bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention and control of HPV infection and HPV-related cancers in Colombia- a meeting report
Authors: Vorsters Alex , Bosch Francesc Xavier , Bonanni Paolo , Franco Eduardo L. , Baay Marc , Simas Clarissa , Waheed Dur-e-Nayab , Castro Carlos , Murillo Raul , Trujillo Lina , Wiesner Carolina , Muñoz Nubia
Published: June 2020

The Human Papillomavirus (HPV) Prevention and Control Board is an independent multidisciplinary board of international experts that disseminates relevant information on HPV to a broad array of stakeholders and provides guidance on strategic, technical and policy issues in the implementation of HPV control programs. In response to drastic drop of vaccine coverage following the adverse event crisis in Carmen del Bolivar, Colombia, the HPV Prevention and Control Board in collaboration with the Colombian National Cancer Institute and Colombian League Against Cancer convened a meeting in Bogota, Columbia (November 2018). The goal of the meeting was to bring together national and international group of experts to report the disease burden, epidemiology and surveillance of HPV and HPV-related cancers, to discuss the successes and especially the challenges of HPV vaccination and screening in Colombia, as well as the lessons learnt from neighbouring countries. The meeting provided a platform to confer various stakeholder’s perspectives, including the role of the Colombian healthcare system and to catalyse various parts of the public health community in Colombia into effective action. The conclusion of the meeting included following suggestions to strengthen HPV prevention and control: 1) Re-introducing school-based vaccine programs, 2) Integrating primary and secondary prevention programs, 3) Developing an innovative crisis communication plan targeting healthcare workers, teachers and general population, 4) Building trust through efficient and timely communication, 5) Building strong relationship with media to ensure a stable vaccination campaign support, and 6) Promoting empathy among healthcare professionals towards patients to build trust and communicate effectively.
ALPPS versus two-stage hepatectomy for colorectal liver metastases—–a comparative retrospective cohort study
Authors: Bednarsch Jan , Czigany Zoltan , Sharmeen Samara , van der Kroft Gregory , Strnad Pavel , Ulmer Tom Florian , Isfort Peter , Bruners Philipp , Lurje Georg , Neumann Ulf Peter
Published: June 2020

Background

Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) and two stage hepatectomy with inter-stage portal vein embolization (TSH/PVE) are surgical maneuvers applied in patients with advanced malignancies considered unresectable by means of conventional liver surgery. The aim of this report is to compare the oncologic outcome and technical feasibility of ALPPS and TSH/PVE in the scenario of colorectal liver metastases (CRLM).

Methods

All consecutive patients who underwent either ALPPS or TSH/PVE for CRLM between 2011 and 2017 in one hepatobiliary center were analyzed and compared regarding perioperative and long-term oncologic outcome.

Results

A cohort of 58 patients who underwent ALPPS (n = 21) or TSH/PVE (n = 37) was analyzed. The median overall survival (OS) was 28 months and 34 months after ALPPS and TSH/PVE (p = 0.963), respectively. The median recurrence-free survival (RFS) was higher following ALPPS with 19 months than following TSH/PVE with 10 months, but marginally failed to achieve statistical significance (p = 0.05). There were no differences in morbidity and mortality after stages 1 and 2. Patients undergoing ALPPS due to insufficient hypertrophy after TSH/PVE (rescue-ALPPS) displayed similar oncologic outcome as patients treated by conventional ALPPS or TSH/PVE (p = 0.971).

Conclusions

ALPPS and TSH/PVE show excellent technical feasibility and comparable long-term oncologic outcome in CRLM. Rescue ALPPS appears to be a viable option for patients displaying insufficient hypertrophy after a TSH/PVE approach.
Development of the WHO Antenatal Care Recommendations Adaptation Toolkit: a standardised approach for countries
Authors: Barreix Maria , Lawrie Theresa A. , Kidula Nancy , Tall Fatim , Bucagu Maurice , Chahar Ram , Tunçalp Özge
Published: June 2020

Background

Increasingly, WHO recommendations are defined by context-specific factors and WHO is developing strategies to ensure that recommendations are successfully adapted and implemented at country level. This manuscript describes the development of a toolkit to support governments to adapt the WHO recommendations on antenatal care (ANC) for a positive pregnancy experience for their context in a systematic manner.

Methods

The toolkit was developed in three steps. It was created with input from methodologists and regional implementation experts (Step 1) followed by a user-testing phase (Step 2), implemented during country stakeholder meetings. User testing consisted of stakeholder interviews that were transcribed, and data was categorised according to the content analysis method. Suggestions for toolkit improvement and issues identified during the interviews were assessed as serious, moderately serious or minor/cosmetic.

Results

A total of 22 stakeholders – comprising five Ministry of Health (MoH) consultants, four MoH policy-makers, and 13 advisors/implementers – from Burkina Faso, India, Rwanda and Zambia participated in user-testing interviews during stakeholder meetings held in each country between August 2018 and February 2019. Most stakeholders had a medical or nursing background and half were women. Overall, responses to the toolkit were positive, with all stakeholders finding it useful and desirable. User testing interviews highlighted four serious, four moderately serious and five minor/cosmetic issues to be managed. These were addressed in the final step (Step 3), an updated version of the WHO ANC Recommendations Adaptation Toolkit, comprised of two main components – a baseline assessment tool with spreadsheets for data entry and a Slidedoc®, a dual-purpose document for reading and presentation, outlining the qualitative data that shaped the women-centred perspective of the guidelines, accompanied by an instruction manual detailing the components’ use.

