Collision Rate Research Articles

Quantum rotational dynamics of linear C5 at low interstellar temperatures for H2 collision.

The quantum dynamics of carbon chains through H2 and He collisions in the interstellar medium (ISM) is an important step toward accurate modeling of their abundance in non-local thermodynamic equilibrium conditions. The C5(Σg+1) molecule is the longest pure carbon chain detected in the ISM to date. While He collisions are computationally easy to perform, the collision with much more abundant H2 is both complicated and computationally demanding. Using templates for approximating p-H2 collisional rates, such as scaling He rates and using a reduced 4D → 2D potential energy surface (PES), has limited applicability. On the other hand, any such approximation does not exist for o-H2. Therefore, a full rotational dynamics of C5 with both p- and o-H2 is performed considering both molecules as rigid-rotors. The PES is calculated using CCSD(T)-F12a/AVTZ, and a neural network fitting model has been carefully chosen to strictly obey spectroscopic accuracy and augment the PES. The augmented PES is then expanded into radial terms using the bispherical harmonics function, and close coupling calculations have been done to get the cross sections and, subsequently, rate coefficients for various rotational transitions of C5.

The multidimensional coagulation and collisional breakage equation with unbounded kernel

Many scientific and technical fields have benefited from the understanding of the Coagulation and Collisional Breakage Equation (CCBE). In one-dimensional CCBE, only one property of the particle (like size or mass of the particle) is considered. However, there are other factors (like including volume, enthalpy, porosity, mole number, binder content, and more) that affect how particle ensembles behave. Therefore the study of multidimensional CCBE is more accurate. For the multi-dimensional (CCBE), we denote the property characteristics vector as x → = ( x 1 , x 2 , … , x d ) ∈ R + d . In this research work, the existence of a continuous solution is investigated where collision rate satisfies C ( x → , y → ) ≤ c ∏ i = 1 d ( 1 + x i ) ν ( 1 + y i ) ν , where c>0 is a constant, 0 ≤ ν ≤ θ and the coagulation kernel satisfies the following, K ( x → , y → ) ≤ k ∏ i = 1 d ( 1 + x i ) α ( 1 + y i ) α , where k is a positive constant, 0 ≤ α ≤ θ and 0 < θ ≤ 1 . Additionally, the uniqueness of the solution is shown. To prove the result, we have defined a new norm and examined the equicontinuity with respect to time and the property characteristics vector and Arzelà–Ascoli theorem is used.

First map of D2H+ emission revealing the true centre of a prestellar core: Further insights into deuterium chemistry

Context. IRAS 16293E is a rare case of a prestellar core being subjected to the effects of at least one outflow. Aims. We want to disentangle the actual structure of the core from the outflow impact and evaluate the evolutionary stage of the core. Methods. Prestellar cores being cold and depleted, the best tracers of their central regions are the two isotopologues of the trihydrogen cation that are observable from the ground: ortho-H2D+ and para-D2H+. We used the Atacama Pathfinder EXperiment (APEX) telescope to map the para-D2H+ emission in IRAS 16293E and collected James Clerk Maxwell Telescope (JCMT) archival data of ortho-H2D+. We compared their emission to that of other tracers, including dust emission, and analysed their abundance with the help of a 1D radiative transfer tool. The ratio of the abundances of ortho-H2D+ to para-D2H+ can be used to estimate the stage of the chemical evolution of the core. Results. We have obtained the first complete map of para-D2H+ emission in a prestellar core. We compare it to a map of ortho-H2D+ and show their partial anti-correlation. This reveals a strongly evolved core with a para-D2H+/ortho-H2D+ abundance ratio towards the centre for which we obtain a conservative lower limit from 3.9 (at 12 K) to 8.3 (at 8 K), while the high extinction of the core is indicative of a central temperature below 10 K. This ratio is higher than predicted by the known chemical models found in the literature. Para-D2H+ (and indirectly ortho-H2D+) is the only species that reveals the true centre of this core, while the emission of other molecular tracers and dust are biased by the temperature structure that results from the impact of the outflow. Conclusions. This study is an invitation to reconsider the analysis of previous observations of this source and possibly questions the validity of the deuteration chemical models or of the reaction and inelastic collisional rate coefficients of the H+3 isotopologue family. This could impact the deuteration clock predictions for all sources.

