89,563 research outputs found
ApuA, a multifunctional x-glucan-degrading enzyme of Streptococcus suis, mediates adhesion to porcine epithelium and mucus
We have identified apuA in Streptococcus suis, which encodes a bifunctional amylopullulanase with conserved -amylase and pullulanase substrate-binding domains and catalytic motifs. ApuA exhibited properties typical of a Gram-positive surface protein, with a putative signal sequence and LPKTGE cell-wall-anchoring motif. A recombinant protein containing the predicted N-terminal -amylase domain of ApuA was shown to have -(1,4) glycosidic activity. Additionally, an apuA mutant of S. suis lacked the pullulanase -(1,6) glycosidic activity detected in a cell-surface protein extract of wild-type S. suis. ApuA was required for normal growth in complex medium containing pullulan as the major carbon source, suggesting that this enzyme plays a role in nutrient acquisition in vivo via the degradation of glycogen and food-derived starch in the nasopharyngeal and oral cavities. ApuA was shown to promote adhesion to porcine epithelium and mucus in vitro, highlighting a link between carbohydrate utilization and the ability of S. suis to colonize and infect the host
Discrepancies in Determinations of the Ginzburg-Landau Parameter
Long-standing discrepancies within determinations of the Ginzburg-Landau
parameter from supercritical field measurements on superconducting
microspheres are reexamined. The discrepancy in tin is shown to result from
differing methods of analyses, whereas the discrepancy in indium is a
consequence of significantly differing experimental results. The reanalyses
however confirms the lower determinations to within experimental
uncertainties.Comment: submitted to Phys. Rev.
Estimating turbulent velocities in the elliptical galaxies NGC 5044 and NGC 5813
The interstellar and intra-cluster medium in giant elliptical galaxies and
clusters of galaxies is often assumed to be in hydrostatic equilibrium.
Numerical simulations, however, show that about 5-30% of the pressure in a
cluster is provided by turbulence induced by, for example, the central AGN and
merger activity. We aim to put constraints on the turbulent velocities and
turbulent pressure in the ICM of the giant elliptical galaxies NGC 5044 and NGC
5813 using XMM-Newton RGS observations. The magnitude of the turbulence is
estimated using the Fe XVII lines at 15.01 A, 17.05 A, and 17.10 A in the RGS
spectra. At low turbulent velocities, the gas becomes optically thick in the
15.01 A line due to resonant scattering, while the 17 A lines remain optically
thin. By comparing the (I(17.05)+I(17.10))/I(15.01) line ratio from RGS with
simulated line ratios for different Mach numbers, the level of turbulence is
constrained. The measurement is limited by systematic uncertainties in the
atomic data, which are at the 20-30% level. We find that the line ratio in NGC
5813 is significantly higher than in NGC 5044. This difference can be explained
by a higher level of turbulence in NGC 5044. The high turbulent velocities and
the fraction of the turbulent pressure support of >40% in NGC 5044, assuming
isotropic turbulence, confirm that it is a highly disturbed system, probably
due to an off-axis merger. The turbulent pressure support in NGC 5813 is more
modest at 15-45%. The (I(17.05)+I(17.10))/I(15.01) line ratio in an optically
thin plasma, calculated using AtomDB v2.0.1, is 2 sigma above the ratio
measured in NGC 5044, which cannot be explained by resonant scattering. This
shows that the discrepancies between theoretical, laboratory, and astrophysical
data on Fe XVII lines need to be reduced to improve the accuracy of the
determination of turbulent velocities using resonant scattering.Comment: 11 pages, 5 figures, accepted for publication in A&
XTE J1550-564: INTEGRAL Observations of a Failed Outburst
The well known black-hole X-ray binary transient XTE J1550-564 underwent an
outburst during the spring of 2003 which was substantially underluminous in
comparison to previous periods of peak activity in that source. In addition,
our analysis shows that it apparently remained in the hard spectral state over
the duration of that outburst. This is again in sharp contrast to major
outbursts of that source in 1998/1999 during which it exhibited an irregular
light curve, multiple state changes and collimated outflows. This leads us to
classify it as a "failed outburst." We present the results of our study of the
spring 2003 event including light curves based on observations from both
INTEGRAL and RXTE. In addition, we studied the evolution of the high-energy
3-300 keV continuum spectrum using data obtained with three main instruments on
INTEGRAL. These spectra are consistent with typical low-hard-state thermal
Comptonization emission. We also consider the 2003 event in the context of a
multi-source, multi-event period-peak luminosity diagram in which it is a clear
outlyer. We then consider the possibility that the 2003 event was due to a
discrete accretion event rather than a limit-cycle instablility. In that
context, we apply model fitting to derive the timescale for viscous propagation
in the disk, and infer some physical characteristics.Comment: 22 pages, 8 figures, to be published in The Astrophysical Journa
Cluster and nebular properties of the central star-forming region of NGC 1140
We present new high spatial resolution HST/ACS imaging of NGC 1140 and high
spectral resolution VLT/UVES spectroscopy of its central star-forming region.
