VLT observations of the highly ionized nebula around Brey2

We present the first high resolution HeII 4686 images of the high excitation nebula around the WR star Brey 2 in the LMC. This nebula presents a striking morphology: a small arc-like feature some 3.6pc in radius is particularly prominent in the HeII 4686 line. We further discover a previously unknown faint HeII emission that extends over an area of 22*17 pc^2. An even fainter HeII emission is apparently associated with the interstellar bubble blown by the progenitor of Brey2. The total HeII flux corresponds to an ionizing flux of 4*10^{47} photons/s. Halpha, [OIII], and HeI 5876 images and long-slit spectra are also examined in this letter, enabling us to investigate the detailed physical properties at various locations of the nebula.Comment: 4 pages, 3 figures (2 in jpg), accepted by A&A Letters, also available from http://vela.astro.ulg.ac.be/Preprints/P80/index.htm

Solidification mechanism of highly undercooled metal alloys

Experiments were conducted on metal droplet undercooling, using Sn-25wt%Pb and Ni-34wt%Sn alloys. To achieve the high degree of undercooling, emulsification treatments were employed. Results show the fraction of supersaturated primary phase is a function of the amount of undercooling, as is the fineness of the structures. The solidification behavior of the tin-lead droplets during recalescence was analyzed using three different hypotheses; (1) solid forming throughout recalescence is of the maximum thermodynamically stable composition; (2) partitionless solidification below the T sub o temperature, and solid forming thereafter is of the maximum thermodynamically stable composition; and (3) partitionless solidification below the T sub o temperature with solid forming thereafter that is of the maximum thermodynamically metastable composition that is possible. The T sub o temperature is calculated from the equal molar free energies of the liquid solid using the regular solution approximation

DC Spin Current Generation in a Rashba-type Quantum Channel

We propose and demonstrate theoretically that resonant inelastic scattering (RIS) can play an important role in dc spin current generation. The RIS makes it possible to generate dc spin current via a simple gate configuration: a single finger-gate that locates atop and orients transversely to a quantum channel in the presence of Rashba spin-orbit interaction. The ac biased finger-gate gives rise to a time-variation in the Rashba coupling parameter, which causes spin-resolved RIS, and subsequently contributes to the dc spin current. The spin current depends on both the static and the dynamic parts in the Rashba coupling parameter, $\alpha_0$ and $\alpha_1$, respectively, and is proportional to $\alpha_0 \alpha_1^2$. The proposed gate configuration has the added advantage that no dc charge current is generated. Our study also shows that the spin current generation can be enhanced significantly in a double finger-gate configuration.Comment: 4 pages,4 figure

Neutron scattering study of novel magnetic order in Na0.5CoO2

We report polarized and unpolarized neutron scattering measurements of the magnetic order in single crystals of Na0.5CoO2. Our data indicate that below T_N=88 K the spins form a novel antiferromagnetic pattern within the CoO2 planes, consisting of alternating rows of ordered and non-ordered Co ions. The domains of magnetic order are closely coupled to the domains of Na ion order, consistent with such a two-fold symmetric spin arrangement. Magnetoresistance and anisotropic susceptibility measurements further support this model for the electronic ground state.Comment: 4 pages, 4 figure

A Morphological Diagnostic for Dynamical Evolution of Wolf-Rayet Bubbles

We have observed H-alpha and [OIII] emission from eight of the most well defined Wolf-Rayet ring nebulae in the Galaxy. We find that in many cases the outermost edge of the [OIII] emission leads the H-alpha emission. We suggest that these offsets, when present, are due to the shock from the Wolf-Rayet bubble expanding into the circumstellar envelope. Thus, the details of the WR bubble morphology at H-alpha and [OIII] can then be used to better understand the physical condition and evolutionary stage of the nebulae around Wolf-Rayet stars, as well as place constraints on the nature of the stellar progenitor and its mass loss history.Comment: 11 pages, LaTex, 8 figures, accepted for publication in AJ, November 200