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EXPERIMENTAL AND THEORETICAL STUDY OF SHYNTESIS OF N-ALKYL-NITROIMIDAZOLES.

M., Constain Salamanca; V., William Tiznado; JARAMILLO, Paula
Fonte: UNIV ANTIOQUIA, FAC QUIMICA FARMACEUTICA Publicador: UNIV ANTIOQUIA, FAC QUIMICA FARMACEUTICA
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
65.65%
In this work we realized and experimental and theoretical study of the N-alkylation of nitroimidazoles. The N-alkyl-2-methyl-nitroimidazoles correspond to biologically active molecules, obtained by reaction of 2-methyl-5-nitroimidazole and different alkyl halides. This reaction showed the formation of a mixture of isomeric products in different proportions, denominated like N-alkyl-2-methyl-4-nitroimidazole and N-alkyl-2-methyl-5-nitroimidazole, respectively. The reaction suggestes the formation of a tautomeric equilibrium, which generates two nucleophilic sites susceptible to electrophilic attack by the alkyl halide. The local nucleophilic reactivity of the nitroimidazole nng is determined using local reactivity indices such as the Fukui function and the electrostatic potential, besides the electronic localization function (ELF). The Fukui function was integrated for each atom using partition schemes based on analysis of Mulliken charges and natural bond orbital (NBO). Finally the reaction profiles were assessed. The results show a minor difference in the local reactivity. Nevertheless a significant difference in energy barriers is observed explaining the formation of an isomeric product over another. These results agree quite well with the experimental data.

A theoretical study of SnF2+, SnCl2+, and SnO2+ and their experimental search

Batista, Ana Paula de Lima; Lima, Jose Carlos Barreto de; Franzreb, Klaus; Ornellas, Fernando R.
Fonte: AMER INST PHYSICS; MELVILLE Publicador: AMER INST PHYSICS; MELVILLE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.66%
We present a detailed theoretical study of the stability of the gas-phase diatomic dications SnF2+, SnCl2+, and SnO2+ using ab initio computer calculations. The ground states of SnF2+, SnCl2+, and SnO2+ are thermodynamically stable, respectively, with dissociation energies of 0.45, 0.30, and 0.42 eV. Whereas SnF2+ dissociates into Sn2+ + F, the long range behaviour of the potential energy curves of SnCl2+ and SnO2+ is repulsive and wide barrier heights due to avoided crossing act as a kind of effective dissociation energy. Their equilibrium internuclear distances are 4.855, 5.201, and 4.852 a(0), respectively. The double ionisation energies (T-e) to form SnF2+, SnCl2+, and SnO2+ from their respective neutral parents are 25.87, 23.71, and 25.97 eV. We combine our theoretical work with the experimental results of a search for these doubly positively charged diatomic molecules in the gas phase. SnO2+ and SnF2+ have been observed for prolonged oxygen (O-16(-)) ion beam sputtering of a tin metal foil and of tin (II) fluoride (SnF2) powder, respectively, for ion flight times of about 10(-5) s through a magnetic-sector mass spectrometer. In addition, SnCl2+ has been detected for O-16(-) ion surface bombardment of stannous (tin (II)) chloride (SnCl2) powder. To our knowledge...

"Estudo experimental e teórico de compostos de bases de Schiff com cobre (II)"; "Experimental and theoretical studies on copper(II) Schiff Bases"

