Similarity and contrasts between thermodynamic properties at the critical point of liquid alkali metals and of electron-hole droplets

The recent experimental study by means of time-resolved luminescence measurements of an electron-hole liquid (EHL) in diamond by Shimano et al. [Phys. Rev. Lett. 88 (2002) 057404] prompts us to compare and contrast critical temperature T_c and critical density n_c relations in liquid alkali metals with those in electron-hole liquids. The conclusion drawn is that these systems have similarities with regard to critical properties. In both cases the critical temperature is related to the cube root of the critical density. The existence of this relation is traced to Coulomb interactions and to systematic trends in the dielectric constant of the electron-hole systems. Finally a brief comparison between the alkalis and EHLs of the critical values for the compressibility ratio Z_c is also given

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of similar to 1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to similar to 4mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O-2 caused by the increasing electrical field, when the discharge is operated in ambient air

Characterization of a planar 8 mm wide radiofrequency atmospheric pressure plasma source by spectroscopy techniques

Atmospheric pressure planar radiofrequency (RF) 13.56 MHz discharge in Ar gas generated in a long gap is investigated. The discharge operation with and without a dielectric barrier on the electrodes is studied as a function of the applied power and gas flow. The source afterglow is characterized and is analyzed for possible large-scale biomedical applications where low gas temperature is required. The discharge is studied by relative and absolute emission spectroscopies. A gas temperature as low as 330 +/- 50 K is determined from the rotational-vibrational band of OH emission. The absolute value of the discharge continuum irradiation is used to determine the electron density and the electron temperature. The electron-atom and electron-ion contributions to the bremsstrahlung radiation are calculated and are compared with measured spectra. The electron density of 1.9 +/- 1 x 10(20) m(-3) and electron temperature of 1.75 +/- 0.25 eV are measured in the discharge without a dielectric barrier. It is found that presence of the dielectric has a negligible effect on electron temperature, whereas the electron number density is almost six times lower in the discharge with the dielectric barrier

Temperature dependence of the electrical conductivity of imidazolium ionic liquids.

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10^7 Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion.ionic liquids; molten salts;