Collision Model Research Articles

Reliability-Based Optimization of a Novel Bumper System Considering Low-Speed Crashworthiness and Pedestrian Protection

In the event of a vehicle collision, the front bumper is the first point of contact with an obstacle, effectively absorbing the energy. Comprehensively considering both low-speed collision and pedestrian protection performance, this paper introduces a novel bumper system featuring variable-section curved foam and an E-shaped section beam. Moreover, the low-speed collision and lower legform collision models are developed, and a sensitivity analysis is conducted to identify critical parameters. Finally, a reliability-based optimization is conducted to determine the optimal structural configurations that enhance the bumper system’s performance and reliability. The results show that the reliability-based optimization significantly improves both pedestrian protection and crashworthiness, achieving a reliability level exceeding 95%.

Merging White Dwarf binaries produce Type Ia Supernovae in elliptical galaxies

Abstract I find that Type Ia supernovae (SNe Ia) with bimodal nebular emission profiles occur almost exclusively in massive ($\hbox{$\rm M_\star $} \gtrsim 10^{11}~\hbox{$\rm M_\odot $}$) galaxies with low star-formation rates (SFR $\lesssim 0.5~\hbox{$\rm M_\odot $}$/yr). The bimodal profiles are likely produced by two white dwarfs that exploded during a merger or collision, supported by a correlation between the peak-to-peak velocity separation (vsep) and the SN Ia peak luminosity (MV) which arises naturally from more massive white dwarf binaries synthesizing more 56Ni during the explosion. The distributions of SNe Ia with and without bimodal nebular lines differ in host mass, SFR, and specific SFR with K-S test probabilities of $3.1{{\%}}$, $0.03{{\%}}$, and $0.02{{\%}}$, respectively. Viewing angle effects can fully explain the SNe Ia in quiescent hosts without bimodal emission profiles and the dearth of merger/collision driven SNe Ia in star-forming hosts requires at least two distinct progenitor channels for normal SNe Ia. $30\!-\!40{{\%}}$ of all SNe Ia originate from mergers or collisions depending on how cleanly host environment distinguishes progenitor scenarios. Existing models for WD mergers and collisions broadly reproduce the vsep–MV correlation and future analyses may be able to infer the masses/mass-ratios of merging white dwarfs in external galaxies.

An off-resonant quantum collision model: Realizing a qubit coupled with an effective negative temperature bath

Abstract Quantum collision model provides a promising tool for investigating system-bath dynamics. Most of the studies on quantum collision models work in the resonant regime. In quantum dynamics, the off-resonant interaction often brings in exciting effects. It is thereby attractive to investigate quantum collision models in the off-resonant regime. On the other hand, a bath with a negative absolute temperature is anticipated to be instrumental in developing thermal devices. The design of an effective bath with negative absolute temperature coupled to a qubit is significant for developing such thermal devices. We establish an effective negative-absolute-temperature bath coupled to a qubit with a quantum collision model in a far-off-resonant regime. We conduct a detailed and systematic investigation on the off-resonant collision model. There is an additional constraint on the collision duration resulting from the far-off resonant collision. The dynamics of the collision model in the far-off-resonant regime are different from the one beyond the far-off-resonant regime. Numerical simulations confirm the validity of the proposed approach.

Classifying Two-Body Hamiltonians for Quantum Darwinism

Quantum Darwinism is a paradigm to understand how classically objective reality emerges from within a fundamentally quantum universe. Despite the growing attention that this field of research has been enjoying, it is currently not known what specific properties a given Hamiltonian describing a generic quantum system must have to allow the emergence of classicality. Therefore, in the present work, we consider a broadly applicable generic model of an arbitrary finite-dimensional system interacting with an environment formed from an arbitrary collection of finite-dimensional degrees of freedom via an unspecified, potentially time-dependent Hamiltonian containing at most two-body interaction terms. We show that such models support quantum Darwinism if the set of operators acting on the system which enter the Hamiltonian satisfy a set of commutation relations with a pointer observable and with one other. We demonstrate our results by analyzing a wide range of example systems: a qutrit interacting with a qubit environment, a qubit-qubit model with interactions alternating in time, and a series of collision models including a minimal model of a quantum Maxwell demon. Published by the American Physical Society 2024

Structural complexity of glyphosate and aminomethylphosphonate metal complexes.

