Search

Excited state van der Waals (vdW) potential energy surfaces (PESs) of the NO A2Σ+ + CO2 X 1 Σ g + system are thoroughly investigated using coupled cluster theory and complete active space perturbation theory to second order (CASPT2). First, it is shown that pair natural orbital coupled cluster singles and doubles with perturbative triples yields comparable accuracy compared to CCSD(T) for molecular properties and vdW-minima at a fraction of computational cost of the latter. Using this method in conjunction with highly diffuse basis sets and counterpoise correction for basis set superposition error, the PESs for different intermolecular orientations are investigated. These show numerous vdW-wells, interconnected for all geometries except one, with a maximum depth of up to 830 cm−1; considerably deeper than those on the ground state surface. Multi-reference effects are investigated with CASPT2 calculations. The long-range vdW-surfaces support recent experimental observations relating to rotational energy transfer due the anisotropy in the potentials. [ABSTRACT FROM AUTHOR]

In the title compound, C16H13Cl4N3, the dihedral angle between the benzene rings of the dichlorophenyl and dimethylaniline groups is 50.85 (13)°. The central –N=N– unit shows an E configuration. In the crystal, molecules form parallel layers to the (100) plane by C—H···π and face-to-face π-π [centroid-to-centroid distances = 4.0538 (17) and 4.0537 (17) Å] interactions. These layers are connected by Van der Waals interactions to stabilize the crystal structure. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from Cl···H/H···Cl (36.4%), H···H (23.3%) and C···H/H···C (15.2%) contacts. [ABSTRACT FROM AUTHOR]

In previous earthquakes, a significant number of adjacent buildings in a series have been damaged due to collisions. Pounding between adjacent structures in a series causes them to inflict multiple blows on one another, which is a complex type of collision. Previous studies have produced inconsistent or conflicting research conclusions due to various parameters of buildings and excitation. It is challenging to determine a universal law of collision reactions between adjacent buildings in a row. To address the complexity of these parameters, the dimensional analysis method is used. This work establishes a mathematical model for the dimensionless collision response of adjacent structures in a row. The layout of the structures is considered through three different configurations, and the effects of unilateral and bilateral collisions are compared. The analysis also considers the impacts of the frequency ratio, mass ratio and gap size of the oscillators. According to the impact of pounding, the displacement and velocity responses of the outer structures with low mass and stiffness can be divided into multiple spectral regions based on the frequency ratio of the structure and excitation. The effects of the mass ratio and frequency ratio on the responses of the outer flexible structures are correlated with the spectral regions. The results indicate that placing a structure with a small mass and stiffness outside is dangerous, since it causes a much larger pounding force and displacement of the outer structure. Compared with the unilateral impact response, the bilateral impact response induces a smaller displacement of the middle structure with a slight mass and stiffness. [ABSTRACT FROM AUTHOR]

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex 'exotic' structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted. [ABSTRACT FROM AUTHOR]

It is vital to analyze ship collision risk for preventing collisions and improving safety at sea. This paper takes Ningbo-Zhoushan Port, a typical complex navigable water, as the research object. Firstly, a probabilistic conflict detection method based on an AIS data-driven dynamic ship domain model is proposed to achieve effective ship conflict detection under uncertain environments. Then, a ship group identification method is proposed, which can extract the ship groups with conflict correlation and space compactness. Finally, according to the characteristics of ship traffic in complex navigable waters, the dynamic calculation of ship collision risk is carried out from individual, regional, and local multi-scale perspectives. The experimental results show that the proposed method can detect the collision risk in a timely, reliable, and effective manner under complex dynamic conditions. As such, they provide valuable insights into ship collision risk prediction and the development of risk mitigation measures. [ABSTRACT FROM AUTHOR]

Decision-making for collision avoidance in complex maritime environments is a critical technology in the field of autonomous ship navigation. However, existing collision avoidance decision algorithms still suffer from unstable strategy exploration and poor compliance with regulations. To address these issues, this paper proposes a novel autonomous ship collision avoidance algorithm, the dynamically adjusted entropy proximal policy optimization (DAE-PPO). Firstly, a reward system suitable for complex maritime encounter scenarios is established, integrating the International Regulations for Preventing Collisions at Sea (COLREGs) with collision risk assessment. Secondly, the exploration mechanism is optimized using a quadratically decreasing entropy method to effectively avoid local optima and enhance strategic performance. Finally, a simulation testing environment based on Unreal Engine 5 (UE5) was developed to conduct experiments and validate the proposed algorithm. Experimental results demonstrate that the DAE-PPO algorithm exhibits significant improvements in efficiency, success rate, and stability in collision avoidance tests. Specifically, it shows a 45% improvement in success rate per hundred collision avoidance attempts compared to the classic PPO algorithm and a reduction of 0.35 in the maximum collision risk (CR) value during individual collision avoidance tasks. [ABSTRACT FROM AUTHOR]

In Automated Fiber Placement (AFP), the substantial structure of the placement robot, the variable mold shapes, and the limited free space pose significant challenges for planning collision-free robot transitions. The task involves planning a collision-free path within the robot's high-dimensional configuration space. Informed RRT* is a common approach for such problems but often struggles with efficiency and path quality in environments with large informed sampling spaces influenced by obstacles. To address these issues, this paper proposes an improved Informed RRT* algorithm with a Local Knowledge Acceleration sampling strategy (LKA-Informed RRT*), aimed at enhancing planning efficiency and adaptability in complex obstacle settings. An Adaptive Sampling Control (ASC) rate is introduced, measuring the algorithm's convergence speed, guides the algorithm to switch between informed and local sampling adaptively. The proposed local sampling method uses failure nodes from the exploration process to estimate obstacle distributions, steering sampling toward regions that expedite path convergence. Experimental results show that LKA-Informed RRT* significantly outperforms state-of-the-art algorithms in convergence efficiency and path cost. Compared to the original Informed RRT*, the proposed method reduces planning time by about 60%, substantially boosting efficiency for collision-free transitions in complex environments. [ABSTRACT FROM AUTHOR]

Measurements of the 0–0 hyperfine resonant frequencies of ground-state 85Rb atoms show a nonlinear dependence on the pressure of the buffer gases Ar, Kr, and Xe. The nonlinearities are similar to those previously observed with 87Rb and 133Cs and presumed to come from alkali-metal–noble-gas van der Waals molecules. However, the shape of the nonlinearity observed for Xe conflicts with previous theory, and the nonlinearities for Ar and Kr disagree with the expected isotopic scaling of previous 87Rb results. Improving the modeling alleviates most of these discrepancies by treating rotation quantum mechanically and considering additional spin interactions in the molecules. Including the dipolar-hyperfine interaction allows simultaneous fitting of the linear and nonlinear shifts of both 85Rb and 87Rb in either Ar, Kr, or Xe buffer gases with a minimal set of shared, isotope-independent parameters. To the limit of experimental accuracy, the shifts in He and N2 were linear with pressure. The results are of practical interest to vapor-cell atomic clocks and related devices. [ABSTRACT FROM AUTHOR]