The central region contains several clusters, the two brightest of which are
clusters 1 and 6 from Hunter, O'Connell & Gallagher, located within
star-forming knots A and B, respectively. Nebular analysis indicates that the
knots have an LMC-like metallicity of 12 + log(O/H) = 8.29 +/- 0.09. According
to continuum subtracted H alpha ACS imaging, cluster 1 dominates the nebular
emission of the brighter knot A. Conversely, negligible nebular emission in
knot B originates from cluster 6. Evolutionary synthesis modelling implies an
age of 5 +/- 1 Myr for cluster 1, from which a photometric mass of (1.1 +/-
0.3) x 10^6 Msun is obtained. For this age and photometric mass, the modelling
predicts the presence of ~5900 late O stars within cluster 1. Wolf-Rayet
features are observed in knot A, suggesting 550 late-type WN and 200 early-type
WC stars. Therefore, N(WR)/N(O) ~ 0.1, assuming that all the WR stars are
located within cluster 1. The velocity dispersions of the clusters were
measured from constituent red supergiants as sigma ~ 23 +/- 1 km/s for cluster
1 and sigma ~ 26 +/- 1 km/s for cluster 6. Combining sigma with half-light
radii of 8 +/- 2 pc and 6.0 +/- 0.2 pc measured from the F625W ACS image
implies virial masses of (10 +/- 3) x 10^6 Msun and (9.1 +/- 0.8) x 10^6 Msun
for clusters 1 and 6, respectively. The most likely reason for the difference
between the dynamical and photometric masses of cluster 1 is that the velocity
dispersion of knot A is not due solely to cluster 1, as assumed, but has an
additional component associated with cluster 2.Comment: 13 pages, 7 figure
Elastic response of a nematic liquid crystal to an immersed nanowire
We study the immersion of a ferromagnetic nanowire within a nematic liquid
crystal using a lattice Boltzmann algorithm to solve the full three-dimensional
equations of hydrodynamics. We present an algorithm for including a moving
boundary, to simulate a nanowire, in a lattice Boltzmann simulation. The
nematic imposes a torque on a wire that increases linearly with the angle
between the wire and the equilibrium direction of the director field. By
rotation of these nanowires, one can determine the elastic constants of the
nematic.Comment: 10 pages, 8 figure
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
The quantum state vector in phase space and Gabor's windowed Fourier transform
Representations of quantum state vectors by complex phase space amplitudes,
complementing the description of the density operator by the Wigner function,
have been defined by applying the Weyl-Wigner transform to dyadic operators,
linear in the state vector and anti-linear in a fixed `window state vector'.
Here aspects of this construction are explored, with emphasis on the connection
with Gabor's `windowed Fourier transform'. The amplitudes that arise for simple
quantum states from various choices of window are presented as illustrations.
Generalized Bargmann representations of the state vector appear as special
cases, associated with Gaussian windows. For every choice of window, amplitudes
lie in a corresponding linear subspace of square-integrable functions on phase
space. A generalized Born interpretation of amplitudes is described, with both
the Wigner function and a generalized Husimi function appearing as quantities
linear in an amplitude and anti-linear in its complex conjugate.
Schr\"odinger's time-dependent and time-independent equations are represented
on phase space amplitudes, and their solutions described in simple cases.Comment: 36 pages, 6 figures. Revised in light of referees' comments, and
further references adde
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