253 research outputs found
Neuromorphic computing for attitude estimation onboard quadrotors
Compelling evidence has been given for the high energy efficiency and update
rates of neuromorphic processors, with performance beyond what standard Von
Neumann architectures can achieve. Such promising features could be
advantageous in critical embedded systems, especially in robotics. To date, the
constraints inherent in robots (e.g., size and weight, battery autonomy,
available sensors, computing resources, processing time, etc.), and
particularly in aerial vehicles, severely hamper the performance of
fully-autonomous on-board control, including sensor processing and state
estimation. In this work, we propose a spiking neural network (SNN) capable of
estimating the pitch and roll angles of a quadrotor in highly dynamic movements
from 6-degree of freedom Inertial Measurement Unit (IMU) data. With only 150
neurons and a limited training dataset obtained using a quadrotor in a real
world setup, the network shows competitive results as compared to
state-of-the-art, non-neuromorphic attitude estimators. The proposed
architecture was successfully tested on the Loihi neuromorphic processor
on-board a quadrotor to estimate the attitude when flying. Our results show the
robustness of neuromorphic attitude estimation and pave the way towards
energy-efficient, fully autonomous control of quadrotors with dedicated
neuromorphic computing systems
Neuromorphic Control using Input-Weighted Threshold Adaptation
Neuromorphic processing promises high energy efficiency and rapid response
rates, making it an ideal candidate for achieving autonomous flight of
resource-constrained robots. It will be especially beneficial for complex
neural networks as are involved in high-level visual perception. However, fully
neuromorphic solutions will also need to tackle low-level control tasks.
Remarkably, it is currently still challenging to replicate even basic low-level
controllers such as proportional-integral-derivative (PID) controllers.
Specifically, it is difficult to incorporate the integral and derivative parts.
To address this problem, we propose a neuromorphic controller that incorporates
proportional, integral, and derivative pathways during learning. Our approach
includes a novel input threshold adaptation mechanism for the integral pathway.
This Input-Weighted Threshold Adaptation (IWTA) introduces an additional weight
per synaptic connection, which is used to adapt the threshold of the
post-synaptic neuron. We tackle the derivative term by employing neurons with
different time constants. We first analyze the performance and limits of the
proposed mechanisms and then put our controller to the test by implementing it
on a microcontroller connected to the open-source tiny Crazyflie quadrotor,
replacing the innermost rate controller. We demonstrate the stability of our
bio-inspired algorithm with flights in the presence of disturbances. The
current work represents a substantial step towards controlling highly dynamic
systems with neuromorphic algorithms, thus advancing neuromorphic processing
and robotics. In addition, integration is an important part of any temporal
task, so the proposed Input-Weighted Threshold Adaptation (IWTA) mechanism may
have implications well beyond control tasks
On the Microscopic Origin of Cholesteric Pitch
We present a microscopic analysis of the instability of the nematic phase to
chirality when molecular chirality is introduced perturbatively. We show that
previously neglected short-range biaxial correlations play a crucial role in
determining the cholesteric pitch. We propose an order parameter which
quantifies the chirality of a molecule.Comment: RevTeX 3.0, 4 pages, one included eps figure. Published versio
Seeking creativity: A case study on information problem solving in professional music
This study explored the information seeking behavior of a professional jazz musician during creative work. It aimed at revealing information seeking activities necessary to execute present-day musical projects. A single case was studied in depth. First, a narrative interview was conducted to reveal project phases and corresponding information seeking behavior. Second, hereupon a semi-structured interview was taken to identify information seeking activities per phase. Results indicate that the musician deliberately searched for musical information especially in the first project phases. The internet was used as main source. Both data and goal driven strategies were applied, of which the latter were relatively scarce. This means that in this case the musician sporadically searched information based on a contemplated search plan. Future research should aim at generalizing findings of this case. It should further validate the underlying analytical framework that proved to be useful for describing and categorizing musical information seeking behavior
