Abstract We present recent developments in Pythia for the modelling of hadronic cascades in a medium. Several improvements have been made in the Angantyr model for collisions with nuclei, especially in the limit of low collision energies, allowing it to be used throughout the hadronic cascades. Also the simplified nuclear model in the PythiaCascade module has been updated. We find that the two models give consistent results for cosmic ray air showers initiated by both high energy protons and nuclei.

A Fourier-based dynamic smooth JKR model for adhesive particle collisions without nonphysical attraction forces

Context . Giant impacts between planetary embryos are a natural step in the terrestrial planet formation process and are expected to create disks of warm debris in the terrestrial regions of their stars. Understanding the gas and dust debris produced in giant impacts is vital for comprehending and constraining models of planetary collisions. Aims . We reveal the distribution of millimeter (mm) grains in the giant impact debris disk of HD 172555 for the first time, using new ALMA 0.87 mm observations at ∼80 mas (2.3 au) resolution. Methods . We modeled the interferometric visibilities to obtain basic spatial properties of the disk and compared these data to the disk’s dust and gas distributions at other wavelengths. Results . We detected the star and dust emission from an inclined disk out to ∼9 au and down to 2.3 au (on-sky) from the central star, with no significant asymmetry in the dust distribution. The radiative transfer modeling of the visibilities indicates the disk surface density distribution of mm grains most likely peaks around ∼5 au, while the width inferred remains model-dependent at the S/N of the data. We highlighted an outward radial offset of the small grains traced by scattered light observations compared to the mm grains, which could be explained by the combined effect of gas drag and radiation pressure in the presence of large enough gas densities. Furthermore, our SED modeling implies a size distribution slope for the mm grains consistent with the expectation of collisional evolution and flatter than inferred for the micron-sized grains, implying a break in the grain size distribution and confirming an overabundance of small grains.

This paper presents a common setting for the collision integrals [Formula: see text] appearing in the kinetic theory of dense gases. It includes the collision integrals of the Enskog equation, of (a variant of) the Povzner equation, and of a model for soft sphere collisions proposed by Cercignani (Comm. Pure Appl. Math. 36 (1983) 479–494). All these collision integrals are “delocalized”, in the sense that they involve products of the distribution functions of gas molecules evaluated at positions whose distance is of the order of the molecular radius. Our first main result is to express these collision integrals as the divergence in [Formula: see text] of some mass current, where [Formula: see text] is the velocity variable, while [Formula: see text] and [Formula: see text] are expressed as the phase space divergence (i.e. divergence in both position and velocity) of appropriate momentum and energy currents. This extends to the case of dense gases an earlier result by Villani (Math. Model. Numer. Anal. M2AN 33 (1999) 209–227) in the case of the classical Boltzmann equation (where the collision integral involves products of the distribution function of gas molecules evaluated at different velocities, but at the same position. Applications of this conservative formulation of delocalized collision integrals include the possibility of obtaining the local conservation laws of momentum and energy starting from this kinetic theory of denses gases. Similarly a local variant of the Boltzmann H Theorem, involving some kind of free energy instead of Boltzmann’s H function, can be obtained in the form of an expression for the entropy production in terms of the phase space divergence of some phase space current, and of a nonpositive term.

Nonequilibrium steady states in multi-bath quantum collision models

Exploring novel surrogate safety indicators measuring conflict riskiness and severity: a case study in Sacramento, United States.

ABSTRACT This study investigates the charging performance of single‐qubit and multi‐qubit quantum batteries in both Markovian and non‐Markovian environments. Using the collision model to simulate a bosonic bath, we provide a detailed study of the impact of temperature on battery performance through both analytical and numerical solutions in a prepared thermal bath, demonstrating that high temperature generally suppresses steady‐state ergotropy of quantum batteries, while also accelerating the convergence to the steady state. By applying the Luo‐Fu‐Song measure of non‐Markovianity, it is found that the information backflow generated in a non‐Markovian environment further enhances the battery's ergotropy and speeds up the approach to the steady state. Additionally, when studying multi‐qubit quantum battery, we consider each individual spin as an independent battery unit. The results show that non‐Markovian memory effects allow spins directly coupled to the bath to store more energy. Notably, with elevated temperature even enhancing their steady‐state ergotropy due to information backflow. Finally, we find that the battery's mixedness is always positively correlated with the unavailable energy. This provides theoretical support for distributed energy extraction in quantum batteries.

