This study investigated features of instructors' classroom discourse on the derivative with the commognitive lens. The analysis focused on how three calculus instructors addressed the derivative as a ...point-specific value and as a function in the beginning lessons about the derivative. The results show that (a) the instructors frequently used secant lines and the tangent line on the graph of a curve to illustrate the symbolic notation for the derivative at a point without making explicit connections between the graphical illustration and the symbolic notations, (b) they made a transition from the point-specific view of the derivative to the interval view mainly by changing the literal symbol for a point to a variable rather than addressing how the quantity that the derivative shows, changes over an interval, (c) they quantified the derivative as a number using functions with limited graphical features, and (d) they often justified the property of the derivative function with the slope of the tangent line at a point as an indication of the universality of the property. These results show that the aspects of the derivative that the past mathematicians and today's students have difficulties with are not explicitly addressed in these three classrooms. They also suggest that making explicit these aspects of the derivative through word use and visual mediators, and making clear connections between the ways that the quantities and properties of the derivative are visually mediated with symbolic, graphical, and algebraic notations would help students to understand why and how the limit component for the derivative are illustrated on graphs and expressed symbolically, and the derivative is expanded from a point to an interval, and properties of the derivative are investigated over an interval. More explicit discussions on these ideas perhaps make them more accessible to students.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Despite the global effort to mitigate the spread, coronavirus disease 2019 (COVID-19) has become a pandemic that took more than 2 million lives. There are numerous ongoing clinical studies aiming to ...find treatment options and many are being published daily. Some effective treatment options, albeit of variable efficacy, have been discovered. Therefore, it is necessary to develop an evidence-based methodology, to continuously check for new evidence, and to update recommendations accordingly. Here we provide guidelines on pharmaceutical treatment for COVID-19 based on the latest evidence.
This paper investigates how three widely used calculus textbooks in the U.S. realize the derivative as a point-specific object and as a function using Sfard's communicational approach. For this ...purpose, the study analyzed word-use and visual mediators for the limit process through which the derivative at a point was objectified, and word-use and visual mediators for the derivative process through which the derivative as a function was objectified. The analysis highlighted inconsistency in realizations of the limit process and object, and derivative process and object found in some instances, and implicit discussion on relations among different visual mediators. Specifically, the results of this study led to four observations about issues suggested by one or more of the textbooks: a) visual mediators of the initial and final objects, and the visual mediators of these processes were often inconsistent; b) transformations of visual mediators from initial object, through process, to final object were often implicit both in one visual mediator and across multiple visual mediators; c) visual mediators for the limit processes were sometimes disconnected from the initial and final objects, or the connections were not explicit; and d) realizations of both the derivative at a point and the derivative of a function were mediated with nearly identical symbols suggesting a possible difficulty with understanding the difference between them.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Exposure to metal arsenic (As) has been proposed as a risk factor for autism spectrum disorders (ASDs), which are neurodevelopmental disorders with worldwide increasing in its incidence. In the ...present study, BTBR T +
tf
/J (BTBR) mice with ASD-like behavioral characteristics and control highly social FVB mice were orally exposed to 0.1 mM arsenic(III)oxide for 4 weeks, and were compared to investigate neuroimmunological or behavioral abnormalities. IgG1:IgG2a ratios in brain tissues from BTBR mice exposed to As (BTBR-As) were significantly higher than those of BTBR-control mice (BTBR-C), but this change did not occur in FVB mice exposed to As. Levels of IL-4, IFN-γ, IL-1β, IL-17, and TNF-α in brain tissue were lowered in BTBR-As relative to BTBR-C, but this tendency was not observed with FVB mice. BTBR-As mice demonstrated decrease in relative travel distance and time spent in the center vs. the periphery of open field arena compared to BTBR-C. Sociability evaluation using three-way chamber test did not clearly demonstrate As-mediated alteration in social interaction in BTBR mice. These findings suggest the potential for As-driven predominant T
