Evolution of Carbon Clusters in the Detonation Products of the Triaminotrinitrobenzene (TATB)-Based Explosive PBX 9502

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watkins, Erik B.; Velizhanin, Kirill A.; Dattelbaum, Dana M.

The detonation of carbon-rich high explosives yields solid carbon as a major constituent of the product mixture and, depending on the thermodynamic conditions behind the shock front, a variety of carbon allotropes and morphologies may form and evolve. We applied time-resolved small angle x-ray scattering (TR-SAXS) to investigate the dynamics of carbon clustering during detonation of PBX 9502, an explosive composed of triaminotrinitrobenzene (TATB) and 5 wt% fluoropolymer binder. Solid carbon formation was probed from 0.1 to 2.0 μs behind the detonation front and revealed rapid carbon cluster growth which reached a maximum after ~200 ns. The late-time carbon clustersmore » had a radius of gyration of 3.3 nm which is consistent with 8.4 nm diameter spherical particles and matched particle sizes of recovered products. Simulations using a clustering kinetics model were found to be in good agreement with the experimental measurements of cluster growth when invoking a freeze-out temperature, and temporal shift associated with the initial precipitation of solid carbon. Product densities from reactive flow models were compared to the electron density contrast obtained from TR-SAXS and used to approximate the carbon cluster composition as a mixture of 20% highly ordered (diamond-like) and 80% disordered carbon forms, which will inform future product equation of state models for solid carbon in PBX 9502 detonation product mixtures.« less

Studies of Atomic Free Radicals Stored in a Cryogenic Environment

NASA Technical Reports Server (NTRS)

Lee, David M.; Hubbard, Dorthy (Technical Monitor); Alexander, Glen (Technical Monitor)

2003-01-01

Impurity-Helium Solids are porous gel-like solids consisting of impurity atoms and molecules surrounded by thin layers of solid helium. They provide an ideal medium for matrix isolation of free radicals to prevent recombination and store chemical energy. In this work electron spin resonance, nuclear magnetic resonance, X-ray diffraction, and ultrasound techniques have all been employed to study the properties of these substances. Detailed studies via electron spin resonance of exchange tunneling chemical reactions involving hydrogen and deuterium molecular and atomic impurities in these solids have been performed and compared with theory. Concentrations of hydrogen approaching the quantum solid criterion have been produced. Structured studies involving X ray diffraction, ultrasound, and electron spin resonance have shown that the impurities in impurity helium solids are predominantly contained in impurity clusters, with each cluster being surrounded by thin layers of solid helium.

Dynamic microscopy of nanoscale cluster growth at the solid-liquid interface.

PubMed

Williamson, M J; Tromp, R M; Vereecken, P M; Hull, R; Ross, F M

2003-08-01

Dynamic processes at the solid-liquid interface are of key importance across broad areas of science and technology. Electrochemical deposition of copper, for example, is used for metallization in integrated circuits, and a detailed understanding of nucleation, growth and coalescence is essential in optimizing the final microstructure. Our understanding of processes at the solid-vapour interface has advanced tremendously over the past decade due to the routine availability of real-time, high-resolution imaging techniques yielding data that can be compared quantitatively with theory. However, the difficulty of studying the solid-liquid interface leaves our understanding of processes there less complete. Here we analyse dynamic observations--recorded in situ using a novel transmission electron microscopy technique--of the nucleation and growth of nanoscale copper clusters during electrodeposition. We follow in real time the evolution of individual clusters, and compare their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth. The experimental technique developed here is applicable to a broad range of dynamic phenomena at the solid-liquid interface.

Critical Analysis of Cluster Models and Exchange-Correlation Functionals for Calculating Magnetic Shielding in Molecular Solids.

PubMed

Holmes, Sean T; Iuliucci, Robbie J; Mueller, Karl T; Dybowski, Cecil

2015-11-10

Calculations of the principal components of magnetic-shielding tensors in crystalline solids require the inclusion of the effects of lattice structure on the local electronic environment to obtain significant agreement with experimental NMR measurements. We assess periodic (GIPAW) and GIAO/symmetry-adapted cluster (SAC) models for computing magnetic-shielding tensors by calculations on a test set containing 72 insulating molecular solids, with a total of 393 principal components of chemical-shift tensors from 13C, 15N, 19F, and 31P sites. When clusters are carefully designed to represent the local solid-state environment and when periodic calculations include sufficient variability, both methods predict magnetic-shielding tensors that agree well with experimental chemical-shift values, demonstrating the correspondence of the two computational techniques. At the basis-set limit, we find that the small differences in the computed values have no statistical significance for three of the four nuclides considered. Subsequently, we explore the effects of additional DFT methods available only with the GIAO/cluster approach, particularly the use of hybrid-GGA functionals, meta-GGA functionals, and hybrid meta-GGA functionals that demonstrate improved agreement in calculations on symmetry-adapted clusters. We demonstrate that meta-GGA functionals improve computed NMR parameters over those obtained by GGA functionals in all cases, and that hybrid functionals improve computed results over the respective pure DFT functional for all nuclides except 15N.

Thermodynamic properties of small aggregates of rare-gas atoms

NASA Technical Reports Server (NTRS)

Etters, R. D.; Kaelberer, J.

1975-01-01

The present work reports on the equilibrium thermodynamic properties of small clusters of xenon, krypton, and argon atoms, determined from a biased random-walk Monte Carlo procedure. Cluster sizes ranged from 3 to 13 atoms. Each cluster was found to have an abrupt liquid-gas phase transition at a temperature much less than for the bulk material. An abrupt solid-liquid transition is observed for thirteen- and eleven-particle clusters. For cluster sizes smaller than 11, a gradual transition from solid to liquid occurred over a fairly broad range of temperatures. Distribution of number of bond lengths as a function of bond length was calculated for several systems at various temperatures. The effects of box boundary conditions are discussed. Results show the importance of a correct description of boundary conditions. A surprising result is the slow rate at which system properties approach bulk behavior as cluster size is increased.

Clustering fossils in solid inflation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akhshik, Mohammad, E-mail: m.akhshik@ipm.ir

In solid inflation the single field non-Gaussianity consistency condition is violated. As a result, the long tenor perturbation induces observable clustering fossils in the form of quadrupole anisotropy in large scale structure power spectrum. In this work we revisit the bispectrum analysis for the scalar-scalar-scalar and tensor-scalar-scalar bispectrum for the general parameter space of solid. We consider the parameter space of the model in which the level of non-Gaussianity generated is consistent with the Planck constraints. Specializing to this allowed range of model parameter we calculate the quadrupole anisotropy induced from the long tensor perturbations on the power spectrum ofmore » the scalar perturbations. We argue that the imprints of clustering fossil from primordial gravitational waves on large scale structures can be detected from the future galaxy surveys.« less

Transport properties of dilute α -Fe (X ) solid solutions (X = C, N, O)

NASA Astrophysics Data System (ADS)

Schuler, Thomas; Nastar, Maylise

2016-06-01

We extend the self-consistent mean field (SCMF) method to the calculation of the Onsager matrix of Fe-based interstitial solid solutions. Both interstitial jumps and substitutional atom-vacancy exchanges are accounted for. A general procedure is introduced to split the Onsager matrix of a dilute solid solution into intrinsic cluster Onsager matrices, and extract from them flux-coupling ratios, mobilities, and association-dissociation rates for each cluster. The formalism is applied to vacancy-interstitial solute pairs in α -Fe (V X pairs, X = C, N, O), with ab initio based thermodynamic and kinetic parameters. Convergence of the cluster mobility contribution gives a controlled estimation of the cluster definition distance, taking into account both its thermodynamic and kinetic properties. Then, the flux-coupling behavior of each V X pair is discussed, and qualitative understanding is achieved from the comparison between various contributions to the Onsager matrix. Also, the effect of low-activation energy second-nearest-neighbor interstitial solute jumps around a vacancy on these results is addressed.

Dynamic Cluster Size Effects on the Glass Transition of Thin Films

NASA Astrophysics Data System (ADS)

Wool, Richard

2013-03-01

During cooling from the melt of amorphous materials, it has been shown experimentally that dynamic rigid clusters form in equilibrium with the liquid and their relaxation behavior determines the kinetic nature of Tg [Stanzione et al, J. Non Cryst Solids 357(2): 311-319 2011]. The fractal clusters of size R ~ 5-60 nm (polystyrene) have relaxation times τ ~ R1.8 (solid-to-liquid). They are analogous to sub critical size embryos during crystallization as the amorphous material tries to crystallize due to the strong intermolecular forces at T < Tm ; they are not related to density fluctuations or surface capillary waves. In free-standing thin films of thickness h, several important events occur: (a) The large clusters with R > h are excluded and the thin films have an average faster relaxation time compared to the bulk; consequently Tg decreases as h decreases. (b) The segmental dynamics at the 1 nm scale are largely not affected by nanoconfinement since Tg is determined only by the cluster dynamics with R >> 1 nm. (c) The mobile layer on the surface of free standing films is due to the presence of smaller clusters on the surface which will disappear with increasing rate of testing. (d) With adhesion to a solid substrate, the surface mobile layer disappears as the surface clusters size grow and the change in Tg is suppressed. (e) Physical aging is controlled by the relaxation of the rigid fractal clusters and in thin films, physical aging will occur more rapidly compared to the bulk. (f) The large effect of molecular weight M on Tg appears to be related to the effect on the cluster size distribution giving smaller clusters and faster relation times with increasing M. These results are in accord with the Twinkling Fractal theory of the glass transition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sehgal, Ray M.; Maroudas, Dimitrios, E-mail: maroudas@ecs.umass.edu, E-mail: ford@ecs.umass.edu; Ford, David M., E-mail: maroudas@ecs.umass.edu, E-mail: ford@ecs.umass.edu

We have developed a coarse-grained description of the phase behavior of the isolated 38-atom Lennard-Jones cluster (LJ{sub 38}). The model captures both the solid-solid polymorphic transitions at low temperatures and the complex cluster breakup and melting transitions at higher temperatures. For this coarse model development, we employ the manifold learning technique of diffusion mapping. The outcome of the diffusion mapping analysis over a broad temperature range indicates that two order parameters are sufficient to describe the cluster's phase behavior; we have chosen two such appropriate order parameters that are metrics of condensation and overall crystallinity. In this well-justified coarse-variable space,more » we calculate the cluster's free energy landscape (FEL) as a function of temperature, employing Monte Carlo umbrella sampling. These FELs are used to quantify the phase behavior and onsets of phase transitions of the LJ{sub 38} cluster.« less

α clustering with a hollow structure: Geometrical structure of α clusters from platonic solids to fullerene shape

NASA Astrophysics Data System (ADS)

Tohsaki, Akihiro; Itagaki, Naoyuki

2018-01-01

We study α -cluster structure based on the geometric configurations with a microscopic framework, which takes full account of the Pauli principle, and which also employs an effective internucleon force including finite-range three-body terms suitable for microscopic α -cluster models. Here, special attention is focused upon the α clustering with a hollow structure; all the α clusters are put on the surface of a sphere. All the platonic solids (five regular polyhedra) and the fullerene-shaped polyhedron coming from icosahedral structure are considered. Furthermore, two configurations with dual polyhedra, hexahedron-octahedron and dodecahedron-icosahedron, are also scrutinized. When approaching each other from large distances with these symmetries, α clusters create certain local energy pockets. As a consequence, we insist on the possible existence of α clustering with a geometric shape and hollow structure, which is favored from Coulomb energy point of view. Especially, two configurations, that is, dual polyhedra of dodecahedron-icosahedron and fullerene, have a prominent hollow structure compared with the other six configurations.

Solid-solid collapse transition in a two dimensional model molecular system.

PubMed

Singh, Rakesh S; Bagchi, Biman

2013-11-21

Solid-solid collapse transition in open framework structures is ubiquitous in nature. The real difficulty in understanding detailed microscopic aspects of such transitions in molecular systems arises from the interplay between different energy and length scales involved in molecular systems, often mediated through a solvent. In this work we employ Monte-Carlo simulation to study the collapse transition in a model molecular system interacting via both isotropic as well as anisotropic interactions having different length and energy scales. The model we use is known as Mercedes-Benz (MB), which, for a specific set of parameters, sustains two solid phases: honeycomb and oblique. In order to study the temperature induced collapse transition, we start with a metastable honeycomb solid and induce transition by increasing temperature. High density oblique solid so formed has two characteristic length scales corresponding to isotropic and anisotropic parts of interaction potential. Contrary to the common belief and classical nucleation theory, interestingly, we find linear strip-like nucleating clusters having significantly different order and average coordination number than the bulk stable phase. In the early stage of growth, the cluster grows as a linear strip, followed by branched and ring-like strips. The geometry of growing cluster is a consequence of the delicate balance between two types of interactions, which enables the dominance of stabilizing energy over destabilizing surface energy. The nucleus of stable oblique phase is wetted by intermediate order particles, which minimizes the surface free energy. In the case of pressure induced transition at low temperature the collapsed state is a disordered solid. The disordered solid phase has diverse local quasi-stable structures along with oblique-solid like domains.

Solid-solid collapse transition in a two dimensional model molecular system

NASA Astrophysics Data System (ADS)

Singh, Rakesh S.; Bagchi, Biman

2013-11-01

Solid-solid collapse transition in open framework structures is ubiquitous in nature. The real difficulty in understanding detailed microscopic aspects of such transitions in molecular systems arises from the interplay between different energy and length scales involved in molecular systems, often mediated through a solvent. In this work we employ Monte-Carlo simulation to study the collapse transition in a model molecular system interacting via both isotropic as well as anisotropic interactions having different length and energy scales. The model we use is known as Mercedes-Benz (MB), which, for a specific set of parameters, sustains two solid phases: honeycomb and oblique. In order to study the temperature induced collapse transition, we start with a metastable honeycomb solid and induce transition by increasing temperature. High density oblique solid so formed has two characteristic length scales corresponding to isotropic and anisotropic parts of interaction potential. Contrary to the common belief and classical nucleation theory, interestingly, we find linear strip-like nucleating clusters having significantly different order and average coordination number than the bulk stable phase. In the early stage of growth, the cluster grows as a linear strip, followed by branched and ring-like strips. The geometry of growing cluster is a consequence of the delicate balance between two types of interactions, which enables the dominance of stabilizing energy over destabilizing surface energy. The nucleus of stable oblique phase is wetted by intermediate order particles, which minimizes the surface free energy. In the case of pressure induced transition at low temperature the collapsed state is a disordered solid. The disordered solid phase has diverse local quasi-stable structures along with oblique-solid like domains.

Photoelectron Spectroscopy Study of [Ta2B6]-: a Hexagonal Bipyramdial Cluster

NASA Astrophysics Data System (ADS)

Jian, Tian; Li, Weili; Romanescu, Constantin; Wang, Lai-Sheng

2014-06-01

It has been a long-sought goal in cluster science to discover stable atomic clusters as building blocks for cluster-assembled nanomaterials, as exemplified by the fullerenes and their subsequent bulk syntheses.[1,2] Clusters have also been considered as models to understand bulk properties, providing a bridge between molecular and solid-state chemistry.[3] Herein we report a joint photoelectron spectroscopy and theoretical study on the [Ta2B6]- and [Ta2B6] clusters.[4] The photoelectron spectrum of [Ta2B6]- displays a simple spectral pattern and a large HOMO-LUMO gap, suggesting its high symmetry. Theoretical calculations show that both the neutral and anion are D6h pyramidal. The chemical bonding analyses for [Ta2B6] revealed the nature of the B6 and Ta interactions and uncovered strong covalent bonding between B6 and Ta. The D6h-[TaB6Ta] gaseous cluster is reminiscent of the structural pattern in the ReB6X6Re core in the [(Cp*Re)2B6H4Cl2] and the TiB6Ti motif in the newly synthesized Ti7Rh4Ir2B8 solid-state compound.[5,6] The current work provides an intrinsic link between a gaseous cluster and motifs for solid materials. Continued investigations of the transition-metal boron clusters may lead to the discovery of new structural motifs involving pure boron clusters for the design of novel boride materials. Reference [1] H.W. Kroto, J. R. Heath, S. C. OBrien, R. F. Curl, R. E. Smalley, Nature 1985, 318, 162 - 163. [2] W. Krtschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nature 1990, 347, 354 - 358. [3] T. P. Fehlner, J.-F. Halet, J.-Y. Saillard, Molecular Clusters: A Bridge to Solid-State Chemitry, Cambridge University Press, UK, 2007. [4] W. L. Li, L. Xie, T. Jian, C. Romanescu, X. Huang, L.-S. Wang, Angew. Chem. Int. Ed. 2014, 126, 1312 - 1316. [5] B. Le Guennic, H. Jiao, S. Kahlal, J.-Y. Saillard, J.-F. Halet, S. Ghosh, M. Shang, A. M. Beatty, A. L. Rheingold, T. P. Fehlner, J. Am. Chem. Soc. 2004, 126, 3203 - 3217. [6] B. P. T. Fokwa, M. Hermus, Angew. Chem. 2012, 124, 1734 - 1737; Angew. Chem. Int. Ed. 2012, 51, 1702 - 1705.

Short-range order in the Ca sub 1-x La sub x F sub 2+x solid solution: 1:0:3 or 1:0:4 clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laval, J.P.; Abaouz, A.; Frit, B.

1989-08-01

The defect structure of the Ca{sub 1-x}La{sub x}F{sub 2+x} solid solution (0 {le} x {le} 0.38) has been examined at room temperature by powder neutron diffraction. Two kinds of (xxx) interstitial anions, whose respective numbers increase linearly with increasing dopant cation concentration, have been found: one labeled F{sup 0} (x {approx} 0.41) is a true interstitial; the other labeled F{sup {prime}{double prime}} (x {approx} 0.31) can be considered a relaxed normal anion. Two 1:0:n defect clusters are compatible, within the experimental errors, with these results: the 1:0:3 (1V{sub F}, OF{prime}, 3F{sup {double prime}}, 2 La{sup 3+}) and the 1:0:4 (1V{submore » F}, OF{prime}, 4F{sup {double prime}}, 3La{sup 3+}) clusters. Charge balance considerations and comparisons with the homologous Ca{sub 1-x}M{sub x}{sup IV}F{sub 2+2x} solid solutions (M{sup IV} = Th, U) allow us to think that the less dense 1:0:3 cluster is present for the whole domain of both kinds of solid solutions.« less

Solid state, thermal synthesis of site-specific protein-boron cluster conjugates and their physicochemical and biochemical properties.

PubMed

Goszczyński, Tomasz M; Kowalski, Konrad; Leśnikowski, Zbigniew J; Boratyński, Janusz

2015-02-01

Boron clusters represent a vast family of boron-rich compounds with extraordinary properties that provide the opportunity of exploitation in different areas of chemistry and biology. In addition, boron clusters are clinically used in boron neutron capture therapy (BNCT) of tumors. In this paper, a novel, in solid state (solvent free), thermal method for protein modification with boron clusters has been proposed. The method is based on a cyclic ether ring opening in oxonium adduct of cyclic ether and a boron cluster with nucleophilic centers of the protein. Lysozyme was used as the model protein, and the physicochemical and biological properties of the obtained conjugates were characterized. The main residues of modification were identified as arginine-128 and threonine-51. No significant changes in the secondary or tertiary structures of the protein after tethering of the boron cluster were found using mass spectrometry and circular dichroism measurements. However, some changes in the intermolecular interactions and hydrodynamic and catalytic properties were observed. To the best of our knowledge, we have described the first example of an application of cyclic ether ring opening in the oxonium adducts of a boron cluster for protein modification. In addition, a distinctive feature of the proposed approach is performing the reaction in solid state and at elevated temperature. The proposed methodology provides a new route to protein modification with boron clusters and extends the range of innovative molecules available for biological and medical testing. Copyright © 2014 Elsevier B.V. All rights reserved.

Evidence that Clouds of keV Hydrogen Ion Clusters Bounce Elastically from a Solid Surface

NASA Technical Reports Server (NTRS)

Lewis, R. A.; Martin, James J.; Chakrabarti, Suman; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

The behavior of hydrogen ion clusters is tested by an inject/hold/extract technique in a Penning-Malmberg trap. The timing pattern of the extraction signals is consistent with the clusters bouncing elastically from a detector several times. The ion clusters behave more like an elastic fluid than a beam of ions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chezhina, N.V., E-mail: chezhina@nc2490.spb.edu; Korolev, D.A.; Zhuk, N.A.

On the basis of the results of magnetic susceptibility and ESR studies of the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions iron atoms in the solid solutions of cubic modification of bismuth niobate were found to exist as Fe(III) monomers and exchange bound Fe(III)-O-Fe(III) dimers with antiferro- and ferromagnetic type of superexchange. The exchange parameters and the distribution of monomers and dimers in the solid solutions were calculated as a function of paramagnetic atom content. - Graphical abstract: The study of the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions showed that the introduction of iron atoms into the structure ofmore » Bi{sub 3}NbO{sub 7} stabilizes the cubic structure of bismuth niobate making the phase transition tetragonal ↔ cubic structure irreversible. In the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions we observe the formation of dimers with antiferro- and ferromagnetic exchange. Such clusters are partially retained even at the infinite dilution of the solid solution, which testifies for their rigidity. A sufficiently high parameter of ferromagnetic exchange in a dimer (+53 cm{sup −1}) seems to result from iron atoms being located in the vicinity of oxygen vacancy. - Highlights: • The reversible transition cubic – tetragonal modifications in Bi{sub 3}NbO{sub 7} becomes irreversible. • Only cubic modification of Bi{sub 3}Nb{sub 1-x}Fe{sub x}O{sub 7-δ} is stable due to clusters of Fe atoms. • These clusters are sufficiently strong and retained even at the infinite dilution. • The calculations of magnetic susceptibility give the distribution of the clusters and single atoms.« less

Modeling of Cluster-Induced Turbulence in Particle-Laden Channel Flow

NASA Astrophysics Data System (ADS)

Baker, Michael; Capecelatro, Jesse; Kong, Bo; Fox, Rodney; Desjardins, Olivier

2017-11-01

A phenomenon often observed in gas-solid flows is the formation of mesoscale clusters of particles due to the relative motion between the solid and fluid phases that is sustained through the dampening of collisional particle motion from interphase momentum coupling inside these clusters. The formation of such sustained clusters, leading to cluster-induced turbulence (CIT), can have a significant impact in industrial processes, particularly in regards to mixing, reaction progress, and heat transfer. Both Euler-Lagrange (EL) and Euler-Euler anisotropic Gaussian (EE-AG) approaches are used in this work to perform mesoscale simulations of CIT in fully developed gas-particle channel flow. The results from these simulations are applied in the development of a two-phase Reynolds-Averaged Navier-Stokes (RANS) model to capture the wall-normal flow characteristics in a less computationally expensive manner. Parameters such as mass loading, particle size, and gas velocity are varied to examine their respective impact on cluster formation and turbulence statistics. Acknowledging support from the NSF (AN:1437865).

Dense flow around a sphere moving into a cloud of grains

NASA Astrophysics Data System (ADS)

Gondret, Philippe; Faure, Sylvain; Lefebvre-Lepot, Aline; Seguin, Antoine

2017-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone of about constant solid fraction builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size that increases with the initial solid fraction ϕ0 of the cloud. A detailed analysis of the local strain rate and local stress fields inside the cluster reveals that, despite different spatial variations of strain and stresses, the local friction coeffcient μ appears to depend only on the local inertial number I as well as the local solid fraction ϕ, which means that a local rheology does exist in the present non parallel flow. The key point is that the spatial variations of I inside the cluster does not depend on the sphere velocity and explore only a small range between about 10-2 and 10-1. The influence of sidewalls is then investigated on the flow and the forces.

Space shuttle with common fuel tank for liquid rocket booster and main engines (supertanker space shuttle)

NASA Technical Reports Server (NTRS)

Thorpe, Douglas G.

1991-01-01

An operation and schedule enhancement is shown that replaces the four-body cluster (Space Shuttle Orbiter (SSO), external tank, and two solid rocket boosters) with a simpler two-body cluster (SSO and liquid rocket booster/external tank). At staging velocity, the booster unit (liquid-fueled booster engines and vehicle support structure) is jettisoned while the remaining SSO and supertank continues on to orbit. The simpler two-bodied cluster reduces the processing and stack time until SSO mate from 57 days (for the solid rocket booster) to 20 days (for the liquid rocket booster). The areas in which liquid booster systems are superior to solid rocket boosters are discussed. Alternative and future generation vehicles are reviewed to reveal greater performance and operations enhancements with more modifications to the current methods of propulsion design philosophy, e.g., combined cycle engines, and concentric propellant tanks.

Characterization of the molecular distribution of drugs in glassy solid dispersions at the nano-meter scale, using differential scanning calorimetry and gravimetric water vapour sorption techniques.

PubMed

van Drooge, D J; Hinrichs, W L J; Visser, M R; Frijlink, H W

2006-03-09

The molecular distribution in fully amorphous solid dispersions consisting of poly(vinylpyrrolidone) (PVP)-diazepam and inulin-diazepam was studied. One glass transition temperature (T(g)), as determined by temperature modulated differential scanning calorimetry (TMDSC), was observed in PVP-diazepam solid dispersions prepared by fusion for all drug loads tested (10-80 wt.%). The T(g) of these solid dispersions gradually changed with composition and decreased from 177 degrees C for pure PVP to 46 degrees C for diazepam. These observations indicate that diazepam was dispersed in PVP on a molecular level. However, in PVP-diazepam solid dispersions prepared by freeze drying, two T(g)'s were observed for drug loads above 35 wt.% indicating phase separation. One T(g) indicated the presence of amorphous diazepam clusters, the other T(g) was attributed to a PVP-rich phase in which diazepam was dispersed on a molecular level. With both the value of the latter T(g) and the DeltaC(p) of the diazepam glass transition the concentrations of molecular dispersed diazepam could be calculated (27-35 wt.%). Both methods gave similar results. Water vapour sorption (DVS) experiments revealed that the PVP-matrix was hydrophobised by the incorporated diazepam. TMDSC and DVS results were used to estimate the size of diazepam clusters in freeze dried PVP-diazepam solid dispersions, which appeared to be in the nano-meter range. The inulin-diazepam solid dispersions prepared by spray freeze drying showed one T(g) for drug loads up to 35 wt.% indicating homogeneous distribution on a molecular level. However, this T(g) was independent of the drug load, which is unexpected because diazepam has a lower T(g) than inulin (46 and 155 degrees C, respectively). For higher drug loads, a T(g) of diazepam as well as a T(g) of the inulin-rich phase was observed, indicating the formation of amorphous diazepam clusters. From the DeltaC(p) of the diazepam glass transition the amount of molecularly dispersed diazepam was calculated (12-27 wt.%). In contrast to the PVP-diazepam solid dispersions, DVS-experiments revealed that inulin was not hydrophobised by diazepam. Consequently, the size of diazepam clusters could not be estimated. It was concluded that TMDSC enables characterization and quantification of the molecular distribution in amorphous solid dispersions. When the hygroscopicity of the carrier is reduced by the drug, DVS in combination with TMDSC can be used to estimate the size of amorphous drug clusters.

A platonic solid templating Archimedean solid: an unprecedented nanometre-sized Ag37 cluster

NASA Astrophysics Data System (ADS)

Li, Xiao-Yu; Su, Hai-Feng; Yu, Kai; Tan, Yuan-Zhi; Wang, Xing-Po; Zhao, Ya-Qin; Sun, Di; Zheng, Lan-Sun

2015-04-01

The spontaneous formation of discrete spherical nanosized molecules is prevalent in nature, but the authentic structural mimicry of such highly symmetric polyhedra from edge sharing of regular polygons has remained elusive. Here we present a novel ball-shaped {(HNEt3)[Ag37S4(SC6H4tBu)24(CF3COO)6(H2O)12]} cluster (1) that is assembled via a one-pot process from polymeric {(HNEt3)2[Ag10(SC6H4tBu)12]}n and CF3COOAg. Single crystal X-ray analysis confirmed that 1 is a Td symmetric spherical molecule with a [Ag36(SC6H4tBu)24] anion shell enwrapping a AgS4 tetrahedron. The shell topology of 1 belongs to one of 13 Archimedean solids, a truncated tetrahedron with four edge-shared hexagons and trigons, which are supported by a AgS4 Platonic solid in the core. Interestingly, the cluster emits green luminescence centered at 515 nm at room temperature. Our investigations have provided a promising synthetic protocol for a high-nuclearity silver cluster based on underlying geometrical principles.The spontaneous formation of discrete spherical nanosized molecules is prevalent in nature, but the authentic structural mimicry of such highly symmetric polyhedra from edge sharing of regular polygons has remained elusive. Here we present a novel ball-shaped {(HNEt3)[Ag37S4(SC6H4tBu)24(CF3COO)6(H2O)12]} cluster (1) that is assembled via a one-pot process from polymeric {(HNEt3)2[Ag10(SC6H4tBu)12]}n and CF3COOAg. Single crystal X-ray analysis confirmed that 1 is a Td symmetric spherical molecule with a [Ag36(SC6H4tBu)24] anion shell enwrapping a AgS4 tetrahedron. The shell topology of 1 belongs to one of 13 Archimedean solids, a truncated tetrahedron with four edge-shared hexagons and trigons, which are supported by a AgS4 Platonic solid in the core. Interestingly, the cluster emits green luminescence centered at 515 nm at room temperature. Our investigations have provided a promising synthetic protocol for a high-nuclearity silver cluster based on underlying geometrical principles. Electronic supplementary information (ESI) available: detailed synthesis procedure, tables, crystal data in CIF files, IR data, TGA results and powder X-ray diffractogram for 1. CCDC 1042228. See DOI: 10.1039/c5nr01222h

Experimental verification of the cluster model of CH3F-(ortho-H2)n in solid para-H2 by using mid-infrared pump-probe laser spectroscopy

NASA Astrophysics Data System (ADS)

Miyamoto, Yuki; Mizoguchi, Asao; Kanamori, Hideto

2017-03-01

The bleaching process in the C-F stretching mode (ν3 band) of CH3F-(ortho-H2)n [n = 0 and 1] clusters in solid para-H2 was monitored using pump and probe laser spectroscopy on the C-H stretching mode (ν1 and 2ν5 bands). From an analysis of the depleted spectral profiles, the transition frequency and linewidth of each cluster were directly determined. The results agree with the values previously derived from a deconvolution analysis of the broadened ν1/2ν5 spectrum observed by FTIR spectroscopy. The complementary increase and decrease between the n = 0 and 1 components were also verified through monitoring the ν1 and 2ν5 bands, which suggests a closed system among the CH3F-(ortho-H2)n clusters. These observations provide experimental verification of the CH3F-(ortho-H2)n cluster model. On the other hand, a trial to observe the bleaching process by pumping the C-H stretching mode was not successful. This result may be important for understanding the dynamics of vibrational relaxation processes in CH3F-(ortho-H2)n in solid para-H2.

Experimental verification of the cluster model of CH3F-(ortho-H2)n in solid para-H2 by using mid-infrared pump-probe laser spectroscopy.

PubMed

Miyamoto, Yuki; Mizoguchi, Asao; Kanamori, Hideto

2017-03-21

The bleaching process in the C-F stretching mode (ν 3 band) of CH 3 F-(ortho-H 2 ) n [n = 0 and 1] clusters in solid para-H 2 was monitored using pump and probe laser spectroscopy on the C-H stretching mode (ν 1 and 2ν 5 bands). From an analysis of the depleted spectral profiles, the transition frequency and linewidth of each cluster were directly determined. The results agree with the values previously derived from a deconvolution analysis of the broadened ν 1 /2ν 5 spectrum observed by FTIR spectroscopy. The complementary increase and decrease between the n = 0 and 1 components were also verified through monitoring the ν 1 and 2ν 5 bands, which suggests a closed system among the CH 3 F-(ortho-H 2 ) n clusters. These observations provide experimental verification of the CH 3 F-(ortho-H 2 ) n cluster model. On the other hand, a trial to observe the bleaching process by pumping the C-H stretching mode was not successful. This result may be important for understanding the dynamics of vibrational relaxation processes in CH 3 F-(ortho-H 2 ) n in solid para-H 2 .

Polymorphism of Lysozyme Condensates.

PubMed

Safari, Mohammad S; Byington, Michael C; Conrad, Jacinta C; Vekilov, Peter G

2017-10-05

Protein condensates play essential roles in physiological processes and pathological conditions. Recently discovered mesoscopic protein-rich clusters may act as crucial precursors for the nucleation of ordered protein solids, such as crystals, sickle hemoglobin polymers, and amyloid fibrils. These clusters challenge settled paradigms of protein condensation as the constituent protein molecules present features characteristic of both partially misfolded and native proteins. Here we employ the antimicrobial enzyme lysozyme and examine the similarities between mesoscopic clusters, amyloid structures, and disordered aggregates consisting of chemically modified protein. We show that the mesoscopic clusters are distinct from the other two classes of aggregates. Whereas cluster formation and amyloid oligomerization are both reversible, aggregation triggered by reduction of the intramolecular S-S bonds is permanent. In contrast to the amyloid structures, protein molecules in the clusters retain their enzymatic activity. Furthermore, an essential feature of the mesoscopic clusters is their constant radius of less than 50 nm. The amyloid and disordered aggregates are significantly larger and rapidly grow. These findings demonstrate that the clusters are a product of limited protein structural flexibility. In view of the role of the clusters in the nucleation of ordered protein solids, our results suggest that fine-tuning the degree of protein conformational stability is a powerful tool to control and direct the pathways of protein condensation.

Synthesis of Densely Packaged, Ultrasmall Pt02 Clusters within a Thioether-Functionalized MOF: Catalytic Activity in Industrial Reactions at Low Temperature.

PubMed

Mon, Marta; Rivero-Crespo, Miguel A; Ferrando-Soria, Jesús; Vidal-Moya, Alejandro; Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino; Hernández-Garrido, Juan C; López-Haro, Miguel; Calvino, José J; Ragazzon, Giulio; Credi, Alberto; Armentano, Donatella; Pardo, Emilio

2018-05-22

The gram-scale synthesis, stabilization, and characterization of well-defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X-ray snapshots of Pt 0 2 clusters, homogenously distributed and densely packaged within the channels of a metal-organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO 2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less-dangerous industrial reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A unifying model for adsorption and nucleation of vapors on solid surfaces.

PubMed

Laaksonen, Ari

2015-04-23

Vapor interaction with solid surfaces is traditionally described with adsorption isotherms in the undersaturated regime and with heterogeneous nucleation theory in the supersaturated regime. A class of adsorption isotherms is based on the idea of vapor molecule clustering around so-called active sites. However, as the isotherms do not account for the surface curvature effects of the clusters, they predict an infinitely thick adsorption layer at saturation and do not recognize the existence of the supersaturated regime. The classical heterogeneous nucleation theory also builds on the idea of cluster formation, but describes the interactions between the surface and the cluster with a single parameter, the contact angle, which provides limited information compared with adsorption isotherms. Here, a new model of vapor adsorption on nonporous solid surfaces is derived. The basic assumption is that adsorption proceeds via formation of molecular clusters, modeled as liquid caps. The equilibrium of the individual clusters with the vapor phase is described with the Frenkel-Halsey-Hill (FHH) adsorption theory modified with the Kelvin equation that corrects for the curvature effect on vapor pressure. The new model extends the FHH adsorption isotherm to be applicable both at submonolayer surface coverages and at supersaturated conditions. It shows good agreement with experimental adsorption data from 12 different adsorbent-adsorbate systems. The model predictions are also compared against heterogeneous nucleation data, and they show much better agreement than predictions of the classical heterogeneous nucleation theory.

Multi-scale study of condensation in water jets using ellipsoidal-statistical Bhatnagar-Gross-Krook and molecular dynamics modeling

NASA Astrophysics Data System (ADS)

Li, Zheng; Borner, Arnaud; Levin, Deborah A.

2014-06-01

Homogeneous water condensation and ice formation in supersonic expansions to vacuum for stagnation pressures from 12 to 1000 mbar are studied using the particle-based Ellipsoidal-Statistical Bhatnagar-Gross-Krook (ES-BGK) method. We find that when condensation starts to occur, at a stagnation pressure of 96 mbar, the increase in the degree of condensation causes an increase in the rotational temperature due to the latent heat of vaporization. The simulated rotational temperature profiles along the plume expansion agree well with measurements confirming the kinetic homogeneous condensation models and the method of simulation. Comparisons of the simulated gas and cluster number densities, cluster size for different stagnation pressures along the plume centerline were made and it is found that the cluster size increase linearly with respect to stagnation pressure, consistent with classical nucleation theory. The sensitivity of our results to cluster nucleation model and latent heat values based on bulk water, specific cluster size, or bulk ice are examined. In particular, the ES-BGK simulations are found to be too coarse-grained to provide information on the phase or structure of the clusters formed. For this reason, molecular dynamics simulations of water condensation in a one-dimensional free expansion to simulate the conditions in the core of a plume are performed. We find that the internal structure of the clusters formed depends on the stagnation temperature. A larger cluster of average size 21 was tracked down the expansion, and a calculation of its average internal temperature as well as a comparison of its radial distribution functions (RDFs) with values measured for solid amorphous ice clusters lead us to conclude that this cluster is in a solid-like rather than liquid form. In another molecular-dynamics simulation at a much lower stagnation temperature, a larger cluster of size 324 and internal temperature 200 K was extracted from an expansion plume and equilibrated to determine its RDF and self-diffusion coefficient. The value of the latter shows that this cluster is formed in a supercooled liquid state rather than in an amorphous solid state.

Characterization of Acousto-Electric Cluster and Array Levitation and its Application to Evaporation

NASA Technical Reports Server (NTRS)

Robert E. Apfel; Zheng, Yibing

2000-01-01

An acousto-electric levitator has been developed to study the behavior of liquid drop and solid particle clusters and arrays. Unlike an ordinary acoustic levitator that uses only a standing acoustic wave to levitate a single drop or particle, this device uses an extra electric static field and the acoustic field simultaneously to generate and levitate charged drops in two-dimensional arrays in air without any contact to a solid surface. This cluster and array generation (CAG) instrument enables us to steadily position drops and arrays to study the behavior of multiple drop and particle systems such as spray and aerosol systems relevant to the energy, environmental, and material sciences.

Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

DOEpatents

Alivisatos, A. Paul; Colvin, Vicki L.

1998-01-01

Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed.

Spherical cluster ensembles with fractal structure in LaSrMnO: New form of self-organization in solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okunev, V. D.; Samoilenko, Z. A.; Burkhovetski, V. V.

The growth of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films in magnetron plasma, in special conditions, leads to the appearance of ensembles of micron-sized spherical crystalline clusters with fractal structure, which we consider to be a new form of self-organization in solids. Each ensemble contains 10{sup 5}-10{sup 6} elementary clusters, 100-250 A in diameter. Interaction of the clusters in the ensemble is realized through the interatomic chemical bonds, intrinsic to the manganites. Integration of peripheral areas of interacting clusters results in the formation of common intercluster medium in the ensemble. We argue that the ensembles with fractal structure built into paramagnetic disorderedmore » matrix have ferromagnetic properties. Absence of sharp borders between elementary clusters and the presence of common intercluster medium inside each ensemble permits to rearrange magnetic order and to change the volume of the ferromagnetic phase, providing automatically a high sensitivity of the material to the external field.« less

Paramagnetic Attraction of Impurity-Helium Solids

NASA Technical Reports Server (NTRS)

Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

2003-01-01

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

Localized Ambient Solidity Separation Algorithm Based Computer User Segmentation.

PubMed

Sun, Xiao; Zhang, Tongda; Chai, Yueting; Liu, Yi

2015-01-01

Most of popular clustering methods typically have some strong assumptions of the dataset. For example, the k-means implicitly assumes that all clusters come from spherical Gaussian distributions which have different means but the same covariance. However, when dealing with datasets that have diverse distribution shapes or high dimensionality, these assumptions might not be valid anymore. In order to overcome this weakness, we proposed a new clustering algorithm named localized ambient solidity separation (LASS) algorithm, using a new isolation criterion called centroid distance. Compared with other density based isolation criteria, our proposed centroid distance isolation criterion addresses the problem caused by high dimensionality and varying density. The experiment on a designed two-dimensional benchmark dataset shows that our proposed LASS algorithm not only inherits the advantage of the original dissimilarity increments clustering method to separate naturally isolated clusters but also can identify the clusters which are adjacent, overlapping, and under background noise. Finally, we compared our LASS algorithm with the dissimilarity increments clustering method on a massive computer user dataset with over two million records that contains demographic and behaviors information. The results show that LASS algorithm works extremely well on this computer user dataset and can gain more knowledge from it.

Localized Ambient Solidity Separation Algorithm Based Computer User Segmentation

PubMed Central

Sun, Xiao; Zhang, Tongda; Chai, Yueting; Liu, Yi

2015-01-01

Most of popular clustering methods typically have some strong assumptions of the dataset. For example, the k-means implicitly assumes that all clusters come from spherical Gaussian distributions which have different means but the same covariance. However, when dealing with datasets that have diverse distribution shapes or high dimensionality, these assumptions might not be valid anymore. In order to overcome this weakness, we proposed a new clustering algorithm named localized ambient solidity separation (LASS) algorithm, using a new isolation criterion called centroid distance. Compared with other density based isolation criteria, our proposed centroid distance isolation criterion addresses the problem caused by high dimensionality and varying density. The experiment on a designed two-dimensional benchmark dataset shows that our proposed LASS algorithm not only inherits the advantage of the original dissimilarity increments clustering method to separate naturally isolated clusters but also can identify the clusters which are adjacent, overlapping, and under background noise. Finally, we compared our LASS algorithm with the dissimilarity increments clustering method on a massive computer user dataset with over two million records that contains demographic and behaviors information. The results show that LASS algorithm works extremely well on this computer user dataset and can gain more knowledge from it. PMID:26221133

Beyond the Young-Laplace model for cluster growth during dewetting of thin films: effective coarsening exponents and the role of long range dewetting interactions.

PubMed

Constantinescu, Adi; Golubović, Leonardo; Levandovsky, Artem

2013-09-01

Long range dewetting forces acting across thin films, such as the fundamental van der Waals interactions, may drive the formation of large clusters (tall multilayer islands) and pits, observed in thin films of diverse materials such as polymers, liquid crystals, and metals. In this study we further develop the methodology of the nonequilibrium statistical mechanics of thin films coarsening within continuum interface dynamics model incorporating long range dewetting interactions. The theoretical test bench model considered here is a generalization of the classical Mullins model for the dynamics of solid film surfaces. By analytic arguments and simulations of the model, we study the coarsening growth laws of clusters formed in thin films due to the dewetting interactions. The ultimate cluster growth scaling laws at long times are strongly universal: Short and long range dewetting interactions yield the same coarsening exponents. However, long range dewetting interactions, such as the van der Waals forces, introduce a distinct long lasting early time scaling behavior characterized by a slow growth of the cluster height/lateral size aspect ratio (i.e., a time-dependent Young angle) and by effective coarsening exponents that depend on cluster size. In this study, we develop a theory capable of analytically calculating these effective size-dependent coarsening exponents characterizing the cluster growth in the early time regime. Such a pronounced early time scaling behavior has been indeed seen in experiments; however, its physical origin has remained elusive to this date. Our theory attributes these observed phenomena to ubiquitous long range dewetting interactions acting across thin solid and liquid films. Our results are also applicable to cluster growth in initially very thin fluid films, formed by depositing a few monolayers or by a submonolayer deposition. Under this condition, the dominant coarsening mechanism is diffusive intercluster mass transport while the cluster coalescence plays a minor role, both in solid and in fluid films.

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds.

PubMed

Perić, Berislav; Gautier, Régis; Pickard, Chris J; Bosiočić, Marko; Grbić, Mihael S; Požek, Miroslav

2014-01-01

Two hexanuclear niobium halide cluster compounds with a [Nb6X12](2+) (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable Bo field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of (95)Mo nuclei in structurally related compounds containing [Mo6Br8](4+) cluster cores. Experimentally determined δiso((93)Nb) values are in the range from 2,400 to 3,000 ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (Vzz and δ33) coinciding with the molecular four-fold axis of the [Nb6X12](2+) unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (Vzz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (Vyy) and the largest CS principal axis (δ11) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by (79/81)Br NQR and (35)Cl solid-state NMR measurements. Copyright © 2014 Elsevier Inc. All rights reserved.

Charging and hybridization in the finite cluster model

NASA Technical Reports Server (NTRS)

Bauschlicher, C. W., Jr.; Bagus, P. S.; Nelin, C. J.

1984-01-01

Cluster wavefunctions which have appropriate hybridization and polarization lead to reasonable properties for the interaction of an adsorbate with a solid surface. However, for Al clusters, it was found that the atomic change distribution is not uniform. The finite cluster size leads to changes not representative for an extended system. This effect appears to be dependent on the particular materials being studied; it does not occur in all cases.

Infrared spectroscopy of solid normal hydrogen doped with CH3F and O2 at 4.2 K: CH3F:O2 complex and CH3F migration

NASA Astrophysics Data System (ADS)

Abouaf-Marguin, L.; Vasserot, A.-M.

2011-04-01

Double doping of solid normal hydrogen with CH3F and O2 at about 4.2 K gives evidence of (ortho-H2)n:CH3F clusters and of O2:CH3F complex formation. FTIR analysis of the time evolution of the spectra in the region of the v3 C-F stretching mode indicates that these clusters behave very differently from (ortho-H2)n:H2O clusters. The main point is the observed migration of CH3F molecules in solid para-H2 at 4.2 K which differs from that of H2O under identical experimental conditions. This is confirmed by an increase over time of the integrated intensity of the CH3F:O2 complex with a rate constant K = 2.7(2) . 10-4 s-1.

Nanothermodynamics of iron clusters: Small clusters, icosahedral and fcc-cuboctahedral structures

NASA Astrophysics Data System (ADS)

Angelié, C.; Soudan, J.-M.

2017-05-01

The study of the thermodynamics and structures of iron clusters has been carried on, focusing on small clusters and initial icosahedral and fcc-cuboctahedral structures. Two combined tools are used. First, energy intervals are explored by the Monte Carlo algorithm, called σ-mapping, detailed in the work of Soudan et al. [J. Chem. Phys. 135, 144109 (2011), Paper I]. In its flat histogram version, it provides the classical density of states, gp(Ep), in terms of the potential energy of the system. Second, the iron system is described by a potential which is called "corrected EAM" (cEAM), explained in the work of Basire et al. [J. Chem. Phys. 141, 104304 (2014), Paper II]. Small clusters from 3 to 12 atoms in their ground state have been compared first with published Density Functional Theory (DFT) calculations, giving a complete agreement of geometries. The series of 13, 55, 147, and 309 atom icosahedrons is shown to be the most stable form for the cEAM potential. However, the 147 atom cluster has a special behaviour, since decreasing the energy from the liquid zone leads to the irreversible trapping of the cluster in a reproducible amorphous state, 7.38 eV higher in energy than the icosahedron. This behaviour is not observed at the higher size of 309 atoms. The heat capacity of the 55, 147, and 309 atom clusters revealed a pronounced peak in the solid zone, related to a solid-solid transition, prior to the melting peak. The corresponding series of 13, 55, and 147 atom cuboctahedrons has been compared, underscoring the unstability towards the icosahedral structure. This unstability occurs clearly in several steps for the 147 atom cluster, with a sudden transformation at a transition state. This illustrates the concerted icosahedron-cuboctahedron transformation of Buckminster Fuller-Mackay, which is calculated for the cEAM potential. Two other clusters of initial fcc structures with 24 and 38 atoms have been studied, as well as a 302 atom cluster. Each one relaxes towards a more stable structure without regularity. The 38 atom cluster exhibits a nearly glassy relaxation, through a cascade of six metastable states of long life. This behaviour, as that of the 147 atom cluster towards the amorphous state, shows that difficulties to reach ergodicity in the lower half of the solid zone are related to particular features of the potential energy landscape, and not necessarily to a too large size of the system. Comparisons of the cEAM iron system with published results about Lennard-Jones systems and DFT calculations are made. The results of the previous clusters have been combined with that of Paper II to plot the cohesive energy Ec and the melting temperature Tm in terms of the cluster atom number Nat. The Nat -1 /3 linear dependence of the melting temperature (Pawlow law) is observed again for Nat > 150. In contrast, for Nat < 150, the curve diverges strongly from the Pawlow law, giving it an overall V-shape, with a linear increase of Tm when Nat goes from 55 to 13 atoms. Surprisingly, the 38 atom cluster is anomalously below the overall curve.

Tunability of the circadian action of tetrachromatic solid-state light sources

NASA Astrophysics Data System (ADS)

Žukauskas, A.; Vaicekauskas, R.

2015-01-01

An approach to the optimization of the spectral power distribution of solid-state light sources with the tunable non-image forming photobiological effect on the human circadian rhythm is proposed. For tetrachromatic clusters of model narrow-band (direct-emission) light-emitting diodes (LEDs), the limiting tunability of the circadian action factor (CAF), which is the ratio of the circadian efficacy to luminous efficacy of radiation, was established as a function of constraining color fidelity and luminous efficacy of radiation. For constant correlated color temperatures (CCTs), the CAF of the LED clusters can be tuned above and below that of the corresponding blackbody radiators, whereas for variable CCT, the clusters can have circadian tunability covering that of a temperature-tunable blackbody radiator.

Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers

DOEpatents

Alivisatos, A.P.; Colvin, V.L.

1998-05-12

Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed. 10 figs.

Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants.

PubMed

Takagiwa, Yoshiki; Kimura, Kaoru

2014-08-01

In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al 12 Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit ( ZT ) by optimizing the bond strengths of intra- and inter-icosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT , materials should form a real gap to obtain a higher Seebeck coefficient.

Effect of Arsenic on the Formation and Adsorption Property of Ferric Hydroxide Precipitates in ZVI Treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Xing; Xi, Beidou; Zhao, Ying

Treatment of arsenic by zerovalent iron (ZVI) has been studied extensively. However, the effect of arsenic on the formation of ferric hydroxide precipitates in the ZVI treatment has not been investigated. We discovered that the specific surface area (ca. 187 m2/g) and arsenic content (ca. 67 mg/g) of the suspended solids (As-containing solids) generated in the ZVI treatment of arsenic solutions were much higher than the specific surface area (ca. 37 m2/g) and adsorption capacity (ca.12 mg/g) of the suspended solids (As-free solids) generated in the arsenic-free solutions. Arsenic in the As-containing solids was much more stable than the adsorbedmore » arsenic in As-free solids. XRD, SEM, TEM, and selected area electron diffraction (SAED) analyses showed that the As-containing solids consisted of amorphous nanoparticles, while the As-free solids were composed of micron particles with weak crystallinity. Extended X-ray absorption fine structure (EXAFS) analysis determined that As(V) was adsorbed on the As-containing suspended solids and magnetic solid surfaces through bidentate binuclear complexation; and As(V) formed a mononuclear complex on the As-free suspended solids. The formation of the surface As(V) complexes retarded the bonding of free FeO6 octahedra to the oxygen sites on FeO6 octahedral clusters and prevented the growth of the clusters and their development into 3-dimensional crystalline phases.« less

Cluster size resolving analysis of CH3F-(ortho-H2)n in solid para-hydrogen using FTIR absorption spectroscopy at 3 μm region.

PubMed

Miyamoto, Yuki; Momose, Takamasa; Kanamori, Hideto

2012-11-21

Infrared absorption spectra of methyl fluoride with ortho-hydrogen (ortho-H(2)) clusters in a solid para-hydrogen (para-H(2)) crystal at 3.6 K were studied in the C-H stretching fundamental region (~3000 cm(-1)) using an FTIR spectrometer. As shown previously, the ν(3) C-F stretching fundamental band of CH(3)F-(ortho-H(2))(n) (n = 0, 1, 2, ...) clusters at 1040 cm(-1) shows a series of n discrete absorption lines, which correspond to different-sized clusters. We observed three unresolved broad peaks in the C-H stretching region and applied this cluster model to them assuming the same intensity distribution function as the ν(3) band. A fitting analysis successfully gave us the linewidth and lineshift of the components in each vibrational band. It was found that the separately determined linewidth, matrix shift of the band origin, and cluster shift are dependent on the vibrational mode. From the transition intensities of the monomer component derived from the fitting analysis, we discuss the mixing ratio of the vibrational modes due to Fermi resonance.

Lack of Dependence of the Sizes of the Mesoscopic Protein Clusters on Electrostatics.

PubMed

Vorontsova, Maria A; Chan, Ho Yin; Lubchenko, Vassiliy; Vekilov, Peter G

2015-11-03

Protein-rich clusters of steady submicron size and narrow size distribution exist in protein solutions in apparent violation of the classical laws of phase equilibrium. Even though they contain a minor fraction of the total protein, evidence suggests that they may serve as essential precursors for the nucleation of ordered solids such as crystals, sickle-cell hemoglobin polymers, and amyloid fibrils. The cluster formation mechanism remains elusive. We use the highly basic protein lysozyme at nearly neutral and lower pH as a model and explore the response of the cluster population to the electrostatic forces, which govern numerous biophysical phenomena, including crystallization and fibrillization. We tune the strength of intermolecular electrostatic forces by varying the solution ionic strength I and pH and find that despite the weaker repulsion at higher I and pH, the cluster size remains constant. Cluster responses to the presence of urea and ethanol demonstrate that cluster formation is controlled by hydrophobic interactions between the peptide backbones, exposed to the solvent after partial protein unfolding that may lead to transient protein oligomers. These findings reveal that the mechanism of the mesoscopic clusters is fundamentally different from those underlying the two main classes of ordered protein solid phases, crystals and amyloid fibrils, and partial unfolding of the protein chain may play a significant role. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Clustering and flow around a sphere moving into a grain cloud.

PubMed

Seguin, A; Lefebvre-Lepot, A; Faure, S; Gondret, P

2016-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.

Structural study of CH4, CO2 and H2O clusters containing from several tens to several thousands of molecules

NASA Astrophysics Data System (ADS)

Torchet, G.; Farges, J.; de Feraudy, M. F.; Raoult, B.

Clusters are produced during the free jet expansion of gaseous CH4, CO2 or H2O. For a given stagnation temperature To, the mean cluster size is easily increased by increasing the stagnation pressure p0. On the other hand, the cluster temperature does not depend on stagnation conditions but mainly on properties of the condensed gas. An electron diffraction analysis provides information about the cluster structure. Depending on whether the diffraction patterns exhibit crystalline lines or not, the structure is worked out either by using crystallographic methods or by constructing cluster models. When they contain more than a few thousand molecules, clusters show a crystalline structure identical to that of one phase, namely, the cubic phase, known in bulk solid: plastic phase (CH4), unique solid phase (CO2) or metastable cubic phase (H2O). When decreasing the cluster size, the studied compounds behave quite differently: CO2 clusters keep the same crystalline structure, CH4 clusters show the multilayer icosahedral structure wich has been found in rare gas clusters, and H2O clusters adopt a disordered structure different from the amorphous structures of bulk ice. Des agrégats sont produits au cours de la détente en jet libre des gaz CH4, CO2 ou H2O. Pour une température initiale donnée To, on accroît facilement la taille moyenne des agrégats en augmentant la pression initiale po . Par contre, la température des agrégats dépend principalement des propriétés du gaz condensé. Une analyse par diffraction électronique permet l'étude de la structure des agrégats. Selon que les diagrammes de diffraction contiennent ou non des raies cristallines, on a recours soit à des méthodes cristallographiques soit à la construction de modèles d'agrégats. Lorsqu'ils renferment plus de quelques milliers de molécules, les agrégats adoptent la structure cristalline de l'une des phases connues du solide massif et plus précisément la phase cubique : phase plastique pour CH4, phase solide unique pour CO2 ou phase cubique métastable pour H2O. Lorsque la taille des agrégats décroît, leurs comportements se révèlent très différents selon les molécules étudiées : les agrégats de CO2 conservent la même structure cristalline, les agrégats de CH4 adoptent la structure icosaédrique multicouche trouvée pour les agrégats de gaz rares, et les agrégats de glace adoptent une structure désordonnée différente des structures amorphes de la glace massive.

Solid State Digital Propulsion "Cluster Thrusters" For Small Satellites Using High Performance Electrically Controlled Extinguishable Solid Propellants (ECESP)

NASA Technical Reports Server (NTRS)

Sawka, Wayne N.; Katzakian, Arthur; Grix, Charles

2005-01-01

Electrically controlled extinguishable solid propellants (ESCSP) are capable of multiple ignitions, extinguishments and throttle control by the application of electrical power. Both core and end burning no moving parts ECESP grains/motors to three inches in diameter have now been tested. Ongoing research has led to a newer family of even higher performance ECESP providing up to 10% higher performance, manufacturing ease, and significantly higher electrical conduction. The high conductivity was not found to be desirable for larger motors; however it is ideal for downward scaling to micro and pico- propulsion applications with a web thickness of less than 0.125 inch/ diameter. As a solid solution propellant, this ECESP is molecularly uniform, having no granular structure. Because of this homogeneity and workable viscosity it can be directly cast into thin layers or vacuum cast into complex geometries. Both coaxial and grain stacks have been demonstrated. Combining individual propellant coaxial grains and/or grain stacks together form three-dimensional arrays yield modular cluster thrusters. Adoption of fabless manufacturing methods and standards from the electronics industry will provide custom, highly reproducible micro-propulsion arrays and clusters at low costs. These stack and cluster thruster designs provide a small footprint saving spacecraft surface area for solar panels and/or experiments. The simplicity of these thrusters will enable their broad use on micro-pico satellites for primary propulsion, ACS and formation flying applications. Larger spacecraft may find uses for ECESP thrusters on extended booms, on-orbit refueling, pneumatic actuators, and gas generators.

Chemistry and Physics of Solid Surfaces 5

DTIC Science & Technology

1984-04-01

associated with dimers and trimers, Type 2 particles form large clusters of 2000-5000 A size in aqueous solution. Luminescence studies carried out with...and rates of energy transfer, real time measurements using ultrashort laser pulses hold great promise. With the possible exception of the stimulated...the dynamic prop- erties of such clusters . The clusters are not stationary entities as origi- nally envisioned. Instead even fairly large aggregates

A new family of Ln₇ clusters with an ideal D(3h) metal-centered trigonal prismatic geometry, and SMM and photoluminescence behaviors.

PubMed

Mazarakioti, Eleni C; Poole, Katye M; Cunha-Silva, Luis; Christou, George; Stamatatos, Theocharis C

2014-08-14

The first use of the flexible Schiff base ligand N-salicylidene-2-aminocyclohexanol in metal cluster chemistry has afforded a new family of Ln7 clusters with ideal D(3h) point group symmetry and metal-centered trigonal prismatic topology; solid-state and solution studies revealed SMM and photoluminescence behaviors.

Space-filling, multifractal, localized thermal spikes in Si, Ge and ZnO

NASA Astrophysics Data System (ADS)

Ahmad, Shoaib; Abbas, Muhammad Sabtain; Yousuf, Muhammad; Javeed, Sumera; Zeeshan, Sumaira; Yaqub, Kashif

2018-04-01

The mechanism responsible for the emission of clusters from heavy ion irradiated solids is proposed to be thermal spikes. Collision cascade-based theories describe atomic sputtering but cannot explain the consistently observed experimental evidence for significant cluster emission. Statistical thermodynamic arguments for thermal spikes are employed here for qualitative and quantitative estimation of the thermal spike-induced cluster emission from Si, Ge and ZnO. The evolving cascades and spikes in elemental and molecular semiconducting solids are shown to have fractal characteristics. Power law potential is used to calculate the fractal dimension. With the loss of recoiling particles' energy the successive branching ratios get smaller. The fractal dimension is shown to be dependent upon the exponent of the power law interatomic potential D = 1/2m. Each irradiating ion has the probability of initiating a space-filling, multifractal thermal spike that may sublime a localized region near the surface by emitting clusters in relative ratios that depend upon the energies of formation of respective surface vacancies.

Abundance gradients in cooling flow clusters: Ginga Large Area Counters and Einstein Solid State Spectrometer spectra of A496, A1795, A2142, and A2199

NASA Technical Reports Server (NTRS)

White, Raymond E., III; Day, C. S. R.; Hatsukade, Isamu; Hughes, John P.

1994-01-01

We analyze the Ginga Large Area Counters (LAC) and Einstein Solid State Spectrometer (SSS) spectra of four cooling flow clusters, A496, A1795, A2142, and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high-energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four clusters, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model dependence in the amount of cold, X-ray-absorbing matter discovered in these clusters by White et al.

Structural properties and glass transition in Aln clusters

NASA Astrophysics Data System (ADS)

Sun, D. Y.; Gong, X. G.

1998-02-01

We have studied the structural and dynamical properties of several Aln clusters by the molecular-dynamics method combined with simulated annealing. The well-fitted glue potential is used to describe the interatomic interaction. The obtained atomic structures for n=13, 55, and 147 are in agreement with results from ab initio calculations. Our results have demonstrated that the disordered cluster Al43 can be considered as a glass cluster. The obtained thermal properties of glass cluster Al43 are clearly different from the results for high-symmetry clusters, its melting behavior has properties similar to those of a glass solid. The present studies also show that the surface melting behavior does not exist in the studied Aln clusters.

Analysis of 3D vortex motion in a dusty plasma

NASA Astrophysics Data System (ADS)

Mulsow, M.; Himpel, M.; Melzer, A.

2017-12-01

Dust clusters of about 50-1000 particles have been confined near the sheath region of a gaseous radio-frequency plasma discharge. These compact clusters exhibit a vortex motion which has been reconstructed in full three dimensions from stereoscopy. Smaller clusters are found to show a competition between solid-like cluster structure and vortex motion, whereas larger clusters feature very pronounced vortices. From the three-dimensional analysis, the dust flow field has been found to be nearly incompressible. The vortices in all observed clusters are essentially poloidal. The dependence of the vorticity on the cluster size is discussed. Finally, the vortex motion has been quantitatively attributed to radial gradients of the ion drag force.

Molecular Clusters: Nanoscale Building Blocks for Solid-State Materials.

PubMed

Pinkard, Andrew; Champsaur, Anouck M; Roy, Xavier

2018-04-17

The programmed assembly of nanoscale building blocks into multicomponent hierarchical structures is a powerful strategy for the bottom-up construction of functional materials. To develop this concept, our team has explored the use of molecular clusters as superatomic building blocks to fabricate new classes of materials. The library of molecular clusters is rich with exciting properties, including diverse functionalization, redox activity, and magnetic ordering, so the resulting cluster-assembled solids, which we term superatomic crystals (SACs), hold the promise of high tunability, atomic precision, and robust architectures among a diverse range of other material properties. Molecular clusters have only seldom been used as precursors for functional materials. Our team has been at the forefront of new developments in this exciting research area, and this Account focuses on our progress toward designing materials from cluster-based precursors. In particular, this Account discusses (1) the design and synthesis of molecular cluster superatomic building blocks, (2) their self-assembly into SACs, and (3) their resulting collective properties. The set of molecular clusters discussed herein is diverse, with different cluster cores and ligand arrangements to create an impressive array of solids. The cluster cores include octahedral M 6 E 8 and cubane M 4 E 4 (M = metal; E = chalcogen), which are typically passivated by a shell of supporting ligands, a feature upon which we have expanded upon by designing and synthesizing more exotic ligands that can be used to direct solid-state assembly. Building from this library, we have designed whole families of binary SACs where the building blocks are held together through electrostatic, covalent, or van der Waals interactions. Using single-crystal X-ray diffraction (SCXRD) to determine the atomic structure, a remarkable range of compositional variability is accessible. We can also use this technique, in tandem with vibrational spectroscopy, to ascertain features about the constituent superatomic building blocks, such as the charge of the cluster cores, by analysis of bond distances from the SCXRD data. The combination of atomic precision and intercluster interactions in these SACs produces novel collective properties, including tunable electrical transport, crystalline thermal conductivity, and ferromagnetism. In addition, we have developed a synthetic strategy to insert redox-active guests into the superstructure of SACs via single-crystal-to-single-crystal intercalation. This intercalation process allows us to tune the optical and electrical transport properties of the superatomic crystal host. These properties are explored using a host of techniques, including Raman spectroscopy, SQUID magnetometry, electrical transport measurements, electronic absorption spectroscopy, differential scanning calorimetry, and frequency-domain thermoreflectance. Superatomic crystals have proven to be both robust and tunable, representing a new method of materials design and architecture. This Account demonstrates how precisely controlling the structure and properties of nanoscale building blocks is key in developing the next generation of functional materials; several examples are discussed and detailed herein.

A Novel Acousto-Electric Levitator for Studies of Drop and Particle Clusters and Arrays

NASA Technical Reports Server (NTRS)

Tian, Yuren; Apfel, Robert E.; Zheng, Yibing

1999-01-01

A novel and compact instrumentation for studying the behavior of drop sprays and of clusters of drops now permits fundamental research into the behavior of reacting and non-reacting fluid and solid species. The new capability is made possible by simultaneous acousto-electric levitation and charging of "seed" droplets (10-30 microns in diameter) which come together in 2-D clusters (with up to 300 droplets). These clusters are interesting in their own right because of their crystalline and quasi-crystalline forms, which depend on the acoustic and electric field parameters. By varying the electric and acoustic field intensities, one can cause a cluster of droplets to condense into larger drops (e.g. 50-300 microns) which, because of their charge, form uniformly spaced 2-D arrays of monodispersed drops (e.g. 30-40 array drops in preliminary experiments). One or more layers of these 2-D arrays can form in the acoustic standing wave. Such a configuration permits a wide range of fundamental studies of drop evaporation, combustion, and nucleation. The drops can be single or multicomponent. Therefore, fundamental materials studies can also be performed. Using this same Cluster and Array Generation (CAG) instrumentation, it has been also possible in preliminary experiments to demonstrate the clustering and arraying of solid particles, both coated with an electrically conducting layer and uncoated, and both charged and uncharged.

Analysis of LAC Observations of Clusters of Galaxies and Supernova Remnants

NASA Technical Reports Server (NTRS)

Hughes, J.

1996-01-01

The following publications are included and serve as the final report: The X-ray Spectrum of Abell 665; Clusters of Galaxies; Ginga Observation of an Oxygen-rich Supernova Remnant; Ginga Observations of the Coma Cluster and Studies of the Spatial Distribution of Iron; A Measurement of the Hubble Constant from the X-ray Properties and the Sunyaev-Zel'dovich Effect of Abell 2218; Non-polytropic Model for the Coma Cluster; and Abundance Gradients in Cooling Flow Clusters: Ginga LAC (Large Area Counter) and Einstein SSS (Solid State Spectrometer) Spectra of A496, A1795, A2142, and A2199.

Energy Characteristics of Small Metal Clusters Containing Vacancies

NASA Astrophysics Data System (ADS)

Reva, V. I.; Pogosov, V. V.

2018-02-01

Self-consistent calculations of spatial distributions of electrons, potentials, and energies of dissociation, cohesion, vacancy formation, and electron attachment, as well as the ionization potential of solid Al N , Na N clusters ( N ≥ 254), and clusters containing a vacancy ( N ≥ 12) have been performed using a model of stable jellium. The contribution of a monovacancy to the energy of the cluster, the size dependences of the characteristics, and their asymptotic forms have been considered. The calculations have been performed on the SKIT-3 cluster at the Glushkov Institute of Cybernetics, National Academy of Sciences of Ukraine (Rpeak = 7.4 Tflops).

Infrared spectra of N2O-(ortho-D2)N and N2O-(HD)N clusters trapped in bulk solid parahydrogen.

PubMed

Lorenz, Britney D; Anderson, David T

2007-05-14

High-resolution infrared spectra of the clusters N2O-(ortho-D2)N and N2O-(HD)N, N=1-4, isolated in bulk solid parahydrogen at liquid helium temperatures are studied in the 2225 cm-1 region of the nu3 antisymmetric stretch of N2O. The clusters form during vapor deposition of separate gas streams of a precooled hydrogen mixture (ortho-D2para-H2 or HDpara-H2) and N2O onto a BaF2 optical substrate held at approximately 2.5 K in a sample-in-vacuum liquid helium cryostat. The cluster spectra reveal the N2O nu3 vibrational frequency shifts to higher energy as a function of N, and the shifts are larger for ortho-D2 compared to HD. These vibrational shifts result from the reduced translational zero-point energy for N2O solvated by the heavier hydrogen isotopomers. These spectra allow the N=0 peak at 2221.634 cm-1, corresponding to the nu3 vibrational frequency of N2O isolated in pure solid parahydrogen, to be assigned. The intensity of the N=0 absorption feature displays a strong temperature dependence, suggesting that significant structural changes occur in the parahydrogen solvation environment of N2O in the 1.8-4.9 K temperature range studied.

Extended utility of molten-salt chemistry: unprecedented synthesis of a water-soluble salt-inclusion solid comprised of high-nuclearity vanadium oxide clusters.