Small differences in the structure and subsequent reactivity of glyphosate complexes can have a highly consequential impact due to the enormous quantities of glyphosate used globally. The gas phase metal speciation of glyphosate and its abundant metabolite, aminomethylphosphonic acid (AMPA), were determined using cross-platform electrospray ionisation ion mobility mass spectrometry. Monomeric [M + L - H]+ complexes, and both larger, and/or higher order clusters formed with divalent metals (M = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Cu2+, and Zn2+; and L = glyphosate and AMPA). Complexation occurred at more than one ligand donor site for [M + L - H]+, resulting in multidentate complexes. The type of complex depended on M, with central positions maximizing the interactions of the M with donor sites of the L preferred. The isomers were separated by ion mobility and experimental collisional cross sections (N2CCSexp) were derived for all isolated species. An energy threshold DFT approach located the structural families and potential lowest energy forms; these were found to be consistent with confirmed condensed phase (reported crystal structures) and gas phase structures (via infrared multiple photon dissociation, IRMPD). Theoretical nitrogen collisional cross sections (N2CCScalc) of these confirmed structures tended to underestimate the N2CCSexp for both [M + glyphosate - H]+ and [M + AMPA - H]+ complexes. Underestimation ranged between 1-20%, and was not uniform between species. By comparison, helium collisional cross sections (HeCCSexp and HeCCScalc) were in better agreement (within 1-3%). These findings suggest further refinements are needed to collisional cross section modelling for metal containing species, in particular for nitrogen drift gas.

Some Physics of Small Collision Systems

In recent years, certain experimental results from small collision systems (e.g. p-p, d-Au, p-Pb) at the RHIC and LHC have been reinterpreted as evidence for the formation, therein, of a dense flowing medium (QGP) despite small collision volumes. Systems that had been assigned as simple references (e.g., cold nuclear matter) for larger A-A collisions would then no longer play that role. This article examines conventional interpretations of certain data features in the context of a two-component (soft + hard) collision model. Specific topics include centrality determination for p-Pb collisions, interpretation (or not) of nuclear modification factors, significance of claims for strangeness enhancement, and interpretation of the “ridge” in p-p collisions. For p-p and p-Pb data analysis results indicate that p-Pb collisions are simple linear superpositions of p-N collisions, and N–N collisions within small systems generally follow simple and consistent rules. However, there is more to be learned about “basic” QCD in small systems with improved analysis methods.

The Impact of Shear on Disk Galaxy Star Formation Rates

Abstract Determining the physical processes that control galactic-scale star formation rates is essential for an improved understanding of galaxy evolution. The role of orbital shear is currently unclear, with some models expecting reduced star formation rates and efficiencies with increasing shear, e.g., if shear stabilizes gas against gravitational collapse, while others predicting enhanced rates, e.g., if shear-driven collisions between giant molecular clouds trigger star formation. Expanding on the analysis of 16 galaxies by C. Suwannajak et al., we assess the shear dependence of star formation efficiency (SFE) per orbital time (ϵ orb) in 49 galaxies selected from the PHANGS-ALMA survey. In particular, we test a prediction of the shear-driven giant molecular cloud​​​​​​ (GMC) collision model that ϵ orb ∝ (1–0.7β), where β ≡ d ln v circ / d ln r , i.e., SFE per orbital time declines with decreasing shear. We fit the function ϵ orb = ϵ orb,0(1 − α CC β) finding α CC ≃ 0.76 ± 0.16; an alternative fit with ϵ orb normalized by the median value in each galaxy yields α CC * = 0.80 ± 0.15 . These results are in good agreement with the prediction of the shear-driven GMC collision theory. We also examine the impact of a galactic bar on ϵ orb finding a modest decrease in SFE in the presence of a bar, which can be attributed to lower rates of shear in these regions. We discuss the implications of our results for the GMC life cycle and environmental dependence of star formation activity.

