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I present a critical overview of so-called "{\it ab initio}" DFT (density fuctional theory) based calculation schemes for the description of the electronic structure, energy spectrum, and optical response for strongly correlated 3$d$ oxides, in particular, crystal-field and charge transfer transitions as compared with an "old"\, cluster model that does generalize crystal-field and ligand-field theory. As a most instructive illustration of validity of numerous calculation techniques I address the prototypical 3$d$ insulator NiO predicted to be a metal in frames of a standard LDA (local density approximation) band theory., Comment: 21 pages, 1 figure

Three-body $AAB$ model for the $NN{\bar K}(s_{NN}=0)$ kaonic cluster is considered based on the configuration space Faddeev equations. Within a single-channel approach, the difference between masses of nucleons and kaons and the charge independence breaking of nucleon-nucleon interaction are taken into consideration. We definite the particle configurations in the system according to the particle masses and pair potentials. There are two sets of the particle configurations, $ ppK^-$, $np \bar{K^0}$ and $nn {\bar K}^0$, $npK^-$, charged and neutral. The three-body calculations are performed by applying $NN$ and $N\bar K$ phenomenological isospin-dependent potentials. The mass and energy spectra related to the particle configurations are presented. We evaluate the mass and energy uncertainties for the $NN\bar K$ model. An analogy to $NNN$ model for the $^3$H and $^3$He nuclei is proposed.

A 2D cluster-based coordination polymer of {Fe5}-2D was developed by hierarchical dimension augmentation from its 1D coordination polymer of {Fe5}-1D and discrete 0D cluster of {Fe5}-0D. And a possible bottom-up synthesis mechanism was proposed.

The results of the calculation on magnetization (M) for diluted magnetic semiconductor Pb1-xEuxSe are reported. Our calculation includes two distinct contributions namely contribution from the localized magnetic impurity (Mi) and contribution from the band effect (Mb). Mi has been calculated using a three-spin cluster model which comprises the clusters consisting of one-spin (M1), two-spins (M2) and three-spins (M3). Moreover, M3 includes both open triplets (Mot) and closed triplets (Mct). The statistical distribution of the different clusters has been considered using random distribution approximation in the dilute limit. The contributions from these clusters to the magnetization have been evaluated using a modified Heisenberg's exchange Hamiltonian in the nearest approximation. The magnetization has been calculated as a function of magnetic field and impurity concentration. The band effect includes the contribution from lattice diamagnetism( χ l a t t ) . This mechanism has been considered in the effective mass formalism using a two-band k → . π → model. Our calculated values of M compare very well with experimental data where available.

The charge distributions and elastic electron form factors for 18O, 42,44Ca, 58Ni, and 118Sn nuclei were considered using the cluster expansion of the 1- and 2-body terms. Inelastic electron form factors to 2+ states with core-polarization effects were studied, where the nuclear collective modes were considered alongside the shell model transition density. The influence of short-range correlations (SRCs) was calculated by the parameter β, which was introduced into the ground-state charge distribution and concluded the Jastrow-type function. It is found that the inclusion of 2-body correlations is necessary to describe the observed data of elastic and inelastic form factors at high momentum transfer q > 3 fm–1.

Here, we conducted a photometric and astrometric study of two open stellar clusters Dolidze-18 and Ruprecht-70, which have not been photometrically studied before. The most important thing for using Gaia (DR2) database lies in the positions, parallax, and proper motions, which make us split cluster members from the field ones and get precise astrophysical parameters. On studying the radial density profiles of these clusters, the actual sizes are estimated and found larger using Gaia. From the color-magnitude diagrams and theoretical isochrones, we simultaneously determined the ages, distance moduli, and reddening of the two clusters. However, considering the parallaxes of Gaia (DR2) for the cluster members, we calculated the cluster distance and confirmed what we obtained from the color-magnitude diagram. Then, the Cartesian galactocentric coordinates (Xo, Yo, Zo), and the distances from the galactic center (Rg) were also estimated. According to the luminosity and mass functions, the total luminosity and total mass of the clusters are estimated. Our study shows that Ruprecht-70 is recently dynamically relaxed, while Dolidze 18 is not relaxed yet., Comment: 17 pages, 8 figures, 1 table

As a subsequent paper for “type-A-choking-oriented unified model for fast fluidization dynamics”, the present work aims to provide more systematic mesoscale analyses on clusters. Starting from theoretical derivations on idealized flow patterns of gas and solids around a single falling cluster; the momentum consumption due to particle circulation in clouds and the modification of flows by the constraint of driving force available in the bed were addressed. Complete compensation of the pressure-drop driven percolated gas in clusters by the reversely-penetrating particles was used for the ultimate closure of the model. An important finding of the present work, different from most empirical correlations, but verified by Wei and Zhu's latest experimental data and others, is that the cluster diameter does not vary monotonically with the mean solids holdup of the bed, but has a maximum value in between. Demonstrative calculations show that it is easy for Group A particles to enter the flow regime of high-density fast-fluidization as the circulating solids flux increases continuously, while fast fluidization for Group B particles tends to be stopped at Type C choking in advance. Compared with Group A particles, the clusters for Group B particles are less dense, but the penetration velocities of particles are higher, resulting in much larger dimensionless diameters of clusters. Finally, issues of pseudo-2D fast-bed modeling were discussed, and modeling of fast-beds with uneven flow fields was outlook briefly.