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2-like reactivity profile in the brain microenvironment of BTBR mice and for As-mediated locomotive impairment probably associated with ASD.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Methyl bromide (MB) has been used in a wide range of applications, but since it was determined to be an ozone-depleting compound, it has only been used for pre-shipment and quarantine purposes in ...trade. Phosphine (PH3) is currently the ideal fumigant as an MB alternative worldwide. However, the development of PH3 resistance in the target insect pest and longer PH3 fumigation treatment times raise questions about the continued use of PH3. This study attempted to shorten treatment time via combination treatment with ethyl formate (EF). Planococcus citri was used as the main quarantine pest in Korea, and the acute toxicity of EF, PH3, and EF + PH3 was determined at every developmental stage. EF treatment at 4 h showed LCT99 values of 45.85~65.43 mg∙h/L, and PH3 treatment at 20 h showed that of 0.13~0.83 mg∙h/L depending on the developmental stage. The efficacy of PH3 decreased after reducing the treatment time, but synergistic effects were observed at all stages of development of P. citri when both fumigants were used simultaneously for 4 h. After combined treatment, dihydrolipoyl dehydrogenase expression and the production of two phospholipids, PI(O-16:0) and PC(18:2), were significantly reduced in treated P. citri adults compared with the control. Therefore, combined treatments might be key to reducing the treatment time and resistance of PH3 in the field.
Methyl benzoate (MB) is a small, hydrophobic organic compound that is isolated from the freshwater fern, Salvinia molesta. Because of its pleasant odor, it has been used as a fragrance and flavor ...enhancer. In addition, it is used to attract orchid bees for pollination in the farm and has been tested for its potential to be developed as a green pesticide targeting a diverse group of insects. In spite of its wide applications, the safety of MB to humans remains poorly understood. In this study, we tested the cytotoxicity of MB against cultured human cells, including kidney, colon, and neuronal cells. Furthermore, other natural and synthetic benzoic acids such as ethyl benzoate (EB) and vinyl benzoate (VB) were compared with MB for their similarity and broad commercial and industrial applications. We found that MB and VB have the least and most overall toxicity to the tested human cells, respectively. In addition, the expression of some genes involved in cell cycle, protein quality control, and neurotransmission such as cyclin D1, HSP70, and ACHE genes was differentially expressed in the presence of these chemicals, most noticeably in treatment of VB. Our study provided the LC50 values of these benzoic acids for human cells in vitro and suggested their mild toxicity that should be considered in the industrial and agricultural applications to be within safe limits.
Agricultural science; Pesticide; Environmental health; Toxicology; Methyl benzoate; Cytotoxicity; Gene expression.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Deep blue PHOLEDs with over 20% of external quantum efficiency is achieved.•We examined optimized device structure of PHOLEDs and doping concentration.•The color coordinates(x, y) of new ...heteroleptic Ir(III) complex is (0.13,0.18).
Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) using two heteroleptic iridium compounds, (dfpypy)2Ir(acac) and (dfpypy)2Ir(dpm), as a dopant and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material have been developed. The electroluminescent device of (dfpypy)2Ir(dpm) at the doping level of 3wt% shows the best performance with external quantum efficiency of 18.5–20.4% at the brightness of 100–1000cd/m2 and the color coordinate of (0.14,0.18) at 1000cd/m2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Given the importance of the ability to use variables flexibly in Calculus and students' difficulties related to various uses of variables, this study examined how variables are treated in calculus ...class. Data for this study came from graduate teaching assistants' (TAs') classroom teaching, which plays a crucial role in undergraduate students' learning of entry-level mathematics, but of which we still have a limited understanding. We analyzed TAs' uses of variables in terms of prior literature examining how students use variables and what uses of variables cause difficulties for students. Our results show that the uses of variables by the TAs in this study typically aligned with students' dominant conception of variables as symbols to be manipulated and did not give students many opportunities to consider the uses of variables that commonly cause difficulties for students.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
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