Collisional Fragmentation Research Articles

1I/‘Oumuamua as an N2 Ice Fragment of an Exo‐Pluto Surface II: Generation of N2 Ice Fragments and the Origin of ‘Oumuamua

AbstractThe origin of the interstellar object 1I/‘Oumuamua has defied explanation. In a companion paper (Jackson & Desch, 2021), we show that a body of N2 ice with axes 45 m × 44 m × 7.5 m at the time of observation would be consistent with its albedo, nongravitational acceleration, and lack of observed CO or CO2 or dust. Here we demonstrate that impacts on the surfaces of Pluto‐like Kuiper belt objects (KBOs) would have generated and ejected ∼1014 collisional fragments—roughly half of them H2O ice fragments and half of them N2 ice fragments—due to the dynamical instability that depleted the primordial Kuiper belt. We show consistency between these numbers and the frequency with which we would observe interstellar objects like 1I/‘Oumuamua, and more comet‐like objects like 2I/Borisov, if other stellar systems eject such objects with efficiency like that of the Sun; we infer that differentiated KBOs and dynamical instabilities that eject impact‐generated fragments may be near‐universal among extrasolar systems. Galactic cosmic rays would erode such fragments over 4.5 Gyr, so that fragments are a small fraction (∼0.1%) of long‐period Oort comets, but C/2016 R2 may be an example. We estimate ‘Oumuamua was ejected about 0.4–0.5 Gyr ago, from a young (∼108 yr) stellar system, which we speculate was in the Perseus arm. Objects like ‘Oumuamua may directly probe the surface compositions of a hitherto‐unobserved type of exoplanet: “exo‐Plutos.” ‘Oumuamua may be the first sample of an exoplanet brought to us.

Anomeric Retention of Carbohydrates in Multistage Cyclic Ion Mobility (IMSn): De Novo Structural Elucidation of Enzymatically Produced Mannosides

Carbohydrates are complex structures that still challenge analysts today because of their different levels of isomerism, notably the anomerism of the glycosidic bond. It has been shown recently that anomerism is preserved upon gas-phase fragmentation and that high-resolution ion mobility (IMS) can distinguish anomers. However, these concepts have yet to be applied to complex biological products. We have used high-resolution IMS on a cyclic device to characterize the reaction products of Uhgb_MS, a novel mannoside synthase of the GH130 family. We designed a so-called IMSn sequence consisting of (i) separating and isolating specific IMS peaks, (ii) ejecting ions to a pre-array store cell depending on their arrival time, (iii) inducing collisional activation upon reinjection, and (iv) performing multistage IMS analysis of the fragments. First, we applied IMS2 sequences to purely linked α1,2- and β1,2-mannooligosaccharides, which provided us with reference drift times for fragments of known conformation. Then, we performed IMSn analyses of enzymatically produced mannosides and, by comparison with the references, we succeeded in determining the intrachain anomerism of a α1,2-mannotriose and a mix-linked β/α1,2-mannotetraose-a first for a crude biological medium. Our results show that the anomerism of glycosides is maintained through multiple stages of collisional fragmentation, and that standalone high-resolution IMS and IMSn can be used to characterize the intrachain anomerism in tri- and tetrasaccharides in a biological medium. This is also the first evidence that a single carbohydrate-active enzyme can synthesize both α- and β-glycosidic linkages.

On the scaling of fragmentation and energy dissipation in collisions of dust aggregates

Fragmentation of granular clusters may be studied by experiments and by granular mechanics simulation. When comparing results, it is often assumed that results can be compared when scaled to the same value of E/E_{mathrm{sep}}, where E denotes the collision energy and E_{mathrm{sep}} is the energy needed to break every contact in the granular clusters. The ratio E/E_{mathrm{sep}}propto v^2 depends on the collision velocity v but not on the number of grains per cluster, N. We test this hypothesis using granular-mechanics simulations on silica clusters containing a few thousand grains in the velocity range where fragmentation starts. We find that a good parameter to compare different systems is given by E/(N^{alpha }E_{mathrm{sep}}), where alpha sim 2/3. The occurrence of the extra factor N^{alpha } is caused by energy dissipation during the collision such that large clusters request a higher impact energy for reaching the same level of fragmentation than small clusters. Energy is dissipated during the collision mainly by normal and tangential (sliding) forces between grains. For large values of the viscoelastic friction parameter, we find smaller cluster fragmentation, since fragment velocities are smaller and allow for fragment recombination.Graphic abstract