Ellipse in Discrete Element Method simulation can be modelled by a cluster of sub-spheres under the multi-sphere approach or one elliptical entity under the single-particle approach. However, due to multiple sub-contacts, the cluster response is over-stiff and over-damped, compared with the particle response (i.e., ground truth). The equalized method was proposed to solve the problem, where the stiffness and damping coefficient for each sub-contact is equally reduced from the ground truths by a factor of the sub-contact number. Alternatively, the best-fit method was proposed to determine the sub-contact stiffness and damping coefficient using the series of sub-contact overlapping with different orders. In scenarios of ellipse-wall/inter-ellipse collision, the equalized method tuned the cluster responses to closely match to the ground truths, with various errors commonly

Low-frequency hysteresis loops and specific absorption rate (SAR) of various assemblies of elongated spheroidal magnetite nanoparticles have been calculated for a range of particle semiaxis ratios a/b = 1.0–3.0. The SAR of a dilute randomly oriented assembly of magnetite nanoparticles in an alternating magnetic field of moderate frequency, f = 300 kHz, and amplitude H0 = 100–200 Oe is shown to decrease significantly with an increase in the aspect ratio of nanoparticles. In addition, there is a narrowing and shift of the intervals of optimal particle diameters towards smaller particle sizes. However, the orientation of a dilute assembly of elongated nanoparticles in a magnetic field leads to an almost twofold increase in SAR at the same frequency and amplitude of the alternating magnetic field, the range of optimal particle diameters remaining unchanged. The effect of the magneto-dipole interaction on the SAR of a dilute assembly of oriented clusters of elongated magnetite nanoparticles has also been investigated depending on the volume fraction of nanoparticles in a cluster. It has been found that the SAR of the assembly of oriented clusters decreases by approximately an order of magnitude with an increase in the volume fraction of nanoparticles in a cluster in the range of 0.04–0.2.

We have investigated the structure of the Hercules supercluster (SCL160) based on data originally extracted from the Sloan Digital Sky Survey SDSS-DR7. We have traced the mass distribution in the field through the numerical density-weighted by the $r^\prime$-luminosity of the galaxies and classified them based on their spatial position and redshift. This has allowed us not only to address the kinematics of the supercluster as a whole, but also the internal kinematic of each cluster, which was no further explored before. We have confirmed that the Hercules supercluster is composed of the galaxy clusters A2147, A2151, and A2152. A2151 consists of five subclusters, A2147 on two and A2152 on at least two. They form the heart of the Hercules supercluster. We also have found two other gravitationally bond clusters, increasing, therefore, the known members of the supercluster. We have estimated a total mass of $2.1\pm0.2 \times 10^{15}$ M$_\odot$ for the Hercules supercluster. To determine the dynamical masses in this work, we have resorted to the $M_{200}-\sigma$ scaling relation and the caustic technique. Comparing both methods with simulated data of bimodal merging clusters, we found the caustic, as well as the $\sigma$-based masses, are biased through the merger age, showing a boost just after the pericentric passage. This is not in line with the principle of the caustic method that affirms it is not depending on the cluster dynamical state., Comment: 20 pages, 11 figures, 7 tables - Accepted for publication in MNRAS

The quantum chemical version of the density matrix renormalization group (DMRG) method has established itself as one of the methods of choice for calculations of strongly correlated molecular systems. Despite its great ability to capture strong electronic correlation in large active spaces, it is not suitable for computations of dynamical electron correlation. In this work, we present a new approach to the electronic structure problem of strongly correlated molecules, in which DMRG is responsible for a proper description of the strong correlation, whereas dynamical correlation is computed via the recently developed adiabatic connection (AC) technique which requires only up to two-body active space reduced density matrices. We report the encouraging results of this approach on typical candidates for DMRG computations, namely, n-acenes (n = 2 → 7), Fe(II)-porphyrin, and the Fe3S4 cluster.

Intense light traps and binds small particles, offering unique control to the microscopic world. With incoming illumination and radiative losses, optical forces are inherently nonconservative, thus non-Hermitian. Contrary to conventional systems, the operator governing time evolution is real and asymmetric (i.e., non-Hermitian), which inevitably yield complex eigenvalues when driven beyond the exceptional points, where light pumps in energy that eventually “melts” the light-bound structures. Surprisingly, unstable complex eigenvalues are prevalent for clusters with ~10 or more particles, and in the many-particle limit, their presence is inevitable. As such, optical forces alone fail to bind a large cluster. Our conclusion does not contradict with the observation of large optically-bound cluster in a fluid, where the ambient damping can take away the excess energy and restore the stability. The non-Hermitian theory overturns the understanding of optical trapping and binding, and unveils the critical role played by non-Hermiticity and exceptional points, paving the way for large-scale manipulation., Non-conservativeness plays a mysterious role in optical trapping. Applying the non-Hermitian theory, the authors showed that the existence of exceptional points drives the Lorentz force to lose its ability to bind clusters of ~10 or more microparticles, unless remedied by dissipative forces.

We investigate dynamics and bifurcations in a mathematical model that captures electrochemical experiments on arrays of microelectrodes. In isolation, each individual microelectrode is described by a one-dimensional unit with a bistable current-potential response. When an array of such electrodes is coupled by controlling the total electric current, the common electric potential of all electrodes oscillates in some interval of the current. These coupling-induced collective oscillations of bistable one-dimensional units are captured by the model. Moreover, any equilibrium is contained in a cluster subspace, where the electrodes take at most three distinct states. We systematically analyze the dynamics and bifurcations of the model equations: We consider the dynamics on cluster subspaces of successively increasing dimension and analyze the bifurcations occurring therein. Most importantly, the system exhibits an equivariant transcritical bifurcation of limit cycles. From this bifurcation, several limit cycles branch, one of which is stable for arbitrarily many bistable units.

