Clusters Of Different Sizes Research Articles

Nanostructural investigation of slightly altered rhyolitic volcanic glass

Silica rich volcanic glass is investigated by selected area electron diffraction (SAED) and high resolution electron microscopy (HRTEM), and nanostructural characterization is presented. In freshly crushed glass shards the presence of amorphous and randomly oriented nanocrystalline component was detected, the latter one enriched in iron with respect to the amorphous regions. To interpret the iron containing nanocrystalline structure, model clusters of different size, shape and composition were constructed and used to calculate scattered electron intensity. According to our calculations, already a single ring of six interconnected SiO4 tetrahedra results a separate broad peak at ~5Å which reflects nicely the main diffraction feature of amorphous silica. Inserting two dimensional iron array between two neighbouring silica layers produces a less compact structure and the first diffraction peak shifts towards larger values with respect to the pure silica. For smaller clusters (number of atoms<250) first peak position shows a remarkable dependence on the structure and size of the cluster. The pair distribution analysis of SAED and HRTEM data indicates a certain degree of ordering with a domain size of ~2nm.

Short Communication: HIV-1 Transmission Networks Across South Korea.

Molecular epidemiology can help clarify the properties and dynamics of HIV-1 transmission networks in both global and regional scales. We studied 143 HIV-1-infected individuals recruited from four medical centers of three cities in South Korea between April 2013 and May 2014. HIV-1 env V3 sequence data were generated (337-793 bp) and analyzed using a pairwise distance-based clustering approach to infer putative transmission networks. Participants whose viruses were ≤2.0% divergent according to Tamura-Nei 93 genetic distance were defined as clustering. We collected demographic, risk, and clinical data and analyzed these data in relation to clustering. Among 143 participants, we identified nine putative transmission clusters of different sizes (range 2-4 participants). The reported risk factor of participants were concordant in only one network involving two participants, that is, both individuals reported homosexual sex as their risk factor. The participants in the other eight networks did not report concordant risk factors, although they were phylogenetically linked. About half of the participants refused to report their risk factor. Overall, molecular epidemiology provides more information to understand local transmission networks and the risks associated with these networks.

Increased absorption in InAsSb nanowire clusters through coupled optical modes

Nanowires can act as efficient light absorbers where waveguide modes are resonant to specific wavelengths. This resonant wavelength can easily be tuned by the nanowire dimensions, but the absorption of infrared radiation requires diameters of hundreds of nm, which is difficult to achieve using epitaxial growth. Here, we demonstrate that infrared absorption in InAsSb nanowires with the diameters of only 140 nm grown on Si substrates can be enhanced resonantly by placing them closely packed in clusters of different sizes. We find that coating the nanowires with a dielectric to optically connect them results in an efficient absorption diameter far exceeding the diameter of the constituent nanowires and that the cut-off wavelength is redshifted with an increasing cluster diameter. Numerical simulations are in agreement with the experimental results and demonstrate that if nanowires are positioned in clusters, a peak absorptance of 20% is possible at 5.6 μm with only 3% surface coverage. This absorptance is 200 times higher than for wires placed in an equidistant pattern. Our findings have direct implications for the design of efficient nanowire based photodetectors and solar cells.

Effect of graphite size on the tribological behavior of Ti (C, N)-based cermets self-mated wear pairs

In the present work, graphite of different particle size ranging from 2μm to 32μm is added into the system to lubricate the Ti (C, N) cermets, but the addition amount is fixed at 1wt%. The sliding wear tests were carried out using block-on-ring equipment. The distribution morphology of graphite, mechanical properties and wear behavior were studied in this paper. The results indicate that when the graphite is added into the cermet, graphite particles join together and are distributed to clusters of different size which are like bird nests. The range of the “bird-nest” clusters increase with the improvement of graphite size when the graphite particle size is smaller than 12μm but decrease when larger than 12μm. Furthermore when the graphite grain size increase to 32μm, most of the particles exist in the cermets individually instead of distributing like bird nest The mechanical properties decrease with the improvement of graphite size, and when the particles size of graphite increase to 32μm the mechanical properties get worse sharply. The wear mechanism of the cermets with graphite, adhesion and plastic deformation are dominated. The extruded graphite forms a tribofilm, and protects the surface from the hard abrasive particles ploughing. When the particles size of graphite added is 22μm, cermets which have coarser graphite particles and more but moderate-in-size graphite clusters possess the best effect of lubrication

Multimodal porous carbon derived from ionic liquids: correlation between pore sizes and ionic clusters.

