7,740 research outputs found
Traction force microscopy with optimized regularization and automated Bayesian parameter selection for comparing cells
Adherent cells exert traction forces on to their environment, which allows
them to migrate, to maintain tissue integrity, and to form complex
multicellular structures. This traction can be measured in a perturbation-free
manner with traction force microscopy (TFM). In TFM, traction is usually
calculated via the solution of a linear system, which is complicated by
undersampled input data, acquisition noise, and large condition numbers for
some methods. Therefore, standard TFM algorithms either employ data filtering
or regularization. However, these approaches require a manual selection of
filter- or regularization parameters and consequently exhibit a substantial
degree of subjectiveness. This shortcoming is particularly serious when cells
in different conditions are to be compared because optimal noise suppression
needs to be adapted for every situation, which invariably results in systematic
errors. Here, we systematically test the performance of new methods from
computer vision and Bayesian inference for solving the inverse problem in TFM.
We compare two classical schemes, L1- and L2-regularization, with three
previously untested schemes, namely Elastic Net regularization, Proximal
Gradient Lasso, and Proximal Gradient Elastic Net. Overall, we find that
Elastic Net regularization, which combines L1 and L2 regularization,
outperforms all other methods with regard to accuracy of traction
reconstruction. Next, we develop two methods, Bayesian L2 regularization and
Advanced Bayesian L2 regularization, for automatic, optimal L2 regularization.
Using artificial data and experimental data, we show that these methods enable
robust reconstruction of traction without requiring a difficult selection of
regularization parameters specifically for each data set. Thus, Bayesian
methods can mitigate the considerable uncertainty inherent in comparing
cellular traction forces
Optimal adaptive control with separable drift uncertainty
We consider a problem of stochastic optimal control with separable drift
uncertainty in strong formulation on a finite horizon. The drift coefficient of
the state is multiplicatively influenced by an unknown random variable
, while admissible controls are required to be adapted to the
observation filtration. Choosing a control actively influences the state and
information acquisition simultaneously and comes with a learning effect. The
problem, initially non-Markovian, is embedded into a higher-dimensional
Markovian, full information control problem with control-dependent filtration
and noise. To that problem, we apply the stochastic Perron method to
characterize the value function as the unique viscosity solution to the HJB
equation, explicitly construct -optimal controls and show that the
values of strong and weak formulations agree. Numerical illustrations show a
significant difference between the adaptive control and the certainty
equivalence control
Tube Width Fluctuations in F-Actin Solutions
We determine the statistics of the local tube width in F-actin solutions,
beyond the usually reported mean value. Our experimental observations are
explained by a segment fluid theory based on the binary collision approximation
(BCA). In this systematic generalization of the standard mean-field approach
effective polymer segments interact via a potential representing the
topological constraints. The analytically predicted universal tube width
distribution with a stretched tail is in good agreement with the data.Comment: Final version, 5 pages, 4 figure
Use of Web-Based Learning Modules for a General Medicine Advanced Pharmacy Practice Experience.
Objective. To implement and assess web-based learning modules on baseline pharmacy student knowledge prior to a general medicine advanced pharmacy practice experience (APPE).
Methods. Three web-based learning modules were developed for use prior to a general medicine APPE. Students completed pre- and post-assessments specific to each learning module. Additionally, students completed perception surveys at the conclusion of the APPE to determine the utility of these modules and the impact on student learning experiences.
Results. Use of the web-based training (WBT) modules resulted in a statistically significant improvement in post-assessment scores for two of the three modules (p \u3c 0.001). Student participants found the modules easy to use and helpful in APPE preparation.
Conclusions. Utilization of a WBT module prior to a general medicine APPE improves baseline knowledge among pharmacy students
Attractive instability of oppositely charged membranes induced by charge density fluctuations
We predict the conditions under which two oppositely charged membranes show a
dynamic, attractive instability. Two layers with unequal charges of opposite
sign can repel or be stable when in close proximity. However, dynamic charge
density fluctuations can induce an attractive instability and thus facilitate
fusion. We predict the dominant instability modes and timescales and show how
these are controlled by the relative charge and membrane viscosities. These
dynamic instabilities may be the precursors of membrane fusion in systems where
artificial vesicles are engulfed by biological cells of opposite charge
Gauss sum factorization with cold atoms
We report the first implementation of a Gauss sum factorization algorithm by
an internal state Ramsey interferometer using cold atoms. A sequence of
appropriately designed light pulses interacts with an ensemble of cold rubidium
atoms. The final population in the involved atomic levels determines a Gauss
sum. With this technique we factor the number N=263193.Comment: 4 pages, 5 figure
Direct observation of the tube model in F-actin solutions
Mutual uncrossability of polymers generates topological constraints on their
conformations and dynamics, which are generally described using the tube model.
We imaged confinement tubes for individual polymers within a F-actin solution
by sampling over many successive micrographs of fluorescently labeled probe
filaments. The resulting average tube width shows the predicted scaling
behavior. Unexpectedly, we found an exponential distribution of tube curvatures
which is attributed to transient entropic trapping in network void spaces.Comment: 6 pages, 4 figure
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