A recent study suggests that the observed multiplicity of super-Earth (SE) systems is correlated with stellar overdensities: field stars in high phase-space density environments have an excess of single-planet systems compared to stars in low density fields. This correlation is puzzling as stellar clustering is expected to influence mostly the outer part of planetary systems. Here we examine the possibility that stellar flybys indirectly excite the mutual inclinations of initially coplanar SEs, breaking their co-transiting geometry. We propose that flybys excite the inclinations of exterior substellar companions, which then propagate the perturbation to the inner SEs. Using analytical calculations of the secular coupling between SEs and companions, together with numerical simulations of stellar encounters, we estimate the expected number of "effective" flybys per planetary system that lead to the destruction of the SE co-transiting geometry. Our analytical results can be rescaled easily for various SE and companion properties (masses and semi-major axes) and stellar cluster parameters (density, velocity dispersion and lifetime). We show that for a given SE system, there exists an optimal companion architecture that leads to the maximum number of effective flybys; this results from the trade-off between the flyby cross section and the companion's impact on the inner system. Subject to uncertainties in the cluster parameters, we conclude that this mechanism is inefficient if the SE system has a single exterior companion, but may play an important role in "SE + two companions" systems that were born in dense stellar clusters. Whether this effect causes the observed correlation between planet multiplicity and stellar overdensities remains to be confirmed., Comment: 16 pages, 18 figures, accepted in MNRAS

We present original Giant Metrewave Radio Telescope (GMRT) radio observations of the galaxy cluster Abell 725, at a redshift (z) of 0.09, along with other archival observations. Our GMRT maps reveal two steep-spectrum diffuse filaments in the cluster, along with a previously reported arc-like structure, and a wide-angle-tail (WAT) radio source associated with the brightest cluster galaxy (BCG) at the periphery of the cluster. The bent morphology of the WAT indicates that its jets have been swept back by the dynamic pressure resulting from the motion of the BCG through the surrounding intracluster medium. The BCG associated with the WAT hosts a black hole whose mass we estimate to be 1.4 $\ \pm\ 0.4 \times 10^{9}\,\rm M_{\odot }$. We observe a 2 arcmin (195 kpc in projection) offset between the BCG and the X-ray centroid of the galaxy cluster, which, along with other dynamic features, indicates the cluster’s early stage of evolution. The WAT radio galaxy, the arc, and the filaments have spectral indices $\alpha _{612}^{240}= -0.46\ \pm\ 0.15$, −0.8 ± 0.3, and (−1.13 ± 0.48, −1.40 ± 0.50), respectively. The WAT and the arc are connected structures, while the filaments are detached from them, but are found to be along the trail of the WAT. Based on the morphology of the components, and the progressive steepening of the components from the core of the WAT to the filaments, we propose that this system is a radio galaxy with trailing antique filaments.

We analyse the surface brightness profiles of disc-type galaxies in the EAGLE simulations in order to investigate the effects of galaxy mass and environment on galaxy profile types. Following observational works, we classify the simulated galaxies by their disc surface brightness profiles into single exponential (Type I), truncated (Type II) and anti-truncated (Type III) profiles. In agreement with previous observation and theoretical work, we find that Type II discs result from truncated star-forming discs that drive radial gradients in the stellar populations. In contrast, Type III profiles result from galaxy mergers, extended star-forming discs or the late formation of a steeper, inner disc. We find that the EAGLE simulations qualitatively reproduce the observed trends found between profile type frequency and galaxy mass, morphology and environment, such as the fraction of Type III galaxies increasing with galaxy mass, and the the fraction of Type II galaxies increasing with Hubble type. We investigate the lower incidence of Type II galaxies in galaxy clusters, finding, in a striking similarity to observed galaxies, that almost no S0-like galaxies in clusters have Type II profiles. Similarly, the fraction of Type II profiles for disc-dominated galaxies in clusters is significantly decreased relative to field galaxies. This difference between field and cluster galaxies is driven by star formation quenching. Following the cessation of star formation upon entering a galaxy cluster, the young stellar populations of Type II galaxies simply fade, leaving behind Type I galaxies., 11 pages, 10 figures. Accepted for publication in MNRAS

We measure the projected half-light radii of young star clusters in 31 galaxies from the Legacy Extragalactic UV Survey (LEGUS). We implement a custom pipeline specifically designed to be robust against contamination, which allows us to measure radii for 6097 clusters. This is the largest sample of young star cluster radii currently available. We find that most (but not all) galaxies share a common cluster radius distribution, with the peak at around 3 pc. We find a clear mass-radius relation of the form $R_{\mathrm{eff}} \propto M^{0.24}$. This relation is present at all cluster ages younger than 1 Gyr, but with a shallower slope for clusters younger than 10 Myr. We present simple toy models to interpret these age trends, finding that high-mass clusters are more likely to be not tidally limited and expand. We also find that most clusters in LEGUS are gravitationally bound, especially at older ages or higher masses. Lastly, we present the cluster density and surface density distributions, finding a large scatter that appears to decrease with cluster age. The youngest clusters have a typical surface density of 100 $M_\odot$ pc$^{-2}$., Accepted by MNRAS. Cluster catalogs available at https://gillenbrown.github.io/LEGUS-sizes/

The sedimentation level of blue straggler stars (BSS) has been shown to be a great tool to investigate the dynamical states of globular clusters (GCs). The area enclosed between the cumulative radial distributions of BSS and a reference population up to the half-mass radius of the clusters, $A^+_{\mathrm{rh}}$, is known to be a measure of the sedimentation of BSS in GCs. In this work, we calculate $A^+_{\mathrm{rh}}$ for 11 open clusters (OCs) using a combined list of main-sequence turn-off stars, sub-giant branch stars, and red giant branch stars as reference population. The BSS, the reference populations, and the cluster members are identified using the proper motions and parallaxes from the Gaia DR2 data. In a subset of clusters, the BSS are confirmed cluster members on the basis of radial velocity information available in the literature. Using the Pearson and Spearman rank correlation coefficients, we find weak correlations between the estimated values of $A^+_{\mathrm{rh}}$ and other markers of dynamical ages of the clusters, i.e. the number of central relaxations a cluster has experienced since its formation, and the structural parameters of the clusters. Based on statistical tests, we find that these correlations are similar to the corresponding correlations among the less evolved GCs, albeit within large errors.

