Collision Dynamics Research Articles

Analysis of the cross section and characteristic of fluorescence emission of the He atom confined in the plasma conditions

The structural properties, angle-integrated total and magnetic sublevel excitation cross sections, alignments of the residual ion, and polarization properties of the line emission are investigated for the plasma-embedded atomic system. This is done using the developed distorted wave approach which solves the Dirac equation by employing a modified Debye potential to represent the screened interaction in plasmas. The effective Hamiltonian is employed to obtain the level energies as functions of the screening parameters. The Coulomb interaction is replaced by shielded Coulomb interaction during the collision dynamics. As an illustrating example, detailed calculations are carried out for the 1s2→1s2p3,1P1 excitations of the plasma-embedded He atom by electron impact. Our results suggest that the energy levels are pushed towards continuum as the effect of (plasma) confinement increases. The cross sections decreases monotonically if the screening effect is enhanced continuously, while the alignments of the residual He+ ion and polarizations of the fluorescence emission change slightly for the corresponding screening parameters. A comparison of our results in the absence of the screening potential with other available experimental and theoretical data shows satisfactory agreement. The present study not only provides a helpful approach to study the influence of plasma effect, but also has important applications in laser produced plasmas, stellar atmospheres, fusion research plasmas and so on.

Remediation of a non-steroidal anti-inflammatory drug from aqueous solutions using cobalt ferrite-photocatalytic membranes

CoFe2O4-PES photocatalytic membranes were assessed for Naproxen degradation in water. The degradation obeyed first-order reaction kinetics (Kapp: 1.25 × 10−3 min−1 - 3.90 × 10−3 min−1). Surface roughness altered the collision dynamics of reactive species. It enhanced the chances of successful collision between Naproxen and reactive radicals. Membrane hydrophilicity improved the generation of reactive radicals by minimizing the blockage of active sites. Intermediates detected by Quadrupole Time-of-Flight Mass Spectrometry showed that Naproxen degraded via demethylation, hydroxylation, and ring-opening reactions. Leaching studies investigated the stability of the prepared membranes. CoFe2O4-PES membranes can be used in advanced oxidation technologies for water treatment.

B meson production in Pb+Pb at 5.02 ATeV at LHC: Estimating the diffusion coefficient in the infinite mass limit

In the last decade a Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions supplying a satisfactory description of the main observables for D meson and providing an estimate of the space-diffusion coefficient Ds(T) from the phenomenology. In this paper, we extend the approach to bottom quarks describing their propagation in the quark-gluon plasma within an event-by-event full Boltzmann transport approach followed by a coalescence plus fragmentation hadronization. We find that QPM approach is able to correctly predict the first available data on RAA(pT) and v2(pT) of single-electron from B decays without any parameter modification w.r.t. the charm. We show also predictions for centralities where data are not yet available for both v2(pT) and v3(pT). Moreover, we discuss the significant breaking of the expected scaling of the thermalization time τth with MQ/T, discussing the evolution with mass of Ds(T) to better assess the comparison to lQCD calculations. We find that at T=Tc charm quark Ds(T) is about a factor of 2 larger than the asymptotic value for M→∞, while bottom Ds(T) is only a 20% higher. This implies a Ds(T) which is consistent within the current uncertainty to the most recent lattice QCD calculations with dynamical quarks for M→∞.

On the collision dynamics in a molecular model

We study the problem of the hydrogen atom submitted to a circularly polarized microwave field. This problem, analyzed from a classical mechanics approach, can be modeled by an autonomous Hamiltonian depending on one parameter K>0. The paper is focused on the so called n-ejection–collision orbits (n-EC orbits), that is orbits that the electron describes when it ejects from the nucleus and collides with it at the n relative minimum in the distance with respect to the nucleus. In this work, we analyze the evolution of the families of n-EC orbits. We conduct a comprehensive numerical analysis of the bifurcations, which involves multiple precision computations, to characterize the successive bifurcation families that emerge. Additionally, we examine the periodic and quasi-periodic motion of the n-EC orbits belonging to these bifurcation families.

Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

Characterizing nuclear modification effects in high-energy O-O collisions at energies available at the CERN Large Hadron Collider: A transport model perspective

The present work focuses on oxygen-oxygen (O-O) collisions, which are planned at the CERN Large Hadron Collider. Oxygen, being a doubly magic number nucleus, has some very unique features. This study attempts to probe the exotic state of QCD matter in O-O collisions. Additionally, the role of different nuclear density profiles in governing the final-state dynamics in ultrarelativistic nuclear collisions is also explored. Using a multiphase transport model, we obtain the nuclear modification factor (RAA) for all charged hadrons and identified particles for O-O collisions at sNN = 7 TeV. Furthermore, we investigate the behavior of RAA as a function of transverse momentum (pT) for three centralities (most central, mid-central, and peripheral) considering both α-cluster and Woods-Saxon nuclear density profiles. We also extend this work to study the rapidity dependence of RAA for all charged hadrons. To better understand our findings of O-O collisions, the results are confronted with the available data of RAA for Pb-Pb collisions. The present study sheds light on particle production mechanisms, emphasizing factors influencing particle yield from precollision to postcollision stages in the context of O-O collisions. Published by the American Physical Society 2024

Binary collision dynamics of equal-sized nanodroplets

Binary nanodroplet collisions have received increasing attention, whilst the identification of collision outcomes and the viscous dissipation mechanism have remained poorly understood. Using molecular dynamics simulations, this study investigates binary nanodroplet collisions over wide ranges of Weber number (We), Ohnesorge number (Oh) and off-centre distances. Coalescence, stretching separation and shattering are identified; however, bouncing, reflexive separation and rotational separation reported for millimetre-sized collisions are not observed, which is attributed to the enhanced viscous effect caused by the ‘natural’ high-viscosity characteristics of nanodroplets. Intriguingly, as an intermediate outcome, holes form in retracting films at relatively high We, arising from the vibration and thermal fluctuation of the films. Due to the combined effects of inertial, capillary and viscous forces, binary nanodroplet collisions fall into the cross-over regime, so estimating viscous dissipation becomes extremely important for distinguishing outcome boundaries. Based on the criterion that stretching separation is triggered only when the residual off-centre kinetic energy exceeds the surface energy required for separation, the boundary equation between coalescence and stretching separation is established. Here, viscous dissipation is calculated by the extracted flow feature from simulations, showing that the ratio of viscous dissipation to the initial kinetic energy depends only on Oh, not on We. Because of complex viscous dissipation mechanisms, the same boundary equation in the cross-over regime has also not been satisfactorily revealed for macroscale collisions. Therefore, the proposed equation is tested for wide data sources from both macroscale and nanoscale collisions, and satisfying agreement is achieved, demonstrating the universality of the equation.

Obstacle Intention Awareness in Automatic Ship Collision Avoidance: Full-Scale Experiments in Confined Waters

In this article, full-scale experiments with a dynamic obstacle intention-aware Collision Avoidance System (CAS) are presented. The CAS consists of the Probabilistic Scenario-Based Model Predictive Control (PSB-MPC) for trajectory planning, dynamic obstacle avoidance, and antigrounding, with a Dynamic Bayesian Network (DBN) used for inferring obstacle intentions online. The novelty of this article lies in the utilization of intention information in deliberate collision-free planning. By inferring multiple different intention states on how and if nearby obstacles adhere to the COLREGS, the PSB-MPC can plan COLREGS-compliant avoidance maneuvers when possible, taking into account its awareness of the situation. The experiments put emphasis on hazardous situations where this intention information is both useful and necessary in order to avoid high collision risk. To the authors’ knowledge, the work is the first field experimental validation of such a probabilistic intention-aware CAS with consideration of multiple intention states. The experimental results demonstrate the validity of the proposed CAS scheme, with adherence to the traffic rules (COLREGS) 7, 8 and 13–17 in a diverse set of situations. The strengths and weaknesses of the proposed CAS are also discussed, giving insights that can be useful for researchers and practitioners in the field. Here, challenges related to detecting obstacle maneuvers and making the intention inference more robust to noise should be addressed as future work to make the scheme better suited for general usage on ships engaged in real traffic.

