Collisional Fragmentation Research Articles

Numerical simulations on effects of turbulence on the size spectrum of sinking particles in ocean surface boundary layer

Sinking particles in the ocean play a crucial role in the climate system by transporting materials, such as carbon, deep into the ocean. The amount of this transport is influenced by the net sinking speed of the particles and the amount of material attached to them, both of which are determined by the size spectrum of the particles. The spectrum is shaped by aggregation and disaggregation processes, which are typically most active in the ocean surface boundary layer (OSBL), where intense turbulent flows can enhance both particle collision (aggregation) and particle fragmentation (disaggregation). This study aims to reveal the mechanism by which turbulence transforms the size spectrum through these competing processes and to determine whether turbulence alters the downward material transport from the OSBL. To achieve this, we performed large-eddy simulations to reproduce wind- and wave-induced turbulent flows, employing a Lagrangian particle model to track passive particles in the flow and simulate their aggregation and disaggregation. The model tracked groups of particles rather than individual ones. The results revealed that the shape of the simulated size spectrum was characterized by two length scales, the compensation radius (characterizing the particle floatability) and the Kolmogorov scale, which define the shear range where the turbulent shear shapes the spectrum, the sinking range where the gravitational sinking of particles shapes the spectrum, and the transition range between them. The findings revealed that turbulence tends to increase the terminal velocity and decrease the specific surface area of sinking particles when turbulent aggregation dominates over disaggregation, and vice versa. Although these results may be influenced by uncertain parameterizations (e.g., disaggregation parameterization), the study demonstrates the effectiveness of the numerical approach in investigating the fundamental processes governing particle sinking in turbulent flows.

On the Local Formation of the TRAPPIST-1 Exoplanets

The discovery of seven approximately Earth-mass planets orbiting the 0.09 M ⊙ M dwarf TRAPPIST-1 captivated the public and sparked a proliferation of investigations into the system’s origins. Among other properties, the resonant architecture of the planets has been interpreted to imply that orbital migration played a dominant role in the system’s early formation. If correct, this hypothesis could imply that all of the seven worlds formed far from the star, and might harbor enhanced inventories of volatile elements. However, multiple factors also contradict this interpretation. In particular, the planets’ apparent rocky compositions and nonhierarchical mass distribution might be evidence that they formed closer to their current orbital locations. In this paper, we investigate the latter possibility with over 600 accretion simulations that model the effects of collisional fragmentation. In addition to producing multiple TRAPPIST-like configurations, we experiment with a number of different models for tracking the evolution of the planets’ volatile contents and bulk iron-to-silicate ratios. We conclude that a trend in bulk iron contents is the more likely explanation for the observed radial trend of decreasing uncompressed densities in the real system. Given the degree of radial mixing that occurs in our simulations, in most cases we find that all seven planets finish with similar volatile contents. Another confounding quality of the TRAPPIST-1 system is the fact that the innermost planets are not in first-order resonances with one another. By applying a tidal migration model to our most promising accretion model results, we demonstrate cases where higher-order resonances are populated.

Fragmentation in Collisions of Snow with Graupel/Hail: New Formulation from Field Observations

Abstract Secondary ice production (SIP) has been attributed to the generation of most ice particles observed in precipitating clouds with cloud tops warmer than −36°C, from various aircraft- and ground-based field observations across the globe. One of the known SIP mechanisms is fragmentation during collisions among ice particles. It has been studied with our theoretical formulation, which has been applied in microphysical schemes of atmospheric models in a few studies. These have predicted an extensive impact on cloud glaciation and radiative properties. However, there has been a lack of experimental field studies, especially involving naturally falling snowflakes, to better understand this particular mechanism of SIP. This study reports the first field measurements with modern technology for fragmentation during collisions between naturally falling snowflakes and graupel/hail particles. This was observed with an innovatively designed portable chamber that was deployed outdoors in northern Sweden. Applying the observations from this field-based study, we optimized the existing formulation for predicting numbers of fragments from collisions of snow with graupel/hail. The observations show the average numbers of fragments per collision for dendritic (3–12 mm) and nondendritic (1–3 mm) snow were about 12 and 1, respectively. This represents a boost of predicted fragment numbers relative to our original formulation published in 2017. The updated formulation for breakup in ice–ice collisions can be implemented in the microphysical schemes of atmospheric models.

