Simultaneous Collisions Research Articles

I2DM: A Monte Carlo framework for ion irradiation on two-dimensional materials

Recent years have witnessed a surge of research on the structure, property and performance engineering of two-dimensional (2D) materials by ion irradiation. Compared to the 3D counterparts, 2D systems exhibit drastically different and even counter-intuitive irradiation response, and an atomic insight into the ion bombardment and defect formation is essential. In this work, we develop a theoretical framework I2DM for simulating ion irradiation on two-dimensional (2D) materials using Monte Carlo (MC) algorithm. I2DM can generate incident ions with adjustable ion species, incident energy, ion fluence and incident angle. Based on binary collision approximation (BCA), the primary collisions, cascade collisions and defect recombination during irradiation process are explicitly described. As output, details on the defect type/yield and morphology of irradiated material are provided. We have performed systematic simulations on three typical 2D structures, including graphene, h-BN, and MoS2 under different ion irradiation conditions, and reveal that the obtained results are in excellent agreement with the available experimental measurements and molecular dynamics data. The developed framework is generally applicable and computationally efficient, highly valuable for understanding the fundamental mechanism of ion irradiation on 2D systems and designing/optimizing low-dimensional structures for nanoelectronics, spintronics, optics, energy storage and environmental protection. Program SummaryProgram Title: I2DM.CPC Library link to program files:https://doi.org/10.17632/pf2pz4fxj3.1.Licensing provisions: GPLv2.Programming language: Python.Supplementary material: Supplementary material is available.Nature of problem: A general MC framework for simulating ion irradiation on 2D materials; calculate the energy loss by nuclear stopping and electronic stopping; simulate primary/cascade collisions and defect recombination; predict defect type/yield and morphology of 2D target.Solution method: This framework uses BCA to describe nuclear stopping for the irradiation process; the energy loss by electronic stopping is computed by a semiempirical model combining Oen-Robinson model and Lindhard-Scharff model; simultaneous collision is included for describing many-body interaction; capture radius is introduced to simulate defect recombination.

Regularizable collinear periodic solutions in the n-body problem with arbitrary masses

For n-body problem with arbitrary positive masses, we prove there are regularizable collinear periodic solutions for any ordering of the masses, going from a simultaneous binary collision to another in half of a period with half of the masses moving monotonically to the right and the other half monotonically to the left. When the masses satisfy certain equality condition, the solutions have extra symmetry. This also gives a new proof of the existence of Schubart orbit, when n=3.

Maximal Codimension Collisions and Invariant Measures for Hard Spheres on a Line

For any N≥3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N\\ge 3$$\\end{document}, we study invariant measures of the dynamics of N hard spheres whose centres are constrained to lie on a line. In particular, we study the invariant submanifold M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {M}$$\\end{document} of the tangent bundle of the hard sphere billiard table comprising initial data that lead to the simultaneous collision of all N hard spheres. Firstly, we obtain a characterisation of those continuously-differentiable N-body scattering maps which generate a billiard dynamics on M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {M}$$\\end{document} admitting a canonical weighted Hausdorff measure on M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {M}$$\\end{document} (that we term the Liouville measure onM\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {M}$$\\end{document}) as an invariant measure. We do this by deriving a second boundary-value problem for a fully nonlinear PDE that all such scattering maps satisfy by necessity. Secondly, by solving a family of functional equations, we find sufficient conditions on measures which are absolutely continuous with respect to the Hausdorff measure in order that they be invariant for billiard flows that conserve momentum and energy. Finally, we show that the unique momentum- and energy-conserving linearN-body scattering map yields a billiard dynamics which admits the Liouville measure on M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {M}$$\\end{document} as an invariant measure.

Machine Learning for Real-Time Processing of ATLAS Liquid Argon Calorimeter Signals with FPGAs

With the High-Luminosity upgrade of the LHC, the number of simultaneous proton-proton collisions will be increased to up to 200. This requires an extensive overhaul of the detector systems. For the ATLAS Liquid Argon calorimeter electronics, 556 high performance FPGAs will be installed to reconstruct the energy for all 182 468 cells at the LHC bunch crossing frequency of 40 MHz. However, the current digital filter used for energy reconstruction (optimal filter) decreases in performance under these high pileup conditions. We demonstrate, that small recurrent or convolutional neural networks can outperform the optimal filter. Prototype implementations of the respective inference code in VHDL show, that the use of these networks on FPGAs is feasible and the resulting firmware fits onto the planned Intel Agilex devices. The full design is capable of processing 384 detector cells per FPGA, by combining parallel instances of the firmware with time division multiplexing.