With high-quality data from programs like the Hubble Frontier Fields, cluster lensing has reached the point that models are dominated by systematic rather than statistical uncertainties. We introduce a Bayesian framework to quantify systematic effects by determining how different lens modelling choices affect the results. Our framework includes a new two-sample test for quantifying the difference between posterior probability distributions that are sampled by methods like Monte Carlo Markov chains. We use the framework to examine choices related to the selection and treatment of cluster member galaxies in two of the Frontier Field clusters: Abell 2744 and MACS J0416.1–2403. When selecting member galaxies, choices about depth and area affect the models; we find that model results are robust for an I-band magnitude limit of mlim ≥ 22.5 mag and a radial cut of rlim ≥ 90 arcsec (from the centre of the field), although the radial limit likely depends on the spatial extent of lensed images. Mass is typically assigned to galaxies using luminosity/mass scaling relations. We find that the slopes of the scaling relations can have significant effects on lens model parameters but only modest effects on lensing magnifications. Interestingly, scatter in the scaling relations affects the two fields differently. This analysis illustrates how our framework can be used to analyse lens modelling choices and guide future cluster lensing programs.

Cluster lens models are affected by a variety of choices in the lens modelling process. We have begun a programme to develop a systematic error budget for cluster lens modelling. Here, we examine the selection of image constraints as a potential systematic effect. For constraining the mass model, we find that it is more important to have images be spatially distributed around the cluster than to have them distributed in redshift. We also find that some image sets appear to be more important than others in terms of how well they constrain the models; the ‘important’ image sets typically include an image that lies close to a lensing critical curve as well as an image that is relatively isolated from other images (providing constraints in a region that would otherwise lack lensing information). These conclusions can help guide observing programmes that seek follow-up data for candidate lensed images.

A clump moving through the intracluster medium of a galaxy cluster can drive a bow shock trailed by a bullet-like core. In some cases, such as in the prototypical Bullet cluster, X-rays show a gas bullet with a protruding head and pronounced shoulders. We point out that these features, while difficult to explain without dark matter (DM), naturally arise as the head of the slowed-down gas is gravitationally pulled forward toward its unhindered DM counterpart. X-ray imaging thus provides a unique, robust probe of the offset, collisionless DM, even without gravitational lensing or other auxiliary data. Numerical simulations and a toy model suggest that the effect is common in major mergers, is often associated with a small bullet-head radius of curvature, and may lead to distinct bullet morphologies, consistent with observations., Comment: 9 pages, 3 figures, comments welcome

We analyzed the largest Small Magellanic Cloud (SMC) cluster sample (32) with proper motions and radial velocity measurements, from which we obtained their space velocity components. By adopting as a reference the recent best-fitted rotating disc of SMC star clusters as a function of the position angle, we computed their residual velocity vectors, and compared their magnitudes ($\Delta$V) with that of a cluster with residual velocity components equal to the velocity dispersions along the three independent SMC rotating disc axes of motion ($\Delta$V = 60 km/s). We found that clusters that belong to SMC tidally induced structures have $\Delta$V > 50 km/s, which suggests that space velocities of clusters in the process of escaping the rotating disc kinematics, are measurably different. Studied clusters pertaining to a northern branch of the Magellanic Bridge, the main Magellanic Bridge, the Counter-Bridge and the West halo give support to these findings. NGC 121, the oldest known SMC cluster, does not belong to any SMC tidal feature, and has $\Delta$V = 64 km/s, slightly above the boundary between bound and kinematically perturbed clusters., Comment: 7 pages, 4 figures. Accepted for publication in MNRAS

[4Fe-4S]-dependent radical S-adenosylmethionine (SAM) proteins are a superfamily of oxidoreductases that can catalyze a series of challenging transformations using the common 5-dAdo radical intermediate. Although the structures and functions of radical SAM enzymes have been extensively studied, the electronic state-dependent reactions of the [4Fe-4S] clusters in these enzymes are still elusive. Herein we performed QM/MM calculations to elucidate the electronic state-dependent reactivity of the [4Fe-4S] cluster in pyruvate-formate lyase activating enzyme. Our calculations show that the electronic state-dependent SAM activation by the [4Fe-4S] clusters in radical SAM enzyme is determined by both the super-exchange and exchange-enhanced reactivities. The super-exchange coupling in the [4Fe-4S] cluster favors the antiferromagnetic coupling between two neighbouring pairs, which results in the \begin{document}$\alpha$\end{document} -electron rather than the \begin{document}$\beta$\end{document} -electron donation from the [4Fe-4S] \begin{document}$^{1+}$\end{document} cluster toward the SAM activation. Meanwhile, in the most favorable electronic state for the reductive cleavage of S \begin{document}$-$\end{document} C5 \begin{document}$'$\end{document} , Fe4 would donate its \begin{document}$\alpha$\end{document} -electron to gain the maximum exchange interactions in the Fe4-block. Such super-exchange and exchange-enhanced reactivity could be the general principles for reactivities of [4Fe-4S] cluster in RS enzymes.

