3,484 research outputs found
Absence of Localization in Certain Field Effect Transistors
We review some experimental and theoretical results on the metal-to-insulator
transition (MIT) observed at zero magnetic field (B=0) in several
two-dimensional electron systems (2DES). Scaling of the conductance and
magnetic field dependence of the conductance provide convincing evidence that
the MIT is driven by Coulomb interactions among the carriers and is
dramatically sensitive to spin polarization of the carriers.Comment: 8 pages, LaTeX, figure label change
Metal-insulator transition and glassy behavior in two-dimensional electron systems
Studies of low-frequency resistance noise demonstrate that glassy freezing
occurs in a two-dimensional electron system in silicon in the vicinity of the
metal-insulator transition (MIT). The width of the metallic glass phase, which
separates the 2D metal and the (glassy) insulator, depends strongly on
disorder, becoming extremely small in high-mobility (low-disorder) samples. The
glass transition is manifested by a sudden and dramatic slowing down of the
electron dynamics, and by a very abrupt change to the sort of statistics
characteristic of complicated multistate systems. In particular, the behavior
of the second spectrum, an important fourth-order noise statistic, indicates
the presence of long-range correlations between fluctuators in the glassy
phase, consistent with the hierarchical picture of glassy dynamics.Comment: Contribution to conference on "Noise as a tool for studying
materials" (SPIE), Santa Fe, New Mexico, June 2003; 15 pages, 12 figs.
(includes some low-quality figs; send e-mail to get high-quality figs.
The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
By taking into account relativistic corrections to the magnetic dipole
operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98
is obtained. In order to check this new value using AGN spectra we present the
measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a
sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database
and from published observations. We select only high signal-to-noise ratio
spectra for which the line shapes of the [OIII] 4959,5007 lines are the same.
We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good
agreement with the theoretical one.Comment: Accepted for publication in the MNRA
Using the Fermilab Proton Source for a Muon to Electron Conversion Experiment
The Fermilab proton source is capable of providing 8 GeV protons for both the
future long-baseline neutrino program (NuMI), and for a new program of low
energy muon experiments. In particular, if the 8 GeV protons are rebunched and
then slowly extracted into an external beamline, the resulting proton beam
would be suitable for a muon-to-electron conversion experiment designed to
improve on the existing sensitivity by three orders of magnitude. We describe a
scheme for the required beam manipulations. The scheme uses the Accumulator for
momentum stacking, and the Debuncher for bunching and slow extraction. This
would permit simultaneous operation of the muon program with the future NuMI
program, delivering 10^20 protons per year at 8 GeV for the muon program at the
cost of a modest (~10%) reduction in the protons available to the neutrino
program.Comment: 18 pages, 7 figure
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