Rapid destruction of planetary debris around white dwarfs through aeolian erosion

ABSTRACTThe discovery of numerous debris discs around white dwarfs (WDs) gave rise to extensive study of such discs and their role in polluting WDs, but the formation and evolution of these discs is not yet well understood. Here, we study the role of aeolian (wind) erosion in the evolution of solids in WD debris discs. Aeolian erosion is a destructive process that plays a key role in shaping the properties and size distribution of planetesimals, boulders, and pebbles in gaseous protoplanetary discs. Our analysis of aeolian erosion in WD debris discs shows that it can also play an important role in these environments. We study the effects of aeolian erosion under different conditions of the disc and its erosive effect on planetesimals and boulders of different sizes. We find that solid bodies smaller than $\sim \! 5 \, \rm {km}$ will be eroded within the short disc lifetime. We compare the role of aeolian erosion in respect to other destructive processes such as collisional fragmentation and thermal ablation. We find that aeolian erosion is the dominant destructive process for objects with radius $\lesssim \! 10^3 \, \rm {cm}$ and at distances $\lesssim \! 0.6 \, \mathrm{R}_\odot$ from the WD. Thereby, aeolian erosion constitutes the main destructive pathway linking fragmentational collisions operating on large objects with sublimation of the smallest objects and Poynting–Robertson drag, which leads to the accretion of the smallest particles on to the photosphere of WDs, and the production of polluted WDs.

Mass spectral studies on the human skin surface for mosquito vector control applications.

Human skin surface chemical cues comprise a complex mixture of compounds that mosquitoes use to locate and select their human host, based on inter- and intra-human variation in chemical profiles. The complexity of the skin surface matrix calls for advanced analytical techniques to enable separation and identification of biomarkers, which may be used as topical attractants and repellants in future mosquito vector control programmes. The perceived mosquito attractiveness between 20 volunteers and the preference of mosquitoes to bite certain regions, namely, ankle versus wrist, of the human host were investigated in this study, by comparing skin surface chemical profiles. Ion mobility was combined with high resolution mass spectrometry to provide additional confidence in biological marker discovery and identification of human skin surface compounds. This study employed a non-intrusive sampling scheme using a polydimethylsiloxane (PDMS) sampler and solvent desorption analysed with ultra-performance liquid chromatography with ion mobility high-resolution mass spectrometry (UPLC-IMS-HRMS). Statistical approaches guided the identification of 14 biological markers discerning difference in perceived mosquito attractiveness and 20 biomarkers associated with the different skin regions sampled. A broad range (m/z 96.0437 to 788.6095) of chemical compounds was detected from a variety of classes (including sugars, steroids, fatty acids, peptides and peptide derivatives, and compounds of food origin). Ten compounds were unequivocally identified on the human skin surface, and caffeine was reported on the human skin surface for the first time. Furthermore, 77 compounds, of which 64 to the authors' knowledge have not previously been reported, were detected on the human skin surface using accurate mass, collision cross section (CCS) values and fragmentation patterns. This approach enabled comprehensive human skin surface chemical profiling and provides an extensive list of tentatively identified skin surface compounds together with accurate mass values and adducts with their corresponding CCS values.

Multiple thrust systems from the Southern Granulite Terrane, India: Insights on Precambrian convergent margin tectonics