Conclusions

The WHO ANC Recommendations Adaptation Toolkit was developed to support countries to systematically adapt the WHO ANC recommendations for country contexts. Using this approach, similar tools can be developed to support guideline implementation across different health domains and the continuum of care.
WT1 facilitates the self-renewal of leukemia-initiating cells through the upregulation of BCL2L2: WT1-BCL2L2 axis as a new acute myeloid leukemia therapy target
Authors: Zhou Bin , Jin Xianghong , Jin Weiwei , Huang Xingzhou , Wu Yanfei , Li Haiying , Zhu Weijian , Qin Xiaoyi , Ye Haige , Gao Shenmeng
Published: June 2020

Background

Overexpression of Wilms’ tumor-1 (WT1) transcription factor facilitates proliferation in acute myeloid leukemia (AML). However, whether WT1 is enriched in the leukemia-initiating cells (LICs) and leukemia stem cells (LSCs) and facilitates the self-renewal of LSCs remains poorly understood.

Methods

MLL-AF9-induced murine leukemia model was used to evaluate the effect of knockdown of wt1 on the self-renewal ability of LSC. RNA sequencing was performed on WT1-overexpressing cells to select WT1 targets. Apoptosis and colony formation assays were used to assess the anti-leukemic potential of a deubiquitinase inhibitor WP1130. Furthermore, NOD/SCID-IL2Rγ (NSG) AML xenotransplantation and MLL-AF9-induced murine leukemia models were used to evaluate the anti-leukemogenic potential of WP1130 in vivo.

Results

We found that wt1 is highly expressed in LICs and LSCs and facilitates the maintenance of leukemia in a murine MLL-AF9-induced model of AML. WT1 enhanced the self-renewal of LSC by increasing the expression of BCL2L2, a member of B cell lymphoma 2 (BCL2) family, by direct binding to its promoter region. Loss of WT1 impaired self-renewal ability in LSC and delayed the progression of leukemia. WP1130 was found to modify the WT1-BCL2L2 axis, and WP1130-induced anti-leukemic activity was mediated by ubiquitin proteasome-mediated destruction of WT1 protein. WP1130 induced apoptosis and decreased colony formation abilities of leukemia cells and prolonged the overall survival in the THP1-based xenograft NSG mouse model. WP1130 also decreased the frequency of LSC and prolonged the overall survival in MLL-AF9-induced murine leukemia model. Mechanistically, WP1130 induced the degradation of WT1 by positively affecting the ubiquitination of WT1 protein.

Conclusions

Our results indicate that WT1 is required for the development of AML. WP1130 exhibits anti-leukemic activity by inhibiting the WT1-BCL2L2 axis, which may represent a new acute myeloid leukemia therapy target.
Oscillation of solutions of third order nonlinear neutral differential equations
Authors: Sallam Ragaa A. , Salem Shaimaa , El-Sheikh Mohamed M. A.
Published: June 2020

The main objective of this article is to improve and complement some of the oscillation criteria published recently in the literature for third order differential equation of the form $$ \bigl( r(t) \bigl( z^{\prime \prime }(t) \bigr) ^{\alpha } \bigr) ^{\prime }+q(t)f \bigl(x \bigl(\sigma (t) \bigr) \bigr)=0,\quad t\geq t_{0}>0, $$(r(t)(z″(t))α)′+q(t)f(x(σ(t)))=0,t≥t0>0, where $z(t)=x(t)+p(t)x(\tau (t))$z(t)=x(t)+p(t)x(τ(t)) and α is a ratio of odd positive integers in the two cases $\int _{t_{0}}^{\infty }r^{\frac{-1}{\alpha } }(s)\,\mathrm {d}s<\infty $∫t0∞r−1α(s)ds<∞ and $\int _{t_{0}}^{\infty }r^{\frac{-1}{\alpha } }(s)\,\mathrm {d}s=\infty $∫t0∞r−1α(s)ds=∞. Some illustrative examples are presented.
Serum DHEA-S levels could be used as a comparable diagnostic test to assess the pubertal growth spurt in dentofacial orthopedics
Authors: Anusuya V. , Nagar Amit , Tandon Pradeep , Singh G. K. , Singh Gyan Prakash , Mahdi A. A.
Published: June 2020

Background

Pubertal growth spurt assessment guides the timing of intervention for correcting the skeletal discrepancies in dentofacial orthopedics. Serum hormones are being studied for the skeletal age assessment to avoid unnecessary radiographic exposure. The present study is to evaluate the relationship of serum hormones dehydroepiandrosterone-sulfate (DHEA-S), insulin-like growth factor (IGF-1), and cervical vertebral stages (CS stages) in the skeletal age assessment of orthodontics patients around the circumpubertal age.