This work is devoted to the study of the star formation histories (SFHs) of the brightest cluster galaxies (BCGs) with intermediate central ages (from 5 to 10Gyr), to confirm if BCGs with these ages represent different accretion histories or simply a stochastic effect. The sample is composed of 6 BCGs with intermediate central ages and 3 BCGs with old central ages (> 12Gyr) as comparison galaxies. The galaxies were observed with the integrated field spectrograph VIMOS installed in the Very Large Telescope (VLT). The SFHs were obtained with the full spectrum fitting technique using the star population code STARLIGHT. The BCGs of intermediate central age analyzed formed almost 100% of their stars at z > 2 and their SFHs are similar to the SFHs of BCGs of old central ages and elliptical galaxies of similar mass (MDyn > 1011 Mʘ); therefore, these BCGs do not represent different SFHs.

We present the v1.0 release of CLMM, an open source Python library for the estimation of the weak lensing masses of clusters of galaxies. CLMM is designed as a standalone toolkit of building blocks to enable end-to-end analysis pipeline validation for upcoming cluster cosmology analyses such as the ones that will be performed by the LSST-DESC. Its purpose is to serve as a flexible, easy-to-install and easy-to-use interface for both weak lensing simulators and observers and can be applied to real and mock data to study the systematics affecting weak lensing mass reconstruction. At the core of CLMM are routines to model the weak lensing shear signal given the underlying mass distribution of galaxy clusters and a set of data operations to prepare the corresponding data vectors. The theoretical predictions rely on existing software, used as backends in the code, that have been thoroughly tested and cross-checked. Combined, theoretical predictions and data can be used to constrain the mass distribution of galaxy clusters as demonstrated in a suite of example Jupyter Notebooks shipped with the software and also available in the extensive online documentation., 21 pages, 6 figures, accepted for publication by MNRAS

The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H+(H2O)n extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H+(H2O)21 cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster. Protonated water species have been the subject of numerous experimental and computational studies. Here the authors provide a nearly complete assignment of the experimental IR spectrum of the H+(H2O)21 water cluster based on high-level wavefunction theory and anharmonic vibrational quasi-degenerate perturbation theory.

Many-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system. Emergent phenomena in complex many-body systems driven far from equilibrium are currently a subject of intense study. Here, the authors report on a nonlinear current-density relationship in experiments of magnetic colloids driven above disordered energy landscapes, and explain the underlying mechanisms through analytical modeling.

As an important class of carbon reservoirs in the interstellar medium (ISM), polycyclic aromatic hydrocarbon (PAH) molecules play an important role in the evolutionary network of prebiotic molecules. Here, the experimental evidence of astronomically relevant amino-acid derivatives – PAH/amino-acid clusters – is provided, and we study their ion–molecular collision reactions in the gas phase. With the initial molecular precursors dicoronylene (DC, C48H20)/alanine (Ala, C3H7NO2) and DC/isoleucine (Ile, C6H13NO2), the experiments indicate that PAH–amino-acid cluster cations (e.g. (Ala)C48H$_{(0-19)}\, ^+$ and (Ile)C48H$_{(0-19)}\, ^+$) and graphene–amino-acid cluster cations (e.g. (Ala)nC$_{48}\, ^+$ and (Ile)nC$_{48}\, ^+$, n = 1, 2, 3, 4) are efficiently formed in a strong interstellar radiation field. In addition, the structure of clusters and the binding energy of their formation pathways are studied by a quantum chemistry calculation method: gas-phase reactions (ion–molecule reactions) between PAH cations with amino acids readily occur (exothermic energy around 2.0–4.7 eV), and these newly formed clusters have a complex molecular configuration (C–O and C–N bond type). These laboratory studies provide a cluster growth pathway (through an ion–molecule reaction) towards the formation of amino-acid derivatives in a bottom-up process and insight into their chemical-evolution behaviour, opening up aromatic-based chemistry that is available to the species (dehydrogenated PAHs or graphene molecules) that formed from the photofragmentation process of PAHs in interstellar environments. When conditions are suitable (e.g. have similar molecular abundance spatial distributions in the ISM), amino-acid derivatives can form efficiently, and newly built large PAH/amino-acid clusters may be widespread in space.

Gravitational Wave (GW) astronomy promises to observe different kinds of astrophysical sources. Here we explore the possibility of detection of GWs from hyperbolic interactions of compact stars with ground-based interferometric detectors. It is believed that a bound compact cluster, such as a globular cluster, can be a primary environment for these interactions. We estimate the detection rates for such events by considering local geometry within the cluster, accounting for scattering probability of compact stars at finite distances, and assuming realistic cluster properties guided by available numerical models, their formation times, and evolution of stars inside them. We find that, even in the conservative limit, it may be possible to detect such black hole encounters in the next few years by the present network of observatories with the ongoing sensitivity upgrades and one to few events per year with the next generation observatories. In practice, actual detection rates can significantly surpass the estimated average rates, since the chances of finding outliers in a very large population can be high. Such observations (or, no observation) may provide crucial constraints to estimate the number of isolated compact stars in the universe. These detections will be exciting discoveries on their own and will be complimentary to observations of binary mergers bringing us one step closer to address a fundamental question, how many black holes are there in the observable universe., 10 pages, 4 figures