• Field relationships as shown in structural cross sections indicate thrust-nappe tectonics. • Multiple thrusting and associated features reveal that the granulitic units are allochthonous in nature. • The charnockite massifs represent nappes of volcanic arcs and/or microcontinents. • The Neoproterozoic-Cambrian evolution of the SGT involved the closure of the Mozambique Ocean. The geological and structural complexities of the Southern Granulite Terrane (SGT) of India, a key Gondwana collisional orogenic belt, are increasingly recognized and our understanding is still evolving despite several multidisciplinary efforts. Six important structural cross sections along some critical geological corridors have been reconstructed covering the entire stretch of SGT. We propose subduction related multiple thrust systems for the evolution of the SGT, based on the salient features derived from the structural cross sections and the currently available geoscientific data sets. The presence of tectonic windows and klippe structures in Madurai block and unusual occurrence of high strain zones on top of some of the highly elevated quartzite hills support the thrust-nappe tectonic model for the SGT implying possible allochthonous nature of many of the supracrustals and granulitic units involving multiphases of thrusting. The evolution of the SGT involves converging accretionary processes of island arc magmatic intrusives, thrust stacking, crustal coupling, granitic emplacement and the obduction of ophiolite complexes indicating a complete range of geological processes encountered in modern orogenic belts. These features could thus be representative of multiple thrusting related to south directed subduction processes followed by wide scale collision of Gondwana fragments during the end Precambrian.

Linking planetary embryo formation to planetesimal formation

Context. The growth-timescales of planetary embryos and their formation process are imperative for our understanding on how planetary systems form and develop. They determine the subsequent growth mechanisms during the life stages of a circumstellar disk. Aims. We quantify the timescales and spatial distribution of planetary embryos through collisional growth and fragmentation of dynamically forming 100 km sized planetesimals. In our study, the formation timescales of viscous disk evolution and planetesimal formation are linked to the formation of planetary embryos in the terrestrial planet zone. Methods. We connected a one-dimensional model for viscous gas evolution, dust and pebble dynamics, and pebble flux-regulated planetesimal formation to the N-body code LIPAD. Our framework enabled us to study the formation, growth, fragmentation, and evolution of planetesimals with an initial size of 100 km in diameter for the first million years of a viscous disk. Results. Our study shows the effect of the planetesimal surface density evolution on the preferential location and timescales of planetary embryo formation. Only the innermost embryos (<2 au) in our study form well within the lifetime of an active pebble flux for any disk studied. Higher planetesimal disk masses and steeper planetesimal surface density profiles result in more massive embryos within a larger area, rather than in a higher number of embryos. A one-dimensional analytically derived model for embryo formation based on the local planetesimal surface density evolution is presented. This model can reproduce the spatial distribution, formation rate, and total number of planetary embryos at a fraction of the computational cost of the N-body simulations. Conclusions. The formation of planetary embryos in the terrestrial planet zone occurs simultaneously with the formation of planetesimals. The local planetesimal surface density evolution and the orbital spacing of planetary embryos in the oligarchic regime are good constraints for modeling planetary embryo formation analytically. Our embryo formation model is a valuable asset in future studies of planet formation.

Análisis de clústeres para simulaciones de mecánica granular mediante algoritmos de aprendizaje automático

Las simulaciones de dinámica molecular (MD) en colisiones de granos permiten incorporar propiedades complejas de interacciones de polvo. Realizamos simulaciones de colisiones de granos porosos, cada uno con muchas partículas, utilizando el software LAMMPS de MD. Las simulaciones consistieron en un grano de proyectil que golpeó un grano objetivo inmóvil más grande, con diferentes velocidades de impacto. La desventaja de este método es el gran costo computacional debido a que se modela una gran cantidad de partículas. Machine Learning (ML) tiene el poder de manipular grandes datos y construir modelos predictivos que podrían reducir los tiempos de simulación MD. Usando algoritmos ML (Support Vector Machine y Random Forest) podemos predecir el resultado de las simulaciones MD con respecto a la formación de fragmentos, después de varios pasos más pequeños que en las simulaciones MD habituales. Logramos una reducción de tiempo de al menos un 46%, para una precisión del 90%. Estos resultados muestran que SVM y RF pueden ser herramientas poderosas pero simples para reducir el costo computacional en simulaciones de fragmentación de colisiones.

Semiautomated glycoproteomics data analysis workflow for maximized glycopeptide identification and reliable quantification.

