The real and imaginary parts of the frequency dependent response of YBaCuO samples doped with scandium are measured over a wide frequency range (5 Hz to 13 MHz) both, in the normal (at 298 K) and in the superconducting (at 77 K) states. An attempt is made to identify the relaxation mechanisms responsible for ac conduction in the samples. It is suggested that 2p hole-polarons associated with the oxygen atoms play an important role in determining the frequency dependent behaviour in the normal state as well as at their superconductivity.Der Real-und Tmaginiiranteil der frequenzabhingigen Kennlinie von mit Scandium dotierten YBaCuO-Proben werden uber einen groRen Frequenzbereich (5 Hz bis 13 MHz) sowohl im Normal-(bei 298 K) als auch im Supraleitungsiustand (bei 77 K) gemessen. Es wird versucht, den fur die Wechselstromleitfiihigkeit verantwortlichen Relaxationsmechanismus zu identifizieren. Es wird angenommen, dalj 2p-Locherpolaronen, die mit den Sauerstoffatomen verknupft sind, einc wesentliche Rolle bei der Bestimmung des frequenzabhangigen Verhaltens im Normalzustand sowie bei ihrer Supraleitfahigkeit spielen.

No abstract

Reflectance measurements at room temperature (298 K) on ceramic YBa,Cu,O, --x in the spectral range 0.6 to 6.1 eV and subsequent Kramers-Kronig analyses of the spectra indicate the presence of excitations at 1.0, 2.1, 3.6, and 5.7 eV. It is argued that there is enough evidence to consider the 1.0 and 2.1 eV excitations as excitons.Messungen des Reflexionsvermogens bei Zimmertemperatur (298 K) an YBa2Cu,0, -,-Keramiken im Spektralbereich von 0,6 bis 6,l eV und anschliel3ende Kramers-Kronig-Analyse der Spektren ergeben die Existenz von Anregungen bei 1,0, 2,1, 3,6 und 5,7 eV. Es wird angenommen, daR geniigend Hinweise existieren, um die Anregungen bei 1,0 und 2,l eV als Exzitonen zu betrachten.

No abstract

A simple, sensitive, quick, easy and efficient (SSQuEE) analytical technique based on cloud point extraction (CPE) has been developed for the determination of different pesticides present in soil and water with high performance liquid chromatography separation and ultraviolet detection. The environmentally friendliness surfactant like Triton X -100, compared to Tween series of non-ionic surfactant can effectively extract imidacloprid (insecticide), flusilazole (fungicide) and atrazine (herbicide) at cloud point temperature at 67 ºC, 82 ºC and 62 ºC, respectively. To reach the optimum extraction efficiency, different experimental parameters like surfactant concentration, salt type and its concentration, equilibrium time and temperature, pH were observed. At the optimum conditions, linear regression coefficient of the standard curves was greater than 0.9924. The limit of detection of imidacloprid, flusilazole and atrazine were 0.10 μg L-1, 0.24 μg L-1, 0.15 μg L-1 and recovery percent are 99.71 %, 88.1% and 89.74%, respectively.