Utilizando a relação que fornece a irradiância devida à interferência de fontes pontuais, mostramos por meio de gráficos como o princípio de Huygens-Fresnel funciona quando é aplicado para determinar o padrão de difração de Fraunhofer gerado por uma onda plana que incide perpendicularmente em um anteparo que contém apenas uma fenda. Desta forma, somos capazes de identificar como se originam os picos principal e secundários de difração, o que não é entendido claramente a partir da obtenção analítica do padrão de difração em questão.

Using the relation for the irradiance due to the interference of point sources, we show through graphs how the Huygens-Fresnel principle works when it is applied to determine the Fraunhofer diffraction pattern due to a normally incident plane wave on a single slit. In this way, we are able to identify the origins of the principal and secondary peaks of diffraction, which is not clearly understood from the analytical determination of the present diffraction pattern.

Giant extracellular hemoglobins are considered the summit of complexity in systems that carry oxygen, constituting an extraordinary model system to the study of hemoproteins. This class includes the hemoglobin of the annelid Glossoscolex paulistus that presents high cooperativity, great oligomeric and redox stabilities and ability of oligomeric reassociation. These properties have motivated evaluations about its utilization as prototype of artificial blood and biosensor. Kinetic studies involving autoxidation and detailed spectroscopic characterizations of its ferrous and ferric species have propitiated information about the structure-activity relationship of this macromolecule. The present review analyzes several biochemical issues, evaluating the state-of-art of this subject.

In this paper we deal with the problem of controlling some Chaplygin systems in the framework of the vakonomic approach for nonholonomic systems. Equations of motion for these systems are obtained which contain a free parameter that permits to control the system. It is show that given a prescribed path it is possible to determine the parameter of control which inserted in the equations of motion compel the trajectory of the system to follow the input function.