Recent advancements in materials science have shed light on the potential of exploring hierarchical assemblies of molecules on surfaces, driven by both fundamental and applicative challenges. This field encompasses diverse areas including molecular storage, drug delivery, catalysis, and nanoscale chemical reactions. In this context, the utilization of nanotube templates (NTs) has emerged as promising platforms for achieving advanced one-dimensional (1D) molecular assemblies. NTs offer cylindrical, crystalline structures with high aspect ratios, capable of hosting molecules both externally and internally (Mol@NT). Furthermore, NTs possess a wide array of available diameters, providing tunability for tailored assembly. This review underscores recent breakthroughs in the field of Mol@NT. The first part focuses on the diverse panorama of structural properties in Mol@NT synthesized in the last decade. The advances in understanding encapsulation, adsorption, and ordering mechanisms are detailed. In a second part, the review highlights the physical interactions and photophysics properties of Mol@NT obtained by the confinement of molecules and nanotubes in the van der Waals distance regime. The last part of the review describes potential applicative fields of these 1D heterostructures, providing specific examples in photovoltaics, luminescent materials, and bio-imaging. A conclusion gathers current challenges and perspectives of the field to foster discussion in related communities. [ABSTRACT FROM AUTHOR]

Ship path planning is the core problem of autonomous driving of smart ships and the basis for avoiding obstacles and other ships reasonably. To achieve this goal, this study improved the traditional A* algorithm to propose a new method for ship collision avoidance path planning by combining the multi-target point artificial potential field algorithm (MPAPF). The global planning path was smoothed and segmented into multi-target sequence points with the help of an improved A* algorithm and fewer turning nodes. The improved APF algorithm was used to plan the path of multi-target points locally, and the ship motion constraints were considered to generate a path that was more in line with the ship kinematics. In addition, this method also considered the collision avoidance situation when ships meet, carried out collision avoidance operations according to the International Regulations for Preventing Collisions at Sea (COLREGs), and introduced the collision risk index (CRI) to evaluate the collision risk and obtain a safe and reliable path. Through the simulation of a static environment and ship encounter, the experimental results show that the proposed method not only has good performance in a static environment but can also generate a safe path to avoid collision in more complex encounter scenarios. [ABSTRACT FROM AUTHOR]

In this paper, we propose an approach based on parameter β, which equals the free volume in a unit cell normalized to the van der Waals volume of the molecules. The analysis was carried out within a cluster including two-component crystals [CF1 + CF2], in which one of the components remains constant (CF1) and the other varies (CF2). Linear correlation equations, such as β(CC) = C + D·β(CF2), linking the β(CC) parameter of the two-component crystals with the similar parameter β(CF2) of the single-component crystal for the strictly fixed temperatures were derived on the basis of the crystallographic experimental data. The coefficients of the correlation equations for different clusters were analyzed. A relationship was discovered between the correlation coefficient D and the HYBOT descriptor describing the donor and acceptor interactions with the other molecules. A graphic method was developed for analyzing the β(CC) parameter for the cocrystals belonging to the same cluster relative to the β parameter values of the individual compounds β(CF1) and β(CF2). The correlation equations derived in the study give an opportunity to evaluate the unit cell volume of a hypothetical cocrystal knowing only the crystal structure of a single-component crystal of one of the cocrystal components. [ABSTRACT FROM AUTHOR]

An accurate and computationally efficient determination of the cross sections for electron collision ionization of molecules has various applications, such as plasma physics and atmospheric science. In the case of large molecules, ab initio calculations are often difficult and time‐consuming. Here, we develop a feed forward neural network to predict the electron impact ionization cross sections of complex molecules. The training (predicting) set in the method consists of a series of theoretical ionization cross sections for small (large) molecules obtained from the combined model, which integrates the Binary‐Encounter‐Bethe and Deutsch‐Märk models. Several complex systems or targets involving electron collision ionization are evaluated, including molecules such as CH4$$ {}_4 $$, C3$$ {}_3 $$H8$$ {}_8 $$, C5$$ {}_5 $$H8$$ {}_8 $$, C6$$ {}_6 $$H10$$ {}_{10} $$, C6$$ {}_6 $$, C2$$ {}_2 $$H6$$ {}_6 $$O, and C6$$ {}_6 $$H6$$ {}_6 $$O. The root mean square errors of the trained and predicted cross sections by the 2×3×3×1$$ 2\times 3\times 3\times 1 $$ neural network (compared to the values from the combined model) are found to be approximately.0086 and.0930 (in 10−20$$ {}^{-20} $$ cm2$$ {}^2 $$), respectively, (using the C2$$ {}_2 $$H6$$ {}_6 $$O molecule as an example), indicating our results are very high accuracy. The excellent agreement between the predicted values and the actual values indicates that the neural network is a practical and powerful tool for determining the electron collision ionization cross sections of complex molecules and can provide valuable insights into the dynamics process. Apart from its fundamental importance, this study has far‐reaching implications for gas discharge, low‐temperature plasmas, and fusion edge plasmas and so forth. [ABSTRACT FROM AUTHOR]

To accurately map weak D2–Ne long-range interactions, we have studied rotationally inelastic cold scattering of D2 prepared in the vibrationally excited (v = 4) and rotationally aligned (j = 2, m) quantum state within the moving frame of a supersonically expanded mixed molecular beam. In contrast to earlier high energy D2–Ne collision experiments, the (j = 2 → j′ = 0) cold scattering produced highly symmetric angular distributions that strongly suggest a resonant quasi-bound collision complex that lives long enough to make a few rotations. Our partial wave analysis indicates that the scattering dynamics is dominated by a single resonant l = 2 orbital, even in the presence of a broad temperature (0–5 K) distribution that allows incoming orbitals up to l = 5. The dominance of a single orbital suggests that the resonant complex stabilizes through the coupling of the internal (j = 2) and orbital (l = 2) angular momentum to produce a total angular momentum of J = 0 for the D2–Ne complex. [ABSTRACT FROM AUTHOR]