Tozzo, Érica
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/09/2006 PT
Relevância na Pesquisa
45.66%
Neste trabalho inicialmente foi feita uma breve apresentação sobre a utilização de compostos de bases de Schiff e Cobre(II) como catalisadores na reação de oxidação de sulfetos. Foi feita a determinação das estruturas cristalinas dos compostos: N,N'-bis(3-etoxisalicilideno)-(1,2etileno- diamina) Cu(II), sistema cristalino ortorrômbico grupo espacial Pbcn a = 7.639(5); b= 12.760(5); c= 19.733(5)Å; V = 1923.4(15) (3)Å3; Dcalc = 1.505 Mg/m3; MM = 435.96; e m = 1.170 mm-1, N,N'-bis (4-dietilaminasalicilideno) - (1,2etilenodiamina) Cu(II), sistema monoclínico, C2/c, a = 19.571(2); b=9.8514(2)=; c=12.4552(4) Å; Beta = 93.705(9)o; V =2396.4(5) Å3; Dcalc=1.358 Mg.m-3; MM= 490.10; e m = 0.944 mm-1, N,N'-bis(3-metoxisalicilideno)-(1,2etilenodiamina)Cu(II), sistema ortorrômbico, Pna21, a = 7.5140(6); b= 9.2629(9); c= 24.721(3)Å; V =1720.6(3) Å3; Dcalc = 1.575 Mg,m-1; MM = 407.91; e m = 1.302 mm1 e (SALAHE)Cu(II), monoclínico, P21/C, a = 18.3216(2) Å; b=4.804(3) Å; c=19.801(2)Å; Beta = 98.908(6)o; V =2396.4(5) Å3; Dcalc=1.358 Mg.m-3; MM= 490.10; e m = 0.944 mm-1. Os cálculos teóricos para as quatro moléculas foram efetuados partindo-se das coordenadas atômicas cristalográficas. Foram modeladas, para posterior estudo teórico...

Estudo teórico e experimental de estruturas supramoleculares obtidas com clusters trinucleares de rutênio e porfirinas; Theoretical and experimental study on supramolecular structures obtained with trinuclear ruthenium clusters and porphyrins

Formiga, André Luiz Barboza
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/09/2005 PT
Relevância na Pesquisa
45.69%
A química supramolecular de porfirinas e clusters trinucleares de rutênio foi investigada sob o ponto de vista teórico-experimental. Através do desenvolvimento de uma nova metodologia baseada em ferramentas teóricas, as propriedades desses sistemas puderam ser explicadas à luz da mecânica quântica, revelando os mecanismos eletrônicos envolvidos na modificação das propriedades dos anéis porfirínicos pelos compostos de coordenação. As geometrias, a dinâmica e as estruturas eletrônicas desses sistemas foram obtidas através do desenvolvimento de novos parâmetros para campos de força empíricos, e da utilização de métodos semi-empíricos e ab initio. Essas foram utilizadas para interpretar as propriedades físico-químicas dos mesmos, como por exemplo a associação intermolecular em solução e na forma de filmes finos obtidos sobre superfícies não rugosas. O estudo teórico detalhado das estruturas eletrônicas dessas espécies comprovou que a influência supramolecular dos compostos de coordenação se dá através de orbitais de simetria π, representando o principal mecanismo de ativação de anéis porfirínicos por compostos de coordenação. Essa ativação diferenciada pôde ser evidenciada experimentalmente pela aplicação dessas espécies em células fotoeletroquímicas e em sistemas de catálise com atividade citocromo P-450.; The supramolecular chemistry of porphyrins and trinuclear ruthenium clusters has been investigated by a theoretical-experimental approach. Through the development of a new methodology based on theoretical tools...

Estudo teórico da reação do radical metila com nitrogênio atômico (4S): aspectos estruturais, energéticos, espectroscópicos e cinéticos; Theoretical study of reaction between methyl radicals and atomic nitrogen (4S): structural, energetic, spectroscopy and kinetic aspects

Alves, Tiago Vinicius
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/05/2008 PT
Relevância na Pesquisa
45.67%
A busca de uma melhor compreensão dos ciclos químicos que ocorrem na atmosfera de Titan, um dos satélites naturais de Saturno, tem posto em relevância a importância de reações químicas envolvendo nitrogênio atômico e hidrocarbonetos, principalmente o radical metila. Além desta ênfase astroquìmica, essa reação tem também um papel importante no estudo da decomposição de metano em plasma pós-descarga de nitrogênio e no entendimento de processos de combustão. Neste trabalho, dando continuidade a estudos teóricos envolvendo reações de espécies atômicas com hidrocarbonetos realizados por este grupo e utilizando o estado da arte em termos de cálculos de estrutura eletrônica, realizou-se uma ampla investigação da superfície tripleto de energia potencial 3[H3, C, N] com ênfase nos aspectos estruturais, energéticos e espectroscópicos dos pontos estacionários e na cinética global da reação. Nesta superfície de energia potencial, foram caracterizados 7 pontos estacionários, sendo 3 estados de transição e 4 mínimos. No melhor nível de cálculo, CCSD(T)/CBS, o mínimo global corresponde à formação do radical metilnitreno, 71,01 kcal/mol mais estável do que o canal de entrada N(4S) + CH3 (2A2"). Entretanto...