In this proof of concept study on the synthesis of ionic liquid (IL)-derived multimodal porous carbon using ionic clusters of different sizes as porogens, the carbonization behaviors of binary IL mixtures of 1-ethyl-3-methylimidazolium dicyanamide (EMIM-dca) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-Tf2N) were systematically investigated to demonstrate the formation of multimodal porous carbons with hierarchical structures originating from the ionic cluster porogens. The multimodal porous structures of the resulting IL-derived porous carbons were characterized based on the quenched solid density functional theory, and the role of the ionic clusters as porogens is discussed. From the viewpoint of green and sustainable chemistry, the IL-based synthesis using ionic clusters as porogens is a simple, effective, and sustainable technique for synthesizing multimodal porous carbons with hierarchical structures. To the best of our knowledge, this is the first study demonstrating that a multimodal porous structure of IL-derived porous carbons could be systematically manipulated with the aid of ionic clusters of different sizes as porogens.

TIME-DRIVEN opportunistic routing protocol for ultra-wideband indoor positioning

The scope of a single regional indoor positioning network is often restricted to its main anchor communication range and more susceptible to obstacles. Multiple main anchors can be the basis of an indoor positioning network’s extensibility and can adapt to the complex communication environment. In this article, a novel TIME-DRIVEN opportunistic routing protocol with intelligent response is proposed. First, an extendable ultra-wideband positioning system is modeled. In two or more communication cells, anchors can act as a main or slave anchor in different areas, respectively, and a forward clock check package from the initial district to its surrounding area. They can also achieve the clock synchronization of the entire network. In this model, the anchors will be divided into different sizes of clusters, and the main anchor is elected according to the broadcast time. Furthermore, the relay anchor will be intelligently selected according to the opportunistic probability based on the received signal strength indicator. Finally, experiments are conducted to verify the performance of the method.

Retention and thermal desorption of helium in pure tungsten

Tungsten (W) is cited as a candidate first-wall material in fusion reactors owing to its outstanding thermal properties and erosion resistance. An important issue is that the energetic isotopes of hydrogen, tritium (T) and deuterium (D) and helium (He) particles damage the surface of W in fusion reactors. He particles cause more notable damage than D or T because the binding energy of defects and He is larger than that of defects and D or T. In this study, well-annealed W specimens were implanted with 5 keV He ions at room temperature and irradiation dosages of 1.0 × 1020 and 2.5 × 1021 ions/m2. Then, thermal desorption spectroscopy analysis was performed by heating the samples to 1973 K at a ramping rate of 0.5 K/s. Thermal desorption of He in the sample irradiated with a low dosage occurred at 1400 and 1960 K, whereas that in the sample irradiated with a high dosage occurred at 740, 1050 and 1500 K. According to the microstructures observed using transmission electron microscopy, both peaks in the former case were attributed to He de-trapping from irradiation to nduced helium-vacancy clusters of different sizes, whereas the peaks in the latter case were attributed to He de-trapping from surface defects, irradiation-induced dislocation loops and tiny helium-vacancy clusters, respectively.