PubMed

Queen, Wendy L; West, J Palmer; Hudson, Joan; Hwu, Shiou-Jyh

2011-11-07

Polyoxometallates (POMs) are desirable in materials applications ranging from uses as catalysts in selective oxidation reactions to molecular-like building blocks for the preparation of new extended solids. With the use of an unprecedented approach involving high temperature, molten salt methods, a fascinating series of salt-inclusion solids (SISs) that contain high nuclearity POMs has been isolated for the first time. Cs(11)Na(3)(V(15)O(36))Cl(6) (1) was synthesized using the eutectic NaCl/CsCl flux (mp 493 °C) which serves as a reactive solvent in crystal growth and allows for the SIS formation. Its framework can be viewed as an "ionic" lattice composed of alternately packed counterions of Cl-centered [V(15)O(36)Cl](9-) clusters (V15; S = 11/2) and multinuclear [Cs(9)Na(3)Cl(5)](7+) cations. In light of the structural analysis, 1 was proven to be soluble in water giving rise to a dark green solution that is similar in color to single crystals of the title compound. Infrared spectroscopy of the solid formed from fast evaporation of the solution supports the presence of dissolved V15 clusters. Also noteworthy is the magnetization of 1 at 2 K, which reveals an s-shaped plot resembling that of superparamagnetic materials. © 2011 American Chemical Society

Development of a two-fluid drag law for clustered particles using direct numerical simulation and validation through experiments

NASA Astrophysics Data System (ADS)

Abbasi Baharanchi, Ahmadreza

This dissertation focused on development and utilization of numerical and experimental approaches to improve the CFD modeling of fluidization flow of cohesive micron size particles. The specific objectives of this research were: (1) Developing a cluster prediction mechanism applicable to Two-Fluid Modeling (TFM) of gas-solid systems (2) Developing more accurate drag models for Two-Fluid Modeling (TFM) of gas-solid fluidization flow with the presence of cohesive interparticle forces (3) using the developed model to explore the improvement of accuracy of TFM in simulation of fluidization flow of cohesive powders (4) Understanding the causes and influential factor which led to improvements and quantification of improvements (5) Gathering data from a fast fluidization flow and use these data for benchmark validations. Simulation results with two developed cluster-aware drag models showed that cluster prediction could effectively influence the results in both the first and second cluster-aware models. It was proven that improvement of accuracy of TFM modeling using three versions of the first hybrid model was significant and the best improvements were obtained by using the smallest values of the switch parameter which led to capturing the smallest chances of cluster prediction. In the case of the second hybrid model, dependence of critical model parameter on only Reynolds number led to the fact that improvement of accuracy was significant only in dense section of the fluidized bed. This finding may suggest that a more sophisticated particle resolved DNS model, which can span wide range of solid volume fraction, can be used in the formulation of the cluster-aware drag model. The results of experiment suing high speed imaging indicated the presence of particle clusters in the fluidization flow of FCC inside the riser of FIU-CFB facility. In addition, pressure data was successfully captured along the fluidization column of the facility and used as benchmark validation data for the second hybrid model developed in the present dissertation. It was shown the second hybrid model could predict the pressure data in the dense section of the fluidization column with better accuracy.

Group IIB-VIA semiconductor oxide cluster ions

NASA Astrophysics Data System (ADS)

Jayasekharan, Thankan

2018-05-01

Metal oxide cluster ions, MnOm± (M = Zn, Cd) and HgnOm- of various stoichiometry have been generated from solid IIB-VIA semiconductor oxides targets, (ZnO(s), CdO(s), and HgO(s)) by using pulse laser desorption ionization time of flight mass spectrometry with a laser of λ = 355 nm. Analysis of mass spectral data indicates the formation of stoichiometric cluster ions viz., (ZnO)n=1-30+ and (CdO)n=1-40+ along with -O bound anions, (ZnO)n=1-30O-, (CdO)n=1-40O- and (HgO)n=1-36O- from their respective solids. Further, metal oxoanions such as ZnOn=2,3-, CdOn=2,3,6-, and HgOn=2,3,6,7- have also been noted signifying the higher coordination ability of both Cd and Hg with O/O2/O3 species.

Average structure and local configuration of excess oxygen in UO(2+x).

PubMed

Wang, Jianwei; Ewing, Rodney C; Becker, Udo

2014-03-19

Determination of the local configuration of interacting defects in a crystalline, periodic solid is problematic because defects typically do not have a long-range periodicity. Uranium dioxide, the primary fuel for fission reactors, exists in hyperstoichiometric form, UO(2+x). Those excess oxygen atoms occur as interstitial defects, and these defects are not random but rather partially ordered. The widely-accepted model to date, the Willis cluster based on neutron diffraction, cannot be reconciled with the first-principles molecular dynamics simulations present here. We demonstrate that the Willis cluster is a fair representation of the numerical ratio of different interstitial O atoms; however, the model does not represent the actual local configuration. The simulations show that the average structure of UO(2+x) involves a combination of defect structures including split di-interstitial, di-interstitial, mono-interstitial, and the Willis cluster, and the latter is a transition state that provides for the fast diffusion of the defect cluster. The results provide new insights in differentiating the average structure from the local configuration of defects in a solid and the transport properties of UO(2+x).

Structural evolution in the crystallization of rapid cooling silver melt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Z.A., E-mail: ze.tian@gmail.com; Laboratory for Simulation and Modelling of Particulate Systems School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052; Dong, K.J.

2015-03-15

The structural evolution in a rapid cooling process of silver melt has been investigated at different scales by adopting several analysis methods. The results testify Ostwald’s rule of stages and Frank conjecture upon icosahedron with many specific details. In particular, the cluster-scale analysis by a recent developed method called LSCA (the Largest Standard Cluster Analysis) clarified the complex structural evolution occurred in crystallization: different kinds of local clusters (such as ico-like (ico is the abbreviation of icosahedron), ico-bcc like (bcc, body-centred cubic), bcc, bcc-like structures) in turn have their maximal numbers as temperature decreases. And in a rather wide temperaturemore » range the icosahedral short-range order (ISRO) demonstrates a saturated stage (where the amount of ico-like structures keeps stable) that breeds metastable bcc clusters. As the precursor of crystallization, after reaching the maximal number bcc clusters finally decrease, resulting in the final solid being a mixture mainly composed of fcc/hcp (face-centred cubic and hexagonal-closed packed) clusters and to a less degree, bcc clusters. This detailed geometric picture for crystallization of liquid metal is believed to be useful to improve the fundamental understanding of liquid–solid phase transition. - Highlights: • A comprehensive structural analysis is conducted focusing on crystallization. • The involved atoms in our analysis are more than 90% for all samples concerned. • A series of distinct intermediate states are found in crystallization of silver melt. • A novelty icosahedron-saturated state breeds the metastable bcc state.« less

Coupling microscopic and mesoscopic scales to simulate chemical equilibrium between a nanometric carbon cluster and detonation products fluid.

PubMed

Bourasseau, Emeric; Maillet, Jean-Bernard

2011-04-21

This paper presents a new method to obtain chemical equilibrium properties of detonation products mixtures including a solid carbon phase. In this work, the solid phase is modelled through a mesoparticle immersed in the fluid, such that the heterogeneous character of the mixture is explicitly taken into account. Inner properties of the clusters are taken from an equation of state obtained in a previous work, and interaction potential between the nanocluster and the fluid particles is derived from all-atoms simulations using the LCBOPII potential (Long range Carbon Bond Order Potential II). It appears that differences in chemical equilibrium results obtained with this method and the "composite ensemble method" (A. Hervouet et al., J. Phys. Chem. B, 2008, 112.), where fluid and solid phases are considered as non-interacting, are not significant, underlining the fact that considering the inhomogeneity of such system is crucial.

Cluster-distinguishing genotypic and phenotypic diversity of carbapenem-resistant Gram-negative bacteria in solid-organ transplantation patients: a comparative study.

PubMed

Karampatakis, Theodoros; Geladari, Anastasia; Politi, Lida; Antachopoulos, Charalampos; Iosifidis, Elias; Tsiatsiou, Olga; Karyoti, Aggeliki; Papanikolaou, Vasileios; Tsakris, Athanassios; Roilides, Emmanuel

2017-07-31

Solid-organ transplant recipients may display high rates of colonization and/or infection by multidrug-resistant bacteria. We analysed and compared the phenotypic and genotypic diversity of carbapenem-resistant (CR) strains of Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii isolated from patients in the Solid Organ Transplantation department of our hospital. Between March 2012 and August 2013, 56 CR strains from various biological fluids underwent antimicrobial susceptibility testing with VITEK 2, molecular analysis by PCR amplification and genotypic analysis with pulsed-field gel electrophoresis (PFGE). They were clustered according to antimicrobial drug susceptibility and genotypic profiles. Diversity analyses were performed by calculating Simpson's diversity index and applying computed rarefaction curves.Results/Key findings. Among K. pneumoniae, KP-producers predominated (57.1 %). VIM and OXA-23 carbapenemases prevailed among P. aeruginosa and A. baumannii (89.4 and 88.9 %, respectively). KPC-producing K. pneumoniae and OXA-23 A. baumannii were assigned in single PFGE pulsotypes. VIM-producing P. aeruginosa generated multiple pulsotypes. CR K. pneumoniae strains displayed phenotypic diversity in tigecycline, colistin (CS), amikacin (AMK), gentamicin (GEN) and co-trimoxazole (SXT) (16 clusters); P. aeruginosa displayed phenotypic diversity in cefepime (FEP), ceftazidime, aztreonam, piperacillin, piperacillin-tazobactam, AMK, GEN and CS (9 clusters); and A. baumannii displayed phenotypic diversity in AMK, GEN, SXT, FEP, tobramycin and rifampicin (8 clusters). The Simpson diversity indices for the interpretative phenotype and PFGE analysis were 0.89 and 0.6, respectively, for K. pneumoniae strains (P<0.001); 0.77 and 0.6 for P. aeruginosa (P=0.22); and 0.86 and 0.19 for A. baumannii (P=0.004). The presence of different antimicrobial susceptibility profiles does not preclude the possibility that two CR K. pneumoniae or A. baumannii isolates are clonally related.

Pivot method for global optimization: A study of structures and phase changes in water clusters

NASA Astrophysics Data System (ADS)

Nigra, Pablo Fernando

In this thesis, we have carried out a study of water clusters. The research work has been developed in two stages. In the first stage, we have investigated the properties of water clusters at zero temperature by means of global optimization. The clusters were modeled by using two well known pairwise potentials having distinct characteristics. One is the Matsuoka-Clementi-Yoshimine potential (MCY) that is an ab initio fitted function based on a rigid-molecule model, the other is the Sillinger-Rahman potential (SR) which is an empirical function based on a flexible-molecule model. The algorithm used for the global optimization of the clusters was the pivot method, which was developed in our group. The results have shown that, under certain conditions, the pivot method may yield optimized structures which are related to one another in such a way that they seem to form structural families. The structures in a family can be thought of as formed from the aggregation of single units. The particular types of structures we have found are quasi-one dimensional tubes built from stacking cyclic units such as tetramers, pentamers, and hexamers. The binding energies of these tubes form sequences that span smooth curves with clear asymptotic behavior; therefore, we have also studied the sequences applying the Bulirsch-Stoer (BST) algorithm to accelerate convergence. In the second stage of the research work, we have studied the thermodynamic properties of a typical water cluster at finite temperatures. The selected cluster was the water octamer which exhibits a definite solid-liquid phase change. The water octamer also has several low lying energy cubic structures with large energetic barriers that cause ergodicity breaking in regular Monte Carlo simulations. For that reason we have simulated the octamer using paralell tempering Monte Carlo combined with the multihistogram method. This has permited us to calculate the heat capacity from very low temperatures up to T = 230 K. We have found the melting temperature to be 178.5 K. In addition, we have been able to estimate at 12 K the onset temperature of a solid-solid phase change between the two lowest energy lying isomers.

High Intensity Femtosecond XUV Pulse Interactions with Atomic Clusters: Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ditmire, Todd

We propose to expand our recent studies on the interactions of intense extreme ultraviolet (XUV) femtosecond pulses with atomic and molecular clusters. The work described follows directly from work performed under BES support for the past grant period. During this period we upgraded the THOR laser at UT Austin by replacing the regenerative amplifier with optical parametric amplification (OPA) using BBO crystals. This increased the contrast of the laser, the total laser energy to ~1.2 J , and decreased the pulse width to below 30 fs. We built a new all reflective XUV harmonic beam line into expanded lab space. This enabled an increase influence by a factor ofmore » 25 and an increase in the intensity by a factor of 50. The goal of the program proposed in this renewal is to extend this class of experiments to available higher XUV intensity and a greater range of wavelengths. In particular we plan to perform experiments to confirm our hypothesis about the origin of the high charge states in these exploding clusters, an effect which we ascribe to plasma continuum lowering (ionization potential depression) in a cluster nano-­plasma. To do this we will perform experiments in which XUV pulses of carefully chosen wavelength irradiate clusters composed of only low-Z atoms and clusters with a mixture of this low-­Z atom with higher Z atoms. The latter clusters will exhibit higher electron densities and will serve to lower the ionization potential further than in the clusters composed only of low Z atoms. This should have a significant effect on the charge states produced in the exploding cluster. We will also explore the transition of explosions in these XUV irradiated clusters from hydrodynamic expansion to Coulomb explosion. The work proposed here will explore clusters of a wider range of constituents, including clusters from solids. Experiments on clusters from solids will be enabled by development we performed during the past grant period in which we constructed and tested a cluster generator based on the Laser Ablation of Microparticles (LAM) method.« less

On the calculation of the energies of dissociation, cohesion, vacancy formation, electron attachment, and the ionization potential of small metallic clusters containing a monovacancy

NASA Astrophysics Data System (ADS)

Pogosov, V. V.; Reva, V. I.

2017-09-01

In terms of the model of stable jellium, self-consistent calculations of spatial distributions of electrons and potentials, as well as of energies of dissociation, cohesion, vacancy formation, electron attachment, and ionization potentials of solid clusters of Mg N , Li N (with N ≤ 254 ) and of clusters containing a vacancy ( N ≥ 12) have been performed. The contribution of a monovacancy to the energy of the cluster and size dependences of its characteristics and of asymptotics have been discussed. Calculations have been performed using a SKIT-3 cluster at Glushkov Institute of Cybernetics, National Academy of Sciences, Ukraine (Rpeak = 7.4 Tflops).

Sequential desorption energy of hydrogen from nickel clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deepika,; Kumar, Rakesh, E-mail: rakesh@iitrpr.ac.in; R, Kamal Raj.

2015-06-24

We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage andmore » regeneration of Hydrogen as a clean energy carrier.« less

Self-assembly of a tetrahedral 58-nuclear barium vanadium oxide cluster.

PubMed

Kastner, Katharina; Puscher, Bianka; Streb, Carsten

2013-01-07

We report the synthesis and characterization of a molecular barium vanadium oxide cluster featuring high nuclearity and high symmetry. The tetrameric, 2.3 nm cluster H(5)[Ba(10)(NMP)(14)(H(2)O)(8)[V(12)O(33)](4)Br] is based on a bromide-centred, octahedral barium scaffold which is capped by four previously unknown [V(12)O(33)](6-) clusters in a tetrahedral fashion. The compound represents the largest polyoxovanadate-based heterometallic cluster known to date. The cluster is formed in organic solution and it is suggested that the bulky N-methyl-2-pyrrolidone (NMP) solvent ligands allow the isolation of this giant molecule and prevent further condensation to a solid-state metal oxide. The cluster is fully characterized using single-crystal XRD, elemental analysis, ESI mass spectrometry and other spectroscopic techniques.

Transition mechanism of the reaction interface of the thermal decomposition of calcite

NASA Astrophysics Data System (ADS)

Li, Zhi; Zhao, Zhen; Wang, Qi; Wang, Guocheng

2018-06-01

Even the reaction layer (excited state CaCO3) is so thin that it is difficult to detect, it is significantly restrict the orientation of the solid product (excited state CaO) of the thermal decomposition of calcite. Quantum chemical calculation with GGA-PW91 functional reveals that the ground-state (CaCO3)m clusters are more stable than the hybrid objects (CaCO3)m-(CaO)n clusters. The lowest-energy (CaCO3)m clusters are more kinetically stable than that of (CaCO3)m-n(CaO)n clusters and then than that of (CaO)n clusters except (CaCO3)(CaO)3 clusters from the HOMO-LUMO gaps. (CaCO3)2 clusters should co-exist at room temperature and they prefer to decompose with the temperature increasing.

A novel approach to the theory of homogeneous and heterogeneous nucleation.

PubMed

Ruckenstein, Eli; Berim, Gersh O; Narsimhan, Ganesan

2015-01-01

A new approach to the theory of nucleation, formulated relatively recently by Ruckenstein, Narsimhan, and Nowakowski (see Refs. [7-16]) and developed further by Ruckenstein and other colleagues, is presented. In contrast to the classical nucleation theory, which is based on calculating the free energy of formation of a cluster of the new phase as a function of its size on the basis of macroscopic thermodynamics, the proposed theory uses the kinetic theory of fluids to calculate the condensation (W(+)) and dissociation (W(-)) rates on and from the surface of the cluster, respectively. The dissociation rate of a monomer from a cluster is evaluated from the average time spent by a surface monomer in the potential well as obtained from the solution of the Fokker-Planck equation in the phase space of position and momentum for liquid-to-solid transition and the phase space of energy for vapor-to-liquid transition. The condensation rates are calculated using traditional expressions. The knowledge of those two rates allows one to calculate the size of the critical cluster from the equality W(+)=W(-) as well as the rate of nucleation. The developed microscopic approach allows one to avoid the controversial application of classical thermodynamics to the description of nuclei which contain a few molecules. The new theory was applied to a number of cases, such as the liquid-to-solid and vapor-to-liquid phase transitions, binary nucleation, heterogeneous nucleation, nucleation on soluble particles and protein folding. The theory predicts higher nucleation rates at high saturation ratios (small critical clusters) than the classical nucleation theory for both solid-to-liquid as well as vapor-to-liquid transitions. As expected, at low saturation ratios for which the size of the critical cluster is large, the results of the new theory are consistent with those of the classical one. The present approach was combined with the density functional theory to account for the density profile in the cluster. This approach was also applied to protein folding, viewed as the evolution of a cluster of native residues of spherical shape within a protein molecule, which could explain protein folding/unfolding and their dependence on temperature. Copyright © 2014 Elsevier B.V. All rights reserved.

Grape cluster microclimate influences the aroma composition of Sauvignon blanc wine.

PubMed

Martin, Damian; Grose, Claire; Fedrizzi, Bruno; Stuart, Lily; Albright, Abby; McLachlan, Andrew

2016-11-01

New Zealand Sauvignon blanc (SB) wines are characterised by a distinctive combination of tropical-fruity and green-herbaceous aromatic compounds. The influence of sunlight exposure of grape clusters on juice and wine composition was investigated, with the aim of manipulating aromatic compounds in SB wine. In the absence of basal leaf removal SB clusters naturally exposed to sunlight were riper than shaded clusters, evidenced by higher total soluble solids (TSS) and proline, and lower malic acid, 3-isobutyl-2-methoxypyrazine (IBMP) and arginine. Volatile thiols in wines did not differ between shaded and exposed clusters. At equivalent TSS, cluster exposure had little or no effect on malic acid concentration. Conversely, wine from shaded clusters had almost double the IBMP concentration of wine from exposed clusters at equivalent TSS. The effects on SB juice and wine composition of natural variations in cluster microclimate are not comparable with the effects of cluster exposure created through leaf removal. Copyright © 2016 Elsevier Ltd. All rights reserved.

Low work function, stable compound clusters and generation process

DOEpatents

Dinh, Long N.; Balooch, Mehdi; Schildbach, Marcus A.; Hamza, Alex V.; McLean, II, William

2000-01-01

Low work function, stable compound clusters are generated by co-evaporation of a solid semiconductor (i.e., Si) and alkali metal (i.e., Cs) elements in an oxygen environment. The compound clusters are easily patterned during deposition on substrate surfaces using a conventional photo-resist technique. The cluster size distribution is narrow, with a peak range of angstroms to nanometers depending on the oxygen pressure and the Si source temperature. Tests have shown that compound clusters when deposited on a carbon substrate contain the desired low work function property and are stable up to 600.degree. C. Using the patterned cluster containing plate as a cathode baseplate and a faceplate covered with phosphor as an anode, one can apply a positive bias to the faceplate to easily extract electrons and obtain illumination.

A Computational Study of Rare Gas Clusters: Stepping Stones to the Solid State

ERIC Educational Resources Information Center

Glendening, Eric D.; Halpern, Arthur M.

2012-01-01

An upper-level undergraduate or beginning graduate project is described in which students obtain the Lennard-Jones 6-12 potential parameters for Ne[subscript 2] and Ar[subscript 2] from ab initio calculations and use the results to express pairwise interactions between the atoms in clusters containing up to N = 60 atoms. The students use simulated…

Analysis of the bond-valence method for calculating (29) Si and (31) P magnetic shielding in covalent network solids.

PubMed

Holmes, Sean T; Alkan, Fahri; Iuliucci, Robbie J; Mueller, Karl T; Dybowski, Cecil

2016-07-05

(29) Si and (31) P magnetic-shielding tensors in covalent network solids have been evaluated using periodic and cluster-based calculations. The cluster-based computational methodology employs pseudoatoms to reduce the net charge (resulting from missing co-ordination on the terminal atoms) through valence modification of terminal atoms using bond-valence theory (VMTA/BV). The magnetic-shielding tensors computed with the VMTA/BV method are compared to magnetic-shielding tensors determined with the periodic GIPAW approach. The cluster-based all-electron calculations agree with experiment better than the GIPAW calculations, particularly for predicting absolute magnetic shielding and for predicting chemical shifts. The performance of the DFT functionals CA-PZ, PW91, PBE, rPBE, PBEsol, WC, and PBE0 are assessed for the prediction of (29) Si and (31) P magnetic-shielding constants. Calculations using the hybrid functional PBE0, in combination with the VMTA/BV approach, result in excellent agreement with experiment. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Hot and solid gallium clusters: too small to melt.

PubMed

Breaux, Gary A; Benirschke, Robert C; Sugai, Toshiki; Kinnear, Brian S; Jarrold, Martin F

2003-11-21

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.

Iron-carbide cluster thermal dynamics for catalyzed carbon nanotube growth

NASA Astrophysics Data System (ADS)

Ding, Feng; Bolton, Kim; Rosén, Arne

2004-07-01

Molecular dynamics simulations have been used to study the thermal behavior of FeN-mCm clusters where N, the total number of atoms, extends up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid-solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculation indicates that, when carbon nanotubes (CNTs) are grown on large (>3-4 nm) catalyst particles at low temperatures (<1200 K), the catalyst particles are not completely molten. It is argued that the mechanism of CNT growth under these conditions may be governed by the surface melting of the cluster. .

Two-Dimensional Fullerene Assembly from an Exfoliated van der Waals Template.

PubMed

Lee, Kihong; Choi, Bonnie; Plante, Ilan Jen-La; Paley, Maria V; Zhong, Xinjue; Crowther, Andrew C; Owen, Jonathan S; Zhu, Xiaoyang; Roy, Xavier

2018-05-22

Two-dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom-up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C 60 as a polymerizable monomer. The C 60 building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C 60 monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C 60 . The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Supercritical fluid molecular spray film deposition and powder formation

DOEpatents

Smith, Richard D.

1986-01-01

Solid films are deposited, or fine powders formed, by dissolving a solid material into a supercritical fluid solution at an elevated pressure and then rapidly expanding the solution through a short orifice into a region of relatively low pressure. This produces a molecular spray which is directed against a substrate to deposit a solid thin film thereon, or discharged into a collection chamber to collect a fine powder. Upon expansion and supersonic interaction with background gases in the low pressure region, any clusters of solvent are broken up and the solvent is vaporized and pumped away. Solute concentration in the solution is varied primarily by varying solution pressure to determine, together with flow rate, the rate of deposition and to control in part whether a film or powder is produced and the granularity of each. Solvent clustering and solute nucleation are controlled by manipulating the rate of expansion of the solution and the pressure of the lower pressure region. Solution and low pressure region temperatures are also controlled.

Method and apparatus for offloading compute resources to a flash co-processing appliance

DOEpatents

Tzelnic, Percy; Faibish, Sorin; Gupta, Uday K.; Bent, John; Grider, Gary Alan; Chen, Hsing -bung

2015-10-13

Solid-State Drive (SSD) burst buffer nodes are interposed into a parallel supercomputing cluster to enable fast burst checkpoint of cluster memory to or from nearby interconnected solid-state storage with asynchronous migration between the burst buffer nodes and slower more distant disk storage. The SSD nodes also perform tasks offloaded from the compute nodes or associated with the checkpoint data. For example, the data for the next job is preloaded in the SSD node and very fast uploaded to the respective compute node just before the next job starts. During a job, the SSD nodes perform fast visualization and statistical analysis upon the checkpoint data. The SSD nodes can also perform data reduction and encryption of the checkpoint data.

Adatom lifetime in film growth at solid surfaces in the framework of the Johnson Mehl Avrami Kolmogorov model

NASA Astrophysics Data System (ADS)

Tomellini, M.; Fanfoni, M.

1999-10-01

On the basis of the quasi-static approximation and for simultaneous nucleation the adatom lifetime, τ, during film growth at solid surfaces has been computed by Monte Carlo (MC) simulation. The quantity DN0τ, N0 and D being respectively the cluster density and the adatom diffusion coefficient, is found to depend upon the portion of surface covered by clusters and, very weakly, on N0. Moreover, a stochastic approach based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory has been developed to obtain the analytical expression of the MC curve. The collision factor of the mean island has been calculated and compared with those previously obtained from the uniform depletion approximation and the lattice approximation.

The model of the long-range effect in solids: Evolution of structure, clusters of internal boundaries, and their statistical descriptors

NASA Astrophysics Data System (ADS)

Herega, Alexander; Sukhanov, Volodymyr; Vyrovoy, Valery

2017-12-01

It is known that the multifocal mechanism of genesis of structure of heterogeneous materials provokes intensive formation of internal boundaries. In the present papers, the dependence of the structure and properties of material on the characteristic size and shape, the number and size distribution, and the character of interaction of individual internal boundaries and their clusters is studied. The limitation on the applicability of the material damage coefficient is established; the effective information descriptor of internal boundaries is proposed. An idea of the effect of long-range interaction in irradiated solids on the realization of the second-order phase transition is introduced; a phenomenological percolation model of the effect is proposed.

Iterative local Gaussian clustering for expressed genes identification linked to malignancy of human colorectal carcinoma

PubMed Central

Wasito, Ito; Hashim, Siti Zaiton M; Sukmaningrum, Sri

2007-01-01

Gene expression profiling plays an important role in the identification of biological and clinical properties of human solid tumors such as colorectal carcinoma. Profiling is required to reveal underlying molecular features for diagnostic and therapeutic purposes. A non-parametric density-estimation-based approach called iterative local Gaussian clustering (ILGC), was used to identify clusters of expressed genes. We used experimental data from a previous study by Muro and others consisting of 1,536 genes in 100 colorectal cancer and 11 normal tissues. In this dataset, the ILGC finds three clusters, two large and one small gene clusters, similar to their results which used Gaussian mixture clustering. The correlation of each cluster of genes and clinical properties of malignancy of human colorectal cancer was analysed for the existence of tumor or normal, the existence of distant metastasis and the existence of lymph node metastasis. PMID:18305825

Iterative local Gaussian clustering for expressed genes identification linked to malignancy of human colorectal carcinoma.

PubMed

Wasito, Ito; Hashim, Siti Zaiton M; Sukmaningrum, Sri

2007-12-30

Gene expression profiling plays an important role in the identification of biological and clinical properties of human solid tumors such as colorectal carcinoma. Profiling is required to reveal underlying molecular features for diagnostic and therapeutic purposes. A non-parametric density-estimation-based approach called iterative local Gaussian clustering (ILGC), was used to identify clusters of expressed genes. We used experimental data from a previous study by Muro and others consisting of 1,536 genes in 100 colorectal cancer and 11 normal tissues. In this dataset, the ILGC finds three clusters, two large and one small gene clusters, similar to their results which used Gaussian mixture clustering. The correlation of each cluster of genes and clinical properties of malignancy of human colorectal cancer was analysed for the existence of tumor or normal, the existence of distant metastasis and the existence of lymph node metastasis.

A phase field model for segregation and precipitation induced by irradiation in alloys

NASA Astrophysics Data System (ADS)

Badillo, A.; Bellon, P.; Averback, R. S.

2015-04-01

A phase field model is introduced to model the evolution of multicomponent alloys under irradiation, including radiation-induced segregation and precipitation. The thermodynamic and kinetic components of this model are derived using a mean-field model. The mobility coefficient and the contribution of chemical heterogeneity to free energy are rescaled by the cell size used in the phase field model, yielding microstructural evolutions that are independent of the cell size. A new treatment is proposed for point defect clusters, using a mixed discrete-continuous approach to capture the stochastic character of defect cluster production in displacement cascades, while retaining the efficient modeling of the fate of these clusters using diffusion equations. The model is tested on unary and binary alloy systems using two-dimensional simulations. In a unary system, the evolution of point defects under irradiation is studied in the presence of defect clusters, either pre-existing ones or those created by irradiation, and compared with rate theory calculations. Binary alloys with zero and positive heats of mixing are then studied to investigate the effect of point defect clustering on radiation-induced segregation and precipitation in undersaturated solid solutions. Lastly, irradiation conditions and alloy parameters leading to irradiation-induced homogeneous precipitation are investigated. The results are discussed in the context of experimental results reported for Ni-Si and Al-Zn undersaturated solid solutions subjected to irradiation.

Synthesis and Structure of an Extended Cluster Lead(II) Carboxylate, [Pb{(CO)(9)Co(3)(&mgr;(3)-CCO(2))}(2)](n)(). Role of Core Metals in Cluster-Derived Hydrogenation Catalysts.

PubMed

Lei, Xinjian; Shang, Maoyu; Patil, Atul; Wolf, Eduardo E.; Fehlner, Thomas P.

1996-05-22

The reaction of lead acetate with (CO)(9)Co(3)(&mgr;(3)-CCOOH) leads to the formation of [Pb{(CO)(9)Co(3)(&mgr;(3)-CCO(2))}(2)](n)(), I, in high yield. The structure of I exhibits unusual six-coordinate Pb(II) centers with two asymmetrical chelating cluster carboxylates (C(22)Co(6)PbO(22); triclinic P&onemacr;; a = 8.119(1), b = 14.346(2), c = 14.660(2) Å; alpha = 102.18(1), beta = 99.01(1), gamma = 97.30(1) degrees; Z = 2). One oxygen of each cluster carboxylate ligand bridges between adjacent lead atoms such that a chainlike extended structure is found in the solid state without the presence of solvent or water. I is converted stepwise on pyrolysis into two metastable forms of solid materials (designated LT and HT), each of which has been characterized spectroscopically. The hydrogenation of 2-butenal as a test reaction shows that the LT catalyst exhibits selectivities similar to previous LT materials derived from other cobalt cluster metal carboxylates and that the HT material is totally inactive. The observed release of the lead core metal under HT activation conditions totally inactivates the catalyst and demonstrates exposure of the core metal in the HT form of these novel catalysts.

Ge(14)[Ge(SiMe(3))(3)](5)Li(3)(THF)(6): the largest metalloid cluster compound of germanium: on the way to fullerene-like compounds?

PubMed

Schenk, Christian; Schnepf, Andreas

2008-10-14

The reaction of GeBr with LiGe(SiMe(3))(3) yields the largest metalloid cluster compound of germanium Ge(14)[Ge(SiMe(3))(3)](5)Li(3)(THF)(6), in which 14 germanium atoms are arranged as a hollow sphere in the cluster core, showing that in the case of germanium also fullerene-like compounds might be present in the borderland between the molecular and solid states.

Reversible Electrochemical Lithium-Ion Insertion into the Rhenium Cluster Chalcogenide-Halide Re6Se8Cl2.

PubMed

Bruck, Andrea M; Yin, Jiefu; Tong, Xiao; Takeuchi, Esther S; Takeuchi, Kenneth J; Szczepura, Lisa F; Marschilok, Amy C

2018-05-07

The cluster-based material Re 6 Se 8 Cl 2 is a two-dimensional ternary material with cluster-cluster bonding across the a and b axes capable of multiple electron transfer accompanied by ion insertion across the c axis. The Li/Re 6 Se 8 Cl 2 system showed reversible electron transfer from 1 to 3 electron equivalents (ee) at high current densities (88 mA/g). Upon cycling to 4 ee, there was evidence of capacity degradation over 50 cycles associated with the formation of an organic solid-electrolyte interface (between 1.45 and 1 V vs Li/Li + ). This investigation highlights the ability of cluster-based materials with two-dimensional cluster bonding to be used in applications such as energy storage, showing structural stability and high rate capability.

Study of cluster behavior in the riser of CFB by the DSMC method

NASA Astrophysics Data System (ADS)

Liu, H. P.; Liu, D. Y.; Liu, H.

2010-03-01

The flow behaviors of clusters in the riser of a two-dimensional (2D) circulating fluidized bed was numerically studied based on the Euler-Lagrangian approach. Gas turbulence was modeled by means of Large Eddy Simulation (LES). Particle collision was modeled by means of the direct simulation Monte Carlo (DSMC) method. Clusters' hydrodynamic characteristics are obtained using a cluster identification method proposed by sharrma et al. (2000). The descending clusters near the wall region and the up- and down-flowing clusters in the core were studied separately due to their different flow behaviors. The effects of superficial gas velocity on the cluster behavior were analyzed. Simulated results showed that near wall clusters flow downward and the descent velocity is about -45 cm/s. The occurrence frequency of the up-flowing cluster is higher than that of down-flowing cluster in the core of riser. With the increase of superficial gas velocity, the solid concentration and occurrence frequency of clusters decrease, while the cluster axial velocity increase. Simulated results were in agreement with experimental data. The stochastic method used in present paper is feasible for predicting the cluster flow behavior in CFBs.

Matrix Assisted and/or Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of WO3 Clusters Formation in Gas Phase. Nanodiamonds, Fullerene, and Graphene Oxide Matrices

NASA Astrophysics Data System (ADS)

Ausekar, Mayuri Vilas; Mawale, Ravi Madhukar; Pazdera, Pavel; Havel, Josef

2018-03-01

The formation of W x O y +●/-● clusters in the gas phase was studied by laser desorption ionization (LDI) and matrix assisted laser desorption ionization (MALDI) of solid WO3. LDI produced (WO3) n + ●/- ● ( n = 1-7) clusters. In MALDI, when using nano-diamonds (NDs), graphene oxide (GO), or fullerene (C60) matrices, higher mass clusters were generated. In addition to (WO3) n -● clusters, oxygen-rich or -deficient species were found in both LDI and MALDI (with the total number of clusters exceeding one hundred ≈ 137). This is the first time that such matrices have been used for the generation of(WO3) n + ●/-● clusters in the gas phase, while new high mass clusters (WO3) n -● ( n = 12-19) were also detected. [Figure not available: see fulltext.

Quantum phase transition between cluster and antiferromagnetic states

NASA Astrophysics Data System (ADS)

Son, W.; Amico, L.; Fazio, R.; Hamma, A.; Pascazio, S.; Vedral, V.

2011-09-01

We study a Hamiltonian system describing a three-spin-1/2 cluster-like interaction competing with an Ising-like exchange. We show that the ground state in the cluster phase possesses symmetry protected topological order. A continuous quantum phase transition occurs as result of the competition between the cluster and Ising terms. At the critical point the Hamiltonian is self-dual. The geometric entanglement is also studied and used to investigate the quantum phase transition. Our findings in one dimension corroborate the analysis of the two-dimensional generalization of the system, indicating, at a mean-field level, the presence of a direct transition between an antiferromagnetic and a valence bond solid ground state.

SU-E-J-03: A Comprehensive Comparison Between Alpha and Beta Emitters for Cancer Radioimmunotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, C.Y.; Guatelli, S; Oborn, B

2014-06-01

Purpose: The purpose of this study is to perform a comprehensive comparison of the therapeutic efficacy and cytotoxicity of alpha and beta emitters for Radioimmunotherapy (RIT). For each stage of cancer development, specific models were built for the separate objectives of RIT to be addressed:a) kill isolated cancer cells in transit in the lymphatic and vascular circulation,b) regress avascular cell clusters,c) regress tumor vasculature and tumors. Methods: Because of the nature of short range, high LET alpha and long energy beta radiation and heterogeneous antigen expression among cancer cells, the microdosimetric approach is essential for the RIT assessment. Geant4 basedmore » microdosimetric models are developed for the three different stages of cancer progression: cancer cells, cell clusters and tumors. The energy deposition, specific energy resulted from different source distribution in the three models was calculated separately for 4 alpha emitting radioisotopes ({sup 211}At, {sup 213}Bi, {sup 223}Ra and {sup 225}Ac) and 6 beta emitters ({sup 32}P, {sup 33}P, {sup 67}Cu, {sup 90}Y, {sup 131}I and {sup 177}Lu). The cell survival, therapeutic efficacy and cytotoxicity are determined and compared between alpha and beta emitters. Results: We show that internal targeted alpha radiation has advantages over beta radiation for killing isolated cancer cells, regressing small cell clusters and also solid tumors. Alpha particles have much higher dose specificity and potency than beta particles. They can deposit 3 logs more dose than beta emitters to single cells and solid tumor. Tumor control probability relies on deep penetration of radioisotopes to cancer cell clusters and solid tumors. Conclusion: The results of this study provide a quantitative understanding of the efficacy and cytotoxicity of RIT for each stage of cancer development.« less

Techniques to derive geometries for image-based Eulerian computations

PubMed Central

Dillard, Seth; Buchholz, James; Vigmostad, Sarah; Kim, Hyunggun; Udaykumar, H.S.

2014-01-01

Purpose The performance of three frequently used level set-based segmentation methods is examined for the purpose of defining features and boundary conditions for image-based Eulerian fluid and solid mechanics models. The focus of the evaluation is to identify an approach that produces the best geometric representation from a computational fluid/solid modeling point of view. In particular, extraction of geometries from a wide variety of imaging modalities and noise intensities, to supply to an immersed boundary approach, is targeted. Design/methodology/approach Two- and three-dimensional images, acquired from optical, X-ray CT, and ultrasound imaging modalities, are segmented with active contours, k-means, and adaptive clustering methods. Segmentation contours are converted to level sets and smoothed as necessary for use in fluid/solid simulations. Results produced by the three approaches are compared visually and with contrast ratio, signal-to-noise ratio, and contrast-to-noise ratio measures. Findings While the active contours method possesses built-in smoothing and regularization and produces continuous contours, the clustering methods (k-means and adaptive clustering) produce discrete (pixelated) contours that require smoothing using speckle-reducing anisotropic diffusion (SRAD). Thus, for images with high contrast and low to moderate noise, active contours are generally preferable. However, adaptive clustering is found to be far superior to the other two methods for images possessing high levels of noise and global intensity variations, due to its more sophisticated use of local pixel/voxel intensity statistics. Originality/value It is often difficult to know a priori which segmentation will perform best for a given image type, particularly when geometric modeling is the ultimate goal. This work offers insight to the algorithm selection process, as well as outlining a practical framework for generating useful geometric surfaces in an Eulerian setting. PMID:25750470

Architecture and method for a burst buffer using flash technology

DOEpatents

Tzelnic, Percy; Faibish, Sorin; Gupta, Uday K.; Bent, John; Grider, Gary Alan; Chen, Hsing-bung

2016-03-15

A parallel supercomputing cluster includes compute nodes interconnected in a mesh of data links for executing an MPI job, and solid-state storage nodes each linked to a respective group of the compute nodes for receiving checkpoint data from the respective compute nodes, and magnetic disk storage linked to each of the solid-state storage nodes for asynchronous migration of the checkpoint data from the solid-state storage nodes to the magnetic disk storage. Each solid-state storage node presents a file system interface to the MPI job, and multiple MPI processes of the MPI job write the checkpoint data to a shared file in the solid-state storage in a strided fashion, and the solid-state storage node asynchronously migrates the checkpoint data from the shared file in the solid-state storage to the magnetic disk storage and writes the checkpoint data to the magnetic disk storage in a sequential fashion.

Nitrogen-rich heterocycles as reactivity retardants in shocked insensitive explosives.

PubMed

Manaa, M Riad; Reed, Evan J; Fried, Laurence E; Goldman, Nir

2009-04-22

We report the first quantum-based multiscale simulations to study the reactivity of shocked perfect crystals of the insensitive energetic material triaminotrinitrobenzene (TATB). Tracking chemical transformations of TATB experiencing overdriven shock speeds of 9 km/s for up to 0.43 ns and 10 km/s for up to 0.2 ns reveal high concentrations of nitrogen-rich heterocyclic clusters. Further reactivity of TATB toward the final decomposition products of fluid N(2) and solid carbon is inhibited due to the formation of these heterocycles. Our results thus suggest a new mechanism for carbon-rich explosive materials that precedes the slow diffusion-limited process of forming the bulk solid from carbon clusters and provide fundamental insight at the atomistic level into the long reaction zone of shocked TATB.

Molecular growth from a Mo176 to a Mo248 cluster

NASA Astrophysics Data System (ADS)

Müller, A.; Shah, Syed Q. N.; Bögge, H.; Schmidtmann, M.

1999-01-01

In polyoxometalate chemistry a large variety of compounds, clusters and solid-state structures can be formed by the linking together of well-defined metal-oxygen building blocks, . These species exhibit unusual topological and electronic properties, andfind applications ranging from medicine to industrial processes. The recently reported ring-shaped mixed-valence polyoxomolybdates of the type {Mo154} (refs 5, 6) and {Mo176} (refs 7, 8) represent a new class of giant clusters with nanometre-sized cavities and interesting properties for host-guest chemistry. Here we describe the formation of related clusters of the type {Mo248} formed by addition of further units to the inner surface of the {Mo176 } `wheel'. The additional units arrange themselves into two {Mo36} `hub-caps' on the initial wheel-clusters that are not stable in isolation. These findings reveal a new pathway to the development of complex coordination clusters.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bunkin, N. F., E-mail: nbunkin@kapella.gpi.ru; Suyazov, N. V.; Shkirin, A. V.

Experiments using phase-modulation interference microscopy and Mueller-matrix polarimetry show that double-distilled water free of foreign solid matter contains macroscopic light scatterers. Numerical calculations suggest that these scatterers can be represented as micrometer-size clusters of polydisperse air bubbles with effective radii between 70 and 90 nm. The fractal dimension of the clusters varies from 2.4 to 2.8, and their concentration is on the order of 10{sup 6} cm{sup -3}.

Clustering and phase behaviour of attractive active particles with hydrodynamics.

PubMed

Navarro, Ricard Matas; Fielding, Suzanne M

2015-10-14

We simulate clustering, phase separation and hexatic ordering in a monolayered suspension of active squirming disks subject to an attractive Lennard-Jones-like pairwise interaction potential, taking hydrodynamic interactions between the particles fully into account. By comparing the hydrodynamic case with counterpart simulations for passive and active Brownian particles, we elucidate the relative roles of self-propulsion, interparticle attraction, and hydrodynamic interactions in determining clustering and phase behaviour. Even in the presence of an attractive potential, we find that hydrodynamic interactions strongly suppress the motility induced phase separation that might a priori have been expected in a highly active suspension. Instead, we find only a weak tendency for the particles to form stringlike clusters in this regime. At lower activities we demonstrate phase behaviour that is broadly equivalent to that of the counterpart passive system at low temperatures, characterized by regimes of gas-liquid, gas-solid and liquid-solid phase coexistence. In this way, we suggest that a dimensionless quantity representing the level of activity relative to the strength of attraction plays the role of something like an effective non-equilibrium temperature, counterpart to the (dimensionless) true thermodynamic temperature in the passive system. However there are also some important differences from the equilibrium case, most notably with regards the degree of hexatic ordering, which we discuss carefully.

A ground truth based comparative study on clustering of gene expression data.

PubMed

Zhu, Yitan; Wang, Zuyi; Miller, David J; Clarke, Robert; Xuan, Jianhua; Hoffman, Eric P; Wang, Yue

2008-05-01

Given the variety of available clustering methods for gene expression data analysis, it is important to develop an appropriate and rigorous validation scheme to assess the performance and limitations of the most widely used clustering algorithms. In this paper, we present a ground truth based comparative study on the functionality, accuracy, and stability of five data clustering methods, namely hierarchical clustering, K-means clustering, self-organizing maps, standard finite normal mixture fitting, and a caBIG toolkit (VIsual Statistical Data Analyzer--VISDA), tested on sample clustering of seven published microarray gene expression datasets and one synthetic dataset. We examined the performance of these algorithms in both data-sufficient and data-insufficient cases using quantitative performance measures, including cluster number detection accuracy and mean and standard deviation of partition accuracy. The experimental results showed that VISDA, an interactive coarse-to-fine maximum likelihood fitting algorithm, is a solid performer on most of the datasets, while K-means clustering and self-organizing maps optimized by the mean squared compactness criterion generally produce more stable solutions than the other methods.

X-ray tomography studies on porosity and particle size distribution in cast in-situ Al-Cu-TiB{sub 2} semi-solid forged composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mathew, James; Mandal, Animesh

X-ray computed tomography (XCT) was used to characterise the internal microstructure and clustering behaviour of TiB{sub 2} particles in in-situ processed Al-Cu metal matrix composites prepared by casting method. Forging was used in semi-solid state to reduce the porosity and to uniformly disperse TiB{sub 2} particles in the composite. Quantification of porosity and clustering of TiB{sub 2} particles was evaluated for different forging reductions (30% and 50% reductions) and compared with an as-cast sample using XCT. Results show that the porosity content was decreased by about 40% due to semi-solid forging as compared to the as-cast condition. Further, XCT resultsmore » show that the 30% forging reduction resulted in greater uniformity in distribution of TiB{sub 2} particles within the composite compared to as-cast and the 50% forge reduction in semi-solid state. These results show that the application of forging in semi-solid state enhances particle distribution and reduces porosity formation in cast in-situ Al-Cu-TiB{sub 2} metal matrix composites. - Highlights: •XCT was used to visualise 3D internal structure of Al-Cu-TiB{sub 2} MMCs. •Al-Cu-TiB{sub 2} MMC was prepared by casting using flux assisted synthesis method. •TiB{sub 2} particles and porosity size distribution were evaluated. •Results show that forging in semi-solid condition decreases the porosity content and improve the particle dispersion in MMCs.« less

A combined experimental and theoretical spectroscopic protocol for determination of the structure of heterogeneous catalysts: developing the information content of the resonance Raman spectra of M1 MoVO x .

PubMed

Kubas, Adam; Noak, Johannes; Trunschke, Annette; Schlögl, Robert; Neese, Frank; Maganas, Dimitrios

2017-09-01

Absorption and multiwavelength resonance Raman spectroscopy are widely used to investigate the electronic structure of transition metal centers in coordination compounds and extended solid systems. In combination with computational methodologies that have predictive accuracy, they define powerful protocols to study the spectroscopic response of catalytic materials. In this work, we study the absorption and resonance Raman spectra of the M1 MoVO x catalyst. The spectra were calculated by time-dependent density functional theory (TD-DFT) in conjunction with the independent mode displaced harmonic oscillator model (IMDHO), which allows for detailed bandshape predictions. For this purpose cluster models with up to 9 Mo and V metallic centers are considered to represent the bulk structure of MoVO x . Capping hydrogens were used to achieve valence saturation at the edges of the cluster models. The construction of model structures was based on a thorough bonding analysis which involved conventional DFT and local coupled cluster (DLPNO-CCSD(T)) methods. Furthermore the relationship of cluster topology to the computed spectral features is discussed in detail. It is shown that due to the local nature of the involved electronic transitions, band assignment protocols developed for molecular systems can be applied to describe the calculated spectral features of the cluster models as well. The present study serves as a reference for future applications of combined experimental and computational protocols in the field of solid-state heterogeneous catalysis.

Rotational symmetry breaking toward a string-valence bond solid phase in frustrated J1 -J2 transverse field Ising model

NASA Astrophysics Data System (ADS)

Sadrzadeh, M.; Langari, A.

2018-06-01

We study the effect of quantum fluctuations by means of a transverse magnetic field (Γ) on the highly degenerate ground state of antiferromagnetic J1 -J2 Ising model on the square lattice, at the limit J2 /J1 = 0.5 . We show that harmonic quantum fluctuations based on single spin flips can not lift such degeneracy, however an-harmonic quantum fluctuations based on multi spin cluster flip excitations lift the degeneracy toward a unique ground state with string-valence bond solid (VBS) nature. A cluster operator formalism has been implemented to incorporate an-harmonic quantum fluctuations. We show that cluster-type excitations of the model lead not only to lower the excitation energy compared with a single-spin flip but also to lift the extensive degeneracy in favor of a string-VBS state, which breaks lattice rotational symmetry with only two fold degeneracy. The tendency toward the broken symmetry state is justified by numerical exact diagonalization. Moreover, we introduce a map to find the relation between the present model on the checkerboard and square lattices.

Recent developments in the kinetic theory of nucleation.

PubMed

Ruckenstein, E; Djikaev, Y S

2005-12-30

A review of recent progress in the kinetics of nucleation is presented. In the conventional approach to the kinetic theory of nucleation, it is necessary to know the free energy of formation of a new-phase particle as a function of its independent variables at least for near-critical particles. Thus the conventional kinetic theory of nucleation is based on the thermodynamics of the process. The thermodynamics of nucleation can be examined by using various approaches, such as the capillarity approximation, density functional theory, and molecular simulation, each of which has its own advantages and drawbacks. Relatively recently a new approach to the kinetics of nucleation was proposed [Ruckenstein E, Nowakowski B. J Colloid Interface Sci 1990;137:583; Nowakowski B, Ruckenstein E. J Chem Phys 1991;94:8487], which is based on molecular interactions and does not employ the traditional thermodynamics, thus avoiding such a controversial notion as the surface tension of tiny clusters involved in nucleation. In the new kinetic theory the rate of emission of molecules by a new-phase particle is determined with the help of a mean first passage time analysis. This time is calculated by solving the single-molecule master equation for the probability distribution function of a surface layer molecule moving in a potential field created by the rest of the cluster. The new theory was developed for both liquid-to-solid and vapor-to-liquid phase transitions. In the former case the single-molecule master equation is the Fokker-Planck equation in the phase space which can be reduced to the Smoluchowski equation owing to the hierarchy of characteristic time scales. In the latter case, the starting master equation is a Fokker-Planck equation for the probability distribution function of a surface layer molecule with respect to both its energy and phase coordinates. Unlike the case of liquid-to-solid nucleation, this Fokker-Planck equation cannot be reduced to the Smoluchowski equation, but the hierarchy of time scales does allow one to reduce it to the Fokker-Plank equation in the energy space. The new theory provides an equation for the critical radius of a new-phase particle which in the limit of large clusters (low supersaturations) yields the Kelvin equation and hence an expression for the macroscopic surface tension. The theory was illustrated with numerical calculations for a molecular pair interaction potential combining the dispersive attraction with the hard-sphere repulsion. The results for the liquid-to-solid nucleation clearly show that at given supersaturation the nucleation rate depends on the cluster structure (for three cluster structures considered-amorphous, fcc, and icosahedral). For both the liquid-to-solid and vapor-to-liquid nucleation, the predictions of the theory are consistent with the results of classical nucleation theory (CNT) in the limit of large critical clusters (low supersaturations). For small critical clusters the new theory provides higher nucleation rates than CNT. This can be accounted for by the fact that CNT uses the macroscopic interfacial tension which presumably overpredicts the surface tension of small clusters, and hence underpredicts nucleation rates.

Truncated Dual-Cap Nucleation Site Development

NASA Technical Reports Server (NTRS)

Matson, Douglas M.; Sander, Paul J.

2012-01-01

During heterogeneous nucleation within a metastable mushy-zone, several geometries for nucleation site development must be considered. Traditional spherical dual cap and crevice models are compared to a truncated dual cap to determine the activation energy and critical cluster growth kinetics in ternary Fe-Cr-Ni steel alloys. Results of activation energy results indicate that nucleation is more probable at grain boundaries within the solid than at the solid-liquid interface.

Synthesis, characterization, and tuning of the liquid crystal properties of ionic materials based on the cyclic polyoxothiometalate [{Mo4O4S4(H2O)3(OH)2}2(P8W48O184)](36-).

PubMed

Watfa, Nancy; Floquet, Sébastien; Terazzi, Emmanuel; Haouas, Mohamed; Salomon, William; Korenev, Vladimir S; Taulelle, Francis; Guénée, Laure; Hijazi, Akram; Naoufal, Daoud; Piguet, Claude; Cadot, Emmanuel

2015-02-14

A series of compounds resulting from the ionic association of a nanoscopic inorganic cluster of formula [K2NaxLiy{Mo4O4S4(OH)2(H2O)3}2(HzP8W48O184)]((34-x-y-z)-), 1, with several organic cations such as dimethyldioctadecylammonium DODA(+), trimethylhexadecylammonium TMAC16(+), alkylmethylimidazoliums mimCn(+) (n = 12-20) and alkyl-dimethylimidazoliums dmimCn(+) (n = 12 and 16) was prepared and characterized in the solid state by FT-IR, EDX, Elemental analysis, TGA and solid state NMR. The solid state NMR experiments performed on (1)H, (13)C and (31)P nuclei evidenced the interactions between the cations and 1 as well as the organization of the alkyl chains of the cations within the solid. Polarized optical microscopy, DSC and SA-XRD experiments implicated mesomorphic phases for DODA(+) and mimCn(+) salts of 1. The crystallographic parameters were determined and demonstrated that the inter-lamellar spacing could be controlled upon changing the length of the alkyl chain, a very interesting result if we consider the huge size of the inorganic cluster 1 and the simple nature of the cations.

CO2 in solid para-hydrogen: spectral splitting and the CO2···(o-H2)n clusters.

PubMed

Du, Jun-He; Wan, Lei; Wu, Lei; Xu, Gang; Deng, Wen-Ping; Liu, An-Wen; Chen, Yang; Hu, Shui-Ming

2011-02-17

Complicated high-resolution spectral structures are often observed for molecules doped in solid molecular hydrogen. The structures can result from miscellaneous effects and are often interpreted differently in references. The spectrum of the ν(3) band of CO(2) in solid para-H(2) presents a model system which exhibits rich spectral structures. With the help of the potential energy simulation of the CO(2) molecule doped in para-hydrogen matrix, and extensive experiments with different CO(2) isotopologues and different ortho-hydrogen concentrations in the matrix, the spectral features observed in p-H(2) matrix are assigned to the CO(2)···(o-H(2))(n) clusters and also to energy level splitting that is due to different alignments of the doped CO(2) molecules in the matrix. The assignments are further supported by the dynamics analysis and also by the spectrum recorded with sample codoped with O(2) which serves as catalyst transferring o-H(2) to p-H(2) in the matrix at 4 K temperature. The observed spectral features of CO(2)/pH(2) can potentially be used as an alternative readout of the temperature and orthohydrogen concentration in the solid para-hydrogen.

Cluster A personality pathology in social anxiety disorder: a comparison with panic disorder.

PubMed

O'Toole, Mia Skytte; Arendt, Mikkel; Fentz, Hanne Nørr; Hougaard, Esben; Rosenberg, Nicole K

2014-10-01

Social anxiety disorder (SAD) has been associated with cluster A personality disorder (PD) traits, mainly paranoid and schizoid traits. The aim of the study was to further investigate cluster A personality pathology in patients with SAD. Self-reported PD traits were investigated in a clinical sample of 161 participants with SAD and in a clinical comparison group of 145 participants with panic disorder with or without agoraphobia (PAD). A diagnosis of SAD was associated with more paranoid and schizotypal PD traits, and an association between depression and personality pathology could indicate a state-effect of depression on PD traits. Patients with SAD had more cluster A personality pathology than patients with PAD, with the most solid indication for paranoid personality pathology.

Simulation of hydrodynamics using large eddy simulation-second-order moment model in circulating fluidized beds

NASA Astrophysics Data System (ADS)

Juhui, Chen; Yanjia, Tang; Dan, Li; Pengfei, Xu; Huilin, Lu

2013-07-01

Flow behavior of gas and particles is predicted by the large eddy simulation of gas-second order moment of solid model (LES-SOM model) in the simulation of flow behavior in CFB. This study shows that the simulated solid volume fractions along height using a two-dimensional model are in agreement with experiments. The velocity, volume fraction and second-order moments of particles are computed. The second-order moments of clusters are calculated. The solid volume fraction, velocity and second order moments are compared at the three different model constants.

Structural, thermodynamic, and mechanical properties of WCu solid solutions

NASA Astrophysics Data System (ADS)

Liang, C. P.; Wu, C. Y.; Fan, J. L.; Gong, H. R.

2017-11-01

Various properties of Wsbnd Cu solid solutions are systematically investigated through a combined use of first-principles calculation, cluster expansion, special quasirandom structures (SQS), and lattice dynamics. It is shown that SQS are effective to unravel the intrinsic nature of solid solutions, and that BCC and FCC W100-xCux solid solutions are energetically more stable when 0 ≤ x ≤ 70 and 70 < x ≤ 100, respectively. Calculations also reveal that the Debye model should be appropriate to derive thermodynamic properties of Wsbnd Cu, and that the coefficients of thermal expansion of W100-xCux solid solutions are much lower than those of corresponding mechanical mixtures. In addition, the G/B values of W100-xCux solid solutions reach a minimum at x = 50, which is fundamentally due to the softening of phonons as well as strong chemical bonding between W and Cu with a mainly metallic feature.

Structural characterization of a magnetic granular system under a time-dependent magnetic field: Voronoi tessellation and multifractal analysis

NASA Astrophysics Data System (ADS)

Moctezuma, R. E.; Arauz-Lara, J. L.; Donado, F.

2018-04-01

The structure of a two-dimensional magnetic granular system was determined by multifractal and Voronoi polygon analysis for a wide range of particle concentrations. Randomizing of the particle motions are produced by applying to the system a time-dependent sinusoidal magnetic field directed along the vertical direction. Both repulsive and attractive short-range interactions between the particles are induced. A direct observation of such system shows qualitatively that, as particle concentration increases, the structure evolves from being liquid-like at low particle concentrations to solid-like at high concentrations. We observe the formation of clusters which are small and weakly bonded and short-lived at low concentrations. Above a threshold particle concentration, clusters grow larger and are more strongly attached. In the system, one can distinguish the mobile particles from the immobile particles belonging to clusters, they can be considered separately as two different phases, a fluid and a solid. We determined the information entropy of the system as a whole and separately from each phase as particle concentration increases. The distribution of the Voronoi polygon areas are well fitted by a two-parameter gamma distribution and we have found that the regularity factor shows a notable change when pieces of the solid phase start to form. The methods we use here show that they can use even when the system is heterogeneous and they provide information when changes start.

Uranyl peroxide nanoclusters at high-pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turner, Katlyn M.; Szymanowski, Jennifer E. S.; Zhang, Fuxiang

Here, U 60 ([UO 2(O 2)(OH)] 60 60– in water) is a uranyl peroxide nanocluster with a fullerene topology and O h symmetry. U 60 clusters can exist in crystalline solids or in liquids; however, little is known of their behavior at high pressures. We compressed the U 60-bearing material: Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 ( Fm3¯; a = 37.884 Å) in a diamond anvil cell to determine its response to increasing pressure. Three length scales and corresponding structural features contribute to the compression response: uranyl peroxide bonds (<0.5 nm), isolated single nanoclusters (2.5 nm), andmore » the long-range periodicity of nanoclusters within the solid (>3.7 nm). Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 transformed to a tetragonal structure below 2 GPa and irreversibly amorphized between 9.6 and 13 GPa. The bulk modulus of the tetragonal U 60-bearing material was 25 ± 2 GPa. The pressure-induced amorphous phase contained intact U 60 clusters, which were preserved beyond the loss of long-range periodicity. The persistence of U 60 clusters at high pressure may have been enhanced by the interaction between U 60 nanoclusters and the alcohol pressure medium. Once formed, U 60 nanoclusters persist regardless of their associated long-range ordering—in crystals, amorphous solids, or solutions.« less

Electron spin resonance study of atomic hydrogen stabilized in solid neon below 1 K

NASA Astrophysics Data System (ADS)

Sheludiakov, S.; Ahokas, J.; Järvinen, J.; Lehtonen, L.; Vasiliev, S.; Dmitriev, Yu. A.; Lee, D. M.; Khmelenko, V. V.

2018-03-01

We report on an electron spin resonance study of atomic hydrogen stabilized in solid Ne matrices carried out at a high field of 4.6 T and temperatures below 1 K . The films of Ne, slowly deposited on the substrate at a temperature of ˜1 K , exhibited a high degree of porosity. We found that H atoms may be trapped in two different substitutional positions in the Ne lattice as well as inside clusters of pure molecular H2 in the pores of the Ne film. The latter type of atoms was very unstable against recombination at temperatures 0.3-0.6 K . Based on the observed nearly instant decays after rapid small increases of temperature, we evaluate the lower limit of the recombination rate constant kr≥5 ×10-20cm3s-1 at 0.6 K , five orders of magnitude larger than that previously found in the thin films of pure H2 at the same temperature. Such behavior assumes a very high mobility of atoms and may indicate a solid-to-liquid transition for H2 clusters of certain sizes, similar to that observed in experiments with H2 clusters inside helium droplets [Phys. Rev. Lett. 101, 205301 (2008), 10.1103/PhysRevLett.101.205301]. We found that the efficiency of dissociation of H2 in neon films is enhanced by two orders of magnitude compared to that in pure H2 as a result of the strong action of secondary electrons.

Uranyl peroxide nanoclusters at high-pressure

DOE PAGES

Turner, Katlyn M.; Szymanowski, Jennifer E. S.; Zhang, Fuxiang; ...

2017-08-14

Here, U 60 ([UO 2(O 2)(OH)] 60 60– in water) is a uranyl peroxide nanocluster with a fullerene topology and O h symmetry. U 60 clusters can exist in crystalline solids or in liquids; however, little is known of their behavior at high pressures. We compressed the U 60-bearing material: Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 ( Fm3¯; a = 37.884 Å) in a diamond anvil cell to determine its response to increasing pressure. Three length scales and corresponding structural features contribute to the compression response: uranyl peroxide bonds (<0.5 nm), isolated single nanoclusters (2.5 nm), andmore » the long-range periodicity of nanoclusters within the solid (>3.7 nm). Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 transformed to a tetragonal structure below 2 GPa and irreversibly amorphized between 9.6 and 13 GPa. The bulk modulus of the tetragonal U 60-bearing material was 25 ± 2 GPa. The pressure-induced amorphous phase contained intact U 60 clusters, which were preserved beyond the loss of long-range periodicity. The persistence of U 60 clusters at high pressure may have been enhanced by the interaction between U 60 nanoclusters and the alcohol pressure medium. Once formed, U 60 nanoclusters persist regardless of their associated long-range ordering—in crystals, amorphous solids, or solutions.« less

Quantum model of a solid-state spin qubit: Ni cluster on a silicon surface by the generalized spin Hamiltonian and X-ray absorption spectroscopy investigations

NASA Astrophysics Data System (ADS)

Farberovich, Oleg V.; Mazalova, Victoria L.; Soldatov, Alexander V.

2015-11-01

We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density-functional scheme for the calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange coupling parameters linking the nickel ions with a silicon substrate. In this model the interaction of a spin qubit with substrate is considered in GSH at the calculation of exchange integrals Jij of the nanosystem Ni7-Si in the one-electron approach taking into account chemical bonds of all Si-atoms of a substrate (environment) with atoms of the Ni7-cluster. The energy pattern was found from the effective GSH Hamiltonian acting in the restricted spin space of the Ni ions by the application of the irreducible tensor operators (ITO) technique. In this paper we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on the silicon surface. The solution of the problem of the entanglement between spin states in the N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement (DOE). In this study we have developed and used the advanced high-precision numerical techniques to accurately assess the details of the decoherence process governing the dynamics of the N-spin qubits interacting with a silicon surface. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time (0.327 μs). The comparison of the energy pattern with the anisotropic exchange models conventionally used for the analysis of this system and, with the results of the experimental XANES spectra, shows that our complex investigations provide a good description of the pattern of the spin levels and the spin structures of the nanomagnetic Ni7 qubit. The results are discussed in the view of the general problem of the solid-state spin qubits and the spin structure of the Ni cluster.

Packing the silica colloidal crystal beads: a facile route to superhydrophobic surfaces.

PubMed

Sun, Cheng; Gu, Zhong-Ze; Xu, Hua

2009-11-03

To mimic the structure of the lotus leaf, we present a facile route to prepare superhydrophobic surfaces by depositing nanoparticle clusters onto a solid surface. These clusters were fabricated via solidification of an emulsion droplet containing a nanoparticle in silicone oil. Thus, the microsized clusters and nanoparticles form dual-scale roughness structures. The surface is modified by fluoroalkylsilane and exhibits superhydrophobicity, with a contact angle greater than 165 degrees as well as a sliding angle less than 1 degrees . On the basis of size tuning of the nano/microstructures, various contact angles and sliding angles were investigated. Furthermore, the influence of micro/nanostructures on superhydrophobicity is discussed.

Postcollision interaction in noble gas clusters: observation of differences in surface and bulk line shapes.

PubMed

Lindblad, A; Fink, R F; Bergersen, H; Lundwall, M; Rander, T; Feifel, R; Ohrwall, G; Tchaplyguine, M; Hergenhahn, U; Svensson, S; Björneholm, O

2005-12-01

The surface and bulk components of the x-ray photoelectron spectra of free noble gas clusters are shown to display differences in the influence of postcollision interaction between the photoelectron and the Auger electron on the spectral line shape; the bulk component is observed to be less affected than the surface and atomic parts of the spectra. A model for postcollision interaction in nonmetallic solids and clusters is also provided which takes the polarization screening into account. Core-level photoelectron spectra of Ar, Kr, and Xe have been recorded to verify the dependence of the postcollision interaction effect on the polarizability of the sample.

Vent modification of large ribbon parachutes to enhance cluster performance

NASA Technical Reports Server (NTRS)

Kolega, D. J.; Woodis, W. R.; Reuter, J. D.

1986-01-01

Due to uneven load sharing and lagging inflation rates, the design of the Large Main Parachute (LMP) cluster, used to recover the Space Shuttle steel case Solid Rocket Boosters, had to be modified. The cause of the problem was excessive variation in effective porosity in the crown area of the LMP during first stage inflation. The design modification consisted of adding horizontal ribbons above the existing vent band to reduce the vent porosity and better control the position and attitude of the vent lines. Performance of modified LMP's since introduction indicates that the load sharing between the clustered chutes has been significantly improved.

Giant Spherical Cluster with I-C140 Fullerene Topology**

PubMed Central

Heinl, Sebastian; Peresypkina, Eugenia; Sutter, Jörg; Scheer, Manfred

2015-01-01

We report on an effective cluster expansion of CuBr-linked aggregates by the increase of the steric bulk of the CpR ligand in the pentatopic molecules [CpRFe(η5-P5)]. Using [CpBIGFe(η5-P5)] (CpBIG=C5(4-nBuC6H4)5), the novel multishell aggregate [{CpBIGFe(η5:2:1:1:1:1:1-P5)}12(CuBr)92] is obtained. It shows topological analogy to the theoretically predicted I-C140 fullerene molecule. The spherical cluster was comprehensively characterized by various methods in solution and in the solid state. PMID:26411255

Metal-atom Interactions and Clustering in Organic Semiconductor Systems

NASA Astrophysics Data System (ADS)

Tomita, Yoko; Park, Tea-uk; Nakayama, Takashi

2017-07-01

The interatomic interactions and clustering of metal atoms have been studied by first-principles calculations in graphene, pentacene, and polyacetylene as representative organic systems. It is shown that long-range repulsive Coulomb interaction appears between metal atoms with small electronegativity such as Al due to their ionization on host organic molecules, inducing their scattered distribution in organic systems. On the other hand, metal atoms with large electronegativity such as Au are weakly bonded to organic molecules, easily diffuse in molecular solids, and prefer to combine with each other owing to their short-range strong metallic-bonding interaction, promoting metal cluster generation in organic systems.

Polymorphism of Ag29(BDT)12(TPP)43- cluster: interactions of secondary ligands and their effect on solid state luminescence.

PubMed

Nag, Abhijit; Chakraborty, Papri; Bodiuzzaman, Mohammad; Ahuja, Tripti; Antharjanam, Sudhadevi; Pradeep, Thalappil

2018-05-31

We present the first example of polymorphism (cubic & trigonal) in single crystals of an atomically precise monolayer protected cluster, Ag29(BDT)12(TPP)43-. We demonstrate that C-Hπ interactions of the secondary ligands (TPP) are dominant in a cubic lattice compared to a trigonal lattice, resulting in a greater rigidity of the structure, which in turn, results in a higher luminescence efficiency in it.

Assessing the capability of continuum and discrete particle methods to simulate gas-solids flow using DNS predictions as a benchmark

DOE PAGES

Lu, Liqiang; Liu, Xiaowen; Li, Tingwen; ...

2017-08-12

For this study, gas–solids flow in a three-dimension periodic domain was numerically investigated by direct numerical simulation (DNS), computational fluid dynamic-discrete element method (CFD-DEM) and two-fluid model (TFM). DNS data obtained by finely resolving the flow around every particle are used as a benchmark to assess the validity of coarser DEM and TFM approaches. The CFD-DEM predicts the correct cluster size distribution and under-predicts the macro-scale slip velocity even with a grid size as small as twice the particle diameter. The TFM approach predicts larger cluster size and lower slip velocity with a homogeneous drag correlation. Although the slip velocitymore » can be matched by a simple modification to the drag model, the predicted voidage distribution is still different from DNS: Both CFD-DEM and TFM over-predict the fraction of particles in dense regions and under-predict the fraction of particles in regions of intermediate void fractions. Also, the cluster aspect ratio of DNS is smaller than CFD-DEM and TFM. Since a simple correction to the drag model can predict a correct slip velocity, it is hopeful that drag corrections based on more elaborate theories that consider voidage gradient and particle fluctuations may be able to improve the current predictions of cluster distribution.« less

Constrained Sintering in Fabrication of Solid Oxide Fuel Cells

PubMed Central

Lee, Hae-Weon; Park, Mansoo; Hong, Jongsup; Kim, Hyoungchul; Yoon, Kyung Joong; Son, Ji-Won; Lee, Jong-Ho; Kim, Byung-Kook

2016-01-01

Solid oxide fuel cells (SOFCs) are inevitably affected by the tensile stress field imposed by the rigid substrate during constrained sintering, which strongly affects microstructural evolution and flaw generation in the fabrication process and subsequent operation. In the case of sintering a composite cathode, one component acts as a continuous matrix phase while the other acts as a dispersed phase depending upon the initial composition and packing structure. The clustering of dispersed particles in the matrix has significant effects on the final microstructure, and strong rigidity of the clusters covering the entire cathode volume is desirable to obtain stable pore structure. The local constraints developed around the dispersed particles and their clusters effectively suppress generation of major process flaws, and microstructural features such as triple phase boundary and porosity could be readily controlled by adjusting the content and size of the dispersed particles. However, in the fabrication of the dense electrolyte layer via the chemical solution deposition route using slow-sintering nanoparticles dispersed in a sol matrix, the rigidity of the cluster should be minimized for the fine matrix to continuously densify, and special care should be taken in selecting the size of the dispersed particles to optimize the thermodynamic stability criteria of the grain size and film thickness. The principles of constrained sintering presented in this paper could be used as basic guidelines for realizing the ideal microstructure of SOFCs. PMID:28773795

Assessing the capability of continuum and discrete particle methods to simulate gas-solids flow using DNS predictions as a benchmark

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Liqiang; Liu, Xiaowen; Li, Tingwen

For this study, gas–solids flow in a three-dimension periodic domain was numerically investigated by direct numerical simulation (DNS), computational fluid dynamic-discrete element method (CFD-DEM) and two-fluid model (TFM). DNS data obtained by finely resolving the flow around every particle are used as a benchmark to assess the validity of coarser DEM and TFM approaches. The CFD-DEM predicts the correct cluster size distribution and under-predicts the macro-scale slip velocity even with a grid size as small as twice the particle diameter. The TFM approach predicts larger cluster size and lower slip velocity with a homogeneous drag correlation. Although the slip velocitymore » can be matched by a simple modification to the drag model, the predicted voidage distribution is still different from DNS: Both CFD-DEM and TFM over-predict the fraction of particles in dense regions and under-predict the fraction of particles in regions of intermediate void fractions. Also, the cluster aspect ratio of DNS is smaller than CFD-DEM and TFM. Since a simple correction to the drag model can predict a correct slip velocity, it is hopeful that drag corrections based on more elaborate theories that consider voidage gradient and particle fluctuations may be able to improve the current predictions of cluster distribution.« less

Analysis of S-band solid-state transmitters for the solar power satellite

NASA Technical Reports Server (NTRS)

Belohoubek, E. F.; Ettenberg, M.; Huang, H. C.; Nowogrodzki, M.; Sechi, F. N.