Methods

A total of ninety subjects with age ranging from 7 to 21 years were selected and divided into two groups based on the sex (45 males, 45 females). They were further distributed in each group based on the six CS stages determined from the lateral cephalogram. Blood samples from each subject were collected to evaluate the serum DHEA-S and IGF-1 levels by using the enzyme-linked immunosorbent assay (ELISA). Collected data were analyzed in SPSS software with a test of normalcy, unpaired t test, and one-way analysis of variance (ANOVA) followed by the least significant difference (LSD) post hoc comparison test and univariate regression analysis.

Results

The highest mean serum hormone levels were found in CS 4 in group A (male) and CS 3 in group B (female). ANOVA results showed that there was a significant difference in the serum hormone levels among the different CS stages in both the groups for both the hormones. Statistically, a significant difference was found between each CS stages for both the hormones except in the DHEA-S levels between CS 5 and CS 6.

Conclusions

The mean serum DHEA-S levels followed a typical pattern from the CS 1 till CS 6 which was comparable and similar to the mean serum IGF-1 levels in respect to CS stages. Thus, serum DHEA-S levels could be used as a possible diagnostic test for the assessment of the skeletal pubertal growth spurt in dentofacial orthopedics.
The effect of an in-school versus after-school delivery on students’ social and motivational outcomes in a technology-based physical activity program
Authors: McDavid Lindley , Carleton Parker Loran , Li Weiling , Bessenbacher Ann , Randolph Anthony , Harriger Alka , Harriger Brad
Published: June 2020

Background

Expanding opportunities to experience engaging STEM educational programs is an important pathway to increasing students’ interest and competencies in STEM and, ultimately, motivation to pursue STEM careers. After-school programs offer one means to achieve this aim, but barriers such as a lack of transportation or available teachers may limit participation for some students in this context. Transitioning after-school STEM programs to in-school can provide opportunities to increase reach by removing these and other barriers. However, it is likely that this change in the learning context, from after-school to in-school, impacts student experiences and, ultimately, program efficacy by altering how students and teachers interact; as teachers and students adjust their behaviors and expectations to a more traditional learning context. To examine this potential effect, self-determination theory was used to frame how the learning context influences the social and motivational outcomes of a STEM program for underserved youth. In-school (N = 244; 39% girls, Mage = 13, 63% Caucasian, 18% African American, 6% Multiracial) and after-school (N = 70, 33% girls, Mage = 12, 55% Caucasian, 16% Multiracial, 13% Latino/a) program students completed surveys that assessed teacher-student interactions, and student psychological needs and motivation. In a structural equation model, student perceptions of teachers were entered as predictors of motivation for the program directly and mediated by psychological need satisfaction. Learning context (0 = in-school, 1 = after-school) was entered as a ubiquitous predictor.

Results

Findings support the theorized model where perceptions of teachers positively predicted psychological need satisfaction (R2 = .20), and both variables positively predicted more self-determined motivation (R2 = .30–.35). Findings also demonstrate an effect of learning context where learning context negatively predicted the less self-determined motivations only (R2 = .06–.10) (i.e., in-school contexts are associated with less desirable motivational outcomes).

Conclusion

Findings reinforce the instrumental role of students’ positive perceptions of teachers in fostering a more desirable self-determined motivation for STEM program participation. Additionally, in-school programs must consider and integrate novel approaches that mitigate the negative impact of established in-school structures and processes (e.g., grades and mandatory participation) on student motivation for these programs and, potentially, interest in STEM careers.
The association between weather and the number of daily shootings in Chicago (2012–2016)
Authors: Reeping Paul M. , Hemenway David
Published: June 2020

Background

Previous studies have linked weather to crime and aggression but have not considered the causal structure of the variables included in the model(s).

Methods

This cross-sectional study used data from 2012 to 2016 to measure the association between weather and the number of shootings in Chicago. The number of shootings per day was obtained via the Chicago Tribune (2012–2016). Daily high temperature, humidity, wind speed, difference in temperature from historical average, precipitation type and amount, were extracted via The Weather Underground. Weekend, holidays, and other non-school days were also included as possible effect measure modifiers. Causally-adjusted negative binomial regressions were used to evaluate the associations between the exposures of interest and daily number of shootings.

Results

A 10-degree (°C) higher temperature was significantly associated with 34% more shootings on weekdays, and 42% more shootings on weekends or holidays. A 10-degree higher temperature than average was also associated with 33.8% higher rate of shootings.

Conclusion

In recent years, shootings in Chicago were more likely to happen on warm days and especially during the weekend or holidays. This finding is in-line with studies that have linked crime to higher temperature and also suggests that shootings may be related to when individuals are outside and more likely to encounter violence. Interventions that keep people inside, such as air-conditioning and summer programs for students, might be effective in reducing the number of shootings in Chicago. We believe using a causal structure is useful for understanding the link between weather and shootings.
Practice parameters for the use of actigraphy in the military operational context: the Walter Reed Army Institute of Research Operational Research Kit-Actigraphy (WORK-A)
Authors: Devine Jaime K. , Choynowski Jake , Burke Tina , Carlsson Kajsa , Capaldi Vincent F. , McKeon Ashlee B. , Sowden Walter J.
Published: June 2020

Background

The Walter Reed Army Institute of Research (WRAIR) Operational Research Kit-Actigraphy (WORK-A) is a set of unique practice parameters and actigraphy-derived measures for the analysis of operational military sleep patterns. The WORK-A draws on best practices from the literature and comprises 15 additional descriptive variables. Here, we demonstrate the WORK-A with a sample of United States Army Reserve Officers’ Training Corps (ROTC) cadets (n = 286) during a month-long capstone pre-commissioning training exercise.

