Observation of the morphology of thin films of solid helium deposited from the fluid onto sapphire

Thin layers of solid helium were grown on sapphire single-crystal substrates at pressures from about 500 bar to 9 kbar. Grain boundaries can be observed in these layer crystals. The morphology of the grains depends on the crystal modification. In the hcp phase (below about 1.13 kbar) a system of parallel bands is observed, probably due to slip and twinning. In the fcc phase (above 1.13 kbar) a polygonal structure similar to a helium froth is found. Melting of this froth in the fcc phase shows grain boundary melting; fluid helium is wetting the fcc grains. Grain boundaries in the hcp phase are, in contrast, not wetted by fluid helium. Near the triple point at 1.13 kbar and 15.0 K one can deposit both crystalline phases side by side. In such structures, the transition fcc hcp⁴He can be observed during isothermal holding. The transition proceeds by the parallel motion of low-energy grain boundaries.     

Diagonal horn integrated with micromachined waveguide forsubmillimetre applications

The feasibility of coupling silicon micromachines rectangular waveguide to a modified diagonal horn antenna using a model at 110 GHz is demonstrated. The antenna patterns obtained are similar to those obtained with a standard diagonal horn. A method of reducing the on-axis cross polarization response of diagonal horns is also presented     

Design and results for a 345 GHz sis focal plane array using planar technology

We describe a focal plane array using antenna elements and SIS junctions photo-etched on a quartz substrate. The etched antenna is of a new strip-line type in which a two-dimensional corrugated horn is phase-corrected with a strip-line lens. Good beam efficiency is indicated by the measured antenna patterns. A DSB receiver temperature of 225 K was obtained with a number of imperfections still present.     

A study of bubble nucleation in tungsten using thermal desorption spectrometry: Clusters of 2 to 100 helium atoms

The attachment of helium to annealed inert gas impurity atom traps in tungsten has been measured by thermal desorption spectrometry. For the first helium atom trapped, all five impurities (the substitutional He atom HeV, Ne, Ar, Kr and Xe) were found to have approximately the same trapping radius (≈2.8 Å). The binding energy, however, decreased monotonically with increasing impurity mass from 3.1 eV for HeV to 1.2 eV for Xe. All were found able to trap at least i = 100 helium atoms with no evidence of saturation. On the contrary, for i > 10 the trapping characteristics, essentially the same for all five traps, were a gradual increase in binding energy from ~2.2 eV at i = 10 to ~4.5 eVati = 100, and an increase in the average trapping radius to ~12.5 Å when the average number of trapped He atoms per trap was 62. The results thus describe the first stages of helium bubble formation in tungsten at room temperature.     

Integrated Josephson effect suppression electromagnets for sis receivers

We describe a method for integrating a Josephson current suppression electromagnet along with a superconductor-insulator-superconductor (SIS) mixer. In this technique, circuitry already in place for matching the SIS mixing device with the antenna is used as the conductor for an electromagnet. Reduced cost and size are among the advantages achieved by elimination of external magnets.     

Synthesis review on groundwater discharge to surface water in the Great Lakes Basin

Groundwater in the Great Lakes Basin (GLB) serves as a reservoir of approximately 4000 to 5500 km³ of water and is a significant source of water to the Great Lakes. Indirect groundwater inflow from tributaries of the Great Lakes may account for 5–25% of the total water inflow to the Great Lakes and in Lake Michigan it is estimated that groundwater directly contributes 2–2.5% of the total water inflow. Despite these estimates, there is great uncertainty with respect to the impact of groundwater on surface water in the GLB. In terms of water quantity, groundwater discharge is spatially and temporally variable from the reach to the basin scale. Reach scale preferential flow pathways in the sub-surface play an important role in delivering groundwater to surface water bodies, however their identification is difficult a priori with existing data and their impact at watershed to basin scale is unknown. This variability also results in difficulty determining the location and contribution of groundwater to both point and non-point source surface water contamination. With increasing human population in the GLB and the hydrological changes brought on by continued human development and climate change, sound management of water resources will require a better understanding of groundwater surface–water interactions as heterogeneous phenomena both spatially and temporally. This review provides a summary of the scientific knowledge and gaps on groundwater–surface water interactions in the GLB, along with a discussion on future research directions.