252 research outputs found
Trajectory tracking control of a quadrotor UAV based on sliding mode active disturbance rejection control
This paper proposes a sliding mode active disturbance rejection control scheme to deal with trajectory tracking control problems for the quadrotor unmanned aerial vehicle (UAV). Firstly, the differential signal of the reference trajectory can be obtained directly by using the tracking differentiator (TD), then the design processes of the controller can be simplified. Secondly, the estimated values of the UAV's velocities, angular velocities, total disturbance can be acquired by using extended state observer (ESO), and the total disturbance of the system can be compensated in the controller in real time, then the robustness and anti-interference capability of the system can be improved. Finally, the sliding mode controller based on TD and ESO is designed, the stability of the closed-loop system is proved by Lyapunov method. Simulation results show that the control scheme proposed in this paper can make the quadrotor track the desired trajectory quickly and accurately.
 
Unified linear time-invariant model predictive control for strong nonlinear chaotic systems
It is well known that an alone linear controller is difficult to control a chaotic system, because intensive nonlinearities exist in such system. Meanwhile, depending closely on a precise mathematical modeling of the system and high computational complexity, model predictive control has its inherent drawback in controlling nonlinear systems. In this paper, a unified linear time-invariant model predictive control for intensive nonlinear chaotic systems is presented. The presented model predictive control algorithm is based on an extended state observer, and the precise mathematical modeling is not required. Through this method, not only the required coefficient matrix of impulse response can be derived analytically, but also the future output prediction is explicitly calculated by only using the current output sample. Therefore, the computational complexity can be reduced sufficiently. The merits of this method include, the Diophantine equation needing no calculation, and independence of precise mathematical modeling. According to the variation of the cost function, the order of the controller can be reduced, and the system stability is enhanced. Finally, numerical simulations of three kinds of chaotic systems confirm the effectiveness of the proposed method
Enhancing Spoofing Speech Detection Using Rhythm Information
Current spoofing speech detection systems need more convincing evidence. In
this paper, the flaws of rhythm information inherent in the TTS-generated
speech are analyzed to increase the reliability of detection systems. TTS
models take text as input and utilize acoustic models to predict rhythm
information, which introduces artifacts in the rhythm information. By filtering
out vocal tract response, the remaining glottal flow with rhythm information
retains detection ability for TTS-generated speech. Based on these analyses, a
rhythm perturbation module is proposed to enhance the copy-synthesis data
augmentation method. Fake utterances generated by the proposed method force the
detecting model to pay attention to the artifacts in rhythm information and
effectively improve the ability to detect TTS-generated speech of the
anti-spoofing countermeasures.Comment: Five pages, two figure
Ultimate boundary estimations and topological horseshoe analysis of a new 4D hyper-chaotic system
In this paper, we first estimate the boundedness of a new proposed 4-dimensional (4D) hyper-chaotic system with complex dynamical behaviors. For this system, the ultimate bound set Ω1 and globally exponentially attractive set Ω2 are derived based on the optimization method, Lyapunov stability theory and comparison principle. Numerical simulations are presented to show the effectiveness of the method and the boundary regions. Then, to prove the existence of hyper-chaos, the hyper-chaotic dynamics of the 4D nonlinear system is investigated by means of topological horseshoe theory and numerical computation. Based on the algorithm for finding horseshoes in three-dimensional hyper-chaotic maps, we finally find a horseshoe with two-directional expansions in the 4D hyper-chaotic system, which can rigorously prove the existence of the hyper-chaos in theory
Receding Horizon Trajectory Optimization with Terminal Impact Specifications
The trajectory optimization problem subject to terminal impact time and angle specifications can be reformulated as a nonlinear programming problem using the Gauss pseudospectral method. The cost function of the trajectory optimization problem is modified to reduce the terminal control energy. A receding horizon optimization strategy is implemented to reject the errors caused by the motion of a surface target. Several simulations were performed to validate the proposed method via the C programming language. The simulation results demonstrate the effectiveness of the proposed algorithm and that the real-time requirement can be easily achieved if the C programming language is used to realize it
Sleep duration in Chinese adolescents: biological, environmental, and behavioral predictors
