820 research outputs found
Polarimetric modeling of corotating interaction regions (CIRs) threading massive-star winds
Massive star winds are complex radiation-hydrodynamic (sometimes
magnetohydrodynamic) outflows that are propelled by their enormously strong
luminosities. The winds are often found to be structured and variable, but can
also display periodic or quasi-periodic behavior in a variety of wind
diagnostics. The regular variations observed in putatively single stars,
especially in UV wind lines, have often been attributed to corotating
interaction regions (CIRs) like those seen in the solar wind. We present light
curves for variable polarization from winds with CIR structures. We develop a
model for a time-independent CIR based on a kinematical description. Assuming
optically thin electron scattering, we explore the range of polarimetric light
curves that result as the curvature, latitude, and number of CIRs are varied.
We find that a diverse array of variable polarizations result from an
exploration of cases. The net polarization from an unresolved source is
weighted more toward the inner radii of the wind. Given that most massive stars
have relatively fast winds compared to their rotation speeds, CIRs tend to be
conical at inner radii, transitioning to a spiral shape at a few to several
stellar radii in the wind. Winds with a single CIR structure lead to easily
identifiable polarization signatures. By contrast allowing for multiple CIRs,
all emerging from a range of azimuth and latitude positions at the star, can
yield complex polarimetric behavior. Although our model is based on some
simplifying assumptions, it produces qualitative behavior that we expect to be
robust, and this has allowed us to explore a wide range of CIR configurations
that will prove useful for interpreting polarimetric data.Comment: accepted to A&
Fast Mesh Refinement in Pseudospectral Optimal Control
Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy
--- simply increase the order of the Lagrange interpolating polynomial and
the mathematics of convergence automates the distribution of the grid points.
Unfortunately, as increases, the condition number of the resulting linear
algebra increases as ; hence, spectral efficiency and accuracy are lost in
practice. In this paper, we advance Birkhoff interpolation concepts over an
arbitrary grid to generate well-conditioned PS optimal control discretizations.
We show that the condition number increases only as in general, but
is independent of for the special case of one of the boundary points being
fixed. Hence, spectral accuracy and efficiency are maintained as increases.
The effectiveness of the resulting fast mesh refinement strategy is
demonstrated by using \underline{polynomials of over a thousandth order} to
solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201
Alien Registration- Proulx, Joseph Ludger N. (Madawaska, Aroostook County)
https://digitalmaine.com/alien_docs/35147/thumbnail.jp
The right way to kiss: directionality bias in head-turning during kissing
Humans have a bias for turning to the right in a number of settings. Here we document a bias in head-turning to the right in adult humans, as tested in the act of kissing. We investigated head-turning bias in both kiss initiators and kiss recipients for lip kissing, and took into consideration differences due to sex and handedness, in 48 Bangladeshi heterosexual married couples. We report a significant male bias in the initiation of kissing and a significant bias in head-turning to the right in both kiss initiators and kiss recipients, with a tendency among kiss recipients to match their partners’ head-turning direction. These interesting outcomes are explained by the influences of societal learning or cultural norms and the potential neurophysiological underpinnings which together offer novel insights about the mechanisms underlying behavioral laterality in humans
Stellar Collisions and Ultracompact X-ray Binary Formation
(abridged) We report the results of SPH calculations of parabolic collisions
between a subgiant or slightly evolved red-giant star and a neutron star (NS).
Such collisions are likely to form ultracompact X-ray binaries (UCXBs) observed
today in old globular clusters. In particular, we compute collisions of a 1.4
Msun NS with realistically modelled parent stars of initial masses 0.8 and 0.9
Msun, each at three different evolutionary stages (corresponding to three
different radii R). The distance of closest approach for the initial orbit
varies from 0.04 R (nearly head-on) to 1.3 R (grazing). These collisions lead
to the formation of a tight binary, composed of the NS and the subgiant or
red-giant core, embedded in an extremely diffuse common envelope (CE) typically
of mass ~0.1 to 0.3 Msun. Our calculations follow the binary for many hundreds
of orbits, ensuring that the orbital parameters we determine at the end of the
calculations are close to final. Some of the fluid initially in the envelope of
the (sub)giant, from 0.003 to 0.023 Msun in the cases we considered, is left
bound to the NS. The eccentricities of the resulting binaries range from about
0.2 for our most grazing collision to about 0.9 for the nearly head-on cases.
