Exploring mathematical connections of pre-university students through tasks involving rates of change

This paper reports the results of a research exploring the mathematical connections of pre-university students while they solving tasks which involving rates of change. We assume mathematical connections as a cognitive process through which a person finds real relationships between two or more ideas, concepts, definitions, theorems, procedures, representations or meanings or with other disciplines or the real-world. Four tasks were proposed to the 33 pre-university students that participated in this research; the central concept of the first task is the slope, the last three tasks contain concepts like velocity, speed and acceleration. Task-based interviews were conducted to collect data and later analysed with thematic analysis. Results showed most of the students made mathematical connections of the procedural type, the mathematical connections of the common features type are made in smaller quantities and the mathematical connection of the generalization type is scarcely made. Furthermore, students considered slope as a concept disconnected from velocity, speed and acceleration.     

Gate-induced drain leakage (GIDL) in MFMIS and MFIS negative capacitance FinFETs

The gate induced drain leakage (GIDL) effect in negative capacitance (NC) FinFET is investigated. A Landau–Ginzburg–Devonshire equation (which considers the polarization gradient in ferroelectric material) is used to estimate the characteristics of the NC FinFET. Specifically, metal-ferroelectric-metal-insulator-semiconductor (MFMIS) and metal-ferroelectric-insulator-semiconductor (MFIS) NC FinFETs are compared, in order to figure out the effect of the internal metal layer on the GIDL effect. To analyze the impact of the polarization gradient on the GIDL effect in NC FinFET, a polarization gradient coefficient is varied. For MFMIS, the polarization gradient doesn't significantly affect the device performance. The subthreshold swing improves but the GIDL effect deteriorates because of the “uniform” NC effect in channel region. For MFIS, the device performance is explicitly affected by the polarization gradient. Smaller polarization gradients result in non-uniform NC effect in channel region, resulting in severe GIDL effects. On the other hand, higher polarization gradients alleviate GIDL effects.     

pH-sensing properties of PbO<Subscript>2</Subscript> thin film electrodeposited on carbon ceramic electrode

In this paper, a new highly sensitive potentiometric pH electrode is proposed based on the solid-state PbO₂ film electrodeposited on carbon ceramic electrode (CCE). Two different crystal structures of PbO₂, α and β were examined and the similar results were obtained. Moreover, the experimental results obtained for the proposed pH sensor and a conventional glass pH electrode were in good agreement. The electromotive force (emf) signal between the pH-sensitive PbO₂-coated CCE and SCE reference electrode was linear over the pH range of 1.5–12.5. Near-Nernstian slopes of −64.82 and −57.85 mV/pH unit were obtained for α- and β-PbO₂ electrodes, respectively. The interferences of some mono-valence and multi-valence ions on potentiometric response of the sensor were studied. The proposed pH sensor displayed high ion selectivity with respect to K⁺, Na⁺, Ca²⁺, and Li⁺, with log values around −12 and has a working lifetime of about 30 days. Key parameters important for the pH sensor performance, including kind of PbO₂ film, selectivity, response time, stability, and reproducibility, have been characterized. The proposed electrode showed a good efficiency for direct pH-metry after calibration and pH-metric titrations without calibration step. The response time was about 1 s in acidic medium and less than 30 s in alkaline solutions. The pH values of complex matrix samples such as fruit juices measured by the proposed sensor and a conventional glass pH electrode were in good agreement.     

New figuring model based on surface slope profile for grazing‐incidence reflective optics

Surface slope profile is widely used in the metrology of grazing‐incidence reflective optics instead of surface height profile. Nevertheless, the theoretical and experimental model currently used in deterministic optical figuring processes is based on surface height, not on surface slope. This means that the raw slope profile data from metrology need to be converted to height profile to perform the current height‐based figuring processes. The inevitable measurement noise in the raw slope data will introduce significant cumulative error in the resultant height profiles. As a consequence, this conversion will degrade the determinism of the figuring processes, and will have an impact on the ultimate surface figuring results. To overcome this problem, an innovative figuring model is proposed, which directly uses the raw slope profile data instead of the usual height data as input for the deterministic process. In this paper, first the influence of the measurement noise on the resultant height profile is analyzed, and then a new model is presented; finally a demonstration experiment is carried out using a one‐dimensional ion beam figuring process to demonstrate the validity of our approach.     

