Active Collision Avoidance System Design Based on Model Predictive Control with Varying Sampling Time

In active collision avoidance,the trajectory tracking controller determines the deviation from the reference path and the vehicle stability.The main objective of this study was to reduce the tracking error and improve the tracking performance in collision avoidance.Unlike the previously proposed model predictive control(MPC)strategies with constant sampling time,an improved MPC controller with varying sampling time based on the hierarchical control framework was proposed in this paper.Compared with the original MPC tracking controller,the improved MPC controller demonstrated better adaptive capability for the varying road adhesion coefficients and vehicle speed on a curved road.The simulation results revealed that the hierarchical control framework generated an optimal trajectory for collision avoidance in real-time by minimizing the potential field energy.

Impacts of sampling design on the abundance estimation of Portunus trituberculatus using crab pots

Fishery-independent surveys can provide high-quality data and support fishery assessment and management.Optimization of sampling design is crucial to increase the quality of fishery surveys.Crab pots are important fishing gears used to catch crabs.We analyzed the impacts of sampling design of crab pots on the abundance of Portunus trituberculatus in the Changjiang(Yangtze)River estuary to the Hangzhou Bay and its adjacent waters in East China Sea.The crab pots were cylindrical,240 mm in height and 600 mm in diameter of the iron ring.Our sampling designs(including fixed-station sampling,simple random sampling,stratified fixed-station sampling,and stratified random sampling),three number of stations(9,16,and 24),and three numbers of crab pots(500,1000,and 3000)were simulated and compared with the“true”abundance that obtained from bottom trawl surveys in the study area in 2007.The scenarios with 16 stations were set in stratification as a control group for comparison with unstratified designs.Results show that simple random sampling can obtain more stable results than fixed-station sampling in the abundance estimation of P.trituberculatus.In addition,stratified sampling resulted in more accurate abundance than unstratified sampling.The accuracy of the simulated results improved with the increase of the number of stations.No remarkable differences in the results were found among the scenarios of different number of crab pots at each station.However,resource-intensive areas exerted great impacts on simulation results.Thus,prior information or pre-survey results about resource abundance and density distribution are necessary.This study may serve as a reference for future sampling designs of crab pots of P.trituberculatus and other species.

An On-Line Modeling Based Kalman Filtering Process for Time-Interval-Variable Sequences with Application to Astronomic Surveying

The problem of variable sampling time interval which appears in application of Kalman Filtering is analyzed and the corresponding filtering process with or without present transition matrix is suggested, then an application experiment for astronomical surveying is introduced. In this process, the known stochastically variable sampling time intervals play the roles as deterministic input sequences of the state-space description, and the corresponding matrix and (if needed) state transition matrix can be established by performing real-time and structure-linear system identification.

Diurnal variation in fecal concentrations of acid-detergent insoluble ash and alkaline-peroxide lignin from cattle fed bermudagrass hays of varying nutrient content

Background： The effect of time of fecal sampling on the accuracy of acid-detergent insoluble ash （ADIA） and alkaline-peroxide lignin （APL） for the prediction of fecal output （FO） in cattle was evaluated. Eight ruminally cannulated cows （594 _＋ 35.5 kg） were allocated randomly to 4 bermudagrass [Cynodon dactylon （L.） Pers.] hay diets markedly different in crude protein concentration （79-164 g/kg） with 2 replicates per diet for 3 periods. Cows were offered hay individually at 20 g DM/kg of body weight daily in equal feedings at 08：00 and 16：00 h for a 10-d adaptation period followed by 5-d of total fecal collection. Fecal grab samples also were taken each day during the fecal collection period at 06：00, 12：00, 18：00, and 24：00 h either directly from the rectum or from freshly voided feces. Samples were composited within cow and time across the 5 d total fecal collection period. Additionally, forage, ort, and fecal samples were analyzed for concentrations of APL and ADIA. Results： Fecal concentrations of ADIA and APL were not affected by sampling time （P 〉 0.22）, even though diet affected （P 〈 0.01） fecal ADIA and APL concentrations. There were no diet x sampling time interactions （P ≥ 0.60）. Estimates of FO and dry matter digestibility （DMD） from ADIA and APL were not affected （P 〉 0.16） by sampling time or the diet x sampling time interaction （P 〉 0.74）. Estimates of FO and DMD from markers from different sampling times or all different combinations of sampling time were not different （P 〉 0.72） from those of total collection among internal markers. Conclusion： Little variation in concentrations of ADIA and APL in daily fecal excretion across time increases flexibility in fecal grab sampling schedules for predicting FO and DMD.

