Showing papers on "Cluster (physics) published in 2018"

Integration K-Means Clustering Method and Elbow Method For Identification of The Best Customer Profile Cluster

Abstract: Clustering is a data mining technique used to analyse data that has variations and the number of lots. Clustering was process of grouping data into a cluster, so they contained data that is as similar as possible and different from other cluster objects. SMEs Indonesia has a variety of customers, but SMEs do not have the mapping of these customers so they did not know which customers are loyal or otherwise. Customer mapping is a grouping of customer profiling to facilitate analysis and policy of SMEs in the production of goods, especially batik sales. Researchers will use a combination of K-Means method with elbow to improve efficient and effective k-means performance in processing large amounts of data. K-Means Clustering is a localized optimization method that is sensitive to the selection of the starting position from the midpoint of the cluster. So choosing the starting position from the midpoint of a bad cluster will result in K-Means Clustering algorithm resulting in high errors and poor cluster results. The K-means algorithm has problems in determining the best number of clusters. So Elbow looks for the best number of clusters on the K-means method. Based on the results obtained from the process in determining the best number of clusters with elbow method can produce the same number of clusters K on the amount of different data. The result of determining the best number of clusters with elbow method will be the default for characteristic process based on case study. Measurement of k-means value of k-means has resulted in the best clusters based on SSE values on 500 clusters of batik visitors. The result shows the cluster has a sharp decrease is at K = 3, so K as the cut-off point as the best cluster.

Clustering huge protein sequence sets in linear time

Abstract: Metagenomic datasets contain billions of protein sequences that could greatly enhance large-scale functional annotation and structure prediction. Utilizing this enormous resource would require reducing its redundancy by similarity clustering. However, clustering hundreds of millions of sequences is impractical using current algorithms because their runtimes scale as the input set size N times the number of clusters K, which is typically of similar order as N, resulting in runtimes that increase almost quadratically with N. We developed Linclust, the first clustering algorithm whose runtime scales as N, independent of K. It can also cluster datasets several times larger than the available main memory. We cluster 1.6 billion metagenomic sequence fragments in 10 h on a single server to 50% sequence identity, >1000 times faster than has been possible before. Linclust will help to unlock the great wealth contained in metagenomic and genomic sequence databases. Billions of metagenomic and genomic sequences fill up public datasets, which makes similarity clustering an important and time-critical analysis step. Here, the authors develop Linclust, an algorithm with linear time complexity that can cluster over a billion sequences within hours on a single server.

Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials

Abstract: Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. One of the early motivations in studying clusters was to understand how the properties of matter evolve as a function of size, shape, and composition. Over the past few decades, more than 200 000 papers have been published in this field. These studies have not only led to a considerable understanding of this evolution from clusters to crystals, but also have revealed many unusual size-specific properties that make cluster science an interdisciplinary field on its own, bridging physics, chemistry, materials science, biology, and medicine. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties. This Review focuses on the properties ...

A catalogue of masses, structural parameters, and velocity dispersion profiles of 112 Milky Way globular clusters

Abstract: We have determined masses, stellar mass functions, and structural parameters of 112 Milky Way globular clusters by fitting a large set of N-body simulations to their velocity dispersion and surface density profiles. The velocity dispersion profiles were calculated based on a combination of more than 15000 high-precision radial velocities which we derived from archival ESO/VLT and Keck spectra together with similar to 20000 published radial velocities from the literature. Our fits also include the stellar mass functions of the globular clusters, which are available for 47 clusters in our sample, allowing us to self-consistently take the effects of mass segregation and ongoing cluster dissolution into account. We confirm the strong correlation between the global mass functions of globular clusters and their relaxation times recently found by Sollima & Baumgardt (2017). We also find a correlation of the escape velocity from the centre of a globular cluster and the fraction of first generation stars (FG) in the cluster recently derived for 57 globular clusters by Milone et al. (2017), but no correlation between the FG star fraction and the global mass function of a globular cluster. This could indicate that the ability of a globular cluster to keep the wind ejecta from the polluting star(s) is the crucial parameter determining the presence and fraction of second-generation stars and not its later dynamical mass loss.

