Collision Processes Research Articles

Global tensor polarization of spin 3/2 hadrons and quark spin correlations in relativistic heavy ion collisions

We study the global polarization of spin-3/2 hadrons in relativistic heavy ion collisions. We show in particular that the global tensor polarizations of rank two or three for spin-3/2 hadrons are sensitive to the local two or three quark spin correlations respectively in the quark gluon plasma produced in the collision processes. We present the relationships between these measurable tensor polarizations and quark spin correlations in the quark matter system. Published by the American Physical Society 2024

Integrated detrital rutile and detrital zircon ages: a new perspective on the tectonic evolution of South China

Abstract Paleogeographic reconstructions are of key importance for understanding the history of continental breakups and amalgamations during the whole history of the Earth. A special case is the history of the Asian continent, which, compared to other continents, consists of several large cratons and numerous smaller continental blocks. The history of the assembly of South China remains controversial in terms of the timing, Late Neoproterozoic or Early Paleozoic, and the participating continental blocks, e.g., Yangtze, Cathaysia, India and/or Australia. Detrital rutile U-Pb dating possesses a significant potential for deciphering tectonic settings as rutile frequently crystallizes during orogenic events associated with the processes of collision and subduction. Detrital zircon U-Pb dating is a perfect instrument for identifying provenance characteristics and age characteristics of sedimentary sources. An integration of these two methods of dating offers better opportunities for reconstructing tectonic settings. This paper presents a first attempt to reconstruct the Neoproterozoic to Early Palaeozoic tectonic history and paleogeography of the whole South China Block based on U-Pb geochronology of rutile and zircon and Hf-in-zircon isotopes from Lower Jurassic Baitianba Formation sedimentary rocks of the western margin of the Yangtze Block, a major part of South China. Our obtained integrated U-Pb rutile and zircon age data show three main age populations of 960-940 Ma, 630-610 Ma and 530-520 Ma. The new U-Pb detrital rutile and zircon ages, compared with former data from Gondwana and Australia, suggest that Yangtze amalgamated with Cathaysia to form South China during the Sibao orogeny at 960-940 Ma. The detrital rutile and zircons of the new 630-610 Ma age group could have been delivered from western Australia during Late Neoproterozoic to Cambrian Paterson-Petermann orogeny. The abundant 530-520 Ma detrital rutile and zircon ages fit well the coeval zircon age populations recorded in Gondwana-derived terranes, like India and Indochina.

Investigation of Impact Contact Force Testing and Damage Analysis on Potatoes

To investigate the influencing factors and intrinsic relationships between potato impact force and impact damage during potato soil separation, a testing system for potato impact force was established. The impact force test system is composed of a base, a height adjustment device, a simple separation screen, a soil storage tank, an impact force sensor, and so on. By allowing potatoes to fall freely to simulate the collision process, impact force data are collected, and a high-speed camera is used to locate the impact position and analyze the degree of damage. Through the response surface analysis method, the influencing factors and laws of the impact force and impact damage during the collision process between potatoes and rods under soil and no-soil conditions were studied. The results of the response surface analysis indicate that when the screen inclination is within the range of 14.12° to 14.77°, falling height ranges from 453.83 mm to 500 mm, screen rod spacing falls within 36.50 mm to 40 mm, and the screen rod material is rubber. Potatoes can still be at a relatively low damage level when enduring a large impact force. This study has significant implications for reducing potato impact damage during harvesting, enhancing economic benefits in the potato industry, and advancing the technical level of potato harvesting equipment. In the future, based on the results of this study, further exploration can be made to optimize the design of potato harvesting equipment so as to better reduce the damage to potatoes during harvesting and subsequent processing processes and promote the sustainable development of the potato industry.