Theoretical study of MgO(001) surfaces: Pure, doped with Fe, Ca, and Al, and with and without adsorbed water

Almeida, A. L.; Martins, JBL; Longo, Elson; Furtado, N. C.; Taft, C. A.; Sambrano, JR; Lester, W. A.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 705-713
ENG
Relevância na Pesquisa
55.59%
Ab initio calculations of large cluster models have been performed in order to study water adsorption at the five-fold coordinated adsorption site on pure Mg(001) and MgO(001) surfaces doped with Fe, Ca, and Al. The geometric parameters of the adsorbed water molecule have been optimized preparatory to analysis of binding energies, charge transfer, preferential sites of interaction, and bonding distances. We have used Mulliken population analysis methods in order to analyze charge distributions and the direction of charge transfer. We have also investigated energy gaps, HOMO energies, and SCF orbital energies as well as the acid-base properties of our cluster model. Numerical results are compared, where possible, with experiment and interpreted in the framework of various analytical models. (C) 2001 John Wiley & Sons, Inc.

Basis sets applied to the theoretical study of the vibrational structure of hexaaquaaluminum(III) ion

Treu, O.; Pinheiro, J. C.; Kondo, R. T.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 109-112
ENG
Relevância na Pesquisa
65.69%
Gaussian basis sets were developed with the Generator Coordinate Hartree-Fock (GCHF) method for the atoms from H (14s), O (23s16p), and Al (29sl9p) in the ground state. These basis sets were then contracted to 3s (12,1,1), 5s3p (18,2,1,1,1/14,1,1), and 7s5p (20,3,2,1,1,1,1/14,2,1,1,1) for H, O and Al atoms, respectively, by a standard procedure. The quality of contracted basis sets in molecular calculations was evaluated through studies of the total and orbital (epsilon(HOMO) and epsilon(HOMO-1)) energies at the HF level for the hexaaquaaluminum(III) ion, [AI(H(2)O)(6)](3+). For the O atom, the 5s3p was supplemented with d polarization function and it was used in combination with 3s, and 7s5p for H and Al atoms was used to the theoretical interpretation of the Infrared (IR) spectrum of hexaaquaaluminum(III) ion. The calculations of the IR-spectrum were also performed at the HF level and it showed that the basis sets obtained with the aid of GCHF method lead to the selection of useful contracted Gaussian basis sets for the theoretical study of vibrational property of ionic specie of our interest. (C) 2004 Elsevier B.V. All rights reserved.

Theoretical and experimental evaluation of the influence of the length of drill rods in the SPT-T test

Peixoto, Anna Silvia Palcheco; Oliveira Neto, Luttgardes de; Antenor, Valéria Borin
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 23-31
ENG
Relevância na Pesquisa
55.69%
The influence of soil drill rod length on the N value in the SPT-T test has been studied extensively by Mello (1971), Schmertmann & Palacios (1979), Odebrecht et al. (2002) and Cavalcante (2002). This paper presents an analysis of the Standard Penetration Test supplemented with torque measurement (SPT-T). A theoretical study of the resistance of the rod material to torsion and bending indicated that the shear stress caused by the rod self-weight represents less than 1% of that caused by the torsional moment. An experimental study with electric torquemeters attached to a horizontal rod system, as well as two field tests in the vertical direction, were also carried out to compare and substantiate the results. The purpose of these tests was to analyze changes along the length of the rod in response to successive increments at 1-meter intervals. Torque measurements were taken at each increment of the length to ascertain the accuracy of the theoretical data. The difference between the applied torque and the measured torque at the end of rod system was lower than the minimum scale of mechanical torquemeters used in practice.