State-to-state cross sections and rate coefficients for transitions between rotational/fine-structure levels of OH(X2Π) induced by collisions with atomic hydrogen are reported in this work. The scattering calculations take into account the full open-shell character of the OH + H system and include the four potential energy surfaces (1A′, 1A″, 3A′, 3A″) that correlate with the OH(X2Π) + H(2S) asymptote. Three of these surfaces are repulsive, while the deep H2O well is present on one surface (1A′). The OH + H potential energy curves calculated by Alexander et al. [J. Chem. Phys. 121, 5221 (2004)] are employed in this work. Time independent quantum scattering calculations were performed using the quantum statistical method of Rackham and co-workers [Chem. Phys. Lett. 343, 356 (2001)] because of the presence of the deep H2O well. The computed cross sections include contributions from direct scattering, as well formation and decay of a transient collision complex since the transient HO–H complex is expected to decay nonreactively. Rate coefficients for OH–H inelastic collisions are of interest for astrophysical applications. [ABSTRACT FROM AUTHOR]

Recent advances in synthetic methods, combined with tip‐induced on‐surface chemistry, have enabled the formation of numerous cyclocarbon molecules. Here, we investigate computationally the experimentally studied C16 and C18 molecules as well as their van der Waals (vdW) complexes with several typical donor and acceptor molecules. Our results demonstrate a remarkable electron‐withdrawing ability of cyclocarbon molecules. The vdW complexes of C16 and C18 exhibit a thermodynamically favorable photoinduced electron transfer (ET) from the donor partner to the cyclocarbons that occurs on a picosecond time scale. The lower reorganization energy of C16 compared to C18 leads to a significant acceleration of the ET reactions. [ABSTRACT FROM AUTHOR]

Recent advances in synthetic methods, combined with tip‐induced on‐surface chemistry, have enabled the formation of numerous cyclocarbon molecules. Here, we investigate computationally the experimentally studied C16 and C18 molecules as well as their van der Waals (vdW) complexes with several typical donor and acceptor molecules. Our results demonstrate a remarkable electron‐withdrawing ability of cyclocarbon molecules. The vdW complexes of C16 and C18 exhibit a thermodynamically favorable photoinduced electron transfer (ET) from the donor partner to the cyclocarbons that occurs on a picosecond time scale. The lower reorganization energy of C16 compared to C18 leads to a significant acceleration of the ET reactions. [ABSTRACT FROM AUTHOR]

The reaction of the 1-propynyl radical (CH3CC; X2A1) with propylene (CH3CHCH2; X1A′) was studied in a crossed molecular beam machine at a collision energy of 37 ± 1 kJ mol−1. Experimental data combined with high-level electronic structure (CCSD(T)-F12/cc-pVTZ-F12//ωB97X-D/6-311G(d,p)) and RRKM calculations reveal the reaction mechanism. The overall barrierless and exoergic reaction involves indirect reaction dynamics and commences preferentially with addition of 1-propynyl with its radical centre to the carbon–carbon double bond at the terminal carbon atom of propylene. This work focuses on molecular mass growth process (hydrogen loss channels) although theory suggests methyl loss as a prevalent channel. In these processes, the C6H9 collision complexes either emit atomic hydrogen or undergo isomerisation followed by atomic hydrogen loss to preferentially yield the cis/trans isomers of 1,3-dimethylvinylacetylene (2-hexen-4-yne) as the primary product. Analysis of reaction dynamics of 1-propynyl and ethynyl radicals with propylene along with their fractional abundance in deep space suggests formation of methyl- and dimethyl derivatives of vinylacetylene in cold molecular clouds. Once formed they may engage in fundamental molecular mass growth processes via the barrierless Hydrogen Abstraction Vinylacetylene Addition mechanism that leads to the formation of methyl- and dimethylnaphthalenes thus providing a versatile route to methyl-substituted PAHs in interstellar medium. [ABSTRACT FROM AUTHOR]

Two-dimensional materials have aroused the attention of many scientists due to its remarkable chemical, magnetic, optical, and electronic characteristics. However, the specific interaction mechanism between various amino acids with arsenene surfaces has not been explored. We systematically investigated the interactions of 20 amino acids with arsenene by calculating the adsorption energy, electronic structure, sensitivity, and recovery time using density functional theory with Grimme's dispersion correction. Moreover, applying biaxial strains can drastically change the adsorption energy. For the first time, it was discovered that the arsenene monolayer has strong adsorption specificity, high sensitivity, and short recovery time for amino acid molecules through van der Waals interactions. Our findings indicate that the arsenene may be used as a sensing medium for amino acids. [ABSTRACT FROM AUTHOR]

Spectroscopic properties and potential energy curves of alkali metal (M = Na and K) – rare gas (Rg = He, Ne, Ar, Kr, Xe and Rn) van der Waals molecules in their ground states have been studied in detail using spin-restricted open-shell coupled cluster with single and double excitations and perturbative contribution of connected triple excitations (RCCSD(T)) methods. The core-valence correlation (CV) effect was found to be crucial for M-RG molecules containing heavy rare gas atoms. The electronic energies were corrected for the basis set superposition error (BSSE) using the counterpoise method. Energies were extrapolated to the complete basis set (CBS) limit using a two-point scheme. The permanent electric dipole moments, static electric dipole polarizabilities and long-range dispersion coefficients were also calculated. The computed spectroscopic constants, vibrational levels and rotational constants were reported for M-RG and good agreement with the available experimental and theoretical values were found. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) and phenolics are pollutants found ubiquitously in freshwater systems. MPs oftentimes serve as a vector for pollutants across ecosystems and are now being explored as alternative adsorbents for pollutant removal. This strategy would reflect the 'reuse' of an existing waste stream into a potentially useful product while at the same time helping to minimize plastic waste in the marine environment. In this study, the adsorption of phenol onto pristine (Pr-PET), modified (Mod-PET), and aged (Ag-PET) Polyethylene Terephthalate (PET) microplastics was examined experimentally and theoretically. Kinetics, isotherms, and thermodynamics models were used to investigate the adsorption process while Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were employed to investigate molecular level alterations. The result showed that the Ag-PET MPs had the best removal efficiency due larger surface area and the adsorption occurred in a pseudo-second-order manner, showing that the rate of phenol adsorption is directly proportional to the number of surface-active sites on the surface of PET MPs while the intraparticle diffusion defined rate-limiting step. However, the maximum monolayer adsorption capacity followed Mod-PET (38.02 mg/g) > Ag-PET (8.08 mg/g) > Pr-PET (6.84 mg/g). The adsorption process proceeded spontaneously and thermodynamically favourable. GCMC-MD simulations revealed that PET MPs are capable of successfully adsorbing the phenol molecule through Van der Waals and electrostatic interactions and can be adopted as novel adsorbents for phenol removal in aqueous solutions. [ABSTRACT FROM AUTHOR]