Oriented electron transmission in polyoxometalate-metalloporphyrin organic framework for highly selective electroreduction of CO 2

Abstract: The design of highly stable, selective and efficient electrocatalysts for CO2 reduction reaction is desirable while largely unmet. In this work, a series of precisely designed polyoxometalate-metalloporphyrin organic frameworks are developed. Noted that the integration of {e-PMo8VMo4VIO40Zn4} cluster and metalloporphyrin endows these polyoxometalate-metalloporphyrin organic frameworks greatly advantages in terms of electron collecting and donating, electron migration and electrocatalytic active component in the CO2 reduction reaction. Thus-obtained catalysts finally present excellent performances and the mechanisms of catalysis processes are discussed and revealed by density functional theory calculations. Most importantly, Co-PMOF exhibits remarkable faradaic efficiency ( > 94%) over a wide potential range (−0.8 to −1.0 V). Its best faradaic efficiency can reach up to 99% (highest in reported metal-organic frameworks) and it exhibits a high turnover frequency of 1656 h−1 and excellent catalysis stability ( > 36 h). While CO2 reduction provides a way to remove carbon from the atmosphere, it is challenging to design effective, selective materials for this process. Here, authors construct metal-organic frameworks from polyoxometalates and porphryins to direct electron flow and improve CO2 reduction efficiencies.

Atomic-Level Doping of Metal Clusters.

Abstract: ConspectusAtomically precise noble metal (mainly silver and gold) nanoclusters are an emerging category of promising functional materials for future applications in energy, sensing, catalysis, and nanoelectronics. These nanoclusters are protected by ligands such as thiols, phosphines, and hydride and have sizes between those of atoms and plasmonic nanoparticles. In metallurgy, the properties of a pure metal are modified by the addition of other metals, which often offers augmented characteristics, making them more utilizable for real-life applications. In this Account, we discuss how the incorporation of various metal atoms into existing protected nanoclusters tunes their structure and properties.The process of incorporating metals into an existing cluster is known as doping; the product is known as a doped cluster, and the incorporated metal atom is called a dopant/foreign atom. We first present a brief historical overview of protected clusters and the need for doping and explain (with examples) the diff...

Alloy Clusters: Precise Synthesis and Mixing Effects

Abstract: ConspectusMetal alloys exhibit functionalities unlike those of single metals. Such alloying has drawn considerable research interest, particularly for nanoscale particles (metal clusters/nanoparticles), from the viewpoint of creating new functional nanomaterials. In gas phase cluster research, generated alloy clusters can be spatially separated with atomic precision in vacuum. Thus, the influences of increases or decreases in each element on the overall electronic structure of the cluster can be elucidated. However, to further understand the related mixing and synergistic effects, alloy clusters need to be produced on a large scale and characterized by various techniques. Because alloy clusters protected by thiolate (SR) can be synthesized by chemical methods and are stable in both solution and the solid state, these clusters are ideal study materials to better understand the mixing and synergistic effects. Moreover, the alloy clusters thus created have potential applications as functional materials. Ther...

PCL: Proposal Cluster Learning for Weakly Supervised Object Detection

Abstract: Weakly Supervised Object Detection (WSOD), using only image-level annotations to train object detectors, is of growing importance in object recognition. In this paper, we propose a novel deep network for WSOD. Unlike previous networks that transfer the object detection problem to an image classification problem using Multiple Instance Learning (MIL), our strategy generates proposal clusters to learn refined instance classifiers by an iterative process. The proposals in the same cluster are spatially adjacent and associated with the same object. This prevents the network from concentrating too much on parts of objects instead of whole objects. We first show that instances can be assigned object or background labels directly based on proposal clusters for instance classifier refinement, and then show that treating each cluster as a small new bag yields fewer ambiguities than the directly assigning label method. The iterative instance classifier refinement is implemented online using multiple streams in convolutional neural networks, where the first is an MIL network and the others are for instance classifier refinement supervised by the preceding one. Experiments are conducted on the PASCAL VOC, ImageNet detection, and MS-COCO benchmarks for WSOD. Results show that our method outperforms the previous state of the art significantly.

