5,357 research outputs found
The 2D dynamics of radiative zones of low-mass stars
In the context of secular evolution, we describe the dynamics of the
radiative core of low-mass stars to understand the internal transport of
angular momentum in such stars which results in a solid rotation in the Sun
from 0.7R_sun to 0.2R_sun and a weak radial core-envelope differential rotation
in solar-type stars. This study requires at least a 2D description to capture
the latitudinal variations of the differential rotation. We build 2D numerical
models of a radiative core on the top of which we impose a latitudinal shear so
as to reproduce a cylindrical differential rotation in a convective envelope.
We perform a systematic study over the Rossby number measuring the latitudinal
differential rotation at the radiative-convective interface. The imposed shear
generates a geostrophic flow implying a cylindrical differential rotation. When
compared to the baroclinic flow that arises from the stable stratification, we
find that the geostrophic flow is dominant when the Rossby number is high
enough with a cylindrical rotation profile. For low Rossby numbers, the
baroclinic solution dominates with a quasi-shellular rotation profile. Using
scaling laws from 3D simulations, we show that slow rotators are expected to
have a cylindrical rotation profile. Fast rotators may have a shellular profile
at the beginning of the main-sequence in stellar radiative zones. This study
enables us to predict different types of differential rotation and emphasizes
the need of a new generation of 2D rotating stellar models developed in synergy
with 3D numerical simulations. The shear induced by a surface convective zone
has a strong impact on the dynamics of the underlying radiative zone in
low-mass stars. But, it cannot produce a flat internal rotation profile in a
solar configuration calling for additional processes for the transport of
angular momentum in both radial and latitudinal directions.Comment: 12 pages, 7 figures, accepted for publication in A&
Divergence in credit ratings
During the recent credit crisis credit rating agencies (CRAs) became increas-
ingly lax in their rating of structured products, yet increasingly stringent
in their rating of corporate bonds. We examine a model in which a CRA
operates in both the market for structured products and for corporate debt,
and shares a common reputation across the two markets. We find that, as a
CRA s reputation becomes good enough, it can be optimal for it to infl ate its
ratings with probability one in the structured products market, but in flate
its ratings with a probability zero in the corporate bond market
Sub-Inertial Gravity Modes in the B8V Star KIC 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing
KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36
consecutive dipole () gravity (g-) modes. The monotonically decreasing
period spacing of the series, in addition to the local dips in the pattern
confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in
chemically inhomogeneous layers. We employ the traditional approximation of
rotation to incorporate rotational effects on g-mode frequencies. Our detailed
forward asteroseismic modelling of this g-mode series reveals that KIC 7760680
is a moderately rotating B star with mass M. By
simultaneously matching the slope of the period spacing, and the number of
modes in the observed frequency range, we deduce that the equatorial rotation
frequency of KIC 7760680 is 0.4805 day, which is 26\% of its Roche break
up frequency. The relative deviation of the model frequencies and those
observed is less than one percent. We succeed to tightly constrain the
exponentially-decaying convective core overshooting parameter to . This means that convective core overshooting can
coexist with moderate rotation. Moreover, models with exponentially-decaying
overshoot from the core outperform those with the classical step-function
overshoot. The best value for extra diffusive mixing in the radiatively stable
envelope is confined to (with in cm sec), which is notably smaller than theoretical
predictions.Comment: 12 Figures, 2 Tables, all data publicly available for download;
accepted for publication in Astrophysical Journa
Charismatic and Expository Preaching: A Case Study of Two Preaching Methods within the Local Church
Preaching by far is the primary tool used within the Body of Christ to spread the gospel throughout the world and draw people to the ecclesia (church). For centuries the fundamental approach to heralding the Word of God has been rooted in expository preaching. This theologically sound approach has been shadowed by the rise of the Charismatic Movement and its preaching. Therefore, this thesis project study foci will be on Charismatic and Expository Preaching: A Case Study of Two Preaching Methods within the Local Church. This study is necessary to determine if these two forms of preaching can co-exist or if charismatic preaching can be incorporated as sound doctrinal preaching to edify the Body of Christ. The case study will be accomplished by theoretically and theologically comparing the data, biblical research, and the visitation of charismatic churches, particularly churches grounded in sound expository preaching. This research aims to compare the two by evaluating the churches\u27 growth and decline using these forms of preaching and how the congregants receive the preaching of the two. The results will be valuable to the ministry in understanding the effectiveness of the two as it pertains to the church\u27s growth and Christ as its foundation. New Hope Missionary Baptist Church was once considered charismatic with tremendous growth, with its pastor being charismatic and possessing many of the spiritual gifts that congregants gravitated to with awe. With his departure, the church had a significant decline
CP and related phenomena in the context of Stellar Evolution
We review the interaction in intermediate and high mass stars between their
evolution and magnetic and chemical properties. We describe the theory of