Pulsed field studies of the magnetization reversal in molecular nanomagnets
We report experimental studies of crystals of Mn12 molecular magnetic
clusters in pulsed magnetic fields with sweep rates up to 4x10^3 T/s. The steps
in the magnetization curve are observed at fields that are shifted with respect
to the resonant field values. The shift systematically increases as the rate of
the field sweep goes up. These data are consistent with the theory of the
collective dipolar relaxation in molecular magnets.Comment: 4 pages, 4 figure
Polydispersity and ordered phases in solutions of rodlike macromolecules
We apply density functional theory to study the influence of polydispersity
on the stability of columnar, smectic and solid ordering in the solutions of
rodlike macromolecules. For sufficiently large length polydispersity (standard
deviation ) a direct first-order nematic-columnar transition is
found, while for smaller there is a continuous nematic-smectic and
first-order smectic-columnar transition. For increasing polydispersity the
columnar structure is stabilized with respect to solid perturbations. The
length distribution of macromolecules changes neither at the nematic-smectic
nor at the nematic-columnar transition, but it does change at the
smectic-columnar phase transition. We also study the phase behaviour of binary
mixtures, in which the nematic-smectic transition is again found to be
continuous. Demixing according to rod length in the smectic phase is always
preempted by transitions to solid or columnar ordering.Comment: 13 pages (TeX), 2 Postscript figures uuencode
Antibodies against Platelet Glycoproteins in Clinically Suspected VITT Patients
Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare but severe complication following COVID-19 vaccination, marked by thrombocytopenia and thrombosis. Analogous to heparin-induced thrombocytopenia (HIT), VITT shares similarities in anti-platelet factor 4 (PF4) IgG-mediated platelet activation via the FcγRIIa. To investigate the involvement of platelet-antibodies in VITT, we analyzed the presence of platelet-antibodies directed against glycoproteins (GP)IIb/IIIa, GPV and GPIb/IX in the serum of 232 clinically suspected VITT patients determined based on (suspicion of) occurrence of thrombocytopenia and/or thrombosis in relation to COVID-19 vaccination. We found that 19% of clinically suspected VITT patients tested positive for anti-platelet GPs: 39%, 32% and 86% patients tested positive for GPIIb/IIIa, GPV and GPIb/IX, respectively. No HIT-like VITT patients (with thrombocytopenia and thrombosis) tested positive for platelet-antibodies. Therefore, it seems unlikely that platelet-antibodies play a role in HIT-like anti-PF4-mediated VITT. Platelet-antibodies were predominantly associated with the occurrence of thrombocytopenia. We found no association between the type of vaccination (adenoviral vector vaccine versus mRNA vaccine) or different vaccines (ChAdOx1 nCoV-19, Ad26.COV2.S, mRNA-1273, BTN162b2) and the development of platelet-antibodies. It is essential to conduct more research on the pathophysiology of VITT, to improve diagnostic approaches and identify preventive and therapeutic strategies.</p
Advances in preclinical therapeutics development using small animal imaging and molecular analyses: the gastrointestinal stromal tumors model
The large use of target therapies in the treatment of gastrointestinal stromal tumors (GISTs) highlighted the urgency to integrate new molecular imaging technologies, to develop new criteria for tumor response evaluation and to reach a more comprehensive definition of the molecular target. These aspects, which come from clinical experiences, are not considered enough in preclinical research studies which aim to evaluate the efficacy of new drugs or new combination of drugs with molecular target. We developed a xenograft animal model GIST882 using nude mice. We evaluated both the molecular and functional characterization of the tumor mass. The mutational analysis of KIT receptor of the GIST882 cell lines and tumor mass showed a mutation on exon 13 that was still present after in vivo cell growth. The glucose metabolism and cell proliferation was evaluated with a small animal PET using both FDG and FLT. The experimental development of new therapies for GIST treatment requires sophisticated animal models in order to represent the tumor molecular heterogeneity already demonstrated in the clinical setting and in order to evaluate the efficacy of the treatment also considering the inhibition of tumor metabolism, and not only considering the change in size of tumors. This approach of cancer research on GISTs is crucial and essential for innovative perspectives that could cross over to other types of cancer
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