The E-MOSAICS project: simulating the formation and co-evolution of galaxies and their star cluster populations

Abstract: We introduce the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) project. E-MOSAICS incorporates models describing the formation, evolution, and disruption of star clusters into the EAGLE galaxy formation simulations, enabling the examination of the co-evolution of star clusters and their host galaxies in a fully cosmological context. A fraction of the star formation rate of dense gas is assumed to yield a cluster population; this fraction and the population’s initial properties are governed by the physical properties of the natal gas. The subsequent evolution and disruption of the entire cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. This introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ∼L galaxies with disc-like morphologies atz = 0. The simulations broadly reproduce key observed characteristics of young star clusters and globular clusters (GCs), without invoking separate formation mechanisms for each population. The simulated GCs are the surviving population of massive clusters formed at early epochs (z 1–2), when the characteristic pressures and surface densities of star-forming gas were significantly higher than observed in local galaxies. We examine the influence of the star formation and assembly histories of galaxies on their cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient cluster population, while galaxies with late mergers are capable of forming massive clusters even at late cosmic epochs. We find that the phenomenological treatment of interstellar gas in EAGLE precludes the accurate modelling of cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome this shortcoming.

A stellar census in globular clusters with MUSE: The contribution of rotation to cluster dynamics studied with 200 000 stars

Abstract: This is the first of a series of papers presenting the results from our survey of 25 Galactic globular clusters with the MUSE integral-field spectrograph. In combination with our dedicated algorithm for source deblending, MUSE provides unique multiplex capabilities in crowded stellar fields and allows us to acquire samples of up to 20 000 stars within the half-light radius of each cluster. The present paper focuses on the analysis of the internal dynamics of 22 out of the 25 clusters, using about 500 000 spectra of 200 000 individual stars. Thanks to the large stellar samples per cluster, we are able to perform a detailed analysis of the central rotation and dispersion fields using both radial profiles and two-dimensional maps. The velocity dispersion profiles we derive show a good general agreement with existing radial velocity studies but typically reach closer to the cluster centres. By comparison with proper motion data we derive or update the dynamical distance estimates to 14 clusters. Compared to previous dynamical distance estimates for 47 Tuc, our value is in much better agreement with other methods. We further find significant (>3sigma) rotation in the majority (13/22) of our clusters. Our analysis seems to confirm earlier findings of a link between rotation and the ellipticities of globular clusters. In addition, we find a correlation between the strengths of internal rotation and the relaxation times of the clusters, suggesting that the central rotation fields are relics of the cluster formation that are gradually dissipated via two-body relaxation.

Atom-Precise Modification of Silver(I) Thiolate Cluster by Shell Ligand Substitution: A New Approach to Generation of Cluster Functionality and Chirality.

Abstract: To realize the molecular design of new functional silver(I) clusters, a new synthetic approach has been proposed, by which the weakly coordinating ligands NO3– in a Ag20 thiolate cluster precursor can be substituted by carboxylic ligands while keeping its inner core intact. By rational design, novel atom-precise carboxylic or amino acid protected 20-core Ag(I)-thiolate clusters have been demonstrated for the first time. The fluorescence and electrochemical activity of the postmodified Ag20 clusters can be modulated by alrestatin or ferrocenecarboxylic acid substitution. More strikingly, when chiral amino acids were used as postmodified ligands, CD-activity was observed for the Ag20 clusters, unveiling an efficient way to obtain atom-precise chiral silver(I) clusters.

