6,832 research outputs found
Origin of the unusually low nitrogen abundances in young populations of the Large Magellanic Cloud
It is a longstanding problem that HII regions and very young stellar
populations in the Large Magellanic Cloud (LMC) have the nitrogen abundances
([N/H]) by a factor of ~7 lower than the solar value. We here discuss a new
scenario in which the observed unusually low nitrogen abundances can be closely
associated with recent collision and subsequent accretion of HI high velocity
clouds (HVCs) that surround the Galaxy and have low nitrogen abundances. We
show that if the observed low [N/H] is limited to very young stars with ages
less than ~10^7 yr, then the collision/accretion rate of the HVCs onto the LMC
needs to be ~ 0.2 M_sun/yr (corresponding to the total HVC mass of 10^6-10^7
M_sun) to dilute the original interstellar medium (ISM) before star formation.
The required accretion rate means that even if the typical mass of HVCs
accreted onto the LMC is ~ 10^7 M_sun, the Galaxy needs to have ~2500 massive
HVCs within the LMC's orbital radius with respect to the Galactic center. The
required rather large number of massive HVCs drives us to suggest that the HVCs
are not likely to efficiently dilute the ISM of the LMC and consequently lower
the [N/H]. We thus suggest the transfer of gas with low [N/H] from the Small
Magellanic Cloud (SMC) to the LMC as a promising scenario that can explain the
observed low [N/H].Comment: 24pages, 6 figures, accepted in Ap
Morse homology for the heat flow
We use the heat flow on the loop space of a closed Riemannian manifold to
construct an algebraic chain complex. The chain groups are generated by
perturbed closed geodesics. The boundary operator is defined in the spirit of
Floer theory by counting, modulo time shift, heat flow trajectories that
converge asymptotically to nondegenerate closed geodesics of Morse index
difference one.Comment: 89 pages, 3 figure
Multiphase Gas In Galaxy Halos: The OVI Lyman-limit System toward J1009+0713
We have serendipitously detected a strong O VI-bearing Lyman limit system at
z_abs = 0.3558 toward the QSO J1009+0713 (z_em = 0.456) in our survey of
low-redshift galaxy halos with the Hubble Space Telescope's Cosmic Origins
Spectrograph. Its rest-frame equivalent width of W_r = 835 +/- 49 mA is the
highest for an intervening absorber yet detected in any low-redshift QSO
sightline, with absorption spanning 400 km s^-1 in its rest frame. HST/WFC3
images of the galaxy field show that the absorber is associated with two
galaxies lying at 14 and 46 kpc from the QSO line of sight. The bulk of the
absorbing gas traced by H I resides in two strong, blended component groups
that possess a total logN(HI) = 18 - 18.8. The ion ratios and column densities
of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a
simple photoionization model in which diffuse, low-metallicity halo gas is
exposed to a photoionizing field from stars in the nearby galaxies that
propagates into the halo at 10% efficiency. We constrain the metallicity firmly
within the range 0.1 - 1 Zsun, and photoionization modeling indirectly
indicates a subsolar metallicity of 0.05 - 0.5 Zsun. The appearance of strong O
VI and nine Mg II components and our review of similar systems in the
literature support the "interface" picture of high-velocity O VI: the total
strength of the O VI shows a positive correlation with the number of detected
components in the low-ionization gas, however the total O VI column densities
still far exceed the values expected from interface models for the number of
detected clouds.Comment: 20 pages, 11 figures, accepted for publication in Ap
Inconsistent recognition of uncertainty in studies of climate change impacts on forests
Petr, M., Vacchiano, G., Thom, D., Mairota, P., Kautz, M., Gonçalves, L. M. D. S., ... Reyer, C. P. O. (2019). Inconsistent recognition of uncertainty in studies of climate change impacts on forests. Environmental Research Letters, 14(11), 1-13. [113003]. https://doi.org/10.1088/1748-9326/ab4670Background. Uncertainty about climate change impacts on forests can hinder mitigation and adaptation actions. Scientific enquiry typically involves assessments of uncertainties, yet different uncertainty components emerge in different studies. Consequently, inconsistent understanding of uncertainty among different climate impact studies (from the impact analysis to implementing solutions) can be an additional reason for delaying action. In this review we (a) expanded existing uncertainty assessment frameworks into one harmonised framework