This article examines the local history of the Northern Sea Route using the Yamal settlement of Novy Port as a case study. Shifting the focus of research from the capital-based decision-making centers to the anchor points of the Transpolar Route makes it possible to see complex collisions, alternative options, deviations from plans, and other failures, without which it is impossible to implement such large-scale projects as the Northern Sea Route. Novy Port was assigned the role of one of the outposts of the Soviet colonization of the Arctic. At each of the identified stages of the history of Novy Port, its modus vivendi was formulated anew, which reflected a change in paradigms in the development of the Northern Sea Route. [ABSTRACT FROM AUTHOR]

We investigate the prospect of using a two-dimensional material, fluorographene, to mimic the light-harvesting function of natural photosynthetic antennas. We show by quantum chemical calculations that isles of graphene in a fluorographene sheet can act as quasi-molecules similar to natural pigments from which the structures similar in function to photosynthetic antennas can be built. The graphene isles retain enough identity so that they can be used as building blocks to which intuitive design principles of natural photosynthetic antennas can be applied. We examine the excited state properties, stability, and interactions of these building blocks. Constraints put on the antenna structure by the two-dimensionality of the material as well as the discrete nature of fluorographene sheet are studied. We construct a hypothetical energetic funnel out of two types of quasi-molecules to show how a limited number of building blocks can be arranged to bridge the energy gap and spatial separation in excitation energy transfer. Energy transfer rates for a wide range of the system–environment interaction strengths are predicted. We conclude that conditions for the near unity quantum efficiency of energy transfer are likely to be fulfilled in fluorographene with the controlled arrangement of quasi-molecules. [ABSTRACT FROM AUTHOR]

We consider the origin of nonlinear collision shifts for the 0–0 hyperfine transition in alkali/noble-gas systems due to van der Waals molecule formation. Developing a semi-empirical model, we describe the shift as arising from three fundamental interactions: (1) a fractional change in the alkali's valence electron density at the alkali nucleus, η, which affects the hyperfine contact term; (2) a mixing of p-wavefunction character into the alkali ground state (characterized by the probability for p-state character appearing in the perturbed wavefunction ξ12), which gives rise to an electric quadrupole term in the ground-state hyperfine splitting; and (3) an interaction of the alkali's valence electron with the magnetic field produced by molecular rotation, characterized by a magnetic field strength BvdW. In addition to these molecular parameters, the model also depends on the formation rate of van der Waals molecules, kfP2, and the breakup rate of the molecules, kbP, where P is the noble-gas pressure. Fitting the model to the 85Rb/Xe and 87Rb/Xe experimental data of McGuyer and co-workers (and taking previously measured values for kf and BvdW), we find that η = 9 × 10−3, ξ12 = 5 × 10−3, and kb = 2.9×107 s−1/Torr. [ABSTRACT FROM AUTHOR]

We show that the integral cross sections for state-to-state quantum scattering of cold molecules in a magnetic field can be efficiently computed using the total angular momentum representation despite the presence of unphysical Zeeman states in the eigenspectrum of the asymptotic Hamiltonian. We demonstrate that the unphysical states arise due to the incompleteness of the space-fixed total angular momentum basis caused by using a fixed cutoff value Jmax for the total angular momentum of the collision complex J. As a result, certain orbital angular momentum (l) basis states lack the full range of J values required by the angular momentum addition rules, resulting in the appearance of unphysical states. We find that by augmenting the basis with a full range of J-states for every l, it is possible to completely eliminate the unphysical states from quantum scattering calculations on molecular collisions in external magnetic fields. To illustrate the procedure, we use the augmented basis sets to calculate the state-to-state cross sections for rotational and spin relaxation in cold collisions of 40CaH(X2Σ+, v = 0, N = 1, MN = 1, MS = 1/2) molecules with 4He atoms in a magnetic field. We find excellent agreement with benchmark calculations, validating our proposed procedure. We find that N-conserving spin relaxation from the highest-energy to the lowest-energy Zeeman state of the N = 1 manifold, | 11 1 2 〉 → | 1 − 1 − 1 2 〉 is nearly completely suppressed due to the lack of spin–rotation coupling between the fully spin-stretched Zeeman states. Our results demonstrate the possibility of rigorous, computationally efficient, and unphysical state-free quantum calculations on cold molecular collisions and on near-threshold energy levels of strongly anisotropic atom-molecule collision complexes in an external magnetic field. [ABSTRACT FROM AUTHOR]

Based on theoretical calculations and experimental characterizations, the extraction of heavy oil components using subcritical water (Sub-CW) as an extraction solvent was studied in the temperature range of 250–325 °C. According to theoretical calculations, small-scale polycyclic aromatic hydrocarbons (PAHs) are preferentially dissolved in Sub-CW. Meanwhile, the dissolution of heavy oil molecules with large-scale aromatic structures and heterocyclic rings in Sub-CW is hindered. The increase in temperature reduces the hydrogen bonding force between water molecules and the van der Waals repulsion between Sub-CW and PAHs, promoting the dissolution of PAHs in Sub-CW. Extraction experiments applied in a semi-continuous device confirm that Sub-CW selectively extracts aromatic hydrocarbons from heavy oil. Increasing extraction temperature increases the yield of the extract. The aromatic hydrocarbon content in the extract at 325 °C reaches 80 wt%, which is 27 wt% higher than feedstock value. In addition, the asphaltene content in the extract is reduced from the feedstock value of 14 wt% to 2 wt%. • Sub-CW was used as a property-tunable solvent for extracting heavy oil components. • Sub-CW selectively extracts aromatic hydrocarbons from heavy oil. • The yield and composition of the extract are sensitive to extraction temperature. • Opposite distribution of HSP hinders dissolution of PAHs/hetero-PAHs in Sub-CW. • Destruction of hydrogen bonds promotes dissolution of PAHs/hetero-PAHs in Sub-CW. [ABSTRACT FROM AUTHOR]

Diacetylenedisalicylic acid is a new rigid linker molecule, capable of forming strong chelate bonds with metal cations. Its monosubstituted salts with dimethylamine and sodium form 1D and 2D coordination polymers, whose structures were solved from single crystals, along with the dimethyl ester of diacetylenedisalicylic acid. The structure of the dimethyl ester is characterized by a dense co‐facial π‐stacking of molecules with a dominance of van der Waals interactions between the stacks. The angle between the stack direction and the butadiyne groups does not meet the Enkelmann criterion for polymerization in a crystal. In contrast to the dimethyl ester, both salts have a rigid framework with channels filled with disordered solvent molecules. Photoluminescence spectra of the acid and its dimethyl ester have been studied. Thermal analysis of the acid confirms its high thermal stability to 286°C. The acid and its dimethyl ester are prone to polymerization on further heating followed by 50–52% mass loss, forming an amorphous carbon residue at 1000°C. [ABSTRACT FROM AUTHOR]

