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The temperature evolution of dilute soft inertial gas-solid suspensions is theoretically analyzed when the gas particles are influenced by a nonlinear drag force from a background fluid. The kinetic theory is extended to this system, and the time evolutions of the temperature and the kurtosis of the velocity distribution are derived. Molecular dynamics simulations are also performed to check the validity of the theory, and they show good agreement with the theoretical predictions.

The drag acting on an intruder in a three-dimensional frictionless dry granular environment is numerically studied. It is found the followings: (1) There is no yield force for the motion of the intruder without the gravity. (2) The drag is proportional to the cross section of the moving intruder. (3) If the intruder is larger than surrounding grains, the drag is proportional to the moving speed V of the intruder for dense systems, but it exhibits a crossover from quadratic to linear dependences of the moving speed when the volume fraction of the surrounding grains is much lower than the jamming point. (4) There is a plateau regime where the drag is almost independent of V if the size of the intruder is identical to those of the environmental grains and the volume fraction is near the jamming point.

In this paper, we present a comprehensive investigation of stress propagation in a two-dimensional elastic circular disk. To accurately describe the displacements and stress fields within the disk, we employ a scalar and vector potential approach, representing them as sums of Bessel functions. The determination of the coefficients for these expansions is accomplished in the Laplace space, where we compare the boundary conditions. By converting the inverse Laplace transforms into complex integrals using residue calculus, we successfully derive explicit expressions for the displacements and stress fields. Notably, these expressions encompass primary, secondary, and surface waves, providing a thorough characterization of the stress propagation phenomena within the disk. Our findings contribute to the understanding of mechanical behavior in disk-shaped components and can be valuable in the design and optimization of such structures across various engineering disciplines.

The kinetic theory of dilute granular gases with hard-core and inverse power-law potentials is developed. The scattering process is studied theoretically, which yields the relative speed and the impact parameter dependence of the scattering angle. The viscosity is derived from the Boltzmann equation and its temperature dependence is plotted. We also perform the direct simulation Monte Carlo to check the validity of the theory.

This paper investigates the stress and displacement distribution in a two-dimensional elastic hollow disk subjected to distributed diametric loading, extending our previous analysis of concentrated loading [Okamura et al. Strength Mater. 57, 102–114 (2025)]. The study provides deeper insights into the mechanical behavior of materials such as concrete and rock by examining the effects of load distribution on stress localization and displacement patterns. Using elastodynamic theory, we derive the static stress distributions and identify key differences from the concentrated loading case, particularly in the locations and magnitudes of stress extrema. This work contributes to a more comprehensive understanding of stress behavior in elastic disks under realistic loading conditions.

We demonstrate that discontinuous shear thickening (DST) can occur even in moderately dense, inertial suspensions of hydrodynamically interacting, frictionless soft particles. Using the Lubrication-Friction Discrete Element Method, our simulations reveal that DST can emerge at lower particle densities, provided that both the inertia of the suspended particles and their softness are sufficiently pronounced. Furthermore, we show that, under these conditions, the DST behavior obtained from the simulation qualitatively agrees with that predicted by kinetic theory, even without accounting for hydrodynamic interactions. These findings expand the understanding of DST in soft particle systems and highlight the importance of particle inertia and softness in controlling rheological behavior.

Abstract A kinetic theory for a dilute inertial suspension under a simple shear is developed. With the aid of the corresponding Boltzmann equation, it is found that the flow curves (the relations between the stress and the strain rate) exhibit the crossovers from the Newtonian to the Bagnoldian for a granular suspension and from the Newtonian to a fluid having a viscosity proportional to the square of the shear rate for a suspension consisting of elastic particles, respectively. The existence of the negative slope in the flow curve directly leads to a discontinuous shear thickening (DST). This DST corresponds to the discontinuous transition of the kinetic temperature between a quenched state and an ignited state. The results of the event-driven Langevin simulation of hard spheres perfectly agree with the theoretical results without any fitting parameter. The introduction of an attractive interaction between particles is also another source of the DST in dilute suspensions. Namely, there are two discontinuous jumps in the flow curve if the suspension particles have the attractive interaction.

Background Limited lumbar fusion surgery for adult spinal deformity (ASD) increases the risk of proximal junctional failure (PJF) at the thoracolumbar junction due to preserved mobility in this region. The majority of the extant research on PJF focuses on cases where the upper instrumented vertebra (UIV) is in the thoracic spine, whereas the aim of this study was to evaluate the correlation between Hounsfield Unit (HU) values around the thoracolumbar junction and the incidence of PJF following limited lumbar fusion. Methods A retrospective review identified patients aged ≥ 40 years who underwent fusion surgery spanning ≥ 3 levels with a UIV in the upper lumbar spine (L1-L3) and had a follow-up of at least two years. Demographic data, surgical factors, and spinopelvic parameters were analyzed. HU values were measured at the UIV, UIV + 1, and lower instrumented vertebra and were assessed for their association with PJF. Results Of 50 patients, 46 were included after excluding 4 who required reoperation for distal junctional failure. The mean age was 65.9 years, with a mean follow-up of 6.3 years. PJF was observed in 17 patients (36.9%). While most demographic and surgical factors were similar between groups, age was significantly associated with PJF ( p  = 0.024). Preoperative parameters significantly differed, including PT ( p  = 0.011), PI-LL ( p  = 0.010), SVA ( p  = 0.008), and HU at UIV/UIV + 1 ( p  = 0.006). Postoperative differences included PT ( p  = 0.007), PI-LL ( p  = 0.005), proximal junctional angle ( p  = 0.021), SVA ( p  = 0.021), and the global alignment and proportion (GAP) score ( p  = 0.001). Logistic regression identified low HU at UIV/UIV + 1 as the only independent PJF risk factor (OR: 0.975, 95% CI: 0.950–0.996, p  = 0.016), with a cutoff value of 97.8 HU (AUC = 0.745, p  = 0.022). PJF rates were 73.3%, 26.7%, and 12.5% for patients with HU < 98, 98–134, and > 134, respectively. Conclusion Preoperative low HU values at UIV/UIV + 1 independently predict PJF risk. HU assessment via preoperative CT imaging offers a critical tool for surgical planning in ASD limited lumbar fusion cases. Clinical trial number Not applicable.

Abstract We demonstrate that discontinuous shear thickening (DST) can take place even in a moderately dense inertial suspension consisting of frictionless soft particles. This DST can be regarded as ignited–quenched or exploded–continous shear thickening (CST) transitions in the inertial suspension. An approximate kinetic theory well recovers the results of the Langevin simulation in the wide range of the volume fraction without any fitting parameters.