Numerical Investigation of the transient process of direct collision between two droplets

Abstract The use of spray systems finds widespread applications in fields such as national defense and industry. These systems are employed for spray cooling, spray forming, spray coating, and inkjet painting. Within spray systems, atomized droplets play a crucial role, either impacting surfaces or colliding with each other. Understanding the impact process of these droplets is essential for optimizing spray system performance. In this study, computational simulations focus on direct collision of two droplets. Numerical methods are employed, including structured single-block and staggered grid systems for discretizing the spatial domain. The finite volume method iteratively solves the governing equations of mass and momentum. The coupling between velocities and pressure is handled using SIMPLER methods. During droplet collision, phenomena like deformation, breakup, and merging occur at the boundary. To accurately capture these movements, a level set function approach is utilized. Numerical simulations of a water droplet impinging on a flat surface are compared with experimental results for verification. When two droplets collide head-on with the same Reynolds number and Weber number, they merge into a single oscillating droplet at a fixed position. Increasing the Reynolds number of the two colliding droplets intensifies the oscillation phenomenon in the merged droplet. Even when two droplets collide at an angle or have different sizes, they still merge into a single oscillating droplet. The merged droplet moves in a direction where the original two droplets’ momentum cannot be fully offset.

Collisional orogeny between the Siberian and Sino-Korean paleoplates: Evidence from geochronology and metamorphism of the metamorphic ophiolite mélange in the Banlashan area near the Xar Moron River in the southeastern Central Asian orogenic belt

As the largest Phanerozoic accretionary orogenic belt, whether the Central Asian Orogenic Belt (CAOB) experienced a strong collisional orogenic process after Paleo-Asian Ocean (PAO) closure remains controversial. The age and P-T conditions recorded by metamorphic rocks could be used to study the thermal and tectonic regimes during orogenic processes, providing constraints for orogenic evolution. In this paper, the geochronology and metamorphism of a newly discovered metamorphic ophiolite mélange in the Banlashan area near the Xar Moron River in the southeastern CAOB were studied. The association and age of the metamorphic ophiolite mélange protoliths are similar to those of the Xar Moron River ophiolite belt to the north. The metamorphic ages of different ophiolite mélange lithologies are all late Permian (250.2–256.5 Ma), indicating that the Siberian and Sino-Korean paleoplates collided during the late Permian. The metamorphic pressure and temperature recorded by the garnet amphibolite block in the ophiolite mélange could reach 8.5–8.8 kbar and 700–725 ℃. The core-to-rim zoning of garnet indicates that the garnet amphibolite underwent a clockwise P–T path, which is the typical metamorphic feature of collisional orogens. The ophiolite mélange metamorphic features, combined with regional magmatic, metamorphic, sedimentary and tectonic deformation data, indicate that a strong collisional orogeny occurred rather than a soft orogeny between the Siberian and Sino-Korean paleoplates after the PAO closure.

Very Extended Ionized Gas Discovered around NGC 1068 with the Circumgalactic Hα Spectrograph

We have performed wide-field, ultra-low-surface-brightness Hα emission-line mapping around NGC 1068 with the newly commissioned Circumgalactic Hα Spectrograph. NGC 1068 is notable for its active galactic nucleus, which globally ionizes gas in the disk and halo. Line-emitting diffuse ionized gas is distributed throughout the galactic disk and large-scale ionized filaments are found well beyond the disk, aligned with the cone angle of the central jet. We report the discovery of a new ribbon of ionized gas around NGC 1068 beyond even the known outer filamentary structure, located 20 kpc from the galaxy. The Hα surface brightness of this ribbon is on the order of the bright telluric lines, ranging from 4 to 16 R, with fainter regions on the order of the sky background continuum. Unlike previous extended emission, the ribbon is not as well aligned with the current axis of the central jet. It is not associated with any galactic structure or known tidal features in the halo of NGC 1068, though it may originate from a larger distribution of unmapped neutral atomic or molecular gas in the halo. The morphology of the ribbon emission in Hα is correlated with extended UV emission around NGC 1068. Hα-to-UV flux ratios in the ribbon are comparable to extended emission-line ratios in the halos of NGC 5128, NGC 253, and M82. The Hα excess in the ribbon gas suggests ionization by slow shocks or a mixture of in situ star formation and photoionization and collisional ionization processes.

