570 research outputs found

    Black shale lithofacies prediction and distribution Pattern analysis of middle Devonian Marcellus Shale in the Appalachian Basin, northeastern U.S.A.

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    The Marcellus Shale, marine organic-rich mudrock deposited during Middle Devonian in the Appalachian basin, is considered the largest unconventional shale-gas resource in United State. Although homogeneous in the appearance, the mudstone shows heterogeneity in mineral composition, organic matter richness, gas content, and fracture density. Two critical factors for unconventional mudstone reservoirs are units amenable to hydraulic fracture stimulation and rich of organic matter. The effectiveness of hydraulic fracture stimulation is influenced by rock geomechanical properties, which are related to rock mineralogy. The natural gas content in mudrock reservoirs has a strong relationship with organic matter, which is measured by total organic carbon (TOC). In place of using petrographic information and sedimentary structures, Marcellus Shale lithofacies were based on mineral composition and organic matter richness and were predicted by conventional logs to make the lithofacies \u27meaningful’, ‘predictable’ and ‘mappable’ at multiple scales from the well bore to basin. Core X-ray diffraction (XRD) and TOC data was used to classify Marcellus Shale into seven lithofacies according to three criteria: clay volume, the ratio of quartz to carbonate, and TOC. Pulsed neutron spectroscopy (PNS) logs provide similar mineral concentration and TOC content, and were used to classify shale lithofacies by the same three criteria. Artificial neural network (ANN) with improvements (i.e., learning algorithms, performance function and topology design) was utilized to predict Marcellus Shale lithofacies in 707 wells with conventional logs. To improve the effectiveness of wireline logs to predict lithofacies, the effects of barite and pyrite were partly removed and eight petrophysical parameters commonly used for a conventional reservoir analysis were derived from conventional logs by petrophysical analysis. These parameters were used as input to the ANN analysis. Geostatistical analysis was used to develop the experimental variogram models and vertical proportion of each lithofacies. Indictor kriging, truncated Gaussian simulation (TGS), and sequential indicator simulation (SIS) were compared, and SIS algorithm performed well for modeling Marcellus Shale lithofacies in three-dimensions. Controlled primarily by sediment dilution, organic matter productivity, and organic matter preservation/decomposition, Marcellus Shale lithofacies distribution was dominantly affected by the water depth and the distance to shoreline. The Marcellus Shale lithofacies with the greatest organic content and highest measure of brittleness is concentrated along a crescent shape region paralleling the inferred shelf and shoreline, showing shape of crescent paralleling with shoreline. The normalized average gas production rate from horizontal wells supported the proposed approach to modeling Marcellus Shale lithofacies. The proposed 3-D modeling approach may be helpful for (1) investigating the distribution of each lithofacies at a basin-scale; (2) developing a better understanding of the factors controlling the deposition and preservation of organic matter and the depositional model of marine organic-rich mudrock; (3) identifying organic-rich units and areas and brittle units and areas in shale-gas reservoirs; (4) assisting in the design of horizontal drilling trajectories and location of stimulation activity; and (5) providing input parameters for the simulation of gas flow and production in mudrock (e.g., porosity, permeability and fractures)

    Essays on the effects of parental education and private tutoring on children's education outcomes, and the rural-urban student achievement differential in China

