When a tunnel boring machine (TBM) is applied to the tunnel constructed in the mixed-face ground, the ground conditions ahead of tunnel face have a key impact on the operation performance and safety. ...Aiming to establish an automatic prediction model for geological conditions based on the operational data of TBM, the first step is to conduct clustering analysis using Canopy and K-means algorithms to recognize ground types based on geological data. Then, the ground type obtained by clustering analysis and corresponding operational parameters of tunneling machine are combined to construct a sample set. The outlier detection and synthetic minority oversampling technique (SMOTE) were used to preprocess the sample set. To obtain the best prediction effect, three different classifiers were applied for the model selection. By comparing the prediction performance of these three classifiers models, the gradient boosting decision tree (GBDT) model with accuracy of 0.804 shows the best performance as the geological prediction model. The test results of the prediction model show a low sensitivity when training set is small (set as 20%). The analysis of the importance of the model inputs showed that among the six machine parameters used in this study, the total thrust force, penetration rate and ratio of thrust to torque, are the three most influential inputs on the ground condition prediction results. Hence, the proposed prediction procedure can be applied to characterized and predicted ground conditions to ensure the safety and efficiency of tunneling.
Highlights
Clustering algorithms are used to distinguish the geological types of tunneling faces.
A GBDT-based recognize model for geological conditions in TBMs tunneling process is developed.
The proposed model is examined by different sizes of training sets for testing sensibility.
The importance analysis of TBM operational parameters is conducted.
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As a common phenomenon in landslides, entrainment of loose bed material along the sliding path can enhance both the volume and mobility of the sliding mass, posing a great threat to the life and ...property safety of people in the affected area. For the purpose of revealing the mechanism of entrainment phenomenon of sliding material in the runout process, a dynamic slice-based model was firstly proposed in the present study. In this model, the motion of landslide body is assumed to follow the rheological law proposed by Voellmy. Additionally, through Voellmy model, the increase in kinetic energy, mass and volume of landslide body and entrainment depth caused by the entrainment phenomenon were taken into consideration. Subsequently, on the basis of the dynamic slice-based model, back-analyses were performed on the Wenjia gully landslide. The effect of entrainment phenomenon on the post-failure motion was analyzed. The calculated results shows that the travel distance obtained from proposed model is closer to field data than that resulted from Scheidegger’s empirical method. Moreover, the peak value of the maximum velocity calculated by this model is in good agreement with that get from the dynamic analysis model (DAN3D). When considering the entrainment phenomenon, the volume of sliding mass increases greatly in post-failure motion. This paper provides a new method for analyzing the entrainment phenomenon in landslide motion.
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Due to the voluntary nature of open source software, it can be hard to find a developer to work on a particular task. For example, some issue reports may be too cumbersome and unexciting for someone ...to volunteer to do them, yet these issue reports may be of high priority to the success of a project. To provide an incentive for implementing such issue reports, one can propose a monetary reward, i.e., a bounty, to the developer who completes that particular task. In this paper, we study bounties in open source projects on GitHub to better understand how bounties can be leveraged to evolve such projects in terms of addressing issue reports. We investigated 5,445 bounties for GitHub projects. These bounties were proposed through the Bountysource platform with a total bounty value of 406,425. We find that 1) in general, the timing of proposing bounties is the most important factor that is associated with the likelihood of an issue being addressed. More specifically, issue reports are more likely to be addressed if they are for projects in which bounties are used more frequently and if they are proposed earlier. 2) The bounty value of an issue report is the most important factor that is associated with the issue-addressing likelihood in the projects in which no bounties were used before. 3) There is a risk of wasting money for backers who invest money on long-standing issue reports.
CrSBr is a recently discovered two-dimensional anti-ferromagnet. It has attracted much attention due to its superior properties for potential optoelectronic and spintronic applications. However, its ...complex refractive index with layer dependence has not been systematically studied yet. In this work, we studied the room-temperature complex refractive indices of thin CrSBr flakes of different thicknesses in the visible light range. Using micro-reflectance spectroscopy, we measured the optical contrast of thin CrSBr flakes with respect to different substrates. The complex refractive index was extracted by modeling the optical contrast with the Fresnel equations. We extracted the band gap values of CrSBr in the few-layer limit. We determined the band gaps for monolayer, bilayer, and trilayer CrSBr to be 1.88 eV, 1.81 eV, and 1.77 eV, respectively. As a comparison, the band gap for multilayer CrSBr is outside our measured range, that is, below 1.55 eV. Our results suggest that the band gap of CrSBr decreases as thickness increases.