Abstract Metronome synchronization and the transition between the in-phase and anti-phase synchronization have been observed in classical systems. We demonstrate the quantum analog of this phenomenon in a two-qubit system coupled to a common environment. Tracing out the environment in the quantum collision model, we obtain an effective master equation with a two-body dissipator for two qubits. Quenching the two-body dissipator, we demonstrate controlled transitions from in-phase to anti-phase synchronization. This synchronization transition is robust against noise. Signatures of the transition are observed through Pearson correlation coefficient measurements obtained via quantum simulations on superconducting circuits. Future experiments employing qutrit systems are expected to yield a more pronounced effect.

Abstract The repeated interaction model provides a framework for emulating and analyzing the dynamics of open quantum systems. We explore here the dynamics generated by this protocol in a system that is simultaneously coupled to two baths through noncommuting system operators. One bath is made to couple to nondiagonal elements of the system, thus it induces dissipative dynamics, while the other couples to diagonal elements, and by itself it generates pure dephasing. By solving the problem analytically exactly, we show that when both baths act concurrently, a strong systembath coupling gives rise to nonadditive effects in the dynamics. A prominent signature of this nonadditivity is the characteristic slowing down of population relaxation, driven by the influence of the dephasing bath. Beyond dynamics, we investigate the thermodynamic behavior of the model. Previous studies, using quantum master equations, showed that strong system-bath coupling created bath-cooperativity in this model, allowing heat exchange to the dephasing (diagonally coupled) bath. We find instead that, under the repeated interaction scheme, heat flows exclusively to the dissipative bath (coupled through nondiagonal elements). Our results highlight the need for a deeper understanding of the types of open quantum system dynamics and steady-state phenomena that emerge within the repeated interaction framework and the relation of this protocol to other common open quantum system techniques.

Abstract The total electron detachment cross section for the O 2 - + O 2 collision system has been measured with the beam attenuation method and with the signal growth rate method in the energy range of 1.5 to 10 keV. Given the loose nature of the extra attached electron on the oxygen molecule, it is demonstrated that at the present kinetic energy range, the cross-section velocity dependence can be understood under the framework of a collision between a quasi-free electron and the molecular target within the free collision model. Comparison between the O 2 - + O 2 and the e - + O 2 collision systems highlights the importance of the resonant behavior of the interaction between the quasi-free electron of the O 2 - projectile and the O 2 target. In addition, differences between detachment data obtained using the two experimental methods is analysed and attributed to the role played by long-lived metastable auto-detaching states in each method.

Carroll hydrodynamics arises in the [Formula: see text] limit of relativistic hydrodynamics. Instances of its relevance include the Bjorken and Gubser flow models of heavy-ion collisions, where the ultrarelativistic nature of the flow makes the physics effectively Carrollian. In this paper, we explore the structure of hydrodynamics in what can be termed as the Carrollian regime, where instead of keeping only the leading terms in the [Formula: see text] limit of relativistic hydrodynamics, we perform a small-c expansion and retain the subleading terms as well. We do so both for perfect fluids as well as viscous fluids incorporating first-order derivative corrections. As apposite applications of the formalism, we utilize the subleading terms to compute modifications to the Bjorken and Gubser flow equations which bring in, in particular, dependence on rapidity.

