1,374 research outputs found
Modeling human trophoblast, the placental epithelium at the maternal fetal interface.
Appropriate human trophoblast lineage specification and differentiation is crucial for the establishment of normal placentation and maintenance of pregnancy. However, due to the lack of proper modeling systems, the molecular mechanisms of these processes are still largely unknown. Much of the early studies in this area have been based on animal models and tumor-derived trophoblast cell lines, both of which are suboptimal for modeling this unique human organ. Recent advances in regenerative and stem cell biology methods have led to development of novel in vitro model systems for studying human trophoblast. These include derivation of human embryonic and induced pluripotent stem cells and establishment of methods for the differentiation of these cells into trophoblast, as well as the more recent derivation of human trophoblast stem cells. In addition, advances in culture conditions, from traditional two-dimensional monolayer culture to 3D culturing systems, have led to development of trophoblast organoid and placenta-on-a-chip model, enabling us to study human trophoblast function in context of more physiologically accurate environment. In this review, we will discuss these various model systems, with a focus on human trophoblast, and their ability to help elucidate the key mechanisms underlying placental development and function. This review focuses on model systems of human trophoblast differentiation, including advantages and limitations of stem cell-based culture, trophoblast organoid, and organ-on-a-chip methods and their applications in understanding placental development and disease
Toward a unified light curve model for multi-wavelength observations of V1974 Cygni (Nova Cygni 1992)
We present a unified model for optical, ultraviolet (UV), and X-ray light
curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model
of nova outbursts, we have calculated light curves and searched for the best
fit model that is consistent with optical, UV, and X-ray observations. Our best
fit model is a white dwarf (WD) of mass 1.05 M_\sun with a chemical composition
of X=0.46, C+N+O=0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and
continuum UV 1455 \AA light curves are well reproduced. Supersoft X-rays
emerged on day ~ 250 after outburst, which is naturally explained by our model:
our optically thick winds cease on day 245 and supersoft X-rays emerge from
self-absorption by the winds. The X-ray flux keeps a constant peak value for ~
300 days followed by a quick decay on day ~ 600. The duration of X-ray flat
peak is well reproduced by a steady hydrogen shell burning on the WD. Optical
light curve is also explained by the same model if we introduce free-free
emission from optically thin ejecta. A t^{-1.5} slope of the observed optical
and infrared fluxes is very close to the slope of our modeled free-free light
curve during the optically thick wind phase. Once the wind stops, optical and
infrared fluxes should follow a t^{-3} slope, derived from a constant mass of
expanding ejecta. An abrupt transition from a t^{-1.5} slope to a t^{-3} slope
at day ~ 200 is naturally explained by the change from the wind phase to the
post-wind phase on day ~ 200. The development of hard X-ray flux is also
reasonably understood as shock-origin between the wind and the companion star.
The distance to V1974 Cyg is estimated to be ~ 1.7 kpc with E(B-V)= 0.32 from
the light curve fitting for the continuum UV 1455 \AA.Comment: 8 pages, 4 figures, to appear in the Astrophysical Journa
A Modeling of the Super-Eddington Luminosity in Nova Outbursts: V1974 Cygni
We have modeled nova light curves exceeding the Eddington luminosity. It has
been suggested that a porous structure develops in nova envelopes during the
super Eddington phase and the effective opacity is much reduced for such a
porous atmosphere. Based on this reduced opacity model, we have calculated
envelope structures and light curves of novae. The optically thick wind model
is used to simulate nova winds. We find that the photospheric luminosity and
the wind mass-loss rate increase inversely proportional to the reducing factor
of opacities, but the wind velocity hardly changes. We also reproduce the
optical light curve of V1974 Cygni (Nova Cygni 1992) in the super-Eddington
phase, which lasts 13 days from the optical peak 1.7 mag above the Eddington
luminosity.Comment: 8 pages, 4 figures, to appear in ApJ
FINANCIAL PROFITABILITY OF MALI-SUD BAS-FOND RICE PRODUCTION SYSTEMS
The high costs of rehabilitating and/or expanding government-managed irrigated schemes in Mali (Office du Niger) has prompted policy-makers and researchers to explore the potential for the underdeveloped farmer-managed bas-fond to contribute to ensure an adequate rice supply and increase rural households' incomes. Because little is known about nas-fond rice production in Mali, this paper analyzes its financial profitability based on data collected from a random sample of 221 farmers. Data analysis revealed that there are numerous rice production systems in the bas-fond. Budget analysis showed that the four most common bas-fond production systems yield higher returns than the opportunity cost of labor and they are more profitable than the main upland crops competing with rice for farmers labor (cotton, sorghum/millet, and maize). Within a given bas-fond system, however, profitability varies considerably across farms.Agricultural Finance, Crop Production/Industries,
Kawm Ntawv Qib Siab Understanding the psychosociocultural educational experiences of Hmong American undergraduates
Using a psychosociocultural framework, this study examined the educational experiences of 85 Hmong American undergraduates attending a predominantly-White university. Differences in class standing indicated that upper-division students reported higher confidence in college-related tasks than their lower-division counterparts, yet the upper-division students perceived a less-welcoming university environment that was incongruent with their cultural values than the lower-division undergraduates. Peer support, college self-efficacy and cultural congruity were salient variables in understanding Hmong American undergraduate’s educational experiences. The study’s limitations, future research directions, and implications for college administrators and faculty are discussed
A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Austrinae
A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae
(V394 CrA) is modeled to obtain various physical parameters of this recurrent
nova. We then apply the same set of parametersto a quiescent phase and confirm
that these parameters give a unified picture of the binary. The early visual
light curve (1-10 days after the optical maximum) is well reproduced by a
thermonuclear runaway model on a very massive WD close to the Chandrasekhar
limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also
reproduced by the combination of a slightly irradiated MS and a fully
irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The
best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun
(0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68
degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass
at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an
average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent
phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed
light curve can be reproduced with a disk size of 0.7 times the Roche lobe size
and a rather slim thickness of 0.05 times the accretion disk size at the rim.
