36,635 research outputs found
Universal scale factors relating mesonic fields and quark operators
Scale factor matrices relating mesonic fields in chiral Lagrangians and
quark-level operators of QCD sum-rules are shown to be constrained by chiral
symmetry, resulting in universal scale factors for each chiral nonet. Built
upon this interplay between chiral Lagrangians and QCD sum-rules, the scale
factors relating the isotriplet scalar mesons to their underlying quark
composite field were recently determined. It is shown that the same technique
when applied to isodoublet scalars reproduces the same scale factors,
confirming the universality property and further validating this connection
between chiral Lagrangians and QCD sum-rules which can have nontrivial impacts
on our understanding of the low-energy QCD, in general, and the physics of
scalar mesons in particular.Comment: 5 pages, 1 figure. arXiv admin note: text overlap with
arXiv:1909.0724
Biodegradable Polylactic Acid (PLA) Microstructures for Scaffold Applications
In this research, we present a simple and cost effective soft lithographic
process to fabricate PLA scaffolds for tissue engineering. In which, the
negative photoresist JSR THB-120N was spun on a glass subtract followed by
conventional UV lithographic processes to fabricate the master to cast the PDMS
elastomeric mold. A thin poly(vinyl alcohol) (PVA) layer was used as a mode
release such that the PLA scaffold can be easily peeled off. The PLA precursor
solution was then cast onto the PDMS mold to form the PLA microstructures.
After evaporating the solvent, the PLA microstructures can be easily peeled off
from the PDMS mold. Experimental results show that the desired microvessels
scaffold can be successfully transferred to the biodegradable polymer PLA.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Estimating Black Hole Masses in Active Galaxies Using the Halpha Emission Line
It has been established that virial masses for black holes in low-redshift
active galaxies can be estimated from measurements of the optical continuum
strength and the width of the broad Hbeta line. Under various circumstances,
however, both of these quantities can be challenging to measure or can be
subject to large systematic uncertainties. To mitigate these difficulties, we
present a new method for estimating black hole masses. From analysis of a new
sample of broad-line active galactic nuclei, we find that Halpha luminosity
scales almost linearly with optical continuum luminosity and that a strong
correlation exists between Halpha and Hbeta line widths. These two empirical
correlations allow us to translate the standard virial mass system to a new one
based solely on observations of the broad Halpha emission line.Comment: to appear in Apj; 8 pages; 5 figures; uses emulateapj5.st
Equilibrium spin pulsars unite neutron star populations
Many pulsars are formed with a binary companion from which they can accrete
matter. Torque exerted by accreting matter can cause the pulsar spin to
increase or decrease, and over long times, an equilibrium spin rate is
achieved. Application of accretion theory to these systems provides a probe of
the pulsar magnetic field. We compare the large number of recent torque
measurements of accreting pulsars with a high-mass companion to the standard
model for how accretion affects the pulsar spin period. We find that many long
spin period (P > 100 s) pulsars must possess either extremely weak (B < 10^10
G) or extremely strong (B > 10^14 G) magnetic fields. We argue that the
strong-field solution is more compelling, in which case these pulsars are near
spin equilibrium. Our results provide evidence for a fundamental link between
pulsars with the slowest spin periods and strong magnetic fields around
high-mass companions and pulsars with the fastest spin periods and weak fields
around low-mass companions. The strong magnetic fields also connect our pulsars
to magnetars and strong-field isolated radio/X-ray pulsars. The strong field
and old age of our sources suggests their magnetic field penetrates into the
superconducting core of the neutron star.Comment: 6 pages, 4 figures; to appear in MNRA
Kinematics of Circumgalactic Gas: Feeding Galaxies and Feedback
We present observations of 50 pairs of redshift z ~ 0.2 star-forming galaxies
and background quasars. These sightlines probe the circumgalactic medium (CGM)
out to half the virial radius, and we describe the circumgalactic gas
kinematics relative to the reference frame defined by the galactic disks. We
detect halo gas in MgII absorption, measure the equivalent-width-weighted
Doppler shifts relative to each galaxy, and find that the CGM has a component
of angular momentum that is aligned with the galactic disk. No net
counter-rotation of the CGM is detected within 45 degrees of the major axis at
any impact parameter. The velocity offset of the circumgalactic gas correlates
with the projected rotation speed in the disk plane out to disk radii of
roughly 70 kpc. We confirm previous claims that the MgII absorption becomes
stronger near the galactic minor axis and show that the equivalent width
correlates with the velocity range of the absorption. We cannot directly
measure the location of any absorber along the sightline, but we explore the
hypothesis that individual velocity components can be associated with gas
orbiting in the disk plane or flowing radially outward in a conical outflow. We
conclude that centrifugal forces partially support the low-ionization gas and
galactic outflows kinematically disturb the CGM producing excess absorption.
Our results firmly rule out schema for the inner CGM that lack rotation and
suggest that angular momentum as well as galactic winds should be included in
any viable model for the low-redshift CGM.Comment: Accepted for publication in the Astrophysical Journa
Numerical analysis of the Iosipescu specimen for composite materials
A finite element analysis of the Iosipescu shear tests for unidirectional and cross-ply composites is presented. It is shown that an iterative analysis procedure must be used to model the fixture-specimen kinematics. The correction factors which are needed to compensate for the nonuniformity of stress distribution in calculating shear modulus are shown to be dependent on the material orthotropic ratio and the finite element loading models. Test section strain distributions representative of typical graphite-epoxy specimens are also presented
Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic Cloud
We report on the long-term average spin period, rate of change of spin period
and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the
Small Magellanic Cloud. We also collect and calculate parameters of each system
and use these data to determine that all systems contain a neutron star which
is accreting via a disc, rather than a wind, and that if these neutron stars
are near spin equilibrium, then over half of them, including all with spin
periods over about 100 s, have magnetic fields over the quantum critical level
of 4.4x10^13 G. If these neutron stars are not close to spin equilibrium, then
their magnetic fields are inferred to be much lower, of the order of 10^6-10^10
G, comparable to the fields of neutron stars in low-mass X-ray binaries. Both
results are unexpected and have implications for the rate of magnetic field
decay and the isolated neutron star population.Comment: 22 pages, 50 figures; to appear in MNRA
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