1,745 research outputs found
Religiosity and Sexual Risk Behaviors Among Latina Adolescents: Trends from 1995 to 2008
Purpose: The purpose of this study was to determine trends in the influence of religiosity on sexual activity of Latina adolescents in the United States from 1995 to 2008 and to determine if differences existed between the Mexican American and other Latina groups.
Methods: The sample comprised the subset of unmarried, 15–21-year-old (mean 17 years) Latina female respondents in the 1995 (n=267), 2002 (n=306), and 2006–2008 (n=400) National Survey of Family Growth (NSFG) datasets. Associations between religiosity (importance of religion and service attendance) and history of ever having sex, number of sex partners, and age of sexual debut were investigated.
Results: Less than one half of Latinas in 1995 (44%) and in 2006–2008 (44%) reported that religion was very important to them, whereas in 2002, 50% reported it was important. Only in 1995 did Latinas who viewed religion as very important have a significantly lower level of sexual initiation. In 1995 and in 2006–2008, Latinas who held religion as very important had significantly fewer partners. In all three cohorts, the higher religious importance group had higher virgin survival rates. Across cohorts, approximately one third of respondents reported frequent religious attendance. In all cohorts, frequent attenders were less likely to have had sex, had fewer partners, and had older age at sexual debut. The survival rate as virgins for Mexican origin Latinas was higher in 1995 and 2002 compared to non-Mexican Latinas but was almost the same in 2006–2008.
Conclusions: Religiosity had a protective association with sexual activity among Latina adolescents. The association of importance of religion with sexual activity has diminished from 1995 to 2008, however, whereas the importance of service attendance has remained stable. The influence of religion was more apparent among the Latinas of Mexican origin, but this greater influence also diminished by 2006–2008
Expanding hot flow in the black hole binary SWIFT J1753.5-0127: evidence from optical timing
We describe the evolution of optical and X-ray temporal characteristics
during the outburst decline of the black hole X-ray binary SWIFT J1753.5-0127.
The optical/X-ray cross-correlation function demonstrates a single positive
correlation at the outburst peak, then it has multiple dips and peaks during
the decline stage, which are then replaced by the precognition dip plus peak
structure in the outburst tail. Power spectral densities and phase lags show a
complex evolution, revealing the presence of intrinsically connected optical
and X-ray quasi-periodic oscillations. For the first time, we quantitatively
explain the evolution of these timing properties during the entire outburst
within one model, the essence of which is the expansion of the hot accretion
flow towards the tail of the outburst. The pivoting of the spectrum produced by
synchrotron Comptonization in the hot flow is responsible for the appearance of
the anti-correlation with the X-rays and for the optical quasi-periodic
oscillations. Our model reproduces well the cross-correlation and phase lag
spectrum during the decline stage, which could not be understood with any model
proposed before.Comment: 13 pages, 11 figures, MNRAS submitte
Ulcerative enteritis in quail
Publication authorized January 31, 1941.Digitized 2007 AES.Includes bibliographical references (page 27)
Adjusting particle-size distributions to account for aggregation in tephra-deposit model forecasts
Volcanic ash transport and dispersion (VATD) models are used to forecast tephra deposition during volcanic eruptions. Model accuracy is limited by the fact that fine-ash aggregates (clumps into clusters), thus altering patterns of deposition. In most models this is accounted for by ad hoc changes to model input, representing fine ash as aggregates with density ρagg, and a log-normal size distribution with median μagg and standard deviation σagg. Optimal values may vary between eruptions. To test the variance, we used the Ash3d tephra model to simulate four deposits: 18 May 1980 Mount St. Helens; 16-17 September 1992 Crater Peak (Mount Spurr); 17 June 1996 Ruapehu; and 23 March 2009 Mount Redoubt. In 192 simulations, we systematically varied μagg and σagg, holding ρagg constant at 600 kgm-3. We evaluated the fit using three indices that compare modeled versus measured (1) mass load at sample locations; (2) mass load versus distance along the dispersal axis; and (3) isomass area. For all deposits, under these inputs, the best-fit value of μagg ranged narrowly between ∼2.3 and 2.7φ (0.20-0.15 mm), despite large variations in erupted mass (0.25-50 Tg), plume height (8.5- 25 km), mass fraction of fine ( \u3c 0.063 mm) ash (3-59 %), atmospheric temperature, and water content between these eruptions. This close agreement suggests that aggregation may be treated as a discrete process that is insensitive to eruptive style or magnitude. This result offers the potential for a simple, computationally efficient parameterization scheme for use in operational model forecasts. Further research may indicate whether this narrow range also reflects physical constraints on processes in the evolving cloud
Kinematic and morphological modeling of the bipolar nebula Sa2-237
We present [OIII]500.7nm and Halpha+[NII] images and long-slit, high
resolution echelle spectra in the same spectral regions of Sa2--237, a possible
bipolar planetary nebula. The image shows a bipolar nebula of about 34" extent,
with a narrow waist, and showing strong point symmetry about the central
object, indicating it's likely binary nature. The long slit spectra were taken
over the long axis of the nebula, and show a distinct ``eight'' shaped pattern
in the velocity--space plot, and a maximum projected outflow velocity of
V=106km/s, both typical of expanding bipolar planetary nebulae. By model
fitting the shape and spectrum of the nebula simultaneously, we derive the
inclination of the long axis to be 70 degrees, and the maximum space velocity
of expansion to be 308 km/s. Due to asymmetries in the velocities we adopt a
new value for the system's heliocentric radial velocity of -30km/s. We use the
