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Low energy consumption is one of the main challenges for wireless video transmission on battery limited devices. The energy invested at the lower layers of the protocol stack involved in data communication, such as link and physical layer, represent an important part of the total energy consumption. This communication energy highly depends on the channel conditions and on the transmission data rate. Traditionally, video coding is unaware of varying channel conditions. In this paper, we propose a cross-layer approach in which the rate control mechanism of the video codec becomes channel-aware and steers the instantaneous output rate according to the channel conditions to reduce the communication energy. Our results show that energy savings of up to 30% can be obtained with a reduction of barely 0.1 dB on the average video quality. The impact of feedback delays is shown to be small. In addition, this adaptive mechanism has low complexity, which makes it suitable for real-time applications. 相似文献
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Sofie Frederickx Francis Tuerlinckx Paul De Boeck David Magis 《Journal of Educational Measurement》2010,47(4):432-457
In this paper we present a new methodology for detecting differential item functioning (DIF). We introduce a DIF model, called the random item mixture (RIM), that is based on a Rasch model with random item difficulties (besides the common random person abilities). In addition, a mixture model is assumed for the item difficulties such that the items may belong to one of two classes: a DIF or a non-DIF class. The crucial difference between the DIF class and the non-DIF class is that the item difficulties in the DIF class may differ according to the observed person groups while they are equal across the person groups for the items from the non-DIF class. Statistical inference for the RIM is carried out in a Bayesian framework. The performance of the RIM is evaluated using a simulation study in which it is compared with traditional procedures, like the likelihood ratio test, the Mantel-Haenszel procedure and the standardized p -DIF procedure. In this comparison, the RIM performs better than the other methods. Finally, the usefulness of the model is also demonstrated on a real life data set. 相似文献
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The big-fish-little-pond effect (BFLPE) model predicts students’ academic self-concept to be negatively predicted by the achievement level of their reference group, controlling for individual achievement. Despite an abundance of empirical evidence supporting the BFLPE, there have been relatively few studies searching for possible moderators. Integrating the BFLPE model with Achievement Goal Theory, the present study aims to determine whether the negative effect of class-average achievement on academic self-concept is moderated by individual and class-average achievement goals. Our sample comprised of 2987 students (50% boys) from Grade 6 in 112 elementary schools in the Flemish region of Belgium (174 classes). Applying multilevel modelling, we found a stronger BFLPE when students’ individual achievement goals were higher, regardless of the specific nature of these goals. The BFLPE was not moderated by class-average levels of achievement goals. Overall, our findings demonstrate that the BFLPE is moderated by individual goal-related factors. 相似文献
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According to the big-fish-little-pond (BFLP) model, the self-concept is not only influenced in a positive way by one’s own achievement, but also in a negative way by one’s relative achievement in comparison with one’s immediate peers. This study investigates whether the BFLP effect also holds for second language acquisition. A random sample of 9167 Dutch-speaking students from Grade 8 took a reading comprehension test in French followed by a short background questionnaire in which they were asked for their self-concept of reading French. Multilevel regressions of the latter on individual and group achievement confirmed the BFLP effect but did not confirm an interaction of the effect with gender, individual achievement or class size. Moreover, in line with the local dominance hypothesis, it was shown that the negative effect of the average performance of peers is stronger for classmates than for schoolmates. 相似文献
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A straightforward way to prevent students from leaving education without a higher secondary diploma is increasing the compulsory education age. The idea is that, by staying longer in school, more students eventually obtain a higher secondary diploma. This paper examines the impact of a one-year increase in compulsory school-age on dropping out of secondary education by a difference-in-differences analysis. For this, we exploit a recent compulsory education policy reform in the Netherlands. After controlling for confounding factors and observable covariates, we find that the one year increase in compulsory school-age reduces dropout by 2.5 percentage points. The effect, however, is entirely situated in the group non-liable to the policy reform. We observe that native Dutch vocational students, mostly without retention in grade, but also without a higher secondary diploma at hand, more often left school in the immediate period before the policy reform. Given the economic revival at that time, this may reflect anticipation of labor market opportunities. 相似文献
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The present study investigated relationships between students’ conceptions of constructivist learning on the one hand, and their regulation and processing strategies on the other hand. Students in a constructivist, problem-based learning curriculum were questioned about their conceptions of knowledge construction and self-regulated learning, as well as their beliefs regarding their own (in)ability to learn and motivation to learn. Two hypothesized models were tested within 98 psychology students, using a structural equation modelling approach: The first model implemented regulation and processing variables of the Inventory of Learning Styles [ILS, Vermunt (Learning styles and regulation of learning in higher education – towards process-oriented instruction in autonomous thinking, 1992)], the second model of the Motivated Strategies for Learning Questionnaire [MSLQ, Pintrich and de Groot (Journal of Educational Psychology, 82, 33–40, 1990)]. Results showed that structural relations exist between conceptions of constructivist learning and regulation and processing strategies. Furthermore, students who express doubt with regard to their own learning capacities are at risk for adopting an inadequate regulation strategy. A three-tiered structure of conceptual, controlling, and operational level appeared valid for the MSLQ variables, but not entirely for those of the ILS. 相似文献
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