1,720,962 research outputs found
Development and Validation of a Parameter-Free Model Chemistry for the Computation of Reliable Reaction Rates
Get PDFA recently developed model chemistry (jun-Cheap) has been slightly modified and proposed as an effective, reliable, and parameter-free scheme for the computation of accurate reaction rates with special reference to astrochemical and atmospheric processes. Benchmarks with different sets of state-of-the-art energy barriers spanning a wide range of values show that, in the absence of strong multireference contributions, the proposed model outperforms the most well-known model chemistries, reaching a subchemical accuracy without any empirical parameter and with affordable computer times. Some test cases show that geometries, energy barriers, zero point energies, and thermal contributions computed at this level can be used in the framework of the master equation approach based on the ab initio transition-state theory for obtaining accurate reaction rates
TRAJETÓRIA DA SALTA-Z NO MUNICÍPIO DE PORTO VELHO: RELATO DE EXPERIÊNCIA
No full textNeste artigo visamos analisar de forma clara e objetiva a trajetória da salta-z no município de Porto Velho. Trata-se de um relato de experiência construído a partir da coleta de dados pela observação participante nas incursões até as comunidades beneficiadas pela tecnologia salta-z e através da análise documental de arquivos escritos e acumulados na experiência tais como atas de reuniões, relatórios, informações divulgadas pela imprensa, dentre outros registros disponíveis. Através da articulação entre a Prefeitura do Município de Porto Velho e a Fundação Nacional de Saúde – FUNASA foi possível a implantação de quatro unidades da solução alternativa simplificada de tratamento de água com zeólita – salta-z em comunidades mais afastadas da capital de Rondônia. A utilização de tecnologias sociais de baixo custo e fácil aplicabilidade tais como a Salta-z desenvolvida pela Funasa/Superintendência Estadual do Pará – Suest/PA mostrou-se uma solução alternativa eficiente e capaz de amenizar o problema existente na acessibilidade ao serviços de abastecimento de água tratada e segura na capital Porto Velho. A Salta-Z é uma importante ferramenta para o acesso a água tratada capaz de promover uma série de mudanças e melhorias na comunidade onde é implantada impactando positivamente na promoção da saúde, nas relações comunitárias, na consciência ambiental e principalmente na compreensão de que a água é um recurso finito e imprescindívelKeywords: Drinking Water. Sanitation. Riverside communities. Salta-z
A twist on the reaction of the CN radical with methylamine in the interstellar medium: New hints from a state-of-the-art quantum-chemical study
Get PDFDespite the fact that the majority of current models assume that interstellar complex organic molecules (iCOMs) are formed on dust-grain surfaces, there is some evidence that neutral gas-phase reactions play an important role. In this paper, we investigate the reaction occurring in the gas phase between methylamine (CH3NH2) and the cyano (CN) radical, for which only fragmentary and/or inaccurate results have been reported to date. This case study allows us to point out the pivotal importance of employing quantum-chemical calculations at the state of the art. Since the two major products of the CH3NH2 + CN reaction, namely the CH3NH and CH2NH2 radicals, have not been spectroscopically characterized yet, some effort has been made for filling this gap
H-Abstraction from Dimethyl Sulfide in the Presence of an Excess of Hydroxyl Radicals. A Quantum Chemical Evaluation of Thermochemical and Kinetic Parameters Unveils an Alternative Pathway to Dimethyl Sulfoxide
Get PDFElucidation of the oxidation mechanism of naturally emitted reduced sulfur compounds, especially dimethyl sulfide, plays a central role in understanding background acid precipitation in the natural environment. Most frequently, theoretical studies of the addition and H-elimination reactions of dimethyl sulfide with hydroxyl radicals are studied considering the presence of oxygen that further reacts with the radicals formed in the initial steps. Although the reaction of intermediate species with additional hydroxyl radicals has been considered as part of the global mechanism of oxidation, little if any attention has been dedicated to the possibility of reactions of the initial radicals with a second OH molecule. In