for characterizing uncertainty, (b) used this framework to identify and classify uncertainties in climate change impacts studies on forests, and (c) summarised the uncertainty assessment methods applied in those studies. Methods. We systematically reviewed climate change impact studies published between 1994 and 2016. We separated these studies into those generating information about climate change impacts on forests using models -'modelling studies', and those that used this information to design management actions-'decision-making studies'. We classified uncertainty across three dimensions: nature, level, and location, which can be further categorised into specific uncertainty types. Results. We found that different uncertainties prevail in modelling versus decision-making studies. Epistemic uncertainty is the most common nature of uncertainty covered by both types of studies, whereas ambiguity plays a pronounced role only in decision-making studies. Modelling studies equally investigate all levels of uncertainty, whereas decision-making studies mainly address scenario uncertainty and recognised ignorance. Finally, the main location of uncertainty for both modelling and decision-making studies is within the driving forces-representing, e.g. socioeconomic or policy changes. The most frequently used methods to assess uncertainty are expert elicitation, sensitivity and scenario analysis, but a full suite of methods exists that seems currently underutilized. Discussion & Synthesis. The misalignment of uncertainty types addressed by modelling and decision-making studies may complicate adaptation actions early in the implementation pathway. Furthermore, these differences can be a potential barrier for communicating research findings to decision-makers.publishersversionpublishe
The Gas-Galaxy Connection at z = 0.35: OVI and HI Absorption Towards J0943+0531
We present observations of HI and OVI absorption systems proximate to a
galaxy at z_gal = 0.3529. The absorption was detected serendipitously in Cosmic
Origins Spectrograph observations of the low-z QSO J0943+0531 (z_qso = 0.564).
The data show two separate clouds along the sightline at an impact parameter of
95kpc from the galaxy. The first is likely low-metallicity gas falling onto the
galaxy. This assessment is based on the high velocity offset of the cloud from
the galaxy (delta_v = 365kms) and the weak metal line absorption, combined with
photoionization modeling. The second cloud, with only a modest velocity
separation from the galaxy (delta_v = 85kms), exhibits very strong OVI
absorption qualitatively similar to OVI absorption seen in the Milky Way halo.
Collisional ionization equilibrium models are ruled out by the metal line
column density ratios. Photoionization modeling implies a length-scale for the
OVI cloud of ~0.1-1.2Mpc, which indicates the absorbing gas most likely resides
within the local filamentary structure. This system emphasizes that kinematic
association alone is not sufficient to establish a physical connection to
galaxies, even at small impact parameters and velocity separations.
Observations such as these, connecting galaxies with their gaseous
environments, are becoming increasingly important for understanding galaxy
evolution and provide constraints for cosmological simulations.Comment: ApJ in press. 11 pages, 7 figure
Evidence for Cold Accretion: Primitive Gas Flowing onto a Galaxy at z~0.274
We present UV and optical observations from the Cosmic Origins Spectrograph
on the Hubble Space Telescope and Keck of a z= 0.27395 Lyman limit system (LLS)
seen in absorption against the QSO PG1630+377. We detect H I absorption with
log N(HI)=17.06\pm0.05 as well as Mg II, C III, Si III, and O VI in this
system. The column densities are readily explained if this is a multi-phase
system, with the intermediate and low ions arising in a very low metallicity
([Mg/ H] =-1.71 \pm 0.06) photoionized gas. We identify via Keck spectroscopy
and Large Binocular Telescope imaging a 0.3 L_* star-forming galaxy projected
37 kpc from the QSO at nearly identical redshift (z=0.27406, \Delta v = -26
\kms) with near solar metallicity ([O/ H]=-0.20 \pm 0.15). The presence of very
low metallicity gas in the proximity of a near-solar metallicity, sub-L_*
galaxy strongly suggests that the LLS probes gas infalling onto the galaxy. A
search of the literature reveals that such low metallicity LLSs are not
uncommon. We found that 50% (4/8) of the well-studied z < 1 LLSs have
metallicities similar to the present system and show sub-L_* galaxies with rho
