Accurate simulations of pure-viscoacoustic wave propagation in tilted transversely isotropic media

Forward modeling of seismic wave propagation is crucial for the realization of reverse time migration(RTM) and full waveform inversion(FWI) in attenuating transversely isotropic media. To describe the attenuation and anisotropy properties of subsurface media, the pure-viscoacoustic anisotropic wave equations are established for wavefield simulations, because they can provide clear and stable wavefields. However, due to the use of several approximations in deriving the wave equation and the introduction of a fractional Laplacian approximation in solving the derived equation, the wavefields simulated by the previous pure-viscoacoustic tilted transversely isotropic(TTI) wave equations has low accuracy. To accurately simulate wavefields in media with velocity anisotropy and attenuation anisotropy, we first derive a new pure-viscoacoustic TTI wave equation from the exact complex-valued dispersion formula in viscoelastic vertical transversely isotropic(VTI) media. Then, we present the hybrid finite-difference and low-rank decomposition(HFDLRD) method to accurately solve our proposed pure-viscoacoustic TTI wave equation. Theoretical analysis and numerical examples suggest that our pure-viscoacoustic TTI wave equation has higher accuracy than previous pure-viscoacoustic TTI wave equations in describing q P-wave kinematic and attenuation characteristics. Additionally, the numerical experiment in a simple two-layer model shows that the HFDLRD technique outperforms the hybrid finite-difference and pseudo-spectral(HFDPS) method in terms of accuracy of wavefield modeling.

Overview of computation strategies on the dispersion analysis for explicit finite difference solution of acoustic wave equation

Finite-difference(FD)method is the most extensively employed numerical modeling technique.Nevertheless,when using the FD method to simulate the seismic wave propagation,the large spatial or temporal sampling interval can lead to dispersion errors and numerical instability.In the FD scheme,the key factor in determining both dispersion errors and stability is the selection of the FD weights.Thus,How to obtain appropriate FD weights to guarantee a stable numerical modeling process with minimum dispersion error is critical.The FD weights computation strategies can be classified into three types based on different computational ideologies,window function strategy,optimization strategy,and Taylor expansion strategy.In this paper,we provide a comprehensive overview of these three strategies by presenting their fundamental theories.We conduct a set of comparative analyses of their strengths and weaknesses through various analysis tests and numerical modelings.According to these comparisons,we provide two potential research directions of this field:Firstly,the development of a computational strategy for FD weights that enhances stability;Secondly,obtaining FD weights that exhibit a wide bandwidth while minimizing dispersion errors.

Regularized least-squares migration of simultaneous-source seismic data with adaptive singular spectrum analysis

Simultaneous-source acquisition has been recog- nized as an economic and efficient acquisition method, but the direct imaging of the simultaneous-source data produces migration artifacts because of the interference of adjacent sources. To overcome this problem, we propose the regularized least-squares reverse time migration method （RLSRTM） using the singular spectrum analysis technique that imposes sparseness constraints on the inverted model. Additionally, the difference spectrum theory of singular values is presented so that RLSRTM can be implemented adaptively to eliminate the migration artifacts. With numerical tests on a fiat layer model and a Marmousi model, we validate the superior imaging quality, efficiency and convergence of RLSRTM compared with LSRTM when dealing with simultaneoussource data, incomplete data and noisy data.

3D elastic waveform modeling with an optimized equivalent staggered-grid finite-difference method

Equivalent staggered-grid(ESG) as a new family of schemes has been utilized in seismic modeling,imaging,and inversion.Traditionally,the Taylor series expansion is often applied to calculate finite-difference(FD) coefficients on spatial derivatives,but the simulation results suffer serious numerical dispersion on a large frequency zone.We develop an optimized equivalent staggered-grid(OESG) FD method that can simultaneously suppress temporal and spatial dispersion for solving the second-order system of the 3 D elastic wave equation.On the one hand,we consider the coupling relations between wave speeds and spatial derivatives in the elastic wave equation and give three sets of FD coefficients with respect to the P-wave,S-wave,and converted-wave(C-wave) terms.On the other hand,a novel plane wave solution for the 3 D elastic wave equation is derived from the matrix decomposition method to construct the time-space dispersion relations.FD coefficients of the OESG method can be acquired by solving the new dispersion equations based on the Newton iteration method.Finally,we construct a new objective function to analyze P-wave,S-wave,and C-wave dispersion concerning frequencies.The dispersion analyses show that the presented method produces less modeling errors than the traditional ESG method.The synthetic examples demonstrate the effectiveness and superiority of the presented method.

