A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction

We describe the equipment, observational method and reduction procedure of an absolutely calibrated radio continuum survey of the South Celestial Hemisphere at a frequency of 1420 MHz. These observations cover the area 0h < R.A. < 24h for declinations less than -10 degree. The sensitivity is about 50 mK T_B (full beam brightness) and the angular resolution (HPBW) is 35.4', which matches the existing northern sky survey at the same frequency.Comment: 9 pages with 9 figures, A&A, in pres

Observation of magnetism in Au thin films

Direct magnetization measurements of thin gold films are presented. These measurements integrate the signal from the thin film under study and the magnetic contribution of the film's interface with the substrate. The diamagnetic contribution to the signal from the bulk substrate is of the same order as the noise level. we find that thin gold films can exhibit positive magnetization. The character of their magnetic behavior is strongly substrate dependent.Comment: 9 pages, 4 figure

Spectral Index of the Diffuse Radio Background Measured From 100 to 200 MHz

The mean absolute brightness temperature of the diffuse radio background was measured as a function of frequency in a continuous band between 100 and 200 MHz over an effective solid angle of ~pi str at high Galactic latitude. A spectral brightness temperature index of beta = 2.5 +/- 0.1 (alpha_s = 0.5) was derived from the observations, where the error limits are 3-sigma and include estimates of the instrumental systematics. Zenith drift scans with central declinations of -26.5 degrees and spanning right ascensions 0 to 10 hours yielded little variation in the mean spectral index. The mean absolute brightness temperature at 150 MHz was found to reach a minimum of T = 237 +/- 10 K at a right ascension of 2.5 hours. Combining these measurements with those of Haslam et al. 1982 yields a spectral index of beta = 2.52 +/- 0.04 between 150 and 408 MHz.Comment: 8 pages including 7 figures and 4 tables. Accepted by A

HI ``Tails'' from Cometary Globules in IC1396

IC 1396 is a relatively nearby (750 pc), large (>2 deg), HII region ionized by a single O6.5V star and containing bright-rimmed cometary globules. We have made the first arcmin resolution images of atomic hydrogen toward IC 1396, and have found remarkable ``tail''-like structures associated with some of the globules and extending up to 6.5 pc radially away from the central ionizing star. These HI ``tails'' may be material which has been ablated from the globule through ionization and/or photodissociation and then accelerated away from the globule by the stellar wind, but which has since drifted into the ``shadow'' of the globules. This report presents the first results of the Galactic Plane Survey Project recently begun by the Dominion Radio Astrophysical Observatory.Comment: 11 pages, 5 postscript figures, uses aaspp4.sty macros, submitted in uuencoded gzipped tar format, accepted for publication in Astrophysical Journal Letters, colour figures available at http://www.drao.nrc.ca/~schieven/news_sep95/ic1396.htm

Exciton binding energies in carbon nanotubes from two-photon photoluminescence

One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.Comment: 5 pages, 4 figure

A New System of Parallel Isolated Nonthermal Filaments Near the Galactic Center: Evidence for a Local Magnetic Field Gradient

We report the discovery of a system of isolated nonthermal filaments approximately 0.5 deg. northwest (75 pc in projection) of Sgr A. Unlike other isolated nonthermal filaments which show subfilamentation, braiding of subfilaments, and flaring at their ends, these filaments are simple linear structures and more closely resemble the parallel bundled filaments in the Galactic center radio arc. However, the most unusual feature of these filaments is that the 20/90 cm spectral index uniformly decreases as a function of length, in contrast to all other nonthermal filaments in the Galactic center. This spectral gradient may not be due to simple particle aging but could be explained by a curved electron energy spectrum embedded in a diverging magnetic field. If so, the scale of the magnetic gradient is not consistent with a large scale magnetic field centered on Sgr A* suggesting that this filament system is tracing a local magnetic field.Comment: 10 pages, AASTeX 5.01 LaTeX2e; 7 figures in 9 PostScript files; scheduled for publication in the 2001 December 10, v. 563 issue of Ap

One-dimensional pinning behavior in Co-doped BaFe2As2 thin films

Angle-resolved transport measurements revealed that planar defects dominate flux pinning in the investigated Co-doped BaFe2As2 thin film. For any given field and temperature, the critical current depends only on the angle between the crystallographic c-axis and the applied magnetic field but not on the angle between the current and the field. The critical current is therefore limited only by the in-plane component of the Lorentz force but independent of the out-of-plane component, which is entirely balanced by the pinning force exerted by the planar defects. This one-dimensional pinning behavior shows similarities and differences to intrinsic pinning in layered superconductors.Comment: 8 pages, 6 figure

Scaling of the conductance in gold nanotubes

A new form of gold nanobridges has been recently observed in ultrahigh-vacuum experiments, where the gold atoms rearrange to build helical nanotubes, akin in some respects to carbon nanotubes. The good reproducibility of these wires and their unexpected stability will allow for conductance measurements and make them promising candidates for future applications . We present here a study of the transport properties of these nanotubes in order to understand the role of chirality and of the different orbitals in quantum transport observables. The conductance per atomic row shows a light decreasing trend as the diameter grows, which is also shown through an analytical formula based on a one-orbital model.Comment: 5 pages, 6 figure