StaR-LIF: State-resolved laser-induced fluorescence modeling for diatomic molecules

This study introduced a new model for quantitative analysis of the state-resolved laser-induced fluorescence signal of diatomic molecules, namely StaR-LIF. This model is built upon a master equation of the collisional-radiative transfer processes, which incorporated the latest data on the collisional energy transfer rates between individual spin- and parity-resolved rovibronic quantum levels, together with the most recent updates on the energy levels, line strengths and broadening/shift parameters of the relevant absorption and fluorescence transitions. To facilitate the use of this model, a web-based graphic user interface has been developed and made available at https://starlif.pku.edu.cn. Example applications of the current model have been demonstrated for NO, OH and CH, including parametric studies on the effects of variable pulse width and saturating excitation, as well as the temporal evolution of fluorescence spectrum during collisional transfer. The StaR-LIF model can provide quantitative modeling and analysis capabilities over a wide range of gasdynamic and excitation conditions, and promises to be useful in future LIF studies of complex reacting flows.

MASER and dasar lines of disilicon carbide (SiCSi) using accurate collisional rate coefficients

MASER and dasar lines of disilicon carbide (SiCSi) using accurate collisional rate coefficients

Rotational excitation of methyl mercaptan (CH3SH) in collisions with molecular hydrogen

Abstract This paper presents the calculation of rate coefficients for transitions between rotational levels of the A-type and E-type levels of methyl mercaptan (CH3SH) resulting from collisions with molecular hydrogen. Radiative transfer modeling requires both radiative and collisional rates to describe the rotational populations under the usual conditions in interstellar clouds where LTE conditions do not apply. To compute the intermolecular interaction between CH3SH and H2, the explicitly correlated CCSD(T)-F12a coupled-cluster method which utilized a correlation-consistent aug-cc-pVTZ basis was employed. The computed energies were fit to a functional form suitable for use in scattering calculations. Rate coefficients were calculated over the temperature range from 5 to 100 K for transitions between the 110 lowest CH3SH rotational levels (having energies less than 107 cm−1 (ca. 150 K) within both the A-type and E-type manifolds caused by collisions with para- and ortho-H2. The rate coefficients were obtained through time-independent quantum close coupling quantum scattering calculations utilizing the calculated PES.

Methanimine in Cool Cosmic Objects Using Accurate Collisional Rate Coefficients

Methanimine in Cool Cosmic Objects Using Accurate Collisional Rate Coefficients

Size distribution of aggregates across different aquatic systems around Japan shows that stronger aggregates are formed under turbulence

AbstractMarine aggregates, composed of various particles, play a crucial role in ocean carbon storage. The overall size distribution of the aggregates (number size spectra) is controlled by the balance between aggregation and disaggregation processes. Turbulence has been proposed to facilitate both aggregation and disaggregation by increasing the collision rate of aggregates or sometimes directly tearing them apart. Predominant processes driven by turbulence typically depend on the level of turbulence—relatively weak turbulence is associated with aggregation while stronger turbulence promotes disaggregation. Aggregate strength also plays a key role, as strongly bonded aggregates can withstand turbulence better, leading to lower disaggregation rates. While the relationship between turbulence and aggregate strength has been studied numerically and experimentally, field measurements remain limited. Here, we compare our number size spectra to turbulence intensity from the field measurements across different environmental settings around Japan to determine the effect of turbulence on aggregate strength. We combined measurements from 10 sites with different environmental settings and observed the flatter slopes (higher net aggregation rate) and shifts in the intersection lengths with an increase of turbulence, while strong turbulence is typically linked with disaggregation. Our findings suggested that stronger aggregates are formed under stronger turbulence and the overall population of strong aggregates also increases with an increase of turbulence intensity. We also compared our number size spectra with three other confounding factors (fluorescence, salinity, and aggregate compositions) to confirm the effects of turbulence are dominant in our aggregate dynamics.

A performant energy-conserving particle reweighting method for Particle-in-Cell simulations

A new particle-based reweighting method is developed and demonstrated in the Aleph Particle-in-Cell with Direct Simulation Monte Carlo (PIC-DSMC) program. Novel splitting and merging algorithms ensure that modified particles maintain physically consistent positions and velocities. This method allows a single reweighting simulation to efficiently model plasma evolution over orders of magnitude variation in density, while accurately preserving energy distribution functions (EDFs). Demonstrations on electrostatic sheath and collisional rate dynamics show that reweighting simulations achieve accuracy comparable to fixed weight simulations with substantial computational time savings. This highly performant reweighting method is recommended for modeling plasma applications that require accurate resolution of EDFs or exhibit significant density variations in time or space.

