Small Cluster Sizes Research Articles

Fast Columnar Physics Analyses of Terabyte-Scale LHC Data on a Cache-Aware Dask Cluster

The development of an LHC physics analysis involves numerous investigations that require the repeated processing of terabytes of data. Thus, a rapid completion of each of these analysis cycles is central to mastering the science project. We present a solution to efficiently handle and accelerate physics analyses on small-size institute clusters. Our solution uses three key concepts: vectorized processing of collision events, the “MapReduce” paradigm for scaling out on computing clusters, and efficiently utilized SSD caching to reduce latencies in IO operations. This work focuses on the latter key concept, its underlying mechanism, and its implementation. Using simulations from a Higgs pair production physics analysis as an example, we achieve an improvement factor of 6.3 in the runtime for reading all input data after one cycle and even an overall speedup of a factor of 14.9 after 10 cycles, reducing the runtime from hours to minutes.

Regulated adsorption sites using atomically single cluster over biochar for efficient elemental mercury uptake

Carbon-based materials have been widely used in gaseous pollutant removal because of their sufficient surface functional groups; however, its removal efficiency for elemental mercury (Hg0) is low. In this study, we fabricated biomass using a chelated coupled pyrolysis strategy and further constructed the regulated adsorption sites for gaseous Hg0 uptake. A series of Mnδ-N2O2/BC with different manganese cluster sizes demonstrated that manganese clusters anchored on biochar acted as highly active and durable adsorbents for Hg0 immobilization, which increased the adsorption efficiency of Hg0 by up to 50%. Shrimp- and crab-based biochar adsorbents exhibited excellent Hg0 removal because of their chitosan-like structure. In particular, small Mn clusters and oxygen species around the defect led to a boost in the Hg0 adsorption by carbon. The results of density functional theory calculation revealed that the presence of oxygen in the carbon skeleton can tune the electrons of small-sized Mn clusters, thereby promoting the affinity of mercury atoms. The newly developed Mnδ-N2O2/BCshrimp had an adsorption capacity of 7.98–11.52 mg g−1 over a broad temperature range (50–200 °C) and showed a high tolerance to different industrial flue gases (H2O, NO, HCl, and SO2). These results provide novel green and low-carbon disposal methods for biomass resource utilization and industrial Hg0 emission control.Graphical

A theoretical study of the functionalized carbon dots surfaces binding with silver nanostructures

Density functional theory (DFT) calculations were carried out to evaluate the interaction of silver nanostructures on non-functionalized and functionalized carbon dots (Cdots) surfaces. Coronene and coronene with an epoxy functional group are used to model the Cdots surfaces and small size clusters of Agn (n = 1.0.3) are employed to represent the silver nanostructures. A theoretical study of the stability and structure of the composite Ag@Cdots material is performed. The essential role of oxygenated functional groups of Cdots functionalized surfaces to attach silver clusters is systematically evaluated with focus on the understanding of the mechanism intervening on the Cdots surfaces and silver nanostructures interaction. The electronic structure and charge distribution are analyzed. Additionally a bonding investigation is also developed as an attempt to characterize the most relevant bonds contributing to anchor silver nanostructures on Cdots surfaces.

Cascade Reaction of Ethanol to Butadiene over Ag-Promoted, Silica- or Zeolite-Supported Ta, Y, Pr, or La Oxide Catalysts

Ethanol converts to 1,3-butadiene in the presence of suitable multifunctional catalysts. In this work, Lewis acid cations Ta, Y, Pr, and La were dispersed on amorphous silica or β zeolite, and after physically mixing with silica-supported Ag nanoparticles, were tested in the cascade reaction of ethanol to butadiene at 573 K. The Lewis acid catalysts were characterized by X-ray fluorescence, N2 physisorption, scanning transmission electron microscopy (STEM), X-ray diffraction, and diffuse reflectance (DR) UV–vis and X-ray photoelectron spectroscopies. High-resolution STEM images confirmed the small oxide cluster size on the silica support. Results from DR UV–vis spectroscopy showed that zeolite-supported Ta and Pr catalysts had a smaller metal oxide cluster size, relative to their SiO2 counterparts. X-ray photoelectron spectroscopy confirmed that the oxidation state of the cations supported on the zeolite remained the same as that of their SiO2-supported analogues. The selectivity of the C4 coupling products toward butadiene relative to butanol correlated with the acid strength of the Lewis acid cations, as evaluated by the 2-propanol decomposition reaction to propene and acetone, with Ta being the most selective. The rate of C–C coupling over the zeolite-supported cations was enhanced by an order of magnitude compared to those cations supported on amorphous SiO2.