Target-oriented Gaussian beam migration using a modif ied ray tracing scheme

For large-scale 3D seismic data,target-oriented reservoir imaging is more attractive than conventional full-volume migration,in terms of computation efficiency.Gaussian beam migration(GBM)is one of the most robust depth imaging method,which not only keeps the advantages of ray methods,such as high efficiency and flexibility,but also allows us to solve caustics and multipathing problems.But conventional Gaussian beam migration requires slant stack for prestack data,and ray tracing from beam center location to subsurface,which is not easy to be directly applied for target-oriented imaging.In this paper,we modify the conventional Gaussian beam migration scheme,by shooting rays from subsurface image points to receivers to implement wavefield back-propagation.This modification helps us to achieve a better subsurface illumination in complex structure and allows simple implementation for target reservoir imaging.Significantly,compared with the wavefi eld-based GBM,our method does not reconstruct the subsurface snapshots,which has higher efficiency.But the proposed method is not as efficient as the conventional Gaussian beam migration.Synthetic and field data examples demonstrate the validity and the target-oriented imaging capability of our method.

3D variable-grid full-waveform inversion on GPU

Full-waveform inversion(FWI)is a powerful tool to reconstruct subsurface geophysical parameters with high resolution.As3 D surveys become widely implemented,corresponding 3 D processing techniques are required to solve complex geological cases,while a large amount of computation is the most challenging problem.We propose an adaptive variable-grid 3 D FWI on graphics processing unit devices to improve computational efficiency without losing accuracy.The irregular-grid discretization strategy is based on a dispersion relation,and the grid size adapts to depth,velocity,and frequency automatically.According to the transformed grid coordinates,we derive a modified acoustic wave equation and apply it to full wavefield simulation.The 3 D variable-grid modeling is conducted on several 3 D models to validate its feasibility,accuracy and efficiency.Then we apply the proposed modeling method to full-waveform inversion for source and residual wavefield propagation.It is demonstrated that the adaptive variable-grid FWI is capable of decreasing computing time and memory requirements.From the inversion results of the 3 D SEG/EAGE overthrust model,our method retains inversion accuracy when recovering both thrust and channels.

Convolution-based multi-scale envelope inversion

Envelope inversion(El)is an efficient tool to mitigate the nonlinearity of conventional full waveform inversion(FWI)by utilizing the ultralow-frequency component in the seismic data.However,the performance of envelope inversion depends on the frequency component and initial model to some extent.To improve the convergence ability and avoid the local minima issue,we propose a convolution-based envelope inversion method to update the low-wavenumber component of the velocity model.Besides,the multi-scale inversion strategy(MCEI)is also incorporated to improve the inversion accuracy while guaranteeing the global convergence.The success of this method relies on modifying the original envelope data to expand the overlap region between observed and modeled envelope data,which in turn expands the global minimum basin of misfit function.The accurate low-wavenumber component of the velocity model provided by MCEI can be used as the migration model or an initial model for conventional FWI.The numerical tests on simple layer model and complex BP 2004 model verify that the proposed method is more robust than El even when the initial model is coarse and the frequency component of data is high.

Stable attenuation-compensated reverse time migration and its application to land seismic data

Intrinsic attenuation of the earth causes energy loss and phase distortion in seismic wave propagation.To obtain high-resolution imaging results,these negative effects must be considered during reverse time migration(RTM).We can easily implement attenuation-compensated RTM using the constant Q viscoacoustic wave equation with decoupled amplitude attenuation and phase dispersion terms.However,the nonphysical amplitude-compensation process will inevitably amplify the high-frequency noise in the wavefield in an exponential form,causing the numerical simulation to become unstable.This is due to the fact that the amplitude of the compensation grows exponentially with frequency.In order to achieve stable attenuation-compensated RTM,we modify the analytic expression of the attenuation compensation extrapolation operator and make it only compensate for amplitude loss within the effective frequency band.Based on this modified analytic formula,we then derive an explicit time-space domain attenuation compensation extrapolation operator.Finally,the implementation procedure of stable attenuation-compensated RTM is presented.In addition to being simple to implement,the newly proposed attenuation-compensated extrapolation operator is superior to the conventional low-pass filter in suppressing random noise,which will further improve the imaging resolution.We use two synthetic and one land seismic datasets to verify the stability and effectiveness of the proposed attenuationcompensated RTM in improving imaging resolution in viscous media.

