13,223 research outputs found
Study to define and verify the personal oral hygiene requirements for extended manned space flight Annual report, 1 Jul. 1968 - 30 Jun. 1969
Astronaut oral hygiene requirements for extended manned space fligh
Preliminary study of minimum performance approaches to automated Mars sample return missions Final report, 19 Oct. - 20 Nov. 1970
Alternative mission/system approaches to automated Mars surface sample return based on utilization of Titan 3 or Saturn Intermediate-20 launch vehicle
FINDCHIRP: an algorithm for detection of gravitational waves from inspiraling compact binaries
Matched-filter searches for gravitational waves from coalescing compact
binaries by the LIGO Scientific Collaboration use the FINDCHIRP algorithm: an
implementation of the optimal filter with innovations to account for unknown
signal parameters and to improve performance on detector data that has
nonstationary and non-Gaussian artifacts. We provide details on the FINDCHIRP
algorithm as used in the search for subsolar mass binaries, binary neutron
stars, neutron star-black hole binaries, and binary black holes.Comment: 19 pages, 1 figure, journal version with Creative Commons 4.0
open-access license adde
Packing Fractions and Maximum Angles of Stability of Granular Materials
In two-dimensional rotating drum experiments, we find two separate influences
of the packing fraction of a granular heap on its stability. For a fixed grain
shape, the stability increases with packing fraction. However, in determining
the relative stability of different grain shapes, those with the lowest average
packing fractions tend to form the most stable heaps. We also show that only
the configuration close to the surface of the pile figures prominently.Comment: 4 pages, 4 figure
The Size Distribution of Trans-Neptunian Bodies
[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with
m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are
discovered, roughly 25 times fewer than expected from extrapolation of the
differential sky density Sigma(m) of brighter objects. The ACS and other recent
TNO surveys show departures from a power law size distribution. Division of the
TNO sample into ``classical Kuiper belt'' (CKB) and ``Excited'' samples reveals
that Sigma(m) differs for the two populations at 96% confidence. A double power
law adequately fits all data. Implications include: The total mass of the CKB
is ~0.010 M_Earth, only a few times Pluto's mass, and is predominately in the
form of ~100 km bodies. The mass of Excited objects is perhaps a few times
larger. The Excited class has a shallower bright-end size distribution; the
largest objects, including Pluto, comprise tens of percent of the total mass
whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the
largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times
less massive. The deficit of small TNOs occurs for sizes subject to disruption
by present-day collisions, suggesting extensive depletion by collisions. Both
accretion and erosion appearing to have proceeded to more advanced stages in
the Excited class than the CKB. The absence of distant TNOs implies that any
distant (60 AU) population must have less than the CKB mass in the form of
objects 40 km or larger. The CKB population is sparser than theoretical
estimates of the required precursor population for short period comets, but the
Excited population could be a viable precursor population.Comment: Revised version accepted to the Astronomical Journal. Numerical
results are very slightly revised. Implications for the origins of
short-period comets are substantially revised, and tedious material on
statistical tests has been collected into a new Appendi
BRST quantization of the massless minimally coupled scalar field in de Sitter space (zero modes, euclideanization and quantization)
We consider the massless scalar field on the four-dimensional sphere .
Its classical action is degenerate
under the global invariance . We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form where
is a gauge parameter and is the volume of . It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of , and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space - the lorentzian version of - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on and
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).Comment: This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)
Age validation of quillback rockfish (Sebastes maliger) using bomb radiocarbon
Rockfishes (Sebastes spp.) support one of the most economically important f isheries of the Pacific Northwest and it is essential for sustainable management that age estimation procedures be validated for these species. Atmospheric testing of thermonuclear devices during the
1950s and 1960s created a global radiocarbon (14C) signal in the ocean environment that scientists have identified
as a useful tracer and chronological marker in natural systems. In this study, we first demonstrated that fewer samples are necessary for age validation using the bomb-generated 14C signal by emphasizing the utility of the time-specific marker created by the initial rise of bomb-14C. Second, the bomb-generated 14C signal retained in fish otoliths was used to validate the age and age estimation method of the quillback rockfish (Sebastes maliger) in the
waters of southeast Alaska. Radiocarbon values from the first year’s growth of quillback rockfish otoliths were plotted against estimated birth year to produce a 14C time series spanning 1950 to 1985. The initial rise in bomb-14C from prebomb levels (~ –90‰) occurred in 1959 [±1 year]
and 14C levels rose relatively rapidly to peak Δ14C values in 1967 (+105.4‰) and subsequently declined through the end of the time series in 1985 (+15.4‰). The agreement between the year of initial rise of 14C levels from the quillback rockfish time series and the chronology determined for the waters of southeast Alaska from yelloweye rockfish (S. ruberrimus) otoliths validated the aging method for the quillback rockfish. The concordance of the entire quillback rockfish 14C time series with the yelloweye rockfish time series demonstrated the effectiveness of this age validation
technique, confirmed the longevity of the quillback rockfish up to a minimum of 43 years, and strongly confirms higher age estimates of u
SDSS J013655.91+242546.0 - an A-type hyper-velocity star from the outskirts of the Galaxy
Hyper-velocity stars (HVS) are moving so fast that they are unbound to the
Galaxy. Dynamical ejection by a supermassive black hole is favoured to explain
their origin. Locating the place of birth of an individual HVS is of utmost
importance to understanding the ejection mechanism. SDSS J013655.91+242546.0
(J0136+2425 for short) was found amongst three high-velocity stars (drawn from
a sample of more than 10000 blue stars), for which proper motions were
measured. A kinematical as well as a quantitative NLTE spectral analysis was
performed. When combined with the radial velocity (RV) and the spectroscopic
distance, the trajectory of the star in the Galactic potential was
reconstructed. J0136+2425 is found to be an A-type main-sequence star
travelling at 590 \kms, possibly unbound to the Galaxy and originating
in the outer Galactic rim nowhere near the Galactic centre. J0136+2425 is the
second HVS candidate with measured proper motion, besides the massive B star HD
271791, and also the second for which its proper motion excludes a Galactic
centre origin and, hence, the SMBH slingshot mechanism. Most known HVS are late
B-type stars of about 3 M. With a mass of 2.45 M, J0136+2425
resembles a typical HVS far more than HD 271791 does. Hence, this is the first
time that a typical HVS is found not to originate in the Galactic centre. Its
ejection velocity from the disk is so high (550 \kms) that the extreme
supernova binary scenario proposed for HD 271791 is very unlikely.Comment: 4 pages, 5 figures, accepted for publication in A&
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