496 research outputs found
Inequalities for nucleon generalized parton distributions with helicity flip
Several positivity bounds are derived for generalized parton distributions
(GPDs) with helicity flip.Comment: 20 page
Mitochondrial DNA data indicate an introduction through Mainland Southeast Asia for Australian dingoes and Polynesian domestic dogs
In the late stages of the global dispersal of dogs, dingoes appear in the Australian archaeological record 3500 years BP, and dogs were one of three domesticates brought with the colonization of Polynesia, but the introduction routes to this region remain unknown. This also relates to questions about human history, such as to what extent the Polynesian culture was introduced with the Austronesian expansion from Taiwan or adopted en route, and whether pre-Neolithic Australia was culturally influenced by the surrounding Neolithic world. We investigate these questions by mapping the distribution of the mtDNA founder haplotypes for dingoes (A29) and ancient Polynesian dogs (Arc1 and Arc2) in samples across Southern East Asia (n = 424) and Island Southeast Asia (n = 219). All three haplotypes were found in South China, Mainland Southeast Asia and Indonesia but absent in Taiwan and the Philippines, and the mtDNA diversity among dingoes indicates an introduction to Australia 4600–18 300 years BP. These results suggest that Australian dingoes and Polynesian dogs originate from dogs introduced to Indonesia via Mainland Southeast Asia before the Neolithic, and not from Taiwan together with the Austronesian expansion. This underscores the complex origins of Polynesian culture and the isolation from Neolithic influence of the pre-Neolithic Australian culture
Baxter operators for the quantum sl(3) invariant spin chain
The noncompact homogeneous sl(3) invariant spin chains are considered. We
show that the transfer matrix with generic auxiliary space is factorized into
the product of three sl(3) invariant commuting operators. These operators
satisfy the finite difference equations in the spectral parameters which follow
from the structure of the reducible sl(3) modules.Comment: 20 pages, 4 figures, references adde
Time-of-flight spectroscopy of ultracold neutrons at the PSI UCN source
The ultracold neutron (UCN) source at the Paul Scherrer Institute (PSI)
provides high intensities of storable neutrons for fundamental physics
experiments. The neutron velocity spectrum parallel to the beamline axis was
determined by time-of-flight spectroscopy using a neutron chopper. In
particular, the temporal evolution of the spectrum during neutron production
and UCN storage in the source storage volume was investigated and compared to
Monte Carlo simulation results. A softening of the measured spectrum from a
mean velocity of 7.7(1) m s to 5.1(1) m s occurred within the
first 30 s after the proton beam pulse had impinged on the spallation target. A
spectral hardening was observed over longer time scales of one measurement day,
consistent with the effect of surface degradation of the solid deuterium
moderator
Factorization of the transfer matrices for the quantum sl(2) spin chains and Baxter equation
It is shown that the transfer matrices of homogeneous sl(2) invariant spin
chains with generic spin, both closed and open, are factorized into the product
of two operators. The latter satisfy the Baxter equation that follows from the
structure of the reducible representations of the sl(2) algebra.Comment: 14 pages, 9 figures, typos correcte
Characterization of ultracold neutron production in thin solid deuterium films at the PSI UCN source
We determined the ultracold neutron (UCN) production rate by superthermal
conversion in the solid deuterium (sD) moderator of the UCN source at the
Paul Scherrer Institute (PSI). In particular, we considered low amounts of less
than mol of D, deposited on the cooled moderator vessel surfaces in
thin films of a few mm thickness. We measured the isotopic () and isomeric () purity of the deuterium
to conclude that absorption and up-scattering at K have a negligible
effect on the UCN yield from the thin films. We compared the calculated UCN
yield based on the previously measured thermal neutron flux from the heavy
water thermal moderator with measurements of the UCN count rates at the
beamports. We confirmed our results and thus demonstrate an absolute
characterization of the UCN production and transport in the source by
simulations
Molecular Population Structure for Feral Swine in the United States
Feral swine (Sus scrofa) have invaded most of the United States and continue to expand throughout North America. Given the ecological and economic threats posed by increasing feral swine abundance, it is imperative to develop an understanding of their patterns of natural range expansion and human-mediated introductions. Towards this goal, we used molecular markers to elucidate the genetic structure of feral swine populations throughout the United States and evaluated the association between historical introductions and contemporary patterns of genetic organization. We used STRUCTURE and discriminant analysis of principal components (DAPC) to delineate genetic clusters for 959 individuals genotyped at 88 single nucleotide polymorphism loci. We identified 10 and 12 genetic clusters for the 2 clustering approaches, respectively. We observed strong agreement in clusters across approaches, with both describing clusters having strong geographic association at regional levels reflecting past introduction and range expansion patterns. In addition, we evaluated patterns of isolation by distance to test for and estimate spatial scaling of population structure within western, central, and eastern regions of North America. We found contrasting spatial patterns of genetic relatedness among regions, suggesting differences in the invasion process, likely as a result of regional variation in landscape heterogeneity and the influence of human mediated introductions. Our results indicate that molecular analyses of population genetic structure can provide reliable insights into the invasion processes of feral swine, thus providing a useful basis for management focused on minimizing continued range expansion by this problematic species
A highly stable atomic vector magnetometer based on free spin precession
We present a magnetometer based on optically pumped Cs atoms that measures
the magnitude and direction of a 1 T magnetic field. Multiple circularly
polarized laser beams were used to probe the free spin precession of the Cs
atoms. The design was optimized for long-time stability and achieves a scalar
resolution better than 300 fT for integration times ranging from 80 ms to 1000
s. The best scalar resolution of less than 80 fT was reached with integration
times of 1.6 to 6 s. We were able to measure the magnetic field direction with
a resolution better than 10 rad for integration times from 10 s up to 2000
s
Solid deuterium surface degradation at ultracold neutron sources
Solid deuterium (sD_2) is used as an efficient converter to produce ultracold
neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high
purity and mostly in its ortho-state in order to guarantee long lifetimes of
UCN in the solid from which they are extracted into vacuum. Also the UCN
transparency of the bulk sD_2 material must be high because crystal
inhomogeneities limit the mean free path for elastic scattering and reduce the
extraction efficiency. Observations at the UCN sources at Paul Scherrer
Institute and at Los Alamos National Laboratory consistently show a decrease of
the UCN yield with time of operation after initial preparation or later
treatment (`conditioning') of the sD_2. We show that, in addition to the
quality of the bulk sD_2, the quality of its surface is essential. Our
observations and simulations support the view that the surface is deteriorating
due to a build-up of D_2 frost-layers under pulsed operation which leads to
strong albedo reflections of UCN and subsequent loss. We report results of UCN
yield measurements, temperature and pressure behavior of deuterium during
source operation and conditioning, and UCN transport simulations. This,
together with optical observations of sD_2 frost formation on initially
transparent sD_2 in offline studies with pulsed heat input at the North
Carolina State University UCN source results in a consistent description of the
UCN yield decrease.Comment: 15 pages, 22 figures, accepted by EPJ-
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