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1. Photoproduction of Axionlike Particles

   https://doi.org/10.1103/PhysRevLett.123.071801  

   Aloni, Daniel; Fanelli, Cristiano; Soreq, Yotam; Williams, Mike (August 2019, Physical Review Letters)
2. Mechanical properties of particles

   https://doi.org/10.22323/1.346.0066  

   Polyakov, Maxim; Schweitzer, Peter (August 2019, 23rd International Symposium on Spin Physics (SPIN 2018))

   Selected topics related to the physics of the energy-momentum tensor (EMT) form factors are discussed. The topics are: 1) Fundamental mechanical properties of particles and gravity 2) Mechanical properties of non-spherical particles 3) Gravitational form factors of Goldstone bosons 4) Nucleon's seismology? 

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3. Spectral emissivities and temperatures of burning iron as single particles or groups of particles

   https://doi.org/10.1016/j.fuel.2024.132537  

   Yao, Yuan; Chang, Di; Panahi, Aidin; Levendis, Yiannis A (November 2024, Fuel)

   Nimmo, Bill (Ed.)

   This manuscript reports on the combustion of powdered iron, for the purpose of utilizing it as an environmentally friendly circular energy carrier. The conducted research investigated the spectral emissivity and temperature of iron particles, burned either individually or in groups. Combustion experiments were conducted under high heating rates in an externally-heated drop tube furnace. The pressure was atmospheric and the axial temperature was nearly-constant at ~1350 K. The oxidizer gas contained 15-100% oxygen in nitrogen diluent. Iron particles were sieve-classified in the 44-53 µm range. Results showed that, depending on the oxygen concentration, and consequently the particle temperature, the average spectral emissivities of single burning particles varied between 0.18 and 0.46, in the 600-1000 nm wavelength range. Corresponding temperatures of single particles varied between 2300 K and 2800 K, increasing with increasing oxygen concentration in the gas. In the case of groups of iron particles burning in air at different particle number densities, average spectral emissivities were found to be in the range of 0.42-0.45, with the upper value associated with denser particle clouds. Corresponding peak temperatures of particle burning in groups were found to be in the range of 2160 K to 2100 K, with the lower value attributed to denser particle clouds. 

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4. Hopper flows of deformable particles

   https://doi.org/10.1039/d2sm01079h  

   Cheng, Yuxuan; Treado, John D.; Lonial, Benjamin F.; Habdas, Piotr; Weeks, Eric R.; Shattuck, Mark D.; O'Hern, Corey S. (November 2022, Soft Matter)

   Numerous experimental and computational studies show that continuous hopper flows of granular materials obey the Beverloo equation that relates the volume flow rate Q and the orifice width w : Q ∼ ( w / σ avg − k ) β , where σ avg is the average particle diameter, kσ avg is an offset where Q ∼ 0, the power-law scaling exponent β = d − 1/2, and d is the spatial dimension. Recent studies of hopper flows of deformable particles in different background fluids suggest that the particle stiffness and dissipation mechanism can also strongly affect the power-law scaling exponent β . We carry out computational studies of hopper flows of deformable particles with both kinetic friction and background fluid dissipation in two and three dimensions. We show that the exponent β varies continuously with the ratio of the viscous drag to the kinetic friction coefficient, λ = ζ / μ . β = d − 1/2 in the λ → 0 limit and d − 3/2 in the λ → ∞ limit, with a midpoint λ c that depends on the hopper opening angle θ w . We also characterize the spatial structure of the flows and associate changes in spatial structure of the hopper flows to changes in the exponent β . The offset k increases with particle stiffness until k ∼ k max in the hard-particle limit, where k max ∼ 3.5 is larger for λ → ∞ compared to that for λ → 0. Finally, we show that the simulations of hopper flows of deformable particles in the λ → ∞ limit recapitulate the experimental results for quasi-2D hopper flows of oil droplets in water. 

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5. The color of aerosol particles

   https://doi.org/10.1038/s41598-023-28823-6  

   Giri, Ramesh; Berg, Matthew J. (December 2023, Scientific Reports)

   Abstract Digital in-line holography (DIH) is an established method to image small particles in a manner where image reconstruction is performed computationally post-measurement. This ability renders it ideal for aerosol characterization, where particle collection or confinement is often difficult, if not impossible. Conventional DIH provides a gray-scale image akin to a particle’s silhouette, and while it gives the particle size and shape, there is little information about the particle material. Based on the recognition that the spectral reflectance of a surface is partly determined by the material, we demonstrate a method to image free-flowing particles with DIH in color with the eventual aim to differentiate materials based on the observed color. Holograms formed by the weak backscattered light from individual particles illuminated by red, green, and blue lasers are recorded by a color sensor. Images are reconstructed from the holograms and then layered to form a color image, the color content of which is quantified by chromaticity analysis to establish a representative signature. A variety of mineral dust aerosols are studied where the different signatures suggest the possibility to differentiate particle material. The ability of the method to resolve the inhomogeneous composition within a single particle in some cases is shown as well. 

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