Range Of Impact Parameters Research Articles

On the Origin of the Ancient, Large-scale Cold Front in the Perseus Cluster of Galaxies

The intracluster medium of the Perseus Cluster exhibits spiral-shaped X-ray surface brightness discontinuities known as “cold fronts,” which simulations indicate are caused by the sloshing motion of the gas after the passage of a subcluster. Recent observations of Perseus have shown that these fronts extend to large radii. In this work, we present simulations of the formation of sloshing cold fronts in Perseus using the AREPO magnetohydrodynamics code, to produce a plausible scenario for the formation of the large front at a radius of 700 kpc. Our simulations explore a range of subcluster masses and impact parameters. We find that low-mass subclusters cannot generate a cold front that can propagate to such a large radius, and that small impact parameters create too much turbulence, which leads to the disruption of the cold front before it reaches such a large distance. Subclusters that make only one core passage produce a stable initial front that expands to large radii, but without a second core passage of the subcluster, other fronts are not created at a later time in the core region. We find a small range of simulations with subclusters with mass ratios of R ∼ 1:5 and an initial impact parameter of θ ∼ 20°–25° that not only produce the large cold front but a second set in the core region at later times. These simulations indicate that the “ancient” cold front is ∼6–8.5 Gyr old. For the simulations providing the closest match with observations, the subcluster has completely merged into the main cluster.

The South Pole‐Aitken Basin: Constraints on Impact Excavation, Melt, and Ejecta

AbstractThe formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact.

Atomistic simulations of oblique collisions between crystalline and amorphous SiC nanoparticles: Mechanisms of deformation and scaling coefficients of restitutions

Systematic atomistic simulations of oblique collisions between spherical crystalline, 6H and 3C, and amorphous SiC nanoparticles (NPs) are performed in the bouncing and fragmentation regimes for the particles with diameters from 8 nm to 30 nm, impact velocities from 100 ms−1 to 5000 ms−1, and in the whole range of the geometric impact parameter. The critical sticking velocity of 6H-SiC NPs reduces from ∼490 ms−1 to ∼150 ms−1 when the NP diameter increases from 10 nm to 30 nm. Below the melting threshold, the collision of crystalline NPs induces the formation of localized zones of densified material, while the remaining parts of NPs are not affected by plastic deformations. The impact of amorphous NPs results in the plastic deformation of significant parts of the NP material and much larger irreversible losses of mechanical energy. The post-collision translational and rotational velocities of crystalline NPs as well as coefficients of restitution (CORs) demonstrate weak dependence on the NP size if the NP diameter is greater than 20 nm. At constant impact velocity, the normal COR only marginally varies for head-on and oblique collisions, when the collision angle is smaller than ∼53°. The tangential center-of-mass and point-of-contact CORs, as functions of the impact parameter, demonstrate extremal behavior with the minima at collision angles from ∼27° to ∼37°. The normal COR exhibits a linear decay as a function of the impact velocity where the slope coefficient is different below and above the melting threshold. The tangential CORs attain the minimum values at the impact velocity of ∼300 ms−1. The obtained results are summarized in the form of fitting equations for CORs as functions of the impact parameter and velocity, which can be readily used to predict the post-collision translational and angular velocities of NPs in large-scale simulations of granular gas flows.