Methods

The sleep of ROTC cadets (n = 286) was measured by Philips Actiwatch devices during the 31-day training exercise. The preliminary effectiveness of the WORK-A was tested by comparing differences in sleep measures collected by Actiwatches as calculated by Philips Actiware software against WORK-A-determined sleep measures and self-report sleep collected from a subset of ROTC cadets (n = 140).

Results

Actiware sleep summary statistics were significantly different from WORK-A measures and self-report sleep (all P ≤ 0.001). Bedtimes and waketimes as determined by WORK-A major sleep intervals showed the best agreement with self-report bedtime (22:21 ± 1:30 vs. 22:13 ± 0:40, P = 0.21) and waketime (04:30 ± 2:17 vs. 04:31 ± 0:47, P = 0.68). Though still significantly different, the discrepancy was smaller between the WORK-A measure of time in bed (TIB) for major sleep intervals (352 ± 29 min) and self-report nightly sleep duration (337 ± 57 min, P = 0.006) than that between the WORK-A major TIB and Actiware TIB (177 ± 42, P ≤ 0.001).

Conclusions

Default actigraphy methods are not the most accurate methods for characterizing soldier sleep, but reliable methods for characterizing operational sleep patterns is a necessary first step in developing strategies to improve soldier readiness. The WORK-A addresses this knowledge gap by providing practice parameters and a robust variety of measures with which to profile sleep behavior in service members.
Intraprocedural guidance for recanalization of post-thrombotic venous lesions using live overlay of center lines from pre-operative cross-sectional imaging: a preliminary experience
Authors: Sundararajan Sri Hari , Doustaly Raphael , Avignon Gregoire , Madoff David C. , Winokur Ronald S.
Published: June 2020

Purpose

Pre-procedural contrast-enhanced CT and MRI imaging is typically acquired prior to deep venous recanalization procedures for post-thrombotic syndrome. This technical note reports the utility of live-overlay of augmented centerlines extracted from pre-procedural CT and MRI imaging in facilitating fluoroscopic-guided recanalization of post-thrombotic venous lesions.

Methods and materials

Six patients with pre-procedural CT or MR venography data were incorporated into a commercially available 3D overlay software (Vessel Assist, GE Healthcare, Buc, France) during venous disease interventions for post-thrombotic venous lesions. Procedures were performed on the GE Discovery IGS 740 fluoroscopy system. After manual determination of the vasculature from preprocedural CT or MR, centerlines were created representing the location and trajectory of the vessels. Steps showcasing the creation of centerlines and their representation during overlay with real-time fluoroscopic guidance in these cases are outlined. Time required to cross the post-thrombotic and occlusive venous segments were reviewed.

Results

All iliocaval recanalization procedures were successfully performed utilizing vessel centerline 3D overlay. In one case where occlusion extended to the femoral vein, mis-registration was identified over the femoral anatomy due to a complex leg rotation compared to pre-procedural imaging. No procedural complications related to utilization of software were noted. Average crossing time for occlusions was 3.4 min (range 1.6–5.2).

Conclusion

3D overlay with vessel tracking from pre-procedural CT and MRI imaging is technically feasible and assists in catheter navigation for post-thrombotic venous segments. While results from these preliminary experiences support the continued use of this technology, further prospective and comparative evaluation of this technique is warranted to assess for added value in technical success, reductions in procedure time or reductions in radiation exposure.
Novel opportunities for NGS-based one health surveillance of foodborne viruses
Authors: Desdouits Marion , de Graaf Miranda , Strubbia Sofia , Oude Munnink Bas B. , Kroneman Annelies , Le Guyader Françoise S. , Koopmans Marion P. G.
Published: June 2020

Foodborne viral infections rank among the top 5 causes of disease, with noroviruses and hepatitis A causing the greatest burden globally. Contamination of foods by infected food handlers or through environmental pollution are the main sources of foodborne illness, with a lesser role for consumption of products from infected animals. Viral partial genomic sequencing has been used for more than two decades to track foodborne outbreaks and whole genome or metagenomics next-generation-sequencing (NGS) are new additions to the toolbox of food microbiology laboratories. We discuss developments in the field of targeted and metagenomic NGS, with an emphasis on application in food virology, the challenges and possible solutions towards future routine application.
Spinal muscular atrophy in Venezuela: quantitative analysis of SMN1 and SMN2 genes
Authors: Yépez Yuri , Paradisi Irene , Arias Sergio
Published: June 2020

Background

Spinal muscular atrophy (SMA) is mostly caused by homozygous deletions in the survival motor neuron 1 (SMN1) gene. SMN2, its paralogous gene, is a genetic modifier of the disease phenotype, and its copy number is correlated with SMA severity. The purpose of the study was to investigate the number of copies of the SMN1 and SMN2 genes in a Venezuelan population control sample and in patients with a presumptive diagnosis of SMA, besides estimating the frequency of mutation carriers in the population.