Research on robust decision making for intelligent connected vehicle at highway on-ramp

Reinforcement learning has demonstrated its potential in the decision-making field of autonomous driving. By engaging in trial-and-error learning and interacting with the environment, we can adapt our behavioral strategies based on reward and enhance driving decisions. Nevertheless, real-world vehicle decision-making involves intricate and diverse information, and the limited state information hinders agents from making optimal decisions, which may result in catastrophic consequences like collisions. Therefore, this paper proposes a robust deep reinforcement learning method based on the Soft Actor-Critic (SAC) algorithm for highway intelligent connected vehicle ramp merging decision-making. The model represents the vehicle features of the target lane and its adjacent lanes as an environmental state space. Additionally, a hybrid action space is designed, which combines discrete lateral actions and continuous longitudinal actions. Finally, an on-ramp simulation platform is built using actual roads and SUMO to verify the feasibility of the model. Multiple sets of comparative analysis experimental results demonstrate that the proposed method outperforms others in terms of the average reward return value, robustness value, collision rate, and success rate. Moreover, the model exhibits a stable lane change success rate under various road traffic density conditions, which indicates its robustness. The code can be obtained at https://github.com/ColinFanghz/sac-on-ramp.git .

Distributions and collision rates of ALP stars in the Milky Way

Distributions and collision rates of ALP stars in the Milky Way

Intensification of fine particle flotation with less energy input using vortex generators

The separation of fine mineral particles has always been challenging in flotation. Previous studies generally believed that intensifying fine particle flotation necessarily involves higher energy expenditure. To explore the more effective intensification, this study measured the flotation performance of diaspore particles smaller than 20 μm in a mineralization pipe. The energy input was regulated by varying the slurry flow rate in the mineralization pipe and incorporating wedge-shaped vortex generator (VG) with different pinch angles. The results of flotation tests indicated that introduction of VG can achieve superior flotation performance with reduced energy input. A flotation rate of 0.86/min was obtained in the mineralization pipe with VG and a pinch angle of 60° (VGP-60) at an energy input of 27.29 W, much higher than that of 0.53 /min in empty pipe at 37.59 W. The more effective intensification is attributed to the high turbulent dissipation rate (ε) induced by VG. The volume-averaged ε in VGP-60 is 31.8 m2/s3 at an energy input of 27.29W, exceeding that in empty pipe at 37.59 W. The increased ε enhances the collision rate between particles and bubbles, thus causing the flotation rate to grow as a power function with exponent of 0.5.

The Densities in Diffuse and Translucent Molecular Clouds: Estimates from Observations of C2 and from Three-dimensional Extinction Maps

Newly computed collisional rate coefficients for the excitation of C2 in collisions with H2, presented recently by Najar & Kalugina, are significantly larger than the values adopted previously in models for the excitation of the C2 molecule, a widely used probe of the interstellar gas density. With these new rate coefficients, we have modeled the C2 rotational distributions inferred from visible and ultraviolet absorption observations of electronic transitions of C2 toward a collection of 46 nearby background sources. The inferred gas densities in the foreground interstellar clouds responsible for the observed C2 absorption are a factor 4–7 smaller than those inferred previously, a direct reflection of the larger collisional rate coefficients computed by Najar & Kalugina. These lower-density estimates are generally in good agreement with the peak densities inferred from 3D extinction maps for the relevant sight lines. In cases where H3+ absorption has also been observed and used to estimate the cosmic-ray ionization rate (CRIR), our estimates of the latter will also decrease accordingly because the H3+ abundance is a function of the ratio of the CRIR to the gas density.

Methanimine in cool cosmic objects using accurate collisional rate coefficients

Methanimine in cool cosmic objects using accurate collisional rate coefficients

Ideal Collision Rate of Symmetric Hexapods in a Simple Shear Flow.