Dynamic short-term crash analysis and prediction at toll plazas for proactive safety management

Toll plazas are commonly recognized as bottlenecks on toll roads, where vehicles are prone to crashes. However, there has been a lack of research analyzing and predicting dynamic short-term crash risk specifically at toll plazas. This study utilizes traffic, geometric, and weather data to analyze and predict dynamic short-term collision occurrence probability at mainline toll plazas. A random-effects logit regression model is employed to identify crash precursors and assess their impacts on the probability of crash occurrence at toll plazas. Meanwhile, a Long Short-Term Memory Convolutional Neural Network (LSTM-CNN) network is applied for crash prediction. The results of random-effects logit regression model indicate that the flow standard deviation of downstream, upstream occupancy, speed difference and occupancy difference between upstream and downstream positively influence the probability of crash occurrence. Conversely, an increase in the proportion of ETC lanes negatively impacts the probability of crash occurrence. Additionally, there appears a higher likelihood of crashes occurring during summer at toll plaza area. Furthermore, to address the issue of data imbalance, Synthetic Minority Oversampling Techniques (SMOTE) and class weight methods were employed. Stacked Sparse AutoEncoder-Long Short-Term Memory (SSAE-LSTM) and CatBoost were developed and their performance was compared with the proposed model. The results demonstrated that the LSTM-CNN model outperformed the other models in terms of the Area Under the Curve (AUC) values and the true positive rate. The findings of this study can assist engineers in selecting suitable traffic control strategies to improve traffic safety in toll plaza areas. Moreover, the developed collision prediction model can be incorporated into a real-time safety management system to proactively prevent traffic crash.

Automated guided vehicle dispatching and routing integration via digital twin with deep reinforcement learning

The manufacturing industry has witnessed a significant shift towards high flexibility and adaptability, driven by personalized demands. However, automated guided vehicle (AGV) dispatching optimization is still challenging when considering AGV routing with the spatial-temporal and kinematics constraints in intelligent production logistics systems, limiting the evolving industry applications. Against this backdrop, this paper presents a digital twin (DT)-enhanced deep reinforcement learning-based optimization framework to integrate AGV dispatching and routing at both horizontal and vertical levels. First, the proposed framework leverages a digital twin model of the shop floor to provide a simulation environment that closely mimics the actual manufacturing process, enabling the AGV dispatching agent to be trained in a realistic setting, thus reducing the risk of finding unrealistic solutions under specific shop-floor settings and preventing time-consuming trial-and-error processes. Then, the AGV dispatching with the routing problem is modeled as a Markov Decision Process to optimize tardiness and energy consumption. An improved dueling double deep Q network algorithm with count-based exploration is developed to learn a better-dispatching policy by interacting with the high-fidelity DT model that integrates a static path planning agent using A* and a dynamic collision avoidance agent using a deep deterministic policy gradient to prevent the congestion and deadlock. Experimental results show that our method outperforms four state-of-the-art methods with shorter tardiness, lower energy consumption, and better stability. The proposed method provides significant potential to utilize the digital twin and reinforcement learning in the decision-making and optimization of manufacturing processes.

