Multiple Collisions Research Articles

Classical Modelling of a Bosonic Sampler with Photon Collisions

The original formulation of the boson sampling problem assumed that little or no photon collisions occur. However, modern experimental realizations rely on setups where collisions are quite common, i.e., the number of photons M injected into the circuit is close to the number of detectors N. Here we present a classical algorithm that simulates a bosonic sampler: it calculates the probability of a given photon distribution at the interferometer outputs for a given distribution at the inputs. This algorithm is most effective in cases with multiple photon collisions, and in those cases, it outperforms known algorithms.

Multiple vehicle cooperation and collision avoidance in automated vehicles: survey and an AI-enabled conceptual framework

Prospective customers are becoming more concerned about safety and comfort as the automobile industry swings toward automated vehicles (AVs). A comprehensive evaluation of recent AVs collision data indicates that modern automated driving systems are prone to rear-end collisions, usually leading to multiple-vehicle collisions. Moreover, most investigations into severe traffic conditions are confined to single-vehicle collisions. This work reviewed diverse techniques of existing literature to provide planning procedures for multiple vehicle cooperation and collision avoidance (MVCCA) strategies in AVs while also considering their performance and social impact viewpoints. Firstly, we investigate and tabulate the existing MVCCA techniques associated with single-vehicle collision avoidance perspectives. Then, current achievements are extensively evaluated, challenges and flows are identified, and remedies are intelligently formed to exploit a taxonomy. This paper also aims to give readers an AI-enabled conceptual framework and a decision-making model with a concrete structure of the training network settings to bridge the gaps between current investigations. These findings are intended to shed insight into the benefits of the greater efficiency of AVs set-up for academics and policymakers. Lastly, the open research issues discussed in this survey will pave the way for the actual implementation of driverless automated traffic systems.

Spin-polarization after scattering

This paper deals with the spin-polarization change of an electron beam after elastic scattering with a neutral atom. The first part of the paper is devoted to summarizing the Kessler theory of the elastic scattering of spin-polarized electron beams. After a general description of the dependence on the polar and azimuthal angles of the spin-polarization after scattering, the effects on the spin-polarization of multiple elastic collisions occurring in the same scattering plane and with identical scattering angles are also treated. In particular, we show that, in this case, an initially unpolarized beam becomes fully polarized in the direction normal to the scattering plane after a number of collisions. The number of collisions necessary to reach full (transverse) polarization is a function of the common scattering angle. We also demonstrate that spin-polarization is conserved for forward and backward elastic scattering.

Study on crashworthiness of nature-inspired functionally graded lattice metamaterials for bridge pier protection against ship collision

Lightweight lattice metamaterials can effectively enhance the impact resistance of thin-walled structures. With the aim of further investigating the potential of lattice-filled composite structures, an innovative nature-inspired functionally graded lattice filled protection structure (FGLPS) is proposed in this paper to enhance structural energy absorption characteristics under ship impact loadings. At this point, two different graded patterns (i.e. increasing graded pattern and decreasing graded pattern with partition design) for lattice metamaterial fillers are established, then the effects of gradient model and impact angle on energy absorption characteristics of lattice-filled structures are studied using ship impact finite element model with multiple collision conditions. The results show that the novel functionally graded lattice filled thin-walled structure can significantly reduce the peck impact force, prolong the impact time and play prominent protective role. Especially, the peak impact force generated during the vessel impact on bridge pier can be reduced by up to 60.01% through zonal gradient design. Besides, FGPLS can absorb up to 33.15% of total impact energy by plastic deformation, and both increasing and decreasing gradient structure have the potential ability to significantly reduce the impact damage. The findings of this study provide a new approach to the engineering applications of collision-resistant structures with high energy absorption capacity.