IRAS and 21cm radio fluxes, the energy distribution, and the projected size of
Sa2-237 to estimate it's distance to be 2.1+-0.37kpc. At this distance Sa2-237
has a luminosity of 340 Lsun, a size of 0.37pc, and -- assuming constant
expansion velocity -- a nebular age of 624 years. The above radial velocity and
distance place Sa2--237 in the disk of the Galaxy at z=255pc, albeit with
somewhat peculiar kinematics.Comment: 10pp, 4 fig
Ice nucleation and overseeding of ice in volcanic clouds
Water is the dominant component of volcanic gas emissions, and water phase transformations, including the formation of ice, can be significant in the dynamics of volcanic clouds. The effectiveness of volcanic ash particles as ice-forming nuclei (IN) is poorly understood and the sparse data that exist for volcanic ash IN have been interpreted in the context of meteorological, rather than volcanic clouds. In this study, single-particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature. Measured freezing temperatures show only weak correlations with ash IN composition and surface area. Our measurements, together with a review of previous volcanic ash IN measurements, suggest that fine-ash particles (equivalent diameters between approximately 1 and 1000 μm) from the majority of volcanoes will exhibit an onset of freezing between ∼250–260 K. In the context of explosive eruptions where super-micron particles are plentiful, this result implies that volcanic clouds are IN-rich relative to meteorological clouds, which typically are IN-limited, and therefore should exhibit distinct microphysics. We can expect that such “overseeded” volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size, relative to dynamically similar meteorological clouds, and that glaciation will tend to occur over a relatively narrow altitude range
The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio,
millimeter, and infrared (IR) wavelengths, with the aim of learning about its
broad-band spectrum. At the IRAM 30m telescope, we have detected the magnetar
at 88 and 144GHz, the highest radio-frequency emission ever seen from a pulsar.
At 88GHz we detected numerous individual pulses, with typical widths ~2ms and
peak flux densities up to 45Jy. Together with nearly contemporaneous
observations with the Parkes, Nancay, and Green Bank telescopes, we find that
in late 2006 July the spectral index of the pulsar was -0.5<alpha<0 over the
range 1.4-144GHz. Nine dual-frequency Very Large Array and Australia Telescope
Compact Array observations in 2006 May-September are consistent with this
finding, while showing variability of alpha with time. We infer from the IRAM
observations that XTE J1810-197 remains highly linearly polarized at millimeter
wavelengths. Also, toward this pulsar, the transition frequency between strong
and weak scattering in the interstellar medium may be near 50GHz. At Gemini, we
detected the pulsar at 2.2um in 2006 September, at the faintest level yet
observed, K_s=21.89+-0.15. We have also analyzed four archival IR Very Large
Telescope observations (two unpublished), finding that the brightness
fluctuated within a factor of 2-3 over a span of 3 years, unlike the monotonic
decay of the X-ray flux. Thus, there is no correlation between IR and X-ray
flux, and it remains uncertain whether there is any correlation between IR and
radio flux.Comment: Accepted for publication in ApJ; contains improved discussion of
infrared uncertaintie
Asynchronous food-web pathways could buffer the response of Serengeti predators to El Niño southern oscillation
Understanding how entire ecosystems maintain stability in the face of climatic and human disturbance is one of the most fundamental challenges in ecology. Theory suggests that a crucial factor determining the degree of ecosystem stability is simply the degree of synchrony with which different species in ecological food webs respond to environmental stochasticity. Ecosystems in which all food-web pathways are affected similarly by external disturbance should amplify variability in top carnivore abundance over time due to population interactions, whereas ecosystems in which a large fraction of pathways are nonresponsive or even inversely responsive to external disturbance will have more constant levels of abundance at upper trophic levels. To test the mechanism underlying this hypothesis, we used over half a century of demographic data for multiple species in the Serengeti (Tanzania) ecosystem to measure the degree of synchrony to variation imposed by an external environmental driver, the El Niño Southern Oscillation (ENSO). ENSO effects were mediated largely via changes in dry-season vs. wet-season rainfall and consequent changes in vegetation availability, propagating via bottom-up effects to higher levels of the Serengeti food web to influence herbivores, predators and parasites. Some species in the Serengeti food web responded to the influence of ENSO in opposite ways, whereas other species were insensitive to variation in ENSO. Although far from conclusive, our results suggest that a diffuse mixture of herbivore responses could help buffer top carnivores, such as Serengeti lions, from variability in climate. Future global climate changes that favor some pathways over others, however, could alter the effectiveness of such processes in the future
Real-Space Observation of Quantum Tunneling by a Carbon Atom: Flipping Reaction of Formaldehyde on Cu(110)
We
present a direct observation of carbon-atom tunneling in the
flipping reaction of formaldehyde between its two mirror-reflected
states on a Cu(110) surface using low-temperature scanning tunneling
microscopy (STM). The flipping reaction was monitored in real time,
and the reaction rate was found to be temperature independent below
10 K. This indicates that this reaction is governed by quantum mechanical
tunneling, albeit involving a substantial motion of the carbon atom
(∼1 Å). In addition, deuteration of the formaldehyde molecule
resulted in a significant kinetic isotope effect (<i>R</i><sub>CH<sub>2</sub>O</sub>/<i>R</i><sub>CD<sub>2</sub>O</sub> ≈ 10). The adsorption structure, reaction pathway, and tunneling
probability were examined by density functional theory calculations,
which corroborate the experimental observations
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