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41.
42.
A Stable Q Compensated Reverse Time Migration Method Based on Excitation Amplitude Imaging Condition
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Qingqing Li Li-Yun Fu Weijia Sun Wei Wei & Wanting Hou 《Communications In Computational Physics》2020,28(1):141-166
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
43.
OBJECTIVES: To assess the effectiveness and safety of additional bedtime H2‐receptor antagonists (H2RAs) in suppressing nocturnal gastric acid breakthrough (NAB) via a systematic review. METHODS: Eligible trials were identified by searching the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library Issue 2, 2004), MEDLINE (January 1966–June 2004), EMBASE (January 1980–June 2004) and CINAHL (January 1982–June 2004). Additional hand‐searching was conducted on the proceedings of correlated conferences, eight important Chinese journals and references of all included trials. All randomized controlled trials evaluating H2RAs for the control of NAB were eligible for inclusion. The systematic review was conducted using methods recommended by The Cochrane Collaboration. RESULTS: Only two randomized crossover studies, comprising 32 participants, met the inclusion criteria. Because the design, dosage and duration of the treatments were different between the studies, it was not possible to conduct meta‐analysis. There were no consistent conclusions found between the two included studies in evaluating H2RAs for the control of NAB. CONCLUSIONS: No implications for practice at this stage can be concluded. Appropriately designed large‐scale randomized controlled trials with long‐term follow up are needed to determine the effects of additional bedtime H2RAs in suppressing NAB. 相似文献
44.
Dexamethasone treatment attenuates early seawater instillation-induced acute lung injury in rabbits. 总被引:8,自引:0,他引:8
Ding Xinmin Duan Yunyou Peng Chaosheng Feng Huasong Zhou Pingkun Meng Jiguang Xue Zhiqian Xu Qinzhi 《Pharmacological research》2006,53(4):372-379
There is very little evidence on the value of giving corticoids in cases of seawater drowning induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Therefore, this study aimed to investigate whether dexamethasone treatment can attenuate seawater instillation-induced acute lung injury in rabbits. Seawater (4 ml/kg body weight) was instilled into the lower trachea of ventilated, anesthetized rabbits. Then these rabbits were assigned randomly 20 min later to receive intravenous injection of 1mg/kg body weight of dexamethasone (dissolving in 2 ml of normal saline) or 2 ml of normal saline. All animals demonstrated immediate drops in arterial oxygen tension (PaO2) and the total thoracic compliance, which were significantly improved after 2 h of dexamethasone treatment. Histopathological study also indicated that dexamethasone treatment markedly attenuated lung histopathological changes, alveolar hemorrhage and inflammatory cells infiltration with evidence of decreasing of myeloperoxidase (MPO) activity and tumor necrosis factor-alpha (TNF-alpha) concentration in lung tissue. In addition, dexamethasone treatment reduced extravascular lung water and lung epithelial-endothelial barrier permeability, up-regulated the expression of surfactant protein-A (SP-A) and alpha-epithelial Na+ channel, and increased Na+/K+-adenosine triphosphatase (Na+/K+-ATPase) activity and Na+/K+-ATPase-alpha1 protein abundance. Thus, these data indicate that dexamethasone treatment might be of benefit in patients with seawater aspiration-induced ALI. 相似文献
45.
目的对年轻患者肩关节脱位进行系统的康复治疗,以检验系统康复疗法疗效优于单纯固定的假设。方法根据所采用的治疗方法,将43例40岁以下的急性肩关节脱位患者分成实验组23例,对照组20例。实验组患者进行包括关节活动范围锻炼、发展肩胛骨周围肌的肌力训练、发展肩袖肌的肌力、适度的外展、外旋锻炼及耐力训练在内的系统康复治疗。对照组只进行单纯固定后未经系统康复治疗。对两组患者的临床效果进行比较。结果实验组复发率为17%(4/23),对照组复发率为45%(9/20),两组复发率比较差异有显著性意义(χ2=3.866,P<0.05);随访结果显示肩关节ASES评分实验组为90.9±4.87,对照组为75.4±4.94,两组差异有非常显著性意义(t=9.94,P=2.99×10-12<0.01)。结论肩关节脱位年轻患者进行系统的康复锻炼,可以提高患肩的稳定性。 相似文献
46.
目的:构建人IL-1Ra和人IL-10真核表达质粒载体并检测其表达。方法:用双酶切方法切取PCDI-IL-1Ra和PCDI-IL-10质粒中包含人IL-1Ra和人IL-10 CDS全长序列的cD-NA片段,并分别连接到真核表达质粒pcDNA3.1上,然后用壳聚糖转染上述质粒到原代软骨细胞,RT-PCR检测其mRNA水平的表达。结果:成功将人IL-1Ra和IL-10 CDS全长序列的cDNA片段克隆到真核表达载体,mRNA水平检测到目的基因的表达明显提高。结论:真核表达质粒可以用于外源基因的原代软骨细胞导入和表达,为进一步的基因治疗研究提供依据。 相似文献
47.
目的:探讨椎管扩大成形术治疗腰椎管狭窄的效果。方法:椎板减压后复位,用棘突或髂骨植于一侧开槽处扩大椎管,并进行椎板及关节突关节植骨,对54例随访病人的手术前后临床表现及X线和CT进行比较。结果:随访6—39个月,临床优良率为81.1%。随访X线片显示椎板明显后移,CT测量与术前对比显示椎管内径扩大明显。结论:椎管扩大成形术操作简单,效果满意,术后并发症少,是治疗腰椎管狭窄的又一选择。 相似文献
48.
骨质疏松相关基因的研究进展 总被引:3,自引:1,他引:2
骨质疏松(osteoporosis,OP)在很大程度上受基因的影响。在OP的相关基因中,维生素D受体(VDR)基因、雌激素受体(ER)基因、Ⅰ型胶原基因及转化生长因子基因都是重要的候选基因。VDR基因中BB基因型者比Bb及bb基因型者的腰椎骨密度(bone mineral density,BMD)低,骨丢失率高。FokⅠ基因型与腰椎BMD降低有明显相关性,ff基因型者腰椎BMDXx基因型者>xx基因型者。Ⅰ型胶原基因与骨量呈显著相关性,COLIA1基因突变可致低骨量、骨脆性增加。转化生长因子β(TGF-β)基因对调节骨形成和骨吸收有重要作用,TGF-β基因中可发生碱基丢失,这种变异多见于OP患者。 相似文献
49.
50.