Showing papers on "Cluster (physics) published in 2021"

Fully Exposed Cluster Catalyst (FECC): Toward Rich Surface Sites and Full Atom Utilization Efficiency

Abstract: Increasing attention has been paid to single-atom catalysts (SACs) in heterogeneous catalysis because of their unique electronic properties, maximized atomic utilization efficiency, and potential to serve as a bridge between the heterogeneous and homogeneous catalysis. However, SACs can have limited advantages or even constrained applications for the reactions that require designated metallic states with multiple atoms or surface sites with metal-metal bonds. As a cross-dimensional extension to the concept of SACs, fully exposed cluster catalysts (FECCs) offer diverse surface sites formed by an ensemble of metal atoms, for the adsorption and transformation of reactants/intermediates. More importantly, FECCs have the advantage of maximized atom utilization efficiency. Thus, FECCs provide a novel platform to design effective and efficient catalysts for certain chemical processes. This outlook summarizes recent advances and proposes prospective research directions in the design of catalysts and characterizations of FECCs, together with potential challenges.

Shell engineering to achieve modification and assembly of atomically-precise silver clusters.

Abstract: Continuing research on the preparation and structural determination of monolayer-protected silver clusters has been performed. The compounds include mixed-valence Ag0/1+ clusters and single-valence Ag1+ clusters, which contain a few to tens or hundreds of Ag atoms that are protected by organic ligands. Sometimes, counter ions and extraneous species appear in their crystalline state. These non-metal parts define the shell layers of silver clusters. Strong coordination bonds and weak supramolecular interactions have been employed not only to modify the shell configurations and components of discrete silver clusters but also to hierarchically assemble silver clusters, producing novel cluster-based functional materials with unexpected physical and chemical properties. Atomically-precise structures help to map out definite electronic structures and structure-property correlations, enabling precise control of shell layers to achieve desired stability and specific functionalities. In this Tutorial Review, based on classic silver cluster paradigms, we first summarize the strategies and recent advances in precise modification and hierarchical assembly of well-defined silver clusters through shell engineering. Second, the correlations of structure-property and structure-functionality are summarized. Of these, the most important is structure-luminescence relationship, which is discussed in detail. In this topic, the uniqueness and prospect of silver clusters as potential lighting materials are scrutinized. Finally, the existing challenges and perspectives of functional silver clusters are presented. The general strategic design presented in this Review will motivate researchers to exploit the development of functionality-oriented materials based on nanosized building blocks in the enrichment of nanotechnology and material science.

Structural and electronic properties of medium-sized beryllium doped magnesium BeMgn clusters and their anions

Abstract: Bimetallic clusters have attracted much attention because of the structural and property changes that occur: cluster size and doping. Here, we performed a structural search of the global minimum for bimetallic BeMgn0/− (n = 10–20) clusters by utilizing efficient CALYPSO structural searching program with subsequent DFT calculations. A large number of low energetic isomers converge and the most stable structures are confirmed by comparing the total energies for different cluster sizes. Satisfactory agreement between theoretical and experimental PES spectra demonstrates the validity of our predicted global minimum structures. It is found that the most stable structures of BeMgn0/− clusters are filled cage-like frameworks at n = 10–20. The localized position of Be atoms changes from completely encapsulated sites to surface sites, after which the position reverts to the caged Mg motif. In all BeMgn0/− clusters, the charge transfers from the Mgn motif to Be atoms. Increasing occupations of p orbitals manifest their increasing metallic behaviors. A stability analysis revealed that the D4d symmetric BeMg16 caged structure with one centred Be atom has robust stability, which can be because BeMg16 possesses a closed electronic shell of 1S21P61D101F42S21F10 filled with 34 valence electrons and strong Be-Mg bonds due to s-p hybridization. This finding is supported by multi-centre bonds and Mayer bond order analyses.

