8,505 research outputs found
The influence of a single defect in composite gate insulators on the performance of nanotube transistors
The current through a carbon nanotube field-effect transistor (CNFET) with
cylindrical gate electrode is calculated using the nonequilibrium Greens
function method in a tight-binding approximation. The obtained result is in
good agreement with the experimental data. The space radiation and nuclear
radiation are known to cause defects in solids. The theoretical approach is
used to calculate the amplitude of the random-telegraph-signal (RTS) noise due
to a single defect in the gate oxide of a long channel p-type CNFET. We
investigate how the amplitude of the RTS noise is affected by the composite
structure of gate insulators, which contains an inner insulator with a
dielectric constant larger than 3.9 and an outer insulator with a dielectric
constant of 3.9 (as for SiO2). It is found that the RTS amplitude increases
apparently with the decreasing thickness of the inner gate insulator. If the
inner insulator is too thin, even though its dielectric constant is as large as
80, the amplitude of the RTS noise caused by the charge of Q = +1e may amount
to around 80% in the turn-on region. Due to strong effects of defects in
CNFETs, CNFETs have a potential to be used for detecting the space radiation or
nuclear radiation.Comment: 8 Figure
Semiclassical Approach to Survival Probability at Quantum Phase Transitions
We study the decay of survival probability at quantum phase transitions
(QPT). The semiclassical theory is found applicable in the vicinities of
critical points with infinite degeneracy. The theory predicts a power law decay
of the survival probability for relatively long times in systems with d=1 and
an exponential decay in systems with sufficiently large d, where d is the
degrees of freedom of the underlying classical dynamics. The semiclassical
predictions are checked numerically in four models.Comment: 4 pages, 3 figures; published versio
Optimal Drug Policy in Low-Income Neighborhoods
Part of the debate over the control of drug activity in cities is concerned with the effectiveness of implementing demand- versus supply-side drug policies. This paper is motivated by the relative lack of research providing formal economic underpinning for the implementation of either policy. We construct a simple model of drug activity, in which the drug price and the distribution of population in a community are determined according to a career choice rule and a predetermined drug demand. Three potential government objectives are considered. We find that both demand- and supply-side policies have theoretical support under different community conditions. While the demand-side policy discourages active drug sellers, the supply-side policy has an additional drug-dealing replacement effect on inducing potential entry of drug dealers. In low-income neighborhoods, demand-side policy is more effective if the drug problem is more sever or if the government objective is to deter dealer entry or to promote community's aggregate income rather than minimizing active drug selling.
Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
We present optical and near-infrared stellar polarization observations toward
the dark filamentary clouds associated with IC5146. The data allow us to
investigate the dust properties (this paper) and the magnetic field structure
(Paper II). A total of 2022 background stars were detected in -, -,
-, and/or -bands to mag. The ratio of the polarization
percentage at different wavelengths provides an estimate of ,
the wavelength of peak polarization, which is an indicator of the small-size
cutoff of the grain size distribution. The grain size distribution seems to
significantly change at 3 mag, where both the average and dispersion
of decrease. In addition, we found
0.6-0.9 m for mag, which is larger than the 0.55 m
in the general ISM, suggesting that grain growth has already started in low
regions. Our data also reveal that polarization efficiency (PE ) decreases with as a power-law in -, -, and
-bands with indices of -0.710.10, -1.230.10 and -0.530.09.
However, -band data show a power index change; the PE varies with
steeply (index of -0.950.30) when mag but softly
(index of -0.250.06) for greater values. The soft decay of PE in
high regions is consistent with the Radiative Aligned Torque model,
suggesting that our data trace the magnetic field to mag.
Furthermore, the breakpoint found in -band is similar to the where we
found the dispersion significantly decreased. Therefore, the
flat PE- in high regions implies that the power index changes result
from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap
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