Collision Conditions Research Articles

Constraining timing and P-T conditions of continental collision and late overprinting in the Southern Brasília Orogen (SE-Brazil): U-Pb zircon ages and geothermobarometry of the Andrelândia Nappe System

The Andrelândia Nappe System (ANS) is an important component of the Neoproterozoic Southern Brasília Orogen (SBO) in SE Brazil and its evolution is related to the convergence and subsequent collision between the passive margin of the São Francisco paleocontinent and Paranapanema block during the Brasiliano Orogeny. The ANS is mainly composed of a pile of deformed meta-sedimentary rocks that record an inverted metamorphic pattern, ranging respectively from amphibolite facies at the bottom to high-P granulite conditions at the top. The ANS is here simplified into the lower, middle and upper nappes. Four samples from different tectonic settings within the ANS were collected for zircon isotopic investigation. In addition, geothermobarometry modelling were performed on seven samples from the middle nappe. Retro-eclogite slices associated to basement gneissic rocks occur along the contact between the upper and middle nappes and have zircon grains with metamorphic rims grown in high-P conditions of 12–16kbar with temperatures of ∼700–800°C, during the continental subduction dated here by U-Pb SHRIMP in zircon at 625±6Ma. A period of nappe emplacement accompanied by melting in the middle nappe is evidenced by a garnet-muscovite-staurolite-kyanite schist with leucosome parallel to the main foliation dated by U-Pb SHRIMP in zircon at 618±5Ma. Re-equilibrium at pressures of 4–7kbar with temperatures of ∼500–700°C is ascribed to a second heat pulse under lower pressure conditions. The period of melting associated to this event in the middle nappe occurred at 586±9Ma and is marked by an anatectic tourmaline-garnet-muscovite bearing S-type granite. This granite body is part of a NE-SW belt of granites, with ages between 605 and 563Ma and covering both the Central Ribeira Orogen (CRO) and the SBO. The age and the alignment of this granite belt justify the interpretation that it is genetically related to the CRO. Thus, the new data provide evidence that tectonothermal events related to the collisional front of the CRO extended up to ∼200km overlapping the consolidated SBO at ca. 580Ma.

Freeze-out conditions in proton-proton collisions at the highest energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

The freezeout conditions in proton-proton collisions at $\sqrt{s_{\textrm{NN}}}= 200$, $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields at mid-rapidity within the framework of the statistical model of an ideal gas of hadrons and resonances in the grand canonical ensemble. The variation of the extracted freezeout thermal parameters and the goodness of the fits with $\sqrt{s_{\textrm{NN}}}$ are discussed. We find the extracted temperature and baryon chemical potential of the freezeout surface to be similar in p+p and heavy ion collisions. On the other hand, the thermal behaviour of the strange hadrons is qualitatively different in p+p as compared to A+A. We find an additional parameter accounting for non-equilibrium strangeness production is essential for describing the p+p data. This is in contrast to A+A where the non-equilibrium framework could be successfully replaced by a sequential and complete equilibrium model with an early freezeout of the strange hadrons.

Experimental and theoretical modeling of behavior of 3D-printed polymers under collision with a rigid rod

The behavior of five different 3D-printed polymers has been analyzed both theoretically and experimentally under low-speed collision conditions. The impact of a rigid rod with a flat specimen fabricated of 3D-printed materials was analyzed. An experimental setup has been designed in order to capture the motion of the rod during the impact using a high-speed camera. Image processing algorithms were developed to estimate the velocity before and after the impact as well as the coefficient of restitution. Also, permanent deformations after the impact were scanned with an optical profilometer. In this work, a theoretical formulation for the contact force during the impact is proposed. The impact was divided into two phases, compression and restitution, in which materials considered elastic–plastic in the first and fully elastic in the second one. The experimental results are used to measure the damping coefficient. Results show a good correlation between the proposed formulation for the contact force and the behavior of materials.

