Hermann von Helmholtz

Résumé

Hermann von Helmholtz est un scientifique (physiologiste et physicien) prussien, né le à Potsdam et mort le à Berlin-Charlottenburg. Il a notamment apporté d'importantes contributions à l'étude de la perception des sons et des couleurs ainsi qu'à la thermodynamique. Biographie Hermann Helmholtz était le fils aîné d'un professeur de . La condition de ses parents ne lui permettant pas de poursuivre des études de physique, il s'inscrivit à l’École de médecine militaire Frédéric-Guillaume sous la direction de Johannes Müller où, après un concours, il pourrait devenir fonctionnaire : c'est ainsi qu'il fut médecin militaire de 1843 à 1848, affecté à la garnison de Potsdam. Il devint membre de la Deutsche Physikalische Gesellschaft de Berlin qui venait de se créer, et y fut d'abord actif comme rapporteur des publications savantes, où se trouvaient beaucoup d'articles mathématiques. Au cours de ces lectures, il développa un intérêt particulier pour la question de l'existence d'u

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https://fr.wikipedia.org/wiki/Hermann_von_Helmholtz

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Studies on the Interfacial Electric Field and Stark Effect at the TiO2/Dye/Electrolyte Interface

Anna Eriksson, Nikolaos Vlachopoulos

Interfaces of dye-sensitized TiO2 nanoparticles with electrolytes or hole conductors have been widely applied in photoelectrochemical cells. However, the fundamental understanding of their properties and function is still poor. Herein, we demonstrate that the spectral changes that occur in the-visible spectrum of dye-sensitized TiO2 films upon (a) Li+ titration, (b) potentiostatic electron accumulation in mesoporous TiO2, and (c) photoinduced electron injection into TiO2 can be explained by the Stark effect, which can then be used to characterize the change in the local electric field at the TiO2/dye/electrolyte interface. A quantitative analysis of the Stark effect indicates that the compact (Helmholtz) layer capacitance at the TiO2/dye/electrolyte interface strongly affects the strength of the local electric field. Systematic studies show that the Helmholtz layer capacitance depends strongly on the Li+ concentration and surface dye coverage but is independent of the concentrations of other electrolytic species and the light intensity. These results illustrate the potential of Stark spectroscopy for the in situ study of the TiO2/dye/electrolyte interfaces and provide substantial new insights into these widely applied interfaces related to photoelectrochemistry and other research fields.

American Chemical Society2016

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NMR-microprobes based on solenoids and Helmholtz coils have been microfabricated and NMR-spectra of mammalian cells have successfully been taken. The microfabrication technology developed for these probes consists of three electroplated copper levels for low resistance coils and three SU-8 layers for the integration of microchannels. This technology allows fabricating solenoids, Helmholtz and planar coils on the same wafer. The coils have inner diameters in the range of 160 to 400 microm and detection volumes of 5 to 22 nL. The solenoid and Helmholtz coils show improved RF-field characteristics compared to a planar coil fabricated with the same process. The fabricated solenoid has a particularly low resistance of only 0.46 Omega at 300 MHz. Moreover, it is very sensitive and has a very uniform RF-field, but shows large line width. The Helmholtz coils are slightly less sensitive, but display a far narrower line width, and are therefore a good compromise. With a Helmholtz coil, a SNR of 620 has been measured after one scan on 9 nL pure water. An NMR-microprobe based on a Helmholtz coil has also been used to take spectra of CHO cells that have been concentrated in the sensitive region of the coil with a mechanical filter integrated into the channel.

2007

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Uniform magnetic fields are desired in a wide range of applications. The most known device achieving such a purpose is the pair of Helmholtz coils. It consists of two identical circular coils, with their main axis aligned and placed at a distance equal to their common radius from each other. The goal of this research is to find another arrangement of the coils in space so as to achieve the largest region possible with a uniform magnetic field. A topology optimization framework is developed for this purpose. It investigates the ideal distribution of current densities in an axisymmetric 2D domain. The designed topology provides a significant improvement of the volume with a uniform field, which is 6.37 times larger than the reference one obtained with Helmholtz coils.

2022

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