Redesign an aircraft windshield to improve its mechanical resistance against simultaneous bird impacts

The bird impact on aircraft components is one of the most serious accidents which can happen in the aviation industry. Among the various parts of an aircraft, the bird impact on the windshield is more important due to the possibility of causing injury to the pilot. Standard windshields are designed to withstand a bird strike, however, in a group flight of birds, several birds can strike the windshield at the same time. The results of practical tests and simulations show that the current windshields are seriously damaged in the simultaneous collision of several birds and the possibility of birds penetrating the cabin is very high. In this research the mechanical properties of standard windshield constituent materials are obtained. Initially practical tests are carried out and simulation results are verified for single bird strike. Using these results, the simultaneous impact of three birds on a windshield is simulated. It was shown that the resistance of the standard windshield against simultaneous collisions is insufficient. So the thicknesses of the windshield layers are determined in such a way that the new windshield is resistant and bird penetration into the cabin does not happen.

Simple Analytical Expressions for Steady-State Vapor Growth and Collision–Coalescence Particle Size Distribution Parameter Profiles

Abstract This study derives simple analytical expressions for the theoretical height profiles of particle number concentrations (Nt) and mean volume diameters (Dm) during the steady-state balance of vapor growth and collision–coalescence with sedimentation. These equations are general for both rain and snow gamma size distributions with size-dependent power-law functions that dictate particle fall speeds and masses. For collision–coalescence only, Nt (Dm) decreases (increases) as an exponential function of the radar reflectivity difference between two height layers. For vapor deposition only, Dm increases as a generalized power law of this reflectivity difference. Simultaneous vapor deposition and collision–coalescence under steady-state conditions with conservation of number, mass, and reflectivity fluxes lead to a coupled set of first-order, nonlinear ordinary differential equations for Nt and Dm. The solutions to these coupled equations are generalized power-law functions of height z for Dm(z) and Nt(z) whereby each variable is related to one another with an exponent that is independent of collision–coalescence efficiency. Compared to observed profiles derived from descending in situ aircraft Lagrangian spiral profiles from the CRYSTAL-FACE field campaign, these analytical solutions can on average capture the height profiles of Nt and Dm within 8% and 4% of observations, respectively. Steady-state model projections of radar retrievals aloft are shown to produce the correct rapid enhancement of surface snowfall compared to the lowest-available radar retrievals from 500 m MSL. Future studies can utilize these equations alongside radar measurements to estimate Nt and Dm below radar tilt elevations and to estimate uncertain microphysical parameters such as collision–coalescence efficiencies. Significance Statement While complex numerical models are often used to describe weather phenomenon, sometimes simple equations can instead provide equally good or comparable results. Thus, these simple equations can be used in place of more complicated models in certain situations and this replacement can allow for computationally efficient and elegant solutions. This study derives such simple equations in terms of exponential and power-law mathematical functions that describe how the average size and total number of snow or rain particles change at different atmospheric height levels due to growth from the vapor phase and aggregation (the sticking together) of these particles balanced with their fallout from clouds. We catalog these mathematical equations for different assumptions of particle characteristics and we then test these equations using spirally descending aircraft observations and ground-based measurements. Overall, we show that these mathematical equations, despite their simplicity, are capable of accurately describing the magnitude and shape of observed height and time series profiles of particle sizes and numbers. These equations can be used by researchers and forecasters along with radar measurements to improve the understanding of precipitation and the estimation of its properties.

Low energy ion-solid interactions: a quantitative experimental verification of binary collision approximation simulations

Ultra-low energy ion implantation has become an attractive method for doping of two-dimensional materials and ultra-thin films. The new dynamic Monte Carlo program IMINTDYN based on the binary collision approximation allows a reliable prediction of low energy implantation profiles and target compositional changes, as well as efficient simulation of high energy light ion scattering. To demonstrate the quality of these predictions and simulations, we present a model case experiment where we implanted W ions into tetrahedral amorphous carbon with low (10 keV) and ultra-low (20 eV) ion energies and analyzed the W implantation profiles with high resolution Rutherford backscattering spectrometry (HR-RBS). This experiment is compared with a complete simulation of all aspects of ion-solid-interactions of the experiment using the new IMINTDYN program. A unique novel simulation option, also relevant for implantation into 2D materials, is the inclusion of the vacancy as target species with dynamic vacancy generation and annihilation. Whereas simulations neglecting vacancy formation cannot reproduce the measured implantation profiles, we find excellent agreement between simulated and measured HR-RBS spectra. We also demonstrate the important role of simultaneous weak collisions in the binary collision approximation at low projectile energies.