Extended stellar systems in the solar neighborhood - V. Discovery of coronae of nearby star clusters

Abstract: We present a novel view on the morphology and dynamical state of ten prominent, nearby (≤500 pc), and young (∼30–300 Myr) open star clusters with Gaia DR2: α Per, Blanco 1, IC 2602, IC 2391, Messier 39, NGC 2451A, NGC 2516, NGC 2547, Platais 9, and the Pleiades. We introduce a pioneering member-identification method that is informed by cluster bulk velocities and deconvolves the spatial distribution with a mixture of Gaussians. Our approach enables inferring the true spatial distribution of the clusters by effectively filtering field star contaminants while at the same time mitigating the effect of positional errors along the line of sight. This first application of the method reveals vast stellar coronae that extend for ≳100 pc and surround the cluster cores, which are comparatively tiny and compact. The coronae and cores form intertwined, coeval, and comoving extended cluster populations, each encompassing tens of thousands of cubic parsec and stretching across tens of degrees on the sky. Our analysis shows that the coronae are gravitationally unbound but largely comprise the bulk of the stellar mass of the populations. Most systems are in a highly dynamic state, showing evidence of expansion and sometimes simultaneous contraction along different spatial axes. The velocity field of the extended populations for the cluster cores appears asymmetric but is aligned along a spatial axis unique to each cluster. The overall spatial distribution and the kinematic signature of the populations are largely consistent with the differential rotation pattern of the Milky Way. This finding underlines the important role of global Galactic dynamics in the fate of stellar systems. Our results highlight the complexity of the Milky Way’s open cluster population and call for a new perspective on the characterization and dynamical state of open clusters.

Automatic clustering algorithms: a systematic review and bibliometric analysis of relevant literature

Abstract: Cluster analysis is an essential tool in data mining. Several clustering algorithms have been proposed and implemented, most of which are able to find good quality clustering results. However, the majority of the traditional clustering algorithms, such as the K-means, K-medoids, and Chameleon, still depend on being provided a priori with the number of clusters and may struggle to deal with problems where the number of clusters is unknown. This lack of vital information may impose some additional computational burdens or requirements on the relevant clustering algorithms. In real-world data clustering analysis problems, the number of clusters in data objects cannot easily be preidentified and so determining the optimal amount of clusters for a dataset of high density and dimensionality is quite a difficult task. Therefore, sophisticated automatic clustering techniques are indispensable because of their flexibility and effectiveness. This paper presents a systematic taxonomical overview and bibliometric analysis of the trends and progress in nature-inspired metaheuristic clustering approaches from the early attempts in the 1990s until today’s novel solutions. Finally, key issues with the formulation of metaheuristic algorithms as a clustering problem and major application areas are also covered in this paper.

Cosmological implications of the anisotropy of ten galaxy cluster scaling relations

Abstract: The hypothesis that the late Universe is isotropic and homogeneous is adopted by most cosmological studies, including studies of galaxy clusters. The cosmic expansion rate H 0 is thought to be spatially constant, while bulk flows are often presumed to be negligible compared to the Hubble expansion, even at local scales. The effects of bulk flows on the redshift–distance conversion are hence usually ignored. Any deviation from this consensus can strongly bias the results of such studies, and thus the importance of testing these assumptions cannot be understated. Scaling relations of galaxy clusters can be effectively used for this testing. In previous works, we observed strong anisotropies in cluster scaling relations, whose origins remain ambiguous. By measuring many different cluster properties, several scaling relations with different sensitivities can be built. Nearly independent tests of cosmic isotropy and large bulk flows are then feasible. In this work, we make use of up to 570 clusters with measured properties at X-ray, microwave, and infrared wavelengths to construct ten different cluster scaling relations and test the isotropy of the local Universe; to our knowedge, we present five of these scaling relations for the first time. Through rigorous and robust tests, we ensure that our analysis is not prone to generally known systematic biases and X-ray absorption issues. By combining all available information, we detect an apparent 9% spatial variation in the local H 0 between (l , b )∼(280° , −15° ) and the rest of the sky. The observed anisotropy has a nearly dipole form. Using isotropic Monte Carlo simulations, we assess the statistical significance of the anisotropy to be > 5σ . This result could also be attributed to a ∼900 km s−1 bulk flow, which seems to extend out to at least ∼500 Mpc. These two effects will be indistinguishable until more high-z clusters are observed by future all-sky surveys such as eROSITA.

Substantial π-aromaticity in the anionic heavy-metal cluster [Th@Bi12]4.

