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Dynamic light scattering (DLS) is a commonly used analytical tool for characterizing the size distribution of colloids in a dispersion or a solution. Typically, the intensity of a scattering produced from the sample at a fixed angle from an incident laser beam is recorded as a function of time and converted into time autocorrelation data, which can be inverted to estimate the distribution of colloid diffusivity to estimate the colloid size distribution. For polydisperse samples, this inversion problem, being a Fredholm integral equation of the first kind, is ill-posed and is typically handled using cumulant expansions or regularization methods. Here, we introduce a user-friendly graphical user interface (GUI) for analyzing the measured scattering intensity time autocorrelation data using both the cumulant expansion method and regularization methods, with the latter implemented using various commonly employed algorithms, including NNLS, CONTIN, REPES, and DYNALS. The GUI allows the user to modulate any and all of the fit parameters, offering extreme flexibility. Additionally, the GUI also enables a comparison of the size distributions generated by various algorithms and an evaluation of their performance. We present the fit results obtained from the GUI for model monomodal and bimodal dispersions to highlight the strengths, limitations, and scope of applicability of these algorithms for analyzing time autocorrelation data from DLS.
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Visualizing the Hydrogen Atomic Orbitals: A Tool for Undergraduate Physical Chemistry
Despite the prominence of orbitals throughout the undergraduate chemistry curriculum, high-quality visualization of atomic orbitals is out of reach for most scientists. Rigorously visualizing the atomic orbitals even for simple hydrogen-like atoms and ions is rather challenging due to the complex 3-D structure and geometric variability of the orbitals across three distinct quantum numbers. In this work, a graphical user interface (GUI)-based tool for visualizing 3-D volumetric density plots of hydrogen atomic orbitals is introduced. This tool is written in Python, and a Jupyter notebook version with explanatory blocks interspersed in the code is included for pedagogical purposes. The user can manipulate a large number of features using the GUI, which allows customization of the orbital illustrations. Because this visualizer is capable of visualizing orbitals with any quantum numbers and showing their nodal surfaces, it can serve as a supplement to students’ lecture and textbook education on this topic.
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- Award ID(s):
- 2142874
- PAR ID:
- 10548153
- Publisher / Repository:
- Journal of Chemical Education
- Date Published:
- Journal Name:
- Journal of Chemical Education
- Volume:
- 101
- Issue:
- 8
- ISSN:
- 0021-9584
- Page Range / eLocation ID:
- 3539 to 3546
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jchemed.4c00547