An amplitude-preserved adaptive focused beam seismic migration method

Gaussian beam migration （GBM） is an effec- tive and robust depth seismic imaging method, which overcomes the disadvantage of Kirchhoff migration in imaging multiple arrivals and has no steep-dip limitation of one-way wave equation migration. However, its imaging quality depends on the initial beam parameters, which can make the beam width increase and wave-front spread with the propagation of the central ray, resulting in poor migration accuracy at depth, especially for exploration areas with complex geological structures. To address this problem, we present an adaptive focused beam method for shot-domain prestack depth migration. Using the infor- mation of the input smooth velocity field, we first derive an adaptive focused parameter, which makes a seismic beam focused along the whole central ray to enhance the wave- field construction accuracy in both the shallow and deep regions. Then we introduce this parameter into the GBM, which not only improves imaging quality of deep reflectors but also makes the shallow small-scale geological struc- tures well-defined. As well, using the amplitude-preserved extrapolation operator and deconvolution imaging condi- tion, the concept of amplitude-preserved imaging has been included in our method. Typical numerical examples and the field data processing results demonstrate the validity and adaptability of our method.

2D Q-compensated multi-component elastic Gaussian beam migration

Elastic waves are affected by viscoelasticity during the propagation through the Earth,resulting in energy attenuation and phase distortion,in turn resulting in low seismic imaging accuracy.Therefore,viscoelasticity should be considered in seismic migration imaging.We propose a Q compensated multicomponent elastic Gaussian beam migration(Q-EGBM)method to(1)separate the elastic-wave data into longitudinal(P)and transverse(S)waves to perform PP-wave and PS-wave imaging;(2)recover the amplitude loss caused by attenuation;(3)correct phase distortions caused by dispersion;(4)improve the resolution of migration imaging.In this paper,to accomplish(2),(3),and(4),we derive complex-valued traveltimes in viscoelastic media.The results of numerical experiments using a simple five-layer model and a sophisticated BP gas model show that the method presented here has significant advantages in recovering energy decay and correcting phase distortion,as well as significantly improving imaging resolution.

A fast space-time-domain Gaussian beam migration approach using the dominant frequency approximation

The Gaussian beam migration(GBM) is a steady imaging approach, which has high accuracy and efficiency. Its implementation mainly includes the traditional frequency domain and the recent popular space-time domain. Firstly, we use the upward ray tracing strategy to get the backward wavefields. Then,we use the dominant frequency of the seismic data to simplify the imaginary traveltime calculation of the wavefields, which can cut down the Fourier transform number compared with the traditional GBM in the space-time domain. In addition, we choose an optimized parameter for the take-off angle increment of the up-going and down-going rays. These optimizations help us get an efficient space-time-domain acoustic GBM approach. Typical four examples show that the proposed method can significantly improve the computational efficiency up to one or even two orders of magnitude in different models with different model parameters and produce good imaging results with comparable accuracy and resolution with the traditional GBM in the space-time domain.

α-Pyrone Derivatives from a Streptomyces Strain Resensitize Tamoxifen Resistance in Breast Cancer Cells

Tamoxifen resistance(TamR)is the underlying cause of treatment failure in many breast cancer patients receiving tamoxifen.In order to look for noncytotoxic natural products with the ability to reverse TamR,an extract from strain Streptomyces sp.KIB-H0495 was detected to be active.Subsequent large scale fermentation and isolation led to the isolation of four a-pyrone derivatives including two new compounds,violapyrones J(2)and K(3),and two known analogues,violapyrones B(1)and I(4).Further bioactivity assays indicated that only 1 and 3 exerted potent resensitization effects on MCF-7/TamR cells at a concentration of 1 lM.Owing to the simple structures of 1 and 3,these two compounds might have potential for further investigation as novel tamoxifen resensitization agent in breast cancer chemotherapy.

A computational method for wide-azimuth 3D dip-angle gathers using Gaussian beam migration

The dip-angle-domain common-image gather(DDCIG)is a key tool to separate the diffraction and reflection imaging results.Reflectors with different spatial geometries produce different responses in DDCIGs.Compared with Kirchhoff migration,Gaussian beam migration(GBM)is more effective and robust to overcome the multipathing problem.As a ray-based method,it has explicit angle information naturally during the propagation.We have developed a 3D DDCIG computational method using GBM,which obtain both the imaging result and angle-domain gathers with only one pass of calculation.The angle-gather computation is based on geometrical optics,and multiple angle conversions are implemented under the rules of space geometry,which helps to avoid rounding errors and improve accuracy.Additionally,the multi-azimuth joint presentation strategy is proposed to describe the characteristic of omnidirectional dip angles using a finite number of gathers.After using a 2D model to illustrate application advantages of DDCIG,we apply the proposed method to two 3D models to test its feasibility and accuracy.A field data example further demonstrates the adaptability of our method to seismic imaging for a land survey.