The scaling exponent of residual nonwetting phase cluster size distributions in porous media

AbstractDuring an imbibition process in two‐phase subsurface flow the imbibing phase can displace the nonwetting phase up to an endpoint at which a residual saturation is reached (which cannot be reduced further by additional wetting phase flow due to the complex pore network of the rock and associated strong capillary forces which trap the nonwetting phase). The residual nonwetting phase is split into many disconnected clusters of different sizes. This size distribution is of key importance, for instance, in the context of hydrocarbon recovery, contaminant transport, or CO2 geostorage; and it is well established that this size distribution follows a power law. However, there is significant uncertainty associated with the exact value of the distribution exponent τ, which mathematically describes the size distribution. To reduce this uncertainty and to better constrain τ, we analyzed a representative experimental data set with mathematically rigorous methods, and we demonstrate that τ is substantially smaller (≈1.1) than previously suggested. This raises increasing doubt that simple percolation models can accurately predict subsurface fluid flow behavior; and this has serious consequences for subsurface flow processes: hydrocarbon recovery is easier than predicted, but CO2 geostorage dissolution trapping capacities are significantly reduced and potential remobilization of residual CO2 is more likely than previously believed.

Energy deposition clustering as a functional radiation quality descriptor for modeling relative biological effectiveness.

To explore the use of the frequency of the energy deposition (ED) clusters of different sizes (cluster order, CO) as a surrogate (instead of, e.g., LET) classification of the physical characteristics of ionizing radiation at a nanometer scale, to construct a framework for the calculation of relative biological effectiveness (RBE) with cell survival as endpoint. The frequency of cluster order fCO is calculated by sorting the ED sites generated with the Monte Carlo track structure code LIonTrack into clusters based on a single parameter called the cluster distance dC being the maximum allowed distance between two neighboring EDs belonging to a cluster. Published cell survival data parameterized with the linear-quadratic (LQ) model for V79 cells exposed to 15 different radiation qualities (including brachytherapy sources, proton, and carbon ions) were used as input to a fitting procedure, designed to determine a weighting function wCO that describes the capacity of a cluster of a certain CO to damage the cell's sensitive volume. The proposed framework uses both fCO and wCO to construct surrogate based functions for the LQ parameters α and β from which RBE values can be derived. The results demonstrate that radiation quality independent weights wCO exist for both the α and β parameters. This enables the calculation of α values that correlate to their experimental counterparts within experimental uncertainties (relative residual of 15% for dC = 2.5 nm). The combination of both α and β surrogate based functions, despite the higher relative residuals for β values, yielded an RBE function that correlated to experimentally derived RBE values (relative residual of 16.5% for dC = 2.5 nm) for all radiation qualities included in this work. The fCO cluster characterization of ionizing radiation at a nanometer scale can effectively be used to calculate particle and energy dependent α and β values to predict RBE values with potential applications to, e.g., treatment planning systems in radiotherapy.

Comparison of S-adsorption on (111) and (100) facets of Cu nanoclusters.

In order to gain insight into the nature of chemical bonding of sulfur atoms on coinage metal surfaces, we compare the adsorption energy and structural parameters for sulfur at four-fold hollow (4fh) sites on (100) facets and at three-fold hollow (3fh) sites on (111) facets of Cu nanoclusters. Consistent results are obtained from localized atomic orbital and plane-wave based density functional theory using the same functionals. PBE and its hybrid counterpart (PBE0 or HSE06) also give similar results. 4fh sites are preferred over 3fh sites with stronger bonding by ∼0.6 eV for nanocluster sizes above ∼280 atoms. However, for smaller sizes there are strong variations in the binding strength and the extent of the binding site preference. We show that suitable averaging over clusters of different sizes, or smearing the occupancy of orbitals, provide useful strategies to aid assessment of the behavior in extended surface systems. From site-projected density of states analysis using the smearing technique, we show that S adsorbed on a 4fh site has similar bonding interactions with the substrate as that on a 3fh site, but with much weaker antibonding interactions.

Síntese do cerato de bário pelo método de complexação combinando EDTA-citrato e avaliação catalítica na oxidação do monóxido de carbono testada em reator de leito fixo

