Dissolution Of Clusters Research Articles

Defective Phosphorene as a Promising Anchoring Material for Lithium–Sulfur Batteries

The lithium–sulfur battery, despite having considerable advantages, is still far from its practical applications, which is primarily caused by the dissolution of polysulfide clusters of lithium (Li...

The survival of star clusters with black hole subsystems

Abstract Recent observations have detected top-heavy IMFs in dense star forming regions like the Arches cluster. Whether such IMFs also exist in old dense stellar systems like globular clusters is difficult to constrain, because massive stars already became black holes (BHs) and neutron stars (NSs). However, studies of stellar dynamics find that BHs/NSs influence the long-term evolution of star clusters. Following Breen & Heggie (2013) and by carrying out two-component N-body simulations, we demonstrate how this dynamical impact connects with the shape of IMFs. By investigating the energy balance between the BH subsystem and the global, we find that to properly describe the evolution of clusters, a corrected two-body relaxation time, Trh, p = Trh/ψ, is necessary. Because ψ depends on the total mass fraction of BHs, M2/M, and the mass ratio, m2/m1, the cluster dissolution time is sensitive to the property of BHs or IMFs. Especially, the escape rate of BHs via ejections from few-body encounters are linked to mass segregation. In strong tidal fields, top-heavy IMFs easily lead to the fast dissolution of star clusters and the formation of BH-dominant dark clusters, which suggests that the observed massive GCs with dense cores are unlikely to have extreme top-heavy IMFs. With the future observations of gravitational waves providing unique information of BHs/NSs, it is possible to combine the multi-message observations to have better constrains on the IMFs of old star clusters.

Hybrid kinetic Monte Carlo algorithm for strongly trapping alloy systems

Abstract Selected solute atoms can strongly interact with and slow down the diffusion of point defects in alloy systems. While such additions can be beneficial, for instance to promote microstructural stability during thermal annealing or during irradiation by energetic particles, they create significant computational challenges when simulating these evolutions using atomistic techniques such as kinetic Monte Carlo (KMC) simulations. Point defect trapping in energy basins created by clusters of solute atoms leads to frequent re-visiting of states with short residence times, which dramatically reduces the efficiency of traditional KMC algorithms. We introduce here a hybrid algorithm that combines and expand on two prior KMC algorithms, the Chain KMC and the equilibrating basin KMC. This hybrid algorithm, referred to as the Equilibrating Chain algorithm, utilizes Chain KMC as previously reported, but leverages the data-handling framework to build an occupation distribution of the basin, allowing the equilibrating basin assumption to be statistically tested and applied. For a model A-B trapping alloy system on a face-centered cubic lattice, statistical comparisons of basin exit and cluster dissolution kinetics between traditional and accelerated KMC algorithms are presented to demonstrate the accuracy and the efficiency of the new algorithm. We also discuss our algorithm in the context of other accelerated KMC algorithms.

A kinematically unbiased, all-sky search for nearby, young, low-mass stars

ABSTRACT The past two decades have seen dramatic progress in our knowledge of the population of young stars of age $\lt \!200\,$ Myr that lie within $150\,$ pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the opportunity to explore (among many other things) the dissolution of stellar clusters and their diffusion into the field star population. Here, we exploit the combination of astrometric and photometric data from Gaia and photometric data from GALEX (UV) and 2MASS (near-IR) in an attempt to identify additional nearby, young, late-type stars. Specifically, we present a sample of 146 GALEX UV-selected late-type (predominantly K-type) field stars with Gaia-based distances $\lt \!125\,$ pc (based on Gaia Data Release 1) that have isochronal ages $\lt \!80\,$ Myr even if equal-components binaries. We investigate the spectroscopic and kinematic properties of this sample. Despite their young isochronal ages, only ∼10 per cent of stars among this sample can be confidently associated with established nearby, young moving groups (MGs). These candidate MG members include five stars newly identified in this study. The vast majority of our sample of 146 nearby young star candidates have anomalous kinematics relative to the known MGs. These stars may hence represent a previously unrecognized population of young stars that has recently mixed into the older field star population. We discuss the implications and caveats of such a hypothesis – including the intriguing fact that, in addition to their non-young-star-like kinematics, the majority of the UV-selected, isochronally young field stars within $50\,$ pc appear surprisingly X-ray faint.