An analytic approach for nonlinear collisional fragmentation model arising in bubble column

The phenomenon of coagulation and breakage of particles plays a pivotal role in diverse fields. It aids in tracking the development of aerosols and granules in the pharmaceutical sector, coagulation or breakage of droplets in chemical engineering, understanding blood clotting mechanisms in biology, and facilitating cheese production through the action of enzymes within the dairy industry. A significant portion of research in this direction concentrates on coagulation or linear breakage processes. In the case of linear case, bubble particles break down due to inherent stresses or specific conditions of the breakage event. However, in many practical situations, particle division is primarily due to forces exerted during collisions between particles, necessitating an approach that accounts for nonlinear collisional breakage. Despite its critical role in a wide array of engineering and physical operations, the study of this nonlinear fragmentation phenomenon has not been extensively pursued. This article introduces an innovative semi-analytical method that leverages the beyond linear use of equation superposition function to address the nonlinear integro-partial differential model of collisional breakage population balance. This approach is versatile, allowing for the resolution of both linear/nonlinear equations while sidestepping the complexities associated with discretization of domain. To assess the precision of this method, we conduct a thorough convergence analysis. This process utilizes the principle of contractive mapping in the Banach space, a globally recognized strategy for verifying convergence. We explore a variety of kernel parameters associated with collisional kernels, alongside breakage and initial distribution functions, to derive novel iterative solutions. Comparing our findings with those obtained through the finite volume method regarding number density functions and their integral moments, we demonstrate the reliability and accuracy of our approach. The consistency and correctness of our method are further validated by depicting the errors between the exact and approximated solutions in graphical and tabular formats.

Dust evolution during a protostellar collapse: Influence on the coupling between the neutral gas and magnetic field

Context. The extent of the coupling between the magnetic field and the gas during the collapsing phase of star-forming cores is strongly affected by the dust size distribution, which is expected to evolve by means of coagulation, fragmentation, and other collision outcomes. Aims. We aim to investigate the influence of key parameters on the evolution of the dust distribution, as well as on the magnetic resistivities during protostellar collapse. Methods. We performed a set of collapsing single-zone simulations with shark. The code computes the evolution of the dust distribution, accounting for different grain growth and destruction processes, with the grain collisions being driven by brownian motion, turbulence, and ambipolar drift. It also computes the charges carried by each grain species and the ion and electron densities, as well as the magnetic resistivities. Results. We find that the dust distribution significantly evolves during the protostellar collapse, shaping the magnetic resistivities. The peak size of the distribution, population of small grains, and, consequently, the magnetic resistivities are controlled by both coagulation and fragmentation rates. Under standard assumptions, the small grains coagulate very early as they collide by ambipolar drift, yielding magnetic resistivities that are many orders of magnitude apart from the non-evolving dust case. In particular, the ambipolar resistivity, ηAD, is very high prior to nH = 1010 cm−3. As a consequence, magnetic braking is expected to be ineffective. In this case, large size protoplanetary discs should result, which is inconsistent with recent observations. To alleviate this tension, we identified mechanisms that are capable of reducing the ambipolar resistivity during the ensuing protostellar collapse. Among them, electrostatic repulsion and grain-grain erosion feature as the most promising approaches. Conclusions. The evolution of the magnetic resistivities during the protostellar collapse and consequently the shape of the magnetic field in the early life of the protoplanetary disc strongly depends on the possibility to repopulate the small grains or to prevent their early coagulation. Therefore, it is crucial to better constrain the collision outcomes and the dust grain’s elastic properties, especially the grain’s surface energy based on both theoretical and experimental approaches.