Crashworthiness of a Truck Cabin using Finite Element Simulation

A crash test is a form of destructive testing in order to ensure safe design in case of an impact or collision. These impact tests are carried out to understand a components structural behaviour and its response under different collision conditions. But it is not always economical to destroy a specimen to ensure its safety, especially in case of small scale production. Moreover actual crash testing in different conditions requires high resources and time. Crash simulation is very popular now a days because it is a virtual representation of a destructive crash test of a vehicle using a computer simulation in order to examine the level of safety of the vehicle and its occupants in different conditions like collision velocity, collision direction, colliding object, material and number of component of colliding object etc and hence saves the time and cost. Data obtained from a crash simulation indicate the capability of the vehicle body to protect the vehicle occupants during a collision against injury. In this study a FE crash analysis of commercial truck cabin in two different cases (Bare cabin and loaded cabin) using Finite Element Approach (FEA) is focused. Crash analysis of truck cab is performed using FEA in order to predict the design parameters for minimization harm to the occupants of the vehicle. A bare truck cabin and a rigid wall were used to simulate crash conditions with different crashing velocity and impact angles. CATIA V5R20 CAD software is used for the modeling of the selected cabin components followed by FE meshing through Hypermesh and then analysis is done using LS-DYNA by setting the boundary conditions, material properties etc. appropriately.

The study of initial conditions in collisions of light, intermediate and heavy nuclei

The system size dependence for multiparticle processes has been recognized in both cosmic ray (“Stratosphere” collaboration) and at accelerator (“EMU” collaboration) experiments. The strong enhancement in multiplicity fluctuations for the most central light-light – (C, O, Ne) + (C/N/O) – collisions has been revealed at JINR-AGS-SPS energies. The sharp difference of light nuclear interactions are interpreted as the sign of intrinsic alpha-clustering in light nuclei.

The study of initial conditions in collisions of light, intermediate and heavy nuclei

The system size dependence for multiparticle processes has been recognized in both cosmic ray (“Stratosphere” collaboration) and at accelerator (“EMU” collaboration) experiments. The strong enhancement in multiplicity fluctuations for the most central light-light – (C, O, Ne) + (C/N/O) – collisions has been revealed at JINR-AGS-SPS energies. The sharp difference of light nuclear interactions are interpreted as the sign of intrinsic alpha-clustering in light nuclei.

Effect of the crack propagation behavior depend on collision condition

Effect of the crack propagation behavior depend on collision condition

Solid-fluid Transition in Granular Flows: MPM Simulations with a New Constitutive Approach

Many natural phenomena (rock or snow avalanches, and debris flows) as well as industrial processes are characterized by the flow of solid particles. A key issue in the development of a numerical tool for the study of this problem is the implementation of a suitable constitutive model, capable of capturing the complex rheological behaviour of the granular material in a wide range of strain rates. At the micro-scale level, the grains interacts by enduring frictional contacts or by nearly instantaneous collisions. The first mechanism prevails at low shear rates, when the material behaves like a solid (quasi-static conditions); the latter prevails at high shear rates, when it behaves like a fluid or a granular gas (collisional conditions). This paper presents a new constitutive model able to describe the behaviour of granular materials from quasi-static to collisional conditions and the transition in between. The stress tensor is assumed to be the sum of a quasi-static and a collisional contribution: the former one is modelled by adopting an elasto-plastic model incorporating the critical state concept, whereas the latter stems from the kinetic theory of granular gases. The features of the constitutive model are illustrated with a volume element test; moreover the model has been implemented in the MPM code Anura3D and applied to the simulation of triaxial tests.

Tracking properties of the ATLAS Transition Radiation Tracker (TRT)

The tracking performance parameters of the ATLAS Transition Radiation Tracker (TRT) as part of the ATLAS Inner Detector (ID) are described for different data taking conditions in proton-proton collisions at the Large Hadron Collider (LHC). These studies are performed using data collected during the first (Run 1) and the second (Run 2) periods of LHC operation and are compared with Monte Carlo simulations. The performance of the TRT, operating with xenon-based (Xe-based) and argon-based (Ar-based) gas mixtures and its dependence on the TRT occupancy is presented. No significant degradation of position measurement accuracy was found up to occupancies of about 20% in Run 1. The relative number of reconstructed tracks in ID that also have a extension in the TRT was observed to be almost constant with the increase of occupancies up to 50%. Even in configurations where tracks are close to each other, the reconstruction algorithm is still able to find the correct TRT hits and properly reconstruct the tracks.