Graphene to fluorographene and fluorographane: A theoretical study

Paupitz, R.; Autreto, P. A S; Legoas, S. B.; Srinivasan, S Goverapet; Van Duin, A. C T; Galvão, D. S.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.59%
We report here a fully reactive molecular dynamics study on the structural and dynamical aspects of the fluorination of graphene membranes (fluorographene). Our results show that fluorination tends to produce defective areas on the graphene membranes with significant distortions of carbon-carbon bonds. Depending on the amount of incorporated fluorine atoms, large membrane holes were observed due to carbon atom losses. These results may explain the broad distribution of the structural lattice parameter values experimentally observed. We have also investigated the effects of mixing hydrogen and fluorine atoms on the graphene functionalization. Our results show that, when in small amounts, the presence of hydrogen atoms produces a significant decrease in the rate of fluorine incorporation onto the membrane. On the other hand, when fluorine is the minority element, it produces a significant catalytic effect on the rate of hydrogen incorporation. We have also observed the spontaneous formation of new hybrid structures with different stable configurations (chair-like, zigzag-like and boat-like) which we named fluorographane. © 2013 IOP Publishing Ltd.

Hydrogen oxidation on ordered intermetallic phases of platinum and tin - A combined experimental and theoretical study

Santos, E.; Pinto, L. M C; Soldano, G.; Innocente, A. F.; Ângelo, A. C D; Schmickler, W.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 191-196
ENG
Relevância na Pesquisa
55.66%
Hydrogen oxidation on the surfaces of the intermetallic compounds Pt 3Sn, PtSn and PtSn2 has been studied by the rotating disc electrode technique. Pt3Sn and PtSn were found to be good catalysts, about as good as Pt, while PtSn2 was inactive over the investigated range of potentials. Underpotential deposition of hydrogen is observed only on Pt3Sn. These results are explained by theoretical calculations based on a theory developed within our own group, and by density functional theory. © 2012 Elsevier B.V.

A theoretical and experimental study to unequivocal structural assignment of tetrahydroquinoline derivatives

da Silva, Bruno Henrique Sacoman Torquato; Marana, Naiara Letícia; Mafud, Ana Carolina; da Silva-Filho, Luiz Carlos
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1-11
ENG
Relevância na Pesquisa
45.69%
The tetrahydroquinoline derivatives can be easily synthesized through Povarov reaction and have several important biological activities. This work describes a comparative study for the unequivocal assignment of molecular structure of different tetrahydroquinoline derivatives, through a complete analysis of NMR 1D and 2D NMR spectra (1H, 13C, COSY, HSQC, and HMBC), and the correlation this data with theoretical calculations of energy-minimization and chemical shift (δ), employing the theory level of DFT/B3LYP with set of the cc-pVDZ basis. For these derivatives the experimental analyses and the theoretical model adopted were sufficient to obtain a good description of its structures, and these results can be used to assign the structure of various others tetrahydroquinoline derivatives. © 2013 Springer Science+Business Media New York.

Entropic and Electrostatic Effects on the Folding Free Energy of a Surface-Attached Biomolecule: An Experimental and Theoretical Study

Watkins, Herschel M.; Vallée-Bélisle, Alexis; Ricci, Francesco; Makarov, Dmitrii E.; Plaxco, Kevin W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.69%
Surface-tethered biomolecules play key roles in many biological processes and biotechnologies. However, while the physical consequences of such surface attachment have seen significant theoretical study, to date this issue has seen relatively little experimental investigation. In response we present here a quantitative experimental and theoretical study of the extent to which attachment to a charged –but otherwise apparently inert– surface alters the folding free energy of a simple biomolecule. Specifically, we have measured the folding free energy of a DNA stem loop both in solution and when site-specifically attached to a negatively charged, hydroxyl-alkane-coated gold surface. We find that, whereas surface attachment is destabilizing at low ionic strength it becomes stabilizing at ionic strengths above ~130 mM. This behavior presumably reflects two competing mechanisms: excluded volume effects, which stabilize the folded conformation by reducing the entropy of the unfolded state, and electrostatics, which, at lower ionic strengths, destabilizes the more compact folded state via repulsion from the negatively charged surface. To test this hypothesis we have employed existing theories of the electrostatics of surface-bound polyelectrolytes and the entropy of surface-bound polymers to model both effects. Despite lacking any fitted parameters...

