From antinode clusters to node clusters: the concentration-dependent transition of floaters on a standing Faraday wave.

PubMed

Sanlı, Ceyda; Lohse, Detlef; van der Meer, Devaraj

2014-05-01

A hydrophilic floating sphere that is denser than water drifts to an amplitude maximum (antinode) of a surface standing wave. A few identical floaters therefore organize into antinode clusters. However, beyond a transitional value of the floater concentration ϕ, we observe that the same spheres spontaneously accumulate at the nodal lines, completely inverting the self-organized particle pattern on the wave. From a potential energy estimate we show (i) that at low ϕ antinode clusters are energetically favorable over nodal ones and (ii) how this situation reverses at high ϕ, in agreement with the experiment.

Atomic dynamics and the problem of the structural stability of free clusters of solidified inert gases

NASA Astrophysics Data System (ADS)

Verkhovtseva, É. T.; Gospodarev, I. A.; Grishaev, A. V.; Kovalenko, S. I.; Solnyshkin, D. D.; Syrkin, E. S.; Feodos'ev, S. B.

2003-05-01

The dependence of the rms amplitudes of atoms in free clusters of solidified inert gases on the cluster size is investigated theoretically and experimentally. Free clusters are produced by homogeneous nucleation in an adiabatically expanding supersonic stream. Electron diffraction is used to measure the rms amplitudes of the atoms; the Jacobi-matrix method is used for theoretical calculations. A series of distinguishing features of the atomic dynamics of microclusters was found. This was necessary to determine the character of the formation and the stability conditions of the crystal structure. It wass shown that for clusters consisting of less than N˜103 atoms, as the cluster size decreases, the rms amplitudes grow much more rapidly than expected from the increase in the specific contribution of the surface. It is also established that an fcc structure of a free cluster, as a rule, contains twinning defects (nuclei of an hcp phase). One reason for the appearance of such defects is the so-called vertex instability (anomalously large oscillation amplitudes) of the atoms in coordination spheres.

Galaxy clusters in local Universe simulations without density constraints: a long uphill struggle

NASA Astrophysics Data System (ADS)

Sorce, Jenny G.

2018-06-01

Galaxy clusters are excellent cosmological probes provided that their formation and evolution within the large scale environment are precisely understood. Therefore studies with simulated galaxy clusters have flourished. However detailed comparisons between simulated and observed clusters and their population - the galaxies - are complicated by the diversity of clusters and their surrounding environment. An original way initiated by Bertschinger as early as 1987, to legitimize the one-to-one comparison exercise down to the details, is to produce simulations constrained to resemble the cluster under study within its large scale environment. Subsequently several methods have emerged to produce simulations that look like the local Universe. This paper highlights one of these methods and its essential steps to get simulations that not only resemble the local Large Scale Structure but also that host the local clusters. It includes a new modeling of the radial peculiar velocity uncertainties to remove the observed correlation between the decreases of the simulated cluster masses and of the amount of data used as constraints with the distance from us. This method has the particularity to use solely radial peculiar velocities as constraints: no additional density constraints are required to get local cluster simulacra. The new resulting simulations host dark matter halos that match the most prominent local clusters such as Coma. Zoom-in simulations of the latter and of a volume larger than the 30h-1 Mpc radius inner sphere become now possible to study local clusters and their effects. Mapping the local Sunyaev-Zel'dovich and Sachs-Wolfe effects can follow.

Kinetics and Structure of Superagglomerates Produced by Silane and Acetylene

NASA Technical Reports Server (NTRS)

Mulholland, G. W.; Hamins, A.; Sivathanu, Y.

1999-01-01

The evolution of smoke in a laminar diffusion flame involves several steps. The first step is particle inception/nucleation in the high-temperature fuel-rich region of the flame followed by surface growth and coagulation/coalescence of the small particles. As the primary spheres grow in size and lose hydrogen, the colliding particles no longer coalesce but retain their identity as a cluster of primary spheres, termed an agglomerate. Finally, in the upper portion of the flame, the particles enter an oxidizing environment which may lead to partial or complete burnout of the agglomerates. Currently there is no quantitative model for describing the growth of smoke agglomerates up to superagglomerates with an overall dimension of 10 microns and greater. Such particles are produced during the burning of acetylene and fuels containing benzene rings such as toluene and polystyrene. In the case of polystyrene, smoke agglomerates in excess of 1 mm have been observed "raining" out from large fires. Evidence of the formation of superagglomerates in a laminar acetylene/air diffusion flame has been recently reported. Acetylene was chosen as the fuel since the particulate loading in acetylene/air diffusion flames is very high. Photographs were obtained by Sorensen using a microsecond xenon lamp of the "stream" of soot just above the flame. For low flow rates of acetylene, only submicrometer soot clusters are produced and they give rise to the homogeneous appearance of the soot stream. When the flow rate is increased to 1.7 cu cm/s, soot clusters up to 10 microns are formed and they are responsible for the graininess and at a flow rate of 3.4 cu cm/s, a web of interconnected clusters as large as the width of the flame is seen. This interconnecting web of superagglomerates is described as a gel state by Sorensen et al (1998). This is the first observation of a gel for a gas phase system. It was observed that this gel state immediately breaks up into agglomerates due to buoyancy induced turbulence and gravitational sedimentation.

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-07-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star-forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

The early dynamical evolution of star clusters near the Galactic Centre

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2018-04-01

We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ˜2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ˜ 600 M⊙ pc-3 if the Arches is at 30 pc from the GC, or ˜ 200 M⊙ pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

Analysis of gamma-ray energies for 56 excited superdeformed rotational bands of nuclei of lanthanons La to Dy and of Hg, Tl, and Pb on the basis of the two-revolving-cluster model, with evaluation of moments of inertia and radii of revolution and assignment of nucleonic compositions to the clusters and the central sphere.

PubMed

Pauling, L

1992-08-01

Analysis of the gamma-ray energies of 28 excited superdeformed bands of lanthanon nuclei by application of the two-revolving-cluster model yields the result that the central sphere for all 28 has the semimagic-magic composition p40n50, with the range p8n12 to p14n18 for the clusters and the radius of revolution increasing from 7.31 to 7.76 fm. Similar analysis of 28 excited bands of Hg, Tl, and Pb nuclei leads to p56n82 (semimagic-magic) for the central sphere of 24 bands, p64n82 (semimagic-magic) for 2, and p64n90 (doubly semimagic) for 2, with cluster range p8n12 to p14n16 and values of the radius of revolution from 8.70 to 8.92 fm for 26 bands and 9.2 fm for 2.

Analysis of gamma-ray energies for 56 excited superdeformed rotational bands of nuclei of lanthanons La to Dy and of Hg, Tl, and Pb on the basis of the two-revolving-cluster model, with evaluation of moments of inertia and radii of revolution and assignment of nucleonic compositions to the clusters and the central sphere.

PubMed Central

Pauling, L

1992-01-01

Analysis of the gamma-ray energies of 28 excited superdeformed bands of lanthanon nuclei by application of the two-revolving-cluster model yields the result that the central sphere for all 28 has the semimagic-magic composition p40n50, with the range p8n12 to p14n18 for the clusters and the radius of revolution increasing from 7.31 to 7.76 fm. Similar analysis of 28 excited bands of Hg, Tl, and Pb nuclei leads to p56n82 (semimagic-magic) for the central sphere of 24 bands, p64n82 (semimagic-magic) for 2, and p64n90 (doubly semimagic) for 2, with cluster range p8n12 to p14n16 and values of the radius of revolution from 8.70 to 8.92 fm for 26 bands and 9.2 fm for 2. PMID:11607313

Condensation and dissociation rates for gas phase metal clusters from molecular dynamics trajectory calculations

DOE PAGES

Yang, Huan; Goudeli, Eirini; Hogan, Christopher J.

2018-04-24

In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we present a collision rate theory-Molecular Dynamics simulation approach to calculate condensation probabilities and condensation rate coefficients; we use this approach to examine atomic condensation onto 6-56 atom Au and Mg clusters. The probability of condensation depends upon the initial relative velocity ( v) between atom and cluster andmore » the initial impact parameter ( b). In all cases there is a well-defined region of b-v space where condensation is highly probable, and outside of which the condensation probability drops to zero. For Au clusters with more than 10 atoms, we find that at gas temperatures in the 300-1200 K range, the condensation rate coefficient exceeds the hard sphere rate coefficient by a factor of 1.5-2.0. Conversely, for Au clusters with 10 or fewer atoms, and for 14 atom and 28 atom Mg clusters, as cluster equilibration temperature increases the condensation rate coefficient drops to values below the hard sphere rate coefficient. Calculations also yield the self-dissociation rate coefficient, which is found to vary considerably with gas temperature. Finally, calculations results reveal that grazing (high b) atom-cluster collisions at elevated velocity (> 1000 m s -1) can result in the colliding atom rebounding (bounce) from the cluster surface or binding while another atom dissociates (replacement). In conclusion, the presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.« less

Condensation and dissociation rates for gas phase metal clusters from molecular dynamics trajectory calculations.

PubMed

Yang, Huan; Goudeli, Eirini; Hogan, Christopher J

2018-04-28

In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard-sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we present a collision rate theory-molecular dynamics simulation approach to calculate condensation probabilities and condensation rate coefficients. We use this approach to examine atomic condensation onto 6-56-atom Au and Mg clusters. The probability of condensation depends upon the initial relative velocity (v) between atom and cluster and the initial impact parameter (b). In all cases, there is a well-defined region of b-v space where condensation is highly probable, and outside of which the condensation probability drops to zero. For Au clusters with more than 10 atoms, we find that at gas temperatures in the 300-1200 K range, the condensation rate coefficient exceeds the hard-sphere rate coefficient by a factor of 1.5-2.0. Conversely, for Au clusters with 10 or fewer atoms and for 14- and 28-atom Mg clusters, as cluster equilibration temperature increases, the condensation rate coefficient drops to values below the hard-sphere rate coefficient. Calculations also yield the self-dissociation rate coefficient, which is found to vary considerably with gas temperature. Finally, calculations results reveal that grazing (high b) atom-cluster collisions at elevated velocity (>1000 m s -1 ) can result in the colliding atom rebounding (bounce) from the cluster surface or binding while another atom dissociates (replacement). The presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.

Condensation and dissociation rates for gas phase metal clusters from molecular dynamics trajectory calculations

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

Yang, Huan; Goudeli, Eirini; Hogan, Christopher J.

In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we present a collision rate theory-Molecular Dynamics simulation approach to calculate condensation probabilities and condensation rate coefficients; we use this approach to examine atomic condensation onto 6-56 atom Au and Mg clusters. The probability of condensation depends upon the initial relative velocity ( v) between atom and cluster andmore » the initial impact parameter ( b). In all cases there is a well-defined region of b-v space where condensation is highly probable, and outside of which the condensation probability drops to zero. For Au clusters with more than 10 atoms, we find that at gas temperatures in the 300-1200 K range, the condensation rate coefficient exceeds the hard sphere rate coefficient by a factor of 1.5-2.0. Conversely, for Au clusters with 10 or fewer atoms, and for 14 atom and 28 atom Mg clusters, as cluster equilibration temperature increases the condensation rate coefficient drops to values below the hard sphere rate coefficient. Calculations also yield the self-dissociation rate coefficient, which is found to vary considerably with gas temperature. Finally, calculations results reveal that grazing (high b) atom-cluster collisions at elevated velocity (> 1000 m s -1) can result in the colliding atom rebounding (bounce) from the cluster surface or binding while another atom dissociates (replacement). In conclusion, the presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.« less

Condensation and dissociation rates for gas phase metal clusters from molecular dynamics trajectory calculations

NASA Astrophysics Data System (ADS)

Yang, Huan; Goudeli, Eirini; Hogan, Christopher J.

2018-04-01

In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard-sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we present a collision rate theory-molecular dynamics simulation approach to calculate condensation probabilities and condensation rate coefficients. We use this approach to examine atomic condensation onto 6-56-atom Au and Mg clusters. The probability of condensation depends upon the initial relative velocity (v) between atom and cluster and the initial impact parameter (b). In all cases, there is a well-defined region of b-v space where condensation is highly probable, and outside of which the condensation probability drops to zero. For Au clusters with more than 10 atoms, we find that at gas temperatures in the 300-1200 K range, the condensation rate coefficient exceeds the hard-sphere rate coefficient by a factor of 1.5-2.0. Conversely, for Au clusters with 10 or fewer atoms and for 14- and 28-atom Mg clusters, as cluster equilibration temperature increases, the condensation rate coefficient drops to values below the hard-sphere rate coefficient. Calculations also yield the self-dissociation rate coefficient, which is found to vary considerably with gas temperature. Finally, calculations results reveal that grazing (high b) atom-cluster collisions at elevated velocity (>1000 m s-1) can result in the colliding atom rebounding (bounce) from the cluster surface or binding while another atom dissociates (replacement). The presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.

Porous Ceramic Spheres From Cation Exchange Beads

NASA Technical Reports Server (NTRS)

Dynys, Fred

2005-01-01

This document is a slide presentation that examines the use of a simple templating process to produce hollow ceramic spheres with a pore size of 1 to 10 microns. Using ion exchange process it was determined that the method produces porous ceramic spheres with a unique structure: (i.e., inner sphere surrounded by an outer sphere.)

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.

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.

Predicting tensorial electrophoretic effects in asymmetric colloids

NASA Astrophysics Data System (ADS)

Mowitz, Aaron J.; Witten, T. A.

2017-12-01

We formulate a numerical method for predicting the tensorial linear response of a rigid, asymmetrically charged body to an applied electric field. This prediction requires calculating the response of the fluid to the Stokes drag forces on the moving body and on the countercharges near its surface. To determine the fluid's motion, we represent both the body and the countercharges using many point sources of drag known as Stokeslets. Finding the correct flow field amounts to finding the set of drag forces on the Stokeslets that is consistent with the relative velocities experienced by each Stokeslet. The method rigorously satisfies the condition that the object moves with no transfer of momentum to the fluid. We demonstrate that a sphere represented by 1999 well-separated Stokeslets on its surface produces flow and drag force like a solid sphere to 1% accuracy. We show that a uniformly charged sphere with 3998 body and countercharge Stokeslets obeys the Smoluchowski prediction [F. Morrison, J. Colloid Interface Sci. 34, 210 (1970), 10.1016/0021-9797(70)90171-2] for electrophoretic mobility when the countercharges lie close to the sphere. Spheres with dipolar and quadrupolar charge distributions rotate and translate as predicted analytically to 4% accuracy or better. We describe how the method can treat general asymmetric shapes and charge distributions. This method offers promise as a way to characterize and manipulate asymmetrically charged colloid-scale objects from biology (e.g., viruses) and technology (e.g., self-assembled clusters).

Exploring gravitational lensing model variations in the Frontier Fields galaxy clusters

NASA Astrophysics Data System (ADS)

Harris James, Nicholas John; Raney, Catie; Brennan, Sean; Keeton, Charles

2018-01-01

Multiple groups have been working on modeling the mass distributions of the six lensing galaxy clusters in the Hubble Space Telescope Frontier Fields data set. The magnification maps produced from these mass models will be important for the future study of the lensed background galaxies, but there exists significant variation in the different groups’ models and magnification maps. We explore the use of two-dimensional histograms as a tool for visualizing these magnification map variations. Using a number of simple, one- or two-halo singular isothermal sphere models, we explore the features that are produced in 2D histogram model comparisons when parameters such as halo mass, ellipticity, and location are allowed to vary. Our analysis demonstrates the potential of 2D histograms as a means of observing the full range of differences between the Frontier Fields groups’ models.This work has been supported by funding from National Science Foundation grants PHY-1560077 and AST-1211385, and from the Space Telescope Science Institute.

Orientational ordering of lamellar structures on closed surfaces

NASA Astrophysics Data System (ADS)

PÈ©kalski, J.; Ciach, A.

2018-05-01

Self-assembly of particles with short-range attraction and long-range repulsion interactions on a flat and on a spherical surface is compared. Molecular dynamics simulations are performed for the two systems having the same area and the density optimal for formation of stripes of particles. Structural characteristics, e.g., a cluster size distribution, a number of defects, and an orientational order parameter (OP), as well as the specific heat, are obtained for a range of temperatures. In both cases, the cluster size distribution becomes bimodal and elongated clusters appear at the temperature corresponding to the maximum of the specific heat. When the temperature decreases, orientational ordering of the stripes takes place and the number of particles per cluster or stripe increases in both cases. However, only on the flat surface, the specific heat has another maximum at the temperature corresponding to a rapid change of the OP. On the sphere, the crossover between the isotropic and anisotropic structures occur in a much broader temperature interval; the orientational order is weaker and occurs at significantly lower temperature. At low temperature, the stripes on the sphere form spirals and the defects resemble defects in the nematic phase of rods adsorbed at a sphere.

Tidal disruption of open clusters in their parent molecular clouds

NASA Technical Reports Server (NTRS)

Long, Kevin

1989-01-01

A simple model of tidal encounters has been applied to the problem of an open cluster in a clumpy molecular cloud. The parameters of the clumps are taken from the Blitz, Stark, and Long (1988) catalog of clumps in the Rosette molecular cloud. Encounters are modeled as impulsive, rectilinear collisions between Plummer spheres, but the tidal approximation is not invoked. Mass and binding energy changes during an encounter are computed by considering the velocity impulses given to individual stars in a random realization of a Plummer sphere. Mean rates of mass and binding energy loss are then computed by integrating over many encounters. Self-similar evolutionary calculations using these rates indicate that the disruption process is most sensitive to the cluster radius and relatively insensitive to cluster mass. The calculations indicate that clusters which are born in a cloud similar to the Rosette with a cluster radius greater than about 2.5 pc will not survive long enough to leave the cloud. The majority of clusters, however, have smaller radii and will survive the passage through their parent cloud.

Filtered back-projection algorithm for Compton telescopes

DOEpatents

Gunter, Donald L [Lisle, IL

2008-03-18

A method for the conversion of Compton camera data into a 2D image of the incident-radiation flux on the celestial sphere includes detecting coincident gamma radiation flux arriving from various directions of a 2-sphere. These events are mapped by back-projection onto the 2-sphere to produce a convolution integral that is subsequently stereographically projected onto a 2-plane to produce a second convolution integral which is deconvolved by the Fourier method to produce an image that is then projected onto the 2-sphere.

Method for producing small hollow spheres

DOEpatents

Hendricks, C.D.

1979-01-09

Method is disclosed for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T [approx gt] 600 C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10[sup 3] [mu]m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants. 1 fig.

Method and apparatus for producing small hollow spheres

DOEpatents

Hendricks, Charles D.

1979-01-01

Method and apparatus for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T.gtoreq.600.degree. C.). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.

Method for producing small hollow spheres

DOEpatents

Hendricks, Charles D. [Livermore, CA

1979-01-09

Method for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T .gtorsim. 600.degree. C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.

Monte Carlo simulation of Hamaker nanospheres coated with dipolar particles

NASA Astrophysics Data System (ADS)

Meyra, Ariel G.; Zarragoicoechea, Guillermo J.; Kuz, Victor A.

2012-01-01

Parallel tempering Monte Carlo simulation is carried out in systems of N attractive Hamaker spheres dressed with n dipolar particles, able to move on the surface of the spheres. Different cluster configurations emerge for given values of the control parameters. Energy per sphere, pair distribution functions of spheres and dipoles as function of temperature, density, external electric field, and/or the angular orientation of dipoles are used to analyse the state of aggregation of the system. As a consequence of the non-central interaction, the model predicts complex structures like self-assembly of spheres by a double crown of dipoles. This interesting result could be of help in understanding some recent experiments in colloidal science and biology.

Corrected Mean-Field Model for Random Sequential Adsorption on Random Geometric Graphs

NASA Astrophysics Data System (ADS)

Dhara, Souvik; van Leeuwaarden, Johan S. H.; Mukherjee, Debankur

2018-03-01

A notorious problem in mathematics and physics is to create a solvable model for random sequential adsorption of non-overlapping congruent spheres in the d-dimensional Euclidean space with d≥ 2 . Spheres arrive sequentially at uniformly chosen locations in space and are accepted only when there is no overlap with previously deposited spheres. Due to spatial correlations, characterizing the fraction of accepted spheres remains largely intractable. We study this fraction by taking a novel approach that compares random sequential adsorption in Euclidean space to the nearest-neighbor blocking on a sequence of clustered random graphs. This random network model can be thought of as a corrected mean-field model for the interaction graph between the attempted spheres. Using functional limit theorems, we characterize the fraction of accepted spheres and its fluctuations.

Influence of the electron density on the characteristics of terahertz waves generated under laser–cluster interaction

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

Frolov, A. A., E-mail: frolov@ihed.ras.ru

2016-12-15

A theory of generation of terahertz radiation under laser–cluster interaction, developed earlier for an overdense cluster plasma [A. A. Frolov, Plasma Phys. Rep. 42. 637 (2016)], is generalized for the case of arbitrary electron density. The spectral composition of radiation is shown to substantially depend on the density of free electrons in the cluster. For an underdense cluster plasma, there is a sharp peak in the terahertz spectrum at the frequency of the quadrupole mode of a plasma sphere. As the electron density increases to supercritical values, this spectral line vanishes and a broad maximum at the frequency comparable withmore » the reciprocal of the laser pulse duration appears in the spectrum. The dependence of the total energy of terahertz radiation on the density of free electrons is analyzed. The radiation yield is shown to increase significantly under resonance conditions, when the laser frequency is close to the eigenfrequency of the dipole or quadrupole mode of a plasma sphere.« less

Diverse assembly behavior in colloidal Platonic polyhedral sphere clusters

NASA Astrophysics Data System (ADS)

Marson, Ryan; Teich, Erin; Dshemuchadse, Julia; Glotzer, Sharon; Larson, Ronald

We simulate the self-assembly of colloidal ``polyhedral sphere clusters (PSCs)'', which consist of equal-sized spheres placed at the vertices of a polyhedron such that they just touch along each edge. These colloidal building blocks have recently been experimentally fabricated; here we predict crystal structures that would appear in the phase diagram of resulting particle assemblies. We use Brownian dynamics (BD) simulations of rigid body clusters performed in the open-source GPU-based HOOMD-Blue particle simulation package to show the assembly behavior of the 5 Platonic PSCs. The simulations contain as many as 4096 individual polyhedra, across over 30 different densities per cluster geometry, with some ordered phases possessing unit cells with 20 or more particles. We observe the formation of not only traditional cubic structures such as BCC and FCC, but also more complex phases having structure symmetries with Pearson symbols - hP7, cP20, cI2, mP6, and hR3. The observations reported here will serve as a guide for future colloidal assembly experiments using an expanded library of PSCs, consisting of other regular and irregular polyhedra, allowing researchers to target specific arrangements of ``halo'' and ``core'' particles for technologically relevant applications including photonics and structural color.

Accelerating the coupled-cluster singles and doubles method using the chain-of-sphere approximation

NASA Astrophysics Data System (ADS)

Dutta, Achintya Kumar; Neese, Frank; Izsák, Róbert

2018-06-01

In this paper, we present a chain-of-sphere implementation of the external exchange term, the computational bottleneck of coupled-cluster calculations at the singles and doubles level. This implementation is compared to standard molecular orbital, atomic orbital and resolution of identity implementations of the same term within the ORCA package and turns out to be the most efficient one for larger molecules, with a better accuracy than the resolution-of-identity approximation. Furthermore, it becomes possible to perform a canonical CC calculation on a tetramer of nucleobases in 17 days, 20 hours.

Interaction and charge transfer between dielectric spheres: Exact and approximate analytical solutions.

PubMed

Lindén, Fredrik; Cederquist, Henrik; Zettergren, Henning

2016-11-21

We present exact analytical solutions for charge transfer reactions between two arbitrarily charged hard dielectric spheres. These solutions, and the corresponding exact ones for sphere-sphere interaction energies, include sums that describe polarization effects to infinite orders in the inverse of the distance between the sphere centers. In addition, we show that these exact solutions may be approximated by much simpler analytical expressions that are useful for many practical applications. This is exemplified through calculations of Langevin type cross sections for forming a compound system of two colliding spheres and through calculations of electron transfer cross sections. We find that it is important to account for dielectric properties and finite sphere sizes in such calculations, which for example may be useful for describing the evolution, growth, and dynamics of nanometer sized dielectric objects such as molecular clusters or dust grains in different environments including astrophysical ones.

Incidence of the muffin-tin approximation on the electronic structure of large clusters calculated by the MS-LSD method: The typical case of C{sub 60}

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

Razafinjanahary, H.; Rogemond, F.; Chermette, H.

The MS-LSD method remains a method of interest when rapidity and small computer resources are required; its main drawback is some lack of accuracy, mainly due to the muffin-tin distribution of the potential. In the case of large clusters or molecules, the use of an empty sphere to fill, in part, the large intersphere region can improve greatly the results. Calculations bearing on C{sub 60} has been undertaken to underline this trend, because, on the one hand, the fullerenes exhibit a remarkable possibility to fit a large empty sphere in the center of the cluster and, on the other hand,more » numerous accurate calculations have already been published, allowing quantitative comparison with results. The author`s calculations suggest that in case of added empty sphere the results compare well with the results of more accurate calculations. The calculated electron affinity for C{sub 60} and C{sub 60}{sup {minus}} are in reasonable agreement with experimental values, but the stability of C{sub 60}{sup 2-} in gas phase is not found. 35 refs., 3 figs., 5 tabs.« less

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.

Sector and Sphere: the design and implementation of a high-performance data cloud

PubMed Central

Gu, Yunhong; Grossman, Robert L.

2009-01-01

Cloud computing has demonstrated that processing very large datasets over commodity clusters can be done simply, given the right programming model and infrastructure. In this paper, we describe the design and implementation of the Sector storage cloud and the Sphere compute cloud. By contrast with the existing storage and compute clouds, Sector can manage data not only within a data centre, but also across geographically distributed data centres. Similarly, the Sphere compute cloud supports user-defined functions (UDFs) over data both within and across data centres. As a special case, MapReduce-style programming can be implemented in Sphere by using a Map UDF followed by a Reduce UDF. We describe some experimental studies comparing Sector/Sphere and Hadoop using the Terasort benchmark. In these studies, Sector is approximately twice as fast as Hadoop. Sector/Sphere is open source. PMID:19451100

Whole genome sequencing as a tool to investigate a cluster of seven cases of listeriosis in Austria and Germany, 2011-2013.

PubMed

Schmid, D; Allerberger, F; Huhulescu, S; Pietzka, A; Amar, C; Kleta, S; Prager, R; Preußel, K; Aichinger, E; Mellmann, A

2014-05-01

A cluster of seven human cases of listeriosis occurred in Austria and in Germany between April 2011 and July 2013. The Listeria monocytogenes serovar (SV) 1/2b isolates shared pulsed-field gel electrophoresis (PFGE) and fluorescent amplified fragment length polymorphism (fAFLP) patterns indistinguishable from those from five food producers. The seven human isolates, a control strain with a different PFGE/fAFLP profile and ten food isolates were subjected to whole genome sequencing (WGS) in a blinded fashion. A gene-by-gene comparison (multilocus sequence typing (MLST)+) was performed, and the resulting whole genome allelic profiles were compared using SeqSphere(+) software version 1.0. On analysis of 2298 genes, the four human outbreak isolates from 2012 to 2013 had different alleles at ≤6 genes, i.e. differed by ≤6 genes from each other; the dendrogram placed these isolates in between five Austrian unaged soft cheese isolates from producer A (≤19-gene difference from the human cluster) and two Austrian ready-to-eat meat isolates from producer B (≤8-gene difference from the human cluster). Both food products appeared on grocery bills prospectively collected by these outbreak cases after hospital discharge. Epidemiological results on food consumption and MLST+ clearly separated the three cases in 2011 from the four 2012-2013 outbreak cases (≥48 different genes). We showed that WGS is capable of discriminating L. monocytogenes SV1/2b clones not distinguishable by PFGE and fAFLP. The listeriosis outbreak described clearly underlines the potential of sequence-based typing methods to offer enhanced resolution and comparability of typing systems for public health applications. © 2014 The Authors Clinical Microbiology and Infection © 2014 European Society of Clinical Microbiology and Infectious Diseases.

The quest for inorganic fullerenes

NASA Astrophysics Data System (ADS)

Pietsch, Susanne; Dollinger, Andreas; Strobel, Christoph H.; Park, Eun Ji; Ganteför, Gerd; Seo, Hyun Ook; Kim, Young Dok; Idrobo, Juan-Carlos; Pennycook, Stephen J.

2015-10-01

Experimental results of the search for inorganic fullerenes are presented. MonSm- and WnSm- clusters are generated with a pulsed arc cluster ion source equipped with an annealing stage. This is known to enhance fullerene formation in the case of carbon. Analogous to carbon, the mass spectra of the metal chalcogenide clusters produced in this way exhibit a bimodal structure. The species in the first maximum at low mass are known to be platelets. Here, the structure of the species in the second maximum is studied by anion photoelectron spectroscopy, scanning transmission electron microscopy, and scanning tunneling microcopy. All experimental results indicate a two-dimensional structure of these species and disagree with a three-dimensional fullerene-like geometry. A possible explanation for this preference of two-dimensional structures is the ability of a two-element material to saturate the dangling bonds at the edges of a platelet by excess atoms of one element. A platelet consisting of a single element only cannot do this. Accordingly, graphite and boron might be the only materials forming nano-spheres because they are the only single element materials assuming two-dimensional structures.

The Structure of the Young Star Cluster NGC 6231. II. Structure, Formation, and Fate

NASA Astrophysics Data System (ADS)

Kuhn, Michael A.; Getman, Konstantin V.; Feigelson, Eric D.; Sills, Alison; Gromadzki, Mariusz; Medina, Nicolás; Borissova, Jordanka; Kurtev, Radostin

2017-12-01

The young cluster NGC 6231 (stellar ages ˜2-7 Myr) is observed shortly after star formation activity has ceased. Using the catalog of 2148 probable cluster members obtained from Chandra, VVV, and optical surveys (Paper I), we examine the cluster’s spatial structure and dynamical state. The spatial distribution of stars is remarkably well fit by an isothermal sphere with moderate elongation, while other commonly used models like Plummer spheres, multivariate normal distributions, or power-law models are poor fits. The cluster has a core radius of 1.2 ± 0.1 pc and a central density of ˜200 stars pc-3. The distribution of stars is mildly mass segregated. However, there is no radial stratification of the stars by age. Although most of the stars belong to a single cluster, a small subcluster of stars is found superimposed on the main cluster, and there are clumpy non-isotropic distributions of stars outside ˜4 core radii. When the size, mass, and age of NGC 6231 are compared to other young star clusters and subclusters in nearby active star-forming regions, it lies at the high-mass end of the distribution but along the same trend line. This could result from similar formation processes, possibly hierarchical cluster assembly. We argue that NGC 6231 has expanded from its initial size but that it remains gravitationally bound.

A volumetric conformal mapping approach for clustering white matter fibers in the brain

PubMed Central

Gupta, Vikash; Prasad, Gautam; Thompson, Paul

2017-01-01

The human brain may be considered as a genus-0 shape, topologically equivalent to a sphere. Various methods have been used in the past to transform the brain surface to that of a sphere using harmonic energy minimization methods used for cortical surface matching. However, very few methods have studied volumetric parameterization of the brain using a spherical embedding. Volumetric parameterization is typically used for complicated geometric problems like shape matching, morphing and isogeometric analysis. Using conformal mapping techniques, we can establish a bijective mapping between the brain and the topologically equivalent sphere. Our hypothesis is that shape analysis problems are simplified when the shape is defined in an intrinsic coordinate system. Our goal is to establish such a coordinate system for the brain. The efficacy of the method is demonstrated with a white matter clustering problem. Initial results show promise for future investigation in these parameterization technique and its application to other problems related to computational anatomy like registration and segmentation. PMID:29177252

Ceramic Spheres From Cation Exchange Beads

NASA Technical Reports Server (NTRS)

Dynys, F. W.

2003-01-01

Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.

Electric-field-induced association of colloidal particles

NASA Astrophysics Data System (ADS)

Fraden, Seth; Hurd, Alan J.; Meyer, Robert B.

1989-11-01

Dilute suspensions of micron diameter dielectric spheres confined to two dimensions are induced to aggregate linearly by application of an electric field. The growth of the average cluster size agrees well with the Smoluchowski equation, but the evolution of the measured cluster size distribution exhibits significant departures from theory at large times due to the formation of long linear clusters which effectively partition space into isolated one-dimensional strips.

Gel Fabrication of Molybdenum “Beads”

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

Lowden, Richard Andrew; Armstrong, Beth L.; Cooley, Kevin M.

2016-11-01

Spherical molybdenum particles or “beads” of various diameters are of interest as feedstock materials for the additive manufacture of targets and assemblies used in the production of 99Mo medical isotopes using accelerator technology. Small metallic beads or ball bearings are typically fabricated from wire; however, small molybdenum spheres cannot readily be produced in this manner. Sol-gel processes are often employed to produce small dense microspheres of metal oxides across a broad diameter range that in the case of molybdenum could be reduced and sintered to produce metallic spheres. These Sol-gel type processes were examined for forming molybdenum oxide beads; however,more » the molybdenum trioxide was chemically incompatible with commonly used gelation materials. As an alternative, an aqueous alginate process being assessed for the fabrication of oxide spheres for catalyst applications was employed to form molybdenum trioxide beads that were successfully reduced and sintered to produce small molybdenum spheres.« less

Periodic and Aperiodic Close Packing: A Spontaneous Hard-Sphere Model.

ERIC Educational Resources Information Center

van de Waal, B. W.

1985-01-01

Shows how to make close-packed models from balloons and table tennis balls to illustrate structural features of clusters and organometallic cluster-compounds (which are of great interest in the study of chemical reactions). These models provide a very inexpensive and tactile illustration of the organization of matter for concrete operational…

Hydration entropy change from the hard sphere model.

PubMed

Graziano, Giuseppe; Lee, Byungkook

2002-12-10

The gas to liquid transfer entropy change for a pure non-polar liquid can be calculated quite accurately using a hard sphere model that obeys the Carnahan-Starling equation of state. The same procedure fails to produce a reasonable value for hydrogen bonding liquids such as water, methanol and ethanol. However, the size of the molecules increases when the hydrogen bonds are turned off to produce the hard sphere system and the volume packing density rises. We show here that the hard sphere system that has this increased packing density reproduces the experimental transfer entropy values rather well. The gas to water transfer entropy values for small non-polar hydrocarbons is also not reproduced by a hard sphere model, whether one uses the normal (2.8 A diameter) or the increased (3.2 A) size for water. At least part of the reason that the hard sphere model with 2.8 A size water produces too small entropy change is that the size of water is too small for a system without hydrogen bonds. The reason that the 3.2 A model also produces too small entropy values is that this is an overly crowded system and that the free volume introduced in the system by the addition of a solute molecule produces too much of a relief to this crowding. A hard sphere model, in which the free volume increase is limited by requiring that the average surface-to-surface distance between the solute and water molecules is the same as that between the increased-size water molecules, does approximately reproduce the experimental hydration entropy values. Copyright 2002 Elsevier Science B.V.

Initial Dynamical Evolution of Star Clusters with Tidal Field

NASA Astrophysics Data System (ADS)

Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

2017-03-01

Observations have been suggested that star clusters could form from the rapid collapse and violent relaxation of substructured distributions. We investigate the collapse of fractal stellar distributions in no, weak, and very strong tidal fields. We find that the rapid collapse of substructure into spherical clusters happens quickly with no or a weak tidal field, but very strong tidal fields prevent a cluster forming. However, we also find that dense Plummer spheres are also rapidly destroyed in strong tidal fields. We suggest that this is why the low-mass star clusters cannot survive near the galactic centre which has strong tidal field.

Coffee-rings and glasses: Colloids out of equilibrium

NASA Astrophysics Data System (ADS)

Yunker, Peter Joseph

This thesis describes experiments that utilize colloids to explore nonequilibrium phenomena. Specifically, the deposition of particles during evaporation and the glass transition are explored. In the first set of experiments, we found that particle shape has a profound effect on particle deposition. We evaporated drops of colloidal suspensions containing micron-sized particles that range in shape from isotropic spheres to very anisotropic ellipsoids. For sessile drops, i.e., drops sitting on a solid surface, spheres are deposited in a ring-like stain, while ellipsoids are deposited uniformly. We also confined drops between glass plates and allowed them to evaporate. During evaporation, colloidal particles coat the air-water interface, forming colloidal monolayer membranes (CMMs). As particle anisotropy increases, CMM bending rigidity was found to increase. This increase in bending rigidity provides a new mechanism that produces a uniform deposition of ellipsoids and a heterogeneous deposition of spheres. In the second set of experiments, we employed colloidal suspensions to investigate the character of glassy materials. "Anisotropic glasses'' were investigated with ellipsoidal particles confined to two-dimensional chambers at high packing fractions; this system enabled the study of the effects of particle shape on the vibrational properties of colloidal glasses. Low frequency modes in glasses composed of slightly anisotropic particles are found to have predominantly rotational character. Conversely, low frequency modes in glasses of highly anisotropic particles exhibit a mix of rotational and translational character. Aging effects in glasses were explored using suspensions of temperature-sensitive microgel spheres. We devised a method to rapidly quench from liquid to glass states, and then observed the resultant colloidal glasses as they aged. Particle rearrangements in glasses occur collectively, i.e., many particles move in a correlated manner. During aging, we observed that the size of these collective rearrangements increases. Thus, the slowing dynamics of aging appear governed by growing correlated domains of particles required for relaxation. Using the same microgel particles, the transformation of a crystal into a glass due to added disorder was investigated by adding smaller particles into a quasi-two-dimensional colloidal crystal. The crystal-glass transition bears structural signatures similar to those of the crystal-fluid transition, but also exhibits a sharp change in dynamic heterogeneity which ``turns-on'' abruptly as a function of increasing disorder. Finally, we investigated the influence of morphology and size on the vibrational properties of disordered clusters of colloidal particles. Spectral features of cluster vibrational modes are found to depend strongly on the average number of nearest neighbors but only weakly on the number of particles in each glassy cluster. The scaling of the median phonon frequency with nearest neighbor number is reminiscent of athermal simulations of the jamming transition.

Release of sperm clusters in spheres by the black coral Cupressopathes pumila (Anthozoa, Antipatharia)

NASA Astrophysics Data System (ADS)

Gaino, E.; Scoccia, F.

2009-12-01

Fecund polyps from a bottlebrush-shaped colony of black coral Cupressopathes pumila (Brook 1889) from Ambon Island (Maluku Archipelago, Indonesia) were studied at the structural and ultrastructural levels. Five fragments, each 5 cm long and containing about 60 polyps, were cut from a single parental colony. The fragments underwent different treatments: two were fixed in 70% alcohol for species identification; the remaining three were reared in aerated aquaria and then processed for anatomic studies by light and transmission electron microscopy. Some polyps from one of these reared fragments displayed spheres of various sizes protruding from the mouth. Four hours after sampling, spheres settled on the bottom of the aquarium. Comparative analysis of the fecund polyps showed: (i) the differentiation of spermatocysts inside the transverse primary mesenteries that separate the lateral tentacles from one another; (ii) spermatocysts entering the gastric cavity after breakage of the mesentery wall and (iii) location of spermatocysts close to the basal part of the pharynx. Analysis of the largest spheres, both close to the external surface of the mouth and settled on the bottom of the small aerated aquaria, showed that they were irregularly bordered with residual mesentery tissue and contained clusters of spermatocysts. Gametes presented various phases of differentiation up to the final sperm, as it occurs in the spermatocysts developing inside the mesenteries of the fecund polyps. In consideration of the particular distribution of the colonies of C. pumila, which grow very far apart, the release of buoyant spheres is a particular modality of spawning which can be viewed as a strategy for successful fertilisation over long distances.

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor

NASA Technical Reports Server (NTRS)

Scott, Carl D.; Povitsky, Alexander; Dateo, Christopher; Gokcen, Tahir; Willis, Peter A.; Smalley, Richard E.

2003-01-01

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Apoptosis of Trypanosoma musculi co-cultured with LPS activated macrophages: enhanced expression of nitric oxide synthase INF-gamma and caspase.

PubMed

Gugssa, A; Gebru, S; Lee, C M; Baccetti, B; Anderson, W

2005-08-01

Trypanosoma musculi-macrophage co-cultures were studied to investigate the biological role of lipopolysaccharide (LPS) induced cytokines in controlling the proliferation of parasites in vitro. Macrophages, isolated by peritoneal lavage, sustained the growth and proliferation of the parasites. Macrophages activated with LPS were characterized by up-regulation of nitric oxide synthase (iNOS) and phagocytosis of fluorescent latex spheres. Activated macrophages showed marked inhibition of the association and proliferation of the parasites. The LPS treated macrophages produced cytokines, especially interferon gamma (INF-gamma), which was detected by Western blot. Trypanosomes, inhibited from association with macrophages, did not proliferate and instead formed clusters held together by their flagella. Cells in these clusters were apoptotic, as demonstrated by the Apoptag reaction and gel fragmentation assay. In addition, high levels of caspase 8 and caspase 3 were shown in floating trypanosome clusters. The results would suggest that INF-gamma and other cytokines released by activated macrophages, possibly functioning through the INF-gammaR1, Fas ligand, CD95 or other death ligands in the trypanosome plasma membrane initiates the apoptosis cascade in trypanosomes.

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor.

PubMed

Scott, Carl D; Povitsky, Alexander; Dateo, Christopher; Gökçen, Tahir; Willis, Peter A; Smalley, Richard E

2003-01-01

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

The quest for inorganic fullerenes

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

Pietsch, Susanne; Dollinger, Andreas; Strobel, Christoph H.

2015-10-02

Experimental results of the search for inorganic fullerenes are presented. Mo nS m - and W nS m - clusters are generated with a pulsed arc cluster ion source equipped with an annealing stage. This is known to enhance fullerene formation in the case of carbon. Analogous to carbon, the mass spectra of the metal chalcogenide clusters produced in this way exhibit a bimodal structure. Moreover, the species in the first maximum at low mass are known to be platelets. The structure of the species in the second maximum is studied by anion photoelectron spectroscopy, scanning transmission electron microscopy,more » and scanning tunneling microcopy. All experimental results indicate a two-dimensional structure of these species and disagree with a three-dimensional fullerene-like geometry. A possible explanation for this preference of two-dimensional structures is the ability of a two-element material to saturate the dangling bonds at the edges of a platelet by excess atoms of one element. A platelet consisting of a single element only cannot do this. Likewise, graphite and boron might be the only materials forming nano-spheres because they are the only single element materials assuming two-dimensional structures.« less

The quest for inorganic fullerenes

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

Pietsch, Susanne; Dollinger, Andreas; Strobel, Christoph H.

2015-10-07

Experimental results of the search for inorganic fullerenes are presented. Mo{sub n}S{sub m}{sup −} and W{sub n}S{sub m}{sup −} clusters are generated with a pulsed arc cluster ion source equipped with an annealing stage. This is known to enhance fullerene formation in the case of carbon. Analogous to carbon, the mass spectra of the metal chalcogenide clusters produced in this way exhibit a bimodal structure. The species in the first maximum at low mass are known to be platelets. Here, the structure of the species in the second maximum is studied by anion photoelectron spectroscopy, scanning transmission electron microscopy, andmore » scanning tunneling microcopy. All experimental results indicate a two-dimensional structure of these species and disagree with a three-dimensional fullerene-like geometry. A possible explanation for this preference of two-dimensional structures is the ability of a two-element material to saturate the dangling bonds at the edges of a platelet by excess atoms of one element. A platelet consisting of a single element only cannot do this. Accordingly, graphite and boron might be the only materials forming nano-spheres because they are the only single element materials assuming two-dimensional structures.« less

Free energy of singular sticky-sphere clusters.

PubMed

Kallus, Yoav; Holmes-Cerfon, Miranda

2017-02-01

Networks of particles connected by springs model many condensed-matter systems, from colloids interacting with a short-range potential and complex fluids near jamming, to self-assembled lattices and various metamaterials. Under small thermal fluctuations the vibrational entropy of a ground state is given by the harmonic approximation if it has no zero-frequency vibrational modes, yet such singular modes are at the epicenter of many interesting behaviors in the systems above. We consider a system of N spherical particles, and directly account for the singularities that arise in the sticky limit where the pairwise interaction is strong and short ranged. Although the contribution to the partition function from singular clusters diverges in the limit, its asymptotic value can be calculated and depends on only two parameters, characterizing the depth and range of the potential. The result holds for systems that are second-order rigid, a geometric characterization that describes all known ground-state (rigid) sticky clusters. To illustrate the applications of our theory we address the question of emergence: how does crystalline order arise in large systems when it is strongly disfavored in small ones? We calculate the partition functions of all known rigid clusters up to N≤21 and show the cluster landscape is dominated by hyperstatic clusters (those with more than 3N-6 contacts); singular and isostatic clusters are far less frequent, despite their extra vibrational and configurational entropies. Since the most hyperstatic clusters are close to fragments of a close-packed lattice, this underlies the emergence of order in sticky-sphere systems, even those as small as N=10.

Free energy of singular sticky-sphere clusters

NASA Astrophysics Data System (ADS)

Kallus, Yoav; Holmes-Cerfon, Miranda

2017-02-01

Networks of particles connected by springs model many condensed-matter systems, from colloids interacting with a short-range potential and complex fluids near jamming, to self-assembled lattices and various metamaterials. Under small thermal fluctuations the vibrational entropy of a ground state is given by the harmonic approximation if it has no zero-frequency vibrational modes, yet such singular modes are at the epicenter of many interesting behaviors in the systems above. We consider a system of N spherical particles, and directly account for the singularities that arise in the sticky limit where the pairwise interaction is strong and short ranged. Although the contribution to the partition function from singular clusters diverges in the limit, its asymptotic value can be calculated and depends on only two parameters, characterizing the depth and range of the potential. The result holds for systems that are second-order rigid, a geometric characterization that describes all known ground-state (rigid) sticky clusters. To illustrate the applications of our theory we address the question of emergence: how does crystalline order arise in large systems when it is strongly disfavored in small ones? We calculate the partition functions of all known rigid clusters up to N ≤21 and show the cluster landscape is dominated by hyperstatic clusters (those with more than 3 N -6 contacts); singular and isostatic clusters are far less frequent, despite their extra vibrational and configurational entropies. Since the most hyperstatic clusters are close to fragments of a close-packed lattice, this underlies the emergence of order in sticky-sphere systems, even those as small as N =10 .

Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

PubMed Central

Petrenko, Alexander; Stein, Matthias

2017-01-01

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. PMID:28067774

Colloidal alloys with preassembled clusters and spheres.

PubMed

Ducrot, Étienne; He, Mingxin; Yi, Gi-Ra; Pine, David J

2017-06-01

Self-assembly is a powerful approach for constructing colloidal crystals, where spheres, rods or faceted particles can build up a myriad of structures. Nevertheless, many complex or low-coordination architectures, such as diamond, pyrochlore and other sought-after lattices, have eluded self-assembly. Here we introduce a new design principle based on preassembled components of the desired superstructure and programmed nearest-neighbour DNA-mediated interactions, which allows the formation of otherwise unattainable structures. We demonstrate the approach using preassembled colloidal tetrahedra and spheres, obtaining a class of colloidal superstructures, including cubic and tetragonal colloidal crystals, with no known atomic analogues, as well as percolating low-coordination diamond and pyrochlore sublattices never assembled before.

Archimedean Synthesis and Magic Numbers: "Sizing" Giant Molybdenum-Oxide-Based Molecular Spheres of the Keplerate Type.

PubMed

Müller; Sarkar; Shah; Bögge; Schmidtmann; Kögerler; Hauptfleisch; Trautwein; Schünemann

1999-11-02

Pythagorean harmony can be found in the spherical polyoxometalate clusters described here (see illustration for an example of a structure), since there are interesting relationships between the so-called magic numbers (12, 32, 42, 72, 132) relevant for spherical viruses and the number of the building blocks in the cluster. The size of these Keplerate clusters can be tailored by varying the type of connections between the pentagons by means of different spacers.

Directional Cluster Analysis on a Sphere: Retrieval of Archean Magnetic Directions from Data with High Dispersion

NASA Astrophysics Data System (ADS)

Bono, R. K.; Dare, M. S.; Tarduno, J. A.; Cottrell, R. D.

2016-12-01

Magnetic directions from coarse clastic rocks are typically highly scattered, to the point that the null hypothesis that they are drawn from a random distribution, using the iconic test of Watson (1956), cannot be rejected at a high confidence level (e.g. 95%). Here, we use an alternative approach of searching for directional clusters on a sphere. When applied to a new data set of directions from quartzites from the Jack Hills of Western Australia, we find evidence for distinct and meaningful magnetic directions at low (200 to 300 degrees C) and intermediate ( 350 to 450 degrees C) unblocking temperatures, whereas the test of Watson (1956) fails to draw a distinction from random distributions for the ensemble of directions at these unblocking temperature ranges. The robustness of the directional groups identified by the cluster analysis is confirmed by non-parametric resampling tests. The lowest unblocking temperature directional mode appears related to the present day field, perhaps contaminated by viscous magnetizations. The intermediate temperature magnetization matches an overprint recorded by the secondary mineral fuchsite (Cottrell et al., 2016) acquired at ca. 2.65 Ga. These data thus indicate that the Jack Hills carry an overprint at intermediate unblocking temperatures of Archean age. We find no evidence for a 1 Ga remagnetization. In general, the application of cluster analysis on a sphere, with directions confirmed by nonparametric tests, represents a new approach that should be applied when evaluating data with high dispersion, such as those that typically come from weak coarse-grained clastic sedimentary rocks, and/or rocks that have seen several tectonic events that could have imparted multiple magnetic overprints.

Improved Bonner sphere neutron spectrometry measurements for the nuclear industry

NASA Astrophysics Data System (ADS)

Roberts, N. J.; Thomas, D. J.; Visser, T. P. P.

2017-11-01

A novel, two-stage approach has been developed for producing the a priori spectrum for Bonner sphere unfolding in a case where neutrons are produced by spontaneous fission and (α,n) reactions, e.g. in UF6. The code SOURCES 4C is first used to obtain the energy spectrum of the neutrons inside the material, which is then fed into a MCNP model of the entire geometry to derive the neutron spectrum at the location of the Bonner sphere. Using this as the a priori spectrum produces a much more detailed unfolded Bonner sphere spectrum retaining fine structure from the calculation that would not be present if a simple estimated spectrum had been used as the a priori spectrum. This is illustrated using a Bonner sphere measurement of the neutron energy spectrum produced by a 48Y cylinder of UF6. From the unfolded spectrum an estimate has been made of the neutron ambient dose equivalent, i.e. the quantity which a neutron survey instrument should measure. The difference in the ambient dose equivalent of the unfolded spectrum is over 10% when using the novel approach instead of using a simpler estimate consisting of a single high energy peak, 1/E continuum, and thermal peak.

I. Excluded volume effects in Ising cluster distributions and nuclear multifragmentation. II. Multiple-chance effects in alpha-particle evaporation

NASA Astrophysics Data System (ADS)

Breus, Dimitry Eugene

In Part I, geometric clusters of the Ising model are studied as possible model clusters for nuclear multifragmentation. These clusters may not be considered as non-interacting (ideal gas) due to excluded volume effect which predominantly is the artifact of the cluster's finite size. Interaction significantly complicates the use of clusters in the analysis of thermodynamic systems. Stillinger's theory is used as a basis for the analysis, which within the RFL (Reiss, Frisch, Lebowitz) fluid-of-spheres approximation produces a prediction for cluster concentrations well obeyed by geometric clusters of the Ising model. If thermodynamic condition of phase coexistence is met, these concentrations can be incorporated into a differential equation procedure of moderate complexity to elucidate the liquid-vapor phase diagram of the system with cluster interaction included. The drawback of increased complexity is outweighted by the reward of greater accuracy of the phase diagram, as it is demonstrated by the Ising model. A novel nuclear-cluster analysis procedure is developed by modifying Fisher's model to contain cluster interaction and employing the differential equation procedure to obtain thermodynamic variables. With this procedure applied to geometric clusters, the guidelines are developed to look for excluded volume effect in nuclear multifragmentation. In Part II, an explanation is offered for the recently observed oscillations in the energy spectra of alpha-particles emitted from hot compound nuclei. Contrary to what was previously expected, the oscillations are assumed to be caused by the multiple-chance nature of alpha-evaporation. In a semi-empirical fashion this assumption is successfully confirmed by a technique of two-spectra decomposition which treats experimental alpha-spectra as having contributions from at least two independent emitters. Building upon the success of the multiple-chance explanation of the oscillations, Moretto's single-chance evaporation theory is augmented to include multiple-chance emission and tested on experimental data to yield positive results.

Method for producing dustless graphite spheres from waste graphite fines

DOEpatents

Pappano, Peter J [Oak Ridge, TN; Rogers, Michael R [Clinton, TN

2012-05-08

A method for producing graphite spheres from graphite fines by charging a quantity of spherical media into a rotatable cylindrical overcoater, charging a quantity of graphite fines into the overcoater thereby forming a first mixture of spherical media and graphite fines, rotating the overcoater at a speed such that the first mixture climbs the wall of the overcoater before rolling back down to the bottom thereby forming a second mixture of spherical media, graphite fines, and graphite spheres, removing the second mixture from the overcoater, sieving the second mixture to separate graphite spheres, charging the first mixture back into the overcoater, charging an additional quantity of graphite fines into the overcoater, adjusting processing parameters like overcoater dimensions, graphite fines charge, overcoater rotation speed, overcoater angle of rotation, and overcoater time of rotation, before repeating the steps until graphite fines are converted to graphite spheres.

Broadband radiometer

DOEpatents

Cannon, Theodore W.

1994-01-01

A broadband radiometer including (a) an optical integrating sphere having a enerally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample.

Broadband radiometer

DOEpatents

Cannon, T.W.

1994-07-26

A broadband radiometer is disclosed including (a) an optical integrating sphere having generally spherical integrating chamber and an entry port for receiving light (e.g., having visible and ultraviolet fractions), (b) a first optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to broadband radiation, (c) a second optical radiation detector for receiving light from the sphere and producing an electrical output signal corresponding to a predetermined wavelength fraction of the broadband radiation, and (d) an output for producing an electrical signal which is proportional to the difference between the two electrical output signals. The radiometer is very useful, for example, in measuring the absolute amount of ultraviolet light present in a given light sample. 8 figs.

Phononic crystals of spherical particles: A tight binding approach

NASA Astrophysics Data System (ADS)

Mattarelli, M.; Secchi, M.; Montagna, M.

2013-11-01

The vibrational dynamics of a fcc phononic crystal of spheres is studied and compared with that of a single free sphere, modelled either by a continuous homogeneous medium or by a finite cluster of atoms. For weak interaction among the spheres, the vibrational dynamics of the phononic crystal is described by shallow bands, with low degree of dispersion, corresponding to the acoustic spheroidal and torsional modes of the single sphere. The phonon displacements are therefore related to the vibrations of a sphere, as the electron wave functions in a crystal are related to the atomic wave functions in a tight binding model. Important dispersion is found for the two lowest phonon bands, which correspond to zero frequency free translation and rotation of a free sphere. Brillouin scattering spectra are calculated at some values of the exchanged wavevectors of the light, and compared with those of a single sphere. With weak interaction between particles, given the high acoustic impedance mismatch in dry systems, the density of phonon states consist of sharp bands separated by large gaps, which can be well accounted for by a single particle model. Based on the width of the frequency gaps, tunable with the particle size, and on the small number of dispersive acoustic phonons, such systems may provide excellent materials for application as sound or heat filters.

Desmoplastic small round cell tumor with sphere-like clusters mimicking adenocarcinoma.

PubMed

Hattori, Yukinori; Yoshida, Akihiko; Sasaki, Naoshi; Shibuki, Yasuo; Tamura, Kenji; Tsuta, Koji

2015-03-01

Desmoplastic small round cell tumor (DSRCT) is a rare and aggressive neoplasm that predominantly affects young men. DSRCT often presents as multiple nodules on the serosal surface and is histologically categorized as a small round cell tumor. However, the cytological spectrum of DSRCT is not fully understood because of its rarity. Here, we report an unusual case of DSRCT that showed spheres of cells without stromal cores in pleural fluid cytology material, a finding that is typically associated with metastatic adenocarcinoma and mesothelioma. The specimen from a simultaneous needle biopsy showed the classic histology of DSRCT, comprising nests of small round cells set in desmoplasia. The diagnosis of DSRCT was further supported by immunohistochemical coexpression of cytokeratin and desmin, as well as Ewing sarcoma breakpoint region 1 gene rearrangement, which was determined by fluorescence in situ hybridization. The unusual cytological finding in this case illustrates a potential pitfall of the cytological diagnosis of pleural fluid or ascites. DSRCT should not be excluded from the differential diagnosis when sphere-like round cell clusters are observed in pleural or abdominal effusion, particularly in young male patients. © 2014 Wiley Periodicals, Inc.

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.

Close-packed floating clusters: granular hydrodynamics beyond the freezing point?

PubMed

Meerson, Baruch; Pöschel, Thorsten; Bromberg, Yaron

2003-07-11

Monodisperse granular flows often develop regions with hexagonal close packing of particles. We investigate this effect in a system of inelastic hard spheres driven from below by a "thermal" plate. Molecular dynamics simulations show, in a wide range of parameters, a close-packed cluster supported by a low-density region. Surprisingly, the steady-state density profile, including the close-packed cluster part, is well described by a variant of Navier-Stokes granular hydrodynamics (NSGH). We suggest a simple explanation for the success of NSGH beyond the freezing point.

Role of radial nonuniformities in the interaction of an intense laser with atomic clusters

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

Holkundkar, Amol R.; Gupta, N. K.

A model for the interaction of an intense laser with atomic clusters is presented. The model takes into account the spatial nonuniformities of the cluster as it evolves in time. The cluster is treated as a stratified sphere having an arbitrary number of layers. Electric and magnetic fields are obtained by solving the vector Helmholtz equation coupled with one-dimensional Lagrangian hydrodynamics. Results are compared with the uniform density nanoplasma model. Enhancement in the amount of energy absorbed is seen over the uniform density model. In some cases the absorbed energy increases by as much as a factor of 40.

Cavitation and radicals drive the sonochemical synthesis of functional polymer spheres

DOE PAGES

Narayanan, Badri; Deshmukh, Sanket A.; Shrestha, Lok Kumar; ...

2016-07-25

Sonochemical synthesis can lead to a dramatic increase in the kinetics of formation of polymer spheres (templates for carbon spheres) compared to the modified Stober silica method applied to produce analogous polymer spheres. Reactive molecular dynamics simulations of the sonochemical process indicate a significantly enhanced rate of polymer sphere formation starting from resorcinol and formaldehyde precursors. The associated chemical reaction kinetics enhancement due to sonication is postulated to arise from the localized lowering of atomic densities, localized heating, and generation of radicals due to cavitation collapse in aqueous systems. This dramatic increase in reaction rates translates into enhanced nucleation andmore » growth of the polymer spheres. Finally, the results are of broad significance to understanding mechanisms of sonication induced synthesis as well as technologies utilizing polymers spheres.« less

Cavitation and radicals drive the sonochemical synthesis of functional polymer spheres

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

Narayanan, Badri, E-mail: bnarayanan@anl.gov; Deshmukh, Sanket A.; Sankaranarayanan, Subramanian K. R. S., E-mail: ssankaranarayanan@anl.gov

2016-07-25

Sonochemical synthesis can lead to a dramatic increase in the kinetics of formation of polymer spheres (templates for carbon spheres) compared to the modified Stöber silica method applied to produce analogous polymer spheres. Reactive molecular dynamics simulations of the sonochemical process indicate a significantly enhanced rate of polymer sphere formation starting from resorcinol and formaldehyde precursors. The associated chemical reaction kinetics enhancement due to sonication is postulated to arise from the localized lowering of atomic densities, localized heating, and generation of radicals due to cavitation collapse in aqueous systems. This dramatic increase in reaction rates translates into enhanced nucleation andmore » growth of the polymer spheres. The results are of broad significance to understanding mechanisms of sonication induced synthesis as well as technologies utilizing polymers spheres.« less

Mechanical contact induced transformation from the amorphous to the crystalline state in metallic glass

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1984-01-01

Friction and wear tests were conducted with 3.2- and 6.4-millimeter-diameter aluminum oxide spheres sliding, in reciprocating motion, on a Fe67Co18B14Si1 metallic foil. Crystallites with a size range of 10 to 150 nanometers were produced on the wear surface of the amorphous alloy. A strong interaction between transition metals and metalloids such as silicon and boron results in strong segregation during repeated sliding, provides preferential transition metal-metalloid clustering in the amorphous alloy, and subsequently produces the diffused honeycomb structure formed by dark grey bands and primary crystals, that is, alpha-Fe in the matrix. Large plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminum oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris, and/or powdery-whiskery oxide debris.

An analytical model for the calculation of the change in transmembrane potential produced by an ultrawideband electromagnetic pulse.

PubMed

Hart, Francis X; Easterly, Clay E

2004-05-01

The electric field pulse shape and change in transmembrane potential produced at various points within a sphere by an intense, ultrawideband pulse are calculated in a four stage, analytical procedure. Spheres of two sizes are used to represent the head of a human and the head of a rat. In the first stage, the pulse is decomposed into its Fourier components. In the second stage, Mie scattering analysis (MSA) is performed for a particular point in the sphere on each of the Fourier components, and the resulting electric field pulse shape is obtained for that point. In the third stage, the long wavelength approximation (LWA) is used to obtain the change in transmembrane potential in a cell at that point. In the final stage, an energy analysis is performed. These calculations are performed at 45 points within each sphere. Large electric fields and transmembrane potential changes on the order of a millivolt are produced within the brain, but on a time scale on the order of nanoseconds. The pulse shape within the brain differs considerably from that of the incident pulse. Comparison of the results for spheres of different sizes indicates that scaling of such pulses across species is complicated. Published 2004 Wiley-Liss, Inc.

Improved method for producing small hollow spheres

DOEpatents

Rosencwaig, A.; Koo, J.C.; Dressler, J.L.

An improved method and apparatus for producing small hollow spheres of glass having an outer diameter ranging from about 100..mu.. to about 500..mu.. with a substantially uniform wall thickness in the range of about 0.5 to 20..mu.. are described. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions.

Computational study of the electronic structure and magnetic properties of the Ni-C state in [NiFe] hydrogenases including the second coordination sphere.

PubMed

Kampa, Mario; Lubitz, Wolfgang; van Gastel, Maurice; Neese, Frank

2012-12-01

[NiFe] hydrogenases catalyze the reversible formation of H(2). The [NiFe] heterobimetallic active site is rich in redox states. Here, we investigate the key catalytic state Ni-C of Desulfovibrio vulgaris Miyazaki F hydrogenase using a cluster model that includes the truncated amino acids of the entire second coordination sphere of the enzyme. The optimized geometries, computed g tensors, hyperfine coupling constants, and IR stretching frequencies all agree well with experimental values. For the hydride in the bridging position, only a single minimum on the potential energy surface is found, indicating that the hydride bridges and binds to both nickel and iron. The influence of the second coordination sphere on the electronic structure is investigated by comparing results from the large cluster models with truncated models. The largest interactions of the second coordination sphere with the active site concern the hydrogen bonds with the cyanide ligands, which modulate the bond between iron and these ligands. Secondly, the electronic structure of the active site is found to be sensitive to the protonation state of His88. This residue forms a hydrogen bond with the spin-carrying sulfur atom of Cys549, which in turn tunes the spin density at the nickel and coordinating sulfur atoms. In addition, the unequal distribution of spin density over the equatorial cysteine residues results from different orientations of the cysteine side chains, which are kept in their particular orientation by the secondary structure of the protein.

Template-free magnesium oxide hollow sphere inclusion in organic-inorganic hybrid films via sol-gel reaction.

PubMed

Kang, Eun-Seok; Takahashi, Masahide; Tokuda, Yomei; Yoko, Toshinobu

2006-06-06

Magnesium oxide hollow spheres without a template core were conveniently prepared by stabilized bubble formation in a hybrid solution containing a magnesium acetate precursor, thus avoiding the complicated preparation process using a template. The hollow sphere could be aligned along the radial striation by spin coating, and its diameter from a micrometer to submicrometer dimension could be easily modified by the solution composition. It was also possible to control the open or closed hollow sphere by changing the solvent. Thus, the produced magnesium oxide hollow sphere is envisioned to have applications in many areas such as medicine, analysis, optics, and so on.

The [4Fe-4S](2+) cluster in reconstituted biotin synthase binds S-adenosyl-L-methionine.