Globular clusters contain a finite number of stars. As a result, they inevitably undergo secular evolution (`relaxation') causing their mean distribution function (DF) to evolve on long timescales. On one hand, this long-term evolution may be interpreted as driven by the accumulation of local deflections along each star's mean field trajectory -- so-called `non-resonant relaxation'. On the other hand, it can be thought of as driven by non-local, collectively dressed and resonant couplings between stellar orbits, a process termed `resonant relaxation'. In this paper we consider a model globular cluster represented by a spherical, isotropic isochrone DF, and compare in detail the predictions of both resonant and non-resonant relaxation theories against tailored direct $N$-body simulations. In the space of orbital actions (namely the radial action and total angular momentum), we find that both resonant and non-resonant theories predict the correct morphology for the secular evolution of the cluster's DF, although non-resonant theory over-estimates the amplitude of the relaxation rate by a factor ${\sim 2}$. We conclude that the secular relaxation of hot isotropic spherical clusters is not dominated by collectively amplified large-scale potential fluctuations, despite the existence of a strong ${\ell = 1}$ damped mode. Instead, collective amplification affects relaxation only marginally even on the largest scales. The predicted contributions to relaxation from smaller scale fluctuations are essentially the same from resonant and non-resonant theories., Comment: 26 pages, 14 figures, submitted to MNRAS

In 2016, Li et al. [Int. J. Theor. Phys. 55, 1820–1823 (2016)] proposed schemes for quantum teleportation of certain class of three and four qubit states by utilizing four- and five- qubit cluster states, respectively, as the quantum channels. Moreover, their teleportation-schemes necessitates multi-qubit entangled states. In the present study, it has been demonstrated that these authors committed trivial errors while designing their teleportation schemes and, hence, quantum teleportation could not be perfectly achieved. It is seen that the tasks of teleporting aforementioned class of three and four qubit states can be accomplished by applying only a two-qubit maximally entangled states, i.e., single Bell state as the quantum channel. It is, therefore, an improvement on Li et al. teleportation-schemes is proposed, which not only reduces quantum resource consumption but also operation complexity.

We present a detailed analysis of the velocity structure of the Virgo cluster using {\it XMM-Newton} observations. Using a novel technique which uses uses the Cu K$\alpha$ instrumental line to calibrate the EPIC-pn energy scale, we are able to obtain velocity measurements with uncertainties down to $\Delta v \sim 100$ km/s. We created 2D projected maps for the velocity, temperature, metallicity, density, pressure and entropy with an spatial resolution of 0.25$'$. We have found that in the innermost gas there is a high velocity structure, most likely indicating the presence of an outflow from the AGN while our analysis of the cluster cool core using RGS data indicates that the velocity of the gas agrees with the M87 optical redshift. An overall gradient in the velocity is seen, with larger values as we move away from the cluster core. The hot gas located within the western radio flow is redshifted, moving with a velocity $\sim 331$ km/s while the hot gas located within the eastern radio flow is blueshifted, with a velocity $\sim 258$ km/s, suggesting the presence of backflows. Our results reveal the effects of both AGN outflows and gas sloshing, in the complex velocity field of the Virgo cluster., Comment: 19 pages, 21 figures; This paper is part of a series on the ICM velocity structure using XMM-Newton observations. Related series papers: arXiv:2203.12635, arXiv:2303.17556

Young solar-type stars are known to be strong X-ray emitters and their X-ray spectra have been widely studied. X-rays from the central star may play a crucial role in the thermodynamics and chemistry of the circumstellar material as well as in the atmospheric evolution of young planets. In this paper we present model spectra based on spectral parameters derived from the observations of young stars in the Orion Nebula Cluster from the Chandra Orion Ultradeep Project (COUP). The spectra are then used to calculate new photoevaporation prescriptions that can be used in disc and planet population synthesis models. Our models clearly show that disc wind mass loss rates are controlled by the stellar luminosity in the soft (100 eV - 1 keV) X- ray band. New analytical relations are provided for the mass loss rates and profiles of photoevaporative winds as a function of the luminosity in the soft X-ray band. The agreement between observed and predicted transition disc statistics moderately improved using the new spectra, but the observed population of strongly accreting large cavity discs can still not be reproduced by these models. Furthermore, our models predict a population of non-accreting transition discs that are not observed. This highlights the importance of considering the depletion of millimeter-sized dust grains from the outer disc, which is a likely reason why such discs have not been detected yet., Comment: 12 pages, 7 tables, 9 figures, accepted for publication in MNRAS

Many young and intermediate age massive stellar clusters host bimodal distributions in the rotation rates of their stellar populations, with a dominant peak of rapidly rotating stars and a secondary peak of slow rotators. The origin of this bimodal rotational distribution is currently debated and two main theories have been put forward in the literature. The first is that all/most stars are born as rapid rotators and that interacting binaries brake a fraction of the stars, resulting in two populations. The second is that the rotational distribution is a reflection of the early evolution of pre-main sequence stars, in particular, whether they are able to retain or lose their protoplanetary discs during the first few Myr. Here, we test the binary channel by exploiting multi-epoch VLT/MUSE observations of NGC 1850, a 100Myr massive cluster in the LMC, to search for differences in the binary fractions of the slow and fast rotating populations. If binarity is the cause of the rotational bimodality, we would expect that the slowly rotating population should have a much larger binary fraction than the rapid rotators. However, in our data we detect similar fractions of binary stars in the slow and rapidly rotating populations (5.9+/-1.1% and 4.5+/-0.6%, respectively).Hence, we conclude that binarity is not a dominant mechanism in the formation of the observed bimodal rotational distributions., Comment: 5 pages, 2 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We present a detailed study of the shapes and alignments of different galaxy cluster components using hydrodynamical simulations. We compute shape parameters from the Dark Matter (DM) distribution, the galaxy members and the intra-cluster light (ICL). We assess how well the DM cluster shape can be constrained by means of the identified galaxy member positions and the ICL. Further, we address the dilution factor introduced when estimating the cluster elongation using weak-lensing stacking techniques, which arises due to the misalignment between the total surface mass distribution and the distribution of luminous tracers. The dilution is computed considering the alignment between the DM and the Brightest Cluster Galaxy, the galaxy members and the ICL. Our study shows that distributions of galaxy members and ICL are less spherical than the DM component, although both are well aligned with the semi-major axis of the later. We find that the distribution of galaxy members hosted in more concentrated subhalos is more elongated than the distribution of the DM. Moreover, these galaxies are better aligned with the dark matter component compared to the distribution of galaxies hosted in less concentrated subhalos. We conclude that the positions of galaxy members can be used as suitable tracers to estimate the cluster surface density orientation, even when a low number of members is considered. Our results provide useful information for interpreting the constraints on the shapes of galaxy clusters in observational studies., Comment: Submitted MNRAS. 12 pages, 7 figures (+ appendix)

