Os argumentos físicos fundamentais para a descrição da linha de ressonância resultante de transições de estados quânticos induzidos por radiações eletromagnéticas não são, muitas vezes, suficientemente bem compreendidos por estudantes iniciantes em ciências naturais ou não-especialistas em espectroscopia. Livros didáticos em geral tendem a tratar o problema com base em formalismos teóricos complexos, inacessíveis a todos aqueles que não estão suficientemente familiarizados com os argumentos físicos e matemáticos avançados da mecânica quântica. Neste artigo, são apresentados desenvolvimentos algébricos mais diretos e mais simples, com a intenção de oferecer uma alternativa didática e servir como fonte de referência a leitores com graus variáveis de domínio teórico em física avançada. O ponto central é mostrar que a largura da linha de ressonância da radiação gama é conceitualmente o dobro da largura de linha natural para a energia relacionada ao estado nuclear excitado da transição. Os argumentos algébricos são utilizados de modo a oferecer uma via direta e dedutiva, intencionalmente mais prontamente alcançáveis do que os ora encontrados na literatura científica. Este estudo de caso foi escolhido na perspectiva particular do princípio físico correspondente à espectroscopia nuclear Mössbauer.
Recebido em 23/6/03; aceito em 21/11/03 REFLECTIONS ON THE CONTRIBUTION OF CARNOT TO THE FIRST LAW OF THERMODYNAMICS. The classical interpretations of Nicolas Léonard Sadi Carnot on some physical principles involved in the operation of heat engines were fundamental to the development and formulation of the Second Law of Thermodynamics. Moreover, an accurate historical survey clearly reveals that Carnot was, by that time, also well aware about some new concepts, which were further worked out by other scientists to lead to what was, some time later, known as the mechanical equivalent of heat and the conservation of energy. Benoit Paul Émile Clapeyron recognized these original concepts in the first of Carnot´s monographs, published in 1824, but no explicit citation is found in any post-Carnot classical texts dealing with the First Law of Thermodynamics, including those by Julius Robert Mayer, James Prescott Joule and Hermann Ludwig Ferdinand von Helmholtz. The main objective of the present work is to point out some historical evidences of the pioneering contribution of Carnot to the modern concept of the First Law of Thermodynamics.
is known to have established the basis for the third law of thermodynamics and also as one of the founders of the modern physical chemistry. For his work in chemical thermodynamics, he was awarded the Nobel Prize in chemistry, in 1920. An important fact about this scientist life, not always realized, was his stay in Brazil, in 1914, for a short period. He went to the city of São Paulo, where he gave a conference at the Faculdade São Bento. He talked about thermodynamics to a very selected audience. The work presented here explores this visit to Brazil, the importance the newspaper gave to this important visitor, and the community present at his lecture. His impression of Brazil was certainly positive, since one of his daughter immigrates to Brazil in 1939. It is hoped the material will add relevant information to the history of chemistry in Brazil.
FRITZ HABER VISIT TO BRAZIL. Fritz Haber was awarded with the Nobel Prize in Chemistry in 1918 for the ammonia synthesis from its gaseous components. This work was fundamental to stop starvation around the world. On the opposite, his engagement to produce chemical weapons during the First World War is also an important fact in the life of this scientist. This polemic scientist visited Brazil in 1923, carrying out a project to extract gold from the sea. The present work tries to recover the historical fact behind the visit of this scientist to Brazil.
Investigations based on 57 Fe Mössbauer spectroscopy and powder X-ray diffraction report the existence of siderite in a manganese ore deposit in the city of Conselheiro Lafaiete, Minas Gerais, Brazil. Mössbauer parameters at 110 K indicated the isomorphous substitution of Fe 2+ in siderite structure by other cations such as Ca 2+ and Mg 2+ , resulting in the distortion of siderite structure. The proposed mechanism suggests the formation of siderite and it is consistent with the process of carbonate formation in reducing environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.