Advances in chemistry and bioactivity of the genus Erythroxylum

Erythroxylum P.Browne is the largest and most representative genus of Erythroxylaceae family.It contains approxi-mately 230 species that are mainly distributed in tropical and subtropical regions.Some species in this genus,such as E.monogynum and E.coca,have been used as folk medicines in India or South America for a long history.It is well known that Erythroxylum plants are rich in tropane alkaloids,and the representative member cocaine shows remarka-ble activity in human central nervous system.However,many other types of active compounds have also been found in Erythroxylum along with the broadening and deepening of phytochemical research.To date,a total of 383 com-pounds from Erythroxylum have been reported,among which only 186 tropane alkaloids have been reviewed in 2010.In this review,we summarized all remained 197 compounds characterized from 53 Erythroxylum species from 1960 to 2021,which include diterpenes,triterpenes,alkaloids,flavonoids,and other derivates,providing a comprehensive overview of phytoconstituents profile of Erythroxylum plants.In addition,the biological activities of representative phytochemicals and crude extracts were also highlighted.

Development status and trend of traditional Chinese medicine database

Following the trend of information technology,the development of traditional Chinese medicine(TCM)databases has led to great changes in terms of data.For example,the storage and dissemination medium of data has achieved a shift from paper books to the internet,and the content has expanded from basic information to comprehensive information such as targets and molecular structures of modern medicine.In recent years,the amount of information contained in the TCM databases has grown at an unparalleled rate.However,there are still challenges correlated with the database construction,including insufficient data volume,inconsistent construction standards,and a low level of platformization.Additionally,the prevalence of applications in the field of TCM like network pharmacology,bioinformatics,and artificial intelligence requires a large volume of high-quality data.Generally speaking,the advancements in life science and artificial intelligence technology have outpaced the development of TCM databases.Therefore,this paper compiled the current status of TCM databases,discussed the benefits and drawbacks of various databases,and concluded that the development trend should be comprehensive,platform-based,and tightly integrated with modern life science technology and artificial intelligence technology,so as to provide assistance to the modernization research of TCM.

Identification and characterization of camptothecin tailoring enzymes in Nothapodytes tomentosa

Camptothecin is a complex monoterpenoid indole alkaloid with remarkable antitumor activity.Given that two C-10 modified camptothecin derivatives,topotecan and irinotecan,have been approved as potent anticancer agents,there is a critical need for methods to access other aromatic ringfunctionalized congeners(e.g.,C-9,C-10,etc.).However,contemporary methods for chemical oxidation are generally harsh and low-yielding when applied to the camptothecin scaffold,thereby limiting the development of modified derivatives.Reported herein,we have identified four tailoring enzymes responsible for C-9 modifications of camptothecin from Nothapodytes tomentosa,via metabolomic and transcriptomic analysis.These consist of a cytochrome P450(Nt CPT9H)which catalyzes the regioselective oxidation of camptothecin to 9-hydroxycamptothecin,as well as two methyltransferases(Nt OMT1/2,converting 9-hydroxycamptothecin to 9-methoxycamptothecin),and a uridine diphosphate-glycosyltransferase(Nt UGT5,decorating 9-hydroxycamptothecin to9-β-D-glucosyloxycamptothecin).Importantly,the critical residues that contribute to the specific catalytic activity of Nt CPT9H have been elucidated through molecular docking and mutagenesis experiments.This work provides a genetic basis for producing camptothecin derivatives through metabolic engineering.This will hasten the discovery of novel C-9 modified camptothecin derivatives,with profound implications for pharmaceutical manufacture.

Combined impacts of aerosols and urbanization on a highly threatened extreme precipitation event in Beijing,China

On July 21,2012,a catastrophic precipitation event occurred in Beijing,highlighting the serious threat of extreme precipitation on socio-economic development and human health under climate change.Nevertheless,whether,how and to what extent aerosols and urbanization,as the two main influencing factors of urban extreme precipitation,have affected this highly damaging extreme event remains largely unex-plored.Here,we employed the weather research and forecasting model coupled with chemistry(WRF-Chem)and a single-layer urban canopy model to investigate the influences of urbanization,aerosols and their interactions on this extreme precipitation event.We found that the joint intensification effects of urbanization and aerosols on extreme precipitation events greatly enhance its negative influence on megacities.The results indicate that aerosols are enhanced by increasing cloud droplet numbers,thereby intensifying the feedback between precipitation and latent heating.Consequently,the total precipitation increased by 22.6%,raising the precipitation in the Beijing area increase by at least 50 mm.By stimulating atmospheric instability and strengthening vertical air motion(over 0.25 m s^(-1)),the urban heat island effect considerably in-fluences the temporal and spatial distributions of extreme precipitation events,resulting in an increase in warm cloud precipitation(80%)and a decrease(30%)in frontal precipitation.Consequently,joint intensification effects resulted in more concentrated precipitation in the southwest of Beijing,leading to a substantial increase(more than 40%,~80 mm).This condition may be an important reason for the most severe disasters in the southwest of Beijing.

