Phase-sensitive fat suppression steady-state free procession sequence with phase correction

Robust and fast fat suppression is a challenge in balanced steady-state free precession （SSFP） magnetic resonance imaging. Although single-acquisition phase-sensitive SSFP can provide fat-suppressed images in short scan time, phase errors, especially spatially-dependent phase shift, caused by a variety of factors may result in misplacement of fat and water voxels. In this paper, a novel phase correction algorithm was used to calibrate those phase errors during image reconstruction. This algorithm corrects phase by region growing, employing both the magnitude and the phase information of image pixels. Phantom and in vivo imagings were performed to validate the technique. As a result, excellent fat-suppressed images were acquired by using single-acquisition phase-sensitive SSFP with phase correction.

Amplitude spectrum compensation and phase spectrum correction of seismic data based on the generalized S transform

We propose a method for the compensation and phase correction of the amplitude spectrum based on the generalized S transform. The compensation of the amplitude spectrum within a reliable frequency range of the seismic record is performed in the S domain to restore the amplitude spectrum of reflection. We use spectral simulation methods to fit the time-dependent amplitude spectrum and compensate for the amplitude attenuation owing to absorption. We use phase scanning to select the time-, space-, and frequencydependent phases correction based on the parsimony criterion and eliminate the residual phase effect of the wavelet in the S domain. The method does not directly calculate the Q value; thus, it can be applied to the case of variable Q. The comparison of the theory model and field data verify that the proposed method can recover the amplitude spectrum of the strata reflectivity, while eliminating the effect of the residual phase of the wavelet. Thus, the wavelet approaches the zero-phase wavelet and, the seismic resolution is improved.

Structure-preserving properties of Strmer-Verlet scheme for mathematical pendulum

The structure-preserving property, in both the time domain and the frequency domain, is an important index for evaluating validity of a numerical method. Even in the known structure-preserving methods such as the symplectic method, the inherent conser- vation law in the frequency domain is hardly conserved. By considering a mathematical pendulum model, a Stormer-Verlet scheme is first constructed in a Hamiltonian frame- work. The conservation law of the StSrmer-Verlet scheme is derived, including the total energy expressed in the time domain and periodicity in the frequency domain. To track the structure-preserving properties of the Stormer-Verlet scheme associated with the con- servation law, the motion of the mathematical pendulum is simulated with different time step lengths. The numerical results illustrate that the StSrmer-Verlet scheme can preserve the total energy of the model but cannot preserve periodicity at all. A phase correction is performed for the StSrmer-Verlet scheme. The results imply that the phase correction can improve the conservative property of periodicity of the Stormer-Verlet scheme.

High efficiency spreading spectrum modulation using double orthogonal complex sequences

This paper presents a novel scheme of high efficiency spreading spectrum modulation using double orthogonal complex sequences （DoCS）. In this scheme, input data bit-stream is split into many groups with length M. Each group is then mapped into a word of width M and then utihzed to select one sequence from 2u-2 DoCS sequences each with length L. After that, the selected sequence is modulated on carrier in quadrature phase shift keying （QPSK） mode. In addition, a new method named forward phase correction （FPC） is put forward for carrier recovery. Theoretical analysis and bit-error-ratio（BER） experiment results indicate that the proposed scheme has better performance than the conventional direct sequence spread spectrum（DSSS） scheme both in bandwidth efficiency and processing gain of the receiver.

A VHF RFPGA with adaptive phase-correction technique

This paper presents a VHF（30-300 MHz） RF programmable gain amplifier（PGA） with an adaptive phase correction technique.The proposed technique effectively mitigates phase errors over the VHF band,and the RFPGA as a whole satisfies all the specifications of the China mobile multimedia broadcasting VHF band applications.The RFPGA is implemented with a TSMC 0.25μm CMOS process.Measurement results reveal a gain range of around 61 dB,an ⅡP3 of-7 dBm at maximum gain,a power consumption of 10.2 mA at maximum gain,and a phase imbalance of less than 0.3 degrees.