Aggregation-fragmentation and individual dynamics of active clusters.

Abstract: A remarkable feature of active matter is the propensity to self-organize. One striking instance of this ability to generate spatial structures is the cluster phase, where clusters broadly distributed in size constantly move and evolve through particle exchange, breaking or merging. Here we propose an exhaustive description of the cluster dynamics in apolar active matter. Exploiting large statistics gathered on thousands of Janus colloids, we measure the aggregation and fragmentation rates and rationalize the resulting cluster size distribution and fluctuations. We also show that the motion of individual clusters is entirely consistent with a model positing random orientation of colloids. Our findings establish a simple, generic model of cluster phase, and pave the way for a thorough understanding of clustering in active matter.

Central Doping of a Foreign Atom into the Silver Cluster for Catalytic Conversion of CO2 toward C-C Bond Formation.

Abstract: Clusters with an exact number of atoms are of particular interest in catalysis. Their catalytic behaviors can be potentially altered with the addition or removal of a single atom. Now the effects of doping with a single foreign atom (Au, Pd, and Pt) into the core of an Ag cluster with 25 atoms on the catalytic properties are explored, where the foreign atom is protected by 24 Ag atoms (Au@Ag24 , Pd@Ag24 , and Pt@Ag24 ). The central doping of a single atom into the Ag25 cluster has a substantial influence on the catalytic performance in the carboxylation reaction of CO2 with terminal alkyne through C-C bond formation to produce propiolic acid. These studies reveal that the catalytic properties of the cluster catalysts can be dramatically changed with the subtle alteration by a single atom away from the active sites.

Structural Stability and Evolution of Medium-Sized Tantalum-Doped Boron Clusters: A Half-Sandwich-Structured TaB12 – Cluster

Abstract: Transition-metal (TM)-doped boron clusters have received considerable attention in recent years, in part, because of their remarkable size-dependent structural and electronic properties. However, the structures of medium-sized boron clusters doped with TM atoms are still not well-known because of the much increased complexity of the potential surface as well as the rapid increase in the number of low-energy isomers, which are the challenges in cluster structural searches. Here, by means of an unbiased structure search, we systematically investigated the structural evolution of medium-sized tantalum-doped boron clusters, TaBn0/- (n = 10-20). The results revealed that TaBn0/- (n = 10-15) clusters adopt half-sandwich molecular geometries, with the notable exception of TaB10-, while for n = 16-18 and 19-20, the lowest-energy clusters are characterized by drum-type geometries and tubular molecules with two B atoms on the top, respectively. Good agreement between the calculated and experimental photoelectron spectra strongly support the validity of our global minimum structures. Molecular orbital and adaptive natural density partitioning analyses indicate that the enhanced stability of half-sandwich TaB12- is due to the strong interaction of the Ta atom (5d orbitals) with surrounding B atoms (2p orbitals) and σ B-B bonds in the B12 moiety.

Metastable Structures in Cluster Catalysis from First-Principles: Structural Ensemble in Reaction Conditions and Metastability Triggered Reactivity

Abstract: Reactivity studies on catalytic transition metal clusters are usually performed on a single global minimum structure. With the example of a Pt13 cluster under a pressure of hydrogen, we show from first-principle calculations that low energy metastable structures of the cluster can play a major role for catalytic reactivity and that hence consideration of the global minimum structure alone can severely underestimate the activity. The catalyst is fluxional with an ensemble of metastable structures energetically accessible at reaction conditions. A modified genetic algorithm is proposed to comprehensively search for the low energy metastable ensemble (LEME) structures instead of merely the global minimum structure. In order to reduce the computational cost of density functional calculations, a high dimensional neural network potential is employed to accelerate the exploration. The presence and influence of LEME structures during catalysis is discussed by the example of H covered Pt13 clusters for two reactions of major importance: hydrogen evolution reaction and methane activation. The results demonstrate that although the number of accessible metastable structures is reduced under reaction condition for Pt13 clusters, these metastable structures can exhibit high activity and dominate the observed activity due to their unique electronic or structural properties. This underlines the necessity of thoroughly exploring the LEME structures in catalysis simulations. The approach enables one to systematically address the impact of isomers in catalysis studies, taking into account the high adsorbate coverage induced by reaction conditions.