Nonuniversality of heavy quark hadronization in elementary high-energy collisions

It has been traditionally hypothesized that the heavy quark (charm c and bottom b) fragmentation is universal across different collision systems, based on the notion that hadronization as a soft process should occur at the characteristic nonperturbative quantum chromodynamics (QCD) scale, ΛQCD. However, this universality hypothesis has recently been challenged by the observation that the c- and b-baryon production relative to their meson counterparts in minimum bias proton-proton (pp) collisions at the CERN Large Hadron Collider (LHC) energies is significantly enhanced as compared to the electron-positron (e+e−) collisions. The conception of nonuniversality is unambiguously reinforced by the latest measurement of the charged-particle multiplicity dependence of the b-baryon–to–meson yield ratio, Λb/B, by the LHCb experiment in s=13TeVpp collisions at the LHC, evolving continuously from the saturation value in minimum bias pp collisions toward the small value in e+e− collisions as the system size gradually reduces. We address the multiplicity dependence of b-baryon production in the canonical statistical hadronization model with input b-hadron spectrum augmented with many hitherto unobserved states from quark model predictions. We demonstrate that the decreasing trend of the Λb/B toward low multiplicities can be quantitatively understood from the canonical suppression on the yield of Λb, as caused by the requirement of strict conservation of baryon number in sufficiently small systems. We have therefore proposed a plausible scenario for understanding the origin of the nonuniversality of heavy quark fragmentation in elementary collisions. Published by the American Physical Society 2024

Compaction during fragmentation and bouncing produces realistic dust grain porosities in protoplanetary discs

Context. In protoplanetary discs, micron-sized dust grows to form millimetre- to centimetre-sized pebbles but encounters several barriers during its evolution. Collisional fragmentation and radial drift impede further dust growth to planetesimal size. Fluffy grains have been hypothesised to solve these problems. While porosity leads to faster grain growth, the implied porosity values obtained from previous simulations were larger than suggested by observations. Aims. In this paper, we study the influence of porosity on dust evolution, taking into account growth, bouncing, fragmentation, compaction, rotational disruption, and snow lines, in order to understand their impact on dust evolution. Methods. We developed a module for porosity evolution for the 3D smoothed particle hydrodynamics code PHANTOM that accounts for dust growth and fragmentation. This mono-disperse model is integrated into both a 1D code and the 3D code to capture the overall evolution of dust and gas. Results. We show that porosity helps dust growth and leads to the formation of larger solids than when considering compact grains, as predicted by previous work. Our simulations taking into account compaction during fragmentation show that large millimetre grains are still formed but are ten to 100 times more compact. Thus, millimetre sizes with typical filling factors of ~0.1 match the values measured on comets or via polarimetric observations of protoplanetary discs.

Crust and Upper Mantle of the South China Sea (probabilistic-deterministic gravity model)

Rheological layering of a tectonosphere of the South China Sea (SCS) on the crust rigid (the depth interval of 5–30 km), viscous subcrustal (the depth interval of 30–70 km), rigid lower lithospheric (50–90 km), astenospheric (80–150 km) and rigid subastenospheric (the depth interval is more than 150 km) is established. Distributions of the density inhomogeneities connecting with the main tectonic events in SCS are caused by the Paleo-Pacific’s convergence, and later — the Philippine’a oceanic plate with the Philippine archipelago and further — with the Asian margin. In this zone by distributions of density contrast in a tectonosphere are tracing Cenozoic processes of a subduction, stretching, transformic shift and structure of the central type of the probable plume nature which form an evolutionary sequence: back arc, or paleo-oceanic spreading → the Philippine subduction → NE-stretching with shift → formation of the structure of the central type of a probable plume origin. The structures caused by convergence of the Asian continent with the Indo-Australian plate are isolated from the West Pacific margin, and the underthrsting of rigid lithospheric plates from the South under a lithosphere of the margin sea reflects traces of more ancient collision of fragments of the Gondwana with Asian continent.

