Numerical investigation of penetration performance of non-ideal segmented-rod projectiles

The design of a segmented-rod projectile is often simplified into an ideal one in theoretical analysis for the convenience of modeling of its performance. But the actual performance of non-ideal segmented-rod projectiles over the impact velocity range in practical applications was rarely explored. AUTODYN numerical code is used to investigate the influence of the component design upon the penetration performance of non-ideal segmented-rod projectiles over a wide range of impact velocities, which can be used to guide the optimal design of weaponry segmented-rod projectiles.     

New modeling approach of secondary control layer for autonomous single-phase microgrids

In a microgrid (MG) topology, the secondary control is introduced to compensate for the voltage amplitude and frequency deviations, mainly caused by the inherent characteristics of the droop control strategy. This paper proposes an accurate approach to derive small signal models of the frequency and amplitude voltage at the point of common coupling (PCC) of a single-phase MG by analyzing the dynamics of the second-order generalized integrator-based frequency-locked loop (SOGI-FLL). The frequency estimate model is then introduced in the frequency restoration control loop, while the derived model of the amplitude estimate is introduced for the voltage restoration loop. Based on the obtained models, the MG stability analysis and proposed controllers’ parameters tuning are carried out. Also, this study includes the modeling and design of the synchronization control loop that enables a seamless transition from island mode to grid-connected mode operation. Simulation and practical experiments of a hierarchical control scheme, including traditional droop control and the proposed secondary control for two single-phase parallel inverters, are implemented to confirm the effectiveness and the robustness of the proposal under different operating conditions. The obtained results validate the proposed modeling approach to provide the expected transient response and disturbance rejection in the MG.     

Principals' and teachers' attitudes and knowledge of inclusive education as predictors of effective teaching practices in Ghana

Surveys and observations were undertaken in selected primary schools in Ghana to determine whether principals' and teachers' attitudes towards and knowledge of inclusive education, as well as principals' expectations of teachers in implementing inclusion, were predictors of effective teaching practices in their classrooms. The sample of 128 educators (20 principals and 108 teachers) drawn from 20 primary schools in two districts, were required to respond to questionnaire measures of Attitude Towards Inclusive Education Scale (ATIES), Knowledge of Inclusive Education Scale (KIES) and Principals' Expectations Scale (PES). Of the total number of teachers ( N  = 108), 37 were observed during instructional delivery in their classrooms. The data were analysed by a variety of statistical procedures including Regression Analysis and Discriminant Function Analysis. In the context of the Theory of Planned Behaviour (Ajzen, 1985), the results showed that whilst attitudes towards inclusion (attitude element) and knowledge of inclusion (perceived behavioural control element) predicted effective teaching practices, principals' expectations (subjective norm) did not. Implications for the implementation of effective inclusive practices in Ghanaian schools and the need for future research are discussed.     

Parent and Student Voices on the First Year of the DC Opportunity Scholarship Program

In January 2004 President Bush authorized the DC School Choice Incentive Act, an initiative funded at $14 million that created a scholarship program providing 1,700 low-income Washington, DC, children the opportunity to attend participating K–12 nonpublic schools in the district. In addition to offering opportunities to participating children, the DC Opportunity Scholarship Program opens a door for examining the implications when more families are given the opportunity to select private schools for their children. This article reviews the results of a qualitative assessment aimed at understanding how families experienced their first year in the program. Referencing direct quotes from families that took part in focus groups, we address the following areas of participants' experience: reaction to the choice opportunity, motivation for participation, what was valued in schools, how information was received, selection of final school, reaction to new school environment, parent responses to new challenges, student–school responses to new challenges, financial policies, and overall satisfaction. Each section contains family responses juxtaposed with popular literature on school choice. This report is the first in a series that will monitor the experiences of families during the first 5 years of this program.