whereby the method operates, besides getting a better picture of the pertinent parameters value range that allows sintering prevention.Sintering e um processo pelo qual nanopartíıculas aumentam o seu tamanho e reduzem seu numero sob altas temperaturas. Como a atividade catalítica depende do número de síıtios ativos, e estes se encontram na superfície das nanopartículas, a consequência mais prejudicial do sintering para catalise é a perda de área superficial, que reduz o número de sítios ativos. Sintering e a principal causa de desativacão de catalisadores e as estratégias de prevenção atuais demandam métodos de síntese específicas, modificação das propriedades quíımicas das nanopartíıculas ou nanoestruturação dos suportes. Uma nova proposta para a prevenção de sintering de nanopartículas, facilmente reproduzível, e apresentada e aplicada a nanopartículas de Cu suportadas em MgO. Uma combinação de medidas de XRD, EXAFS in situ e TEM demonstra a prevenção de sintering das nanopartículas de Cu sob atmosfera de H2 a 300◦C. As técnicas de XANES in situ resolvido no tempo e XPS foram utilizadas para explorar a possibilidade de envenenamento do catalisador devido a estratégia empregada. Os resultados indicam que não há qualquer composto envenenado. Ademais, modelando o sistema utilizando simulações de Monte Carlo foi possível reproduzir a prevenção de sintering e propôr um mecanismo pelo qual o método opera, além de se obter uma figura mais ampla do intervalo de valores de parâmetros que permitem a prevenção de sintering

Lateral Resistance of Buried Pipes by Frictional Limit Analysis

Pipelines are vital means of transportation of liquids and gases over large geographical areas. Regarding buried pipes, they are submitted to thermal and mechanical loads due to their support conditions, pipe-soil friction and the surrounding soil mass. Under high compressive loads carried out by these efforts, loss of stability and buckling may occur. Then, the evaluation of soil lateral resistance that will cause a imminent breakout is important. This work aims the analysis of the soil lateral resistance by frictional limit analysis formulation, considering the soil mass as a deformable body and the pipe as a rigid one. An yield function considering material porosity and material friction angle is considered. The soil lateral resistance forces obtained from the proposed formulation are compared to a those ones considering the limit analysis lower bound found in literature. The fully bounded condition observed in most models is also discussed

Controle de sintering em nanopartículas de Cu/MgO

Sintering é o aumento do tamanho médio de partículas, que ocorre tipicamente em altas temperaturas. Esse efeito é a principal causa de desativação de catalisadores, dado que reações catalíticas geralmente necessitam de temperaturas elevadas. O sintering provoca a redução de área superficial, onde ocorrem as reações, levando à perda de atividade catalítica. Dado que o sintering é geralmente irreversível, sua prevenção é essencial para o desenvolvimento de catalisadores mais eficientes e duradouros. Os métodos abordados na literatura para prevenir sintering geralmente envolvem mudanças nas propriedades químicas e físicas das nanopartículas, podendo levar à prejuízos na atividade catalítica e seletividade. Neste trabalho, um método inédito é proposto com o intuito de prevenir a ocorrência de sintering em nanopartículas de Cu/MgO. As amostras foram expostas a uma atmosfera de H2 à 300 C. Nessa reação química, o H2 tende a ceder elétrons para algumas espécies da amostra, levando à diminuição da carga formal destas espécies. Denomina-se essa reação por tratamento redutor, que é um procedimento muito comum para a ativação de catalisadores. As técnicas de difração de raios X e microscopia eletrônica de transmissão foram usadas para determinar o tamanho médio das nanopartículas antes e após a redução. Os resultados obtidos mostram a prevenção de sintering em ao menos uma das amostras, indicando que o método é promissor no combate ao sintering. O método pode ser aplicado para outros sistemas, impactando fortemente no desenvolvimento de novos catalisadores.Sintering is the increase of the mean particle size, which typically occurs at high temperatures. It is the main reason for catalyst deactivation, since catalytic reactions usually occur at elevated temperature regimes. Sintering leads to reduction of superficial area, where the reactions occur, resulting in a decrease of the catalytic activity. Since sintering is generally irreversible, its prevention is essential for the development of more efficient and lasting catalysts. The main approaches found in the literature for sintering prevention involve changes in chemical and physical properties of nanoparticles, potentially leading to damage for the catalytic activity and selectivity. In this work, a new method is proposed aiming to prevent sintering in Cu/MgO nanoparticles. The samples were exposed to a reduction treatment at 300 C. In this chemical reaction, H2 tends to give electrons to some species of the sample, leading to the decrease of formal charge in this species. This reaction is denominated by reducing treatment, which is a very common procedure for the activation of catalysts. X-ray diffraction and transmission electron microscopy techniques were used to determine nanoparticles mean size before and after reduction treatment. The results show no signs of sintering in at least one of the samples, indicating that this is a promising method for sintering prevention. The method could possibly be adapted to other systems, impacting strongly on the development of new catalysts

Strengthening of damaged low strength concrete beams using PTMS or NSM techniques