New 40Ar/39Ar Dating and Paleomagnetism of the Pana Formation Rocks From the Linzhou Basin, Lhasa Block: Implications for the India‐Asia Collision

AbstractThe India‐Asia collision onset and cessation of the Neo‐Tethyan oceanic subduction are pivotal for understanding the collision processes, Tibetan Plateau uplift and global climate change, yet they remain hotly debated. The mostly cited ∼60–50 Ma initial collision age would require a ca. 20 Ma delay of the orogenic responses in Asia. Besides, the majority of the Cretaceous and Paleogene paleomagnetic data from the Lhasa Block (LB) indicates a “Greater” and “Quiescent” Asia prior to the India‐Asia collision, conflicting with the widely observed latest Cretaceous intense deformation within the block. To address these paradoxes, we present new paleomagnetic results on the Pana Formation volcanic rocks from the Linzhou basin, southern LB, with 40Ar/39Ar dating results indicating emplacement around ∼53 Ma. Combined with previous paleomagnetic results, the updated mean ChRM direction indicates the LB at 31.4°N (28.9–33.9°N) in the early Eocene. This indicates a minimal amount of crustal shortening (1.2 ± 3.8° or 0.9 ± 3.8°) in the northern Plateau since the early Eocene, and a substantial N‐S distance of 1,880 ± 420 km between the Indian and Asian leading margins at that time. Reassessed paleomagnetic data from LB, in conjunction with current knowledge on the original size of Greater India, fit well with a two‐stage collision model. This model suggests a ∼55 Ma collision between India and an intra‐oceanic arc, followed by a ∼34 Ma final collision between India and Asia, aligning well with the collision‐related responses in the plateau.

Injection, confinement, and diagnosis of electrons and positrons in a permanent magnet dipole trap

Prerequisites for the goal of studying long-lived, magnetically confined, electron–positron pair plasmas in the laboratory include the injection of both species into the trap, long trapping times, and suitable diagnostic methods. Here we report recent progress on these tasks achieved in a simple dipole trap based on a supported permanent magnet. For the injection of electrons, both an E×B drift technique (of a ∼2–μA, 6-eV beam) and “edge injection” (from a filament emitting a few mA and biased to some tens of volts) have been demonstrated; the former is suitable for low-density beams with smaller spatial and velocity spreads, while the latter employs fluctuations arising from collective behavior. To diagnose the edge-injected electrons, image potentials and currents induced on a wall probe, the magnet case, and wall electrodes were measured. Confinement of drift-injected positrons, measured experimentally, exhibited at least two well-separated timescales. Simulations reproduced this qualitatively, using a simple model of elastic collisions with residual background gas, and point to small adjustments for increasing trapping times. In a major upgrade to diagnostic capabilities, 25 bismuth germanate detectors, placed in three reentrant ports, are able to localize annihilation gammas, which will be used in future experiments to distinguish between different loss channels.Graphical abstract

Kinetic simulations of nuclear burning plasmas in inertial confinement fusions taking into account the large-angle collisions

Although ignition had been achieved at the National Ignition Facility (NIF), recent observations of the experiments indicate novel physics that beyond theoretical predictions emerge, e.g., the neutron analysis of experiments has revealed deviations from the Maxwellian distributions in ion relative kinetic energies of burning plasmas, with the surprising emergence of supra-thermal deuterium and tritium (DT) ions that fall outside the predictions of macroscopic statistical hydrodynamic models. Via our newly developed hybrid-particle-in-cell code, incorporating the newly-proposed model of large-angle collisions, we infer that this could be attributed to the increased significance of large-angle collisions among DT ions and α-particles in the burning plasma. Extensive and unprecedented kinetic investigations into the implications of large-angle collisions in the burning plasma have yield several key findings, including an ignition moment promotion by ∼10ps, the presence of supra-thermal ions below an energy threshold, and approximately twice the expected deposition of α-particles densities. The rationality of our findings is confirmed through the congruency between the neutron spectral moment analyses conducted by the NIF and our kinetic simulations, both highlighting progressively widening disparities between neutron spectral moment analyses and hydrodynamics predictions, which becomes more pronounced as the yield increases. Our kinetic simulations with large-angle collisions not only provide novel insights for experiment interpretation but also open new research opportunities for the largely unexplored regime of the nuclear burning plasmas, which are distinguished by their exceptionally high energy densities and hold immense potential for illuminating the intricate physics that underpins the evolution of the early universe.

