Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges

A new traceability chain for the derivation of the farad from dc quantum Hall effect has been implemented at INRIM. Main components of the chain are two new coaxial transformer bridges: a resistance ratio bridge, and a quadrature bridge, both operating at 1541 Hz. The bridges are energized and controlled with a polyphase direct-digital-synthesizer, which permits to achieve both main and auxiliary equilibria in an automated way; the bridges and do not include any variable inductive divider or variable impedance box. The relative uncertainty in the realization of the farad, at the level of 1000 pF, is estimated to be 64E-9. A first verification of the realization is given by a comparison with the maintained national capacitance standard, where an agreement between measurements within their relative combined uncertainty of 420E-9 is obtained.Comment: 15 pages, 11 figures, 3 table

Stable electron beams from laser wakefield acceleration with few-terawatt driver using a supersonic air jet

International audienceThe generation of stable electron beams produced by the laser wakefield acceleration mechanism with a few-terawatt laser system (600 mJ, 50 fs) in a supersonic synthetic air jet is reported and the requirements necessary to build such a stable electron source are experimentally investigated in conditions near the bubble regime threshold. The resulting electron beams have stable energies of (17.4 +/- 1.1) MeV and an energy spread of (13.5 +/- 1.5) MeV (FWHM), which has been achieved by optimizing the properties of the supersonic gas jet target for the given laser system. Due to the availability of few-terawatt laser systems in many laboratories around the world these stable electron beams open possibilities for applications of this type of particle source

Strontium ferrite nanoparticles synthesized in presence of polyvinylalcohol: Phase composition, microstructural and magnetic properties

Systematic study was devoted to the synthesis of hexagonal strontium ferrite nanoparticles employing polyvinylalcohol as stabilizing agent. Preliminary experiments allowed to select an optimal sol having molar ratio Sr2+/Fe3+=12, weight ratio PVA/[Sr2++Fe3+]=1.4 and pH=2.1. The obtained sol were transformed to gels by an evaporation of water at 100 °C and drying at 112 °C under vacuum. The subsequent calcination was carried out for 3 h at 400 °C, achieved by heating rate of 17 K/min. The obtained precursor was used for a detail study of influence of annealing conditions (temperature range 600–700 °C, annealing time 10–190 min) on the resulting properties. Semiquantitative X-ray phase analysis approved a gradual increase of the M-phase content and a gradual growth of M-phase crystallites with temperature and time. Magnetic measurements showed a distinct influence of the phase composition, namely ratio of the contents of M-phase and maghemite on the shape of the magnetic loops, while the crystallite sizes have only a slight effect

Komplexní geochemický výzkum interakcí a migrací organických a anorganických látek v horninovém prostředí:Sorpce organických polutantů přírodními sorbenty

Zpráva se zabývá problematikou charakterizace organické hmoty hornin, sedimentů a půd jako přírodních sorbentů a interakcemi těchto materiálů s organickými polutanty v modelových systémech hornina - voda. Výsledky analýz byly podrobeny auditu jakosti a spolehlivosti statistickým hodnocením údajů včetně vyšetření korelací mezi definitivně příbuznými analytickými veličinami. Byly validovány metody stanovení triazinových herbicidů ve vodách a zeminách pomocí HPLC. Výsledky jsou uvedeny v přílohách