Droplet positive collision is a complex process involving heat transfer in gas-liquid-solid three-phase flow and droplet collide dynamics. In order to study the kinetic behavior of droplets under positive collision in low velocity (v < 2 m/s), this paper focuses on the spreading, vibration, and fracture characteristics of double droplets by numerical simulation. First, the accuracy of the model is verified by experimental comparison. The effects of droplet diameters, collision velocities and wall contact angles on the spreading process are analyzed, and the spreading factor curves are plotted. Then, the droplet rebound vibration after collision fusion is equated to a single-degree-of-freedom damped vibration system, and the peak vibration height variation curve of the fused droplet is obtained by non-linear fitting. Considering the droplet phase change, the influence law of different conditions on the vibration damping factor and vibration time of the fused droplet is studied. Finally, it is found that rebound fracture and spreading fracture occur after the fusion of double droplets under positive collision, and the critical values of collide velocity required for the occurrence of the aforementioned phenomenon are found. To provide a reliable theoretical basis for the study of heat and mass transfer processes after multiple droplets collide the wall. [ABSTRACT FROM AUTHOR]

Using the concept of quasi‐molecule ("tile") and the database of quasi‐molecules embedded on a parent molecule, it is discussed whether the latter can attain linear form or otherwise. Besides anew accurate optimization of all tiles (quasi‐triatomics) at various levels of ab initio theory and basis‐sets, the nature of the predicted stationary points for the title parent molecules is probed through a priori calculations here too reported. Also discussed is the common rule that even‐nCnH− anions are linear while odd‐numbered ones tend to have nonlinear isomers. The reported quasi‐molecule approach is general, and allow the prediction of linearity or otherwise of the parent systems prior to calculations on them. When based on an extension of the bisection method (Varandas, Int. J. Quantum Chem.2023, 123, e27036.), it is easy to use even for large parent molecules, as illustrated for neutral and anionic carbon clusters with n≥9. [ABSTRACT FROM AUTHOR]

For more than half a century, networks of radiative association, dissociative recombination, and bimolecular reactions have been postulated to drive the low-temperature chemistry of cold molecular clouds. Third-body stabilizations of collision complexes have been assumed to be 'irrelevant' due to short lifetime of such complexes. Here, we conduct crossed molecular beam studies of ground state atomic silicon with diacetylene in combination with electronic structure calculations and microcanonical kinetics models operating under cold molecular cloud conditions. Our combined experimental, electronic structure, and microcanonical kinetics modelling investigations provide compelling evidence that three-body collisions of molecular hydrogen with long-lived reaction intermediates accessed through intersystem crossing are prevalent deep inside molecular clouds. This concept might be exportable to reactions involving polycyclic aromatic hydrocarbons thus affording a versatile machinery to complex organics via third-body stabilizations of bimolecular collision complexes deep inside cold molecular clouds. [ABSTRACT FROM AUTHOR]

With the implementation of AGV technology and automated scheduling, storage and retrieval systems have become widely utilized in warehouse management. However, due to the use of unidirectional channels, AGV movement is restricted, and detours may occur frequently. Additionally, as the number of AGVs increases, deadlocks can arise, which lead to delays in order packaging and a decrease in overall warehouse performance. Hence, this paper proposes a dynamic scheduling method for task assignment and route optimization of AGVs to prevent collisions. The routing optimization method is based on an improved A* algorithm, which takes into account the dynamic map as input. Moreover, this paper investigates highly complex collision scenarios in bidirectional channels. Through simulation experiments, it is evident that scheduling methods based on bidirectional channels offer a clear advantage in terms of efficiency compared to those based on unidirectional channels. [ABSTRACT FROM AUTHOR]

The fragmentation/adhesion behavior of nanoparticle agglomerate collision, which is challenging to model, is a crucial factor affecting fluidization. In this study, a discrete‐finite element method (FDEM) based cohesive crack model is developed to simulate normal collisions between a complex agglomerate (around 1 mm) and a wall. In the FDEM model, the complex agglomerate is built from primary agglomerates (around a few micrometers), whose adhesive force and Young's modulus are measured by an atomic force microscope (AFM). The simulation results including fragmentation morphology and plastic deformation agree well with the collision experiments. Finally, the sensitivity of the model is tested, including adhesive force, solid holdup, and Young's modulus. Fragment distribution is found to fit well with a two‐parameter Weibull function and damage ratio is found to have a polynomial relation with a modified Weber number. The model output shows a potential to be utilized in macroscopic model. [ABSTRACT FROM AUTHOR]

Inelastic collisions and elementary chemical reactions proceeding through the formation and subsequent decay of an intermediate collision complex, with an associated deep well on the potential energy surface, pose a challenge for accurate fully quantum mechanical approaches, such as the close-coupling method. In this study, we report on the theoretical prediction of temperature-dependent state-to-state rate coefficients for these complex-mode processes, using a statistical quantum method. This statistical adiabatic channel model is benchmarked by a direct comparison using accurate rate coefficients from the literature for a number of systems (H2 + H+, HD + H+, SH+ + H, and CH+ + H) of interest in astrochemistry and astrophysics. For all of the systems considered, an error of less than factor 2 was found, at least for the dominant transitions and at low temperatures, which is sufficiently accurate for applications in the above mentioned disciplines. [ABSTRACT FROM AUTHOR]

We study the role of pairwise long-range interactions in the formation of van der Waals molecules through direct three-body recombination processes A + B + B → AB + B, based on a classical trajectory method in hyperspherical coordinates developed in our earlier works [J. Pérez-Ríos et al., J. Chem. Phys. 140, 044307 (2014); M. Mirahmadi and J. Pérez-Ríos, J. Chem. Phys. 154, 034305 (2021)]. In particular, we find the effective long-range potential in hyperspherical coordinates with an exact expression in terms of dispersion coefficients of pairwise potentials. Exploiting this relation, we derive a classical threshold law for the total cross section and the three-body recombination rate yielding an analytical expression for the three-body recombination rate as a function of the pairwise long-range coefficients of the involved partners. [ABSTRACT FROM AUTHOR]