The Vagueness of COLREG versus Collision Avoidance Techniques—A Discussion on the Current State and Future Challenges Concerning the Operation of Autonomous Ships

With the development of Maritime Autonomous Surface Ships (MASS), considerable research is undertaken to secure their safety. One of the critical aspects of MASS is collision avoidance, and multiple collision avoidance algorithms have been developed. However, due to various reasons, collision avoidance of autonomous merchant vessels appears to be far from resolved. With this study, we aim to discuss the current state of Collision Avoidance Methods (CAMs) and the challenges lying ahead—from a joint academic and practical point of view. To this end, the key Rules from International Regulations for Preventing Collisions at Sea (COLREG) have been reviewed with a focus on their practical application for MASS. Moreover, the consideration of the COLREG Rules in contemporary collision avoidance algorithms has been reviewed. The ultimate objective is to identify aspects of COLREG requiring additional attention concerning MASS developments in terms of collision avoidance. Our conclusions indicate that although a lot of progress has been achieved recently, the feasibility of CAMs for MASS remains questionable. Reasons for so are the ambiguous character of the regulations, especially COLREG, as well as virtually all existing CAMs being at best only partly COLREG-compliant.

The trajectory of bio-carriers in periodic energy landscape regulated by the multiple collision history in a magnetophoretic system

Analysis of changes in particle trajectories due to collision is essential to understanding the physical information such as energy or mass exchange during collisions between particles. Most of the research has studied particles with initial energies in a relatively uniform or gradient static energy landscape. However, compared to the particle collisions of a static energy landscape, the movement becomes more diverse in a complex magnetic energy landscape. We designed micro-magnet arrays to create complex energy landscapes with temporal and spatial periodicity. Magnetic particles draw distinctly different trajectories in this magnetophoretic system depending on the coupling number. When the particles collide with each other, an immediate shift to a classified trajectory was confirmed according to the collision type. This study analyzes the particle trajectory shift that includes various information. Therefore, we inversely calculate the coupling history, such as the coupling number, time, and order due to collision. This investigation represents a unique analysis of the dynamics change of particles within a complex magnetic energy landscape.

Analysis of Transport and Vehicular Road Crash Cases in Metro Manila from 2016 to 2020

Introduction. Metro Manila, the metropolitan center and seat of the national government, is composed of 16 cities and 1 municipality, and considered as the second-most populous region in the Philippines. Transport is a key sector that is needed for accessibility and economic progress. Yet, the question on safety of the roads of Manila remains as road crashes continue to be reported.Objective. The study aims to determine the trend of road crashes in Metro Manila, and the factors associated with both fatality and injury among three types of road users – the drivers, the passengers, and the pedestrians.Methods. A retrospective analysis of 523,059 road crash data between 2016 to 2020 was done. Using descriptive statistics, the road crash variables analyzed in the study were (1) crash classification according to damage to property, fatal, and non-fatal crash, (2) road user type according to driver, passenger, and pedestrian, (3) vehicle type, (4) junction type, and (5) risky road user behavior. Logistic and multinomial regression models were used to determine whether these variables were significant with road user fatality and injury.Results. The analysis of the MMARAS database (n=523,059) showed an increasing trend of road crashes occurred since 2016 and peaked in 2019, and declined in 2020. Majority (436,367, 83.426%) were damage to property, followed by non-fatal or injurious cases (84751, 16.203%) and fatal outcomes (1941, 0.371%). Drivers have the greatest number of fatalities and injuries compared to passengers and pedestrians. Cars (513482 52.322%) and motorcycles (136641, 13.923%) remain the major types of vehicles involved in road crashes. The factors that were significantly associated with increased odds ratio for driver death were involvement of pedicabs (OR=10.937, p=0.000), motorcycles (OR=55.061, p=0.000), bus (OR=5.835, p=0.000), truck (OR=7.073, p=0.000), hit object (OR=11.007, p=0.000), self-accident (OR=6.149, p=0.000), and collisions in bridges/flyovers (OR=2.713, p=0.010)). The factors that were significantly associated with increased odds ratio for passenger fatality were the involvement of motorcycle (OR=3.75, p=0.021), angle impact (OR=42.01, p=0.002), multiple collision (OR=18.42, p=0.040), self-accident (OR=32.66, p=0.010), and lost control (OR=82.98, p=0.001). The factors significantly associated with pedestrian fatality were hit and run (OR=56.04, p=0.000), hit pedestrian (OR=1085.17, p=0.000), and crashes in bridges/flyover (OR=4.20, p=0.025). Meanwhile, multinomial regression showed that classification of crash and vehicle type were significantly associated with fatal and non-fatal crashes.Conclusion. The study showed the trend of fatality and injury among drivers, passengers, and pedestrians from2016-2020, and factors of road crashes in Metro Manila including vehicle type, road behaviors, collision type and junction type.

