Electromagnetic response function for the semi-annual variations estimated by the single-station method using the night-time values of the geomagnetic fields

The geomagnetic night-time values were used to estimate the electromagnetic response function Q1 for half-year period. If the spatial structure of the source field can be described by the approximation, one can estimate the Q1 value using the single-station Z/H method. This technique enables us to carry out regional deep gcomagnetic sounding by the method. The data used for analyses are geomagnetic night-time values for about, typically, 26 years from 5 good-quality stations and for several years from 34 stations distributed over the globe. The results indicate that the night-time values yield more reliable response estimates for half-year period compared to the usual estimates obtained from daily means. It implies that the approximation for the night-time fields holds good for the half-year period, but the daily means are not suitable for estimating the response function of the semi-annual variations by using the single-station method. Source field analyses for daily means data and night-time means data have also been carried out in this paper.

Extraction of Alpha transmitter signals from single-station observations using the direction-finding method

For the applications of Alpha very-low-frequency(VLF) systems consisting of multiple transmitters, determining the origin transmitter station of received signals is a crucial problem. Based on single-station observations, this study develops a directionfinding method to extract Russian Alpha transmitter signals. First, the amplitudes of Alpha signals received in Suizhou City,Hubei Province(31.57°N, 113.32°E) in the east-west(EW) and north-south(NS) directions are obtained by the power spectrum method. The amplitude ratios of signals in the two directions are subsequently adopted to estimate the propagation angles of the signals with respect to the NS direction of the VLF receiver station. Phase ambiguity in our system is eliminated by comparing Alpha signal waveform with that from the VTX transmitter in India(8.39°N, 77.75°E) as a reference station. Finally, we can determine the quadrant where the incoming wave signals are located relative to the receiver and eventually distinguish the exact Alpha transmitters. Based on the direction-finding results, the amplitudes of each Alpha signal are extracted, and their diurnal variation features are analyzed to verify the performance of our method. These results are of great significance for the further study of Alpha signals and VLF long-distance communication.

A new method of discovering new meteor showers from the IMO single-station video meteor database

It has been found that unknown meteor showers could be efficiently discovered from the single station video meteor database of the International Meteor Organization(IMO) by assuming the geocentric velocity and adjusting it within the dynamically permitted range. The mean geocentric velocities of new meteor showers can be obtained,as well as the coordinates of the radiants. The activity period and maximum time can also be obtained if there are sufficient shower meteors. All single station video meteor observations between February 13 and 17(from 2000 to 2005) in IMO's database are processed with this method. As a result,two new meteor showers,one near RA=245.10°,Dec=41.82° in Hercules and the other near RA=233.03°,Dec=17.04° in Serpenids,are discovered. Some dynamical characteristics of the new meteor showers are also determined. Considering the random nature on the selection of period in this work,it is expected that there are some more potential new meteor showers in IMO's video database.

A Modified-Simplified MPPT Technique for Three-Phase Single-State Grid-Connected PV Systems

Nowadays,the single state inverter for the grid-connected photovoltaic(PV)systems is becoming more and more popular as they can reduce circuit complexity resulting in less power losses of the inverter.This paper focuses on the use of model predictive control(MPC)to control a 3-phase and 2-level single-state grid-connected inverter in order to regulate the PV maximum power point(MPP).The algorithm of MPC scheme was done to measure the simultaneous current signal including predicting the next sampling current flow.The reference current(Id∗)was used to control the distribution of electrical power from the solar cell to the grid.To be able to control the maximum power point tracking(MPPT)when the sunlight suddenly changes,so that a developing MPPT based on estimation current perturbation and observation(ECP&O-MPPT)technique was used to control the reference current.This concept was experimented by using MATLAB/Simulink software package.The proposed technique was tested and compared with the old technique.The simulation results showed that the developed MPPT technique can track the MPP faster when the light changes rapidly under 1,000W/m2,25℃ standard climatic conditions.The MPPT time was 0.015 s.The total harmonic distortion(THD)was 2.17%and the power factor was 1.

Comparative Study on Torque Performance of Five-phase Single-Stator and Double-Stator Permanent Magnet Synchronous Motors

This paper compares the torque characteristics of single stator permanent magnet synchronous motor(PMSM)and double-stator PMSM under different split-ratios,air-gap lengths and shaft diameters by finite element method.Firstly,the effects of split-ratio towards the torque characteristics of the two motor structures under different air-gap lengths are researched,the results show that the optimal split-ratios of the two motor structures do not change under different air-gap lengths,and the optimal split-ratio of the double-stator motor is greater than that of single-stator,and the torque of the double-stator motor is greater than that of single-stator motor with arbitrary split-ratio under the same air-gap length;Finally,the effects of the shaft diameter to the torque of the two motor structures are investigated,obtaining that with the increasing of shaft diameter,the electromagnetic torque of the single-stator motor is almost unchanged,however,the torque of the double-stator is gradually reduced,when the shaft diameter reached a certain extent,the electromagnetic torque of the double-stator motor is smaller than that of single-stator motor with the split ratio within a certain range,and the torque/quality ratio of the double-stator motor is smaller than that of single-stator motor with their optimal split ratio separately.

Status of UnDifferenced and Uncombined GNSS Data Processing Activities in China

With the continued development of multiple Global Navigation Satellite Systems(GNSS)and the emergence of various frequencies,UnDifferenced and UnCombined(UDUC)data processing has become an increasingly attractive option.In this contribution,we provide an overview of the current status of UDUC GNSS data processing activities in China.These activities encompass the formulation of Precise Point Positioning(PPP)models and PPP-Real-Time Kinematic(PPP-RTK)models for processing single-station and multi-station GNSS data,respectively.Regarding single-station data processing,we discuss the advancements in PPP models,particularly the extension from a single system to multiple systems,and from dual frequencies to single and multiple frequencies.Additionally,we introduce the modified PPP model,which accounts for the time variation of receiver code biases,a departure from the conventional PPP model that typically assumes these biases to be time-constant.In the realm of multi-station PPP-RTK data processing,we introduce the ionosphere-weighted PPP-RTK model,which enhances the model strength by considering the spatial correlation of ionospheric delays.We also review the phase-only PPP-RTK model,designed to mitigate the impact of unmodelled code-related errors.Furthermore,we explore GLONASS PPP-RTK,achieved through the application of the integer-estimable model.For large-scale network data processing,we introduce the all-in-view PPP-RTK model,which alleviates the strict common-view requirement at all receivers.Moreover,we present the decentralized PPP-RTK data processing strategy,designed to improve computational efficiency.Overall,this work highlights the various advancements in UDUC GNSS data processing,providing insights into the state-of-the-art techniques employed in China to achieve precise GNSS applications.

Investigations of the seismomagnetic effect in the geomagnetic diurnal variations

In this paper we attempt to Abstract seismomagnetic signals from geomagnetic diurnal variations of three components in quiet days before and after great earthquakes. The method employed here is to examine the ratio of apparent depths between two geomagnetic observatories using the single-station Z/H method. We first estimate the apparent depth for the period of 24 h for two observatories which are located at almost the same latitude. Then we analyse the time changes of the apparent-depth-ratio between these stations. In the interval of 1962 1988, the time variation of apparent-depth-ratio between the Beijing and Lanzhou observatories seems to be related to the three great earthquakes occurred near Beijing. Roughly speaking, the anomalous change in apparentdepth-ratio appears to be positive before earthquake, and appears to be negative after earthquake.