PubMed

Cosper, Michele Mader; Jameson, Guy N L; Davydov, Roman; Eidsness, Marly K; Hoffman, Brian M; Huynh, Boi Hanh; Johnson, Michael K

2002-11-27

The combination of resonance Raman, electron paramagnetic resonance and Mössbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes.

Relative range error evaluation of terrestrial laser scanners using a plate, a sphere, and a novel dual-sphere-plate target.

PubMed

Muralikrishnan, Bala; Rachakonda, Prem; Lee, Vincent; Shilling, Meghan; Sawyer, Daniel; Cheok, Geraldine; Cournoyer, Luc

2017-12-01

Terrestrial laser scanners (TLS) are a class of 3D imaging systems that produce a 3D point cloud by measuring the range and two angles to a point. The fundamental measurement of a TLS is range. Relative range error is one component of the overall range error of TLS and its estimation is therefore an important aspect in establishing metrological traceability of measurements performed using these systems. Target geometry is an important aspect to consider when realizing the relative range tests. The recently published ASTM E2938-15 mandates the use of a plate target for the relative range tests. While a plate target may reasonably be expected to produce distortion free data even at far distances, the target itself needs careful alignment at each of the relative range test positions. In this paper, we discuss relative range experiments performed using a plate target and then address the advantages and limitations of using a sphere target. We then present a novel dual-sphere-plate target that draws from the advantages of the sphere and the plate without the associated limitations. The spheres in the dual-sphere-plate target are used simply as fiducials to identify a point on the surface of the plate that is common to both the scanner and the reference instrument, thus overcoming the need to carefully align the target.

Effective conductivity of suspensions of overlapping spheres

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

Kim, I.C.; Torquato, S.

1992-03-15

An accurate first-passage simulation technique formulated by the authors (J. Appl. Phys. {bold 68}, 3892 (1990)) is employed to compute the effective conductivity {sigma}{sub {ital e}} of distributions of penetrable (or overlapping) spheres of conductivity {sigma}{sub 2} in a matrix of conductivity {sigma}{sub 1}. Clustering of particles in this model results in a generally intricate topology for virtually the entire range of sphere volume fractions {phi}{sub 2} (i.e., 0{le}{phi}{sub 2}{le}1). Results for the effective conductivity {sigma}{sub {ital e}} are presented for several values of the conductivity ratio {alpha}={sigma}{sub 2}/{sigma}{sub 1}, including superconducting spheres ({alpha}={infinity}) and perfectly insulating spheres ({alpha}=0), andmore » for a wide range of volume fractions. The data are shown to lie between rigorous three-point bounds on {sigma}{sub {ital e}} for the same model. Consistent with the general observations of Torquato (J. Appl. Phys. {bold 58}, 3790 (1985)) regarding the utility of rigorous bounds, one of the bounds provides a good estimate of the effective conductivity, even in the extreme contrast cases ({alpha}{much gt}1 or {alpha}{congruent}0), depending upon whether the system is below or above the percolation threshold.« less

Clustering impact regime with shocks in freely evolving granular gas

NASA Astrophysics Data System (ADS)

Isobe, Masaharu

2017-06-01

A freely cooling granular gas without any external force evolves from the initial homogeneous state to the inhomogeneous clustering state, at which the energy decay deviates from the Haff's law. The asymptotic behavior of energy in the inelastic hard sphere model have been predicted by several theories, which are based on the mode coupling theory or extension of inelastic hard rods gas. In this study, we revisited the clustering regime of freely evolving granular gas via large-scale molecular dynamics simulation with up to 16.7 million inelastic hard disks. We found novel regime regarding on collisions between "clusters" spontaneously appearing after clustering regime, which can only be identified more than a few million particles system. The volumetric dilatation pattern of semicircular shape originated from density shock propagation are well characterized on the appearing of "cluster impact" during the aggregation process of clusters.

Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.

PubMed

Rodríguez-López, Tonalli; del Río, Fernando

2012-01-28

In this work we study a set of soft-sphere systems characterised by a well-defined variation of their softness. These systems represent an extension of the repulsive Lennard-Jones potential widely used in statistical mechanics of fluids. This type of soft spheres is of interest because they represent quite accurately the effective intermolecular repulsion in fluid substances and also because they exhibit interesting properties. The thermodynamics of the soft-sphere fluids is obtained via an effective hard-sphere diameter approach that leads to a compact and accurate equation of state. The virial coefficients of soft spheres are shown to follow quite simple relationships that are incorporated into the equation of state. The approach followed exhibits the rescaling of the density that produces a unique equation for all systems and temperatures. The scaling is carried through to the level of the structure of the fluids.

Fabrication of hexagonal star-shaped and ring-shaped patterns arrays by Mie resonance sphere-lens-lithography

NASA Astrophysics Data System (ADS)

Liu, Xianchao; Wang, Jun; Li, Ling; Gou, Jun; Zheng, Jie; Huang, Zehua; Pan, Rui

2018-05-01

Mie resonance sphere-lens-lithography has proved to be a good candidate for fabrication of large-area tunable surface nanopattern arrays. Different patterns on photoresist surface are obtained theoretically by adjusting optical coupling among neighboring spheres with different gap sizes. The effect of light reflection from the substrate on the pattern produced on the photoresist with a thin thickness is also discussed. Sub-micron hexagonal star-shaped and ring-shaped patterns arrays are achieved with close-packed spheres arrays and spheres arrays with big gaps, respectively. Changing of star-shaped vertices is induced by different polarization of illumination. Experimental results agree well with the simulation. By using smaller resonance spheres, sub-400 nm star-shaped and ring-shaped patterns can be realized. These tunable patterns are different from results of previous reports and have enriched pattern morphology fabricated by sphere-lens-lithography, which can find application in biosensor and optic devices.

PREPARATION OF HIGH-DENSITY THORIUM OXIDE SPHERES

DOEpatents

McNees, R.A. Jr.; Taylor, A.J.

1963-12-31

A method of preparing high-density thorium oxide spheres for use in pellet beds in nuclear reactors is presented. Sinterable thorium oxide is first converted to free-flowing granules by means such as compression into a compact and comminution of the compact. The granules are then compressed into cubes having a density of 5.0 to 5.3 grams per cubic centimeter. The cubes are tumbled to form spheres by attrition, and the spheres are then fired at 1250 to 1350 deg C. The fired spheres are then polished and fired at a temperature above 1650 deg C to obtain high density. Spherical pellets produced by this method are highly resistant to mechanical attrition hy water. (AEC)

Enteric coated spheres produced by extrusion/spheronization provide effective gastric protection and efficient release of live therapeutic bacteria.

PubMed

de Barros, João M S; Lechner, Tabea; Charalampopoulos, Dimitrios; Khutoryanskiy, Vitaliy V; Edwards, Alexander D

2015-09-30

We present a novel but simple enteric coated sphere formulation containing probiotic bacteria (Lactobacillus casei). Oral delivery of live bacterial cells (LBC) requires live cells to survive firstly manufacturing processes and secondly GI microbicidal defenses including gastric acid. We incorporated live L. casei directly in the granulation liquid, followed by granulation, extrusion, spheronization, drying and spray coating to produce dried live probiotic spheres. A blend of MCC, calcium-crosslinked alginate, and lactose was developed that gave improved live cell survival during manufacturing, and gave excellent protection from gastric acid plus rapid release in intestinal conditions. No significant loss of viability was observed in all steps except drying, which resulted in approximately 1 log loss of viable cells. Eudragit coating was used to protect dried live cells from acid, and microcrystalline cellulose (MCC) was combined with sodium alginate to achieve efficient sphere disintegration leading to rapid and complete bacterial cell release in intestinal conditions. Viability and release of L. casei was evaluated in vitro in simulated GI conditions. Uncoated spheres gave partial acid protection, but enteric coated spheres effectively protected dried probiotic LBC from acid for 2h, and subsequently released all viable cells within 1h of transfer into simulated intestinal fluid. Copyright © 2015 Elsevier B.V. All rights reserved.

New Convex and Spherical Structures of Bare Boron Clusters

NASA Astrophysics Data System (ADS)

Boustani, Ihsan

1997-10-01

New stable structures of bare boron clusters can easily be obtained and constructed with the help of an "Aufbau Principle" suggested by a systematicab initioHF-SCF and direct CI study. It is concluded that boron cluster formation can be established by elemental units of pentagonal and hexagonal pyramids. New convex and small spherical clusters different from the classical known forms of boron crystal structures are obtained by a combination of both basic units. Convex structures simulate boron surfaces which can be considered as segments of open or closed spheres. Both convex clusters B16and B46have energies close to those of their conjugate quasi-planar clusters, which are relatively stable and can be considered to act as a calibration mark. The closed spherical clusters B12, B22, B32, and B42are less stable than the corresponding conjugated quasi-planar structures. As a consequence, highly stable spherical boron clusters can systematically be predicted when their conjugate quasi-planar clusters are determined and energies are compared.

Probability of lensing magnification by cosmologically distributed galaxies

NASA Technical Reports Server (NTRS)

Pei, Yichuan C.

1993-01-01

We present the analytical formulae for computing the magnification probability caused by cosmologically distributed galaxies. The galaxies are assumed to be singular, truncated-isothermal spheres without both evolution and clustering in redshift. We find that, for a fixed total mass, extended galaxies produce a broader shape in the magnification probability distribution and hence are less efficient as gravitational lenses than compact galaxies. The high-magnification tail caused by large galaxies is well approximated by an A exp -3 form, while the tail by small galaxies is slightly shallower. The mean magnification as a function of redshift is, however, found to be independent of the size of the lensing galaxies. In terms of the flux conservation, our formulae for the isothermal galaxy model predict a mean magnification to within a few percent with the Dyer-Roeder model of a clumpy universe.

Cluster formation and phase separation in heteronuclear Janus dumbbells

NASA Astrophysics Data System (ADS)

Munaò, G.; O'Toole, P.; Hudson, T. S.; Costa, D.; Caccamo, C.; Sciortino, F.; Giacometti, A.

2015-06-01

We have recently investigated the phase behavior of model colloidal dumbbells constituted by two identical tangent hard spheres, with the first being surrounded by an attractive square-well interaction (Janus dumbbells, Munaó et al 2014 Soft Matter 10 5269). Here we extend our previous analysis by introducing in the model the size asymmetry of the hard-core diameters and study the enriched phase scenario thereby obtained. By employing standard Monte Carlo simulations we show that in such ‘heteronuclear Janus dumbbells’ a larger hard-sphere site promotes the formation of clusters, whereas in the opposite condition a gas-liquid phase separation takes place, with a narrow interval of intermediate asymmetries wherein the two phase behaviors may compete. In addition, some peculiar geometrical arrangements, such as lamellæ, are observed only around the perfectly symmetric case. A qualitative agreement is found with recent experimental results, where it is shown that the roughness of molecular surfaces in heterogeneous dimers leads to the formation of colloidal micelles.

High pressure gas spheres for neutron and photon experiments

NASA Astrophysics Data System (ADS)

Rupp, G.; Petrich, D.; Käppeler, F.; Kaltenbaek, J.; Leugers, B.; Reifarth, R.

2009-09-01

High pressure gas spheres have been designed and successfully used in several nuclear physics experiments on noble gases. The pros and cons of this solution are the simple design and the high reliability versus the fact that the density is limited to 40-60% of liquid or solid gas samples. Originally produced for neutron capture studies at keV energies, the comparably small mass of the gas spheres were an important advantage, which turned out to be of relevance for other applications as well. The construction, performance, and operation of the spheres are described and examples for their use are presented.

Superelastic carbon spheres under high pressure

NASA Astrophysics Data System (ADS)

Li, Meifen; Guo, Junjie; Xu, Bingshe

2013-03-01

We report a superelastic deformation behavior of carbon spheres by the in situ Raman spectroscopy in a high-pressure diamond anvil cell. The carbon spheres produced by arc discharging in toluene have a mean diameter of 200 nm and an onion-like multilayer graphitic structure. We find that the elastic coefficients, during both the compression and decompression processes, remain a constant up to 10 GPa, indicating a superior high-pressure structural stability. Such superelastic behavior is related to the isotropic and concentric configuration of carbon spheres and provides additional insight into improving the microscopic mechanical properties of small-scale particles.

Stabilizing ultrasmall Au clusters for enhanced photoredox catalysis.

PubMed

Weng, Bo; Lu, Kang-Qiang; Tang, Zichao; Chen, Hao Ming; Xu, Yi-Jun

2018-04-18

Recently, loading ligand-protected gold (Au) clusters as visible light photosensitizers onto various supports for photoredox catalysis has attracted considerable attention. However, the efficient control of long-term photostability of Au clusters on the metal-support interface remains challenging. Herein, we report a simple and efficient method for enhancing the photostability of glutathione-protected Au clusters (Au GSH clusters) loaded on the surface of SiO 2 sphere by utilizing multifunctional branched poly-ethylenimine (BPEI) as a surface charge modifying, reducing and stabilizing agent. The sequential coating of thickness controlled TiO 2 shells can further significantly improve the photocatalytic efficiency, while such structurally designed core-shell SiO 2 -Au GSH clusters-BPEI@TiO 2 composites maintain high photostability during longtime light illumination conditions. This joint strategy via interfacial modification and composition engineering provides a facile guideline for stabilizing ultrasmall Au clusters and rational design of Au clusters-based composites with improved activity toward targeting applications in photoredox catalysis.

Co-clustering directed graphs to discover asymmetries and directional communities

PubMed Central

Rohe, Karl; Qin, Tai; Yu, Bin

2016-01-01

In directed graphs, relationships are asymmetric and these asymmetries contain essential structural information about the graph. Directed relationships lead to a new type of clustering that is not feasible in undirected graphs. We propose a spectral co-clustering algorithm called di-sim for asymmetry discovery and directional clustering. A Stochastic co-Blockmodel is introduced to show favorable properties of di-sim. To account for the sparse and highly heterogeneous nature of directed networks, di-sim uses the regularized graph Laplacian and projects the rows of the eigenvector matrix onto the sphere. A nodewise asymmetry score and di-sim are used to analyze the clustering asymmetries in the networks of Enron emails, political blogs, and the Caenorhabditis elegans chemical connectome. In each example, a subset of nodes have clustering asymmetries; these nodes send edges to one cluster, but receive edges from another cluster. Such nodes yield insightful information (e.g., communication bottlenecks) about directed networks, but are missed if the analysis ignores edge direction. PMID:27791058

Co-clustering directed graphs to discover asymmetries and directional communities.

PubMed

Rohe, Karl; Qin, Tai; Yu, Bin

2016-10-21

In directed graphs, relationships are asymmetric and these asymmetries contain essential structural information about the graph. Directed relationships lead to a new type of clustering that is not feasible in undirected graphs. We propose a spectral co-clustering algorithm called di-sim for asymmetry discovery and directional clustering. A Stochastic co-Blockmodel is introduced to show favorable properties of di-sim To account for the sparse and highly heterogeneous nature of directed networks, di-sim uses the regularized graph Laplacian and projects the rows of the eigenvector matrix onto the sphere. A nodewise asymmetry score and di-sim are used to analyze the clustering asymmetries in the networks of Enron emails, political blogs, and the Caenorhabditis elegans chemical connectome. In each example, a subset of nodes have clustering asymmetries; these nodes send edges to one cluster, but receive edges from another cluster. Such nodes yield insightful information (e.g., communication bottlenecks) about directed networks, but are missed if the analysis ignores edge direction.

A Review of Discrete Element Method (DEM) Particle Shapes and Size Distributions for Lunar Soil

NASA Technical Reports Server (NTRS)

Lane, John E.; Metzger, Philip T.; Wilkinson, R. Allen

2010-01-01

As part of ongoing efforts to develop models of lunar soil mechanics, this report reviews two topics that are important to discrete element method (DEM) modeling the behavior of soils (such as lunar soils): (1) methods of modeling particle shapes and (2) analytical representations of particle size distribution. The choice of particle shape complexity is driven primarily by opposing tradeoffs with total number of particles, computer memory, and total simulation computer processing time. The choice is also dependent on available DEM software capabilities. For example, PFC2D/PFC3D and EDEM support clustering of spheres; MIMES incorporates superquadric particle shapes; and BLOKS3D provides polyhedra shapes. Most commercial and custom DEM software supports some type of complex particle shape beyond the standard sphere. Convex polyhedra, clusters of spheres and single parametric particle shapes such as the ellipsoid, polyellipsoid, and superquadric, are all motivated by the desire to introduce asymmetry into the particle shape, as well as edges and corners, in order to better simulate actual granular particle shapes and behavior. An empirical particle size distribution (PSD) formula is shown to fit desert sand data from Bagnold. Particle size data of JSC-1a obtained from a fine particle analyzer at the NASA Kennedy Space Center is also fitted to a similar empirical PSD function.

Size-controlled, magnetic, and core-shell nanoparticles synthesized by inert-gas condensation

NASA Astrophysics Data System (ADS)

Koten, Mark A.

Interest in nanoparticles (2 to 100 nm in diameter) and clusters of atoms (0.5 to 2 nm in diameter) has heightened over the past two and a half decades on both fundamental and functional levels. Nanoparticles and clusters of atoms are an exciting branch of materials science because they do not behave like normal bulk matter, nor do they act like molecules. They can have shockingly different physical, chemical, optical, or magnetic properties from the same material at a larger scale. In the case of nanoparticles, the surface-to-volume ratio can change fundamental properties like melting temperature, binding energy, or electron affinity. The definitions of markers used to distinguish between metallic, semiconducting, and insulating bulk condensed matter, such as the band gap and polarizability, can even be blurred or confused on the nanoscale. Similarly, clusters of atoms can form in structures that are only stable at finite sizes, and do not translate to bulk condensed matter. Thermodynamics of finite systems changes dramatically in nanovolumes such as wires, rods, cubes, and spheres, which can lead to complex core-shell and onion-like nanostructures. Consequently, these changes in properties and structure have led to many new possibilities in the field of materials engineering. Inert-gas condensation (IGC) is a well-established method of producing nanoparticles that condense from the gas phase. Its first use dates back to the early 1990s, and it has been used to fabricate nanoparticles both commercially and in research and development for applications in magnetism, biomedicine, and catalysts. In this dissertation, IGC was used to produce a wide variety of nanoparticles. First, control over the size distributions of Cu nanoparticles and how it relates to the plasma properties inside the nucleation chamber was investigated. Next, the formation of phase pure WFe2 nanoparticles revealed that this Laves phase is ferromagnetic instead of non-magnetic. Finally, core-shell nanoparticles were produced using three thermodynamically different systems, which showed that IGC could be used to produce a wide variety of core-shell particles. These three projects are presented in the context of size-dependent structural and magnetic properties.

Cohesion of Bubbles in Foam

ERIC Educational Resources Information Center

Ross, Sydney

1978-01-01

The free-energy change, or binding energy, of an idealized bubble cluster is calculated on the basis of one mole of gas, and on the basis of a single bubble going from sphere to polyhedron. Some new relations of bubble geometry are developed in the course of the calculation. (BB)

Crystallization of hard spheres revisited. I. Extracting kinetics and free energy landscape from forward flux sampling.

PubMed

Richard, David; Speck, Thomas

2018-03-28

We investigate the kinetics and the free energy landscape of the crystallization of hard spheres from a supersaturated metastable liquid though direct simulations and forward flux sampling. In this first paper, we describe and test two different ways to reconstruct the free energy barriers from the sampled steady state probability distribution of cluster sizes without sampling the equilibrium distribution. The first method is based on mean first passage times, and the second method is based on splitting probabilities. We verify both methods for a single particle moving in a double-well potential. For the nucleation of hard spheres, these methods allow us to probe a wide range of supersaturations and to reconstruct the kinetics and the free energy landscape from the same simulation. Results are consistent with the scaling predicted by classical nucleation theory although a quantitative fit requires a rather large effective interfacial tension.

Crystallization of hard spheres revisited. I. Extracting kinetics and free energy landscape from forward flux sampling

NASA Astrophysics Data System (ADS)

Richard, David; Speck, Thomas

2018-03-01

We investigate the kinetics and the free energy landscape of the crystallization of hard spheres from a supersaturated metastable liquid though direct simulations and forward flux sampling. In this first paper, we describe and test two different ways to reconstruct the free energy barriers from the sampled steady state probability distribution of cluster sizes without sampling the equilibrium distribution. The first method is based on mean first passage times, and the second method is based on splitting probabilities. We verify both methods for a single particle moving in a double-well potential. For the nucleation of hard spheres, these methods allow us to probe a wide range of supersaturations and to reconstruct the kinetics and the free energy landscape from the same simulation. Results are consistent with the scaling predicted by classical nucleation theory although a quantitative fit requires a rather large effective interfacial tension.

A Unique 3D Nitrogen-Doped Carbon Composite as High-Performance Oxygen Reduction Catalyst

PubMed Central

Karunagaran, Ramesh; Tung, Tran Thanh; Tran, Diana; Coghlan, Campbell; Doonan, Christian

2017-01-01

The synthesis and properties of an oxygen reduction catalyst based on a unique 3-dimensional (3D) nitrogen doped (N-doped) carbon composite are described. The composite material is synthesised via a two-step hydrothermal and pyrolysis method using bio-source low-cost materials of galactose and melamine. Firstly, the use of iron salts and galactose to hydrothermally produceiron oxide (Fe2O3) magnetic nanoparticle clusters embedded carbon spheres. Secondly, magnetic nanoparticles diffused out of the carbon sphere when pyrolysed in the presence of melamine as nitrogen precursor. Interestingly, many of these nanoparticles, as catalyst-grown carbon nanotubes (CNTs), resulted in the formation of N-doped CNTs and N-doped carbon spheres under the decomposition of carbon and a nitrogen environment. The composite material consists of integrated N-doped carbon microspheres and CNTs show high ORR activity through a predominantly four-electron pathway. PMID:28792432

Hunting high and low: disentangling primordial and late-time non-Gaussianity with cosmic densities in spheres

NASA Astrophysics Data System (ADS)

Uhlemann, C.; Pajer, E.; Pichon, C.; Nishimichi, T.; Codis, S.; Bernardeau, F.

2018-03-01

Non-Gaussianities of dynamical origin are disentangled from primordial ones using the formalism of large deviation statistics with spherical collapse dynamics. This is achieved by relying on accurate analytical predictions for the one-point probability distribution function and the two-point clustering of spherically averaged cosmic densities (sphere bias). Sphere bias extends the idea of halo bias to intermediate density environments and voids as underdense regions. In the presence of primordial non-Gaussianity, sphere bias displays a strong scale dependence relevant for both high- and low-density regions, which is predicted analytically. The statistics of densities in spheres are built to model primordial non-Gaussianity via an initial skewness with a scale dependence that depends on the bispectrum of the underlying model. The analytical formulas with the measured non-linear dark matter variance as input are successfully tested against numerical simulations. For local non-Gaussianity with a range from fNL = -100 to +100, they are found to agree within 2 per cent or better for densities ρ ∈ [0.5, 3] in spheres of radius 15 Mpc h-1 down to z = 0.35. The validity of the large deviation statistics formalism is thereby established for all observationally relevant local-type departures from perfectly Gaussian initial conditions. The corresponding estimators for the amplitude of the non-linear variance σ8 and primordial skewness fNL are validated using a fiducial joint maximum likelihood experiment. The influence of observational effects and the prospects for a future detection of primordial non-Gaussianity from joint one- and two-point densities-in-spheres statistics are discussed.

A preliminary investigation of projectile shape effects in hypervelocity impact of a double-sheet structure

NASA Technical Reports Server (NTRS)

Morrison, R. H.

1972-01-01

Impact tests of a sphere and several cylinders of various masses and fineness ratios, all of aluminum, fired into an aluminum double-sheet structure at velocities near 7 km/sec, show that a cylinder, impacting in the direction of its axis, is considerably more effective as a penetrator than a sphere. Impacts of three cylinders of equal mass, but different fineness ratios, produced holes through the structures' rear sheet, whereas impact of a sphere of the same mass did not. Moreover, it was found that to prevent rear-sheet penetration, the mass of the 1/2-fineness-ratio cylinder had to be reduced by a factor greater than three. Further tests wherein the cylinder diameter was held constant while the cylinder length was systematically reduced showed that a cylinder with a fineness ratio of 0.07 and a mass of only 1/7 that of the sphere was still capable of producing a hole in the rear sheet.

SU-E-T-504: Intensity-Modulated Radiosurgery Treatments Derived by Optimizing Delivery of Sphere Packing Treatment Plans

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

Hermansen, M; Bova, F; John, T St.

2015-06-15

Purpose To minimize the number of monitor units required to deliver a sphere packing stereotactic radiosurgery (SRS) plan by eliminating overlaps of individual beam projections. Methods An algorithm was written in C{sup ++} to calculate SRS treatment doses using sphere packing. Three fixed beams were used to approximate each arc in a typical SRS treatment plan. For cases involving multiple isocenters, at each gantry and table angle position beams directed to individual spheres overlap to produce regions of high dose, resulting in intensity modulated beams. These high dose regions were dampened by post-processing of the combined beam profile. The post-processmore » dampening involves removing the excess overlapping fluence from all but the highest contributing beam. The dampened beam profiles at each table and gantry angle position were then summed to produce the new total dose distribution. Results Delivery times for even the most complex multiple sphere plans can be reduced to consistent times of about 20 to 30 minutes. The total MUs required to deliver the plan can also be reduced by as much as 85% of the original plan’s MUs. Conclusion Regions of high dose are removed. Dampening overlapping radiation fluence can produce the new beam profiles that have more uniform dose distributions using less MUs. This results in a treatment that requires significantly fewer intensity values than traditional IMRT or VAMT planning.« less

Self-organization of silver nanoparticles forming on chemical reduction to give monodisperse spheres

NASA Astrophysics Data System (ADS)

Yakutik, I. M.; Shevchenko, G. P.

2004-09-01

It was found possible to produce monodisperse spherical silver particles using K-Na-tartrate as the reductant for Ag + in the presence of gelatin. It was shown that the silver spheres form in the process of spontaneous self-organization of 10-15 nm-sized primary particles. The conditions making it possible to control the sizes of the monodisperse spheres in the range from 150 nm to 1.5 μm were specified.

Osteogenic potency of a 3-dimensional scaffold-free bonelike sphere of periodontal ligament stem cells in vitro.

PubMed

Singhatanadgit, Weerachai; Varodomrujiranon, Manatsanan

2013-12-01

The present study aimed to investigate the osteogenic potency of scaffold-free 3-dimensional (3D) spheres of periodontal ligament stem cells (PDLSCs). The osteogenic potency of PDLSC spheres was determined by the ability to form mineralization and to express key osteogenesis-associated genes. The alkaline phosphatase (ALP) activity and the protein content of PDLSC spheres were also measured. The 3D sphere developed its osteogenic potency in a time-dependent manner, containing approximately 10-fold higher mineralization, 5-fold higher protein content, and 4-fold greater ALP activity than those in the controls. The expression of key osteogenic genes was also upregulated in the 3D PDLSC spheres. Cellular outgrowth was observed when reintroduced into 2D culture. PDLSCs were able to undergo osteogenic differentiation in a scaffold-free 3D culture, producing bonelike mineralization in vitro. This suggests, at least in vitro, the osteogenic potency of the 3D PDLSC spheres. Copyright © 2013 Elsevier Inc. All rights reserved.

Towards DNA-Based Programmable Matter

DTIC Science & Technology

2012-02-28

optics. Nature 2003, 424, 824–830. (2) Xu, H. X.; Bjerneld, E. J.; Kall , M.; Borjesson, L. Spectroscopy of single hemoglobin molecules by surface...Brenner, M. P.; Manoharan, V. N. The Free-energy Landscape of Clusters of Attractive Hard Spheres. Science 2010, 327, 560–563. (35) Xu, H. X.; Kall , M

Edible oil structures at low and intermediate concentrations. I. Modeling, computer simulation, and predictions for X ray scattering

NASA Astrophysics Data System (ADS)

Pink, David A.; Quinn, Bonnie; Peyronel, Fernanda; Marangoni, Alejandro G.

2013-12-01

Triacylglycerols (TAGs) are biologically important molecules which form the recently discovered highly anisotropic crystalline nanoplatelets (CNPs) and, ultimately, the large-scale fat crystal networks in edible oils. Identifying the hierarchies of these networks and how they spontaneously self-assemble is important to understanding their functionality and oil binding capacity. We have modelled CNPs and studied how they aggregate under the assumption that all CNPs are present before aggregation begins and that their solubility in the liquid oil is very low. We represented CNPs as rigid planar arrays of spheres with diameter ≈50 nm and defined the interaction between spheres in terms of a Hamaker coefficient, A, and a binding energy, VB. We studied three cases: weak binding, |VB|/kBT ≪ 1, physically realistic binding, VB = Vd(R, Δ), so that |VB|/kBT ≈ 1, and Strong binding with |VB|/kBT ≫ 1. We divided the concentration of CNPs, ϕ, with 0≤ϕ= 10-2 (solid fat content) ≤1, into two regions: Low and intermediate concentrations with 0<ϕ<0.25 and high concentrations with 0.25 < ϕ and considered only the first case. We employed Monte Carlo computer simulation to model CNP aggregation and analyzed them using static structure functions, S(q). We found that strong binding cases formed aggregates with fractal dimension, D, 1.7≤D ≤1.8, in accord with diffusion limited cluster-cluster aggregation (DLCA) and weak binding formed aggregates with D =3, indicating a random distribution of CNPs. We found that models with physically realistic intermediate binding energies formed linear multilayer stacks of CNPs (TAGwoods) with fractal dimension D =1 for ϕ =0.06,0.13, and 0.22. TAGwood lengths were greater at lower ϕ than at higher ϕ, where some of the aggregates appeared as thick CNPs. We increased the spatial scale and modelled the TAGwoods as rigid linear arrays of spheres of diameter ≈500 nm, interacting via the attractive van der Waals interaction. We found that TAGwoods aggregated via DLCA into clusters with fractal dimension D =1.7-1.8. As the simulations were run further, TAGwoods relaxed their positions in order to maximize the attractive interaction making the process look like reaction limited cluster-cluster aggregation with the fractal dimension increasing to D =2.0-2.1. For higher concentrations of CNPs, many TAGwood clusters were formed and, because of their weak interactions, were distributed randomly with D =3.0. We summarize the hierarchy of structures and make predictions for X-ray scattering.

Evaluation of hierarchical agglomerative cluster analysis methods for discrimination of primary biological aerosol

NASA Astrophysics Data System (ADS)

Crawford, I.; Ruske, S.; Topping, D. O.; Gallagher, M. W.

2015-07-01

In this paper we present improved methods for discriminating and quantifying Primary Biological Aerosol Particles (PBAP) by applying hierarchical agglomerative cluster analysis to multi-parameter ultra violet-light induced fluorescence (UV-LIF) spectrometer data. The methods employed in this study can be applied to data sets in excess of 1×106 points on a desktop computer, allowing for each fluorescent particle in a dataset to be explicitly clustered. This reduces the potential for misattribution found in subsampling and comparative attribution methods used in previous approaches, improving our capacity to discriminate and quantify PBAP meta-classes. We evaluate the performance of several hierarchical agglomerative cluster analysis linkages and data normalisation methods using laboratory samples of known particle types and an ambient dataset. Fluorescent and non-fluorescent polystyrene latex spheres were sampled with a Wideband Integrated Bioaerosol Spectrometer (WIBS-4) where the optical size, asymmetry factor and fluorescent measurements were used as inputs to the analysis package. It was found that the Ward linkage with z-score or range normalisation performed best, correctly attributing 98 and 98.1 % of the data points respectively. The best performing methods were applied to the BEACHON-RoMBAS ambient dataset where it was found that the z-score and range normalisation methods yield similar results with each method producing clusters representative of fungal spores and bacterial aerosol, consistent with previous results. The z-score result was compared to clusters generated with previous approaches (WIBS AnalysiS Program, WASP) where we observe that the subsampling and comparative attribution method employed by WASP results in the overestimation of the fungal spore concentration by a factor of 1.5 and the underestimation of bacterial aerosol concentration by a factor of 5. We suggest that this likely due to errors arising from misatrribution due to poor centroid definition and failure to assign particles to a cluster as a result of the subsampling and comparative attribution method employed by WASP. The methods used here allow for the entire fluorescent population of particles to be analysed yielding an explict cluster attribution for each particle, improving cluster centroid definition and our capacity to discriminate and quantify PBAP meta-classes compared to previous approaches.

VizieR Online Data Catalog: HD61005 SPHERE H and Ks images (Olofsson+, 2016)

NASA Astrophysics Data System (ADS)

Olofsson, J.; Samland, M.; Avenhaus, H.; Caceres, C.; Henning, T.; Moor, A.; Milli, J.; Canovas, H.; Quanz, S. P.; Schreiber, M. R.; Augereau, J.-C.; Bayo, A.; Bazzon, A.; Beuzit, J.-L.; Boccaletti, A.; Buenzli, E.; Casassus, S.; Chauvin, G.; Dominik, C.; Desidera, S.; Feldt, M.; Gratton, R.; Janson, M.; Lagrange, A.-M.; Langlois, M.; Lannier, J.; Maire, A.-L.; Mesa, D.; Pinte, C.; Rouan, D.; Salter, G.; Thalmann, C.; Vigan, A.

2016-05-01

The fits files contains the reduced ADI and DPI SPHERE observations used to produce Fig. 1 of the paper. Besides the primary card, the files consists of 6 additional ImageHDU. The first and second one contain the SPHERE IRDIS ADI H band observations and the noise map. The third and fourth contain the SPHERE IRDIS ADI Ks band observations and the corresponding noise map. Finally, the fifth and sixth ImageHDU contain the SPHERE IRDIS DPI H band data as well as the noise map. Each ADI image has 1024x1024 pixels, while the DPI images have 1800x1800 pixels. The header of the primary card contains the pixel sizes for each datasets and the wavelengths of the H and K band observations. (2 data files).

Interaction of a shock wave with multiple spheres suspended in different arrangements

NASA Astrophysics Data System (ADS)

Zhang, Li-Te; Sui, Zhen-Zhen; Shi, Hong-Hui

2018-03-01

In this study, the unsteady drag force, Fd, drag coefficient, Cd, and the relevant dynamic behaviors of waves caused by the interaction between a planar incident shock wave and a multi-sphere model are investigated by using imbedded accelerometers and a high-speed Schlieren system. The shock wave is produced in a horizontal 200 mm inner diameter circular shock tube with a 2000 mm × 200 mm × 200 mm transparent test section. The time history of Cd is obtained based on band-block and low-pass Fast Fourier Transformation filtering combined with Savitzky-Golay polynomial smoothing for the measured acceleration. The effects of shock Mach number, Ms, geometry of multi-sphere model, nondimensional distance between sphere centers, H, and channel blockage are analyzed. We find that all time histories of Cd have a similar double-peak shaped main structure. It is due to wave reflection, diffraction, interference, and convergence at different positions of the spheres. The peak Fd increases, whereas the peak Cd decreases monotonically with increasing Ms. The increase of shock strength due to shock focusing by upstream spheres increases the peak Fd of downstream spheres. Both the increase in sphere number and the decrease in distance between spheres promote wave interference between neighboring spheres. As long as the wave interference times are shorter than the peak times, the peak Fd and Cd are higher compared to a single sphere.

Hydrodynamic clustering of droplets in turbulence

NASA Astrophysics Data System (ADS)

Kunnen, Rudie; Yavuz, Altug; van Heijst, Gertjan; Clercx, Herman

2017-11-01

Small, inertial particles are known to cluster in turbulent flows: particles are centrifuged out of eddies and gather in the strain-dominated regions. This so-called preferential concentration is reflected in the radial distribution function (RDF; a quantitative measure of clustering). We study clustering of water droplets in a loudspeaker-driven turbulence chamber. We track the motion of droplets in 3D and calculate the RDF. At moderate scales (a few Kolmogorov lengths) we find the typical power-law scaling of preferential concentration in the RDF. However, at even smaller scales (a few droplet diameters), we encounter a hitherto unobserved additional clustering. We postulate that the additional clustering is due to hydrodynamic interactions, an effect which is typically disregarded in modeling. Using a perturbative expansion of inertial effects in a Stokes-flow description of two interacting spheres, we obtain an expression for the RDF which indeed includes the additional clustering. The additional clustering enhances the collision probability of droplets, which enhances their growth rate due to coalescence. The additional clustering is thus an essential effect in precipitation modeling.

Water Surface Impact and Ricochet of Deformable Elastomeric Spheres

NASA Astrophysics Data System (ADS)

Hurd, Randy C.

Soft and deformable silicone rubber spheres ricochet from a water surface when rigid spheres and disks (or skipping stones) cannot. This dissertation investigates why these objects are able to skip so successfully. High speed cameras allow us to see that these unique spheres deform significantly as they impact the water surface, flattening into pancake-like shapes with greater area. Though the water entry behavior of deformable spheres deviates from that of rigid spheres, our research shows that if this deformation is accounted for, their behavior can be predicted from previously established methods. Soft spheres skip more easily because they deform significantly when impacting the water surface. We present a diagram which enables the prediction of a ricochet from sphere impact conditions such as speed and angle. Experiments and mathematical representations of the sphere skipping both show that these deformable spheres skip more readily because deformation momentarily increases sphere area and produces an attack angle with the water which is favorable to skipping. Predictions from our mathematical representation of sphere skipping agree strongly with observations from experiments. Even when a sphere was allowed to skip multiple times in the laboratory, the mathematical predictions show good agreement with measured impact conditions through subsequent skipping events. While studying multiple impact events in an outdoor setting, we discovered a previously unidentified means of skipping, which is unique to deformable spheres. This new skipping occurs when a relatively soft sphere first hits the water at a high speed and low impact angle and the sphere begins to rotate very quickly. This quick rotation causes the sphere to stretch into a shape similar to an American football and maintain this shape while it spins. The sphere is observed to move nearly parallel with the water surface with the tips of this "football" dipping into the water as it rotates and the sides passing just over the surface. This sequence of rapid impact events give the impression that the sphere is walking across the water surface.

Cosmic-string-induced hot dark matter perturbations

NASA Technical Reports Server (NTRS)

Van Dalen, Anthony

1990-01-01

This paper investigates the evolution of initially relativistic matter, radiation, and baryons around cosmic string seed perturbations. A detailed analysis of the linear evolution of spherical perturbations in a universe is carried out, and this formalism is used to study the evolution of perturbations around a sphere of uniform density and fixed radius, approximating a loop of cosmic string. It was found that, on scales less than a few megaparsec, the results agree with the nonrelativistic calculation of previous authors. On greater scales, there is a deviation approaching a factor of 2-3 in the perturbation mass. It is shown that a scenario with cosmic strings, hot dark matter, and a Hubble constant greater than 75 km/sec per Mpc can generally produce structure on the observed mass scales and at the appropriate time: 1 + z = about 4 for galaxies and 1 + z = about 1.5 for Abell clusters.

Pentachlorophenol radical cations generated on Fe(III)-montmorillonite initiate octachlorodibenzo-p-dioxin formation in clays: DFT and FTIR studies

PubMed Central

Gu, Cheng; Liu, Cun; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.

2011-01-01

Octachlorodibenzodioxin (OCDD) forms spontaneously from pentachlorophenol (PCP) on the surfaces of Fe(III)-saturated smectite clay (1). Here, we used in situ FTIR methods and quantum mechanical calculations to determine the mechanism by which this reaction is initiated. As the clay was dehydrated, vibrational spectra showed new peaks that grew and then reversibly disappeared as the clay rehydrated. First principle DFT calculations of hydrated Fe-PCP clusters reproduced these transient FTIR peaks when inner-sphere complexation and concomitant electron transfer produced Fe(II) and PCP radical cations. Thus, our experimental (FTIR) and theoretical (quantum mechanical) results mutually support the hypothesis that OCDD formation on Fe-smectite surfaces is initiated by the reversible formation of metastable PCP radical cations via single electron transfer from PCP to Fe(III). The negatively charged clay surface apparently selects for this reaction mechanism by stabilizing PCP radical cations. PMID:21254769

Image method for electrostatic energy of polarizable dipolar spheres

NASA Astrophysics Data System (ADS)

Gustafson, Kyle S.; Xu, Guoxi; Freed, Karl F.; Qin, Jian

2017-08-01

The multiple-scattering theory for the electrostatics of many-body systems of monopolar spherical particles, embedded in a dielectric medium, is generalized to describe the electrostatics of these particles with embedded dipoles and multipoles. The Neumann image line construction for the electrostatic polarization produced by one particle is generalized to compute the energy, forces, and torques for the many-body system as functions of the positions of the particles. The approach is validated by comparison with direct numerical calculation, and the convergence rate is analyzed and expressed in terms of the discontinuity in dielectric contrast and particle density. As an illustration of this formalism, the stability of small particle clusters is analyzed. The theory is developed in a form that can readily be adapted to Monte Carlo and molecular dynamics simulations for polarizable particles and, more generally, to study the interactions among polarizable molecules.

Pore configuration landscape of granular crystallization.

PubMed

Saadatfar, M; Takeuchi, H; Robins, V; Francois, N; Hiraoka, Y

2017-05-12

Uncovering grain-scale mechanisms that underlie the disorder-order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics.

Pore configuration landscape of granular crystallization

PubMed Central

Saadatfar, M.; Takeuchi, H.; Robins, V.; Francois, N.; Hiraoka, Y.

2017-01-01

Uncovering grain-scale mechanisms that underlie the disorder–order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics. PMID:28497794

Pore configuration landscape of granular crystallization

NASA Astrophysics Data System (ADS)

Saadatfar, M.; Takeuchi, H.; Robins, V.; Francois, N.; Hiraoka, Y.

2017-05-01

Uncovering grain-scale mechanisms that underlie the disorder-order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics.

A discrete in continuous mathematical model of cardiac progenitor cells formation and growth as spheroid clusters (Cardiospheres).

PubMed

Di Costanzo, Ezio; Giacomello, Alessandro; Messina, Elisa; Natalini, Roberto; Pontrelli, Giuseppe; Rossi, Fabrizio; Smits, Robert; Twarogowska, Monika

2018-03-14

We propose a discrete in continuous mathematical model describing the in vitro growth process of biophsy-derived mammalian cardiac progenitor cells growing as clusters in the form of spheres (Cardiospheres). The approach is hybrid: discrete at cellular scale and continuous at molecular level. In the present model, cells are subject to the self-organizing collective dynamics mechanism and, additionally, they can proliferate and differentiate, also depending on stochastic processes. The two latter processes are triggered and regulated by chemical signals present in the environment. Numerical simulations show the structure and the development of the clustered progenitors and are in a good agreement with the results obtained from in vitro experiments.

Method and means for producing solid evacuated microspheres of hydrogen

DOEpatents

Turnbull, Robert J.; Foster, Christopher A.; Hendricks, Charles D.

1976-01-01

A method is provided for producing solid, evacuated microspheres comprised of hydrogen. The spheres are produced by forming a jet of liquid hydrogen and exciting mechanical waves on the jet of appropriate frequency so that the jet breaks up into drops with a bubble formed in each drop by cavitation. The drops are exposed to a pressure less than the vapor pressure of the liquid hydrogen so that the bubble which is formed within each drop expands. The drops which contain bubbles are exposed to an environment having a pressure just below the triple point of liquid hydrogen and they thereby freeze giving solid, evacuated spheres of hydrogen.

Development of a Thin-Film Solar Cell Interconnect for the Powersphere Concept

NASA Technical Reports Server (NTRS)

Simburger, Edward J.; Matsumoto, James H.; Giants, Thomas W.; Garcia, Alexander, III; Liu, Simon; Rawal, Suraj P.; Perry, Alan R.; Marshall, Craig; Lin, John K.; Scarborough, Stephen E.

2005-01-01

Dual junction amorphous silicon (a-Si) solar cells produced on polyimide substrate have been selected as the best candidate to produce a lightweight solar array for the PowerSphere program. The PowerSphere concept features a space-inflatable, geodetic solar array approximately 0.6 meters in diameter and capable of generating about 20W of electrical power. Trade studies of various wiring concepts and connection methods led to an interconnect design with a copper contact that wraps around the edge, to the back of the solar cell. Applying Plasma Vapor Deposited (PVD) copper film to both sides and the edge of the solar cell produces the wrap around contact. This procedure results in a contact pad on the back of the solar cell, which is then laser welded to a flex circuit material. The flex circuit is constructed of copper in a custom designed routing pattern, and then sandwiched in a Kapton insulation layer. The flex circuit then serves as the primary power distribution system between the solar cells and the spacecraft. Flex circuit material is the best candidate for the wiring harness because it allows for low force deployment of the solar cells by the inflatable hinges on the PowerSphere. An additional frame structure, fabricated and assembled by ILC Dover, will reinforce the wrap around contact-flex blanket connection, thus providing a mechanically robust solar cell interconnect for the PowerSphere multifunctional program. The PowerSphere team will use the wraparound contact design approach as the primary solution for solar cell integration and the flex blanket for power distribution.

A comparison of the fragmentation thresholds and inertial cavitation doses of different ultrasound contrast agents

NASA Astrophysics Data System (ADS)

Chen, Wen-Shiang; Matula, Thomas J.; Brayman, Andrew A.; Crum, Lawrence A.

2003-01-01

Contrast bubble destruction is important in several new diagnostic and therapeutic applications. The pressure threshold of destruction is determined by the shell material, while the propensity for of the bubbles to undergo inertial cavitation (IC) depends both on the gas and shell properties of the ultrasound contrast agent (UCA). The ultrasonic fragmentation thresholds of three specific UCAs (Optison, Sonazoid, and biSpheres), each with different shell and gas properties, were determined under various acoustic conditions. The acoustic emissions generated by the agents, or their derivatives, characteristic of IC after fragmentation, was also compared, using cumulated broadband-noise emissions (IC ``dose''). Albumin-shelled Optison and surfactant-shelled Sonazoid had low fragmentation thresholds (mean=0.13 and 0.15 MPa at 1.1 MHz, 0.48 and 0.58 MPa at 3.5 MHz, respectively), while polymer-shelled biSpheres had a significant higher threshold (mean=0.19 and 0.23 MPa at 1.1 MHz, 0.73 and 0.96 MPa for thin- and thick-shell biSpheres at 3.5 MHz, respectively, p<0.01). At comparable initial concentrations, surfactant-shelled Sonazoid produced a much larger IC dose after shell destruction than did either biSpheres or Optison (p<0.01). Thick-shelled biSpheres had the highest fragmentation threshold and produced the lowest IC dose. More than two and five acoustic cycles, respectively, were necessary for the thin- and thick-shell biSpheres to reach a steady-state fragmentation threshold.

Mean and Fluctuating Force Distribution in a Random Array of Spheres

NASA Astrophysics Data System (ADS)

Akiki, Georges; Jackson, Thomas; Balachandar, Sivaramakrishnan

2015-11-01

This study presents a numerical study of the force distribution within a cluster of mono-disperse spherical particles. A direct forcing immersed boundary method is used to calculate the forces on individual particles for a volume fraction range of [0.1, 0.4] and a Reynolds number range of [10, 625]. The overall drag is compared to several drag laws found in the literature. As for the fluctuation of the hydrodynamic streamwise force among individual particles, it is shown to have a normal distribution with a standard deviation that varies with the volume fraction only. The standard deviation remains approximately 25% of the mean streamwise force on a single sphere. The force distribution shows a good correlation between the location of two to three nearest upstream and downstream neighbors and the magnitude of the forces. A detailed analysis of the pressure and shear forces contributions calculated on a ghost sphere in the vicinity of a single particle in a uniform flow reveals a mapping of those contributions. The combination of the mapping and number of nearest neighbors leads to a first order correction of the force distribution within a cluster which can be used in Lagrangian-Eulerian techniques. We also explore the possibility of a binary force model that systematically accounts for the effect of the nearest neighbors. This work was supported by the National Science Foundation (NSF OISE-0968313) under Partnership for International Research and Education (PIRE) in Multiphase Flows at the University of Florida.

Formation of aggregated nanoparticle spheres through femtosecond laser surface processing

NASA Astrophysics Data System (ADS)

Tsubaki, Alfred T.; Koten, Mark A.; Lucis, Michael J.; Zuhlke, Craig; Ianno, Natale; Shield, Jeffrey E.; Alexander, Dennis R.

2017-10-01

A detailed structural and chemical analysis of a class of self-organized surface structures, termed aggregated nanoparticle spheres (AN-spheres), created using femtosecond laser surface processing (FLSP) on silicon, silicon carbide, and aluminum is reported in this paper. AN-spheres are spherical microstructures that are 20-100 μm in diameter and are composed entirely of nanoparticles produced during femtosecond laser ablation of material. AN-spheres have an onion-like layered morphology resulting from the build-up of nanoparticle layers over multiple passes of the laser beam. The material properties and chemical composition of the AN-spheres are presented in this paper based on scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) analysis. There is a distinct difference in the density of nanoparticles between concentric rings of the onion-like morphology of the AN-sphere. Layers of high-density form when the laser sinters nanoparticles together and low-density layers form when nanoparticles redeposit while the laser ablates areas surrounding the AN-sphere. The dynamic nature of femtosecond laser ablation creates a variety of nanoparticles that make-up the AN-spheres including Si/C core-shell, nanoparticles that directly fragmented from the base material, nanoparticles with carbon shells that retarded oxidation, and amorphous, fully oxidized nanoparticles.

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.

Percolation study for the capillary ascent of a liquid through a granular soil

NASA Astrophysics Data System (ADS)

Cárdenas-Barrantes, Manuel Antonio; Muñoz, José Daniel; Araujo, Nuno Machado

2017-06-01

Capillary rise plays a crucial role in the construction of road embankments in flood zones, where hydrophobic compounds are added to the soil to suppress the rising of water and avoid possible damage of the pavement. Water rises through liquid bridges, menisci and trimers, whose width and connectivity depends on the maximal half-length λ of the capillary bridges among grains. Low λs generate a disconnect structure, with small clusters everywhere. On the contrary, for high λ, create a percolating cluster of trimers and enclosed volumes that form a natural path for capillary rise. Hereby, we study the percolation transition of this geometric structure as a function of λ on a granular media of monodisperse spheres in a random close packing. We determine both the percolating threshold λc = (0.049 ± 0.004)R (with R the radius of the granular spheres), and the critical exponent of the correlation length v = 0.830 ± 0.051, suggesting that the percolation transition falls into the universality class of ordinary percolation.

Metallic-nanoparticles-enhanced fluorescence from individual micron-sized aerosol particles on-the-fly.

PubMed

Sivaprakasam, Vasanthi; Hart, Matthew B; Jain, Vaibhav; Eversole, Jay D

2014-08-11

Fluorescence spectra from individual aerosol particles that were either coated or embedded with metallic nanoparticles (MNPs) was acquired on-the-fly using 266 nm and 355 nm excitation. Using aqueous suspensions of MNPs with either polystyrene latex (PSL) spheres or dissolved proteins (tryptophan or ovalbumin), we generated PSL spheres coated with MNPs, or protein clusters embedded with MNPs as aerosols. Both enhanced and quenched fluorescence intensities were observed as a function of MNP concentration. Optimizing MNP material, size and spacing should yield enhanced sensitivity for specific aerosol materials that could be exploited to improve detection limits of single-particle, on-the-fly fluorescence or Raman based spectroscopic sensors.

Structure and anomalous solubility for hard spheres in an associating lattice gas model.

PubMed

Szortyka, Marcia M; Girardi, Mauricio; Henriques, Vera B; Barbosa, Marcia C

2012-08-14

In this paper we investigate the solubility of a hard-sphere gas in a solvent modeled as an associating lattice gas. The solution phase diagram for solute at 5% is compared with the phase diagram of the original solute free model. Model properties are investigated both through Monte Carlo simulations and a cluster approximation. The model solubility is computed via simulations and is shown to exhibit a minimum as a function of temperature. The line of minimum solubility (TmS) coincides with the line of maximum density (TMD) for different solvent chemical potentials, in accordance with the literature on continuous realistic models and on the "cavity" picture.

Support Vector Data Descriptions and k-Means Clustering: One Class?

PubMed

Gornitz, Nico; Lima, Luiz Alberto; Muller, Klaus-Robert; Kloft, Marius; Nakajima, Shinichi

2017-09-27

We present ClusterSVDD, a methodology that unifies support vector data descriptions (SVDDs) and k-means clustering into a single formulation. This allows both methods to benefit from one another, i.e., by adding flexibility using multiple spheres for SVDDs and increasing anomaly resistance and flexibility through kernels to k-means. In particular, our approach leads to a new interpretation of k-means as a regularized mode seeking algorithm. The unifying formulation further allows for deriving new algorithms by transferring knowledge from one-class learning settings to clustering settings and vice versa. As a showcase, we derive a clustering method for structured data based on a one-class learning scenario. Additionally, our formulation can be solved via a particularly simple optimization scheme. We evaluate our approach empirically to highlight some of the proposed benefits on artificially generated data, as well as on real-world problems, and provide a Python software package comprising various implementations of primal and dual SVDD as well as our proposed ClusterSVDD.

Down-to-earth studies of carbon clusters

NASA Technical Reports Server (NTRS)

Smalley, R. E.

1990-01-01

Recent advances in supersonic beam experiments with laser-vaporization sources of clusters have provided some interesting new insights into the nature of the small clusters of carbon, and the processes through which carbon condenses. One cluster in particular, C(sub 60), appears to play a central role. It is argued that this cluster takes the shape of a soccerball: a hollow sphere composed of a shell of 60 carbon atoms connected by a lattice of hexagonal and pentagonal rings, in a pattern of overall icosahedral symmetry. Although C(sub 60) appears to be uniquely stable due to its perfect symmetry, all other even-numbered carbon clusters in the 32 to 100+ atom size range seem to favor similar closed spheroidal forms. These species are interpreted as relatively unreactive side products in condensation reactions of carbon vapor involving spiraling graphitic sheets. The prevalence of C(sub 60) in laser-vaporized carbon vapors and sooting flames suggests that it may be formed readily whenever carbon condenses. Such ready formation and extraordinary stability may have substantial astrophysical implications.

Down-to-earth studies of carbon clusters

NASA Astrophysics Data System (ADS)

Smalley, R. E.

1990-04-01

Recent advances in supersonic beam experiments with laser-vaporization sources of clusters have provided some interesting new insights into the nature of the small clusters of carbon, and the processes through which carbon condenses. One cluster in particular, C60, appears to play a central role. It is argued that this cluster takes the shape of a soccer ball: a hollow sphere composed of a shell of 60 carbon atoms connected by a lattice of hexagonal and pentagonal rings, in a pattern of overall icosahedral symmetry. Although C60 appears to be uniquely stable due to its perfect symmetry, all other even-numbered carbon clusters in the 32 to 100+ atom size range seem to favor similar closed spheroidal forms. These species are interpreted as relatively unreactive side products in condensation reactions of carbon vapor involving spiraling graphitic sheets. The prevalence of C60 in laser-vaporized carbon vapors and sooting flames suggests that it may be formed readily whenever carbon condenses. Such ready formation and extraordinary stability may have substantial astrophysical implications.

Cryochemical and CVD processing of shperical carbide fuels for propulsion reactors

NASA Astrophysics Data System (ADS)

Blair, H. Thomas; Carroll, David W.; Matthews, R. Bruce

1991-01-01

Many of the nuclear propulsion reactor concepts proposed for a manned mission to Mars use a coated spherical particle fuel form similar to that used in the Rover and NERVA propulsion reactors. The formation of uranium dicarbide microspheres using a cryochemical process and the coating of the UC2 spheres with zirconium carbide using chemical vapor deposition are being developed at Los Alamos National Laboratory. The cryochemical process is described with a discussion of the variables affecting the sphere formation and carbothermic reduction to produce UC2 spheres from UO2. Emphasis is placed on minimizing the wastes produced by the process. The ability to coat particles with ZrC was recaptured, and improvements in the process and equipment were developed. Volatile organometallic precursors were investigated as alternatives to the original ZrCl4 precursor.

Effect of laser irradiation on the early-stage seed formation of laser-induced submicrometer-scale silica spheres

NASA Astrophysics Data System (ADS)

Kim, H. J.; Ha, S. Y.; Hong, Y. J.; Nam, S.; Oh, S. Y.; Lim, C.

2014-04-01

We describe the effect of irradiation on the early-stage seed formation of submicrometer-scale (SS) SiO2 spheres by a laser-induced process. A quartz cell containing chemical reagents was exposed to a pulsed laser (Nd:YAG, 532 nm) tuned to various energy densities, while SiO2 SS spheres are synthesized in the quartz cell by the Stöber, Fink, and Bohn method. Higher laser energy densities typically produce wider size distributions. In particular, bidisperse SiO2 spheres were obtained when the laser energy density was 1.15 J/cm2. The size distributions were widest with 1.15 J/cm2 and narrowest with 0.33 J/cm2 laser energy density. However, the compositions of the SiO2 SS spheres were not affected by laser irradiation, and we observed by the energy-dispersive X-ray spectroscopy that the compositions of the irradiated and nonirradiated SiO2 SS spheres were the same.

Novel one-step route for synthesizing CdS/polystyrene nanocomposite hollow spheres.

PubMed

Wu, Dazhen; Ge, Xuewu; Zhang, Zhicheng; Wang, Mozhen; Zhang, Songlin

2004-06-22

CdS/polystyrene nanocomposite hollow spheres with diameters between 240 and 500 nm were synthesized under ambient conditions by a novel microemulsion method in which the polymerization of styrene and the formation of CdS nanoparticles were initiated by gamma-irradiation. The product was characterized by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA), which show the walls of the hollow spheres are porous and composed of polystyrene containing homogeneously dispersed CdS nanoparticles. The quantum-confined effect of the CdS/polystyrene nanocomposite hollow spheres is confirmed by the ultraviolet-visible (UV-vis) and photoluminescent (PL) spectra. We propose that the walls of these nanocomposite hollow spheres originate from the simultaneous synthesis of polystyrene and CdS nanoparticles at the interface of microemulsion droplets. This novel method is expected to produce various inorganic/polymer nanocomposite hollow spheres with potential applications in the fields of materials science and biotechnology.

Structure and thermodynamics of a mixture of patchy and spherical colloids: A multi-body association theory with complete reference fluid information

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

Bansal, Artee; Asthagiri, D.; Cox, Kenneth R.

A mixture of solvent particles with short-range, directional interactions and solute particles with short-range, isotropic interactions that can bond multiple times is of fundamental interest in understanding liquids and colloidal mixtures. Because of multi-body correlations, predicting the structure and thermodynamics of such systems remains a challenge. Earlier Marshall and Chapman [J. Chem. Phys. 139, 104904 (2013)] developed a theory wherein association effects due to interactions multiply the partition function for clustering of particles in a reference hard-sphere system. The multi-body effects are incorporated in the clustering process, which in their work was obtained in the absence of the bulk medium.more » The bulk solvent effects were then modeled approximately within a second order perturbation approach. However, their approach is inadequate at high densities and for large association strengths. Based on the idea that the clustering of solvent in a defined coordination volume around the solute is related to occupancy statistics in that defined coordination volume, we develop an approach to incorporate the complete information about hard-sphere clustering in a bulk solvent at the density of interest. The occupancy probabilities are obtained from enhanced sampling simulations but we also develop a concise parametric form to model these probabilities using the quasichemical theory of solutions. We show that incorporating the complete reference information results in an approach that can predict the bonding state and thermodynamics of the colloidal solute for a wide range of system conditions.« less

Close-packed monolayer self-assembly of silica nanospheres assisted by infrared irradiation

NASA Astrophysics Data System (ADS)

Minh, Nguyen Van; Hue, Nguyen Thi; Lien, Nghiem Thi Ha; Hoang, Chu Manh

2018-01-01

In this paper, we report on a fast and cost-effective drop coating technique for the self-assembly of silica nano-spheres from a mono-dispersed colloidal suspension into close-packed monolayer (CMP) on hydrophilic single-crystal silicon substrate. The technique includes the self-assembly of silica nano-spheres on slanted silicon substrate and infrared irradiation during evaporation process of the coated droplet. The influence of the substrate slant angle and infrared irradiation on the formation of silica nano-sphere monolayer is investigated. This achievement is promising for various applications, such as a mask layer for nano-sphere lithography that is employed for producing fundamental elements in photonics, plasmonics, and solar cell. [Figure not available: see fulltext.

Method of preparing copper-dendritic composite alloys for mechanical reduction

DOEpatents

Verhoeven, John D.; Gibson, Edwin D.; Schmidt, Frederick A.; Spitzig, William A.

1988-01-01

Copper-dendritic composite alloys are prepared for mechanical reduction to increase tensile strength by dispersing molten droplets of the composite alloy into an inert gas; solidifying the droplets in the form of minute spheres or platelets; and compacting a mass of the spheres or platelets into an integrated body. The spheres preferably have diameters of from 50 to 2000 .mu.m, and the platelets thicknesses of 100 to 2000 .mu.m. The resulting spheres or platelets will contain ultra-fine dendrites which produce higher strengths on mechanical reduction of the bodies formed therefrom, or comparable strengths at lower reduction values. The method is applicable to alloys of copper with vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron and cobalt.

Method of preparing copper-dendritic composite alloys for mechanical reduction

DOEpatents

Verhoeven, J.D.; Gibson, E.D.; Schmidt, F.A.; Spitzig, W.A.

1988-09-13

Copper-dendritic composite alloys are prepared for mechanical reduction to increase tensile strength by dispersing molten droplets of the composite alloy into an inert gas; solidifying the droplets in the form of minute spheres or platelets; and compacting a mass of the spheres or platelets into an integrated body. The spheres preferably have diameters of from 50 to 2,000 [mu]m, and the platelets thicknesses of 100 to 2,000 [mu]m. The resulting spheres or platelets will contain ultra-fine dendrites which produce higher strengths on mechanical reduction of the bodies formed therefrom, or comparable strengths at lower reduction values. The method is applicable to alloys of copper with vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron and cobalt. 3 figs.

Neck formation and deformation effects in a preformed cluster model of exotic cluster decays

NASA Astrophysics Data System (ADS)

Kumar, Satish; Gupta, Raj K.

1997-01-01

Using the nuclear proximity approach and the two center nuclear shape parametrization, the interaction potential between two deformed and pole-to-pole oriented nuclei forming a necked configuration in the overlap region is calculated and its role is studied for the cluster decay half-lives. The barrier is found to move to a larger relative separation, with its proximity minimum lying in the neighborhood of the Q value of decay and its height and width reduced considerably. For cluster decay calculations in the preformed cluster model of Malik and Gupta, due to deformations and orientations of nuclei, the (empirical) preformation factor is found to get reduced considerably and agrees nicely with other model calculations known to be successful for their predictions of cluster decay half-lives. Comparison with the earlier case of nuclei treated as spheres suggests that the effects of both deformations and neck formation get compensated by choosing the position of cluster preformation and the inner classical turning point for penetrability calculations at the touching configuration of spherical nuclei.

Spontaneous emergence of catalytic cycles with colloidal spheres

NASA Astrophysics Data System (ADS)

Zeravcic, Zorana; Brenner, Michael P.

2017-04-01

Colloidal particles endowed with specific time-dependent interactions are a promising route for realizing artificial materials that have the properties of living ones. Previous work has demonstrated how this system can give rise to self-replication. Here, we introduce the process of colloidal catalysis, in which clusters of particles catalyze the creation of other clusters through templating reactions. Surprisingly, we find that simple templating rules generically lead to the production of huge numbers of clusters. The templating reactions among this sea of clusters give rise to an exponentially growing catalytic cycle, a specific realization of Dyson’s notion of an exponentially growing metabolism. We demonstrate this behavior with a fixed set of interactions between particles chosen to allow a catalysis of a specific six-particle cluster from a specific seven-particle cluster, yet giving rise to the catalytic production of a sea of clusters of sizes between 2 and 11 particles. The fact that an exponentially growing cycle emerges naturally from such a simple scheme demonstrates that the emergence of exponentially growing metabolisms could be simpler than previously imagined.

Kinematics of the Doped Quantum Vortices in Superfluid Helium Droplets

NASA Astrophysics Data System (ADS)

Bernando, Charles; Vilesov, Andrey F.

2018-05-01

Recent observation of quantum vortices in superfluid 4He droplets measuring a few hundreds of nanometers in diameter involved decoration of vortex cores by clusters containing large numbers of Xe atoms, which served as X-ray contrast agents. Here, we report on the study of the kinematics of the combined vortex-cluster system in a cylinder and in a sphere. Equilibrium states, characterized by total angular momentum, L, were found by minimizing the total energy, E, which sums from the kinetic energy of the liquid due to the vortex and due to orbiting Xe clusters, as well as solvation energy of the cluster in the droplet. Calculations show that, at small mass of the cluster, the equilibrium displacement of the system from the rotation axis is close to that for the bare vortex. However, upon decrease in L beyond certain critical value, which is larger for heavier clusters, the displacement bifurcates toward the surface region, where the motion of the system is governed by the clusters. In addition, at even smaller L, bare orbiting clusters become energetically favorable, opening the possibility for the vortex to detach from the cluster and to annihilate at the droplet's surface.