Dynamic obstacle avoidance for Multi-rotor UAV using chance-constraints based on obstacle velocity

To ensure the safety of autonomous Multi-rotor UAVs flying in urban airspace, they should be capable of avoiding collisions with unpredictable dynamic obstacles, such as birds. UAVs must consider both relative position and relative velocity to avoid moving obstacles. Model predictive control (MPC) can consider the multiple collision avoidance constraints in a constrained optimisation framework. This study proposes a chance-constraints based on obstacle velocity (CCOV) method, which can be combined with previous positional chance constraint methods to account for uncertainty in both position and velocity. This effectively prevents collision with high-velocity obstacles, even in a noisy environment. The proposed method has been performed on a numerical simulation built in MATLAB.

Instantaneous support propagation for [formula omitted]-Fleming–Viot processes

For a probability-measure-valued neutral Fleming–Viot process (Zt:t≥0) with Lévy mutation and resampling mechanism associated to a general Λ-coalescent with multiple collisions, we prove the instantaneous propagation of supports. That is, at any fixed time t>0, with probability one the closed support S(Zt) of the Fleming–Viot process satisfies S(ν∗Zt)⊆S(Zt), where ν is the Lévy measure of the mutation process. To show this result, we apply Donnelly–Kurtz’s lookdown particle representation for Fleming–Viot processes.

Molecular Dynamics Simulation of Scattering and Surface Diffusion of Oxygen Molecules on Ionomers in Catalyst Layers of PEFCs

Polymer electrolyte fuel cells (PEFCs) are used in fuel cell vehicles and households stationary power sources because of their low operating temperatures, small size, and light weight. For further development of PEFCs, it is necessary to reduce the amount of platinum used in the catalyst layers. If the amount of platinum used in the catalyst layers is reduced, the current density per mass of platinum increases. The effect of diffusion polarization then becomes dominant in the overall voltage drop. One factor that causes diffusion polarization is the transport resistance of oxygen molecules in the catalyst layers. Therefore, an understanding of the transport of oxygen molecules in the catalyst layers is necessary to improve the performance of PEFCs under high current density conditions. The catalyst layers comprise porous structures by aggregation of ionomer-coated platinum-supported carbon. The Knudsen number is important for gas diffusion phenomena in porous structures. The Knudsen number is the ratio of the representative length of the system to the mean free path of gas molecules, and when this value is sufficiently small, the gas diffusion phenomenon can be regarded as molecular diffusion. When the Knudsen number is sufficiently large, the gas diffusion phenomenon becomes Knudsen diffusion, in which collisions with solid walls are more dominant than collisions between gas molecules. The Knudsen number is sufficiently large in the porous structure of the catalyst layer. Therefore, the effect of collision with solid surfaces is important in the oxygen transport in the catalyst layer. In previous studies, it has been clarified that the behavior of oxygen molecules incident on an ionomer thin film includes surface scattering, in which diffuse reflection occurs on the surface, and surface diffusion, in which oxygen molecules trapped on the surface move across the surface in a series of multiple collisions. However, the effect of surface diffusion on oxygen transport across the catalyst layer is not clear. The purpose of this study is to analyze the effect of oxygen molecules and ionomer conditions on surface diffusion using the MD simulation. We analyze the behavior of oxygen molecules impinging on ionomers in a computational system that reproduces the pores of the catalyst layer. The simulation system consists of polymer chains, solvent molecules (water molecules and hydronium ions), and oxygen molecules. Periodic boundary conditions were applied in the x-, y-, and z-directions. The behavior of oxygen molecules after they impact the ionomer wall such as their residence time during surface diffusion and the surface diffusion coefficient will be analyzed.AcknowledgmentsThis work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan, Grant number JPNP20003. It was performed on the Supercomputer system “AFI-NITY” at the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University. Figure 1

