Measurement and analysis of earth's magnetic field based on low-magnetic field standards
The Cheongyang (CYG) observatory has been built to measure earth's magnetic field and to study prediction of earthquake and space weather. The equipments of the CYG observatory are a 3-axis fluxgate magnetometer, an overhauser effect proton magnetometer, a declination/inclination magnetometer and a data logger. A Cs-4He atomic magnetic resonance magnetometer was used to correct the measured data obtained by the proton magnetometer. All the measurement equipments were calibrated using magnetic field standard system maintained at KRISS. The Measurement results show a variation of the baselines less than 5 nT within one year, which is the most critical requirement criteria for joining the INTERMAGNET (International Real-time Magnetic Observatory Network).
Research on a secondary tuning algorithm based on SVD & STFT for FID signal
The tuning precision of a Proton precession magnetometer’s sensor is the key to getting the best signal to noise ratio (SNR) of free induction decay (FID) signals. By analyzing the noises of the magnetometer’s sensor and conditioning circuit, this paper introduces the principle of tuning and proposes a secondary tuning algorithm based on the singular value decomposition (SVD) and short-time Fourier transform (STFT), targeting the current lack of a tuning method. Moreover, the STFT for an FID signal’s feature analysis is applied for the first time. First, the space matrix is constructed by the acquisition of ADC for the untuned FID signal, and then the SVD is performed to eliminate the noise and obtain the useful signal. Finally, the STFT technique is applied to the denoised signal to extract the time-frequency feature. By theory analysis, simulation modeling and the testing of an actual FID signal, the results show that, compared with general tuning methods such as peak detection and fast Fourier transform (FFT), the proposed algorithm improves the sensor’s tuning precision, and the time of the tuning process is no more than one second. Furthermore, the problem of mistuning in strong-disturbance environments is solved. Thus, the secondary tuning algorithm based on the SVD and STFT is more practical.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)