A coherence-based phase aberration correction method in medical ultrasound

A coherence-based correction method was proposed in order to improve the lateral resolution and enhance the contrast of medical ultrasound imaging in the presence of phase aberration. The averaged coherence factor was proposed at first and used as a metric to evaluate phase aberration correction. By maximizing the averaged coherence factor, the time delay parameter of each channel was adjusted. A new set of coherence factors was calculated and the corrected data was optimized to form the final B-mode image. The simulations on point targets and a cyst phantom showed that the proposed method outperformed the nearest neighboring cross correlation method and conventional coherence-weighting method, and the lateral resolution and contrast ratio was improved by approximately 0.24mm and 18dB respectively. The proposed method combined the advantages of phase error correction and coherence-weighting, which could improve imaging qualities effectively in medical ultrasound.

A Novel Offset Fresnel Zone Plate Antenna

A novel offset Fresnel Zone Plate reflector Antenna ( FZPA ) is proposed, the phase correcting zone of this FZPA is elliptic. Based on Physical Optics Method, the focusing characteristics of the reflector are analyzed. The comparison of this new FZPA with the circular FZPA and Mawzones FZPA is made.

A New Reflector Antenna Based on the Fresnel Principle

A new type of reflector antenne is proposed, which applies the 1 D Fresnel zone phase correction to the classical parabolic cylindrical reflector, providing an alternative to the dual parabolic cylindrical ones discussed by Sanad and Shafai [1] . The focusing characteristics of the new reflector are analyzed by physical optics method, and numerical results are illustrated to evaluate its applicability.

Precise orbit determination for BDS satellites

Since the frst pair of BeiDou satellites was deployed in 2000,China has made continuous eforts to establish its own independent BeiDou Navigation Satellite System(BDS)to provide the regional radio determination satellite service as well as regional and global radio navigation satellite services,which rely on the high quality of orbit and clock products.This article summarizes the achievements in the precise orbit determination(POD)of BDS satellites in the past decade with the focus on observation and orbit dynamic models.First,the disclosed metadata of BDS satellites is presented and the contribution to BDS POD is addressed.The complete optical properties of the satellite bus as well as solar panels are derived based on the absorbed parameters as well the material properties.Secondly,the status and tracking capabilities of the L-band data from accessible ground networks are presented,while some low earth orbiter satellites with onboard BDS tracking capability are listed.The topological structure and measurement scheme of BDS Inter-Satellite-Link(ISL)data are described.After highlighting the progress on observation models as well as orbit perturbations for BDS,e.g.,phase center corrections,satellite attitude,and solar radiation pressure,diferent POD strategies used for BDS are summarized.In addition,the urgent requirement for error modeling of the ISL data is emphasized based on the analysis of the observation noises,and the incompatible characteristics of orbit and clock derived with L-band and ISL data are illuminated and discussed.The further researches on the improvement of phase center calibration and orbit dynamic models,the refnement of ISL observation models,and the potential contribution of BDS to the estimation of geodetic parameters based on L-band or ISL data are identifed.With this,it is promising that BDS can achieve better performance and provides vital contributions to the geodesy and navigation.

Multi-antenna synchronized global navigation satellite system receiver and its advantages in high-precision positioning applications

The multi-antenna synchronized global navi- gation satellite system receiver is a high precision, low cost, and widely used emerging receiver. Using this type of receiver, the satellite and receiver clock errors can be eliminated simultaneously by forming between antenna single-differences, which is equivalent to the conventional double-difference model. However, current multi-antenna synchronized global navigation satellite system receiver products have not fully realized their potential to achieve better accuracy, efficiency, and broader applications. This paper introduces the conceptual design and derivable products of multi-antenna synchronized global navigation satellite system receivers involving the aspects of attitude determination, multipath effect mitigation, phase center variation correction, and ground-based carrier phase wind- up calibration. Through case studies, the advantages of multi-antenna synchronized global navigation satellite system receivers in high-precision positioning applications are demonstrated.