Reactions of fused dihydro-1,2,4-thiadiazoles with isocyanates and isothiocyanates to give 6aλ4-thia-1,3,4,6-tetraazapentalene derivatives

3-Methyl-6,7-dihydro-5H-1,2,4-thiadiazolo[4,5-a]pyrimidine 4a reacted with isocyanates and isothiocyanates with elimination of acetonitrile and concomitant addition of two molecules of the heterocumulene to give the 2,3-disubstituted-6,7-dihydro-5H-2aλ⁴-thia-2, 3, 4a, 7a-tetraazacyclopent[cd]indene-1 (2H), 4(3H)-diones 8a–8e and the corresponding dithiones 9a–9h , respectively. 3-Methyl-5, 10-dihydrobenzo[e]-1,2,4-thiadiazolo[4,5-a][1,3]diazepine 5a likewise reacted with isocyanates and isothiocyanates to give the 2,3-disubstituted-5,10-dihydro-2aλ⁴-thia-2,3, 4a, 10a-tetraazapentaleno[3, 3a, 4-gh]benzocyclopheptene-1, 4-diones 10a–10f and the corresponding dithiones 11a–11f . The base 4a reacted with phenyl isocyanate, methyl isothiocyanate, and phenyl isothiocyanate in toluene at room temperature to give the zwitterions 14a , 14b , and 14c , respectively, and the diazepine 5a reacted with phenyl isothiocyanate to give the zwitterion 17 .     

A Hybrid Method for Low Reynolds Number Flow Past an Asymmetric Cylindrical Body

Low Reynolds number fluid flow past a cylindrical body of arbitrary shape in an unbounded, two-dimensional domain is a singular perturbation problem involving an infinite logarithmic expansion in the small parameter ε, representing the Reynolds number. We apply a hybrid asymptotic–numerical method to compute the drag coefficient, C _D and lift coefficient C _L to within all logarithmic terms. The hybrid method solution involves a matrix M , depending only on the shape of the body, which we compute using a boundary integral method. We illustrate the hybrid method results on an elliptic object and on a more complicated profile.     

Synthesis and Stereochemistry of Exogonic Acid

Exogonic Acid (1) was isolated from the Brazilian tree, Ipomoea operculata. Dahlke and Graf first characterized (1) in 1964. Despite some subsequent work, it was not until 1992 that we determined the absolute stereochemistry of (1) by synthesis of enantiomers of (1) and application of enantioselective gas chromatographic technique. Here we wish to report our new seterocontrolled synthesis of (1) and its methyl ester.     

Discovery Learning Using Chemland Simulation Software

We describe in this paper a set of computer-based simulations for use in general chemistry courses. We detail a discovery-based method of teaching, whereby students are led to discover concepts through guided-inquiry use of the simulation modules. Three methods of using the software are described, as is the development process we have employed. Finally, we describe our evaluation studies of the effects of our methodology and the use of a scientific reasoning instrument. The software is available free for download as part of this article.     

1,6‐Interactions between di­methyl­amino and aldehyde groups in two bi­phenyl derivatives

The title compounds, 2‐(di­methyl­amino)­bi­phenyl‐2′‐carbox­aldehyde, C₁₅H₁₅NO, and 2‐(di­methyl­amino)­bi­phenyl‐2′,6′‐dicarbox­aldehyde, C₁₆H₁₅­NO₂, show similar 1,6‐interactions [N?C=O 2.929 (3) to 3.029 (3) Å] between the di­methyl­amino and aldehyde groups located in the ortho positions of the two rings, which lie at 58.1 (1)–62.4 (1)° to each other.     

The Influence of Positivism on the Teaching of Mathematics in Brazil: 1870–1930

This article describes the strong influence of positivism on the teaching of mathematics in Brazil. The dissemination of positivism occurred in a very intensive way from 1870 to 1930, due mainly to the strong leadership of teachers at the military and engineering academies. From its firmly entrenched position in these institutions, the positivistic ideology affected the social, political, pedagogical, and ideological life in Brazil. Here, I identify the main representatives of positivism, who focused their research on Auguste Comte's concept of mathematics. They oriented curricula and programs according to Comte's principles as well as produced mathematics with a distinct positivist bent. Although a marked decline occurred after 1930, the positivistic phenomenon was not exhausted as a research topic, and, indeed, it still has not been entirely extinguished in Brazilian life. Copyright 1999 Academic Press.Este trabalho descreve a forte influência do positivismo no ensino da Matemática no Brasil. A difusão do positivismo aconteceu de forma muita intensa entre 1870 e 1930, devido principalmente a atuação dos docentes-militares, que mantinham uma liderança forte nas academias militares e de engenharia. Nestas instituições a ideologia positivista encontrou uma forte sustentação e pode, então, ter efeitos na vida social, polı́tica, pedagógica e ideológica brasileira. Identificamos os principais representantes do positivismo no cı́rculo acadêmico. Detectamos as primeiras manifestações da concepção de Matemática de Auguste Comte em livros-texto. Identificamos a orientação de currı́culos e programas segundo os preceitos de Comte e analisamos principalmente as obras de Matemática de autores positivistas. O declı́nio do positivismos depois de 1930 também é registrado. O fenômeno positivismo não foi esgotado como tema de pesquisa e tudo indica que ainda não se extinguiu completamente da vida brasileira. Copyright 1999 Academic Press.MSC 1991 subject classifications: 01A55, 01A70.     

Steady-state aeroelasticity of fluid flow over a laminated composite plate

A stress-function-based variational approach is used to determine the interlaminar stresses in a multilayered strip of laminate subject to arbitrary combinations of axial extension, bending, and the steady-state aerodynamic loading of fluid flow over the upper surface of laminated composite plate. Symmetric four-layer, cross-ply and angle-ply laminates are considered in details. Some numerical solutions by using a personal computer are obtained. The present results for four-layer laminates show that the aerodynamic loading has significant effects on the interlaminar stresses near the free-edge regions.     

Students’ Microscopic, Macroscopic, and Symbolic Representations of Chemical Reactions

This study examined the mental representations of chemical reactions used by six students (three male, three female) who achieved above-average grades in a college freshman chemistry class at a large midwestern university. The representations expressed by the students in structured interviews were categorized as microscopic, macroscopic, or symbolic representations of chemical reactions. The study revealed that the participants did make at least some use of each of the three representations; however, there were wide variations among participants in the sophistication of the various representations they used and in their understanding of the relationships between representations. Also, participants receiving very similar course grades sometimes demonstrated very different conceptual understandings of chemical reactions.