Resumo A perovskita de cerato de bário foi sintetizada com base no método de complexação combinando EDTA-citrato e suas propriedades catalíticas testadas na reação de oxidação do monóxido de carbono em um reator de leito fixo variando a vazão de alimentação (50 e 100 mL.min-1) e a temperatura (100 a 550 °C). A fase cristalina de interesse foi obtida com tamanho de cristalito de 133 nm, junto com uma pequena quantidade de BaCO3 (3%). Quando sintetizado pelo método de complexação combinando EDTA-citrato, o cerato de bário apresenta um formato esférico irregular com aglomerados de diferentes tamanhos e com a presença de poros de diferentes tamanhos distribuídos aleatoriamente, sendo sua área superficial específica igual a 2,61 m2.g-1. Na vazão de 50 mL.min-1 ocorreu maior conversão quando comparado com a de 100 mL.min-1, sendo mais evidente entre 300 e 400 °C. Além disso, na vazão de 50 mL.min-1 ocorreu conversão total de CO em CO2 a 400 °C, enquanto que em 100 mL.min-1 a conversão foi de aproximadamente 60%. Com o uso da perovskita como catalisador o processo de oxidação é completo a 400 °C, enquanto que na reação sem catalisador a conversão completa é alcançada somente a 550 °C. Apesar da sua pequena área superficial, o BaCeO3 é altamente reativo na oxidação do monóxido de carbono.

In Situ-Raman Spectroscopy and Comparison with DFT Computational and Experimental Study of Electroless Nickel Deposition

The kinetic mechanism of the electroless deposition of NiP from hypophosphite solutions was investigated from first principles with the intent of determining a set of elementary reactions that could effectively identify the most relevant steps of this complex process. The outcome of the computational approach is discussed in terms of experimental results obtained by electrochemical methods and surface analysis techniques [1,2]. Simulations were performed with Density Functional Theory DFT using the B3LYP exchange and correlation functionals [3], the 6-311+G(d,p) basis set for P,C,H and O atoms [4], and the Stuttgart effective core potential basis sets for Ni [5]). The interaction of Ni++ and H2PO2- with the Ni surface was studied using Ni clusters of different sizes (from 4 to 12 atoms). Solvation in water was modeled using the implicit polarizable continuum model [6]; calculations were performed using the G09 computational suite [7]. Simulations were initially devoted to the identification of the first reaction steps that lead to the adsorption of Ni++ on the Ni surface and to its successive reduction by means of the hypophosphite anion. Though several theories were proposed to describe this key step in the literature, our search was guided by the original insight published several years ago [8], according to which the reduction of Ni++ requires the formation of an intermediate species containing the NiOH group. Such species would then take active part in the transfer of the OH group to H2PO2-, thus favoring its oxidation to H2PO3-. In addition, it was imposed that the searched elementary mechanism satisfies the experimental observation, obtained with marked deuterium species, that each molecule of hydrogen that is evolved contextually to the deposition of NiP contains two H atoms coming from two H2PO2- anions. The possibility that NiOH+ is formed in solution prior to deposition was investigated determining computationally the pKa of Ni++. Results revealed that the formation of NiOH+ is not favored in the pH ranges in which NiP is usually deposited. A similar result was obtained when considering the possibility that NiOH+, after being formed in solution, is stabilized through the formation of a complex with H2PO2-. A thermodynamically favored set of reactions was instead found when it was investigated the possibility that NiOH is formed at the surface contextually with a Ni-H2PO2 complex. It was in fact found that the following set of reactions has a globally slightly negative (≈ -5 ± 5 kcal/mol) free energy change: R1) Ni ++ + surf ® Niads ++ R2) Niads ++ + 2 H2O + H2PO2 - ® NiOH(H2PO2)ads + H3O+ The minimum energy structure of the surface NiOH(H2PO2)ads species optimized at the B3LYP level on a Ni8 cluster in implicit water. The two reactions set R1-R2 provides a mechanism for the initial step of reduction of Ni++, thermodynamically viable and consistent with the hypotheses formulated above. The results of this analysis suggest therefore that the initial step of Ni++ reduction during NiP deposition involves a concerted mechanism in which adsorbed Ni++ contextually reacts with H2PO2- and a water molecule. This mechanism can be also supported by electrochemical measurements, indicating the need of OH funtionalization of the catalytic surface in order to have the reaction of hyposphite. In order to understand completely the adsorption phenomena on the electrode surface during the electroless deposition process, in situ-Raman analyses were performed. The purpose of this experimental section is to discern the different complexes adsorbed on the electrode surface while the reaction proceeds. These tests were carried out at different temperature, starting from the ambient temperature to the effective process temperature. The effect of each complexing agent dissolved into electroless NiP bath on complexes adsorbed on the electrode surface and the comparison with the DFT computational analysis will be presented.

