Multichannel singular spectrum analysis of the axial atmospheric angular momentum

Earth＇s variable rotation is mainly produced by the variability of the AAM（atmospheric angular momentum）. In particular, the axial AAM component X_3, which undergoes especially strong variations,induces changes in the Earth＇s rotation rate. In this study we analysed maps of regional input into the effective axial AAM from 1948 through 2011 from NCEP/NCAR reanalysis. Global zonal circulation patterns related to the LOD（length of day） were described. We applied MSSA（Multichannel Singular Spectrum Analysis） jointly to the mass and motion components of AAM, which allowed us to extract annual, semiannual, 4-mo nth, quasi-biennial, 5-year, and low-frequency oscillations. PCs（Principal components） strongly related to ENSO（El Nino southern oscillation） were released. They can be used to study ENSO-induced changes in pressure and wind fields and their coupling to LOD. The PCs describing the trends have captured slow atmospheric circulation changes possibly related to climate variability.

Discharge and flow characterizations of the double-side sliding discharge plasma actuator

We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current(DC)voltage.The discharge tests show that sliding discharge and extended discharge are filamentary discharge.The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle,ultimately expands the discharge channel.The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge(DBD).The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge,which causes a bulge structure in the discharge channel.The bias DC electrode can deflect the direction of the induced jet,then modifying the properties of the boundary layer.Extended discharge can accelerate the velocity of the starting vortex,improving the horizontal velocity profile by 203%.The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate,compared with sliding discharge and DBD.However,the momentum growth of sliding discharge lasts longer in the whole pulsed cycle,indicating that sliding discharge can also inject more momentum.

Numerical investigation of the control factors driving Zhe-Min Coastal Current

During the northeast monsoon season,Zhe-Min Coastal Current(ZMCC)travels along the Chinese mainland coast and carries fresh,cold,and eutrophic water.ZMCC is significantly important for the hydrodynamic processes and marine ecosystems along its path.Thus,this bottom-trapped plume deserves to be further discussed in terms of the major driving factor,for which different opinions exist.For this purpose,in this study,a high resolution Semi-implicit Cross-scale Hydroscience Integrated System Model(SCHISM)is established and validated.High correlation coefficients exist between along-shelf wind speeds and seasonal variations of both ZMCC volume transport and the freshwater signal.These coefficients imply that the wind is important in regulating ZMCC.However,for similar annual mean ZMCC volume transports,the extreme south boundaries of Zhe-Min Coastal Water(ZMCW)are different among different years.This difference is attracting attention and is explored in this study.According to the low wind/discharge experiment,it was found that although the volume transport of ZMCC is more sensitive to the variation of local wind speeds,the carried freshwater is limited by the Changjiang River discharge,which ultimately determines the south boundary of ZMCW.The momentum analysis at transects I and II shows that,for driving ZMCC,the along-shore wind forcing is as important as the buoyancy forcing.Note that this conclusion is supported by a zero-discharge experiment.It was also found that the buoyancy forcing varies with respect to time and space,which is due to variations of the discharge of Changjiang River.In addition,a particle tracking experiment shows that the substance carried by the Changjiang River diluted water would distribute along the Zhe-Min coastal region during the northeast monsoon season and it may escape due to the wind relaxation.

Analysis and Testing of Microvibrations Produced by Momentum Wheel Assemblies

The microvibrations produced by momentum wheel assemblies（MWA） can degrade the performance of instruments with high pointing precision and stability on spacecraft.This paper concentrates on analyzing and testing the microvibrations produced by MWA.We analyze the disturbance sources produced by mass imbalance,structural mode,bearing irregularity and nonlinear stiffness,and random noise;then,test a well-balanced MWA by a highly sensitive measurement system consisting of a Kistler table and an optical tabletop.The results show that the test system has a resolution of less than 0.003 N in the frequency range of 3-300 Hz.The dynamic imbalance of the MWA cannot excite the radial rocking mode,but there are dynamic amplifications when the poly-harmonic disturbances intersect with the structural modes.Especially at high rotational speed（〉3 000 rev/min）,the main disturbance sources of the MWA come from the bearing irregularity interacting with radial translation mode in the high frequency range.Thus,bearing noise deserves more attention for the well-balanced MWA,and alternative of high quality bearings are proposed to reduce the microvibrations.

The imminent weakening of export momentum The analysis of China’s foreign trade of textiles from January to August

The weakening of export momentumAnalysts anticipated an imminent weakeningof export momentum for China’s textile and