Results

SMN1 and SMN2 gene copies were assessed in 49 Venezuelan dweller unrelated normal individuals and in 94 subjects from 29 families with a SMA presumptive diagnosis, using the quantitative PCR method. A SMN1 deletion carrier frequency of 0.01 and 0.163 of homozygous absence of the SMN2 gene were found in the Venezuelan control sample. Deletion of SMN1 exon 7 was confirmed in 15 families; the remaining 14 index cases had two SMN1 copies and a heterogeneous phenotype not attributable to SMN deletions. Based on clinical features of the index cases and the SMN2 copy number, a positive phenotype-genotype correlation was demonstrated. No disease geographical aggregation was found in the country.

Conclusion

The frequency of carriers of the deletion of exon 7 in SMN1 in the Venezuelan control population was similar to that observed in populations worldwide, while the frequency of 0 copies of the SMN2 gene (16.3 %) seems to be relatively high. All these findings have pertinent implications for the diagnosis and genetic counseling on SMA in Venezuela.
A statistics-based descriptor for automatic classification of scatterers in seismic sections
Authors: Maciel Susanne , Biloti Ricardo
Published: June 2020

Discontinuities and small structures induce diffractions on seismic or ground-penetrating radar (GPR) acquisitions. Therefore, diffraction images can be used as a tool to access valuable information concerning subsurface scattering features, such as pinch outs, fractures, and edges. Usually, diffraction-imaging methods operate on diffraction events previously detected. Pattern-recognition methods are efficient to detect, image, and characterize diffractions. The use of this kind of approach, though, requires a numerical description of image points on a seismic section or radargram. We have investigated a new descriptor for seismic/GPR data that distinguishes diffractions from reflections. The descriptor consists of a set of statistical measures from diffraction operators sensitive to kinematic and dynamic aspects of an event. We develop experiments in which the proposed descriptor was incorporated into a pattern-recognition routine for diffraction imaging. The obtained method is useful for performing the automatic classification of image points using supervised and unsupervised algorithms, as a complementary step to Kirchhoff imaging. We also develop a new type of filtering, designed to address anomalies on the diffraction operators caused by interfering events. We evaluate the method using synthetic seismic data and real GPR data. Our results indicate that the descriptor correctly discriminates diffractions and shows promising results for low signal-to-noise-ratio situations.
Time-domain induced polarization forward modeling and an apparent spectral parameter solution based on the Weibull growth model
Authors: Meng Qingxin , Hu Xiangyun , Pan Heping , Ma Huolin , Luo Miao
Published: June 2020

The application of the Cole-Cole model within time-domain induced polarization (TDIP) forward field modeling shows that the model parameters can characterize time-varying states of the TDIP field and support observed data analysis. The Cole-Cole model contains real and imaginary parts, and it requires a frequency-to-time conversion for TDIP forward modeling. However, the TDIP field is usually expressed by a real number, and its intuitive time-varying states field intensity increases with charging time. Therefore, the forward model should be constructed in a simpler form. We have aimed to develop a forward model using mathematical functions not based on physical principles. The Weibull (WB) growth model, which is primarily used to describe the time-varying curve features in regression analysis, is introduced into the basic algorithm of the TDIP forward model. Subsequently, a forward expression of the TDIP effect is established. Based on the time-varying shape and scale parameters, this expression describes the time-varying rate and relaxation states of the TDIP fields. Furthermore, based on the extensively used conjugate gradient optimization, an apparent WB parameter scheme is initiated to calculate the spectral parameters that represent the relaxation and time-varying rate obtained from the multi-time-channel TDIP data. Finally, this scheme is applied to interpret the different simulated and actual TDIP data. The results demonstrate that the WB growth model can be used for the TDIP forward model without involving physical principles, the model parameters without specific physical significance can be used to represent the time-varying states of TDIP fields, and apparent WB parameters can be used to discern different TDIP observed data. The setting of the TDIP forward model and model parameters can actually be more flexible and diverse, so as to obtain simpler forward expressions and ensure a highly efficient inverse solution.
On the seismic wavelet estimative and reflectivity recovering based on linear inversion: Well-to-seismic tie on a real data set from Viking Graben, North Sea
Authors: de Macedo Isadora A. S. , de Figueiredo José Jadsom S.
Published: June 2020

Tying seismic data to well data is critical in reservoir characterization. In general, the main factors controlling a successful seismic well tie are an accurate time-depth relationship and a coherent wavelet estimate. Wavelet estimation methods are divided into two major groups: statistical and deterministic. Deterministic methods are based on using the seismic trace and the well data to estimate the wavelet. Statistical methods use only the seismic trace and generally require assumptions about the wavelet’s phase or a random process reflectivity series. We have compared the estimation of the wavelet for seismic well tie purposes through least-squares minimization and zero-order quadratic regularization with the results obtained from homomorphic deconvolution. Both methods make no assumption regarding the wavelet’s phase or the reflectivity. The best-estimated wavelet is used as the input to sparse-spike deconvolution to recover the reflectivity near the well location. The results show that the wavelets estimated from both deconvolutions are similar, which builds our confidence in their accuracy. The reflectivity of the seismic section is recovered according to known stratigraphic markers (from gamma-ray logs) present in the real data set from the Viking Graben field, Norway.
3D inversion of magnetotelluric data by using a hybrid forward-modeling approach and mesh decoupling
Authors: Varılsüha Deniz
Published: June 2020

