1,561 research outputs found
Undulations on the surface of elongated bubbles in confined gas-liquid flows
© 2017 American Physical Society. A systematic analysis is presented of the undulations appearing on the surface of long bubbles in confined gas-liquid flows. CFD simulations of the flow are performed with a self-improved version of the open-source solver ESI OpenFOAM (release 2.3.1), for Ca=0.002-0.1 and Re=0.1-1000, where Ca=μU/σ and Re=2ρUR/μ, with μ and ρ being, respectively, the viscosity and density of the liquid, σ the surface tension, U the bubble velocity, and R the tube radius. A model, based on an extension of the classical axisymmetric Bretherton theory, accounting for inertia and for the curvature of the tube's wall, is adopted to better understand the CFD results. The thickness of the liquid film, and the wavelength and decay rate of the undulations extracted from the CFD simulations, agree well with those obtained with the theoretical model. Inertial effects appear when the Weber number of the flow We=CaRe=O(10-1) and are manifest by a larger number of undulation crests that become evident on the surface of the rear meniscus of the bubble. This study demonstrates that the necessary bubble length for a flat liquid film region to exist between the rear and front menisci rapidly increases above 10R when Ca>0.01 and the value of the Reynolds number approaches 1000
Signaling Cascade Involved in Rapid Stimulation of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) by Dexamethasone
Impairment of mucociliary clearance with reduced airway fluid secretion leads to
chronically inflamed airways. Cystic fibrosis transmembrane conductance regulator (CFTR) is
crucially involved in airway fluid secretion and dexamethasone (dexa) has previously been shown to
elevate CFTR activity in airway epithelial cells. However, the pathway by which dexa increases CFTR
activity is largely unknown. We aimed to determine whether the increase of CFTR activity by dexa
is achieved by non-genomic signaling and hypothesized that the phosphoinositide 3-kinase (PI3K)
pathway is involved in CFTR stimulation. Primary rat airway epithelial cells and human bronchial
submucosal gland-derived Calu-3 cells were analyzed in Ussing chambers and kinase activation was
determined byWestern blots. Results demonstrated a critical involvement of PI3K and protein kinase
B (AKT) signaling in the dexa-induced increase of CFTR activity, while serum and glucocorticoid
dependent kinase 1 (SGK1) activity was not essential. We further demonstrated a reduced neural
precursor cell expressed, developmentally downregulated 4-like (NEDD4L) ubiquitin E3 ligase
activity induced by dexa, possibly responsible for the elevated CFTR activity. Finally, increases of
CFTR activity by dexa were demonstrated within 30 min accompanied by rapid activation of AKT.
In conclusion, dexa induces a rapid stimulation of CFTR activity which depends on PI3K/AKT
signaling in airway epithelial cells. Glucocorticoids might thus represent, in addition to their
immunomodulatory actions, a therapeutic strategy to rapidly increase airway fluid secretion
Glucocorticoids Equally Stimulate Epithelial Na+ Transport in Male and Female Fetal Alveolar Cells
Preterm infants frequently suffer from respiratory distress syndrome (RDS), possibly due
to lower expression of epithelial Na+ channels (ENaC). RDS incidence is sex-specific, affecting males
almost twice as often. Despite the use of antenatal glucocorticoids (GCs), the sex difference persists.
It is still controversial whether both sexes benefit equally from GCs. We previously showed that
Na+ transport is higher in female compared with male fetal distal lung epithelial (FDLE) cells.
Since GCs increase Na+ transport, we hypothesized that their stimulating effect might be sex-specific.
We analyzed FDLE cells with Ussing chambers and RT-qPCR in the presence or absence of fetal serum.
In serum-free medium, GCs increased the ENaC activity and mRNA expression, independent of sex.
