Does Taking One Step Back Get You Two Steps Forward? Grade Retention and School Performance in Poor Areas in Rural China

Despite the rise in grade retention in poor areas in rural China recently, little work has been done to understand the impact of grade retention on the educational performance of students in these areas in rural China. This paper seeks to redress this shortcoming and examines the effect of grade retention on educational performance on 1649 students in 36 elementary schools in Shaanxi province. With a dataset that was collected from a survey designed specifically to capture school performance of students before and after they were retained, we use Differences-in-Differences, Propensity Score Matching and Differences-in-Differences Matching approaches to analyze the effect of grade retention on school performance. Although the descriptive analysis shows that grade retention helps to improve the scores of the students that were retained, somewhat surprisingly, the results from the multivariate analysis consistently show that there is no significant positive effect of grade retention on school performance of the students. In fact, in some cases (e.g., for the students who repeat grade 2), grade retention is shown to hurt school performance.

SPICE-Compatible Cavity and Transmission Line Model for Power Bus with Narrow Slots

Segmental lumped circuits are derived from coupled transmission line model for a narrow slot on the power bus. Both electric and magnetic coupling are taken into account by distributed inductances and capacitances. Then a SPICE- compatible circuit model for the power bus with the narrow slot is proposed. In this model, the segmental lumped circuits are connected to the equivalent circuit, which is derived by a hybrid cavity model and segmentation method for irregular power/ground planes. The model is validated by comparing with the calculations of finite element method (FEM) for the self or mutual impedances of the two port networks located in the power bus

Transfer Paths and Academic Performance: The Primary School Merger Program in China

In the late 1990s and early 2000s, China's Ministry of Education embarked on an ambitious program of elementary school mergers by shutting down small village schools and opening up larger centralized schools in towns and county seats. The goal of the program was to improve the teacher and building resources in an attempt to raise the human capital of students in poor rural areas, although it was recognized that students would lose the opportunity to learn in the settings of their own familiar villages. Because of the increased distances to the new centralized schools, the merger program also entailed building boarding facilities and encouraging or mandating that students live at school during the week away from their family. Given the magnitude of the program and the obvious mix of benefits and costs that such a program entails there has been surprisingly little effort to evaluate the impact of creating a new system that transfers students from school to school during their elementary school period of education and, in some cases, making student live in boarding facilities at school. In this paper, our overall goal is to examine the impact of the Rural Primary School Merger Program on academic perfirmance of students using a dataset from a survey that we designed to reflect transfer paths and boarding statuses of students. We use OLS and Propensity Score Matching approaches and demonstrate that there is a large 'resource effect' (that is, an effect that appears to be associated with the better facilities and higher quality of teachers in the town and county schools) that appears to be associated with the transfers of students from less centralized schools (such as, village schools) to more centralized schools. Boarding, however, is shown to have negative impacts on academic perfirmance. However, students who transfer to county school benefit from the transfer no matter where they start and whether they board or not

Differential Vias Transition Modeling in a Multilayer Printed Circuit Board

A 26-layer printed circuit board including several test sites has been analyzed. All the sites have a transition from coupled microstrips to coupled striplines through signal vias. Differential measurements have been performed on some of these test sites to estimate the effect on S-parameters and eye diagrams due to via and antipad radius variation, and different lengths of via stub. The focus of this paper is on a test site with a transition from top to the sixth layer. At the same time, a physics based circuit model has been assembled in a spice-based simulation tool and a full-wave model has been generated as well. The paper will show that the process of modeling can require a series of adjustments to get reasonable results. A brief discussion about possible issues associated with fabrication tolerances is presented in the last chapter

Analytical Evaluation of Via-Plate Capacitance for Multilayer Printed Circuit Boards and Packages

The via-plate capacitance for a via transition to a multilayer printed circuit board is evaluated analytically in terms of higher order parallel-plate modes. The Green\u27s function in a bounded coaxial cavity for a concentric magnetic ring current is first derived by introducing reflection coefficients for cylindrical waves at the inner and outer cavity walls. These walls can be perfect electric conductor (PEC)/perfect magnetic conductor(PMC) or a nonreflective perfectly matched layer. by further assuming a magnetic frill current on the via-hole in the metal plate, an analytical formula is derived for the via barrel-plate capacitance by summing the higher order modes in the bounded coaxial cavity. The convergence of the formula with the number of modes, as well as with the radius of the outer PEC/PMC wall is discussed. The analytical formula is validated by both quasi-static numerical methods and measurements. Furthermore, the formula allows the investigation of the frequency dependence of the via-plate capacitance, which is not possible with quasi-static methods

Numerical simulation of gas migration rules and comparison between U shape and U+L shape ventilation system

This paper offers an overview of numerical simulation with the aim of improving the knowledge and reference of coal mine gas distribution rule, and providing a case study of the optimization of ventilation system and environment protection. The numerical simulation experiments based on U shape ventilation system and U+L shape ventilation system are performed respectively. The results indicate that U+L shape ventilation system is more effective than its counterpart in terms of accelerating the gas flow, balancing the air pressure, and lowering the gas content of the upper corner. Besides, the field verification shows that the average gas content of tail airway, upper corner and air outlet have decreased from 1.86%, 0.79% and 0.58% (U shape ventilation system) to 1.68%, 0.75% and 0.55% (U+L shape ventilation system) respectively, and the average gas drainage rate of special drilling tunnel has increased from 43.4 m3·min-1 (U shape ventilation system) to approximately 51.8 m3·min-1 (U+L shape ventilation system).Postprint (published version

Noise Coupling Between Power/Ground Nets Due to Differential Vias Transitions in a Multilayer PCB

Due to the increase in board density, routing traces on different layers becomes a widely used strategy. Through-hole vias are often used to connect these traces. Those vias that penetrate power/ground plane pairs could cause noise coupling between signal and power/ground nets. At the same time, the need for clean signal transmitted to receivers results in a wide use of differential signals. This paper studies the noise coupling mechanism caused by a differential pair of vias penetrating power/ground plane pair using a physics-based via-plane model combined with transmission line models for traces. A 26-layer printed circuit board with a pair of differential vias have been modeled. The simulated results clearly demonstrate the impact of ground vias and via stubs on noise coupling