Syntheses of NCN and NC₃N from ionic precursors in the gas phase and an unusual arrangement of neutral NC₃N: A joint experimental and theoretical study; Syntheses of NCN and NC(3)N from ionic precursors in the gas phase and an unusual arrangement of neutral NC(3)N: A joint experimental and theoretical study

Blanksby, S.; Dua, S.; Bowie, J.; Schroder, D.; Schwarz, H.
Fonte: Amer Chemical Soc Publicador: Amer Chemical Soc
Tipo: Artigo de Revista Científica
Publicado em //2000 EN
Relevância na Pesquisa
45.69%
Neutral NCN is made in a mass spectrometer by charge stripping of NCN-•, while neutral dicyanocarbene NCCCN can be formed by neutralization of either the corresponding anionic and cationic species, NCCCN-• and NCCCN+•. Theoretical calculations at the RCCSD(T)/aug-cc-pVTZ//B3LYP/6-31+G(d) level of theory indicate that the 3Σg- state of NCCCN is 18 kcal mol-1 more stable than the 1A1 state. While the majority of neutrals formed from either NCCCN-• or NCCCN+• correspond to NCCCN, a proportion of the neutral NCCCN molecules have sufficient excess energy to effect rearrangement, as evidenced by a loss of atomic carbon in the neutralization reionization (NR) spectra of either NCCCN+• and NCCCN-•. 13C labeling studies indicate that loss of carbon occurs statistically following or accompanied by scrambling of all three carbon atoms. A theoretical study at the B3LYP/6-31+G(d)//B3LYP/6-31+G(d) level of theory indicates that C loss is a consequence of the rearrangement sequence NCCCN → CNCCN → CNCNC and that C scrambling occurs within singlet CNCCN via the intermediacy of a four-membered C2v-symmetrical transition structure.; Stephen J. Blanksby, Suresh Dua, and John H. Bowie, Detlef Schröder and Helmut Schwarz; Web Release Date: November 5...

Theoretical studies for ozonide formation during the ozonolysis of bicyclic endoperoxides

Cain, N.; Hixson, J.; Taylor, D.
Fonte: C S I R O Publishing Publicador: C S I R O Publishing
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
45.66%
Theoretical investigations on the treatment of bicyclic endoperoxides (1,2-dioxines) with ozone at the HF/6-31G*, MP2/6-31G*or 6-311G*, and DFT(B3LYP)/6-31G*levels of theory indicate that the estimated activation energies for formation of the possible endo-endo, endo-exo, exo-endo, or exo-exo transition states along with the formation of the primary ozonides and product ozonides are very sensitive to effects of electron correlation and basis set. This study suggests that MP2/6-311G*is the best level of theory for evaluating such systems. At the MP2/6-311G*level of theory it was found that the transition state for primary ozonide formation was lowest in energy when ozone approaches in an endo facial fashion with a further 3kJmol-1 stabilisation seen when the central oxygen within the primary ozonide protrudes outwards (exo) as opposed to inwards (endo). The product ozonides are predicted to be more stable than the combined starting materials by some 380-580kJmol-1 depending on the level of theory, clearly highlighting the substantive exothermic nature of this type of ozonolysis reaction.; Nicole M. Cain, Josh L. Hixson, and Dennis K. Taylor