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    This thesis includes three empirical chapters, which are self-contained but all related to education inequality in China. Chapter 2 aims to examine the causal effect (nurture effect) of parental education on children's education. Parents and their children share many common characteristics which are often unobserved -- this causes the omitted-variable bias. To eliminate this bias, this chapter uses school interruption during the Chinese Cultural Revolution (CR) as an instrument. The Chinese Cultural Revolution (1966-1976) significantly interrupted one generation's education, but has had no direct effect on the next generation. It naturally provides a valid instrument. The empirical results suggest that in urban China, an one year decrease in parent's schooling because of school interruption during the CR leads to a 0.27-0.38 year decrease in the child's schooling; if a parent did not obtain a university degree because of school interruption during the CR, the child is 35-53 percent less likely to obtain a university degree. The results also suggest that maternal education has a greater influence on children's education than paternal education. Overall, for the particular group whose parental education was changed by the CR, this chapter confirms a significant and sizable nurture effect. Chapter 3 estimates the causal effect of private tutoring on Chinese and mathematics test scores of primary school students in urban China. Because the unobserved determinants of schooling achievement often influence private tutoring expenditure, OLS cannot provide a consistent estimate. This chapter adopts a heteroskedasticity based identification strategy proposed by Lewbel (2012) to handle this problem. The estimation results show that, on average, private tutoring expenditure has a small but statistically significant effect on the mathematics test scores of primary school students, but has no statistically significant effect on the Chinese test scores. A 1000 yuan (about 55% of a standard deviation) increase in private tutoring expenditure raises the primary school students' mathematics test scores by 0.80-0.87 percentage point (about 11% of a standard deviation). The instrumental variable quantile regression combined with the Lewbel method suggests that private tutoring is more likely to improve student achievement at the bottom end of test score distribution. When moving upward to the top end, the effect becomes smaller and even negative, despite not being significant. Chapter 4 measures and analyzes the rural-urban schooling achievement gap in primary education in China. Using the RUMiC 2010 data, this chapter finds that the test scores of urban children are on average about 5.7 percentage points higher than that of rural children. This is approximately equivalent to 54-56% and 65-72% of the standard deviations of urban and rural children's test scores, respectively. The regression analysis and Oaxaca-Blinder decomposition analysis suggest that urban children outperform their rural counterparts mainly because of their better socio-economic background (e.g. parental education and family income per capita), better school quality and higher government budgetary spending on education per student in cities

    Rates of Return to University Education: the Regression Discontinuity Design

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    Estimating the rate of return to a university degree has always been difficult due to the problem of omitted variable biases. Benefiting from a special feature of the University Admission system in China, which has clear cutoffs for university entry, combined with a unique data set with information on individual National College Entrance Examination (NCEE) scores, we estimate the Local Average Treatment Effects (LATE) of university education based on a Regression Discontinuity design. To the best of our knowledge, this is the first study to use RD design to estimate the causal effect of a university education on earnings. Our results show that the rates of return to 4-year university education relative to 3-year college education are 40 and 60 per cent for the compliers in the male and female samples, respectively, which are much larger than the simple OLS estimations revealed in previous literature. Since in our sample a large proportion of individuals are compliers (45 per cent for males and 48 per cent for females), the LATEs estimated in this paper have a relatively general implication. In addition, we find that the LATEs are likely to be larger than ATEs, suggesting that the inference drawn from average treatment effects might understate the true effects of the university expansion program introduced in China in 1999 and thereafter.Rate of return to education, Regression Discontinuity Design, China

    Rates of Return to University Education: The Regression Discontinuity Design

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    Estimating the rate of return to a university degree has always been difficult due to the problem of omitted variable biases. Benefiting from a special feature of the University Admission system in China, which has clear cutoffs for university entry, combined with a unique data set with information on individual National College Entrance Examination (NCEE) scores, we estimate the Local Average Treatment Effects (LATE) of university education based on a Regression Discontinuity design. To the best of our knowledge, this is the first study to use RD design to estimate the causal effect of a university education on earnings. Our results show that the rates of return to 4-year university education relative to 3-year college education are 40 and 60 per cent for the compliers in the male and female samples, respectively, which are much larger than the simple OLS estimations revealed in previous literature. Since in our sample a large proportion of individuals are compliers (45 per cent for males and 48 per cent for females), the LATEs estimated in this paper have a relatively general implication. In addition, we find that the LATEs are likely to be larger than ATEs, suggesting that the inference drawn from average treatment effects might understate the true effects of the university expansion program introduced in China in 1999 and thereafter.rate of return to education, regression discontinuity design, China

    The Long Shadow of the Chinese Cultural Revolution: The Intergenerational Transmission of Education

