Moho depth inversion in the Tibetan Plateau from high-precision gravity data

The Tibetan Plateau(TP)is the youngest orogenic belt resulting from a continental collision on the Earth.It is a natural laboratory for studying continental dynamics,such as continental convergence,plate subduction,and plateau uplift.Investigating the deep structure of the TP has always been a popular issue in geological research.The Moho is the boundary between the crust and the mantle and therefore plays a crucial role in the Earth’s structure.Parameters such as depth and lateral variation,as well as the fine structure of the crust-mantle interface,reveal the lithospheric dynamics in the TP.Two methods are generally employed to study the Moho surface:seismic detection and gravity inversion.Seismic detection has the characteristic of high precision,but it is limited to a few cross-sectional lines and is quite costly.It is not suitable for and cannot be carried out over a large area of the TP.The Moho depth over a large area can be obtained through gravity inversion,but this method is affected by the nature of gravity data,and the accuracy of the inversion method is lower than that of seismic detection.In this work,a high-precision gravity field model was selected.The Parker-Oldenburg interface inversion method was used,within the constraints of seismic observations,and the Bott iteration method was introduced to enhance the inversion efficiency.The Moho depth in the TP was obtained with high precision,consistent with the seismic detection results.The research results showed that the shape of the Moho in the TP is complex and the variation range is large,reaching 60−80 km.In contrast with the adjacent area,a clear zone of sharp variation appears at the edge of the plateau.In the interior of the TP,the buried depth of the Moho is characterized by two depressions and two uplifts.To the south of the Yarlung Zangbo River,the Moho inclines to the north,and to the north,the Moho depresses downward,which was interpreted as the Indian plate subducting to the north below Tibet.The Moho depression on the north side of the Qiangtang block,reaching 72 km deep,may be a result of the southward subduction of the lithosphere.The Moho uplift of the Qiangtang block has the same strike as the Bangong−Nujiang suture zone,which may indicate that the area is compensated by a low-density and low-velocity mantle.

Precise geoid computation using Stokes-Helmert’s scheme and strict integrals of topographic effects

The high-precision local geoid model was computed based on the improved Stokes-Helmert0 s boundary value problem and strict integrals of topographic effects. This proposed method involves three steps.First, the mathematical form of Stokes-Helmert0 s boundary value problem was derived, and strict computational formulas regarding topographic effects were provided to overcome the disadvantage of planar approximations. Second, a gravimetric geoid model was constructed using the proposed StokesHelmert0 s scheme with a heterogeneous data set. Third, a least squares adjustment method combined with a multi-surface function model was employed to remove the bias between the gravimetric geoid model and the GNSS/leveling data and to refine the final local geoid model. The accuracy of the final geoid model was evaluated using independent GNSS/leveling data. Numerical results show that an external precision of 1.45 cm is achievable.

Evaluation of spiral CT imaging in the diagnosis of the primary ureteral carcinoma

Objective: To explore the characteristics of the primary ureteral carcinoma (PUC) and discuss the value of spiral CT (SCT) in the diagnosis of PUC. Methods: The SCT findings of the primary ureteral carcinoma in 16 cases were analyzed and compared with the histopathological diagnosis and staging. Results: The transverse diameters of the lesions were 1.0–2.1 cm, and the longitudinal lengths were 1.5–15.2 cm. There were no statistically significant differences (P>0.1) in diam- eters and lengths among the low staging group (pT0–T2) and the high staging group (pT3–T4). The average CT value of the lesions was 43 HU on plain scanning, and 73 HU on CE scanning. The increment was 30 HU. The lesions were clearer on CE scanning. Curved planar reconstruction (CPR) could show the entire course of the urinary tract. Among 6 cases of pT3 stage, CT gave a correct diagnosis in 1 case. For 2 cases of pT4 stage, CT gave correct diagnoses in both cases. Conclusion: The carcinomatous lesions spread along the ureter. The longitudinal length of each lesion is longer than its transverse diameter. Tumor cannot be staged merely according to its diameter and length. CT is difficult to differentiate stage T0–T3, while for stage T4, CT diagnosis is accurate. Contrast enhancement CT scanning has the confirming and differentiating roles. CPR offers direct and easy observing images for clinical doctors.

Detection of Huanglongbing(citrus greening) based on hyperspectral image analysis and PCR

Huanglongbing (HLB, citrus greening) is one of the most serious quarantine diseases of citrus worldwide. To monitor in real-time, recognize diseased trees, and efficiently prevent and control HLB disease in citrus, it is necessary to develop a rapid diagnostic method to detect HLB infected plants without symptoms. This study used Newhall navel orange plants as the research subject, and collected normal color leaf samples and chlorotic leaf samples from a healthy orchard and an HLB-infected orchard, respectively. First, hyperspectral data of the upper and lower leaf surfaces were obtained, and then the polymerase chain reaction (PCR) was used to detect the HLB bacterium in each leaf. The PCR test results showed that all samples from the healthy orchard were negative, and a portion of the samples from the infected orchard were positive. According to these results, the leaf samples from the orchards were divided into disease-free leaves and HLB-positive leaves, and the least squares support vector machine recognition model was established based on the leaf hyperspectral reflectance. The effect on the model of the spectra obtained from the upper and lower leaf surfaces was investigated and different pretreatment methods were compared and analyzed. It was observed that the HLB recognition rate values of the calibration and validation sets based on upper leaf surface spectra under 9-point smoothing pretreatment were 100% and 92.5%, respectively. The recognition rate values based on lower leaf surface spectra under the second-order derivative pretreatment were also 100% and 92.5%, respectively. Both upper and lower leaf surface spectra were available for recognition of HLB-infected leaves, and the HLB PCR-positive leaves could be distinguished from the healthy by the hyperspectral modeling analysis. The results of this study show that early and nondestructive detection of HLBinfected leaves without symptoms is possible, which provides a basis for the hyperspectral diagnosis of citrus with HLB.

Development of High Temperature Acoustic Emission Sensing System Using Fiber Bragg Grating

In some applications in structural health monitoring （SHM）, the acoustic emission （AE） detection technology is used in the high temperature environment. In this paper, a high-temperature-resistant AE sensing system is developed based on the fiber Bragg grating （FBG） sensor. A novel high temperature FBG AE sensor is designed With a high signal-to-noise ratio （SNR） compared with the traditional FBG AE sensor. The output responses of the designed sensors with different sensing fiber lengths also are investigated both theoretically and experimentally. Excellent AE detection results are obtained using the proposed FBG AE sensing system over a temperature range from 25℃ to 200℃. The experimental results indicate that this FBG AE sensing system can well meet the application requirement in AE detecting areas at high temperature.