Diffusion-mediated processes in Pt/Cu(001) surface alloy

In this paper we present the investigation of the diffusion-mediated processes in a Pt/Cu(001) surface alloy. We use the interatomic semiempirical TB-SMA interatomic potentials and the self-learning kinetic Monte Carlo method to investigate the following processes: order-disorder phase transition in the Pt/Cu(001) surface alloy, dissolution of small Pt clusters, and electromigration of small vacancy clusters in the topmost layer of the Pt/Cu(001) surface alloy. We have fitted the universal parameters of the interatomic TB-SMA potentials for the Pt–Cu system. The potentials reproduce bulk properties of copper and platinum as well as properties of the Pt/Cu(001) and Pt/Cu(111) surface alloys.

Radiation induced solute clustering in high-Ni reactor pressure vessel steel

The thermal stability and the structure of solute-vacancy clusters formed by neutron irradiation are studied by means of positron annihilation spectroscopy and hardness measurements of post-irradiation annealed reactor pressure vessel steels with high and low Ni contents. Two distinct recovery stages were observed and assigned to (a) the dissolution of vacancy clusters at about 650 K, and (b) the dissolution of solute-vacancy clusters at about 750 K. In steels with high Ni content, hardening mainly recovers during the second stage. Atomistic and coarse grain models suggest that during this stage, the removal of vacancies from vacancy-solute clusters leads to complete cluster dissolution, which indicates that solute clusters are radiation induced.

Transient crosslinking kinetics optimize gene cluster interactions.

Our understanding of how chromosomes structurally organize and dynamically interact has been revolutionized through the lens of long-chain polymer physics. Major protein contributors to chromosome structure and dynamics are condensin and cohesin that stochastically generate loops within and between chains, and entrap proximal strands of sister chromatids. In this paper, we explore the ability of transient, protein-mediated, gene-gene crosslinks to induce clusters of genes, thereby dynamic architecture, within the highly repeated ribosomal DNA that comprises the nucleolus of budding yeast. We implement three approaches: live cell microscopy; computational modeling of the full genome during G1 in budding yeast, exploring four decades of timescales for transient crosslinks between 5kbp domains (genes) in the nucleolus on Chromosome XII; and, temporal network models with automated community (cluster) detection algorithms applied to the full range of 4D modeling datasets. The data analysis tools detect and track gene clusters, their size, number, persistence time, and their plasticity (deformation). Of biological significance, our analysis reveals an optimal mean crosslink lifetime that promotes pairwise and cluster gene interactions through “flexible” clustering. In this state, large gene clusters self-assemble yet frequently interact (merge and separate), marked by gene exchanges between clusters, which in turn maximizes global gene interactions in the nucleolus. This regime stands between two limiting cases each with far less global gene interactions: with shorter crosslink lifetimes, “rigid” clustering emerges with clusters that interact infrequently; with longer crosslink lifetimes, there is a dissolution of clusters. These observations are compared with imaging experiments on a normal yeast strain and two condensin-modified mutant cell strains. We apply the same image analysis pipeline to the experimental and simulated datasets, providing support for the modeling predictions.

Modelling the Effects of Dark Matter Substructure on Globular Cluster Evolution with the Tidal Approximation

Abstract We present direct N-body simulations of tidally filling 30,000 M⊙ star clusters orbiting between 10 kpc and 100 kpc in galaxies with a range of dark matter substructure properties. The time-dependent tidal force is determined based on the combined tidal tensor of the galaxy’s smooth and clumpy dark matter components, the latter of which causes fluctuations in the tidal field that can heat clusters. The strength and duration of these fluctuations are sensitive to the local dark matter density, substructure fraction, sub-halo mass function, and the sub-halo mass-size relation. Based on the cold dark matter framework, we initially assume sub-halos are Hernquist spheres following a power-law mass function between 105 and 1011M⊙ and find that tidal fluctuations are too weak and too short to affect star cluster evolution. Treating sub-halos as point masses, to explore how denser sub-halos affect clusters, we find that only sub-halos with masses greater than 106M⊙ will cause cluster dissolution times to decrease. These interactions can also decrease the size of a cluster while increasing the velocity dispersion and tangential anisotropy in the outer regions via tidal heating. Hence increased fluctuations in the tidal tensor, especially fluctuations that are due to low-mass halos, do not necessarily translate into mass loss. We further conclude that the tidal approximation can be used to model cluster evolution in the tidal fields of cosmological simulations with a minimum cold dark matter sub-halo mass of 106M⊙, as the effect of lower-mass sub-halos on star clusters is negligible.

