908 research outputs found
Cell migration on material-driven fibronectin microenvironments
Cell migration is a fundamental process involved in a wide range of biological phenomena. However, how the underlying mechanisms that control migration are orchestrated is not fully understood. In this work, we explore the migratory characteristics of human fibroblasts using different organisations of fibronectin (FN) triggered by two chemically similar surfaces, poly(ethyl acrylate) (PEA) and poly(methyl acrylate) (PMA); cell migration is mediated via an intermediate layer of fibronectin (FN). FN is organised into nanonetworks upon simple adsorption on PEA whereas a globular conformation is observed on PMA. We studied cell speed over the course of 24 h and the morphology of focal adhesions in terms of area and length. Additionally, we analysed the amount of cell-secreted FN as well as FN remodelling. Velocity of human fibroblasts was found to exhibit a biphasic behaviour on PEA, whereas it remained fairly constant on PMA. FA analysis revealed more mature focal adhesions on PEA over time contrary to smaller FAs found on PMA. Finally, human fibroblasts seemed to remodel adsorbed FN more on PMA than on PEA. Overall, these results indicate that the cell–protein–material interface affects cell migratory behaviour. Analysis of FAs together with FN secretion and remodelling were associated with differences in cell velocity providing insights into the factors that can modulate cell motility
Semiclassical and quantum Liouville theory
We develop a functional integral approach to quantum Liouville field theory
completely independent of the hamiltonian approach. To this end on the sphere
topology we solve the Riemann-Hilbert problem for three singularities of finite
strength and a fourth one infinitesimal, by determining perturbatively the
Poincare' accessory parameters. This provides the semiclassical four point
vertex function with three finite charges and a fourth infinitesimal. Some of
the results are extended to the case of n finite charges and m infinitesimal.
With the same technique we compute the exact Green function on the sphere on
the background of three finite singularities. Turning to the full quantum
problem we address the calculation of the quantum determinant on the background
of three finite charges and of the further perturbative corrections. The zeta
function regularization provides a theory which is not invariant under local
conformal transformations. Instead by employing a regularization suggested in
the case of the pseudosphere by Zamolodchikov and Zamolodchikov we obtain the
correct quantum conformal dimensions from the one loop calculation and we show
explicitly that the two loop corrections do not change such dimensions. We then
apply the method to the case of the pseudosphere with one finite singularity
and compute the exact value for the quantum determinant. Such results are
compared to those of the conformal bootstrap approach finding complete
agreement.Comment: 12 pages, 1 figure, Contributed to 5th Meeting on Constrained
Dynamics and Quantum Gravity (QG05), Cala Gonone, Sardinia, Italy, 12-16 Sep
200
First test of a high voltage feedthrough for liquid Argon TPCs connected to a 300 kV power supply
Voltages above a hundred kilo-volt will be required to generate the drift
field of future very large liquid Argon Time Projection Chambers. The most
delicate component is the feedthrough whose role is to safely deliver the very
high voltage to the cathode through the thick insulating walls of the cryostat
without compromising the purity of the argon inside. This requires a
feedthrough that is typically meters long and carefully designed to be vacuum
tight and have small heat input. Furthermore, all materials should be carefully
chosen to allow operation in cryogenic conditions. In addition, electric fields
in liquid argon should be kept below a threshold to reduce risks of discharges.
The combination of all above requirements represents significant challenges
from the design and manufacturing perspective. In this paper, we report on the
successful operation of a feedthrough satisfying all the above requirements.
The details of the feedthrough design and its manufacturing steps are provided.
Very high voltages up to unprecedented voltages of -300 kV could be applied
during long periods repeatedly. A source of instability was observed, which was
specific to the setup configuration which was used for the test and not due to
the feedthrough itself.Comment: 13 pages, 9 figure
Hamiltonian solutions of the 3-body problem in (2+1)-gravity
We present a full study of the 3-body problem in gravity in flat
(2+1)-dimensional space-time, and in the nonrelativistic limit of small
velocities. We provide an explicit form of the ADM Hamiltonian in a regular
coordinate system and we set up all the ingredients for canonical quantization.
We emphasize the role of a U(2) symmetry under which the Hamiltonian is
invariant and which should generalize to a U(N-1) symmetry for N bodies. This
symmetry seems to stem from a braid group structure in the operations of
looping of particles around each other, and guarantees the single-valuedness of
the Hamiltonian. Its role for the construction of single-valued energy
eigenfunctions is also discussed.Comment: 25 pages, no figure. v2: some calculation details removed to make the
paper more concise (see v1 for the longer version), minor correction in a
formula in the section on quantization, references added; results and
conclusions unchange
Digital Recording of Historical Defensive Structures in Mountainous Areas Using Drones: Considerations and Comparisons
Digital recording of historic buildings and sites in mountainous areas could be challenging. The paper considers and discusses the case of historical defensive structures in the Italian Alps, designed and built to be not accessible. Drone images and photogrammetric techniques for 3D modeling play a fundamental role in the digital documentation of fortified constructions with non-contact techniques. This manuscript describes the use of drones for reconstructing the external surfaces of some fortified structures using traditional photogrammetric/SfM solutions and novel methods based on NeRFs. The case of direct orientation based on PPK and traditional GCPs placed on the ground is also discussed, considering the difficulties in placing and measuring control points in such environments
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