Glycoproteomic data are often very complex, reflecting the high structural diversity of peptide and glycan portions. The use of glycopeptide-centered glycoproteomics by mass spectrometry is rapidly evolving in many research areas, leading to a demand in reliable data analysis tools. In recent years, several bioinformatic tools were developed to facilitate and improve both the identification and quantification of glycopeptides. Here, a selection of these tools was combined and evaluated with the aim of establishing a robust glycopeptide detection and quantification workflow targeting enriched glycoproteins. For this purpose, a tryptic digest from affinity-purified immunoglobulins G and A was analyzed on a nano-reversed-phase liquid chromatography–tandem mass spectrometry platform with a high-resolution mass analyzer and higher-energy collisional dissociation fragmentation. Initial glycopeptide identification based on MS/MS data was aided by the Byonic software. Additional MS1-based glycopeptide identification relying on accurate mass and retention time differences using GlycopeptideGraphMS considerably expanded the set of confidently annotated glycopeptides. For glycopeptide quantification, the performance of LaCyTools was compared to Skyline, and GlycopeptideGraphMS. All quantification packages resulted in comparable glycosylation profiles but featured differences in terms of robustness and data quality control. Partial cysteine oxidation was identified as an unexpectedly abundant peptide modification and impaired the automated processing of several IgA glycopeptides. Finally, this study presents a semiautomated workflow for reliable glycoproteomic data analysis by the combination of software packages for MS/MS- and MS1-based glycopeptide identification as well as the integration of analyte quality control and quantification.

Fragment emission and critical behavior in light and heavy charged systems * *Supported Council of Scientific and Industrial Research (CSIR), Govt. of India (03 (1388)/16/EMR-II)

We study the emission of fragments in central collisions of light and heavily charged systems of 40Ar+45Sc and 84Kr+197Au, respectively, using the Quantum Molecular Dynamics (QMD) model as the primary model. The fragments are identified using an energy based clusterization algorithm, i.e., the Simulated Annealing Clusterization Algorithm (SACA). The charge distributions of intermediate mass fragments [3≤ ≤12] are fitted with power-law ( ) and exponential ( ) fits in order to extract the parameters τ and whose minimum values are also sometimes linked with the onset of fragmentation or the critical point for a liquid-gas phase transition. Other parameters such as the normalized second moment , , average size of the second largest cluster , phase separation parameter ( ), bimodal parameter (P), information entropy (H), and Zipf's law are also analyzed to find the exact energy of the onset of fragmentation. Our detailed analysis predicts that an energy point exists between 20-23.1 MeV/nucleon, which is very close to the experimentally observed value of 23.9 MeV/nucleon for the 40Ar+45Sc reaction. We also find that the critical energy deduced using Zipf's law is higher than those predicted from other critical exponents. Moreover, no minimum is found for τ values of the highly charged system of 84Kr+197Au, in agreement with experimental findings and various theoretical calculations. We observe that the QMD + SACA model calculations are in agreement with the experimental observations. This agreement supports our results regarding the energy point of the liquid-gas phase transition and the onset of fragmentation.

Holistic quality evaluation of Saposhnikoviae Radix (Saposhnikovia divaricata) by reversed-phase ultra-high performance liquid chromatography and hydrophilic interaction chromatography coupled with ion mobility quadrupole time-of-flight mass spectrometry-based untargeted metabolomics

Untargeted metabolomics more suits the quality evaluation of TCM because of its holistic property. To assess the holistic quality difference of Saposhnikoviae Radix (the roots of Saposhnikovia divaricata), we integrate ultra-high-performance liquid chromatography coupled with ion mobility/quadrupole time-of-flight mass spectrometry (UHPLC/IM-QTOF-MS)-based untargeted metabolomics and quantitative assay. A BEH C18 column in the reversed-phase mode and a BEH Amide column in Hydrophilic Interaction Chromatography (HILIC) mode were utilized for metabolites profiling, which enabled high coverage of the non-polar to polar components in Saposhnikoviae Radix. Moreover, the application of major components knockout strategy enlarged the exposure of those minor components. Integrated use of high-definition MSE (HDMSE) and data-dependent acquisition (DDA) could enhance the metabolites characterization by providing reliable fragmentation information and collision cross section values. Computational in-house library-driven automated peak annotation of the HDMSE and DDA data assisted to characterize 104 components from Saposhnikoviae Radix. Chemometric analyses of the commercial Saposhnikoviae Radix samples (64 batches collected from 11 cultivars aging from 1 to 4 years), based on the positive MSE data, in general could indicate large discrimination between Guan-Fang-Feng (from Heilongjiang) and the others, but negligible difference among Saposhnikoviae Radix from the other ten provinces of China and with different ages. Quantitative assays of prim-O-glucosylcimifugin and 4′-O-β-D-glucosyl-5-O-methylvisamminol, by a rapid and fully validated UHPLC-UV method, could primarily deduce that Guan-Fang-Feng aging 2 and 3 years exhibited better quality. The methods established can holistically assess the quality of TCM with wide spans of plant metabolites covered.

