333 research outputs found
The Nature of Interstellar Gas toward the Pleiades Revealed in Absorption Lines
We present high-resolution, high signal to noise absorption-line observations
of CN, Ca II, Ca I, CH^+, and CH along twenty lines of sight toward members of
the Pleiades. The acquired data enable the most detailed study to date of the
interaction between cluster stars and the surrounding interstellar gas. Total
equivalent widths are consistent with previous investigations except where
weaker features are detected owing to our greater sensitivity. Mean b-values
for the molecular species indicate that toward most of the Pleiades CH is
associated with the production of CH^+ rather than CN. An analysis of radial
velocities reveals a kinematic distinction between ionized atomic gas and
molecular and neutral gas. Molecular components are found with velocities in
the local standard of rest of either ~ +7 km s^-1 or ~ +9.5 km s^-1, with the
higher-velocity components associated with the strongest absorption. Atomic gas
traced by Ca II shows a strong central component at v_LSR ~ +7 km s^-1
exhibiting velocity gradients indicative of cloud-cluster interactions. Gas
density estimates derived from measured CH/CH^+ column density ratios show good
agreement with those inferred from H_2 rotational populations, yielding typical
values of n ~ 50 cm^-3. Our models do not include the important time-dependent
effects on CH^+ formation which may ultimately be needed to extract physical
conditions in these clouds.Comment: 18 pages, 10 figures, emulateapj style, Accepted for publication in
Ap
Yearling Beef Cattle Grazing Diverse Summer Annual Swards
Utilizing summer annuals is often regarded as “a breakeven proposition at best” due to high establishment costs. This study investigated using botanical diversity to increase forage yield or animal performance to improve the economic feasibility of grazing summer annual forages in western Kentucky, USA. Sorghum-sudangrass (Sorghum bicolor x S. bicolor spp. drummondii)-based treatments included a monoculture, a three-species mixture (two grasses, one legume), and a 12-species mixture (five grasses, four legumes, two brassicas, and one forb). Angus-cross yearling beef calves (329, 366, and 297 kg in 2017, 2018, and 2019, respectively) grazed summer annuals in 2017-2019 for an average of 40 days each year without supplementation. Pastures were stocked when forage was approximately 1 m tall and calves were removed when forage was 2-2.5 m tall (seedheads present). In all years, forage dry matter yield was not different between treatments (p \u3e 0.85) and both mixtures were dominated by sorghum-sudangrass. In 2017 (p \u3c 0.03) and 2019 (p \u3c 0.03), calves grazing the 12-species mixture had lower average daily gains (ADG) than the monoculture and 3-species mixture, while there was no difference in 2018 (p \u3e 0.3). Average daily gains were suboptimal for stocker calves in all years (0.75, 0.01, 0.54 kg day-1 in 2017, 2018, and 2019). The extremely low ADG in 2018 was likely a result of stocking pastures late in the season when grasses were at physiological maturity. Additional species increased seed cost but did not contribute significantly to forage production and did not result in increased animal production. Unless greater forage yield or livestock gains are attained, planting mixtures may not provide any economic benefit. However, adjusting seeding rates to favor less dominant species may provide a more accurate representation of species diversity manipulation effects on forage and livestock production
Quantum Interference on the Kagom\'e Lattice
We study quantum interference effects due to electron motion on the Kagom\'e
lattice in a perpendicular magnetic field. These effects arise from the
interference between phase factors associated with different electron
closed-paths. From these we compute, analytically and numerically, the
superconducting-normal phase boundary for Kagom\'e superconducting wire
networks and Josephson junction arrays. We use an analytical approach to
analyze the relationship between the interference and the complex structure
present in the phase boundary, including the origin of the overall and fine
structure. Our results are obtained by exactly summing over one thousand
billion billions () closed paths, each one weighted by its
corresponding phase factor representing the net flux enclosed by each path. We
expect our computed mean-field phase diagrams to compare well with several
proposed experiments.Comment: 9 pages, Revtex, 3 figures upon reques
Geometrical frustration induced (semi-)metal to insulator transition
We study the low-energy properties of the geometrically frustrated Hubbard
model on a three-dimensional pyrochlore lattice and a two-dimensional
checkerboard lattice on the basis of the renormalization group method and mean
field analysis. It is found that in the half-filling case, a (semi-)metal to
insulator transition (MIT) occurs. Also, in the insulating phase, which has a
spin gap, the spin rotational symmetry is not broken, while charge ordering
exists. The results are applied to the description of the MIT observed in the
pyrochlore system .Comment: 4 pages, 5 figure
Large- limit of a Hubbard model in a magnetic field: chiral spin interactions and paramagnetism
We consider the large- limit of the one-band Hubbard model at half-filling
on a non-bipartite two-dimensional lattice. An external magnetic field can
induce a three-spin chiral interaction at order . We discuss
situations in which, at low temperatures, the chiral term may have a larger
effect than the Pauli coupling of electron spins to a magnetic field. We
present a model which explicitly demonstrates this. The ground state is a
singlet with a gap; hence the spin susceptibility is zero while the chiral
susceptibility is finite and paramagnetic.Comment: 12 pages, plain TeX, one figure available on request, to appear in
Phys. Rev.