About 0.5 mag sinusoidal variation of the light curve requires the mass
accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent
with the above estimation from the 1987 outburst. These newly obtained
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.Comment: 9 pages including 4 figures, to appear in the Astrophysical Journal,
Part
A Time-Motion Study of Emergency and Hospitalist Physicians in a Community Hospital Setting
Introduction: Research has shown that low physician work satisfaction correlates with burnout. Having sufficient time at the patient’s bedside is one element that contributes to work satisfaction. Interruptions, on the other hand, have been implicated as a potential cause of both worker dissatisfaction and clinical error. Better understanding how direct patient care and interruptions affect physician satisfaction may aid in developing future interventions to reduce burnout and improve patient safety.
Methods: We conducted an observational, time-motion study to assess how physicians spend their time and correlated these findings to physician satisfaction. This study was conducted in July 2020 (7/1/20 - 7/15/20) at a 591-bed community hospital. A total of 114 emergency medicine (EM) physicians and hospitalists were eligible for participation. Participants were recruited by email. Two trained medical students categorized and recorded the activities of 13 EM and 8 hospitalist physicians and documented the number of interruptions they experienced. An anonymous survey was also employed to investigate participants’ perceptions about interruptions and how they spend their time. We compared the responses from the subjective survey to the objective data to identify activities that may positively or negatively impact participant satisfaction.
Results: 18.4% of all eligible physicians participated in the study. In summary, our study showed that EM and hospitalist physicians dedicate roughly double the amount of time to indirect patient care (56.3%) compared to direct patient care (25.8%). EM physicians had more than twice the number of interruptions as hospitalists (every 4.4 minutes vs. every 11.3 minutes). From our survey results, we found no statistically significant difference between the perceived and observed proportion of time spent on direct and indirect patient care for EM physicians (p = 0.62 direct; 0.21 indirect) or hospitalists (p = 0.82 direct; 0.69 indirect). However, there was a statistically significant difference between perceived (overestimated) and observed number of interruptions reported by EM physicians (p = 0.02).
Conclusion: The observational data along with the survey results indicate a desire to reduce indirect patient care and increase time at the bedside — suggesting that interventions that target this discrepancy may increase physician work satisfaction and therefore decrease burnout. Additionally, we found that EM physicians far overestimate the actual number of interruptions they experience —however, EM does still engender more than double the interruptions as hospitalists encounter, despite experiencing similar percentages of direct and indirect patient care
A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf
A new interpretation for the second peak of T Coronae Borealis (T CrB)
outbursts is proposed based on a thermonuclear runaway (TNR) model. The system
consists of a very massive white dwarf (WD) with a tilting accretion disk and a
lobe-filling red-giant. The first peak of the visual light curve of T CrB
outbursts is well reproduced by the TNR model on a WD close to the
Chandrasekhar mass (), while the second peak
is reproduced by the combination of the irradiated M-giant and the irradiated
tilting disk. The derived fitting parameters are the WD mass , the M-giant companion mass
( is acceptable), the inclination angle of the orbit i \sim
70 \arcdeg, and the tilting angle of the disk i_{\rm prec} \sim 35 \arcdeg.
These parameters are consistent with the recently derived binary parameters of
T CrB.Comment: 6 pages including 2 figures, to be published in ApJ Letter
Intraocular human cytomegaloviruses of ocular diseases are distinct from those of viremia and are capable of escaping from innate and adaptive immunity by exploiting HLA-E-mediated peripheral and central tolerance
Human cytomegalovirus (HCMV) infections develop into CMV diseases that result in various forms of manifestations in local organs. CMV-retinitis is a form of CMV disease that develops in immunocompromised hosts with CMV-viremia after viruses in the peripheral circulation have entered the eye. In the HCMV genome, extensive diversification of the UL40 gene has produced peptide sequences that modulate NK cell effector functions when loaded onto HLA-E and are subsequently recognized by the NKG2A and NKG2C receptors. Notably, some HCMV strains carry UL40 genes that encode peptide sequences identical to the signal peptide sequences of specific HLA-A and HLA-C allotypes, which enables these CMV strains to escape HLA-E-restricted CD
Nucleosynthesis in Baryon-Rich Outflows Associated With Gamma-Ray Bursts
Robust generation of gamma-ray bursts (GRBs) implies the formation of
outflows with very low baryon loads and highly relativistic velocities, but
more baryon-rich, slower outflows are also likely to occur in most GRB central
engine scenarios, either as ``circum-jet winds'' or ``failed GRBs''. Here we
study the possibility of nucleosynthesis within such baryon-rich outflows by
conducting detailed reaction network calculations in the framework of the basic
fireball model. It is shown that high baryon load fireballs attaining mildly
relativistic velocities can synthesize appreciable quantities of heavy neutron
capture elements with masses up to the platinum peak and beyond. Small but
interesting amounts of light elements such as deuterium and boron can also be
produced. Depending on the neutron excess and baryon load, the combination of
high entropy, rapid initial expansion and gradual expansion at later times can
cause the reaction flow to reach the fission regime, and its path can be
intermediate between those of the - and -processes (``-process''). The
nucleosynthetic signature of these outflows may be observable in the companion
stars of black hole binary systems and in the most metal-poor stars,
potentially offering an important probe of the inner conditions of the GRB
source. Contribution to the solar abundances for some heavy elements may also
be possible. The prospects for further developments in various directions are
discussed.Comment: ApJ, in press; 11 pages, 3 figure
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