160 research outputs found
Practical Stabilization of Uncertain Nonholonomic Mobile Robots Based on Visual Servoing Model with Uncalibrated Camera Parameters
The practical stabilization problem is addressed for a class of uncertain nonholonomic mobile robots with uncalibrated visual parameters. Based on the visual servoing kinematic model, a new switching controller is presented in the presence of parametric uncertainties associated with the camera system. In comparison with existing methods, the new design method is directly used to control the original system without any state or input transformation, which is effective to avoid singularity. Under the proposed control law, it is rigorously proved that all the states of closed-loop system can be stabilized to a prescribed arbitrarily small neighborhood of the zero equilibrium point. Furthermore, this switching control technique can be applied to solve the practical stabilization problem of a kind of mobile robots with uncertain parameters (and angle measurement disturbance) which appeared in some literatures such as Morin et al. (1998), Hespanha et al. (1999), Jiang (2000), and Hong et al. (2005). Finally, the simulation results show the effectiveness of the proposed controller design approach
Numerical Simulation Study on Propeller Slipstream Interference of High Altitude Long Endurance Unmanned Air Vehicle
AbstractIn this paper,thecontrol equation of Multiple Reference Frame(MRF) as the propeller calculation model was present and analyzed, the propeller slipstream interference on HALE UAV was studied with three-dimensional numerical simulation. It is shown that the flow field of the MRF model is good consistent with true propeller flow, and MRF can accurately simulate aerodynamic interference on the aircraft. The stream traces on the V-tail surface were deflected and shrank, pressure distribution,Cmx and Cmzon V-tail surface was changed apparently too.Butslipstream had little effect on wing. The influence of propeller slipstream on the aerodynamic performance of the UAV at the status of taking off is biggest, become weaker at status of climbing and smallest at the status of cruising. The influence of propeller slipstream is enhanced with increment of propeller thrust and basically familiar in the same thrust between the two blade attack angle. The pressure drag on aft of UAV fuselage increased rapidly by the interference of propeller slipstream, leading aerodynamic performance of UAV become badly
TransTailor: Pruning the Pre-trained Model for Improved Transfer Learning
The increasing of pre-trained models has significantly facilitated the
performance on limited data tasks with transfer learning. However, progress on
transfer learning mainly focuses on optimizing the weights of pre-trained
models, which ignores the structure mismatch between the model and the target
task. This paper aims to improve the transfer performance from another angle -
in addition to tuning the weights, we tune the structure of pre-trained models,
in order to better match the target task. To this end, we propose TransTailor,
targeting at pruning the pre-trained model for improved transfer learning.
Different from traditional pruning pipelines, we prune and fine-tune the
pre-trained model according to the target-aware weight importance, generating
an optimal sub-model tailored for a specific target task. In this way, we
transfer a more suitable sub-structure that can be applied during fine-tuning
to benefit the final performance. Extensive experiments on multiple pre-trained
models and datasets demonstrate that TransTailor outperforms the traditional
pruning methods and achieves competitive or even better performance than other
state-of-the-art transfer learning methods while using a smaller model.
