151 research outputs found
Neural Network Control for the Probe Landing Based on Proportional Integral Observer
For the probe descending and landing safely, a neural network control method based on proportional integral observer (PIO) is proposed. First, the dynamics equation of the probe under the landing site coordinate system is deduced and the nominal trajectory meeting the constraints in advance on three axes is preplanned. Then the PIO designed by using LMI technique is employed in the control law to compensate the effect of the disturbance. At last, the neural network control algorithm is used to guarantee the double zero control of the probe and ensure the probe can land safely. An illustrative design example is employed to demonstrate the effectiveness of the proposed control approach
Safety Index Synthesis via Sum-of-Squares Programming
Control systems often need to satisfy strict safety requirements. Safety
index provides a handy way to evaluate the safety level of the system and
derive the resulting safe control policies. However, designing safety index
functions under control limits is difficult and requires a great amount of
expert knowledge. This paper proposes a framework for synthesizing the safety
index for general control systems using sum-of-squares programming. Our
approach is to show that ensuring the non-emptiness of safe control on the safe
set boundary is equivalent to a local manifold positiveness problem. We then
prove that this problem is equivalent to sum-of-squares programming via the
Positivstellensatz of algebraic geometry. We validate the proposed method on
robot arms with different degrees of freedom and ground vehicles. The results
show that the synthesized safety index guarantees safety and our method is
effective even in high-dimensional robot systems
State-wise Constrained Policy Optimization
Reinforcement Learning (RL) algorithms have shown tremendous success in
simulation environments, but their application to real-world problems faces
significant challenges, with safety being a major concern. In particular,
enforcing state-wise constraints is essential for many challenging tasks such
as autonomous driving and robot manipulation. However, existing safe RL
algorithms under the framework of Constrained Markov Decision Process (CMDP) do
not consider state-wise constraints. To address this gap, we propose State-wise
Constrained Policy Optimization (SCPO), the first general-purpose policy search
algorithm for state-wise constrained reinforcement learning. SCPO provides
guarantees for state-wise constraint satisfaction in expectation. In
particular, we introduce the framework of Maximum Markov Decision Process, and
prove that the worst-case safety violation is bounded under SCPO. We
demonstrate the effectiveness of our approach on training neural network
policies for extensive robot locomotion tasks, where the agent must satisfy a
variety of state-wise safety constraints. Our results show that SCPO
significantly outperforms existing methods and can handle state-wise
constraints in high-dimensional robotics tasks.Comment: arXiv admin note: text overlap with arXiv:2305.1368
Migration direction in a songbird explained by two loci
Migratory routes and remote wintering quarters in birds are often species and even population specific. It has been known for decades that songbirds mainly migrate solitarily, and that the migration direction is genetically controlled. Yet, the underlying genetic mechanisms remain unknown. To investigate the genetic basis of migration direction, we track genotyped willow warblers Phylloscopus trochilus from a migratory divide in Sweden, where South-West migrating, and South-East migrating subspecies form a hybrid swarm. We find evidence that migration direction follows a dominant inheritance pattern with epistatic interaction between two loci explaining 74% of variation. Consequently, most hybrids migrate similarly to one of the parental subspecies, and therefore do not suffer from the cost of following an inferior, intermediate route. This has significant implications for understanding the selection processes that maintain narrow migratory divides
Robust Linear Quadratic Regulator via Sliding Mode Guidance for Spacecraft Orbiting a Tumbling Asteroid
Aiming to ensure the stability of the spacecraft with multiuncertainties and mitigate the threat of the initial actuator saturation,
a Robust Linear Quadratic Regulator (RLQR) via sliding mode guidance (SMG) for orbiting a tumbling asteroid is proposed
in this paper. The orbital motion of the spacecraft near a tumbling asteroid is modelled in the body-fixed frame considering the
sun-relative effects, and the orbiting control problem is formulated as a stabilization of a nonlinear time-varying system. RLQR
based on the adaptive feedback linearization is proposed to stabilize the spacecraft orbiting with the uncertainties of the asteroid’s
rotation and gravitational field. In order to avoid the initial actuator saturation, SMG is applied to generate the transition process
trajectory of the closed-loop system. The effectiveness of the proposed control scheme is verified by the simulations of orbiting the
asteroid Toutatis 4179
Identification of DYNLT1 associated with proliferation, relapse, and metastasis in breast cancer
BackgroundBreast cancer (BC) is the most common malignant disease worldwide. Although the survival rate is improved in recent years, the prognosis is still bleak once recurrence and metastasis occur. It is vital to investigate more efficient biomarkers for predicting the metastasis and relapse of BC. DYNLT1 has been reported that participating in the progression of multiple cancers. However, there is still a lack of study about the correlation between DYNLT1 and BC.MethodsIn this study, we evaluated and validated the expression pattern and prognostic implication of DYNLT1 in BC with multiple public cohorts and BC tumor microarrays (TMAs) of paraffin-embedded tissues collected from the Affiliated Hospital of Jining Medical University. The response biomarkers for immune therapy, such as tumor mutational burden (TMB), between different DYNLT1 expression level BC samples were investigated using data from the TCGA-BRCA cohort utilizing public online tools. In addition, colony formation and transwell assay were conducted to verify the effects of DYNLT1 in BC cell line proliferation and invasion.ResultsThe results demonstrated that DYNLT1 overexpressed in BC and predicted poor relapse-free survival in our own BC TMA cohort. In addition, DYNLT1 induced BC development by promoting MDA-MB-231 cell proliferation migration, and metastasis.ConclusionAltogether, our findings proposed that DYNLT1 could be a diagnostic and prognostic indicator in BC
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