24,886 research outputs found
Elucidating the Correlation of the Quasar \ion{Fe}{2}/\ion{Mg}{2} Ratio with Redshift
Interpretation of the \ion{Fe}{2}(UV)/\ion{Mg}{2} emission ratios from
quasars has a major cosmological motivation. Both Fe and Mg are produced by
short-lived massive stars. In addition, Fe is produced by accreting white dwarf
supernovae somewhat after star formation begins. Therefore, we expect that the
Fe/Mg ratio will gradually decrease with redshift. We have used data from the
Sloan Digital Sky Survey to explore the dependence of the
\ion{Fe}{2}(UV)/\ion{Mg}{2} ratio on redshift and on luminosity in the redshift
range of , and we have used predictions from our 830-level model
for the \ion{Fe}{2} atom in photoionization calculations to interpret our
findings.
We have split the quasars into several groups based upon the value of their
\ion{Fe}{2}(UV)/\ion{Mg}{2} emission ratios, and then checked to see how the
fraction of quasars in each group varies with the increase of redshift. We next
examined the luminosity dependence of the \ion{Fe}{2}(UV)/\ion{Mg}{2} ratio,
and we found that beyond a threshold of \ion{Fe}{2}(UV)/\ion{Mg}{2} =~ 5, and
, the \ion{Fe}{2}(UV)/\ion{Mg}{2} ratio increases with
luminosity, as predicted by our model.
We interpret our observed variation of the \ion{Fe}{2}(UV)/\ion{Mg}{2} ratio
with redshift as a result of the correlation of redshift with luminosity in a
magnitude limited quasar sample.Comment: ApJL accepte
Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor
For a systematic assessment of submillimeter observing conditions at
different sites, we constructed tipping radiometers to measure the broad band
atmospheric transparency in the window around 350 m wavelength. The
tippers were deployed on Maunakea, Hawaii, at the South Pole, and in the
vicinity of Cerro Chajnantor in northern Chile. Identical instruments permit
direct comparison of these sites. Observing conditions at the South Pole and in
the Chajnantor area are better than on Maunakea. Simultaneous measurements with
two tippers demonstrate conditions at the summit of Cerro Chajnantor are
significantly better than on the Chajnantor plateau.Comment: Accepted by PAS
The Intergenerational Effects of Early Childbearing
Since World War II, the average age at which women experience their first birth has drifted up, but since 1986 there has been a resurgence of births to teenagers. Just as early fertility appears to adversely affect the life chances of the teen mother, it may also have negative effects on her children. We hypothesize that when the children of teen mothers are young adults, they will tend to have lower education, and will be more likely to be economically inactive, to have children when they are teens, and to have children out of wedlock when they are teens. In this paper, we present several models designed to reveal the impact that being born to a teenage mother has on children's chances for success as young adults. Our findings indicate that the children of mothers who first gave birth as teens are adversely affected as young adults.
Do Teens Make Rational Choices? The Case of Teen Nonmarital Childbearing
With emphasis on the role of economic incentives, we explore the determinants of a woman’s choice of whether or not to give birth as an unmarried teenager. Our data are taken from the Panel Study of Income Dynamics. Guided by a simple utility-maximization model, we represent the income possibilities available to teenaged women if they do and do not give birth out of wedlock. We estimate these choice-conditioned income possibilities through a two-stage probit procedure, relying on the observed incomes of a secondary sample of somewhat older women. The response of the young women in our primary sample to these income expectations is measured after controlling for the effects of a variety of other factors, including the characteristics of the girl’s family, the social and economic environment in which she lives (including such policy-related factors as expenditures by states on family planning programs and education), and her own prior choices. We use the estimated structural parameters from our model to simulate the effects of a variety of policy interventions on the probability of becoming an unmarried teen mother. Our estimations provide evidence that income expectations have a persistent influence on the childbearing decision. They also provide evidence that the provision of public family planning expenditures and increases in parental education could reduce the prevalence of teen nonmarital births.
