A real-time performance improvement method for composite time scale

The composite time scale(CTS)provides a stable,accurate,and reliable time scale for modern society.The improvement of CTS’s real-time performance will improve its stability,which strengths related applications’performance.Aiming at this goal,a method achieved by determining the optimal calculation interval and accelerating adjustment stage is proposed in this paper.The determinants of the CTS’s calculation interval(characteristics of the clock ensemble,the measurement noise,the time and frequency synchronization system’s noise and the auxiliary output generator noise floor)are studied and the optimal calculation interval is obtained.We also investigate the effect of ensemble algorithm’s initial parameters on the CTS’s adjustment stage.A strategy to get the reasonable initial parameters of ensemble algorithm is designed.The results show that the adjustment stage can be finished rapidly or even can be shorten to zero with reasonable initial parameters.On this basis,we experimentally generate a distributed CTS with a calculation interval of 500 s and its stability outperforms those of the member clocks when the averaging time is longer than1700 s.The experimental result proves that the CTS’s real-time performance is significantly improved.

Real-time damage analysis of 2D C/SiC composite based on spectral characters of acoustic emission signals using pattern recognition

In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.

MODULATION OF MADDEN-JULIAN OSCILLATION ON TIBETAN PLATEAU VORTEX

This study uses NCEP/NCAR daily reanalysis data,NOAA outgoing long-wave radiation(OLR) data,the real-time multivariate MJO(RMM) index from the Australian Bureau of Meteorology and Tibetan Plateau vortex(TPV)data from the Chengdu Institute of Plateau Meteorology to discuss modulation of the Madden-Julian Oscillation(MJO)on the Tibetan Plateau Vortex(TPV).Wavelet and composite analysis are used.Results show that the MJO plays an important role in the occurrence of the TPV that the number of TPVs generated within an active period of the MJO is three times as much as that during an inactive period.In addition,during the active period,the number of the TPVs generated in phases 1 and 2 is larger than that in phases 3 and 7.After compositing phases 1 and 7 separately,all meteorological elements in phase 1 are apparently conducive to the generation of the TPV,whereas those in phase 7 are somewhat constrained.With its eastward propagation process,the MJO convection centre spreads eastward,and the vertical circulation within the tropical atmosphere changes.Due to the interaction between the mid-latitude and low-latitude atmosphere,changes occur in the baroclinic characteristics of the atmosphere,the available potential energy and eddy available potential energy of the atmosphere,and the circulation structures of the atmosphere over the Tibetan Plateau(TP) and surrounding areas.This results in significantly different water vapour transportation and latent heat distribution.Advantageous and disadvantageous conditions therefore alternate,leading to a significant difference among the numbers of plateau vortex in different phases.

Techniques and instruments used for real-time analysis of atmospheric nanoscale molecular clusters: A review

The extremely high concentrations of PM2.5(particulate matter with an aerodynamic meter≤2.5 mm)during severe and persistent haze events in China have been closely related to the formation of secondary aerosols(SA).New particle formation(NPF)is the critical initial step of SA formation.New particles are commonly formed from gas-phase precursors(e.g.,SO2,volatile organic compounds)via nucleation and initial growth,in which molecular clusters with a mobility diameter smaller than 3 nm(hereafter referred to nanoscale molecular clusters)will be involved throughout the whole process.Recently,significant breakthroughs have been obtained on NPF studies,which are mostly attributed to the technical development in the real-time analysis of size-resolved number concentration and chemical composition of nanoscale molecular clusters.Regarding the detection of size-resolved number concentrations of nanoscale molecular clusters,both methods and instruments have been well built up;practical application in laboratory-scale experiments and field measurements have also been successfully demonstrated.In contrast,real-time analysis of chemical composition of nanoscale molecular clusters has still encountered the great challenges caused by the complex organic compositions of the clusters,and improvement of present analytical strategies is urgently required.The better understanding in NPF will not only benefit the atmospheric modeling and climate predictions but also the source control of SA.

Heterogeneous parallel computing accelerated iterative subpixel digital image correlation

Parallel computing techniques have been introduced into digital image correlation(DIC) in recent years and leads to a surge in computation speed. The graphics processing unit(GPU)-based parallel computing demonstrated a surprising effect on accelerating the iterative subpixel DIC, compared with CPU-based parallel computing. In this paper, the performances of the two kinds of parallel computing techniques are compared for the previously proposed path-independent DIC method, in which the initial guess for the inverse compositional Gauss-Newton(IC-GN) algorithm at each point of interest(POI) is estimated through the fast Fourier transform-based cross-correlation(FFT-CC) algorithm. Based on the performance evaluation, a heterogeneous parallel computing(HPC) model is proposed with hybrid mode of parallelisms in order to combine the computing power of GPU and multicore CPU. A scheme of trial computation test is developed to optimize the configuration of the HPC model on a specific computer. The proposed HPC model shows excellent performance on a middle-end desktop computer for real-time subpixel DIC with high resolution of more than 10000 POIs per frame.

Analysis of the Mechanism Underlying Tibetan Plateau Vortex Frequency Difference between Strong and Weak MJO Periods

In this paper, the NCEP/DOE reanalysis data, OLR data from NOAA, Australian Meteorological Bureau real-time multivariate MJO index, and Tibetan Plateau vortex （TPV） statistical data from the Chengdu Institute of Plateau Met- eorology, are used to discuss the modulation of the TPV by the MJO, through applying the wavelet analysis and com- posite analysis. The results show that： （1） The MJO plays an important role in modulating the TPV, as the number of TPVs generated in strong MJO periods is three times that in weak periods. （2） During strong （weak） MJO periods, the Tibetan Plateau （TP） is in control of a low-frequency, low-pressure cyclone （high-pressure, anticyclone） system, and thus the atmospheric circulation conditions over the plateau are conducive （inconducive） to the generation of TPVs. （3） During strong （weak） MJO periods, southerly （northerly） winds prevail in the east of the TP, while north- erly （southerly） winds in the west. Over the northern part of the TP, easterly （westerly） flow is predominant, while westerly （easterly） flow prevails over the south, thus conducive （inconducive） to the formation of cyclonic circula- tion （i.e., TPVs） at low altitude over the TP. （4） In strong MJO periods, water vapor is relatively less abundant over most of the TP, inconducive to the generation of TPVs; however, moisture transported by the south branch trough and the low-frequency, high-pressure anticyclone system from the Bay of Bengal, are very important for the develop- ment of TPVs. As the strength of the MJO changes continuously during its eastward propagation, the inten- sity of tropical convection and vertical circulation structures of the tropical atmosphere also change accordingly. Al- ternation between favorable and unfavorable conditions for the generation of TPVs occurs, thus resulting in signifi- cant frequency differences of TPVs between strong and weak MJO periods.