Characterizing the response of Timepix solid state detectors to dust impacts

Timepix Solid State Detectors (TSSDs) are used in a range of applications, including high energy particle physics, x-ray imaging spectroscopy, medical imaging, radiation monitors and compact dosimeters. In space sciences, such detectors have been used for characterizing the radiation environments of the Earth and lunar surface. This study is a pilot investigation of the response of TSSDs to high-velocity dust impacts. The setup used for the measurements is a silicon slab with 500μm thickness combined with the Timepix 2 read-out chip with a pixel size of 55×55 μm2. The outer surface of the SSD is coated with a 150 nm thick layer of aluminum to eliminate the sensitivity to light. The dust accelerator facility operated at the University of Colorado is used to expose the TSSD to micron- and sub-micron sized iron particles in a velocity range of 1–10 km/s. A fraction (5%) of the impacting dust particles were detected by the TSSD. The primary mechanism of the detection is through the light generated upon the impact and the charge signal spreads over multiple pixels. The fraction of dust particles kinetic energy that is converted to detectable charge on the TSSD is small, in the range of 10−3−10−6. The largest craters generated by the dust impacts were examined using a scanning electron microscope (SEM). The SEM images confirm that the particles penetrated the aluminum layer and the craters contain iron residue from the dust material. Over the investigated impact parameter range, the TSSD does not suffer a permanent damage from the dust impacts. Due to their small size and relatively low sensitivity to dust impacts, TSSDs could be used as dust detectors only in environments with high dust fluxes (e.g., in cometary trails), or where the precision measurements of the impact location are desired.

Photon-photon fusion and tau g-2 measurement in ATLAS

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons. New measurements of exclusive dilepton production (electron, muon, and tau pairs) performed by the ATLAS experiment are discussed. We present the photon-induced production of tau pairs and constraints on the tau lepton’s anomalous magnetic dipole moment. In addition, measurements of photon-induced electron and muon pair production are presented, which provide strong constraints on the nuclear photon flux and its dependence on the impact parameter and photon energy. Forward neutrons are utilised to provide an experimental handle on the impact parameter range sampled in the events.

Black hole binaries in AGN accretion discs – II. Gas effects on black hole satellite scatterings

ABSTRACT The black hole (BH) binaries in active galactic nuclei (AGN) are expected to form mainly through scattering encounters in the ambient gaseous medium. Recent simulations, including our own, have confirmed this formation pathway is highly efficient. We perform 3D smoothed particle hydrodynamics (SPH) simulations of BH scattering encounters in AGN discs. Using a range of impact parameters, we probe the necessary conditions for binary capture and how different orbital trajectories affect the dissipative effects from the gas. We identify a single range of impact parameters, typically of width ∼0.86−1.59 binary Hill radii depending on AGN disc density, that reliably leads to binary formation. The periapsis of the first encounter is the primary variable that determines the outcome of the initial scattering. We find an associated power law between the energy dissipated and the periapsis depth to be ΔE ∝ r−b with b = 0.42 ± 0.16, where deeper encounters dissipate more energy. Excluding accretion physics does not significantly alter these results. We identify the region of parameter space in initial energy versus impact parameter where a scattering leads to binary formation. Based on our findings, we provide a ready-to-use analytic criterion that utilizes these two pre-encounter parameters to determine the outcome of an encounter, with a reliability rate of >90 per cent. As the criterion is based directly on our simulations, it provides a reliable and highly physically motivated criterion for predicting binary scattering outcomes which can be used in population studies of BH binaries and mergers around AGN.

Mapping circumgalactic medium observations to theory using machine learning

ABSTRACT We present a random forest (RF) framework for predicting circumgalactic medium (CGM) physical conditions from quasar absorption line observables, trained on a sample of Voigt profile-fit synthetic absorbers from the simba cosmological simulation. Traditionally, extracting physical conditions from CGM absorber observations involves simplifying assumptions such as uniform single-phase clouds, but by using a cosmological simulation we bypass such assumptions to better capture the complex relationship between CGM observables and underlying gas conditions. We train RF models on synthetic spectra for H i and selected metal lines around galaxies across a range of star formation rates, stellar masses, and impact parameters, to predict absorber overdensities, temperatures, and metallicities. The models reproduce the true values from simba well, with normalized transverse standard deviations of 0.50–0.54 dex in overdensity, 0.32–0.54 dex in temperature, and 0.49–0.53 dex in metallicity predicted from metal lines (not H i), across all ions. Examining the feature importance, the RF indicates that the overdensity is most informed by the absorber column density, the temperature is driven by the line width, and the metallicity is most sensitive to the specific star formation rate. Alternatively examining feature importance by removing one observable at a time, the overdensity and metallicity appear to be more driven by the impact parameter. We introduce a normalizing flow approach in order to ensure the scatter in the true physical conditions is accurately spanned by the network. The trained models are available online.