Mocca survey data base– i. Dissolution of tidally filling star clusters harbouring black hole subsystems

We investigate the dissolution process for dynamically evolving star clusters embedded in an external tidal field by exploring the MOCCA Survey Database I, with focus on the presence and evolution of a stellar-mass black hole subsystem. We argue that the presence of a black hole subsystem can lead to the dissolution of tidally filling star clusters and this can be regarded as a third type of cluster dissolution mechanism (in addition to well-known mechanisms connected with strong mass loss due to stellar evolution and mass loss connected with the relaxation process). This third process is characterized by abrupt cluster dissolution connected with the loss of dynamical equilibrium. The abrupt dissolution is powered by strong energy generation from a stellar-mass black hole subsystem accompanied by tidal stripping. Additionally, we argue that such a mechanism should also work for even tidally under-filling clusters with top-heavy initial mass function. Observationally, star clusters which undergo dissolution powered by the third mechanism would look as a 'dark cluster' i.e. composed of stellar mass black holes surrounded by an expanding halo of luminous stars (Banerjee & Kroupa 2011), and they should be different from 'dark clusters' harbouring intermediate mass black holes as discussed by Askar et al. (2017a). An additional observational consequence of an operation of the third dissolution mechanism should be a larger than expected abundance of free floating black holes in the Galactic halo.

Orbits of Open Star Clusters NGC 6067, NGC 2506 ANG IC 465

The studies of the orbits of star clusters are very important to understand the evolution of these objects. The survival or dissolution of star clusters in galactic tides within which they orbit depends on their orbit history. The orbits of three galactic clusters namely NGC 6067, NGC 2506 and IC 4651 are calculated using newly available proper motion data taken from GAIA data. These orbits are traced backwards in time which is equal to the age of the clusters. The main parameters of the orbits such as eccentricity, apogalactic distance and perigalactic distance are calculated.

Orbits of Open Star Clusters NGC 6067, NGC 2506 ANG IC 465

The studies of the orbits of star clusters are very important to understand the evolution of these objects. The survival or dissolution of star clusters in galactic tides within which they orbit depends on their orbit history. The orbits of three galactic clusters namely NGC 6067, NGC 2506 and IC 4651 are calculated using newly available proper motion data taken from GAIA data. These orbits are traced backwards in time which is equal to the age of the clusters. The main parameters of the orbits such as eccentricity, apogalactic distance and perigalactic distance are calculated.

Radiation Induced Solute Clustering in High-Ni Reactor Pressure Vessel Steel

The thermal stability and the structure of solute-vacancy clusters formed by neutron irradiation are studied by means of positron annihilation spectroscopy and hardness measurements of post-irradiation annealed reactor pressure vessel steels with high and low Ni contents. Two distinct recovery stages were observed and assigned to (a) the dissolution of vacancy clusters at about 650 K, and (b) the dissolution of solute-vacancy clusters at about 750 K. In steels with high Ni content, hardening mainly recovers during the second stage. Atomistic and coarse grain models suggest that during this stage, the removal of vacancies from vacancy-solute clusters leads to complete cluster dissolution, which indicates that solute clusters are radiation induced.

