We describe a new integrated optical spectroscopy facility for high-pressure research in materials research and mineral science located at the beamline BL01B of the Shanghai Synchrotron Radiation Facility. The system combines infrared synchrotron Fourier-Transform spectroscopy with broadband laser visible/near infrared and conventional laser Raman spectroscopy in one instrument. The system utilizes a custom-built microscope optics designed for a variety of diamond anvil cell experiments, which include low-temperature and ultrahigh pressure studies. We demonstrate the capabilities of the facility for studies of a variety of high-pressure phenomena such as phase and electronic transitions and chemical transformations.

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm (230 GHz) observations of the HD 32297 and HD 61005 debris disks, two of the most iconic debris disks because of their dramatic swept-back wings seen in scattered light images. These observations achieve sensitivities of 14 and 13 mu Jy beam(-1) for HD. 32297 and HD. 61005, respectively, and provide the highest resolution images of these two systems at millimeter wavelengths to date. By adopting a Markov Chain Monte Carlo modeling approach, we determine that both disks are best described by a two-component model consisting of a broad (Delta R/R > 0.4) planetesimal belt with a rising surface density gradient and a steeply falling outer halo aligned with the scattered light disk. The inner and outer edges of the planetesimal belt are located at 78.5 +/- 8.1 au and 122 +/- 3 au for HD 32297, and 41.9 +/- 0.9 au and 67.0 +/- 0.5 au for HD 61005. The halos extend to 440 +/- 32 au and 188 +/- 8 au, respectively. We also detect (CO)-C-12 J = 2-1 gas emission from HD 32297 co-located with the dust continuum. These new ALMA images provide observational evidence that larger, millimeter-sized grains may also populate the extended halos of these two disks previously thought to only be composed of small, micron-sized grains. We discuss the implications of these results for potential shaping and sculpting mechanisms of asymmetric debris disks.

The phase diagrams of Na2CO3 and K2CO3 have been determined with multianvil (MA) and diamond anvil cell (DAC) techniques. In MA experiments with heating, gamma-Na2CO3 is stable up to 12 GPa and above this pressure transforms to P6(3)/mcm-phase. At 26 GPa, Na2CO3-P6(3)/mcm transforms to the new phase with a diffraction pattern similar to that of the theoretically predicted Na2CO3-P21/m. On cold compression in DAC experiments, gamma-Na2CO3 is stable up to the maximum pressure reached of 25 GPa. K2CO3 shows a more complex sequence of phase transitions. Unlike gamma-Na2CO3, gamma-K2CO3 has a narrow stability field. At 3 GPa, K2CO3 presents in the form of the new phase, called K2CO3-III, which transforms into another new phase, K2CO3-IV, above 9 GPa. In the pressure range of 9-15 GPa, another new phase or the mixture of phases III and IV is observed. The diffraction pattern of K2CO3-IV has similarities with that of the theoretically predicted K2CO3-P2(1)/m and most of the diffraction peaks can be indexed with this structure. Water has a dramatic effect on the phase transitions of K2CO3. Reconstruction of the diffraction pattern of gamma-K2CO3 is observed at pressures of 0.5-3.1 GPa if the DAC is loaded on the air.

The light scattered from dust grains in debris disks is typically modeled as compact spheres using the Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work we examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross-sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross-sections are necessary to calculate the beta-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.

Alternative technologies are required in order to meet a worldwide demand for clean non-polluting energy sources. Thermoelectric generators, which generate electricity from heat in a compact and reliable manner, are potential devices for waste heat recovery. However, thermoelectric performance, as encapsulated by the figure of merit ZT, has remained at around 1.0 at room temperature, which has limited practical applications. Here, we study the effects of pressure on ZT in Cr-doped PbSe, which has a maximum ZT of less than 1.0 at a temperature of about 700 K. By applying external pressure using a diamond anvil cell, we obtained a room-temperature ZT value of about 1.7. From thermoelectric, magnetoresistance and Raman measurements, as well as density functional theory calculations, a pressure-driven topological phase transition is found to enable this enhancement. Experiments also support the appearance of a topological crystalline insulator after the transition. These findings point to the possibility of using compression to increase not just ZT in existing thermoelectric materials, but also the possibility of realizing topological crystalline insulators.