Biodiversity on the line: life cycle impact assessment of power lines on birds and mammals in Norway

The global shift towards renewable energy plays an important role in fighting climate change. To facilitate the global growth of renewable energy production, the expansion of the electric grid becomes inevitable. Yet further construction of power lines poses a risk to biodiversity. Power lines traverse natural habitats and can lead to habitat conversion, fragmentation, and loss. Moreover, due to collisions and electrocutions, power lines kill hundreds of millions of birds each year. These impacts, however, have so far not been incorporated into decision-making. Life cycle assessment (LCA) is a widely used framework to compare environmental impacts and support decision-makers in planning and promoting sustainable strategies. We adapted existing life cycle impact assessment (LCIA) models to quantify the three main impacts of power lines on biodiversity: collision, electrocution, and habitat conversion and fragmentation. Our models incorporated species-area and species-habitat relationships to assess the effects of power lines on the diversity of birds and non-flying mammals in Norway, as the country is currently committed to reducing its emissions by expanding its renewable energy capacity. Overall, habitat conversion and fragmentation had the highest impact across the three impact categories, particularly affecting mammal richness. Furthermore, distribution lines often affected species richness more than transmission lines. The effect of the three impact pathways varied among different species groups, highlighting the vulnerability of certain species to habitat change, collision, and electrocution. Integrating LCIA models that quantify the impacts of power lines on biodiversity into LCA can support decision-makers with tools to promote the development of the electric grid without overlooking its effect on species richness. In addition, our models set the stage for a comprehensive assessment of the effects of electricity generation and transmission on biodiversity.

Heavy quark fragmentation in e+e− collisions to NNLO+NNLL accuracy in perturbative QCD

Fragmentation of heavy quarks into heavy-flavoured hadrons receives both perturbative and non-perturbative contributions. We consider perturbative QCD corrections to heavy quark production in e+e− collisions to next-to-next-to-leading order accuracy in QCD with next-to-next-to-leading-logarithmic resummation of quasi-collinear and soft emissions. We study multiple matching schemes, and multiple regularisations of the soft resummation, and observe a significant dependence of the perturbative results on these ingredients, suggesting that NNLO+NNLL perturbative accuracy may not lead to real gains unless the interface with non-perturbative physics is properly analysed. We confirm previous evidence that D*+ experimental data from CLEO/BELLE and from LEP are not reconcilable with perturbative predictions employing standard DGLAP evolution. We extract non-perturbative contributions from e+e− experimental data for both D and B meson fragmentation. Such contributions can be used to predict heavy-quark fragmentation in other processes, e.g. DIS and proton-proton collisions.

Operational Angular Track Reconstruction in Space Surveillance Radars through an Adaptive Beamforming Approach

In the last few years, many space surveillance initiatives have started to consider the problem represented by resident space object overpopulation. In particular, the European Space Surveillance and Tracking (EUSST) consortium is in charge of providing services like collision avoidance, fragmentation analysis, and re-entry, which rely on measurements obtained through ground-based sensors. BIRALES is an Italian survey radar belonging to the EUSST framework and is capable of providing measurements including Doppler shift, slant range, and angular profile. In recent years, the Music Approach for Track Estimate and Refinement (MATER) algorithm has been developed to retrieve angular tracks through an adaptive beamforming technique, guaranteeing the generation of more accurate and robust measurements with respect to the previous static beamforming approach. This work presents the design of a new data processing chain to be used by BIRALES to compute the angular track. The signal acquired by the BIRALES receiver array is down-converted and the receiver bandwidth is split into multiple channels, in order to maximize the signal-to-noise ratio of the measurements. Then, the signal passes through a detection block, where an isolation procedure creates, for each epoch, signal correlation matrices (CMs) related to the channels involved in the detection and then processes them to isolate the data stream related to a single detected source. Consequently, for each epoch and for each detected source, just the CM featuring the largest signal contribution is kept, allowing deriving the Doppler shift measurement from the channel illumination sequence. The MATER algorithm is applied to each CM stream, first estimating the signal directions of arrival, then grouping them in the observation time window, and eventually returning the target angular track. Ambiguous estimates may be present due to the configuration of the receiver array, which cause spatial aliasing phenomena. This problem can be addressed by either exploiting transit prediction (in the case of cataloged objects), or by applying tailored criteria (for uncatalogued objects). The performance of the new architecture was assessed in real operational scenarios, demonstrating the enhancement represented by the implementation of the channelization strategy, as well as the angular measurement accuracy returned by MATER, in both nominal and off-nominal scenarios.