Abstract: The concept of aromaticity was originally defined as a property of unsaturated, cyclic planar organic molecules like benzene, which gain stability by the inherent delocalization of 4n + 2 π-electrons over the ring atoms. Since then, π-aromaticity has been observed for a large variety of organic and inorganic non-metal compounds, yet, for molecules consisting only of metal atoms, it has remained restricted to systems with three to five atoms. Here, we present the straightforward synthesis of a metal 12-ring that exhibits 2π-aromaticity and has a ring current much stronger than that of benzene (6π) and equivalent to that of porphine (26π), despite these organic molecules having (much) larger numbers of π-electrons. Highly reducing reaction conditions allowed access to the heterometallic anion [Th@Bi12]4−, with interstitial Th4+ stabilizing a Bi128− moiety. Our results show that it is possible to design and generate substantial π-aromaticity in large metal rings, and we hope that such π-aromatic heavy-metal cycles will eventually find use in cluster-based reactions. A wide variety of organic and inorganic compounds show π-aromaticity, yet for all-metal systems it has remained restricted to compounds with three to five atoms. Now, the anionic cluster [Th@Bi12]4− has been shown to exhibit π-aromaticity, with a significant ring current despite relying on the delocalization of only two π-electrons.

Assembly‑Induced Strong Circularly Polarized Luminescence of Spirocyclic Chiral Silver(I) Clusters

Abstract: Spirocyclic Ag9 clusters, as a new form of intrinsically chiral metal clusters, were constructed through vertex-sharing of two in-situ-generated heteroaryl diide-centered metal rings. Such core-peripheral type clusters exhibit versatile photoluminescent and chiroptical behavior under different aggregation conditions. In contrast to a ligand-based fluorescence emission in a diluted solution of the clusters, a solvent polarity-caused assembly gives rise to new cluster-based phosphorous luminescence owing to radiative mode switching and aggregation-induced emission. Assembly of cluster enantiomers leads to micrometer-long helical nanofibers, whose handedness is determined by absolute configuration of individual spirocyclic clusters. Benefiting from exciton couplings of helical arrangements of chelating ligands at molecular and microscopic levels, the assembled film of cluster enantiomers exhibits circularly polarized luminescence with a high anisotropy factor (0.16).

SharPer: Sharding Permissioned Blockchains Over Network Clusters

Abstract: Scalability is one of the main roadblocks to business adoption of blockchain systems. Despite recent intensive research on using sharding techniques to enhance the scalability of blockchain systems, existing solutions do not efficiently address cross-shard transactions. In this paper, we introduce SharPer, a scalable permissioned blockchain system. In SharPer, nodes are clustered and each data shard is replicated on the nodes of a cluster. SharPer supports networks consisting of either crash-only or Byzantine nodes. In SharPer, the blockchain ledger is formed as a directed acyclic graph and each cluster maintains only a view of the ledger. SharPer incorporates decentralized flattened protocols to establish cross-shard consensus. The decentralized nature of the cross-shard consensus in SharPer enables parallel processing of transactions with nonoverlapping clusters. Furthermore, SharPer provides deterministic safety guarantees. The experimental results reveal the efficiency of SharPer in terms of performance and scalability especially in workloads with a low percentage of cross-shard transactions.

B48−: a bilayer boron cluster

Abstract: Size-selected negatively-charged boron clusters (Bn−) have been found to be planar or quasi-planar in a wide size range Even though cage structures emerged as the global minimum at B39−, the global minimum of B40− was in fact planar Only in the neutral form did the B40 borospherene become the global minimum How the structures of larger boron clusters evolve is of immense interest Here we report the observation of a bilayer B48− cluster using photoelectron spectroscopy and first-principles calculations The photoelectron spectra of B48− exhibit two well-resolved features at low binding energies, which are used as electronic signatures to compare with theoretical calculations Global minimum searches and theoretical calculations indicate that both the B48− anion and the B48 neutral possess a bilayer-type structure with D2h symmetry The simulated spectrum of the D2h B48− agrees well with the experimental spectral features, confirming the bilayer global minimum structure The bilayer B48−/0 clusters are found to be highly stable with strong interlayer covalent bonding, revealing a new structural type for size-selected boron clusters The current study shows the structural diversity of boron nanoclusters and provides experimental evidence for the viability of bilayer borophenes

Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different β-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours.

