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 $T_b = 7.5\times 10^5$ 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 12^{12}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 $^{12}$CO ($J$=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 $^{12}$CO ($J$=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} $\times$ \timeform{2.D3}, corresponding to 12 pc $\times$ 17 pc) and the highest-sensitivity ($\sim$9 mJy beam$^{-1}$) 1.1 mm dust-continuum imaging of the Orion-A GMC with an effective spatial resolution of $\sim$ 40\arcsec. The $^{12}$CO ($J$=1-0) image was taken over the northern \timeform{1D.2} \times\timeform{1D.2} (corresponding 9 pc $\times$ 9 pc) area with a sensitivity of 0.93 K in $T_{\rm MB}$, a velocity resolution of 1.0 km s$^{-1}$, and an effective spatial resolution of 21\arcsec. With these data, together with the MSX 8 $\mu$m, Spitzer 24 $\mu$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 $\gamma$-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 $\bf \sim$ 1 $\cdot$ 10$^{-11}$ photons cm$^{-2}$ s$^{-1}$, 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 $\gamma$-rays from PSR1706-44, pulsed and unpulsed. The energy output in the TeV region corresponds to about 10$^{-3}$ of the spin down energy loss rate of the neutron star.Comment: 13 pages, latex format (article), 2 figures include