In the Multi-Axis Differential Absorption Spectroscopy (MAX-DOAS) trace gas and aerosol profile inversion algorithm, the vertical resolution and the observation information obtained through a series of continuous observations with multiple elevation angles (EAs) can affect the accuracy of an aerosol profile, thus further affecting the results of the gas profile. Therefore, this study examined the effect of the vertical resolution of an aerosol profile and EAs on the NO2 profile retrieval by combining simulations and measurements. Aerosol profiles were retrieved from MAX-DOAS observations and co-observed using light detection and ranging (Lidar). Three aerosol profile shapes (Boltzmann, Gaussian, and exponential) with vertical resolutions of 100 and 200 m were used in the atmospheric radiative transfer model. Firstly, the effect of the vertical resolution of the input aerosol profile on the retrieved aerosol profile with a resolution of 200 m was studied. The retrieved aerosol profiles from the two vertical resolution aerosol profiles as input were similar. The aerosol profile retrieved from a 100 m resolution profile as input was slightly overestimated compared to the input value, whereas that from a 200 m resolution input was slightly underestimated. The relative deviation of the aerosol profile retrieved from the 100 m resolution as input was higher than that of the 200 m. MAX-DOAS observations in Hefei city on 4 September 2020 were selected to verify the simulation results. The aerosol profiles retrieved from the oxygen collision complex (O4) differential slant column density derived from MAX-DOAS observations and Lidar simulation were compared with the input Lidar aerosol profiles. The correlation between the retrieved and input aerosol profiles was high, with a correlation coefficient R > 0.99. The aerosol profiles retrieved from the Lidar profile at 100 and 200 m resolutions as input closely matched the Lidar aerosol profiles, consistent with the simulation result. However, aerosol profiles retrieved from MAX-DOAS measurements differed from the Lidar profiles due to the influence of the averaging kernel matrix smoothing, the different location and viewing geometry, and uncertainties associated with the Lidar profiles. Next, NO2 profiles of different vertical resolutions were used as input profiles to retrieve the NO2 profiles under a single aerosol profile scenario. The effect of the vertical resolution on the retrieval of NO2 profiles was found to be less significant compared to aerosol retrievals. Using the Lidar aerosol profile as the a priori aerosol information had little effect on NO2 profile retrieval. Additionally, the retrieved aerosol profiles and aerosol optical depths varied under different EAs. Ten EAs (i.e., 1, 2, 3, 4, 5, 6, 8, 15, 30, and 90°) were found to obtain more information from observations. [ABSTRACT FROM AUTHOR]

Path planning is the core technology to realize mobile robot navigation. The enhanced A* algorithm with a time elastic band method (TEB) is utilized to aim at the collision problem in a complex environment. A grid-based method transfers the complex environment to a simple grid-based map. The mobile robot's position is determined based on information from the given maps. Optimizing the search point strategy and removing redundant path points reduces the path length and computational scale. The approach yields a safe trajectory in the local path using a time elastic band. The collision cost function combined with the preview deviation angle tracking method ensures the minimum collision-free distance to obstacles and the shortest path. Furthermore, the third-degree B-spline curve will improve the performance of the mobile robot path at the steering angles. Simulated results illustrate the correctness of the proposed method. [ABSTRACT FROM AUTHOR]

The European Alps formed at the boundary between the Eurasian plate and Adriatic microplate within a complex system of collision and subduction. However, the large‐scale three‐dimensional mantle‐flow field related to the underlying geodynamic processes has not yet been resolved in detail. In this study, we present the first comprehensive analysis of layered anisotropy for the complete Alpine range from shear‐wave splitting measurements at 591 seismic stations of the AlpArray experiment. Our findings suggest a combination of asthenospheric and distinct lithospheric contributions to the splitting observations, which can be seen as a generalization of previously reported models of single‐layer anisotropy. The enhanced vertical resolution exposes the impact of successive Mediterranean tectonic episodes, such as the opening of the Provençal‐Ligurian and Tyrrhenian Basins alongside the Adriatic slab retreat, as well as the Pannonian Basin opening and the Aegean slab retreat, resulting in deformation of the lithosphere and flow in the asthenospheric mantle. The dominant role of the larger scale Mediterranean subduction systems on mantle dynamics becomes evident. The observations provide supporting evidence that the Eurasian slab has broken off at its boundaries and that the resulting gaps channel flow from the mantle beneath the Eurasian plate to the Adriatic and Aegean subduction systems. The results provide new constraints on geodynamic processes involved in forming the European Alps, as previous tectonic episodes are preserved in the anisotropic fabric of the lithosphere‐asthenosphere system. This raises new questions regarding their geochemical and geophysical conditions, and their larger‐scale impact on the formation of the Alpine orogeny. Plain Language Summary: The European Alps are located along the contact of the Eurasian continental plate to the North and the Adriatic plate to the South. This zone is subject of a complicated history of their collision, in which the rigid plates are consumed into the more flexible and softer underlying mantle. In this work, we look at seismic anisotropy which describes the property of rocks to allow body waves to travel with different speeds when passing through the rock at different directions. This is mostly produced by a flow of softer rock beneath the rigid outer shell of the Earth. In our analysis of anisotropy, we also allow for its change with depth. We find that the anisotropy is not only produced by flow, but in part also by separate volumes of the rigid outer shell. This is a result from a history of deformation. While the location of the Eurasian and Adriatic plates remains unchanged, heavy parts of the plates descent. As a result, the plates are stretched forming the thinned Liguro‐Provençal and Pannonian Basin. In addition, the descending Eurasian plate is breaking off at its boundaries, which allows the softer rock at larger depth to flow through the resulting gaps. Key Points: This study presents the first comprehensive analysis of layered anisotropy for the entire Alpine range based on shear‐wave splittingThe anisotropy patterns within the asthenosphere and lithosphere suggest a relation to large‐scale Mediterranean tectonic processesOur findings allow discrimination between subduction‐controlled asthenospheric flow and tectonic deformation of the lithosphere [ABSTRACT FROM AUTHOR]

In this work, we show that van der Waals molecules X–RG (where RG is the rare gas atom) may be created through direct three-body recombination collisions, i.e., X + RG + RG → X–RG + RG. In particular, the three-body recombination rate at temperatures relevant for buffer gas cell experiments is calculated via a classical trajectory method in hyperspherical coordinates [Pérez-Ríos et al., J. Chem. Phys. 140, 044307 (2014)]. As a result, it is found that the formation of van der Waals molecules in buffer gas cells (1 K ≲ T ≲ 10 K) is dominated by the long-range tail (distances larger than the LeRoy radius) of the X–RG interaction. For higher temperatures, the short-range region of the potential becomes more significant. Moreover, we notice that the rate of formation of van der Walls molecules is of the same order of the magnitude independent of the chemical properties of X. As a consequence, almost any X–RG molecule may be created and observed in a buffer gas cell under proper conditions. [ABSTRACT FROM AUTHOR]

