3,915 research outputs found
Collagen-mimetic peptide-modifiable hydrogels for articular cartilage regeneration
Regenerative medicine strategies for restoring articular cartilage face significant challenges to recreate the complex and dynamic biochemical and biomechanical functions of native tissues. As an approach to recapitulate the complexity of the extracellular matrix, collagen-mimetic proteins offer a modular template to incorporate bioactive and biodegradable moieties into a single construct. We modified a Streptococcal collagen-like 2 protein with hyaluronic acid (HA) or chondroitin sulfate (CS)-binding peptides and then cross-linked with a matrix metalloproteinase 7 (MMP7)-sensitive peptide to form biodegradable hydrogels. Human mesenchymal stem cells (hMSCs) encapsulated in these hydrogels exhibited improved viability and significantly enhanced chondrogenic differentiation compared to controls that were not functionalized with glycosaminoglycan-binding peptides. Hydrogels functionalized with CS-binding peptides also led to significantly higher MMP7 gene expression and activity while the HA-binding peptides significantly increased chondrogenic differentiation of the hMSCs. Our results highlight the potential of this novel biomaterial to modulate cell-mediated processes and create functional tissue engineered constructs for regenerative medicine applications
High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822-37
We present a preliminary analysis of the X-ray spectrum of the accretion disk
corona source, 4U 1822-37, obtained with the High Energy Transmission Grating
Spectrometer onboard the Chandra X-ray Observatory. We detect discrete emission
lines from photoionized iron, silicon, magnesium, neon, and oxygen, as well as
a bright iron fluorescence line. Phase-resolved spectroscopy suggests that the
recombination emission comes from an X-ray illuminated bulge located at the
predicted point of impact between the disk and the accretion stream. The
fluorescence emission originates in an extended region on the disk that is
illuminated by light scattered from the corona.Comment: 12 pages, 6 figures; Accepted for publication in ApJ Letter
Development of a public audiology service in Southern Malawi: profile of patients across two years
Objective
To describe the profile of patients attending the Queen Elizabeth Central Hospital (QECH) audiology clinic in Malawi, over a two-year period (2016â2017).
Design
A retrospective patient record review.
Study sample
There were 2299 patients assessed at the QECH audiology department between January 2016 and December 2017. Adult patientsâ ages ranged from 18 to 94âyears (Mâ=â45.8, SD = 19.22). The mean age of children included in this study was 7.7âyears (SD= 5.21). Overall, 45.4% of patients were female.
Results
Of the 61.6% of adults and 41.7% of children found to have some degree of hearing loss, 28.3% and 15.4% were fitted with hearing aids, respectively. The number of patients seen in 2017 (nâ=â1385) was 34% higher than that of 2016 (nâ=â914).
Conclusion
This study found that demand for hearing services is increasing in this public sector Malawian audiology department but uptake of hearing aids for those in need is low. Future evaluation of service provision and treatment outcomes is needed. Results from this study can be used to inform the development of future audiology clinics in low resource settings
A supernova remnant coincident with the slow X-ray pulsar AX J1845-0258
We report on Very Large Array observations in the direction of the
recently-discovered slow X-ray pulsar AX J1845-0258. In the resulting images,
we find a 5-arcmin shell of radio emission; the shell is linearly polarized
with a non-thermal spectral index. We class this source as a previously
unidentified, young (< 8000 yr), supernova remnant (SNR), G29.6+0.1, which we
propose is physically associated with AX J1845-0258. The young age of G29.6+0.1
is then consistent with the interpretation that anomalous X-ray pulsars (AXPs)
are isolated, highly magnetized neutron stars ("magnetars"). Three of the six
known AXPs can now be associated with SNRs; we conclude that AXPs are young
(~<10 000 yr) objects, and that they are produced in at least 5% of
core-collapse supernovae.Comment: 4 pages, 1 embedded EPS file, uses emulateapj.sty. Accepted to ApJ
Letter
Effects of Strong Magnetic Fields on Neutron Star Structure
We study static neutron stars with poloidal magnetic fields and a simple
class of electric current distributions consistent with the requirement of
stationarity. For this class of electric current distributions, we find that
magnetic fields are too large for static configurations to exist when the
magnetic force pushes a sufficient amount of mass off-center that the
gravitational force points outward near the origin in the equatorial plane. (In
our coordinates an outward gravitational force corresponds to , where and are respectively time and radial
coordinates and is coefficient of in the line element.) For the
equations of state (EOSs) employed in previous work, we obtain configurations
of higher mass than had been reported; we also present results with more recent
EOSs. For all EOSs studied, we find that the maximum mass among these static
configurations with magnetic fields is noticeably larger than the maximum mass
attainable by uniform rotation, and that for fixed values of baryon number the
maximum mass configurations are all characterized by an off-center density