We have developed a new algorithm for the inversion of magnetotelluric (MT) data. The developed algorithm is built to be fast, versatile, and accurate. A fast inversion algorithm has to include a fast forward-modeling routine. To achieve that, a hybrid approach consisting of finite-difference (FD) and finite-element (FE) methods is used to benefit from the speed of the FD method and the flexibility to add topographic features of the FE method. To reduce the number of cells, and thus reducing the size of the system to be solved in the forward and pseudoforward solutions, different meshes for various groups of frequencies are used. Then, these are mapped onto the inversion mesh by a mesh-decoupling technique to further accelerate the inversion. To build a versatile inversion algorithm, the capability of using different data types is implemented. In addition to the impedance tensor and the magnetic transfer function, the algorithm also computes the phase tensor and phase vector, which are distortion-free forms of MT data. It is also possible to invert intersite data and their respective phase tensors using the developed code. Furthermore, the distortion matrix can also be estimated as a parameter. The new code is tested with different noisy and distorted synthetic data measured on a surface with topography to evaluate the inversion accuracy and computational efficiency. The results indicate that the code is accurate and that the runtimes are reasonable for the large 3D models considered. Using four graphics processing units, the hybrid forward-modeling approach and the mesh-decoupling technique together result in a 12 times speedup for the examples presented in this study.
Traveltime-table compression using artificial neural networks for Kirchhoff-migration processing of microseismic data
Authors: Grubas Serafim I. , Loginov Georgy N. , Duchkov Anton A.
Published: June 2020

Massive computation of seismic traveltimes is widely used in seismic processing, for example, for the Kirchhoff migration of seismic and microseismic data. Implementation of the Kirchhoff migration operators uses large precomputed traveltime tables (for all sources, receivers, and densely sampled imaging points). We have tested the idea of using artificial neural networks for approximating these traveltime tables. The neural network has to be trained for each velocity model, but then the whole traveltime table can be compressed by several orders of magnitude (up to six orders) to the size of less than 1 MB. This makes it convenient to store, share, and use such approximations for processing large data volumes. We evaluate some aspects of choosing neural-network architecture, training procedure, and optimal hyperparameters. On synthetic tests, we find a reasonably accurate approximation of traveltimes by neural networks for various velocity models. A final synthetic test shows that using the neural-network traveltime approximation results in good accuracy of microseismic event localization (within the grid step) in the 3D case.
A robust first-arrival picking workflow using convolutional and recurrent neural networks
Authors: Yuan Pengyu , Wang Shirui , Hu Wenyi , Wu Xuqing , Chen Jiefu , Van Nguyen Hien
Published: June 2020

A deep-learning-based workflow is proposed in this paper to solve the first-arrival picking problem for near-surface velocity model building. Traditional methods, such as the short-term average/long-term average method, perform poorly when the signal-to-noise ratio is low or near-surface geologic structures are complex. This challenging task is formulated as a segmentation problem accompanied by a novel postprocessing approach to identify pickings along the segmentation boundary. The workflow includes three parts: a deep U-net for segmentation, a recurrent neural network (RNN) for picking, and a weight adaptation approach to be generalized for new data sets. In particular, we have evaluated the importance of selecting a proper loss function for training the network. Instead of taking an end-to-end approach to solve the picking problem, we emphasize the performance gain obtained by using an RNN to optimize the picking. Finally, we adopt a simple transfer learning scheme and test its robustness via a weight adaptation approach to maintain the picking performance on new data sets. Our tests on synthetic data sets reveal the advantage of our workflow compared with existing deep-learning methods that focus only on segmentation performance. Our tests on field data sets illustrate that a good postprocessing picking step is essential for correcting the segmentation errors and that the overall workflow is efficient in minimizing human interventions for the first-arrival picking task.
A modified numerical-flux-based discontinuous Galerkin method for 2D wave propagations in isotropic and anisotropic media
Authors: He Xijun , Yang Dinghui , Ma Xiao , Qiu Chujun
Published: June 2020

We have developed a new discontinuous Galerkin (DG) method to solve the 2D seismic wave equations in isotropic and anisotropic media. This method uses a modified numerical flux that is based on a linear combination of the Godunov and the centered fluxes. A weighting factor is introduced in this modified numerical flux that is expected to be optimized to some extent. Through the investigations on the considerations of numerical stability, numerical dispersion, and dissipation errors, we develop a possible choice of optimal weighting factor. Several numerical experiments confirm the effectiveness of the proposed method. We evaluate a convergence test based on cosine wave propagation without the source term, which shows that the numerical errors in the modified flux-based DG method and the Godunov-flux-based method are quite similar. However, the improved computational efficiency of the modified flux over the Godunov flux can be demonstrated only at a small sampling rate. Then, we apply the proposed method to simulate the wavefields in acoustic, elastic, and anisotropic media. The numerical results show that the modified DG method produces small numerical dispersion and obtains results in good agreement with the reference solutions. Numerical wavefield simulations of the Marmousi model show that the proposed method also is suitable for the heterogeneous case.
A nonlinear solution to 3D seismic data conditioning using trained dictionaries
Authors: Yu Zhou , Johnston Rodney , Etgen John , Reitz Anya
Published: June 2020