Initial conditions in AA and pA collisions

A full understanding of the spacetime evolution of the QCD matter created in a heavy ion collision requires understanding the properties of the initial stages. In the weak coupling picture these are dominated by classical gluon fields, whose properties can also be studied via the scattering of dilute probes off a high energy hadron or nucleus. A particular challenge is understanding small systems, where LHC data is also showing signs of collective behavior. We discuss some recent results of on the initial matter production and thermalization in heavy ion collisions, in particular in the gluon saturation framework.

Exploring the Gas Phase Synthesis of the Elusive Class of Boronyls and the Mechanism of Boronyl Radical Reactions under Single Collision Conditions.

Until recently, the chemistry of boronyl (BO), a diatomic radical isolectronic with the cyano (CN) species, has remained unknown. The boronyl group is characterized by a boron-oxygen multiple bond, and because of the inherent electron deficiency of the boron atom, boronyls (RBO) are highly reactive and typically only exist in their cyclotrimeric form (RBO)3. Due to their invaluable role as reactants, the isolation of the monomers in gas phase experiments has been extensively sought after by the organic synthesis and physical organic chemistry communities but never achieved. Besides the interests from a physical organic and synthetic point of view, boronyls also play a role as reaction intermediates in boron-assisted rocket propulsion systems. In this Account, we review recent experimental work in which gas phase organo boronyl monomers (RBO) are formed via bimolecular reactions of the boronyl radical (BO) with C2-C6 unsaturated hydrocarbons. The investigated hydrocarbons are widely exploited as fuels, and their reactions with boronyl radicals under single collision conditions lead to the formation of organo boronyls. Our studies also elucidate the mechanisms of their formation reactions thus furnishing a comprehension at the molecular level of this reaction class. The variety of the employed hydrocarbon substrates has allowed us to systematically classify the chemical behavior of the boronyl radicals. With the exception of the case of the dimethylacetylene reaction, the boron monoxide radical versus atomic hydrogen exchange mechanisms were always open leading to the formation of highly unsaturated organo boronyl monomers (RBO), which could be easily identified because they cannot trimerize under single collision conditions. Besides the hydrogen displacement pathway, methylacetylene, dimethylacetylene, and propylene, carrying one or two methyl groups, were also found to eliminate a methyl group. In all systems, the reactions were barrierless, indirect, and initiated by addition of the boron monoxide radical to the π electron density of the hydrocarbon molecule, with the radical center located at the boron atom of the BO radical, thus leading to doublet radical intermediates. These intermediates either decompose via hydrogen or methyl loss or isomerize prior to their decomposition via atomic hydrogen or migration of the BO moiety. A consistent trend suggests that all exit transition states are rather tight with those involved in the hydrogen atom loss depicting exit barriers of typically 25 to 35 kJ mol-1, whereas the methyl loss pathways are associated with tighter exit transition states located about 30-50 kJ mol-1 above the separated products. Further, the overall energetics suggest that those bimolecular reactions are exoergic by 40-90 kJ mol-1. These findings confirm that this reaction class leads to the formation of highly unsaturated organo boronyl molecules.

Intense ion-beam dynamics in the NICA collider

The problems of intense ion-beam dynamics in the developed and optimized optical structure of the NICA collider are considered. Conditions for beam collisions and obtaining the required parameters of luminosity in the operation energy range are discussed. The restriction on collider luminosity is related to effects of the domination of the space charge and intrabeam scattering. Applying methods of cooling, electron and stochastic ones, will permit one to suppress these effects and reach design luminosity. The work also deals with systems of magnetic field correction and problems of calculating the dynamic aperture of the collider.

