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1. Detection of the 4.4-MeV gamma rays from 16O( ν, ν ′)16O(12.97 MeV, 2−) with a water Cherenkov detector in supernova neutrino bursts

   https://doi.org/10.1093/ptep/ptac168  

   Sakuda, Makoto; Suzuki, Toshio; Reen, Mandeep Singh; Nakazato, Ken’ichiro; Suzuki, Hideyuki (January 2023, Progress of Theoretical and Experimental Physics)

   Abstract We first discuss and determine the isospin mixing of the two 2− states (12.53 MeV and 12.97 MeV) of the16O nucleus using inelastic electron scattering data. We then evaluate the cross section of 4.4-MeV γ rays produced in the neutrino neutral-current (NC) reaction 16O(ν, ν′)16O(12.97 MeV, 2−) in a water Cherenkov detector at a low energy, below 100 MeV. The detection of γ rays for Eγ > 5 MeV from the NC reaction 16O(ν, ν′)16O(Ex > 16 MeV, T = 1) with a water Cherenkov detector in supernova neutrino bursts has been proposed and discussed by several authors previously. In this article, we discuss a new NC reaction channel from 16O(12.97 MeV, 2−) producing a 4.4-MeV γ ray, the cross section of which is more robust and even larger at low energy (Eν < 25 MeV) than the NC cross section from 16O(Ex > 16 MeV, T = 1). We also evaluate the number of such events induced by neutrinos from supernova explosion which can be observed by the Super-Kamiokande, an Earth-based 32-kton water Cherenkov detector. 

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2. Size-Dependent Diffusion and Dispersion of Particles in Mucin

   https://doi.org/10.3390/polym15153241  

   Kumar, Parveen; Tamayo, Joshua; Shiu, Ruei-Feng; Chin, Wei-Chun; Gopinath, Arvind (August 2023, Polymers)

   Mucus, composed significantly of glycosylated mucins, is a soft and rheologically complex material that lines respiratory, reproductive, and gastrointestinal tracts in mammals. Mucus may present as a gel, as a highly viscous fluid, or as a viscoelastic fluid. Mucus acts as a barrier to the transport of harmful microbes and inhaled atmospheric pollutants to underlying cellular tissue. Studies on mucin gels have provided critical insights into the chemistry of the gels, their swelling kinetics, and the diffusion and permeability of molecular constituents such as water. The transport and dispersion of micron and sub-micron particles in mucin gels and solutions, however, differs from the motion of small molecules since the much larger tracers may interact with microstructure of the mucin network. Here, using brightfield and fluorescence microscopy, high-speed particle tracking, and passive microrheology, we study the thermally driven stochastic movement of 0.5–5.0 μm tracer particles in 10% mucin solutions at neutral pH, and in 10% mucin mixed with industrially relevant dust; specifically, unmodified limestone rock dust, modified limestone, and crystalline silica. Particle trajectories are used to calculate mean square displacements and the displacement probability distributions; these are then used to assess tracer diffusion and transport. Complex moduli are concomitantly extracted using established microrheology techniques. We find that under the conditions analyzed, the reconstituted mucin behaves as a weak viscoelastic fluid rather than as a viscoelastic gel. For small- to moderately sized tracers with a diameter of lessthan 2 μm, we find that effective diffusion coefficients follow the classical Stokes–Einstein relationship. Tracer diffusivity in dust-laden mucin is surprisingly larger than in bare mucin. Probability distributions of mean squared displacements suggest that heterogeneity, transient trapping, and electrostatic interactions impact dispersion and overall transport, especially for larger tracers. Our results motivate further exploration of physiochemical and rheological mechanisms mediating particle transport in mucin solutions and gels. 

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3. Mercury’s Chaotic Secular Evolution as a Subdiffusive Process

   https://doi.org/10.3847/1538-4357/ad3e5f  

   Abbot, Dorian S; Webber, Robert J; Hernandez, David M; Hadden, Sam; Weare, Jonathan (May 2024, The Astrophysical Journal)

   Abstract Mercury’s orbit can destabilize, generally resulting in a collision with either Venus or the Sun. Chaotic evolution can causeg₁to decrease to the approximately constant value ofg₅and create a resonance. Previous work has approximated the variation ing₁as stochastic diffusion, which leads to a phenomological model that can reproduce the Mercury instability statistics of secular andN-body models on timescales longer than 10 Gyr. Here we show that the diffusive model significantly underpredicts the Mercury instability probability on timescales less than 5 Gyr, the remaining lifespan of the solar system. This is becauseg₁exhibits larger variations on short timescales than the diffusive model would suggest. To better model the variations on short timescales, we build a new subdiffusive phenomological model forg₁. Subdiffusion is similar to diffusion but exhibits larger displacements on short timescales and smaller displacements on long timescales. We choose model parameters based on the behavior of theg₁trajectories in theN-body simulations, leading to a tuned model that can reproduce Mercury instability statistics from 1–40 Gyr. This work motivates fundamental questions in solar system dynamics: why does subdiffusion better approximate the variation ing₁than standard diffusion? Why is there an upper bound ong₁, but not a lower bound that would prevent it from reachingg₅? 

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4. Vertical velocity of a small sphere in a sheared granular bed

   https://doi.org/10.1103/PhysRevResearch.6.L022015  

   Gao, Song; Ottino, Julio M; Lueptow, Richard M; Umbanhowar, Paul B (April 2024, Physical Review Research)

   Small particles fall through sheared beds of larger particles in settings ranging from geophysics to industry, but the study of large-to-small size ratios $R$, spanning the trapping threshold $R_t,$has been neglected. In simulations of noncohesive spheres for $R<R_t,$the small-sphere vertical velocity $v_p$first increases with shear rate $\dot{\gamma }$as trapping time decreases, but $v_p$then decreases as velocity fluctuations frustrate downward mobility. For $R>R_t, v_p$is constant at low $\dot{\gamma },$but again decreases at high $\dot{\gamma }$. We model these behaviors and discuss analogies with electron transport in solids. Published by the American Physical Society2024 

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5. P-V-T equation of state of boron carbide

   Somayazulu, M.; Ahart, M.; Meng, Y.; Ciezak, J.; Velisavlevic, N.; Hemley, R. J. (October 2023, Philosophical transactions A)

   We report the P-V-T equation of state measurements of B4C to 50GPa and approximately 2500K in laser-heated diamond anvil cells. We obtain an ambient temperature, third-order Birch–Murnaghan fit to the P-V data that yields a bulk modulus K0 of 221(2) GPa and derivative, (dK/dP)0 of 3.3(1). These were used in fits with both a Mie–Grüneisen– Debye model and a temperature-dependent, Birch– Murnaghan equation of state that includes thermal pressure estimated by thermal expansion (α) and a temperature-dependent bulk modulus (dK0/dT). The ambient pressure thermal expansion coefficient (α0+α1T), Grüneisen γ (V)=γ 0(V/V0)q and volumedependent Debye temperature, were used as input parameters for these fits and found to be sufficient to describe the data in the whole P-T range of this study. 

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