Tensional homeostasis in endothelial cells is a multicellular phenomenon.

Mammalian cells of various types exhibit the remarkable ability to adapt to externally applied mechanical stresses and strains. Because of this adaptation, cells can maintain their endogenous mechanical tension at a preferred (homeostatic) level, which is essential for normal physiological functions of cells and tissues and provides protection against various diseases, including atherosclerosis and cancer. Conventional wisdom is that the cell possesses the ability to maintain tensional homeostasis on its own. Recent findings showed, however, that isolated cells cannot maintain tensional homeostasis. Here we studied the effect of multicellular interactions on tensional homeostasis by measuring traction forces in isolated bovine aortic endothelial cells and in confluent and nonconfluent cell clusters of different sizes. We found that, in isolated cells, the traction field exhibited a highly dynamic and erratic behavior. However, in cell clusters, dynamic fluctuations of the traction field became attenuated with increasing cluster size, at a rate that was faster in nonconfluent than confluent clusters. The driving mechanism of attenuation of traction field fluctuations was statistical averaging of the noise, and the impeding mechanism was nonuniform stress distribution in the clusters, which resulted from intercellular force transmission, known as a "global tug-of-war." These results show that isolated cells could not maintain tensional homeostasis, which confirms previous findings, and that tensional homeostasis is a multicellular phenomenon, which is a novel finding.

Role of F− ions in the structure and properties of BaF2[sbnd]B2O3 glasses

XRD, TEM, SEM, FTIR and NMR spectroscopies have been used to explore the role of F− ions in structure of BaF2B2O3 glasses. Up to BaF2≈35mol% the majority of fluorine enters the glass network to convert BO3 units into Ba1/22+BO3F− (B4 units) with BF linkages. For BaF2>35mol%, a part of BaF2 forms its own matrix in the form of amorphous and crystalline phase, built of BaF4 tetrahedra. Calculated N4 values from IR spectra agree well with the data obtained from NMR spectroscopy. SEM shows clusters of different size separated from the amorphous phase. Changes in Tg reveal that the BF bonds are weaker than BO bonds. Density and molar volume calculated on the basis of the presented model are in excellent agreement with the experimental data. Abrupt changes in conductivity and activation energy for BaF2>35mol% are correlated with the presence of BaF4 clusters and changes in free volume and packing density. As far the authors know, BaF2B2O3 glasses are investigated for the first time.

Detecting protein complexes from DPINs by density based clustering with Pigeon-Inspired Optimization Algorithm

Detecting protein complexes is crucial to understand principles of cellular organization. Plenty evidences have indicated that sub-graphs with high density in protein-protein interaction (PPI) network, especially dynamic PPI network (DPIN), usually correspond to protein complexes. As a well-known density-based clustering algorithm, Density-Based Spatial Clustering of Applications with Noise (DBSCAN) has been used in many areas due to its simplicity and the ability to detect clusters of different sizes and shapes. However, one of its limitations is that the performance of DBSCAN depends on two specified parameters $\varepsilon$ and MinPts, where $\varepsilon$ represents the maximum radius of a neighborhood from an observing point while MinPts means the minimum number of data points contained in such a neighborhood. In this article, we develop a new method named as P-DBSCAN to detect protein complexes in DPIN by using Pigeon-Inspired Optimization (PIO) Algorithm to optimize the parameters $\varepsilon$ and MinPts in DBSCAN. The experiments on DIP and MIPS datasets show that P-DBSCAN outperforms the state-of-the-art methods for protein complex detection in terms of several criteria such as precision, recall and f-measure.