Numerical study on melt drop collision and hydraulic fragmentation during FCI of a nuclear reactor severe accident

Melt drop collision is an important phenomenon in the circumstance of pressure wave propagation during fuel–coolant interaction (FCI). The deformation and fragmentation of melt drops can increase the contact area with coolant, and as a result will affect the heat transfer and melt oxidation. In this study, a numerical model was established by considering surface tension and validated with the experimental results that were obtained from water droplet collision in gaseous environment. Then, the head-on collision of two UO2 melt drops in water pool was investigated at different Weber numbers, and the melt morphology, contact area, and the number and size distribution of children droplets were analyzed. The results show that interfacial waves and wrinkles could be clearly observed on the melt film, and the finger structures presented at the rim of melt film and finally separated into children melt droplets. The increase of fuel–coolant contact area could be divided into the inducements by deformation and fragmentation. The melt deformation only had influence to the area increase at intermediate process but no effect to that at steady state. By contrast, the final fuel–coolant contact area was determined by the intensity of melt fragmentation. The size distribution of melt children droplets was like an off-centered normal distribution, where the maximum number of children droplets existed in the size range of 0.03 < D/D0 < 0.045, but the droplets in this size range contributed little to the fuel–coolant contact area. With the above analysis, an empirical model to calculate the contact area was developed. The model had a discrepancy of ±10% in the range of Wec = 290–1815 that the model was established in, but the discrepancies were about 13.3% and 19.3% for the cases of Wec at 2196 and 2612, respectively.

Evidence for early fragmentation-reassembly of ordinary chondrite (H, L, and LL) parent bodies from REE-in-two-pyroxene thermometry

Ordinary chondrites (OCs) are variably thermally metamorphosed meteorites thought to originate from at least three different parent bodies (H, L, and LL) in the Main Belt of asteroids. The thermal evolutions of OC parent bodies are frequently explained by the onion shell model; however, a competing hypothesis is the fragmentation-reassembly model. The onion shell model proposes undisrupted, internally heated parent bodies with concentrically stratified thermal structure, and posits that OC petrologic types (i.e., 3–6) develop with increasing temperature and burial depth. In this model, petrologic types are inversely correlated with cooling rate in the parent body. The alternative fragmentation-reassembly model invokes catastrophic collisional disruption of parent bodies that initially possessed onion shell structures, followed by rapid reaccretion of hot fragments, forming rubble pile bodies. Fragmentation would result in fast cooling (quenching) of collisional fragments from the temperature experienced by the parent body at the time of collision. Discrimination between these two models may be possible via investigation of the thermal histories of OCs by application of geothermometry and geospeedometry, which are used to constrain the temperatures and rates through which igneous and metamorphic rock samples cool. Most published cooling rate data for OC parent bodies are based on methods that record rates through low closure temperatures (∼500–200 °C) rather than from peak metamorphic temperatures. Recently, a rare earth element (REE)-in-two-pyroxene thermometer has been shown to establish peak or magmatic temperatures (TREE; Liang et al. [2013]) for rocks that cooled at moderate to fast geologic rates. We applied the REE-in-two-pyroxene method to determine peak temperatures for 18 OC samples (mostly type 6), in conjunction with conventional two-pyroxene thermometry (TBKN; Brey and Köhler [1990]) and Ca-in-olivine thermometry (TCa-Ol; Köhler and Brey [1990]), to determine closure temperatures and estimate cooling rates for OC parent bodies. Inconsistent with slow cooling rates expected within an onion shell structure, we obtain fast cooling at rates ≳0.3 °C/y from peak temperatures of ∼900 °C. Corroborating the TREE and TBKN measurements, TCa-Ol suggests that the OCs cooled through TCa-Ol closure temperatures (∼700 to 800 °C) at ∼10−2 to 10−1 °C/y. These cooling rates are three to six orders of magnitude faster than rates determined using methods sensitive to low temperature (≤500 °C) cooling (e.g., metallography, 40Ar–39Ar ages, 244Pu fission track). We developed a novel numerical thermal model that incorporates fragmentation of an initial onion shell body and reassembly into a rubble pile body that reproduces both the fast cooling from high temperatures and the slow cooling through low temperatures observed in chondritic meteorites. We hypothesize that OC parent bodies initially possessed onion shell thermal structures, but later experienced collisional breakup, then reaccreted rapidly to form thermally stable rubble-pile asteroids.