Alkali-activation of CaO-FeOx-SiO2 slag: Formation mechanism from in-situ X-ray total scattering

The pursuit of low-CO2 technologies has led to a surge in research on alternative cementitious materials, of which alkali-activated materials are a large family. In recent years alkali-activated materials have expanded to encompass Fe-rich precursors in addition to the more commonly employed aluminosilicate precursors. The formation mechanism of alkali-activated materials from two Fe-rich synthetic slags has been assessed by employing in-situ X-ray total scattering and subsequent pair distribution function analysis. The evolution of the local atom-atom correlations reveals three reaction stages. After the dissolution of Fe-silicate clusters from the slag, a binder phase is formed with Fe in both Fe2+ and Fe3+ oxidation states. The Fe2+ state is present in the form of trioctahedral layers, similar to those in Fe(OH)2, while the Fe3+ is likely located in the polymerized silicate network. Exposure to air causes the Fe2+ species to transition to the Fe3+ state.

MOCCA-SURVEY Database I: Dissolution of tidally filling star clusters harboring black hole subsystem

AbstractWe investigate the dissolution process of star clusters embedded in an external tidal field and harboring a subsystem of stellar-mass black hole. For this purpose we analyzed the MOCCA models of real star clusters contained in the Mocca Survey Database I. We showed that the presence of a stellar-mass black hole subsystem in tidally filling star cluster can lead to abrupt cluster dissolution connected with the loss of cluster dynamical equilibrium. Such cluster dissolution can be regarded as a third type of cluster dissolution mechanism. We additionally argue that such a mechanism should also work for tidally under-filling clusters with a top-heavy initial mass function.

Digoxin Induced Dissolution of CTC Clusters

Digoxin Induced Dissolution of CTC Clusters

Effects of H2O2 Concentration on Formation of Uranyl Peroxide Species Probed by Dissolution of Uranium Nitride and Uranium Dioxide.

Dissolution of uranium materials in alkaline aqueous conditions containing H2O2 results in uranyl peroxide species in solution, including anionic uranyl peroxide cage clusters. Uranyl peroxide cage clusters are generally highly soluble in water, where they persist as aqueous macroanions. Previous studies indicate that uranyl cluster speciation and dissolution of uranium materials is impacted by the concentration of alkali metal in solution, but in these studies, high concentrations of H2O2 were used. Herein, the role of hydrogen peroxide concentration is examined relative to the dissolution of powdered UN and UO2. Lower initial H2O2 concentrations reduce dissolution of UO2 and UN and tend to produce simple (small) uranyl peroxide species rather the highly soluble uranyl peroxide clusters. H2O2 availability will have implications for uranyl speciation and solubility where spent nuclear fuel is in contact with water and where alkaline peroxide conditions are used in dissolution of nuclear material.

Effect of Ar Post-irradiations on Magnetic Properties of Cu-Implanted ZnO Single Crystals

Ar+ post-irradiation effects on magnetic behavior of Cu+-implanted ZnO single crystals were studied. It was found that Cu+-implanted and Ar+-irradiated samples, even the primary sample, showed a magnetic moment (MM), but the saturation magnetization (MS) of Ar+ post-irradiated on Cu+ as-implanted one drastically decreased. Based on the first-principle method, it was drawn to the incomplete filling electronic configuration of the substituted Cu ion whose 3d orbital hybridized with O-2p contributing to the magnetism. The MM induced by the substituted Cu+ ion was much less than that induced by the substituted Cu2+ and Cu3+ ion, so the ratio of Cu2+,3+/Cu+ decreased after Ar+ post-irradiation, leading to the decrease of MS. The excessive concentration of O vacancy induced by post-irradiation also weakened the MM by their compensating electrons, and decreased the effective magnetic exchange coupling interaction. Cu-related clusters dissolution was also a critical reason for the reduction of MS.

Conversion of InP Clusters to Quantum Dots.

