7,070 research outputs found
ATRAN3S: An unsteady transonic code for clean wings
The development and applications of the unsteady transonic code ATRAN3S for clean wings are discussed. Explanations of the unsteady, transonic small-disturbance aerodynamic equations that are used and their solution procedures are discussed. A detailed user's guide, along with input and output for a sample case, is given
Reinventing Westminster Abbey 1642-1660: a house of kings from revolution to restoration
While historians are familiar with the destruction wrought on the nation's cathedrals during the Civil War, the rather different fate experienced by Westminster Abbey--an important symbolic building that tied together royal and religious authority--has been strangely neglected. This article argues that the Abbey played an important and distinctive role in the religious and cultural politics of the nation during the 1640s and 1650s. It uncovers the Abbey’s role in helping to legitimise successive non-monarchical regimes and ultimately explains how efforts to ‘reclaim’ the Abbey at the Restoration formed part of broader efforts to renegotiate and reinterpret the nation’s past
Radial Velocities of Stars in the Galactic Center
We present results from K band slit scan observations of a ~20''x20'' region
of the Galactic center (GC) in two separate epochs more than five years apart.
The high resolution (R>=14,000) observations allow the most accurate radial
velocity and acceleration measurements of the stars in the central parsec of
the Galaxy. Detected stars can be divided into three groups based on the CO
absorption band heads at ~2.2935 microns and the He I lines at ~2.0581 microns
and ~2.112, 2.113 microns: cool, narrow-line hot and broad-line hot. The radial
velocities of the cool, late-type stars have approximately a symmetrical
distribution with its center at ~-7.8(+/-10.3) km/s and a standard deviation
~113.7(+/-10.3) km/s. Although our statistics are dominated by the brightest
stars, we estimate a central black hole mass of 3.9(+/-1.1) million solar
masses, consistent with current estimates from complete orbits of individual
stars. Our surface density profile and the velocity dispersion of the late type
stars support the existence of a low density region at the Galactic center
suggested by earlier observations. Many hot, early-type stars show radial
velocity changes higher than maximum values allowed by pure circular orbital
motions around a central massive object, suggesting that the motions of these
stars greatly deviate from circular orbital motions around the Galactic center.
The correlation between the radial velocities of the early type He I stars and
their declination offsets from Sagittarius A* suggests that a systematic
rotation is present for the early-type population. No figure rotation around
the Galactic center for the late type stars is supported by the new
observations.Comment: 61 pages, 18 figures, 7 tables; accepted for publication in
Astrophysical Journa
Long-Term Evolution of Massive Black Hole Binaries. II. Binary Evolution in Low-Density Galaxies
We use direct-summation N-body integrations to follow the evolution of binary
black holes at the centers of galaxy models with large, constant-density cores.
Particle numbers as large as 400K are considered. The results are compared with
the predictions of loss-cone theory, under the assumption that the supply of
stars to the binary is limited by the rate at which they can be scattered into
the binary's influence sphere by gravitational encounters. The agreement
between theory and simulation is quite good; in particular, we are able to
quantitatively explain the observed dependence of binary hardening rate on N.
We do not verify the recent claim of Chatterjee, Hernquist & Loeb (2003) that
the hardening rate of the binary stabilizes when N exceeds a particular value,
or that Brownian wandering of the binary has a significant effect on its
evolution. When scaled to real galaxies, our results suggest that massive black
hole binaries in gas-poor nuclei would be unlikely to reach gravitational-wave
coalescence in a Hubble time.Comment: 13 pages, 8 figure
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Effect of a Fruit and Vegetable Prescription Program on Children's Fruit and Vegetable Consumption.
