11,227 research outputs found
Astrometric Effects of Gravitational Wave Backgrounds with non-Luminal Propagation Speeds
A passing gravitational wave causes a deflection in the apparent astrometric positions of distant stars. The effect of the speed of the gravitational wave on this astrometric shift is discussed. A stochastic background of gravitational waves would result in a pattern of astrometric deflections which are correlated on large angular scales. These correlations are quantified and investigated for backgrounds of gravitational waves with sub- and super-luminal group velocities. The statistical properties of the correlations are depicted in two equivalent and related ways: as correlation curves and as angular power spectra. Sub-(super-)luminal gravitational wave backgrounds have the effect of enhancing (suppressing) the power in low-order angular modes. Analytical representations of the redshift-redshift and redshift-astrometry correlations are also derived. The potential for using this effect for constraining the speed of gravity is discussed
A search for evidence of large body Earth impacts associated with biological crisis zones in the fossil record
The natural history of the Earth, how the present plant and animal species developed, how others completely died out, etc., was studied. The rock strata sampled and studied were at the time of deposition at sea bottom. It was found that, exactly at the stratigraphic level corresponding to the extinction, a thin clay layer was greatly enriched in the the rare element iridium. It was hypothesized that the excess irridium at the boundary came from a large steroid like object that hit the earth, and that the impact of this object threw up a dust cloud dense enough and long lasting enough to bring about the extinction of a wide variety of plants and animals, producing the unique break in in the fossil record, the cretaceous-tertiary boundary. The same iridium and platinum metals enrichement are found in a thin clay layer that corresponds with the boundary as difined by sudden radical changes in plant populations. The irridium enrichement is confirmed at other fresh water origin rites in the Raton Basin
Developing an embedded nursing service within a homeless shelter: Client's perspectives
This phenomenological case study of a newly developed nursing service, embedded within a homeless shelter in the South East of England, uses semi-structured to elicit experiences and perceptions of clients within the service. Participants ( = 6) were interviewed using a semi-structured approach and identified three broad themes: impact of previous healthcare experiences, benefits of embedding healthcare within the shelter, and future service development. The study illuminates the diversity and complexity of healthcare needs of homeless people, as well as offers a unique insight into the service user's perception of the service
Multi-chord fiber-coupled interferometer with a long coherence length laser
This paper describes a 561 nm laser heterodyne interferometer that provides
time-resolved measurements of line-integrated plasma electron density within
the range of 10^15-10^18 cm^(-2). Such plasmas are produced by railguns on the
Plasma Liner Experiment (PLX), which aims to produce \mu s-, cm-, and
Mbar-scale plasmas through the merging of thirty plasma jets in a spherically
convergent geometry. A long coherence length, 320 mW laser allows for a strong,
sub-fringe phase-shift signal without the need for closely-matched probe and
reference path lengths. Thus only one reference path is required for all eight
probe paths, and an individual probe chord can be altered without altering the
reference or other probe path lengths. Fiber-optic decoupling of the probe
chord optics on the vacuum chamber from the rest of the system allows the probe
paths to be easily altered to focus on different spatial regions of the plasma.
We demonstrate that sub-fringe resolution capability allows the interferometer
to operate down to line-integrated densities of order 10^15 cm^(-2).Comment: submitted to Rev. Sci. Instrum. (2011
Regioselective Reactions of Highly Substituted Arynes
The fully regioselective reactivity of four new highly substituted silyl aryl triflate aryne precursors in aryne acyl-alkylation, acyl-alkylation/condensation, and heteroannulation reactions is reported. The application of these more complex arynes provides access to diverse natural product scaffolds and obviates late-stage functionalization of aromatic rings
Accelerated return to sport after osteochondral autograft plug transfer
Background:Previous studies have reported varying return-to-sport protocols after knee cartilage restoration procedures.Purpose:To (1) evaluate the time for return to sport in athletes with an isolated chondral injury who underwent an accelerated return-to-sport protocol after osteochondral autograft plug transfer (OAT) and (2) evaluate clinical outcomes to assess for any consequences from the accelerated return to sport.Study Design:Case series; Level of evidence, 4.Methods:An institutional cohort of 152 OAT procedures was reviewed, of which 20 competitive athletes met inclusion and exclusion criteria. All patients underwent a physician-directed accelerated rehabilitation program after their procedure. Return to sport was determined for all athletes. Clinical outcomes were assessed using International Knee Documentation Committee (IKDC) and Tegner scores as well as assessment of level of participation on return to sport.Results:Return-to-sport data were available for all 20 athletes; 13 of 20 athletes (65%) were available for clinical evaluation at a mean 4.4-year follow-up. The mean time for return to sport for all 20 athletes was 82.9 ± 25 days (range, 38-134 days). All athletes were able to return to sport at their previous level and reported that they were satisfied or very satisfied with their surgical outcome and ability to return to sport. The mean postoperative IKDC score was 84.5 ± 9.5. The mean Tegner score prior to injury was 8.9 ± 1.7; it was 7.7 ± 1.9 at final follow-up.Conclusion:Competitive athletes with traumatic chondral defects treated with OAT managed using this protocol had reduced time to preinjury activity levels compared with what is currently reported, with excellent clinical outcomes and no serious long-term sequelae.</jats:sec
The Influence of Binary Stars on Dwarf Spheroidal Galaxy Kinematics
We have completed a Monte-Carlo simulation to estimate the effect of binary
star orbits on the measured velocity dispersion in dwarf spheroidal galaxies.
This paper analyses previous attempts at this calculation, and explains the
simulations which were performed with mass, period and ellipticity
distributions similar to that measured for the solar neighbourhood. The
conclusion is that with functions such as these, the contribution of binary
stars to the velocity dispersion is small. The distributions are consistent
with the percentage of binaries detected by observations, although this is
quite dependent on the measuring errors and on the number of years over which
measurements have been taken. For binaries to be making a significant
contribution to the dispersion measured in dSph galaxies, the distributions of
the orbital parameters would need to be very different from those of stars in
the solar neighbourhood. In particular more smaller period orbits with higher
mass secondaries would be required. The shape of the velocity distribution may
help to resolve this issue when more data becomes available. In general, the
scenarios producing a larger apparent dispersion have a velocity distribution
which deviates more clearly from Gaussian.Comment: MNRAS in press, uuencoded ps fil
The channels of technology acquisition in commercial firms, and the NASA dissemination program
Technology acquisition in commercial firms, and NASA dissemination progra
Overcoming the su(2^n) sufficient condition for the coherent control of n-qubit systems
We study quantum systems with even numbers N of levels that are completely
state-controlled by unitary transformations generated by Lie algebras
isomorphic to sp(N) of dimension N(N+1)/2. These Lie algebras are smaller than
the respective su(N) with dimension N^2-1. We show that this reduction
constrains the Hamiltonian to have symmetric energy levels. An example of such
a system is an n-qubit system. Using a geometric representation for the quantum
wave function of a finite system, we present an explicit example that shows a
two-qubit system can be controlled by the elements of the Lie algebra sp(4)
(isomorphic to spin(5) and so(5)) with dimension ten rather than su(4) with
dimension fifteen. These results enable one to envision more efficient
algorithms for the design of fields for quantum-state engineering, and they
provide more insight into the fundamental structure of quantum control.Comment: 13 pp., 2 figure
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