An ideal collision rate (ICR) is defined as the average rate of contact between two particles that translate and rotate with the imposed fluid flow in the absence of interparticle interactions. ICR in a simple shear flow provides an estimate of the collision rate in a flowing dilute particle suspension, and its value is known only for traditional convex shapes such as spheres and cylinders. In this work, we compute the ICR for a family of symmetric hexapods (shown in Figure 1) that are particles composed of three orthogonal cylinders with coinciding centers (forming six arms) with at least two cylinders having the same length. We employed the finite-element method to obtain the rotational dynamics of hexapods and Monte Carlo simulations to calculate their ICR. Our results indicate that the ICR for hexapods is not directly proportional to the volume of the particle, in contrast to what is observed for convex shapes such as spheres and cylinders. For hexapods of the same size, the ICR could be similar for particles with order-of-magnitude differences in their volumes and it could also vary by an order of magnitude for particles with similar volumes. Specifically for hexapods termed branched fibers, which have one longer cylinder, the ICR changes by an order of magnitude even when the shorter cylinders are significantly smaller than the longer cylinder. This change is attributed to the increase in the tumbling frequency of the particle due to hydrodynamic forces acting on the shorter arms, in addition to the increased probability of collision afforded by them. Using asymptotic theory for high-aspect ratio cylinders, we showed that the tumbling period of hexapods was proportional to an algebraic power of the ratio of its arm lengths and has a weaker logarithm relationship with the aspect ratio of its arms. The collision cross-section provided the relative cross-streamline particle separations for the most likely binary collisions in the suspensions, and its value was sensitive to the arm lengths, as well. The collision rate of hexapods also could not be estimated within an order of magnitude from existing geometric models, such as the ICR of a circumscribing convex shape, ICR for one of the individual cylinders of the hexapod, or using the particle volume times the shear rate. Our work indicates that collision rate for non-convex particles in shear flows critically depends on the shape of the particle due to nontrivial changes in the particle's orientational dynamics, and the ICR calculation serves as a more reliable method for estimating their true collision rates in the suspension.

Safety, Efficiency, and Mental Workload in Simulated Teledriving of a Vehicle as Functions of Camera Viewpoint.

Teleoperation services are expected to operate on-road and often in urban areas. In current teleoperation applications, teleoperators gain a higher viewpoint of the environment from a camera on the vehicle's roof. However, it is unclear how this viewpoint compares to a conventional viewpoint in terms of safety, efficiency, and mental workload. In the current study, teleoperators (n = 148) performed driving tasks in a simulated urban environment with a conventional viewpoint (i.e., the simulated camera was positioned inside the vehicle at the height of a driver's eyes) and a higher viewpoint (the simulated camera was positioned on the vehicle roof). The tasks required negotiating road geometry and other road users. At the end of the session, participants completed the NASA-TLX questionnaire. Results showed that participants completed most tasks faster with the higher viewpoint and reported lower frustration and mental demand. The camera position did not affect collision rates nor the probability of hard braking and steering events. We conclude that a viewpoint from the vehicle roof may improve teleoperation efficiency without compromising driving safety, while also lowering the teleoperators' mental workload.

Multiagent trajectory decision‐making for complex systems based on transformer large model structure

AbstractThe article explores the application of transformer‐based large models for trajectory decision‐making in complex decision systems, focusing on multiagent nodes in a topological structure. By leveraging the capabilities of large models, the proposed approach enhances decision‐making in model‐free control environments characterized by numerous agents, diverse internal tasks, and unknown conditions. The proposed framework integrates advanced transformer models with a sophisticated decision‐making framework to enhance the efficiency, safety, and reliability of multiagent operations in dynamic environments. The results demonstrate the superior performance of the transformer model, achieving a trajectory decision‐making accuracy of 97.8%, significantly outperforming other models such as long short‐term memory (LSTM), gate recurrent unit (GRU), and traditional approaches. The visualizations highlight the close alignment between the true and predicted outcomes of complex decision‐making systems, showcasing the model's ability to capture complex dependencies and interactions within the multiagent environment. High task completion rates and low collision rates further underscore the effectiveness of the decision‐making framework in optimizing agent coordination and ensuring safe operations.