AN IMPROVED APPROACH IN THE APPLICATIONOF AN ELASTIC-PLASTIC CONTACT FORCE MODELIN THE MODELLING OF MULTIPLE IMPACTS

This paper presents the modelling of a simultaneous multiple collision occurring between several bodies ofa kinematic chain. An algorithm is proposed that when used with an elastoplastic contact model, allows thephenomena that can occur during a multiple-body collision to be taken into account. These phenomena includethe transition of the collision state from the restitution phase directly to the compression phase or successivecollisions occurring along the same normal. The proposed algorithm can be used with any elastoplastic contactmodel. This paper presents its use with a selected model in a three-body system. Numerical calculations basedon the model have been verified using the Finite Element Method (FEM). The use of the proposed improvedapproach reduces the post-collision velocity prediction error by 2.34% compared to the baseline descriptionof collisions known from the literature.

Simultaneous Collision Avoiding and Target Tracking for Unmanned Ground Vehicle with Velocity and Heading Rate Constraints

Simultaneous Collision Avoiding and Target Tracking for Unmanned Ground Vehicle with Velocity and Heading Rate Constraints

Developing GPU-compliant algorithms for CMS ECAL local reconstruction during LHC Run 3 and Phase 2

The higher LHC luminosities foreseen in Run 3 (2022+) and during the Phase 2 of the LHC (2029+), and the consequently larger number of simultaneous proton-proton collisions per event, pose significant challenges for the CMS event reconstruction. In particular maintaining the strict time budget for reconstruction algorithms at the CMS software high level trigger will not be possible considering only the expected increase of processing power from conventional CPUs. Therefore, CMS is investigating the use of heterogeneous architectures, including GPU accelerators, to satisfy the needs of the Phase 2 reconstruction. The local reconstruction algorithm of the CMS electromagnetic calorimeter (ECAL) is among the first to be implemented on heterogeneous platforms for LHC Run 3. This article discusses the necessary changes to the CMS software framework that support the execution of code on accelerators. The current development status of the ECAL local reconstruction algorithm is described and first performance results of GPU enabled code are presented.

TCLink: A Fully Integrated Open Core for Timing Compensation in FPGA-Based High-Speed Links

The high luminosity expected in the second phase of the upgrades of the Large Hadron Collider (LHC phase-2 upgrades) will pose unprecedented challenges to its four experiments in terms of collisions density – also known as pileup – per beam crossing. Disentangling the vertices of 200 simultaneous collisions every 25 ns requires high granularity in the detectors, as well as extremely precise and stable timing. While short-term timing stability is usually a concern addressed in timing distribution systems, long-term variations due to changing environmental conditions can accumulate through distribution chains and can dominate the overall timing stability of the systems they serve. Timing distribution systems in LHC experiments typically use high-speed links and clock recovery. This paper presents a logic core that can be used to mitigate long-term temperature variations in high-speed links. The Timing Compensated Link (TCLink) is an open-source firmware core fully integrated in Xilinx Ultrascale Field Programmable Gate Arrays (FPGAs). It demonstrates picosecond-level phase precision over timing distribution systems, improving the overall timing stability in physics experiments.

An advanced dual APF-based controller for efficient simultaneous collision and singularity avoidance for human-robot collaborative assembly processes

Immersive coexistence between humans and robots is key for next generations of assembly processes. Accounting for human behavior in a shared working space demands for the prevention of collisions in a persistently changing environment along with the avoidance of robot singularities. This work presents a dual Artificial Potential Fields (d-APF) controller for efficient simultaneous singularity and collision avoidance in human cobot blended assembly tasks. The benefits of the controller have been benchmarked to the damped least square and the artificial potential fields methods and validated with respect to an industrial use case addressing the disassembly of battery packs for e-cars.

