Radiative lifetimes in Zn(II), Cd(II) and Hg(II) measured by fast-beam zero-field level-crossing technique

The zero-field level-crossing technique has been used to determine radiative lifetimes of excited states in singly ionized zinc, cadmium, and mercury. The excited levels in Zn(II), Cd(II) and Hg(II) were populated by collisions between fast ions and helium gas. Particular attention has been paid to the systematic errors occurring in radiative lifetimes by this technique. The results are compared with the lifetimes obtained by beam-foil, phase-shift, delayed-coincidence techniques and theoretical calculations.     

Measurements of angular distributions of sputtered material as a new tool for surface-segregation studies: Segregation in CuPt alloys

The angular distribution of copper and platinum sputtered by argon ions from polycrystalline CuPt targets at 77 K has been measured by a collection technique. The argon-ion energy has been varied from 1.25 to 320 keV. For bombardment energies above 20 keV, differences in the angular distributions for the two elements indicate a strong copper segregation to the surface during bombardment.     

The mathematical technique in Fermat's deduction of the law of refraction

This article attempts to explain Fermat's not quite obvious calculations connected with his deduction of the law of refraction in Analysis ad refractiones (1662), and to describe the development which led to these calculations. In 1657 Fermat tried to deduce a law of refraction based on the principle that light follows the quickest path between two given points. He did not succeed because he found that the calculations were too long and tedious. The calculations are indeed complicated, but if Fermat, in 1657, had been willing to accept Descartes' law of refraction he would probably also have seen that it solved his problem. However, Fermat was of the opinion that Descartes' law was wrong and, therefore, he did not expect that solution. Only in 1662, when he succeeded in reducing the calculations substantially, did he realize that they led to the sine law of Descartes.     

The differential equations of the Voigt function

The three second-order partial differential equations of the Voigt function are presented, leading to a powerful and accurate method of determining the Voigt function in the calculation of a line profile in a stellar atmosphere.     

Hydrogen-bond topology and the ice VII/VIII and ice Ih/XI proton-ordering phase transitions

The existence of an ice Ih/XI proton-ordering transition to a low-temperature ferroelectric phase has sparked considerable debate in the literature. Electronic density functional theory calculations, extended using graph invariants, confirm that a transition to a low-temperature ferroelectric phase should occur. The predicted transition at 98 K is in qualitative agreement with the observed transition at 72 K, and the low-temperature phase is the ferroelectric phase determined in diffraction experiments. The theoretical methods used to predict the phase transition are validated by comparing their prediction to the well-characterized ice VII/VIII proton-ordering transition.     

Sensitivity of a tucuxi (Sotalia fluviatilis guianensis) to airborne sound

Auditory systems of cetaceans are considered highly specialized for underwater sound processing, whereas the extent of their hearing capacity in air is still a point of issue. In this study, the sensitivity to airborne sound in a male tucuxi (Sotalia fluviatilis guianensis) was tested by means of a go/no go response paradigm. Auditory thresholds were obtained from 2 to 31.5 kHz. Compared to the hearing thresholds of other dolphins as well as of amphibian mammals, the sensitivity to airborne sound of the test subject is low from 2 to 8 kHz, with the highest threshold at 4 kHz. Thresholds at 16 and 31.5 kHz reveal a sharp increase in hearing sensitivity. Thus, although not obtained in this study, the upper aerial hearing limit is in the ultrasonic range. A comparison of the present data with the underwater audiogram of the same test subject referred to sound intensity indicates that the sensitivity of Sotalia to underwater sound is generally better than to airborne sound.