Abstract: A series of tetranuclear lanthanide-based clusters [Ln4(dbm)6(L)2(CH3OH)4]·2CH3OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H3L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln8(HL)10(CH3O)4(CH3OH)2]·6CH3OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H3L and two different β-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, β-diketones play an important role in assembling and affecting the structures of Ln4 to Ln8 clusters. This is the first use of β-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln4 clusters to Ln8 clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd4 and 4-Gd8. More importantly, clusters 1-Gd4 and 4-Gd8 display significant cryogenic magnetic refrigeration properties (-ΔSm = 24.88 J kg-1 K-1 for 1-Gd4 and -ΔSm = 32.52 J kg-1 K-1 for 4-Gd8); the results show that cluster 4-Gd8 exhibits a larger magnetocaloric effect than 1-Gd4. Cluster 2-Dy4 shows remarkable single-molecule magnet (SMM) behavior (ΔE/kB = 67.5 K and τ0 = 3.06 × 10-7 s) under a zero dc field, and 5-Dy8 exhibits a field-induced SMM-like behavior (ΔE/kB = 39.83 K and τ0 = 2.12 × 10-7 s) under a 5000 Oe dc field.

Irradiation resistance mechanism of the CoCrFeMnNi equiatomic high-entropy alloy.

Abstract: When face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE) are irradiated by high-energy particles or deformed at high speed, stacking fault tetrahedra (SFTs), which are a type of vacancy cluster defect, are often formed. Therefore, SFTs were expected to form in the CoCrFeMnNi equiatomic high-entropy alloy (HEA). However, no SFT was observed in the CoCrFeMnNi HEA with high-speed plastic deformation even after annealing at 873 K. To elucidate this mechanism, the binding energy of vacancy clusters in the CoCrFeMnNi HEA was calculated based on first principles. The binding energy of the di-vacancy cluster was positive (average of 0.25 eV), while that of the tri-vacancy cluster was negative (average of − 0.44 eV), suggesting that the possibility of formation of a tri-vacancy cluster was low. The inability to form a cluster containing three vacancies is attributed to the excellent irradiation resistance of the CoCrFeMnNi HEA. However, if an extra vacancy is added to a tri-vacancy cluster (with negative binding energy), the binding energy of the subsequent tetra-vacancy cluster may become positive. This suggests that it is possible to form vacancy clusters in the CoCrFeMnNi HEA when high-energy ion or neutron irradiation causes cascade damage.

Entrepreneurial fintech clusters

Abstract: We study the formation and dynamics of entrepreneurial clusters in the emerging fintech industry. Using detailed data on the almost 1000 fintech startups in France to date, we find that most fintechs are geographically clustered and that the location of new fintech startups is affected, among other things, by the size of clusters and the presence of incubators. Larger clusters attract more new fintech startups, and incubators are shown to be an effective mechanism to attract new fintech startups. We further examine entrepreneurial exits of fintechs and find that being located in a larger cluster reduces the risk of failure but increases the likelihood of being acquired. Increased competition within a given segment of fintech increases failure rates. Moreover, the risk of failure is significantly lower for fintech startups that have been developed in an incubator.

The ThreeHundred: the structure and properties of cosmic filaments in the outskirts of galaxy clusters

Abstract: Galaxy cluster outskirts are described by complex velocity fields induced by diffuse material collapsing towards filaments, gas and galaxies falling into clusters, and gas shock processes triggered by substructures. A simple scenario that describes the large-scale tidal fields of the cosmic web is not able to fully account for this variety, nor for the differences between gas and collisionless dark matter. We have studied the filamentary structure in zoom-in resimulations centred on 324 clusters from The ThreeHundred project, focusing on differences between dark and baryonic matter. This paper describes the properties of filaments around clusters out to five $R_{200}$, based on the diffuse filament medium where haloes had been removed. For this, we stack the remaining particles of all simulated volumes to calculate the average profiles of dark matter and gas filaments. We find that filaments increase their thickness closer to nodes and detect signatures of gas turbulence at a distance of $\sim 2 h^{-1}\rm{Mpc}$ from the cluster. These are absent in dark matter. Both gas and dark matter collapse towards filament spines at a rate of $\sim 200 h^{-1} \rm{km ~ s^{-1}} $. We see that gas preferentially enters the cluster as part of filaments, and leaves the cluster centre outside filaments. We further see evidence for an accretion shock just outside the cluster. For dark matter, this preference is less obvious. We argue that this difference is related to the turbulent environment. This indicates that filaments act as highways to fuel the inner regions of clusters with gas and galaxies.