Young stellar clusters across nearly five orders of magnitude in mass appear to follow a power-law mass-radius relationship (MRR), $R_{\star} \propto M_{\star}^{\alpha}$, with $\alpha \approx 0.2 - 0.33$. We develop a simple analytic model for the cluster mass-radius relation. We consider a galaxy disc in hydrostatic equilibrium, which hosts a population of molecular clouds that fragment into clumps undergoing cluster formation and feedback-driven expansion. The model predicts a mass-radius relation of $R_{\star} \propto M_{\star}^{1/2}$ and a dependence on the kpc-scale gas surface density $R_{\star} \propto \Sigma_{\rm g}^{-1/2}$, which results from the formation of more compact clouds (and cluster-forming clumps within) at higher gas surface densities. This environmental dependence implies that the high-pressure environments in which the most massive clusters can form also induce the formation of clusters with the smallest radii, thereby shallowing the observed MRR at high-masses towards the observed $R_{\star} \propto M_{\star}^{1/3}$. At low cluster masses, relaxation-driven expansion induces a similar shallowing of the MRR. We combine our predicted MRR with a simple population synthesis model and apply it to a variety of star-forming environments, finding good agreement. Our model predicts that the high-pressure formation environments of globular clusters at high redshift naturally led to the formation of clusters that are considerably more compact than those in the local Universe, thereby increasing their resilience to tidal shock-driven disruption and contributing to their survival until the present day., Comment: Accepted to MNRAS. Revised model incorporates a new dependence on Toomre Q

Ultra-diffuse galaxies (UDGs) are the lowest-surface brightness galaxies known, with typical stellar masses of dwarf galaxies but sizes similar to larger galaxies like the Milky Way. The reason for their extended sizes is debated, with suggested internal processes like angular momentum, feedback or mergers versus external mechanisms or a combination of both. Observationally, we know that UDGs are red and quiescent in groups and clusters while their counterparts in the field are blue and star-forming. This dichotomy suggests environmental effects as main culprit. However, this scenario is challenged by recent observations of isolated quiescent UDGs in the field. Here we use $\Lambda$CDM cosmological hydrodynamical simulation to show that isolated quenched UDGs are formed as backsplash galaxies that were once satellites of another galactic, group or cluster halo but are today a few Mpc away from them. These interactions, albeit brief, remove the gas and tidally strip the outskirts of the dark matter haloes of the now quenched seemingly-isolated UDGs, which are born as star-forming field UDGs occupying dwarf-mass dark matter haloes. Quiescent UDGs may therefore be found in non-negligible numbers in filaments and voids, bearing the mark of past interactions as stripped outer haloes devoid of dark matter and gas compared to dwarfs with similar stellar content., Comment: Author's version for the main article and supplementary information (13 pages, 10 figures). Accepted for publication in Nature Astronomy

We present an analysis of the galaxy population in XLSSC 122, an X-ray selected, virialized cluster at redshift $z=1.98$. We utilize HST WFC3 photometry to characterize the activity and morphology of spectroscopically confirmed cluster members. The quiescent fraction is found to be $88^{+4}_{-20}$ per cent within 0.5$r_{500}$, significantly enhanced over the field value of $20^{+2}_{-2}$ per cent at $z\sim2$. We find an excess of "bulge-like" quiescent cluster members with Sersic index $n>2$ relative to the field. These galaxies are found to be larger than their field counterparts at 99.6 per cent confidence, being on average $63^{+31}_{-24}$ per cent larger at a fixed mass of $M_\star = 5\times10^{10} M_\odot$. This suggests that these cluster member galaxies have experienced an accelerated size evolution relative to the field at $z>2$. We discuss minor mergers as a possible mechanism underlying this disproportionate size growth., 9 pages, 7 figures, accepted for publication in MNRAS

In this paper the influence of the inlet and outlet configurations of a pseudo-2D fluidized riser on the hydrodynamics (i.e. flow pattern and cluster characteristics) are studied. A detailed comparison between experimental data and full 3D CFD-DEM simulation results is performed. Solids volume fraction and mass flux are characterized and particle clusters are detected in our CFD-DEM simulations and compared to experimental data. It is shown that a correct representation of the outlet is very important for a correct simulation of the solids holdup in the top section of the riser. The core-annulus flow behavior is generally well predicted by the model and cluster characteristics such as cluster occurance and velocity are also in good agreement with experimental data. Finally, an outlook is given for the future use of CFD-DEM simulation approaches to study riser flows.

The reconstruction of charged particle trajectories at the Large Hadron Collider and future colliders relies on energy depositions in sensors placed at distances ranging from a centimeter to a meter from the colliding beams. We propose a method of detecting charged particles that decay invisibly after traversing a short distance of about 25 cm inside the experimental apparatus. One of the decay products may constitute the dark matter known to be 84% of all matter at galactic and cosmological distance scales. Our method uses graph computing to cluster spacepoints recorded by two-dimensional silicon pixel sensors into mathematically-defined patterns. The algorithm may be implemented on silicon-based integrated circuits using field-programmable gate array technology to augment or replace traditional computing platforms.

