236 research outputs found
Stochastic coarse-grained simulations of polyelectrolytes
Stochastic coarse-grained simulations are implemented to investigate the behavior of both strong
and weak polyelectrolytes in acqueous solution. A primitive electrolyte model is used to represent
polyeletrolytes and mobile ions, whereas the solvent is implcitly represented by a dielectric
continuum. The polyelectrolytes dissociation equilibria are taken into account by the constant-pH
method where necessary. Several different chemico-physical systems have been investigated:
1. linear and star weak polyelectrolytes (both in solutions or confined in semi-permeable
spherical cavities) able to interact via charged hydrogen bonds;
2. linear and star weak polyelectrolytes interacting with an oppositely charged macroion, the
latter represented either via the usual charge-centered model or via monovalent charges
tethered to (but free to move and rearrange on) its surface:
3. linear and star strong polyelectrolytes interacting with a primitive model of a zwitterionic
micelle;
4. mixtures of oppositely charged star-shaped strong polyelectrolytes that self-assemble to
form gel-like phases at the free swelling equilibrium;
5. weak knotted ring polyelectrolytes, the latter showing a non monotonic behavior of their
size versus their ionization degree, an evidence that was not predicted by mean-filed
approaches.
Overall, our simulations demonstrated that the polyelectrolytes behavior often deviates from the one
expected for "canonical" polyelectrolytes in diluted aqueous solutions when chemically specific
interactions (such as charged hydrogen bonds) have to be taken into account, or when charge
correlation play a fiundamental role
Sensation seeking, non-contextual decision making, and driving abilities as measured through a moped simulator.
The general aim of the present study was to explore the relations between driving style (assessed through a moped riding simulator) and psychological variables such as sensation seeking and decision making. Because the influences of sensation seeking and decision making on driving styles have been studied separately in the literature, we have tried to investigate their mutual relations so as to include them in a more integrated framework. Participants rode the Honda Riding Trainer (HRT) simulator, filled in the Sensation Seeking Scale V (SSS V), and performed the Iowa Gambling Task (IGT). A cluster analysis of the HRT riding indexes identified three groups: Prudent, Imprudent, and Insecure riders. First, the results showed that Insecure males seek thrills and adventure less than both Prudent males and Insecure females, whereas Prudent females are less disinhibited than both Prudent males and Insecure females. Moreover, concerning the relations among SSS, decision making as measured by the IGT, and riding performance, high thrill and adventure seekers performed worse in the simulator only if they were also bad decision makers, indicating that these two traits jointly contribute to the quality of riding performance. From an applied perspective, these results also provide useful information for the development of protocols for assessing driving abilities among novice road users. Indeed, the relation between risk proneness and riding style may allow for the identification of road-user populations who require specific training
Efficient Deep Learning of Robust Policies from MPC using Imitation and Tube-Guided Data Augmentation
Imitation Learning (IL) has been increasingly employed to generate
computationally efficient policies from task-relevant demonstrations provided
by Model Predictive Control (MPC). However, commonly employed IL methods are
often data- and computationally-inefficient, as they require a large number of
MPC demonstrations, resulting in long training times, and they produce policies
with limited robustness to disturbances not experienced during training. In
this work, we propose an IL strategy to efficiently compress a computationally
expensive MPC into a Deep Neural Network (DNN) policy that is robust to
previously unseen disturbances. By using a robust variant of the MPC, called
Robust Tube MPC (RTMPC), and leveraging properties from the controller, we
introduce a computationally-efficient Data Aggregation (DA) method that enables
a significant reduction of the number of MPC demonstrations and training time
required to generate a robust policy. Our approach opens the possibility of
zero-shot transfer of a policy trained from a single MPC demonstration
collected in a nominal domain, such as a simulation or a robot in a
lab/controlled environment, to a new domain with previously-unseen bounded
model errors/perturbations. Numerical and experimental evaluations performed
using linear and nonlinear MPC for agile flight on a multirotor show that our
method outperforms strategies commonly employed in IL (such as DAgger and DR)
in terms of demonstration-efficiency, training time, and robustness to
perturbations unseen during training.Comment: Under review. arXiv admin note: text overlap with arXiv:2109.0991
Efficient Deep Learning of Robust, Adaptive Policies using Tube MPC-Guided Data Augmentation
The deployment of agile autonomous systems in challenging, unstructured
environments requires adaptation capabilities and robustness to uncertainties.
Existing robust and adaptive controllers, such as the ones based on MPC, can
achieve impressive performance at the cost of heavy online onboard
computations. Strategies that efficiently learn robust and onboard-deployable
policies from MPC have emerged, but they still lack fundamental adaptation
capabilities. In this work, we extend an existing efficient IL algorithm for
robust policy learning from MPC with the ability to learn policies that adapt
to challenging model/environment uncertainties. The key idea of our approach
consists in modifying the IL procedure by conditioning the policy on a learned
lower-dimensional model/environment representation that can be efficiently
estimated online. We tailor our approach to the task of learning an adaptive
position and attitude control policy to track trajectories under challenging
disturbances on a multirotor. Our evaluation is performed in a high-fidelity
simulation environment and shows that a high-quality adaptive policy can be
obtained in about hours. We additionally empirically demonstrate rapid
adaptation to in- and out-of-training-distribution uncertainties, achieving a
cm average position error under a wind disturbance that corresponds to
about of the weight of the robot and that is larger than the
maximum wind seen during training.Comment: 8 pages, 6 figure
Modulation of DNA repair genes induced by TLR9 agonists: A strategy to eliminate “altered” cells?
We provided evidence that the TLR9 engagement of innate immune cells present in the tumor microenvironment by CpG-oligodeoxynucleotide (CpG-ODN) induces down-modulation of DNA repair gene expression in tumor cells, sensitizing cancer cells to DNA-damaging chemotherapy. These findings expand the benefits of CpG-ODN therapy beyond induction of a strong immune response
Touch the Wind: Simultaneous Airflow, Drag and Interaction Sensing on a Multirotor
Disturbance estimation for Micro Aerial Vehicles (MAVs) is crucial for
robustness and safety. In this paper, we use novel, bio-inspired airflow
sensors to measure the airflow acting on a MAV, and we fuse this information in
an Unscented Kalman Filter (UKF) to simultaneously estimate the
three-dimensional wind vector, the drag force, and other interaction forces
(e.g. due to collisions, interaction with a human) acting on the robot. To this
end, we present and compare a fully model-based and a deep learning-based
strategy. The model-based approach considers the MAV and airflow sensor
dynamics and its interaction with the wind, while the deep learning-based
strategy uses a Long Short-Term Memory (LSTM) neural network to obtain an
estimate of the relative airflow, which is then fused in the proposed filter.
We validate our methods in hardware experiments, showing that we can accurately
estimate relative airflow of up to 4 m/s, and we can differentiate drag and
interaction force.Comment: The first two authors contributed equall
An innovative 8 channels system for time-resolved diffuse optical tomography based on SiPMs
We present the design of a novel 8 channels system for time resolved optical tomography based on Silicon Photomultipliers (SiPMs), therefore knocking down cost and complexity of this technique and paving the way to a widespread diffusion. We validated the system performances on phantoms
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