Mechanical properties, electrochemical performance and interfacial contact resistance of as-deposited and annealed NbxAlyC and CrxAlyC coatings on stainless steel 316L substrates

NbxAlyC and CrxAlyC coatings (where x is the Nb or Cr target current and y is the Al target current) were deposited on stainless steel 316L substrates using a radio frequency unbalanced magnetron sputtering system. The sputtered NbxAlyC and CrxAlyC coatings were vacuum annealed at 800°C and 750°C for 1 h, respectively. The cross-sectional and surface morphologies of the as-deposited coatings showed a columnar structure and a loose surface, respectively. The X-ray diffraction results showed that the annealed NbxAlyC and CrxAlyC coatings contained Nb2AlC and Cr2AlC MAX crystalline phases, respectively, The MAX crystalline phase improved the hardness, corrosion resistance, and electrical conductivity of the coatings. The annealed coatings also formed an Al2O3 layer with a small cluster size and a dense surface, which significantly improved the corrosion resistance compared to that of the as-deposited coatings. The electrochemical test results showed that the corrosion current density (Icorr) and interfacial contact resistance (ICR) values of all the annealed coatings were lower than those of the as-deposited coatings and were consistent with the standard for the bipolar plates in commercial proton exchange membrane fuel cells. Among all the coatings, the annealed Nb2.5Al0.5C-H coating showed the lowest Icorr and ICR values.

An atomic/molecular-level strategy for the design of a preferred nitrogen-doped carbon nanotube cathode for Li-O2 batteries

The formation and growth of Li2O2, the primary discharge product with extremely low conductivity, will cause the passivation of the cathode and the failure or even death of Li-O2 batteries. In this paper, by means of molecular dynamics and density functional theory, we systematically investigated the morphology evolution and electron transport pathway of (Li2O2)n on the surface of nitrogen-doped carbon nanotubes (NCNTs) and the effects of the possible N configuration on the growth stability of (Li2O2)n. Our results demonstrated that the morphology of (Li2O2)n on the surface of NCNTs undergos a process from scattered small-sized clusters to film-like (axial) and toroidal (circumferential) large clusters, and finally completely surrounded the NCNTs. Compared with graphitic N1 and graphitic N2, Li2O2 tends to aggregate stably on the surface of pyridinic N3 and pyridinic N4, which can effectively reduce the capacity loss caused by Li2O2 branches and free state Li2O2. In addition, a stable gap exists between Li2O2 and NCNTs, which is attributed to the Coulomb force and van der Waals interaction. Importantly, (Li2O2)n with p-type semiconductor characteristics acts as a bridge between NCNTs, and electrons are mainly transferred along the surface of (Li2O2)n clusters. Moreover, increasing the wall number of NCNTs and using NCNT bundles were found to be beneficial to improving the deposition stability of (Li2O2)n. Notably, pyrrolic N3 with unstable structure is not recommended for practical application. These results offer general guidelines for designing highly active catalysts for Li-O2 batteries in terms of the optimization of the NCNT-based cathode, and the unique research methods also shed more light on the analysis of the discharge product behavior of other potential metal-air batteries.

Tube geometry controls protein cluster conformation and stability on the endoplasmic reticulum surface.

