LAMOST spectral survey——An overview

LAMOST （Large sky Area Multi-Object fiber Spectroscopic Telescope） is a Chinese national scientific research facility operated by National Astronomical Observatories, Chinese Academy of Sciences （NAOC）. After two years of commis- sioning beginning in 2009, the telescope, instruments, software systems and opera- tions are nearly ready to begin the main science survey. Through a spectral survey of millions of objects in much of the northern sky, LAMOST will enable research in a number of contemporary cutting edge topics in astrophysics, such as discovery of the first generation stars in the Galaxy, pinning down the formation and evolution history of galaxies - especially the Milky Way and its central massive black hole, and look- ing for signatures of the distribution of dark matter and possible sub-structures in the Milky Way halo. To maximize the scientific potential of the facility, wide national par- ticipation and international collaboration have been emphasized. The survey has two major components： the LAMOST ExtraGAlactic Survey （LEGAS） and the LAMOST Experiment for Galactic Understanding and Exploration （LEGUE）. Until LAMOST reaches its full capability, the LEGUE portion of the survey will use the available ob- serving time, starting in 2012. An overview of the LAMOST project and the survey that will be carried out in the next five to six years is presented in this paper. The sci- ence plan for the whole LEGUE survey, instrumental specifications, site conditions, and the descriptions of the current on-going pilot survey, including its footprints and target selection algorithm, will be presented as separate papers in this volume.

A revised rotation curve of the Milky Way with maser astrometry

We reconstruct the rotation curve of the Milky Way using the new trigono-metric parallax and proper motion data for masers in 43 high-mass star-forming re-gions obtained by VLBI, as well as the existing data from the literature, based on a new set of galactic constants （R0, -0） = （8.4 kpc, 254 km s^-1） measured by Reid et al. The revised rotation curve of the Milky Way is almost fiat or slightly rising in the region from about 6 to 15 kpc. The rotation velocities within 5 kpc of the Galactic center, as determined by VLBI, differ from those obtained by measurement of the HI-and CO-line tangent velocities. We fitted the revised rotation curve arising from three mass components： the bulge, disk and dark matter halo. The total mass of the Milky Way is found to be 2.3× 10^11 M⊙ （20 kpc）. This is about 10% larger than that from Sofue et al, and is comparable with the mass of M31, 3.4× 10^11 M⊙ （35 kpc）, given by Carignan et al. The limited accurate observational data, especially the VLBI data, do not permit a fully satisfactory fit to the rotation curve. The extensive par-allax and proper motion data that will be produced by the Bar and Spiral Structure Legacy Survey project in the next few years should lead to considerable progress in understanding the rotation curve and dark matter halo of the Milky Way.

Continuous-wave and Q-switched performance of an Yb:YAG/YAG composite thin disk ceramic laser pumped with 970-nm laser diode

Using front face-pumped compact active mirror laser （CAMIL） structure, we have demonstrated an Yb：YAG/YAG composite ceramic disk laser with pumping wavelength at 970 nm. The laser has been operated in both continuous-wave （CW） and Q-switching modes. Under CW operation, laser output power of 1.05 W with 2% transmission output coupler was achieved at the wavelength of 1031 nm. Q- switched laser output was gotten by using an acousto-optic Q-switch. The repetition rate ranged from 1 to 30 kHz and the pulse width varied from 166 to 700 ns.

Structural optimization of uniaxial symmetry non-circular bolt clearance hole on turbine disk

This study proposes a parameterized model of a uniaxial symmetry non-circular hole, to improve conventional circular bolt clearance holes on turbine disks. The profile of the model consists of eight smoothly connected arcs, the radiuses of which are determined by 5 design variables.By changing the design variables, the profile of the non-circular hole can be transformed to accommodate different load ratios, thereby improving the stress concentration of the area near the hole and that of the turbine disk. The uniaxial symmetry non-circular hole is optimized based on finite element method（FEM）, in which the maximum first principal stress is taken as the objective function. After optimization, the stress concentration is evidently relieved; the maximum first principal stress and the maximum von Mises stress on the critical area are reduced by 30.39% and 25.34%respectively, showing that the uniaxial symmetry non-circular hole is capable of reducing the stress level of bolt clearance holes on the turbine disk.