1979-01-01

The possibility of replacing the Reference System antenna in which thermionic devices are used for the dc-to-microwave conversion, with solid-state elements was explored. System, device, and antenna module tradeoff investigations strongly point toward the desirability of changing the transmitter concept to a distributed array of relatively low power elements, deriving their dc power directly from the solar cell array and whose microwave power outputs are combined in space. The approach eliminates the thermal, weight, and dc-voltage distribution problems of a system in which high power tubes are simply replaced with clusters of solid state amplifiers. The proposed approach retains the important advantages of a solid state system: greatly enhanced reliability and graceful degradation of the system.

Group additivity-Pourbaix diagrams advocate thermodynamically stable nanoscale clusters in aqueous environments

PubMed Central

Wills, Lindsay A.; Qu, Xiaohui; Chang, I-Ya; Mustard, Thomas J. L.; Keszler, Douglas A.; Persson, Kristin A.; Cheong, Paul Ha-Yeon

2017-01-01

The characterization of water-based corrosion, geochemical, environmental and catalytic processes rely on the accurate depiction of stable phases in a water environment. The process is aided by Pourbaix diagrams, which map the equilibrium solid and solution phases under varying conditions of pH and electrochemical potential. Recently, metastable or possibly stable nanometric aqueous clusters have been proposed as intermediate species in non-classical nucleation processes. Herein, we describe a Group Additivity approach to obtain Pourbaix diagrams with full consideration of multimeric cluster speciation from computations. Comparisons with existing titration results from experiments yield excellent agreement. Applying this Group Additivity-Pourbaix approach to Group 13 elements, we arrive at a quantitative evaluation of cluster stability, as a function of pH and concentration, and present compelling support for not only metastable but also thermodynamically stable multimeric clusters in aqueous solutions. PMID:28643782

Mechanical gate control for atom-by-atom cluster assembly with scanning probe microscopy.

PubMed

Sugimoto, Yoshiaki; Yurtsever, Ayhan; Hirayama, Naoki; Abe, Masayuki; Morita, Seizo

2014-07-11

Nanoclusters supported on substrates are of great importance in physics and chemistry as well as in technical applications, such as single-electron transistors and nanocatalysts. The properties of nanoclusters differ significantly from those of either the constituent atoms or the bulk solid, and are highly sensitive to size and chemical composition. Here we propose a novel atom gating technique to assemble various atom clusters composed of a defined number of atoms at room temperature. The present gating operation is based on the transfer of single diffusing atoms among nanospaces governed by gates, which can be opened in response to the chemical interaction force with a scanning probe microscope tip. This method provides an alternative way to create pre-designed atom clusters with different chemical compositions and to evaluate their chemical stabilities, thus enabling investigation into the influence that a single dopant atom incorporated into the host clusters has on a given cluster stability.

Group additivity-Pourbaix diagrams advocate thermodynamically stable nanoscale clusters in aqueous environments

NASA Astrophysics Data System (ADS)

Wills, Lindsay A.; Qu, Xiaohui; Chang, I.-Ya; Mustard, Thomas J. L.; Keszler, Douglas A.; Persson, Kristin A.; Cheong, Paul Ha-Yeon

2017-06-01

The characterization of water-based corrosion, geochemical, environmental and catalytic processes rely on the accurate depiction of stable phases in a water environment. The process is aided by Pourbaix diagrams, which map the equilibrium solid and solution phases under varying conditions of pH and electrochemical potential. Recently, metastable or possibly stable nanometric aqueous clusters have been proposed as intermediate species in non-classical nucleation processes. Herein, we describe a Group Additivity approach to obtain Pourbaix diagrams with full consideration of multimeric cluster speciation from computations. Comparisons with existing titration results from experiments yield excellent agreement. Applying this Group Additivity-Pourbaix approach to Group 13 elements, we arrive at a quantitative evaluation of cluster stability, as a function of pH and concentration, and present compelling support for not only metastable but also thermodynamically stable multimeric clusters in aqueous solutions.

Electronic effects on melting: Comparison of aluminum cluster anions and cations

NASA Astrophysics Data System (ADS)

Starace, Anne K.; Neal, Colleen M.; Cao, Baopeng; Jarrold, Martin F.; Aguado, Andrés; López, José M.

2009-07-01

Heat capacities have been measured as a function of temperature for aluminum cluster anions with 35-70 atoms. Melting temperatures and latent heats are determined from peaks in the heat capacities; cohesive energies are obtained for solid clusters from the latent heats and dissociation energies determined for liquid clusters. The melting temperatures, latent heats, and cohesive energies for the aluminum cluster anions are compared to previous measurements for the corresponding cations. Density functional theory calculations have been performed to identify the global minimum energy geometries for the cluster anions. The lowest energy geometries fall into four main families: distorted decahedral fragments, fcc fragments, fcc fragments with stacking faults, and "disordered" roughly spherical structures. The comparison of the cohesive energies for the lowest energy geometries with the measured values allows us to interpret the size variation in the latent heats. Both geometric and electronic shell closings contribute to the variations in the cohesive energies (and latent heats), but structural changes appear to be mainly responsible for the large variations in the melting temperatures with cluster size. The significant charge dependence of the latent heats found for some cluster sizes indicates that the electronic structure can change substantially when the cluster melts.

Synthesis and structure of an extended cluster lead(II) carboxylate, [Pb((CO){sub 9}Co{sub 3}({mu}{sub 3}-CCO{sub 2})){sub 2}]{sub n}. Role of core metals in cluster-derived hydrogenation catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xinjian Lei; Maoyu Shang; Fehlner, T.P.

The reaction of lead acetate with (CO){sub 9}Co{sub 3}({mu}{sub 3}-CCOOH) leads to the formation of [Pb((CO){sub 9}Co{sub 3}({mu}{sub 3}-CCO{sub 2})){sub 2}]{sub n}, I, in high yield. The structure of I exhibits unusual six-coordinate Pb(II) centers with two asymmetrical chelating cluster carboxylates (C{sub 22}Co{sub 6}PbO{sub 22}; triclinic P1; a = 8.119(1), b = 14.346(2), c = 14.660(2) {Angstrom}; {alpha} = 102.18(1), {beta} = 99.01(1), {gamma} = 97.30(1){degrees}; Z = 2). One oxygen of each cluster carboxylate ligand bridges between adjacent lead atoms such that a chainlike extended structure is found in the solid state without the presence of solvent or water.more » I is converted stepwide on pyrolysis into two metastable forms of solid materials (designated LT and HT), each of which has been characterized spectroscopically. The hydrogenation of 2-butenal as a test reaction shows that the LT catalyst exhibits selectivities similar to previous LT materials derived from other cobalt cluster metal carboxylates and that the HT material is totally inactive. The observed release of the lead core metal under HT activation conditions totally inactivates the catalyst and demonstrates exposure of the core metal in the HT form of these novel catalysts.« less

Study of methods to increase cluster/dislocation loop densities in electrodes

NASA Astrophysics Data System (ADS)

Yang, Xiaoling; Miley, George H.

2009-03-01

Recent research has developed a technique for imbedding ultra-high density deuterium ``clusters'' (50 to 100 atoms per cluster) in various metals such as Palladium (Pd), Beryllium (Be) and Lithium (Li). It was found the thermally dehydrogenated PdHx retained the clusters and exhibited up to 12 percent lower resistance compared to the virginal Pd samplesootnotetextA. G. Lipson, et al. Phys. Solid State. 39 (1997) 1891. SQUID measurements showed that in Pd these condensed matter clusters approach metallic conditions, exhibiting superconducting propertiesootnotetextA. Lipson, et al. Phys. Rev. B 72, 212507 (2005ootnotetextA. G. Lipson, et al. Phys. Lett. A 339, (2005) 414-423. If the fabrication methods under study are successful, a large packing fraction of nuclear reactive clusters can be developed in the electrodes by electrolyte or high pressure gas loading. This will provide a much higher low-energy-nuclear- reaction (LENR) rate than achieved with earlier electrodeootnotetextCastano, C.H., et al. Proc. ICCF-9, Beijing, China 19-24 May, 2002..

Why are para-hydrogen clusters superfluid? A quantum theorem of corresponding states study.

PubMed

Sevryuk, Mikhail B; Toennies, J Peter; Ceperley, David M

2010-08-14

The quantum theorem of corresponding states is applied to N=13 and N=26 cold quantum fluid clusters to establish where para-hydrogen clusters lie in relation to more and less quantum delocalized systems. Path integral Monte Carlo calculations of the energies, densities, radial and pair distributions, and superfluid fractions are reported at T=0.5 K for a Lennard-Jones (LJ) (12,6) potential using six different de Boer parameters including the accepted value for hydrogen. The results indicate that the hydrogen clusters are on the borderline to being a nonsuperfluid solid but that the molecules are sufficiently delocalized to be superfluid. A general phase diagram for the total and kinetic energies of LJ (12,6) clusters encompassing all sizes from N=2 to N=infinity and for the entire range of de Boer parameters is presented. Finally the limiting de Boer parameters for quantum delocalization induced unbinding ("quantum unbinding") are estimated and the new results are found to agree with previous calculations for the bulk and smaller clusters.

X-ray emission from clusters of galaxies

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.

1983-01-01

Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlations between X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or KT and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores of several clusters is discussed based on spectral observations with the Einstein solid state spectrometer.

Structure and dynamics of ND3BF3 in the solid and gas phases: a combined NMR, neutron diffraction, and Ab initio study.

PubMed

Penner, Glenn H; Ruscitti, Bruno; Reynolds, Julie; Swainson, Ian

2002-12-30

The decrease in D-->A bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND(3)BF(3) by powder neutron diffraction. The B-N internuclear distance is 1.554(3) A, 0.118 A shorter than the most recent gas-phase microwave value and 0.121 A shorter than the single molecule geometry optimized (1.672 A, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D.F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen ((15)N and (14)N) and boron ((11)B and (10)B) chemical shifts should be rather insensitive to changes in r(BN) and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the (11)B and (14)N QCCs show large changes because of both effects. An analysis of the (10)B[(19)F] line shape in solid ND(3)(10)BF(3) yields a (11)B QCC of +/-0.130 MHz. This is reasonably close an earlier value of +/-0.080 MHz and the value of +/-0.050 MHz calculated for a [NH(3)BF(3)](4) cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T(1) measurements yield an activation energy for rotation of the ND(3) group in solid ND(3)BF(3) of 9.5 +/- 0.1 kJ/mol. Simulations of the temperature-dependent T(1) anisotropy gave an E(a) of 9.5 +/- 0.2 kJ/mol and a preexponential factor, A, of 3.0 +/- 0.1 x 10(12) s(-)(1). Our calculated value for a [NH(3)BF(3)](4) cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T(1) measurements.

Compact near-IR and mid-IR cavity ring down spectroscopy device

NASA Technical Reports Server (NTRS)

Miller, J. Houston (Inventor)

2011-01-01

This invention relates to a compact cavity ring down spectrometer for detection and measurement of trace species in a sample gas using a tunable solid-state continuous-wave mid-infrared PPLN OPO laser or a tunable low-power solid-state continuous wave near-infrared diode laser with an algorithm for reducing the periodic noise in the voltage decay signal which subjects the data to cluster analysis or by averaging of the interquartile range of the data.

D2O clusters isolated in rare-gas solids: Dependence of infrared spectrum on concentration, deposition rate, heating temperature, and matrix material

NASA Astrophysics Data System (ADS)

Shimazaki, Yoichi; Arakawa, Ichiro; Yamakawa, Koichiro

2018-04-01

The infrared absorption spectra of D2O monomers and clusters isolated in rare-gas matrices were systematically reinvestigated under the control of the following factors: the D2O concentration, deposition rate, heating temperature, and rare-gas species. We clearly show that the cluster-size distribution is dependent on not only the D2O concentration but also the deposition rate of a sample; as the rate got higher, smaller clusters were preferentially formed. Under the heating procedures at different temperatures, the cluster-size growth was successfully observed. Since the monomer diffusion was not enough to balance the changes in the column densities of the clusters, the dimer diffusion was likely to contribute the cluster growth. The frequencies of the bonded-OD stretches of (D2O)k with k = 2-6 were almost linearly correlated with the square root of the critical temperature of the matrix material. Additional absorption peaks of (D2O)2 and (D2O)3 in a Xe matrix were assigned to the species trapped in tight accommodation sites.

Stepwise assembly of a semiconducting coordination polymer [Cd8S(SPh)14(DMF)(bpy)]n and its photodegradation of organic dyes.

PubMed

Xu, Chao; Hedin, Niklas; Shi, Hua-Tian; Xin, ZhiFeng; Zhang, Qian-Feng

2015-04-14

Chalcogenolate clusters can be interlinked with organic linkers into semiconducting coordination polymers with photocatalytic properties. Here, discrete clusters of Cd8S(SPh)14(DMF)3 were interlinked with 4,4'-bipyridine into a one dimensional coordination polymer of [Cd8S(SPh)14(DMF)(bpy)]n with helical chains. A stepwise mechanism for the assembly of the coordination polymer in DMF was revealed by an ex situ dynamic light scattering study. The cluster was electrostatically neutral and showed a penta-supertetrahedral structure. During the assembly each cluster was interlinked with two 4,4'-bipyridine molecules, which replaced the two terminal DMF molecules of the clusters. In their solid-state forms, the cluster and the coordination polymer were semiconductors with wide band gaps of 3.08 and 2.80 ev. They photocatalytically degraded rhodamine B and methylene blue in aqueous solutions. The moderate conditions used for the synthesis could allow for further in situ studies of the reaction-assembly of related clusters and coordination polymers.

Role of distortion in the hcp vs fcc competition in rare-gas solids

NASA Astrophysics Data System (ADS)

Krainyukova, N. V.

2011-05-01

As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.

Free energy reconstruction from steered dynamics without post-processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Athenes, Manuel, E-mail: Manuel.Athenes@cea.f; Condensed Matter and Materials Division, Physics and Life Sciences Directorate, LLNL, Livermore, CA 94551; Marinica, Mihai-Cosmin

2010-09-20

Various methods achieving importance sampling in ensembles of nonequilibrium trajectories enable one to estimate free energy differences and, by maximum-likelihood post-processing, to reconstruct free energy landscapes. Here, based on Bayes theorem, we propose a more direct method in which a posterior likelihood function is used both to construct the steered dynamics and to infer the contribution to equilibrium of all the sampled states. The method is implemented with two steering schedules. First, using non-autonomous steering, we calculate the migration barrier of the vacancy in Fe-{alpha}. Second, using an autonomous scheduling related to metadynamics and equivalent to temperature-accelerated molecular dynamics, wemore » accurately reconstruct the two-dimensional free energy landscape of the 38-atom Lennard-Jones cluster as a function of an orientational bond-order parameter and energy, down to the solid-solid structural transition temperature of the cluster and without maximum-likelihood post-processing.« less

An ``Alternating-Curvature'' Model for the Nanometer-scale Structure of the Nafion Ionomer, Based on Backbone Properties Detected by NMR

NASA Astrophysics Data System (ADS)

Schmidt-Rohr, Klaus; Chen, Q.

2006-03-01

The perfluorinated ionomer, Nafion, which consists of a (-CF2-)n backbone and charged side branches, is useful as a proton exchange membrane in H2/O2 fuel cells. A modified model of the nanometer-scale structure of hydrated Nafion will be presented. It features hydrated ionic clusters familiar from some previous models, but is based most prominently on pronounced backbone rigidity between branch points and limited orientational correlation of local chain axes. These features have been revealed by solid-state NMR measurements, which take advantage of fast rotations of the backbones around their local axes. The resulting alternating curvature of the backbones towards the hydrated clusters also better satisfies the requirement of dense space filling in solids. Simulations based on this ``alternating curvature'' model reproduce orientational correlation data from NMR, as well as scattering features such as the ionomer peak and the I(q) ˜ 1/q power law at small q values, which can be attributed to modulated cylinders resulting from the chain stiffness. The shortcomings of previous models, including Gierke's cluster model and more recent lamellar or bundle models, in matching all requirements imposed by the experimental data will be discussed.

Efficient neutron generation from solid-nanoparticle explosions driven by DPSSL-pumped high-repetition rate femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Watari, T.; Matsukado, K.; Sekine, T.; Takeuchi, Y.; Hatano, Y.; Yoshimura, R.; Satoh, N.; Nishihara, K.; Takagi, M.; Kawashima, T.

2016-03-01

We propose novel neutron source using high-intensity laser based on the cluster fusion scheme. We developed DPSSL-pumped high-repetition-rate 20-TW laser system and solid nanoparticle target for neutron generation demonstration. In our neutron generation experiment, high-energy deuterons were generated from coulomb explosion of CD solid- nanoparticles and neutrons were generated by DD fusion reaction. Efficient and stable neutron generation was obtained by irradiating an intense femtosecond laser pulse of >2×1018 W/cm2. A yield of ∼105 neutrons per shot was stably observed during 0.1-1 Hz continuous operation.

Triosmium Clusters on a Support: Determination of Structure by X-Ray Absorption Spectroscopy and High-Resolution Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shareghe, Mehraeen; Chi, Miaofang; Browning, Nigel D.

2011-01-01

The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration-corrected STEM. The samples were synthesized from [Os{sub 3}(CO){sub 12}] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high-angle annular dark-field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root-mean-square (rms) radii of 2.03 {+-} 0.06 {angstrom}. The EXAFS OsOs coordination number ofmore » 2.1 {+-} 0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02 {+-} 0.04 {angstrom}. The high-resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining OsOs distances of 2.80 {+-} 0.14 {angstrom}, matching the EXAFS value of 2.89 {+-} 0.06 {angstrom}. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters.« less

Towards a comprehensive knowledge of the star cluster population in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Piatti, A. E.

2018-07-01

The Small Magellanic Cloud (SMC) has recently been found to harbour an increase of more than 200 per cent in its known cluster population. Here, we provide solid evidence that this unprecedented number of clusters could be greatly overestimated. On the one hand, the fully automatic procedure used to identify such an enormous cluster candidate sample did not recover ˜50 per cent, on average, of the known relatively bright clusters located in the SMC main body. On the other hand, the number of new cluster candidates per time unit as a function of time is noticeably different from the intrinsic SMC cluster frequency (CF), which should not be the case if these new detections were genuine physical systems. We found additionally that the SMC CF varies spatially, in such a way that it resembles an outside-in process coupled with the effects of a relatively recent interaction with the Large Magellanic Cloud. By assuming that clusters and field stars share the same formation history, we showed for the first time that the cluster dissolution rate also depends on position in the galaxy. The cluster dissolution becomes higher as the concentration of galaxy mass increases or if external tidal forces are present.

Jammed systems of oriented needles always percolate on square lattices

NASA Astrophysics Data System (ADS)

Kondrat, Grzegorz; Koza, Zbigniew; Brzeski, Piotr

2017-08-01

Random sequential adsorption (RSA) is a standard method of modeling adsorption of large molecules at the liquid-solid interface. Several studies have recently conjectured that in the RSA of rectangular needles, or k -mers, on a square lattice, percolation is impossible if the needles are sufficiently long (k of order of several thousand). We refute these claims and present rigorous proof that in any jammed configuration of nonoverlapping, fixed-length, horizontal, or vertical needles on a square lattice, all clusters are percolating clusters.

Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach

NASA Astrophysics Data System (ADS)

Pan, Weichun; Kolomeisky, Anatoly B.; Vekilov, Peter G.

2005-05-01

Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.

Temperature invariance of NaCl solubility in water: inferences from salt-water cluster behavior of NaCl, KCl, and NH4Cl.

PubMed

Bharmoria, Pankaj; Gupta, Hariom; Mohandas, V P; Ghosh, Pushpito K; Kumar, Arvind

2012-09-27

The growth and stability of salt-water clusters have been experimentally studied in aqueous solutions of NaCl, KCl, and NH(4)Cl from dilute to near-saturation conditions employing dynamic light scattering and zeta potential measurements. In order to examine cluster stability, the changes in the cluster sizes were monitored as a function of temperature. Compared to the other cases, the average size of NaCl-water clusters remained almost constant over the studied temperature range of 20-70 °C. Information obtained from the temperature-dependent solution compressibility (determined from speed of sound and density measurements), multinuclear NMR ((1)H, (17)O, (35)Cl NMR), and FTIR were utilized to explain the cluster behavior. Comparison of NMR chemical shifts of saturated salt solutions with solid-state NMR data of pure salts, and evaluation of spectral modifications in the OH stretch region of saturated salt solutions as compared to that of pure water, provided important clues on ion pair-water interactions and water structure in the clusters. The high stability and temperature independence of the cluster sizes in aqueous NaCl shed light on the temperature invariance of its solubility.

Fictitious domain method for fully resolved reacting gas-solid flow simulation

NASA Astrophysics Data System (ADS)

Zhang, Longhui; Liu, Kai; You, Changfu

2015-10-01

Fully resolved simulation (FRS) for gas-solid multiphase flow considers solid objects as finite sized regions in flow fields and their behaviours are predicted by solving equations in both fluid and solid regions directly. Fixed mesh numerical methods, such as fictitious domain method, are preferred in solving FRS problems and have been widely researched. However, for reacting gas-solid flows no suitable fictitious domain numerical method has been developed. This work presents a new fictitious domain finite element method for FRS of reacting particulate flows. Low Mach number reacting flow governing equations are solved sequentially on a regular background mesh. Particles are immersed in the mesh and driven by their surface forces and torques integrated on immersed interfaces. Additional treatments on energy and surface reactions are developed. Several numerical test cases validated the method and a burning carbon particles array falling simulation proved the capability for solving moving reacting particle cluster problems.

The influence of containerless undercooling and rapid solid-state quenching on the superconductive and magnetic properties of some clustering alloy systems

NASA Technical Reports Server (NTRS)

Collings, E. W.

1984-01-01

The properties of clustering alloy systems and the manner in which they are influenced by rapid quenching from a containerless undercooled melt are discussed. It was postulated that rapid quenching under such conditions would result in highly disordered metastable alloys, and furthermore, that alloys in such conditions would possess physical properties characteristically different from those of alloys in the annealed equilibrium state. The scope of the program is essentially to gauge the influence of containerless undercooling on the submicrostructure of clustering-type alloys, using certain physical properties as diagnostic tools. Microstructures and macrostructures were to be examined using optical- and scanning-electron microscopy.

Giant Spherical Cluster with I-C140 Fullerene Topology.

PubMed

Heinl, Sebastian; Peresypkina, Eugenia; Sutter, Jörg; Scheer, Manfred

2015-11-02

We report on an effective cluster expansion of CuBr-linked aggregates by the increase of the steric bulk of the Cp(R) ligand in the pentatopic molecules [Cp(R)Fe(η(5)-P5)]. Using [Cp(BIG)Fe(η(5)-P5)] (Cp(BIG)=C5(4-nBuC6H4)5), the novel multishell aggregate [{Cp(BIG)Fe(η(5:2:1:1:1:1:1)-P5)}12(CuBr)92] is obtained. It shows topological analogy to the theoretically predicted I-C140 fullerene molecule. The spherical cluster was comprehensively characterized by various methods in solution and in the solid state. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficient quantum circuits for one-way quantum computing.

PubMed

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-13

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.

New triethoxysilylated 10-vertex closo-decaborate clusters. Synthesis and controlled immobilization into mesoporous silica.

PubMed

Abi-Ghaida, Fatima; Laila, Zahra; Ibrahim, Ghassan; Naoufal, Daoud; Mehdi, Ahmad

2014-09-14

Novel silylated hydroborate clusters comprising the closo-decaborate cage were prepared and characterized by (1)H, (13)C, (11)B, (29)Si NMR and mass spectroscopy ESI. The synthesis of such silylated clusters was achieved using reactive derivatives of [B10H10](2-), [1-B10H9N2](-) and [2-B10H9CO](-). These silylated decaborate clusters constitute a new class of precursors that can be covalently anchored onto various silica supports without any prior surface modification. As a proof of concept, the synthesized precursors were successfully anchored on mesoporous silica, SBA-15 type, in different percentages, where the mesoporous material retained its structure. All materials modified with closo-decaborate were characterized by (11)B and (29)Si solid state NMR, XRD, TEM and nitrogen sorption.

The first octahedral cluster complexes with terminal formate ligands: synthesis, structure, and properties of K4[Re6S8(HCOO)6] and Cs4[Re6S8(HCOO)6].

PubMed

Brylev, Konstantin A; Mironov, Yuri V; Kozlova, Svetlana G; Fedorov, Vladimir E; Kim, Sung-Jin; Pietzsch, Hans-Jürgen; Stephan, Holger; Ito, Akitaka; Ishizaka, Shoji; Kitamura, Noboru

2009-03-02

The hexarhenium anionic cluster complex with terminal formate ligands [Re6S8(HCOO)6]4- was obtained by the room-temperature reaction between [Re6S8(OH)6]4- and formic acid in an aqueous solution. The cluster was crystallized as a potassium or cesium salt and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV/vis, and luminescence spectroscopies. In particular, the emission quantum yield of the potassium salt of the Re6 cluster anion in the solid phase was determined for the first time. The electronic structures of [Re6S8(HCOO)6]4- and [Re6S8(OH)6]4- were also elucidated by DFT calculations.

A combined experimental and theoretical spectroscopic protocol for determination of the structure of heterogeneous catalysts: developing the information content of the resonance Raman spectra of M1 MoVOx † †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc01771e Click here for additional data file.

PubMed Central

Kubas, Adam; Noak, Johannes

2017-01-01

Absorption and multiwavelength resonance Raman spectroscopy are widely used to investigate the electronic structure of transition metal centers in coordination compounds and extended solid systems. In combination with computational methodologies that have predictive accuracy, they define powerful protocols to study the spectroscopic response of catalytic materials. In this work, we study the absorption and resonance Raman spectra of the M1 MoVOx catalyst. The spectra were calculated by time-dependent density functional theory (TD-DFT) in conjunction with the independent mode displaced harmonic oscillator model (IMDHO), which allows for detailed bandshape predictions. For this purpose cluster models with up to 9 Mo and V metallic centers are considered to represent the bulk structure of MoVOx. Capping hydrogens were used to achieve valence saturation at the edges of the cluster models. The construction of model structures was based on a thorough bonding analysis which involved conventional DFT and local coupled cluster (DLPNO-CCSD(T)) methods. Furthermore the relationship of cluster topology to the computed spectral features is discussed in detail. It is shown that due to the local nature of the involved electronic transitions, band assignment protocols developed for molecular systems can be applied to describe the calculated spectral features of the cluster models as well. The present study serves as a reference for future applications of combined experimental and computational protocols in the field of solid-state heterogeneous catalysis. PMID:28989667

The Twinkling Fractal Theory of the Glass Transition: Applications to Soft Matter

NASA Astrophysics Data System (ADS)

Wool, Richard

2012-02-01

The Twinkling Fractal Theory (TFT) of the glass transition has recently been demonstrated experimentally [J.F. Stanzione et al., J. Non Cryst. Sol., (2011, 357,311]. The hard to-soft matter transition is characterized by the presence of solid fractal clusters with liquid-like pools that are dynamically interchanging via their anharmonic intermolecular potentials with Boltzmann energy populations with a characteristic temperature dependent vibrational density of states g(φ) ˜ φ^df . The twinkling fractal frequencies φ cover a range of 10^12 Hz to 10-10Hz and the fractal solid clusters of size R have a lifetime τ ˜ R^Df/df, where the fractal dimension Df 2.4 and the fracton dimension df = 4/3. Here we explore its application to a number of soft matter issues. These include (a) Confinement effects on Tg reduction in thin films of thickness h, where by virtue of large cluster exclusion, δTg ˜ 1/h^Df/df; (b) Tg gradients near bulk surfaces, where the smaller clusters on the surface have a faster relaxation time; (c) Effect of twinkling surfaces on cell growth, where at T Tg + 20 C, there exists a twinkling fractal range that leads to bell-shaped enhancement of cell growth and chemical up-regulation via the twinkling surfaces ``communicating `` with the cells through their vibrations; and (d) adhesion above and below Tg where topological fluctuations associated with g(φ) promotes the development of nano-nails at the interface.

Analysis of local bond-orientational order for liquid gallium at ambient pressure: Two types of cluster structures.

PubMed

Chen, Lin-Yuan; Tang, Ping-Han; Wu, Ten-Ming

2016-07-14

In terms of the local bond-orientational order (LBOO) parameters, a cluster approach to analyze local structures of simple liquids was developed. In this approach, a cluster is defined as a combination of neighboring seeds having at least nb local-orientational bonds and their nearest neighbors, and a cluster ensemble is a collection of clusters with a specified nb and number of seeds ns. This cluster analysis was applied to investigate the microscopic structures of liquid Ga at ambient pressure (AP). The liquid structures studied were generated through ab initio molecular dynamics simulations. By scrutinizing the static structure factors (SSFs) of cluster ensembles with different combinations of nb and ns, we found that liquid Ga at AP contained two types of cluster structures, one characterized by sixfold orientational symmetry and the other showing fourfold orientational symmetry. The SSFs of cluster structures with sixfold orientational symmetry were akin to the SSF of a hard-sphere fluid. On the contrary, the SSFs of cluster structures showing fourfold orientational symmetry behaved similarly as the anomalous SSF of liquid Ga at AP, which is well known for exhibiting a high-q shoulder. The local structures of a highly LBOO cluster whose SSF displayed a high-q shoulder were found to be more similar to the structure of β-Ga than those of other solid phases of Ga. More generally, the cluster structures showing fourfold orientational symmetry have an inclination to resemble more to β-Ga.

Melting and glass transition for Ni clusters.

PubMed

Teng, Yuyong; Zeng, Xianghua; Zhang, Haiyan; Sun, Deyan

2007-03-08

The melting of NiN clusters (N = 29, 50-150) has been investigated by using molecular dynamics (MD) simulations with a quantum corrected Sutton-Chen (Q-SC) many-body potential. Surface melting for Ni147, direct melting for Ni79, and the glass transition for Ni29 have been found, and those melting points are equal to 540, 680, and 940 K, respectively. It shows that the melting temperatures are not only size-dependent but also a symmetrical structure effect; in the neighborhood of the clusters, the cluster with higher symmetry has a higher melting point. From the reciprocal slopes of the caloric curves, the specific heats are obtained as 4.1 kB per atom for the liquid and 3.1 kB per atom for the solid; these values are not influenced by the cluster size apart in the transition region. The calculated results also show that latent heat of fusion is the dominant effect on the melting temperatures (Tm), and the relationship between S and L is given.

Formation and emission mechanisms of Ag nanoclusters in the Ar matrix assembly cluster source

NASA Astrophysics Data System (ADS)

Zhao, Junlei; Cao, Lu; Palmer, Richard E.; Nordlund, Kai; Djurabekova, Flyura

2017-11-01

In this paper, we study the mechanisms of growth of Ag nanoclusters in a solid Ar matrix and the emission of these nanoclusters from the matrix by a combination of experimental and theoretical methods. The molecular dynamics simulations show that the cluster growth mechanism can be described as "thermal spike-enhanced clustering" in multiple sequential ion impact events. We further show that experimentally observed large sputtered metal clusters cannot be formed by direct sputtering of Ag mixed in the Ar. Instead, we describe the mechanism of emission of the metal nanocluster that, at first, is formed in the cryogenic matrix due to multiple ion impacts, and then is emitted as a result of the simultaneous effects of interface boiling and spring force. We also develop an analytical model describing this size-dependent cluster emission. The model bridges the atomistic simulations and experimental time and length scales, and allows increasing the controllability of fast generation of nanoclusters in experiments with a high production rate.

Real time dynamics of Si magic clusters mediating phase transformation: Si(111)-(1 × 1) to (7 × 7) reconstruction revisited

NASA Astrophysics Data System (ADS)

Ong, Wei Jie; Tok, Eng Soon

2012-07-01

Using Scanning Tunneling Microscope (STM), we show that the surface undergoes phase transformation from disordered "1 × 1" to (7 × 7) reconstruction which is mediated by the formation of Si magic clusters. Mono-disperse Si magic clusters of size ~ 13.5 ± 0.5 Å can be formed by heating the Si(111) surface to 1200 °C and quenching it to room temperature at cooling rates of at least 100 °C/min. The structure consists of 3 tetra-clusters of size ~ 4.5 Ǻ similar to the Si magic clusters that were formed from Si adatoms deposited by Si solid source on Si(111)-(7 × 7) [1]. Using real time STM scanning to probe the surface at ~ 400 °C, we show that Si magic clusters pop up from the (1 × 1) surface and form spontaneously during the phase transformation. This is attributed to the difference in atomic density between "disordered 1 × 1" and (7 × 7) surface structures which lead to the release of excess Si atoms onto the surface as magic clusters.

Performance evaluation of Space Shuttle SRB parachutes from air drop and scaled model wind tunnel tests. [Solid Rocket Booster recovery system

NASA Technical Reports Server (NTRS)

Moog, R. D.; Bacchus, D. L.; Utreja, L. R.

1979-01-01

The aerodynamic performance characteristics have been determined for the Space Shuttle Solid Rocket Booster drogue, main, and pilot parachutes. The performance evaluation on the 20-degree conical ribbon parachutes is based primarily on air drop tests of full scale prototype parachutes. In addition, parametric wind tunnel tests were performed and used in parachute configuration development and preliminary performance assessments. The wind tunnel test data are compared to the drop test results and both sets of data are used to determine the predicted performance of the Solid Rocket Booster flight parachutes. Data from other drop tests of large ribbon parachutes are also compared with the Solid Rocket Booster parachute performance characteristics. Parameters assessed include full open terminal drag coefficients, reefed drag area, opening characteristics, clustering effects, and forebody interference.

A novel approach to model the transient behavior of solid-oxide fuel cell stacks

NASA Astrophysics Data System (ADS)

Menon, Vikram; Janardhanan, Vinod M.; Tischer, Steffen; Deutschmann, Olaf

2012-09-01

This paper presents a novel approach to model the transient behavior of solid-oxide fuel cell (SOFC) stacks in two and three dimensions. A hierarchical model is developed by decoupling the temperature of the solid phase from the fluid phase. The solution of the temperature field is considered as an elliptic problem, while each channel within the stack is modeled as a marching problem. This paper presents the numerical model and cluster algorithm for coupling between the solid phase and fluid phase. For demonstration purposes, results are presented for a stack operated on pre-reformed hydrocarbon fuel. Transient response to load changes is studied by introducing step changes in cell potential and current. Furthermore, the effect of boundary conditions and stack materials on response time and internal temperature distribution is investigated.

Dielectric constant adjustments in computations of the scattering properties of solid ice crystals using the Generalized Multi-particle Mie method

NASA Astrophysics Data System (ADS)

Lu, Yinghui; Aydin, Kültegin; Clothiaux, Eugene E.; Verlinde, Johannes

2014-03-01

Ice crystal scattering properties at microwave radar wavelengths can be modeled with the Generalized Multi-particle Mie (GMM) method by decomposing an ice crystal into a cluster of tiny spheres composed of solid ice. In this decomposition the mass distribution of the tiny spheres in the cluster is no longer equivalent to that in the original ice crystal because of gaps between the tiny spheres. To compensate for the gaps in the cluster representation of an ice crystal in the GMM computation of crystal scattering properties, the Maxwell Garnett approximation is used to estimate what the dielectric function of the tiny spheres (i.e., the inclusions) in the cluster must be to make the cluster of tiny spheres with associated air gaps (i.e., the background matrix) dielectrically equivalent to the original solid ice crystal. Overall, compared with the T-matrix method for spheroids outside resonance regions this approach agrees to within mostly 0.3 dB (and often better) in the horizontal backscattering cross section σhh and the ratio of horizontal and vertical backscattering cross sections σhh/σvv, and 6% for the amplitude scattering matrix elements Re{S22-S11} and Im{S22} in the forward direction. For crystal sizes and wavelengths near resonances, where the scattering parameters are highly sensitive to the crystal shape, the differences are generally within 1.2 dB for σhh and σhh/σvv, 20% for Re{S22-S11} and 6% for Im{S22}. The Discrete Dipole Approximation (DDA) results for the same spheroids are generally closer than those of GMM to the T-matrix results. For hexagonal plates the differences between GMM and the DDA at a W-band wavelength (3.19 mm) are mostly within 0.6 dB for σhh, 1 dB for σhh/σvv, 11% for Re{S22-S11} and 12% for Im{S22}. For columns the differences are within 0.3 dB for σhh and σhh/σvv, 8% for Re{S22-S11} and 4% for Im{S22}. This method shows higher accuracy than an alternative method that artificially increases the thickness of ice plates to provide the same mass as the original ice crystal.

Antioxidants (carotenoids and phenolics) profile of cherry tomatoes as influenced by deficit irrigation, ripening and cluster.

PubMed

Coyago-Cruz, Elena; Corell, Mireia; Moriana, Alfonso; Hernanz, Dolores; Benítez-González, Ana M; Stinco, Carla M; Meléndez-Martínez, Antonio J

2018-02-01

The purpose of this study was to assess the relationship between the effect of regulated deficit irrigation, cluster, developmental stages and two seasons (autumn 2015 and spring 2016) on the commercial and functional quality (carotenoids and plenolics levels) in 'Lazarino' and 'Summerbrix' tomatoes. Autumn had a positive effect on the commercial quality, with larger fruits (22% in 'Summerbrix'; 26% in 'Lazarino') and higher soluble solids (16% in 'Summerbrix'; 12% in 'Lazarino'). Total carotenoids did not change significantly with irrigation and variety while total phenolics did with the cluster and season. In most cases, the main amounts of carotenoids and phenolic were found in the higher cluster and carotenoids in ripe fruit. Thus, irrigation of such varieties could be reduced drastically (ca. 80%) without affecting considerably the overall quality of their fruits (changes not greater than 30%). Copyright © 2017 Elsevier Ltd. All rights reserved.

Melting and Freezing of Metal Clusters

NASA Astrophysics Data System (ADS)

Aguado, Andrés; Jarrold, Martin F.

2011-05-01

Recent developments allow heat capacities to be measured for size-selected clusters isolated in the gas phase. For clusters with tens to hundreds of atoms, the heat capacities determined as a function of temperature usually have a single peak attributed to a melting transition. The melting temperatures and latent heats show large size-dependent fluctuations. In some cases, the melting temperatures change by hundreds of degrees with the addition of a single atom. Theory has played a critical role in understanding the origin of the size-dependent fluctuations, and in understanding the properties of the liquid-like and solid-like states. In some cases, the heat capacities have extra features (an additional peak or a dip) that reveal a more complex behavior than simple melting. In this article we provide a description of the methods used to measure the heat capacities and provide an overview of the experimental and theoretical results obtained for sodium and aluminum clusters.

Identifying Few-Molecule Water Clusters with High Precision on Au(111) Surface.

PubMed

Dong, Anning; Yan, Lei; Sun, Lihuan; Yan, Shichao; Shan, Xinyan; Guo, Yang; Meng, Sheng; Lu, Xinghua

2018-06-01

Revealing the nature of a hydrogen-bond network in water structures is one of the imperative objectives of science. With the use of a low-temperature scanning tunneling microscope, water clusters on a Au(111) surface were directly imaged with molecular resolution by a functionalized tip. The internal structures of the water clusters as well as the geometry variations with the increase of size were identified. In contrast to a buckled water hexamer predicted by previous theoretical calculations, our results present deterministic evidence for a flat configuration of water hexamers on Au(111), corroborated by density functional theory calculations with properly implemented van der Waals corrections. The consistency between the experimental observations and improved theoretical calculations not only renders the internal structures of absorbed water clusters unambiguously, but also directly manifests the crucial role of van der Waals interactions in constructing water-solid interfaces.

Disorder-induced stiffness degradation of highly disordered porous materials

NASA Astrophysics Data System (ADS)

Laubie, Hadrien; Monfared, Siavash; Radjaï, Farhang; Pellenq, Roland; Ulm, Franz-Josef

2017-09-01

The effective mechanical behavior of multiphase solid materials is generally modeled by means of homogenization techniques that account for phase volume fractions and elastic moduli without considering the spatial distribution of the different phases. By means of extensive numerical simulations of randomly generated porous materials using the lattice element method, the role of local textural properties on the effective elastic properties of disordered porous materials is investigated and compared with different continuum micromechanics-based models. It is found that the pronounced disorder-induced stiffness degradation originates from stress concentrations around pore clusters in highly disordered porous materials. We identify a single disorder parameter, φsa, which combines a measure of the spatial disorder of pores (the clustering index, sa) with the pore volume fraction (the porosity, φ) to scale the disorder-induced stiffness degradation. Thus, we conclude that the classical continuum micromechanics models with one spherical pore phase, due to their underlying homogeneity assumption fall short of addressing the clustering effect, unless additional texture information is introduced, e.g. in form of the shift of the percolation threshold with disorder, or other functional relations between volume fractions and spatial disorder; as illustrated herein for a differential scheme model representative of a two-phase (solid-pore) composite model material.

Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster

NASA Technical Reports Server (NTRS)

Lea, S. M.; Mushotzky, R.; Holt, S. S.

1982-01-01

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 arcmin from the center of M87 are reported. X-ray spectra were obtained at these two locations with the Solid State Spectrometer onboard the Einstein Observatory. Emission lines were observed in both locations, indicating the presence of heavy elements at abundances near solar. There is no strong abundance gradient, within the errors. A temperature gradient has been detected: T increases from about 1.4 keV at the position of M87 to about 3.35 keV 7 arcmin away. There is lower temperature thermal emission at the center of M87 with T about 0.6 keV, consistent with models for cooling flows in this cluster. A mass infall rate of nearly 20 solar masses/yr has been obtained. In addition to the thermal emission, a power-law component has been detected in the spectrum of M87, consistent with that observed by HEAO 1, indicating that this component probably originates in the galaxy itself. Comparison of the results with those of other observers and with theoretical models for this source indicates the presence of intracluster gas having density near 1/1000 per cu cm and temperature of about 30,000,000 K.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Rong; Wu, Yongquan, E-mail: yqwu@shu.edu.cn; Xiao, Junjiang

We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clustersmore » and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.« less

Fullerene faraday cage keeps magnetic properties of inner cluster pristine.

PubMed

Avdoshenko, Stanislav M

2018-04-21

Any single molecular magnets (SMMs) perspective for application is as good as its magnetization stability in ambient conditions. Endohedral metallofullerenes (EMFs) provide a solid basis for promising SMMs. In this study, we investigated the behavior of functionalized EMFs on a gold surface (EMF-L-Au). Having followed the systems molecular dynamics paths, we observed that the chemically locked inner cluster inside fullerene cage will remain locked even at room temperature due to the ligand-effect. We have located multiple possible minima with different charge arrangements between EMF-L-Au fragments. Remarkably, the charge state of the EMF inner cluster remained virtually constant and so magnetic properties are expected to be untouched. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

A Hundred-Year-Old Experiment Re-evaluated: Accurate Ab-Initio Monte-Carlo Simulations of the Melting of Radon.

PubMed

Schwerdtfeger, Peter; Smits, Odile; Pahl, Elke; Jerabek, Paul

2018-06-12

State-of-the-art relativistic coupled-cluster theory is used to construct many-body potentials for the rare gas element radon in order to determine its bulk properties including the solid-to-liquid phase transition from parallel tempering Monte Carlo simulations through either direct sampling of the bulk or from a finite cluster approach. The calculated melting temperature are 201(3) K and 201(6) K from bulk simulations and from extrapolation of finite cluster values, respectively. This is in excellent agreement with the often debated (but widely cited) and only available value of 202 K, dating back to measurements by Gray and Ramsay in 1909. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Relativistic coupled-cluster and density-functional studies of argon at high pressure

NASA Astrophysics Data System (ADS)

Schwerdtfeger, Peter; Steenbergen, Krista G.; Pahl, Elke

2017-06-01

The equation of state P (V ,T ) for solid argon is determined by the calculation of accurate static and vibrational terms in the free energy. The static component comes from a quantum theoretical many-body expansion summing over all energetic contributions from two-, three-, and four-body fragments treated with relativistic coupled cluster theory, while the lattice vibrations are described at an anharmonic level including two- and three-body forces as well as temperature effects. The dynamic part is calculated within the Debye and Einstein approximation, as well as by a more accurate phonon treatment where the vibrational motions in the lattice are coupled. Our results are in good agreement with room-temperature high-pressure experimental data up to ˜20 GPa. In the 20-100 GPa pressure range, however, we see considerable deviations between experiment and theory, perhaps indicating missing four-body contributions (beyond the quadruple dipole terms included here), missing five and higher-body effects, and the need to go beyond the coupled cluster singles-doubles with perturbative triples treatment in such higher-body forces. This contrasts with the results for solid neon, where excellent agreement has been achieved taking only two- and three-body forces into account [P. Schwerdtfeger and A. Hermann, Phys. Rev. B 80, 064106 (2009), 10.1103/PhysRevB.80.064106]. We demonstrate that the phase transition from fcc to hcp cannot account for the large discrepancies observed. Density functional calculations give very mixed results in the high-pressure region, but some functionals such as optB88-vdW (proposed by Lundqvist and co-workers) describe the many-body forces in argon reasonably well over the range of pressures investigated. Theoretical investigations of the heavier rare gas solids reaching experimental accuracy in the high-pressure regime therefore remain a significant challenge.

In situ solid-state electrochemistry of mass-selected ions at well-defined electrode–electrolyte interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prabhakaran, Venkateshkumar; Johnson, Grant E.; Wang, Bingbing

2016-11-07

Molecular-level understanding of electrochemical processes occurring at electrode-electrolyte interfaces (EEI) is key to the rational development of high-performance and sustainable electrochemical technologies. This article reports the development and first application of solid-state in situ electrochemical probes to study redox and catalytic processes occurring at well-defined EEI generated using soft-landing of mass- and charge-selected cluster ions (SL). In situ electrochemical probes with excellent mass transfer properties are fabricated using carefully-designed nanoporous ionic liquid membranes. SL enables deposition of pure active species that are not obtainable with other techniques onto electrode surfaces with precise control over charge state, composition, and kinetic energy.more » SL is, therefore, a unique tool for studying fundamental processes occurring at EEI. For the first time using an aprotic electrochemical probe, the effect of charge state (PMo12O403-/2-) and the contribution of building blocks of Keggin polyoxometalate (POM) clusters to redox processes are characterized by populating EEI with novel POM anions generated by electrospray ionization and gas phase dissociation. Additionally, a proton conducting electrochemical probe has been developed to characterize the reactive electrochemistry (oxygen reduction activity) of bare Pt clusters (Pt40 ~1 nm diameter), thus demonstrating the capability of the probe for studying reactions in controlled gaseous environments. The newly developed in situ electrochemical probes combined with ion SL provide a versatile method to characterize the EEI in solid-state redox systems and reactive electrochemistry at precisely-defined conditions. This capability will advance molecular-level understanding of processes occurring at EEI that are critical to many energy-related technologies.« less

Some properties of solid helium and helium nanoclusters using the effective HFD-like interaction potential: Adsorption and desorption inside carbon nanotube

NASA Astrophysics Data System (ADS)

Abbaspour, M.; Akbarzadeh, H.; Banihashemi, S. Z.; Sotoudeh, A.

2018-02-01

We have calculated the zero equation of state of solid helium using a two-body Hartree-Fock dispersion (HFD)-like potential from molecular dynamics (MD) simulation. To take many-body forces into account, our simple and accurate empirical expression is used with the HFD-like potential without requiring an expensive three-body calculation. This potential model also includes the quantum effects for helium at low temperatures. The results indicate that our effective HFD-like potential improves the prediction of the classical two-body results to get better agreement with experiment than many other two-body and three-body potentials of helium reported in the literature. We have also simulated the adsorption and desorption processes of the (He)55, (He)147, (He)309, (He)561, and (He)923 icosahedral nanoclusters confined into the different armchair and zigzag CNTs from 0 to 50 K using our effective model. We have observed an interesting phenomenon at 0 K for helium. The nanoclusters adsorb to the inner CNT wall as a melting process. But, the heavier noble gas clusters (such as Ne and Xe) show the different behavior than the He clusters. They form a multilayered solid structure into the CNT at zero temperature and adsorb into the inner wall of the CNT at higher temperatures. Our results for He clusters show that the absolute value of the adsorption energy increases as the size of the nanocluster increases. The desorption process begins at a certain temperature and represents itself by a jump in the configurational energy values. We have also investigated the structural and dynamical properties of the confined helium nanoclusters during the adsorption and desorption processes at different temperatures.

State of the metal core in nanosecond exploding wires and related phenomena

NASA Astrophysics Data System (ADS)

Sarkisov, G. S.; Sasorov, P. V.; Struve, K. W.; McDaniel, D. H.

2004-08-01

Experiments show that an expanding metal wire core that results from a nanosecond electrical explosion in vacuum consists primarily of three different states: solid, microdrop, and gas-plasma. The state of the wire core depends both on the amount of energy deposited before the voltage breakdown and on the heating conditions. For small amounts of deposited energy (on the order of solid-stage enthalpy), the wire core remains in a solid state or is partially disintegrated. For a high level of deposited energy (more than vaporization energy) the wire core is in a gas-plasma state. For an intermediate level of deposited energy (more than melting but less than vaporization), the wire disintegrates into hot liquid microdrops or clusters of submicron size. For a wire core in the cluster state, interferometry demonstrates weak (or even absent) phaseshift. Light emission shows a "firework effect"—the long late-time radiation related to the emission by the expanding cylinder of hot microparticles. For the wire core in a gas-plasma state, interferometry demonstrates a large phaseshift and a fast reduction in light emission due to adiabatic cooling of the expanding wire core. The simulation of this firework effect agrees well with experimental data, assuming submicron size and a temperature approaching boiling for the expanded microparticles cylinder.

Canard-Elevon Interactions on a Hypersonic Vehicle

DTIC Science & Technology

2010-01-01

AIAA. †Professor, Department of Aerospace Engineering, 1320 Beal Avenue, 3024 Francois-Xavier Bagnoud Building; cesnik@umich.edu. Associate Fellow...high number of grid points on each airfoil face, the CFD squares are clustered close together and, therefore, appear to be a solid line. V . Parametric

Tribological coatings for complex mechanical elements produced by supersonic cluster beam deposition of metal dichalcogenide nanoparticles

NASA Astrophysics Data System (ADS)

Piazzoni, C.; Buttery, M.; Hampson, M. R.; Roberts, E. W.; Ducati, C.; Lenardi, C.; Cavaliere, F.; Piseri, P.; Milani, P.

2015-07-01

Fullerene-like MoS2 and WS2 nanoparticles can be used as building blocks for the fabrication of fluid and solid lubricants. Metal dichalcogenide films have a very low friction coefficient in vacuum, therefore they have mostly been used as solid lubricants in space and vacuum applications. Unfortunately, their use is significantly hampered by the fact that in the presence of humidity, oxygen and moisture, the low-friction properties of these materials rapidly degrade due to oxidation. The use of closed-cage MoS2 and WS2 nanoparticles may eliminate this problem, although the fabrication of lubricant thin films starting from dichalcogenide nanoparticles is, to date, a difficult task. Here we demonstrate the use of supersonic cluster beam deposition for the coating of complex mechanical elements (angular contact ball bearings) with nanostructured MoS2 and WS2 thin films. We report structural and tribological characterization of the coatings in view of the optimization of tribological performances for aerospace applications.

Magnetic properties of solid oxygen under pressure (Review Article)

NASA Astrophysics Data System (ADS)

Freiman, Yu. A.

2015-11-01

Solid oxygen is a unique crystal combining properties of a simple molecular solid and a magnet. Unlike ordinary magnets, the exchange interaction in solid oxygen acts on a background of weak Van der Waals forces, providing a significant part of the total lattice energy. Therefore, the magnetic and lattice properties of solid oxygen are very closely related. This manifests itself in a very rich phase diagram and numerous anomalies of thermal, magnetic and optical properties. Low-temperature low-pressure α-O2 is a two-sublattice collinear Neel antiferromagnet. At a pressure of ˜6 GPa, α-O2 is transformed into δ-O2, in which three different magnetic structures are realized upon increasing temperature. At ˜8 GPa δ-O2 is transformed into ɛ-O2. In this transition, O2 molecules combine into four-molecule clusters (O2)4. This transformation is accompanied by a magnetic collapse. This review describes the evolution of the magnetic structure with increasing pressure, and analyzes the causes behind this behavior.

Melting of size-selected gallium clusters with 60-183 atoms.

PubMed

Pyfer, Katheryne L; Kafader, Jared O; Yalamanchali, Anirudh; Jarrold, Martin F

2014-07-10

Heat capacities have been measured as a function of temperature for size-selected gallium cluster cations with between 60 and 183 atoms. Almost all clusters studied show a single peak in the heat capacity that is attributed to a melting transition. The peaks can be fit by a two-state model incorporating only fully solid-like and fully liquid-like species, and hence no partially melted intermediates. The exceptions are Ga90(+), which does not show a peak, and Ga80(+) and Ga81(+), which show two peaks. For the clusters with two peaks, the lower temperature peak is attributed to a structural transition. The melting temperatures for clusters with less than 50 atoms have previously been shown to be hundreds of degrees above the bulk melting point. For clusters with more than 60 atoms the melting temperatures decrease, approaching the bulk value (303 K) at around 95 atoms, and then show several small upward excursions with increasing cluster size. A plot of the latent heat against the entropy change for melting reveals two groups of clusters: the latent heats and entropy changes for clusters with less than 94 atoms are distinct from those for clusters with more than 93 atoms. This observation suggests that a significant change in the nature of the bonding or the structure of the clusters occurs at 93-94 atoms. Even though the melting temperatures are close to the bulk value for the larger clusters studied here, the latent heats and entropies of melting are still far from the bulk values.

A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tingwen; Zhang, Yongmin

2013-10-11

Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve themore » 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.« less

Final Scientific/Technical Report: Breakthrough Design and Implementation of Many-Body Theories for Electron Correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

So Hirata

2012-01-03

This report discusses the following highlights of the project: (1) grid-based Hartree-Fock equation solver; (2) explicitly correlated coupled-cluster and perturbation methods; (3) anharmonic vibrational frequencies and vibrationally averaged NMR and structural parameters of FHF; (4) anharmonic vibrational frequencies and vibrationally averaged structures of hydrocarbon combustion species; (5) anharmonic vibrational analysis of the guanine-cytosine base pair; (6) the nature of the Born-Oppenheimer approximation; (7) Polymers and solids Brillouin-zone downsampling - the modulo MP2 method; (8) explicitly correlated MP2 for extended systems; (9) fast correlated method for molecular crystals - solid formic acid; and (10) fast correlated method for molecular crystals -more » solid hydrogen fluoride.« less

The isoelectric point/point-of zero-charge of interfaces formed by aqueous solutions and nonpolar solids, liquids, and gases.

PubMed

Healy, Thomas W; Fuerstenau, Douglas W

2007-05-01

From our previous work on the role of the electrostatic field strength in controlling the pH of the iso-electric point (iep)/point-of-zero-charge (pzc) of polar solids we have extended the analysis to predict that the pH of the iep/pzc of a nonpolar solid, liquid or gas-aqueous interface should occur at pH 1.0-3.0, dependent on the value assigned to water molecules or clusters at the interface. Consideration of a wide range of experimental results covering nonpolar solids such as molybdenite, stibnite, paraffin, etc. as well as hydrocarbon liquids such as xylene, decalin, and long chain (>C8) alkane oils, as well as nitrogen and hydrogen gases, all in various simple 1:1 electrolyte solutions confirm the general validity of the result. We further consider various models of the origin of the charge on nonpolar material-water interfaces.

Porphyrin network materials: Chemical exploration in the supramolecular solid-state

NASA Astrophysics Data System (ADS)

Kosal, Margaret Elizabeth

Rational design of solid-state materials from molecular building blocks possessing desired physical and chemical characteristics remains among the most challenging tasks for the synthetic chemist. Using p-carboxylic acid tetraphenyl porphyrin molecules, H2T(p-CO 2H)PP, as the organic building block, the synthesis of novel microporous coordination framework materials has been pursued for this work. The self-assembly of the anionic carboxylate with divalent alkaline earth or transition metal cations yielded clathrate, lamellar and three-dimensional network materials. The solvothermal synthesis, characterization, and selective sorption properties of a 3-dimensional metalloporphyrin network solid, [CoT( p-CO2)PPCo1.5], named PIZA-1 for Porphyrinic Illinois Zeolite Analogue 1, have been investigated. The extended structure reveals a single, independent, neutral network with large, bi-directional oval-shaped channels (9 x 7 A) along the crystallographic b - and c-axes and another set of channels (14 x 7 A) along the a-axis. At the intersection of channels, an internal chamber (31 x 31 x 10 A) is realized. Channel-shape is attributable to ruffling of the metalloporphyrin macrocycles when coordinated to the bridging trinuclear Co(II)-carboxylate clusters. The void volume of the stable, thermally robust, solvate-free material is calculated to be 74% of the total unit cell volume. Size-, shape- and functional-group-selective sorption indicates a preference for water and amines. This organic zeolite analogue also demonstrates remarkable ability as a molecular sieve for removal of water from common organic solvents. By powder X-ray diffraction, BET gas adsorption studies and FTIR, this material has been shown to maintain its porous structure as a guest-free solid when heated under vacuum to 250°C. PIZA-1 demonstrates extremely high capacity for repeated selective sorption of water. In comparison to 4A molecular sieves, PIZA-1 exhibits higher capacity and faster response for the selective adsorption of water from common organic solvents. Molecular modeling of corroborates experimental results. The large internal cavities of PIZA-1 are a consequence of the trinuclear Co(II)carboxylate cluster forcing the ruffling of the porphyrin building blocks. The linear trinuclear metal-carboxylate cluster of PIZA-1 is contrasted with the bent trinuclear M(II) carboxylate clusters (M = Co, Mn) of isostructural 3-dimensional frameworks: PIZA-2 and PIZA-3. Containing near-planar metalloporphyrin macrocycles, PIZA-2 and PIZA-3 manifest lower void volumes (56%).

Growth and properties of silicon heterostructures with buried nanosize Mg2Si clusters

NASA Astrophysics Data System (ADS)

Galkin, N. G.; Galkin, K. N.

2005-06-01

The technology of solid-phase growth of nanosize islands of magnesium suicide on Si (111) 7x7 with narrow distributions of lateral size and height (60 - 80 and 5 - 7 nanometers, respectively) and density of up to 2x 109 sm-2 is proposed. A 20-50 nm thick Si layer has been grown upon these islands. Basing on the data of AES, EELS, AFM and JR spectroscopy, a conclusion is made that the Mg2Si islands remain in depth of the Si layer. The suggestion is made that sizes, density and crystal structure of the buried magnesium suicide clusters preserves. It is shown, that the system of three as-grown layers of buried clusters has smoother surface than the one layer system. The contribution of the Mg2Si clusters into the dielectric function is observed at the energy 0.8-1.2 eV, it is maximal if the clusters are localized on the silicon surface. It is shown, that with increase of the number of Mg2Si cluster layers their contribution increases into the effective number of electrons per a unit cell and effective dielectric function of the sample.

Radiation-induced microcrystal shape change as a mechanism of wasteform degradation

NASA Astrophysics Data System (ADS)

Ojovan, Michael I.; Burakov, Boris E.; Lee, William E.

2018-04-01

Experiments with actinide-containing insulating wasteforms such as devitrified glasses containing 244Cm, Ti-pyrochlore, single-phase La-monazite, Pu-monazite ceramics, Eu-monazite and zircon single crystals containing 238Pu indicate that mechanical self-irradiation-induced destruction may not reveal itself for many years (even decades). The mechanisms causing these slowly-occurring changes remain unknown therefore in addition to known mechanisms of wasteform degradation such as matrix swelling and loss of solid solution we have modelled the damaging effects of electrical fields induced by the decay of radionuclides in clusters embedded in a non-conducting matrix. Three effects were important: (i) electric breakdown; (ii) cluster shape change due to dipole interaction, and (iii) cluster shape change due to polarisation interaction. We reveal a critical size of radioactive clusters in non-conducting matrices so that the matrix material can be damaged if clusters are larger than this critical size. The most important parameters that control the matrix integrity are the radioactive cluster (inhomogeneity) size, specific radioactivity, and effective matrix electrical conductivity. We conclude that the wasteform should be as homogeneous as possible and even electrically conductive to avoid potential damage caused by electrical charges induced by radioactive decay.

Infrared spectroscopy of water clusters isolated in methane matrices: Effects of isotope substitution and annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamakawa, Koichiro, E-mail: koichiro.yamakawa@gakushuin.ac.jp; Ehara, Namika; Ozawa, Nozomi

2016-07-15

Using infrared-active solvents of CH{sub 4} and CD{sub 4} for matrix isolation, we measured infrared spectra of H{sub 2}O and D{sub 2}O clusters at 7 K. The solute-concentration dependence of the spectrum of H{sub 2}O clusters in a CH{sub 4} matrix was investigated and was used for the peak assignment. Annealing procedures were found to promote the size growth of water clusters in methane matrices for all the combinations of (H{sub 2}O, CH{sub 4}), (H{sub 2}O, CD{sub 4}), (D{sub 2}O, CH{sub 4}), and (D{sub 2}O, CD{sub 4}). We also monitored the ν{sub 3} absorption due to methane to find themore » annealing-induced structural change only of solid CH{sub 4}. The matrix effects on the vibrations of the clusters are discussed on the basis of “T{sub c} plots”, where their frequencies are plotted as a function of the square root of the matrix critical temperature, T{sub c}. The obtained plots assure the validity of the assignment of the cluster peaks.« less

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

NASA Astrophysics Data System (ADS)

Wang, Guangshuo; Ma, Yingying; Li, Meixia; Cui, Guohua; Che, Hongwei; Mu, Jingbo; Zhang, Xiaoliang; Tong, Yu; Dong, Xufeng

2017-01-01

In this study, magnesium ferrite (MgFe2O4) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe2O4 nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe2O4 nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe2O4 nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe2O4 nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.

A Theoretical Study of Structural, Electronic and Vibrational Properties of Small Fluoride Clusters

NASA Astrophysics Data System (ADS)

Waters, Kevin; Pandey, Ratnesh; Nigam, Sandeep; He, Haiying; Pingle, Subhash; Pandey, Avinash; Pandey, Ravindra

2014-03-01

Alkaline earth metal fluorides are an interesting family of ionic crystals having a wide range of applications in solid state lasers, luminescence, scintillators, to name just a few. In this work, small stoichiometric clusters of (MF2)n (M = Mg, Ca Sr, Ba, n =1-6) were studied for structural, vibrational and electronic properties using first-principles methods based on density functional theory. A clear trend of structural and electronic structure evolution was found for all the alkaline earth metal fluorides when the cluster size n increases from 1 to 6. Our study reveals that these fluoride clusters mimic the bulk-like behavior at the very small size. Among the four series of metal fluorides, however, (MgF2)n clusters stands out to be different in its preference of equilibrium structures owing to the much smaller ionic radius of Mg and the higher degree of covalency in the Mg-F bonding. The calculated binding energy, highest stretching frequency, ionization potential, and HOMO-LUMO gap decrease from MgF2 to BaF2 for the same cluster size. These variations are explained in terms of the change in the ionic radius and the basicity of the metal ions.

Thermal Considerations of Space Solar Power Concepts with 3.5 GW RF Output

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2000-01-01

This paper presents the thermal challenge of the Space Solar Power (SSP) design concepts with a 3.5 GW radio-frequency (RF) output. High efficiency klystrons are thermally more favored than solid state (butterstick) to convert direct current (DC) electricity to radio-frequency (RF) energy at the transmitters in these concepts. Using klystrons, the heat dissipation is 0.72 GW. Using solid state, the heat dissipation is 2.33 GW. The heat dissipation of the klystrons is 85% at 500C, 10% at 300C, and 5% at 125C. All the heat dissipation of the solid state is at 100C. Using klystrons, the radiator area is 74,500 square m Using solid state, the radiator area is 2,362,200 square m Space constructable heat pipe radiators are assumed in the thermal analysis. Also, to make the SSP concepts feasible, the mass of the heat transport system must be minimized. The heat transport distance from the transmitters to the radiators must be minimized. It can be accomplished by dividing the radiator into a cluster of small radiators, so that the heat transport distances between the klystrons and radiators can be minimized. The area of each small radiator is on the order of 1 square m. Two concepts for accommodating a cluster of small radiators are presented. If the distance between the transmitters and radiators is 1.5 m or less, constant conductance heat pipes (CCHPs) are acceptable for heat transport. If the distance exceeds 1.5 m, loop heat pipes (LHPs) are needed.

Evolution of the Contact Area with Normal Load for Rough Surfaces: from Atomic to Macroscopic Scales.

PubMed

Huang, Shiping

2017-11-13

The evolution of the contact area with normal load for rough surfaces has great fundamental and practical importance, ranging from earthquake dynamics to machine wear. This work bridges the gap between the atomic scale and the macroscopic scale for normal contact behavior. The real contact area, which is formed by a large ensemble of discrete contacts (clusters), is proven to be much smaller than the apparent surface area. The distribution of the discrete contact clusters and the interaction between them are key to revealing the mechanism of the contacting solids. To this end, Green's function molecular dynamics (GFMD) is used to study both how the contact cluster evolves from the atomic scale to the macroscopic scale and the interaction between clusters. It is found that the interaction between clusters has a strong effect on their formation. The formation and distribution of the contact clusters is far more complicated than that predicted by the asperity model. Ignorance of the interaction between them leads to overestimating the contacting force. In real contact, contacting clusters are smaller and more discrete due to the interaction between the asperities. Understanding the exact nature of the contact area with the normal load is essential to the following research on friction.

Do Clustering Monoclonal Antibody Solutions Really Have a Concentration Dependence of Viscosity?

PubMed Central

Pathak, Jai A.; Sologuren, Rumi R.; Narwal, Rojaramani

2013-01-01

Protein solution rheology data in the biophysics literature have incompletely identified factors that govern hydrodynamics. Whereas spontaneous protein adsorption at the air/water (A/W) interface increases the apparent viscosity of surfactant-free globular protein solutions, it is demonstrated here that irreversible clusters also increase system viscosity in the zero shear limit. Solution rheology measured with double gap geometry in a stress-controlled rheometer on a surfactant-free Immunoglobulin solution demonstrated that both irreversible clusters and the A/W interface increased the apparent low shear rate viscosity. Interfacial shear rheology data showed that the A/W interface yields, i.e., shows solid-like behavior. The A/W interface contribution was smaller, yet nonnegligible, in double gap compared to cone-plate geometry. Apparent nonmonotonic composition dependence of viscosity at low shear rates due to irreversible (nonequilibrium) clusters was resolved by filtration to recover a monotonically increasing viscosity-concentration curve, as expected. Although smaller equilibrium clusters also existed, their size and effective volume fraction were unaffected by filtration, rendering their contribution to viscosity invariant. Surfactant-free antibody systems containing clusters have complex hydrodynamic response, reflecting distinct bulk and interface-adsorbed protein as well as irreversible cluster contributions. Literature models for solution viscosity lack the appropriate physics to describe the bulk shear viscosity of unstable surfactant-free antibody solutions. PMID:23442970

X-ray spectral observations of clusters of galaxies undergoing merger events

NASA Astrophysics Data System (ADS)

Henriksen, Mark J.

1993-09-01

We have analyzed the HEAO 1 A2 observations of two clusters whose optical and X-ray isophotes are suggestive of merging subclusters, A119 and A754, and find evidence of nonisothermal X-ray emission from both clusters. The X-ray spectrum of both clusters, when fitted with a single isothermal model, shows residual soft X-ray emission. There is a statistically significant reduction in chi-squared (98 percent probability based on the F-test) when a second temperature component is added. If the asymmetric isophotes seen in the soft X-ray image are indicative of merging subclusters, then our analysis of the Einstein IPC spectra and Solid State Spectrometer observations of A754, which provide some spatial and spectral resolution, suggests that the two temperature components seen in the HEAO 1 A2 spectra are associated with gas trapped in the subcluster potential wells. The implied subcluster isothermal masses suggest that a more massive cluster is accreting a less massive companion in A754. The present observations cannot rule out the alternative possibility that the cooler gas is associated with the outer cluster atmosphere rather than individual subclusters, as appears to be the case for A119. Astro D observations will be necessary to distinguish between these two possibilities for both clusters.

