Calculus as taught by mathematicians typically involves a large toolbox of algebraic manipulations. Almost all computations are done using rectangular coordinates and, later, the associated standard basis of unit vectors. Vector calculus as used by physicists, on the other hand, typically involves geometric reasoning, and the frequent use of coordinates and basis vectors adapted to the symmetries that are present. Thermodynamics goes even further, fundamentally altering the notion of “standard coordinates.” These treatments are sufficiently different from each other that they constitute different languages; students are often unable to translate.

Our research group at Oregon State University has been working to bridge this gap between mathematics and physics for more than two decades, primarily by restructuring upper-division physics courses, but also by developing materials for second-year calculus that emphasize geometric reasoning. The Paradigms in Physics project, continuously supported since 1997 by the NSF, has evolved from “merely” designing novel curricula to studying student learning of mathematical concepts such as partial derivatives.

This talk describes several examples of these language differences, the curricular materials we have developed to help students bridge this gap (including an online textbook and a website featuring more than 300 classroom activities), and some of the education research in which our materials are grounded.

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The mechanisms which control the growth of nanocrystals are difficult to investigate because nanocrystals occupy a position awkwardly intermediate between molecules and solids. Two case studies highlight these difficulties and their solution.

(1) Cation exchange is a chemical reaction in which all the cations of a material are replaced by different cations, thus creating a new material. In semiconductor nanocrystals, cation exchange happens extremely fast – many orders of magnitude faster than for macroscopic crystals and far faster than simple size-scaling would suggest. I propose a theoretical mechanism for cation exchange in nanocrystals that reveals a surprising consequence of Coulomb interactions acting at nanometer length scales.

(2) Semiconductor nanostructures take a wide variety of physical forms. One of the most active areas of this research focuses on semiconductor “nanoplatelets,” the name given to nanostructures that are very thin and very wide. An early question asked by researchers was, what causes materials to form these very thin shapes in the first place? The question is even more puzzling when you learn that even materials with an underlying isotropic crystal structure form these extremely asymmetrical shapes. I will propose an explanation of this “kinetic instability” in the growth and show how this theory can be be used by researchers to create new families of nanoplatelet materials.

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In traditional optoelectronics the ability to downscale critical device dimensions has proven extremely successful over the past sixty years in increasing their functionality and performance. These extraordinary developments have been achieved through a virtuous circle of scientific and engineering breakthroughs which have led to the proliferation of information & communication technologies with an extraordinary impact on our daily life and society. However, adopting established manufacturing methods to emerging technologies such as printed optoelectronics, has proven challenging both in terms of technology and economics. This talk will focus on progress being made downscaling emerging forms of large-area optoelectronics through a new fabrication paradigm and their application in a variety of functional devices including, light-emitting nanogap diodes, photo-detectors and rectifying diodes.

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The need for exquisite control of light is ubiquitous in energy-relevant applications, optoelectronics, and information science. In this talk, I will discuss how hybrid materials consisting of distinct sub-lattices and periodically nanostructured materials allow for dramatically enhanced light absorption, emission, and charge carrier generation at various time- and length-scales. I will first focus on hybrid organic-inorganic perovskites. These solution-processed, scalable materials exhibit remarkable optoelectronic properties such as strong light absorption, defect tolerance, and long carrier lifetimes. I will describe how electronic excitations in these materials are coupled to and influenced by the vibrational degrees of freedom of the organic and inorganic sublattices, investigated using an array of optical spectroscopic techniques. The unique soft nature of the lead-halide octahedral framework gives rise to dynamic fluctuations in the electronic bandgap, which distinguishes hybrid perovskites from traditional inorganic semiconductors. Furthermore, strong quantum confinement can be easily imparted to hybrid perovskites with the use of organic spacer-cations, leading to hyperbolic dispersion relation and enhanced light-emitting properties. Beyond solution-processed semiconductors, I will demonstrate how widely-used materials, such as indium-tin-oxide (ITO), can be grown in ordered, nanoscale array form by chemical vapor phase epitaxy to exhibit well-defined localized surface plasmon resonances in the infrared spectral range. The unique band structure and carrier concentration of ITO result in an unusual type of optical nonlinearity that is significantly larger and faster than the noble metal counterparts. I will conclude by discussing how such material platforms open new avenues for infrared molecular sensing, ultrafast optical switching and active photonic devices.

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Many people believe that the detonation of an Improvised Nuclear Device (IND) will automatically result in massive death and destruction.  Such an event will almost certainly result in many deaths, but many other people will survive IF they know what to do to protect themselves.  The key message is to “Go in, stay in, and tune in” (see https://emergency.cdc.gov/radiation/). The purpose of this presentation is to explain what an IND is, how it works, what its impact will be, and how, because some of the effects of an IND decreases with time, people can survive the initial impact if they act quickly and appropriately.  This presentation will also discuss the role that scientifically literate citizens can have in helping to educate their family members, friends, and neighbors on these important concepts.

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The ability to reconfigure nanoscale building blocks into different architectures, as if they were Lego pieces, has enormous potential for nanoscience. The development of colloidal synthesis has largely increased the availability of nanocrystals with well-controlled sizes and shapes. Bottom-up assembly of these nanoscale building blocks opens the prospect of creating novel artificial materials and systems with unusual properties and functionalities. However, it is still a great challenge to achieve precise, controlled, and reconfigurable assembly of nanomaterials. This seminar will introduce an optical approach to address this fundamental challenge in nanoscience. My research group exploits light-driven self-organization to create artificial nanomaterials. Shaped optical fields are created by modulating the intensity, phase, and polarization of laser beams in space and time. Self-organization arises from electrodynamic interactions among strongly scattering plasmonic nanoparticles, leading to a new type of material: reconfigurable optical matter with nanoparticle superlattices. New science has emerged in these artificial materials, for example, negative optical torque in optical matter arrays, and the developed optical methods will lead to more research opportunities and applications in microfluidics, microrheology, optical physics, and cell biology.

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