The endoplasmic reticulum (ER), a cellular organelle that forms a cell-spanning network of tubes and sheets, is an important location of protein synthesis and folding. When the ER experiences sustained unfolded protein stress, IRE1 proteins embedded in the ER membrane activate and assemble into clusters as part of the unfolded protein response (UPR). We use kinetic Monte Carlo simulations to explore IRE1 clustering dynamics on the surface of ER tubes. While initially growing clusters are approximately round, once a cluster is sufficiently large a shorter interface length can be achieved by 'wrapping' around the ER tube. A wrapped cluster can grow without further interface length increases. Relative to wide tubes, narrower tubes enable cluster wrapping at smaller cluster sizes. Our simulations show that wrapped clusters on narrower tubes grow more rapidly, evaporate more slowly, and require a lower protein concentration to grow compared to equal-area round clusters on wider tubes. These results suggest that cluster wrapping, facilitated by narrower tubes, could be an important factor in the growth and stability of IRE1 clusters and thus impact the persistence of the UPR, connecting geometry to signaling behavior. This work is consistent with recent experimental observations of IRE1 clusters wrapped around narrow tubes in the ER network.

Modeling and Analysis of UAV-Assisted Mobile Network with Imperfect Beam Alignment

With the rapid development of emerging 5G and beyond (B5G), Unmanned Aerial Vehicles (UAVs) are increasingly important to improve the performance of dense cellular networks. As a conventional metric, coverage probability has been widely studied in communication systems due to the increasing density of users and complexity of the heterogeneous environment. In recent years, stochastic geometry has attracted more attention as a mathematical tool for modeling mobile network systems. In this paper, an analytical approach to the coverage probability analysis of UAV-assisted cellular networks with imperfect beam alignment has been proposed. An assumption was considered that all users are distributed according to Poisson Cluster Process (PCP) around base stations, in particular, Thomas Cluster Process (TCP). Using this model, the impact of beam alignment errors on the coverage probability was investigated. Initially, the Probability Density Function (PDF) of directional antenna gain between the user and its serving base station was obtained. Then, association probability with each tier was achieved. A tractable expression was derived for coverage probability in both Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) condition links. Numerical results demonstrated that at low UAVs altitude, beam alignment errors significantly degrade coverage performance. Moreover, for a small cluster size, alignment errors do not necessarily affect the coverage performance.

Design of Lanthanide Single-Chain Magnets Based on Tubular Segment Clusters

One-dimensional (1D) atomic chains that exhibit large magnetic anisotropy are highly relevant to spintronic applications. Such 1D magnetic systems have usually been produced by atom/molecular assembling on solid surfaces or by coordination polymers. Here, we demonstrate an alternative approach for the formation of a confined ferromagnetic holmium (Ho) atom chain, which is composed of repeating units of the tubular Ho doped boron (B) cluster HoB20. The tubular HoB20 is discovered by the global structural search of a series of small-sized boron clusters doped by a single Ho atom (HoBn, n = 12, 14, 16, 18, 20) using ab initio calculations. Electronic analysis reveals that the individual HoB20 cluster is stabilized by the double σ + π aromaticity. Extending the tubular structure results in a single Ho atom chain being confined inside a boron nanotube, which shows ferromagnetic behaviors and a large magnetic anisotropy of more than 40 meV/atom. Our findings indicate that the magnetic lanthanide chain is a promising candidate for high-density magnetic information storage.

An adaptive mutual K-nearest neighbors clustering algorithm based on maximizing mutual information

Clustering based on Mutual K-nearest Neighbors (CMNN) is a classical method of grouping data into different clusters. However, it has two well-known limitations: (1) the clustering results are very much dependent on the parameter k; (2) CMNN assumes that noise points correspond to clusters of small sizes according to the Mutual K-nearest Neighbors (MKNN) criterion, but some data points in small size clusters are wrongly identified as noises. To address these two issues, we propose an adaptive improved CMNN algorithm (AVCMNN), which consists of two parts: (1) improved CMNN algorithm (abbreviated as VCMNN) and (2) adaptive VCMNN algorithm (abbreviated as AVCMNN). Specifically, the first part is VCMNN algorithm, we first reassign the data points in some small-size clusters by a novel voting strategy because some of them are wrongly identified as noise points, and the clustering results are improved. Then, the second part is AVCMNN, we use maximizing mutual information to construct an objective function to optimize the parameters of the proposed method and finally obtain the better parameters values and clustering results. We conduct extensive experiments on twenty datasets, including six synthetic datasets, ten UCI datasets, and four image datasets. The experimental results show that VCMNN and AVCMNN outperforms three classical algorithms (i.e., CMNN, DPC, and DBSCAN) and six state-of-the-art (SOTA) clustering algorithms in most cases.

