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Author(s):  
Yi Luan ◽  
Hongfeng Yang ◽  
Baoshan Wang ◽  
Wei Yang ◽  
Weitao Wang ◽  
...  

Abstract Temporal changes of seismic velocities in the Earth’s crust can be induced by stress perturbations or material damage from reasons such as strong ground motion, volcanic activities, and atmospheric effects. However, monitoring the temporal changes remains challenging, because most of them generally exist in small travel-time differences of seismic data. Here, we present an excellent case of daily variations of the subsurface structure detected using a large-volume air-gun source array of one-month experiment in Binchuan, Yunnan, southwestern China. The seismic data were recorded by 12 stations within ∼10 km away from the source and used to detect velocity change in the crust using the deconvolution method and sliding window cross-correlation method, which can eliminate the “intercept” error when cutting the air-gun signals and get the real subsurface variations. Furthermore, the multichannel singular spectral analysis method is used to separate the daily change (∼1 cycle per day) from the “long-period” change (<1 cycle per day) or noise. The result suggests that the daily velocity changes at the two nearest stations, 53277 (offset ∼700 m) and 53278 (offset ∼2.3 km), are well correlated with air temperature variation with a time lag of 5.0 ± 1.5 hr, which reflects that the velocity variations at the subsurface are likely attributed to thermoelastic strain. In contrast, both daily and long-period velocity changes at distant stations correlate better with the varying air pressure than the temperature, indicating that the velocity variations at deeper depth are dominated by the elastic loading of air pressure. Our results demonstrate that the air-gun source is a powerful tool to detect the velocity variation of the shallow crust media.


Author(s):  
Robin Zatta ◽  
Daniel Headland ◽  
Eamal Ashna ◽  
Ritesh Jain ◽  
Philipp Hillger ◽  
...  

AbstractArrays of terahertz (THz) sources provide a pathway to overcoming the radiation power limitations of single sources. Several independent sources of THz radiation may be implemented in a single integrated circuit, thereby realizing a monolithic THz source array of high output power. Integrated THz sources must generally be backside-coupled to extended hemispherical dielectric lenses in order to suppress substrate modes and extract THz power. However, this lens also increases antenna gain and thereby produces several non-overlapping beams. This is because individual source pixels are relatively large. Hence, their spatial separation on-chip translates to angular separation in the far-field. In other words, there are gaps in their field of view into which very little THz power is projected. Therefore, they cannot homogeneously illuminate an imaging target. This article presents a simple, practical, and scalable method to convert arrays of incoherent THz sources into a diffuse, uniform illumination source without the need for reducing pixel size. Briefly, individual beam divergence is optimized by tailoring the dimensions of the extended hemispherical dielectric lens such that the far-field beams of adjacent source pixels overlap and combine to form a uniform far-field beam. We applied this method to an incoherent 8 × 8-pixel THz source array radiating 10.3 dBm at 0.42 THz as a proof of concept and thereby realized a 10.3-dBm 0.42-THz diffuse, uniform illumination source that was then deployed in a demonstration of THz active imaging.


2021 ◽  
Vol 40 (10) ◽  
pp. 759-767
Author(s):  
Rolf H. Baardman ◽  
Rob F. Hegge

Machine learning (ML) has proven its value in the seismic industry with successful implementations in areas of seismic interpretation such as fault and salt dome detection and velocity picking. The field of seismic processing research also is shifting toward ML applications in areas such as tomography, demultiple, and interpolation. Here, a supervised ML deblending algorithm is illustrated on a dispersed source array (DSA) data example in which both high- and low-frequency vibrators were deployed simultaneously. Training data pairs of blended and corresponding unblended data were constructed from conventional (unblended) data from another survey. From this training data, the method can automatically learn a deblending operator that is used to deblend for both the low- and the high-frequency vibrators of the DSA data. The results obtained on the DSA data are encouraging and show that the ML deblending method can offer a good performing, less user-intensive alternative to existing deblending methods.