Tracking Cardiac Rehabilitation Utilization in Medicare Beneficiaries: 2017 UPDATE
PURPOSE: This study updates cardiac rehabilitation (CR) utilization data in a cohort of Medicare beneficiaries hospitalized for CR-eligible events in 2017, including stratification by select patient demographics and state of residence.
METHODS: We identified Medicare fee-for-service beneficiaries who experienced a CR-eligible event and assessed their CR participation (≥1 CR sessions in 365 d), engagement, and completion (≥36 sessions) rates through September 7, 2019. Measures were assessed overall, by beneficiary characteristics and state of residence, and by primary (myocardial infarction; coronary artery bypass surgery; heart valve repair/replacement; percutaneous coronary intervention; or heart/heart-lung transplant) and secondary (angina; heart failure) qualifying event type.
RESULTS: In 2017, 412 080 Medicare beneficiaries had a primary CR-eligible event and 28.6% completed ≥1 session of CR within 365 d after discharge from a qualifying event. Among beneficiaries who completed ≥1 CR session, the mean total number of sessions was 25 ± 12 and 27.6% completed ≥36 sessions. Nebraska had the highest enrollment rate (56.1%), with four other states also achieving an enrollment rate \u3e50% and 23 states falling below the overall rate for the United States.
CONCLUSIONS: The absolute enrollment, engagement, and program completion rates remain low among Medicare beneficiaries, indicating that many patients did not benefit or fully benefit from a class I guideline-recommended therapy. Additional research and continued widespread adoption of successful enrollment and engagement initiatives are needed, especially among identified populations
Aging in a topological spin glass
We have examined the nonconventional spin glass phase of the 2-dimensional
kagome antiferromagnet (H_3 O) Fe_3 (SO_4)_2 (OH)_6 by means of ac and dc
magnetic measurements. The frequency dependence of the ac susceptibility peak
is characteristic of a critical slowing down at Tg ~ 18K. At fixed temperature
below Tg, aging effects are found which obey the same scaling law as in spin
glasses or polymers. However, in clear contrast with conventional spin glasses,
aging is remarkably insensitive to temperature changes. This particular type of
dynamics is discussed in relation with theoretical predictions for highly
frustrated non-disordered systems.Comment: 4 pages, 4 figure
Long range Neel order in the triangular Heisenberg model
We have studied the Heisenberg model on the triangular lattice using several
Quantum Monte Carlo (QMC) techniques (up to 144 sites), and exact
diagonalization (ED) (up to 36 sites). By studying the spin gap as a function
of the system size we have obtained a robust evidence for a gapless spectrum,
confirming the existence of long range Neel order. Our best estimate is that in
the thermodynamic limit the order parameter m= 0.41 +/- 0.02 is reduced by
about 59% from its classical value and the ground state energy per site is
e0=-0.5458 +/- 0.0001 in unit of the exchange coupling. We have identified the
important ground state correlations at short distance.Comment: 4 pages, RevTeX + 4 encapsulated postscript figure
Spin chirality on a two-dimensional frustrated lattice
The collective behavior of interacting magnetic moments can be strongly
influenced by the topology of the underlying lattice. In geometrically
frustrated spin systems, interesting chiral correlations may develop that are
related to the spin arrangement on triangular plaquettes. We report a study of
the spin chirality on a two-dimensional geometrically frustrated lattice. Our
new chemical synthesis methods allow us to produce large single crystal samples
of KFe3(OH)6(SO4)2, an ideal Kagome lattice antiferromagnet. Combined
thermodynamic and neutron scattering measurements reveal that the phase
transition to the ordered ground-state is unusual. At low temperatures,
application of a magnetic field induces a transition between states with
different non-trivial spin-textures.Comment: 7 pages, 4 figure
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