Effects of environment on the electron-impact ionization dynamics of argon clusters

Ionization of the $3p$ orbital of argon (Ar) monomers, dimers (${\mathrm{Ar}}_{2}$), and small-size Ar clusters (${\mathrm{Ar}}_{n},\phantom{\rule{0.16em}{0ex}}\ensuremath{\langle}n\ensuremath{\rangle}\ensuremath{\approx}15$) is investigated for 90-eV electron impact. Experimentally, the three-dimensional momentum vectors of the two outgoing electrons and the residual ion are measured in triple coincidence, as is the mass-over-charge ratio of the ion, using a reaction microscope that covers a large part of the final-state phase space. The triple-differential cross sections (TDCS) are obtained for almost the full solid angle of the ejected electron, in which the data for Ar monomers are well reproduced by $B$-spline $R$-matrix calculations for ejected electron energies of 3 eV, 5 eV, and 10 eV, and projectile scattering angles of ${10}^{\ensuremath{\circ}}$ and ${20}^{\ensuremath{\circ}}$. Compared to the Ar monomer, the cross sections for ${\mathrm{Ar}}_{2}$ and ${\mathrm{Ar}}_{n}$ exhibit effects due to the neighboring atoms by the suppression of binary and recoil lobes and the enhanced electron emission out of the projectile scattering plane. These environmental effects are further investigated using a multicenter three-distorted-wave theory, which can generate the TDCSs for electron-impact ionization of ${\mathrm{Ar}}_{2}$. These studies reveal an important role of multicenter scattering reactions on the ionization dynamics of Ar clusters. Moreover, a two-center interference is not found in the TDCS of ${\mathrm{Ar}}_{2}$. This is interpreted as due to the involvement of orbitals with both gerade and ungerade symmetries in the ionization process.

Molecular dynamics simulations of irradiated defect clusters evolution in different crystal structures

Irradiation damage is an important cause of material failure in in-service nuclear reactors. It is important to explore the resistance to irradiation of metals with different crystal structures. As the formation and evolution of point defects on the atomic scale caused by cascade collisions in the early stages of irradiation are currently difficult to observe experimentally, it is currently possible to simulate the dynamic process of irradiation damage on the atomic scale by means of molecular dynamics (MD) methods. In this paper, some atomic scale numerical simulations are performed to study the irradiation behaviour and displacement cascades in metals with different crystal structures of bcc-Fe, hcp-Ti, hcp-Zr and fcc-Ni by the MD methods. The effect of temperature and the magnitude of the primary knock-on atom (PKA) energy on the generation and evolution of point defects is mainly studied. Results show that an increase in cascade energies from 0.5 keV to 10 keV can significantly promote defect formation for different crystal structures, while ambient temperature (T) has a slight effect on the number of surviving defects. The simulations also illustrate that high-energy cascades can significantly promote the formation of defect clusters. Statistical results of the displacement cascades show that bcc-Fe produces a small number of stable defects, a small cluster size and number relative to fcc-Ni, hcp-Ti, and hcp-Zr structures, which indicates that the bcc-Fe structure has a good radiation resistance. These findings could provide an appropriate idea for obtaining potential radiation-resistant materials for nuclear reactors.

Effect of immersion time and pH variation on the inhibition of AA2198-T851 alloy by leaching of anticorrosion pigments from free-standing films of organic coatings