Ap-star `fossil' fields, before touching on the expected secular diffusive
processes which give rise to evolution of the field. We then present recent
results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that
magnetic fields of the kind seen on the main-sequence already exist during the
pre-main sequence phase, in agreement with fossil field theory, and that the
origin of the slow rotation of Ap/Bp stars also lies early in the pre-main
sequence evolution; we also present results confirming a lack of stars with
fields below a few hundred gauss. We then seek which macroscopic motions
compete with atomic diffusion in determining the surface abundances of AmFm
stars. While turbulent transport and mass loss, in competition with atomic
diffusion, are both able to explain observed surface abundances, the interior
abundance distribution is different enough to potentially lead to a test using
asterosismology. Finally we review progress on the turbulence-driving and
mixing processes in stellar radiative zones.Comment: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figure
The Warm Ionized Medium in the Milky Way and Other Galaxies
Observations of the "Warm Ionized Medium" (or, equivalently, the "Diffuse
Ionized Gas") of the local ISM, the Perseus arm in the Milky Way, and also in
several other galaxies show strong [NII]6563 (~H-alpha in some cases) and
[SII]6717/[NII]6583 = 0.6 - 0.7 in all locations and objects. Other line ratios
(e.g., [O III]5007/H-beta) vary considerably. Simple photoionization models
reproduce the observed spectra, providing extra heating beyond that supplied by
photoionization is assumed (Reynolds, Haffner, & Tufte 1999). With observed
gas-phase abundances (not solar), the line ratios in the local arm at b = 0 deg
are fitted with no extra heating and (S/H) = 13 ppm (solar is 20 ppm). Local
gas observed at b = -35 deg requires extra heating of about gamma = 0.75, where
gamma is the extra heating in units of 10^{-25} erg H^{-1} s^{-1}. In the
Perseus arm, there are similar results, with a domposition consistent with the
Galactic abundance gradient. The requirements for NGC 891 are similar to the
Perseus arm: little or no extra heating at |z| = 1 kpc and gamma 3 at 2 kpc. In
NGC 891 there is also an increase of 5007/H-alpha with |z| that can only come
about if most of the ionizing radiation is supplied by stars with T~50000 K.
Either their radiation must propagate from the plane to high |z| through very
little intervening matter, or else the stars are located at high |z|. The total
power requirement of the extra heating is <15% of the photoionization power.
[O~II]3727/H-beta can serve as a useful diagnostic of extra heating, but
[S~III] 9065,9531/H-alpha is not useful in this regard.Comment: 32 pages, including 2 figures. To appear in November 20 Ap
In situ ozone data for evaluation of the laser absorption spectrometer ozone remote sensor: 1979 southeastern Virginia urban plume study summer field program
Ozone data from the 1979 Southeastern Virginia Urban Study (SEV-UPS) field program are presented. The SEV-UPS was conducted for evaluation of an ozone remote sensor, the Laser Absorption Spectrometer. During the measurement program, remote-sensor evaluation was in two areas; (1) determination of the remote sensor's accuracy, repeatability, and operational characteristics, and (2) demonstration of the application of remotely sensed ozone data in air-quality studies. Data from six experiments designed to provide in situ ozone data for evaluation of the sensor in area 1, above, are presented. Experiments consisted of overflights of a test area with the remote sensor aircraft while in situ measurements with a second aircraft and selected surface stations provided correlative ozone data within the viewing area of the remote sensor
Summary of aircraft results for 1978 southeastern Virginia urban plume measurement study of ozone, nitrogen oxides, and methane
Ozone production was determined from aircraft and surface in situ measurements, as well as from an airborne laser absorption spectrometer. Three aircraft and approximately 10 surface stations provided air-quality data. Extensive meteorological, mixing-layer-height, and ozone-precursor data were also measured. Approximately 50 hrs (9 flight days) of data from the aircraft equipped to monitor ozone, nitrogen oxides, dewpoint temperature, and temperature are presented. In addition, each experiment conducted is discussed
Commercial Fishing Port Development in North Florida
The author has identified the following significant results. Seven major counties were examined: Escambia, Bay, Gulf, Franklin, Wakulla, Nassau, and Duval. Population and economic activity were reviewed, along with commercial fishing and port facilities. Recommendations for five northwest Florida counties were based on interpretation of aerial photographs, satellite imagery, an aerial survey site visit, and published data. Major needs in Pensacola included docking, ice supply, and net and engine repair services. Costs for additional docks, an ice plant, and gear storage were estimated at 2,860,000. Added docking, gear storage, and ice supply, as well as gear electronics and diesel repair were needed in Port St. Joe. Costs were calculated at 1,107,000 for docks and gear storage, Eastpoint - 2,824,100 for docks, gear storage, and ice plant)
Spousal Violence and Outcome in Custody and Visitation Mediation
To examine whether custody and visitation mediation is appropriate in cases with a history of spousal violence, the outcomes of 49 self-reported violent couples were compared to those of 29 never-violent couples in court-ordered mediation. Outcomes were not adversely affected significantly except in chronic cases where incidents had occurred both during the marriage and after separation (p - .011). This report calls for standardized screening to identify chronically violent spouses as well as for modified approaches to treatment of such cases
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