Evolution of the Contact Area with Normal Load for Rough Surfaces: from Atomic to Macroscopic Scales

NASA Astrophysics Data System (ADS)

Huang, Shiping

2017-11-01

The evolution of the contact area with normal load for rough surfaces has great fundamental and practical importance, ranging from earthquake dynamics to machine wear. This work bridges the gap between the atomic scale and the macroscopic scale for normal contact behavior. The real contact area, which is formed by a large ensemble of discrete contacts (clusters), is proven to be much smaller than the apparent surface area. The distribution of the discrete contact clusters and the interaction between them are key to revealing the mechanism of the contacting solids. To this end, Green's function molecular dynamics (GFMD) is used to study both how the contact cluster evolves from the atomic scale to the macroscopic scale and the interaction between clusters. It is found that the interaction between clusters has a strong effect on their formation. The formation and distribution of the contact clusters is far more complicated than that predicted by the asperity model. Ignorance of the interaction between them leads to overestimating the contacting force. In real contact, contacting clusters are smaller and more discrete due to the interaction between the asperities. Understanding the exact nature of the contact area with the normal load is essential to the following research on friction.

A self-consistent density based embedding scheme applied to the adsorption of CO on Pd(111)

NASA Astrophysics Data System (ADS)

Lahav, D.; Klüner, T.

2007-06-01

We derive a variant of a density based embedded cluster approach as an improvement to a recently proposed embedding theory for metallic substrates (Govind et al 1999 J. Chem. Phys. 110 7677; Klüner et al 2001 Phys. Rev. Lett. 86 5954). In this scheme, a local region in space is represented by a small cluster which is treated by accurate quantum chemical methodology. The interaction of the cluster with the infinite solid is taken into account by an effective one-electron embedding operator representing the surrounding region. We propose a self-consistent embedding scheme which resolves intrinsic problems of the former theory, in particular a violation of strict density conservation. The proposed scheme is applied to the well-known benchmark system CO/Pd(111).

Ferromagnetism and spin glass ordering in transition metal alloys (invited)

NASA Astrophysics Data System (ADS)

Crane, S.; Carnegie, D. W., Jr.; Claus, H.

1982-03-01

Magnetic properties of transition metal alloys near the percolation threshold are often complicated by metallurgical effects. Alloys like AuFe, VFe, CuNi, RhNi, and PdNi are in general not random solid solutions but have various degrees of atomic clustering or short-range order (SRO), depending on the heat treatment. First, it is shown how the magnetic ordering temperature of these alloys varies with the degree of clustering or SRO. Second, by systematically changing this degree of clustering or SRO, important information can be obtained about the magnetic phase diagram. In all these alloys below the percolation limit, the onset of ferromagnetic order is probably preceded by a spin glass-type ordering. However, details of the magnetic phase diagram near the critical point can be quite different alloy systems.

One-step generation of continuous-variable quadripartite cluster states in a circuit QED system

NASA Astrophysics Data System (ADS)

Yang, Zhi-peng; Li, Zhen; Ma, Sheng-li; Li, Fu-li

2017-07-01

We propose a dissipative scheme for one-step generation of continuous-variable quadripartite cluster states in a circuit QED setup consisting of four superconducting coplanar waveguide resonators and a gap-tunable superconducting flux qubit. With external driving fields to adjust the desired qubit-resonator and resonator-resonator interactions, we show that continuous-variable quadripartite cluster states of the four resonators can be generated with the assistance of energy relaxation of the qubit. By comparison with the previous proposals, the distinct advantage of our scheme is that only one step of quantum operation is needed to realize the quantum state engineering. This makes our scheme simpler and more feasible in experiment. Our result may have useful application for implementing quantum computation in solid-state circuit QED systems.

Interaction of Boron Clusters with Oxygen: a DFT Study

NASA Astrophysics Data System (ADS)

Salavitabar, Kamron; Boggavarapu, Kiran; Kandalam, Anil

A controlled combustion involving aluminum nanoparticles has often been the focus of studies in the field of solid fuel propellants. However very little focus has been given to the study of boron nanoparticles in controlled combustion. In contrast to aluminum nanoclusters, boron nanoclusters (Bn) are known to exhibit a planar geometries even at the size of n = 19 - 20, and thus offer a greater surface area for interaction with oxygen. Earlier experimental studies have shown that boron nanoclusters exhibit different reactivity with oxygen depending on their size and charge. In this poster, we present our recent density functional theory based results, focusing on the reactivity patterns of neutral and negatively charged B5 cluster with On, where n = 1 - 5; and B6 cluster with On (n = 1 - 2). The effect of charge on the reactivity of boron cluster, variation in the stability of product clusters, i e., neutral and negatively charged B5On (n = 1 - 5) and B6On (n = 1 - 2) are also examined. Financial Support from West Chester University Foundation under FaStR grant is acknowledged.

Multiplexed immunofluorescence delineates proteomic cancer cell states associated with metabolism

PubMed Central

Sood, Anup; Miller, Alexandra M.; Brogi, Edi; Sui, Yunxia; Armenia, Joshua; McDonough, Elizabeth; Santamaria-Pang, Alberto; Stamper, Aleksandra; Campos, Carl; Pang, Zhengyu; Li, Qing; Port, Elisa; Graeber, Thomas G.; Schultz, Nikolaus; Ginty, Fiona; Larson, Steven M.

2016-01-01

The phenotypic diversity of cancer results from genetic and nongenetic factors. Most studies of cancer heterogeneity have focused on DNA alterations, as technologies for proteomic measurements in clinical specimen are currently less advanced. Here, we used a multiplexed immunofluorescence staining platform to measure the expression of 27 proteins at the single-cell level in formalin-fixed and paraffin-embedded samples from treatment-naive stage II/III human breast cancer. Unsupervised clustering of protein expression data from 638,577 tumor cells in 26 breast cancers identified 8 clusters of protein coexpression. In about one-third of breast cancers, over 95% of all neoplastic cells expressed a single protein coexpression cluster. The remaining tumors harbored tumor cells representing multiple protein coexpression clusters, either in a regional distribution or intermingled throughout the tumor. Tumor uptake of the radiotracer 18F-fluorodeoxyglucose was associated with protein expression clusters characterized by hormone receptor loss, PTEN alteration, and HER2 gene amplification. Our study demonstrates an approach to generate cellular heterogeneity metrics in routinely collected solid tumor specimens and integrate them with in vivo cancer phenotypes. PMID:27182557

Speckle reduction of OCT images using an adaptive cluster-based filtering

NASA Astrophysics Data System (ADS)

Adabi, Saba; Rashedi, Elaheh; Conforto, Silvia; Mehregan, Darius; Xu, Qiuyun; Nasiriavanaki, Mohammadreza

2017-02-01

Optical coherence tomography (OCT) has become a favorable device in the dermatology discipline due to its moderate resolution and penetration depth. OCT images however contain grainy pattern, called speckle, due to the broadband source that has been used in the configuration of OCT. So far, a variety of filtering techniques is introduced to reduce speckle in OCT images. Most of these methods are generic and can be applied to OCT images of different tissues. In this paper, we present a method for speckle reduction of OCT skin images. Considering the architectural structure of skin layers, it seems that a skin image can benefit from being segmented in to differentiable clusters, and being filtered separately in each cluster by using a clustering method and filtering methods such as Wiener. The proposed algorithm was tested on an optical solid phantom with predetermined optical properties. The algorithm was also tested on healthy skin images. The results show that the cluster-based filtering method can reduce the speckle and increase the signal-to-noise ratio and contrast while preserving the edges in the image.

Density Functional Investigation of the Inclusion of Gold Clusters on a CH 3 S Self-Assembled Lattice on Au(111)

DOE PAGES

Allen, Darnel J.; Archibald, Wayne E.; Harper, John A.; ...

2016-01-01

We employ first-principles density functional theoretical calculations to address the inclusion of gold (Au) clusters in a well-packed CH 3 S self-assembled lattice. We compute CH 3 S adsorption energies to quantify the energetic stability of the self-assembly and gold adsorption and dissolution energies to characterize the structural stability of a series of Au clusters adsorbed at the SAM-Au interface. Our results indicate that the inclusion of Au clusters with less than four Au atoms in the SAM-Au interface enhances the binding of CH 3 S species. In contrast, larger Au clusters destabilize the self-assembly. We attribute this effect tomore » the low-coordinated gold atoms in the cluster. For small clusters, these low-coordinated sites have significantly different electronic properties compared to larger islands, which makes the binding with the self-assembly energetically more favorable. Our results further indicate that Au clusters in the SAM-Au interface are thermodynamically unstable and they will tend to dissolve, producing Au adatoms incorporated in the self-assembly in the form of CH 3 S-Au-SCH 3 species. This is due to the strong S-Au bond which stabilizes single Au adatoms in the self-assembly. Our results provide solid insight into the impact of adatom islands at the CH 3 S-Au interface.« less

The effect of the residues of vineyard fungicides on postharvest decay, 2011

USDA-ARS?s Scientific Manuscript database

The purpose for this experiment was to quantify the effect of residues of vineyard fungicides on control of postharvest decay of table grapes. Mature (22% soluble solids content), freshly harvested ‘Princess Seedless’ grape clusters were arranged on metal racks. Fungicides were applied with an air b...

First-principles melting of gallium clusters down to nine atoms: structural and electronic contributions to melting.

PubMed

Steenbergen, Krista G; Gaston, Nicola

2013-10-07

First-principles Born-Oppenheimer molecular dynamics simulations of small gallium clusters, including parallel tempering, probe the distinction between cluster and molecule in the size range of 7-12 atoms. In contrast to the larger sizes, dynamic measures of structural change at finite temperature demonstrate that Ga7 and Ga8 do not melt, suggesting a size limit to melting in gallium exists at 9 atoms. Analysis of electronic structure further supports this size limit, additionally demonstrating that a covalent nature cannot be identified for clusters larger than the gallium dimer. Ga9, Ga10 and Ga11 melt at greater-than-bulk temperatures, with no evident covalent character. As Ga12 represents the first small gallium cluster to melt at a lower-than-bulk temperature, we examine the structural properties of each cluster at finite temperature in order to probe both the origins of greater-than-bulk melting, as well as the significant differences in melting temperatures induced by a single atom addition. Size-sensitive melting temperatures can be explained by both energetic and entropic differences between the solid and liquid phases for each cluster. We show that the lower-than-bulk melting temperature of the 12-atom cluster can be attributed to persistent pair bonding, reminiscent of the pairing observed in α-gallium. This result supports the attribution of greater-than-bulk melting in gallium clusters to the anomalously low melting temperature of the bulk, due to its dimeric structure.

Radiation-induced segregation on defect clusters in single-phase concentrated solid-solution alloys

DOE PAGES

Lu, Chenyang; Yang, Taini; Jin, Ke; ...

2017-01-12

A group of single-phase concentrated solid-solution alloys (SP-CSAs), including NiFe, NiCoFe, NiCoFeCr, as well as a high entropy alloy NiCoFeCrMn, was irradiated with 3 MeV Ni 2+ ions at 773 K to a fluence of 5 10 16 ions/cm 2 for the study of radiation response with increasing compositional complexity. Advanced transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) was used to characterize the dislocation loop distribution and radiation-induced segregation (RIS) on defect clusters in the SP-CSAs. The results show that a higher fraction of faulted loops exists in the more compositionally complex alloys, which indicate that increasingmore » compositional complexity can extend the incubation period and delay loop growth. The RIS behaviors of each element in the SP-CSAs were observed as follows: Ni and Co tend to enrich, but Cr, Fe and Mn prefer to deplete near the defect clusters. RIS level can be significantly suppressed by increasing compositional complexity due to the sluggish atom diffusion. According to molecular static (MS) simulations, disk like segregations may form near the faulted dislocation loops in the SP-CSAs. Segregated elements tend to distribute around the whole faulted loop as a disk rather than only around the edge of the loop.« less

Cluster analysis of dynamic contrast enhanced MRI reveals tumor subregions related to locoregional relapse for cervical cancer patients.

PubMed

Torheim, Turid; Groendahl, Aurora R; Andersen, Erlend K F; Lyng, Heidi; Malinen, Eirik; Kvaal, Knut; Futsaether, Cecilia M

2016-11-01

Solid tumors are known to be spatially heterogeneous. Detection of treatment-resistant tumor regions can improve clinical outcome, by enabling implementation of strategies targeting such regions. In this study, K-means clustering was used to group voxels in dynamic contrast enhanced magnetic resonance images (DCE-MRI) of cervical cancers. The aim was to identify clusters reflecting treatment resistance that could be used for targeted radiotherapy with a dose-painting approach. Eighty-one patients with locally advanced cervical cancer underwent DCE-MRI prior to chemoradiotherapy. The resulting image time series were fitted to two pharmacokinetic models, the Tofts model (yielding parameters K trans and ν e ) and the Brix model (A Brix , k ep and k el ). K-means clustering was used to group similar voxels based on either the pharmacokinetic parameter maps or the relative signal increase (RSI) time series. The associations between voxel clusters and treatment outcome (measured as locoregional control) were evaluated using the volume fraction or the spatial distribution of each cluster. One voxel cluster based on the RSI time series was significantly related to locoregional control (adjusted p-value 0.048). This cluster consisted of low-enhancing voxels. We found that tumors with poor prognosis had this RSI-based cluster gathered into few patches, making this cluster a potential candidate for targeted radiotherapy. None of the voxels clusters based on Tofts or Brix parameter maps were significantly related to treatment outcome. We identified one group of tumor voxels significantly associated with locoregional relapse that could potentially be used for dose painting. This tumor voxel cluster was identified using the raw MRI time series rather than the pharmacokinetic maps.

Cluster Dynamics Modeling with Bubble Nucleation, Growth and Coalescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Almeida, Valmor F.; Blondel, Sophie; Bernholdt, David E.

The topic of this communication pertains to defect formation in irradiated solids such as plasma-facing tungsten submitted to helium implantation in fusion reactor com- ponents, and nuclear fuel (metal and oxides) submitted to volatile ssion product generation in nuclear reactors. The purpose of this progress report is to describe ef- forts towards addressing the prediction of long-time evolution of defects via continuum cluster dynamics simulation. The di culties are twofold. First, realistic, long-time dynamics in reactor conditions leads to a non-dilute di usion regime which is not accommodated by the prevailing dilute, stressless cluster dynamics theory. Second, long-time dynamics callsmore » for a large set of species (ideally an in nite set) to capture all possible emerging defects, and this represents a computational bottleneck. Extensions beyond the dilute limit is a signi cant undertaking since no model has been advanced to extend cluster dynamics to non-dilute, deformable conditions. Here our proposed approach to model the non-dilute limit is to monitor the appearance of a spatially localized void volume fraction in the solid matrix with a bell shape pro le and insert an explicit geometrical bubble onto the support of the bell function. The newly cre- ated internal moving boundary provides the means to account for the interfacial ux of mobile species into the bubble, and the growth of bubbles allows for coalescence phenomena which captures highly non-dilute interactions. We present a preliminary interfacial kinematic model with associated interfacial di usion transport to follow the evolution of the bubble in any number of spatial dimensions and any number of bubbles, which can be further extended to include a deformation theory. Finally we comment on a computational front-tracking method to be used in conjunction with conventional cluster dynamics simulations in the non-dilute model proposed.« less

Quantitative analysis of impact of awareness-raising activities on organic solid waste separation behaviour in Balikpapan City, Indonesia.

PubMed

Murase, Noriaki; Murayama, Takehiko; Nishikizawa, Shigeo; Sato, Yuriko

2017-10-01

Many cities in Indonesia are under pressure to reduce solid waste and dispose of it properly. In response to this pressure, the Japan International Cooperation Agency and the Indonesian Government have implemented a solid waste separation and collection project to reduce solid waste in the target area (810 households) of Balikpapan City. We used a cluster randomised controlled trial method to measure the impact of awareness-raising activities that were introduced by the project on residents' organic solid waste separation behaviour. The level of properly separated organic solid waste increased by 6.0% in areas that conducted awareness-raising activities. Meanwhile, the level decreased by 3.6% in areas that did not conduct similar activities. Therefore, in relative comparison, awareness-raising increased the level by 9.6%. A comparison among small communities in the target area confirmed that awareness-raising activities had a significant impact on organic solid waste separation. High frequencies of monitoring at waste stations and door-to-door visits by community members had a positive impact on organic solid waste separation. A correlation between the proximity of environmental volunteers' houses to waste stations and a high level of separation was also confirmed. The awareness-raising activities introduced by the project led to a significant increase in the separation of organic solid waste.

Martensitic transformations in Ag-Au bimetallic core-shell nanoalloys

NASA Astrophysics Data System (ADS)

Chen, Fuyi; Johnston, Roy L.

2008-01-01

Combining the Gupta potential and bond order analysis in a molecular dynamics simulation, a martensitic transformation is observed in the 147-atom AucoreAgshell nanostructure at 328K. The response time for this transformation is about 7ps at 350K. In pure gold clusters, it was previously thought that a similar solid-to-solid transformation is a prelude to melting transitions. In the present case, atomic pathway snapshots show that the heating energy is used to overcome the energy barrier for initiating the spontaneous process. The subsequent twist-deformation propagation and termination are clearly observed.

The effect of size and composition on structural transitions in monometallic nanoparticles

NASA Astrophysics Data System (ADS)

Rossi, Kevin; Pavan, Luca; Soon, YeeYeen; Baletto, Francesca

2018-02-01

Predicting the morphological stability of nanoparticles is an essential step towards the accurate modelling of their chemophysical properties. Here we investigate solid-solid transitions in monometallic clusters of 0.5-2.0 nm diameter at finite temperatures and we report the complex dependence of the rearrangement mechanism on the nanoparticle's composition and size. The concerted Lipscomb's Diamond-Square-Diamond mechanisms which connects the decahedral or the cuboctahedral to the icosahedral basins, take place only below a material dependent critical size above which surface diffusion prevails and leads to low-symmetry and defected shapes still belonging to the initial basin.

A theoretical study of water equilibria: The cluster distribution versus temperature and pressure for (H2O)n, n=1-60, and ice

NASA Astrophysics Data System (ADS)

Lenz, Annika; Ojamäe, Lars

2009-10-01

The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0-120 K) and 28-mer (100-260 K)] dominate at low temperatures and separate to smaller clusters [21-22-mer (170-280 K) and 4-6-mer (270-320 K) and to monomers (300-350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20-22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (Cp, ΔH) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

A theoretical study of water equilibria: the cluster distribution versus temperature and pressure for (H2O)n, n = 1-60, and ice.

PubMed

Lenz, Annika; Ojamäe, Lars

2009-10-07

The size distribution of water clusters at equilibrium is studied using quantum-chemical calculations in combination with statistical thermodynamics. The necessary energetic data is obtained by quantum-chemical B3LYP computations and through extrapolations from the B3LYP results for the larger clusters. Clusters with up to 60 molecules are included in the equilibrium computations. Populations of different cluster sizes are calculated using both an ideal gas model with noninteracting clusters and a model where a correction for the interaction energy is included analogous to the van der Waals law. In standard vapor the majority of the water molecules are monomers. For the ideal gas model at 1 atm large clusters [56-mer (0-120 K) and 28-mer (100-260 K)] dominate at low temperatures and separate to smaller clusters [21-22-mer (170-280 K) and 4-6-mer (270-320 K) and to monomers (300-350 K)] when the temperature is increased. At lower pressure the transition from clusters to monomers lies at lower temperatures and fewer cluster sizes are formed. The computed size distribution exhibits enhanced peaks for the clusters consisting of 21 and 28 water molecules; these sizes are for protonated water clusters often referred to as magic numbers. If cluster-cluster interactions are included in the model the transition from clusters to monomers is sharper (i.e., occurs over a smaller temperature interval) than when the ideal-gas model is used. Clusters with 20-22 molecules dominate in the liquid region. When a large icelike cluster is included it will dominate for temperatures up to 325 K for the noninteracting clusters model. Thermodynamic properties (C(p), DeltaH) were calculated with in general good agreement with experimental values for the solid and gas phase. A formula for the number of H-bond topologies in a given cluster structure is derived. For the 20-mer it is shown that the number of topologies contributes to making the population of dodecahedron-shaped cluster larger than that of a lower-energy fused prism cluster at high temperatures.

Effect of two different treatments for reducing grape yield in Vitis vinifera cv Syrah on wine composition and quality: berry thinning versus cluster thinning.

PubMed

Gil, M; Esteruelas, M; González, E; Kontoudakis, N; Jiménez, J; Fort, F; Canals, J M; Hermosín-Gutiérrez, I; Zamora, F

2013-05-22

The influence of two treatments for reducing grape yield, cluster thinning and berry thinning, on red wine composition and quality were studied in a Vitis vinifera cv Syrah vineyard in AOC Penedès (Spain). Cluster thinning reduced grape yield per vine by around 40% whereas berry thinning only reduced it by around 20%. Cluster thinning grapes had higher soluble solids content than control grapes, and their resultant wines have greater anthocyanin and polysaccharide concentrations than the control wine. Wine obtained from berry thinning grapes had a higher total phenolic index, greater flavonol, proanthocyanidin, and polysaccharide concentrations, and lower titratable acidity than the control wine. Wines obtained from both treatments were sufficiently different from the control wine to be significantly distinguished by a trained panel in a triangular test. Even though both treatments seem to be effective at improving the quality of wine, berry thinning has the advantage because it has less impact on crop yield reduction.

The Open Connectome Project Data Cluster: Scalable Analysis and Vision for High-Throughput Neuroscience.

PubMed

Burns, Randal; Roncal, William Gray; Kleissas, Dean; Lillaney, Kunal; Manavalan, Priya; Perlman, Eric; Berger, Daniel R; Bock, Davi D; Chung, Kwanghun; Grosenick, Logan; Kasthuri, Narayanan; Weiler, Nicholas C; Deisseroth, Karl; Kazhdan, Michael; Lichtman, Jeff; Reid, R Clay; Smith, Stephen J; Szalay, Alexander S; Vogelstein, Joshua T; Vogelstein, R Jacob

2013-01-01

We describe a scalable database cluster for the spatial analysis and annotation of high-throughput brain imaging data, initially for 3-d electron microscopy image stacks, but for time-series and multi-channel data as well. The system was designed primarily for workloads that build connectomes - neural connectivity maps of the brain-using the parallel execution of computer vision algorithms on high-performance compute clusters. These services and open-science data sets are publicly available at openconnecto.me. The system design inherits much from NoSQL scale-out and data-intensive computing architectures. We distribute data to cluster nodes by partitioning a spatial index. We direct I/O to different systems-reads to parallel disk arrays and writes to solid-state storage-to avoid I/O interference and maximize throughput. All programming interfaces are RESTful Web services, which are simple and stateless, improving scalability and usability. We include a performance evaluation of the production system, highlighting the effec-tiveness of spatial data organization.

The Open Connectome Project Data Cluster: Scalable Analysis and Vision for High-Throughput Neuroscience

PubMed Central

Burns, Randal; Roncal, William Gray; Kleissas, Dean; Lillaney, Kunal; Manavalan, Priya; Perlman, Eric; Berger, Daniel R.; Bock, Davi D.; Chung, Kwanghun; Grosenick, Logan; Kasthuri, Narayanan; Weiler, Nicholas C.; Deisseroth, Karl; Kazhdan, Michael; Lichtman, Jeff; Reid, R. Clay; Smith, Stephen J.; Szalay, Alexander S.; Vogelstein, Joshua T.; Vogelstein, R. Jacob

2013-01-01

We describe a scalable database cluster for the spatial analysis and annotation of high-throughput brain imaging data, initially for 3-d electron microscopy image stacks, but for time-series and multi-channel data as well. The system was designed primarily for workloads that build connectomes— neural connectivity maps of the brain—using the parallel execution of computer vision algorithms on high-performance compute clusters. These services and open-science data sets are publicly available at openconnecto.me. The system design inherits much from NoSQL scale-out and data-intensive computing architectures. We distribute data to cluster nodes by partitioning a spatial index. We direct I/O to different systems—reads to parallel disk arrays and writes to solid-state storage—to avoid I/O interference and maximize throughput. All programming interfaces are RESTful Web services, which are simple and stateless, improving scalability and usability. We include a performance evaluation of the production system, highlighting the effec-tiveness of spatial data organization. PMID:24401992

Distributions of methyl group rotational barriers in polycrystalline organic solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beckmann, Peter A., E-mail: pbeckman@brynmawr.edu, E-mail: wangxianlong@uestc.edu.cn; Conn, Kathleen G.; Division of Education and Human Services, Neumann University, One Neumann Drive, Aston, Pennsylvania 19014-1298

We bring together solid state {sup 1}H spin-lattice relaxation rate measurements, scanning electron microscopy, single crystal X-ray diffraction, and electronic structure calculations for two methyl substituted organic compounds to investigate methyl group (CH{sub 3}) rotational dynamics in the solid state. Methyl group rotational barrier heights are computed using electronic structure calculations, both in isolated molecules and in molecular clusters mimicking a perfect single crystal environment. The calculations are performed on suitable clusters built from the X-ray diffraction studies. These calculations allow for an estimate of the intramolecular and the intermolecular contributions to the barrier heights. The {sup 1}H relaxation measurements,more » on the other hand, are performed with polycrystalline samples which have been investigated with scanning electron microscopy. The {sup 1}H relaxation measurements are best fitted with a distribution of activation energies for methyl group rotation and we propose, based on the scanning electron microscopy images, that this distribution arises from molecules near crystallite surfaces or near other crystal imperfections (vacancies, dislocations, etc.). An activation energy characterizing this distribution is compared with a barrier height determined from the electronic structure calculations and a consistent model for methyl group rotation is developed. The compounds are 1,6-dimethylphenanthrene and 1,8-dimethylphenanthrene and the methyl group barriers being discussed and compared are in the 2–12 kJ mol{sup −1} range.« less

From the Superatom Model to a Diverse Array of Super-Elements: A Systematic Study of Dopant Influence on the Electronic Structure of Thiolate-Protected Gold Clusters.

PubMed

Schacht, Julia; Gaston, Nicola

2016-10-18

The electronic properties of doped thiolate-protected gold clusters are often referred to as tunable, but their study to date, conducted at different levels of theory, does not allow a systematic evaluation of this claim. Here, using density functional theory, the applicability of the superatomic model to these clusters is critically evaluated, and related to the degree of structural distortion and electronic inhomogeneity in the differently doped clusters, with dopant atoms Pd, Pt, Cu, and Ag. The effect of electron number is systematically evaluated by varying the charge on the overall cluster, and the nominal number of delocalized electrons, employed in the superatomic model, is compared to the numbers obtained from Bader analysis of individual atomic charges. We find that the superatomic model is highly applicable to all of these clusters, and is able to predict and explain the changing electronic structure as a function of charge. However, significant perturbations of the model arise due to doping, due to distortions of the core structure of the Au 13 [RS(AuSR) 2 ] 6 - cluster. In addition, analysis of the electronic structure indicates that the superatomic character is distributed further across the ligand shell in the case of the doped clusters, which may have implications for the self-assembly of these clusters into materials. The prediction of appropriate clusters for such superatomic solids relies critically on such quantitative analysis of the tunability of the electronic structure. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ligand combination strategy for the preparation of novel low-dimensional and open-framework metal cluster materials

NASA Astrophysics Data System (ADS)

Anokhina, Ekaterina V.

Low-dimensional and open-framework materials containing transition metals have a wide range of applications in redox catalysis, solid-state batteries, and electronic and magnetic devices. This dissertation reports on research carried out with the goal to develop a strategy for the preparation of low-dimensional and open-framework materials using octahedral metal clusters as building blocks. Our approach takes its roots from crystal engineering principles where the desired framework topologies are achieved through building block design. The key idea of this work is to induce directional bonding preferences in the cluster units using a combination of ligands with a large difference in charge density. This investigation led to the preparation and characterization of a new family of niobium oxychloride cluster compounds with original structure types exhibiting 1ow-dimensional or open-framework character. Most of these materials have framework topologies unprecedented in compounds containing octahedral clusters. Comparative analysis of their structural features indicates that the novel cluster connectivity patterns in these systems are the result of complex interplay between the effects of anisotropic ligand arrangement in the cluster unit and optimization of ligand-counterion electrostatic interactions. The important role played by these factors sets niobium oxychloride systems apart from cluster compounds with one ligand type or statistical ligand distribution where the main structure-determining factor is the total number of ligands. These results provide a blueprint for expanding the ligand combination strategy to other transition metal cluster systems and for the future rational design of cluster-based materials.

Comparison of spray drying, electroblowing and electrospinning for preparation of Eudragit E and itraconazole solid dispersions.

PubMed

Sóti, Péter Lajos; Bocz, Katalin; Pataki, Hajnalka; Eke, Zsuzsanna; Farkas, Attila; Verreck, Geert; Kiss, Éva; Fekete, Pál; Vigh, Tamás; Wagner, István; Nagy, Zsombor K; Marosi, György

2015-10-15

Three solvent based methods: spray drying (SD), electrospinning (ES) and air-assisted electrospinning (electroblowing; EB) were used to prepare solid dispersions of itraconazole and Eudragit E. Samples with the same API/polymer ratios were prepared in order to make the three technologies comparable. The structure and morphology of solid dispersions were identified by scanning electron microscopy and solid phase analytical methods such as, X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and Raman chemical mapping. Moreover, the residual organic solvents of the solid products were determined by static headspace-gas chromatography/mass spectroscopy measurements and the wettability of samples was characterized by contact angle measurement. The pharmaceutical performance of the three dispersion type, evaluated by dissolution tests, proved to be very similar. According to XRPD and DSC analyses, made after the production, all the solid dispersions were free of any API crystal clusters but about 10 wt% drug crystallinity was observed after three months of storage in the case of the SD samples in contrast to the samples produced by ES and EB in which the polymer matrix preserved the API in amorphous state. Copyright © 2015 Elsevier B.V. All rights reserved.

The [(AI 2O 3) 2] - Anion Cluster: Electron Localization-Delocalization Isomerism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierka, Marek; Dobler, Jens; Sauer, Joachim

2009-10-05

Three-dimensional bulk alumina and its two-dimensional thin films show great structural diversity, posing considerable challenges to their experimental structural characterization and computational modeling. Recently, structural diversity has also been demonstrated for zerodimensional gas phase aluminum oxide clusters. Mass-selected clusters not only make systematic studies of the structural and electronic properties as a function of size possible, but lately have also emerged as powerful molecular models of complex surfaces and solid catalysts. In particular, the [(Al 2O 3) 3-5] + clusters were the first example of polynuclear maingroup metal oxide cluster that are able to thermally activate CH 4. Over themore » past decades gas phase aluminum oxide clusters have been extensively studied both experimentally and computationally, but definitive structural assignments were made for only a handful of them: the planar [Al 3O 3] - and [Al 5O 4] - cluster anions, and the [(Al 2O 3) 1-4(AlO)] + cluster cations. For stoichiometric clusters only the atomic structures of [(Al 2O 3) 4] +/0 have been nambiguously resolved. Here we report on the structures of the [(Al 2O 3) 2] -/0 clusters combining photoelectron spectroscopy (PES) and quantum chemical calculations employing a genetic algorithm as a global optimization technique. The [(Al 2O 3) 2] - cluster anion show energetically close lying but structurally distinct cage and sheet-like isomers which differ by delocalization/localization of the extra electron. The experimental results are crucial for benchmarking the different computational methods applied with respect to a proper description of electron localization and the relative energies for the isomers which will be of considerable value for future computational studies of aluminum oxide and related systems.« less

Synthesis and characterization of transition metal clusters: From the isolation of ligand-stabilized solid fragments to the tuning of magnetic anisotropy and host-guest selectivity, and, Approaches to science teaching: Development of an observation instrument with a measurement model based on item response theory

NASA Astrophysics Data System (ADS)

Hee, Allan George

Part I. The work presented herein describes efforts to develop general techniques for the synthesis of transition metal clusters and the manipulation of their properties. In Chapter 2, it is demonstrated that a modified metal atom reactor allows for the vaporization, passivation, and isolation of metal-chalcogenide clusters from their parent binary solids. Among the clusters produced by this method were Cr6S8(PEt3)6, Fe4S 4(PEt3)4, Co6S8(PEt 3)6, Cu6S4(PEt3)6, Cu12S6(PEt3)8, and Cu26Se 13(PEt3)14. To create single-molecule magnets with higher demagnetization barriers, we are developing metal-cyanide systems which exhibit highly adjustable magnetic behavior. Chapter 3 reports an attempt to introduce magnetic anisotropy into a MnCr6 cluster. Replacement of CrIII with Mo III resulted in the assembly of K[(Me3tacn)6MnMo 6(CN)18](ClO4)3 (Me3tacn = N,N',N″ -trimethyl-1,4,7-triazacyclononane)---the first well-documented example of a cyano-bridged single-molecule magnet. Recently, it was demonstrated that replacing Me3tacn with the less sterically hindering tach (tach = cis,cis-1,3,5-triaminocyclohexane) in the face-centered cubic cluster [(tach)8Cr8Ni 6(CN)24]Br12 provides greater access to the cluster cavity. Chapter 4 describes my efforts to probe the selectivity of this cluster toward inclusion of various guests. Part II. Successful implementation of student-centered curricula reforms requires the creation of a measurement instrument for monitoring whether the curricula are being used as intended. The creation and development of an observation instrument would greatly contribute to this effort. To develop a theoretically sound construct map, it is necessary to review the literature and conduct our own investigations of approaches to science teaching. Chapter 2 presents the findings of these investigations and their contributions to our understanding of the construct. Using these findings, the Science Teaching Observation Protocol (STOP) was created and designed to measure two subconstructs: intentions and strategies. Chapter 3 details the first pilot test of STOP and analysis of the collected data. In Chapter 4, the theoretical shortcomings of the instrument are analyzed and discussed. Modified versions of the intention and strategy subconstruct maps are presented.

Four-body interaction energy for compressed solid krypton from quantum theory.

PubMed

Tian, Chunling; Wu, Na; Liu, Fusheng; Saxena, Surendra K; Zheng, Xingrong

2012-07-28

The importance of the four-body contribution in compressed solid krypton was first evaluated using the many-body expansion method and the coupled cluster theory with full single and double excitations plus perturbative treatment of triples. All different four-atom clusters existing in the first- and second-nearest neighbor shells of face-centered cubic krypton were considered, and both self-consistent-field Hartree-Fock and correlation parts of the four-body interaction were accurately determined from the ambient conditions up to eightfold volume compression. We find that the four-body interaction energy is negative at compression ratio lower than 2, where the dispersive forces play a dominant role. With increasing the compression, the four-body contribution becomes repulsive and significantly cancels the over-softening effects of the three-body potential. The obtained equation of state (EOS) was compared with the experiments and the density-functional theory calculations. It shows that combination of the four-body effects with two- and three-body interactions leads to an excellent agreement with EOS measurements throughout the whole experimental range 0-130 GPa, and extends the prediction to 300 GPa.

Relating dynamics of model unentangled, crystallizable polymeric liquids to their local structure

NASA Astrophysics Data System (ADS)

Nguyen, Hong T.; Hoy, Robert S.

We study the liquid-state dynamics of a recently developed, crystallizable bead-spring polymer model. The model possesses a single ground state (NCP, wherein monomers close-pack and chains are nematically aligned) for all finite bending stiffnesses kb, but the solid morphologies formed under cooling vary strongly with kb, varying from NCP to amorphous. We find that systems with kb producing amorphous order are good glass-formers exhibiting the classic Vogel-Fulcher slowdown with decreasing temperature T. In contrast, systems with kb producing crystalline solids exhibit a simpler dynamics when kb is small. Larger kb produce more complex dynamics, but these are associated with the existence of an intermediate nematic liquid rather than glassy slowdown. We relate these differences to local, cluster-level structure measured via TCC analyses. Formation propensities and lifetimes of various clusters (associated with amorphous or crystalline order) vary strongly with kb and T. We relate these differences to those measured by the self-intermediate scattering function and other macroscopic measures of dynamics. Our results should aid in understanding the competition between crystallization and glass-formation in synthetic polymers.

Rationalizing the role of structural motif and underlying electronic structure in the finite temperature behavior of atomic clusters

NASA Astrophysics Data System (ADS)

Susan, Anju; Joshi, Kavita

2014-04-01

Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al36 which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature.

Simulation studies of glassy nanoclusters

NASA Astrophysics Data System (ADS)

Bowles, Richard

2015-03-01

Glassy materials are amorphous solids usually formed by rapidly cooling a liquid below its equilibrium freezing temperature, trapping the particles in a liquid-like structure at the glass transition temperature. While appearing throughout nature and industry, these systems continue to challenge the way we think about the dynamics and thermodynamics of condensed matter and a fundamental understanding of the glass state remains elusive. This talk describes molecular simulation studies of glassy behaviour in binary Lennard-Jones nanoclusters. We show that the relaxation dynamics of the clusters is nonuniform and the core of the cluster goes through a glass transition at higher temperatures than at the surface. As the nanoclusters are cooled, they also exhibit a fragile-strong crossover in their dynamics and we explore how this phenomena is linked to the potential energy landscape of the clusters. Finally, we compare the properties of nanoclusters formed through vapour condensation, directly to the glassy state, with those of glassy clusters formed through traditional supercooling. The condensation clusters are shown to form ultra-stable glassy states analogous to the ultra-stable glasses formed by thin film vapour deposition onto a cold substrate. In all, our work suggests that nanoscale clusters exhibit some unique glassy features, while also offering potential insights into the fundamental nature of the glass transition.

Photoionization of rare gas clusters

NASA Astrophysics Data System (ADS)

Zhang, Huaizhen

This thesis concentrates on the study of photoionization of van der Waals clusters with different cluster sizes. The goal of the experimental investigation is to understand the electronic structure of van der Waals clusters and the electronic dynamics. These studies are fundamental to understand the interaction between UV-X rays and clusters. The experiments were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory. The experimental method employs angle-resolved time-of-flight photoelectron spectrometry, one of the most powerful methods for probing the electronic structure of atoms, molecules, clusters and solids. The van der Waals cluster photoionization studies are focused on probing the evolution of the photoelectron angular distribution parameter as a function of photon energy and cluster size. The angular distribution has been known to be a sensitive probe of the electronic structure in atoms and molecules. However, it has not been used in the case of van der Waals clusters. We carried out outer-valence levels, inner-valence levels and core-levels cluster photoionization experiments. Specifically, this work reports on the first quantitative measurements of the angular distribution parameters of rare gas clusters as a function of average cluster sizes. Our findings for xenon clusters is that the overall photon-energy-dependent behavior of the photoelectrons from the clusters is very similar to that of the corresponding free atoms. However, distinct differences in the angular distribution point at cluster-size-dependent effects were found. For krypton clusters, in the photon energy range where atomic photoelectrons have a high angular anisotropy, our measurements show considerably more isotropic angular distributions for the cluster photoelectrons, especially right above the 3d and 4p thresholds. For the valence electrons, a surprising difference between the two spin-orbit components was found. For argon clusters, we found that the angular distribution parameter values of the two-spin-orbit components from Ar 2p clusters are slightly different. When comparing the beta values for Ar between atoms and clusters, we found different results between Ar 3s atoms and clusters, and between Ar 3p atoms and clusters. Argon cluster resonance from surface and bulk were also measured. Furthermore, the angular distribution parameters of Ar cluster photoelectrons and Ar atom photoelectrons in the 3s → np ionization region were obtained.

An approach for drag correction based on the local heterogeneity for gas-solid flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tingwen; Wang, Limin; Rogers, William

2016-09-22

The drag models typically used for gas-solids interaction are mainly developed based on homogeneous systems of flow passing fixed particle assembly. It has been shown that the heterogeneous structures, i.e., clusters and bubbles in fluidized beds, need to be resolved to account for their effect in the numerical simulations. Since the heterogeneity is essentially captured through the local concentration gradient in the computational cells, this study proposes a simple approach to account for the non-uniformity of solids spatial distribution inside a computational cell and its effect on the interaction between gas and solid phases. Finally, to validate this approach, themore » predicted drag coefficient has been compared to the results from direct numerical simulations. In addition, the need to account for this type of heterogeneity is discussed for a periodic riser flow simulation with highly resolved numerical grids and the impact of the proposed correction for drag is demonstrated.« less

A smoothed particle hydrodynamics framework for modelling multiphase interactions at meso-scale

NASA Astrophysics Data System (ADS)

Li, Ling; Shen, Luming; Nguyen, Giang D.; El-Zein, Abbas; Maggi, Federico

2018-01-01

A smoothed particle hydrodynamics (SPH) framework is developed for modelling multiphase interactions at meso-scale, including the liquid-solid interaction induced deformation of the solid phase. With an inter-particle force formulation that mimics the inter-atomic force in molecular dynamics, the proposed framework includes the long-range attractions between particles, and more importantly, the short-range repulsive forces to avoid particle clustering and instability problems. Three-dimensional numerical studies have been conducted to demonstrate the capabilities of the proposed framework to quantitatively replicate the surface tension of water, to model the interactions between immiscible liquids and solid, and more importantly, to simultaneously model the deformation of solid and liquid induced by the multiphase interaction. By varying inter-particle potential magnitude, the proposed SPH framework has successfully simulated various wetting properties ranging from hydrophobic to hydrophilic surfaces. The simulation results demonstrate the potential of the proposed framework to genuinely study complex multiphase interactions in wet granular media.

Cluster Analysis Identifies Distinct Pathogenetic Patterns in C3 Glomerulopathies/Immune Complex-Mediated Membranoproliferative GN.

PubMed

Iatropoulos, Paraskevas; Daina, Erica; Curreri, Manuela; Piras, Rossella; Valoti, Elisabetta; Mele, Caterina; Bresin, Elena; Gamba, Sara; Alberti, Marta; Breno, Matteo; Perna, Annalisa; Bettoni, Serena; Sabadini, Ettore; Murer, Luisa; Vivarelli, Marina; Noris, Marina; Remuzzi, Giuseppe

2018-01-01

Membranoproliferative GN (MPGN) was recently reclassified as alternative pathway complement-mediated C3 glomerulopathy (C3G) and immune complex-mediated membranoproliferative GN (IC-MPGN). However, genetic and acquired alternative pathway abnormalities are also observed in IC-MPGN. Here, we explored the presence of distinct disease entities characterized by specific pathophysiologic mechanisms. We performed unsupervised hierarchical clustering, a data-driven statistical approach, on histologic, genetic, and clinical data and data regarding serum/plasma complement parameters from 173 patients with C3G/IC-MPGN. This approach divided patients into four clusters, indicating the existence of four different pathogenetic patterns. Specifically, this analysis separated patients with fluid-phase complement activation (clusters 1-3) who had low serum C3 levels and a high prevalence of genetic and acquired alternative pathway abnormalities from patients with solid-phase complement activation (cluster 4) who had normal or mildly altered serum C3, late disease onset, and poor renal survival. In patients with fluid-phase complement activation, those in clusters 1 and 2 had massive activation of the alternative pathway, including activation of the terminal pathway, and the highest prevalence of subendothelial deposits, but those in cluster 2 had additional activation of the classic pathway and the highest prevalence of nephrotic syndrome at disease onset. Patients in cluster 3 had prevalent activation of C3 convertase and highly electron-dense intramembranous deposits. In addition, we provide a simple algorithm to assign patients with C3G/IC-MPGN to specific clusters. These distinct clusters may facilitate clarification of disease etiology, improve risk assessment for ESRD, and pave the way for personalized treatment. Copyright © 2018 by the American Society of Nephrology.

The structure of deposited metal clusters generated by laser evaporation

NASA Astrophysics Data System (ADS)

Faust, P.; Brandstättner, M.; Ding, A.

1991-09-01

Metal clusters have been produced using a laser evaporation source. A Nd-YAG laser beam focused onto a solid silver rod was used to evaporate the material, which was then cooled to form clusters with the help of a pulsed high pressure He beam. TOF mass spectra of these clusters reveal a strong occurrence of small and medium sized clusters ( n<100). Clusters were also deposited onto grid supported thin layers of carbon-films which were investigated by transmission electron microscopy. Very high resolution pictures of these grids were used to analyze the size distribution and the structure of the deposited clusters. The diffraction pattern caused by crystalline structure of the clusters reveals 3-and 5-fold symmetries as well as fcc bulk structure. This can be explained in terms of icosahedron and cuboctahedron type clusters deposited on the surface of the carbon layer. There is strong evidence that part of these cluster geometries had already been formed before the depostion process. The non-linear dependence of the cluster size and the cluster density on the generating conditions is discussed. Therefore the samples were observed in HREM in the stable DEEKO 100 microscope of the Fritz-Haber-Institut operating at 100 KV with the spherical aberration c S =0.5 mm. The quality of the pictures was improved by using the conditions of minimum phase contrast hollow cone illumination. This procedure led to a minimum of phase contrast artefacts. Among the well-crystallized particles were a great amount of five- and three-fold symmetries, icosahedra and cuboctahedra respectively. The largest clusters with five- and three-fold symmetries have been found with diameters of 7 nm; the smallest particles displaying the same undistorted symmetries were of about 2 mm. Even smaller ones with strong distortions could be observed although their classification is difficult. The quality of the images was improved by applying Fourier filtering techniques.

Notes from the Field: Probable Mucormycosis Among Adult Solid Organ Transplant Recipients at an Acute Care Hospital - Pennsylvania, 2014-2015.

PubMed

Novosad, Shannon A; Vasquez, Amber M; Nambiar, Atmaram; Arduino, Matthew J; Christensen, Erick; Moulton-Meissner, Heather; Keckler, M Shannon; Miller, Jeffrey; Perz, Joseph F; Lockhart, Shawn R; Chiller, Tom; Gould, Carolyn; Sehulster, Lynne; Brandt, Mary E; Weber, J Todd; Halpin, Alison Laufer; Mody, Rajal K

2016-05-13

On September 17, 2015, the Pennsylvania Department of Health (PADOH) notified CDC of a cluster of three potentially health care-associated mucormycete infections that occurred among solid organ transplant recipients during a 12-month period at hospital A. On September 18, hospital B reported that it had identified an additional transplant recipient with mucormycosis. Hospitals A and B are part of the same health care system and are connected by a pedestrian bridge. PADOH requested CDC's assistance with an on-site investigation, which started on September 22, to identify possible sources of infection and prevent additional infections.

Nonclassical nucleation pathways in protein crystallization

NASA Astrophysics Data System (ADS)

Zhang, Fajun

2017-11-01

Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

Nonclassical nucleation pathways in protein crystallization.

PubMed

Zhang, Fajun

2017-11-08

Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high density liquid phase, mesoscopic clusters, or a pre-ordered state. In this review, we focus on the studies of nonclassical pathways in protein crystallization and discuss the applications of the various scenarios of two-step nucleation theory. In particular, we focus on protein solutions in the presence of multivalent salts, which serve as a model protein system to study the nucleation pathways. We wish to point out the unique features of proteins as model systems for further studies.

The XXL Survey: First Results and Future

NASA Technical Reports Server (NTRS)

Pierre, M.; Adami, C.; Birkinshaw, M.; Chiappetti, L.; Ettori, S.; Evrard, A.; Faccioli, L.; Gastaldello, F.; Giles, P.; Horellou, C.;

Electrical probing of field-driven cascading quantized transitions of skyrmion cluster states in MnSi nanowires

NASA Astrophysics Data System (ADS)

Du, Haifeng; Liang, Dong; Jin, Chiming; Kong, Lingyao; Stolt, Matthew J.; Ning, Wei; Yang, Jiyong; Xing, Ying; Wang, Jian; Che, Renchao; Zang, Jiadong; Jin, Song; Zhang, Yuheng; Tian, Mingliang

2015-07-01

Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future spintronic devices. To enable such applications, particular attention has been focused on the properties of skyrmions in highly confined geometries such as one-dimensional nanowires. Hitherto, it is still experimentally unclear what happens when the width of the nanowire is comparable to that of a single skyrmion. Here, we achieve this by measuring the magnetoresistance in ultra-narrow MnSi nanowires. We observe quantized jumps in magnetoresistance versus magnetic field curves. By tracking the size dependence of the jump number, we infer that skyrmions are assembled into cluster states with a tunable number of skyrmions, in agreement with the Monte Carlo simulations. Our results enable an electric reading of the number of skyrmions in the cluster states, thus laying a solid foundation to realize skyrmion-based memory devices.

Silver-induced reconstruction of an adeninate-based metal-organic framework for encapsulation of luminescent adenine-stabilized silver clusters.

PubMed

Jonckheere, Dries; Coutino-Gonzalez, Eduardo; Baekelant, Wouter; Bueken, Bart; Reinsch, Helge; Stassen, Ivo; Fenwick, Oliver; Richard, Fanny; Samorì, Paolo; Ameloot, Rob; Hofkens, Johan; Roeffaers, Maarten B J; De Vos, Dirk E

2016-05-21

Bright luminescent silver-adenine species were successfully stabilized in the pores of the MOF-69A (zinc biphenyldicarboxylate) metal-organic framework, starting from the intrinsically blue luminescent bio-MOF-1 (zinc adeninate 4,4'-biphenyldicarboxylate). Bio-MOF-1 is transformed to the MOF-69A framework by selectively leaching structural adenine linkers from the original framework using silver nitrate solutions in aqueous ethanol. Simultaneously, bright blue-green luminescent silver-adenine clusters are formed inside the pores of the recrystallized MOF-69A matrix in high local concentrations. The structural transition and concurrent changes in optical properties were characterized using a range of structural, physicochemical and spectroscopic techniques (steady-state and time-resolved luminescence, quantum yield determination, fluorescence microscopy). The presented results open new avenues for exploring the use of MOFs containing luminescent silver clusters for solid-state lighting and sensor applications.

Crystallization process of a three-dimensional complex plasma

NASA Astrophysics Data System (ADS)

Steinmüller, Benjamin; Dietz, Christopher; Kretschmer, Michael; Thoma, Markus H.

2018-05-01

Characteristic timescales and length scales for phase transitions of real materials are in ranges where a direct visualization is unfeasible. Therefore, model systems can be useful. Here, the crystallization process of a three-dimensional complex plasma under gravity conditions is considered where the system ranges up to a large extent into the bulk plasma. Time-resolved measurements exhibit the process down to a single-particle level. Primary clusters, consisting of particles in the solid state, grow vertically and, secondarily, horizontally. The box-counting method shows a fractal dimension of df≈2.72 for the clusters. This value gives a hint that the formation process is a combination of local epitaxial and diffusion-limited growth. The particle density and the interparticle distance to the nearest neighbor remain constant within the clusters during crystallization. All results are in good agreement with former observations of a single-particle layer.

Numerical determination of the interfacial energy and nucleation barrier of curved solid-liquid interfaces in binary systems

NASA Astrophysics Data System (ADS)

Kundin, Julia; Choudhary, Muhammad Ajmal

2016-07-01

The phase-field crystal (PFC) technique is a widely used approach for modeling crystal growth phenomena with atomistic resolution on mesoscopic time scales. We use a two-dimensional PFC model for a binary system based on the work of Elder et al. [Phys. Rev. B 75, 064107 (2007), 10.1103/PhysRevB.75.064107] to study the effect of the curved, diffuse solid-liquid interface on the interfacial energy as well as the nucleation barrier. The calculation of the interfacial energy and the nucleation barrier certainly depends on the proper definition of the solid-liquid dividing surface and the corresponding nucleus size. We define the position of the sharp interface at which the interfacial energy is to be evaluated by using the concept of equimolar dividing surface (re) and the minimization of the interfacial energy (rs). The comparison of the results based on both radii shows that the difference re-rs is always positive and has a limit for large cluster sizes which is comparable to the Tolman length. Furthermore, we found the real nucleation barrier for small cluster sizes, which is defined as a function of the radius rs, and compared it with the classical nucleation theory. The simulation results also show that the extracted interfacial energy as function of both radii is independent of system size, and this dependence can be reasonably described by the nonclassical Tolman formula with a positive Tolman length.

Estimating carbon cluster binding energies from measured Cn distributions, n <= 10

NASA Astrophysics Data System (ADS)

Pargellis, A. N.

1990-08-01

Experimental data are presented for the cluster distribution of sputtered negative carbon clusters, C-n, with n≤10. Additionally, clusters have been observed with masses indicating they are CsC-2n, with n≤4. The C-n data are compared with the data obtained by other groups, for neutral and charged clusters, using a variety of sources such as evaporation, sputtering, and laser ablation. The data are used to estimate the cluster binding energies En, using the universal relation, En=(n-1)ΔHn+RTe [ln(Jn/J1)+0.5 ln(n)-α-(ΔSn-ΔS1)/R], derived from basic kinetic and thermodynamic relations. The estimated values agree astonishingly well with values from the literature, varying from published values by at most a few percent. In this equation, Jn is the observed current of n-atom clusters, ΔHn is the heat of vaporization, ΔH1=7.41 eV, and Te ≊0.25 eV (2900 K) is the effective source temperature. The relative change in cluster entropy during sublimation from the solid to vapor phase is approximated to first order by the relation (ΔSn-ΔS1)/R =3.1+0.9(n-2), and is fit to published data for n between 2 and 5 and temperatures between 2000 and 4000 K. The parameter α is empirical, obtained by fitting the data to known binding energies for Cn≤5 clusters. For evaporation sources, α must be zero, but α˜7 when sputtering with Cs+ ions, indicating the sputtered clusters appear to be in thermodynamic equilibrium, but not the atoms. Several possible mechanisms for the formation of clusters during sputtering are examined. One plausible mechanism is that atoms diffuse on the graphite surface to form clusters which are then desorbed by energetic, recoil atoms created in subsequent sputtering events.

Influence of Winemaking Processing Steps on the Amounts of (E)-2-Decenal and Tridecane as Off-Odorants Caused by Brown Marmorated Stink Bug (Halyomorpha halys).

PubMed

Mohekar, Pallavi; Osborne, James; Wiman, Nik G; Walton, Vaughn; Tomasino, Elizabeth

2017-02-01

Brown marmorated stink bugs (BMSB) release stress compounds, tridecane and (E)-2-decenal, that affect final wine quality. This study focuses on determining the effect of wine processing on (E)-2-decenal and tridecane release in both red and white wines. Wines were produced by adding live BMSB to grape clusters at densities of 0, 0.3, 1, and 3 bugs/cluster. Compound concentrations were measured using headspace solid phase microextraction with multidimensional gas chromatography and mass spectrometry. For red wines, the highest levels of stress compounds were found using 3 BMSB/cluster [tridecane, 614 μg/L; (E)-2-decenal, 2.0 μg/L]. Pressing was found to be the critical process point for stress compound release, and additional pressing processes, press types, and press fractions were investigated. BMSB taint for white wines was not found to be problematic with respect to wine quality. An action control of 3 BMSB/cluster is recommended as this was related to the known consumption rejection threshold for (E)-2-decenal.

First Principles Studies for Lithium Intercalation and Diffusion Behaviors in MoS2 treated with the Compressive Sensing Cluster Expansion

NASA Astrophysics Data System (ADS)

Liu, Chi-Ping; Zhou, Fei; Ozolins, Vidvuds

2014-03-01

Molybdenum disulfide (MoS2) is a good candidate electrode material for high capacity energy storage applications, such as lithium ion batteries and supercapacitors. In this work, we investigate lithium intercalation and diffusion kinetics in MoS2 by using first-principles density-functional theory (DFT) calculations. Two different lithium intercalation sites (1-H and 2-T) in MoS2 are found to be stable for lithium intercalation at different van der Waals' (vdW) gap distances. It is found that both thermodynamic and kinetic properties are highly related to the interlayer vdW gap distance, and that the optimal gap distance leads to effective solid-state diffusion in MoS2. Additionally, through the use of compressive sensing, we build accurate cluster expansion models to study the thermodynamic properties of MoS2 at high lithium content by truncating the higher order effective clusters with significant contributions. The results show that compressive sensing cluster expansion is a rigorous and powerful tool for model construction for advanced electrochemical applications in the future.

Energy-saving approaches to solid state street lighting

NASA Astrophysics Data System (ADS)

Vitta, Pranciškus; Stanikūnas, Rytis; Tuzikas, Arūnas; Reklaitis, Ignas; Stonkus, Andrius; Petrulis, Andrius; Vaitkevičius, Henrikas; Žukauskas, Artūras

2011-10-01

We consider the energy-saving potential of solid-state street lighting due to improved visual performance, weather sensitive luminance control and tracking of pedestrians and vehicles. A psychophysical experiment on the measurement of reaction time with a decision making task was performed under mesopic levels of illumination provided by a highpressure sodium (HPS) lamp and different solid-state light sources, such as daylight and warm-white phosphor converted light-emitting diodes (LEDs) and red-green-blue LED clusters. The results of the experiment imply that photopic luminances of road surface provided by solid-state light sources with an optimized spectral power distribution might be up to twice as low as those provided by the HPS lamp. Dynamical correction of road luminance against road surface conditions typical of Lithuanian climate was estimated to save about 20% of energy in comparison with constant-level illumination. The estimated energy savings due to the tracking of pedestrians and vehicles amount at least 25% with the cumulative effect of intelligent control of at least 40%. A solid-state street lighting system with intelligent control was demonstrated using a 300 m long test ground consisting of 10 solid-state street luminaires, a meteorological station and microwave motion sensor network operated via power line communication.

Waste management in primary healthcare centres of Iran.

PubMed

Mesdaghinia, Alireza; Naddafi, Kazem; Mahvi, Amir Hossein; Saeedi, Reza

2009-06-01

The waste management practices in primary healthcare centres of Iran were investigated in the present study. A total of 120 primary healthcare centres located across the country were selected using the cluster sampling method and the current situation of healthcare waste management was determined through field investigation. The quantities of solid waste and wastewater generation per outpatient were found to be 60 g outpatient(-1) day(-1) and 26 L outpatient(-1) day(-1), respectively. In all of the facilities, sharp objects were separated almost completely, but separation of other types of hazardous healthcare solid waste was only done in 25% of the centres. The separated hazardous solid waste materials were treated by incineration, temporary incineration and open burning methods in 32.5, 8.3 and 42.5% of the healthcare centres, respectively. In 16.7% of the centres the hazardous solid wastes were disposed of without any treatment. These results indicate that the management of waste materials in primary healthcare centres in Iran faced some problems. Staff training and awareness, separation of healthcare solid waste, establishment of the autoclave method for healthcare solid waste treatment and construction of septic tanks and disinfection units in the centres that were without access to a sewer system are the major measures that are suggested for improvement of the waste management practices.

Modelling solid solutions with cluster expansion, special quasirandom structures, and thermodynamic approaches

NASA Astrophysics Data System (ADS)

Saltas, V.; Horlait, D.; Sgourou, E. N.; Vallianatos, F.; Chroneos, A.

2017-12-01

Modelling solid solutions is fundamental in understanding the properties of numerous materials which are important for a range of applications in various fields including nanoelectronics and energy materials such as fuel cells, nuclear materials, and batteries, as the systematic understanding throughout the composition range of solid solutions for a range of conditions can be challenging from an experimental viewpoint. The main motivation of this review is to contribute to the discussion in the community of the applicability of methods that constitute the investigation of solid solutions computationally tractable. This is important as computational modelling is required to calculate numerous defect properties and to act synergistically with experiment to understand these materials. This review will examine in detail two examples: silicon germanium alloys and MAX phase solid solutions. Silicon germanium alloys are technologically important in nanoelectronic devices and are also relevant considering the recent advances in ternary and quaternary groups IV and III-V semiconductor alloys. MAX phase solid solutions display a palette of ceramic and metallic properties and it is anticipated that via their tuning they can have applications ranging from nuclear to aerospace industries as well as being precursors for particular MXenes. In the final part, a brief summary assesses the limitations and possibilities of the methodologies discussed, whereas there is discussion on the future directions and examples of solid solution systems that should prove fruitful to consider.

The distribution of saturated clusters in wetted granular materials

NASA Astrophysics Data System (ADS)

Li, Shuoqi; Hanaor, Dorian; Gan, Yixiang

2017-06-01

The hydro-mechanical behaviour of partially saturated granular materials is greatly influenced by the spatial and temporal distribution of liquid within the media. The aim of this paper is to characterise the distribution of saturated clusters in granular materials using an optical imaging method under different water drainage conditions. A saturated cluster is formed when a liquid phase fully occupies the pore space between solid grains in a localized region. The samples considered here were prepared by vibrating mono-sized glass beads to form closely packed assemblies in a rectangular container. A range of drainage conditions were applied to the specimen by tilting the container and employing different flow rates, and the liquid pressure was recorded at different positions in the experimental cell. The formation of saturated clusters during the liquid withdrawal processes is governed by three competing mechanisms arising from viscous, capillary, and gravitational forces. When the flow rate is sufficiently large and the gravity component is sufficiently small, the viscous force tends to destabilize the liquid front leading to the formation of narrow fingers of saturated material. As the water channels along these liquid fingers break, saturated clusters are formed inside the specimen. Subsequently, a spatial and temporal distribution of saturated clusters can be observed. We investigated the resulting saturated cluster distribution as a function of flow rate and gravity to achieve a fundamental understanding of the formation and evolution of such clusters in partially saturated granular materials. This study serves as a bridge between pore-scale behavior and the overall hydro-mechanical characteristics in partially saturated soils.

Inferring Viral Dynamics in Chronically HCV Infected Patients from the Spatial Distribution of Infected Hepatocytes

DOE PAGES

Graw, Frederik; Balagopal, Ashwin; Kandathil, Abraham J.; ...

2014-11-13

Chronic liver infection by hepatitis C virus (HCV) is a major public health concern. Despite partly successful treatment options, several aspects of intrahepatic HCV infection dynamics are still poorly understood, including the preferred mode of viral propagation, as well as the proportion of infected hepatocytes. Answers to these questions have important implications for the development of therapeutic interventions. In this study, we present methods to analyze the spatial distribution of infected hepatocytes obtained by single cell laser capture microdissection from liver biopsy samples of patients chronically infected with HCV. By characterizing the internal structure of clusters of infected cells, wemore » are able to evaluate hypotheses about intrahepatic infection dynamics. We found that individual clusters on biopsy samples range in size from 4-50 infected cells. In addition, the HCV RNA content in a cluster declines from the cell that presumably founded the cluster to cells at the maximal cluster extension. These observations support the idea that HCV infection in the liver is seeded randomly (e.g. from the blood) and then spreads locally. Assuming that the amount of intracellular HCV RNA is a proxy for how long a cell has been infected, we estimate based on models of intracellular HCV RNA replication and accumulation that cells in clusters have been infected on average for less than a week. Further, we do not find a relationship between the cluster size and the estimated cluster expansion time. Lastly, our method represents a novel approach to make inferences about infection dynamics in solid tissues from static spatial data.« less

Effect of the non-thermal Sunyaev-Zel'dovich effect on the temperature determination of galaxy clusters

NASA Astrophysics Data System (ADS)

Marchegiani, P.; Colafrancesco, S.

2017-08-01

A recent stacking analysis of Planck HFI data of galaxy clusters led to the derivation of the cluster temperatures using the relativistic corrections to the Sunyaev-Zel'dovich effect (SZE). However, the temperatures of high-temperature clusters, as derived from this analysis, were basically higher than the temperatures derived from X-ray measurements, at a moderate statistical significance of 1.5σ. This discrepancy has been attributed by Hurier to calibration issues. In this paper, we discuss an alternative explanation for this discrepancy in terms of a non-thermal SZE astrophysical component. We find that this explanation can work if non-thermal electrons in galaxy clusters have a low minimum momentum (p1 ˜ 0.5-1), and if their pressure is of the order of 20-30 per cent of the thermal gas pressure. Both these conditions are hard to obtain if the non-thermal electrons are mixed with the hot gas in the intracluster medium, but can be possibly obtained if the non-thermal electrons are mainly confined in bubbles with a high amount of non-thermal plasma and a low amount of thermal plasma, or are in giant radio lobes/relics in the outskirts of the clusters. To derive more precise results on the properties of the non-thermal electrons in clusters, and in view of more solid detections of a discrepancy between X-ray- and SZE-derived cluster temperatures that cannot be explained in other ways, it would be necessary to reproduce the full analysis done by Hurier by systematically adding the non-thermal component of the SZE.

Inferring Viral Dynamics in Chronically HCV Infected Patients from the Spatial Distribution of Infected Hepatocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graw, Frederik; Balagopal, Ashwin; Kandathil, Abraham J.

Chronic liver infection by hepatitis C virus (HCV) is a major public health concern. Despite partly successful treatment options, several aspects of intrahepatic HCV infection dynamics are still poorly understood, including the preferred mode of viral propagation, as well as the proportion of infected hepatocytes. Answers to these questions have important implications for the development of therapeutic interventions. In this study, we present methods to analyze the spatial distribution of infected hepatocytes obtained by single cell laser capture microdissection from liver biopsy samples of patients chronically infected with HCV. By characterizing the internal structure of clusters of infected cells, wemore » are able to evaluate hypotheses about intrahepatic infection dynamics. We found that individual clusters on biopsy samples range in size from 4-50 infected cells. In addition, the HCV RNA content in a cluster declines from the cell that presumably founded the cluster to cells at the maximal cluster extension. These observations support the idea that HCV infection in the liver is seeded randomly (e.g. from the blood) and then spreads locally. Assuming that the amount of intracellular HCV RNA is a proxy for how long a cell has been infected, we estimate based on models of intracellular HCV RNA replication and accumulation that cells in clusters have been infected on average for less than a week. Further, we do not find a relationship between the cluster size and the estimated cluster expansion time. Lastly, our method represents a novel approach to make inferences about infection dynamics in solid tissues from static spatial data.« less

Recent Progress in Studies of Nanostructured Impurity Helium Solids

NASA Astrophysics Data System (ADS)

Khmelenko, V. V.; Kunttu, H.; Lee, D. M.

2007-07-01

Impurity helium (Im He) solids are porous materials formed inside superfluid 4He by nanoclusters of impurities injected from the gas phase. The results of studies of these materials have relevance to soft condensed matter physics, matrix isolation of free radicals and low temperature chemistry. Recent studies by a variety of experimental techniques, including CW and pulse ESR, X-ray diffraction, ultrasound and Raman spectroscopy allow a better characterization of the properties of Im He solids. The structure of Im He solids, the trapping sites of stabilized atoms and the possible energy content of the samples are analyzed on the basis of experimental data. The kinetics of exchange tunneling reactions of hydrogen isotopes in nanoclusters and the changes of environment of the atoms during the course of these reactions are reviewed. Analysis of the ESR data shows that very large fraction of the stabilized atoms in Im He solids reside on the surfaces of impurity nanoclusters. The future directions for studying Im He solids are described. Among the most attractive are the studies of Im He solids with high concentrations of stabilized atoms at ultralow (10 20 mK) temperature for the observation of new collective quantum phenomena, the studies of practical application of Im He solids as a medium in neutron moderator for efficient production of ultracold (˜1 mK) neutrons, and the possibilities of obtaining high concentration of atomic nitrogen embedded in N2 clusters for energy storage.

From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

NASA Astrophysics Data System (ADS)

Schwartzkopf, Matthias; Buffet, Adeline; Körstgens, Volker; Metwalli, Ezzeldin; Schlage, Kai; Benecke, Gunthard; Perlich, Jan; Rawolle, Monika; Rothkirch, André; Heidmann, Berit; Herzog, Gerd; Müller-Buschbaum, Peter; Röhlsberger, Ralf; Gehrke, Rainer; Stribeck, Norbert; Roth, Stephan V.

2013-05-01

The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources. Electronic supplementary information (ESI) available: The full GISAXS image sequence of the experiment, the model-based IsGISAXS-simulation sequence as movie files for comparison and detailed information about sample cleaning, XRR, FESEM, IsGISAXS, comparison μGIWAXS/μGISAXS, and sampling statistics. See DOI: 10.1039/c3nr34216f

Implications of hydrogen/halogen-bond in the stabilization of confined water and anion-water clusters by a cationic receptor

NASA Astrophysics Data System (ADS)

Hoque, Md. Najbul; Das, Gopal

2016-03-01

Anion complexation of benzene capped flexible tripodal receptor and solid state stabilization of discrete hybrid anion-water or infinite water clusters by various supramolecular interactions are reported here. The crystal structure of the receptor in protonated states shows all the three arms projected in one direction. We structurally demonstrate discrete fluoride-water cluster [F2-H2O]2- and square shaped chloride-water cluster [Cl2-(H2O)2]2- inside the cationic channel of the receptor. Structural analysis also reveals that these clusters are stabilized inside the channel through active participation of N/C/Ow‧H⋯Ow, N/C/Ow‧H⋯X- (X- = F-, Cl- and I-) H-bonds and electrostatic interactions. Moreover, C-H⋯π and π⋯π types weak intermolecular interactions appear to play crucial role in supramolecular assembly of receptor. Additionally, on treatment with hydroiodic acid (HI) L resulted zwitterionic iodide complex. Crystal structure reveals the presence of S···I halogen bonded dimer, I2···I halogen bond, 1D infinite water chain and neutral iodine molecules. It is comprehensible that ligand basal structure (benzene capped and N-bridge head in two tripodal) play crucial roles in the formation of diverse halide-water cluster. All structures were well examined by different techniques such as NMR, IR, TGA, DSC, PXRD and XRD.

SLURM: Simple Linux Utility for Resource Management

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jette, M; Dunlap, C; Garlick, J

2002-04-24

Simple Linux Utility for Resource Management (SLURM) is an open source, fault-tolerant, and highly scalable cluster management and job scheduling system for Linux clusters of thousands of nodes. Components include machine status, partition management, job management, and scheduling modules. The design also includes a scalable, general-purpose communication infrastructure. Development will take place in four phases: Phase I results in a solid infrastructure; Phase II produces a functional but limited interactive job initiation capability without use of the interconnect/switch; Phase III provides switch support and documentation; Phase IV provides job status, fault-tolerance, and job queuing and control through Livermore's Distributed Productionmore » Control System (DPCS), a meta-batch and resource management system.« less

Long-living nanobubbles of dissolved gas in aqueous solutions of salts and erythrocyte suspensions.

PubMed

Bunkin, Nikolai F; Ninham, Barry W; Ignatiev, Pavel S; Kozlov, Valery A; Shkirin, Alexey V; Starosvetskij, Artem V

2011-03-01

Results of experiments combining laser modulation interference microscopy and Mueller matrix scatterometry show that macroscopic scatterers of light are present in liquids free of external solid impurities. Experimental data on distilled water and aqueous NaCl solutions of various concentrations as well as physiological saline solution are reported. The experimental data can be interpreted by using a model of micron-scale clusters composed of polydisperse air nanobubbles having effective radii of 70-100 nm. Their concentration increases with the growth of ionic content. We hypothesize that under certain conditions those clusters of nanobubbles can affect the erythrocyte structure. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Visualising crystal packing interactions in solid-state NMR: Concepts and applications

NASA Astrophysics Data System (ADS)

Zilka, Miri; Sturniolo, Simone; Brown, Steven P.; Yates, Jonathan R.