Hierarchical Self-Organization of Perylene Bisimides into Supramolecular Spheres and Periodic Arrays Thereof.

PubMed

Sahoo, Dipankar; Peterca, Mihai; Aqad, Emad; Partridge, Benjamin E; Heiney, Paul A; Graf, Robert; Spiess, Hans W; Zeng, Xiangbing; Percec, Virgil

2016-11-09

Perylene bisimide derivatives (PBIs) are known to form only columnar or lamellar assemblies. There is no known example of a PBI self-assembling into a supramolecular sphere. Therefore, periodic and quasiperiodic arrays generated from spherical assemblies produced from PBIs are also not known. Here, a PBI functionalized at its imide groups with a second generation self-assembling dendron is reported to self-assemble into supramolecular spheres. These spheres self-organize in a body-centered cubic (BCC) periodic array, rarely encountered for self-assembling dendrons but often encountered in block copolymers. These supramolecular spheres also assemble into a columnar hexagonal array in which the supramolecular columns are unexpectedly and unprecedentedly made from spheres. At lower temperature, two additional columnar hexagonal phases consisting of symmetric and asymmetric tetrameric crowns of PBI are observed. Structural and retrostructural analysis via X-ray diffraction (XRD), molecular modeling, molecular simulation, and solid state NMR suggests that inversion of the symmetric tetrameric crowns at high temperature mediates their transformation into supramolecular spheres. The tetrameric crowns of PBIs are able to form an isotropic sphere in the cubic phase due to rapid molecular motion at high temperature, unobservable by XRD but demonstrated by solid state NMR studies. This mechanism of hierarchical self-organization of PBI into supramolecular spheres is most probably general and can be applied to other related planar molecules to generate new functions.

Feminist Attitudes and Support for Gender Equality: Opinion Change in Women and Men, 1974-1998

ERIC Educational Resources Information Center

Bolzendahl, Catherine I.; Myers, Daniel J.

2004-01-01

This article examines attitudes related to feminism and gender equality by evaluating the trends in, and determinants of, women and men's attitudes from 1974 to 1998. Past accounts suggest two clusters of explanations based on interests and exposure. Using these, we examine opinions on abortion, sexual behavior, public sphere gender roles, and…

Cluster analysis of multiple planetary flow regimes

NASA Technical Reports Server (NTRS)

Mo, Kingtse; Ghil, Michael

1987-01-01

A modified cluster analysis method was developed to identify spatial patterns of planetary flow regimes, and to study transitions between them. This method was applied first to a simple deterministic model and second to Northern Hemisphere (NH) 500 mb data. The dynamical model is governed by the fully-nonlinear, equivalent-barotropic vorticity equation on the sphere. Clusters of point in the model's phase space are associated with either a few persistent or with many transient events. Two stationary clusters have patterns similar to unstable stationary model solutions, zonal, or blocked. Transient clusters of wave trains serve as way stations between the stationary ones. For the NH data, cluster analysis was performed in the subspace of the first seven empirical orthogonal functions (EOFs). Stationary clusters are found in the low-frequency band of more than 10 days, and transient clusters in the bandpass frequency window between 2.5 and 6 days. In the low-frequency band three pairs of clusters determine, respectively, EOFs 1, 2, and 3. They exhibit well-known regional features, such as blocking, the Pacific/North American (PNA) pattern and wave trains. Both model and low-pass data show strong bimodality. Clusters in the bandpass window show wave-train patterns in the two jet exit regions. They are related, as in the model, to transitions between stationary clusters.

Morphology of clusters of attractive dry and wet self-propelled spherical particle suspensions.

PubMed

Alarcón, Francisco; Valeriani, Chantal; Pagonabarraga, Ignacio

2017-01-25

In order to assess the effect of hydrodynamics in the assembly of active attractive spheres, we simulate a semi-dilute suspension of attractive self-propelled spherical particles in a quasi-two dimensional geometry comparing the case with and without hydrodynamics interactions. To start with, independent of the presence of hydrodynamics, we observe that depending on the ratio between attraction and propulsion, particles either coarsen or aggregate forming finite-size clusters. Focusing on the clustering regime, we characterize two different cluster parameters, i.e. their morphology and orientational order, and compare the case when active particles behave either as pushers or pullers (always in the regime where inter-particle attractions compete with self-propulsion). Studying cluster phases for squirmers with respect to those obtained for active Brownian disks (indicated as ABPs), we have shown that hydrodynamics alone can sustain a cluster phase of active swimmers (pullers), while ABPs form cluster phases due to the competition between attraction and self-propulsion. The structural properties of the cluster phases of squirmers and ABPs are similar, although squirmers show sensitivity to active stresses. Active Brownian disks resemble weakly pusher squirmer suspensions in terms of cluster size distribution, structure of the radius of gyration on the cluster size and degree of cluster polarity.

Controlled Expansion of a Strong-Field Iron Nitride Cluster: Multi-Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity.

PubMed

Drance, Myles J; Mokhtarzadeh, Charles C; Melaimi, Mohand; Agnew, Douglas W; Moore, Curtis E; Rheingold, Arnold L; Figueroa, Joshua S

2018-05-02

Multimetallic clusters have long been investigated as molecular surrogates for reactive sites on metal surfaces. In the case of the μ 4 -nitrido cluster [Fe 4 (μ 4 -N)(CO) 12 ] - , this analogy is limited owing to the electron-withdrawing effect of carbonyl ligands on the iron nitride core. Described here is the synthesis and reactivity of [Fe 4 (μ 4 -N)(CO) 8 (CNAr Mes2 ) 4 ] - , an electron-rich analogue of [Fe 4 (μ 4 -N)(CO) 12 ] - , where the interstitial nitride displays significant nucleophilicity. This characteristic enables rational expansion with main-group and transition-metal centers to yield unsaturated sites. The resulting clusters display surface-like reactivity through coordination-sphere-dependent atom rearrangement and metal-metal cooperativity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Regularities in the sequences of the number of nucleons in the revolving clusters for the ground-state energy bands of the even-even nuclei with neutron number equal to or greater than 126.

PubMed

Pauling, L

1990-06-01

Values of m, the number of nucleons in the revolving cluster, and of R, the radius of revolution of the cluster about the center of mass of the spherical part of the nucleus, are calculated from the observed values of the energy for the ground-state bands of all nuclei with neutron number N >/= 126 on the basis of the assumptions (i) that both m and R change in a reasonable way with increase in the angular momentum quantum number J and with change in the proton number Z and the neutron number N, (ii) that m is usually an even integer, (iii) that certain clusters are especially stable, and (iv) that there is a special stability of the doubly magic sphere p82n126.

Regularities in the sequences of the number of nucleons in the revolving clusters for the ground-state energy bands of the even-even nuclei with neutron number equal to or greater than 126.

PubMed Central

Pauling, L

1990-01-01

Values of m, the number of nucleons in the revolving cluster, and of R, the radius of revolution of the cluster about the center of mass of the spherical part of the nucleus, are calculated from the observed values of the energy for the ground-state bands of all nuclei with neutron number N >/= 126 on the basis of the assumptions (i) that both m and R change in a reasonable way with increase in the angular momentum quantum number J and with change in the proton number Z and the neutron number N, (ii) that m is usually an even integer, (iii) that certain clusters are especially stable, and (iv) that there is a special stability of the doubly magic sphere p82n126. PMID:11607085

Mapping the formation areas of giant molybdenum blue clusters: a spectroscopic study

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

Botar, Bogdan; Ellern, Arkady; Kogerler, Paul

2012-05-18

The self-assembly of soluble molybdenum blue species from simple molybdate solutions has primarily been associated with giant mixed-valent wheel-shaped cluster anions, derived from the {MoV/VI154/176} archetypes, and a {MoV/VI368} lemon-shaped cluster. The combined use of Raman spectroscopy and kinetic precipitation as self-assembly monitoring techniques and single-crystal X-ray diffraction is key to mapping the realm of molybdenum blue species by establishing spherical {MoV/VI102}-type Keplerates as an important giant molybdenum blue-type species. We additionally rationalize the empirical effect of reducing agent concentration on the formation of all three relevant skeletal types: wheel, lemon and spheres. Whereas both wheels and the lemon-shaped {MoV/VI368}more » cluster are obtained from weakly reduced molybdenum blue solutions, considerably higher reduced solutions lead to {MoV/VI102}-type Keplerates.« less

Preparation of Geophysical Fluid Flow Experiments With The Rotating Spherical Gap Flow Model In Space

NASA Astrophysics Data System (ADS)

Egbers, C.

The'GeoFlow' is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluid Mechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field simi- lar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment re- quires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth`s liquid core the experiment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heat- ing the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number.

Two Ti13-oxo-clusters showing non-compact structures, film electrode preparation and photocurrent properties.

PubMed

Hou, Jin-Le; Luo, Wen; Wu, Yin-Yin; Su, Hu-Chao; Zhang, Guang-Lin; Zhu, Qin-Yu; Dai, Jie

2015-12-14

Two benzene dicarboxylate (BDC) and salicylate (SAL) substituted titanium-oxo-clusters, Ti13O10(o-BDC)4(SAL)4(O(i)Pr)16 (1) and Ti13O10(o-BDC)4(SAL-Cl)4(O(i)Pr)16 (2), are prepared by one step in situ solvothermal synthesis. Single crystal analysis shows that the two Ti13 clusters take a paddle arrangement with an S4 symmetry. The non-compact (non-sphere) structure is stabilized by the coordination of BDC and SAL. Film photoelectrodes are prepared by the wet coating process using the solution of the clusters and the photocurrent response properties of the electrodes are studied. It is found that the photocurrent density and photoresponsiveness of the electrodes are related to the number of coating layers and the annealing temperature. Using ligand coordinated titanium-oxo-clusters as the molecular precursors of TiO2 anatase films is found to be effective due to their high solubility, appropriate stability in solution and hence the easy controllability.

Experimental study of the oscillation of spheres in an acoustic levitator.

PubMed

Andrade, Marco A B; Pérez, Nicolás; Adamowski, Julio C

2014-10-01

The spontaneous oscillation of solid spheres in a single-axis acoustic levitator is experimentally investigated by using a high speed camera to record the position of the levitated sphere as a function of time. The oscillations in the axial and radial directions are systematically studied by changing the sphere density and the acoustic pressure amplitude. In order to interpret the experimental results, a simple model based on a spring-mass system is applied in the analysis of the sphere oscillatory behavior. This model requires the knowledge of the acoustic pressure distribution, which was obtained numerically by using a linear finite element method (FEM). Additionally, the linear acoustic pressure distribution obtained by FEM was compared with that measured with a laser Doppler vibrometer. The comparison between numerical and experimental pressure distributions shows good agreement for low values of pressure amplitude. When the pressure amplitude is increased, the acoustic pressure distribution becomes nonlinear, producing harmonics of the fundamental frequency. The experimental results of the spheres oscillations for low pressure amplitudes are consistent with the results predicted by the simple model based on a spring-mass system.

Volume determination of two spheres of the new 28Si crystal of PTB

NASA Astrophysics Data System (ADS)

Nicolaus, A.; Bartl, G.; Peter, A.; Kuhn, E.; Mai, T.

2017-08-01

In the scope of the redetermination of Avogadro’s constant N A, a new isotopically enriched silicon crystal has been produced, from which two spheres were manufactured. After the crystal properties, the lattice parameter and molar mass, as well as the masses of the two spheres have been determined, the volume of the spheres was also measured. For this, the sphere interferometer of PTB was used. The methods of the interferometric measurements have been improved and the major contributions to the uncertainty have been investigated thoroughly. As a result, the total uncertainty could be reduced significantly, yielding a substantial impact on the determination of Avogadro’s constant. The mean diameter of each sphere was measured twice with a repeatability of  ±2  ×  10-10, and the relative uncertainty of the ‘apparent’ volume, which disregards the comparatively small influence of the optical effects of surface layers, was reduced to 7  ×  10-9. The final results of the volumes and comments on their uncertainties are given.

The statistical average of optical properties for alumina particle cluster in aircraft plume

NASA Astrophysics Data System (ADS)

Li, Jingying; Bai, Lu; Wu, Zhensen; Guo, Lixin

2018-04-01

We establish a model for lognormal distribution of monomer radius and number of alumina particle clusters in plume. According to the Multi-Sphere T Matrix (MSTM) theory, we provide a method for finding the statistical average of optical properties for alumina particle clusters in plume, analyze the effect of different distributions and different detection wavelengths on the statistical average of optical properties for alumina particle cluster, and compare the statistical average optical properties under the alumina particle cluster model established in this study and those under three simplified alumina particle models. The calculation results show that the monomer number of alumina particle cluster and its size distribution have a considerable effect on its statistical average optical properties. The statistical average of optical properties for alumina particle cluster at common detection wavelengths exhibit obvious differences, whose differences have a great effect on modeling IR and UV radiation properties of plume. Compared with the three simplified models, the alumina particle cluster model herein features both higher extinction and scattering efficiencies. Therefore, we may find that an accurate description of the scattering properties of alumina particles in aircraft plume is of great significance in the study of plume radiation properties.

Evaluation of hierarchical agglomerative cluster analysis methods for discrimination of primary biological aerosol

NASA Astrophysics Data System (ADS)

Crawford, I.; Ruske, S.; Topping, D. O.; Gallagher, M. W.

2015-11-01

In this paper we present improved methods for discriminating and quantifying primary biological aerosol particles (PBAPs) by applying hierarchical agglomerative cluster analysis to multi-parameter ultraviolet-light-induced fluorescence (UV-LIF) spectrometer data. The methods employed in this study can be applied to data sets in excess of 1 × 106 points on a desktop computer, allowing for each fluorescent particle in a data set to be explicitly clustered. This reduces the potential for misattribution found in subsampling and comparative attribution methods used in previous approaches, improving our capacity to discriminate and quantify PBAP meta-classes. We evaluate the performance of several hierarchical agglomerative cluster analysis linkages and data normalisation methods using laboratory samples of known particle types and an ambient data set. Fluorescent and non-fluorescent polystyrene latex spheres were sampled with a Wideband Integrated Bioaerosol Spectrometer (WIBS-4) where the optical size, asymmetry factor and fluorescent measurements were used as inputs to the analysis package. It was found that the Ward linkage with z-score or range normalisation performed best, correctly attributing 98 and 98.1 % of the data points respectively. The best-performing methods were applied to the BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen-Rocky Mountain Biogenic Aerosol Study) ambient data set, where it was found that the z-score and range normalisation methods yield similar results, with each method producing clusters representative of fungal spores and bacterial aerosol, consistent with previous results. The z-score result was compared to clusters generated with previous approaches (WIBS AnalysiS Program, WASP) where we observe that the subsampling and comparative attribution method employed by WASP results in the overestimation of the fungal spore concentration by a factor of 1.5 and the underestimation of bacterial aerosol concentration by a factor of 5. We suggest that this likely due to errors arising from misattribution due to poor centroid definition and failure to assign particles to a cluster as a result of the subsampling and comparative attribution method employed by WASP. The methods used here allow for the entire fluorescent population of particles to be analysed, yielding an explicit cluster attribution for each particle and improving cluster centroid definition and our capacity to discriminate and quantify PBAP meta-classes compared to previous approaches.

Density functional theory studies on the solvent effects in Al(H2O)63+ water-exchange reactions: the number and arrangement of outer-sphere water molecules.

PubMed

Liu, Li; Zhang, Jing; Dong, Shaonan; Zhang, Fuping; Wang, Ye; Bi, Shuping

2018-03-07

Density functional theory (DFT) calculations combined with cluster models are performed at the B3LYP/6-311+G(d,p) level for investigating the solvent effects in Al(H 2 O) 6 3+ water-exchange reactions. A "One-by-one" method is proposed to obtain the most representative number and arrangement of explicit H 2 Os in the second hydration sphere. First, all the possible ways to locate one explicit H 2 O in second sphere (N m ' = 1) based on the gas phase structure (N m ' = 0) are examined, and the optimal pathway (with the lowest energy barrier) for N m ' = 1 is determined. Next, more explicit H 2 Os are added one by one until the inner-sphere is fully hydrogen bonded. Finally, the optimal pathways with N m ' = 0-7 are obtained. The structural and energetic parameters as well as the lifetimes of the transition states are compared with the results obtained with the "Independent-minimum" method and the "Independent-average" method, and all three methods show that the pathway with N m ' = 6 may be representative. Our results give a new idea for finding the representative pathway for water-exchange reactions in other hydrated metal ion systems.

LOW VELOCITY SHPERE IMPACT OF SODA LIME SILICATE GLASS

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

Morrissey, Timothy G; Fox, Ethan E; Wereszczak, Andrew A

2012-01-01

This report summarizes TARDEC-sponsored work at Oak Ridge National Laboratory (ORNL) during the FY11 involving low velocity ( 30 m/s or 65 mph) ball impact testing of Starphire soda lime silicate glass. The intent was to better understand low velocity impact response in the Starphire for sphere densities that bracketed that of rock. Five sphere materials were used: borosilicate glass, soda-lime silicate glass, steel, silicon nitride, and alumina. A gas gun was fabricated to produce controlled velocity delivery of the spheres against Starphire tile targets. Minimum impact velocities to initiate fracture in the Starphire were measured and interpreted in contextmore » to the kinetic energy of impact and the elastic property mismatch between the any of the five sphere-Starphire-target combinations.« less

Method for producing small hollow spheres

DOEpatents

Rosencwaig, Allen; Koo, Jackson C.; Dressler, John L.

1981-01-01

A method for producing small hollow spheres of glass having an outer diameter ranging from about 100.mu. to about 500.mu. with a substantially uniform wall thickness in the range of about 0.5-20.mu.. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions. In one embodiment, one of the temperature regions is lower than both the preceeding region and the subsequent region. One region utilizes a temperature of at least 200.degree. C. higher than the melting point of the glass-forming material in the solution and, for example, may be at least 3 times higher than the temperature of the preceeding region. In addition, there is a sharp temperature gradient between these regions. As each droplet of solution passes through a first region it forms into a gel membrane having a spherical shape and encapsulates the rest of the drop retained in the elastic outer surface and the water entrapped within diffuses rapidly through the thin gel membrane which causes more of the glass-forming material to go out of solution and is incorporated into the gel membrane causing it to grow in size and become hollow. thus produced hollow glass sphere has a sphericity, concentricity, and wall uniformity of better than 5%. The sphere is capable of retaining material of up to at least 100 atmospheres therein over long periods of time. In one embodiment.

Criticality in charge-asymmetric hard-sphere ionic fluids.

PubMed

Aqua, Jean-Noël; Banerjee, Shubho; Fisher, Michael E

2005-10-01

Phase separation and criticality are analyzed in z:1 charge-asymmetric ionic fluids of equisized hard spheres by generalizing the Debye-Hückel approach combined with ionic association, cluster solvation by charged ions, and hard-core interactions, following lines developed by Fisher and Levin for the 1:1 case (i.e., the restricted primitive model). Explicit analytical calculations for 2:1 and 3:1 systems account for ionic association into dimers, trimers, and tetramers and subsequent multipolar cluster solvation. The reduced critical temperatures, Tc* (normalized by z), decrease with charge asymmetry, while the critical densities increase rapidly with . The results compare favorably with simulations and represent a distinct improvement over all current theories such as the mean spherical approximation, symmetric Poisson-Boltzmann theory, etc. For z not equal to 1, the interphase Galvani (or absolute electrostatic) potential difference, Deltaphi(T), between coexisting liquid and vapor phases is calculated and found to vanish as absolute value (T-Tc) beta when T-->Tc-with, since our approximations are classical, beta = (1/2). Above Tc, the compressibility maxima and so-called k-inflection loci (which aid the fast and accurate determination of the critical parameters) are found to exhibit a strong z dependence.

Sphere-shaped nano-hydroxyapatite/chitosan/gelatin 3D porous scaffolds increase proliferation and osteogenic differentiation of human induced pluripotent stem cells from gingival fibroblasts.

PubMed

Ji, Jun; Tong, Xin; Huang, Xiaofeng; Wang, Tiancong; Lin, Zitong; Cao, Yazhou; Zhang, Junfeng; Dong, Lei; Qin, Haiyan; Hu, Qingang

2015-07-08

Hydroxyapatite (HA) is an important component of human bone and bone tissue engineering scaffolds. A plethora of bone tissue engineering scaffolds have been synthesized so far, including nano-HA/chitosan/gelatin (nHA/CG) scaffolds; and for seeding cells, stem cells, especially induced pluripotent stem cells (iPSCs), have been a promising cell source for bone tissue engineering recently. However, the influence of different HA nano-particle morphologies on the osteogenic differentiation of human iPSCs (hiPSCs) from human gingival fibroblasts (hGFs) is unknown. The purpose of this study was to investigate the osteogenic differentiation of hiPSCs from hGFs seeded on nHA/CG scaffolds with 2 shapes (rod and sphere) of nHA particles. Firstly, hGFs isolated from discarded normal gingival tissues were reprogrammed into hiPSCs. Secondly, hiPSCs were seeded on rod-like nHA/CG (rod-nHA/CG) and sphere-shaped nHA/CG (sphere-nHA/CG) scaffolds respectively and then cell/scaffold complexes were cultured in vitro. Scanning electron microscope, hematoxyline and eosin (HE) staining, Masson's staining, and quantitative real-time polymerase chain reaction techniques were used to examine hiPSC morphology, proliferation, and differentiation on rod-nHA/CG and sphere-nHA/CG scaffolds. Finally, hiPSCs composited with 2 kinds of nHA/CG were transplanted in vivo in a subcutaneous implantation model for 12 weeks; pure scaffolds were also transplanted as a blank control. HE, Masson's, and immunohistochemistry staining were applied to detect new bone regeneration ability. The results showed that sphere-nHA/CG significantly increased hiPSCs from hGF proliferation and osteogenic differentiation in vitro. hiPSCs and sphere-nHA/CG composities generated large bone, whereas hiPSCs and rod-nHA/CG composities produced tiny bone in vivo. Moreover, pure scaffolds without cells almost produced no bone. In conclusion, our work provided a potential innovative bone tissue engineering approach using clinically discarded gingival tissues and sphere-nHA/CG scaffolds.

[Impact of point spread function correction in standardized uptake value quantitation for positron emission tomography images: a study based on phantom experiments and clinical images].

PubMed

Nakamura, Akihiro; Tanizaki, Yasuo; Takeuchi, Miho; Ito, Shigeru; Sano, Yoshitaka; Sato, Mayumi; Kanno, Toshihiko; Okada, Hiroyuki; Torizuka, Tatsuo; Nishizawa, Sadahiko

2014-06-01

While point spread function (PSF)-based positron emission tomography (PET) reconstruction effectively improves the spatial resolution and image quality of PET, it may damage its quantitative properties by producing edge artifacts, or Gibbs artifacts, which appear to cause overestimation of regional radioactivity concentration. In this report, we investigated how edge artifacts produce negative effects on the quantitative properties of PET. Experiments with a National Electrical Manufacturers Association (NEMA) phantom, containing radioactive spheres of a variety of sizes and background filled with cold air or water, or radioactive solutions, showed that profiles modified by edge artifacts were reproducible regardless of background μ values, and the effects of edge artifacts increased with increasing sphere-to-background radioactivity concentration ratio (S/B ratio). Profiles were also affected by edge artifacts in complex fashion in response to variable combinations of sphere sizes and S/B ratios; and central single-peak overestimation up to 50% was occasionally noted in relatively small spheres with high S/B ratios. Effects of edge artifacts were obscured in spheres with low S/B ratios. In patient images with a variety of focal lesions, areas of higher radioactivity accumulation were generally more enhanced by edge artifacts, but the effects were variable depending on the size of and accumulation in the lesion. PET images generated using PSF-based reconstruction are therefore not appropriate for the evaluation of SUV.

Bushy sphere dendrites with husk-shaped branches axially spreading out from the core for photo-catalytic oxidation/remediation of toxins.

PubMed

Shenashen, Mohamed A; Kawada, Satoshi; Selim, Mahmoud M; Morsy, Wafaa M; Yamaguchi, Hitoshi; Alhamid, Abdulaziz A; Ohashi, Naoki; Ichinose, Izumi; El-Safty, Sherif A

2017-06-14

This work describes densely interlinked bushy "tree-like chains" characterized by neatly branched sphere dendrites (bushy sphere dendrites, BSD) with long fan-like, husk-shaped branching paths that extend longitudinally from the core axis of the {110}-exposed plane. We confirmed that the hierarchical dendrite surfaces created bowls of swirled caves along the tree-tube in the mat-like branches. These surfaces had high-index catalytic site facets associated with the formation of ridges/defects on the dominant {110}-top-cover surface. These swirled caves along the branches were completely filled with 50-100 nm poly-CN nano-sphere-fossils with orb-like appearance. Such structural features are key issues of the inherent surface reactivity of a powerful catalyst/trapper, enabling photocatalytic oxidation and trapping of extremely toxic arsenite (AsO 3 3- ) species and photo-induced recovery of arsenate (AsO 4 3- ) products from catalyst surfaces. The light-induced release of produced AsO 4 3- from BSD indicates (i) highly controlled waste collection/management (i.e., recovery), (ii) low cost and ecofriendly photo-adsorbent, (iii) selective trapping of real sample water to produce water-free arsenite species; (iv) multiple reuse cycles of catalysts (i.e., reduced waste volume). Matrixed dendrites, covered with 3D microscopic sphere cores that capture solar-light, trap toxins, and are triggered by light, were designed. These dendrites can withstand indoor and outdoor recovery of toxins from water sources.

Mesoporous carbon spheres with controlled porosity for high-performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Wang, Dexian; Fu, Aiping; Li, Hongliang; Wang, Yiqian; Guo, Peizhi; Liu, Jingquan; Zhao, Xiu Song

2015-07-01

Mesoporous carbon (MC) spheres with hierarchical pores, controlled pore volume and high specific surface areas have been prepared by a mass-producible spray drying assisted template method using sodium alginate as carbon precursor and commercial colloidal silica particles as hard template. The resulting MC spheres, possessing hierarchical pores in the range of 3-30 nm, are employed as conductive matrices for the preparation of cathode materials for lithium-sulfur batteries. A high pressure induced one-step impregnation of elemental sulfur into the pore of the MC spheres has been exploited. The electrochemical performances of sulfur-impregnated MC spheres (S-MC) derived from MC spheres with different pore volume and specific surface area but with the same sulfur loading ratio of 60 wt% (S-MC-X-60) have been investigated in details. The S-MC-4-60 composite cathode material displayed a high initial discharge capacity of 1388 mAhg-1 and a good cycling stability of 857 mAhg-1 after 100 cycles at 0.2C, and shows also excellent rate capability of 864 mAhg-1 at 2C. More importantly, the sulfur loading content in MC-4 spheres can reach as high as 80%, and it still can deliver a capacity of 569 mAhg-1 after 100 cycles at 0.2C.

Tunable elastin-like polypeptide hollow sphere as a high payload and controlled delivery gene depot.

PubMed

Dash, Biraja C; Mahor, Sunil; Carroll, Oliver; Mathew, Asha; Wang, Wenxin; Woodhouse, Kimberly A; Pandit, Abhay

2011-06-30

Self-assembly driven processes can be utilized to produce a variety of nanostructures useful for various in vitro and in vivo applications. Characteristics such as size, stability, biocompatibility, high therapeutic loading and controlled delivery of these nanostructures are particularly crucial in relation to in vivo applications. In this study, we report the fabrication of tunable monodispersed elastin-like polypeptide (ELP) hollow spheres of 100, 300, 500 and 1000 nm by exploiting the self-assembly property and net positive charge of ELP. The microbial transglutaminase (mTGase) cross-linking provided robustness and stability to the hollow spheres while maintaining surface functional groups for further modifications. The resulting hollow spheres showed a higher loading efficiency of plasmid DNA (pDNA) by using polyplex (~70 μg pDNA/mg of hollow sphere) than that of self-assembled ELP particles and demonstrated controlled release triggered by protease and elastase. Moreover, polyplex-loaded hollow spheres showed better cell viability than polyplex alone and yielded higher luciferase expression by providing protection against endosomal degradation. Overall, the monodispersed, tunable hollow spheres with a capability of post-functionalization can provide an exciting new opportunity for use in a range of therapeutic and diagnostic applications. Copyright © 2011 Elsevier B.V. All rights reserved.

Solid evacuated microspheres of hydrogen

DOEpatents

Turnbull, Robert J.; Foster, Christopher A.; Hendricks, Charles D.

1982-01-01

A method is provided for producing solid, evacuated microspheres comprised of hydrogen. The spheres are produced by forming a jet of liquid hydrogen and exciting mechanical waves on the jet of appropriate frequency so that the jet breaks up into drops with a bubble formed in each drop by cavitation. The drops are exposed to a pressure less than the vapor pressure of the liquid hydrogen so that the bubble which is formed within each drop expands. The drops which contain bubbles are exposed to an environment having a pressure just below the triple point of liquid hydrogen and they thereby freeze giving solid, evacuated spheres of hydrogen.

Low-energy collisions of helium clusters with size-selected cobalt cluster ions

NASA Astrophysics Data System (ADS)

Odaka, Hideho; Ichihashi, Masahiko

2017-04-01

Collisions of helium clusters with size-selected cobalt cluster ions, Com+ (m ≤ 5), were studied experimentally by using a merging beam technique. The product ions, Com+Hen (cluster complexes), were mass-analyzed, and this result indicates that more than 20 helium atoms can be attached onto Com+ at the relative velocities of 103 m/s. The measured size distributions of the cluster complexes indicate that there are relatively stable complexes: Co2+Hen (n = 2, 4, 6, and 12), Co3+Hen (n = 3, 6), Co4+He4, and Co5+Hen (n = 3, 6, 8, and 10). These stabilities are explained in terms of their geometric structures. The yields of the cluster complexes were also measured as a function of the relative velocity (1 × 102-4 × 103 m/s), and this result demonstrates that the main interaction in the collision process changes with the increase of the collision energy from the electrostatic interaction, which includes the induced deformation of HeN, to the hard-sphere interaction. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80015-0

Experimental investigation of shock wave diffraction over a single- or double-sphere model

NASA Astrophysics Data System (ADS)

Zhang, L. T.; Wang, T. H.; Hao, L. N.; Huang, B. Q.; Chen, W. J.; Shi, H. H.

2017-01-01

In this study, the unsteady drag produced by the interaction of a shock wave with a single- and a double-sphere model is measured using imbedded accelerometers. The shock wave is generated in a horizontal circular shock tube with an inner diameter of 200 mm. The effect of the shock Mach number and the dimensionless distance between spheres is investigated. The time-history of the drag coefficient is obtained based on Fast Fourier Transformation (FFT) band-block filtering and polynomial fitting of the measured acceleration. The measured peak values of the drag coefficient, with the associated uncertainty, are reported.

Porous cobalt spheres for high temperature gradient magnetically assisted fluidized beds

NASA Technical Reports Server (NTRS)

Atwater, James E.; Akse, James R.; Jovanovic, Goran N.; Wheeler, Richard R Jr; Sornchamni, Thana

2003-01-01

Porous metallic cobalt spheres have been prepared as high temperature capable media for employment in gradient magnetically assisted fluidization and filtration technologies. Cobalt impregnated alginate beads are first formed by extrusion of an aqueous suspension of Co3O4 into a Co(II) chloride solution. The organic polymer is thermally decomposed yielding cobalt oxide spheres, followed by reduction to the metallic state, and densification. Cobalt beads have been produced with porosities ranging between 10 and 50%, depending upon sintering conditions. The product media have been characterized by scanning electron microscopy (SEM), nitrogen adsorption porosimetry, and vibrating sample magnetometry. c2003 Elsevier Science Ltd. All rights reserved.

Water walking - an evolution of water surface skipping

NASA Astrophysics Data System (ADS)

Hurd, Randy; Belden, Jesse; Jandron, Michael; Bower, Allan; Holekamp, Sean; Truscott, Tadd

2017-11-01

Previous work has shown that elastomeric spheres skip more easily than disk-shaped stones. This is due to increased lift stemming from sphere deformation, which provides an increased cross-sectional area and favorable attack angle upon impact. We extend lift models developed for individual impacts to long-range multiple impact events and compare the estimates to experimental results, which show good agreement. Additionally, a surprising new mode of skipping is observed that resembles water-walking, wherein a quickly rotating sphere produces small successive impacts allowing it to move parallel to the water surface. The dynamics of this new multiple skip behavior are rationalized analytically and tested experimentally.

Percolation of disordered jammed sphere packings

NASA Astrophysics Data System (ADS)

Ziff, Robert M.; Torquato, Salvatore

2017-02-01

We determine the site and bond percolation thresholds for a system of disordered jammed sphere packings in the maximally random jammed state, generated by the Torquato-Jiao algorithm. For the site threshold, which gives the fraction of conducting versus non-conducting spheres necessary for percolation, we find {{p}\\text{c}}=0.3116(3) , consistent with the 1979 value of Powell 0.310(5) and identical within errors to the threshold for the simple-cubic lattice, 0.311 608, which shares the same average coordination number of 6. In terms of the volume fraction ϕ, the threshold corresponds to a critical value {φ\\text{c}}=0.199 . For the bond threshold, which apparently was not measured before, we find {{p}\\text{c}}=0.2424(3) . To find these thresholds, we considered two shape-dependent universal ratios involving the size of the largest cluster, fluctuations in that size, and the second moment of the size distribution; we confirmed the ratios’ universality by also studying the simple-cubic lattice with a similar cubic boundary. The results are applicable to many problems including conductivity in random mixtures, glass formation, and drug loading in pharmaceutical tablets.

Optical waveguide loop for planar trapping of blood cells and microspheres

NASA Astrophysics Data System (ADS)

Ahluwalia, Balpreet S.; Hellesø, Olav G.

2013-09-01

The evanescent field from a waveguide can be used to trap and propel a particle. An optical waveguide loop with an intentional gap at the center is used for planar transport and stable trapping of particles. The waveguide acts as a conveyor belt to trap and deliver spheres towards the gap. At the gap, the counter-diverging light fields hold the sphere at a fixed position. Numerical simulation based on the finite element method was performed in three dimensions using a computer cluster. The field distribution and optical forces for rib and strip waveguide designs are compared and discussed. The optical force on a single particle was computed for various positions of the particle in the gap. Simulation predicted stable trapping of particles in the gap. Depending on the gap separation (2-50 μm) a single or multiple spheres and red blood cells were trapped at the gap. Waveguides were made of tantalum pentaoxide material. The waveguides are only 180 nm thick and thus could be integrated with other functions on the chip.

Long-Term, Low-Frequency Cluster of a German-Imipenemase-1-Producing Enterobacter hormaechei ssp. steigerwaltii ST89 in a Tertiary Care Hospital in Germany.

PubMed

Wendel, Andreas F; Meyer, Sebastian; Deenen, René; Köhrer, Karl; Kolbe-Busch, Susanne; Pfeffer, Klaus; Willmann, Matthias; Kaasch, Achim J; MacKenzie, Colin R

2018-05-11

Enterobacter cloacae complex is a common cause of hospital outbreaks. A retrospective and prospective molecular analysis of carbapenem-resistant clinical isolates in a tertiary care center demonstrated an outbreak of a German-imipenemase-1 (GIM-1) metallo-beta-lactamase-producing Enterobacter hormaechei ssp. steigerwaltii affecting 23 patients between 2009 and 2016. Thirty-three isolates were sequence type 89 by conventional multilocus sequence typing (MLST) and displayed a maximum difference of 49 out of 3,643 targets in the ad-hoc core-genome MLST (cgMLST) scheme (SeqSphere+ software; Ridom, Münster, Germany). The relatedness of all isolates was confirmed by further maximum-likelihood phylogeny. One clonal complex of highly related isolates (≤15 allele difference in cgMLST) contained 17 patients, but epidemiological data only suggested five transmission events. The bla GIM-1 -gene was embedded in a class-1-integron (In770) and the Tn21-subgroup transposon Tn6216 (KC511628) on a 25-kb plasmid. Environmental screening detected one colonized sink trap in a service room. The outbreak was self-limited as no further bla GIM-1 -positive E. hormaechei has been isolated since 2016. Routine molecular screening of carbapenem-nonsusceptible gram-negative isolates detected a long-term, low-frequency outbreak of a GIM-1-producing E. hormaechei ssp. steigerwaltii clone. This highlights the necessity of molecular surveillance.

The mechanism of CO2 hydration: a porous metal oxide nanocapsule catalyst can mimic the biological carbonic anhydrase role.

PubMed

Bandeira, Nuno A G; Garai, Somenath; Müller, Achim; Bo, Carles

2015-11-04

The mechanism for the hydration of CO2 within a Keplerate nanocapsule is presented. A network of hydrogen bonds across the water layers in the first metal coordination sphere facilitates the proton abstraction and nucleophilic addition of water. The highly acidic properties of the polyoxometalate cluster are crucial for explaining the catalysed hydration.

The single scattering properties of the aerosol particles as aggregated spheres

NASA Astrophysics Data System (ADS)

Wu, Y.; Gu, X.; Cheng, T.; Xie, D.; Yu, T.; Chen, H.; Guo, J.

2012-08-01

The light scattering and absorption properties of anthropogenic aerosol particles such as soot aggregates are complicated in the temporal and spatial distribution, which introduce uncertainty of radiative forcing on global climate change. In order to study the single scattering properties of anthorpogenic aerosol particles, the structures of these aerosols such as soot paticles and soot-containing mixtures with the sulfate or organic matter, are simulated using the parallel diffusion limited aggregation algorithm (DLA) based on the transmission electron microscope images (TEM). Then, the single scattering properties of randomly oriented aerosols, such as scattering matrix, single scattering albedo (SSA), and asymmetry parameter (AP), are computed using the superposition T-matrix method. The comparisons of the single scattering properties of these specific types of clusters with different morphological and chemical factors such as fractal parameters, aspect ratio, monomer radius, mixture mode and refractive index, indicate that these different impact factors can respectively generate the significant influences on the single scattering properties of these aerosols. The results show that aspect ratio of circumscribed shape has relatively small effect on single scattering properties, for both differences of SSA and AP are less than 0.1. However, mixture modes of soot clusters with larger sulfate particles have remarkably important effects on the scattering and absorption properties of aggregated spheres, and SSA of those soot-containing mixtures are increased in proportion to the ratio of larger weakly absorbing attachments. Therefore, these complex aerosols come from man made pollution cannot be neglected in the aerosol retrievals. The study of the single scattering properties on these kinds of aggregated spheres is important and helpful in remote sensing observations and atmospheric radiation balance computations.

Classical plasma dynamics of Mie-oscillations in atomic clusters

NASA Astrophysics Data System (ADS)

Kull, H.-J.; El-Khawaldeh, A.

2018-04-01

Mie plasmons are of basic importance for the absorption of laser light by atomic clusters. In this work we first review the classical Rayleigh-theory of a dielectric sphere in an external electric field and Thomson’s plum-pudding model applied to atomic clusters. Both approaches allow for elementary discussions of Mie oscillations, however, they also indicate deficiencies in describing the damping mechanisms by electrons crossing the cluster surface. Nonlinear oscillator models have been widely studied to gain an understanding of damping and absorption by outer ionization of the cluster. In the present work, we attempt to address the issue of plasmon relaxation in atomic clusters in more detail based on classical particle simulations. In particular, we wish to study the role of thermal motion on plasmon relaxation, thereby extending nonlinear models of collective single-electron motion. Our simulations are particularly adopted to the regime of classical kinetics in weakly coupled plasmas and to cluster sizes extending the Debye-screening length. It will be illustrated how surface scattering leads to the relaxation of Mie oscillations in the presence of thermal motion and of electron spill-out at the cluster surface. This work is intended to give, from a classical perspective, further insight into recent work on plasmon relaxation in quantum plasmas [1].

Biomimetic Inspired Core-Canopy Quantum Dots: Ions Trapped in Voids Induce Kinetic Fluorescence Switching.

PubMed

Saha, Arpita; Oleshkevich, Elena; Vinas, Clara; Teixidor, Francesc

2017-12-01

Closely packed hollow spheres connected through pillars to a CdSe quantum dot (QD) core produce channels through which ions navigate. This particular structure is well represented by [CdSe@CarbOPH(O)]@Cl/[N(Caprylyl) 3 Me 1 ] indicating that in the channels between the canopy made by the carboranyl spheres (carboranylphosphinate, CarbOPH(O)) and the CdSe core exist chloride anions. Due to the close packing, the spheres produce openings. These are converted into gates because [N(Caprylyl) 3 Me 1 ] acts as a plug. The [CdSe@CarbOPH(O)]@Cl/assembly is negatively charged because the Cd positive charges are outnumbered by the negative charges due to the Se, the phosphinic acid and, very importantly, the trapped chloride anions, and this negative load is compensated by the cationic surfactant. Here, it is shown that this synergism produces an unprecedented phenomenon, namely, kinetic fluorescence switching. It is observed that the material shines brightly then loses its brightness and, upon the application of kinetic energy, shines back to the maximum power. This process continues for an extended period of time, up to half a year, at least. This new type of architecture in QDs is named as core-canopy QDs. In this case, this study demonstrates one property, the kinetic fluorescence switching, as a consequence of the trapping of Cl - in the QDs channels, but other properties can be envisaged with the judicious choice of the anions or even the pillar connecting the hollow sphere with the ground. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A galactic mega-merger

NASA Image and Video Library

2016-01-11

The subject of this NASA/ESA Hubble Space Telescope image is known as NGC 3597. It is the product of a collision between two good-sized galaxies, and is slowly evolving to become a giant elliptical galaxy. This type of galaxy has grown more and more common as the Universe has evolved, with initially small galaxies merging and progressively building up into larger galactic structures over time. NGC 3597 is located approximately 150 million light-years away in the constellation of Crater (The Cup). Astronomers study NGC 3597 to learn more about how elliptical galaxies form — many ellipticals began their lives far earlier in the history of the Universe. Older ellipticals are nicknamed “red and dead” by astronomers because these bloated galaxies are not anymore producing new, bluer, stars in ages, and are thus packed full of old and redder stellar populations. Before infirmity sets in, some freshly formed elliptical galaxies experience a final flush of youth, as is the case with NGC 3597. Galaxies smashing together pool their available gas and dust, triggering new rounds of star birth. Some of this material ends up in dense pockets initially called proto-globular clusters, dozens of which festoon NGC 3597. These pockets will go on to collapse and form fully-fledged globular clusters, large spheres that orbit the centres of galaxies like satellites, packed tightly full of millions of stars.

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.

Vacuum injection of hydrogen micro-sphere beams

NASA Astrophysics Data System (ADS)

Trostell, Bertil

1995-02-01

The design, construction and operation of a facility producing hydrogen micro-sphere beams in vacuum are summarized. A scheme is utilized, where a liquid hydrogen jet is broken up into droplets, which are injected into vacuum through a capillary at continuum gas flow conditions. In a typical beam, 40 μm diameter micro-spheres, generated at a frequency of 70 kHz, travel at free flight speeds of 60 m/s. The angular divergence of the beam amounts to ±0.04°. The intention is to use the micro-sphere beams as high luminosity internal targets in the WASA experimental station at the CELSIUS cooler storage ring in Uppsala. A time averaged target density profile, having a FWHM and peak density of 3.5 mm and 5 × 10 16 atoms/cm 2, respectively, is obtained 2.5 m downstream of the capillary exit.

A study of nondiffracting Lommel beams propagating in a medium containing spherical scatterers

NASA Astrophysics Data System (ADS)

Belafhal, A.; Ez-zariy, L.; Hricha, Z.

2016-11-01

By means of the expansion of the nondiffracting beams on plane waves with help of the Whittaker integral, an exact analytical expression of the far-field form function of the scattering of the acoustic and optical nondiffracting Lommel beams propagating in a medium containing spherical particles, considered as rigid and single spheres, is investigated in this work. The form function of the scattering of the high order Bessel beam by a rigid and isolated sphere is deduced, from our finding, as a special case. The effects of the wave number-sphere radius product (ka) , the polar angle (φ) , the propagation half-cone angle (β) and the scattering angle (θ) on the far-field form function of the scattered wave have been analyzed and discussed numerically. The numerical results show that the illumination of a rigid sphere by Lommel beams produces asymmetrical scattering.

Close packing of rods on spherical surfaces

NASA Astrophysics Data System (ADS)

Smallenburg, Frank; Löwen, Hartmut

2016-04-01

We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry of the closest-packed configuration as a function of the aspect ratio L/D, where L is the cylinder length and D the diameter of the rods. We find a rich variety of cluster structures. For larger clusters, we find that the best-packed configurations up to around 100 particles are highly dependent on the exact number of particles and aspect ratio. For even larger clusters, we find largely disordered clusters for very short rods (L/D = 0.25), while slightly longer rods (L/D = 0.5 or 1) prefer a global baseball-like geometry of smectic-like domains, similar to the behavior of large-scale nematic shells. Intriguingly, we observe that when compared to their optimal flat-plane packing, short rods adapt to the spherical geometry more efficiently than both spheres and longer rods. Our results provide predictions for experimentally realizable systems of colloidal rods trapped at the interface of emulsion droplets.

Spatially-Resolved Observations of Giant Stars with SPHERE

NASA Astrophysics Data System (ADS)

Khouri, Theo

2018-04-01

SPHERE on the VLT is an extreme adaptive optics instrument that produces images with unprecedented angular resolution at visible and near-infrared wavelengths. Its primary goal is imaging, low-resolution spectroscopic, and polarimetric characterization of extra-solar planetary systems. Nonetheless, the high spatial resolution and the instrument design optimized for observations in a narrow field of view around bright targets make SPHERE the perfect instrument for obtaining spatially-resolved images of close-by giant, evolved stars. This is particularly true at the shortest wavelengths available with SPHERE, where the angular resolution is best (> 20 mas) and these stars appear larger (< 70 mas). In this talk, I will review how SPHERE has been used to study the surfaces and extended atmospheres of evolved stars and how these observations advance our understanding of the stellar pulsations and convective motions that shape these stars. Moreover, I will present recent results from a monitoring campaign of the star R Doradus using SPHERE with observations taken at twelve epochs over eight months that reveal features on the stellar disc varying on timescales of a few weeks. Finally, I will present quasi-simultaneous observations with SPHERE and ALMA that spatially resolve the stellar discs of two asymptotic giant branch stars, Mira and R Doradus, and discuss what such multi-wavelength observation campaigns can teach us about the processes that shape evolved stars.

Space Inside a Liquid Sphere Transforms into De Sitter Space by Hilbert Radius

NASA Astrophysics Data System (ADS)

Rabounski, Dmitri; Borissova, Larissa

2010-04-01

Consider space inside a sphere of incompressible liquid, and space surrounding a mass-point. Metrics of the spaces were deduced in 1916 by Karl Schwarzschild. 1) Our calculation shows that a liquid sphere can be in the state of gravitational collapse (g00 = 0) only if its mass and radius are close to those of the Universe (M = 8.7x10^55 g, a = 1.3x10^28 cm). However if the same mass is presented as a mass-point, the radius of collapse rg (Hilbert radius) is many orders lesser: g00 = 0 realizes in a mass-point's space by other conditions. 2) We considered a liquid sphere whose radius meets, formally, the Hilbert radius of a mass-point bearing the same mass: a = rg, however the liquid sphere is not a collapser (see above). We show that in this case the metric of the liquid sphere's internal space can be represented as de Sitter's space metric, wherein λ = 3/a^2 > 0: physical vacuum (due to the λ-term) is the same as the field of an ideal liquid where ρ0 < 0 and p = -ρ0 c^2 > 0 (the mirror world liquid). The gravitational redshift inside the sphere is produced by the non-Newtonian force of repulsion (which is due to the λ-term, λ = 3/a^2 > 0); it is also calculated.

Weak-Lensing Detection of Cl 1604+4304 at z=0.90

NASA Astrophysics Data System (ADS)

Margoniner, V. E.; Lubin, L. M.; Wittman, D. M.; Squires, G. K.

2005-01-01

We present a weak-lensing analysis of the high-redshift cluster Cl 1604+4304. At z=0.90, this is the highest redshift cluster yet detected with weak lensing. It is also one of a sample of high-redshift, optically selected clusters whose X-ray temperatures are lower than expected based on their velocity dispersions. Both the gas temperature and galaxy velocity dispersion are proxies for its mass, which can be determined more directly by a lensing analysis. Modeling the cluster as a singular isothermal sphere, we find that the mass contained within projected radius R is (3.69+/-1.47)[R/(500 kpc)]×1014 Msolar. This corresponds to an inferred velocity dispersion of 1004+/-199 km s-1, which agrees well with the velocity dispersion of 989+98-76 km s-1 recently measured by Gal & Lubin. These numbers are higher than the 575+110-85 km s-1 inferred from Cl 1604+4304's X-ray temperature; however, all three velocity dispersion estimates are consistent within ~1.9 σ.

Analysis of a hyperdeformed band of 152(66)Dy86 on the basis of a structure with two revolving clusters, each with a previously unrecognized two-tiered structure.

PubMed

Pauling, L

1994-02-01

Analysis on the basis of the two-revolving-cluster model has been made of a cascade of 11 gamma-rays constituting a hyperdeformed band of 152(66)Dy86 (or possibly 153Dy) reported by Galindo-Uribarri et al. [Galindo-Uribarri, A., et al. (1993) Phys. Rev. Lett. 73, 231-234], leading to the conclusions that the band extends from values K approximately 82-104 for the angular-momentum quantum number, that the moment of inertia is approximately 5650 Da.fm2, that the composition of the central sphere is p40n50 and that of each of the clusters is p13n18, that each of the clusters consists of two tiers of spherons, and that the radii of revolution of the inner and outer tiers have values of about 8.00 and 11.20 fm, respectively.

Analysis of a hyperdeformed band of 152(66)Dy86 on the basis of a structure with two revolving clusters, each with a previously unrecognized two-tiered structure.

PubMed Central

Pauling, L

1994-01-01

Analysis on the basis of the two-revolving-cluster model has been made of a cascade of 11 gamma-rays constituting a hyperdeformed band of 152(66)Dy86 (or possibly 153Dy) reported by Galindo-Uribarri et al. [Galindo-Uribarri, A., et al. (1993) Phys. Rev. Lett. 73, 231-234], leading to the conclusions that the band extends from values K approximately 82-104 for the angular-momentum quantum number, that the moment of inertia is approximately 5650 Da.fm2, that the composition of the central sphere is p40n50 and that of each of the clusters is p13n18, that each of the clusters consists of two tiers of spherons, and that the radii of revolution of the inner and outer tiers have values of about 8.00 and 11.20 fm, respectively. PMID:11607453

Some constructions of biharmonic maps and Chen’s conjecture on biharmonic hypersurfaces

NASA Astrophysics Data System (ADS)

Ou, Ye-Lin

2012-04-01

We give several construction methods and use them to produce many examples of proper biharmonic maps including biharmonic tori of any dimension in Euclidean spheres (Theorem 2.2, Corollaries 2.3, 2.4 and 2.6), biharmonic maps between spheres (Theorem 2.9) and into spheres (Theorem 2.10) via orthogonal multiplications and eigenmaps. We also study biharmonic graphs of maps, derive the equation for a function whose graph is a biharmonic hypersurface in a Euclidean space, and give an equivalent formulation of Chen's conjecture on biharmonic hypersurfaces by using the biharmonic graph equation (Theorem 4.1) which paves a way for the analytic study of the conjecture.

Experiments with a Sphere from which the Boundary Layer Is Removed by Suction

NASA Technical Reports Server (NTRS)

Schrenk, Oskar

1926-01-01

The task of removing the boundary layer by suction consists in producing, in place of the ordinary flow with the formation of vortices, another kind of flow in which the vortices are eliminated by drawing small quantities of fluid from certain points on the surface into the interior of the body. The experiments with a sphere, which constitute the subject of this report, were made early in the present year .

Electrochemical characteristics of discrete, uniform, and monodispersed hollow mesoporous carbon spheres in double-layered supercapacitors.

PubMed

Chen, Xuecheng; Kierzek, Krzysztof; Wenelska, Karolina; Cendrowski, Krzystof; Gong, Jiang; Wen, Xin; Tang, Tao; Chu, Paul K; Mijowska, Ewa

2013-11-01

Core-shell-structured mesoporous silica spheres were prepared by using n-octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core-shell-structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double-layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer-Emmett-Teller (BET) area and larger pore size. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radiation torque on an absorptive spherical drop centered on an acoustic helicoidal Bessel beam

NASA Astrophysics Data System (ADS)

Zhang, Likun; Marston, Philip L.

2009-11-01

Circularly polarized electromagnetic waves carry axial angular momentum and analysis shows that the axial radiation torque on an illuminated sphere is proportional to the power absorbed by the sphere [1]. Helicoidal acoustic beams also carry axial angular momentum and absorption of such a beam should also produce an axial radiation torque [2]. In the present work the acoustic radiation torque on solid spheres and spherical drops centered on acoustic helicoidal Bessel beams is examined. The torque is predicted to be proportional to the ratio of the absorbed power to the acoustic frequency. Depending on the beam helicity, the torque is parallel or anti-parallel to the beam axis. The analysis uses a relation between the scattering and the partial wave coefficients for a sphere in a helicoidal Bessel beam. Calculations suggest that beams with a low topological charge are more efficient for generating torques on solid spheres.[4pt] [1] P. L. Marston and J. H. Crichton, Phys. Rev. A. 30, 2508-2516 (1984).[0pt] [2] B. T. Hefner and P. L. Marston, J. Acoust. Soc. Am. 106, 3313-3316 (1999).

Auxiliary iron-sulfur cofactors in radical SAM enzymes.

PubMed

Lanz, Nicholas D; Booker, Squire J

2015-06-01

A vast number of enzymes are now known to belong to a superfamily known as radical SAM, which all contain a [4Fe-4S] cluster ligated by three cysteine residues. The remaining, unligated, iron ion of the cluster binds in contact with the α-amino and α-carboxylate groups of S-adenosyl-l-methionine (SAM). This binding mode facilitates inner-sphere electron transfer from the reduced form of the cluster into the sulfur atom of SAM, resulting in a reductive cleavage of SAM to methionine and a 5'-deoxyadenosyl radical. The 5'-deoxyadenosyl radical then abstracts a target substrate hydrogen atom, initiating a wide variety of radical-based transformations. A subset of radical SAM enzymes contains one or more additional iron-sulfur clusters that are required for the reactions they catalyze. However, outside of a subset of sulfur insertion reactions, very little is known about the roles of these additional clusters. This review will highlight the most recent advances in the identification and characterization of radical SAM enzymes that harbor auxiliary iron-sulfur clusters. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases. Copyright © 2015 Elsevier B.V. All rights reserved.

The mond external field effect on the dynamics of the globular clusters: general considerations and application to NGC 2419

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

Derakhshani, Kamran, E-mail: kderakhshani@iasbs.ac.ir

2014-03-01

In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer partsmore » of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ{sup 2} of surface brightness and velocity dispersion.« less

The MOND External Field Effect on the Dynamics of the Globular Clusters: General Considerations and Application to NGC 2419

NASA Astrophysics Data System (ADS)

Derakhshani, Kamran

2014-03-01

In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer parts of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ2 of surface brightness and velocity dispersion.

Cholangiocarcinoma stem-like subset shapes tumor-initiating niche by educating associated macrophages

PubMed Central

Raggi, Chiara; Correnti, Margherita; Sica, Antonio; Andersen, Jesper B.; Cardinale, Vincenzo; Alvaro, Domenico; Chiorino, Giovanna; Forti, Elisa; Glaser, Shannon; Alpini, Gianfranco; Destro, Annarita; Sozio, Francesca; Di Tommaso, Luca; Roncalli, Massimo; Banales, Jesus M.; Coulouarn, Cédric; Bujanda, Luis; Torzilli, Guido; Invernizzi, Pietro

2017-01-01

Background & Aims A therapeutically challenging subset of cells, termed cancer stem cells (CSCs) are responsible for cholangiocarcinoma (CCA) clinical severity. Presence of tumor-associated macrophages (TAMs) has prognostic significance in CCA and other malignancies. Thus, we hypothesized that CSCs may actively shape their tumor-supportive immune niche. Methods CCA cells were cultured in 3D conditions to generate spheres. CCA sphere analysis of in vivo tumorigenic-engraftment in immune-deficient mice and molecular characterization was performed. The in vitro and in vivo effect of CCA spheres on macrophage precursors was tested after culturing healthy donor cluster of differentiation (CD)14+ with CCA-sphere conditioned medium. Results CCA spheres engrafted in 100% of transplanted mice and revealed a significant 20.3-fold increase in tumor-initiating fraction (p = 0.0011) and a sustained tumorigenic potential through diverse xenograft-generations. Moreover, CCA spheres were highly enriched for CSC, liver cancer and embryonic stem cell markers both at gene and protein levels. Next, fluorescence-activated cell sorting analysis showed that in the presence of CCA sphere conditioned medium, CD14+ macrophages expressed key markers (CD68, CD115, human leukocyte antigen-D related, CD206) indicating that CCA sphere conditioned medium was a strong macrophage-activator. Gene expression profile of CCA sphere activated macrophages revealed unique molecular TAM-like features confirmed by high invasion capacity. Also, freshly isolated macrophages from CCA resections recapitulated a similar molecular phenotype of in vitro-educated macrophages. Consistent with invasive features, the largest CD163+ set was found in the tumor front of human CCA specimens (n = 23) and correlated with a high level of serum cancer antigen 19.9 (n = 17). Among mediators released by CCA spheres, only interleukin (IL)13, IL34 and osteoactivin were detected and further confirmed in CCA patient sera (n = 12). Surprisingly, a significant association of IL13, IL34 and osteoactivin with sphere stem-like genes was provided by a CCA database (n = 104). In vitro combination of IL13, IL34, osteoactivin was responsible for macrophage-differentiation and invasion, as well as for in vivo tumor-promoting effect. Conclusion CCA-CSCs molded a specific subset of stem-like associated macrophages thus providing a rationale for a synergistic therapeutic strategy for CCA-disease. Lay summary Immune plasticity represents an important hallmark of tumor outcome. Since cancer stem cells are able to manipulate stromal cells to their needs, a better definition of the key dysregulated immune subtypes responsible for cooperating in supporting tumor initiation may facilitate the development of new therapeutic approaches. Considering that human cholangiocarcinoma represents a clinical emergency, it is essential to move to predictive models in order to understand the adaptive process of macrophage component (imprinting, polarization and maintenance) engaged by tumor stem-like compartment. PMID:27593106

Thermodynamics of gravitational clustering phenomena: N-body self-gravitating gas on the sphere {{{S}}^{3}}\\subset {{{R}}^{4}}

NASA Astrophysics Data System (ADS)

Tello-Ortiz, F.; Velazquez, L.

2016-10-01

This work is devoted to the thermodynamics of gravitational clustering, a collective phenomenon with a great relevance in the N-body cosmological problem. We study a classical self-gravitating gas of identical non-relativistic particles defined on the sphere {{{S}}3}\\subset {{{R}}4} by considering gravitational interaction that corresponds to this geometric space. The analysis is performed within microcanonical description of an isolated Hamiltonian system by combining continuum approximation and the steepest descend method. According to numerical solution of resulting equations, the gravitational clustering can be associated with two microcanonical phase transitions. A first phase transition with a continuous character is associated with breakdown of SO(4) symmetry of this model. The second one is the gravitational collapse, whose continuous or discontinuous character crucially depends on the regularization of short-range divergence of gravitation potential. We also derive the thermodynamic limit of this model system, the astrophysical counterpart of the Gibbs-Duhem relation, the order parameters that characterize its phase transitions and the equation of state. Other interesting behavior is the existence of states with negative heat capacities, which appear when the effects of gravitation turn dominant for energies sufficiently low. Finally, we comment on the relevance of some of these results in the study of astrophysical and cosmological situations. Special interest deserves the gravitational modification of the equation of state due to the local inhomogeneities of matter distribution. Although this feature is systematically neglected in studies about universe expansion, the same one is able to mimic an effect that is attributed to the dark energy: a negative pressure.

Low Velocity Sphere Impact of a Soda Lime Silicate Glass

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

Wereszczak, Andrew A; Fox, Ethan E; Morrissey, Timothy G

2011-10-01

This report summarizes TARDEC-sponsored work at Oak Ridge National Laboratory (ORNL) during the FY11 involving low velocity (< 30 m/s or < 65 mph) ball impact testing of Starphire soda lime silicate glass. The intent was to better understand low velocity impact response in the Starphire for sphere densities that bracketed that of rock. Five sphere materials were used: borosilicate glass, soda-lime silicate glass, steel, silicon nitride, and alumina. A gas gun was fabricated to produce controlled velocity delivery of the spheres against Starphire tile targets. Minimum impact velocities to initiate fracture in the Starphire were measured and interpreted inmore » context to the kinetic energy of impact and the elastic property mismatch between the any of the five sphere-Starphire-target combinations. The primary observations from this low velocity (< 30 m/s or < 65 mph) testing were: (1) Frictional effects contribute to fracture initiation. (2) Spheres with a lower elastic modulus require less force to initiate fracture in the Starphire than spheres with a higher elastic modulus. (3) Contact-induced fracture did not initiate in the Starphire SLS for impact kinetic energies < 150 mJ. Fracture sometimes initiated or kinetic energies between {approx} 150-1100 mJ; however, it tended to occur when lower elastic modulus spheres were impacting it. Contact-induced fracture would always occur for impact energies > 1100 mJ. (4) The force necessary to initiate contact-induced fracture is higher under dynamic or impact conditions than it is under quasi-static indentation conditions. (5) Among the five used sphere materials, silicon nitride was the closest match to 'rock' in terms of both density and (probably) elastic modulus.« less

Large-scale synthesis of a novel tri(8-hydroxyquioline) aluminum nanostructure.

PubMed

Tian, Xike; Fei, Jinbo; Pi, Zhenbang; Yang, Chao; Xiao, Zhidong; Zhang, Lide

2006-08-01

A novel tri(8-hydroxyquioline) aluminum (AlQ3) nanostructure was prepared on large scale at low cost by low-temperature physical vapor deposition (PVD). The morphologies, the chemical bondings, and photoluminescence of the AlQ3 nanostructure were investigated by environmental scanning electronic microscopy (ESEM), Fourier transform infrared spectrum (FT-IR), and photoluminescence (PL) spectra, respectively. The AlQ3 nanostructure was composed of micro-sphere with nanowire-cluster growing on the surface. The diameter of micro-sphere and nanowire were about 5 microm and 80 nm, respectively. FT-IR results indicated that the AlQ3 molecule had a strong thermal stability under research conditions. The growth mechanism of the novel nanostructure was discussed. The novel organic nanostructure would be believed to attractive building field-emission devices and other optical devices.

Modeling of light scattering by icy bodies

NASA Astrophysics Data System (ADS)

Kolokolova, L.; Mackowski, D.; Pitman, K.; Verbiscer, A.; Buratti, B.; Momary, T.

2014-07-01

As a result of ground-based, space-based, and in-situ spacecraft mission observations, a great amount of photometric, polarimetric, and spectroscopic data of icy bodies (satellites of giant planets, Kuiper Belt objects, comet nuclei, and icy particles in cometary comae and rings) has been accumulated. These data have revealed fascinating light-scattering phenomena, such as the opposition surge resulting from coherent backscattering and shadow hiding and the negative polarization associated with them. Near-infrared (NIR) spectra of these bodies are especially informative as the depth, width, and shape of the absorption bands of ice are sensitive not only to the ice abundance but also to the size of icy grains. Numerous NIR spectra obtained by Cassini's Visual and Infrared Mapping Spectrometer (VIMS) have been used to map the microcharacteristics of the icy satellites [1] and rings of Saturn [2]. VIMS data have also permitted a study of the opposition surge for icy satellites of Saturn [3], showing that coherent backscattering affects not only brightness and polarization of icy bodies but also their spectra [4]. To study all of the light-scattering phenomena that affect the photopolarimetric and spectroscopic characteristics of icy bodies, including coherent backscattering, requires computer modeling that rigorously considers light scattering by a large number of densely packed small particles that form either layers (in the case of regolith) or big clusters (ring and comet particles) . Such opportunity has appeared recently with a development of a new version MSTM4 of the Multi-Sphere T-Matrix code [5]. Simulations of reflectance and absorbance spectra of a ''target'' (particle layer or cluster) require that the dimensions of the target be significantly larger than the wavelength, sphere radius, and layer thickness. For wavelength-sized spheres and packing fractions typical of regolith, targets can contain dozens of thousands of spheres that, with the original MSTM code, would require enormous computer RAM and CPU. MSTM4 adopts a discrete Fourier convolution (DFC), implemented using a fast Fourier transform (FFT), for the evaluation of the exciting field. This approach is very similar to that used in the discrete-dipole approximation (DDA) codes, with the difference that it considers multipole nature of the translation operators, and does not require that the sphere origins be located on a regular lattice. The MSTM4 code not only allows us to consider a larger number of constituent particles but also is about 100 times faster in wall-clock time than the original version of the MSTM code. Example of MSTM4 modeling is shown in the Figure.