Modeling Dense Star Clusters in the Milky Way and Beyond with the Cluster Monte Carlo Code

Abstract: We describe the public release of the Cluster Monte Carlo Code (CMC) a parallel, star-by-star $N$-body code for modeling dense star clusters. CMC treats collisional stellar dynamics using Henon's method, where the cumulative effect of many two-body encounters is statistically reproduced as a single effective encounter between nearest-neighbor particles on a relaxation timescale. The star-by-star approach allows for the inclusion of additional physics, including strong gravitational three- and four-body encounters, two-body tidal and gravitational-wave captures, mass loss in arbitrary galactic tidal fields, and stellar evolution for both single and binary stars. The public release of CMC is pinned directly to the COSMIC population synthesis code, allowing dynamical star cluster simulations and population synthesis studies to be performed using identical assumptions about the stellar physics and initial conditions. As a demonstration, we present two examples of star cluster modeling: first, we perform the largest ($N = 10^8$) star-by-star $N$-body simulation of a Plummer sphere evolving to core collapse, reproducing the expected self-similar density profile over more than 15 orders of magnitude; second, we generate realistic models for typical globular clusters, and we show that their dynamical evolution can produce significant numbers of black hole mergers with masses greater than those produced from isolated binary evolution (such as GW190521, a recently reported merger with component masses in the pulsational pair-instability mass gap).

Density peaks clustering based on k-nearest neighbors and self-recommendation

Abstract: Density peaks clustering (DPC) model focuses on searching density peaks and clustering data with arbitrary shapes for machine learning. However, it is difficult for DPC to select a cut-off distance in the calculation of a local density of points, and DPC easily ignores the cluster centers with lower density in datasets with variable densities. In addition, for clusters with complex shapes, DPC selects only one cluster center for a cluster, meaning that the structure of the whole cluster is not fully reflected. To overcome these drawbacks, this paper presents a novel DPC model that merges microclusters based on k-nearest neighbors (kNN) and self-recommendation, called DPC-MC for short. First, the kNN-based neighbourhood of point is defined and the mutual neighbour degree of point is presented in this neighbourhood, and then a new local density based on the mutual neighbour degree is proposed. This local density does not need to set the cut-off distance manually. Second, to address the artificial setting of cluster centers, a self-recommendation strategy for local centers is provided. Third, after the selection of multiple local centers, the binding degree of microclusters is developed to quantify the combination degree between a microcluster and its neighbour clusters. After that, homogeneous clusters are found according to the binding degree of microclusters during the process of deleting boundary points layer by layer. The homologous clusters are merged, the points in the abnormal clusters are reallocated, and then the clustering process ends. Finally, the DPC-MC algorithm is designed, and nine synthetic datasets and twenty-seven real-world datasets are used to verify the effectiveness of our algorithm. The experimental results demonstrate that the presented algorithm outperforms other compared algorithms in terms of several evaluation metrics for clustering.

A series of dysprosium clusters assembled by a substitution effect-driven out-to-in growth mechanism

Abstract: Although the design and synthesis of high-nuclear lanthanide clusters with specific shapes and functions have been an active area of research, effective experience and rules to guide further systematic expansion of lanthanide clusters with different connections are lacking. Herein, we adjusted the steric hindrance effects on the substituents of diacylhydrazone ligands (H4L1, N′2,N′9-bis((E)-2-hydroxybenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide; H4L2, N′2,N′9-bis((E)-2-hydroxy-3-methylbenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide; H4L3, N′2,N′9-bis((E)-3-(tert-butyl)-2-hydroxybenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide) and reacted them with Dy(NO3)3·6H2O under solvothermal conditions to obtain three dysprosium clusters (1–3) with different shapes. The molecular formulas of the abovementioned clusters are [Dy16(L1)3(μ3-OH)25(NO3)11(H2O)10]·4CH3CN·8CH3OH, [Dy10(L2)4(μ2-OH)2(μ3-O)4(NO3)4(CH3CN)2(CH3OH)4(H2O)8]·CH3OH·8H2O, and [Dy5(L3)2(μ2-CH3O)(μ2-OH)2(μ4-O)(NO3)2(CH3OH)2]·6CH3OH·2CH3CN. Cluster 1 with a brucite-like planar structure crystallizes in the P21/n space group of the monoclinic system. The Dy(III) ions in the cluster 1 structure are bridged by μ3-OH− to form a plane triangle shape. In addition, the structure of cluster 1 contains three layers of Dy(III) ions (1 + 6 + 9) with different coordination environments. Cluster 2 crystallizes in the P space group of the triclinic system. The cluster core in cluster 2 is composed of two molecules of missing cubane Dy4O6 and two Dy(III) ions. The ligand (L2)4− adopts two coordination modes (μ3-η1:η1:η2:η1:η1:η2:η1:η1 and μ5-η2:η1:η1:η1:η1:η1:η1:η1:η1:η2) to chelate Dy(III) ions. In addition, Dy(III) ions in Dy4O6 are connected by μ2-OH− and μ3-OH−. Two molecules of planar Dy3L3 intersect to form cluster 3, and it crystallizes in the I2/a space group of the monoclinic system. The analysis of the structure of clusters 1–3 shows that they are formed by a stepwise assembly process from outside to inside. To the best of our knowledge, a very small number of examples have reported that a series of differently connected dysprosium clusters were obtained through the regulation of substitution effects. Notably, we are the first to propose the out-to-in growth mechanism of planar high-nucleus dysprosium clusters. The results of the variable temperature AC susceptibility test show that clusters 1, 2, and 3 exhibit single-molecule magnet-like behavior under zero-field conditions.

