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1. Streaming Instability and Turbulence: Conditions for Planetesimal Formation

   https://doi.org/10.3847/1538-4357/ad47a2  

   Lim_임, Jeonghoon 정훈; Simon, Jacob B; Li_李, Rixin 日新; Armitage, Philip J; Carrera, Daniel; Lyra, Wladimir; Rea, David G; Yang_楊, Chao-Chin 朝欽; Youdin, Andrew N (July 2024, The Astrophysical Journal)

   Abstract The streaming instability (SI) is a leading candidate for planetesimal formation, which can concentrate solids through two-way aerodynamic interactions with the gas. The resulting concentrations can become sufficiently dense to collapse under particle self-gravity, forming planetesimals. Previous studies have carried out large parameter surveys to establish the critical particle to gas surface density ratio (Z), above which SI-induced concentration triggers planetesimal formation. The thresholdZdepends on the dimensionless stopping time (τ_s, a proxy for dust size). However, these studies neglected both particle self-gravity and external turbulence. Here, we perform 3D stratified shearing box simulations with both particle self-gravity and turbulent forcing, which we characterize via a turbulent diffusion parameter,α_D. We find that forced turbulence, at amplitudes plausibly present in some protoplanetary disks, can increase the thresholdZby up to an order of magnitude. For example, forτ_s= 0.01, planetesimal formation occurs whenZ≳ 0.06, ≳0.1, and ≳0.2 atα_D= 10⁻⁴, 10^−3.5, and 10⁻³, respectively. We provide a single fit to the criticalZrequired for the SI to work as a function ofα_Dandτ_s(although limited to the rangeτ_s= 0.01–0.1). Our simulations also show that planetesimal formation requires a mid-plane particle-to-gas density ratio that exceeds unity, with the critical value being largely insensitive toα_D. Finally, we provide an estimation of particle scale height that accounts for both particle feedback and external turbulence. 

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2. Coupled Self‐Scintillation and Photodetection in PbS Quantum Dots/Graphene X‐Ray Detectors

   https://doi.org/10.1002/adom.202503700  

   Shultz, Andrew; Gong, Maogang; Maroufian, Seyed A; Takacs, Fir; Wu, Judy Z (February 2026, Advanced Optical Materials)

   ABSTRACT Colloidal quantum dot/graphene (QD/Gr) nanohybrids rely on strong quantum confinement and offer a promising platform to design high‐performance quantum sensors such as photodetectors. In QD/Gr nanohybrid photodetectors, QDs absorb the incident light, and the spectral range is determined by the QD's semiconductor bandgap with moderate tunability by QD size, which presents a challenge for QDs/Gr nanohybrids to be used for detection of photons beyond such a conventional bandgap‐determined spectral range. In this work, we explored coupled self‐scintillation and X‐ray photodetection in PbS QD/Gr nanohybrids of sub‐micron active layer thickness for compromised X‐ray self‐scintillation by Pb of high X‐ray cross section and high‐gain detection enabled by graphene on both rigid and flexible substrates. An additional critical step found to suppress noise induced by interaction of polar molecules with dangling bonds on the QD surface was achieved by a poly(methyl methacrylate) capping layer, resulting in significantly improved signal‐to‐noise ratio. This allows a maximum X‐ray sensitivity of 280 C Gy⁻¹cm⁻², together with high responsivity in visible to infrared range on the order of 10 A/W. This result has demonstrated that the conventional bandgap‐determined spectral range can be significantly expanded through design of the QD/Gr nanohybrids. The demonstrated performance and mechanical flexibility provide a pathway toward durable, flexible quantum dot‐based detectors for multi‐spectrum sensing. 

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3. Mesoscopic flow simulation to understand the percolation through fine-ground electronic waste particle bed

   https://doi.org/10.1016/j.powtec.2025.120703  

   Diermyer, Zachary; Xia, Yidong; Hamed, Ahmed; Klinger, Jordan; Thompson, Vicki; Li, Zhen; Li, Jiaoyan (March 2025, Powder Technology)

   Mechanical size reduction is a critical pretreatment for hydrometallurgical recovery of valuable metals in electronic waste. The particle size resulting from milling ranges from a few micrometers to a few millimeters, presenting challenges of achieving sufficient leaching percolation in portions occupied by fine particles. This work investigates the hydrodynamics of percolation through micrometer-sized fine particle beds by using many-body dissipative particle dynamics flow simulations. The results show that higher effective pore size resulting from high aspect-ratio particle packing contributes to higher permeability than spherical particle packing. Increasing surface wettability enhances maximum saturation rates but reduces permeability. Moreover, increasing tortuosity negatively impacts permeability and the degree of reduction in permeability caused by increased surface wettability decreases with increasing tortuosity. These findings imply possible complex relationships between tortuosity, pore size, and surface wettability that collectively impact percolation in loosely packed fine particle beds and can be used to guide improvement in pretreatment. 

