Broadband, millimeter-wave antireflection coatings for large-format, cryogenic aluminum oxide optics.

We present two prescriptions for broadband ($ {\sim} 77 - 252\;{\rm GHz} $), millimeter-wave antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide optics: one for large-format (700 mm diameter) planar and plano-convex elements, the other for densely packed arrays of quasi-optical elements-in our case, 5 mm diameter half-spheres (called "lenslets"). The coatings comprise three layers of commercially available, polytetrafluoroethylene-based, dielectric sheet material. The lenslet coating is molded to fit the 150 mm diameter arrays directly, while the large-diameter lenses are coated using a tiled approach. We review the fabrication processes for both prescriptions, then discuss laboratory measurements of their transmittance and reflectance. In addition, we present the inferred refractive indices and loss tangents for the coating materials and the aluminum oxide substrate. We find that at 150 GHz and 300 K the large-format coating sample achieves $ (97 \pm 2)\% $ transmittance, and the lenslet coating sample achieves $ (94 \pm 3)\% $ transmittance.

Calorimetric Observation of Single He 2 ∗ Excimers in a 100-mK He Bath.

We report the first calorimetric detection of individual He 2 ∗ excimers within a bath of superfluid 4 He . The detector used in this work is a single superconducting titanium transition edge sensor (TES) with an energy resolution of ∼ 1 eV , immersed directly in the helium bath. He 2 ∗ excimers are produced in the surrounding bath using an external gamma-ray source. These excimers exist either as short-lived singlet or long-lived triplet states. We demonstrate detection (and discrimination) of both states: In the singlet case the calorimeter records the absorption of a prompt ≈ 15 eV photon, and in the triplet case the calorimeter records a direct interaction of the molecule with the TES surface, which deposits a distinct fraction of the ≈ 15 eV , released upon decay, into the surface. We also briefly discuss the detector fabrication and characterization.

Poland's migration problems: a post-communist legacy.

PIP: "Poland's geographical location and the fall of communism has turned the country into a significant area for would-be migrants. This has changed the once predominant character of Poland as a ¿sending' migrant country into a ¿sending' and 'receiving' one. The extra burden of additional temporary or permanent migrants from neighboring East and Central European states is, together with the expanding number of asylum seekers, placing further strains on the country's economy. It also has changed the demographic structure of the nation-state as well as the social and economic (trade) structure and traffic patterns." (EXCERPT)^ieng

Ethnicity as a cause of migration in Eastern Europe.

"Migration within and from Eastern Europe [including Yugoslavia] has recently risen as a topic of significance on the European political agenda. One aspect of this complex migration matrix relates to ethnic unrest. This paper examines the scale and spatial ramifications of this movement.... An attempt is made to divide the ethnic quilt of Eastern Europe into those countries with few such problems and those with many. It is possible then to define areas of active migration (hot spots) from those of potential migration ([flammable] spots) based on predictions from the current situation."

Cervical spine strength after facet injury and spine plate application.

Although metallic plates are used for cervical spine stabilization, few biomechanical studies have been done to evaluate their efficiency. A previous study indicated that one half of the facet joint may be destroyed before compromise in strength occurs. Isolated motion segments in which one half of the facet joint was resected bilaterally were used. A two-hole Roy-Camille plate was attached bilaterally with 3.5-mm-diameter, 16-mm-long screws and the construct loaded in shear. Failure occurred at 415.6 N by fracture through the screw holes of the damaged joint, compared to a failure load of 699.6 N in specimens without screws and plates but in which 75% of the joint had been destroyed. Results were significant at the 95% confidence level. A second group of specimens using C2-3-4 and C5-6-7 was tested after 50% facet resection and application of a three-segment plate. Failure again occurred by fracture through the screw hole at the damaged joint. We conclude that, if significant facet destruction is present, screw holes for plate application further weakens the bone. The desired biomechanical stability may not be present.