Dynamics of periodic wave evolution and collision for a two-component Ablowitz–Ladik system on the two physically uncoupled chains with the next-to-neighboring dispersion

Dynamics of periodic wave evolution and collision for a two-component Ablowitz–Ladik system on the two physically uncoupled chains with the next-to-neighboring dispersion

Finite element analysis and clinical study of chest wall reconstruction using carbon fiber artificial rib

Carbon fiber composites are emerging as a promising new biomaterial for chest wall reconstruction implants due to their mechanical properties and biocompatibility. This work evaluates the biomechanics of carbon fiber artificial ribs using finite element analysis and clinical implementation. Static simulations of normal breathing process show the maximum stress on the implant is only 2.83 MPa, far below the material ultimate strength of 60 MPa, indicating the excellent fit for maintaining respiratory function. Dynamic collision simulations demonstrate the artificial rib model could withstand a 4 kg rigid object impact at 2 m/s without fracture. Reconstructing the artificial rib with a human rib in the finite element analysis model increases the overall stress tolerance. The impact force required for fracture increases 48% compared to the artificial rib alone, suggesting improved strength from rib integration. Clinically, 10 of 13 patients receiving the artificial rib implants show no significant loss of pulmonary function based on spirometry tests. Based on our findings, the combined simulations and clinical results validate the strong mechanical performance and biocompatibility of the carbon fiber artificial ribs for chest wall reconstruction under static and dynamic loading while maintaining normal respiratory function.

3D multi-system Bayesian calibration with energy conservation to study rapidity-dependent dynamics of nuclear collisions

Considerable information about the early-stage dynamics of heavyion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems — large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition, which we calibrate on the hadron multiplicity and anisotropic flow coefficients. We utilize Bayesian inference to constrain properties of the early- and late-time dynamics of the system, and highlight the impact of enforcing global energy conservation in our 3D model.

Dynamics of collisions and uptake of alcohol molecules with hydrated nitric acid clusters.

We investigate the collisions of different alcohol molecules with hydrated nitric acid clusters using a molecular beam experiment and molecular dynamics simulations. The uptake cross sections σp for the molecules evaluated from the experiment are in excellent agreement with the simulations. This suggests that (i) the nontrivial assumptions implemented in the evaluation procedure of the experimental data are valid, and (ii) the simulations describe correctly the major processes in the molecule-cluster collisions. We observe that σp decreases with the increasing alkyl chain length of the alcohol, and also with the branching of the molecules that have the same mass but different structures. These systematic trends can be rationalized based on the accessibility of the hydrophilic OH group, which decreases with the increasing chain length and steric hindrance. The observed trends and their interpretation differ significantly from the simple model of hard-sphere collisions. The obtained data shall be beneficial not only for the fundamental understanding of the molecule-cluster collisions, but also in the modelling of atmospheric new-particle formation and aerosol growth.

Mixed quantum/classical theory (MQCT) approach to the dynamics of molecule-molecule collisions in complex systems.

We developed a general theoretical approach and a user-ready computer code that permit study of the dynamics of collisional energy transfer and ro-vibrational energy exchange in complex molecule-molecule collisions. The method is a mixture of classical and quantum mechanics. The internal ro-vibrational motion of collision partners is treated quantum mechanically using a time-dependent Schrödinger equation that captures many quantum phenomena including state quantization and zero-point energy, propensity and selection rules for state-to-state transitions, quantum symmetry and interference phenomena. A significant numerical speed up is obtained by describing the translational motion of collision partners classically, using the Ehrenfest mean-field trajectory approach. Within this framework a family of approximate methods for collision dynamics is developed. Several benchmark studies for diatomic and triatomic molecules, such as H2O and ND3 collided with He, H2 and D2, show that the results of MQCT are in good agreement with full-quantum calculations in a broad range of energies, especially at high collision energies where they become nearly identical to the full quantum results. Numerical efficiency of the method and massive parallelism of the MQCT code permit us to embrace some of the most complicated collisional systems ever studied, such as C6H6 + He, CH3COOH + He and H2O + H2O. Application of MQCT to the collisions of chiral molecules such as CH3CHCH2O + He, and to molecule-surface collisions is also possible and will be pursued in the future.

