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1. ‘Golden Ratio Yoshimura’ for meta-stable and massively reconfigurable deployment

   https://doi.org/10.1098/rsta.2024.0009  

   Deshpande, Vishrut; Phalak, Yogesh; Zhou, Ziyang; Walker, Ian; Li, Suyi (October 2024, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   Yoshimura origami is a classical folding pattern that has inspired many deployable structure designs. Its applications span from space exploration, kinetic architectures and soft robots to even everyday household items. However, despite its wide usage, Yoshimura has been fixated on a set of design constraints to ensure its flat foldability. Through extensive kinematic analysis and prototype tests, this study presents a new Yoshimura that intentionally defies these constraints. Remarkably, one can impart a unique meta-stability by using the Golden Ratio angle ( ${\cot }^{-1}1.618\approx {31.72}^{\circ }$) to define the triangular facets of a generalized Yoshimura (with $n=3$, where $n$is the number of rhombi shapes along its cylindrical circumference). As a result, when its facets are strategically popped out, a ‘Golden Ratio Yoshimura’ boom with $m$modules can be theoretically reconfigured into $8^m$geometrically unique and load-bearing shapes. This result not only challenges the existing design norms but also opens up a new avenue to create deployable and versatile structural systems. This article is part of the theme issue ‘Origami/Kirigami-inspired structures: from fundamentals to applications’. 

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2. Observation of a pseudoscalar excess at the top quark pair production threshold

   https://doi.org/10.1088/1361-6633/adf7d3  

   Collaboration, The_CMS (August 2025, Reports on Progress in Physics)

   Abstract A search for resonances in top quark pair ( $\mathrm{t}\bar{\mathrm{t}}$) production in final states with two charged leptons and multiple jets is presented, based on proton–proton collision data collected by the CMS experiment at the CERN LHC at $\sqrt{s}=13\text{TeV}$, corresponding to 138 fb⁻¹. The analysis explores the invariant mass of the $\mathrm{t}\bar{\mathrm{t}}$system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic $\mathrm{t}\bar{\mathrm{t}}$threshold compared to the non-resonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar ( ${}^1{\text{S}}_0^{\left[1\right]}$) quasi-bound toponium state, as predicted by non-relativistic quantum chromodynamics. Using a simplified model for ${}^1{\text{S}}_0^{\left[1\right]}$toponium, the cross section of the excess above the pQCD prediction is measured to be $8.8{}_{-1.4}^{+1.2}\text{pb}$. 

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3. Electron impact excitation of allowed and forbidden transitions between fine-structure levels in Ti III

   https://doi.org/10.1088/1361-6595/ad95b8  

   Wang, Yang; Cao, Qiu-Yao; Zhu, Xi-Ming; Du, Chun-Meng; Bartschat, Klaus (November 2024, Plasma Sources Science and Technology)

   Abstract Introduction: We present an extensive theoretical investigation of the electron impact excitation of doubly-ionized titanium (Ti III) to meet the needs of spectral analysis and plasma modeling. OBJECTIVES: The main objective of this work is to extend the currently scarce database of both structure and collision data for Ti III. METHODS: The calculation was performed in the close-coupling approximation using theB-splineR-matrix method. The multi-configuration Hartree–Fock method in combination withB-spline configuration interaction expansions and the non-orthogonal orbitals technique is employed for accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target states. Relativistic effects are treated at the semi-relativistic Breit-Pauli approximation level. RESULTS: The present close-coupling expansion includes 138 fine-structure levels of Ti III belonging to the $3d^2$, $4s^2$, $4s4p$, $3d4l$( $l=0-3$), $3d5l$( $l=0-3$), $3d6s$, and $3d6p$configurations. Comprehensive sets of radiative and electron collisional data are reported for all of the possible transitions between the 138 fine-structure levels. Thermally averaged collision strengths are determined using a Maxwellian distribution for a wide range of temperatures from ${10}^2$K to ${10}^5$K. The accuracy of the calculated radiative parameters is validated by comparing with available values from the NIST database and previous literature. CONCLUSION: Given the lack of sufficient currently available experimental and theoretical data, the electron impact excitation cross sections of the Ti III fine-structure levels presented here are systematic, extensive, and internally consistent, thus making them suitable for many modeling applications. 

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4. Sub-1 V/cm E-FISH-based picosecond electric field measurements in atmospheric pressure air

   https://doi.org/10.1088/1361-6595/adae32  

   LaCombe, Grayson; Wang, Jianan; Frederickson, Kraig; Simeni_Simeni, Marien (February 2025, Plasma Sources Science and Technology)

   Abstract We report on the development of a highly sensitive electric field induced second harmonic generation diagnostic setup capable of measuring electric field strengths as low as 1 $\mathrm{V}{\mathrm{cm}}^{-1}$at the picosecond time scale under atmospheric pressure conditions. This unprecedented sensitivity is achieved through passive homodyne detection, which utilizes stray signals generated by an optical component in the beam path. Our detection limit of 0.3–0.5 $\mathrm{V}{\mathrm{cm}}^{-1}$represents an improvement of over 2–3 orders of magnitude compared to previous reports (100–1000 $\mathrm{V}{\mathrm{cm}}^{-1}$) in the literature. Additionally, we demonstrate sensitivity to the polarity of the electric field. Experimental results are corroborated by simulations of the 400 ps time-resolved homodyne process, offering deeper insights into the enhanced detection capabilities and the system’s ability to resolve the field sign. 

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5. Convolution identities for divisor sums and modular forms

   https://doi.org/10.1073/pnas.2322320121  

   Fedosova, Ksenia; Klinger-Logan, Kim; Radchenko, Danylo (October 2024, Proceedings of the National Academy of Sciences)

   Ribet, Kenneth (Ed.)

   We consider certain convolution sums that are the subject of a conjecture by Chester, Green, Pufu, Wang, and Wen in string theory. We prove a generalized form of their conjecture, explicitly evaluating absolutely convergent sums $\sum _{n_1\in \mathbb{Z}\setminus \{0,n\}}\phi (n_1,n-n_1){\sigma }_{2m_1}\left(n_1\right){\sigma }_{2m_2}(n-n_1),$ where $\phi (n_1,n_2)$is a Laurent polynomial with logarithms. Contrary to original expectations, such convolution sums, suitably extended to $n_1\in \{0,n\}$, do not vanish, but instead, they carry number theoretic meaning in the form of Fourier coefficients of holomorphic cusp forms. 

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