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[en] Conceptual understanding is one of the main topics in science and physics education research. In the majority of conceptual understanding studies, students’ understanding levels were categorized dichotomously, either as alternative or scientific understanding. Although they are invaluable in many ways, namely developing new instructional materials and assessment instruments, students’ alternative understandings alone are not sufficient to describe students’ conceptual understanding in detail. This paper introduces an example of a study in which a method was developed to assess and describe students’ conceptual understanding beyond alternative and scientific understanding levels. In this study, six undergraduate students’ conceptual understanding levels of direct current electricity concepts were assessed and described in detail by using their answers to qualitative problems. In order to do this, conceptual understanding indicators are described based on science and mathematics education literature. The students’ understanding levels were analysed by assertion analysis based on the conceptual understanding indicators. The results indicated that the participants demonstrated three intermediate understanding levels in addition to alternative and scientific understanding. This paper presents the method and its application to direct current electricity concepts. (paper)
[en] Highlights: • The differences between charge and discharge was explored using dynamic EIS;. • At the same SOC, Rct during charge was usually smaller than that during discharge due to surface concentration change;. • The charge transfer resistance decreased with the charging/discharging current. - Abstract: The electrochemical impedance spectroscopy (EIS) of a lithium-ion battery is usually measured at open-circuit state under a constant state-of-charge (SOC). In this way, the differences between charge and discharge cannot be distinguished, because they both occur in one cycle of the alternating current. To explore the differences, in this study, we propose a new implementation method measuring the dynamic EIS (DEIS) of a LiMn2O4/Li half-cell (0.8 mAh) in the galvanostatic mode while the cell is under charging or discharging at a series of direct currents (DC). The results show the charge transfer resistance, Rct, decreases with the increased DC. Also, Rct during charging is usually smaller than that during discharging. The dependency of Rct on the DC can be explained according to the Butler-Volmer equation. The difference in Rct between charge and discharge, ΔRct, is ascribed to a significant surface concentration variation caused by the DC
[en] The main causes of residual activation currents in dc mean current ionisation chambers are briefly discussed. Theoretical and experimental aspects of fission product and wall activation effects are considered and performance data for a typical chamber derived. The likely ways in which this performance can be changed by modifications to the design are stated. (author)
[en] This paper presents a dual voltage-controlled-delay-line (VCDL) delay-lock-loop (DLL) based gate driver for a zero-voltage-switching (ZVS) DC-DC converter. Using the delay difference of two VCDLs for the dead time control, the dual VCDL DLL is able to implement ZVS control with high accuracy while keeping good linearity performance of the DLL and low power consumption. The design is implemented in the CSM 2P4M 0.35 μm CMOS process. The measurement results indicate that an efficiency improvement of 2%-4% is achieved over the load current range from 100 to 600 mA at 4 MHz switching frequency with 3.3 V input and 1.3 V output voltage.
[en] An electrotransport apparatus for purifying reactive metals is described. A large d.c. current (approximately 10 A/mm2) is applied to the specimen inside an ultra high vacuum chamber. This chamber is evacuated using an ion pump and a titanium sublimation pump. It is bakeable to 650K and is capable of maintaining a vacuum of 7 x 10-8 Pa. Resistivity ratio results from several preliminary runs in zirconium indicate a reduction in overall impurity level by 60 percent after a typical run at 1750K for approximately 120h