2021 ◽  
Author(s):  
Minghao Yu ◽  
Xiangbo Gong ◽  
Zhuo Xu ◽  
Xiaojie Wan

2021 ◽  
pp. 110-129
Author(s):  
Volodymyr Drahan

Summary. Purpose of the study – on the basis of a significant source array and historiography, to outline the main well-known and little-known facts from the life and various activities of a prominent public and educational figure, publicist and writer – Stefan Kovaliv. The research methodology involves the use of general scientific principles of historicism, objectivity and systematicity. We used general scientific (analysis and synthesis), general (problem-chronological and periodization) and special-historical (historical-comparative and historical-genetic) methods. Theoretical and methodological principles of "intellectual history" and "intellectual biography" became the basis in the process of the research. The scientific novelty of the proposed article is manifested primarily in the fact that based on a multifaceted analysis of a significant source array, for the first time an attempt was made to cover a more comprehensive biographical portrait of Stefan Kovalіv with the introduction of little-known facts from his life and work. Conclusions. The materials presented in the article to the biographical portrait of Stefan Kovalіv, give every reason to say that his life and multifaceted activities have significantly influenced, and he left a diverse creative heritage and continues to affect the formation of socio-cultural development of different generations and segments of Ukrainian society. In addition, it is proved that during the last third of the XIX – early XX century, Stefan Kovalіv was an active driving force in the historical progress of the Galician region being a manysided personality.


Author(s):  
Kai Sun ◽  
Yongpin Chen ◽  
Sihao Liu ◽  
Yanwen Zhao ◽  
Deqiang Yang

2021 ◽  
Vol 186 (Supplement_1) ◽  
pp. 745-750
Author(s):  
Christina R Inscoe ◽  
Yueh Lee ◽  
Alex J Billingsley ◽  
Connor Puett ◽  
Daniel Nissman ◽  
...  

ABSTRACT Introduction Musculoskeletal injury to extremities is a common issue for both stateside and deployed military personnel, as well as the general public. Superposition of anatomy can make diagnosis difficult using standard clinical techniques. There is a need for increased diagnostic accuracy at the point-of-care for military personnel in both training and operational environments, as well as assessment during follow-up treatment to optimize care and expedite return to service. Orthopedic tomosynthesis is rapidly emerging as an alternative to digital radiography (DR), exhibiting an increase in sensitivity for some clinical tasks, including diagnosis and follow-up of fracture and arthritis. Commercially available digital tomosynthesis systems are large complex devices. A compact device for extremity tomosynthesis (TomoE) was previously demonstrated using carbon nanotube X-ray source array technology. The purpose of this study was to prepare and evaluate the prototype device for an Institutional Review Board-approved patient wrist imaging study and provide initial patient imaging results. Materials and Methods A benchtop device was constructed using a carbon nanotube X-ray source array and a flat panel digital detector. Twenty-one X-ray projection images of cadaveric specimens and human subjects were acquired at incident angles from −20 to +20 degrees in various clinical orientations, with entrance dose calibrated to commercial digital tomosynthesis wrist scans. The projection images were processed with an iterative reconstruction algorithm in 1 mm slices. Reconstruction slice images were evaluated by a radiologist for feature conspicuity and diagnostic accuracy. Results The TomoE image quality was found to provide more diagnostic information than DR, with reconstruction slices exhibiting delineation of joint space, visual conspicuity of trabecular bone, bone erosions, fractures, and clear depiction of normal anatomical features. The scan time was 15 seconds and the skin entrance dose was verified to be 0.2 mGy. Conclusions The TomoE device image quality has been evaluated using cadaveric specimens. Dose was calibrated for a patient imaging study. Initial patient images depict a high level of anatomical detail and an increase in diagnostic value compared to DR.


2020 ◽  
Author(s):  
Derrek Spronk ◽  
Yueting Luo ◽  
Christina R. Inscoe ◽  
Yueh Z. Lee ◽  
Jianping Lu ◽  
...  

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