An evaluation model for the recreational carrying capacity of urban aerial trails

Different from traditional trails, urban aerial trails are limited by the carrying capacity of visitors. Therefore, it is necessary to research the recreational carrying capacity of aerial trails, in order to provide satisfactory recreational experiences to the visitors. This study took Xiamen Mountains-to-Sea Trail as the research target, and obtained the number of visitors and acceptability data based on visual assessment and questionnaire survey. Based on the data, a social carrying capacity model of the aerial trail in combination with Cifuentes' carrying capacity calculation method was proposed. The research results show that the trail's social carrying capacity is much lower than the physical carrying capacity without affecting tourists' recreational experience. The findings of this study explain the reasonable impact parameter range of the social carrying capacity, and further optimize the trail's recreational carrying capacity.

Multi-objective optimization of multiple droplet impacts on a molten PCM using NSGA-II optimizer and artificial neural network

Embracing an interaction between the phase change material (PCM) and the droplets of a heat transfer fluid, the direct contact (DC) method suggests a cutting-edge solution for expediting the phase change rates of PCMs in thermal energy storage (TES) units. In the direct contact TES configuration, when impacting the molten PCM pool, droplets evaporate, provoking the formation of a solidified PCM area (A). Then, they reduce the created solid temperature, leading to a minimum temperature value (Tmin). As a novelty, this research intends to maximize A and minimize Tmin since augmenting A expedites the discharge rate, and by lowering Tmin, the generated solid is preserved longer, resulting in a higher storage efficacy. To take the influences of interaction between droplets into account, the simultaneous impingement of two ethanol droplets on a molten paraffin wax is surveyed. Impact parameters (Weber number, impact spacing, and the pool temperature) govern the objective functions (A and Tmin). Initially, through high-speed and IR thermal imaging, the experimental values of objective functions are achieved for a wide range of impact parameters. Afterward, exploiting an artificial neural network (ANN), two models are fitted to A and Tmin, respectively. Subsequently, the models are provided for the NSGA-II algorithm to implement multi-objective optimization (MOO). Eventually, utilizing two different final decision-making (FDM) approaches (LINMAP and TOPSIS), optimized impact parameters are attained from the Pareto front. Regarding the results, the optimum amount of Weber number, impact spacing, and pool temperature accomplished by LINMAP and TOPSIS procedures are 309.44, 2.84 mm, 66.89 °C, and 294.98, 2.78 mm, 66.89 °C, respectively. This is the first investigation delving into the optimization of multiple droplet impacts for TES applications.

A Time-Dependent-Density-Functional-Theory Study of Charge Transfer Processes of Li2+ Colliding with Ar in the MeV Region

We study charge transfer of a multi-electron collision system Li2+ + Ar using the time-dependent density functional theory non-adiabatically coupled to the molecular dynamics. By implementing the particle number projection method, the single- and double-charge transfer cross sections are extracted at MeV energies, which are in good agreement with the experimental data available. The analysis of charge transfer probabilities shows that for energies higher than 1.0 MeV, the single-charge transfer occurs for a broader range of impact parameters, while the double-charge transfer is dominated by close collisions. To gain the population of captured electrons on the projectile, we compute the orbital projection probabilities. It is found that the electrons of the Ar atom will most possibly transfer to the 2p orbitals of the Li2+, and only a small portion of captured electrons distribute on the s orbitals. This work verifies the capability of the present methodology in dealing with charge transfer in dressed ion collisions at MeV energies.

