1,377 research outputs found
Design and Stability Analysis of Uncertain Networked Predictive Control Systems with Multiple Forward Channels
This paper is concerned with the design and stability of networked predictive control for uncertain systems with multiple forward channels. The delays and packet dropouts are distributed such that the classic networked predictive control (NPC) needs modifications to be implemented. An improved control signal selection scheme with distributed prediction length is proposed to increase the prediction accuracy and hence achieve better control performance. Moreover, stability analysis results are obtained for both constant and random cases. Interestingly, it is shown that the stability of the closed-loop NPC system is not related to the distributed delays when they are constant and the system model is accurate. Finally, a two-axis milling machine example is given to illustrate the effectiveness of the proposed method
Integrating Second Life into an EFL Program: Studentsâ Perspectives
Second Life (SL) is a three dimension virtual world imagined and created by its users. To explore various facets of language learning within SL, faculty members of an American university and a Chinese university took an evaluation research approach to search for appropriate ways to integrate SL into an EFL (English as a Foreign Language) program. This paper reports a part of the research efforts with a focus on the Chinese studentsâ perspectives of an EFL Program in SL. Specifically included in this paper are (a) the Chinese studentsâ perceived technology readiness to use SL for EFL learning, (b) their perceptions of SL, and (c) the EFL Program implemented in SL. The paper reviews related literature and theoretical support, describes the studyâs context and its implementation procedures, and discusses the evaluation results and implications. Finally, the paper shares with the audience some considerations for integrating SL into an EFL progra
Correcting soft errors online in fast fourier transform
While many algorithm-based fault tolerance (ABFT) schemes have been proposed to detect soft errors offline in the fast Fourier transform (FFT) after computation finishes, none of the existing ABFT schemes detect soft errors online before the computation finishes. This paper presents an online ABFT scheme for FFT so that soft errors can be detected online and the corrupted computation can be terminated in a much more timely manner. We also extend our scheme to tolerate both arithmetic errors and memory errors, develop strategies to reduce its fault tolerance overhead and improve its numerical stability and fault coverage, and finally incorporate it into the widely used FFTW library - one of the today's fastest FFT software implementations. Experimental results demonstrate that: (1) the proposed online ABFT scheme introduces much lower overhead than the existing offline ABFT schemes; (2) it detects errors in a much more timely manner; and (3) it also has higher numerical stability and better fault coverage
Multi-step prediction of chlorophyll concentration based on Adaptive Graph-Temporal Convolutional Network with Series Decomposition
Chlorophyll concentration can well reflect the nutritional status and algal
blooms of water bodies, and is an important indicator for evaluating water
quality. The prediction of chlorophyll concentration change trend is of great
significance to environmental protection and aquaculture. However, there is a
complex and indistinguishable nonlinear relationship between many factors
affecting chlorophyll concentration. In order to effectively mine the nonlinear
features contained in the data. This paper proposes a time-series decomposition
adaptive graph-time convolutional network ( AGTCNSD ) prediction model.
Firstly, the original sequence is decomposed into trend component and periodic
component by moving average method. Secondly, based on the graph convolutional
neural network, the water quality parameter data is modeled, and a parameter
embedding matrix is defined. The idea of matrix decomposition is used to assign
weight parameters to each node. The adaptive graph convolution learns the
relationship between different water quality parameters, updates the state
information of each parameter, and improves the learning ability of the update
relationship between nodes. Finally, time dependence is captured by time
convolution to achieve multi-step prediction of chlorophyll concentration. The
validity of the model is verified by the water quality data of the coastal city
Beihai. The results show that the prediction effect of this method is better
than other methods. It can be used as a scientific resource for environmental
management decision-making.Comment: 12 pages, 10 figures, 3 tables, 45 reference
Gradient damage spreading of molten volcanic ash on thermal barrier coatings
