Sulfoxides in the allylation of aldehydesin the presence of silicon tetrachlorideand allyltributylstannane

SiCl4 can be conveniently activated by catalytic amounts of dimethyl sulfoxide or other readily-available sulfoxides for the allylation of aromatic, hetero-aromatic and unsaturated aldehydes in the presence of allyltributyl stannane. Chiral aryl methyl sulfoxides have been used to develop asymmetric allylation methods, as well as probe the aldehyde substrate scop

La resolución numérica de ecuaciones de Viète y su difusión en el curso matemático de Hérigone

Postprint (published version

A problem on the approximation of n-roots based on the Viète's work

In this paper, after giving a brief approach about the historical question of how different authors and cultures handled approximations of the n-th root of N := An + R, we consider the particular case of the approximation of n v N by A + R d (here n, A, d are positive integers, with n = 2, d = (A + 1)n - An - 1, and 0 < R = d), explicitly considered by Viète in his De Numerosa Potestatum. Viète established in one of the precepts of his work that the n-th root is placed between A + R d+1 and A+ R d . Indeed, it is easily seen that, of course, A + R d+1 = n v N , but unfortunately n v N can be greater than A + R d when n = 3. Then the question arises whether we are able or not of determining what values of R (fixing the integer values n and A, so also d) give a true approximation by excess when n v N is estimated as A + R d , that is, to find those values of R producing an excess in relation with the exact value of the root. We give a complete answer to the cases n = 7, and we present without proof the main result for a general n.This work has been supported by the grant MTM2017-84079-P (AEI/FEDER, UE) from Ministerio de Ciencia, Innovación y Universidades (Spain).Postprint (published version

Avaliação de desempenho mecânico e térmico de material compósito para envoltória de habitações visando eficiência energética

The research work evaluates the mechanical and thermal performance of a cementitious composite for the preparation of wrapping panels, applied to the architectural design of a prefabricated housing for tropical climate, aiming at the improvement of the thermal and energetic efficiency in the internal environments as an option to the ceramic building blocks. It studies the constructive viability and sustainability of the composite, which uses materials with known thermoisolating properties (vermiculite, expanded clay and metaculin) allied to the projective strategies of the Bioclimatic Architecture, in order to minimize the absorption and transfer of heat incident on the roofs and walls to the internal environments, seeking contributions for studies of these factors in the prefabricated construction process committed to the reduction of material waste. The research methodology is based on the ABNT bibliography and standards conducted the comparative tests for the characterization of composite materials, following a sequence of mix tests where a three-point scale was selected for weighing, axial compression and density tests , with comparative results of 59% lighter weight and 50% resistance of the parameters set for a traditional concrete Pilot trait, surpassing the results of these indicators for masonry of ceramic blocks. The thermal efficiency tests of the composite were initially performed on three series of test specimens submitted to the tests of the Hot Wire and the K 30 Conductivity Meter with coherent comparative results of resistance and thermal conductivity, followed by the molding of three wall prototypes with the respective traces for tests in a thermal chamber simulating and simultaneously recording the daytime and nighttime thermal variation on the two faces of the wall tested, with thermal efficiency results compatible with those of a ceramic block wall. Compounding the final results of weight, strength and thermal performance of the prototype walls compared to a traditional wall of ceramic blocks, the compatibility of the composite for the design of the prefabricated house was evident.NenhumaO trabalho de pesquisa avalia o desempenho mecânico e térmico de um compósito cimentício para a confecção de painéis envoltórios, aplicados ao projeto arquitetônico de uma habitação popular pré-fabricada para clima tropical, objetivando o melhoramento da eficiência térmica e energética nos ambientes internos como opção ao sistema construtivo tradicional de blocos cerâmicos. Estuda a viabilidade construtiva e a sustentabilidade do compósito, que utiliza materiais com reconhecidas propriedades termoisolantes (vermiculita, argila expandida e metaculim) aliadas às estratégias projetivas da Arquitetura Bioclimática, com o objetivo de minimizar a absorção e transferência de calor incidente nas cobertas e vedações para os ambientes internos, buscando contribuições para estudo desses fatores no processo construtivo pré-fabricado comprometido com a redução dos desperdícios de materiais. A metodologia investigativa fundamentada na bibliografia e nas normas da ABNT conduziu os ensaios comparativos para a caracterização dos materiais integrantes do compósito, seguindo uma sequência de testes de misturas onde foi selecionada uma escala de três traços para ensaios de pesagem, resistência à compressão axial e densidade, com resultados comparativos de peso 59% mais leve e resistência de 50% dos parâmetros fixados para um traço piloto de concreto tradicional, superando os resultados desses indicadores para a alvenaria de blocos cerâmicos. Os testes de eficiência térmica do compósito foram realizados inicialmente em três séries de corpos de prova submetidos aos ensaios do Fio Quente e do Condutivímetro K 30 com resultados comparativos de resistência e condutividade térmica coerentes, seguiu-se a moldagem de três protótipos de paredes com os respectivos traços para ensaios em uma câmara térmica, que simula e registra simultaneamente a variação térmica diurna e noturna nas duas faces da parede testada, com resultados de eficiência térmica compatíveis aos de uma parede de blocos cerâmicos. Compilados os resultados finais de peso, resistência e desempenho térmico das paredes protótipos comparados aos de uma parede tradicional de blocos cerâmicos ficou evidente a compatibilidade do compósito para a estruturação do projeto da casa pré-fabricada

Chiral sulfoxides in the enantioselective allylation of aldehydes with allyltrichlorosilane: a kinetic study

The mechanism of the allylation of aldehydes in the presence of allyltrichlorosilane employing the commercially available (R)-methyl p-tolyl sulfoxide as a Lewis base has been investigated. The combination of kinetic measurements, conductivity analysis and quantum chemical calculations indicates that the reaction proceeds through a dissociative pathway in which an octahedral cationic complex with two sulfoxides is involved. The lack of turnover is ascribed to the formation of neutral sulfurane derivatives

Constructal approach to bioengineering: the ocular anterior chamber temperature

The aim of this work was to analyse the pressure inside the eyes anterior chamber, namedintraocular pressure (IOP), in relation to the biomechanical properties of corneas. The approach used was based on the constructal law, recently introduced in vision analysis. Results were expressed as the relation between the temperature of the ocular anterior chamber and the biomechanical properties of the cornea. The IOP, the elastic properties of the cornea, and the related refractive properties of the eye were demonstrated to be dependent on the temperature of the ocular anterior chamber. These results could lead to new perspectives for experimental analysis of the IOP in relation to the properties of the cornea

A re-investigation of Modena’s protocol for the asymmetric oxidation of prochiral sulfides

The reactivity of commercially available or easily accessible hydroperoxides has been conveniently exploited for the achievement of highly efficient and enantioselective catalytic modifications of Modenas protocol for the asymmetric oxidation of sulfides. A notably enhanced enantioselectivity has been obtained by exploiting a concomitant process of stereoconvergent kinetic resolution taking place under catalytic conditions