1,715 research outputs found
Nucleons, Nuclear Matter and Quark Matter: A unified NJL approach
We use an effective quark model to describe both hadronic matter and
deconfined quark matter. By calculating the equations of state and the
corresponding neutron star properties, we show that the internal properties of
the nucleon have important implications for the properties of these systems.Comment: 17 pages, 5 figures, Section 5 extended, references adde
Hubble Space Telescope Imaging of Bright Lyman-break Galaxy Candidates from the Sloan Digital Sky Survey: Not LBGs After All
We present deep Hubble Space Telescope ACS and NICMOS images of six bright
Lyman-break galaxy candidates that were previously discovered in the Sloan
Digital Sky Survey. We find that five of the objects are consistent with
unresolved point sources. Although somewhat atypical of the class, they are
most likely LoBAL quasars, perhaps FeLoBALs. The sixth object, J1147, has a
faint companion galaxy located ~0.8 arcsec to the southwest. The companion
contributes ~8% of the flux in the observed-frame optical and infrared. It is
unknown whether this companion is located at the same redshift as J1147.Comment: 16 pages, 8 figures, 3 tables; accepted for publication in A
An Alternative Approach To Measuring Reverberation Lags in Active Galactic Nuclei
Motivated by recent progress in the statistical modeling of quasar
variability, we develop a new approach to measuring emission-line reverberation
lags to estimate the size of broad-line regions (BLRs) in active galactic
nuclei. Assuming that all emission-line light curves are scaled, smoothed, and
displaced versions of the continuum, this alternative approach fits the light
curves directly using a damped random walk model and aligns them to recover the
time lag and its statistical confidence limits. We introduce the mathematical
formalism of this approach and demonstrate its ability to cope with some of the
problems for traditional methods, such as irregular sampling, correlated
errors, and seasonal gaps. We redetermine the lags for 87 emission lines in 31
quasars and reassess the BLR size--luminosity relationship using 60 H-beta
lags. We confirm the general results from the traditional cross-correlation
methods, with a few exceptions. Our method, however, also supports a broad
range of extensions. In particular, it can simultaneously fit multiple lines
and continuum light curves which improves the lag estimate for the lines and
provides estimates of the error correlations between them. Determining these
correlations is of particular importance for interpreting emission-line
velocity--delay maps. We can also include parameters for luminosity-dependent
lags or line responses. We use this to detect the scaling of the BLR size with
continuum luminosity in NGC 5548.Comment: match to the version accepted to ApJ. New code release available at
http://www.astronomy.ohio-state.edu/~yingzu/spear.htm
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Multicomponent metal-organic framework membranes for advanced functional composites.
The diverse chemical and structural properties of metal-organic frameworks (MOFs) make them attractive for myriad applications, but their native powder form is limiting for industrial implementation. Composite materials of MOFs hold promise as a means of exploiting MOF properties in engineered forms for real-world applications. While interest in MOF composites is growing, research to date has largely focused on utilization of single MOF systems. The vast number of different MOF structures provides ample opportunity to mix and match distinct MOF species in a single composite to prepare multifunctional systems. In this work, we describe the preparation of three types of multi-MOF composites with poly(vinylidene fluoride) (PVDF): (1) co-cast MOF MMMs, (2) mixed MOF MMMs, and (3) multilayer MOF MMMs. Finally, MOF MMMs are explored as catalytic membrane reactors for chemical transformations
Telescope Parallel Actuator Mount: Control and Testing
This thesis approaches the task of designing a control system for the Parallel Actuator Mount developed by Dr. John Ridgely and Mr. Garrett Gudgel. It aims to create a base framework that directly controls the telescope and can be expanded to accept external command. It incorporates lower priced components and develops more easily approachable software with great functionality. An open-loop method for velocity control is established. Developing repeatable tests is a major focus. Testing finds the control methods developed result in velocity error of less than 5% and position error of less than 1.5% despite several mechanical issues and inaccuracies. Design guidelines are established that allow for the easy implementation of a Parallel Actuator Mount on other systems.