< 100 kpc in those fields where redshifts have been surveyed. We argue that the
properties of these primitive LLSs and their host galaxies are consistent with
those of cold mode accretion streams seen in galaxy simulations.Comment: Accepted for publication in the Astrophysical Journa
The COS-Halos Survey: Keck LRIS and Magellan MagE Optical Spectroscopy
We present high signal-to-noise optical spectra for 67 low-redshift (0.1 < z
< 0.4) galaxies that lie within close projected distances (5 kpc < rho < 150
kpc) of 38 background UV-bright QSOs. The Keck LRIS and Magellan MagE data
presented here are part of a survey that aims to construct a statistically
sampled map of the physical state and metallicity of gaseous galaxy halos using
the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). We
provide a detailed description of the optical data reduction and subsequent
spectral analysis that allow us to derive the physical properties of this
uniquely data-rich sample of galaxies. The galaxy sample is divided into 38
pre-selected L ~ L*, z ~ 0.2 "target" galaxies and 29 "bonus" galaxies that lie
in close proximity to the QSO sightlines. We report galaxy spectroscopic
redshifts accurate to +/- 30 km s-1, impact parameters, rest-frame colors,
stellar masses, total star formation rates, and gas-phase interstellar medium
oxygen abundances. When we compare the distribution of these galaxy
characteristics to those of the general low-redshift population, we find good
agreement. The L ~ L* galaxies in this sample span a diverse range of color
(1.0 < u-r < 3.0), stellar mass (10^9.5 < M/M_sun < 10^11.5), and SFRs (0.01 -
20 M_sun yr-1). These optical data, along with the COS UV spectroscopy,
comprise the backbone of our efforts to understand how halo gas properties may
correlate with their host galaxy properties, and ultimately to uncover the
processes that drive gas outflow and/or are influenced by gas inflow.Comment: 20 pages, 12 Figures, Submitted to ApJ
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Women’s pelvic floor muscle strength and urinary and anal incontinence after childbirth: a cross-sectional study
Abstract OBJECTIVE To analyse pelvic floor muscle strength (PFMS) and urinary and anal incontinence (UI and AI) in the postpartum period. METHOD Cross-sectional study carried out with women in their first seven months after child birth. Data were collected through interviews, perineometry (Peritron™), and the International Consultation on Incontinence Questionnaire-Short Form (ICIQ-SF). RESULTS 128 women participated in the study. The PFMS mean was 33.1 (SD=16.0) cmH2O and the prevalence of UI and AI was 7.8% and 5.5%, respectively. In the multiple analyses, the variables associated with PFMS were type of birth and cohabitation with a partner. Newborn’s weight, previous pregnancy, UI during pregnancy, and sexual activity showed an association with UI after child birth. Only AI prior to pregnancy was associated with AI after childbirth. CONCLUSION Vaginal birth predisposes to the reduction of PFMS, and caesarean section had a protective effect to its reduction. The occurrence of UI during pregnancy is a predictor of UI after childbirth, and women with previous pregnancies and newborns with higher weights are more likely to have UI after childbirth.AI prior to pregnancy is the only risk factor for its occurrence after childbirth. Associations between PFMS and cohabitation with a partner, and between UI and sexual activity do not make possible to conclude that these variables are directly associated
Quasi-classical approximation in vortex filament dynamics. Integrable systems, gradient catastrophe and flutter
Quasiclassical approximation in the intrinsic description of the vortex
filament dynamics is discussed. Within this approximation the governing
equations are given by elliptic system of quasi-linear PDEs of the first order.
Dispersionless Da Rios system and dispersionless Hirota equation are among
them. They describe motion of vortex filament with slow varying curvature and
torsion without or with axial flow. Gradient catastrophe for governing
equations is studied. It is shown that geometrically this catastrophe manifests
as a fast oscillation of a filament curve around the rectifying plane which
resembles the flutter of airfoils. Analytically it is the elliptic umbilic
singularity in the terminology of the catastrophe theory. It is demonstrated
that its double scaling regularization is governed by the Painleve' I equation.Comment: 25 pages, 5 figures, minor typos correcte
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