Time evolutions of information entropies in a one-dimensional Vlasov–Poisson system

A one-dimensional Vlasov–Poisson system is considered to elucidate how the information entropies of the probability distribution functions of the electron position and velocity variables evolve in the Landau damping process. Considering the initial condition given by the Maxwellian velocity distribution with the spatial density perturbation in the form of the cosine function of the position, we derive linear and quasilinear analytical solutions that accurately describe both early and late time behaviors of the distribution function and the electric field. The validity of these solutions is confirmed by comparison with numerical simulations based on contour dynamics. Using the quasilinear analytical solution, the time evolutions of the velocity distribution function and its kurtosis indicating deviation from the Gaussian distribution are evaluated with the accuracy of the squared perturbation amplitude. We also determine the time evolutions of the information entropies of the electron position and velocity variables and their mutual information. We further consider Coulomb collisions that relax the state in the late-time limit in the collisionless process to the thermal equilibrium state. In this collisional relaxation process, the mutual information of the position and velocity variables decreases to zero, while the total information entropy of the phase-space distribution function increases by the decrease in the mutual information and demonstrates the validity of Boltzmann's H-theorem.

Analysis of waves dynamics in a rotating detonation combustor fueled by kerosene

The wave dynamics play a crucial role in the operation characteristics of the rotating detonation engine. We conducted numerical simulations of a rotating detonation combustor (RDC) using multicomponent reactive Navier–Stokes equations coupled with a discrete phases model. The RDC in this research employs a configuration with multiple coaxial injectors supplying oxygen-enriched air and kerosene spray at room temperature. To accurately identify and analyze waves within the RDC, we proposed a three-dimensional transient detonation wave detection method based on the combined parameters of normal Mach number and heat release rate in the flow field. Two typical wave modes, referred to as single-wave mode and counter-waves mode, are identified and then selected to conduct a detailed wave dynamics analysis. The general wave behavior is discussed, and velocity deficit is compared for these two wave modes. For the single-wave mode, intermittent micro-explosions are observed generating retonation waves periodically in the unburnt pockets behind the rotating detonation shock front. For the counter-waves mode, we analyzed the collision process of the two waves and the coupling/decoupling of the shock front with the detonative heat release zone, revealing the reason for significant velocity deficits in this wave mode. This research demonstrates that micro-explosions intermittently occur in the multiphase RDC in both single-wave and counter-waves modes and generate micro explosion shock waves periodically, which influence the complicated wave dynamics behavior.

Predicting Collision-Induced-Dissociation Tandem Mass Spectra (CID-MS/MS) Using Ab Initio Molecular Dynamics.

Compound identification is at the center of metabolomics, usually by comparing experimental mass spectra against library spectra. However, most compounds are not commercially available to generate library spectra. Hence, for such compounds, MS/MS spectra need to be predicted. Machine learning and heuristic models have largely failed except for lipids. Here, quantum chemistry software can be used to predict mass spectra. However, quantum chemistry predictions for collision induced dissociation (CID) mass spectra in LC-MS/MS are rare. We present the CIDMD (Collision-Induced Dissociation via Molecular Dynamics) framework to model CID-based MS/MS spectra. It uses first-principles molecular dynamics (MD) to simulate the physical process of molecular collisions in CID tandem mass spectrometry. First, molecular ions are constructed at specific protonation sites. Using density functional theory, these protonated ions are targeted by argon collider gas atoms at user-specified velocities. Subsequent bond breakages are simulated over time for at least 1,000 fs. Each simulation is repeated multiple times from various collisional directions. Fragmentations are accumulated over those repeated collisions to generate CIDMD in silico mass spectra. Twelve small metabolites (<205 Da) were selected to test the accuracy of this framework in comparison to experimental MS/MS spectra. When testing different protomers, collider velocities, number of simulations, simulation time and impact factor b cutoffs, we yielded 261 predicted mass spectra. These in silico spectra resulted in entropy similarity scores of an average 624 ± 189 for all 261 spectra compared to their corresponding experimental spectra, which improved to 828 ± 77 when using optimal parameters of the most probable protomers for 12 molecules. With increasing molecular mass, higher velocities achieved better results. Similarly, different protomers showed large differences in fragmentation; hence, with increasing numbers of protomers and tautomers, the average CIDMD prediction accuracy decreased. Mechanistic details showed that specific fragment ions can be produced from different protomers via multiple fragmentation pathways. We propose that CIDMD is a suitable tool to predict mass spectra of small metabolites like produced by the gut microbiome.