2017-10-01

In this article, we introduce and apply a methodology, based on density functional theory and the gauge-including projector augmented wave approach, to explore the effects of packing interactions on solid-state nuclear magnetic resonance (NMR) parameters. A visual map derived from a so-termed "magnetic shielding contribution field" can be made of the contributions to the magnetic shielding of a specific site—partitioning the chemical shift to specific interactions. The relation to the established approaches of examining the molecule to crystal change in the chemical shift and the nuclear independent chemical shift is established. The results are applied to a large sample of 71 molecular crystals and three further specific examples from supermolecular chemistry and pharmaceuticals. This approach extends the NMR crystallography toolkit and provides insight into the development of both cluster based approaches to the predictions of chemical shifts and for empirical predictions of chemical shifts in solids.

Concept considerations for a small orbital transfer vehicle

NASA Technical Reports Server (NTRS)

Green, M.; Sibila, A. I.

1979-01-01

This paper summarizes a study of small orbital transfer vehicles to place payloads in orbits with altitudes above those of the standard Shuttle operations. The overall objective of the study is to examine the role of the small orbital transfer vehicle (SOTV) in Shuttle operations and to identify typical propulsion concepts for accomplishing the mission. Consideration is given to existing and planned systems and upper stages, along with new propulsion stages. The new propulsion concept development examines tandem and clustered solids, controlled solids, monopropellant and bipropellant liquids, and staged solid/liquid combinations. The paper presents considerations of the mission requirements, tradeoffs of the various configurations, and candidate selections. For the selected candidate concepts the performance, support equipment, operational considerations and program costs were determined. The results show that a new modular liquid stage system is cost effective in handling the majority of the payloads considered. The remainder of the payloads can be accomodated by existing systems.

Effect of nanostructure on rapid boiling of water on a hot copper plate: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Fu, Ting; Mao, Yijin; Tang, Yong; Zhang, Yuwen; Yuan, Wei

2016-08-01

Molecular dynamic simulations are performed to study the effects of nanostructure on rapid boiling of water that is suddenly heated by a hot copper plate. The results show that the nanostructure has significant effects on energy transfer from solid copper plate to liquid water and phase change process from liquid water to vapor. The liquid water on the solid surface rapidly boil after contacting with an extremely hot copper plate and consequently a cluster of liquid water moves upward during phase change. The temperature of the water film when it separates from solid surface and its final temperature when the system is at equilibrium strongly depend on the size of the nanostructure. These temperatures increase with increasing size of nanostructure. Furthermore, a non-vaporized molecular layer is formed on the surface of the copper plate even continuous heat flux is passing into water domain through the plate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez, Y.; Carriazo, J.G.; Almanza, O.

Materials from a mining process, in which ferronickel metal extraction is the principal aim, were studied. The residual solid (scum) obtained in this process leads to large-scale accumulation of a vitreous material (pollutant) which creates an environmental problem. These materials were characterized by EPR, X-ray diffraction and X-ray fluorescence. The results indicate that the analyzed solids are rich in Fe{sub 2}O{sub 3} and NiO among other oxides. The scum material shows diffraction signals corresponding to the minerals enstatite (pyroxene) and {alpha}-alumina. Moreover, the scum EPR analysis showed a broad line around g = 2.1 corresponding to Fe{sup 3+} clusters inmore » a complex glassy matrix. An analysis of EPR at different temperatures was also performed. The objective of this work, as a first exploratory stage, is to develop a better understanding of the residual solids in order to identify potential applications.« less

Evaluation of a buried vertical well leachate recirculation system for municipal solid waste landfills.

PubMed

Kadambala, Ravi; Powell, Jon; Singh, Karamjit; Townsend, Timothy G

2016-12-01

Vertical liquids addition systems have been used at municipal landfills as a leachate management method and to enhance biostabilization of waste. Drawbacks of these systems include a limitation on pressurized injection and the occurrence of seepage. A novel vertical well system that employed buried wells constructed below a lift of compacted waste was operated for 153 days at a landfill in Florida, USA. The system included 54 wells installed in six clusters of nine wells connected with a horizontally-oriented manifold system. A cumulative volume of 8430 m 3 of leachate was added intermittently into the well clusters over the duration of the project with no incidence of surface seeps. Achievable average flow rates ranged from 9.3 × 10 -4 m 3 s -1 to 14.2 × 10 -4 m 3 s -1 , which was similar to or greater than flow rates achieved in a previous study using traditional vertical wells at the same landfill site. The results demonstrated that pressurized liquids addition in vertical wells at municipal solid waste landfills can be achieved while avoiding typical operational and maintenance issues associated with seeps. © The Author(s) 2016.

Accelerated transport and growth with symmetrized dynamics

NASA Astrophysics Data System (ADS)

Merikoski, Juha

2013-12-01

In this paper we consider a model of accelerated dynamics with the rules modified from those of the recently proposed [Dong et al., Phys. Rev. Lett. 109, 130602 (2012), 10.1103/PhysRevLett.109.130602] accelerated exclusion process (AEP) such that particle-vacancy symmetry is restored to facilitate a mapping to a solid-on-solid growth model in 1+1 dimensions. In addition to kicking a particle ahead of the moving particle, as in the AEP, in our model another particle from behind is drawn, provided it is within the "distance of interaction" denoted by ℓmax. We call our model the doubly accelerated exclusion process (DAEP). We observe accelerated transport and interface growth and widening of the cluster size distribution for cluster sizes above ℓmax, when compared with the ordinary totally asymmetric exclusion process (TASEP). We also characterize the difference between the TASEP, AEP, and DAEP by computing a "staggered" order parameter, which reveals the local order in the steady state. This order in part explains the behavior of the particle current as a function of density. The differences of the steady states are also reflected by the behavior of the temporal and spatial correlation functions in the interface picture.

Salient concerns in using analgesia for cancer pain among outpatients: A cluster analysis study.

PubMed

Meghani, Salimah H; Knafl, George J

2017-02-10

To identify unique clusters of patients based on their concerns in using analgesia for cancer pain and predictors of the cluster membership. This was a 3-mo prospective observational study ( n = 207). Patients were included if they were adults (≥ 18 years), diagnosed with solid tumors or multiple myelomas, and had at least one prescription of around-the-clock pain medication for cancer or cancer-treatment-related pain. Patients were recruited from two outpatient medical oncology clinics within a large health system in Philadelphia. A choice-based conjoint (CBC) analysis experiment was used to elicit analgesic treatment preferences (utilities). Patients employed trade-offs based on five analgesic attributes (percent relief from analgesics, type of analgesic, type of side-effects, severity of side-effects, out of pocket cost). Patients were clustered based on CBC utilities using novel adaptive statistical methods. Multiple logistic regression was used to identify predictors of cluster membership. The analyses found 4 unique clusters: Most patients made trade-offs based on the expectation of pain relief (cluster 1, 41%). For a subset, the main underlying concern was type of analgesic prescribed, i.e ., opioid vs non-opioid (cluster 2, 11%) and type of analgesic side effects (cluster 4, 21%), respectively. About one in four made trade-offs based on multiple concerns simultaneously including pain relief, type of side effects, and severity of side effects (cluster 3, 28%). In multivariable analysis, to identify predictors of cluster membership, clinical and socioeconomic factors (education, health literacy, income, social support) rather than analgesic attitudes and beliefs were found important; only the belief, i.e ., pain medications can mask changes in health or keep you from knowing what is going on in your body was found significant in predicting two of the four clusters [cluster 1 (-); cluster 4 (+)]. Most patients appear to be driven by a single salient concern in using analgesia for cancer pain. Addressing these concerns, perhaps through real time clinical assessments, may improve patients' analgesic adherence patterns and cancer pain outcomes.

Effective cluster model of dielectric enhancement in metal-insulator composites

NASA Astrophysics Data System (ADS)

Doyle, W. T.; Jacobs, I. S.

1990-11-01

The electrical permittivity of a suspension of conducting spheres at high volume loading exhibits a large enhancement above the value predicted by the Clausius-Mossotti approximation. The permittivity enhancement is a dielectric anomaly accompanying a metallization transition that occurs when conducting particles are close packed. In disordered suspensions, close encounters can cause a permittivity enhancement at any volume loading. We attribute the permittivity enhancements typically observed in monodisperse disordered suspensions of conducting spheres to local metallized regions of high density produced by density fluctuations. We model a disordered suspension as a mixture, or mesosuspension, of isolated spheres and random close-packed spherical clusters of arbitrary size. Multipole interactions within the clusters are treated exactly. External interactions between clusters and isolated spheres are treated in the dipole approximation. Model permittivities are compared with Guillien's experimental permittivity measurements [Ann. Phys. (Paris) Ser. 11, 16, 205 (1941)] on liquid suspensions of Hg droplets in oil and with Turner's conductivity measurements [Chem. Eng. Sci. 31, 487 (1976)] on fluidized bed suspensions of ion-exchange resin beads in aqueous solution. New permittivity measurements at 10 GHz on solid suspensions of monodisperse metal spheres in polyurethane are presented and compared with the model permittivities. The effective spherical cluster model is in excellent agreement with the experiments over the entire accessible range of volume loading.

Approximate kernel competitive learning.

PubMed

Wu, Jian-Sheng; Zheng, Wei-Shi; Lai, Jian-Huang

2015-03-01

Kernel competitive learning has been successfully used to achieve robust clustering. However, kernel competitive learning (KCL) is not scalable for large scale data processing, because (1) it has to calculate and store the full kernel matrix that is too large to be calculated and kept in the memory and (2) it cannot be computed in parallel. In this paper we develop a framework of approximate kernel competitive learning for processing large scale dataset. The proposed framework consists of two parts. First, it derives an approximate kernel competitive learning (AKCL), which learns kernel competitive learning in a subspace via sampling. We provide solid theoretical analysis on why the proposed approximation modelling would work for kernel competitive learning, and furthermore, we show that the computational complexity of AKCL is largely reduced. Second, we propose a pseudo-parallelled approximate kernel competitive learning (PAKCL) based on a set-based kernel competitive learning strategy, which overcomes the obstacle of using parallel programming in kernel competitive learning and significantly accelerates the approximate kernel competitive learning for large scale clustering. The empirical evaluation on publicly available datasets shows that the proposed AKCL and PAKCL can perform comparably as KCL, with a large reduction on computational cost. Also, the proposed methods achieve more effective clustering performance in terms of clustering precision against related approximate clustering approaches. Copyright © 2014 Elsevier Ltd. All rights reserved.

The cluster compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} containing Mo{sub 14} clusters and the new mono- and bi-capped trioctahedral Mo{sub 15} and Mo{sub 16} clusters: Synthesis, crystal structure, and electrical and magnetic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gall, Philippe; Guizouarn, Thierry; Gougeon, Patrick, E-mail: Patrick.Gougeon@univ-rennes1.fr

2015-07-15

Single crystals of the new quaternary compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. The crystal structure was determined by single-crystal X-ray diffraction. In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} crystallizes in the orthorhombic space group Pbca with unit-cell parameters a=9.4432(14) Å, b=11.4828(12) Å, c=20.299(4) Å and Z=4. Full-matrix least-squares refinement on F{sup 2} using 3807 independent reflections for 219 refinable parameters resulted in R{sub 1}=0.0259 and wR{sub 2}=0.0591. The crystal structure contains in addition to Mo{sub 14} clusters the first examples of mono- and bi-capped trioctahedral Mo{sub 14} i.e. Mo{sub 15} and Mo{sub 16} clusters.more » The oxygen framework derives from a stacking along the a direction of close-packed layers with sequence (…ABAC…). The Mo–Mo distances range between 2.6938(5) and 2.8420(6) Å and the Mo–O distances between 1.879(5) and 2.250(3) Å, as usually observed in molybdenum oxide clusters. The indium atoms form In{sub 4}{sup 6+} bent chains with In–In distances of 2.6682(5) and 2.6622(8) Å and the Ti atoms are in highly distorted octahedral sites of oxygen atoms with Ti–O distances ranging between 1.865(4) and 2.161(4) Å. Magnetic susceptibility measurements confirm the presence of Ti{sup 4+} cations and the absence of localized moments on the Mo network. Electrical resistivity measurements on a single crystal of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} show a semimetallic behavior. - Graphical abstract: We present here the synthesis, the crystal structure, and the electrical and magnetic properties of the new compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} in which Mo{sub 14} clusters coexist statistically with mono- and bi-capped trioctahedral Mo{sub 14} that is Mo{sub 15} and Mo{sub 16} clusters. - Highlights: • Single crystals of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. • The crystal structure contains Mo{sub 14}, Mo{sub 15} and Mo{sub 16} clusters. • The indium atoms form In{sub 4}{sup 6+} bent chains. • Poorly metallic behavior. • Absence of localized moments on the Mo network as well as on the Ti atoms.« less

Extended Fenske-Hall LCAO MO calculations of core-level shifts in solid P compounds

NASA Astrophysics Data System (ADS)

Franke, R.; Chassé, T.; Reinhold, J.; Streubel, P.; Szargan, R.

1997-08-01

Extended Fenske-Hall LCAO-MO ΔSCF calculations on solids modelled as H-pseudoatom saturated clusters are reported. The computational results verify the experimentally obtained initial-state (effective atomic charges, Madelung potential) and relaxation-energy contributions to the XPS phosphorus core-level binding energy shifts measured in Na 3PO 3S, Na 3PO 4, Na 2PO 3F and NH 4PF 6 in reference to red phosphorus. It is shown that the different initial-state contributions observed in the studied phosphates are determined by local and nonlocal terms while the relaxation-energy contributions are mainly dependent on the nature of the nearest neighbors of the phosphorus atom.

Chaotic Exchange of Solid Material Between Planetary Systems: Implications for Lithopanspermia

PubMed Central

Belbruno, Edward; Malhotra, Renu; Savransky, Dmitry

2012-01-01

Abstract We examined a low-energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we found that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology, as it addresses whether life on Earth could have been transferred to other planetary systems in the Solar System's birth cluster and whether life on Earth could have been transferred from beyond the Solar System. In the Solar System, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8–4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (∼100–500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt objects and theoretical coagulation models, and taking into account Oort Cloud formation models, we discerned that the expected number of bodies with mass>10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 1014 to 3·1016, with transfer timescales of tens of millions of years. We estimate that of the order of 3·108·l (km) could potentially be life-bearing, where l is the depth of Earth's crust in kilometers that was ejected as the result of the early bombardment. Key Words: Extrasolar planets—Interplanetary dust—Interstellar meteorites—Lithopanspermia. Astrobiology 12, 754–774. PMID:22897115

Community mobilization and household level waste management for dengue vector control in Gampaha district of Sri Lanka; an intervention study.

PubMed

Abeyewickreme, W; Wickremasinghe, A R; Karunatilake, K; Sommerfeld, J; Axel, Kroeger

2012-12-01

Waste management through community mobilization to reduce breeding places at household level could be an effective and sustainable dengue vector control strategy in areas where vector breeding takes place in small discarded water containers. The objective of this study was to assess the validity of this assumption. An intervention study was conducted from February 2009 to February 2010 in the populous Gampaha District of Sri Lanka. Eight neighborhoods (clusters) with roughly 200 houses each were selected randomly from high and low dengue endemic areas; 4 of them were allocated to the intervention arm (2 in the high and 2 in the low endemicity areas) and in the same way 4 clusters to the control arm. A baseline household survey was conducted and entomological and sociological surveys were carried out simultaneously at baseline, at 3 months, at 9 months and at 15 months after the start of the intervention. The intervention programme in the treatment clusters consisted of building partnerships of local stakeholders, waste management at household level, the promotion of composting biodegradable household waste, raising awareness on the importance of solid waste management in dengue control and improving garbage collection with the assistance of local government authorities. The intervention and control clusters were very similar and there were no significant differences in pupal and larval indices of Aedes mosquitoes. The establishment of partnerships among local authorities was well accepted and sustainable; the involvement of communities and households was successful. Waste management with the elimination of the most productive water container types (bowls, tins, bottles) led to a significant reduction of pupal indices as a proxy for adult vector densities. The coordination of local authorities along with increased household responsibility for targeted vector interventions (in our case solid waste management due to the type of preferred vector breeding places) is vital for effective and sustained dengue control.

Community mobilization and household level waste management for dengue vector control in Gampaha district of Sri Lanka; an intervention study

PubMed Central

Abeyewickreme, W; Wickremasinghe, A R; Karunatilake, K; Sommerfeld, Johannes; Kroeger, Axel

2012-01-01

Introduction Waste management through community mobilization to reduce breeding places at household level could be an effective and sustainable dengue vector control strategy in areas where vector breeding takes place in small discarded water containers. The objective of this study was to assess the validity of this assumption. Methods An intervention study was conducted from February 2009 to February 2010 in the populous Gampaha District of Sri Lanka. Eight neighborhoods (clusters) with roughly 200 houses each were selected randomly from high and low dengue endemic areas; 4 of them were allocated to the intervention arm (2 in the high and 2 in the low endemicity areas) and in the same way 4 clusters to the control arm. A baseline household survey was conducted and entomological and sociological surveys were carried out simultaneously at baseline, at 3 months, at 9 months and at 15 months after the start of the intervention. The intervention programme in the treatment clusters consisted of building partnerships of local stakeholders, waste management at household level, the promotion of composting biodegradable household waste, raising awareness on the importance of solid waste management in dengue control and improving garbage collection with the assistance of local government authorities. Results The intervention and control clusters were very similar and there were no significant differences in pupal and larval indices of Aedes mosquitoes. The establishment of partnerships among local authorities was well accepted and sustainable; the involvement of communities and households was successful. Waste management with the elimination of the most productive water container types (bowls, tins, bottles) led to a significant reduction of pupal indices as a proxy for adult vector densities. Conclusion The coordination of local authorities along with increased household responsibility for targeted vector interventions (in our case solid waste management due to the type of preferred vector breeding places) is vital for effective and sustained dengue control. PMID:23318240

Ionic and Covalent Stabilization of Intermediates and Transition States in Catalysis by Solid Acids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshlahra, Prashant; Carr, Robert T.; Iglesia, Enrique

Reactivity descriptors describe catalyst properties that determine the stability of kinetically relevant transition states and adsorbed intermediates. Theoretical descriptors, such as deprotonation energies (DPE), rigorously account for Brønsted acid strength for catalytic solids with known structure. Here, mechanistic interpretations of methanol dehydration turnover rates are used to assess how charge reorganization (covalency) and electrostatic interactions determine DPE and how such interactions are recovered when intermediates and transition states interact with the conjugate anion in W and Mo polyoxometalate (POM) clusters and gaseous mineral acids. Turnover rates are lower and kinetically relevant species are less stable on Mo than W POMmore » clusters with similar acid strength, and such species are more stable on mineral acids than that predicted from W-POM DPE–reactivity trends, indicating that DPE and acid strength are essential but incomplete reactivity descriptors. Born–Haber thermochemical cycles indicate that these differences reflect more effective charge reorganization upon deprotonation of Mo than W POM clusters and the much weaker reorganization in mineral acids. Such covalency is disrupted upon deprotonation but cannot be recovered fully upon formation of ion pairs at transition states. Predictive descriptors of reactivity for general classes of acids thus require separate assessments of the covalent and ionic DPE components. Here, we describe methods to estimate electrostatic interactions, which, taken together with energies derived from density functional theory, give the covalent and ionic energy components of protons, intermediates, and transition states. In doing so, we provide a framework to predict the reactive properties of protons for chemical reactions mediated by ion-pair transition states.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prabhakaran, Venkateshkumar; Johnson, Grant E.; Wang, Bingbing

Molecular-level understanding of electrochemical processes occurring at electrode-electrolyte interfaces (EEI) is key to the rational development of high-performance and sustainable electrochemical technologies. This article reports the development and first application of solid-state in situ electrochemical probes to study redox and catalytic processes occurring at well-defined EEI generated using soft-landing of mass- and charge-selected cluster ions (SL). In situ electrochemical probes with excellent mass transfer properties are fabricated using carefully-designed nanoporous ionic liquid membranes. SL enables deposition of pure active species that are not obtainable with other techniques onto electrode surfaces with precise control over charge state, composition, and kinetic energy.more » SL is, therefore, a unique tool for studying fundamental processes occurring at EEI. For the first time using an aprotic electrochemical probe, the effect of charge state (PMo12O403-/2-) and the contribution of building blocks of Keggin polyoxometalate (POM) clusters to redox processes are characterized by populating EEI with novel POM anions generated by electrospray ionization and gas phase dissociation. Additionally, a proton conducting electrochemical probe has been developed to characterize the reactive electrochemistry (oxygen reduction activity) of bare Pt clusters (Pt40 ~1 nm diameter), thus demonstrating the capability of the probe for studying reactions in controlled gaseous environments. The newly developed in situ electrochemical probes combined with ion SL provide a versatile method to characterize the EEI in solid-state redox systems and reactive electrochemistry at precisely-defined conditions. This capability will advance molecular-level understanding of processes occurring at EEI that are critical to many energy-related technologies.« less

Multiple bud cultures of 'Barhee' date palm (Phoenix dactylifera) and physiological status of regenerated plants.

PubMed

Fki, Lotfi; Bouaziz, Neila; Kriaa, Walid; Benjemaa-Masmoudi, Raja; Gargouri-Bouzid, Radhia; Rival, Alain; Drira, Noureddine

2011-09-15

Adventitious bud clusters of date palm 'Barhee' were successfully established from juvenile leaves (<1cm) using reduced amounts of 2,4-D (0.2mgL(-1)) to limit the risk of somaclonal variation. An average of 8.4 adventitious buds per explant were obtained. Histological examination showed that the superficial cell layers of leaves had the highest caulogenic capacity. High sucrose concentration (70gL(-1)) was used for the conversion of initial buds to multiple bud clusters. The promoting effect of temporary immersion on shoot proliferation was found to be significant when compared to cultivation on solid media. Elongation of shoots was also better using a thin film of PGR-free liquid medium instead of a solid medium. Anatomical observations indicated that roots from vitroplants were potentially functional at various developmental stages. However, only 12-month-old vitroplants were found to be physiologically able to control transpirational vapor loss. Additionally, the photochemical activity of photosystem II in these vitroplants was close to that measured in plants that were already acclimatized. As a result, 83.3% of regenerated plants were successfully acclimatized. No phenotypic variation was observed among more than 500 adventitious bud-derived plants. All regenerants survived after field transplantation. We found that the production of adventitious bud clusters in small bioreactors was able to provide an efficient micropropagation system for date palm cv. 'Barhee'. An in vitro hardening step was a prerequisite for the successful transfer of vitroplants in soil. Copyright © 2011 Elsevier GmbH. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laskin, Julia; Johnson, Grant E.; Prabhakaran, Venkateshkumar

Immobilization of complex molecules and clusters on supports plays an important role in a variety of disciplines including materials science, catalysis and biochemistry. In particular, deposition of clusters on surfaces has attracted considerable attention due to their non-scalable, highly size-dependent properties. The ability to precisely control the composition and morphology of clusters and small nanoparticles on surfaces is crucial for the development of next generation materials with rationally tailored properties. Soft- and reactive landing of ions onto solid or liquid surfaces introduces unprecedented selectivity into surface modification by completely eliminating the effect of solvent and sample contamination on the qualitymore » of the film. The ability to select the mass-to-charge ratio of the precursor ion, its kinetic energy and charge state along with precise control of the size, shape and position of the ion beam on the deposition target makes soft-landing an attractive approach for surface modification. High-purity uniform thin films on surfaces generated using mass-selected ion deposition facilitate understanding of critical interfacial phenomena relevant to catalysis, energy generation and storage, and materials science. Our efforts have been directed toward understanding charge retention by soft-landed metal and metal-oxide cluster ions, which may affect both their structure and reactivity. Specifically, we have examined the effect of the surface on charge retention by both positively and negatively charged cluster ions. We found that the electronic properties of the surface play an important role in charge retention by cluster cations. Meanwhile, the electron binding energy is a key factor determining charge retention by cluster anions. These findings provide the scientific foundation for the rational design of interfaces for advanced catalysts and energy storage devices. Further optimization of electrode-electrolyte interfaces for applications in energy storage and electrocatalysis may be achieved by understanding and controlling the properties of soft-landed cluster ions.« less

Structural Evolution and Atom Clustering in β-SiAlON: β-Si 6–z Al z O z N 8–z

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cozzan, Clayton; Griffith, Kent J.; Laurita, Geneva

2017-02-06

SiAlON ceramics, solid solutions based on the Si 3N 4 structure, are important, lightweight structural materials with intrinsically high strength, high hardness, and high thermal and chemical stability. Described by the chemical formula β-Si 6–zAl zO zN 8–z, from a compositional viewpoint, these materials can be regarded as solid solutions between Si 3N 4 and Al 3O 3N. A key aspect of the structural evolution with increasing Al and O (z in the formula) is to understand how these elements are distributed on the β-Si 3N 4 framework. The average and local structural evolution of highly phase-pure samples of β-Simore » 6–zAl zO zN 8–z with z = 0.050, 0.075, and 0.125 are studied here, using a combination of X-ray diffraction, NMR studies, and density functional theory calculations. Synchrotron X-ray diffraction establishes sample purity and indicates subtle changes in the average structure with increasing Al content in these compounds. Solid-state magic-angle-spinning 27Al NMR experiments, coupled with detailed ab initio calculations of NMR spectra of Al in different AlO qN 4–q tetrahedra (0 ≤ q ≤ 4), reveal a tendency of Al and O to cluster in these materials. Independently, the calculations suggest an energetic preference for Al–O bond formation, instead of a random distribution, in the β-SiAlON system.« less

Lipid-Mediated Clusters of Guest Molecules in Model Membranes and Their Dissolving in the Presence of Lipid Rafts.

PubMed

Kardash, Maria E; Dzuba, Sergei A

2017-05-25

The clustering of molecules is an important feature of plasma membrane organization. It is challenging to develop methods for quantifying membrane heterogeneities because of their transient nature and small size. Here, we obtained evidence that transient membrane heterogeneities can be frozen at cryogenic temperatures which allows the application of solid-state experimental techniques sensitive to the nanoscale distance range. We employed the pulsed version of electron paramagnetic resonance (EPR) spectroscopy, the electron spin echo (ESE) technique, for spin-labeled molecules in multilamellar lipid bilayers. ESE decays were refined for pure contribution of spin-spin magnetic dipole-dipolar interaction between the labels; these interactions manifest themselves at a nanometer distance range. The bilayers were prepared from different types of saturated and unsaturated lipids and cholesterol (Chol); in all cases, a small amount of guest spin-labeled substances 5-doxyl-stearic-acid (5-DSA) or 3β-doxyl-5α-cholestane (DChl) was added. The local concentration found of 5-DSA and DChl molecules was remarkably higher than the mean concentration in the bilayer, evidencing the formation of lipid-mediated clusters of these molecules. To our knowledge, formation of nanoscale clusters of guest amphiphilic molecules in biological membranes is a new phenomenon suggested only recently. Two-dimensional 5-DSA molecular clusters were found, whereas flat DChl molecules were found to be clustered into stacked one-dimensional structures. These clusters disappear when the Chol content is varied between the boundaries known for lipid raft formation at room temperatures. The room temperature EPR evidenced entrapping of DChl molecules in the rafts.

Development of clinical dosage forms for a poorly water-soluble drug II: formulation and characterization of a novel solid microemulsion preconcentrate system for oral delivery of a poorly water-soluble drug.

PubMed

Li, Ping; Hynes, Sara R; Haefele, Thomas F; Pudipeddi, Madhu; Royce, Alan E; Serajuddin, Abu T M

2009-05-01

The solution of a poorly water-soluble drug in a liquid lipid-surfactant mixture, which served as a microemulsion preconcentrate, was converted into a solid form by incorporating it in a solid polyethylene glycol (PEG) matrix. The solid microemulsion preconcentrates thus formed consisted of Capmul PG8 (propylene glycol monocaprylate) as oil, Cremophor EL (polyoxyl 35 castor oil) as surfactant, and hydrophilic polymer PEG 3350 as solid matrix. The drug (aqueous solubility: 0.17 microg/mL at pH 1-8 and 25 degrees C) was dissolved in a melt of the mixture at 65-70 degrees C and then the hot solution was filled into hard gelatin capsules; the liquid gradually solidified upon cooling below 55 degrees C. The solid system was characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), confocal Raman microscopy (CRM), and the dispersion testing in water. It was confirmed that a solid microemulsion preconcentrate is a two-phase system, where clusters of crystalline PEG 3350 formed the solid structure (m.p. 55-60 degrees C) and the liquid microemulsion preconcentrate dispersed in between PEG 3350 crystals as a separate phase. The drug remained dissolved in the liquid phase. In vitro release testing showed that the preconcentrate dispersed readily in water forming a microemulsion with the drug dissolved in the oil particles (<150 nm) and the presence of PEG 3350 did not interfere with the process of self-microemulsification.

Modeling the self-assembly of functionalized fullerenes on solid surfaces using Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Bubnis, Gregory J.

Since their discovery 25 years ago, carbon fullerenes have been widely studied for their unique physicochemical properties and for applications including organic electronics and photovoltaics. For these applications it is highly desirable for crystalline fullerene thin films to spontaneously self-assemble on surfaces. Accordingly, many studies have functionalized fullerenes with the aim of tailoring their intermolecular interactions and controlling interactions with the solid substrate. The success of these rational design approaches hinges on the subtle interplay of intermolecular forces and molecule-substrate interactions. Molecular modeling is well-suited to studying these interactions by directly simulating self-assembly. In this work, we consider three different fullerene functionalization approaches and for each approach we carry out Monte Carlo simulations of the self-assembly process. In all cases, we use a "coarse-grained" molecular representation that preserves the dominant physical interactions between molecules and maximizes computational efficiency. The first approach we consider is the traditional gold-thiolate SAM (self-assembled monolayer) strategy which tethers molecules to a gold substrate via covalent sulfur-gold bonds. For this we study an asymmetric fullerene thiolate bridged by a phenyl group. Clusters of 40 molecules are simulated on the Au(111) substrate at different temperatures and surface coverage densities. Fullerenes and S atoms are found to compete for Au(111) surface sites, and this competition prevents self-assembly of highly ordered monolayers. Next, we investigate self-assembled monolayers formed by fullerenes with hydrogen-bonding carboxylic acid substituents. We consider five molecules with different dimensions and symmetries. Monte Carlo cooling simulations are used to find the most stable solid structures of clusters adsorbed to Au(111). The results show cases where fullerene-Au(111) attraction, fullerene close-packing, and hydrogen-bonding interactions can cooperate to guide self-assembly or compete to hinder it. Finally, we consider three bis-fullerene molecules, each with a different "bridging group" covalently joining two fullerenes. To effectively study the competing "standing-up" and "lying-down" morphologies, we use Monte Carlo simulations in conjunction with replica exchange and force field biasing methods. For clusters adsorbed to smooth model surfaces, we determine free energy landscapes and demonstrate their utility for rationalizing and predicting self-assembly.

The simulation and experimental validation on gas-solid two phase flow in the riser of a dense fluidized bed

NASA Astrophysics Data System (ADS)

Wang, Xue-Yao; Jiang, Fan; Xu, Xiang; Wang, Sheng-Dian; Fan, Bao-Guo; Xiao, Yun-Han

2009-06-01

Gas-solid flow in dense CFB (circulating fluidized bed)) riser under the operating condition, superficial gas 15.5 m/s and solid flux 140 kg/m2s using Geldart B particles (sand) was investigated by experiments and CFD (computational fluid dynamics) simulation. The overall and local flow characteristics are determined using the axial pressure profiles and solid concentration profiles. The cold experimental results indicate that the axial solid concentration distribution contains a dilute region towards the up-middle zone and a dense region near the bottom and the top exit zones. The typical core-annulus structure and the back-mixing phenomenon near the wall of the riser can be observed. In addition, owing to the key role of the drag force of gas-solid phase, a revised drag force coefficient, based on the EMMS (energy-minimization multi-scale) model which can depict the heterogeneous character of gas-solid two phase flow, was proposed and coupled into the CFD control equations. In order to find an appropriate drag force model for the simulation of dense CFB riser, not only the revised drag force model but some other kinds of drag force model were used in the CFD. The flow structure, solid concentration, clusters phenomenon, fluctuation of two phases and axial pressure drop were analyzed. By comparing the experiment with the simulation, the results predicted by the EMMS drag model showed a better agreement with the experimental axial average pressure drop and apparent solid volume fraction, which proves that the revised drag force based on the EMMS model is an appropriate model for the dense CFB simulation.

Evolution of irradiation-induced strain in an equiatomic NiFe alloy

DOE PAGES

Ullah, Mohammad W.; Zhang, Yanwen; Sellami, Neila; ...

2017-07-10

Here, we investigate the formation and accumulation of irradiation-induced atomic strain in an equiatomic NiFe concentrated solid-solution alloy using both atomistic simulations and x-ray diffraction (XRD) analysis of irradiated samples. Experimentally, the irradiations are performed using 1.5 MeV Ni ions to fluences ranging from 1 × 10 13 to 1 × 10 14 cm -2. The irradiation simulations are carried out by overlapping 5 keV Ni recoils cascades up to a total of 300 recoils. An increase of volumetric strain is observed at low dose, which is associated with production of point defects and small clusters. A relaxation of strainmore » occurs at higher doses, when large defect clusters, like dislocation loops, dominate.« less

Surface passivation for tight-binding calculations of covalent solids.

PubMed

Bernstein, N

2007-07-04

Simulation of a cluster representing a finite portion of a larger covalently bonded system requires the passivation of the cluster surface. We compute the effects of an explicit hybrid orbital passivation (EHOP) on the atomic structure in a model bulk, three-dimensional, narrow gap semiconductor, which is very different from the wide gap, quasi-one-dimensional organic molecules where most passivation schemes have been studied in detail. The EHOP approach is directly applicable to minimal atomic orbital basis methods such as tight-binding. Each broken bond is passivated by a hybrid created from an explicitly expressed linear combination of basis orbitals, chosen to represent the contribution of the missing neighbour, e.g. a sp(3) hybrid for a single bond. The method is tested by computing the forces on atoms near a point defect as a function of cluster geometry. We show that, compared to alternatives such as pseudo-hydrogen passivation, the force on an atom converges to the correct bulk limit more quickly as a function of cluster radius, and that the force is more stable with respect to perturbations in the position of the cluster centre. The EHOP method also obviates the need for parameterizing the interactions between the system atoms and the passivating atoms. The method is useful for cluster calculations of non-periodic defects in large systems and for hybrid schemes that simulate large systems by treating finite regions with a quantum-mechanical model, coupled to an interatomic potential description of the rest of the system.

Surface passivation for tight-binding calculations of covalent solids

NASA Astrophysics Data System (ADS)

Bernstein, N.

2007-07-01

Simulation of a cluster representing a finite portion of a larger covalently bonded system requires the passivation of the cluster surface. We compute the effects of an explicit hybrid orbital passivation (EHOP) on the atomic structure in a model bulk, three-dimensional, narrow gap semiconductor, which is very different from the wide gap, quasi-one-dimensional organic molecules where most passivation schemes have been studied in detail. The EHOP approach is directly applicable to minimal atomic orbital basis methods such as tight-binding. Each broken bond is passivated by a hybrid created from an explicitly expressed linear combination of basis orbitals, chosen to represent the contribution of the missing neighbour, e.g. a sp3 hybrid for a single bond. The method is tested by computing the forces on atoms near a point defect as a function of cluster geometry. We show that, compared to alternatives such as pseudo-hydrogen passivation, the force on an atom converges to the correct bulk limit more quickly as a function of cluster radius, and that the force is more stable with respect to perturbations in the position of the cluster centre. The EHOP method also obviates the need for parameterizing the interactions between the system atoms and the passivating atoms. The method is useful for cluster calculations of non-periodic defects in large systems and for hybrid schemes that simulate large systems by treating finite regions with a quantum-mechanical model, coupled to an interatomic potential description of the rest of the system.

Understanding the Cu-Zn brass alloys using a short-range-order cluster model: significance of specific compositions of industrial alloys

PubMed Central

Hong, H. L.; Wang, Q.; Dong, C.; Liaw, Peter K.

2014-01-01

Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1~6 and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys. PMID:25399835

Understanding the Cu-Zn brass alloys using a short-range-order cluster model: Significance of specific compositions of industrial alloys

DOE PAGES

Hong, H. L.; Wang, Q.; Dong, C.; ...

2014-11-17

Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu 12]Zn 1~6 and [Zn-Cu 12](Zn,Cu) 6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent themore » 1 st-neighbor cluster, and each cluster is matched with one to six 2 nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1 st- and 2 nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. As a result, the revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.« less

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D.

PubMed

Liu, Lichen; Díaz, Urbano; Arenal, Raul; Agostini, Giovanni; Concepción, Patricia; Corma, Avelino

2017-01-01

Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene.

Cryopreservation of human insulin expressing cells macro-encapsulated in a durable therapeutic immunoisolating device theracyte.

PubMed

Yakhnenko, Ilya; Wong, Wallace K; Katkov, Igor I; Itkin-Ansari, Pamela

2012-01-01

Encapsulating insulin producing cells (INPCs) in an immunoisolation device have been shown to cure diabetes in rodents without the need for immunosuppression. However, micro-encapsulation in semi-solid gels raises longevity and safety concerns for future use of stem cell derived INPCs. We have focused on a durable and retrievable macro-encapsulation (> 10(6) cells) device (TheraCyte). Cryopreservation (CP) of cells preloaded into the device is highly desirable but may require prolonged exposure to cryoprotectants during loading and post-thaw manipulations. Here, we are reporting survival and function of a human islet cell line frozen as single cells or as islet-like cell clusters. The non-clusterized cells exhibited high cryosurvival after prolonged pre-freeze or post-thaw exposure to 10 percent DMSO. However, both clusterization and especially loading INPCs into the device reduced viable yield even without CP. The survived cryopreserved macro-encapsulated INPCs remained fully functional suggesting that CP of macro-encapsulated cells is a promising tool for cell based therapies.

Development of a Hybrid Piezo Natural Rubber Piezoelectricity and Piezoresistivity Sensor with Magnetic Clusters Made by Electric and Magnetic Field Assistance and Filling with Magnetic Compound Fluid

PubMed Central

Shimada, Kunio; Saga, Norihiko

2017-01-01

Piezoelements used in robotics require large elasticity and extensibility to be installed in an artificial robot skin. However, the piezoelements used until recently are vulnerable to large forces because of the thin solid materials employed. To resolve this issue, we utilized a natural rubber and applied our proposed new method of aiding with magnetic and electric fields as well as filling with magnetic compound fluid (MCF) and doping. We have verified the piezoproperties of the resulting MCF rubber. The effect of the created magnetic clusters is featured in a new two types of multilayered structures of the piezoelement. By measuring the piezoelectricity response to pressure, the synergetic effects of the magnetic clusters, the doping and the electric polymerization on the piezoelectric effect were clarified. In addition, by examining the relation between the piezoelectricity and the piezoresistivity created in the MCF piezo element, we propose a hybrid piezoelement. PMID:28208625

The GSAM software: A global search algorithm of minima exploration for the investigation of low lying isomers of clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchal, Rémi; Carbonnière, Philippe; Pouchan, Claude

2015-01-22

The study of atomic clusters has become an increasingly active area of research in the recent years because of the fundamental interest in studying a completely new area that can bridge the gap between atomic and solid state physics. Due to their specific properties, such compounds are of great interest in the field of nanotechnology [1,2]. Here, we would present our GSAM algorithm based on a DFT exploration of the PES to find the low lying isomers of such compounds. This algorithm includes the generation of an intial set of structure from which the most relevant are selected. Moreover, anmore » optimization process, called raking optimization, able to discard step by step all the non physically reasonnable configurations have been implemented to reduce the computational cost of this algorithm. Structural properties of Ga{sub n}Asm clusters will be presented as an illustration of the method.« less

Low-temperature 1H NMR spectroscopic study of hydration properties of a hybrid system based on nanosilica, DNA and doxorubicin in the presence of C60 fullerene

NASA Astrophysics Data System (ADS)

Turov, V. V.; Prylutskyy, Yu. I.; Ugnivenko, A. P.; Barvinchenko, V. N.; Krupskaya, T. V.; Tsierkezos, N. G.; Ritter, U.

2014-03-01

The structure of hydrate cover layers of SiO2-DNA-Dox (where Dox: doxorubicin) and SiO2-DNA-Dox-C60 fullerene hybrids was studied by means of low-temperature 1H NMR spectroscopy in tetrachloromethane. The hydration properties of SiO2-DNA-Dox nanomaterials combined with fullerenes and their derivatives are extremely important for their further use as therapeutics in cancer treatment and for safety reasons. The findings reveal that the hydration properties of the hybrids differ from those of the solid DNA particulates or SiO2-DNA systems due to the existence of different types of water clusters, namely the weakly (WAW) and strongly associated water (SAW) clusters. For SAW clusters the radial distributions as well as the distributions of change in Gibbs free energy due to adsorptive interactions at the surfaces of the investigated systems were obtained.

Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tench, R. J.; Balooch, M.; Bernardez, L.; Allen, Mike J.; Siekhaus, W. J.; Olander, D. R.; Wang, W.

1990-04-01

Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4 to 100 microns diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO 2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10(exp -5) Torr by 1 to 3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10(exp -8) Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with angstrom resolution. Clusters up to 30 A in diameter were observed.

Effect of the fruit position on the cluster on fruit quality, carotenoids, phenolics and sugars in cherry tomatoes (Solanum lycopersicum L.).

PubMed

Coyago-Cruz, Elena; Corell, Mireia; Moriana, Alfonso; Hernanz, Dolores; Stinco, Carla M; Meléndez-Martínez, Antonio J

2017-10-01

Cherry tomato varieties are widely consumed in many countries. They contain nutrients and health-promoting compounds like phenolics and carotenoids. The main purpose of this study was to determine how the fruit position on the cluster affected quality parameters of diverse nature (weight, soluble solids, firmness, colour, carotenoids, phenolic compounds and sugars). For this purpose the fourth cluster of two cherry varieties (Summerbrix and Lazarino) were studied. The results indicated that the fruit position on the cluster decreased the fruit size between 14 and 16% and weight 40%; firmness in 'Lazarino' increased 56%; C* ab increased 12% in 'Lazarino' and decreased 13% in 'Summerbrix'; h ab increased 9% in 'Summerbrix'. Total carotenoid levels were not statistically different in two positions, and in the other position the contents were higher, with a difference of 36% between these two values. The highest total phenolic levels were observed in the PII position. However, total sugars increased 36%, fructose 36% and glucose 35% from the PI to PIII position in 'Lazarino', while, in 'Summerbrix' higher values were observed in the PIII position. Copyright © 2017 Elsevier Ltd. All rights reserved.

The bacterial species definition in the genomic era

PubMed Central

Konstantinidis, Konstantinos T; Ramette, Alban; Tiedje, James M

2006-01-01

The bacterial species definition, despite its eminent practical significance for identification, diagnosis, quarantine and diversity surveys, remains a very difficult issue to advance. Genomics now offers novel insights into intra-species diversity and the potential for emergence of a more soundly based system. Although we share the excitement, we argue that it is premature for a universal change to the definition because current knowledge is based on too few phylogenetic groups and too few samples of natural populations. Our analysis of five important bacterial groups suggests, however, that more stringent standards for species may be justifiable when a solid understanding of gene content and ecological distinctiveness becomes available. Our analysis also reveals what is actually encompassed in a species according to the current standards, in terms of whole-genome sequence and gene-content diversity, and shows that this does not correspond to coherent clusters for the environmental Burkholderia and Shewanella genera examined. In contrast, the obligatory pathogens, which have a very restricted ecological niche, do exhibit clusters. Therefore, the idea of biologically meaningful clusters of diversity that applies to most eukaryotes may not be universally applicable in the microbial world, or if such clusters exist, they may be found at different levels of distinction. PMID:17062412

Synthesis, crystal structure and third-order non-linear optical property of heterobimetallic cluster compound [MoOICu 3S 3(2,2'-bipy) 2

NASA Astrophysics Data System (ADS)

Li, Yong; Lu, Jing; Xu, Jiqing; Cui, Xiaobing; Sun, Yinghua; Yang, Qingxin; Pan, Lingyun

2004-03-01

Nest-shaped cluster [MoOICu 3S 3(2,2'-bipy) 2] ( 1) was synthesized by the treatment of (NH 4) 2MoS 4, CuI, ( n-Bu) 4NI, and 2,2'-bipyridine (2,2'-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2 1/ n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) Å3, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2'-bipy ligand. The non-linear optical (NLO) property of [MoOICu 3S 3(2,2'-bipy) 2] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its α2 and n2 values were calculated as 6.2×10 -10 and -3.8×10 -17 m 2 W -1 in a 3.7×10 -4 M DMF solution.

OCCAM: a flexible, multi-purpose and extendable HPC cluster

NASA Astrophysics Data System (ADS)

Aldinucci, M.; Bagnasco, S.; Lusso, S.; Pasteris, P.; Rabellino, S.; Vallero, S.

2017-10-01

The Open Computing Cluster for Advanced data Manipulation (OCCAM) is a multipurpose flexible HPC cluster designed and operated by a collaboration between the University of Torino and the Sezione di Torino of the Istituto Nazionale di Fisica Nucleare. It is aimed at providing a flexible, reconfigurable and extendable infrastructure to cater to a wide range of different scientific computing use cases, including ones from solid-state chemistry, high-energy physics, computer science, big data analytics, computational biology, genomics and many others. Furthermore, it will serve as a platform for R&D activities on computational technologies themselves, with topics ranging from GPU acceleration to Cloud Computing technologies. A heterogeneous and reconfigurable system like this poses a number of challenges related to the frequency at which heterogeneous hardware resources might change their availability and shareability status, which in turn affect methods and means to allocate, manage, optimize, bill, monitor VMs, containers, virtual farms, jobs, interactive bare-metal sessions, etc. This work describes some of the use cases that prompted the design and construction of the HPC cluster, its architecture and resource provisioning model, along with a first characterization of its performance by some synthetic benchmark tools and a few realistic use-case tests.

Structural motifs of pre-nucleation clusters.

PubMed

Zhang, Y; Türkmen, I R; Wassermann, B; Erko, A; Rühl, E

2013-10-07

Structural motifs of pre-nucleation clusters prepared in single, optically levitated supersaturated aqueous aerosol microparticles containing CaBr2 as a model system are reported. Cluster formation is identified by means of X-ray absorption in the Br K-edge regime. The salt concentration beyond the saturation point is varied by controlling the humidity in the ambient atmosphere surrounding the 15-30 μm microdroplets. This leads to the formation of metastable supersaturated liquid particles. Distinct spectral shifts in near-edge spectra as a function of salt concentration are observed, in which the energy position of the Br K-edge is red-shifted by up to 7.1 ± 0.4 eV if the dilute solution is compared to the solid. The K-edge positions of supersaturated solutions are found between these limits. The changes in electronic structure are rationalized in terms of the formation of pre-nucleation clusters. This assumption is verified by spectral simulations using first-principle density functional theory and molecular dynamics calculations, in which structural motifs are considered, explaining the experimental results. These consist of solvated CaBr2 moieties, rather than building blocks forming calcium bromide hexahydrates, the crystal system that is formed by drying aqueous CaBr2 solutions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rioux, Robert M.

In this work, we have primarily utilized isothermal titration calorimetry (ITC) and complimentary catalyst characterization techniques to study and assess the impact of solution conditions (i.e., solid-liquid) interface on the synthesis of heterogeneous and electro-catalysts. Isothermal titration calorimetry is well-known technique from biochemistry/physics, but has been applied to a far lesser extent to characterize buried solid-liquid interfaces in materials science. We demonstrate the utility and unique information provided by ITC for two distinct catalytic systems. We explored the thermodynamics associated catalyst synthesis for two systems: (i) ion-exchange or strong electrostatic adsorption for Pt and Pd salts on silica and aluminamore » materials (ii) adsorption to provide covalent attachment of metal and metal-oxo clusters to Dion-Jacobsen perovskite materials.« less

Delocalization via Sliding in Solid 4He: Is It Plausible?

NASA Astrophysics Data System (ADS)

Krainyukova, N. V.

2010-02-01

The modified Debye approach was used to calculate the Gibbs free energy for solid 4He and energetic profiles for different atomic displacements with respect to an equilibrium lattice. Atoms interact via the applied Aziz potential. We have found that individual atomic displacements may hardly give rise to any delocalization because of huge barriers but cooperative plane sliding is highly plausible especially in the intermediate phase, which was found to be more favorable than hcp for small cluster sizes. In the latter case the roughness of the potential profile is less than one kelvin. In some particular sliding cases the energy levels in the nearest wells nearly coincide that is a well-known precursor for the delocalization effect.

Nucleation of the diamond phase in aluminium-solid solutions

NASA Technical Reports Server (NTRS)

Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

1993-01-01

Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

Artwork visualization using a solid-state lighting engine with controlled photochemical safety.

PubMed

Tuzikas, Arūnas; Žukauskas, Artūras; Vaicekauksas, Rimantas; Petrulis, Andrius; Vitta, Pranciškus; Shur, Michael

2014-07-14

A concept of a solid-state lighting engine for artwork-specific illumination with controlled photochemical safety is introduced. The engine is based on a tetrachromatic cluster of colored light-emitting diodes wirelessly controlled via an external smart device. By using an instantaneous dimming functionality, the driving software allows for maintaining the damage irradiance relevant to a particular type of photosensitive artwork material at a constant value, while varying the chromaticity and color rendition properties of the generated light. The effect of the constant damage irradiance on the visual impression from artworks is demonstrated for the lighting engine operating in three modes, such as selecting color temperature, tuning color saturating ability, and shifting chromaticity outside white light locus, respectively.

Investigating the Co-Adsorption Behavior of Nucleic-Acid Base (Thymine and Cytosine) and Melamine at Liquid/Solid Interface

NASA Astrophysics Data System (ADS)

Zhao, Huiling; Li, Yinli; Chen, Dong; Liu, Bo

2016-12-01

The co-adsorption behavior of nucleic-acid base (thymine; cytosine) and melamine was investigated by scanning tunneling microscopy (STM) technique at liquid/solid (1-octanol/graphite) interface. STM characterization results indicate that phase separation happened after dropping the mixed solution of thymine-melamine onto highly oriented pyrolytic graphite (HOPG) surface, while the hetero-component cluster-like structure was observed when cytosine-melamine binary assembly system is used. From the viewpoints of non-covalent interactions calculated by using density functional theory (DFT) method, the formation mechanisms of these assembled structures were explored in detail. This work will supply a methodology to design the supramolecular assembled structures and the hetero-component materials composed by biological and chemical compound.

The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids.

PubMed

Novikov, Alexey; Caroff, Martine; Della-Negra, Serge; Depauw, Joël; Fallavier, Mireille; Le Beyec, Yvon; Pautrat, Michèle; Schultz, J Albert; Tempez, Agnès; Woods, Amina S

2005-01-01

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents. Copyright (c) 2005 John Wiley & Sons, Ltd.

Role of clusters in nonclassical nucleation and growth of protein crystals

PubMed Central

Sleutel, Mike; Van Driessche, Alexander E. S.

2014-01-01

The development of multistep nucleation theory has spurred on experimentalists to find intermediate metastable states that are relevant to the solidification pathway of the molecule under interest. A great deal of studies focused on characterizing the so-called “precritical clusters” that may arise in the precipitation process. However, in macromolecular systems, the role that these clusters might play in the nucleation process and in the second stage of the precipitation process, i.e., growth, remains to a great extent unknown. Therefore, using biological macromolecules as a model system, we have studied the mesoscopic intermediate, the solid end state, and the relationship that exists between them. We present experimental evidence that these clusters are liquid-like and stable with respect to the parent liquid and metastable compared with the emerging crystalline phase. The presence of these clusters in the bulk liquid is associated with a nonclassical mechanism of crystal growth and can trigger a self-purifying cascade of impurity-poisoned crystal surfaces. These observations demonstrate that there exists a nontrivial connection between the growth of the macroscopic crystalline phase and the mesoscopic intermediate which should not be ignored. On the other hand, our experimental data also show that clusters existing in protein solutions can significantly increase the nucleation rate and therefore play a relevant role in the nucleation process. PMID:24449867

On the coherent rotation of diffuse matter in numerical simulations of clusters of galaxies

NASA Astrophysics Data System (ADS)

Baldi, Anna Silvia; De Petris, Marco; Sembolini, Federico; Yepes, Gustavo; Lamagna, Luca; Rasia, Elena

2017-03-01

We present a study on the coherent rotation of the intracluster medium and dark matter components of simulated galaxy clusters extracted from a volume-limited sample of the MUSIC project. The set is re-simulated with three different recipes for the gas physics: (I) non-radiative, (II) radiative without active galactic nuclei (AGN) feedback and (III) radiative with AGN feedback. Our analysis is based on the 146 most massive clusters identified as relaxed, 57 per cent of the total sample. We classify these objects as rotating and non-rotating according to the gas spin parameter, a quantity that can be related to cluster observations. We find that 4 per cent of the relaxed sample is rotating according to our criterion. By looking at the radial profiles of their specific angular momentum vector, we find that the solid body model is not a suitable description of rotational motions. The radial profiles of the velocity of the dark matter show a prevalence of the random velocity dispersion. Instead, the intracluster medium profiles are characterized by a comparable contribution from the tangential velocity and the dispersion. In general, the dark matter component dominates the dynamics of the clusters, as suggested by the correlation between its angular momentum and the gas one, and by the lack of relevant differences among the three sets of simulations.

From solid solution to cluster formation of Fe and Cr in α-Zr

NASA Astrophysics Data System (ADS)

Burr, P. A.; Wenman, M. R.; Gault, B.; Moody, M. P.; Ivermark, M.; Rushton, M. J. D.; Preuss, M.; Edwards, L.; Grimes, R. W.

2015-12-01

To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques - atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.

Effect of mixing, concentration and temperature on the formation of mesostructured solutions and their role in the nucleation of DL-valine crystals.

PubMed

Jawor-Baczynska, Anna; Moore, Barry D; Sefcik, Jan

2015-01-01

We report investigations on the formation of mesostructured solutions in DL-valine-water-2-propanol mixtures, and the crystallization of DL-valine from these solutions. Mesostructured liquid phases, similar to those previously observed in aqueous solutions of glycine and DL-alanine, were observed using Dynamic Light Scattering and Brownian microscopy, in both undersaturated and supersaturated solutions below a certain transition temperature. Careful experimentation was used to demonstrate that the optically clear mesostructured liquid phase, comprising colloidal mesoscale clusters dispersed within bulk solution, is thermodynamically stable and present in equilibrium with the solid phase at saturation conditions. Solutions prepared by slow cooling contained mesoscale clusters with a narrow size distribution and a mean hydrodynamic diameter of around 200 nm. Solutions of identical composition prepared by rapid isothermal mixing of valine aqueous solutions with 2-propanol contained mesoscale clusters which were significantly larger than those observed in slowly cooled solutions. The presence of larger mesoscale clusters was found to correspond to faster nucleation. Observed induction times were strongly dependent on the rapid initial mixing step, although solutions were left undisturbed afterwards and the induction times observed were up to two orders of magnitude longer than the initial mixing period. We propose that mesoscale clusters above a certain critical size are likely to be the location of productive nucleation events.

Genomic analyses of bacterial porin-cytochrome gene clusters

DOE PAGES

Shi, Liang; Fredrickson, James K.; Zachara, John M.

2014-11-26

In this study, the porin-cytochrome (Pcc) protein complex is responsible for trans-outer membrane electron transfer during extracellular reduction of Fe(III) by the dissimilatory metal-reducing bacterium Geobacter sulfurreducens PCA. The identified and characterized Pcc complex of G. sulfurreducens PCA consists of a porin-like outer-membrane protein, a periplasmic 8-heme c type cytochrome (c-Cyt) and an outer-membrane 12-heme c-Cyt, and the genes encoding the Pcc proteins are clustered in the same regions of genome (i.e., the pcc gene clusters) of G. sulfurreducens PCA. A survey of additionally microbial genomes has identified the pcc gene clusters in all sequenced Geobacter spp. and other bacteriamore » from six different phyla, including Anaeromyxobacter dehalogenans 2CP-1, A. dehalogenans 2CP-C, Anaeromyxobacter sp. K, Candidatus Kuenenia stuttgartiensis, Denitrovibrio acetiphilus DSM 12809, Desulfurispirillum indicum S5, Desulfurivibrio alkaliphilus AHT2, Desulfurobacterium thermolithotrophum DSM 11699, Desulfuromonas acetoxidans DSM 684, Ignavibacterium album JCM 16511, and Thermovibrio ammonificans HB-1. The numbers of genes in the pcc gene clusters vary, ranging from two to nine. Similar to the metal-reducing (Mtr) gene clusters of other Fe(III)-reducing bacteria, such as Shewanella spp., additional genes that encode putative c-Cyts with predicted cellular localizations at the cytoplasmic membrane, periplasm and outer membrane often associate with the pcc gene clusters. This suggests that the Pcc-associated c-Cyts may be part of the pathways for extracellular electron transfer reactions. The presence of pcc gene clusters in the microorganisms that do not reduce solid-phase Fe(III) and Mn(IV) oxides, such as D. alkaliphilus AHT2 and I. album JCM 16511, also suggests that some of the pcc gene clusters may be involved in extracellular electron transfer reactions with the substrates other than Fe(III) and Mn(IV) oxides.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gobrecht, David; Cristallo, Sergio; Piersanti, Luciano

Silicon carbide (SiC) grains are a major dust component in carbon-rich asymptotic giant branch stars. However, the formation pathways of these grains are not fully understood. We calculate ground states and energetically low-lying structures of (SiC){sub n}, n = 1, 16 clusters by means of simulated annealing and Monte Carlo simulations of seed structures and subsequent quantum-mechanical calculations on the density functional level of theory. We derive the infrared (IR) spectra of these clusters and compare the IR signatures to observational and laboratory data. According to energetic considerations, we evaluate the viability of SiC cluster growth at several densities andmore » temperatures, characterizing various locations and evolutionary states in circumstellar envelopes. We discover new, energetically low-lying structures for Si{sub 4}C{sub 4}, Si{sub 5}C{sub 5}, Si{sub 15}C{sub 15}, and Si{sub 16}C{sub 16} and new ground states for Si{sub 10}C{sub 10} and Si{sub 15}C{sub 15}. The clusters with carbon-segregated substructures tend to be more stable by 4–9 eV than their bulk-like isomers with alternating Si–C bonds. However, we find ground states with cage geometries resembling buckminsterfullerens (“bucky-like”) for Si{sub 12}C{sub 12} and Si{sub 16}C{sub 16} and low-lying stable cage structures for n ≥ 12. The latter findings thus indicate a regime of cluster sizes that differ from small clusters as well as from large-scale crystals. Thus—and owing to their stability and geometry—the latter clusters may mark a transition from a quantum-confined cluster regime to a crystalline, solid bulk-material. The calculated vibrational IR spectra of the ground-state SiC clusters show significant emission. They include the 10–13 μ m wavelength range and the 11.3 μm feature inferred from laboratory measurements and observations, respectively, although the overall intensities are rather low.« less

Structure and Bonding in Noncrystalline Solids Abstracts

DTIC Science & Technology

1983-06-02

displacement cascades are unlikely. Related damage studies as diffuse X- ray scattering, magnetic susceptibility and positron - annihilation lifetime...the positron annihilation lifetime data; diffuse X-ray scattering studies give evidence for "amorphized" clusters in neutron but not in elec-ron...feldspar glasses and glasses in the system CaO- MgO -SiO 2 . These results indicate that the nearest-neighbor and next- nearest-neighbor environments are very

Application of Diffusion Monte Carlo to Materials Dominated by van der Waals Interactions

DOE PAGES

Benali, Anouar; Shulenburger, Luke; Romero, Nichols A.; ...

2014-06-12

Van der Waals forces are notoriously difficult to account for from first principles. We perform extensive calculation to assess the usefulness and validity of diffusion quantum Monte Carlo when applied to van der Waals forces. We present results for noble gas solids and clusters - archetypical van der Waals dominated assemblies, as well as a relevant pi-pi stacking supramolecular complex: DNA + intercalating anti-cancer drug Ellipticine.

Quantum-Chemical Approach to NMR Chemical Shifts in Paramagnetic Solids Applied to LiFePO4 and LiCoPO4.

PubMed

Mondal, Arobendo; Kaupp, Martin

2018-04-05

A novel protocol to compute and analyze NMR chemical shifts for extended paramagnetic solids, accounting comprehensively for Fermi-contact (FC), pseudocontact (PC), and orbital shifts, is reported and applied to the important lithium ion battery cathode materials LiFePO 4 and LiCoPO 4 . Using an EPR-parameter-based ansatz, the approach combines periodic (hybrid) DFT computation of hyperfine and orbital-shielding tensors with an incremental cluster model for g- and zero-field-splitting (ZFS) D-tensors. The cluster model allows the use of advanced multireference wave function methods (such as CASSCF or NEVPT2). Application of this protocol shows that the 7 Li shifts in the high-voltage cathode material LiCoPO 4 are dominated by spin-orbit-induced PC contributions, in contrast with previous assumptions, fundamentally changing interpretations of the shifts in terms of covalency. PC contributions are smaller for the 7 Li shifts of the related LiFePO 4 , where FC and orbital shifts dominate. The 31 P shifts of both materials finally are almost pure FC shifts. Nevertheless, large ZFS contributions can give rise to non-Curie temperature dependences for both 7 Li and 31 P shifts.

Spatial and temporal variation of water quality of a segment of Marikina River using multivariate statistical methods.

PubMed

Chounlamany, Vanseng; Tanchuling, Maria Antonia; Inoue, Takanobu

2017-09-01

Payatas landfill in Quezon City, Philippines, releases leachate to the Marikina River through a creek. Multivariate statistical techniques were applied to study temporal and spatial variations in water quality of a segment of the Marikina River. The data set included 12 physico-chemical parameters for five monitoring stations over a year. Cluster analysis grouped the monitoring stations into four clusters and identified January-May as dry season and June-September as wet season. Principal components analysis showed that three latent factors are responsible for the data set explaining 83% of its total variance. The chemical oxygen demand, biochemical oxygen demand, total dissolved solids, Cl - and PO 4 3- are influenced by anthropogenic impact/eutrophication pollution from point sources. Total suspended solids, turbidity and SO 4 2- are influenced by rain and soil erosion. The highest state of pollution is at the Payatas creek outfall from March to May, whereas at downstream stations it is in May. The current study indicates that the river monitoring requires only four stations, nine water quality parameters and testing over three specific months of the year. The findings of this study imply that Payatas landfill requires a proper leachate collection and treatment system to reduce its impact on the Marikina River.

New double molybdate Na9Fe(MoO4)6: Synthesis, structure, properties

NASA Astrophysics Data System (ADS)

Savina, Aleksandra A.; Solodovnikov, Sergey F.; Basovich, Olga M.; Solodovnikova, Zoya A.; Belov, Dmitry A.; Pokholok, Konstantin V.; Gudkova, Irina A.; Stefanovich, Sergey Yu.; Lazoryak, Bogdan I.; Khaikina, Elena G.

2013-09-01

A new double molybdate Na9Fe(MoO4)6 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mössbauer and dielectric impedance spectroscopy. Single crystals of Na9Fe(MoO4)6 were obtained and its structure was solved (the space group R3¯, a=14.8264(2), c=19.2402(3) Å, V=3662.79(9) Å3, Z=6, R=0.0132). The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. The basic structure units are polyhedral clusters composed of central FeО6 octahedron sharing edges with three Na(1)О6 octahedra. The clusters share common vertices with bridging МоО4 tetrahedra to form an open 3D framework where the cavities are occupied by Na(2) and Na(3) atoms. The compound melts incongruently at 904.7±0.2 K. Arrhenius type temperature dependence of electric conductivity σ has been registered in solid state (σ=6.8×10-2 S сm-1 at 800 K), thus allowing considering Na9Fe(MoO4)6 as a new sodium ion conductor.

Full-potential theoretical investigations of electron inelastic mean free paths and extended x-ray absorption fine structure in molybdenum.

PubMed

Chantler, C T; Bourke, J D

2014-04-09

X-ray absorption fine structure (XAFS) spectroscopy is one of the most robust, adaptable, and widely used structural analysis tools available for a range of material classes from bulk solids to aqueous solutions and active catalytic structures. Recent developments in XAFS theory have enabled high-accuracy calculations of spectra over an extended energy range using full-potential cluster modelling, and have demonstrated particular sensitivity in XAFS to a fundamental electron transport property-the electron inelastic mean free path (IMFP). We develop electron IMFP theory using a unique hybrid model that simultaneously incorporates second-order excitation losses, while precisely accounting for optical transitions dictated by the complex band structure of the solid. These advances are coupled with improved XAFS modelling to determine wide energy-range absorption spectra for molybdenum. This represents a critical test case of the theory, as measurements of molybdenum K-edge XAFS represent the most accurate determinations of XAFS spectra for any material. We find that we are able to reproduce an extended range of oscillatory structure in the absorption spectrum, and demonstrate a first-time theoretical determination of the absorption coefficient of molybdenum over the entire extended XAFS range utilizing a full-potential cluster model.

Interaction of intense ultrashort pulse lasers with clusters.

NASA Astrophysics Data System (ADS)

Petrov, George

2007-11-01

The last ten years have witnessed an explosion of activity involving the interaction of clusters with intense ultrashort pulse lasers. Atomic or molecular clusters are targets with unique properties, as they are halfway between solid and gases. The intense laser radiation creates hot dense plasma, which can provide a compact source of x-rays and energetic particles. The focus of this investigation is to understand the salient features of energy absorption and Coulomb explosion by clusters. The evolution of clusters is modeled with a relativistic time-dependent 3D Molecular Dynamics (MD) model [1]. The Coulomb interaction between particles is handled by a fast tree algorithm, which allows large number of particles to be used in simulations [2]. The time histories of all particles in a cluster are followed in time and space. The model accounts for ionization-ignition effects (enhancement of the laser field in the vicinity of ions) and a variety of elementary processes for free electrons and charged ions, such as optical field and collisional ionization, outer ionization and electron recapture. The MD model was applied to study small clusters (1-20 nm) irradiated by a high-intensity (10^16-10^20 W/cm^2) sub-picosecond laser pulse. We studied fundamental cluster features such as energy absorption, x-ray emission, particle distribution, average charge per atom, and cluster explosion as a function of initial cluster radius, laser peak intensity and wavelength. Simulations of novel applications, such as table-top nuclear fusion from exploding deuterium clusters [3] and high power synchrotron radiation for biological applications and imaging [4] have been performed. The application for nuclear fusion was motivated by the efficient absorption of laser energy (˜100%) and its high conversion efficiency into ion kinetic energy (˜50%), resulting in neutron yield of 10^6 neutrons/Joule laser energy. Contributors: J. Davis and A. L. Velikovich. [1] G. M. Petrov, et al Phys. Plasmas 12 063103 (2005); 13 033106 (2006) [2] G. M. Petrov, J. Davis, European Phys. J. D 41 629 (2007) [3] G. M. Petrov, J. Davis, A. L. Velikovich, Plasma Phys. Contr. Fusion 48 1721 (2006) [4] G. M. Petrov, J. Davis, A. L. Velikovich, J. Phys. B 39 4617 (2006)

Development of a Two-fluid Drag Law for Clustered Particles using Direct Numerical Simulation and Validation through Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gokaltun, Seckin; Munroe, Norman; Subramaniam, Shankar

2014-12-31

This study presents a new drag model, based on the cohesive inter-particle forces, implemented in the MFIX code. This new drag model combines an existing standard model in MFIX with a particle-based drag model based on a switching principle. Switches between the models in the computational domain occur where strong particle-to-particle cohesion potential is detected. Three versions of the new model were obtained by using one standard drag model in each version. Later, performance of each version was compared against available experimental data for a fluidized bed, published in the literature and used extensively by other researchers for validation purposes.more » In our analysis of the results, we first observed that standard models used in this research were incapable of producing closely matching results. Then, we showed for a simple case that a threshold is needed to be set on the solid volume fraction. This modification was applied to avoid non-physical results for the clustering predictions, when governing equation of the solid granular temperate was solved. Later, we used our hybrid technique and observed the capability of our approach in improving the numerical results significantly; however, improvement of the results depended on the threshold of the cohesive index, which was used in the switching procedure. Our results showed that small values of the threshold for the cohesive index could result in significant reduction of the computational error for all the versions of the proposed drag model. In addition, we redesigned an existing circulating fluidized bed (CFB) test facility in order to create validation cases for clustering regime of Geldart A type particles.« less

Experimental and theoretical study on Raman spectra of magnesium fluoride clusters and solids.

PubMed

Neelamraju, S; Bach, A; Schön, J C; Fischer, D; Jansen, M

2012-11-21

In this study, the Raman and IR spectra of a large number of isomers of MgF(2) clusters and of possible bulk polymorphs of MgF(2) are calculated and compared with experimental data observed using a low-temperature atom beam deposition. The bulk polymorphs were taken from earlier work, while the cluster modifications for the neutral (MgF(2))(n) (n = 1-10) clusters and charged clusters (up to the trimer anion and cation, (Mg(3)F(7))(-) and (Mg(3)F(5))(+), respectively) are determined in the present work by global energy landscape explorations using simulated annealing. These theoretical calculations are complemented by an experimental study on both the vapor phase and the deposited films of MgF(2), which are generated in a low-temperature atom beam deposition setup for the synthesis of MgF(2) bulk phases. The MgF(2) vapor and film are characterized via Raman spectroscopy of the MgF(2) gas phase species embedded in an Ar-matrix and of the MgF(2)-films deposited onto a cooled substrate, respectively. We find that, in the vapor phase, there are monomers and dimers and charged species to be present in our experimental setup. Furthermore, the results suggest that in the amorphous bulk MgF(2), rutile-like domains are present and MgF(2) clusters similar to those in the matrix. Finally, peaks at about 800 cm(-1), which are in the same range as the A(g) modes of clusters with dangling fluorine atoms connected to three-coordinated Mg atoms, indicate that such dangling bonds are also present in amorphous MgF(2).

Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

DOE PAGES

Fleischmann, Ernst; Miller, Michael K.; Affeldt, Ernst; ...

2015-01-31

Here, the solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980 °C and 30–75 MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is moremore » than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ' precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.« less

Experimental evidence for an absorbing phase transition underlying yielding of a soft glass

NASA Astrophysics Data System (ADS)

Nagamanasa, K. Hima; Gokhale, Shreyas; Sood, A. K.; Ganapathy, Rajesh

2014-03-01

A characteristic feature of solids ranging from foams to atomic crystals is the existence of a yield point, which marks the threshold stress beyond which a material undergoes plastic deformation. In hard materials, it is well-known that local yield events occur collectively in the form of intermittent avalanches. The avalanche size distributions exhibit power-law scaling indicating the presence of self-organized criticality. These observations led to predictions of a non-equilibrium phase transition at the yield point. By contrast, for soft solids like gels and dense suspensions, no such predictions exist. In the present work, by combining particle scale imaging with bulk rheology, we provide a direct evidence for a non-equilibrium phase transition governing yielding of an archetypal soft solid - a colloidal glass. The order parameter and the relaxation time exponents revealed that yielding is an absorbing phase transition that belongs to the conserved directed percolation universality class. We also identified a growing length scale associated with clusters of particles with high Debye-Waller factor. Our findings highlight the importance of correlations between local yield events and may well stimulate the development of a unified description of yielding of soft solids.

Molecular Syntheses of Extended Materials

NASA Astrophysics Data System (ADS)

Paley, Daniel W.

Bottom-up molecular synthesis is a route to chemically and crystallographically uniform polymers and solid-state materials. Through the use of molecular precursors, we gain atomic-level control of functionality and fine-tuning of the collective properties of materials. This dissertation presents two studies that demonstrate this approach. Ring-opening alkyne metathesis polymerization is a possible approach to monodisperse conjugated polymers, but its applications have been limited by difficult syntheses and high air sensitivity of known organometallic ROAMP initiators. We designed a dimeric, air-stable molybdenum alkylidyne with a tris(phenolate) supporting ligand. The precatalyst is activated by addition of methanol and polymerizes cyclooctynes with excellent chemical selectivity and functional group tolerance. The Nuckolls and Roy groups have introduced a new family of solid-state compounds synthesized from cobalt chalcogenide clusters Co6Q 8(PR3)6 and fullerenes. The first examples of these materials crystallized in superatom lattices with the symmetry of simple inorganic solids CdI2 (P-3m1) and NaCl (Fm-3m). This dissertation reveals that further members of the family feature extraordinary diversity of structure, including a pseudo-trigonal array of fulleride dimers in [Co 6Te8(PEt3)6]2[C140 ][C70]2 and a heterolayered van der Waals cocrystal [Co6Se8(PEt2phen)6][C 60]5. In addition to these unusual crystal structures, this dissertation presents a method for assigning redox states from crystallographic data in Co6Q8 clusters. Finally, a detailed guide to the collection and solution of single-crystal X-ray data is presented. The guide is intended for independent study by new crystallographers.

Assessment of the impact of landfill on groundwater quality: a case study of the Pirana site in western India.

PubMed

Singh, Umesh Kumar; Kumar, Manish; Chauhan, Rita; Jha, Pawan Kumar; Ramanathan, Al; Subramanian, V

2008-06-01

In present study focus has been given on estimating quality and toxicity of waste with respect to heavy metals and its impact on groundwater quality, using statistical and empirical relationships between different hydrochemical data, so that easy monitoring may be possible which in turn help the sustainable management of landfill site and municipal solid waste. Samples of solid waste, leachate and groundwater were analyzed to evaluate the impact of leachates on groundwater through the comparison of their hydrochemical nature. Results suggest the existence of an empirical relationship between some specific indicator parameters like heavy metals of all three above mentioned sample type. Further, K/Mg ratio also indicates three groundwater samples heavily impacted from leachate contamination. A good number of samples are also showing higher values for NO(3)(-) and Pb than that of World Health Organization (WHO) drinking water regulation. Predominance of Fe and Zn in both groundwater and solid waste samples may be due to metal plating industries in the area. Factor analysis is used as a tool to explain observed relation between numerous variables in term of simpler relation, which may help to deduce the strength of relation. Positive loading of most of the factors for heavy metal clearly shows landfill impact on ground water quality especially along the hydraulic gradient. Cluster analysis, further substantiates the impact of landfill. Two major groups of samples obtained from cluster analysis suggest that one group comprises samples that are severely under the influence of landfill and contaminated leachates along the groundwater flow direction while other assorted with samples without having such influence.

The characterization of photographic materials as substrates for surface enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Vaughan, J.; Hortin, N.; Christie, S.; Kvasnik, F.; Scully, P. J.

2005-06-01

In this study, five types of photographic materials were obtained from commercial sources and characterized for use as substrates for surface enhanced Raman spectroscopy. The substrates are photographic emulsions coated on glass or paper support. The emulsions were developed to maximize the amount of metallic silver aggregated into clusters. The test analyte, Cresyl Violet, was deposited directly onto the substrate surface. The permeable nature of the supporting gelatin matrix enables the interaction between the target analyte and the solid silver clusters. The surface enhanced Raman spectra of a 2.75 × 10-7 M concentration of Cresyl Violet in ethanol were obtained using these photographic substrates. The Raman and resonant Raman enhancement of Cresyl Violet varies from substrate to substrate, as does the ratio of Raman to resonant Raman peak heights.

Ro-vibrational Spectra of (para-H2 )N -CH4 in He Droplets.

PubMed

Hoshina, Hiromichi; Sliter, Russell; Ravi, Aakash; Kuma, Susumu; Momose, Takamasa; Vilesov, Andrey F

2016-11-18

In this work, we report on the infrared spectroscopic study of clusters of CH 4 molecules with up to N=80 para-hydrogen molecules assembled inside He droplets. Upon increase of the number of the added para-hydrogen molecules up to about N=12, both the rotational constant, B, and the origin frequency of the υ 3 band of CH 4 decrease gradually. In the range of 6 ≤N≤12, the spectra indicate some abrupt changes of B and υ 3 with both values being approximately constant at N≥12. The origin of this effect is discussed. Comparison of the spectra of methane molecules in para-hydrogen clusters to that in solid para-hydrogen is also presented. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-leg SU ( 2 n ) spin ladder: A low-energy effective field theory approach

DOE PAGES

Lecheminant, P.; Tsvelik, A. M.

2015-05-07

We present a field-theory analysis of a model of two SU( 2n)-invariant magnetic chains coupled by a generic interaction preserving time reversal and inversion symmetry. Contrary to the SU(2)-invariant case the zero-temperature phase diagram of such two-leg spin ladder does not contain topological phases. Thus, only generalized Valence Bond Solid phases are stabilized when n > 1 with different wave vectors and ground-state degeneracies. In particular, we find a phase which is made of a cluster of 2n spins put in an SU( 2n) singlet state. For n = 3, this cluster phase is relevant to ¹⁷³Yb ultracold atoms, withmore » an emergent SU(6) symmetry, loaded in a double-well optical lattice.« less

Voltage-dependent cluster expansion for electrified solid-liquid interfaces: Application to the electrochemical deposition of transition metals

NASA Astrophysics Data System (ADS)

Weitzner, Stephen E.; Dabo, Ismaila

2017-11-01

The detailed atomistic modeling of electrochemically deposited metal monolayers is challenging due to the complex structure of the metal-solution interface and the critical effects of surface electrification during electrode polarization. Accurate models of interfacial electrochemical equilibria are further challenged by the need to include entropic effects to obtain accurate surface chemical potentials. We present an embedded quantum-continuum model of the interfacial environment that addresses each of these challenges and study the underpotential deposition of silver on the gold (100) surface. We leverage these results to parametrize a cluster expansion of the electrified interface and show through grand canonical Monte Carlo calculations the crucial need to account for variations in the interfacial dipole when modeling electrodeposited metals under finite-temperature electrochemical conditions.

Theoretical investigations of open-shell systems: 1. Spectral simulation of the 2s(2)p(2) (2)D <- 2s(2)2p (2)P(o) valence transition in the boron diargon cluster, and 2. Quantum Monte Carlo calculations of boron in solid molecular hydrogen

NASA Astrophysics Data System (ADS)

Krumrine, Jennifer Rebecca

This dissertation is concerned in part with the construction of accurate pairwise potentials, based on reliable ab initio potential energy surfaces (PES's), which are fully anisotropic in the sense that multiple PES's are accessible to systems with orientational electronic properties. We have carried out several investigations of B (2s 22p 2Po) with spherical ligands: (1)an investigation of the electronic spectrum of the BAr2 complex and (2)two related studies of the equilibrium properties and spectral simulation of B embedded in solid pH 2. Our investigations suggest that it cannot be assumed that nuclear motion in an open-shell system occurs on a single PES. The 2s2p2 2 D <-- 2s22p 2Po valence transition in the BAr 2 cluster is investigated. The electronic transition within BAr 2 is modeled theoretically; the excited potential energy surfaces of the five-fold degenerate B(2s2p2 2D) state within the ternary complex are computed using a pairwise-additive model. A collaborative path integral molecular dynamics investigation of the equilibrium properties of boron trapped in solid para-hydrogen (pH2) and a path integral Monte Carlo spectral simulation. Using fully anisotropic pair potentials, coupling of the electronic and nuclear degrees of freedom is observed, and is found to be an essential feature in understanding the behavior and determining the energy of the impure solid, especially in highly anisotropic matrices. We employ the variational Monte Carlo method to further study the behavior of ground state B embedded in solid pH2. When a boron atom exists in a substitutional site in a lattice, the anisotropic distortion of the local lattice plays a minimal role in the energetics. However, when a nearest neighbor vacancy is present along with the boron impurity, two phenomena are found to influence the behavior of the impure quantum solid: (1)orientation of the 2p orbital to minimize the energy of the impurity and (2)distortion of the local lattice structure to promote an energetically favorable nuclear configuration. This research was supported by the Joint Program for Atomic, Molecular and Optical Science sponsored by the University of Maryland at College Park and the National Insititute of Standards and Technology, and by the U.S. Air Force Office of Scientific Research. (Abstract shortened by UMI.)

First-principles energetics of water clusters and ice: A many-body analysis

NASA Astrophysics Data System (ADS)

Gillan, M. J.; Alfè, D.; Bartók, A. P.; Csányi, G.

2013-12-01

Standard forms of density-functional theory (DFT) have good predictive power for many materials, but are not yet fully satisfactory for cluster, solid, and liquid forms of water. Recent work has stressed the importance of DFT errors in describing dispersion, but we note that errors in other parts of the energy may also contribute. We obtain information about the nature of DFT errors by using a many-body separation of the total energy into its 1-body, 2-body, and beyond-2-body components to analyze the deficiencies of the popular PBE and BLYP approximations for the energetics of water clusters and ice structures. The errors of these approximations are computed by using accurate benchmark energies from the coupled-cluster technique of molecular quantum chemistry and from quantum Monte Carlo calculations. The systems studied are isomers of the water hexamer cluster, the crystal structures Ih, II, XV, and VIII of ice, and two clusters extracted from ice VIII. For the binding energies of these systems, we use the machine-learning technique of Gaussian Approximation Potentials to correct successively for 1-body and 2-body errors of the DFT approximations. We find that even after correction for these errors, substantial beyond-2-body errors remain. The characteristics of the 2-body and beyond-2-body errors of PBE are completely different from those of BLYP, but the errors of both approximations disfavor the close approach of non-hydrogen-bonded monomers. We note the possible relevance of our findings to the understanding of liquid water.

Cluster structure of anaerobic aggregates of an expanded granular sludge bed reactor.

PubMed

Gonzalez-Gil, G; Lens, P N; Van Aelst, A; Van As, H; Versprille, A I; Lettinga, G

2001-08-01

The metabolic properties and ultrastructure of mesophilic aggregates from a full-scale expanded granular sludge bed reactor treating brewery wastewater are described. The aggregates had a very high methanogenic activity on acetate (17.19 mmol of CH(4)/g of volatile suspended solids [VSS].day or 1.1 g of CH(4) chemical oxygen demand/g of VSS.day). Fluorescent in situ hybridization using 16S rRNA probes of crushed granules showed that 70 and 30% of the cells belonged to the archaebacterial and eubacterial domains, respectively. The spherical aggregates were black but contained numerous whitish spots on their surfaces. Cross-sectioning these aggregates revealed that the white spots appeared to be white clusters embedded in a black matrix. The white clusters were found to develop simultaneously with the increase in diameter. Energy-dispersed X-ray analysis and back-scattered electron microscopy showed that the whitish clusters contained mainly organic matter and no inorganic calcium precipitates. The white clusters had a higher density than the black matrix, as evidenced by the denser cell arrangement observed by high-magnification electron microscopy and the significantly higher effective diffusion coefficient determined by nuclear magnetic resonance imaging. High-magnification electron microscopy indicated a segregation of acetate-utilizing methanogens (Methanosaeta spp.) in the white clusters from syntrophic species and hydrogenotrophic methanogens (Methanobacterium-like and Methanospirillum-like organisms) in the black matrix. A number of physical and microbial ecology reasons for the observed structure are proposed, including the advantage of segregation for high-rate degradation of syntrophic substrates.

Cluster Structure of Anaerobic Aggregates of an Expanded Granular Sludge Bed Reactor

PubMed Central

Gonzalez-Gil, G.; Lens, P. N. L.; Van Aelst, A.; Van As, H.; Versprille, A. I.; Lettinga, G.

2001-01-01

The metabolic properties and ultrastructure of mesophilic aggregates from a full-scale expanded granular sludge bed reactor treating brewery wastewater are described. The aggregates had a very high methanogenic activity on acetate (17.19 mmol of CH4/g of volatile suspended solids [VSS]·day or 1.1 g of CH4 chemical oxygen demand/g of VSS·day). Fluorescent in situ hybridization using 16S rRNA probes of crushed granules showed that 70 and 30% of the cells belonged to the archaebacterial and eubacterial domains, respectively. The spherical aggregates were black but contained numerous whitish spots on their surfaces. Cross-sectioning these aggregates revealed that the white spots appeared to be white clusters embedded in a black matrix. The white clusters were found to develop simultaneously with the increase in diameter. Energy-dispersed X-ray analysis and back-scattered electron microscopy showed that the whitish clusters contained mainly organic matter and no inorganic calcium precipitates. The white clusters had a higher density than the black matrix, as evidenced by the denser cell arrangement observed by high-magnification electron microscopy and the significantly higher effective diffusion coefficient determined by nuclear magnetic resonance imaging. High-magnification electron microscopy indicated a segregation of acetate-utilizing methanogens (Methanosaeta spp.) in the white clusters from syntrophic species and hydrogenotrophic methanogens (Methanobacterium-like and Methanospirillum-like organisms) in the black matrix. A number of physical and microbial ecology reasons for the observed structure are proposed, including the advantage of segregation for high-rate degradation of syntrophic substrates. PMID:11472948

Inclusion evolution in molten and solidifying steel

NASA Astrophysics Data System (ADS)

Wang, Yan

Cleanliness, with respect to impurities and nonmetallic inclusions in the melt, is an important issue in steel production. The commercial interest in controlling steel cleanliness has been growing rapidly, because clean steel exhibits a highly attractive combination of corrosion resistance, good formability, pleasing appearance, and a wide range of strength levels. In order to satisfy the requirements for the degree of cleanliness in steel, controlling the size distribution, chemistry and shape of inclusions are of great importance in the steelmaking process. A knowledge of the formation of nonmetallic inclusions and their chemical and morphological evolution during the steelmaking and casting process is necessary in order to minimize the inclusion size and also try to promote potentially beneficial properties of inclusions, such as grain-refining. In this research, the evolution of inclusions in molten and solidifying steels was investigated through in-situ observations using a high temperature Confocal Scanning Laser Microscope (CSLM). The study focused on solid Al2O3 and liquid Al 2O3-CaO inclusions on low carbon steel melt surfaces. Firstly, the agglomeration and clustering of inclusions on steel surfaces were quantified and compared to predictions according to capillary depression driven attraction forces. A strong agglomeration was observed between the solid Al2O33 particle pairs. However, the liquid Al 2O3-CaO inclusions were not prone to agglomeration due to their lens-like morphology, which causes the absence of capillary force. Secondly, the pushing vs. engulfment and entrapment of both liquid Al 2O3-CaO and solid Al2O3 inclusions by advancing planar and cellular delta-ferrite solidification fronts was studied and compared to model predictions based on the force balances acting on the inclusions at the solid/melt interface. The critical velocity, above which the inclusions get engulfed, was observed to be slower at the cellular front than at the planar interface for liquid Al2O3-CaO inclusions. This indicates that these inclusions tend to more easily get engulfed at inter-cellular boundaries. However, there was no appreciable difference observed about the critical velocity for the large solid Al2O 3 inclusion clusters at the cellular boundary with that at the planar interface. The pushed liquid Al2O3-CaO inclusions were subject to a chemical and morphological change during solidification. (Abstract shortened by UMI.)

Production and composition of pyrogenic dissolved organic matter from a logical series of laboratory-generated chars

NASA Astrophysics Data System (ADS)

Bostick, Kyle W.; Zimmerman, Andrew R.; Wozniak, Andrew. S.; Mitra, Siddhartha; Hatcher, Patrick G.

2018-04-01

Though pyrogenic carbon (pyC) has been assumed to be predominantly stable, degradation and transfers of pyC between various pools have been found to influence its cycling and longevity in the environment. Dissolution via leaching may be the main control on loss processes such as microbial or abiotic oxidation, mineral sorption, or export to aquatic systems. Yet, little is known of the controls on pyrogenic dissolved organic matter (pyDOM) generation or composition. Here, the yield and composition of pyDOM generated through batch leaching of a thermal series of oak and grass biochars, as well as several non-pyrogenic reference materials, was compared to that of their parent solids. Over 17 daily leaching cycles, biochars made from oak at 250 to 650° C released decreasing amounts of C on both a weight (16.9 to 0.3%, respectively) and C yield basis (7.4 to 0.2% C, respectively). Aryl-C represented an estimated 32 to 82% of C in the parent solids (identified by 13C-NMR), but only 7 to 38% in the leachates (identified by 1H-NMR), though both increased with pyrolysis temperature. PyC, often operationally defined as condensed aromatic carbon (ConAC), was quantified using the benzenepolycarboxylic acid (BPCA) method. Tri- and tetra-carboxylated BPCAs were formed from non-pyrogenic reference materials, thus, only penta- and hexa-carboxylated BPCAs were used to derive a BPCA-C to ConAC conversion factor of 7.04. ConAC made up 24 to 57% of the pyrogenic solid C (excluding the 250 °C biochar), but only about 9 to 23% of their respective leachates' DOC, though both proportions generally increased with pyrolysis temperature. Weighted BPCA compound distributions, or the BPCA Aromatic Condensation (BACon) Index, indicate that ConAC cluster size increased in pyrogenic solids but not in leachates. Additional evidence presented suggests that both aromatic cluster size and O-containing functional group contents in the pyrogenic solid control pyC solubility. Overall, pyDOM was found to be compositionally dissimilar from its parent chars and contained a complex mixture of organic compound groups. Thus, it is expected that estimates of dissolved pyC production and export, made only by detection of ConAC, are too low by factors of 4 to 11.

Ionic Solid Hydrogen Fuel: Experimental Investigation of Cluster-Impact Fusion

DTIC Science & Technology

1991-01-24

LOX/H2 (1.6 x 106 J/kg). For missions with IT less than 100,000 s, the CIF rocket performance will be essentially identical to that of antimatter Under...Another concept utilizing antimatter was proposed, but it is limited by the technological difficulties in producing, bunching, and storing antimatter ...of high Isp and thrust comparable with that of antimatter . Conventional fusion devices with magnetic or inertial confinement schemes, however, seem

The old open cluster NGC 2112: updated estimates of fundamental parameters based on a membership analysis†

NASA Astrophysics Data System (ADS)

Carraro, G.; Villanova, S.; Demarque, P.; Moni Bidin, C.; McSwain, M. V.

2008-05-01

We report on a new, wide-field (20 × 20 arcmin2), multicolour (UBVI), photometric campaign in the area of the nearby old open cluster NGC 2112. At the same time, we provide medium-resolution spectroscopy of 35 (and high-resolution of additional 5) red giant and turn-off stars. This material is analysed with the aim to update the fundamental parameters of this traditionally difficult cluster, which is very sparse and suffers from heavy field star contamination. Among the 40 stars with spectra, we identified 21 bona fide radial velocity members which allow us to put more solid constraints on the cluster's metal abundance, long suggested to be as low as the metallicity of globulars. As indicated earlier by us on a purely photometric basis, the cluster [Fe/H] abundance is slightly supersolar ([Fe/H] = 0.16 +/- 0.03) and close to the Hyades value, as inferred from a detailed abundance analysis of three of the five stars with higher resolution spectra. Abundance ratios are also marginally supersolar. Based on this result, we revise the properties of NGC 2112 using stellar models from the Padova and Yale-Yonsei groups. For this metal abundance, we find that the cluster's age, reddening and distance values are 1.8 Gyr, 0.60 mag and 940 pc, respectively. Both the Yale-Yonsei and Padova models predict the same values for the fundamental parameters within the errors. Overall, NGC 2112 is a typical solar neighbourhood, thin-disc star cluster, sharing the same chemical properties of F-G stars and open clusters close to the Sun. This investigation outlines the importance of a detailed membership analysis in the study of disc star clusters. This paper includes data gathered with the 6.5 Magellan Telescopes, located at Las Campanas Observatory, Chile. The data discussed in this paper will be made available at the WEBDA open cluster data base http://www.univie.ac.at/webda, which is maintained by E. Paunzen and J.-C. Mermilliod. ‡ E-mail: gcarraro@eso.org (GC); sandro.villanova@unipd.it (SV); demarque@astro.yale.edu (PD); mbidin@das.uchile.cl (CMB); mcswain@lehigh.edu(MVM)

Calorimetric determination of energetics of solid solutions of UO 2+ x with CaO and Y 2O 3

NASA Astrophysics Data System (ADS)

Mazeina, Lena; Navrotsky, Alexandra; Greenblatt, Martha

2008-02-01

Quantitative study of thermodynamic properties of solid solutions of UO 2+ x with divalent and trivalent oxides is important for predicting the behavior of oxide fuel. Although early literature work measured vapor pressure in some of these solid solutions, direct calorimetric measurements of enthalpies of formation have been hampered by the refractory nature of such oxides. First measurements of the enthalpies of formation in the systems UO 2+ x-CaO and UO 2+ x-YO 1.5, obtained by high-temperature oxide melt solution calorimetry, are reported. Both systems show significantly negative (exothermic) heats of formation from binary oxides (UO 2, plus O 2 and CaO or YO 1.5, as well as from UO 2 plus UO 3 and CaO or YO 1.5), consistent with reported free energy measurements in the urania-yttria system. The energetic contributions of oxygen content (oxidation of U 4+) and of charge balanced ionic substitution as well as defect clustering are discussed. Behavior of urania-yttria is compared to that of corresponding systems in which the tetravalent ion is Ce, Zr, or Hf. The substantial additional stability in the solid solutions compared to pure UO 2+ x may retard, in both thermodynamic and kinetic sense, the oxidation and leaching of spent fuel to form aqueous U 6+ and solid uranyl phases.

Solid oxygen revisited

NASA Astrophysics Data System (ADS)

Freiman, Yu. A.; Jodl, H. J.; Crespo, Yanier

2018-05-01

The paper provides an up-to-date review of the experimental and theoretical works on solid oxygen published over the past decade. The most important results presented in this review are the following: Detection of magnetic collapse in neutron studies under the delta-epsilon transition. Identification of the lattice structure of the ɛ phase. In this structure the O2 molecules retain their individuality, but there is an additional link leading to the formation of clusters of molecular quartets with the structural formula (O2)4. Discovery of the unique magnetic properties of the delta phase, which hosts three different magnetic structures in the domain of the same crystallographic structure. The extension of the phase diagram to the high-pressure high-temperature region which was previously beyond the reach for experiment; the molecular η and η‧ phases were found and their structures were identified. Behavior of the melting line up to 60 GPa (1750 K). Discovery of a new molecular θ phase in ultrahigh magnetic fields up to over 190 T and the construction of the thermodynamical magnetic-field-temperature H- T phase diagram on the base of the ultrahigh-field magnetization, optical magneto-transmission, and adiabatic magnetocaloric effect measurements. Prediction of the persistence of the molecular state of solid oxygen up to the pressure of 1.9 TPa which is significantly higher than the corresponding limits in solid hydrogen and nitrogen, other generic molecular solids.

Fine structure of Fe-Co-Ga and Fe-Cr-Ga alloys with low Ga content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleinerman, Nadezhda M., E-mail: kleinerman@imp.uran.ru; Serikov, Vadim V., E-mail: kleinerman@imp.uran.ru; Vershinin, Aleksandr V., E-mail: kleinerman@imp.uran.ru

2014-10-27

Investigation of Ga influence on the structure of Fe-Cr and Fe-Co alloys was performed with the use of {sup 57}Fe Mössbauer spectroscopy and X-ray diffraction methods. In the alloys of the Fe-Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The analysis of Mössbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to entermore » the nearest surroundings of iron atoms, thus forming binary Fe-Ga regions (or phases)« less

Characterisation of volatile profiles in 50 native Peruvian chili pepper using solid phase microextraction-gas chromatography mass spectrometry (SPME-GCMS).

PubMed

Patel, Kirti; Ruiz, Candy; Calderon, Rosa; Marcelo, Mavel; Rojas, Rosario

2016-11-01

The volatiles were characterised by headspace solid phase micro extraction (HS-SPME), gas chromatography mass spectrometry (GC-FID/MS). A total of 127 compounds were identified with terpenes (including mono terpenes and sesquiterpenes - a total of 45 compounds), esters (31 compounds) and hydrocarbons (20 compounds) were the predominant volatile compounds. Principal component analysis (PCA) of the volatile compounds yielded 2 significant PC's, which together accounted for 90.3% of the total variance in the data set and the scatter plot generated between PC1 and PC2 successfully segregated the 50 chili pepper samples into 7 groups. Clusters of hydrocarbons, esters, terpenes, aldehyde and ketones formed the major determinants of the difference. Copyright © 2016 Elsevier Ltd. All rights reserved.

The Influence of Vanadium on Ferrite and Bainite Formation in a Medium Carbon Steel

NASA Astrophysics Data System (ADS)

Sourmail, T.; Garcia-Mateo, C.; Caballero, F. G.; Cazottes, S.; Epicier, T.; Danoix, F.; Milbourn, D.

2017-09-01

The influence of vanadium additions on transformation kinetics has been investigated in a medium carbon forging steel. Using dilatometry to track transformation during continuous cooling or isothermal transformation, the impact of vanadium on both ferrite-pearlite and bainite has been quantified. Transmission electron microscopy and atom probe tomography have been used to establish whether vanadium was present in solid solution, or as clusters and precipitates. The results show that vanadium in solid solution has a pronounced retarding influence on ferrite-pearlite formation and that, unlike in the case of niobium, this effect can be exploited even during relatively slow cooling. The influence on bainite transformation was found to depend on temperature; an explanation in terms of the effect of vanadium on heterogeneous nucleation is tentatively proposed.

Understanding the high pressure properties of molecular solids and molecular surfaces deposited on hetrogeneous substrates

NASA Technical Reports Server (NTRS)

Etters, R. D.

1985-01-01

Work directed toward understanding the high pressure properties of molecular solids and molecular surfaces deposited on hetrogeneous substrates is reported. The motivation, apart from expanding our basic knowledge about these systems, was to understand and predict the properties of new materials synthesized at high pressure, including pressure induced metallic and superconducting states. As a consequence, information about the states of matter of the Jovian planets and their satellites, which are natural high pressure laboratories was also provided. The work on molecular surfaces and finite two and three dimensional clusters of atoms and molecules was connected with the composition and behavior of planetary atmospheres and on the processes involved in forming surface layers, which is vital to the development of composite materials and microcircuitry.

StarBooster Demonstrator Cluster Configuration Analysis/Verification Program

NASA Technical Reports Server (NTRS)

DeTurris, Dianne J.

2003-01-01

In order to study the flight dynamics of the cluster configuration of two first stage boosters and upper-stage, flight-testing of subsonic sub-scale models has been undertaken using two glideback boosters launched on a center upper-stage. Three high power rockets clustered together were built and flown to demonstrate vertical launch, separation and horizontal recovery of the boosters. Although the boosters fly to conventional aircraft landing, the centerstage comes down separately under its own parachute. The goal of the project has been to collect data during separation and flight for comparison with a six degree of freedom simulation. The configuration for the delta wing canard boosters comes from a design by Starcraft Boosters, Inc. The subscale rockets were constructed of foam covered in carbon or fiberglass and were launched with commercially available solid rocket motors. The first set of boosters built were 3-ft tall with a 4-ft tall centerstage, and two additional sets of boosters were made that were each over 5-ft tall with a 7.5 ft centerstage. The rocket cluster is launched vertically, then after motor bum out the boosters are separated and flown to a horizontal landing under radio-control. An on-board data acquisition system recorded data during both the launch and glide phases of flight.

Homochiral coordination polymers with helixes and metal clusters based on lactate derivatives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zhong-Xuan, E-mail: xuzhongxuan4201@163.com; Ma, Yu-Lu; Lv, Guo-ling

2017-05-15

Utilizing the lactic acid derivatives (R)-4-(1-carboxyethoxy)benzoic acid (denoted: (R)-H{sub 2}CBA) and (S)-4-(1-carboxyethoxy)benzoic acid (denoted: (S)-H{sub 2}CBA)as chiral linkers to self-assemble with 4, 4′-bipyridine (denoted: BIP) and Cd(II) ions, a couple of three-dimensional homochiral coordination polymers, namely [Cd{sub 3}((R)-CBA){sub 3} (BIP){sub 2}(H{sub 2}O)]·xGuest (1-D) and [Cd{sub 3}((S)-CBA){sub 3}(BIP){sub 2}(H{sub 2}O)]·xGuest (1-L), have been synthesized under solvothermal reaction condition. Single crystal X-ray diffraction analysis reveals the two complexes contain single helical chains based on enantiopure ligands and cadmium clusters. Moreover, some physical characteristics such as PXRD, thermal stability, solid-state circular dichroism (CD) and luminescent were also investigated. - Graphical abstract: Utilizing enantiomericmore » lactic acid derivatives (R)-H{sub 2}CBA and (S)-H{sub 2}CBA to assemble with Cd{sup 2+} ions and ancillary BIP ligands, a couple of 3D homochiral coordination polymers with metal clusters and helical chains have been prepared by hydrothermal reaction. - Highlights: • Chiral lactic acid derivative. • Enantiomeric coordination polymer. • Helical chain. • Trinuclear cadmium cluster.« less

Optical amplification of photothermal therapy with gold nanoparticles and nanoclusters

NASA Astrophysics Data System (ADS)

Khlebtsov, Boris; Zharov, Vladimir; Melnikov, Andrei; Tuchin, Valery; Khlebtsov, Nikolai

2006-10-01

Recently, several groups (Anderson, Halas, Zharov, and their co-workers, 2003; El-Sayed and co-workers, 2006) demonstrated, through pioneering results, the great potential of photothermal (PT) therapy for the selective treatment of cancer cells, bacteria, viruses, and DNA targeted with gold nanospheres, nanoshells, nanorods, and nanosphere clusters. However, the current understanding of the relationship between the nanoparticle/cluster parameters (size, shape, particle/cluster structure, etc) and the efficiency of PT therapy is limited. Here, we report theoretical simulations aimed at finding the optimal single-particle and cluster structures to achieve its maximal absorption, which is crucial for PT therapeutic effects. To characterize the optical amplification in laser-induced thermal effects, we introduce relevant parameters such as the ratio of the absorption cross section to the gold mass of a single-particle structure and absorption amplification, defined as the ratio of cluster absorption to the total absorption of non-interacting particles. We consider the absorption efficiency of single nanoparticles (gold spheres, rods, and silica/gold nanoshells), linear chains, 2D lattice arrays, 3D random volume clusters, and the random aggregated N-particle ensembles on the outer surface of a larger dielectric sphere, which mimic aggregation of nanosphere bioconjugates on or within cancer cells. The cluster particles are bare or biopolymer-coated gold nanospheres. The light absorption of cluster structures is studied by using the generalized multiparticle Mie solution and the T-matrix method. The gold nanoshells with (silica core diameter)/(gold shell thickness) parameters of (50-100)/(3-8) nm and nanorods with minor/major sizes of (15-20)/(50-70) nm are shown to be more efficient PT labels and sensitizers than the equivolume solid single gold spheres. In the case of nanosphere clusters, the interparticle separations and the short linear-chain fragments are the main structural parameters determining the absorption efficiency and its spectral shifting to the red. Although we have not found a noticeable dependence of absorption amplification on the cluster sphere size, 20-40 nm particles are found to be most effective, in accordance with our experimental observations. The long-wavelength absorption efficiency of random clusters increases with the cluster particle number N at small N and reveals a saturation behaviour at N>20.

The role of FeS(aq) molecular clusters in microbial redox cycling and iron mineralization.

NASA Astrophysics Data System (ADS)

Druschel, G.; Oduro, H.; Sperling, J.; Johnson, C.

2008-12-01

Iron sulfide molecular clusters, FeS(aq), are a group of polynuclear Fe-S complexes varying in size between a few and a few hundred molecules that occur in many environments and are critical parts of cycling between soluble iron and iron sulfide minerals. These clusters react uniquely with voltammetric Au-amalgam electrodes, and the signal for these molecules has now been observed in many terrestrial and marine aquatic settings. FeS(aq) clusters form when aqueous sulfide and iron(II) interact, but the source of those ions can come from abiotic or microbial sulfate and iron reduction or from the abiotic non-oxidative dissolution of iron sulfide minerals. Formation of iron sulfide minerals, principally mackinawite as the first solid nanocrystalline phase in many settings, is necessarily preceeded by formation and evolution of these molecular clusters as mineralization proceeds, and the clusters have been suggested to additionally be part of the pyritization process (Rickard and Luther, 1997; Luther and Rickard, 2005). In several systems, we have also observed FeS(aq) clusters to be the link between Fe-S mineral dissolution and oxidation of iron and sulfide, with important implications for changes to the overall oxidation pathway. Microorganisms can clearly be involved in the formation of FeS(aq) through iron and sulfate reduction, but it is not clear to date if organisms can utilize these clusters either as metabolic components or as anabolic 'building blocks' for enzyme production. Cycling of iron in the Fe-S system linked to FeS(aq) would clearly be a critical part of understanding iron isotope dynamics preserved in iron sulfide minerals. We will review ongoing work towards understanding the role of FeS(aq) in iron cycling and isotope fractionation as well as the measurement and characterization of this key class of iron complexes using environmental voltammetry.

Tumour compartment transcriptomics demonstrates the activation of inflammatory and odontogenic programmes in human adamantinomatous craniopharyngioma and identifies the MAPK/ERK pathway as a novel therapeutic target.

PubMed

Apps, John R; Carreno, Gabriela; Gonzalez-Meljem, Jose Mario; Haston, Scott; Guiho, Romain; Cooper, Julie E; Manshaei, Saba; Jani, Nital; Hölsken, Annett; Pettorini, Benedetta; Beynon, Robert J; Simpson, Deborah M; Fraser, Helen C; Hong, Ying; Hallang, Shirleen; Stone, Thomas J; Virasami, Alex; Donson, Andrew M; Jones, David; Aquilina, Kristian; Spoudeas, Helen; Joshi, Abhijit R; Grundy, Richard; Storer, Lisa C D; Korbonits, Márta; Hilton, David A; Tossell, Kyoko; Thavaraj, Selvam; Ungless, Mark A; Gil, Jesus; Buslei, Rolf; Hankinson, Todd; Hargrave, Darren; Goding, Colin; Andoniadou, Cynthia L; Brogan, Paul; Jacques, Thomas S; Williams, Hywel J; Martinez-Barbera, Juan Pedro

2018-05-01

Adamantinomatous craniopharyngiomas (ACPs) are clinically challenging tumours, the majority of which have activating mutations in CTNNB1. They are histologically complex, showing cystic and solid components, the latter comprised of different morphological cell types (e.g. β-catenin-accumulating cluster cells and palisading epithelium), surrounded by a florid glial reaction with immune cells. Here, we have carried out RNA sequencing on 18 ACP samples and integrated these data with an existing ACP transcriptomic dataset. No studies so far have examined the patterns of gene expression within the different cellular compartments of the tumour. To achieve this goal, we have combined laser capture microdissection with computational analyses to reveal groups of genes that are associated with either epithelial tumour cells (clusters and palisading epithelium), glial tissue or immune infiltrate. We use these human ACP molecular signatures and RNA-Seq data from two ACP mouse models to reveal that cell clusters are molecularly analogous to the enamel knot, a critical signalling centre controlling normal tooth morphogenesis. Supporting this finding, we show that human cluster cells express high levels of several members of the FGF, TGFB and BMP families of secreted factors, which signal to neighbouring cells as evidenced by immunostaining against the phosphorylated proteins pERK1/2, pSMAD3 and pSMAD1/5/9 in both human and mouse ACP. We reveal that inhibiting the MAPK/ERK pathway with trametinib, a clinically approved MEK inhibitor, results in reduced proliferation and increased apoptosis in explant cultures of human and mouse ACP. Finally, we analyse a prominent molecular signature in the glial reactive tissue to characterise the inflammatory microenvironment and uncover the activation of inflammasomes in human ACP. We validate these results by immunostaining against immune cell markers, cytokine ELISA and proteome analysis in both solid tumour and cystic fluid from ACP patients. Our data support a new molecular paradigm for understanding ACP tumorigenesis as an aberrant mimic of natural tooth development and opens new therapeutic opportunities by revealing the activation of the MAPK/ERK and inflammasome pathways in human ACP.

Old metal oxide clusters in new applications: spontaneous reduction of Keggin and Dawson polyoxometalate layers by a metallic electrode for improving efficiency in organic optoelectronics.

PubMed

Vasilopoulou, Maria; Douvas, Antonios M; Palilis, Leonidas C; Kennou, Stella; Argitis, Panagiotis

2015-06-03

The present study is aimed at investigating the solid state reduction of a representative series of Keggin and Dawson polyoxometalate (POM) films in contact with a metallic (aluminum) electrode and at introducing them as highly efficient cathode interlayers in organic optoelectronics. We show that, upon reduction, up to four electrons are transferred from the metallic electrode to the POM clusters of the Keggin series dependent on addenda substitution, whereas a six electron reduction was observed in the case of the Dawson type clusters. The high degree of their reduction by Al was found to be of vital importance in obtaining effective electron transport through the cathode interface. A large improvement in the operational characteristics of organic light emitting devices and organic photovoltaics based on a wide range of different organic semiconducting materials and incorporating reduced POM/Al cathode interfaces was achieved as a result of the large decrease of the electron injection/extraction barrier, the enhanced electron transport and the reduced recombination losses in our reduced POM modified devices.

Computational studies of small neutral vanadium oxide clusters and their reactions with sulfur dioxide

NASA Astrophysics Data System (ADS)

Jakubikova, Elena; He, Sheng-Gui; Xie, Yan; Matsuda, Yoshiyuki; Bernstein, Elliot

2007-03-01

Vanadium oxide is a catalytic system that plays an important role in the conversion of SO2 to SO3. Density functional theory at the BPW91/LANL2DZ level is employed to obtain structures of VOy (y=1,,5), V2Oy (y=2,,7), V3Oy (y=4,,9), V4Oy (y=7,,12) and their complexes with SO2. BPW91/LANL2DZ is insufficient to describe properly relative V-O and S-O bond strengths of vanadium and sulfur oxides. Calibration of theoretical results with experimental data is necessary to compute enthalpies of reactions between VxOy and SO2. Theoretical results indicate SO2 to SO conversion occurs for oxygen-deficient clusters and SO2 to SO3 conversion occurs for oxygen-rich clusters. Subsequent experimental studies confirm the presence of SO in the molecular beam as well as the presence of VxOy complexes with SO2. Some possible mechanisms for SO3 formation and catalyst regeneration for solids are also suggested.

Microscopic mechanism of nanocrystal formation from solution by cluster aggregation and coalescence

PubMed Central

Hassan, Sergio A.

2011-01-01

Solute-cluster aggregation and particle fusion have recently been suggested as alternative routes to the classical mechanism of nucleation from solution. The role of both processes in the crystallization of an aqueous electrolyte under controlled salt addition is here elucidated by molecular dynamics simulation. The time scale of the simulation allows direct observation of the entire crystallization pathway, from early events in the prenucleation stage to the formation of a nanocrystal in equilibrium with concentrated solution. The precursor originates in a small amorphous aggregate stabilized by hydration forces. The core of the nucleus becomes crystalline over time and grows by coalescence of the amorphous phase deposited at the surface. Imperfections of ion packing during coalescence promote growth of two conjoint crystallites. A parameter of order and calculated cohesive energies reflect the increasing crystalline order and stress relief at the grain boundary. Cluster aggregation plays a major role both in the formation of the nucleus and in the early stages of postnucleation growth. The mechanism identified shares common features with nucleation of solids from the melt and of liquid droplets from the vapor. PMID:21428633

Preparation and electrical-property characterization of poly(vinyl chloride)-derived carbon nanosheet by ion beam irradiation-induced carbon clustering and carbonization

NASA Astrophysics Data System (ADS)

Jung, Chan-Hee; Sohn, Joon-Yong; Kim, Hyo-Sub; Hwang, In-Tae; Lee, Hong-Joon; Shin, Junhwa; Choi, Jae-Hak

2018-05-01

In this work, we demonstrated that carbon nanosheet (CNS) can easily be produced by a room-temperature, solid-state proton irradiation-induced clustering of poly(vinyl chloride) (PVC) films followed by carbonization. The results of the optical, chemical, and structural analyses revealed that oxidized and sp2-hybridized carbon clusters were effectively created in the PVC thin film by combined dehydrochlorination and inter-coupling reactions during proton irradiation. This was further converted to pseudo-hexagonally-structured nano-crystalline CNS with 2-D symmetry and metallic transporting character by high-temperature treatment. As a result, the CNS exhibited a very high electrical conductivity (587 S/cm) without a significant change in their thickness, a low surface roughness (0.36 nm), and a high work function (5.11 eV). These findings demonstrate that the radiation-based approach opens new avenues for the design and development of 2-D CNS as a graphene allotrope for the application of electronic devices, including field-effect transistors, electric heating devices, biosensors, supercapacitors, and fuel cells.

Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster

NASA Technical Reports Server (NTRS)

Lea, S. M.; Mushotzky, R. F.; Holt, S. S.

1982-01-01

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 minutes from the center of M87 are presented. X-ray spectra are obtained at these two locations with the slid state spectrometer onboard the Einstein Observatory. Emission lines were observed in both locations, indicating the presence of heavy elements at abundances approximately solar (to within a factor of 2). A temperature gradient, T increases from approximately 1.4 keV at the position of M87 to T approximately 3.35 keV 7' away, was detected. There is lower temperature thermal emission at the center of M87 with T approximately 0.6 keV, consistent with models for cooling flows in this cluster. In addition to the thermal emission, a power law component in the spectrum of M87, was detected consistent with that observed by HEAO-1, indicating that this component probably originates in the galaxy itself. The presence of intracluster gas having density approximately .001 cu cm and temperature approximately 30 million K is indicated.

Future Power Production by LENR with Thin-Film Electrodes

NASA Astrophysics Data System (ADS)

Miley, George H.; Hora, Heinz; Lipson, Andrei; Luo, Nie; Shrestha, P. Joshi

2007-03-01

PdD cluster reaction theory was recently proposed to explain a wide range of Low energy Nuclear Reaction (LENR) experiments. If understood and optimized, cluster reactions could lead to a revolutionary new power source of nuclear energy. The route is two-fold. First, the excess heat must be obtained reproducibly and over extended run times. Second, the percentage of excess must be significantly (order of magnitude or more) higher than the 20-50% typically today. The thin film methods described here have proven to be quite reproducible, e.g. providing excess heat of 20-30% in nine consecutive runs of several weeks each. However, mechanical separation of the films occurs over long runs due to the severe mechanical stresses created.. Techniques to overcome these problems are possible using graded bonding techniques similar to that used in high temperature solid oxide fuel cells. Thus the remaining key issue is to increase the excess heat. The cluster model provides import insight into this. G. H. Miley, H. Hora, et al., 233rd Amer Chem Soc Meeting, Chicago, IL, March 25-29, 2007.

Point defect evolution in Ni, NiFe and NiCr alloys from atomistic simulations and irradiation experiments

DOE PAGES

Aidhy, Dilpuneet S.; Lu, Chenyang; Jin, Ke; ...

2015-08-08

Using molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni 0.5Fe 0.5, and Ni 0.8Cr 0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3 <111>{111}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller andmore » more clusters are observed in the alloys. The vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to formation of stacking fault tetrahedra, also consistent with our experiments. The results also show that the surviving Frenkel pairs are composition-dependent and are largely Ni dominated.« less

DNA-Mediated Self-Organization of Polymeric Nanocompartments Leads to Interconnected Artificial Organelles.

PubMed

Liu, Juan; Postupalenko, Viktoriia; Lörcher, Samuel; Wu, Dalin; Chami, Mohamed; Meier, Wolfgang; Palivan, Cornelia G

2016-11-09

Self-organization of nanocomponents was mainly focused on solid nanoparticles, quantum dots, or liposomes to generate complex architectures with specific properties, but intrinsically limited or not developed enough, to mimic sophisticated structures with biological functions in cells. Here, we present a biomimetic strategy to self-organize synthetic nanocompartments (polymersomes) into clusters with controlled properties and topology by exploiting DNA hybridization to interconnect polymersomes. Molecular and external factors affecting the self-organization served to design clusters mimicking the connection of natural organelles: fine-tune of the distance between tethered polymersomes, different topologies, no fusion of clustered polymersomes, and no aggregation. Unexpected, extended DNA bridges that result from migration of the DNA strands inside the thick polymer membrane (about 12 nm) represent a key stability and control factor, not yet exploited for other synthetic nano-object networks. The replacement of the empty polymersomes with artificial organelles, already reported for single polymersome architecture, will provide an excellent platform for the development of artificial systems mimicking natural organelles or cells and represents a fundamental step in the engineering of molecular factories.

Self-assembly of [Pt(3n)(CO)(6n)]2- (n = 4-8) carbonyl clusters: from molecules to conducting molecular metal wires.

PubMed

Femoni, Cristina; Iapalucci, Maria Carmela; Longoni, Giuliano; Lovato, Tatiana; Stagni, Stefano; Zacchini, Stefano

2010-07-05

A comprehensive study discussing the different parameters that influence the self-assembly of [Pt(3n)(CO)(6n)](2-) (n = 4-8) clusters with miscellaneous mono- and dications into 0-D, 1-D, 2-D, and 3-D materials is herein reported. As an unexpected bonus, the use of Ru(II) dications allowed the first structural characterization of the previously unknown [Pt(21)(CO)(42)](2-) dianion. 0-D structures, which contain isolated ions, are electrical insulators in solid form. Conversely, as soon as infinite chains of clusters are formed, the electrical resistivity, measured in pressed pellets, decreases to 10(5)-10(6), 10(4), and 10(2) ohms cm for discontinuous, semicontinuous, and continuous chains, respectively. Therefore, the resemblance of these materials to molecular metal wires is not only morphological but also functional. Preliminary results of possible self-assembly phenomena in a solution of [Pt(15)(CO)(30)](2-) and [Pt(18)(CO)(36)](2-) according to dynamic light scattering experiments are also reported.

Clustered Mutation Signatures Reveal that Error-Prone DNA Repair Targets Mutations to Active Genes.

PubMed

Supek, Fran; Lehner, Ben

2017-07-27

Many processes can cause the same nucleotide change in a genome, making the identification of the mechanisms causing mutations a difficult challenge. Here, we show that clustered mutations provide a more precise fingerprint of mutagenic processes. Of nine clustered mutation signatures identified from >1,000 tumor genomes, three relate to variable APOBEC activity and three are associated with tobacco smoking. An additional signature matches the spectrum of translesion DNA polymerase eta (POLH). In lymphoid cells, these mutations target promoters, consistent with AID-initiated somatic hypermutation. In solid tumors, however, they are associated with UV exposure and alcohol consumption and target the H3K36me3 chromatin of active genes in a mismatch repair (MMR)-dependent manner. These regions normally have a low mutation rate because error-free MMR also targets H3K36me3 chromatin. Carcinogens and error-prone repair therefore redistribute mutations to the more important regions of the genome, contributing a substantial mutation load in many tumors, including driver mutations. Copyright © 2017 Elsevier Inc. All rights reserved.

Measurement of high-dynamic range x-ray Thomson scattering spectra for the characterization of nano-plasmas at LCLS

DOE PAGES

MacDonald, M. J.; Gorkhover, T.; Bachmann, B.; ...

2016-08-08

Atomic clusters can serve as ideal model systems for exploring ultrafast (~100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano plasmas was limited to coherent x-ray imaging. Here we present the first measurement of spectrally-resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities and ionization. Single shot x-ray Thomson scatterings signals were recorded at 120 Hz using a crystal spectrometer in combination withmore » a single-photon counting and energy-dispersive pnCCD. A precise pump laser collimation scheme enabled recording near background-free scattering spectra from Ar clusters with an unprecedented dynamic range of more than 3 orders of magnitude. As a result, such measurements are important for understanding collective effects in laser-matter interactions on femtosecond timescales, opening new routes for the development of schemes for their ultrafast control.« less

Greater-than-bulk melting temperatures explained: Gallium melts Gangnam style

NASA Astrophysics Data System (ADS)

Gaston, Nicola; Steenbergen, Krista

2014-03-01

The experimental discovery of superheating in gallium clusters contradicted the clear and well-demonstrated paradigm that the melting temperature of a particle should decrease with its size. However the extremely sensitive dependence of melting temperature on size also goes to the heart of cluster science, and the interplay between the effects of electronic and geometric structure. We have performed extensive first-principles molecular dynamics calculations, incorporating parallel tempering for an efficient exploration of configurational phase space. This is necessary, due to the complicated energy landscape of gallium. In the nanoparticles, melting is preceded by a transitions between phases. A structural feature, referred to here as the Gangnam motif, is found to increase with the latent heat and appears throughout the observed phase changes of this curious metal. We will present our detailed analysis of the solid-state isomers, performed using extensive statistical sampling of the trajectory data for the assignment of cluster structures to known phases of gallium. Finally, we explain the greater-than-bulk melting through analysis of the factors that stabilise the liquid structures.

Measurement of high-dynamic range x-ray Thomson scattering spectra for the characterization of nano-plasmas at LCLS

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDonald, M. J., E-mail: macdonm@umich.edu; SLAC National Accelerator Laboratory, Menlo Park, California 94025; Gorkhover, T.

2016-11-15

Atomic clusters can serve as ideal model systems for exploring ultrafast (∼100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano-plasmas was limited to coherent x-ray imaging. Here we present the first measurement of spectrally resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities, and ionization. Single shot x-ray Thomson scattering signals were recorded at 120 Hz using a crystal spectrometer in combination withmore » a single-photon counting and energy-dispersive pnCCD. A precise pump laser collimation scheme enabled recording near background-free scattering spectra from Ar clusters with an unprecedented dynamic range of more than 3 orders of magnitude. Such measurements are important for understanding collective effects in laser-matter interactions on femtosecond time scales, opening new routes for the development of schemes for their ultrafast control.« less

Understanding boron through size-selected clusters: structure, chemical bonding, and fluxionality.

PubMed

Sergeeva, Alina P; Popov, Ivan A; Piazza, Zachary A; Li, Wei-Li; Romanescu, Constantin; Wang, Lai-Sheng; Boldyrev, Alexander I

2014-04-15

Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar structures, stabilized by localized two-center-two-electron (2c-2e) σ bonds on the periphery and delocalized multicenter-two-electron (nc-2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron's electron deficiency and leads to fluxional behavior, which has been observed in B13(+) and B19(-). A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B(-), formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B(-)/C analogy. It is believed that the electronic transmutation concept will be effective and valuable in aiding the design of new boride materials with predictable properties. The study of boron clusters with intermediate properties between those of individual atoms and bulk solids has given rise to a unique opportunity to broaden the frontier of boron chemistry. Understanding boron clusters has spurred experimentalists and theoreticians to find new boron-based nanomaterials, such as boron fullerenes, nanotubes, two-dimensional boron, and new compounds containing boron clusters as building blocks. Here, a brief and timely overview is presented addressing the recent progress made on boron clusters and the approaches used in the authors' laboratories to determine the structure, stability, and chemical bonding of size-selected boron clusters by joint photoelectron spectroscopy and theoretical studies. Specifically, key findings on all-boron hydrocarbon analogues, metal-centered boron wheels, and electronic transmutation in boron clusters are summarized.

Understanding Boron through Size-Selected Clusters: Structure, Chemical Bonding, and Fluxionality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sergeeva, Alina P.; Popov, Ivan A.; Piazza, Zachary A.

Conspectus Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar structures, stabilized by localized two-center–two-electron (2c–2e) σ bonds on the periphery and delocalized multicenter–two-electron (nc–2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron’s electron deficiency and leads to fluxional behavior, which has been observed in B13+ and B19–. A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiationmore » has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B–, formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B–/C analogy. It is believed that the electronic transmutation concept will be effective and valuable in aiding the design of new boride materials with predictable properties. The study of boron clusters with intermediate properties between those of individual atoms and bulk solids has given rise to a unique opportunity to broaden the frontier of boron chemistry. Understanding boron clusters has spurred experimentalists and theoreticians to find new boron-based nanomaterials, such as boron fullerenes, nanotubes, two-dimensional boron, and new compounds containing boron clusters as building blocks. Here, a brief and timely overview is presented addressing the recent progress made on boron clusters and the approaches used in the authors’ laboratories to determine the structure, stability, and chemical bonding of size-selected boron clusters by joint photoelectron spectroscopy and theoretical studies. Specifically, key findings on all-boron hydrocarbon analogues, metal-centered boron wheels, and electronic transmutation in boron clusters are summarized.« less

A Co16 cluster and a 1-D Mn chain complex supported by benzohydroxamic acid.

PubMed

Cao, Yanyuan; Chen, Yanmei; Li, Lei; Gao, Dandan; Liu, Wei; Hu, Hailiang; Li, Wu; Li, Yahong

2013-08-14

The syntheses, crystal structures and magnetic properties are described for a {Co16} cluster [Co(II)16O(OH)2(bha)12(PhCO2)4(Phen)2(MeOH)4]·2MeOH (1) and a 1-D Mn(II) chain complex [Mn(Hbha)2]n·(2MeOH)n (2) (H2bha = benzohydroxamic acid; Phen = 1,10-phenanthroline). The 1 : 1 : 0.5 reaction of Co(O2CMe)2·4H2O, H2bha and 1,10-phenanthroline in MeOH at 100 °C under autogenous pressure gave cluster 1. Complex 2 was obtained from the 1 : 1 reaction mixture of Mn(O2CMe)2·2H2O and H2bha in MeOH under solvothermal conditions. The {Co16} cluster can be thought as a face-centered cube with two wings. The H2bha ligands show hydroximic form in 1 and exhibit hydroxamic mode in 2. The hydroximate ligands in 1 display three distinct binding modes, one of which is novel. Variable-temperature solid-state dc magnetic susceptibility studies have been performed in the 2.0-300 K range for complexes 1 and 2. Antiferromagnetic M(II)···M(II) exchange interactions were found for both 1 and 2. This work also demonstrates that solvothermal method is a potential synthetic approach for the design and growth of high nuclearity clusters or chain complexes of the H2bha ligand.

Altered Actin Centripetal Retrograde Flow in Physically Restricted Immunological Synapses

PubMed Central

Yu, Cheng-han; Wu, Hung-Jen; Kaizuka, Yoshihisa; Vale, Ronald D.; Groves, Jay T.

2010-01-01

Antigen recognition by T cells involves large scale spatial reorganization of numerous receptor, adhesion, and costimulatory proteins within the T cell-antigen presenting cell (APC) junction. The resulting patterns can be distinctive, and are collectively known as the immunological synapse. Dynamical assembly of cytoskeletal network is believed to play an important role in driving these assembly processes. In one experimental strategy, the APC is replaced with a synthetic supported membrane. An advantage of this configuration is that solid structures patterned onto the underlying substrate can guide immunological synapse assembly into altered patterns. Here, we use mobile anti-CD3ε on the spatial-partitioned supported bilayer to ligate and trigger T cell receptor (TCR) in live Jurkat T cells. Simultaneous tracking of both TCR clusters and GFP-actin speckles reveals their dynamic association and individual flow patterns. Actin retrograde flow directs the inward transport of TCR clusters. Flow-based particle tracking algorithms allow us to investigate the velocity distribution of actin flow field across the whole synapse, and centripetal velocity of actin flow decreases as it moves toward the center of synapse. Localized actin flow analysis reveals that, while there is no influence on actin motion from substrate patterns directly, velocity differences of actin are observed over physically trapped TCR clusters. Actin flow regains its velocity immediately after passing through confined TCR clusters. These observations are consistent with a dynamic and dissipative coupling between TCR clusters and viscoelastic actin network. PMID:20686692

Parallel implementation of D-Phylo algorithm for maximum likelihood clusters.

PubMed

Malik, Shamita; Sharma, Dolly; Khatri, Sunil Kumar

2017-03-01

This study explains a newly developed parallel algorithm for phylogenetic analysis of DNA sequences. The newly designed D-Phylo is a more advanced algorithm for phylogenetic analysis using maximum likelihood approach. The D-Phylo while misusing the seeking capacity of k -means keeps away from its real constraint of getting stuck at privately conserved motifs. The authors have tested the behaviour of D-Phylo on Amazon Linux Amazon Machine Image(Hardware Virtual Machine)i2.4xlarge, six central processing unit, 122 GiB memory, 8  ×  800 Solid-state drive Elastic Block Store volume, high network performance up to 15 processors for several real-life datasets. Distributing the clusters evenly on all the processors provides us the capacity to accomplish a near direct speed if there should arise an occurrence of huge number of processors.

Monitoring the solid-state electrochemistry of Cu(2,7-AQDC) (AQDC = anthraquinone dicarboxylate) in a lithium battery: coexistence of metal and ligand redox activities in a metal-organic framework.

PubMed

Zhang, Zhongyue; Yoshikawa, Hirofumi; Awaga, Kunio

2014-11-19

By adopting a facile synthetic strategy, we obtained a microporous redox-active metal-organic framework (MOF), namely, Cu(2,7-AQDC) (2,7-H2AQDC = 2,7-anthraquinonedicarboxylic acid) (1), and utilized it as a cathode active material in lithium batteries. With a voltage window of 4.0-1.7 V, both metal clusters and anthraquinone groups in the ligands exhibited reversible redox activity. The valence change of copper cations was clearly evidenced by in situ XANES analysis. By controlling the voltage window of operation, extremely high recyclability of batteries was achieved, suggesting the framework was robust. This MOF is the first example of a porous material showing independent redox activity on both metal cluster nodes and ligand sites.

Imaging Atomic-Scale Clustering in III–V Semiconductor Alloys

DOE PAGES

Hirst, Louise C.; Kotulak, Nicole A.; Tomasulo, Stephanie; ...

2017-03-13

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III–V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this paper, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Finally, image quantification of atomicmore » column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.« less

Domain and network aggregation of CdTe quantum rods within Langmuir Blodgett monolayers

NASA Astrophysics Data System (ADS)

Zimnitsky, Dmitry; Xu, Jun; Lin, Zhiqun; Tsukruk, Vladimir V.

2008-05-01

Control over the organization of quantum rods was demonstrated by changing the surface area at the air-liquid interface by means of the Langmuir-Blodgett (LB) technique. The LB isotherm of CdTe quantum rods capped with a mixture of alkylphosphines shows a transition point in the liquid-solid state, which is caused by the inter-rod reorganization. As we observed, at low surface pressure the quantum rods are assembled into round-shaped aggregates composed of a monolayer of nanorods packed in limited-size clusters with random orientation. The increase of the surface pressure leads to the rearrangement of these aggregates into elongated bundles composed of uniformly oriented nanorod clusters. Further compression results in denser packing of nanorods aggregates and in the transformation of monolayered domains into a continuous network of locally ordered quantum rods.

Solid-phase arsenic speciation in aquifer sediments: A micro-X-ray absorption spectroscopy approach for quantifying trace-level speciation

USGS Publications Warehouse

Nicholas, Sarah L.; Erickson, Melinda L.; Woodruff, Laurel G.; Knaeble, Alan R.; Marcus, Matthew A.; Lynch, Joshua K.; Toner, Brandy M.

2017-01-01

e of this research is to identify the solid-phase sources and geochemical mechanisms of release of As in aquifers of the Des Moines Lobe glacial advance. The overarching concept is that conditions present at the aquifer-aquitard interfaces promote a suite of geochemical reactions leading to mineral alteration and release of As to groundwater. A microprobe X-ray absorption spectroscopy (lXAS) approach is developed and applied to rotosonic drill core samples to identify the solid-phase speciation of As in aquifer, aquitard, and aquifer-aquitard interface sediments. This approach addresses the low solid-phase As concentrations, as well as the fine-scale physical and chemical heterogeneity of the sediments. The spectroscopy data are analyzed using novel cosine-distance and correlation-distance hierarchical clustering for Fe 1s and As 1s lXAS datasets. The solid-phase Fe and As speciation is then interpreted using sediment and well-water chemical data to propose solid-phase As reservoirs and release mechanisms. The results confirm that in two of the three locations studied, the glacial sediment forming the aquitard is the source of As to the aquifer sediments. The results are consistent with three different As release mechanisms: (1) desorption from Fe (oxyhydr)oxides, (2) reductive dissolution of Fe (oxyhydr)oxides, and (3) oxidative dissolution of Fe sulfides. The findings confirm that glacial sediments at the interface between aquifer and aquitard are geochemically active zones for As. The diversity of As release mechanisms is consistent with the geographic heterogeneity observed in the distribution of elevated-As wells.

Numerical Modeling of Reactive Multiphase Flow for FCC and Hot Gas Desulfurization Circulating Fluidized Beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Aubrey L.

2005-07-01

This work was carried out to understand the behavior of the solid and gas phases in a CFB riser. Only the riser is modeled as a straight pipe. A model with linear algebraic approximation to solids viscosity of the form, {musubs} = 5.34{epsisubs}, ({espisubs} is the solids volume fraction) with an appropriate boundary condition at the wall obtained by approximate momentum balance solution at the wall to acount for the solids recirculation is tested against experimental results. The work done was to predict the flow patterns in the CFB risers from available experimental data, including data from a 7.5-cm-ID CFBmore » riser at the Illinois Institute of Technology and data from a 20.0-cm-ID CFB riser at the Particulate Solid Research, Inc., facility. This research aims at modeling the removal of hydrogen sulfide from hot coal gas using zinc oxide as the sorbent in a circulating fluidized bed and in the process indentifying the parameters that affect the performance of the sulfidation reactor. Two different gas-solid reaction models, the unreacted shrinking core (USC) and the grain model were applied to take into account chemical reaction resistances. Also two different approaches were used to affect the hydrodynamics of the process streams. The first model takes into account the effect of micro-scale particle clustering by adjusting the gas-particle drag law and the second one assumes a turbulent core with pseudo-steady state boundary condition at the wall. A comparison is made with experimental results.« less

Hybrid De Novo Genome Assembly Using MiSeq and SOLiD Short Read Data

PubMed Central

Ikegami, Tsutomu; Inatsugi, Toyohiro; Kojima, Isao; Umemura, Myco; Hagiwara, Hiroko; Machida, Masayuki; Asai, Kiyoshi

2015-01-01

A hybrid de novo assembly pipeline was constructed to utilize both MiSeq and SOLiD short read data in combination in the assembly. The short read data were converted to a standard format of the pipeline, and were supplied to the pipeline components such as ABySS and SOAPdenovo. The assembly pipeline proceeded through several stages, and either MiSeq paired-end data, SOLiD mate-paired data, or both of them could be specified as input data at each stage separately. The pipeline was examined on the filamentous fungus Aspergillus oryzae RIB40, by aligning the assembly results against the reference sequences. Using both the MiSeq and the SOLiD data in the hybrid assembly, the alignment length was improved by a factor of 3 to 8, compared with the assemblies using either one of the data types. The number of the reproduced gene cluster regions encoding secondary metabolite biosyntheses (SMB) was also improved by the hybrid assemblies. These results imply that the MiSeq data with long read length are essential to construct accurate nucleotide sequences, while the SOLiD mate-paired reads with long insertion length enhance long-range arrangements of the sequences. The pipeline was also tested on the actinomycete Streptomyces avermitilis MA-4680, whose gene is known to have high-GC content. Although the quality of the SOLiD reads was too low to perform any meaningful assemblies by themselves, the alignment length to the reference was improved by a factor of 2, compared with the assembly using only the MiSeq data. PMID:25919614

Anomaly Detection for Data Reduction in an Unattended Ground Sensor (UGS) Field

DTIC Science & Technology

2014-09-01

information (shown with solid lines in the diagram). Typically, this would be a mobile ad - hoc network (MANET). The clusters are connected to other nodes...interquartile ranges MANET mobile ad - hoc network OSUS Open Standards for Unattended Sensors TOC tactical operations center UAVs unmanned aerial vehicles...19b. TELEPHONE NUMBER (Include area code ) 301-394-1221 Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 iii Contents List of

General, Unified, Multiscale Modeling to Predict the Sensitivity of Energetic Materials

DTIC Science & Technology

2011-10-05

Time dependence of molecular carbon cluster size in solid methane shocked with a piston velocity up =11 km /s. The initial temperature and density were...Galilean in- variant in configuration space, but the kinetic energy of the system depends on the scalar product of the total momentum with U. To... dependent superheating of the x-component shock direction of kinetic energy . This 224513-4 Dawes et al. J. Chem. Phys. 131, 224513 2009 Author

DFT study of benzyl alcohol/TiO2 interfacial surface complex: reaction pathway and mechanism of visible light absorption.

PubMed

Zhao, Lei; Gu, Feng Long; Kim, Minjae; Miao, Maosheng; Zhang, Rui-Qin

2017-09-24

We propose a new pathway for the adsorption of benzyl alcohol on the surface of TiO 2 and the formation of interfacial surface complex (ISC). The reaction free energies and reaction kinetics were thoroughly investigated by density functional calculations. The TiO 2 surfaces were modeled by clusters consisting of 4 Ti atoms and 18 O atoms passivated by H, OH group and H 2 O molecules. Compared with solid-state calculations utilizing the periodicity of the materials, such cluster modeling allows inclusion of the high-order correlation effects that seem to be essential for the adsorption of organic molecules onto solid surfaces. The effects of both acidity and solvation are included in our calculations, which demonstrate that the new pathway is competitive with a previous pathway. The electronic structure calculations based on the relaxed ISC structures reveal that the chemisorption of benzyl alcohol on the TiO 2 surface greatly alters the nature of the frontier molecular orbitals. The resulted reduced energy gap in ISC matches the energy of visible light, showing how the adsorption of benzyl alcohol sensitizes the TiO 2 surface. Graphical Abstract The chemisorption of benzyl alcohol on TiO 2 surface greatly alters the nature of the frontier molecular orbitals and the formed interfacial surface complex can be sensitized by visible light.

The effect of coumaryl alcohol incorporation on the structure and composition of lignin dehydrogenation polymers.

PubMed

Harman-Ware, Anne E; Happs, Renee M; Davison, Brian H; Davis, Mark F

2017-01-01

Lignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processes. Here, DHPs were synthesized using a Zutropfverfahren method with horseradish peroxidase and three lignin monomers, sinapyl (S), coumaryl (H), and coniferyl (G) alcohols, in the presence of hydrogen peroxide. The H monomer was reacted with G and a 1:1 molar mixture of S:G monomers at H molar compositions of 0, 5, 10, and 20 mol% to study how the presence of the H monomer affected the structure and composition of the recovered polymers. At low H concentrations, solid-state NMR spectra suggest that the H and G monomers interact to form G:H polymers that have a lower average molecular weight than the solely G-based polymer or the G:H polymer produced at higher H concentrations. Solid-state NMR and pyrolysis-MBMS analyses suggest that at higher H concentrations, the H monomer primarily self-polymerizes to produce clusters of H-based polymer that are segregated from clusters of G- or S:G-based polymers. Thioacidolysis generally showed higher recoveries of thioethylated products from S:G or S:G:H polymers made with higher H content, indicating an increase in the linear ether linkages. Overall, the experimental results support theoretical predictions for the reactivity and structural influences of the H monomer on the formation of lignin-like polymers.

Theoretical and experimental insights into the origin of the catalytic activity of subnanometric gold clusters: attempts to predict reactivity with clusters and nanoparticles of gold.

PubMed

Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino

2014-03-18

Particle size is one of the key parameters determining the unexpected catalytic activity of gold, with reactivity improving as the particle gets smaller. While this is valid in the 1-5 nm range, chemists are now investigating the influence of particle size in the subnanometer regime. This is due to recent advances in both characterization techniques and synthetic routes capable of stabilizing these size-controlled gold clusters. Researchers reported in early studies that small clusters or aggregates of a few atoms can be extremely active in some reactions, while 1-2 nm nanoparticles are catalytically more efficient for other reactions. Furthermore, the possibility that small gold clusters generated in situ from gold salts or complexes could be the real active species in homogeneous gold-catalyzed organic reactions should be considered. In this Account, we address two questions. First, what is the origin of the enhanced reactivity of gold clusters on the subnanometer scale? And second, how can we predict the reactions where small clusters should work better than larger nanoparticles? Both geometric factors and electronic or quantum size effects become important in the subnanometer regime. Geometric reasons play a key role in hydrogenation reactions, where only accessible low coordinated neutral Au atoms are needed to dissociate H2. The quantum size effects of gold clusters are important as well, as clusters formed by only a few atoms have discrete molecule-like electronic states and their chemical reactivity is related to interactions between the cluster's frontier molecular orbitals and those of the reactant molecules. From first principles calculations, we predict an enhanced reactivity of small planar clusters for reactions involving activation of CC multiple bonds in alkenes and alkynes through Lewis acid-base interactions, and a better catalytic performance of 3D gold nanoparticles in redox reactions involving bond dissociation by oxidative addition and new bond formation by reductive elimination. In oxidation reactions with molecular O2, initial dissociation of O2 into basic oxygen atoms would be more effectively catalyzed by gold nanoparticles of ∼1 nm diameter. In contrast, small planar clusters should be more active for reactions following a radical pathway involving peroxo or hydroperoxo intermediates. We have experimentally confirmed these predictions for a series of Lewis acid and oxidation reactions catalyzed by gold clusters and nanoparticles either in solution or supported on solid carriers.

