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  • 1
    ISSN: 1573-6857
    Keywords: cessation of reproduction ; genetics of longevity ; heritability ; maximum life span ; mice ; 4-way-cross
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We found high narrow-sense heritability of life span based on the regression of offspring on average parental (midparent) life spans. In two mouse populations prepared using the 4-way-cross design, mean ± SE heritabilities were 62 ± 11% (P ≤ 0.001) and 44 ± 15% (P ≤ 0.01). To reflect inherited rates of aging, rather than resistance to early disease, data from the first 25% to die were deleted, so that only about 40% of families were used for offspring-midparent regressions. Heritabilities still remained high, 38% and 55%, for the same two populations, respectively. Populations studied in two other experiments did not show nearly as high heritabilities; in one case probably due to environmental stress, and in the other probably because the strains used did not have sufficient additive variance in genes regulating longevity. Significant heritabilities occurred only when a wild derived inbred strain was included in the 4-way cross. The age when a female ceased to reproduce appeared to be related to the life spans of her offspring, but only weakly, not approaching significance for any individual experiment. The age when a female became infertile was related to her life span, but the relationship disappeared when short-lived mice were excluded from the analysis. Our findings indicate that, in sufficiently diverse mouse populations, selection for increased longevity should be possible and that the direct selection for parental life span will be a more efficient strategy than selection for female reproductive life span.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9559
    Keywords: SIS receiver ; twin-slot planar antenna ; NbTiN superconductor ; bandgap energy ; AlN tunnel barrier ; RF loss ; cooled optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have developed a niobium titanium nitride (NbTiN) based superconductor-insulator-superconductor (SIS) receiver to cover the 350 micron atmospheric window. This frequency band lies entirely above the energy gap of niobium (700 GHz), a commonly used SIS superconductor. The instrument uses an open structure twin-slot SIS mixer that consists of two Nb/AlN/NbTiN tunnel junctions, NbTiN thin-film microstrip tuning elements, and a NbTiN ground plane. The optical configuration is very similar to the 850 GHz waveguide receiver that was installed at the Caltech Submillimeter Observatory (CSO) in 1997. To minimize front-end loss, we employed reflecting optics and a cooled beamsplitter at 4 K. The instrument has an uncorrected receiver noise temperature of 205K DSB at 800 GHz and 410K DSB at 900 GHz. The degradation in receiver sensitivity with frequency is primarily due to an increase in the mixer conversion loss, which is attributed to the mismatch between the SIS junction and the twin-slot antenna impedance. The overall system performance has been confirmed through its use at the telescope to detect a wealth of new spectroscopic lines.
    Type of Medium: Electronic Resource
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