Thermalization of gluons in spatially homogeneous systems

We investigate thermalization of gluons in spatially homogeneous systems using the Boltzmann equation in diffusion approximation. A complete picture on thermalization is obtained for both initially under- and over-populated systems. In an initially under-populated system, we find that its soft sector undergoes three stages: overheating, cooling/overcooling and reheating before full thermalization is achieved. In an initially over-populated system, we find that its soft sector only undergoes two stages towards full thermalization: overheating and cooling. The cooling stage is consistently driven by momentum broadening due to multiple elastic collisions, manifest as a non-thermal scaling solution.

Use of climatic cold in scientific research

A review of scientific research data on the use of climatic cold carried out on the basis of institutes of the Federal research center «Yakut Scientific Center» Siberian Branch of the Russian Academy of Science is presented, natural low temperatures being used both as testing conditions and as a tool for experimental studies. The results of full-scale hydraulic tests of pressure vessels and pipes under conditions of low climatic temperatures, and under internal pressure created due to the effect of ice formation in closed cavities are presented. The results made it possible to determine the limit states of large-diameter pipelines, simulate the stress-strain state of the pipeline in thawed, freezing and frozen soils, substantiate the extension of the lifetime of pressure vessels, develop a technology for their welding, and determine the allowable size of defects in welded joints. It is shown that climatic tests of polymer, composite, construction, welding and other classes of materials provide for estimation of their service life under the impact of climatic factors. An experimental study of the response of solids to multiple collisions with ice granules at low climatic temperatures has been carried out along with the study of the processes of brittle fracture of their surface with the formation of splintery particles. Study of the effect of fibrous fillers of natural origin on the strength properties of fresh-ice based composition material revealed that introduction of fillers increases the strength characteristics of fresh ice by 2 – 3 times. It is shown that climatic features and a significant scientific potential of the Sakha (Yakutia) Republic provide for effective use of climatic cold as a tool for scientific research and solution of engineering problems in various sectors of the national economy.

Autonomous Trajectory Generation Comparison for De-Orbiting with Multiple Collision Avoidance.

Over the past four decades, space debris has been identified as a growing hazard for near-Earth space systems. With limited access to space debris tracking databases and only recent policy advancements made to secure a sustainable space environment and mission architecture, this manuscript aims to establish an autonomous trajectory maneuver to de-orbit spacecrafts back to Earth using collision avoidance techniques for the purpose of decommissioning or re-purposing spacecrafts. To mitigate the risk of colliding with another object, the spacecraft attitude slew maneuver requires high levels of precision. Thus, the manuscript compares two autonomous trajectory generations, sinusoidal and Pontragin’s method. In order to determine the Euler angles (roll, pitch, and yaw) necessary for the spacecraft to safely maneuver around space debris, the manuscript incorporates way-point guidance as a collision avoidance approach. When the simulation compiled with both sinusoidal and Pontryagin trajectories, there were differences within the Euler angle spacecraft tracking that could be attributed to the increased fuel efficiency by over five orders of magnitude and lower computation time by over 15 min for that of Pontryagin’s trajectory compared with that of the sinusoidal trajectory. Overall, Pontryagin’s method produced an autonomous trajectory that is more optimal by conserving 37.9% more fuel and saving 40.5% more time than the sinusoidal autonomous trajectory.

Measurements of rolling friction with a stringless pendulum

Experimental results are presented on the coefficient of rolling friction, μ R, measured for a variety of different balls using a stringless pendulum. A wide range of results was obtained, depending on ball stiffness, surface roughness, ball radius and ball speed. Soft balls dissipate energy as a result of hysteresis losses in the contact region and have relative high values of μ R. Hard balls rolling on a hard surface dissipate energy by multiple collisions between asperities, with low values of μ R that increase with rolling speed and surface roughness. The experiment is very easy to set up and would be a useful addition in a student laboratory or as a lecture demonstration.

