The singing cymbal: Is it really photon momentum?

A simple demonstration that is occasionally used in the classroom to show that light carries momentum involves making an orchestral cymbal audibly ring using light from a common photoflash. A metal plate or a piece of foil can also be used, however, it appears that many people use a cymbal because the sound is easily heard at a reasonable distance. It is such an impressive example of the effects attributable to photon momentum that it is posted on the CERN website for educational under the name “singing cymbal.” Although it is an impressive demonstration, a series of simple classroom experiments can show that the sound of the singing cymbal is not due to the transfer of photon momentum

Coupling of Transverse and Longitudinal Waves in Piano Strings

The existence of longitudinal waves in vibrating piano strings has been previously established, as has their importance in producing the characteristic sound of the piano. Modeling of the coupling between the transverse and longitudinal motion of strings indicates that the amplitude of the longitudinal waves are quadratically related to the transverse displacement of the string, however, experimental verification of this relationship is lacking. In the work reported here this relationship is tested by driving the transverse motion of a piano string at only two frequencies, which simplifies the task of unambiguously identifying the constituent signals. The results indicate that the generally accepted relationship between the transverse motion and the longitudinal motion is valid. It is further shown that this dependence on transverse displacement is a good approximation when a string is excited by the impact of the hammer during normal play

Multiphoton Excitation of Upconverting Nanoparticles in Pulsed Regime

Upconverting nanoparticles (UCNPs) present emission in the visible region upon irradiation with NIR light through a multiphoton mechanism. However, the long characteristic time of their emission has prevented the use of this kind of entities as multiphoton probes. We present a study on the use of erbium-containing UCNPs under pulsed excitation, showing that both the power density and the duration of the excitation pulse are key factors to understand the emission behavior. By adjusting power and excitation rate, we can obtain typical multiphoton z-axis focal exclusive excitation. These findings open the possibility of using UCNPs as probes for controlled localization of uncaging and imaging with multiphoton z-axis sectioning. We show that this can be achieved even at power densities several orders of magnitude lower than traditional multiphoton microscopies.Fil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Chen, Zhijun. Max Planck Institute for Polymer Research; AlemaniaFil: Wu, Si. Max Planck Institute for Polymer Research; AlemaniaFil: Etchenique, Roberto Argentino. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentin

In situ characterization of phospholipid coated electrodes

Four in situ techniques, quartz crystal microbalance, electrochemical impedance spectroscopy, ellipsometry and atomic force microscopy, have been used to study the deposition of dioleoylphosphatidylglycerol (DOPG) films from vesicle solution onto 1-decanethiol coated gold surfaces. The experiments show that, although no one technique can give an unequivocal picture of the deposition process and structure of the final film, by combining the results from the four different techniques a consistent picture emerges. Initially, over the first 200 s a monolayer of DOPG is formed on the 1-decanethiol coated surface. Then at longer times and in the presence of 0.1 M NaCl and 0.1 M TRIS buffer at pH 8 a further bilayer of DOPG is deposited on top of this initially formed monolayer. Evidence for this is provided by the quartz crystal microbalance measurements and from atomic force microscopy. The results from electrochemical impedance measurements and ellipsometry are consistent with these findings but these two methods are less able to distinguish between the formation of the monolayer and subsequent deposition of the bilayer on top of the monolayer. For DOPG films, where the head group is negatively charged at pH 8, the ionic strength of the solution has an important effect in controlling the deposition of the bilayer on top of the initially formed monolayer