3,424 research outputs found
Vascular networks due to dynamically arrested crystalline ordering of elongated cells
Recent experimental and theoretical studies suggest that crystallization and
glass-like solidification are useful analogies for understanding cell ordering
in confluent biological tissues. It remains unexplored how cellular ordering
contributes to pattern formation during morphogenesis. With a computational
model we show that a system of elongated, cohering biological cells can get
dynamically arrested in a network pattern. Our model provides a new explanation
for the formation of cellular networks in culture systems that exclude
intercellular interaction via chemotaxis or mechanical traction.Comment: 11 pages, 4 figures. Published as: Palm and Merks (2013) Physical
Review E 87, 012725. The present version includes a correction in the
calculation of the nematic order parameter. Erratum submitted to PRE on Jun
5th 2013. The correction does not affect the conclusion
Genesis of Atlantic Lows Experiment NASA Electra Boundary Layer Flights Data Report
The objective of this research was to obtain high resolution measurements of the height of the Marine Atmospheric Boundary Layer (MABL) during cold air outbreaks using an Airborne Lidar System. The research was coordinated with other investigators participating in the Genesis of Atlantic Lows Experiment (GALE). An objective computerized scheme was developed to obtain the Boundary Layer Height from the Lidar Data. The algorithm was used on each of the four flight days producing a high resolution data set of the MABL height over the GALE experiment area. Plots of the retrieved MABL height as well as tabular data summaries are presented
Time-Resolved PIV Measurements of Ship Airwakes with Quartering Winds
The unsteady, three-dimensional, turbulent airwake over the Simple Frigate Ship No. 2 (SFS2) with quartering wind flow directions was studied in a low-speed wind tunnel facility. Surface oil flow visualization and time-resolved stereoscopic and planar particle image velocimetry (PIV) measurements were made for three crosswise planes and a single centerline streamwise plane. Measurements included various configurations with the bow of the ship model at two different quartering wind conditions of 10 and 20 degrees, as well as cases with and without the effects of a simulated atmospheric boundary layer (ABL). A comparative analysis of the time-averaged flow structures between the quartering wind cases and the pure headwind measurements showed significant differences in the development of the airwake. For both quartering wind cases, the funnel wake had a trailing vortex on the windward side and large cross-sectional velocity magnitudes. The flight deck recirculation region decreased in size and became asymmetric for both quartering wind cases. Different flight deck vortical structures were found, indicating a difference within the flow field based on the yaw angle. A spectral analysis showed the streamwise fluctuations contained more energy for the quartering wind cases in the funnel wake region, which was also seen in the turbulent fluctuations. Two-point velocity correlations revealed large-scale coherent motion in the streamwise direction. The coherent behavior was further related to the observed time-averaged flow field structures through proper orthogonal decomposition (POD). The POD analysis highlighted the nontrivial behavior that was inherent to the airwake. These findings further emphasize the complexity of the airwake and necessity of understanding the development of the airwake under a broad range of conditions
Designing Synthetic Pathways for Several 2-Thio-Substituted-3H-Phenothiazin-3-ones in Preparation for Testing in Treatment of Central Nervous System Disorders
This paper investigates possible synthetic pathways for two 2-thio-substituted-3H-phenothiazin-3-ones (7). A two step reaction in which 1,4-benzoquinone (1) is first reacted with an alkylthiol (2) in the presence of sodium periodate (NaIO4) and then treated with 2-aminothiophenol (5) followed by a second oxidation with sodium periodate was demonstrated to be effective in synthesizing 2-(phenylthio)-3H-phenothiazin-3-one (12). The same synthetic approach was shown to be ineffective in the synthesis of 2-(cyclopentylthio)-3H-phenothiazin-3-one (16) due to the fact that the first step was incapable of synthesizing 2-(cyclopentylthio)-1,4-benzoquinone (14). Several other synthetic routes were also proven to be ineffective. This investigation is part of a larger effort to create a vast library of 2-thio-substituted-3H-phenothiazin-3-ones (7) for testing in leukotriene inhibition and treatment of neurodegenerative disorders
Computational Screening of Tip and Stalk Cell Behavior Proposes a Role for Apelin Signaling in Sprout Progression
Angiogenesis involves the formation of new blood vessels by sprouting or
splitting of existing blood vessels. During sprouting, a highly motile type of
endothelial cell, called the tip cell, migrates from the blood vessels followed
by stalk cells, an endothelial cell type that forms the body of the sprout. To
get more insight into how tip cells contribute to angiogenesis, we extended an
existing computational model of vascular network formation based on the
cellular Potts model with tip and stalk differentiation, without making a
priori assumptions about the differences between tip cells and stalk cells. To
predict potential differences, we looked for parameter values that make tip
cells (a) move to the sprout tip, and (b) change the morphology of the
angiogenic networks. The screening predicted that if tip cells respond less
effectively to an endothelial chemoattractant than stalk cells, they move to
the tips of the sprouts, which impacts the morphology of the networks. A
comparison of this model prediction with genes expressed differentially in tip
and stalk cells revealed that the endothelial chemoattractant Apelin and its
receptor APJ may match the model prediction. To test the model prediction we
inhibited Apelin signaling in our model and in an \emph{in vitro} model of
angiogenic sprouting, and found that in both cases inhibition of Apelin or of
its receptor APJ reduces sprouting. Based on the prediction of the
computational model, we propose that the differential expression of Apelin and
APJ yields a "self-generated" gradient mechanisms that accelerates the
extension of the sprout.Comment: 48 pages, 10 figures, 8 supplementary figures. Accepted for
publication in PLoS ON
Genetic evidence of farmed straying and introgression in Swedish wild salmon populations
Escaped farmed Atlantic salmon represent a well-documented and ongoing threat to wild conspecific populations. In Norway, the world-leading producer of farmed salmon, annual monitoring of straying and genetic introgression by farmed escapees in wild salmon rivers has been carried out since the late 1980s. In this study, we applied molecular and statistical methods routinely used in the Norwegian monitoring programme to investigate the magnitude of escaped farmed salmon and genetic introgression in salmon rivers on the west coast of Sweden, where suspected escapees have been observed. Our results confirm that escaped farmed salmon stray, successfully spawn, and produce offspring at levels similar to those observed in neighbouring Norway. These findings raise concerns over population productivity and long-term viability and highlight the need for more permanent monitoring of the presence and consequences of escaped farmed salmon in Swedish salmon rivers. Our results further illustrate that farmed gene flow may constitute a transboundary problem with potential international implications
- …