In this work, organic coating films loaded with leachable anticorrosive pigments, cerium 4-hydroxycinnamate (Ce(4OHCin)3) and strontium zinc phosphosilicate (SZP 391) were immersed in 3.5% NaCl solution at pH 3, pH 5.6, and pH 10. Extracts from each bulk solutions were taken after 24 h, 72 h, 168 h, 240 h, and 336 h to quantitatively measure the leaching of the inhibitive species as a function of time using inductively coupled plasma optical emission spectroscopy (ICP-OES). Other part of the extracts was also employed as test solution to monitor the inhibitive properties of the leached species on AA2198-T851 substrates using electrochemical impedance spectroscopy (EIS). After the immersion process, the unexposed and exposed film surfaces were characterized using optical microscopy, transmission, and scanning electron microscopy (TEM & SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The leaching test results confirmed the release of inhibitive species from the coating films into the test solutions, whose rate increased with immersion time but decrease with increasing pH of the bulk solution. Greater leaching rate was observed at the lowest pH, whose release follows non-Fickian diffusion. Furthermore, the EIS results indicated significant protection of the alloy and the efficiency increased with increasing immersion time and decreasing pH. The extract with Ce(4OHCin)3 pigment shows comparatively higher release rate and better inhibitive properties, with the best at the lowest pH 3. This is attributed to its smaller cluster size and high solubility. The optical and electron Microscopy, XRD and FT-IR of coating films have further complemented the leaching process by revealing pores left behind due to dissolution of large clusters. The pores networks provided excellent transport path for both inward migration of aggressive solution and the release of dissolved inhibitive species.

Effect of Ligand Structures on Ligand-Protected Gold Clusters: [Au-(p-/m-/o-MBT)]1-8 Clusters.

The controllable preparation of ligand-protected clusters is still an unresolved problem, which may be due to that their formation mechanism is unclear. We propose that the ligand is the key to solve the above problems. Here, by using p-, m-, and o-methylbenzenethiol ligand protected gold clusters as examples, we try to explore the effect of ligand structures on ligand-protected gold clusters. The geometrical structures, relative stabilities and surface properties of small-sized ligand-protected gold clusters [Au-SR]1-8 (SR = p-/m-/o-MBT) have been systematically studied based on the density functional theory. The results show that the ground state structures of [Au-SR]1-8 clusters tend to form closed rings except for [Au-SR]1,2. The different structures of ligand have significant effect on the structures and stabilities of ligand-protected clusters. By analyzing their surface properties and possible growth patterns, it is found that [Au-SR]1,2 clusters serve as the basic building blocks, and the larger clusters can be regarded as the combinations of them. This study provides some insights into the effect of ligands on ligand-protected clusters, which is useful for understanding the formation mechanism of ligand-protected clusters.

Revealing the activity origin of oxygen-doped amorphous carbon material for SO2 catalytic oxidation: A descriptor considering dynamic electron transfer during O2 activation

Carbon-based catalytic oxidation widely exists in contamination control, energy conversion and chemical production, in which amorphous carbon containing heteroatom is commonly used carbocatalyst. Compared with crystalline carbon, small-sized aromatic carbon clusters in amorphous carbon exhibit edge and size effect for catalytic oxidation; however, the activity origin, especially accurate activity descriptor remains to be explored. Herein, using SO2 catalytic oxidation as the probe reaction, a combined computational and experimental investigation was conducted to reveal the activity origin of oxygen-doped amorphous carbon. By density functional theory calculations on various oxygen-doped carbon clusters, a site-specific descriptor considering dynamic electron transfer effect was proposed via combining Fukui function and Mulliken electronegativity, based on which the catalytic activity is found to be determined by both oxygen groups and edges. The configuration with cyclic ether embedded into K-region edge is predicted to own the highest activity with O2 activation and SO2 oxidation barrier as low as 35.4 and 89.3 kJ mol−1. SO2 catalytic oxidation dynamic experiments using model amorphous carbocatalysts further validate the favorable role of ether group and edges. This work demonstrates quantitative descriptor for O2 activation and catalytic oxidation on amorphous carbocatalyst, providing guidance for designing high-performance carbocatalyst considering size and edge effect.

Gold-Hydrogen Analogy in Small-Sized Hydrogen-Doped Gold Clusters Revisited.

The analogy between gold and hydrogen is a subject of long-standing debate. In the present work, we examine the validity of the gold-hydrogen analogy in a series of small-sized H-doped gold clusters, Aun-1 H with n varying between 2 and 10 and also investigate its dependence on the cluster size. Keeping in mind the importance of the role of structures, we make use of the genetic algorithm coupled with a density functional theory based method to exhaustively search and identify the energetically low-lying structures of each of the H-doped gold clusters. These lower energy structures of H-doped and pristine gold clusters are then employed to carry out the calculations of their electronic properties, stability analysis as well as their reactivity towards the adsorption and activation of CO and O2 molecules. Our study shows that in line with the gold-hydrogen analogy, both electronic properties and the adsorption/activation characteristics of H-doped gold clusters remain very similar to those of pristine gold clusters.