Impact of aeolian erosion on dust evolution in protoplanetary discs

Context. Many barriers prevent dust from forming planetesimals via coagulation in protoplanetary discs, such as bouncing, collisional fragmentation, or aeolian erosion. Modelling dust and the different phenomena that can alter its evolution is therefore necessary. Multiple solutions have been proposed, but they still need to be confirmed. Aims. In this paper, we explore the role that aeolian erosion plays in the evolution of dust. Methods. We used a mono-disperse model to account for dust growth and fragmentation, implemented in a 1D code to compute the evolution of single grains and in a 3D smoothed particle hydrodynamics (SPH) code to compute the global evolution of dust and gas. We tested the erosion model in our code and ensured it matched previous results. Results. With a disc model that reproduces observations, we show with both 1D and 3D studies that erosion is not significant during the evolution of dust when we take fragmentation into consideration. With a low-viscosity disc, fragmentation is less of a problem, but grain growth is also less important, which prevents the formation of large objects. In dust traps, close to the star, erosion is also not impactful, even when fragmentation is turned off. Conclusions. We show in this paper that aeolian erosion is negligible when radial drift, fragmentation, and dust traps are taken into account and that it does not alter the dust evolution in the disc. However, it can have an impact on later stages, when the streaming instability forms large clumps close to the star, or when planetesimals are captured.

Dust-gas coupling in turbulence- and MHD wind-driven protoplanetary disks: Implications for rocky planet formation

The degree of coupling between dust particles and their surrounding gas in protoplanetary disks is quantified by the dimensionless Stokes number. The Stokes number (St) governs particle size and spatial distributions, in turn establishing the dominant mode of planetary accretion in different disk regions. In this paper, we model the characteristic St of particles across time in disks evolving under both turbulent viscosity and magnetohydrodynamic (MHD) disk winds. In both turbulence- and wind-dominated disks, we find that collisional fragmentation is the limiting mechanism of particle growth. The water-ice sublimation line constitutes a critical transition point in dust settling, drift, and size regimes. For a fiducial disk evolution parameter α̃≃10−3, silicate particles inteior to the ice-line are characterized by low St (≲10−2) and sizes in the sub-mm- to 1cm-scale. Icy particles/boulders beyond the ice-line are characterized by high St (≳10−2) and sizes in the cm to dm size range. Hence, icy particles settle into a thin layer at the outer disk midplane and drift inward at velocities exceeding the gaseous accretionary flow due to substantial headwind drag. Silicate particles in the inner disk remain relatively well dispersed and are to a large extent advected inward with their surrounding gas.The St dichotomy across the ice-line translates to distinct planet formation pathways between the inner and outer disk. While pebble accretion proceeds slowly for rocky embryos within the ice-line (across most of parameter space), it does so rapidly for volatile-rich embryos beyond it, allowing for the growth of giant planet cores before disk dissipation. Through simulations of rocky planet growth, we evaluate the competition between pebble accretion and classical pairwise collisions between planetesimals. We conclude that the dominance of pebble accretion can only be realized in disks that are driven by MHD winds, slow-evolving (α̃≲10−3.5), and devoid of pressure maxima that may concentrate solids and give rise of planetesimal rings in which classical growth is enhanced. Such disks are extremely quiescent, with Shakura-Sunyaev turbulence parameters αν≲10−4. We conclude that for most of parameter space corresponding to values of αν reflected in observations of protoplanetary disks (≳10−4), pairwise planetesimal collisions constitute the dominant pathway of rocky planet accretion. Our results are discussed in the context of super-Earth origins, and lend support to the emerging view that they formed in planetesimal rings. Moreover, these results argue against a significant contribution (≳ 10%) of outer disk, carbonaceous material to the proto-Earth in the form of pebbles, in agreement with chemical and isotopic investigations of Earth’s accretion history.