A Node Overhaul Scheme for Energy Efficient Clustering in Wireless Sensor Networks

Abstract: Clustering of wireless sensor network nodes, a fundamental operation, is aimed at achieving load balancing and prolonged network lifetime. Low-energy adaptive clustering hierarchy protocol, the prominent standard, achieves these. An improved protocol, balance cluster formation, provides the additional advantage of equal size clusters, but at the cost of overlapping of clusters. This letter presents a node overhaul scheme that achieves load balancing and energy efficiency while also maintaining uniform size clusters without any overlapping. The proposed solution first forms initial clusters and later refurbishes the initial clusters based on a second best choice cluster head, wherever applicable. The results so obtained show a substantial improvement in network lifetime and node death rate as compared to other simulated methods.

Threefold Collaborative Stabilization of Ag14 -Nanorods by Hydrophobic Ti16 -Oxo Clusters and Alkynes: Designable Assembly and Solid-State Optical-Limiting Application.

Abstract: Ag nanoclusters have received increasing attention due to their atomically precise and diverse structures and intriguing optical properties. Nevertheless, the inherent instability of Ag nanoclusters has seriously hindered their practical application. In this work, for the first time, Ag clusters are collaboratively protected by hydrophobic Ti-oxo clusters and alkyne ligands. Initially, a pyramidal Ag5 cluster terminated with t BuC≡C- and CH3 CN was inserted into the cavity of a Ti8 -oxo nanoring to form Ag5 @Ti8 . To overcome the instability of acetonitrile-terminated silver site, such two Ag5 @Ti8 clusters could sandwich an Ag4 unit to form Ag14 -nanorod@Ti16 -oxo-nanoring (Ag14 @Ti16 ), which is peripherally protected by fluorophenyl groups and alkyne caps. This threefold protected (hydrophobic fluorinated organic layer, Ti-O shell, and terminal alkyne ligands) Ag14 @Ti16 exhibits superhydrophobicity and excellent ambient stability, endowing it with solid-state optical limiting characteristics.

Examination of coalescence as the origin of nuclei in hadronic collisions

Abstract: The origin of weakly bound nuclear clusters in hadronic collisions is a key question to be addressed by heavy-ion collision (HIC) experiments. The measured yields of clusters are approximately consistent with expectations from phenomenological statistical hadronization models (SHMs), but a theoretical understanding of the dynamics of cluster formation prior to kinetic freeze-out is lacking. The competing model is nuclear coalescence, which attributes cluster formation to the effect of final state interactions (FSI) during the propagation of the nuclei from kinetic freeze-out to the observer. This phenomenon is closely related to the effect of FSI in imprinting femtoscopic correlations between continuum pairs of particles at small relative momentum difference. We give a concise theoretical derivation of the coalescence-correlation relation, predicting nuclear cluster spectra from femtoscopic measurements. We review the fact that coalescence derives from a relativistic Bethe-Salpeter equation, and recall how effective quantum mechanics controls the dynamics of cluster particles that are nonrelativistic in the cluster center-of-mass frame. We demonstrate that the coalescence-correlation relation is roughly consistent with the observed cluster spectra in systems ranging from PbPb to $p\mathrm{Pb}$ and $pp$ collisions. Paying special attention to nuclear wave functions, we derive the coalescence prediction for the hypertriton and show that it, too, is roughly consistent with the data. Our work motivates a combined experimental programme addressing femtoscopy and cluster production under a unified framework. Upcoming $pp, p\mathrm{Pb}$, and peripheral PbPb data analyzed within such a program could stringently test coalescence as the origin of clusters.