Standards for the preparation and writing of Psychology review articles

Fern??ndez-R??os, Luis; Buela-Casal, Gualberto
Fonte: Asociaci??n Espa??ola de Psicolog??a Conductual Publicador: Asociaci??n Espa??ola de Psicolog??a Conductual
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.67%
The synthesis of bibliographical resources addressing a topic is an interesting subject for research. It is included as part of literature reviews. The aim of this theoretical study is to establish a series of standards for planning, preparing and writing Psychology review articles. With this aim, the study suggests a set of guidelines for the structuring and justification of content for these types of articles: organisation of the article, background understanding of the topic, literature review, style and understanding of argumentative structure, theoretical and practical relevance of conclusions, the critical and interdisciplinary perspectives of the article, recommendations for future research and what the article can bring to the future advancement of the discipline. The work concludes on the relevance of the study undertaken and accepts the importance of undertaking the necessary reviews from the interdisciplinary perspective of building psychological understanding.; La s??ntesis de recursos bibliogr??ficos acerca de un tema es una interesante actividad de investigaci??n. Se incluye dentro de las revisiones de bibliograf??a. El objetivo del presente estudio te??rico es establecer la estructura de una serie de normas para planificar...

Theoretical Study of Chloroperoxidase Catalyzed Chlorination of beta-Cyclopentanedione and Role of Water in the Chlorination Mechanism

D'Cunha, Cassian
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
55.59%
Chloroperoxidase (CPO) is a potential biocatalyst for use in asymmetric synthesis. The mechanisms of CPO catalysis are therefore of interest. The halogenation reaction, one of several chemical reactions that CPO catalyzes, is not fully understood and is the subject of this dissertation. The mechanism by which CPO catalyzes halogenation is disputed. It has been postulated that halogenation of substrates occurs at the active site. Alternatively, it has been proposed that hypochlorous acid, produced at the active site via oxidation of chloride, is released prior to reaction, so that halogenation occurs in solution. The free-solution mechanism is supported by the observation that halogenation of most substrates often occurs non-stereospecifically. On the other hand, the enzyme-bound mechanism is supported by the observation that some large substrates undergo halogenation stereospecifically. The major purpose of this research is to compare chlorination of the substrate beta-cyclopentanedione in the two environments. One study was of the reaction with limited hydration because such a level of hydration is typical of the active site. For this work, a purely quantum mechanical approach was used. To model the aqueous environment, the limited hydration environment approach is not appropriate. Instead...

Estudo experimental de teórico das constantes de acoplamento n ANTPOT. ('J IND. ch') (n= 1,2,3) em adamantanos substituídos; Experimental and theoretical study of n ANTPOT. ('J IND. ch') (n= 1,2,3) spin-spin coupling constants in substituted adamantane

Caio Ricardo Faiad da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/12/2011 PT
Relevância na Pesquisa
45.66%
A introdução da dissertação consiste na breve descrição da racionalização de acoplamentos JCH (n = 1, 2 e 3), das etapas de cálculos teóricos e das duas técnicas recentemente implementadas no IQ-Unicamp: HSQC-TOCSY-IPAP e IPAP-HSQMBC. A primeira parte da seção Resultados e Discussão trata da determinação experimental dos acoplamentos nos derivados de adamantano. Na parte que aborda as constantes calculadas é mostrado que não há necessidade de alto rigor teórico nos cálculos de otimização de geometria para moléculas rígidas em estudos de constante de acoplamento. As estruturas otimizadas nos níveis de teoria PM3 e B3LYP não apresentaram diferenças nos parâmetros geométricos e nem nas constantes de acoplamento teóricas. Sendo assim, o tempo para a obtenção dos resultados utilizando o método PM3 é drasticamente diminuído. A última parte dos Resultados e Discussão consiste na racionalização os JCH. A introdução do substituinte no adamantano não provoca modificação estrutural e por isso as variações das JCH são atribuídas às interações hiperconjugativas. O aumento do JCßHß para todos os derivados e devido a interação do substituinte com o sCC ou sCC*. Já para os JCaHb e JCaHg é observado que para os substituintes CN...

