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1. Dispersive nonreciprocity between a qubit and a cavity

   https://doi.org/10.1126/sciadv.adj8796  

   Wang, Ying-Ying; Wang, Yu-Xin; van_Geldern, Sean; Connolly, Thomas; Clerk, Aashish A; Wang, Chen (April 2024, Science Advances)

   The dispersive interaction between a qubit and a cavity is ubiquitous in circuit and cavity quantum electrodynamics. It describes the frequency shift of one quantum mode in response to excitations in the other and, in closed systems, is necessarily bidirectional, i.e., reciprocal. Here, we present an experimental study of a nonreciprocal dispersive-type interaction between a transmon qubit and a superconducting cavity, arising from a common coupling to dissipative intermediary modes with broken time reversal symmetry. We characterize the qubit-cavity dynamics, including asymmetric frequency pulls and photon shot noise dephasing, under varying degrees of nonreciprocity by tuning the magnetic field bias of a ferrite component in situ. We introduce a general master equation model for nonreciprocal interactions in the dispersive regime, providing a compact description of the observed qubit-cavity dynamics agnostic to the intermediary system. Our result provides an example of quantum nonreciprocal phenomena beyond the typical paradigms of non-Hermitian Hamiltonians and cascaded systems. 

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2. Hydrodynamic interactions between a sedimenting squirmer and a planar wall

   https://doi.org/10.1017/jfm.2025.260  

   Shum, Henry; Palaniappan, D; Young, Yuan-Nan (May 2025, Journal of Fluid Mechanics)

   The hydrodynamic interactions between a sedimenting microswimmer and a solid wall have ubiquitous biological and technological applications. A plethora of gravity-induced swimming dynamics near a planar no-slip wall provide a platform for designing artificial microswimmers that can generate directed propulsion through their translation–rotation coupling near a wall. In this work, we provide exact solutions for a squirmer (a model swimmer of spherical shape with a prescribed slip velocity) facing either towards or away from a planar wall perpendicular to gravity. These exact solutions are used to validate a numerical code based on the boundary integral method with an adaptive mesh for distances from the wall down to 0.1 % of the squirmer radius. This boundary integral code is then used to investigate the rich gravity-induced dynamics near a wall, mapping out the detailed bifurcation structures of the swimming dynamics in terms of orientation and distance to the wall. Simulation results show that a squirmer may traverse the wall, move to a fixed point at a given height with a fixed orientation in a monotonic way or in an oscillatory fashion, or oscillate in a limit cycle in the presence of wall repulsion. 

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3. A Bijection Between Evil-Avoiding and Rectangular Permutations

   https://doi.org/10.37236/11841  

   Tung, Katherine (October 2023, The Electronic Journal of Combinatorics)

   Evil-avoiding permutations, introduced by Kim and Williams in 2022, arise in the study of the inhomogeneous totally asymmetric simple exclusion process. Rectangular permutations, introduced by Chirivì, Fang, and Fourier in 2021, arise in the study of Schubert varieties and Demazure modules. Taking a suggestion of Kim and Williams, we supply an explicit bijection between evil-avoiding and rectangular permutations in $$S_n$$ that preserves the number of recoils. We encode these classes of permutations as regular languages and construct a length-preserving bijection between words in these regular languages. We extend the bijection to another Wilf-equivalent class of permutations, namely the $$1$$-almost-increasing permutations, and exhibit a bijection between rectangular permutations and walks of length $2n-2$ in a path of seven vertices starting and ending at the middle vertex. 

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4. Sparking a sulfur war between plants and pathogens

   https://doi.org/10.1016/j.tplants.2022.07.007  

   Wang, Wei; Liu, Jinbao; Mishra, Bharat; Mukhtar, M. Shahid; McDowell, John M. (December 2022, Trends in Plant Science)
5. Tradeoffs between safety and time: A routing view

   https://doi.org/10.1016/j.trc.2019.09.020  

   Carmody, Daniel R.; Sowers, Richard B. (November 2019, Transportation research Part C Emerging technologies)

   This article proposes a data-driven combination of travel times, distance, and collision counts in urban mobility datasets, with the goal of quantifying how intertwined traffic accidents are in the road network of a city. We devise a bi-attribute routing problem to capture the tradeoff between travel time and accidents. We apply this to a dataset from New York City. By visualizing the results of this computation in a normalized way, we provide a comparative tool for studies of urban traffic. 

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