An improved method to access initial states in relativistic heavy-ion collisions

Observables in heavy-ion collisions are generally categorized into centralities, which reflect an average over events within a range of impact parameters including a wide variety of initial-state configurations. A multiple binning method using spectator neutrons within each centrality has been shown to provide access to events with rare initial-state conditions. This work suggests an improvement in quantifying the difference between standard centrality and spectator neutron binning towards accessing the initial-state properties. A selection of events with higher initial-state density at a fixed participating nucleon number was observed to result in larger final-state particle production and smaller elliptic flow. The relative difference between observables in centrality and spectator binning shows reduced sensitivity for the observables dominated by impact parameter fluctuations in the initial state, such as triangular flow. This property renders the spectator binning method a good candidate for separating geometric contributions from random fluctuations in the initial state towards final-state observables.

Modeling approaches for atmospheric ion–dipole collisions: all-atom trajectory simulations and central field methods

Abstract. Ion–dipole collisions can facilitate the formation of atmospheric aerosol particles and play an important role in their detection in chemical ionization mass spectrometers. Conventionally, analytical models, or simple parametrizations, have been used to calculate the rate coefficients of ion–dipole collisions in the gas phase. Such models, however, neglect the atomistic structure and charge distribution of the collision partners. To determine the accuracy and applicability of these approaches under atmospheric conditions, we calculated collision cross sections and rate coefficients from all-atom molecular dynamics collision trajectories, sampling the relevant range of impact parameters and relative velocities, and from a central field model using an effective attractive interaction fitted to the long-range potential of mean force between the collision partners. We considered collisions between various atmospherically relevant molecular ions and dipoles and charged and neutral dipolar clusters. Based on the good agreement between collision cross sections and rate coefficients obtained from molecular dynamics trajectories and a generalized central field model, we conclude that the effective interactions between the collision partners are isotropic to a high degree, and the model is able to capture the relevant physicochemical properties of the systems. In addition, when the potential of mean force is recalculated at the respective temperatures, the central field model exhibits the correct temperature dependence of the collision process. The classical parametrization by Su and Chesnavich (1982), which combines a central field model with simplified trajectory simulations, is able to predict the collision rate coefficients and their temperature dependence quite well for molecular systems, but the agreement worsens for systems containing clusters. Based on our results, we propose the combination of potential of mean force calculation and a central field model as a viable and elegant alternative to the brute force sampling of individual collision trajectories over a large range of impact parameters and relative velocities.

Semiclassical Trajectory Studies of Reactive and Nonreactive Scattering of OH(A 2 Σ+ ) by H2 Based on an Improved Full-Dimensional Ab Initio Diabatic Potential Energy Matrix.

We present a new full-dimensional diabatic potential energy matrix (DPEM) for electronically nonadiabatic collisions of OH(A 2 Σ+ ) with H2 , and we calculate the probabilities of electronically adiabatic inelastic collisions, nonreactive quenching, and reactive quenching to form H2 O+H. The DPEM was fitted using a many-body expansion with permutationally invariant polynomials in bond-order functions to represent the many-body part. The dynamics calculations were carried out with the fewest-switches with time uncertainty and stochastic decoherence (FSTU/SD) semiclassical trajectory method. We present results both for head-on collisions (impact parameter b equal to zero) and for a full range of impact parameters. The results are compared to experiment and to earlier FSTU/SD and quantum dynamics calculations with a previously published DPEM. The various theoretical results all agree that nonreactive quenching dominates reactive quenching, but there are quantitative differences between the two DPEMs and between the b=0 results and the all-b results, especially for the probability of reactive quenching.