Efficacy and safety of Tianqi Pingchan Granule,a compound Chinese herbal medicine,for levodopa-induced dyskinesia in Parkinson’s disease:A randomized double-blind placebo-controlled trial

Background Patients with Parkinson’s disease(PD)undergoing long-term levodopa therapy are prone to develop levodopa-induced dyskinesia(LID).Amantadine is the main drug recommended for the treatment of LID by current guidelines,but it is far from meeting clinical needs.Tianqi Pingchan Granule(TPG),a compound Chinese herbal medicine,has been developed to relieve symptom of LID.Objective This randomized controlled trial evaluated the efficacy and safety of the combination of TPG and amantadine for LID.Design,setting,participants and interventions This is a randomized double-blind placebo-controlled trial,conducted from January 2020 to August 2021 at 6 sites in Jiangsu,Zhejiang and Shanghai,China.One hundred PD patients with≥0.5 h of LID were randomly assigned to either the TPG plus amantadine group(TPG group)or the placebo plus amantadine group(placebo group),and treated for a period of 12 weeks.To ensure unbiased results,all study participants,investigators and sponsors were unaware of group allocations.Additionally,the data analysts remained blinded until the analysis was finalized.Main outcome measures The primary outcome was assessed using the Unified Dyskinesia Rating Scale(UDysRS)(Range 0–104).The key secondary end point was improvement of motor and non-motor symptoms.Safety analyses included all enrolled patients.Results One hundred patients were enrolled and randomized into the two treatment groups.The changes in UDysRS at week 12 were–11.02 for the TPG group and–4.19 for the placebo group(treatment difference–6.83[–10.53 to–3.12];P=0.0004).Adverse events were reported for 2 of 50 patients(4.0%)in each of the groups.Conclusion This study indicated that a 12-week treatment of amantadine plus TPG effectively reduced UDysRS scores and was well tolerated,demonstrating the efficacy and safety of TPG for the treatment of LID in PD.

Posterior reversible encephalopathy syndrome in patients with hematologic tumor confers worse outcome

Background:This study aimed to evaluate the clinical features of posterior reversible encephalopathy syndrome(PRES)in children.Methods:The medical records of 31 patients from five medical centers who were diagnosed with PRES from 2001 to 2013 were retrospectively analyzed.In the 31 patients,16 were males,and 15 females,with a median age of 7 years(3-12 years).Patients younger than 10 years accounted for 74.2%of the 31 patients.Results:Seizure,the most common clinical sign,occurred in 29 of the 31 patients.Visual disturbances were also observed in 20 patients.Cerebral imaging abnormalities were bilateral and predominant in the parietal and occipital white matter.In this series,three patients died in the acute phase of PRES.One patient had resolution of neurologic presentation within one week,but no apparent improvement in radiological abnormalities was observed at eight months.One patient showed gradual recovery of both neurologic presentation and radiological abnormalities during follow-up at eight months.One patient developed long-term cortical blindness.All of the PRES patients with hematologic tumor had a worse prognosis than those without hematologic tumor.Conclusions:Seizure is a prevalent characteristic of children with PRES.Poor prognosis can be seen in PRES patients with hematologic tumor.

Segmentation and focus-point location based on boundary analysis in forest canopy hemispherical photography

Analysis of forest canopy hemisphere images is one of the most important methods for measuring forest canopy structure parameters. In this study, our main focus was on using circular image region segmentation, which is the basis of forest canopy hemispherical photography. The boundary of a forest canopy hemisphere image was analyzed via histogram, rectangle, and Fourier descriptors. The image boundary characteristics were defined and obtained based on the following：（1） an edge model that contains three parts, i.e., step, ramp, and roof;（2） boundary points of discontinuity;（3） an edge that has a linear distribution of scattering points. On this basis, we proposed a segmentation method for the circular region in a forest canopy hemisphere image, fitting the circular boundary and computing the center and radius by the least squares method. The method was unrelated to the parameters of the image acquisition device. Hence, this study lays a foundation for automatically adjusting the parameters of high-performance image acquisition devices used in forest canopy hemispherical photography.