Collision rate coefficients for C7N− and C10H− with H2

ABSTRACT The anions C$_7$N$^-$ and C$_{10}$H$^-$ are the two longest of the linear (C,N)-bearing and (C,H)-bearing chains that have so far been detected in the interstellar medium (ISM). In order to glean information on their collision-induced rotational state-changing processes, we analyse the general features of new ab initio potentials describing the interaction of both linear anions with H$_2$, one of the most abundant partners in their ISM environment. We employ an artificial neural network fit of the reduced-dimensionality potential energy surface for C$_7$N$^-$...H$_2$ interaction and discuss in detail the spatial features in terms of multipolar radial coefficients. For the C$_{10}$H$^-$...H$_2$ interaction, we use the initial grid of two-dimensional raw points to generate by quadrature the Legendre expansion directly, further including the long-range terms as discussed in the main text. Quantum scattering calculations are employed to obtain rotationally inelastic cross-sections, for collision energies in the range of 10$^{-4}$ to 400 cm$^{-1}$. From them we generate the corresponding inelastic rate coefficients as a function of temperature covering the range from 10 to 50 K. The results for the rate coefficients for the longest cyanopolyyne are compared with the earlier results obtained for the smaller terms of the same series, also in collision with H$_2$. We obtain that the inelastic rate coefficients for the long linear anions are all fairly large compared with the earlier systems. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are illustrated in our conclusions.

Inelastic scattering of PO+ by H2 at interstellar temperatures

ABSTRACT Phosphorous species are of great interest in interstellar chemistry since they are the basic blocks for building life here on Earth. Modelling the abundance and environment of recently detected PO$^{+}$ under non-local thermodynamic equilibrium (LTE) requires rotational spectra of the molecule along with accurate collisional rates with the most abundant species, hydrogen and helium. A new 4D ab initio potential energy surface (PES) of PO$^{+}$ – H$_{2}$ collision is calculated using CCSD(T)/CBS(DTQ) methodology considering rigid rotor approximation. The region containing the minima of the PES is augmented using neural networks (NNs) model while very high potentials ($\gt 2500$ cm$^{-1}$) and asymptotic region have been approximated using Slater and R$^{-4}$ functions, respectively. The close coupling calculations have been performed using molscat software for both ortho and para-H$_{2}$. The rate coefficients have been reported for transitions $j-j^{\prime }=$$1-0$, $2-1$, $3-2$, and $5-4$ through which PO$^{+}$ has been experimentally detected in interstellar medium (ISM). The rate coefficients for even and odd transitions of PO$^{+}$ with para-H$_{2}$ are compared with that of helium and are found to be 1.1–2.0 times higher. For even transitions ($\Delta j = 2$), the ortho-H$_{2}$ rates are 10 per cent higher than para-H$_{2}$ rates. However, the trend reverses in the case of odd transitions ($\Delta j = 1$) when higher J transitions are considered at low temperatures. At higher temperatures, the ortho rates cross the para-H$_{2}$ rates and become larger than the latter. The new rate coefficients with both ortho and para-H$_{2}$ will enable accurate modelling of the PO$^{+}$ abundance in the ISM under non-LTE conditions.

Change in the collision avoidance performance of autonomous emergency braking systems

Objective This study quantifies the change in collision avoidance performance of autonomous emergency braking (AEB) systems for traffic accidents in Japan since 2015. Method This study used data on Japanese traffic accidents compiled by Japan’s National Police Agency. The data included only accidents involving loss of or injury to human life; accidents involving only property damage were excluded. We restricted our analysis to collisions between two 4-wheel vehicles and considered only collisions for which we could determine whether the primary party’s car was equipped with an AEB system. Both Poisson and negative binomial mixed-effects regression analyses were conducted using the data for 2021 and 2022 to measure the collision avoidance performance of first registered cars in 2015 to 2020 equipped with AEB systems compared with cars without AEB systems first registered in 2015. Collision avoidance performance was measured for 2 types of intervehicle collisions: rear-end collisions and right-turn collisions. Collision avoidance performance for rear-end collisions was also measured for each of the 3 car types—Standard, small, and light cars. Results The collision reduction rate for rear-end collisions increases with the year of first registration and for cars equipped with AEB systems first registered in 2020 compared with non-AEB-equipped cars first registered in 2015 is 69.2% (95% confidence interval [CI] 67.0%–71.1%), indicating that the performance of AEB systems has dramatically improved in terms of preventing rear-end collisions. For right-turn collisions, the rate increased to 20.4% (95% CI 5.9%–32.6%) for cars equipped with AEB systems first registered in 2019. However, no clear trend is observed. Conclusions This study evaluated a time series of the collision reduction performance of AEB systems using an original methodology. Japan’s New Car Assessment Program (JNCAP) has included AEB’s effectiveness in reducing damage from traffic collisions as an evaluation item since FY2014. The results could demonstrate the effectiveness of JNCAP.