52 research outputs found
Many-body interactions between contracting living cells
The organization of live cells into tissues and their subsequent biological
function involves inter-cell mechanical interactions, which are mediated by
their elastic environment. To model this interaction, we consider cells as
spherical active force dipoles surrounded by an unbounded elastic matrix. Even
though we assume that this elastic medium responds linearly, each cell's
regulation of its mechanical activity leads to nonlinearities in the emergent
interactions between cells. We study the many-body nature of these interactions
by considering several geometries that include three or more cells. We show
that for different regulatory behaviors of the cells' activity, the total
elastic energy stored in the medium differs from the superposition of all
two-body interactions between pairs of cells within the system. Specifically,
we find that the many-body interaction energy between cells that regulate their
position is smaller than the sum of interactions between all pairs of cells in
the system, while for cells that do not regulate their position, the many-body
interaction is larger than the superposition prediction. Thus, such
higher-order interactions should be considered when studying the mechanics of
multiple cells in proximity
FlowNet: Learning Optical Flow with Convolutional Networks
Convolutional neural networks (CNNs) have recently been very successful in a
variety of computer vision tasks, especially on those linked to recognition.
Optical flow estimation has not been among the tasks where CNNs were
successful. In this paper we construct appropriate CNNs which are capable of
solving the optical flow estimation problem as a supervised learning task. We
propose and compare two architectures: a generic architecture and another one
including a layer that correlates feature vectors at different image locations.
Since existing ground truth data sets are not sufficiently large to train a
CNN, we generate a synthetic Flying Chairs dataset. We show that networks
trained on this unrealistic data still generalize very well to existing
datasets such as Sintel and KITTI, achieving competitive accuracy at frame
rates of 5 to 10 fps.Comment: Added supplementary materia
Learning-based Ensemble Average Propagator Estimation
By capturing the anisotropic water diffusion in tissue, diffusion magnetic
resonance imaging (dMRI) provides a unique tool for noninvasively probing the
tissue microstructure and orientation in the human brain. The diffusion profile
can be described by the ensemble average propagator (EAP), which is inferred
from observed diffusion signals. However, accurate EAP estimation using the
number of diffusion gradients that is clinically practical can be challenging.
In this work, we propose a deep learning algorithm for EAP estimation, which is
named learning-based ensemble average propagator estimation (LEAPE). The EAP is
commonly represented by a basis and its associated coefficients, and here we
choose the SHORE basis and design a deep network to estimate the coefficients.
The network comprises two cascaded components. The first component is a
multiple layer perceptron (MLP) that simultaneously predicts the unknown
coefficients. However, typical training loss functions, such as mean squared
errors, may not properly represent the geometry of the possibly non-Euclidean
space of the coefficients, which in particular causes problems for the
extraction of directional information from the EAP. Therefore, to regularize
the training, in the second component we compute an auxiliary output of
approximated fiber orientation (FO) errors with the aid of a second MLP that is
trained separately. We performed experiments using dMRI data that resemble
clinically achievable -space sampling, and observed promising results
compared with the conventional EAP estimation method.Comment: Accepted by MICCAI 201
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