Cosmological distance indicators

We review three distance measurement techniques beyond the local universe: (1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and (3) HI intensity mapping. We describe the principles and theory behind each method, the ingredients needed for measuring such distances, the current observational results, and future prospects. Time delays from strongly lensed quasars currently provide constraints on $H_0$ with < 4% uncertainty, and with 1% within reach from ongoing surveys and efforts. Recent exciting discoveries of strongly lensed supernovae hold great promise for time-delay cosmography. BAO features have been detected in redshift surveys up to z <~ 0.8 with galaxies and z ~ 2 with Ly-$\alpha$ forest, providing precise distance measurements and $H_0$ with < 2% uncertainty in flat $\Lambda$CDM. Future BAO surveys will probe the distance scale with percent-level precision. HI intensity mapping has great potential to map BAO distances at z ~ 0.8 and beyond with precisions of a few percent. The next years ahead will be exciting as various cosmological probes reach 1% uncertainty in determining $H_0$, to assess the current tension in $H_0$ measurements that could indicate new physics.Comment: Review article accepted for publication in Space Science Reviews (Springer), 45 pages, 10 figures. Chapter of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Ag

MODEL STUDIES OF FLOW AND MIXING IN THE PARTIALLY ENRICHED GAS-COOLED POWER REACTOR

A quarter-scale flow model, using air as a working fluid, was used to obtain design data for the PEGCPR program. A design for the core-support cylinder, to provide optimum mixing and core-flow distribution, was developed, following which experimentul studies of core-flow distribution, mixing of flow from the two inlets, flow patterns in plenum spaces, flow patterns in the thermal- shield-coolant passage, and pressure drops throughout the model were carried out. Results obtained in the model were then converted to values applicable to helium flow in the prototype. (auth

PWR CORE 2 MODEL STUDIES TO IMPROVE INLETPLENUM-CHAMBER MIXING

In the course of the PWR Core 2 study program, studies to improve mixing in the lower plenum were carried out using a quarter-scale air-flow model. By use of vanes to form a strong vortex in the lower plenum, excellent lower-plenum mixing was obtained with only slight increase in pressure drop. For the studies relating to a 9-ft core design, the model core was extended downward 4 1/2 in. below the Core I position. The flow baffle used for this configuration extended below the four inlets, with the result that considerable pressure loss occurred in the lower plenum. It was found that mixing could be greatly improved by use of deflectors to divert the inlet flow in a tangential direction. Data on lower- plenum mixing, core-flow distribution, thermal-shield-flow directions and velocities, flowbaffle orifice coefficients, and pressure losses were obtained for the 9-ft core configuration both with flow deflectors and without them. The flow deflectors greatly improved mixing at the expense of increased lowerplenum pressure loss. For the studies relating to a 7.5-ft core design, the core was extended downward 2 1/4 in. The flow baffle used for this core design extended to about the center line of the inlets, so that restriction of inlet flow was less than for the 9-ft core. Data for the basic configuration were obtained, following which many types of mixing devices were studied. Use of a vaned ring to produce a strong vortex in the lower plenum resulted in excellent mixing with only slight increase in pressure drop. A similar vaned ring was designed for the prototype by Westinghouse and incorporated in the quarter-scale model. Detailed studies of model performance proved this design satisfactory. (auth