The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude

NASA Technical Reports Server (NTRS)

Johnston, M. D.; Bradt, H. V.; Doxsey, R. E.; Marshall, F. E.; Schwartz, D. A.; Margon, B.

1981-01-01

The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.

Future Achievements, Passion and Motivation in the Transition from Junior-to-Senior Sport in Spanish Young Elite Soccer Players.

PubMed

Chamorro, José L; Torregrosa, Miquel; Sánchez Oliva, David; García Calvo, Tomás; León, Benito

2016-10-20

Within the context of the transition from junior-to-senior sport, this study aims in first place to explore differences in young Spanish elite soccer players based on the importance given to getting different achievements in their future (including sport, studies and private life) and, in second place, to explore differences among those players in levels of passion, motivation and basic psychological need. 478 elite youth soccer filled out a questionnaire based on the presented theoretical models. A cluster analysis shows a sport oriented group (N = 98) only interested in becoming a professional, a life spheres balance group (N = 288) characterized by balancing the importance of achievements in the sport sphere, as well as in education and a private life and a group (N = 91) only interested in private life achievements. The life spheres balance group shows higher levels of harmonious passion (η2 = .06, F(2, 475) = 9.990, p < .001) than the players of the other groups. The life spheres balance group shows higher levels of autonomous motivation (η2 = .10, F(2, 475) = 13.597, p < .001), autonomy (η2 = .07, F(2, 475) = 6.592, p < .01) and relatedness satisfaction (η2 = .07, F(2, 475) = 5.603, p < .01) than the sport oriented group as well as lower levels of amotivation (η2 = .04, F(2, 475) = 6.665, p < .01) than the private life oriented group. This study suggests players who perceive equal future importance in their life spheres appear to be more resourceful than the other two groups regarding athletes' internal resources, such as passion and motivation, to cope with the transition to professional soccer.

Preparation and Properties of C/C Hollow Spheres and the Energy Absorption Capacity of the Corresponding Aluminum Syntactic Foams.

PubMed

Yu, Qiyong; Zhao, Yan; Dong, Anqi; Li, Ye

2018-06-12

The present study focuses on the preparation and characterization of lab-scale aluminum syntactic foams (ASFs) filled with hollow carbon spheres (HCSs). A new and original process for the fabrication of HCSs was explored. Firstly, expanded polystyrene beads with an average diameter of 6 mm and coated with carbon fibers/thermoset phenolic resin were produced by the “rolling ball” method. In the next step, the spheres were cured and post-cured, and then carbonized at 1050 °C under vacuum to form the HCSs. The porosity in the shell of the HCSs was decreased by increasing the number of impregnation⁻carbonization cycles. The aluminum syntactic foams were fabricated by casting the molten aluminum into a crucible filled with HCSs. The morphology of the hollow spheres before and after carbonization was investigated by scanning electron microscope (SEM). The compressive properties of the ASF were tested and the energy absorption capacities were calculated according to stress⁻strain curves. The results showed that the ASF filled with HCSs which had been treated by more cycles of impregnation⁻carbonization had higher energy absorption capacity. The aluminum syntactic foam absorbed 34.9 MJ/m³ (28.8 KJ/Kg) at 60% strain, which was much higher than traditional closed cell aluminum foams without particles. The HCSs have a promising future in producing a novel family of metal matrix syntactic foams.

Processing and properties of Ti-6Al-4V hollow sphere foams from hydride powder

NASA Astrophysics Data System (ADS)

Hardwicke, Canan Uslu

Honeycomb structures currently used in aerospace systems are expensive to manufacture, limited to sheet form, and present joining problems and mechanical anisotropy that promotes shear failure at low stresses. Metallic foams produced by point contact bonding of monosized hollow spheres offer an alternative if they can be processed into strong, light-weight, and reasonably priced structural materials. In this work, technology has been established for fabricating good quality, Ti-6Al-4V hollow sphere foams using the coaxial nozzle powder slurry technique. It was shown that hydride form of Ti-ELI can be used as the starting precursor powder and processed into fine particles of 1-10 mum size range without increasing the impurity levels. Hydride dispersion in acetone was provided by the addition of polyester/polyamine copolymers through electrosteric stabilization. Addition of PMMA to the pseudoplastically dispersed organic slurries helped bind hydride powder spherical shells. Furthermore, monosized Ti-6Al-4V hollow spheres were sintered to 98% dense cell walls in Ar and point-contact bonded into closed-cell foams through solid-state diffusion. These findings suggest that near-net shape Ti-6Al-4V structures may be produced with isotropic properties, strength, toughness, and densities as low as 10% of the bulk. Findings concerning the optimum processing parameters and implications for future research are discussed.

Preparation of Geophysical Fluid Flow Experiments ( GeoFlow ) in the Fluid Science Laboratory on ISS

NASA Astrophysics Data System (ADS)

Egbers, C.

The ,,GeoFlow" is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluidmechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field similar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment requires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth's liquid core the exp eriment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heating the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number. Results of preparatory experiments and numerical simulation of the space experiment will be presented. Funding from DLR under grant 50 WM 0122 is greatfully ackwnoledged.

Pilot Scale Production of Activated Carbon Spheres Using Fluidized Bed Reactor and Its Evaluation for the Removal of Hexavalent Chromium from Aqueous Solutions

NASA Astrophysics Data System (ADS)

Tripathi, Nagesh Kumar; Sathe, Manisha

2017-12-01

Large scale production of activated carbon is need of ongoing research due to its excellent adsorption capacity for removal of heavy metals from contaminated solutions. In the present study, polymeric precursor polystyrene beads [Brunauer Emmett Teller (BET) surface area, 46 m2/g; carbon content, 40.64%; crushing strength, 0.32 kg/sphere] were used to produce a new variant of activated carbon, Activated Carbon Spheres (ACS) in a pilot scale fluidized bed reactor. ACS were prepared by carbonization of polymeric precursor at 850 °C followed by activation of resultant material with steam. Prepared ACS were characterized using scanning electron microscope, CHNS analyzer, thermogravimetric analyzer, surface area analyzer and crushing strength tester. The produced ACS have 1009 m2/g BET surface area, 0.89 cm3/g total pore volume, 92.32% carbon content and 1.1 kg/sphere crushing strength with less than 1% of moisture and ash content. The ACS were also evaluated for its potential to remove hexavalent chromium [Cr(VI)] from contaminated solutions. The chromium removal is observed to be 99.1% at initial concentration 50 mg/l, pH 2, ACS dose 1 g/l, contact time 2 h, agitation 120 rpm and temperature 30 °C. Thus ACS can be used as an adsorbent material for the removal of Cr(VI) from contaminated solutions.

Adamantyl- and Furanyl-Protected Nanoscale Silver Sulfide Clusters.

PubMed

Bestgen, Sebastian; Yang, Xiaoxun; Issac, Ibrahim; Fuhr, Olaf; Roesky, Peter W; Fenske, Dieter

2016-07-11

The silver salts of 1-adamantanethiol (AdSH) and furan-2-ylmethanethiol (FurCH2 SH) were successfully applied as building blocks for ligand-protected Ag2 S nanoclusters. The reaction of the silver thiolates [AgSAd]x and [AgSCH2 Fur]x with S(SiMe3 )2 and 1,5-bis(diphenylphosphino)pentane (dpppt) afforded three different clusters with 58, 94 and, 190 silver atoms. The intensely colored compounds [Ag58 S13 (SAd)32 ] (1), [Ag94 S34 (SAd)26 (dpppt)6 ] (2), and [Ag190 S58 (SCH2 Fur)74 (dpppt)8 ] (3) were structurally characterized by single-crystal X-ray diffraction and exhibit different cluster core geometries and ligand shells. The diameters of the well-defined sphere-shaped nanoclusters range from 2.2 nm to 3.5 nm. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Impact of Horizontal and Temporal Resolution on Convection and Precipitation with High-Resolution GEOS-5

NASA Technical Reports Server (NTRS)

Putman, William P.

2012-01-01

Using a high-resolution non-hydrostatic version of GEOS-5 with the cubed-sphere finite-volume dynamical core, the impact of spatial and temporal resolution on cloud properties will be evaluated. There are indications from examining convective cluster development in high resolution GEOS-5 forecasts that the temporal resolution within the model may playas significant a role as horizontal resolution. Comparing modeled convective cloud clusters versus satellite observations of brightness temperature, we have found that improved. temporal resolution in GEOS-S accounts for a significant portion of the improvements in the statistical distribution of convective cloud clusters. Using satellite simulators in GEOS-S we will compare the cloud optical properties of GEOS-S at various spatial and temporal resolutions with those observed from MODIS. The potential impact of these results on tropical cyclone formation and intensity will be examined as well.

Coordinated Hard Sphere Mixture (CHaSM): A simplified model for oxide and silicate melts at mantle pressures and temperatures

NASA Astrophysics Data System (ADS)

Wolf, Aaron S.; Asimow, Paul D.; Stevenson, David J.

2015-08-01

We develop a new model to understand and predict the behavior of oxide and silicate melts at extreme temperatures and pressures, including deep mantle conditions like those in the early Earth magma ocean. The Coordinated Hard Sphere Mixture (CHaSM) is based on an extension of the hard sphere mixture model, accounting for the range of coordination states available to each cation in the liquid. By utilizing approximate analytic expressions for the hard sphere model, this method is capable of predicting complex liquid structure and thermodynamics while remaining computationally efficient, requiring only minutes of calculation time on standard desktop computers. This modeling framework is applied to the MgO system, where model parameters are trained on a collection of crystal polymorphs, producing realistic predictions of coordination evolution and the equation of state of MgO melt over a wide range of pressures and temperatures. We find that the typical coordination number of the Mg cation evolves continuously upward from 5.25 at 0 GPa to 8.5 at 250 GPa. The results produced by CHaSM are evaluated by comparison with predictions from published first-principles molecular dynamics calculations, indicating that CHaSM is accurately capturing the dominant physics controlling the behavior of oxide melts at high pressure. Finally, we present a simple quantitative model to explain the universality of the increasing Grüneisen parameter trend for liquids, which directly reflects their progressive evolution toward more compact solid-like structures upon compression. This general behavior is opposite that of solid materials, and produces steep adiabatic thermal profiles for silicate melts, thus playing a crucial role in magma ocean evolution.

Crystallization and dynamical arrest of attractive hard spheres.

PubMed

Babu, Sujin; Gimel, Jean-Christophe; Nicolai, Taco

2009-02-14

Crystallization of hard spheres interacting with a square well potential was investigated by numerical simulations using so-called Brownian cluster dynamics. The phase diagram was determined over a broad range of volume fractions. The crystallization rate was studied as a function of the interaction strength expressed in terms of the second virial coefficient. For volume fractions below about 0.3 the rate was found to increase abruptly with increasing attraction at the binodal of the metastable liquid-liquid phase separation. The rate increased until a maximum was reached after which it decreased with a power law dependence on the second virial coefficient. Above a critical percolation concentration, a transient system spanning network of connected particles was formed. Crystals were formed initially as part of the network, but eventually crystallization led to the breakup of the network. The lifetime of the transient gels increased very rapidly over a small range of interaction energies. Weak attraction destabilized the so-called repulsive crystals formed in pure hard sphere systems and shifted the coexistence line to higher volume fractions. Stronger attraction led to the formation of a denser, so-called attractive, crystalline phase. Nucleation of attractive crystals in the repulsive crystalline phase was observed close to the transition.

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

Ebeida, Mohamed S.; Mitchell, Scott A.; Swiler, Laura P.

We introduce a novel technique, POF-Darts, to estimate the Probability Of Failure based on random disk-packing in the uncertain parameter space. POF-Darts uses hyperplane sampling to explore the unexplored part of the uncertain space. We use the function evaluation at a sample point to determine whether it belongs to failure or non-failure regions, and surround it with a protection sphere region to avoid clustering. We decompose the domain into Voronoi cells around the function evaluations as seeds and choose the radius of the protection sphere depending on the local Lipschitz continuity. As sampling proceeds, regions uncovered with spheres will shrink,more » improving the estimation accuracy. After exhausting the function evaluation budget, we build a surrogate model using the function evaluations associated with the sample points and estimate the probability of failure by exhaustive sampling of that surrogate. In comparison to other similar methods, our algorithm has the advantages of decoupling the sampling step from the surrogate construction one, the ability to reach target POF values with fewer samples, and the capability of estimating the number and locations of disconnected failure regions, not just the POF value. Furthermore, we present various examples to demonstrate the efficiency of our novel approach.« less

Röntgen spheres around active stars

NASA Astrophysics Data System (ADS)

Locci, Daniele; Cecchi-Pestellini, Cesare; Micela, Giuseppina; Ciaravella, Angela; Aresu, Giambattista

2018-01-01

X-rays are an important ingredient of the radiation environment of a variety of stars of different spectral types and age. We have modelled the X-ray transfer and energy deposition into a gas with solar composition, through an accurate description of the electron cascade following the history of the primary photoelectron energy deposition. We test and validate this description studying the possible formation of regions in which X-rays are the major ionization channel. Such regions, called Röntgen spheres may have considerable importance in the chemical and physical evolution of the gas embedding the emitting star. Around massive stars the concept of Röntgen sphere appears to be of limited use, as the formation of extended volumes with relevant levels of ionization is efficient just in a narrow range of gas volume densities. In clouds embedding low-mass pre-main-sequence stars significant volumes of gas are affected by ionization levels exceeding largely the cosmic-ray background ionization. In clusters arising in regions of vigorous star formation X-rays create an ionization network pervading densely the interstellar medium, and providing a natural feedback mechanism, which may affect planet and star formation processes.

The influence of particle shape on dielectric enhancement in metal-insulator composites

NASA Astrophysics Data System (ADS)

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

1992-04-01

Disordered suspensions of conducting particles exhibit substantial permittivity enhancements beyond the predictions of the Clausius-Mossotti equation and other purely dipolar approximations. The magnitude of the enhancement depends upon the shape of the particles. A recently developed effective cluster model for spherical particles [Phys. Rev. B 42, 9319 (1990)] that treats a disordered suspension as a mixture, or mesosuspension, of isolated spheres and close-packed spherical clusters of arbitrary size is in excellent agreement with experiments on well-stirred suspensions of spheres over the entire accessible range of volume loading. In this paper, the effective cluster model is extended to be applicable to disordered suspensions of arbitrarily shaped conducting particles. Two physical parameters are used to characterize a general suspension: the angular average polarizability of an isolated particle, and the volume loading at closest packing of the suspension. Multipole interactions within the clusters are treated exactly. External particle-shape-dependent interactions between clusters and isolated particles are treated in the dipole approximation in two ways: explicitly, using the Clausius-Mossotti equation, and implicitly, using the Wiener equation. Both versions of the model are used to find the permittivity of a monodisperse suspension of conducting spheroids, for which the model parameters can be determined independently. The two versions are in good agreement when the axial ratio of the particles is not extreme. The Clausius-Mossotti version of the model yields a mesoscopic analogue of the dielectric virial expansion. It is limited to small volume loadings when the particles have an extremely nonspherical shape. The Wiener equation version of the model holds at all volume loadings for particles of arbitrary shape. Comparison of the two versions of the model leads to a simple physical interpretation of Wiener's equation. The models are compared with experiments of Kelly, Stenoien, and Isbell [J. Appl. Phys. 24, 258 (1953)] on aluminum and zinc particles in paraffin, with Nasuhoglu's experiments on iron particles in oil [Commun. Fac. Sci. Univ. Ankara 4, 108 (1952)], and with new X-band and Kα-band permittivity measurements on Ni-Cr alloy particles in a polyurethane binder.

Fabrication of sub-micrometer-sized jingle bell-shaped hollow spheres from multilayered core-shell particles.

PubMed

Gu, Shunchao; Kondo, Tomohiro; Mine, Eiichi; Nagao, Daisuke; Kobayashi, Yoshio; Konno, Mikio

2004-11-01

Jingle bell-shaped hollow spheres were fabricated starting from multilayered particles composed of a silica core, a polystyrene inner shell, and a titania outer shell. Composite particles of silica core-polystyrene shell, synthesized by coating a 339-nm-sized silica core with a polystyrene shell of thickness 238 nm in emulsion polymerization, were used as core particles for a succeeding titania-coating. A sol-gel method was employed to form the titania outer shell with a thickness of 37 nm. The inner polystyrene shell in the multilayered particles was removed by immersing them in tetrahydrofuran. These successive procedures could produce jingle bell-shaped hollow spheres that contained a silica core in the titania shell.

Transmission spectra changes produced by decreasing compactness of opal-like structures

NASA Astrophysics Data System (ADS)

Andueza, A.; Echeverría, R.; Morales, P.; Sevilla, J.

2009-01-01

Artificial opal-like structures based on spheres and colloidal particles have been fabricated in a controlled way, presenting optical band-gap properties in the optical frequency range. Nonclose packed artificial opals have also been fabricated and studied recently. In order to gain a better understanding of these phenomena, we have studied macroscopic models of nonclose packed fcc lattices using glass spheres (ɛ =7) of 8 mm diameter, and measuring in the microwave region (from 10 to 30 GHz). The results have shown a Bragg resonance tunable with filling factor of the opal, and a strong rejected band similar, also present in close packed samples, much less affected by compactness. The relation of this high order band with spheres single layer behavior is also discussed.

Directed Self-Assembly of Gradient Concentric Carbon Nanotube Rings

NASA Astrophysics Data System (ADS)

Hong, Suck Won; Jeong, Wonje; Ko, Hyunhyub; Tsukruk, Vladimir; Kessler, Michael; Lin, Zhiqun

2008-03-01

Hundreds of gradient concentric rings of linear conjugated polymer, (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene], i.e., MEH-PPV) with remarkable regularity over large areas were produced by controlled, repetitive ``stick- slip'' motions of the contact line in a confined geometry consisting of a sphere on a flat substrate (i.e., sphere-on-flat geometry). Subsequently, MEH-PPV rings exploited as template to direct the formation of gradient concentric rings of multiwalled carbon nanotubes (MWNTs) with controlled density. This method is simple, cost effective, and robust, combining two consecutive self-assembly processes, namely, evaporation-induced self- assembly of polymers in a sphere-on-flat geometry, followed by subsequent directed self-assembly of MWNTs on the polymer- templated surfaces.

Coulomb Fission in Multiply-Charged Ammonia Clusters: Accurate Measurements of the Rayleigh Instability Limit from Fragmentation Patterns.

PubMed

Harris, Christopher; Stace, Anthony J

2018-03-15

A series of experiments have been undertaken on the fragmentation of multiply charged ammonia clusters, (NH 3 ) n z+ , where z ≤ 8 and n ≤ 850, to establish Rayleigh instability limits, whereby clusters at certain critical sizes become unstable due to Coulomb repulsion between the resident charges. Experimental results on size-selected clusters are found to be in excellent agreement with theoretical predictions of Rayleigh instability limits at all values of the charge. Electrostatic theory has been used to help identify fragmentation patterns on the assumption that the clusters separate into two dielectric spheres, and the predicted Coulomb repulsion energies used to establish pathways and the sizes of cluster fragments. The results show that fragmentation is very asymmetric in terms of both the numbers of molecules involved and the amount of charge each fragment accommodates. For clusters carrying a charge ≤+4, the results show that fragmentation proceeds via the loss of small, singly charged clusters. When clusters carry a charge of +5 or more, the experimental observations suggest a marked switch in behavior. Although the laboratory measurements equate to fragmentation via the loss of a large dication cluster, electrostatic theory supports an interpretation that involves the sequential loss of two smaller, singly charged clusters possibly accompanied by the extensive evaporation of neutral molecules. It is suggested that this change in fragmentation pattern is driven by the channelling of Coulomb repulsion energy into intermolecular modes within these larger clusters. Overall, the results appear to support the ion evaporation model that is frequently used to interpret electrospray experiments.

Morphology of single inhalable particle in the air polluted city of Shijiazhuang, China.

PubMed

Wang, Zanhong; Zhang, Lingzhi; Zhang, Yuliang; Zhao, Zhou; Zhang, Sumin

2008-01-01

In the typical air polluted city of Shijiazhuang, single inhalable particle samples in non-heating period, heating period, dust storm days, and snowy days were collected and detected by SEM/EDS (scanning electron microscopy and energy dispersive X-ray spectrometry). The particle morphology was characterized by the 6 shape clusters, which are: irregular square, agglomerate, sphere, floccule, column or stick, and unknown, by quantitative order. The irregular square particles are common in all kinds of samples; sphere particles are more, and column or stick are less in winter samples; in the wet deposit samples, agglomerate and floccule particles are not found. The surface of most particles is coarse with fractal edge, which can provide suitable chemical reaction bed in the polluted atmospheric environment. New formed calcium crystal is found to demonstrate the existence of neutralized reaction, explaining the reason for the high SO2 emission and low acid rain frequency in Shijiazhuang. The three sorts of surface patterns of spheres are smooth, semi-smooth, and coarse, corresponding to the element of Si-dominant, Si-Al-dominant, and Fe-dominant. The soot particle is present as floccule with average size around 10 microm, considerably larger than the former reported results, but wrapped or captured with other fine particles to make its appearance unique and enhance its toxicity potentially. The new formed calcium crystal, the 3 sorts of sphere surface patterns, and the unique soot appearance represent the single inhalable particle's morphology characteristics in Shijiazhuang City.

Placers of cosmic dust in the blue ice lakes of Greenland

NASA Technical Reports Server (NTRS)

Maurette, M.; Hammer, C.; Reeh, N.; Brownlee, D. E.; Thomsen, H. H.

1986-01-01

A concentration process occurring in the melt zone of the Greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth. Extraterrestrial particles collected from this region are well preserved and are collectable in large quantities. The collected particles are generally identical to cosmic spheres found on the ocean floor, but a pure glass type was discovered that has not been seen in deep-sea samples. Iron-rich spheres are conspicuously rare in the collected material.

Multiregion bicentric-spheres models of the head for the simulation of bioelectric phenomena.

PubMed

Vatta, Federica; Bruno, Paolo; Inchingolo, Paolo

2005-03-01

Equations are derived for the electric potentials [electroencephalogram (EEG)] produced by dipolar sources in a multiregion bicentric-spheres volume-conductor head model. Being the equations valid for an arbitrary number of regions, our proposal is a generalization of many spherical models presented so far in literature, each of those regarded as a particular case of our multiregion model. Moreover, our approach allows considering new features of the head volume-conductor to better approximate electrical properties of the real head.

Wetting, meniscus structure, and capillary interactions of microspheres bound to a cylindrical liquid interface.

PubMed

Kim, Paul Y; Dinsmore, Anthony D; Hoagland, David A; Russell, Thomas P

2018-03-14

Wetting, meniscus structure, and capillary interactions for polystyrene microspheres deposited on constant curvature cylindrical liquid interfaces, constructed from nonvolatile ionic or oligomeric liquids, were studied by optical interferometry and optical microscopy. The liquid interface curvature resulted from the preferential wetting of finite width lines patterned onto planar silicon substrates. Key variables included sphere diameter, nominal (or average) contact angle, and deviatoric interfacial curvature. Menisci adopted the quadrupolar symmetry anticipated by theory, with interfacial deformation closely following predicted dependences on sphere diameter and nominal contact angle. Unexpectedly, the contact angle was not constant locally around the contact line, the nominal contact angle varied among seemingly identical spheres, and the maximum interface deviation did not follow the predicted dependence on deviatoric interfacial curvature. Instead, this deviation was up to an order-of-magnitude larger than predicted. Trajectories of neighboring microspheres visually manifested quadrupole-quadrupole interactions, eventually producing square sphere packings that foreshadow interfacial assembly as a potential route to hierarchical 2D particle structures.

Method and apparatus for producing gas-filled hollow spheres. [target pellets for inertial confinement fusion

NASA Technical Reports Server (NTRS)

Wang, T. G.; Elleman, D. D. (Inventor)

1982-01-01

A system for forming hollow spheres containing pressured gas is described which includes a cylinder device containing a molten solid material with a nozzle at its end. A second gas nozzle, lying slightly upstream from the tip of the first nozzle, is connected to a source that applies pressured filler gas that is to fill the hollow spheres. High pressure is applied to the molten metal, as by moving a piston within the cylinder device, to force the molten material out of the first nozzle. At the same time, pressured gas fills the center of the extruded hollow liquid pipe that breaks into hollow spheres. The environment outside the nozzles contains gas at a high pressure such as 100 atmospheres. Gas is supplied to the gas nozzle at a slightly higher pressure such as 101 atmospheres. The pressure applied to the molten material is at a still higher pressure such as 110 atmospheres.

Theoretical Elastic Stress Distributions Arising from Discontinuities and Edge Loads in Several Shell-Type Structures

NASA Technical Reports Server (NTRS)

Johns, Robert H.; Orange, Thomas W.

1961-01-01

The deformation and complete stress distribution are determined for each of the following edge loaded thin shells of revolution: (1) a right circular cylinder, (2) a frustum of a right circular cone, and (3) a portion of a sphere. The locations of the maximum circumferential and meridional stresses on both the inner and outer surfaces are also found. The basic equations for the above were selected from the published literature on the subject and expanded to produce to resultant-stress equations in closed from where practicable to do so. Equations are also developed for the discontinuity shear force and bending moment at each of the following junction: (1) axial change of thickness in a circular cylinder, (2) axial change of thickness in a cone, (3) change of thickness in a portion of a sphere, (4) a cylinder and a cone, (5) a cylinder and a portion of a sphere(6) a cylinder and a flat head, and (7) a cone and a portion of a sphere.

A resonance shift prediction based on the Boltzmann-Ehrenfest principle for cylindrical cavities with a rigid sphere.

PubMed

Santillan, Arturo O; Cutanda-Henríquez, Vicente

2008-11-01

An investigation on the resonance frequency shift for a plane-wave mode in a cylindrical cavity produced by a rigid sphere is reported in this paper. This change of the resonance frequency has been previously considered as a cause of oscillational instabilities in single-mode acoustic levitation devices. It is shown that the use of the Boltzmann-Ehrenfest principle of adiabatic invariance allows the derivation of an expression for the resonance frequency shift in a simpler and more direct way than a method based on a Green's function reported in literature. The position of the sphere can be any point along the axis of the cavity. Obtained predictions of the resonance frequency shift with the deduced equation agree quite well with numerical simulations based on the boundary element method. The results are also confirmed by experiments. The equation derived from the Boltzmann-Ehrenfest principle appears to be more general, and for large spheres, it gives a better approximation than the equation previously reported.

A general route to hollow mesoporous rare-earth silicate nanospheres as a catalyst support.

PubMed

Jin, Renxi; Yang, Yang; Zou, Yongcun; Liu, Xianchun; Xing, Yan

2014-02-17

Hollow mesoporous structures have recently aroused intense research interest owing to their unique structural features. Herein, an effective and precisely controlled synthesis of hollow rare-earth silicate spheres with mesoporous shells is reported for the first time, produced by a simple hydrothermal method, using silica spheres as the silica precursors. The as-prepared hollow rare-earth silicate spheres have large specific surface area, high pore volume, and controllable structure parameters. The results demonstrate that the selection of the chelating reagent plays critical roles in forming the hollow mesoporous structures. In addition, a simple and low-energy-consuming approach to synthesize highly stable and dispersive gold nanoparticle-yttrium silicate (AuNPs/YSiO) hollow nanocomposites has also been developed. The reduction of 4-nitrophenol with AuNPs/YSiO hollow nanocomposites as the catalyst has clearly demonstrated that the hollow rare-earth silicate spheres are good carriers for Au nanoparticles. This strategy can be extended as a general approach to prepare multifunctional yolk-shell structures with diverse compositions and morphologies simply by replacing silica spheres with silica-coated nanocomposites. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Retuning the Catalytic Bias and Overpotential of a [NiFe]-Hydrogenase via a Single Amino Acid Exchange at the Electron Entry/Exit Site

PubMed Central

2017-01-01

The redox chemistry of the electron entry/exit site in Escherichia coli hydrogenase-1 is shown to play a vital role in tuning biocatalysis. Inspired by nature, we generate a HyaA-R193L variant to disrupt a proposed Arg–His cation−π interaction in the secondary coordination sphere of the outermost, “distal”, iron–sulfur cluster. This rewires the enzyme, enhancing the relative rate of H2 production and the thermodynamic efficiency of H2 oxidation catalysis. On the basis of Fourier transformed alternating current voltammetry measurements, we relate these changes in catalysis to a shift in the distal [Fe4S4]2+/1+ redox potential, a previously experimentally inaccessible parameter. Thus, metalloenzyme chemistry is shown to be tuned by the second coordination sphere of an electron transfer site distant from the catalytic center. PMID:28697596

Kinetics of motility-induced phase separation and swim pressure

NASA Astrophysics Data System (ADS)

Patch, Adam; Yllanes, David; Marchetti, M. Cristina

Active Brownian particles (ABPs) represent a minimal model of active matter consisting of self-propelled spheres with purely repulsive interactions and rotational noise. We correlate the time evolution of the mean pressure towards its steady state value with the kinetics of motility-induced phase separation. For parameter values corresponding to phase separated steady states, we identify two dynamical regimes. The pressure grows monotonically in time during the initial regime of rapid cluster formation, overshooting its steady state value and then quickly relaxing to it, and remains constant during the subsequent slower period of cluster coalescence and coarsening. The overshoot is a distinctive feature of active systems. NSF-DMR-1305184, NSF-DGE-1068780, ACI-1341006, FIS2015-65078-C02, BIFI-ZCAM.

Coordinating the Provision of Health Services in Humanitarian Crises: a Systematic Review of Suggested Models.

PubMed

Lotfi, Tamara; Bou-Karroum, Lama; Darzi, Andrea; Hajjar, Rayan; El Rahyel, Ahmed; El Eid, Jamale; Itani, Mira; Brax, Hneine; Akik, Chaza; Osman, Mona; Hassan, Ghayda; El-Jardali, Fadi; Akl, Elie

2016-08-03

Our objective was to identify published models of coordination between entities funding or delivering health services in humanitarian crises, whether the coordination took place during or after the crises. We included reports describing models of coordination in sufficient detail to allow reproducibility. We also included reports describing implementation of identified models, as case studies. We searched Medline, PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CINAHL, PsycINFO, and the WHO Global Health Library. We also searched websites of relevant organizations. We followed standard systematic review methodology. Our search captured 14,309 citations. The screening process identified 34 eligible papers describing five models of coordination of delivering health services: the "Cluster Approach" (with 16 case studies), the 4Ws "Who is Where, When, doing What" mapping tool (with four case studies), the "Sphere Project" (with two case studies), the "5x5" model (with one case study), and the "model of information coordination" (with one case study). The 4Ws and the 5x5 focus on coordination of services for mental health, the remaining models do not focus on a specific health topic. The Cluster approach appears to be the most widely used. One case study was a mixed implementation of the Cluster approach and the Sphere model. We identified no model of coordination for funding of health service. This systematic review identified five proposed coordination models that have been implemented by entities funding or delivering health service in humanitarian crises. There is a need to compare the effect of these different models on outcomes such as availability of and access to health services.

Grid-Sphere Electrodes for Contact with Ionospheric Plasma

NASA Technical Reports Server (NTRS)

Stone, Nobie H.; Poe, Garrett D.

2010-01-01

Grid-sphere electrodes have been proposed for use on the positively biased end of electrodynamic space tethers. A grid-sphere electrode is fabricated by embedding a wire mesh in a thin film from which a spherical balloon is formed. The grid-sphere electrode would be deployed from compact stowage by inflating the balloon in space. The thin-film material used to inflate the balloon is formulated to vaporize when exposed to the space environment. This would leave the bare metallic spherical grid electrode attached to the tether, which would present a small cross-sectional area (essentially, the geometric wire shadow area only) to incident neutral atoms and molecules. Most of the neutral particles, which produce dynamic drag when they impact a surface, would pass unimpeded through the open grid spaces. However, partly as a result of buildup of a space charge inside the grid-sphere, and partially, the result of magnetic field effects, the electrode would act almost like a solid surface with respect to the flux of electrons. The net result would be that grid-sphere electrodes would introduce minimal aerodynamic drag, yet have effective electrical-contact surface areas large enough to collect multiampere currents from the ionospheric plasma that are needed for operation of electrodynamic tethers. The vaporizable-balloon concept could also be applied to the deployment of large radio antennas in outer space.

Some mechanisms for the formation of octopus-shaped iron micro-particles

NASA Astrophysics Data System (ADS)

Bica, Ioan

2004-08-01

Fluid spheres (micro-spheres or/and drops) are formed out of the metallic solid (the carbon steel semi-finished product) in the argon plasma of the transferred electric arc. For short intervals of time, the spheres are at rest with relation to vapors. The movement of the vapors around the spheres is in the same plane. It consists of a movement around a circle combined with the movement produced by a definitely located whirl. The molar concentration of the vapors is small in comparison with the molar density of the mixture formed of vapors and gas. At the intersection of the sphere and the plane of movement of the vapors, distinct stagnation point is formed. They constitute points of the beginning/and end of the current lines. Each current line is a carrier of a vapor cylinder. In time, the cylinder-gas interface reaches points of temperature equal to that of the "dew point" for iron. On this occasion a liquid membrane is formed. It delimits the vapor-gas mixture from the rest of the gas. Subsequent to the process of diffusion in non-stationary condition, the membrane becomes thicker and no vapors exist inside the tube. Needle-shaped micro-tubes are formed, in liquid phase, around the fluid sphere. By solidification, micro-particles occur, consisting of a central nucleus around which ligaments branch out.

Low pressure radon diffusion - A laboratory study and its implications for lunar venting

NASA Technical Reports Server (NTRS)

Friesen, L. J.; Adams, J. A. S.

1976-01-01

Results of a study of radon migration through columns of fine particulate materials, at total pressures of 0.02-0.2 torr, are reported. Materials studied were: NBS Glass Spheres (SRM 1003), Emerson & Cuming Eccospheres (IG-101), activated coconut charcoal, Lipaci obsidian, and W-1 Standard Diabase. Rates of diffusion were used to derive heats of adsorption for radon on the materials tested. The most reliable values found clustered around 8-9 kcal/mole. These high heats of adsorption, if typical for most materials, combined with low percentages of radon emanation by lunar soils found by other researchers, imply that random walk diffusion will not be an important mechanism for redistributing the radon and the radon daughters produced in the lunar regolith. In particular, since random walk migration is not a sufficient mechanism to account for localized high concentrations of radon-222 and its daughter polonium-210 observed by the Apollo 15 and 16 command modules, an alternative mechanism is proposed, in which radon would be swept to the surface by other gases during intermittent venting events.

Scattering on hyperbolic microspheres: From photonic nanojets to Poisson-Arago bright spots

NASA Astrophysics Data System (ADS)

Hodges, Reed; Dean, Cleon; Durach, Maxim

We investigate optical properties of metal-dielectric metamaterial microspheres composed of subwavelength spherical shells of two different materials alternating in an onion-layer fashion. Recently such metamaterial spheres were considered as cavities and their whispering gallery modes were investigated. We focus on the scattering of external radiation by the meta-micropheres in this work. We show that different scenarios are produced by altering the metal fraction in the spheres: as the microsphere transitions from all-dielectric to hyperbolic to all-metal, the photonic nanojets transform into Poisson-Arago bright spots. A new phenomenon also emerges as the percentage of metal in the microsphere increases. ``Hot spots'' of optical fields intensity appear at the center of the sphere. Their intensity is much higher than that of the incident plane wave.

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

Krasniak, S. R.; Smith, R. D.

Enzymatic hydrolysis of biomass to produce glucose may become feasible if an inexpensive method to reuse the enzyme can be found. This study investigated one such method whereby ..beta..-D-glucosidase (E.C. 3.2.1.21) was immobilized in calcium alginate gel spheres, which were shown to catalyze the hydrolysis of cellobiose to glucose. There was a loss of 49% of the enzyme from the alginate slurry during gelation. After gelation, in the stable gel spheres, there was a 37% retention of the enzyme activity that was actually immobilized. The reason for the loss in activity was investigated and may be caused by inhibition ofmore » the enzyme within the sphere by the calcium cations and the alginate anions also present. Mass transfer effects were minimal in this system and were not responsible for the activity loss.« less

Scattering properties of alumina particle clusters with different radius of monomers in aerocraft plume

NASA Astrophysics Data System (ADS)

Li, Jingying; Bai, Lu; Wu, Zhensen; Guo, Lixin; Gong, Yanjun

2017-11-01

In this paper, diffusion limited aggregation (DLA) algorithm is improved to generate the alumina particle cluster with different radius of monomers in the plume. Scattering properties of these alumina clusters are solved by the multiple sphere T matrix method (MSTM). The effect of the number and radius of monomers on the scattering properties of clusters of alumina particles is discussed. The scattering properties of two types of alumina particle clusters are compared, one has different radius of monomers that follows lognormal probability distribution, another has the same radius of monomers that equals the mean of lognormal probability distribution. The result show that the scattering phase functions and linear polarization degrees of these two types of alumina particle clusters are of great differences. For the alumina clusters with different radius of monomers, the forward scatterings are bigger and the linear polarization degree has multiple peaks. Moreover, the vary of their scattering properties do not have strong correlative with the change of number of monomers. For larger booster motors, 25-38% of the plume being condensed alumina. The alumina can scatter radiation from other sources present in the plume and effect on radiation transfer characteristics of plume. In addition, the shape, size distribution and refractive index of the particles in the plume are estimated by linear polarization degree. Therefore, accurate scattering properties calculation is very important to decrease the deviation in the related research.

Self-renewal and multilineage differentiation of mouse dental epithelial stem cells.

PubMed

Chang, Julia Yu Fong; Wang, Cong; Jin, Chengliu; Yang, Chaofeng; Huang, Yanqing; Liu, Junchen; McKeehan, Wallace L; D'Souza, Rena N; Wang, Fen

2013-11-01

Understanding the cellular and molecular mechanisms underlying the self-renewal and differentiation of dental epithelial stem cells (DESCs) that support the unlimited growth potential of mouse incisors is critical for developing novel tooth regenerative therapies and unraveling the pathogenesis of odontogenic tumors. However, analysis of DESC properties and regulation has been limited by the lack of an in vitro assay system and well-documented DESC markers. Here, we describe an in vitro sphere culture system to isolate the DESCs from postnatal mouse incisor cervical loops (CLs) where the DESCs are thought to reside. The dissociated cells from CLs were able to expand and form spheres for multiple generations in the culture system. Lineage tracing indicated that DESC within the spheres were epithelial in origin as evident by lineage tracing. Upon stimulation, the sphere cells differentiated into cytokeratin 14- and amelogenin-expressing and mineral material-producing cells. Compared to the CL tissue, sphere cells expressed high levels of expression of Sca-1, CD49f (also designated as integrin α6), and CD44. Fluorescence-activated cell sorting (FACS) analyses of mouse incisor CL cells further showed that the CD49f(Bright) population was enriched in sphere-forming cells. In addition, the CD49f(Bright) population includes both slow-cycling and Lgr5(+) DESCs. The in vitro sphere culture system and identification of CD49f(Bright) as a DESC marker provide a novel platform for enriching DESCs, interrogating how maintenance, cell fate determination, and differentiation of DESCs are regulated, and developing tooth regenerative therapies. © 2013.

Self-renewal and Multilineage Differentiation of Mouse Dental Epithelial Stem Cells

PubMed Central

Chang, Julia Yu Fong; Wang, Cong; Jin, Chengliu; Yang, Chaofeng; Huang, Yanqing; Liu, Junchen; McKeehan, Wallace L.; D’Souza, Rena N.; Wang, Fen

2013-01-01

Understanding the cellular and molecular mechanisms underlying the self-renewal and differentiation of dental epithelial stem cells (DESCs) that support the unlimited growth potential of mouse incisors is critical for developing novel tooth regenerative therapies and unraveling the pathogenesis of odontogenic tumors. However, analysis of DESC properties and regulation has been limited by the lack of an in vitro assay system and well-documented DESC markers. Here, we describe an in vitro sphere culture system to isolate the DESCs from postnatal mouse incisor cervical loops (CLs) where the DESCs are thought to reside. The dissociated cells from CLs were able to expand and form spheres for multiple generations in the culture system. Lineage tracing indicated that DESC within the spheres were epithelial in origin as evident by lineage tracing. Upon stimulation, the sphere cells differentiated into cytokeratin 14- and amelogenin-expressing and mineral material-producing cells. Compared to the CL tissue, sphere cells expressed high levels of expression of Sca-1, CD49f (also designated as integrin α6), and CD44. Fluorescence-activated cell sorting (FACS) analyses of mouse incisor CL cells further showed that the CD49fBright population was enriched in sphere-forming cells. In addition, the CD49fBright population includes both slow-cycling and Lgr5+ DESCs. The in vitro sphere culture system and identification of CD49fBright as a DESC marker provide a novel plateform for enriching DESCs, interrogating how maintenance, cell fate determination, and differentiation of DESCs are regulated, and developing tooth regenerative therapies. PMID:23906788

Are the stratospheric dust particles meteor ablation debris or interplanetary dust?

NASA Technical Reports Server (NTRS)

Blanchard, M. B.; Kyte, F. T.

1978-01-01

Natural and laboratory created fusion crusts and debris from artificial meteor samples were used to develop criteria for recognizing meteor ablation debris in a collection of 5 to 50 micron particles from the stratosphere. These laboratory studies indicate that meteor ablation debris from nickel-iron meteoroids produce spherules containing taenite, wuestite, magnetite, and hematite. These same studies also indicate that ablation debris from chondritic meteoroids produce spheres and fragmentary debris. The spheres may be either silicate rich, containing zoned olivine, magnetite, and glass, or sulfide rich, containing iron oxides (e.g., magnetite, wuestite) and iron sulfides (e.g., pyrrhotite, pentlandite). The fragmentary debris may be either fine-grained aggregates of olivine, magnetite, pyroxene, and occasionally pyrrhotite (derived from the meteorite matrix) or individual olivine and pyroxene grains (derived from meteorite inclusions).

Information-educational environment with adaptive control of learning process

NASA Astrophysics Data System (ADS)

Modjaev, A. D.; Leonova, N. M.

2017-01-01

Recent years, a new scientific branch connected with the activities in social sphere management developing intensively and it is called "Social Cybernetics". In the framework of this scientific branch, theory and methods of management of social sphere are formed. Considerable attention is paid to the management, directly in real time. However, the decision of such management tasks is largely constrained by the lack of or insufficiently deep study of the relevant sections of the theory and methods of management. The article discusses the use of cybernetic principles in solving problems of control in social systems. Applying to educational activities a model of composite interrelated objects representing the behaviour of students at various stages of educational process is introduced. Statistical processing of experimental data obtained during the actual learning process is being done. If you increase the number of features used, additionally taking into account the degree and nature of variability of levels of current progress of students during various types of studies, new properties of students' grouping are discovered. L-clusters were identified, reflecting the behaviour of learners with similar characteristics during lectures. It was established that the characteristics of the clusters contain information about the dynamics of learners' behaviour, allowing them to be used in additional lessons. The ways of solving the problem of adaptive control based on the identified dynamic characteristics of the learners are planned.

Cluster Bean—A Ureide- or Amide-Producing Legume? 1

PubMed Central

Sheoran, Inder S.; Luthra, Yash P.; Kuhad, Mohinder S.; Singh, Randhir

1982-01-01

Xylem sap of cluster bean (Cyamopsis tetragonoloba L. cv FS-277) and pigeonpea (Cajanus cajan cv UPAS-120) were analyzed for total nitrogen, amide nitrogen, and ureide nitrogen at flowering stage. Nitrogenase, uricase, and allantoinase were compared in nodules of cluster bean and pigeonpea. Xylem sap of cluster bean exhibited higher amounts of amides as compared to ureides, and the activities of uricase and allantoinase (ureide-producing enzymes) in nodules were also low, whereas the reverse was the case for pigeonpea. Based on these investigations, it has been concluded that cluster bean is an amide-producing legume rather than ureide-producing as had been reported earlier. PMID:16662600

Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications.

PubMed

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua; Keum, Jong K; Naskar, Amit K

2018-05-29

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads with micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. The renewable carbon product demonstrated a desirable surface area of 872 m 2 /g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.

Production of Large-Particle-Size Monodisperse Latexes in Microgravity

NASA Technical Reports Server (NTRS)

Vanderhoff, J. W.; Micale, F. J.; El-Aasser, M. S.; Kornfeld, M.

1985-01-01

A latex is a suspension of very tiny (micrometer-size) plastic spheres in water, stabilized by emulsifiers. The growth of billions of these tiny plastic spheres to sizes larger than can be grown on Earth is attempted while keeping all of them exactly the same size and perfectly spherical. Thus far on several of the Monodisperse Latex Reactor (MLR) flights, the latex spheres have been returned to Earth with standard deviations of better than 1.4%. In microgravity the absence of buoyancy effects has allowed growth of the balls up to 30 micrometers in diameter thus far. The MLR has now flown 5 times on the Shuttle. The MLR has now produced the first commercial space product; that is the first commercial material ever manufactured in space and marketed on Earth. Once it is demonstrated that these large-size-monodisperse latexes can be routinely produced in quantity and quality, they can be marketed for many types of scientific applications. They can be used in biomedical research for such things as drug carriers and tracers in the body, human and animal blood flow studies, membrane and pore-sizing in the body, and medical diagnostic tests.

Complex Refractive Index of Ice Fog at a Radio Wavelength of 3 mm

DTIC Science & Technology

1974-10-01

particles on mirror surface 55 41. Liberally dusting mirror with 3-// polystyrene dust produces almost no effect 56 —" -.-.—-- ■ .■..^„^-^aa...spheres, as Debye (1929) did in his original theory. The rotation of these spheres in a viscous medium is opposed by forces related by Stoke’s law to...given by a relation of the form ,_ C „D/kT E/RT Z 0 where R k ■ M.C \\s only slightly temperature dependent, and n/w is the average time required by

High-level waste program progress report, January 1, 1980-March 31, 1980

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

Not Available

1980-05-01

FUETAP concretes cured at 100/sup 0/C and 0.1 or 0.6 MPa had essentially the same physical properties as those cured at higher temperatures and pressures. Standard specimens containing high concentrations of /sup 244/Cm showed little gasification after 1 month. The large (23-cm ID) spray calciner has been completed and is operating satisfactorily. Construction was completed on a sphere-forming system capable of producing 100-g batches of Synroc spheres by internal gelation, and several runs were made. Preparations for the compatibilty tests are underway. (DLC)

POF-Darts: Geometric adaptive sampling for probability of failure

DOE PAGES

Ebeida, Mohamed S.; Mitchell, Scott A.; Swiler, Laura P.; ...

2016-06-18

We introduce a novel technique, POF-Darts, to estimate the Probability Of Failure based on random disk-packing in the uncertain parameter space. POF-Darts uses hyperplane sampling to explore the unexplored part of the uncertain space. We use the function evaluation at a sample point to determine whether it belongs to failure or non-failure regions, and surround it with a protection sphere region to avoid clustering. We decompose the domain into Voronoi cells around the function evaluations as seeds and choose the radius of the protection sphere depending on the local Lipschitz continuity. As sampling proceeds, regions uncovered with spheres will shrink,more » improving the estimation accuracy. After exhausting the function evaluation budget, we build a surrogate model using the function evaluations associated with the sample points and estimate the probability of failure by exhaustive sampling of that surrogate. In comparison to other similar methods, our algorithm has the advantages of decoupling the sampling step from the surrogate construction one, the ability to reach target POF values with fewer samples, and the capability of estimating the number and locations of disconnected failure regions, not just the POF value. Furthermore, we present various examples to demonstrate the efficiency of our novel approach.« less

The astronomy of Andean myth: The history of a cosmology

NASA Astrophysics Data System (ADS)

Sullivan, William F.

It is shown that Andean myth, on one level, represents a technical language recording astronomical observations of precession and, at the same time, an historical record of simultaneous social and celestial transformations. Topographic and architectural terms of Andean myth are interpreted as a metaphor for the organization of and locations on the celestial sphere. Via ethoastronomical date, mythical animals are identified as stars and placed on the celestial sphere according to their topographical location. Tested in the planetarium, these arrays generate cluster of dates - 200 B.C. and 650 A.D. Analysis of the names of Wiraqocha and Manco Capac indicates they represent Saturn and Jupiter and that their mythical meeting represents their conjunction in 650 A.D. The astronomy of Andean myth is then used as an historical tool to examine how the Andean priest-astronomers recorded the simultaneous creation of the avllu and of this distinctive astronomical system about 200 B.C. The idea that the agricultural avllu, with its double descent system stressing the importance of paternity, represents a transformation of society from an earlier matrilineal/horticultural era is examined in light of the sexual imagery employed in myth. Wiraqocha's androgyny and the division of the celestial sphere into male (ecliptic) and female (celestial equator = earth) are interpreted as cosmological validations of the new social structure.

Modeling Spectra of Icy Satellites and Cometary Icy Particles Using Multi-Sphere T-Matrix Code

NASA Astrophysics Data System (ADS)

Kolokolova, Ludmilla; Mackowski, Daniel; Pitman, Karly M.; Joseph, Emily C. S.; Buratti, Bonnie J.; Protopapa, Silvia; Kelley, Michael S.

2016-10-01

The Multi-Sphere T-matrix code (MSTM) allows rigorous computations of characteristics of the light scattered by a cluster of spherical particles. It was introduced to the scientific community in 1996 (Mackowski & Mishchenko, 1996, JOSA A, 13, 2266). Later it was put online and became one of the most popular codes to study photopolarimetric properties of aggregated particles. Later versions of this code, especially its parallelized version MSTM3 (Mackowski & Mishchenko, 2011, JQSRT, 112, 2182), were used to compute angular and wavelength dependence of the intensity and polarization of light scattered by aggregates of up to 4000 constituent particles (Kolokolova & Mackowski, 2012, JQSRT, 113, 2567). The version MSTM4 considers large thick slabs of spheres (Mackowski, 2014, Proc. of the Workshop ``Scattering by aggregates``, Bremen, Germany, March 2014, Th. Wriedt & Yu. Eremin, Eds., 6) and is significantly different from the earlier versions. It adopts a Discrete Fourier Convolution, implemented using a Fast Fourier Transform, for evaluation of the exciting field. MSTM4 is able to treat dozens of thousands of spheres and is about 100 times faster than the MSTM3 code. This allows us not only to compute the light scattering properties of a large number of electromagnetically interacting constituent particles, but also to perform multi-wavelength and multi-angular computations using computer resources with rather reasonable CPU and computer memory. We used MSTM4 to model near-infrared spectra of icy satellites of Saturn (Rhea, Dione, and Tethys data from Cassini VIMS), and of icy particles observed in the coma of comet 103P/Hartley 2 (data from EPOXI/DI HRII). Results of our modeling show that in the case of icy satellites the best fit to the observed spectra is provided by regolith made of spheres of radius ~1 micron with a porosity in the range 85% - 95%, which slightly varies for the different satellites. Fitting the spectra of the cometary icy particles requires icy aggregates of size larger than 40 micron with constituent spheres in the micron size range.

Anomalous optical scattering from intersecting fine particles

NASA Astrophysics Data System (ADS)

Paley, Alina V.; Radchik, Alex V.; Smith, Geoffrey B.

1995-09-01

There are many areas of science and technology where the scattering of electromagnetic waves by clusters or merging particles are of interest. The merging particles under study might be inclusions in high-density composites, liquid drops, biological cells, macroscopic ceramic particles, etc. As intersecting particles are bounded by a complex physical surface, the problem of scattering from these particles valid for any degree of merging, including touching, and for arbitrary materials of the constituents, has received limited attention. Here we present solutions which are valid and exact in the long wavelength limit compared with the size of intersecting spherical particles and cardioidal particles of similar dimensions. Both shapes are almost coincident everywhere except in the region of intersection. We treat the case when the waves are polarized along the common axis (longitudinal field). The solutions of Laplace's equation are integrals (spheres) or sums (cardioids) over continuous or discrete eigenvalue spectra respectively. The spectral dependencies of the resulting extinction coefficients and the scattering for the spherical and cardioidal particles are quite distinct. There is an enormous difference in the magnitude of absorption responses. Overall the cardioidal particle behaves as if it is almost invisible in terms of effects on the external field for a very broad band of optical frequencies. THe latter result was checked for a number of dielectric permittivities and seems to be universal. It scatters far more weakly than the isolated sphere. In constrast the intersecting sphere has an extinction band which is broad and is much enhanced at longer wavelegnths relative to the simple sphere. This result has significant implications for the design of surfaces with minimum scattering.

Workplace testing of the new single sphere neutron spectrometer based on Dysprosium activation foils (Dy-SSS)

NASA Astrophysics Data System (ADS)

Bedogni, R.; Gómez-Ros, J. M.; Esposito, A.; Gentile, A.; Chiti, M.; Palacios-Pérez, L.; Angelone, M.; Tana, L.

2012-08-01

A photon insensitive passive neutron spectrometer consisting of a single moderating polyethylene sphere with Dysprosium activation foils arranged along three perpendicular axes was designed by CIEMAT and INFN. The device is called Dy-SSS (Dy foil-based Single Sphere Spectrometer). It shows nearly isotropic response in terms of neutron fluence up to 20 MeV. The first prototype, previously calibrated with 14 MeV neutrons, has been recently tested in workplaces having different energy and directional distributions. These are a 2.5 MeV nearly mono-chromatic and mono-directional beam available at the ENEA Frascati Neutron Generator (FNG) and the photo-neutron field produced in a 15 MV Varian CLINAC DHX medical accelerator, located in the Ospedale S. Chiara (Pisa). Both neutron spectra are known through measurements with a Bonner Sphere Spectrometer. In both cases the experimental response of the Dy-SSS agrees with the reference data. Moreover, it is demonstrated that the spectrometric capability of the new device are independent from the directional distribution of the neutron field. This opens the way to a new generation of moderation-based neutron instruments, presenting all advantages of the Bonner sphere spectrometer without the disadvantage of the repeated exposures. This concept is being developed within the NESCOFI@BTF project of INFN (Commissione Scientifica Nazionale 5).

Hubble Sees an Ancient Globular Cluster

NASA Image and Video Library

2017-12-08

This image captures the stunning NGC 6535, a globular cluster 22,000 light-years away in the constellation of Serpens (The Serpent) that measures one light-year across. Globular clusters are tightly bound groups of stars which orbit galaxies. The large mass in the rich stellar centre of the globular cluster pulls the stars inward to form a ball of stars. The word globulus, from which these clusters take their name, is Latin for small sphere. Globular clusters are generally very ancient objects formed around the same time as their host galaxy. To date, no new star formation has been observed within a globular cluster, which explains the abundance of aging yellow stars in this image, most of them containing very few heavy elements. NGC 6535 was first discovered in 1852 by English astronomer John Russell Hind. The cluster would have appeared to Hind as a small, faint smudge through his telescope. Now, over 160 years later, instruments like the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3) on the NASA/ European Space Agency (ESA) Hubble Space Telescope allow us to marvel at the cluster and its contents in greater detail. Credit: ESA/Hubble & NASA, Acknowledgement: Gilles Chapdelaine NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Analysis of the energy of the first four excited states of the ground-state rotational bands of the even-even nuclei from 6C8 to 56Ba90 with the model of a single cluster of nucleons revolving about a sphere.

PubMed Central

Pauling, L

1991-01-01

The results of the analysis of the first four energy levels of the ground-state rotational bands of even-even nuclei from 6C8 to 56Ba90 on the basis of the revolving-cluster model are reported. Values of the nucleon number of the revolving cluster are assigned on the basis in part of the shell model and in part of the expectation that the corresponding values of the radius of revolution would change only slightly from one energy level to an adjacent level or from one nucleus to an adjacent nucleus. The values of the radius of revolution are found to change gradually from about 5 to 6 fm for the lighter nuclei to 7 to 8 fm for the heavier nuclei in the sequence studied. PMID:11607232

Nanoscale surface modification of glass using a 1064 nm pulsed laser

NASA Astrophysics Data System (ADS)

Theppakuttai, Senthil; Chen, Shaochen

2003-07-01

We report a method to produce nanopatterns on borosilicate glass by a Nd:yttrium-aluminum-garnet laser (10 ns, 1064 nm), using silica nanospheres. Nonlinear absorption of the enhanced optical field between the spheres and glass sample is believed to be the primary reason for the creation of nanofeatures on the glass substrate. By shining the laser beam from the backside of the glass sample, the scattering effects are minimized and only the direct field enhancement due to the spheres is utilized for surface patterning. To confirm this, calculations based on the Mie scattering theory were performed, and the resulting intensity as a function of scattering angles are presented. The nanofeatures thus obtained by this method are 350 nm in diameter and the distance between them is around 640 nm, which is same as the size of spheres used.

Study of cluster formation in a quasi-square well model of Janus ellipsoids

NASA Astrophysics Data System (ADS)

Ruth, Donovan; Rickman, Jeffrey; Gunton, James; Li, Wei

2014-03-01

We investigate the effect of geometry and range of attractive interaction on the self-assembly of Janus particles. In particular, we consider Janus spheroids with an aspect ratio of 0.6 and a quasi-square well model with a short range attractive interaction of 0.2 sigma where sigma is the characteristic length of the spheroid. We find that below a certain transition temperature the system forms orientationally ordered micelles and vesicles, with a cluster distribution qualitatively similar to that found in an earlier study of Janus spheres. (Phys. Chem. Chem. Phys. (2010) vol 12, 11869-11877, F. Sciortino, A. Giacometti and G. Pastore) Finally we discuss the implications of our work for encapsulation by self-assembly. Acknowledgement: This work was supported by a grant from the Mathers Foundation.

Simulation of moving boundaries interacting with compressible reacting flows using a second-order adaptive Cartesian cut-cell method

NASA Astrophysics Data System (ADS)

Muralidharan, Balaji; Menon, Suresh

2018-03-01

A high-order adaptive Cartesian cut-cell method, developed in the past by the authors [1] for simulation of compressible viscous flow over static embedded boundaries, is now extended for reacting flow simulations over moving interfaces. The main difficulty related to simulation of moving boundary problems using immersed boundary techniques is the loss of conservation of mass, momentum and energy during the transition of numerical grid cells from solid to fluid and vice versa. Gas phase reactions near solid boundaries can produce huge source terms to the governing equations, which if not properly treated for moving boundaries, can result in inaccuracies in numerical predictions. The small cell clustering algorithm proposed in our previous work is now extended to handle moving boundaries enforcing strict conservation. In addition, the cell clustering algorithm also preserves the smoothness of solution near moving surfaces. A second order Runge-Kutta scheme where the boundaries are allowed to change during the sub-time steps is employed. This scheme improves the time accuracy of the calculations when the body motion is driven by hydrodynamic forces. Simple one dimensional reacting and non-reacting studies of moving piston are first performed in order to demonstrate the accuracy of the proposed method. Results are then reported for flow past moving cylinders at subsonic and supersonic velocities in a viscous compressible flow and are compared with theoretical and previously available experimental data. The ability of the scheme to handle deforming boundaries and interaction of hydrodynamic forces with rigid body motion is demonstrated using different test cases. Finally, the method is applied to investigate the detonation initiation and stabilization mechanisms on a cylinder and a sphere, when they are launched into a detonable mixture. The effect of the filling pressure on the detonation stabilization mechanisms over a hyper-velocity sphere launched into a hydrogen-oxygen-argon mixture is studied and a qualitative comparison of the results with the experimental data are made. Results indicate that the current method is able to correctly reproduce the different regimes of combustion observed in the experiments. Through the various examples it is demonstrated that our method is robust and accurate for simulation of compressible viscous reacting flow problems with moving/deforming boundaries.

Fuzzy spaces topology change as a possible solution to the black hole information loss paradox

NASA Astrophysics Data System (ADS)

Silva, C. A. S.

2009-06-01

The black hole information loss paradox is one of the most intricate problems in modern theoretical physics. A proposal to solve this is one related with topology change. However it has found some obstacles related to unitarity and cluster decomposition (locality). In this Letter we argue that modelling the black hole's event horizon as a noncommutative manifold - the fuzzy sphere - we can solve the problems with topology change, getting a possible solution to the black hole information loss paradox.

On the Effect of Sphere-Overlap on Super Coarse-Grained Models of Protein Assemblies

NASA Astrophysics Data System (ADS)

Degiacomi, Matteo T.

2018-05-01

Ion mobility mass spectrometry (IM/MS) can provide structural information on intact protein complexes. Such data, including connectivity and collision cross sections (CCS) of assemblies' subunits, can in turn be used as a guide to produce representative super coarse-grained models. These models are constituted by ensembles of overlapping spheres, each representing a protein subunit. A model is considered plausible if the CCS and sphere-overlap levels of its subunits fall within predetermined confidence intervals. While the first is determined by experimental error, the latter is based on a statistical analysis on a range of protein dimers. Here, we first propose a new expression to describe the overlap between two spheres. Then we analyze the effect of specific overlap cutoff choices on the precision and accuracy of super coarse-grained models. Finally, we propose a method to determine overlap cutoff levels on a per-case scenario, based on collected CCS data, and show that it can be applied to the characterization of the assembly topology of symmetrical homo-multimers. [Figure not available: see fulltext.

Preparation of UC0.07-0.10N0.90-0.93 spheres for TRISO coated fuel particles

NASA Astrophysics Data System (ADS)

Hunt, R. D.; Silva, C. M.; Lindemer, T. B.; Johnson, J. A.; Collins, J. L.

2014-05-01

The US Department of Energy is considering a new nuclear fuel that would be less susceptible to ruptures during a loss-of-coolant accident. The fuel would consist of tristructural isotropic coated particles with dense uranium nitride (UN) kernels with diameters of 650 or 800 μm. The objectives of this effort are to make uranium oxide microspheres with adequately dispersed carbon nanoparticles and to convert these microspheres into UN spheres, which could be then sintered into kernels. Recent improvements to the internal gelation process were successfully applied to the production of uranium gel spheres with different concentrations of carbon black. After the spheres were washed and dried, a simple two-step heat profile was used to produce porous microspheres with a chemical composition of UC0.07-0.10N0.90-0.93. The first step involved heating the microspheres to 2023 K in a vacuum, and in the second step, the microspheres were held at 1873 K for 6 h in flowing nitrogen.

Photothermal therapy of Lewis lung carcinoma in mice using gold nanoshells on carboxylated polystyrene spheres

NASA Astrophysics Data System (ADS)

Liu, Huiyu; Chen, Dong; Tang, Fangqiong; Du, Gangjun; Li, Linlin; Meng, Xianwei; Liang, Wei; Zhang, Yangde; Teng, Xu; Li, Yi

2008-11-01

A new approach towards the design of gold nanoshells on carboxylated polystyrene spheres (GNCPSs) is reported here. Gold nanoshells were self-assembled on the surface of carboxylated polystyrene spheres by a seed growth method. Chitosan (CHI) was used as a functional agent of carboxylated polystyrene spheres for attaching gold seeds. The surface plasmon resonance (SPR) peak of GNCPSs can be tuned, greatly redshifted, over a broad spectral range including the near-infrared (NIR) wavelength region, which provides maximal penetration of light through tissue. Irradiation of GNCPSs at their peak extinction coefficient results in the conversion of light to heat energy that produces a local rise in temperature. Our study revealed that the Lewis lung carcinoma (LLC) in mice treated with GNCPSs exposed to a low dose of NIR light (808 nm, 4 W cm-2) induced irreversible tissue damage. The tumor volumes of the treatment group by GNCPSs were significantly lower than those of control groups, with an average inhibition rate over 55% (P<0.005). This study proves that GNCPSs are promising in plasmonic photothermal tumor therapy.

Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage.

PubMed

Min, Xin; Fang, Minghao; Huang, Zhaohui; Liu, Yan'gai; Huang, Yaoting; Wen, Ruilong; Qian, Tingting; Wu, Xiaowen

2015-08-11

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage

PubMed Central

Min, Xin; Fang, Minghao; Huang, Zhaohui; Liu, Yan’gai; Huang, Yaoting; Wen, Ruilong; Qian, Tingting; Wu, Xiaowen

2015-01-01

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG. PMID:26261089

Multifunctional Inflatable Structure Being Developed for the PowerSphere Concept

NASA Technical Reports Server (NTRS)

Peterson, Todd T.