Understanding and deconvoluting the different mechanisms involved in the synthesis of nanomaterials is necessary to make uniform materials with desirable function. In this study, in situ spectroscopic methods were used to study exchange reactions at the surface of indium phosphide clusters, revealing that the cluster surface lacks significant dynamics on the NMR time-scale at room temperature. The exchange of surface carboxylate ligands can be induced at elevated temperatures and with the addition of carboxylic acid and indium carboxylate. These studies suggest that carboxylate may be a key ingredient in promoting cluster dissolution to larger nanostructures. Toward this end, the evolution of InP clusters was examined by in situ UV-vis spectroscopy, revealing cluster dissolution and renucleation that is dramatically dependent on the concentration of carboxylate. In addition to the concentration of exogenous ligands, the rate of particle growth and final product distribution were dependent on temperature and initial cluster concentration. These results, taken together, suggest a mechanism of cluster evolution involving cluster dissociation to form multiple reactive monomer species that renucleate and grow to larger nanomaterials. Nonproductive monomer degradation is observed in the lower temperature regime (<200 °C), suggesting a critical temperature threshold for efficient cluster to quantum dot conversion.

Size-dependent variability in the formation and trade-offs of facultative aggregations in golden orb-web spiders (Nephila clavipes)

The vast majority (> 99.99%) of spiders are solitary, but in some species, individuals form stable groups or, alternatively, looser aggregations that fluctuate over space and time. While previous work has documented trade-offs associated with being part of intraspecific groups, rather than being solitary, we know less about why grouping behavior would be facultative. Residing in a group can reduce predation risk, but also lead to competition for food, and we hypothesized that variation in these trade-offs could provide insights into the optional nature of clustering. We used a Costa Rican population of golden orb-web spiders, Nephila clavipes, to ask two questions. First, we tested whether a spider’s size influenced the trade-offs of clustering, and second, whether inter-annual variation in predator and prey abundance could help explain clustering patterns. We also examined the process of cluster formation and dissolution in relation to spider size. Data collected on over 1500 spiders over 4 years indicated that in each year, small spiders experienced the greatest reduction in predation if clustered and also were most likely to initiate aggregations. Overall rates of predation varied significantly among years, and small spiders were most likely to cluster in the year with highest predation. We also detected a cost of clustering in the form of reduced prey capture, but only in years with relatively high overall prey acquisition. Together, these findings suggest that trade-offs that vary individually and over time could influence a spider’s decision to cluster and, hence, explain the facultative nature of aggregating in this population. Animals within a population can show variability in a range of behaviors, such as foraging and predator avoidance, and at times, the ideal way of behaving depends on individual or environmental conditions. In this study, we asked why some female golden orb-web spiders (Nephila clavipes) form groups, while in the same population, others are solitary. This is an interesting question given how rare aggregations are among spiders. In our study, small spiders benefited most from clustering in terms of higher survival when aggregated compared to when solitary. At the same time, spiders of all sizes captured less prey when aggregated, although this cost was only detected in years with relatively abundant prey. Together, these findings suggest that trade-offs that vary individually and over time could influence a spider’s decision to cluster and, hence, explain the optional nature of aggregating in this population.

The Long-term Evolution of Star Clusters Formed with a Centrally Peaked Star Formation Efficiency Profile

Abstract We have studied the long-term evolution of star clusters of the solar neighborhood, starting from their birth in gaseous clumps until their complete dissolution in the Galactic tidal field. We have combined the “local-density-driven cluster formation model” of Parmentier &amp; Pfalzner with direct N-body simulations of clusters following instantaneous gas expulsion. We have studied the relation between cluster dissolution time, t dis, and cluster “initial” mass, M init, defined as the cluster mass at the end of the dynamical response to gas expulsion (i.e., violent relaxation), when the cluster age is 20–30 Myr. We consider the “initial” mass to be consistent with other works that neglect violent relaxation. The model clusters formed with a high star formation efficiency (SFE, i.e., gas mass fraction converted into stars) follow a tight mass-dependent relation, in agreement with previous theoretical studies. However, the low-SFE models present a large scatter in both the “initial” mass and the dissolution time, a shallower mass-dependent relation than high-SFE clusters, and most dissolve within 1 Gyr (cluster teenage mortality). Both groups differ in their structural properties on average. Combining two populations of clusters, high- and low-SFE ones, with domination of the latter, yields a cluster dissolution time for the solar neighborhood in agreement with that inferred from observations, without any additional destructive processes such as giant molecular cloud encounters. An apparent mass-independent relation may emerge for our low-SFE clusters when we neglect low-mass clusters (as expected for extragalactic observations), although more simulations are needed to investigate this aspect.