A Continuous 100-mK Helium-Light Cooling System for MUSCAT on the LMT

The MUSCAT instrument is a large-format camera planned for installation on the Large Millimeter Telescope (LMT) in 2018. MUSCAT requires continuous cooling of several large-volume stages to sub-Kelvin temperatures, with the focal plane cooled to 100 mK. Through the use of continuous sorption coolers and a miniature dilution refrigerator, the MUSCAT project can fulfil its cryogenic requirements at a fraction of the cost and space required for conventional dilution systems. Our design is a helium-light system, using a total of only 9 litres of helium-3 across several continuous cooling systems, cooling from 4 K to 100 mK. Here we describe the operation of both the continuous sorption and the miniature dilution refrigerator systems used in this system, along with the overall thermal design and budgeting of MUSCAT. MUSCAT will represent the first deployment of these new technologies in a science-grade instrument and will prove the concept as a viable option for future large-scale experiments such as CMB-S4.Comment: Presented at 17th International Workshop on Low-Temperature Detectors. Published in Journal of Low Temperature Physics, 201

Nuclear Officer Bonus & Incentive Pay (NOBIP) and Retention

NPS NRP Executive SummaryRetaining top-quality nuclear officers is critical to mission readiness. To facilitate officer retention, the Navy offers a bonus, the Nuclear Officer Continuation Bonus (COBO), to officers who have fulfilled the minimum service requirement (MSR). The Navy recently raised the amount of the bonus in the hope of increasing retention. It is mission-critical to understand how responsive retention rates have been to COBO, particularly in light of the recent changes. This study examines the efficacy of the most recent bonus policy for nuclear officers, NAVPOL 20241 and its immediate predecessor. Specifically, we used sponsor-provided data on 2,058 nuclear officers across seven year groups to assess the impact of the latest NAVPOL on nuclear officer retention relative to the immediately prior policy. Statistical analyses using survivorship modeling revealed that individual characteristics, such as the overall unemployment rate, marital status, presence of dependents, length of military tenure, and membership in certain racial/ethnic ­­groups are all positively and statistically significantly associated with nuclear officer retention. We recommend the Navy commission additional studies to obtain a deeper understanding of the non-monetary factors influencing nuclear officer retention, rather than a simple increase in the dollar amount of the COBO.N1 - Manpower, Personnel, Training & EducationThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

Nuclear Officer Bonus & Incentive Pay (NOBIP) and Retention

NPS NRP Project PosterRetaining top-quality nuclear officers is critical to mission readiness. To facilitate officer retention, the Navy offers a bonus, the Nuclear Officer Continuation Bonus (COBO), to officers who have fulfilled the minimum service requirement (MSR). The Navy recently raised the amount of the bonus in the hope of increasing retention. It is mission-critical to understand how responsive retention rates have been to COBO, particularly in light of the recent changes. This study examines the efficacy of the most recent bonus policy for nuclear officers, NAVPOL 20241 and its immediate predecessor. Specifically, we used sponsor-provided data on 2,058 nuclear officers across seven year groups to assess the impact of the latest NAVPOL on nuclear officer retention relative to the immediately prior policy. Statistical analyses using survivorship modeling revealed that individual characteristics, such as the overall unemployment rate, marital status, presence of dependents, length of military tenure, and membership in certain racial/ethnic ­­groups are all positively and statistically significantly associated with nuclear officer retention. We recommend the Navy commission additional studies to obtain a deeper understanding of the non-monetary factors influencing nuclear officer retention, rather than a simple increase in the dollar amount of the COBO.N1 - Manpower, Personnel, Training & EducationThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

