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1. Ferroelectric nematic liquids with conics

   https://doi.org/10.1038/s41467-023-36326-1  

   Kumari, Priyanka; Basnet, Bijaya; Wang, Hao; Lavrentovich, Oleg D. (February 2023, Nature Communications)

   Abstract Spontaneous electric polarization of solid ferroelectrics follows aligning directions of crystallographic axes. Domains of differently oriented polarization are separated by domain walls (DWs), which are predominantly flat and run along directions dictated by the bulk translational order and the sample surfaces. Here we explore DWs in a ferroelectric nematic (N_F) liquid crystal, which is a fluid with polar long-range orientational order but no crystallographic axes nor facets. We demonstrate that DWs in the absence of bulk and surface aligning axes are shaped as conic sections. The conics bisect the angle between two neighboring polarization fields to avoid electric charges. The remarkable bisecting properties of conic sections, known for millennia, play a central role as intrinsic features of liquid ferroelectrics. The findings could be helpful in designing patterns of electric polarization and space charge. 

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2. Imaging the Néel vector switching in the monolayer antiferromagnet MnPSe3 with strain-controlled Ising order

   https://doi.org/10.1038/s41565-021-00885-5  

   Ni, Zhuoliang; Haglund, A. V.; Wang, H.; Xu, B.; Bernhard, C.; Mandrus, D. G.; Qian, X.; Mele, E. J.; Kane, C. L.; Wu, Liang (April 2021, Nature Nanotechnology)

   null (Ed.)

   Antiferromagnets are interesting materials for spintronics because of their faster dynamics and robustness against perturbations from magnetic fields. Control of the antiferromagnetic order constitutes an important step towards applications, but has been limited to bulk materials so far. Here, using spatially resolved second-harmonic generation, we show direct evidence of long-range antiferromagnetic order and Ising-type Néel vector switching in monolayer MnPSe3 with large XY anisotropy. In additional to thermally induced switching, uniaxial strain can rotate the Néel vector, aligning it to a general in-plane direction irrespective of the crystal axes. A change of the universality class of the phase transition in the XY model under uniaxial strain causes this emergence of strain-controlled Ising order in the XY magnet MnPSe3. Our discovery is a further ingredient for compact antiferromagnetic spintronic devices in the two-dimensional limit. 

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3. First law and quantum correction for holographic entanglement contour

   https://doi.org/10.21468/SciPostPhys.11.3.058  

   Han, Muxin; Wen, Qiang (January 2021, SciPost Physics)

   Entanglement entropy satisfies a first law-like relation, whichequates the first order perturbation of the entanglement entropy for theregion A A to the first order perturbation of the expectation value of the modularHamiltonian, \delta S_{A}=\delta \langle K_A \rangle δ S A = δ ⟨ K A ⟩ .We propose that this relation has a finer version which states that, thefirst order perturbation of the entanglement contour equals to the firstorder perturbation of the contour of the modular Hamiltonian,i.e.  \delta s_{A}(\textbf{x})=\delta \langle k_{A}(\textbf{x})\rangle δ s A ( 𝐱 ) = δ ⟨ k A ( 𝐱 ) ⟩ .Here the contour functions s_{A}(\textbf{x}) s A ( 𝐱 ) and k_{A}(\textbf{x}) k A ( 𝐱 ) capture the contribution from the degrees of freedom at \textbf{x} 𝐱 to S_{A} S A and K_A K A respectively. In some simple cases k_{A}(\textbf{x}) k A ( 𝐱 ) is determined by the stress tensor. We also evaluate the quantumcorrection to the entanglement contour using the fine structure of theentanglement wedge and the additive linear combination (ALC) proposalfor partial entanglement entropy (PEE) respectively. The fine structurepicture shows that, the quantum correction to the boundary PEE can beidentified as a bulk PEE of certain bulk region. While the shows thatthe quantum correction to the boundary PEE comes from the linearcombination of bulk entanglement entropy. We focus on holographictheories with local modular Hamiltonian and configurations of quantumfield theories where the applies. 

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4. 3D printing‐based full‐scale human brain for diverse applications

   https://doi.org/10.1002/brx2.5  

   Hua, Weijian; Zhang, Cheng; Raymond, Lily; Mitchell, Kellen; Wen, Lai; Yang, Ying; Zhao, Danyang; Liu, Shu; Jin, Yifei (April 2023, Brain‐X)

   Abstract Surgery is the most frequent treatment for patients with brain tumors. The construction of full‐scale human brain models, which is still challenging to realize via current manufacturing techniques, can effectively train surgeons before brain tumor surgeries. This paper aims to develop a set of three‐dimensional (3D) printing approaches to fabricate customized full‐scale human brain models for surgery training as well as specialized brain patches for wound healing after surgery. First, a brain patch designed to fit a wound's shape and size can be easily printed in and collected from a stimuli‐responsive yield‐stress support bath. Then, an inverse 3D printing strategy, called “peeling‐boiled‐eggs,” is proposed to fabricate full‐scale human brain models. In this strategy, the contour layer of a brain model is printed using a sacrificial ink to envelop the target brain core within a photocurable yield‐stress support bath. After crosslinking the contour layer, the as‐printed model can be harvested from the bath to photo crosslink the brain core, which can be eventually released by liquefying the contour layer. Both the brain patch and full‐scale human brain model are successfully printed to mimic the scenario of wound healing after removing a brain tumor, validating the effectiveness of the proposed 3D printing approaches. 

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5. Self-regulated non-reciprocal motions in single-material microstructures

   https://doi.org/10.1038/s41586-022-04561-z  

   Li, Shucong; Lerch, Michael M.; Waters, James T.; Deng, Bolei; Martens, Reese S.; Yao, Yuxing; Kim, Do Yoon; Bertoldi, Katia; Grinthal, Alison; Balazs, Anna C.; et al (May 2022, Nature)

   paired with distinct reverse arcs1,2. Efforts to mimic such dynamics synthetically rely on multimaterial designs but face limits to programming arbitrary motions or diverse behaviours in one structure3–8. Here we show how diverse, complex, non-reciprocal, stroke-like trajectories emerge in a single-material system through self-regulation. When a micropost composed of photoresponsive liquid crystal elastomer with mesogens aligned oblique to the structure axis is exposed to a static light source, dynamic dances evolve as light initiates a travelling order-to-disorder transition front, transiently turning the structure into a complex evolving bimorph that twists and bends via multilevel opto-chemo-mechanical feedback. As captured by our theoretical model, the travelling front continuously reorients the molecular, geometric and illumination axes relative to each other, yielding pathways composed from series of twisting, bending, photophobic and phototropic motions. Guided by the model, here we choreograph a wide range of trajectories by tailoring parameters, including illumination angle, light intensity, molecular anisotropy, microstructure geometry, temperature and irradiation intervals and duration. We further show how this opto-chemo-mechanical self-regulation serves as a foundation for creating self-organizing deformation patterns in closely spaced microstructure arrays via light-mediated interpost communication, as well as complex motions of jointed microstructures, with broad implications for autonomous multimodal actuators in areas such as soft robotics7,9,10, biomedical devices11,12 and energy transductionmaterials13, and for fundamental understanding of self-regulated systems14,15 

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