A Multilevel Point-Cluster-Based Discriminative Feature for ALS Point Cloud Classification

Point cloud classification plays a critical role in point cloud processing and analysis. Accurately classifying objects on the ground in urban environments from airborne laser scanning (ALS) point clouds is a challenge because of their large variety, complex geometries, and visual appearances. In this paper, a novel framework is presented for effectively extracting the shape features of objects from an ALS point cloud, and then, it is used to classify large and small objects in a point cloud. In the framework, the point cloud is split into hierarchical clusters of different sizes based on a natural exponential function threshold. Then, to take advantage of hierarchical point cluster correlations, latent Dirichlet allocation and sparse coding are jointly performed to extract and encode the shape features of the multilevel point clusters. The features at different levels are used to capture information on the shapes of objects of different sizes. This way, robust and discriminative shape features of the objects can be identified, and thus, the precision of the classification is significantly improved, particularly for small objects.

Physicochemical characterization of a new raw material obtained from leaves of Syzygium cumini (L.) Skeel (Myrtaceae)

The aim of this study was to determine the physicochemical characteristics of leaves of Syzygium cumini L. Skeels plant and characterize the extract of this plant by analytical techniques. Pharmacopeial methods of physicochemical analysis were used, including morphological characterization of the particle, thermal analysis, infrared spectroscopy and X-ray diffraction. The plant drug was presented as a coarse powder, within the appropriate Brazilian Pharmacopoeia parameters. The X-ray diffraction, optical microscopy and scanning electron microscopy suggested that the extract particles are amorphous and have irregular shapes, so that clusters of different sizes and morphologies are displayed. Thermal decomposition of the organic components in the sample started in a step that occurred between 151.64 and 209.27 °C with mass loss of 9.08 %, followed by another step with more significant mass loss (28.16 %). The infrared spectrum, in turn, showed many functional groups of compounds present in the lyophilized extract in different absorption bands. The results showed that the analytical techniques allowed us to characterize the physicochemical properties of the plant leaves, which may be useful in the production of new herbal medicines.

Size dependence of vacancy migration energy in ionic nano particles: A potential energy landscape perspective

Size dependence of vacancy migration energy in ionic nano particles is investigated by analysis of potential energy surfaces in potassium chloride clusters. Numerical methods are used to find almost all local minima and transition states for vacancy migration in clusters of different sizes, and reveal characteristic features of energy surface structure. It is shown that migration energy is significantly lower near a cluster surface than near a cluster core, and the mean first-passage time for migration of a vacancy decreases with cluster size. These results are consistent with observations of high diffusion rates in small clusters.

ChemInform Abstract: Rare‐Earth Metal Oxo/Hydroxo Clusters — Synthesis, Structures, and Applications

AbstractReview: 122 refs.

The effect of electron irradiation on the structure and the optical properties of silver particulate films deposited on modified thermoplastic polymer substrates

The silver (Ag) particulate films are prepared by the vacuum evaporation onto polystyrene (PS) substrates modified with 3-mercaptopropyltrimethoxysilane (MPTMS), pre-irradiated with the 8-MeV electron beam, held at a temperature 453 K. The effect of organosilane and electron irradiation dose on the Ag particulate structure is studied through optical spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with selected area electron diffraction (SAED) pattern, atomic-force microscopy (AFM), and X-ray diffraction (XRD). The flat spectrum observed for the lower irradiation doses may be due to the formation of the clusters of different sizes and shapes. The band shift toward the higher wavelength is attributed to the increased aggregation leading to the formation of the larger-sized nanoclusters. A long tail extending to the higher wavelength region is also observed due to aggregation process. The FESEM studies indicate the formation of the silver nanoclusters. The decrease in the particle size with the increase in irradiation dose as seen through TEM studies is interpreted on the basis of polymer–metal particle interaction caused by the free radicals formed due to the electron irradiation of the MPTMS-modified PS substrates. The SAED pattern shows the crystalline nature of the silver particles formed on the pure PS and the MPTMS-modified PS substrates irradiated with the electron beam. The AFM studies show an increase in the average surface roughness of the silver films with the electron irradiation dose and the MPTMS concentration. XRD indicated the polycrystalline nature of silver film on the pre-irradiated PS substrates and formation of nanocrystallites of silver with preferred orientation on the MPTMS-modified PS substrates pre-irradiated with electron beam.