Ten-moment fluid model for low-temperature magnetized plasmas

In this paper, a one-dimensional 10-moment multi-fluid plasma model is developed and applied to low-temperature magnetized plasmas. The 10-moment model solves for six anisotropic pressure terms, in addition to density and three components of fluid momentum, which allows the model to capture finite kinetic effects. The results are benchmarked against a 5-moment model, which assumes that the gas constituents follow a Maxwellian velocity distribution function (VDF), and a particle-in-cell Monte Carlo collision model that allows for arbitrary non-Maxwellian VDFs. The models are compared in a one-dimensional, low-temperature, partially magnetized plasma test case. The 10-moment results accurately reproduce the anisotropic temperature profile in low-temperature magnetized plasmas, where shear gradients exist due to the E×B drift. We discuss the mechanisms by which the anisotropic pressure can be generated in low-temperature magnetized plasmas. In addition, the importance of a self-consistent heat flux closure to the 10-moment model is studied, showing consistency with other models only when the assumptions of the underlying model are met. The 10-moment model allows for study of electron inertia effects and non-Maxwellian VDFs without the need for kinetic methods that are more computationally expensive.

Interaction-aware control for robotic vegetation override in off-road environments

Robotic systems tasked with completing off-road economic, military, or humanitarian missions often encounter environmental objects when traversing unstructured terrains. Certain objects (e.g. safety cones) must be avoided to ensure operational integrity, but others (e.g. small vegetation) can be interacted with (e.g. overridden/pushed) safely. Pure object-avoidance assumptions in conventional robotic system navigation policies may lead to inefficient (slow) or overly-cautious (immobilized) traversal behaviors in off-road terrains. To address this gap in system performance, we draw inspiration from existing hybrid dynamic system control literature. We have designed a nonlinear trajectory optimization controller that utilizes vegetation-interaction models as a jump map in the dynamics constraint. In contrast to purely vision-based navigation policies which classify the traversability of obstacles, the allowable subset of objects with which the vehicle can safely interact is now characterized by a data-driven collision model and the existence of a dynamically-feasible trajectory which satisfies the contact constraints. The controller’s capabilities are demonstrated on a full-sized autonomous utility task vehicle where objects including posts and trees of up to 25.4 [mm] and 81.8 [mm] diameter are overridden.

Simulating Non-Markovian Dynamics in Multidimensional Electronic Spectroscopy via Quantum Algorithm.

Including the effect of the molecular environment in the numerical modeling of time-resolved electronic spectroscopy remains an important challenge in computational spectroscopy. In this contribution, we present a general approach for the simulation of the optical response of multichromophore systems in a structured environment and its implementation as a quantum algorithm. A key step of the procedure is the pseudomode embedding of the system-environment problem resulting in a finite set of quantum states evolving according to a Markovian quantum master equation. This formulation is then solved by a collision model integrated into a quantum algorithm designed to simulate linear and nonlinear response functions. The workflow is validated by simulating spectra for the prototypical excitonic dimer interacting with fast (memoryless) and finite-memory environments. The results demonstrate, on the one hand, the potential of the pseudomode embedding for simulating the dynamical features of nonlinear spectroscopy, including lineshape, spectral diffusion, and relaxations along delay times. On the other hand, the explicit synthesis of quantum circuits provides a fully quantum simulation protocol of nonlinear spectroscopy harnessing the efficient quantum simulation of many-body dynamics promised by the future generation of fault-tolerant quantum computers.

Atomistic simulations of low energy ion irradiation of 2D materials: From ab-initio molecular dynamics to simple binary collision model

Atomistic simulations of low energy ion irradiation of 2D materials: From <i>ab-initio</i> molecular dynamics to simple binary collision model

Quantum switch instabilities with an open control

The superposition of causal orders shows promise in various quantum technologies. However, the fragility of quantum systems arising from environmental interactions, leading to dissipative behavior and irreversibility, demands a deeper understanding of the possible instabilities in the coherent control of causal orders. In this work, we employ a collisional model to investigate the impact of an open control system on the generation of interference between two causal orders. We present the environmental instabilities for the switch of two arbitrary quantum operations and examine the influence of environmental temperature on each potential outcome of control post-selection. Additionally, we explore how environmental instabilities affect protocol performance, including switching between mutually unbiased measurement observables and refrigeration powered by causal order superposition, providing insights into broader implications.

