11,280 research outputs found
Optical Lattice Induced Light Shifts in an Yb Atomic Clock
We present an experimental study of the lattice induced light shifts on the
1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The
``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394
799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz
on the 518 THz clock transition. Also investigated were the hyperpolarizability
shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2
two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By
tuning the lattice frequency over the two-photon resonances and measuring the
corresponding clock transition shifts, the hyperpolarizability shift was
estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the
magic wavelength. In addition, we have confirmed that a circularly polarized
lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate
that the differential polarizability and hyperpolarizability frequency shift
uncertainties in a Yb lattice clock could be held to well below 10^-17.Comment: Accepted to PR
Frequency evaluation of the doubly forbidden transition in bosonic Yb
We report an uncertainty evaluation of an optical lattice clock based on the
transition in the bosonic isotope Yb by use
of magnetically induced spectroscopy. The absolute frequency of the
transition has been determined through comparisons
with optical and microwave standards at NIST. The weighted mean of the
evaluations is (Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty
due to systematic effects has been reduced to less than 0.8 Hz, which
represents in fractional frequency.Comment: 4 pages, 3 figure -Submitted to PRA Rapid Communication
Holocene variations in the Scottish marine radiocarbon reservoir effect
We assessed the evidence for variations in the marine radiocarbon reservoir effect (MRE) at coastal, archaeological Iron Age sites in north and west Scotland by comparing AMS measurements of paired marine and terrestrial materials (4 pairs per context). DeltaR values were calculated from measurements on material from 3 sites using 6 sets of samples, all of which were deposited around 2000 BP. The weighted mean of the DeltaR determinations was -79 +/- 17 C-14 yr, which indicates a consistent, reduced offset between atmospheric and surface ocean C-14 specific activity for these sites during this period, relative to the present day (DeltaR = similar to0 C-14 yr). We discuss the significance of this revised AR correction by using the example of wheelhouse chronologies at Hornish Point and their development in relation to brochs. In addition, we assess the importance of using the concepts of MRE correction and AR variations when constructing chronologies using C-14 measurements made on materials that contain marine- derived carbon
\u3ci\u3eHaplosporidium nelsoni\u3c/i\u3e (MSX) Epizootic in the Piscataqua River Estuary (Maine/New Hampshire, U.S.A.)
A major epizootic of Haplosporidium nelsoni occurred during 1995 in the Piscataqua River Estuary, near the northern distributional limit of the parasite. Prevalence of H. nelsoni in samples of oysters, Crassostrea virginica, collected between 5 September and 18 December 1995 from sites in Maine and New Hampshire ranged from 15 to 81 %, with up to 50% systemic infections. Associated proportions of dead oysters ranged from 25 to 83%. The epizootic was most likely triggered by unusually warm and dry climatic conditions in 1995 that resulted in a temperature and salinity regime in the estuary that favored the parasite
Quasiperiodic spin-orbit motion and spin tunes in storage rings
We present an in-depth analysis of the concept of spin precession frequency
for integrable orbital motion in storage rings. Spin motion on the periodic
closed orbit of a storage ring can be analyzed in terms of the Floquet theorem
for equations of motion with periodic parameters and a spin precession
frequency emerges in a Floquet exponent as an additional frequency of the
system. To define a spin precession frequency on nonperiodic synchro-betatron
orbits we exploit the important concept of quasiperiodicity. This allows a
generalization of the Floquet theorem so that a spin precession frequency can
be defined in this case too. This frequency appears in a Floquet-like exponent
as an additional frequency in the system in analogy with the case of motion on
the closed orbit. These circumstances lead naturally to the definition of the
uniform precession rate and a definition of spin tune. A spin tune is a uniform
precession rate obtained when certain conditions are fulfilled. Having defined
spin tune we define spin-orbit resonance on synchro--betatron orbits and
examine its consequences. We give conditions for the existence of uniform
precession rates and spin tunes (e.g. where small divisors are controlled by
applying a Diophantine condition) and illustrate the various aspects of our
description with several examples. The formalism also suggests the use of
spectral analysis to ``measure'' spin tune during computer simulations of spin
motion on synchro-betatron orbits.Comment: 62 pages, 1 figure. A slight extension of the published versio
Queensland Drug Trends 2019: Key Findings from the Ecstasy and Related Drugs Reporting System (EDRS) Interviews
This report describes annual data and 20-year trends in the use of ecstasy and related drugs, harms associated with use, and drug markets in Queensland.\ua0 It forms part of a nationwide, annual series of reports prepared for the Commonwealth Government and distributed widely to state government health and law enforcement agencies, and is used to inform policy and treatment responses.\ua0In the 2019 sample, cannabis and ecstasy were the drugs of choice nominated\ua0(28% and 23%), while cannabis and alcohol were the drugs used most often\ua0(54% and 21%). A quarter of recent users consumed ecstasy weekly or more often; most perceived it easy or very easy to obtain. One in 4 participants had recently used methamphetamine, 67% cocaine, 53% LSD, 56% nitrous oxide and 27% ketamine
SEROLOGIC SURVEY OF SELECTED PATHOGENS IN WHITE-TAILED AND MULE DEER IN WESTERN NEBRASKA
Exposure of free-ranging white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus) in western Nebraska to selected livestock pathogens was determined by serology and attempted virus isolation. Antibodies to bluetongue virus, epizootic hemorrhagic disease virus, and bovine respiratory syncytial virus were present in both species of deer. No serologic reactors to Brucella or Anaplasma were found. Attempts to isolate bluetongue virus were negative
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