Notably, on the Stanford Dogs dataset, TransTailor can achieve 2.7% accuracy
improvement over other transfer methods with 20% fewer FLOPs.Comment: This paper has been accepted by AAAI202
Effect of Recession on the Re-entry Capsule Aerodynamic Characteristic
AbstractNumerical simulation and analysis of aerodynamic characteristics of Soyuz ablation shape is carried out in this paper for the adverse influence coming from recession. The result indicates that the shape change caused by the recession will increase absolute value of trim angle of attack and trim lift-drag ratio. The conclusion offers reference for the aerodynamic layout design and improve of the Soyuz re-entry capsule
The Effect of Temperature and Strain Rate on the Interfacial Behavior of Glass Fiber Reinforced Polypropylene Composites: A Molecular Dynamics Study
To make better use of fiber reinforced polymer composites in automotive applications, a clearer knowledge of its interfacial properties under dynamic and thermal loadings is necessary. In the present study, the interfacial behavior of glass fiber reinforced polypropylene (PP) composites under different loading temperatures and strain rates were investigated via molecular dynamics simulation. The simulation results reveal that PP molecules move easily to fit tensile deformation at higher temperatures, resulting in a lower interfacial strength of glass fiber–PP interface. The interfacial strength is enhanced with increasing strain rate because the atoms do not have enough time to relax at higher strain rates. In addition, the non-bonded interaction energy plays a crucial role during the tensile deformation of composites. The damage evolution of glass fiber–PP interface follows Weibull’s distribution. At elevated temperatures, tensile loading is more likely to cause cohesive failure because the mechanical property of PP is lower than that of the glass fiber–PP interface. However, at higher strain rates, the primary failure mode is interfacial failure because the strain rate dependency of PP is more pronounced than that of the glass fiber–PP interface. The relationship between the failure modes and loading conditions obtained by molecular dynamics simulation is consistent with the author’s previous experimental studies
Paste structure and rheological properties of lotus seed starch–glycerin monostearate complexes formed by high-pressure homogenization
peer-reviewedStarch–lipid complexes were prepared using lotus seed starch (LS) and glycerin monostearate (GMS) via a high-pressure homogenization (HPH) process, and the effect of HPH on the paste structure and rheological properties of LS–GMS was investigated. Rapid Visco Analyser (RVA) profiles showed that HPH treatment inhibited the formation of the second viscosity peak of the LS–GMS paste, and the extent of this change was dependent on the level of homogenized pressure. Analysis of the size-exclusion chromatography, light microscopy, and low-field 1H nuclear magnetic resonance results revealed that high homogenized pressure (70–100 MPa) decreased molecular weight and size by degrading the branch structure of amylopectin; however, intact LS–GMS granules can optimize the network structure by filler–matrix interaction, which causes free water to transition into immobile water in the starch paste. The steady-shear results showed that the LS–GMS pastes presented non-Newtonian shear-thinning behavior, with higher homogenized pressure producing a smaller hysteresis loop area. During the oscillation process, the LS–GMS pastes prepared at 100 MPa exhibited the lowest loss tangent values in all the complexes, indicating a stronger resistance to vibration
Preparation and characterization of lotus seed starch-fatty acid complexes formed by microfluidization
peer-reviewedUsing dynamic high pressure microfluidization, we prepared starch-lipid complexes from lotus seed starch (LS) and six saturated fatty acids (FAs) of different carbon chain length and analyzed their semi-crystalline structure and digestibility. Iodine blue value analysis showed the highest complex index (86.3%) was observed between LS and octanoic acid (C8). X-ray diffraction analysis showed crystal structure changed from V6II to V6I type with decreasing FA chain length. Small angle x-ray scattering and differential scanning calorimetry analyses confirmed the presence of a strong V6I-type mass fractal structure with a Bragg distance of 12.3 nm in LS-C8, which can be considered to be a type-II complex with high melting temperature (Tp = 123.98 °C). Scanning electron microscopy results showed the complexes had more spherocrystals with decreasing FA chain length. Compared to other FAs, C8 significantly reduced the LS susceptibility to digestive enzymes, increased slowly digestion starch content (26.06%) and decreased digestion rate (3.59 × 10−2)
PAI-Diffusion: Constructing and Serving a Family of Open Chinese Diffusion Models for Text-to-image Synthesis on the Cloud
Text-to-image synthesis for the Chinese language poses unique challenges due
to its large vocabulary size, and intricate character relationships. While
existing diffusion models have shown promise in generating images from textual
descriptions, they often neglect domain-specific contexts and lack robustness
in handling the Chinese language. This paper introduces PAI-Diffusion, a
comprehensive framework that addresses these limitations. PAI-Diffusion
incorporates both general and domain-specific Chinese diffusion models,
enabling the generation of contextually relevant images. It explores the
potential of using LoRA and ControlNet for fine-grained image style transfer
and image editing, empowering users with enhanced control over image
generation. Moreover, PAI-Diffusion seamlessly integrates with Alibaba Cloud's
Machine Learning Platform for AI, providing accessible and scalable solutions.
All the Chinese diffusion model checkpoints, LoRAs, and ControlNets, including
domain-specific ones, are publicly available. A user-friendly Chinese WebUI and
the diffusers-api elastic inference toolkit, also open-sourced, further
facilitate the easy deployment of PAI-Diffusion models in various environments,
making it a valuable resource for Chinese text-to-image synthesis
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