A Fast Markov Decision Process-Based Algorithm for Collision Avoidance in Urban Air Mobility

Multiple aircraft collision avoidance is a challenging problem due to a stochastic environment and uncertainty in the intent of other aircraft. Traditionally a layered approach to collision avoidance has been employed using a centralized air traffic control system, established rules of the road, separation assurance, and last minute pairwise collision avoidance. With the advent of Urban Air Mobility (air taxis), the expected increase in traffic density in urban environments, short time scales, and small distances between aircraft favor decentralized decision making on-board the aircraft. In this paper, we present a Markov Decision Process (MDP) based method, named FastMDP, which can solve a certain subclass of MDPs quickly, and demonstrate using the algorithm online to safely maintain separation and avoid collisions with multiple aircraft (1-on-n) while remaining computationally efficient. We compare the FastMDP algorithm’s performance against two online collision avoidance algorithms that have been shown to be both efficient and scale to large numbers of aircraft: Optimal Reciprocal Collision Avoidance (ORCA) and Monte Carlo Tree Search (MCTS). Our simulation results show that under the assumption that aircraft do not have perfect knowledge of other aircraft intent FastMDP outperforms ORCA and MCTS in collision avoidance behavior in terms of loss of separation and near mid-air collisions while being more computationally efficient. We further show that in our simulation FastMDP behaves nearly as well as MCTS with perfect knowledge of other aircraft intent. Our results show that FastMDP is a promising algorithm for collision avoidance that is also computationally efficient.

Adaptive moving environment for efficient molecular dynamics simulations of high-fluence ion irradiation

Ion-beam processing of materials is widely supported by atomistic simulations by means of molecular dynamics. Although the approach has given several valuable insights, it has a limited operational window in both time and length scales. In particular, for high-fluence ion irradiation with multiple consecutive cascades, the direct molecular dynamics method becomes prohibitively time consuming.In this work, we propose a speed-up algorithm for molecular-dynamics simulations of multiple consecutive collision cascades employing an adaptive moving environment model. In the model, the computational power is primarily focused on calculating the atomic movement in the propagating cascade regions, while thermally equilibrated regions outside the cascades are excluded. Up to a five-fold efficiency increase was seen with the adaptive moving environment compared to classical molecular dynamics, without any significant statistical difference in the results of multiple individual ion-cascade simulations in a heterostructure of alternating Si and SiO2 layers. Simulations of temperature-driven dynamic annealing during high-fluence ion irradiation of Si nanopillars at elevated temperatures using the adaptive moving environment showed similar trends as experiments with respect to temperature dependence. The model is included in the atomistic simulator toolkit, COSIRMA (COmputer Simulator for IRradiation of MAterials), and can easily be enabled through the user-friendly graphical interface.

Explaining mercury via a single giant impact is highly unlikely

ABSTRACTThe classical scenario of terrestrial planet formation is characterized by a phase of giant impacts among Moon-to-Mars mass planetary embryos. While the classic model and its adaptations have produced adequate analogues of the outer three terrestrial planets, Mercury’s origin remains elusive. Mercury’s high-core mass fraction compared to the Earth’s is particularly outstanding. Among collisional hypotheses, this feature has been long interpreted as the outcome of an energetic giant impact among two massive protoplanets. Here, we revisit the classical scenario of terrestrial planet formation with focus on the outcome of giant impacts. We have performed a large number of N-body simulations considering different initial distributions of planetary embryos and planetesimals. Our simulations tested the effects of different giant planet configurations, from virtually circular to very eccentric configurations. We compare the giant impacts produced in our simulations with those that are more likely to account for the formation of Mercury and the Moon according to smoothed hydrodynamic simulations. Impact events that could lead to Moon’s formation are observed in all our simulations with up to ∼20 per cent of all giant impacts, consistent with the range of the expected Moon-forming event conditions. On the other hand, Mercury-forming events via a single giant impact are extremely rare, accounting for less than ∼1 per cent of all giant impacts. Our results suggest that producing Mercury as a remnant of a single giant impact that strips out the mantle of a differentiated planetary object with Earth-like iron-silicate ratio is challenging and alternative scenarios may be required (e.g. multiple collisions).

