3,732 research outputs found
Synergistic interaction between the Arp2/3 complex and cofilin drives stimulated lamellipod extension
Both the Arp2/3 complex and cofilin are believed to be important for the generation of protrusive force at the leading edge; however, their relative contributions have not been explored in vivo. Our results with living cells show that cofilin enters the leading edge immediately before the start of lamellipod extension, slightly earlier than Arp2/3, which begins to be recruited slightly later as the lamellipod is extended. Blocking either the Arp2/3 complex or cofilin function in cells results in failure to extend broad lamellipods and inhibits free barbed ends, suggesting that neither factor on its own can support actin polymerization-mediated protrusion in response to growth factor stimulation. High-resolution analysis of the actin network at the leading edge supports the idea that both the severing activity of cofilin and the specific branching activity of the Arp2/3 complex are essential for lamellipod protrusion. These results are the first to document the relative contributions of cofilin and Arp2/3 complex in vivo and indicate that cofilin begins to initiate the generation of free barbed ends that act in synergy with the Arp2/3 complex to create a large burst in nucleation activity
B\,^1\Sigma^{+}_{u} and EF\,^{1}\Sigma^{+}_{g} level energies of D
Accurate absolute level energies of the B\,^1\Sigma^{+}_{u}, and
EF\,^{1}\Sigma^{+}_{g}, rovibrational quantum states of molecular
deuterium are derived by combining results from a Doppler-free two-photon laser
excitation study on several lines in the
(0,0) band, with results
from a Fourier-transform spectroscopic emission study on a low-pressure
hydrogen discharge. Level energy uncertainties as low as 0.0005 cm are
obtained for some low-lying E\,^{1}\Sigma^{+}_{g} inner-well rovibrational
levels, while uncertainties for higher-lying rovibrational levels and those of
the F\,^{1}\Sigma^{+}_{g} outer-well states are nominally 0.005 cm.
Level energies of B\,^1\Sigma^{+}_{u} rovibrational levels, for
and are determined at an accuracy of 0.001 cm. Computed
wavelengths of D Lyman transitions in the
B\,^1\Sigma^{+}_{u}-X\,^{1}\Sigma^{+}_{g} () bands are also tabulated
for future applications.Comment: appears in Journal of Molecular Spectroscopy (2014
Mesoscale modeling of the rheology of pressure sensitive adhesives through inclusion of transient forces
For optimal application, pressure-sensitive adhesives must have rheological
properties in between those of a viscoplastic solid and those of a viscoelastic
liquid. Such adhesives can be produced by emulsion polymerisation, resulting in
latex particles which are dispersed in water and contain long-chain acrylic
polymers. When the emulsion is dried, the latex particles coalesce and an
adhesive film is formed. The rheological properties of the dried samples are
believed to be dominated by the interface regions between the original latex
particles, but the relation between rheology and latex particle properties is
poorly understood. In this paper we show that it is possible to describe the
bulk rheology of a pressure-sensitive adhesive by means of a mesoscale
simulation model. To reach experimental time and length scales, each latex
particle is represented by just one simulated particle. The model is subjected
to oscillatory shear flow and extensional flow. Simple order of magnitude
estimates of the model parameters already lead to semi-quantitative agreement
with experimental results. We show that inclusion of transient forces in the
model, i.e. forces with memory of previous configurations, is essential to
correctly predict the linear and nonlinear properties.Comment: 29 pages, 8 figure
Actin at cell-cell junctions is composed of two dynamic and functional populations
The ability of epithelial cells to polarize requires cell-cell adhesion mediated by cadherin receptors. During cell-cell contact, the mechanism via which a flat, spread cell shape is changed into a tall, cuboidal epithelial morphology is not known. We found that cadherin-dependent adhesion modulates actin dynamics by triggering changes in actin organization both locally at junctions and within the rest of the cell. Upon induction of cell-cell contacts, two spatial actin populations are distinguishable: junctional actin and peripheral thin bundles. With time, the relative position of these two populations changes and becomes indistinguishable to form a cortical actin ring that is characteristic of mature, fully polarized epithelial cells. Junctional actin and thin actin bundles differ in their actin dynamics and mechanism of formation, and interestingly, have distinct roles during epithelial polarization. Whereas junctional actin stabilizes clustered cadherin receptors at cell-cell contacts, contraction of peripheral actin bundle is essential for an increase in the maximum height at the lateral domain during polarization (cuboidal morphology). Thus, both junctional actin and thin bundles are necessary, and cooperate with each other to generate a polarized epithelial morphology
Reduced dimension modeling of leading edge turbulent interaction noise
A computational aeroacoustics approach is used to model the effects of real airfoil geometry on leading edge turbulent interaction noise for symmetric airfoils at zero angle of attack. For the first time, one-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulent disturbances are modeled instead of single frequency transverse gusts, which previous computational studies of leading edge noise have been confined to. The effects of the inclusion of streamwise and spanwise disturbances on the noise are assessed, and it is shown that accurate noise predictions for symmetric airfoils can be made by modeling only the transverse disturbances, which reduces the computational expense of simulations. Additionally, the two-component turbulent synthesis method is used to model the effects of airfoil thickness on the noise for thicknesses ranging from 2% to 12%. By using sufficient airfoil thicknesses to show trends, it is found that airfoil thickness will reduce the noise at high frequency, and that the sound power P will reduce linearly with increasing airfoil thickness
A 16-channel Digital TDC Chip with internal buffering and selective readout for the DIRC Cherenkov counter of the BABAR experiment
A 16-channel digital TDC chip has been built for the DIRC Cherenkov counter
of the BaBar experiment at the SLAC B-factory (Stanford, USA). The binning is
0.5 ns, the conversion time 32 ns and the full-scale 32 mus. The data driven
architecture integrates channel buffering and selective readout of data falling
within a programmable time window. The time measuring scale is constantly
locked to the phase of the (external) clock. The linearity is better than 80 ps
rms. The dead time loss is less than 0.1% for incoherent random input at a rate
of 100 khz on each channel. At such a rate the power dissipation is less than
100 mw. The die size is 36 mm2.Comment: Latex, 18 pages, 13 figures (14 .eps files), submitted to NIM
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