Three-Mediator Enhanced Collisions on an Ultramicroelectrode for Selective Identification of Single Saccharomyces cerevisiae.

Selective detection of colliding entities, especially cells and microbes, is of great challenge in single-entity electrochemistry. Herein, based on the different cellular electron transport pathways between microbes and mediators, we report a three-mediator system [K3Fe(CN)6, K4Fe(CN)6, and menadione] to achieve redox activity analysis and selective identification of single Saccharomyces cerevisiae without the usage of antibodies. K4Fe(CN)6 in the three-mediator system will oxidize near the electrode surface and increase the local concentration of K3Fe(CN)6, which will promote the redox reaction of S. cerevisiae. The hydrophobic mediator─menadione─can selectively penetrate through the S. cerevisiae membrane and get access to its intracellular redox center and can further react with K3Fe(CN)6 in the bulk solution. In contrast, the mediator can only get access to the bacterial membranes of Escherichia coli and Staphylococcus aureus, which results in different electrochemical collision signals between the above microbes. In the three-mediator system, upward step-like collision signals were observed in S. cerevisiae suspension, which are related to their microbial redox activity. In comparison, E. coli or S. aureus only generated downward current steps because the blockage effect of mediator diffusion suppresses their redox activities. When S. cerevisiae co-existed with E. coli or S. aureus, transients generated by both blockage and redox activity were observed. The approach enables us to trace the collision behaviors of different microbes and distinguish their simultaneous collisions, which is the foundation for further application of electrochemical collision technique in the specific identification of single biological entities.

Colliding and Fixed Target Mode in a Single Experiment—A Novel Approach to Study the Matter under New Extreme Conditions

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300 MeV and baryonic charge density over three times the values of the normal nuclear density. According to contemporary theoretical knowledge, such conditions were not accessible during the early Universe evolution and are not accessible now in the known astrophysical phenomena. To achieve these new extreme conditions, we proposed performing high-luminosity experiments at LHC or other colliders by means of scattering the two colliding beams at the nuclei of a solid target that is fixed at their interaction region. Under plausible assumptions, we estimate the reaction rate for the p+C+p and Pb+Pb+Pb reactions and discuss the energy deposition into the target and possible types of fixed targets for such reactions. To simulate the triple nuclear collisions, we employed the well-known UrQMD 3.4 model for the beam center-of-mass collision energies sNN = 2.76 TeV. As a result of our modeling, we found that, in the most central and simultaneous triple nuclear collisions, the initial baryonic charge density is approximately three times higher than the one achieved in the ordinary binary nuclear collisions at this energy.

ATLAS LAr Calorimeter commissioning for LHC Run-3

The ATLAS experiment at the Large Hadron Collider (LHC) measures proton-proton collisions at high energies. Within the Phase-I upgrade of the LHC before the start of Run-3 in 2022, the trigger system of the Liquid Argon calorimeter of ATLAS is being prepared to cope with an increased number of simultaneous proton-proton collisions. In the back-end of this new trigger system, the LATOME boards will be responsible for the computation of the energies deposited in the calorimeter. The commissioning of this computation within the LATOME is presented.

CMS ECAL upgrade for precision timing and energy measurements at the High-Luminosity LHC

The High Luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous luminosity of ∼5 × 1034 cm−2 s−1, leading to an average of 150–200 simultaneous collisions. This high instantaneous luminosity scenario presents a significant challenge for the detectors. The barrel region of the CMS electromagnetic calorimeter (ECAL) will be preserved but will be operated at a lower temperature and with a completely new readout and trigger electronics. A dual gain transimpedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be used in the new readout electronics. The trigger decision will be moved off-detector and performed by powerful and flexible FPGA processors, allowing for more sophisticated trigger algorithms to be applied. The upgraded ECAL will be capable of high-precision energy measurements throughout HL-LHC and will greatly improve the time resolution for photons and electrons above 10 GeV. The performance obtained with the new electronics has been tested at CERN under an electron beam with a matrix of ECAL crystals equipped with APDs.

