29,157 research outputs found
The swine flu alert: keeping Asia safe
After years of concern about H5N1 bird flu, the new flu causing global alarm is a pig virus of the H1N1 family. As influenza reports erupt around the world, inevitable questions are arising. Is this the big one? Are we prepared
A uvbyCaHbeta Analysis of the Old Open Cluster, NGC 6819
NGC 6819 is a richly populated, older open cluster situated within the Kepler
field. A CCD survey of the cluster on the uvbyCaHbeta system, coupled with
proper-motion membership, has been used to isolate 382 highly probable,
single-star unevolved main-sequence members over a 20-arcminute field centered
on the cluster. From 278 F dwarfs with high precision photometry in all
indices, a mean reddening of E(b-y) = 0.117 +/- 0.005 or E(B-V) = 0.160 +/-
0.007 is derived, where the standard errors of the mean include both internal
errors and the photometric zero-point uncertainty. With the reddening fixed,
the metallicity derived from the same 278 stars is [Fe/H] = -0.116 +/- 0.101
from m_1 and -0.055 +/- 0.033 from hk, for a weighted average of [Fe/H] = -0.06
+/- 0.04, where the quoted standard errors of the mean values include the
internal errors from the photometric scatter plus the uncertainty in the
photometric zero points. If metallicity is derived using individual reddening
values for each star to account for potential reddening variation across the
face of the cluster, the analogous result is unchanged. The cluster members at
the turnoff of the color-magnitude diagram are used to test and confirm the
recently discovered variation in reddening across the face of the cluster, with
a probable range in the variation of Delta[E(B-V)] = 0.045 +/-0.015. With the
slightly higher reddening and lower [Fe/H] compared to commonly adopted values,
isochrone fitting leads to an age of 2.3 +/- 0.2 Gyr for an apparent modulus of
(m-M) = 12.40 +/-0.12.Comment: WIYN Open Cluster Study LXI; accepted to Astronomical Journal. 11
figures, 2 table
Relativistic Quasilinear Diffusion in Axisymmetric Magnetic Geometry for Arbitrary-Frequency Electromagnetic Fluctuations
A relativistic bounce-averaged quasilinear diffusion equation is derived to
describe stochastic particle transport associated with arbitrary-frequency
electromagnetic fluctuations in a nonuniform magnetized plasma. Expressions for
the elements of a relativistic quasilinear diffusion tensor are calculated
explicitly for magnetically-trapped particle distributions in axisymmetric
magnetic geometry in terms of gyro-drift-bounce wave-particle resonances. The
resonances can destroy any one of the three invariants of the unperturbed
guiding-center Hamiltonian dynamics.Comment: 22 pages, Latex, to appear in Physics of Plasma
Impact of stout-link smearing in lattice fermion actions
The impact of stout-link smearing in lattice fermion actions is examined
through the consideration of the mass and renormalization functions of the
overlap quark propagator over a variety of smeared configurations. Up to six
sweeps of stout-link smearing are investigated. For heavy quark masses, the
quark propagator is strongly affected by the smearing procedure. For moderate
masses, the effect appears to be negligible. A small effect is seen for light
quark masses, where dynamical mass generation is suppressed through the
smearing procedure.Comment: 7 pages, 3 figures, presented at the XXVII International Symposium on
Lattice Field Theory - LAT2009, July 26-31 2009, Peking University, Beijing,
Chin
Stout-link smearing in lattice fermion actions
The properties of the momentum space quark propagator in Landau gauge are
studied for the overlap quark action in quenched lattice QCD. Numerical
calculations are performed over four ensembles of gauge configurations, where
three are smeared using either 1, 3, or 6 sweeps of stout-link smearing. We
calculate the non-perturbative wave function renormalization function
and the non-perturbative mass function for a variety of bare quark
masses. We find that the wave-function renormalization function is slightly
sensitive to the number of stout-link smearing sweeps. For the mass function we
find the effect of the stout-link smearing algorithm to be small for moderate
to light bare quark masses. For a heavy bare quark mass we find a strong
dependence on the number of smearing sweeps.Comment: 8 pages, 4 figure
Spectral pitch distance and microtonal melodies
We present an experiment designed to test the effectiveness of spectral pitch distance at modeling the degree of “affinity” or “fit” of pairs of successively played tones or chords (spectral pitch distance is the cosine distance between salience-weighted, Gaussian-smoothed, pitch domain embeddings of spectral pitches—typically the first eight to ten partials of a tone). The results of a previously conducted experiment, which collected ratings of the perceived similarity and fit of root-position major and minor triads, suggest the model works well for pairs of triads in standard 12-tone equal temperament tunings.
The new experiment has been designed to test the effectiveness of spectral pitch distance at modeling the affinity of tones in microtonal melodies where the partials of the tones can be variably tempered between being perfectly harmonic and perfectly matched to the underlying microtonal tuning. The use of microtonal tunings helps to disambiguate innate perceptual (psychoacoustical) responses from learned (cultural) responses.
Participants are presented with a software synthesizer containing two unlabeled controls: one adjusts the precise tuning of the tones; the other adjusts the extent to which the spectrum is tempered to match the tuning (as set by the first control). A selection of microtonal melodies are played in different tunings, and the participants adjust one, or both, controls until they find a “sweet spot” at which the music sounds most “in-tune” and the notes best “fit” together. The results of these experiments will be presented and discussed
A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, NGC 752
Precision uvbyCaHbeta photometry of the nearby old open cluster, NGC 752, is
presented. The mosaic of CCD fields covers an area ~42' on a side with internal
precision at the 0.005 to 0.010 mag level for the majority of stars down to
V~15. The CCD photometry is tied to the standard system using an extensive set
of published photoelectric observations adopted as secondary standards within
the cluster. Multicolor indices are used to eliminate as nonmembers a large
fraction of the low probability proper-motion members near the faint end of the
main sequence, while identifying 24 potential dwarf members between V=15.0 and
16.5, eight of which have been noted before from Vilnius photometry. From 68
highly probable F dwarf members, we derive a reddening estimate of E(b-y)=
0.025 +/- 0.003 (E(B-V) = 0.034 +/- 0.004), where the error includes the
internal photometric uncertainty and the systematic error arising from the
choice of the standard (b-y), Hbeta relation. With reddening fixed, [Fe/H] is
derived from the F dwarf members using both m_1 and hk, leading to [Fe/H] =
-0.071 +/-0.014 (sem) and -0.017 +/- 0.008 (sem), respectively. Taking the
internal precision and possible systematics in the standard relations into
account, [Fe/H] for NGC 752 becomes -0.03 +/-0.02. With the reddening and
metallicity defined, we use the Victoria-Regina isochrones on the Stromgren
system and find an excellent match for (m-M) = 8.30 +/- 0.05 and an age of 1.45
+/- 0.05 Gyr at the appropriate metallicity.Comment: 37 pages, 11 figures, 4 tables. Accepted to Astronomical Journa
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