1D modeling of plasma streamers at ammonia-air flame conditions

Abstract This work is a self-consistent 1D modeling of streamers in ammonia-oxygen-nitrogen-water mixtures. A fluid model that includes species transport, electrostatic potential, and detailed chemistry was developed and verified. This model is then used to simulate the avalanche, streamer formation and propagation phases, driven by a nanosecond voltage pulse, at different thermochemical conditions derived from a 1D laminar premixed ammonia-air flame. The applicability of the Meek’s criterion in predicting the streamer inception location was successfully confirmed. Streamer formation and propagation duration were found to vary significantly with different thermochemical conditions, due to the difference in ionization rates. The thermochemical state also affected the breakdown characteristics which was tested by maintaining the background reduced electric field constant. Detailed kinetic analyses revealed the importance of O(1D) in the production of key radicals, such as O, OH, and NH2. Furthermore, the contributions of the dissociative electronic excitation of NH3 towards the production of H and NH2 radicals have also been reported. Spatial and temporal evolution of the electron energy loss fractions for various inelastic collision processes at different thermochemical states uncovered the input plasma energy spent of fuel dissociation and the large variability in the dominant processes during the avalanche and streamer propagation phases. The methodology and analyses reported in this work are key towards developing effective strategies for controlled nanosecond-pulsed non-equilibrium plasma sources used for ammonia ignition and flame stabilization.

Factorization of photon induced processes in ultra-peripheral heavy ion collisions

In this study, we investigate photon-photon scattering in ultra-peripheral heavy ion collisions (UPCs). We start by deriving an effective Lagrangian from first principles and then apply factorization techniques from Soft-Collinear effective theory (SCET). This approach allows us to decompose the photon-photon scattering cross-section into two primary factors: the generalized transverse momentum distributions (GTMDs) and the hard scattering amplitude. We further analyze the emission of soft photons by final state leptons, incorporating a soft function into the cross section through an evolution method. Our analysis yields detailed predictions for observable angular correlations among the final state leptons. Specifically, we calculate the angular correlations characterized by the azimuthal parameters 〈cos⁡2ϕ〉 and 〈cos⁡4ϕ〉, highlighting the influence of initial photons polarization and recoil effects from final state soft photons.

On the elastoplastic behavior in collisional compression of spherical dust aggregates

Aggregates consisting of submicron-sized cohesive dust grains are ubiquitous, and understanding the collisional behavior of dust aggregates is essential. It is known that low-speed collisions of dust aggregates result in either sticking or bouncing, and local and permanent compaction occurs near the contact area upon collision. In this study, we perform numerical simulations of collisions between two aggregates and investigate their compressive behavior. We find that the maximum compression length is proportional to the radius of aggregates and increases with the collision velocity. We also reveal that a theoretical model of contact between two elastoplastic spheres successfully reproduces the size- and velocity-dependence of the maximum compression length observed in our numerical simulations. Our findings on the plastic deformation of aggregates during collisional compression provide a clue to understanding the collisional growth process of aggregates.Graphic abstract

Study of the heavy quarks energy loss through medium polarization, elastic collision and radiative processes

Study of the heavy quarks energy loss through medium polarization, elastic collision and radiative processes

Electrothermal filamentation of igniting plasmas.