The small class of known stars with unusually warm, dusty debris disks is a key sample to probe in order to understand cascade models and the extreme collisions that likely lead to the final configurations of planetary systems. Because of its extreme dustiness and small radius, the disk of BD +20 307 has a short predicted collision time and is therefore an interesting target in which to look for changes in dust quantity and composition over time. To compare with previous ground and Spitzer Space Telescope data, Stratospheric Observatory for Infrared Astronomy (SOFIA) photometry and spectroscopy were obtained. The system's 8.8-12.5 mu m infrared emission increased by 10 +/- 2% over nine years between the SOFIA and earlier Spitzer measurements. In addition to an overall increase in infrared excess, there is a suggestion of a greater increase in flux at shorter wavelengths (less than 10.6 mu m) compared to longer wavelengths (greater than 10.6 mu m). Steady-state collisional cascade models cannot explain the increase in BD +20 307's disk flux over such short timescales. A catastrophic collision between planetary-scale bodies is still the most likely origin for the system's extreme dust; however, the cause for its recent variation requires further investigation.

We performed Raman and infrared (IR) spectroscopy measurements of hydrogen at 295 K up to 280 GPa at an IR synchrotron facility of the Shanghai Synchrotron Radiation Facility (SSRF). To reach the highest pressure, hydrogen was loaded into toroidal diamond anvils with 30-mu m central culet. The intermolecular coupling has been determined by concomitant measurements of the IR and Raman vibron modes. In phase IV, we find that the intermolecular coupling is much stronger in the graphenelike layer (G layer) of elongated molecules compared to the Br2-like layer (B layer) of shortened molecules and it increases with pressure much faster in the G layer compared to the B layer. These heterogeneous lattice dynamical properties are unique features of highly fluxional hydrogen phase IV.

The fate of subducted carbonates in the lower mantle and at the core-mantle boundary was modelled via experiments in the MgCO3-Fe-0 system at 70-150 GPa and 800-2600 K in a laser-heated diamond anvil cell. Using in situ synchrotron X-ray diffraction and ex situ transmission electron microscopy we show that the reduction of Mg-carbonate can be exemplified by: 6MgCO(3) + 19Fe = 8FeO +10(Mg0.6Fe0.4)O + Fe7C3 + 3C. The presented results suggest that the interaction of carbonates with Fe-0 or Fe-0-bearing rocks can produce Fe-carbide and diamond, which can accumulate in the D '' region, depending on its carbon to Fe ratio. Due to the sluggish kinetics of the transformation, diamond can remain metastable at the core-mantle boundary (CMB) unless it is in a direct contact with Fe-metal. In addition, it can be remobilized by redox melting accompanying the generation of mantle plumes. (C) 2019, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Young, low-mass stars in the solar neighborhood are vital for completing the mass function for nearby, young coeval groups, establishing a more complete census for evolutionary studies, and providing targets for direct-imaging exoplanet and/or disk studies. We present properties derived from high-resolution optical spectra for 336 candidate young nearby, low-mass stars. These include measurements of radial velocities and age diagnostics such as H alpha and Li lambda 6707 equivalent widths. Combining our radial velocities with astrometry from Gaia DR2, we provide full 3D kinematics for the entire sample. We combine the measured spectroscopic youth information with additional age diagnostics (e.g., X-ray and UV fluxes, color-magnitude diagram positions) and kinematics to evaluate potential membership in nearby, young moving groups and associations. We identify 77 objects in our sample as bona fide members of 10 different moving groups, 14 of which are completely new members or have had their group membership reassigned. We also reject 44 previously proposed candidate moving group members. Furthermore, we have newly identified or confirmed the youth of numerous additional stars that do not belong to any currently known group and find 69 comoving systems using Gaia DR2 astrometry. We also find evidence that the Carina association is younger than previously thought, with an age similar to the beta Pictoris moving group (similar to 22 Myr).