Magic number colloidal clusters as minimum free energy structures.

Abstract: Clusters in systems as diverse as metal atoms, virus proteins, noble gases, and nucleons have properties that depend sensitively on the number of constituent particles. Certain numbers are termed ‘magic’ because they grant the system with closed shells and exceptional stability. To this point, magic number clusters have been exclusively found with attractive interactions as present between atoms. Here we show that magic number clusters exist in a confined soft matter system with negligible interactions. Colloidal particles in an emulsion droplet spontaneously organize into a series of clusters with precisely defined shell structures. Crucially, free energy calculations demonstrate that colloidal clusters with magic numbers possess higher thermodynamic stability than those off magic numbers. A complex kinetic pathway is responsible for the efficiency of this system in finding its minimum free energy configuration. Targeting similar magic number states is a strategy towards unique configurations in finite self-organizing systems across the scales. Magic number cluster with closed shells and increased stability often result from potential energy minimization between attractive atoms or particles. Here, Wang et al. show that such magic number clusters can also result from entropy maximization in colloidal systems with negligible interactions.

Phosphine-Ligated Gold Clusters with Core+ exo Geometries: Unique Properties and Interactions at the Ligand-Cluster Interface.

Abstract: ConspectusOver recent years, research on the structures and properties of ligand-protected gold cluster molecules has gained significant interest. The crystal structure information accumulated to date has revealed the structural preference to adopt closed polyhedral geometries, but the use of multidentate ligands sometimes leads to the formation of exceptional structures. This Account describes results of our studies on diphosphine-coordinated [core+exo]-type gold clusters featuring extra gold atoms outside the polyhedral cores, highlighting (1) their distinct optical properties due to the unique electronic structures generated by the exo gold atoms and (2) electronic/attractive ligand–cluster interactions that cause definite perturbation effects on the cluster properties.Subnanometer gold clusters with [core+exo]-type geometries (nuclearity = 6, 7, 8, and 11) commonly displayed single absorption bands in the visible region, which are distinct in patterns from those of conventional polyhedral-only homolog...

CE3: A three-way clustering method based on mathematical morphology

Abstract: Many existing clustering methods produce clusters with clear and sharp boundaries, which does not truly reflect the fact that a cluster may not necessarily have a well-defined boundary in many real world situations. In this paper, by combining ideas of erosion and dilation from mathematical morphology and principles of three-way decision, we propose a framework of a contraction-and-expansion based three-way clustering called CE3. A three-way cluster is defined by a nested pair of sets called the core and the support of the cluster, respectively. A stronger relationship holds between objects in the core and a weaker relationship holds between objects in the support. Given a cluster obtained from a hard clustering method, CE3 uses a contraction operation to shrink the cluster into the core of a three-way cluster and uses an expansion operation to enlarge the cluster into the support. The difference between the support and the core is called the fringe region, representing an unsharp boundary of a cluster. Within the CE3 framework, we can define different types of contraction and expansion operations. We can apply the CE3 framework on the top of any existing clustering method. As examples for demonstration, we introduce a pair of neighbor-based contraction and expansion operations and apply the CE3 framework on the top of k-means and spectral clustering, respectively. We use one synthetic data set, five UCI data sets, and three USPS data sets to evaluate experimentally the performance of CE3. The results show that CE3 is in fact effective in revealing cluster structures.