2004-01-01

NASA has funded a collaborative team of The Aerospace Corporation, ILC Dover, Lockheed Martin, and NASA Glenn Research Center to develop the Multifunctional Inflatable Structure (MIS) for a "PowerSphere" concept through a NASA Research Announcement. This power system concept has several advantages, including a high collection area, low weight and stowage volume, and the elimination of all solar array pointing mechanisms. The current 3-year effort will culminate with the fabrication and testing of a fully functional engineering development unit. The baseline design of the Power-Sphere consists of two opposing semispherical domes connected to a central spacecraft. Each semispherical dome consists of hexagonal and pentagonal solar cell panels that together form a geodetic sphere. Inflatable ultraviolet (UV) rigidizable tubular hinges between the solar cell panels and UV rigidizable isogrid center columns with imbedded flex circuitry form the MIS. The reference configuration for the PowerSphere is a 0.6-m-diameter (fully deployed) spacecraft with a total mass budget of 4 kg (1 kg for PowerSphere, 3 kg for spacecraft) capable of producing 29 W of electricity with 10-percent-efficient thin-film solar cells. In a stowed configuration, the solar cell panels will be folded sequentially to the outside of the instrument decks. The center column will be z-folded between the instrument decks and the spacecraft housing for packaging. The instrument panel will secure the z-folded stack with launch ties. After launch, once the release tie is triggered, the center column and hinge tubes will inflate and be rigidized in their final configurations by ultraviolet radiation. The overall PowerSphere deployment sequence is shown pictorially in the following illustration.

Study of lithium cation in water clusters: based on atom-bond electronegativity equalization method fused into molecular mechanics.

PubMed

Li, Xin; Yang, Zhong-Zhi

2005-05-12

We present a potential model for Li(+)-water clusters based on a combination of the atom-bond electronegativity equalization and molecular mechanics (ABEEM/MM) that is to take ABEEM charges of the cation and all atoms, bonds, and lone pairs of water molecules into the intermolecular electrostatic interaction term in molecular mechanics. The model allows point charges on cationic site and seven sites of an ABEEM-7P water molecule to fluctuate responding to the cluster geometry. The water molecules in the first sphere of Li(+) are strongly structured and there is obvious charge transfer between the cation and the water molecules; therefore, the charge constraint on the ionic cluster includes the charged constraint on the Li(+) and the first-shell water molecules and the charge neutrality constraint on each water molecule in the external hydration shells. The newly constructed potential model based on ABEEM/MM is first applied to ionic clusters and reproduces gas-phase state properties of Li(+)(H(2)O)(n) (n = 1-6 and 8) including optimized geometries, ABEEM charges, binding energies, frequencies, and so on, which are in fair agreement with those measured by available experiments and calculated by ab initio methods. Prospects and benefits introduced by this potential model are pointed out.

Benzoate-Induced High-Nuclearity Silver Thiolate Clusters.

PubMed

Su, Yan-Min; Liu, Wei; Wang, Zhi; Wang, Shu-Ao; Li, Yan-An; Yu, Fei; Zhao, Quan-Qin; Wang, Xing-Po; Tung, Chen-Ho; Sun, Di

2018-04-03

Compared with the well-known anion-templated effects in shaping silver thiolate clusters, the influence from the organic ligands in the outer shell is still poorly understood. Herein, three new benzoate-functionalized high-nuclearity silver(I) thiolate clusters are isolated and characterized for the first time in the presence of diverse anion templates such as S 2- , α-[Mo 5 O 18 ] 6- , and MoO 4 2- . Single-crystal X-ray analysis reveals that the nuclearities of the three silver clusters (SD/Ag28, SD/Ag29, SD/Ag30) vary from 32 to 38 to 78 with co-capped tBuS - and benzoate ligands on the surface. SD/Ag28 is a turtle-like cluster comprising a Ag 29 shell caging a Ag 3 S 3 trigon in the center, whereas SD/Ag29 is a prolate Ag 38 sphere templated by the α-[Mo 5 O 18 ] 6- anion. Upon changing from benzoate to methoxyl-substituted benzoate, SD/Ag30 is isolated as a very complicated core-shell spherical cluster composed of a Ag 57 shell and a vase-like Ag 21 S 13 core. Four MoO 4 2- anions are arranged in a supertetrahedron and located in the interstice between the core and shell. Introduction of the bulky benzoate changes elaborately the nuclearity and arrangements of silver polygons on the shell of silver clusters, which is exemplified by comparing SD/Ag28 and a known similar silver thiolate cluster. The three new clusters emit luminescence in the near-infrared (NIR) region and show different thermochromic luminescence properties. This work presents a flexible approach to synthetic studies of high-nuclearity silver clusters decorated by different benzoates, and structural modulations are also achieved. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The structure of clusters of galaxies

NASA Astrophysics Data System (ADS)

Fox, David Charles

When infalling gas is accreted onto a cluster of galaxies, its kinetic energy is converted to thermal energy in a shock, heating the ions. Using a self-similar spherical model, we calculate the collisional heating of the electrons by the ions, and predict the electron and ion temperature profiles. While there are significant differences between the two, they occur at radii larger than currently observable, and too large to explain observed X-ray temperature declines in clusters. Numerical simulations by Navarro, Frenk, & White (1996) predict a universal dark matter density profile. We calculate the expected number of multiply-imaged background galaxies in the Hubble Deep Field due to foreground groups and clusters with this profile. Such groups are up to 1000 times less efficient at lensing than the standard singular isothermal spheres. However, with either profile, the expected number of galaxies lensed by groups in the Hubble Deep Field is at most one, consistent with the lack of clearly identified group lenses. X-ray and Sunyaev-Zel'dovich (SZ) effect observations can be combined to determine the distance to clusters of galaxies, provided the clusters are spherical. When applied to an aspherical cluster, this method gives an incorrect distance. We demonstrate a method for inferring the three-dimensional shape of a cluster and its correct distance from X-ray, SZ effect, and weak gravitational lensing observations, under the assumption of hydrostatic equilibrium. We apply this method to simple, analytic models of clusters, and to a numerically simulated cluster. Using artificial observations based on current X-ray and SZ effect instruments, we recover the true distance without detectable bias and with uncertainties of 4 percent.

Broad spectrum antibiotic compounds and use thereof

DOEpatents

Koglin, Alexander; Strieker, Matthias

2016-07-05

The discovery of a non-ribosomal peptide synthetase (NRPS) gene cluster in the genome of Clostridium thermocellum that produces a secondary metabolite that is assembled outside of the host membrane is described. Also described is the identification of homologous NRPS gene clusters from several additional microorganisms. The secondary metabolites produced by the NRPS gene clusters exhibit broad spectrum antibiotic activity. Thus, antibiotic compounds produced by the NRPS gene clusters, and analogs thereof, their use for inhibiting bacterial growth, and methods of making the antibiotic compounds are described.

Displaying Planetary and Geophysical Datasets on NOAAs Science On a Sphere (TM)

NASA Astrophysics Data System (ADS)

Albers, S. C.; MacDonald, A. E.; Himes, D.

2005-12-01

NOAAs Science On a Sphere(TM)(SOS)was developed to educate current and future generations about the changing Earth and its processes. This system presents NOAAs global science through a 3D representation of our planet as if the viewer were looking at the Earth from outer space. In our presentation, we will describe the preparation of various global datasets for display on Science On a Sphere(TM), a 1.7-m diameter spherical projection system developed and patented at the Forecast Systems Laboratory (FSL) in Boulder, Colorado. Four projectors cast rotating images onto a spherical projection screen to create the effect of Earth, planet, or satellite floating in space. A static dataset can be prepared for display using popular image formats such as JPEG, usually sized at 1024x2048 or 2048x4096 pixels. A set of static images in a directory will comprise a movie. Imagery and data for SOS are obtained from a variety of government organizations, sometimes post-processed by various individuals, including the authors. Some datasets are already available in the required cylindrical projection. Readily available planetary maps can often be improved in coverage and/or appearance by reprojecting and combining additional images and mosaics obtained by various spacecraft, such as Voyager, Galileo, and Cassini. A map of Mercury was produced by blending some Mariner 10 photo-mosaics with a USGS shaded-relief map. An improved high-resolution map of Venus was produced by combining several Magellan mosaics, supplied by The Planetary Society, along with other spacecraft data. We now have a full set of Jupiter's Galilean satellite imagery that we can display on Science On a Sphere(TM). Photo-mosaics of several Saturnian satellites were updated by reprojecting and overlaying recently taken Cassini flyby images. Maps of imagery from five Uranian satellites were added, as well as one for Neptune. More image processing was needed to add a high-resolution Voyager mosaic to a pre-existing map of Neptune's moon Triton. A map of the cosmic background radiation was produced that shows the early universe from an external perspective. Full details and credits for these maps may be viewed online at http://laps.fsl.noaa.gov/albers/sos/sos.html. Geophysical imagery recently added to SOS includes a real-time global infrared weather satellite animation of Earth. This is a 15-minute, quality controlled animation spanning the most recent month, which draws on a number of geosynchronous and polar-orbiting weather satellites for data. Other meteorological and oceanographic datasets can be displayed, such as animations depicting the three-dimensional drifting of the ARGO buoy network through the oceans. Oceanic buoy observations were overlaid on the "Blue Marble" Earth imagery displayed on Science On a Sphere(TM). A static image shows locations for five different global buoy networks. We also produced two movies that show the drift of >1000 ARGO buoys over a period of several months. The first movie shows only the horizontal buoy drift, and the second modulates the intensities to represent the timing of each buoy dive cycle. Animations in real time are also being produced for sea surface temperatures (and anomalies). These analyses are obtained from web displays provided by the DOD Fleet Numerical Operations Center. With advanced technologies, the possibilities are limitless for displaying additional global datasets on Science On a Sphere(TM) and other spherical projection screens.

Nonthermal Particles and Radiation Produced by Cluster Merger Shocks

DTIC Science & Technology

2003-09-10

NONTHERMAL PARTICLES AND RADIATION PRODUCED BY CLUSTER MERGER SHOCKS Robert C. Berrington and Charles D. Dermer Naval Research Laboratory, Code 7653...of the merging cluster and is assumed to be constant as the shock propagates outward from the cluster center. In this paper , we model the cluster ...emission in the60–250 eV band for a number of clus- ters. These clusters include Virgo , Coma, Fornax, A2199, A1795, and A4059 (Lieu et al. 1996a, 1996b

Reentrant and Isostructural Transitions in the Cluster-Crystal Forming GEM-4

NASA Astrophysics Data System (ADS)

Zhang, Kai; Charbonneau, Patrick; Mladek, Bianca

2011-03-01

Systems governed by soft, bounded, purely repulsive interactions show two possible equilibrium behaviors under compression: reentrant melting, as in the Gaussian core model (GCM), or clustering, as in the penetrable sphere model (PSM). The generalized exponential model of power 4 (GEM-4), which is the intermedia of the GCM and PSM with a simple isotropic pair interaction u (r) ~e-r4 , is thought to belong to the second family and was indeed found to form clusters at sufficiently high densities at high temperatures. Here, we present the low-temperature behavior of GEM-4 through Monte Carlo simulations using a specially developed free energy integration scheme. We find the phase behavior to be hybrid between the GCM and the PSM limits, showing a surprisingly rich phase behavior in spite of the simplicity of the interaction form. For instance, S- shaped doubly reentrant phase sequences and evidence of a cascade of critical isostructural transitions between crystals of different average lattice site occupancy are observed. The possible annihilation of lattice sites and accompanying clustering moreover leads to an unusual softening upon compression, which suggest that these materials may have interesting mechanical properties. We discuss possible experimental realizations and challenges of this class of materials.

Modulation of Active Site Electronic Structure by the Protein Matrix to Control [NiFe] Hydrogenase Reactivity

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

Smith, Dayle MA; Raugei, Simone; Squier, Thomas C.

2014-09-30

Control of the reactivity of the nickel center of the [NiFe] hydrogenase and other metalloproteins commonly involves outer coordination sphere ligands that act to modify the geometry and physical properties of the active site metal centers. We carried out a combined set of classical molecular dynamics and quantum/classical mechanics calculations to provide quantitative estimates of how dynamic fluctuations of the active site within the protein matrix modulate the electronic structure at the catalytic center. Specifically we focused on the dynamics of the inner and outer coordination spheres of the cysteinate-bound Ni–Fe cluster in the catalytically active Ni-C state. There aremore » correlated movements of the cysteinate ligands and the surrounding hydrogen-bonding network, which modulate the electron affinity at the active site and the proton affinity of a terminal cysteinate. On the basis of these findings, we hypothesize a coupling between protein dynamics and electron and proton transfer reactions critical to dihydrogen production.« less

Modulation of active site electronic structure by the protein matrix to control [NiFe] hydrogenase reactivity.

PubMed

Smith, Dayle M A; Raugei, Simone; Squier, Thomas C

2014-11-21

Control of the reactivity of the nickel center of the [NiFe] hydrogenase and other metalloproteins commonly involves outer coordination sphere ligands that act to modify the geometry and physical properties of the active site metal centers. We carried out a combined set of classical molecular dynamics and quantum/classical mechanics calculations to provide quantitative estimates of how dynamic fluctuations of the active site within the protein matrix modulate the electronic structure at the catalytic center. Specifically we focused on the dynamics of the inner and outer coordination spheres of the cysteinate-bound Ni-Fe cluster in the catalytically active Ni-C state. There are correlated movements of the cysteinate ligands and the surrounding hydrogen-bonding network, which modulate the electron affinity at the active site and the proton affinity of a terminal cysteinate. On the basis of these findings, we hypothesize a coupling between protein dynamics and electron and proton transfer reactions critical to dihydrogen production.

Parallel, Gradient-Based Anisotropic Mesh Adaptation for Re-entry Vehicle Configurations

NASA Technical Reports Server (NTRS)

Bibb, Karen L.; Gnoffo, Peter A.; Park, Michael A.; Jones, William T.

2006-01-01

Two gradient-based adaptation methodologies have been implemented into the Fun3d refine GridEx infrastructure. A spring-analogy adaptation which provides for nodal movement to cluster mesh nodes in the vicinity of strong shocks has been extended for general use within Fun3d, and is demonstrated for a 70 sphere cone at Mach 2. A more general feature-based adaptation metric has been developed for use with the adaptation mechanics available in Fun3d, and is applicable to any unstructured, tetrahedral, flow solver. The basic functionality of general adaptation is explored through a case of flow over the forebody of a 70 sphere cone at Mach 6. A practical application of Mach 10 flow over an Apollo capsule, computed with the Felisa flow solver, is given to compare the adaptive mesh refinement with uniform mesh refinement. The examples of the paper demonstrate that the gradient-based adaptation capability as implemented can give an improvement in solution quality.

Fabrication of hierarchical porous hollow carbon spheres with few-layer graphene framework and high electrochemical activity for supercapacitor

NASA Astrophysics Data System (ADS)

Chen, Jing; Hong, Min; Chen, Jiafu; Hu, Tianzhao; Xu, Qun

2018-06-01

Porous amorphous carbons with large number of defects and dangling bonds indicate great potential application in energy storage due to high specific surface area and strong adsorption properties, but poor conductivity and pore connection limit their practical application. Here few-layer graphene framework with high electrical conductivity is embedded and meanwhile hierarchical porous structure is constructed in amorphous hollow carbon spheres (HCSs) by catalysis of Fe clusters of angstrom scale, which are loaded in the interior of crosslinked polystyrene via a novel method. These unique HCSs effectively integrate the inherent properties from two-dimensional sp2-hybridized carbon, porous amorphous carbon, hierarchical pore structure and thin shell, leading to high specific capacitance up to 561 F g-1 at a current density of 0.5 A g-1 as an electrode of supercapacitor with excellent recyclability, which is much higher than those of other reported porous carbon materials up to present.

A Mechanistic Investigation of the Gold(III)-Catalyzed Hydrofurylation of C-C Multiple Bonds.

PubMed

Hossein Bagi, Amin; Khaledi, Yousef; Ghari, Hossein; Arndt, Sebastian; Hashmi, A Stephen K; Yates, Brian F; Ariafard, Alireza

2016-11-09

The gold-catalyzed direct functionalization of aromatic C-H bonds has attracted interest for constructing organic compounds which have application in pharmaceuticals, agrochemicals, and other important fields. In the literature, two major mechanisms have been proposed for these catalytic reactions: inner-sphere syn-addition and outer-sphere anti-addition (Friedel-Crafts-type mechanism). In this article, the AuCl 3 -catalyzed hydrofurylation of allenyl ketone, vinyl ketone, ketone, and alcohol substrates is investigated with the aid of density functional theory calculations, and it is found that the corresponding functionalizations are best rationalized in terms of a novel mechanism called "concerted electrophilic ipso-substitution" (CEIS) in which the gold(III)-furyl σ-bond produced by furan auration acts as a nucleophile and attacks the protonated substrate via an outer-sphere mechanism. This unprecedented mechanism needs to be considered as an alternative plausible pathway for gold(III)-catalyzed arene functionalization reactions in future studies.

Three-sphere low-Reynolds-number swimmer with a passive elastic arm.

PubMed

Montino, Alessandro; DeSimone, Antonio

2015-05-01

One of the simplest model swimmers at low Reynolds number is the three-sphere swimmer by Najafi and Golestanian. It consists of three spheres connected by two rods which change their lengths periodically in non-reciprocal fashion. Here we investigate a variant of this model in which one rod is periodically actuated while the other is replaced by an elastic spring. We show that the competition between the elastic restoring force and the hydrodynamic drag produces a delay in the response of the passive elastic arm with respect to the active one. This leads to non-reciprocal shape changes and self-propulsion. After formulating the equations of motion, we study their solutions qualitatively and numerically. The leading-order term of the solution is computed analytically. We then address questions of optimization with respect to both actuation frequency and swimmer's geometry. Our results can provide valuable conceptual guidance in the engineering of robotic microswimmers.

Origin of the sphere-to-rod transition in cationic micelles with aromatic counterions: specific ion hydration in the interfacial region matters.

PubMed

Geng, Yan; Romsted, Laurence S; Froehner, Sandro; Zanette, Dino; Magid, Linda J; Cuccovia, Iolanda M; Chaimovich, Hernan

2005-01-18

Sphere-to-rod transitions of cetyltrimethylammonium (CTA+) micelles with dichlorobenzoate counterions are remarkably substituent dependent. Simultaneous estimates of the interfacial molarities of H2O, MeOH, and Cl- and 2,6- and 3,5-dichlorobenzoate (2,6OBz and 3,5OBz) counterions were obtained by the chemical trapping method in mixed micelles of CTACl/CTA3,5OBz and CTACl/CTA2,6OBz without added salt. Increasing the CTA3,5OBz mole fraction produces a marked concurrent increase in interfacial 3,5OBz- and a decrease in interfacial H2O concentrations through the sphere-to-rod transition. No abrupt concentration changes are observed with increasing CTA2,6OBz mole fraction. Counterion-specific changes in the interfacial water concentration may be a major contributor to the delicate balance of forces governing micellar morphology.

Discriminative echolocation in a porpoise, 12

PubMed Central

Turner, Ronald N.; Norris, Kenneth S.

1966-01-01

Operant conditioning techniques were used to establish a discriminative echolocation performance in a porpoise. Pairs of spheres of disparate diameters were presented in an under-water display, and the positions of the spheres were switched according to a scrambled sequence while the blindfolded porpoise responded on a pair of submerged response levers. Responses which identified the momentary state of the display were food-reinforced, while those which did not (errors) produced time out. Errors were then studied in relation to decreased disparity between the spheres. As disparity was decreased, errors which terminated runs of correct responses occurred more frequently and were followed by longer strings of consecutive errors. Increased errors and disruption of a stable pattern of collateral behavior were associated. Since some sources of error other than decreased disparity were present, the porpoise's final performance did not fully reflect the acuity of its echolocation channel. PMID:5964509

Simulation of perturbation produced by an absorbing spherical body in collisionless plasma

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

Krasovsky, V. L., E-mail: vkrasov@iki.rssi.ru; Kiselyov, A. A., E-mail: alexander.kiselyov@stonehenge-3.net.ru; Dolgonosov, M. S.

2017-01-15

A steady plasma state reached in the course of charging of an absorbing spherical body is found using computational methods. Numerical simulations provide complete information on this process, thereby allowing one to find the spatiotemporal dependences of the physical quantities and observe the kinetic phenomena accompanying the formation of stable electron and ion distributions in phase space. The distribution function of trapped ions is obtained, and their contribution to the screening of the charged sphere is determined. The sphere charge and the charge of the trapped-ion cloud are determined as functions of the unperturbed plasma parameters.

Metal Alloy ICF Capsules Created by Electrodeposition

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

Horwood, Corie; Stadermann, Michael; Bunn, Thomas L.

Electrochemical deposition is an attractive alternative to physical vapor deposition and micromachining to produce metal capsules for inertial confinement fusion (ICF). Electrochemical deposition (also referred to as electrodeposition or plating) is expected to produce full-density metal capsules without seams or inclusions of unwanted atomic constituents, the current shortcomings of micromachine and physical vapor deposition, respectively. In this paper, we discuss new cathode designs that allow for the rapid electrodeposition of gold and copper alloys on spherical mandrels by making transient contact with the constantly moving spheres. Electrodeposition of pure gold, copper, platinum, and alloys of gold-copper and gold-silver are demonstrated,more » with nonporous coatings of >40 µm achieved in only a few hours of plating. The surface roughness of the spheres after electrodeposition is comparable to the starting mandrel, and the coatings appear to be fully dense with no inclusions. A detailed understanding of the electrodeposition conditions that result in different alloy compositions and plating rates will allow for the electrodeposition of graded alloys on spheres in the near future. Finally, this report on the electrodeposition of metals on spherical mandrels is an important first step toward the fabrication of graded-density metal capsules for ICF experiments at the National Ignition Facility.« less

Optical characterization of a light guide for the polymerization of root canal fillers: preliminary results

NASA Astrophysics Data System (ADS)

Munin, Egberto; Lupato Conrado, Luis A.; Alves, Leandro P.; Zangaro, Renato A.

2004-05-01

The sealing cements used in endodontics are commonly of the type activated by chemical reactions. During polymerization, mechanical contractions are not uncommon, leading to non-perfect sealing or treatment failure. Photopolymerizable cements usually presents superior performance as compared to those chemically activated. However, difficulties in carrying-up the light to difficult-to-reach regions like the dental apex preclude those material of being accepted in the dental office routine. Recently, a novel technique for the light curing of photopolymerizable cements in endodontic applications has been proposed. Such a technique makes use of a polymeric light guide to deliver the curing light to the apex region, for a single step polymerization of the canal filler. For this work, a 28 mm long polymer light-guide, has been produced. The polymer surface was roughened to produce light scattering and allow the light to escape from the guide. The light scattering profile along the body of the guide is an important property for the proposed application. We used an integrating sphere to measure the irradiation profile for the proposed endodontic device. It was found that the experimental data for the amount of light coupled into the integrating sphere as a function of the length of the cone inside the sphere fits to a double exponential model.

Metal Alloy ICF Capsules Created by Electrodeposition

DOE PAGES

Horwood, Corie; Stadermann, Michael; Bunn, Thomas L.

2017-12-04

Electrochemical deposition is an attractive alternative to physical vapor deposition and micromachining to produce metal capsules for inertial confinement fusion (ICF). Electrochemical deposition (also referred to as electrodeposition or plating) is expected to produce full-density metal capsules without seams or inclusions of unwanted atomic constituents, the current shortcomings of micromachine and physical vapor deposition, respectively. In this paper, we discuss new cathode designs that allow for the rapid electrodeposition of gold and copper alloys on spherical mandrels by making transient contact with the constantly moving spheres. Electrodeposition of pure gold, copper, platinum, and alloys of gold-copper and gold-silver are demonstrated,more » with nonporous coatings of >40 µm achieved in only a few hours of plating. The surface roughness of the spheres after electrodeposition is comparable to the starting mandrel, and the coatings appear to be fully dense with no inclusions. A detailed understanding of the electrodeposition conditions that result in different alloy compositions and plating rates will allow for the electrodeposition of graded alloys on spheres in the near future. Finally, this report on the electrodeposition of metals on spherical mandrels is an important first step toward the fabrication of graded-density metal capsules for ICF experiments at the National Ignition Facility.« less

How should spin-weighted spherical functions be defined?

NASA Astrophysics Data System (ADS)

Boyle, Michael

2016-09-01

Spin-weighted spherical functions provide a useful tool for analyzing tensor-valued functions on the sphere. A tensor field can be decomposed into complex-valued functions by taking contractions with tangent vectors on the sphere and the normal to the sphere. These component functions are usually presented as functions on the sphere itself, but this requires an implicit choice of distinguished tangent vectors with which to contract. Thus, we may more accurately say that spin-weighted spherical functions are functions of both a point on the sphere and a choice of frame in the tangent space at that point. The distinction becomes extremely important when transforming the coordinates in which these functions are expressed, because the implicit choice of frame will also transform. Here, it is proposed that spin-weighted spherical functions should be treated as functions on the spin or rotation groups, which simultaneously tracks the point on the sphere and the choice of tangent frame by rotating elements of an orthonormal basis. In practice, the functions simply take a quaternion argument and produce a complex value. This approach more cleanly reflects the geometry involved, and allows for a more elegant description of the behavior of spin-weighted functions. In this form, the spin-weighted spherical harmonics have simple expressions as elements of the Wigner 𝔇 representations, and transformations under rotation are simple. Two variants of the angular-momentum operator are defined directly in terms of the spin group; one is the standard angular-momentum operator L, while the other is shown to be related to the spin-raising operator ð.

Women in Radio Soap Operas: A Historical Perspective of the Image of Women's "Sphere" in the "Golden Age."

ERIC Educational Resources Information Center

St John, Jacqueline

Radio's "Golden Age," the 1930s and 1940s produced numerous successful and profitable daytime serials, called "soap operas" because they were most often sponsored by firms selling laundry products. Among the most popular of these series were those produced by the team of Anne and Frank Hummert. Working through the…

Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications

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

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads withmore » micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. As a result, the renewable carbon product demonstrated a desirable surface area of 872 m 2/g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.« less

Amending the Structure of Renewable Carbon from Biorefinery Waste-Streams for Energy Storage Applications

DOE PAGES

Ho, Hoi Chun; Goswami, Monojoy; Chen, Jihua; ...

2018-05-29

Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads withmore » micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. As a result, the renewable carbon product demonstrated a desirable surface area of 872 m 2/g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.« less

Approximating a free-field blast environment in the test section of an explosively driven conical shock tube

NASA Astrophysics Data System (ADS)

Stewart, J. B.

2018-02-01

This paper presents experimental data on incident overpressures and the corresponding impulses obtained in the test section of an explosively driven 10° (full angle) conical shock tube. Due to the shock tube's steel walls approximating the boundary conditions seen by a spherical sector cut out of a detonating sphere of energetic material, a 5.3-g pentolite shock tube driver charge produces peak overpressures corresponding to a free-field detonation from an 816-g sphere of pentolite. The four test section geometries investigated in this paper (open air, cylindrical, 10° inscribed square frustum, and 10° circumscribed square frustum) provide a variety of different time histories for the incident overpressures and impulses, with a circumscribed square frustum yielding the best approximation of the estimated blast environment that would have been produced by a free-field detonation.

Long-Ranged Oppositely Charged Interactions for Designing New Types of Colloidal Clusters

NASA Astrophysics Data System (ADS)

Demirörs, Ahmet Faik; Stiefelhagen, Johan C. P.; Vissers, Teun; Smallenburg, Frank; Dijkstra, Marjolein; Imhof, Arnout; van Blaaderen, Alfons

2015-04-01

Getting control over the valency of colloids is not trivial and has been a long-desired goal for the colloidal domain. Typically, tuning the preferred number of neighbors for colloidal particles requires directional bonding, as in the case of patchy particles, which is difficult to realize experimentally. Here, we demonstrate a general method for creating the colloidal analogs of molecules and other new regular colloidal clusters without using patchiness or complex bonding schemes (e.g., DNA coating) by using a combination of long-ranged attractive and repulsive interactions between oppositely charged particles that also enable regular clusters of particles not all in close contact. We show that, due to the interplay between their attractions and repulsions, oppositely charged particles dispersed in an intermediate dielectric constant (4 <ɛ <10 ) provide a viable approach for the formation of binary colloidal clusters. Tuning the size ratio and interactions of the particles enables control of the type and shape of the resulting regular colloidal clusters. Finally, we present an example of clusters made up of negatively charged large and positively charged small satellite particles, for which the electrostatic properties and interactions can be changed with an electric field. It appears that for sufficiently strong fields the satellite particles can move over the surface of the host particles and polarize the clusters. For even stronger fields, the satellite particles can be completely pulled off, reversing the net charge on the cluster. With computer simulations, we investigate how charged particles distribute on an oppositely charged sphere to minimize their energy and compare the results with the solutions to the well-known Thomson problem. We also use the simulations to explore the dependence of such clusters on Debye screening length κ-1 and the ratio of charges on the particles, showing good agreement with experimental observations.

Dynamical resonance shift and unification of resonances in short-pulse laser-cluster interaction

NASA Astrophysics Data System (ADS)

Mahalik, S. S.; Kundu, M.

2018-06-01

Pronounced maximum absorption of laser light irradiating a rare-gas or metal cluster is widely expected during the linear resonance (LR) when Mie-plasma wavelength λM of electrons equals the laser wavelength λ . On the contrary, by performing molecular dynamics (MD) simulations of an argon cluster irradiated by short 5-fs (FWHM) laser pulses it is revealed that, for a given laser pulse energy and a cluster, at each peak intensity there exists a λ —shifted from the expected λM—that corresponds to a unified dynamical LR at which evolution of the cluster happens through very efficient unification of possible resonances in various stages, including (i) the LR in the initial time of plasma creation, (ii) the LR in the Coulomb expanding phase in the later time, and (iii) anharmonic resonance in the marginally overdense regime for a relatively longer pulse duration, leading to maximum laser absorption accompanied by maximum removal of electrons from cluster and also maximum allowed average charge states for the argon cluster. Increasing the laser intensity, the absorption maxima is found to shift to a higher wavelength in the band of λ ≈(1 -1.5 ) λM than permanently staying at the expected λM. A naive rigid sphere model also corroborates the wavelength shift of the absorption peak as found in MD and unequivocally proves that maximum laser absorption in a cluster happens at a shifted λ in the marginally overdense regime of λ ≈(1 -1.5 ) λM instead of λM of LR. The present study is important for guiding an optimal condition laser-cluster interaction experiment in the short-pulse regime.

Differentiation of human-induced pluripotent stem cells into insulin-producing clusters.

PubMed

Shaer, Anahita; Azarpira, Negar; Vahdati, Akbar; Karimi, Mohammad Hosein; Shariati, Mehrdad

2015-02-01

In diabetes mellitus type 1, beta cells are mostly destroyed; while in diabetes mellitus type 2, beta cells are reduced by 40% to 60%. We hope that soon, stem cells can be used in diabetes therapy via pancreatic beta cell replacement. Induced pluripotent stem cells are a kind of stem cell taken from an adult somatic cell by "stimulating" certain genes. These induced pluripotent stem cells may be a promising source of cell therapy. This study sought to produce isletlike clusters of insulin-producing cells taken from induced pluripotent stem cells. A human-induced pluripotent stem cell line was induced into isletlike clusters via a 4-step protocol, by adding insulin, transferrin, and selenium (ITS), N2, B27, fibroblast growth factor, and nicotinamide. During differentiation, expression of pancreatic β-cell genes was evaluated by reverse transcriptase-polymerase chain reaction; the morphologic changes of induced pluripotent stem cells toward isletlike clusters were observed by a light microscope. Dithizone staining was used to stain these isletlike clusters. Insulin produced by these clusters was evaluated by radio immunosorbent assay, and the secretion capacity was analyzed with a glucose challenge test. Differentiation was evaluated by analyzing the morphology, dithizone staining, real-time quantitative polymerase chain reaction, and immunocytochemistry. Gene expression of insulin, glucagon, PDX1, NGN3, PAX4, PAX6, NKX6.1, KIR6.2, and GLUT2 were documented by analyzing real-time quantitative polymerase chain reaction. Dithizone-stained cellular clusters were observed after 23 days. The isletlike clusters significantly produced insulin. The isletlike clusters could increase insulin secretion after a glucose challenge test. This work provides a model for studying the differentiation of human-induced pluripotent stem cells to insulin-producing cells.

Percolation, phase separation, and gelation in fluids and mixtures of spheres and rods

NASA Astrophysics Data System (ADS)

Jadrich, Ryan; Schweizer, Kenneth S.

2011-12-01

The relationship between kinetic arrest, connectivity percolation, structure and phase separation in protein, nanoparticle, and colloidal suspensions is a rich and complex problem. Using a combination of integral equation theory, connectivity percolation methods, naïve mode coupling theory, and the activated dynamics nonlinear Langevin equation approach, we study this problem for isotropic one-component fluids of spheres and variable aspect ratio rigid rods, and also percolation in rod-sphere mixtures. The key control parameters are interparticle attraction strength and its (short) spatial range, total packing fraction, and mixture composition. For spherical particles, formation of a homogeneous one-phase kinetically stable and percolated physical gel is predicted to be possible, but depends on non-universal factors. On the other hand, the dynamic crossover to activated dynamics and physical bond formation, which signals discrete cluster formation below the percolation threshold, almost always occurs in the one phase region. Rods more easily gel in the homogeneous isotropic regime, but whether a percolation or kinetic arrest boundary is reached first upon increasing interparticle attraction depends sensitively on packing fraction, rod aspect ratio and attraction range. Overall, the connectivity percolation threshold is much more sensitive to attraction range than either the kinetic arrest or phase separation boundaries. Our results appear to be qualitatively consistent with recent experiments on polymer-colloid depletion systems and brush mediated attractive nanoparticle suspensions.

Models of metal binding structures in fulvic acid from the Suwannee River, Georgia

USGS Publications Warehouse

Leenheer, J.A.; Brown, G.K.; MacCarthy, P.; Cabaniss, S.E.

1998-01-01

Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The 'metal binding' fraction was characterized by quantitative 13C NMR, 1H NMR, and FT-1R spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl groups were clustered in short- chain aliphatic dibasic acid structures. The Ca2+ binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Structural models were derived based upon oxidation and photolytic rearrangements of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate binding sites with the potential for both inner-sphere and outer-sphere type binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The `metal binding' fraction was characterized by quantitative 13C NMR, 1H NMR, and FT-IR spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl groups were clustered in short-chain aliphatic dibasic acid structures. The Ca2+ binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Structural models were derived based upon oxidation and photolytic rearrangements of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate binding sites with the potential for both inner-sphere and outer-sphere type binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.

Method for introduction of gases into microspheres

DOEpatents

Hendricks, C.D.; Koo, J.C.; Rosencwaig, A.

A method is described for producing small hollow glass spheres filled with a gas by introduction of the gas during formation of the hollow glass spheres. Hollow glass microspheres having a diameter up to about 500..mu.. with both thin walls (0.5 to 4/sub ..mu../) and thick walls (5 to 20/sub ..mu../) that contain various fill gases, such as Ar, Kr, Xe, Br, D, H/sub 2/, DT, He, N/sub 2/, Ne, CO/sub 2/, etc., in the interior thereof, can be produced by the diffusion of the fill gas or gases into the microsphere during the formation thereof from a liquid droplet of glass-form-forming solution. This is accomplished by filling at least a portion of the multiple-zone drop-furnace used in producing hollow microspheres with the gas or gases of interest, and then taking advantage of the high rate of gaseous diffusion of the fill gas through the wall of the gel membrane before it transforms into a glass microsphere as it is processed in the multiple-zone furnace.

Beta-Tin Grain Formation in Aluminum-Modified Lead-Free Solder Alloys

NASA Astrophysics Data System (ADS)

Reeve, Kathlene N.; Handwerker, Carol A.

2018-01-01

The limited number of independent β-Sn grain orientations that typically form during solidification of Sn-based solders and the resulting large β-Sn grain size have major effects on overall solder performance and reliability. This study analyzes whether additions of Al to Sn-Cu and Sn-Cu-Ag alloys can be used to change the grain size, morphology, and twinning structures of atomized (as-solidified) and re-melted (reflowed) β-Sn dendrites as determined using scanning electron microscopy and electron backscatter diffraction for as-solidified and reflow cycled (20-250°C, 1-5 cycles) Sn-Cu-Al and Sn-Ag-Cu-Al drip atomized spheres (260 μm diameter). The resulting microstructures were compared to as-solidified and reflow cycled Sn-Ag-Cu spheres (450 μm diameter) as well as as-solidified Sn-Ag-Cu, Sn-Cu, and Sn-Ag microstructures from the literature. Previous literature observations reporting reductions in undercooling and β-Sn grain size with Al micro-alloying additions could not be correlated to the presence of the Cu9Al4 phase or Al solute. The as-solidified spheres displayed no change in β-Sn dendrite structure or grain size when compared to non-Al-modified alloys, and the reflow cycled spheres produced high undercoolings (22-64°C), indicating a lack of potent nucleation sites. The current findings highlighted the role of Ag in the formation of the interlaced twinning structure and demonstrated that with deliberate compositional choices, formation of the alloy's β-Sn grain structure (cyclical twinning versus interlaced twinning) could be influenced, in both the as-solidified and reflow cycled states, though still not producing the fine-grain sizes and multiple orientations desired for improved thermomechanical properties.

Aperture excited dielectric antennas

NASA Technical Reports Server (NTRS)

Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

1974-01-01

The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

Proton transport facilitating water-oxidation: the role of second sphere ligands surrounding the catalytic metal cluster.

PubMed

Bao, Han; Dilbeck, Preston L; Burnap, Robert L

2013-10-01

The ability of PSII to extract electrons from water, with molecular oxygen as a by-product, is a remarkable biochemical and evolutionary innovation. From an evolutionary perspective, the invention of PSII approximately 2.7 Ga led to the accelerated accumulation of biomass in the biosphere and the accumulation of oxygen in the atmosphere, a combination that allowed for the evolution of a much more complex and extensive biosphere than would otherwise have been possible. From the biochemical and enzymatic perspective, PSII is remarkable because of the thermodynamic and kinetic obstacles that needed to have been overcome to oxidize water as the ultimate photosynthetic electron donor. This article focuses on how proton release is an integral part of how these kinetic and thermodynamic obstacles have been overcome: the sequential removal of protons from the active site of H2O-oxidation facilitates the multistep oxidation of the substrate water at the Mn4CaOx, the catalytic heart of the H2O-oxidation reaction. As noted previously, the facilitated deprotonation of the Mn4CaOx cluster exerts a redox-leveling function preventing the accumulation of excess positive charge on the cluster, which might otherwise hinder the already energetically difficult oxidation of water. Using recent results, including the characteristics of site-directed mutants, the role of the second sphere of amino acid ligands and the associated network of water molecules surrounding the Mn4CaOx is discussed in relation to proton transport in other systems. In addition to the redox-leveling function, a trapping function is assigned to the proton release step occurring immediately prior to the dioxygen chemistry. This trapping appears to involve a yet-to-be clarified gating mechanism that facilitates to coordinated release of a proton from the neighborhood of the active site thereby insuring that the backward charge-recombination reaction does not out-compete the forward reaction of dioxygen chemistry during this final step of H2O-oxidation.

Holographic Characterization of Colloidal Fractal Aggregates

NASA Astrophysics Data System (ADS)

Wang, Chen; Cheong, Fook Chiong; Ruffner, David B.; Zhong, Xiao; Ward, Michael D.; Grier, David G.

In-line holographic microscopy images of micrometer-scale fractal aggregates can be interpreted with the Lorenz-Mie theory of light scattering and an effective-sphere model to obtain each aggregate's size and the population-averaged fractal dimension. We demonstrate this technique experimentally using model fractal clusters of polystyrene nanoparticles and fractal protein aggregates composed of bovine serum albumin and bovine pancreas insulin. This technique can characterize several thousand aggregates in ten minutes and naturally distinguishes aggregates from contaminants such as silicone oil droplets. Work supported by the SBIR program of the NSF.

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

Switchable molecular magnets

PubMed Central

SATO, Osamu

2012-01-01

Various molecular magnetic compounds whose magnetic properties can be controlled by external stimuli have been developed, including electrochemically, photochemically, and chemically tunable bulk magnets as well as a phototunable antiferromagnetic phase of single chain magnet. In addition, we present tunable paramagnetic mononuclear complexes ranging from spin crossover complexes and valence tautomeric complexes to Co complexes in which orbital angular momentum can be switched. Furthermore, we recently developed several switchable clusters and one-dimensional coordination polymers. The switching of magnetic properties can be achieved by modulating metals, ligands, and molecules/ions in the second sphere of the complexes. PMID:22728438

Composition of clusters and building blocks in amylopectins from maize mutants deficient in starch synthase III.

PubMed

Zhu, Fan; Bertoft, Eric; Seetharaman, Koushik

2013-12-18

Branches in amylopectin are distributed along the backbone. Units of the branches are building blocks (smaller) and clusters (larger) based on the distance between branches. In this study, composition of clusters and building blocks of amylopectins from dull1 maize mutants deficient in starch synthase III (SSIII) with a common genetic background (W64A) were characterized and compared with the wild type. Clusters were produced from amylopectins by partial hydrolysis using α-amylase of Bacillus amyloliquefaciens and were subsequently treated with phosphorylase a and β-amylase to produce φ,β-limit dextrins. Clusters were further extensively hydrolyzed with the α-amylase to produce building blocks. Structures of clusters and building blocks were analyzed by diverse chromatographic techniques. The results showed that the dull1 mutation resulted in larger clusters with more singly branched building blocks. The average cluster contained ~5.4 blocks in dull1 mutants and ~4.2 blocks in the wild type. The results are compared with previous results from SSIII-deficient amo1 barley and suggest fundamental differences in the cluster structures.

Comparison of the response to phosphorus deficiency in two lupin species, Lupinus albus and L. angustifolius, with contrasting root morphology.

PubMed

Funayama-Noguchi, Sachiko; Noguchi, Ko; Terashima, Ichiro

2015-03-01

White lupin (Lupinus albus) produces cluster roots, an adaptation to low soil phosphorus (P). Cluster roots exude large levels of P-solubilizing compounds such as citrate and malate. In contrast, narrow leaf lupin (L. angustifolius) is closely related to L. albus, but does not produce cluster roots. To examine the different strategies for P acquisition, we compared the growth, biomass allocation, respiratory properties and construction cost between L. albus and L. angustifolius under P-deficient conditions. Both Lupinus species were grown in hydroponic culture with 1 or 100 μM P. Under the P-deficient regime, L. albus produced cluster roots with little change in biomass allocation, while L. angustifolius significantly increased biomass allocation to roots. The rate of cyanide-resistant SHAM (salicylhydroxamic acid)-sensitive respiration was high in cluster roots and very low in roots of L. angustifolius. These results suggest a low alternative oxidase (AOX) activity in L. angustifolius roots, and thus, ATP would be produced efficiently in L. angustifolius roots. The construction cost was highest in cluster roots and lowest in L. angustifolius roots. This study shows that under P deficiency, L. albus produces high-cost cluster roots to increase the P availability, while L. angustifolius produces large quantities of low-cost roots to enhance P uptake. © 2014 John Wiley & Sons Ltd.

The WHISPER Relaxation Sounder and the CLUSTER Active Archive

NASA Astrophysics Data System (ADS)

Trotignon, J. G.; Décréau, P. M. E.; Rauch, J. L.; Vallières, X.; Rochel, A.; Kougblénou, S.; Lointier, G.; Facskó, G.; Canu, P.; Darrouzet, F.; Masson, A.

The Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation (WHISPER) instrument is part of the Wave Experiment Consortium (WEC) of the CLUSTER mission. With the help of the long double sphere antennae of the Electric Field and Wave (EFW) instrument and the Digital Wave Processor (DWP), it delivers active (sounding) and natural (transmitter off) electric field spectra, respectively from 4 to 82 kHz, and from 2 to 80 kHz. These frequency ranges have been chosen to include the electron plasma frequency, which is closely related to the total electron density, in most of the regions encountered by the CLUSTER spacecraft. Presented here is an overview of the WHISPER data products available in the CLUSTER Active Archive (CAA). The instrument and its performance are first recalled. The way the WHISPER products are obtained is then described, with particular attention being paid to the density determination. Both sounding and natural measurements are commonly used in this process, which depends on the ambient plasma regime. This is illustrated using drawings similar to the Bryant plots commonly used in the CLUSTER master science plan. These give a clear overview of typical density values and the parts of the orbits where they are obtained. More information on the applied software or on the quality/reliability of the density determination can also be highlighted.

Growth Behavior and Electronic Structure of Noble Metal-Doped Germanium Clusters.

PubMed

Mahtout, Sofiane; Siouani, Chaouki; Rabilloud, Franck

2018-01-18

Structures, energetics, and electronic properties of noble metal-doped germanium (MGe n with M = Cu, Ag, Au; n = 1-19) clusters are systematically investigated by using the density functional theory (DFT) approach. The endohedral structures in which the metal atom is encapsulated inside of a germanium cage appear at n = 10 when the dopant is Cu and n = 12 for M = Ag and Au. While Cu doping enhances the stability of the corresponding germanium frame, the binding energies of AgGe n and AuGe n are always lower than those of pure germanium clusters. Our results highlight the great stability of the CuGe 10 cluster in a D 4d structure and, to a lesser extent, that of AgGe 15 and AuGe 15 , which exhibits a hollow cage-like geometry. The sphere-type geometries obtained for n = 10-15 present a peculiar electronic structure in which the valence electrons of the noble metal and Ge atoms are delocalized and exhibit a shell structure associated with the quasi-spherical geometry. It is found that the coinage metal is able to give both s- and d-type electrons to be reorganized together with the valence electrons of Ge atoms through a pooling of electrons. The cluster size dependence of the stability, the frontier orbital energy gap, the vertical ionization potentials, and electron affinities are given.

Polymer depletion-driven cluster aggregation and initial phase separation in charged nanosized colloids

NASA Astrophysics Data System (ADS)

Gögelein, Christoph; Nägele, Gerhard; Buitenhuis, Johan; Tuinier, Remco; Dhont, Jan K. G.

2009-05-01

We study polymer depletion-driven cluster aggregation and initial phase separation in aqueous dispersions of charge-stabilized silica spheres, where the ionic strength and polymer (dextran) concentration are systematically varied, using dynamic light scattering and visual observation. Without polymers and for increasing salt and colloid content, the dispersions become increasingly unstable against irreversible cluster formation. By adding nonadsorbing polymers, a depletion-driven attraction is induced, which lowers the stabilizing Coulomb barrier and enhances the cluster growth rate. The initial growth rate increases with increasing polymer concentration and decreases with increasing polymer molar mass. These observations can be quantitatively understood by an irreversible dimer formation theory based on the classical Derjaguin, Landau, Verwey, and Overbeek pair potential, with the depletion attraction modeled by the Asakura-Oosawa-Vrij potential. At low colloid concentration, we observe an exponential cluster growth rate for all polymer concentrations considered, indicating a reaction-limited aggregation mechanism. At sufficiently high polymer and colloid concentrations, and lower salt content, a gas-liquidlike demixing is observed initially. Later on, the system separates into a gel and fluidlike phase. The experimental time-dependent state diagram is compared to the theoretical equilibrium phase diagram obtained from a generalized free-volume theory and is discussed in terms of an initial reversible phase separation process in combination with irreversible aggregation at later times.

Polymer depletion-driven cluster aggregation and initial phase separation in charged nanosized colloids.

PubMed

Gögelein, Christoph; Nägele, Gerhard; Buitenhuis, Johan; Tuinier, Remco; Dhont, Jan K G

2009-05-28

We study polymer depletion-driven cluster aggregation and initial phase separation in aqueous dispersions of charge-stabilized silica spheres, where the ionic strength and polymer (dextran) concentration are systematically varied, using dynamic light scattering and visual observation. Without polymers and for increasing salt and colloid content, the dispersions become increasingly unstable against irreversible cluster formation. By adding nonadsorbing polymers, a depletion-driven attraction is induced, which lowers the stabilizing Coulomb barrier and enhances the cluster growth rate. The initial growth rate increases with increasing polymer concentration and decreases with increasing polymer molar mass. These observations can be quantitatively understood by an irreversible dimer formation theory based on the classical Derjaguin, Landau, Verwey, and Overbeek pair potential, with the depletion attraction modeled by the Asakura-Oosawa-Vrij potential. At low colloid concentration, we observe an exponential cluster growth rate for all polymer concentrations considered, indicating a reaction-limited aggregation mechanism. At sufficiently high polymer and colloid concentrations, and lower salt content, a gas-liquidlike demixing is observed initially. Later on, the system separates into a gel and fluidlike phase. The experimental time-dependent state diagram is compared to the theoretical equilibrium phase diagram obtained from a generalized free-volume theory and is discussed in terms of an initial reversible phase separation process in combination with irreversible aggregation at later times.

Synthesis of Fe3O4 cluster microspheres/graphene aerogels composite as anode for high-performance lithium ion battery

NASA Astrophysics Data System (ADS)

Zhou, Shuai; Zhou, Yu; Jiang, Wei; Guo, Huajun; Wang, Zhixing; Li, Xinhai

2018-05-01

Iron oxides are considered as attractive electrode materials because of their capability of lithium storage, but their poor conductivity and large volume expansion lead to unsatisfactory cycling stability. We designed and synthesized a novel Fe3O4 cluster microspheres/Graphene aerogels composite (Fe3O4/GAs), where Fe3O4 nanoparticles were assembled into cluster microspheres and then embedded in 3D graphene aerogels framework. In the spheres, the sufficient free space between Fe3O4 nanoparticles could accommodate the volume change during cycling process. Graphene aerogel works as flexible and conductive matrix, which can not only significantly increase the mechanical stress, but also further improve the storage properties. The Fe3O4/GAs composite as an anode material exhibits high reversible capability and excellent cyclic capacity for lithium ion batteries (LIBs). A reversible capability of 650 mAh g-1 after 500 cycles at a current density of 1 A g-1 can be maintained. The superior storage capabilities of the composites make them potential anode materials for LIBs.

Viscoelasticity of Depletion-Induced Emulsion Gels

NASA Astrophysics Data System (ADS)

Meller, Amit; Stavans, Joel; Gisler, Thomas; Weitz, David A.

1997-03-01

The presence of non-adsorbing polymer in an oil-in-water emulsion results in a depletion attraction between the emulsion droplets, causing a phase separation into an droplet-rich phase and a polymer-rich phase largely devoid of emulsion droplets. At high enough droplet concentration, however, this phase separation is kinetically arrested to a gel-like state where large (diameter>50 μm) clusters of droplets are weakly connected via ramifications, leading to a measurable elastic modulus. We measure the mean-square displacement <Δ r ^2 (t)> of a droplet of size a inside a cluster using diffusing wave spectroscopy (DWS); by means of a generalized Stokes-Einstein relation we obtain frequency dependent storage and loss moduli G'(ω) and G''(ω), respectively. G'(ω) reaches a plateau at frequencies between 1 rad/s and 100 rad/s; this plateau modulus is found to scale with the hard-sphere energy density k_BT/a^3; within the clusters the droplets are densely packed, yet remain undeformed, the droplet volume fraction being determined by the osmotic pressure exerted by the polymer.

Radiometric Measurement Comparisons Using Transfer Radiometers in Support of the Calibration of NASA's Earth Observing System (EOS) Sensors

NASA Technical Reports Server (NTRS)

Butler, James J.; Johnson, B. Carol; Brown, Steven W.; Yoon, Howard W.; Barnes, Robert A.; Markham, Brian L.; Biggar, Stuart F.; Zalewski, Edward F.; Spyak, Paul R.; Cooper, John W.;

One-pot, single-component synthesis of functional emulsion-templated hybrid inorganic-organic polymer capsules.

PubMed

Harbron, Rachel L; McDonald, Tom O; Rannard, Steve P; Findlay, Paul H; Weaver, Jonathan V M

2012-02-01

Multi-purpose amphiphilic branched copolymer surfactants can be used to simultaneously stabilise and cross-link emulsion droplets to produce encapsulated spheres and hollow capsules. This journal is © The Royal Society of Chemistry 2012

Measurement of the neutron fields produced by a 62 MeV proton beam on a PMMA phantom using extended range Bonner sphere spectrometers

NASA Astrophysics Data System (ADS)

Amgarou, K.; Bedogni, R.; Domingo, C.; Esposito, A.; Gentile, A.; Carinci, G.; Russo, S.

2011-10-01

The experimental characterization of the neutron fields produced as parasitic effect in medical accelerators is assuming an increased importance for either the patient protection or the facility design aspects. Medical accelerators are diverse in terms of particle type (electrons or hadrons) and energy, but the radiation fields around them have in common (provided that a given threshold energy is reached) the presence of neutrons with energy span over several orders of magnitude. Due to the large variability of neutron energy, field or dosimetry measurements in these workplaces are very complex, and in general, cannot be performed with ready-to-use commercial instruments. In spite of its poor energy resolution, the Bonner Sphere Spectrometer (BSS) is the only instrument able to simultaneously determine all spectral components in such workplaces. The energy range of this instrument is limited to E<20 MeV if only polyethylene spheres are used, but can be extended to hundreds of MeV by including metal-loaded spheres (extended range BSS, indicated with ERBSS). With the aim of providing useful data to the scientific community involved in neutron measurements at hadron therapy facilities, an ERBSS experiment was carried out at the Centro di AdroTerapia e Applicazioni Nucleari Avanzate (CATANA) of INFN—LNS (Laboratori Nazionali del Sud), where a proton beam routinely used for ophthalmic cancer treatments is available. The 62 MeV beam was directed towards a PMMA phantom, simulating the patient, and two neutron measurement points were established at 0° and 90° with respect to the beam-line. Here the ERBSS of UAB (Universidad Autónoma de Barcelona— Grup de Física de les Radiacions) and INFN (Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Frascati) were exposed to characterize the "forward" and "sideward" proton-induced neutron fields. The use of two ERBSS characterized by different set of spheres, central detectors, and independently established and calibrated, is important for guaranteeing the robustness of the measured spectra and estimating their overall uncertainties.

Directionally Interacting Spheres and Rods Form Ordered Phases

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

Liu, Wenyan; Mahynski, Nathan A.; Gang, Oleg

The structures formed by mixtures of dissimilarly shaped nanoscale objects can significantly enhance our ability to produce nanoscale architectures. However, understanding their formation is a complex problem due to the interplay of geometric effects (entropy) and energetic interactions at the nanoscale. Spheres and rods are perhaps the most basic geometrical shapes and serve as convenient models of such dissimilar objects. The ordered phases formed by each of these individual shapes have already been explored, but, when mixed, spheres and rods have demonstrated only limited structural organization to date. We show using experiments and theory that the introduction of directional attractionsmore » between rod ends and isotropically interacting spherical nanoparticles (NPs) through DNA base pairing leads to the formation of ordered three-dimensional lattices. The spheres and rods arrange themselves in a complex alternating manner, where the spheres can form either a face-centered cubic (FCC) or hexagonal close-packed (HCP) lattice, or a disordered phase, as observed by in situ X-ray scattering. Increasing NP diameter at fixed rod length yields an initial transition from a disordered phase to the HCP crystal, energetically stabilized by rod-rod attraction across alternating crystal layers, as revealed by theory. In the limit of large NPs, the FCC structure is instead stabilized over the HCP by rod entropy. Thus, we propose that directionally specific attractions in mixtures of anisotropic and isotropic objects offer insight into unexplored self-assembly behavior of noncomplementary shaped particles.« less

Directionally Interacting Spheres and Rods Form Ordered Phases

DOE PAGES

Liu, Wenyan; Mahynski, Nathan A.; Gang, Oleg; ...

2017-05-10

The structures formed by mixtures of dissimilarly shaped nanoscale objects can significantly enhance our ability to produce nanoscale architectures. However, understanding their formation is a complex problem due to the interplay of geometric effects (entropy) and energetic interactions at the nanoscale. Spheres and rods are perhaps the most basic geometrical shapes and serve as convenient models of such dissimilar objects. The ordered phases formed by each of these individual shapes have already been explored, but, when mixed, spheres and rods have demonstrated only limited structural organization to date. We show using experiments and theory that the introduction of directional attractionsmore » between rod ends and isotropically interacting spherical nanoparticles (NPs) through DNA base pairing leads to the formation of ordered three-dimensional lattices. The spheres and rods arrange themselves in a complex alternating manner, where the spheres can form either a face-centered cubic (FCC) or hexagonal close-packed (HCP) lattice, or a disordered phase, as observed by in situ X-ray scattering. Increasing NP diameter at fixed rod length yields an initial transition from a disordered phase to the HCP crystal, energetically stabilized by rod-rod attraction across alternating crystal layers, as revealed by theory. In the limit of large NPs, the FCC structure is instead stabilized over the HCP by rod entropy. Thus, we propose that directionally specific attractions in mixtures of anisotropic and isotropic objects offer insight into unexplored self-assembly behavior of noncomplementary shaped particles.« less

Kinetics of motility-induced phase separation and swim pressure

NASA Astrophysics Data System (ADS)

Patch, Adam; Yllanes, David; Marchetti, M. Cristina

2017-01-01

Active Brownian particles (ABPs) represent a minimal model of active matter consisting of self-propelled spheres with purely repulsive interactions and rotational noise. Here we examine the pressure of ABPs in two dimensions in both closed boxes and systems with periodic boundary conditions and show that its nonmonotonic behavior with density is a general property of ABPs and is not the result of finite-size effects. We correlate the time evolution of the mean pressure towards its steady-state value with the kinetics of motility-induced phase separation. For parameter values corresponding to phase-separated steady states, we identify two dynamical regimes. The pressure grows monotonically in time during the initial regime of rapid cluster formation, overshooting its steady-state value and then quickly relaxing to it, and remains constant during the subsequent slower period of cluster coalescence and coarsening. The overshoot is a distinctive feature of active systems.

Superlattices assembled through shape-induced directional binding

NASA Astrophysics Data System (ADS)

Lu, Fang; Yager, Kevin G.; Zhang, Yugang; Xin, Huolin; Gang, Oleg

2015-04-01

Organization of spherical particles into lattices is typically driven by packing considerations. Although the addition of directional binding can significantly broaden structural diversity, nanoscale implementation remains challenging. Here we investigate the assembly of clusters and lattices in which anisotropic polyhedral blocks coordinate isotropic spherical nanoparticles via shape-induced directional interactions facilitated by DNA recognition. We show that these polyhedral blocks--cubes and octahedrons--when mixed with spheres, promote the assembly of clusters with architecture determined by polyhedron symmetry. Moreover, three-dimensional binary superlattices are formed when DNA shells accommodate the shape disparity between nanoparticle interfaces. The crystallographic symmetry of assembled lattices is determined by the spatial symmetry of the block's facets, while structural order depends on DNA-tuned interactions and particle size ratio. The presented lattice assembly strategy, exploiting shape for defining the global structure and DNA-mediation locally, opens novel possibilities for by-design fabrication of binary lattices.

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

Lu, Fang; Yager, Kevin G.; Zhang, Yugang

Organization of spherical particles into lattices is typically driven by packing considerations. Although the addition of directional binding can significantly broaden structural diversity, nanoscale implementation remains challenging. Here we investigate the assembly of clusters and lattices in which anisotropic polyhedral blocks coordinate isotropic spherical nanoparticles via shape-induced directional interactions facilitated by DNA recognition. We show that these polyhedral blocks—cubes and octahedrons—when mixed with spheres, promote the assembly of clusters with architecture determined by polyhedron symmetry. Moreover, three-dimensional binary superlattices are formed when DNA shells accommodate the shape disparity between nanoparticle interfaces. The crystallographic symmetry of assembled lattices is determined bymore » the spatial symmetry of the block’s facets, while structural order depends on DNA-tuned interactions and particle size ratio. Lastly, the presented lattice assembly strategy, exploiting shape for defining the global structure and DNA-mediation locally, opens novel possibilities for by-design fabrication of binary lattices.« less

Radiative properties of flame-generated soot

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

Koeylue, U.O.; Faeth, G.M.

1993-05-01

Approximate methods for estimating the optical properties of flame-generated soot aggregates were evaluated using existing computer simulations and measurements in the visible and near-infrared portions of the spectrum. The following approximate methods were evaluated for both individual aggregates and polydisperse aggregate populations: the Rayleigh scattering approximation, Mie scattering for an equivalent sphere, and Rayleigh-Debye-Gans (R-D-G) scattering for both given and fractal aggregates. Results of computer simulations involved both prescribed aggregate geometry and numerically generated aggregates by cluster-cluster aggregation; multiple scattering was considered exactly using the mean-field approximation, and ignored using the R-D-G approximation. Measurements involved the angular scattering properties ofmore » soot in the postflame regions of both premixed and nonpremixed flames. The results show that available computer simulations and measurements of soot aggregate optical properties are not adequate to provide a definitive evaluation of the approximate prediction methods. 40 refs., 7 figs., 1 tab.« less

Superlattices assembled through shape-induced directional binding

DOE PAGES

Lu, Fang; Yager, Kevin G.; Zhang, Yugang; ...

2015-04-23

Organization of spherical particles into lattices is typically driven by packing considerations. Although the addition of directional binding can significantly broaden structural diversity, nanoscale implementation remains challenging. Here we investigate the assembly of clusters and lattices in which anisotropic polyhedral blocks coordinate isotropic spherical nanoparticles via shape-induced directional interactions facilitated by DNA recognition. We show that these polyhedral blocks—cubes and octahedrons—when mixed with spheres, promote the assembly of clusters with architecture determined by polyhedron symmetry. Moreover, three-dimensional binary superlattices are formed when DNA shells accommodate the shape disparity between nanoparticle interfaces. The crystallographic symmetry of assembled lattices is determined bymore » the spatial symmetry of the block’s facets, while structural order depends on DNA-tuned interactions and particle size ratio. Lastly, the presented lattice assembly strategy, exploiting shape for defining the global structure and DNA-mediation locally, opens novel possibilities for by-design fabrication of binary lattices.« less

Mössbauer spectroscopy of the chloroplast-targeted DnaJ-like proteins CDJ3 and CDJ4

NASA Astrophysics Data System (ADS)

Auerbach, H.; Kalienkova, V.; Schroda, M.; Schünemann, V.

2017-11-01

The heat shock protein 70 (HSP70) in the chloroplast of Chlamydomonas reinhardtii, termed HSP70B, interacts with chloroplast-targeted DnaJ-like proteins (CDJs). In this work we focus on two CDJ co-chaperones (CDJ3 and CDJ4) of HSP70B which contain a redox-active Fe-S cluster (Dorn et al. Biochem. J. 427, 205 [2010]). We have performed Mössbauer spectroscopy on 57Fe enriched CDJ3 an) CDJ4. Our results indicate that both proteins have unusual [4Fe4S] 2+ clusters showing structural inhomogeneity of the two [Fe 2.5+-Fe 2.5+] pairs. The spectra have been analyzed by means of two components with δ-values characteristic for Fe 2.5+ centers, but the differences in Δ E Q indicate variations in their tetrahedral coordination spheres.

A preliminary assessment of asteroid shapes produced by impact disruption and re-creation: Application to the AIDA target.

NASA Astrophysics Data System (ADS)

Barnouin, Olivier; Michel, Patrick; Richardson, Derek

2016-04-01

In order to understand the origin of the 65803 Didymos, the target of the Asteroid Impact and Deflection Assessment mission, and gain insights on the origin and evolution of the asteroid's162173 Ryugu and 101955 Bennu, we investigate systematically the shapes of all re-accumulated fragments produced by the catastrophic disruption of a parent body that is 1 km in diameter or larger. These new fragments eventually become new asteroids of the size that current sample-return missions plan to explore. We choose a range of impact conditions by varying the parent bodies' strength, size and porosity, and the velocity and size of the projectile. Impact conditions range from near the catastrophic threshold, usually designated by Q*, where half of the target's mass escapes, to far greater values above this threshold. Our numerical investigations of the catastrophic disruption, which are undertaken using an SPH hydrocode, include a model of fragmentation for porous materials. The gravitationally dominated phase of reaccumulation of our asteroids is computed using the N-body code pkdgrav. At sufficiently slow impact speeds in the N-body model, particles are permitted to stick, forming irregular, competent pieces that can gather into non-idealized rubble piles as a result of re-accumulation. Shape and spin information of re-accumulated bodies are thus preserved. Due to numerical expense, this first study uses what we call a hard-sphere model, rather than a soft-sphere spring and dashpot model. This latter model is more commonly used in granular flow simulations for which detailed treatment of the multicontact physics is needed, which is not the case here, and comes at the expense of much smaller timesteps. With the hard-sphere model, there are three supported collision outcomes for bonded aggregates: sticking on contact (to grow the aggregate); bouncing (computed for these generally non-central impacts); and fragmentation (wherein the particles involved become detached from their respective aggregates and proceed to bounce as rigid spheres, possibly releasing more particles). We adjusted the strength of the forming aggregates to the measured strength of materials in the lab, scaled to the aggregate size, by using strength size scaling rules. In the future we expect to compare our hard-sphere models to a few soft-sphere for reasonable granular materials to best characterize differences between the two approaches, if any. Our results indicate that while 25143 Itokawa-like potato-shaped asteroids are typically the outcome of disruption, often more spherical or "top-shaped" asteroids can also be produced. Our results confirm what others have already noted, namely that a "top-shaped" or diamond shaped asteroid is not necessarily the result of the formation of YORP spin-up. Other criteria besides just shape need to be developed to determine whether or not the evolution of an asteroid and its surface geology have been dominated by YORP-related processes or by impact-derived re-accretion.