Hydraulics of stepped chutes: experimental-numerical-theoretical study; Hidráulica dos descarregadores em degraus: estudo expermental-numérico-teórico

Meireles, Inês Osório de Castro
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
45.76%
O estudo de escoamentos turbulentos em descarregadores em degraus tem sido um desafio para os investigadores. A macro-rugosidade do leito, a ondulação da superfície livre, a intermitência da localização da secção inicial de entrada de ar e o escoamento bi-fásico a jusante da secção inicial de entrada de ar fazem com que a caracterização do escoamento deslizante sobre turbilhões em descarregadores em degraus não seja simples. Actualmente, é possível combinar técnicas de medição fiáveis com simulações numéricas e análise teórica. Nesta dissertação, o estudo experimental baseia-se em resultados experimentais obtidos em duas instalações experimentais: a instalação A, do Laboratório Nacional de Engenharia Civil (LNEC), dotada de um descarregador em degraus com declive de 1V:0.75H e a instalação B, do Instituto Superior Técnico (IST), dotada de um descarregador em degraus com declive de 1V:2H. Uma sonda de ar, um tubo de Pitot modificado e vários hidrómetros permitiram o estudo do escoamento deslizante sobre turbilhões mono- e bifásico ao longo do descarregador em degraus da instalação A. Na bacia de dissipação de energia, a observação visual do escoamento foi auxiliada pelas leituras efectuadas em tomadas de pressão localizadas na soleira da bacia e pelas leituras da altura do escoamento efectuadas em réguas graduadas localizadas nas paredes da bacia. Na instalação B foram utilizados um tubo de Pitot e vários hidrómetros para estudar a região não arejada do escoamento deslizante sobre turbilhões no descarregador em degraus. O estudo numérico é baseado em simulações numéricas da região não arejada do escoamento deslizante sobre turbilhões sobre descarregadores em degraus com o código comercial de CFD FLOW-3D® de modo a reproduzir as condições ensaiadas experimentalmente. As simulações beneficiaram da técnica de blocos múltiplos (multi-block) num sistema de coordenadas cartesianas...

Distribution of carbon atoms in iron-carbon fcc phase: an experimental and theoretical study

Laneri, K. F.; Desimoni, J.; Zarragoicoechea, G. J.; Fernandez-Guillermet, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/03/2002
Relevância na Pesquisa
45.69%
This paper presents an experimental and theoretical study of the distribution of carbon atoms in the octahedral interstitial sites of the face-centered cubic (fcc) phase of the iron-carbon system. The experimental part of the work consists of Mossbauer measurements in Fe-C alloys with up to about 12 atomic percent C, which are interpreted in terms of two alternative models for the distribution of C atoms in the interstitial sites. The theoretical part combines an analysis of the chemical potential of C based on the quasichemical approximation to the statistical mechanics of interstitial solutions, with three-dimensional Monte Carlo simulations. The latter were performed by assuming a gas like mixture of C atoms and vacancies (Va) in the octahedral interstitial sites. The number of C-C, C-Va and Va-Va pairs calculated using Monte Carlo simulations are compared with those given by the quasichemical model. Furthermore, the relative fraction of the various Fe environments were calculated and compared with those extracted from the Mossbauer spectra. The simulations reproduce remarkably well the relative fractions obtained assuming the Fe(8)C(1-y) model for Mossbauer spectra, which includes some blocking of the nearest neighbour interstitial sites by a C atom. With the new experimental and theoretical information obtained in the present study...

Experimental and theoretical study of horizontal-axis wind turbines

Anderson, Michael Broughton
Fonte: University of Cambridge Publicador: University of Cambridge
Tipo: Thesis; doctoral; PhD
EN
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An experimental and theoretical study of horizontal-axis wind turbines is undertaken. The theoretical analyses cover the four major areas of aerodynamics, turbulence. aeroelasticity and blade optimisation. EXisting aerodynamic theories based on blade-element theory for predicting the loads on a wind turbine blade are reviewed and extended to include non-uniform flow, tip losses and the 'turbulent wake' state. A theoretical model based on a free vortex representation of a turbine wake is developed enabling the flow field within the vicinity of a turbine to be ascertained and also providing an important cross-check with the far simpler blade~lement theory. The turbulent variations in the wind velocity over the rotor swept area are considered and in particular their effects on the loads and available energy. A simple numerical solution of the dynamics of a two-bladed rotor is developed enabling the loads within the rotor blade to be determined and also those which are transferred to the supporting structure. Three rotor configurations are examined in detail; hingeless, hinged and teetered. The important problem of determining the appropriate blade shape for a particular application is considered. In parallel with the theoretical study an experimental program is also undertaken. This includes the design...