The XXL Survey : XX : the 365 cluster catalogue

Abstract: Context. In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical.Aims. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detected clusters suitable for cosmological studies. The main goal of present article is to make public and describe the properties of the cluster catalogue in its present state, as well as of associated catalogues of more specific objects such as super-clusters and fossil groups.Methods. Following from the publication of the hundred brightest XXL clusters, we now release a sample containing 365 clusters in total, down to a flux of a few 10−15 erg s−1 cm−2 in the [0.5–2] keV band and in a 1′ aperture. This release contains the complete subset of clusters for which the selection function is well determined plus all X-ray clusters which are, to date, spectroscopically confirmed. In this paper, we give the details of the follow-up observations and explain the procedure adopted to validate the cluster spectroscopic redshifts. Considering the whole XXL cluster sample, we have provided two types of selection, both complete in a particular sense: one based on flux-morphology criteria, and an alternative based on the [0.5–2] keV flux within 1 arcmin of the cluster centre. We have also provided X-ray temperature measurements for 80% of the clusters having a flux larger than 9 × 10−15 erg s−1 cm−2 .Results. Our cluster sample extends from z ~ 0 to z ~ 1.2, with one cluster at z ~ 2. Clusters were identified through a mean number of six spectroscopically confirmed cluster members. The largest number of confirmed spectroscopic members in a cluster is 41. Our updated luminosity function and luminosity–temperature relation are compatible with our previous determinations based on the 100 brightest clusters, but show smaller uncertainties. We also present an enlarged list of super-clusters and a sample of 18 possible fossil groups.Conclusions. This intermediate publication is the last before the final release of the complete XXL cluster catalogue when the ongoing C2 cluster spectroscopic follow-up is complete. It provides a unique inventory of medium-mass clusters over a 50 deg2 area out to z ~ 1.

Integration of Lanthanide–Transition-Metal Clusters onto CdS Surfaces for Photocatalytic Hydrogen Evolution

Abstract: Heterometallic lanthanide-transition-metal (4f-3d) clusters with well-defined crystal structures integrate multiple metal centers and provide a platform for achieving synergistic catalytic effects. Herein, we present a strategy for enhanced hydrogen evolution by loading atomically precise 4f-3d clusters Ln52 Ni56 on a CdS photoabsorber surface. Interestingly, some Ni2+ ions in the clusters Ln52 Ni56 were exchanged by the Cd2+ to form Ln52 Ni56-x Cdx /CdS composites. Photocatalytic studies show that the efficient synergistic multipath charge separation and transfer from CdS to the Eu52 Ni56-x Cdx cluster enable high visible-light-driven hydrogen evolution at 25 353 μmol h-1 g-1 . This work provides the strategy to design highly active photocatalytic hydrogen evolution catalysts by assembling heterometallic 4f-3d clusters on semiconductor materials.

Formation of globular cluster candidates in merging proto-galaxies at high redshift: a view from the FIRE cosmological simulations

Abstract: Using a state-of-the-art cosmological simulation of merging proto-galaxies at high redshift from the FIRE project, with explicit treatments of star formation and stellar feedback in the interstellar medium, we investigate the formation of star clusters and examine one of the formation hypotheses of present-day metal-poor globular clusters. We find that frequent mergers in high-redshift proto-galaxies could provide a fertile environment to produce long-lasting bound star clusters. The violent merger event disturbs the gravitational potential and pushes a large gas mass of ≳ 10^(5–6) M⊙ collectively to high density, at which point it rapidly turns into stars before stellar feedback can stop star formation. The high dynamic range of the reported simulation is critical in realizing such dense star-forming clouds with a small dynamical time-scale, t_(ff)≲ 3 Myr, shorter than most stellar feedback time-scales. Our simulation then allows us to trace how clusters could become virialized and tightly bound to survive for up to ∼420 Myr till the end of the simulation. Because the cluster's tightly bound core was formed in one short burst, and the nearby older stars originally grouped with the cluster tend to be preferentially removed, at the end of the simulation the cluster has a small age spread.

The XXL Survey XX: The 365 cluster catalogue.

