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1. Analysis of signal-to-noise ratio of angle of polarization and degree of polarization

   https://doi.org/10.1364/OSAC.422541  

   Chen, Yingkai; Zhu, Zhongmin; Liang, Zuodong; Iannucci, Leanne_E; Lake, Spencer_P; Gruev, Viktor (April 2021, OSA Continuum)

   Recent advancements in nanofabrication technology has led to commercialization of single-chip polarization and color-polarization imaging sensors in the visible spectrum. Novel applications have arisen with the emergence of these sensors leading to questions about noise in the reconstructed polarization images. In this paper, we provide theoretical analysis for the input and output referred noise for the angle and degree of linear polarization information. We validated our theoretical model with experimental data collected from a division of focal plane polarization sensor. Our data indicates that the noise in the angle of polarization images depends on both incident light intensity and degree of linear polarization and is independent of the incident angle of polarization. However, noise in degree of linear polarization images depends on all three parameters: incident light intensity, angle and degree of linear polarization. This theoretical model can help guide the development of imaging setups to record optimal polarization information. 

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2. Spectra of products of digraphs

   https://doi.org/10.13001/ela.2020.5243  

   Catral, Minerva; Ciardo, Lorenzo; Hogben, Leslie; Reinhart, Carolyn (January 2020, The Electronic Journal of Linear Algebra)

   null (Ed.)

   A unified approach to the determination of eigenvalues and eigenvectors of specific matrices associated with directed graphs is presented. Matrices studied include the new distance matrix, with natural extensions to the distance Laplacian and distance signless Laplacian, in addition to the new adjacency matrix, with natural extensions to the Laplacian and signless Laplacian. Various sums of Kronecker products of nonnegative matrices are introduced to model the Cartesian and lexicographic products of digraphs. The Jordan canonical form is applied extensively to the analysis of spectra and eigenvectors. The analysis shows that Cartesian products provide a method for building infinite families of transmission regular digraphs with few distinct distance eigenvalues. 

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3. The size of the class of countable sequences of ordinals

   https://doi.org/10.1090/tran/8573  

   Chan, William; Jackson, Stephen; Trang, Nam (January 2021, Transactions of the American Mathematical Society)

   Assume . There is no injection of (the set of countable length sequences of countable ordinals) into (the class of length sequences of ordinals). There is no injection of (the powerset of ) into (the class of countable length sequences of ordinals). 

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4. Stability of the centers of group algebras of $$GL_n(q)$$

   https://doi.org/https://doi.org/10.1016/j.aim.2019.04.026  

   Wan, Jinkui; Wang, Weiqiang (April 2019, Advances in mathematics)

   The center $$Z_n(q)$$ of the integral group algebra of the general linear group $$GL_n(q)$$ over a finite field admits a filtration with respect to the reflection length. We show that the structure constants of the associated graded algebras $$\mathscr{G}_n(q)$$ are independent of $$n$$, and this stability leads to a universal stable center with positive integer structure constants which governs the algebras $$\mathscr{G}_n(q)$$ for all $$n$$. Various structure constants of the stable center are computed and several conjectures are formulated. Analogous stability properties for symmetric groups and wreath products were established earlier by Farahat-Higman and the second author. 

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5. Systematic Variation of Friction of Rods

   https://doi.org/10.1115/1.4055544  

   Ibrahim Khalil, Md; Tong, Dezhong; Wang, Guanjin; Khalid Jawed, Mohammad; Khoda, Bashir (November 2022, Journal of Applied Mechanics)

   Abstract The mechanical response of a knot tied in elastic rods strongly depends on the frictional force due to rod–rod contact. The behavior of a knot can be qualitatively different based on the frictional coefficient of the elastic rod. Systematic variation of friction during rod–rod contact is a crucial component of any experimental design to uncover the underlying ingredients behind the mechanics of knots. In this paper, we demonstrate a novel process of controlling the friction of a continuous rod by adhering non-spherical inorganic micro-particles. Polymeric binder is used to deliver the particles as asperities over the rod substrate and by controlling their size and distribution the coefficient of friction of the rod is determined. In parallel, numerical simulations with the discrete elastic rods algorithm are used to reproduce the experimental observations. Tabletop experiments are performed where overhand knots with a variety of unknotting numbers are pulled tight. The force–extension curve of these experiments shows that the proposed process can successfully tune the friction between rods. 

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