656 research outputs found
A graphene bilayer channel transistor with a very high Ion/Ioff ratio, graphene single electron devices and graphene nano-mechanical structures for NEMS
The 2006 Radio Outburst of a Microquasar Cyg X-3: Observation and Data
We present the results of the multi-frequency observations of radio outburst
of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m
telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope.
Since the prediction of a flare by RATAN-600, the source has been monitored
from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the
quench of the activity, successive flares exceeding 1 Jy were observed
successfully. The time scale of the variability in the active phase is
presumably shorter in higher frequency bands.
We also present the result of a follow-up VLBI observation at 8.4 GHz with
the Japanese VLBI Network (JVN) 2.6 days after the first rise. The VLBI image
exhibits a single core with a size of <8 mas (80 AU). The observed image was
almost stable, although the core showed rapid variation in flux density. No jet
structure was seen at a sensitivity of K.Comment: 17 pages,6 figures; accepted by PAS
Multiple Functionality in Nanotube Transistors
Calculations of quantum transport in a carbon nanotube transistor show that
such a device offers unique functionality. It can operate as a ballistic
field-effect transistor, with excellent characteristics even when scaled to 10
nm dimensions. At larger gate voltages, channel inversion leads to resonant
tunneling through an electrostatically defined nanoscale quantum dot. Thus the
transistor becomes a gated resonant tunelling device, with negative
differential resistance at a tunable threshold. For the dimensions considered
here, the device operates in the Coulomb blockade regime, even at room
temperature.Comment: To appear in Phys. Rev. Let
Microwave Transport in Metallic Single-Walled Carbon Nanotubes
The dynamical conductance of electrically contacted single-walled carbon
nanotubes is measured from dc to 10 GHz as a function of source-drain voltage
in both the low-field and high-field limits. The ac conductance of the nanotube
itself is found to be equal to the dc conductance over the frequency range
studied for tubes in both the ballistic and diffusive limit. This clearly
demonstrates that nanotubes can carry high-frequency currents at least as well
as dc currents over a wide range of operating conditions. Although a detailed
theoretical explanation is still lacking, we present a phenomenological model
of the ac impedance of a carbon nanotube in the presence of scattering that is
consistent with these results.Comment: Added reference
New Panoramic View of CO and 1.1 mm Continuum Emission in the Orion A Molecular Cloud. I. Survey Overview and Possible External Triggers of Star Formation
We present new, wide and deep images in the 1.1 mm continuum and the
CO (=1-0) emission toward the northern part of the Orion A Giant
Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera
mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope
in Chile, and the CO (=1-0) data were with the 25 beam receiver
(BEARS) on the NRO 45 m telescope in the On-The-Fly (OTF) mode. The present
AzTEC observations are the widest (\timeform{1.D7}
\timeform{2.D3}, corresponding to 12 pc 17 pc) and the
highest-sensitivity (9 mJy beam) 1.1 mm dust-continuum imaging of
the Orion-A GMC with an effective spatial resolution of 40\arcsec. The
CO (=1-0) image was taken over the northern \timeform{1D.2}
\times\timeform{1D.2} (corresponding 9 pc 9 pc) area with a
sensitivity of 0.93 K in , a velocity resolution of 1.0 km
s, and an effective spatial resolution of 21\arcsec. With these data,
together with the MSX 8 m, Spitzer 24 m and the 2MASS data, we have
investigated the detailed structure and kinematics of molecular gas associated
with the Orion-A GMC and have found evidence for interactions between molecular
clouds and the external forces that may trigger star formation. Two types of
possible triggers were revealed; 1) Collision of the diffuse gas on the cloud
surface, particularly at the eastern side of the OMC-2/3 region, and 2)
Irradiation of UV on the pre-existing filaments and dense molecular cloud
cores. Our wide-field and high-sensitivity imaging have provided the first
comprehensive view of the potential sites of triggered star formation in the
Orion-A GMC.Comment: 32 pages, 20 figures, accepted for publication in PAS
Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes
For spin-polarized junctions of ferromagnetically contacting multiple
conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon
nanotubes/FM junctions, we theoretically investigate spin-dependent transport
to elucidate the intrinsic relation between the number of paths and conduction,
and to enhance the magnetoresistance (MR) ratio. When many paths are randomly
located between the two FMs, electronic wave interference between the FMs
appears, and then the MR ratio increases with increasing number of paths.
Furthermore, at each number of paths, the MR ratio for carbon nanotubes becomes
larger than that for atomic wires, reflecting the characteristic shape of
points in contact with the FM.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.
Ferromagnetism in multi--band Hubbard models: From weak to strong Coulomb repulsion
We propose a new mechanism which can lead to ferromagnetism in Hubbard models
containing triangles with different on-site energies. It is based on an
effective Hamiltonian that we derive in the strong coupling limit. Considering
a one-dimensional realization of the model, we show that in the quarter-filled,
insulating case the ground-state is actually ferromagnetic in a very large
parameter range going from Tasaki's flat-band limit to the strong coupling
limit of the effective Hamiltonian. This result has been obtained using a
variety of analytical and numerical techniques. Finally, the same results are
shown to apply away from quarter-filling, in the metallic case.Comment: 12 pages, revtex, 12 figures,needs epsf and multicol style file
Very High Energy Gamma Rays from PSR1706-44
We have obtained evidence of gamma-ray emission above 1 TeV from PSR1706-44,
using a ground-based telescope of the atmospheric \v{C}erenkov imaging type
located near Woomera, South Australia. This object, a -ray source
discovered by the COS B satellite (2CG342-02), was identified with the radio
pulsar through the discovery of a 102 ms pulsed signal with the EGRET
instrument of the Compton Gamma Ray Observatory. The flux of the present
observation above a threshold of 1 TeV is 1 10
photons cm s, which is two orders of magnitude smaller than the
extrapolation from GeV energies. The analysis is not restricted to a search for
emission modulated with the 102 ms period, and the reported flux is for all
-rays from PSR1706-44, pulsed and unpulsed. The energy output in the
TeV region corresponds to about 10 of the spin down energy loss rate of
the neutron star.Comment: 13 pages, latex format (article), 2 figures include
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