Steep pulsed electric fields modulate cell apoptosis through the change of intracellular calcium concentration

A steep electric pulsed field with low intensity (150–250 V/cm) and relative long time (10 min) was applied to adherent liver cancer cell line SMMC-7721 and the liver cell line HL-7702. Results showed that the electric field with intensity of 200 and 250 V/cm could trigger cell apoptosis, whereas the SMMC-7721 cell was more sensitive to the electric stimulation than the HL-7702 cell. Laser Scanning Confocal Microscope (LSCM) was used to measuring the real-time change of cytosolic free Ca²⁺ concentration. When cells were exposed electric pulses with 100 V/cm intensity for 10 min, there was no significant change of intracellular calcium concentration. With the intensity increased to 200 and 250 V/cm, intracellular calcium concentration decreased significantly. Results demonstrated the relationship between the apoptosis and change of intracellular calcium concentration. And the steep electric pulsed field can be used to the cancer therapy.     

Computing boundary slopes of 2-bridge links

We describe an algorithm for computing boundary slopes of 2-bridge links. As an example, we work out the slopes of the links obtained by surgery on one component of the Borromean rings. A table of all boundary slopes of all 2-bridge links with 10 or less crossings is also included.

     

海底边坡稳定分析方法综述

本文指出海底边坡与陆上边坡的不同点,对一个完整的海底边坡稳定问题从几何形状和载荷情况两个方面进行了描述。由于波浪影响是海底边坡问题的最大特点,因此回顾了计算海底压力的各种方法以及在海底压力作用下海底土层产生的瞬态和残余孔隙压力。然后对极限平衡、静态变形分析和动力分析三大类边坡稳定分析方法进行了评述,并指出各自的适用范围。海底边坡破坏后的行为尤其复杂,指出用流变模型预测泥流性质的可能性。最后提出了海底边坡稳定性课题的当前致力方向。      

地质工程自动监测硬件系统若干技术问题

地质工程自动监测系统具有监测对象信息变化差异大,监测环境恶劣等显着特点。其硬件系统须具备监测范围广,抗干扰能力强,抗雷击等特殊功能。同时,为了适应现代化工程建设的要求,还应具备先进的智能化和网络化等功能。为此,本文对地质工程自动监测系统的功能和组成、当前的发展趋势及所涉及到一些关键硬件技术问题展开了讨论,着重总结了作者有关地质工程自动监测硬件系统关键技术问题的研究。最后介绍了作者为五强溪水电站边坡工程建立的自动监测系统,以及该系统双端防雷保护和模块化信号调理等难题的解决。     

Global composite element iteration for analysis of seepage free surface

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隧道洞口段非均质及各向异性土质裂缝仰坡稳定性上限解

针对忽略岩土体非均质和各向异性将导致边坡稳定性评价产生误差的问题,应用极限分析上限理论及抗剪强度系数折减法,推导土体强度非均质和各向异性影响下隧道洞口含裂缝仰坡稳定性解析式,探究土体强度非均质和各向异性对仰坡稳定性系数、坡顶裂缝位置、隧道拱顶失稳范围及仰坡安全系数的影响。结果表明,裂缝深度及坡角越大,仰坡稳定性系数越小;非均质系数越大和各向异性系数越小,维持仰坡稳定的临界坡高越大;非均质系数及各向异性系数越大,裂缝距坡顶边缘越远,隧道拱顶失稳范围越大;非均质系数增大有利于仰坡稳定,而各向异性系数越大仰坡越易失稳。