Congo Red as a Supramolecular Carrier System for Doxorubicin: An Approach to Understanding the Mechanism of Action.

The uptake and distribution of doxorubicin in the MCF7 line of breast-cancer cells were monitored by Raman measurements. It was demonstrated that bioavailability of doxorubicin can be significantly enhanced by applying Congo red. To understand the mechanism of doxorubicin delivery by Congo red supramolecular carriers, additional monolayer measurements and molecular dynamics simulations on model membranes were undertaken. Acting as molecular scissors, Congo red particles cut doxorubicin aggregates and incorporated them into small-sized Congo red clusters. The mixed doxorubicin/Congo red clusters were adsorbed to the hydrophilic part of the model membrane. Such behavior promoted transfer through the membrane.

Effect of plasma treatment on nucleation of Au nanoparticles

Nucleation is a basic issue in film science and technology, and it plays a vital role in the field of functional devices characterized in ultra-thin and continuous thin films. In this paper, Au clusters were deposited on three different substrates (BOPP, Si (100) and carton support film) by means of magnetron sputtering with or without air plasma pretreatment. The results show that plasma treatment conducted on BOPP substrate decreased the water contact angle significantly, indicating an enhanced surface energy of BOPP substrate. The introduction of polar groups (C–O/C–N, C=O/N–C=O and O–C=O) as well as a modified topology were responsible for the improvement of hydrophilicity. Au nanoparticles prepared on untreated substrates exhibited a non-uniform topology independent of substrate type. After plasma treatment, Au nucleation densities were increased greatly, and the nucleus sizes were much smaller. Based on the thermodynamics theory of heterogeneous nucleation, by means of plasma treatment, the substrate surface energy was enhanced and the film-substrate interfacial energy was decreased simultaneously, and both of them contributed to the higher nucleation density and smaller cluster size.

Momentum signatures of site percolation in disordered two-dimensional ferromagnets

In this work, we consider a two-dimensional square lattice of pinned magnetic spins with nearest-neighbour interactions and we randomly replace a fixed proportion of spins with nonmagnetic defects carrying no spin. We focus on the linear spin-wave regime and address the propagation of a spin-wave excitation with initial momentum $k_0$. We compute the disorder-averaged momentum distribution obtained at time $t$ and show that the system exhibits two regimes. At low defect density, typical disorder configurations only involve a single percolating magnetic cluster interspersed with single defects essentially and the physics is driven by Anderson localization. In this case, the momentum distribution features the emergence of two known emblematic signatures of coherent transport, namely the coherent backscattering (CBS) peak located at $-k_0$ and the coherent forward scattering (CFS) peak located at $k_0$. At long times, the momentum distribution becomes stationary. However, when increasing the defect density, site percolation starts to set in and typical disorder configurations display more and more disconnected clusters of different sizes and shapes. At the same time, the CFS peak starts to oscillate in time with well defined frequencies. These oscillation frequencies represent eigenenergy differences in the regular, disorder-immune, part of the Hamiltonian spectrum. This regular spectrum originates from the small-size magnetic clusters and its weight grows as the system undergoes site percolation and small clusters proliferate. Our system offers a unique spectroscopic signature of cluster formation in site percolation problems.

Concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in ferritic steel containing copper during aging

ABSTRACT The concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in the ferritic steel containing copper after aging at 400°C for 4000 h have been investigated using transmission electron microscopy (TEM) and atom probe tomography (APT). The results show that spinodal decomposition and an atomic ordering reaction occur in the ferritic steel containing copper. After aging, the retained austenite decomposed by the spinodal mechanism into C-rich and C-lean regions. The C-rich phase transforms into the (Fe,Mo)2C carbides via the ordering reaction, while Cu-rich clusters formed in the C-lean regions. The experimental results can be interpreted on the basis of phase separation via spinodal decomposition followed by chemical ordering. The small size of Cu-rich clusters can be attributed to the lower diffusion coefficient of Cu in the retained austenite.