Quantitative atomic-scale structure characterization of ordered mesoporous carbon materials by solid state NMR

DOE PAGES

Wang, Zhuoran; Opembe, Naftali; Kobayashi, Takeshi; ...

2018-02-03

In this study, solid-state (SS)NMR techniques were applied to characterize the atomic-scale structures of ordered mesoporous carbon (OMC) materials prepared using Pluronic F127 as template with resorcinol and formaldehyde as polymerizing precursors. A rigorous quantitative analysis was developed using a combination of 13C SSNMR spectra acquired with direct polarization and cross polarization on natural abundant and selectively 13C-enriched series of samples pyrolyzed at various temperatures. These experiments identified and counted the key functional groups present in the OMCs at various stages of preparation and thermal treatment. Lastly, the chemical evolution of molecular networks, the average sizes of aromatic clusters andmore » the extended molecular structures of OMCs were then inferred by coupling this information with the elemental analysis results.« less

Quantitative atomic-scale structure characterization of ordered mesoporous carbon materials by solid state NMR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhuoran; Opembe, Naftali; Kobayashi, Takeshi

In this study, solid-state (SS)NMR techniques were applied to characterize the atomic-scale structures of ordered mesoporous carbon (OMC) materials prepared using Pluronic F127 as template with resorcinol and formaldehyde as polymerizing precursors. A rigorous quantitative analysis was developed using a combination of 13C SSNMR spectra acquired with direct polarization and cross polarization on natural abundant and selectively 13C-enriched series of samples pyrolyzed at various temperatures. These experiments identified and counted the key functional groups present in the OMCs at various stages of preparation and thermal treatment. Lastly, the chemical evolution of molecular networks, the average sizes of aromatic clusters andmore » the extended molecular structures of OMCs were then inferred by coupling this information with the elemental analysis results.« less

Low energy stage study. Volume 1: Executive summary. [propulsion system configurations for orbital launching of space shuttle payloads

NASA Technical Reports Server (NTRS)

1978-01-01

Cost effective approaches for placing automated payloads into circular and elliptical orbits using energy requirements significantly lower than that provided by the smallest, currently planned shuttle upper stage, SSUS-D, were investigated. Launch costs were derived using both NASA existing/planned launch approaches as well as new propulsion concepts meeting low-energy regime requirements. Candidate new propulsion approaches considered were solid (tandem, cluster, and controlled), solid/liquid combinations and all-liquid stages. Results show that the most economical way to deliver the 129 low energy payloads is basically with a new modular, short liquid bipropellant stage system for the large majority of the payloads. For the remainder of the payloads, use the shuttle with integral OMS and the Scout form for a few specialized payloads until the Shuttle becomes operational.

Transient lattice contraction in the solid-to-plasma transition

PubMed Central

Ferguson, Ken R.; Bucher, Maximilian; Gorkhover, Tais; Boutet, Sébastien; Fukuzawa, Hironobu; Koglin, Jason E.; Kumagai, Yoshiaki; Lutman, Alberto; Marinelli, Agostino; Messerschmidt, Marc; Nagaya, Kiyonobu; Turner, Jim; Ueda, Kiyoshi; Williams, Garth J.; Bucksbaum, Philip H.; Bostedt, Christoph

2016-01-01

In condensed matter systems, strong optical excitations can induce phonon-driven processes that alter their mechanical properties. We report on a new phenomenon where a massive electronic excitation induces a collective change in the bond character that leads to transient lattice contraction. Single large van der Waals clusters were isochorically heated to a nanoplasma state with an intense 10-fs x-ray (pump) pulse. The structural evolution of the nanoplasma was probed with a second intense x-ray (probe) pulse, showing systematic contraction stemming from electron delocalization during the solid-to-plasma transition. These findings are relevant for any material in extreme conditions ranging from the time evolution of warm or hot dense matter to ultrafast imaging with intense x-ray pulses or, more generally, any situation that involves a condensed matter-to-plasma transition. PMID:27152323

Photon emission from massive projectile impacts on solids.

PubMed

Fernandez-Lima, F A; Pinnick, V T; Della-Negra, S; Schweikert, E A

2011-01-01

First evidence of photon emission from individual impacts of massive gold projectiles on solids for a number of projectile-target combinations is reported. Photon emission from individual impacts of massive Au(n) (+q) (1 ≤ n ≤ 400; q = 1-4) projectiles with impact energies in the range of 28-136 keV occurs in less than 10 ns after the projectile impact. Experimental observations show an increase in the photon yield from individual impacts with the projectile size and velocity. Concurrently with the photon emission, electron emission from the impact area has been observed below the kinetic emission threshold and under unlikely conditions for potential electron emission. We interpret the puzzling electron emission and correlated luminescence observation as evidence of the electronic excitation resulting from the high-energy density deposited by massive cluster projectiles during the impact.

Photon emission from massive projectile impacts on solids

PubMed Central

Fernandez-Lima, F. A.; Pinnick, V. T.; Della-Negra, S.; Schweikert, E. A.

2011-01-01

First evidence of photon emission from individual impacts of massive gold projectiles on solids for a number of projectile-target combinations is reported. Photon emission from individual impacts of massive Aun+q (1 ≤ n ≤ 400; q = 1–4) projectiles with impact energies in the range of 28–136 keV occurs in less than 10 ns after the projectile impact. Experimental observations show an increase in the photon yield from individual impacts with the projectile size and velocity. Concurrently with the photon emission, electron emission from the impact area has been observed below the kinetic emission threshold and under unlikely conditions for potential electron emission. We interpret the puzzling electron emission and correlated luminescence observation as evidence of the electronic excitation resulting from the high-energy density deposited by massive cluster projectiles during the impact. PMID:21603128

Solid oxide fuel cell anode image segmentation based on a novel quantum-inspired fuzzy clustering

NASA Astrophysics Data System (ADS)

Fu, Xiaowei; Xiang, Yuhan; Chen, Li; Xu, Xin; Li, Xi

2015-12-01

High quality microstructure modeling can optimize the design of fuel cells. For three-phase accurate identification of Solid Oxide Fuel Cell (SOFC) microstructure, this paper proposes a novel image segmentation method on YSZ/Ni anode Optical Microscopic (OM) images. According to Quantum Signal Processing (QSP), the proposed approach exploits a quantum-inspired adaptive fuzziness factor to adaptively estimate the energy function in the fuzzy system based on Markov Random Filed (MRF). Before defuzzification, a quantum-inspired probability distribution based on distance and gray correction is proposed, which can adaptively adjust the inaccurate probability estimation of uncertain points caused by noises and edge points. In this study, the proposed method improves accuracy and effectiveness of three-phase identification on the micro-investigation. It provides firm foundation to investigate the microstructural evolution and its related properties.

Inert-Gas Condensed Co-W Nanoclusters: Formation, Structure and Magnetic Properties

NASA Astrophysics Data System (ADS)

Golkar-Fard, Farhad Reza

Rare-earth permanent magnets are used extensively in numerous technical applications, e.g. wind turbines, audio speakers, and hybrid/electric vehicles. The demand and production of rare-earth permanent magnets in the world has in the past decades increased significantly. However, the decrease in export of rare-earth elements from China in recent time has led to a renewed interest in developing rare-earth free permanent magnets. Elements such as Fe and Co have potential, due to their high magnetization, to be used as hosts in rare-earth free permanent magnets but a major challenge is to increase their magnetocrystalline anisotropy constant, K1, which largely drives the coercivity. Theoretical calculations indicate that dissolving the 5d transition metal W in Fe or Co increases the magnetocrystalline anisotropy. The challenge, though, is in creating a solid solution in hcp Co or bcc Fe, which under equilibrium conditions have negligible solubility. In this dissertation, the formation, structure, and magnetic properties of sub-10 nm Co-W clusters with W content ranging from 4 to 24 atomic percent were studied. Co-W alloy clusters with extended solubility of W in hcp Co were produced by inert gas condensation. The different processing conditions such as the cooling scheme and sputtering power were found to control the structural state of the as-deposited Co-W clusters. For clusters formed in the water-cooled formation chamber, the mean size and the fraction crystalline clusters increased with increasing power, while the fraction of crystalline clusters formed in the liquid nitrogen-cooled formation chamber was not as affected by the sputtering power. For the low W content clusters, the structural characterization revealed clusters predominantly single crystalline hcp Co(W) structure, a significant extension of W solubility when compared to the equilibrium solubility, but fcc Co(W) and Co3W structures were observed in very small and large clusters, respectively. At high W content, clusters with hcp Co(W), fcc Co(W) or Co3W structures were observed. The magnetic measurements at 10 K and 300 K revealed that the coercivity, saturation magnetization and magnetocrystalline anisotropy of the clusters formed in the water-cooled formation chamber were higher than for clusters formed in the liquid nitrogen-cooled formation chamber. The coercivity and magnetocrystalline anisotropy of the clusters increased as long as W was dissolved into the hcp Co structure. With increasing fraction of Co3W and fcc Co(W) clusters, as observed in the high-W content sample, the magnetic properties deteriorated significantly. The highest coercivity and magnetocrystalline anisotropy of 893 Oe and 3.9 x 106 ergs/cm3, respectively, was obtained at 10 K for the 5 at.% W clusters sputtered at 150 W in the water-cooled formation chamber.

The Inorganic Illustrator: A 3-D Graphical Supplement for Inorganic and Bioinorganic Chemistry Courses Distributed on CD-ROM

NASA Astrophysics Data System (ADS)

Childs, Scott L.; Hagen, Karl S.

1996-10-01

The visualization of molecular and solid state chemical structures in three dimensions is a particularly difficult problem for students to overcome when the primary means of communication is the two-dimensional world of textbooks, blackboards, and overhead projector screens. Recent editions of popular textbooks in organic, inorganic, and biochemistry have included stereoviews of molecules to aid the student, and stereoviews of crystal structures have been used in inorganic chemistry publications for many years. These are powerful aids for visualizing complex molecules, but with the exception of the biochemistry text mentioned above, they are limited to single, static images generally in black and white. Molecular model kits are routinely used very effectively in organic chemistry but their utility in inorganic chemistry is limited to all but the most simple molecules encountered. Now that personal computers are generally accessible and multimedia tools are starting to make an appearance in chemistry lecture halls (1), we can make our inorganic and bioinorganic chemistry and crystallography lectures come alive with the aid of the computer-based resources, which are the essence of this project. As part of this project we are accumulating a database of representative crystal structures of main group molecules, coordination complexes, organometallic compounds, small metalloproteins, bioinorganic model complexes, clusters, and solid state materials in Chem3D Plus format to be viewed with Chem3D Viewer, which is free software from Cambridge Scientific Computing. We are also generating a library of high-quality graphic images of these same molecules and structures using Cerius2 package from Molecular Simulations. These include polyhedral representations of clusters and solid state structures (see Fig. 1). Figure 1. Representation of the user interface: the title page and an example of polyhedral and ball-and-stick representation of an octanuclear iron-oxo cluster. The files of solid state structures will not be limited to single unit cells that are common in textbooks, but will present multiple cells such that the extended lattice of the material is evident. Navigation through these resources is through a unique open hypertext-based interface using Authorware, which allows the user to create complex applications that support movies, animation, and other graphics seamlessly. Chem3D Viewer is a powerful program that allows not only multiple visualization modes, but also the detailed analysis of both bonded and nonbonded distances and angles. This is particularly useful for recognizing symmetry elements within molecules, as the student can precisely align atoms along the screen's Cartesian axes or within its planes and subsequently rotate the molecules about the axes at precise angles. We are developing stand-alone interactive tutorials to assign point groups to molecules and clusters. In addition, tutorials are being developed that show how the Chem3D Viewer software can be most effectively used in a classroom setting for lectures or for home or lab use by the students. The Inorganic Illustrator will be made available to the education community for the cost of materials plus shipping and handling. Acknowledgment We would like to thank the NSF for financial support through the Division of Undergraduate Education Course and Curriculum Program (DUE-CCD 9455567). Literature Cited 1. Illman, D. L. Chem. Eng. News 1994, 72(May 9), 34.

In-line solid state prediction during pharmaceutical hot-melt extrusion in a 12 mm twin screw extruder using Raman spectroscopy.

PubMed

Saerens, Lien; Ghanam, Dima; Raemdonck, Cedric; Francois, Kjell; Manz, Jürgen; Krüger, Rainer; Krüger, Susan; Vervaet, Chris; Remon, Jean Paul; De Beer, Thomas

2014-08-01

The aim of this research was to use Raman spectroscopy for the in-line monitoring of the solid state of materials during pharmaceutical hot-melt extrusion in the die head of a 12 mm (development scale) twin-screw extruder during formulation development. A full factorial (mixed) design was generated to determine the influence of variations in concentration of Celecoxib (CEL) in Eudragit® E PO, three different screw configurations and varying barrel temperature profiles on the solid state, 'melt temperature' and die pressure of continuously produced extrudates in real-time. Off-line XRD and DSC analysis were used to evaluate the suitability of Raman spectroscopy for solid state predictions. First, principal component analysis (PCA) was performed on all in-line collected Raman spectra from the experimental design. The resulting PC 1 versus PC 2 scores plot showed clustering according to solid state of the extrudates, and two classes, one class where crystalline CEL is still present and a second class where no crystalline CEL was detected, were found. Then, a soft independent modelling of class analogy (SIMCA) model was developed, by modelling these two classes separately by disjoint PCA models. These two separate PCA models were then used for the classification of new produced extrudates and allowed distinction between glassy solid solutions of CEL and crystalline dispersions of CEL. All extrudates were classified similarly by Raman spectroscopy, XRD and DSC measurements, with exception of the extrudates with a 30% CEL concentration extruded at 130 °C. The Raman spectra of these experiments showed bands which were sharper than the amorphous spectra, but broader than the crystalline spectra, indicating the presence of CEL that has dissolved into the matrix and CEL in its crystalline state. XRD and DSC measurements did not detect this. Modifications in the screw configuration did not affect the solid state and did not have an effect on the solid state prediction of new produced extrudates. Secondly, the influence of variations in die pressure on the Raman spectra was examined. The applied drug concentration, processing temperature and feeder performance influence the die pressure, which is reflected in the Raman spectra as a change in spectral intensity. When applying PCA on the raw spectra from the experimental design, the first principal component describes the influence of die pressure on the spectra, which was seen as a decrease in Raman intensity of the whole spectrum when the pressure in the sample increased. Clustering according to processing temperature was found, although the temperature in the die remained constant, indicating that a difference in viscosity, resulting in a changed die pressure, was detected. When the feeder was stopped, the score values of the first principal component almost simultaneously decreased, and only stabilized once the die pressure became stable. Since Raman spectra collected in the extrusion die are influenced by changes in die pressure, disturbances upstream of the extrusion process can be observed and identified in the Raman measurements. Copyright © 2014 Elsevier B.V. All rights reserved.

Formation of solid Kr nanoclusters in MgO

NASA Astrophysics Data System (ADS)

van Huis, M. A.; van Veen, A.; Schut, H.; Kooi, B. J.; de Hosson, J. Th.

2003-06-01

The phenomenon of positron confinement enables us to investigate the electronic structure of nanoclusters embedded in host matrices. Solid Kr nanoclusters are a very interesting subject of investigation because of the very low predicted value of the positron affinity of bulk Kr. In this work, positron trapping in solid Kr nanoclusters embedded in MgO is investigated. The Kr nanoclusters were created by means of 280 keV Kr ion implantation in single crystals of MgO(100) and subsequent thermal annealing at a temperature of 1100 K. The nanoclusters were observed by cross-sectional transmission electron microscopy in high-resolution mode. The fcc Kr nanoclusters are rectangularly shaped with sizes of 2 to 5 nm and are in a cube-on-cube orientation relationship with the MgO host matrix. From the Moiré fringes in high-resolution recordings, the lattice parameter of the solid Kr was deduced and found to vary from 5.3 to 5.8 Å. The corresponding pressures are 0.6 2.5 GPa as found using the Ronchi equation of state. The relationship between lattice parameter and cluster size was investigated and it was found that the lattice parameter increases linearly with increasing nanocluster size. The defect evolution during annealing was monitored by means optical absorption spectroscopy and positron beam analysis. No evidence of positron trapping was found despite the very low positron affinity of solid Kr. Alternative definitions of the positron affinity are proposed for application to insulator materials.

Properties of solid solutions, doped film, and nanocomposite structures based on zinc oxide

NASA Astrophysics Data System (ADS)

Lashkarev, G. V.; Shtepliuk, I. I.; Ievtushenko, A. I.; Khyzhun, O. Y.; Kartuzov, V. V.; Ovsiannikova, L. I.; Karpyna, V. A.; Myroniuk, D. V.; Khomyak, V. V.; Tkach, V. N.; Timofeeva, I. I.; Popovich, V. I.; Dranchuk, N. V.; Khranovskyy, V. D.; Demydiuk, P. V.

2015-02-01

A study of the properties of materials based on the wide bandgap zinc oxide semiconductor, which are promising for application in optoelectronics, photovoltaics and nanoplasmonics. The structural and optical properties of solid solution Zn1-xCdxO films with different cadmium content, are studied. The samples are grown using magnetron sputtering on sapphire backing. Low-temperature photoluminescence spectra revealed emission peaks associated with radiative recombination processes in those areas of the film that have varying amounts of cadmium. X-ray phase analysis showed the presence of a cadmium oxide cubic phase in these films. Theoretical studies of the solid solution thermodynamic properties allowed for a qualitative interpretation of the observed experimental phenomena. It is established that the growth of the homogeneous solid solution film is possible only at high temperatures, whereas regions of inhomogeneous composition can be narrowed through elastic deformation, caused by the mismatch of the film-backing lattice constants. The driving forces of the spinodal decomposition of the Zn1-xCdxO system are identified. Fullerene-like clusters of Znn-xCdxOn are used to calculate the bandgap and the cohesive energy of ZnCdO solid solutions. The properties of transparent conductive ZnO films, doped with Group III donor impurities (Al, Ga, In), are examined. It is shown that oxygen vacancies are responsible for the hole trap centers in the zinc oxide photoconductivity process. We also examine the photoluminescence properties of metal-ZnO nanocomposite structures, caused by surface plasmons.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marlow, W.H.

An aerosol here is understood to be a two-component system comprised of gaseous and condensed phases with the characteristic that the condensed phase is not an equilibrium subsystem. In contrast to the usual definitions based upon geometrical or mechanical variables, this quasi-thermodynamic formulation is framed to emphasize the dynamical behavior of aerosols by allowing for coagulation and other aerosol evolutionary processes as natural consequences of the interactions and state variables appropriate to the system. As will become clear later, it also provides a point of departure for distinguishing aerosol particles from unstable gas-phase cluster systems. The question of accommodation inmore » particle collisions must be addressed as a prelude to the discussion of the role of long-range forces. Microscopic reversibility is frequently assumed for molecular collisions with either molecules or solid surfaces. In the case of aerosol collisions, the implication of this assumption is that collisions are elastic, which is contrary to the evidence from coagulation experiments and the conventional operational assumption of sticking upon collision. Gay and Berne have performed computer simulations of the collision of two clusters consisting of a total of 135 molecules interacting via Lennard-Jones potentials. That work showed that complete accommodation, accompanied by overall heating of the unified cluster, occurred. Since heating represents an irreversible degradation of the kinetic energy of the collision, the hamiltonian of the two-cluster system should be considered as dissipative and therefore microscopic reversibility does not apply.« less

Communities of ammonia-oxidizing bacteria in activated sludge of various sewage treatment plants in Tokyo.

PubMed

Limpiyakorn, Tawan; Shinohara, Yuko; Kurisu, Futoshi; Yagi, Osami

2005-10-01

We investigated ammonia-oxidizing bacteria in activated sludge collected from 12 sewage treatment systems, whose ammonia removal and treatment processes differed, during three different seasons. We used real-time PCR quantification to reveal total bacterial numbers and total ammonia oxidizer numbers, and used specific PCR followed by denaturing gel gradient electrophoresis, cloning, and sequencing of 16S rRNA genes to analyze ammonia-oxidizing bacterial communities. Total bacterial numbers and total ammonia oxidizer numbers were in the range of 1.6 x 10(12) - 2.4 x 10(13) and 1.0 x 10(9) - 9.2 x 10(10)cellsl(-1), respectively. Seasonal variation was observed in the total ammonia oxidizer numbers, but not in the ammonia-oxidizing bacterial communities. Members of the Nitrosomonas oligotropha cluster were found in all samples, and most sequences within this cluster grouped within two of the four sequence types identified. Members of the clusters of Nitrosomonas europaea-Nitrosococcus mobilis, Nitrosomonas cryotolerans, and unknown Nitrosomonas, occurred solely in one anaerobic/anoxic/aerobic (A2O) system. Members of the Nitrosomonas communis cluster occurred almost exclusively in association with A2O and anaerobic/aerobic systems. Solid residence time mainly influenced the total numbers of ammonia-oxidizing bacteria, whereas dissolved oxygen concentration primarily affected the ammonia-oxidizing activity per ammonia oxidizer cell.

Insights into the Li Intercalation and SEI Formation on LiSi Nanoclusters

DOE PAGES

Hankins, Kie; Soto, Fernando A.; Balbuena, Perla B.

2017-01-01

We report a first-principles atomic level assessment of the lithiation and reactivity of pre-lithiated Si clusters. Density functional theory formation energy calculations reveal that the pre-lithiated Li 16Si 16 cluster exposed to two different Li fluxes can store Li between the concentrations of Li 2.5Si and Li 3.5Si. This increase in storage capacity is attributed to the start of an amorphization process in the cluster, and more importantly these results show that the intercalation reaction can be controlled by the flux of the Li-ions. However, in a real battery, the lithiation of the anode occurs simultaneously to the electrode-electrolyte reactions.more » Here we simulate the solid-electrolyte interphase (SEI) formation and simultaneous lithiation of a Li 16Si 16 cluster in contact with two different electrolyte solutions: one with pure ethylene carbonate (EC), and another with a 1 M solution of LiPF 6 in EC. Our ab initio molecular dynamics simulations show that the solvent and salt are decomposed leading to the initial stages of the SEI layer formation and large part of the added Li becomes part of the SEI. Interestingly, the pure EC solution results in lower storage capacity and higher reactivity, whereas the presence of the salt causes the opposite effect: higher lithiation and reduced reactivity.« less

Discrete Element Model for Suppression of Coffee-Ring Effect

NASA Astrophysics Data System (ADS)

Xu, Ting; Lam, Miu Ling; Chen, Ting-Hsuan

2017-02-01

When a sessile droplet evaporates, coffee-ring effect drives the suspended particulate matters to the droplet edge, eventually forming a ring-shaped deposition. Because it causes a non-uniform distribution of solid contents, which is undesired in many applications, attempts have been made to eliminate the coffee-ring effect. Recent reports indicated that the coffee-ring effect can be suppressed by a mixture of spherical and non-spherical particles with enhanced particle-particle interaction at air-water interface. However, a model to comprehend the inter-particulate activities has been lacking. Here, we report a discrete element model (particle system) to investigate the phenomenon. The modeled dynamics included particle traveling following the capillary flow with Brownian motion, and its resultant 3D hexagonal close packing of particles along the contact line. For particles being adsorbed by air-water interface, we modeled cluster growth, cluster deformation, and cluster combination. We found that the suppression of coffee-ring effect does not require a circulatory flow driven by an inward Marangoni flow at air-water interface. Instead, the number of new cluster formation, which can be enhanced by increasing the ratio of non-spherical particles and the overall number of microspheres, is more dominant in the suppression process. Together, this model provides a useful platform elucidating insights for suppressing coffee-ring effect for practical applications in the future.

Ensemble averaged structure–function relationship for nanocrystals: effective superparamagnetic Fe clusters with catalytically active Pt skin [Ensemble averaged structure-function relationship for composite nanocrystals: magnetic bcc Fe clusters with catalytically active fcc Pt skin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petkov, Valeri; Prasai, Binay; Shastri, Sarvjit

Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure–function relationship for metallic NCs is to be quantified precisely. In this paper, we address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction,more » respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Lastly, we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure–function relationship for the increasingly complex metallic NCs explored for practical applications.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellis, D.E.; Gubanov, V.A.; Rosen, A.

The electronic structure of actinide monoxides AcO and dioxides AcO/sub 2/, where Ac = Th, U, Np, Pu, Am, Cm and Bk has been studied by molecular cluster methods based on the first-principles one-electron local density theory. Molecular orbitals for nearest neighbor clusters AcO/sup 10 -//sub 6/ and AcO/sup 12 -//sub 8/ representative of monoxide and dioxide lattices were obtained using non-relativistic spin-restricted and spin-polarized Hartree-Fock-Slater models for the entire series. Fully relativistic Dirac-Slater calculations were performed for ThO, UO and NpO in order to explore magnitude of spin-orbit splittings and level shifts in valence structure. Self-consistent iterations were carriedmore » out for NpO, in which the NpO/sub 6/ cluster was embedded in the molecular field of the solid. Finally, a ''moment polarized'' model which combines both spin-polarization and relativistic effects in a consistent fashion was applied to the NpO system. Covalent mixing of oxygen 2p and Ac 5f orbitals was found to increase rapidly across the actinide series; metal s,p,d covalency was found to be nearly constant. Mulliken atomic population analysis of cluster eigenvectors shows that free-ion crystal field models are unreliable, except for the light actinides. X-ray photoelectron line shapes have been calculated and are found to compare rather well with experimental data on the dioxides.« less

Clusters and holes: Exchange networks in hematite-ilmenite solid solutions

NASA Astrophysics Data System (ADS)

Fabian, K.; McEnroe, S. A.; Robinson, P.

2009-04-01

Holes and clusters of exchange networks dominate the low-temperature, metastable phase diagram of the system (1 - x)Fe2O3 xF eTiO3 (Ilmx ). By our measurements we have probed and extended the phase diagram of Ishikawa et al. (1985) in the light of magnetic influences of the random exchange links, which originate either by replacing random pairs of Fe2+ and Ti4+ ions in the ordered ilmenite lattice by two Fe3+ions (ordered Ilmx phase), or by randomly replacing two Fe3+ ions in the hematite lattice by a pair of Fe2+ and Ti4+ ions (disordered Ilmx phase). Now a large dataset is available from these measurements, and we propose several new ideas to interpret the sometimes unexpected results. By refining a method of Ishikawa (1967), we analyze the PM' region of the phase diagram in terms of a mean field theory of interacting clusters. This allows to determine cluster sizes and interaction field distribution by inverting hysteresis measurements of Ilm92 and Ilm97. To understand the relation between ordered and disordered phases we design a mean field theory to determine Neel and Curie temperatures of both. An especially interesting finding is that the experimentally observed intersection of PM-PM' crossover with the AF phase boundary close to Ilm97 can be explained by analyzing average exchange interaction strengths.

Transient enhancement and spectral narrowing of the photothermal effect of plasmonic nanoparticles under pulsed excitation.

PubMed

Lukianova-Hleb, Ekaterina Y; Volkov, Alexey N; Wu, Xiangwei; Lapotko, Dmitri O

2013-02-06

The transient 100-fold enhancement and spectral narrowing to 2 nm of the photothermal conversion by solid gold nanospheres under near-infrared excitation with a short laser pulse is reported. This non-stationary effect was observed for a wide range of optical fluences starting from 10 mJ cm(-2) for single nanospheres, their ensembles and aggregated clusters in water, in vitro and in vivo. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Monoclonal antibodies as cancer therapeutics.

PubMed

Elloumi, Jihene; Jellali, Karim; Jemel, Ikram; Aifa, Sami

2012-04-01

Three main targets were subjected for the most approved monoclonal antibodies (mAbs) in cancer therapy: EGFR in solid cancer, the clusters of differentiation in blood cancer and VEGF in angiogenesis. Meanwhile side effects, the elevated costs and resistance problems are limiting the efficiency of mAbs as targeted therapy. The combinatory therapy with chemo or radiotherapy has improved the efficiency of mAbs. The present review aims to shed more light on the immunotherapy and the related patents that were developed for cancer treatment.

Installation Restoration Program (IRP). Phase 2. Confirmation/Quantification. Stage 1. McEntire Air National Guard Base, Eastover, South Carolina.

DTIC Science & Technology

1986-06-10

Environmental Research Group (ERG) Laboratories of Ann Arbor, Michigan, and a duplicate set sent to OEHL’s laboratory in San Antonio, Texas. The remainder of...sites and well clusters , and the overall sparsity of data points at the base, a water table aquifer potentiometric surface map for the entire base could...L _ MW2-34 The predominant solid wastes disposed at this site were paper and domestic refuse, old wood from demolished structures, general

First International Conference on Organic Nonlinear Optics. Section B: Nonlinear Optics, Principles, Materials, Phenomena, and Devices.

DTIC Science & Technology

1994-01-01

kET/T1T 2 ) (solid lines). clusters of guest molecules with local concentrations exceeding the average value of about 1 pentacene /(50 ,A) in the highest...that the transport topology of singlet excitation energy is determined by the local distribu- tions of pentacene guests in the crystal. A singlet...Pullman, USA S. Miyata (co-chair), Tokyo University of Technology and Agriculture, Tokyo, Japan Local Organizing Committee F. Charra (secretary) P.-A

Tunable Magnetic Exchange Interactions in Manganese-Doped Inverted Core-Shell ZnSe-CdSe Nanocrystals

DTIC Science & Technology

2009-01-01

exchange coupling even for a singlemagnetic dopant atom12,17. Whereas magnetically doped monocomponent nanocrystals are well established16, wavefunction...Solid State Commun. 114, 547–550 (2000). 13. Radovanovic, P. V. & Gamelin, D. R. Electronic absorption spectroscopy of cobalt ions in diluted magnetic...D. R. Inorganic cluster syntheses of TM2+-doped quantum dots (CdSe, CdS, CdSe/CdS): Physical property dependence on dopant locale. J. Am. Chem. Soc

Early stages of the oxidation of metal surfaces. [photoelectron spectroscopy of zinc oxide

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Johnson, K. H.

1978-01-01

Photoemission cross sections were calculated for the ZnO4(-6) cluster using the self consistent-chi alpha- scattered wave theory to display the main features of the ultraviolet and X-ray photoemission data from ZnO. A solid model is suggested for an absolute photoemission intensity comparison resulting in chi alpha intensities which are roughly 70% of the experimental values. Together with the experimental data, the calculations allow a complete determination of the electronic structure of a ZnO surface.

Soil chemistry and pollution study of a closed landfill site at Ampar Tenang, Selangor, Malaysia.

PubMed

Mohd Adnan, Siti Nur Syahirah Binti; Yusoff, Sumiani; Piaw, Chua Yan

2013-06-01

A total of 20 landfills are located in State of Selangor, Malaysia. This includes the Ampar Tenang landfill site, which was closed on 26 January 2010. It was reported that the landfill has been upgraded to a level I type of sanitary classification. However, the dumpsite area is not being covered according to the classification. In addition, municipal solid waste was dumped directly on top of the unlined natural alluvium formation. This does not only contaminate surface and subsurface soils, but also initiates the potential risk of groundwater pollution. Based on previous studies, the Ampar Tenang soil has been proven to no longer be capable of preventing pollution migration. In this study, metal concentrations of soil samples up to 30 m depth were analyzed based on statistical analysis. It is very significant because research of this type has not been carried out before. The subsurface soils were significantly polluted by arsenic (As), lead (Pb), iron (Fe), copper (Cu) and aluminium (Al). As and Pb exceeded the safe limit values of 5.90 mg/kg and 31.00 mg/kg, respectively, based on Provincial Sediment Quality Guidelines for Metals and the Interim Sediment Quality Values. Furthermore, only Cu concentrations showed a significantly decreasing trend with increasing depth. Most metals were found on clay-type soils based on the cluster analysis method. Moreover, the analysis also differentiates two clusters: cluster I-Pb, As, zinc, Cu, manganese, calcium, sodium, magnesium, potassium and Fe; cluster II-Al. Different clustering may suggest a different contamination source of metals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olawoyin, L.

The unattached environmental radioactive particles/clusters, produced mainly by {sup 222}Rn in indoor air, are usually few nanometers in size. The inhalation of these radioactive clusters can lead to deposition of radioactivity on the mucosal surface of the tracheobronchial tree. The ultimate size of the cluster together with the flow characteristics will determine the depositional site in the human lung and thus, the extent of damage that can be caused. Thus, there exists the need for the determination of the size of the radioactive clusters. However, the existing particle measuring device have low resolution in the sub-nanometer range. In this research,more » a system for the alternative detection and measurement of the size of particles/cluster in the less than 2 nm range have been developed. The system is a one stage impactor which has a solid state spectrometer as its impaction plate. It`s major feature is the nozzle-to-plate separation, L. The particle size collected changes with L and thus, particle size spectroscopy is achieved by varying L. The number of collected particles is determined by alpha spectroscopy. The size-discriminating ability of the system was tested with laboratory generated radon particles and it was subsequently used to characterize the physical (size) changes associated with the interaction of radon progeny with water vapor and short chain alcohols in various support gases. The theory of both traditional and high velocity jet impactors together with the design and evaluation of the system developed in this study are discussed in various chapters of this dissertation. The major results obtained in the course of the study are also presented.« less

Plasmonic nanoparticles for a bottom-up approach to fabricate optical metamaterials

NASA Astrophysics Data System (ADS)

Dintinger, José; Scharf, Toralf

2012-03-01

We investigate experimentally metallic nanoparticle composites fabricated by bottom-up techniques as potential candidates for optical metamaterials. Depending on the plasmonic resonances sustained by individual NPs and their nanoscale organization into larger meta-atoms, various properties might emerge. Here, the focus of our contribution is on the fabrication and optical characterization of silver NP clusters with a spherical shape. We start with the characterisation of the "bulk" dielectric constants of silver NP inks by spectroscopic ellipsometry for different nanoparticle densities (i.e from strongly diluted dispersions to solid randomly packed films). The inks are then used to prepare spherical nanoparticle clusters by an oil-in water emulsion technique. The study of their optical properties demonstrates their ability to support Mie resonances in the visible. These resonances are associated with the excitation of a magnetic dipole, which constitutes a prerequisite to the realization of metamaterials with negative permeability.

Aerodynamic Analysis of Tektites and Their Parent Bodies

NASA Technical Reports Server (NTRS)

Adams, E. W.; Huffaker, R. M.

1962-01-01

Experiment and analysis indicate that the button-type australites were derived from glassy spheres which entered or re-entered the atmosphere as cold solid bodies; in case of average-size specimens, the entry direction was nearly horizontal and the entry speed between 6.5 and 11.2 km/sec. Terrestrial origin of such spheres is impossible because of extremely high deceleration rates at low altitudes. The limited extension of the strewn fields rules out extraterrestrial origin of clusters of such spheres because of stability considerations for clusters in space. However, tektites may have been released as liquid droplets from glassy parent bodies ablating in the atmosphere of the earth. The australites then have skipped together with the parent body in order to re-enter as cold spheres. Terrestrial origin of a parent body would require an extremely violent natural event. Ablation analysis shows that fusion of opaque siliceous stone into glass by aerodynamic heating is impossible.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhancedmore » swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. Finally, the results suggest design criteria for next generation radiation tolerant structural alloys.« less

A relativistic coupled-cluster interaction potential and rovibrational constants for the xenon dimer

NASA Astrophysics Data System (ADS)

Jerabek, Paul; Smits, Odile; Pahl, Elke; Schwerdtfeger, Peter

2018-01-01

An accurate potential energy curve has been derived for the xenon dimer using state-of-the-art relativistic coupled-cluster theory up to quadruple excitations accounting for both basis set superposition and incompleteness errors. The data obtained is fitted to a computationally efficient extended Lennard-Jones potential form and to a modified Tang-Toennies potential function treating the short- and long-range part separately. The vibrational spectrum of Xe2 obtained from a numerical solution of the rovibrational Schrödinger equation and subsequently derived spectroscopic constants are in excellent agreement with experimental values. We further present solid-state calculations for xenon using a static many-body expansion up to fourth-order in the xenon interaction potential including dynamic effects within the Einstein approximation. Again we find very good agreement with the experimental (face-centred cubic) lattice constant and cohesive energy.

Spin-orbit effects on the (119)Sn magnetic-shielding tensor in solids: a ZORA/DFT investigation.

PubMed

Alkan, Fahri; Holmes, Sean T; Iuliucci, Robbie J; Mueller, Karl T; Dybowski, Cecil

2016-07-28

Periodic-boundary and cluster calculations of the magnetic-shielding tensors of (119)Sn sites in various co-ordination and stereochemical environments are reported. The results indicate a significant difference between the predicted NMR chemical shifts for tin(ii) sites that exhibit stereochemically-active lone pairs and tin(iv) sites that do not have stereochemically-active lone pairs. The predicted magnetic shieldings determined either with the cluster model treated with the ZORA/Scalar Hamiltonian or with the GIPAW formalism are dependent on the oxidation state and the co-ordination geometry of the tin atom. The inclusion of relativistic effects at the spin-orbit level removes systematic differences in computed magnetic-shielding parameters between tin sites of differing stereochemistries, and brings computed NMR shielding parameters into significant agreement with experimentally-determined chemical-shift principal values. Slight improvement in agreement with experiment is noted in calculations using hybrid exchange-correlation functionals.

Emerging Multifunctional Metal-Organic Framework Materials.

PubMed

Li, Bin; Wen, Hui-Min; Cui, Yuanjing; Zhou, Wei; Qian, Guodong; Chen, Banglin

2016-10-01

Metal-organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self-assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre-designing or post-synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evolution of an adenine-copper cluster to a highly porous cuboidal framework: solution-phase ripening and gas-adsorption properties.

PubMed

Venkatesh, V; Pachfule, Pradip; Banerjee, Rahul; Verma, Sandeep

2014-09-15

The synthesis and directed evolution of a tetranuclear copper cluster, supported by 8-mercapto-N9-propyladenine ligand, to a highly porous three-dimensional cubic framework in the solid state is reported. The structure of this porous framework was unambiguously characterized by X-ray crystallography. The framework contains about 62 % solvent-accessible void; the presence of a free exocyclic amino group in the porous framework facilitates reversible adsorption of gas and solvent molecules. Oriented growth of framework in solution was also tracked by force and scanning electron microscopy studies, leading to identification of an intriguing ripening process, over a period of 30 days, which also revealed formation of cuboidal aggregates in solution. The elemental composition of these cuboidal aggregates was ascertained by EDAX analysis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Mobility in Concentrated Pyroclastic Density Currents: An Examination of a Self-Fluidization Mechanism

NASA Astrophysics Data System (ADS)

Breard, Eric C. P.; Dufek, Josef; Lube, Gert

2018-01-01

Pyroclastic density currents (PDCs) are a significant volcanic hazard. However, their dominant transport mechanisms remain poorly understood, in part because of the large variability of PDC types and deposits. Here we combine field data with experimental and numerical simulations to illuminate the twofold fate of particles settling from an ash cloud to form the dense PDC basal flow. At solid fractions >1 vol %, heterogeneous drag leads to formation of mesoscale particle clusters that favor rapid particle settling and result in a mobile dense layer with significant bed weight support. Conversely, at lower concentrations the absence of particle clusters typically leads to formation of poorly mobile dense beds that deposit massive layers. Based on this transport dichotomy, we present a numerical dense-dilute parameter that allows a PDC's dominant transport mechanism to be determined directly from the deposit geometry and grainsize characteristics.

Enhancing radiation tolerance by controlling defect mobility and migration pathways in multicomponent single-phase alloys

NASA Astrophysics Data System (ADS)

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun; Jin, Ke; Yang, Taini; Xiu, Pengyuan; Zhang, Yanwen; Gao, Fei; Bei, Hongbin; Shi, Shi; He, Mo-Rigen; Robertson, Ian M.; Weber, William J.; Wang, Lumin

2016-12-01

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhanced swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. The results suggest design criteria for next generation radiation tolerant structural alloys.

Characterization of the Polyoxin Biosynthetic Gene Cluster from Streptomyces cacaoi and Engineered Production of Polyoxin H*S⃞

PubMed Central

Chen, Wenqing; Huang, Tingting; He, Xinyi; Meng, Qingqing; You, Delin; Bai, Linquan; Li, Jialiang; Wu, Mingxuan; Li, Rui; Xie, Zhoujie; Zhou, Huchen; Zhou, Xiufen; Tan, Huarong; Deng, Zixin

2009-01-01

A gene cluster (pol) essential for the biosynthesis of polyoxin, a nucleoside antibiotic widely used for the control of phytopathogenic fungi, was cloned from Streptomyces cacaoi. A 46,066-bp region was sequenced, and 20 of 39 of the putative open reading frames were defined as necessary for polyoxin biosynthesis as evidenced by its production in a heterologous host, Streptomyces lividans TK24. The role of PolO and PolA in polyoxin synthesis was demonstrated by in vivo experiments, and their functions were unambiguously characterized as O-carbamoyltransferase and UMP-enolpyruvyltransferase, respectively, by in vitro experiments, which enabled the production of a modified compound differing slightly from that proposed earlier. These studies should provide a solid foundation for the elucidation of the molecular mechanisms for polyoxin biosynthesis, and set the stage for combinatorial biosynthesis using genes encoding different pathways for nucleoside antibiotics. PMID:19233844

Chemical and nanometer-scale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy

USGS Publications Warehouse

Mao, J.; Fang, X.; Lan, Y.; Schimmelmann, A.; Mastalerz, Maria; Xu, L.; Schmidt-Rohr, K.

2010-01-01

We have used advanced and quantitative solid-state nuclear magnetic resonance (NMR) techniques to investigate structural changes in a series of type II kerogen samples from the New Albany Shale across a range of maturity (vitrinite reflectance R0 from 0.29% to 1.27%). Specific functional groups such as CH3, CH2, alkyl CH, aromatic CH, aromatic C-O, and other nonprotonated aromatics, as well as "oil prone" and "gas prone" carbons, have been quantified by 13C NMR; atomic H/C and O/C ratios calculated from the NMR data agree with elemental analysis. Relationships between NMR structural parameters and vitrinite reflectance, a proxy for thermal maturity, were evaluated. The aromatic cluster size is probed in terms of the fraction of aromatic carbons that are protonated (???30%) and the average distance of aromatic C from the nearest protons in long-range H-C dephasing, both of which do not increase much with maturation, in spite of a great increase in aromaticity. The aromatic clusters in the most mature sample consist of ???30 carbons, and of ???20 carbons in the least mature samples. Proof of many links between alkyl chains and aromatic rings is provided by short-range and long-range 1H-13C correlation NMR. The alkyl segments provide most H in the samples; even at a carbon aromaticity of 83%, the fraction of aromatic H is only 38%. While aromaticity increases with thermal maturity, most other NMR structural parameters, including the aromatic C-O fractions, decrease. Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity. In this series of samples, thermal maturation mostly increases aromaticity by reducing the length of the alkyl chains attached to the aromatic cores, not by pronounced growth of the size of the fused aromatic ring clusters. ?? 2010 Elsevier Ltd. All rights reserved.

Diffusion and Clustering of Carbon Dioxide on Non-porous Amorphous Solid Water

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Jiao; Emtiaz, Shahnewaj M.; Vidali, Gianfranco

2017-03-01

Observations by ISO and Spitzer toward young stellar objects showed that CO{sub 2} segregates in the icy mantles covering dust grains. Thermal processing of the ice mixture was proposed as being responsible for the segregation. Although several laboratories studied thermally induced segregation, a satisfying quantification is still missing. We propose that the diffusion of CO{sub 2} along pores inside water ice is the key to quantify segregation. We combined Temperature Programmed Desorption and Reflection Absorption InfraRed Spectroscopy to study how CO{sub 2} molecules interact on a non-porous amorphous solid water (np-ASW) surface. We found that CO{sub 2} diffuses significantly onmore » an np-ASW surface above 65 K and clusters are formed at well below one monolayer. A simple rate equation simulation finds that the diffusion energy barrier of CO{sub 2} on np-ASW is 2150 ± 50 K, assuming a diffusion pre-exponential factor of 10{sup 12} s{sup −1}. This energy should also apply to the diffusion of CO{sub 2} on the wall of pores. The binding energy of CO{sub 2} from CO{sub 2} clusters and CO{sub 2} from H{sub 2}O ice has been found to be 2415 ± 20 K and 2250 ± 20 K, respectively, assuming the same prefactor for desorption. CO{sub 2}–CO{sub 2} interaction is stronger than CO{sub 2}–H{sub 2}O interaction, in agreement with the experimental finding that CO{sub 2} does not wet the np-ASW surface. For comparison, we carried out similar experiments with CO on np-ASW, and found that the CO–CO interaction is always weaker than CO–H{sub 2}O. As a result, CO wets the np-ASW surface. This study should be of help to uncover the thermal history of CO{sub 2} on the icy mantles of dust grains.« less

Measurement of Mechanical Coherency Temperature and Solid Volume Fraction in Al-Zn Alloys Using In Situ X-ray Diffraction During Casting

NASA Astrophysics Data System (ADS)

Drezet, Jean-Marie; Mireux, Bastien; Kurtuldu, Güven; Magdysyuk, Oxana; Drakopoulos, Michael

2015-09-01

During solidification of metallic alloys, coalescence leads to the formation of solid bridges between grains or grain clusters when both solid and liquid phases are percolated. As such, it represents a key transition with respect to the mechanical behavior of solidifying alloys and to the prediction of solidification cracking. Coalescence starts at the coherency point when the grains begin to touch each other, but are unable to sustain any tensile loads. It ends up at mechanical coherency when the solid phase is sufficiently coalesced to transmit macroscopic tensile strains and stresses. Temperature at mechanical coherency is a major input parameter in numerical modeling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. This temperature has been determined for Al-Zn alloys using in situ X-ray diffraction during casting in a dog-bone-shaped mold. This setup allows the sample to build up internal stress naturally as its contraction is prevented. The cooling on both extremities of the mold induces a hot spot at the middle of the sample which is irradiated by X-ray. Diffraction patterns were recorded every 0.5 seconds using a detector covering a 426 × 426 mm2 area. The change of diffraction angles allowed measuring the general decrease of the lattice parameter of the fcc aluminum phase. At high solid volume fraction, a succession of strain/stress build up and release is explained by the formation of hot tears. Mechanical coherency temperatures, 829 K to 866 K (556 °C to 593 °C), and solid volume fractions, ca. 98 pct, are shown to depend on solidification time for grain refined Al-6.2 wt pct Zn alloys.

Colossal permittivity behavior and its origin in rutile (Mg1/3Ta2/3)xTi1-xO2.

PubMed

Dong, Wen; Chen, Dehong; Hu, Wanbiao; Frankcombe, Terry J; Chen, Hua; Zhou, Chao; Fu, Zhenxiao; Wei, Xiaoyong; Xu, Zhuo; Liu, Zhifu; Li, Yongxiang; Liu, Yun

2017-08-30

This work investigates the synthesis, chemical composition, defect structures and associated dielectric properties of (Mg 2+ , Ta 5+ ) co-doped rutile TiO 2 polycrystalline ceramics with nominal compositions of (Mg 2+ 1/3 Ta 5+ 2/3 ) x Ti 1-x O 2 . Colossal permittivity (>7000) with a low dielectric loss (e.g. 0.002 at 1 kHz) across a broad frequency/temperature range can be achieved at x = 0.5% after careful optimization of process conditions. Both experimental and theoretical evidence indicates such a colossal permittivity and low dielectric loss intrinsically originate from the intragrain polarization that links to the electron-pinned [Formula: see text] defect clusters with a specific configuration, different from the defect cluster form previously reported in tri-/pent-valent ion co-doped rutile TiO 2 . This work extends the research on colossal permittivity and defect formation to bi-/penta-valent ion co-doped rutile TiO 2 and elucidates a likely defect cluster model for this system. We therefore believe these results will benefit further development of colossal permittivity materials and advance the understanding of defect chemistry in solids.

View of the Skylab 1 space station cluster from the Skylab 2 Command Module

NASA Image and Video Library

1973-05-25

S73-26738 (25 May 1973) --- A close-up view of the Skylab 1 space station cluster can be seen in this reproduction taken from a color television transmission made by a TV camera aboard the Skylab 2 Command Module during its ?fly-around? inspection of the cluster. The numbers across the top of the picture indicate the Skylab 1 ground lapse time. Note the missing portion of the micrometeoroid shield on the Orbital Workshop. The shield area was reported to be solid gold by the Skylab 2 crewmen. A cable appears to be wrapped around the damaged OWS solar array system wing. The crewmen reported that the other OWS solar panel was completely gone, with only tubes and wiring sticking out. One of the discone antennas extends out form the Airlock Module. The Multiple Docking Adapter is in the lower left corner of the picture. A portion of a solar panel on the Apollo Telescope Mount is visible at the bottom and at the left edge. In their ?fly around? inspection the crewmen noted that portions of the micrometeoroid shield had slid back underneath the OWS solar wing. Photo credit: NASA

Antimicrobial-Resistant Bacterial Populations and Antimicrobial Resistance Genes Obtained from Environments Impacted by Livestock and Municipal Waste

PubMed Central

Durso, Lisa M.; Harhay, Dayna M.; Schmidt, John W.

2015-01-01

This study compared the populations of antimicrobial-resistant bacteria and the repertoire of antimicrobial resistance genes in four environments: effluent of three municipal wastewater treatment facilities, three cattle feedlot runoff catchment ponds, three swine waste lagoons, and two “low impact” environments (an urban lake and a relict prairie). Multiple liquid and solid samples were collected from each environment. The prevalences and concentrations of antimicrobial-resistant (AMR) Gram-negative (Escherichia coli and Salmonella enterica) and Gram-positive (enterococci) bacteria were determined from individual samples (n = 174). The prevalences of 84 antimicrobial resistance genes in metagenomic DNA isolated from samples pooled (n = 44) by collection date, location, and sample type were determined. The prevalences and concentrations of AMR E. coli and Salmonella were similar among the livestock and municipal sample sources. The levels of erythromycin-resistant enterococci were significantly higher in liquid samples from cattle catchment ponds and swine waste lagoons than in liquid samples from municipal wastewater treatment facilities, but solid samples from these environments did not differ significantly. Similarly, trimethoprim/sulfamethoxazole-resistant E. coli concentrations were significantly higher in swine liquid than in municipal liquid samples, but there was no difference in solid samples. Multivariate analysis of the distribution of antimicrobial resistance genes using principal coordinate analysis showed distinct clustering of samples with livestock (cattle and swine), low impact environment and municipal samples forming three separate clusters. The numbers of class A beta-lactamase, class C beta-lactamase, and fluoroquinolone resistance genes detected were significantly higher (P < 0.05) in municipal samples than in cattle runoff or swine lagoon samples. In conclusion, we report that AMR is a very widespread phenomenon and that similar prevalences and concentrations of antimicrobial-resistant bacteria and antimicrobial resistance genes exist in cattle, human, and swine waste streams, but a higher diversity of antimicrobial resistance genes are present in treated human waste discharged from municipal wastewater treatment plants than in livestock environments. PMID:26197056

Antimicrobial-Resistant Bacterial Populations and Antimicrobial Resistance Genes Obtained from Environments Impacted by Livestock and Municipal Waste.

PubMed

Agga, Getahun E; Arthur, Terrance M; Durso, Lisa M; Harhay, Dayna M; Schmidt, John W

2015-01-01

This study compared the populations of antimicrobial-resistant bacteria and the repertoire of antimicrobial resistance genes in four environments: effluent of three municipal wastewater treatment facilities, three cattle feedlot runoff catchment ponds, three swine waste lagoons, and two "low impact" environments (an urban lake and a relict prairie). Multiple liquid and solid samples were collected from each environment. The prevalences and concentrations of antimicrobial-resistant (AMR) Gram-negative (Escherichia coli and Salmonella enterica) and Gram-positive (enterococci) bacteria were determined from individual samples (n = 174). The prevalences of 84 antimicrobial resistance genes in metagenomic DNA isolated from samples pooled (n = 44) by collection date, location, and sample type were determined. The prevalences and concentrations of AMR E. coli and Salmonella were similar among the livestock and municipal sample sources. The levels of erythromycin-resistant enterococci were significantly higher in liquid samples from cattle catchment ponds and swine waste lagoons than in liquid samples from municipal wastewater treatment facilities, but solid samples from these environments did not differ significantly. Similarly, trimethoprim/sulfamethoxazole-resistant E. coli concentrations were significantly higher in swine liquid than in municipal liquid samples, but there was no difference in solid samples. Multivariate analysis of the distribution of antimicrobial resistance genes using principal coordinate analysis showed distinct clustering of samples with livestock (cattle and swine), low impact environment and municipal samples forming three separate clusters. The numbers of class A beta-lactamase, class C beta-lactamase, and fluoroquinolone resistance genes detected were significantly higher (P < 0.05) in municipal samples than in cattle runoff or swine lagoon samples. In conclusion, we report that AMR is a very widespread phenomenon and that similar prevalences and concentrations of antimicrobial-resistant bacteria and antimicrobial resistance genes exist in cattle, human, and swine waste streams, but a higher diversity of antimicrobial resistance genes are present in treated human waste discharged from municipal wastewater treatment plants than in livestock environments.

Carbon solids in oxygen-deficient explosives (LA-UR-13-21151)

NASA Astrophysics Data System (ADS)

Peery, Travis

2013-06-01

The phase behavior of excess carbon in oxygen-deficient explosives has a significant effect on detonation properties and product equations of state. Mixtures of fuel oil in ammonium nitrate (ANFO) above a stoichiometric ratio demonstrate that even small amounts of graphite, on the order of 5% by mole fraction, can substantially alter the Chapman-Jouget (CJ) state properties, a central ingredient in modeling the products equation of state. Similar effects can be seen for Composition B, which borders the carbon phase boundary between graphite and diamond. Nano-diamond formation adds complexity to the product modeling because of surface adsorption effects. I will discuss these carbon phase issues in our equation of state modeling of detonation products, including our statistical mechanics description of carbon clustering and surface chemistry to properly treat solid carbon formation. This work is supported by the Advanced Simulation and Computing Program, under the NNSA.

Scaled Rocket Testing in Hypersonic Flow

NASA Technical Reports Server (NTRS)

Dufrene, Aaron; MacLean, Matthew; Carr, Zakary; Parker, Ron; Holden, Michael; Mehta, Manish

2015-01-01

NASA's Space Launch System (SLS) uses four clustered liquid rocket engines along with two solid rocket boosters. The interaction between all six rocket exhaust plumes will produce a complex and severe thermal environment in the base of the vehicle. This work focuses on a recent 2% scale, hot-fire SLS base heating test. These base heating tests are short-duration tests executed with chamber pressures near the full-scale values with gaseous hydrogen/oxygen engines and RSRMV analogous solid propellant motors. The LENS II shock tunnel/Ludwieg tube tunnel was used at or near flight duplicated conditions up to Mach 5. Model development was strongly based on the Space Shuttle base heating tests with several improvements including doubling of the maximum chamber pressures and duplication of freestream conditions. Detailed base heating results are outside of the scope of the current work, rather test methodology and techniques are presented along with broader applicability toward scaled rocket testing in supersonic and hypersonic flow.

Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework.

PubMed

Berger, Daniel; Logsdail, Andrew J; Oberhofer, Harald; Farrow, Matthew R; Catlow, C Richard A; Sherwood, Paul; Sokol, Alexey A; Blum, Volker; Reuter, Karsten

2014-07-14

We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110).

Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, Daniel, E-mail: daniel.berger@ch.tum.de; Oberhofer, Harald; Reuter, Karsten

2014-07-14

We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capabilitymore » by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO{sub 2}(110)« less

Structural and mechanical design challenges of space shuttle solid rocket boosters separation and recovery subsystems

NASA Technical Reports Server (NTRS)

Woodis, W. R.; Runkle, R. E.

1985-01-01

The design of the space shuttle solid rocket booster (SRB) subsystems for reuse posed some unique and challenging design considerations. The separation of the SRBs from the cluster (orbiter and external tank) at 150,000 ft when the orbiter engines are running at full thrust meant the two SRBs had to have positive separation forces pushing them away. At the same instant, the large attachments that had reacted launch loads of 7.5 million pounds thrust had to be servered. These design considerations dictated the design requirements for the pyrotechnics and separation rocket motors. The recovery and reuse of the two SRBs meant they had to be safely lowered to the ocean, remain afloat, and be owed back to shore. In general, both the pyrotechnic and recovery subsystems have met or exceeded design requirements. In twelve vehicles, there has only been one instance where the pyrotechnic system has failed to function properly.

The effect of injected interstitials on void formation in self-ion irradiated nickel containing concentrated solid solution alloys

DOE PAGES

Yang, Tai-ni; Lu, Chenyang; Jin, Ke; ...

2017-02-21

Pure nickel and three nickel containing single-phase concentrated solid solution alloys (SP-CSAs) have been irradiated using 3 MeV Ni 2+ ions at 500 C to fluences of 1.5 x 10 16 and 5.0 x 10 16 cm 2. We characterized the radiation-induced voids using cross sectional transmission electron microscopy that distributions of voids and dislocation loops were presented as a function of depth. We also observed a various degree of void suppression on the tested samples and a defect clusters migration mechanism was proposed for NiCo. Furthermore, in order to sufficiently understand the defect dynamics in these SP-CSAs, the injectedmore » interstitial effect has been taken into account along with the 1-dimentional (1-D) and 3-dimentional (3-D) interstitial movement mechanisms.« less

Two-dimensional freezing criteria for crystallizing colloidal monolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Ziren; Han Yilong; Alsayed, Ahmed M.

Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At themore » freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.« less

Biofilm growth program and architecture revealed by single-cell live imaging

NASA Astrophysics Data System (ADS)

Yan, Jing; Sabass, Benedikt; Stone, Howard; Wingreen, Ned; Bassler, Bonnie

Biofilms are surface-associated bacterial communities. Little is known about biofilm structure at the level of individual cells. We image living, growing Vibrio cholerae biofilms from founder cells to ten thousand cells at single-cell resolution, and discover the forces underpinning the architectural evolution of the biofilm. Mutagenesis, matrix labeling, and simulations demonstrate that surface-adhesion-mediated compression causes V. cholerae biofilms to transition from a two-dimensional branched morphology to a dense, ordered three-dimensional cluster. We discover that directional proliferation of rod-shaped bacteria plays a dominant role in shaping the biofilm architecture, and this growth pattern is controlled by a single gene. Competition analyses reveal the advantages of the dense growth mode in providing the biofilm with superior mechanical properties. We will further present continuum theory to model the three-dimensional growth of biofilms at the solid-liquid interface as well as solid-air interface.

Reversibility and criticality in amorphous solids

DOE PAGES

Regev, Ido; Weber, John; Reichhardt, Charles; ...

2015-11-13

The physical processes governing the onset of yield, where a material changes its shape permanently under external deformation, are not yet understood for amorphous solids that are intrinsically disordered. Here, using molecular dynamics simulations and mean-field theory, we show that at a critical strain amplitude the sizes of clusters of atoms undergoing cooperative rearrangements of displacements (avalanches) diverges. We compare this non-equilibrium critical behaviour to the prevailing concept of a ‘front depinning’ transition that has been used to describe steady-state avalanche behaviour in different materials. We explain why a depinning-like process can result in a transition from periodic to chaoticmore » behaviour and why chaotic motion is not possible in pinned systems. As a result, these findings suggest that, at least for highly jammed amorphous systems, the irreversibility transition may be a side effect of depinning that occurs in systems where the disorder is not quenched.« less

Rate Dependence of Elementary Rearrangements and Spatiotemporal Correlations in the 3D Flow of Soft Solids

NASA Astrophysics Data System (ADS)

Vasisht, Vishwas V.; Dutta, Sudeep K.; Del Gado, Emanuela; Blair, Daniel L.

2018-01-01

We use a combination of confocal microscopy, rheology, and molecular dynamics simulations to investigate jammed emulsions under shear, by analyzing the 3D droplets rearrangements in the shear frame. Our quantitative analysis of local dynamics reveals elementary nonaffine rearrangements that underlie the onset of the flow at small strains. We find that the mechanism of unjamming and the upturn in the material flow curve are associated to a qualitative change in spatiotemporal correlations of such rearrangements with the applied shear rate. At high shear rates, droplet clusters follow coordinated, stringlike motion. Conversely, at low shear rates, the elementary nonaffine rearrangements exhibit longer-ranged correlations, with complex spatiotemporal patterns. The 3D microscopic details provide novel insights into the specific features of the material flow curve, common to a large class of technologically relevant soft disordered solids and new fundamental ingredients for constitutive models.

Development and parallelization of a direct numerical simulation to study the formation and transport of nanoparticle clusters in a viscous fluid

NASA Astrophysics Data System (ADS)

Sloan, Gregory James

The direct numerical simulation (DNS) offers the most accurate approach to modeling the behavior of a physical system, but carries an enormous computation cost. There exists a need for an accurate DNS to model the coupled solid-fluid system seen in targeted drug delivery (TDD), nanofluid thermal energy storage (TES), as well as other fields where experiments are necessary, but experiment design may be costly. A parallel DNS can greatly reduce the large computation times required, while providing the same results and functionality of the serial counterpart. A D2Q9 lattice Boltzmann method approach was implemented to solve the fluid phase. The use of domain decomposition with message passing interface (MPI) parallelism resulted in an algorithm that exhibits super-linear scaling in testing, which may be attributed to the caching effect. Decreased performance on a per-node basis for a fixed number of processes confirms this observation. A multiscale approach was implemented to model the behavior of nanoparticles submerged in a viscous fluid, and used to examine the mechanisms that promote or inhibit clustering. Parallelization of this model using a masterworker algorithm with MPI gives less-than-linear speedup for a fixed number of particles and varying number of processes. This is due to the inherent inefficiency of the master-worker approach. Lastly, these separate simulations are combined, and two-way coupling is implemented between the solid and fluid.

Brief report: Lymphocytic choriomeningitis virus transmitted through solid organ transplantation--Massachusetts, 2008.

PubMed

2008-07-25

Lymphocytic choriomeningitis virus (LCMV) is a rodent-borne arenavirus found worldwide. House mice (Mus musculus) are the natural reservoir, but LCMV also can infect other wild, pet, and laboratory rodents (e.g., rats, mice, guinea pigs, and hamsters). Humans can be infected through exposure to rodent excreta. Person-to-person transmission has occurred only through maternal-fetal transmission and solid organ transplantation. LCMV infection in humans can be asymptomatic or cause a spectrum of illness ranging from isolated fever to meningitis and encephalitis. Overall case fatality is <1%. Fetal infections can result in congenital abnormalities or death. Immunosuppressed patients, such as organ transplant recipients, can develop fatal hemorrhagic fever-like disease. Transmission of LCMV and an LCMV-like arenavirus via organ transplantation has been documented in three previous clusters. Of 11 recipients described in those clusters, 10 died of multisystem organ failure, with LCMV-associated hepatitis as a prominent feature. The surviving patient was treated with ribavirin (an antiviral with in vitro activity against LCMV) and reduction of immunosuppressive therapy. On April 15, 2008, an organ procurement organization (OPO) notified CDC of severe illness in two kidney transplant recipients from a common donor; at the time of notification, one of the recipients had died. Samples from the donor and both recipients were tested at CDC; on April 22, test results revealed evidence of acute LCMV infection in the donor and both recipients. This report summarizes the results of the subsequent public health investigation.

The effect of coumaryl alcohol incorporation on the structure and composition of lignin dehydrogenation polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harman-Ware, Anne E.; Happs, Renee M.; Davison, Brian H.

Lignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processes. Here, DHPs were synthesized using a Zutropfverfahren method with horseradish peroxidase and three lignin monomers, sinapyl (S), coumaryl (H) and coniferyl (G) alcohols, in the presence of hydrogen peroxide. The H monomer was reacted with G and a 1:1 molar mixture of S:G monomers at H molar compositions of 0, 5, 10 and 20 mol% to study how the presence of the H monomer affected the structure and composition of the recovered polymers. At low H concentrations, solid state NMRmore » spectra suggest that the H and G monomers interact to form G:H polymers that have a lower average molecular weight than the solely G-based polymer or the G:H polymer produced at higher H concentrations. Solid-state NMR and pyrolysis-MBMS analyses suggest that at higher H concentrations, the H monomer primarily self-polymerizes to produce clusters of H-based polymer that are segregated from clusters of G- or S:G-based polymers. Thioacidolysis generally showed higher recoveries of thioethylated products from S:G or S:G:H polymers made with higher H content, indicating an increase in the linear ether linkages. Overall, the experimental results support theoretical predictions for the reactivity and structural influences of the H monomer on the formation of lignin-like polymers.« less

Study of the optical properties and the carbonaceous clusters in DAM-ADC solid state nuclear track detectors

NASA Astrophysics Data System (ADS)

Rammah, Y. S.; Abdalla, A. M.

2017-12-01

The optical properties of DAM-ADC solid state nuclear track detectors (SSNTDs) were investigated. Samples of DAM-ADC detector were irradiated at room temperature with gamma doses in the range of 100-500 kGy using 1.25 MeV 60Co source of dose rate 4 kGy/h. The optical characterization of these detectors have been studied through the measurements of UV-visible absorption spectra of blank and γ- irradiated samples. The optical energy band gaps, Eg for the detectors were obtained from the direct and the indirect allowed transitions in K-space using two methods (Tauc's model and absorption spectrum fitting (ASF) method). The absorbance of DAM-ADC detector was found to increase with increasing of the gamma absorbed dose. The width of the tail of localized states in the band gap, Eu was evaluated with the Urbach's method. The number of carbon atoms per conjugated length (N), the number of carbon atoms per cluster (M), and refractive index (n) for the present samples were determined. Both of the direct and the indirect band gaps of DAM-ADC detector decrease with increasing of the gamma absorbed dose. Urbach's energy decreased significantly for the detector. An increase in N, M, and n with increasing of the gamma absorbed dose was noticed. Results shed light on the effect of gamma irradiations of DAM-ADC SSNTDs to suitable industrial applications and to modify the optical properties through gamma-induced modifications of the polymer structure.

Locational Determinants of Emissions from Pollution-Intensive Firms in Urban Areas

PubMed Central

Zhou, Min; Tan, Shukui; Guo, Mingjing; Zhang, Lu

2015-01-01

Industrial pollution has remained as one of the most daunting challenges for many regions around the world. Characterizing the determinants of industrial pollution should provide important management implications. Unfortunately, due to the absence of high-quality data, rather few studies have systematically examined the locational determinants using a geographical approach. This paper aimed to fill the gap by accessing the pollution source census dataset, which recorded the quantity of discharged wastes (waste water and solid waste) from 717 pollution-intensive firms within Huzhou City, China. Spatial exploratory analysis was applied to analyze the spatial dependency and local clusters of waste emissions. Results demonstrated that waste emissions presented significantly positive autocorrelation in space. The high-high hotspots generally concentrated towards the city boundary, while the low-low clusters approached the Taihu Lake. Their locational determinants were identified by spatial regression. In particular, firms near the city boundary and county road were prone to discharge more wastes. Lower waste emissions were more likely to be observed from firms with high proximity to freight transfer stations or the Taihu Lake. Dense populous districts saw more likelihood of solid waste emissions. Firms in the neighborhood of rivers exhibited higher waste water emissions. Besides, the control variables (firm size, ownership, operation time and industrial type) also exerted significant influence. The present methodology can be applicable to other areas, and further inform the industrial pollution control practices. Our study advanced the knowledge of determinants of emissions from pollution-intensive firms in urban areas. PMID:25927438

The effect of coumaryl alcohol incorporation on the structure and composition of lignin dehydrogenation polymers

DOE PAGES

Harman-Ware, Anne E.; Happs, Renee M.; Davison, Brian H.; ...

2017-11-30

Lignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processes. Here, DHPs were synthesized using a Zutropfverfahren method with horseradish peroxidase and three lignin monomers, sinapyl (S), coumaryl (H) and coniferyl (G) alcohols, in the presence of hydrogen peroxide. The H monomer was reacted with G and a 1:1 molar mixture of S:G monomers at H molar compositions of 0, 5, 10 and 20 mol% to study how the presence of the H monomer affected the structure and composition of the recovered polymers. At low H concentrations, solid state NMRmore » spectra suggest that the H and G monomers interact to form G:H polymers that have a lower average molecular weight than the solely G-based polymer or the G:H polymer produced at higher H concentrations. Solid-state NMR and pyrolysis-MBMS analyses suggest that at higher H concentrations, the H monomer primarily self-polymerizes to produce clusters of H-based polymer that are segregated from clusters of G- or S:G-based polymers. Thioacidolysis generally showed higher recoveries of thioethylated products from S:G or S:G:H polymers made with higher H content, indicating an increase in the linear ether linkages. Overall, the experimental results support theoretical predictions for the reactivity and structural influences of the H monomer on the formation of lignin-like polymers.« less

Growth of High-Density Zinc Oxide Nanorods on Porous Silicon by Thermal Evaporation

PubMed Central

Rusli, Nurul Izni; Tanikawa, Masahiro; Mahmood, Mohamad Rusop; Yasui, Kanji; Hashim, Abdul Manaf

2012-01-01

The formation of high-density zinc oxide (ZnO) nanorods on porous silicon (PS) substrates at growth temperatures of 600–1000 °C by a simple thermal evaporation of zinc (Zn) powder in the presence of oxygen (O2) gas was systematically investigated. The high-density growth of ZnO nanorods with (0002) orientation over a large area was attributed to the rough surface of PS, which provides appropriate planes to promote deposition of Zn or ZnOx seeds as nucleation sites for the subsequent growth of ZnO nanorods. The geometrical morphologies of ZnO nanorods are determined by the ZnOx seed structures, i.e., cluster or layer structures. The flower-like hexagonal-faceted ZnO nanorods grown at 600 °C seem to be generated from the sparsely distributed ZnOx nanoclusters. Vertically aligned hexagonal-faceted ZnO nanorods grown at 800 °C may be inferred from the formation of dense arrays of ZnOx clusters. The formation of disordered ZnO nanorods formed at 1000 °C may due to the formation of a ZnOx seed layer. The growth mechanism involved has been described by a combination of self-catalyzed vapor-liquid-solid (VLS) and vapor-solid (VS) mechanism. The results suggest that for a more precise study on the growth of ZnO nanostructures involving the introduction of seeds, the initial seed structures must be taken into account given their significant effects.