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Technical question and answer (Q&A) websites provide a platform for developers to communicate with each other by asking and answering questions. Stack Overflow is the most prominent of such websites. ...With the rapidly increasing number of questions on Stack Overflow, it is becoming difficult to get an answer to all questions and as a result, millions of questions on Stack Overflow remain unsolved. In an attempt to improve the visibility of unsolved questions, Stack Overflow introduced a bounty system to motivate users to solve such questions. In this bounty system, users can offer reputation points in an effort to encourage users to answer their question. In this paper, we study 129,202 bounty questions that were proposed by 61,824 bounty backers. We observe that bounty questions have a higher solving-likelihood than non-bounty questions. This is particularly true for long-standing unsolved questions. For example, questions that were unsolved for 100 days for which a bounty is proposed are more likely to be solved (55%) than those without bounties (1.7%). In addition, we studied the factors that are important for the solving-likelihood and solving-time of a bounty question. We found that: (1) Questions are likely to attract more traffic after receiving a bounty than non-bounty questions. (2) Bounties work particularly well in very large communities with a relatively low question solving-likelihood. (3) High-valued bounties are associated with a higher solving-likelihood, but we did not observe a likelihood for expedited solutions. Our study shows that while bounties are not a silver bullet for getting a question solved, they are associated with a higher solving-likelihood of a question in most cases. As questions that are still unsolved after two days hardly receive any traffic, we recommend that Stack Overflow users propose a bounty as soon as possible after those two days for the bounty to have the highest impact.
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The fetal growth charts in widest use in China were published by Hadlock >35 years ago and were established on data from several hundred of American pregnant women. After that, >100 fetal growth ...charts were published around the world. We attempted to assess the impact of applying the long-standing Hadlock charts and other charts in a Chinese population and to compare their ability to predict newborn small for gestational age (SGA).
For this retrospective observational study, we reviewed all pregnant women ( n = 106,455) who booked prenatal care with ultrasound measurements for fetal biometry at the Shenzhen Maternity and Child Healthcare Hospital between 2012 and 2019. A fractional polynomial regression model was applied to generate Shenzhen fetal growth chart ranges for head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL). The differences between Shenzhen charts and published charts were quantified by calculating the Z -score. The impact of applying these published charts was quantified by calculating the proportions of fetuses with biometric measurements below the 3rd centile of these charts. The sensitivity and area under the receiver operating characteristic curves of published charts to predict neonatal SGA (birthweight <10th centile) were assessed.
Following selection, 169,980 scans of fetal biometry contributed by 41,032 pregnancies with reliable gestational age were analyzed. When using Hadlock references (<3rd centile), the proportions of small heads and short femurs were as high as 8.9% and 6.6% in late gestation, respectively. The INTERGROWTH-21st standards matched those of our observed curves better than other charts, in particular for fat-free biometry (HC and FL). When using AC<10th centile, all of these references were poor at predicting neonatal SGA.
Applying long-standing Hadlock references could misclassify a large proportion of fetuses as SGA. INTERGROWTH-21st standard appears to be a safe option in China. For fat-based biometry, AC, a reference based on the Chinese population is needed. In addition, when applying published charts, particular care should be taken due to the discrepancy of measurement methods.
Operating an open source project requires not only intrinsic motivation (e.g., the joy of participation) but also extrinsic motivation (e.g., financial incentives). Almost 95% of open source projects ...are no longer maintained after a year. Nowadays, although donations start to play an important role in operating open source projects, there is little knowledge about the characteristics of donors and the usage of donations. A better understanding of the characteristics of donations, their donors, and the usage of donations in open source projects is needed to provide insights to the stakeholders of open source projects to help them operate their projects more sustainably. In this paper, we study the donations that are received through the Open Collective platform (i.e., an online crowdfunding platform) to support open source projects, to understand the characteristics of these donations, their donors, and the usage of these donations. To do so, we investigate 225 GitHub open source projects that received 54,889 donations with a total value of $2,537,281 through the Open Collective platform. We find that: 1) In general, corporate donors tend to donate more money than individual donors in a single donation. However, in a collective, the total donation amount from individual donors is more than corporate donors, suggesting the importance of individual donors. Moreover, individual donors are more likely to redonate to the same collective compared to corporate donors. 2) Non-engineering-related expenses take up to 54.0% of the total number of all expenses that are filtered against donation. For instance, “Web services”, “marketing”, and “travel” expenses are the three most frequent and costly non-engineering-related expense types. For engineering-related expenses, the most frequent expenses are related to development and maintenance. Interestingly, we also observe that 18% of the engineering expenses were spent to propose bounties for addressing issues with a median cost of $95 per proposed bounty. We further analyze the differences between individual-supported collectives (i.e., collectives where more than 80% of their donation amount is from individual donors) and corporate-supported collectives (i.e., collectives where more than 80% of their donation amount is from corporate donors). We observe that corporate-supported collectives tend to receive a higher donation amount than individual-supported collectives and the monthly received donation amounts are positively associated with the levels of community and maintenance activities in corporate-supported collectives. They have no significant difference in terms of popularity (e.g., the number of pull requests) of their associated GitHub projects. Our findings suggest that the stakeholders of GitHub open source projects should try to attract more individual donors. Collectives should not expect to receive a large amount of funds overall from donations unless their projects are very popular or are mainly supported by corporations. Projects should budget for a reasonable amount (e.g., 13% of total funds) of non-engineering expenses (e.g., marketing and traveling).
