Properties of nanoparticles generated during femtosecond laser machining in air and water

Femtosecond laser ablation is used to generate nanoparticle aerosols and colloids from solid targets of various materials (Ti, Ag, Au, Co, etc.) in air and water ambience. We determine the influence of different laser parameters (pulse energy, pulse overlap) and properties of media (air, airbrush, water) on the rate of production and size distribution of the laser-generated nanoparticles. It is shown that the pulse overlap and laser fluence are the parameters determining the nanoparticle size. At optimum conditions the nanoparticle productivity can be increased by 150–300%. The generation of multimaterial nanoparticle dispersions is demonstrated. Being free of toxic impurities, the laser-produced nanoparticles may be promising for biomedical applications. PACS 79.20.Ds; 81.16.Mk; 81.16.-c; 52.38.Ph; 06.60.Jn     

Aminyloxide (nitroxide)—XXIV: Empirische ermittlung der spindichteverteilung in aminyloxiden

¹⁷O-Labelled aminyloxides 1–8 (dialkyl-, alkylaryl-, diaryl-, acylaminyloxides and amidinyloxides) have been prepared by various methods. The ESR spectra of 1a and 4 have been measured in various solvents, showing a very good correlation between a^N respectively a^O and the E_T-values of solvents. From the solvent-dependence of the coupling constants of 1a Q-values have been evaluated for the simplified equation aⁱ = Q_iiⁱ × pⁱ (Q_NN^N = 33.1 G; Q_oo^o = 35.3 G). These values were used to calculate the spin density ?^N and ?^o of the aminyloxides 1–8. The Q-values are shown to be reasonable by summation of the spin density of all positions for the radicals 4–7. which gives one with only small deviations. In most of these radicals in which the unpaired electron is delocalized into the conjugated π-system ?^N is reduced significantly, as compared to dialkyl-ammyloxides, whereas ?⁰ is only lowered to a small extent.     

On the Present Status of the Problem of Charge Dependence and Charge Asymmetry of the Nucleon-Nucleon Force

The charge dependence of the nucleon-nucleon force can be derived from the low-energy scattering parameters. The p-p and n-p parameters were measured in direct scattering experiments. The n-n parameters a_nn = (-16.70 ± 0.38) fm and r_nn = (2.78 ± 0.13) fm have been determined from few particle reactions. The difference of the scattering lengths (a_nn - a_nn) ≈ 7 fm demonstrates the violation of the charge independence. Information on the charge symmetry is still doubtful due to the inaccuracy of the charge correction for the p-p parameters. Whereas the n-n and the charge corrected p-p parameters known at present yield a weaker n-n force than the p-p force, the opposite result follows from the binding energy difference for ³He and ³H and the meson theory of the nuclear forces.     

Zum Lumineszenzmodell manganaktivierter Titanate

The emission spectra and the temperature dependence of the relative intensity of luminescence of three manganese activated titanate phosphors [Zn₂TiO₄, (Mg, Zn)₂TiO₄, Mg₂TiO₄] after optical excitation with radiation from 300–500 nm were measured for various temperatures above 4,2 °K. The luminescence of the Mn⁴⁺-centre is influenced by the cations (Mg²⁺ or Zn²⁺) of the lattice. The temperature dependence of the relative intensity of the luminescence depends on the excitation wavelength. The results are discussed and found to be in good agreement with those of aC-C-model which assumes two energy parabolas for the excited state.     

An experimental limit on production of axions in a fission reactor

We report on an experiment conducted at the ILL reactor aimed at searching for coincident gamma-ray events from axion decay. No such events are seen and our results are interpreted, using the calculations by Donnelly et al., as an upper limit of the axion mass of 280 keV.     

Darstellung und Kristallstruktur der Phasen Zr3S4 und Hf3S4

The crystal structure of the Zr₃S₄ phase was confirmed by single crystal work. The structure parameters were refined. An isotypic phase forming a microcrystalline powder could be prepared in the system hafnium/sulphur.