The inelastic scattering dynamics of the isobaric molecules, naphthalene (C10H8) and 2-octanone (C8H16O), on highly oriented pyrolytic graphite (HOPG) have been investigated as part of a broader effort to inform the inlet design of a mass spectrometer for the analysis of atmospheric gases during a flyby mission through the atmosphere of a planet or moon. Molecular beam–surface scattering experiments were conducted, and the scattered products were detected with the use of a rotatable mass spectrometer detector. Continuous, supersonic beams were prepared, with average incident translational energies, ⟨Ei⟩, of 247.3 kJ mol−1 and 538.2 kJ mol−1 for naphthalene and 268.6 kJ mol−1 and 433.8 kJ mol−1 for 2-octanone. These beams were directed toward an HOPG surface, held at 530 K, at incident angles, θi, of 30°, 45°, and 70°, and scattered products were detected as functions of their translational energies and scattering angles. The scattering dynamics of both molecules are very similar and mimic the scattering of atoms and small molecules on rough surfaces, where parallel momentum is not conserved, suggesting that the dynamics are dominated by a corrugated interaction potential between the incident molecule and the surface. The effective corrugation of the molecule–surface interaction is apparently caused by the structure of the incident molecule and the consequent myriad available energy transfer pathways between the molecule and the surface during a complex collision event. In addition, the HOPG surface contributes to the corrugation of the interaction potential because it can absorb significant energy from collisions with incident molecules that have high mass and incident energy. Small differences in the scattering dynamics of the two molecules are inferred to arise from the details of the molecule–surface interaction potential, with 2-octanone exhibiting dynamics that suggest a slightly stronger interaction with the surface than naphthalene. These results add to a growing body of work on the scattering dynamics of organic molecules on HOPG, from which insight into the hypervelocity sampling and analysis of such molecules may be obtained. [ABSTRACT FROM AUTHOR]

In this paper, we present a GPU algorithm for finite element hyperelastic simulation. We show that the interior-point method, known to be effective for robust collision resolution, can be coupled with non-Newton procedures and be massively sped up on the GPU. Newton's method has been widely chosen for the interior-point family, which fully solves a linear system at each step. After that, the active set associated with collision/contact constraints is updated. Mimicking this routine using a non-Newton optimization (like gradient descent or ADMM) unfortunately does not deliver expected accelerations. This is because the barrier functions employed in an interior-point method need to be updated at every iteration to strictly confine the search to the feasible region. The associated cost (e.g., per-iteration CCD) quickly overweights the benefit brought by the GPU, and a new parallelism modality is needed. Our algorithm is inspired by the domain decomposition method and designed to move interior-point-related computations to local domains as much as possible. We minimize the size of each domain (i.e., a stencil) by restricting it to a single element, so as to fully exploit the capacity of modern GPUs. The stencil-level results are integrated into a global update using a novel hybrid sweep scheme. Our algorithm is locally second-order offering better convergence. It enables simulation acceleration of up to two orders over its CPU counterpart. We demonstrate the scalability, robustness, efficiency, and quality of our algorithm in a variety of simulation scenarios with complex and detailed collision geometries. [ABSTRACT FROM AUTHOR]

Non-covalent interactions such as van der Waals interactions and hydrogen bonds are crucial for the chiral induction and control of molecules, but it remains difficult to study them at the single-molecule level. Here, we report a carbene molecule on a copper surface as a prototype of an anchored molecule with a facile chirality change. We examine the influence of the attractive van der Waals interactions on the chirality change by regulating the tip-molecule distance, resulting in an excess of a carbene enantiomer. Our model study provides insight into the change of molecular chirality controlled by van der Waals interactions, which is fundamental for understanding the mechanisms of chiral induction and amplification. The control of molecular chirality is of great interest in stereochemistry and biochemistry. Here, the authors show how to alter the chirality dynamics of a single molecule through tip-induced van der Waals interactions. [ABSTRACT FROM AUTHOR]

We used stochastic simulations and experimental data from E. coli, K. aerogenes, Synechococcus PCC 7002 and Synechocystis PCC 6803 to provide evidence that transcriptional interference via the collision mechanism is likely a prevalent mechanism for bacterial gene regulation. Rifampicin time-series data can be used to globally monitor and quantify collision between sense and antisense transcription-complexes. Our findings also highlight that transcriptional events, such as differential RNA decay, partial termination, and internal transcriptional start sites often deviate from gene annotations. Consequently, within a single gene annotation, there exist transcript segments with varying half-lives and transcriptional properties. To address these complexities, we introduce 'rifi', an R-package that analyzes transcriptomic data from rifampicin time series. 'rifi' employs a dynamic programming-based segmentation approach to identify individual transcripts, enabling accurate assessment of RNA stability and detection of diverse transcriptional events. RNA time-series data using rifampicin (an inhibitor of transcription initiation) give insight into transcriptional interference, e.g. by sense/asRNA complex collision, and other features of RNA. The R-package rifi analyses these complex data. [ABSTRACT FROM AUTHOR]

By using CCSD(T) and EOM-CCSD methods together with quasirelativistic energy-consistent small-core pseudopotentials and large atom-centered basis sets as well as bond functions, the potential energy curves (PECs) for the ground state and several low-lying singlet excited states of the van der Waals molecular systems between cadmium atom interacting with RG atoms (RG = He, Ne, Ar, Kr, Xe and Rn) are obtained. The dispersion coefficients of ground state for Cd-RG have been computed. And the spectroscopic constants of the bound states of Cd-RG molecules have been calculated, the spectroscopic constants of ground state and C1Π state of Cd-RG complexes are in reasonable agreement with the available theoretical and experimental results; the vertical excitation energies of singlet low-lying excited states are also obtained. And the transition dipole moments (TDMs) of (3)1Σ+-X1Σ+ and (4)1Σ+-X1Σ+ transitions are discussed, which would be helpful to understand the transition properties of Cd-RG complex. Furthermore, frequencies of vibrational transitions, rotational constants, Franck-Condon factors (FCFs) of C1Π-X1Σ+ transition and oscillator strengths of Cd-RG have also been acquired. The present work would be of value to understand on the electronically excited states of Cd-RG molecule, especially the electronic structure and spectroscopic characteristics of the singlet excited states. [ABSTRACT FROM AUTHOR]

