1,434 research outputs found
A supersymmetric model for triggering Supernova Ia in isolated white dwarfs
We propose a model for supernovae Ia explosions based on a phase transition
to a supersymmetric state which becomes the active trigger for the deflagration
starting the explosion in an isolated sub-Chandrasekhar white dwarf star. With
two free parameters we fit the rate and several properties of type Ia
supernovae and address the gap in the supermassive black hole mass
distribution. One parameter is a critical density fit to about
g/cc while the other has the units of a space time volume and is found to be of
order Gyr where is the earth radius. The model involves
a phase transition to an exact supersymmetry in a small core of a dense star.Comment: 20 pages, 5 figures, expanded version to be published in Physical
Review
Quantum confinement corrections to the capacitance of gated one-dimensional nanostructures
With the help of a multi-configurational Green's function approach we
simulate single-electron Coulomb charging effects in gated ultimately scaled
nanostructures which are beyond the scope of a selfconsistent mean-field
description. From the simulated Coulomb-blockade characteristics we derive
effective system capacitances and demonstrate how quantum confinement effects
give rise to corrections. Such deviations are crucial for the interpretation of
experimentally determined capacitances and the extraction of
application-relevant system parameters
Direct and Heterodyne Detection of Microwaves in a Metallic Single Wall Carbon Nanotube
This letter reports measurements of microwave (up to 4.5 GHz) detection in
metallic single-walled carbon nanotubes. The measured voltage responsivity was
found to be 114 V/W at 77K. We also demonstrated heterodyne detection at 1 GHz.
The detection mechanism can be explained based on standard microwave detector
theory and the nonlinearity of the DC IV-curve. We discuss the possible causes
of this nonlinearity. While the frequency response is limited by circuit
parasitics in this measurement, we discuss evidence that indicates that the
effect is much faster and that applications of carbon nanotubes as terahertz
detectors are feasible
Lateral scaling in carbon nanotube field-effect transistors
We have fabricated carbon nanotube (CN) field-effect transistors with
multiple, individually addressable gate segments. The devices exhibit markedly
different transistor characteristics when switched using gate segments
controlling the device interior versus those near the source and drain. We
ascribe this difference to a change from Schottky barrier modulation at the
contacts to bulk switching. We also find that the current through the bulk
portion is independent of gate length for any gate voltage, offering direct
evidence for ballistic transport in semiconducting CNs over at least a few
hundred nanometers, even for relatively small carrier velocities.Comment: 4 pages, 4 figure
On the Performance of Single-Gated Ultrathin-Body SOI Schottky-Barrier MOSFETs
The authors study the dependence of the performance of silicon-on-insulator (SOI) Schottky-barrier (SB) MOSFETs on the SOI body thickness and show a performance improvement for decreasing SOI thickness. The inverse subthreshold slopes S extracted from the experiments are compared with simulations and an analytical approximation. Excellent agreement between experiment, simulation, and analytical approximation is found, which shows that S scales approximately as the square root of the gate oxide and the SOI thickness. In addition, the authors study the impact of the SOI thickness on the variation of the threshold voltage V-th of SOI SB-MOSFETs and find a non-monotonic behavior of V-th. The results show that to avoid large threshold voltage variations and achieve high-performance devices, the gate oxide thickness should be as small as possible, and the SOI thickness should be similar to 3 nm
A Fully Tunable Single-Walled Carbon Nanotube Diode
We demonstrate a fully tunable diode structure utilizing a fully suspended
single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward
bias can be continuously tuned up to 4.3 V by controlling gate voltages, which
is ~6 times the nanotube bandgap energy. Furthermore, the same device design
can be configured into a backward diode by tuning the band-to-band tunneling
current with gate voltages. A nanotube backward diode is demonstrated for the
first time with nonlinearity exceeding the ideal diode. These results suggest
that a tunable nanotube diode can be a unique building block for developing
next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure
A comparative study of satellite and ground-based phenology
Long time series of ground-based plant phenology, as well as more than two decades of satellite-derived phenological metrics, are currently available to assess the impacts of climate variability and trends on terrestrial vegetation. Traditional plant phenology provides very accurate information on individual plant species, but with limited spatial coverage. Satellite phenology allows monitoring of terrestrial vegetation on a global scale and provides an integrative view at the landscape level. Linking the strengths of both methodologies has high potential value for climate impact studies. We compared a multispecies index from ground-observed spring phases with two types (maximum slope and threshold approach) of satellite-derived start-of-season (SOS) metrics. We focus on Switzerland from 1982 to 2001 and show that temporal and spatial variability of the multispecies index correspond well with the satellite-derived metrics. All phenological metrics correlate with temperature anomalies as expected. The slope approach proved to deviate strongly from the temporal development of the ground observations as well as from the threshold-defined SOS satellite measure. The slope spring indicator is considered to indicate a different stage in vegetation development and is therefore less suited as a SOS parameter for comparative studies in relation to ground-observed phenology. Satellite-derived metrics are, however, very susceptible to snow cover, and it is suggested that this snow cover should be better accounted for by the use of newer satellite sensor
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