Dense, hot plasmas are susceptible to the electrothermal instability: a collisional process which permits temperature perturbations in electron currents to grow. It is shown here that linearizing a system comprised of two opposing currents and a mobile ion background as three distinct fluids yields unstable modes with rapid growth rates (∼10^{13}s^{-1}) for wavenumbers below a threshold k_{th}. An analytical threshold condition is derived, this being surpassed for typical hot-spot and shell parameters. Particle-in-cell simulations successfully benchmark the predicted growth rates and threshold behavior. Electrothermal filamentation within the shell will impact the burn wave propagation into the cold fuel and resulting burn dynamics.

Description of Short-Range Interactions of Carbon-Based Materials with a Combined AIREBO and ZBL Potential.

An accurate description of short-range interactions among atoms is crucial for simulating irradiation effects in applications related to ion modification techniques. A smooth integration of the Ziegler-Biersack-Littmark (ZBL) potential with the adaptive intermolecular reactive empirical bond-order (AIREBO) potential was achieved to accurately describe the short-range interactions for carbon-based materials. The influence of the ZBL connection on potential energy, force, and various AIREBO components, including reactive empirical bond-order (REBO), Lennard-Jones (LJ), and the torsional component, was examined with configurations of the dimer structure, tetrahedron structure, and monolayer graphene. The REBO component is primarily responsible for the repulsive force, while the LJ component is mainly active in long-range interactions. It is shown that under certain conditions, the torsional energy can lead to a strong repulsive force at short range. Molecular dynamics simulations were performed to study the collision process in configurations of the C-C dimer and bulk graphite. Cascade collisions in graphite with kinetic energies of 1 keV and 10 keV for primary knock-on atoms showed that the short-range description can greatly impact the number of generated defects and their morphology.

Effects of Particle Migration on the Relaxation of Shock Wave Collisions.

The non-equilibrium characteristics during the shock relaxation process hold a foundational position in various fields. In contrast to the propagation of a single shock wave, the collision process of two shock waves exhibits distinct non-equilibrium features. Employing non-equilibrium molecular dynamics, we simulated the collision of ultra-strong shock waves in a classical gas system, investigating the relationship between equilibrium relaxation time and shock intensity. Tracking the spatial migration of microscopic particles in the shock collision region during the relaxation process, we observed a significant contribution of particle migration to the average energy changes during relaxation. The discussion on particle migration provides a valuable new perspective for understanding the microscopic mechanisms of the relaxation process.

Opening and Closure of the Sulu Sea: Revealed by Its Peripheral Subduction and Collision Processes

The Sulu Sea is a small marginal sea in the western Pacific, but it is a very complex and tectonically active region, situated amidst the convergence of the Eurasian, Pacific, and India-Australian plates. Deciphering its geodynamic evolution is crucial, but our understanding of its opening, closure, and tectonic history remains inadequate. The main aim of this study was to systematically study the opening and subsequent closure of the Sulu Sea though discerning tectonic unconformities, structural features, and subduction-collision tectonic zones around margins of the sea. The interpreted sections and gravity anomaly data indicate that the NE Sulu Sea has undergone Neogene extension and contraction due to subduction and collision along the northern margins of the Sulu Sea, whereas the SE Sulu Sea gradually extended from northwest to southeast during the Middle Miocene and has subsequently subducted since the Middle Miocene along the southeastern margins of the Sulu Sea. Several subduction and collision boundaries with different characteristics were developed including continent-continent collision, arc-continent collision, and ocean-arc subduction. The different margins of the Sulu Sea showed distinct asynchronous subduction and collision processes. The northern margins of the Sulu Sea can be divided into three subduction-collision tectonic zones from west to east: the Sabah-Nansha block collision has occurred in NE Borneo since the Early Miocene, followed by the SW Palawan-Cagayan arc collision in SW Palawan Island since the Middle Miocene, and the NW Palawan-Mindoro arc collision since the Late Miocene with further oblique subduction of the Philippine Sea Plate. The southeastern margins can also be divided into two subduction tectonic zones from south to east: the SE Sulu Sea has subducted southward beneath the Celebes Sea since the Middle Miocene, followed by the southeastward subduction beneath the Philippine Sea Plate since the Pliocene. Since the Miocene, the interactions among the Australia-India, the Philippine Sea, and the Eurasian plates have formed the circum-Sulu Sea subduction-collisional margins characterized by microplate collisions, deep-sea trough development, and thick sediments filling in the orogenic foreland. This study is significant for gaining insights into the opening and closure of marginal seas and the dynamics of multiple microplates in Southeast Asia.