Clustered Genes Involved in Cyclopiazonic Acid Production are Next to the Aflatoxin Biosynthesis Gene Cluster in Aspergillus flavus

USDA-ARS?s Scientific Manuscript database

Cyclopiazonic acid (CPA), an indole-tetramic acid toxin, is produced by many species of Aspergillus and Penicillium. In addition to CPA Aspergillus flavus produces polyketide-derived carcinogenic aflatoxins (AFs). AF biosynthesis genes form a gene cluster in a subtelomeric region. Isolates of A. fla...

Total growth and root-cluster production by legumes and proteas depends on rhizobacterial strain, host species and nitrogen level

PubMed Central

Lamont, Byron B.; Pérez-Fernández, María

2016-01-01

Background Root clusters are bunches of hairy rootlets produced by >1800 species in nine families. The possible involvement of micro-organisms in root-cluster formation has produced conflicting results over the last 40 years. In addition, any effect of rhizobacteria on overall plant growth of root-cluster-bearing species remains unknown. Aims To evaluate the effect of seven rhizobacteria on total plant size, and relative cluster production, by three species, and relate outcomes to their indole-3-acetic acid (IAA)-producing ability as part explanation of past disparate results. Methods We grew Leucadendron salicifolium (from South Africa), Viminaria juncea (Australia) and Lupinus albus (Europe) in gnotobiotic, hydroponic culture at two nitrogen (N) levels and inoculated them with seven bacterial strains and harvested the plants after 13 weeks. Key Results Following inoculation with all seven bacteria individually, plant growth sometimes greatly exceeded that of the aseptic controls, but, under other conditions, growth was less than the controls. Leucadendron and Lupinus failed to produce root clusters in the –N aseptic controls and Viminaria in the +N controls that was overcome by inoculating them with selected bacteria. Six bacteria were able to induce far more root clusters than those of the aseptic controls, while all bacteria sometimes suppressed cluster production in other treatments. All nine possible combinations of resource (plant size, indirect) and morphogenetic (relative cluster production, direct) effects were represented among the results, especially positive synergism (larger plants with a greater density of clusters). There was no clear relationship with IAA-producing ability of the seven bacteria, but low IAA strains of Pseudomonas putida and Bacillus magetarium were associated with greatest cluster production. Conclusions While root-cluster formation can sometimes be induced by introducing rhizobacteria to aseptic culture, the growth-promoting properties of apparently beneficial bacteria on general growth and root-cluster production are best described as facultative, as their promotory effects depend on host species, growing conditions and index of plant response used. PMID:27288511

Structure-related frustrated magnetism of nanosized polyoxometalates: aesthetics and properties in harmony.

PubMed

Kögerler, Paul; Tsukerblat, Boris; Müller, Achim

2010-01-07

The structural versatility characterizing polyoxometalate chemistry, in combination with the option to deliberately use well-defined building blocks, serves as the foundation for the generation of a large family of magnetic clusters, frequently comprising highly symmetric spin arrays. If the spin centers are coupled by antiferromagnetic exchange, some of these systems exhibit spin frustration, which can result in novel magnetic properties of purely molecular origins. We discuss here the magnetic properties of selected nanosized polyoxometalate clusters featuring spin triangles as their magnetic 'building blocks' or fragments. This includes unique porous Keplerate clusters of the type {(Mo)Mo(5)}(12)M(30) (M = Fe(III), Cr(III), V(IV)) with the spin centers defining a regular icosidodecahedron and the {V(15)As(6)}-type cluster sphere containing a single equilateral spin triangle; these species are widely discussed and studied in the literature for their role in materials science as molecular representations of Kagomé lattices and in relation to quantum computing, respectively. Exhibiting fascinating and unique structural features, these magnetic molecules allow the study of the implications of frustrated spin ordering. Furthermore, this perspective covers the impact of spin frustration on the degeneracy of the ground state and related problems, namely strong magnetic anisotropy and the interplay of antisymmetric exchange and structural Jahn-Teller effects.

Importance of Interaction between Integrin and Actin Cytoskeleton in Suspension Adaptation of CHO cells.

PubMed

Walther, Christa G; Whitfield, Robert; James, David C

2016-04-01

The biopharmaceutical production process relies upon mammalian cell technology where single cells proliferate in suspension in a chemically defined synthetic environment. This environment lacks exogenous growth factors, usually contributing to proliferation of fibroblastic cell types such as Chinese hamster ovary (CHO) cells. Use of CHO cells for production hence requires a lengthy 'adaptation' process to select clones capable of proliferation as single cells in suspension. The underlying molecular changes permitting proliferation in suspension are not known. Comparison of the non-suspension-adapted clone CHO-AD and a suspension-adapted propriety cell line CHO-SA by flow cytometric analysis revealed a highly variable bi-modal expression pattern for cell-to-cell contact proteins in contrast to the expression pattern seen for integrins. Those have a uni-modal expression on suspension and adherent cells. Integrins showed a conformation distinguished by regularly distributed clusters forming a sphere on the cell membrane of suspension-adapted cells. Actin cytoskeleton analysis revealed reorganisation from the typical fibrillar morphology found in adherent cells to an enforced spherical subcortical actin sheath in suspension cells. The uni-modal expression and specific clustering of integrins could be confirmed for CHO-S, another suspension cell line. Cytochalasin D treatment resulted in breakdown of the actin sheath and the sphere-like integrin conformation demonstrating the link between integrins and actin in suspension-adapted CHO cells. The data demonstrates the importance of signalling changes, leading to an integrin rearrangement on the cell surface, and the necessity of the reinforcement of the actin cytoskeleton for proliferation in suspension conditions.

Hierarchical self-assembly of nanoparticles in polymer matrix and the nature of the interparticle interaction

NASA Astrophysics Data System (ADS)

Lin, Yu-Chiao; Chen, Chun-Yu; Chen, Hsin-Lung; Hashimoto, Takeji; Chen, Show-An; Li, Yen-Cheng

2015-06-01

Using small angle X-ray scattering (SAXS), we elucidated the spatial organization of palladium (Pd) nanoparticles (NPs) in the polymer matrix of poly(2-vinylpyridine) (P2VP) and the nature of inter-nanoparticle interactions, where the NPs were synthesized in the presence of P2VP by the reduction of palladium acetylacetonate (Pd(acac)2). The experimental SAXS profiles were analysed on the basis of a hierarchical structure model considering the following two types of interparticle potential: (i) hard-core repulsion only (i.e., the hard-sphere interaction) and (ii) hard-core repulsion together with an attractive potential well (i.e., the sticky hard-sphere interaction). The corresponding theoretical scattering functions, which were used for analysing the experimental SAXS profiles, were obtained within the context of the Percus-Yevick closure and the Ornstein-Zernike equation in the fundamental liquid theory. The analyses revealed that existence of the attractive potential well is indispensable to account for the experimental SAXS profiles. Moreover, the morphology of the hybrids was found to be characterized by a hierarchical structure with three levels, where about six primary NPs with the diameter of ca. 1.8 nm (level one) formed local clusters (level two), and these clusters aggregated to build up a large-scale mass-fractal structure (level three) with the fractal dimension of ca. 2.3. The scattering function developed here is of general use for quantitatively characterizing the morphological structures of polymer/NP hybrids and, in particular, for exploring the interaction potential of the NPs on the basis of the fundamental liquid theory.

FAST TRACK COMMUNICATION: Shear coordinate description of the quantized versal unfolding of a D4 singularity

NASA Astrophysics Data System (ADS)

Chekhov, Leonid; Mazzocco, Marta

2010-11-01

In this communication, by using Teichmüller theory of a sphere with four holes/orbifold points, we obtain a system of flat coordinates on the general affine cubic surface having a D4 singularity at the origin. We show that the Goldman bracket on the geodesic functions on the four-holed/orbifold sphere coincides with the Etingof-Ginzburg Poisson bracket on the affine D4 cubic. We prove that this bracket is the image under the Riemann-Hilbert map of the Poisson-Lie bracket on \\oplus _{1}^3\\mathfrak {sl}^\\ast (2,{{\\bb C}}) . We realize the action of the mapping class group by the action of the braid group on the geodesic functions. This action coincides with the procedure of analytic continuation of solutions of the sixth Painlevé equation. Finally, we produce the explicit quantization of the Goldman bracket on the geodesic functions on the four-holed/orbifold sphere and of the braid group action.

3-D Printed Ultem 9085 Testing and Analysis

NASA Technical Reports Server (NTRS)

Aguilar, Daniel; Christensen, Sean; Fox, Emmet J.

2015-01-01

The purpose of this document is to analyze the mechanical properties of 3-D printed Ultem 9085. This document will focus on the capabilities, limitations, and complexities of 3D printing in general, and explain the methods by which this material is tested. Because 3-D printing is a relatively new process that offers an innovative means to produce hardware, it is important that the aerospace community understands its current advantages and limitations, so that future endeavors involving 3-D printing may be completely safe. This document encompasses three main sections: a Slosh damage assessment, a destructive test of 3-D printed Ultem 9085 samples, and a test to verify simulation for the 3-D printed SDP (SPHERES Docking Port). Described below, 'Slosh' and 'SDP' refer to two experiments that are built using Ultem 9085 for use with the SPHERES (Synchronized Position Hold, Engage, Reorient, Experimental Satellites) program onboard the International Space Station (ISS) [16]. The SPHERES Facility is managed out of the National Aeronautics and Space Administration (NASA) Ames Research Center in California.

Critical Dimensions of Water-tamped Slabs and Spheres of Active Material

DOE R&D Accomplishments Database

Greuling, E.; Argo, H.: Chew, G.; Frankel, M. E.; Konopinski, E.J.; Marvin, C.; Teller, E.

1946-08-06

The magnitude and distribution of the fission rate per unit area produced by three energy groups of moderated neutrons reflected from a water tamper into one side of an infinite slab of active material is calculated approximately in section II. This rate is directly proportional to the current density of fast neutrons from the active material incident on the water tamper. The critical slab thickness is obtained in section III by solving an inhomogeneous transport integral equation for the fast-neutron current density into the tamper. Extensive use is made of the formulae derived in "The Mathematical Development of the End-Point Method" by Frankel and Goldberg. In section IV slight alterations in the theory outlined in sections II and III were made so that one could approximately compute the critical radius of a water-tamper sphere of active material. The derived formulae were applied to calculate the critical dimensions of water-tamped slabs and spheres of solid UF{sub 6} leaving various (25) isotope enrichment fractions. Decl. Dec. 16, 1955.

Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser.

PubMed

Bang, W; Dyer, G; Quevedo, H J; Bernstein, A C; Gaul, E; Donovan, M; Ditmire, T

2013-02-01

The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6×10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed.

Production of monodisperse cerium oxide microspheres with diameters near 100 μm by internal-gelation sol–gel methods

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

Katalenich, Jeffrey A.; Kitchen, Brian B.; Pierson, Bruce D.

Internal gelation sol-gel methods have used a variety of sphere forming methods in the past to produce metal oxide microspheres, but typically with poor control over the size uniformity at diameters near 100 µm. This work describes efforts to make and measure internal gelation, sol-gel microspheres with very uniform diameters in the 100 – 200 µm size range using a two-fluid nozzle. A custom apparatus was used to form aqueous droplets of sol-gel feed solutions in silicone oil and heat them to cause gelation of the spheres. Gelled spheres were washed, dried, and sintered prior to mounting on glass slidesmore » for optical imaging and analysis. Microsphere diameters and shape factors were determined as a function of silicone oil flow rate in a two-fluid nozzle and the size of a needle dispensing the aqueous sol-gel solution. Nine batches of microspheres were analyzed and had diameters ranging from 65.5 ± 2.4 µm for the smallest needle and fastest silicone oil flow rate to 211 ± 4.7 µm for the largest needle and slowest silicone oil flow rate. Standard deviations for measured diameters were less than 8% for all samples and most were less than 4%. Microspheres had excellent circularity with measured shape factors of 0.9 – 1. However, processing of optical images was complicated by shadow effects in the photoresist layer on glass slides and by overlapping microspheres. Based on calculated flow parameters, microspheres were produced in a simple dripping mode in the two-fluid nozzle. Using flow rates consistent with a simple dripping mode in a two-fluid nozzle configuration allows for very uniform oxide microspheres to be produced using the internal-gelation sol-gel method.« less

Production of Monodisperse Cerium Oxide Microspheres with Diameters near 100 µm by Internal Gelation Sol-Gel Methods

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

Katalenich, Jeffrey A.; Kitchen, Brian B.; Pierson, Bruce

2018-05-01

Internal gelation sol-gel methods have used a variety of sphere forming methods in the past to produce metal oxide microspheres, but typically with poor control over the size uniformity at diameters near 100 µm. This work describes efforts to make and measure internal gelation, sol-gel microspheres with very uniform diameters in the 100 – 200 µm size range using a two-fluid nozzle. A custom apparatus was used to form aqueous droplets of sol-gel feed solutions in silicone oil and heat them to cause gelation of the spheres. Gelled spheres were washed, dried, and sintered prior to mounting on glass slidesmore » for optical imaging and analysis. Microsphere diameters and shape factors were determined as a function of silicone oil flow rate in a two-fluid nozzle and the size of a needle dispensing the aqueous sol-gel solution. Nine batches of microspheres were analyzed and had diameters ranging from 65.5 ± 2.4 µm for the smallest needle and fastest silicone oil flow rate to 211 ± 4.7 µm for the largest needle and slowest silicone oil flow rate. Standard deviations for measured diameters were less than 8% for all samples and most were less than 4%. Microspheres had excellent circularity with measured shape factors of 0.9 – 1. However, processing of optical images was complicated by shadow effects in the photoresist layer on glass slides and by overlapping microspheres. Based on calculated flow parameters, microspheres were produced in a simple dripping mode in the two-fluid nozzle. Using flow rates consistent with a simple dripping mode in a two-fluid nozzle configuration allows for very uniform oxide microspheres to be produced using the internal-gelation sol-gel method.« less

Two-State Reactivity in Low-Valent Iron-Mediated C-H Activation and the Implications for Other First-Row Transition Metals.

PubMed

Sun, Yihua; Tang, Hao; Chen, Kejuan; Hu, Lianrui; Yao, Jiannian; Shaik, Sason; Chen, Hui

2016-03-23

C-H bond activation/functionalization promoted by low-valent iron complexes has recently emerged as a promising approach for the utilization of earth-abundant first-row transition metals to carry out this difficult transformation. Herein we use extensive density functional theory and high-level ab initio coupled cluster calculations to shed light on the mechanism of these intriguing reactions. Our key mechanistic discovery for C-H arylation reactions reveals a two-state reactivity (TSR) scenario in which the low-spin Fe(II) singlet state, which is initially an excited state, crosses over the high-spin ground state and promotes C-H bond cleavage. Subsequently, aryl transmetalation occurs, followed by oxidation of Fe(II) to Fe(III) in a single-electron transfer (SET) step in which dichloroalkane serves as an oxidant, thus promoting the final C-C coupling and finalizing the C-H functionalization. Regeneration of the Fe(II) catalyst for the next round of C-H activation involves SET oxidation of the Fe(I) species generated after the C-C bond coupling. The ligand sphere of iron is found to play a crucial role in the TSR mechanism by stabilization of the reactive low-spin state that mediates the C-H activation. This is the first time that the successful TSR concept conceived for high-valent iron chemistry is shown to successfully rationalize the reactivity for a reaction promoted by low-valent iron complexes. A comparative study involving other divalent middle and late first-row transition metals implicates iron as the optimum metal in this TSR mechanism for C-H activation. It is predicted that stabilization of low-spin Mn(II) using an appropriate ligand sphere should produce another promising candidate for efficient C-H bond activation. This new TSR scenario therefore emerges as a new strategy for using low-valent first-row transition metals for C-H activation reactions.

Variation in the fumonisin biosynthetic gene cluster in fumonisin-producing and nonproducing black aspergilli.

PubMed

Susca, Antonia; Proctor, Robert H; Butchko, Robert A E; Haidukowski, Miriam; Stea, Gaetano; Logrieco, Antonio; Moretti, Antonio

2014-12-01

The ability to produce fumonisin mycotoxins varies among members of the black aspergilli. Previously, analyses of selected genes in the fumonisin biosynthetic gene (fum) cluster in black aspergilli from California grapes indicated that fumonisin-nonproducing isolates of Aspergillus welwitschiae lack six fum genes, but nonproducing isolates of Aspergillus niger do not. In the current study, analyses of black aspergilli from grapes from the Mediterranean Basin indicate that the genomic context of the fum cluster is the same in isolates of A. niger and A. welwitschiae regardless of fumonisin-production ability and that full-length clusters occur in producing isolates of both species and nonproducing isolates of A. niger. In contrast, the cluster has undergone an eight-gene deletion in fumonisin-nonproducing isolates of A. welwitschiae. Phylogenetic analyses suggest each species consists of a mixed population of fumonisin-producing and nonproducing individuals, and that existence of both production phenotypes may provide a selective advantage to these species. Differences in gene content of fum cluster homologues and phylogenetic relationships of fum genes suggest that the mutation(s) responsible for the nonproduction phenotype differs, and therefore arose independently, in the two species. Partial fum cluster homologues were also identified in genome sequences of four other black Aspergillus species. Gene content of these partial clusters and phylogenetic relationships of fum sequences indicate that non-random partial deletion of the cluster has occurred multiple times among the species. This in turn suggests that an intact cluster and fumonisin production were once more widespread among black aspergilli. Copyright © 2014 Elsevier Inc. All rights reserved.

The structure and properties of a simple model mixture of amphiphilic molecules and ions at a solid surface

NASA Astrophysics Data System (ADS)

Pizio, O.; Sokołowski, S.; Sokołowska, Z.

2014-05-01

We investigate microscopic structure, adsorption, and electric properties of a mixture that consists of amphiphilic molecules and charged hard spheres in contact with uncharged or charged solid surfaces. The amphiphilic molecules are modeled as spheres composed of attractive and repulsive parts. The electrolyte component of the mixture is considered in the framework of the restricted primitive model (RPM). The system is studied using a density functional theory that combines fundamental measure theory for hard sphere mixtures, weighted density approach for inhomogeneous charged hard spheres, and a mean-field approximation to describe anisotropic interactions. Our principal focus is in exploring the effects brought by the presence of ions on the distribution of amphiphilic particles at the wall, as well as the effects of amphiphilic molecules on the electric double layer formed at solid surface. In particular, we have found that under certain thermodynamic conditions a long-range translational and orientational order can develop. The presence of amphiphiles produces changes of the shape of the differential capacitance from symmetric or non-symmetric bell-like to camel-like. Moreover, for some systems the value of the potential of the zero charge is non-zero, in contrast to the RPM at a charged surface.

Large-area photonic crystals

NASA Astrophysics Data System (ADS)

Ruhl, Tilmann; Spahn, Peter; Hellmann, Gotz P.; Winkler, Holger

2004-09-01

Materials with a periodically modulated refractive index, with periods on the scale of light wavelengths, are currently attracting much attention because of their unique optical properties which are caused by Bragg scattering of the visible light. In nature, 3d structures of this kind are found in the form of opals in which monodisperse silica spheres with submicron diameters form a face-centered-cubic (fcc) lattice. Artificial opals, with the same colloidal-crystalline fcc structure, have meanwhile been prepared by crystallizing spherical colloidal particles via sedimentation or drying of dispersions. In this report, colloidal crystalline films are introduced that were produced by a novel technique based on shear flow in the melts of specially designed submicroscopic silica-polymer core-shell hybrid spheres: when the melt of these spheres flows between the plates of a press, the spheres crystallize along the plates, layer by layer, and the silica cores assume the hexagonal order corresponding to the (111) plane of the fcc lattice. This process is fast and yields large-area films, thin or thick. To enhance the refractive index contrast in these films, the colloidal crystalline structure was inverted by etching out the silica cores with hydrofluoric acid. This type of an inverse opal, in which the fcc lattice is formed by mesopores, is referred to as a polymer-air photonic crystal.

Mechanism of the quasi-zero axial acoustic radiation force experienced by elastic and viscoelastic spheres in the field of a quasi-Gaussian beam and particle tweezing.

PubMed

Mitri, F G; Fellah, Z E A

2014-01-01

The present analysis investigates the (axial) acoustic radiation force induced by a quasi-Gaussian beam centered on an elastic and a viscoelastic (polymer-type) sphere in a nonviscous fluid. The quasi-Gaussian beam is an exact solution of the source free Helmholtz wave equation and is characterized by an arbitrary waist w₀ and a diffraction convergence length known as the Rayleigh range z(R). Examples are found where the radiation force unexpectedly approaches closely to zero at some of the elastic sphere's resonance frequencies for kw₀≤1 (where this range is of particular interest in describing strongly focused or divergent beams), which may produce particle immobilization along the axial direction. Moreover, the (quasi)vanishing behavior of the radiation force is found to be correlated with conditions giving extinction of the backscattering by the quasi-Gaussian beam. Furthermore, the mechanism for the quasi-zero force is studied theoretically by analyzing the contributions of the kinetic, potential and momentum flux energy densities and their density functions. It is found that all the components vanish simultaneously at the selected ka values for the nulls. However, for a viscoelastic sphere, acoustic absorption degrades the quasi-zero radiation force. Copyright © 2013 Elsevier B.V. All rights reserved.

Micro-heterogeneity of Cellulosic Fiber Biopolymer Prepared from Corn Hulls

USDA-ARS?s Scientific Manuscript database

Z-trim is a zero calorie cellulosic fiber biopolymer produced from corn hulls. The micro-structural heterogeneities of Z-trim biopolymer were investigated by monitoring the thermally driven displacements of well-dispersed micro-spheres via video fluorescence microscopy named multiple-particle track...

Micro-Heterogeneity of Cellulosic Fiber Biopolymer Prepared from Corn Hulls

USDA-ARS?s Scientific Manuscript database

Z-trim is a zero calorie cellulosic fiber biopolymer produced from corn hulls. The micro-structural heterogeneities of Z-trim biopolymer were investigated by monitoring the thermally driven displacements of well-dispersed micro-spheres via video fluorescence microscopy named multiple-particle track...

Interaction Heterogeneity can Favorably Impact Colloidal Crystal Nucleation

NASA Astrophysics Data System (ADS)

Jenkins, Ian C.; Crocker, John C.; Sinno, Talid

2017-10-01

Colloidal particles with short-ranged attractions, e.g., micron-scale spheres functionalized with single-stranded DNA oligomers, are susceptible to becoming trapped in disordered configurations even when a crystalline arrangement is the ground state. Moreover, for reasons that are not well understood, seemingly minor variations in the particle formulation can lead to dramatic changes in the crystallization outcome. We demonstrate, using a combination of equilibrium and nonequilibrium computer simulations, that interaction heterogeneity—variations in the energetic interactions among different particle pairs in the population—may favorably impact crystal nucleation. Specifically, interaction heterogeneity is found to lower the free energy barrier to nucleation via the formation of clusters comprised preferentially of strong-binding particle pairs. Moreover, gelation is inhibited by "spreading out over time" the nucleation process, resulting in a reduced density of stable nuclei, allowing each to grow unhindered and larger. Our results suggest a simple and robust approach for enhancing colloidal crystallization near the "sticky sphere" limit, and support the notion that differing extents of interaction heterogeneity arising from various particle functionalization protocols may contribute to the otherwise unexplained variations in crystallization outcomes reported in the literature.

Unsteady sedimentation of flocculating non-Brownian suspensions

NASA Astrophysics Data System (ADS)

Zinchenko, Alexander

2017-11-01

Microstructural evolution and temporal dynamics of the sedimentation rate U(t) are studied for a monodisperse suspension of non-Brownian spherical particles subject to van der Waals attraction and electrostatic repulsion in the realistic range of colloidal parameters (Hamaker constant, surface potential, double layer thickness etc.). A novel economical high-order multipole algorithm is used to fully resolve hydrodynamical interactions in the dynamical simulations with up to 500 spheres in a periodic box and O(106) time steps, combined with geometry perturbation to incorporate lubrication and extend the solution to arbitrarily small particle separations. The total colloidal force near the secondary minimum often greatly exceeds the effective gravity/buoyancy force, resulting in the formation of strong but flexible bonds and large clusters as the suspension evolves from an initial well-mixed state of non-aggregated spheres. Ensemble averaging over many initial configurations is used to predict U(t) for particle volume fractions between 0.1 and 0.25. The results are fully convergent, system-size independent and cover a 2-2.5 fold growth of U(t) after a latency time.

Surface complexation model for multisite adsorption of copper(II) onto kaolinite

NASA Astrophysics Data System (ADS)

Peacock, Caroline L.; Sherman, David M.

2005-08-01

We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO 4H n) n-6 and binuclear (Cu 2O 6H n) n-8 inner-sphere complexes on variable-charge ≡AlOH sites and as Cu 2+ on ion exchangeable ≡X-H + sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH) 6 polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH) 2Cu(OH) 20, tridentate (≡Al 3O(OH) 2)Cu 2(OH) 30 and ≡X-Cu 2+ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions

Compressive Properties of Metal Matrix Syntactic Foams in Free and Constrained Compression

NASA Astrophysics Data System (ADS)

Orbulov, Imre Norbert; Májlinger, Kornél

2014-06-01

Metal matrix syntactic foam (MMSF) blocks were produced by an inert gas-assisted pressure infiltration technique. MMSFs are advanced hollow sphere reinforced-composite materials having promising application in the fields of aviation, transport, and automotive engineering, as well as in civil engineering. The produced blocks were investigated in free and constrained compression modes, and besides the characteristic mechanical properties, their deformation mechanisms and failure modes were studied. In the tests, the chemical composition of the matrix material, the size of the reinforcing ceramic hollow spheres, the applied heat treatment, and the compression mode were considered as investigation parameters. The monitored mechanical properties were the compressive strength, the fracture strain, the structural stiffness, the fracture energy, and the overall absorbed energy. These characteristics were strongly influenced by the test parameters. By the proper selection of the matrix and the reinforcement and by proper design, the mechanical properties of the MMSFs can be effectively tailored for specific and given applications.

From linking of metal-oxide building blocks in a dynamic library to giant clusters with unique properties and towards adaptive chemistry.

PubMed

Müller, Achim; Gouzerh, Pierre

2012-11-21

Following Nature's lessons, today chemists can cross the boundary of the small molecule world to construct multifunctional and highly complex molecular nano-objects up to protein size and even cell-like nanosystems showing responsive sensing. Impressive examples emerge from studies of the solutions of some oxoanions of the early transition metals especially under reducing conditions which enable the controlled linking of metal-oxide building blocks. The latter are available from constitutional dynamic libraries, thus providing the option to generate multifunctional unique nanoscale molecular systems with exquisite architectures, which even opens the way towards adaptive and evolutive (Darwinian) chemistry. The present review presents the first comprehensive report of current knowledge (including synthesis aspects not discussed before) regarding the related giant metal-oxide clusters mainly of the type {Mo(57)M'(6)} (M' = Fe(III), V(IV)) (torus structure), {M(72)M'(30)} (M = Mo, M' = V(IV), Cr(III), Fe(III), Mo(V)), {M(72)Mo(60)} (M = Mo, W) (Keplerates), {Mo(154)}, {Mo(176)}, {Mo(248)} ("big wheels"), and {Mo(368)} ("blue lemon") - all having the important transferable pentagonal {(M)M(5)} groups in common. These discoveries expanded the frontiers of inorganic chemistry to the mesoscopic world, while there is probably no collection of discrete inorganic compounds which offers such a versatile chemistry and the option to study new phenomena of interdisciplinary interest. The variety of different properties of the sphere- and wheel-type metal-oxide-based clusters can directly be related to their unique architectures: The spherical Keplerate-type capsules having 20 crown-ether-type pores and tunable internal functionalities allow the investigation of confined matter as well as that of sphere-surface-supramolecular and encapsulation chemistry - including related new aspects of the biologically important hydrophobic effects - but also of nanoscale ion transport and separation. The wheel-type molybdenum-oxide clusters exhibiting complex landscapes do not only have well-defined reaction sites but also show unprecedented adaptability regarding the integration of various kinds of matter. Applications in different fields, e.g. in materials science and catalysis including those in small spaces, investigated by several groups, are discussed while possible directions for future work are outlined.

The Vela Cloud: A Giant H I Anomaly in the NGC 3256 GROUP

NASA Astrophysics Data System (ADS)

English, Jayanne; Koribalski, B.; Bland-Hawthorn, J.; Freeman, K. C.; McCain, Claudia F.

2010-01-01

We present Australia Telescope Compact Array (ATCA) observations of a galaxy-sized intergalactic H I cloud ("the Vela Cloud") in the NGC 3256 galaxy group. The group contains the prominent merging galaxy NGC 3256, which is surrounded by a number of H I fragments, the tidally disturbed galaxy NGC 3263, and several other peculiar galaxies. The Vela Cloud, with an H I mass of 3-5 × 10^9 M_{⊙}, resides southeast of NGC 3256 and west of NGC 3263, within an area of 9' × 16' (100 kpc × 175 kpc for an adopted distance of 38 Mpc). In our ATCA data the Vela Cloud appears as three diffuse components and contains four density enhancements. The Vela Cloud's properties, together with its group environment, suggest that it has a tidal origin. Each density enhancement contains ˜ 10^{8} M_{⊙} of H I gas, which is sufficient material for the formation of globular cluster progenitors. However, if we represent the enhancements as Bonnor-Ebert spheres, then the pressure of the surrounding H I would need to increase by at least a factor of 9 in order to cause the collapse of an enhancement. Thus we do not expect them to form massive bound stellar systems like super star clusters or tidal dwarf galaxies. Since the H I density enhancements have some properties in common with high-velocity clouds, we explore whether they may evolve to be identified with these starless clouds instead. Original plate material is copyright © the Royal Observatory Edinburgh and the Anglo-Australian Observatory. The plates were processed into the present compressed digital form with their permission. The Digitized Sky Survey was produced at the Space Telescope Science Institute under US Government grant NAG W-2166.

Hubble Views a Galactic Mega-merger

NASA Image and Video Library

2016-01-15

The subject of this NASA/ESA Hubble Space Telescope image is known as NGC 3597. It is the product of a collision between two good-sized galaxies, and is slowly evolving to become a giant elliptical galaxy. This type of galaxy has grown more and more common as the universe has evolved, with initially small galaxies merging and progressively building up into larger galactic structures over time. NGC 3597 is located approximately 150 million light-years away in the constellation of Crater (The Cup). Astronomers study NGC 3597 to learn more about how elliptical galaxies form — many ellipticals began their lives far earlier in the history of the universe. Older ellipticals are nicknamed “red and dead” by astronomers because these bloated galaxies are not anymore producing new, bluer stars, and are thus packed full of old and redder stellar populations. Before infirmity sets in, some freshly formed elliptical galaxies experience a final flush of youth, as is the case with NGC 3597. Galaxies smashing together pool their available gas and dust, triggering new rounds of star birth. Some of this material ends up in dense pockets initially called proto-globular clusters, dozens of which festoon NGC 3597. These pockets will go on to collapse and form fully-fledged globular clusters, large spheres that orbit the centers of galaxies like satellites, packed tightly full of millions of stars. Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Euler-Vector Clustering of GPS Velocities Defines Microplate Geometry in Southwest Japan

NASA Astrophysics Data System (ADS)

Savage, J. C.

2018-02-01

I have used Euler-vector clustering to assign 469 GEONET stations in southwest Japan to k clusters (k = 2, 3,..., 9) so that, for any k, the velocities of stations within each cluster are most consistent with rigid-block motion on a sphere. That is, I attempt to explain the raw (i.e., uncorrected for strain accumulation), 1996-2006 velocities of those 469 Global Positioning System stations by rigid motion of k clusters on the surface of a spherical Earth. Because block geometry is maintained as strain accumulates, Euler-vector clustering may better approximate the block geometry than the values of the associated Euler vectors. The microplate solution for each k is constructed by merging contiguous clusters that have closely similar Euler vectors. The best solution consists of three microplates arranged along the Nankaido Trough-Ryukyu Trench between the Amurian and Philippine Sea Plates. One of these microplates, the South Kyushu Microplate (an extension of the Ryukyu forearc into the southeast corner of Kyushu), had previously been identified from paleomagnetic rotations. Relative to ITRF2000 the three microplates rotate at different rates about neighboring poles located close to the northwest corner of Shikoku. The microplate model is identical to that proposed in the block model of Wallace et al. (2009, https://doi.org/10.1130/G2522A.1) except in southernmost Kyushu. On Shikoku and Honshu, but not Kyushu, the microplate model is consistent with that proposed in the block models of Nishimura and Hashimoto (2006, https://doi.org/10.1016/j.tecto.2006.04.017) and Loveless and Meade (2010, https://doi.org/10.1029/2008JB006248) without the low-slip-rate boundaries proposed in the latter.

Hydration of Atmospheric Molecular Clusters: Systematic Configurational Sampling.

PubMed

Kildgaard, Jens; Mikkelsen, Kurt V; Bilde, Merete; Elm, Jonas

2018-05-09

We present a new systematic configurational sampling algorithm for investigating the potential energy surface of hydrated atmospheric molecular clusters. The algo- rithm is based on creating a Fibonacci sphere around each atom in the cluster and adding water molecules to each point in 9 different orientations. To allow the sam- pling of water molecules to existing hydrogen bonds, the cluster is displaced along the hydrogen bond and a water molecule is placed in between in three different ori- entations. Generated redundant structures are eliminated based on minimizing the root mean square distance (RMSD) of different conformers. Initially, the clusters are sampled using the semiempirical PM6 method and subsequently using density func- tional theory (M06-2X and ωB97X-D) with the 6-31++G(d,p) basis set. Applying the developed algorithm we study the hydration of sulfuric acid with up to 15 water molecules. We find that the additions of the first four water molecules "saturate" the sulfuric acid molecule and are more thermodynamically favourable than the addition of water molecule 5-15. Using the large generated set of conformers, we assess the performance of approximate methods (ωB97X-D, M06-2X, PW91 and PW6B95-D3) in calculating the binding energies and assigning the global minimum conformation compared to high level CCSD(T)-F12a/VDZ-F12 reference calculations. The tested DFT functionals systematically overestimates the binding energies compared to cou- pled cluster calculations, and we find that this deficiency can be corrected by a simple scaling factor.

Application of a Bonner sphere spectrometer for the determination of the angular neutron energy spectrum of an accelerator-based BNCT facility.

PubMed

Mirzajani, N; Ciolini, R; Di Fulvio, A; Esposito, J; d'Errico, F

2014-06-01

Experimental activities are underway at INFN Legnaro National Laboratories (LNL) (Padua, Italy) and Pisa University aimed at angular-dependent neutron energy spectra measurements produced by the (9)Be(p,xn) reaction, under a 5MeV proton beam. This work has been performed in the framework of INFN TRASCO-BNCT project. Bonner Sphere Spectrometer (BSS), based on (6)LiI (Eu) scintillator, was used with the shadow-cone technique. Proper unfolding codes, coupled to BSS response function calculated by Monte Carlo code, were finally used. The main results are reported here. Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.

Clustered DNA damages induced in human hematopoietic cells by low doses of ionizing radiation

NASA Technical Reports Server (NTRS)

Sutherland, Betsy M.; Bennett, Paula V.; Cintron-Torres, Nela; Hada, Megumi; Trunk, John; Monteleone, Denise; Sutherland, John C.; Laval, Jacques; Stanislaus, Marisha; Gewirtz, Alan

2002-01-01

Ionizing radiation induces clusters of DNA damages--oxidized bases, abasic sites and strand breaks--on opposing strands within a few helical turns. Such damages have been postulated to be difficult to repair, as are double strand breaks (one type of cluster). We have shown that low doses of low and high linear energy transfer (LET) radiation induce such damage clusters in human cells. In human cells, DSB are about 30% of the total of complex damages, and the levels of DSBs and oxidized pyrimidine clusters are similar. The dose responses for cluster induction in cells can be described by a linear relationship, implying that even low doses of ionizing radiation can produce clustered damages. Studies are in progress to determine whether clusters can be produced by mechanisms other than ionizing radiation, as well as the levels of various cluster types formed by low and high LET radiation.

Benchmark Comparison of Dual- and Quad-Core Processor Linux Clusters with Two Global Climate Modeling Workloads

NASA Technical Reports Server (NTRS)

McGalliard, James

2008-01-01

This viewgraph presentation details the science and systems environments that NASA High End computing program serves. Included is a discussion of the workload that is involved in the processing for the Global Climate Modeling. The Goddard Earth Observing System Model, Version 5 (GEOS-5) is a system of models integrated using the Earth System Modeling Framework (ESMF). The GEOS-5 system was used for the Benchmark tests, and the results of the tests are shown and discussed. Tests were also run for the Cubed Sphere system, results for these test are also shown.

Optimal approximation of harmonic growth clusters by orthogonal polynomials

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

Teodorescu, Razvan

2008-01-01

Interface dynamics in two-dimensional systems with a maximal number of conservation laws gives an accurate theoreticaI model for many physical processes, from the hydrodynamics of immiscible, viscous flows (zero surface-tension limit of Hele-Shaw flows), to the granular dynamics of hard spheres, and even diffusion-limited aggregation. Although a complete solution for the continuum case exists, efficient approximations of the boundary evolution are very useful due to their practical applications. In this article, the approximation scheme based on orthogonal polynomials with a deformed Gaussian kernel is discussed, as well as relations to potential theory.

Neurokinin B-producing projection neurons in the lateral stripe of the striatum and cell clusters of the accumbens nucleus in the rat.

PubMed

Zhou, Ligang; Furuta, Takahiro; Kaneko, Takeshi

2004-12-06

Neurons producing preprotachykinin B (PPTB), the precursor of neurokinin B, constitute 5% of neurons in the dorsal striatum and project to the substantia innominata (SI) selectively. In the ventral striatum, PPTB-producing neurons are collected mainly in the lateral stripe of the striatum (LSS) and cell clusters of the accumbens nucleus (Acb). In the present study, we first examined the distribution of PPTB-immunoreactive neurons in rat ventral striatum and found that a large part of the PPTB-immunoreactive cell clusters was continuous to the LSS, but a smaller part was not. Thus, we divided the PPTB-immunoreactive cell clusters into the LSS-associated and non-LSS-associated ones. We next investigated the projection targets of the PPTB-producing ventral striatal neurons by combining immunofluorescence labeling and retrograde tracing. After injection of Fluoro-Gold into the basal component of the SI (SIb) and medial part of the interstitial nucleus of posterior limb of the anterior commissure, many PPTB-immunoreactive neurons were retrogradely labeled in the LSS-associated cell clusters and LSS, respectively. When the injection site included the ventral part of the sublenticular component of the SI(SIsl), retrogradely labeled neurons showed PPTB-immunoreactivity frequently in non-LSS-associated cell clusters. Furthermore, these PPTB-immunoreactive projections were confirmed by the double-fluorescence method after anterograde tracer injection into the ventral striatum containing the cell clusters. Since the dorsalmost part of the SIsl is known to receive strong inputs from PPTB-producing dorsal striatal neurons, the present results indicate that PPTB-producing ventral striatal neurons project to basal forebrain target regions in parallel with dorsal striatal neurons without significant convergence. 2004 Wiley-Liss, Inc.

Application of clustering methods: Regularized Markov clustering (R-MCL) for analyzing dengue virus similarity

NASA Astrophysics Data System (ADS)

Lestari, D.; Raharjo, D.; Bustamam, A.; Abdillah, B.; Widhianto, W.

2017-07-01

Dengue virus consists of 10 different constituent proteins and are classified into 4 major serotypes (DEN 1 - DEN 4). This study was designed to perform clustering against 30 protein sequences of dengue virus taken from Virus Pathogen Database and Analysis Resource (VIPR) using Regularized Markov Clustering (R-MCL) algorithm and then we analyze the result. By using Python program 3.4, R-MCL algorithm produces 8 clusters with more than one centroid in several clusters. The number of centroid shows the density level of interaction. Protein interactions that are connected in a tissue, form a complex protein that serves as a specific biological process unit. The analysis of result shows the R-MCL clustering produces clusters of dengue virus family based on the similarity role of their constituent protein, regardless of serotypes.

Preparation of Gelatin Layer Film with Gold Clusters in Using Photographic Film

NASA Astrophysics Data System (ADS)

Kuge, Ken'ichi; Arisawa, Michiko; Aoki, Naokazu; Hasegawa, Akira

2000-12-01

A gelatin layer film with gold clusters is produced by taking advantage of the photosensitivity of silver halide photography. Through exposure silver specks, which are called latent-image specks and are composed of several reduced silver atoms, are formed on the surface of silver halide grains in the photographic film. As the latent-image specks act as a catalyst for redox reaction, reduced gold atoms are deposited on the latent-image specks when the exposed film is immersed in a gold (I) thiocyanate complex solution for 5-20 days. Subsequently, when the silver halide grains are dissolved and removed, the gelatin layer film with gold clusters remains. The film produced by this method is purple and showed an absorption spectrum having a maximum of approximately 560 nm as a result of plasmon absorption. The clusters continued to grow with immersion time, and the growth rate increased as the concentration of the gold complex solution was increased. The cluster diameter changed from 20 nm to 100 nm. By this method, it is possible to produce a gelatin film of a large area with evenly dispersed gold clusters, and since it is produced only on the exposed area, pattern forming is also possible.

A Framework for Testing Scientific Software: A Case Study of Testing Amsterdam Discrete Dipole Approximation Software

NASA Astrophysics Data System (ADS)

Shao, Hongbing

Software testing with scientific software systems often suffers from test oracle problem, i.e., lack of test oracles. Amsterdam discrete dipole approximation code (ADDA) is a scientific software system that can be used to simulate light scattering of scatterers of various types. Testing of ADDA suffers from "test oracle problem". In this thesis work, I established a testing framework to test scientific software systems and evaluated this framework using ADDA as a case study. To test ADDA, I first used CMMIE code as the pseudo oracle to test ADDA in simulating light scattering of a homogeneous sphere scatterer. Comparable results were obtained between ADDA and CMMIE code. This validated ADDA for use with homogeneous sphere scatterers. Then I used experimental result obtained for light scattering of a homogeneous sphere to validate use of ADDA with sphere scatterers. ADDA produced light scattering simulation comparable to the experimentally measured result. This further validated the use of ADDA for simulating light scattering of sphere scatterers. Then I used metamorphic testing to generate test cases covering scatterers of various geometries, orientations, homogeneity or non-homogeneity. ADDA was tested under each of these test cases and all tests passed. The use of statistical analysis together with metamorphic testing is discussed as a future direction. In short, using ADDA as a case study, I established a testing framework, including use of pseudo oracles, experimental results and the metamorphic testing techniques to test scientific software systems that suffer from test oracle problems. Each of these techniques is necessary and contributes to the testing of the software under test.

Experimental transient and permanent deformation studies of steel-sphere-impacted or impulsively-loaded aluminum beams with clamped ends

NASA Technical Reports Server (NTRS)

Witmer, E. A.

1975-01-01

The sheet explosive loading technique (SELT) was employed to obtain elastic-plastic, large-deflection transient and/or permanent strain data on simple well-defined structural specimens and materials: initially-flat 6061-T651 aluminum beams with both ends ideally clamped via integral construction. The SELT loading technique was chosen since it is both convenient and provides forcing function information of small uncertainty. These data will be useful for evaluating pertinent structural response prediction methods. A second objective was to obtain high-quality transient-strain data for a well-defined structural/material model subjected to impact by a rigid body of known mass, impact velocity, and geometry; large-deflection, elastic-plastic transient response conditions are of primary interest. The beam with both ends clamped and a steel sphere as the impacting body were chosen. The steel sphere was launched vertically by explosive propulsion to achieve various desired impact velocities. The sphere/beam impact tests resulted in producing a wide range of structural responses and permanent deformations, including rupture of the beam from excessive structural response in two cases. The transient and permanent strain data as well as the permanent deflection data obtained are of high quality and should be useful for checking and evaluating methods for predicting the responses of simple 2-d structures to fragment (sphere) impact. Transient strain data very close to the point of impact were not obtained over as long a time as desirable because the gage(s) in that region became detached during the transient response.

Processing of cenosphere-cement/asphalt composite materials and evaluation of their mechanical and acoustic properties

DOT National Transportation Integrated Search

2004-04-09

Cenospheres are hollow, aluminum silicate spheres, between 10-300mm in diameter. Their low specific gravity (0.67) make them ideal replacements for fine sand for producing low density concrete. In this research, the moisture uptake and loss by cenosp...

Constraining the Mass of the Spectacular Pandora's Cluster, Abell 2744

NASA Astrophysics Data System (ADS)

Carrasco, Rodrigo; Frye, Brenda; Coe, Dan; Dupke, Renato; Merten, Julian; Sodre, Laerte; Massey, Richard; Braglia, Filberto; Cypriano, Eduardo; Zitrin, Adi; Krick, Jessica; Benitez, Narciso

2011-08-01

Violent cluster mergers provide a unique opportunity to study the interplay between dark matter (DM) and ICM and to set constraints on the nature of DM. In particular, cluster mergers near first core passage allow us to ``see'' DM by comparing the spatial distribution of the intra-cluster gas (baryonic) to that of DM. We have recently finished a lensing analysis of the particularly interesting merging system, A2744, the Pandora cluster. We found that it is the result of a spectacular merging event, significantly more complex than the "Bullet Cluster", that produced a wide variety of new phenomenologies, among them, a Bullet, a Dark sub-cluster (no gas), a Ghost sub-cluster (no DM), which can provide fundamental insights to the physics of the ICM, and begs further observations. Our analyses revealed 34 arcs produced by strong gravitational lensing, none of which had been published to date. Spectroscopic redshifts of these arcs are essential to determine precise masses of the main merging system providing crucial information for further numerical simulations and to set stronger constraints on the DM self-interaction cross-section. Therefore we are requesting 17.2 hours on Gemini+GMOS-S, primarily to obtain spectroscopic redshifts of multiply strongly lensed arcs produced by this impressive cluster.

Photochemical cleavage of metal--carbon nanocrystals and their reconstruction into met--cars clusters

NASA Astrophysics Data System (ADS)

Pilgrim, J. S.; Duncan, M. A.

1994-10-01

Titanium and zirconium metal--carbon clusters are produced by laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. In addition to the now-familiar "met-cars" stoichiometry (M8C12), larger magic number clusters are produced with near 1:1 metal--carbon ratios. The special stoichiometries observed correspond to face-centered cubic crystal fragments, with a strong preference for fragments with symmetrical x,y,z dimensions. Mass-selected photodissociation experiments are used to investigate the structural patterns and stabilities of these systems. Photodissociation of the larger "nanocrystal" clusters leads to cleavage along crystal planes, producing smaller crystals also having highly symmetric dimensions. Photoexcitation of all these crystallites, in particular the 3 × 3 × 3 species, also leads to surface reconstruction, forming the M8C12 met-cars cluster and/or the M8C13 cluster, the latter of which is assigned to a met--cars cage with an endohedral carbon atom.

Clustering Methods with Qualitative Data: A Mixed Methods Approach for Prevention Research with Small Samples

PubMed Central

Henry, David; Dymnicki, Allison B.; Mohatt, Nathaniel; Allen, James; Kelly, James G.

2016-01-01

Qualitative methods potentially add depth to prevention research, but can produce large amounts of complex data even with small samples. Studies conducted with culturally distinct samples often produce voluminous qualitative data, but may lack sufficient sample sizes for sophisticated quantitative analysis. Currently lacking in mixed methods research are methods allowing for more fully integrating qualitative and quantitative analysis techniques. Cluster analysis can be applied to coded qualitative data to clarify the findings of prevention studies by aiding efforts to reveal such things as the motives of participants for their actions and the reasons behind counterintuitive findings. By clustering groups of participants with similar profiles of codes in a quantitative analysis, cluster analysis can serve as a key component in mixed methods research. This article reports two studies. In the first study, we conduct simulations to test the accuracy of cluster assignment using three different clustering methods with binary data as produced when coding qualitative interviews. Results indicated that hierarchical clustering, K-Means clustering, and latent class analysis produced similar levels of accuracy with binary data, and that the accuracy of these methods did not decrease with samples as small as 50. Whereas the first study explores the feasibility of using common clustering methods with binary data, the second study provides a “real-world” example using data from a qualitative study of community leadership connected with a drug abuse prevention project. We discuss the implications of this approach for conducting prevention research, especially with small samples and culturally distinct communities. PMID:25946969

Clustering Methods with Qualitative Data: a Mixed-Methods Approach for Prevention Research with Small Samples.

PubMed

Henry, David; Dymnicki, Allison B; Mohatt, Nathaniel; Allen, James; Kelly, James G

2015-10-01

Qualitative methods potentially add depth to prevention research but can produce large amounts of complex data even with small samples. Studies conducted with culturally distinct samples often produce voluminous qualitative data but may lack sufficient sample sizes for sophisticated quantitative analysis. Currently lacking in mixed-methods research are methods allowing for more fully integrating qualitative and quantitative analysis techniques. Cluster analysis can be applied to coded qualitative data to clarify the findings of prevention studies by aiding efforts to reveal such things as the motives of participants for their actions and the reasons behind counterintuitive findings. By clustering groups of participants with similar profiles of codes in a quantitative analysis, cluster analysis can serve as a key component in mixed-methods research. This article reports two studies. In the first study, we conduct simulations to test the accuracy of cluster assignment using three different clustering methods with binary data as produced when coding qualitative interviews. Results indicated that hierarchical clustering, K-means clustering, and latent class analysis produced similar levels of accuracy with binary data and that the accuracy of these methods did not decrease with samples as small as 50. Whereas the first study explores the feasibility of using common clustering methods with binary data, the second study provides a "real-world" example using data from a qualitative study of community leadership connected with a drug abuse prevention project. We discuss the implications of this approach for conducting prevention research, especially with small samples and culturally distinct communities.

Uncrowding R 136 from VLT/SPHERE extreme adaptive optics

NASA Astrophysics Data System (ADS)

Khorrami, Z.; Vakili, F.; Lanz, T.; Langlois, M.; Lagadec, E.; Meyer, M. R.; Robbe-Dubois, S.; Abe, L.; Avenhaus, H.; Beuzit, J. L.; Gratton, R.; Mouillet, D.; Origné, A.; Petit, C.; Ramos, J.

2017-06-01

This paper presents the sharpest near-IR images of the massive cluster R 136 to date, based on the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode.The crowded stellar population in the core of the R 136 starburst compact cluster remains still to be characterized in terms of individual luminosities, age, mass and multiplicity. SPHERE/VLT and its high contrast imaging possibilities open new windows to make progress on these questions.Stacking-up a few hundreds of short exposures in J and Ks spectral bands over a field of view (FoV) of 10.9″ × 12.3″ centered on the R 136a1 stellar component, enabled us to carry a refined photometric analysis of the core of R 136. We detected 1110 and 1059 sources in J and Ks images respectively with 818 common sources. Thanks to better angular resolution and dynamic range, we found that more than 62.6% (16.5%) of the stars, detected both in J and Ks data, have neighbours closer than 0.2'' (0.1''). The closest stars are resolved down to the full width at half maximum (FWHM) of the point spread function (PSF) measured by Starfinder. Among resolved and/or detected sources R 136a1 and R 136c have optical companions and R 136a3 is resolved as two stars (PSF fitting) separated by 59 ± 2 mas. This new companion of R 136a3 presents a correlation coefficient of 86% in J and 75% in Ks. The new set of detected sources were used to re-assess the age and extinction of R 136 based on 54 spectroscopically stars that have been recently studied with HST slit-spectroscopy (Crowther et al. 2016, MNRAS, 458, 624) of the core of this cluster. Over 90% of these 54 sources identified visual companions (closer than 0.2''). We found the most probable age and extinction for these sources are Myr, AJ = (0.45 ± 0.5) mag and AK = (0.2 ± 0.5) mag within the photometric and spectroscopic error-bars. Additionally, using PARSEC evolutionary isochrones and tracks, we estimated the stellar mass range for each detected source (common in J and K data) and plotted the generalized histogram of mass (MF with error-bars). Using SPHERE data, we have gone one step further and partially resolved and studied the initial mass function covering mass range of (3-300) M⊙ at the age of 1 and 1.5 Myr. The density in the core of R 136 (0.1-1.4 pc) is estimated and extrapolated in 3D and larger radii (up to 6 pc). We show that the stars in the core are still unresolved due to crowding, and the results we obtained are upper limits. Higher angular resolution is mandatory to overcome these difficulties. Based on data collected at the European Southern Observatory, Chile, Guaranteed Time Observation 095.D-0309(K).The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A56

Compaction of granular materials: numerical simulation of "elastic" compression and pressure solution creep

NASA Astrophysics Data System (ADS)

Bernabe, Y.; Evans, J.

2012-12-01

In a previous work we investigated stress transfer in a pair of grain contacts undergoing pressure solution (PS) creep, showed that stress transfer resulted in a significant decrease in overall strain rate, and concluded that PS creep rates of a randomly packed granular aggregate should be affected by packing evolution and the formation of new contacts during creep. To test these conclusions further, we are numerically simulating the "elastic" hydrostatic compression of a random pack of spheres, using a numerical method similar to that of Cundall and Strack [1979]. We assumed that the spheres were frictionless (i.e., spheres in contact only interacted through normal forces) and that the contact forces obeyed the non-linear Digby [1981] model. In order to determine the PS creep compression of the sphere pack subjected to a constant confining pressure pc, we calculated the thicknesses of the dissolved layers at each individual grain contact during a small time increment and, from these, the overall deformation of the sphere pack. We used an analytical expression discussed in our previous paper and originating from Lehner and Leroy [2004]. During these simulations, we also computed the mean coordination number of the grain contact z, the effective bulk modulus K of the sphere pack and others parameters characterizing the topological and mechanical properties of the sphere assembly. Our results show strong non-linear increase of z and K with pc during "elastic" compression and, with time, during PS creep. The packing rearrangements associated with PS creep produce complex time dependence of the overall deformation ɛ(t). We observed a regular transition from ɛ∝t^3/4 at early times (i.e., less than 0.1 years) and ɛ∝t^1/3 at late times (i.e., more than 1000 years). Cundall, P.A., and O.D.L. Strack (1979), A discrete numerical model for granular assemblies, Geotech., 29, 47-65. Digby, P.J. (1981), The effective elastic moduli of porous rocks, J. Appl. Mech., 48, 803-808. Lehner, F.K., and Y. Leroy (2004), Sandstone compaction by intergranular pressure solution, In Mech. Fluid Saturated Rocks (eds. Y. Guéguen and M. Boutéca), Elsevier.

Acquisition of /s/-Clusters in Dutch-Speaking Children with Phonological Disorders

ERIC Educational Resources Information Center

Gerrits, Ellen

2010-01-01

This study investigated the acquisition of word initial s clusters of 3-5 year old Dutch children with phonological disorders. Within these clusters, sl was produced correctly most often, whereas sn and sx were the more difficult clusters. In cluster reductions, s+obstruent and sl clusters reduction patterns followed the Sonority Sequencing…

Hyperfine coupling constants on inner-sphere water molecules of Gd(III)-based MRI contrast agents.

PubMed

Esteban-Gómez, David; de Blas, Andrés; Rodríguez-Blas, Teresa; Helm, Lothar; Platas-Iglesias, Carlos

2012-11-12

Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Gd(H(2)O)(8)](3+) and different Gd(III)-based magnetic resonance imaging contrast agents such as [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)]. DFT calculations performed on the [Gd(H(2)O)(8)](3+) model system show that both hybrid-GGA functionals (BH&HLYP, B3PW91 and PBE1PBE) and the hybrid meta-GGA functional TPSSh provide (17)O HFCCs in close agreement with the experimental data. The use of all-electron relativistic approaches based on the DKH2 approximation and the use of relativistic effective core potentials (RECP) provide results of essentially the same quality. The accurate calculation of HFCCs on the [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)] complexes requires an adequate description of solvent effects. This was achieved by using a mixed cluster/continuum approach that includes explicitly two second-sphere water molecules. The calculated isotropic (17)O HFCCs (A(iso)) fall within the range 0.40-0.56 MHz, and show deviations from the corresponding experimental values typically lower than 0.05 MHz. The A(iso) values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Gd(III) ion, as well as by the orientation of the water molecule plane with respect to the Gd-O vector. (1)H HFCCs of coordinated water molecules and (17)O HFCCs of second-sphere water molecules take values close to zero. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Torsional Alfvén Waves in a Dipolar Magnetic Field

NASA Astrophysics Data System (ADS)

Nataf, H. C.; Tigrine, Z.; Cardin, P.; Schaeffer, N.

2017-12-01

The discovery of torsional Alfvén waves in the Earth's core (Gillet et al, 2010) is a strong motivation for investigating the properties of these waves. Here, we report on the first experimental study of such waves. Alfvén waves are difficult to excite and observe in liquid metals because of their high magnetic diffusivity. Nevertheless, we obtained clear signatures of such diffusive waves in our DTS experiment. In this setup, some 40 liters of liquid sodium are contained between a ro = 210 mm-radius stainless steel outer shell, and a ri = 74 mm-radius copper inner sphere. Both spherical boundaries can rotate independently around a common vertical axis. The inner sphere shells a strong permanent magnet, which produces a nearly dipolar magnetic field whose intensity falls from 175 mT at ri to 8 mT at ro in the equatorial plane. We excite Alfvén waves in the liquid sodium by applying a sudden jerk of the inner sphere. To study the effect of global rotation, which leads to the formation of geostrophic torsional Alfvén waves, we spin the experiment at rotation rates fo = fi up to 15 Hz. The Alfvén wave produces a clear azimuthal magnetic signal on magnetometers installed in a sleeve inside the fluid. We also probe the associated azimuthal velocity field using ultrasound Doppler velocimetry. Electric potentials at the surface of the outer sphere turn out to be very revealing as well. In parallel, we use the XSHELLS magnetohydrodynamics spherical code to model torsional Alfvén waves in the experimental conditions, and beyond. We explore both linear and non-linear regimes. We observe a strong excitation of inertial waves in the equatorial plane, where the wave transits from a region of strong magnetic field to a region dominated by rotation (see figure of meridian map of azimuthal velocity). These novel observations should help deciphering the dynamics of Alfvén waves in planetary cores.

Biosynthetic Genes for the Tetrodecamycin Antibiotics

PubMed Central

Gverzdys, Tomas

2016-01-01

ABSTRACT We recently described 13-deoxytetrodecamycin, a new member of the tetrodecamycin family of antibiotics. A defining feature of these molecules is the presence of a five-membered lactone called a tetronate ring. By sequencing the genome of a producer strain, Streptomyces sp. strain WAC04657, and searching for a gene previously implicated in tetronate ring formation, we identified the biosynthetic genes responsible for producing 13-deoxytetrodecamycin (the ted genes). Using the ted cluster in WAC04657 as a reference, we found related clusters in three other organisms: Streptomyces atroolivaceus ATCC 19725, Streptomyces globisporus NRRL B-2293, and Streptomyces sp. strain LaPpAH-202. Comparing the four clusters allowed us to identify the cluster boundaries. Genetic manipulation of the cluster confirmed the involvement of the ted genes in 13-deoxytetrodecamycin biosynthesis and revealed several additional molecules produced through the ted biosynthetic pathway, including tetrodecamycin, dihydrotetrodecamycin, and another, W5.9, a novel molecule. Comparison of the bioactivities of these four molecules suggests that they may act through the covalent modification of their target(s). IMPORTANCE The tetrodecamycins are a distinct subgroup of the tetronate family of secondary metabolites. Little is known about their biosynthesis or mechanisms of action, making them an attractive subject for investigation. In this paper we present the biosynthetic gene cluster for 13-deoxytetrodecamycin in Streptomyces sp. strain WAC04657. We identify related clusters in several other organisms and show that they produce related molecules. PMID:27137499

Low-temperature transonic cooling flows in galaxy clusters

NASA Technical Reports Server (NTRS)

Sulkanen, Martin E.; Burns, Jack O.; Norman, Michael L.

1989-01-01

Calculations are presented which demonstrate that cooling flow models with large sonic radii may be consistent with observed cluster gas properties. It is found that plausible cluster parameters and cooling flow mass accretion rates can produce sonic radii of 10-20 kpc for sonic point temperatures of 1-3 x 10 to the 6th K. The numerical calculations match these cooling flows to hydrostatic atmosphere solutions for the cluster gas beyond the cooling flow region. The cooling flows produce no appreciable 'holes' in the surface brightness toward the cluster center, and the model can be made to match the observed X-ray surface brightness of three clusters in which cooling flows had been believed to be absent. It is suggested that clusters with low velocity dispersion may be the natural location for such 'cool' cooling flows, and fits of these models to the X-ray surface brightness profiles for three clusters are presented.

Electromagnetic Levitation of a Disc

ERIC Educational Resources Information Center

Valle, R.; Neves, F.; de Andrade, R., Jr.; Stephan, R. M.

2012-01-01

This paper presents a teaching experiment that explores the levitation of a disc of ferromagnetic material in the presence of the magnetic field produced by a single electromagnet. In comparison to the classical experiment of the levitation of a sphere, the main advantage of the proposed laboratory bench is that the uniform magnetic field…

Evaluation of head and face injury potential of current airline seats during crash decelerations.

DOT National Transportation Integrated Search

1966-06-01

A large percentage of deaths in commercial-airline crashes is produced as the body and lower limbs flail around the seat belt. According to a previous study, a 10-foot-diameter sphere of clear area would be necessary to prevent a person from striking...

A Unit Cell Laboratory Experiment: Marbles, Magnets, and Stacking Arrangements

ERIC Educational Resources Information Center

Collins, David C.

2011-01-01

An undergraduate first-semester general chemistry laboratory experiment introducing face-centered, body-centered, and simple cubic unit cells is presented. Emphasis is placed on the stacking arrangement of solid spheres used to produce a particular unit cell. Marbles and spherical magnets are employed to prepare each stacking arrangement. Packing…

Crystal growth of artificial snow

NASA Technical Reports Server (NTRS)

Kimura, S.; Oka, A.; Taki, M.; Kuwano, R.; Ono, H.; Nagura, R.; Narimatsu, Y.; Tanii, J.; Kamimiytat, Y.

1984-01-01

Snow crystals were grown onboard the space shuttle during STS-7 and STS-8 to facilitate the investigation of crystal growth under conditions of weightlessness. The experimental design and hardware are described. Space-grown snow crystals were polyhedrons looking like spheres, which were unlike snow crystals produced in experiments on Earth.

Using cuttlefish ink as an additive to produce -non-iridescent structural colors of high color visibility.

PubMed

Zhang, Yafeng; Dong, Biqin; Chen, Ang; Liu, Xiaohan; Shi, Lei; Zi, Jian

2015-08-26

Non-iridescent structural colors of high color visibility are produced by amorphous photonic structures, in which -natural cuttlefish ink is used as an additive to break down the long-range order of the structures. The color hue and its spectral purity can be tuned by adjusting the diameter of the polystyrene (PS) spheres and the proportion of ink particles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Methods for quantitative infrared directional-hemispherical and diffuse reflectance measurements using an FTIR and a commercial integrating sphere

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

Blake, Thomas A.; Johnson, Timothy J.; Tonkyn, Russell G.

Infrared integrating sphere measurements of solid samples are important in providing reference data for contact, standoff and remote sensing applications. At the Pacific Northwest National Laboratory (PNNL) we have developed protocols to measure both the directional-hemispherical ( and diffuse (d) reflectances of powders, liquids, and disks of powders and solid materials using a commercially available, matte gold-coated integrating sphere and Fourier transform infrared spectrometer. Detailed descriptions of the sphere alignment and its use for making these reflectance measurements are given. Diffuse reflectance values were found to be dependent on the bidirectional reflection distribution function (BRDF) of the sample and themore » solid angle intercepted by the sphere’s specular exclusion port. To determine how well the sphere and protocols produce quantitative reflectance data, measurements were made of three diffuse and two specular standards prepared by the National institute of Standards and Technology (NIST, USA), LabSphere Infragold and Spectralon standards, hand-loaded sulfur and talc powder samples, and water. The five NIST standards behaved as expected: the three diffuse standards had a high degree of “diffuseness,” d/ = D > 0.9, whereas the two specular standards had D ≤ 0.03. The average absolute differences between the NIST and PNNL measurements of the NIST standards for both directional-hemispherical and diffuse reflectances are on the order of 0.01 reflectance units. Other quantitative differences between the PNNL-measured and calibration (where available) or literature reflectance values for these standards and materials are given and the possible origins of discrepancies are discussed. Random uncertainties and estimates of systematic uncertainties are presented. Corrections necessary to provide better agreement between the PNNL reflectance values as measured for the NIST standards and the NIST reflectance values for these same standards are also discussed.« less

Toward GEOS-6, A Global Cloud System Resolving Atmospheric Model

NASA Technical Reports Server (NTRS)

Putman, William M.