This paper proves that the Parallel Actuator Mount is a potentially viable system for aiming a telescope when an astronomer does not require full sky coverage. The tests showed too much error to fully recommend the system as built and tested, but there are paths to increase accuracy of the system without greatly increasing the complexity or cost. The inclusion of a method of feedback, including a plate solver and an inertial measurement unit, would greatly improve the system. It may also be of use to modify the software to include a variable time step for the velocity control
Neutron Star Properties from an NJL Model Modified to Simulate Confinement
The NJL model has recently been extended with a method to simulate
confinement. This leads in mean field approximation to a natural mechanism for
the saturation of nuclear matter. We use the model to investigate the equation
of state of asymmetric nuclear matter and then use it to compute the properties
of neutron stars.Comment: 5 pages, 6 figures, to be published in the proceedings for QCD Down
Under Workshop, Adelaide, March 10-19, 200
BLR kinematics and Black Hole Mass in Markarian 6
We present results of the optical spectral and photometric observations of
the nucleus of Markarian 6 made with the 2.6-m Shajn telescope at the Crimean
Astrophysical Observatory. The continuum and emission Balmer line intensities
varied more than by a factor of two during 1992-2008. The lag between the
continuum and Hbeta emission line flux variations is 21.1+-1.9 days. For the
Halpha line the lag is about 27 days but its uncertainty is much larger. We use
Monte-Carlo simulation of the random time series to check the effect of our
data sampling on the lag uncertainties and we compare our simulation results
with those obtained by random subset selection (RSS) method of Peterson et al.
(1998). The lag in the high-velocity wings are shorter than in the line core in
accordance with the virial motions. However, the lag is slightly larger in the
blue wing than in the red wing. This is a signature of the infall gas motion.
Probably the BLR kinematic in the Mrk 6 nucleus is a combination of the
Keplerian and infall motions. The velocity-delay dependence is similar for
individual observational seasons. The measurements of the Hbeta line width in
combination with the reverberation lag permits us to determine the black hole
mass, M_BH=(1.8+-0.2)x10^8 M_sun. This result is consistent with the AGN
scaling relationships between the BLR radius and the optical continuum
luminosity (R_BLR is proportional to L^0.5) as well as with the black-hole
mass-luminosity relationship (M_BH-L) under the Eddington luminosity ratio for
Mrk 6 to be L_bol/L_Edd ~ 0.01.Comment: 17 pages, 10 figures, accepted for publication in MNRA
Implementing PCAC in Nonperturbative Models of Pion Production
Traditional few-body descriptions of pion production use integral equations
to sum the strong interactions nonperturbatively. Although much physics is
thereby included, there has not been a practical way of incorporating the
constraints of chiral symmetry into such approaches. Thus the traditional
few-body descriptions fail to reflect the underlying theory of strong
interactions, QCD, which is largely chirally symmetric. In addition, the lack
of chiral symmetry in the few-body approaches means that their predictions of
pion production are in principle not consistent with the partial conservation
of axial current (PCAC), a fact that has especially large consequences at low
energies. We discuss how the recent introduction of the ``gauging of equations
method'' can be used to include PCAC into traditional few-body descriptions and
thereby solve this long standing problemComment: Contribution to Proceedings, 1st Asia-Pacific Conference on Few-Body
Problems in Physics, Noda/Kashiwa, Japan, 23-28 August 1999, to be published
by Springer-Verlag as "Few-Body Systems Supplement". 7 pages, revtex, epsf, 3
Postscript figure
Calculating Kaon Fragmentation Functions from NJL-Jet Model
The Nambu--Jona-Lasinio (NJL) - Jet model provides a sound framework for
calculating the fragmentation functions in an effective chiral quark theory,
where the momentum and isospin sum rules are satisfied without the introduction
of ad hoc parameters. Earlier studies of the pion fragmentation functions using
the NJL model within this framework showed qualitative agreement with the
empirical parameterizations. Here we extend the NJL-Jet model by including the
strange quark. The corrections to the pion fragmentation functions and
corresponding kaon fragmentation functions are calculated using the elementary
quark to quark-meson fragmentation functions from NJL. The results for the kaon
fragmentation functions exhibit a qualitative agreement with the empirical
parameterizations, while the unfavored strange quark fragmentation to pions is
shown to be of the same order of magnitude as the unfavored light quark's. The
results of these studies are expected to provide important guidance for the
analysis of a large variety of semi-inclusive data.Comment: 9 pages, 14 figure
Monte Carlo Simulations of Hadronic Fragmentation Functions using NJL-Jet Model
The recently developed Nambu-Jona-Lasinio (NJL) - Jet model is used as an
effective chiral quark theory to calculate the quark fragmentation functions to
pions, kaons, nucleons, and antinucleons. The effects of the vector mesons rho,
K* and phi on the production of secondary pions and kaons are included. The
fragmentation processes to nucleons and antinucleons are described by using the
quark-diquark picture, which has been shown to give a reasonable description of
quark distribution functions. We incorporate effects of next-to-leading order
(NLO) in the Q^2 evolution, and compare our results with the empirical
fragmentation functions.Comment: 27 pages, 13 figure
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