目的:探讨妊高征患者母体循环中脐动脉(U m A)、双侧子宫动脉(U t A )及髂内动脉(Il A)的收缩期/舒张期比值(S/ D)和血流量(△Q )在预测围产儿结局方面的诊断价值。方法:采用多普勒超声检测4 8例妊高征患者U m A、U t A及Il A的S/ D和...目的:探讨妊高征患者母体循环中脐动脉(U m A)、双侧子宫动脉(U t A )及髂内动脉(Il A)的收缩期/舒张期比值(S/ D)和血流量(△Q )在预测围产儿结局方面的诊断价值。方法:采用多普勒超声检测4 8例妊高征患者U m A、U t A及Il A的S/ D和△Q,并与6 2例正常单胎妊娠孕妇对比。结果:U m A S/ D的敏感度(82 .1% )、阳性似然比(4.4 9)及约登指数(0 .6 38)均高于U t A S/ D;Um A△Q的敏感度(85 .7% )、特异度(82 .9% )、阳性似然比(5 .0 1)及约登指数(0 .6 86 )均高于U t A△Q ,且U m A△Q和U t A△Q各项指标分别高于U m A S/ D和U t A S/ D;Il A S/ D及Il A△Q各指标均较低。结论:△Q对妊高征患者围产儿结局的诊断价值优于S/ D;Il A S/ D和△Q的诊断价值较U m A和U t A低。展开更多
In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be a...In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be able to achieve acquisition in a very short time in spite of large Doppler frequencies. However, the traditional methods cannot solve it well. This work describes a new method that uses a differential decoding technique for Doppler mitigation and a batch process of FFT (fast Fourier transform) and IFFT (invert FFT) for the purpose of parallel code phase search by frequency domain correlation. After the code phase is estimated, another FFT process is carried out to search the Doppler frequency. Since both code phase and Doppler frequency domains are searched in parallel, this architecture can provide acquisition fifty times faster than conventional FFT methods. The performance in terms of the probability of detection and false alarm are also analyzed and simulated, showing that a signal-to-noise ratio (SNR) loss of 3 dB is introduced by the differential decoding. The proposed method is an efficient way to shorten the acquisition time with slightly hardware increasing.展开更多
文摘目的:探讨妊高征患者母体循环中脐动脉(U m A)、双侧子宫动脉(U t A )及髂内动脉(Il A)的收缩期/舒张期比值(S/ D)和血流量(△Q )在预测围产儿结局方面的诊断价值。方法:采用多普勒超声检测4 8例妊高征患者U m A、U t A及Il A的S/ D和△Q,并与6 2例正常单胎妊娠孕妇对比。结果:U m A S/ D的敏感度(82 .1% )、阳性似然比(4.4 9)及约登指数(0 .6 38)均高于U t A S/ D;Um A△Q的敏感度(85 .7% )、特异度(82 .9% )、阳性似然比(5 .0 1)及约登指数(0 .6 86 )均高于U t A△Q ,且U m A△Q和U t A△Q各项指标分别高于U m A S/ D和U t A S/ D;Il A S/ D及Il A△Q各指标均较低。结论:△Q对妊高征患者围产儿结局的诊断价值优于S/ D;Il A S/ D和△Q的诊断价值较U m A和U t A低。
基金Project(60904090) supported by the National Natural Science Foundation of China
文摘In low earth orbit (LEO) satellite or missile communication scenarios, signals may experience extremely large Doppler shifts and have short visual time. Thus, direct sequence spread spectrum (DSSS) systems should be able to achieve acquisition in a very short time in spite of large Doppler frequencies. However, the traditional methods cannot solve it well. This work describes a new method that uses a differential decoding technique for Doppler mitigation and a batch process of FFT (fast Fourier transform) and IFFT (invert FFT) for the purpose of parallel code phase search by frequency domain correlation. After the code phase is estimated, another FFT process is carried out to search the Doppler frequency. Since both code phase and Doppler frequency domains are searched in parallel, this architecture can provide acquisition fifty times faster than conventional FFT methods. The performance in terms of the probability of detection and false alarm are also analyzed and simulated, showing that a signal-to-noise ratio (SNR) loss of 3 dB is introduced by the differential decoding. The proposed method is an efficient way to shorten the acquisition time with slightly hardware increasing.