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4. Comparison of surface energy and adhesion energy of surface-treated particles

   Sansao, B.; Kellar, J.; Cross, W.; Romkes, A. (February 2021, Powder technology)

   null (Ed.)

   The mineral industry uses tremendous amounts of water every year in the processing of ores. Sustainable practices associated with the processing of ores are, therefore, of critical importance. The project described herein is the first step toward producing a dry, particle-separation process based upon control and exploitation of adhesive forces. In this research, the goal is to determine the surface energy of particles, and further, whether the solid sur- face energy can be used to understand the adhesion between these particles and surface-modified substrates. Glass spheres were chosen to represent silicate minerals, the most abundant type of minerals found in mineral deposits. The solid surface energy was found by using contact angle measurements and by applying the van Oss-Good-Chaudhury (VOGC) method. The VOGC method utilizes three-liquid triads to determine the Lifshitz- van der Waals, Lewis acid and Lewis base surface energy components. Surface energies from plasma-cleaned glass were between 40.2 and 60.2 mJ/m2; for the same glass with a hydrophobic chemical surface treatment, trichloro(octadecyl)silane (TCOD), the surface energy was between 20.8 and 20.9 mJ/m2; and for the glass with a hydrophilic chemical surface treatment (n1-(3-trimethoxysilylpropyl) diethylenetriamine (TMPA)) the surface energy was between 46.3 and 61.6 mJ/m2. The particle-substrate adhesion was also measured using a mechanical impact tester. Glass disks and beads were used, cleaned and surface treated with TCOD and TMPA. A custom horizontal impact tester was designed and used to measure the adhesion force between the glass spheres and a glass disk substrate. Impact of the disk/particle puck causes particle removal as tensile forces act on the particles. The tensile detachment force and adhesive force are equal at a critical particle size. Johnson- Kendall-Roberts (JKR) theory was used to determine the interfacial energy between the particles and the surface. The average interfacial energy of plasma cleaned glass, glass treated with TCOD and with TMPA were 44.8 mJ/m2, 21.6 mJ/m2, and 40.1 mJ/m2, respectively. These values are in good agreement with the literature values and with the interfacial energy determined using the VOGC method described above, demonstrating that two approaches compare favorably, despite the dramatically different methods (molecular vs mechanical) utilized. 

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5. Controlling Surface of Rods With Entrained Particle as Asperities

   https://doi.org/10.1115/1.4064646  

   Khalil, Md Ibrahim; Islam, Md Akibul; Tong, Dezhong; Jawed, Mohammad Khalid; Khoda, Bashir (March 2023, Journal of Micro- and Nano-Manufacturing)

   Abstract Changing the surface properties (i.e., roughness or friction) can be instrumental for many applications but can be a complex and resource-intensive process. In this paper, we demonstrate a novel process of controlling the friction of a continuous rod by delivering inorganic microparticles. A standardized continuous particle transfer protocol has been developed in our laboratory for depositing particles from a liquid carrier system (LCS) to the cylindrical rod substrate. The particle transfer process can produce controllable and tunable surface properties. Polymeric binder is used to deliver the particles as asperities over the rod substrate and by controlling their size, shape, and distribution, the coefficient of friction of the rod is determined. Tabletop experiments are designed and performed to measure the friction coefficient following the Capstan equation. The entrained particles on the substrate will create size- and shape-based asperities, which will alter the surface morphology toward the desired direction. Both oblique and direct quantitative measurements are performed at different particles and binder concentrations. A systematic variation in the friction coefficient is observed and reported in the result section. It is observed from the capstan experiment that adding only 1% irregular shaped particles in the suspension changes the friction coefficient of the rods by almost 115%. The proposed friction control technique is a simple scale-up, low-cost, low-waste, and low-energy manufacturing method for controlling the surface morphology. 

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