Context: Singly ionized carbon ̧ii is theorized to be the brightest emission line feature in star-forming galaxies, and hence an excellent tracer of the evolution of cosmic star formation. Archival maps from far-infrared and submillimeter surveys potentially contain the redshifted ̧iiumns, hidden in the much-brighter continuum emission. Aim: We present a search for aggregate ̧iium line emission across the predicted peak of star formation history by tomographically stacking a high-completeness galaxy catalog on broadband deep maps of the COSMOS field and constraining residual excess emission after subtracting the continuum spectral energy distribution (SED). Methods: The COSMOS equatorial 2 , , and SCUBA2/JCMT. Using the high precision UV-O-IR photometry catalog COSMOS2020, we performed unbiased simultaneous stacking of sim360,000 photometric redshifts on these confusion-limited maps to resolve the sub-THz radiation background. By subtracting a continuum SED model with conservative uncertainty estimation and completeness correction through comparison to the /FIRAS monopole spectrum, we obtain tomographic constraints on the sky-averaged ̧iium signal within the three SPIRE maps: 11.8 ± 10.2, 11.0 ± 8.7, 9.6 ± 9.8, and 9.2 ± 6.6 kJy/sr at redshifts z∼ 0.65, sim1.3, sim2.1, and sim2.6, respectively, corresponding to 1-1.4σ significance in each bin. patch has been mapped by Spitzer Herschel COBE Results: Our 3σ upper limits are in tension with past z∼ 2.6 results from cross-correlating SDSS-BOSS quasars with high-frequency maps, and indicate a much less dramatic evolution (∼times 7.5) of the mean ̧ii intensity across the peak of star formation history than collisional excitation models or frameworks calibrated to the tentative xBOSS measurement. We discuss this tension, particularly in the context of in-development surveys (TIM, EXCLAIM) that will map this ̧ii at high redshift resolution. Planck Planck Conclusion: Having demonstrated stacking in broadband deep surveys as a complementary methodology to next-generation spectrometers for line intensity mapping, these novel methods can be extended to upcoming galaxy surveys such as , as well as to place upper limits on fainter atomic and molecular lines. Euclid

Abstract The paper presents a constraint-based collision model for Cosserat rods, able to handle dynamic or static contact between a large number of highly flexible structures. The model provides the required collision impulses prior to updating the solution of the rods, with the impulses accounted for as external loads. The procedure avoids the need to modify the structure solver itself and circumvents any iteration between the collision model and the solver for the Cosserat rods, maintaining the efficiency of any chosen Cosserat solver. The collision model is adopted from Tschisgale et al. (Arch. Appl. Mech. 89(2):167–193, 2019) and extended towards higher stability, which is found necessary in the case of very flexible rods. Furthermore, the model is supplemented with additional terms that arise when the colliding rods are immersed in a fluid. The latter is accounted for by an immersed-boundary method. A large number of tests are conducted to demonstrate the functionality of the final model. Beyond the present study, this set of cases may constitute a suitable test bench for dry and wet collisions of flexible structures.

Statistical hadronization model for low-energy heavy-ion collisions

Developed DNS-DEM coupling model for normal collisions of ellipsoidal particles on wet surfaces

To address the issues of severe local erosion and uneven service life of flow components in mining metal slurry pumps, this article aims to utilize biomimetic methods to design the biomimetic schemes, reveal the biomimetic erosion reduction mechanism, and achieve erosion reduction and balance. First, a solid–liquid two-phase flow numerical calculation model is established based on the irregular particle collision model. Hydraulic performance and erosion law experiments are conducted to verify the model's accuracy, and the erosion laws of the traditional mining metal slurry pump are revealed. Subsequently, different biomimetic configurations, directions, and combinations are carried out for the impeller and sheath's design based on the shell surface morphology. Then, the erosion distribution and amount of the impeller and sheath, the particle motion behaviors, and the flow field flow characteristics are explored under different biomimetic schemes. Finally, the biomimetic scheme with optimal erosion reduction and balance is obtained, and the erosion reduction mechanism of different biomimetic designs is revealed. The experimental results show that when using the groove biomimetic configuration, perpendicular direction, and impeller+sheath combination scheme, the mining metal slurry pump has relatively optimal erosion reduction and balance. Compared to the non-biomimetic design scheme, the total erosion decreases by 24.0%, and the difference in erosion between the impeller and sheath decreases by 77.4%. This study presents a new technological path and entry point for reducing erosion and extending the service life of mining metal slurry pumps and other turbine machinery.

