2,075 research outputs found
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
Multiple regions of quantum criticality in YbAgGe
Dilation and thermopower measurements on YbAgGe, a heavy-fermion
antiferromagnet, clarify and refine the magnetic field-temperature (H-T) phase
diagram and reveal a field-induced phase with T-linear resistivity. On the
low-H side of this phase we find evidence for a first-order transition and
suggest that YbAgGe at 4.5 T may be close to a quantum critical end point. On
the high-H side our results are consistent with a second-order transition
suppressed to a quantum critical point near 7.2 T. We discuss these results in
light of global phase diagrams proposed for Kondo lattice systems
A versatile and compact capacitive dilatometer
We describe the design, construction, calibration, and operation of a
relatively simple differential capacitive dilatometer suitable for measurements
of thermal expansion and magnetostriction from 300 K to below 1 K with a
low-temperature resolution of about 0.05 angstroms. The design is characterized
by an open architecture permitting measurements on small samples with a variety
of shapes. Dilatometers of this design have operated successfully with a
commercial physical property measurement system, with several types of
cryogenic refrigeration systems, in vacuum, in helium exchange gas, and while
immersed in liquid helium (magnetostriction only) to temperatures of 30 mK and
in magnetic fields to 45 T.Comment: 8 pages, incorporating 6 figures, submitted to Rev. Sci. Instru
Localized f electrons in CexLa1-xRhIn5: dHvA Measurements
Measurements of the de Haas-van Alphen effect in CexLa1-xRhIn5 reveal that
the Ce 4f electrons remain localized for all x, with the mass enhancement and
progressive loss of one spin from the de Haas-van Alphen signal resulting from
spin fluctuation effects. This behavior may be typical of antiferromagnetic
heavy fermion compounds, inspite of the fact that the 4f electron localization
in CeRhIn5 is driven, in part, by a spin-density wave instability.Comment: 4 pages, 4 figures, submitted to PR
Field-Orientation Dependent Heat Capacity Measurements at Low Temperatures with a Vector Magnet System
We describe a heat capacity measurement system for the study of the
field-orientation dependence for temperatures down to 50 mK. A "Vector Magnet"
combined with a mechanical rotator for the dewar enables the rotation of the
magnetic field without mechanical heating in the cryostat by friction. High
reproducibility of the field direction, as well as an angular resolution of
better than 0.01 degree, is obtained. This system is applicable to other kinds
of measurements which require a large sample space or an adiabatic sample
environment, and can also be used with multiple refrigerator inserts
interchangeably.Comment: 7 pages, 8 figure
Time-resolved dynamics of electron wave packets in chaotic and regular quantum billiards with leads
We perform numerical studies of the wave packet propagation through open
quantum billiards whose classical counterparts exhibit regular and chaotic
dynamics. We show that for t less or similar to tau (tau being the Heisenberg
time), the features in the transmitted and reflected currents are directly
related to specific classical trajectories connecting the billiard leads. In
contrast, the long-time asymptotics of the wave packet dynamics is
qualitatively different for classical and quantum billiards. In particularly,
the decay of the quantum system obeys a power law that depends on the number of
decay channels, and is not sensitive to the nature of classical dynamics
(chaotic or regular).Comment: 5 pages, 4 figure
Time Structure of Particle Production in the Merit High-Power Target Experiment
The MERIT experiment is a proof-of-principle test of a target system for high power proton beam to be used as front-end for a neutrino factory complex or amuon collider. The experiment took data in autumn 2007 with the fast extracted beam from the CERN Proton Synchrotron (PS) to a maximum intensity of about 30 Ă 1012 protons per pulse. We report results from the portion of the MERIT experiment in which separated beam pulses were delivered to a free mercury jet target with time intervals between pulses varying from 2 to 700 ÎŒs. The analysis is based on the responses of particle detectors placed along side and downstream of the target
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