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1. Electrohydrodynamic flow about a colloidal particle suspended in a non-polar fluid

   https://doi.org/10.1017/jfm.2024.997  

   Wang, Zhanwen; Miksis, Michael J; Vlahovska, Petia M (December 2024, Journal of Fluid Mechanics)

   Nonlinear electrokinetic phenomena, where electrically driven fluid flows depend nonlinearly on the applied voltage, are commonly encountered in aqueous suspensions of colloidal particles. A prime example is the induced-charge electro-osmosis, driven by an electric field acting on diffuse charge induced near a polarizable surface. Nonlinear electrohydrodynamic flows also occur in non-polar fluids, driven by the electric field acting on space charge induced by conductivity gradients. Here, we analyse the flows about a charge-neutral spherical solid particle in an applied uniform electric field that arise from conductivity dependence on local field intensity. The flow pattern varies with particle conductivity: while the flow about a conducting particle has a quadrupolar pattern similar to induced-charge electro-osmosis, albeit with opposite direction, the flow about an insulating particle has a more complex structure. We find that this flow induces a force on a particle near an electrode that varies non-trivially with particle conductivity: while it is repulsive for perfectly insulating particles and particles more conductive than the suspending medium, there exists a range of particle conductivities where the force is attractive. The force decays as the inverse square of the distance to the electrode and thus can dominate the dielectrophoretic attraction due to the image dipole, which falls off with the fourth power with the distance. This electrohydrodynamic lift opens new possibilities for colloidal manipulation and driven assembly by electric fields. 

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2. A perspective on nonlinear, microwave, and quantum photonics with Kerr microcombs

   https://doi.org/10.1063/5.0181707  

   Chembo, Yanne K; Heidari, Elham; Menyuk, Curtis R (December 2023, Applied Physics Letters)

   Microresonator Kerr optical frequency combs currently constitute a well-established research area in integrated, nonlinear, and quantum photonics. These systems have found a plethora of technological applications, while serving as an excellent platform to investigate fundamental scientific topics such as light–matter interactions, pattern formation in driven-dissipative systems, or entangled twin-photon generation. We here provide a brief overview of the topic, highlight some of the most recent advances, and discuss a few of the main challenges ahead in this field. 

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3. A strontium-rich ultra-metal-poor star in the Atari disc component

   https://doi.org/10.1093/mnrasl/slad197  

   Mardini, Mohammad K.; Frebel, Anna; Chiti, Anirudh (December 2023, Monthly Notices of the Royal Astronomical Society: Letters)

   ABSTRACT We report on the discovery of the first ultra-metal-poor (UMP) star 2MASS J20500194−6613298 (J2050−6613; [Fe/H] = −4.05) selected from the Gaia BP/RP spectral catalogue that belongs to the ancient Atari disc component. We obtained a high-resolution spectrum for the star with the MIKE spectrograph on the Magellan-Clay telescope. J2050−6613 displays a typical chemical abundance pattern for UMP stars, including carbon and zinc enhancements. In contrast, J2050−6613 shows extremely high [Sr/Fe] and [Sr/Ba] ratios compared to other stars in the [Fe/H] < −4.0 regime. J2050−6613 is most likely an early Population II star that formed from a gas cloud that was chemically enriched by a massive Population III hypernova (E > 1052 erg). Such a Population III core-collapse hypernova could simultaneously explain the origin of the abundance pattern of light and heavy elements of 2MASS J2050−6613 if a large amount of Sr of ∼10−5 M⊙ was produced, possibly by neutrino-driven (wind) ejecta. Therefore, the abundance pattern of 2MASS J2050−6613 places important constraints on Sr-producing nucleosynthesis sources operating in the Atari progenitor at the earliest times. 

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4. Rise and fall of patterns in driven-dissipative Rydberg polaritons

   https://doi.org/10.1103/PhysRevResearch.6.033065  

   Alaeian, Hadiseh; Walther, Valentin (July 2024, Physical Review Research)

   In this study, we present an exploration of spontaneous symmetry breaking and pattern formation in the driven-dissipative system of Rydberg exciton polaritons with long-range interactions. Our investigation unravels the pattern formations through modulational instability, characterized by scales in the micron range. We observe the dynamics of the polariton ensemble, studying the emergence of metastable patterns and their eventual collapse in the long-time limit. This phenomenon is attributed to the destructive interference between the polariton state and the external drive within the ensemble. Further, we delineate conditions conducive to the stable formation of patterns under incoherent pumping. These findings open up various avenues for delving into the burgeoning realm of driven-dissipative and long-range interacting gases through the unique characteristics of Rydberg excitons. Published by the American Physical Society2024 

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5. Lianas decelerate tropical forest thinning during succession

   https://doi.org/10.1111/ele.14008  

   Medina‐Vega, José A.; van der Heijden, Geertje M. F.; Schnitzer, Stefan A.; Penuelas, ed., Josep (April 2022, Ecology Letters)

   Abstract The well‐established pattern of forest thinning during succession predicts an increase in mean tree biomass with decreasing tree density. The forest thinning pattern is commonly assumed to be driven solely by tree‐tree competition. The presence of non‐tree competitors could alter thinning trajectories, thus altering the rate of forest succession and carbon uptake. We used a large‐scale liana removal experiment over 7 years in a 60‐ to 70‐year‐old Panamanian forest to test the hypothesis that lianas reduce the rate of forest thinning during succession. We found that lianas slowed forest thinning by reducing tree growth, not by altering tree recruitment or mortality. Without lianas, trees grew and presumably competed more, ultimately reducing tree density while increasing mean tree biomass. Our findings challenge the assumption that forest thinning is driven solely by tree‐tree interactions; instead, they demonstrate that competition from other growth forms, such as lianas, slow forest thinning and ultimately delay forest succession. 

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