On isotropic cylindrically symmetric stellar models

We attempt to match the most general cylindrically symmetric vacuum space-time with a Robertson-Walker interior. The matching conditions show that the interior must be dust filled and that the boundary must be comoving. Further, we show that the vacuum region must be polarized. Imposing the condition that there are no trapped cylinders on an initial time slice, we can apply a result of Thorne's and show that trapped cylinders never evolve. This results in a simplified line element which we prove to be incompatible with the dust interior. This result demonstrates the impossibility of the existence of an isotropic cylindrically symmetric star (or even a star which has a cylindrically symmetric portion). We investigate the problem from a different perspective by looking at the expansion scalars of invariant null geodesic congruences and, applying to the cylindrical case, the result that the product of the signs of the expansion scalars must be continuous across the boundary. The result may also be understood in relation to recent results about the impossibility of the static axially symmetric analogue of the Einstein-Straus model.Comment: 13 pages. To appear in Classical and Quantum Gravit

Pre-cooling a 3He/4He dilutor module with a sealed closed-cycle continuous cooler

A continuous closed cycle cooler to operate at a base temperature below 300 mK has been successfully designed and tested by Chase Research Cryogenics in collaboration with Cardiff University Astronomical Instrumentation Group. This compact, relatively low-cost unit has temperature and heat load capability of around 200 µW at 340 mK, and 400 µW at 450 mK. Here we discuss the suitability of this unit for precooling a miniature self-contained dilution module to produce a cryogen-free cooling platform capable of achieving a useful cooling power at temperatures of less than 100 mK

The Central Singularity in Spherical Collapse

The gravitational strength of the central singularity in spherically symmetric space-times is investigated. Necessary conditions for the singularity to be gravitationally weak are derived and it is shown that these are violated in a wide variety of circumstances. These conditions allow conclusions to be drawn about the nature of the singularity without having to integrate the geodesic equations. In particular, any geodesic with a non-zero amount of angular momentum which impinges on the singularity terminates in a strong curvature singularity.Comment: 17 pages; revised and corrected with improved result

A Characterisation of Strong Wave Tails in Curved Space-Times

A characterisation of when wave tails are strong is proposed. The existence of a curvature induced tail (i.e. a Green's function term whose support includes the interior of the light-cone) is commonly understood to cause backscattering of the field governed by the relevant wave equation. Strong tails are characterised as those for which the purely radiative part of the field is backscattered. With this definition, it is shown that electromagnetic waves in asymptotically flat space-times and fields governed by tail-free propagation have weak tails, but minimally coupled scalar fields in a cosmological scenario have strong tails.Comment: 17 pages, Revtex, to appear in Classical and Quantum Gravit

Molecular Genetic Influences on Normative and Problematic Alcohol Use in a Population-Based Sample of College Students

Background: Genetic factors impact alcohol use behaviors and these factors may become increasingly evident during emerging adulthood. Examination of the effects of individual variants as well as aggregate genetic variation can clarify mechanisms underlying risk. Methods: We conducted genome-wide association studies (GWAS) in an ethnically diverse sample of college students for three quantitative outcomes including typical monthly alcohol consumption, alcohol problems, and maximum number of drinks in 24 h. Heritability based on common genetic variants (h2SNP) was assessed. We also evaluated whether risk variants in aggregate were associated with alcohol use outcomes in an independent sample of young adults. Results: Two genome-wide significant markers were observed: rs11201929 in GRID1 for maximum drinks in 24 h, with supportive evidence across all ancestry groups; and rs73317305 in SAMD12 (alcohol problems), tested only in the African ancestry group. The h2SNP estimate was 0.19 (SE = 0.11) for consumption, and was non-significant for other outcomes. Genome-wide polygenic scores were significantly associated with alcohol outcomes in an independent sample. Conclusions: These results robustly identify genetic risk for alcohol use outcomes at the variant level and in aggregate. We confirm prior evidence that genetic variation in GRID1impacts alcohol use, and identify novel loci of interest for multiple alcohol outcomes in emerging adults. These findings indicate that genetic variation influencing normative and problematic alcohol use is, to some extent, convergent across ancestry groups. Studying college populations represents a promising avenue by which to obtain large, diverse samples for gene identification