Hadronization conditions in relativistic nuclear collisions and the QCD pseudo-critical line

We compare the reconstructed hadronization conditions in relativistic nuclear collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in terms of temperature and baryon-chemical potential with lattice QCD calculations, by using hadronic multiplicities. We obtain hadronization temperatures and baryon chemical potentials with a fit to measured multiplicities by correcting for the effect of post-hadronization rescattering. The post-hadronization modification factors are calculated by means of a coupled hydrodynamical-transport model simulation under the same conditions of approximate isothermal and isochemical decoupling as assumed in the statistical hadronization model fits to the data. The fit quality is considerably better than without rescattering corrections, as already found in previous work. The curvature of the obtained "true" hadronization pseudo-critical line kappa is found to be 0.0048 +- 0.0026, in agreement with lattice QCD estimates; the pseudo-critical temperature at vanishing mu_B is found to be 164.3+-1.8 MeV.

Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments.

Product detection studies of C(3P) atom reactions with butene (C4H8) isomers (but-1-ene, cis-but-2-ene, trans-but-2-ene) are carried out in a flow tube reactor at 353 K and 4 Torr under multiple collision conditions. Ground state carbon atoms are generated by 248 nm laser photolysis of tetrabromomethane, CBr4, in a buffer of helium. Thermalized reaction products are detected using synchrotron tunable VUV photoionization and time-of-flight mass spectrometry. The temporal profiles of the detected ions are used to discriminate products from side or secondary reactions. For the C(3P) + trans-but-2-ene and C(3P) + cis-but-2-ene reactions, various isomers of C4H5 and C5H7 are identified as reaction products formed via CH3 and H elimination. Assuming equal ionization cross sections for all C4H5 and C5H7 isomers, C4H5:C5H7 branching ratios of 0.63:1 and 0.60:1 are derived for the C(3P) + trans-but-2-ene and the C(3P) + cis-but-2-ene reactions, respectively. For the C(3P) + but-1-ene reaction, two reaction channels are observed: the H-elimination channel, leading to the formation of the ethylpropargyl isomer, and the C3H3 + C2H5 channel. Assuming equal ionization cross sections for ethylpropargyl and C3H3 radicals, a branching ratio of 1:0.95 for the C3H3 + C2H5 and H + ethylpropargyl channels is derived. The experimental results are compared to previous H atom branching ratios and used to propose the most likely mechanisms for the reaction of ground state carbon atoms with butene isomers.

Growth in the quantity of debris in Space as AN effect of mutual mechanical collisions of various types

Estimates are determined of the potential consequences of mutual collisions of dangerous space objects both among themselves and with operating space systems. Research extrapolating the existing objective estimates and supervision of pollution in low Earth orbits shows the probability of catastrophic growth in the number of objects and orbital debris in low orbits leading to the practical impossibility of further peaceful scientific exploration of space. The development of methodologies and technologies regarding the comprehensive investigation of shock impacts on space objects and systems becomes the actual task for the creation of conditions for the safe development of peaceful space explorations. Research involving the collision processes, including the dynamics and associated consequences, developing means and pathways of protection for spaceships, protection of structures and systems from the influence of high-speed objects, means and methods to remove debris from space, and the use of dangerous objects. The technology of measurements with applications in tensometry provides data acquisition concerning the shock impulse in a wide range of collision conditions, and ensuring a physical and constructive variety of the impacting objects is considered.

Data-driven train set crash dynamics simulation

ABSTRACTTraditional finite element (FE) methods are arguably expensive in computation/simulation of the train crash. High computational cost limits their direct applications in investigating dynamic behaviours of an entire train set for crashworthiness design and structural optimisation. On the contrary, multi-body modelling is widely used because of its low computational cost with the trade-off in accuracy. In this study, a data-driven train crash modelling method is proposed to improve the performance of a multi-body dynamics simulation of train set crash without increasing the computational burden. This is achieved by the parallel random forest algorithm, which is a machine learning approach that extracts useful patterns of force–displacement curves and predicts a force–displacement relation in a given collision condition from a collection of offline FE simulation data on various collision conditions, namely different crash velocities in our analysis. Using the FE simulation results as a benchmark, we compared our method with traditional multi-body modelling methods and the result shows that our data-driven method improves the accuracy over traditional multi-body models in train crash simulation and runs at the same level of efficiency.