Aviation safety and aero engine life are always threatened by dust or ash suspending in the air route which derive from inevitable natural phenomena (volcanic eruption and sand storm) and human productive activity (run way debris, industrial fumes, and coal ash emission). Those floating silicate ash with the low melt temperature (lower than 1100 ÂșC) will be easily ingested into jet engine and quickly melted due to the fact that the turbine inlet temperature of the current advanced jet engine at cruising altitude (1200-1450 ÂșC) far exceed the melting point of those silicate ash. Subsequently, these molten ash are deposited on the surface of thermal barrier coatings (TBCs). TBCs is a refractory ceramic layer deposited on the surface of super alloy and can protect these metal at the hot parts (such as combustion chamber, blade and nozzle) from high temperature. However, these silicate deposits will lead to serious spallation and even failure of TBCs. Once the TBCs exfoliate under stress or chemical corrosion because of ash deposition, the engine may stop running during the flight and cause air disaster. Therefore, silicate ash deposition undoubtedly pose a huge obstacle in the development of jet engine. Here, to comprehensively understand the effect of silicate deposits on TBCs, we investigated the subsurface-transverse spreading ring of re-melted volcanic ash (obtained from Tungurahua Volcano, Ecuador, 2014) with various droplet size on the APS TBCs and EB-PVD TBCs respectively at the temperature from 1200 ÂșC to 1600 ÂșC over a wide range of duration (Figs. 1a and b). Our results demonstrate that the gradient change of concentration of volcanic ash melt onto TBCs directly leads to the formation of spreading ring in the subsurface-transverse of molten volcanic ash located in the edge of main spreading area (Fig. 1c). These observations imply that the interaction process of molten silicate ash with TBCs is driven not only by vertical infiltration due to gravitation but also by horizontal spreading owing to capillary force. Notably, the infiltration depth of the ring area was deeper than that of the main liquid area, which closely resembles previously observed in ceramic plate (Figs. 1d and e). Overall, we summaries the influence of temperature, holding time and size of droplet on spreading radius and conclude the mechanism of vertical infiltration. Those work is the first step to improving the TBCs and serve as the basic of developing the new generation of aeroengines.
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Research on dedicated rail power supply system for electric cars
in order to improve the endurance capacity and driving safety of electric vehicles, a special track power supply system for
electric cars on expressways is studied. The working principle of the main components of the system, such as sliding contact charging track
and mechanical charging arm, is simulated and analyzed by using SolidWorks software. The results show that the charging function of the
contact track can provide unlimited endurance for electric vehicles, and the guidance function of the track can also ensure the safety of highspeed driving
DifferSketching: How Differently Do People Sketch 3D Objects?
Multiple sketch datasets have been proposed to understand how people draw 3D
objects. However, such datasets are often of small scale and cover a small set
of objects or categories. In addition, these datasets contain freehand sketches
mostly from expert users, making it difficult to compare the drawings by expert
and novice users, while such comparisons are critical in informing more
effective sketch-based interfaces for either user groups. These observations
motivate us to analyze how differently people with and without adequate drawing
skills sketch 3D objects. We invited 70 novice users and 38 expert users to
sketch 136 3D objects, which were presented as 362 images rendered from
multiple views. This leads to a new dataset of 3,620 freehand multi-view
sketches, which are registered with their corresponding 3D objects under
certain views. Our dataset is an order of magnitude larger than the existing
datasets. We analyze the collected data at three levels, i.e., sketch-level,
stroke-level, and pixel-level, under both spatial and temporal characteristics,
and within and across groups of creators. We found that the drawings by
professionals and novices show significant differences at stroke-level, both
intrinsically and extrinsically. We demonstrate the usefulness of our dataset
in two applications: (i) freehand-style sketch synthesis, and (ii) posing it as
a potential benchmark for sketch-based 3D reconstruction. Our dataset and code
are available at https://chufengxiao.github.io/DifferSketching/.Comment: SIGGRAPH Asia 2022 (Journal Track
Evolutionary-Based Online Motion Planning Framework for Quadruped Robot Jumping
Offline evolutionary-based methodologies have supplied a successful motion
planning framework for the quadrupedal jump. However, the time-consuming
computation caused by massive population evolution in offline
evolutionary-based jumping framework significantly limits the popularity in the
quadrupedal field. This paper presents a time-friendly online motion planning
framework based on meta-heuristic Differential evolution (DE), Latin hypercube
sampling, and Configuration space (DLC). The DLC framework establishes a
multidimensional optimization problem leveraging centroidal dynamics to
determine the ideal trajectory of the center of mass (CoM) and ground reaction
forces (GRFs). The configuration space is introduced to the evolutionary
optimization in order to condense the searching region. Latin hypercube
sampling offers more uniform initial populations of DE under limited sampling
points, accelerating away from a local minimum. This research also constructs a
collection of pre-motion trajectories as a warm start when the objective state
is in the neighborhood of the pre-motion state to drastically reduce the
solving time. The proposed methodology is successfully validated via real robot
experiments for online jumping trajectory optimization with different jumping
motions (e.g., ordinary jumping, flipping, and spinning).Comment: IROS202
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