A Geometrically Motivated Two-Dimensional Collisional Abrasion Model to Resolve the Evolution of Natural Fragment Shapes

A Geometrically Motivated Two-Dimensional Collisional Abrasion Model to Resolve the Evolution of Natural Fragment Shapes

Self-organization in collisionless, high-β turbulence

The magnetohydrodynamic (MHD) equations, as a collisional fluid model that remains in local thermodynamic equilibrium (LTE), have long been used to describe turbulence in myriad space and astrophysical plasmas. Yet, the vast majority of these plasmas, from the solar wind to the intracluster medium (ICM) of galaxy clusters, are only weakly collisional at best, meaning that significant deviations from LTE are not only possible but common. Recent studies have demonstrated that the kinetic physics inherent to this weakly collisional regime can fundamentally transform the evolution of such plasmas across a wide range of scales. Here, we explore the consequences of pressure anisotropy and Larmor-scale instabilities for collisionless, $\beta \gg 1$ , turbulence, focusing on the role of a self-organizational effect known as ‘magneto-immutability’. We describe this self-organization analytically through a high- $\beta$ , reduced ordering of the Chew–Goldberger–Low-MHD (CGL-MHD) equations, finding that it is a robust inertial-range effect that dynamically suppresses magnetic-field-strength fluctuations, anisotropic-pressure stresses and dissipation due to heat fluxes. As a result, the turbulent cascade of Alfvénic fluctuations continues below the putative viscous scale to form a robust, nearly conservative, MHD-like inertial range. These findings are confirmed numerically via Landau-fluid CGL-MHD turbulence simulations that employ a collisional closure to mimic the effects of microinstabilities. We find that microinstabilities occupy a small ( ${\sim }5\,\%$ ) volume-filling fraction of the plasma, even when the pressure anisotropy is driven strongly towards its instability thresholds. We discuss these results in the context of recent predictions for ion-vs-electron heating in low-luminosity accretion flows and observations implying suppressed viscosity in ICM turbulence.

A general continuous contact force model for contact collisions of soft and hard materials

A general continuous contact force model for contact collisions of soft and hard materials

Covariant formulation of spinodal decomposition in rapidly expanding quark gluon plasma

Quantum chromodynamics (QCD) is expected to have a first order phase transition between the confined hadron gas and the deconfined quark gluon plasma at high baryon densities. This will result in phase boundary effects in the metastable and unstable regions. It is important to include these effects in phenomenological models of heavy ion collisions to identify experimental signatures of a phase transition. This requires building intuition on phase separation in rapidly expanding fluids. In this work we present the covariant equations of relativistic hydrodynamics with a phase boundary, provide prescriptions to extend the equation of state to metastable and unstable regions, and show the effects of spinodal separation in a Bjorken flow. Published by the American Physical Society 2024

Large time solution for collisional breakage model: Laplace transformation based accelerated homotopy perturbation method

The behavior of several particulate processes, such as cell interaction, blood clotting, bubble formation, grain breakage, and cheese formation from milk, have been studied using coagulation and fragmentation models (Fogelson and Guy, 2008 [1]; Pazmiño et al., 2022 [2]; Chen et al., [3]). Various studies utilize the linear fragmentation model to simplify the underlying physics. However, in real-life scenarios, particles form due to the collision of two particles, leading to a non-linear collisional breakage model. Unfortunately, the collisional breakage model is less explored due to its complex behavior. While analytical solutions are difficult to compute and are still missing in the literature, this article proposes an approximate solution for the model using the Laplace-based accelerated homotopy perturbation method. Further, coupling with Padé approximant, the accuracy of the solution is extended for the longer time. Considering various physically relevant kernels, the approximate series solutions are compared with the well known finite-volume solutions to measure the accuracy in terms of qualitative and quantitative errors. The article also encompasses theoretical convergence analysis and error estimations to enhance comprehension of the proposed formulation.