156 research outputs found
Reflections on methodology for assessing campus sustainability from a Turkish perspective
No full textAim: The author provides a critical reflection of the questionnaire discussed at the workshop “Methodology for assessing the campus sustainability from the perspective of multi-level antifragility” held on Friday 13 May at the WSB University in Wrocław. The author reflects from the background of his experience in Turkey. Design / Research methods: The author provides his own reflections and opinions, based on the discussions at the workshop. Conclusions / findings: It is very difficult to create a set of indicators making campus sustainability internationally comparable, as well as finding proper sources of information. A starting point in creating such indicators may be mistakes threatening organizational viability and external sustainability Originality / value of the article: The article provides critical feedback on an innovative approach towards research on campus sustainability. </jats:p
Measuring Nature of Science Views of Middle School Students
No full textDeveloping scientific literacy for all students is the most often stated purpose of contemporary science education. Nature of science (NOS) is seen as an important component of scientific literacy. There are various perceptions of NOS in the science education community and NOS itself is an ever-changing construct. This makes it challenging to develop instruments for measuring understanding of NOS at different levels. Many instruments have been developed and are being developed to assess NOS learning, which indicates the importance attributed to this subject. In this study, we developed a multiple-choice test to measure NOS understanding of middle school students. The instrument was applied to 1397 middle school students. The 24 item multiple-choice test had KR-20 reliability coefficient of 0.74. A 12 item multiple-choice test created as a subset of the 24 items of the original test. This test was easier and had higher discrimination, which can provide useful measurement data about students' understanding of NOS for diagnostic or formative purposes
A multiphase phase-field study of three-dimensional martensitic twinned microstructures at large strains
No full textA thermodynamically consistent multiphase phase-field approach for stress and temperature-induced martensitic phase transformation at the nanoscale and under large strains is developed. A total of N independent order parameters are considered for materials with N variants, where one of the order parameters describes A M transformations and the remaining N-1 independent order parameters describe the transformations between the variants. A non-contradictory gradient energy is used within the free energy of the system to account for the energies of the interfaces. In addition, a non-contradictory kinetic relationships for the rate of the order parameters versus thermodynamic driving forces is suggested. As a result, a system of consistent coupled Ginzburg-Landau equations for the order parameters are derived. The crystallographic solution for twins within twins is presented for the cubic to tetragonal transformations. A 3D complex twins within twins microstructure is simulated using the developed phase-field approach and a large-strain-based nonlinear finite element method. A comparative study between the crystallographic solution and the simulation result is presented.This is a pre-print of the article Basak, Anup, and Valery I. Levitas. "A multiphase phase-field study of three-dimensional martensitic twinned microstructures at large strains." arXiv preprint arXiv:2206.12576 (2022).
DOI: 10.48550/arXiv.2206.12576.
Copyright 2022 The Author(s).
Attribution 4.0 International (CC BY 4.0).
Posted with permission
Failure mechanisms in lithium silicon batteries
No full textLithium silicon (Li-Si) batteries offer more than ten times the theoretical specific capacity compared to current lithium ion battery technologies, by using a silicon anode. In practice however, the cycle life of Li-Si batteries is very limited. The large volume change of the silicon anode is known to be the main reason for this. Research on the volume changes during varying cell cycles and voltages is presented in this thesis and an experimental set up for a quasi in situ study of the SEI layer is suggested. Cycling tests with an amorphous silicon thin film of 220 nm deposited using magnetron sputtering on a copper foil current collector confirmed that the major cause of capacity loss is swelling of the silicon during lithiation, causing the silicon to detach from the current collector and resulting in significant capacity loss. Increasing the lower cut off voltage from 0 V to 0.2 V resulted in a slight improvement of cycle life. Silicon detachment also decreased as determined by SEM images. EFTEM and EDX mapping showed a clear split between a partially lithiated silicon layer on the surface and a pure silicon layer on the current collector side. It can be concluded that discharging Li-Si batteries to 0.2 V instead of 0 V is a promising method to reduce the swelling of silicon during lithiation.HREMQuantum NanoscienceApplied Science
Making Better Batteries: Following Electrochemistry at the Nano Scale with Electron Microscopy
No full textWith the focus in automobile industry to switch from petroleum-based vehicles to all electric vehicles, the increasing demand on harvesting energy from renewable sources for a safer and greener future and the ever-increasing demand of the portable electronics systems, the need for better batteries is eminent. The ultimate aim of battery research is to develop a low cost, light and small battery that can deliver high-capacity and/or high power. Lithium and sodium batteries are the frontrunners in achieving this ultimate battery. A macro battery is composed of thousands of millions of nanoparticles. Thus, to prepare a better battery we must determine the respective effects of electrode nanoparticle size, shape, structure, grain–grain boundary, defects and doping on the battery performance. To do so electrode nanoparticles need to be probed at the nano-scale to find out the correlation between their morphology, structure and chemical properties and their evolution due to the battery charging-discharging with battery performance. In this thesis we have utilized the unique capability of electron microscope to resolve the microstructural and chemical information at the (sub)nanometer scale to probe the electrode nanoparticles for making better batteries
Effects of surface capping with Poly-vinyl butyral (PVB) on the ultraviolet photosensing properties of ZnO nanorods
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