maximum.Comment: Submitted to the Astrophysical Journal. 37 pages, 8 figures, uses
aastex macro
The "K-Correction" for Irradiated Emission Lines in LMXBs: Evidence for a Massive Neutron Star in X1822-371 (V691 CrA)
We study the K-correction for the case of emission lines formed in the X-ray
illuminated atmosphere of a Roche lobe filling star. We compute the
K-correction as function of the mass ratio 'q' and the disc flaring angle
'alpha' using a compact binary code where the companion's Roche lobe is divided
into 10^5 resolution elements. We also study the effect of the inclination
angle in the results. We apply our model to the case of the neutron star
low-mass X-ray binary X1822-371 (V691 CrA), where a K-emission velocity
K_em=300 +-8 km/s has been measured by Casares et al. (2003). Our numerical
results, combined with previous determination of system parameters, yields
1.61Msun < M_NS < 2.32Msun and 0.44Msun < M_2 < 0.56Msun for the two binary
components(i. e. 0.24 < q < 0.27), which provide a compelling evidence for a
massive neutron star in this system. We also discuss the implications of these
masses into the evolutionary history of the binary.Comment: 6 pages, 5 figures. Accepted for publication in Ap
Discovery of a ~1 Hz quasi-periodic oscillation in the low-mass X-ray binary 4U 1746-37
We have discovered a ~1 Hz quasi-periodic oscillation (QPO) in the persistent
X-ray emission and during type I X-ray bursts of the globular cluster source,
dipper and low-mass X-ray binary (LMXB) 4U 1746-37. The QPO properties resemble
those of QPOs found recently in the LMXB dippers 4U 1323-62, and EXO 0748-676,
which makes 4U 1746-37 the third source known to exhibit this type of QPOs. We
present evidence for X-ray spectral changes in this source similar to those
observed in LMXBs referred to as atoll sources. We detect two states, a low
intensity and spectrally hard state, and a higher intensity and spectrally soft
state. This may explain the different spectral characteristics reported for 4U
1746-37 earlier. The high intensity state resembles the banana branch state of
atoll sources. The QPOs are only seen in the low intensity state, and are
absent when the source is in the banana branch. This strongly suggests that
either the accretion disk or an extended central source change shape between
the low intensity state and the banana branch. Twelve bursts were detected, of
which 5 took place while the source was on the banana branch and 7 when the
source was in the low intensity state. The bursts occurring on the banana
branch had an e-folding time ~3 times longer than those which occurred in the
low intensity state. Whereas previously detected dips showed only a decrease in
count rate of ~15%, we found in one observation a dip in which the count rate
dropped from ~200 counts per second to ~20 counts per second. This dip lasted
only ~250 seconds, during which clear spectral hardening occured. This is the
first time strong evidence for spectral changes during a dip are reported for
this source.Comment: 17 pages, accepted for publication in Ap
ASCA and BeppoSAX observations of the peculiar X-ray source 4U1700+24/HD154791
The X-ray source 4U1700+24/HD154791 is one of the few galactic sources whose
counterpart is an evolved M star. In X-rays the source shows extreme erratic
variability and a complex and variable spectrum. While this strongly suggests
accretion onto a compact object, no clear diagnosis of binarity was done up to
now. We report on ASCA and BeppoSAX X-ray broad band observations of this
source and on ground optical observations from the Loiano 1.5 m telescope.Comment: 5 pages, 4 figures, uses aipproc.sty, to appear in Proceedings of the
Fifth Compton Symposiu
Implications of X-Ray Line Variations for 4U1822-371
4U 1822-371 is one of the proto-type accretion disk coronal sources with an
orbital period of about 5.6 hours. The binary is viewed almost edge-on at a
high inclination angle of 83 degrees, which makes it a unique candidate to
study binary orbital and accretion disk dynamics in high powered X-ray sources.
We observed the X-ray source in 4U 1822-371 with the Chandra High Energy
Transmission Grating Spectrometer (HETGS) for almost nine binary orbits. X-ray
eclipse times provide an update of the orbital ephemeris. We find that our
result follows the quadratic function implied by previous observations;
however, it suggests a flatter trend. Detailed line dynamics also confirm a
previous suggestion that the observed photo-ionized line emission originates
from a confined region in the outer edge of the accretion disk near the hot
spot. Line properties allow us to impose limits on the size of accretion disk,
the central corona, and the emission region. The photo-ionized plasma is
consistent with ionization parameters of log(xi) > 2, and when combined with
disk size and reasonable assumptions for the plasma density, this suggests
illuminating disk luminosities which are over an order of magnitude higher than
what is actually observed. That is, we do not directly observe the central
emitting X-ray source. The spectral continua are best fit by a flat power law
with a high energy cut-off and partial covering absorption (N_H ranging from
5.4-6.3x10^{22} cm^{-2}) with a covering fraction of about 50%. We discuss some
implications of our findings with respect to the photo-ionized line emission
for the basic properties of the X-ray source.Comment: Submitted to the Astrophysical Journa
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