Delineation of the boundaries of a buried pre-glacial valley with LANDSAT-1 data
The continuity of a narrow meandering strip of Udoll (prairie) soils running east and west for approximately 40 miles across north central Indiana in an area predominantly of Udalfs (timber soils) was detected from LANDSAT-1 data taken on June 9, 1973. This data was processed through a clustering procedure and classified with resulting increased definition of the boundaries among soils grouped according to nine categories and vegetation to two categories of reflectance. This dark stretch of prairie soil is believed to have formed in the heavy textured, poorly drained glacial debris which filled a major pre-glacial tributary of the Teays River System. Ready identification and location of the valley has significance to soil survey and land classification people as a guide to soil classification and land use and to geologists as a guide to location of a potentially economically significant aquifer
Evaluation of materials and design modifications for aircraft brakes
A test program is described which was carried out to evaluate several proposed design modifications and several high-temperature friction materials for use in aircraft disk brakes. The evaluation program was carried out on a specially built test apparatus utilizing a disk brake and wheel half from a small het aircraft. The apparatus enabled control of brake pressure, velocity, and braking time. Tests were run under both constant and variable velocity conditions and covered a kinetic energy range similar to that encountered in aircraft brake service. The results of the design evaluation program showed that some improvement in brake performance can be realized by making design changes in the components of the brake containing friction material. The materials evaluation showed that two friction materials show potential for use in aircraft disk brakes. One of the materials is a nickel-based sintered composite, while the other is a molybdenum-based material. Both materials show much lower wear rates than conventional copper-based materials and are better able to withstand the high temperatures encountered during braking. Additional materials improvement is necessary since both materials show a significant negative slope of the friction-velocity curve at low velocities
Diagnostics of the structure of AGN's broad line regions with reverberation mapping data: confirmation of the two-component broad line region model
We re-examine the ten Reverberation Mapping (RM) sources with public data
based on the two-component model of the Broad Line Region (BLR). In fitting
their broad H-beta lines, six of them only need one Gaussian component, one of
them has a double-peak profile, one has an irregular profile, and only two of
them need two components, i.e., a Very Broad Gaussian Component (VBGC) and an
Inter-Mediate Gaussian Component (IMGC). The Gaussian components are assumed to
come from two distinct regions in the two-component model; they are Very Broad
Line Region (VBLR) and Inter-Mediate Line region (IMLR). The two sources with a
two-component profile are Mrk 509 and NGC 4051. The time lags of the two
components of both sources satisfy ,
where and are the lags of the two components while
and represent the mean gas velocities of the two regions,
supporting the two-component model of the BLR of Active Galactic Nuclei (AGN).
The fact that most of these ten sources only have the VBGC confirms the
assumption that RM mainly measures the radius of the VBLR; consequently, the
radius obtained from the R-L relationship mainly represent the radius of VBLR.
Moreover, NGC 4051, with a lag of about 5 days in the one component model, is
an outlier on the R-L relationship as shown in Kaspi et al. (2005); however
this problem disappears in our two-component model with lags of about 2 and 6
days for the VBGC and IMGC, respectively.Comment: 7 pages, 5 figures. Accepted for publication in the Special Issue of
Science in China (G) "Astrophysics of Black holes and Related Compact
Objects
Stress, coping, and emotional distress of medically underserved lung and head-and-neck cancer patients
2019 Summer.Includes bibliographical references.The intent of this study was to investigate how lung cancer (LC) and head and neck cancer (HNC) patients who are medically underserved (i.e. uninsured, underinsured, low income) experience emotional distress (symptoms of depression and anxiety) after being diagnosed with LC or HNC. Participants were recruited from four Colorado hospitals. They completed a baseline survey which included measures of perceived stress, coping self-efficacy, depression symptoms, and anxiety symptoms. The Transactional Model of Stress and Coping (TMSC) was used as a theoretical guide for analyses about the relations of stress coping and emotional distress. When age, sex, and stage of cancer were controlled for, levels of perceived stress were observed to be positively associated with experience of emotional distress. Further, coping was shown to be an effective moderator of the relation of perceived stress to emotional distress. The TMSC is a functional theoretical model for organizing the understanding of stress, coping and emotional distress for medically underserved LC and HNC patients. Further research should be conducted to assess for changes in these variables overtime, particularly if psychological interventions can be used to influence each variable
Aerodynamic design of the contoured wind-tunnel liner for the NASA supercritical, laminar-flow-control, swept-wing experiment
An overview is presented of the entire procedure developed for the aerodynamic design of the contoured wind tunnel liner for the NASA supercritical, laminar flow control (LFC), swept wing experiment. This numerical design procedure is based upon the simple idea of streamlining and incorporates several transonic and boundary layer analysis codes. The liner, presently installed in the Langley 8 Foot Transonic Pressure Tunnel, is about 54 ft long and extends from within the existing contraction cone, through the test section, and into the diffuser. LFC model testing has begun and preliminary results indicate that the liner is performing as intended. The liner design results presented in this paper, however, are examples of the calculated requirements and the hardware implementation of them
- …