In almost all the cases we consider, gravitational radiation alone will cause
sufficiently fast orbital decay to form a UCXB within a Hubble time, and often
on a much shorter timescale. Our hydrodynamics code implements the recent SPH
equations of motion derived with a variational approach by Springel & Hernquist
and by Monaghan. Numerical noise is reduced by enforcing an analytic constraint
equation that relates the smoothing lengths and densities of SPH particles. We
present tests of these new methods to help demonstrate their improved accuracy.Comment: 41 pages, 17 figures, accepted by Ap
Both Reintroduction and Recolonization Likely Contributed to the Re-establishment of a Fisher Population in East-central Alberta
Recently, Stewart et al. (2017) investigated the origins of contemporary fisher populations in the Cooking Lake Moraine (CLM) of east-central Alberta, Canada, where fishers (Pekania pennanti) from Ontario and Manitoba, Canada were reintroduced in the early 1990s. To address this objective, Stewart et al. (2017) compared microsatellite alleles from extant fisher populations in the CLM to those from Ontario, Manitoba, and other Alberta populations. They reported that the CLM population clustered with adjacent native Alberta populations, consistent with recolonization, but also that 2 of 109 microsatellite alleles in the CLM occurred only in the source populations from Ontario and Manitoba. Rather than allowing for the possibility that these alleles descended from reintroduced fishers, the authors speculated that they represented random mutations among fishers that recolonized the area naturally from nearby populations in Alberta, and concluded that the reintroduction had failed completely. We disagree with this conclusion for 2 reasons. We contend it is more likely that the 2 alleles represent a genetic signature from the individuals released during the reintroduction, rather than being the result of mutations. We further suggest that, irrespective of the genetic legacy of introduced fishers in the recovered population, the presence of reintroduced fishers in the CLM may have helped facilitate natural recolonization of the area by fishers from surrounding areas. In our view, Stewart et al.’s (2017) findings do not demonstrate conclusively that the reintroduction program failed; on the contrary, we argue that their findings indicate that reintroduced fishers likely contributed to the long-term persistence of fishers in the CLM. The uncertainty surrounding this case underscores the importance of genetic monitoring following reintroductions.https://digitalcommons.snc.edu/faculty_staff_works/1032/thumbnail.jp
MAIT cells are activated in acute Dengue virus infection and after in vitro Zika virus infection.
Dengue virus (DENV) and Zika virus (ZIKV) are members of the Flaviviridae and are predominantly transmitted via mosquito bites. Both viruses are responsible for a growing number of infections in tropical and subtropical regions. DENV infection can cause lethargy with severe morbidity and dengue shock syndrome leading to death in some cases. ZIKV is now linked with Guillain-Barré syndrome and fetal malformations including microcephaly and developmental disorders (congenital Zika syndrome). The protective and pathogenic roles played by the immune response in these infections is unknown. Mucosal-associated invariant T (MAIT) cells are a population of innate T cells with potent anti-bacterial activity. MAIT cells have also been postulated to play a role in the immune response to viral infections. In this study, we evaluated MAIT cell frequency, phenotype, and function in samples from subjects with acute and convalescent DENV infection. We found that in acute DENV infection, MAIT cells had elevated co-expression of the activation markers CD38 and HLA-DR and had a poor IFNγ response following bacterial stimulation. Furthermore, we found that MAIT cells can produce IFNγ in response to in vitro infection with ZIKV. This MAIT cell response was independent of MR1, but dependent on IL-12 and IL-18. Our results suggest that MAIT cells may play an important role in the immune response to Flavivirus infections
Shut Up & Write!® builds writing self-efficacy and self-regulation in early-career researchers
Abstract
Introduction:
High writing self-efficacy and self-regulation are tied to publication and grant submission. Writers with these attributes are more productive. We investigated whether participating in a Shut Up & Write!®-style intervention (SUAW) would produce statistically significant gains in writing self-efficacy and self-regulation when comparing pre-post-participation surveys.
Methods:
Forty-seven medical students, TL1/KL2, and early-career faculty from across the USA expressed interest in participating, with 37 completing the pre-survey. We conducted (on Zoom) a 12-week SUAW series and measured the effect using a pre-post survey adapted from the Writer Self-Perception Scale. Paired t-tests (α = 0.05) were conducted on three subscales to test for significant differences between pre- and post-test means. The subscales reflected writing attitudes, writing strategies, and avoiding writing distractions. Subscales showed acceptable internal consistency with Cronbach’s alphas of 0.80, 0.71, and 0.72, respectively.
Results:
Twenty-seven participants attended at least one session. Of these, 81% presented as female, and 60% were from NIH-defined Underrepresented Backgrounds and/or were from Minority-Serving Institutions. Twenty-four completed both the pre- and post-surveys. Sixty percent previously participated in an activity similar to SUAW. We found significant improvements in writing attitudes (p = 0.020) and writing strategies (p = 0.041) for those who previously participated. For those who had not previously participated, we found improved writing strategies (p = 0.002). Eighty percent were very satisfied/satisfied with SUAW.
Discussion:
Researchers have tied writing self-efficacy and self-regulation to timely publication and grant submission. We found significant gains in self-efficacy and self-regulation, suggesting that participation in a SUAW-style intervention may increase writing productivity
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