Methanogenic pathway and community structure in a thermophilic anaerobic digestion process of organic solid waste.

PubMed

Sasaki, Daisuke; Hori, Tomoyuki; Haruta, Shin; Ueno, Yoshiyuki; Ishii, Masaharu; Igarashi, Yasuo

2011-01-01

The methanogenic pathway and microbial community in a thermophilic anaerobic digestion process of organic solid waste were investigated in a continuous-flow stirred-tank reactor using artificial garbage slurry as a feedstock. The decomposition pathway of acetate, a significant precursor of CH(4) and a key intermediate metabolite in the anaerobic digestion process, was analyzed by using stable isotopes. A tracer experiment using (13)C-labeled acetate revealed that approximately 80% of the acetate was decomposed via a non-aceticlastic oxidative pathway, whereas the remainder was converted to methane via an aceticlastic pathway. Archaeal 16S rRNA analyses demonstrated that the hydrogenotrophic methanogens Methanoculleus spp. accounted for >90% of detected methanogens, and the aceticlastic methanogens Methanosarcina spp. were the minor constituents. The clone library targeting bacterial 16S rRNA indicated the predominance of the novel Thermotogales bacterium (relative abundance: ~53%), which is related to anaerobic acetate oxidizer Thermotoga lettingae TMO, although the sequence similarity was low. Uncultured bacteria that phylogenetically belong to municipal solid waste cluster I were also predominant in the microflora (~30%). These results imply that the microbial community in the thermophilic degrading process of organic solid waste consists exclusively of unidentified bacteria, which efficiently remove acetate through a non-aceticlastic oxidative pathway. Copyright © 2010 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

The quataron concept: a key to solve the problem of the nanostate

NASA Astrophysics Data System (ADS)

Askhabov, A. M.

2003-04-01

In a number of our works (Askhabov, 1998-2002) we have described a set of ideas and principles dealing with structural organization of substance in the nanorange and its role for formation of crystalline and noncrystalline materials. These ideas have been collectively referred to as the “quataron concept”. Central in this new concept is the idea that there are specific nanosize clusters arising under non-equilibrium conditions. These clusters are understood as a peculiar form of structural organization of substance at the nanolevel and referred to as "hidden" phase clusters or quatarons. As inequilibrium objects, quatarons are capable of self-organization and self-development. With their valencies fully realized (in covalent interactions), they can become large molecules; with a three-dimensional ordering (atom arrangement in a crystal lattice) they will produce crystalline particles. Quatarons are the basis for all kinds of equilibrium nanostructures from ordinary tetra- and octahedral groupings to the widely known fullerenes or dense dodecahedral and icosahedral clusters, colloidal, fractal particles. In particular, the quataron theory offers a very simple solution to the fullerene problem. Quatarons are fullerene predecessors. The fullerene architecture is dictated by hollow quatarons. Besides, it has been found that only clusters more than ~1.2 nm in size can become potenial centers of crystallization. Thus, quatarons seem to be behind all the rest of nanoparticles, including nanocrystals. This theory also broadens our understanding of the amorphous state. If for some reason quatarons or their aggregates fail to crystallize, for example, as a result of the fractal structure of the cluster surface or owing to their non-crystallographic (icosahedral) shape, then in the condensed state they give rise to a special class of solid ultradisperse materials (quatarites) of various degrees of ordering. The closest analogue of such materials is opal, a material made up of one-size spherical silica particles. A well-ordered material composed of carbon fullerenes is known as fullerite. The quataron concept will produce a profound effect on the mineralogical science, physics and chemistry of minerals. Already now we have obviously reached the point where we need to revise some of the fundamental genetic, structural and classificational issues. In particular, what was said above about the structure and formation of noncrystalline materials dictates the necessity of a broader understanding of the mineral. This would result in that a large number of materials now referred to as mineraloids will fall into the area of minerals and will be considered as new mineral species, which would mean that minerals are not only natural objects (chemical compounds) of crystalline structure but also X-ray amorphous solids of certain arrangement of elements (fullerites, quatarites, opals, etc.). The work was done with financial support from RFBI (grant N. 02-05-64688) and INTAS (grant N. 99-0247).

Quantum-Mechanical Combinatorial Design of Solids having Target Properties

NASA Astrophysics Data System (ADS)

Zunger, Alex

2007-03-01

(1) One of the most striking aspects of solid state physics is the diversity of structural forms in which crystals appear in Nature. Not only are there many distinct crystal-types, but combinations of two or more crystalline materials (alloys) give rise to various local geometric atomic patters. The already rich repertoire of such forms has recently been significantly enhanced by the advent of artificial crystal growth techniques (MBE, STM- atom positioning, etc.) that can create desired structural forms, such as superlattices and impurity clusters even in defiance of the rules of equilibrium thermodynamics. (2) At the same time, the fields of chemistry of nanostructures and physics of structural phase-transitions have long revealed that different atomic configurations generally lead to different physical properties even without altering the chemical makeup. While the most widely - known illustration of such ``form controls function'' rule is the dramatically different color, conductivity and hardness of the allotropical forms of pure carbon (diamond,graphite, C60), the physics of semiconductor superstructures and nanostructures is full of striking examples of how optical, magnetic and transport properties depend sensitively on atomic configuration. (3) Yet, the history of material research has generally occurred via accidental discoveries of material structures having interesting physical property (semiconductivity, ferromagnetism; superconductivity etc.). This begs the question: can this discovery process be inverted, i.e. can we first articulate a desired target physical property, then search (within a class) for the configuration that has this property? (4) The number of potentially interesting atomic configurations exhibits a combinatorial explosion, so even fast synthesis or fast computations can not survey all. (5) This talk describes the recent steps made by solid state theory + computational physics to address this ``Inverse Design'' (Franceschetti & Zunger, Nature, 402, 60 (1999) problem. I will show how Genetic Algorithms, in combination with efficient (``Order N'') solutions to the Pseudopotential Schrodinger equation allow us to investigate astronomical spaces of atomic configurations in search of the structure with a target physical property. Only a small fraction of all (˜ 10**14 in our case) configurations need to be examined. Physical properties are either calculated on-the-fly (if it's easy), or first ``Cluster-Expanded'' (if the theory is difficult). I will illustrate this Inverse Band Structure approach for (a) Design of required band-gaps in semiconductor superlattices; (b) architecture of impurity --clusters with desired optical properties (PRL 97, 046401, 2006) (c) search for configuration of magnetic ions in semiconductors that maximize the ferromagnetic Curie temperature (PRL, 97, 047202, 2006).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mirjankar, Nikhil S.; Fraga, Carlos G.; Carman, April J.

Chemical attribution signatures (CAS) for chemical threat agents (CTAs) are being investigated to provide an evidentiary link between CTAs and specific sources to support criminal investigations and prosecutions. In a previous study, anionic impurity profiles developed using high performance ion chromatography (HPIC) were demonstrated as CAS for matching samples from eight potassium cyanide (KCN) stocks to their reported countries of origin. Herein, a larger number of solid KCN stocks (n = 13) and, for the first time, solid sodium cyanide (NaCN) stocks (n = 15) were examined to determine what additional sourcing information can be obtained through anion, carbon stablemore » isotope, and elemental analyses of cyanide stocks by HPIC, isotope ratio mass spectrometry (IRMS), and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. The HPIC anion data was evaluated using the variable selection methods of Fisher-ratio (F-ratio), interval partial least squares (iPLS), and genetic algorithm-based partial least squares (GAPLS) and the classification methods of partial least squares discriminate analysis (PLSDA), K nearest neighbors (KNN), and support vector machines discriminate analysis (SVMDA). In summary, hierarchical cluster analysis (HCA) of anion impurity profiles from multiple cyanide stocks from six reported country of origins resulted in cyanide samples clustering into three groups: Czech Republic, Germany, and United States, independent of the associated alkali metal (K or Na). The three country groups were independently corroborated by HCA of cyanide elemental profiles and corresponded to countries with known solid cyanide factories. Both the anion and elemental CAS are believed to originate from the aqueous alkali hydroxides used in cyanide manufacture. Carbon stable isotope measurements resulted in two clusters: Germany and United States (the single Czech stock grouped with United States stocks). The carbon isotope CAS is believed to originate from the carbon source and process used to make the HCN utilized in cyanide synthesis. Classification errors for two validation studies using anion impurity profiles collected over five years on different instruments were as low as zero for KNN and SVMDA, demonstrating the excellent reliability (so far) of using anion impurities for matching a cyanide sample to its country of manufacture (i.e., factory). Variable selection reduced errors for those classification methods having errors greater than zero with iPLS-forward selection, and F-ratio typically providing the lowest errors. Finally, using anion profiles to match cyanides to a specific stock or stock group resulted in cross-validation errors ranging from zero to 5.3%.« less

The Role of Carboxydothermus hydrogenoformans in the Conversion of Calcium Phosphate from Amorphous to Crystalline State

PubMed Central

Haddad, Mathieu; Vali, Hojatollah; Paquette, Jeanne; Guiot, Serge R.

2014-01-01

Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30–50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process. PMID:24586811

Municipal solid waste generation in Kathmandu, Nepal.

PubMed

Dangi, Mohan B; Pretz, Christopher R; Urynowicz, Michael A; Gerow, Kenneth G; Reddy, J M

2011-01-01

Waste stream characteristics must be understood to tackle waste management problems in Kathmandu Metropolitan City (KMC), Nepal. Three-stage stratified cluster sampling was used to evaluate solid waste data collected from 336 households in KMC. This information was combined with data collected regarding waste from restaurants, hotels, schools and streets. The study found that 497.3 g capita(-1) day(-1) of solid waste was generated from households and 48.5, 113.3 and 26.1 kg facility(-1) day(-1) of waste was generated from restaurants, hotels and schools, respectively. Street litter measured 69.3 metric tons day(-1). The average municipal solid waste generation rate was 523.8 metric tons day(-1) or 0.66 kg capita(-1) day(-1) as compared to the 320 metric tons day(-1) reported by the city. The coefficient of correlation between the number of people and the amount of waste produced was 0.94. Key household waste constituents included 71% organic wastes, 12% plastics, 7.5% paper and paper products, 5% dirt and construction debris and 1% hazardous wastes. Although the waste composition varied depending on the source, the composition analysis of waste from restaurants, hotels, schools and streets showed a high percentage of organic wastes. These numbers suggest a greater potential for recovery of organic wastes via composting and there is an opportunity for recycling. Because there is no previous inquiry of this scale in reporting comprehensive municipal solid waste generation in Nepal, this study can be treated as a baseline for other Nepalese municipalities. Copyright © 2010 Elsevier Ltd. All rights reserved.

Thermodynamic approach to the paradox of diamond formation with simultaneous graphite etching in the low pressure synthesis of diamond

NASA Astrophysics Data System (ADS)

Hwang, Nong M.; Yoon, Duk Y.

1996-03-01

In spite of the critical handicap from the thermodynamic point of view, the atomic hydrogen hypothesis is strongly supported by experimental observations of diamond deposition with simultaneous graphite etching. Thermodynamic analysis of the CH system showed that at ˜ 1500 K, carbon solubility in the gas phase is minimal and thus, the equilibrium fraction of solid carbon is maximal. Depending on whether gas phase nucleation takes place or not, the driving force is for deposition or for etching of solid carbon below ˜ 1500 K for the input gas of the typical mixture of 1% CH 499% H 2. The previous observation of etching of the graphite substrate is not expected unless solid carbon precipitated in the gas phase. By rigorous thermodynamic analysis of the previous experimental observations of diamond deposition with simultaneous graphite etching, we suggested that the previous implicit assumption that diamond deposits by an atomic unit should be the weakest point leading to the thermodynamic paradox. The experimental observations could be successfully explained without violating thermodynamics by assuming that the diamond phase had nucleated in the gas phase as fine clusters.

Investigating aquifer contamination and groundwater quality in eastern Terai region of Nepal.

PubMed

Mahato, Sanjay; Mahato, Asmita; Karna, Pankaj Kumar; Balmiki, Nisha

2018-05-21

This study aims at assessing the groundwater quality of the three districts of Eastern Terai region of Nepal viz. Morang, Jhapa, Sunsari using physicochemical characteristics and statistical approach so that possible contamination of water reservoir can be understood. pH, temperature, conductivity, turbidity, color, total dissolved solids, fluorides, ammonia, nitrates, chloride, total hardness, calcium hardness, calcium, magnesium, total alkalinity, iron, manganese, arsenic have to be analyzed to know the present status of groundwater quality. Results revealed that the value of analyzed parameters were within the acceptable limits for drinking water recommended by World Health Organization except for pH, turbidity, ammonia and iron. As per Nepal Drinking Water Quality Standards, fluoride and manganese too were not complying with the permissible limit. Electrical conductivity, total dissolved solids, chloride, total hardness, calcium hardness, manganese, and total alkalinity show good positive correlation with major water quality parameters. Calcium, magnesium, total hardness, calcium hardness and total alkalinity greatly influences total dissolved solids and electrical conductivity. ANOVA, Tukey, and clustering highlight the significance of three districts. Groundwater can be considered safe, but there is always a chance of contamination through chemical wastes in the heavily industrialized area of Morang and Sunsari Industrial corridor.

Coarsening in Solid-liquid Mixtures: Overview of Experiments on Shuttle and ISS

NASA Technical Reports Server (NTRS)

Duval, Walter M. B.; Hawersaat, Robert W.; Lorik, T.; Thompson, J.; Gulsoy, B.; Voorhees, P. W.

2013-01-01

The microgravity environment on the Shuttle and the International Space Station (ISS) provides the ideal condition to perform experiments on Coarsening in Solid-Liquid Mixtures (CSLM) as deleterious effects such as particle sedimentation and buoyancy-induced convection are suppressed. For an ideal system such as Lead-Tin in which all the thermophysical properties are known, the initial condition in microgravity of randomly dispersed particles with local clustering of solid Tin in eutectic liquid Lead-Tin matrix, permitted kinetic studies of competitive particle growth for a range of volume fractions. Verification that the quenching phase of the experiment had negligible effect of the spatial distribution of particles is shown through the computational solution of the dynamical equations of motion, thus insuring quench-free effects from the coarsened microstructure measurements. The low volume fraction experiments conducted on the Shuttle showed agreement with transient Ostwald ripening theory, and the steady-state requirement of LSW theory was not achieved. More recent experiments conducted on ISS with higher volume fractions have achieved steady-state condition and show that the kinetics follows the classical diffusion limited particle coarsening prediction and the measured 3D particle size distribution becomes broader as predicted from theory.

Accessing the dark exciton spin in deterministic quantum-dot microlenses

NASA Astrophysics Data System (ADS)

Heindel, Tobias; Thoma, Alexander; Schwartz, Ido; Schmidgall, Emma R.; Gantz, Liron; Cogan, Dan; Strauß, Max; Schnauber, Peter; Gschrey, Manuel; Schulze, Jan-Hindrik; Strittmatter, Andre; Rodt, Sven; Gershoni, David; Reitzenstein, Stephan

2017-12-01

The dark exciton state in semiconductor quantum dots (QDs) constitutes a long-lived solid-state qubit which has the potential to play an important role in implementations of solid-state-based quantum information architectures. In this work, we exploit deterministically fabricated QD microlenses which promise enhanced photon extraction, to optically prepare and read out the dark exciton spin and observe its coherent precession. The optical access to the dark exciton is provided via spin-blockaded metastable biexciton states acting as heralding states, which are identified by deploying polarization-sensitive spectroscopy as well as time-resolved photon cross-correlation experiments. Our experiments reveal a spin-precession period of the dark exciton of (0.82 ± 0.01) ns corresponding to a fine-structure splitting of (5.0 ± 0.7) μeV between its eigenstates |↑ ⇑ ±↓ ⇓ ⟩. By exploiting microlenses deterministically fabricated above pre-selected QDs, our work demonstrates the possibility to scale up implementations of quantum information processing schemes using the QD-confined dark exciton spin qubit, such as the generation of photonic cluster states or the realization of a solid-state-based quantum memory.

Computer-assisted cytologic diagnosis in pancreatic FNA: An application of neural networks to image analysis.

PubMed

Momeni-Boroujeni, Amir; Yousefi, Elham; Somma, Jonathan

2017-12-01

Fine-needle aspiration (FNA) biopsy is an accurate method for the diagnosis of solid pancreatic masses. However, a significant number of cases still pose a diagnostic challenge. The authors have attempted to design a computer model to aid in the diagnosis of these biopsies. Images were captured of cell clusters on ThinPrep slides from 75 pancreatic FNA cases (20 malignant, 24 benign, and 31 atypical). A K-means clustering algorithm was used to segment the cell clusters into separable regions of interest before extracting features similar to those used for cytomorphologic assessment. A multilayer perceptron neural network (MNN) was trained and then tested for its ability to distinguish benign from malignant cases. A total of 277 images of cell clusters were obtained. K-means clustering identified 68,301 possible regions of interest overall. Features such as contour, perimeter, and area were found to be significantly different between malignant and benign images (P <.05). The MNN was 100% accurate for benign and malignant categories. The model's predictions from the atypical data set were 77% accurate. The results of the current study demonstrate that computer models can be used successfully to distinguish benign from malignant pancreatic cytology. The fact that the model can categorize atypical cases into benign or malignant with 77% accuracy highlights the great potential of this technology. Although further study is warranted to validate its clinical applications in pancreatic and perhaps other areas of cytology as well, the potential for improved patient outcomes using MNN for image analysis in pathology is significant. Cancer Cytopathol 2017;125:926-33. © 2017 American Cancer Society. © 2017 American Cancer Society.

A two-stage model of fracture of rocks

USGS Publications Warehouse

Kuksenko, V.; Tomilin, N.; Damaskinskaya, E.; Lockner, D.

1996-01-01

In this paper we propose a two-stage model of rock fracture. In the first stage, cracks or local regions of failure are uncorrelated occur randomly throughout the rock in response to loading of pre-existing flaws. As damage accumulates in the rock, there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop. Based on statistical arguments, a critical density of damage will occur where clusters of flaws become large enough to lead to larger-scale failure of the rock (stage two). While crack interaction and cooperative failure is expected to occur within clusters of closely spaced cracks, the initial development of clusters is predicted based on the random variation in pre-existing Saw populations. Thus the onset of the unstable second stage in the model can be computed from the generation of random, uncorrelated damage. The proposed model incorporates notions of the kinetic (and therefore time-dependent) nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation. The advantage offered by this model is that its salient features are valid for fracture processes occurring over a wide range of scales including earthquake processes. A notion of the rank of fracture (fracture size) is introduced, and criteria are presented for both fracture nucleation and the transition of the failure process from one scale to another.

The energy landscape of glassy dynamics on the amorphous hafnium diboride surface

NASA Astrophysics Data System (ADS)

Nguyen, Duc; Mallek, Justin; Cloud, Andrew N.; Abelson, John R.; Girolami, Gregory S.; Lyding, Joseph; Gruebele, Martin

2014-11-01

Direct visualization of the dynamics of structural glasses and amorphous solids on the sub-nanometer scale provides rich information unavailable from bulk or conventional single molecule techniques. We study the surface of hafnium diboride, a conductive ultrahigh temperature ceramic material that can be grown in amorphous films. Our scanning tunneling movies have a second-to-hour dynamic range and single-point current measurements extend that to the millisecond-to-minute time scale. On the a-HfB2 glass surface, two-state hopping of 1-2 nm diameter cooperatively rearranging regions or "clusters" occurs from sub-milliseconds to hours. We characterize individual clusters in detail through high-resolution (<0.5 nm) imaging, scanning tunneling spectroscopy and voltage modulation, ruling out individual atoms, diffusing adsorbates, or pinned charges as the origin of the observed two-state hopping. Smaller clusters are more likely to hop, larger ones are more likely to be immobile. HfB2 has a very high bulk glass transition temperature Tg, and we observe no three-state hopping or sequential two-state hopping previously seen on lower Tg glass surfaces. The electronic density of states of clusters does not change when they hop up or down, allowing us to calibrate an accurate relative z-axis scale. By directly measuring and histogramming single cluster vertical displacements, we can reconstruct the local free energy landscape of individual clusters, complete with activation barrier height, a reaction coordinate in nanometers, and the shape of the free energy landscape basins between which hopping occurs. The experimental images are consistent with the compact shape of α-relaxors predicted by random first order transition theory, whereas the rapid hopping rate, even taking less confined motion at the surface into account, is consistent with β-relaxations. We make a proposal of how "mixed" features can show up in surface dynamics of glasses.

Three-Dimensional Modeling of Fracture Clusters in Geothermal Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghassemi, Ahmad

The objective of this is to develop a 3-D numerical model for simulating mode I, II, and III (tensile, shear, and out-of-plane) propagation of multiple fractures and fracture clusters to accurately predict geothermal reservoir stimulation using the virtual multi-dimensional internal bond (VMIB). Effective development of enhanced geothermal systems can significantly benefit from improved modeling of hydraulic fracturing. In geothermal reservoirs, where the temperature can reach or exceed 350oC, thermal and poro-mechanical processes play an important role in fracture initiation and propagation. In this project hydraulic fracturing of hot subsurface rock mass will be numerically modeled by extending the virtual multiplemore » internal bond theory and implementing it in a finite element code, WARP3D, a three-dimensional finite element code for solid mechanics. The new constitutive model along with the poro-thermoelastic computational algorithms will allow modeling the initiation and propagation of clusters of fractures, and extension of pre-existing fractures. The work will enable the industry to realistically model stimulation of geothermal reservoirs. The project addresses the Geothermal Technologies Office objective of accurately predicting geothermal reservoir stimulation (GTO technology priority item). The project goal will be attained by: (i) development of the VMIB method for application to 3D analysis of fracture clusters; (ii) development of poro- and thermoelastic material sub-routines for use in 3D finite element code WARP3D; (iii) implementation of VMIB and the new material routines in WARP3D to enable simulation of clusters of fractures while accounting for the effects of the pore pressure, thermal stress and inelastic deformation; (iv) simulation of 3D fracture propagation and coalescence and formation of clusters, and comparison with laboratory compression tests; and (v) application of the model to interpretation of injection experiments (planned by our industrial partner) with reference to the impact of the variations in injection rate and temperature, rock properties, and in-situ stress.« less

Multifunctional Metal-Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters.

PubMed

Litvinova, Yulia M; Gayfulin, Yakov M; Kovalenko, Konstantin A; Samsonenko, Denis G; van Leusen, Jan; Korolkov, Ilya V; Fedin, Vladimir P; Mironov, Yuri V

2018-02-19

The redox-active rhenium octahedral cluster unit [Re 6 Se 8 (CN) 6 ] 4- was combined with Gd 3+ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H 2 O) 3 } 2 (L)Re 6 Se 8 (CN) 6 ]·nH 2 O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H 2 O) 3 } 2 (L)] 4+ are connected by [Re 6 Se 8 (CN) 6 ] 4- clusters. Frameworks contain spacious channels filled with H 2 O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO 2 uptake and remarkable CO 2 /N 2 selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br 2 , yielding dark-green powders of [{Gd(H 2 O) 3 } 2 (L)Re 6 Se 8 (CN) 6 ]Br·nH 2 O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br - leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.

Mesoscale energy deposition footprint model for kiloelectronvolt cluster bombardment of solids.

PubMed

Russo, Michael F; Garrison, Barbara J

2006-10-15

Molecular dynamics simulations have been performed to model 5-keV C60 and Au3 projectile bombardment of an amorphous water substrate. The goal is to obtain detailed insights into the dynamics of motion in order to develop a straightforward and less computationally demanding model of the process of ejection. The molecular dynamics results provide the basis for the mesoscale energy deposition footprint model. This model provides a method for predicting relative yields based on information from less than 1 ps of simulation time.

A three-dimensional structured/unstructured hybrid Navier-Stokes method for turbine blade rows

NASA Technical Reports Server (NTRS)

Tsung, F.-L.; Loellbach, J.; Kwon, O.; Hah, C.

1994-01-01

A three-dimensional viscous structured/unstructured hybrid scheme has been developed for numerical computation of high Reynolds number turbomachinery flows. The procedure allows an efficient structured solver to be employed in the densely clustered, high aspect-ratio grid around the viscous regions near solid surfaces, while employing an unstructured solver elsewhere in the flow domain to add flexibility in mesh generation. Test results for an inviscid flow over an external transonic wing and a Navier-Stokes flow for an internal annular cascade are presented.

DOE Office of Scientific and Technical Information (OSTI.GOV)

ALAM,TODD M.

Monte Carlo simulations of phosphate tetrahedron connectivity distributions in alkali and alkaline earth phosphate glasses are reported. By utilizing a discrete bond model, the distribution of next-nearest neighbor connectivities between phosphate polyhedron for random, alternating and clustering bonding scenarios was evaluated as a function of the relative bond energy difference. The simulated distributions are compared to experimentally observed connectivities reported for solid-state two-dimensional exchange and double-quantum NMR experiments of phosphate glasses. These Monte Carlo simulations demonstrate that the polyhedron connectivity is best described by a random distribution in lithium phosphate and calcium phosphate glasses.

Improving the stability of subnano-MoO3/meso-SiO2 catalyst through amino-functionalization

NASA Astrophysics Data System (ADS)

Wang, Jiasheng; Wu, Wenpei; Yang, Qianfan; Wang, Wan-Hui; Bao, Ming

Subnano-MoO3 clusters (below 1nm) have excellent catalytic activity on oxidative desulfurization (ODS). However, the stability is not very satisfactory due to the leaching of MoO3 during the reaction. To enhance the stability, here we developed a method by grafting NH2 to silica. NH2 could form coordination bond with MoO3, as proved by solid state 1H NMR, which can prevent MoO3 from leaching and thus significantly enhance the stability.

Hydrothermal Synthesis of Nanostructured Vanadium Oxides

PubMed Central

Livage, Jacques

2010-01-01

A wide range of vanadium oxides have been obtained via the hydrothermal treatment of aqueous V(V) solutions. They exhibit a large variety of nanostructures ranging from molecular clusters to 1D and 2D layered compounds. Nanotubes are obtained via a self-rolling process while amazing morphologies such as nano-spheres, nano-flowers and even nano-urchins are formed via the self-assembling of nano-particles. This paper provides some correlation between the molecular structure of precursors in the solution and the nanostructure of the solid phases obtained by hydrothermal treatment. PMID:28883325

A High Performance Computing Approach to the Simulation of Fluid Solid Interaction Problems with Rigid and Flexible Components (Open Access Author’s Manuscript)

DTIC Science & Technology

2014-08-01

searchrequired for SPH are described in Sect. 3. Section 4 contains aperformance analysis of the algorithm using Kepler -type GPUcards. 2. Numerical...generation of Kepler architecture, code nameGK104, which is also implemented in Tesla K10. The Keplerarchitecture relies on a Graphics Processing Cluster (GPC...lat-ter is 512 KB large and has a bandwidth of 512 B/clockcycle. Constant memory (read only per grid): 48 KB per Kepler SM.Used to hold constants

Experimental research of phase transitions in a melt of high-purity aluminum

NASA Astrophysics Data System (ADS)

Vorontsov, V. B.; Pershin, V. K.

2017-12-01

This scientific work is devoted to the studying of the genetic connection structures of solid and liquid phases. In this paper Fourier analysis of acoustic emission (AE) signals accompanying heating of high purity aluminum from the melting point up to 860 °C was performed. The experimental data allowed to follow the dynamics of disorder zones in the melt with increasing melt temperature up to their complete destruction. The presented results of spectral analysis of the signals were analyzed from the standpoint of the theory of cluster melting metals.

Classical vs. non-classical pathways of mineral formation (Invited)

NASA Astrophysics Data System (ADS)

De Yoreo, J. J.

2013-12-01

Recent chemical analyses, microscopy studies and computer simulations suggest many minerals nucleate through aggregation of pre-nucleation clusters and grow by particle-mediated processes that involve amorphous or disordered precursors. Still other analyses, both experimental and computational, conclude that even simple mineral systems like calcium carbonate form via a barrier-free process of liquid-liquid separation, which is followed by dehydration of the ion-rich phase to form the solid products. However, careful measurements of calcite nucleation rates on a variety of ionized surfaces give results that are in complete agreement with the expectations of classical nucleation theory, in which clusters growing through ion-by-ion addition overcome a free energy barrier through the natural microscopic density fluctuations of the system. Here the challenge of integrating these seemingly disparate observations and analyses into a coherent picture of mineral formation is addressed by considering the energy barriers to calcite formation predicted by the classical theory and the changes in those barriers brought about by the introduction of interfaces and clusters, both stable and metastable. Results from a suite of in situ TEM, AFM, and optical experiments combined with simulations are used to illustrate the conclusions. The analyses show that the expected barrier to homogeneous calcite nucleation is prohibitive even at concentrations exceeding the solubility limit of amorphous calcium carbonate. However, as demonstrated by experiments on self-assembled monolayers, the introduction of surfaces that moderately decrease the interfacial energy associated with the forming nucleus can reduce the magnitude of the barrier to a level that is easily surmounted under typical laboratory conditions. In the absence of such surfaces, experiments that proceed by continually increasing supersaturation with time can easily by-pass direct nucleation of calcite and open up pathways through all other solid phases, as well as dense liquid phases associated with a spinodal. Simulations predict that this phase boundary lies within the region of the calcium carbonate - water phase diagram accessible at room temperature. AFM and TEM analyses of other mineral systems, particularly calcium phosphate, suggest cluster aggregation can play important roles both in modifying barriers and in biasing pathways towards or away from amorphous phases. Most importantly, analysis of the energetic changes shows that barriers are only reduced if the clusters are metastable relative to the free ions and that the reduction is naturally accompanied by a bias towards formation of amorphous precursors. Finally, results from in situ TEM observations of nanoparticle interactions are used to understand the mechanisms controlling particle-mediated growth following formation of primary nuclei of either crystalline phases or disordered precursors. Measurements of the particle speeds and accelerations are used to estimate the magnitude of the attractive potential that drives particle-particle aggregation.

Iron-Rhodium and Iron-Iridium Mixed-Metal Nitrido-Carbonyl Clusters. Synthesis, Characterization, Redox Properties, and Solid-State Structure of the Octahedral Clusters [Fe(5)RhN(CO)(15)](2)(-), [Fe(5)IrN(CO)(15)](2)(-), and [Fe(4)Rh(2)N(CO)(15)](-). Infrared and Nuclear Magnetic Resonance Spectroscopic Studies on the Interstitial Nitride.

PubMed

Della Pergola, Roberto; Cinquantini, Arnaldo; Diana, Eliano; Garlaschelli, Luigi; Laschi, Franco; Luzzini, Paola; Manassero, Mario; Repossi, Andrea; Sansoni, Mirella; Stanghellini, Pier Luigi; Zanello, Piero

1997-08-13

The cluster [Fe(5)RhN(CO)(15)](2)(-) was synthesized in 40% yield from [Fe(4)N(CO)(12)](-) and [Rh(CO)(4)](-) in refluxing tetrahydrofuran, whereas the analogous anion [Fe(5)IrN(CO)(15)](2)(-) was prepared in CH(3)CN at room temperature from [Fe(6)N(CO)(15)](3)(-) and [Ir(C(8)H(14))(2)Cl](2); the yields are higher than 60%. The monoanion [Fe(4)Rh(2)N(CO)(15)](-) was obtained in 70% yield from [Fe(5)RhN(CO)(15)](2)(-) and hydrated RhCl(3). The solid-state structures of the three anions were determined on their [PPh(4)](+) salts: the six metal atoms are arranged in octahedral cages and are coordinated to 3 edge-bridging and 12 terminal carbonyl ligands and to a &mgr;(6)-N ligand. The Rh and Ir atoms have less terminal COs than Fe, in order to equalize the excess electrons at the d(9) metal centers. The two rhodium atoms in [Fe(4)Rh(2)N(CO)(15)](-) are directly bound. The (15)N NMR spectra of the three compounds have been recorded; the signals of the nitride ligands were found at delta = 514 ppm for the dianions and 470 ppm for [Fe(4)Rh(2)N(CO)(15)](-); any group 9 atom shifts the resonance of nitrogen to higher fields. The coupling constants J((15)N-(103)Rh) are 8-9 Hz. The vibrational patterns of the metal cores have been interpreted on the basis of an idealized M(6) octahedral arrangement, subsequently modified by the perturbations given by different atomic masses and M-M stretching force constants. The motions of the nitrogen are related to the idealized symmetry of the cage; the M-N force constant values depend on the type of metal and on the charge of the anion. The dianions [Fe(5)MN(CO)(15)](2)(-) can be electrochemically oxidized at -20 degrees C to their short-lived monoanions, which can be characterized by EPR spectroscopy. In contrast, the cluster [Fe(4)Rh(2)N(CO)(15)](-) undergoes a single-step 2-electron reduction to the partially stable trianion [Fe(4)Rh(2)N(CO)(15)](3)(-), which was also characterized by EPR spectroscopy. The Fe-Rh nitride clusters are active catalysts for the hydroformylation of 1-pentene, but display low selectivity (35-65%) in n-hexanal and are demolished under catalytic conditions.

Analysis of long-term water quality for effective river health monitoring in peri-urban landscapes--a case study of the Hawkesbury-Nepean river system in NSW, Australia.

PubMed

Pinto, U; Maheshwari, B L; Ollerton, R L

2013-06-01

The Hawkesbury-Nepean River (HNR) system in South-Eastern Australia is the main source of water supply for the Sydney Metropolitan area and is one of the more complex river systems due to the influence of urbanisation and other activities in the peri-urban landscape through which it flows. The long-term monitoring of river water quality is likely to suffer from data gaps due to funding cuts, changes in priority and related reasons. Nevertheless, we need to assess river health based on the available information. In this study, we demonstrated how the Factor Analysis (FA), Hierarchical Agglomerative Cluster Analysis (HACA) and Trend Analysis (TA) can be applied to evaluate long-term historic data sets. Six water quality parameters, viz., temperature, chlorophyll-a, dissolved oxygen, oxides of nitrogen, suspended solids and reactive silicates, measured at weekly intervals between 1985 and 2008 at 12 monitoring stations located along the 300 km length of the HNR system were evaluated to understand the human and natural influences on the river system in a peri-urban landscape. The application of FA extracted three latent factors which explained more than 70 % of the total variance of the data and related to the 'bio-geographical', 'natural' and 'nutrient pollutant' dimensions of the HNR system. The bio-geographical and nutrient pollution factors more likely related to the direct influence of changes and activities of peri-urban natures and accounted for approximately 50 % of variability in water quality. The application of HACA indicated two major clusters representing clean and polluted zones of the river. On the spatial scale, one cluster was represented by the upper and lower sections of the river (clean zone) and accounted for approximately 158 km of the river. The other cluster was represented by the middle section (polluted zone) with a length of approximately 98 km. Trend Analysis indicated how the point sources influence river water quality on spatio-temporal scales, taking into account the various effects of nutrient and other pollutant loads from sewerage effluents, agriculture and other point and non-point sources along the river and major tributaries of the HNR. Over the past 26 years, water temperature has significantly increased while suspended solids have significantly decreased (p < 0.05). The analysis of water quality data through FA, HACA and TA helped to characterise the key sections and cluster the key water quality variables of the HNR system. The insights gained from this study have the potential to improve the effectiveness of river health-monitoring programs in terms of cost, time and effort, particularly in a peri-urban context.

An aggregation-volume-bias Monte Carlo investigation on the condensation of a Lennard-Jones vapor below the triple point and crystal nucleation in cluster systems: an in-depth evaluation of the classical nucleation theory.

PubMed

Chen, Bin; Kim, Hyunmi; Keasler, Samuel J; Nellas, Ricky B

2008-04-03

The aggregation-volume-bias Monte Carlo based simulation technique, which has led to our recent success in vapor-liquid nucleation research, was extended to the study of crystal nucleation processes. In contrast to conventional bulk-phase techniques, this method deals with crystal nucleation events in cluster systems. This approach was applied to the crystal nucleation of Lennard-Jonesium under a wide range of undercooling conditions from 35% to 13% below the triple point. It was found that crystal nucleation in these model clusters proceeds initially via a vapor-liquid like aggregation followed by the formation of crystals inside the aggregates. The separation of these two stages of nucleation is distinct except at deeper undercooling conditions where the crystal nucleation barrier was found to diminish. The simulation results obtained for these two nucleation steps are separately compared to the classical nucleation theory (CNT). For the vapor-liquid nucleation step, the CNT was shown to provide a reasonable description of the critical cluster size but overestimate the barrier heights, consistent with previous simulation studies. On the contrary, for the crystal nucleation step, nearly perfect agreement with the barrier heights was found between the simulations and the CNT. For the critical cluster size, the comparison is more difficult as the simulation data were found to be sensitive to the definition of the solid cluster, but a stringent criterion and lower undercooling conditions generally lead to results closer with the CNT. Additional simulations at undercooling conditions of 40% or above indicate a nearly barrierless transition from the liquid to crystalline-like structure for sufficiently large clusters, which leads to further departure of the barrier height predicted by the CNT from the simulation data for the aggregation step. This is consistent with the latest experimental results on argon that show an unusually large underestimation of the nucleation rate by the CNT toward deep undercooling conditions.

Cluster analysis of phytoplankton data collected from the National Stream Quality Accounting Network in the Tennessee River basin, 1974-81

USGS Publications Warehouse

Stephens, D.W.; Wangsgard, J.B.

1988-01-01

A computer program, Numerical Taxonomy System of Multivariate Statistical Programs (NTSYS), was used with interfacing software to perform cluster analyses of phytoplankton data stored in the biological files of the U.S. Geological Survey. The NTSYS software performs various types of statistical analyses and is capable of handling a large matrix of data. Cluster analyses were done on phytoplankton data collected from 1974 to 1981 at four national Stream Quality Accounting Network stations in the Tennessee River basin. Analysis of the changes in clusters of phytoplankton genera indicated possible changes in the water quality of the French Broad River near Knoxville, Tennessee. At this station, the most common diatom groups indicated a shift in dominant forms with some of the less common diatoms being replaced by green and blue-green algae. There was a reduction in genera variability between 1974-77 and 1979-81 sampling periods. Statistical analysis of chloride and dissolved solids confirmed that concentrations of these substances were smaller in 1974-77 than in 1979-81. At Pickwick Landing Dam, the furthest downstream station used in the study, there was an increase in the number of genera of ' rare ' organisms with time. The appearance of two groups of green and blue-green algae indicated that an increase in temperature or nutrient concentrations occurred from 1974 to 1981, but this could not be confirmed using available water quality data. Associations of genera forming the phytoplankton communities at three stations on the Tennessee River were found to be seasonal. Nodal analysis of combined data from all four stations used in the study did not identify any seasonal or temporal patterns during 1974-81. Cluster analysis using the NYSYS programs was effective in reducing the large phytoplankton data set to a manageable size and provided considerable insight into the structure of phytoplankton communities in the Tennessee River basin. Problems encountered using cluster analysis were the subjectivity introduced in the definition of meaningful clusters, and the lack of taxonomic identification to the species level. (Author 's abstract)

Design of hydrophobic polyoxometalate hybrid assemblies beyond surfactant encapsulation.

PubMed

Song, Yu-Fei; McMillan, Nicola; Long, De-Liang; Thiel, Johannes; Ding, Yulong; Chen, Haisheng; Gadegaard, Nikolaj; Cronin, Leroy

2008-01-01

Grafting of C-6, C-16 and C-18 alkyl chains onto the hydrophilic Mn-Anderson clusters (compounds 2-4) has been achieved. Exchange of the tetrabutyl ammonium (TBA) with dimethyldioctadecyl ammonium (DMDOA) results in the formation of new polyoxometalate (POM) assemblies (compounds 5-6), in which the POM cores are covalently functionalized by hydrophilic alkyl-chains and enclosed by surfactant of DMDOABr. As a result, we have been able to design and synthesize POM-containing hydrophobic materials beyond surfactant encapsulation. In solid state, scanning electron and transmission electron microscopy (SEM and TEM) studies of the TBA salts of compounds 3 and 4 show highly ordered, uniform, reproducible assemblies with unique segmented rodlike morphology. SEM and TEM studies of the DMDOA salts of compounds 5 and 6 show that they form spherical and sea urchin 3D objects in different solvent systems. In solution, the physical properties of compound 5 and 6 (combination of surfactant-encapsulated cluster (SEC) and surface-grafted cluster (SGC)) show a liquid-to-gel phase transition in pure chloroform below 0 degrees C, which are much lower than other reported SECs. By utilizing light scattering measurements, the nanoparticle size for compounds 5 and 6 were measured at 5 degrees C and 30 degrees C, respectively. Other physical properties including differential scanning calorimetry have been reported.

Ensemble averaged structure–function relationship for nanocrystals: effective superparamagnetic Fe clusters with catalytically active Pt skin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petkov, Valeri; Prasai, Binay; Shastri, Sarvjit

2017-09-12

Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure–function relationship for metallic NCs is to be quantified precisely. In this paper, we address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction,more » respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Lastly, we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure–function relationship for the increasingly complex metallic NCs explored for practical applications.« less

Applicability of Hydrologic Landscapes for Model Calibration ...

EPA Pesticide Factsheets

The Pacific Northwest Hydrologic Landscapes (PNW HL) at the assessment unit scale has provided a solid conceptual classification framework to relate and transfer hydrologically meaningful information between watersheds without access to streamflow time series. A collection of techniques were applied to the HL assessment unit composition in watersheds across the Pacific Northwest to aggregate the hydrologic behavior of the Hydrologic Landscapes from the assessment unit scale to the watershed scale. This non-trivial solution both emphasizes HL classifications within the watershed that provide that majority of moisture surplus/deficit and considers the relative position (upstream vs. downstream) of these HL classifications. A clustering algorithm was applied to the HL-based characterization of assessment units within 185 watersheds to help organize watersheds into nine classes hypothesized to have similar hydrologic behavior. The HL-based classes were used to organize and describe hydrologic behavior information about watershed classes and both predictions and validations were independently performed with regard to the general magnitude of six hydroclimatic signature values. A second cluster analysis was then performed using the independently calculated signature values as similarity metrics, and it was found that the six signature clusters showed substantial overlap in watershed class membership to those in the HL-based classes. One hypothesis set forward from thi

Formation, dissolution and properties of surface nanobubbles

NASA Astrophysics Data System (ADS)

Che, Zhizhao; Theodorakis, Panagiotis E.

2017-02-01

Surface nanobubbles are stable gaseous phases in liquids that form on solid substrates. While their existence has been confirmed, there are many open questions related to their formation and dissolution processes along with their structures and properties, which are difficult to investigate experimentally. To address these issues, we carried out molecular dynamics simulations based on atomistic force fields for systems comprised of water, air (N2 and O2), and a Highly Oriented Pyrolytic Graphite (HOPG) substrate. Our results provide insights into the formation/dissolution mechanisms of nanobubbles and estimates for their density, contact angle, and surface tension. We found that the formation of nanobubbles is driven by an initial nucleation process of air molecules and the subsequent coalescence of the formed air clusters. The clusters form favorably on the substrate, which provides an enhanced stability to the clusters. In contrast, nanobubbles formed in the bulk either move randomly to the substrate and spread or move to the water--air surface and pop immediately. Moreover, nanobubbles consist of a condensed gaseous phase with a surface tension smaller than that of an equivalent system under atmospheric conditions, and contact angles larger than those in the equivalent nanodroplet case. We anticipate that this study will provide useful insights into the physics of nanobubbles and will stimulate further research in the field by using all-atom simulations.

Imprinted gene expression in fetal growth and development.

PubMed

Lambertini, L; Marsit, C J; Sharma, P; Maccani, M; Ma, Y; Hu, J; Chen, J

2012-06-01

Experimental studies showed that genomic imprinting is fundamental in fetoplacental development by timely regulating the expression of the imprinted genes to overlook a set of events determining placenta implantation, growth and embryogenesis. We examined the expression profile of 22 imprinted genes which have been linked to pregnancy abnormalities that may ultimately influence childhood development. The study was conducted in a subset of 106 placenta samples, overrepresented with small and large for gestational age cases, from the Rhode Island Child Health Study. We investigated associations between imprinted gene expression and three fetal development parameters: newborn head circumference, birth weight, and size for gestational age. Results from our investigation show that the maternally imprinted/paternally expressed gene ZNF331 inversely associates with each parameter to drive smaller fetal size, while paternally imprinted/maternally expressed gene SLC22A18 directly associates with the newborn head circumference promoting growth. Multidimensional Scaling analysis revealed two clusters within the 22 imprinted genes which are independently associated with fetoplacental development. Our data suggest that cluster 1 genes work by assuring cell growth and tissue development, while cluster 2 genes act by coordinating these processes. Results from this epidemiologic study offer solid support for the key role of imprinting in fetoplacental development. Copyright © 2012 Elsevier Ltd. All rights reserved.

Isostructural solid-solid phase transition in monolayers of soft core-shell particles at fluid interfaces: structure and mechanics.

PubMed

Rey, Marcel; Fernández-Rodríguez, Miguel Ángel; Steinacher, Mathias; Scheidegger, Laura; Geisel, Karen; Richtering, Walter; Squires, Todd M; Isa, Lucio

2016-04-21

We have studied the complete two-dimensional phase diagram of a core-shell microgel-laden fluid interface by synchronizing its compression with the deposition of the interfacial monolayer. Applying a new protocol, different positions on the substrate correspond to different values of the monolayer surface pressure and specific area. Analyzing the microstructure of the deposited monolayers, we discovered an isostructural solid-solid phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases corresponded to shell-shell and core-core inter-particle contacts, respectively; with increasing surface pressure the former mechanically failed enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore measured the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer. The interfaces always showed a strong elastic response, with a dip in the shear elastic modulus in correspondence with the melting of the shell-shell phase, followed by a steep increase upon the formation of a percolating network of the core-core contacts. These results demonstrate that the core-shell nature of the particles leads to a rich mechanical and structural behavior that can be externally tuned by compressing the interface, indicating new routes for applications, e.g. in surface patterning or emulsion stabilization.

Growth and melting of droplets in cold vapors.

PubMed

L'Hermite, Jean-Marc

2009-11-01

A model has been developed to investigate the growth of droplets in a supersaturated cold vapor taking into account their possible solid-liquid phase transition. It is shown that the solid-liquid phase transition is nontrivially coupled, through the energy released in attachment, to the nucleation process. The model is based on the one developed by J. Feder, K. C. Russell, J. Lothe, and G. M. Pound [Adv. Phys. 15, 111 (1966)], where the nucleation process is described as a thermal diffusion motion in a two-dimensional field of force given by the derivatives of a free-energy surface. The additional dimension accounts for droplets internal energy. The solid-liquid phase transition is introduced through a bimodal internal energy distribution in a Gaussian approximation derived from small clusters physics. The coupling between nucleation and melting results in specific nonequilibrium thermodynamical properties, exemplified in the case of water droplets. Analyzing the free-energy landscapes gives an insight into the nucleation dynamics. This landscape can be complex but generally exhibits two paths: the first one can generally be ascribed to the solid state, while the other to the liquid state. Especially at high supersaturation, the growth in the liquid state is often favored, which is not unexpected since in a supersaturated vapor the droplets can stand higher internal energy than at equilibrium. From a given critical temperature that is noticeably lower than the bulk melting temperature, nucleation may end in very large liquid droplets. These features can be qualitatively generalized to systems other than water.

ASA-FTL: An adaptive separation aware flash translation layer for solid state drives

DOE PAGES

Xie, Wei; Chen, Yong; Roth, Philip C

2016-11-03

Here, the flash-memory based Solid State Drive (SSD) presents a promising storage solution for increasingly critical data-intensive applications due to its low latency (high throughput), high bandwidth, and low power consumption. Within an SSD, its Flash Translation Layer (FTL) is responsible for exposing the SSD’s flash memory storage to the computer system as a simple block device. The FTL design is one of the dominant factors determining an SSD’s lifespan and performance. To reduce the garbage collection overhead and deliver better performance, we propose a new, low-cost, adaptive separation-aware flash translation layer (ASA-FTL) that combines sampling, data clustering and selectivemore » caching of recency information to accurately identify and separate hot/cold data while incurring minimal overhead. We use sampling for light-weight identification of separation criteria, and our dedicated selective caching mechanism is designed to save the limited RAM resource in contemporary SSDs. Using simulations of ASA-FTL with both real-world and synthetic workloads, we have shown that our proposed approach reduces the garbage collection overhead by up to 28% and the overall response time by 15% compared to one of the most advanced existing FTLs. We find that the data clustering using a small sample size provides significant performance benefit while only incurring a very small computation and memory cost. In addition, our evaluation shows that ASA-FTL is able to adapt to the changes in the access pattern of workloads, which is a major advantage comparing to existing fixed data separation methods.« less

Robust Superhydrophobic Carbon Nanotube Film with Lotus Leaf Mimetic Multiscale Hierarchical Structures.

PubMed

Wang, Pengwei; Zhao, Tianyi; Bian, Ruixin; Wang, Guangyan; Liu, Huan

2017-12-26

Superhydrophobic carbon nanotube (CNT) films have demonstrated many fascinating performances in versatile applications, especially for those involving solid/liquid interfacial processes, because of their ability to affect the material/energy transfer at interfaces. Thus, developing superhydrophobic CNTs has attracted extensive research interests in the past decades, and it could be achieved either by surface coating of low-free energy materials or by constructing micro/nanohierarchical structures via various complicated processes. So far, developing a simple approach to fabricate stable superhydrophobic CNTs remains a challenge because the capillary force induced coalescence frequently happens when interacting with liquid. Herein, drawing inspirations from the lotus leaf, we proposed a simple one-step chemical vapor deposition approach with programmable controlled gas flow to directly fabricate a CNT film with rather stable superhydrophobicity, which can effectively prevent even small water droplets from permeating into the film. The robust superhydrophobicity was attributable to typical lotus-leaf-like micro/nanoscale hierarchical surface structures of the CNT film, where many microscale clusters composed of entangled nanotubes randomly protrude out of the under-layer aligned nanotubes. Consequently, dual-scale air pockets were trapped within each microscale CNT cluster and between, which could largely reduce the liquid/solid interface, leading to a Cassie state. Moreover, the superhydrophobicity of the CNT film showed excellent durability after long time exposure to air and even to corrosive liquids with a wide range of pH values. We envision that the approach developed is advantageous for versatile physicochemical interfacial processes, such as drag reduction, electrochemical catalysis, anti-icing, and biosensors.

Poly(vinylpyrrolidone) supported copper nanoclusters: glutathione enhanced blue photoluminescence for application in phosphor converted light emitting devices

NASA Astrophysics Data System (ADS)

Wang, Zhenguang; Susha, Andrei S.; Chen, Bingkun; Reckmeier, Claas; Tomanec, Ondrej; Zboril, Radek; Zhong, Haizheng; Rogach, Andrey L.

2016-03-01

Poly(vinylpyrrolidone) supported Cu nanoclusters were synthesized by reduction of Cu(ii) ions with ascorbic acid in water, and initially showed blue photoluminescence with a quantum yield of 8%. An enhancement of the emission quantum yield has been achieved by treatment of Cu clusters with different electron-rich ligands, with the most pronounced effect (photoluminescence quantum yield of 27%) achieved with glutathione. The bright blue emission of glutathione treated Cu NCs is fully preserved in the solid state powder, which has been combined with commercial green and red phosphors to fabricate down-conversion white light emitting diodes with a high colour rendering index of 92.Poly(vinylpyrrolidone) supported Cu nanoclusters were synthesized by reduction of Cu(ii) ions with ascorbic acid in water, and initially showed blue photoluminescence with a quantum yield of 8%. An enhancement of the emission quantum yield has been achieved by treatment of Cu clusters with different electron-rich ligands, with the most pronounced effect (photoluminescence quantum yield of 27%) achieved with glutathione. The bright blue emission of glutathione treated Cu NCs is fully preserved in the solid state powder, which has been combined with commercial green and red phosphors to fabricate down-conversion white light emitting diodes with a high colour rendering index of 92. Electronic supplementary information (ESI) available: The optical spectra of control experiments for Cu NC synthesis, optimization of the reaction conditions, and spectra for LEDs chips and blue LEDs. See DOI: 10.1039/c6nr00806b

Atomistic Modeling of Cation Diffusion in Transition Metal Perovskites La1-xSrxMnO3+/-δfor Solid Oxide Fuel Cell Cathodes Applications

NASA Astrophysics Data System (ADS)

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane; Sorescu, Dan; Abernathy, Harry

Cation diffusion in La1-xSrxMnO3+/-δ (LSM) and in related perovskite materials play an important role in controlling long term performance and stability of solid oxide fuel cell (SOFCs) cathodes. Due to sluggish rates of cation diffusion and complex coupling between defect chemistry and cation diffusion pathways, currently there is still lack of quantitative theoretical model predictions on cation diffusivity vs. T and P(O2) to describe experimental cation tracer diffusivities. In this work, based on ab initio modeling of LSM defect chemistry and migration barriers of the possible cation diffusion pathways, we assess the rates of A-site and B-site cation diffusion in a wide range of T and P(O2) at x =0.0 and 0.2 for SOFC applications. We demonstrate the active cation diffusion pathways in LSM involve cation defect clusters as cation transport carriers, where reduction in the cation migration barriers, which are governed by the steric effect associated with the metal-oxygen cage in the perovskite lattice, is much greater than the penalty of repulsive interaction in the A-site and B-site cation vacancy clusters, leading to higher cation diffusion rates as compared to those of single cation vacancy hopping mechanisms. The predicted Mn and La/Sr cation self-diffusion coefficients of LSM at at x =0.0 and 0.2 along with their 1/T and P(O2) dependences, are in good agreement with the experimental tracer diffusion coefficients.

Interactions between glycine and amorphous solid water nanoscale films

NASA Astrophysics Data System (ADS)

Tzvetkov, George; Koller, Georg; Netzer, Falko P.

2012-12-01

The interactions of glycine (Gly) with amorphous solid water (ASW) nanolayers (≤ 100 ML), vapor-deposited on single crystalline AlOx surfaces at 100 K, have been investigated by near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K-edge, temperature-programmed thermal desorption (TPD), X-ray photoelectron spectroscopy (XPS), and temperature-dependent work function measurements. Gly-on-ASW, ASW-on-Gly, and Gly on top of ASW-on-Gly ultrathin films have been fabricated. In contrast to the uniform ASW films grown directly on the hydrophilic AlOx, water molecules adsorb on the hydrophobic Gly films in the form of 3D ASW clusters. This leads to significant differences in the NEXAFS and work function data obtained from ASW-on-AlOx and ASW-on-Gly films, respectively. Furthermore, these structural differences influence the chemical state of Gly molecules (neutral vs. zwitterionic) adsorbed on top of ASW films. N1s XPS measurements revealed an increased amount of neutral Gly molecules in the film top-deposited on the ASW-on-Gly structure in comparison to the neutral Gly in the films directly condensed on AlOx or grown on the ASW substrate. H2O TPD spectra demonstrate that the crystallization and desorption processes of ASW are affected in a different way by the Gly layers, top-deposited on to ASW-on-AlOx and ASW-on-Gly films. At the same time, Gly adlayers sink into the ASW film during crystallization/desorption of the latter and land softly on the alumina surface in the form of zwitterionic clusters.

Ab initio investigation of Ti2Al(C,N) solid solutions

NASA Astrophysics Data System (ADS)

Arróyave, Raymundo; Radovic, Miladin

2011-10-01

Mn+1AXn phases (M: early transition metal, A: IIIA- or IVA-group element, X: carbon or nitrogen) are layered ternary compounds that possess both metal- and ceramic-like properties with numerous potential applications in bulk and thin film forms, particularly under high-temperature conditions. In this work, we use the cluster expansion formalism to investigate the energetics of C-N interactions across the entire Ti2AlC-Ti2AlN composition range. It is shown that there is a definite tendency for ordering in the C,N sublattice. However, the molar volume and bulk modulus of the ordered structures found along the Ti2AlC-Ti2AlN composition range show small deviations from the (linear) rule of mixing, indicating that despite the ordering tendencies, the C-N interactions are not strong and the solution becomes disordered at relatively low temperatures. Random solid solutions of Ti2AlC1-xNx are simulated using special quasirandom structures (SQS) with x=0.25, 0.50, and 0.75. The thermodynamic properties of these structures are compared to those of the structures found to belong to the ground state through the cluster expansion approach. It is found that the structural properties of these approximations to random alloys do not deviate significantly from Vegard's law. The trend in the structural parameters of these SQS are found to agree well with available experimental data and the predictions of the bulk modulus suggest a very weak alloying effect—with respect to Vegard's law—on the elastic properties of Ti2AlC1-xNx.

Modeling and simulation of the data communication network at the ASRM Facility

NASA Technical Reports Server (NTRS)

Nirgudkar, R. P.; Moorhead, R. J.; Smith, W. D.

1994-01-01

This paper describes the modeling and simulation of the communication network for the NASA Advanced Solid Rocket Motor (ASRM) facility under construction at Yellow Creek near Luka, Mississippi. Manufacturing, testing, and operations at the ASRM site will be performed in different buildings scattered over an 1800 acre site. These buildings are interconnected through a local area network (LAN), which will contain one logical Fiber Distributed Data Interface (FDDI) ring acting as a backbone for the whole complex. The network contains approximately 700 multi-vendor workstations, 22 multi-vendor workcells, and 3 VAX clusters interconnected via Ethernet and FDDI. The different devices produce appreciably different traffic patterns, each pattern will be highly variable, and some patterns will be very bursty. Most traffic is between the VAX clusters and the other devices. Comdisco's Block Oriented Network Simulator (BONeS) has been used for network simulation. The two primary evaluation parameters used to judge the expected network performance are throughput and delay.

Numerical studies from quantum to macroscopic scales of carbon nanoparticules in hydrogen plasma

NASA Astrophysics Data System (ADS)

Lombardi, Guillaume; Ngandjong, Alain; Mezei, Zsolt; Mougenot, Jonathan; Michau, Armelle; Hassouni, Khaled; Seydou, Mahamadou; Maurel, François

2016-09-01

Dusty plasmas take part in large scientific domains from Universe Science to nanomaterial synthesis processes. They are often generated by growth from molecular precursor. This growth leads to the formation of larger clusters which induce solid germs nucleation. Particle formed are described by an aerosol dynamic taking into account coagulation, molecular deposition and transport processes. These processes are controlled by the elementary particle. So there is a strong coupling between particle dynamics and plasma discharge equilibrium. This study is focused on the development of a multiscale physic and numeric model of hydrogen plasmas and carbon particles around three essential coupled axes to describe the various physical phenomena: (i) Macro/mesoscopic fluid modeling describing in an auto-coherent way, characteristics of the plasma, molecular clusters and aerosol behavior; (ii) the classic molecular dynamics offering a description to the scale molecular of the chains of chemical reactions and the phenomena of aggregation; (iii) the quantum chemistry to establish the activation barriers of the different processes driving the nanopoarticule formation.

Intra-amoeba multiplication induces chemotaxis and biofilm colonization and formation for Legionella.

PubMed

Bigot, Renaud; Bertaux, Joanne; Frere, Jacques; Berjeaud, Jean-Marc

2013-01-01

Legionella pneumophila, a facultative intracellular bacterium, is the causative agent of legionellosis. In the environment this pathogenic bacterium colonizes the biofilms as well as amoebae, which provide a rich environment for the replication of Legionella. When seeded on pre-formed biofilms, L. pneumophila was able to establish and survive and was only found at the surface of the biofilms. Different phenotypes were observed when the L. pneumophila, used to implement pre-formed biofilms or to form mono-species biofilms, were cultivated in a laboratory culture broth or had grown intracellulary within the amoeba. Indeed, the bacteria, which developed within the amoeba, formed clusters when deposited on a solid surface. Moreover, our results demonstrate that multiplication inside the amoeba increased the capacity of L. pneumophila to produce polysaccharides and therefore enhanced its capacity to establish biofilms. Finally, it was shown that the clusters formed by L. pneumophila were probably related to the secretion of a chemotaxis molecular agent.

Intra-Amoeba Multiplication Induces Chemotaxis and Biofilm Colonization and Formation for Legionella

PubMed Central

Bigot, Renaud; Bertaux, Joanne; Frere, Jacques; Berjeaud, Jean-Marc

2013-01-01

Legionella pneumophila, a facultative intracellular bacterium, is the causative agent of legionellosis. In the environment this pathogenic bacterium colonizes the biofilms as well as amoebae, which provide a rich environment for the replication of Legionella. When seeded on pre-formed biofilms, L. pneumophila was able to establish and survive and was only found at the surface of the biofilms. Different phenotypes were observed when the L. pneumophila, used to implement pre-formed biofilms or to form mono-species biofilms, were cultivated in a laboratory culture broth or had grown intracellulary within the amoeba. Indeed, the bacteria, which developed within the amoeba, formed clusters when deposited on a solid surface. Moreover, our results demonstrate that multiplication inside the amoeba increased the capacity of L. pneumophila to produce polysaccharides and therefore enhanced its capacity to establish biofilms. Finally, it was shown that the clusters formed by L. pneumophila were probably related to the secretion of a chemotaxis molecular agent. PMID:24205008

Nickel-aluminum alloy clusters -- structural and dynamical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jellinek, J.; Krissinel, E.B.

1997-08-01

Structural and dynamical properties of mixed Ni{sub n}Al{sub m} alloy clusters mimicked by a many-body potential are studied computationally for all the possible compositions n and m such that n + m = 13. It is shown that the manifold of the usually very large number of the different possible structural forms can be systematized by introducing classes of structures corresponding to the same concentration of the components, geometry and type of the central atom. General definitions of mixing energy and mixing coefficient are introduced, and it is shown that the energy ordering of the structural forms within each classmore » is governed by the mixing coefficient. The peculiarities of the solid-to-liquid-like transition are described as a function of the concentration of the two types of atoms. These peculiarities are correlated with and explained in terms of the energy spectra of the structural forms. Class-dependent features of the dynamics are described and analyzed.« less

Molecular Occupancy of Nanodot Arrays.

PubMed

Cai, Haogang; Wolfenson, Haguy; Depoil, David; Dustin, Michael L; Sheetz, Michael P; Wind, Shalom J

2016-04-26

Single-molecule nanodot arrays, in which a biomolecule of choice (protein, nucleic acid, etc.) is bound to a metallic nanoparticle on a solid substrate, are becoming an increasingly important tool in the study of biomolecular and cellular interactions. We have developed an on-chip measurement protocol to monitor and control the molecular occupancy of nanodots. Arrays of widely spaced nanodots and nanodot clusters were fabricated on glass surfaces by nanolithography and functionalized with fluorescently labeled proteins. The molecular occupancy was determined by monitoring individual fluorophore bleaching events, while accounting for fluorescence quenching effects. We found that the occupancy can be interpreted as a packing problem, and depends on nanodot size and binding ligand concentration, where the latter is easily adjusted to compensate the flexibility of dimension control in nanofabrication. The results are scalable with nanodot cluster size, extending to large area close packed arrays. As an example, the nanoarray platform was used to probe the geometric requirement of T-cell activation at the single-molecule level.

Aggregation in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Meyer, Abigail

Organic light emitting diode (OLED) technology has great potential for becoming a solid state lighting source. However, there are inefficiencies in OLED devices that need to be understood. Since these inefficiencies occur on a nanometer scale there is a need for structural data on this length scale in three dimensions which has been unattainable until now. Local Electron Atom Probe (LEAP), a specific implementation of Atom Probe Tomography (APT), is used in this work to acquire morphology data in three dimensions on a nanometer scale with much better chemical resolution than is previously seen. Before analyzing LEAP data, simulations were used to investigate how detector efficiency, sample size and cluster size affect data analysis which is done using radial distribution functions (RDFs). Data is reconstructed using the LEAP software which provides mass and position data. Two samples were then analyzed, 3% DCM2 in C60 and 2% DCM2 in Alq3. Analysis of both samples indicated little to no clustering was present in this system.

Reactive molecular dynamics simulation of solid nitromethane impact on (010) surfaces induced and nonimpact thermal decomposition.

PubMed

Guo, Feng; Cheng, Xin-lu; Zhang, Hong

2012-04-12

Which is the first step in the decomposition process of nitromethane is a controversial issue, proton dissociation or C-N bond scission. We applied reactive force field (ReaxFF) molecular dynamics to probe the initial decomposition mechanisms of nitromethane. By comparing the impact on (010) surfaces and without impact (only heating) for nitromethane simulations, we found that proton dissociation is the first step of the pyrolysis of nitromethane, and the C-N bond decomposes in the same time scale as in impact simulations, but in the nonimpact simulation, C-N bond dissociation takes place at a later time. At the end of these simulations, a large number of clusters are formed. By analyzing the trajectories, we discussed the role of the hydrogen bond in the initial process of nitromethane decompositions, the intermediates observed in the early time of the simulations, and the formation of clusters that consisted of C-N-C-N chain/ring structures.

Formation of a sodium bicarbonate cluster in the structure of sodium-substituted hydroxyapatite

NASA Astrophysics Data System (ADS)

Tkachenko, M. V.; Kamzin, A. S.

2015-02-01

Ceramic sodium-substituted carbonated hydroxyapatite has been synthesized using the method of the solid-phase reaction in the temperature range of 640-820°C in water vapor. It has been established that substitutions of Ca2+ ions in the cation and anion subsystems with Na+ ions and the PO{4/3-} and OH- groups with CO{3/2-} ions lead to a considerable acceleration of the shrinkage and synthesis of dense ceramics at substantially lower temperatures than in the case of unsubstituted hydroxyapatite. Sintering in water vapor leads to densification of carbonate groups in channel positions, which induces the appearance of orderings of A2 and B2 types (bands with wave numbers 867 and 865 cm-1 in IR spectra, respectively) as well as the protonation of carbonate groups both in A and B sites and the formation of sodium bicarbonate clusters (856 and 859 cm-1) in addition to carbonate ordering of A1 and B1 types (879 and 872 cm-1).

High multiplicity α-particle breakup measurements to study α-condensate states

NASA Astrophysics Data System (ADS)

Bishop, J.; Kokalova, Tz; Freer, M.; Assie, M.; Acosta, L.; Bailey, S.; Cardella, G.; Curtis, N.; De Filippo, E.; Dell'Aquila, D.; De Luca, S.; Francalanza, L.; Gnoffo, B.; Lanzalone, G.; Lombardo, I.; Martorana, N.; Norella, S.; Pagano, A.; Pagano, E. V.; Papa, M.; Pirrone, S.; Politi, G.; Rizzo, F.; Russotto, P.; Quattrocchi, L.; Smith, R.; Stefan, I.; Trifirò, A.; Trimarchì, M.; Verde, G.; Vigilante, M.; Wheldon, C.

2017-06-01

An experiment was performed to investigate α-condensate states via high α-particle multiplicity breakup. The nucleus of interest was 28Si therefore to measure multiplicity 7 particle breakup events, a highly granular detector with a high solid angle coverage was required. For this purpose, the CHIMERA and FARCOS detectors at INFN LNS were employed. Particle identification was achieved through ΔE-E energy loss. The α-particle multiplicity was measured at three beam energies to investigate different excitation regimes in 28Si. At a beam energy where the energy is sufficient to provide the 7 α-particles with enough energy to be identified using the ΔE-E method, multiplicity 7 events can be seen. Given these high multiplicity events, the particles can be reconstructed to investigate the breakup of α-condensate states. Analysing the decay paths of these states can elucidate whether the state of interest corresponds to a non-cluster, clustered or condensed state.

Enhancing radiation tolerance by controlling defect mobility and migration pathways in multicomponent single-phase alloys

DOE PAGES

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun; ...

2016-12-15

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhancedmore » swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. Finally, the results suggest design criteria for next generation radiation tolerant structural alloys.« less

Clustering of particles and pathogens within evaporating drops

NASA Astrophysics Data System (ADS)

Park, Jaebum; Kim, Ho-Young

2017-11-01

The evaporation of sessile suspension drops leads to accumulation of the particles around the pinned contact line, which is widely termed the coffee ring effect. However, the evaporation behavior of a liquid drop containing a small number of particles with the size comparable to the host drop is unclear yet. Thus, here we investigate the motion and spatial distribution of large particles within a sessile drop. The spherical particles cluster only when their initial distance is below a critical value, which is a function of the diameter and wettability of particle as well as the surface tension and size of the host drop. We rationalize such a critical distance for self-assembly based on the balance of the capillary force and the frictional resistance to sliding and rolling of the particles on a solid substrate. We further discuss the physical significance of this drop-mediated ``Cheerios effect'' in connection with the fate of pathogens residing in drops as a result of sneezing and coughing.

Radial macrosegregation and dendrite clustering in directionally solidified Al-7Si and Al-19Cu alloys

NASA Astrophysics Data System (ADS)

Ghods, M.; Johnson, L.; Lauer, M.; Grugel, R. N.; Tewari, S. N.; Poirier, D. R.

2016-05-01

Hypoeutectic Al-7 wt% Si and Al-19 wt% Cu alloys were directionally solidified upward in a Bridgman furnace through a range of constant growth speeds and thermal gradients. Though processing is thermo-solutally stable, flow initiated by gravity-independent advection at, slightly leading, central dendrites moves rejected solute out ahead and across the advancing interface. Here any lagging dendrites are further suppressed which promotes a curved solid-liquid interface and the eventual dendrite "clustering" seen in transverse sections (dendrite "steepling" in longitudinal orientations) as well as extensive radial macrosegregation. Both aluminum alloys showed considerable macrosegregation at the low growth speeds (10 and 30 μm s-1) but not at higher speed (72 μm s-1). Distribution of the fraction eutectic-constituent on transverse sections was determined in order to quantitatively describe radial macrosegregation. The convective mechanisms leading to dendrite-steepling were elucidated with numerical simulations, and their results compared with the experimental observations.