Overview of Spacecraft-Fragmentation Testing

Spacecraft fragmentation due to collisions with space debris is a major concern for space agencies and commercial entities, since in the next years the production of collisional fragments is expected to become the major source of space debris. Experimental studies have shown that the fragmentation process is highly complex and influenced by various factors, such as the satellite design, the material properties, the velocity and angle of the debris impact, and the point of collision (e.g., central, glancing, on spacecraft appendages). This paper summarizes the current state of research in spacecraft fragmentation, including the methods and techniques used to simulate debris impacts, the characterization of fragment properties and the analysis of the resulting debris cloud. It provides an overview of the main experiments performed, underlining the most critical issues observed. Moreover, it presents a set of experiments performed at the University of Padova and proposes some future directions for this research.

JWST Near-infrared Spectroscopy of the Lucy Jupiter Trojan Flyby Targets: Evidence for OH Absorption, Aliphatic Organics, and CO2

We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft—the Patroclus–Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7–5.3 μm reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 μm that is most prominent on the less-red objects Eurybates, Patroclus–Menoetius, and Polymele. An additional absorption feature at 3.3–3.6 μm, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 μm that we attribute to bound or trapped CO2. Comparisons with other solar system small bodies reveal broad similarities in the 2.7–3.6 μm bands with analogous features on Centaurs, Kuiper Belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7–3.6 μm absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans’ surfaces at the higher temperatures of the Jupiter region. The CO2 band manifested on the surface of Eurybates suggests that CO2 may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.

Characterization of PEGylation sites in Neulasta and a biosimilar candidate with a combined fragmentation strategy in mass spectrometry analysis.

In the development of biosimilar products to Neulasta, it is essential to determine the intact molecular mass and confirm precise PEGylation sites. In this study, we applied a combination of techniques, including post-column addition of triethylamine in reversed-phase liquid chromatography-mass spectrometry (RPLC-MS) to determine the intact molecular mass, and in-source fragmentation (ISF) and higher-energy collision dissociation-tandem mass spectrometry (HCD-MS/MS) to identify the PEGylation site. Our results show that both the pegfilgrastim biosimilar candidate and Neulasta lots are mono-PEGylated at the N-terminal end. Furthermore, we show that the combined ISF and HCD-MS/MS method can be used for identifying the PEGylation sites in the diPEGylated variant of pegfilgrastim. The diPEGylated variant has modification sites at the N-terminal end and a lysine at position 35 in the protein sequence.

Ultrastructural and glycoproteomic characterization of Prevotella intermedia: Insights into O-glycosylation and outer membrane vesicles.