this work, we performed a computational study using quantum-chemical methods, of the mechanism of H-abstraction from dimethyl sulfide under normal atmospheric conditions and in reaction chambers at different O2 partial pressure, including complete absence of oxygen. Additionally, important rate coefficients were computed using canonical and variational transition state theory. The rate coefficient for abstraction affords a 4.72 × 10-12 cm3 molecule-1 s-1 value, very close to the most recent experimental one (4.13 × 10-12 cm3 molecule-1 s-1). According to our best results, the initial methyl thiomethyl radical was obtained at-25.2 kcal/mol (experimentally-22.4 kcal/mol), and four important paths were identified on the potential energy surface. From the interplay of thermochemical and kinetic arguments, it was possible to demonstrate that the preferred product of the reaction of dimethyl sulfide with two hydroxyl radicals is actually dimethyl sulfoxide
Performance evaluation of the simplified collective alternative solution for water treatment for small communities (Salta-z)
Get PDFCom o objetivo de alcançar a universalização do acesso à água potável, a Fundação Nacional da Saúde (Funasa) desenvolveu e vem implementando no Brasil a Solução Alternativa Coletiva Simplificada para Tratamento de Água em Pequenas Comunidades (Salta-z). Apesar de sua crescente aplicação, reconheceu-se a necessidade de uma avaliação apurada de seu desempenho. Sendo assim, o objetivo desse trabalho foi avaliar o desempenho da Salta-z em diferentes condições operacionais, além de indicar possíveis intervenções e boas práticas. Foi instalada uma unidade da Salta-z nas dependências da estação de tratamento de água da Universidade Federal de Viçosa com os mesmos elementos daquelas distribuídas pela Funasa, acrescidos de um filtro de areia (em paralelo ao de zeólita) e dois tanques de contato após cada filtro. Foram realizadas três etapas de experimentação. Na etapa 1, definiu-se que o melhor arranjo operacional para realização da desinfecção é a desinfecção pós-filtração, com uso do tanque de contato operado em batelada e do dosador de coagulante para dosagem do desinfetante. Na etapa 2, definiu-se o procedimento operacional para realização da dosagem de coagulante e avaliou-se a capacidade do sistema quanto à remoção de turbidez, esporos de bactérias aeróbias (EBA), coliformes totais e E. coli em diferentes condições de turbidez da água bruta, materiais filtrantes e taxas de filtração. Por fim, na etapa 3 o objetivo foi avaliar o desempenho dos filtros em condições de turbidez mais elevada na água decantada e em carreiras longas de filtração. Seguindo-se os procedimentos e arranjos operacionais definidos e recomendados neste trabalho, a Salta-z foi capaz de alcançar elevada eficiência em todas as condições avaliadas, alcançando de 86,7 a 98,5% de remoção de turbidez, 3,6 a 4,8 log1 0 e 3,4 a 4,7 10 log de remoção de EBA no sistema operado com o filtro de areia e com o de zeólita, respectivamente, e ausência de coliformes totais e E. coli em todas as amostras de água desinfetada. O filtro de areia foi mais eficiente na operação de retrolavagem e na remoção de EBA (2,5 log 10 em média) do que o de zeólita (2,0 log 10 em média), apesar de que, após a desinfecção, a remoção total foi similar entre ambos os sistemas. Mesmo na etapa 3, a turbidez da água filtrada foi mantida abaixo de 0,30 uT em ambos os filtros, na maior parte do tempo, e o término das carreiras de filtração se deu por esgotamento da carga hidráulica, sem ocorrência de trespasse, o que evidencia a resiliência do sistema. A Salta-z demonstrou, portanto, ser uma tecnologia eficiente e com potencial de ser aplicada em diferentes condições e mananciais de água. Entretanto, para a confirmação desse potencial, recomenda-se a realização de estudos para avaliar alternativas de flexibilidade operacional e remoção simultânea de diferentes variáveis, além de uma melhor apropriação das condições hidrodinâmicas da floculação e dos mecanismos de filtração em zeólita. Palavras-chave: Saneamento rural. Tratamento de água. Turbidez. Esporos de bactérias aeróbias.With the aim of universalizing the access to potable water, Brazil’s National Health Foundation (Funasa) developed the Simplified Collective Alternative Solution for Water Treatment for Small Communities (Salta-z). Despite the increasing implementation of this solution, the need for an accurate