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1. Atmospheric effects on the laser-driven avalanche-based remote detection of radiation

   https://doi.org/10.1364/OL.488346  

   Zingale, A.; Waczynski, S.; Sears, J.; Lakis, R_E; Milchberg, H_M (May 2023, Optics Letters)

   The effect of realistic atmospheric conditions on mid-IR (λ = 3.9 µm) and long-wave-IR (λ = 10 µm) laser-induced avalanche breakdown for the remote detection of radioactive material is examined experimentally and with propagation simulations. Our short-range in-lab mid-IR laser experiments show a correlation between increasing turbulence level and a reduced number of breakdown sites associated with a reduction in the portion of the focal volume above the breakdown threshold. Simulations of propagation through turbulence are in excellent agreement with these measurements and provide code validation. We then simulate propagation through realistic atmospheric turbulence over a long range (0.1–1 km) in the long-wave-IR regime (λ = 10 µm). The avalanche threshold focal volume is found to be robust even in the presence of strong turbulence, only dropping by ∼50% over a propagation length of ∼0.6 km. We also experimentally assess the impact of aerosols on avalanche-based detection, finding that, while background counts increase, a useful signal is extractable even at aerosol concentrations 10⁵times greater than what is typically observed in atmospheric conditions. Our results show promise for the long-range detection of radioactive sources under realistic atmospheric conditions. 

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2. Observations of River Plume Mixing in the Surf Zone

   https://doi.org/10.1175/JPO-D-21-0286.1  

   Kastner, S. E.; Horner-Devine, A. R.; Thomson, J. M.; Giddings, S. N. (March 2023, Journal of Physical Oceanography)

   We use salinity observations from drifters and moorings at the Quinault River mouth to investigate mixing and stratification in a surf-zone-trapped river plume. We quantify mixing based on the rate of change of salinity DS/Dt in the drifters’ quasi-Lagrangian reference frame. We estimate a constant value of the vertical eddy diffusivity of salt of Kz=(2.2 +/- 0.6) x 10^-3 m^2 s^-1, based on the relationship between vertically integrated DS/Dt and stratification, with values as high as 1 x 10^-2 m^2 s^-1 when stratification is low. Mixing, quantified as DS/Dt, is directly correlated to surf-zone stratification, and is therefore modulated by changes in stratification caused by tidal variability in freshwater volume flux. High DS/Dt is observed when the near-surface stratification is high and salinity gradients are collocated with wave-breaking turbulence. We observe a transition from low stratification and low DS/Dt at low tidal stage to high stratification and high DS/Dt at high tidal stage. Observed wave-breaking turbulence does not change significantly with stratification, tidal stage, or offshore wave height; as a result, we observe no relationship between plume mixing and offshore wave height for the range of conditions sampled. Thus, plume mixing in the surf zone is altered by changes in stratification; these are due to tidal variability in freshwater flux from the river and not wave conditions, presumably because depth-limited wave breaking causes sufficient turbulence for mixing to occur during all observed conditions. 

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3. Spectra of Magnetic Turbulence in a Relativistic Plasma

   https://doi.org/10.3847/2041-8213/ac6cde  

   Vega, Cristian; Boldyrev, Stanislav; Roytershteyn, Vadim (May 2022, The Astrophysical Journal Letters)

   Abstract We present a phenomenological and numerical study of strong Alfvénic turbulence in a magnetically dominated collisionless relativistic plasma with a strong background magnetic field. In contrast with the nonrelativistic case, the energy in such turbulence is contained in magnetic and electric fluctuations. We argue that such turbulence is analogous to turbulence in a strongly magnetized nonrelativistic plasma in the regime of broken quasi-neutrality. Our 2D particle-in-cell numerical simulations of turbulence in a relativistic pair plasma find that the spectrum of the total energy has the scalingk^−3/2, while the difference between the magnetic and electric energies, the so-called residual energy, has the scalingk^−2.4. The electric and magnetic fluctuations at scaleℓexhibit dynamic alignment with the alignment angle scaling close to $\cos {\varphi }_{\mathit{\ell }}\propto {\mathit{\ell }}^{1/4}$. At scales smaller than the (relativistic) plasma inertial scale, the energy spectrum of relativistic inertial Alfvén turbulence steepens tok^−3.5. 

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4. Positive feedback: How a synergy between the streaming instability and dust coagulation forms planetesimals

   https://doi.org/10.1051/0004-6361/202554100  

   Carrera, Daniel; Lim, Jeonghoon; Eriksson, Linn_E J; Lyra, Wladimir; Simon, Jacob B (April 2025, Astronomy & Astrophysics)

   Context.One of the most important open questions in planet formation is how dust grains in a protoplanetary disk manage to overcome growth barriers and form the ∼100 km planet building blocks that we call planetesimals. There appears to be a gap between the largest grains that can be produce by coagulation, and the smallest grains that are needed for the streaming instability (SI) to form planetesimals. Aims.Here we explore the novel hypothesis that dust coagulation and the SI work in tandem; in other words, they form a feedback loop where each one boosts the action of the other to bridge the gap between dust grains and planetesimals. Methods.We developed a semi-analytical model of dust concentration due to the SI, and an analytic model of how the SI affects the fragmentation and radial drift barriers. We then combined them to model our proposed feedback loop. Results.In the fragmentation-limited regime, we find a powerful synergy between the SI and dust growth that drastically increases both grain sizes and densities. We find that a midplane dust-to-gas ratio ofϵ ≥ 0.3 is a sufficient condition for the feedback loop to reach the planetesimal-forming region for turbulence values 10⁻⁴ ≤ α ≤ 10⁻³and grain sizes 0.01 ≤ St ≤ 0.1. In contrast, the drift-limited regime only shows grain growth without significant dust accumulation. In other words, planetesimal formation remains challenging in the drift-dominated regime and dust traps may be required to allow planet formation at wide orbital distances. 

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5. Long-range nonspreading propagation of sound beam through periodic layered structure

   https://doi.org/10.1038/s42005-020-00422-1  

   Zubov, Yurii; Djafari-Rouhani, Bahram; Jin, Yuqi; Sofield, Mathew; Walker, Ezekiel; Neogi, Arup; Krokhin, Arkadii (September 2020, Communications Physics)

   Abstract Linear spreading of a wave packet or a Gaussian beam is a fundamental effect known in evolution of quantum state and propagation of optical/acoustic beams. The rate of spreading is determined by the diffraction coefficientDwhich is proportional to the curvature of the isofrequency surface. Here, we analyzed dispersion of sound in a solid-fluid layered structure and found a flex point on the isofrequency curve whereDvanishes for given direction of propagation and frequency. Nonspreading propagation is experimentally observed in a water steel lattice of 75 periods (~1 meter long) and occurs in the regime of anomalous dispersion and strong acoustic anisotropy when the effective mass along periodicity is close to zero. Under these conditions the incoming beam experiences negative refraction of phase velocity leading to backward wave propagation. The observed effect is explained using a complete set of dynamical equations and our effective medium theory. 

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