Superfluid liquid helium control for the primordial inflation polarization explorer balloon payload.

The Primordial Inflation Polarization Explorer (PIPER) is a stratospheric balloon payload to measure the polarization of the cosmic microwave background. Twin telescopes mounted within an open-aperture bucket dewar couple the sky to bolometric detector arrays. We reduce detector loading and photon noise by cooling the entire optical chain to 1.7 K or colder. A set of fountain-effect pumps sprays superfluid liquid helium onto each optical surface, producing helium flows of 50-100 cm3 s-1 at heights up to 200 cm above the liquid level. We describe the fountain-effect pumps and the cryogenic performance of the PIPER payload during two flights in 2017 and 2019.

The balloon-borne cryogenic telescope testbed mission: Bulk cryogen transfer at 40 km altitude.

The balloon-borne cryogenic telescope testbed is a stratospheric balloon payload intended to develop technology for a future cryogenic suborbital observatory. A series of flights are intended to establish ultra-light dewar performance and open-aperture observing techniques for large (3 m-5 m diameter) cryogenic telescopes at infrared wavelengths. An initial flight in 2019 demonstrated bulk transfer of liquid nitrogen and liquid helium at stratospheric altitudes. An 827 kg payload carried 14 l of liquid nitrogen (LN2) and 268 l of liquid helium (LHe) in pressurized storage dewars to an altitude of 39.7 km. Once at float altitude, liquid nitrogen transfer cooled a separate, unpressurized bucket dewar to a temperature of 65 K, followed by the transfer of 32 l of liquid helium from the storage dewar into the bucket dewar. Calorimetric tests measured the total heat leak to the LHe bath within the bucket dewar. A subsequent flight will replace the receiving bucket dewar with an ultra-light dewar of similar size to compare the performance of an ultra-light design dewar to that of conventional superinsulated dewars.

Sub-Kelvin cooling for two kilopixel bolometer arrays in the PIPER receiver.

The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne telescope mission to search for inflationary gravitational waves from the early universe. PIPER employs two 32 × 40 arrays of superconducting transition-edge sensors, which operate at 100 mK. An open bucket Dewar of liquid helium maintains the receiver and telescope optics at 1.7 K. We describe the thermal design of the receiver and sub-Kelvin cooling with a continuous adiabatic demagnetization refrigerator (CADR). The CADR operates between 70 and 130 mK and provides ≈10 µW cooling power at 100 mK, nearly five times the loading of the two detector assemblies. We describe electronics and software to robustly control the CADR, overall CADR performance in flightlike integrated receiver testing, and practical considerations for implementation in the balloon float environment.

Variable-delay polarization modulators for cryogenic millimeter-wave applications.

We describe the design, construction, and initial validation of the variable-delay polarization modulator (VPM) designed for the PIPER cosmic microwave background polarimeter. The VPM modulates between linear and circular polarization by introducing a variable phase delay between orthogonal linear polarizations. Each VPM has a diameter of 39 cm and is engineered to operate in a cryogenic environment (1.5 K). We describe the mechanical design and performance of the kinematic double-blade flexure and drive mechanism along with the construction of the high precision wire grid polarizers.

[Results of regular dental care of mental and physical handicapped patients]. / Ergebnisse einer regelmässigen zahnärztlichen Betreuung geistig und körperlich behinderter Patienten.

The results of the regular dental care of 192 mental and physical handicapped patients were analysed in a 5-year-period. The care system in which the prevention, the therapy in narcosis and the annual control are combined is very effective on a long-term basis. The handicapped patients had a lower prevalence of caries, a higher percentage of filled teeth and less extractions compared to a group of handicapped patients without continuous dental care.

[Indications for restorative treatment with posterior composite resins]. / Zur Indikation zahnfarbener plastischer Füllungsmaterialien fur Seintenzahndefekte.

The authors discuss the advantages and disadvantages of the restorative treatment with posterior composite resins. They warn against the uncritical application of such materials and formulate directions for their use.