evaluation of its performance in water treatment was recognized. Therefore, the aim of this work was to evaluate the performance of Salta-z under different operating conditions and to indicate possible interventions and good operational practices. A unit of the Salta-z was installed on the premises of the water treatment plant of the Federal University of Viçosa, with the same elements as the ones distributed by Funasa, with the addition of a sand filter (in parallel with the zeolite one) and two contact tanks after each filter. Three stages of experimentation were conducted. At Stage 1, it was defined that the best operational arrangement for carrying out disinfection was the post-filtration disinfection, with the contact tank operated in a batch flow and using the coagulant dosing device for disinfectant dosing. At Stage 2, the operational procedure for the coagulant dosing was defined and the system's ability to remove turbidity, aerobic spore bacteria (ASB), total coliforms and E. coli under different conditions of turbidity of the raw water, filter media and filtration rates were evaluated. Finally, at Stage 3 the aim was to evaluate the performance of the filters in conditions of higher turbidity in decanted water and in longer filtration runs. Following the procedures and operational designs defined and recommended in this work, the Salta-z was able to achieve high efficiency in all the conditions assessed. The system achieved turbidity removals of 86.7% to 98.5% with both filter medias, overall ASB removals of 3.6 to 4.8 log and 3.4 to 4.7 log with the system operated with the sand and zeolite filter, respectively, and, in all of the disinfected water samples was detected the absence of total coliforms and E. coli. The difference between the two systems was that the sand filter achieved higher efficiency at the backwash operation and higher ASB removal (an average of 2.5 log) than the zeolite one (an average of 2.0 log), although, after disinfection, the overall removal of ASB was similar. Even at Stage 3, the filtered water turbidity, for both filter medias, were lower than 0.30 uT for most of the time. Moreover, the filter runs ended with the hydraulic load depletion and not with turbidity breakthrough. These observations point to the resilience of the filters. Therefore, the Salta-z proved to be an efficient technology with the potential for implementation in different conditions and water sources. However, to confirm this potential, there are some recommendations, such as to carry out studies to evaluate alternatives of operational flexibility and simultaneous removal of different parameters, in addition to a better appropriation of the hydrodynamic conditions of flocculation and of the filtration mechanisms in the zeolite filter. Keywords: Rural sanitation. Water treatment. Turbidity. Aerobic spore-forming bacteriaCoordenação de Aperfeiçoamento de Pessoal de Nível Superio
Exploring the Maze of C2N2H5Radicals and Their Fragments in the Interstellar Medium with the Help of Quantum-Chemical Computations
Get PDFAmong the species discovered in the interstellar medium and planetary atmospheres, a crucial role is played by the so-called "interstellar"complex organic molecules (iCOMs) because they are the signature of the increasing molecular complexity in space. Indeed, they may represent the connection between simple molecules and biochemical species like amino acids and nucleobases. In particular, HCN and the related CN radical are the starting points of rich nitrile chemistry. In this framework, we have undertaken a computational investigation of the gas-phase reaction mechanisms involving different C2N2H5 radicals and their fragments, stemming from the addition of the cyano radical to the nitrogen atom of methylamine. Aiming at exploiting an accurate yet cost-effective protocol, a combination of CCSD(T)-based composite schemes and density functional theory has been employed. The exploration of the plausible chemical reaction channels has led to the identification of 12 different products, as well as 28 transition states connecting reactants, intermediates, and products. Aminoacetonitrile (H2NCH2CN), proposed as an intermediate in the formation of the smallest amino acid glycine, and the CH2NH2 radical appear as products energetically accessible under astrophysical conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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