Abstract Compared to conventional hydraulic machinery, pump-turbines located in sediment-laden rivers face more severe sediment erosion risks in their flow-passing components, owing to their frequent start-stop cycles, highly variable operating conditions, and bidirectional flow characteristics. The guide vane opening is a critical parameter for mitigating sediment wear severity, optimizing the internal flow field, and enhancing hydraulic efficiency. The influence mechanism of guide vane opening variations on sediment erosion characteristics was systematically investigated under both turbine and pump modes using a pump-turbine model from a pumped-storage power station. An Eulerian-Lagrangian approach, integrated with the Grant & Tabakoff particle collision model and Oka erosion model, was employed to evaluate wear depth distribution patterns across distinct working surfaces of runner blades. Research indicates that under turbine mode, as the guide vane opening increases, the erosion zone on the runner blade suction surface gradually shifts from the leading edge toward the trailing edge, accompanied by an increasing trend in average wear rate. In pump mode, the wear rate on the blade suction surfaces exhibits a relatively more minor increase with larger openings. Primary erosion areas include the band-proximal region and 0.6-1.0 chord position on runner blade suction surfaces, as well as leading-to-trailing edge zones on guide vane suction surfaces. These findings provide a theoretical basis for optimizing pump-turbine anti-erosion designs.

ABSTRACT Based on the developed multi‐cavity rotating charger, an investigation into the triboelectric charging of PA, PP, PU, and ABS particles was conducted. First, the force and motion models of the particles were established. A collision model of particles inside the charger has been established, and the effects of rotational speed, tilt angle, and inner cavity diameter on the triboelectric collision of particles have been explored. Second, the triboelectric charging experiments of polymers were carried out using the developed multi‐cavity rotating charger. Single‐factor and orthogonal experiments revealed that factors influencing on charge‐to‐mass difference as: tilt angle > inner cavity diameter > rotational speed. Finally, the optimal charging parameter combination for the four‐component polymer particles was determined through experiments. The research on particle charging provides theoretical and experimental support for their subsequent electrostatic separation.

Collision integrals related to transport properties are calculated for O2+N collisions using quasi-classical trajectory molecular dynamics simulations on high-accuracy ab initio potential energy surfaces for the 2A', 4A', and 6A' electronic states. The influence of O2 vibrational excitation on collision integrals is investigated within the framework of state-to-state kinetic theory, with inelastic contributions incorporated using the Wang-Chang and Uhlenbeck formulation. Under vibrational nonequilibrium conditions (with vibrational temperatures up to 20,000 K), the thermally averaged diffusion and viscosity collision integrals deviate from their equilibrium values by at most 12 and 17%, respectively. For moderate nonequilibrium (|T - Tv| ≤ 5000 K), deviations remain below 5%, indicating that the equilibrium assumption provides an adequate description. Furthermore, approximating vibrational state-specific collision integrals by those of the vibrational ground state yields results that reproduce the detailed calculations, with only minor errors across the considered temperature range. This approximation provides sufficient accuracy for estimating thermally averaged collision integrals, even when the vibrational distribution function deviates significantly from the Boltzmann distribution, and can substantially simplify state-specific modeling of transport properties in hypersonic flow simulations. For practical implementation, the mean collision integrals are fitted as functions of temperature, and the resulting data are further used to reparameterize widely used collision models.

This study addresses the critical issue of high casualty rates in frontal collisions by proposing structural optimization methods for the energy-absorbing box of lightweight electric vehicles. A small pure electric car was selected as the research object. A finite element model for frontal collision was established in HyperMesh and solved using the LS-DYNA explicit dynamics solver. The parameters such as the acceleration of the B-pillar of the vehicle, the compression distance of the energy absorption box and the energy absorption are analyzed in this study. Energy absorption was used as the primary crashworthiness indicator while ensuring that the peak collision force, compression distance of the energy-absorbing box, and acceleration of the B-pillar complied with safety standards. Results demonstrate that Scheme 2 (featuring reduced wall thickness and a single induced groove) outperformed other designs, increasing energy absorption by 3% and reducing mass by 17% compared to the baseline model. This conclusion can provide a reference basis for the subsequent vehicle collision analysis.