A higher probability of detecting lensed supermassive black hole binaries by LISA

ABSTRACT Gravitational lensing of gravitational waves (GWs) is a powerful probe of the matter distribution in the universe. Here we revisit the wave-optics effects induced by dark matter (DM) haloes on the GW signals of merging massive black hole binaries (MBHBs), and we study the possibility of discerning these effects using the Laser Interferometer Space Antenna (LISA). In particular, we include the haloes in the low-mass range of $10^5\!-\!10^8\, \mathrm{M}_\odot$ since they are the most numerous according to the cold DM model. We simulate the lensed signals corresponding to a wide range of impact parameters, and we find distinguishable deviation from the standard best-fitting GW templates even when the impact parameter is as large y ≃ 50. Consequently, we estimate that over $(0.1\!-\!1.6){{\ \rm per\ cent}}$ of the MBHBs in the mass range of $10^{5.0}\!-\!10^{6.5}\, \mathrm{M}_\odot$ and the redshift range of 4 − 10 should show detectable wave-optics effects. This probability is one order of magnitude higher than that derived in previous works. The uncertainty comes mainly from the mass function of the DM haloes. Not detecting any signal during the LISA mission would imply that DM haloes with $10^5\!-\!10^8\, \mathrm{M}_\odot$ are less numerous than what the cold DM model predicts.

An advanced bath model to simulate association followed by ensuing dissociation dynamics of benzene + benzene system: a comparative study of gas and condensed phase results.

The role of the environment (N2 molecules) on the association followed by the ensuing dissociation reaction of benzene + benzene system is studied here with the help of a new code setup. Chemical dynamics simulations are performed to investigate this reaction in vacuum as well as in a bath of 1000 N2 molecules, equilibrated at 300 K. Bath densities of 20 and 324 kg m-3 are considered with a few results from the latter density. The simulations are performed at three different excitation temperatures of benzene, namely, 1000, 1500, and 2000 K, with an impact parameter range of 0-12 Å for both vacuum and bath models. Higher association probabilities and hence, higher temperature dependent association rate constants are obtained in the condensed phase. In the condensed phase, when a trajectory takes a longer time for the monomers to associate, the associated complex is formed with a longer lifetime and provides a lower rate of ensuing dissociation. Higher association rate and lower dissociation rate in condensed phase dynamics are due to the energy transfer process. Hence, the energy transfer phenomenon plays a decisive role in the association/dissociation dynamics, which is completely ignored in the same reaction when studied in vacuum.

Stars Crushed by Black Holes. I. On the Energy Distribution of Stellar Debris in Tidal Disruption Events

Abstract The distribution of orbital energies imparted into stellar debris following the close encounter of a star with a supermassive black hole is the principal factor in determining the rate of return of debris to the black hole, and thus in determining the properties of the resulting lightcurves from such events. We present simulations of tidal disruption events for a range of β ≡ r t/r p where r p is the pericenter distance and r t the tidal radius. We perform these simulations at different spatial resolutions to determine the numerical convergence of our models. We compare simulations in which the heating due to shocks is included or excluded from the dynamics. For β ≲ 8, the simulation results are well-converged at sufficiently moderate-to-high spatial resolution, while for β ≳ 8, the breadth of the energy distribution can be grossly exaggerated by insufficient spatial resolution. We find that shock heating plays a non-negligible role only for β ≳ 4, and that typically the effect of shock heating is mild. We show that self-gravity can modify the energy distribution over time after the debris has receded to large distances for all β. Primarily, our results show that across a range of impact parameters, while the shape of the energy distribution varies with β, the width of the energy spread imparted to the bulk of the debris is closely matched to the canonical spread, Δ E = GM • R ⋆ / r t 2 , for the range of β we have simulated.

New explicit correlations for the critical sticking velocity and restitution coefficient of small adhesive particles: A finite element study and validation

The collision between small adhesive particles and flat substrate is a fundamental phenomenon in both natural and industrial processes. Due to the complex coupling among the elastic deformation, surface adhesion and viscoelastic damping, a great gap still exists for directly obtaining a universal correlation for the restitution coefficient. In this work, we use the finite element method (FEM) to numerically investigate the wall collision of small adhesive particles. The surface adhesion is directly incorporated by the Hamaker theory and the viscoelastic dissipation is coupled to the local strain, stress and strain rate. The results show that the FEM model naturally captures the coupling between the surface adhesion and viscoelastic damping, and thus is capable to predict the proper restitution coefficient by directly using the surface energy of bulk materials, without any adjustment or fitting. By simulating a large number of wall collision cases in a wide range of impact parameters, we present new universal correlations for the restitution coefficient and critical sticking velocity, which agree well with the classic experimental data in a wide range of the incident velocity, particle size and particle/substrate material properties. Our explicit correlations can be easily incorporated into Eulerian-Lagrangian simulations for quantitatively describing the sticking/rebound behaviors of laden aerosol particles.