“On the Foundation of Transport-Driven Diffusion for Neutron Transport Problems”

The article presents the foundation of a novel methodology developed for the solution of the neutron transport equation, named the transport driven-diffusion approach, which can be considered as an evolution of the classic multiple collision method. The idea behind this method is based on the expansion of the full solution in terms of the contributions of the particles emitted by successive collisions plus a residual term, accounting for particles which have undergone more than a predefined number of collisions. In order to determine the contribution at each collision order, a transport equation with a source term is solved, while the estimation of the residue is based on a diffusion theory model. The physical rationale for the choice of the diffusion model for the residue is discussed and justified, as physics suggests that the diffusion assumptions become more applicable for the description of the particles having suffered a certain number of collisions rather than to the original transport problem. Some results are presented for a set of steady-state and time-dependent test cases. Their analysis shows the remarkable advantage of the method proposed in terms of accuracy and computational time, when compared to standard diffusion and multiple collision at the same order.

Gravitational wave of intermediate-mass black holes in Population III star clusters

ABSTRACT Previous theoretical studies suggest that the Population III (Pop3) stars tend to form in extremely metal-poor gas clouds with approximately $10^5 \ \mathrm{M}_\odot$ embedded in mini dark matter haloes. Very massive stars can form via multiple collisions in Pop3 star clusters and eventually evolve to intermediate-mass black holes (IMBHs). In this work, we conduct star-by-star N-body simulations for modelling the long-term evolution of Pop3 star clusters. We find that if the mini dark matter haloes can survive today, these star clusters can avoid tidal disruption by the galactic environment and can efficiently produce IMBH–black hole (BH) mergers among a wide range of redshift from 0 to 20. The average gravitational wave event rate is estimated to be $0.1\!-\!0.8\ \mathrm{yr}^{-1} \,\mathrm{Gpc}^{-3}$, and approximately 40–80 per cent of the mergers occur at high redshift (z > 6). The characteristic strain shows that a part of low-redshift mergers can be detected by LISA, TianQin, and Taiji, whereas most mergers can be covered by DECIGO and advanced LIGO/Virgo/KAGRA. Mergers with pair-instability BHs have a rate of approximately 0.01–0.15 yr−1 Gpc−3, which can explain the GW190521-like events.

Simulation of Energy-Resolved Mass Spectrometry Distributions from Surface-Induced Dissociation.

Understanding the relationship between protein structure and experimental data is crucial for utilizing experiments to solve biochemical problems and optimizing the use of sparse experimental data for structural interpretation. Tandem mass spectrometry (MS/MS) can be used with a variety of methods to collect structural data for proteins. One example is surface-induced dissociation (SID), which is used to break apart protein complexes (via a surface collision) into intact subcomplexes and can be performed at multiple laboratory frame SID collision energies. These energy-resolved MS/MS experiments have shown that the profile of the breakages depends on the acceleration energy of the collision. It is possible to extract an appearance energy (AE) from energy-resolved mass spectrometry (ERMS) data, which shows the relative intensity of each type of subcomplex as a function of SID acceleration energy. We previously determined that these AE values for specific interfaces correlated with structural features related to interface strength. In this study, we further examined the structural relationships by developing a method to predict the full ERMS plot from the structure, rather than extracting a single value. First, we noted that for proteins with multiple interface types, we could reproduce the correct shapes of breakdown curves, further confirming previous structural hypotheses. Next, we demonstrated that interface size and energy density (measured using Rosetta) correlated with data derived from the ERMS plot (R2 = 0.71). Furthermore, based on this trend, we used native crystal structures to predict ERMS. The majority of predictions resulted in good agreement, and the average root-mean-square error was 0.20 for the 20 complexes in our data set. We also show that if additional information on cleavage as a function of collision energy could be obtained, the accuracy of predictions improved further. Finally, we demonstrated that ERMS prediction results were better for the native than for inaccurate models in 17/20 cases. An application to run this simulation has been developed in Rosetta, which is freely available for use.