For an integer k ≥ 2, let S(1); S(2);: ::; S(k) be k independent simple symmetric random walks on Z. A pair (n; z) is called a collision event if there are at least two distinct random walks, namely, S(i); S(j) satisfying S(i) n = S(j) n = z. We show that under the same scaling as in Donsker's theorem, the sequence of random measures representing these collision events converges to a nontrivial random measure on [0; 1]xR. Moreover, the limit random measure can be characterized using Wiener chaos. The proof is inspired by methods from statistical mechanics, especially, by a partition function that has been developed for the study of directed polymers in random environments. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The research on decision-making models of ship collision avoidance is confronted with numerous challenges. These challenges encompass inadequate consideration of complex factors, including but not limited to open water scenarios, the absence of static obstacle considerations, and insufficient attention given to avoiding collisions between manned ships and MASSs. A decision model for MASS collision avoidance is proposed to overcome these limitations by integrating the strengths of model-based and model-free methods in reinforcement learning. This model incorporates S-57 chart information, AIS data, and the Dyna framework to improve effectiveness. (1) When the MASS's navigation task is known, a static navigation environment is built based on S-57 chart information, and the Voronoi diagram and improved A* algorithm are used to obtain the energy-saving optimal static path as the planned sea route. (2) Given the small main dimensions of an MASS, which is easily affected by wind and current factors, the motion model of an MASS is established based on the MMG model considering wind and current factors. At the same time, AIS data are used to extract the target ship (manned ship) data. (3) According to the characteristics of the actual navigation of ships at sea, the state space, action space, and reward function of the reinforcement learning algorithm are designed. The MASS collision avoidance decision model based on the Dyna-DQN model is established. Based on the DQN algorithm, the agent (MASS) and the environment interact continuously, and the actual interaction data generated are used for the iterative update of the collision avoidance strategy and the training of the environment model. Then, the environment model is used to generate a series of simulated empirical data to promote the iterative update of the strategy. Using the waters near the South China Sea as the research object for simulation verification, the navigation tasks are divided into three categories: only considering static obstacles, following the planned sea route considering static obstacles, and following the planned sea route considering both static and dynamic obstacles. The results show that through repeated simulation experiments, an MASS can complete the navigation task without colliding with static and dynamic obstacles. Therefore, the proposed method can be used in the intelligent collision avoidance module of MASSs and is an effective MASS collision avoidance method. [ABSTRACT FROM AUTHOR]

Fast and accurate treatment of collisions in the context of modern N -body planet formation simulations remains a challenging task due to inherently complex collision processes. We aim to tackle this problem with machine learning (ML), in particular via residual neural networks. Our model is motivated by the underlying physical processes of the data-generating process and allows for flexible prediction of post-collision states. We demonstrate that our model outperforms commonly used collision handling methods such as perfect inelastic merging and feed-forward neural networks in both prediction accuracy and out-of-distribution generalization. Our model outperforms the current state of the art in 20/24 experiments. We provide a data set that consists of 10164 Smooth Particle Hydrodynamics (SPH) simulations of pairwise planetary collisions. The data set is specifically suited for ML research to improve computational aspects for collision treatment and for studying planetary collisions in general. We formulate the ML task as a multi-task regression problem, allowing simple, yet efficient training of ML models for collision treatment in an end-to-end manner. Our models can be easily integrated into existing N -body frameworks and can be used within our chosen parameter space of initial conditions, i.e. where similar-sized collisions during late-stage terrestrial planet formation typically occur. [ABSTRACT FROM AUTHOR]

Space debris represent a threat to satellites in orbit around Earth. In the case of impact, satellites can be subjected to damage spanning from localized craterization to subsystem failure, to complete loss of the vehicle; large collision events may lead to fragmentation of the spacecraft. Simulating and testing debris impacts may help in understanding the physics behind these events, modelling the effects, and developing dedicated protection systems and mitigation strategies. In this context, the Space Debris group at the University of Padova investigates in-space collisions with experimental campaigns performed in a dedicated Hypervelocity Impact Facility and with numerical simulations with commercial and custom software. In this paper, an overview is given of the last 10 years of research activities performed at the University of Padova. First, the hypervelocity impact testing facility is described and the main experimental campaigns performed in the last few years are summarized. The second part of this work describes impact modelling research advances, focusing on the simulation of complex collision scenarios. [ABSTRACT FROM AUTHOR]

Ship motion planning is a core issue of autonomous navigation for maritime autonomous surface ships (MASS). This paper proposes a novel model predictive artificial potential field (MPAPF) motion planning method for complex encounter scenarios considering collision avoidance rules. A new ship domain is established, in which a closed interval potential field function is designed to represent the inviolable properties of the ship domain. A Nomoto model with a predefined speed during motion planning is adopted to generate followable paths conforming to the ship kinematics. To solve the local optima problem of traditional artificial potential field (APF) method and guarantee the collision avoidance safety in complex encounter scenarios, a motion planning method based on model predictive strategy and artificial potential field, i.e., MPAPF, is proposed. In this method, the ship motion planning problem is transformed to a non-linear optimization problem with multiple constraints including maneuverability, navigation rules, navigable waterway, etc. Simulation results from 4 case studies show that the proposed MPAPF algorithm can solve the problems above and generate feasible motion paths to avoid ship collision in complex encounter scenarios compared to variants of APF, A-star and rapidly-exploring random trees (RRT). • Path planning is converted to a non-linear receding optimization problem. • An eccentric ship domain conforming to COLREGs rules is generated. • A new APF function for different types of encounter obstacles is proposed. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) radicals are ubiquitous chemical intermediates present in the atmosphere and in combustion processes, where laser-induced fluorescence is extensively used on the NO (A2Σ+ ← X2Π) band to report on fuel-burning properties. However, accurate fluorescence quantum yields and NO concentration measurements are impeded by electronic quenching of NO (A2Σ+) to NO (X2Π) with colliding atomic and molecular species. To improve predictive combustion models and develop a molecular-level understanding of NO (A2Σ+) quenching, we report the velocity map ion images and product state distributions of NO (X2Π, v″ = 0, J″, Fn, Λ) following nonreactive collisional quenching of NO (A2Σ+) with molecular oxygen, O2 (X3Σg−). A novel dual-flow pulse valve nozzle is constructed and implemented to carry out the NO (A2Σ+) electronic quenching studies and to limit NO2 formation. The isotropic ion images reveal that the NO–O2 system evolves through a long-lived NO3 collision complex prior to formation of products. Furthermore, the corresponding total kinetic energy release distributions support that O2 collision coproducts are formed primarily in the c1Σu− electronic state with NO (X2Π, v″ = 0, J″, Fn, Λ). The product state distributions also indicate that NO (X2Π) is generated with a propensity to occupy the Π(A″) Λ-doublet state, which is consistent with the NO π* orbital aligned perpendicular to nuclear rotation. The deviations between experimental results and statistical phase space theory simulations illustrate the key role that the conical intersection plays in the quenching dynamics to funnel population to product rovibronic levels. [ABSTRACT FROM AUTHOR]