We review one-dimensional lattice models and the corresponding results that describe the low-temperature properties of quasi-one-dimensional lattice systems with long-range interaction. A widely known example is narrow-band low-dimensional conductors with long-range interelectron repulsion. The models deal with particles that live on the one-dimensional host lattice (chain), translation invariant or disordered, and interact via the long-range repulsive potential. The results are presented concerning the translation invariant host chain, in particular: the low-temperature thermodynamics incommensurable ground states and related devil-staircase form of various characteristics as functions of pertinent parameters, the self-localization of particles, a new branch of elementary excitations, etc. In the disordered case, where the sites of the host chain fluctuate randomly around the sites of the periodic chain, the low-temperature thermodynamics and the structure of the ground state are discussed in the framework of a certain model, which we call the cluster model and which seems to be a fairly reasonable approximation for low temperatures and small concentration of particles. Using analytical and numerical tools we analyze the thermodynamics and the ground state of the model. The latter proves to be a sequence of random domains and we study in detail their distribution.

We consider a model for an N × N lattice network of weakly coupled neural oscilla- tors with periodic boundary conditions (2D square torus), where the coupling between neurons is assumed to be within a von Neumann neighborhood of size r, denoted as von Neumann r-neighborhood. Using the phase model reduction technique, we study the existence of cluster solutions with constant phase differences (Ψh, Ψv) between adjacent oscillators along the horizontal and vertical directions in our network, where Ψh and Ψv are not necessarily to be identical. Applying the Kronecker production representation and the circulant matrix theory, we develop a novel approach to analyze the stability of cluster solutions with constant phase difference (i.e., Ψh,Ψv are equal). We begin our analysis by deriving the precise conditions for stability of such cluster solutions with von Neumann 1-neighborhood and 2 neighborhood couplings, and then we generalize our result to von Neumann r-neighborhood coupling for arbitrary neighborhood size r ≥ 1. This developed approach for the stability analysis indeed can be extended to an arbitrary coupling in our network. Finally, numerical simulations are used to validate the above analytical results for various values of N and r by considering an inhibitory network of Morris-Lecar neurons.

The need to consider vibrational motions of molecules in bound states of a vapor–liquid system in order to calculate its thermodynamic functions (TFs) raises the question of possibly isolating them from the collective kinetic contribution and describing them. An attempt is made to do so using a molecular kinetic theory based on the cluster approach (CA) in the lattice gas model (LGM). The existence of physically bound groups of fluid particles forming associates, which is observed for rarefied vapor, is extended to the range of densities of a vapor–liquid system. An associative model of a fluid is proposed that reflects regions of rarefied and dense fluids, different types of molecular motions, and the effects of anharmonic vibrations of atoms in bound states. Starting from an isolated dimer to a dense phase, particle vibrations are calculated in a quasi-dimer model reflecting average local vibrational frequencies. In dense fluids, local density fluctuations characterize representations of associates. Under the effect of vibration anharmonism in bound associates, molecular pair interaction potentials are renormalized into many-particle potentials. The problem of calculating TFs according to correlation functions, which is done extensively in fluid theory and CA in the LGM, is discussed. The problem lies in two ways of calculating the free energy: using molecular distribution functions or thermodynamic relationships. An approach is formulated for strictly calculating TFs with the use of model free energies. A statistical sum is introduced into the theory of fluids and ensures a self-consistent description of equilibria and kinetics.

The main stages of constructing a theory of high-order elastic moduli are considered. The first stage is developing a way to determine the dependence of the irreducible energies of interaction between atoms in each cluster. The second stage is finding a way of summing the irreducible potential energies of all clusters so that the result is equal to the total potential energy of the crystal, even though some clusters contain the same atoms.

We present the analysis of deep X-ray observations of 10 massive galaxy clusters at redshifts $1.05 < z < 1.71$, with the primary goal of measuring the metallicity of the intracluster medium (ICM) at intermediate radii, to better constrain models of the metal enrichment of the intergalactic medium. The targets were selected from X-ray and Sunyaev-Zel'dovich (SZ) effect surveys, and observed with both the \textit{XMM-Newton} and \textit{Chandra} satellites. For each cluster, a precise gas mass profile was extracted, from which the value of $r_{500}$ could be estimated. This allows us to define consistent radial ranges over which the metallicity measurements can be compared. In general, the data are of sufficient quality to extract meaningful metallicity measurements in two radial bins, $r, Comment: 10 pages, 5 figures

In recent years, Higher Order Modes Cluster (HOMC) guided waves have been considered for ultrasonic testing of plates and pipes. HOMC guided waves consist of higher order Lamb wave modes that travel together as a single nondispersive wave packet. The objective of this paper is to investigate the effect of frequency-thickness value on the contribution of Lamb wave modes in an HOMC guided wave. This is an important issue that has not been thoroughly investigated before. The contribution of each Lamb wave mode in an HOMC guided wave is studied by using a two-dimensional finite element model. The level of contribution of various Lamb wave modes to the wave cluster is verified by using a 2D FFT analysis. The results show that by increasing the frequency-thickness value, the order of contributing modes in the HOMC wave packet increases. The number of modes that comprise a cluster also increases up to a specific frequency-thickness value and then it starts to decrease. Plotting of the cross-sectional displacement patterns along the HOMC guided wave paths confirms the shifting of dominant modes from lower to higher order modes with increase of frequency-thickness value. Experimental measurements conducted on a mild steel plate are used to verify the finite element simulations. The experimental results are found to be in good agreement with simulations and confirm the changes observed in the level of contribution of Lamb wave modes in a wave cluster by changing the frequency-thickness value.