Seismic analysis for reservoir characterization has been a primary focus for the geophysical community for decades. One of the critical steps in delivering high-quality processed seismic data for seismic analysis is to remove undesirable prestack seismic phenomena prior to amplitude variation with offset (AVO) analysis. Contrary to the conventional approach, which is mainly 2D gather-based and assumes flat events, we have developed a 3D nonlinear approach with a single principle: the 3D geologic structure should be invariant from offset to offset. Trained dictionaries, generated by 3D complex wavelet transformation over pilot volumes, are progressively constructed by stacking over selected offsets or angles. A sparse nonlinear approximation using the L0 norm is imposed on the data against the trained dictionaries after applying a 3D complex wavelet transform to the data. The final step is to apply an inverse 3D complex wavelet transform to the sparsified coefficients to return to the data space. This workflow is repeated for all offsets or angles. The workflow is automatic and requires minimal user input, resulting in a fast and efficient process. Multiple field data examples have demonstrated significant signal-to-noise ratio uplift, AVO and azimuthal AVO conservation, preservation of steeply dipping structural events, and multiple suppression. The processing time is significantly shorter compared with alternative conventional processes.
Wavefield decomposition in arbitrary direction and an imaging condition based on stratigraphic dip
Authors: Guo Xuebao , Shi Ying , Wang Weihong , Jing Hongliang , Zhang Zhen
Published: June 2020

In reverse time migration (RTM), wavefield decomposition can play an important role in addressing the issue of migration noise, especially low-frequency noise. The complete wavefield decomposition based on the Hilbert transform is a commonly used method in RTM, but it is accompanied by extra wavefield simulation and wavefield storage. We have developed three distinct methods. The first is a convenient method for wavefield decomposition, which is based on Poynting vectors. Only the unit vector in one direction is needed to realize the wavefield decomposition in an arbitrary direction by this method. It breaks through the limitation that the Hilbert transform-based method is applicable only to the up- and downgoing wave or left- and right-going wave decomposition, and the calculation cost is negligible compared with RTM. The second is a method based on the instantaneous wavenumber, which we developed for calculating the wave propagation direction. On the basis of wavefield decomposition, the imaging angle gather from the new method performs better than that of the Poynting vector method. Meanwhile, it also is used for generating the incident angle gather and dip angle gather. The latter expresses the dip angle of underground strata. More importantly, the above methods allow us to control the wavefield decomposition direction and three angles at any position underground. The third adopts a stratigraphic imaging condition method, and we briefly analyze the relationship between the new method and the inverse-scattering imaging condition. The stratigraphic imaging condition maps the results to the dip angle of the stratum through a spatial gradient wavefield, which can enhance the effective imaging information. The above three kinds of angle gathers also can be constructed by the stratigraphic imaging condition. Numerical experiments demonstrate that the imaging results and the angle gathers obtained by our proposed method have higher accuracy and resolution.
Elastic properties as indicators of heat flux into cold near-surface Arctic sediments
Authors: Stemland Helene Meling , Johansen Tor Arne , Ruud Bent Ole , Mavko Gary
Published: June 2020

Temperatures in the terrestrial Arctic today are increasing at the highest rate on earth, and heat flux into the cold sediments may result in extensive thawing. Thawing sediments lose their mechanical strength; therefore, warming has significant geomorphic consequences. We have combined heat flux, rock physics, and seismic modeling to estimate the change in elastic properties related to various published future climate scenarios in the Arctic, and we thus investigate the feasibility of exposing thawing rates from seismic data. The heat-flux model was validated using temperature data continuously recorded at the surface and within a well in Adventdalen, Svalbard. We estimated the evolving temperatures in an upper vertical section of the well using the heat-flux model, and we compared them with actual measured well temperatures. The modeled and measured data were consistent, even though our simplified model ignores heat transport due to fluid flow and the effects of clay. The heat-flux modeling resulted in subsurface isotherms that were input to rock-physics modeling based on two-end-member mixing of fully frozen and unfrozen composites to delineate possible climate effects on the seismic properties of the sediments. The results show that the elastic and seismic properties of (partly) frozen unconsolidated near-surface saline sediments strongly depend on heat flux into the subsurface, and they vary seasonally and between different climate scenarios. Seismic data obtained by full-waveform modeling and real experiments in Adventdalen show that time-lapse analysis of Rayleigh waves may be an efficient tool for monitoring heat flux into the terrestrial Arctic.
Locating passive sources on seismic reflection image in the presence of velocity errors
Authors: Liu Yujin , Ma Yue , Han Song , Luo Yi
Published: June 2020