Abstract: In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detected clusters suitable for cosmological studies. The main goal of present article is to make public and describe the properties of the cluster catalogue in its present state, as well as of associated catalogues as super-clusters and fossil groups. We release a sample containing 365 clusters in total. We give the details of the follow-up observations and explain the procedure adopted to validate the cluster spectroscopic redshifts. Considering the whole XXL cluster sample, we have provided two types of selection, both complete in a particular sense: one based on flux-morphology criteria, and an alternative based on the [0.5-2] keV flux within one arcmin of the cluster centre. We have also provided X-ray temperature measurements for 80$\%$ of the clusters having a flux larger than 9$\times$10$^{-15}$$\rm \thinspace erg \, s^{-1} \, cm^{-2}$. Our cluster sample extends from z$\sim$0 to z$\sim$1.2, with one cluster at z$\sim$2. Clusters were identified through a mean number of six spectroscopically confirmed cluster members. Our updated luminosity function and luminosity-temperature relation are compatible with our previous determinations based on the 100 brightest clusters, but show smaller uncertainties. We also present an enlarged list of super-clusters and a sample of 18 possible fossil groups. This intermediate publication is the last before the final release of the complete XXL cluster catalogue when the ongoing C2 cluster spectroscopic follow-up is complete. It provides a unique inventory of medium-mass clusters over a 50~\dd\ area out to z$\sim$1.

Deciphering synergetic core-shell transformation from [Mo 6 O 22 @Ag 44 ] to [Mo 8 O 28 @Ag 50 ].

Abstract: The structural transformation of high-nuclearity silver clusters from one to another induced by specific stimuli is of scientific significance in terms of both cluster synthesis and reactivity. Herein, we report two silver-thiolate clusters, [Mo6O22@Ag44] and [Mo8O28@Ag50], which are templated by isopolymolybdates inside and covered by iPrS− and PhCOO− ligands on the surfaces. Amazingly, the [Mo8O28@Ag50] can be transformed from [Mo6O22@Ag44] by adding PhCOOH which increases the degree of condensation of molybdates template from Mo6O228- to Mo8O288-, then enlarging the outer silver shell from Ag44 to Ag50. The evolution of solution species revealed by time-dependent electrospray ionization mass spectrometry (ESI-MS) suggests a breakage-growth-reassembly (BGR) transformation mechanism. These results not only provide a combined assembly strategy (anion-template + induced transformation) for the synthesis of silver-thiolate clusters but also help us to better understand the complex transformation process underpinning the assembly system. Understanding how one metal nanocluster transforms into another is of synthetic and fundamental importance. Here, the authors use mass spectrometry to reveal an acid-induced structural transformation between two Ag clusters that proceeds via a breakage-growth-reassembly mechanism.

Cluster phases and bubbly phase separation in active fluids: Reversal of the Ostwald process

Abstract: A new analysis shows how to describe microphase-separated states in active matter systems, and that they should be expected generically in active fluids.

Perspective: Size selected clusters for catalysis and electrochemistry

Abstract: Size-selected clusters containing a handful of atoms may possess noble catalytic properties different from nano-sized or bulk catalysts. Size- and composition-selected clusters can also serve as models of the catalytic active site, where an addition or removal of a single atom can have a dramatic effect on their activity and selectivity. In this perspective, we provide an overview of studies performed under both ultra-high vacuum and realistic reaction conditions aimed at the interrogation, characterization, and understanding of the performance of supported size-selected clusters in heterogeneous and electrochemical reactions, which address the effects of cluster size, cluster composition, cluster–support interactions, and reaction conditions, the key parameters for the understanding and control of catalyst functionality. Computational modeling based on density functional theory sampling of local minima and energy barriers or ab initio molecular dynamics simulations is an integral part of this research by providing fundamental understanding of the catalytic processes at the atomic level, as well as by predicting new materials compositions which can be validated in experiments. Finally, we discuss approaches which aim at the scale up of the production of well-defined clusters for use in real world applications.

