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1. Global hypersurfaces of section in the spatial restricted three-body problem

   https://doi.org/10.1088/1361-6544/ac692b  

   Moreno, Agustin; van Koert, Otto (May 2022, Nonlinearity)

   We propose a contact-topological approach to the spatial circular restricted three-body problem, for energies below and slightly above the first critical energy value. We prove the existence of a circle family of global hypersurfaces of section for the regularized dynamics. Below the first critical value, these hypersurfaces are diffeomorphic to the unit disk cotangent bundle of the 2-sphere, and they carry symplectic forms on their interior, which are each deformation equivalent to the standard symplectic form. The boundary of the global hypersurface of section is an invariant set for the regularized dynamics that is equal to a level set of the Hamiltonian describing the regularized planar problem. The first return map is Hamiltonian, and restricts to the boundary as the time-1 map of a positive reparametrization of the Reeb flow in the planar problem. This construction holds for any choice of mass ratio, and is therefore non-perturbative. We illustrate the technique in the completely integrable case of the rotating Kepler problem, where the return map can be studied explicitly. 

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2. Compression Acceleration of Protons and Heavier Ions at the Heliospheric Current Sheet

   https://doi.org/10.3847/1538-4357/ad6e80  

   Murtas, Giulia; Li, Xiaocan; Guo, Fan (October 2024, The Astrophysical Journal)

   Abstract Recent observations by the Parker Solar Probe (PSP) suggest that protons and heavier ions are accelerated to high energies by magnetic reconnection at the heliospheric current sheet (HCS). By solving the energetic particle transport equation in large-scale MHD simulations, we study the compression acceleration of protons and heavier ions in the reconnecting HCS. We find that the acceleration of multispecies ions results in nonthermal power-law distributions with a spectral index consistent with the PSP observations. Our study shows that the high-energy cutoff of protons can reach $E_{\max }\sim 0.1$–1 MeV depending on the particle diffusion coefficients. We also study how the high-energy cutoff of different ion species scales with the charge-to-mass ratio $E_{\max }\propto {\left(Q/M\right)}^{\alpha }$. When determining the diffusion coefficients from the quasi-linear theory with a Kolmogorov magnetic power spectrum, we find thatα∼ 0.4, which is somewhat smaller thanα∼ 0.7 observed by PSP. 

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3. Conditional $$L^{\infty }$$ Estimates for the Non-cutoff Boltzmann Equation in a Bounded Domain

   https://doi.org/10.1007/s00205-024-02002-x  

   Ouyang, Zhimeng; Silvestre, Luis (August 2024, Archive for Rational Mechanics and Analysis)

   We consider weak solutions of the inhomogeneous non-cutoff Boltzmann equa- tion in a bounded domain with any of the usual physical boundary conditions: in-flow, bounce-back, specular-reflection and diffuse-reflection. When the mass, energy and entropy densities are bounded above, and the mass density is bounded away from a vacuum, we obtain an estimate of the L∞ norm of the solution de- pending on the macroscopic bounds on these hydrodynamic quantities only. This is a regularization effect in the sense that the initial data is not required to be bounded. We present a proof based on variational ideas, which is fundamentally different to the proof that was previously known for the equation in periodic spatial domains 

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4. Cauchy problems for Einstein equations in three-dimensional spacetimes

   https://doi.org/10.1088/1361-6382/adc4b7  

   Chruściel, Piotr T; Cong, Wan; Quéau, Théophile; Wutte, Raphaela (April 2025, Classical and Quantum Gravity)

   Abstract We analyze existence and properties of solutions of two-dimensional general relativistic initial data sets with a negative cosmological constant, both on spacelike and characteristic surfaces. A new family of such vacuum spacelike data parameterised by poles at the conformal boundary at infinity is constructed. We review the notions of global Hamiltonian charges, emphasizing the difficulties arising in this dimension, both in a spacelike and characteristic setting. One or two, depending upon the topology, lower bounds for energy in terms of angular momentum, linear momentum, and center of mass are established. 

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5. Generation of fast photoelectrons in strong-field emission from metal nanoparticles

   https://doi.org/10.1515/nanoph-2024-0719  

   Saydanzad, Erfan; Powell, Jeffrey; Renner, Tim; Summers, Adam; Rolles, Daniel; Trallero-Herrero, Carlos; Kling, Matthias F; Rudenko, Artem; Thumm, Uwe (April 2025, Nanophotonics)

   We investigated the generation and control of fast photoelectrons (PEs) by exposing plasmonic nanoparticles (NPs) to short infrared (IR) laser pulses with peak intensities between 10¹²and 3 × 10¹³ W/cm². Our measured and numerically simulated PE momentum distributions demonstrate the extent to which PE yields and cutoff energies are controlled by the NP size, material, and laser peak intensity. For strong-field photoemission from spherical silver, gold, and platinum NPs with diameters between 10 and 100 nm our results confirm and surpass extremely high PEs cutoff energies, up to several hundred times the incident laser-pulse ponderomotive energy, found recently for gold nanospheres [Saydanzad et al., Nanophotonics12, 1931 (2023)]. As reported previously for dielectric NPs [Rupp et al., J. Mod. Opt.64, 995 (2017)], at higher intensities the cutoff energies we deduce from measured and simulated PE spectra tend to converge to a metal-independent limit. We expect these characteristics of light-induced electron emission from prototypical plasmonic metallic nanospheres to promote the understanding of the electronic dynamics in more complex plasmonic nanostructures and the design of nanoscale light-controlled plasmonic electron sources for photoelectronic devices of applied interest. 

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