Modeling chiral criticality and its consequences for heavy-ion collisions

We explore the critical fluctuations near the chiral critical endpoint (CEP) in a chiral effective model and discuss possible signals of the CEP, recently explored experimentally in nuclear collision. Particular attention is paid to the dependence of such signals on the location of the phase boundary and the CEP relative to the chemical freeze-out conditions in nuclear collisions. We argue that in effective models, standard freeze-out fits to heavy-ion data should not be used directly. Instead, the relevant quantities should be examined on lines in the phase diagram that are defined self-consistently, within the framework of the model. We discuss possible choices for such an approach.

Development of the collision ratio to infer the time at which to begin a collision avoidance of a ship

A prior study attempted to solve the intrinsic problem of a critical collision condition including the slower ship’s dilemma by considering the maneuverability of the own ship and the International Regulations for Preventing Collisions at Sea (COLREGs). The collision ratio proposed in the previous study provided insight into the solution of the intrinsic problem, but it was not suitable as an index to determine the time at which to begin the maneuver to avoid the collision.This paper develops a collision ratio as an index that can be used to determine the time at which to begin the collision avoidance maneuver. The collision ratio is calculated by considering the maneuverability of the own ship, the COLREGs, and three virtual intrusion domains (VIDs). The validity of the inferred collision ratio is then assessed according to the dynamic characteristics of the own ship and the basic knowledge of the collision avoidance algorithm. The results indicate that the proposed collision ratio is suitable for use as a new index to determine the time at which to begin the collision avoidance maneuver.

Thermal Methane Conversion to Syngas Mediated by Rh1-Doped Aluminum Oxide Cluster Cations RhAl3O4.

Laser ablation generated RhAl3O4+ heteronuclear metal oxide cluster cations have been mass-selected using a quadrupole mass filter and reacted with CH4 or CD4 in a linear ion trap reactor under thermal collision conditions. The reactions have been characterized by state-of-the-art mass spectrometry and quantum chemistry calculations. The RhAl3O4+ cluster can activate four C-H bonds of a methane molecule and convert methane to syngas, an important intermediate product in methane conversion to value-added chemicals. The Rh atom is the active site for activation of the C-H bonds of methane. The high electron-withdrawing capability of Rh atom is the driving force to promote the conversion of methane to syngas. The polarity of Rh oxidation state is changed from positive to negative after the reaction. This study has provided the first example of methane conversion to syngas by heteronuclear metal oxide clusters under thermal collision conditions. Furthermore, the molecular level origin has been revealed for the condensed-phase experimental observation that trace amounts of Rh can promote the participation of lattice oxygen of chemically very inert support (Al2O3) to oxidize methane to carbon monoxide.

Fast particle loss channels in Wendelstein 7-X

One of the main goals of Wendelstein 7-X (W7-X) is to demonstrate the fast particle confinement properties of the quasi-isodynamic stellarator concept. Fast particle populations will be produced either by Neutral Beam Injection (NBI) or by minority Ion Cyclotron Resonant Heating (ICRH). A fraction of these particles are expected to be lost (even without collisions), despite the optimisation procedure used for the W7-X design. Confinement properties of NBI particles in W7-X were presented in the paper of Drevlak et al (2014 Nucl. Fusion 54 073002). A detailed study is presented here where the loss patterns of an NBI population are described. In particular, focussing on a high-mirror equilibrium, the confinement of fast ions with varying energy injection is studied under collisional conditions. It is found that collisions are not only responsible for classical transport losses but also enhance drift induced losses caused by trapped particles. Moreover, an asymmetry is found in the toroidal position of particle losses which can be explained by local variation in the equilibrium field. The effects of a neoclassically resolved radial electric field are also investigated. Fast particle confinement is significantly improved by the associated drift. In particular, an increasing radial electric field helps to reduce and even stop the losses due to the 3D equilibrium structure for times comparable to slowing down time.