Co-crystallization of atomically precise metal nanoparticles driven by magic atomic and electronic shells

Abstract: This paper reports co-crystallization of two atomically precise, different-size ligand-stabilized nanoclusters, a spherical (AuAg)267(SR)80 and a smaller trigonal-prismatic (AuAg)45(SR)27(PPh3)6 in 1:1 ratio, characterized fully by X-ray crystallographic analysis (SR = 2,4-SPhMe2). The larger cluster has a four concentric-shell icosahedral structure of Ag@M12@M42@M92@Ag120(SR)80 (M = Au or Ag) with the inner-core M147 icosahedron observed here for metal nanoparticles. The cluster has an open electron shell of 187 delocalized electrons, fully metallic, plasmonic behavior, and a zero HOMO-LUMO energy gap. The smaller cluster has an 18-electron shell closing, a notable HOMO-LUMO energy gap and a molecule-like optical spectrum. This is the first direct demonstration of the simultaneous presence of competing effects (closing of atom vs. electron shells) in nanocluster synthesis and growth, working together to form a co-crystal of different-sized clusters. This observation suggests a strategy that may be helpful in the design of other nanocluster systems via co-crystallization.

The Lithium Depletion Boundary and the Age of the Hyades Cluster

Abstract: Determination of the lithium depletion boundary (LDB), i.e., the observational limit below which the cores of very low-mass objects do not reach high enough temperatures for Li destruction, has been used to obtain ages for several open clusters and stellar associations younger than 200 Myr—which until now has been considered the practical upper limit on the range of applicability of this method. In this work, we show that the LDB method can be extended to significant older ages than previously thought. Intermediate resolution optical spectra of six L-type candidate members in the Hyades cluster obtained using Optical System for Imaging and Low Resolution Integrated Spectroscopy at the 10.4 m Gran Telescopio Canarias are presented. The 670.8 nm resonance doublet is clearly detected only in the two faintest and coolest of these objects, which are classified as L3.5 to L4 brown dwarf (BD) cluster members with luminosities around 10−4 solar. Lithium depletion factors are estimated for our targets with the aid of synthetic spectra and they are compared with predictions from evolutionary models. An LDB age of 650 ± 70 Myr for the Hyades provides a consistent description of our data using a set of state-of-the-art evolutionary models for BDs calculated by Baraffe et al.

Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range of 1-2 GHz

Abstract: We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts a bright radio relic, known as the Toothbrush, and an elongated giant radio halo. These new observations allow us to study the surface brightness distribution down to one arcsec resolution with very high sensitivity. Our images provide an unprecedented detailed view of the Toothbrush, revealing enigmatic filamentary structures. To study the spectral index distribution, we complement our analysis with published LOFAR and GMRT observations. The bright ‘brush’ of the Toothbrush shows a prominent narrow ridge to its north with a sharp outer edge. The spectral index at the ridge is in the range −0.70 ≤ α ≤ −0.80. We suggest that the ridge is caused by projection along the line of sight. With a simple toy model for the smallest region of the ridge, we conclude that the magnetic field is below 5μG and varies significantly across the shock front. Our model indicates that the actual Mach number is higher than that obtained from the injection index and agrees well with the one derived from the overall spectrum, namely M = 3.78 −0.2. The radio halo shows an average spectral index of α = −1.16 ± 0.05 and a slight gradient from north to south. The southernmost part of the halo is steeper and possibly related to a shock front. Excluding the southernmost part, the halo morphology agrees very well with the X-ray morphology. A power-law correlation is found between the radio and X-ray surface brightness. Subject headings: Galaxies: clusters: individual (1RXS J0603.3+4214) − Galaxies: clusters: intracluster medium − large-scale structures of universe − Acceleration of particles − Radiation mechanism: non-thermal: magnetic fields