Event-by-event heavy-flavour dynamics: Estimating the spatial diffusion coefficient Ds from charm to the infinite mass limit

Quasi-Particle Model (QPM) has been developed to study charm quark dynamics in ultra-relativistic heavy-ion collisions with good description of D mesons RAA(pT) and v2,3(pT) and leading to the evaluation of the spatial diffusion coefficient Ds(T). With an event-by-event full Boltzmann transport approach followed by a hybrid hadronization via coalescence plus fragmentation, we show RAA(pT), v2(pT) down to pT → 0 for D and B mesons. We find that QPM approach is able to correctly predict first available data on RAA(pT) and v2(pT) of single-electron from B mesons decays measured by ALICE. A significant breaking of the expected scaling of the thermalization time τth with MQ/T is found. Charm quark Ds(T) is about 50% larger than the asymptotic value for MQ → ∞, while the bottom Ds(T) is only 20% higher. In the infinite mass limit the Ds(T) is consistent with recent lQCD calculations with dynamical quarks.

Collective dynamics - Theoretical overview

I overview the recent progress of phenomenological studies exploring collective dynamics in relativistic nuclear collisions to understand various QCD properties. Originally, collectivity was interpreted as a manifestation of the hydrodynamic behaviour of the QGP as a response to the initial collision geometry. Over the past decade, however, particularly following the experimental observation of momentum azimuthal anisotropy in small colliding systems, pioneering studies have demonstrated the possibility of other interpretations. In this talk, I highlight recent studies aimed at understanding various QCD properties at different collision stages through the lens of collectivity and emphasize the importance of establishing Monte Carlo event generators for relativistic nuclear collisions.

Establishing the Range of Applicability of Hydrodynamics in High-Energy Collisions

We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number Re−1 is sufficiently small and the early pre-equilibrium stage is properly accounted for. By determining the breakdown of hydrodynamics as a function of system size and energy, we find that it is quantitatively accurate in central lead-lead collisions at LHC energies, but should not be used in typical proton-lead or proton-proton collisions, where the development of collective flow cannot accurately be described within hydrodynamics.

Event-by-event kinetic description of pre-equilibrium charge evolution in QCD plasma

We use QCD effective kinetic theory to calculate far-fromequilibrium dynamics on an event-by-event basis within the KøMPøST framework. We present non-equilibrium charge response functions and the dynamical evolution of the conserved charge current pertinent to the early-time dynamics of heavy-ion collisions at the highest energies. The KøMPøST framework with conserved baryon, strangeness, and electric charges can then be readily implemented into a multistage model allowing for the initialization of a nonequilibrium charge current in hydrodynamic simulations.

First close-coupling study of the excitation of a large cyclic molecule: collision of c-C5H6 with He.

Recent astronomical observations revealed an increasing molecular complexity in the interstellar medium through the detection of a series of large cyclic carbon species. To correctly interpret these detections, a complex analysis is necessary that takes into account the non-local thermodynamic equilibrium (non-LTE) conditions of the emitting media (e.g. when energy level populations deviate from a Boltzman distribution). This requires proper state-to-state collisional data for the excitation and de-excitation processes of the molecular levels. Cyclopentadiene (c-C5H6), which was recently detected in cold interstellar clouds, is extensively studied in many aspects due to its large importance for chemistry in general. At the same time, there are no collisional data available for this species, which are necessary for a more precise interpretation of the corresponding detections. In this work, we first provide an accurate 3D rigid-rotor interaction potential for the [c-C5H6 + He] complex from high-level of ab initio theories, which has been used to study their inelastic collision by the exact close coupling quantum scattering method. To the best of our knowledge, this is the first study where this method is systematically applied to treat the dynamics of molecular collisions involving more than ten atoms. We also analyse the collisional propensity rules and the differences in contrast to calculations, where the approximate coupled states scattering methods is used.