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    Between 1966 and 1976, China experienced a Cultural Revolution (CR). During this period, the education of around 17 birth cohorts was interrupted by between 1 and 8 years. In this paper we examine whether, and by how much, this large-scale schooling interruption affected their children's education. We find a strong effect: more interrupted education for parents, less completed education for their children. On average the CR cohort had 2.9 years interrupted education. If they failed to catch up after the CR, this translates to a reduction of 0.87 years of schooling and a 9 percentage points (or 50%) reduction in the probability of completing a university degree for their children relative to the children whose parents did not have interrupted schooling. Our results have strong implications for developing countries prone to long-term conflicts which often adversely affect children's education. As human capital accumulation is one of the main drivers of economic development, these negative schooling shocks affecting current generation education levels will have an impact far beyond the immediate economic development of these war-torn economies and extend to the next generation

    Helmert Variance Component Estimation for Multi-GNSS Relative Positioning

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    The Multi-constellation Global Navigation Satellite System (Multi-GNSS) has become the standard implementation of high accuracy positioning and navigation applications. It is well known that the noise of code and phase measurements depend on GNSS constellation. Then, Helmert variance component estimation (HVCE) is usually used to adjust the contributions of di¿erent GNSS constellations by determining their individual variances of unit weight. However, HVCE requires a heavy computation load. In this study, the HVCE posterior weighting was employed to carry out a kinematic relative Multi-GNSS positioning experiment with six short-baselines from day of year (DoY) 171 to 200 in 2019. As a result, the HVCE posterior weighting strategy improved Multi-GNSS positioning accuracy by 20.5%, 15.7% and 13.2% ineast-north-up(ENU) components, compared to an elevation-dependent (ED) priori weighting strategy. We observed that the weight proportion of both code and phase observations for each GNSS constellation were consistent during the entire 30 days, which indicates that the weight proportions of both code and phase observations are stable over a long period of time. It was also found that the quality of a phase observation is almost equivalent in each baseline and GNSS constellation, whereas that of a code observation is different. In order to reduce the time consumption off the HVCE method without sacrificing positioning accuracy, the stable variances of unit weights of both phase and code observations obtained over 30 days were averaged and then frozen as a priori information in the positioning experiment. The result demonstrated similar ENU improvements of 20.0%, 14.1% and 11.1% with respect to the ED method but saving 88% of the computation time of the HCVE strategy. Our study concludes with the observations that the frozen variances of unit weight (FVUW) could be applied to the positioning experiment for the next 30 days, that is, from DoY 201 to 230 in 2019, improving the positioning ENU accuracy of the ED method by 18.1%, 13.2% and 10.6%, indicating the effectiveness of the FVUW.Peer ReviewedPostprint (published version

    Two sufficient conditions in frequency domain for Gabor frames

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    AbstractTwo sufficient conditions for the Gabor system to be a frame for L2(R) are presented in this note. The conditions proposed are stated in terms of the Fourier transforms of the Gabor system’s generating functions. It is also shown that these conditions are better than the known result

    A multiscale non-orthogonal model for tensile properties of uncoated and coated F-12 aramid fabric

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    Coated F-12 aramid fabric can be used as the balloon envelopes material because of the high strength and light weight performance. In this paper, a multiscale non-orthogonal material model was established to capture the tensile properties of F-12 fabric with and without polyethylene terephthalate-aluminum (PET-Al) coating. Off-axial monotonic tensile tests were carried out to validate the material model. The nonlinearity and anisotropic properties of the coated and uncoated fabrics were investigated. In this model, the stress was obtained based on the equilibrium equations and yarn constitutive model in mesoscale. The mesoscale configuration was observed through optical microscope and SEM. The material orientation was aligned with the yarn directions and the stress was updated in real time. The material model was implemented by user material subroutine in ABAQUS and simulate fabric off-axial tensile test. In addition, a theory model to calculate the elastic property of the fabric was also set up using the mesoscale deformation mechanism. The simulation results were compared with the test and theory results. Results suggest that simulation results were agree well with test results. The fabrics were nearly linearity in weft direction, while the stressstrain curve exhibited obvious nonlinearity in warp direction. The tensile modulus of the fabric showed orthotropic behaviour rather than the strength. The coating can affect the strength and failure model of F-12 fabric. Yarn slip was the mostly failure model in uncoated fabric while break in coated fabric. Research in this study provides certain reference in analysis and design for balloon envelops
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