AbstractObjectiveTo examine sleep duration-related risk factors from multidimensional domains among Chinese adolescents.MethodsA random sample of 4801 adolescents aged 11–20 years participated in a cross-sectional survey. A self-reported questionnaire was used to collect information about the adolescents' sleep behaviors and possible related factors from eight domains.ResultsIn all, 51.0% and 9.8% of adolescents did not achieve optimal sleep duration (defined as <8.0 h per day) on weekdays and on weekends, respectively. According to multivariate logistic regression models, after adjusting for all possible confounders, 17 factors were associated with sleep duration <8 h. Specifically, 13 factors from five domains were linked to physical and psychosocial condition, environment, and behaviors. These factors were overweight/obesity, chronic pain, bedtime anxiety/excitement/depression, bed/room sharing, school starting time earlier than 07:00, cram school learning, more time spent on homework on weekdays, television viewing ≥2 h/day, physical activity <1 h/day, irregular bedtime, and shorter sleep duration of father.ConclusionBiological and psychosocial conditions, sleep environments, school schedules, daily activity and behaviors, and parents' sleep habits significantly may affect adolescents' sleep duration, indicating that the existing chronic sleep loss in adolescents could be, at least partly, intervened by improving adolescents' physical and psychosocial conditions, controlling visual screen exposure, regulating school schedules, improving sleep hygiene and daytime behaviors, and changing parents' sleep habits
SAMUS: Adapting Segment Anything Model for Clinically-Friendly and Generalizable Ultrasound Image Segmentation
Segment anything model (SAM), an eminent universal image segmentation model,
has recently gathered considerable attention within the domain of medical image
segmentation. Despite the remarkable performance of SAM on natural images, it
grapples with significant performance degradation and limited generalization
when confronted with medical images, particularly with those involving objects
of low contrast, faint boundaries, intricate shapes, and diminutive sizes. In
this paper, we propose SAMUS, a universal model tailored for ultrasound image
segmentation. In contrast to previous SAM-based universal models, SAMUS pursues
not only better generalization but also lower deployment cost, rendering it
more suitable for clinical applications. Specifically, based on SAM, a parallel
CNN branch is introduced to inject local features into the ViT encoder through
cross-branch attention for better medical image segmentation. Then, a position
adapter and a feature adapter are developed to adapt SAM from natural to
medical domains and from requiring large-size inputs (1024x1024) to small-size
inputs (256x256) for more clinical-friendly deployment. A comprehensive
ultrasound dataset, comprising about 30k images and 69k masks and covering six
object categories, is collected for verification. Extensive comparison
experiments demonstrate SAMUS's superiority against the state-of-the-art
task-specific models and universal foundation models under both task-specific
evaluation and generalization evaluation. Moreover, SAMUS is deployable on
entry-level GPUs, as it has been liberated from the constraints of long
sequence encoding. The code, data, and models will be released at
https://github.com/xianlin7/SAMUS
Expressive paragraph text-to-speech synthesis with multi-step variational autoencoder
Neural networks have been able to generate high-quality single-sentence
speech with substantial expressiveness. However, it remains a challenge
concerning paragraph-level speech synthesis due to the need for coherent
acoustic features while delivering fluctuating speech styles. Meanwhile,
training these models directly on over-length speech leads to a deterioration
in the quality of synthesis speech. To address these problems, we propose a
high-quality and expressive paragraph speech synthesis system with a multi-step
variational autoencoder. Specifically, we employ multi-step latent variables to
capture speech information at different grammatical levels before utilizing
these features in parallel to generate speech waveform. We also propose a
three-step training method to improve the decoupling ability. Our model was
trained on a single-speaker French audiobook corpus released at Blizzard
Challenge 2023. Experimental results underscore the significant superiority of
our system over baseline models.Comment: 5 pages, 1 figure, 2 table
Structural Controllability of Discrete-Time Linear Control Systems with Time-Delay: A Delay Node Inserting Approach
This paper is concerned with the structural controllability analysis for discrete-time linear control systems with time-delay. By adding virtual delay nodes, the linear systems with time-delay are transformed into corresponding linear systems without time-delay, and the structural controllability of them is equivalent. That is to say, the time-delay does not affect or change the controllability of the systems. Several examples are also presented to illustrate the theoretical results
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