Water worlds in N-body simulations with fragmentation in systems without gaseous giants

Aims. We analyze the formation and evolution of terrestrial-like planets around solar-type stars in the absence of gaseous giants. In particular, we focus on the physical and dynamical properties of those that survive in the system’s habitable zone (HZ). This investigation is based on a comparative study between N-body simulations that include fragmentation and others that consider all collisions as perfect mergers. Methods. We use an N-body code, presented in a previous paper, that allows planetary fragmentation. We carry out three sets of 24 simulations for 400 Myr. Two sets are developed adopting a model that includes hit-and-run collisions and planetary fragmentation, each one with different values of the individual minimum mass allowed for the fragments. For the third set, we considered that all collisions lead to perfect mergers. Results. The planetary systems produced in N-body simulations with and without fragmentation are broadly similar, though with some differences. In simulations with fragmentation, the formed planets have lower masses since part of them is distributed among collisional fragments. Additionally, those planets presented lower eccentricities, presumably due to dynamical friction with the generated fragments. Lastly, perfect mergers and hit-and-run collisions are the most common outcome. Regardless of the collisional treatment adopted, most of the planets that survive in the HZ start the simulation beyond the snow line, having very high final water contents. Such planets are called water worlds. The fragments’ contribution to their final mass and water content is negligible. Finally, the individual minimum mass for fragments may play an important role in the planets’ collisional history. Conclusions. Collisional models that incorporate fragmentation and hit-and-run collisions lead to a more detailed description of the physical properties of the terrestrial-like planets formed. We conclude that planetary fragmentation is not a barrier to the formation of water worlds in the HZ. The results shown in this work suggest that further refinement is necessary to have a more realistic model of planetary formation.

Evolution of an Asteroid Family under YORP, Yarkovsky, and Collisions

Abstract Any population of asteroids, like asteroid families, will disperse in semimajor axis due to the Yarkovsky effect. The amount of drift is modulated by the asteroid spin state evolution, which determines the balance between the diurnal and seasonal Yarkovsky forces. The asteroid’s spin state is, in turn, controlled in part by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. The otherwise smooth evolution of an asteroid can be abruptly altered by collisions, which can cause impulsive changes in the spin state and can move the asteroid onto a different YORP track. In addition, collisions may also alter the YORP parameters by changing the superficial features and overall shape of the asteroid. Thus, the coupling between YORP and Yarkovsky is also strongly affected by the impact history of each body. To investigate this coupling, we developed a statistical code modeling the time evolution of semimajor axis under YORP–Yarkovsky coupling. It includes the contributions of NYORP (normal YORP), TYORP (tangential YORP), and collisions whose effects are deterministically calculated and not added in a statistical way. We find that both collisions and TYORP increase the dispersion of a family in semimajor axis by making the spin axis evolution less smooth and regular. We show that the evolution of a family’s structure with time is complex and collisions randomize the YORP evolution. In our test families, we do not observe the formation of a “YORP-eye” in the semimajor axis versus diameter distribution, even after a long period of time. If present, the “YORP-eye” might be a relic of an initial ejection velocity pattern of the collisional fragments.