2010-01-01

NASA is committed to observing and understanding the weather and climate of our home planet through the use of multi-scale modeling systems and space-based observations. Global climate models have evolved to take advantage of the influx of multi- and many-core computing technologies and the availability of large clusters of multi-core microprocessors. GEOS-6 is a next-generation cloud system resolving atmospheric model that will place NASA at the forefront of scientific exploration of our atmosphere and climate. Model simulations with GEOS-6 will produce a realistic representation of our atmosphere on the scale of typical satellite observations, bringing a visual comprehension of model results to a new level among the climate enthusiasts. In preparation for GEOS-6, the agency's flagship Earth System Modeling Framework [JDl] has been enhanced to support cutting-edge high-resolution global climate and weather simulations. Improvements include a cubed-sphere grid that exposes parallelism; a non-hydrostatic finite volume dynamical core, and algorithm designed for co-processor technologies, among others. GEOS-6 represents a fundamental advancement in the capability of global Earth system models. The ability to directly compare global simulations at the resolution of spaceborne satellite images will lead to algorithm improvements and better utilization of space-based observations within the GOES data assimilation system

Cluster beam targets for laser plasma extreme ultraviolet and soft x-ray sources

DOEpatents

Kublak, G.D.; Richardson, M.C.

1996-11-19

Method and apparatus for producing extreme ultraviolet (EUV) and soft x-ray radiation from an ultra-low debris plasma source are disclosed. Targets are produced by the free jet expansion of various gases through a temperature controlled nozzle to form molecular clusters. These target clusters are subsequently irradiated with commercially available lasers of moderate intensity (10{sup 11}--10{sup 12} watts/cm{sup 2}) to produce a plasma radiating in the region of 0.5 to 100 nanometers. By appropriate adjustment of the experimental conditions the laser focus can be moved 10--30 mm from the nozzle thereby eliminating debris produced by plasma erosion of the nozzle. 5 figs.

Cluster beam targets for laser plasma extreme ultraviolet and soft x-ray sources

DOEpatents

Kublak, Glenn D.; Richardson, Martin C. (CREOL

1996-01-01

Method and apparatus for producing extreme ultra violet (EUV) and soft x-ray radiation from an ultra-low debris plasma source are disclosed. Targets are produced by the free jet expansion of various gases through a temperature controlled nozzle to form molecular clusters. These target clusters are subsequently irradiated with commercially available lasers of moderate intensity (10.sup.11 -10.sup.12 watts/cm.sup.2) to produce a plasma radiating in the region of 0.5 to 100 nanometers. By appropriate adjustment of the experimental conditions the laser focus can be moved 10-30 mm from the nozzle thereby eliminating debris produced by plasma erosion of the nozzle.

Polyhedral protein cages encase synaptic vesicles and participate in their attachment to the active zone.

PubMed

Zampighi, G A; Fisher, R S

1997-08-01

In an effort to elucidate the interactions between synaptic vesicles and the membrane of the active zone, we have investigated the structure of interneuronal asymmetric synapses in the neocortex of adult rats using thin-sectioning, freeze-fracture, and negative staining electron microscopy. We identified three subtypes of spherical synaptic vesicles. Type I were agranular vesicles of 47.5 +/- 3.8 nm (mean SD, n = 24) in diameter usually seen aggregated in clusters in the presynaptic bouton. Type II synaptic vesicles were composed of a approximately 45-nm-diameter lipid bilayer sphere encased in a cage 77 +/- 4.6 nm (mean SD, n = 42) in diameter. The cage was composed of open-faced pentamers 20-22 nm/side arranged as a regular polyhedron. Type II caged vesicles were found in clusters at the boutons, adhered to the active zone, and were also present in axons. Type III synaptic vesicles appeared as electron-dense spheres 60-75 nm in diameter abutted to the membrane of the active zone. Clathrin-coated vesicles and pits of 116.6 +/- 9 nm (mean SD, n = 14) in diameter were also present in both the pre- and postsynaptic sides. Freeze-fracture showed that some intrinsic membrane proteins in the active zone were arranged as pentamers exhibiting the same dimension of those forming cages (approximately 22 nm/side). From these data, we concluded that: (a) the presynaptic bouton contains a heterogeneous population of "caged" and "plain" synaptic vesicles and (b) type II synaptic vesicles bind to receptors in the active zone. Therefore, current models of transmitter release should take into account the substantial heterogeneity of the vesicle population and the binding of vesicular cages to the membrane of the active zone.

Convergence of QM/MM and Cluster Models for the Spectroscopic Properties of the Oxygen-Evolving Complex in Photosystem II.

PubMed

Retegan, Marius; Neese, Frank; Pantazis, Dimitrios A

2013-08-13

The latest crystal structure of photosystem II at 1.9 Å resolution, which resolves the topology of the Mn4CaO5 oxygen evolving complex (OEC) at atomistic detail, enables a better correlation between structural features and spectroscopic properties than ever before. Building on the refined crystallographic model of the OEC and the protein, we present combined quantum mechanical/molecular mechanical (QM/MM) studies of the spectroscopic properties of the natural catalyst embedded in the protein matrix. Focusing on the S2 state of the catalytic cycle, we examine the convergence of not only structural parameters but also of the intracluster magnetic interactions in terms of exchange coupling constants and of experimentally relevant (55)Mn, (17)O, and (14)N hyperfine coupling constants with respect to QM/MM partitioning using five QM regions of increasing size. This enables us to assess the performance of the method and to probe second sphere effects by identifying amino acid residues that principally affect the spectroscopic properties of the OEC. Comparison between QM-only and QM/MM treatments reveals that whereas QM/MM models converge quickly to stable values, the QM cluster models need to incorporate significantly larger parts of the second coordination sphere and surrounding water molecules to achieve convergence for certain properties. This is mainly due to the sensitivity of the QM-only models to fluctuations in the hydrogen bonding network and ligand acidity. Additionally, a hydrogen bond that is typically omitted in QM-only treatments is shown to determine the hyperfine coupling tensor of the unique Mn(III) ion by regulating the rotation plane of the ligated D1-His332 imidazole ring, the only N-donor ligand of the OEC.

Sub-10 nm Silicon Nanopillar Fabrication Using Fast and Brushless Thermal Assembly of PS-b-PDMS Diblock Copolymer.

PubMed

Garnier, Jérôme; Arias-Zapata, Javier; Marconot, Olivier; Arnaud, Sandrine; Böhme, Sophie; Girardot, Cécile; Buttard, Denis; Zelsmann, Marc

2016-04-20

A new approach to obtaining spherical nanodomains using polystyrene-block-polydimethylsiloxane (PS-b-PDMS) is proposed. To reduce drastically the process time, we blended a copolymer with cylindrical morphology with a PS homopolymer. Adding PS homopolymer into a low-molar-mass cylindrical morphology PS-b-PDMS system drives it toward a spherical morphology. Besides, by controlling the as-spun state, spherical PDMS nanodomains could be kept and thermally arranged. This PS-homopolymer addition allows not only an efficient, purely thermal arrangement process of spheres but also the ability to work directly on nontreated silicon substrates. Indeed, as shown by STEM measurements, no PS brush surface treatment was necessary in our study to avoid a PDMS wetting layer at the interface with the Si substrate. Our approach was compared to a sphere-forming diblock copolymer, which needs a longer thermal annealing. Furthermore, GISAXS measurements provided complete information on PDMS sphere features. Excellent long-range order spherical microdomains were therefore produced on flat surfaces and inside graphoepitaxy trenches with a period of 21 nm, as were in-plane spheres with a diameter of 8 nm with a 15 min thermal annealing. Finally, direct plasma-etching transfer into the silicon substrate was demonstrated, and 20 nm high silicon nanopillars were obtained, which are very promising results for various nanopatterning applications.

Enhanced removal of toxic Cr(VI) in tannery wastewater by photoelectrocatalysis with synthetic TiO2 hollow spheres

NASA Astrophysics Data System (ADS)

Zhao, Yang; Chang, Wenkai; Huang, Zhiding; Feng, Xugen; Ma, Lin; Qi, Xiaoxia; Li, Zenghe

2017-05-01

Owing to the acute toxicity and mobility, the Cr(VI) in tannery wastewater is a huge threat to biological and environmental systems. Herein, an effective photoelectrocatalytic reduction of Cr(VI) was carried out by applying electric field to photocatalysis of as-prepared TiO2 spheres. The synthesis of spherical TiO2 catalytic materials with hollow structure and high surface areas was based on a self-assembly process induced by a mixture of organic acetic acid and ethanol. The possible formation mechanism of TiO2 spheres was proposed and verified by acid concentration-dependent and temperature-dependent experiments. It was found that the reaction rate constant of photoelectrocatalytic reduction of Cr(VI) exhibited an almost 3 fold improvement (0.0362 min-1) as compared to that of photocatalysis (0.0126 min-1). As a result, the mechanism of photoelectrocatalytic reduction of Cr(VI) was described according to the simultaneous determination of Cr(VI), Cr(III) and total Cr in the system. In addition, the effect of pH value and voltage of potential were also discussed. Moreover, this photoelectrocatalysis with TiO2 hollow spheres exhibited excellent activity for reduction of Cr(VI) in actual tannery wastewater produced from three different tanning procedures. These attributes suggest that this photoelectrocatalysis has strong potential applications in the treatment of tannery pollutants.

Boiling characteristics of dilute polymer solutions and implications for the suppression of vapor explosions

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

Bang, K.H.; Kim, M.H.

Quenching experiments of hot solid spheres in dilute aqueous solutions of polyethylene oxide polymer have been conducted for the purpose of investigating the physical mechanisms of the suppression of vapor explosions in this polymer solutions. Two spheres of 22.2mm and 9.5mm-diameter were tested in the polymer solutions of various concentrations at 30{degrees}C. Minimum film boiling temperature ({Delta}T{sub MFB}) in this highly-subcooled liquid rapidly decreased from over 700{degrees}c for pure water to about 150{degrees}C as the polymer concentration was increased up to 300ppm for 22.2mm sphere, and it decreased to 350{degrees}C for 9.5mm sphere. This rapid reduction of minimum film boilingmore » temperature in the PEO aqueous solutions can explain its ability of the suppression of spontaneous vapor explosions. The ability of suppression of vapor explosions by dilute polyethylene oxide solutions against an external trigger pressure was tested by dropping molten tin into the polymer solutions at 25{degrees}C. It was observed that in 50ppm solutions more mass fragmented than in pure water, but produced weaker explosion pressures. The explosion was completely suppressed in 300ppm solutions with the external trigger. The debris size distributions of fine fragments smaller than 0.7mm were shown almost identical regardless of the polymer concentrations.« less

The ergot alkaloid gene cluster: functional analyses and evolutionary aspects.

PubMed

Lorenz, Nicole; Haarmann, Thomas; Pazoutová, Sylvie; Jung, Manfred; Tudzynski, Paul

2009-01-01

Ergot alkaloids and their derivatives have been traditionally used as therapeutic agents in migraine, blood pressure regulation and help in childbirth and abortion. Their production in submerse culture is a long established biotechnological process. Ergot alkaloids are produced mainly by members of the genus Claviceps, with Claviceps purpurea as best investigated species concerning the biochemistry of ergot alkaloid synthesis (EAS). Genes encoding enzymes involved in EAS have been shown to be clustered; functional analyses of EAS cluster genes have allowed to assign specific functions to several gene products. Various Claviceps species differ with respect to their host specificity and their alkaloid content; comparison of the ergot alkaloid clusters in these species (and of clavine alkaloid clusters in other genera) yields interesting insights into the evolution of cluster structure. This review focuses on recently published and also yet unpublished data on the structure and evolution of the EAS gene cluster and on the function and regulation of cluster genes. These analyses have also significant biotechnological implications: the characterization of non-ribosomal peptide synthetases (NRPS) involved in the synthesis of the peptide moiety of ergopeptines opened interesting perspectives for the synthesis of ergot alkaloids; on the other hand, defined mutants could be generated producing interesting intermediates or only single peptide alkaloids (instead of the alkaloid mixtures usually produced by industrial strains).

Various nanoparticle morphologies and surface properties of waterborne polyurethane controlled by water

PubMed Central

Zhou, Xing; Fang, Changqing; Lei, Wanqing; Du, Jie; Huang, Tingyi; Li, Yan; Cheng, Youliang

2016-01-01

Water plays important roles in organic reactions such as polyurethane synthesis, and the aqueous solution environment affects polymer morphology and other properties. This paper focuses on the morphology and surface properties of waterborne polyurethane resulting from the organic reaction in water involving different forms (solid and liquid), temperatures and aqueous solutions. We provide evidence from TEM observations that the appearance of polyurethane nanoparticles in aqueous solutions presents diverse forms, including imperfect spheres, perfect spheres, perfect and homogenous spheres and tubes. Based on the results on FTIR, GPC, AFM and XRD experiments, we suggest that the shape of the nanoparticles may be decided by the crimp degree (i.e., the degree of polyurethane chains intertangling in the water environment) and order degree, which are determined by the molecular weight (Mn) and hydrogen bonds. Meanwhile, solid water and high-temperature water can both reduce hard segments that gather on the polyurethane film surface to reduce hydrophilic groups and produce a soft surface. Our findings show that water may play key roles in aqueous polymer formation and bring order to molecular chains. PMID:27687001

Light diffusing films fabricated by strawberry-like PMMA/SiO₂ composite microspheres for LED application.

PubMed

Guo, Shuang; Zhou, Shuxue; Li, Huijing; You, Bo

2015-06-15

This paper presents a facile method to fabricate volumetric light diffusing films with high transmittance and haze simultaneously by mimicking the micro- and nanostructure of compound eyes. Strawberry-like polymethyl methacrylate/SiO2 composite microspheres were first prepared via the electrostatic attraction between positively charged PMMA spheres and negatively charged SiO2 nanoparticles, and further blended with polyacrylate latex to produce light diffusing coatings. A novel light diffusing film with hemispherical surface was built by casting the light diffusing coatings on optical-grade PET film. Effects of the sizes of PMMA spheres and SiO2 nanoparticles on the optical properties of light diffusing film were investigated by a haze meter and application on a LED lamp. The best result (transmittance 94.6% and haze 84.2%) was achieved for the strawberry-like composite microspheres based on 1 μm PMMA spheres and 50 nm SiO2 nanoparticles. The light-diffusing mechanism of the strawberry-like microspheres in the film was discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

Synthesis and characterizations of spherical hollow composed of AgI nanoparticle using AgBr as the precursor

NASA Astrophysics Data System (ADS)

Yang, Ming; Zhou, Kui

2011-01-01

Hollow spheres of AgI with an average radius of 100-200 nm have been prepared by a simple reaction between AgBr suspension and KI in the presence of gelatin. Gelatin played a decisive role as an inhibitor of the direct attack of I- ions to AgBr surfaces and coagulation of the growing AgI in producing the spherical AgI particles. The products were characterized by X-ray powder diffraction, transmission electron microscopy, UV-vis absorption spectroscopy and X-ray photoelectron spectra techniques. The band gaps are estimated to be 2.95 eV according to the results of optical measurements of the hollow spheres of AgI.

The sirodesmin biosynthetic gene cluster of the plant pathogenic fungus Leptosphaeria maculans.

PubMed

Gardiner, Donald M; Cozijnsen, Anton J; Wilson, Leanne M; Pedras, M Soledade C; Howlett, Barbara J

2004-09-01

Sirodesmin PL is a phytotoxin produced by the fungus Leptosphaeria maculans, which causes blackleg disease of canola (Brassica napus). This phytotoxin belongs to the epipolythiodioxopiperazine (ETP) class of toxins produced by fungi including mammalian and plant pathogens. We report the cloning of a cluster of genes with predicted roles in the biosynthesis of sirodesmin PL and show via gene disruption that one of these genes (encoding a two-module non-ribosomal peptide synthetase) is essential for sirodesmin PL biosynthesis. Of the nine genes in the cluster tested, all are co-regulated with the production of sirodesmin PL in culture. A similar cluster is present in the genome of the opportunistic human pathogen Aspergillus fumigatus and is most likely responsible for the production of gliotoxin, which is also an ETP. Homologues of the genes in the cluster were also identified in expressed sequence tags of the ETP producing fungus Chaetomium globosum. Two other fungi with publicly available genome sequences, Magnaporthe grisea and Fusarium graminearum, had similar gene clusters. A comparative analysis of all four clusters is presented. This is the first report of the genes responsible for the biosynthesis of an ETP. Copyright 2004 Blackwell Publishing Ltd

An insight into the distribution, genetic diversity, and mycotoxin production of Aspergillus section Flavi in soils of pistachio orchards.

PubMed

Jamali, Mojdeh; Ebrahimi, Mohammad-Ali; Karimipour, Morteza; Shams-Ghahfarokhi, Masoomeh; Dinparast-Djadid, Navid; Kalantari, Sanaz; Pilehvar-Soltanahmadi, Yones; Amani, Akram; Razzaghi-Abyaneh, Mehdi

2012-01-01

In the present study, 193 Aspergillus strains were isolated from a total of 100 soil samples of pistachio orchards, which all of them were identified as Aspergillus flavus as the most abundant species of Aspergillus section Flavi existing in the environment. Approximately 59%, 81%, and 61% of the isolates were capable of producing aflatoxins (AFs), cyclopiazonic acid (CPA), and sclerotia, respectively. The isolates were classified into four chemotypes (I to IV) based on the ability to produce AFs and CPA. The resulting dendrogram of random amplified polymorphic DNA (RAPD) analysis of 24 selected A. flavus isolates demonstrated the formation of two separate clusters. Cluster 1 contained both aflatoxigenic and non-aflatoxigenic isolates (17 isolates), whereas cluster 2 comprised only aflatoxigenic isolates (7 isolates). All the isolates of cluster 2 produced significantly higher levels of AFs than those of cluster 1 and the isolates that produced both AFB(1) and AFB(2) were found only in cluster 2. RAPD genotyping allowed the differentiation of A. flavus from Aspergillus parasiticus as a closely related species within section Flavi. The present study has provided for the first time the relevant information on distribution and genetic diversity of different A. flavus populations from nontoxigenic to highly toxigenic enable to produce hazardous amounts of AFB(1) and CPA in soils of pistachio orchards. These fungi, either toxigenic or not-toxigenic, should be considered as potential threats for agriculture and public health.

Hubble Admires a Youthful Globular Star Cluster

NASA Image and Video Library

2017-12-08

Hubble sees an unusal global cluster that is enriching the interstellar medium with metals Globular clusters offer some of the most spectacular sights in the night sky. These ornate spheres contain hundreds of thousands of stars, and reside in the outskirts of galaxies. The Milky Way contains over 150 such clusters — and the one shown in this NASA/ESA Hubble Space Telescope image, named NGC 362, is one of the more unusual ones. As stars make their way through life they fuse elements together in their cores, creating heavier and heavier elements — known in astronomy as metals — in the process. When these stars die, they flood their surroundings with the material they have formed during their lifetimes, enriching the interstellar medium with metals. Stars that form later therefore contain higher proportions of metals than their older relatives. By studying the different elements present within individual stars in NGC 362, astronomers discovered that the cluster boasts a surprisingly high metal content, indicating that it is younger than expected. Although most globular clusters are much older than the majority of stars in their host galaxy, NGC 362 bucks the trend, with an age lying between 10 and 11 billion years old. For reference, the age of the Milky Way is estimated to be above 13 billion years. This image, in which you can view NGC 362’s individual stars, was taken by Hubble’s Advanced Camera for Surveys (ACS). Credit: ESA/Hubble& NASA NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Impact of heuristics in clustering large biological networks.

PubMed

Shafin, Md Kishwar; Kabir, Kazi Lutful; Ridwan, Iffatur; Anannya, Tasmiah Tamzid; Karim, Rashid Saadman; Hoque, Mohammad Mozammel; Rahman, M Sohel

2015-12-01

Traditional clustering algorithms often exhibit poor performance for large networks. On the contrary, greedy algorithms are found to be relatively efficient while uncovering functional modules from large biological networks. The quality of the clusters produced by these greedy techniques largely depends on the underlying heuristics employed. Different heuristics based on different attributes and properties perform differently in terms of the quality of the clusters produced. This motivates us to design new heuristics for clustering large networks. In this paper, we have proposed two new heuristics and analyzed the performance thereof after incorporating those with three different combinations in a recently celebrated greedy clustering algorithm named SPICi. We have extensively analyzed the effectiveness of these new variants. The results are found to be promising. Copyright © 2015 Elsevier Ltd. All rights reserved.

Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition.

PubMed

Emery, S B; Xin, Y; Ridge, C J; Buszek, R J; Boatz, J A; Boyle, J M; Little, B K; Lindsay, C M

2015-02-28

We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structure at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.

Process for Making a Noble Metal on Tin Oxide Catalyst

NASA Technical Reports Server (NTRS)

Davis, Patricia; Miller, Irvin; Upchurch, Billy

2010-01-01

To produce a noble metal-on-metal oxide catalyst on an inert, high-surface-area support material (that functions as a catalyst at approximately room temperature using chloride-free reagents), for use in a carbon dioxide laser, requires two steps: First, a commercially available, inert, high-surface-area support material (silica spheres) is coated with a thin layer of metal oxide, a monolayer equivalent. Very beneficial results have been obtained using nitric acid as an oxidizing agent because it leaves no residue. It is also helpful if the spheres are first deaerated by boiling in water to allow the entire surface to be coated. A metal, such as tin, is then dissolved in the oxidizing agent/support material mixture to yield, in the case of tin, metastannic acid. Although tin has proven especially beneficial for use in a closed-cycle CO2 laser, in general any metal with two valence states, such as most transition metals and antimony, may be used. The metastannic acid will be adsorbed onto the high-surface-area spheres, coating them. Any excess oxidizing agent is then evaporated, and the resulting metastannic acid-coated spheres are dried and calcined, whereby the metastannic acid becomes tin(IV) oxide. The second step is accomplished by preparing an aqueous mixture of the tin(IV) oxide-coated spheres, and a soluble, chloride-free salt of at least one catalyst metal. The catalyst metal may be selected from the group consisting of platinum, palladium, ruthenium, gold, and rhodium, or other platinum group metals. Extremely beneficial results have been obtained using chloride-free salts of platinum, palladium, or a combination thereof, such as tetraammineplatinum (II) hydroxide ([Pt(NH3)4] (OH)2), or tetraammine palladium nitrate ([Pd(NH3)4](NO3)2).

Detachable microsphere scalpel tips for potential use in ophthalmic surgery with the erbium:YAG laser.

PubMed

Hutchens, Thomas C; Darafsheh, Arash; Fardad, Amir; Antoszyk, Andrew N; Ying, Howard S; Astratov, Vasily N; Fried, Nathaniel M

2014-01-01

Vitreoretinal surgery is performed using mechanical dissection that sometimes results in iatrogenic complications, including vitreous hemorrhage, retinal breaks, incomplete membrane delamination, retinal distortion, microscopic damage, etc. An ultraprecise laser probe would be an ideal tool for cutting away pathologic membranes; however, the depth of surgery should be precisely controlled to protect the sensitive underlying retina. The ultraprecise surgical microprobe formed by chains of dielectric spheres for use with the erbium:YAG laser source (λ=2940  nm), with extremely short optical penetration depth in tissue, was optimized. Numerical modeling demonstrated a potential advantage of five-sphere focusing chains of sapphire spheres with index n=1.71 for ablating the tissue with self-limited depth around 10 to 20 μm. Novel detachable microsphere scalpel tips formed by chains of 300 μm sapphire (or ruby) spheres were tested on ophthalmic tissues, ex vivo. Detachable scalpel tips could allow for reusability of expensive mid-infrared trunk fibers between procedures, and offer more surgical customization by interchanging various scalpel tip configurations. An innovative method for aiming beam integration into the microsphere scalpel to improve the illumination of the surgical site was also shown. Single Er:YAG pulses of 0.2 mJ and 75-μs duration produced ablation craters in cornea epithelium for one, three, and five sphere structures with the latter generating the smallest crater depth (10 μm) with the least amount of thermal damage depth (30 μm). Detachable microsphere laser scalpel tips may allow surgeons better precision and safety compared to mechanical scalpels when operating on delicate or sensitive areas like the retina.

Pancreatic islet-like clusters from bone marrow mesenchymal stem cells of human first-trimester abortus can cure streptozocin-induced mouse diabetes.

PubMed

Zhang, Yihua; Shen, Wenzheng; Hua, Jinlian; Lei, Anmin; Lv, Changrong; Wang, Huayan; Yang, Chunrong; Gao, Zhimin; Dou, Zhongying

2010-12-01

Bone marrow mesenchymal stem cells (BMSCs) have been reported to possess low immunogenicity and cause immunosuppression of recipients when allografted. They can differentiate into insulin-producing cells and may be a valuable source for islet formation. However, the extremely low differentiating rate of adult BMSCs toward insulin-producing cells and the insufficient insulin secretion of the differentiated BMSCs in vitro prevent their clinical use in diabetes treatment. Little is known about the potential of cell replacement therapy with human BMSCs. Previously, we isolated and identified human first-trimester fetal BMSCs (hfBMSCs). Under a novel four-step induction procedure established in this study, the hfBMSCs effectively differentiated into functional pancreatic islet-like cell clusters that contained 62 ± 14% insulin-producing cells, expressed a broad gene profile related to pancreatic islet β-cell development, and released high levels of insulin (2.245 ± 0.222 pmol/100 clusters per 30 min) and C-peptide (2.200 ± 0.468 pmol/100 clusters per 30 min) in response to 25 mmol/L glucose stimulus in vitro. The pancreatic islet-like cell clusters normalized the blood glucose level of diabetic model mice for at least 9 weeks when xenografted; blood glucose levels in these mice rose abnormally again when the grafts were removed. Examination of the grafts indicated that the transplanted cells survived in recipients and produced human insulin and C-peptide in situ. These results demonstrate that hfBMSCs derived from a human first-trimester abortus can differentiate into pancreatic islet-like cell clusters following an established four-step induction. The insulin-producing clusters present advantages in cell replacement therapy of type 1 diabetic model mice.

Parametric strong gravitational lensing analysis of Abell 1689

NASA Astrophysics Data System (ADS)

Halkola, A.; Seitz, S.; Pannella, M.

2006-11-01

We have derived the mass distribution of galaxy cluster Abell 1689 within 0.3h-170Mpc of the cluster centre using its strong lensing (SL) effect on 32 background galaxies, which are mapped in altogether 107 multiple images. The multiple images are based on some from the literature with modifications to both include new and exclude some of the original image systems. The cluster profile is explored further out to ~2.5h-170Mpc with weak lensing (WL) shear measurements from the literature. The masses of ~200 cluster galaxies are measured with the Fundamental Plane (FP) in order to model accurately the small-scale mass structure in the cluster. The cluster galaxies are modelled as elliptical truncated isothermal spheres. The scalings of the truncation radii with the velocity dispersions of galaxies are assumed to match those of: (i) field galaxies; and (ii) theoretical expectations for galaxies in dense environments. The dark matter (DM) component of the cluster is described by either non-singular isothermal ellipsoids (NSIE) or elliptical versions of the universal DM profile (elliptical Navarro, Frenk & White, ENFW). To account for substructure in the DM we allow for two DM haloes. The fitting of a non-singular isothermal sphere (NSIS) to the smooth DM component results in a velocity dispersion of 1450+39-31kms-1 and a core radius of 77+10-8h-170kpc, while a Navarro, Frenk & White (NFW) profile has an r200 of 2.86 +/- 0.16h-170Mpc (M200 = 3.2 × 1015Msolarh70) and a concentration of 4.7+0.6-0.5. The total mass profile is well described by either a NSIS profile with σ = 1514+18-17kms-1 and a core radius of rc = 71 +/- 5h-170kpc, or an NFW profile with C = 6.0 +/- 0.5 and r200 = 2.82 +/- 0.11h-170Mpc (M200 = 3.0 × 1015Msolarh70). The errors are assumed to be due to the error in assigning masses to the individual galaxies in the galaxy component. Their small size is due to the very strong constraints imposed by multiple images and the ability of the smooth DM component to adjust to uncertainties in the galaxy masses. The agreement in the total mass profile between this work and that of the literature is better than 1σ at all radii, despite the considerable differences in the methodology used. Using the same image configuration as used in the literature, we obtain a SL model that is superior to some in the literature (rms of 2.7 compared to 3.2arcsec). This is very surprising considering the larger freedom in the surface mass profile in their grid modelling. The difference is most likely a result of the careful inclusion of the cluster galaxies. Using also WL shear measurements from the literature, we can constrain the profile further out to r ~ 2.5h-170Mpc. The best-fitting parameters change to σ = 1499 +/- 15kms-1 and rc = 66 +/- 5h-170kpc for the NSIS profile and C = 7.6 +/- 0.5 and r200 = 2.55 +/- 0.07h-170Mpc (M200 = 2.3 × 1015Msolarh70) for the NFW profile.

Hierarchic Agglomerative Clustering Methods for Automatic Document Classification.

ERIC Educational Resources Information Center

Griffiths, Alan; And Others

1984-01-01

Considers classifications produced by application of single linkage, complete linkage, group average, and word clustering methods to Keen and Cranfield document test collections, and studies structure of hierarchies produced, extent to which methods distort input similarity matrices during classification generation, and retrieval effectiveness…

Biosynthetic Genes for the Tetrodecamycin Antibiotics.

PubMed

Gverzdys, Tomas; Nodwell, Justin R

2016-07-15

We recently described 13-deoxytetrodecamycin, a new member of the tetrodecamycin family of antibiotics. A defining feature of these molecules is the presence of a five-membered lactone called a tetronate ring. By sequencing the genome of a producer strain, Streptomyces sp. strain WAC04657, and searching for a gene previously implicated in tetronate ring formation, we identified the biosynthetic genes responsible for producing 13-deoxytetrodecamycin (the ted genes). Using the ted cluster in WAC04657 as a reference, we found related clusters in three other organisms: Streptomyces atroolivaceus ATCC 19725, Streptomyces globisporus NRRL B-2293, and Streptomyces sp. strain LaPpAH-202. Comparing the four clusters allowed us to identify the cluster boundaries. Genetic manipulation of the cluster confirmed the involvement of the ted genes in 13-deoxytetrodecamycin biosynthesis and revealed several additional molecules produced through the ted biosynthetic pathway, including tetrodecamycin, dihydrotetrodecamycin, and another, W5.9, a novel molecule. Comparison of the bioactivities of these four molecules suggests that they may act through the covalent modification of their target(s). The tetrodecamycins are a distinct subgroup of the tetronate family of secondary metabolites. Little is known about their biosynthesis or mechanisms of action, making them an attractive subject for investigation. In this paper we present the biosynthetic gene cluster for 13-deoxytetrodecamycin in Streptomyces sp. strain WAC04657. We identify related clusters in several other organisms and show that they produce related molecules. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Quality Evaluation of Agricultural Distillates Using an Electronic Nose

PubMed Central

Dymerski, Tomasz; Gębicki, Jacek; Wardencki, Waldemar; Namieśnik, Jacek

2013-01-01

The paper presents the application of an electronic nose instrument to fast evaluation of agricultural distillates differing in quality. The investigations were carried out using a prototype of electronic nose equipped with a set of six semiconductor sensors by FIGARO Co., an electronic circuit converting signal into digital form and a set of thermostats able to provide gradient temperature characteristics to a gas mixture. A volatile fraction of the agricultural distillate samples differing in quality was obtained by barbotage. Interpretation of the results involved three data analysis techniques: principal component analysis, single-linkage cluster analysis and cluster analysis with spheres method. The investigations prove the usefulness of the presented technique in the quality control of agricultural distillates. Optimum measurements conditions were also defined, including volumetric flow rate of carrier gas (15 L/h), thermostat temperature during the barbotage process (15 °C) and time of sensor signal acquisition from the onset of the barbotage process (60 s). PMID:24287525

Enhancement of photothermal heat generation by metallodielectric nanoplasmonic clusters.

PubMed

Ahmadivand, Arash; Pala, Nezih; Güney, Durdu Ö

2015-06-01

A four-member homogenous quadrumer composed of silver core-shell nanostructures is tailored to enhance photothermal heat generation efficiency in sub-nanosecond time scale. Calculating the plasmonic and photothermal responses of metallic cluster, we show that it is possible to achieve thermal heat flux generation of 64.7 μW.cm^-2 and temperature changes in the range of ΔT = 150 K, using Fano resonant effect. Photothermal heat generation efficiency is even further enhanced by adding carbon nanospheres to the offset gap between particles and obtained thermal heat flux generation of 93.3 μW.cm^-2 and temperature increase of ΔT = 172 K. It is also shown that placement of dielectric spheres gives rise to arise collective magnetic dark plasmon modes that improves the quality of the observed Fano resonances. The presented data attests the superior performance of the proposed metallodielectric structures to utilize in practical tumor and cancer therapies and drug delivery applications.

Scaling, clustering and avalanches for steel beads in an external magnetic field

NASA Astrophysics Data System (ADS)

Marquinez, Alyse; Thvedt, Ingrid; Lehman, S. Y.; Jacobs, D. T.

2011-03-01

We investigated avalanches using uniform 3mm steel spheres (``beads'') dropped onto a conical bead pile within a uniform magnetic field. The bead pile is built by pouring beads onto a circular base where the bottom layer of beads had been glued randomly. Beads are then individually dropped from a fixed height after which the pile is massed. This process is repeated for thousands of bead drops. By measuring the number of avalanches of a given size that occurred during the experiment, the resulting avalanche size distribution was compared to a power law description as predicted by self-organized criticality. As the magnetic field intensity increased, the beads clustered to give a larger angle of repose and we measured the change in the avalanche size distribution. The moments of the distribution give a sensitive test of mean-field theory as the universality class for these bead piles. We acknowledge support from Research Corporation and NSF-REU grant DMR 0649112.

Galactic Tidal Shocks Effects in Globular Clusters

NASA Astrophysics Data System (ADS)

Cruz, F.; Aguilar, L.

2001-07-01

We present results of a set of N--Body simulations of 105--particle King models in the presence of a realistic Galactic tidal field. Tidal effects over a cluster are dominated by two processes, differentiated by the way they produc e mass loss in the system. The first one is the Roche lobe overflow, which depend s directly on the ratio of cluster to the Roche lobe size. The second process is tidal heating, produced by the time varying part of the Galactic tide, which injects energy directly on the orbits of the stars inside the cluster.

Scattering Amplitudes from Intersection Theory

NASA Astrophysics Data System (ADS)

Mizera, Sebastian

2018-04-01

We use Picard-Lefschetz theory to prove a new formula for intersection numbers of twisted cocycles associated with a given arrangement of hyperplanes. In a special case when this arrangement produces the moduli space of punctured Riemann spheres, intersection numbers become tree-level scattering amplitudes of quantum field theories in the Cachazo-He-Yuan formulation.

Micro-heterogeneity of corn hulls cellulosic fiber biopolymer studied by multiple-particle tracking (MPT)

USDA-ARS?s Scientific Manuscript database

A novel technique named multiple-particle tracking (MPT) was used to investigate the micro-structural heterogeneities of Z-trim, a zero calorie cellulosic fiber biopolymer produced from corn hulls. The principle of MPT technique is to monitor the thermally driven motion of inert micro-spheres, which...

Tricky Circuitry

ERIC Educational Resources Information Center

Davies, Tony

2014-01-01

Teaching children about circuits and the way electricity works is a "tricky business" because it is invisible. Just imagine all eyes are on the teacher as he or she produces for the class what looks like a ping-pong ball and then, with a wave of their hand, the incredible happens! This wonderful white sphere begins to glow red and a…

The Market Transformation of the System of Education in Russia

ERIC Educational Resources Information Center

Lukashenko, M.

2004-01-01

The market of educational services represents a socially oriented mechanism that ensures a constant link between the producers and consumers of economic goods in the sphere of education. For the purpose of guarding against negative effects of a purely market mechanism, it is supplemented by elements of state regulation. In other countries, the…

Antiques Roadshow visits Stennis

NASA Image and Video Library

2010-07-23

Associate producer Adam Monahan (right) looks on as Antiques Roadshow Host Mark Walberg (left) discusses space toys with expert toy appraiser Noel Barrett in the StenniSphere visitor center and museum at Stennis Space Center. The Antiques Roadshow program shown on Public Broadcasting System stations across the nation visited Stennis to film a space toy segment on July 23.

GEOMAG[TM] Paradoxes

ERIC Educational Resources Information Center

Defrancesco, Silvia; Logiurato, Fabrizio; Karwasz, Grzegorz

2007-01-01

As often happens, a lot of physics can come out of a toy. What we found interesting is the observation of the magnetic field produced by different configurations built with GEOMAG[TM]. This toy provides small magnetic bars and steel spheres to play with. Amusing 3-D structures can be built; nevertheless, this possibility is not so obvious. Indeed,…

orbis (sphaera), circulus, via, iter, orbita -- on the terminological identification of the essential paradigm change in astronomy by Johannes Kepler. (German Title: orbis (sphaera), circulus, via, iter, orbita} -- zur terminologischen Kennzeichnung des wesentlichsten Paradigmawechsels in der Astronomie durch Johannes Kepler)

NASA Astrophysics Data System (ADS)

Krafft, Fritz

2011-08-01

The use of modern terminology hinders to understand historical astronomical texts and often misleads the reader. Therefore, this study tries to reconstruct the ideas of the way the planets seem to move against the sphere of fixed stars in a non-teleological manner, that means in the original view and with original terms. The study proceeds historically and explains: (1) Aristotle's system of homocentric spheres being hollow spheres of ether turning equally round the earth in the centre of the world, a number of which makes the apparatus of the movement of a planet which produces its apparently unequal motion. (2) Ptolemy's reductionistic system of geometric circles (eccentric deferents, epicycles etc.), which are indeed great circles on non-concentric hollow spheres, whereupon they turn around equally. The space which they take up in all is surrounded by an inner and an outer concentric spherical surface and makes the sphere of the planet. (3) John's of Sacrobosco transferring of the geometric astronomy to the Latin of Middle Ages and the commentators' precision of the Greek-Latin terms. (4) The tradition of the "Theorica planetarum" which makes this geometry physics by allotting every partial moving to a partial material hollow sphere (with spherical surfaces of different centricity) or full sphere of an epicycle (orbes particulares or partialis), a number of which makes the entire sphere of each planet (orbis totalis or totus). - Copernicus also stood within this tradition, except that his entire spheres differ from the earlier ones in size or thickness (because he eliminated the partly very big synodic epicycles and allocated their effect as a mere parallactic one to the yearly moving of the earth) and in the great intervening spaces between each other (a result of measuring the true distances of the planets on the basis of these parallactic effects). (5) Tycho Brahe's refutation of the unchangingness and unpermeableness and therefore solidity of all etherial spheres, what had been the fundamental condition for creating the indirect ways of the planets in all astronomical systems with partial or entire spheres engaging one another. It was particularly Kepler who recognizes that as a result celestial physics requires a complete change. (6) Kepler's replacement of celestial physics. He did not think any more that the apparent (unequal) way of a planet indirectly results from the combination of several equal movements of etherial partial and entire spheres. His planets move their true and real way caused directly by the joint effect of two corporal forces moving the planets both around the sun and to and from it, which latter makes the planet's speed indeed naturally unequal. For this "real way" he coins in late 1604 the specific term "orbita" (the modern "orbit", the German "Bahn". This term then little by little replaced the former non-specific, general description of the apparent or real way (as "via, iter, ambitus, circulus, circuitus" etc.), and Kepler used it increasingly from its introduction (initially frequently joined to a describing definition of this "way") up to the exclusive use in the fifth book of the "Epitome", after this "orbita" had changed its shape from a perfect eccentric circle to an oval and finally an elliptic form. This way Kepler marks the paradigm change of astronomy caused by himself also terminologically.

Big Data is a powerful tool for environmental improvements in the construction business

NASA Astrophysics Data System (ADS)

Konikov, Aleksandr; Konikov, Gregory

2017-10-01

The work investigates the possibility of applying the Big Data method as a tool to implement environmental improvements in the construction business. The method is recognized as effective in analyzing big volumes of heterogeneous data. It is noted that all preconditions exist for this method to be successfully used for resolution of environmental issues in the construction business. It is proven that the principal Big Data techniques (cluster analysis, crowd sourcing, data mixing and integration) can be applied in the sphere in question. It is concluded that Big Data is a truly powerful tool to implement environmental improvements in the construction business.

Structure of the Hf nucleus in high rotational states.

PubMed

Pauling, L

1984-05-01

The values of the moment of inertia of the ground-state band of (168)Hf from J = 0(+) to 22(+) are interpreted as involving a revolving cluster with composition increasing steadily from p(10.5)n(14) to p(20.5)n(24), with radius of revolution 6.390 fm. The excited bands from 14(+) to 34(+), 21(-) to 33(-), and 18(-) to 30(-) have nearly the same very large moment of inertia. It is interpreted as involving two caps, each consisting of 11 tritons, on opposite sides of the nearly doubly magic sphere p(50)n(52), the value of the radius of revolution being 6.445 fm.

Large stability and high catalytic activities of sub-nm metal (0) clusters: implications into the nucleation and growth theory.

PubMed

Piñeiro, Yolanda; Buceta, David; Calvo, Javier; Huseyinova, Shahana; Cuerva, Miguel; Pérez, Ángel; Domínguez, Blanca; López-Quintela, M Arturo

2015-07-01

Clusters are stable catalytic species, which are produced during the synthesis of nanoparticles (NPs). Their existence contradicts the thermodynamic principles used to explain the formation of NPs by the classical nucleation and growth theories (NGTs). Using chemical and electrochemical methods we will show that depending on the experimental conditions one can produce either Ag clusters or Ag NPs. Moreover, using already prepared Ag clusters one can observe the disappearance of the usual induction period observed for the kinetics of NP formation, indicating that clusters catalyze the formation of NPs. Taking these data together with some previous examples of cluster-catalyzed anisotropic growth, we derived a qualitative approach to include the catalytic activities of clusters into the formation of NPs, which is incorporated into the NGT. Some qualitative conclusions about the main experimental parameters, which affect the formation of clusters versus NPs, as well as the catalytic mechanism versus the non-catalytic one, are also described. Copyright © 2015 Elsevier Inc. All rights reserved.

Synthesis and Characterization of Novel Compound Clusters

DTIC Science & Technology

1997-08-26

also be intrinsically stable, they cannot be formed by this plasma chemistry presumably because the metals are less reactive. Plasma chemistry reactions...samples without the presence of hydrogen. Vaporization of these composite samples produces the metal carbide clusters in many cases where plasma chemistry does...antimony or bismuth cannot be produced by the hydrocarbon plasma chemistry method, but they are produced readily from composite sample (metal film on

JaSTA-2: Second version of the Java Superposition T-matrix Application

NASA Astrophysics Data System (ADS)

Halder, Prithish; Das, Himadri Sekhar

2017-12-01

In this article, we announce the development of a new version of the Java Superposition T-matrix App (JaSTA-2), to study the light scattering properties of porous aggregate particles. It has been developed using Netbeans 7.1.2, which is a java integrated development environment (IDE). The JaSTA uses double precision superposition T-matrix codes for multi-sphere clusters in random orientation, developed by Mackowski and Mischenko (1996). The new version consists of two options as part of the input parameters: (i) single wavelength and (ii) multiple wavelengths. The first option (which retains the applicability of older version of JaSTA) calculates the light scattering properties of aggregates of spheres for a single wavelength at a given instant of time whereas the second option can execute the code for a multiple numbers of wavelengths in a single run. JaSTA-2 provides convenient and quicker data analysis which can be used in diverse fields like Planetary Science, Atmospheric Physics, Nanoscience, etc. This version of the software is developed for Linux platform only, and it can be operated over all the cores of a processor using the multi-threading option.

Static electric dipole polarizabilities of tri- and tetravalent U, Np, and Pu ions.

PubMed

Parmar, Payal; Peterson, Kirk A; Clark, Aurora E

2013-11-21

High-quality static electric dipole polarizabilities have been determined for the ground states of the hard-sphere cations of U, Np, and Pu in the III and IV oxidation states. The polarizabilities have been calculated using the numerical finite field technique in a four-component relativistic framework. Methods including Fock-space coupled cluster (FSCC) and Kramers-restricted configuration interaction (KRCI) have been performed in order to account for electron correlation effects. Comparisons between polarizabilities calculated using Dirac-Hartree-Fock (DHF), FSCC, and KRCI methods have been made using both triple- and quadruple-ζ basis sets for U(4+). In addition to the ground state, this study also reports the polarizability data for the first two excited states of U(3+/4+), Np(3+/4+), and Pu(3+/4+) ions at different levels of theory. The values reported in this work are the most accurate to date calculations for the dipole polarizabilities of the hard-sphere tri- and tetravalent actinide ions and may serve as reference values, aiding in the calculation of various electronic and response properties (for example, intermolecular forces, optical properties, etc.) relevant to the nuclear fuel cycle and material science applications.

Phase behaviour in complementary DNA-coated gold nanoparticles and fd-viruses mixtures: a numerical study.

PubMed

Chiappini, Massimiliano; Eiser, Erika; Sciortino, Francesco

2017-01-01

A new gel-forming colloidal system based on a binary mixture of fd-viruses and gold nanoparticles functionalized with complementary DNA single strands has been recently introduced. Upon quenching below the DNA melt temperature, such a system results in a highly porous gel state, that may be developed in a new functional material of tunable porosity. In order to shed light on the gelation mechanism, we introduce a model closely mimicking the experimental one and we explore via Monte Carlo simulations its equilibrium phase diagram. Specifically, we model the system as a binary mixture of hard rods and hard spheres mutually interacting via a short-range square-well attractive potential. In the experimental conditions, we find evidence of a phase separation occurring either via nucleation-and-growth or via spinodal decomposition. The spinodal decomposition leads to the formation of small clusters of bonded rods and spheres whose further diffusion and aggregation leads to the formation of a percolating network in the system. Our results are consistent with the hypothesis that the mixture of DNA-coated fd-viruses and gold nanoparticles undergoes a non-equilibrium gelation via an arrested spinodal decomposition mechanism.

Optical signatures of molecular particles via mass-selected cluster spectroscopy

NASA Technical Reports Server (NTRS)

Duncan, Michael A.

1990-01-01

A new molecular beam apparatus was developed to study optical absorption in cold (less than 100 K) atomic clusters and complexes produced by their condensation with simple molecular gases. In this instrument, ionized clusters produced in a laser vaporization nozzle source are mass selected and studied with photodissociation spectroscopy at visible and ultraviolet wavelengths. This new approach can be applied to synthesize and characterize numerous particulates and weakly bound complexes expected in planetary atmospheres and in comets.

Text analysis of MEDLINE for discovering functional relationships among genes: evaluation of keyword extraction weighting schemes.

PubMed

Liu, Ying; Navathe, Shamkant B; Pivoshenko, Alex; Dasigi, Venu G; Dingledine, Ray; Ciliax, Brian J

2006-01-01

One of the key challenges of microarray studies is to derive biological insights from the gene-expression patterns. Clustering genes by functional keyword association can provide direct information about the functional links among genes. However, the quality of the keyword lists significantly affects the clustering results. We compared two keyword weighting schemes: normalised z-score and term frequency-inverse document frequency (TFIDF). Two gene sets were tested to evaluate the effectiveness of the weighting schemes for keyword extraction for gene clustering. Using established measures of cluster quality, the results produced from TFIDF-weighted keywords outperformed those produced from normalised z-score weighted keywords. The optimised algorithms should be useful for partitioning genes from microarray lists into functionally discrete clusters.

Regulatory Feedback Loop of Two phz Gene Clusters through 5′-Untranslated Regions in Pseudomonas sp. M18

PubMed Central

Li, Yaqian; Du, Xilin; Lu, Zhi John; Wu, Daqiang; Zhao, Yilei; Ren, Bin; Huang, Jiaofang; Huang, Xianqing; Xu, Yuhong; Xu, Yuquan

2011-01-01

Background Phenazines are important compounds produced by pseudomonads and other bacteria. Two phz gene clusters called phzA1-G1 and phzA2-G2, respectively, were found in the genome of Pseudomonas sp. M18, an effective biocontrol agent, which is highly homologous to the opportunistic human pathogen P. aeruginosa PAO1, however little is known about the correlation between the expressions of two phz gene clusters. Methodology/Principal Findings Two chromosomal insertion inactivated mutants for the two gene clusters were constructed respectively and the correlation between the expressions of two phz gene clusters was investigated in strain M18. Phenazine-1-carboxylic acid (PCA) molecules produced from phzA2-G2 gene cluster are able to auto-regulate expression itself and activate the expression of phzA1-G1 gene cluster in a circulated amplification pattern. However, the post-transcriptional expression of phzA1-G1 transcript was blocked principally through 5′-untranslated region (UTR). In contrast, the phzA2-G2 gene cluster was transcribed to a lesser extent and translated efficiently and was negatively regulated by the GacA signal transduction pathway, mainly at a post-transcriptional level. Conclusions/Significance A single molecule, PCA, produced in different quantities by the two phz gene clusters acted as the functional mediator and the two phz gene clusters developed a specific regulatory mechanism which acts through 5′-UTR to transfer a single, but complex bacterial signaling event in Pseudomonas sp. strain M18. PMID:21559370

Magnetic behavior in Cr{sub 2}@Ge{sub n} (1≤n≤12) clusters: A density functional investigation

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

Dhaka, Kapil, E-mail: kapil.dhaka@pilani.bits-pilani.ac.in; Trivedi, Ravi, E-mail: kapil.dhaka@pilani.bits-pilani.ac.in; Bandyopadhyay, Debashis, E-mail: kapil.dhaka@pilani.bits-pilani.ac.in

2014-04-24

With a goal to produce magnetic moment in Cr{sub 2} Doped Ge{sub n} clusters which will be useful for practical applications, we have considered the structure and magnetic properties of Pure Germanium clusters and substitutionally doped it with Cr dimer to produce Cr{sub 2}@Ge{sub n} clusters. As the first step of calculation, geometrical optimizations of the nanoclusters have been done. These optimized geometries have been used in calculate the average binding energy per atom (BE), HOMO-LUMO gap and hence the relative stability of the clusters. These parameters have been demonstrated as structural and electronic properties of the clusters. Gap betweenmore » highest occupied molecular orbital and lowest unoccupied molecular orbital indicate cluster to be a potential motif for generating magnetic cluster assembled materials. Based on these values a comparative study on different sized clusters has been done in order to understand the origin of structures, electronic and magnetic properties of Cr{sub 2}@Ge{sub n} nanoclusters.« less

Interactive visual exploration and refinement of cluster assignments.

PubMed

Kern, Michael; Lex, Alexander; Gehlenborg, Nils; Johnson, Chris R

2017-09-12

With ever-increasing amounts of data produced in biology research, scientists are in need of efficient data analysis methods. Cluster analysis, combined with visualization of the results, is one such method that can be used to make sense of large data volumes. At the same time, cluster analysis is known to be imperfect and depends on the choice of algorithms, parameters, and distance measures. Most clustering algorithms don't properly account for ambiguity in the source data, as records are often assigned to discrete clusters, even if an assignment is unclear. While there are metrics and visualization techniques that allow analysts to compare clusterings or to judge cluster quality, there is no comprehensive method that allows analysts to evaluate, compare, and refine cluster assignments based on the source data, derived scores, and contextual data. In this paper, we introduce a method that explicitly visualizes the quality of cluster assignments, allows comparisons of clustering results and enables analysts to manually curate and refine cluster assignments. Our methods are applicable to matrix data clustered with partitional, hierarchical, and fuzzy clustering algorithms. Furthermore, we enable analysts to explore clustering results in context of other data, for example, to observe whether a clustering of genomic data results in a meaningful differentiation in phenotypes. Our methods are integrated into Caleydo StratomeX, a popular, web-based, disease subtype analysis tool. We show in a usage scenario that our approach can reveal ambiguities in cluster assignments and produce improved clusterings that better differentiate genotypes and phenotypes.

Does tidal capture produce cataclysmic variables?

NASA Technical Reports Server (NTRS)

Bailyn, Charles D.; Grindlay, Jonathan E.; Garcia, Michael R.

1990-01-01

It is shown that earlier estimates of the number of cataclysmic variables (CVs) to be expected from tidal capture in globular clusters may have been considerably too high, since many such binaries will result in unstable mass transfer, and thus not become CVs after all. In particular, CVs with white dwarf masses less than or obout 1.0 solar mass will be supressed. Such unstable mass transfer events may produce some of the cluster mass loss required to stabilize the cluster core. The smaller number of stable CVs predicted may suggest a reconsideration of the nature of some of the low-luminosity cluster X-ray sources.

Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition

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

Emery, S. B., E-mail: samuel.emery@navy.mil; Little, B. K.; Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542

2015-02-28

We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structuremore » at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.« less

Biodiversity and γ-aminobutyric acid production by lactic acid bacteria isolated from traditional alpine raw cow's milk cheeses.

PubMed

Franciosi, Elena; Carafa, Ilaria; Nardin, Tiziana; Schiavon, Silvia; Poznanski, Elisa; Cavazza, Agostino; Larcher, Roberto; Tuohy, Kieran M

2015-01-01

"Nostrano-cheeses" are traditional alpine cheeses made from raw cow's milk in Trentino-Alto Adige, Italy. This study identified lactic acid bacteria (LAB) developing during maturation of "Nostrano-cheeses" and evaluated their potential to produce γ-aminobutyric acid (GABA), an immunologically active compound and neurotransmitter. Cheese samples were collected on six cheese-making days, in three dairy factories located in different areas of Trentino and at different stages of cheese ripening (24 h, 15 days, and 1, 2, 3, 6, and 8 months). A total of 1,059 LAB isolates were screened using Random Amplified Polymorphic DNA-PCR (RAPD-PCR) and differentiated into 583 clusters. LAB strains from dominant clusters (n = 97) were genetically identified to species level by partial 16S rRNA gene sequencing. LAB species most frequently isolated were Lactobacillus paracasei, Streptococcus thermophilus, and Leuconostoc mesenteroides. The 97 dominant clusters were also characterized for their ability in producing GABA by high-performance liquid chromatography (HPLC). About 71% of the dominant bacteria clusters evolving during cheeses ripening were able to produce GABA. Most GABA producers were Lactobacillus paracasei but other GABA producing species included Lactococcus lactis, Lactobacillus plantarum, Lactobacillus rhamnosus, Pediococcus pentosaceus, and Streptococcus thermophilus. No Enterococcus faecalis or Sc. macedonicus isolates produced GABA. The isolate producing the highest amount of GABA (80.0±2.7 mg/kg) was a Sc. thermophilus.

N, S co-doped carbon spheres with highly dispersed CoO as non-precious metal catalyst for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Chen, Linlin; Guo, Xingpeng; Zhang, Guoan

2017-08-01

It is still a great challenge in preparing non-precious metal catalysts with high activity and long-term stability to substitute for precious metal catalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, we report a novel and facile catalyst-N, S co-doped carbon spheres with highly dispersed CoO (CoO@NS-CSs), where biomass glucose spheres act as carbon precursor and H2S, NH3 derived from the decomposition of thiourea not only provide N, S sources but also can etch carbon spheres to produce nanoporous structure. CoO@NS-CSs catalyst exhibits excellent ORR activity with a high onset potential of 0.946 V vs. RHE (reversible hydrogen electrode) and a half-wave potential of 0.821 V vs. RHE through a four-electron pathway in alkaline solution, which is comparable to commercial Pt/C catalyst (onset potential: 0.926 V vs. RHE, half-wave potential: 0.827 V vs. RHE). Furthermore, both the long-term stability and methanol-tolerance of CoO@NS-CSs catalyst are superior to those of commercial Pt/C catalyst. The excellent ORR performance of CoO@NS-CSs catalyst can be attributed to its micro-mesopore structure, high specific surface area (667 m2 g-1), and highly dispersed CoO. This work manifests that the obtained CoO@NS-CSs catalyst is promising to be applied to fuel cells.

Production of metal particles and clusters

NASA Technical Reports Server (NTRS)

Mcmanus, S. P.

1982-01-01

The feasibility of producing novel metals or metal clusters in a low gravity environment was studied. The production of coordinately unsaturated metal carbonyls by thermolysis or photolysis of stable metal carbonyls has the potential to generate novel catalysts by this technique. Laser irradiation of available metal carbonyls was investigated. It is found that laser induced decomposition of metal carbonyls is feasible for producing a variety of coordinately unsaturated species. Formation of clustered species does occur but is hampered by weak metal-metal bonds.

ΛGR Centennial: Cosmic Web in Dark Energy Background

NASA Astrophysics Data System (ADS)

Chernin, A. D.

The basic building blocks of the Cosmic Web are groups and clusters of galaxies, super-clusters (pancakes) and filaments embedded in the universal dark energy background. The background produces antigravity, and the antigravity effect is strong in groups, clusters and superclusters. Antigravity is very weak in filaments where matter (dark matter and baryons) produces gravity dominating in the filament internal dynamics. Gravity-antigravity interplay on the large scales is a grandiose phenomenon predicted by ΛGR theory and seen in modern observations of the Cosmic Web.

X-Ray Gas Temperatures in the Arc Clusters MS0440+204 and MS0302+1658

NASA Technical Reports Server (NTRS)

Gioia, Isabella M.; White, Nicholas

1997-01-01

The cluster of galaxies MS0440+02, originally discovered through its X-ray emission, was part of an optical observational program to search for arcs and arclets in a complete sample of X-ray luminous, medium-distant clusters of galaxies. Mauna Kea CCD images of MS0440+02 showed a remarkable optical morphology. The core of the cluster contains 6 bright galaxies and numerous fainter ones embedded in a low surface brightness halo. Besides, MS0440+02 is the most spectacular example that we have found of an arc system in a compact condensed cluster, with arcs symmetrically distributed to draw almost perfect circles around the cluster center. Giant arcs are magnified images of distant galaxies, gravitationally distorted by massive foreground clusters. It is of great importance to compare the results of the lensing studies with those derived from X-ray observations, as the two are independent methods of studying the mass distribution. Thus MS0440+02 was the ideal target to obtain temperature measurement with ASCA and good spatial resolution X-ray observations with ROSAT. The X-ray data have been used in conjunction with Hubble Space Telescope observations to put more stringent constrains on the mass estimates. Most of the different wavelength datasets have been reduced and analyzed. Mass determinations have been separately obtained from galaxy virial motions and X-ray profile fitting using the cluster gas temperature as measured by the ASCA satellite. Assuming that the hot gas is in hydrostatic equilibrium and in a spherical potential, we find from the X-ray data a mass distribution profile that is well described by a Beta model. From the multiple images formed by gravitational lensing (HST data) using the modelling of the gravitational lensed arcs, we have derived Beta model. To reconcile the mass estimates we have explored the possibility of having a supercluster surrounding the MOS0440 cluster, that is a model with two isothermal spheres, one embedded inside the other. These results have been published or are in press.

Cluster structures influenced by interaction with a surface.

PubMed

Witt, Christopher; Dieterich, Johannes M; Hartke, Bernd

2018-05-30

Clusters on surfaces are vitally important for nanotechnological applications. Clearly, cluster-surface interactions heavily influence the preferred cluster structures, compared to clusters in vacuum. Nevertheless, systematic explorations and an in-depth understanding of these interactions and how they determine the cluster structures are still lacking. Here we present an extension of our well-established non-deterministic global optimization package OGOLEM from isolated clusters to clusters on surfaces. Applying this approach to intentionally simple Lennard-Jones test systems, we produce a first systematic exploration that relates changes in cluster-surface interactions to resulting changes in adsorbed cluster structures.

The Effect of Metal Oxide on Nanoparticles from Thermite Reactions

ERIC Educational Resources Information Center

Moore, Lewis Ryan

2006-01-01

The purpose of this research was to determine how metal oxide used in a thermite reaction can impact the production of nanoparticles. The results showed the presence of nanoparticles (less than 1 micron in diameter) of at least one type produced by each metal oxide. The typical particles were metallic spheres, which ranged from 300 nanometers in…

Personal Meaning in the Public Sphere: The Standardisation and Rationalisation of Biodiversity Data in the UK and the Netherlands

ERIC Educational Resources Information Center

Lawrence, Anna; Turnhout, Esther

2010-01-01

The demand for biodiversity data is increasing. Governments require standardised, objective data to underpin planning and conservation decisions. These data are produced by large numbers of (volunteer) natural historians and non-governmental organisations. This article analyses the interface between the state and the volunteer naturalists to…

"No tempo de Zicartola": Locating Cultural Mediation and Social Change, 1963-65

ERIC Educational Resources Information Center

Dietrich, Elise M.

2017-01-01

In 1960s Rio de Janeiro, the Brazilian white middle class embraced the samba music written by working-class blacks as a source of authentic national culture. Cultural mediators, or individuals that bridged sociocultural spheres and negotiated the terms in which work was produced and circulated, were essential to samba's mainstream acceptance. This…

Living in the Age of Imposed Amnesia: The Eclipse of Democratic Formative Culture

ERIC Educational Resources Information Center

Giroux, Henry A.

2011-01-01

This article argues that under neoliberal casino capitalism there has been a wholesale attack not only on the social state but also on those public spheres that enable the formative cultures necessary to produce critical agents, engaged subjects, and the literacies necessary to make power and authority accountable. In this instance, the struggle…

Testing prediction methods: Earthquake clustering versus the Poisson model

USGS Publications Warehouse

Michael, A.J.

1997-01-01

Testing earthquake prediction methods requires statistical techniques that compare observed success to random chance. One technique is to produce simulated earthquake catalogs and measure the relative success of predicting real and simulated earthquakes. The accuracy of these tests depends on the validity of the statistical model used to simulate the earthquakes. This study tests the effect of clustering in the statistical earthquake model on the results. Three simulation models were used to produce significance levels for a VLF earthquake prediction method. As the degree of simulated clustering increases, the statistical significance drops. Hence, the use of a seismicity model with insufficient clustering can lead to overly optimistic results. A successful method must pass the statistical tests with a model that fully replicates the observed clustering. However, a method can be rejected based on tests with a model that contains insufficient clustering. U.S. copyright. Published in 1997 by the American Geophysical Union.

Cluster correlation and fragment emission in 12C+12C at 95 MeV/nucleon

NASA Astrophysics Data System (ADS)

Tian, G.; Chen, Z.; Han, R.; Shi, F.; Luo, F.; Sun, Q.; Song, L.; Zhang, X.; Xiao, G. Q.; Wada, R.; Ono, A.

2018-03-01

The impact of cluster correlations has been studied in the intermediate mass fragment (IMF) emission in 12C+12C at 95 MeV/nucleon, using antisymmetrized molecular dynamics (AMD) model simulations. In AMD, the cluster correlation is introduced as a process to form light clusters with A ≤4 in the final states of a collision induced by the nucleon-nucleon residual interaction. Correlations between light clusters are also considered to form light nuclei with A ≤9 . This version of AMD, combined with GEMINI to calculate the decay of primary fragments, reproduces the experimental energy spectra of IMFs well overall with reasonable reproduction of light charged particles when we carefully analyze the excitation energies of primary fragments produced by AMD and their secondary decays. The results indicate that the cluster correlation plays a crucial role for producing fragments at relatively low excitation energies in the intermediate-energy heavy-ion collisions.

A Fast Implementation of the ISODATA Clustering Algorithm

NASA Technical Reports Server (NTRS)

Memarsadeghi, Nargess; Mount, David M.; Netanyahu, Nathan S.; LeMoigne, Jacqueline

2005-01-01

Clustering is central to many image processing and remote sensing applications. ISODATA is one of the most popular and widely used clustering methods in geoscience applications, but it can run slowly, particularly with large data sets. We present a more efficient approach to ISODATA clustering, which achieves better running times by storing the points in a kd-tree and through a modification of the way in which the algorithm estimates the dispersion of each cluster. We also present an approximate version of the algorithm which allows the user to further improve the running time, at the expense of lower fidelity in computing the nearest cluster center to each point. We provide both theoretical and empirical justification that our modified approach produces clusterings that are very similar to those produced by the standard ISODATA approach. We also provide empirical studies on both synthetic data and remotely sensed Landsat and MODIS images that show that our approach has significantly lower running times.