In contrast, GCs did not increase the Na+ transport in serum-supplemented media and abolished the
otherwise observed sex difference. Inhibition of the GC receptor in the presence of serum did not
equalize Na+ transport between male and female cells. The GC-induced surfactant protein mRNA
expression was concentration and sex-specific. In conclusion, female and male FDLE cells exhibit no
sex difference in response to GCs with regard to Na+ transport, and GR activity does not contribute
to the higher Na+ transport in females
Development and Functional Characterization of Fetal Lung Organoids
Preterminfants frequently suffer frompulmonary complications due to a physiological and
structural lung immaturity resulting in significant morbidity and mortality. Novel in vitro and
in vivo models are required to study the underlying mechanisms of late lung maturation
and to facilitate the development of new therapeutic strategies. Organoids recapitulate
essential aspects of structural organization and possibly organ function, and can be
used to model developmental and disease processes. We aimed at generating fetal
lung organoids (LOs) and to functionally characterize this in vitro model in comparison
to primary lung epithelial cells and lung explants ex vivo. LOs were generated with
alveolar and endothelial cells from fetal rat lung tissue, using a Matrigel-gradient and
air-liquid-interface culture conditions. Immunocytochemical analysis showed that the LOs
consisted of polarized epithelial cell adhesion molecule (EpCAM)-positive cells with the
apical membrane compartment facing the organoid lumen. Expression of the alveolar
type 2 cell marker, RT2-70, and the Club cell marker, CC-10, were observed. Na+
transporter and surfactant protein mRNA expression were detected in the LOs. First
time patch clamp analyses demonstrated the presence of several ion channels with
specific electrophysiological properties, comparable to vital lung slices. Furthermore, the
responsiveness of LOs to glucocorticoids was demonstrated. Finally, maturation of LOs
induced by mesenchymal stem cells confirmed the convenience of the model to test and
establish novel therapeutic strategies. The results showed that fetal LOs replicate key
biological lung functions essential for lung maturation and therefore constitute a suitable
in vitro model system to study lung development and related diseases
A model of non-perturbative gluon emission in an initial state parton shower
We consider a model of transverse momentum production in which
non-perturbative smearing takes place throughout the perturbative evolution, by
a simple modification to an initial state parton shower algorithm. Using this
as the important non-perturbative ingredient, we get a good fit to data over a
wide range of energy. Combining it with the non-perturbative masses and cutoffs
that are a feature of conventional parton showers also leads to a reasonable
fit. We discuss the extrapolation to the LHC.Comment: 14 pages, 6 figures; version accepted by JHE
Aquilegia, Vol. 29 No. 3, May-July 2005: Newsletter of the Colorado Native Plant Society
https://epublications.regis.edu/aquilegia/1105/thumbnail.jp
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Dynamics of long gas bubbles rising in a vertical tube in a cocurrent liquid flow
© 2019 American Physical Society. When a confined long gas bubble rises in a vertical tube in a cocurrent liquid flow, its translational velocity is the result of both buoyancy and mean motion of the liquid. A thin film of liquid is formed on the tube wall and its thickness is determined by the interplay of viscous, inertial, capillary and buoyancy effects, as defined by the values of the Bond number (Bo≡ρgR2/σ with ρ being the liquid density, g the gravitational acceleration, R the tube radius, and σ the surface tension), capillary number (Cab≡μUb/σ with Ub being the bubble velocity and μ the liquid dynamic viscosity), and Reynolds number (Reb≡2ρUbR/μ). We perform experiments and numerical simulations to investigate systematically the effect of buoyancy (Bo=0-5) on the shape and velocity of the bubble and on the thickness of the liquid film for Cab=10-3-10-1 and Reb=10-2-103. A theoretical model, based on an extension of Bretherton's lubrication theory, is developed and utilized for parametric analyses; its predictions compare well with the experimental and numerical data. This study shows that buoyancy effects on bubbles rising in a cocurrent liquid flow make the liquid film thicker and the bubble rise faster, when compared to the negligible gravity case. In particular, gravitational forces impact considerably the bubble dynamics already when B
Uncertainties on Central Exclusive Scalar Luminosities from the unintegrated gluon distributions
In a previous report we used the Linked Dipole Chain model unintegrated gluon
densities to investigate the uncertainties in the predictions for central
exclusive production of scalars at hadron colliders. Here we expand this
investigation by also looking at other parameterizations of the unintegrated
gluon density, and look in more detail on the behavior of these at small k_T.
We confirm our conclusions that the luminosity function for central exclusive
production is very sensitive to this behavior. However, we also conclude that
the available densities based on the CCFM and LDC evolutions are not
constrained enough to give reliable predictions even for inclusive Higgs
production at the LHC
The Newly Active R Coronae Borealis Star, V2552 Oph
In 2001, V2552 Oph (CD -22 12017, HadV98) quickly faded by several magnitudes
in a manner typical of the R Coronae Borealis (RCB) stars. Photometry of V2552
Oph obtained over 70 years previous to 2001 shows no indication of variability.
Optical spectra of this star subsequently confirmed that V2552 Oph is a member
of the hydrogen deficient, carbon-rich RCB class of variables. It resembles the
warm (T 7000 K) RCB stars such as R Coronae Borealis itself. Other
RCB stars, such as XX Cam and Y Mus, have experienced similar periods of
inactivity, going decades without significant dust formation. Further
observations of V2552 Oph will be of great interest since there is an
opportunity to monitor an RCB star that may be moving from prolonged inactivity
into an active phase of dust production.Comment: 12 pages, 2 figures, PASP in pres
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