Discrete-time based sliding-mode control of robot manipulators

Purpose-The purpose of this paper is to develop sliding mode control with linear and nonlinear manifolds in discrete-time domain for robot manipulators.Design/methodology/approach–First,a discrete linear sliding mode controller is designed to an n-link robot based on Gao’s reaching law.In the second step,a discrete terminal sliding mode controller is developed to design a finite time and high precision controller.The stability analysis of both controllers is presented in the presence of model uncertainties and external disturbances.Finally,sampling time effects on the continuous-time system outputs and sliding surfaces are discussed.Findings–Computer simulations on a three-link SCARA robot show that the proposed controllers are robust against model uncertainties and external disturbance.It was also shown that the sampling time has important effects on the closed loop system stability and convergence.Practical implications-The proposed controllers are low cost and easily implemented in practice in comparison with continuous-time ones.Originality/value-The novelty associated with this paper is the development of an approach to finite time and robust control of n-link robot manipulators in discrete-time domain.Also,obtaining an upper bound for the sampling time is another contribution of this work.

Design of the sample cell in near-field surface-enhanced Raman scattering by finite difference time domain method

The rational design of the sample cell may improve the sensitivity of surface-enhanced Raman scattering （SERS） detection in a high degree. Finite difference time domain （FDTD） simulations of the configuration of Ag film-Ag particles illuminated by plane wave and evanescent wave are performed to provide physical insight for design of the sample cell. Numerical solutions indicate that the sample cell can provide more ＂hot spots＂ and the massive field intensity enhancement occurs in these ＂hot spots＂. More information on the nanometer character of the sample can be got because of gradient-field Raman （GFR） of evanescent wave. OCIS codes： 290.5860, 240.0310, 240.6680, 999.9999 （surface-enhanced Raman scattering）.

Influence of sampling frequency on detectability of fish community and fish species in a fishery-independent survey

Understanding the dynamics and regulation of a particular ecological process requires monitoring of the process at appropriate spatial and temporal scales.Information collected at an inappropriate spatiotemporal scale may be insufficient for capturing spatio-temporal dynamics of fish populations and community.In this study,a Monte Carlo method was developed to evaluate the detectability performances of different sampling frequencies,sampling timings and sampling intensities on fish community indices and fish species.Species richness indices tended to decrease with an increased sampling frequency,while species diversity indices had small changes in response to changes in sampling frequency.The diversity index was more likely to be influenced by the choice of sampling timing compared to the richness index.The total number of species,especially seasonal and rare species present in the simulated sampling,increased with sampling frequency.Although sampling frequency is more important than sampling intensity,sampling intensity is also important for the detectability of fish species.This study showed that sampling frequency and intensity could greatly influence the estimation of fish community.Choices of sampling timing,sampling frequency and intensity may result in different estimates of fish species compositions and community structure.It is very necessary to consider the importance of sufficient sampling frequency and intensity in a survey program.

Cross-calibration on the electromagnetic field detection payloads of the China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic Satellite(CSES)deploys three payloads to detect the electromagnetic environment in the ionosphere.The tri-axial fluxgate magnetometers(FGM),as part of the high precision magnetometer(HPM),measures the Earth magnetic vector field in a frequency range from direct current(DC)to 15 Hz.The tri-axial search coil magnetometer(SCM)detects the alternating current(AC)related magnetic field in a frequency range from several Hz to 20 k Hz,and the electric field detector(EFD)measures the spatial electric field in a broad frequency band from DC to 3.5 MHz.This work mainly crosscalibrates the consistency of these three payloads in their overlapped detection frequency range and firstly evaluates CSES’s timing system and the sampling time differences between EFD and SCM.A sampling time synchronization method for EFD and SCM waveform data is put forward.The consistency between FGM and SCM in the ultra-low-frequency(ULF)range is validated by using the magnetic torque(MT)signal as a reference.A natural quasiperiodic electromagnetic wave event verifies SCM and EFD’s consistency in extremely low-frequency and very low-frequency(ELF/VLF)bands.This cross-calibration work is helpful to upgrade the data quality of CSES and brings valuable insights to similar electromagnetic detection solutions by low earth orbit satellites.