*41%*:**NTNU Java: Carnot Cycle (Heat Engine)***35%*:**Development and assessment of research-based tutorials on heat engines and the second law of thermodynamics***34%*:**Flashlets: Carnot Cycle***32%*:**Concept substitution: A teaching strategy for helping students disentangle related physics concepts***31%*:**Development of a concept inventory to assess students' understanding and reasoning difficulties about the properties and formation of stars***30%*:**Investigation of Studentsâ€™ Preconceptions and Difficulties with the Vector Direction Concept at a Mexican University***29%*:**Students' concepts of force as applied to related physical systems: a search for consistency***29%*:**Facilitating model-building of electrostatics concepts related to conductors***28%*:**Student Difficulties with Wave Concepts***28%*:**Improving Students' Understanding of Quantum Mechanics***28%*:**They Still Remember What I Never Taught Them: Student Understanding of Entropy***26%*:**Investigating the Relationship Between Student Difficulties with the Concept of Electric Potential and the Concept of Rate of Change***26%*:**Student understanding of basic probability concepts in an upper-division thermal physics course***25%*:**Exploring the development of conceptual ecologies: communities of concepts related to convection and heat***25%*:**An investigation of student thinking regarding calorimetry, entropy, and the second law of thermodynamics***25%*:**Student Difficulties with Graphical Representations of Negative Values of Velocity***25%*:**Addressing Student Difficulties with Buoyancy***25%*:**Students' difficulties with unit vectors and scalar multiplication of a vector***25%*:**Testing Studentsâ€™ Understanding of Vector Concepts**