Locating passive-source positions by using microseismic events is essential for monitoring hydraulic fractures. Among all microseismic source locating approaches, time-reversal imaging (TRI) is a promising one that is based on the principle that all of the back-propagated receiver wavefields should coincide at the source position when the velocity is accurate. It can image microseismic sources by applying a focusing imaging condition to the reconstructed receiver wavefields. However, the TRI method is highly sensitive to velocity errors and it is time-consuming or even challenging to refine the velocity model when the subsurface structure is complex. Instead of updating the velocity model, we have adopted a new method to locate microseismic events on a seismic reflection image under the condition that the seismic data are colocated with surface or near-surface microseismic observations. This method does not correctly place the microseismic events in depth; rather, it makes them consistent with the seismic reflection image; thus, it is still capable of providing correct local structure information around the passive source without the need of building an accurate velocity model. We have theoretically analyzed the variation of the imaged source location when the velocity model is inaccurate. Our result shows that faster velocities cause shallower depths whereas slower velocities cause deeper depths of source locations on the image. This is similar to the behavior of the focusing depth, but it is opposite to that of the migration depth in active-source seismic reflection imaging. Then, we match the locations of microseismic events with the well-focused seismic reflection image, which is extracted by slicing the time-shift common-image gathers at the time lag where the image has the maximal energy. Finally, synthetic tests validate the effectiveness of the proposed approach.
Delaying the source ghost to improve the ultralow-frequency response of a marine air-gun source
Authors: Shen Honglei , Elboth Thomas , Tao Chunhui , Tian Gang , Wang Hanchuang , Zhang Guoyin
Published: June 2020

The competing effect between the fundamental bubble and its source-ghost response results in a strong attenuation of the lowest frequencies (below 7 Hz). This loss cannot be compensated easily by adjusting the source depth. Consequently, the low-frequency content in marine seismic data is not optimal, degrading the performance of low-frequency dependent processing approaches, such as full-waveform inversion. To overcome this, we have developed an additional source to counteract the ghost from the main source. In this situation, the fundamental bubble is characterized by the depth of the main source, whereas the ghost response is characterized by the summed depth of the main and additional sources. This source setup mitigates the competing effect and reduces the suppression of ultralow frequencies. Compared with a conventional horizontal source, our source design will reduce the mid- to high-frequency output, which may be beneficial in situations in which environmental constraints limit the maximum allowed output of a marine source.
P-wave velocity profile at very shallow depths in sand dunes
Authors: Hanafy Sherif M. , El-Husseiny Ammar , Benaafi Mohammed , Al-Shuhail Abdullatif , Dvorkin Jack
Published: June 2020

We have addressed the problem of measuring the compressional wave velocity at a very shallow depth in unconsolidated dune sand. Because the overburden stress is very small at shallow depths, the respective velocity is small and the seismic signal is weak. This is why such data are scarce, in the lab and in the field. Our approach is to stage a high-resolution seismic experiment with a dense geophone line with spacing varying between 10 and 25 cm, allowing us to produce a velocity-depth relation in the upper 1 m interval. These results are combined with another survey in which the geophone spacing is 2 m and the dominant frequency is an order of magnitude lower than in the first survey. The latter results give us the velocity profile in the deeper interval between 1 and 7 m, down to the base of the dune. The velocity rapidly increases from about 48 m/s in the first few centimeters to 231 m/s at 1 m depth and then gradually increases to 425 m/s at 7 m depth. This is the first time when such a low velocity has been recorded at extremely shallow depths in sand in situ. The velocity profile thus generated is statistically fitted with a simple analytical equation. Our velocity values are higher than those published previously for beach sand. We find that using replacement or tomogram velocities instead of an accurately measured velocity profile may result in 23%–44% error in the static correction.
Least-squares diffraction imaging using shaping regularization by anisotropic smoothing
Authors: Merzlikin Dmitrii , Fomel Sergey , Wu Xinming
Published: June 2020

We have used least-squares migration to emphasize edge diffractions. The inverted forward-modeling operator is the chain of three operators: Kirchhoff modeling, azimuthal plane-wave destruction, and the path-summation integral filter. Azimuthal plane-wave destruction removes reflected energy without damaging edge-diffraction signatures. The path-summation integral guides the inversion toward probable diffraction locations. We combine sparsity constraints and anisotropic smoothing in the form of shaping regularization to highlight edge diffractions. Anisotropic smoothing enforces continuity along edges. Sparsity constraints emphasize diffractions perpendicular to edges and have a denoising effect. Synthetic and field data examples illustrate the effectiveness of the proposed approach in denoising and highlighting edge diffractions, such as channel edges and faults.
Robust vector median filtering with a structure-adaptive implementation
Authors: Wang Yanghua , Liu Xiwu , Gao Fengxia , Rao Ying
Published: June 2020

The 3D seismic data in the prestack domain are contaminated by impulse noise. We have adopted a robust vector median filter (VMF) for attenuating the impulse noise from 3D seismic data cubes. The proposed filter has two attractive features. First, it is robust; the vector median that is the output of the filter not only has a minimum distance to all input data vectors, but it also has a high similarity to the original data vector. Second, it is structure adaptive; the filter is implemented following the local structure of coherent seismic events. The application of the robust and structure-adaptive VMF is demonstrated using an example data set acquired from an area with strong sedimentary rhythmites composed of steep-dipping thin layers. This robust filter significantly improves the signal-to-noise ratio of seismic data while preserving any discontinuity of reflections and maintaining the fidelity of amplitudes, which will facilitate the reservoir characterization that follows.