Late Mesozoic ductile deformation and exhumation along the Shangdan suture zone in the Qinling Orogenic Belt, China

The Qinling Orogenic Belt (QOB) is a multi‐stage orogenic belt recording subduction and collision processes. The ductile shearing deformation with different properties and ages is developed on the boundary of the different litho‐tectonic units, which can be used to decipher the tectonic evolution of the QOB. Previous studies mainly concentrated on the pre‐Late Mesozoic shearing deformation, while the Late Mesozoic shearing deformation received less attention. It restricts the understanding of the Late Mesozoic tectonic evolution of the QOB. Hence, we conducted detailed field structural analysis and laboratory analysis of the Shagou shear zone (SGSZ) in the middle part of the Shangdan suture zone (SDSZ). The SGSZ, developed in the southern margin of the Baliping pluton, is an S–SSW‐dipping sinistral strike‐slip ductile shear zone with a top‐to‐the‐ESE shear sense. The mylonite protoliths are voluminous Late Triassic granites (200–215 Ma) and a small amount of Neoproterozoic granites (759 Ma) and Early Cretaceous granites (145 Ma). Microstructures and geothermobarometer results suggest that the ductile shearing deformation occurred under high greenschist–low amphibolite‐facies conditions (400–650°C) at middle crustal depths (13–21 km). Zircon U–Pb and amphibole‐biotite 40Ar/39Ar dating results constrain the timing of shearing deformation to 135–145 Ma and the rapid exhumation of the SGSZ to 115–135 Ma. Combining with the regional data, we consider that the sinistral strike‐slip shearing deformation in the SGSZ controls and accommodates the south‐eastward extrusion of the East SQB under the intracontinental compression. Subsequently, the intracontinental extension led to the rapid exhumation of the SGSZ.

Effect of surface pore on bubble–solid surface collisional interaction and adhesion process

ABSTRACT In low-rank and oxidized coal flotation, the pore structure on particle surfaces can significantly affect the bubble-particle collisional adhesion process, which in turn affects the flotation performance. In this study, to understand its mechanism, the collisional interaction process between bubbles and substrates with a single pore was observed throjugh a self-made system, and the interaction force was measured during the adhesion and detachment process. The results proved that the pore accelerated the kinetic energy dissipation of the bubbles after collision and largely shortened the induction time during the adhhesion process. The induction time on the perforated substrate was an order of magnitude shorter than that on the smooth surface. The interaction force measurement results showed that bubble interaction behavior on smooth and perforated surfaces was essentially the same, which suggests that the single pore on hydrophobic surface can accelerate bubble adhesion without affecting adhesion stability, thus strengthening bubble – particle adhesion.

Emergence of Amphiphilicity on Surfaces of Pure Cellulose Nanofibrils Directly Generated by Aqueous Counter Collision Process.

The present paper describes a downsizing mechanism of an aqueous counter collision (ACC) process that enables the rapid preparation of cellulose nanofibrils (CNFs) as an aqueous dispersion solely by impinging a pair of water jets containing the raw materials. Extensive studies have revealed that the resulting CNFs by ACC have amphiphilic fiber surfaces, in which two kinds of faces with different natures are present along the entire fiber axis. They therefore have superior adsorption to surfaces of various conventional polymer plastics. These characteristic adsorption behaviors, which are totally different from those for other CNFs prepared by other means, are attributable to their hydrophobic surfaces. In the present study, high-resolution microscopy, including atomic force microscopy, confocal laser scanning microscopy, and scanning electron microscopy with broad argon ion beam milling, was used to determine how the emergence of such hydrophobic characteristics in a nanofibril face occurs in relation to the ACC nanopulverization mechanism due to the collision of the pair of water jets.