This article presents the results of an analytical and experimental study on the performance of rectangular reinforced concrete (RC) beams strengthened using either post-tension metal strapping (PTMS) or side-near surface mounted (SNSM) FRP bars. Four low-strength (15.3 MPa) medium-scale beams were tested in four-point bending in two phases. In Phase I, one control beam was tested up to failure, whereas three beams were tested up to yielding of the main flexural reinforcement. In Phase II, the three pre-cracked beams were strengthened using PTMS or SNSM techniques, and then retested up to failure. The results indicate that the capacity of the pre-cracked PTMS-strengthened beam was only 8 % higher than the control counterpart. Conversely, the SNSM strengthening solution increased the beam capacity by up to 55 %, which is due to additional flexural reinforcement provided by the FRP bars. Moreover, the predictions given by linear cracked sectional analysis and the current ACI guidelines match well the deflection response of the strengthened beams but only up to the yielding load

Foraging behavior of Scaptotrigona depilis (Hymenoptera, Apidae, Meliponini) and its relationship with temporal and abiotic factors

Stingless bees play an important role in Tropical and Subtropical ecosystems as pollinators of many plants. The aim of this study was to characterize the pattern of flight activity and foraging for pollen by Scaptotrigona depilis workers and their relation with climatic and temporal factors. We observed flight activity from July 2001 to June 2002 and pollen collection by scoring the flow of workers entering and exiting the colonies. We tested whether environmental (temperature, relative humidity, pluviosity and luminosity) and temporal predictors (month and time of day) affected bees’ activities. The study was conducted during one year and the records of observations showed that during the dry season when the length of light is longer, the external activity was more intensive, while during cold months with shorter light period, foraging activity was reduced. Pollen collection showed a peak in February, but in general this activity was regulated by temperature, humidity and daily luminosity

Solitary fibrous tumor of the tongue

Solitary fibrous tumor (SFT) is a benign mesenchymal neoplasm originally described in pleura with a rare presentation in the oral cavity. Herein, we report a case of a 28-year-old male patient who presented an asymptomatic slow-growing mass in the anterior part of the tongue. Intraoral examination revealed a well-circumscribed mass covered by normal mucosa with a fibrous consistency. Due to non-specific clinical findings, the initial diagnostic hypotheses include benign submucosal neoplasms such as leiomyoma, neurofibroma, SFT, and others. An excisional biopsy was performed. Microscopically, the tumor was surrounded by a thick fibrous capsule; hypo and hypercellular areas were arranged in a storiform pattern with a stroma formed by collagen and abundant vascularization. Tumor cells showed immunopositivity for CD34 and STAT-6 and no expression of CD99, AML, S-100, and Ki-67. According to these findings, the diagnosis of SFT was established. After 24 months, the patient is asymptomatic and has no evidence of recurrence. Although oral involvement is rare, SFT should be included in the differential diagnosis of oral submucosal lesions

CARACTERIZAÇÃO DOS AGLOMERADOS AGROINDUSTRIAIS DE MATO GROSSO DO SUL

O objetivo deste artigo foi caracterizar os aglomerados agroindustriais de Mato Grosso do Sul (MS), baseado nas metodologias disponíveis de desenvolvimento local. A importância deste estudo se deu pelo fato de identificar os aglomerados industriais (Sistemas Locais de Produção) distribuídos pelo território do estado de MS, caracterizá-los e divulgar as políticas públicas existentes e sugerir novas que possam viabilizar os atuais aglomerados e atrair novos investimentos. Trata-se de uma pesquisa exploratória, conduzida em dois momentos: o primeiro baseou-se em pesquisa de dados secundários, sobretudo no relatório de pesquisa de onze cadeias produtivas efetuada pelo Governo de MS e UFMS. No segundo momento foram feitas entrevistas com quatro especialistas da Federação das Indústrias de MS e Secretaria de Estado de Produção. Pode-se concluir que inexistem clusters no estado de MS; quanto aos pólos de crescimento, foi identificado em Ivinhema, o Pólo mandioqueiro, sem empresa motriz; Pólos industriais com empresa motrix foram identificados em São Gabriel do Oeste (suinocultura) e Dourados (avicultura); O tipo meio novador foi identificado na região de Dourados (piscicultura), além de Campo Grande (indústria coureira); por fim, o formato distrito industrial ficou caracterizado na região central de Campo Grande, pela agregação de mais de vinte empresas.-----------------------------------------------The objective of this paper was to characterize the agro-industrial clusters of Mato Grosso of Sul (MS), based of the available methodologies of local development. The importance of this study if it gave for the fact to identify the industrial clusters (Local Systems of Production) distributed by the territory of the state of MS, to characterize them and to divulge the public politics existing and to suggest new that they can make possible the current clusters and attract new investments. One is about a exploratória research, lead at two moments: the first one was based on research of secondary data, over all in the report of research of eleven productive chains effected by the Government of MS and UFMS. At as the moment interviews with four specialists of the Federacy of the Industries of MS and State secretary of Production had been made. It can be concluded that they inexist clusters in the MS state; in relation to the growth polar regions, it was identified in Ivinhema, the cassava Polar region, without focal company; Industrial polar regions with focal company had been identified in São Gabriel do Oeste (meat pork industry) and Dourados (poultry industry); The innovation type was identified in the region of Dourados (meat fish industry), beyond Campo Grande (leather industry); finally, the format industrial district was characterized in the central region of Campo Grande, by the aggregation of more than twenty companies.Aglomerados industriais, sistemas locais de produção, clusters, agro-industrial clusters, local systems of production, clusters, Community/Rural/Urban Development,