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Issue addressing is a vital task in the evolution of software projects. However, in practice, not all issues can be addressed on time. To facilitate the issue addressing process, monetary incentives ...(e.g., bounties) are used to attract developers to address issues. There are two types of core roles who are involved in this process:
bounty backers
, who propose bounties for an issue report via bounty platforms (e.g., Bountysource), and
bounty hunters
, who address the bounty issues and win the bounties. We wish to study the process of bounty issue addressing from the angle of two important roles (i.e., backers and hunters) and their related behaviors. With a better understanding of how they address bounty issues, stakeholders (e.g., operators and developers) of open source projects may have a reasonable estimation of what they can expect from backers and hunters. In this study, we investigate 2,955 bounty backers and 882 bounty hunters, and their associated 3,579 GitHub issue reports with 5,589 bounties that were proposed on Bountysource. We find that: 1) Overall, the value of a bounty is small (median bounty value of $20). Both individual and corporate backers prefer to support implementing new features rather than fixing bugs. Corporate backers tend to propose larger bounties and propose bounties more frequently than individual backers. 2) 85.0% of the bounty hunters addressed less than 3 bounty issues. The income of 56.7% of the bounty hunters is no more than $100 and only 2.7% of the hunters have earned more than $2,000. In addition, most of the regular hunters and big hunters are developers that made at least one commit before addressing a bounty issue. 3) The value of a bounty issue is not a statistically significant factor that attracts developers that have never made any commit before to address an issue. Based on our findings, we provide several suggestions for stakeholders of open source projects and hunters.
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As reported, 27-93 % of pregnant women take at least one drug during pregnancy. However, drug exposure during pregnancy still lacks sufficient foetal safety evidence of human origin. It is urgent to ...fill the knowledge gap about medication safety during pregnancy for optimization of maternal disease treatment and pregnancy drug consultation.
The China Teratology Birth Cohort (CTBC) was established in 2019 and is a hospital-based open-ended prospective cohort study with the aim of assessing drug safety during pregnancy. Pregnant women who set up the pregnancy health records in the first trimester or who seek drug consultation regardless of gestational age in the member hospitals are recruited. Enrolled pregnant women need to be investigated four times, namely, 6-14 and 24-28 weeks of gestational age, before discharge after hospital delivery, and 28-42 days after birth. Maternal medication exposure during pregnancy is the focus of the CTBC. For drugs, information on the type, name, and route of medication; start and end time of medication; single dose; frequency of medication; dosage form; manufacturer; and reason for medication is collected. The adverse pregnancy outcomes collected in the study include birth defects, stillbirth, spontaneous abortion, preterm birth, post-term birth, low birth weight, macrosomia, small for gestational age, large for gestational age and low Apgar score. CTBC uses an electronic questionnaire for data collection and a cloud system for data management. Biological samples are collected if informed consents are obtained. Multi-level logistic regression, mixed-effect negative binomial distribution regression and spline function regression are used to explore the effect of drugs on the occurrence of birth defects.
The findings of the study will assist in further understanding the risk of birth defects and other adverse pregnancy outcomes associated with maternal drug exposure and developing the optimal treatment plans and drug counselling for pregnant women.
This study was approved by the Research Ethics Committee of the West China Second Hospital of Sichuan University and registered at the Chinese Clinical Trial Registry ( http://www.chictr.org.cn/index.aspx , registration number ChiCTR1900022569 ).
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