Prevotella intermedia, a Gram-negative bacterium from the Bacteroidota phylum, is associated with periodontitis. Other species within this phylum are known to possess the general O-glycosylation system. The O-glycoproteome has been characterized in several species, including Tannerella forsythia, Porphyromonas gingivalis, and Flavobacterium johnsoniae. In our study, we used electron cryotomography (cryoET) and glycoproteomics to reveal the ultrastructure of P. intermedia and characterize its O-glycoproteome. Our cryoET analysis unveiled the ultrastructural details of the cell envelope and outer membrane vesicles (OMVs) of P. intermedia. We observed an electron-dense surface layer surrounding both cells and OMVs. The OMVs were often large (>200 nm) and presented two types, with lumens being either electron-dense or translucent. LC-MS/MS analyses of P. intermedia fractions led to the identification of 1655 proteins, which included 62 predicted T9SS cargo proteins. Within the glycoproteome, we identified 443 unique O-glycosylation sites within 224 glycoproteins. Interestingly, the O-glycosylation motif exhibited a broader range than reported in other species, with O-glycosylation found at D(S/T)(A/I/L/M/T/V/S/C/G/F/N/E/Q/D/P). We identified a single O-glycan with a delta mass of 1531.48 Da. Its sequence was determined by MS2 and MS3 analyses using both collision-induced dissociation and high-energy collisional dissociation fragmentation modes. After partial deglycosylation with trifluoromethanesulfonic acid, the O-glycan sequence was confirmed to be dHex-dHex-HexNAc (HPO3 -C6 H12 O5 )-dHex-Hex-HexA-Hex(dHex). Bioinformatic analyses predicted the localization of O-glycoproteins, with 73 periplasmic proteins, 53 inner membrane proteins, 52 lipoproteins, 26 outer membrane proteins, and 14 proteins secreted by the T9SS.

The evolution of collision debris near the ν6 secular resonance and its role in the origin of terrestrial water

ABSTRACT This work presents novel findings that broaden our understanding of the amount of water that can be transported to the Earth. The key innovation lies in the combined usage of smoothed particle hydrodynamics (SPH) and N-body codes to assess the role of collision fragments in water delivery. We also present a method for generating initial conditions that enables the projectile to impact at the designated location on the target’s surface with the specified velocity. The primary objective of this study is to simulate giant collisions between two Ceres-sized bodies by SPH near the ν6 secular resonance and follow the evolution of the ejected debris by numerical N-body code. With our method 6 different initial conditions for the collision were determined, and the corresponding impacts were simulated by SPH. Examining the orbital evolution of the debris ejected after collisions, we measured the amount of water delivered to the Earth, which is broadly 0.001 ocean equivalents of water, except in one case where one large body transported 7 per cent oceans of water to the planet. Based on this and taking into account the frequency of collisions, the amount of delivered water varies between 1.2 and 8.3 ocean’s worth of water, depending on the primordial disc mass. According to our results, the prevailing external pollution model effectively accounts for the assumed water content on the Earth, whether it’s estimated at 1 or 10 ocean’s worth of water.

Ab initio study of nuclear clustering in hot dilute nuclear matter

We present a systematic ab initio study of clustering in hot dilute nuclear matter using nuclear lattice effective field theory with an SU(4)-symmetric interaction. We introduce a method called light-cluster distillation to determine the abundances of dimers, trimers, and alpha clusters as a function of density and temperature. Our lattice results are compared with an ideal gas model composed of free nucleons and clusters. Excellent agreement is found at very low density, while deviations from ideal gas abundances appear at increasing density due to cluster-nucleon and cluster-cluster interactions. In addition to determining the composition of hot dilute nuclear matter as a function of density and temperature, the lattice calculations also serve as benchmarks for virial expansion calculations, statistical models, and transport models of fragmentation and clustering in nucleus-nucleus collisions.

Heavy-flavour production as a function of event activity in pp collisions with the ALICE experiment

Due to their large masses, the production of heavy-flavour quarks can be computed perturbatively, thus providing a powerful tool to test the corresponding QCD calculations. Additionally, measurements of heavy-flavour hadrons are useful to reveal the details of heavy-quark fragmentation in pp collisions at LHC energies. Event-activity-dependent measurements of heavy-flavour production may shed light on the mechanisms of interplay between soft and hard processes. In this contribution, we present recent measurements of the ALICE experiment on charm-hadron production as a function of charged-particle multiplicity in pp collisions at various energies, including the measurements of charm baryon-to-meson production yield ratios. New results of D-meson production as a function of the transverse spherocity of the event, as well as of the transverse event-activity classifier RT, are also presented.