Numerical Simulation of Mechanical Coupling for Low-Back Booster with a 6-Year-Old Child during a Crash Test

This research assessed a mechanical coupling for the ISOFIX Child Restraint System using the Finite Element Method (FEM) in a critical condition (simultaneous frontal and lateral collision). The mechanism was designed according to the R129 standard, and it consists of a set of springs and dampers that allows displacements in the three Cartesian axes (x, y, z) to dissipate a portion of the energy produced by a traffic accident. Two case studies are presented. The first one evaluates the behavior of the mechanism by applying the equivalent weight of a child and the LBB during a frontal and lateral impact according to the FMVSS 213 standard. The second evaluates the injuries generated in the head, neck, and thorax with a six-year Hybrid III model during a frontal impact when implementing the coupling system. The outcomes show that both axes reach a maximum deceleration of 23 G, and it remains from 17 G to 21 G in 30 ms. After 65 ms, it decreases from 17 G to 0 G. Overall, the injury rates are compared when using mechanical coupling with LBB and only LBB to analyze the system’s efficiency, showing a significant reduction in head and neck injuries, obtaining a 24% variation in the HIC36, and reducing the neck range motion by 19.3°.

Asymptotic genealogies for a class of generalized Wright–Fisher models

A class of Cannings models is studied, with population size N having a mixed multinomial offspring distribution with random success probabilities ${W_{1}},\dots ,{W_{N}}$ induced by independent and identically distributed positive random variables ${X_{1}},{X_{2}},\dots $ via ${W_{i}}:={X_{i}}/{S_{N}}$, $i\in \{1,\dots ,N\}$, where ${S_{N}}:={X_{1}}+\cdots +{X_{N}}$. The ancestral lineages are hence based on a sampling with replacement strategy from a random partition of the unit interval into N subintervals of lengths ${W_{1}},\dots ,{W_{N}}$. Convergence results for the genealogy of these Cannings models are provided under assumptions that the tail distribution of ${X_{1}}$ is regularly varying. In the limit several coalescent processes with multiple and simultaneous multiple collisions occur. The results extend those obtained by Huillet [J. Math. Biol. 68 (2014), 727–761] for the case when ${X_{1}}$ is Pareto distributed and complement those obtained by Schweinsberg [Stoch. Process. Appl. 106 (2003), 107–139] for models where sampling is performed without replacement from a supercritical branching process.

Intelligent controller for nonholonomic wheeled mobile robot: A fuzzy path following combination

This research article presents a novel solution of controller design for the autonomous path-following maneuver of a nonholonomic wheeled mobile robotic (WMR) system subjected to static and dynamic obstacles. Currently, autonomously operated nonholonomic vehicles, capable of completing tasks avoiding collisions, are deployed for low-profile household applications to sophisticated space missions. The geometrically constrained path-following controller with embedded intelligence for collision avoidance is designed based on a twofold hybrid control law. The hybrid control law combines the feedback linearization controller (FBC) with the fuzzy logic controller (FLC). The feedback linearization controller helps the mobile robot to remain on its desired path, while the fuzzy logic controller helps the mobile robot to avoid critical obstacles around the reference path. It is analytically proven that the proposed hybrid control law converges the robot asymptotically to the desired path when it is safely away from obstacles. Further, when the robot detects an obstacle in its sensing range, obstacle avoidance control law acts locally and it deviates itself from the desired path to avoid collision assuring stability through a bounded tracking control law. Considering bounded sensor measurement uncertainties during obstacle detection, it is observed that the fuzzy logic-based collision-avoidance algorithm behaves in a robust manner. The hybrid controller is designed and tested in a simulated environment with the real-life parameters of a nonholonomic wheeled mobile robot. The robot is capable of traversing through the geometrically constrained desired paths avoiding obstacles in an improved manner compared to the existing method. Moreover, the robot is also capable of returning back to its original path when obstacles are safely away. The performance of the novel hybrid control strategy is illustrated for several geometrically constrained paths via simulation to show its effectiveness in terms of fulfilling dual objectives of path following and simultaneous collision avoidance in an improved manner.

Crisis-induced flow reversals in magnetoconvection.

We report the occurrence of flow reversals induced by the attractor-merging crisis in Rayleigh-Bénard convection of electrically conducting low-Prandtl-number fluids in the presence of a uniform external horizontal magnetic field. The simultaneous collision of two coexisting chaotic attractors with an unstable fixed point and its associated stable manifold takes place in the higher-dimensional phase space of the system, leading to a single merged chaotic attractor. The effect of strength of the magnetic field on the flow reversal phenomena is also explored in detail.