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1. Flows of Co-closed G2-Structures

   https://doi.org/10.1007/978-1-0716-0577-6_12  

   Grigorian, Sergey (January 2020, Fields Institute communications)

   Karigiannis, S.; Leung, N.; Lotay, J. (Ed.)

   We survey recent progress in the study of G2-structure Laplacian coflows, that is, heat flows of co-closed G2-structures. We introduce the properties of the original Laplacian coflow of G2-structures as well as the modified coflow, reviewing short-time existence and uniqueness results for the modified coflow and well as recent Shi-type estimates that apply to a more general class of G2-structure flows. 

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2. Scaling of ctenes and consequences for swimming performance in the ctenophore Pleurobrachia bachei

   https://doi.org/10.1111/ivb.12297  

   Heimbichner Goebel, Wyatt L.; Colin, Sean P.; Costello, John H.; Gemmell, Brad J.; Sutherland, Kelly R. (August 2020, Invertebrate Biology)

   Abstract Ctenophores coordinate large macrociliary structures called ctenes to propel themselves through the water. The morphology and kinematics of the ctenes mediate swimming performance. We investigated morphological and kinematic factors affecting swimming performance in free‐swimming ctenophores (Pleurobrachia bachei) using high speed videography. Our morphological results showed that the relationship between body size and ctene morphology and arrangement inP. bacheiwere well described using linear (i.e., isometric) relationships, which suggests functional limitations of ctenes that vary among individuals of different sizes. Our kinematic results showed that isometric constraints on swimming performance can potentially be overcome by alterations in kinematics: (a) swimming speed inP. bacheiincreased with ctene beat frequency over a range of body lengths, and (b) the separation of ctenes into clumps of cilia allowed the ctene to increase in width during the effective stroke and decrease in width during recovery. Separation increases the surface area of the ctene during the effective stroke, likely increasing the thrust produced. The finding that ctenes are not monoliths and instead are separated into clumps of cilia has not been previously described, and we subsequently observed this trait in three other ctenophore species:Euplokamis dunlapae,Bolinopsis infundibulum,andBeroe mitrata. Flexibility in function may be a necessary corollary to isometric development of the ctenes as propulsive structures. 

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3. Ring-Opening Metathesis Polymerization of the Dewar Isomer of 1,2-Azaborinine, a B–N Isostere of Benzene

   https://doi.org/10.1021/acsmacrolett.3c00601  

   Lin, Huina; Yang, Xinyu; Liu, Shih-Yuan; Jäkle, Frieder (December 2023, ACS Macro Letters)

   The successful polymerization of the Dewar isomer of an azaborinine heterocycle is reported. Controlled ring-opening metathesis polymerization was accomplished with Grubbs and Hoveya−Grubbs second generation catalysts (G2, HG2), as well as a Z-selective Ru catalyst (HGM2001). The structure of the polymers containing 4-membered B−N heterocycles was verified by GPC and multinuclear and 2D NMR. Differences in stereochemistry of polymers derived from G2/HG2 versus the Z-selective catalyst HGM2001 were substantiated by 2D NOESY, FT-IR, and Raman analyses. The incorporation of B−N heterocycles into these polymer structures is promising as a route to functional polymers that contain polar side groups. 

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4. Almost isotropy-maximal manifolds of non-negative curvature

   https://doi.org/10.1090/9100  

   Dong, Zheting; Escher, Christine; Searle, Catherine (May 2024, Transactions of the American Mathematical Society)

   We extend the equivariant classification results of Escher and Searle for closed, simply connected, Riemannian $n$-manifolds with non-negative sectional curvature admitting isometric isotropy-maximal torus actions to the class of such manifolds admitting isometric strictly almost isotropy-maximal torus actions. In particular, we prove that any such manifold is equivariantly diffeomorphic to the free, linear quotient by a torus of a product of spheres of dimensions greater than or equal to three. 

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5. Generalizability of muscle synergies in isometric force generation versus point-to-point reaching in the human upper extremity workspace

   https://doi.org/10.3389/fnhum.2023.1144860  

   Pham, Katherine; Portilla-Jiménez, Manuel; Roh, Jinsook (July 2023, Frontiers in Human Neuroscience)

   Isometric force generation and kinematic reaching in the upper extremity has been found to be represented by a limited number of muscle synergies, even across task-specific variations. However, the extent of the generalizability of muscle synergies between these two motor tasks within the arm workspace remains unknown. In this study, we recorded electromyographic (EMG) signals from 13 different arm, shoulder, and back muscles of ten healthy individuals while they performed isometric and kinematic center-out target matches to one of 12 equidistant directional targets in the horizontal plane and at each of four starting arm positions. Non-negative matrix factorization was applied to the EMG data to identify the muscle synergies. Five and six muscle synergies were found to represent the isometric force generation and point-to-point reaches. We also found that the number and composition of muscle synergies were conserved across the arm workspace per motor task. Similar tuning directions of muscle synergy activation profiles were observed at different starting arm locations. Between the isometric and kinematic motor tasks, we found that two to four out of five muscle synergies were common in the composition and activation profiles across the starting arm locations. The greater number of muscle synergies that were involved in achieving a target match in the reaching task compared to the isometric task may explain the complexity of neuromotor control in arm reaching movements. Overall, our results may provide further insight into the neuromotor compartmentalization of shared muscle synergies between two different arm motor tasks and can be utilized to assess motor disabilities in individuals with upper limb motor impairments. 

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