Grain size distribution and sedimentology in volcanic mass-wasting flows: implications for propagation and mobility

The sedimentological characteristics of mass-wasting flow deposits are important for assessing the differences between phenomena and their propagation and emplacement mechanisms. In the present study, nine volcanic debris avalanche deposits and eight lahar deposits are considered, from the literature. Their sedimentology is expressed in the descriptive statistics: median grain size, sand, gravel and finer particle fractions, skewness and sorting. Analysis of the data confirms that lahars and debris avalanches diverge in their grain size distribution and in their evolution during propagation. Water saturation in lahars is the main factor enabling debulking, a mechanism that is not recorded in the data derived from debris avalanches deposits. On the contrary, evidence of comminution of particles due to particle-particle interactions is observed in debris avalanches, and not in lahars. These findings support previous studies suggesting that although water content in debris avalanches plays a role in propagation, the effects of inertial collision of solid fragments are more important than fluid effects, confirming that particle-particle interactions are the main factor influencing the mobility of non-saturated mass wasting flows.

Strangeness enhancement due to string fluctuations

We study string fragmentation in high multiplicity proton-proton collisions in a model where the string tension fluctuates. These fluctuations produce exponential pion spectra which are fitted to the transverse momentum distributions of charged particles for different multiplicities. For each multiplicity the so obtained hadronic slope parameter defines the magnitude of the string fluctuations which in turn determines the produced ratio of strange to light quarks. PYTHIA string decay simulations are used to convert each ratio of strange to light quarks to the appropriate ratio of strange hadrons to pions.

Mass Spectral Library of Acylcarnitines Derived from Human Urine.

We describe the creation of a mass spectral library of acylcarnitines and conjugated acylcarnitines from the LC-MS/MS analysis of six NIST urine reference materials. To recognize acylcarnitines, we conducted in-depth analyses of fragmentation patterns of acylcarnitines and developed a set of rules, derived from spectra in the NIST17 Tandem MS Library and those identified in urine, using the newly developed hybrid search method. Acylcarnitine tandem spectra were annotated with fragments from carnitine and acyl moieties as well as neutral loss peaks from precursors. Consensus spectra were derived from spectra having similar retention time, fragmentation pattern, and the same precursor m/z and collision energy. The library contains 157 different precursor masses, 586 unique acylcarnitines, and 4 332 acylcarnitine consensus spectra. Furthermore, from spectra that partially satisfied the fragmentation rules of acylcarnitines, we identified 125 conjugated acylcarnitines represented by 987 consensus spectra, which appear to originate from Phase II biotransformation reactions. To our knowledge, this is the first report of conjugated acylcarnitines. The mass spectra provided by this work may be useful for clinical screening of acylcarnitines as well as for studying relationships among fragmentation patterns, collision energies, structures, and retention times of acylcarnitines. Further, these methods are extensible to other classes of metabolites.

Physical and mathematical models for space objects breakup and fragmentation in hypervelocity collisions

The paper presents results of analysis of existing mathematical models for orbital debris fragments breakup in high velocity collisions. The breakup models are modified and updated taking into account the latest breakup criteria, experimental data and basic conservation laws. The model examples are analyzed, the criterion is developed for distinguishing fragments, which will stay in orbit after collision event.

Forward production of nuclear fragments in CC collisions at beam energy 20.5 GeV/nucleon

The inclusive differential cross sections for forward production of nuclear fragments at an angle of 0∘ in CC collisions at beam energy 20.5 GeV/nucleon (SNN=6.3GeV) are presented. Measurements have been performed at the U-70 Accelerator Complex (Protvino) using a combined spectrometer on base of the beamline. Fragments selection was carried out by measuring of ionization in scintillation counters taking into account the data from threshold Cherenkov counters and hadron calorimeter. Fragment mass was determined through Cherenkov light emission angle measured in the spectrometer of ring imaging Cherenkov radiation. Data are given for fragments with charge 1≤Z≤6, atomic number 1≤A≤10 and A/Z<3.4 with momenta from 20 to 210 GeV/c. The measurements are compared with Fritiof model, statistical models and theoretical parameterizations. The discovered differences between theory and experiment are discussed.