The stability and efficiency, especially the stability, are generally concerned
issues in Q compensated reverse time migration (Q-RTM). The instability occurs because of the exponentially boosted high frequency ambient noise during the forward
or backward seismic wavefield propagation. The regularization and low-pass filtering
methods are two effective strategies to control the instability of the wave propagation in Q-RTM. However, the regularization parameters are determined experimentally, and the wavefield cannot be recovered accurately. The low-pass filtering method
cannot balance the selection of cutoff frequency for varying Q values, and may damage
the effective signals, especially when the signal-to-noise ratio (SNR) of the seismic data
is low, the Q-RTM will be a highly unstable process. In order to achieve the purpose
of stability, the selection of cutoff frequency will be small enough, which can cause
great damage to the effective high frequency signals. In this paper, we present a stable Q-RTM algorithm based on the excitation amplitude imaging condition, which can
compensate both the amplitude attenuation and phase dispersion. Unlike the existing Q-RTM algorithms enlarging the amplitude, the exponentially attenuated seismic
wavefield will be used during both the forward and backward wavefield propagation
of Q-RTM. Therefore, the new Q-RTM algorithm is relative stable, even for the low
SNR seismic data. In order to show the accuracy and stability of our stable Q-RTM
algorithm clearly, an example based on Graben model will be illustrated. Then, a realistic BP gas chimney model further demonstrates that the proposed method enjoys
good stability and anti-noise performance compared with the traditional Q-RTM with
amplitude amplification. Compare the Q-RTM images of these two models to the reference images obtained by the acoustic RTM with acoustic seismic data, the new Q-RTM
results match the reference images quite well. The proposed method is also tested
using a field seismic data, the result shows the effectiveness of our proposed method. 相似文献
Objective: To report a case of labour induction during extracorporeal membrane oxygenation (ECMO) support in a patient with acute respiratory distress syndrome (ARDS) caused by influenza and review of the literature.
Methods: Case report and the literature search of all English articles on delivery while on ECMO in patients with ARDS caused by influenza.
Results: A 25-year-old pregnant woman was initiated with ECMO due to severe ARDS caused by influenza A (H1N1) virus. When the patient had symptoms of colporrhagia and uterine contractions, the medical team decided to start labour induction while on ECMO. There were in total five case reports identified. Maternal oxygenation was improved after delivery and ECMO was successfully discontinued.
Conclusions: Maternal oxygenation was improved after delivery, which may be beneficial to reduce the duration of ECMO. Caesarean section (CS) may be the most used mode and labour induction could be another option. The procedure should be performed by an experienced ECMO team, cooperating with the obstetrician, anaesthesiologist, and ICU doctors. 相似文献
Background Intravitreal triamcinolone acetonide (TA) has been widely used as a therapeutic method for many ocular diseases, but a consensus on an appropriate safe therapeutic window of dosage for intravitreal injection, and whether vehicle of TA should be reduced or eliminated, has not yet been reached. The aim of this article is to investigate these issues.Methods Forty New Zealand white rabbits were divided into four experimental groups and one control group. Four or 25 mg TA, with vehicle either reduced or not, was injected into the vitreous cavity of rabbits in experimental groups. Rabbits in the control group received 0.2 ml intravitreal sterile saline solution. Intraocular pressures (IOP) were measured by a Tonopen tonometer. Values of lens density were measured by a Pentacam system. Soluble protein, total antioxidation capacity, reduced glutathione (GSH), glutathion peroxidase (GSH-px), and superoxide dismutase (SOD) in lens were measured by specific kits. ERG and pathological examinations, including light and electron microscopy of the retina, were also performed.Results Elevation of IOP was noted in all experimental groups after intravitreal TA (P<0.01, paired t-test). Significant increase of lens density was noticed at 1 week after intravitreal TA in the 25 mg vehicle-containing group (P<0.0001, paired t-test). Significant loss of GSH-px activity was noticed at the end of the study (P<0.05, paired t-test), while SOD activity increased (P<0.05, paired t-test). Amplitudes of ERG waves declined significantly in vehicle-containing groups (P<0.01, paired t-test) at the end of the study. Pathological examination showed obvious retinal toxicity in vehicle-containing groups.Conclusions Vehicle of TA should be eliminated or reduced before intravitreal injection to avoid potential retinal toxicity and transient increase in lens density.Presented at Chinese Academy of Fundus Disease Meeting, April, 2005.This study was supported by the 985 Fund of Peking University, Beijing.The authors have no financial interest in any instruments or drugs mentioned in this study. 相似文献