CGM2 I: The Extent of the Circumgalactic Medium Traced by Neutral Hydrogen

Abstract We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM2) survey. The CGM2 survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z ≲ 1 quasars, all with a signal-to-noise ratio of ∼10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 107 M ⊙ < M ⋆ < 1011 M ⊙ and z ≲ 0.5, we show that the H i covering fraction above a threshold of N HI > 1014cm−2 is ≳0.5 within 1.5 virial radii (R vir ∼ R 200m). We examine the H i kinematics and find that the majority of absorption lies within ±250 km s−1 of the galaxy systemic velocity. We examine H i covering fractions over a range of impact parameters to infer a characteristic size of the CGM, , as a function of galaxy mass. is the impact parameter at which the probability of observing an absorber with N HI >1014 cm−2 is >50%. In this framework, the radial extent of the CGM of M ⋆ > 109.9 M ⊙ galaxies is kpc or . Intermediate-mass galaxies with 109.2 < M ⋆/M ⊙ < 109.9 have an extent of kpc or . Low-mass galaxies, M ⋆ < 109.2 M ⊙, show a smaller physical scale of kpc and extend to . Our analysis suggests that using R vir as a proxy for the characteristic radius of the CGM likely underestimates its extent.

A study of cool core resiliency and entropy mixing in simulations of galaxy cluster mergers

ABSTRACT We present results from a suite of binary merging cluster simulations. The hydrodynamical cluster simulations are performed employing a smoothed particle hydrodynamics formulation in which gradient errors are strongly reduced by means of an integral approach. We consider adiabatic as well as radiative simulations, in which we include gas cooling, star formation, and energy feedback from supernovae. We explore the effects of merging on the thermodynamic structure of the intracluster gas of the final merger remnant. In particular, we study how core entropy is generated during the merging and the stability properties of the initial cool-core profile against disruption. To this end, we consider a range of initial mass ratio and impact parameters. Final entropy profiles of our adiabatic merging simulations are in good accord with previous findings, with cool-cores being disrupted for all of the initial merging setups. For equal-mass off-axis mergers, we find that a significant contribution to the final primary core entropy is due to hydrodynamic instabilities generated by rotational motions, which are induced by tidal torques during the first pericentre passage. In radiative simulations, cool-cores are more resilient against heating processes; none the less, they are able to maintain their integrity only in the case of off-axis mergers with very unequal masses. We suggest that these results are robust against changes in the gas physical modelling, in particular to the inclusion of AGN thermal feedback. Our findings support the view that the observed core cluster morphology emerges naturally in a merging cluster context, and conclude that the merging angular momentum is a key parameter in shaping the thermodynamical properties of the final merger remnant.

Close encounters with the Death Star: Interactions between collapsed bodies and the Solar System

Aims. We aim to investigate the consequences of a fast massive stellar remnant – a black hole (BH) or a neutron star (NS) – encountering a planetary system. Methods. We modelled a close encounter between the actual Solar System (SS) and a 2 M⊙ NS and a 10 M⊙ BH, using a few-body symplectic integrator. We used a range of impact parameters, orbital phases at the start of the simulation derived from the current SS orbital parameters, encounter velocities, and incidence angles relative to the plane of the SS. Results. We give the distribution of possible outcomes, such as when the SS remains bound, when it suffers a partial or complete disruption, and in which cases the intruder is able to capture one or more planets, yielding planetary systems around a BH or a NS. We also show examples of the long-term stability of the captured planetary systems.