Room-temperature continuous-wave operation of large-area (120 ,m X 980 ,um) GaAs/AlGaAs graded-refractiveindex separate-confinement heterostructure lasers on (100) Si substrates has been obtained. Minimum threshold- as a test of material quality.14 Dislocations, strain, and other defects present in the material, however, have kept the threshold-current densities high and limited the measurements to pulsed conditions. In this Letter we present results on extremely lowthreshold current lasers and the first report to our knowledge of continuous wave (cw) operation of a GaAs/AlGaAs/Si injection laser at room temperature. The epitaxial structures were grown by molecularbeam epitaxy (MBE) on (100) Si tilted by 4° toward (110). The substrate cleaning procedure and growth conditions used were similar to those of Ref. 5. The graded-refractive-index separate-confinement heterostructure laser consisted of a 7-nm quantum-well, 350-nm parabolic graded region and a 1.5-,um cladding AlGaAs layer on each side of the confining structure.

The structures of the neutron-rich 69,71,73 Co isotopes were investigated via (p, 2p) knockout reactions at the Radioactive Isotope Beam Factory, RIKEN. Isotopes of interest were studied using the DALI2 γ-ray detector array combined with the MINOS target and tracker system. Level schemes were reconstructed using the γ-γ coincidence technique, with tentative spin-parity assignments based on the measured inclusive and exclusive cross sections. Comparison with shell-model calculations using the Lenzi-Nowacki-Poves-Sieja LNPS and PFSDG-U interactions suggests coexistence of spherical and deformed shapes at low excitation energies in the 69,71,73 Co isotopes. The distorted-wave impulse approximation (DWIA) framework was used to calculate the single-particle cross sections. These values were compared with the experimental findings.

We have measured the proper motion of magnetic elements on the quiet Sun by means of local correlation tracking. The existence of a pattern in the intranetwork (IN) flow is confirmed. This velocity field is consistent with the direct Doppler measurement of the horizontal component of the supergranular velocity field. The IN elements generally move toward the network boundaries. By tracking test points we confirm that the magnetic elements converge in areas corresponding to the magnetic network. But because the IN elements are of random polarity, they cannot contribute to the growth or maintenance of the magnetic network.By calculating the cross correlation between the magnetogram and Dopplergram, we confirm that the supergranule boundaries and the magnetic network are roughly correlated.

Parthenogenetic embryonic stem (pES) cells are pluripotent stem cells derived from artificially activated oocytes without embryo destruction, thus eliciting less ethic concerns, and have been demonstrated promising for autologous stem cell therapy. However, pES cells could carry inappropriate imprinting such as relatively high expression of H19, a paternal imprinted gene, and may negatively influence their lineage differentiation. We show that knockdown of H19 by shRNA in mouse pES cells does not alter self-renewal and expression of genes associated with pluripotency. We find that down-regulation of H19 promotes differentiation of pES cells to epidermis. In addition, H19 depletion also facilitates differentiation of pES cells to cardiomyocytes and strong heart-like beating. Our data support the notion that reduction of H19 improves pES cell differentiation in the lineages of ectoderm and mesoderm, and provide further evidence suggesting that defective imprinting can be manipulated to allow potential application of pES cells for stem cell therapy.

No abstract