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891.
Hsin-Mei E. Huang 《International Journal of Science and Mathematics Education》2017,15(7):1323-1341
This study examined the effectiveness of 3 curriculum interventions focused on strengthening children’s ability to solve area measurement problems and explored the instructional perspectives of the instructor who implemented the interventions. The interventions involved various degrees of emphasis on area measurement and knowledge of 2-dimensional geometry. Participants were 131 fourth graders, recruited from a city in northern Taiwan, and 1 instructor. The results confirmed the effectiveness of an enriched curriculum integrating knowledge of 2-dimensional geometry in enhancing children’s conceptual understanding of area measurement. The group that received the enriched curriculum outperformed the other groups that received the curricula stressing only 2-dimensional geometry or numerical calculations for area measurement in solving the area problems requiring mathematical judgments and explanations. The curriculum also facilitated children’s reasoning in distinguishing between the perimeter and area of a rectangle, which required higher-order mathematical thinking. Interview data revealed that approximately all children from the 3 intervention groups could identify the mathematical subject-matter components highlighted in the curricula. Interviewees tended to consider the use of formulae to solve area measurement problems to be important, despite some differences in learning gains among the 3 groups. In interviews, the participating instructor revealed a change of perspective regarding the importance of offering students opportunities for manipulation and geometric operations when teaching area measurement, prompted by curriculum enactment. 相似文献
892.
S M Srivastava 《Resonance》2007,12(2):59-70
In 1931, the great Austrian mathematician Kurt Gödel proved “all consistent axiomatic formulations of number theory include undecidable propositions”. This discovery of Gödel and its proof had enormous repercussions in mathematics and computer science. The proof hinged upon the writing of a self-referential mathematical statement, in the same way as the liar’s paradox — I am lying — is a self-referential statement. In this three-part article, we describe Gödel’s discovery and his famous proof. 相似文献
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Andrew Post J. Michio Clark D. G. E. Robertson T. Blaine Hoshizaki Michael D. Gilchrist 《Sports Engineering》2017,20(2):111-119
Brain injury research in sport employs a variety of physical models equipped with accelerometers. These acceleration signals are commonly processed using filters. The purpose of this research was to determine the effect of applying filters with different cutoff frequencies to the acceleration signals used as input for finite element modeling of the brain. Signals were generated from reconstructions of concussion events from American football and ice hockey in the laboratory using a Hybrid III headform. The resulting acceleration signals were used as input for the University College Dublin Brain Trauma Model after being processed with filters. The results indicated that using a filter with a cutoff of 300 Hz or higher had little effect on the resulting strain measures. In some cases there was some effect of the filters on the peak linear (8–30g) and rotational measures (1000–4000 rad/s2), but little effect on the finite element strain result (approximately 2–6 %). The short duration and high magnitude accelerations, such as the puck impact, were most affected by the cutoff frequency of different filters. 相似文献
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Liquid or gaseous fuel scramjet technology has made great progress, and there has been some research attention to solid-fuel scramjet. A new scramjet configuration using solid fuel as propellant, namely solid-fuel rocket scramjet, is tested experimentally. It consists of two combustors. One is a rocket combustor used as gas generator, and the other is a supersonic combustor used for secondary combustion. The experiment simulates a flight Mach number of 4 at high altitude (stagnation temperature and pressure are 1170 K and 1.16 MPa, respectively), and metalized solid fuel is used as propellant. The results reveal that fuel-rich gas from the gas generator can burn with air in the supersonic combustor. Preliminary evaluation results show that the combustion efficiency of the propellant is about 90%, and the total pressure recovery coefficient in the supersonic combustor is about 0.6. These results indicate that the configuration of solid-fuel rocket scramjet is feasible. 相似文献
899.
The combustion performance of hydrogen fuel in a scramjet combustor has been a popular focus for scholars all over the world. In this study, the influence of the jet-to-crossflow pressure ratio on combustion performance in a scramjet combustor was investigated numerically, and the influence of a wall-mounted cavity was evaluated. The simulations were conducted using the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the renormalization group (RNG) k-ε turbulence model and the single-step chemical reaction mechanism. This numerical approach was validated by comparing predicted results with published experimental shadowgraphs and velocity and temperature measurements. When the pressure of the wall-injector increases, the performance of the combustor decreases. At the same inflow condition, this may lead to a scram-to-ram mode transition. The cavity adopted in this study would prevent pre-combustion shock waves from pushing out of the isolator and help to stabilize the flow field, but it would decrease the mixing and combustion efficiencies. 相似文献
900.
Eleni Morfidi Anastasios Mikropoulos Aspasia Rogdaki 《Education and Information Technologies》2018,23(1):271-286
The present study examined whether the use of concept mapping is more effective in teaching expository material in comparison to a traditional, lecture only, approach. Its objective was threefold. First, to determine if multimedia concept mapping produces differential learning outcomes compared to digital text-based concept mapping. Secondly, to compare the above experimental approaches to traditional teaching and finally to demonstrate if there are significant differences in the level of satisfaction reported by children under the three instructional approaches used. Thirty fifth grade children participated from which three groups of poor readers were formed, matched on age, gender and reading ability. The two experimental groups were taught with the use of digital text-based and multimedia concept maps respectively and the control group was subjected to the traditional teaching method of expository material. Each group had three sessions of instruction on three different expository texts. The results indicated that concept mapping can be an effective means for teaching expository content. However, there were no differential learning outcomes when adding multimedia elements to concept maps. Moderate satisfaction was reported for all three approaches. The findings coincide with the body of literature emphasizing the importance of concept mapping in the learning and instruction of children with reading difficulties. The study’s results inform potential educators on the use of multimedia with poor readers in elementary school. 相似文献