A Fast Implementation of the Isodata Clustering Algorithm

NASA Technical Reports Server (NTRS)

Memarsadeghi, Nargess; Le Moigne, Jacqueline; Mount, David M.; Netanyahu, Nathan S.

2007-01-01

Clustering is central to many image processing and remote sensing applications. ISODATA is one of the most popular and widely used clustering methods in geoscience applications, but it can run slowly, particularly with large data sets. We present a more efficient approach to IsoDATA clustering, which achieves better running times by storing the points in a kd-tree and through a modification of the way in which the algorithm estimates the dispersion of each cluster. We also present an approximate version of the algorithm which allows the user to further improve the running time, at the expense of lower fidelity in computing the nearest cluster center to each point. We provide both theoretical and empirical justification that our modified approach produces clusterings that are very similar to those produced by the standard ISODATA approach. We also provide empirical studies on both synthetic data and remotely sensed Landsat and MODIS images that show that our approach has significantly lower running times.

The ergot alkaloid gene cluster in Claviceps purpurea: extension of the cluster sequence and intra species evolution.

PubMed

Haarmann, Thomas; Machado, Caroline; Lübbe, Yvonne; Correia, Telmo; Schardl, Christopher L; Panaccione, Daniel G; Tudzynski, Paul

2005-06-01

The genomic region of Claviceps purpurea strain P1 containing the ergot alkaloid gene cluster [Tudzynski, P., Hölter, K., Correia, T., Arntz, C., Grammel, N., Keller, U., 1999. Evidence for an ergot alkaloid gene cluster in Claviceps purpurea. Mol. Gen. Genet. 261, 133-141] was explored by chromosome walking, and additional genes probably involved in the ergot alkaloid biosynthesis have been identified. The putative cluster sequence (extending over 68.5kb) contains 4 different nonribosomal peptide synthetase (NRPS) genes and several putative oxidases. Northern analysis showed that most of the genes were co-regulated (repressed by high phosphate), and identified probable flanking genes by lack of co-regulation. Comparison of the cluster sequences of strain P1, an ergotamine producer, with that of strain ECC93, an ergocristine producer, showed high conservation of most of the cluster genes, but significant variation in the NRPS modules, strongly suggesting that evolution of these chemical races of C. purpurea is determined by evolution of NRPS module specificity.

Carbon-shell-constrained silicon cluster derived from Al-Si alloy as long-cycling life lithium ion batteries anode

NASA Astrophysics Data System (ADS)

Su, Junming; Zhang, Congcong; Chen, Xiang; Liu, Siyang; Huang, Tao; Yu, Aishui

2018-03-01

Although silicon is the most promising anode material for Li-ion batteries, large volume expansion during lithiation and delithiation is the main obstacle limiting the commercial application of silicon anodes. There are two ways to alleviate volume expansion and prevent further pulverization of a Si anode: fabrication of a rational nanostructure possessing void spaces and uniform distribution of the conducting sites, without a good balance effect in mitigating the limiting factors and enhancing battery performance. In this paper, we propose a novel nanostructure - a carbon-shell-constrained Si cluster (Si/C shell) with both adequate void space and good distribution of electrical contact sites to guarantee homogeneous lithiation in the initial cycle. Benefiting from the ability to maintain electrical conductivity of the outer carbon shell, even after cluster fragmentation, the Si/C shell synthesized from low-cost commercial Al-Si alloy spheres can deliver 0.03% capacity loss from 100th to 1000th cycles at a current density of 1 A g-1. The Si/C shell sample with the dual functional structure mentioned above can also maintain its own nanostructure during cycling and deliver excellent rate performance. It is a concise and scalable strategy which can simplify the preparation of other alloy anode materials for Li-ion batteries.

Why do ultrasoft repulsive particles cluster and crystallize? Analytical results from density-functional theory.

PubMed

Likos, Christos N; Mladek, Bianca M; Gottwald, Dieter; Kahl, Gerhard

2007-06-14

We demonstrate the accuracy of the hypernetted chain closure and of the mean-field approximation for the calculation of the fluid-state properties of systems interacting by means of bounded and positive pair potentials with oscillating Fourier transforms. Subsequently, we prove the validity of a bilinear, random-phase density functional for arbitrary inhomogeneous phases of the same systems. On the basis of this functional, we calculate analytically the freezing parameters of the latter. We demonstrate explicitly that the stable crystals feature a lattice constant that is independent of density and whose value is dictated by the position of the negative minimum of the Fourier transform of the pair potential. This property is equivalent with the existence of clusters, whose population scales proportionally to the density. We establish that regardless of the form of the interaction potential and of the location on the freezing line, all cluster crystals have a universal Lindemann ratio Lf=0.189 at freezing. We further make an explicit link between the aforementioned density functional and the harmonic theory of crystals. This allows us to establish an equivalence between the emergence of clusters and the existence of negative Fourier components of the interaction potential. Finally, we make a connection between the class of models at hand and the system of infinite-dimensional hard spheres, when the limits of interaction steepness and space dimension are both taken to infinity in a particularly described fashion.

Optical and Atomic Force Microscopy Characterization of PbI2 Quantum Dots

NASA Technical Reports Server (NTRS)

Mu, R.; Tung, Y. S.; Ueda, A.; Henderson, D. O.

1997-01-01

Lead iodide (PbI2) clusters were synthesized from the chemical reaction of NaI (or KI) with Pb(NO3)2 in H2O, D2O, CH3OH, and C3H7OH media. The observation of the absorption features above 350 nm with the help of integrating sphere accessory strongly suggests the quantum dot formation of PbI2 in solution. Spectral comparison between the synthesized PbI2 clusters in solution and PbI2 nanophase by impregnation of PbI2 in four different pore-sized porous silica indicates that the PbI2 cluster size in solution is less than 2.5 nm in lateral dimension. Atomic force microscopy (AFM) measurements show that the PbL clusters deposited onto three different molecularly flat surfaces are single-layered. The measured height is 1.0 - 0.1 nm. The swollen layer thickness can be attributed to the intralayer contraction from the strong lateral interaction among PbI2 molecules, which is supported by ab initio calculation. Raman scattering measurement of LO and TO modes of PbI2 in bulk and in the confined state were also conducted in 50-150 cu cm region. The observed three bands at 74, %, 106 1/cm are assigned to TO2, LO2, and LO, mode, respectively. The relatively small red-shift in LO modes may be caused by the surface phonon polaritons of PbI2 nanophase in the porous silica.

Representational momentum in perception and grasping: translating versus transforming objects.

PubMed

Brouwer, Anne-Marie; Franz, Volker H; Thornton, Ian M

2004-07-14

Representational momentum is the tendency to misremember the stopping point of a moving object as further forward in the direction of movement. Results of several studies suggest that this effect is typical for changes in position (e.g., translation) and not for changes in object shape (transformation). Additionally, the effect seems to be stronger in motor tasks than in perceptual tasks. Here, participants judged the final distance between two spheres after this distance had been increasing or decreasing. The spheres were two separately translating objects or were connected to form a single transforming object (a dumbbell). Participants also performed a motor task in which they grasped virtual versions of the final objects. We found representational momentum for the visual judgment task for both stimulus types. As predicted, it was stronger for the spheres than for the dumbbells. In contrast, for grasping, only the dumbbells produced representational momentum (larger maximum grip aperture when the dumbbells had been growing compared to when they had been shrinking). Because type of stimulus change had these different effects on representational momentum for perception and action, we conclude that different sources of information are used in the two tasks or that they are governed by different mechanisms.

RadBall Technology Testing and MCNP Modeling of the Tungsten Collimator.

PubMed

Farfán, Eduardo B; Foley, Trevor Q; Coleman, J Rusty; Jannik, G Timothy; Holmes, Christopher J; Oldham, Mark; Adamovics, John; Stanley, Steven J

2010-01-01

The United Kingdom's National Nuclear Laboratory (NNL) has developed a remote, non-electrical, radiation-mapping device known as RadBall(™), which can locate and quantify radioactive hazards within contaminated areas of the nuclear industry. RadBall(™) consists of a colander-like outer shell that houses a radiation-sensitive polymer sphere. The outer shell works to collimate radiation sources and those areas of the polymer sphere that are exposed react, becoming increasingly more opaque, in proportion to the absorbed dose. The polymer sphere is imaged in an optical-CT scanner, which produces a high resolution 3D map of optical attenuation coefficients. Subsequent analysis of the optical attenuation matrix provides information on the spatial distribution of sources in a given area forming a 3D characterization of the area of interest. RadBall(™) has no power requirements and can be positioned in tight or hard-to reach locations. The RadBall(™) technology has been deployed in a number of technology trials in nuclear waste reprocessing plants at Sellafield in the United Kingdom and facilities of the Savannah River National Laboratory (SRNL). This study focuses on the RadBall(™) testing and modeling accomplished at SRNL.

RadBall™ Technology Testing and MCNP Modeling of the Tungsten Collimator

PubMed Central

Farfán, Eduardo B.; Foley, Trevor Q.; Coleman, J. Rusty; Jannik, G. Timothy; Holmes, Christopher J.; Oldham, Mark; Adamovics, John; Stanley, Steven J.

2010-01-01

The United Kingdom’s National Nuclear Laboratory (NNL) has developed a remote, non-electrical, radiation-mapping device known as RadBall™, which can locate and quantify radioactive hazards within contaminated areas of the nuclear industry. RadBall™ consists of a colander-like outer shell that houses a radiation-sensitive polymer sphere. The outer shell works to collimate radiation sources and those areas of the polymer sphere that are exposed react, becoming increasingly more opaque, in proportion to the absorbed dose. The polymer sphere is imaged in an optical-CT scanner, which produces a high resolution 3D map of optical attenuation coefficients. Subsequent analysis of the optical attenuation matrix provides information on the spatial distribution of sources in a given area forming a 3D characterization of the area of interest. RadBall™ has no power requirements and can be positioned in tight or hard-to reach locations. The RadBall™ technology has been deployed in a number of technology trials in nuclear waste reprocessing plants at Sellafield in the United Kingdom and facilities of the Savannah River National Laboratory (SRNL). This study focuses on the RadBall™ testing and modeling accomplished at SRNL. PMID:21617740

Effects of Group Size and Lack of Sphericity on the Recovery of Clusters in K-Means Cluster Analysis

ERIC Educational Resources Information Center

de Craen, Saskia; Commandeur, Jacques J. F.; Frank, Laurence E.; Heiser, Willem J.

2006-01-01

K-means cluster analysis is known for its tendency to produce spherical and equally sized clusters. To assess the magnitude of these effects, a simulation study was conducted, in which populations were created with varying departures from sphericity and group sizes. An analysis of the recovery of clusters in the samples taken from these…

Wide Distribution of Foxicin Biosynthetic Gene Clusters in Streptomyces Strains – An Unusual Secondary Metabolite with Various Properties

PubMed Central

Greule, Anja; Marolt, Marija; Deubel, Denise; Peintner, Iris; Zhang, Songya; Jessen-Trefzer, Claudia; De Ford, Christian; Burschel, Sabrina; Li, Shu-Ming; Friedrich, Thorsten; Merfort, Irmgard; Lüdeke, Steffen; Bisel, Philippe; Müller, Michael; Paululat, Thomas; Bechthold, Andreas

2017-01-01

Streptomyces diastatochromogenes Tü6028 is known to produce the polyketide antibiotic polyketomycin. The deletion of the pokOIV oxygenase gene led to a non-polyketomycin-producing mutant. Instead, novel compounds were produced by the mutant, which have not been detected before in the wild type strain. Four different compounds were identified and named foxicins A–D. Foxicin A was isolated and its structure was elucidated as an unusual nitrogen-containing quinone derivative using various spectroscopic methods. Through genome mining, the foxicin biosynthetic gene cluster was identified in the draft genome sequence of S. diastatochromogenes. The cluster spans 57 kb and encodes three PKS type I modules, one NRPS module and 41 additional enzymes. A foxBII gene-inactivated mutant of S. diastatochromogenes Tü6028 ΔpokOIV is unable to produce foxicins. Homologous fox biosynthetic gene clusters were found in more than 20 additional Streptomyces strains, overall in about 2.6% of all sequenced Streptomyces genomes. However, the production of foxicin-like compounds in these strains has never been described indicating that the clusters are expressed at a very low level or are silent under fermentation conditions. Foxicin A acts as a siderophore through interacting with ferric ions. Furthermore, it is a weak inhibitor of the Escherichia coli aerobic respiratory chain and shows moderate antibiotic activity. The wide distribution of the cluster and the various properties of the compound indicate a major role of foxicins in Streptomyces strains. PMID:28270798

Apparatus for producing carbon-coated nanoparticles and carbon nanospheres

DOEpatents

Perry, W. Lee; Weigle, John C.; Phillips, Jonathan

2015-10-20

An apparatus for producing carbon-coated nano- or micron-scale particles comprising a container for entraining particles in an aerosol gas, providing an inlet for carbon-containing gas, providing an inlet for plasma gas, a proximate torch for mixing the aerosol gas, the carbon-containing gas, and the plasma gas, bombarding the mixed gases with microwaves, and providing a collection device for gathering the resulting carbon-coated nano- or micron-scale particles. Also disclosed is a method and apparatus for making hollow carbon nano- or micro-scale spheres.

Butyrate production in phylogenetically diverse Firmicutes isolated from the chicken caecum

PubMed Central

Eeckhaut, Venessa; Van Immerseel, Filip; Croubels, Siska; De Baere, Siegrid; Haesebrouck, Freddy; Ducatelle, Richard; Louis, Petra; Vandamme, Peter

2011-01-01

Summary Sixteen butyrate‐producing bacteria were isolated from the caecal content of chickens and analysed phylogenetically. They did not represent a coherent phylogenetic group, but were allied to four different lineages in the Firmicutes phylum. Fourteen strains appeared to represent novel species, based on a level of ≤ 98.5% 16S rRNA gene sequence similarity towards their nearest validly named neighbours. The highest butyrate concentrations were produced by the strains belonging to clostridial clusters IV and XIVa, clusters which are predominant in the chicken caecal microbiota. In only one of the 16 strains tested, the butyrate kinase operon could be amplified, while the butyryl‐CoA : acetate CoA‐transferase gene was detected in eight strains belonging to clostridial clusters IV, XIVa and XIVb. None of the clostridial cluster XVI isolates carried this gene based on degenerate PCR analyses. However, another CoA‐transferase gene more similar to propionate CoA‐transferase was detected in the majority of the clostridial cluster XVI isolates. Since this gene is located directly downstream of the remaining butyrate pathway genes in several human cluster XVI bacteria, it may be involved in butyrate formation in these bacteria. The present study indicates that butyrate producers related to cluster XVI may play a more important role in the chicken gut than in the human gut. PMID:21375722

STELLAR ENCOUNTER RATE IN GALACTIC GLOBULAR CLUSTERS

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

Bahramian, Arash; Heinke, Craig O.; Sivakoff, Gregory R.

2013-04-01

The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed 'King-model' profiles for all clusters. By deprojecting cluster surface brightness profilesmore » to estimate luminosity density profiles, we treat 'King-model' and 'core-collapsed' clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.« less

EMBLA 2002: an Optical and Ground Survey in Hessdalen

NASA Astrophysics Data System (ADS)

Teodorani, M.; Nobili, G.

2002-10-01

A two-weeks scientific expedition to Hessdalen, aimed at investigating on field mysterious atmospheric light-phenomena, was carried out in August 2002 by the physics section of an italian team of scientists. Results are presented and discussed. Photometric analysis shows that the light-phenomenon is able to produce a luminous power of up-to 100 kW. A 3-D analysis of photo frames shows that the luminous phenomenon doesn't resemble canonical plasma features (a sharply gaussian PSF) unless the light phenomenon is caused by one recently discovered natural light-ball of BL type whose light-distribution (PSF) might be able to simulate an uniformly illuminated solid. A comparison of the light-distribution in different time-sequential frames shows that apparent slightly exponential wings of the PSF features are probably due to variations of atmospheric turbulence and transparency and not to intrinsic properties. Maximum phases of luminosity of the radiating surface are demonstrated to be due to the sudden apparition of a cluster of co-existing light-balls at constant temperature, while the inflation of light-balls is ruled out. Spectra show no resolved lines but a three-peaked feature which might be attributed both to some kind of artificial illumination system and to a mixture of many blended lines due to several chemical elements (more possibly: silicon). The results of a lab analysis of ground samples shows that some powder which was collected near a river contains an anomalous iron sphere of micrometric dimensions. A biophysical research-proposal aimed at studying the relation between the EM field produced by the phenomenon and the electrical activity of the human body is also presented. On the basis of this third explorative experience, the importance of having at disposal a sophisticated opto-electronic portable station (missing at present) is stressed for the future.

Numerical simulation of a sphere moving down an incline with identical spheres placed equally apart

USGS Publications Warehouse

Ling, Chi-Hai; Jan, Chyan-Deng; Chen, Cheng-lung; Shen, Hsieh Wen

1992-01-01

This paper describes a numerical study of an elastic sphere moving down an incline with a string of identical spheres placed equally apart. Two momentum equations and a moment equation formulated for the moving sphere are solved numerically for the instantaneous velocity of the moving sphere on an incline with different angles of inclination. Input parameters for numerical simulation include the properties of the sphere (the radius, density, Poison's ratio, and Young's Modulus of elasticity), the coefficient of friction between the spheres, and a damping coefficient of the spheres during collision.

The WRAIR projectile concussive impact model of mild traumatic brain injury: re-design, testing and preclinical validation.

PubMed

Leung, Lai Yee; Larimore, Zachary; Holmes, Larry; Cartagena, Casandra; Mountney, Andrea; Deng-Bryant, Ying; Schmid, Kara; Shear, Deborah; Tortella, Frank

2014-08-01

The WRAIR projectile concussive impact (PCI) model was developed for preclinical study of concussion. It represents a truly non-invasive closed-head injury caused by a blunt impact. The original design, however, has several drawbacks that limit the manipulation of injury parameters. The present study describes engineering advancements made to the PCI injury model including helmet material testing, projectile impact energy/head kinematics and impact location. Material testing indicated that among the tested materials, 'fiber-glass/carbon' had the lowest elastic modulus and yield stress for providing an relative high percentage of load transfer from the projectile impact, resulting in significant hippocampal astrocyte activation. Impact energy testing of small projectiles, ranging in shape and size, showed the steel sphere produced the highest impact energy and the most consistent impact characteristics. Additional tests confirmed the steel sphere produced linear and rotational motions on the rat's head while remaining within a range that meets the criteria for mTBI. Finally, impact location testing results showed that PCI targeted at the temporoparietal surface of the rat head produced the most prominent gait abnormalities. Using the parameters defined above, pilot studies were conducted to provide initial validation of the PCI model demonstrating quantifiable and significant increases in righting reflex recovery time, axonal damage and astrocyte activation following single and multiple concussions.

Swarm: robust and fast clustering method for amplicon-based studies.

PubMed

Mahé, Frédéric; Rognes, Torbjørn; Quince, Christopher; de Vargas, Colomban; Dunthorn, Micah

2014-01-01

Popular de novo amplicon clustering methods suffer from two fundamental flaws: arbitrary global clustering thresholds, and input-order dependency induced by centroid selection. Swarm was developed to address these issues by first clustering nearly identical amplicons iteratively using a local threshold, and then by using clusters' internal structure and amplicon abundances to refine its results. This fast, scalable, and input-order independent approach reduces the influence of clustering parameters and produces robust operational taxonomic units.

Density profiles of a self-gravitating lattice gas in one, two, and three dimensions

NASA Astrophysics Data System (ADS)

Bakhti, Benaoumeur; Boukari, Divana; Karbach, Michael; Maass, Philipp; Müller, Gerhard

2018-04-01

We consider a lattice gas in spaces of dimensionality D =1 ,2 ,3 . The particles are subject to a hardcore exclusion interaction and an attractive pair interaction that satisfies Gauss' law as do Newtonian gravity in D =3 , a logarithmic potential in D =2 , and a distance-independent force in D =1 . Under mild additional assumptions regarding symmetry and fluctuations we investigate equilibrium states of self-gravitating material clusters, in particular radial density profiles for closed and open systems. We present exact analytic results in several instances and high-precision numerical data in others. The density profile of a cluster with finite mass is found to exhibit exponential decay in D =1 and power-law decay in D =2 with temperature-dependent exponents in both cases. In D =2 the gas evaporates in a continuous transition at a nonzero critical temperature. We describe clusters of infinite mass in D =3 with a density profile consisting of three layers (core, shell, halo) and an algebraic large-distance asymptotic decay. In D =3 a cluster of finite mass can be stabilized at T >0 via confinement to a sphere of finite radius. In some parameter regime, the gas thus enclosed undergoes a discontinuous transition between distinct density profiles. For the free energy needed to identify the equilibrium state we introduce a construction of gravitational self-energy that works in all D for the lattice gas. The decay rate of the density profile of an open cluster is shown to transform via a stretched exponential for 1

Cysteine as a ligand platform in the biosynthesis of the FeFe hydrogenase H cluster

DOE PAGES

Suess, Daniel L. M.; Bürstel, Ingmar; De La Paz, Liliana; ...

2015-08-31

Hydrogenases catalyze the redox interconversion of protons and H 2, an important reaction for a number of metabolic processes and for solar fuel production. In FeFe hydrogenases, catalysis occurs at the H cluster, a metallocofactor comprising a [4Fe–4S] H subcluster coupled to a [2Fe] H subcluster bound by CO, CN–, and azadithiolate ligands. The [2Fe] H subcluster is assembled by the maturases HydE, HydF, and HydG. HydG is a member of the radical S-adenosyl-L-methionine family of enzymes that transforms Fe and L-tyrosine into an [Fe(CO) 2(CN)] synthon that is incorporated into the H cluster. Though it is thought that themore » site of synthon formation in HydG is the “dangler” Fe of a [5Fe] cluster, many mechanistic aspects of this chemistry remain unresolved including the full ligand set of the synthon, how the dangler Fe initially binds to HydG, and how the synthon is released at the end of the reaction. In order to address these questions, we show in this paper that L-cysteine (Cys) binds the auxiliary [4Fe–4S] cluster of HydG and further chelates the dangler Fe. We demonstrate that a [4Fe–4S] aux[CN] species is generated during HydG catalysis, a process that entails the loss of Cys and the [Fe(CO) 2(CN)] fragment; on this basis, we suggest that Cys likely completes the coordination sphere of the synthon. Finally, through spectroscopic analysis of HydG before and after the synthon is formed, we conclude that Cys serves as the ligand platform on which the synthon is built and plays a role in both Fe 2+ binding and synthon release.« less

Magnetic separation of Dy(III) ions from homogeneous aqueous solutions

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

Pulko, B., E-mail: Barbara.Pulko@tu-dresden.de; Yang, X.; Lei, Z.

2014-12-08

The possibility to enrich paramagnetic dysprosium(III) ions in a magnetic field gradient is proved by means of interferometry, which may open the route for a magnetic separation of rare earth ions from aqueous solutions. The separation dynamics are studied for three different concentrations of DyCl{sub 3} and compared with those found recently in a sulphate solution of the 3d ion Mn(II). In view of the similar-sized hydration spheres for Dy(III) and Mn(II), the slower separation dynamics in DyCl{sub 3} is attributed to both a higher densification coefficient and the strong impact of Brownian motion due to the absence of ion-pairmore » clusters.« less

Heterobimetallic Catalysis: Platinum-Gold-Catalyzed Tandem Cyclization/C-X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles.

PubMed

Alonso, José Miguel; Muñoz, María Paz

2018-04-16

Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt-Au heterobimetallic catalyst system for the synthesis of a family of multi-heteroaromatic structures through tandem cyclization/C-X coupling reaction. Au-catalyzed 6-endo-cyclization takes place as the first fast step. Pt-Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer-sphere mechanism by hybrid homogeneous-heterogeneous catalysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure of the 168Hf nucleus in high rotational states

PubMed Central

Pauling, Linus

1984-01-01

The values of the moment of inertia of the ground-state band of 168Hf from J = 0+ to 22+ are interpreted as involving a revolving cluster with composition increasing steadily from p10.5n14 to p20.5n24, with radius of revolution 6.390 fm. The excited bands from 14+ to 34+, 21- to 33-, and 18- to 30- have nearly the same very large moment of inertia. It is interpreted as involving two caps, each consisting of 11 tritons, on opposite sides of the nearly doubly magic sphere p50n52, the value of the radius of revolution being 6.445 fm. PMID:16593470

Analytical solution to the fractional polytropic gas spheres

NASA Astrophysics Data System (ADS)

Nouh, Mohamed I.; Abdel-Salam, Emad A.-B.

2018-04-01

The Lane-Emden equation can be used to model stellar interiors, star clusters and many configurations in astrophysics. Unfortunately, there is an exact solution only for the polytropic indices n = 0, 1 and 5. In the present paper, a series solution for the fractional Lane-Emden equation is presented. The solution is performed in the frame of modified Rienmann Liouville derivatives. The obtained results recover the well-known series solutions when α =1. The fractional model of n = 3 is calculated and the mass-radius relation, density ratio, pressure ratio and temperature ratio are investigated. The fractional star appears much different than the integer star, as it is denser, more stressed and hotter than the integer star.

Photometry of Standard Stars and Open Star Clusters

NASA Astrophysics Data System (ADS)

Jefferies, Amanda; Frinchaboy, Peter

2010-10-01

Photometric CCD observations of open star clusters and standard stars were carried out at the McDonald Observatory in Fort Davis, Texas. This data was analyzed using aperture photometry algorithms (DAOPHOT II and ALLSTAR) and the IRAF software package. Color-magnitude diagrams of these clusters were produced, showing the evolution of each cluster along the main sequence.

Learner Typologies Development Using OIndex and Data Mining Based Clustering Techniques

ERIC Educational Resources Information Center

Luan, Jing

2004-01-01

This explorative data mining project used distance based clustering algorithm to study 3 indicators, called OIndex, of student behavioral data and stabilized at a 6-cluster scenario following an exhaustive explorative study of 4, 5, and 6 cluster scenarios produced by K-Means and TwoStep algorithms. Using principles in data mining, the study…

Biodiversity and γ-Aminobutyric Acid Production by Lactic Acid Bacteria Isolated from Traditional Alpine Raw Cow's Milk Cheeses

PubMed Central

Nardin, Tiziana; Schiavon, Silvia; Cavazza, Agostino; Larcher, Roberto; Tuohy, Kieran M.

2015-01-01

“Nostrano-cheeses” are traditional alpine cheeses made from raw cow's milk in Trentino-Alto Adige, Italy. This study identified lactic acid bacteria (LAB) developing during maturation of “Nostrano-cheeses” and evaluated their potential to produce γ-aminobutyric acid (GABA), an immunologically active compound and neurotransmitter. Cheese samples were collected on six cheese-making days, in three dairy factories located in different areas of Trentino and at different stages of cheese ripening (24 h, 15 days, and 1, 2, 3, 6, and 8 months). A total of 1,059 LAB isolates were screened using Random Amplified Polymorphic DNA-PCR (RAPD-PCR) and differentiated into 583 clusters. LAB strains from dominant clusters (n = 97) were genetically identified to species level by partial 16S rRNA gene sequencing. LAB species most frequently isolated were Lactobacillus paracasei, Streptococcus thermophilus, and Leuconostoc mesenteroides. The 97 dominant clusters were also characterized for their ability in producing GABA by high-performance liquid chromatography (HPLC). About 71% of the dominant bacteria clusters evolving during cheeses ripening were able to produce GABA. Most GABA producers were Lactobacillus paracasei but other GABA producing species included Lactococcus lactis, Lactobacillus plantarum, Lactobacillus rhamnosus, Pediococcus pentosaceus, and Streptococcus thermophilus. No Enterococcus faecalis or Sc. macedonicus isolates produced GABA. The isolate producing the highest amount of GABA (80.0±2.7 mg/kg) was a Sc. thermophilus. PMID:25802859

Microgravity acoustic mixing for particle cloud combustors

NASA Technical Reports Server (NTRS)

Pla, Frederic; Rubinstein, Robert I.

1990-01-01

Experimental and theoretical investigations of acoustic mixing procedures designed to uniformly distribute fuel particles in a combustion tube for application in the proposed Particle Cloud Combustion Experiment (PCCE) are described. Two acoustic mixing methods are investigated: mixing in a cylindrical tube using high frequency spinning modes generated by suitably phased, or quadrature speakers, and acoustic premixing in a sphere. Quadrature mixing leads to rapid circumferential circulation of the powder around the tube. Good mixing is observed in the circulating regions. However, because axial inhomogeneities are necessarily present in the acoustic field, this circulation does not extend throughout the tube. Simultaneous operation of the quadrature-speaker set and the axial-speaker was observed to produce considerably enhanced mixing compared to operation of the quadrature-speaker set alone. Mixing experiments using both types of speakers were free of the longitudinal powder drift observed using axial-speakers alone. Vigorous powder mixing was obtained in the sphere for many normal modes: however, in no case was the powder observed to fill the sphere entirely. Theoretical analysis indicated that mixing under steady conditions cannot fill more than a hemisphere except under very unusual conditions. Premixing in a hemisphere may be satisfactory; otherwise, complete mixing in microgravity might be possible by operating the speaker in short bursts. A general conclusion is that acoustic transients are more likely to produce good mixing than steady state conditions. The reason is that in steady conditions, flow structures like nodal planes are possible and often even unavoidable. These tend to separate the mixing region into cells across which powder cannot be transferred. In contrast, transients not only are free of such structures, they also have the characteristics, desirable for mixing, of randomness and disorder. This conclusion is corroborated by mixing experiments using axial waves.

Thermal noise calculation method for precise estimation of the signal-to-noise ratio of ultra-low-field MRI with an atomic magnetometer.

PubMed

Yamashita, Tatsuya; Oida, Takenori; Hamada, Shoji; Kobayashi, Tetsuo

2012-02-01

In recent years, there has been considerable interest in developing an ultra-low-field magnetic resonance imaging (ULF-MRI) system using an optically pumped atomic magnetometer (OPAM). However, a precise estimation of the signal-to-noise ratio (SNR) of ULF-MRI has not been carried out. Conventionally, to calculate the SNR of an MR image, thermal noise, also called Nyquist noise, has been estimated by considering a resistor that is electrically equivalent to a biological-conductive sample and is connected in series to a pickup coil. However, this method has major limitations in that the receiver has to be a coil and that it cannot be applied directly to a system using OPAM. In this paper, we propose a method to estimate the thermal noise of an MRI system using OPAM. We calculate the thermal noise from the variance of the magnetic sensor output produced by current-dipole moments that simulate thermally fluctuating current sources in a biological sample. We assume that the random magnitude of the current dipole in each volume element of the biological sample is described by the Maxwell-Boltzmann distribution. The sensor output produced by each current-dipole moment is calculated either by an analytical formula or a numerical method based on the boundary element method. We validate the proposed method by comparing our results with those obtained by conventional methods that consider resistors connected in series to a pickup coil using single-layered sphere, multi-layered sphere, and realistic head models. Finally, we apply the proposed method to the ULF-MRI model using OPAM as the receiver with multi-layered sphere and realistic head models and estimate their SNR. Copyright © 2011 Elsevier Inc. All rights reserved.

A Bonner Sphere Spectrometer based on a large 6LiI(Eu) scintillator: Calibration in reference monoenergetic fields

NASA Astrophysics Data System (ADS)

Bedogni, R.; Pola, A.; Costa, M.; Monti, V.; Thomas, D. J.

2018-07-01

A Bonner Sphere spectrometer employing a large, 11 mm diameter × 3 mm thickness, 6LiI(Eu) scintillator (LL-BSS), was assembled. The purpose was to produce a BSS similar in sensitivity to those based on 3He sensors, but using alternative sensors. With respect to the traditional BSS based on the 4 mm (diameter) × 4 mm (height) 6LiI(Eu), this new BSS is a factor of 3 more sensitive. LL-BSS response matrix, determined with MCNPX, was experimentally evaluated with monoenergetic reference neutron fields of 144 keV, 565 keV and 1.2 MeV available at NPL (Teddington, UK). The results of the experiment confirmed the correctness of the response matrix within an overall uncertainty lower than ±2%.

Fabrication of Pt/Au concentric spheres from triblock copolymer.

PubMed

Koh, Haeng-Deog; Park, Soojin; Russell, Thomas P

2010-02-23

Dispersion of an aqueous H(2)PtCl(6) solution into a trifluorotoluene (TFT) solution of a polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) triblock copolymer produced an emulsion-induced hollow micelle (EIHM), comprising a water nanodroplet stabilized by PEO, H(2)PtCl(6)/P2VP, and PS, sequentially. The following addition of an aqueous LiAuCl(4) solution into the dispersion led to a coordination of LiAuCl(4) and PEO. The resulting spherical EIHM structure was transformed to a hollow cylindrical micelle by the fusion of spherical EIHM with the addition of methanol. This structural transition was reversible by the alternative addition of methanol and TFT. Oxygen plasma was used to generate Pt/Au concentric spheres and hollow cylindrical Pt/Au nano-objects.

Flash Kα radiography of laser-driven solid sphere compression for fast ignition

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

Sawada, H.; Lee, S.; Shiroto, T.

2016-06-20

Time-resolved compression of a laser-driven solid deuterated plastic sphere with a cone was measured with flash Kα x-ray radiography. A spherically converging shockwave launched by nanosecond GEKKO XII beams was used for compression while a flash of 4.51 keV Ti Kα x-ray backlighter was produced by a high-intensity, picosecond laser LFEX (Laser for Fast ignition EXperiment) near peak compression for radiography. Areal densities of the compressed core were inferred from two-dimensional backlit x-ray images recorded with a narrow-band spherical crystal imager. The maximum areal density in the experiment was estimated to be 87 ± 26 mg/cm 2. Lastly, the temporalmore » evolution of the experimental and simulated areal densities with a 2-D radiation-hydrodynamics code is in good agreement.« less

A New Hybrid Viscoelastic Soft Tissue Model based on Meshless Method for Haptic Surgical Simulation

PubMed Central

Bao, Yidong; Wu, Dongmei; Yan, Zhiyuan; Du, Zhijiang

2013-01-01

This paper proposes a hybrid soft tissue model that consists of a multilayer structure and many spheres for surgical simulation system based on meshless. To improve accuracy of the model, tension is added to the three-parameter viscoelastic structure that connects the two spheres. By using haptic device, the three-parameter viscoelastic model (TPM) produces accurate deformationand also has better stress-strain, stress relaxation and creep properties. Stress relaxation and creep formulas have been obtained by mathematical formula derivation. Comparing with the experimental results of the real pig liver which were reported by Evren et al. and Amy et al., the curve lines of stress-strain, stress relaxation and creep of TPM are close to the experimental data of the real liver. Simulated results show that TPM has better real-time, stability and accuracy. PMID:24339837

Flash Kα radiography of laser-driven solid sphere compression for fast ignition

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

Sawada, H.; Lee, S.; Nagatomo, H.

2016-06-20

Time-resolved compression of a laser-driven solid deuterated plastic sphere with a cone was measured with flash Kα x-ray radiography. A spherically converging shockwave launched by nanosecond GEKKO XII beams was used for compression while a flash of 4.51 keV Ti Kα x-ray backlighter was produced by a high-intensity, picosecond laser LFEX (Laser for Fast ignition EXperiment) near peak compression for radiography. Areal densities of the compressed core were inferred from two-dimensional backlit x-ray images recorded with a narrow-band spherical crystal imager. The maximum areal density in the experiment was estimated to be 87 ± 26 mg/cm{sup 2}. The temporal evolution of the experimental andmore » simulated areal densities with a 2-D radiation-hydrodynamics code is in good agreement.« less

Mechanical Characterization of Partially Crystallized Sphere Packings

NASA Astrophysics Data System (ADS)

Hanifpour, M.; Francois, N.; Vaez Allaei, S. M.; Senden, T.; Saadatfar, M.

2014-10-01

We study grain-scale mechanical and geometrical features of partially crystallized packings of frictional spheres, produced experimentally by a vibrational protocol. By combining x-ray computed tomography, 3D image analysis, and discrete element method simulations, we have access to the 3D structure of internal forces. We investigate how the network of mechanical contacts and intergranular forces change when the packing structure evolves from amorphous to near perfect crystalline arrangements. We compare the behavior of the geometrical neighbors (quasicontracts) of a grain to the evolution of the mechanical contacts. The mechanical coordination number Zm is a key parameter characterizing the crystallization onset. The high fluctuation level of Zm and of the force distribution in highly crystallized packings reveals that a geometrically ordered structure still possesses a highly random mechanical backbone similar to that of amorphous packings.

Draft genome sequence of Streptomyces sp. strain SS, which produces a series of uridyl peptide antibiotic sansanmycins.

PubMed

Wang, Lifei; Xie, Yunying; Li, Qinglian; He, Ning; Yao, Entai; Xu, Hongzhang; Yu, Ying; Chen, Ruxian; Hong, Bin

2012-12-01

Streptomyces sp. SS produces a series of uridyl peptide antibiotic sansanmycins. Here, we present a draft genome sequence of Streptomyces sp. SS containing the biosynthetic gene cluster for the antibiotics. The identification of the biosynthetic gene cluster of sansanmycins may provide further insight into biosynthetic mechanisms for uridyl peptide antibiotics.

Test Equipment and Method to Characterize a SWIR Digital Imaging System

DTIC Science & Technology

2014-06-01

based on Gallium Arsenide (GaAs) detectors are sensitive in the visible and near infrared (NIR) bands, and used only at night. They produce images from... current from the silicon sensor located on the sphere. The irradiance responsivity, Rn, is the ratio of the silicon detector current and the absolute...silicon detector currents , in accordance with equation 1: ( , ,)[ 2⁄ ] = [] ( ,

NASA Technology Transfer - Human Robot Teaming

NASA Image and Video Library

2016-12-23

Produced for Intelligent Robotics Group to show at January 2017 Consumer Electronics Show (CES). Highlights development of VERVE (Visual Environment for Remote Virtual Exploration) software used on K-10, K-REX, SPHERES and AstroBee projects for 3D awareness. Also mentions transfer of software to Nissan for their development in their Autonomous Vehicle project. Video includes Nissan's self-driving car around NASA Ames.

Corporate Testing: Standards, Profits, and the Demise of the Public Sphere

ERIC Educational Resources Information Center

Leistyna, Pepi

2007-01-01

This article examines the standardized high-stakes testing in the wake of the No Child Left Behind (NCLB) movement. It focuses on the political economy of the testing industry; that is, a look into the ownership, intent, and regulation of the private forces that produce, provide materials, prep sessions, and tutorials for and evaluate, report on,…

Wear Particle Atlas. Revised

DTIC Science & Technology

1982-06-28

known to be generated by cavitation erosion and more importantly by welding or grinding processes. Spheres produced in fatigue cracks may be...generated by welding , grinding, and erosion are frequently over 10/vm. Lubricating oils, as supplied by manufacturers, frequently contain metal...coefficient of friction in nonlubricated contacts If a test is conducted in vacuum, adhesive wear (metal-to-metal welding ) will occur much more rapidly

Planetary Education and Outreach Using the NOAA Science on a Sphere

NASA Technical Reports Server (NTRS)

Simon-Miller, A. A.; Williams, D. R.; Smith, S. M.; Friedlander, J. S.; Mayo, L. A.; Clark, P. E.; Henderson, M. A.

2011-01-01

Science On a Sphere (SOS) is a large visualization system, developed by the National Oceanic and Atmospheric Administration (NOAH), that uses computers running Redhat Linux and four video projectors to display animated data onto the outside of a sphere. Said another way, SOS is a stationary globe that can show dynamic, animated images in spherical form. Visualization of cylindrical data maps show planets, their atmosphere, oceans, and land, in very realistic form. The SOS system uses 4 video projectors to display images onto the sphere. Each projector is driven by a separate computer, and a fifth computer is used to control the operation of the display computers. Each computer is a relatively powerful PC with a high-end graphics card. The video projectors have native XGA resolution. The projectors are placed at the corners of a 30' x 30' square with a 68" carbon fiber sphere suspended in the center of the square. The equator of the sphere is typically located 86" off the floor. SOS uses common image formats such as JPEG, or TIFF in a very specific, but simple form; the images are plotted on an equatorial cylindrical equidistant projection, or as it is commonly known, a latitude/longitude grid, where the image is twice as wide as it is high (rectangular). 2048x] 024 is the minimum usable spatial resolution without some noticeable pixelation. Labels and text can be applied within the image, or using a timestamp-like feature within the SOS system software. There are two basic modes of operation for SOS: displaying a single image or an animated sequence of frames. The frame or frames can be setup to rotate or tilt, as in a planetary rotation. Sequences of images that animate through time produce a movie visualization, with or without an overlain soundtrack. After the images are processed, SOS will display the images in sequence and play them like a movie across the entire sphere surface. Movies can be of any arbitrary length, limited mainly by disk space and can be animated at frame rates up to 30 frames per second. Transitions, special effects, and other computer graphics techniques can be added to a sequence through the use of off-the-shelf software, like Final Cut Pro. However, one drawback is that the Sphere cannot be used in the same manner as a flat movie screen; images cannot be pushed to a "side", a highlighted area must be viewable to all sides of the room simultaneously, and some transitions do not work as well as others. We discuss these issues and workarounds in our poster.

Particle shape inhomogeneity and plasmon-band broadening of solar-control LaB6 nanoparticles

NASA Astrophysics Data System (ADS)

Machida, Keisuke; Adachi, Kenji

2015-07-01

An ensemble inhomogeneity of non-spherical LaB6 nanoparticles dispersion has been analyzed with Mie theory to account for the observed broad plasmon band. LaB6 particle shape has been characterized using small-angle X-ray scattering (SAXS) and electron tomography (ET). SAXS scattering intensity is found to vary exponentially with exponent -3.10, indicating the particle shape of disk toward sphere. ET analysis disclosed dually grouped distribution of nanoparticle dispersion; one is large-sized at small aspect ratio and the other is small-sized with scattered high aspect ratio, reflecting the dual fragmentation modes during the milling process. Mie extinction calculations have been integrated for 100 000 particles of varying aspect ratio, which were produced randomly by using the Box-Muller method. The Mie integration method has produced a broad and smooth absorption band expanded towards low energy, in remarkable agreement with experimental profiles by assuming a SAXS- and ET-derived shape distribution, i.e., a majority of disks with a little incorporation of rods and spheres for the ensemble. The analysis envisages a high potential of LaB6 with further-increased visible transparency and plasmon peak upon controlled particle-shape and its distribution.

Advanced Electrochemistry of Individual Metal Clusters Electrodeposited Atom by Atom to Nanometer by Nanometer.

PubMed

Kim, Jiyeon; Dick, Jeffrey E; Bard, Allen J

2016-11-15

Metal clusters are very important as building blocks for nanoparticles (NPs) for electrocatalysis and electroanalysis in both fundamental and applied electrochemistry. Attention has been given to understanding of traditional nucleation and growth of metal clusters and to their catalytic activities for various electrochemical applications in energy harvesting as well as analytical sensing. Importantly, understanding the properties of these clusters, primarily the relationship between catalysis and morphology, is required to optimize catalytic function. This has been difficult due to the heterogeneities in the size, shape, and surface properties. Thus, methods that address these issues are necessary to begin understanding the reactivity of individual catalytic centers as opposed to ensemble measurements, where the effect of size and morphology on the catalysis is averaged out in the measurement. This Account introduces our advanced electrochemical approaches to focus on each isolated metal cluster, where we electrochemically fabricated clusters or NPs atom by atom to nanometer by nanometer and explored their electrochemistry for their kinetic and catalytic behavior. Such approaches expand the dimensions of analysis, to include the electrochemistry of (1) a discrete atomic cluster, (2) solely a single NP, or (3) individual NPs in the ensemble sample. Specifically, we studied the electrocatalysis of atomic metal clusters as a nascent electrocatalyst via direct electrodeposition on carbon ultramicroelectrode (C UME) in a femtomolar metal ion precursor. In addition, we developed tunneling ultramicroelectrodes (TUMEs) to study electron transfer (ET) kinetics of a redox probe at a single metal NP electrodeposited on this TUME. Owing to the small dimension of a NP as an active area of a TUME, extremely high mass transfer conditions yielded a remarkably high standard ET rate constant, k 0 , of 36 cm/s for outer-sphere ET reaction. Most recently, we advanced nanoscale scanning electrochemical microscopy (SECM) imaging to resolve the electrocatalytic activity of individual electrodeposited NPs within an ensemble sample yielding consistent high k 0 values of ≥2 cm/s for the hydrogen oxidation reaction (HOR) at different NPs. We envision that our advanced electrochemical approaches will enable us to systematically address structure effects on the catalytic activity, thus providing a quantitative guideline for electrocatalysts in energy-related applications.

Model business intelligence system design of quality products by using data mining in R Bakery Company

NASA Astrophysics Data System (ADS)

Fitriana, R.; Saragih, J.; Luthfiana, N.

2017-12-01

R Bakery company is a company that produces bread every day. Products that produced in that company have many different types of bread. Products are made in the form of sweet bread and wheat bread which have different tastes for every types of bread. During the making process, there were defects in the products which the defective product turns into reject product. Types of defects that are produced include burnt, sodden bread and shapeless bread. To find out the information about the defects that have been produced then by applying a designed model business intelligence system to create database and data warehouse. By using model business Intelligence system, it will generate useful information such as how many defect that produced by each of the bakery products. To make it easier to obtain such information, it can be done by using data mining method which data that we get is deep explored. The method of data mining is using k-means clustering method. The results of this intelligence business model system are cluster 1 with little amount of defect, cluster 2 with medium amount of defect and cluster 3 with high amount of defect. From OLAP Cube method can be seen that the defect generated during the 7 months period of 96,744 pieces.

Collinear swimmer propelling a cargo sphere at low Reynolds number.

PubMed

Felderhof, B U

2014-11-01

The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes equations in the presence of a sphere with a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.

Discovery of Gene Cluster for Mycosporine-Like Amino Acid Biosynthesis from Actinomycetales Microorganisms and Production of a Novel Mycosporine-Like Amino Acid by Heterologous Expression

PubMed Central

Miyamoto, Kiyoko T.; Komatsu, Mamoru

2014-01-01

Mycosporines and mycosporine-like amino acids (MAAs), including shinorine (mycosporine-glycine-serine) and porphyra-334 (mycosporine-glycine-threonine), are UV-absorbing compounds produced by cyanobacteria, fungi, and marine micro- and macroalgae. These MAAs have the ability to protect these organisms from damage by environmental UV radiation. Although no reports have described the production of MAAs and the corresponding genes involved in MAA biosynthesis from Gram-positive bacteria to date, genome mining of the Gram-positive bacterial database revealed that two microorganisms belonging to the order Actinomycetales, Actinosynnema mirum DSM 43827 and Pseudonocardia sp. strain P1, possess a gene cluster homologous to the biosynthetic gene clusters identified from cyanobacteria. When the two strains were grown in liquid culture, Pseudonocardia sp. accumulated a very small amount of MAA-like compound in a medium-dependent manner, whereas A. mirum did not produce MAAs under any culture conditions, indicating that the biosynthetic gene cluster of A. mirum was in a cryptic state in this microorganism. In order to characterize these biosynthetic gene clusters, each biosynthetic gene cluster was heterologously expressed in an engineered host, Streptomyces avermitilis SUKA22. Since the resultant transformants carrying the entire biosynthetic gene cluster controlled by an alternative promoter produced mainly shinorine, this is the first confirmation of a biosynthetic gene cluster for MAA from Gram-positive bacteria. Furthermore, S. avermitilis SUKA22 transformants carrying the biosynthetic gene cluster for MAA of A. mirum accumulated not only shinorine and porphyra-334 but also a novel MAA. Structure elucidation revealed that the novel MAA is mycosporine-glycine-alanine, which substitutes l-alanine for the l-serine of shinorine. PMID:24907338

Discovery of gene cluster for mycosporine-like amino acid biosynthesis from Actinomycetales microorganisms and production of a novel mycosporine-like amino acid by heterologous expression.

PubMed

Miyamoto, Kiyoko T; Komatsu, Mamoru; Ikeda, Haruo

2014-08-01

Mycosporines and mycosporine-like amino acids (MAAs), including shinorine (mycosporine-glycine-serine) and porphyra-334 (mycosporine-glycine-threonine), are UV-absorbing compounds produced by cyanobacteria, fungi, and marine micro- and macroalgae. These MAAs have the ability to protect these organisms from damage by environmental UV radiation. Although no reports have described the production of MAAs and the corresponding genes involved in MAA biosynthesis from Gram-positive bacteria to date, genome mining of the Gram-positive bacterial database revealed that two microorganisms belonging to the order Actinomycetales, Actinosynnema mirum DSM 43827 and Pseudonocardia sp. strain P1, possess a gene cluster homologous to the biosynthetic gene clusters identified from cyanobacteria. When the two strains were grown in liquid culture, Pseudonocardia sp. accumulated a very small amount of MAA-like compound in a medium-dependent manner, whereas A. mirum did not produce MAAs under any culture conditions, indicating that the biosynthetic gene cluster of A. mirum was in a cryptic state in this microorganism. In order to characterize these biosynthetic gene clusters, each biosynthetic gene cluster was heterologously expressed in an engineered host, Streptomyces avermitilis SUKA22. Since the resultant transformants carrying the entire biosynthetic gene cluster controlled by an alternative promoter produced mainly shinorine, this is the first confirmation of a biosynthetic gene cluster for MAA from Gram-positive bacteria. Furthermore, S. avermitilis SUKA22 transformants carrying the biosynthetic gene cluster for MAA of A. mirum accumulated not only shinorine and porphyra-334 but also a novel MAA. Structure elucidation revealed that the novel MAA is mycosporine-glycine-alanine, which substitutes l-alanine for the l-serine of shinorine. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Effective, Low-Cost Recovery of Toxic Arsenate Anions from Water by Using Hollow-Sphere Geode Traps.

PubMed

Shenashen, Mohamed A; Akhtar, Naeem; Selim, Mahmoud M; Morsy, Wafaa M; Yamaguchi, Hitoshi; Kawada, Satoshi; Alhamid, Abdulaziz A; Ohashi, Naoki; Ichinose, Izumi; Alamoudi, Ahmad S; El-Safty, Sherif A

2017-08-04

Because of the devastating impact of arsenic on terrestrial and aquatic organisms, the recovery, removal, disposal, and management of arsenic-contaminated water is a considerable challenge and has become an urgent necessity in the field of water treatment. This study reports the controlled fabrication of a low-cost adsorbent based on microscopic C-,N-doped NiO hollow spheres with geode shells composed of poly-CN nanospherical nodules (100 nm) that were intrinsically stacked and wrapped around the hollow spheres to form a shell with a thickness of 500-700 nm. This C-,N-doped NiO hollow-sphere adsorbent (termed CNN) with multiple diffusion routes through open pores and caves with connected open macro/meso windows over the entire surface and well-dispersed hollow-sphere particles that create vesicle traps for the capture, extraction, and separation of arsenate (AsO 4 3- ) species from aqueous solution. The CNN structures are considered to be a potentially attractive adsorbent for AsO 4 3- species due to 1) superior removal and trapping capacity from water samples and 2) selective trapping of AsO 4 3- from real water samples that mainly contained chloride and nitrate anions and Fe 2+ , and Mn 2+ , Ca 2+ , and Mg 2+ cations. The structural stability of the hierarchal geodes was evident after 20 cycles without any significant decrease in the recovery efficiency of AsO 4 3- species. To achieve low-cost adsorbents and toxic-waste management, this superior CNN AsO 4 3- dead-end trapping and recovery system evidently enabled the continuous control of AsO 4 3- disposal in water-scarce environments, presents a low-cost and eco-friendly adsorbent for AsO 4 3- species, and selectively produced water-free arsenate species. These CNN geode traps show potential as excellent adsorbent candidates in environment remediation tools and human healthcare. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Identification and onset of inertial modes in the wide-gap spherical Couette system

NASA Astrophysics Data System (ADS)

Barik, A.; Wicht, J.; Triana, S. A.; Hoff, M.

2016-12-01

The spherical Couette system consists of two concentric rotating spheres with a fluid filling the shell in between. The system has been studied for a long time by fluid dynamicists and is ideal for studying flow instabilities due to differential rotation and the interaction of the same with magnetic fields - important for understanding dynamics of planetary and stellar interiors. The system is also a basis for a new generation of dynamo experiments because of its closer geometrical resemblance to real astrophysical objects as compared to past experiments. We simulate this system using the two different pseudo-spectral codes MagIC and XSHELLS. We focus here on a very interesting and general instability in this system - inertial modes. A rotating body of fluid is known to sustain oscillatory waves due to the restoring action of the Coriolis force. In a bounded container, these form a discrete spectrum called inertial modes. These modes have been analytically known for a rotating full sphere for over a century now. In a spherical shell, they cannot be formulated analytically. However, many of these inertial modes are observed in spherical Couette experiments as well as in simulations. Past studies have tried to explain the onset of these modes invoking wave over-reflection or critical layer instabilities on the cylinder tangent to the inner sphere. In this study, we present the inertial modes found in our simulations and try to explain their onset as secondary instabilities due to the destabilization of the fundamental non-axisymmetric instability, forming a triadic resonance with the fundamental instability. We run various simulations varying the rotation rate of the inner sphere, while keeping the rotation rate of the outer sphere constant. We track velocities and induced magnetic field and produce spectrograms similar to those of the experiments. Our results match very well the experimental data from spherical Couette set-ups at BTU Cottbus and the University of Maryland.

Stopped-flow kinetic studies of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt.

PubMed

Zhang, Jingyan; Ge, Zhishen; Jiang, Xiaoze; Hassan, P A; Liu, Shiyong

2007-12-15

The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS], chi(PTHC)=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time, tau(g), for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson-Wall (A-W) theory. At chi(PTHC) > or = 0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtained tau(g) decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. At chi(PTHC)=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at low chi(PTHC) and the sphere-to-rod transition at high chi(PTHC) further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain lengths, the slower the sphere-to-rod transition.

A new method to prepare colloids of size-controlled clusters from a matrix assembly cluster source

NASA Astrophysics Data System (ADS)

Cai, Rongsheng; Jian, Nan; Murphy, Shane; Bauer, Karl; Palmer, Richard E.

2017-05-01

A new method for the production of colloidal suspensions of physically deposited clusters is demonstrated. A cluster source has been used to deposit size-controlled clusters onto water-soluble polymer films, which are then dissolved to produce colloidal suspensions of clusters encapsulated with polymer molecules. This process has been demonstrated using different cluster materials (Au and Ag) and polymers (polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol). Scanning transmission electron microscopy of the clusters before and after colloidal dispersion confirms that the polymers act as stabilizing agents. We propose that this method is suitable for the production of biocompatible colloids of ultraprecise clusters.

M31 Globular Clusters and Galaxy Formation

NASA Astrophysics Data System (ADS)

Gregg, M. D.; Karick, A. M.

2005-12-01

The brightest globular cluster in the halo of M31, cluster G1, has properties which suggest that it is not an ordinary globular but an ultra-compact dwarf galaxy: its velocity dispersion, M/L, and ellipticity are all atypically large, and its color-magnitude diagram suggests an abundance spread. Using the Keck Laser Guide Star Adaptive Optics system with NIRC2, we have begun an imaging campaign of globular clusters in M31 to measure their core sizes. Combining these data with high dispersion spectroscopy will produce masses and M/L ratios to determine if there are additional UCDs masquerading as M31 globulars. UCDs are thought to be the remnant nuclei from tidally stripped dwarf ellipticals or small spirals; finding additional examples in the cluster system of M31 has implications for galaxy formation processes. The K-band image quality during our first LGS run was very stable over many hours, with Strehl ratios of 0.35 or better, producing point sources with FWHM of 0\\farcs05. The core sizes of the clusters, which range from 0\\farcs2 to 0\\farcs8 can be easily measured from these data. The observing conditions were nearly as good in the J-band, and we obtained both colors for a number of clusters. We discuss our efforts to produce photometrically-calibrated color-magnitude diagrams of the clusters. This work is supported by National Science Foundation Grant No. 0407445 and was done at the Institute of Geophysics and Planetary Physics, under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Mapping coexistence lines via free-energy extrapolation: application to order-disorder phase transitions of hard-core mixtures.

PubMed

Escobedo, Fernando A

2014-03-07

In this work, a variant of the Gibbs-Duhem integration (GDI) method is proposed to trace phase coexistence lines that combines some of the advantages of the original GDI methods such as robustness in handling large system sizes, with the ability of histogram-based methods (but without using histograms) to estimate free-energies and hence avoid the need of on-the-fly corrector schemes. This is done by fitting to an appropriate polynomial function not the coexistence curve itself (as in GDI schemes) but the underlying free-energy function of each phase. The availability of a free-energy model allows the post-processing of the simulated data to obtain improved estimates of the coexistence line. The proposed method is used to elucidate the phase behavior for two non-trivial hard-core mixtures: a binary blend of spheres and cubes and a system of size-polydisperse cubes. The relative size of the spheres and cubes in the first mixture is chosen such that the resulting eutectic pressure-composition phase diagram is nearly symmetric in that the maximum solubility of cubes in the sphere-rich solid (∼20%) is comparable to the maximum solubility of spheres in the cube-rich solid. In the polydisperse cube system, the solid-liquid coexistence line is mapped out for an imposed Gaussian activity distribution, which produces near-Gaussian particle-size distributions in each phase. A terminal polydispersity of 11.3% is found, beyond which the cubic solid phase would not be stable, and near which significant size fractionation between the solid and isotropic phases is predicted.

Eddy currents in the measurement of magnetic susceptibility of rocks

NASA Astrophysics Data System (ADS)

Ježek, Josef; Hrouda, František

2018-01-01

The in-phase and out-of-phase susceptibility of rocks is determined by the magnetic permeability of minerals, their viscous relaxation, and by eddy currents in electrically conductive minerals induced by the applied field. The last effect has been modelled by analytical solution of Maxwell equations for a conductive sphere immersed in a homogeneous, non-conductive medium with given permeability, in presence of an alternating field. The solution is a complex function of parameters describing the sphere (its size, conductivity and permeability), surrounding medium (permeability) and applied field (frequency). Without numerical evaluations, it is difficult to distinguish in-phase and out-of-phase (OPS) susceptibility. In this paper, approximate equations are derived for both susceptibility components, which depend only on the permeability contrast between the sphere and the surrounding medium, and the skin ratio, defined as the ratio between sphere radius and skin depth of the induced currents. These equations are used to obtain a systematic assessment of the role of electrical conductivity in determining the susceptibility of rock samples. The contribution of eddy currents to the susceptibility of diluted (<5%) magnetite particle dispersions is negligible at 1 kHz, but not at higher frequencies. Common rock-forming paramagnetic and diamagnetic minerals with weak electrical conductivity and magnetic permeability are characterized by negligible OPS at 1 kHz. Theoretically, measurable OPS and high phase angles can be produced by paramagnetic conductive minerals in certain combinations with a diamagnetic matrix. This can be excluded from practical point of view for paramagnetic minerals with susceptibilities >0.003 and conductivities not exceeding 5000 S/m.

The implementation of hybrid clustering using fuzzy c-means and divisive algorithm for analyzing DNA human Papillomavirus cause of cervical cancer

NASA Astrophysics Data System (ADS)

Andryani, Diyah Septi; Bustamam, Alhadi; Lestari, Dian

2017-03-01

Clustering aims to classify the different patterns into groups called clusters. In this clustering method, we use n-mers frequency to calculate the distance matrix which is considered more accurate than using the DNA alignment. The clustering results could be used to discover biologically important sub-sections and groups of genes. Many clustering methods have been developed, while hard clustering methods considered less accurate than fuzzy clustering methods, especially if it is used for outliers data. Among fuzzy clustering methods, fuzzy c-means is one the best known for its accuracy and simplicity. Fuzzy c-means clustering uses membership function variable, which refers to how likely the data could be members into a cluster. Fuzzy c-means clustering works using the principle of minimizing the objective function. Parameters of membership function in fuzzy are used as a weighting factor which is also called the fuzzier. In this study we implement hybrid clustering using fuzzy c-means and divisive algorithm which could improve the accuracy of cluster membership compare to traditional partitional approach only. In this study fuzzy c-means is used in the first step to find partition results. Furthermore divisive algorithms will run on the second step to find sub-clusters and dendogram of phylogenetic tree. To find the best number of clusters is determined using the minimum value of Davies Bouldin Index (DBI) of the cluster results. In this research, the results show that the methods introduced in this paper is better than other partitioning methods. Finally, we found 3 clusters with DBI value of 1.126628 at first step of clustering. Moreover, DBI values after implementing the second step of clustering are always producing smaller IDB values compare to the results of using first step clustering only. This condition indicates that the hybrid approach in this study produce better performance of the cluster results, in term its DBI values.

Unsupervised Cryo-EM Data Clustering through Adaptively Constrained K-Means Algorithm

PubMed Central

Xu, Yaofang; Wu, Jiayi; Yin, Chang-Cheng; Mao, Youdong

2016-01-01

In single-particle cryo-electron microscopy (cryo-EM), K-means clustering algorithm is widely used in unsupervised 2D classification of projection images of biological macromolecules. 3D ab initio reconstruction requires accurate unsupervised classification in order to separate molecular projections of distinct orientations. Due to background noise in single-particle images and uncertainty of molecular orientations, traditional K-means clustering algorithm may classify images into wrong classes and produce classes with a large variation in membership. Overcoming these limitations requires further development on clustering algorithms for cryo-EM data analysis. We propose a novel unsupervised data clustering method building upon the traditional K-means algorithm. By introducing an adaptive constraint term in the objective function, our algorithm not only avoids a large variation in class sizes but also produces more accurate data clustering. Applications of this approach to both simulated and experimental cryo-EM data demonstrate that our algorithm is a significantly improved alterative to the traditional K-means algorithm in single-particle cryo-EM analysis. PMID:27959895

Unsupervised Cryo-EM Data Clustering through Adaptively Constrained K-Means Algorithm.

PubMed

Xu, Yaofang; Wu, Jiayi; Yin, Chang-Cheng; Mao, Youdong

2016-01-01

In single-particle cryo-electron microscopy (cryo-EM), K-means clustering algorithm is widely used in unsupervised 2D classification of projection images of biological macromolecules. 3D ab initio reconstruction requires accurate unsupervised classification in order to separate molecular projections of distinct orientations. Due to background noise in single-particle images and uncertainty of molecular orientations, traditional K-means clustering algorithm may classify images into wrong classes and produce classes with a large variation in membership. Overcoming these limitations requires further development on clustering algorithms for cryo-EM data analysis. We propose a novel unsupervised data clustering method building upon the traditional K-means algorithm. By introducing an adaptive constraint term in the objective function, our algorithm not only avoids a large variation in class sizes but also produces more accurate data clustering. Applications of this approach to both simulated and experimental cryo-EM data demonstrate that our algorithm is a significantly improved alterative to the traditional K-means algorithm in single-particle cryo-EM analysis.

Stem/progenitor cells derived from the cochlear sensory epithelium give rise to spheres with distinct morphologies and features.

PubMed

Diensthuber, Marc; Oshima, Kazuo; Heller, Stefan

2009-06-01

Nonmammalian vertebrates regenerate lost sensory hair cells by means of asymmetric division of supporting cells. Inner ear or lateral line supporting cells in birds, amphibians, and fish consequently serve as bona fide stem cells resulting in high regenerative capacity of hair cell-bearing organs. Hair cell regeneration does not happen in the mammalian cochlea, but cells with proliferative capacity can be isolated from the neonatal cochlea. These cells have the ability to form clonal floating colonies, so-called spheres, when cultured in nonadherent conditions. We noticed that the sphere population derived from mouse cochlear sensory epithelium cells was heterogeneous, consisting of morphologically distinct sphere types, hereby classified as solid, transitional, and hollow. Cochlear sensory epithelium-derived stem/progenitor cells initially give rise to small solid spheres, which subsequently transition into hollow spheres, a change that is accompanied by epithelial differentiation of the majority of sphere cells. Only solid spheres, and to a lesser extent, transitional spheres, appeared to harbor self-renewing stem cells, whereas hollow spheres could not be consistently propagated. Solid spheres contained significantly more rapidly cycling Pax-2-expressing presumptive otic progenitor cells than hollow spheres. Islet-1, which becomes upregulated in nascent sensory patches, was also more abundant in solid than in hollow spheres. Likewise, hair cell-like cells, characterized by the expression of multiple hair cell markers, differentiated in significantly higher numbers in cell populations derived from solid spheres. We conclude that cochlear sensory epithelium cell populations initially give rise to small solid spheres that have self-renewing capacity before they subsequently convert into hollow spheres, a process that is accompanied by loss of stemness and reduced ability to spontaneously give rise to hair cell-like cells. Solid spheres might, therefore, represent the most suitable sphere type for cell-based assays or animal model transplantation studies aimed at development of cell replacement therapies.