Browsing by Subject "Coulomb potential"
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Item Asteroseismological Study on PG 0112+104 with Pure and Screened Coulomb Potential(2018-07) Chen, Y.H.; Castanheira, B.; Vanderbosch, Z.; Montgomery, M.With 78.7 days of observations by Kepler space telescope, Hermes et al. (2017) made a detailed mode identification on a hot DBV star PG 0112+104. In total, 11 likely m = 0 components with 5 triplets and 3 quintuplets were identified. Those modes can be used to constrain fitting models. A grid of main sequence stars are evolved to be white dwarfs by MESA. Being results of thermal nuclear burning, the core compositions are taken out and added into WDEC to evolve grids of DBV stars. The element diffusion effect adopting pure Coulomb potential and screened Coulomb potential are added into WDEC. Two grids of DBV star models are evolved with the two Coulomb potential scenarios. The eigenfrequencies are calculated and used to fit the 11 observed modes. Two preferredmodels with pure and screened Coulomb potential scenarios are selected. They are consistent with previous spectral and asteroseismological results. The root-mean-square residual is improved by 27%. The differences for the two scenarios are obvious at the C/O-He interface area. Long-period modes are sensitive to this area, but most of the observed modes are short-period modes. DBV stars with lots of long-period modes should be found in future work to study the effect.Item Magnetic field enhancement of Coulomb blockade conductance oscillations in metal-metal oxide double barrier tunnel devices fabricated using atomic force microscope nanolithography(2005) Wiemeri, Jeffrey Charles; Shih, Chih-KangMagnetic field enhancement of Coulomb blockade conductance oscillations in metal oxide double barrier tunnel devices fabricated using atomic force microscope nanolithography is reported for the first time. Anodic oxidation by this method was accomplished on lithographically patterned Ti and Ni device layers. This is the first time Ni has been reported to be oxidized via scanning probe lithography. Magnetoresistance measurements were taken on selected devices in a Hall effect cryogenic system where tunneling conductance behavior was observed at 1.8, 10, 25, and 50 K in the Ti devices and 150 K in the Ni devices. Coulomb blockade conductance features were observed at vii 1.8, 10 and 50 K in the Ti devices and 10 and 25 K in the Ni devices. Applying a 9T magnetic field enhanced the conductance oscillations and clarified the Coulomb staircase apparent in the I-V curves for both devices. From theoretical fits of the experimental conductance behavior for the Ti devices, this is attributed to a suppression of cotunneling currents in the device. Additionally, in multiple Ti devices, a zero-bias anomaly peak was observed at ~ 2 K and is attributed to contaminant particles in the metal oxide barrier creating a localized magnetic moment in the junction leading to spin-flip and s-d exchange scattering assisted tunneling according to the Anderson-Appelbaum model. This is the first time these zero-bias anomalies have been observed and reported in planar tunnel junctions.