IntroductionMost children in families with low income do not meet dietary guidance on fruit and vegetable consumption. Fruit and vegetable prescription programs improve access to and affordability of health-supporting foods for adults, but their effect on dietary behavior among children is not known. The objective of this study was to describe the extent to which exposure to a fruit and vegetable prescription program was associated with changes in consumption among participants aged 2 to 18.MethodsWe used data from a modified National Cancer Institute screener to calculate fruit and vegetable intake among 883 children who were overweight or had obesity and participated in a 4- to 6-month fruit and vegetable prescription program at federally qualified health centers during 4 years (2012-2015). Secondary analyses in 2017 included paired t tests to compare change in fruit and vegetable consumption (cups/day) between first and last visits and multivariable linear regressions, including propensity dose-adjusted models, to model this change as a function of sociodemographic and program-specific covariates, such as number of clinical visits and value of prescription redemption.ResultsWe found a dose propensity-adjusted increase of 0.32 cups (95% confidence interval, 0.19-0.45 cups) for each additional visit while holding constant the predicted number of visits and site. An equal portion of the change-score increase was attributed to vegetable consumption and fruit consumption (β = 0.16 for each).ConclusionFruit and vegetable prescription programs in clinical settings may increase fruit and vegetable consumption among children in low-income households. Future research should use a comparison group and consider including qualitative analysis of site-specific barriers and facilitators to success
Polymers near Metal Surfaces: Selective Adsorption and Global Conformations
We study the properties of a polycarbonate melt near a nickel surface as a
model system for the interaction of polymers with metal surfaces by employing a
multiscale modeling approach. For bulk properties a suitably coarse grained
bead spring model is simulated by molecular dynamics (MD) methods with model
parameters directly derived from quantum chemical calculations. The surface
interactions are parameterized and incorporated by extensive quantum mechanical
density functional calculations using the Car-Parrinello method. We find strong
chemisorption of chain ends, resulting in significant modifications of the melt
composition when compared to an inert wall.Comment: 8 pages, 3 figures (2 color), 1 tabl
Contested legitimacy and the ambiguous rise of vestries in early modern London
Studies of the rise of London's vestries in the period to 1640 have tended to discuss them in terms of the inexorable rise of oligarchy and state formation. This article re-examines the emergence of the vestries in several ways, moving beyond this traditional focus on oligarchy, and noting how London's vestries raised much broader issues concerning law, custom, and lay religious authority. The article reveals a notable contrast between the widespread influence and activities of London vestries and the questionable legal framework in which they operated. The political and ecclesiastical authorities – and in particular Archbishop Laud – are also shown to have had very mixed attitudes towards the legitimacy and desirability of powerful vestries. The apparently smooth and relentless spread of select vestries in the pre-war period is also shown to be illusory. The granting of vestry ‘faculties’ by the authorities ceased abruptly at the end of the 1620s, amid a series of serious legal challenges, on both local and ideological grounds, to the existence of vestries. Their rise had thus been seriously contested and stymied well before the upheavals of the 1640s, although opposition to them came from multiple sources – Laudians, Henry Spelman and the royal Commission on Fees, and local parishioners – whose objectives could vary
Evolution of Supermassive Black Hole Binary and Acceleration of Jet Precession in Galactic Nuclei
Supermassive black hole binary (SMBHB) is expected with the hierarchical
galaxy formation model. Currently, physics processes dominating the evolution
of a SMBHB are unclear. An interesting question is whether we could
observationally determine the evolution of SMBHB and give constraints on the
physical processes. Jet precession have been observed in many AGNs and
generally attributed to disk precession. In this paper we calculate the time
variation of jet precession and conclude that jet precession is accelerated in
SMBHB systems but decelerated in others. The acceleration of jet precession
is related to jet precession timescale and
SMBHB evolution timescale , . Our calculations based on the models
for jet precession and SMBHB evolution show that can be as
high as about with a typical value -0.2 and can be easily detected. We
discussed the differential jet precession for NGC1275 observed in the
literature. If the observed rapid acceleration of jet precession is true, the
jet precession is due to the orbital motion of an unbound SMBHB with mass ratio
. When jets precessed from the ancient bubbles to the currently
active jets, the separation of SMBHB decrease from about to
with an averaged decreasing velocity and evolution timescale . However, if we assume a steady jet precession for many cycles,
the observations implies a hard SMBHB with mass ratio and
separation .Comment: 29 pages, no figure, Accepted for publication in Ap
Spin Evolution of Supermassive Black Holes and Galactic Nuclei
The spin angular momentum S of a supermassive black hole (SBH) precesses due
to torques from orbiting stars, and the stellar orbits precess due to dragging
of inertial frames by the spinning hole. We solve the coupled post-Newtonian
equations describing the joint evolution of S and the stellar angular momenta
Lj, j = 1...N in spherical, rotating nuclear star clusters. In the absence of
gravitational interactions between the stars, two evolutionary modes are found:
(1) nearly uniform precession of S about the total angular momentum vector of
the system; (2) damped precession, leading, in less than one precessional
period, to alignment of S with the angular momentum of the rotating cluster.
Beyond a certain distance from the SBH, the time scale for angular momentum
changes due to gravitational encounters between the stars is shorter than
spin-orbit precession times. We present a model, based on the
Ornstein-Uhlenbeck equation, for the stochastic evolution of star clusters due
to gravitational encounters and use it to evaluate the evolution of S in nuclei
where changes in the Lj are due to frame dragging close to the SBH and to
encounters farther out. Long-term evolution in this case is well described as
uniform precession of the SBH about the cluster's rotational axis, with an
increasingly important stochastic contribution when SBH masses are small. Spin
precessional periods are predicted to be strongly dependent on nuclear
properties, but typical values are 10-100 Myr for low-mass SBHs in dense
nuclei, 100 Myr - 10 Gyr for intermediate mass SBHs, and > 10 Gyr for the most
massive SBHs. We compare the evolution of SBH spins in stellar nuclei to the
case of torquing by an inclined, gaseous accretion disk.Comment: 25 page
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